JPH09283181A - Non-aqueous electrolyte secondary battery and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: In a non-aqueous electrolyte secondary battery with a positive electrode capacity regulation using a material containing lithium in the positive electrode and a carbon material mainly in the negative electrode, the lithium supplied from the positive electrode to the negative electrode during the first charge An object of the present invention is to provide a non-aqueous electrolyte secondary battery that suppresses a part of the battery from being consumed without being used for discharging, has a high energy density, and has excellent cycle characteristics. SOLUTION: At least one of a positive electrode, a negative electrode, and a nonaqueous electrolyte has the following formula (wherein R ₁ , R ₂ , R ₃ , and R ₄ are:
Each independently represents a methyl group, an ethyl group, a butyl group or a hydrogen atom. ) The alkylammonium oxalate salt shown in (1) is added, and the total addition amount of the alkylammonium oxalate salt is not more than half of the lithium amount corresponding to the irreversible capacity of the negative electrode material. Embedded image

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high energy density non-aqueous electrolyte secondary battery having improved discharge capacity and charge / discharge cycle characteristics, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium metal as a negative electrode have high electromotive force and are expected to have higher energy density than conventional nickel-cadmium storage batteries and lead storage batteries, and many studies have been conducted. . However, when metallic lithium is used for the negative electrode, dendrites are generated during charging, and a short circuit easily occurs inside the battery, resulting in a battery with low reliability. In order to solve this problem, the use of an alloy negative electrode of lithium and aluminum (Al) or lead (Pb) was studied. When these alloy negative electrodes are used, Li is occluded in the negative electrode alloy upon charging, and a highly reliable battery without dendrite generation is obtained. However, since the discharge potential of the alloy negative electrode is about 0.5 V more noble than that of metallic Li, the voltage of the battery is less than 0.
It drops by 5 V, which also reduces the energy density of the battery.

[0003] On the other hand, researches using an intercalation compound of a carbon material such as graphite and Li as a negative electrode active material have been actively conducted. Even in the case of this compound anode, Li does not enter the carbon layer and generate dendrites during charging. Since the discharge potential is about 0.1 V more noble than that of metallic Li, the decrease in battery voltage is small. This can be said to be a more preferable negative electrode. Generally, the carbonaceous material contains organic substances in an inert atmosphere flow of about 400 to 300.
It can be obtained by decomposing by heating at 0 ° C. for carbonization and further graphitization. The starting material for the carbonaceous material is almost always an organic matter, which is a carbonization process 1500
By heating up to around 0 ° C, almost only carbon atoms remain, and heating up to a high temperature near 3000 ° C develops a graphite structure. As the organic material, pitch in the liquid phase,
A coal tar, a mixture of coke and pitch, etc. are used. In the solid phase, wood raw material, furan resin, phenol
Examples thereof include resin, epoxy resin, cellulose, polyacrylonitrile and rayon. In the gas phase, hydrocarbon gas such as methane and propane is used. At present, both carbon materials obtained at a relatively low temperature of up to about 1500 ° C. and carbon materials having a crystal structure close to a graphite structure after firing up to around 3000 ° C. are applied to non-aqueous electrolyte secondary batteries, especially lithium It has been put to practical use under the trade name of ion secondary battery.

[0004]

It is known that all carbon materials have a larger charge capacity than the discharge capacity in the first charge / discharge. In other words, the amount of electricity that does not contribute to discharging is consumed in the first charging.
This charge / discharge capacity difference is often referred to as “capacity loss” or “retention”. This difference in charge and discharge capacity is a serious problem in a lithium ion secondary battery in which a material containing lithium is used for the positive electrode, for example, LiCoO ₂ , and a carbon material is used for the negative electrode. Since the capacity of this battery is controlled by the positive electrode, part of the lithium given from the positive electrode to the negative electrode during the first charging is consumed without being used for discharging. As a result, the battery capacity is reduced by the amount of lithium consumed.

In order to solve this problem, an object of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery having higher energy density, good cycle characteristics, and high reliability.

[0006]

In order to achieve the above object, the present invention comprises a positive electrode having reversibility for charge and discharge,
A non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing a Li salt and having a negative electrode having reversibility for charge and discharge, wherein at least one of the positive electrode, the negative electrode, and the non-aqueous electrolyte has the following formula (1 ) It is characterized by containing an oxalic acid alkyl ammonium salt.

[0007]

Embedded image

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently a methyl group, an ethyl group, a butyl group or a hydrogen atom.) The method for producing the non-aqueous electrolyte secondary battery of the present invention Is a step of accommodating a power generation element containing an alkylammonium oxalate salt in a battery case, a step of charging at least the first cycle in a state where the upper part of the case is opened to release the produced gas, and then sealing the case. Have steps. Here, it is preferable that the total amount of the alkyl ammonium oxalate salt added is not more than half of the amount of lithium corresponding to the irreversible capacity of the negative electrode material. Since the chemical equivalent of oxalic acid alkylammonium salt is 2, the irreversible capacity of lithium is completely supplemented by adding half the number of moles of lithium corresponding to the irreversible capacity of the negative electrode material. be able to. All of the alkylammonium oxalate salt is decomposed during the charge in the first cycle, and does not act as an effective solute of the electrolyte in the subsequent charge / discharge.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The alkylammonium oxalate salt may be added to any of the positive electrode, the negative electrode and the non-aqueous electrolyte that constitute the power generating element. Further, even when the amount of the alkyl ammonium oxalate salt added does not reach half of the amount of lithium corresponding to the irreversible capacity of the negative electrode material, as compared with the case where no alkyl ammonium oxalate salt is added, The effect can be partially obtained.
As the negative electrode, any carbon material may be used, and further, a carbon material containing 10.5 to 18.3 wt% nitrogen, 7
~ 35 wt% sulfur containing carbon material, 6.5-25 wt
It is desirable to include at least one of the carbon materials containing% oxygen. The total amount of alkylammonium oxalate salt to be added is determined according to the irreversible capacity of these negative electrode materials used.

The positive electrode material may be any material having reversibility with respect to charge and discharge, but a material containing lithium is particularly preferable. For example, LiCoO ₂ , LiNiO ₂ ,
LiMn ₂ O ₄ and LiFeO _2, gamma-type LiV ₂ O _5, LiM
A positive electrode having reversibility with respect to charge / discharge such as nO ₂ is suitable, and an intercalation compound containing these composite metal oxides or lithium is suitable. The non-aqueous electrolyte used is one in which an electrolyte salt is dissolved in an organic solvent. As the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-dimethoxytan, γ-butyrolactone, tetrahydrofuran, 2-
Methyl tetrahydrofuran, 1,3-dioxolane, 4
-Methyl-1,3-dioxolane, 4-methyl-1,3
Examples include dioxolane, diethyl ether and sulfolane. Electrolyte salts include LiCiO ₄ , LiAsF ₆ , Li
BF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO
₃ ) etc. The shape of the battery according to the present invention is not limited to a cylindrical shape, a coin shape, a square shape, a flat shape and the like, and any shape is possible.

Alkyl ammonium oxalate salt is used as a positive electrode,
When added to the negative electrode and the electrolyte, the following effects can be considered. (1) When an oxalic acid alkylammonium salt is added to the positive electrode: The oxalic acid alkylammonium salt added to the positive electrode is oxidized and decomposed in the charging process of the first cycle to generate an alkylammonium ion and carbon dioxide. Moreover, since the oxidative decomposition potential of the oxalic acid alkyl ammonium salt is lower than the lithium desorption potential from the positive electrode, the oxidative decomposition of the oxalic acid alkyl ammonium salt occurs preferentially. The generated alkyl ammonium ion reaches the surface of the negative electrode and cancels the irreversible capacity. Therefore, all the lithium ions desorbed from the positive electrode can contribute to the charge / discharge reaction. (2) When oxalic acid alkylammonium salt is added to the negative electrode: The oxalic acid alkylammonium salt added to the negative electrode undergoes reductive decomposition in the first cycle charging process to generate alkylammonium ions and carbon dioxide. Here, initially, the reaction potential of inserting (charging) lithium into the negative electrode is higher, but the negative electrode potential sharply decreases as the reaction progresses, and reductive decomposition of the alkylammonium oxalate salt immediately occurs preferentially. The generated alkyl ammonium ion is
The irreversible capacity is offset on the negative electrode surface. (3) When an oxalic acid alkyl ammonium salt is added to the non-aqueous electrolyte: The oxalic acid alkyl ammonium salt added to the non-aqueous electrolyte dissolves and dissociates into oxalate ions and alkyl ammonium ions. This alkylammonium ion reaches the surface of the negative electrode in the charging process of the first cycle and can also offset the irreversible capacity. In any case, the alkylammonium generated by decomposition reaches the surface of the negative electrode material and causes irreversible capacity. Lithium during the first cycle charging and the reaction active point on the surface of the negative electrode material are replaced with lithium from the positive electrode. It is presumed that the lithium ion from the positive electrode is not consumed as a result.

[0012]

Embodiments of the present invention will be described below. Example 1 In this example, an example in which tetrabutylammonium oxalate salt is added to the negative electrode will be described. Graphite was used as the carbon material of the negative electrode. The irreversible capacity of this graphite is 50 mAh per 1 g of graphite. A battery was manufactured according to the following procedure. The negative electrode is graphite powder 1 which is the negative electrode active material.
Styrene-butadiene rubber was mixed with 00 g as a binder, a petroleum solvent was further added, and the mixture was sufficiently stirred to obtain a paste-like mixture. The mixing ratio of graphite and the binder was 100: 5 in terms of solid content weight ratio. A predetermined amount of tetrabutylammonium oxalate salt was added to this paste-like mixture and mixed thoroughly. As shown in Table 1, the amount of tetrabutylammonium oxalate added was 0.0037 mol, 0.0037 mol, corresponding to half the amount of lithium in the irreversible capacity of graphite.
Two kinds of 18 mol were used. The above paste was applied to a copper core material, dried at 120 ° C., rolled and cut to obtain a negative electrode plate. In addition, as comparative examples, those in which the tetrabutylammonium oxalate salt was not added to the negative electrode, and 0.0037 mol, 0.003 mol of lithium oxalate in the negative electrode were used.
Two types with 18 mol added were prepared. The weight of graphite was 2 g in each of the negative electrode plates.

LiMn _1.8 Co _0.2 O ₄ which is the positive electrode active material
Was synthesized by mixing Li ₂ CO ₃ , Mn ₃ O ₄ and CoCO ₃ in a predetermined molar ratio and heating at 900 ° C. Further, this was classified into 100 mesh or less. To 100 g of this positive electrode active material, 10 g of carbon powder as a conductive agent, 8 g of polytetrafluoroethylene as a binder, and a petroleum solvent were added to form a paste, which was applied to a titanium core material, dried and rolled. To obtain a positive electrode plate. The weight of the positive electrode active material was 5 g. The non-aqueous electrolyte was a mixed solution of ethylene carbonate and dimethoxyethane in an equal volume ratio in which 1 mol / l of lithium perchlorate was dissolved.

Assembly of the battery is carried out as follows.
The cylindrical battery shown in was constructed. First, the positive electrode plate 1 and the negative electrode plate 2 were spirally wound via a separator 3 made of a microporous polypropylene film to form an electrode group. Insulating plates 6 and 7 made of polypropylene are placed on the upper and lower sides of this electrode group and inserted into a battery case 8 to form a battery case 8
After forming a step on the upper part of the above, 2.6 ml of non-aqueous electrolyte was injected. Then, the first cycle of charging and discharging was performed with the upper part of the battery case open, the reaction product gas was released, and then the battery was sealed with the sealing plate 9. The positive electrode lead 4 attached to the positive electrode plate is connected to the positive electrode terminal 10 attached to the sealing plate 9, and the negative electrode lead 5 attached to the negative electrode plate is connected to the battery case 8. The charging / discharging condition in this case was constant current charging / discharging, and the current value was 100 mA. The charge and discharge cut voltage has an upper limit of 4.2 V and a lower limit of 3.
0 V was applied. The battery thus sealed was subjected to a charge / discharge cycle test under the same conditions as above. Table 1 shows the initial capacity and the capacity retention rate after 100 cycles.

[0015]

[Table 1]

The battery of this embodiment has an initial discharge capacity and 1
The discharge capacity retention rate at the 00th cycle is also superior to the comparative example. In the case of the comparative battery in which lithium oxalate is added to the negative electrode, the irreversible capacity of the negative electrode can be compensated by lithium generated during the first cycle charging, but the effect is not as good as that of alkylammonium oxalate.

Example 2 In this example, an example in which tetrabutylammonium oxalate salt is added to the positive electrode will be described. The negative electrode was produced in exactly the same manner as in Example 1 except that tetrabutylammonium oxalate salt was not added. The positive electrode is an active material LiMn classified to 100 mesh or less.
_1.8 g of Co _0.2 O ₄ to 10 g of carbon powder as a conductive agent, 8 g of polytetrafluoroethylene as a binder,
And a petroleum solvent were added, and the mixture was sufficiently stirred to obtain a paste-like mixture. A predetermined amount of tetrabutylammonium oxalate salt was added to this paste-like mixture and mixed thoroughly. The amount of tetrabutylammonium oxalate salt added is
As shown in Table 2, 0.0037 mol and 0.001
Two types of 8 mol were used. This paste was applied to a titanium core material, dried at 250 ° C., and rolled to obtain a positive electrode plate.
The weight of the positive electrode active material was 5 g. It should be noted that a comparative example was one in which tetrabutylammonium oxalate salt was not added to the positive electrode. The battery assembling method, the charge / discharge test method and the like were exactly the same as in Example 1. Table 2 shows the initial discharge capacity, and 10
The capacity retention rate after 0 cycle is shown.

[0018]

[Table 2]

The initial discharge capacity and the discharge capacity retention rate at the 100th cycle were high values for the battery of this example.

Example 3 In this example, an example in which tetrabutylammonium oxalate salt is added to a non-aqueous electrolyte will be described. An ammonium oxalate salt was added to a mixed solution of ethylene carbonate and dimethoxyethane in an equal volume in which 1 mol / l of lithium perchlorate was dissolved, and they were mixed sufficiently. As shown in Table 3, the amount of ammonium oxalate added was two kinds of 0.0037 mol and 0.0018 mol. A battery was assembled in the same manner as in Example 1 except that the above non-aqueous electrolyte was used with the addition of the tetrabutylammonium oxalate salt, and the negative electrode without the addition of the tetrabutylammonium oxalate salt was used. A charge / discharge cycle test was conducted under exactly the same conditions as above. A non-aqueous electrolyte to which no tetrabutylammonium oxalate salt was added was used as a comparative example. Table 3 shows the initial discharge capacity and the capacity retention rate after 100 cycles. Both the initial discharge capacity and the discharge capacity retention rate at the 100th cycle showed the highest value in the battery of this example.

[0021]

[Table 3]

Example 4 In this example, a negative electrode, a positive electrode,
An example in which oxalic acid tetrabutylammonium salt is added to at least two of the nonaqueous electrolyte will be described. A negative electrode, a positive electrode, and a nonaqueous electrolyte to which tetrabutylammonium oxalate salt was added were prepared in exactly the same manner as in Examples 1, 2, and 3, respectively. The battery assembling method, the charge / discharge test method and the like were exactly the same as in Example 1. In addition, the thing which does not add oxalic acid tetrabutylammonium salt was made into the comparative example. Table 4 shows the portion to which tetrabutylammonium oxalate salt was added, and the addition amount thereof, and Table 5
Shows the initial discharge capacity and the capacity retention rate after 100 cycles. The discharge capacity and the discharge capacity retention rate at the 100th cycle were both high in the battery of this example.

[0023]

[Table 4]

[0024]

[Table 5]

Example 5 In this example, oxalic acid tetrabutylammonium salt was added to at least one of the positive electrode, the negative electrode, and the non-aqueous electrolyte constituting the power generation element, and the oxalic acid tetrabutylammonium salt was added. The upper limit of the total amount added is half the number of moles of lithium, which corresponds to the irreversible capacity of the negative electrode material.
A method for manufacturing a non-aqueous electrolyte secondary battery in which a reaction product gas is released by performing first-cycle charging / discharging with the upper part of the battery open and then sealed is examined. In this example, tetrabutylammonium oxalate salt was added to the negative electrode. That is, the same negative electrode, positive electrode, and electrolyte as in Example 1 were housed in a battery case, the first cycle was charged and discharged with the upper case opened to release the reaction product gas, and then sealed. A comparative example was prepared by starting the charge and discharge of the first cycle after sealing and sealing the upper part of the case. The charge / discharge test method is exactly the same as in Example 1. Table 6 shows the initial discharge capacity and the capacity retention rate after 100 cycles.

[0026]

[Table 6]

There is no difference in discharge capacity between the battery of Example and the battery of Comparative Example, but in the discharge capacity retention ratio at the 100th cycle,
The batteries of the examples showed high values. The reason for this is that charging and discharging in the first cycle are performed with the upper case opened to release the reaction product gas and then the gas is sealed, so that the inside of the battery becomes stable and the reaction product gas and the battery It is considered that this is because the side reaction with the internal substance does not occur. Further, in the case of this type of battery, when the charge / discharge cycle is repeated, gas generation may be observed with the decomposition reaction or the like of the electrolytic solution, although only slightly. Therefore, when the first cycle charging / discharging is performed with the battery sealed, the reaction product gas increases the internal pressure of the battery. When the charge / discharge cycle is further repeated in this state, the newly generated gas is difficult to be desorbed from the electrode surface or the like because the internal pressure is already high, and the gas remains on the electrode surface or the like for a long period of time. As a result, the battery reaction may be adversely affected. In the above examples, tetrabutylammonium oxalate was used as the alkylammonium oxalate salt, but the same effect can be obtained for oxalic acid alkylammonium salts having various alkyl groups shown in the above formula (1). Is obtained.

Example 6 In this example, an example in which various alkylammonium oxalate salts are added to the negative electrode will be described. The battery manufacturing method and charge / discharge test conditions are the same as in Example 1. Table 7 shows the types of alkylammonium oxalate salts examined and the corresponding battery numbers. Table 8 shows the initial discharge capacity of each battery and the capacity retention rate after 100 cycles.

[0029]

[Table 7]

[0030]

[Table 8]

Each battery has a large initial discharge capacity and excellent cycle characteristics. In addition, in this embodiment, the alkyl groups contained in the salt have been described as being of the same type, but any combination of a methyl group, an ethyl group and a butyl group has the same effect. Furthermore, in this example, the case where the oxalic acid alkyl ammonium salt was added to the positive electrode was explained, but it was confirmed that the same effect was obtained when the oxalic acid alkyl ammonium salt was added to the negative electrode and the non-aqueous electrolyte. There is.

[0032]

As described above, according to the present invention, a non-aqueous electrolyte secondary battery having high energy density and good cycle characteristics can be obtained.

[Brief description of drawings]

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

[Explanation of symbols]

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Ito 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In the company

Claims (4)

[Claims] 1. A positive electrode having reversibility to charge and discharge, a non-aqueous electrolyte containing a lithium salt, and a negative electrode having reversibility to charge and discharge, the positive electrode, the negative electrode, and the non-aqueous electrolyte. At least one contains the alkyl ammonium oxalate salt represented by following formula (1), The non-aqueous electrolyte secondary battery characterized by the above-mentioned. Embedded image (In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently a methyl group, an ethyl group, a butyl group or a hydrogen atom.) 2. The total addition amount of the alkylammonium oxalate salt is set to a number of moles less than half of the amount of lithium corresponding to the irreversible capacity (charge capacity-discharge capacity in the first cycle) of the negative electrode. Non-aqueous electrolyte secondary battery. 3. A positive electrode having reversibility for charge and discharge, a negative electrode having reversibility for charge and discharge, a separator for separating both electrodes, a non-aqueous electrolyte containing a lithium salt, and the positive electrode. A step of accommodating an alkylammonium oxalate salt represented by the following formula (1) contained in at least one of a negative electrode, a negative electrode, and a non-aqueous electrolyte in a battery case; at least the first cycle with the case above being open. The method for producing a non-aqueous electrolyte secondary battery, comprising the steps of: charging the battery, releasing the generated gas, and then sealing the gas. Embedded image (In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently a methyl group, an ethyl group, a butyl group or a hydrogen atom.) 4. The method for producing a non-aqueous electrolyte secondary battery according to claim 4, wherein the total amount of the alkylammonium oxalate salt added is set to a number of moles that is half or less of the amount of lithium corresponding to the irreversible capacity of the negative electrode.