JP2002015776A - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary cell with high energy density having higher safety. SOLUTION: The nonaqueous electrolyte secondary cell comprises a positive electrode 4 including lithium containing compound, a negative electrode 5, and a nonaqueous electrolyte, and the surface of active material particle contained in the positive electrode 4 contains lanthanoid and covered by lithium containing conductive compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonaqueous electrolyte secondary battery provided with a positive electrode containing a lithium-containing compound as an active material.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries have attracted attention. This is probably because the successful development of a relatively safe negative electrode material and the realization of a high-voltage battery by increasing the decomposition voltage of the non-aqueous electrolyte were considered. Among them, a secondary battery using lithium ions has a particularly high discharge potential, and thus is expected to realize a battery having a high energy density. The positive electrode of a non-aqueous electrolyte secondary battery using lithium ions has a transition element oxide called an active material, a binder, and a conductive agent having high conductivity due to insufficient conductivity of the active material in general. Is given. In addition to high conductivity, the conductive agent is required to have oxidation resistance that is not oxidized by contact with the active material, and further has a structure, such as a fibrous shape, for facilitating electrical contact between the active materials. Is required.

[0003] Under the above conditions, it is necessary to further reduce the weight.
Considering cost, etc., carbon-based acetylene
Conductive agents such as racks have been used. Actually LiC
oO ₂This battery is used in batteries that use
Satisfactory characteristics have been obtained using an electric agent.

[0004]

In recent years, due to the high material cost of Co, there has been a demand for batteries using less expensive materials, batteries with higher energy density and batteries with higher output density. Some of these new active materials have high energy density, but have poor thermal stability after charging compared to Co-based active materials, or have poor electron conductivity, so that the generation of Joule heat cannot be ignored. Has been found to have For this reason, other methods are required in addition to attempts to improve the active material itself.

Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having higher safety in a battery having a high energy density.

[0006]

In order to achieve the above object, a non-aqueous electrolyte secondary battery of the present invention comprises a non-aqueous electrolyte comprising a positive electrode containing a lithium-containing compound, a negative electrode, and a non-aqueous electrolyte. A liquid secondary battery, wherein the surface of the active material particles contained in the positive electrode is coated with a conductive compound containing Li represented by the following formula.

Li _1-x A _y BO _3-z F _z (0 ≦ x <1, 0 ≦ y <1, 0 <z ≦ 3) (where A is a monovalent or divalent typical element, a lanthanoid element) Or at least one selected from the group consisting of combinations thereof, wherein B is of the genus IVa, Va, or VI
a, VIIa, 8 and Ib).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery (for example, a cylindrical non-aqueous electrolyte secondary battery) according to the present invention will be described below with reference to FIG. For example, a cylindrical container 1 with a bottom made of stainless steel has an insulator 2 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes:
It has a structure in which a belt-like material in which the positive electrode 4, the separator 5, and the negative electrode 6 are laminated in this order is spirally wound so that the negative electrode 6 is located outside. The separator 5 is formed of, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, or a polypropylene porous film.

An electrolyte is contained in the container 1. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8
The sealing plate 8 is disposed at the upper opening of the container 1 and caulked in the vicinity of the upper opening inward.
Is fixed to the container 1 in a liquid-tight manner. The positive terminal 9 is
It is fitted to the center of the insulating sealing plate 8. One end of the positive electrode lead 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9. The negative electrode 6 is connected to the container 1 as a negative electrode terminal via a negative electrode lead (not shown). Next, the configurations of the positive electrode 4, the negative electrode 6, and the non-aqueous electrolyte will be specifically described. 1) Configuration of Positive Electrode 4 The positive electrode 4 uses the above-described lithium-containing conductive compound having a specific resistance of 1 × 10 ⁻³ (Ωm) or less as a conductive agent for coating the active material surface.

The positive electrode 4 is made of, for example, a lithium-containing cobalt oxide (LiCoO ₂ ), a lithium-containing nickel oxide (LiNiO ₂ ), a lithium-containing manganese oxide (LiMn ₂ O ₄ ) or a crystal of the active material. A material in which another element is added or partially substituted can be used.

[0011] Further, as a conductive agent coated on these surfaces or as an active material itself, lanthanum lithium nickel composite fluorine oxide ((La, Li) Ni (O, F) ₃ ) or lanthanum lithium copper fluoride ((La) , Li) Cu
(O, F) ₃ ), lanthanum lithium vanadium fluoride ((La, Li) V (O, F) ₃ ), lanthanum lithium manganese fluoride ((La, Li) Mn (O,
F) ₃ ), lanthanum lithium iron fluoride ((La,
Li) Fe (O, F) ₃ ), lanthanum lithium titanium fluoride ((La, Li) Ti (O, F) ₃ ), lanthanum lithium chromium fluoride ((La, Li) Cr
(O, F) ₃ ), lanthanum lithium ruthenium fluoride ((La, Li) Ru (O, F) ₃ ), lanthanum lithium iridium fluoride ((La, Li) Ir
A lithium-containing conductive compound such as (O, F) ₃ ) can be used.

Preferably, the thickness of the film is 0.3 nm or more. This is due to the following reasons.
When the thickness of the film is less than 0.3 nm, it is difficult to form a low-resistance film due to mutual diffusion of the active material and the material of the film. A more preferable film thickness is a range of 10 nm or more as a range that can be manufactured more stably and has high mass productivity.
Further, since these lithium-containing conductive compounds have both lithium ion conductivity and electron conductivity, they can be used as active materials themselves.

The active material, a carbon-based conductive agent such as acetylene black and a binder are suspended in a suitable solvent,
The positive electrode 4 is produced by applying the suspension to a current collector and drying the suspension to form a thin plate.

As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) and the like are used. it can.

As the current collector, it is preferable to use, for example, an aluminum foil, a stainless steel foil, a titanium foil or the like. 2) Configuration of Negative Electrode 6 As the negative electrode 6, for example, a material containing a substance that absorbs and desorbs lithium ions (for example, a carbonaceous material or a chalcogen compound), a material containing a light metal, or the like can be used.
Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound which stores and desorbs lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.

Examples of the carbonaceous material for storing and desorbing lithium ions include coke, carbon fiber, pyrolytic vapor-grown carbon material, graphite, fired resin, fired mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. Can be mentioned. Above all, mesophase pitch-based carbon fibers or mesophase spherical carbon graphitized at 2500 ° C. or higher are preferable because the electrode capacity is increased.

[0017] The carbonaceous material is particularly 700 ppm by differential thermal analysis.
It has an exothermic peak at a temperature of 800 ° C. or more, more preferably an exothermic peak at a temperature of 800 ° C. or more.
Diffraction peak (P101) and (100) diffraction peak (P1
00) is preferably in the range of 0.7 to 2.2. Since the negative electrode containing such a carbonaceous material can rapidly store and remove lithium ions,
The rapid charge / discharge performance of the secondary battery is improved.

The chalcogen compounds that occlude and desorb lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe).
₂ ) and the like. When used for such a chalcogen compound negative electrode, although the voltage of the secondary battery decreases, the capacity of the negative electrode increases, so that the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like. A negative electrode containing a substance that occludes and desorbs lithium ions is produced by, for example, suspending the substance and a binder in an appropriate solvent, applying the suspension to a current collector, drying, and pressing. You.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used. As the current collector, for example, a copper foil, a stainless steel foil, a nickel foil, or the like is preferably used. 3) Configuration of Non-Aqueous Electrolyte As the non-aqueous electrolyte, a solution in which an electrolyte (lithium salt) is dissolved in a non-aqueous solvent is used.

Examples of the non-aqueous solvent include ethylene carbonate (EC) and propylene carbonate (PC).
And cyclic carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and linear chains such as dimethoxyethane (DME), diethoxyethane (DEE), and ethoxymethoxyethane. Ethers, cyclic ethers and crown ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), fatty acid esters such as γ-butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfolane (SL) And dimethyl sulfoxide (DMSO).
The non-aqueous solvents may be used alone or in combination of two or more. Above all, one consisting of at least one selected from EC, PC, γ-BL, EC, PC, γ-BL
-At least one selected from BL and DMC, EMC,
DEC, DME, DEE, THF, 2-MeTHF, A
It is desirable to use a mixed solvent composed of at least one selected from N. Further, when using a negative electrode containing a carbonaceous material that occludes and desorbs lithium ions, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC and γ-BL, and EC and PC EMC, E
C and PC and DEC, EC and PC and DEE, EC and AN,
EC and EMC, PC and DMC, PC and DEC, EC and D
It is desirable to use a mixed solvent composed of EC.

The electrolyte may be, for example, lithium perchlorate.
(LiClO₄), Lithium hexafluorophosphate (Li
PF₆), Lithium borofluoride (LiBF₄), Six foot
Lithium arsenide arsenide (LiAsF6), trifluorometas
Lithium sulfonate (LiCF ₃SO₃), Bistriflu
Oromethylsulfonylimide lithium (LiN (CF ₃
SO₂)₂) And the like.
Among them, LiPF₆, LiBF₄, LiN (CF₃S
O₂)₂Is used to improve conductivity and safety
preferable. The amount of the electrolyte dissolved in the non-aqueous solvent is
It is preferred to be in the range of 0.1 mol / l to 3.0 mol / l.
Good.

[0023] Making lithium-containing conductive as described above
The positive electrode with the compound coated on the surface of the positive electrode active material is assembled into a secondary battery.
To increase the capacity of secondary batteries
However, high security can be achieved. In fact, Table 1
As shown in the figure, the secondary battery according to the present invention has a nail
In the test, the heat generation of the electrode is suppressed.
The electrodes of conventional secondary batteries that do not use
Heat or combustion reactions occur. Also contains lithium
Cycle characteristics compared to using non-conductive oxide
Is good. Embodiments of the present invention will be described below in detail with reference to the drawings.
Will be described. The present invention is not limited to the following examples.
Not to change the gist.
It can be changed and implemented. (Example 1) <Preparation of positive electrode> LiCoO as positive electrode active material₂Powder
Carefully grind and measure appropriately with a particle size distribution analyzer,
Continue grinding until no longer present. Then to this active material
Lanthanum nitrate and lithium nitrate in a molar ratio of about 1%
Dissolve ammonium fluoride and copper nitrate in water
Make a liquid. Add this active material powder to this aqueous solution and stir
While heating, remove the solvent. This is further added in oxygen
Heat to 400 ° C to remove nitric acid and ammonia components
Lanthanum lithium copper fluoride ((L
a _0.8, Li_0.2) Cu (O_2.6, F_0.4))
Is formed. The active material powder and the conductive agent
Tylene black powder and graphite powder, binder
And PVDF powder as the
Disperse in a 2pyrrolidone solvent to form a positive electrode mixture slurry.
Was. This slurry was applied on aluminum foil and dried
Thereafter, rolling and cutting were performed to produce a positive electrode. <Preparation of negative electrode> Negative electrode active material and graphite as conductive agent
Powder and styrene-butadiene rubber as binder in an appropriate ratio
Mix, add water and carefully disperse to form negative electrode mixture slurry.
After coating and drying on copper foil, rolling and cutting
Produced. <Preparation of non-aqueous electrolyte> Propylene carbonate and
LiP as electrolyte in mixed solvent consisting of toxicethane
F₆Is dissolved to a concentration of 1 mol / l
A non-aqueous electrolyte was prepared. <Preparation of battery for evaluation>
After the generator has dried sufficiently, the positive electrode
And the negative electrode facing each other, wound and inserted between stainless steel
And inject electrolyte in an argon atmosphere and seal
An evaluation battery was manufactured. (Example 2) The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG. Coating on active material surface
Lanthanum lithium vanadium fluoride
Oxide ((La_0.4, Li_0.6) V (O_2.8, F
_0.2)) Powder was used. (Example 3) The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG.

As a conductive agent for coating the surface of the active material,
Tantalum manganese fluoride ((La_0.5, L
i_0.5) Mn (O_2.6, F_0.4)) Using powder
Was. Example 4 The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG. Coating on active material surface
Lanthanum lithium chromium fluoridation as conductive agent
Things ((La_0.4, Li_0.6) Cr (O_2.8, F
_0.2)) Powder was used. Example 5 Example 5 was repeated except that the following active materials were used.
1. The positive electrode evaluation battery shown in FIG.
Assembled. LiMn as positive electrode active material₂O₄Powder
Was used. (Example 6) Example 6 was repeated except that the following active materials were used.
1. The positive electrode evaluation battery shown in FIG.
Assembled. LiNi as the positive electrode active material_0.4Mn
_1.6O₄Powder was used. Example 7 The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG. Coating on active material surface
Neodymium lithium copper fluoride as conductive agent
((Nd _0.8, Li_0.2) Cu (O_2.6, F
_0.4)) Powder was used. Example 8 The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG. Coating on active material surface
Neodymium lithium vanadium fluoride
Oxide ((Nd_0.4, Li_0.6) V (O_2.8, F
_0.2)) Powder was used. Example 9 The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG. Coating on active material surface
Neodymium lithium manganese fluoride as conductive agent
((Nd_0.5, Li_0.5) Mn (O_2.6, F
_0.4)) Powder was used. (Example 10) The following conductive agent was coated on the surface of a positive electrode active material.
The above-mentioned figure has the same configuration as in Example 1 except that it is used for clothes.
1 was assembled. Active material surface
Neodymium lithium chromium fluoride as conductive agent to cover
((Nd_0.4, Li_0.6) Cr (O_2.8, F
_0.2)) Powder was used. (Example 11) Except that the following active materials were used,
The positive electrode evaluation battery shown in FIG. 1 described above with the same configuration as in Example 7.
Was assembled. LiMn as a positive electrode active material₂O₄Powder
Was used. Example 12 Example 12 was repeated except that the following active materials were used.
The positive electrode evaluation battery shown in FIG. 1 described above with the same configuration as in Example 7.
Was assembled. LiNi as the positive electrode active material_0.4Mn
_1.6O₄Powder was used. (Example 13) A conductive agent shown below was coated on the surface of a positive electrode active material.
The above-mentioned figure has the same configuration as in Example 1 except that it is used for clothes.
1 was assembled. Active material surface
Strontium lithium copper fluoride
Oxide ((Sr_0.8, Li_0.2) Cu (O_1.8,
F_1.2)) Powder was used. (Example 14) A conductive agent shown below was coated on the surface of a positive electrode active material.
The above-mentioned figure has the same configuration as in Example 1 except that it is used for clothes.
1 was assembled. Active material surface
Strontium lithium vanadium as conductive agent to cover
Fluoride oxide ((Sr_0.8, Li_0.2) V (O
_1.8, F_0.2)) Powder was used. (Example 15) A conductive agent shown below was coated on the surface of a positive electrode active material.
The above-mentioned figure has the same configuration as in Example 1 except that it is used for clothes.
1 was assembled. Active material surface
Strontium lithium manganese as conductive agent to cover
Fluoride oxide ((Sr_0.8, Li_0.2) Mn (O
_2.0, F_1.0)) Powder was used. (Example 16) A conductive agent shown below was coated on the surface of a positive electrode active material.
The above-mentioned figure has the same configuration as in Example 1 except that it is used for clothes.
1 was assembled. Active material surface
Strontium lithium chromium
Oxide ((Sr_0.8, Li_0.2) Cr (O
_2.8, F_0.2)) Powder was used. (Example 17) Except that the following active materials were used,
The positive electrode evaluation electrode shown in FIG.
Assembled the pond. LiMn as positive electrode active material₂O₄
Powder was used. Example 18 Example 18 was repeated except that the following active materials were used.
The positive electrode evaluation electrode shown in FIG.
Assembled the pond. LiNi as the positive electrode active material_0.4
Mn_1.6O₄Powder was used. (Comparative Example 1) The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG. Coating on active material surface
Iron oxide (Fe)₃O₄Use powder
Was. (Comparative Example 2) The reason why the surface coating of the positive electrode active material was not performed
Outside, the positive electrode shown in FIG.
An evaluation battery was assembled. (Comparative Example 3) Agglomerates of about 100μ were used as the positive electrode active material.
The same configuration as in the first embodiment except that the
The assembled positive electrode evaluation battery shown in FIG. 1 was assembled. (Comparative Example 4) The following conductive agent was coated on the surface of a positive electrode active material.
1 except that it was used in FIG.
The positive electrode evaluation battery shown in FIG.

Lanthanum nickelate (LaNiO ₃ ) powder was used as a conductive agent for coating the surface of the active material. (Comparative Example 5) The positive electrode evaluation battery shown in FIG. 1 described above was assembled with the same configuration as in Example 1 except that the following conductive agent was used to cover the surface of the positive electrode active material.

As a conductive agent for coating the active material surface, lanthanum strontium manganate ((La, Sr) MnO)
₃ ) Powder was used. (Comparative Example 6) The same configuration as in Example 1 except that the following conductive agent was used for coating the surface of the positive electrode active material was used.
The positive electrode evaluation battery shown in FIG.

Strontium chromate (SrCrO ₃ ) powder was used as a conductive agent for coating the active material surface.

After charging the batteries obtained in Example 1 and Comparative Example 6 to reach 4.4 V at a current value of 0.5 C, current was continuously supplied so as to maintain the voltage, and the total charging time became 5 hours. Then stop the current. In Examples 6, 12, and 18, after charging reached 4.6 V at a current value of 0.5 C, the current was continued to maintain the voltage, and the current was stopped when the total charging time reached 5 hours. Thereafter, the thermal stability of the battery is measured as follows. A thermocouple was immediately attached to the battery that had been subjected to the above-described charging treatment, a nail was inserted from the side of the battery, and a temporal change in the temperature of the battery was measured. At the same time, the charge / discharge cycle characteristics were measured using another battery manufactured under the same conditions. The results are shown in Tables 1 and 2 below.

As is clear from Tables 1 and 2, Examples 1 to
It can be seen that the electrodes 18 and Comparative Examples 4 to 6 have low exothermic peak temperatures.

However, the electrodes of Comparative Examples 1 to 3 had insufficient conductivity of the conductive agent, and the electrodes of Comparative Examples 4 to 6 had insufficient conductivity of lithium ions. Is inferior. Further, the electrode of Comparative Example 2 was not preferable because ignition was avoided, but the temperature reached was high and gas was ejected. It is considered that the battery of Comparative Example 3 ignited because the peak heat generation temperature was too high.

As a result of the comprehensive judgment, it was judged that all of the examples were superior to the comparative example.

[Table 1]

[Table 2]

[0032]

As described in detail above, according to the nonaqueous electrolyte secondary battery of the present invention, by using a conductive oxide for the surface coating of the active material, the thermal stability of the battery in a charged state can be more assured. Thus, a highly safe secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a non-aqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 1-container, 3-electrode group, 4-positive electrode, 5-negative electrode, 6-separator, 8--sealing plate

Continuing from the front page (72) Inventor Shuji Yamada 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Research and Development Center Co., Ltd. F-term in Toshiba R & D Center (reference) 5H029 AJ12 AK03 AL04 AL06 AL07 AM02 AM03 AM04 AM05 AM07 BJ02 BJ14 DJ08 DJ16 EJ04 EJ05 HJ02 5H050 AA15 BA17 CA08 CB05 CB07 CB08 DA02 DA10 EA08 EA12 FA17 HA02

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a lithium-containing compound, a negative electrode, and a non-aqueous electrolyte, wherein the surface of active material particles contained in the positive electrode is represented by the following formula:非 A non-aqueous electrolyte secondary battery characterized by being coated with a conductive compound having a lobskite structure, containing Li, and having free electrons. _{Li 1-x A y BO 3} -z F z (0 ≦ x <1,0 ≦ y <1,0 <z ≦ 3) ( however, A is a monovalent or divalent typical elements, lanthanoid elements or their At least one member selected from the group consisting of combinations, wherein B is of the genus IVa, Va, or VI
a, VIIa, VIII and Ib). 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the active material comprises only primary particles formed by crystal growth or particles having a smooth surface without gaps such as phases. . 3. The non-aqueous electrolyte secondary battery according to claim 1, further comprising a positive electrode having a carbon-based conductive agent interposed between all the particles of the active material.