JP7413296B2 - Electrode groups, secondary batteries, battery packs, and vehicles - Google Patents

Description

Embodiments of the present invention relate to an electrode group, a secondary battery, a battery pack, and a vehicle.

Lithium ion batteries, such as nonaqueous electrolyte batteries, in which charging and discharging are performed by lithium ions moving between a negative electrode and a positive electrode, are being actively researched as high energy density batteries.

In addition to being used as a power source for small electronic devices, this non-aqueous electrolyte battery is also expected to be used as a medium- to large-sized power source for in-vehicle and stationary applications. Such medium- and large-sized applications require long-life performance and high safety. Higher energy density and input/output performance are also required.

Japanese Patent Application Publication No. 2010-186683 JP2017-208255A

“Powder X-ray Analysis in Practice” First Edition (2002) Edited by the Japanese Society of Analytical Chemistry X-ray Analysis Research Council Edited by Izumi Nakai and Fujio Izumi (Asakura Shoten)

It is an object of the present invention to provide an electrode group, a secondary battery, and a battery pack that exhibit excellent output performance, as well as a vehicle that includes this battery pack.

According to embodiments, an electrode group including a positive electrode and a negative electrode including a titanium-containing oxide is provided. The electrode group has a flat wound structure in which a laminate including a positive electrode and a negative electrode is wound such that the center thereof is located along the first direction. A winding section perpendicular to the first direction of the winding structure includes an innermost circumference and an outermost circumference. For the thickness t from the innermost circumference to the outermost circumference along the longest straight line in the winding cross section, the thickness of the portion of the negative electrode located within 0.2t from the innermost circumference along the longest straight line. At least a portion has a cut along the first direction.

According to another embodiment, a secondary battery is provided that includes the electrode group and electrolyte according to the above embodiments.

According to yet another embodiment, a battery pack including the secondary battery according to the above embodiment is provided.

According to yet another embodiment, a vehicle is provided that includes the battery pack according to the above embodiment.

FIG. 1 is a perspective view schematically showing an example of an electrode group according to an embodiment. FIG. 2 is a schematic cross-sectional view taken along virtual plane II shown in FIG. 1; FIG. 3 is an enlarged cross-sectional view of part A of the electrode group shown in FIG. 2; 1 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment. FIG. 5 is an enlarged cross-sectional view of part B of the secondary battery shown in FIG. 4. FIG. 1 is a perspective view schematically showing an example of an assembled battery according to an embodiment. FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. 8 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 7. FIG. 1 is a partially transparent view schematically showing an example of a vehicle according to an embodiment. 1 is a diagram schematically showing an example of a control system related to an electrical system in a vehicle according to an embodiment.

As a nonaqueous electrolyte battery that has long life performance and high safety, there is a nonaqueous electrolyte battery that uses a titanium-containing composite oxide as a negative electrode. In order to obtain even higher energy density, measures such as increasing the amount of electrode mixture and increasing electrode density can be considered. However, an increase in the electrode mixture or electrode density may lead to an increase in battery resistance, resulting in a decrease in input/output performance.

Examples of common types of electrode groups contained in non-aqueous electrolyte batteries include a wound type and a laminated type. The wound type has excellent productivity, but impregnation with electrolyte is low. Further, in the portion of the wound electrode group where an arc-shaped curved surface is formed, reaction between opposing electrodes (for example, a negative electrode and a positive electrode as its counter electrode) is difficult to occur, and battery resistance tends to increase. The innermost circumference of the electrode group is less likely to cause a reaction between opposing electrodes.

Embodiments will be described below with reference to the drawings. Note that common components throughout the embodiments are denoted by the same reference numerals, and redundant explanations will be omitted. In addition, each figure is a schematic diagram for explaining the embodiment and promoting understanding thereof, and the shape, dimensions, ratio, etc. may differ from the actual device, but these are in accordance with the following explanation and known technology. The design can be changed as appropriate by taking into consideration.

[First embodiment]
The electrode group according to the first embodiment includes a positive electrode and a negative electrode. The negative electrode includes a titanium-containing oxide. The electrode group has a flat wound structure in which a laminate including a positive electrode and a negative electrode is wound such that the center thereof is located along the first direction. A winding section perpendicular to the first direction of the winding structure includes an innermost circumference and an outermost circumference. Among the negative electrodes included in the electrode group, the thickness t from the innermost circumference to the outermost circumference along the longest straight line in the winding cross section is within 0.2t from the innermost circumference. There is a cut along the first direction in at least a part of the portion located at .

Such an electrode group may be a battery electrode group. The term "battery" as used herein includes, for example, secondary batteries such as lithium ion secondary batteries and non-aqueous electrolyte batteries. By using such an electrode group, the battery resistance value of the secondary battery can be reduced and high output performance can be obtained.

The electrode group can further include a separator.

An electrode group according to an embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a perspective view schematically showing an example of an electrode group according to an embodiment. FIG. 2 is a schematic cross-sectional view taken along virtual plane II shown in FIG. FIG. 3 is an enlarged cross-sectional view of section A of the electrode group shown in FIG.

The illustrated electrode group 1 has a flat wound structure wound around an imaginary winding axis C along the first direction 11, as shown in FIG. Further, in the wound type structure, as shown in FIGS. 2 and 3, a laminate including a negative electrode 3, a positive electrode 5, and a separator 4 provided between the negative electrode 3 and the positive electrode 5 has a flat shape. It has a rolled structure. The negative electrode 3, the positive electrode 5, and the separator 4 each include a plurality of windings, and within the electrode group 1, -the negative electrode 3, the separator 4, the positive electrode 5, the separator 4, the negative electrode 3, the separator 4, the positive electrode 5, the separator They are arranged repeatedly in the order of 4-. A space 9 exists around the winding axis C.

FIG. 2 shows a winding section of the electrode group 1 perpendicular to the first direction 11. As shown in FIG. A broken line 10 shown in FIG. 2 represents the position along which the longest straight line from one end of the electrode group 1 to the other end runs along this winding cross section. The electrode group 1 includes curved surface portions 13 in which the negative electrode 3, the separator 4, and the positive electrode 5 are curved in a curved shape at both ends along the second direction 12 parallel to this longest straight line, and there is a space between them. The negative electrode 3, the separator 4, and the positive electrode 5 include a flat portion 14 that is flat or substantially flat.

In the electrode group 1, the distance from the innermost periphery 15 to the outermost periphery 16 in the curved surface portion 13 where the negative electrode 3, separator 4, and positive electrode 5 are curved is the wall portion of the electrode group 1 surrounding the space 9. Let the thickness be t. Specifically, the thickness t refers to the thickness along the longest straight line mentioned above. The thickness t may be the thickness of the laminate including the negative electrode 3, the separator 4, and the positive electrode 5 in the stacking direction before winding. At a portion with a thickness of 0.2t from the innermost circumference 15 to the outermost circumference 16 along the longest straight line in the winding section of the electrode group 1, a portion of the negative electrode 3 located at this portion has a cut 8. including. That is, the negative electrode 3 has the cut 8 in the arc-shaped curved surface portion 13 of the wall portion of the electrode group 1 in a region from the innermost circumferential side to one-fifth of the wall thickness. Although only one location is shown in FIG. 3, each of the arc-shaped curved surface portions 13 that the electrode group 1 has at both ends along the second direction 12 has a thickness of 0.2t from the innermost periphery 15 toward the outer periphery. There is a cut 8 at the point.

In the flat portion 14 where the negative electrode 3, separator 4, and positive electrode 5 are flat (or substantially flat), the surfaces of each member are likely to come into close contact with each other. Therefore, the charging and discharging reaction between the negative electrode 3 and the positive electrode 5 can proceed smoothly in the flat portion 14 located in the middle along the second direction. On the other hand, in the curved surface section 13 that is composed of the negative electrode 3, separator 4, and positive electrode 5, each of which has a curved surface shape, the contact between each member tends to be poor. Therefore, the charging/discharging reaction progresses less easily in the curved portion 13 than in the flat portion 14. The charging/discharging reaction is more difficult to proceed on the innermost circumference 15 side than on the outermost circumference 16 side, and the reaction is less likely to proceed at a position closer to the innermost circumference 15 side. Due to this, in an electrode group that does not include the cut 8 at the above position, battery resistance may locally increase.

As in the illustrated example, the negative electrode 3 is connected to the negative electrode 3 at a thickness of 0.2t from the innermost periphery 15 toward the outer periphery along the longest straight line of the winding cross section, that is, near the innermost periphery 15 of the curved surface portion 13. In the electrode group 1 having the cuts 8, local increases in resistance can be suppressed. By providing the cut 8, the stress and rigidity of the portion of the negative electrode 3 adjacent to the cut 8 are alleviated, and that portion is easily brought into close contact with the positive electrode 5 via the separator 4. That is, by including the cut 8, it is possible to reduce the number of locations in the curved surface portion 13 where the charging/discharging reaction does not proceed easily.

The term "cut" here refers to a notch and/or a cut in the negative electrode. The “cut portion” may refer to a portion where a part of the negative electrode is cut by a method described below, for example. These notches and cut portions are provided in a part of the negative electrode 3 along the first direction 11 of the electrode group 1 . As described below, the negative electrode 3 can include a negative electrode current collector and a negative electrode active material-containing layer provided thereon. The cut 8 indicates a notch and/or a cut portion extending over the entire thickness direction of the negative electrode 3 including the negative electrode current collector and the negative electrode active material-containing layer. That is, at the position where the cut 8 exists, a notch and/or a cut portion is provided in both the negative electrode current collector and the negative electrode active material-containing layer.

The cut 8 may be present in one or more of the plurality of winding circumferences included in the negative electrode 3 at a position within a thickness of 0.2 t toward the outside from the innermost circumference 15. The cut 8 may be provided all along the circumference from the innermost circumference 15 to the thickness of 0.2t, or the cut 8 may be provided in a part of the circumference. When the cut 8 is provided in a part of the winding circumference of the negative electrode 3 at a position up to a thickness of 0.2t, the position of the cut 8 is not particularly limited as long as it falls within the thickness range up to 0.2t. For example, the position of the cut 8 may be biased towards the innermost circumference 15 side. Alternatively, the position of the cut 8 may be biased toward the outermost circumference within the thickness range up to 0.2t. Moreover, the cuts 8 may be provided on adjacent circumferences among the winding circumferences of the negative electrode 3, and the circumferences provided with the cuts 8 do not have to be adjacent to each other. It is preferable that the positions of the cuts 8 are concentrated on the innermost circumference 15 side.

In the electrode group 1, the cut 8 is not included in the portion outside the thickness of 0.2 t from the innermost circumference 15. In other words, neither incisions nor cut portions are provided in the region other than the region from the innermost circumference 15 to the outermost circumference 16 up to a thickness of 0.2t. Even within the curved surface portion 13, charging and discharging reactions occur relatively smoothly in the portions closer to the outermost periphery 16, and the effect obtained by providing the cuts 8 decreases as the portion approaches the outermost periphery 16. Making a cut in a location that contributes to charging and discharging is equivalent to cutting off an electronic conduction path. By keeping the range in which the cut 8 is provided within a thickness of 0.2 t, the above-mentioned effects can be obtained while suppressing deterioration of battery performance.

As illustrated by the arrangement on the broken line 10 in FIG. 3, the position of the cuts 8 may overlap with the longest straight line in the winding section. The position of the cut 8 does not have to overlap with the longest straight line. The cut 8 is included in a portion of the negative electrode 3 extending outward from the innermost periphery 15 to a thickness of 0.2t along the longest straight line, and is located within the portion along the longest straight line. In other words, the cut 8 is located within 20% of the innermost circumference of the number of turns of the negative electrode 3, and at a position included in the curved surface portion 13 in the innermost circumference. It is desirable that the position of the cut 8 be at least adjacent to the longest straight line in the winding section. In other words, it is desirable that the cut 8 be adjacent to and/or overlap the longest straight line. More preferably, the position of the cut 8 overlaps with the longest straight line in the winding cross section.

The cut 8 provided in the negative electrode 3 may span the entire first length _LA of the electrode group in the first direction 11, or may span a part of the first length _LA . good. For example, as will be described later, the negative electrode current collector that the negative electrode 3 may include may include a portion that is not provided with a negative electrode active material-containing layer and can function as a negative electrode current collecting tab, but the cut 8 is a portion that can function as a negative electrode current collecting tab. It may extend over the entire negative electrode 3 along the first direction 11. The length of the cut 8 along the first direction 11 is preferably 0.3L _A or more and 0.8L _A or less with respect to the first length _LA .

When the electrode group 1 includes a plurality of cuts 8, the lengths of each cut 8 along the first direction 11 may be the same or different. When there is a plurality of cuts 8, the length of the cuts 8 refers to the average length of the cuts 8. The cut 8 along the first direction 11 may not be continuous, and may include a plurality of notches and/or cut portions divided along the first direction 11. For locations in the negative electrode 3 where the cut 8 is divided into a plurality of notches and/or cut portions along the first direction 11, the length of each cut and/or cut portion in the first direction 11 The sum of is considered to be the length of cut 8. That is, it is preferable that the average total length of each cut 8 is 0.3L _A or more and 0.8L _A or less with respect to the first length _LA . It is more preferable that the total length of all the cuts 8 is 0.3L _A or more and 0.8L _A or less with respect to the first length _LA .

The effect obtained by providing the cut 8 in the innermost peripheral portion of the negative electrode 3 within the thickness of 0.2t is that the first length LA in the first direction 11 and the second length _LA in the second direction 12 are This is preferably achieved in the electrode group 1 in which the length L _B satisfies the relationship 1<L _A /L _B <5. A large ratio of the first length _LA to the second length _LB means that the ratio of the curved surface portion 13 to the flat portion 14 is relatively large. Furthermore, the longer the first length _{LA is} , the longer the distance that the liquid electrolyte permeates into the electrode group from the end face intersecting the first direction 11, and the more places in the electrode group are likely to be short of electrolyte. Therefore, among general electrode groups, electrode groups with a long first length L _A in the first direction 11 are more likely to cause local resistance increases than electrode groups with a short first length L _A. . In the electrode group 1 according to the embodiment, by providing the cuts 8 at the above-mentioned locations, it is possible to suppress a local increase in resistance even when the first length _LA is relatively long. In the electrode group 1 in which the ratio of the first length L _A to the second length L _B is less than 5, a greater effect can be obtained by providing the cuts 8 . Note that the second direction 12 is orthogonal to the first direction 11.

Hereinafter, the negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be explained in detail.

1) Negative electrode The negative electrode can include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer can contain a negative electrode active material and optionally a conductive agent and a binder.

The negative electrode active material-containing layer contains a titanium-containing oxide as a negative electrode active material. Examples of titanium-containing oxides include lithium titanate having a ramsdellite structure (e.g. Li _2+w Ti ₃ O ₇ , 0≦w≦3), lithium titanate having a spinel structure (e.g. Li _4+w Ti ₅ O ₁₂ , 0≦w≦3), monoclinic titanium dioxide (TiO ₂ ), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, orthorhombic titanium composite oxide, and monoclinic niobium titanium composite oxide.

An example of the rectangular titanium-containing complex oxide is a compound represented by Li _2+a Mα _2-b Ti _6-c Mβ _d O _14+σ . Here, Mα is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. Mβ is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The respective subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and −0.5≦σ≦0.5.

A specific example of the rectangular titanium-containing complex oxide includes a rectangular sodium-containing titanium-containing oxide represented by Li _2+a Na _2-y MA _y Ti _6-z MB _z O ₁₄ . Here, MA is at least one selected from the group consisting of Sr, Ba, K, and Cs. MB is at least one selected from the group consisting of Nb, Ta, Zr, and Mo. The respective subscripts in the composition formula are 0≦a≦6, 0≦y<1, and 0≦z<2. A more specific example is Li _2+a Na ₂ Ti ₆ O ₁₄ (0≦a≦6).

An example of the monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M1 _y+z Nb _2-z O _7-δ . Here, M1 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The respective subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3. A specific example of the monoclinic niobium titanium composite oxide is Li _x Nb ₂ TiO ₇ (0≦x≦5).

Another example of the monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M2 _y Nb _2-z M3 _z O _7+δ . Here, M2 is at least one selected from the group consisting of Zr, Si, and Sn. M3 is at least one selected from the group consisting of V, Ta, and Bi. The respective subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Among the titanium-containing oxides, from the viewpoint of obtaining a high battery voltage, it is preferable to include a rectangular titanium-containing composite oxide, particularly a rectangular sodium-containing titanium-containing oxide, as the negative electrode active material. From the viewpoint of obtaining high capacity, it is preferable to include a monoclinic niobium titanium composite oxide as the negative electrode active material.

In addition to the titanium-containing oxide described above, the negative electrode active material may also contain a niobium oxide such as niobium pentoxide.

The conductive agent is blended to improve current collection performance and suppress contact resistance between the negative electrode active material and the negative electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanofibers, and carbon nanotubes. One of these may be used as a conductive agent, or a combination of two or more may be used as a conductive agent. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with carbon or an electronically conductive inorganic material.

The binder is blended to fill gaps between the dispersed active materials and to bind the negative electrode active material and the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinyl pyrrolidone (PVP), fluorine rubber, styrene butadiene rubber, acrylic resin, and acrylic. These include resin copolymers, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. Examples of acrylic resin copolymers and polyacrylic acid compounds include polyacrylic acid and polyacrylonitrile. One of these may be used as a binder, or a combination of two or more may be used as a binder.

In the negative electrode active material-containing layer, the negative electrode active material, the conductive agent, and the binder are contained in a proportion of 70% by mass or more and 96% by mass or less, 2% by mass or more and 28% by mass or less, and 2% by mass or more and 28% by mass or less, respectively. It is preferable to mix them. By setting the amount of the conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved, and the output performance of a secondary battery using such an electrode group can be improved. Further, by setting the amount of the binder to 2% by mass or more, the binding property between the negative electrode active material-containing layer and the negative electrode current collector becomes sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable that the amount of the conductive agent and the binder be 28% by mass or less, respectively, in order to increase the capacity.

The negative electrode current collector has a potential higher than 0.8 V (vs. Li/Li ⁺ ) with respect to the redox potential of lithium, for example, a potential range of 1 V or more and 3 V or less with respect to the redox potential of lithium (vs. Li/ A material that is electrochemically stable in Li ⁺ ) is used. For example, the negative electrode current collector is preferably made of aluminum or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

Further, the negative electrode current collector can include a portion on the surface of which the negative electrode active material-containing layer is not formed. This part can act as a negative electrode current collection tab.

The density of the negative electrode active material-containing layer (excluding the current collector) is preferably 2.1 g/cm ³ or more and 2.8 g/cm ³ or less. A negative electrode in which the density of the negative electrode active material-containing layer is within this range has excellent energy density and electrolyte retention.

2) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer can contain a positive electrode active material and optionally a conductive agent and a binder.

As the positive electrode active material, for example, oxides or sulfides can be used. The positive electrode may contain one type of compound alone as a positive electrode active material, or may contain a combination of two or more types of compounds. Examples of oxides and sulfides include compounds capable of intercalating and deintercalating Li or Li ions.

Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, and lithium manganese composite oxide (for example, Lip _{Mn 2} O ₄ or _Lip MnO ₂ ; 0<p≦1). , lithium nickel composite oxide (e.g. _Lip NiO ₂ ; 0<p≦1), lithium cobalt complex oxide (e.g. _Lip CoO ₂ ; 0<p≦1), lithium nickel cobalt complex oxide (e.g. _Lip Ni _1-q Co _q O ₂ ; 0<p≦1, 0<q<1), lithium manganese cobalt composite oxide (for example, Li _p Mn _q Co _1-q O ₂ ; 0<p≦1, 0<q< 1), lithium manganese nickel composite oxide having a spinel structure (e.g. Li _p Mn _2-s Ni _s O ₄ ; 0<p≦1, 0<s<2), lithium phosphorous oxide having an olivine structure (e.g. Li _p FePO ₄ ; 0<p≦1, Li _p Fe _{1-t Mnt} PO ₄ ; 0<p≦1, 0<t≦1, Li _p CoPO ₄ ; 0<p≦1), iron sulfate (Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (e.g. V ₂ O ₅ ), and lithium nickel cobalt manganese composite oxide (Lip _{Ni 1-qr} Co _q Mn _r O ₂ ; 0<p≦1, 0<q <1, 0<r<1, q+r<1).

Among the above, examples of compounds more preferable as positive electrode active materials include lithium manganese composite oxides having a spinel structure (e.g., Li _p Mn ₂ O ₄ ; 0<p≦1), lithium nickel composite oxides (e.g., Li _p NiO ₂ ; 0<p≦1), lithium cobalt composite oxide (e.g. Lip CoO ₂ ; 0<p≦ ₁ ), lithium nickel cobalt composite oxide (e.g. Lip _{Ni 1-q} Co _q O ₂ ; 0< p≦1, 0<q<1), lithium manganese nickel composite oxide with spinel structure (e.g. Li _p Mn _2-s Ni _s O ₄ ; 0<p≦1, 0<s<2), lithium manganese cobalt Composite oxides (e.g. _Lip Mn _q Co _1-q O ₂ ; 0<p≦1, 0<q<1), lithium phosphorous oxides having an olivine structure (e.g. _Lip FePO ₄ ; 0<p≦1, Lip _{Fe 1-t Mnt} PO ₄ ; 0<p≦1, 0<t≦1, _Lip CoPO ₄ ; 0<p≦1), and lithium nickel cobalt manganese composite oxide ( _Lip Ni _{1- qr} Co _q Mn _r O ₂ ;0<p≦1, 0<q<1, 0<r<1, q+r<1). When these compounds are used as positive electrode active materials, the positive electrode potential can be increased.

When using room temperature molten salt as the battery electrolyte, lithium iron phosphate, Li _u VPO ₄ F (0≦u≦1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or these It is preferable to use a positive electrode active material containing a mixture of. Since these compounds have low reactivity with salts molten at room temperature, cycle life can be improved. Details of the room temperature molten salt will be described later.

The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material having a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material having a primary particle size of 1 μm or less allows lithium ions to diffuse smoothly in the solid.

The specific surface area of the positive electrode active material is preferably 0.1 m ² /g or more and 10 m ² /g or less. A positive electrode active material having a specific surface area of 0.1 m ² /g or more can sufficiently secure Li ion occlusion/desorption sites. A positive electrode active material having a specific surface area of 10 m ² /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, acrylic resin, copolymers of acrylic resins, polyacrylic acid compounds, and imide compounds. , carboxymethyl cellulose (CMC), and salts of CMC. Examples of acrylic resin copolymers and polyacrylic acid compounds include polyacrylic acid and polyacrylonitrile. One of these may be used as a binder, or a combination of two or more may be used as a binder.

The conductive agent is blended to improve current collection performance and suppress contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanofibers, and carbon nanotubes. One of these may be used as a conductive agent, or a combination of two or more may be used as a conductive agent. Further, the conductive agent can also be omitted.

In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably blended in a proportion of 80% by mass or more and 98% by mass or less, and 2% by mass or more and 20% by mass or less, respectively.

Sufficient electrode strength can be obtained by setting the amount of the binder to 2% by mass or more. The binder can also function as an insulator. Therefore, when the amount of the binder is 20% by mass or less, the amount of insulator included in the electrode is reduced, so that the internal resistance can be reduced.

When adding a conductive agent, the positive electrode active material, the binder, and the conductive agent each have a content of 80% by mass or more and 95% by mass or less, 2% by mass or more and 17% by mass or less, and 3% by mass or more and 18% by mass or less. It is preferable to mix them in proportions.

By setting the amount of the conductive agent to 3% by mass or more, the above-mentioned effects can be exhibited. Furthermore, by controlling the amount of the conductive agent to 18% by mass or less, the proportion of the conductive agent that comes into contact with the electrolyte in the secondary battery can be lowered. When this ratio is low, decomposition of the electrolyte can be reduced when storing the secondary battery in a high temperature environment.

The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. It is preferable that the purity of the aluminum foil is 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

Further, the positive electrode current collector can include a portion on the surface of which the positive electrode active material-containing layer is not formed. This part can act as a positive electrode current collection tab.

3) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of blocking current. Furthermore, a separator made of a porous film coated with an inorganic compound can also be used.

<Method for manufacturing electrode group>
Such an electrode group can be manufactured, for example, as follows.

A negative electrode, a positive electrode, and a separator are prepared.

The negative electrode can be produced, for example, by the following method. First, a slurry is prepared by suspending a negative electrode active material, a conductive agent, and a binder in a solvent. This slurry is applied to one or both sides of the negative electrode current collector. Next, the applied slurry is dried to obtain a composite (laminate) of the negative electrode active material-containing layer and the negative electrode current collector. This composite is then pressed. In this way, a negative electrode is produced.

The positive electrode can be produced by the same method as the negative electrode, for example, using a positive electrode active material instead of the negative electrode active material and using a positive electrode current collector instead of the negative electrode current collector.

The prepared negative electrode, separator, and positive electrode are laminated in the order of negative electrode, separator, positive electrode, and separator to obtain a laminate. Next, this laminate is spirally wound to obtain a wound body. At this time, for example, the laminate can be wound so that a part of the negative electrode becomes the outermost periphery. The obtained wound body is subjected to a press treatment to obtain a flat wound electrode group.

By using an appropriately designed negative electrode and pressing the wound body under appropriate conditions, the negative electrode is cut within a thickness of 0.2t from the innermost circumference as described above, and the cut is made. can be provided. By appropriately adjusting the design of the negative electrode and the press processing conditions for the wound body, it is possible to make cuts in the number of windings in which cuts occur in the negative electrode, that is, in the thickness direction from the innermost circumference to the outermost circumference of the electrode group. You can control the extent to which

For example, in an electrode group using a negative electrode containing copper foil as a negative electrode current collector and a carbon-based material as a negative electrode active material, it is difficult to generate a cut in the negative electrode at a curved surface portion. Cuts are more likely to occur when a less flexible negative electrode is used. Specifically, as the amount of conductive agent and binder included in the negative electrode active material-containing layer increases, the hardness of the negative electrode increases, and the number of windings including cuts increases accordingly. Tend. When the blending ratio of the binder is increased, the strength of the bond between the negative electrode active material-containing layer and the negative electrode current collector increases, and stress is generated in the portion of the wound body that is bent during the pressing process. Since it becomes easier to concentrate, the negative electrode becomes more likely to be disconnected. The hardness of the negative electrode is also affected by the composition and particle morphology of the negative electrode active material. There is a tendency that the higher the density of the negative electrode active material-containing layer, the greater the number of circumferences having cuts, and the smaller the particle size of the negative electrode active material particles, the greater the number of circumferences having cuts. The density of the negative electrode active material-containing layer can be controlled, for example, by adjusting the amount of slurry applied to the current collector and the conditions for pressing the composite of the negative electrode active material-containing layer and the negative electrode current collector.

Also from the viewpoint of cutting the negative electrode by pressing the wound body, it is desirable to use aluminum foil or aluminum alloy foil as the negative electrode current collector. When a thin negative electrode current collector is used, the number of turns having cuts tends to increase.

In the pressing process for the wound body, for example, a load of 80 kN is applied to the wound body for 1 minute or more and 3 minutes or less. By increasing the load during pressing to a specific value or more, it can be expected that cuts along the first direction will occur in the negative electrode. The longer the pressing time, the more turns there are including cuts. Heat pressing may also be performed; in that case, the number of circumferences including cuts in the negative electrode tends to increase.

It is not desirable in the present invention to provide a notch or cut portion in advance in the negative electrode before winding a laminate including a negative electrode, a separator, and a positive electrode, although this does not hinder the present invention. If a notch is provided in the negative electrode or the negative electrode is cut before winding, not only will the workability during winding be hindered, but also the adhesion between each member in the resulting electrode group may deteriorate. As a result, battery resistance may even increase.

<Measurement method>
Various methods of measuring the electrode group will be explained below. Specifically, a method of confirming a break in the negative electrode included in the innermost peripheral portion of the curved surface portion of the electrode group and a method of confirming the negative electrode active material contained in the negative electrode will be described.

If the electrode group to be measured is built into a secondary battery, take out the electrode group as follows. First, put the battery in a discharge state. The discharge state here refers to a state in which a constant current is discharged to a discharge lower limit voltage at a current value of 0.2 C or less in an environment of 25°C. The discharged battery is placed in a glove box with an inert atmosphere, for example, a glove box filled with argon gas. Next, the battery is disassembled in the glove box and the electrode group is taken out from the battery. Specifically, inside the glove box, cut open the battery while being careful not to short-circuit the positive and negative electrodes. The electrode group is taken out from there, and its surface is washed with, for example, methyl ethyl carbonate (MEC) solvent. This cleaning removes Li salt adhering to the surface of the electrode group. After that, the electrode group is dried.

Cleaning of the electrode group may be omitted. However, the electrode for confirming the active material is cleaned after being removed from the electrode group as described later.

(How to check the cut)
The presence or absence of a cut (notch and/or cut portion) in the negative electrode at a portion within a thickness of 0.2 t from the innermost circumference of the electrode group can be confirmed by the following method.

In the wound electrode group, check the number of turns of the laminate of the negative electrode, positive electrode, and separator included in the electrode group. Count the number of windings within 20% of the number of windings of the entire electrode group from the innermost circumference, and among the number of windings within 20% of the innermost circumference, the longest straight line of the winding cross section. It is confirmed whether a part of the negative electrode has a notch or cut portion along the first direction. Based on the number of turns of the entire electrode group and the thickness (t) of the laminate, the number of circumferences in which notches and/or cut portions are confirmed can be converted into a unit for the thickness t. Here, the notch or cut portion refers to a portion where there is a cut or cut portion between the negative electrode active material-containing layer and the current collector, where only the negative electrode active material-containing layer is missing and the current collector is exposed. It does not refer to the part that is For example, if the number of windings in the electrode group is 50, check whether the negative electrode has a notch or a cut portion within 10 windings from the innermost circumference.

(How to check negative electrode active material)
Take out the negative electrode from the electrode group and obtain a measurement sample. For example, cut out the electrode connected to the negative terminal. The electrode taken out is washed with, for example, methyl ethyl carbonate (MEC) solvent. This cleaning removes Li salt adhering to the electrode surface, and then the electrode is dried.

Using the obtained electrode (negative electrode) as a sample, elemental analysis was performed using a scanning electron microscope (SEM-EDX) equipped with an energy dispersive X-ray analyzer, and X-ray diffraction ( By combining X-Ray Diffraction; . By SEM-EDX analysis, it is possible to know the shape of the components contained in the active material-containing layer and the composition (each element of B to U in the periodic table) of the components contained in the active material-containing layer. By ICP measurement, the elements in the active material-containing layer can be quantified. Then, the crystal structure of the material contained in the active material-containing layer can be confirmed by XRD measurement.

The cross section of the electrode taken out as described above is cut out by Ar ion milling. Observe the cut cross section using SEM. Sampling of samples should also be done in an inert atmosphere such as argon or nitrogen, avoiding exposure to the atmosphere. Some particles are selected using a 3000x SEM observation image. At this time, the particles are selected so that the particle size distribution of the selected particles is as wide as possible.

Next, each selected particle is subjected to elemental analysis using EDX. Thereby, the type and amount of elements other than Li among the elements contained in each selected particle can be specified.

Regarding Li, information about the Li content in the entire active material can be obtained by ICP emission spectroscopy. ICP emission spectroscopy is performed according to the following procedure.

A powder sample is prepared from the dried electrode as follows. The active material-containing layer is peeled off from the current collector and ground in a mortar. A liquid sample is prepared by dissolving the ground sample in acid. At this time, as the acid, hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, etc. can be used. By subjecting this liquid sample to ICP emission spectrometry, the concentration of the element contained in the active material to be measured can be determined.

The crystal structure of the compound contained in each particle selected by SEM can be specified by XRD measurement. XRD measurements are performed using CuKα radiation as a radiation source in the measurement range of 2θ=5° to 90°. Through this measurement, an X-ray diffraction pattern of the compound contained in the selected particles can be obtained.

As a device for XRD measurement, SmartLab manufactured by Rigaku is used. The measurement conditions are as follows:
X-ray source: Cu target Output: 45kV, 200mA
Solar slit: 5° for both incident and receiving light
Step width (2θ): 0.02deg
Scan speed: 20deg/min Semiconductor detector: D/teX Ultra 250
Sample plate holder: flat glass sample plate holder (thickness 0.5mm)
Measurement range: 5°≦2θ≦90°.

When using other equipment, perform measurements using standard Si powder for powder X-ray diffraction, and establish conditions that will yield measurement results of peak intensity, half-width, and diffraction angle equivalent to those obtained with the above equipment. Find it and measure the sample under those conditions.

The conditions for XRD measurement are such that an XRD pattern applicable to Rietveld analysis can be obtained. To collect data for Rietveld analysis, specifically, the step width should be 1/3 to 1/5 of the minimum half-width of the diffraction peak, and the intensity at the peak position of the most intense reflection should be 5000 cps or more. Adjust the measurement time or X-ray intensity as appropriate to achieve the desired results.

The XRD pattern obtained as described above is analyzed by the Rietveld method. In the Rietveld method, a diffraction pattern is calculated from a crystal structure model estimated in advance. The estimation of the crystal structure model here is performed based on the analysis results by EDX and ICP. By fitting all of these calculated values and measured values, parameters related to the crystal structure (lattice constant, atomic coordinates, occupancy, etc.) can be precisely analyzed.

XRD measurement can be performed by directly attaching an electrode sample to a glass holder of a wide-angle X-ray diffraction device. At this time, the XRD spectrum is measured in advance according to the type of metal foil of the electrode current collector, and the position where the peak derived from the current collector appears is determined. Also, know in advance whether or not there are peaks of mixtures such as conductive agents and binders. When the peak of the current collector and the peak of the active material overlap, it is desirable to peel off the active material-containing layer from the current collector and perform the measurement. This is to separate overlapping peaks when quantitatively measuring peak intensity. Of course, if you know these things in advance, you can omit this operation.

The electrode group according to the first embodiment includes a positive electrode and a negative electrode containing a titanium-containing oxide, and has a flat wound structure in which a laminate including the positive electrode and the negative electrode is wound. A thickness of 0.2t from the innermost periphery relative to the thickness t from the innermost periphery to the outermost periphery along the longest straight line in the winding cross section perpendicular to the first direction along the winding center of the wound type structure. At least a portion of the negative electrode has a cut along the first direction at a position within the range. Since battery resistance is suppressed in such an electrode group, the electrode group can provide a secondary battery with excellent output performance.

[Second embodiment]
According to the second embodiment, a secondary battery including an electrode group and an electrolyte is provided. The electrode group included in this secondary battery is the electrode group according to the first embodiment. An electrolyte may be retained in the electrode group.

Moreover, the secondary battery according to the second embodiment can further include an exterior member that houses the electrode group and the electrolyte.

Furthermore, the secondary battery according to the second embodiment can further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

The secondary battery according to the second embodiment may be, for example, a lithium secondary battery. Further, the secondary battery includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

Hereinafter, the electrolyte, the exterior member, the negative electrode terminal, and the positive electrode terminal will be explained in detail.

I. Electrolyte As the electrolyte, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol/L or more and 2.5 mol/L or less.

Examples of electrolyte salts include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), and trifluoromethane. Included are lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethylsulfonylimide (LiN(CF ₃ SO ₂ ) ₂ ), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF ₆ is most preferred.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC); diethyl carbonate (DEC), dimethyl carbonate. linear carbonates such as (dimethyl carbonate; DMC), methyl ethyl carbonate (MEC); tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), dioxolane (DOX); cyclic ethers such as dimethoxy ethane (DME), diethoxy ethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (sulfolane; SL) is included. These organic solvents can be used alone or as a mixed solvent.

A gel nonaqueous electrolyte is prepared by combining a liquid nonaqueous electrolyte and a polymer material. Examples of polymeric materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

Alternatively, as the nonaqueous electrolyte, in addition to liquid nonaqueous electrolyte and gel nonaqueous electrolyte, room temperature molten salt containing lithium ions (ionic melt), polymer solid electrolyte, inorganic solid electrolyte, etc. may be used. Good too.

Room temperature molten salt (ionic melt) refers to a compound that can exist as a liquid at room temperature (15° C. or higher and 25° C. or lower) among organic salts consisting of a combination of organic cations and anions. The room temperature molten salt includes a room temperature molten salt that exists as a liquid alone, a room temperature molten salt that becomes a liquid when mixed with an electrolyte salt, a room temperature molten salt that becomes a liquid when dissolved in an organic solvent, or a mixture thereof. It will be done. Generally, the melting point of the room temperature molten salt used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton.

Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymeric material and solidifying it.

The inorganic solid electrolyte is a solid material that has Li ion conductivity.

II. Exterior Member As the exterior member, for example, a container made of a laminate film or a metal container can be used.

The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

As the laminate film, a multilayer film including a plurality of resin layers and a metal layer interposed between these resin layers is used. The resin layer includes a polymer material such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be formed into the shape of the exterior member by sealing it by heat fusion.

The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, still more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. Preferably, the aluminum alloy contains elements such as magnesium, zinc, and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content thereof is preferably 100 mass ppm or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), square, cylindrical, coin, button, or the like. The exterior member can be appropriately selected depending on the battery dimensions and the intended use of the battery.

III. Negative Electrode Terminal The negative electrode terminal can be formed from a material that is electrochemically stable and conductive in a potential range of 1 V to 3 V (vs. Li/Li ⁺ ) with respect to the oxidation-reduction potential of lithium. Specifically, the material of the negative electrode terminal includes copper, nickel, stainless steel, or aluminum, or at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Examples include aluminum alloys. As the material for the negative electrode terminal, it is preferable to use aluminum or an aluminum alloy. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

IV. Positive electrode terminal The positive electrode terminal is electrically stable in a potential range of 3 V or more and 4.5 V or less (vs. Li/Li ⁺ ) with respect to the oxidation-reduction potential of lithium, and can be formed from a material that has conductivity. . Examples of the material for the positive electrode terminal include aluminum or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

Next, the secondary battery according to the second embodiment will be described in more detail with reference to the drawings.

FIG. 4 is a cross-sectional view schematically showing an example of a secondary battery according to the second embodiment. FIG. 5 is an enlarged cross-sectional view of section B of the secondary battery shown in FIG. 4. FIG.

The secondary battery 100 shown in FIGS. 4 and 5 includes the bag-shaped exterior member 2 shown in FIG. 4, the electrode group 1 shown in FIGS. 4 and 5, and an electrolyte not shown. The electrode group 1 and the electrolyte are housed in a bag-like exterior member 2. An electrolyte (not shown) is held in the electrode group 1.

The bag-like exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

As shown in FIG. 4, the electrode group 1 is a flat wound electrode group. The electrode group 1, which is flat and wound, includes a negative electrode 3, a separator 4, and a positive electrode 5, as shown in FIG. Separator 4 is interposed between negative electrode 3 and positive electrode 5.

The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the portion of the negative electrode 3 located at the outermost shell of the wound electrode group 1, a negative electrode active material-containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in FIG. In other parts of the negative electrode 3, negative electrode active material-containing layers 3b are formed on both sides of the negative electrode current collector 3a.

The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both surfaces of the positive electrode current collector 5a.

As shown in FIG. 4, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer peripheral end of the wound electrode group 1. As shown in FIG. This negative electrode terminal 6 is connected to the outermost shell portion of the negative electrode current collector 3a. Further, the positive electrode terminal 7 is connected to the outermost shell portion of the positive electrode current collector 5a. These negative electrode terminal 6 and positive electrode terminal 7 extend outside from the opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat-sealing this layer.

The secondary battery according to the second embodiment includes the electrode group according to the first embodiment. Therefore, battery resistance is suppressed in the secondary battery according to the second embodiment, and the secondary battery can exhibit excellent output performance.

[Third embodiment]
According to the third embodiment, an assembled battery is provided. The assembled battery according to the third embodiment includes a plurality of secondary batteries according to the second embodiment.

In the assembled battery according to the third embodiment, each unit cell may be arranged electrically connected in series or in parallel, or may be arranged in a combination of series connection and parallel connection.

Next, an example of the assembled battery according to the third embodiment will be described with reference to the drawings.

FIG. 6 is a perspective view schematically showing an example of an assembled battery according to the third embodiment. The assembled battery 200 shown in FIG. 6 includes five single cells 100a to 100e, four bus bars 21, a positive lead 22, and a negative lead 23. Each of the five single cells 100a to 100e is a secondary battery according to the second embodiment.

The bus bar 21 connects, for example, the negative terminal 6 of one cell 100a and the positive terminal 7 of the adjacent cell 100b. In this way, the five single cells 100 are connected in series by the four bus bars 21. That is, the assembled battery 200 in FIG. 6 is a five-series assembled battery. Although an example is not shown, in an assembled battery including a plurality of cells electrically connected in parallel, for example, a plurality of negative terminals are connected to each other by a bus bar, and a plurality of positive terminals are connected to each other by a bus bar. This allows a plurality of single cells to be electrically connected.

The positive terminal 7 of at least one of the five single cells 100a to 100e is electrically connected to a positive lead 22 for external connection. Further, the negative terminal 6 of at least one of the five single cells 100a to 100e is electrically connected to a negative lead 23 for external connection.

The assembled battery according to the third embodiment includes the secondary battery according to the second embodiment. In the assembled battery, battery resistance is suppressed, and such an assembled battery can exhibit excellent output performance.

[Fourth embodiment]
According to a fourth embodiment, a battery pack is provided. This battery pack includes the assembled battery according to the third embodiment. This battery pack may include a single secondary battery according to the second embodiment instead of the assembled battery according to the third embodiment.

The battery pack according to the fourth embodiment can further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device (for example, an electronic device, an automobile, etc.) that uses a battery pack as a power source may be used as a protection circuit for the battery pack.

Furthermore, the battery pack according to the fourth embodiment may further include an external terminal for power supply. The external terminal for energization is for outputting current from the secondary battery to the outside and/or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for energization. Furthermore, when charging the battery pack, charging current (including regenerated energy from the motive power of an automobile, etc.) is supplied to the battery pack through an external terminal for energization.

Next, an example of a battery pack according to a fourth embodiment will be described with reference to the drawings.

FIG. 7 is an exploded perspective view schematically showing an example of a battery pack according to the fourth embodiment. FIG. 8 is a block diagram showing an example of the electric circuit of the battery pack shown in FIG. 7.

The battery pack 300 shown in FIGS. 7 and 8 includes a storage container 31, a lid 32, a protective sheet 33, an assembled battery 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown). .

The storage container 31 shown in FIG. 7 is a bottomed square container having a rectangular bottom surface. The storage container 31 is configured to be able to accommodate the protective sheet 33, the assembled battery 200, the printed wiring board 34, and the wiring 35. The lid 32 has a rectangular shape. The lid 32 accommodates the assembled battery 200 and the like by covering the accommodation container 31. Although not shown, the container 31 and the lid 32 are provided with an opening or a connection terminal for connection to an external device or the like.

The assembled battery 200 includes a plurality of single cells 100, a positive lead 22, a negative lead 23, and an adhesive tape 24.

At least one of the plurality of unit cells 100 is a secondary battery according to the second embodiment. Each of the plurality of unit cells 100 is electrically connected in series as shown in FIG. The plurality of unit cells 100 may be electrically connected in parallel, or may be connected in a combination of series connection and parallel connection. When a plurality of single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

The adhesive tape 24 fastens the plurality of unit cells 100 together. Instead of the adhesive tape 24, a heat shrink tape may be used to fix the plurality of cells 100. In this case, the protective sheets 33 are arranged on both sides of the assembled battery 200, and after a heat-shrinkable tape is made to go around, the heat-shrinkable tape is heat-shrinked to bundle the plurality of unit cells 100.

One end of the positive electrode side lead 22 is connected to the assembled battery 200. One end of the positive electrode side lead 22 is electrically connected to the positive electrode of one or more unit cells 100. One end of the negative electrode side lead 23 is connected to the assembled battery 200. One end of the negative electrode side lead 23 is electrically connected to the negative electrode of one or more unit cells 100.

The printed wiring board 34 is installed along one of the inner surfaces of the container 31 in the short side direction. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, and a positive wiring (positive wiring) 348a. and a negative side wiring (negative side wiring) 348b. One main surface of the printed wiring board 34 faces one side of the assembled battery 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the assembled battery 200.

The other end 22 a of the positive lead 22 is electrically connected to the positive connector 342 .
The other end 23 a of the negative lead 23 is electrically connected to the negative connector 343 .

Thermistor 345 is fixed to one main surface of printed wiring board 34. Thermistor 345 detects the temperature of each cell 100 and transmits the detection signal to protection circuit 346.

External terminal 350 for power supply is fixed to the other main surface of printed wiring board 34 . The external terminal 350 for energization is electrically connected to a device existing outside the battery pack 300. External terminal 350 for energization includes a positive terminal 352 and a negative terminal 353.

The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. Furthermore, the protection circuit 346 is electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative electrode side connector 343 via wiring 343a. Further, the protection circuit 346 is electrically connected to each of the plurality of unit cells 100 via the wiring 35.

The protective sheet 33 is disposed on both inner surfaces of the container 31 in the long side direction and on the inner surface of the container 31 in the short side direction facing the printed wiring board 34 with the assembled battery 200 interposed therebetween. The protective sheet 33 is made of resin or rubber, for example.

The protection circuit 346 controls charging and discharging of the plurality of unit cells 100. Furthermore, the protection circuit 346 connects the protection circuit 346 to an external terminal for energizing the external device based on the detection signal transmitted from the thermistor 345 or the detection signal transmitted from the individual cells 100 or the assembled batteries 200. 350 (positive side terminal 352, negative side terminal 353).

Examples of the detection signal transmitted from the thermistor 345 include a signal that detects that the temperature of the unit cell 100 is higher than a predetermined temperature. Examples of the detection signal transmitted from each single cell 100 or assembled battery 200 include signals that detect overcharging, overdischarging, and overcurrent of the single cell 100. When detecting overcharging or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

Note that as the protection circuit 346, a circuit included in a device (eg, an electronic device, an automobile, etc.) that uses the battery pack 300 as a power source may be used.

Moreover, this battery pack 300 is provided with the external terminal 350 for power supply, as described above. Therefore, this battery pack 300 can output current from the assembled battery 200 to an external device and input current from the external device to the assembled battery 200 via the external terminal 350 for energization. In other words, when the battery pack 300 is used as a power source, the current from the assembled battery 200 is supplied to the external device through the external terminal 350 for energization. Further, when charging the battery pack 300, a charging current from an external device is supplied to the battery pack 300 through the external terminal 350 for energization. When this battery pack 300 is used as an on-vehicle battery, regenerated energy from the motive power of the vehicle can be used as the charging current from an external device.

Note that the battery pack 300 may include a plurality of assembled batteries 200. In this case, the plurality of assembled batteries 200 may be connected in series, in parallel, or by a combination of series connection and parallel connection. Further, the printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive side lead 22 and the negative side lead 23 may be used as the positive side terminal 352 and negative side terminal 353 of the external terminal 350 for energization, respectively.

Such a battery pack is used, for example, in applications that require excellent cycle performance when drawing a large current. Specifically, this battery pack is used, for example, as a power source for electronic equipment, a stationary battery, and an in-vehicle battery for various vehicles. An example of the electronic device is a digital camera. This battery pack is particularly suitable for use as a vehicle battery.

The battery pack according to the fourth embodiment includes the secondary battery according to the second embodiment or the assembled battery according to the third embodiment. Therefore, in the battery pack, battery resistance is suppressed, and such a battery pack can exhibit excellent output performance.

[Fifth embodiment]
According to a fifth embodiment, a vehicle is provided. This vehicle is equipped with a battery pack according to the fourth embodiment.

In the vehicle according to the fifth embodiment, the battery pack recovers, for example, regenerated energy of the motive power of the vehicle. The vehicle may include a mechanism (Regenerator) that converts the kinetic energy of the vehicle into regenerative energy.

Examples of the vehicle according to the fifth embodiment include a two-wheel to four-wheel hybrid electric vehicle, a two-wheel to four-wheel electric vehicle, an assisted bicycle, and a railway vehicle.

The mounting position of the battery pack in the vehicle according to the fifth embodiment is not particularly limited. For example, when a battery pack is installed in a car, the battery pack can be installed in the engine compartment of the vehicle, at the rear of the vehicle, or under the seat.

The vehicle according to the fifth embodiment may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically in parallel, or electrically connected by a combination of series and parallel connections. Good too. For example, when each battery pack includes assembled batteries, the assembled batteries may be electrically connected in series or electrically connected in parallel, or a combination of series and parallel connections may be used to electrically connect the assembled batteries. may be connected to. Alternatively, if each battery pack includes a single battery, each battery may be electrically connected in series, electrically in parallel, or a combination of series and parallel connections. may be electrically connected.

Next, an example of a vehicle according to a fifth embodiment will be described with reference to the drawings.

FIG. 9 is a partially transparent view schematically showing an example of a vehicle according to the fifth embodiment.

A vehicle 400 shown in FIG. 9 includes a vehicle main body 40 and a battery pack 300 according to the fourth embodiment. In the example shown in FIG. 9, vehicle 400 is a four-wheeled automobile.

This vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (for example, single cells or assembled batteries) included in the battery pack 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

FIG. 9 illustrates an example in which the battery pack 300 is installed in the engine room located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted at the rear of the vehicle body 40 or under the seat, for example. This battery pack 300 can be used as a power source for the vehicle 400. Further, this battery pack 300 can recover regenerated energy from the motive power of the vehicle 400.

Next, an embodiment of a vehicle according to a fifth embodiment will be described with reference to FIG. 10.

FIG. 10 is a diagram schematically showing an example of a control system related to the electrical system in a vehicle according to the fifth embodiment. Vehicle 400 shown in FIG. 10 is an electric vehicle.

A vehicle 400 shown in FIG. 10 includes a vehicle main body 40, a vehicle power source 41, a vehicle ECU (Electric Control Unit) 42 which is a higher control device of the vehicle power source 41, and an external terminal (external terminal). It includes a terminal (for connection to a power source) 43, an inverter 44, and a drive motor 45.

The vehicle 400 has a vehicle power source 41 mounted, for example, in the engine room, at the rear of the car body, or under the seat. In addition, in the vehicle 400 shown in FIG. 10, the mounting location of the vehicle power source 41 is schematically shown.

The vehicle power source 41 includes a plurality of (for example, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. Battery packs 300a to 300c are battery packs similar to battery pack 300 described above, and battery packs 200a to 200c are battery packs similar to battery pack 200 described above. The battery packs 200a to 200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be independently removed and replaced with another battery pack 300.

Each of the battery packs 200a to 200c includes a plurality of cells connected in series. At least one of the plurality of single cells is a secondary battery according to the second embodiment. The assembled batteries 200a to 200c are charged and discharged through a positive terminal 413 and a negative terminal 414, respectively.

The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c, and collects information regarding the voltage, temperature, etc. of each of the single cells 100 included in the assembled batteries 200a to 200c included in the vehicle power source 41. do. Thereby, the battery management device 411 collects information regarding maintenance of the vehicle power source 41.

The battery management device 411 and the assembled battery monitoring devices 301a to 301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by a plurality of nodes (battery management device 411 and one or more assembled battery monitoring devices 301a to 301c). The communication bus 412 is, for example, a communication bus configured based on the CAN (Control Area Network) standard.

The assembled battery monitoring devices 301a to 301c measure the voltages and temperatures of individual cells forming the assembled batteries 200a to 200c based on commands communicated from the battery management device 411. However, the temperature can be measured at only a few locations per one assembled battery, and it is not necessary to measure the temperature of all single cells.

The vehicle power supply 41 can also include an electromagnetic contactor (for example, a switch device 415 shown in FIG. 10) that switches the presence or absence of electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a precharge switch (not shown) that is turned on when the assembled batteries 200a to 200c are charged, and a precharge switch (not shown) that is turned on when the output from the assembled batteries 200a to 200c is supplied to the load. It includes a main switch (not shown). Each of the precharge switch and the main switch includes a relay circuit (not shown) that is turned on or off by a signal supplied to a coil located near the switch element. The electromagnetic contactor such as the switch device 415 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. Inverter 44 is controlled based on a control signal from battery management device 411 or vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

The drive motor 45 is rotated by electric power supplied from the inverter 44 . The driving force generated by the rotation of the drive motor 45 is transmitted to the axle and the drive wheels W via, for example, a differential gear unit.

Although not shown, the vehicle 400 includes a regenerative brake mechanism (regenerator). The regenerative brake mechanism rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative brake mechanism is input to the inverter 44 and converted into direct current. The converted DC current is input to the vehicle power source 41.

One terminal of the connection line L1 is connected to the negative terminal 414 of the vehicle power source 41. The other terminal of the connection line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection section (current detection circuit) 416 in the battery management device 411 is provided between the negative electrode terminal 414 and the negative electrode input terminal 417 on the connection line L1.

One terminal of the connection line L2 is connected to the positive terminal 413 of the vehicle power source 41. The other terminal of the connection line L2 is connected to the positive input terminal 418 of the inverter 44. A switch device 415 is provided between the positive terminal 413 and the positive input terminal 418 on the connection line L2.

External terminal 43 is connected to battery management device 411 . The external terminal 43 can be connected to an external power source, for example.

The vehicle ECU 42 coordinately controls the vehicle power source 41, the switch device 415, the inverter 44, etc. together with other management devices and control devices including the battery management device 411 in response to operation inputs from the driver or the like. Through cooperative control of the vehicle ECU 42 and the like, output of electric power from the vehicle power source 41, charging of the vehicle power source 41, etc. are controlled, and the entire vehicle 400 is managed. Data regarding maintenance of the vehicle power source 41, such as remaining capacity of the vehicle power source 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

A vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Therefore, a high performance vehicle can be provided.

[Example]
Examples will be described below, but the present invention is not limited to the examples listed below unless it goes beyond the gist of the present invention.

(Example 1)
In Example 1, an electrode group and a nonaqueous electrolyte battery equipped with the electrode group were manufactured using the following procedure.

<Preparation of negative electrode>
As a negative electrode active material, particles of a monoclinic niobium titanium composite oxide having a composition represented by the formula TiNb ₂ O ₇ were prepared. The negative electrode active material particles had a primary particle shape and an average particle diameter of 3 μm. Also, acetylene black as a conductive agent, carboxymethyl cellulose and styrene-butadiene rubber as a binder were prepared. These were mixed in pure water so that the mass ratio of negative electrode active material: acetylene black: carboxymethyl cellulose: styrene butadiene rubber was 90:5:2.5:2.5 to obtain a slurry. This slurry was applied onto both sides of a current collector made of aluminum foil having a thickness of 15 μm, and the coating film was dried. In this way, a composite including a current collector and negative electrode active material-containing layers formed on both sides of the current collector was obtained. The coating amount per one side of the negative electrode active material-containing layer was 90 g/m ² . The width of the negative electrode was adjusted using a slit device, and the negative electrode coating width was 80 mm, and the width of the aluminum foil to which no electrode was applied was 10 mm. Next, the obtained composite was subjected to a roll press so that the density of the negative electrode active material-containing layer was 2.55 g/cm ³ . Next, this composite was further subjected to vacuum drying to obtain a negative electrode.

<Preparation of positive electrode>
As a positive electrode active material, particles of lithium nickel cobalt manganese composite oxide represented by the formula LiNi _0.5 Co _0.2 Mn _0.3 O ₂ were prepared. In addition, acetylene black as a conductive agent and polyvinylidene fluoride (PVdF) as a binder were prepared. These were mixed so that the mass ratio of positive electrode active material:conductive agent:binder was 90:5:5 to obtain a mixture. Next, the resulting mixture was dispersed in n-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This slurry was applied onto both sides of a current collector made of aluminum foil having a thickness of 15 μm, and the coating film was dried. In this way, a composite including a current collector and positive electrode active material-containing layers formed on both sides of the current collector was obtained. The coating amount per one side of the positive electrode active material-containing layer was 100 g/m ² . The width of the positive electrode was adjusted using a slit device, and the width of the positive electrode coating was 80 mm, and the width of the aluminum foil not coated with the electrode was 10 mm. Next, the obtained composite was subjected to a roll press so that the density of the positive electrode active material-containing layer was 3.05 g/cm ³ . Next, this composite was further subjected to vacuum drying to obtain a positive electrode.

<Manufacture of electrode group>
A polyethylene separator having a thickness of 15 μm was prepared. Next, the prepared separator, the negative electrode, and the positive electrode were laminated in the order of negative electrode, separator, positive electrode, and separator to obtain a laminate. Next, this laminate was spirally wound so that a part of the negative electrode was located at the outermost position, to obtain a wound body. The number of turns of the wound body was 60. Next, this wound body was pressed. The wound body was pressed at room temperature (25° C.) by applying a load of 80 kN for 1 minute. In this way, an electrode group was manufactured.

When the electrode group was disassembled, it was confirmed that there were cut portions (cuts) in the negative electrodes with the number of turns up to 3 from the innermost part. Furthermore, the length of the cut portion (average total length of the cut _portion / The first length L _A ) was confirmed.

<Preparation of non-aqueous electrolyte>
A non-aqueous electrolyte was prepared according to the following procedure. First, propylene carbonate (PC) and diethyl carbonate (DEC) were mixed at a volume ratio of PC:DEC of 1:2 to obtain a mixed solvent. Lithium hexafluorophosphate LiPF ₆ was dissolved in this mixed solvent at a concentration of 1M to obtain a liquid nonaqueous electrolyte.

<Battery assembly>
The electrode group manufactured as described above was inserted into a container made of laminate film. The liquid nonaqueous electrolyte prepared as described above was poured into the container. In this way, the electrode group retained the non-aqueous electrolyte. Next, a non-aqueous electrolyte battery was obtained by sealing the container.

(Example 2)
An electrode group and a non-aqueous electrolyte battery were manufactured in the same manner as in Example 1, except that the negative electrode density was adjusted to 2.6 g/cm ³ . When the electrode group was disassembled, it was confirmed that the negative electrode with the number of turns up to 6 from the innermost part had a cut portion.

(Example 3)
An electrode group and a non-aqueous electrolyte battery were manufactured in the same manner as in Example 1, except that the negative electrode density was adjusted to 2.7 g/cm ³ . When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 12 from the innermost part had cut portions.

(Example 4)
The electrode group and non-aqueous electrolyte battery were assembled in the same manner as in Example 1, except that when pressing the rolled negative electrode, positive electrode, and separator laminate, a load of 80 kN was applied for 3 minutes. Manufactured. When the electrode group was disassembled, it was confirmed that the negative electrode with the number of turns up to 6 from the innermost part had a cut portion.

(Example 5)
The electrodes were prepared in the same manner as in Example 1, except that when pressing the rolled negative electrode, positive electrode, and separator laminate, the temperature was set at 60°C and a load of 80 kN was applied for 1 minute. Groups and non-aqueous electrolyte batteries were manufactured. When the electrode group was disassembled, it was confirmed that the negative electrode with the number of turns up to 2 from the innermost part had a cut portion.

(Example 6)
Particles of a monoclinic niobium titanium composite oxide having a composition represented by TiNb ₂ O ₇ were prepared. The prepared composite oxide particles had a primary particle shape and an average particle diameter of 1 μm. The composite oxide particles were used as the negative electrode active material particles in place of those used in Example 1, and the electrode was formed in the same manner as in Example 1, except that the negative electrode density was adjusted to 2.6 g/ ^cm3 . Groups and non-aqueous electrolyte batteries were manufactured. When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 10 from the innermost part had cut portions.

(Example 7)
Particles of a monoclinic niobium titanium composite oxide having a composition represented by TiNb ₂ O ₇ were prepared. The prepared composite oxide particles had a primary particle shape and an average particle diameter of 6 μm. The composite oxide particles were used as the negative electrode active material particles in place of those used in Example 1, and the electrode was formed in the same manner as in Example 1, except that the negative electrode density was adjusted to 2.6 g/ ^cm3 . Groups and non-aqueous electrolyte batteries were manufactured. When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 5 from the innermost part had cut portions.

(Example 8)
The same procedure as in Example 1 was carried out, except that an aluminum foil with a thickness of 20 μm was used as the negative electrode current collector instead of that used in Example 1, and the negative electrode density was adjusted to 2.7 g/cm ³ . An electrode group and a non-aqueous electrolyte battery were manufactured according to the procedure. When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 7 from the innermost part had a cut portion.

(Example 9)
An electrode group and a nonaqueous electrolyte battery were prepared in the same manner as in Example 1, except that the mass ratio of negative electrode active material: acetylene black: carboxymethyl cellulose: styrene butadiene rubber was changed to 85:10:2.5:2.5. Manufactured. When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 9 from the innermost part had cut portions.

(Example 10)
An electrode group and a nonaqueous electrolyte battery were prepared in the same manner as in Example 1, except that the mass ratio of negative electrode active material: acetylene black: carboxymethyl cellulose: styrene butadiene rubber was changed to 85:8:3.5:3.5. Manufactured. When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 12 from the innermost part had cut portions.

(Example 11)
A rectangular Na-containing titanium-niobium composite oxide having a composition represented by Li ₂ Na _1.8 Ti _5.8 Nb _0.2 O ₁₄ was prepared as a negative electrode active material. The prepared composite oxide particles had a primary particle shape and an average particle diameter of 3 μm. These composite oxide particles were used in place of those used in Example 1 as negative electrode active material particles, and the coating amount per side of the negative electrode active material containing layer was changed to 145 g/m ² . An electrode group and a non-aqueous electrolyte battery were manufactured in the same manner as in Example 1, except that the density was adjusted to 2.5 g/cm ³ . When the electrode group was disassembled, it was confirmed that the negative electrode with the number of turns up to 2 from the innermost part had a cut portion.

(Comparative example 1)
The electrode group and the non-aqueous electrolyte battery were prepared in the same manner as in Example 1, except that when pressing the laminate of the negative electrode, positive electrode, and separator after winding, a load of 30 kN was applied for 30 seconds. was manufactured. When the electrode group was disassembled, neither a notch nor a cut portion was observed.

(Comparative example 2)
An electrode group and a nonaqueous electrolyte battery were manufactured in the same manner as in Example 1, except that the mass ratio of negative electrode active material: acetylene black: carboxymethyl cellulose: styrene butadiene rubber was changed to 85:5:5:5. When the electrode group was disassembled, it was confirmed that the negative electrodes with the number of turns up to 16 from the innermost part had cut portions.

(Comparative example 3)
An electrode group and a nonaqueous electrolyte battery were manufactured in the same manner as in Comparative Example 1, except that the negative electrode density was adjusted to 2.3 g/cm ³ . When the electrode group was disassembled, neither a notch nor a cut portion was observed.

<Evaluation>
Using the non-aqueous electrolyte batteries manufactured in Example 1-11 and Comparative Example 1-3, output performance was evaluated as follows. The discharge capacity was measured when discharging from a fully charged state to a discharged state at a 0.2C rate and a 5C rate, respectively. The ratio of the discharge capacity when discharging at a 5C rate to the discharge capacity when discharging at a 0.2C rate ([5C discharge capacity / 0.2C discharge capacity] x 100%), that is, the 5 C / 0.2 C discharge capacity ratio Calculated.

Specifically, charging and discharging were performed under the following conditions, and the discharge capacity was measured during discharge. Charging was performed in constant current/constant voltage mode. The charging rate was 1C. The charging voltage was set to 2.85V. The charging termination condition was the time when the current value reached 0.05C. Discharge was performed in constant current mode at the above discharge rates (0.2 C and 5 C). The discharge end voltage was set to 1.5V.

Tables 1 and 2 below summarize the designs of the electrode groups and non-aqueous electrolyte batteries produced, details of the cut portions confirmed in the disassembled electrode groups, and evaluation results of the non-aqueous electrolyte batteries. Table 1 summarizes the details of the negative electrode. The details of the negative electrode include the composition of the negative electrode active material, the average particle diameter of the negative electrode active material particles (average primary particle diameter), the content of the negative electrode active material, the content of the conductive agent, the content of the binder, and the negative electrode active material. Table 1 shows the density of the containing layer. Table 2 shows the conditions of the press performed after winding the laminate of the negative electrode, positive electrode, and separator when manufacturing the electrode group, the details of the cut part confirmed in the electrode group, and the output of the nonaqueous electrolyte battery. Summarize performance. Pressing conditions include pressing temperature, pressing load, and pressing time. The details of the cut portions in the electrode group are the number of negative electrodes cut from the innermost circumferential side and the value (unit for t) obtained by converting this number of cuts into thickness as described above. Table 2 shows the 5 C/0.2 C discharge capacity ratio as output performance.

Table 3 below shows the length of the cut portion in each electrode group as a ratio to the length of the electrode group (first length _LA ) in the winding axis direction. In addition, the dimensions of the electrode group (first length L _A /second length L _B ) are also shown.

As shown in the table above, when comparing Examples 1-3, it can be seen that the number of cut electrodes increases as the negative electrode density increases. Specifically, as the density increased, the portion where the cut portion was visible expanded to thicknesses of 0.05t, 0.1t, and 0.2t from the innermost circumferential side of the electrode group. The 5 C / 0.2 C discharge capacity ratio increases from Example 1 to Example 3, which indicates that the battery resistance becomes lower when the proportion of the cut portion becomes 0.1 t, and further 0.2 t, than the thickness of 0.05 t. It was done.

In the comparison between Example 1 and Example 4 and the comparison between Example 2 and Example 6, by increasing the pressing time of the electrode group and decreasing the particle size of the negative electrode active material, It was confirmed that the proportion of the cut portion in the thickness direction increased. It was confirmed that in Examples 4 and 6 as well, the 5 C/0.2 C discharge capacity ratio was higher than in Examples 1 and 2, respectively.

In Example 7, contrary to Example 6, it was confirmed that by increasing the particle size of the negative electrode active material, the proportion occupied by the cut portion decreased, and the 5 C / 0.2 C discharge capacity ratio decreased accordingly. It was done. Furthermore, in Example 8, it was confirmed that by increasing the thickness of the current collector, the proportion occupied by the cut portion was reduced. In Example 8, an improvement in the 5 C/0.2 C discharge capacity ratio was observed, which is presumed to be due to an increase in the proportion of the current collector, which is a conductive member, in the negative electrode.

Furthermore, it was confirmed that increasing the amount of the conductive agent or binder contained in the electrode as in Examples 9 and 10 also increased the proportion of the cut portion in the thickness direction. It was confirmed that the 5 C/0.2 C discharge capacity ratio was also higher in Examples 9 and 10 than in Example 1.

Example 11 is an example using a different type of negative electrode active material from Examples 1-10. In Example 11 as well, a cut portion was formed at a distance of 0.2t from the innermost circumference of the electrode group, and a 5 C/0.2 C discharge capacity ratio comparable to that of Examples 1-10 was obtained.

In Comparative Examples 1 and 3, it was confirmed that if the pressing of the electrode group was insufficient, cuts such as cuts and notches were not formed in the innermost portion of the electrode group. In Comparative Examples 1 and 3, the 5 C/0.2 C discharge capacity ratio was lower than that in Examples 1-10, indicating that the battery resistance was higher. From these results, it was found that in the electrode groups manufactured in Comparative Examples 1 and 3, the innermost part of the negative electrode was left intact in the arc-shaped part where the charge/discharge reaction was difficult to proceed. It is assumed that the output performance was limited.

In Comparative Example 2, when the amount of binder was excessive, cuts were formed over a wider range along the thickness of the electrode group, beyond the area up to 0.2t from the innermost circumference of the electrode group. It was confirmed that In Comparative Example 2, the 5 C/0.2 C discharge capacity ratio was lower than that in Examples 1-10, indicating that the battery resistance was higher. From the results, it is presumed that in the electrode group manufactured in Comparative Example 2, the electron conduction path in the negative electrode was impaired and the battery resistance increased.

According to one or more embodiments and examples described above, an electrode group is provided. The electrode group includes a positive electrode and a negative electrode. The negative electrode includes a titanium-containing oxide. The electrode group includes a laminate including a positive electrode and a negative electrode. The electrode group has a flat wound structure in which the laminate is wound so that its center is located along the first direction. The winding cross section perpendicular to the first direction of the winding structure includes an innermost periphery and an outermost periphery. At least a part of the part of the negative electrode located along the longest straight line within a thickness of 0.2t relative to the thickness t from the innermost circumference to the outermost circumference along the longest straight line in the wound cross section. has a cut along the first direction. In such an electrode group, battery resistance is suppressed, and a secondary battery and battery pack with excellent output performance can be provided, and a vehicle including this battery pack can be provided.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1... Electrode group, 2... Exterior member, 3... Negative electrode, 3a... Negative electrode current collector, 3b... Negative electrode active material containing layer, 4... Separator, 5... Positive electrode, 5a... Positive electrode current collector, 5b... Positive electrode active material containing Layer, 6...Negative electrode terminal, 7...Positive electrode terminal, 8...Cut, 9...Space, 11...First direction, 12...Second direction, 13...Curved surface portion, 14...Flat portion, 15...Innermost periphery, 16... Outermost periphery, 21... Bus bar, 22... Positive electrode side lead, 22a... Other end, 23... Negative electrode side lead, 23a... Other end, 24... Adhesive tape, 31... Container, 32... Lid, 33... Protective sheet, 34... Printed wiring board, 35... Wiring, 40... Vehicle main body, 41... Vehicle power supply, 42... Electric control device, 43... External terminal, 44... Inverter, 45... Drive motor, 100... Secondary battery, 200... Assembled battery, 200a... assembled battery, 200b... assembled battery, 200c... assembled battery, 300... battery pack, 300a... battery pack, 300b... battery pack, 300c... battery pack, 301a... assembled battery monitoring device, 301b... assembled battery monitoring device, 301c ...Battery monitoring device, 342...Positive side connector, 343...Negative side connector, 345...Thermistor, 346...Protection circuit, 342a...Wiring, 343a...Wiring, 350...External terminal for energization, 352...Positive side terminal, 353 ...Negative side terminal, 348a...Plus side wiring, 348b...Minus side wiring, 400...Vehicle, 411...Battery management device, 412...Communication bus, 413...Positive terminal, 414...Negative terminal, 415...Switch device, 416...Current Detection unit, 417... Negative input terminal, 418... Positive input terminal, C... Winding shaft, L1... Connection line, L2... Connection line, W... Drive wheel.

Claims (12)

a positive electrode;
A negative electrode containing a titanium-containing oxide,
A laminate including the positive electrode and the negative electrode has a flat wound structure formed by winding the laminate so that the center thereof is located along the first direction,
A winding section of the winding structure perpendicular to the first direction includes an innermost periphery and an outermost periphery,
With respect to the thickness t from the innermost circumference to the outermost circumference along the longest straight line in the winding cross section, the thickness is within 0.2 t from the innermost circumference along the longest straight line among the negative electrodes. an electrode group in which at least a part of the portion located at has a cut along the first direction. A first length L _A of the electrode group in the first direction and a second length L B of the electrode group in a second direction parallel to the longest straight line are 1<L _A / _{L B} The electrode group according to claim 1, which satisfies the relationship <5. The electrode group according to claim 2, wherein the length of the cut is 0.3L _A or more and 0.8L _A or less with respect to the first length _LA . The titanium-containing oxide is represented by Li _x Ti _1-y M1 _y+z Nb _2-z O _7-δ , where M1 is selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. Claims 1 to 3, comprising at least one compound selected from the group consisting of 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. The electrode group according to any one of item 1. The titanium-containing oxide is represented by Li _2+a Mα _2-b Ti _6-c Mβ _d O _14+σ , where Mα is selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K. Mβ is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. Any one of claims 1 to 3, comprising a compound in which 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, -0.5≦σ≦0.5. The electrode group according to item 1. The electrode group according to any one of claims 1 to 5, wherein the positive electrode includes at least one selected from the group consisting of lithium manganese composite oxide and lithium nickel cobalt manganese composite oxide. The electrode group according to any one of claims 1 to 6,
A secondary battery comprising an electrolyte. A battery pack comprising the secondary battery according to claim 7. External terminal for energization,
The battery pack according to claim 8, further comprising a protection circuit. comprising a plurality of the secondary batteries,
The battery pack according to claim 8 or 9, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle comprising the battery pack according to any one of claims 8 to 10. The vehicle according to claim 11, including a mechanism that converts kinetic energy of the vehicle into regenerative energy.