JPH09330720A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the reaction of a positive electrode material with a nonaqueous electrolyte over a long period, and provide a lithium battery excellent in cycle characteristic in which the lowering of the service capacity is minimized even when charging and discharging are repeated by covering the particle surface of a lithium transition metal compound oxide used in a positive electrode with a compound containing lithium and boron. SOLUTION: This lithium battery has a positive electrode 1 using a lithium transition metal compound oxide, a negative electrode 2 using a lithium material or a material capable of storing and releasing lithium ion, and a nonaqueous electrolyte. At least a part of the particle surface of the lithium transition metal compound oxide used in the positive electrode 1 is covered with a compound containing lithium and boron. Thus, it is suppressed that the nonaquous electrolyte is reacted with the lithium transition metal compound oxide of the positive electrode and decomposed, and the drop of the service capacity is moderated to improve the cycle characteristic.

Description

Detailed Description of the Invention

[0002]

TECHNICAL FIELD The present invention comprises a positive electrode using a lithium transition metal composite oxide, a negative electrode using a lithium material or a material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte. The present invention relates to a lithium battery, and relates to a lithium battery in which a positive electrode using a lithium transition metal composite oxide is improved.

[0003]

2. Description of the Related Art In recent years, as a new type of high-output, high-energy-density secondary battery, there has been a lithium battery that uses a non-aqueous electrolyte as an electrolyte and is discharged and charged by utilizing oxidation and reduction of lithium. It came to be used.

In such a lithium battery, a lithium material or a material capable of inserting and extracting lithium is used for the negative electrode, and a lithium transition metal composite oxide containing lithium and a transition metal is used for the positive electrode. What you have done is known.

However, in the case of the conventional lithium battery using the lithium-transition metal composite oxide in the positive electrode as described above, the non-aqueous electrolyte is mixed with the lithium-transition metal composite oxide used in the positive electrode during the cycle of charging and discharging. React and decompose,
When charging and discharging are repeated, there is a problem that the discharge capacity gradually decreases and the cycle characteristics are poor.

Therefore, the surface of the lithium-transition metal composite oxide used for the positive electrode has been conventionally made to be titanium sulfide T.
Partially covered with iS ₂ or molybdenum sulfide MoS ₂
It has been developed to suppress the reaction between the lithium-transition metal composite oxide and the non-aqueous electrolyte.

However, when the surface of the lithium-transition metal composite oxide is coated with TiS ₂ or MoS _{2 as} described above, the reaction between the lithium-transition metal composite oxide and the non-aqueous electrolyte is suppressed to some extent, but the charge and discharge are increased. However, there is a problem that the discharge capacity is lowered due to the decomposition of the non-aqueous electrolyte and the like.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a positive electrode using a lithium-transition metal composite oxide, a negative electrode using a material capable of inserting and extracting lithium or lithium ions,
The object is to solve the above problems in a lithium battery with a non-aqueous electrolyte, the non-aqueous electrolyte is decomposed by reacting with the lithium transition metal composite oxide used for the positive electrode Is sufficiently suppressed, the discharge capacity does not gradually decrease when repeatedly charged and discharged, and it is an object to obtain a lithium battery having excellent cycle characteristics that can be stably used for a long period of time. It is what

[0009]

In the lithium battery of the present invention, in order to solve the above problems, a positive electrode using a lithium transition metal composite oxide and a lithium material or lithium ion storage and release are provided. In a lithium battery provided with a negative electrode using a possible material and a non-aqueous electrolyte, at least a part of the particle surface of the lithium transition metal composite oxide used for the positive electrode is coated with a compound containing lithium and boron. I did it.

Then, as in the lithium battery of the present invention, when at least a part of the surface of the particles of the lithium-transition metal composite oxide used for the positive electrode is coated with a compound containing lithium and boron, the positive electrode material and the non-aqueous material are mixed. The reaction with the electrolytic solution is suppressed for a long time, and even when charging and discharging are repeated, the non-aqueous electrolytic solution decomposes due to the reaction with the positive electrode material and the discharge capacity gradually decreases as in the conventional case. As a result, a lithium battery having excellent cycle characteristics can be obtained.

Here, in the lithium battery according to the present invention, the compound containing lithium and boron for coating the particle surface of the lithium-transition metal composite oxide used for the positive electrode is a composite nitride containing lithium and boron, or lithium. Various compounds such as a complex oxide containing boron and boron can be used, but it is particularly preferable to use a complex oxide containing lithium and boron, and more preferably LiBO.
It is preferable to use ₂ or Li ₂ B ₄ O ₇ . this is,
Compared with a composite nitride containing lithium and boron, a composite oxide containing lithium and boron is superior in lithium ion permeability, deterioration of the positive electrode material due to charge and discharge is suppressed, and more cycle characteristics are obtained. It is expected to improve.

Further, in coating the surface of the above-mentioned lithium-transition metal composite oxide with the compound containing lithium and boron, when the amount of the compound containing lithium and boron is small, the positive electrode material and the non-aqueous material are mixed. While it becomes impossible to sufficiently suppress decomposition of the non-aqueous electrolytic solution due to contact with the electrolytic solution, when the amount of the compound containing lithium and boron becomes too large, the compound itself containing lithium and boron is Since the ability to store and release lithium is low, and the ability to store and release lithium in the positive electrode as a whole is deteriorated to deteriorate cycle characteristics, the amount of the compound containing lithium and boron described above is preferably used for the positive electrode. It is set to a range of 0.1 to 20 mol% with respect to the lithium-transition metal composite oxide.

In the lithium battery of the present invention, the lithium transition metal composite oxide used as the positive electrode material may be one that has been conventionally used as a material capable of inserting and extracting lithium ions. For example, a lithium transition metal composite oxide represented by the following structural formulas (1) and (2) can be used. In particular, when a lithium transition metal composite oxide containing at least lithium, nickel, and cobalt represented by the following structural formula (1) is used, the lithium transition metal composite oxide has excellent ability to store and release lithium ions. Therefore, a lithium battery having more excellent cycle characteristics can be obtained, which is preferable.

Lix Niy Coz M1-yz Oa (1) [In this structural formula (1), M is B, Na, Mg,
Al, Si, K, Ca, Sc, Ti, V, Cr, Mn,
Fe, Cu, Zn, Ga, Ge, Zr, Nb, Ru, A
At least one element selected from g, Ta, Bi, In, Mo and W, and x, y, z and a are 0 <x.
<1.3, 0.5 ≦ y + z ≦ 1, 1.8 ≦ a ≦ 2.2, and x changes depending on charge and discharge. ]

Lix Fey Tiz M1-yz Oa (2) [In this structural formula (2), M is B, Na, Mg,
Al, Si, K, Ca, Sc, V, Cr, Mn, Cu,
Zn, Ga, Ge, Zr, Nb, Ru, Ag, Ta, B
At least one element selected from i, In, Mo, W, Co, and Ni, and x, y, z, and a are 0 <x.
<1.3, 0.5 ≦ y + z ≦ 1, 1.8 ≦ a ≦ 2.2, and x changes depending on charge and discharge. ]

In the lithium battery of the present invention, the negative electrode material used for the negative electrode includes metallic lithium, Li-Al, Li-In, Li-Sn, Li-P.
b, Li-Bi, Li-Ga, Li-Sr, Li-S
i, Li-Zn, Li-Cd, Li-Ca, Li-Ba
In addition to such lithium alloys as described above, a carbon material such as graphite, coke, or an organic material calcined material capable of inserting and extracting lithium ions can be used.

Further, as the non-aqueous electrolytic solution used in the lithium battery of the present invention, a non-aqueous electrolytic solution which has been generally used conventionally can be used.

The solvent in the non-aqueous electrolyte is, for example, an organic material such as propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate, dimethyl sulfoxide, acetonitrile, butylene carbonate, 1,2-dimethoxyethane or diethyl carbonate. The solvent may be used alone or in combination of two or more.

Further, as the solute to be dissolved in the above solvent in this non-aqueous electrolyte, for example, lithium trifluoromethanesulfonate LiCF ₃ SO ₃ , lithium hexafluorophosphate LiPF ₆ , lithium perchlorate Li
ClO ₄ , lithium tetrafluoroborate LiBF ₄ ,
Trifluoromethanesulfonic acid imide lithium LiN
Lithium compounds such as (CF ₃ SO ₂ ) ₂ can be used.

[0020]

EXAMPLES Hereinafter, the lithium battery according to the present invention will be specifically described with reference to examples, and a comparative example showing that the lithium battery according to the examples of the present invention is excellent in terms of cycle characteristics and the like. List and clarify. The lithium battery according to the present invention is not limited to the examples shown below, and can be implemented with appropriate modifications without departing from the scope of the invention.

Example 1 In the lithium battery of this example, the positive electrode and the negative electrode prepared as follows were used, and the non-aqueous electrolyte solution prepared as described below was used. As shown, a flat type lithium secondary battery having a diameter of 24.0 mm and a thickness of 3.0 mm was obtained.

[Preparation of Positive Electrode] In preparing a positive electrode, Li ₂ CO ₃ and Fe ₂ O ₃ were mixed in a mortar at a molar ratio of 1: 1 and the mixture was dried in an atmosphere of dry air. At 850 ° C. for 20 hours and then crushed in an Ishikawa Raikai mortar,
A powder of LiFeO ₂ used for the positive electrode material was obtained.

Then, a composite nitride Li ₃ BN ₂ containing lithium and boron was added to the positive electrode material LiFeO ₂ powder,
Positive electrode material LiFeO ₂ powder and lithium boron composite nitride L
After mixing with i ₃ BN ₂ in a molar ratio of 10: 1, this mixture was heat-treated at 650 ° C. for 10 hours, and the surface of the above-mentioned positive electrode material LiFeO ₂ powder was treated with this lithium-boron composite nitride Li. Coated with ₃ BN ₂ .

Then, in this way, the positive electrode material LiFeO ₂
A material in which the surface of the powder was coated with Li ₃ BN ₂ , acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 90: 6: 4 to form a positive electrode mixture. After adjustment, this positive electrode mixture was pressed at a pressure of 2 ton / cm ² to be molded into a disk shape having a diameter of 20 mm, and this was heat-treated at 250 ° C. for 2 hours to prepare a positive electrode.

[Preparation of Negative Electrode] In preparing the negative electrode, a rolled plate of metallic lithium having a predetermined thickness was punched into a disk shape having a diameter of 20 mm to prepare the negative electrode.

[Preparation of Non-Aqueous Electrolyte] In preparing the non-aqueous electrolyte, a mixed solvent prepared by mixing propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 1 was used. Lithium perchlorate LiClO ₄ was dissolved as a solute at a ratio of 1 mol / l to prepare a non-aqueous electrolyte solution.

[Production of Battery] To produce a battery, as shown in FIG. 1, the above-mentioned nonaqueous electrolytic solution was impregnated between the disk-shaped positive electrode 1 and negative electrode 2 produced as described above. The separator 3 is sandwiched, and these are housed in the battery can 4 formed by the positive electrode can 4a and the negative electrode can 4b.
The positive electrode 1 is connected to the positive electrode can 4a via the positive electrode current collector 5, while the negative electrode 2 is connected to the negative electrode can 4b via the negative electrode current collector 6, and the positive electrode can 4a and the negative electrode can 4b are made of polypropylene. A lithium secondary battery was produced by being electrically insulated by the insulating packing 7. Then, the chemical energy generated inside the lithium secondary battery was taken out as electric energy from both terminals of the positive electrode can 4a and the negative electrode can 4b.

Comparative Example 1 In this comparative example, when a positive electrode was prepared, LiFeO ₂ powder prepared in the same manner as in Example 1 was used as the positive electrode material, while the surface of the positive electrode material LiFeO ₂ powder was prepared as described above. A lithium secondary battery was prepared in the same manner as in Example 1 except that the lithium-boron composite nitride Li ₃ BN ₂ was not coated.

Example 2 In this example, when a positive electrode was prepared, Li ₂ Co ₃ and TiO ₂ were mixed in a mortar in a molar ratio of 1: 2, and The mixture was heat-treated in a dry air atmosphere at 850 ° C. for 20 hours and then crushed in an Ishikawa-type Raikai mortar to prepare LiTi used as a positive electrode material.
To obtain a powder of O _2.

Then, this positive electrode material LiTiO ₂ powder and the lithium-boron composite nitride L used in Example 1 above were used.
After mixing with i ₃ BN ₂ in a molar ratio of 10: 1, this mixture was heat-treated at 650 ° C. for 10 hours to obtain a positive electrode material L.
The surface of the iTiO ₂ powder was coated with lithium boron composite nitride Li ₃
Coated with BN ₂ , otherwise, above Example 1
A lithium secondary battery was produced in the same manner as in.

(Comparative Example 2) In this comparative example, the LiTiO ₂ powder obtained in Example 2 was used as the positive electrode material for producing the positive electrode, while the surface of the positive electrode material LiTiO ₂ powder was coated with the above-mentioned lithium boron. A lithium secondary battery was prepared in the same manner as in Example 1 except that the composite nitride Li ₃ BN ₂ was not coated.

Example 3 In this example, LiOH, Ni (OH) ₂ and Co were used to prepare a positive electrode.
(OH) ₂ was mixed in a mortar in a molar ratio of 2: 1: 1, and this mixture was heat-treated at 750 ° C. for 20 hours in a dry air atmosphere, and then this was mixed with Ishikawa formula. The powder was crushed in a mortar to obtain LiNi _0.5 Co _0.5 O ₂ powder used as a positive electrode material.

Then, this positive electrode material LiNi _0.5 Co
_0.5 O ₂ powder and the lithium-boron composite nitride Li ₃ BN ₂ used in Example 1 above were mixed at a molar ratio of 10: 1, and this mixture was heat treated at 650 ° C. for 10 hours, The surface of the positive electrode material LiNi _0.5 Co _0.5 O ₂ powder was covered with the lithium boron composite nitride Li ₃ BN, and a lithium secondary battery was produced in the same manner as in Example 1 except for the above.

Comparative Example 3 In this Comparative Example, the LiNi _0.5 Co _0.5 O ₂ powder obtained in Example 3 above was used as the positive electrode material in the production of the positive electrode.
A surface of this positive electrode material LiNi _0.5 Co _0.5 O ₂ powder was not covered with the above lithium boron composite nitride Li ₃ BN ₂ , and otherwise a lithium secondary battery was produced in the same manner as in Example 1 above. .

Next, the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 1
Each lithium secondary battery 3, after being charged with the respective charge current density 1 mA / cm ² up to 4.3 V, at a discharge current density of 3mA / cm ² was discharged to 2.5V, this process as one cycle, this A cycle test was performed in which such charging / discharging was repeated for 250 cycles. Then, the discharge capacity of each lithium secondary battery in the first cycle is measured, and the discharge capacity of each lithium secondary battery in the 250th cycle is measured to determine the capacity of the discharge capacity of the 250th cycle with respect to the discharge capacity of the first cycle. The deterioration rate (%) was determined and the results are shown in Table 1 below.

[0036]

[Table 1]

As is clear from these results, Examples 1 to _{3 in} which the lithium-boron composite nitride Li ₃ BN ₂ was adhered to the surface of each positive electrode material composed of the lithium-transition metal composite oxide
In each of the lithium secondary batteries of No. ₃ , the capacity deterioration rate is lower than that of each of the lithium secondary batteries of Comparative Examples 1 to _{3 in} which the lithium boron composite nitride Li ₃ BN ₂ is not attached to the surface of each positive electrode material. The cycle characteristics are improved, and particularly when LiNi _0.5 Co _0.5 O ₂ which is a composite oxide containing lithium, nickel and cobalt is used as the positive electrode material, the capacity deterioration rate is further reduced and the cycle characteristics are It was further improved.

Examples 4 to 8 In these examples, as shown in Table 2 below, the LiNi _0.5 Co _0.5 O ₂ powder used in Example 3 above was used as the positive electrode material. Each type of lithium secondary battery was manufactured in the same manner as in Example 1 except that the type of the compound containing lithium and boron that covers the surface of the positive electrode material was changed.

Here, the above-mentioned positive electrode material LiNi _0.5 Co
_As a coating material for coating the surface of _0.5 O ₂ powder, as shown in Table 2 below, in Example 4, LiB ₃ O _{5 was used.}
In Example 5, Li ₂ B ₈ O ₁₃ , Li ₄ B ₂ O ₅ in Example 6, and LiB in Example 7.
O ₂ and Li ₂ B ₄ O ₇ in Example 8 were used, and the above-mentioned positive electrode material LiNi _0.5 Co _0.5 O ₂ powder and these lithium boron composite oxides were adjusted to a molar ratio of 10: 1. After mixing to 650
After heat treatment at ℃ for 10 hours, the above positive electrode material LiNi _0.5 C
The surface of the o _0.5 O ₂ powder was coated with each of the above lithium boron composite nitrides.

Then, the lithium secondary batteries of Examples 4 to 8 produced as described above were also subjected to a charge / discharge cycle test in the same manner as in the above case, and the discharge capacity of the first cycle was set to 250. The capacity deterioration rate (%) of the discharge capacity at the cycle was calculated, and the result was used in Example 3 above.
It is shown in Table 2 below together with the case of the lithium secondary battery.

[0041]

[Table 2]

As is clear from these results, the compound containing lithium and boron coating the surface of the positive electrode material was added to the lithium-boron composite nitride Li ₃ BN as in Example 3 above.
Compared with the case of using ₂ , the capacity deterioration rate is further reduced by using the lithium-boron composite oxides as shown in Examples 4 to 8, and particularly, by using LiBO ₂ or Li ₂ B ₄ O ₇ . If it is, the capacity deterioration rate is very low,
The cycle characteristics are greatly improved.

(Examples 9 to 13) Also in these Examples, as shown in Table 2 below, LiNi _0.5 Co _0.5 O ₂ used in Example 3 as a positive electrode material was used.
While using powder, as a coating material for coating the surface of this positive electrode material, LiBO ₂ used in the above-mentioned Example 7 was used.
Was used.

In these Examples, the molar ratio of the coating material LiBO ₂ added to the above LiNi _0.5 Co _0.5 O ₂ powder was 0.05 mol in Example 9 as shown in Table 3 below. %, In Example 10 0.1 m
ol%, 2 mol% in Example 11, 2 in Example 12
0 mol%, 22 mol% in Example 13 were mixed, and this mixture was heat-treated at 650 ° C. for 10 hours in the same manner as in Example 7 above, otherwise, in Example 1 above. Each lithium secondary battery was produced in the same manner as.

Then, the lithium secondary batteries of Examples 9 to 13 produced as described above were also subjected to a charge / discharge cycle test in the same manner as described above, and the discharge capacity of the first cycle was set to 250. The capacity deterioration rate (%) of the discharge capacity at the cycle was obtained, and the results are shown in Table 3 below together with the case of the lithium secondary battery of Example 7 described above.

[0046]

[Table 3]

As is clear from this result, the surface of the LiNi _0.5 Co _0.5 O ₂ powder, which is the positive electrode material, was coated with LiBO ₂
The coating amount is 0.1 to 20 mol.
Within the range of%, the capacity deterioration rate was extremely low, and a lithium secondary battery with excellent cycle characteristics was obtained.

[0048]

As described above in detail, in the lithium battery of the present invention, at least a part of the surface of the particles of the lithium transition metal composite oxide used for the positive electrode is coated with the compound containing lithium and boron. The reaction between the positive electrode material and the non-aqueous electrolytic solution will be suppressed for a long period of time, and even when the charging and discharging are repeated, the discharge capacity is unlikely to be gradually reduced unlike the conventional lithium battery, It has become possible to obtain a lithium battery having excellent cycle characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view showing an internal structure of a lithium battery in each of Examples and Comparative Examples.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode

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[Procedure amendment]

[Submission date] August 27, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction contents]

Example 2 In this example, when a positive electrode was prepared, Li ₂ CO ₃ and TiO ₂ were mixed in a mortar at a molar ratio of 1: 2, and then the positive electrode was prepared. The mixture was heat-treated in a dry air atmosphere at 850 ° C. for 20 hours and then crushed in an Ishikawa-type Raikai mortar to prepare LiTi used as a positive electrode material.
To obtain a powder of O _2.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Mikiya Yamazaki 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Toshiyuki Noma 2-chome Keihanhondori, Moriguchi-shi, Osaka No.5-5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A lithium battery comprising a positive electrode using a lithium-transition metal composite oxide, a negative electrode using a lithium material or a material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution. A lithium battery, wherein at least a part of the surface of particles of the lithium-transition metal composite oxide used is coated with a compound containing lithium and boron. 2. The lithium battery according to claim 1, wherein at least a part of the surface of the particles of the lithium transition metal composite oxide used for the positive electrode is coated with the composite oxide containing lithium and boron. Lithium battery. [0001]