JP2000173659A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nonaqueous electrolyte secondary battery which enables improvement in electrochemical characteristics, such as charge and discharge capacity, a charge and discharge cycle lifetime, and so on, by improving a negative electrode material and by restricting a thickness and a piercing strength of a separator located between positive and negative electrodes. SOLUTION: In this non-aqueous electrolyte secondary battery, a negative electrode material comprises a composite particles, each formed by covering all the surface or a part of the surface of a nuclear particle made of a solid phase A with a solid phase B. The solid phase A contains tin as a constituent element, while the solid phase B is a solid solution or an intermetallic compound of tin (i.e., the constituent element of the solid phase A) and at least one element selected from among group II elements, the transition elements, group XII elements, group XIII elements and group XIV elements excepting carbon, of the periodic table except tin. A separator 7 disposed between positive and negative electrodes has a thickness of 15-40 μm and piercing strength of 200 g or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charge / discharge capacity and a charge / discharge cycle life by improving a negative electrode material of a non-aqueous electrolyte secondary battery and by limiting the thickness and piercing strength of a separator located between the positive and negative electrodes. Non-aqueous electrolyte secondary batteries with improved electrochemical characteristics such as portable information terminals, portable electronic devices, small home electric power storage devices, motor-powered motorcycles, electric vehicles, hybrid electric vehicles, etc. It is about.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries used as main power sources for mobile communication devices and portable electronic devices have the characteristics of high electromotive force and high energy density.
A lithium secondary battery using lithium metal as the negative electrode material has a high energy density, but dendrites are deposited on the negative electrode during charging, and may repeatedly break through the separator to reach the positive electrode side by repeated charging and discharging, causing an internal short circuit. there were. Further, the precipitated dendrite has a high specific activity because of its large specific surface area, and reacts with the solvent in the electrolytic solution on its surface to form a solid electrolyte interface film lacking electron conductivity. For this reason, the internal resistance of the battery is increased, and particles isolated from the electron conduction network are present, and these are factors that lower the charge / discharge efficiency. For these reasons, lithium secondary batteries using lithium metal as the negative electrode material have problems with low reliability and short cycle life.

At present, a carbon material capable of occluding and releasing lithium ions is used as a negative electrode material instead of lithium metal, and has been put to practical use. Normally, metallic lithium does not precipitate on the carbon material negative electrode, so there is no problem of internal short circuit due to dendrite. However, the theoretical capacity of graphite, which is one of the carbon materials, is 372 mAh / g, which is as small as about 1/10 of the theoretical capacity of Li metal alone.

As other negative electrode materials, a simple metal material and a simple nonmetal material which form a compound with lithium are known. For example, the composition formula of the most compound including lithium tin (Sn) is a Li ₂₂ Sn _5, the metal lithium in this range because they do not normally deposit, there is no problem of internal short circuit due to dendrite. The electrochemical capacity between these compounds and each single material is 993 mAh / g, which is larger than the theoretical capacity of graphite.

In addition to a simple metal material and a simple non-metal material which form a compound with lithium, as a compound negative electrode material, a non-ferrous metal silicide comprising a transition element is disclosed in JP-A-7-240201. No. 63651 discloses an intermetallic compound containing a group 4B element and at least one of P and Sb, and its crystal structure is CaF ₂ type, ZnS
A negative electrode material made of any one of an aluminum type and an AlLiSi type has been proposed.

[0006]

However, the negative electrode materials having higher capacities than the above-mentioned carbon materials have the following problems, respectively.

[0007] A single metal material and a single nonmetallic negative electrode material which form a compound with lithium commonly have poor charge / discharge cycle characteristics as compared with a carbon negative electrode material. The reason is not clear, but I think as follows.

Tin is a crystallographic unit cell (tetragonal, spatial
Group I4₁/ Amd) contains four tin atoms. Case
A = 0.5820 nm, c = 0.3175 nm
Converted to a unit cell volume of 0.1075 nm^ThreeIn
The volume occupied by one tin atom is 26.9 × 10^-3nm
^ThreeIt is. Judging from the tin-lithium binary system phase diagram,
At room temperature electrochemical compound formation with lithium
In the early stage of the reaction, tin and the compound Li_TwoSn_FiveWith two phases
Are considered to coexist. Li_TwoSn_FiveCrystallography of
10 for a typical unit cell (tetragonal, space group P4 / mbm)
Contains tin atoms. Its lattice constant a = 1.0
274 nm, c = 0.3125 nm
Lattice volume is 0.32986 nm^ThreeAnd one tin atom
Volume per unit (unit cell volume is the number of tin atoms in the unit cell)
Is 33.0 × 10^-3nm ^ThreeIt is. This value
Therefore, from compound tin to compound Li_TwoSn_FiveTo become
Thus, the volume of the material expands 1.23 times. Change
Formation reaction with electrochemical lithium proceeds
And finally the lithium-rich compound Li_{twenty two}Sn
_FiveIs generated. Li_{twenty two}Sn_FiveCrystallographic unit cell (cubic
Crystal, space group F23) contains 80 tin atoms
You. Converted from its lattice constant a = 1.978 nm,
Coordinate lattice volume is 7.739 nm^ThreeAnd one tin atom
Volume of the crust (the unit cell volume is the number of tin atoms in the unit cell
96.7 × 10)^-3nm^ThreeIt is. This value is
3.59 times that of tin alone, the material expands significantly.

As described above, tin undergoes a large change in the volume of the negative electrode material due to the charge / discharge reaction, and repetition of a change in a state in which two phases having a large volume difference coexist causes cracks in the material and fine particles. It is considered something. It is considered that in the miniaturized material, a space is generated between particles, the electron conduction network is divided, a portion that cannot participate in an electrochemical reaction increases, and the charge / discharge capacity decreases.

That is, the large volume change common to the negative electrode materials of a simple metal material and a simple non-metal material forming a compound with lithium and the structural change due to this are the reasons why the charge / discharge cycle characteristics are poor as compared with the carbon negative electrode material. I guess.

On the other hand, unlike the above-mentioned simple material, it is made of a non-ferrous metal silicide composed of a transition element or an intermetallic compound containing at least one of a Group 4B element and P and Sb, and its crystal structure is CaF ₂ type, ZnS A negative electrode material of any one of the negative electrode type and the AlLiSi type has been proposed as a negative electrode material having improved cycle life characteristics in JP-A-7-240201 and JP-A-9-63651, respectively.

Batteries using a non-ferrous metal silicide negative electrode material comprising a transition element disclosed in Japanese Patent Application Laid-Open No. 7-240201 are described in Examples and Comparative Examples at the first cycle, the 50th cycle, and the 100th cycle. From the battery capacity, the charge-discharge cycle characteristics are improved as compared with the lithium metal anode material, but the battery capacity is increased by only about 12% at the maximum as compared with the natural graphite anode material. Therefore, although not explicitly stated in the specification, it is considered that the non-ferrous metal silicide negative electrode material composed of a transition element has not been significantly increased in capacity as compared with the graphite negative electrode material.

Further, the materials disclosed in Japanese Patent Application Laid-Open No. 9-63651 have improved charge-discharge cycle characteristics as compared with the Li-Pb alloy negative electrode material in Examples and Comparative Examples, and have a higher performance than the graphite negative electrode material. It has been shown to be of high capacity.
However, the discharge capacity was significantly reduced in the charge / discharge cycles of 10 to 20 cycles, and Mg ₂ Sn, which is considered to be the best,
Also, after about 20 cycles, the capacity is reduced to about 70% of the initial capacity.

[0014]

According to the present invention, there is provided a composite particle in which the entire surface or a part of a core particle composed of a solid phase A is coated with a solid phase B, wherein the solid phase A is made of silicon, tin or zinc. The solid phase B contains at least one element as a constituent element, and the solid phase B includes any of silicon, tin, and zinc as constituent elements of the solid phase A and, except for the constituent elements, a Group 2 element, a transition element, and a Group 12 element of the periodic table. , Excluding Group 13 elements and carbon
Using a material that is a solid solution or an intermetallic compound with at least one element selected from the group consisting of group III elements, and the thickness of the separator between the positive and negative electrodes is 15 μm or more and 40 μm or more.
μm or less, and the piercing strength of the separator is 200 g or more, whereby an internal short circuit between the positive and negative electrodes caused by expansion of the negative electrode material can be suppressed, and a non-aqueous electrolyte having high capacity and excellent charge / discharge cycle characteristics. It aims to provide a secondary battery.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The negative electrode material used in the present invention is as follows.
Composite particles in which the whole or part of the periphery of the core particles composed of the solid phase A is coated with the solid phase B, wherein the solid phase A contains tin as a constituent element, and the solid phase B is a constituent element of the solid phase A. A certain tin and, except for the above-mentioned constituent elements, elements of group 2 of the periodic table;
1 excluding transition elements, group 12 and 13 elements, and carbon
A material that is a solid solution with at least one element selected from the group consisting of Group 4 elements or a material that is an intermetallic compound
By using “composite particles”), the solid-phase A has a higher capacity, and the solid-phase B has a role of suppressing expansion and contraction caused by charging and discharging of the solid-phase A. A non-aqueous electrolyte secondary battery, wherein the thickness of the separator located between the positive and negative electrodes is 15 μm or more and 40 μm or less, and the piercing strength of the separator is 200 g or more.

Since the solid phase A of the negative electrode material of the present invention contains high-capacity tin as a constituent element, it is considered that the solid-phase A mainly contributes to an increase in the charge / discharge capacity. Further, the solid phase B covering the whole or a part of the periphery of the core particle composed of the solid phase A contributes to the improvement of the charge / discharge cycle characteristics, and the amount of lithium contained in the solid phase B is usually , Solid solution, and intermetallic compound, respectively, are less than in the case where they are used alone.

The negative electrode material used in the present invention is obtained by coating core particles containing high-volume tin as a constituent element with a solid solution or an intermetallic compound that is unlikely to be miniaturized.
The solid solution or the intermetallic compound of the coating layer can restrain the crystal structure change, that is, a large volume change, of the core particles containing tin as a constituent element caused by the electrochemical occlusion and release of lithium. Suppress the miniaturization of the core particles containing as. As a result, a highly efficient electrochemical reaction system can be realized, and a high-capacity non-aqueous electrolyte secondary battery negative electrode material with little charge / discharge capacity deterioration can be obtained. However, although it is possible to constrain a large volume change of core particles containing tin as a constituent element accompanying the occlusion and release of lithium, a certain volume change is still observed in the coated particles as a whole.

Therefore, when the negative electrode material expands during charging, the negative electrode material or conductive material existing on the surface of the negative electrode plate partially breaks through the separator located between the positive and negative electrodes, causing a minute short circuit between the positive and negative electrodes. Problem has occurred. The change in volume of the negative electrode material of the present invention due to charge and discharge is larger than that of the graphite material, and is considered to be a phenomenon that occurs more remarkably than the conventional nonaqueous electrolyte secondary battery using the graphite material for the negative electrode.

At this time, when the thickness of the separator located between the positive and negative electrodes is 15 μm or more and 40 μm or less, and the piercing strength of the separator is 200 g or more, a minute short circuit between the positive and negative electrodes due to expansion during charging of the negative electrode material may occur. It has been found that the charge-discharge cycle characteristics can be suppressed and good charge-discharge cycle characteristics can be obtained.

That is, if the thickness of the separator located between the positive and negative electrodes is 15 μm or less, the thickness of the separator is small, so that the negative electrode material expands during charging, so that the negative electrode material or conductive material existing on the surface of the negative electrode plate is reduced. A phenomenon in which the separator located between the positive and negative electrodes was partially pierced and a minute short circuit occurred between the positive and negative electrodes occurred, and good charge / discharge cycle characteristics could not be obtained. When the thickness of the separator is 15
If it is not less than μm, it is considered that the separator does not break through even if the negative electrode material expands during charging. However, when the thickness of the separator is 40 μm or more, the volume of the separator occupying the battery container increases, and the filling amount of the positive electrode and the negative electrode capable of inserting and extracting lithium decreases accordingly. Thus, the initial charge / discharge capacity is lower than that of the non-aqueous electrolyte secondary battery, and a high-capacity non-aqueous electrolyte secondary battery cannot be realized. Further, the separator used in the present invention has a limited "piercing strength" which is an index of its physical properties. The method of measuring the “piercing strength” is as follows: a separator is cut into 50 mm × 50 mm, both ends are fixed to a jig, and a needle having a diameter of 1 mm and a tip of 0.5 R is pierced at a speed of 2 mm / sec.
A piercing test was performed on the center of the separator, and the piercing strength was calculated by determining the maximum load value that led to breakage. The value of the piercing strength thus obtained is 200 g
In the following cases, even when the thickness of the separator was 15 μm or more, the negative electrode material expanded during charging, causing a phenomenon of causing a minute short circuit between the positive and negative electrodes, and good charge / discharge cycle characteristics could not be obtained.

The separator used in the present invention includes:
Has a large ion permeability, has a predetermined mechanical strength,
An insulating microporous thin film is used. Further, it is preferable to have a function of closing a hole at a certain temperature or higher to increase resistance. Sheets, nonwoven fabrics or woven fabrics made from olefin polymers such as polypropylene and polyethylene alone or in combination or glass fibers are used because of their organic solvent resistance and hydrophobicity. The pore diameter of the separator is desirably in a range in which the positive and negative electrode materials detached from the electrode sheet, the binder, and the conductive agent do not pass.
A thickness of 1 μm is desirable. The porosity is determined according to the electron and ion permeability, the material and the film pressure, but is generally preferably 30 to 80%.

The positive electrode and the negative electrode used in the present invention are composed of a positive electrode active material capable of electrochemically and reversibly inserting and releasing lithium ions and a mixture layer containing a conductive agent, a binder and the like in a negative electrode material. It was prepared by coating on the surface of a.

As one of the methods for producing the composite particles used in the present invention, a melt of the charged composition of each element constituting the composite particles is prepared by a dry spray method, a wet spray method, a roll quenching method and a rotating electrode method. Rapid cooling and solidification by such as
There is a method of performing heat treatment at a temperature lower than the solidus temperature of the solid solution or the intermetallic compound determined by the charged composition. By rapid solidification of the melt, solid phase A particles as core particles and solid phase B covering the entire surface or a part of the periphery of the solid phase A particles are precipitated.
The purpose of the present invention is to increase the uniformity of the composite particles, but the composite particles according to claim 1 can be obtained even without heat treatment. In addition, any method other than the above-mentioned cooling method can be used as long as it can sufficiently cool.

As another production method, an adhesion layer made of an element other than the elements contained in the solid phase A necessary for forming the solid phase B is formed on the surface of the powder of the solid phase A,
There is a method of performing heat treatment at a temperature lower than the solidus temperature of the solid solution or the intermetallic compound determined by the charged composition. By this heat treatment, the component elements in the solid phase A diffuse into the adhesion layer, and the solid phase B is formed as a coating layer. The adhesion layer can be formed by a plating method or a mechanical alloying method. In the mechanical alloying method, heat treatment may not be required. In addition, any method capable of forming an adhesion layer can be used.

The negative electrode conductive agent used in the present invention may be any conductive material as long as it is an electron conductive material. For example, graphites such as natural graphite (flaky graphite etc.), artificial graphite, expanded graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fibers, Conductive fibers such as metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be included alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black and carbon fiber are particularly preferred. The addition amount of the conductive agent is not particularly limited, but may be 1 to 50 with respect to the negative electrode material.
% By weight, and particularly preferably 1 to 30% by weight. Further, since the negative electrode material of the present invention has electronic conductivity itself, it can function as a battery without adding a conductive material.

The binder for the negative electrode used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders in the present invention include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexa Fluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetra Fluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene Polymer, ethylene - chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer,
Ethylene-acrylic acid copolymer or (Na
⁺ ) Ion crosslinked product, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl methacrylate Copolymers or (Na ⁺ ) ion crosslinked products of the above materials can be mentioned, and these materials can be used alone or as a mixture. Further, a more preferable material among these materials is
Styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer or (Na ⁺ )
Ion crosslinked product, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl methacrylate copolymer It is a combined or (Na ⁺ ) ion crosslinked product of the above materials.

As the current collector for the negative electrode used in the present invention, any collector may be used as long as it does not cause a chemical change in the constructed battery. For example, in addition to stainless steel, nickel, copper, titanium, carbon, conductive resin, and the like, a material obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium is used. Particularly, copper or a copper alloy is preferable. The surface of these materials can be oxidized and used. In addition, it is desirable to make the current collector surface uneven by surface treatment. As the shape, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used. The thickness is not particularly limited, but 1 to
Those having a size of 500 μm are used.

As the positive electrode material used in the present invention, a compound containing or not containing lithium can be used. For example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , L
_{i x Co y Ni 1-y} O 2, Li x Co y M 1-y O z, Li x Ni
_{1-y MyO z, Li x} Mn 2 O 4, Li x Mn 2-y M y O 4 (M
= Na, Mg, Sc, Y, Mn, Fe, Co, Ni, C
u, Zn, Al, Cr, Pb, Sb, and B) (where x = 0 to 1.2, y = 0 to 0.9,
z = 2.0 to 2.3). Where x
The value is a value before the start of charge / discharge, and increases / decreases due to charge / discharge. However, it is also possible to use other positive electrode materials such as transition metal chalcogenides, vanadium oxides and lithium compounds thereof, niobium oxides and lithium compounds thereof, conjugated polymers using organic conductive substances, and Chevrel phase compounds. . It is also possible to use a mixture of a plurality of different positive electrode materials. The average particle size of the positive electrode active material particles is not particularly limited, but is preferably 1 to 30 μm.

The conductive agent for the positive electrode used in the present invention may be any electronic conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, graphites such as natural graphite (flaky graphite, etc.), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black,
Carbon blacks such as thermal black, carbon fiber,
Conductive fibers such as metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide and organic conductive materials such as polyphenylene derivatives Materials and the like can be included alone or as a mixture thereof. Among these conductive agents, artificial graphite and acetylene black are particularly preferred. The addition amount of the conductive agent is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 1 to 30% by weight based on the positive electrode material. For carbon and graphite, 2 to 15% by weight is particularly preferred.

The positive electrode binder used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders in the present invention include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene -Hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene -Tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene Polymer, ethylene - chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer,
Ethylene-acrylic acid copolymer or (Na
⁺ ) Ion crosslinked product, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl methacrylate Copolymers or (Na ⁺ ) ion crosslinked products of the above materials can be mentioned, and these materials can be used alone or as a mixture. Among these materials, more preferred materials are polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

The current collector for the positive electrode used in the present invention may be any electronic conductor that does not cause a chemical change in the charge / discharge potential of the positive electrode material used. For example, in addition to stainless steel, aluminum, titanium, carbon, conductive resin, and the like, a material obtained by treating the surface of aluminum or stainless steel with carbon or titanium is used. Particularly, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized and used. In addition, it is desirable to make the current collector surface uneven by surface treatment. The shape is a foil, a film,
A sheet, a net, a punched material, a lath body, a porous body, a foamed body, a fiber group, a molded body of a nonwoven fabric, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

In the electrode mixture, a filler, a dispersant, an ion conductor, a pressure enhancer and other various additives can be used in addition to a conductive agent and a binder. As the filler, any fibrous material that does not cause a chemical change in the configured battery can be used. Usually, fibers such as olefin-based polymers such as polypropylene and polyethylene, glass, and carbon are used. The addition amount of the filler is not particularly limited, but is 0 to 30% by weight based on the electrode mixture.
Is preferred.

The structure of the negative electrode plate and the positive electrode plate in the present invention is as follows.
It is preferable that the negative electrode mixture surface exists at least on the surface opposite to the positive electrode mixture surface.

The non-aqueous electrolyte used in the present invention is composed of a solvent and a lithium salt dissolved in the solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC).
Cyclic carbonates such as dimethyl carbonate (D
MC), linear carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), and aliphatic carboxylic esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate. , Γ-lactones such as γ-butyrolactone, 1,2-dimethoxyethane (DM
E), chain ethers such as 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, Acetamide, dimethylformamide, dioxolan, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-
Aprotic organic solvents such as imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propanesultone, anisole, dimethylsulfoxide, N-methylpyrrolidone; Can be used alone or in combination of two or more. Among them, a mixed system of a cyclic carbonate and a chain carbonate or a mixed system of a cyclic carbonate, a chain carbonate and an aliphatic carboxylic acid ester is preferable.

Examples of the lithium salts soluble in these solvents include, for example, lithium salts soluble in these solvents such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiPF
AlCl ₄ , LiSbF ₆ , LiSCN, LiCl, Li
CF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ ,
LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl
₁₀ , lower aliphatic lithium carboxylate, LiCl, LiB
r, LiI, lithium chloroborane, lithium tetraphenylborate, imides, and the like. These can be used alone or in combination of two or more in an electrolytic solution or the like using them. Particularly, LiPF ₆ is included. More preferably.

A particularly preferred non-aqueous electrolyte in the present invention is an electrolyte containing at least ethylene carbonate and ethyl methyl carbonate, and LiPF ₆ as a supporting salt. The amount of these electrolytes to be added to the battery is not particularly limited, but a required amount can be used depending on the amounts of the positive electrode material and the negative electrode material and the size of the battery. The amount of the supporting electrolyte dissolved in the nonaqueous solvent is not particularly limited.
2-2 mol / l is preferred. In particular, 0.5-1.5m
ol / l is more preferable.

It is also effective to add another compound to the electrolyte for the purpose of improving the discharge and charge / discharge characteristics.
For example, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, pyridine, hexaphosphoric triamide, nitrobenzene derivative, crown ethers, quaternary ammonium salt, ethylene glycol dialkyl ether and the like can be mentioned.

A mixture of a polymer material and an organic electrolyte composed of a solvent and a lithium salt dissolved in the solvent is absorbed and held in the positive electrode mixture and the negative electrode mixture. It is also possible to configure a battery in which a porous separator made of a retained polymer is integrated with a positive electrode and a negative electrode. As the polymer material, any material can be used as long as it can absorb and hold an organic electrolytic solution, and a copolymer of vinylidene fluoride and hexafluoropropylene is particularly preferable.

The shape of the battery can be any of coin type, button type, sheet type, laminated type, cylindrical type, flat type, square type, large type used for electric vehicles and the like.

Further, the non-aqueous electrolyte secondary battery of the present invention can be used for a portable information terminal, a portable electronic device, a small household power storage device,
The present invention can be used for a motorcycle, an electric vehicle, a hybrid electric vehicle, and the like, but is not particularly limited thereto.

[0041]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Table 1 shows the components (simple element, intermetallic compound, solid solution) of the solid phase A and the solid phase B of the negative electrode material (material A to material G) used in this example, the element ratio at the time of preparation, Shows melting temperature and solidus temperature. In this embodiment, a specific manufacturing method will be described below.

The powder or block of each element constituting the negative electrode material is charged into a melting tank at a charging ratio shown in (Table 1), melted at a melting temperature shown in (Table 1), and the melt is rapidly cooled by a roll. The mixture was quenched and solidified by a method to obtain a solidified product. continue,
The solidified product was subjected to a heat treatment for 20 hours in an inert atmosphere at a temperature about 10 ° C. to 50 ° C. lower than the solidus temperature of the solid solution or intermetallic compound determined by the charged composition shown in (Table 1). The heat-treated product was pulverized by a ball mill and classified by a sieve to obtain materials A to G in particles of 45 μm or less. From these electron microscopic observation results, it was confirmed that the entire surface or a part of the solid phase A particles was covered with the solid phase B.

[0044]

[Table 1]

FIG. 1 is a longitudinal sectional view of a cylindrical battery according to the present invention. The positive electrode plate 5 and the negative electrode plate 6 are spirally wound a plurality of times via a separator 7 and housed in the battery case 1. Then, a positive electrode lead 5 a is drawn out from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is drawn out from the negative electrode plate 6 and connected to the bottom of the battery case 1. The battery case and the lead plate can be made of a metal or an alloy having an organic electrolyte resistance and electron conductivity. For example, iron, nickel, titanium, chromium, molybdenum,
Metals such as copper and aluminum or alloys thereof are used. In particular, the battery case is made of stainless steel plate, Al-
A processed Mn alloy plate, most preferably aluminum for the positive electrode lead and nickel for the negative electrode lead. Further, as the battery case, various types of engineering plastics and a combination thereof with a metal can be used to reduce the weight. Reference numeral 8 denotes an insulating ring provided on the upper and lower portions of the electrode plate group 4, respectively. Then, an electrolytic solution is injected, and a battery can is formed using the sealing plate. At this time, the safety valve can be used as a sealing plate. In addition to the safety valve, various conventionally known safety elements may be provided. For example, fuses, bimetals, P
A TC element or the like is used. In addition to the safety valve, as a countermeasure against an increase in the internal pressure of the battery case, a method of making a cut in the battery case, a gasket cracking method, a sealing plate cracking method, or a cutting method with a lead plate can be used. Further, the charger may be provided with a protection circuit incorporating measures for overcharging and overdischarging, or may be connected independently. As a measure against overcharging, a method of interrupting the current by increasing the internal pressure of the battery can be provided. At this time, a compound for increasing the internal pressure can be contained in the mixture or the electrolyte. Compounds for increasing the internal pressure include Li ₂ CO ₃ , LiHCO ₃ , Na ₂ CO ₃ , NaHCO ₃ ,
Carbonates such as CaCO ₃ and MgCO ₃ ;
Cap, battery case, sheet, lead plate welding method,
Known methods (eg, DC or AC electric welding, laser welding, ultrasonic welding) can be used. A conventionally known compound or mixture such as asphalt can be used as the sealing agent for closing.

The negative electrode plate 6 was prepared by mixing 20% by weight of a carbon powder as a conductive agent and 5% by weight of a polyvinylidene fluoride resin as a binder with respect to 75% by weight of the obtained negative electrode material, and dehydrating the mixture. A slurry is prepared by dispersing in methylpyrrolidinone, coated on a negative electrode current collector made of copper foil, dried,
It was produced by rolling.

On the other hand, the positive electrode plate 5 is prepared by mixing 10% by weight of carbon powder as a conductive agent and 5% by weight of polyvinylidene fluoride resin as a binder with respect to 85% by weight of lithium cobalt oxide powder and dehydrated N-methyl. A slurry is prepared by dispersing it in pyrrolidinone and applied on a positive electrode current collector made of aluminum foil,
After drying, it was produced by rolling.

As the organic electrolyte, a solution prepared by dissolving 1.5 mol / l of LiPF ₆ in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1 was used.

Example 1 In Example 1, the piercing strength of the separator located between the positive and negative electrodes was limited to about 300 g, and the thickness of the separator was (1) 10 μm.
(2) 13 μm, (3) 15 μm, (4) 20 μm, (5) 30
μm, (6) 40 μm, and (7) 45 μm. The material of the separator was a microporous polyethylene film.

As described above, the material A shown in (Table 1)
To G were used as the negative electrodes, and batteries having different thicknesses of the separators were produced (for example, when the negative electrode material A was used and the separator was 1
When the thickness is 0 μm, it is represented as Battery A- (1). ). Among these, batteries (3), (4), (5), and (6) are examples, batteries (1),
(2) and (7) are batteries used as comparative examples. The manufactured cylindrical battery had a diameter of 18 mm and a height of 650 mm. These batteries were first charged at 4.1 mA with a constant current of 100 mA.
After charging until the voltage reaches V, a constant current of 100 mA
The charge / discharge cycle of discharging until the voltage reached V was repeated. Charge and discharge were performed in a constant temperature bath at 20 ° C. The charge / discharge was repeated up to 100 cycles, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity is shown in Tables 2 to 8 as a capacity retention ratio.

[0051]

[Table 2]

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

[Table 6]

[0056]

[Table 7]

[0057]

[Table 8]

When a similar cylindrical battery was manufactured using a graphite material as the negative electrode material, the initial discharge capacity was 151%.
A capacity retention of 92% was obtained at 0 mAh and at the 100th cycle.

As is apparent from Tables 2 to 8, when the piercing strength of the separator is about 300 g, the batteries (3) to (6) whose separator thickness is 15 μm or more and 40 μm or less. It was found that the battery had a higher capacity and a capacity retention rate of 85% or more than the battery prepared using the graphite material, and thus had excellent charge / discharge cycle characteristics. On the other hand, in the batteries (1) and (2) in which the thickness of the separator was 15 μm or less, the capacity retention ratio was 60% or less, and sufficient characteristics could not be obtained.

The cause of the capacity deterioration is that each battery (A,
In B, C, D, E, F, G) batteries (1) and (2), the negative electrode material or conductive material existing on the negative electrode plate surface is located between the positive and negative electrodes due to the volume expansion of the negative electrode material during charging. It is considered that a phenomenon occurs in which a short circuit occurs between the positive electrode and the negative electrode due to partial breakthrough of the separator, and good charge / discharge cycle characteristics cannot be obtained.

On the other hand, in the battery (7) of each battery (A, B, C, D, E, F, G), although there is no cycle deterioration due to a minute short circuit, the volume of the separator occupying in the battery container increases, As a result, the filling amount of the positive electrode and the negative electrode capable of inserting and extracting lithium is reduced, so that the initial discharge capacity is almost the same as that of the battery using the graphite material as the negative electrode, and it has been impossible to realize a high-capacity battery.

Example 2 In Example 2, the thickness of the separator located between the positive and negative electrodes was limited to 15 μm, and the piercing strength of the separator was (8) 152 g, (9) 20
4 g, (10) 303 g, and (11) 411 g were prepared. The material of the separator was a microporous polyethylene film.

As described above, the material A shown in (Table 1)
Was used as a negative electrode to produce batteries having different piercing strengths of the separator (for example, when the piercing strength of the separator was 152 g using the negative electrode material A, this was represented as a battery A- (8)). Among these, batteries (9), (10), and (11) are batteries used as examples and battery (8) is a battery used as a comparative example. still,
The manufactured cylindrical battery has a diameter of 18 mm and a height of 650 mm. These batteries were first charged with a constant current of 100 mA.
After charging until 1V, at a constant current of 100mA 2.
The charge / discharge cycle of discharging until the voltage reached 0 V was repeated.
Charge and discharge were performed in a constant temperature bath at 20 ° C. The charge and discharge were repeated up to 100 cycles, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity is shown in Table 9 as a capacity retention ratio.

[0064]

[Table 9]

As is clear from Table 9, batteries (9) to (1) having a separator piercing strength of 200 g or more were obtained.
In 1), it was found that the capacity retention ratio was 85% or more and the charge / discharge cycle characteristics were excellent. On the other hand, in the battery (8) in which the piercing strength of the separator was 200 g or less, the capacity retention ratio was about 40%, and sufficient characteristics could not be obtained.

The cause of the capacity deterioration is that, in the battery (8), since the piercing strength of the separator is small, the negative electrode material or the conductive material existing on the surface of the negative electrode plate between the positive and negative electrodes due to the volume expansion of the negative electrode material during charging. It is considered that a phenomenon occurred in which the separator positioned partially was pierced to cause a minute short circuit between the positive and negative electrodes, and good charge / discharge cycle characteristics could not be obtained.

In the second embodiment, the thickness of the separator is limited to 15 μm, which is the smallest value in the range of 15 μm to 40 μm defined by the present invention, and separators having different piercing strengths are prepared. However, if the piercing strength is 200 g or more at the thickness limited by the present invention, it can be easily inferred from the results of Examples 1 and 2 that a micro short circuit does not occur.

In Example 2, only the material A was used as the negative electrode material. However, the same effect was obtained with the other materials BG.

Further, in this example, a microporous membrane made of polyethylene was used as the material of the separator. However, similar effects were obtained by using an olefin polymer alone or in combination such as polypropylene and polyethylene.

The elements constituting the negative electrode material used in this example were Mg as a Group 2 element which is a constituent element of the solid phase B, and
Fe and Mo as transition elements, Zn as Group 12 element
In addition, although In was used as Cd and a Group 13 element and Pb was used as a Group 14 element, similar effects were obtained by using other Group elements.

Further, the charging ratio of the constituent elements of the negative electrode material is not particularly limited, and the phases become two phases.
One phase (solid phase A) is a phase mainly composed of Sn, and another phase (solid phase B) may be in a state of partially or entirely covering the periphery thereof. Is not particularly limited. Phase B not only consists of the solid solution and intermetallic compound shown in (Table 1), but also includes the case where each of the solid solution and the element constituting the intermetallic compound and a small amount of other elements are present. It is.

[0072]

As described above, according to the present invention, a non-aqueous electrolyte secondary battery having higher capacity and superior cycle characteristics than a conventional carbonaceous material using a negative electrode material can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical battery according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulating packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6a Negative electrode lead 7 Separator 8 Insulating ring

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiaki Nitta 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. EE07 5H029 AJ05 AK03 AL01 AL11 AM03 AM04 AM07 BJ02 BJ14 DJ04 HJ00 HJ04

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery including a non-aqueous electrolyte, a separator, and a positive electrode and a negative electrode capable of inserting and extracting lithium, wherein the negative electrode is formed on the entire surface around the core particles composed of solid phase A or A part of the composite particles is coated with a solid phase B. The solid phase A contains tin as a constituent element, and the solid phase B has a periodic structure except for tin as a constituent element of the solid phase A and the constituent elements. Group 2 element, transition element, group 12 and 1
Group 3 elements, and a solid solution with at least one element selected from the group consisting of Group 14 elements excluding carbon, or a material that is an intermetallic compound, the thickness of the separator is 15 μm or more and 40 μm or less, and A non-aqueous electrolyte secondary battery, wherein the piercing strength of the separator is 200 g or more.