Electrode for lithium-ion secondary batteries, lithium-ion secondary batteries, and manufacturing method of electrodes for lithium-ion secondary batteries

Abstract

This invention provides an electrode for a lithium-ion secondary battery, a lithium-ion secondary battery using the electrode, and a method for manufacturing the electrode. It enables a battery that, even with a high volumetric energy density and a small amount of electrolyte held by the electrode, can suppress capacity reduction caused by repeated charging and discharging. In the lithium-ion secondary battery electrode where a high-dielectric oxide solid and electrolyte are disposed in the gaps between the active material particles in the electrode binder layer, water, which is reactive with the high-dielectric oxide solid, is not used to prepare the electrode binder layer, and the high-dielectric oxide solid is specifically configured within the electrode binder layer.

Description

Technical Field

[0001] This invention relates to an electrode for lithium-ion secondary batteries, a lithium-ion secondary battery using the electrode, and a method for manufacturing the electrode for lithium-ion secondary batteries. Background Technology

[0002] Previously, lithium-ion secondary batteries were widely used as high-energy-density secondary batteries. Lithium-ion secondary batteries that use liquid as electrolyte have the following structure: there is a separator between the positive and negative electrodes, and it is filled with a liquid electrolyte (electrolyte).

[0003] These types of lithium-ion secondary batteries have various requirements depending on their application. For example, in applications such as automobiles, there is a need to further increase the volumetric energy density. One method for increasing the packing density of the electrode active material is described below.

[0004] As a method to increase the filling density of electrode active material, for example, a method has been proposed that controls the particle size and particle shape of active material particles to minimize the gaps between active materials and fill a large number of active material particles in a certain area to achieve high-density filling (see Patent Document 1).

[0005] However, increasing the packing density of the electrode active material reduces the gaps between the active material particles inside the electrode, resulting in a relative decrease in the amount of electrolyte held by the electrode.

[0006] In addition, electrodes with a high density of active material filling material tend to have higher electrode surface pressure due to the expansion of the negative electrode active material during charging and discharging. As a result, the electrolyte existing between the active materials is squeezed out, which can easily lead to electrolyte depletion.

[0007] Furthermore, repeated charging and discharging under conditions of insufficient electrolyte volume or uneven electrolyte distribution at the electrodes can lead to increased resistance and potential deviation due to insufficient lithium ions. As a result, the solvent constituting the electrolyte is easily decomposed, forming a passivation film on the electrodes, gradually increasing internal resistance and causing a decrease in capacity.

[0008] Under the above circumstances, it is currently not possible to fully realize lithium-ion secondary batteries that experience minimal capacity loss due to repeated charging and discharging.

[0009] [Previous Technical Documents]

[0010] (Patent Documents)

[0011] Patent Document 1: Japanese Patent Application Publication No. 2004-192846 Summary of the Invention

[0012] [The problem the invention aims to solve]

[0013] The present invention was made in view of the above background, and its object is to provide an electrode for a lithium-ion secondary battery, a lithium-ion secondary battery using the electrode, and a method for manufacturing the electrode for a lithium-ion secondary battery, which can realize a battery that can suppress capacity reduction caused by repeated charging and discharging even when the volumetric energy density is high and the amount of electrolyte held by the electrode is small.

[0014] [Technical means to solve the problem]

[0015] The inventors have discovered that if not only electrolyte but also high-dielectric solid particles coexist on the electrode for lithium-ion secondary batteries, uneven distribution of electrolyte within the electrode can be prevented and ionic conductivity can be improved. Therefore, the increase in battery internal resistance during repeated charging and discharging can be suppressed. In Japanese Patent Application No. 2018-100590, an electrode for lithium-ion secondary batteries was proposed in which high-dielectric oxide solids and electrolyte are disposed in the gaps between the active material particles in the electrode mixture layer.

[0016] Furthermore, based on the aforementioned insights, the inventors have repeatedly discussed and arrived at the following insights: depending on the type of high dielectric oxide solid, the water in the slurry used to prepare the electrode mixture layer will cause the surface of the solid particles to deteriorate and the activity to decrease, thus reducing the coexistence effect of the electrolyte and the high dielectric oxide solid particles.

[0017] For example, Li7La3Zr2O as a high dielectric oxide solid. 12 When (LLZO) is added to an aqueous slurry, Li reacts with water on the particle surface and dissolves to form LiOH. Therefore, the interaction with the electrolyte decreases, and the improvement in the electrolyte's ionic conductivity is reduced, thus decreasing the effectiveness in suppressing resistance increases. Furthermore, because it readily adheres to the surface of negative electrode active materials such as graphite particles, the dispersion of the particles between them decreases, leading to LiOH being coated onto the surface of the negative electrode active material, thereby hindering the charge-discharge reaction and reducing its contribution to suppressing resistance increases.

[0018] In contrast, a method for fabricating electrodes using non-aqueous organic solvents such as N-methyl-2-pyrrolidone (NMP) instead of non-aqueous slurries is considered. However, LLZO reacts with polyvinylidene fluoride (PVDF) as a binder, causing the slurry to gel and making it difficult to coat onto the current collector. Furthermore, from the viewpoint of manufacturing cost and battery performance, an aqueous slurry method using rubber-based binders such as styrene-butadiene rubber (SBR) is preferred.

[0019] Furthermore, the inventors repeatedly studied the configuration of high-dielectric oxide solids in the electrode mixture layer. The results showed that, in lithium-ion secondary battery electrodes, high-dielectric oxide solids configured on the separator side are more effective in improving battery performance than those configured on the current collector side.

[0020] Especially when a high-dielectric oxide solid with Li ion conductivity is disposed on the membrane-side surface of the electrode mixture layer, when the Li concentration in the electrolyte decreases during fast charging, the Li within the high-dielectric oxide solid migrates to the surface of the high-dielectric oxide solid to mitigate the insufficient Li concentration in the electrolyte, thus limiting the charging reaction on the membrane side. In this case, by sandwiching the high-dielectric oxide solid particles between the electrode active materials on the membrane-side surface of the electrode mixture layer, a channel for the electrolyte to the current collector foil side can be ensured. The results show that the charging reaction on the membrane side can be suppressed while ensuring electrolyte supply to the current collector foil side, suppressing potential deviations in the thickness direction within the electrode mixture layer, thus helping to prevent electrolysis of the negative electrode active material in contact with the membrane side, and contributing to improved cycle durability.

[0021] Based on these new insights, the inventors believe that if the electrode mixture layer is fabricated without using water, which is reactive with high-dielectric oxide solids, and the high-dielectric oxide solids are configured in a specific way in the electrode mixture layer, then even with a high volumetric energy density and a small amount of electrolyte held by the electrode, a battery that suppresses capacity reduction caused by repeated charging and discharging at a higher level can be achieved, thus completing the present invention.

[0022] That is, the present invention provides an electrode for a lithium-ion secondary battery, which includes an electrolyte and has: a current collector and an electrode mixture layer stacked on the current collector; the electrode mixture layer contains an electrode active material and a first high-dielectric oxide solid; and in the electrode mixture layer, the first high-dielectric oxide solid is configured to have a concentration gradient continuously or in stages, decreasing from the surface opposite to the current collector in the thickness direction of the electrode mixture layer.

[0023] Optionally, the first high-dielectric oxide solid is disposed in the gaps between the electrode active materials.

[0024] Optionally, the first high-dielectric oxide solid is disposed in the electrode mixture layer within a region of less than 1 / 2 thickness, along the thickness direction from the surface opposite to the current collector.

[0025] Optionally, the first high-dielectric oxide solid is an oxide solid electrolyte.

[0026] Optionally, the electrode for the lithium-ion secondary battery is a negative electrode.

[0027] Optionally, the first high-dielectric oxide solid is a lithium-ion conductive solid electrolyte resistant to reduction and decomposition.

[0028] Optionally, the reductively resistant lithium-ion conductive solid electrolyte is relative to Li / Li + The equilibrium potential is 1.5V (1.5V vs Li / Li). + The following reduction decomposition potential.

[0029] Optionally, the reductively resistant lithium-ion conductive solid electrolyte is selected from Li7La3Zr2O. 12 Li5La3Ta2O 12 LiNbO3, Li3PO4 and Li 2.9 PO 3.3 N 0.46 At least one of the groups.

[0030] Optionally, the electrode mixture layer further contains a second high-dielectric oxide solid.

[0031] Optionally, the second high-dielectric oxide solid is disposed in the gaps between the electrode active materials.

[0032] Optionally, the second high-dielectric oxide solid is disposed substantially uniformly over the entire electrode mixture layer.

[0033] In another invention, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, a separator electrically insulating the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the electrode for the lithium-ion secondary battery described above.

[0034] Optionally, the lithium-ion secondary battery includes the positive electrode, the negative electrode, the separator, and a container for containing the electrolyte; the separator is in contact with the electrolyte stored in the container.

[0035] Another invention provides a method for manufacturing an electrode for a lithium-ion secondary battery, the electrode having a current collector and an electrode mixture layer laminated on the current collector, the method comprising the following steps: an electrode paste preparation step, which prepares an electrode paste containing an electrode active material and water; an electrode mixture precursor layer formation step, which coats the electrode paste onto the current collector and dries the water to obtain an electrode mixture precursor layer; a high-dielectric oxide dispersion preparation step, which prepares a high-dielectric oxide solid dispersion containing a first high-dielectric oxide solid and an organic solvent; an electrode mixture layer formation step, which contacts the high-dielectric oxide dispersion with a surface of the electrode mixture precursor layer opposite to the current collector side surface and dries the organic solvent to obtain an electrode mixture layer; and a pressing step, which presses the electrode mixture layer to obtain an electrode for a lithium-ion secondary battery.

[0036] Optionally, the contact method in the electrode mixture layer formation step is at least one of the group consisting of dripping, coating, spraying and impregnation.

[0037] Optionally, in the electrode mixture layer forming step, the first high-dielectric oxide solid is configured to have a concentration gradient continuously or in stages, decreasing from the surface opposite to the current collector in the thickness direction of the electrode mixture layer.

[0038] Optionally, the electrode paste further comprises a second high-dielectric oxide solid.

[0039] Optionally, the electrode for the lithium-ion secondary battery is a negative electrode. Attached Figure Description

[0040] Figure 1 A cross-sectional view illustrating one embodiment of the lithium-ion secondary battery of the present invention. Detailed Implementation

[0041] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0042] <Electrodes for Lithium-ion Secondary Batteries>

[0043] The lithium-ion secondary battery electrode of the present invention is a lithium-ion secondary battery electrode containing an electrolyte, having a current collector and an electrode mixture layer stacked on the current collector. The electrode mixture layer contains an electrode active material and a first high-dielectric oxide solid. Furthermore, in the electrode mixture layer, the first high-dielectric oxide solid is configured to have a concentration gradient that decreases continuously or in stages from the surface opposite to the current collector in the thickness direction of the electrode mixture layer.

[0044] The electrode for lithium-ion secondary batteries of the present invention can be either a positive electrode or a negative electrode for lithium-ion secondary batteries. However, from the viewpoint of dealing with the expansion and contraction of the active material of the negative electrode during charging and discharging and suppressing the formation of lithium film, applying it to the negative electrode can better enjoy the effects of the present invention.

[0045] [Current Collector]

[0046] The current collector in the electrode for lithium-ion secondary batteries of the present invention is not particularly limited, and a known current collector used in lithium-ion secondary batteries can be used.

[0047] Materials that can be used as negative electrode current collectors include, for example, SUS, Ni, Cu, Ti, Al, calcined carbon, conductive polymers, conductive glass, and Al-Cd alloys. Materials that can be used as positive electrode current collectors include, for example, metallic materials such as SUS, Ni, Cr, Au, Pt, Al, Fe, Ti, Zn, and Cu.

[0048] In addition, the shape of the current collector can be, for example, foil, plate, mesh, etc. There is no particular limitation on its thickness; for example, 1 to 20 μm can be used, but it can be selected appropriately according to the needs.

[0049] [Electrode Mixture Layer]

[0050] In the electrode for a lithium-ion secondary battery of the present invention, the electrode mixture layer contains an electrode active material and a first high-dielectric oxide solid as essential components. The electrode mixture layer may be formed on at least one side of the current collector, or it may be formed on both sides. The appropriate selection can be made according to the type and structure of the target lithium-ion secondary battery.

[0051] Furthermore, as long as the electrode mixture layer contains the essential components of this invention—namely, the electrode active material and the first high-dielectric oxide solid—it may contain any other constituent components. Examples of such arbitrary components include, for instance, known components such as conductive additives and adhesives.

[0052] [Electrode active material]

[0053] The electrode active material contained in the electrode of the lithium-ion secondary battery of the present invention is not particularly limited as long as it can absorb and release lithium ions, and known materials can be used as electrode active materials for lithium-ion secondary batteries.

[0054] (Negative electrode active material)

[0055] If the electrode for the lithium-ion secondary battery of the present invention is a negative electrode for a lithium-ion secondary battery, then the negative electrode active material can include metallic lithium, lithium alloys, metal oxides, metal sulfides, metal nitrides, silicon oxide, silicon, and carbon materials such as graphite. As the negative electrode active material, a material with a lower potential than the positive electrode can be selected from the materials capable of forming the electrode.

[0056] (Positive electrode active material)

[0057] If the electrode for the lithium-ion secondary battery of the present invention is a positive electrode for a lithium-ion secondary battery, then there are no particular limitations on the positive electrode active material, and examples include LiCoO2, LiCoO4, LiMn2O4, LiNiO2, LiFePO4, lithium sulfide, sulfur, etc. As the positive electrode active material, a material with a higher potential than that of the negative electrode can be selected from the materials that can form the electrode.

[0058] [First High Dielectric Oxide Solid]

[0059] The first high-dielectric oxide solid contained in the electrode for the lithium-ion secondary battery of the present invention can be any oxide with high dielectric properties, and there is no particular limitation. Generally, the dielectric constant of solid particles pulverized from a crystalline state changes from their original crystalline state, and the dielectric constant decreases. Therefore, the first high-dielectric oxide solid used in the present invention is preferably a powder pulverized in a state that can maintain a high dielectric state as much as possible.

[0060] The relative permittivity of the powder of the first high-dielectric oxide solid used in this invention is preferably 10 or more, more preferably 20 or more. As long as the relative permittivity of the powder is 10 or more, the increase in internal resistance can be suppressed even during repeated charge-discharge cycles, thereby enabling a lithium-ion secondary battery with excellent durability to charge-discharge cycles.

[0061] In this specification, the "powder relative permittivity" refers to the value calculated as follows.

[0062] (Method for measuring the relative permittivity of powder)

[0063] The powder is fed into a tablet former with a diameter (R) of 38 mm for measurement, and compressed using a hydraulic press to a thickness (d) of 1–2 mm, forming a compressed powder. The forming conditions for the compressed powder are: powder relative density (D) powder = Powder weight density / Dielectric specific gravity × 100 The content is at least 40%, preferably 50%, and the capacitance C of the molded body at 25°C and 1kHz is measured using an LCR meter with an automatic balancing bridge method. total And calculate the relative permittivity ε of the pressed powder. total To determine the dielectric constant ε of the actual volume fraction based on the obtained relative dielectric constant of the pressed powder.powder The vacuum permittivity ε0 is set to 8.854 × 10⁻⁶. -12 The relative permittivity ε of air air Let ε be 1, and calculate the relative permittivity of the powder using formulas (1) to (3) below. powder ".

[0064] The contact area between the pressed powder and the electrode is A = (R / 2). 2 ×π (1)

[0065] C total =ε total ×ε0×(A / d) (2)

[0066] ε total =ε powder ×D powder +ε air ×(1-D powder (3)

[0067] The particle size of the first high-dielectric oxide solid is not particularly limited, but from the viewpoint of improving the electrode volume fill density of the electrode active material, it is preferably 1 / 5 or less of the particle size of the electrode active material, more preferably in the range of 0.02 to 3 μm. When the particle size of the high-dielectric oxide solid is 0.02 μm or less, it is impossible to maintain high dielectric properties, and it becomes difficult to obtain the effect of improving capacity retention. When the particle size is 3 μm or more, it becomes difficult to effectively arrange it between the active material particles in the electrode binder layer. In addition, in order to impart electronic conductivity to the high-dielectric oxide solid, it is preferable to implement the method known in Japanese Patent Application No. 2018-99451, which involves carbon coating. This allows output performance to be maintained without hindering the electronic conductivity of the electrode body, that is, without increasing the battery resistance.

[0068] (Configuration of the first high-dielectric oxide solid)

[0069] In the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention, the first high-dielectric oxide solid is configured to have a concentration gradient in a manner that decreases from the surface opposite to the current collector in the thickness direction of the electrode mixture layer.

[0070] In the electrode mixture layer, the first high-dielectric oxide solid is configured to be concentrated on the separator side rather than the current collector side, thereby further improving the performance of the lithium-ion secondary battery using the obtained electrode.

[0071] Specifically, when the concentration of Li in the electrolyte decreases due to a reduction in Li ions caused by rapid charging, the presence of high-dielectric oxide solids hinders the charging reaction of Li ions in the electrolyte. Conversely, when the concentration of Li ions in the electrolyte increases due to discharge, the high-dielectric oxide solids prevent ion association of lithium salts, thus promoting the discharge reaction.

[0072] The lithium-ion secondary battery electrode of the present invention, by having high dielectric oxide solid particles present near the separator side surface of the electrode mixture layer, can ensure electrolyte channels. As a result, it can suppress potential deviation in the thickness direction of the electrode mixture layer, suppress electrolysis, and improve the cycle durability of the lithium-ion secondary battery.

[0073] Furthermore, in the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention, the first high-dielectric oxide solid is more preferably disposed in the electrode mixture layer within a region of thickness less than 1 / 2, along the thickness direction from the surface opposite to the current collector. By being disposed within a region of thickness less than 1 / 2, potential deviation in the electrode thickness direction can be sufficiently suppressed even without tilting the dielectric oxide particles throughout the thickness direction.

[0074] Furthermore, in the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention, the first high-dielectric oxide solid is preferably disposed in the gaps between the electrode active materials. The gaps formed between the electrode active material particles can be controlled by the electrode active material filling rate and are related to the density of the electrode mixture layer. In addition, a resin binder as a binder and a carbon material as a conductive aid for providing electronic conductivity can also be disposed in the gaps between the electrode active material particles.

[0075] By distributing a first high-dielectric oxide solid within the gaps between the electrode active material particles, the electrode for the lithium-ion secondary battery of the present invention can suppress the diffusion of lithium ions within the electrode and reduce the increase in resistance, thereby achieving an electrode with a high filling density of the electrode active material. As a result, a lithium-ion secondary battery can be realized that, even with a high volumetric energy density and a small amount of electrolyte held by the electrode, capacity reduction caused by repeated charge-discharge cycles can be suppressed.

[0076] Furthermore, by distributing a first high-dielectric oxide solid within the gaps between the electrode active material particles, the electrolyte permeability of the lithium-ion secondary battery electrode of the present invention is improved. As a result, the uniformity of the electrolyte retention within the electrode is enhanced. Additionally, the electrolyte impregnation time into the electrode can be shortened, thereby improving productivity.

[0077] Furthermore, by distributing a first high-dielectric oxide solid within the gaps between the electrode active material particles, the electrode for lithium-ion secondary batteries of the present invention can suppress the association of lithium ions and anions through dielectric effects. As a result, for example, even when using an electrolyte containing a high concentration of lithium salt, it is possible to exhibit a reduction in resistance during discharge.

[0078] (The first type of high dielectric oxide solid)

[0079] The first high-dielectric-performance oxide solid electrolyte can be any oxide with high dielectric properties, without particular limitation, but oxide solid electrolytes are preferred. Oxide solid electrolytes allow for the preparation of inexpensive crystals and exhibit excellent electrochemical oxidation and reduction resistance. Furthermore, oxide solid electrolytes have a relatively low true gravity, thus suppressing the increase in electrode weight.

[0080] Furthermore, the first high-dielectric oxide solid is preferably an oxide solid electrolyte with lithium-ion conductivity. If a high-dielectric oxide solid electrolyte with lithium-ion conductivity is used, the output of the resulting lithium-ion secondary battery at low temperatures can be further improved. In addition, electrodes for lithium-ion secondary batteries with excellent electrochemical oxidation resistance and reduction resistance can be manufactured at a relatively low cost.

[0081] Examples of high dielectric oxide solids include BaTiO3 and Ba. x Sr 1-x TiO3 (X = 0.4–0.8), BaZr x Ti 1-x O3 (X = 0.2–0.5), KNbO3 and other composite metal oxides with perovskite-type crystal structures, and SrBi2Ta2O9, SrBi2Nb2O9 and other composite metal oxides containing bismuth with layered perovskite-type crystal structures.

[0082] As an example of a highly dielectric oxide solid with lithium-ion conductivity, for example, a product of the chemical formula Li can be used. 7-y La 3-x AxZr 2-y MyO 12 (In the formula, A is any metal selected from the group consisting of Y, Nd, Sm, and Gd, x is the range of 0 ≤ x < 3, M is Nb or Ta, and y is the range of 0 ≤ y < 2) represents a composite metal oxide with a garnet-type structure.

[0083] Additionally, Li can be listed as an example. x Nb y O3, Li x Ta yO3 (x / y = 0.9–1.1) composite oxides with ilmenite structure, Li3PO4, Li x 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 (O≤x≤l, 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.

[0084] More specifically, Li7La3Zr2O can be cited as an example. 12 Li5La3Ta2O 12 Li 2.9 PO 3.3 N 0.46 LiNbO3, Li3PO4, etc.

[0085] As described above, the electrode for lithium-ion secondary batteries of the present invention can be either a positive electrode or a negative electrode for lithium-ion secondary batteries. However, from the viewpoint of suppressing the formation of an SEI film on the negative electrode during charging and discharging, applying it to the negative electrode allows one to better enjoy the effects of the present invention.

[0086] When the electrode for the lithium-ion secondary battery of the present invention is the negative electrode, the high dielectric oxide solid is preferably a lithium-ion conductive solid electrolyte resistant to reduction and decomposition.

[0087] When the negative electrode mixture layer contains a lithium-ion conductive solid electrolyte that is resistant to reduction and decomposition, the reduction and decomposition of high dielectric oxide solids can be suppressed, resulting in better durability for charge-discharge cycles.

[0088] As a reductively resistant lithium-ion conductive solid electrolyte, it is preferably relative to Li / Li + The equilibrium potential is 1.5V (1.5V vs Li / Li). + Substances with a reduction decomposition potential below )

[0089] If the reduction decomposition potential of a lithium-ion conductive solid electrolyte resistant to reduction decomposition is relative to Li / Li + If the equilibrium potential exceeds 1.5V, the constituent metal elements will dissolve due to reduction and decomposition during charging, and the structural changes will lead to a decrease in lithium-ion conductivity. In addition, if the reduction and decomposition-resistant lithium-ion conductive solid electrolyte undergoes reduction and decomposition, the charge will be consumed during this process, making it difficult to charge the active materials. Therefore, the operating potential range of the lithium-ion secondary battery changes, the capacity decreases, and the durability during charge-discharge cycles will deteriorate significantly.

[0090] As a reductively resistant lithium-ion conductive solid electrolyte, it is preferably selected from LLZO (Li7La3Zr2O) 12 ), LLTO(Li5La3Ta2O) 12 LiNbO3, lithium phosphate Li3PO4 and LIPON (Li 2.9 PO 3.3 N 0.46 At least one of the following: . Among them, the redox potential of Li is close to that of Li redox potential of negative electrode active materials such as graphite and hard carbon, therefore LLZO is particularly preferred.

[0091] When the electrode for the lithium-ion secondary battery of the present invention is a positive electrode, the high dielectric oxide solid is preferably a lithium-ion conductive solid electrolyte resistant to oxidation and decomposition.

[0092] When the positive electrode mixture layer contains a lithium-ion conductive solid electrolyte that is resistant to oxidation and decomposition, the oxidation and decomposition of high dielectric oxide solids can be suppressed, resulting in better durability for charge-discharge cycles.

[0093] As a lithium-ion conductive solid electrolyte resistant to oxidation and decomposition, it is preferably relative to Li / Li + The equilibrium potential is 4.5V (4.5V vs Li / Li). + Substances with an oxidation decomposition potential of 1000 or higher.

[0094] If the oxidation decomposition potential of a lithium-ion conductive solid electrolyte with resistance to oxidation decomposition is relative to Li / Li +If the equilibrium potential is less than 4.5V, the constituent metal elements will dissolve due to oxidation and decomposition during charging, and the structural changes will lead to a decrease in lithium-ion conductivity. In addition, if the oxidatively resistant lithium-ion conductive solid electrolyte undergoes oxidation and decomposition, the charge will be consumed in this oxidation and decomposition, making it difficult to charge the active materials. Therefore, the operating potential range of the lithium-ion secondary battery changes, the capacity decreases, and the durability during charge-discharge cycles will deteriorate significantly.

[0095] As a lithium-ion conductive solid electrolyte with resistance to oxidation and decomposition, an oxide-based glass-ceramic electrolyte is preferred, and more preferably, for example, 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).

[0096] 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).

[0097] (The amount of the first high dielectric oxide solid)

[0098] If the electrode for the lithium-ion secondary battery of the present invention is a negative electrode, the amount of the first high-dielectric oxide solid in the electrode mixture layer is preferably in the range of 0.1% to 5% by mass of the total mass of the electrode mixture layer, more preferably in the range of 0.2% to 3% by mass. Particularly preferred is the range of 0.3% to 2% by mass, in which case the increase in electrode volume and weight caused by the combination is small, and the capacity reduction caused by charging and discharging can be minimized.

[0099] [Second Highest Dielectric Oxide Solid]

[0100] In addition to the first high-dielectric oxide solid, which is an essential component, the electrode for the lithium-ion secondary battery of the present invention may optionally contain a second high-dielectric oxide solid. The second high-dielectric oxide solid is not particularly limited as long as it differs from the first high-dielectric oxide solid; lithium triphosphate (Li3PO4) and lithium niobate (LiNbO3) may be used.

[0101] (Configuration of the second high dielectric oxide solid)

[0102] In the case where the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention contains a second high-dielectric oxide solid, the second high-dielectric oxide solid is preferably disposed in the gaps between the electrode active materials.

[0103] Furthermore, in the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention, the second high-dielectric oxide solid is preferably disposed in the same manner as the first high-dielectric oxide solid in the gaps between the electrode active materials. By disposing it in the gaps between the electrode active materials, a lithium-ion secondary battery can be realized that, even with a high volumetric energy density and a small amount of electrolyte held by the electrode, capacity reduction and resistance increase caused by repeated charge-discharge cycles can be suppressed. In addition, while improving the uniformity of electrolyte retention within the electrode, the impregnation time of the electrolyte on the electrode can be shortened, and productivity can be improved.

[0104] When the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention contains a second high-dielectric oxide solid, the second high-dielectric oxide solid is preferably disposed substantially uniformly throughout the entire electrode mixture layer. That is, the electrode mixture layer of the lithium-ion secondary battery electrode of the present invention is configured such that the second high-dielectric oxide solid is disposed substantially uniformly throughout the entire electrode mixture layer, and the first high-dielectric oxide solid has a continuous or phased concentration gradient in the thickness direction of the electrode mixture layer, decreasing from the surface opposite to the current collector towards the current collector.

[0105] Furthermore, when the electrode mixture layer contains a second high-dielectric oxide solid, the second high-dielectric oxide solid is preferably pre-formed in the electrode paste used to form the electrode mixture layer, and the electrode mixture layer is prepared using this electrode paste. By pre-forming the second high-dielectric oxide solid into the electrode paste, the second high-dielectric oxide solid can be easily disposed between the electrode active material particles in the formed electrode mixture layer, and the second high-dielectric oxide solid can be easily and uniformly disposed throughout the entire electrode mixture layer.

[0106] As the second high-dielectric oxide solid, the same material as the first high-dielectric oxide solid described above can be used. However, when pre-compacting the second high-dielectric oxide solid into the electrode paste, it is preferable to use a material with lower reactivity with the solvent constituting the electrode paste than the first high-dielectric oxide solid. When using a high-dielectric oxide solid that is reactive with the solvent constituting the electrode paste, it is difficult to maximize the effect of the added amount.

[0107] Lithium-ion secondary batteries

[0108] The lithium-ion secondary battery of the present invention is a lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator electrically insulating the positive electrode and the negative electrode, and an electrolyte, and is a lithium-ion secondary battery that uses the electrode of the lithium-ion secondary battery of the present invention as the negative electrode.

[0109] One embodiment of the lithium-ion secondary battery of the present invention is as follows: Figure 1 As shown. Figure 1 The lithium-ion secondary battery 1 shown in one 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 that electrically insulates the positive electrode 4 from the negative electrode 7; an electrolyte 9; and a container 10 that houses the positive electrode 4, the negative electrode 7, the separator 8, and the electrolyte 9.

[0110] Inside container 10, positive electrode layer 3 and negative electrode layer 6 sandwich membrane 8 and face each other, with electrolyte 9 stored below positive electrode layer 3 and negative electrode layer 6. Furthermore, the end of membrane 8 is immersed in electrolyte 9.

[0111] In such Figure 1 In the lithium-ion secondary battery shown, the positive electrode layer 3 contains a positive electrode active material, and the negative electrode layer 6 contains a negative electrode active material. Additionally, the negative electrode layer 6 contains a first high-dielectric oxide solid. The presence of this first high-dielectric oxide solid in the negative electrode layer 6 reduces charging deviation and improves fast charging capability and durability.

[0112] Electrolyte

[0113] As the electrolyte used in the lithium-ion secondary battery of the present invention, an electrolyte composed of a non-aqueous solvent and an electrolyte can be used, and the concentration of the electrolyte is preferably in the range of 0.1 to 10 mol / L.

[0114] (Non-aqueous solvent)

[0115] As non-aqueous solvents, examples include aprotic 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.

[0116] (electrolytes)

[0117] Examples of electrolytes mentioned above include LiPF6, LiBF4, LiClO4, LiN(SO2CF3), LiN(SO2C2F5)2, LiCF3SO3, LiC4F9SO3, LiC(SO2CF3)3, LiF, LiCl, Lil, Li2S, Li3N, Li3P, and Li 10 GeP2S 12 (LGPS), Li3PS4, Li6PS5Cl, Li7P2S8I, Li x 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) and other materials, preferably LiPF6, LiBF4 or mixtures thereof.

[0118] In addition, electrolytes can include ionic liquids or electrolytes containing polymers with aliphatic chains, such as polyethylene oxide (PEO) or polyvinylidene fluoride (PVdF) copolymers. Electrolytes containing ionic liquids can flexibly cover the surface of the positive or negative electrode active material.

[0119] In such Figure 1 In one embodiment of the lithium-ion secondary battery 1 shown, electrolyte 9 fills the gaps between the positive electrode binder layer 3 and the negative electrode binder layer 6, and the pores of the separator 8, while being stored at the bottom of the container 10. In this embodiment, the separator 8 contacts the electrolyte 9 stored in the container 10, thereby allowing the electrolyte 9 to be replenished to the positive electrode binder layer 3 and the negative electrode binder layer 6 via the separator 8 when the electrolyte 9 is consumed.

[0120] The mass of the electrolyte 9 stored at the bottom of the container 10 is preferably in the range of 3 to 25% by mass, which fills the gaps between the positive electrode layer 3 and the negative electrode layer 6 and the pores of the diaphragm 8.

[0121] <Manufacturing Method of Electrodes for Lithium-ion Secondary Batteries>

[0122] The method for manufacturing an electrode for a lithium-ion secondary battery according to the present invention is a method for manufacturing an electrode for a lithium-ion secondary battery having a current collector and an electrode mixture layer stacked on the current collector, comprising an electrode paste preparation step, an electrode mixture precursor layer formation step, a high dielectric oxide solid dispersion preparation step, an electrode mixture layer formation step, and a pressing step.

[0123] [Electrode paste preparation steps]

[0124] The electrode paste preparation step involves preparing an electrode paste containing electrode active material and water. From the viewpoints of manufacturing cost, environmental impact, and battery performance, aqueous slurries are preferred when manufacturing the electrode paste layer for lithium-ion secondary batteries. In the manufacturing method of the lithium-ion secondary battery electrode of the present invention, since the electrode paste used to form the electrode paste layer is aqueous, the above-mentioned requirements can be met.

[0125] (Electrode active material)

[0126] The electrode active material used in the electrode paste preparation step is not particularly limited, but preferably is a material that can be applied to the lithium-ion secondary battery electrode of the present invention. Electrode active materials suitable for both the positive and negative electrodes can be appropriately selected.

[0127] (Preparation conditions)

[0128] The concentration of the electrode active material in the electrode paste is not particularly limited and can be appropriately selected based on the conditions in the subsequent electrode preparation precursor layer formation step. Furthermore, the preparation method of the electrode paste is not particularly limited and can be any known method.

[0129] (Coordination of the second highest dielectric oxide solid)

[0130] In the electrode paste preparation step of the present invention, a second high-dielectric oxide solid, different from the first high-dielectric oxide solid used in the high-dielectric oxide solid dispersion preparation step described later, can be combined with the electrode active material in the electrode paste.

[0131] By pre-compacting the second high-dielectric oxide solid into the electrode paste, the second high-dielectric oxide solid can be easily disposed between the electrode active material particles in the formed electrode mixture layer, and the second high-dielectric oxide solid can be easily disposed substantially uniformly throughout the entire electrode mixture layer.

[0132] Therefore, a lithium-ion secondary battery can be realized that suppresses capacity reduction caused by repeated charge-discharge cycles even with a high volumetric energy density and a small amount of electrolyte held in the electrodes. Furthermore, while the electrolyte retention within the electrodes becomes more uniform, the electrolyte impregnation time on the electrodes can be shortened, thus improving productivity.

[0133] There are no particular limitations on the second high-dielectric-strength oxide solid, but a material suitable for use in the electrode of the lithium-ion secondary battery of the present invention is preferred. That is, the same material as the first high-dielectric-strength oxide solid described above can be used.

[0134] Preferably, the substance has low reactivity with water, which is the solvent constituting the electrode paste. When a solid that is reactive with water, which constitutes the electrode paste, is used as the second high dielectric oxide solid, the surface activity of the solid particles decreases, making it difficult to maximize the effect of the added amount.

[0135] (Other ingredients)

[0136] As long as the electrode paste contains electrode active material and water as essential components, it can contain any other constituent components. Examples of such arbitrary components include the aforementioned second-highest dielectric oxide solid, conductive additives, binders, and other known components.

[0137] [Electrode Mixture Precursor Layer Formation Steps]

[0138] The electrode paste precursor layer formation step involves coating the electrode paste prepared in the electrode paste preparation step onto the current collector, and then drying the water contained in the electrode paste to obtain the electrode paste precursor layer.

[0139] There are no particular limitations on the coating method; any known method can be used. For example, roller coating, screen coating, doctor blade coating, spin coating, and bar coating can be listed.

[0140] Furthermore, there are no particular limitations on the method for drying the water contained in the electrode paste after coating; known methods can be used. There are also no particular limitations on the drying conditions. Water can be completely removed in vacuum drying, or it can remain in a pre-drying stage, allowing it to contact the high-dielectric oxide solid dispersion in a subsequent step.

[0141] [Preparation steps for high-dielectric oxide solid dispersions]

[0142] The high-dielectric oxide solid dispersion preparation step is a step of preparing a high-dielectric oxide dispersion containing a first high-dielectric oxide solid and an organic solvent. As described above, in the method for manufacturing an electrode for a lithium-ion secondary battery of the present invention, water is used as a solvent in the electrode paste used to form the electrode paste layer. On the other hand, an organic solvent is used as the solvent for dispersing the first high-dielectric oxide solid.

[0143] (First high dielectric oxide solid)

[0144] The first high-dielectric oxide solid used in the preparation step of the high-dielectric oxide solid dispersion is not particularly limited, but is preferably the solid described above that can be applied to the electrode of the ion secondary battery of the present invention.

[0145] The solvent used to prepare the high-dielectric oxide solid dispersion is an organic solvent rather than water, therefore even high-dielectric oxide solids that react with water can be used. Examples of high-dielectric oxide solids that react with water include Li7La3Zr2O. 12 (LLZO), Li5La3Ta2O 12 (LLTO), etc. In the method for manufacturing electrodes for lithium-ion secondary batteries of the present invention, electrodes can be prepared even with high dielectric oxide solids that are reactive with water without impairing their activity.

[0146] (Organic solvents)

[0147] There are no particular limitations on the organic solvent used to constitute the high-dielectric oxide solid dispersion; examples include alcohols, ketones, carbonates, and nitriles. However, from the viewpoint of reducing surface reactions of the solid oxide, aprotic solvents are preferred. Any aprotic solvent that can be used as an electrolyte in a lithium-ion battery can function as an electrolyte component, even if only a small portion remains, and is therefore particularly preferred.

[0148] More specifically, examples include carbonates. Examples of cyclic carbonates include ethylene carbonate, ethylene carbonate, propylene carbonate, and butyl carbonate. Additionally, cyclic carbonates such as propylene trifluorocarbonate and ethyl fluorocarbonate, in which some or all of their hydrogen groups are fluorinated, can also be examples. Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and isopropyl methyl carbonate.

[0149] (Preparation conditions)

[0150] The concentration of the first high-dielectric oxide solid in the high-dielectric oxide solid dispersion is not particularly limited and can be appropriately selected according to the conditions in the subsequent electrode mixture layer formation step. Furthermore, the preparation method of the high-dielectric oxide solid dispersion is not particularly limited and can be any known method.

[0151] [Electrode Mixture Layer Formation Steps]

[0152] The electrode mixture layer formation step is as follows: the high dielectric oxide dispersion prepared in the high dielectric oxide solid dispersion preparation step is brought into contact with the surface opposite to the current collector side surface of the electrode mixture precursor layer obtained in the electrode mixture precursor layer formation step, and then the organic solvent contained in the high dielectric oxide solid dispersion is dried to obtain the electrode mixture layer.

[0153] In the electrode mixture layer formation step, the method of contacting the high-dielectric oxide dispersion obtained in the high-dielectric oxide solid dispersion preparation step with the surface opposite to the current collector side surface of the electrode mixture precursor layer is not particularly limited, and can preferably be selected from at least one of the group consisting of dripping, coating, spraying and impregnation.

[0154] Furthermore, there are no particular limitations on the method for drying the organic solvent contained in the high-dielectric oxide solid dispersion after contact with it; known methods can be used. There are also no particular limitations on the drying conditions.

[0155] The high-dielectric oxide dispersion is brought into contact only with the surface opposite to the current collector side surface of the electrode mixture precursor layer, and then the organic solvent contained in the high-dielectric oxide solid dispersion is dried. This allows the first high-dielectric oxide solid contained in the high-dielectric oxide solid dispersion to be configured to have a continuous or phased concentration gradient in the thickness direction of the electrode mixture layer, decreasing from the surface opposite to the current collector towards the current collector.

[0156] Furthermore, in the method for manufacturing an electrode for a lithium-ion secondary battery according to the present invention, in the final lithium-ion secondary battery electrode, it is preferable to arrange a first high-dielectric oxide solid in the electrode mixture layer within a region of thickness less than 1 / 2, from the surface opposite to the current collector along the thickness direction. By arranging the first high-dielectric oxide solid within a region of thickness less than 1 / 2, potential deviation in the electrode thickness direction can be sufficiently suppressed even without arranging the dielectric oxide particles obliquely along the entire thickness direction.

[0157] [Suppression Steps]

[0158] The pressing step involves pressing the electrode mixture layer obtained in the electrode mixture layer formation step to finally obtain the electrode for lithium-ion secondary batteries.

[0159] By pressing the electrode mixture layer, the electrode density can be increased to improve the volumetric energy density, and the first high-dielectric oxide solid and the arbitrarily added second high-dielectric oxide solid can be disposed in the gaps between the electrode active materials.

[0160] Furthermore, by pressing, a concentration gradient can be easily formed in which the filling density of the high-dielectric oxide solid on the current collector side is lower than the filling density of the high-dielectric oxide solid near the opposite surface of the electrode mixture layer.

[0161] In the electrode paste preparation step, when a second high-dielectric oxide solid is incorporated, the second high-dielectric oxide solid is generally uniformly present throughout the entire electrode paste layer in the lithium-ion secondary battery electrode obtained after the pressing step. On the other hand, the first high-dielectric oxide solid is present in such a way that it decreases from the surface opposite to the current collector towards the current collector in the thickness direction of the electrode paste layer, and has a continuous or phased concentration gradient.

[0162] There are no particular limitations on the method for pressing the electrode mixture layer; any known method can be used. There are also no particular limitations on the pressing conditions.

[0163] <Manufacturing Method of Lithium-ion Secondary Batteries>

[0164] The manufacturing method of the lithium-ion secondary battery of the present invention is not particularly limited as long as the negative electrode of the present invention is used. Conventional methods in the art can be applied.

[0165] Example

[0166] The present invention will now be described in further detail with reference to embodiments and comparative examples, but the present invention is not limited thereto.

[0167] <Example 1>

[0168] [Preparation of the negative electrode]

[0169] Sodium carboxymethyl cellulose (CMC) as a binder and acetylene black as a conductive additive were mixed and dispersed using a planetary mixer to obtain a mixture. Artificial graphite (AG, D50 = 12 μm) was mixed into the obtained mixture as the negative electrode active material and dispersed again using a planetary mixer to obtain a negative electrode paste. Then, the obtained negative electrode paste was dispersed in water, and styrene-butadiene rubber (SBR) as a binder was added to prepare a negative electrode paste with a mass ratio of negative electrode active material: conductive additive: styrene-butadiene rubber (SBR): binder (CMC) of 96.5:1:1.5:1.

[0170] A 12 μm thick copper foil was prepared as the negative electrode current collector. The prepared negative electrode paste was coated onto one side of the negative electrode current collector. After drying at 100 °C for 10 minutes, it was impregnated with Li7La3Zr2O, which served as the first high-dielectric oxide solid particle with an average particle size of 0.2 μm. 12 LLZO was dispersed in a liquid obtained from N-methyl-2-pyrrolidone (NMP) and infiltrated at a mass ratio of 0.5 wt% of LLZO to the entire negative electrode mixture layer. Next, after drying at 60°C for 10 minutes, it was pressed with a linear pressure of 1 t / cm using a roller press, and then dried under vacuum at 120°C, thereby preparing a negative electrode mixture layer with a density of 1.5 g / cm³. 3 The negative electrode is used in lithium-ion secondary batteries. Furthermore, the prepared negative electrode is stamped to a size of 34mm × 44mm before use.

[0171] [Preparation of the positive electrode]

[0172] LiNi will be used as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (NCM622, D50 = 12 μm), acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder were mixed to a mass ratio of positive electrode active material: conductive additive: PVDF resin binder = 96.5:1.5:2. The mixture was dispersed using a planetary mixer to obtain a positive electrode paste. Then, the obtained positive electrode paste was dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode paste.

[0173] A 12 μm thick aluminum foil was prepared as the positive electrode current collector. The prepared positive electrode paste was coated onto one side of the positive electrode current collector. After drying at 120 °C for 10 minutes, it was pressed with a roller press at a linear pressure of 1 t / cm, and then dried in a vacuum at 120 °C. This yielded a positive electrode paste layer with a density of 3.3 g / cm³.3 This is the positive electrode for lithium-ion secondary batteries. Furthermore, the prepared positive electrode is stamped into a size of 30mm × 40mm before use.

[0174] [Preparation of Lithium-ion Secondary Batteries]

[0175] Prepare a three-layer laminate of polypropylene / polyethylene / polypropylene (20 μm thick) as a separator. Stack the prepared positive electrode, separator, and negative electrode and insert them into a bag-shaped container made of aluminum laminate (manufactured by Dai Nippon Printing) for secondary batteries by heat sealing.

[0176] At this point, the separator is sandwiched between the positive electrode flux layer of the positive electrode and the negative electrode flux layer of the negative electrode, so that the part of the positive current collector that has not formed a positive electrode flux layer and the part of the negative current collector that has not formed a negative electrode flux layer are exposed outside the container. After injecting electrolyte into the container, the container is vacuum sealed to prepare a lithium-ion secondary battery in which the end of the separator is immersed in the electrolyte stored at the bottom.

[0177] As an electrolyte, a solution of 1.0 mol / L LiPF6 is used, which is prepared by dissolving ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:30:40.

[0178] In this embodiment, the lithium-ion secondary battery contains only a high-dielectric oxide solid at the negative electrode. A portion of the negative electrode active material contacts the high-dielectric oxide solid, while the remaining portion contacts the electrolyte. The resulting lithium-ion secondary battery was evaluated as follows. The evaluation results are shown in Table 1.

[0179] <Example 2>

[0180] In the negative electrode, a lithium-ion secondary battery was prepared in the same manner as in Example 1, except that the particle size of the first high-dielectric oxide solid mixed with the negative electrode binder layer was changed as shown in Table 1.

[0181] <Examples 3-4>

[0182] [Preparation of the negative electrode]

[0183] The proportions of negative electrode active material, conductive additive, first conductive particle, second conductive particle, styrene-butadiene rubber (SBR), and binder (CMC) were set in the manner of 95.3:1:0.2:1:1.5:1. Except for the first conductive particle, a negative electrode paste was prepared in the same manner as in Example 1. Lithium triphosphate was used as the second conductive particle in Example 3, and lithium niobate was used in Example 4.

[0184] A 12 μm thick copper foil was prepared as the negative electrode current collector. The prepared negative electrode paste was coated onto one side of the negative electrode current collector. After drying at 100 °C for 10 minutes, it was placed in a glass beaker and dried at 60 °C for 24 hours in a vacuum drying oven. Then, it was impregnated with Li7La3Zr2O, which has an average particle size of 0.2 μm, as the first high-dielectric oxide solid particle. 12 LLZO was dispersed in a liquid obtained by dispersing N-methyl-2-pyrrolidone (NMP) and infiltrated at a mass ratio of 0.2 wt% of LLZO to the entire negative electrode mixture. The solution was added to a beaker and dripped from the top to wet the entire electrode. The electrode was then placed in a vacuum drying oven, where the dispersion was impregnated into the active material within the negative electrode mixture using a vacuum impregnation method. After drying the electrode at 120°C for 10 minutes, it was rolled. This resulted in a negative electrode mixture layer with a density of 1.5 g / cm³. 3 The negative electrode is used in lithium-ion secondary batteries. Furthermore, the prepared negative electrode is stamped to a size of 34mm × 44mm before use.

[0185] [Preparation of the positive electrode]

[0186] The positive electrode was prepared in the same manner as in Example 1.

[0187] [Preparation of Lithium-ion Secondary Batteries]

[0188] A lithium-ion secondary battery was prepared in the same manner as in Example 1.

[0189] <Comparative Example>

[0190] [Preparation of the negative electrode]

[0191] The negative electrode paste was prepared in the same manner as in Example 1. A 12 μm thick copper foil was used as the negative electrode current collector. The prepared negative electrode paste was coated onto one side of the current collector and dried at 100°C for 10 minutes. Instead of immersing it in a dispersion of high-dielectric oxide solid particles, it was pressed using a roller press at a linear pressure of 1 t / cm and then dried under vacuum at 120°C. This resulted in a negative electrode paste layer with a density of 1.5 g / cm³. 3 The negative electrode is used in lithium-ion secondary batteries. Furthermore, the prepared negative electrode is stamped to a size of 34mm × 44mm before use.

[0192] [Preparation of the positive electrode]

[0193] The positive electrode was prepared in the same manner as in Example 1.

[0194] [Preparation of Lithium-ion Secondary Batteries]

[0195] A lithium-ion secondary battery was prepared in the same manner as in Example 1.

[0196] <Assessment>

[0197] The lithium-ion secondary batteries obtained in Examples 1-4 and Comparative Example 1 were evaluated as follows. The evaluation results are shown in Table 1.

[0198] [Observation of the configuration of the first high-dielectric oxide solid (SEM observation)]

[0199] To confirm the dispersion state of the first high-dielectric oxide solid in the prepared lithium-ion secondary battery electrode, a cross-section of the electrode mixture layer was prepared by ion milling and observed using SEM.

[0200] The imaging range of the cross-sectional SEM was selected to be 100% of the thickness direction (vertical direction) of the electrode mixture layer. The magnification was approximately 5000x to 10000x, and multiple images were captured in segments to confirm the configuration state of the first high-dielectric oxide solid, namely LLZO.

[0201] In the negative electrodes for lithium-ion secondary batteries prepared in Examples 1-4, the thickness of the flux layer was 77 μm, and the LLZO particles were concentrated in the upper layer, which is the separator side (opposite to the current collector). In addition, it was confirmed that particles other than LLZO also existed at a depth of 38 μm, about half the thickness of the flux layer on the separator side (opposite to the current collector).

[0202] Furthermore, the thickness of the electrode mixture layer was set to 100. Region A, extending from the surface layer on the diaphragm side (opposite to the current collector) to 25% of the depth, was designated as region A. Region B, extending from 25% to 50% of the depth, was designated as region B. The ratio of LLZO present in region A to that present in region B (A:B) was calculated as the concentration gradient of the first high-dielectric solid oxide configuration. Regarding the A:B ratio, the reflected electron image from the cross-sectional SEM was binarized to create a brightness distribution curve. The A:B ratio was calculated based on the area ratio of LLZO in regions A and B.

[0203] [Initial discharge capacity]

[0204] The obtained lithium-ion secondary battery was placed at the measurement temperature (25℃) for 1 hour, charged at a constant current of 0.33C to 4.2V, and then charged at a constant voltage of 4.2V for 1 hour. After being placed for 30 minutes, it was discharged at a discharge rate of 0.2C to 2.5V, and the initial discharge capacity was measured.

[0205] [Initial battery resistance]

[0206] The lithium-ion rechargeable battery, after initial discharge capacity measurement, was adjusted to 50% charge level (SOC). Next, a 0.2C pulse discharge was performed for 10 seconds, and the voltage at 10 seconds of discharge was measured. Furthermore, the voltage at 0.2C relative to the current for 10 seconds of discharge was plotted with the horizontal axis representing current and the vertical axis representing voltage. Then, after 5 minutes of resting, a supplementary charge was performed to restore the SOC to 50%, followed by another 5 minutes of resting.

[0207] Next, the above operation was performed for each C-rate: 0.5C, 1C, 2C, 3C, and 4C, and the voltage at each C-rate relative to the current after 10 seconds of discharge was plotted. Furthermore, the slope of the approximate straight line obtained from each curve was used as the initial battery resistance of the lithium-ion secondary battery.

[0208] [Discharge capacity after durability]

[0209] As part of the charge-discharge cycle durability test, the battery was charged to 4.2V at a constant current of 1.0C in a constant temperature bath at 45°C, and then discharged to 2.5V at a constant current of 1.5C. This operation was considered one cycle, and the operation was repeated for 500 cycles. After 500 cycles, the constant temperature bath was set to 25°C, and the battery was placed in the 2.5V discharged state for 24 hours. Then, the discharge capacity after durability was measured in the same manner as the initial discharge capacity measurement.

[0210] [Battery resistance after durability]

[0211] After measuring the discharge capacity after durability testing, the lithium-ion secondary battery is adjusted to 50% of its State of Charge (SOC), and the battery resistance after durability testing is calculated using the same method as when measuring the initial battery resistance.

[0212] [Capacity Maintenance Rate]

[0213] The endurance discharge capacity relative to the initial discharge capacity is calculated and used as the capacity retention rate.

[0214] [Battery resistance rise rate]

[0215] Calculate the battery resistance after durability relative to the initial battery resistance, and use it as the rate of increase in battery resistance.

[0216]

[0217]

[0218] Figure Labels

[0219] 1. Lithium-ion secondary battery

[0220] 2 Positive current collector

[0221] 3 Positive electrode mixture layer

[0222] 4 Positive electrode

[0223] 5. Negative current collector

[0224] 6 Negative electrode mixture layer

[0225] 7 Negative electrode

[0226] 8. Diaphragm

[0227] 9 Electrolyte

[0228] 10 containers

Claims

1. An electrode for a lithium-ion secondary battery, comprising an electrolyte and having: Current collector and electrode mixture layer stacked on the current collector; The electrode mixture layer contains an electrode active material and a first high-dielectric oxide solid; and... In the electrode mixture layer, the first high-dielectric oxide solid is configured to have a continuous or phased concentration gradient, decreasing from the surface opposite to the current collector towards the current collector in the thickness direction of the electrode mixture layer. The first high-dielectric oxide solid is disposed in the electrode mixture layer, from the surface opposite to the current collector along the thickness direction, within a region of less than 1 / 2 thickness. When region A is defined as the area extending from the surface layer opposite to the current collector of the electrode mixture layer to 25% of its depth, and region B is defined as the area from 25% to 50% of its depth, the ratio of the first high-dielectric oxide solid present in region A to the first high-dielectric oxide solid present in region B, i.e., A:B, is 81:19 to 87:

13. The first high-dielectric oxide solid is selected from Li7La3Zr2O 12 Li5La3Ta2O 12 and Li 2.9 PO 3.3 N 0.46 At least one of the groups formed in, The electrode mixture layer also contains a second high-dielectric oxide solid. The second high-dielectric oxide solid is Li3PO4 or LiNbO3.

2. The electrode for a lithium-ion secondary battery according to claim 1, wherein, The first high-dielectric oxide solid is disposed in the gaps between the electrode active materials.

3. The electrode for a lithium-ion secondary battery according to claim 1 or 2, wherein, The electrode used in the lithium-ion secondary battery is the negative electrode.

4. The electrode for a lithium-ion secondary battery according to claim 1, wherein, The first high dielectric oxide solid relative to Li / Li + The equilibrium potential is 1.5V (1.5V vs Li / Li). + The following reduction decomposition potential.

5. The electrode for a lithium-ion secondary battery according to claim 1, wherein, The second high-dielectric oxide solid is disposed in the gaps between the electrode active materials.

6. The electrode for a lithium-ion secondary battery according to claim 1, wherein, The second high-dielectric oxide solid is disposed substantially uniformly throughout the entire electrode mixture layer.

7. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator electrically insulating the positive electrode and the negative electrode, and an electrolyte, and wherein, The negative electrode is the electrode for a lithium-ion secondary battery as described in claim 1 or 2.

8. The lithium-ion secondary battery according to claim 7, wherein, It comprises the positive electrode, the negative electrode, the diaphragm, and a container for containing the electrolyte; The diaphragm is in contact with the electrolyte stored in the container.

9. A method for manufacturing an electrode for a lithium-ion secondary battery, the electrode having a current collector and an electrode mixture layer laminated on the current collector, the method comprising the following steps: The electrode paste preparation step involves preparing an electrode paste containing electrode active material, water, and a second high dielectric oxide solid, wherein the second high dielectric oxide solid is Li3PO4 or LiNbO3. The electrode paste precursor layer formation step involves coating the electrode paste onto the current collector and drying the water to obtain the electrode paste precursor layer. The preparation steps of the high-dielectric oxide solid dispersion include preparing a high-dielectric oxide dispersion containing a first high-dielectric oxide solid and an organic solvent, wherein the first high-dielectric oxide solid is selected from Li7La3Zr2O. 12 Li5La3Ta2O 12 and Li 2.9 PO 3.3 N 0.46 At least one of the groups; The electrode mixture layer formation step involves contacting the high-dielectric oxide dispersion with the surface of the electrode mixture precursor layer opposite to the current collector side surface, and drying the organic solvent to obtain the electrode mixture layer. and, The pressing step presses the electrode mixture layer to obtain an electrode for a lithium-ion secondary battery having the electrode mixture layer. The electrode mixture layer is defined as region A from the surface layer opposite to the current collector of the electrode mixture layer to 25% of the depth direction, and region B from 25% to 50% of the depth direction. The ratio of the first high-dielectric oxide solid present in region A to the first high-dielectric oxide solid present in region B, i.e., A:B, is 81:19 to 87:

13.

10. The method for manufacturing an electrode for a lithium-ion secondary battery according to claim 9, wherein, The contact method in the electrode mixture layer formation step is at least one of the group consisting of dripping, coating, spraying and impregnation.

11. The method for manufacturing an electrode for a lithium-ion secondary battery according to claim 9 or 10, wherein, In the electrode mixture layer formation step, the first high-dielectric oxide solid is configured to have a concentration gradient in a manner that decreases from the surface opposite to the current collector in the thickness direction of the electrode mixture layer, either continuously or in stages.

12. The method for manufacturing an electrode for a lithium-ion secondary battery according to claim 9 or 10, wherein, The electrode used in the lithium-ion secondary battery is the negative electrode.

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