JP2000173670A - Charging method for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a charging/discharging cycle life characteristic of a nonaqueous electrolyte secondary battery using tin for a negative electrode. SOLUTION: In charging a secondary battery provided with composite particles, in which the whole or a part of the circumference of a nucleus particle consisting of a solid phase A using tin is covered by a solid phase B, in a negative electrode, a constant current charging area, in which charging is carried out at a fixed current value I until a set voltage E is attained, and a constant voltage charging area, in which charging is carried out at the set voltage E after the set voltage E is attained, are combined together for charging, and a charging current value in the constant current charging area and the fixed voltage charging area is regulated to 5 mA/cm2 or less in the form of current density for a part in which the positive and negative electrodes face each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to composite particles in which the whole or a part of the periphery of a core particle composed of a solid phase A is coated with a solid phase B on a negative electrode material, wherein the solid phase A comprises at least tin. The solid phase B contains tin, which is a constituent element of the solid phase A, and excluding tin, except for Group 2 element, transition element, Group 12 and Group 13 element of the periodic table, and carbon.
The present invention relates to a nonaqueous electrolyte secondary battery, particularly a charging method, using a material that is a solid solution with at least one element selected from the group consisting of group elements or an intermetallic compound.

[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 lithium precipitates in the negative electrode during charging in the form of dendrites, and repeats charging and discharging to reach the positive electrode side through the separator, causing an internal short circuit. There was a risk of causing. The precipitated dendrite-like lithium 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 low reliability and short cycle life characteristics.

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 dendritic lithium. However, the theoretical capacity of graphite, which is one of the carbon materials, is 372 mAh / g, which is about one tenth of the theoretical capacity of Li metal alone. This battery system is particularly called a lithium ion secondary battery.

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 of lithium. 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 forming a compound with lithium, as a compound negative electrode material, Japanese Unexamined Patent Publication No. 7-240201 discloses a non-ferrous metal silicide comprising a transition element. JP-B-63651 discloses an intermetallic compound containing a group 4B element and at least one of P and Sb, and has a crystal structure of CaF ₂ type, ZnS type, or AlL.
Negative electrode materials made of any of the iSi type have been proposed.

[0006] Further, as a method of charging these batteries, when charging a lithium secondary battery, for example, Japanese Patent Application Laid-Open No. 6-98473 discloses a method for suppressing the deposition of lithium in the form of dendrites on a lithium negative electrode. As shown in the gazette, a method of charging by adding a pulse current has been proposed. Further, even in a lithium ion secondary battery using a carbon material for the negative electrode, in order to prevent lithium from being deposited on the carbon negative electrode, for example, as shown in Japanese Patent Application Laid-Open No. It has been proposed to regulate the charging current value to a certain value or less.

[0007]

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

[0008] A single metal material and a single nonmetallic negative electrode material which form a compound with lithium commonly have poorer charge / discharge cycle life characteristics than carbon negative electrode materials. The reason is not clear, but I think as follows.

[0009] For example, tin contains four tin atoms in the crystallographic unit cell (tetragonal, space group I4 ₁ / amd).
Lattice constant a = 0.5820nm, in terms of c = 0.3175nm, unit cell volume is 0.1075nm ^3, the volume occupied by one tin atom is 26.9 × 10 ^-3 nm ^3. Judging from the tin-lithium binary system phase diagram, in the electrochemical compound formation with lithium at room temperature, tin and the compound Li ₂ Sn ₅
It is considered that these two phases coexist. The crystallographic unit cell of Li ₂ Sn ₅ (tetragonal, space group P4 / mbm) contains 10 tin atoms. Its lattice constant a = 1.0274 nm,
Converted from c = 0.3125 nm, the unit cell volume is 0.32986 nm ³ , and the volume per tin atom (the value obtained by dividing the unit cell volume by the number of tin atoms in the unit cell) is 33.0 × 10 ⁻³ nm. ³ Based on this value, the volume of the material expands 1.23 times as the compound changes from tin to Li ₂ Sn ₅ .
Furthermore, when the electrochemical compound formation reaction with lithium proceeds, the lithium-rich compound Li ₂₂ Sn ₅
Is generated. The crystallographic unit cell (cubic, space group F23) of Li ₂₂ Sn ₅ contains 80 tin atoms. Converted from its lattice constant a = 1.978 nm, the unit cell volume is 7.739
nm ³ and the volume per tin atom (the value obtained by dividing the unit cell volume by the number of tin atoms in the unit cell) is 96.7 × 10 ⁻³ nm
³ This value is 3.59 times that of simple tin, and the material expands significantly.

As described above, tin has a large change in volume of the negative electrode material due to a charge / discharge reaction, and repeats a change in a state in which two phases having a large volume difference coexist, thereby causing cracks in the material and making the particles finer. It is thought to be. 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, it is presumed that a large change in volume and a change in structure due to the change in volume are the reason why the charge-discharge cycle life characteristics are poor as compared with the carbon anode material.

On the other hand, unlike a simple material such as tin described above, it is composed 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 or Sb, and its crystal structure is CaF 2. _A negative electrode material made of any of type ₂ , ZnS type, and AlLiSi type has been proposed in JP-A-7-240201 and JP-A-9-63651, respectively, as anode materials having improved cycle life characteristics.

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 the first cycle, the 50th cycle, and the 100th cycle shown in Examples and Comparative Examples. 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.

The materials disclosed in Japanese Patent Application Laid-Open No. 9-63651 have improved charge-discharge cycle life characteristics as compared with the Li-Pb alloy negative electrode material in Examples and Comparative Examples, and have the same characteristics as the graphite negative electrode material. Are also shown to be of high capacity.
However, the discharge capacity is remarkably reduced in the charge / discharge cycles of 10 to 20 cycles, and even for Mg ₂ Sn which is considered to be the best, the capacity is reduced to about 70% of the initial capacity after about 20 cycles.

Further, the charge / discharge cycle life characteristics differ depending on the method of charging the battery. This is because, depending on the negative electrode material, since the oxidation-reduction potential during charging and the overvoltage during electrochemical reaction are different, if the charging current value or charging voltage value exceeds the allowable range, the electrode reaction proceeds unevenly,
This is because side reactions such as lithium deposition, film formation, and gas generation occur, and the charge-discharge cycle life characteristics deteriorate.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a composite particle in which the whole or a part of the periphery of a core particle composed of a solid phase A is coated with a solid phase B, wherein the solid phase A contains at least tin as a constituent element. The solid phase B is composed of tin, which is a constituent element of the solid phase A, and a group 2 element of the periodic table, a transition element, and 12 excluding tin.
The solid-phase A has a higher capacity and a solid-phase B by using a material that is a solid solution or an intermetallic compound with at least one element selected from the group consisting of a group 13 element, a group 13 element, and a group 14 element excluding carbon. Provides a negative electrode material having excellent charge / discharge cycle characteristics by playing a role of suppressing expansion and contraction caused by charge / discharge of solid phase A. Further, when charging a battery using the above negative electrode material, a set voltage Until (E) is reached, a constant current charging region in which charging is performed at a constant current value (I), and after reaching the set voltage (E), the set voltage (E)
The charging is performed in combination with the constant voltage charging region where constant voltage charging is performed, and the charging current value in the constant current charging region and the constant voltage charging region is set to 5 mA / cm ² or less as the current density of the portion where the positive and negative electrodes face each other. By regulating, a conventional problem can be solved, and a non-aqueous electrolyte secondary battery having high energy density and excellent cycle life characteristics and a method for charging the battery can be provided.

In the present invention, since the solid phase A of the negative electrode material contains high-capacity tin as a constituent element, it is considered that the solid-phase A mainly contributes to increasing 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 contains a small amount of lithium and expands and expands the particles.
By suppressing shrinkage, it suppresses the decrease in current collection,
The charge-discharge cycle life characteristics have been improved. Furthermore, by limiting the charging current value in the constant current charging region and the constant voltage charging region to 5 mA / cm ² or less as the current density of the portion where the positive and negative electrodes face each other, side reactions with the electrolytic solution that occur during charging of the negative electrode can be prevented. It suppresses the charge and discharge cycle life characteristics.

Hereinafter, possible embodiments for implementing the present invention will be described. The positive electrode and the negative electrode used in the present invention have a mixture layer containing a conductive agent, a binder and the like in a positive electrode active material or a negative electrode material capable of electrochemically and reversibly inserting and releasing lithium ions on the surface of the current collector. It was produced by coating.

The negative electrode material used in the present invention is a composite particle in which the whole or a part of the periphery of the core particle composed of the solid phase A is coated with the solid phase B, and the solid phase A contains at least tin as a constituent element. The solid phase B is composed of tin, which is a constituent element of the solid phase A, and a group 2 element, a transition element, a group 12, a group 13 element, and a group 14 element excluding carbon except for tin. A material that is a solid solution with at least one selected element or an intermetallic compound (hereinafter, referred to as “composite particles”).

As one of the methods for producing composite particles used in the present invention, a melt having a 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 manufacturing 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 conductive agent for the negative electrode used in the present invention may be any 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
, Li _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, Cu, Zn, Al, Cr, P
b, Sb, B) (where x = 0)
-1.2, y = 0-0.9, z = 2.0-2.3). Here, the above-mentioned x 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 which 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 binder for the positive 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 -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 and 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.

As the electrode mixture, a filler, a dispersant, an ion conductor, a pressure enhancer, and other various additives can be used in addition to the conductive agent and the 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 comprises 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.

As a lithium salt dissolved in these solvents,
Is, for example, LiClO_Four , LiBF _Four , LiPF₆ , L
iAlCl_Four, LiSbF₆, LiSCN, LiCl, L
iCF_Three SO_Three , LiCF_Three CO_Two , Li (CF_ThreeS
O_Two)_Two, LiAsF₆ , LiN (CF_ThreeSO_Two)_Two, Li
B_TenCl_Ten, Lithium lower aliphatic carboxylate, LiC
1, LiBr, LiI, lithium chloroborane,
Lithium nylborate, imides and the like,
These may be used alone or in combination of two or more
It is possible to use₆ Contains
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.

In addition to the electrolyte, the following solid electrolyte is also used.
Can be used. As solid electrolyte, inorganic solid electrolyte
It can be divided into decomposition and organic solid electrolyte. For inorganic solid electrolyte
Is often Li nitride, halide, oxyacid salt, etc.
Are known. Above all, Li_Four SiO_Four , Li_Four Si
O_Four -LiI-LiOH,_x Li_Three PO_Four −_(1-x)Li _Four 
SiO_Four, Li_Two SiS_Three , Li_Three PO_Four −Li_TwoSS
iS_TwoAnd phosphorus sulfide compounds are effective. Organic solid state
In degrading, for example, polyethylene oxide, polypropylene
Pyrene oxide, polyphosphazene, polyaziridi
, Polyethylene sulfide, polyvinyl alcohol,
Polyvinylidene fluoride, polyhexafluoropropylene
And polymers such as their derivatives, mixtures, and composites
The material is effective.

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.

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. Generally, the thickness of the separator is 10 to 300 μm. The porosity is determined according to the electron and ion permeability, the material and the film thickness, but is generally preferably 30 to 80%.

Further, 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 a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, and a large type used for electric vehicles.

The method for charging a non-aqueous electrolyte secondary battery according to the present invention can be used for a portable information terminal, a portable electronic device, a small household power storage device, a motorcycle, an electric vehicle, a hybrid electric vehicle, and the like. However, the present invention is not particularly limited to these.

[0040]

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.

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

Powders or blocks of each element constituting the negative electrode material are 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 is 10 ° C. to 50 ° C. higher than the solid solution temperature of the solid solution or intermetallic compound determined by the charged composition shown in (Table 1).
The heat treatment was performed at a low temperature in an inert atmosphere for 20 hours. 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 periphery of the solid phase A particles was covered with the solid phase B.

[0043]

[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 pulled out from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is connected from the negative electrode plate 6.
Is pulled out 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,
Metals such as nickel, titanium, chromium, molybdenum, copper, and aluminum or alloys thereof are used. In particular, the battery case is preferably made of a stainless steel plate or an Al-Mn alloy plate, and the positive electrode lead is most preferably aluminum and the negative electrode lead is preferably nickel. 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, a fuse, a bimetal, a PTC element, or the like is used as the overcurrent prevention element. 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 that increase the internal pressure include Li ₂ CO ₃ and L
iHCO ₃ , Na ₂ CO ₃ , NaHCO ₃ , CaCO ₃ ,
Carbonates such as MgCO ₃ . cap,
Known methods (eg, DC or AC electric welding, laser welding, ultrasonic welding) can be used for welding the battery case, sheet, and lead plate. 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 was prepared by mixing 10% 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 85% by weight of a lithium cobalt oxide powder, and dehydrated N-methyl. A slurry is prepared by dispersing 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 LiPF6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1 to 1.5 mol / l was used.

As described above, the materials A to G shown in Table 2
Were used as negative electrodes to produce batteries A to G. The manufactured cylindrical battery had a diameter of 18 mm and a height of 650 mm.

Battery Charging Method These batteries were used for charging according to the present invention. Hereinafter, the charging method of the present invention will be described in detail. FIG. 2 shows a schematic diagram of the charging current and the charging voltage of the embodiment of the present invention. A constant current charging area (CC) in which charging is performed at a constant current value (I) until reaching the set voltage (E), and a constant voltage in the set voltage (E) after reaching the set voltage (E). Charging was performed in combination with the constant voltage charging area (CV) to be charged. Termination of charging is performed when the charging current value is 1 in the constant voltage region (E).
The point in time at which the current reached 00 mA was regarded as charging. The charging current value (I) is a current density per area where the positive and negative electrodes face each other.
3, 5, 7 mA / cm ² , and the set voltage (E) was 4.1.
V. The discharge was performed at a constant current of 100 mA, and the discharge end voltage was set to 2.0 V. The charge / discharge cycle life test was performed in an environment at 20 ° C.

(Comparative Example) A battery H prepared in the same manner as in the Example except that the negative electrode material was made of scale-like artificial graphite (average particle diameter 25 μm) was used, and the current density was changed to 3 mA / cm ^2. The test was performed in the same manner as in the example.

Table 2 shows the initial discharge capacity of the battery and 30
The ratio of the discharge capacity at the 300th cycle to the discharge capacity at the 0th cycle and the initial discharge capacity was shown as a capacity retention ratio.

[0052]

[Table 2]

As is clear from Table 2, all of the batteries A to G of the examples of the present invention have a higher initial capacity than the battery H of the comparative example using graphite as the negative electrode material, and have a higher charge / discharge cycle. Regarding the life characteristics, the current density during charging was 5 mA / cm.
^By setting it to ² or less, the capacity retention ratio was 70% or more, which is superior to the battery H of the comparative example.

The batteries A to G at the time of 300 cycles were disassembled, and the state of the positive electrode, the negative electrode, the separator, and the electrolytic solution was visually observed. A substance thought to be a decomposition product of was adhered. It is considered that this decomposition product hindered the electrode reaction and reduced the discharge capacity. It is considered that the decomposition product was generated by the fact that the negative electrode potential was polarized in a negative direction due to an increase in the current density at the time of charging, and a decomposition reaction of the electrolytic solution as a side reaction occurred.

As described above, a composite particle in which the entire surface or a part of the core particle composed of the solid phase A as the negative electrode material is coated with the solid phase B, the solid phase A contains at least tin as a constituent element, The solid phase B is selected from the group consisting of tin, which is a constituent element of the solid phase A, and a group 2 element, a transition element, a group 12, a group 13 element, and a group 14 element except carbon except for tin. A non-aqueous electrolyte secondary battery characterized by using a material that is a solid solution with at least one type of element or an intermetallic compound, and further, when charging the secondary battery, a set voltage ( Until you reach E)
Charging is performed by combining a constant current charging region in which charging is performed at a constant current value (I) and a constant voltage charging region in which constant voltage charging is performed at a predetermined voltage (E) after reaching the set voltage (E). And the charging current value in the constant current charging region and the constant voltage charging region is defined as the current density of the portion where the positive and negative electrodes face each other.
By charging the battery according to the charging method of the present invention, which is regulated to not more than mA / cm ^2, a battery having high energy density and excellent charge-discharge cycle life characteristics can be provided.

In the present embodiment, the lower limit of the current density during charging is 1 mA / cm ² , but a lower value may be used. However, the time until the battery is fully charged becomes longer. Therefore, for the required charging time, 5 mA / c
The current value may be set within the range of m ² . It is clear that the electrode area may be changed from the viewpoint of battery design.

The element constituting the negative electrode material used in the present embodiment is, when the solid phase A is Sn, Mg as a Group 2 element,
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.

The charge ratio of the constituent elements of the negative electrode material is not particularly limited, and two phases are formed, one phase (solid phase A) is mainly composed of Sn, and the other phase is mainly composed of Sn. It is sufficient that another phase (solid phase B) partially or entirely covers the periphery thereof, and the charged composition is not particularly limited. Further, the phase A is formed not only from Sn but also from elements other than the respective elements, for example, O, C, N,
S, Ca, Mg, Al, Fe, W, V, Ti, Cu, C
This includes the case where trace elements such as r, Co, and P are present. The phase B is not only composed of the solid solution and the intermetallic compound shown in (Table 1), but also the element constituting each solid solution and the intermetallic compound and other elements, for example,
O, C, N, S, Ca, Mg, Al, Fe, W, V, T
This includes the case where trace elements such as i, Cu, Cr, Co, and P are present.

[0059]

As described above, according to the present invention, it is possible to improve the charge / discharge cycle life characteristics of a non-aqueous electrolyte secondary battery having a higher energy density than a conventional carbon material using a negative electrode material.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a charging current and a charging voltage in the charging method of the present invention.

[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

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) H02J 7/10 H02J 7/10 B (72) Inventor: Harima Shimamura 1006, Ojimon, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshiaki Nitta 1006 Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.F-term (reference) AA10 AS11 AS14 BB02 FF42

Claims (1)

[Claims] A composite particle comprising a positive electrode material and a negative electrode material capable of inserting and extracting lithium, wherein the negative electrode material covers the whole or a part of a core particle composed of a solid phase A with a solid phase B. The solid phase A contains at least tin as a constituent element, and the solid phase B contains tin, which is a constituent element of the solid phase A, and a group 2 element of the periodic table, a transition element, excluding tin.
Non-aqueous electrolyte secondary battery using a material that is a solid solution with at least one element selected from the group consisting of Group 13 elements, Group 13 elements, and Group 14 elements excluding carbon, or an intermetallic compound When charging, a constant current charging region in which charging is performed at a constant current value until the set voltage is reached, and a constant voltage charging region in which constant voltage charging is performed at the set voltage after reaching the set voltage. Charge, and
The charging current value in the constant current charging region and the constant voltage charging region
The current density at the portion where the positive and negative electrodes face each other is 5 mA / cm ²
A method for charging a non-aqueous electrolyte secondary battery characterized by the following restrictions.