JPH09312159A - Non-aqueous electrolyte liquid secondary battery and manufacture of positive pole active substance for non-aqueous electrolyte liquid secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte liquid secondary battery with its high energy density and good cycle characteristics. SOLUTION: A composite oxide including lithium is employed as a positive pole active substance, the lithium is doped, and a chloride ion of 0.001% or more and 1.0% or less is added to a positive pole active substance of a nonaqueous electrolyte liquid secondary battery in which a carbonic material to be de-doped is employed as a negative pole active substance. The positive pole active substance is thermally treated at 400 deg.C or more after ammonium chloride has been added to the active substance material and contains a chloride ion. An electrode element made of these positive pole active substance and negative pole active substance is stored in a battery can 5, an insulation plate 4 is arranged on both of the top and bottom faces of the electrode element, a nickel lead is led out from a negative pole power collector 10 to correct power from a negative pole 1 and welded to the battery can 5, in addition, to collect power from a positive pole 2 an aluminum lead is lead out from a positive pole power collector 11 and is welded to a battery cap 7. Then an electrolyte liquid is injected, the battery cap 7 and the battery can 5 are engaged with each other via a sealing port gasket 6, and a cylindrical non-aqueous electrolyte liquid secondary battery is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cycle characteristic of a non-aqueous electrolyte secondary battery in which a composite oxide containing lithium is used as a positive electrode active material, and a carbonaceous material for doping and dedoping lithium is used as a negative electrode active material. It is about the improvement of.

[0002]

2. Description of the Related Art Due to recent advances in electronic technology, electronic devices have become smaller, more efficient, and more portable, and there has been an increasing demand for higher energy density of batteries used in these electronic devices. Conventionally, there are nickel-cadmium batteries, lead batteries, etc. as secondary batteries used in these electronic devices, but these batteries have low discharge potential and insufficient energy density, so to obtain the required energy. To increase the battery weight and battery volume,
The fact is that the above-mentioned demands have not been sufficiently met.

[0003] Recently, lithium secondary batteries have attracted attention as a battery system that meets these requirements, and are being actively studied. However, the lithium secondary battery using metal lithium or a lithium alloy as a negative electrode has insufficient cycle life, rapid charging performance, and the like, and has been a problem to be improved for practical use. It is considered that these problems are caused by dissolution of metallic lithium as a negative electrode, generation of dendrites at the time of precipitation, and miniaturization.

In order to solve these problems, research and development of a lithium ion secondary battery, which is a non-aqueous electrolyte secondary battery, in which a substance such as carbonaceous material capable of doping and dedoping lithium ions is used as a negative electrode. Is being done. Since lithium does not exist in a metallic state in this lithium ion secondary battery, there is no problem such as cycle deterioration due to the metallic lithium negative electrode, and excellent secondary battery characteristics are exhibited. In addition, nickel
Compared to a cadmium battery, it has less self-discharge and no memory effect, and therefore has sufficient characteristics required for a secondary battery.

Further, by using a composite oxide containing lithium having a high oxidation-reduction potential for the positive electrode, the voltage of the battery becomes high, so that it has a high energy density. Due to such characteristics, the lithium ion secondary battery has come to be used as a power source for various portable devices.

On the other hand, since the positive electrode of the lithium ion secondary battery has a high oxidation-reduction potential, it exhibits a high potential of 4 V or more with respect to lithium, especially during charging, so that the electrolytic solution is decomposed on the surface of the positive electrode and the surface of the positive electrode active material is decomposed. A highly resistant film is formed. As a result, when the charge / discharge cycle is repeated for a long period of time, the capacity deterioration becomes large, and it is the current situation that sufficient battery characteristics as a secondary battery are not obtained.

[0007] Therefore, improvement of charge / discharge cycle characteristics has been studied from various viewpoints regarding battery materials of lithium ion secondary batteries. For example, non-aqueous electrolytes, positive electrode active materials, negative electrode active materials, electrode structures, etc. have been improved. Among them, active development of stable non-aqueous electrolytes (organic solvents, solutes) with high oxidation resistance is active. Is being advanced to.

For example, Abstract No. 19,
P33 in Extended Abstracts
of the 184th Electrochemi
cal Society, New Orleans
As shown in (1993), as a solute used for the electrolyte of the non-aqueous electrolyte secondary battery, LiC (SO ₂ C
_{F 3) 3, LiC (SO} 2 CF 3) 2 F, LiC (SO
_{Although 2} CF ₃ ) ₂ SO ₂ CH _{3 and the} like have been newly proposed, they have not yet been put to practical use.

[0009]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a non-aqueous electrolyte solution which uses a composite oxide containing lithium as a positive electrode active material and a carbonaceous material capable of doping and dedoping lithium as a negative electrode active material. An object of the present invention is to provide a non-aqueous electrolyte secondary battery which is excellent in cycle characteristics and has little capacity deterioration even after repeated charge / discharge for a long time.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a composite oxide containing lithium is used as a positive electrode active material, and a carbonaceous material that is doped and dedoped with lithium is used as a negative electrode active material. In the non-aqueous electrolyte secondary battery, the positive electrode active material is approximately 0.001% or more, 1.0% or more.
The following chlorine is included.

The positive electrode active material is formed by using a manufacturing method in which ammonium chloride is added to the active material material and then heat-treated at 400 ° C. or more to contain chlorine to solve the above problems.

Therefore, a positive electrode active material containing chlorine can be obtained by the production method of the present invention, and by using this positive electrode active material in a non-aqueous electrolyte secondary battery, high energy density and little capacity deterioration can be obtained. A secondary battery having excellent cycle characteristics can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor uses a composite oxide containing lithium as a positive electrode active material and a carbonaceous material for doping and dedoping lithium as a negative electrode active material in a non-aqueous electrolyte secondary battery. Chlorine in the active material is approximately 0.001% or more,
It was found that the inclusion of 1.0% or less makes it possible to obtain a non-aqueous electrolyte secondary battery with less capacity deterioration and excellent cycle characteristics.

Although there are various methods of introducing chlorine into the positive electrode active material, the present invention is characterized by adding a predetermined amount of ammonium chloride and then performing heat treatment at 400 ° C. or higher. Further, it is preferable that the heat treatment is performed until no decomposition gas is generated.

The reason why the cycle characteristics are improved by heat treatment at 400 ° C. after adding a predetermined amount of ammonium chloride to the positive electrode active material as described above can be considered as follows.

Ammonium chloride has a sublimation temperature of 337.8 ° C.
When it exceeds, it is decomposed into ammonia and hydrogen chloride. At this time, it is considered that the generated hydrogen chloride comes into contact with the surface of the positive electrode active material and adsorbs chloride ions (Cl ⁻ ) that are anions on the surface of the positive electrode active material, thereby suppressing decomposition of the electrolytic solution. Therefore, the heat treatment temperature needs to be higher than the temperature at which ammonium chloride starts to decompose.

That is, by adding ammonium chloride to the positive electrode active material and heat-treating at a temperature not lower than the sublimation temperature, chlorine ions of hydrogen chloride generated by decomposition of ammonium chloride are adsorbed on the surface of the positive electrode active material, and the electrolyte solution is formed. Is suppressed and the cycle characteristics are effectively affected. Therefore, the material to be added is not particularly limited to ammonium chloride, and it is needless to say that it may be hydrogen chloride or a chloride that generates chlorine when heated.

LiCoO ₂ , LiNi as the positive electrode active material
O ₂ , LiNi _X Co _1-X O ₂ (0 <X <1), LiM
Lithium-containing composite oxides such as n ₂ O ₄ can be used, and these include, for example, lithium, cobalt, nickel,
It is possible to synthesize manganese carbonate, nitrate, oxide and hydroxide as starting materials. The above starting materials are weighed and mixed according to the desired composition, and the mixture is mixed in an oxygen-existing atmosphere at
A lithium composite oxide can be obtained by firing at 0 to 1000 ° C. Further, the lithium composite oxide is not limited to the above Co, Ni, and Mn, and other suitable metals can be added.

On the other hand, although a carbonaceous material is used as the active material for the negative electrode, any material capable of doping and dedoping lithium may be used, and pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke). Etc.), graphites, glassy carbons, organic polymer compound fired bodies (furan resin etc. fired at a suitable temperature to be carbonized), carbon fibers, activated carbon and the like can be used. A carbon material having a (002) plane spacing of 3.70 Å or more and a true density of less than 1.70 g / cc and having no exothermic peak at 700 ° C. or more in a differential thermal analysis in an air stream is preferable. Used.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as a supporting electrolyte and this is dissolved in an organic solvent is used.
Here, the organic solvent is not particularly limited, but propylene carbonate, ethylene carbonate, 1,2-
Dimethoxyethane, γ-butyrolactone, tetrahydrofuran, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, etc. may be used alone, or two or more kinds of mixed solvents may be used.

As the electrolyte, LiClO ₄ , LiAsF ₆ and LiPF ₆ which are generally used for lithium batteries are used.
₆ , LiBF ₄ , LiCl, LiBr, CH ₃ SO ₃ L
i, CF ₃ SO ₃ Li and the like can be used alone or in combination of two or more kinds.

The non-aqueous electrolyte is not limited to a liquid state, and it is possible to use a conventionally known solid electrolyte. Further, in order to obtain a more safe sealed non-aqueous electrolyte secondary battery, it is desirable to provide a means for interrupting the current in accordance with an increase in the battery internal pressure when an abnormality occurs during overcharging.

Next, FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG.

Example 1 Negative electrode 1 was prepared as follows. The negative electrode active material uses petroleum pitch as a starting material, and this is converted to a functional group containing oxygen of 10 to 10.
After introducing 20% (oxygen crosslinking), 1000% in an inert gas
A non-graphitizable carbon material having properties close to those of a glassy carbon material obtained by firing at ℃ was used. 90% by weight of the carbon material thus obtained and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to form a slurry. I made it.
Further, this slurry was applied on both sides of a copper foil which is the negative electrode current collector 10, dried and then compression-molded by a roller press machine to obtain a negative electrode 1.

The positive electrode 2 was manufactured as follows. First, LiNi _0.8 Co _0.2 O ₂ was prepared as a positive electrode active material.
This uses lithium hydroxide as a lithium salt, nickel oxide as a nickel salt, and cobalt oxide as a cobalt salt. Lithium hydroxide, nickel oxide, and cobalt oxide have a Li / Ni / Co ratio of 1.0 / 0.80. /0.2
Weigh and mix so that it becomes 0, and 75 in an oxygen atmosphere.
LiNi having this component ratio after firing at 0 ° C. for 5 hours
_0.8 Co _0.2 O ₂ was obtained. Then, it was pulverized to prepare a powder having a predetermined particle size distribution.

After mixing 99% by weight of this positive electrode active material and 1% by weight of ammonium chloride, heat treatment was carried out at 400 ° C. for 10 hours to leave chlorine on the surface of the positive electrode active material. After ultrasonically extracting this active material, the result of quantitative analysis of chlorine by ion chromatography was 0.00
It was 1%.

Next, ammonium chloride was added to the mixture, 91% by weight of the heat-treated positive electrode active material, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride were mixed to prepare a positive electrode mixture. -Methyl-2-pyrrolidone was dispersed into a slurry. Further, this slurry was applied to an aluminum foil which is the positive electrode current collector 11, dried and then compression-molded by a roller press machine to obtain a positive electrode 2.

The spiral-shaped electrode element body is obtained by sequentially laminating the strip-shaped negative electrode 1 and the positive electrode 2 prepared as described above, and the separator 3 made of a microporous polyethylene film having a thickness of 25 μm in sequence and winding a large number of layers. Created.

The spirally wound electrode element body prepared as described above was housed in a nickel-plated iron battery can 5. Insulating plates 4 are arranged on both upper and lower surfaces of the spiral electrode element body,
In order to collect current from the negative electrode 1, the nickel lead is led out from the negative electrode current collector 10 and welded to the battery can 5, and the positive electrode 2
In order to collect current from the aluminum lead, the aluminum lead was led out from the positive electrode current collector 11 and welded to the battery lid 7.

Then, an electrolyte solution in which 1 mol of LiPF ₆ was dissolved in a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate was poured into the battery can 5, and the sealing gasket 6 coated with asphalt was used. By caulking the battery lid 7 and the battery can 5 in which the safety valve device 8 having the current interruption mechanism and the PTC element 9 is arranged,
Was fixed to prepare a cylindrical non-aqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm.

Example 2 A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that 5% by weight of ammonium chloride was added to the positive electrode active material. As a result of analyzing the amount of chlorine contained in the positive electrode active material, it was 0.02%.

Example 3 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 10% by weight of ammonium chloride was added to the positive electrode active material. As a result of analyzing the amount of chlorine contained in the positive electrode active material, it was 0.1%.

Example 4 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 20% by weight of ammonium chloride was added to the positive electrode active material. As a result of analyzing the amount of chlorine contained in the positive electrode active material, it was 1.0%.

Comparative Example 1 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 0.5% by weight of ammonium chloride was added to the positive electrode active material. As a result of analyzing the amount of chlorine contained in the positive electrode active material, it was below the detection limit.

Comparative Example 2 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 30% by weight of ammonium chloride was added to the positive electrode active material. As a result of analyzing the amount of chlorine contained in the positive electrode active material, it was 3.5%.

A cycle life test was performed on the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 under the following conditions. Charging is performed under the conditions of a charging voltage of 4.20V, a charging current of 1000mA, and a charging time of 2.5h, and discharging is repeated under the conditions of a discharge current of 500mA and an end voltage of 2.75V, and the capacity of the second cycle and the capacity of the 1000th cycle. The capacity retention ratio is defined as the ratio with the above, and the results are shown in Table 1.

[0037]

[Table 1]

It can be seen from Table 1 that when the chlorine content is 0.001% or more, the capacity retention rate is high and the capacity deterioration with the cycle is small. It is considered that this is because the presence of chlorine on the surface of the positive electrode active material suppressed the decomposition of the electrolytic solution. However, when the chlorine content exceeds 1% and becomes 3.5%, there is a drawback that the initial capacity of the battery becomes small although the capacity retention rate is high. It is considered that this is because the presence of excess chlorine hinders the doping and dedoping of lithium ions.

Therefore, in order to secure a high capacity retention without deteriorating the capacity of the battery, it is necessary to make the chlorine content in the positive electrode active material 0.001% or more and 1.0% or less. is there.

Example 5 Next, lithium manganese oxide was prepared as a positive electrode active material. Lithium carbonate was used as the lithium salt and manganese dioxide was used as the manganese salt. A mixture of 1 mol of manganese dioxide and 0.25 mol of lithium carbonate was fired in air at 850 ° C. for 5 hours to obtain a massive LiMn ₂ O. Got _four . The lump-shaped active material was crushed and classified by a ball mill to have a predetermined particle size to obtain a positive electrode active material.

99% by weight of this positive electrode active material and 1% by weight of ammonium chloride were mixed and then heat treated at 400 ° C. for 10 hours.
Chlorine remained in the positive electrode active material for a period of time. As a result of quantitative analysis of chlorine of this active material by the above-mentioned method, 0.
It was found to be 001%.

Next, 86% by weight of the chlorine-added positive electrode active material, 10% by weight of graphite as a conductor,
4% by weight of polyvinylidene fluoride was mixed as a binder to prepare a positive electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to form a slurry. This positive electrode mixture slurry was uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil, dried and then compression-molded with a roller press to obtain a strip-shaped positive electrode. A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the above positive electrode was used.

Example 6 Next, lithium cobalt oxide was prepared as a positive electrode active material. This uses lithium carbonate as a lithium salt and cobalt oxide as a cobalt salt. Cobalt oxide and lithium carbonate are mixed so as to have a Li / Co ratio of 1 and calcined in air at 900 ° C. for 5 hours to form LiCoO ₂ . Obtained. The lump-shaped active material was crushed and classified by a ball mill to have a predetermined particle size to obtain a positive electrode active material.

99% by weight of this positive electrode active material and 1% by weight of ammonium chloride were mixed and then heat treated at 400 ° C. for 10 hours.
Chlorine remained in the positive electrode active material for a period of time. As a result of quantitative analysis of chlorine of this active material by the above-mentioned method, 0.
It was found to be 001%. A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the above positive electrode active material was used.

With respect to the cylindrical non-aqueous electrolyte secondary batteries of Examples 5 to 6, the cycle life test was conducted in the same manner as in Examples 1 to 4. The ratio of the capacity at the 2nd cycle and the capacity at the 1000th cycle was taken as the capacity retention rate, and the results are shown in Table 2.

[0046]

[Table 2]

As can be seen from Table 2, even when lithium cobalt oxide and lithium manganese oxide are used as the positive electrode active material, the introduction of chlorine into the active material maintains a high capacity without impairing the initial capacity. You can get a rate.

From the above results, in a non-aqueous electrolyte secondary battery in which a composite oxide containing lithium is used as a positive electrode active material, and a carbonaceous material capable of doping and dedoping lithium is used as a negative electrode active material, By introducing chlorine into the substance, the capacity deterioration of the battery can be suppressed even if the charge / discharge cycle is repeated for a long time. As a method of introducing chlorine, it is preferable to add ammonium chloride and then perform heat treatment at 400 ° C. or higher.

Although a cylindrical battery has been described as an example, it is needless to say that the present invention can be applied to a prismatic, coin-type, or button-type battery and similar effects can be obtained.

[0050]

As is clear from the above description, a non-aqueous electrolyte secondary solution containing a lithium-containing composite oxide as a positive electrode active material and a lithium-doping and de-doping carbonaceous material as a negative electrode active material. In a battery, the positive electrode active material contains approximately 0.00
By containing 1% or more and 1.0% or less of chlorine, it is possible to suppress the capacity deterioration of the battery even after repeating the charge / discharge cycle for a long time, and obtain a secondary battery having a high capacity and excellent cycle characteristics. be able to.

[Brief description of drawings]

FIG. 1 is a side cross-sectional view of a tubular battery that is an embodiment using the present invention.

[Explanation of symbols]

1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Insulating plate, 5
... Battery can 6 ... Sealing gasket, 7 ... Battery lid, 8 ... Safety valve device, 9
... PTC element 10 ... Negative electrode current collector, 11 ... Positive electrode current collector, 12 ... Negative electrode lead, 13 ... Positive electrode lead 14 ... Center pin

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a composite oxide containing lithium is used as a positive electrode active material, and a carbonaceous material that is doped and dedoped with lithium is used as a negative electrode active material, wherein the positive electrode active material is: A non-aqueous electrolyte secondary battery having a structure containing approximately 0.001% or more and 1.0% or less chlorine. 2. The non-aqueous electrolyte secondary according to claim 1, wherein the positive electrode active material is formed by adding ammonium chloride to the active material and then performing a heat treatment at 400 ° C. or higher. A method for producing a positive electrode active material for a battery.