JP2001291519A - Nonaqueous second battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous second battery which is superior in safety and storing nature. SOLUTION: In a nonaqueous second battery which has a positive electrode, a negative electrode and a nonaqueous electrolyte containing a lithium salt, the nonaqueous second battery is constituted from lithium-containing transition metal chalcogenide whose surface is coated with celluloses, as an active material of the positive electrode. As cellulosics, at least one kind of those chosen from a group consisting of carboxymethyl cellulose, carboxymethyl ethly cellulose, ethyl cellulose, hydroxypropylcellulose and their salt is preferable. Further, as the coating amount of celluloses to cost the surface of lithium-containing transition metal chalcogenide, 0.1 to 5% by the weight standard for lithium- containing transition metal chalcogenide is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous secondary battery, and more particularly, to a non-aqueous secondary battery excellent in safety and storability.

[0002]

2. Description of the Related Art Along with the miniaturization of electronic equipment, there is an increasing demand for a lithium secondary battery used as a power source for higher capacity. This lithium secondary battery has a high average driving voltage of 3.6 V, which is about three times the average driving voltage of conventional nickel-cadmium batteries and nickel-hydrogen batteries, and a light carbonaceous material as a negative electrode material. In addition to the use of, the mobility involved in charge and discharge is light metal lithium, so that the weight can be reduced. However,
Regarding electrical capacity, although the capacity per unit weight is higher than that of conventional nickel-cadmium batteries or nickel-hydrogen batteries, only about 60% of the capacity per unit volume of nickel-hydrogen batteries has been commercialized. There is no demand for higher capacity.

To increase the capacity of a lithium secondary battery, for example,
This can be achieved by increasing the amount of the positive electrode active material, but if the amount of the positive electrode active material is too large,
Since the capacity of the negative electrode is insufficient, metal lithium is likely to precipitate on the surface of the negative electrode, and dendrites are formed. Therefore, the charge / discharge characteristics may be reduced and safety may be significantly impaired. Therefore, considering such circumstances, it is necessary to secure sufficient charge / discharge characteristics and safety at the same time when increasing the capacity. Until now, mainly the safety of the positive electrode active material itself has been reduced. Investigations have been made by improving and increasing the capacity of the negative electrode material.

On the other hand, when a lithium secondary battery is stored for a long time in a charged state, decomposition of an electrolytic solution occurs due to a reaction with a positive electrode active material, and a passive product covering the active material in the electrode by the decomposition product. There is a problem that the battery characteristics decrease due to storage, such as an increase in the coating and an increase in the battery resistance, which leads to a decrease in load characteristics and a failure to obtain a discharge capacity as low as before storage.

Further, in this lithium secondary battery,
As the binder for the positive electrode, polyvinylidene fluoride is generally used (Japanese Patent Application Laid-Open No. 4-24959), or fluororubber is used (Japanese Patent Application Laid-Open No. 4-95363). However, with polyvinylidene fluoride, Li
Since the surface of the positive electrode active material such as CoO ₂ can hardly be covered, an active surface is exposed,
Due to the high reactivity between the positive electrode active material and the electrolytic solution, problems tend to occur in terms of safety and storability.On the other hand, fluororubber covers the surface of the positive electrode active material densely, so that the charge-discharge reaction And the load characteristics are degraded.

[0006]

SUMMARY OF THE INVENTION The present invention solves the problems of the non-aqueous secondary battery represented by the lithium secondary battery as described above, and provides a non-aqueous secondary battery excellent in safety and storability. The purpose is to provide.

[0007]

According to the present invention, there is provided a non-aqueous secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt. The above problem has been solved by using a metal chalcogenide.

Examples of the celluloses that coat the surface of the lithium-containing transition metal chalcogenide include at least one selected from the group consisting of carboxymethylcellulose, carboxymethylethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose, and salts thereof. And carboxymethylcellulose and carboxymethylethylcellulose are particularly preferred. The coating amount of the celluloses is 0.1 to 5% by weight based on the total amount of the lithium-containing transition metal chalcogenide (that is, 0.1 to 5 parts by weight of the celluloses per 100 parts by weight of lithium-containing transition metal chalcogenide).
5 parts by weight), and more preferably 0.5 to 2%.

In the nonaqueous secondary battery of the present invention, since the surface of the highly reactive lithium-containing transition metal chalcogenide is coated with cellulose, the lithium-containing transition metal chalcogenide whose surface is not coated with cellulose is used. Higher stability of the positive electrode active material than when used as a positive electrode active material, especially when the lithium is desorbed during overcharge and the reactivity of the positive electrode active material becomes higher, the reaction with the electrolytic solution is suppressed. Is done. Similarly, even during a short circuit or a nail penetration test, rapid decomposition of the electrolyte does not occur, so that the safety of the battery is improved. On the other hand, since the cellulose-containing coating layer has the above-mentioned effect even if it is thin, it does not easily hinder the movement of lithium ions, and does not lower battery characteristics such as load characteristics. It is also considered that the stability is similarly high during storage, and a reaction such as formation of a passive film on the surface of the positive electrode active material is suppressed.

If the amount of the cellulose coating the surface of the lithium-containing transition metal chalcogenide is too small, it is difficult to obtain a sufficient effect. In addition to lowering the capacity, increasing the coating amount also hinders the charge / discharge reaction. Therefore, as described above, the content is preferably set to 0.1 to 5% by weight based on the total amount of the lithium-containing transition metal chalcogenide. Preferably, it is more preferably 0.5 to 2%.

In contrast to the present invention, when fluororubber is used as a binder, it has an effect of coating the surface of the positive electrode active material and improving the stability of the positive electrode active material to some extent, In this case, the effect of suppressing the reaction of the positive electrode active material is not sufficient, and the load characteristics are degraded because it hinders the movement of lithium ions.

In the present invention, since the surface of the lithium-containing transition metal chalcogenide is previously coated with cellulose, the cellulose is present only on the surface of the lithium-containing transition metal chalcogenide. As described in -22693, etc., when carboxymethylcellulose and a fluororesin are mixed to form a binder and carboxymethylcellulose is dispersed throughout the positive electrode mixture, the reaction of the positive electrode active material during overcharge is suppressed. In order to obtain the same effect as the present invention,
It is necessary to increase the coating amount of the cellulose (for example, it is necessary to increase the weight of the lithium-containing transition metal chalcogenide to 10% or more based on the total amount of the lithium-containing transition metal chalcogenide), and further, the cellulose dispersed in the entire positive electrode mixture Is an obstacle to the movement of lithium ions, and when a conductive auxiliary is added to further improve the conductivity of the positive electrode,
Since the cellulose also covers the surface of the conductive additive, the resistance is increased and the load characteristics are reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to only those exemplifications. Further, the feature of the present invention is that a lithium-containing transition metal chalcogenide whose surface is coated with celluloses is used as a positive electrode active material.
For example, other battery components such as a negative electrode, a non-aqueous electrolyte, and a separator are not particularly limited, and various components including those similar to conventional ones can be used.

First, as the lithium-containing transition metal chalcogenide, for example, LiCoO ₂ , LiNiO ₂ , L
LiN such as iMn ₂ O ₄ and LiNi _0.7 Co _0.3 O _{2
i x Co y O 2 (x} + y = 1), LiNi p Co q M r
O ₂ (p + q + r = 1, M is B, Mg, Al, Si,
P, V, Mn, Fe, Cu, Zn, Sr, In, Sn and at least one element selected from the group consisting of lanthanide elements). All of these lithium-containing transition metal chalcogenides have the property of doping and undoping lithium ions.

As described above, the cellulose which coats the surface of the lithium-containing transition metal chalcogenide is selected from the group consisting of, for example, carboxymethylcellulose, carboxymethylethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose and salts thereof. At least one kind is exemplified, and carboxymethylcellulose, carboxymethylethylcellulose and the like are particularly preferable.

As a method for coating the surface of the lithium-containing transition metal chalcogenide with celluloses, for example, the following method can be adopted.

That is, as a method of coating the surface of a lithium-containing transition metal chalcogenide with cellulose, for example, an aqueous solution in which cellulose is dissolved is mixed with a lithium-containing transition metal chalcogenide powder,
After drying to obtain a bulk body, the bulk body is pulverized so as to have the same particle size distribution as before the coating treatment, and a method of obtaining a coating treatment powder, a cellulose powder and a lithium-containing transition metal chalcogenide A method of mechanically mixing the powder with the powder of Example 1 and immersing it in water, followed by drying to obtain a coating-treated powder, while drying while spraying an aqueous solution in which celluloses are dissolved in lithium-containing transition metal chalcogenide powder. For example, a method of obtaining a coating-treated powder by using the method.

For the positive electrode, the coated powder obtained as described above, that is, a lithium-containing transition metal chalcogenide whose surface is coated with celluloses is used as a positive electrode active material, and the positive electrode active material and, if necessary, are added. A positive electrode mixture is prepared by mixing a conductive assistant and a binder, and the mixture is dispersed in a solvent to form a paste (the binder may be dissolved in the solvent in advance and then mixed with the positive electrode active material), The positive electrode mixture-containing paste is applied to a current collector,
It is manufactured by passing through a step of drying to form a positive electrode mixture layer. However, the manufacturing method of the positive electrode is not limited to the above-described example, and another method may be used.

The active material of the negative electrode facing the positive electrode may be, for example, one capable of doping and undoping lithium ions. Specific examples of such a negative electrode active material include graphite, pyrolytic carbon, and the like. , Cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, carbonaceous materials such as activated carbon, and lithium or lithium-containing compounds. Examples of the lithium-containing compound include tin oxide, silicon oxide, nickel-silicon alloy, magnesium-silicon alloy, tungsten oxide, lithium iron composite oxide, and the like, as well as lithium-aluminum, lithium-lead, lithium And lithium alloys such as indium, lithium-gallium and lithium-indium-gallium. Some of these exemplified lithium-containing compounds do not contain lithium at the time of manufacture, but when they act as a negative electrode active material, they contain lithium.

The negative electrode is prepared by mixing the above-mentioned negative electrode active material with a conductive auxiliary and a binder, which are added as necessary, to prepare a negative electrode mixture, and dispersing the mixture in a solvent to form a paste (the binder is previously added to the solvent). A step of forming a negative electrode mixture layer by applying the negative electrode mixture-containing paste to a negative electrode current collector made of a copper foil or the like, and then drying the mixture. It is produced by going through. However, the method for producing the negative electrode is not limited to the method exemplified above, and may be another method.

In the present invention, examples of the binder used for producing the positive electrode and the negative electrode include polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, and styrene-butadiene rubber. Also,
Examples of the conductive assistant include graphite, acetylene black, carbon black, Ketjen black, carbon fiber, metal powder, metal fiber, and the like.

As a current collector used for producing a positive electrode or a negative electrode, for example, aluminum,
Stainless steel, nickel, titanium or a foil made of titanium or an alloy thereof, punched metal, expanded metal, mesh and the like, the negative electrode, for example, copper, stainless steel,
Examples similar to those described above made of nickel, titanium, or an alloy thereof are given.

In the non-aqueous secondary battery of the present invention, a non-aqueous liquid electrolyte (hereinafter referred to as "electrolyte") is usually used as the non-aqueous electrolyte. As the electrolytic solution, an organic solvent-based non-aqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent is used. The organic solvent of the electrolytic solution is not particularly limited, for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, chain esters such as methyl propyl carbonate, or ethylene carbonate, propylene carbonate, butylene carbonate, vinylene Examples include a cyclic ester having a high dielectric constant such as carbonate, or a mixed solvent of a chain ester and a cyclic ester,
Particularly, a mixed solvent with a cyclic ester containing a chain ester as a main solvent is suitable.

The lithium salt to be dissolved in the above-mentioned organic solvent in preparing the electrolytic solution includes, for example, LiPF ₆ , L
iClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiC ₄
F ₉ O ₃ , LiAsF _{6 and the} like.

In the present invention, a solid or gelled non-aqueous electrolyte can be used as the non-aqueous electrolyte, in addition to the above-mentioned electrolytic solution. Examples of such a solid or gelled non-aqueous electrolyte include an inorganic non-aqueous electrolyte, and an organic non-aqueous electrolyte mainly composed of polyethylene oxide, polypropylene oxide or a derivative thereof.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. However, the present invention is not limited to these embodiments, and can be implemented by appropriately changing the scope without changing the gist. .

Example 1 In Example 1, a non-aqueous secondary battery according to the present invention was prepared using LiC having a surface coated with carboxymethyl cellulose.
A cylindrical lithium ion secondary battery was fabricated using oO ₂ as a positive electrode active material. The coating treatment of the surface of LiCoO _{2 with} the carboxymethyl cellulose was performed as follows. First, an aqueous solution in which carboxymethylcellulose was dissolved in an amount equivalent to 1% by weight based on LiCoO ₂ was added to LiCoO ₂ powder and mixed to obtain a bulk body. Then, the bulk body is crushed into powder again,
It was used as a positive electrode active material.

To 91 parts by weight of the positive electrode active material made of LiCoO ₂ whose surface was coated with carboxymethyl cellulose, 4 parts by weight of natural graphite as a conductive aid and 5 parts by weight of polyvinylidene fluoride as a binder were added and mixed. However, for mixing, polyvinylidene fluoride was previously dissolved in N-methyl-2-pyrrolidone,
The positive electrode active material and natural graphite were added to the polyvinylidene fluoride-containing solution and mixed well to prepare a positive electrode mixture-containing paste. The paste containing the positive electrode mixture has a thickness of 20 μm.
Was uniformly applied so as to have a predetermined coating amount on a positive electrode current collector made of an aluminum foil, and dried to form a positive electrode mixture layer. Similarly, the positive electrode mixture-containing paste is applied to the back surface of the positive electrode current collector, dried to form a positive electrode mixture layer, rolled, and then cut into a predetermined size to obtain a band-shaped positive electrode. Was.

In preparing the negative electrode, 10 parts by weight of polyvinylidene fluoride as a binder was mixed with 90 parts by weight of graphite as the negative electrode active material. However, for mixing, as in the case of the positive electrode, polyvinylidene fluoride was previously dissolved in N-methyl-2-pyrrolidone,
A negative electrode active material was added to the polyvinylidene fluoride-containing solution and mixed to prepare a negative electrode mixture-containing paste. The paste containing the negative electrode mixture was uniformly applied onto a negative electrode current collector made of a copper foil having a thickness of 15 μm so as to have a predetermined coating amount, and dried to form a negative electrode mixture layer. Similarly, the negative electrode mixture-containing paste is applied to the back surface of the negative electrode current collector, dried to form a negative electrode mixture layer, rolled, and then cut into a predetermined size to obtain a strip-shaped negative electrode. Was.

Next, a separator made of a microporous polyethylene film having a thickness of 25 μm is disposed between the strip-shaped positive electrode and the strip-shaped negative electrode manufactured as described above, and spirally wound to form a spiral electrode body. After that, outer diameter 18mm, height 67
The positive electrode lead body and the negative electrode lead body were inserted into a cylindrical battery case with a bottom having a diameter of 2 mm.

Thereafter, 1 mol / l L was placed in the battery case.
Electrolyte solution composed of iPF ₆ / EC + DEC (volume ratio 1: 1) [namely, LiPF ₆ is dissolved at 1 mol / l in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1. Nonaqueous electrolyte] was injected.

Then, the opening of the battery case was sealed in a usual manner, and the structure shown in FIG.
A 5 mm cylindrical non-aqueous secondary battery was produced.

Here, the battery shown in FIG. 1 will be described. 1 is the positive electrode and 2 is the negative electrode. However, FIG. 1 does not show the current collectors used for producing the positive electrode 1 and the negative electrode 2 in order to avoid complication.
The positive electrode 1 and the negative electrode 2 are spirally wound with a separator 3 interposed therebetween, and are accommodated in a battery case 5 together with the above-mentioned electrolytic solution 4 as a spiral electrode body.

The battery case 5 is made of stainless steel, and an insulator 6 made of polypropylene is disposed at the bottom of the battery case 5 before the spiral electrode body is inserted. The sealing plate 7
It is made of aluminum and has a disk shape, a thin portion 7a is provided at the center thereof, and a hole is provided around the thin portion 7a as a pressure inlet 7b for applying the internal pressure of the battery to the explosion-proof valve 9. Have been. The projection 9a of the explosion-proof valve 9 is welded to the upper surface of the thin portion 7a to form a welded portion 11. The thin portion 7a provided on the sealing plate 7
As for the projection 9a of the explosion-proof valve 9 and the like, only the cut surface is illustrated for easy understanding in the drawings, and the outline behind the cut surface is omitted. In addition, the thin portion 7 of the sealing plate 7
Also, the welded portion 11 of a and the projection 9a of the explosion-proof valve 9 is shown in an exaggerated state rather than the actual one so that it can be easily understood in the drawings.

The terminal plate 8 is made of rolled steel, nickel-plated on its surface, and has a hat-like shape with a brim-shaped peripheral portion. The terminal plate 8 is provided with a gas outlet 8a. . The explosion-proof valve 9 is made of aluminum and has a disk shape.
In the center thereof, a protruding portion 9a having a tip portion is provided on the power generation element side (the lower side in FIG. 1), and a thin portion 9b is provided, and the lower surface of the protruding portion 9a is closed as described above. It is welded to the upper surface of the thin portion 7a of the plate 7 to form a welded portion 11. The insulating packing 10 is made of polypropylene and has an annular shape. The insulating packing 10 is disposed above the peripheral edge of the sealing plate 7, and the explosion-proof valve 9 is disposed thereon. The gap between the two is sealed so that the electrolyte does not leak from between the two. The annular gasket 12 is made of polypropylene, and the lead body 13 is made of aluminum. The sealing plate 7 and the positive electrode 1 are connected to each other. An insulator 14 is disposed above the spiral electrode body. The bottom portion is connected by a lead body 15 made of nickel.

In this battery, the thin portion 7 of the sealing plate 7
a and the projecting portion 9a of the explosion-proof valve 9 come into contact at the welded portion 11,
Since the peripheral portion of the explosion-proof valve 9 and the peripheral portion of the terminal plate 8 are in contact with each other, and the positive electrode 1 and the sealing plate 7 are connected by the lead 13 on the positive electrode side, in a normal state, the positive electrode 1 and the terminal plate 8 Means a lead body 13, a sealing plate 7, an explosion-proof valve 9, and their welded parts 1
1 provides an electrical connection and functions normally as an electrical circuit.

When an abnormal situation occurs in the battery, such as when the battery is exposed to a high temperature, and gas is generated inside the battery to increase the internal pressure of the battery, the internal pressure rise causes the central portion of the explosion-proof valve 9 to move. It deforms in the direction of the internal pressure (upward direction in FIG. 1), and accordingly, the thin portion 7a integrated at the welded portion 11 is subjected to shearing force to break the thin portion 7a.
Alternatively, after the welding portion 11 between the projecting portion 9a of the explosion-proof valve 9 and the thin portion 7a of the sealing plate 7 is peeled off, the thin portion 9b provided on the explosion-proof valve 9 is torn, and gas is discharged from the terminal plate 8. The battery is designed to be discharged from the outlet 8a to the outside of the battery to prevent the battery from bursting.

Example 2 The amount of carboxymethylcellulose that coats the surface of LiCoO _{2 was set} at 0.1 based on the weight of LiCoO ₂ .
A cylindrical nonaqueous secondary battery was produced in the same manner as in Example 1 except that the content was set to 1%.

Example 3 The amount of carboxymethylcellulose that coats the surface of LiCoO ₂ was 0.1% by weight based on LiCoO ₂ .
A cylindrical non-aqueous secondary battery was manufactured in the same manner as in Example 1 except that the content was set to 5%.

[0040] The coating amount of carboxymethyl cellulose which covers the surface of Example 4 LiCoO _2, 2% by weight relative to LiCoO ₂
A cylindrical non-aqueous secondary battery was fabricated in the same manner as in Example 1 except that the above conditions were satisfied.

[0041] The coating amount of carboxymethyl cellulose which covers the surface of Example 5 LiCoO _2, 5% by weight relative to LiCoO ₂
A cylindrical non-aqueous secondary battery was fabricated in the same manner as in Example 1 except that the above conditions were satisfied.

Example 6 A cylindrical non-aqueous secondary battery was manufactured in the same manner as in Example 1 except that LiNi _0.7 Co _0.3 O ₂ was used instead of LiCoO ₂ . That is, in the non-aqueous secondary battery of the sixth embodiment, L
The surface of iNi _0.7 Co _0.3 O ₂ is coated with carboxymethyl cellulose, and the coating amount of carboxymethyl cellulose is 1% by weight based on LiNi _0.7 Co _0.3 O ₂ .

Examples 7 to 10 The same procedure as in Example 1 was repeated except that the cellulose used for coating the surface of LiCoO ₂ was changed to carboxymethylethylcellulose, methylcellulose, ethylcellulose and hydroxypropylcellulose, respectively. A battery was manufactured.

[0044] The coating amount of carboxymethyl cellulose which covers the surface of Example 11 LiCoO _2, except that the 6% by weight relative to LiCoO ₂ has a cylindrical nonaqueous secondary battery as in Example 1 Produced.

Comparative Example 1 A cylindrical non-aqueous secondary battery was manufactured in the same manner as in Example 1, except that LiCoO ₂ whose surface was not coated with carboxymethyl cellulose was used as the positive electrode active material.

Comparative Example 2 L not coated with carboxymethylcellulose
Example 1 Example 1 was repeated except that iCoO ₂ was used as a positive electrode active material and a positive electrode was prepared using a mixture of 1% carboxymethylcellulose and 4% polytetrafluoroethylene as a binder based on the weight of the positive electrode active material. A cylindrical non-aqueous secondary battery was produced in the same manner as described above.

Examples 1 to 11 manufactured as described above
And a cycle test for each of the batteries of Comparative Examples 1 and 2,
The overcharge test, the storage test, and the load characteristics were evaluated.
The test methods and evaluation methods are as follows.

Cycle test: Each battery was charged at a constant current and a constant voltage to 4.1 V at 1.5 A under an environment of 20 ° C.
The step of discharging to 2.75 V at 5 A is defined as one cycle,
This charge / discharge cycle is repeated, and the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle [(50
(0th cycle discharge capacity / 1st cycle discharge capacity) ×
100] were obtained, and the results are shown in Table 1 as cycle characteristics (capacity retention).

Overcharge test: Each battery was placed in an environment of 20 ° C.
After charging at a constant current and a constant voltage up to 4.1 V at 1.5 A,
The test was started after storing for 4 hours. The current during the overcharge test was 3.0 A, and the evaluation was performed at the maximum temperature of the battery, which is shown in Table 1.

Storage test: Each battery was charged and discharged in the same manner as in the above cycle test for 5 cycles, charged at a constant current and a constant voltage up to 4.1 V, and then stored in a 60 ° C. environment. After storage for 30 days, discharge was performed, and the same charge / discharge as in the above cycle test was performed once again to measure the discharge capacity and the discharge potential at the time of discharge. In addition, the discharge capacity and the discharge potential at the time of discharge were also measured before storage, and the evaluation of the storage test was evaluated by their change due to storage. That is, with respect to the discharge capacity, the ratio of the discharge capacity after storage to the discharge capacity before storage [(discharge capacity after storage / discharge capacity before storage) × 100] was determined, and this was used as the discharge capacity after storage. It was shown to. With respect to the discharge potential at the time of discharge, the difference between the discharge potential before storage and the discharge potential after storage was determined, and the difference was shown in Table 2 as a decrease in the discharge potential after storage.

Evaluation of load characteristics: The same charge / discharge cycle as in the above cycle test was repeated, and discharge was performed at 3.0 A at the 10th and 100th cycles. The average drive voltage at that time was determined. The results are shown in Table 3.

Tables 1 to 3 show the types of lithium-containing transition metal chalcogenides in each of the examples.
The type of celluloses used for coating the surface and the amount of the coating on the lithium-containing transition metal chalcogenide are shown. Due to space limitations, the names of the celluloses are indicated by abbreviations. That is, carboxymethylcellulose is indicated by CMC, carboxymethylethylcellulose is indicated by CMEC, methylcellulose is indicated by MC, ethylcellulose is indicated by EC, and hydroxypropylcellulose is indicated by HP.
Indicated by C. Tables 1 to 3 also show comparative examples.
The type of the lithium-containing transition metal chalcogenide used, the type of the binder, and the amount used (the amount based on the lithium-containing transition metal chalcogenide) are shown. That is, polytetrafluoroethylene is represented by PTFE.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

As is evident from the results shown in Table 1, the batteries of Examples 1 to 11 have lower maximum temperatures at the time of overcharging than the batteries of Comparative Examples 1 and 2, and have improved safety. You can see that it is doing. This is considered to be because the stability of the active material of the positive electrode was improved, and similar effects were also observed when a short-circuit test, a nail penetration test, and the like were performed.

As shown in Table 2, the batteries of Examples 1 to 11 had larger discharge capacities after storage than the batteries of Comparative Examples 1 and 2, and were excellent in storability.
In addition, comparing the batteries using the same lithium-containing transition metal chalcogenide, it was found that the batteries of the examples were able to maintain a higher operating voltage because the decrease in the discharge potential after storage was also smaller than that of the batteries of the comparative examples. Was.

As for the cycle characteristics, as shown in Table 1, the batteries of Examples 1 to 11 had the same or better characteristics as the battery of Comparative Example 1. However, when the coating amount of carboxymethyl cellulose exceeded 5%, various effects tended to be saturated.

Here, the load characteristics shown in Table 3 will be described. In Examples 1 to 11, the average drive voltage at the 10th and 100th cycles was high, and the load characteristics were excellent.

Incidentally, in Comparative Example 2 in which a mixture of carboxymethylcellulose and polytetrafluoroethylene was used as a binder without previously coating the surface of the lithium-containing transition metal chalcogenide, as shown in Table 3, In particular, the load characteristics at the 100th cycle were poor, and therefore, as shown in Table 1, the deterioration of the cycle characteristics became large. This is considered to be because carboxymethylcellulose also covered the conductive auxiliary agent and could not impart sufficient electron conductivity to the positive electrode.

[0061]

As described above, according to the present invention, a non-aqueous secondary battery excellent in safety and storability can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing one example of a non-aqueous secondary battery according to the present invention.

[Explanation of symbols]

 1 positive electrode 2 negative electrode 3 separator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ04 AJ12 AK03 AL06 AM03 AM05 AM07 BJ02 BJ14 DJ08 HJ01 5H050 AA09 AA15 BA17 CA08 CB08 DA02 DA11 EA21 FA18 HA01

Claims (3)

[Claims] 1. A non-aqueous secondary battery having a positive electrode, a negative electrode and a non-aqueous electrolyte containing a lithium salt, wherein a lithium-containing transition metal chalcogenide whose surface is coated with cellulose is used as an active material of the positive electrode. Non-aqueous secondary battery. 2. The non-aqueous secondary battery according to claim 1, wherein the cellulose is at least one selected from the group consisting of carboxymethylcellulose, carboxymethylethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose, and salts thereof. . 3. The active material of the positive electrode according to claim 1, wherein the amount of cellulose coating the surface of the lithium-containing transition metal chalcogenide is 0.1 to 5% by weight based on the lithium-containing transition metal chalcogenide. Non-aqueous secondary battery.