WO2017221677A1 - Lithium secondary battery - Google Patents

Abstract

The objective of the present invention is to reduce the resistance between a positive electrode and a negative electrode. A lithium ion secondary battery which comprises a positive electrode having a positive electrode mixture layer, a negative electrode having a negative electrode mixture layer, and a ceramic layer arranged between the positive electrode mixture layer and the negative electrode mixture layer, and wherein: the ceramic layer contains ceramic particles and dielectric particles represented by Ba_1-xM_xTiO₃ (wherein M is La or Sr, and x is within the range of 0-0.1); the ceramic particles have an average particle diameter (Da) of from 1 μm to 30 μm (inclusive); the relationship between the average particle diameter (Da) of the ceramic particles and the average particle diameter (Db) of the dielectric particles, namely Db/Da satisfies Db/Da ≤ 0.2; and the volume ratio of the dielectric particles relative to the sum of the volume of the ceramic particles and the volume of the dielectric particles is within the range of 1-40 vol%.

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery having excellent output characteristics.

Lithium secondary batteries have high energy density and are attracting attention as batteries for electric vehicles and power storage. In particular, electric vehicles include zero-emission electric vehicles that are not equipped with an engine, hybrid electric vehicles that are equipped with both an engine and a secondary battery, and plug-in electric vehicles that are charged from a system power source. In particular, in a hybrid electric vehicle, output characteristics at a large current are required for a lithium secondary battery.
As described above, there are various means as conventional techniques for improving the output characteristics of the lithium secondary battery, and in particular, there are the following prior arts as means for promoting the reaction of insertion / extraction of lithium ions.

In Patent Document 1, in an all-solid lithium secondary battery, a modifier having a relative dielectric constant higher than that of the solid electrolyte material is arranged at the interface between the positive electrode active material and the solid electrolyte material, and the positive electrode and the solid electrolyte A technique for reducing the interfacial resistance is disclosed.

Patent Document 2 discloses a technique in which a ferroelectric substance is added to a positive electrode to improve ion conductivity and reduce resistance.

In Patent Document 3, a modifier having a relative dielectric constant higher than that of the electrolyte material is disposed at an interface between at least one of the positive electrode active material and the negative electrode active material and the electrolyte material. A technique for reducing the interface resistance is disclosed.

In Patent Document 4, an inorganic particle layer containing a binder and inorganic particles exists between a positive electrode plate and a separator and / or a negative electrode plate and a separator, and LiPF ₂ O ₂ is used as the nonaqueous electrolyte. A technique for adding (lithium difluorophosphate) is disclosed.

JP 2013-062133 A JP 2014-116129 A JP 2012-142268 A JP 2014-35995 A

Prior arts of Patent Documents 1, 2, and 3 relate to all-solid lithium secondary batteries, and attempt to reduce the interface resistance between an active material and an electrolyte. In a lithium ion battery using an electrolytic solution, this interfacial resistance is remarkably small, and technical problems are different. Therefore, these techniques cannot be applied.

Patent Document 4 is an invention related to an increase in the output of a lithium ion battery using an electrolytic solution. However, since inorganic particles are as small as 300 nm, the pores of the inorganic particle layer become too small, and lithium ion permeability (that is, electrolysis). (Liquid resistance) may deteriorate.

An object of the present invention is to reduce resistance between a positive electrode and a negative electrode in a lithium ion secondary battery in which an inorganic particle layer (for example, a ceramic layer) is provided between the positive electrode and the negative electrode and an electrolytic solution is used. .

The means for solving the above problems are, for example, as follows.

A positive electrode having a positive electrode mixture layer; a negative electrode having a negative electrode mixture layer; and a ceramic layer provided between the positive electrode mixture layer and the negative electrode mixture layer. The ceramic layer includes ceramic particles, , Ba _1-x M _x TiO ₃ (M = La or Sr, x = 0 to 0.1), and the ceramic particles have an average particle diameter (Da) of 1 μm or more. The relationship between the average particle diameter (Da) of the ceramic particles and the average particle diameter (Db) of the dielectric particles is 30 μm or less, and Db / Da is in the range of Db / Da ≦ 0.2. And a volume ratio of the dielectric to the sum of the volumes of the dielectric is in the range of 1 to 40 vol%.

According to the present invention, in the lithium ion secondary battery in which the inorganic particle layer is provided between the positive electrode and the negative electrode and the electrolytic solution is used, the resistance between the positive electrode and the negative electrode can be reduced.

Diagram showing lithium ion secondary battery The figure which shows the battery system which uses the lithium ion secondary battery

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible.

Example 1
(Configuration of the battery of the present invention)
FIG. 1 is a diagram schematically showing the internal structure of the lithium secondary battery 101.

The lithium secondary battery 101 is an electrochemical device that can store or use electric energy by occlusion / release of lithium ions to and from an electrode in a non-aqueous electrolyte.

The lithium secondary battery 101 has a configuration in which an electrode group composed of a positive electrode 107, a negative electrode 108, and a ceramic layer 109 is housed in a battery container 102 in a sealed state. The ceramic layer 109 is formed at least on the surface of the positive electrode 107 or the negative electrode 108. The ceramic layer 109 has a function of a layer that allows lithium ions to permeate by electrically insulating the positive electrode 107 and the negative electrode 108 and holding an electrolyte solution described later. The electrode group can employ various configurations such as a configuration in which strip-shaped electrodes are stacked, a configuration in which strip-shaped electrodes are wound and formed into a cylindrical shape or a flat shape.

The battery container 102 can be selected from an arbitrary shape such as a cylindrical shape, a flat oval shape, and a square shape in accordance with the shape of the electrode group. The battery case 102 accommodates the electrode group from the opening provided in the upper part, and then the opening is closed and sealed by the lid 103.

The lid 103 is joined to the opening of the battery case 102 by, for example, welding, caulking, adhesion, or the like, and the outer edge of the lid 103 is hermetically sealed. The lid 103 has a liquid injection port for injecting the electrolyte L into the battery container 102 after sealing the opening of the battery container 102. The liquid injection port is sealed with a liquid injection stopper 106 after the electrolyte L is injected into the battery container 102. It is also possible to add a safety mechanism to the liquid filling plug 106. As a safety mechanism, a pressure valve for releasing the pressure inside the battery container 102 may be provided.

The positive electrode external terminal 104 and the negative electrode external terminal 105 are fixed to the lid 103 via an insulating seal member 112, and a short circuit between both terminals 104 and 105 is prevented by the insulating seal member 112. The positive external terminal 104 is connected to the positive electrode 107 via the positive lead 110 and the negative external terminal 105 is connected to the negative 108 via the negative lead 111. The material of the lead wire insulating seal member 112 can be selected from fluorine resin, thermosetting resin, glass hermetic seal, etc., and any insulating material that does not react with the electrolyte L and has excellent airtightness is used. can do.

The insulating sheet 113 is also inserted between the electrode group and the battery container 102 so that the positive electrode 107 and the negative electrode 108 are not short-circuited through the battery container 102.

(Production of positive electrode and positive electrode)
As the positive electrode 107, a positive electrode current collector in which a positive electrode mixture layer is formed can be used. The positive electrode mixture includes, for example, a positive electrode active material, a conductive agent, a binder, and a current collector. Typical examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . In addition, LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x M _x O ₂ (M = Co, Ni, Fe, Cr, Zn, Ta, x = 0. _{01 ~ 0.2), Li 2 Mn} 3 MO 8 ( although, M = Fe, Co, Ni , Cu, Zn), Li 1-x AxMn 2 O 4 ( provided that, A = Mg, B, Al , Fe, Co, Ni, Cr, Zn, Ca, x = 0.01 to 0.1), LiNi _1-x MxO ₂ (where M = Co, Fe, Ga, x = 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, Mn, x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (where , M = Mn, Fe, Co, Al, Ga, Ca, Mg _{x = 0.01 ~ 0.2), Fe} (MoO 4) 3, FeF 3, LiFePO 4, LiMnPO 4 , etc. can be used. In this example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was selected as the positive electrode active material.

In this example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the active material, but a higher capacity Li ₂ MnO ₃ —LiMnO ₂ solid solution positive electrode can also be used. A high power 5V positive electrode (such as LiNi _0.5 Mn _1.5 O ₄ ) may be used. When these high-capacity materials or high-power materials are used, the above-mentioned mixture thickness can be reduced, and the electrode area that can be stored in the battery can be increased. As a result, the resistance of the battery can be reduced to enable high output, and at the same time, the capacity of the battery can be increased as compared with the case of using a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ positive electrode.

First, a powder of secondary particles (granulated primary particles) of the positive electrode active material is collected. However, some lithium primary phosphates can be used without granulating the primary particle powder. The presence or absence of granulation varies depending on the type of the positive electrode active material, but any can be used as long as an inorganic particle layer can be provided on the surface of the positive electrode mixture.

The particle size of the positive electrode active material is specified to be equal to or less than the thickness of the mixture layer. When there are coarse particles having a size larger than the thickness of the mixture layer in the positive electrode active material powder, the coarse particles are removed in advance by sieving classification, wind classification or the like to produce particles having a thickness of the mixture layer or less.

First, the positive electrode active material may be used as primary particles that are not granulated, or may be granulated to use secondary particles. In this example, a method for producing a positive electrode will be described assuming that secondary particles are used.

The average particle diameter (D ₅₀ ) of the positive electrode active material was measured by a laser scattering method. The average particle diameter D ₅₀ is a sample of the positive electrode active material was suspended in water, a laser scattering type particle size measuring apparatus (for example, Microtrac) are measured using a. D ₅₀ is defined as the particle size when the ratio (volume fraction) to the volume of the entire sample is 50%. If the range is 3 to 20 μm, it is applicable to the present invention. When D ₅₀ is set to a small range of 3 to 8 μm, the output characteristics are improved, which is more preferable. The positive electrode active material of this example is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having a D ₅₀ of 3 to 8 μm.

In order to produce the positive electrode 107, it is necessary to prepare a positive electrode slurry. The positive electrode slurry is applied to the positive electrode current collector and then becomes a positive electrode mixture layer by drying or the like. The positive electrode active material was 88 parts by weight, the conductive agent was 5 parts by weight, and the PVDF (polyvinylidene fluoride) binder was 7 parts by weight. The conductive agent was a mixture of acetylene black and carbon nanotubes (CNT), and the weight composition of each was 4.7: 0.3. In addition, it changes according to the kind of material, a specific surface area, a particle size distribution, etc., and is not limited to the illustrated composition.

The solvent used to prepare the positive electrode slurry may be any solvent that can dissolve the binder, and 1-methyl-2-pyrrolidone was used for PVDF. Depending on the type of binder, the solvent is selected. A known kneader or disperser was used for the dispersion treatment of the positive electrode material.

A positive electrode slurry in which a positive electrode active material, a conductive agent, a binder, and an organic solvent are mixed is attached to a current collector by a doctor blade method, a dipping method, a spray method, etc., and then the organic solvent is dried and the positive electrode is removed by a roll press. A positive electrode can be produced by pressure molding. It is also possible to stack a plurality of mixture layers on a current collector by repeating a plurality of times from application to drying.

Moreover, the mixture density of the positive electrode mixture layer is preferably ³ g / cm ³ or more, and the conductive agent and the positive electrode active material are preferably adhered to each other. By adjusting the density, the electronic resistance of the mixture layer can be reduced.

For the positive electrode current collector, for example, an aluminum foil having a thickness of 10 to 100 μm, or an aluminum perforated foil having a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to aluminum, stainless steel, titanium, and the like are also applicable. In the present invention, any material can be used for the current collector without being limited by the material, shape, manufacturing method, or the like as long as it does not change during the use of the battery, such as dissolution and oxidation.

The thickness of the positive electrode mixture layer is desirably equal to or greater than the average particle diameter. By setting the thickness to the average particle size or less than the average particle size, there is a possibility that the electron conductivity between adjacent particles is deteriorated. The average particle diameter (D ₅₀ ) of the positive electrode active material of the present invention is measured by a laser scattering method, and the range thereof is preferably 3 to 20 μm, particularly preferably 3 to 8 μm.

Using this positive electrode active material, the resistance can be reduced by setting the mixture thickness to 10 μm or more. Further, the upper limit of the thickness of the positive electrode mixture is 40 μm or less, and particularly preferably 30 μm or less. When the positive electrode mixture layer has a thickness of 50 μm or more, unless the conductive agent is added in a large amount to the positive electrode mixture, the charge level of the positive electrode active material near the surface of the mixture and the current collector surface is uneven and uneven. This is because charging / discharging occurs. When the amount of the conductive agent is increased, the positive electrode volume becomes bulky, and the energy density of the battery may decrease.

(Manufacture of negative electrode and negative electrode)
As the negative electrode 108, a negative electrode current collector in which a negative electrode mixture layer is formed can be used. The negative electrode mixture has a negative electrode active material, a binder, and a current collector. As the negative electrode active material, for example, natural graphite coated with amorphous carbon can be used. In this example, natural graphite coated with amorphous carbon was used.

As a method of forming amorphous carbon on the surface of natural graphite, there is a method of depositing pyrolytic carbon on the negative electrode active material powder. By diluting low molecular hydrocarbons such as ethane, propane and butane with an inert gas such as argon and heating to 800 to 1200 ° C., hydrogen is desorbed from the hydrocarbons on the surface of the negative electrode active material particles, and the negative electrode active Carbon is deposited on the surface of the material particles. Carbon is an amorphous form. In addition, after adding organic substances such as polyvinyl alcohol and sucrose, heat treatment is performed at 300 to 1000 ° C. in an inert gas atmosphere, so that hydrogen and oxygen are desorbed in the form of hydrogen, carbon monoxide, and carbon dioxide. Only carbon can be deposited on the surface of the negative electrode active material.

In this example, a gas in which 1% propane and 99% argon were mixed was brought into contact with the negative electrode active material at 1000 ° C. to deposit carbon. The amount of carbon deposited is desirably in the range of 1 to 30% by weight. In this example, 2% by weight of carbon was deposited on the surface of the negative electrode active material. Carbon coating not only increases the discharge capacity at the first cycle, but is also effective for increasing cycle life characteristics and rate characteristics.

In order to produce the negative electrode 112, it is necessary to prepare a negative electrode slurry. After the negative electrode slurry is applied to the negative electrode current collector, it becomes a negative electrode mixture layer by drying or the like. The addition amount of the conductive agent was x, the negative electrode active material was 96-x parts by weight, the conductive agent was x parts by weight, and the PVDF (polyvinylidene fluoride) binder was 4 parts by weight. In this embodiment, since no conductive agent other than the fibrous conductive agent is used for the negative electrode, x is the amount of the fibrous conductive agent added. In this example, carbon nanotubes (CNT) were used as the fibrous carbon, and the addition amount x was 0.1. Note that other conductive agents such as acetylene black may be mixed in the same manner as the positive electrode. In order to prepare an aqueous slurry, a styrene butadiene rubber and carboxymethyl cellulose binder may be used instead of PVDF. In addition, fluorine rubber, ethylene / propylene rubber, polyacrylic acid, polyimide, polyamide and the like can be used, and there is no restriction in the present invention. Any binder that does not decompose on the surface of the negative electrode and does not dissolve in the electrolyte can be used in the present invention.

The solvent used for preparing the negative electrode slurry may be any solvent that can dissolve the binder, and 1-methyl-2-pyrrolidone was used for PVDF. Depending on the type of binder, the solvent is selected. For example, when using a styrene butadiene rubber and carboxymethyl cellulose binder, water is used as a solvent. A known kneader and disperser were used for the dispersion treatment of the negative electrode material.

Also, a known technique such as a doctor blade method, a dipping method, or a spray method can be applied to apply the negative electrode slurry to the negative electrode current collector. It is also possible to form a multilayer mixture layer on the current collector by performing a plurality of times from application to drying. In this example, the coating was performed once on the copper foil by the doctor blade method.

The thickness of the negative electrode mixture layer is desirably equal to or greater than the average particle diameter. When the thickness is equal to or less than the average particle size, the electron conductivity between adjacent particles may be deteriorated. The mixture thickness is preferably 10 μm or more, more preferably 15 μm or more. Further, the upper limit of the negative electrode mixture thickness is desirably 50 μm or less. If the thickness is more than that, unless the conductive agent is added in a large amount to the negative electrode mixture, the charge level of the negative electrode active material near the surface of the mixture and the current collector surface varies, and uneven charge and discharge occur. When the amount of the conductive agent is increased, the negative electrode volume becomes bulky, and the energy density of the battery decreases.

In this embodiment, graphite is used as the negative electrode active material, but silicon, tin, or a compound thereof (oxide, nitride, and alloy with other metals) may be used as the negative electrode active material. These active materials are larger than the theoretical capacity of graphite (372 Ah / kg), and a capacity of 500 to 3600 Ah / kg is obtained. When these high-capacity materials are used, the above-mentioned mixture thickness can be reduced, and the electrode area that can be accommodated in the battery can be increased. As a result, the resistance of the battery can be reduced to enable high output, and at the same time, the capacity of the battery can be increased as compared with the case where a graphite negative electrode is used.

Examples of the negative electrode current collector that can be used in the present invention include a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, and a foam metal plate. In addition to copper, stainless steel, titanium, nickel, etc. are also applicable. An arbitrary current collector can be used without being limited by the material, shape, manufacturing method, and the like. In this example and comparative example, a rolled copper foil having a thickness of 10 μm was used.

(Production of ceramic layer)
On one or both surfaces of the positive electrode 107 (on the positive electrode mixture layer) and the negative electrode 108 (on the negative electrode mixture layer), a ceramic layer 109 is provided as an inorganic particle layer. Thereby, it will be in the state by which the ceramic layer was provided between the positive mix layer and the negative mix layer. In the following description, a method for producing a ceramic layer on both electrodes will be described. In Example 1, the ceramic layer is formed only on the positive electrode mixture layer.

The ceramic layer 109 has ceramic particles and dielectric particles. Ceramic particles and dielectric particles are oxides containing a metal element, and both must be insoluble in the electrolytic solution.

The ceramic particles and the dielectric particles are selected to have an optimal average particle size (D ₅₀ ) ratio. Here, represents a _{D 50} of the ceramic particles and Da, denoted the _{D 50} of the dielectric particles and Db.

Da is preferably 1 μm or more and 30 μm or less. This is because the thickness of the ceramic layer is 30 μm or less. If the ceramic layer becomes too thick, the movement distance of lithium ions that permeate through the pores inside the ceramic layer becomes too long, and the electrolyte resistance may increase. Further, when considering the case where the same battery container is filled with the electrode and the ceramic layer, the increase in the thickness of the ceramic layer relatively decreases the amount of the battery active material and decreases the battery capacity. Therefore, if the insulation between the positive electrode and the negative electrode can be ensured, it can serve as a ceramic layer. Therefore, the thickness of the ceramic layer is preferably 30 μm or less.

From the above viewpoint, the thickness of the ceramic layer may be further reduced to 2 μm. Since Da is 1 μm, the insulation between the positive electrode and the negative electrode can be ensured if at least a thickness equivalent to two ceramic particles can be ensured. When the thickness is equivalent to one ceramic particle (1 μm), a part of the electrode surface is exposed due to dropping of the ceramic particles, and there is a risk of short circuit between the positive electrode and the negative electrode. Moreover, in order to prevent the positive electrode and the negative electrode from being short-circuited due to the mixing of metal foreign matters during production, the thickness of the ceramic layer is desirably 5 μm or more. Considering that the thickness unevenness (unevenness on the surface) between the positive electrode and the negative electrode is 1 to 2 μm, it is more preferable that the thickness of the ceramic layer is 10 μm or more.

The pores of the ceramic layer are determined by the size of the ceramic particles. As D ₅₀ is large, the pore size is _increased, the pore size becomes smaller as _{D 50} is reduced. The lower limit value 1 μm of Da is a limit value at which the pore diameter becomes too small to deteriorate the lithium ion permeability. The ceramic particles not only function as an insulator for the positive electrode and the negative electrode, but also function as a medium for forming pores that allow lithium ions to pass therethrough.

The dielectric particles have a function of promoting the dissociation of the electrolyte in the ceramic layer and reducing the electrolyte resistance of the ceramic layer. Db of the dielectric particles is preferably controlled so as to satisfy Db / Da ≦ 0.2. That is, small Db dielectric particles that are 1/5 or less of the average particle diameter Da of the ceramic particles are used. The dielectric particles are added so as to be incorporated into the ceramic particles. It is undesirable for this to block the pores formed in the gaps between the ceramic particles. In order to avoid clogging of the pores, it is preferable to use dielectric particles having a smaller particle size than ceramic particles.

Furthermore, the volume ratio of the dielectric to the volume of the ceramic layer is preferably in the range of 1 to 40 vol%. When the volume ratio of the dielectric particles is less than 1 vol%, it is difficult to obtain the effect of dissociating the electrolyte. When it exceeds 40 vol%, the ratio of the ceramic particles becomes too small, and the insulating properties of the ceramic layer may be deteriorated. This is because the dielectric has a lower electronic resistance than the ceramic particles, so that the excessively added dielectric particles come into contact with each other, and the electric resistance of the ceramic layer is reduced.

As a dielectric that can be used in this embodiment, for example, a material represented by Ba _1-x M _x TiO ₃ (M = La or Sr, x = 0 to 0.1) can be used.

The ceramic layer is formed on the positive electrode or the negative electrode. First, ceramic particles and dielectric particles are stirred and mixed thoroughly. After adding a PVDF binder to this, 1-methyl-2-pyrrolidone (NMP) is added, dispersed and kneaded to obtain a slurry of the ceramic layer. This processing method is the same as the method for producing the positive electrode slurry.

The prepared ceramic layer slurry is applied to the surface of the positive electrode or the negative electrode, and the NMP is removed by drying to obtain a ceramic layer. After forming the ceramic layer, it may be compressed by a roll press or may be omitted.

(Manufacture of electrolyte)
As a typical example of an electrolyte solution that can be used in the present invention, a solvent obtained by mixing dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like with ethylene carbonate, lithium hexafluorophosphate (LiPF ₆ ), or lithium borofluoride (Li There is a solution in which LiBF ₄ ) is dissolved. The present invention is not limited to the type of solvent and electrolyte, and the mixing ratio of solvents, and other electrolytes can be used. The electrolyte can also be used in a state of being contained in an ion conductive polymer such as polyvinylidene fluoride and polyethylene oxide. Since the ceramic layer 109 of the present invention prevents the positive electrode 107 and the negative electrode 108 from being short-circuited, a conventional resin separator can be dispensed with.

Solvents that can be used for the electrolyte are propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1, 2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl Sulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphate triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1 , Non-aqueous solvents such as 2-diethoxyethane, chloroethylene carbonate, and chloropropylene carbonate. Other solvents may be used as long as they do not decompose on the positive electrode or negative electrode incorporated in the battery of the present invention.

Further, the electrolyte, the chemical formula _{LiPF 6, LiBF 4, LiClO 4} , LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, or multi such imide lithium salts represented by lithium trifluoromethane sulfonimide There are different types of lithium salts. A non-aqueous electrolytic solution obtained by dissolving these salts in the above-described solvent can be used as a battery electrolytic solution. An electrolyte other than this may be used as long as it does not decompose on the positive electrode or the negative electrode incorporated in the battery of the present invention.

When an electrolytic solution and a solid polymer electrolyte (polymer electrolyte) are used, an ion conductive polymer such as ethylene oxide, acrylonitrile, polyvinylidene fluoride, methyl methacrylate, or hexafluoropropylene polyethylene oxide may be used as the polymer electrolyte. it can. These solid polymer electrolytes can be used by impregnating the ceramic layer 109.

Furthermore, an ionic liquid can be used. For example, 1-ethyl-3-methylimidazole tetrafluoroborate (EMI-BF ₄ ), a mixed complex of lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), triglyme and tetraglyme, a cyclic quaternary ammonium cation (N— The combination of methyl-N-propylpyrrolidinium and imide anion (exemplified by bis (fluorosulfonyl) imide) that does not decompose at the positive electrode and the negative electrode is selected to provide the lithium secondary battery of the present invention. Can be used.

Instead of the non-aqueous electrolyte, a solid polymer electrolyte (polymer electrolyte) or a gel electrolyte can be used. As the solid polymer electrolyte, a known polymer electrolyte such as polyethylene oxide or a mixture (gel electrolyte) of polyvinylidene fluoride and a nonaqueous electrolytic solution can be used. An ionic liquid may be used. These ceramic layers 109 can be impregnated and used.

In this example, an electrolytic solution in which 1 mol concentration (1M = 1 mol / dm ³ ) of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (denoted as EC) and ethyl methyl carbonate (denoted as EMC) was used. . The mixing ratio of EC and EMC was 1: 2. The electrolyte concentration was 1 molar as a reference value. Further, 1% vinylene carbonate was added to the electrolytic solution. Electrolytic solution L is held on the surface of ceramic layer 109 and electrodes 107 and 108 and in the pores.

(Battery assembly)
In this embodiment, the positive electrode 107 and the negative electrode 108 on which the ceramic layer 109 is formed are stacked. In FIG. 1, the ceramic layer 109 may be formed on either surface of the positive electrode 107 and the negative electrode 108, or may be formed on both surfaces. The ceramic layer 109 prevents a short circuit between the positive electrode 107 and the negative electrode 108.

Since the ceramic layer 109 needs to allow lithium ions to permeate during charging and discharging of the battery, it can be used if the pore diameter is generally 0.01 to 10 μm and the porosity is 20 to 90%. In this embodiment, the thickness is 2 μm to 30 μm, desirably 5 μm to 30 μm, and more preferably 10 μm to 30 μm. The porosity of the ceramic layer is 30% or more and 90% or less.

An insulating sheet 113 is inserted between the electrode disposed at the end of the electrode group and the battery container 102 so that the positive electrode 107 and the negative electrode 108 are not short-circuited through the battery container 102.

The upper part of the laminate is electrically connected to an external terminal via a lead wire. The positive electrode 107 is connected to the positive electrode external terminal 104 of the lid 103 via the positive electrode lead wire 110. The negative electrode 108 is connected to the negative electrode external terminal 105 of the lid 103 via the negative electrode lead wire 111. Note that the lead wires 110 and 111 can take any shape such as a wire shape or a plate shape. The lead wires 110 and 111 may have any shape and material depending on the structure of the battery can 113 as long as the structure can reduce the ohmic loss when an electric current is applied and does not react with the electrolyte. You can choose.

The material of the battery container 102 is selected from materials that are corrosion resistant to non-aqueous electrolytes, such as aluminum, stainless steel, steel, and nickel-plated steel.

Thereafter, the lid 103 is brought into close contact with the battery container 102 and the whole battery is sealed. In this embodiment, the lid 103 is attached to the battery container 102 by caulking. A known technique such as welding or adhesion may be applied to the method for sealing the battery.

There are two methods for injecting the electrolytic solution: a method in which the lid 103 is removed from the battery container 102 and added directly to the electrode group, or a method in which the lid 103 is added from the liquid inlet 106. The rated capacity (calculated value) of the battery manufactured as an example is 3 Ah.

Hereinafter, other embodiments will be described. Each numerical value, compound and the like in each example are shown in Table 1. From the left side of the table, the type and composition of ceramic particles used in the ceramic layer and the average particle size Da, the type and composition of dielectric particles and the average particle size Db, the ratio of Db / Da, the volume of the ceramic particles and the dielectric particles. The volume ratio of dielectric particles to the sum, the type and composition of the binder, the type of electrode on which the ceramic layer was formed and the thickness of the ceramic layer, and finally the initial value of the DC resistance (DCR) of the lithium secondary battery and 1 at 50 ° C. The DCR measured after standing for a week is shown.

The reference value of DCR is the initial DCR value of Comparative Example 1 (Table 2), and this is taken as 100%, and the ratios of all other measured values are expressed as percentages.

(Examples 2 to 5)
In Example 1, the volume ratio of the dielectric particles was changed from 1.1 to 40%, and the influence of the addition amount of the dielectric particles on the DCR was evaluated. From these examples, the volume ratio of the dielectric particles to the sum of the volume of the ceramic particles and the dielectric particles is in the range of 1 to 40%, and the initial DCR is smaller than 100% (reference value of Comparative Example 1). became. That is, in these examples, it can be seen that the electrolyte resistance in the ceramic layer was reduced. Even when left at 50 ° C. for one week, the increase rate of DCR was as small as 8% or less. Compared with the results of Comparative Examples 1 to 3 (Table 2), which will be described later, these Examples were superior in durability at the initial stage and after standing at high temperature.

(Examples 6 to 10)
In Example 1, DCR when the ceramic particles were changed to SiO ₂ , ZrO ₂ , TiO ₂ , MgO, AlO (OH) was evaluated.

Even when the ceramic particles were changed, the initial DCR was smaller than 100%, and the DCR increase rate after being left at 50 ° C. was as small as 1%. In these examples, a single dielectric was used, but similar results were obtained even when two or more kinds of mixtures were used, and the DCR substantially coincided with the average value when added alone.

(Examples 11 to 12)
In Example 1, the DCR when the Ba element of the dielectric particle BaTiO ₃ was replaced with La and Sr was evaluated. Compared with Example 1, it was found that the initial DCR was further reduced, and the electrolyte resistance of the ceramic layer was reduced. Also, the DCR increase rate after leaving at 50 ° C. was small.

(Examples 13 to 14)
In Example 1, the average particle diameter Db of the dielectric was changed to 0.3 μm and 0.1 μm, and Db / Da was examined up to a small value of 0.03. There was a tendency for the initial DCR to decrease as Db / Da decreased. It is presumed that the DCR decreased because the void volume between the ceramic particles increased due to the decrease in the dielectric particle size.

(Examples 15 to 16)
In Example 15, the ceramic layer formed on the positive electrode in Example 2 was provided on the negative electrode. In Example 16, the ceramic layer formed on the positive electrode in Example 3 was provided on the negative electrode. The same results as in Example 2 and Example 3 were obtained, and it was shown that even when a ceramic layer was formed on the negative electrode, the electrolyte resistance of the ceramic layer was reduced and the DCR was reduced.

(Examples 17 to 18)
In Example 3, ceramic layers were formed on both the positive electrode and the negative electrode. 1/2 of the thickness of the ceramic layer described in the table was prepared on each surface of the positive electrode and the negative electrode. In Example 17, a 10 μm ceramic layer was formed on the positive electrode and the negative electrode. In Example 18, a 15 μm ceramic layer was formed on the positive electrode and the negative electrode.

Even when the total thickness of the ceramic layer was increased to 30 μm, the initial DCR was as low as 84 to 87%, and the DCR increase rate after being left at 50 ° C. was as small as 1%. In addition, although electrolyte solution resistance increases with the increase in the thickness of a ceramic layer, since electrode resistance occupies most of DCR rather than electrolyte solution resistance, the increase in DCR by increase in electrolyte solution resistance was only 1%.

(Example 19)
The average particle diameter of Al ₂ O ₃ used in Example 18 was 30 μm, and a ceramic layer having a thickness of 30 μm was formed only on the negative electrode. The average particle diameter Db of BaTiO ₃ added to the ceramic layer was 6 μm, and Db / Da = 0.2. No ceramic layer was produced on the positive electrode. Other manufacturing conditions were the same as those in Example 18.

The initial DCR was 80%, which was slightly larger than Example 17, but the DCR increase after being left at 50 ° C. could be suppressed to 1%.

2 are the batteries of Example 14, and FIG. 2 is the battery system of the present invention in which these are connected in series.

Each of the lithium ion batteries 201a and 201b has an electrode group having the same specifications including a positive electrode 207, a negative electrode 208, and a ceramic layer 209, and a positive external terminal 204 and a negative external terminal 205 are provided on the upper part. An insulating seal member 212 is inserted between each external terminal and the battery container so that the external terminals are not short-circuited. In FIG. 2, components corresponding to the positive electrode lead wire 110 and the negative electrode lead wire 111 in FIG. 1 are omitted, but the internal structure of the lithium ion batteries 201a and 201b is the same as that in FIG.

The negative external terminal 205 of the lithium ion battery 201a is connected to the negative input terminal of the charge controller 216 by the power cable 213. The positive external terminal 204 of the lithium ion battery 201a is connected to the negative external terminal 205 of the lithium ion battery 201b via the power cable 214. A positive external terminal 204 of the lithium ion battery 201 b is connected to a positive input terminal of the charge controller 216 by a power cable 215. With such a wiring configuration, the two lithium ion batteries 201a and 201b can be charged or discharged.

The charge / discharge controller 216 exchanges power with an externally installed device (hereinafter referred to as an external device) 219 via the power cables 217 and 218. The external device 219 includes various electric devices such as an external power source and a regenerative motor for supplying power to the charge / discharge controller 216, and an inverter, a converter, and a load that supply power from the system. An inverter or the like may be provided depending on the type of AC and DC that the external device supports. As these devices, known devices can be arbitrarily applied.

In addition, a power generation device 222 that simulates the operating conditions of a wind power generator was installed as a device that generates renewable energy, and was connected to the charge / discharge controller 216 via the power cables 220 and 221. When the power generation device 222 generates power, the charge / discharge controller 216 shifts to the charging mode, supplies power to the external device 219, and charges surplus power to the lithium ion batteries 201a and 212b. Further, when the power generation amount simulating the wind power generator is smaller than the required power of the external device 219, the charge / discharge controller 216 operates to discharge the lithium ion batteries 201a and 212b. The power generation device 222 can be replaced with another power generation device, that is, any device such as a solar cell, a geothermal power generation device, a fuel cell, or a gas turbine generator. The charge / discharge controller 216 stores a program that can be automatically operated so as to perform the above-described operation.

The lithium ion batteries 201a and 201b are normally charged so that a rated capacity can be obtained. For example, 2.8V constant voltage charging can be performed for 0.5 hour at a charging current of 1 hour rate. Since the charging conditions are determined by the design of the material and amount of use of the lithium ion battery, the conditions are optimal for each battery specification.

After charging the lithium ion batteries 201a and 201b, the charge / discharge controller 216 is switched to the discharge mode to discharge each battery. Normally, the discharge is stopped when a certain lower limit voltage is reached.

With the system configuration described above, the external device 219 supplies power during charging and consumes power during discharging. In this embodiment, charging is performed at a 2-hour rate, and discharging is performed at a 1-hour rate (1C). The initial discharge capacity was determined. As a result, a capacity of 99.5 to 100% of the design capacity 3Ah of each battery 201a, 201b was obtained.
Thereafter, a charge / discharge cycle test described below was conducted under the condition of an environmental temperature of 20 to 30 ° C. First, charging is performed at a current (1.5 A) of 2 hours rate (2C), and when the charging depth reaches 50% (1.5 Ah charged state), a pulse of 5 seconds is applied in the charging direction, A pulse test for simulating the acceptance of power from the power generation device 222 and the power supply to the external device 219 was performed by applying a 5 second pulse to the batteries 201a and 201b. The magnitude of the current pulse was 15A for both. This current is a large current with a 0.2 hour rate. Subsequently, the remaining capacity of 1.5 Ah is charged at a current of 2 hours (1.5 A) until the voltage of each battery reaches 4.2 V, and after constant voltage charging for 1 hour at that voltage, charging is performed. Was terminated. Thereafter, the voltage of each battery was discharged to 3 V at a current of 1 hour rate (3 A). When a series of such charge / discharge cycle tests were repeated 500 times, a capacity of 97 to 98% of the initial discharge capacity was obtained. It was found that the performance of the system was hardly degraded when the battery was given a current pulse of power acceptance and power supply.

Hereinafter, a comparative example will be described. Each numerical value, compound, etc. in each example are shown in Table 2.

(Comparative Example 1)
Comparative Example 1 is a result obtained when no dielectric particles were used in Example 1. The initial DCR was set to 100%, which was the reference value for all examples and comparative examples. Based on this, the DCR after standing at 50 ° C. increased to 130%.

(Comparative Example 2)
Comparative Example 2 is a DCR measurement result when the volume ratio of the dielectric to the sum of the ceramic particles and the dielectric is 0.1%. Compared with Example 1, it can be seen that the DCR is large.

(Comparative Example 3)
Comparative Example 3 shows the battery specifications and DCR measurement results when the amount of dielectric added is increased and the volume ratio (composition) is 40% in Example 1. Although the initial DCR is low, the dielectric particles are connected to each other, and the battery voltage after being left at 50 ° C. is 1 V or less due to a minute leakage current. That is, overdischarge occurred and the electrode deteriorated. As a result, the DCR significantly increased after standing at 50 ° C.

(Comparative Example 4)
Comparative Example 4 is a DCR measurement result when Db / Da is increased to 0.33 in Example 1. When Db approaches Da, the dielectric particles close the pores formed by the ceramic particles, and the diffusion of lithium ions is easily inhibited. As a result, it is estimated that the initial DCR increased and the DCR after standing at 50 ° C. also deteriorated.

101 lithium ion battery, 102 battery container, 103 lid, 104 positive external terminal, 105 negative external terminal, 106 liquid inlet, 107 positive electrode, 108 negative electrode, 109 ceramic layer, 110 positive electrode lead wire, 111 negative electrode lead wire, 112 insulation Seal material, 113 insulating sheet, 201a lithium ion battery, 201b lithium ion battery, 202 battery container, 204 positive external terminal, 205 negative external terminal, 206 liquid inlet, 207 positive electrode, 208 negative electrode, 209 ceramic layer, 212 insulating seal Materials, 213 power cable, 214 power cable, 215 power cable, 216 charge / discharge controller, 217 power cable, 218 power cable, 219 external device, 220 power cable, 221 power cable, 22 renewable energy power generation device

Claims (4)

1. A positive electrode having a positive electrode mixture layer;
   A negative electrode having a negative electrode mixture layer;
   A ceramic layer provided between the positive electrode mixture layer and the negative electrode mixture layer;
   The ceramic layer has ceramic particles and dielectric particles represented by Ba _1-x M _x TiO ₃ (M = La or Sr, x = 0 to 0.1 range),
   The average particle diameter (Da) of the ceramic particles is 1 μm or more and 30 μm or less,
   The relationship Db / Da between the average particle size (Da) of the ceramic particles and the average particle size (Db) of the dielectric particles is in the range of Db / Da ≦ 0.2,
   A lithium ion secondary battery in which a volume ratio of the dielectric to a sum of volumes of the ceramic particles and the dielectric is in a range of 1 to 40 vol%.
2. In claim 1,
   The ceramic particle is a lithium ion secondary battery having at least one of SiO ₂ , Al ₂ O ₃ , AlO (OH), ZrO ₂ , MgO, and TiO ₂ .
3. In claim 2,
   The ceramic layer is a lithium ion secondary battery having a size of 2 μm or more and 30 μm or less.
4. A battery system having the lithium ion secondary battery according to claim 3.

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