JP2000156221A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop heat generation so as to prevent thermorunaway even if overcharge or an internal short-circuit occurs by covering a part or the entire part of the surface of a lithium containing metal oxide with a metal and/or carbon material mixture layer having a dissolving potential larger by a certain potential than that of lithium, and by setting the specific resistance of a positive electrode mixture layer to a specific value or less. SOLUTION: In order to restrain the interaction of a lithium containing metal oxide with a solvent of a nonaqueous electrolyte in an overcharge and an internal short circuit, a part or the entire part of the surface of the lithium containing metal oxide is covered with a metal and/or carbon material mixture layer having a dissolving potential larger by three or more volts than that of lithium. Thereby, a heat generation rate is restrained by forming an electrolyte diffusion barrier between the lithium containing metal oxide surface layer and a bulk electrolyte layer. The increase of contact resistance in conjunction with the expansion and contraction of the lithium containing metal oxide is restrained by covering it with the metal and/or carbon material mixture layer and by setting the specific resistance of a depolarizing mixture layer to 1 Ωm or less.

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.

[0002]

2. Description of the Related Art As electronic devices have rapidly become smaller and lighter, there is an increasing demand for secondary batteries that are small, lightweight, have a high energy density, and can be repeatedly charged and discharged. . In addition, due to environmental problems such as air pollution and an increase in carbon dioxide, early commercialization of electric vehicles is desired, and development of excellent secondary batteries having characteristics such as high efficiency, high output, high energy density, and light weight. Is required.

As a secondary battery satisfying these requirements, a secondary battery using a non-aqueous electrolyte has been put to practical use. This battery has several times the energy density of a battery using a conventional aqueous electrolyte solution. For example, a non-aqueous electrolyte as the electrolyte, a cobalt composite oxide or nickel composite oxide or a spinel-type lithium manganese oxide for the positive electrode, and a long life using a carbon material capable of storing and releasing lithium for the negative electrode. 4 V class non-aqueous electrolyte secondary batteries have been put to practical use.

[0004]

In such a non-aqueous electrolyte secondary battery, a high-capacity non-aqueous electrolyte secondary battery using a high-capacity amorphous carbon or / and oxide as a negative electrode has been developed. The development of technology for miniaturization and high capacity is rapidly progressing. As described above, the prevention of overcharge and overdischarge, the prevention of an internal short circuit, and the like have become major issues with the increase in size and capacity, that is, the dramatic increase in volume energy density. As a measure to prevent overcharge, a method of controlling a charging voltage by a charger and a measure to prevent an overdischarge by controlling a cutoff voltage at the time of discharge have become mainstream. Also, in preparation for a failure of control of the charger or the like or the occurrence of a large current due to an internal short circuit, the battery side is provided with a safety valve and a current cut-off means that are opened when a predetermined battery internal pressure is reached. However, even if these measures are taken, the heat generated during overcharging or internal short circuit is extremely rapid, so that safety valves and current interrupting means do not work effectively, often causing troubles such as causing thermal runaway. . Therefore, the present invention provides a battery that can effectively suppress heat generation so as not to cause thermal runaway even if a charger fails and becomes overcharged or an internal short circuit occurs for some reason. The purpose is to:

[0005]

A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode on which a positive electrode mixture layer containing a lithium-containing metal oxide capable of inserting and extracting lithium ions is formed;
A negative electrode on which a negative electrode mixture layer having a host material capable of inserting and extracting lithium ions is formed, and a part or all of the surface of the lithium-containing metal oxide has an elution potential of 3 V with respect to the lithium elution potential. The metal and / or carbon material mixture layer within the above range is covered, and the specific resistance of the positive electrode mixture layer is 1 Ωm or less.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the case where a charger has failed, if a non-aqueous electrolyte secondary battery is charged with a predetermined amount or more of electricity, the battery will generate heat and, in the worst case, may ignite. Also,
Even if an internal short circuit occurs for some reason during charging,
In the worst case, a fire may occur. The present inventor has investigated this cause in detail, and found that when overcharging, the lithium-containing metal oxide, which is a positive electrode host material that absorbs and releases lithium ions, becomes thermally unstable and the battery temperature rises. Clarified that the main cause was a large exothermic decomposition reaction caused by the interaction of the non-aqueous electrolyte with the solvent. In addition, it was clarified that the exothermic reaction due to the interaction between the charged lithium-containing metal oxide and the solvent of the non-aqueous electrolyte is the main cause of thermal escape even when the internal short circuit occurs. Therefore, the present inventor promotes thermal escape at the time of overcharging or internal short-circuit, in order to suppress the interaction between the lithium-containing metal oxide and the solvent of the non-aqueous electrolyte, the surface of the lithium-containing metal oxide is By covering a part or the whole with a metal and / or carbon material mixture layer having an elution potential in the range of 3 V or more with respect to the lithium elution potential, electrolysis between the lithium-containing metal oxide surface layer and the bulk electrolyte layer is performed. By providing a liquid diffusion barrier, the heat generation rate was suppressed. The reason for using a metal having an elution potential in the range of 3 V or more with respect to the lithium elution potential as a metal covering part or all of the surface of the lithium-containing metal oxide is that in this type of nonaqueous electrolyte secondary battery, Since a normal discharge end voltage is 3 V or less, when a metal having an elution potential of less than 3 V with respect to the lithium elution potential is used, the metal elutes at the end of discharge and the surface of the lithium-containing metal oxide This is because the effect of covering is lost. When the surface of the lithium-containing metal oxide is covered with a metal and / or carbon material mixture layer having an elution potential in the range of 3 V or more with respect to the lithium elution potential, a part of the surface of the lithium-containing metal oxide is used. May be covered, or the whole may be covered. However, in order to increase the safety of the battery, it is necessary to minimize the contact area between the lithium-containing metal oxide and the electrolytic solution. Preferably, it is covered with a carbon material. Further, when the surface of the lithium-containing metal oxide is covered with a metal or a carbon material, the surface may be covered with a metal alone or a carbon material alone, or may be covered with a metal and further covered with a carbon material, or may be covered with a carbon material first. It may be a two-layer structure of covering with a metal, or may be further covered with a mixed layer of a metal and a carbon material. Further, the surface layer of the lithium-containing metal oxide is covered with the above-mentioned metal and / or carbon material having excellent electron conductivity, and the specific resistance of the positive electrode mixture layer is set to 1 Ωm or less. This suppresses an increase in contact resistance due to this. If the specific resistance of the positive electrode mixture layer is larger than 1 Ωm, the voltage drop due to the resistance becomes large in the case of high-rate discharge, which causes a problem when the battery is actually used. Therefore, the safety valve and the current cutoff means operate effectively, and the explosive exothermic decomposition reaction at the time of overcharge or internal short circuit, which occurs in the conventional battery, can be effectively suppressed. Furthermore, since a substance having a low specific resistance is always interposed between the particles, an increase in contact resistance between the particles due to expansion and contraction of the lithium-containing metal oxide due to charge and discharge is suppressed, and a long cycle life. Performance has also improved.

The lithium-containing metal oxide used as the positive electrode active material in the present invention is lithium spinel manganese oxide or a small amount of cobalt, nickel, aluminum, or manganese atoms in the crystal of the compound. Compounds substituted with atoms such as chromium, iron, magnesium, calcium, LixMn ₂ O ₄ and LixM
Various lithium manganese composite oxides such as nO ₂ , other composite oxides, oxides having tunnel-like vacancies, and the like can be used. As a specific example, LiCo
O ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , M
nO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO _{2 and the} like. The negative electrode host material used in the present invention may be any material as long as it can occlude and release lithium ions. For example, graphite, coke, carbon, amorphous carbon, SnO, SnO ₂ , Sn
_1-x O (0 ≦ x <1), Si _1-x O (0
≦ x <1). Even when a high-capacity battery is formed using an oxide, safety can be improved by applying the present invention. In the present invention, as the non-aqueous solvent for the electrolytic solution, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane , 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate and the like, and a polar solvent alone or a mixture thereof may be used. Further, a lithium ion conductive solid polymer electrolyte membrane can be used as the electrolyte. In this case, the concentrations of the electrolyte solvent and the supporting salt may be different between the electrolyte contained in the polymer and the electrolyte contained in the pores of the solid polymer electrolyte membrane.
Lithium salts dissolved in organic solvents include LiP
F ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , Li
CF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C
F ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (C
Salts such as OCF ₂ CF ₃ ) ₂ or mixtures thereof may be used. Furthermore, in the examples, as the separator, a porous microporous membrane of polyolefin such as a microporous polypropylene membrane can be used in addition to a microporous polyethylene membrane having insulating properties. Alternatively, two or more types of microporous polyolefin membranes may be used in combination. Further, these polyolefin microporous membranes may be used in combination with a solid polymer electrolyte. The non-aqueous electrolyte secondary battery according to the present invention has a configuration in which a positive electrode, a negative electrode and a separator are combined with a non-aqueous electrolyte, or an organic or inorganic solid electrolyte as a positive electrode, a negative electrode and a separator is combined with a non-aqueous electrolyte. May be used in combination. Any known inorganic solid powder or non-aqueous electrolyte bound by a separator or an organic or inorganic solid electrolyte or an organic binder as a separator can be used.

Hereinafter, the present invention will be described with reference to preferred embodiments. However, it is needless to say that the present invention is not limited to the following without departing from the gist of the present invention.

The present invention will be described below with reference to an embodiment in which a lithium-containing metal oxide according to the present invention is coated. [Example 1] A procedure for manufacturing a nonaqueous electrolyte secondary battery according to the present invention will be described. A lithium-cobalt composite oxide was used as the lithium-containing metal oxide. First, about 50 nm of gold plating was applied to the particle surface of the lithium-cobalt composite oxide by a vacuum evaporation method, and a uniform carbonaceous layer was coated over the entire particle surface by a CVD method. The average thickness of this carbonaceous layer was 1 μm. This is referred to as a positive electrode host material (a). (Vacuum deposition conditions) Degree of vacuum: 5 × 10 ⁻² torr Discharge current: 15 mA × 50 seconds (CVD conditions) Degree of vacuum: 5 × 10 ⁻¹ torr Benzene gas flow: 50 ml / min, Ar gas flow: 100 ml / min Temperature: 200 ° C. The positive electrode plate is made of polyvinylidene fluoride (PVd) as a binder.
F) 6 parts by weight and 3 parts by weight of acetylene black as a conductive agent are mixed together with 91 parts by weight of an active material,
-Methylpyrrolidone (NMP) was appropriately added to prepare a paste, and then applied to both surfaces of the current collector material and dried.
Then, it was manufactured by pressing to a thickness of 180 μm and cutting it to a width of 24 mm leaving a rectangular lead portion.
An aluminum foil having a thickness of 20 μm was used as a current collector material. The specific resistance of the mixture layer in the completed positive electrode plate is
It was 0.5 Ωm. The negative electrode plate has 92 parts by weight of graphite as a host material and polyvinylidene fluoride (PVd) as a binder on both sides of a current collector made of a copper foil having a thickness of 10 μm.
F) 8 parts by weight, mixed with N-methylpyrrolidone (NMP) as a solvent to form a paste, coated on both sides, dried, rolled to a thickness of 220 μm, and formed into a rectangular lead. Was cut to a width of 26 mm.

The separator has a thickness of 25 μm and a width of 28 μm.
Was used.

FIG. 1 is a sectional view of a non-aqueous electrolyte secondary battery according to the present invention. In FIG. 1, 1 is a non-aqueous electrolyte battery,
Reference numeral 2 denotes an electrode group, 3 denotes a negative electrode plate, 4 denotes a positive electrode plate, 5 denotes a separator, and 6 denotes a battery case. The configuration of the non-aqueous electrolyte secondary battery 1 is a prismatic battery in which a spiral electrode group 2 including a positive electrode plate 4, a negative electrode plate 3, and a separator 5 and an electrolyte are accommodated in a battery case 6, and 7 is a lid, 8 is a safety valve, 10 is a negative electrode terminal, and 11 is a negative electrode lead wire.

The battery case 6 has a thickness of 0.3 mm and an inner size of 3 mm.
The surface of an iron main body of 0 × 40 × 8 mm is plated with nickel having a thickness of 5 μm, and a hole (not shown) for injecting an electrolytic solution is provided at an upper side portion.

The electrolyte is ethylene carbonate: diethyl carbonate = 1: 1 containing 1 mol / l of LiPF _6.
The mixed solution (volume ratio) was used. The electrolyte and the separator were sufficiently wetted, and the amount of free electrolyte which did not exist outside the electrode group was injected under reduced pressure to seal the hole, and the designed dose was 900
30 cells of the battery (A) of mAh were manufactured.

Comparative Example 1 A conventional battery (B) was prepared in the same manner as in Example 1 except that a lithium-cobalt composite oxide (b) whose particle surface was not covered with gold or carbon was used as a positive electrode host material. 30 cells were produced.

[Tests and Results] Each of these batteries A and B was set to 10 cells, and the power supply voltage was set to 10 V.
When the battery (A) of Example 1 according to the present invention was continuously charged with a current of C for 2 hours, no abnormality such as smoke and ignition was observed in all the batteries, whereas the conventional Comparative Example 1
In battery (B), the battery temperature rose to 200 ° C. or higher, and smoke was observed. Further, after charging each of these batteries A and B to 1350 mAh by 10 cells,
When the center of the battery was penetrated with a SUS nail, the battery (A) of Example 1 according to the present invention did not show any abnormality such as smoke and ignition in all cases, whereas the conventional comparative example 1
In the battery (B), smoke emission was observed in half of the batteries. In addition, these batteries A and B are each 10 cells,
Table 1 shows the results of comparing the initial discharge capacity and the 300th discharge capacity when the charge / discharge cycle of charging at 900 mA to 4.3 V and then discharging at 900 mA to 2.75 V was repeated 300 times.

[0015]

[Table 1]

Table 1 shows that the battery (A) of Example 1 according to the present invention has a small capacity deterioration.

[0017]

According to the present invention, a lithium-containing metal which promotes thermal escape at the time of overcharge or internal short circuit by providing an electrolyte diffusion barrier between the surface layer of the lithium-containing metal oxide and the bulk electrolyte layer. Interaction between the oxide and the non-aqueous electrolyte can be suppressed. Therefore, the safety valve and the current cutoff means operate effectively, and the explosive exothermic decomposition reaction at the time of overcharging or internal short circuit which occurs in the conventional battery can be prevented, and the safety of the battery can be increased. In addition, since a substance having a low specific resistance is necessarily interposed between the particles of the lithium-containing metal oxide, an increase in contact resistance between the particles due to expansion and contraction of the lithium-containing metal oxide due to charge and discharge is suppressed. Thus, it is possible to improve the cycle life performance over a long period of time. Therefore, the industrial value of the present invention is extremely high.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Negative electrode plate 4 Positive electrode plate 5 Separator 6 Battery case 7 Lid 9 Safety valve 10 Negative electrode terminal 11 Negative electrode lead wire

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Taku Aoki 5th, Kichijoin Nitta Ichidandancho, Minami-ku, Kyoto-shi, Kyoto Inside GE Melcotec Co., Ltd. (72) Inventor Kazuhiro Nakamitsu Kyoto, Kyoto 5F003 (reference) 5K003 AA10 BB05 BB14 BB15 BC05 BD00 5H014 AA02 CC01 EE05 EE07 HH00 5H029 AJ05 AJ12 AK02 AK03 AL02 AL06 AL07 AL08 AM02 AM03 AM04 AM05 AM07 CJ22 DJ08 EJ01 EJ04 HJ20

Claims (1)

[Claims] 1. A positive electrode having a positive electrode mixture layer containing a lithium-containing metal oxide capable of inserting and extracting lithium ions,
A negative electrode on which a negative electrode mixture layer having a host material capable of inserting and extracting lithium ions is provided, and a part or the whole of the surface of the lithium-containing metal oxide has an elution potential of 3 V or more with respect to the lithium elution potential. Covered with the metal and / or carbon material mixture layer within the range, and the specific resistance of the positive electrode mixture layer is 1 Ωm
A nonaqueous electrolyte secondary battery characterized by the following.