JP2014011023A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having improved thermal stability.SOLUTION: A nonaqueous electrolyte secondary battery 1 includes a positive electrode 12, a negative electrode 11, and a nonaqueous electrolyte. The positive electrode 12 includes a lithium transition metal composite oxide as a positive electrode active material. The negative electrode 11 includes a negative electrode active material. The nonaqueous electrolyte includes a solute and a nonaqueous solvent. The nonaqueous solvent includes γ-butyrolactone, a cyclic halogenated carbonate and a chain carbonate. The solute includes a lithium salt including an oxalate complex.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Conventionally, non-aqueous electrolyte secondary batteries have been widely used in electronic devices such as mobile phones, notebook computers, and PDAs. For example, Patent Document 1 discloses using a nonaqueous electrolytic solution containing a cyclic carbonate, a chain carbonate, a cyclic ester, or the like as the nonaqueous electrolytic solution.

JP 2010-113952 A

  In recent years, further improvement in the thermal stability of nonaqueous electrolyte secondary batteries has been demanded.

  A main object of the present invention is to provide a non-aqueous electrolyte secondary battery having improved thermal stability.

  The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a lithium transition metal composite oxide as a positive electrode active material. The negative electrode includes a negative electrode active material. The nonaqueous electrolytic solution includes a solute and a nonaqueous solvent. Nonaqueous solvents include γ-butyrolactone, cyclic halogenated carbonates, and chain carbonates. The solute includes a lithium salt containing an oxalate complex.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having improved thermal stability.

1 is a schematic cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

  Hereinafter, an example of the preferable form which implemented this invention is demonstrated. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

  The drawings referred to in the embodiments are schematically described, and the ratio of the dimensions of the objects drawn in the drawings may be different from the ratio of the dimensions of the actual objects. The specific dimensional ratio of the object should be determined in consideration of the following description.

  As shown in FIG. 1, the nonaqueous electrolyte secondary battery 1 includes a battery container 17. In the present embodiment, the battery case 17 is a cylindrical shape. However, in the present invention, the shape of the battery container is not particularly limited. The battery container 17 may be, for example, a flat type or a square type.

  An electrode body 10 impregnated with a non-aqueous electrolyte is accommodated in the battery container 17.

  The nonaqueous electrolytic solution includes a nonaqueous solvent and a solute. The solute includes a lithium salt containing at least an oxalate complex. Nonaqueous solvents include γ-butyrolactone, cyclic halogenated carbonates, and chain carbonates.

  As described above, non-aqueous electrolytes for non-aqueous electrolyte secondary batteries include non-aqueous electrolytes containing cyclic carbonates such as ethylene carbonate, chain carbonates such as dimethyl carbonate, and cyclic esters such as γ-butyrolactone. It has been. For example, γ-butyrolactone is considered to be able to improve the thermal stability of the battery because it has the effect of reducing the reactivity between the non-aqueous electrolyte and the positive electrode. However, the present inventors have examined that γ-butyrolactone is highly reactive with the negative electrode, and therefore it is difficult to improve the thermal stability of the battery simply by blending γ-butyrolactone with the non-aqueous electrolyte. Became clear. For example, fluorinated ethylene carbonate is known to form a protective film on the surface of the negative electrode. This protective film is stably present in the nonaqueous electrolytic solution within a range of about 60 ° C to 80 ° C. Therefore, it is considered that the storage characteristics at high temperature of the battery can be improved by blending fluorinated ethylene carbonate or the like into the non-aqueous electrolyte. However, even when fluorinated ethylene carbonate is blended with the non-aqueous electrolyte, for example, when an internal short circuit occurs, and the battery temperature becomes higher than 150 ° C., the thermal stability of the battery is poor. May be sufficient.

  On the other hand, in the nonaqueous electrolyte secondary battery 1, the nonaqueous solvent of the nonaqueous electrolyte includes γ-butyrolactone, cyclic halogenated carbonate, and chain carbonate, and the solute of the nonaqueous electrolyte is Includes lithium salts containing oxalate complexes. Thereby, the thermal stability of the nonaqueous electrolyte secondary battery 1 is effectively improved. The details of this reason are not necessarily clear, but can be considered as follows, for example.

  The film formed by the decomposition of both the lithium salt containing the oxalate complex and the cyclic halogenated carbonate by coexisting the lithium salt containing the oxalate complex and the cyclic halogenated carbonate is formed only by the decomposition of the cyclic halogenated carbonate. It is considered that the thermal stability is further improved. Furthermore, by using a chain carbonate with a low dielectric constant as the main solvent (more than 50% by volume), decomposition of the coating at high temperatures and dissolution in the electrolyte accompanying decomposition are suppressed, and the coating is maintained. Therefore, it is considered that the reaction between γ-butyrolactone and the negative electrode at a high temperature is suppressed, and the thermal stability of the battery is improved.

In order to further improve the thermal stability of the nonaqueous electrolyte secondary battery 1, lithium bisoxalate borate (LiB (C ₂ O ₄ ) ₂ : LiBOB) is preferable as the lithium salt containing an oxalate complex.

  In order to further improve the thermal stability of the nonaqueous electrolyte secondary battery 1, it is preferable that the lithium salt containing an oxalate complex is contained in an amount of 0.01 mol / l to 0.5 mol / l, More preferably, it is 1 to 0.2 mol / l.

In addition, as a lithium salt containing other oxalate complexes, for example, Li [M (C ₂ O ₄ ) _x R _y ] (wherein, M is a transition metal, from group IIIb, IVb, Vb of the periodic table) element selected, R represents halogen, an alkyl group, a group selected from halogen-substituted alkyl group, x is a positive integer, y is represented by a 0 or a positive integer.), C ₂ O ₄ to the central atom Examples thereof include lithium salts having an anion coordinated with ^2- . Specific examples of lithium salts containing other oxalate complexes include Li [B (C ₂ O ₄ ) F ₂ ], Li [P (C ₂ O ₄ ) F ₄ ], Li [P (C ₂ O ₄ ) _2. F ₂ ] and the like.

The solute may further contain a lithium salt other than the lithium salt containing the oxalate complex. Examples of such other lithium salts include other lithium salts used in conventionally known nonaqueous electrolyte secondary batteries. Examples of the other lithium salt include lithium salts containing at least one element among P, B, F, O, S, N, and Cl. Specific examples of other lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ( CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , and a mixture of at least two of these. In particular, in order to improve the charge / discharge characteristics and durability of the nonaqueous electrolyte secondary battery 1, the solute preferably further contains LiPF ₆ .

  In order to further improve the thermal stability of the nonaqueous electrolyte secondary battery 1, the nonaqueous solvent preferably contains 5% by volume or more and 30% by volume or less of γ-butyrolactone, and is preferably 10% by volume or more and 20% by volume or less. More preferably. When the non-aqueous solvent contains 5% by volume or more of γ-butyrolactone, the reaction between the positive electrode 12 and the non-aqueous electrolyte can be more effectively suppressed. Further, when the non-aqueous solvent contains γ-butyrolactone in an amount of 30% by volume or less, heat generation due to the reaction between γ-butyrolactone and the negative electrode 11 can be suppressed.

  In order to further improve the thermal stability of the nonaqueous electrolyte secondary battery 1, cyclic fluorinated carbonate is preferable as the cyclic halogenated carbonate. Specific examples of the cyclic fluorinated carbonate include fluorinated ethylene carbonate such as monofluoroethylene carbonate and difluoroethylene carbonate. The cyclic halogenated carbonate may be only one type or a mixture of two or more types.

  In order to further improve the thermal stability of the nonaqueous electrolyte secondary battery 1, the nonaqueous solvent preferably contains 0.5% by volume or more and 20% by volume or less of cyclic halogenated carbonate, and is preferably 1% by volume or more and 10% by volume or more. It is more preferable to contain the volume% or less. When the non-aqueous solvent contains 0.5% by volume or more of the cyclic halogenated carbonate, a protective film is effectively formed on the negative electrode 11, and the thermal stability of the non-aqueous electrolyte secondary battery 1 can be further improved. Moreover, when the non-aqueous solvent contains 20% by volume or less of the cyclic halogenated carbonate, it is possible to suppress a decrease in the ionic conductivity of the non-aqueous electrolyte and a decrease in the output characteristics of the non-aqueous electrolyte secondary battery 1. .

  Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like. Only one type of chain carbonate may be used, or a mixture of two or more types may be used. In order to further improve the thermal stability of the non-aqueous electrolyte secondary battery 1, the non-aqueous solvent preferably contains 50% by volume or more and 90% by volume or less of a chain carbonate, and is 60% by volume or more and 80% by volume or less. More preferably. The non-aqueous solvent contains 50% by volume or more and 90% by volume or less of chain carbonate, thereby improving the thermal stability of the non-aqueous electrolyte secondary battery 1 and improving the output characteristics of the non-aqueous electrolyte secondary battery 1. Reduction can be suppressed.

  The non-aqueous solvent may contain a non-aqueous solvent other than γ-butyrolactone, cyclic halogenated carbonate, and chain carbonate. Examples of such other non-aqueous solvents include non-aqueous solvents used in conventionally known non-aqueous electrolyte secondary batteries. Specific examples of other non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate.

  The electrode body 10 is formed by winding a negative electrode 11, a positive electrode 12, and a separator 13 disposed between the negative electrode 11 and the positive electrode 12.

  The separator 13 is not particularly limited as long as it can suppress a short circuit due to contact between the negative electrode 11 and the positive electrode 12 and can impregnate a non-aqueous electrolyte to obtain lithium ion conductivity. Separator 13 can be constituted by a porous film made of resin, for example. Specific examples of the resin porous membrane include, for example, polypropylene and polyethylene porous membranes, and laminates of polypropylene porous membranes and polyethylene porous membranes.

  The negative electrode 11 includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be composed of, for example, a foil made of a metal such as Cu or an alloy containing a metal such as Cu.

  The negative electrode active material layer includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can reversibly store and release lithium. Examples of the negative electrode active material include a carbon material, a material alloyed with lithium, and a metal oxide. Among these, a carbon material is preferable as the negative electrode active material. Specific examples of the carbon material include natural graphite, artificial graphite, mesophase pitch-based carbon fiber (MCF), mesocarbon microbeads (MCMB), coke, and hard carbon. Examples of the material to be alloyed with lithium include one or more metals selected from the group consisting of silicon, germanium, tin, and aluminum, or one or more types selected from the group consisting of silicon, germanium, tin, and aluminum. The thing which consists of an alloy containing a metal is mentioned. In order to improve the charge / discharge characteristics of the nonaqueous electrolyte secondary battery 1, it is particularly preferable to use a carbon material obtained by coating a graphite material with low crystalline carbon as the negative electrode active material.

  The negative electrode active material layer may contain a carbon conductive agent such as graphite, a binder such as sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

  The positive electrode 12 includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector can be made of, for example, a metal such as Al or an alloy containing a metal such as Al.

  The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer may contain appropriate materials such as a binder and a conductive agent in addition to the positive electrode active material. Specific examples of the binder preferably used include, for example, polyvinylidene fluoride. Specific examples of the conductive agent preferably used include carbon materials such as graphite and acetylene black.

The positive electrode active material includes a lithium transition metal composite oxide. The positive electrode active material preferably has a layered structure. The lithium transition metal composite oxide preferably contains Li, Ni, and Mn and has a layered structure. The lithium transition metal composite oxide has a general formula: Li _{1 + x} Ni _a Mn _b Co _c O _{2 + d} [wherein x, a, b, c and d are x + a + b + c = 1, 0 <x ≦ 0.1, 0 ≦ The conditions of c / (a + b) <0.65, 0.7 ≦ a / b ≦ 2.0, and −0.1 ≦ d ≦ 0.1 are satisfied. It is more preferable that it has a layered structure. In the lithium transition metal composite oxide represented by the above general formula, the composition ratio c of cobalt, the composition ratio a of nickel, and the composition ratio b of manganese are 0 ≦ c / (a + b) <0. By satisfying the condition of 65, the proportion of cobalt can be reduced, the material cost can be reduced, and it can be suitably used as a power source for tools and automobiles.

  In the lithium transition metal composite oxide represented by the above general formula, the composition ratio a of nickel and the composition ratio b of manganese satisfy the condition of 0.7 ≦ a / b ≦ 2.0, The thermal stability of the nonaqueous electrolyte secondary battery 1 can be improved. In addition, when the value of a / b is less than 0.7, the ratio of the manganese composition increases, an impurity layer may be generated, and the capacity may be reduced. In order to increase the thermal stability of the nonaqueous electrolyte secondary battery 1 and suppress the decrease in capacity, in the lithium transition metal composite oxide represented by the above general formula, 0.7 ≦ a / b ≦ 1.5 It is more preferable to satisfy the condition.

  In the lithium transition metal composite oxide represented by the above general formula, x in the lithium composition ratio (1 + x) satisfies the condition of 0 <x ≦ 0.1, so that the non-aqueous electrolyte secondary battery 1 The output characteristics can be further improved. When x> 0.1, the amount of alkali remaining on the surface of the lithium transition metal composite oxide increases, and gelation occurs in the slurry in the process of manufacturing the battery, and the amount of transition metal that undergoes a redox reaction May decrease and the battery capacity may decrease. In the lithium transition metal composite oxide represented by the above general formula, it is more preferable that the condition of 0.05 ≦ x ≦ 0.1 is satisfied.

  Further, in the lithium transition metal composite oxide represented by the above general formula, when d in the oxygen composition ratio (2 + d) satisfies the condition of −0.1 ≦ d ≦ 0.1, the lithium transition metal It can be prevented that the complex oxide is in an oxygen deficient state or an oxygen excess state and its crystal structure is damaged.

  The lithium transition metal composite oxide includes boron (B), fluorine (F), magnesium (Mg), aluminum (Al), titanium (Ti), chromium (Cr), vanadium (V), iron ( Fe), copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo), zirconium (Zr), tin (Sn), tungsten (W), sodium (Na), and potassium (K) At least one selected from the group may be included.

  Hereinafter, the present invention will be described in more detail based on specific examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without departing from the scope of the invention.

Example 1
[Production of positive electrode]
Li ₂ CO ₃ and Ni _0.46 Co _0.28 Mn _0.26 (OH) ₂ obtained by the coprecipitation method were mixed at a predetermined ratio. The obtained mixture was fired at 900 ° C. in the air to obtain Li _1.08 Ni _0.43 Co _0.26 Mn _0.24 O ₂ as a positive electrode active material having a layered structure. The average particle diameter of the obtained positive electrode active material was about 8 μm. The positive electrode active material, carbon black as a conductive agent, and N-methyl-2-pyrrolidone solution in which polyvinylidene fluoride as a binder is dissolved, the mass of the positive electrode active material, the conductive agent, and the binder. The ratio was adjusted to 92: 5: 3, and these were kneaded to prepare a positive electrode mixture slurry. Next, this slurry was applied onto a positive electrode current collector made of aluminum foil, and dried. Then, it rolled with the rolling roller and attached the current collection tab of aluminum to this, and produced the positive electrode.

[Production of negative electrode]
Graphite powder was put into a solution in which CMC (carboxymethylcellulose) as a thickener was dissolved in water, and the mixture was stirred and mixed. Next, SBR (styrene butadiene rubber) as a binder was mixed to prepare a slurry. The mass ratio of graphite, CMC, and SBR was 98: 1: 1. This slurry was applied onto a negative electrode current collector made of copper foil, and dried. Then, it rolled with the rolling roller and attached the current collection tab of nickel to this, and produced the negative electrode.

[Preparation of non-aqueous electrolyte]
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), γ-butyrolactone (γ-BL), and fluorinated ethylene carbonate (FEC) in a volume ratio of 22.5: 22.5: 30, respectively. : The mixture so that it might become 20: 5 was used as the non-aqueous solvent. LiPF ₆ as a solute was dissolved in 1 mol / l of the obtained non-aqueous solvent, and 1% by mass of vinylene carbonate was further added. Further, lithium bisoxalate borate (LiBOB) as a solute was added so as to be 0.1 mol / l in the non-aqueous electrolyte to prepare a non-aqueous electrolyte.

[Production of non-aqueous electrolyte secondary battery]
The positive electrode and the negative electrode prepared above were wound up so as to face each other with a polyethylene separator interposed therebetween to prepare a wound body. Next, in a dry box under an argon atmosphere, the wound body is sealed in a battery can together with a non-aqueous electrolyte solution, so that a cylindrical 18650-size non-aqueous electrolyte secondary battery A (end-of-charge voltage: 4. 2V, discharge final voltage: rated capacity at 2.5 V: 1200 mAh).

(Comparative Example 1)
The non-aqueous electrolyte was prepared in the same manner as the battery A, except that in the preparation of the non-aqueous electrolyte, EC, MEC, and DMC were mixed in a volume ratio of 30:30:40 and used as the non-aqueous solvent. A secondary battery B was produced.

(Comparative Example 2)
In the preparation of the non-aqueous electrolyte, the battery A and the battery A were used except that EC, MEC, DMC, and γ-BL were mixed in a volume ratio of 24: 24: 32: 20, respectively, as the non-aqueous solvent. Similarly, a nonaqueous electrolyte secondary battery C was produced.

(Comparative Example 3)
In the preparation of the non-aqueous electrolyte, the battery A and the battery A were used except that EC, MEC, DMC and FEC were mixed in a volume ratio of 28.5: 28.5: 38: 5, respectively. Similarly, a nonaqueous electrolyte secondary battery D was produced.

[Nail penetration test in a charged state]
Battery A to Battery D were each charged with a constant current until the voltage reached 4.2 V at a charging current of 1200 mA. Next, it was charged at a constant voltage until the charging current reached 20 mA at a voltage of 4.2 V. The battery A to the battery D after charging were each made to reach the maximum temperature of the battery A to the battery D after passing a nail of φ = 2.45 mm at a speed of 1 mm / sec with a nail penetration test device manufactured by Toyo System Co., Ltd. Was measured. The maximum temperature reached in the nail penetration test for batteries A to D is summarized in Table 1 based on the temperature reached for battery B.

  As shown in Table 1, battery A containing EC, MEC, DMC, γ-BL, and FEC, and further containing LiBOB has a maximum ultimate temperature of 20 ° C. lower than battery B not containing γ-BL and FEC. The heat stability was high. Further, in the battery C containing γ-BL but not containing FEC, the maximum temperature reached was 100 ° C. higher than that of the battery B, and the thermal stability of the battery was lower. In addition, the battery D containing FEC but not γ-BL had the highest temperature reached that of the battery B, and the effect of improving the thermal stability of the battery was not confirmed.

(Example 2)
[Production of positive electrode]
Li ₂ CO ₃ and Ni _0.50 Co _0.20 Mn _0.30 (OH) ₂ obtained by the coprecipitation method were mixed at a predetermined ratio. The obtained mixture was fired in air at 900 ° C. to obtain Li _1.07 Ni _0.46 Co _0.18 Mn _0.28 O ₂ as a positive electrode active material having a layered structure. The average particle diameter of the positive electrode active material was about 8 μm. The positive electrode active material, carbon black as a conductive agent, and N-methyl-2-pyrrolidone solution in which polyvinylidene fluoride as a binder is dissolved, the mass of the positive electrode active material, the conductive agent, and the binder. The ratio was adjusted to 92: 5: 3, and these were kneaded to prepare a positive electrode mixture slurry. This slurry was applied on a positive electrode current collector made of aluminum foil, and dried. Then, it rolled with the rolling roller and attached the current collection tab of aluminum to this, and produced the positive electrode.

[Production of negative electrode]
Graphite powder was put into a solution in which CMC (carboxymethylcellulose) as a thickener was dissolved in water, and after stirring and mixing, SBR (styrene butadiene rubber) as a binder was mixed to prepare a slurry. The mass ratio of graphite, CMC, and SBR was 98: 1: 1. This slurry was applied onto a negative electrode current collector made of copper foil, and dried. Then, it rolled with the rolling roller and attached the current collection tab of nickel to this, and produced the negative electrode.

[Preparation of non-aqueous electrolyte]
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), γ-butyrolactone (γ-BL), and fluorinated ethylene carbonate (FEC) in a volume ratio of 22.5: 22.5: 30, respectively. : The mixture so that it might become 20: 5 was used as the non-aqueous solvent. 1 mol / l of LiPF ₆ as a solute was dissolved in the non-aqueous solvent thus prepared, and 1% by mass of vinylene carbonate was further added. Further, lithium bisoxalate borate (LiBOB) as a solute was added so as to be 0.1 mol / l in the non-aqueous electrolyte to prepare a non-aqueous electrolyte.

[Production of non-aqueous electrolyte secondary battery]
The wound body (electrode body) was fabricated by winding so as to face each other through the positive electrode and the negative electrode produced above and a polyethylene separator. Next, in a dry box under an argon atmosphere, the wound body is enclosed in a laminate outer package together with an electrolytic solution, whereby a non-aqueous electrolyte secondary battery E having a rated capacity of 16 mAh at 4.1 V charging is obtained. Produced.

(Example 3)
In the preparation of the non-aqueous electrolyte, EC, MEC, DMC, γ-BL, and FEC were mixed in a volume ratio of 15: 50: 20: 10: 5, respectively, except that a non-aqueous solvent was used. A nonaqueous electrolyte secondary battery F was produced in the same manner as the battery E.

(Comparative Example 4)
In the preparation of the non-aqueous electrolyte, the non-aqueous electrolyte secondary was the same as the battery E, except that EC, MEC, and DMC were mixed in a volume ratio of 30:30:40 as the solvent. Battery G was produced.

(Calorimetric measurement using a Calve calorimeter)
The batteries E to G were each charged with a constant current until the voltage reached 4.1 V at a charging current of 4 mA. Next, the battery was charged at a constant voltage until the charging current became 0.8 mA at a voltage of 4.1 V, and after resting, the battery was discharged to a voltage of 2.5 V at a current of 4 mA. After performing this charging / discharging cycle twice, constant current charging was performed until the voltage reached 4.1 V at a charging current of 4 mA. Furthermore, the battery was charged at a constant voltage until the charging current reached 0.8 mA at a voltage of 4.1 V. The laminates of batteries E to G, each in a fully charged state, were opened, and the wound body was taken out. Next, the wound body was put in a pressure-resistant container for calorimetry, and a calorific value of 160 ° C. to 290 ° C. was obtained. The calorific value was measured by using a Calbe calorimeter C-80 manufactured by Setaram under the conditions of 30 ° C. to 300 ° C. and a heating rate of 1.0 ° C./min. Table 2 shows the relative calorific value of each battery determined with the calorific value of battery G as 100.

  As shown in Table 2, the battery E and the battery F including EC, MEC, DMC, γ-BL, and FEC, and further including LiBOB have a lower heating value than the battery G not including γ-BL and FEC. The heat stability was high. It can be seen that this result corresponds to the result of the nail penetration test. That is, in battery A, it is considered that the maximum temperature reached was lowered as a result of the reduction in the amount of heat generated in the nail penetration test. In the battery F in which the proportion of the chain carbonate in the non-aqueous solvent (total amount of MEC and DMC) was larger than that in the battery E, the calorific value was lower than that in the battery E, and the thermal stability was further higher.

DESCRIPTION OF SYMBOLS 1 ... Nonaqueous electrolyte secondary battery 10 ... Electrode body 11 ... Negative electrode 12 ... Positive electrode 13 ... Separator 17 ... Battery container

Claims (10)

A positive electrode comprising a lithium transition metal composite oxide as a positive electrode active material;
A negative electrode containing a negative electrode active material;
A non-aqueous electrolyte containing a solute and a non-aqueous solvent;
With
The non-aqueous solvent includes γ-butyrolactone, a cyclic halogenated carbonate, and a chain carbonate,
The solute is a nonaqueous electrolyte secondary battery including a lithium salt containing an oxalate complex.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous solvent contains 50% by volume to 90% by volume of chain carbonate.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the cyclic halogenated carbonate is a cyclic fluorinated carbonate.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the lithium salt containing the oxalate complex is lithium bisoxalate borate.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the lithium transition metal composite oxide includes Li, Ni, and Mn and has a layered structure. The lithium transition metal composite oxide has a general formula:
Li _{1 + x} Ni _a Mn _b Co _c O _{2 + d}
[Wherein, x, a, b, c and d are x + a + b + c = 1, 0 <x ≦ 0.1, 0 ≦ c / (a + b) <0.65, 0.7 ≦ a / b ≦ 2. 0, −0.1 ≦ d ≦ 0.1 is satisfied. ]
The nonaqueous electrolyte secondary battery of Claim 5 represented by these.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the nonaqueous solvent contains a chain carbonate in an amount of 60% by volume to 80% by volume.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the nonaqueous solvent contains γ-butyrolactone in an amount of 5% by volume to 30% by volume.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein the nonaqueous solvent contains a cyclic halogenated carbonate in an amount of 0.5% by volume or more and 20% by volume or less.   10. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte solution includes a lithium salt containing an oxalate complex in an amount of 0.01 mol / l or more and 0.5 mol / l or less.