JPH0845509A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] [Structure] A lithium-containing composite oxide to which boron is added is used as a positive electrode active material of a non-aqueous electrolyte secondary battery.
Examples of the lithium-containing composite oxide include Li _w Ni _x C
o _y B _z O ₂ (where x, y, z and w are 0.05 ≦ w ≦
1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦
0.20, the condition of x + y + z = 1) is preferable. [Effect] A non-aqueous electrolyte secondary battery can be obtained in which the positive electrode active material functions normally, the high capacity is maintained, and good cycle characteristics are exhibited even when the battery is stored in a high temperature environment or repeatedly charged and discharged. To be Since such a non-aqueous electrolyte secondary battery can be used regardless of the usage environment, it is suitable as a power supply for portable devices.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, due to advances in electronic technology, electronic devices have been improved in performance, downsized, and made portable, and even for batteries used as power supplies for these portable electronic devices,
Increasing energy densities are increasingly required.

Secondary batteries used in these electronic devices so far include aqueous battery such as nickel-cadmium battery and lead battery. However, these aqueous solution type batteries have a low discharge potential and a large battery weight and battery volume, so that it is difficult to secure the energy density required for the above portable electronic device.

On the other hand, recently, a lithium secondary battery comprising a negative electrode made of lithium metal or a lithium alloy, a positive electrode made of a lithium-containing composite oxide, and a non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent. Secondary batteries have attracted attention as a battery system capable of obtaining high energy density and are being actively researched.

However, in this lithium secondary battery, when the negative electrode is made of metallic lithium, for example, when the metallic lithium is dissolved and deposited during the charge / discharge reaction,
There is a problem in that lithium grows from the negative electrode in the form of dendrite and reaches the positive electrode, causing an internal short circuit. In addition, when the negative electrode is made of a lithium alloy, a phenomenon in which the negative electrode is miniaturized as the charge / discharge reaction proceeds is observed. Such dendrite-like crystal growth of lithium and miniaturization of the negative electrode become more remarkable when rapid charging is performed. For this reason, the lithium secondary battery in which the negative electrode is composed of these metallic lithium or lithium alloy lacks cycle life, safety, quick charging performance, and the like, and is only partially put into practical use as a coin type.

Therefore, in order to solve the problems of the dendrite-like crystal growth of lithium and the miniaturization of the negative electrode as described above, lithium ions such as carbonaceous material may be doped or dedoped instead of lithium metal or the like. Research and development of lithium-ion secondary batteries in which the negative electrode is made of a possible substance has been actively conducted.

Since this lithium ion secondary battery is a battery reaction in which lithium does not exist in a metallic state, dendrite-like crystal growth of lithium hardly occurs, and the negative electrode does not become fine. Therefore, excellent cycle characteristics and high safety can be obtained. Moreover, it has the advantage that it has less self-discharge and no memory effect. In such a lithium-ion secondary battery, the positive electrode to be combined with the negative electrode made of the carbonaceous material is a lithium-containing composite oxide having a high redox potential (for example, a lithium transition metal composite represented by Li _X MO _2). Oxide) is used to increase the battery voltage and improve the energy density.

[0008]

By the way, it is assumed that the above-mentioned portable electronic device to which the secondary battery is applied is used not only in a normal temperature environment but also in various environments ranging from low temperature to high temperature. For example, it is in a high temperature environment such as in an automobile or in a hot and humid environment such as in a warehouse. For this reason, the secondary battery is also required to function normally in such a severe environment, particularly in a high temperature environment.

However, the above lithium-ion secondary battery, when used or stored in a high temperature environment,
There is a drawback that the battery performance is relatively impaired. This is because the electrolytic solution and the positive electrode active material are unstable in a high temperature environment, and therefore, the search for a stable material that can withstand high temperatures and the study of the electrode structure are being actively pursued.

For example, Japanese Unexamined Patent Publication (Kokai) No. 4-184872 proposes a mixed solvent of propylene carbonate and diethyl carbonate as a non-aqueous solvent for a lithium ion secondary battery. This publication describes that use of a mixed solvent of propylene carbonate and diethyl carbonate makes it possible to maintain normal battery performance even at a temperature of 45 ° C. However, even if this mixed solvent is used, if the battery is stored or used at a higher temperature of 60 ° C. or higher,
After all, the battery performance is deteriorated and it is not a sufficient countermeasure.

Also, Abstract No19, p3
3 in Extended Abstracts o
f the 184th Electrochemical
alSociety, New Orleans (199
In 3), LiC (SO ₂ C
_{F 3) 3, LiC (SO} 2 CF 3) 2 F, LiC (SO
Etc. _{2 CF 3) 2 SO 2 CH} 3 are mentioned. However, these are still in the development stage, and further study is necessary before putting them into practical use.

In addition, JP-A-5-151988 discloses that by specifying the particle size distribution of the positive electrode active material, cycle characteristics and storage performance at high temperature can be improved. However, it is very difficult to pulverize the positive electrode active material and adjust the particle size distribution as shown in the above publication,
It is not a realistic method.

Thus, in the lithium ion secondary battery,
Various studies have been conducted to improve the high temperature characteristics, but the actual situation is that satisfactory results have not been obtained.

Therefore, the present invention has been proposed in view of such a conventional situation, and maintains a high capacity even when it is stored in a high temperature environment or repeatedly charged and discharged, and has good cycle characteristics. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery that can obtain the above.

[0015]

Means for Solving the Problems As a result of intensive studies made by the present inventors in order to achieve the above-mentioned object, as a result of using a lithium-containing composite oxide containing boron as a positive electrode active material, We have come to the conclusion that the performance in the high temperature environment is significantly improved.

The present invention has been completed on the basis of such findings, and a lithium-containing composite oxide is used as a positive electrode active material, and a carbonaceous material capable of doping / dedoping lithium is used as a negative electrode active material. In the non-aqueous electrolyte secondary battery described above, boron is added to the lithium-containing composite oxide serving as the positive electrode active material.

The lithium-containing composite oxide which is the positive electrode active material is Li _w Ni _x Co _y B _z O ₂ (where x,
y, z and w are 0.05 ≦ w ≦ 1.10 and 0.5 ≦ x ≦
0.995, 0.005 ≦ z ≦ 0.20, x + y + z =
The condition 1 is satisfied).

The present invention is applied to a lithium ion secondary battery (non-aqueous electrolyte secondary battery) using a carbonaceous material capable of being doped and dedoped with lithium as a negative electrode active material.

In the present invention, in order to improve the performance of such a non-aqueous electrolyte secondary battery in a high temperature environment, a lithium-containing composite oxide to which boron is added is used as a positive electrode active material.

Conventionally, in a lithium ion secondary battery, a lithium-containing composite oxide having a high redox potential has been used as a positive electrode active material because a high battery voltage can be obtained.
However, this lithium-containing composite oxide is a crystal having a hexagonal layered structure in a room temperature environment, but when boron is not added, it is stored in a high temperature environment or subjected to lithium doping / dedoping. Then, the crystallinity decreases. As a result, lithium doping / dedoping is not normally performed, and the performance as a positive electrode active material is impaired.

On the other hand, the lithium-containing composite oxide to which boron is added does not deteriorate in crystallinity not only under normal temperature environment but also under lithium doping / dedoping under high temperature environment, and the normal crystallinity is obtained. Doping / dedoping performance is maintained. Therefore, by using such a lithium-containing composite oxide to which boron is added, it is possible to obtain a non-aqueous electrolyte secondary battery that maintains a high capacity even under a high temperature environment and exhibits good cycle characteristics. It will be.

Here, as the lithium-containing composite oxide to which boron is added, for example, Li _w Ni _x Co _y B
A composite oxide of Li, Ni, and Co represented by _z O ₂ is suitable because a high battery voltage can be obtained.

The amount of boron added is important in order to obtain the above effects by using the positive electrode active material for the lithium-containing composite oxide to which boron is added. If the amount of boron added to the lithium-containing composite oxide is too small, boron hardly contributes to stabilization of the crystal structure, and the high temperature characteristics of the battery are not sufficiently improved. On the other hand, when the amount of boron added is too large, the crystal structure is sufficiently stabilized, but the charge / discharge performance specific to the positive electrode active material is impaired.

That is, there is an optimum range for the amount of boron added. For example, in the case of a lithium-containing composite oxide represented by Li _w Ni _x Co _y B _z O ₂ , w, x, y, z are 0. .05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995,
It is preferable to set so as to satisfy the conditions of 0.005 ≦ z ≦ 0.20 and x + y + z = 1. By setting the composition ratio of each element to satisfy such a condition, it is possible to suppress the capacity deterioration in a high temperature atmosphere without impairing normal charge / discharge characteristics.

The lithium-containing composite oxide represented by Li _w Ni _x Co _y B _z O ₂ is, for example, lithium, cobalt, nickel carbonate, nitrate, oxide, hydroxide, or It is synthesized by adding boric acid, boron oxide, and lithium borate, and firing the mixture as a starting material in a temperature range of 600 ° C. to 1000 ° C. in an oxygen-present atmosphere.

The composition ratio of each element of the lithium-containing composite oxide to be synthesized can be adjusted to the above-mentioned optimum range by controlling the mixing ratio of the starting materials.

On the other hand, as the negative electrode active material, a carbonaceous material capable of doping / dedoping lithium is used. Examples of such carbonaceous materials include pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), graphites, glassy carbons, organic polymer compound fired bodies (furan resin, etc.). Carbonized by firing at an appropriate temperature), carbon fiber, activated carbon and the like can be used. In particular, the plane spacing of the (002) plane is 3.70 or more,
A carbonaceous material having a true density of less than 1.70 g / cc and having no exothermic peak at 700 ° C. or higher in a differential thermal analysis in an air stream is suitable.

As the electrolytic solution, a non-aqueous electrolytic solution in which a lithium salt is used as a supporting electrolyte and this is dissolved in a non-aqueous solvent is used.

The non-aqueous solvent is not particularly limited,
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 as a mixed solvent of two or more thereof.

As the electrolyte, those generally used in lithium batteries can be used, such as LiClO ₄ ,
LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCl, L
iBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like are used alone or in combination of two or more.

A solid electrolyte may be used instead of the non-aqueous electrolyte.

In a battery, the positive electrode made of the positive electrode active material, the negative electrode made of the negative electrode active material and the non-aqueous electrolyte are housed in, for example, an iron battery can, and the battery can and the battery lid are caulked and hermetically sealed. Consists of The positive electrode and the negative electrode are connected to the battery lid and the battery can by a lead member, respectively, and are energized from the outside through the battery lid and the battery can and the lead member. Note that such a battery may be provided with a current interrupting mechanism that interrupts the current in the battery system in response to an increase in the internal pressure of the battery when an abnormality such as overcharging occurs, thereby improving safety.

[0033]

[Function] The lithium-containing composite oxide is a crystal having a hexagonal layered structure, but when boron is not added, it is crystallized when stored in a high temperature environment or when lithium is doped or dedoped. Sex decreases. by this,
Lithium doping and dedoping will not be performed normally,
The performance as the positive electrode active material is impaired.

On the other hand, the lithium-containing composite oxide to which boron is added has stable performance as a positive electrode active material not only in a room temperature environment but also in a high temperature environment where lithium is doped and dedoped. Maintained. this is,
It is considered that the solid solution of boron stabilizes the hexagonal crystal structure and maintains the crystal structure even in a high temperature environment. In a non-aqueous electrolyte secondary battery using a material as a positive electrode active material, even in a high temperature environment,
High capacity is maintained and good cycle characteristics are obtained.

[0035]

EXAMPLES Specific examples to which the present invention is applied will be described below based on experimental results.

The structure of the battery prepared in this example is shown in FIG. In this example, a battery having such a structure was prepared as follows.

First, the positive electrode 2 was manufactured as follows.

Lithium hydroxide, nickel oxide, cobalt oxide and boric acid were mixed so that the Li / Ni / Co / B (molar ratio) was the value shown in Table 1, and the mixture was mixed in an oxygen atmosphere at a temperature of 750 ° C. for 5 hours. A positive electrode active material was synthesized by firing for a time.

[0039]

[Table 1]

91% by weight of the obtained positive electrode active material, 6% by weight of graphite as a conductive material, and 3% by weight of vinylidene borofluoride were mixed to prepare a positive electrode mixture, and N-methyl-2 was used.
-Dispersed in pyrrolidone to obtain a positive electrode mixture slurry. Then, the positive electrode mixture slurry was applied to an aluminum foil to be the positive electrode current collector 10, dried, and compression-molded with a roller press to produce a strip-shaped positive electrode 2.

Next, the negative electrode 1 was produced as follows.

Petroleum pitch was used as a starting material, and 10 to 20% of oxygen-containing functional groups were introduced into this (oxygen cross-linking).
The negative electrode active material was produced by firing at a temperature of 1000 ° C. in an inert gas. The obtained negative electrode active material is a non-graphitizable carbon material having properties close to those of a glassy carbon material.

90% by weight of this carbonaceous material 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 obtain a negative electrode mixture slurry. Further, the negative electrode mixture slurry was applied onto both surfaces of a copper foil which will be the negative electrode current collector 9, dried, and then compression-molded by a roll press machine to prepare a strip-shaped negative electrode 1.

The strip-shaped negative electrode 1 and positive electrode 2 produced as described above are laminated in order with the separator 3 made of a microporous polypropylene film having a thickness of 25 μm interposed therebetween, and are wound many times to form a spiral electrode. The body was made. In addition, in this spiral electrode body, the negative electrode was dimensioned so that both the width and the length were larger than the positive electrode.

The spirally wound electrode body thus produced was housed in a nickel-plated iron battery can 5,
Insulating plates 4 were arranged on the upper and lower surfaces of the spiral electrode body. And
Aluminum lead 1 for collecting positive and negative electrodes
3 was drawn out from the positive electrode current collector 11, welded to the safety valve device 8 connected to the battery lid 7 via the PTC element 9, and the nickel lead 12 was drawn out from the negative electrode current collector 10 and welded to the battery can 5. .

Then, an electrolytic solution in which 1 mol of LiPF ₆ was dissolved in a mixed solvent of propylene carbonate 50% by volume and diethyl carbonate 50% by volume was injected into the battery can 5. Next, the battery lid 7 is fixed by caulking the battery lid 7 and the battery can 5 through the asphalt-coated sealing gasket 6, and a cylindrical battery having a diameter of 18 mm and a height of 65 mm (sample battery 1 to sample battery 14) It was created.

With respect to each of the batteries produced as described above, the initial capacity and the capacity retention rate under a high temperature environment were examined.

The initial capacity and the capacity retention rate in a high temperature environment were such that after charging for 2.5 hours under the conditions of a charging voltage of 4.20 V and a charging current of 1000 A, a discharging current of 500 mA,
After performing two charge / discharge cycles under the condition of a final voltage of 2.75 V under a normal temperature environment, a temperature of 60
The test was conducted by performing 300 cycles under a temperature environment of 300 ° C. and measuring the discharge capacity at that time. The initial capacity is the discharge capacity of the second cycle when such charging and discharging are performed for two cycles, and the capacity retention rate is the ratio of the discharge capacity of the 300th cycle of charging and discharging to the discharge capacity of the second cycle of charging and discharging. is there.
Regarding the measured discharge capacity and capacity retention rate, the results of Sample Battery 1 to Sample Battery 8 are shown in Table 2 and Sample Battery 9
~ The results of the sample battery 14 are shown in Table 3, respectively.

[0049]

[Table 2]

[0050]

[Table 3]

First, as shown in Table 2, when the ratios of B and Co in the positive electrode active material are changed and the ratios of Ni are fixed, the measurement results of sample batteries 1 to 8 are compared. It can be seen that the capacity retention rate increases as the ratio of B in the positive electrode active material increases, and that by setting the molar ratio of B to 0.005 or more, a capacity retention rate of 87% or more can be obtained.

From this, it is effective to add B to the lithium composite oxide serving as the positive electrode active material in a molar ratio of 0.005 or more, in order to improve the cycle characteristics of the battery in a high temperature environment. It is shown that there is. It is considered that this is because B has a function of stabilizing the crystallinity of the lithium composite oxide.

However, the molar ratio of B in the positive electrode active material is 0.
In the sample battery 8 of No. 25, although the capacity retention rate in a high temperature environment is excellent, the initial capacity is 1050 mAh, which is a relatively small value.

Therefore, if the molar ratio of B in the positive electrode active material is too large, it is not preferable, and in order to improve the high temperature characteristics while maintaining the charge and discharge performance, the range is 0.005 to 0.20. Appropriate.

Next, as shown in Table 3, when the ratio of Ni and Co in the positive electrode active material is changed and the ratio of B is fixed, the measurement results of sample batteries 9 to 14 are compared.
It can be seen that the capacity retention ratio in a high temperature environment also changes depending on the ratio of Ni in the positive electrode active material, and if this Ni ratio becomes too small, a sufficient capacity retention ratio cannot be obtained and the initial capacity also decreases. . For example, N in the positive electrode active material
In the sample battery 14 in which the molar ratio of i is 0.40, 7
Only a capacity retention rate of about 5% is obtained. This is B
It is considered that Ni is involved in the effect of stabilizing crystallinity due to Ni.

Therefore, in the lithium-containing composite oxide serving as the positive electrode active material, B is added in a molar ratio of 0.005 to 0.2 and Ni is contained in a molar ratio of 0.50 to 0.995. That is, Li _w Ni _x Co
_y B _z O ₂ (where x, y, z and w are 0.05 ≦ w ≦
1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦
It can be seen that it is appropriate that the composition is such that 0.20 and the condition of x + y + z = 1 is satisfied.

[0057]

As is apparent from the above description, in the non-aqueous electrolyte secondary battery of the present invention, a carbonaceous material capable of being doped / dedoped with lithium as a negative electrode active material is used.
Since a lithium-containing composite oxide to which boron is added is used as the positive electrode active material, a high energy density can be obtained, and the positive electrode active material can function properly even when stored in a high temperature environment or repeatedly charged and discharged. However, high capacity is maintained and good cycle characteristics are obtained. Therefore, it can be used regardless of the usage environment and is suitable as a power supply for portable devices.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing one structural example of a non-aqueous electrolyte secondary battery to which the present invention is applied.

[Explanation of symbols]

 1 Negative electrode 2 Positive electrode 3 Separator

[Procedure amendment]

[Submission date] December 27, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

On the other hand, as the negative electrode active material, a carbonaceous material capable of doping and dedoping lithium is used. For example, as such a carbonaceous material, pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), graphites, glassy carbons, organic polymer compound fired bodies (furan resin, etc.) are suitable. Carbonized by firing at various temperatures), carbon fiber, activated carbon, etc. can be used. In particular, a carbonaceous material having a (002) plane spacing of 3.70 angstroms 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. Is.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction content]

91% by weight of the obtained 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, and N-methyl-2 was used.
-Dispersed in pyrrolidone to obtain a positive electrode mixture slurry. Then, the positive electrode mixture slurry was applied to an aluminum foil to be the positive electrode current collector 10, dried, and compression-molded with a roller press to produce a strip-shaped positive electrode 2.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0048

[Correction method] Change

[Correction content]

The initial capacity and the capacity retention rate in a high temperature environment were as follows: after charging for 2.5 hours under conditions of a charging voltage of 4.20 V and a charging current of 1000 mA, a discharging current of 500 m
A, charge and discharge cycles such as discharging under the condition of a final voltage of 2.75 V were carried out for 2 cycles under a normal temperature environment, then for 300 cycles under a temperature of 60 ° C., and the discharge capacity at that time was measured. . The initial capacity is the discharge capacity of the second cycle when such charging and discharging are performed for two cycles, and the capacity retention rate is the ratio of the discharge capacity of the 300th cycle of charging and discharging to the discharge capacity of the second cycle of charging and discharging. is there. Regarding the measured discharge capacity and capacity retention rate, Table 2 shows the results of Sample Battery 1 to Sample Battery 8 and Table 3 shows the results of Sample Battery 9 to Sample Battery 14, respectively.

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a lithium-containing composite oxide as a positive electrode active material and a carbonaceous material capable of doping and dedoping lithium as a negative electrode active material, which serves as a positive electrode active material. A non-aqueous electrolyte secondary battery in which boron is added to a lithium-containing composite oxide. 2. The lithium-containing composite oxide, which is the positive electrode active material, is a hexagonal crystal.
The non-aqueous electrolyte secondary battery described. 3. A lithium-containing composite oxide as a positive electrode active material is Li _w Ni _x Co _y B _z O ₂ (provided that x, y,
z and w are 0.05 ≦ w ≦ 1.10 and 0.5 ≦ x ≦ 0.9.
95, 0.005 ≦ z ≦ 0.20, x + y + z = 1 are satisfied), The non-aqueous electrolyte secondary battery according to claim 1.