JPH04249074A - Manufacture of non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To prevent drop of the capacity and achieve excellent charging/ discharging cycle characteristics by synthesizing LiMO2 as pos. electrode active substance from Li compound and a compound incl. transfer metal in an atmosphere which has a specific oxygen concentration value in %. CONSTITUTION:LixMO2 as active substance of pos. electrode 2, where M is one or more sorts of transfer metal, and 0.05<=x<=1.10), is synthesized in an atmosphere whose oxygen concentration ranges 0.01-1.0%. That is, the synthetization is made by mixing and baking according to the composition of Li/transfer metal composite oxides with Li2CO3, Li2O, etc., and the atmosphere is prepared by including the oxygen in an inert gas such as Ar. Metal Li, Li alloy, etc., are used to neg. electrode 1, while a solution of the electrolyte such as Li salt in a non-aqueous (organic) solvent is used to the non-aqueous electrolyte. Thereby drop of the capacity associate with progress of the charging/discharging cycles is precluded, and a lightweight battery with excellent cycle characteristic is obtained.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention provides Lix MO2 (M
is at least one type of transition metal) as a positive electrode active material, particularly Lix
The present invention relates to a method for producing MO2. [0002] In recent years, the number of portable electronic devices such as video camera recorders and laptop computers has been increasing, and with this, the demand for batteries as portable power sources has rapidly increased. There is. Batteries that are popular as these portable power sources include Ni-Cd batteries,
Secondary batteries such as lead batteries are examples, but they still have the problem of being difficult to reduce weight. Due to this situation, titanium disulfide,
Non-aqueous electrolyte secondary batteries using metal sulfides such as molybdenum disulfide as positive electrode active materials have been proposed. However, with these metal sulfide-based positive electrode active materials, only batteries with a battery voltage of 3 V or less can be obtained, and there is a problem in that the battery voltage is low from the viewpoint of obtaining a battery with high energy density. Therefore, in order to obtain a battery with higher energy density, in Japanese Patent Publication No. 63-59507, etc., lithium composite oxide (for example, LiC) is used as a positive electrode active material.
A non-aqueous electrolyte secondary battery using oO2 has been proposed. This battery exhibits a high charge/discharge voltage and has the advantage of providing high energy density. In order to obtain a lithium composite oxide as a positive electrode active material, for example, in the case of LiCoO2, it can be produced by firing lithium carbonate and cobalt carbonate in air as shown in the above-mentioned patent publication. [0005] Portable power supplies for electronic devices such as those described above are required to have as long a lifespan as possible. That is, in a secondary battery, it is necessary to prevent a decrease in capacity due to repeated charge/discharge cycles. In this respect, the non-aqueous electrolyte secondary batteries using the above-mentioned lithium composite oxide as a positive electrode active material cannot necessarily be said to have sufficient characteristics. An object of the present invention is to provide a method for manufacturing a non-aqueous electrolyte secondary battery that can prevent a decrease in capacity and has excellent cycle characteristics. [Means for Solving the Problems] In order to achieve the above object, the present invention provides LixMO2 (M is at least one type of transition metal, and x satisfies 0.05≦x≦1.10). ) as a positive electrode active material, the Lix MO2 is made from a lithium compound and a compound containing the transition metal in an atmosphere with an oxygen concentration of 0.01% or more and less than 1.0%. This is a method for manufacturing a non-aqueous electrolyte secondary battery, which is characterized in that the non-aqueous electrolyte secondary battery is synthesized in a liquid electrolyte. [0008] Examples of the lithium compound include lithium carbonate (Li2 CO3) and lithium oxide (Li2O).
and lithium hydroxide (LiOH). In addition, examples of compounds containing the transition metal include carbonates, oxides, and hydroxides of the transition metal. [0009] Lix MO2 can be synthesized by mixing the above-mentioned compounds according to the composition of the composite oxide of lithium and transition metal to be obtained and firing the mixture. In this case, the atmosphere is preferably an inert gas such as argon. This gas contains oxygen in the range mentioned above. Further, the firing temperature is appropriately set depending on each of the above-mentioned compounds as starting materials, but is usually preferably in the range of 600 to 1100°C. [0010] Lix MO2 obtained as above
As a specific example, lithium cobalt oxide (Li
CoO2 ), lithium nickel oxide (Lix N
iO2 ), lithium nickel cobalt oxide (L
Examples include ixNiyCo(1-y)O2;0<y<1). As can be seen from these oxides, M in Lix MO2 is preferably Co and/or Ni. [0011] For the negative electrode in the non-aqueous electrolyte secondary battery of the present invention, a carbon material such as metallic lithium, a lithium alloy (for example, a lithium-aluminum alloy), or a fired body of organic matter such as pitch, tar, or coke is used. be able to. All of these can be doped and dedoped with lithium. Furthermore, as the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery according to the present invention, a nonaqueous electrolyte in which an electrolyte such as a lithium salt is dissolved in a nonaqueous solvent (organic solvent) can be used. [0013] The organic solvent here is not particularly limited, but includes, for example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2
-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3
-Dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, etc. can be used alone or in combination of two or more. [0014] Furthermore, any conventionally known electrolyte can be used as the electrolyte to be dissolved in the organic solvent, including LiClO4,
LiAsF6, LiPF6, LiBF4, LiB
(C6 H5)4, LiCl, LiBr, CH3
There are SO3 Li, CF3 SO3 Li, etc. [0015] Furthermore, the non-aqueous electrolyte may be fixed, such as a polymer complex solid electrolyte. [Operation] As mentioned above, a non-aqueous electrolyte secondary using Lix MO2 as a positive electrode active material synthesized in an atmosphere with an oxygen concentration of 0.01% or more and less than 1.0%. According to the battery, there is little decrease in capacity due to charge/discharge cycles. The reason for this is not clear, but the Li
This is presumed to be because the specific surface area of x MO2 changes depending on the oxygen concentration during synthesis. It is believed that when the oxygen concentration during synthesis is within an appropriate range, the specific surface area of the positive electrode active material in a nonaqueous electrolyte secondary battery will be an appropriate value. [Embodiments] Examples according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic vertical cross-sectional view of the non-aqueous electrolyte secondary battery of this example, and this battery was manufactured as follows. The positive electrode 2 was produced as follows. Lithium carbonate and cobalt carbonate were weighed so that the atomic ratio of lithium to cobalt was 1:1, and thoroughly mixed using a vibration mill. This mixture was fired at 900°C for 48 hours in an inert gas atmosphere with an oxygen concentration of 0.1% to obtain LiCoO2.
2 was crushed. The above powdered LiCoO2 is used as a positive electrode active material, and 91 parts by weight of this LiCoO2 is mixed with 6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride (PVDF) as a binder. This was used as a positive electrode mixture. This positive electrode mixture was dispersed in a solvent N-methyl-2-pyrrolidone to form a slurry (paste). This positive electrode mixture slurry is uniformly applied to both sides of the positive electrode current collector 10, which is a band-shaped aluminum foil, and dried. After drying, compression molding is performed using a roller press machine to form a positive electrode mixture layer 2 on both sides.
A strip-shaped positive electrode 2 having a was obtained. LiCoO2 is present in a powder state in the positive electrode mixture layer 2a, bound together with a conductive agent by a binder. Next, negative electrode 1 was produced as follows. Pitch coke (carbonaceous material) was used as a negative electrode active material carrier, and this pitch coke was ground into powder. 90 parts by weight of such powdered pitch coke and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed to prepare a negative electrode mixture. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone, which is a solvent, to form a slurry (paste). This negative electrode mixture slurry was uniformly applied to both sides of the negative electrode current collector 9, which was a strip-shaped copper foil, and dried. After drying, compression molding was performed using a roller press machine to produce a strip-shaped negative electrode 1. The strip-shaped negative electrode 1, the strip-shaped positive electrode 2, and a pair of separators 3a and 3b made of a microporous polypropylene film having a thickness of 25 μm, which were prepared as described above, were assembled into a negative electrode 1, a separator 3a, a positive electrode 2, and a separator. A spirally wound electrode body 15 was produced by winding a stacked electrode body having a four-layer structure in the order of 3b in a spiral shape along the length direction with the negative electrode 1 inside. . In addition, 33
is the winding core. The spirally wound electrode body 15 manufactured as described above was housed in a nickel-plated iron battery can 5, as shown in FIG. Further, in order to collect current from the negative electrode 1 and the positive electrode 2, a nickel negative electrode lead 11 is attached to the negative electrode current collector 9 in advance, led out from the negative electrode 1, and welded to the bottom surface of the battery can 5. In addition, an aluminum positive electrode lead 12 was attached to the positive electrode current collector 10 in advance, led out from the positive electrode 2, and welded to the protrusion 34a of the metal safety valve 34. [0024] Thereafter, a non-aqueous electrolyte in which lithium salt LiPF6 was dissolved at a ratio of 1 mole/liter in an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane was injected into the battery can 5. The wound electrode body 15 was impregnated. Before and after this, disc-shaped insulating plates 4a and 4b were disposed inside the battery can 5 so as to face the upper and lower end surfaces of the wound electrode body 15, respectively. Thereafter, the battery can 5, the safety valve 34 whose outer peripheries are in close contact with each other, and the metal battery lid 7 are each caulked through an insulating sealing gasket 6 whose surface is coated with asphalt. 5 was sealed. As a result, the battery lid 7 and the safety valve 34 were fixed, and the airtightness inside the battery can 5 was maintained. Further, at this time, the lower end of the gasket 6 in FIG. 1 comes into contact with the outer peripheral surface of the insulating plate 4a, so that the insulating plate 4a comes into close contact with the upper end side of the wound electrode body 15. In the manner described above, a cylindrical non-aqueous electrolyte secondary battery having a diameter of 13.8 mm and a height of 50 mm was manufactured. This battery will be referred to as Battery A for convenience, as shown in Table 1 below. [0028] The cylindrical non-aqueous electrolyte secondary battery has the following characteristics:
In order to constitute a double safety device, a safety valve 34, a stripper 36, and an intermediate fitting body 35 made of an insulating material for integrating these safety valves 34 and the stripper 36 are provided. Although not shown, the safety valve 34 has this safety valve 3
A hole is provided in the battery lid 7 to form a cleavage portion that ruptures when the battery 4 is deformed. In the unlikely event that the internal pressure of the battery rises for some reason, the safety valve 34 will move around its protrusion 34a as shown in FIG.
By deforming upward, the connection between the positive electrode lead 12 and the protrusion 34a is severed and the battery current is cut off, or the cleavage part of the safety valve 34 is ruptured and the gas generated in the battery is exhausted. They are each composed of . Next, the oxygen concentration when firing the LiCoO2 mentioned above was set to 0.5%, 0.8%, and 0.01%, respectively.
Table 1 below was performed in the same manner as for Battery A above, except that
Cylindrical nonaqueous electrolyte secondary batteries B, C, and D were prepared as shown in FIG. In addition, as a comparative example for confirming the effect of the present invention, the oxygen concentration when firing the LiCoO2 mentioned above was 1.0%, 5%, 10%, 20%, and 0.0%, respectively.
Cylindrical non-aqueous electrolyte secondary batteries E, F,
G, H and I were produced respectively. Note that the LiCoO2 pulverization conditions in the nine types of batteries described above were all the same. For each of the above nine types of batteries A to I, after setting the upper limit voltage to 4.1V and charging at a constant current of 500mA for 2 hours, the final voltage was 2.75V at a constant load of 18Ω.
The charge/discharge cycle was repeated until the battery was discharged. In this charge/discharge cycle, the capacity at 10 cycles was measured as the initial capacity, and the capacity at 200 cycles was further measured,
The ratio of the capacity at 200 cycles to the initial capacity (capacity at 200 cycles/initial capacity) was determined, and this was taken as the capacity retention rate. The capacity retention rate of each battery is shown in Table 1 below. [Table 1] [0034] As can be seen from Table 1, Li
There is a clear correlation between the oxygen concentration during CoO2 synthesis and the capacity retention rate after 200 cycles. That is, when the oxygen concentration is 0.005%, the capacity retention rate is low, but when the oxygen concentration ranges from 0.01% to 0.08%, the capacity retention rate becomes about 97% or more, showing good results. When the oxygen concentration becomes 1.0% or more, the capacity retention rate decreases. Therefore, it can be seen that the optimal oxygen concentration during synthesis of LiCoO2 is 0.01% or more and less than 1.0%. Next, the following measurements and considerations were made regarding the existence of a preferable oxygen concentration during the synthesis of a lithium composite oxide as a positive electrode active material. When the specific surface area of LiCoO2 in each of the above-mentioned batteries A, B, C, E, F, G and H was measured, they were 0.07, 0.22, 0.35, and 0.44, respectively.
, 0.61, 0.7, 0.73 m2/g. FIG. 2 shows the relationship between the oxygen concentration and the above-mentioned specific surface area during the synthesis of LiCoO2 for each battery. As can be seen from FIG. 2, as the oxygen concentration increases, the specific surface area of LiCoO2 increases. This tendency is particularly remarkable when the oxygen concentration is less than 1%, and when the oxygen concentration is 1% or more, the specific surface area increases slowly. It is presumed that by synthesizing LiCoO2 as a positive electrode active material in an atmosphere with an oxygen concentration of less than 1%, the specific surface area is reduced, and therefore, unnecessarily finer size of the positive electrode active material is suppressed. [0038] The cause of the capacity reduction of non-aqueous electrolyte secondary batteries is that the specific surface area of the positive electrode active material is larger than necessary (that is, the particles of the positive electrode active material are made finer than necessary).
It is conceivable that the electrolyte becomes more likely to be oxidized due to an oxidation reaction between the positive electrode active material and the electrolyte. If the oxygen concentration during the synthesis of the positive electrode active material is within an appropriate range, as mentioned above, the specific surface area of the positive electrode active material will not become larger than necessary (i.e., the unnecessarily finer size of the positive electrode active material will be suppressed). ), it is estimated that the reaction area between the positive electrode active material and the electrolyte becomes appropriate, reducing deterioration of the electrolyte. Note that LiCoO2 in each of the above-mentioned batteries
When we performed X-ray diffraction measurements on LiCoO2 (used in Battery I), the oxygen concentration at the time of synthesis was 0.005%, we found that cobalt oxide (Co3
It was found that O4) remained. This is considered to be because when the oxygen concentration is less than 0.01%, cobalt oxide remains due to insufficient oxygen in the atmosphere. Such cobalt oxide is an impurity in LiCoO2 as a positive electrode active material, and does not contribute to the charging/discharging reaction of the battery. In addition, other LiCoO2
In the X-ray diffraction measurement, no significant difference was observed between each LiCoO2. Furthermore, although the battery in this example was a cylindrical non-aqueous electrolyte secondary battery, the present invention is not limited to this; for example, it may be of a prismatic type;
It can also be applied to button-type and coin-type batteries. [0041] According to the method for manufacturing a non-aqueous electrolyte secondary battery of the present invention, a battery can be manufactured that can prevent a decrease in capacity as the charge/discharge cycle progresses. Therefore, in addition to the characteristics of high energy density and light weight,
It is possible to provide a non-aqueous electrolyte secondary battery with little capacity loss and excellent cycle characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the oxygen concentration during synthesis of each LiCoO2 obtained in this example and the specific surface area of each LiCoO2.

[Explanation of symbols]

1 Negative electrode 2 Positive electrode 2a Positive electrode mixture layer

Claims (1)

[Claims] Claim 1: A method for manufacturing a nonaqueous electrolyte secondary battery using Lix MO2 (M is at least one type of transition metal, and x satisfies 0.05≦x≦1.10) as a positive electrode active material. , manufacturing a nonaqueous electrolyte secondary battery, characterized in that the Lix MO2 is synthesized from a lithium compound and a compound containing the transition metal in an atmosphere with an oxygen concentration of 0.01% or more and less than 1.0%. Method.