JPH08222269A - Manufacture of nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolyte lithium secondary battery which is excellent in thermal stability in the last stage of the cycle service life and having a carbon negative electrode by using a material which is formed by dissolving electrolyte in a mixed solvent containing an ethylene carbonate by a specific quantity and is dissolved by blowing in carbon dioxide under normal pressure, as electrolytic solution. CONSTITUTION: In manufacturing a nonaqueous electrolyte secondary battery having a positive electrode composed of a lithium-containing metallic oxide, a negative electrode composed of a carbon material which can intercalate and deintercalate lithium and nonaqueous electrolyte, the following means is used. That is, an electrolytic solution which is formed by dissolving inorganic salt being electrolyte in a mixed solvent containing an ethylene carbonate by 20 to 40% in the volume ratio and is dissolved by blowing in carbon dioxide under normal pressure, is injected by a specific quantity into a battery can in which a power generating element is housed. Solvent of the nonaqueous electrolyte is preferable to be a mixed solvent containing at least a single kind of an ethylene carbonate and a chain carbonate or aliphatic carboxylic acid ester.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery, and more particularly to improving the safety of a new non-aqueous electrolyte secondary battery which is small and lightweight.

[0002]

2. Description of the Related Art In recent years, electronic devices have been rapidly reduced in size and weight and have become cordless, and there has been an urgent need to develop a secondary battery having a high energy density which serves as a power source for driving the electronic device.

A lithium secondary battery is being developed as a battery that meets such demands. Conventionally, 3V class active materials such as manganese dioxide and vanadium pentoxide have been used as positive electrode active materials of lithium secondary batteries. A battery was constituted by these positive electrodes, a lithium negative electrode and an organic electrolytic solution, and charging and discharging were repeated.

However, generally, in a lithium secondary battery using lithium metal for the negative electrode, when the battery is heated or ignited by an internal short circuit due to dendrite-like lithium generated on the surface of the negative electrode during charging, or when the battery is heated. In addition, heat is generated due to a chemical reaction between the lithium negative electrode and the electrolytic solution, which may lead to ignition due to thermal runaway, and it is very difficult to ensure safety.

Recently, a carbon material capable of reversibly intercalating / deintercalating lithium has attracted attention as a negative electrode material of a lithium secondary battery and has been partially put into practical use. When a carbon material is used as the negative electrode, lithium, which is the active material during charging, is intercalated between the negative electrode carbon layers, so that metal lithium does not precipitate, and an internal short circuit or lithium metal due to the dendrite-like lithium as described above occurs. The problem of chemical reaction between the electrolyte and the electrolyte can now be prevented.

[0006]

However, when these carbon materials are used for the negative electrode, there is a problem that the negative electrode gradually deteriorates as the charge and discharge cycles are repeated, and the lithium acceptability during charging is lowered. At the end of the cycle life, lithium intercalated only between the carbon layers up to the 2nd stage, and the remaining lithium was deposited as metallic lithium on the surface of the negative electrode. This is because in the deteriorated state of the negative electrode, precipitation proceeds more easily than intercalation. When the battery at the end of the cycle life is heated, heat may be generated due to the chemical reaction between the deposited lithium metal and the electrolytic solution as described above, resulting in a thermal runaway state and ignition of the battery.

The present invention is to solve such a problem, and relates to a negative electrode using a carbon material, which inactivates metallic lithium deposited on the surface of the negative electrode and is excellent in thermal safety even at the end of cycle life. The present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery.

[0008]

In order to solve the above problems, the method for producing a non-aqueous electrolyte secondary battery according to the present invention uses an electrolyte in a mixed solvent containing 20% to 40% by volume of ethylene carbonate. Power generation of a positive electrode made of a lithium-containing metal oxide and an anode made of a carbon material capable of intercalating / deintercalating lithium in an electrolytic solution obtained by dissolving an inorganic salt and blowing carbon dioxide gas under normal pressure. A certain amount of liquid is poured into a battery can containing the elements.

[0009]

[Function] As described above, in the non-aqueous electrolyte secondary battery using a carbon material capable of intercalating / deintercalating lithium in the negative electrode, metal lithium deposition is observed on the negative electrode carbon surface at the end of the cycle life as described above. Will be available. However, a step of returning to normal pressure by injecting a certain amount of an electrolytic solution containing EC in which carbon dioxide gas of the present invention is dissolved under normal pressure into a battery can and then evacuating and then filling the system with carbon dioxide gas In the non-aqueous electrolyte secondary battery manufactured through the above, the deposited metal lithium reacts gently with carbon dioxide gas in the electrolyte solution, and partly produces thermally inactive lithium carbonate, so that the negative electrode heat Stability is increased. Therefore, when the battery at the end of the cycle life is heated, the reaction between the precipitated lithium and the electrolytic solution is less likely to occur, and as a result, a phenomenon such as thermal runaway and ignition of the battery is observed in the temperature range up to about 200 ° C. Disappear.

In the present invention, the selection of the solvent is very important, and the effect can be obtained by dissolving carbon dioxide gas mainly in ethylene carbonate (hereinafter abbreviated as EC).
It is required to include C. However, since EC has a very high melting point and is a solid at room temperature, it is difficult to use it as a single solvent. From these facts, the EC ratio is preferably 20% to 40% by volume, and more preferably 25% to 35%. If it is less than 20%, carbon dioxide cannot be sufficiently dissolved, and the effect of the present invention cannot be obtained. On the other hand, when it exceeds 40%, the high melting point property of EC becomes large, resulting in poor charge and discharge characteristics at a high rate. In order to improve the property of this melting point, a chain carbonate having a low melting point and a low viscosity such as diethyl carbonate (hereinafter abbreviated as DEC) and an aliphatic carboxylic acid such as methyl propionate (hereinafter abbreviated as MP) It is preferable to use a three-component electrolytic solution in which an ester is mixed. Also, D
Ethyl methyl carbonate (hereinafter abbreviated as EMC), which is a chain carbonate similar to EC, can also be used.
It is preferred to use a two-component system or a three-component system electrolytic solution in which an aliphatic carboxylic acid ester is added.

Although carbon dioxide gas is dissolved in the electrolytic solution, it is required to dissolve the inorganic salt of lithium as the electrolyte in the above mixed solvent and to dissolve the carbon dioxide gas by bubbling carbon dioxide gas under normal pressure. JP-A-6-1509
Japanese Patent Laid-Open No. 75-75 discloses that an electrolyte solution is pressurized and filled with carbon dioxide gas in the battery. However, in such a method, the carbon dioxide gas is hardly dissolved in the electrolyte solution and the effect of the present invention cannot be obtained. .

The present invention also relates to a negative electrode material, and the negative electrode is required to be a carbon material capable of intercalating / deintercalating lithium.
Among them, a material having a developed graphite layer structure is advantageous in obtaining a high capacity, and mesophase small spheres graphitized at a high temperature can be used. Japanese Unexamined Patent Publication No. 59-134567 discloses that metallic lithium is used for the negative electrode and an organic electrolytic solution in which carbon dioxide gas is dissolved is used. When such metallic lithium or lithium alloy is used for the negative electrode. The effect of the present invention cannot be obtained. It is considered that the effect of the present invention is that graphite acts as a catalyst for lithium deposited on the surface of graphite, carbon dioxide gas reacts gently to inactivate lithium, and therefore graphite exists in the negative electrode. It is considered that carbon dioxide gas loses reactivity in the non-operating system and does not contribute to the inactivation of lithium.

The inorganic salt of lithium, which is soluble in the electrolyte, is especially
Without limitation, LiPF ₆, LiBF_Four, Li
ClO_FourAny of the conventionally known ones can be used.
is there.

[0014]

【Example】

(Embodiment 1) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a vertical sectional view of a cylindrical battery used in this embodiment. In the figure, 1 is a battery case formed by processing an organic electrolyte resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. 4 is a plate group,
The positive electrode and the negative electrode are spirally wound a plurality of times with a separator interposed therebetween and housed in the battery case 1. A positive electrode lead 5 is drawn out from the positive electrode and connected to the sealing plate 2, and a negative electrode lead 6 is drawn out from the negative electrode and connected to the bottom of the battery case 1. Insulating rings 7 are provided on the upper and lower portions of the electrode plate group 4, respectively. The positive and negative electrodes will be described in detail below.

The positive electrode is a mixture of Li ₂ CO ₃ and Co ₃ O ₄ ,
100 parts by weight of LiCoO ₂ powder synthesized by firing at 900 ° C. for 10 hours, 3 parts by weight of acetylene black and 7 parts by weight of fluororesin binder were mixed and suspended in an aqueous carboxymethylcellulose solution to form a paste. . Apply this paste to both sides of 0.03mm thick aluminum foil,
After drying, it is rolled to a thickness of 0.18 mm, a width of 37 mm, and a length of 2.
It was a 40 mm positive electrode plate.

The negative electrode is formed by graphitizing mesophase small spheres at a high temperature of 2800 ° C. (hereinafter referred to as mesophase graphite).
It was used. (D002) by wide-angle X-ray diffraction is 3.3
It was 7Å. 100 parts by weight of this mesophase graphite was mixed with 3 parts by weight of styrene / butadiene rubber and suspended in an aqueous carboxymethyl cellulose solution to form a paste. Then, this paste was applied to both sides of a copper foil having a thickness of 0.02 mm, dried, and used as a negative electrode plate having a thickness of 0.20 mm, a width of 39 mm and a length of 260 mm.

Aluminum leads are attached to the positive electrode plate, and nickel leads are attached to the negative electrode plate. The leads are spirally wound through a polyethylene separator having a thickness of 0.025 mm, a width of 45 mm, and a length of 730 mm, and a diameter is formed. 1
It was delivered to a battery case with a height of 4.0 mm and a height of 50 mm.

As the electrolytic solution, EC, DEC and MP are 30:
1 mol / l of LiPF ₆ was dissolved as an electrolyte in a solvent mixed in a volume ratio of 50:20. Then, the carbon dioxide gas that had been sufficiently dried and dehydrated was treated with 1 l / min. At the speed of about 3
It was dissolved in the electrolytic solution by blowing at room temperature and atmospheric pressure for 0 minutes. After injecting 2.0 cc of the electrolyte solution thus adjusted into the battery case and evacuating for about 1 minute, the system was filled with carbon dioxide gas to return the battery to normal pressure and sealed. The battery of Example 1 was used.

(Example 2) A battery was constructed in the same manner as in Example 1 except that a solvent obtained by mixing EC and EMC in a volume ratio of 20:80 was used as the solvent of the electrolytic solution. The battery of Example 2 was used.

Comparative Example 1 Instead of the electrolytic solution of the battery of Example 1, an electrolytic solution was used in which 1 mol / l of LiPF ₆ as an electrolyte was dissolved and then carbon dioxide gas was not dissolved.
This electrolyte is poured into the battery case that has delivered the electrode plate group at room temperature and atmospheric pressure, and after evacuation for about 1 minute, the system is returned to normal pressure by filling dry air into the system and sealed. Then, the battery of Comparative Example 1 was obtained.

(Comparative Example 2) In the battery of Example 1, the battery case to which the electrode plate group was delivered was evacuated, and then 12 k of the electrolyte solution in which 1 mol / l of LiPF ₆ as the electrolyte was dissolved was used.
The solution was pressurized and filled with carbon dioxide at a pressure of g / cm ² to inject the solution. Then, the battery was sealed to obtain a battery of Comparative Example 2.

(Comparative Example 3) In the battery of Example 1, EC, DEC, and MP were used as solvents for the electrolytic solution at 10:60:
A battery was constructed in the same manner as in Example 1 except that the solvent mixed in a volume ratio of 30 was used, and the battery of Comparative Example 3 was obtained.

(Comparative Example 4) In the battery of Example 1, EC, DEC, and MP were used as the solvent of the electrolytic solution at 50:30:
A battery was constructed in the same manner as in Example 1 except that a solvent mixed in a volume ratio of 20 was used, and a battery of Comparative Example 4 was obtained.

Next, each of the batteries of this example and the comparative example was replaced with two batteries.
A cell was prepared and a charge / discharge cycle test was performed. In the charge / discharge test, constant voltage charging was performed at 20 ° C. with a charging voltage of 4.1 V and a charging time of 2 hours, the limiting current was 350 mA, and the discharging was a constant current discharge with a discharge current of 500 mA and a discharge end voltage of 3.0 V. Then, the discharge capacity at the 10th cycle was set as the initial capacity, and when the capacity deteriorated to half or less of the initial capacity, the end of the cycle life was determined and the cycle test was stopped in the charged state. One of two batteries at the end of cycle life
One was decomposed, and it was examined whether metallic lithium was deposited on the negative electrode plate. The other battery has a UL standard heating test (room temperature rises from 5 ° C to 165 ° C at 5 ° C / min and is maintained for 10 minutes).
Then, the presence or absence of ignition was examined. The results of the initial capacity, the presence / absence of metallic lithium deposition on the negative electrode at the end of the cycle life, and the presence / absence of ignition in the heating test are shown in (Table 1).

[0026]

[Table 1]

Precipitation of metallic lithium was observed on the surface of the negative electrode of the disassembled battery at the end of cycle life in the battery of the present invention and all the batteries of the comparative examples.

In the batteries of Examples 1 and 2 of the present invention, the initial capacity was as large as 500 mAh or more, and no ignition was observed in the heating test of the battery at the end of cycle life.
When the infrared absorption spectrum of the negative electrode surface of this end-of-cycle battery was measured, an absorption spectrum attributable to lithium carbonate was detected. From this, it is considered that the metallic lithium deposited on the negative electrode reacted with the carbon dioxide gas dissolved in the electrolytic solution, became thermally inactive, and did not ignite. On the other hand, the battery of Comparative Example 1 has ignited in the heating test, which causes a chemical reaction with the electrolytic solution because the deposited metal lithium is thermally active,
It is probable that a fire occurred due to thermal runaway. Also,
The battery of Comparative Example 2 also ignited in the heating test. This is because the carbon dioxide gas is not sufficiently dissolved in the electrolyte solution in the method of pressurizing and filling the electrolyte solution with carbon dioxide gas as described above. It is thought that it cannot be obtained. The battery of Comparative Example 3 also ignited in the heating test, but this is because the carbon dioxide gas was not sufficiently dissolved because the ratio of EC in the solvent component of the electrolytic solution was as low as 10%. Conceivable. In the batteries of Comparative Examples 1 to 3, the presence of lithium carbonate was not recognized from the surface of the negative electrode of the battery at the end of cycle life. In the battery of Comparative Example 4, no ignition was observed in the heating test of the battery at the end of cycle life,
The initial capacity was reduced to 450 mAh. It is considered that this is because the ratio of EC in the electrolytic solution is as large as 50%, so that the viscosity of the electrolytic solution is increased, and the polarization of the battery is increased under a high rate discharge of 1 hour rate and the capacity is reduced.

In this example, diethyl carbonate and ethyl methyl carbonate were used as the chain carbonate of the solvent of the electrolytic solution, and methyl propionate was used as the aliphatic carboxylic acid ester. However, other chain carbonates and aliphatic carboxylic acids were used. Almost the same effect can be obtained by using an ester.

In this embodiment and the comparative example, the positive electrode is L
Although iCoO ₂ is used, almost the same effect can be obtained when another lithium-containing metal oxide is used.

[0031]

As described above, according to the production method of the present invention,
It is possible to thermally inactivate metallic lithium deposited on the negative electrode at the end of the cycle life, and it is possible to provide a non-aqueous electrolyte secondary battery having excellent safety even at the end of the cycle life.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Insulation Packing 4 Electrode Plate Group 5 Positive Electrode Lead 6 Negative Electrode Lead 7 Insulation Ring

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akikatsu Morita 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A positive electrode comprising a lithium-containing metal oxide,
A method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode made of a carbon material capable of intercalating / deintercalating lithium, and a non-aqueous electrolyte, wherein ethylene carbonate is contained in a volume ratio of 20% to 40%. % A non-aqueous electrolyte secondary solution that dissolves an inorganic salt that is an electrolyte in a mixed solvent containing carbon dioxide and injects a fixed amount of the dissolved electrolyte solution into a battery can containing a power generation element by blowing carbon dioxide gas under normal pressure. Battery manufacturing method. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the solvent of the non-aqueous electrolyte is a mixed solvent containing ethylene carbonate and at least one of a chain carbonate and an aliphatic carboxylic acid ester. Manufacturing method. 3. The chain carbonate is diethyl carbonate or ethyl methyl carbonate.
A method for producing the non-aqueous electrolyte secondary battery described.