JPH06290809A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a non-aqueous electrolyte secondary battery, which has a long life and is excellent in capacity retention, by improving solvent composition of an electrolyte. CONSTITUTION:A non-aqueous electrolyte secondary battery is provided with a negative electrode 3 consisting of a carbon material, which can storage/discharge a lithium ion, and a positive electrode 1 consisting of a non-aqueous electrolyte and oxide including lithium. A titanium positive electrode lead plate 2 is spot-welded in the upper part of the positive electrode 1 while a nickel negative electrode lead plate 4 is spot- welded on the lower side of the negative electrode 3, and a separator 5 is arranged between the positive electrode 1 and the negative electrode 3, and a group of electrode plates is constructed by winding the whole of them spirally. A solvent of the non- aqueous electrolyte includes a mixed solvent of cyclic carbonate and chain carbonate represented by a general formula ROCOR' (Rnot equal to R', R, R'represent alkyl groups of carbon number 1-4), and a rate of the volume of the chain carbonate to the volume of the cyclic carbonate is 1-9. When spacing of 002 face (d002) by X-ray diffraction method in the negative electrode carbon material is 3.39Angstrom or less, the cyclic carbonate and ethylene carbonate are used, while propylene carbonate is used when spacing is 3.39Angstrom or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improving the cycle life and capacity characteristics of this battery at low temperatures.

[0002]

2. Description of the Related Art In recent years, portable electronic devices and cordless electronic devices have been rapidly developed, and there is a great demand for a small and lightweight secondary battery having high energy density as a power source for driving these electronic devices. In this regard, non-aqueous electrolyte secondary batteries,
In particular, lithium secondary batteries are highly expected as batteries having high voltage and high energy density.

When making a non-aqueous electrolyte battery into a secondary battery, it is desired that the positive electrode active material has a high capacity and a high voltage.
LiCoO ₂ and LiMn ₂ O satisfy the requirements.
A material showing a high voltage of 4V of ₄ series is mentioned.

On the other hand, as negative electrode materials, metallic lithium, lithium alloys, and carbon materials capable of absorbing and releasing lithium ions have been investigated. However, metallic lithium has a problem of short-circuiting due to dendritic products (dendrites) associated with charge and discharge, and lithium alloy has a problem of electrode collapse due to expansion and contraction associated with charge and discharge. Therefore, recently, carbon materials that do not cause these problems have been regarded as promising as negative electrode materials for lithium secondary batteries.

Generally, when metallic lithium is used as the negative electrode material, active dendrites generated on the negative electrode surface during charging react with a non-aqueous solvent to cause a decomposition reaction in a part of the solvent, which increases charging efficiency. Lowering is well known. As a measure for solving this, Japanese Patent Laid-Open No. 1704646/1982.
In the publication, attention is paid to the fact that ethylene carbonate is excellent in charging efficiency, and it is proposed to use a mixed solvent of ethylene carbonate and propylene carbonate. Further, in JP-A-3-55770, in order to improve low temperature characteristics of a battery, 2-methyltetrahydrofuran, 1,2-dimethoxyethane, 4-methyl-1,3-dioxolane, etc. are mixed in a mixed solvent of ethylene carbonate and diethyl carbonate, It has been proposed to use it as a solvent for non-aqueous electrolytes.

However, even if these systems are used, the charging efficiency is limited to about 98 to 99% at the maximum, and the charging efficiency is not yet sufficiently increased. This is the same even when a lithium alloy is used for the negative electrode.

[0007]

When a carbon material is used as the negative electrode material, the charging reaction is a reaction in which lithium ions in the electrolytic solution intercalate between the layers of the carbon material, so that dendrite of lithium is produced. Therefore, the decomposition reaction of the solvent on the surface of the negative electrode should not occur.
However, in reality, the charging efficiency is less than 100%, and the same problem as in the case of using lithium or a lithium alloy for the negative electrode remains.

The present inventors have not found that this phenomenon is due to the decomposition reaction of the solvent on the surface of the negative electrode as in the case where lithium metal is used for the negative electrode, and does not occur when lithium intercalates between the layers of the negative electrode carbon material. It was thought that this is because not only the solvent coordinated with lithium was also drawn between the layers, causing a decomposition reaction in part of the solvent.

That is, the solvent having a large molecular radius is not smoothly intercalated between the layers of the negative electrode carbon material and is decomposed at the inlet between the layers of the negative electrode material.

Generally, a requirement for a good solvent as an electrolyte for a lithium battery is that it has a large dielectric constant, that is, it can dissolve a large amount of an inorganic salt as a solute. Cyclic carbonates such as propylene carbonate and ethylene carbonate are said to be excellent solvents that satisfy this requirement, but these all have a large molecular radius because of their cyclic structure, and when a carbon material is used for the negative electrode, As described above, there is a problem that the decomposition reaction of the solvent accompanies the charging. However, in that case, if an amorphous carbon material having a relatively large interlayer distance is used as the carbon material of the negative electrode, the degree of decomposition of the solvent tends to decrease.

Further, since these solvents are highly viscous,
When used alone, it has a drawback that the viscosity of the electrolyte is high and charging and discharging at a high rate is difficult, and the battery capacity at low temperature is small. Especially ethylene carbonate has a freezing point of 36.4 ° C.
It is high and cannot be used alone. As a method of compensating for this drawback, as described above, a method of mixing ethers such as 2 methyltetrahydrofuran, 1,2 dimethoxyethane and 4 methyl 1,3 dioxolane is generally used. On the other hand, these ethers have a low oxidative decomposition voltage, and when used in a secondary battery, their decomposition reaction occurs during battery charging, resulting in a short cycle life.

On the other hand, due to the structure of the chain carbonate, it is easy to enter between the layers of the carbonaceous material, and the decomposition reaction during charging is unlikely to occur. On the contrary, these solvents have a relatively low dielectric constant, and an inorganic salt that is a solute is formed. It has the drawback of being difficult to dissolve. In particular, a symmetrical carbonate in which the hydrocarbon groups R and R'in the structural formula ROCOOR 'are the same, for example, dimethyl carbonate in which R has 1 carbon atom has a high melting point of 0.5 ° C. because of its structurally good symmetry. Due to its low temperature characteristics, it is difficult to use as a solvent for lithium secondary batteries. Diethyl carbonate having 2 carbon atoms has a high degree of structural freedom and a low melting point as the number of carbon atoms is large, but on the contrary, the dielectric constant is low and the solubility of the electrolyte is low, which makes it difficult to use as a solvent.

Compared with these symmetric chain carbonates, asymmetric carbonates in which R and R'in the above structural formula are different, for example, ethyl methyl carbonate in which R and R'have 1 and 2 carbon atoms, respectively, are superior. It has been reported in JP-A-2-148665 that it is a solvent, but if it is used alone, the solute-dissolving ability at low temperatures is insufficient, so there was a problem with the discharge characteristics at low temperatures.

Furthermore, when cyclic and chain carbonates are mixed and used, it is possible to solve the above-mentioned problems that occur when each is used alone, and it is possible to improve the charge / discharge characteristics of the battery at room temperature. It is described in Kaihei 2-289150. The present invention finds and reports that the asymmetric chain carbonate is particularly excellent among them.

The present invention solves the above-mentioned problems.
The main object of the present invention is to provide a non-aqueous electrolyte secondary battery having a long life and an excellent capacity retention rate at low temperatures.

Another object of the present invention is to provide a solvent composition of the non-aqueous electrolyte solution which is preferable for the non-aqueous electrolyte secondary battery.

[0017]

In order to solve the above problems and achieve the above-mentioned objects, the present invention provides a general formula ROCO.
The solvent of the electrolytic solution contains a chain carbonate represented by OR '(where R ≠ R', R and R'are alkyl groups having 1 to 4 carbon atoms) and a cyclic carbonate. Particularly, the ratio of the volume of chain carbonate / the volume of ethylene carbonate is set to 1 or more and 9 or less, and the total volume is 70% in all solvents.
When it is at least%, an excellent electrolytic solution for a non-aqueous electrolytic solution secondary battery is provided.

At that time, when a carbon material having a 002 plane spacing (d002) of 3.39Å or less by X-ray diffraction method is used for the negative electrode, the cyclic carbonate is a carbon material of ethylene carbonate of 3.40Å or more. Propylene carbonate is an optimal combination as the cyclic carbonate when is used for the negative electrode.

[0019]

[Function] The cyclic carbonate in the electrolytic solution is effective in increasing the conductivity of the electrolytic solution by dissolving a large amount of the inorganic salt that is a solute, and the chain carbonate easily coordinates with lithium during battery charging. In addition, since the carbonaceous material can enter the interlayer, the decomposition of the solvent can be suppressed.

In particular, by using an asymmetric chain carbonate, an electrolytic solution having a high conductivity and a low melting point can be obtained, and as a result, excellent low temperature characteristics are exhibited.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. In these examples, a cylindrical battery was constructed and evaluated.

(Embodiment 1) FIG. 1 shows a vertical sectional view of a cylindrical battery. In the figure, 1 indicates a positive electrode, which is an active material Li.
CoO ₂ mixed with carbon black as a conductive material and an aqueous dispersion of polytetrafluoroethylene as a binder in a weight ratio of 100: 3: 10 was applied to both sides of an aluminum foil and dried, After being rolled, it is cut into a predetermined size. To this, 2 titanium lead plates are spot welded. The mixing ratio of the aqueous dispersion of polytetrafluoroethylene as the binder is calculated by its solid content. 3 is a negative electrode, which is obtained by heat-treating mesocarbon microbeads at 2800 ° C. and graphitized (d
002 = 3.38Å) as a main material, and a mixture of this and an acrylic binder in a weight ratio of 100: 5 was applied on both sides of a nickel foil, dried, and rolled to a predetermined size. It is cut into pieces. Also, a nickel negative electrode lead plate shown by 4 is spot-welded to the lower side of this. 5
Is a separator made of a polypropylene microporous film, which is interposed between the positive electrode 1 and the negative electrode 3 and is wholly wound in a spiral to form an electrode plate group. Insulating plates 6 and 7 made of polypropylene are arranged at the upper and lower ends of the electrode plate group, respectively, and inserted into a case 8 made of nickel plated with iron. The positive electrode lead 2 is attached to the titanium sealing plate 10 and the negative electrode lead 4 is attached.
After spot welding to the bottom of the case 8, a predetermined amount of electrolytic solution is injected into the case, and the battery is sealed with the sealing plate 10 through the gasket 9 to complete the battery. The dimensions of this battery are 14 mm in diameter and 50 mm in height. In addition, 11 is a positive electrode terminal of the battery, and the battery case 8 also serves as a negative electrode terminal.

Example 1-1 will be described below. (Example 1-1) Ethylene carbonate (hereinafter referred to as EC) which is a cyclic carbonate, tetrahydrofuran (hereinafter referred to as THF) which is a cyclic ether, and dimethoxyethane (hereinafter referred to as D) which is a chain ether are used as the solvent of the electrolytic solution.
Cylindrical batteries A to E shown below were manufactured by using ME) and ethyl methyl carbonate (hereinafter referred to as EMC) which is a chain carbonate. The mixing ratio is shown by volume ratio. Lithium hexafluorophosphate was used as the solute of the electrolytic solution, and the concentration was adjusted to 1 mol / l. Hereinafter, the type and concentration of the solute were the same in all the examples.

Battery A ... EC = 100 Battery B ... EC: THF = 20: 80 Battery C ... EC: DME = 20: 80 Battery D ... EC: EMC = 20: 80 Battery E ... EMC = 100 The battery characteristics evaluated are cycle life characteristics and low temperature characteristics.

The test conditions were a charge / discharge current of 100 mA, a charge end voltage of 4.2 V, and a discharge end voltage of 3.0 V. Charging / discharging was performed once at 20 ° C., and after further charging, the temperature was −10 ° C.
The discharge temperature was changed to, and the low temperature characteristics were evaluated by the magnitude of the discharge capacity. Thereafter, the temperature was returned to 20 ° C., charging and discharging were repeated under the same voltage and current conditions, the test was terminated when the discharge capacity deteriorated to 50% of the initial value, and the number of cycles was taken as the cycle life. In all the following examples, the tests were conducted under the same conditions.

The cycle life characteristics of the batteries A to E are shown in FIG. From FIG. 2, in order of good cycle life characteristics, DEA-A-
It became CB. Among them, the cycle life of B and C containing the ether solvent was short, but it is considered that this is because the ether or THF or DME is decomposed during charging as described above. Next, the cycle life of A in which the cyclic ester was used alone was short. At the time of charging, at the negative electrode, a reaction occurs in which lithium ions intercalate between the layers of the carbon material, but at that time the solvent molecules coordinated with the lithium ions also try to be drawn into the layers, and thus have a cyclic structure and molecular It is considered that the large solvent partially decomposes, resulting in deterioration of cycle characteristics. In addition, chain carbonate alone E
Had the second longest cycle life, but the discharge capacity was small. It is considered that this is because the conductivity of the electrolytic solution was low due to the low dielectric constant of the solvent, the polarization of the battery was large, and the discharge end voltage was reached quickly. The mixed system of cyclic carbonate and chain carbonate of D has the effect of increasing the conductivity of the electrolytic solution by dissolving a large amount of the inorganic salt that is a solute of the cyclic ester, and the lithium carbonate is distributed when the battery of chain carbonate is charged. The cycle life was the longest due to the effect of suppressing the decomposition of the solvent due to the fact that it can easily enter the layers of the carbon material.

Next, referring to FIG. 3, in the order of good low temperature characteristics, BC
-D-A, E, and A and E did not work at low temperature. A is a high freezing point solvent alone, so the electrolyte does not work at low temperature and does not work, and E is a low dielectric constant solvent alone, so it has a low electrical conductivity at low temperature and therefore a large polarization of the battery It is considered that the discharge could not be completed because the discharge end voltage was reached immediately after the flow of the current.

On the other hand, the cyclic carbonate and ether mixed systems B and C showed good low temperature characteristics because they had relatively high electric conductivity even at low temperature. Compared to B and C, the mixed system of the cyclic carbonate and the chain carbonate of D has a lower electric conductivity and a higher viscosity than that of the ether system, so that the low temperature characteristics are slightly inferior.

From the above results, it was the mixed system of cyclic carbonate and chain carbonate that was excellent in both cycle life characteristics and low temperature characteristics.

Next, Example 1-2 will be described. (Example 1-2) In addition to EC and EMC used in Example 1-1 as a solvent of an electrolytic solution, propylene carbonate (hereinafter referred to as PC) which is a cyclic carbonate, dimethyl carbonate (hereinafter referred to as DMC) which is a chain carbonate. The above cylindrical battery was prototyped for the following 6 types of mixed solvent systems prepared by combining diethyl carbonate (hereinafter referred to as DEC) and propylethyl carbonate (hereinafter referred to as PEC).

Battery F ... EC: DMC = 20: 80 Battery G ... EC: EMC = 20: 80 Battery H ... EC: DEC = 20: 80 Battery I ... EC: PEC = 20: 80 Battery J ... PC: DMC = 20: 80 Battery K ... PC: EMC = 20: 80 Battery L ... PC: DEC = 20: 80 Battery M ... PC: PEC = 20: 80 Cycle life characteristics of batteries F to M Figure 4, Figure 5 shows the low temperature characteristics
Shown in.

From FIG. 4, F-
G-HI-J-J, K, L, M, and all of J, K, L, M were found to leak into the battery by 5 cycles. This is the Journal of Electrochemi
cal Science vol, 117 No. 2 (1
970). N. As described by Dey et al., The decomposition reaction of PC occurred on graphite and gas was generated, so that the battery was opened (vented) and leaked, and thereafter charge / discharge was impossible.

Further, when compared by the EC system, no large difference was observed, but the tendency was that the chain carbonate having a smaller molecular structure had better cycle life characteristics. This is presumably because the smaller the solvent molecules are when the intercalating with the lithium ions into the carbon material layer of the negative electrode during charging, the more difficult the solvent is to decompose.

From the above results, when mesocarbon microbeads (d002 = 3.38Å) were used for the negative electrode, the cycle life characteristics were good when ethylene carbonate was used for the cyclic carbonate, and the chain carbonate to be mixed was used. Has been found to be better the smaller the molecule.

Next, referring to FIG.
-L-G-I-H-J-F and F did not work at all. This is because both EC and DMC have a high freezing point of 0 ° C. or higher, so that the electrolytic solution is solidified at −10 ° C. J, which is a mixed system of PC and DMC, was next bad. In contrast, KM or GI using low freezing point EMC, PEC, and DEC exhibited relatively good low-temperature characteristics. In particular, the low-temperature characteristics were particularly good when EMC and PEC asymmetric chain carbonates were used. When PC is used as the cyclic carbonate, the low temperature characteristics are superior to when EC is used, and it is considered that this is because the viscosity of the electrolytic solution at low temperature is lower when PC is used.

From the above results, when mesocarbon microbeads (d002 = 3.38Å) were used for the negative electrode, both the cycle life characteristics and the low temperature characteristics at −10 ° C. exhibited a mixed system of EC and an asymmetric chain carbonate. Was good, and especially the mixed system of EC and EMC was good.

Next, Examples 1-3 will be described. (Example 1-3) Using the EC and EMC that showed the best characteristics in Example 1-2 as the solvent for the electrolytic solution, the above cylindrical battery was prototyped for the following six mixed solvent systems. It was

Battery N ... EC: EMC = 5: 95 Battery O ... EC: EMC = 10: 90 Battery P ... EC: EMC = 20: 80 Battery Q ... EC: EMC = 30: 70 Battery R ... ... EC: EMC = 40: 60 Battery S ... EC: EMC = 50: 50 Battery T ... EC: EMC = 60: 40 Battery N to T cycle life characteristics are shown in FIG. 6 and low temperature characteristics are shown in FIG.
Are shown respectively.

From FIG. 6, O-
It became P-Q-R-S-N-T. The life of T is short because the solvent molecules are large and the ratio of EC that is easily decomposed during charging is large, and the life of N is short because the ratio of EC is small and the solute dissolving ability is insufficient. It is considered that the conductivity of the electrolyte was lowered, the charge / discharge reaction did not occur uniformly in the battery, and the capacity deterioration due to the cycle of the portion having a deep reaction depth increased, and the capacity deterioration of the battery as a whole also increased. In other batteries of O to S, the solvent molecules were small, and the larger the ratio of EMC, which is considered to be less likely to be decomposed during charging, was, the better the cycle life characteristics were.

Next, as shown in FIG. 7, P-O-
Q-R-S-N, T, and N and T did not work at all. The reason why T did not work was that the proportion of EC in the high freezing point solvent was large, so that the electrolytic solution solidified at a low temperature.
On the other hand, it is considered that the reason why N did not work was that the solute dissolving ability was insufficient due to the small proportion of EC, and the electrical conductivity of the electrolytic solution was reduced accordingly. In the other batteries of O to S, the composition having higher conductivity had better low temperature characteristics.

From the above results, it was found that the mixing ratio of EC and EMC is preferably such that the value of EC / EMC is 1 or more and 9 or less.

Next, the crystallinity of the carbon material of the negative electrode and the optimum kind of cyclic carbonate were examined.

Vapor grown carbon fiber (VGCF) was used for the negative electrode, and the firing temperature was changed in the range of 1400 to 2800 ° C. to change the interplanar spacing (d002) value of the 002 plane by the X-ray diffraction method. EC + E for the negative electrode of
The suitability of two types of electrolytic solutions, MC and PC + EMC, was examined.

The second embodiment will be described below. (Example 2) A battery was prepared under exactly the same conditions as in Example 1 except that the negative electrode material and the solvent in the electrolytic solution were different. The contents of the trial manufacture of the battery are shown in (Table 1) below. The mixing ratio of the solvents was 20:80 by volume.

[0045]

[Table 1]

FIG. 8 shows the cycle life characteristics of the batteries a to j, and FIG. 9 shows the discharge capacity at the 10th cycle of each battery.

From FIG. 8, all the batteries except f and g had a long cycle life, but with f and g, leakage was recognized in the battery by the 5th cycle. From this, when the interplanar spacing (d002) value of the 002 surface by the X-ray diffraction method of the negative electrode is 3.39 Å or less, gas is generated when PC is used as the solvent of the electrolytic solution
It has been found that when the pressure is 3.43 Å or more, good cycle life characteristics can be obtained without generating gas. It is considered that the reason why the cycle life of the battery h is slightly short is that a part of the PC generates gas.

Although there is no big difference, the cycle life of the battery tends to be longer as the d002 value of the negative electrode is larger.
It is considered that this is because the larger the carbon layer is, the less likely the solvent is decomposed.

On the other hand, from FIG. 9, the discharge capacity of the battery is d of the negative electrode.
It was found that the smaller the value of 002, that is, the higher the crystallinity of the negative electrode, the larger the value is, and that the cyclic carbonate used in the electrolytic solution is PC rather than EC.

From the above results, when the value of the spacing (d002) of the 002 plane of the carbon material of the negative electrode by the X-ray diffraction method is 3.39Å or less, the cyclic carbonate as the solvent of the electrolytic solution becomes E.
By using C and using PC in the case of 3.40 Å or more, excellent cycle life characteristics and capacity characteristics can be obtained.

Although the composite oxide of lithium and cobalt was used as the positive electrode active material in the examples, other composite oxides of lithium and nickel, composite oxides of lithium and manganese, and composite oxides of lithium and iron were used. Lithium-containing oxides such as, or cobalt of each of the above composite oxides,
Similar results were obtained with nickel, manganese, and iron partially replaced with other transition metals.

Although lithium hexafluorophosphate was used as the solute of the electrolytic solution, other lithium-containing salts such as lithium borofluoride, lithium perchlorate, lithium trifluoromethanesulfonate, and lithium hexafluoroarsenate were used. Almost similar results were obtained by using

Although ethyl methyl carbonate and propyl ethyl carbonate were used as the asymmetric chain carbonates, other similar results were obtained with propyl methyl carbonate, for example. However, its structural formula R
When the carbon number in R and R'in OCOOR 'becomes 5 or more, the dielectric constant decreases, so that the carbon number is preferably 4 or less.

Further, the sum of the volumes of the cyclic carbonate and the chain carbonate needs to be a main component of the solvent for good cycle characteristics of the battery, and the above sum is 70% or more of the total volume of the solvent. It is desirable to occupy.

[0055]

As is apparent from the above description, according to the present invention, the binary carbonate mixed solvent of the cyclic carbonate and the asymmetric chain carbonate is used as the solvent of the electrolytic solution, and the volume of the chain carbonate / cyclic carbonate is increased. When the ratio is 1 or more and 9 or less and the total volume (sum) occupies 70% or more of the total solvent volume, it is possible to provide a non-aqueous electrolyte secondary battery having excellent cycle life characteristics and low temperature characteristics. .

At that time, when a carbon material having a 002 plane spacing (d002) of 3.39Å or less by the X-ray diffraction method is used for the negative electrode, the cyclic carbonate contains ethylene carbonate of 3.40Å or more. Propylene carbonate is the optimal combination of cyclic carbonates when materials are used.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a cylindrical battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the cycle life of the battery in Example 1-1 at 20 ° C.

FIG. 3 is a graph showing changes in the discharge voltage at −10 ° C. of the battery in Example 1-1.

FIG. 4 is a diagram showing the cycle life of the battery in Example 1-2 at 20 ° C.

FIG. 5 is a graph showing changes in the discharge voltage at −10 ° C. of the battery in Example 1-2.

FIG. 6 is a diagram showing the cycle life of the battery in Example 1-3 at 20 ° C.

FIG. 7 is a graph showing changes in discharge voltage at −10 ° C. of the battery in Example 1-3.

FIG. 8 is a diagram showing the cycle life of the battery in Example 2 at 20 ° C.

9 is a diagram showing the discharge capacity at the 10th cycle of the battery in Example 2. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode lead plate 3 Negative electrode 4 Negative electrode lead plate 5 Separator 6 Upper insulating plate 7 Lower insulating plate 8 Case 9 Gasket 10 Sealing plate 11 Positive electrode terminal

Claims (11)

[Claims] 1. A negative electrode made of a carbon material capable of inserting and extracting lithium ions, a non-aqueous electrolytic solution, and a positive electrode made of a lithium-containing oxide. The non-aqueous electrolytic solution is used as a solvent for the non-aqueous electrolytic solution.
A non-aqueous liquid containing a mixed solvent of an asymmetric chain carbonate and a cyclic carbonate represented by the general formula ROCOOR '(where R ≠ R', R and R'are alkyl groups having 1 to 4 carbon atoms). Electrolyte secondary battery. 2. The non-aqueous electrolyte solution according to claim 1, wherein the asymmetric chain carbonate which is a solvent component of the electrolyte solution is one of the group consisting of ethylmethyl carbonate, propylmethyl carbonate and propylethyl carbonate. Secondary battery. 3. The volume ratio of the asymmetric chain carbonate / volume of the cyclic carbonate, which is the solvent component of the electrolytic solution, is 1
The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the total volume of the asymmetric chain carbonate and the cyclic carbonate accounts for 70% or more of the total solvent. 4. The non-aqueous electrolyte contains at least one of the group consisting of lithium hexafluorophosphate, lithium borofluoride, lithium perchlorate and lithium trifluoromethanesulfonate as a solute. The non-aqueous electrolyte secondary battery according to any one of 1. 5. The positive electrode active material is a composite oxide of lithium and cobalt, a composite oxide of lithium and nickel, a composite oxide of lithium and manganese, a composite oxide of lithium and iron, and cobalt of each of the above composite oxides. ,nickel,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, which is any one of the group consisting of manganese and iron partially substituted with other transition metals. 6. The carbonaceous material of the negative electrode is one selected from the group consisting of coal coke, petroleum coke, and carbon fiber heat-treated at a temperature of 2000 ° C. or higher, artificial graphite, natural graphite, or two or more kinds. The non-aqueous electrolyte secondary battery according to claim 1, wherein the cyclic carbonate that is a mixture and is a solvent component of the electrolyte is ethylene carbonate. 7. The non-aqueous electrolyte secondary battery according to claim 6, wherein the carbonaceous material of the negative electrode has a 002 plane spacing (d002) of 3.39 Å or less according to the X-ray diffraction method. 8. The negative electrode carbonaceous material has an interplanar spacing (d002) of 002 planes of 3.36 Å or more by X-ray diffractometry 3.3 or more.
The non-aqueous electrolyte secondary battery according to claim 6, which has a height of 9 Å or less. 9. The carbonaceous material of the negative electrode is mesocarbon microbeads made of mesophase microspheres produced in the carbonization process of pitch as a raw material and heat-treated at a temperature of 2000 ° C. or higher to be graphitized, and X The 002 plane spacing (d002) measured by the line wide-angle diffraction method is 3.36 Å or more.
The non-aqueous electrolyte secondary battery according to claim 8, which has a volume ratio of 38 Å or less. 10. The carbonaceous material of the negative electrode has an interplanar spacing (d002) of 002 planes of 3.40Å or more by an X-ray diffraction method, and a cyclic carbonate which is a solvent component of the electrolytic solution is propylene carbonate. Item 6. A non-aqueous electrolyte secondary battery according to any one of items 1 to 5. 11. The negative electrode carbonaceous material has an 002 plane spacing (d002) of 3.43 Å or more as determined by an X-ray diffraction method, and a cyclic carbonate which is a solvent component of the electrolytic solution is propylene carbonate. Item 6. A non-aqueous electrolyte secondary battery according to any one of items 1 to 5.