JP2017073329A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is high in capacity, superior in charge/discharge cycle characteristic and high in continuous charging characteristic.SOLUTION: A nonaqueous electrolyte secondary battery comprises: a positive electrode; a negative electrode; a nonaqueous electrolyte; and a separator. The positive electrode includes: a positive electrode current collector; and a positive electrode mixture layer on one or each of opposing faces of the positive electrode current collector. The positive electrode mixture layer includes at least a positive electrode active material and a binder. The positive electrode active material is 0.25 m/g or more in specific surface area. The positive electrode mixture layer is 4.0 g/cmor more in density. The nonaqueous electrolyte contains a compound expressed by the following general formula (1): NC-CH-CN (1) (where n is 5 to 10).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having a high capacity, excellent charge / discharge cycle characteristics, and high continuous charge characteristics.

  Nonaqueous electrolyte secondary batteries have been widely deployed not only for consumer devices such as mobile phones and laptop computers, but also for industrial applications such as in-vehicle applications and robot applications because of their high volumetric energy density and weight energy density. Therefore, there are a wide variety of required characteristics, and various characteristic improvements are required by various means.

  In order to improve the volume energy density of a battery, means for increasing the electrode density of the positive electrode and the negative electrode are known, but when the electrode density of the positive electrode and the negative electrode is increased, various battery characteristics are deteriorated. There are, and we are working on countermeasures.

  Patent Document 1 discloses a compound containing two or more nitrile groups in a non-aqueous electrolyte using a specific positive electrode active material in order to prevent deterioration of charge / discharge cycle characteristics and storage characteristics accompanying the increase in density of batteries. Including a non-aqueous secondary battery is disclosed.

In Patent Document 2, a negative electrode suitable for a lithium secondary battery in which deterioration in rapid charge / discharge characteristics and cycle characteristics is small when the negative electrode density is increased, and a high-capacity lithium secondary battery in which the energy density per volume of the secondary battery is improved. Therefore, a negative electrode having a diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode of 500 or less is disclosed.

JP 2013-145752 A JP, 2004-55139, A By the way, as it is in patent documents 1, when a compound which contains two or more nitrile groups in a molecule is used, a fall of storage characteristics can be controlled. On the other hand, for example, when the positive electrode density is 4.0 g / cm 3 or more and the positive electrode active material has a specific surface area of 0.25 m 2 / g or more, there is a nitrile group in the molecule for improving continuous charge characteristics and high-temperature cycle characteristics. The inventors have found that there are more optimal ones of two or more compounds.

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery having a high capacity, excellent charge / discharge cycle characteristics, and high continuous charge characteristics.

The nonaqueous electrolyte secondary battery of the present invention that achieves the above object includes a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator, and the positive electrode includes a positive electrode mixture layer on one or both sides of a positive electrode current collector, The positive electrode mixture layer includes at least a positive electrode active material and a binder, the specific surface area of the positive electrode active material is 0.25 m ² / g or more, and the density of the positive electrode mixture layer is 4.0 g / cm ³ or more. In addition, the non-aqueous electrolyte includes a compound represented by the general formula (1).

_{NC-C n H 2n -CN (} 1)
(However, n is 5 or more and 10 or less.)

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having high capacity, excellent charge / discharge cycle characteristics, and high continuous charge characteristics.

The sectional view of the nonaqueous electrolyte secondary battery which is an example of the embodiment of the present invention is represented. The perspective view of the nonaqueous electrolyte secondary battery which is an example of the embodiment of this invention is represented.

The non-aqueous electrolyte secondary battery of the present invention includes, for example, a laminated electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, a wound structure electrode body obtained by further winding the electrode body, and the like. It has a configuration in which it is enclosed in an exterior body together with a non-aqueous electrolyte.
[Non-aqueous electrolyte]
As the non-aqueous electrolyte according to the non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF _{6 and} other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. be able to.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Examples thereof include sulfites such as glycol sulfite, and these may be used as a mixture of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  In the non-aqueous electrolyte solution (non-aqueous electrolyte) according to the present invention, it is necessary to contain the compound of the general formula (1).

_{NC-C n H 2n -CN (} 1)
(However, n is 5 or more and 10 or less.)
The compound of the general formula (1) has a function of forming a surface protective film on the surface of the positive electrode active material, and the direct contact between the positive electrode and the nonaqueous electrolyte is suppressed by the surface protective film. Using this compound, the specific surface area of the positive electrode active material is 0.25 m ² / g or more, and the density of the positive electrode mixture layer is combined with a positive electrode mixture layer using a positive electrode active material of 4.0 g / cm ³ or more. Thus, a nonaqueous electrolyte secondary battery having excellent high-temperature charge / discharge cycle characteristics and high continuous charge characteristics is obtained. The reason why such an effect can be obtained is not clear, but the following may be considered.

  For example, when compared with a compound in which n in the general formula (1) is 4 or less, the compound in the general formula (1) has a larger number of carbon atoms, and thus the reactivity at the first charge is further improved. Therefore, a film can be easily formed on the positive electrode surface. In particular, since a positive electrode active material having a high specific surface area is used in the present invention, the area on which the film is to be formed is large. However, the compound of the general formula (1) is a film that covers a wide range of areas quickly due to its high reactivity. Can be formed.

  Therefore, as in the case of using a compound having two or more nitrile groups in the molecule as in the prior art, the storage characteristics and cycle characteristics are improved, and in the present invention, the use of a specific positive electrode further increases the continuous charge. The characteristics and cycle characteristics at high temperatures are also excellent.

  Specific examples of the dinitrile compound represented by the general formula (1) include 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1, Examples include 8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, 2,4-dimethylglutaronitrile and the like. . Among these, 1,5-dicyanopentane (pimelonitrile) and 1,6-dicyanohexane (suberonitrile) are preferable because of high versatility.

  The method for preparing the nonaqueous electrolytic solution containing the compound of the general formula (1) is not particularly limited. For example, a compound having two or more nitrile groups in the molecule in the solvent exemplified above and the electrolyte salt exemplified above. May be dissolved according to a conventional method.

The addition amount of the compound of the general formula (1) is preferably 0.05% by mass or more, more preferably 0.1% in the total amount of the non-aqueous electrolyte from the viewpoint of more effectively exerting the action of the addition of these compounds. It is at least 0.5 mass%, more preferably at least 0.5 mass%. Further, in the total amount of the non-aqueous electrolyte, it is preferably 10% by mass or less, more preferably 8% by mass, and further preferably 6% by mass or less. When the compound of the general formula (1) is included in this range, the continuous charge characteristics and the cycle characteristics at high temperatures are good when combined with the positive electrode of the present invention.

You may use common nonaqueous electrolyte additives other than the compound of General formula (1) to such an extent that the effect of this invention is not inhibited. For example, additives such as vinylene carbonate, fluoroethylene carbonate, 1,3-dioxane, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene are appropriately added to the non-aqueous electrolyte. It can also be added.
[Positive electrode]
For the positive electrode according to the nonaqueous electrolyte secondary battery of the present invention, for example, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a conductive additive, a binder, etc. on one side or both sides of a current collector is used. Is done.

<Positive electrode active material>
The positive electrode active material used for the positive electrode is not particularly limited, and a known active material such as a lithium-containing transition metal oxide may be used. Specific examples of the lithium-containing transition metal oxide include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _2. , etc. _{Li x Ni 1-y M y} O 2, Li x Mn y Ni z Co 1-y-z O 2, Li x Mn 2 O 4, Li x Mn 2-y M y O 4 is illustrated. However, in each of the above structural formulas, M is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, Ti, Zr, Ge, and Cr. 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 <z <1.0. From the viewpoint of energy density, a layered compound containing lithium and cobalt (general formula LiCo _1-y M ² _y O ₂ ; M ² is obtained by removing Co from M and y is the same as y described above) preferable.

<Binder>
As the binder used for the positive electrode, any of a thermoplastic resin and a thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), styrene-butadiene rubber (SBR), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoro Ethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene- Tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, Len - methyl acrylate copolymer, ethylene - one or more Na ion crosslinked body and the like of the methyl methacrylate copolymer and their copolymers can be used.

<Conductive aid>
As a conductive support agent used for the said positive electrode, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metal powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives, etc. You may use independently and may use 2 or more types together. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

<Current collector>
The current collector used for the positive electrode can be the same as that used for the positive electrode of a conventionally known nonaqueous electrolyte secondary battery. For example, an aluminum foil having a thickness of 8 to 30 μm can be used. preferable.

<Method for producing positive electrode>
The positive electrode is prepared, for example, as a paste-like or slurry-like positive electrode mixture-containing composition in which the above-described positive electrode active material, conductive additive and binder are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). (However, the binder may be dissolved in a solvent.) After applying this to one or both sides of the current collector and drying, it can be produced through a process of calendering if necessary. .

<Positive electrode mixture layer>
In the positive electrode mixture layer, the total amount of the positive electrode active material is 92 to 99% by weight, the amount of the conductive auxiliary agent is 0.5 to 6% by weight, and the amount of the binder is 0.5 to 6% by weight. Is preferred. The thickness of the positive electrode mixture layer is preferably 40 to 300 μm per one side of the current collector after the calendar treatment.

The positive electrode mixture layer of the present invention is 4.0 g / cm ³ or more. In order to increase the density of the positive electrode mixture layer, two or more types of positive electrode active material particles having different average particle diameters are generally used. If it does so, since the particle | grains smaller than it can be filled between large particles, a positive mix layer becomes high density.

In order to realize a high density of 4.0 g / cm ³ or more, the particle size ratio between the positive electrode active material particles having the largest average particle diameter and the positive electrode active material particles having the smallest average particle diameter, This can be realized by controlling the content ratio of the positive electrode active material particles having the largest average particle diameter and the smallest positive electrode active material particles in the positive electrode active material. On the other hand, when controlled in this way, the specific surface area of the positive electrode active material tends to be 0.25 m ² / g or more.

When the battery is exposed to high temperature and high pressure, the positive electrode and the non-aqueous electrolyte react with each other, and the decomposition reaction of the non-aqueous electrolyte easily occurs. When the non-aqueous electrolyte is decomposed, gas is generated and the battery swells or the non-aqueous electrolyte is reduced by the decomposition, so that the cycle characteristics are deteriorated. In order to suppress these, in the present invention, when the compound of the general formula (1) is used for film formation on the positive electrode, the specific surface area of the positive electrode active material is 0.25 m ² / g or more and the surface area of the positive electrode surface is large. However, it is possible to quickly form a film covering a wide area with high reactivity of the compound of the general formula (1). Therefore, when the battery is exposed to a high voltage or a high temperature state for a long time, such as during continuous charging, high temperature charge / discharge cycle, and high temperature storage, a remarkable improvement effect is seen.

  The “average particle size” as used in this specification refers to the volume-based integrated amount when the integrated volume is obtained from particles having a small particle size distribution measured using a microtrack particle size distribution measuring apparatus “HRA9320” manufactured by Nikkiso Co., Ltd. 50% diameter value (d50) in median is the median diameter.

  Moreover, the density of the mixture layer as used in this specification is a value calculated | required with the following measuring methods. The positive electrode is cut out in a predetermined area, the weight thereof is measured using an electronic balance having a minimum scale of 1 mg, and the weight of the positive electrode mixture layer is calculated by subtracting the weight of the current collector from this weight. Further, the total thickness of the positive electrode was measured at 10 points with a micrometer having a minimum scale of 1 μm, and the volume of the positive electrode mixture layer was calculated from the average value and the area obtained by subtracting the thickness of the current collector from this thickness. The density of the positive electrode mixture layer is calculated by dividing the weight of the positive electrode mixture layer. The mixture layer density of the negative electrode is calculated by the same method.

  In addition, the specific surface area of the positive electrode active material in the present specification is the specific surface area of the positive electrode active material particles contained in the positive electrode mixture layer. When a plurality of positive electrode active material particles are used, the specific surface area of the mixture is determined. say. The specific surface area is measured by the BET method. An example of the apparatus is “Bell Soap Mini” manufactured by Bell Japan.

In order to set the density of the positive electrode mixture layer to 4.0 g / cm ³ or more and the specific surface area of the positive electrode active material to 0.25 m ² / g or more, for example, the following means can be considered.

  <Example 1> Positive electrode active material particles having a small average particle diameter are preferably 1 to 10 μm, and positive electrode active material particles having a large average particle diameter are preferably combined with two positive electrode active material particles having a different average particle diameter of 20 to 30 μm. . By using such large and small positive electrode active material particles, since the small particles fill the gaps between the large particles and the large particles, the positive electrode mixture layer density increases. Furthermore, since the specific surface area of the positive electrode active material particles themselves having an average particle diameter of 1 to 10 μm is large, the specific surface area as the positive electrode active material is also increased.

  <Example 2> A combination of two positive electrode active material particles having different average particle diameters, the positive electrode active material particles having a small average particle diameter and the average particle diameter dlμm of the positive electrode active material particles having a large average particle diameter are dl / ds is preferably 3 to 15. In such a relationship, the density of the positive electrode mixture layer increases because small particles tend to enter the gap between the large particles and the large particles with high density. Further, the specific surface area of the positive electrode active material is increased due to the size of the specific surface area of the small particles.

  <Example 3> Two positive electrode active material particles having different average particle diameters are combined, and the mixing ratio of positive electrode active material particles having a small average particle diameter and positive electrode active material particles having a large average particle diameter is 40:60 to 5:95. Preferably it is in the range. At such a mixing ratio, the density of the positive electrode mixture layer is increased because the small particles can just fill the gaps between the large particles and the large particles. Further, the specific surface area increases due to the size of the specific surface area of the small particles.

  Although several means have been exemplified as described above, the use of a plurality of exemplified means makes it easier to control the density of the positive electrode mixture layer and the specific surface area of the positive electrode active material within a predetermined range. Adopting all three methods is the easiest to control.

In addition to Examples 1 to 3 described above, the density of the positive electrode mixture layer is 4.0 g / cm ³ or more, the specific surface area of the positive electrode active material is 0.25 m ² / g or more, and the compound of the general formula (1) is used. Thus, the problems of the present invention can be solved.

In consideration of feasibility, the density of the positive electrode mixture layer is preferably 5.0 g / cm ³ or less, and the specific surface area of the positive electrode active material is preferably 1.0 m ² / g or less.

[Negative electrode]
The negative electrode used in the non-aqueous electrolyte secondary battery of the present invention has a structure having, for example, a negative electrode active material, a binder, and a negative electrode mixture layer containing a conductive auxiliary agent, if necessary, on one side or both sides of the current collector. Things can be used.

<Negative electrode active material>
The negative electrode active material is not particularly limited as long as it is a negative electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, that is, a material capable of inserting and extracting lithium ions. For example, carbon-based materials that can occlude and release lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One kind or a mixture of two or more kinds is used as the negative electrode active material. In addition, elements such as silicon (Si), tin (Sn), germanium (Ge), bismuth (Bi), antimony (Sb), indium (In) and alloys thereof, lithium such as lithium-containing nitride or lithium-containing oxide A compound that can be charged and discharged at a low voltage close to that of a metal, or a lithium metal or a lithium / aluminum alloy can also be used as the negative electrode active material. Among these, as the negative electrode active material, a material represented by SiO _x containing silicon and oxygen as constituent elements is preferable.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, the SiO _x to SiO ₂ matrix of amorphous Si (e.g., microcrystalline Si) is include the dispersed structure, the SiO ₂ of the amorphous, dispersed therein It is only necessary that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

The SiO _x is preferably a composite that is combined with a carbon material. For example, the surface of the SiO _x is preferably covered with the carbon material. Usually, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. If it is a composite in which SiO _x is combined with a carbon material, for example, a conductive network in the negative electrode is better than when a material obtained by simply mixing SiO _x and a conductive material such as a carbon material is used. Formed.

<Binder>
Examples of the binder include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, and diacetyl cellulose, and modified products thereof; polyvinyl chloride, polyvinyl pyrrolidone (PVP), Thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide, and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber ( SBR), butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and other polymers having rubber-like elasticity and their modifications; It can be used or two or more. "
<Conductive aid>
A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon It is possible to use one or more materials such as fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (described in JP-A-59-20971). it can. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

<Current collector>
As the current collector, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 5 μm in order to ensure mechanical strength. Is desirable.

<Method for producing negative electrode>
The negative electrode is, for example, a paste or slurry in which the above-described negative electrode active material and binder and, if necessary, a conductive assistant are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. A negative electrode mixture-containing composition is prepared, applied to one or both sides of a current collector, dried, and then subjected to a calendering process as necessary. The manufacturing method of a negative electrode is not necessarily restricted to said manufacturing method, It can also manufacture with another manufacturing method.

<Negative electrode mixture layer>
In the said negative mix layer, it is preferable that the total amount of a negative electrode active material shall be 80-99 mass%, and the quantity of a binder shall be 1-20 mass%. In addition, when a conductive material is separately used as a conductive auxiliary agent, these conductive materials in the negative electrode mixture layer are used in such a range that the total amount of the negative electrode active material and the binder amount satisfy the above-described preferable values. It is preferable. In consideration of the thickness of the positive electrode mixture layer, the thickness of the negative electrode mixture layer is preferably 40 to 400 μm, for example.

  By the way, it is thought that the compound of General formula (1) acts on a negative electrode, and cycling characteristics improve. Although details are unknown, it is presumed that the compound of the general formula (1) undergoes reductive decomposition at the negative electrode to form a film, and thus the reaction resistance between the negative electrode and the electrolytic solution can be reduced, and the cycle characteristics are improved.

In the positive electrode of the present invention, the positive electrode mixture layer has a very high density of 4.0 g / cm ³ or more. Therefore, if the negative electrode mixture layer serving as the counter electrode is also high in density, the volume energy density of the entire battery is improved. preferable. For example, the density of the negative electrode mixture layer, 1.5 g / cm ³ or more is good, preferably 1.6 g / cm ³ or more, more preferably 1.65 g / cm ³ or more. Moreover, from a viewpoint of feasibility, 2.0 g / cm ³ or less is preferable.

In order to increase the density of the negative electrode mixture layer in this way, means for increasing the calendar pressure during the above-described calendar processing is known. However, when natural natural graphite is used as the negative electrode active material for a high density of 1.6 g / cm ³ or more, the natural graphite is crushed and the basal plane is parallel to the surface direction of the negative electrode mixture layer. Oriented in the direction. Since Li ions are inserted and desorbed from the edge surface of natural graphite to the interlayer, if they are oriented in this way, the insertion and desorption of Li ions does not go smoothly, and the resistance value of the negative electrode increases, resulting in an increase in overall battery resistance. End up. This tendency becomes more prominent as the calendar pressure is higher.

  Therefore, when natural graphite and MCMB are contained as a negative electrode active material in a mass ratio of 80:20 to 0: 100, a high-density negative electrode mixture layer is obtained without inhibiting smooth insertion / extraction of Li ions. It is possible and preferable. The reason is as follows.

  Natural graphite is easily crushed and its density is easily improved. However, as described above, depending on the calendar pressure, smooth insertion / extraction of Li ions may be inhibited accordingly.

  On the other hand, MCMB has a feature that MCMB is not easily broken or deformed because of its high compressive fracture strength (particle hardness) with respect to the calender pressure when producing the negative electrode. Therefore, the resistance value does not increase greatly.

When natural graphite and MCMB are mixed at a mass ratio of 80:20 to 0: 100 so that the advantages of each of these negative electrode active materials can be used successfully, the density of the negative electrode mixture layer increases and the resistance value of the negative electrode increases. Suppression can be realized at the same time, which is preferable. In the case of such a negative electrode, the surface of the negative electrode becomes rough due to the high particle hardness of MCMB. When the surface of the negative electrode mixture layer is rough, the electrolytic solution easily permeates, and the high temperature cycle characteristics are improved. For this reason, combining with the compound of the general formula (1) described above is preferable because the high-temperature cycle characteristics are synergistically improved.
[Separator]
As the separator for the non-aqueous electrolyte secondary battery of the present invention, conventionally known separators can be used, for example, polyolefins such as polyethylene, polypropylene and ethylene-propylene copolymer; polyesters such as polyethylene terephthalate and copolymer polyester; It is preferable that the porous film be made. In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator is composed of a thermoplastic resin having a melting point, that is, a melting temperature of 100 to 140 ° C. measured using a differential scanning calorimeter (DSC) in accordance with the provisions of Japanese Industrial Standard (JIS) K7121. It is more preferable that it is a single layer porous film mainly composed of polyethylene or a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-exemplified thermoplastic resin used in conventionally known non-aqueous electrolyte secondary batteries, that is, a solvent extraction method, An ion-permeable porous membrane produced by a dry or wet stretching method can be used. Moreover, what improves the heat resistance by providing a heat-resistant layer containing inorganic particles on the porous layer composed of the above-described resin, and what improves adhesion with an electrode by providing an adhesive layer can also be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

In addition, as a characteristic of the separator, a Gurley value represented by the number of seconds that 100 mL of air permeates through the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  There is no restriction | limiting in particular about the form of the nonaqueous electrolyte secondary battery of this invention. For example, any of a coin shape, a button shape, a sheet shape, a laminated shape, a cylindrical shape, a flat shape, a square shape, a large size used for an electric vehicle, etc. may be used.

  In general, the nonaqueous electrolyte secondary battery is ready for shipment after an activation process after assembling the battery in these forms. This activation process mainly includes an initial charge process and an aging process. Through this activation step, the density of the mixture layer tends to decrease in the positive electrode mixture layer and the negative electrode mixture layer through absorption of the non-aqueous electrolyte and migration of Li ions. Generally, the density decreases by about 5 to 10% for the positive electrode and about 10 to 20% for the negative electrode.

  The nonaqueous electrolyte secondary battery of the present invention can be used with the end voltage at the time of charging set to about 4.2 V, similarly to the conventional nonaqueous electrolyte secondary battery. It may be used by a method of charging with a final voltage of 3 V or more, and even when charged by such a method and used at a high temperature, good charge / discharge cycle characteristics and storage characteristics can be exhibited. However, it is preferable that the end voltage at the time of charge of a non-aqueous secondary battery is 4.6V or less.

  The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as conventionally known non-aqueous electrolyte secondary batteries. According to the present invention, since the density of the positive electrode mixture layer is high, the energy density per volume can be improved with a high capacity. Therefore, it is particularly effective for devices that require a high capacity for a limited volume, such as mobile devices, small devices, and robot applications that combine multiple cells in series.

<Preparation of positive electrode>
LiCoO _{2 having} an average particle diameter of 5 μm and 27 μm were mixed at a ratio (mass ratio) of 15:85. The specific surface area of this mixture (positive electrode active material) was 0.25 m ² / g. 96 parts by mass of this positive electrode active material, 20 parts by mass of an NMP solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite and 1 part by mass of Ketjen Black, which are conductive assistants, are biaxial. The mixture was kneaded using a kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

The positive electrode mixture-containing paste is applied to both surfaces and a part of one surface of an aluminum foil (positive electrode current collector) having a thickness of 12 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a positive electrode composite on both surfaces of the aluminum foil. An agent layer was formed. Then, the calendar process was adjusted to adjust the thickness and density of the positive electrode mixture layer. The positive electrode mixture layer in the obtained positive electrode had a density of 4.00 g / cm ³ and a thickness per one side of 70 μm. A positive electrode current collector tab made of um was welded to aluminum on the exposed aluminum foil portion of the positive electrode to produce a strip-shaped positive electrode having a length of 1000 mm and a width of 54 mm.

<Production of negative electrode>
A mixture of MCMB (average particle diameter 20 μm) as a negative electrode active material and natural graphite (average particle diameter 20 μm) in a mass ratio of 6: 4: 97.5 parts by mass, and SBR as a binder: 1. Water was added to and mixed with 5 parts by mass and CMC as a thickener: 1 part by mass to prepare a negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a negative electrode composite on both sides and part of the copper foil. An agent layer was formed. Then, the calendar process was performed and the thickness and density of the negative mix layer were adjusted. At this time, a negative electrode current collector tab made of nickel was welded to the exposed portion of the positive electrode copper foil, and the negative electrode mixture layer in the obtained negative electrode had a density of 1.65 g / cm ³ and a thickness of one side of 86 μm. It was. A strip-shaped negative electrode having a length of 990 mm and a width of 55 mm was produced.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7 at a concentration of 1.1 mol / L, 2% by weight of vinylene carbonate, 2% by weight of fluoroethylene carbonate and 2% by weight of pimelonitrile (general formula Compound (1) n = 5) was added to prepare a non-aqueous electrolyte.

<Preparation of separator>
To 5 kg of boehmite having an average particle diameter d ₅₀ of 1 μm, 5 kg of ion exchange water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) are added, and the internal volume is 20 L, the number of turns is 40 times. A dispersion was prepared by pulverizing with a ball mill for 10 hours per minute. The treated dispersion was vacuum-dried at 120 ° C. and observed with a scanning electron microscope (SEM). As a result, the boehmite was almost plate-shaped.

  To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added and stirred with a three-one motor for 3 hours to form a uniform slurry. [Slurry for forming porous layer (II), solid content ratio: 50% by mass] was prepared.

PE microporous separator for non-aqueous electrolyte secondary battery (porous layer (I): thickness 12 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.) the amount 40W · min / m ²⁾ and subjected to the treated surface porous layer (II) forming slurry was coated by a micro gravure coater, the thickness and dried to form a porous layer of 4μm to (II), A laminated separator was obtained. The mass per unit area of the porous layer (II) in this separator was 5.5 g / m ² , the boehmite volume content was 95% by volume, and the porosity was 45%.

<Battery assembly>
The strip-shaped positive electrode and the strip-shaped positive electrode are overlapped with the laminated separator so that the porous layer (II) is on the positive electrode side, wound in a spiral shape, and then added in a flat shape. The wound electrode body was pressed to form a wound electrode body having a flat wound structure, and this wound electrode body was fixed with an insulating tape made of polypropylene. Next, the wound electrode body was inserted into a rectangular battery case made of aluminum alloy, the lead body was welded, and the lid plate made of aluminum alloy was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte is injected from the inlet provided on the cover plate, and left to stand for 1 hour. The inlet is then sealed, and the structure shown in FIG. A secondary battery was produced.

  The nonaqueous electrolyte secondary battery will be described with reference to FIGS. FIG. 1 is a partial cross-sectional view thereof. A positive electrode 1 and a negative electrode 2 are wound in a spiral shape via a separator 3 and then pressed so as to be flattened to form a flat wound electrode body 6 having a rectangular shape ( (Rectangular cylindrical) battery case 4 is housed together with a non-aqueous electrolyte. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The outer can 4 also serves as a positive electrode terminal. And the insulator 5 which consists of PE sheets is arrange | positioned at the bottom part of the battery case 4, and it connects to each one end of the positive electrode 1 and the negative electrode 2 from the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a PP insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. As a result, the battery is sealed by welding. Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Example 1, the battery case 4 and the cover plate 9 function as positive terminals by directly welding the positive electrode lead body 7 to the cover plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the battery case 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional. Also, the separator does not show each layer separately.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7 at a concentration of 1.1 mol / L, and 2% by mass of vinylene carbonate, 2% by mass of fluoroethylene carbonate and 2% by mass of suberonitrile (general formula Compound (1) n = 6) was added to prepare a non-aqueous electrolyte.

  A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this nonaqueous electrolyte was used.

LiCoO _{2 having} an average particle diameter of 3 μm and 29 μm were mixed at a ratio (mass ratio) of 15:85. The specific surface area of this mixture (positive electrode active material) was 0.35 m ² / g. 96 parts by mass of this positive electrode active material, 20 parts by mass of an NMP solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite and 1 part by mass of Ketjen Black, which are conductive assistants, are biaxial. The mixture was kneaded using a kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

The positive electrode mixture-containing paste is applied to both surfaces and a part of one surface of an aluminum foil (positive electrode current collector) having a thickness of 12 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a positive electrode composite on both surfaces of the aluminum foil. An agent layer was formed. Then, the calendar process was adjusted to adjust the thickness and density of the positive electrode mixture layer. The positive electrode mixture layer in the obtained positive electrode had a density of 4.00 g / cm ³ and a thickness per one side of 70 μm. A positive electrode current collector tab made of um was welded to aluminum on the exposed aluminum foil portion of the positive electrode to produce a strip-shaped positive electrode having a length of 1000 mm and a width of 54 mm.

  A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this positive electrode was used.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7 at a concentration of 1.1 mol / L, and 2% by mass of vinylene carbonate, 2% by mass of fluoroethylene carbonate and 2% by mass of suberonitrile (general formula Compound (1) n = 6) was added to prepare a non-aqueous electrolyte.

  A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the positive electrode prepared in Example 3 and this nonaqueous electrolyte were used.

LiCoO _{2 having} an average particle size of 3 μm and 29 μm were mixed at a ratio (mass ratio) of 15:85. The specific surface area of this mixture (positive electrode active material) was 0.35 m ² / g. 96 parts by mass of this positive electrode active material, 20 parts by mass of an NMP solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite and 1 part by mass of Ketjen Black, which are conductive assistants, are biaxial. The mixture was kneaded using a kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

The positive electrode mixture-containing paste is applied to both surfaces and a part of one surface of an aluminum foil (positive electrode current collector) having a thickness of 12 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a positive electrode composite on both surfaces of the aluminum foil. An agent layer was formed. Then, the calendar process was adjusted to adjust the thickness and density of the positive electrode mixture layer. The positive electrode mixture layer in the obtained positive electrode had a density of 4.11 g / cm ³ and a thickness per side of 68 μm. A positive electrode current collector tab made of um was welded to aluminum on the exposed aluminum foil portion of the positive electrode to produce a strip-shaped positive electrode having a length of 1000 mm and a width of 54 mm.

  A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this positive electrode was used.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7 at a concentration of 1.1 mol / L, and 2% by mass of vinylene carbonate, 2% by mass of fluoroethylene carbonate and 2% by mass of suberonitrile (general formula Compound (1) n = 6) was added to prepare a non-aqueous electrolyte.

  A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the positive electrode prepared in Example 5 and this nonaqueous electrolyte were used.

<Production of negative electrode>
A mixture of MCMB (average particle diameter 20 μm) as a negative electrode active material and natural graphite (average particle diameter 20 μm) in a mass ratio of 6: 4: 97.5 parts by mass, and SBR as a binder: 1. Water was added to and mixed with 5 parts by mass and CMC as a thickener: 1 part by mass to prepare a negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a negative electrode composite on both sides and part of the copper foil. An agent layer was formed. Then, the calendar process was adjusted and the thickness and density of the negative mix layer were adjusted. A negative electrode current collector tab made of nickel was welded to the exposed portion of the copper foil at this time, and the negative electrode mixture layer in the obtained negative electrode had a density of 1.55 g / cm ³ and a thickness of one side of 91 μm. . A strip-shaped negative electrode having a length of 990 mm and a width of 55 mm was produced.

  A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 6 except that this negative electrode was used.

<Production of negative electrode>
Water was added to natural graphite (average particle size 20 μm) as negative electrode active material: 97.5 parts by mass, SBR as binder: 1.5 parts by mass, and CMC as thickener: 1 part by mass. The mixture was mixed to prepare a negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a negative electrode composite on both sides and part of the copper foil. An agent layer was formed. Then, the calendar process was adjusted and the thickness and density of the negative mix layer were adjusted. At this time, a negative electrode current collector tab made of nickel was welded to the exposed portion of the copper foil, and the negative electrode mixture layer in the obtained negative electrode had a density of 1.65 g / cm ³ and a thickness of one side of 86 μm. . A strip-shaped negative electrode having a length of 990 mm and a width of 55 mm was produced.

A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 6 except that this negative electrode was used.
(Comparative Example 1)
<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1.1 mol / L in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7, and 2% by mass of vinylene carbonate, 2% by mass of fluoroethylene carbonate, and 2% by mass of adiponitrile (general formula Compound (1) n = 4) was added to prepare a non-aqueous electrolyte.

A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this nonaqueous electrolyte was used.
(Comparative Example 2)
<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1.1 mol / L in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7, and 2% by mass of vinylene carbonate, 2% by mass of fluoroethylene carbonate, and 2% by mass of adiponitrile (general formula Compound (1) n = 4) was added to prepare a non-aqueous electrolyte.

The same positive electrode as in Example 5 was used. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this positive electrode and this nonaqueous electrolyte were used.
(Comparative Example 3)
<Production of negative electrode>
A mixture of MCMB (average particle diameter 20 μm) as a negative electrode active material and natural graphite (average particle diameter 20 μm) in a mass ratio of 6: 4: 97.5 parts by mass, and SBR as a binder: 1. Water was added to and mixed with 5 parts by mass and CMC as a thickener: 1 part by mass to prepare a negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a negative electrode composite on both sides and part of the copper foil. An agent layer was formed. Then, the calendar process was adjusted and the thickness and density of the negative mix layer were adjusted. A negative electrode current collector tab made of nickel was welded to the exposed portion of the copper foil at this time, and the negative electrode mixture layer in the obtained negative electrode had a density of 1.55 g / cm ³ and a thickness of 91 μm per side. A strip-shaped negative electrode having a length of 990 mm and a width of 55 mm was produced.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Comparative Example 2 except that this negative electrode was used.

  The following evaluations were performed on the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples.

<Charge / discharge cycle characteristics at 45 ° C.>
3. Each non-aqueous electrolyte secondary battery of Example and Comparative Example was left in a 45 ° C. constant temperature bath for 5 hours, and then each battery was charged at a constant current of 1.0 C up to 4.40 V. After reaching 40V, constant voltage charging was performed at 4.40V until the current reached 0.05C. Each of the batteries thereafter was discharged at a constant current of 1.0 C until the voltage reached 3.0V. A series of these charging and discharging operations was taken as one cycle, and charging / discharging was repeated while confirming the discharge capacity. And about each battery, the cycle number which becomes 70% of discharge capacity from the discharge capacity of the 1st cycle was calculated | required.

<Storage characteristics evaluation>
Example Each battery of the comparative example was charged at a constant current of 1.0 C up to 4.40 V at room temperature, and after reaching 4.40 V, the voltage was constant at 4.40 V until the current reached 0.05 C. Charged. Each of the batteries thereafter was discharged at a constant current of 1.0 C until the voltage reached 3.0V. Thereafter, charging was performed at a constant current of 1.0 C up to 4.40 V at room temperature, and after reaching 4.40 V, constant voltage charging was performed at 4.40 V until the current reached 0.05 C. The battery thickness (thickness before storage) at that time was measured. Each battery after thickness measurement was stored in a thermostatic bath at 85 ° C. for 24 hours, taken out of the thermostatic bath and allowed to stand for 4 hours, and then the thickness of the battery (thickness after storage) was measured again. From the thickness before storage and the thickness after storage, the rate of change in thickness of the battery due to storage was determined according to the following formula.

  Thickness change rate (%) = (thickness after storage) ÷ (thickness before storage) × 100-100.

<Continuous charging test>
About each nonaqueous electrolyte secondary battery of an Example and a comparative example, after carrying out constant current charge to 4.45V at a current value of 1.0C at 60 ° C, constant voltage charge was continued at 4.45V, The time until the increase in value (leakage current generation time) was measured.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (3)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
The positive electrode comprises a positive electrode mixture layer on one or both sides of a positive electrode current collector,
The positive electrode mixture layer includes at least a positive electrode active material, a binder, and a conductive additive,
The positive electrode active material has a specific surface area of 0.25 m ² / g or more,
The density of the positive electrode mixture layer is 4.0 g / cm ³ or more,
The nonaqueous electrolyte secondary battery includes a compound represented by the general formula (1).
_{NC-C n H 2n -CN (} 1)
(However, n is 5 or more and 10 or less.) The negative electrode comprises a negative electrode mixture layer on one or both sides of a negative electrode current collector,
The nonaqueous electrolyte secondary battery according to claim 1, wherein a mixture density of the negative electrode mixture layer is 1.6 g / cm ³ or more. The negative electrode mixture layer includes at least a negative electrode active material and a binder,
The negative electrode active material includes natural graphite and mesocarbon microbeads,
2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material includes natural graphite and mesocarbon microbeads in a mass ratio of 80:20 to 0: 100. 3.

Images