JP7142585B2 - SECONDARY BATTERY AND METHOD FOR MANUFACTURING SECONDARY BATTERY - Google Patents

Description

The present disclosure relates to a secondary battery and a method for manufacturing the secondary battery.

For the purpose of improving the reliability of a secondary battery, it has been studied to provide a reference electrode in the battery to control the potentials of the positive and negative electrodes during charging and discharging. An example of the reference electrode is lithium titanate, and in order to stabilize the potential of the reference electrode, lithium titanate must be doped with lithium ions. In Patent Document 1, a reference electrode containing lithium titanate and a fourth electrode are installed in a battery, and after the battery is hermetically sealed, a voltage is applied between the reference electrode and the fourth electrode to A method of doping lithium ions into lithium oxide and a method of separately preparing a reference electrode doped with lithium ions and incorporating it into a secondary battery are disclosed.

Japanese Patent Publication No. 2010-539657

However, the method disclosed in Patent Document 1 has a problem that a space for the fourth electrode must be secured in the battery case. An object of the present disclosure is to provide a secondary battery in which a reference electrode can be doped with lithium ions by a simple method.

A secondary battery that is one aspect of the present disclosure includes an electrode body having a positive electrode and a negative electrode, a conductive battery case that houses the electrode body, and a composition formula Li _{4+x Ti 5} My O ₁₂ (wherein M is one or more elements selected from Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, 0.3≦x≦2.8 and 0≦y≦1); and, wherein the reference electrode layer is formed on the inner wall of the battery case and faces the positive electrode.

A method for manufacturing a secondary battery, which is one aspect of the present disclosure, comprises forming Li _{4+x Ti 5} My O ₁₂ (wherein M is Mg, Nb, Cu, Mn, Ni) on the inner wall of a conductive battery case. , Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, and 0≦x<0.3, 0 forming a reference electrode layer containing a compound that satisfies ≤ y ≤ 1; a step of housing the lithium ion-containing electrolyte into the battery case so that at least the reference electrode layer is immersed in the battery case; are respectively connected to the positive pole of the power source to dope the reference electrode layer with lithium ions.

According to one aspect of the present disclosure, it is possible to provide a secondary battery in which a reference electrode layer can be doped with lithium ions by a simple method.

1 is a perspective view of a secondary battery that is an example of an embodiment, showing the internal structure of a battery case and a first reference electrode formation region with the front side of a rectangular outer package removed. FIG. 1 is a perspective view of an electrode body that is an example of an embodiment; FIG. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1; FIG. 10 is a perspective view of a secondary battery that is another example of the embodiment, showing a first reference electrode formation region and a second reference electrode formation region with the front side of the rectangular outer package removed. . FIG. 3 is a cross-sectional view of a secondary battery that is another example of an embodiment; FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, showing a state when a reference electrode layer is doped with lithium ions;

When a secondary battery is overcharged, gas may be generated on the positive electrode side due to oxidative decomposition of the electrolyte, or the positive electrode active material may dissolve, and metallic lithium may precipitate on the negative electrode side. there is a possibility. Conventionally, overcharging is suppressed by monitoring the potential difference between the positive and negative electrodes, but the electrodes deteriorate with use. Battery reliability can be further improved. Patent Document 1 discloses a method of providing a reference electrode containing lithium titanate and a fourth electrode for doping the reference electrode with lithium ions. However, since the volume inside the battery case is very limited, installing the fourth electrode, which is used only for doping lithium ions before the actual use of the battery, will affect the output characteristics of the battery. There is a problem from your point of view.

A secondary battery that is one aspect of the present disclosure includes an electrode body having a positive electrode and a negative electrode, a conductive battery case that houses the electrode body, and a composition formula Li _{4+x Ti 5} My O ₁₂ (wherein M is one or more elements selected from Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, 0.3≦x≦2.8 and 0≦y≦1); and, wherein the reference electrode layer is formed on the inner wall of the battery case and faces the positive electrode.

Since the reference electrode layer and the positive electrode face each other through the electrolyte containing lithium ions, when a voltage is applied between the reference electrode layer and the positive electrode, the lithium ions contained in the electrolyte move to the reference electrode layer. Cheap. Therefore, since the reference electrode layer can be doped with a sufficient amount of lithium ions, the potential of the reference electrode layer is stabilized, and the potentials of the positive and negative electrodes can be measured with high accuracy.

An example of an embodiment of the present disclosure will be described in detail below. In this embodiment, a prismatic battery including a battery case 200 that is a prismatic metal case is exemplified, but the battery case is not limited to a prismatic shape. may be When using a battery case made of a laminate sheet, the resin layer should not be provided on the portion where the reference electrode layer is formed and the portion where the negative electrode of the power supply is brought into contact. Moreover, although the winding-type electrode body 3 is exemplified, a laminated-type electrode body may be used. In both the positive electrode and the negative electrode, the case where each active material layer is formed on both sides of each core is exemplified, but each active material layer is not limited to the case where it is formed on both sides of each core. It may be formed on at least one surface.

As exemplified in FIG. 1, the secondary battery 100 includes a wound electrode body 3 formed in a flat shape having a flat portion and a pair of curved portions, in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; It includes an electrolyte, and a battery case 200 that houses the electrode body 3 and the electrolyte. The battery case 200 includes a bottomed tubular prismatic exterior body 1 having an opening and a sealing plate 2 that seals the opening of the prismatic exterior body 1 . Both the rectangular exterior body 1 and the sealing plate 2 are made of metal, preferably aluminum or aluminum alloy.

The square exterior body 1 has a substantially rectangular bottom when viewed from the bottom, and side walls erected along the periphery of the bottom. The sidewalls are formed perpendicular to the bottom. Although the dimensions of the rectangular exterior body 1 are not particularly limited, for example, the lateral length is 60 to 160 mm, the height is 60 to 100 mm, and the thickness is 10 to 40 mm. In this specification, for convenience of explanation, the direction along the longitudinal direction of the bottom of the prismatic exterior body 1 is the "horizontal direction" of the prismatic exterior body 1, the direction perpendicular to the bottom is the "height direction", the lateral direction and the Let the direction perpendicular to the height direction be the “thickness direction”.

The electrolyte is a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents that can be used include carbonates, esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinylene carbonate; dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate; , ethyl propyl carbonate, and methyl isopropyl carbonate. The non-aqueous solvent may contain a halogen-substituted product obtained by substituting at least part of the hydrogen atoms of the above solvent with halogen atoms such as fluorine. Note that the electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like. Electrolyte salts include lithium salts. LiPF ₆ or the like, which is generally used as a supporting salt in the conventional secondary battery 100, can be used as the lithium salt. Additives such as vinylene carbonate (VC) can also be added as appropriate.

The positive electrode 4 is an elongated body having a positive electrode core made of metal and positive electrode active material layers 41 formed on both sides of the positive electrode core. A strip-shaped positive electrode core exposed portion 42 is formed through which the positive electrode core is exposed (see FIG. 2 described later). In this embodiment, the positive electrode active material layer 41 is provided on both surfaces of the positive electrode core body from the outer end to the inner end of the positive electrode 4 , that is, over both longitudinal ends of the positive electrode 4 . Similarly, the negative electrode 5 is a long body having a negative electrode core made of metal and negative electrode active material layers 51 formed on both sides of the negative electrode core. A strip-shaped negative electrode core exposing portion 52 is formed along which the negative electrode core is exposed. In this embodiment, the negative electrode active material layer 51 is provided on both surfaces of the negative electrode substrate from the outer end of the negative electrode 5 to the inner end of the negative electrode 5 , ie, across both longitudinal ends of the negative electrode 5 . The electrode body 3 has the positive electrode core exposed portion 42 and the negative electrode core exposed portion 52 disposed on the one end side in the winding axis direction and the negative electrode core exposed portion 52, respectively, on the other end side in the winding axis direction. has a wound structure.

The positive electrode current collector 6 is connected to the stacked portion of the positive electrode core exposed portion 42 , and the negative electrode current collector 8 is connected to the stacked portion of the negative electrode core exposed portion 52 . A suitable positive electrode current collector 6 is made of aluminum or an aluminum alloy. A suitable negative electrode current collector 8 is made of copper or a copper alloy. The positive electrode terminal 7 is inserted into a positive electrode external conductive portion 13 arranged on the battery exterior side of the sealing plate 2 , a positive electrode bolt portion 14 connected to the positive electrode external conductive portion 13 , and a through hole provided in the sealing plate 2 . The positive electrode insertion portion 15 is electrically connected to the positive electrode current collector 6 . The negative electrode terminal 9 is connected to a negative electrode external conductive portion 16 arranged on the battery exterior side of the sealing plate 2 , a negative electrode bolt portion 17 connected to the negative electrode external conductive portion 16 , and a through hole provided in the sealing plate 2 . It has a negative electrode insertion part 18 to be inserted, and is electrically connected to the negative electrode current collector 8 .

The positive electrode terminal 7 and the positive electrode current collector 6 are fixed to the sealing plate 2 via the inner side insulating member and the outer side insulating member, respectively. The inner insulating member is arranged between the sealing plate 2 and the positive electrode current collector 6 , and the outer insulating member is arranged between the sealing plate 2 and the positive electrode terminal 7 . Similarly, the negative electrode terminal 9 and the negative electrode current collector 8 are fixed to the sealing plate 2 via the inner side insulating member and the outer side insulating member, respectively. The inner insulating member is arranged between the sealing plate 2 and the negative electrode current collector 8 , and the outer insulating member is arranged between the sealing plate 2 and the negative electrode terminal 9 .

The electrode body 3 is accommodated in the rectangular exterior body 1 . The sealing plate 2 is connected to the edge of the opening of the rectangular exterior body 1 by laser welding or the like. The sealing plate 2 has an electrolyte pouring hole 10. After the electrolyte is injected into the battery case 200, the electrolyte pouring hole 10 is sealed with a sealing plug. The sealing plate 2 is formed with a gas discharge valve 11 for discharging gas when the pressure inside the battery reaches a predetermined value or higher.

The secondary battery 100, which is one aspect of the present disclosure, preferably further includes a porous electrode body holder 12 that is disposed between the electrode body 3 and the battery case 200 and through which lithium ions can pass (Fig. 3). By sandwiching the electrode body holder 12 between the electrode body 3 and the battery case 200, the contact between the electrode body 3 and the battery case 200 can be reliably prevented. The electrode body holder 12 is not particularly limited as long as it is porous and permeable to lithium ions. For example, an insulating porous sheet is used. The electrode body holder 12 is a porous material mainly composed of at least one selected from, for example, polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aramid. Polyolefins are preferred, especially polyethylene and polypropylene, including the substrate. Since the space between the electrode body 3 and the battery case 200 is narrow, it is preferable that the electrode body 3 be covered with the electrode body holder 12 and housed in the rectangular exterior body 1 .

The inner wall surface of the rectangular exterior body 1 has a first reference electrode formation region 20 . The first reference electrode forming region 20 is a region facing the positive electrode core exposed portion 42 . A reference electrode layer is formed in at least one of the first reference electrode formation region 20 and a second reference electrode formation region 21 to be described later.

The electrode body 3 and the reference electrode layer 60 will be described in detail below.

[Electrode body]
FIG. 2 is a perspective view of the electrode body 3, showing the electrode body 3 in the vicinity of the end of the winding. As exemplified in FIG. 1, the electrode body 3 includes the positive electrode 4 and the negative electrode 5 with the separator 30 interposed therebetween such that the positive electrode core exposed portion 42 and the negative electrode core exposed portion 52 are positioned on opposite sides in the axial direction. It has a wound structure. In the electrode body 3 , the negative electrode 5 is one size larger than the positive electrode 4 and is arranged so that the negative electrode active material layer 51 always exists in the region facing the positive electrode active material layer 41 . The electrode body 3 has, for example, an axial length of 50 to 150 mm, a width of 50 to 90 mm, and a thickness of 8 to 38 mm.

The positive electrode 4 has a positive electrode core and a positive electrode active material layer 41 provided on the positive electrode core. For the positive electrode core, a foil of a metal such as aluminum or an aluminum alloy that is stable in the potential range of the positive electrode 4, a film in which the metal is arranged on the surface layer, or the like can be used. The thickness of the positive electrode core is, for example, 10 to 20 μm. The positive electrode active material layer 41 contains a positive electrode active material, a conductive aid such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably provided on both sides of the positive electrode core. The thickness of the positive electrode active material layer 41 is, for example, 50 to 400 μm in total on both sides of the positive electrode core. The positive electrode 4 is formed by coating a positive electrode core with a positive electrode active material slurry containing a positive electrode active material, a conductive aid, a binder, and the like, drying the coating film, and then compressing the positive electrode active material layer 41 to form a positive electrode. It can be produced by forming on both sides of the core.

For example, a lithium metal composite oxide is used as the positive electrode active material. Metal elements contained in the lithium metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. are mentioned. An example of a suitable lithium metal composite oxide is a lithium metal composite oxide containing at least one of Ni, Co and Mn. Specific examples include lithium metal composite oxides containing Ni, Co and Mn, and lithium metal composite oxides containing Ni, Co and Al. Inorganic compound particles such as tungsten oxide, aluminum oxide, and lanthanide-containing compounds may adhere to the surfaces of the lithium metal composite oxide particles.

The negative electrode 5 has a negative electrode core and a negative electrode active material layer 51 provided on the negative electrode core. For the negative electrode core, a foil of a metal such as copper or a copper alloy that is stable in the potential range of the negative electrode 5, a film having the metal on the surface layer, or the like can be used. The thickness of the negative electrode core is, for example, 5 to 15 μm. The negative electrode active material layer 51 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably provided on both sides of the negative electrode core. The thickness of the negative electrode active material layer 51 is, for example, 50 to 400 μm in total on both sides of the negative electrode core. The negative electrode 5 is formed by applying a negative electrode active material slurry containing a negative electrode active material, a binder, etc. on the negative electrode core, drying the coating film, and then compressing the negative electrode active material layer 51 onto both sides of the negative electrode core. can be produced by forming

As the negative electrode active material, for example, graphite such as natural graphite such as flake graphite, massive graphite, and earthy graphite, massive artificial graphite, and artificial graphite such as graphitized mesophase carbon microbeads is used. As the negative electrode active material, a metal such as Si or Sn that is alloyed with lithium, an alloy containing the metal, a compound containing the metal, or the like may be used, and these may be used in combination with graphite. Specific examples of the compound include silicon compounds represented by SiO _x (0.5≦x≦1.6).

A porous sheet having ion permeability and insulation is used for the separator 30 . The separator 30 is a porous substrate containing at least one selected from, for example, polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aramid as a main component. with polyolefins being preferred, particularly polyethylene and polypropylene being preferred.

The separator 30 may be composed only of a resin-made porous substrate, or may have a multilayer structure in which a heat-resistant layer containing inorganic particles or the like is formed on at least one surface of the porous substrate. . Moreover, the resin-made porous substrate may have a multi-layer structure such as polypropylene/polyethylene/polypropylene. The thickness of the separator 30 is, for example, 10-30 μm. The separator 30 has, for example, an average pore diameter of 0.02 to 5 μm and a porosity of 30 to 70%. Generally, the wound electrode body 3 includes two separators 30, but each separator 30 can be the same.

The electrode body 3 is produced by pressing flat a wound body of the positive electrode 4 and the negative electrode 5 wound with the separator 30 interposed therebetween. In this case, for example, a cylindrical wound body is produced using a substantially cylindrical winding core, and after the winding core is removed, the wound body is radially pressed. Alternatively, the positive electrode 4 and the negative electrode 5 may be flatly wound using a flat winding core. In this case, after removing the winding core, it may be further pressed into a flat shape.

In FIG. 2, the outermost periphery of the electrode assembly 3 is the negative electrode 5 . In the present application, the outermost circumference means the positive electrode 4 or the negative electrode 5 arranged on the outermost side of the winding, and excludes the separator 30 . For example, when the outermost periphery of the electrode body 3 is the negative electrode 5 , it means that the negative electrode 5 covers substantially the entire outer surface of the electrode body 3 excluding core exposed portions of both electrodes. The outermost periphery of the electrode body 3 may be either the negative electrode core or the negative electrode active material layer 51 .

[Reference electrode layer]
The reference electrode layer 60 is an electrode that serves as a reference when measuring the absolute values of the potentials of the positive electrode 4 and the negative electrode 5 . Specifically, the potential of the positive electrode 4 with respect to the reference electrode layer 60 can be measured by measuring the voltage between the battery case 200 electrically connected to the reference electrode layer 60 and the positive electrode terminal 7 . The potential of the negative electrode 5 with respect to the reference electrode layer 60 can be calculated by subtracting the previously measured potential of the positive electrode 4 with respect to the reference electrode layer 60 from the separately measured cell voltage. Since the potentials of the positive electrode 4 and the negative electrode 5 are determined based on the potential of the reference electrode, it is preferable that the potential of the reference electrode layer 60 is stable. The reference electrode layer 60 has a composition formula of Li _{4+x Ti 5} My O ₁₂ (wherein M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, One or more elements selected from Y, La, Zn, Al, and Ga, satisfying 0.3 ≤ x ≤ 2.8 and 0 ≤ y ≤ 1, hereinafter sometimes referred to as "lithium titanate" including compounds consisting of The reference electrode layer 60 can be produced by applying a reference electrode slurry containing at least lithium titanate to a predetermined position on the inner wall of the battery case 200 and drying the applied film. The potential of the reference electrode layer 60 is stabilized by doping lithium ions into the lithium titanate contained in the reference electrode layer 60 thus fabricated. The lithium titanate of the above composition formula is lithium titanate after doping with lithium ions.

The reference electrode layer 60 preferably further contains a conductive aid in order to stabilize the potential of the reference electrode layer 60 . Examples of conductive aids include carbon materials such as carbon black, acetylene black, ketjen black, and graphite.

The reference electrode layer 60 can contain a binder such as styrene-butadiene rubber and polyvinylidene fluoride (PVdF), and a thickener such as carboxymethyl cellulose (CMC), in addition to lithium titanate and a conductive aid.

The thickness and size of the reference electrode layer 60 are not particularly limited as long as the potential of the reference electrode layer 60 is stable. For example, the thickness of the reference electrode layer 60 is preferably 1-200 μm, more preferably 1-50 μm, even more preferably 1-10 μm. The thickness of the reference electrode layer 60 is preferably 1 cm ² to 400 cm ² , more preferably 3 cm ² to 150 cm ² , and even more preferably 5 cm ² to 25 cm. Moreover, the proportion of lithium titanate contained in the reference electrode layer 60 is preferably 90% by mass or more.

The position where the reference electrode layer 60 is formed will be described with reference to FIG. FIG. 3 is a cross-sectional view taken along line AA in FIG. The electrode body 3 is installed substantially in the center of the rectangular outer body 1 in the thickness direction so as not to contact the rectangular outer body 1, and is fixed to the sealing plate 2 via a positive electrode current collector 6 (not shown). there is The reference electrode layer 60 is formed on the inner wall of the battery case 200 , more specifically, on the inner sidewall or bottom of the rectangular exterior body 1 . By forming the reference electrode layer 60 in a layered manner on the prismatic exterior body 1, it can be electrically connected to the prismatic exterior body 1, and the volume inside the battery case 200 is not reduced.

The electrode body 3 is a wound type in which the positive electrode 4 and the negative electrode 5 are wound with the separator 30 interposed therebetween. The electrode body 3 has a positive electrode core exposure portion 42 at one end in the winding direction, and has a negative electrode core exposure portion 52 at the other end in the winding direction. Further, the outermost periphery of the electrode body 3 is the negative electrode 5 , and the reference electrode layer 60 faces the positive electrode core exposed portion 42 .

As shown in FIG. 2 , the outermost periphery of the electrode body 3 is the negative electrode 5 , and the portion of the electrode body 3 where the positive electrode 4 exists on the outside of the winding is the positive electrode core exposed portion 42 . In this case, the reference electrode layer 60 is formed at a position facing the positive electrode core exposed portion 42, in other words, at the first reference electrode formation region 20 in FIG. Since the electrolyte containing lithium ions is present between the reference electrode layer 60 and the positive electrode 4 , when a voltage is applied between the reference electrode layer 60 and the positive electrode 4 , the lithium ions contained in the electrolyte are transferred to the reference electrode layer 60 . Easy to move to. Therefore, the reference electrode layer 60 can be doped with a sufficient amount of lithium ions.

Although the separator 30 is laminated on the outermost negative electrode 5 in FIG. 2 , the separator 30 may not be laminated on the negative electrode 5 . In this case, the separator 30 laminated on the negative electrode 5 in FIG. 2 is laminated under the positive electrode 4, or the length of the separator 30 laminated on the negative electrode 5 is shortened. can be done.

<Another example of the embodiment>
FIG. 4 is a perspective view of a secondary battery that is another example of the embodiment, showing a first reference electrode forming region 20 and a second reference electrode forming region 21. As shown in FIG. The second reference electrode formation region 21 is a part of the inner wall surface of the rectangular outer casing 1 and is a region that faces the part of the electrode body 3 excluding the positive electrode core exposed portion 42 and the negative electrode core exposed portion 52 . . 3, the reference electrode layer 60 is formed on the inner wall of the battery case 200, more specifically, on the inner side wall or bottom of the rectangular exterior body 1. As shown in FIG.

The electrode body 3 is a wound type in which the positive electrode 4 and the negative electrode 5 are wound with the separator 30 interposed therebetween, and has a positive electrode core exposed portion 42 and a negative electrode core exposed portion 52 at both ends in the direction of the winding axis. , the outermost periphery of the electrode body 3 is the positive electrode 4 , and the reference electrode layer 60 faces the portion of the electrode body 3 excluding the negative electrode core exposed portion 52 .

When the outermost periphery of the electrode body 3 is the positive electrode 4 , the positive electrode 4 exists on the outer side of the winding of the electrode body 3 except for the negative electrode core exposure portion 52 of the electrode body 3 . In this case, the reference electrode layer 60 is located at a position facing the portion of the electrode body 3 excluding the negative electrode substrate exposed portion 52, in other words, the first reference electrode formation region 20 or the second reference electrode formation region 21 in FIG. formed in Therefore, the position for forming the reference electrode layer 60 can be selected in a wider range than in the case where the outermost circumference is the negative electrode 5 . Further, when the outermost periphery of the electrode body 3 is the positive electrode active material layer 41, the negative electrode active material layer 51 does not exist in the region facing the outermost positive electrode active material layer 41, so the outermost periphery of the electrode body 3 is the positive electrode core. is preferably

Separator 30 is preferably laminated on the outermost periphery. In this case, the contact of the outermost periphery with the rectangular exterior body 1 can be avoided. Note that even when the electrode body holder 12 is between the electrode body 3 and the rectangular exterior body 1, the separator 30 may be laminated on the outermost periphery.

As illustrated in FIG. 5, the reference electrode layer 60 is preferably at least partially formed on the side surface of the bottom side when the secondary battery 100 is divided in half at the center in the height direction. It is more preferable that at least a portion is formed on the side surface closest to the bottom when the battery 100 is divided into four equal parts in the height direction. By forming the reference electrode layer 60 on the bottom side of the prismatic outer casing 1 even when there is a portion not filled with the electrolyte in the battery case 200, the electrolyte is formed between the reference electrode layer 60 and the positive electrode 4. can be ensured to exist.

[Method for manufacturing secondary battery]
The secondary battery 100 having the configuration described above is manufactured, for example, through the following steps.
(1) On the inner wall of the conductive battery case 200, a composition formula _{Li4 + xTi5MyO12 (} wherein M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, one or more elements selected from Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, satisfying 0≦x<0.3 and 0≦y≦1). forming a reference electrode layer 60 comprising;
(2) The electrode body 3 having the positive electrode 4 and the negative electrode 5 is placed in the battery case 200 via the porous electrode body holder 12 adjacent to the outside of the electrode body 3 so that the positive electrode 4 faces the reference electrode layer 60 . The process of housing in
(3) A step of injecting an electrolyte containing lithium ions into the battery case 200 so that at least the reference electrode layer 60 is immersed.
(4) A step of doping the reference electrode layer 60 with lithium ions by connecting the battery case 200 to the negative electrode of the power source and the positive electrode 4 to the positive electrode of the power source, respectively (see FIG. 6).

In particular, the step of doping the reference electrode layer 60 with lithium ions in the manufacturing method of the secondary battery 100 will be described with reference to FIG. Through the steps (1) to (3) described above, the battery case 200 having the rectangular outer body 1 and the sealing plate 2 contains the reference electrode layer 60 formed on the side wall or the bottom surface of the rectangular outer body 1. , the electrode body 3 is fixed to the sealing plate 2 via the positive electrode current collector 6 and the negative electrode current collector 8 so as not to come into contact with the battery case 200 . The positive electrode 4 on the outer side of the electrode body 3 and the reference electrode layer 60 face each other, and an electrolyte containing lithium ions is present between the reference electrode layer 60 and the positive electrode 4 .

Next, in step (4) described above, the battery case 200 is connected to the negative pole of the power supply, and the positive electrode 4 is connected to the positive pole of the power supply. Specifically, the negative pole of the power supply is connected to either the rectangular exterior body 1 or the sealing plate 2 included in the battery case 200 , while the positive pole of the power supply is connected to the positive terminal 7 . Since a potential difference is generated between the reference electrode layer 60 on the battery case 200 and the positive electrode 4 connected to the positive electrode terminal 7, the lithium ions in the electrolyte are attracted to the reference electrode layer 60 on the negative electrode side, The lithium titanate contained in the electrode layer 60 is doped with lithium ions. Since lithium titanate doped with lithium ions stabilizes the potential, the reference electrode layer 60 can be used as a reference electrode for measuring the potential of the positive electrode 4 or the negative electrode 5 .

A step of sealing the battery case 200 can be performed before the step (4). A step of sealing the battery case 200 may be performed after the step (4). For example, the electrolyte injection hole 10 of the battery case 200 may be sealed after the reference electrode layer 60 is doped with lithium ions while the electrolyte injection hole 10 of the battery case 200 is not sealed. In this case, it is preferable to dope the reference electrode layer 60 with lithium ions in a dry environment. However, by performing the step of sealing the battery case 200 before the step (4), the lithium-doped reference electrode layer 60 does not come into contact with moisture in the atmosphere, and the potential of the reference electrode layer 60 is becomes more stable. Therefore, it is more preferable to perform the step of sealing the battery case 200 before the step (4).

EXAMPLES The present disclosure will be further described below with reference to Examples, but the present disclosure is not limited to these Examples. Further, the secondary batteries according to each example and each comparative example were produced in a non-dry environment without using a dry room, and the secondary batteries according to reference examples were produced under a controlled dry environment in a dry room. .

<Example 1>
[Preparation of positive electrode]
As a positive electrode active material, lithium metal composite oxide particles represented by LiNi _0.35 Co _0.35 Mn _0.30 O ₂ were used. The positive electrode active material, polyvinylidene fluoride dispersed in N-methyl-2-pyrrolidone (NMP), and acetylene black were mixed at a solid content mass ratio of 91:2:7 to form a positive electrode active material slurry. prepared. Next, the positive electrode active material slurry was applied to both surfaces of a positive electrode core made of an aluminum alloy and having a thickness of 15 μm, and the coating film was vacuum-dried to remove NMP by volatilization. However, the cathode active material slurry was not coated on both sides of the positive electrode core at one end along the longitudinal direction, and the positive electrode core was exposed to provide a positive electrode core exposed portion. After compressing the dried coating film using a rolling roll, it was cut into a predetermined electrode plate size to prepare a positive electrode plate having positive electrode active material layers formed on both sides of a positive electrode current collector.

[Preparation of negative electrode]
Natural graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed at a solid content mass ratio of 98:1:1, and an appropriate amount of water was added to prepare a negative electrode active material slurry. Next, the negative electrode active material slurry was applied to both sides of a negative electrode core made of a copper foil having a thickness of 8 μm, and the coating film was vacuum-dried to remove water by volatilization. However, a negative electrode core exposed portion was provided by exposing the negative electrode core without coating the negative electrode active material slurry on both sides of the negative electrode core along one end along the longitudinal direction. After compressing the dried coating film using rolling rolls, it was cut into a predetermined electrode size to produce a negative electrode in which a negative electrode active material layer was formed on both sides of a rectangular negative electrode core.

[Fabrication of electrode body]
The positive electrode and the negative electrode were wound with a strip separator made of a polyethylene/polypropylene microporous film interposed therebetween such that the core exposed portions were located on opposite sides of the wound body in the axial direction. After that, the wound body was radially pressed to form a flat shape, thereby producing a wound electrode body. The wound body was formed by winding a stack of separator/positive electrode/separator/negative electrode in this order from the inside of the roll around a cylindrical winding core (the same separator was used for the two separators). The outermost periphery of the electrode body was used as the negative electrode.

[Preparation of reference electrode]
Lithium titanate having the composition formula Li ₄ Ti ₅ O ₁₂ , carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed at a solid content mass ratio of 98.9:0.7:0.4, An appropriate amount of water was added to prepare a reference electrode slurry. Next, the reference electrode slurry was applied to the inner wall of the side surface of the battery case so as to face the exposed portion of the positive electrode core so that the application amount was 1 mg/cm ² . After that, the battery case was dried to remove the water used as the dispersion medium when preparing the reference electrode slurry, thereby producing a reference electrode layer. The formation area of the reference electrode layer was 8 cm ² .

[Preparation of electrolyte]
Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 3:3:4 (25° C., 1 atm). LiPF ₆ was dissolved in the mixed solvent at a concentration of 1 mol/L, and vinylene carbonate (VC) was added in an amount of 0.3% by mass relative to the total mass of the electrolyte to prepare an electrolyte.

[Production of secondary battery]
A secondary battery (a prismatic battery) was produced using the electrode body, the electrolyte, and a prismatic battery case made of aluminum. The electrode body was covered with a porous electrode body holder, and a rectangular bottomed cylindrical outer can (lateral length 148.0 mm (inner dimension 146.8 mm), thickness 17.5 mm (inner dimension 16.8 mm) constituting a battery case was used. 5 mm) and 65.0 mm in height (inner dimension 64.0 mm)). A positive electrode terminal was attached to a sealing plate constituting a battery case, and a positive current collector was connected to the positive electrode terminal. A negative electrode terminal was attached to the sealing plate, and a negative electrode current collector was connected to the negative electrode terminal. Then, the positive electrode current collector was welded to the positive electrode core exposed portion, and the negative electrode current collector was welded to the negative electrode core exposed portion. The electrolyte was injected into the outer can, and the opening of the battery case was closed with a sealing plate.

[Lithium ion doping to reference electrode layer]
By connecting the battery case of the prepared secondary battery to the negative electrode of the power supply and the positive electrode terminal to the positive electrode of the power supply, and charging at 0.0015 It (7.5 mA) for 60 seconds, lithium was added to the reference electrode layer. doped with ions. The potential of the reference electrode layer after doping with lithium ions is assumed to be 1.55V.

<Example 2>
The solid content mass ratio of the reference electrode slurry was 96.9:2.96.9 with lithium titanate of the composition formula Li ₄ Ti ₅ O ₁₂ , acetylene black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). A secondary battery was produced in the same manner as in Example 1, except that the ratio was changed to 0:0.7:0.4.

<Comparative Examples 1 to 3>
In Comparative Examples 1 to 3, secondary batteries were produced in the same manner as in Example 1, except for the following changes.
(1) Comparative Example 1: No reference electrode layer was produced.
(2) Comparative Example 2: A reference electrode layer was formed at a position not facing the exposed portion of the positive electrode core.
(3) Comparative Example 3: The reference electrode layer was formed at a position not facing the exposed portion of the positive electrode core, and the reference electrode layer was not doped with lithium ions.

<Reference example>
After manufacturing the reference electrode layer and before manufacturing the secondary battery, the electrolyte was injected into the outer can, and a separately prepared lithium electrode was inserted so as to face the reference electrode layer via a porous electrode body holder. The outer can was connected to the negative electrode of the power source, the lithium electrode was connected to the positive electrode of the power source, and the reference electrode layer was doped with lithium ions by charging at 0.0015 It (7.5 mA) for 60 seconds. After that, the lithium electrode was removed, and a secondary battery was produced.

10 cells each of the secondary batteries of Examples 1 and 2, Comparative Examples 1 and 3, and Reference Example were prepared, and the stability of the reference electrode layer was evaluated by the following method. The evaluation results are shown in Table 1. rice field.

[Evaluation of stability of reference electrode layer]
Each secondary battery was charged at a constant current of 1 It (5 A) in a temperature environment of 25° C. and then charged at a constant voltage of 3.52 V for 2.5 hours to set the depth of charge (SOC) to 20%. After standing at room temperature for 2.5 hours, the voltage of the positive electrode with respect to the battery case (positive electrode/battery case) was measured. The voltage of the negative electrode with respect to the battery case (negative electrode/battery case) was calculated by subtracting the voltage of the positive electrode with respect to the battery case from the separately measured cell voltage. From the measurement results of 10 cells, the average value of the positive electrode/battery case and the negative electrode/battery case and the standard deviation of the positive electrode/battery case were calculated. In addition, the SOC of the secondary battery was set to 50% in the same manner as in the case of the SOC of 20% except that the voltage during constant-voltage charging was set to 3.69V, and the measurement was performed in the same manner. In addition, the SOC of the secondary battery was set to 80% in the same manner as in the case of the SOC of 20% except that the voltage during constant voltage charging was set to 3.91 V, and the measurement was performed in the same manner.

The secondary batteries of Comparative Examples 1 to 3 all showed different potentials of the positive electrode/battery case and negative electrode/battery case from the secondary batteries of the reference example produced in a dry environment, and the standard deviation was large and unstable.

On the other hand, in the secondary battery of Example 1, substantially the same potentials and standard deviations of the positive electrode/battery case and negative electrode/battery case were obtained as in the secondary battery of the reference example fabricated in a dry environment. In the secondary battery of Example 1, an electrode body having a positive electrode and a negative electrode, a conductive battery case containing the electrode body, and a composition formula _{Li4 + xTi5MyO12 (} wherein M is Mg, Nb , Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, Al, and Ga, and 0.3 ≤ x ≤ 2.8 and 0 ≤ y ≤ 1); , the reference electrode layer is formed on the inner wall of the battery case, and by facing the positive electrode, it is possible to provide a secondary battery in which the reference electrode layer can be doped with lithium ions by a simple method. Furthermore, in the secondary battery of Example 2, the standard deviation was smaller than that of Example 1 and became stable. In order to make the potential more stable, the reference electrode layer preferably further contains a conductive aid.

1 square exterior body, 2 sealing plate, 3 electrode body, 4 positive electrode, 5 negative electrode, 6 positive electrode current collector, 7 positive electrode terminal, 8 negative electrode current collector, 9 negative electrode terminal, 10 electrolyte injection hole, 11 gas discharge valve, 12 electrode body holder 13 positive electrode external conductive portion 14 positive electrode bolt portion 15 positive electrode insertion portion 16 negative electrode external conductive portion 17 negative electrode bolt portion 18 negative electrode insertion portion 20 first reference electrode forming region 21 second Reference electrode formation region 30 Separator 41 Positive electrode active material layer 42 Positive electrode core exposed portion 51 Negative electrode active material layer 52 Negative electrode core exposed portion 60 Reference electrode layer 100 Secondary battery 200 Battery case

Claims (8)

an electrode body having a positive electrode and a negative electrode;
a conductive battery case housing the electrode body;
Composition formula Li _{4+x Ti 5} My O ₁₂ (wherein M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, a reference electrode layer containing a compound consisting of one or more elements selected from Al and Ga and satisfying 0.3≦x≦2.8 and 0≦y≦1;
an electrolyte comprising lithium ions disposed within the battery case such that the reference electrode layer is submerged;
The electrode body is a wound type in which the positive electrode and the negative electrode are wound with a separator interposed therebetween, and has a positive electrode core exposed portion at one end in the direction of the winding axis and the other end in the direction of the winding axis. has a negative electrode core exposed part in the part,
The outermost periphery of the electrode body is the negative electrode,
The secondary battery, wherein the reference electrode layer is formed on the inner wall of the battery case and faces the positive electrode substrate exposed portion . an electrode body having a positive electrode and a negative electrode;
a conductive battery case housing the electrode body;
Composition formula Li _{4+x Ti 5} My O ₁₂ (wherein M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, V, Sc, Y, La, Zn, a reference electrode layer containing a compound consisting of one or more elements selected from Al and Ga and satisfying 0.3≦x≦2.8 and 0≦y≦1;
an electrolyte comprising lithium ions disposed within the battery case such that the reference electrode layer is submerged;
The electrode body is a wound type in which the positive electrode and the negative electrode are wound with a separator interposed therebetween, and has a positive electrode core exposed portion at one end in the direction of the winding axis and the other end in the direction of the winding axis. has a negative electrode core exposed part in the part,
The outermost periphery of the electrode body is the positive electrode,
The reference electrode layer is formed on the inner wall of the battery case, and faces a portion of the electrode body excluding the negative electrode substrate exposed portion of the secondary battery. 3. The secondary battery according to claim 1, further comprising a porous electrode body holder arranged between said electrode body and said battery case and through which lithium ions can pass. The secondary battery according to any one of claims 1 to 3 , wherein said separator is laminated on said outermost periphery. The secondary battery according to any one of claims 1 to 4 , wherein the reference electrode layer further contains a conductive aid. The secondary battery according to any one of claims 1 to 5 , wherein at least part of the reference electrode layer is formed on the side surface of the bottom side when the secondary battery is divided in half at the center in the height direction. next battery. Li _{4+x Ti 5} My O ₁₂ (wherein M is Mg, Nb, Cu, Mn, Ni, Fe, Ru, Zr, B, Ca, Co, Cr, one or more elements selected from V, Sc, Y, La, Zn, Al, and Ga and satisfying 0≦x<0.3 and 0≦y≦1. forming a
housing an electrode body having a positive electrode and a negative electrode in the battery case via a porous electrode body holder adjacent to the outside of the electrode body so that the positive electrode faces the reference electrode layer;
injecting an electrolyte containing lithium ions into the battery case so that at least the reference electrode layer is immersed;
connecting the battery case to a negative electrode of a power source, connecting the positive electrode to a positive electrode of the power source, and doping the reference electrode layer with lithium ions. 8. The method of manufacturing a secondary battery according to claim 7 , further comprising the step of sealing the battery case before the step of doping the reference electrode layer with lithium ions.

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