JPH11273726A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with high cycle characteristics at a high temperature by preventing the decomposition polymerization of a nonaqueous solvent on the surface of a positive electrode of a lithium secondary battery by using an optimum nonaqueous electrolyte. SOLUTION: A nonaqueous electrolyte secondary battery uses a positive active material and a negative active material both capable of intercalating/ deintercalting lithium, and a nonaqueous electrolyte prepared by dissolving an electrolyte in a nonaqueous solvent. Vinylene carbonate(VC) and N-(benzyl oxi carbonyl oxi) succinimide(NBCS) are included in the nonaqueous solvent of the nonaqueous electrolyte in the weight ratio of NBCS/VC=0.02-1.0.

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 an electrolyte solvent capable of improving capacity deterioration due to progress of a cycle in a high temperature state.

[0002]

2. Description of the Related Art In recent years, with the miniaturization, weight reduction, and portability of camera-integrated VTRs, telephones, laptop computers, and the like, there has been a demand for smaller, lighter, higher capacity secondary batteries used as power supplies for these electronic devices. Is growing.

[0003] Examples of the secondary battery include a nickel-cadmium secondary battery, a lead storage secondary battery, a nickel hydride secondary battery, a lithium ion secondary battery and the like. Oxides and lithium ion secondary batteries using carbon materials for the negative electrode are particularly lightweight,
Since a high energy density can be obtained, there is a high demand for a next-generation secondary battery, and research is being conducted with the aim of further improving its characteristics.

This lithium ion secondary battery comprises a positive electrode plate formed by applying a positive electrode mixture containing an oxide containing Li or the like as a positive electrode active material to the surface of a current collector, and a negative electrode sheet made of a carbon material. And a liquid obtained by adding, for example, LiPF ₆ as an electrolyte to an organic solvent such as ethylene carbonate or diethyl carbonate as an electrolyte. Lithium always exists in an ion state inside the battery, and charge and discharge is performed. In this case, only lithium ions (cations) enter and leave by intercalation / deintercalation reactions between the layers of the crystals of the positive electrode and the negative electrode material or between lattice points or lattice gaps.

[0005]

However, when the lithium ion secondary battery is repeatedly charged or discharged or stored in a high temperature state, the electrolyte inside the battery rises because the electrolyte is decomposed on the surface of the positive electrode. Therefore, a change in the lattice size of the positive electrode material (lithium-containing transition metal transition metal oxide) and the negative electrode material (carbon) due to the above-mentioned lithium ion intercalation and deintercalation reactions that occur during charging and discharging of the battery. And the battery capacity is reduced.

[0006] Further, by repeating charge and discharge in a high temperature state, the transition metal element is dissolved from the lithium-containing transition metal transition metal oxide in the positive electrode, and solvates with the electrolyte to form a complex. This complex acts as an initiator of the polymerization reaction of the cyclic carbonate, whereby the polymerized electrolytic solution is clogged in the fine pores of the separator separating the positive electrode and the negative electrode, and the movement of lithium ions between the positive electrode and the negative electrode is prevented. There is a problem that the battery characteristics are deteriorated by the inhibition.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the decomposition and polymerization of a non-aqueous solvent that occurs on the surface of a positive electrode of a lithium secondary battery, and to provide a high-temperature cycle characteristic. An object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of improving as much as possible.

[0008]

In order to achieve the above object, according to the present invention, a material capable of intercalating and deintercalating lithium into a positive electrode active material and a negative electrode active material is used as a non-aqueous electrolyte. In a non-aqueous electrolyte secondary battery using a non-aqueous solvent in which an electrolyte is dissolved, in the non-aqueous solvent of the non-aqueous electrolyte, vinylene carbonate and N-
(Benzyloxycarbonyloxy) succinimide (claim 1).

In the electrolyte, vinylene carbonate and N-
By containing (benzyloxycarbonyloxy) succinimide, vinylene carbonate and N- (benzyloxycarbonyloxy) succinimide are present at a high concentration on the surface of the positive electrode active material, preventing other solvent molecules from approaching the electrode surface. By doing so, it is considered that decomposition of the electrolytic solution and gas generation on the surface of the active material are suppressed. In a high temperature state, at the solid-liquid interface between the active material surface and the electrolyte, the transition metal element existing near the solid-liquid interface of the active material is dissolved in the electrolyte. It is expected that the dissolved transition metal element solvates with the electrolyte to form a complex, and this complex serves as a polymerization initiator, which is expected to cause a polymerization reaction of the electrolyte. It is expected to be attacked and cause a polymerization reaction. However, since N- (benzyloxycarbonyloxy) succinimide is present on vinylene carbonate and the electrode surface, the N- (benzyloxycarbonyloxy) succinimide traps the transition metal element dissolved in the electrolyte and prevents the polymerization reaction of the electrolyte. it can. Therefore, it is considered that the deterioration of the charge / discharge characteristics of the battery in a high temperature state can be suppressed.

In the present invention, the non-aqueous solvent includes vinylene carbonate (denoted by VC) and N- (benzyloxycarbonyloxy) succinimide (denoted by NBCS) in a weight ratio of NBCS / VC = 0.0
What contains at a ratio of 2 to 1.0 and is composed of a cyclic carbonate and a chain ester is used (Claim 2).

As a result, the charge / discharge cycle characteristics of the battery at a higher temperature can be remarkably improved without inhibiting the action of vinylene carbonate.

Here, ethylene carbonate, butylene carbonate, and propylene carbonate are preferably used as the cyclic carbonate. These cyclic carbonates may be used alone or in combination of two or more. Good (claim 3).

The above chain esters include dimethyl carbonate (DMC) and 1,2-dimethoxyethane (DMC).
E), 1,2-diethoxyethane (DEE) and diethyl carbonate (DEC) are preferably used, and these chain esters may be used alone or as a mixture of two or more. Claim 4).

The supporting electrolyte to be dissolved in the above non-aqueous solvent is not particularly limited, and any of those used in non-aqueous electrolyte secondary batteries can be used. Specifically, LiBF
_{4, LiPF 6, LiClO 4,} LiAsF 6, LiN
(CF ₃ SO ₂ ) ₂ and the like.

As the electrode material, a lithium-containing transition metal oxide represented by the composition formula LiMO ₂ or LiM ₂ O ₄ (M is a transition metal, for example, Co, Ni, Mn, etc.) is used as the positive electrode active material. It is desirable to use. The energy density is increased by using a carbon material having a (002) plane spacing of 3.38 angstroms or less, that is, graphite, as the negative electrode active material.

The positive electrode active material includes a conductive agent such as carbon black and polytetrafluoroethylene (PTF).
E), a paste obtained by mixing a binder such as polyvinylidene fluoride (PVDF) or the like is used.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described focusing on examples.

(1) Embodiment 1 Next, another embodiment to which the present invention is applied will be described based on experimental results.

[Preparation of Test Cell] FIG. 1 shows the structure of an AA wound type lithium secondary battery according to the present invention. In FIG. 1, reference numeral 1 denotes a positive electrode plate, and LiCoO _{2 as} a positive electrode active material, a carbon powder as a conductive material, and an aqueous dispersion of PTFE as a binder are mixed at a weight ratio of 100: 10: 10.
A paste kneaded with water was applied to both sides of an aluminum foil having a thickness of 30 μm, dried, rolled, and cut into a predetermined size to prepare a belt-shaped positive electrode sheet. The mixture was scraped off a part of the sheet perpendicularly to the longitudinal direction of the sheet, and a positive electrode lead plate made of titanium was spot-welded on the current collector.

The positive electrode active material, LiCoO ₂ cobalt oxide (CoO) and lithium carbonate (Li ₂ CO ₃ ) were mixed at a molar ratio of 2: 1 and heated in air at 900 ° C. for 9 hours. Also, among the mixing ratios of the above materials, PTF
The proportion of the aqueous dispersion of E is the proportion of the solid content therein.

Reference numeral 2 denotes a carbon material electrode of a negative electrode, which is composed of an aqueous dispersion of graphite powder and PTFE as a binder in a weight ratio of 10%.
The mixture kneaded at a ratio of 0: 5 was pressed into a nickel expanded metal, dried, and cut into a predetermined size to prepare a belt-shaped negative electrode sheet. Natural graphite was used as the graphite powder. A part of this sheet was scraped off the mixture perpendicularly to the longitudinal direction of the sheet, and a nickel negative electrode lead plate was spot-welded on the current collector. In addition, the ratio of PTFE is a ratio of a solid content similarly to the above.

These positive and negative electrodes are spirally wound through a porous film separator 3 made of polypropylene.
Insert into case 4. After the insertion, the lead 5 made of titanium is spot-welded to the sealing plate 6 made of stainless steel. Reference numeral 7 denotes an aluminum positive electrode cap and positive electrode terminal which has been spot-welded to the sealing plate 6 in advance. Further, the negative electrode lead plate 11 is spot-welded to the center position of the circular bottom surface of the case 4 also serving as the negative electrode terminal. Reference numeral 8 denotes a polypropylene insulating gasket. 1
Reference numeral 0 denotes a safety valve attached so that the internal gas is released to the outside when the battery internal pressure increases due to an abnormality in the battery. Reference numeral 12 denotes an insulating bottom plate made of polypropylene, which has a hole so as to have the same area as the space A generated at the time of winding.

After the above operation, an electrolytic solution (2.3 ml) is injected and sealed. The electrolytic solution was prepared by mixing N- (benzyloxycarbonyloxy) succinimide in vinylene carbonate with N- (benzyloxycarbonyloxy) succinimide in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 (hereinafter referred to as solvent A). A solvent (electrolyte solution 1 to electrolyte solution 7) obtained by mixing a mixed solvent (hereinafter referred to as solvent B) dissolved at a ratio of 5: 1 at a predetermined ratio, and vinylene carbonate and N- (benzyloxy Carbonyloxy)
Lithium succinimide was mixed alone with Li
One in which PF ₆ was dissolved so as to be 1 (mol / l) (Comparative Examples 4 and 5) was used. Table 1 shows a list of the mixing ratios of the solvent A and the solvent B in the electrolytic solutions 1 to 7 used in this cell. The size of the completed battery is AA (14.5φm
mx 50 mm).

[0024]

[Table 1]

[Cycle test] For this prototype battery,
At a temperature of 60 ° C., the upper limit voltage is 4.2 V and the lower limit voltage is 3.0.
V is constant current / constant voltage charging with a charging current of 600 mA
Discharge was performed at a constant current of 200 mA. A cycle test was performed in which the above steps were regarded as one cycle.

[0026]

[Table 2]

(Example 1) The test cell described above was prepared using the electrolytic solution 1. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and FIG. 3 shows a graph thereof. In FIG. 3, the abscissa indicates the ratio (volume%) of the solvent B, and the ordinate indicates the capacity maintenance ratio (%). When applied to the case of the electrolytic solution 1 of the first embodiment, the solvent B in the electrolytic solution 1
Is 5% from Table 1, the capacity retention ratio is 90.2% as shown in the plot where the amount of solvent B is 5% in the graph of FIG.

(Example 2) The above-mentioned test cell was prepared using the electrolyte solution 2. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle relative to the first cycle, and graphs thereof are shown in FIGS. Since the amount of the solvent B in the electrolytic solution 2 is 10% from Table 1, the capacity retention ratio is 92.6% shown by a plot where the amount of the solvent B is 10% in the graph of FIG.

(Example 3) The above-described test cell was prepared using the electrolytic solution 3. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and FIG. 3 shows a graph thereof.

(Example 4) The test cell described above was prepared using the electrolytic solution 4. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and FIG. 3 shows a graph thereof.

(Comparative Example 1) The test cell described above was prepared using the electrolytic solution 5. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and FIG. 3 shows a graph thereof.

(Comparative Example 2) The test cell described above was prepared using the electrolytic solution 6. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and FIG. 3 shows a graph thereof.

(Comparative Example 3) The test cell described above was prepared using the electrolytic solution 7. FIG. 2 shows a graph of the cycle characteristics. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and FIG. 3 shows a graph thereof.

Comparative Example 4 LiPF was added to a solvent obtained by mixing solvent A and vinylene carbonate at a volume ratio of 95: 5.
The above-mentioned test cell was prepared by using, as an electrolyte, a solution in which 6 became 1 (mol / l). Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle.
FIG. 4 shows the graph.

Comparative Example 5 Solvent A and N- (benzyloxycarbonyloxy) succinimide in a weight ratio of 99:
LiPF ₆ was added to the solvent dissolved at a ratio of 1 (mol /
Using the solution dissolved so as to become l) as the electrolyte,
The above test cell was created. Table 2 shows the capacity retention ratio at the 100th cycle with respect to the first cycle, and its graph is shown in FIG.

As can be seen from Tables 1 and 2, Example 1
To those of the electrolyte solutions 1 to 4 used in Example 4, that is,
The non-aqueous solvent contains a non-aqueous solvent in which N- (benzyloxycarbonyloxy) succinimide is dissolved in vinylene carbonate at a ratio of 5 to 20% by volume. In this case, good cycle characteristics were obtained in which the capacity maintenance ratio at the 100th cycle with respect to the first cycle was approximately 90% or more.

The general conclusion is that a solvent composed of at least one of a cyclic ester carbonate and a chain ester contains vinylene carbonate and N- (benzyloxycarbonyloxy) succinimide in a total amount of 5 to 20% by volume. When a non-aqueous electrolyte in which a supporting electrolyte is dissolved in a non-aqueous solvent is used, charge-discharge cycle characteristics at high temperatures are improved.

(2) Embodiment 2 [Preparation of Test Cell] AA type wound lithium secondary battery (FIG. 1) different from the embodiment 1 only in the electrolytic solution.
Was prepared.

2.3 ml of the electrolyte was injected and sealed. This electrolytic solution is composed of a mixed solvent (hereinafter referred to as a solvent A) in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1 and N-vinyl alcohol in vinylene carbonate.
A solvent in which (benzyloxycarbonyloxy) succinimide is dissolved (hereinafter referred to as solvent B) is mixed at a volume ratio of 9: 1, and LiPF ₆ is added to the mixed solvent.
(Mol / l) was used. Here, the ratio of the solvent A and the solvent B was set to 9: 1 because the electrolytic solution 2 (the solvent A and the solvent B in the first embodiment) was used.
9: 1), the highest capacity retention rate 9
It is noted that 2.6 (see Table 2) was shown.

N in solvent B relative to vinylene carbonate
Table 3 shows a list of weight ratios of the dissolved amount of-(benzyloxycarbonyloxy) succinimide. The size of the completed battery is AA type (14.5 mm x 50 mm).

[0041]

[Table 3]

[Cycle test] The batteries produced in this way using the electrolytes 8 to 14 were tested at a temperature of 60 ° C, an upper limit voltage of 4.2 V and a lower limit voltage of 3.0 V at a constant charging current of 600 mA. Current / constant voltage charging was performed for 3 hours, and discharging was performed at a constant current of 200 mA. The above steps are
A cycle test was performed as a cycle.

[0043]

[Table 4]

(Conventional Example) The test cell described above was prepared using the electrolyte solution 8. Fig. 5 shows a graph of the cycle characteristics.
Shown in Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

(Comparative Example 6) Using the electrolytic solution 9, the above test cell was prepared. FIG. 5 shows a graph of the cycle characteristics. Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

Example 5 The test cell described above was prepared using the electrolyte 10. FIG. 5 shows a graph of the cycle characteristics. Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

(Example 6) The test cell described above was prepared using the electrolytic solution 11. FIG. 5 shows a graph of the cycle characteristics. Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

(Example 7) The above test cell was prepared using the electrolytic solution 12. FIG. 5 shows a graph of the cycle characteristics. Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

Example 8 The test cell described above was prepared using the electrolyte 13. FIG. 5 shows a graph of the cycle characteristics. Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

(Comparative Example 7) The test cell described above was prepared using the electrolyte solution 14. FIG. 5 shows a graph of the cycle characteristics. Table 4 shows the capacity retention ratio at the 100th cycle relative to the first cycle.

As can be seen from FIG.
-The electrolytes 10 to 13 used in Example 8, that is, the weight ratio of vinylene carbonate (VC) to N- (benzyloxycarbonyloxy) succinimide (NBCS) is NBCS / VC = 0.02 to 1 A ratio of 0.0 showed good cycle characteristics of a capacity maintenance ratio of 90% or more with respect to a capacity maintenance ratio at the 100th cycle relative to the first cycle. In addition, the electrolyte solution 8 of the conventional example does not contain vinylene carbonate (VC) and N- (benzyloxycarbonyloxy) succinimide (NBCS) at all, and its capacity retention ratio is 84%.
Although the capacity retention rate of Comparative Example 7 slightly exceeded the capacity retention rate, a capacity retention rate of the order of 90% as in Examples 5 to 8 was not obtained.

The general conclusion is that the weight ratio of vinylene carbonate and N- (benzyloxycarbonyloxy) succinimide to NBCS / V in a solvent composed of at least one of cyclic carbonate and chain ester.
It is preferable to use a non-aqueous electrolyte obtained by dissolving a supporting electrolyte in a non-aqueous solvent containing a non-aqueous solvent having a ratio of C = 0.02 to 1.0.

[0053]

As described above, according to the present invention, since vinylene carbonate and N- (benzyloxycarbonyloxy) succinimide are contained in the electrolytic solution, decomposition of the electrolytic solution on the surface of the active material, gas Generation is suppressed. In a high temperature state, it is expected that the transition metal element dissolved forms a complex, and this complex serves as a polymerization initiator to cause a polymerization reaction of the electrolytic solution. However, N- (benzyloxycarbonyloxy) succinimide is used. Since it is present on vinylene carbonate and the electrode surface, the transition metal element dissolved in the electrolytic solution is captured, and the polymerization reaction of the electrolytic solution is prevented. Therefore, a decrease in the charge / discharge characteristics of the battery in a high temperature state is suppressed, and a lithium secondary battery having excellent cycle characteristics at a high temperature can be obtained.

The weight ratio of vinylene carbonate (VC) and N- (benzyloxycarbonyloxy) succinimide (NBCS) to the non-aqueous solvent is NB.
By using a cyclic carbonate and a chain ester containing CS / VC at a ratio of 0.02 to 1.0 (Claim 2), the charge / discharge cycle characteristics of the battery in a high temperature state can be improved. Significant improvement can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a graph showing cycle characteristics of the test battery according to the first embodiment of the present invention, with the type of electrolyte used as a parameter.

FIG. 3 is a graph showing cycle characteristics of a test battery in a relationship between a ratio (volume%) of a solvent B and a capacity retention rate (%).

FIG. 4 is a graph showing the cycle characteristics of the test battery according to the first embodiment of the present invention, using a part of the type of the electrolyte as a parameter.

FIG. 5 is a graph showing cycle characteristics of a test battery according to a second embodiment of the present invention, with the type of electrolyte used as a parameter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode 3 Separator 4 Case 5 Lead 6 Sealing plate 7 Positive electrode cap and positive electrode terminal 8 Insulating gasket 10 Safety valve 11 Negative electrode lead plate 12 Insulating bottom plate

Claims (4)

[Claims] 1. A non-aqueous electrolyte using a material capable of intercalating and de-intercalating lithium as a positive electrode active material and a negative electrode active material, and using a non-aqueous solvent in which an electrolyte is dissolved as a non-aqueous electrolyte. In the secondary battery, the non-aqueous electrolyte of the non-aqueous electrolyte contains vinylene carbonate and N- (benzyloxycarbonyloxy) succinimide. 2. The non-aqueous solvent comprises vinylene carbonate (denoted by VC) and N- (benzyloxycarbonyloxy) succinimide (denoted by NBCS).
2. The non-aqueous electrolyte according to claim 1, wherein the weight ratio is NBCS / VC = 0.02 to 1.0, and the mixture is composed of a cyclic carbonate and a chain ester. Rechargeable battery. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the cyclic carbonate is at least one selected from ethylene carbonate, butylene carbonate, and propylene carbonate. 4. The non-aqueous solution according to claim 2, wherein the chain ester is at least one selected from dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, and diethyl carbonate. Electrolyte secondary battery.