Electrodes for lithium-ion secondary batteries

Abstract

The problem this invention aims to solve is to provide an electrode for lithium-ion secondary batteries and a lithium-ion secondary battery that can suppress capacity degradation during repeated charge-discharge cycles and exhibit excellent durability in charge-discharge cycles. To solve the above problem, this invention provides an electrode for lithium-ion secondary batteries, which includes an electrode mixture layer comprising an electrode active material and a high-dielectric inorganic solid. The electrode active material has a surface portion that contacts the high-dielectric inorganic solid and a portion that contacts the electrolyte. The high-dielectric inorganic solid is a Na or Mg-based high-dielectric inorganic solid.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrode for a lithium ion secondary battery and a lithium ion secondary battery. BACKGROUND

[0002] In the past, various lithium ion secondary batteries using a lithium ion-conductive solid electrolyte have been proposed, and for example, a lithium ion secondary battery is known which contains, in a positive electrode or a negative electrode, an active material coated with a coating layer including a conductive aid and a lithium ion-conductive solid electrolyte (for example, see Patent Document 1).

[0003] The lithium ion secondary battery described in Patent Document 1, in which the active material is coated with the coating layer including the conductive aid and the lithium ion-conductive solid electrolyte in the positive electrode or the negative electrode, can reduce internal resistance, and can suppress deformation of the active material at the time of charge and discharge to prevent a decrease in charge-discharge cycle characteristics or high-rate discharge characteristics.

[0004] [PRIOR ART DOCUMENTS]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2003-59492 SUMMARY

[0007] [PROBLEMS TO BE SOLVED BY THE INVENTION]

[0008] However, in the lithium ion secondary battery described in Patent Document 1, although the aforementioned effects can be favorably obtained at the initial stage of charge-discharge cycles, there is a problem in that durability to charge and discharge sharply decreases during use.

[0009] The present application has been made to solve the above-described problems, and aims to provide an electrode for a lithium ion secondary battery and a lithium ion secondary battery which can suppress a decrease in capacity when repeating charge-discharge cycles, and can realize a lithium ion secondary battery having excellent durability to charge-discharge cycles.

[0010] [MEANS OF SOLVING THE PROBLEMS]

[0011] (1) The present application relates to an electrode for a lithium ion secondary battery, comprising an electrode mixture layer including an electrode active material and a high-dielectric inorganic solid, the electrode active material having a site in contact with the high-dielectric inorganic solid on a surface thereof and a site in contact with an electrolyte solution, and the high-dielectric inorganic solid being a Na or Mg-based high-dielectric inorganic solid.

[0012] According to the invention of (1), since Na or Mg-based high dielectric inorganic solids are chemically stable and capture solvents with a high dielectric effect, an electrode for lithium-ion secondary batteries can be provided that can suppress the rise of internal resistance during repeated charge-discharge cycles and achieve excellent durability for charge-discharge cycles.

[0013] (2) The electrode for a lithium-ion secondary battery according to (1), wherein the aforementioned high dielectric inorganic solid is disposed in the gaps between the aforementioned electrode active materials or on the surface of the particles.

[0014] According to the invention of (2), the aforementioned high dielectric inorganic solid is disposed in the gap between the aforementioned electrode active materials, thereby enabling efficient capture of electrolyte inside the electrode and further reducing internal resistance.

[0015] (3) The electrode for lithium-ion secondary batteries according to (1) or (2), wherein the aforementioned high dielectric inorganic solid is any one of oxide, fluoride, chloride, and sulfide.

[0016] According to the invention of (3), the aforementioned high dielectric inorganic solid can also be any one of oxides, fluorides, chlorides, and sulfides.

[0017] (4) The electrode for a lithium-ion secondary battery according to any one of (1) to (3), wherein the aforementioned electrode for a lithium-ion secondary battery is a negative electrode.

[0018] According to the invention of (4), when the electrode for the aforementioned lithium-ion secondary battery is a negative electrode, the charge capacity of the obtained lithium-ion secondary battery at low temperature can be increased, and the fast charging capability and durability can be improved.

[0019] (5) The electrode for lithium-ion secondary batteries according to (4), wherein the high dielectric inorganic solid of the aforementioned negative electrode is a sodium inorganic compound resistant to reduction and decomposition.

[0020] According to the invention of (5), the high dielectric inorganic solid is not easily decomposed, the solvent replenishment effect continues, and the durability of the electrode is further improved.

[0021] (6) The electrode for a lithium-ion secondary battery according to (5), wherein the aforementioned reductive sodium inorganic compound is relative to Li / Li + The equilibrium potential is 1.5 V (vs Li / Li). + The following reduction decomposition potential.

[0022] According to the invention of (6), when the aforementioned electrode for a lithium-ion secondary battery is a negative electrode, if the reduction decomposition potential of the aforementioned antioxidant lithium-ion conductive solid electrolyte is relative to Li / Li +If the equilibrium potential is above 1.5 V, the following situation can be suppressed: the constituent metal elements undergo reduction decomposition and dissolution during charging, resulting in a decrease in lithium-ion conductivity due to structural changes.

[0023] (7) The electrode for a lithium-ion secondary battery according to (5) or (6), wherein the relative permittivity of the aforementioned reductive sodium inorganic compound is 10 or more.

[0024] According to the invention of (7), due to the polarization of the aforementioned sodium inorganic compound particles resistant to reduction and decomposition, acid generated by the decomposition of fluorine anions such as PF6 or solvents can be replenished on the surface of the negative electrode graphite. If acid is formed inside the secondary battery, it will corrode the positive electrode active material. Therefore, by capturing the generated acid to suppress the corrosion of the positive electrode active material, the breakage of the active material or metal dissolution that occurs during charging and discharging can be suppressed, and the increase in the resistance of the secondary battery during charge and discharge cycles can be suppressed.

[0025] (8) The electrode for a lithium-ion secondary battery according to any one of (5) to (7), wherein the aforementioned reductive sodium inorganic compound is composed of Na 3+ x (Sb 1-x Sn x S4(0≦X≦0.1) is composed of.

[0026] According to the invention of (8), the durability of the electrode can be improved.

[0027] (9) The electrode for a lithium-ion secondary battery according to any one of (5) to (8), wherein the content of the aforementioned reductive sodium inorganic compound in the composite of the aforementioned lithium-ion secondary battery electrode is 0.1 wt% or more and 1.0 wt% or less.

[0028] According to the invention of (9), the durability of the electrode can be improved.

[0029] (10) The electrode for a lithium-ion secondary battery according to any one of (1) to (3), wherein the aforementioned electrode for a lithium-ion secondary battery is a positive electrode.

[0030] According to the invention of (10), when the aforementioned lithium-ion secondary battery electrode is a positive electrode, the output of the obtained lithium-ion secondary battery and its durability to charge-discharge cycles can be improved.

[0031] (11) The electrode for a lithium-ion secondary battery according to (10), wherein the high dielectric inorganic solid of the aforementioned positive electrode is an antioxidant sodium inorganic compound.

[0032] According to the invention of (11), the high dielectric inorganic solid is not easily decomposed, the solvent replenishment effect continues, and the durability of the electrode is further improved.

[0033] (12) The electrode for a lithium-ion secondary battery according to (11), wherein the aforementioned antioxidant decomposition sodium inorganic compound relative to Li / Li + The equilibrium potential is 4.5 V (vs Li / Li). + The oxidation decomposition potential is above 1.

[0034] According to the invention of (12), when the electrode for a lithium-ion secondary battery is a positive electrode, if the oxidation decomposition potential of the aforementioned antioxidant lithium-ion conductive solid electrolyte is relative to Li / Li + If the equilibrium potential is above 4.5 V, the following situation can be suppressed: the constituent metal elements will undergo oxidation and decomposition and dissolve during charging, and the lithium-ion conductivity will decrease due to structural changes.

[0035] (13) The electrode for a lithium-ion secondary battery according to (11) or (12), wherein the relative permittivity of the aforementioned antioxidant sodium inorganic compound is 10 or more.

[0036] According to the invention of (13), it is possible to suppress the increase in resistance of secondary batteries during charge-discharge cycles.

[0037] (14) The electrode for a lithium-ion secondary battery according to any one of (11) to (13), wherein the aforementioned antioxidant sodium inorganic compound is Na 3+ x (Sb 1-x Sn x )S4(0≦X≦0.1)、Na3Zr2Si2PO 12 At least one of them.

[0038] According to the invention of (14), the durability of the electrode can be improved.

[0039] (15) The electrode for a lithium-ion secondary battery according to any one of (11) to (14), wherein the content of the aforementioned antioxidant decomposition sodium inorganic compound in the composite of the aforementioned lithium-ion secondary battery electrode is 0.5 wt% or more and 1.0 wt% or less.

[0040] According to the invention of (15), the durability of the electrode can be improved.

[0041] (15) A lithium-ion secondary battery comprising any one of (1) to (14) an electrode for a lithium-ion secondary battery.

[0042] According to the invention of (15), a lithium-ion secondary battery with excellent durability can be obtained. Attached Figure Description

[0043] Figure 1 This is a cross-sectional view of the lithium-ion secondary battery according to this embodiment.

[0044] Figure 2 This is a schematic diagram showing the active material for a lithium-ion secondary battery according to this embodiment.

[0045] Figure 3 This is a schematic diagram illustrating the electrolyte stabilization effect of the Na-based inorganic compound in this embodiment. Detailed Implementation

[0046] Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. The content of the present invention is not limited to the description of the following embodiment.

[0047] <Lithium-ion secondary batteries>

[0048] like Figure 1 As shown, the lithium-ion secondary battery 1 of this embodiment includes: a positive electrode 4 having a positive electrode flux layer 3 formed on a positive electrode current collector 2; a negative electrode 7 having a negative electrode flux layer 6 formed on a negative electrode current collector 5; a separator 8 electrically insulating the positive electrode 4 and the negative electrode 7; an electrolyte 9; and a container 10 containing the positive electrode 4, the negative electrode 7, the separator 8 and the electrolyte 9.

[0049] Inside the container 10, the positive electrode mixture layer 3 and the negative electrode mixture layer 6 face each other in a manner that clamps the diaphragm 8, and the electrolyte 9 is stored below the positive electrode mixture layer 3 and the negative electrode mixture layer 6. Moreover, the end of the diaphragm 8 is immersed in the electrolyte 9.

[0050] (Electrode mixture layer)

[0051] The positive electrode layer 3 is composed of a positive electrode active material 11, a conductive additive, and a binder. The negative electrode layer 6 is composed of a negative electrode active material 12, a conductive additive, and a binder. Furthermore, at least one of the positive electrode layer 3 or the negative electrode layer 6 contains a highly dielectric inorganic solid 13.

[0052] When the positive electrode mixture layer 3 or the negative electrode mixture layer 6 contains a high-dielectric inorganic solid 13, such as Figure 2 As shown, the positive electrode active material 11 or the negative electrode active material 12 has a portion on its surface that contacts the high-dielectric inorganic solid 13 and a portion that contacts the electrolyte 9. That is, the positive electrode active material 11 or the negative electrode active material 12 contacts the high-dielectric inorganic solid 13 with a portion of its surface, and contacts the electrolyte 9 with the remaining portion.

[0053] In the positive electrode 4 or negative electrode 7 of the lithium-ion secondary battery 1 of this embodiment, the surface of the positive electrode active material 11 or negative electrode active material 12 has a portion that contacts the high-dielectric inorganic solid 13 and a portion that contacts the electrolyte 9. This allows the electrolyte 9 to reduce the surface potential of the positive electrode active material 11 or negative electrode active material 12, and reduces the interfacial resistance of lithium ions between the positive electrode active material 11 or negative electrode active material 12 and the high-dielectric inorganic solid 13. As a result, the migration resistance of lithium ions between the positive electrode active material 11 or negative electrode active material 12 and the high-dielectric inorganic solid 13 can be reduced, and the increase in internal resistance can be suppressed during repeated charge-discharge cycles.

[0054] Furthermore, in the positive electrode 4 or negative electrode 7 of the lithium-ion secondary battery 1 of this embodiment, since the positive electrode active material 11 or the negative electrode active material 12 has a portion on its surface that contacts the electrolyte 9, it can fully contact the electrolyte at this portion. Therefore, even on the surface of the active material where the electrolyte impregnation is relatively low in the past, solvent decomposition can be significantly suppressed, and electrolyte consumption can be suppressed.

[0055] Therefore, in the positive electrode 4 or negative electrode 7 of the lithium-ion secondary battery 1 of this embodiment, since the electrolyte 9 does not dry up, the contact state between the surface of the positive electrode active material 11 or the negative electrode active material 12 and the electrolyte 9 is well maintained, the potential within the electrode becomes uniform, and local high or low potentials can be suppressed. As a result, the positive electrode 4 or negative electrode 7 of the lithium-ion secondary battery 1 according to this embodiment can significantly suppress the oxidative decomposition reaction of the active material in the positive electrode or the reductive decomposition reaction of the active material in the negative electrode, and excellent durability for charge-discharge cycles can be obtained.

[0056] In the lithium-ion secondary battery 1, when the positive electrode additive layer 3 contains a high dielectric inorganic solid 13, the positive electrode can achieve the effect of improving output and excellent durability for charge-discharge cycles.

[0057] When the positive electrode additive layer 3 contains a high-dielectric inorganic solid 13, the positive electrode additive layer 3 preferably contains a high-dielectric inorganic solid 13 in the range of 0.5 to 5% by mass relative to the total amount of the positive electrode additive layer 3. This results in improved durability of the positive electrode. The high-dielectric inorganic solid 13 is further preferably coated on the surface of the positive electrode active material 11 in the range of 1 to 80%.

[0058] If the area covered by the high-dielectric inorganic solid 13 exceeds 80% of the surface of the positive electrode active material 11, the resistance when lithium ions reach the positive electrode active material 11 becomes too high, and the durability is reduced. On the other hand, if the area covered by the high-dielectric inorganic solid 13 is less than 1% of the surface of the positive electrode active material 11, the aforementioned effects achieved by using the high-dielectric inorganic solid 13 cannot be obtained.

[0059] In addition, in the lithium-ion secondary battery 1, when the negative electrode compound layer 6 contains a high dielectric inorganic solid 13, the charging capacity at low temperature can be increased, thereby improving the fast charging capability and durability.

[0060] When the negative electrode mixture layer 6 contains a high-dielectric inorganic solid 13, the negative electrode mixture layer 6 preferably contains 0.1 to 1.0% by mass of the high-dielectric inorganic solid 13 relative to the total amount of the negative electrode mixture layer 6, and more preferably contains 0.1 to 0.5% by mass of the high-dielectric inorganic solid 13. This improves the durability of the negative electrode. The high-dielectric inorganic solid 13 preferably covers 1% to 80% of the surface of the negative electrode active material 12.

[0061] If the area covered by the high-dielectric inorganic solid 13 exceeds 80% of the surface of the negative electrode active material 12, the resistance when lithium ions reach the negative electrode active material 12 becomes too high, and the durability also decreases. On the other hand, if the area covered by the high-dielectric inorganic solid 13 is less than 1% of the surface of the negative electrode active material 12, the aforementioned effects achieved by using the high-dielectric inorganic solid 13 cannot be obtained.

[0062] Furthermore, although not illustrated, if the mass ratio of the high-dielectric inorganic solid 13 in the positive electrode mixture layer 3 or the negative electrode mixture layer 6 is increased, the following state is achieved: the high-dielectric inorganic solid 13 is disposed not only on the surface of the positive electrode active material 11 or the negative electrode active material 12, but also in the gaps between the positive electrode active materials 11 or between the negative electrode active materials 12. The high-dielectric inorganic solid 13 disposed in the gaps between the positive electrode active materials 11 or the negative electrode active materials 12 further reduces the internal resistance of the obtained lithium-ion secondary battery.

[0063] When a high-dielectric inorganic solid 13 is disposed in the gaps between the positive electrode active materials 11 or between the negative electrode active materials 12, it is preferable that, when viewed in cross-section of the electrode composite layer, the cross-sectional area of ​​the high-dielectric inorganic solid 13 present in the gap and the cross-sectional area of ​​the electrolyte 9 are in the range of 2 to 20: 98 to 80. With this ratio, the migration of lithium ions in the electrolyte 9 present in the gap is accelerated by the high-dielectric inorganic solid 13, thereby preventing the high-dielectric inorganic solid 13 from hindering lithium ion migration.

[0064] Therefore, by increasing the mass ratio of the high-dielectric inorganic solid 13 in the positive electrode compound layer 3 or the negative electrode compound layer 6, the internal resistance of the lithium-ion secondary battery 1 can be reduced during continuous discharge and continuous charging, such as when driving an EV.

[0065] [Active Substances]

[0066] As a positive electrode active material, lithium composite oxide (LiNi) can be used, for example. x Co y Mn z O2(x+y+z=1), LiNi x Co y Al z O2 (x + y + z = 1) and lithium iron phosphate (LiFePO4 (LFP)). One or more of these can be used together.

[0067] Examples of negative electrode active materials include carbon powder (amorphous carbon) and silicon dioxide (SiO2). x The carbon powder used may include titanium composite oxides (Li4Ti5O7, TiO2, Nb2TiO7), tin composite oxides, lithium alloys, and metallic lithium, among others. One or more of these may be used. As the aforementioned carbon powder, one or more of the following may be used: soft carbon (easily graphitized carbon), hard carbon (difficult-to-graphitize carbon), and graphite.

[0068] [Conductive additives]

[0069] Examples of conductive additives used in the positive electrode flux layer 3 or the negative electrode flux layer 6 include carbon blacks such as acetylene black (AB) and Ketjen black (KB), carbon materials such as graphite powder, and conductive metal powders such as nickel powder. One or more of these additives may be used.

[0070] [Adhesive]

[0071] Examples of adhesives used in the positive electrode binder layer 3 or the negative electrode binder layer 6 include cellulose polymers, fluorinated resins, vinyl acetate copolymers, and rubbers. Specifically, as adhesives used with solvent-based dispersion media, examples include polyvinylidene fluoride (PVdF), polyimide (PI), polyvinylidene chloride (PVdC), and polyethylene oxide (PEO). As adhesives used with aqueous dispersion media, examples include styrene-butadiene rubber (SBR), acrylic-modified SBR resin (SBR-based latex), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), hydroxypropyl methylcellulose (HPMC), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). One or more of these can be used together.

[0072] (current collector)

[0073] Materials used for the positive electrode current collector 2 and the negative electrode current collector 5 can include foils or plates of copper, aluminum, nickel, titanium, stainless steel, carbon sheets, carbon nanotube sheets, etc. These materials can be used individually or, depending on the requirements, metal-coated foils composed of two or more materials. The thickness of the positive electrode current collector 2 and the negative electrode current collector 5 is not particularly limited, and can be, for example, in the range of 5 to 100 μm. From the viewpoint of structure and improved performance, the thickness of the positive electrode current collector 2 and the negative electrode current collector 5 is preferably in the range of 7 to 20 μm.

[0074] (Diaphragm)

[0075] There are no particular limitations on the diaphragm 8, and examples include porous resin sheets (membranes, non-woven fabrics, etc.) composed of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide.

[0076] (Electrolyte)

[0077] As the electrolyte 9, an electrolyte composed of a non-aqueous solvent and an electrolyte can be used. The concentration of the electrolyte is preferably in the range of 0.1 to 10 mol / L.

[0078] [Non-aqueous solvent]

[0079] There are no particular limitations on the non-aqueous solvents included in electrolyte 9, and examples include non-protic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones. Specifically, examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile (AN), propionitrile, nitromethane, N,N-dimethylformamide (DMF), dimethyl sulfoxide, sulfolane, and γ-butyrolactone.

[0080] [Electrolytes]

[0081] Electrolytes included in electrolyte 9 include, for example, LiPF6, LiBF4, LiClO4, LiN(SO2CF3), LiN(SO2C2F5)2, LiCF3SO3, LiC4F9SO3, LiC(SO2CF3)3, LiF, LiCl, LiI, Li2S, Li3N, Li3P, and Li 10 GeP2S 12 (LGPS), Li3PS4, Li6PS5Cl, Li7P2S8I, Lix PO y N z (x=2y+3z-5, LiPON), Li7La3Zr2O 12 (LLZO), Li 3x La 2 / 3-x TiO3(LLTO), Li 1+x Al x Ti 2-x (PO4)3(0≦x≦1, LATP), Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 Li 1+x+y Al x (Ti,Ge) 2-x Si y P 3-y O 12 Li 4-2x Zn x GeO4 (LISICON), etc. Among them, LiPF6, LiBF4, or mixtures thereof are preferred as electrolytes.

[0082] Furthermore, the electrolyte 9 can be an ionic liquid, or an electrolyte containing polymers containing aliphatic chains such as polyethylene oxide (PEO) or polyvinylidene fluoride (PVdF) copolymers. The electrolyte 9 containing the ionic liquid can flexibly cover the surface of the positive electrode active material 11 or the negative electrode active material 12, and can form a contact area between the surface of the positive electrode active material 11 or the negative electrode active material 12 and the electrolyte 9.

[0083] Electrolyte 9 fills the gaps between the positive electrode layer 3 and the negative electrode layer 6, as well as the pores of the separator 8. Furthermore, electrolyte 9 is stored at the bottom of container 10. The mass of electrolyte 9 stored at the bottom of container 10, relative to the mass of electrolyte 9 filling the gaps between the positive electrode layer 3 and the negative electrode layer 6, and the pores of the separator 8, can be in the range of 3 to 25% by mass. The mass of electrolyte 9 filling the gaps between the positive electrode layer 3 and the negative electrode layer 6, and the pores of the separator 8, can be calculated, for example, based on the total volume of the gaps between the positive electrode layer 3 and the negative electrode layer 6, and the pores of the separator 8, as measured by a mercury porosimeter, and its specific gravity. Alternatively, the total volume of the gaps between the positive electrode layer 3 and the negative electrode layer 6, and the pores of the separator 8, can also be calculated based on the density of the positive electrode layer 3 and the negative electrode layer 6, the density of the materials constituting each layer, and the porosity of the separator 8.

[0084] Since the electrolyte 9 is stored in the container 10 and is in contact with the diaphragm 8, when the electrolyte 9 is consumed, the electrolyte 9 can be replenished to the positive electrode mixture layer 3 and the negative electrode mixture layer 6 through the diaphragm 8.

[0085] [Highly dielectric inorganic solids]

[0086] The high-dielectric inorganic solid 13 contained in at least one of the positive electrode mixture layer 3 or the negative electrode mixture layer 6 is a solid with a high dielectric constant. The dielectric constant of the solid particles obtained by pulverizing a crystalline solid is lower than that of the original crystalline solid. Therefore, the high-dielectric inorganic solid in this embodiment is preferably a solid obtained by pulverizing while maintaining a high dielectric state as much as possible.

[0087] The relative permittivity of the high-dielectric inorganic solid powder used in this invention is preferably 10 or higher, more preferably 20 or higher. Due to the polarization of the high-dielectric inorganic solid particles, acid generated by the decomposition of fluorine anions such as PF6 or solvents can be replenished on the negative electrode graphite surface. If acid forms inside the secondary battery, it will corrode the positive electrode active material. Therefore, by capturing the generated acid, the corrosion of the positive electrode active material can be suppressed. This suppresses the breakage of the active material or metal dissolution that occurs during charge and discharge, thereby suppressing the increase in the secondary battery resistance during charge and discharge cycles. Therefore, if the relative permittivity of the powder is 10 or higher, the increase in internal resistance can also be suppressed during repeated charge and discharge cycles, thus achieving a lithium-ion secondary battery with excellent durability against charge and discharge cycles. The high-dielectric inorganic solid particles also capture acid on the positive electrode surface to suppress the corrosion of the positive electrode active material.

[0088] Here, the “relative permittivity of powder” in this specification refers to the value obtained as follows.

[0089] [Methods for determining the relative permittivity of powders]

[0090] The powder is fed into a tablet forming device with a diameter (R) of 38 mm for testing, and compressed using a hydraulic press to a thickness (d) of 1–2 mm, forming compressed powder. The forming conditions for the compressed powder are the relative density (D) of the powder. powder = (Powder weight density / Dielectric specific gravity) × 100, which is over 40%. For this molded body, the electrostatic capacitance C at 25°C and 1 kHz is measured using an LCR meter and an automatic balancing bridge method. total The relative permittivity ε of the pressed powder was calculated. total The dielectric constant ε of the solid volume fraction is determined based on the obtained relative permittivity of the pressed powder. powder Therefore, the dielectric constant ε0 of vacuum is set to 8.854 × 10⁻⁶. -12The relative permittivity ε of air air Let it be 1, and use the following formulas (1) to (3) to calculate the relative permittivity ε of the powder. powder ".

[0091] The contact area between the pressed powder and the electrode is A = (R / 2). 2 *π (1)

[0092] C total =ε total ×ε0×(A / d) (2)

[0093] ε total =ε powder ×D powder +ε air ×(1-D powder (3)

[0094] From the viewpoint of increasing the electrode volume fill density of the active material, the particle size of the high-dielectric inorganic solid 13 is preferably less than 1 / 5 of the particle size of the positive electrode active material 11 or the negative electrode active material 12, and more preferably in the range of 0.02 to 1 μm. When the particle size of the high-dielectric inorganic solid 13 is less than 0.02 μm, the high dielectric constant cannot be maintained, and thus the effect of suppressing the increase in resistance cannot be obtained.

[0095] The high-dielectric inorganic solid 13 preferably possesses ionic conductivity, and more preferably possesses at least one of Li ion conductivity, Na ion conductivity, and Mg ion conductivity. By possessing the aforementioned ionic conductivity, the high-dielectric inorganic solid 13 can capture free solvent present in the electrolyte 9, forming a near-solventized state. This achieves a solvent stabilization effect in the electrolyte 9, suppressing solvent decomposition. From this viewpoint, the aforementioned ionic conductivity is preferably 10. -7 S / cm or higher.

[0096] Here, “ionic conductivity” in this specification refers to the value obtained as follows.

[0097] [Methods for determining ion conductivity]

[0098] Electrodes are fabricated by sputtering Au onto both sides of a pressed powder body obtained by molding a sintered or powdered high-dielectric inorganic solid 13 using a tablet molding machine. Using the fabricated electrodes, an AC two-terminal method is applied at a voltage of 50 mV and a temperature of 25°C, up to frequencies from 1 to 10 to the power of 6 Hz. The ionic conductivity k is calculated from the resistance value Ri by determining the real value at the point where the imaginary component of the impedance is 0. For example, a Solatron 1260 / 1287 can be used as the measuring device. The ionic conductivity k is expressed using the Au area A' and the thickness l of the high-dielectric inorganic solid 13 as shown in the following formula (4).

[0099] k=l / (Ri×A')(S / cm) (4)

[0100] High-dielectric inorganic solid 13 is composed of Na or Mg-based high-dielectric inorganic solids. For example... Figure 3 As shown, Na or Mg-based high-dielectric inorganic solid 13 is easily polarized to δ in the electrolyte. + The electrolyte molecules form a solvation state with the high-dielectric inorganic solid 13, thereby exhibiting chemical stability and a high dielectric effect on the electrolyte. Therefore, Na or Mg-based high-dielectric inorganic solids have a high electrolyte replenishment capacity, improving electrode durability.

[0101] High dielectric inorganic solid 13, preferably Na 3+x (Sb 1-x Sn x S4(0≦X≦0.1), Na 3-x Sb 1-x W x S4 (0≦X≦1). Specifically, examples include Na3SbS4, Na2WS4, and Na 2.88 Sb 0.88 W 0.12 S4, etc.

[0102] Furthermore, the high-dielectric inorganic solid 13 is preferably composed of any one of oxides, fluorides, chlorides, and sulfides. The high-dielectric inorganic solid 13 may or may not have lithium-ion conductivity, but it is preferably a solid electrolyte with lithium-ion conductivity. If it is a high-dielectric inorganic solid with lithium-ion conductivity, the output of the obtained lithium-ion secondary battery at low temperatures can be further improved. Moreover, electrodes for lithium-ion secondary batteries with excellent electrochemical oxidation and reduction resistance can be manufactured relatively inexpensively. Furthermore, since the true specific gravity of oxide solid electrolytes is relatively low, the increase in battery weight can be suppressed.

[0103] In addition, as described above, in the lithium-ion secondary battery 1, it is sufficient that at least one of the positive electrode binder layer 3 or the negative electrode binder layer 6 contains a high-dielectric inorganic solid 13.

[0104] In the lithium-ion secondary battery 1, when the positive electrode agent layer 3 of the positive electrode 4 contains a high dielectric inorganic solid 13, the high dielectric inorganic solid 13 is preferably an antioxidant sodium inorganic compound.

[0105] When the positive electrode compound layer 3 of the positive electrode 4 contains an antioxidant sodium inorganic compound, the oxidative decomposition of high dielectric inorganic solids can be suppressed in the positive electrode, thereby achieving better durability for charge-discharge cycles.

[0106] Antioxidant decomposition sodium inorganic compounds preferably have a relative Li / Li ratio + The equilibrium potential is 4.5 V (4.5 V vs Li / Li). + The oxidation decomposition potential is above 1.

[0107] When the oxidative decomposition potential of antioxidant sodium inorganic compounds is relative to Li / Li + When the equilibrium potential is less than 4.5 V, the constituent metal elements undergo oxidation and decomposition during charging, resulting in a decrease in lithium-ion conductivity due to structural changes. Furthermore, if the oxidatively resistant lithium-ion conductive solid electrolyte undergoes oxidation and decomposition, this decomposition consumes charge, preventing the active materials from being charged. Consequently, the operating potential range of the lithium-ion secondary battery changes, leading to a decrease in capacity and a significant deterioration in durability during charge-discharge cycles.

[0108] As an antioxidant sodium inorganic compound, an oxide-based glass-ceramic is preferred, such as Li. 1.6 Al 0.6 Ti 1.4 (PO4)3 or Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 At least one of (0≦x≦1, 0≦y≦1).

[0109] Among them, LATP (Li) is particularly preferred. 1.6 Al 0.6 Ti 1.4 (PO4)3), LAGP(Li 1.5 Al 0.5 Ge 1.5 (PO4)3) or Li 1+x+ y Al x (Ti,Ge) 2-x Si y P 3-y O 12 (0≦x≦1,0≦y≦1).

[0110] In the lithium-ion secondary battery 1, when the negative electrode agent layer 6 of the negative electrode 7 contains a high-dielectric inorganic solid 13, the high-dielectric inorganic solid 13 is preferably a sodium inorganic compound resistant to reduction and decomposition.

[0111] When the negative electrode compound layer 6 of the negative electrode 7 contains a sodium inorganic compound that resists reduction and decomposition, the reduction and decomposition of high dielectric inorganic solids can be suppressed at the negative electrode, thereby achieving better durability for charge-discharge cycles.

[0112] Sodium inorganic compounds resistant to reductive decomposition preferably have a relative Li / Li ratio. + The equilibrium potential is 1.5 V (1.5 V vs Li / Li). + The following reduction decomposition potential.

[0113] When the reduction decomposition potential of a lithium-ion conductive solid electrolyte resistant to reduction decomposition is relative to Li / Li + When the equilibrium potential exceeds 1.5 V, the constituent metal elements undergo reduction decomposition and dissolve during charging, leading to a decrease in lithium-ion conductivity due to structural changes. Furthermore, if the reduction-resistant sodium inorganic compound undergoes reduction decomposition, this decomposition consumes charge, preventing the active material from being charged. Consequently, the operating potential range of the lithium-ion secondary battery changes, resulting in a decrease in capacity and a significant deterioration in durability during charge-discharge cycles.

[0114] The preferred embodiments of the present invention have been described above, but the content of the present invention is not limited to the above embodiments and can be appropriately modified.

[0115] [Example]

[0116] The present invention will now be described in further detail based on embodiments. However, the present invention is not limited to the embodiments described below.

[0117] Synthesis of High Dielectric Inorganic Solids

[0118] (Synthesis of Na3SbS4)

[0119] Na3SbS4(NSS) was synthesized using the following method: 70.4 g of Na2S, 75 g of Sb2S3, and 21 g of S were dissolved in 2210 ml of ion-exchanged water and stirred at 70 °C for 5 hours. Afterward, the mixture was cooled to 25 °C, and undissolved matter was removed. Then, 1400 ml of acetone was added, and the mixture was stirred for 5 hours, followed by standing for 12 hours. The mixture was dried under reduced pressure at 200 °C to obtain Na3SbS4. XRD analysis of the obtained sample confirmed the formation of the crystalline phase Na3SbS4(H2O)9.

[0120] (Mg) 0.5 Synthesis of Si2(PO4)3

[0121] Mg was synthesized using the following method 0.5Si2(PO4)3 (MSP). 6.07 g of magnesium acetate tetrahydrate, 6.80 g of silica, and 19.52 g of monoammonium phosphate were added to 500 ml of a 5 mmol / L citric acid aqueous solution. The mixture was stirred at 30°C for 2 hours, then refluxed at 70°C for 24 hours. Next, it was heated at 80°C with stirring for 24 hours. Afterward, it was heated at 150°C for 24 hours to remove moisture or organic matter. The heated sample was pulverized using an agate mortar and pestle and then heated at 400°C for 4 hours. The powder was compressed into a tablet using a tablet forming machine at 50 MPa and then heated at 800°C for 3 hours. A small amount of IPA was added to the obtained sample, and it was pulverized for 10 minutes using a planetary ball mill with 2 mm φ Zr balls at 1000 rpm to obtain MSP powder.

[0122] (Mg) 0.5 Synthesis of Zr2(PO4)3

[0123] Mg was synthesized using the following method 0.5 Zr₂(PO₄)₃ (MZP). 23.79 g of zirconium hydroxide acetate was added to 250 ml of nitric acid adjusted to 0.2 mmol / L and stirred for 1 hour to dissolve, forming an aqueous solution. Separately, 4.47 g of magnesium acetate tetrahydrate and 14.3 g of monoammonium phosphate were added to 250 ml of distilled water and stirred for 1 hour to dissolve, forming an aqueous solution. The two aqueous solutions were then mixed and heated at 100°C for 12 hours, followed by further heating at 150°C for 24 hours. The resulting sample was pulverized using an agate mortar and heated at 400°C for 4 hours. The powder was then compressed using a tablet forming machine at 50 MPa to form a pressed powder, and heated at 800°C for 3 hours. IPA was added to the resulting sample, and the powder was pulverized for 10 minutes at 1000 rpm using a small number of planetary ball mills with 2 mm φ Zr balls, thus obtaining MZP powder.

[0124] The ionic conductivity and relative permittivity of the NSS, MSP, MZP, and NZSP obtained above were determined. Additionally, the NZSP used was a commercially available product (manufactured by Toshima Manufacturing Co., Ltd.). The results are shown in Table 1 below.

[0125] Next, using the high-dielectric inorganic solid prepared above, positive and negative electrodes for Examples 1 to 9 and Comparative Example 1 were fabricated. The composition of the electrodes in each example is shown in Table 1.

[0126] (The production of the positive electrode)

[0127] [In the case of dielectric particles]

[0128] The dielectric particles, acetylene black (AB) as an electron-conducting material, and polyvinylidene fluoride (PVDF) as a binder were premixed in N-methyl-2-pyrrolidone (NMP) as a dispersion solvent. Wet mixing was performed using a rotary mixer to obtain a premixed slurry. Next, Li1Ni, as the positive electrode active material, was... 0.6 Co 0.2 Mn 0.2 O2 (NCM622) was mixed with the obtained premixed slurry and dispersed using a planetary mixer to obtain a positive electrode paste. The mass ratios of the components in the positive electrode paste are shown in Table 1, and each example was prepared using the weight ratios shown in Table 1. The median particle size of NCM622 was 12 μm. Next, the obtained positive electrode paste was coated onto an aluminum positive electrode current collector and dried. After being pressed using a roller press, it was dried in a vacuum at 120°C to form a positive electrode plate with a positive electrode paste layer. The obtained positive electrode plate was punched to a size of 30 mm × 40 mm to form a positive electrode.

[0129] (The production of the positive electrode)

[0130] [In the case of no dielectric particles]

[0131] Acetylene black (AB) as an electronically conductive material and polyvinylidene fluoride (PVDF) as a binder were premixed in N-methyl-2-pyrrolidone (NMP) as a dispersion solvent. The mixture was then wet-mixed using a rotary mixer to obtain a premixed slurry. Next, Li1Ni was added as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2 (NCM622) was mixed with the obtained premixed slurry and dispersed using a planetary mixer to obtain a positive electrode paste. The mass ratio of the components in the positive electrode paste was NCM622:AB:PVDF = 94:4.2:1.8. The median particle size of NCM622 was 12 μm. Next, the obtained positive electrode paste was coated onto an aluminum positive electrode current collector and dried. After being pressed using a roller press, it was dried in a vacuum at 120°C to form a positive electrode plate with a positive electrode paste layer. The obtained positive electrode plate was punched to a size of 30 mm × 40 mm to form the positive electrode.

[0132] (Making the negative electrode)

[0133] [In the case of dielectric particles]

[0134] A carboxymethyl cellulose (CMC) aqueous solution as a binder and acetylene black (AB) as an electronically conductive material were premixed using a planetary mixer. Next, natural graphite (NG) was mixed as the negative electrode active material and further mixed using a planetary mixer. Then, water as a dispersion solvent and styrene-butadiene rubber (SBR) as a binder were added, and the mixture was dispersed using a planetary mixer to obtain a negative electrode paste. The mass ratios of the components in the negative electrode paste were as shown in the examples in Table 1. The median particle size of the natural graphite was 12 μm. Next, the obtained negative electrode paste was coated onto a copper negative electrode current collector and dried. After being pressed using a roller press, it was dried in a vacuum at 130°C to form a negative electrode plate with a negative electrode binder layer. The obtained negative electrode plate was punched to a size of 34 mm × 44 mm to form a negative electrode.

[0135] (Making the negative electrode)

[0136] [In the case of no dielectric particles]

[0137] A carboxymethyl cellulose (CMC) aqueous solution as a binder and acetylene black (AB) as an electronically conductive material were premixed using a planetary mixer. Next, natural graphite (NG) was mixed as the negative electrode active material and further premixed using a planetary mixer. Then, water as a dispersion solvent and styrene-butadiene rubber (SBR) as a binder were added, and the mixture was dispersed using a planetary mixer to obtain a negative electrode paste. The mass ratio of the components in the negative electrode paste was NG:AB:CMC:SBR = 96.5:1.0:1.0:1.5. The median particle size of the natural graphite was 12 μm. The obtained negative electrode paste was then coated onto a copper negative electrode current collector and dried. After being pressed using a roller press, it was dried under vacuum at 130°C to form a negative electrode plate with a negative electrode binder layer. The obtained negative electrode plate was punched to a size of 34 mm × 44 mm to form the negative electrode.

[0138] (The manufacture of lithium-ion secondary batteries)

[0139] A lithium-ion secondary battery was fabricated by heat-sealing and processing an aluminum laminate (manufactured by Dai Nippon Printing Co., Ltd.) into a bag-shaped container, into which a membrane sandwiched between the positive and negative electrodes prepared above was introduced. After injecting electrolyte into each electrode interface, the container was depressurized to -95 kPa and sealed, thereby fabricating a lithium-ion secondary battery. As the membrane, a polyethylene microporous membrane with alumina particles of approximately 5 μm on one side was used. As the electrolyte, LiPF6 was dissolved at a concentration of 1.2 mol / L in a mixed solvent prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 30:30:40.

[0140] <Evaluation>

[0141] The lithium-ion secondary batteries fabricated using the electrodes of Examples 1 to 9 and Comparative Example 1 described above were evaluated as follows.

[0142] [Initial performance (discharge capacity)]

[0143] The fabricated lithium-ion secondary battery was placed at the measured temperature (25°C) for 1 hour, then charged at a constant current of 8.4 mA to 4.2 V, followed by constant voltage charging at 4.2 V for 1 hour. After being placed for 30 minutes, it was charged at a constant current of 8.4 mA to 2.5 V. This process was repeated 5 times, and the discharge capacity at the 5th discharge was defined as the initial discharge capacity (mAh). The ratio of the 1st discharge capacity to the charge capacity is expressed as a percentage. The results are shown in Table 1. Furthermore, the current value at which the obtained discharge capacity could be discharged within 1 hour was defined as 1 C.

[0144] [Initial Performance (Initial Battery Resistance Value)]

[0145] After measuring the initial discharge capacity, the lithium-ion secondary battery was placed at the measurement temperature (25°C) for 1 hour, then charged at 0.2 C to adjust the charge level (SOC (State of Charge)) to 50%, and placed for 10 minutes. Next, the C rate was set to 0.5 C, and a pulse discharge was performed for 10 seconds, measuring the voltage after 10 seconds of discharge. The horizontal axis was set to current, and the vertical axis to voltage, plotting the voltage after 10 seconds of discharge corresponding to the current at 0.5 C. After placing for 10 minutes, auxiliary charging was performed to restore the SOC to 50%, followed by another 10 minutes of placement. The above operation was performed at C rates of 1.0 C, 1.5 C, 2.0 C, 2.5 C, and 3.0 C, and the voltage after 10 seconds of discharge corresponding to the current value at each C rate was plotted. The slope of the approximate straight line obtained using the least squares method from each plot was taken as the internal resistance value (Ω) of the lithium-ion secondary battery obtained in this embodiment. The results are shown in Table 1.

[0146] [Post-durability performance (discharge capacity)]

[0147] As part of the charge-discharge cycle durability test, in a constant-temperature bath at 45°C, a cycle was defined as charging at a constant current rate of 1 C to 4.2 V and then discharging at a constant current rate of 2 C to 2.5 V. This operation was repeated for 500 cycles. After 500 cycles, the constant-temperature bath was changed to 25°C and left for 24 hours. Then, it was charged at a constant current rate of 0.2 C to 4.2 V, followed by constant-voltage charging at 4.2 V for 1 hour. After being left for 30 minutes, it was discharged at a constant current rate of 0.2 C to 2.5 V, and the discharge capacity (mAh) after durability was measured. The results are shown in Table 1.

[0148] [Battery resistance value after durability]

[0149] The lithium-ion secondary battery, after its endurance discharge capacity was measured, was charged to 50% (SOC (State of Charge)) using the same method as the initial battery resistance measurement. The endurance battery resistance (Ω) was then calculated using the same method as the initial battery resistance measurement. The results are shown in Table 1.

[0150] [Capacity retention after durability]

[0151] The ratio of the endurance discharge capacity (mAh) to the initial discharge capacity (mAh) is calculated as the endurance capacity retention rate (%). The results are shown in Table 1.

[0152] [Resistance rise rate after durability]

[0153] The ratio of the battery resistance value after durability testing to the initial battery resistance value (Ω) is calculated as the resistance increase rate (%). The results are shown in Table 1.

[0154] [Table 1]

[0155]

[0156] Based on the results in Table 1, the following results were confirmed: Compared with the comparative example lithium-ion secondary battery, the lithium-ion secondary batteries of each embodiment have higher capacity retention and lower resistance rise rate after durability. That is, it was confirmed that the lithium-ion secondary batteries of each embodiment have excellent durability for charge-discharge cycles. Furthermore, it was also confirmed that the initial charge-discharge efficiency is improved.

[0157] Figure Labels

[0158] 1 Lithium-ion secondary battery

[0159] 2 Positive Current Collector

[0160] 3 Positive electrode mixture layer

[0161] 4 positive electrodes

[0162] 5 Negative current collector

[0163] 6 negative electrode mixture layer

[0164] 7 negative electrode

[0165] 8 diaphragms

[0166] 9 Electrolyte

[0167] 10 containers

[0168] 11 Positive Electrode Active Material

[0169] 12 negative electrode active materials

[0170] 13 High-dielectric inorganic solids

Claims

1. A negative electrode for a lithium ion secondary battery, comprising an electrode mixture layer including a negative electrode active material and a high-dielectric inorganic solid, the aforementioned negative electrode active material has a site in contact with the aforementioned high-dielectric inorganic solid and a site in contact with an electrolyte solution on a surface, the aforementioned electrolyte solution contains LiPF6, LiBF4, or a mixture thereof as an electrolyte, The aforementioned high-dielectric inorganic solid is at least any one of Na3SbS4, Na2WS4, and Na 2.88 Sb 0.88 W 0.12 S4, the relative dielectric constant of a powder of the aforementioned high-dielectric inorganic solid is 10 or more, and the content of the aforementioned high-dielectric inorganic solid in the composite material of the aforementioned negative electrode for a lithium-ion secondary battery is 0.1 wt% or more and 1.0 wt% or less.

2. The negative electrode for a lithium-ion secondary battery according to claim 1, wherein the aforementioned high-dielectric inorganic solid is disposed in a gap between the aforementioned negative electrode active materials or on a particle surface.

3. The negative electrode for a lithium-ion secondary battery according to claim 1, wherein the aforementioned high-dielectric inorganic solid possessed by the aforementioned negative electrode is a reduction-decomposition-resistant sodium inorganic compound.

4. The negative electrode for a lithium-ion secondary battery according to claim 3, wherein The aforementioned anti-reduction-decomposable sodium inorganic compound has a reduction-decomposable potential of 1.5 V (vs. Li / Li + The equilibrium potential has a reduction-decomposable potential of 1.5 V (vs. Li / Li + ) or less.

5. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 1.

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