JP2000173669A - Non-aqueous electrolyte secondary battery charging method - Google Patents

Abstract

(57) [Problem] To improve charge / discharge cycle life characteristics of a battery using silicon and zinc for a negative electrode. SOLUTION: When charging a secondary battery provided with a composite particle in which the whole or a part of a core particle composed of solid phase A using silicon or zinc is coated with a solid phase B on a negative electrode, a set voltage is set. Until (E) is reached, a constant current charging region in which charging is performed at a constant current value (I), and constant voltage charging in which, after reaching the set voltage (E), constant voltage charging is performed at the set voltage (E). The charging is performed in combination with the region, and the charging current value in the constant current charging region and the constant voltage charging region is regulated to 5 mA / cm ² or less as the current density of the portion where the positive and negative electrodes face each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a composite particle comprising a negative electrode material and the whole or a part of the periphery of a core particle composed of a solid phase A coated with a solid phase B, wherein the solid phase A is made of silicon or zinc. The solid phase B contains at least one element as a constituent element, and the solid phase B includes any of silicon and zinc as constituent elements of the solid phase A, and, except for the constituent elements, a Group 2 element of the periodic table, a transition element,
A solid solution with at least one element selected from the group consisting of Group 2 and Group 13 elements and Group 14 elements excluding carbon;
Also, the present invention relates to a nonaqueous electrolyte secondary battery using a material that is an intermetallic compound, particularly to a charging method.

[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 formulas of the most lithium-containing compounds of silicon (Si) and zinc (Zn) are Li ₂₂ Si ₅ and LiZn, respectively.
In this range, metallic lithium does not usually precipitate, and there is no problem of internal short circuit due to dendritic lithium. The electrochemical capacities between these compounds and the individual materials are 4199 mAh / g and 410 mAh / g, respectively, which are both 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.

For example, silicon has its crystallographic unit cell
(Cubic, space group Fd-3m) containing 8 silicon atoms
I have. Converted from lattice constant a = 0.5420 nm, unit cell volume
Is 0.1592nm^ThreeAnd the volume occupied by one silicon atom is 19.
9 × 10^-3nm^ThreeIt is. From the phase diagram of the silicon-lithium binary system
Judging, electrochemical compound with lithium at room temperature
In product formation, silicon and the compound Li₁₂Si₇
It is considered that these two phases coexist. Li₁₂Si₇of
56 crystallographic unit cells (rhombic, space group Pnma)
Contains a silicon atom. Its lattice constant a = 0.8610n
Converted from m, b = 1.9737 nm, c = 1.4341 nm, unit lattice
Product is 2.4372nm^ThreeAnd the volume per silicon atom
(The unit cell volume is divided by the number of silicon atoms in the unit cell.
Value) is 43.5 × 10 ^-3nm^ThreeIt is. From this value,
Element to compound Li₁₂Si₇The volume of the material
It will expand 2.19 times. Silicon and compound Li₁₂Si₇
In the coexistence of two phases with
₁₂Si₇These volume differences are large due to the
Large strains, cracks easily, and fine particles
It can be easy to become. More electrochemical lithium
When the compound formation reaction with the
Li-rich compound_{twenty two}Si_FiveIs generated. Li_{twenty two}Si_FiveCrystal
The unit cell (cubic, space group F23) has 80
Contains an iodine atom. From its lattice constant a = 1.8750 nm
Converted, the unit cell volume is 6.5918 nm^ThreeAnd the silicon source
Volume per child (unit cell volume is
82.4 × 10)^-3nm^ThreeIt is. This value
Is 4.14 times that of elemental silicon, and the material is greatly expanded.
You. In the discharge reaction for the negative electrode material, the compound
The material shrinks as the reaction decreases. This
Since the volume difference between charging and discharging is large as in
Large strain occurs, cracks occur and particles become finer
it is considered as. In addition, there is a space between these miniaturized particles
The electron conduction network is disrupted and the electrochemical
The part that cannot participate in the reaction increases and the charge / discharge capacity decreases.
It is considered to be.

[0010] Zinc contains two zinc atoms to the crystallographic unit cell (hexagonal, space group P6 ₃ / mmc). Lattice constant a
= 0.2665 nm, c = 0.4947 nm, the unit cell volume is
0.030428 nm ³ and the volume occupied by one zinc atom is 15.2
× 10 ^-3 nm ³ . Judging from the phase diagram of the zinc-lithium binary system, a lithium-rich compound LiZn is finally produced through several compounds. The crystallographic unit cell of LiZn (cubic, space group Fd-3m) contains eight zinc atoms. Converted from the lattice constant a = 0.6209 nm, the unit cell volume is 0.2394 nm ³ , and the volume per zinc atom (the value obtained by dividing the unit cell volume by the number of zinc atoms in the unit cell) is 29.9 × 10 ^-3 nm ^3. This value is 1.97 times that of elemental zinc, and the material expands.

As described above, similarly to silicon, zinc has a large change in volume of the negative electrode material due to a charge / discharge reaction, and repeatedly changes a state in which two phases having a large volume difference coexist, thereby causing cracks in the material. It is considered that the particles become finer. 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 single metal material and the single nonmetal material negative electrode material forming a compound with lithium and the resulting structural change are caused by poor charge / discharge cycle life characteristics as compared with the carbon negative electrode material. I guess there is.

On the other hand, unlike the above-mentioned simple material, it is composed of a non-ferrous metal silicide composed of a transition element or an intermetallic compound containing at least one of the group 4B element and P or Sb, and has a crystal structure of 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 were used in the first cycle, the 50th cycle, and the 100th cycle shown in Examples and Comparative Examples. Although the charge / discharge cycle life characteristic is improved as compared with the lithium metal negative electrode material, the battery capacity is increased by only about 12% at the maximum as compared with the natural graphite negative electrode 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 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.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a composite particle in which the entire surface or a part of a core particle comprising a solid phase A is coated with a solid phase B, wherein the solid phase A comprises at least one of silicon and zinc. Containing as an element, the solid phase B is one of silicon and zinc, which are constituent elements of the solid phase A, and excluding the constituent elements, a Group 2 element, a transition element, a Group 12 element, a Group 13 element of the periodic table, and By using a material that is a solid solution or an intermetallic compound with at least one element selected from the group consisting of Group 14 elements excluding carbon, the solid phase A has a higher capacity, and the solid phase B is charged and discharged by the solid phase A. It provides a negative electrode material with excellent charge-discharge cycle characteristics by playing a role in suppressing the expansion and contraction that occurs. Further, when charging a battery using the above-described negative electrode material, until the set voltage (E) is reached, Charging with a constant current value (I) The constant-current charging region and the constant-voltage charging region that performs constant-voltage charging at the set voltage (E) after reaching the set voltage (E) are charged. The conventional problem is solved by regulating the charging current value in the region to 5 mA / cm ² or less as the current density of the portion where the positive and negative electrodes are opposed to each other. A secondary battery 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 at least one of silicon and zinc having a high capacity as a constituent element, it is considered that the solid phase A mainly contributes to an increase in the charge / discharge capacity. The solid phase B, which covers the entire surface or a part of the periphery of the core particles composed of the solid phase A, contains a small amount of lithium and plays a role of suppressing the expansion and contraction of the particles, thereby suppressing a decrease in current collection. In addition, the charge-discharge cycle life characteristics are 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.

In the following, possible embodiments of 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 one of silicon and zinc. The solid phase B includes any of silicon and zinc as the constituent elements of the solid phase A, and, except for the constituent elements, a group 2 element of the periodic table, a transition element,
A material that is a solid solution or an intermetallic compound with at least one element selected from the group consisting of Group 13 elements, Group 13 elements, and Group 14 elements excluding carbon (hereinafter, referred to as “composite particles”).

As one of the methods for producing 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 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 a 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.

The current collector for the negative electrode used in the present invention may be any electronic conductor which does not cause a chemical change in the battery constituted. 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 M y O z, Li x Mn 2 O 4, L
_{i x Mn 2-y M y} O 4 (M = Na, Mg, Sc, Y, M
n, 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.

In the electrode mixture, a filler, a dispersant, an ionic 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 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.

As the separator used in the present invention,
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%.

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.

The method of 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.

[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.

Method of manufacturing negative electrode material (Table 1) Components (solid element, intermetallic compound, solid solution) of solid phase A and solid phase B of the negative electrode material (material A to material L) 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.

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 coagulated material was subjected to a heat treatment for 20 hours in an inert atmosphere at a temperature lower by about 10 ° C. to 50 ° C. than the solidus temperature of the solid solution or the intermetallic compound determined from the charged composition shown in Table 1.
This heat-treated product was pulverized with a ball mill and classified with a sieve to obtain materials A to L in the form of 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.

[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 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 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 LiPF ₆ 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 L shown in Table 2
Were used as negative electrodes to produce batteries A to L. 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 M 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.

[0053]

[Table 2]

As is clear from Table 2, all of the batteries A to L of the examples of the present invention have a higher initial capacity than the battery M 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 the value to ² or less, the capacity retention ratio was 70% or more, which is superior to the battery M of the comparative example.

The batteries A to L 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, as the negative electrode material, composite particles in which the whole or part of the periphery of the core particles made of the solid phase A are coated with the solid phase B, and the solid phase A comprises at least one of silicon and zinc The solid phase B is a solid phase A
Any of silicon and zinc which are the constituent elements of the above, and excluding the above constituent elements, a Group 2 element, a transition element, a Group 12 of the periodic table,
A non-aqueous electrolyte secondary battery, characterized by using a material that is a solid solution with at least one element selected from the group consisting of Group 13 elements, and Group 14 elements excluding carbon, or an intermetallic compound, Further, when charging the secondary battery, a constant current charging region in which charging is performed at a constant current value (I) until the set voltage (E) is reached, and the set voltage (E) is reached. Thereafter, charging is performed in combination with a constant voltage charging region in which constant voltage charging is performed at a set voltage (E), and charging current values in the constant current charging region and the constant voltage charging region are determined by current densities in portions where the positive and negative electrodes are opposed. By charging by the charging method of the present invention, which is regulated to 5 mA / cm ² or less, a battery having high energy density and excellent charge-discharge cycle life characteristics can be provided.

In this 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 elements constituting the negative electrode material used in the present embodiment are, when the solid phase A is Si, 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. When the solid phase A is Zn, Mg is used as a Group 2 element, and Fe and Mo are used as transition elements.
Zn and Cd as Group elements, In as Group 13 elements,
Although Pb was used as a Group 14 element, similar effects were obtained by using elements of each group other than these.

The charge ratio of the constituent elements of the negative electrode material is not particularly limited, and two phases are provided, and one phase (solid phase A) is mainly composed of Si and Zn. It is sufficient that another phase (solid phase B) partially or entirely covers the periphery thereof, and there is no particular limitation on the charged composition. Further, the phase A is formed not only from Sn alone but also from elements other than each element, for example, O,
C, N, S, Ca, Mg, Al, Fe, W, V, Ti, C
This includes the case where trace elements such as u, Cr, 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 each element of the 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.

[0060]

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

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 7/10 H02J 7/10 BH (72) Inventor: Harima Shimamura 1006 Kazuma, Kajima, Kadoma, Osaka Matsushita Inside Electric Industrial Co., Ltd. AM05 AM07 BJ02 BJ14 5H030 AA03 AA10 AS08 AS11 AS14 BB02 BB03 BB04 FF42 FF43

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 includes at least one of silicon and zinc as constituent elements, and the solid phase B includes any of silicon and zinc as constituent elements of the solid phase A and 2 in the periodic table except for the constituent elements. A material that is a solid solution or an intermetallic compound with at least one element selected from the group consisting of a group IV element, a transition element, a group XII, a group XIII element, and a group XIV element excluding carbon. When charging the non-aqueous electrolyte secondary battery, 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 in which the charging is performed at a set voltage after reaching the set voltage. Combined with voltage charging area Characterized in that the charging current value in the constant current charging region and the constant voltage charging region is regulated to 5 mA / cm ² or less as the current density of the portion where the positive and negative electrodes face each other. How to charge the next battery.