JPH08162155A - Non-aqueous electrolyte battery - Google Patents

Abstract

(57) [Summary] [Objective] To improve the high rate discharge characteristics by improving the wettability of the electrode with respect to the electrolyte of the non-aqueous electrolyte battery. In addition, a high discharge capacity is ensured even when an electrode having a porosity of 40% or less is used. [Constitution] In a non-aqueous electrolyte battery composed of a positive electrode 2 made of a Li-containing metal oxide, a negative electrode 1 made of a carbon material, and an electrolytic solution in which a lithium salt is dissolved in an organic solvent, a nonionic surfactant is used as the electrolytic solution. Agent is included. The nonionic surfactant is preferably polyoxyethylene sorbitan fatty acid ester (polyoxyethylene sorbitan trioleate).

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, and more particularly to the electrolyte solution thereof.

[0002]

2. Description of the Related Art Since a lithium battery using lithium as a negative electrode active material has high energy, it has been attempted to be used as a secondary battery in various fields. When pure metal lithium is used as the negative electrode active material, needle-like deposition of negative electrode lithium with repeated charging and discharging, that is, generation of so-called dendrites is a problem. That is, needle-like precipitated lithium pierces the separator and reaches the positive electrode, causing a short circuit inside the battery, resulting in a significant decrease in battery performance, and an abnormal rise in temperature due to an excessive current flowing due to the internal short circuit. In this case, volatilization of the organic electrolytic solution occurs, and in the worst case, the rise in the internal pressure of the battery causes the battery to burst or explode, which is a safety issue. Especially in terms of safety,
After the rupture of the battery, the chemically active and highly reactive metallic lithium reacts with the water in the air, resulting in “Li + H ₂ O → LiOH
+ 1 / 2H ₂ "reactions generation of hydrogen gas and reaction heat to further lower the safety due to the.

In order to solve such a problem caused by the generation of dendrites, it has been proposed to use a carbon material capable of inserting and extracting lithium ions in a negative electrode as it is charged and discharged. In addition, both the positive electrode and the negative electrode are manufactured by a method in which an active material, a conductive auxiliary agent and a binder are dispersed in a solvent, the mixture is thinly applied on a current collector, and dried and then pressed.
The volume energy density is being improved. The electrode plate group is formed by a method of winding a positive electrode and a negative electrode with a separator interposed therebetween. As the solvent of the electrolytic solution, cyclic ester (for example, ethylene carbonate, propylene carbonate, γ-butyrolactone) excellent in charge / discharge efficiency and oxidation resistance, chain ester (for example, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propione) is used. It has been proposed to mix two or more kinds selected from methyl acid, ethyl propionate) and chain ethers (for example, 1,2-dimethoxyethane, methyl ethyl ether, diethyl ether, methyl propyl ether). As the electrolyte, LiCl
Lithium salts such as O ₄ , LiBF ₄ , LiPF ₆ , and LiSO ₃ CF ₃ have been proposed.

[0004]

However, the battery using the above electrolytic solution has a problem that the wettability of the electrode with respect to the electrolytic solution is poor and the high rate discharge characteristics are poor. Further, when the porosity of the electrode is lowered to improve the volumetric energy density of the battery, it becomes difficult for the electrolytic solution to permeate into the electrode, and when the porosity is below a certain value, the battery capacity is sufficiently obtained. There is also the problem of being unable to do so. The first problem to be solved by the present invention is to improve the wettability of the electrode with respect to the electrolytic solution of the non-aqueous electrolyte battery to improve the high rate discharge characteristics. The second problem is to make a battery having a high discharge capacity even if an electrode having a low porosity is used.

[0005]

In order to solve the first problem, a non-aqueous electrolyte battery according to the present invention comprises a positive electrode made of a Li-containing metal oxide, a negative electrode made of a carbon material, and an organic solvent. In an electrolyte solution containing a lithium salt dissolved therein, the electrolyte solution contains a nonionic surfactant. When the porosity of the positive electrode and the negative electrode is 40% or less, the second problem is solved. The nonionic surfactant is preferably polyoxyethylene sorbitan fatty acid ester, and more preferably polyoxyethylene sorbitan trioleate.

[0006]

By adding a nonionic surfactant to the electrolytic solution, the wettability of the electrode with respect to the electrolytic solution is improved, so that the electrolytic solution also penetrates into the small gaps between the electrodes where the electrolytic solution should not normally penetrate. Therefore, the utilization rate of the active material is increased even in the high rate discharge, and the high rate discharge characteristics are improved. Further, even in a non-aqueous electrolyte battery using an electrode having a low porosity, it is possible to prevent a decrease in the utilization rate of the active material because the permeability of the electrolyte to the electrode is improved, resulting in a high discharge capacity. Is obtained.

[0007]

EXAMPLE FIG. 1 shows the structure of a cylindrical battery of an example according to the present invention. 1 is a negative electrode, and its manufacturing method is as follows. First, artificial graphite powder (“JS” manufactured by Nippon Graphite Co., Ltd.)
P ”) and polyvinylidene fluoride as a binder are weighed in a weight ratio of 90:10, N-methylpyrrolidone (NMP) is added and wet-mixed. This was applied to both sides of a copper foil as a current collector, dried at 120 ° C. for 30 minutes and then pressed. 2 is a positive electrode, and its manufacturing method is as follows. First, LiCoO ₂ , graphite powder as a conductive additive and a binder were weighed in a weight ratio of 85: 10: 5,
Add NMP and wet mix. This was applied on both sides of an aluminum foil as a current collector, dried at 120 ° C. for 30 minutes, and then pressed. The negative electrode 1 and the positive electrode 2 are vacuum-dried at 200 ° C. for 4 hours, and the positive electrode 2, the separator 3 made of a microporous film made of polypropylene, the negative electrode 1, and the separator 3 are wound in this order in a dry atmosphere, which is then wound. Four
The positive electrode 2 is stored in the positive electrode terminal 5 which also serves as a lid, and the negative electrode 1
Were connected to case 4 by ultrasonic welding. In the above-mentioned constitution, an electrolytic solution was prepared as in the following Examples 1 to 4, and 3 ml of the electrolytic solution was impregnated with the electrolytic solution to prepare a battery having a nominal capacity of 400 mAh.

Example 1 LiPF ₆ was used as an electrolyte in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio 5: 2: 3).
Was dissolved in 1 M, and 5.0% by volume of polyoxyethylene sorbitan monolaurate as polyoxyethylene sorbitan fatty acid esters which are nonionic surfactants was added thereto.

Example 2 Similarly, 7.0% by volume of polyoxyethylene sorbitan trioleate was added as polyoxyethylene sorbitan fatty acid esters, and an electrolyte solution was prepared in the same manner as in Example 1.

Example 3 An electrolytic solution was prepared in the same manner as in Example 1 except that polyoxyethylene lauryl ether was added as a polyoxyethylene alkyl ether which is a nonionic surfactant in a volume ratio of 8.0%.

Example 4 Glycerol monooleate as a glycerin fatty acid ester which is a nonionic surfactant is 6.0 in volume ratio.
%, And an electrolytic solution was prepared in the same manner as in Example 1 except for the above.

A battery (conventional example) produced in the same manner as the battery of the above-mentioned example except that the nonionic surfactant was not contained in the electrolytic solution was used for the battery of the above-mentioned example (conventional example). FIG. 2 shows the high rate discharge characteristics when the battery was charged at a current of 100 mA) for 5 hours and then discharged at a final voltage of 3 V at a current of 1 A. The porosity of each electrode was set to 60%. Also, a constant voltage of 4.15V (limit current 100mA)
FIG. 3 shows the relationship between the porosity of the electrode and the discharge capacity when the battery was charged for 5 hours at 100 mA and then discharged at a final voltage of 3 V with a current of 100 mA. The porosity of the electrodes was adjusted by the force during pressing for both positive and negative electrodes. It can be seen from FIG. 2 that each of the batteries of the examples has a higher discharge capacity than the conventional example in the high rate discharge characteristics. Further, it can be seen from FIG. 3 that in each of the batteries of the examples, even when the porosity of the electrodes is 40% or less, the battery capacity does not sharply decrease as in the conventional example. Both of the above characteristics are particularly remarkable when polyoxyethylene sorbitan fatty acid esters are used as the nonionic surfactant, and furthermore, a high capacity can be maintained regardless of the porosity of the electrode. Among the polyoxyethylene sorbitan fatty acid esters, the effect of using polyoxyethylene sorbitan trioleate is more remarkable.

In addition to the above examples, the solvent of the electrolytic solution is a mixed solvent using propylene carbonate, γ-butyrolactone, etc., and the electrolyte is LiClO 2 in addition to the above examples.
_The same results as above were obtained when the lithium salt was ₄ , LiBF ₄ , LiSO ₃ CF _3, or the like. In addition to the above examples, the nonionic surfactants are polyoxyethylene alkyl allyl ethers, polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene fatty acid esters, Also in the case of oxyethylene alkyl amines and alkyl alkanol amides, better results were obtained than in the conventional example.

[0014]

As described above, the non-aqueous electrolyte battery according to the present invention is characterized in that a nonionic surfactant is added to the electrolyte solution, and the wettability of the electrode with respect to the electrolyte solution is improved. If so, the electrolyte will also penetrate into the small gaps in the electrode where the electrolyte cannot penetrate. As a result, the utilization factor of the active material is increased in the high rate discharge. Further, even when the porosity of the positive electrode and the negative electrode is 40% or less, it is possible to prevent the utilization rate of the active material from decreasing and maintain a high capacity. When the nonionic surfactant is a polyoxyethylene sorbitan fatty acid ester, the effect of ensuring high rate discharge characteristics and high capacity becomes more remarkable, and high capacity is achieved regardless of whether the electrode porosity is high or low. Can be maintained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a non-aqueous electrolyte battery of an example according to the present invention.

FIG. 2 is a high rate discharge characteristic diagram when the porosity of the electrodes is set to 60% in the non-aqueous electrolyte batteries of the example according to the present invention and the conventional example.

FIG. 3 is a curve diagram showing the relationship between the porosity of the electrodes and the battery capacity of the non-aqueous electrolyte batteries of the example according to the present invention and the conventional example.

[Explanation of symbols]

 1 is negative electrode 2 is positive electrode 3 is separator 4 is case 5 is positive electrode terminal

Claims (4)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode made of a Li-containing metal oxide, a negative electrode made of a carbon material, and an electrolyte solution in which a lithium salt is dissolved in an organic solvent. A non-aqueous electrolyte battery containing an agent. 2. The non-aqueous electrolyte battery according to claim 1, wherein the porosity of the positive electrode and the negative electrode is 40% or less. 3. The non-aqueous electrolyte battery according to claim 1, wherein the nonionic surfactant is a polyoxyethylene sorbitan fatty acid ester. 4. The non-aqueous electrolyte battery according to claim 3, wherein the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan trioleate.