JP6790877B2 - Non-aqueous electrolyte power storage element and its manufacturing method - Google Patents

Description

The present invention relates to a non-aqueous electrolyte power storage device and a method for manufacturing the same.

Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally includes an electrode body having a pair of electrodes electrically separated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge by doing so. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than secondary batteries.

The electrode provided in such a non-aqueous electrolyte power storage element generally has a structure in which a mixture layer containing an active material is formed on the surface of a conductive base material such as a metal foil. This mixture layer is formed by applying a slurry-like mixture containing an active material and drying it. For example, in Patent Document 1, a carbon material (amorphous carbon) having an interlayer distance of 0.340 to 0.370 nm as a negative electrode active material, polymer particles as a binder, and a thickener having a specific degree of polymerization. A slurry composition for a negative electrode of a lithium ion secondary battery containing the above, and a negative electrode of a lithium ion secondary battery obtained from the slurry composition have been proposed.

International Publication No. 2011/096463

In the non-aqueous electrolyte power storage element, it is preferable that the output resistance is low in order to enhance the output characteristics. Output resistance tends to decrease by using amorphous carbon with a small particle size, but there is a concern that the life characteristics will decrease. Therefore, a technique for lowering the output resistance while using amorphous carbon particles having substantially the same size is desired.

The present invention has been made based on the above circumstances, and an object of the present invention is a non-aqueous electrolyte power storage device using amorphous carbon as a negative electrode active material, and an amorphous carbon of the same size is used. It is an object of the present invention to provide a non-aqueous electrolyte power storage element capable of lowering the initial low temperature output resistance compared in the case of use, and a method for manufacturing such a non-aqueous electrolyte power storage element.

One aspect of the present invention made to solve the above problems is a non-aqueous electrolyte power storage element including a negative electrode containing amorphous carbon and styrene-butadiene rubber having a glass transition point of 40 ° C. or higher.

Another aspect of the present invention is the manufacture of a non-aqueous electrolyte power storage element comprising applying a mixture containing amorphous carbon and styrene-butadiene rubber having a glass transition point of 40 ° C. or higher to a negative electrode base material. The method.

According to the present invention, it is a non-aqueous electrolyte power storage device using amorphous carbon as a negative electrode active material, and the initial low temperature output resistance can be lowered as compared with the case where amorphous carbon of the same size is used. It is possible to provide a non-aqueous electrolyte storage element and a method for manufacturing such a non-aqueous electrolyte storage element.

FIG. 1 is an external perspective view showing a secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of secondary batteries according to an embodiment of the present invention.

One aspect of the present invention is a non-aqueous electrolyte power storage element including a negative electrode containing amorphous carbon and styrene-butadiene rubber having a glass transition point of 40 ° C. or higher (hereinafter, also referred to as “SBR”).

According to the non-aqueous electrolyte power storage element, by using amorphous carbon and SBR having a relatively high glass transition point of 40 ° C. or higher, the initial low-temperature output when amorphous carbon of the same size is used. The resistance can be lowered. Further, according to the non-aqueous electrolyte power storage element, the initial discharge capacity can be increased when amorphous carbon of the same size is used. These effects are observed when amorphous carbon is used as the negative electrode active material. In addition, the same size means that the median diameter of amorphous carbon is equal.

The reason why the non-aqueous electrolyte power storage element exerts the above effect is not clear, but the SBR is softened in the heat-drying step after application of the mixture containing amorphous carbon and SBR having a glass transition point of 40 ° C. or higher. And by curing, it is presumed that a good adhesion state with amorphous carbon is formed. Further, the effect that the initial low temperature output resistance can be lowered by using SBR having a glass transition point of 40 ° C. or higher does not occur when graphite is used as the negative electrode active material. This is a peculiar effect that occurs when amorphous carbon and a specific SBR are used as the negative electrode active material. It is presumed that the presence or absence of this effect is due to the layer structure or surface state of the negative electrode active material.

The "amorphous carbon" means a carbon material having an interlayer distance (d002) determined by a wide-angle X-ray diffraction method of 3.40 Å or more.

The glass transition point of SBR is determined by differential scanning calorimetry (DSC). Specifically, a differential scanning calorimetry device (Rigaku Thermo plus DSC8230) is used to set the heating rate to 10 ° C./min. The temperature at which the baseline is shifted is defined as the glass transition point. For measurements below room temperature, use liquid nitrogen to create a low temperature atmosphere.

The median diameter of the amorphous carbon is preferably 7 μm or less. As described above, by using amorphous carbon having a small particle size, the initial low temperature output resistance can be further lowered, and the increase in the low temperature output resistance after the charge / discharge cycle can be suppressed. Furthermore, the initial discharge capacity can be increased by using amorphous carbon having a small particle size.

The "median diameter" means a value (D50) at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%. Specifically, the measured value can be obtained by the following method. A laser diffraction type particle size distribution measuring device (“SALD-2200” manufactured by Shimadzu Corporation) is used as a measuring device, and a Wing SALD-2200 is used as measurement control software. A scattering type measurement mode is adopted, and a laser beam is irradiated to a wet cell in which a dispersion liquid in which a measurement target sample (amorphous carbon) is dispersed in a dispersion solvent circulates, and a scattered light distribution is obtained from the measurement sample. Then, the scattered light distribution is approximated by a lognormal distribution, and the particle diameter corresponding to the cumulative degree of 50% (D50) is defined as the median diameter. The median diameter based on the above measurement is the median diameter measured by extracting 100 amorphous carbons from the SEM image of the negative electrode while avoiding extremely large amorphous carbons and extremely small amorphous carbons. It has been confirmed that they almost match.

Another aspect of the present invention is the manufacture of a non-aqueous electrolyte power storage element comprising applying a mixture containing amorphous carbon and styrene-butadiene rubber having a glass transition point of 40 ° C. or higher to a negative electrode base material. The method.

According to the manufacturing method, it is possible to reduce the initial low-temperature output resistance of a non-aqueous electrolyte power storage element using amorphous carbon as the negative electrode active material as compared with the case of using amorphous carbon of the same size. A non-aqueous electrolyte power storage element capable of being produced can be obtained.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a secondary battery will be described as an example of a non-aqueous electrolyte power storage element. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a case, and the case is filled with the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known aluminum case, resin case or the like which is usually used as a case of a secondary battery can be used.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode mixture layer laminated on the negative electrode base material.

(Negative electrode base material)
The negative electrode base material is a base material having conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel and nickel-plated steel or alloys thereof are used, and copper or a copper alloy is preferable. Further, examples of the form of forming the negative electrode base material include foils and thin-film deposition films, and foils are preferable from the viewpoint of cost. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

(Negative electrode mixture layer)
The negative electrode mixture layer is arranged as the outermost layer of the negative electrode. The negative electrode mixture layer contains amorphous carbon and SBR. The amorphous carbon functions as a negative electrode active material. In addition, SBR functions as a binder (binder). The negative electrode mixture layer contains optional components such as the negative electrode active material other than the amorphous carbon, a binder other than SBR, a thickener, a conductive agent, and a filler, if necessary.

(Amorphous carbon)
Examples of the amorphous carbon include non-graphitizable carbon (hard carbon) and easily graphitizable carbon (soft carbon). Examples of the non-graphitizable carbon include a calcined phenol resin, a calcined furan resin, and a calcined furfuryl alcohol resin. Examples of the easily graphitizable carbon include coke and pyrolytic carbon.

The amorphous carbonite preferably contains non-graphitizable carbon. By using non-graphitizable carbon, it is possible to further suppress an increase in the initial low temperature output resistance of the non-aqueous electrolyte power storage element and the low temperature output resistance after the charge / discharge cycle. It is presumed that this is because the graphitizable carbon has a small expansion and contraction during charging and discharging. The content of graphitizable carbon in the amorphous carbon is not particularly limited, but the lower limit is preferably 70% by mass, more preferably 90% by mass, and even more preferably 99% by mass. This upper limit may be 100% by mass. The "graphitizable carbon" refers to amorphous carbon having an interlayer distance (d002) of 3.60 Å or more and which does not convert to graphite even when heated to an ultra-high temperature of around 3300 K under normal pressure.

The upper limit of the median diameter of the amorphous carbon is, for example, 12 μm, preferably 7 μm, and even more preferably 3.5 μm. By using amorphous carbon whose median diameter is less than or equal to the above upper limit, it is possible to further suppress the increase in the initial low temperature output resistance of the non-aqueous electrolyte power storage element and the low temperature output resistance due to the charge / discharge cycle, and increase the discharge capacity. it can.

On the other hand, the lower limit of the median diameter of amorphous carbon is not particularly limited, but is, for example, 0.5 μm, preferably 1 μm, and more preferably 2 μm from the viewpoint of productivity, availability, and the like. By setting the median diameter of the amorphous carbon to the above lower limit or more, it is possible to further suppress an increase in the low temperature output resistance due to the charge / discharge cycle.

As the lower limit of the BET specific surface area of the amorphous carbon, 1 m ² / g is preferable, 2 m ² / g is more preferable, and 4 m ² / g is further preferable. The upper limit of the BET specific surface area is preferably ^{10 m} 2 / g, more preferably ^{9m 2 / g, 8m 2 /} g is more preferred. By setting the BET specific surface area to the above lower limit or more, the initial low temperature output resistance can be made lower, and the increase in the low temperature output resistance due to the charge / discharge cycle can be more effectively suppressed. On the other hand, by setting the BET specific surface area to the above upper limit or less, for example, the reaction with the electrolyte can be suppressed.

The lower limit of the content of the amorphous carbon in the negative electrode mixture layer is preferably 50% by mass, more preferably 65% by mass, further preferably 80% by mass, and particularly preferably 95% by mass. By setting the content of amorphous carbon to the above lower limit or more, it is possible to secure sufficient discharge capacity, conductivity, and the like. On the other hand, the upper limit of this content can be, for example, 99% by mass.

Examples of other negative electrode active materials that may be contained in the negative electrode mixture layer include known materials that are usually used, and examples thereof include metals or semi-metals such as Si and Sn; Si oxide, Sn oxide and the like. Metal oxides or semi-metal oxides; polyphosphate compounds; graphite (graphite) and the like. However, the upper limit of the content of the negative electrode active material other than the amorphous carbon in the negative electrode active material in the negative electrode active material may be preferably 20% by mass or 5% by mass. In some cases,% by mass is preferable.

(SBR)
SBR is a binder for fixing amorphous carbon and other negative electrode active materials contained as needed. SBR is a copolymer of styrene and butadiene, and monomers other than styrene and butadiene may be further copolymerized. SBR is usually used as an aqueous binder. The aqueous binder means a binder that can be dissolved or dispersed in an aqueous solvent when preparing a mixture. The aqueous solvent means water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, an organic solvent (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be exemplified.

The lower limit of the glass transition point (Tg) of SBR is 40 ° C, preferably 45 ° C, and may be 60 ° C. By using SBR having a high glass transition point in this way, the initial low temperature output resistance can be further lowered. On the other hand, the upper limit of the glass transition point can be, for example, 120 ° C., 110 ° C., or 80 ° C. By setting the glass transition point of SBR to the above upper limit or less, it is possible to suppress the occurrence of agglomeration that occurs during storage and the like, and to maintain good coatability and, by extension, good binding property as a binder.

The lower limit of the SBR content in the negative electrode mixture layer is preferably 1% by mass, more preferably 2% by mass. On the other hand, as the upper limit of the SBR content, 10% by mass is preferable, and 5% by mass is more preferable. By setting the SBR content in the above range, it is possible to reduce the low temperature output resistance of the non-aqueous electrolyte power storage element, increase the discharge capacity, and the like.

Other binders that may be contained in addition to SBR include, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer. (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), vinyl acetate copolymer, acrylic acid-modified SBR, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, fluororubber, arabic rubber, polyvinylidene fluoride ( PVDF), polyvinylidene chloride (PVDC), polyethylene, polypropylene, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO) and the like can be used. However, the upper limit of the content of the binder other than SBR is preferably 50 parts by mass, more preferably 10 parts by mass, and even more preferably 1 part by mass with respect to 100 parts by mass of SBR. As described above, the effect of the present invention is more fully exhibited by substantially using only SBR having a glass transition point of 40 ° C. or higher as the binder.

(Thickener)
Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC), CMC salt, and methyl cellulose. Among these, CMC is preferable. A part of CMC (for example, 30 mol% or less, preferably 10 mol% or less, more preferably 1 mol% or less) may be present as a part of an anion or salt. When the negative electrode mixture layer contains amorphous carbon of the same size, the nonionic CMC is contained, so that the effect of suppressing the increase in low temperature output resistance can be further enhanced and the discharge capacity is also enhanced. be able to. The reason for this is not clear, but in the presence of nonionic CMC, the affinity between the CMC and the amorphous carbon becomes good, and the adhesion of the amorphous carbon increases, which is low resistance (conductive). ) Is presumed to contribute.

The lower limit of the degree of etherification of CMC is preferably 0.4, more preferably 0.45, and even more preferably 0.5. The upper limit of the degree of etherification may be 1.5, but 1 is preferable, 0.8 is more preferable, and 0.6 is further preferable. By setting the degree of etherification of CMC within the above range, the low temperature output resistance can be further lowered. The reason for this is not clear, but by setting the degree of etherification of CMC to the above range, the affinity between CMC and amorphous carbon becomes good, and the adhesion of amorphous carbon increases, which is low resistance. It is presumed that it contributes to (conductivity). The degree of etherification of CMC can be calculated by measuring the degree of substitution of the carboxymethyl group bonded to one unit of anhydrous glucose by alkalinity or acidity. The upper limit of the degree of etherification of CMC can theoretically be up to 3.0, but it is very difficult to manufacture.

The lower limit of the CMC content in the negative electrode mixture layer is preferably 0.3% by mass, more preferably 0.5% by mass. On the other hand, as the upper limit of the content of CMC, 5% by mass is preferable, and 3% by mass is more preferable. By setting the CMC content to the above lower limit or higher, the effect of reducing resistance and the like can be made more sufficient. On the other hand, by setting the CMC content to the above upper limit or less, the discharge capacity of the non-aqueous electrolyte power storage element can be made sufficient.

(BET specific surface area of negative electrode)
As the lower limit of the BET specific surface area of the negative electrode, 2.20 m ² / g is preferable, and 2.3 m ² / g is more preferable. By setting the BET specific surface area of the negative electrode to be equal to or higher than the above lower limit, the initial low temperature output resistance can be further lowered and the discharge capacity can be increased. Although the reason is not clear, by using SBR having a high glass transition point, the BET specific surface area of the negative electrode can be increased even when amorphous carbon of the same size is used, and as a result, the initial BET specific surface area can be increased. The low temperature output resistance can be made lower. On the other hand, the upper limit of the BET specific surface area, for example, ^4m 2 / g, may be ^3m 2 / g, it may be 2.5 m ² / g.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture layer arranged directly on the positive electrode base material or via an intermediate layer.

The positive electrode base material has conductivity. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, as a form of forming the positive electrode base material, a foil, a vapor-deposited film and the like can be mentioned, and the foil is preferable from the viewpoint of cost. That is, an aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

The positive electrode mixture layer is formed from a so-called positive electrode mixture containing a positive electrode active material. Further, the positive electrode mixture forming the positive electrode mixture layer contains optional components such as a conductive agent, a binder (binding agent), a thickener, and a filler, if necessary. These optional components can be the same as those of the negative electrode described above.

Examples of the positive electrode active material include composite oxides represented by Li _x MO _y (M represents at least one kind of transition metal) (Li _x CoO ₂ and Li _x NiO having a layered α-NaFeO type ₂ crystal structure). ₂ , Li _x MnO ₃ , Li _x Ni _α Co _(1-α) O ₂ , Li _x Ni _α Mn _β Co _(1-α-β) O _2, etc., Li _x Mn ₂ O ₄ having a spinel type crystal structure , Li _x Ni _α Mn _(2-α) O ₄ etc.), Li _w Me _x (XO _y ) _z (Me represents at least one kind of transition metal, and X represents, for example, P, Si, B, V, etc.) Examples thereof include polyanionic compounds represented by (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode mixture layer, one of these compounds may be used alone, or two or more of these compounds may be mixed and used.

(Separator)
As the material of the separator, for example, a woven fabric, a non-woven fabric, a porous resin film or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the main component of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. Moreover, you may combine these resins.

(Non-aqueous electrolyte)
The non-aqueous electrolyte is a solution in which an electrolyte salt is dissolved in a non-aqueous solvent. The non-aqueous electrolyte may contain components other than the non-aqueous solvent and the electrolyte salt. Examples of other components include various additives used as additives for general non-aqueous electrolytes for power storage devices.

As the non-aqueous solvent, a known non-aqueous solvent usually used as a non-aqueous solvent for a general non-aqueous electrolyte for a power storage element can be used. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones, nitriles and the like. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but is, for example, 5:95 or more and 50:50 or less. Is preferable.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene. Examples thereof include carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate and the like.

As the electrolyte salt, a known electrolyte salt usually used as an electrolyte salt of a general non-aqueous electrolyte for a power storage element can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like, but lithium salt is preferable.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO). ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3 and} other fluorinated hydrocarbon groups Lithium salt having the above can be mentioned. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The lower limit of the content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 M, more preferably 0.3 M, further preferably 0.5 M, and particularly preferably 0.7 M. On the other hand, the upper limit is not particularly limited, but is preferably 2.5M, more preferably 2M, and even more preferably 1.5M.

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for producing a non-aqueous electrolyte power storage element according to an embodiment of the present invention includes coating a negative electrode base material with a mixture containing amorphous carbon and SBR having a glass transition point of 40 ° C. or higher. .. In addition, the manufacturing method usually further comprises drying the coated mixture.

The mixture (negative mixture layer forming material) is a slurry (paste) in which amorphous carbon, SBR, and, if necessary, other components are dispersed in a dispersion medium such as water. The coating of this mixture on the negative electrode base material can be performed by a known method. In addition, this coating includes spraying, dipping and the like.

The above-mentioned drying may be natural drying, heat drying, or the like. The heat drying can be performed, for example, at 40 ° C. or higher, preferably 50 ° C. or higher and 150 ° C. or lower, and 1 minute or longer and 60 minutes or lower. Further, the temperature of heating and drying can be set to be equal to or higher than the glass transition point of SBR. By this heat drying, a negative electrode mixture layer having high adhesion and low resistance is formed. Incidentally, as a thickener, the case of using CMC-NH ₄ salt, ammonia is volatilized during the heat drying, and thus remaining in the negative-electrode mixture layer as the non-ionic CMC.

After the drying, pressing may be performed in the thickness direction of the negative electrode mixture layer in order to improve the adhesion between the negative electrode mixture layer and the negative electrode base material. A negative electrode can be obtained through such a process.

The non-aqueous electrolyte storage element can be produced by the same method as the conventionally known non-aqueous electrolyte storage element, except for the production of the negative electrode. The manufacturing method includes, for example, housing a positive electrode and a negative electrode (electrode body) in a case, and injecting the non-aqueous electrolyte into the case.

<Other Embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in various modifications and improvements in addition to the above-described embodiment. For example, the negative electrode may have a structure in which a negative electrode mixture is supported on a mesh-shaped negative electrode base material. Further, in the above-described embodiment, the non-aqueous electrolyte storage element is mainly a secondary battery, but other non-aqueous electrolyte storage elements may be used. Examples of other non-aqueous electrolyte power storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic view of a rectangular secondary battery 1 which is an embodiment of a non-aqueous electrolyte power storage element according to the present invention. The figure is a perspective view of the inside of the container. In the secondary battery 1 shown in FIG. 1, the electrode body 2 is housed in the battery container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'.

The configuration of the non-aqueous electrolyte power storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above-mentioned non-aqueous electrolyte power storage elements. An embodiment of the power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of secondary batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
First, graphitizable carbon (median diameter: 2.0 μm, BET specific surface area: 7.90 m ² / g) as amorphous carbon, which is a negative electrode active material, and CMC-NH ₄ salt as a thickener (CMC-NH ₄ salt). Using an etherification degree: 0.6) and SBR (Tg: 45 ° C.) as a binder, 95 parts by mass of amorphous carbon, 2 parts by mass of a thickener, 3 parts by mass of a binder, and water are kneaded. A negative electrode mixture was prepared. The median diameter and BET specific surface area of amorphous carbon were measured by the above method. The negative electrode mixture was applied to the surface of a copper foil (thickness 10 μm) as a negative electrode base material, pressure-molded, and then dried at 120 ° C. for 30 minutes to form a negative electrode mixture layer to obtain a negative electrode. ..

A positive electrode mixture containing 90 parts by mass of the above negative electrode and LiNi _0.33 Co _0.33 Mn _0.33 O ₂ as the positive electrode active material, 5 parts by mass of acetylene black as the conductive auxiliary agent, and 5 parts by mass of polyvinylidene fluoride. A positive electrode having a layer, a separator made of polyethylene, and a non-aqueous electrolyte in which 1.0 mol / L of LiPF ₆ was dissolved in a solvent obtained by mixing PC, DMC and EMC in a volume ratio of 30%: 30%: 40% were used. The secondary battery (non-aqueous electrolyte storage element) of Example 1 was produced.

[Examples 2 to 10, Comparative Examples 1 to 4]
The secondary batteries of Examples 2 to 10 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that the negative electrode active material shown in Table 1 and the SBR having Tg were used. In Table 1, "HC" indicates non-graphitizable carbon, "Gr" indicates graphite, and "D50" indicates the median diameter. The measured values are shown in Table 1.

[Evaluation]
The secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 4 were evaluated by the following methods.

(Measurement of initial discharge capacity and low temperature output resistance)
Each secondary battery is charged at 25 ° C. with a constant current of 1 CmA to 4.2 V, further charged with a constant voltage of 4.2 V for a total of 3 hours, and then discharged to a final voltage of 2.25 V with a constant current of 1 CmA. Was repeated 3 times, and the capacity of the 3rd discharge was taken as the initial discharge capacity.
Further, for each secondary battery after the confirmation test of the initial discharge capacity, the charge state (SOC) of the battery was adjusted to 50% by charging 50% of the initial discharge capacity, and the battery was held at −10 ° C. for 4 hours. After that, the voltage (E1) when discharged at 0.2 CmA (I1) for 10 seconds, the voltage (E2) when discharged at 0.5 CmA (I2) for 10 seconds, and the voltage when discharged at 1 CmA (I3) for 10 seconds. The voltage (E3) was measured respectively. The state of charge (SOC) of the battery was adjusted to 50% after each discharge at I1 and I2. The DC resistance was calculated using these measured values (E1, E2, E3). Specifically, the measured values E1, E2, and E3 are plotted on a graph in which the horizontal axis is current and the vertical axis is voltage, and these three points are approximated by a regression line (approximate straight line) by the least squares method. The slope of the straight line was defined as a DC resistance (DCR) having an SOC of 50% at −10 ° C. This is referred to as the low temperature output resistance.

(Charge / discharge cycle test)
In a constant temperature bath at 60 ° C., a cycle test is performed in which a constant current voltage is charged to a voltage corresponding to SOC 80% with a charging current of 2 CmA, and then a constant current discharge is performed to a voltage corresponding to SOC 20% with a discharge current of 2 CmA for 50 cycles. It was.

(Measurement of low temperature output resistance after charge / discharge cycle test)
The low temperature output resistance was measured for each secondary battery after the charge / discharge cycle test by the same method as described in the above "Measurement of initial discharge capacity and low temperature output resistance".

Table 1 shows the measured initial discharge capacity and the low temperature output resistance after the initial and 50 cycles. Table 1 also shows the ratio of the low temperature output resistance after 50 cycles to the initial low temperature output resistance as the low temperature output resistance change rate.

As shown in Table 1, in the negative electrode mixture layer containing amorphous carbon (HC) of the same size, by using SBR having a glass transition point of 40 ° C. or higher, the initial low temperature output characteristics are lowered and the initial low temperature output characteristics are deteriorated. It can be seen that the discharge capacity of is large. Further, it can be seen that the initial low temperature output resistance can be further lowered by using amorphous carbon having a small median diameter. Specifically, in Examples 1, 3 and 5 in which the glass transition point is 45 ° C. and the median diameter is 2.0 to 3.5 μm, the low temperature output resistance is 63 to 77 mΩcm ^2. On the other hand, that of Example 7 having a median diameter of 6.9 μm was 185 mΩcm ² . There was a difference in low temperature output resistance between the median diameter of 3.5 μm and 6.9 μm, which did not simply depend on the proportion of the median diameter. In addition, the ratio of the initial low-temperature output resistance at the glass transition points of 45 ° C and 103 ° C to the glass transition point of -15 ° C at each median diameter tends to be smaller for negative electrode active materials with a median diameter of 3.5 μm or less. It was seen.

The rate of change of the low temperature output resistance after 50 cycles shows a value smaller than 100% for the negative electrode active material having a median diameter of 6.9 μm or less, and by reducing the median diameter of the negative electrode active material to 6.9 μm or less, It was found that the increase in resistance with the cycle can be suppressed.

[Reference example]
Each secondary battery as a reference example was obtained in the same manner as in Example 1 except that graphite was used as the negative electrode active material and SBR having the glass transition point (Tg) shown in Table 2 was used as the binder. .. The initial low temperature output resistance of these secondary batteries was measured. The relative value of the low temperature output resistance of the battery using SBR at each glass transition point (Tg) when the initial low temperature output resistance value of the battery using SBR having the glass transition point (Tg) of 45 ° C. is set to 100. It is shown in Table 2.

As shown in Table 2, when graphite is used instead of amorphous carbon as the negative electrode active material, the low temperature output resistance increases when the glass transition point of SBR is 40 ° C. or higher. That is, it can be said that the effect that the initial low temperature output resistance can be lowered by using SBR having a glass transition point of 40 ° C. or higher is a peculiar effect that occurs when amorphous carbon is used.

The present invention can be applied to non-aqueous electrolyte power storage elements such as non-aqueous electric field secondary batteries used as power sources for personal computers, electronic devices such as communication terminals, automobiles, and the like.

1 Secondary battery 2 Electrode body 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (2)

A negative electrode containing amorphous carbon and styrene-butadiene rubber having a glass transition point of 40 ° C. or higher is provided .
The median diameter of the amorphous carbon Ru der less 7μm nonaqueous electricity storage device. A mixture containing amorphous carbon and styrene-butadiene rubber having a glass transition point of 40 ° C. or higher is applied to the negative electrode base material .
Method of manufacturing a median diameter 7μm or less der Ru nonaqueous electricity storage device of the amorphous carbon.

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