Secondary battery

Abstract

This secondary battery is provided with: a positive electrode collector; a negative electrode collector; an electrolyte layer disposed between the positive electrode collector and the negative electrode collector; a positive electrode electrolyte solution reservoir demarcated by the positive electrode collector and the electrolyte layer; and a negative electrode electrolyte solution reservoir demarcated by the negative electrode collector and the electrolyte layer. The negative electrode solution reservoir comprises: a conduction member that has a mesh structure and is disposed such that the negative electrode collector and the electrolyte layer are conductive; a negative electrode active substance supported by the communicating member; an electrolyte salt; and a nonaqueous solvent that dissolves the electrolyte salt. The negative electrode active substance contains at least one constituent element selected from the group consisting of silicon, tin, and aluminum.

Description

[Technical field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] In recent years, further improvements in performance are being demanded for secondary batteries, such as lithium-ion secondary batteries, due to the widespread use of portable electronic devices, electric vehicles, etc. For example, Patent Document 1 discloses a lithium-ion secondary battery having a negative electrode containing a silicon material, which is a high-capacity negative electrode active material, and which exhibits good cycle characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 221346 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a negative electrode active material containing silicon as a constituent element is used, as described in Patent Document 1, the negative electrode active material expands and contracts greatly during charging and discharging of the secondary battery, so that the negative electrode active material is likely to pulverize (disintegrate). In addition, when a negative electrode active material containing tin or aluminum as a constituent element is used, the same phenomenon is likely to occur. As a result, the negative electrode active material falls off the negative electrode, and the discharge capacity of the secondary battery may decrease.

[0005] Therefore, an object of one aspect of the present invention is to suppress a decrease in discharge capacity in a secondary battery using a negative electrode active material containing silicon, tin, or aluminum as a constituent element. [Means for solving the problem]

[0006] One aspect of the present invention is 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 filled portion partitioned by the positive electrode current collector and the electrolyte layer, and a negative electrode electrolyte filled portion partitioned by the negative electrode current collector and the electrolyte layer, wherein the negative electrode electrolyte filled portion includes a conductive member having a mesh structure disposed so as to provide electrical continuity between the negative electrode current collector and the electrolyte layer, a negative electrode active material held in the conductive member, an electrolyte salt, and a nonaqueous solvent that dissolves the electrolyte salt, and the negative electrode active material contains at least one element selected from the group consisting of silicon, tin, and aluminum.

[0007] In this secondary battery, the conductive member ensures conduction between the negative electrode current collector and the electrolyte layer, while the negative electrode active material is held by the conductive member and coexists with the negative electrode electrolyte in the negative electrode electrolyte filling section, so that the secondary battery operates as a secondary battery. In this secondary battery, since the negative electrode active material is held by the conductive member, even if the negative electrode active material containing silicon, tin, or aluminum as a constituent element is pulverized by charging and discharging the secondary battery, the negative electrode active material is easily captured by the mesh structure of the conductive member and can continue to function as the negative electrode active material. Therefore, in this secondary battery, the decrease in discharge capacity due to pulverization of the negative electrode active material can be suppressed compared to conventional secondary batteries in which the negative electrode active material is held on the negative electrode current collector.

[0008] In addition, since this secondary battery has a positive electrode electrolyte filling section and a negative electrode electrolyte filling section, electrolytes having compositions suitable for the respective electrodes can be used separately as the positive electrode electrolyte and the negative electrode electrolyte, and therefore the performance of the secondary battery can be improved compared to conventional secondary batteries that use a common electrolyte for the positive and negative electrodes.

[0009] The conductive member may be made of a carbon material.

[0010] The non-aqueous solvent may contain 10 mass % or more of fluoroethylene carbonate based on the total amount of the non-aqueous solvent, or may consist solely of fluoroethylene carbonate.

[0011] The non-aqueous solvent may contain 10 mass % or more of vinylene carbonate based on the total amount of the non-aqueous solvent, or may consist solely of vinylene carbonate.

[0012] The non-aqueous solvent may contain at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol, and diaminohexane in an amount of 10 mass% or more based on the total amount of the non-aqueous solvent, or may consist of only at least one of these.

[0013] The negative electrode active material may contain, as a constituent element, 10% by mass or more of silicon based on the total amount of the negative electrode active material.The negative electrode active material may contain, as a constituent element, 10% by mass or more of tin based on the total amount of the negative electrode active material.The negative electrode active material may contain, as a constituent element, 10% by mass or more of aluminum based on the total amount of the negative electrode active material.

[0014] The positive electrode electrolyte filling section may include a conductive member having a mesh structure arranged so as to electrically connect the positive electrode current collector and the electrolyte layer, a positive electrode active material held in the conductive member, an electrolyte salt, and a nonaqueous solvent that dissolves the electrolyte salt.

[0015] The nonaqueous solvent contained in the positive electrode electrolyte filling portion may be different from the nonaqueous solvent contained in the negative electrode electrolyte filling portion.

[0016] The content of fluoroethylene carbonate in the positive electrolyte filling portion may be 0.1 mass % or less based on the total amount of the nonaqueous solvent contained in the positive electrolyte filling portion. The positive electrolyte filling portion does not need to contain fluoroethylene carbonate.

[0017] The content of vinylene carbonate in the positive electrode electrolyte filling portion may be 0.1 mass % or less based on the total amount of the nonaqueous solvent contained in the positive electrode electrolyte filling portion. The positive electrode electrolyte filling portion does not need to contain vinylene carbonate. Effect of the Invention

[0018] 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, a decrease in discharge capacity can be suppressed. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a perspective view showing a secondary battery according to one embodiment. [Diagram 2] Fig. 2 is a cross-sectional view taken along the line II-II in Fig. 1. Fig. 2(a) is a schematic cross-sectional view showing one embodiment of a secondary battery, and Fig. 2(b) is a schematic cross-sectional view showing another embodiment of the secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiment.

[0021] FIG. 1 is a perspective view showing a secondary battery according to an embodiment. As shown in FIG. 1, the secondary battery 1 according to an embodiment is a so-called laminate type secondary battery including an electrode group 2 and a bag-shaped battery exterior body 3 that houses the electrode group 2. The electrode group 2 is provided with a positive electrode current collector tab 4 and a negative electrode current collector tab 5. The positive electrode current collector tab 4 and the negative electrode current collector tab 5 protrude from the inside to the outside of the battery exterior body 3 so that a positive electrode current collector and a negative electrode current collector (described in detail later) can be electrically connected to the outside of the secondary battery 1, respectively. In another embodiment, the secondary battery 1 may be a secondary battery having a shape other than the laminate type (such as a coin type or a cylindrical type).

[0022] The battery exterior body 3 may be, for example, a container formed of a laminated film. The laminated film may be, for example, a laminated film in which a polymer film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

[0023] Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. As shown in Fig. 2, the secondary battery 1 includes, within a battery exterior case 3, a positive electrode current collector 6, a negative electrode current collector 7, an electrolyte layer 8 disposed between the positive electrode current collector 6 and the negative electrode current collector 7, a positive electrode electrolyte filling section 9 partitioned by the positive electrode current collector 6 and the electrolyte layer 8, and a negative electrode electrolyte filling section 10 partitioned by the negative electrode current collector 7 and the electrolyte layer 8.

[0024] The battery exterior body 3 is sealed so that the positive electrode electrolyte and the negative electrode electrolyte do not leak out from the positive electrode electrolyte filling portion 9 and the negative electrode electrolyte filling portion 10, respectively. In one embodiment, as shown in Fig. 2(a), the positive electrode current collector 6 and the negative electrode current collector 7 may be entirely housed inside the battery exterior body 3. In another embodiment, as shown in Fig. 2(b), both end portions of the positive electrode current collector 6 and the negative electrode current collector 7 may protrude outside the battery exterior body 3.

[0025] The positive electrode current collector 6 is formed of, for example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, etc. The thickness of the positive electrode current collector 6 may be, for example, 1 μm or more and 50 μm or less.

[0026] The negative electrode current collector 7 is formed of, for example, copper, stainless steel, nickel, aluminum, titanium, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The thickness of the negative electrode current collector 7 may be, for example, 1 μm or more and 50 μm or less.

[0027] The electrolyte layer 8 is a layer that allows permeation of cations (e.g., lithium cations) derived from the electrolyte salt contained in the positive electrode electrolyte filling section 9 and the negative electrode electrolyte filling section 10, while not allowing permeation of components other than the active materials (positive electrode active material and negative electrode active material) and cations (e.g., the nonaqueous solvent) contained in the positive electrode electrolyte filling section 9 and the negative electrode electrolyte filling section 10. The electrolyte layer 8 may be, for example, a nonporous electrolyte layer 8 (electrolyte layer 8 having no pores). The thickness of the electrolyte layer 8 is preferably 1 μm or more from the viewpoint of obtaining excellent strength, and is preferably 500 μm or less from the viewpoint of reducing the resistance of ion conduction in the electrolyte layer 8 and thus reducing the resistance of the secondary battery 1.

[0028] Such an electrolyte layer 8 may be a solid electrolyte material exhibiting lithium ion conductivity, and may be formed, for example, of an oxide-based solid electrolyte or a polymer. In one embodiment, the electrolyte layer 8 may be, for example, a perfluorosulfonic acid-based ion exchange membrane. The perfluorosulfonic acid-based ion exchange membrane is, for example, composed of a polymer having a structural unit represented by the following formula (1).

[0029] [ka] [In the formula, x represents an integer of 1 to 20, y represents an integer of 1 to 1000, m represents 0 or 1, n represents an integer of 1 to 10, and X represents a hydrogen atom, an alkali metal atom, or an alkaline earth metal atom.]

[0030] Such polymers can be synthesized, for example, by known methods, or can be purchased commercially as Nafion (registered trademark, manufactured by DowDuPont), Dow membrane (manufactured by DowDuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), or Flemion (registered trademark, manufactured by AGC Corporation).

[0031] 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(p-phenylene). These polymers are preferably used after ion exchange.

[0032] A conductive member is disposed in the positive electrolyte filling portion 9 so as to provide electrical continuity between the positive electrode current collector 6 and the electrolyte layer 8. The conductive member has a mesh structure. The conductive member may be provided in a portion of the positive electrolyte filling portion 9, or may be provided so as to fill the entire positive electrolyte filling portion 9. The thickness of the positive electrolyte filling portion 9 may be, for example, 5 μm or more and 2000 μm or less.

[0033] The conductive member may be, for example, in the form of a sheet. The conductive member is made of a conductive material. Examples of the conductive material include a carbon material, a metal material, and a conductive polymer material.

[0034] Examples of carbon materials include carbon black, graphite, soft carbon, hard carbon, carbon nanotubes, carbon nanofibers, graphene, carbon nanohorns, glassy carbon, and expanded graphite.

[0035] Examples of metal materials include nickel, aluminum, copper, stainless steel, gold, and silver.

[0036] Examples of the conductive polymer material include materials obtained by doping a polymer compound such as polyacetylene, poly(p-phenylene vinylene), polypyrrole, polythiophene, polyaniline, and poly(p-phenylene sulfide). The doping method is not particularly limited, and may be a method of adding a compound such as an electron acceptor (acceptor) such as iodine or arsenic pentafluoride, or an electron donor (donor) such as an alkali metal, to the polymer compound.

[0037] In one embodiment, a member previously formed into a mesh structure may be used as the conductive member. Examples of such conductive members include conductive members made of carbon materials such as carbon felt, carbon paper, and carbon cloth, and conductive members made of metal materials such as punched metal (metal plate with a mesh structure formed by punching).

[0038] Positive electrode electrolyte filling section 9 contains a positive electrode electrolyte, and specifically, for example, contains a positive electrode active material, an electrolyte salt, and a non-aqueous solvent.

[0039] In the positive electrode electrolyte filling section 9, the positive electrode active material is preferably present in a state of being dispersed in the positive electrode electrolyte (non-aqueous solvent). In other words, the positive electrode active material is preferably not held (fixed) on the positive electrode current collector 6, and the positive electrode electrolyte filling section 9 preferably does not include a binder for holding (fixing) the positive electrode active material on the positive electrode current collector 6.

[0040] The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxide 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 z , Li 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 (provided that M is an element different from other elements in each formula), x=0 to 1.2, y=0 to 0.9, and z=2.0 to 2.3). x Ni 1-yM y O z Lithium oxide represented by Li x Ni 1-(y1+y2) Co y1 Mn y2 O z (wherein x and z are the same as those described above, y1 = 0 to 0.9, y2 = 0 to 0.9, and y1 + y2 = 0 to 0.9), for example, 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 Li x Ni 1-y M y O z Lithium oxide represented by Li x Ni 1-(y3+y4) Co y3 Al y4 O z (wherein x and z are the same as those described above, y3=0 to 0.9, y4=0 to 0.9, and y3+y4=0 to 0.9), for example, LiNi 0.8 Co 0.15 Al 0.05 It may be O2.

[0041] The positive electrode active material may be, for example, a lithium phosphate. Examples of lithium phosphate include lithium manganese phosphate (LiMnPO4), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), and lithium vanadium phosphate (Li3V2(PO4)3).

[0042] The content of the positive electrode active material may be 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the total of the positive electrode active material, nonaqueous solvent, and conductive member contained in positive electrode electrolyte filling portion 9.

[0043] The electrolyte salt may be, for example, a lithium salt. The lithium salt may 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 bisfluorosulfonylimide), LiN(SO2CF3)2 (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO2CF2CF3)2.

[0044] 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 1.5 mol / L or less, 1.3 mol / L or less, or 1.2 mol / L or less, based on the total amount of the non-aqueous solvent.

[0045] The nonaqueous solvent is a solvent capable of dissolving the electrolyte salt contained in the positive electrode electrolyte filling section 9. Examples of the nonaqueous solvent include nonaqueous solvents that can be suitably used for both the positive electrode electrolyte and the negative electrode electrolyte, and nonaqueous solvents that can be suitably used only for the positive electrode electrolyte (not suitable for the negative electrode electrolyte). The nonaqueous solvents may be used alone or in combination of two or more.

[0046] The non-aqueous solvent suitable for use in both the positive electrode electrolyte and the negative electrode electrolyte may be, for example, an aprotic solvent suitable for both the positive electrode electrolyte and the negative electrode electrolyte, such as diethyl carbonate, dimethyl ether, diethyl ether, dioxolane, 4-methyldioxolane, sulfolane, dimethyl sulfoxide, propionitrile, benzonitrile, N,N-dimethylacetamide, and diethylene glycol.

[0047] A non-aqueous solvent that can be used only for the positive electrode electrolyte (not for the negative electrode electrolyte) may be a solvent that has excellent oxidation resistance but does not have excellent reduction resistance (when contained in the negative electrode electrolyte, decomposition is promoted, increasing the coating resistance). Examples of such solvents include ethylene carbonate, hexafluoroisopropyl-ethylene carbonate, trans-difluoroethylene carbonate, cis-difluoroethylene carbonate, trishexafluoroisopropyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, acetonitrile, succinonitrile, glutaronitrile, adiponitrile, chloroethylene carbonate, nitromethane, and the like. Among these, the nonaqueous solvent that can be suitably used only for the positive electrode electrolyte (not suitable for the negative electrode electrolyte) may be at least one selected from the group consisting of tris(2,2,2-trifluoroethyl)phosphate, acetonitrile, succinonitrile, adiponitrile, chloroethylene carbonate, nitromethane, and ethylene carbonate.

[0048] The content of the nonaqueous solvent that can be suitably used for both the positive electrode electrolyte and the negative electrode electrolyte may be 1 mass % or more, 3 mass % or more, or 5 mass % or more, and may be 95 mass % or less, 90 mass % or less, or 80 mass % or less, based on the total amount of the nonaqueous solvent contained in positive electrode electrolyte filling section 9. The content of the nonaqueous solvent that can be suitably used only for the positive electrode electrolyte (not suitable for the negative electrode electrolyte) may be 0.1 mass % or more, 1 mass % or more, 10 mass % or more, 15 mass % or more, or 20 mass % or more, and may be 100 mass % or less, 95 mass % or less, or 90 mass % or less, based on the total amount of the nonaqueous solvent contained in positive electrode electrolyte filling section 9.

[0049] In one embodiment, the positive electrode electrolyte filling section 9 may not contain a nonaqueous solvent that is suitable for use only with the negative electrode electrolyte (not suitable for the positive electrode electrolyte) described below. In one embodiment, the positive electrode electrolyte filling section 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-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane. In another embodiment, the content of at least one selected from the group consisting of a nonaqueous solvent that can be suitably used only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte), fluoroethylene carbonate, vinylene carbonate, or 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane, may be 0.1 mass % or less based on the total amount of the nonaqueous solvent contained in positive electrode electrolyte filling portion 9.

[0050] As described above, in the secondary battery 1 according to this embodiment, the positive electrode electrolyte filling section 9 and the negative electrode electrolyte filling section 10 are provided independently, so that a nonaqueous solvent that is suitable only for the positive electrode electrolyte can be used in the positive electrode electrolyte filling section 9, and it is not necessary to use a nonaqueous solvent that is suitable only for the negative electrode electrolyte. As a result, the characteristics of the entire secondary battery 1 can be further improved.

[0051] The positive electrode electrolyte filling section 9 may further include a conductive material. The conductive material may be, for example, a carbon material such as carbon black, such as acetylene black or ketjen black, graphite, graphene, carbon nanotubes, or carbon nanofibers. These conductive materials may be dispersed in the positive electrode electrolyte to form an electronic conductive network. The conductive material is preferably in a particulate form, and more preferably in a bulky particulate form. The content of the conductive material may be 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the total mass of the positive electrode active material, the nonaqueous solvent, and the conductive member contained in the positive electrode electrolyte filling section 9.

[0052] A conductive member is disposed in the negative electrolyte filling section 10 so as to electrically connect the negative electrode current collector 7 and the electrolyte layer 8. The conductive member has a mesh structure. The conductive member may be provided in a part of the negative electrolyte filling section 10, or may be provided so as to fill the entire negative electrolyte filling section 10. The thickness of the negative electrolyte filling section 10 may be, for example, 5 μm or more and 2000 μm or less. The conductive member in the negative electrolyte filling section 10 may be the same as that described as the conductive member in the positive electrolyte filling section 9.

[0053] The negative electrode electrolyte filling section 10 contains a negative electrode electrolyte, and specifically, for example, contains a negative electrode active material, an electrolyte salt, and a non-aqueous solvent.

[0054] The negative electrode active material is preferably present in a state dispersed in the negative electrode electrolyte (nonaqueous solvent) in the negative electrode electrolyte filling section 10. In other words, the negative electrode active material is preferably not held (fixed) on the negative electrode current collector 7, and the negative electrode electrolyte filling section 10 preferably does not include a binder for holding (fixing) the negative electrode active material on the negative electrode current collector 7.

[0055] The negative electrode active material contains at least one element selected from the group consisting of silicon, tin, and aluminum. The silicon content may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, and 100% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the negative electrode active material. The tin content may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, and 100% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the negative electrode active material. The aluminum content may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, and 100% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the negative electrode active material.

[0056] The negative electrode active material containing silicon as a constituent element may contain silicon alone or a compound containing silicon as a constituent element (silicon-containing compound).The negative electrode active material containing tin as a constituent element may contain tin alone or a compound containing tin as a constituent element (tin-containing compound).

[0057] The silicon-containing compound or the tin-containing compound may be, for example, an alloy (silicon alloy or tin alloy) containing silicon or tin and at least one selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as a constituent element. The silicon-containing compound or the tin-containing compound may be an oxide, a nitride, or a carbide. 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.

[0058] The negative electrode active material containing aluminum as a constituent element may be, for example, an aluminum alloy such as a lithium aluminum alloy.

[0059] The content of the negative electrode active material may be 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the total of the negative electrode active material, nonaqueous solvent, and conductive member contained in the negative electrode electrolyte filling portion 10.

[0060] 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. 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, based on the total amount of the nonaqueous solvent.

[0061] The nonaqueous solvent is a solvent capable of dissolving the electrolyte salt contained in the negative electrode electrolyte filling section 10. Examples of the nonaqueous solvent include nonaqueous solvents that can be suitably used for both the positive electrode electrolyte and the negative electrode electrolyte, and nonaqueous solvents that can be suitably used only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte). The nonaqueous solvents may be used alone or in combination of two or more.

[0062] A nonaqueous solvent that can be suitably used only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte) may be a solvent that has excellent resistance to reduction but does not have excellent resistance to oxidation (when contained in a positive electrode electrolyte (particularly, a positive electrode electrolyte using a 4V-based positive electrode such as lithium cobalt oxide as the positive electrode active material), oxidative decomposition is promoted, resulting in an increase in resistance).

[0063] Examples of non-aqueous solvents that can be suitably used only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte) include γ-butyrolactone, ethyl acetate, ethyl pentanoate, dimethyl malonate, diethyl malonate, diethyl methylmalonate, diethyl succinate, diethyl glutarate, diethyl azelate, ethyl heptanoate, heptanoic acid, tetrahydrofuran, 1,2-dimethoxyethane, ethyl propyl 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] , 12-crown-4, 18-crown-6, taurine, N-methyltaurine, 2-(methylamino)ethanol, diaminohexane, methylenebis(2-chloroaniline), 1-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, N,N-dimethylformacetamide, N-methyl-piperazine, trimethylamine, triethylamine, N,N-dimethylpropylamine, dimethylformamide, diethylformamide, 1,1,3,3-tetramethylurea, N,N-dimethyl-propyleneurea, cyclohexane, piperidine, cyclopentane, decahydronaphthalene, tetrahydronaphthalene, pyrrolidine, quinoline, 3-pyrroline, and the like. Among these, the nonaqueous solvent that can be suitably used only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte) may be at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile) ether, 2-(methylamino)ethanol, and diaminohexane.

[0064] In addition, examples of non-aqueous solvents suitable for use only in the negative electrode electrolyte (not suitable for the positive electrode electrolyte) include vinylene carbonate, propane sultone, 1,4-butane sultone, 1,3-propene sultone, ethyl methane sultone, ethylene sulfite, trifluoromethane ethylene carbonate, fluorobenzene, fluoroethylene carbonate, etc. Among these, the non-aqueous solvent suitable for use only in the negative electrode electrolyte (not suitable for the positive electrode electrolyte) may be vinylene carbonate or fluoroethylene carbonate.

[0065] The content of the nonaqueous solvent that can be suitably used for both the positive electrode electrolyte and the negative electrode electrolyte may be 1 mass % or more, 3 mass % or more, or 5 mass % or more, and may be 95 mass % or less, 90 mass % or less, or 80 mass % or less, based on the total amount of the nonaqueous solvent contained in the negative electrode electrolyte filling section 10. The content of the nonaqueous solvent that can be suitably used only for the negative electrode electrolyte (not suitable for the positive electrode electrolyte) may be 0.1 mass % or more, 1 mass % or more, 10 mass % or more, 15 mass % or more, or 20 mass % or more, and may be 100 mass % or less, 95 mass % or less, or 90 mass % or less, based on the total amount of the nonaqueous solvent contained in the negative electrode electrolyte filling section 10.

[0066] From the viewpoint of more suitably controlling the formation of a coating called a solid-electrolyte-interface (SEI) on the surface of the negative electrode active material, in one embodiment, the nonaqueous solvent contains 0.1 mass % or more, 1 mass % or more, 10 mass % or more, 15 mass % or more, or 20 mass % or more of vinylene carbonate based on the total amount of the nonaqueous solvent, and more preferably may consist of only vinylene carbonate.

[0067] From the viewpoint of being able to suitably control the formation and disappearance of SEI on the surface of the negative electrode active material, in one embodiment, the nonaqueous solvent contains 0.1 mass % or more, 1 mass % or more, 10 mass % or more, 15 mass % or more, or 20 mass % or more of fluoroethylene carbonate based on the total amount of the nonaqueous solvent, and more preferably may consist of only fluoroethylene carbonate.

[0068] From the viewpoint of suitably controlling the generation and disappearance of SEI on the surface of the negative electrode active material, in one embodiment, the nonaqueous solvent contains at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane in an amount of 0.1 mass % or more, 1 mass % or more, 10 mass % or more, 15 mass % or more, or 20 mass % or more based on the total amount of the nonaqueous solvent, and more preferably may consist of only at least one of these.

[0069] In one embodiment, the negative electrode electrolyte filling section 10 does not need to contain the above-mentioned nonaqueous solvent that is suitable for use only with the negative electrode electrolyte (not suitable for the positive electrode electrolyte). In another embodiment, the content of the nonaqueous solvent that is suitable for use only with the negative electrode electrolyte (not suitable for the positive electrode electrolyte) may be 0.1 mass % or less based on the total amount of the nonaqueous solvent contained in the negative electrode electrolyte filling section 10.

[0070] As described above, in the secondary battery 1 according to this embodiment, the positive electrode electrolyte filling section 9 and the negative electrode electrolyte filling section 10 are provided independently. Therefore, in the negative electrode electrolyte filling section 10, negative electrode A non-aqueous solvent that is only suitable for the electrolyte can be used, positive electrode There is no need to use a non-aqueous solvent that is suitable only for the electrolyte. As a result, the formation of a coating called SEI on the surface of the negative electrode active material is minimized. The SEI is a factor that affects the life characteristics of a secondary battery, and the SEI grows during hundreds of repeated charge and discharge cycles, which may increase the battery resistance and make it difficult to obtain the initial capacity. Therefore, by using a non-aqueous solvent that can suppress the formation of SEI only for the negative electrode electrolyte, the reduction resistance of the negative electrode electrolyte is improved, and the life of the secondary battery 1 is further improved.

[0071] The negative electrode electrolyte filling section 10 may further include a conductive material. The conductive material may be the same as that described as the conductive material contained 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 with respect to 100 parts by mass of the total mass of the negative electrode active material, the nonaqueous solvent, and the conductive member contained in the negative electrode electrolyte filling section 10.

[0072] In the secondary battery described above, the conductive member ensures conduction between the negative electrode current collector 7 and the electrolyte layer 8, while the negative electrode active material is held by the conductive member and coexists with the negative electrode electrolyte in the negative electrode electrolyte filling section 10, thereby allowing the secondary battery to operate. In this secondary battery, since the negative electrode active material is held by the conductive member, even if the negative electrode active material containing silicon, tin, or aluminum as a constituent element is pulverized by charging and discharging the secondary battery, the negative electrode active material is likely to be captured by the network structure of the conductive member and can continue to function as the negative electrode active material.

[0073] On the other hand, in a conventional secondary battery in which the negative electrode active material is held on the negative electrode current collector 7, when the negative electrode active material is pulverized by charging and discharging the secondary battery, the negative electrode active material falls off from the negative electrode current collector 7 and the electrode containing the negative electrode active material becomes unable to function, which may result in a decrease in the discharge capacity, etc. of the secondary battery.

[0074] Therefore, in this secondary battery 1, the negative electrode active material is not fixed to the negative electrode current collector 7 via a binder, but is dispersed in the negative electrode electrolyte, so that it is possible to suppress a decrease in discharge capacity due to pulverization of the negative electrode active material, compared to conventional secondary batteries in which the negative electrode active material is held on the negative electrode current collector.

[0075] In addition, since this secondary battery is provided with the positive electrode electrolyte filling section 9 and the negative electrode electrolyte filling section 10 separately, electrolytes having compositions suitable for the respective electrodes can be used separately as the positive electrode electrolyte and the negative electrode electrolyte. On the other hand, in a conventional secondary battery using an electrolyte common to the positive and negative electrodes, for example, when a component suitable for the negative electrode is added to the electrolyte, if the component is not suitable for the positive electrode, restrictions are imposed on the amount of the electrolyte to be added so as not to deteriorate the performance of the entire secondary battery. Therefore, in the secondary battery of this embodiment, which does not have such restrictions, the performance of the secondary battery can be improved compared to a conventional secondary battery using an electrolyte common to the positive and negative electrodes. EXAMPLES

[0076] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0077] [Example 1] (Secondary battery production) A positive electrode electrolyte was prepared by dispersing 50 parts by mass of lithium cobalt oxide and 20 parts by mass of acetylene black in 30 parts by mass of acetonitrile (dehydrated grade, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 3 parts by mass of LiBF4 (manufactured by Kishida Chemical Co., Ltd.) using a ball mill. In addition, 50 parts by mass of Si (manufactured by Aldrich, nanosilicon (100 nm or less)) and 20 parts by mass of acetylene black were dispersed in 30 parts by mass of 1-methyl-2-pyrrolidinone (dehydrated grade, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 3 parts by mass of LiBF4 while pulverizing them using a bead mill, to prepare a negative electrode electrolyte.

[0078] An electrolyte layer (Dow DuPont, product name Nafion212) measuring 10 cm x 10 cm was prepared, and carbon felt (AvCarb Material Solutions, AvCarb G100 Soft Graphite Battery Felt) was placed on both sides of the electrolyte layer as a conductive member. Next, a 20 μm thick aluminum foil (positive electrode current collector) was placed on the conductive member on one side of the electrolyte layer, and a 20 μm thick copper foil (negative electrode current collector) was placed on the conductive member on the other side to obtain a laminate. Next, the above positive electrode electrolyte was injected between the positive electrode current collector and the electrolyte layer, and the above negative electrode electrolyte was injected between the negative electrode current collector and the electrolyte layer, and then the laminate was heat pressed at 40°C. The laminate was covered with an aluminum laminate bag (exterior body) so that a part of the positive electrode current collector and the negative electrode current collector protruded outward, and sealed to obtain a secondary battery.

[0079] (Evaluation of secondary batteries) At 25°C, the obtained secondary battery was charged to 4.2 V at a current equivalent to 0.1 C, and then discharged to 2.5 V at a current equivalent to 0.1 C, and the initial (first cycle) discharge capacity X was measured. After two cycles of this charge and discharge, 100 cycles of charging at a current equivalent to 0.5 C and discharging at a current equivalent to 0.5 C were performed. The discharge capacity Y after 100 cycles was measured, and the capacity retention rate (= Y / X × 100 (%)) was calculated to be 91%.

[0080] [Example 2] <Example 2-1> (Secondary battery production) LiNi 0.5 Mn 1.5 A positive electrode electrolyte was prepared by dispersing 50 parts by mass of O2 and 20 parts by mass of acetylene black in 30 parts by mass of acetonitrile (dehydrated grade) and 3 parts by mass of LiBF4 (Kishida Chemical Co., Ltd.) using a ball mill. A negative electrode electrolyte was prepared by dispersing 50 parts by mass of Si (Aldrich, nanosilicon (100 nm or less)) and 20 parts by mass of acetylene black in 30 parts by mass of 1,2-dimethoxyethane (Kishida Chemical Co., Ltd.) and 3 parts by mass of LiBF4 while pulverizing them using a bead mill.

[0081] Lithium ion conductive glass (LICGC, manufactured by OHARA Co., Ltd.) was prepared as the electrolyte layer. Carbon felt (AvCarb G100 Soft Graphite Battery Felt, manufactured by AvCarb Material Solutions) was placed on both sides of the electrolyte layer as a conductive member. Next, a 20 μm thick aluminum foil (positive electrode current collector) was placed on the conductive member on one side of the electrolyte layer, and a 20 μm thick copper foil (negative electrode current collector) was placed on the conductive member on the other side to obtain a laminate. Next, the above positive electrode electrolyte was injected between the positive electrode current collector and the electrolyte layer, and the above negative electrode electrolyte was injected between the negative electrode current collector and the electrolyte layer, and then the laminate was hot pressed at 40° C. The laminate was covered with an aluminum laminate bag (exterior body) so that a part of the positive electrode current collector and the negative electrode current collector protruded outward, and then glass plates were sandwiched on both sides, and an external pressure of 0.3 MP was applied and sealed to obtain a secondary battery.

[0082] (Evaluation of secondary batteries) At 25°C, the obtained secondary battery was charged to 5.0 V at a current equivalent to 0.1 C, and then discharged to 3.0 V at a current equivalent to 0.1 C, and the initial (first cycle) discharge capacity X was measured. After two cycles of this charge and discharge, 100 cycles of charging at a current equivalent to 0.5 C and discharging at a current equivalent to 0.5 C were performed. The discharge capacity Y after 100 cycles was measured, and the discharge capacity retention rate (= Y / X × 100 (%)) was calculated to be 91%.

[0083] <Examples 2-2 to 2-9> (Production of secondary batteries and evaluation of secondary batteries) A secondary battery was produced and evaluated in the same manner as in Example 2-1, except that the solvent of the positive electrode electrolyte and the solvent of the negative electrode electrolyte were changed to the solvents shown in Table 1. The electrolyte solvent was used after being dehydrated as necessary. The results of the capacity retention rate are shown in Table 1.

[0084] [Table 1]

[0085] From the above, it was confirmed that a secondary battery according to one aspect of the present invention (a secondary battery using a negative electrode active material containing silicon, tin, or aluminum as a constituent element) can suppress a decrease in discharge capacity. [Explanation of symbols]

[0086] Reference Signs List 1... secondary battery, 2... electrode group, 3... battery exterior, 4... positive electrode current collecting tab, 5... negative electrode current collecting tab, 6... positive electrode current collecting body, 7... negative electrode current collecting body, 8... electrolyte layer, 9... positive electrode electrolyte filling portion, 10... negative electrode electrolyte filling portion.

Claims

1. 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 partitioned by the positive electrode current collector and the electrolyte layer; a negative electrode electrolyte filling portion partitioned by the negative electrode current collector and the electrolyte layer; Equipped with The negative electrode electrolyte filling section is a conductive member having a mesh structure that is disposed so as to electrically connect the negative electrode current collector and the electrolyte layer; a negative electrode active material held by the conductive member; An electrolyte salt; a non-aqueous solvent for dissolving the electrolyte salt; Including, The negative electrode active material contains, as a constituent element, at least one element selected from the group consisting of silicon, tin, and aluminum.

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

3. 3. The secondary battery according to claim 1, wherein the non-aqueous solvent contains 10 mass % or more of fluoroethylene carbonate based on the total amount of the non-aqueous solvent.

4. 4. The secondary battery according to claim 3, wherein the non-aqueous solvent consists solely of fluoroethylene carbonate.

5. 3. The secondary battery according to claim 1, wherein the non-aqueous solvent contains 10 mass % or more of vinylene carbonate based on the total amount of the non-aqueous solvent.

6. 6. The secondary battery according to claim 5, wherein the non-aqueous solvent consists solely of vinylene carbonate.

7. The non-aqueous solvent is selected from the group consisting of γ-butyrolactone, ethyl acetate, ethyl pentanoate, dimethyl malonate, diethyl malonate, diethyl methylmalonate, diethyl succinate, diethyl glutarate, diethyl azelate, ethyl heptanoate, heptanoic acid, tetrahydrofuran, 1,2-dimethoxyethane, ethyl propyl 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, 12-crown-4, 18-crown-6, taurine, butyl ether ... amine, N-methyltaurine, 2-(methylamino)ethanol, diaminohexane, methylenebis(2-chloroaniline), 1-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, N,N-dimethylformacetamide, N-methyl-piperazine, trimethylamine, triethylamine, N,N-dimethylpropylamine, dimethylformamide, diethylformamide, 1,1,3,3-tetramethylurea, N,N-dimethyl-propylene urea, cyclohexane, piperidine, cyclopentane, decahydronaphthalene, tetrahydronaphthalene, pyrrolidine, quinoline, and 3-pyrroline. The secondary battery according to claim 1 or 2,

8. 8. The secondary battery according to claim 7, wherein the non-aqueous solvent contains at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane, in an amount of 10% by mass or more based on the total amount of the non-aqueous solvent.

9. The secondary battery according to any one of claims 1 to 8, wherein the negative electrode active material contains, as a constituent element, 10 mass% or more of silicon based on the total amount of the negative electrode active material.

10. The secondary battery according to any one of claims 1 to 9, wherein the negative electrode active material contains, as a constituent element, 10 mass% or more of tin based on the total amount of the negative electrode active material.

11. The secondary battery according to any one of claims 1 to 10, wherein the negative electrode active material contains, as a constituent element, 10 mass % or more of aluminum based on the total amount of the negative electrode active material.

12. The positive electrode electrolyte filling section is a conductive member having a mesh structure that is disposed so as to electrically connect the positive electrode current collector and the electrolyte layer; A positive electrode active material held by the conductive member; An electrolyte salt; a non-aqueous solvent for dissolving the electrolyte salt; The secondary battery according to any one of claims 1 to 11, comprising:

13. 13. The secondary battery according to claim 12, wherein the nonaqueous solvent contained in the positive electrode electrolyte filling portion is a nonaqueous solvent different from the nonaqueous solvent contained in the negative electrode electrolyte filling portion.

14. 14. The secondary battery according to claim 12, wherein the content of fluoroethylene carbonate in the positive electrode electrolyte filling portion is 0.1 mass% or less based on the total amount of the nonaqueous solvent contained in the positive electrode electrolyte filling portion.

15. The secondary battery according to any one of claims 12 to 14, wherein the positive electrode electrolyte filling section does not contain fluoroethylene carbonate.

16. The secondary battery according to any one of claims 12 to 15, wherein the content of vinylene carbonate in the positive electrode electrolyte filling portion is 0.1 mass% or less based on the total amount of the nonaqueous solvent contained in the positive electrode electrolyte filling portion.

17. The secondary battery according to any one of claims 12 to 16, wherein the positive electrode electrolyte filling section does not contain vinylene carbonate.

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