JPH11111266A - High polymer electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance ion conductivity, and improve a high rate characteristic by using a composite particle on which a specific surface area is covered with an inorganic solid electrolyte particle on which a reversibly lithium storable/releasable active material particle has lithium ion conductivity, as a positive electrode. SOLUTION: In a positive electrode 2, the positive electrode is formed by hardening a high polymer electrolyte monomer by evaporating an organic solvent after coating a surface of a positive electrode current collecting body 1 by forming it in a slurry shape by adding an electrolyte monomer to a material by mixing a conductive agent and a composite particle on which 5 to 85% of the whole surface of an active material particle is covered with an inorganic solid electrolyte particle by heating/melting lithium cobalt composite oxide as an active material particle and a glass inorganic solid electrolyte as an inorganic solid electrolyte particle. In a negative electrode 4, the negative electrode is formed by press-fitting lithium foil to a surface of a negative electrode current collecting body 3. After a separator 5 is arranged/laminated between the positive electrode and the negative electrode, it is wrapped/fused by an aluminium laminate 6, and a high polymer electrolyte secondary battery is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer electrolyte secondary battery, and more particularly, to a polymer electrolyte secondary battery having improved high-rate characteristics.

[0002]

2. Description of the Related Art In recent years, various lithium secondary batteries capable of obtaining a high electromotive force and a high energy density have attracted attention as power supplies for electronic equipment, power storage, and power supplies for electric vehicles, which have been improved in performance and miniaturization. ing.

[0003] Such lithium secondary batteries include those using a non-aqueous liquid electrolyte and those using a polymer solid electrolyte.

A battery using a non-aqueous liquid electrolyte is widely used for loads requiring high-rate discharge because of its good lithium ion conductivity. There is a danger that the battery will be ignited due to the generation of the battery. In recent years, research and development of a polymer-based solid electrolyte that can avoid such a danger has been promoted.

The above-mentioned polymer-based solid electrolytes include:
In a polymer matrix such as polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylonitrile, etc. A complex or crosslinked body obtained by dissolving a supporting electrolyte salt such as lithium methanesulfonate or an imide salt is used. Further, a gel-based polymer matrix containing a highly dielectric solvent such as γ-butyl lactone, ethylene carbonate, propylene carbonate, or acetonitrile as a plasticizer in the polymer matrix is used.

[0006]

However, in the case where the above-mentioned polymer-based solid electrolyte is used, since the active material and the electrolyte are in contact with each other, the lithium ion at the contact interface between the active material and the electrolyte is disadvantageous. Has a problem that the diffusion rate is too low to obtain sufficient high-rate characteristics.

[0007] Further, the above-described one has a problem that the lithium ion conductivity is about 1 to 5 orders of magnitude lower than that of the non-aqueous liquid electrolyte, so that sufficient high rate characteristics cannot be obtained.

[0008]

According to a first aspect of the present invention, there is provided a polymer electrolyte secondary battery comprising a positive electrode containing a polymer electrolyte and a negative electrode. The active material particles capable of occluding and releasing lithium use composite particles in which 5-80% of the total surface area is covered by inorganic solid electrolyte particles having lithium ion conductivity. A junction interface is formed between the positive electrode active material particles and the inorganic solid electrolyte particles to enhance ionic conductivity, thereby obtaining a polymer electrolyte secondary battery having excellent high rate characteristics.

Further, in the polymer electrolyte secondary battery according to the present invention, the average particle diameter of the inorganic solid electrolyte particles is one fifth or less of the average particle diameter of the active material particles. Accordingly, a polymer electrolyte secondary battery having excellent high-rate characteristics can be obtained without reducing the filling ratio of the active material and the energy density of the battery.

A third aspect of the present invention is a polymer electrolyte secondary battery according to the first aspect, wherein the inorganic solid electrolyte particles have an average particle size of 0.01 to 10 μm. Thus, the composite particles in which the active material particles are coated with the inorganic solid electrolyte particles can be easily formed, and the effect of the bonding interface formed by the inorganic solid electrolyte particles can be maximized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on its embodiments.

A feature of an embodiment of the present invention is that in a polymer electrolyte secondary battery including a positive electrode containing a polymer electrolyte and a negative electrode, the positive electrode contains active material particles capable of reversibly storing and releasing lithium. It is characterized by using composite particles in which 5-80% of the total surface area is covered with inorganic solid electrolyte particles having lithium ion conductivity.

As the positive electrode, LiCo is used as active material particles.
Lithium transition metal oxides such as O ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , V ₂ O ₅ , MnO ₂ , M
transition metal oxides such as oO ₃ , TiS ₂ , MoS ₂ , N
A chalcogen compound such as bSe ₃ or a combination thereof is used, and LiI, LiCl
Such as lithium halide or a derivative thereof, lithium nitride, 0.4Li ₃ PO ₄ .0.6Li ₄ SiO ₄ , L
oxygenates such as iTi ₂ (PO ₄ ) ₃ derivatives, derivatives similar to perovskite type Li _0.34 La _0.51 TiO _2.94 ,
_{Li 2 O · B 2 O 3} , Li 2 O · P 2 O 5 oxide glass typified by derivatives, such _{as, Li 2 S · SiS 2,} Li
₂ S · P ₂ sulfide glass represented by derivatives such as S ₅ is used, the active material as particles the method for coating the inorganic solid electrolyte particles, the method according to mechanofusion using high speed mixing rotation (Hosokawa Micron Corporation ; Powder Engineering Laboratory), method by thermal plasma coating (Nissin Flour Milling Co., Ltd .; Ceramics, 31 [3] 195-9)
7) There is a method in which inorganic solid electrolyte particles and active material particles which have been finely divided in advance are mixed at an arbitrary volume ratio, heated, and coated by sintering or melting at the interface between both particles.

As the negative electrode, a lithium alloy such as a lithium-aluminum alloy, a lithium-silicon alloy, and a lithium-indium alloy; a carbon material such as natural graphite, artificial graphite, coke, and a fired organic material; Can be

In the meantime, between the positive electrode and the negative electrode, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluorophosphate, lithium tetrachloride, Lithium trifluoromethanesulfonate, a polymer electrolyte such as a complex or a crosslinked body obtained by dissolving a supporting electrolyte salt such as an imide salt alone or in combination, γ-butyl lactone, ethylene carbonate in the polymer matrix,
As a separator, a gel type in which a high dielectric solvent such as propylene carbonate or acetonitrile is mixed, or a mixture in which a thickener or a strength retaining agent is mixed with the inorganic solid electrolyte particles may be disposed.

[0016]

FIG. 1 is a sectional view of a polymer electrolyte secondary battery according to an embodiment of the present invention.

In FIG. 1, 1 is a positive electrode current collector made of aluminum, 2 is a positive electrode, and the positive electrode 2 is a lithium-cobalt composite oxide LiCoO ₂ having an average particle size of 10 μm as active material particles and inorganic solid electrolyte particles. the average glass inorganic solid electrolyte particle diameter 0.1μm Li ₂ O · B ₂ O of
₃ · SiO ₂ (molar ratio = 60: 32: 8) and was heated and melted, and the composite particle 90 wt% coated with inorganic solid electrolyte particles to about 5% of the surface of the active material particles, acetylene black as a conductive agent And a solution prepared by dissolving lithium tetrafluoroborate having a main chain of polyethylene oxide and polypropylene oxide as polymer electrolyte monomers in N-methyl-2-pyrrolidone as an organic solvent. The slurry was coated on the positive electrode current collector 1,
The organic solvent is evaporated to cure the polymer electrolyte monomer to form a positive electrode having a thickness of 100 μm.
m.

Reference numeral 3 denotes a negative electrode current collector made of copper, 4 denotes a negative electrode, and the negative electrode 4 is a lithium foil having a thickness of 0.05 mm. The electrode was cut into 3.5 cm x 3.5 cm.

Then, a separator 5 made of the same material as the polymer electrolyte monomer used for the positive electrode 2 is arranged and laminated between the cut positive electrode and the negative electrode. The periphery was fused to obtain a polymer electrolyte secondary battery (A1) according to the present invention.

A polymer electrolyte secondary battery (A2) which differs from the polymer electrolyte secondary battery (A1) only in that about 10% of the surface of the active material particles is coated with inorganic solid electrolyte particles;
A polymer electrolyte secondary battery (A3) which differs from the polymer electrolyte secondary battery (A1) only in that about 50% of the surface of the active material particles are coated with inorganic solid electrolyte particles; Battery (A1) is about 75% of the surface of active material particles
And a polymer electrolyte secondary battery (A4) that was different only in that it was coated with inorganic solid electrolyte particles.

The polymer electrolyte secondary battery (A1)
Means that the positive electrode 2 has an average particle diameter of 10 as active material particles.
89% by weight of a lithium-cobalt composite oxide LiCoO ₂ having an average particle diameter of 0.1 μm as inorganic solid electrolyte particles.
m glass-based inorganic solid electrolyte Li ₂ O.B ₂ O ₃ .Si
Polymer electrolyte secondary battery (B1) which differs only in that a mixture of 1% by weight of O ₂ (molar ratio = 60: 32: 8) and 10% by weight of acetylene black as a conductive agent is used.
Was prepared.

Further, the polymer electrolyte secondary battery (A1)
Is different from the polymer electrolyte secondary battery (B) only in that about 2% of the surface of the active material particles is covered with the inorganic solid electrolyte particles.
2) and a polymer electrolyte secondary battery (B3) that was different from the polymer electrolyte secondary battery (A1) only in that 100% of the surface of the active material particles were covered with inorganic solid electrolyte particles. .

Further, the polymer electrolyte secondary battery (A
3) means that the average particle diameter of the inorganic solid electrolyte particles to be coated is 1
Polymer electrolyte secondary battery (B
4) was produced.

3. Each of the polymer electrolyte secondary batteries produced as described above was charged at a constant current of 0.2 C and 0.5 C.
With a constant voltage of 3 V and a constant current of 0.2 C, the discharge current is 3.0
The battery capacity was investigated by conducting a charge / discharge test at a discharge end voltage of V, and the results are shown in Table 1.

[0025]

[Table 1]

From Table 1, it can be seen that the charging current is 0.2 C, 0.5 C
In either case, the polymer electrolyte secondary batteries A1, A
2, A3, A4 battery capacity is polymer electrolyte secondary battery B
It turns out that it becomes higher than 1, B2, B3, B4.

This is because in the polymer electrolyte secondary battery B1, only the active material particles are mixed with the inorganic solid electrolyte particles, so that a good bonding interface is formed between the active material particles and the inorganic solid electrolyte particles. It was thought that it was not
In the polymer electrolyte secondary battery B2, since the ratio of the inorganic solid electrolyte particles covering the surface of the active material particles was small, it was considered that a bonding interface that could contribute to the improvement of ion conductivity was not formed. In the polymer electrolyte secondary battery B3, since the entire surface of the active material particles was covered, it is considered that the electron conductivity was lowered. In the polymer electrolyte secondary battery B4, the average particle size of the inorganic solid electrolyte particles was reduced. It is considered that the reason was that the filling ratio of the active material particles was reduced because of the large size. This means that when the charging current is increased from 0.2 C to 0.5 C in the polymer electrolyte secondary batteries B1, B2, and B3, the battery capacity is greatly reduced, and the charging current is increased from 0.2 C in the polymer electrolyte secondary battery B4. It is clear from the fact that the decrease in battery capacity is small even at 0.5 C.

In the above-described embodiment, the polymer particles are mixed with the composite particles of the positive electrode 2 in the form of a slurry. However, the composite particles may be used alone, and another binder may be used instead of the polymer electrolyte monomer. There may be.

The reason why the battery capacity was increased in the above embodiment is that the surface of the active material particles was coated with inorganic solid electrolyte particles having a lithium ion transport number (cation transport number) close to 1 to thereby increase the polymer capacity. It is considered that the concentration of the anion derived from the supporting electrolyte salt in the electrolyte monomer was prevented from increasing near the active material particles during the lithium ion release reaction.

[0030]

As described above, the first aspect of the present invention provides
A polymer electrolyte secondary battery having excellent high rate characteristics can be obtained, and the invention according to claim 2 can provide a polymer electrolyte secondary battery having excellent high rate characteristics without lowering the energy density of the battery. According to the third aspect of the invention, it is possible to obtain a polymer electrolyte secondary battery capable of maximizing the effect of the bonding interface formed between the active material particles and the inorganic solid electrolyte particles.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a polymer electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode 3 Negative electrode collector 4 Negative electrode 5 Separator 6 Aluminum laminate

Claims (3)

[Claims] 1. A polymer electrolyte secondary battery comprising a positive electrode containing a polymer electrolyte and a negative electrode, wherein an active material particle capable of reversibly occluding and releasing lithium is an inorganic solid having lithium ion conductivity. A polymer electrolyte secondary battery using composite particles in which 5-80% of the total surface area is covered with electrolyte particles. 2. The polymer electrolyte secondary battery according to claim 1, wherein the average particle size of the inorganic solid electrolyte particles is one fifth or less of the average particle size of the active material particles. Rechargeable battery. 3. The polymer electrolyte secondary battery according to claim 1, wherein the average particle size of the inorganic solid electrolyte particles is 0.01 to 1
A polymer electrolyte secondary battery having a thickness of 0 μm.