JPH05315006A - Noaqueous electrolyte cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To get a nonaqueous electrolyte cell whose safety o electrolyte is high, whose charge-and-discharge cycle performance is good by reducing the free acid content of a nonaqueous electrolyte cell to a specified density or less. CONSTITUTION:A belt negative electrode 1 made up of carbonaceous material which can dope.dedope lithium and a belt positive electrode 2 which uses LiCoO2, etc., as active material are spirally wound round through a separator 3 of micro-porous polypropylene to make an electrode element. This is put in a battery can and a positive.negative electrodes leads 11, 12 are led out, and then, a free acid content is adsorbed by Al2O3, etc., to remove it and a nonaqueous electrolyte of 100ppm or less is injected into the can and a cell over 7 fixed through an insulating sealing gasket 6 to make a nonaqueous electrolyte cell. Lowering of capacity to be caused thereby can be prevented by lowering a free acid content so that a good charge-and-discharge cycle characteristic can be demonstrated.

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 battery using a carbonaceous material as a negative electrode and a method for producing the same.

[0002]

2. Description of the Related Art A non-aqueous electrolyte battery using, for example, lithium as a negative electrode material and an electrolyte in which an electrolyte is dissolved in a non-aqueous solvent has low self-discharge, high operating voltage, and excellent storage performance. It has features such as For this reason, it has been used for a long time and is highly reliable, so it is widely used as a power source for clocks and various memory backups.
It has also attracted attention as a power source for portable devices such as microcomputers.

By the way, the non-aqueous electrolyte batteries including the above-mentioned non-aqueous electrolyte batteries are mainly those having primary battery specifications, but they are economically disadvantageous when used as a power source for portable equipment such as video cameras. Considering this, it is desirable that the rechargeable secondary battery has specifications, and further that it is lightweight and has a large capacity. From this point of view, research and development of non-aqueous electrolyte batteries are being promoted to make them secondary batteries, reduce their weight, and increase their capacity.

As the non-aqueous electrolyte battery of the secondary battery specification,
As a negative electrode material, lithium, a lithium alloy or a lithium occlusion material, and as a positive electrode material, MnO ₂ , TiS ₂ , M
Those using oO ₃ , MoS ₂ , V ₂ O ₅ , WO ₃ , LiCoO _{2 and the} like have been proposed.

Among them, in particular, a non-aqueous electrolyte secondary using a carbon material capable of being doped / dedoped with lithium as a negative electrode material and a lithium / cobalt composite oxide or a lithium / nickel / cobalt composite oxide as a positive electrode material. The battery has high operating voltage, high energy density, and excellent cycle performance compared to non-aqueous electrolyte secondary battery using metallic lithium or lithium alloy as the negative electrode active material. Is expected.

[0006]

By the way, in a non-aqueous electrolyte secondary battery using the above-mentioned carbonaceous material as a negative electrode material, the electrolyte is usually a non-aqueous solvent such as LiAsF ₆ , LiPF _{6 as} an electrolyte. ₆ , LiBF ₄ , Li
_{CF 3 SO 3, LiCF 3 CO} 2, LiClO 4, which is formed by dissolving is used, these particular LiAsF
It has been reported that good charge / discharge performance can be obtained by using an electrolytic solution in which ₆ and LiPF ₆ are dissolved.

However, the non-aqueous electrolyte secondary battery using the carbonaceous material as the negative electrode material is LiAsF ₆ , Li
When an electrolytic solution in which PF ₆ and LiBF ₄ LiCF ₃ CO ₂ are dissolved is used, charge and discharge performance can be obtained, but there is a problem that the capacity remarkably decreases when charging and discharging are repeated.

This is because LiAsF ₆ and LiP in the electrolytic solution
It has been found that the cause is the acid content released from F ₆ , LiBF ₄ , and LiCF ₃ CO ₂ , especially the hydrofluoric acid content. That is, as an electrolyte solution, for example, an electrolyte solution in which 1 mol / l of LiPF ₆ was dissolved in an equal amount mixture solution of propylene carbonate (PC) and 1,2 dimethoxyethane (DME) was stored at 45 ° C., the initial free acid content was 200 ppm.
After 10 days, it increases to 2000 ppm. When this electrolytic solution with an increased free acid content is used in the above-mentioned battery and charging / discharging is performed under high temperature conditions, the active material is dissolved or the electrolytic solution is decomposed at a charging voltage of 4.10 V or more, and the discharge capacity of the battery is Markedly reduced.

In a non-aqueous electrolyte battery using metallic lithium as a negative electrode, the content of free hydrofluoric acid in the electrolytic solution reacts with metallic lithium in the negative electrode to form lithium fluoride, which has a particular effect on battery performance. I don't. However, in a non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode, such a formation reaction of a stable compound does not occur, so that the active material is dissolved,
This causes decomposition of the non-aqueous solvent, resulting in a marked decrease in battery capacity. In order to prevent the release of hydrofluoric acid from the electrolyte, a method has been proposed in which various additives are added in order to make the electrolyte stably exist in the electrolytic solution. However, when the additive is added to the electrolytic solution, the effect of the additive itself on the battery performance is large, and satisfactory characteristics cannot be obtained.

Therefore, the present invention has been proposed in view of the above conventional circumstances, and an object thereof is to provide a non-aqueous electrolyte battery having high stability of the electrolyte and excellent charge / discharge cycle performance. To do.

[0011]

In order to achieve the above-mentioned object, the non-aqueous electrolyte battery of the present invention comprises a lithium dope.
In a non-aqueous electrolyte battery comprising a negative electrode made of a carbonaceous material capable of dedoping, a positive electrode, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, a free acid content of the non-aqueous electrolytic solution Is 100 ppm or less.

Further, the production method of the present invention is characterized in that, when preparing the non-aqueous electrolytic solution, the free acid content is removed by chemisorption or chemical reaction after dissolving the electrolyte in the non-aqueous solvent. is there.

In the non-aqueous electrolyte battery of the present invention, a carbonaceous material is used as the negative electrode material. A non-aqueous electrolyte battery using a carbonaceous material as a negative electrode material is LiAsF ₆ , LiPF
Good charge / discharge performance is exhibited when an electrolyte solution in which ₆ , LiBF ₄ , and LiCF ₃ CO ₂ are dissolved is used. However, in such an electrolytic solution, hydrofluoric acid is liberated from the electrolyte, which induces dissolution of the active material and decomposition of the non-aqueous solvent, resulting in a marked decrease in battery capacity.

Therefore, in the present invention, in order to prevent such a decrease in battery capacity, the concentration of free acid in the electrolytic solution is regulated to 100 ppm or less, preferably 50 ppm or less. By limiting the free acid content of the electrolytic solution to 100 ppm or less, dissolution of the active material due to free hydrofluoric acid and decomposition of the non-aqueous solvent are suppressed, and good charge / discharge cycle performance is exhibited.

In order to prepare an electrolytic solution having a free acid content of 100 ppm or less, it is sufficient to dissolve the electrolyte in a non-aqueous solvent and then subject the electrolytic solution to a free acid removal treatment.

As the free acid removal treatment, a powder that chemically adsorbs the free acid is used, a method of adsorbing the free acid to the chemisorbed powder, a method of chemically reacting the free acid to produce a compound, and a distillation. Although there is a method of removing the free acid content by the method, the method of using the chemisorption powder is preferable because the operation is simple and there is almost no influence on the electrolyte. That is, in the method of producing a compound, since the produced compound must be finally removed by a chemisorbed substance or the like, the number of steps is large and the operation is complicated. Since it is unstable, the characteristics of the electrolytic solution may deteriorate.

In the method using the chemically adsorbed powder, the chemically adsorbed powder may be Al ₂ O ₃ , BaO, MgO, activated carbon, molecular sieve, finely divided silicon dioxide, fine powder of various metal oxides, heat-treated acetylene black, coke. Kinds etc. are used.

In order to remove the free acid content in the solution using these chemisorption powders, for example, the chemisorption powder is added to the solution and stirred, and after stirring, the solution is filtered, or the chemisorption powder is removed. It may be packed in a column and the solution may be passed through this column.

The carbonaceous material used as the negative electrode material in the non-aqueous electrolyte battery may be a conductive polymer such as polyacetylene or polypyrrole, or a carbon material such as coke, polymer charcoal or carbon fiber. However, it is desirable to use a carbonaceous material because the energy density per unit volume is large. As the carbonaceous material, pyrolytic carbons, cokes (petroleum coke, pitch coke, coal coke, etc.), carbon black (acetylene black, etc.), glassy carbon, organic polymer material fired body (organic polymer material 500 Carbon fiber or the like is used, which is fired at a suitable temperature of ℃ or higher in an inert gas stream or in a vacuum).

On the other hand, as the positive electrode material, transition metal oxides such as manganese dioxide and vanadium pentoxide, transition metal chalcogenides such as iron sulfide and titanium sulfide, and composite compounds of these with lithium are used. be able to. In particular, high voltage and high energy density are obtained,
Lithium-cobalt composite oxide and lithium-cobalt-nickel composite oxide are preferable because they have excellent cycle characteristics.

The organic solvent used in the electrolytic solution is not particularly limited, but propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran. , 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,
A single solvent or a mixture of two or more kinds of 3-dioxolane, diglymes, triglymes, sulfolane, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and the like can be used.

[0022]

In the present invention, in a non-aqueous electrolyte battery using a carbonaceous material as the negative electrode material, the concentration of free acid in the electrolyte is 10%.
Keep it as low as 0 ppm or less. In a non-aqueous electrolyte battery that uses an electrolyte solution with a high free acid content, the metal components of the active material present in the electrolyte solution are in a state where they are likely to cause a dissolution reaction due to a high potential. The components easily corrode and dissolve, resulting in a large decrease in capacity with charge / discharge cycles.

In a non-aqueous electrolyte battery using an electrolytic solution having a free acid content concentration of 100 ppm or less, such a capacity reduction caused by the free acid content is prevented, and thus good charge / discharge cycle characteristics are exhibited. An electrolytic solution having a free acid content of 100 ppm or less is easily prepared by contacting an electrolyte solution with, for example, Al ₂ O ₃ powder to chemically adsorb the free acid content and removing the free acid content. It

[0024]

EXAMPLES Specific examples of the present invention will be described below based on experimental results.

Example 1 The constitution of the non-aqueous electrolyte battery produced in this example is shown in FIG.

First, the negative electrode 1 was manufactured as follows.
After using petroleum pitch as a starting material and introducing 10 to 20% of a functional group containing oxygen into this (so-called oxygen crosslinking),
Heat treatment was performed at 1000 ° C. in an inert gas stream to obtain a carbon material having properties similar to glassy carbon. As a result of X-ray diffraction measurement of this carbon material, the spacing between (002) planes was 3.76Å. This carbon material was crushed to obtain a carbon material powder having an average particle size of 10 μm.

The carbon material powder thus obtained was used as a negative electrode active material, and 90 parts by weight of this carbon material powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed,
A negative electrode mixture was prepared. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a slurry.
Then, this negative electrode mixture slurry was uniformly applied to both surfaces of a strip-shaped copper foil having a thickness of 10 μm to be the negative electrode current collector 9, dried and then compression-molded by a roll press machine to fabricate a strip-shaped negative electrode 1. ..

Next, the positive electrode 2 was manufactured as follows. The positive electrode active material (LiCoO ₂ ) was obtained by mixing 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate and firing the mixture in air at 900 ° C. for 5 hours. A positive electrode mixture was prepared by mixing 91.0 parts by weight of this LiCoO ₂ and 3 parts by weight of polyvinylidene fluoride serving as a binder. This positive electrode mixture serves as a solvent for N
-Methyl-2-pyrrolidone was dispersed into a slurry. This positive electrode mixture slurry was uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil serving as the positive electrode current collector 10, dried, and then compression-molded by a roll press machine to prepare a strip-shaped positive electrode 2.

Strip negative electrode 1, strip positive electrode 2 and thickness 25 μ
As shown in FIG. 1, the separator 3 made of the microporous polypropylene film of m was laminated in the order of the negative electrode 1, the separator 3, the positive electrode 2, and the separator 3, and the laminated body was wound many times around the spiral body. A spiral electrode element was manufactured.

The spirally-wound electrode element thus produced was housed in a nickel-plated iron container 5. Insulating plates 4 are arranged on both upper and lower surfaces of the spiral electrode element, and the aluminum positive electrode lead 12 is led out from the positive electrode current collector 10 to the battery lid 7, and the nickel negative electrode lead 11 is led out from the negative electrode current collector 9. It was welded to the battery can 5.

Next, an electrolytic solution to be injected into the battery can was prepared as follows. Propylene carbonate (PC)
50% by volume and 1,2-dimethoxyethane (DME) 50
LiPF ₆ was dissolved at 1 mol / l in a solvent mixed with volume%. Then, this solution was passed through a column filled with dried BaO powder to measure the concentration of free acid.

In order to measure the concentration of free acid, first, 10 g of a sample was precisely weighed in a dry stopper (water content of 100 ppm or less) in a flask with a stopper, and collected. Then, cold water mixed in advance with ice: distilled water at a ratio of 50:50 was added to the above sample to make 100 ml, and further 2 mg of bromthymol blue powder was used as an indicator.
0 g was added, and the solution temperature was adjusted to 0 to 5 ° C. Then, for this solution, the factor F for which N is calculated in advance is N / 1.
The neutralization point was determined using 0 NaOH solution. The end point was changed from orange to bluish purple and the bluish purple continued for 5 seconds. From the obtained neutralization point, the acid concentration was calculated based on the following formula.

C = (0.002 × A × F / S) × 100 A: Neutralization point (ml) C: Acid content concentration (wt%) F: Factor of NaOH F S: Sample weight (g) Results The acid concentration of the electrolytic solution was 30 ppm.

The electrolyte thus prepared is poured into a battery can, and the battery can 5 is caulked through an asphalt-coated insulating sealing gasket 6 to fix the battery lid 7, and the diameter is 20 mm, and the height is 20 mm. A 50 mm cylindrical non-aqueous electrolyte battery (Example battery 1) was produced.

A charging / discharging cycle in which the manufactured battery is charged under the conditions of a charging current of 1 A, a charging time of 2.5 hours and an upper limit voltage of 4.1 V, and is discharged under the conditions of a resistance of 6 ohms and an end voltage of 2.5 V. Was repeated. And 1
The discharge capacity at the 0th cycle and the 100th cycle was measured. The results are shown in Table 1.

Example 2 In preparing an electrolytic solution, PC50% by volume, DME50
An electrolyte solution was prepared by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of volume%, and the electrolyte solution was dried with MgO.
A nonaqueous electrolyte battery (Example battery 2) was produced in the same manner as in Example 1 except that the powder was passed through a packed column.
The free acid content of the prepared electrolytic solution was 45 ppm.

Example 1 of the produced non-aqueous electrolyte battery
The charge / discharge cycle was repeated in the same manner as in, and the discharge capacities at the 10th cycle and the 100th cycle were measured.
The results are shown in Table 1.

Example 3 In preparing an electrolytic solution, PC50 volume L% and DME50
Same as Example 1 except that 1 mol / l of LiPF ₆ was dissolved in a solvent mixed with volume% to prepare an electrolyte solution, and the electrolyte solution was passed through a packed column of dried Al ₂ O ₃ powder. And non-aqueous electrolyte battery (Example battery 3)
Was produced. The free acid content of the prepared electrolyte was 35 p.
It was pm.

Example 1 of the produced non-aqueous electrolyte battery
The charge / discharge cycle was repeated in the same manner as in, and the discharge capacities at the 10th cycle and the 100th cycle were measured.
The results are shown in Table 1.

Example 4 In preparing an electrolytic solution, PC50% by volume and DME50 were used.
LiPF ₆ was dissolved in a solvent mixed with 1% by volume of 1 mol / l to prepare an electrolyte solution, and this electrolyte solution was passed through a packed column of dry carbon (activated carbon) powder, as in Example 1. A non-aqueous electrolyte battery (Example battery 4) was produced. The free acid content of this electrolyte is 75 p
It was pm.

Example 1 of the produced non-aqueous electrolyte battery
The charge / discharge cycle was repeated in the same manner as in, and the discharge capacities at the 10th cycle and the 100th cycle were measured.
The results are shown in Table 1.

Example 5 In preparing an electrolytic solution, PC50% by volume and DME50 were used.
LiBF ₆ was dissolved in a solvent mixed with 1% by volume of 1 mol / l to prepare an electrolyte solution, and this electrolyte solution was passed through a packed column of dried Al ₂ O ₃ powder, as in Example 1. Non-aqueous electrolyte battery (Example battery 5)
Was produced. The free acid content of this electrolyte was 30 ppm.
Met.

Example 1 of the produced non-aqueous electrolyte battery
The charge / discharge cycle was repeated in the same manner as in, and the discharge capacities at the 10th cycle and the 100th cycle were measured.
The results are shown in Table 1.

Example 6 In preparing an electrolytic solution, PC50% by volume and DME50 were used.
1 mol of LiCF ₃ CO ₂ was added to the solvent mixed with vol%.
/ L is dissolved to prepare an electrolyte solution, and this electrolyte solution is
Except that passed through a packed column of the dried Al ₂ 0 ₃ powder was formed in the same manner as in a non-aqueous electrolyte battery of Example 1 (Example battery 6). The free acid content of this electrolyte is 60
It was ppm.

Example 1 of the produced non-aqueous electrolyte battery
The charge / discharge cycle was repeated in the same manner as in, and the discharge capacities at the 10th cycle and the 100th cycle were measured.
The results are shown in Table 1.

Example 7 In preparing an electrolytic solution, LiPF ₆ was added to a solvent prepared by mixing 50% by volume of PC and 50% by volume of diethyl carbonate (DEC).
Was dissolved in an amount of 1 mol / l to prepare an electrolyte solution, and this electrolyte solution was passed through a packed column of dried Al ₂ O ₃ powder in the same manner as in Example 1 (non-aqueous electrolyte battery (Example A battery 7) was produced. The free acid content of this electrolytic solution was 25 ppm.

The non-aqueous electrolyte battery thus produced was repeatedly charged and discharged in the same manner as in Example 1, and the discharge capacities at the 10th and 100th cycles were measured. The results are shown in Table 1.

Comparative Example 1 In preparing an electrolytic solution, 50% by volume of PC and 50% of DME were used.
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that 1 mol / l of LiPF ₆ was dissolved in a solvent mixed with a volume percentage, and this electrolyte solution was used as an electrolyte solution as it was without performing a treatment to remove free acid. A battery (Comparative Example Battery 1) was produced. The free acid content of this electrolytic solution was 150 ppm.

The non-aqueous electrolyte battery thus produced was repeatedly charged and discharged in the same manner as in Example 1, and the discharge capacities at the 10th and 100th cycles were measured. The results are shown in Table 1.

Comparative Example 2 In preparing an electrolytic solution, LiPF ₆ was added to a solvent prepared by mixing 50% by volume of PC and 50% by volume of diethyl carbonate (DEC).
Was dissolved in an amount of 1 mol / l, and a non-aqueous electrolyte battery (Comparative battery 2) was prepared in the same manner as in Example 1 except that this electrolyte solution was used as an electrolytic solution as it was without performing a treatment to remove free acid. .. The free acid content of this electrolyte was 105
It was ppm.

The non-aqueous electrolyte battery thus produced was repeatedly charged and discharged in the same manner as in Example 1, and the discharge capacities at the 10th and 100th cycles were measured. The results are shown in Table 1.

Comparative Example 3 When preparing an electrolytic solution, LiPF ₆ was added to a solvent prepared by mixing 50% by volume of PC and 50% by volume of diethyl carbonate (DEC).
Was dissolved in 1 mol / l, and this electrolyte solution was stored at room temperature for 6 months and then used as an electrolyte solution.
A non-aqueous electrolyte battery (Comparative Example Battery 3) was produced in the same manner as in. The free acid content of this electrolytic solution was 250 ppm.

The non-aqueous electrolyte battery thus produced was repeatedly charged and discharged in the same manner as in Example 1, and the discharge capacities at the 10th and 100th cycles were measured. The results are shown in Table 1.

[0054]

[Table 1]

As can be seen from Table 1, in the non-aqueous electrolyte battery, the lower the free acid concentration of the electrolytic solution, the smaller the decrease in capacity with charge / discharge cycles, and the free acid content is 100 ppm or less. Each of the example batteries 1 to 7 using the electrolytic solution has a high capacity retention rate (discharge capacity at 100th cycle / 10 discharge capacity at 10th cycle). Furthermore, the capacity retention of the example batteries 1 to example batteries 3, example batteries 6, and example batteries 7 using the electrolytic solution having a low free acid content of 50 ppm or less is 89% or more.

Therefore, it was found from the above that in the non-aqueous electrolyte battery, controlling the concentration of the free acid component of the electrolyte is effective in improving the capacity retention rate.

[0057]

As is clear from the above description, in the non-aqueous electrolyte battery of the present invention, the concentration of free acid in the electrolyte solution is kept as low as 100 ppm or less. It is possible to improve performance, self-discharge performance, stability of electrolyte, and the like. Moreover, the storage performance of the electrolytic solution itself can be improved.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an example of a non-aqueous electrolyte battery of the present invention.

[Explanation of symbols]

 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 4 ... Insulating plate 5 ... Battery can 6 ... Insulating gasket 7 ... Battery lid 9 ... Negative electrode current collector 10 ... -Positive electrode current collector 11 ... Negative electrode lead 12 ... Positive electrode lead

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Kojima 3-11-1, Mizutani Higashi, Fujimi City, Saitama Prefecture Toyama Yakuhin Kogyo Co., Ltd. Shiki Plant (72) Inventor Takahiro Rokkaku 3-11 Mizutani Higashi, Fujimi City, Saitama Prefecture -1 Toyama Yakuhin Kogyo Co., Ltd. Shiki Factory (72) Inventor Kazuto Ichikawa 3-11-1 Mizutani Higashi, Fujimi City, Saitama Prefecture Toyama Yakuhin Kogyo Co., Ltd. Inside Shiki Factory (72) Inventor Takashi Fujino Fujimi City, Saitama Prefecture 3-11-1 Mizutani Higashi Toyama Yakuhin Kogyo Co., Ltd. Shiki Factory (72) Inventor Yoichi Kagogi 3-11-1 Mizutani Higashi Fujimi, Saitama Prefecture Toyama Yakuhin Kogyo Co., Ltd. Shiki Factory

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery comprising a negative electrode made of a carbonaceous material capable of being doped and dedoped with lithium, a positive electrode, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, A non-aqueous electrolyte battery, wherein the free acid content of the non-aqueous electrolyte is 100 ppm or less. 2. When preparing a non-aqueous electrolyte, the electrolyte is dissolved in a non-aqueous solvent to prepare an electrolyte solution, and then the free acid component in the electrolyte solution is removed by chemisorption or chemical reaction. And a method for manufacturing a non-aqueous electrolyte battery.