Secondary battery

Abstract

The present application provides a secondary battery, which has: a positive electrode current collector; a negative electrode current collector; an electrolyte layer disposed between the positive electrode current collector and the negative electrode current collector; a positive electrolyte filling portion divided by the positive electrode current collector and the electrolyte layer; and a negative electrolyte filling portion divided by the negative electrode current collector and the electrolyte layer. The negative electrolyte filling portion includes: a conduction member disposed in a manner to make the negative electrode current collector and the electrolyte layer conductive and having a mesh structure; a negative active material held in the conduction member; an electrolyte salt; and a nonaqueous solvent dissolving the electrolyte salt. The negative active material contains at least one selected from the group consisting of silicon, tin, and aluminum as a constituent element.

Description

Technical Field

[0001] This invention relates to a secondary battery. Background Technology

[0002] In recent years, with the popularization of portable electronic devices, electric vehicles, etc., there is a demand for further improvement in the performance of secondary batteries, represented by lithium-ion secondary batteries. For example, Patent Document 1 discloses a lithium-ion secondary battery that can obtain good cycle characteristics in a lithium-ion secondary battery having a negative electrode containing silicon material as a high-capacity negative electrode active material.

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2018 / 221346 Summary of the Invention

[0006] The technical problem to be solved by the invention

[0007] However, when using negative electrode active materials containing silicon as a constituent element, as described in Patent Document 1, the negative electrode active material expands and contracts significantly during the charging / discharging of the secondary battery, thus easily leading to micronization (disintegration) of the negative electrode active material. Furthermore, the same phenomenon easily occurs when using negative electrode active materials containing tin or aluminum as constituent elements. As a result, the negative electrode active material detaches from the negative electrode, potentially reducing the discharge capacity of the secondary battery.

[0008] Therefore, one aspect of the object of the present invention is to suppress the decrease in discharge capacity in secondary batteries using negative electrode active materials containing silicon, tin or aluminum as constituent elements.

[0009] means for solving technical problems

[0010] One aspect of the present invention is a secondary battery comprising: a positive current collector; a negative current collector; an electrolyte layer disposed between the positive current collector and the negative current collector; a positive electrolyte filling portion divided by the positive current collector and the electrolyte layer; and a negative electrolyte filling portion divided by the negative current collector and the electrolyte layer, the negative electrolyte filling portion comprising: a conductive member disposed in a manner that enables the negative current collector and the electrolyte layer to conduct and having a mesh structure; a negative active material held in the conductive member; an electrolyte salt; and a non-aqueous solvent for dissolving the electrolyte salt, the negative active material containing at least one constituent element selected from the group consisting of silicon, tin, and aluminum.

[0011] In this secondary battery, the conductive component ensures conductivity between the negative electrode current collector and the electrolyte layer. Furthermore, the negative electrode active material remains in the conductive component and coexists with the negative electrode electrolyte in the negative electrode electrolyte filling section, thereby enabling the secondary battery to operate. Moreover, in this secondary battery, the negative electrode active material is held in the conductive component; therefore, even if the negative electrode active material containing silicon, tin, or aluminum as constituent elements is micronized due to charging / discharging of the secondary battery, the negative electrode active material is easily captured in the mesh structure of the conductive component and can continue to function as a negative electrode active material. Therefore, compared to conventional secondary batteries where the negative electrode active material is held on the negative electrode current collector, this secondary battery can suppress the decrease in discharge capacity caused by the micronization of the negative electrode active material.

[0012] Furthermore, this secondary battery has separate positive electrode electrolyte filling sections and negative electrode electrolyte filling sections, so electrolytes with compositions suitable for each electrode can be used separately as the positive and negative electrode electrolytes. Therefore, compared with conventional secondary batteries that use a common electrolyte for both the positive and negative electrodes, the performance of the secondary battery can be improved.

[0013] The conductive components can be made of carbon materials.

[0014] Based on the total amount of non-aqueous solvents, the non-aqueous solvents may contain more than 10% by mass of fluoroethylene carbonate, or may consist only of fluoroethylene carbonate.

[0015] Based on the total amount of non-aqueous solvents, the non-aqueous solvents may contain more than 10% by mass of vinylene carbonate, or may consist only of vinylene carbonate.

[0016] Based on the total amount of non-aqueous solvents, the non-aqueous solvents may contain more than 10% by mass of at least one selected from the group consisting of 12-crown ether-4, 18-crown ether-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol and diaminohexane, or may consist of only at least one of these.

[0017] Based on the total amount of negative electrode active material, the negative electrode active material may contain more than 10% by mass of silicon as a constituent element. Based on the total amount of negative electrode active material, the negative electrode active material may contain more than 10% by mass of tin as a constituent element. Based on the total amount of negative electrode active material, the negative electrode active material may contain more than 10% by mass of aluminum as a constituent element.

[0018] The positive electrode electrolyte filling portion may include: a conductive component configured to allow the positive electrode current collector to conduct through the electrolyte layer and having a mesh structure; a positive electrode active material held in the conductive component; an electrolyte salt; and a non-aqueous solvent to dissolve the electrolyte salt.

[0019] The non-aqueous solvent contained in the positive electrode electrolyte filling section can be a different non-aqueous solvent than the non-aqueous solvent contained in the negative electrode electrolyte filling section.

[0020] Based on the total amount of non-aqueous solvent contained in the positive electrode electrolyte filling section, the content of fluoroethylene carbonate in the positive electrode electrolyte filling section can be less than 0.1% by mass. The positive electrode electrolyte filling section may not contain fluoroethylene carbonate.

[0021] Based on the total amount of non-aqueous solvents contained in the positive electrode electrolyte filling section, the content of vinylene carbonate in the positive electrode electrolyte filling section can be less than 0.1% by mass. The positive electrode electrolyte filling section may not contain vinylene carbonate.

[0022] Invention Effects

[0023] According to one aspect of the present invention, in a secondary battery using a negative electrode active material containing silicon, tin or aluminum as a constituent element, it is possible to suppress the decrease in discharge capacity. Attached Figure Description

[0024] Figure 1 This is a perspective view of a secondary battery according to one embodiment.

[0025] Figure 2 It is along Figure 1 A sectional view of the section obtained by cutting along line II-II. Figure 2 (a) is a schematic cross-sectional view showing one embodiment of a secondary battery. Figure 2 (b) is a schematic cross-sectional view showing another embodiment of the secondary battery. Detailed Implementation

[0026] Hereinafter, embodiments of the present invention will be described with appropriate reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0027] Figure 1 This is a perspective view showing a secondary battery according to one embodiment. For example... Figure 1As shown, in one embodiment, the secondary battery 1 is a so-called laminated secondary battery comprising an electrode assembly 2 and a pouch-shaped battery casing 3 housing the electrode assembly 2. A positive current collector 4 and a negative current collector 5 are provided in the electrode assembly 2. The positive current collector 4 and the negative current collector 5 protrude from the inside of the battery casing 3 to the outside in such a way that the positive current collector and the negative current collector (details will be described later) can be electrically connected to the outside of the secondary battery 1. In another embodiment, the secondary battery 1 can be a secondary battery of a shape other than laminated (coin-shaped, cylindrical, etc.).

[0028] The battery casing 3 can be, for example, a container formed of a laminated film. The laminated film can be, for example, a laminated film formed by sequentially stacking polymer films such as polyethylene terephthalate (PET) film, metal foils such as aluminum, copper, and stainless steel, and sealant layers such as polypropylene.

[0029] Figure 2 It is along Figure 1 A sectional view obtained by cutting along line II-II. For example... Figure 2 As shown, the secondary battery 1 has a positive current collector 6, a negative current collector 7, an electrolyte layer 8 disposed between the positive current collector 6 and the negative current collector 7, a positive electrolyte filling portion 9 divided by the positive current collector 6 and the electrolyte layer 8, and a negative electrolyte filling portion 10 divided by the negative current collector 7 and the electrolyte layer 8 within the battery casing 3.

[0030] The battery casing 3 is sealed to prevent leakage of the positive electrolyte and negative electrolyte from the positive electrolyte filling portion 9 and the negative electrolyte filling portion 10, respectively. In one embodiment, as... Figure 2 As shown in (a), the positive current collector 6 and the negative current collector 7 can be housed inside the battery casing 3. In another embodiment, as... Figure 2 As shown in (b), the two ends of the positive current collector 6 and the negative current collector 7 can protrude outwards from the battery casing 3.

[0031] The positive current collector 6 is formed of materials such as aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, and conductive glass. The thickness of the positive current collector 6 can be, for example, 1 μm or more, and can be less than 50 μm.

[0032] The negative current collector 7 is formed of, for example, copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The thickness of the negative current collector 7 can be, for example, 1 μm or more, and can be 50 μm or less.

[0033] The electrolyte layer 8 is a layer that allows cations (e.g., lithium cations) from the electrolyte salts contained in the positive electrolyte filling portion 9 and the negative electrolyte filling portion 10 to pass through, but prevents the active materials (positive electrode active material and negative electrode active material) and components other than cations (e.g., the aforementioned non-aqueous solvents) contained in the positive electrolyte filling portion 9 and the negative electrolyte filling portion 10 from passing through. The electrolyte layer 8 can be, for example, a non-porous electrolyte layer 8 (an electrolyte layer 8 without pores). From the viewpoint of obtaining excellent strength, the thickness of the electrolyte layer 8 is preferably 1 μm or more, and from the viewpoint of reducing the resistance of ion conduction in the electrolyte layer 8, which results in a reduction of the resistance of the secondary battery 1, it is preferably 500 μm or less.

[0034] This electrolyte layer 8 can be a solid electrolyte material exhibiting lithium-ion conductivity, for example, it can be formed from an oxide-based solid electrolyte or a polymer. In one embodiment, the electrolyte layer 8 can be, for example, a perfluorosulfonic acid-based ion exchange membrane. A perfluorosulfonic acid-based ion exchange membrane is, for example, composed of a polymer having structural units represented by the following formula (1).

[0035]

[0036] [In the formula, x represents an integer from 1 to 20, y represents an integer from 1 to 1000, m represents 0 or 1, n represents an integer from 1 to 10, and X represents a hydrogen atom, an alkali metal atom, or an alkaline earth metal atom.]

[0037] This polymer can be synthesized, for example, by known methods, and can also be purchased as Nafion (registered trademark, manufactured by DowDuPont, Inc.), Dow membrane (manufactured by DowDuPont, Inc.), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), or Flemion (registered trademark, manufactured by AGC Inc.).

[0038] In another embodiment, the polymer constituting the electrolyte layer 8 may be, for example, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, polyethylene oxide, polyacrylic acid, polymethacrylic acid, sulfonated polyimide, sulfonated poly(ether ether ketone), sulfonated poly(ether sulfone), or sulfonated poly(paraben). These polymers are preferably used via ion exchange.

[0039] A conductive member is provided in the positive electrolyte filling portion 9 to enable the positive current collector 6 to conduct electricity with the electrolyte layer 8. The conductive member has a mesh structure. The conductive member can be provided in a part of the positive electrolyte filling portion 9, or it can be provided in a way that fills the entire positive electrolyte filling portion 9. The thickness of the positive electrolyte filling portion 9 can be, for example, 5 μm or more, and can be 2000 μm or less.

[0040] The conductive component can be, for example, in the form of a sheet. The conductive component is formed of a conductive material. Examples of conductive materials include carbon materials, metallic materials, and conductive polymer materials.

[0041] Examples of carbon materials include carbon black, graphite, soft carbon, hard carbon, carbon nanotubes, carbon nanofibers, graphene, carbon nanohorns, glassy carbon, and expanded graphite.

[0042] Examples of metallic materials include nickel, aluminum, copper, stainless steel, gold, and silver.

[0043] Examples of conductive polymer materials include those doped with polymers such as polyacetylene, poly(p-phenylenevinylene), polypyrrole, polythiophene, polyaniline, and poly(p-phenylene sulfide). The doping method is not particularly limited and can involve adding compounds such as iodine, arsenic pentafluoride (electron acceptors), or alkali metals (electron donors) to the polymer.

[0044] In one embodiment, a component pre-formed into a mesh structure can be used as the conductive component. Examples of such conductive components include conductive components made of carbon materials such as carbon felt, carbon paper, and carbon cloth, and conductive components made of metal materials such as perforated metal plates (metal plates with a mesh structure formed by perforation).

[0045] The positive electrolyte filling section 9 contains a positive electrolyte, specifically, it contains, for example, a positive active material, an electrolyte salt, and a non-aqueous solvent.

[0046] In the positive electrode electrolyte filling portion 9, the positive electrode active material is preferably present in a state dispersed in the positive electrode electrolyte (non-aqueous solvent). In other words, the positive electrode active material is preferably not held (fixed) to the positive electrode current collector 6, and the positive electrode electrolyte filling portion 9 preferably does not contain any binding material for holding (fixing) the positive electrode active material to the positive electrode current collector 6.

[0047] Positive electrode active materials are, for example, lithium oxides. Examples of lithium oxides include Li. x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z Li x Ni 1-y M y O zLi x Mn2O4, Li x Mn 2-y M y O4 (In each formula, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V, and B (where M is an element different from the other elements in the formula). x = 0–1.2, y = 0–0.9, z = 2.0–2.3.) etc. Li x Ni 1-y M y O z The lithium oxide represented can be Li x Ni 1-(y1+y2) Co y1 Mn y2 O z (Where x and z are the same as above, y1 = 0 to 0.9, y2 = 0 to 0.9, and y1 + y2 = 0 to 0.9.) For example, it could be LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O 2、 LiNi 0.8 Co 0.1 Mn 0.1 O2. Li x Ni 1-y M y O z The lithium oxide represented can also be Li x Ni 1-(y3+y4) Co y3 Al y4 O z (Where x and z are the same as above, y3 = 0 to 0.9, y4 = 0 to 0.9, and y3 + y4 = 0 to 0.9.) For example, it could be LiNi. 0.8 Co 0.15 Al 0.05 O2.

[0048] The positive electrode active material can also be a lithium phosphate, for example. Examples of lithium phosphates include lithium manganese phosphate (LiMnPO4), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), and lithium vanadium phosphate (Li3V2(PO4)3).

[0049] Compared to the total mass of 100 parts by mass of the positive electrode active material, non-aqueous solvent, and conductive components contained in the positive electrode electrolyte filling section 9, the content of the positive electrode active material can be 10 parts by mass or more, and can be 80 parts by mass or less.

[0050] The electrolyte salt can be, for example, a lithium salt. The lithium salt can be, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2 (Li[FSI], lithium bis(fluorosulfonyl)imide), LiN(SO2CF3)2 (Li[TFSI], lithium bis(trifluoromethanesulfonyl)imide), and LiN(SO2CF2CF3)2.

[0051] Based on the total amount of non-aqueous solvents, the content of electrolyte salts can be above 0.5 mol / L, above 0.7 mol / L, or above 0.8 mol / L, and can be below 1.5 mol / L, below 1.3 mol / L, or below 1.2 mol / L.

[0052] The non-aqueous solvent is a solvent capable of dissolving the electrolyte salt contained in the positive electrode electrolyte filling section 9. Examples of non-aqueous solvents include those suitable for both positive and negative electrode electrolytes, and those suitable only for positive electrode electrolytes (not suitable for negative electrode electrolytes). One type of non-aqueous solvent may be used alone, or two or more may be used in combination.

[0053] Non-aqueous solvents suitable for use in both positive and negative electrode electrolytes can be used, for example, aprotic solvents suitable for both positive and negative electrode electrolytes. Examples of such aprotic solvents include diethyl carbonate, dimethyl ether, diethyl ether, dioxolane, 4-methyldioxolane, sulfolane, dimethyl sulfoxide, propionitrile, benzyl nitrile, N,N-dimethylacetamide, and diethylene glycol.

[0054] Non-aqueous solvents suitable only for use in positive electrode electrolytes (not suitable for negative electrode electrolytes) can be solvents with excellent oxidation resistance but poor reduction resistance (promoting decomposition and increasing film resistance when contained in negative electrode electrolytes). Examples of such solvents include ethylene carbonate, hexafluoroisopropyl ethylene carbonate, trans-difluoroethylene carbonate, cis-difluoroethylene carbonate, tris(hexafluoroisopropyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, acetonitrile, succinate, glutaronitrile, adiponitrile, chloroethylene carbonate, and nitromethane. Among these, the non-aqueous solvent suitable only for use in positive electrode electrolytes (not suitable for negative electrode electrolytes) can be at least one selected from the group consisting of tri(2,2,2-trifluoroethyl) phosphate, acetonitrile, succinate, adiponitrile, chloroethylene carbonate, nitromethane, and ethylene carbonate.

[0055] Based on the total amount of non-aqueous solvent contained in the positive electrode electrolyte filling section 9, the content of non-aqueous solvent suitable for both positive and negative electrode electrolytes can be 1% or more by mass, 3% or more by mass, or 5% or more by mass, and can be 95% or less by mass, 90% or less by mass, or 80% or less by mass. Based on the total amount of non-aqueous solvent contained in the positive electrode electrolyte filling section 9, the content of non-aqueous solvent suitable only for positive electrode electrolytes (not suitable for negative electrode electrolytes) can be 0.1% or more by mass, 1% or more by mass, 10% or more by mass, 15% or more by mass, or 20% or more by mass, and can be 100% or less by mass, 95% or less by mass, or 90% or less by mass.

[0056] In one embodiment, the positive electrode electrolyte filling portion 9 may not contain a non-aqueous solvent suitable only for use with the negative electrode electrolyte (not suitable for the positive electrode electrolyte) described later. In one embodiment, the positive electrode electrolyte filling portion 9 may not contain fluoroethylene carbonate, may not contain vinylene carbonate, and may not contain at least one selected from the group consisting of 12-crown ether-4, 18-crown ether-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol, and diaminohexane. In another embodiment, the non-aqueous solvent suitable only for use in the negative electrode electrolyte (not suitable for the positive electrode electrolyte) contains at least one selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, or 12-crown ether-4, 18-crown ether-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol, and diaminohexane. The content of the non-aqueous solvent can be less than 0.1% by mass, based on the total amount of non-aqueous solvent contained in the positive electrode electrolyte filling section 9.

[0057] As described above, in the secondary battery 1 according to this embodiment, a positive electrode electrolyte filling section 9 and a negative electrode electrolyte filling section 10 are independently provided. Therefore, a non-aqueous solvent suitable only for the positive electrode electrolyte can be used in the positive electrode electrolyte filling section 9, and a non-aqueous solvent suitable only for the negative electrode electrolyte can be omitted. As a result, the overall characteristics of the secondary battery 1 can be further improved.

[0058] The positive electrode electrolyte filling section 9 may also contain a conductive material. The conductive material may be, for example, carbon black such as acetylene black and Ketjen black, graphite, graphene, carbon nanotubes, carbon nanofibers, or other carbon materials. These conductive materials can form an electron conduction network by dispersing in the positive electrode electrolyte. The conductive material is preferably in particulate form, more preferably in large-volume particulate form. The content of the conductive material may be 5 parts by mass or more, and 50 parts by mass or less, relative to 100 parts by mass of the total mass of the positive electrode active material, non-aqueous solvent, and conductive components contained in the positive electrode electrolyte filling section 9.

[0059] A conductive member is provided in the negative electrode electrolyte filling section 10 to enable the negative electrode current collector 7 to conduct electricity to the electrolyte layer 8. The conductive member has a mesh structure. The conductive member can be provided in a part of the negative electrode electrolyte filling section 10, or it can be provided in a way that fills the entire negative electrode electrolyte filling section 10. The thickness of the negative electrode electrolyte filling section 10 can be, for example, 5 μm or more, and can be 2000 μm or less. The conductive member in the negative electrode electrolyte filling section 10 can be the same as the conductive member described as the conductive member in the positive electrode electrolyte filling section 9.

[0060] The negative electrode electrolyte filling section 10 contains a negative electrode electrolyte, specifically, it contains, for example, a negative electrode active material, an electrolyte salt, and a non-aqueous solvent.

[0061] In the negative electrode electrolyte filling portion 10, the negative electrode active material is preferably present in a state dispersed in the negative electrode electrolyte (non-aqueous solvent). In other words, the negative electrode active material is preferably not held (fixed) to the negative electrode current collector 7, and the negative electrode electrolyte filling portion 10 preferably does not contain any binding material for holding (fixing) the negative electrode active material to the negative electrode current collector 7.

[0062] The negative electrode active material contains at least one constituent element selected from the group consisting of silicon, tin, and aluminum. Based on the total amount of the negative electrode active material, the silicon content can be 10% or more by mass, 15% or more by mass, or 20% or more by mass, and can be less than 100% by mass, 95% by mass, or 90% by mass. Based on the total amount of the negative electrode active material, the tin content can be 10% or more by mass, 15% or more by mass, or 20% or more by mass, and can be less than 100% by mass, 95% by mass, or 90% by mass. Based on the total amount of the negative electrode active material, the aluminum content can be 10% or more by mass, 15% or more by mass, or 20% or more by mass, and can be less than 100% by mass, 95% by mass, or 90% by mass.

[0063] Negative electrode active materials containing silicon as a constituent element may contain silicon monomers or compounds containing silicon as a constituent element (silicon-containing compounds). Negative electrode active materials containing tin as a constituent element may contain tin monomers or compounds containing tin as a constituent element (tin-containing compounds).

[0064] Silicon-containing compounds or tin-containing compounds can be, for example, alloys (silicon alloys or tin alloys) comprising silicon or tin and at least one element selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Silicon-containing compounds or tin-containing compounds can also be oxides, nitrides, or carbides. Examples of such silicon-containing compounds include silicon oxides such as SiO, SiO2, and LiSiO; silicon nitrides such as Si3N4 and Si2N2O; and silicon carbides such as SiC. Examples of such tin-containing compounds include tin oxides such as SnO, SnO2, and LiSnO.

[0065] Anode active materials containing aluminum as a constituent element can be, for example, aluminum alloys such as lithium-aluminum alloys.

[0066] Compared to the total mass of 100 parts by mass of the negative electrode active material, non-aqueous solvent, and conductive components contained in the negative electrode electrolyte filling section 10, the content of the negative electrode active material can be 10 parts by mass or more, and can be 80 parts by mass or less.

[0067] The electrolyte salt may be, for example, a lithium salt. The lithium salt may be the same as the lithium salt described as the electrolyte salt contained in the positive electrode electrolyte filling section 9. Based on the total amount of non-aqueous solvent, the content of the electrolyte salt may be 0.5 mol / L or more, 0.7 mol / L or more, or 0.8 mol / L or more, and may be 5 mol / L or less, 3 mol / L or less, or 2 mol / L or less.

[0068] The non-aqueous solvent is a solvent capable of dissolving the electrolyte salt contained in the negative electrode electrolyte filling section 10. Examples of non-aqueous solvents include those that are suitable for both positive and negative electrode electrolytes, as well as those suitable only for negative electrode electrolytes (not suitable for positive electrode electrolytes). One type of non-aqueous solvent may be used alone, or two or more may be used in combination.

[0069] Non-aqueous solvents suitable only for use in negative electrode electrolytes (not suitable for positive electrode electrolytes) can be solvents with excellent resistance to reduction but poor resistance to oxidation (which, when used in positive electrode electrolytes (especially those using 4V-based positive electrodes such as lithium cobalt oxide as the positive electrode active material), promote oxidative decomposition and lead to an increase in resistance).

[0070] Examples of non-aqueous solvents suitable only for use in negative electrode electrolytes (not suitable for positive electrode electrolytes) include γ-butyrolactone, ethyl acetate, ethyl valerate, dimethyl malonate, diethyl malonate, diethyl methyl malonate, diethyl succinate, diethyl glutarate, diethyl azelaate, ethyl heptanoate, heptanoic acid, tetrahydrofuran, 1,2-dimethoxyethane, ethylpropyl ether, tetraethylene glycol dimethyl ether, ethylene glycol bis(3-aminopropyl) ether, diethylene glycol bis(3-aminopropyl) ether, ethylene glycol bis(propionitrile) ether, bis[2-(2-methoxyethoxy)ethyl ether, 1 2-Crown ether-4, 18-Crown ether-6, Taurine, N-Methyltaurine, 2-(Methylamino)ethanol, Diaminohexane, Methylenebis(2-chloroaniline), 1-Methyl-2-pyrrolidone, 1,3-Dimethyl-2-imidazolium ketone, N,N-Dimethylformamide, N-Methylpiperazine, Trimethylamine, Triethylamine, N,N-Dimethylpropylamine, Dimethylformamide, Diethylformamide, 1,1,3,3-Tetramethylurea, N,N-Dimethyl-propenylurea, Cyclohexane, Piperidine, Cyclopentane, Decahydronaphthalene, Tetrahydronaphthalene, Pyrrolidine, Quinoline, 3-Pyrrolidone, etc. Among these, the non-aqueous solvent suitable only for use in negative electrode electrolytes (not suitable for positive electrode electrolytes) can be at least one selected from the group consisting of 12-crown ether-4, 18-crown ether-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol and diaminohexane.

[0071] Furthermore, examples of non-aqueous solvents suitable only for use in negative electrode electrolytes (not suitable for positive electrode electrolytes) include vinylene carbonate, propane sulpholactone, 1,4-butane sulpholactone, 1,3-propene sulpholactone, ethyl methane sulpholactone, vinyl sulfite, trifluoromethane carbonate, fluorobenzene, and fluoroethylene carbonate. Among these, vinylene carbonate or fluoroethylene carbonate are non-aqueous solvents suitable only for use in negative electrode electrolytes (not suitable for positive electrode electrolytes).

[0072] Based on the total amount of non-aqueous solvent contained in the negative electrode electrolyte filling section 10, the content of non-aqueous solvent suitable for both positive and negative electrode electrolytes can be 1% or more by mass, 3% or more by mass, or 5% or more by mass, and can be 95% or less by mass, 90% or less by mass, or 80% or less by mass. Based on the total amount of non-aqueous solvent contained in the negative electrode electrolyte filling section 10, the content of non-aqueous solvent suitable only for negative electrode electrolytes (not suitable for positive electrode electrolytes) can be 0.1% or more by mass, 1% or more by mass, 10% or more by mass, 15% or more by mass, or 20% or more by mass, and can be 100% or less by mass, 95% or less by mass, or 90% or less by mass.

[0073] From the viewpoint of being able to further and appropriately control the formation of a film called Solid-Electrolyte-Interface (SEI) on the surface of the negative electrode active material, in one embodiment, based on the total amount of non-aqueous solvent, the non-aqueous solvent may contain 0.1% or more by mass, 1% or more by mass, 10% or more by mass, 15% or more by mass, or 20% or more by mass of vinylene carbonate, more preferably consisting only of vinylene carbonate.

[0074] From the viewpoint of being able to properly control the formation and disappearance of SEI on the surface of the negative electrode active material, in one embodiment, based on the total amount of non-aqueous solvent, the non-aqueous solvent may contain 0.1% or more, 1% or more, 10% or more, 15% or more, or 20% or more of fluoroethylene carbonate, more preferably composed only of fluoroethylene carbonate.

[0075] From the viewpoint of being able to appropriately control the formation and disappearance of SEI on the surface of the negative electrode active material, in one embodiment, based on the total amount of non-aqueous solvent, the non-aqueous solvent may contain at least one selected from the group consisting of 12-crown ether-4, 18-crown ether-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol, and diaminohexane, more preferably, only at least one of these.

[0076] In one embodiment, the negative electrode electrolyte filling portion 10 may not contain non-aqueous solvents suitable only for the aforementioned negative electrode electrolyte (not suitable for the positive electrode electrolyte). In another embodiment, based on the total amount of non-aqueous solvents contained in the negative electrode electrolyte filling portion 10, the content of non-aqueous solvents suitable only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte) may be 0.1% by mass or less.

[0077] As described above, in the secondary battery 1 according to this embodiment, a positive electrode electrolyte filling section 9 and a negative electrode electrolyte filling section 10 are independently provided. Therefore, a non-aqueous solvent suitable only for the negative electrode electrolyte can be used in the negative electrode electrolyte filling section 10, and a non-aqueous solvent suitable only for the positive electrode electrolyte can be omitted. As a result, the formation of a film called SEI on the surface of the negative electrode active material is suppressed to a minimum. SEI is a factor that affects the life characteristics of the secondary battery. During repeated charge / discharge cycles, SEI grows, thereby increasing the battery resistance and potentially preventing the output of the initial capacity. Therefore, by using a non-aqueous solvent that can suppress the formation of SEI only in the negative electrode electrolyte, the reduction resistance of the negative electrode electrolyte can be improved, thereby further improving the life of the secondary battery 1.

[0078] The negative electrode electrolyte filling section 10 may also contain a conductive material. The conductive material may be the same as the conductive material described as included in the positive electrode electrolyte filling section 9. The content of the conductive material may be 5 parts by mass or more and 50 parts by mass or less, relative to the total mass of 100 parts by mass of the negative electrode active material, non-aqueous solvent and conductive components included in the negative electrode electrolyte filling section 10.

[0079] In the secondary battery described above, the conductive component ensures conductivity between the negative electrode current collector 7 and the electrolyte layer 8, and the negative electrode active material in the negative electrode electrolyte filling section 10 coexists with the negative electrode electrolyte while remaining in the conductive component, thereby enabling the secondary battery to operate. Furthermore, in this secondary battery, the negative electrode active material is held in the conductive component, so even if the negative electrode active material containing silicon, tin, or aluminum as constituent elements is micronized due to the charging / discharging of the secondary battery, the negative electrode active material is easily captured in the mesh structure of the conductive component and can continue to function as a negative electrode active material.

[0080] On the other hand, in conventional secondary batteries where the negative electrode active material is held on the negative electrode current collector 7, if the negative electrode active material becomes micronized due to the charging / discharging of the secondary battery, the negative electrode active material will fall off from the negative electrode current collector 7, and the electrode containing the negative electrode active material will not be able to function, so the discharge capacity of the secondary battery may be reduced.

[0081] Therefore, in this secondary battery 1, the negative electrode active material is not fixed to the negative electrode current collector 7 by the binder material, but is dispersed in the negative electrode electrolyte. Therefore, compared with conventional secondary batteries in which the negative electrode active material is held on the negative electrode current collector, the reduction in discharge capacity caused by the micronization of the negative electrode active material can be suppressed.

[0082] Furthermore, this secondary battery separately includes a positive electrode electrolyte filling section 9 and a negative electrode electrolyte filling section 10, thus allowing the use of electrolytes with compositions suitable for each electrode individually as the positive and negative electrode electrolytes. On the other hand, in conventional secondary batteries that use a common electrolyte for both the positive and negative electrodes, for example, when a component suitable for the negative electrode is added to the electrolyte, if that component is not suitable for the positive electrode, its addition amount is limited, thus preventing a decrease in the overall performance of the secondary battery. Therefore, in the secondary battery of this embodiment, which does not have this limitation, the performance of the secondary battery can be improved compared to conventional secondary batteries that use a common electrolyte for both the positive and negative electrodes.

[0083] Example

[0084] The present invention will be specifically described below using examples, but the present invention is not limited to the examples.

[0085] [Example 1]

[0086] (Making a secondary battery)

[0087] A positive electrode electrolyte was prepared by dispersing 50 parts by weight of lithium cobalt oxide and 20 parts by weight of acetylene black in 30 parts by weight of acetonitrile (dehydration grade, manufactured by FUJIFILM Wako Pure Chemical Corporation) and 3 parts by weight of LiBF4 (manufactured by Kishida Chemical Co., Ltd.) using a ball mill. Meanwhile, a negative electrode electrolyte was prepared by dispersing 50 parts by weight of Si (manufactured by Aldrich, nano-silicon (below 100 nm)) and 20 parts by weight of acetylene black in 30 parts by weight of 1-methyl-2-pyrrolidone (dehydration grade, manufactured by FUJIFILM Wako Pure Chemical Corporation) and 3 parts by weight of LiBF4 using a ball mill.

[0088] An electrolyte layer (manufactured by DowDuPont, Inc., trade name Nafion212) measuring 10cm × 10cm was prepared. Carbon felt (manufactured by AvCarb Material Solutions, AvCarb G100 SoftGraphite Battery Felt) was placed on both surfaces of the electrolyte layer as conductive components. Next, a 20μm thick aluminum foil (positive current collector) was placed on the conductive component on one surface of the electrolyte layer, and a 20μm thick copper foil (negative current collector) was placed on the conductive component on the other surface, thus obtaining a laminate. Then, the aforementioned positive electrolyte was injected between the positive current collector and the electrolyte layer, and the aforementioned negative electrolyte was injected between the negative current collector and the electrolyte layer. The laminate was then hot-pressed at 40°C. The laminate was sealed by covering it with an aluminum laminated bag (outer casing) with a portion of the positive and negative current collectors protruding outwards, thereby obtaining a secondary battery.

[0089] (Evaluation of secondary batteries)

[0090] The obtained secondary battery was charged to 4.2V at 25°C with a current equivalent to 0.1C, and then discharged to 2.5V with a current equivalent to 0.1C. The initial (first cycle) discharge capacity X was measured. After two cycles of this charge and discharge, 100 cycles of charging and discharging with a current equivalent to 0.5C were performed. The discharge capacity Y after 100 cycles was measured, and the capacity retention rate (=Y / X×100(%)) was calculated, which was 91%.

[0091] [Example 2]

[0092] <Example 2-1>

[0093] (Making a secondary battery)

[0094] Using a ball mill to process LiNi 0.5 Mn 1.5 A positive electrode electrolyte was prepared by dispersing 50 parts by weight of O2 and 20 parts by weight of acetylene black in 30 parts by weight of acetonitrile (dehydrated grade) and 3 parts by weight of LiBF4 (manufactured by Kishida Chemical Co., Ltd.). Meanwhile, a negative electrode electrolyte was prepared by dispersing 50 parts by weight of Si (manufactured by Aldrich, nano-silicon (below 100 nm)) and 20 parts by weight of acetylene black in 1,2-dimethoxyethane (manufactured by Kishida Chemical Co., Ltd.) and 3 parts by weight of LiBF4 using a ball mill.

[0095] Lithium-ion conductive glass (manufactured by OHARA Inc., LICGC) was prepared as the electrolyte layer. Carbon felt (AvCarb G100 Soft Graphite Battery Felt manufactured by AvCarb Material Solutions) was disposed on both surfaces of the electrolyte layer as conductive components. Next, a 20 μm thick aluminum foil (positive current collector) was disposed on the conductive component on one surface of the electrolyte layer, and a 20 μm thick copper foil (negative current collector) was disposed on the conductive component on the other surface, thus obtaining a laminate. Then, the aforementioned positive electrolyte was injected between the positive current collector and the electrolyte layer, and the aforementioned negative electrolyte was injected between the negative current collector and the electrolyte layer, and the laminate was hot-pressed at 40°C. The laminate was covered with an aluminum laminate bag (outer casing) with a portion of the positive and negative current collectors protruding outwards. Then, a glass plate was sandwiched between the two surfaces, and an external pressure of 0.3 MPa was applied to seal it, thereby obtaining a secondary battery.

[0096] (Evaluation of secondary batteries)

[0097] The obtained secondary battery was charged to 5.0V at 25°C with a current equivalent to 0.1C, and then discharged to 3.0V with a current equivalent to 0.1C. The initial (first cycle) discharge capacity X was measured. After two cycles of this charge and discharge, 100 cycles of charging and discharging with a current equivalent to 0.5C were performed. The discharge capacity Y after 100 cycles was measured, and the discharge capacity retention rate (=Y / X×100(%)) was calculated, which was 91%.

[0098] <Examples 2-2 to 2-9>

[0099] (Making and evaluating secondary batteries)

[0100] Except for changing the solvents of the positive and negative electrode electrolytes to those shown in Table 1, the secondary battery was fabricated and evaluated in the same manner as in Example 2-1. Furthermore, the electrolyte solvent was used after dehydration treatment as needed. The capacity retention results are shown in Table 1.

[0101] [Table 1]

[0102]

[0103] Based on the above confirmation, the secondary battery (a secondary battery using a negative electrode active material containing silicon, tin or aluminum as constituent elements) according to one aspect of the present invention can suppress the reduction of discharge capacity.

[0104] Symbol Explanation

[0105] 1-Secondary battery, 2-Electrode assembly, 3-Battery casing, 4-Positive current collector, 5-Negative current collector, 6-Positive current collector, 7-Negative current collector, 8-Electrolyte layer, 9-Positive electrolyte filling part, 10-Negative electrolyte filling part.

Claims

1. A secondary battery comprising: a positive electrode current collector; a negative electrode current collector; an electrolyte layer disposed between the positive electrode current collector and the negative electrode current collector; a positive electrode electrolyte filling portion divided by the positive electrode current collector and the electrolyte layer; and a negative electrode electrolyte filling portion divided by the negative electrode current collector and the electrolyte layer, the positive electrode electrolyte filling portion comprising: a positive electrode active material comprising a lithium oxide and / or a lithium phosphate; an electrolyte salt; and a first nonaqueous solvent dissolving the electrolyte salt, the negative electrode electrolyte filling portion comprising: a conduction member disposed in a manner to make the negative electrode current collector and the electrolyte layer conductive and having a network structure; a negative electrode active material held in the conduction member; an electrolyte salt; and a second nonaqueous solvent dissolving the electrolyte salt, the negative electrode active material containing at least one selected from the group consisting of silicon, tin, and aluminum as a constituent element, the first nonaqueous solvent containing 10% by mass or more of at least one selected from the group consisting of tris(2,2,2-trifluoroethyl) phosphate, acetonitrile, adiponitrile, chloroethylene carbonate, nitromethane, and ethylene carbonate, based on the total amount of the first nonaqueous solvent, the second nonaqueous solvent containing 10% by mass or more of at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, ethyl heptanoate, tetrahydrofuran, and ethylene glycol bis(propionitrile) ether, based on the total amount of the second nonaqueous solvent, and the first nonaqueous solvent being different from the second nonaqueous solvent.

2. The secondary battery according to claim 1, wherein the conduction member is formed of a carbon material.

3. The secondary battery according to claim 1 or 2, wherein the second nonaqueous solvent contains 10% by mass or more of fluoroethylene carbonate, based on the total amount of the second nonaqueous solvent.

4. The secondary battery according to claim 1 or 2, wherein the second nonaqueous solvent contains 10% by mass or more of vinylene carbonate, based on the total amount of the second nonaqueous solvent.

5. The secondary battery according to claim 1 or 2, wherein the negative electrode active material contains 10% by mass or more of silicon as a constituent element, based on the total amount of the negative electrode active material.

6. The secondary battery according to claim 1 or 2, wherein the negative electrode active material contains 10% by mass or more of tin as a constituent element, based on the total amount of the negative electrode active material.

7. The secondary battery according to claim 1 or 2, wherein the negative electrode active material contains 10% by mass or more of aluminum as a constituent element, based on the total amount of the negative electrode active material.

8. The secondary battery according to claim 1 or 2, wherein the positive electrode electrolyte filling portion comprises a conduction member disposed in a manner to make the positive electrode current collector and the electrolyte layer conductive and having a network structure, and the positive electrode active material is held in the conduction member.

9. The secondary battery according to claim 8, wherein the content of fluoroethylene carbonate in the positive electrode electrolyte filling portion is 0.1% by mass or less, based on the total amount of the first nonaqueous solvent. ​ ​ ​ ​ ​ ​ ​ wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 10. The secondary battery according to claim 8, wherein The positive electrode electrolyte filling portion does not contain fluoroethylene carbonate.

11. The secondary battery according to claim 8, wherein The content of the vinylene carbonate in the positive electrode electrolyte filling portion is 0.1 mass% or less based on the total amount of the first nonaqueous solvent.

12. The secondary battery according to claim 8, wherein The positive electrode electrolyte filling portion does not contain vinylene carbonate.

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