Electrolyte absorbing particles, self-supporting sheet, electrode for lithium ion secondary battery, separator for lithium ion secondary battery, and lithium ion secondary battery

Abstract

The present application provides an electrolyte absorbing particle, a self-supporting sheet containing the electrolyte absorbing particle, an electrode for a lithium ion secondary battery containing the electrolyte absorbing particle, a separator using the electrolyte absorbing particle, and a lithium ion secondary battery using the electrolyte absorbing particle, the electrolyte absorbing particle having a liquid retention property of an electrolyte and being capable of improving transport properties of lithium ions. A particle is produced in which a resin layer capable of absorbing an electrolyte is provided on the surface of a high-dielectric oxide solid. Specifically, an electrolyte absorbing particle is produced which has a resin layer capable of absorbing an electrolyte on the surface of a high-dielectric oxide solid.

Description

Technical Field

[0001] The present invention relates to an electrolyte absorber particle, a self-standing sheet containing the electrolyte absorber particle, an electrode for a lithium-ion secondary battery containing the electrolyte absorber particle, a separator using the electrolyte absorber particle, and a lithium-ion secondary battery using the electrolyte absorber particle. Background Technology

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

[0003] The electrolyte in lithium-ion secondary batteries is typically a flammable organic solvent, and safety, especially regarding heat, can sometimes be a concern. Therefore, a solid-state battery has been proposed that uses a flame-retardant solid electrolyte instead of an organic liquid electrolyte.

[0004] These lithium-ion rechargeable batteries have various requirements depending on their application. For example, in applications such as automobiles, the ideal battery is one with high energy density and minimal degradation in output characteristics even after repeated charge-discharge cycles.

[0005] However, generally speaking, the output characteristics of lithium-ion secondary batteries tend to decrease with repeated charge and discharge cycles. This is because repeated charge and discharge cause the electrolyte to decompose, forming a passivation film on the electrodes, which gradually increases the internal resistance, and the amount of electrolyte decreases, resulting in insufficient electrolyte.

[0006] To address this, a method is proposed that promotes electrolyte dissociation and replenishes free solvent by containing a solid electrolyte within the electrode, thereby maintaining the properties (see Patent Document 1). Solid electrolytes readily polarize electrons and ions, and thus replenish the electrolyte by counteracting anions and free solvents that act as lithium diffusion hindrances, thereby improving lithium diffusivity.

[0007] [Previous Technical Documents]

[0008] (Patent Documents)

[0009] Patent Document 1: Japanese Patent Application Publication No. 2016-167457 Summary of the Invention

[0010] [The problem the invention aims to solve]

[0011] However, while solid electrolyte particles exhibit high wettability of the electrolyte, they lack the ability to immobilize the electrolyte. Therefore, due to gravity and the expansion and contraction of the electrodes accompanying the charging and discharging of lithium-ion secondary batteries, the electrolyte easily disappears from the surface of the solid electrolyte particles. Consequently, even with the addition of solid electrolyte, the effect is limited.

[0012] The present invention was made in view of the above circumstances, and aims to provide an electrolyte absorbing particle, a self-standing sheet containing the electrolyte absorbing particle, an electrode for a lithium-ion secondary battery containing the electrolyte absorbing particle, a separator using the electrolyte absorbing particle, and a lithium-ion secondary battery using the electrolyte absorbing particle, wherein the electrolyte absorbing particle has electrolyte liquid retention properties and can improve lithium-ion transport characteristics.

[0013] [Technical means to solve the problem]

[0014] The inventors conducted active research to solve the above-mentioned problems. They then concluded that if a resin layer capable of absorbing electrolyte is incorporated onto the surface of particles composed of highly dielectric oxide solids, the resulting particles would possess electrolyte retention properties and enhance lithium-ion transport characteristics, thus completing this invention.

[0015] That is, the present invention is an electrolyte absorbing particle having a resin layer on the surface of a high dielectric oxide solid capable of absorbing electrolyte.

[0016] In the aforementioned electrolyte absorber particles, the aforementioned high dielectric oxide solid can also be an oxide with lithium ion conductivity.

[0017] In the aforementioned electrolyte absorber particles, the aforementioned high dielectric oxide solid can also be a strong dielectric oxide with a relative dielectric constant of 10 or more.

[0018] In the aforementioned electrolyte absorber particles, the aforementioned high-dielectric oxide solid can also exhibit a dielectric constant of 10 at 25°C. -7 Lithium-ion conductivity above S / cm.

[0019] In the aforementioned electrolyte absorber particles, the aforementioned high-dielectric oxide solid can also be composed of the chemical formula Li 7- y La 3-x A x Zr 2-y M y O 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 garnet-type composite metal oxide.

[0020] In the aforementioned electrolyte absorber particles, the aforementioned high-dielectric oxide solid can also contain substances with the chemical formula Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 The composite metal oxide of the crystal is represented by (where 0≦x≦1, 0≦y≦1).

[0021] In the aforementioned electrolyte absorber particles, the aforementioned resin layer may also have fine pores, which are filled with and absorb electrolyte.

[0022] The volume of the aforementioned pores can also be 30 vol% or more relative to the volume of the aforementioned resin layer.

[0023] Another invention is a self-standing sheet comprising the aforementioned electrolyte-absorbing particles.

[0024] Another invention is an electrode for a lithium-ion secondary battery, which includes an electrode active material and the aforementioned electrolyte absorber particles.

[0025] In the aforementioned electrode for lithium-ion secondary batteries, the amount of electrolyte absorbent particles prepared relative to 100 parts by mass of the aforementioned electrode for lithium-ion secondary batteries may be 0.1 parts by mass or more and 5 parts by mass or less.

[0026] In the aforementioned electrodes for lithium-ion secondary batteries, the aforementioned electrode active material can also be a positive electrode active material.

[0027] In the aforementioned electrodes for lithium-ion secondary batteries, the aforementioned electrode active material can also be a negative electrode active material.

[0028] Another invention relates to an electrode for a lithium-ion secondary battery, comprising: a current collector; and an electrode active material layer formed on at least one side of the current collector and comprising the electrode active material; and having an electrolyte absorption layer on the electrode active material layer, the electrolyte absorption layer comprising the electrolyte absorption particles.

[0029] In the aforementioned electrode for lithium-ion secondary batteries, the electrolyte absorption layer can also come into contact with the separator when the lithium-ion secondary battery is formed.

[0030] In the aforementioned electrodes for lithium-ion secondary batteries, the aforementioned electrode active material can also be a positive electrode active material.

[0031] In the aforementioned electrodes for lithium-ion secondary batteries, the aforementioned electrode active material can also be a negative electrode active material.

[0032] Another invention is a separator for lithium-ion secondary batteries, which has an electrolyte absorption layer on at least one side of a substrate, the electrolyte absorption layer comprising the aforementioned electrolyte absorption particles.

[0033] Another invention relates to a lithium-ion secondary battery comprising: a positive electrode layer for a lithium-ion secondary battery, having a positive active material layer comprising a positive active material; a negative electrode layer for a lithium-ion secondary battery, having a negative active material layer comprising a negative active material; a separator disposed between the aforementioned positive electrode layer and the aforementioned negative electrode layer for a lithium-ion secondary battery; and an electrolyte; and an electrolyte absorption layer comprising electrolyte absorption particles is provided between the aforementioned positive electrode layer and / or the aforementioned negative electrode layer for a lithium-ion secondary battery and the aforementioned separator.

[0034] (The effect of the invention)

[0035] The electrolyte-absorbing particles of the present invention possess electrolyte liquid retention properties, thus preventing electrolyte loss from the particle surface. As a result, the lithium-ion transport characteristics can be improved, thereby reducing the initial resistance of the lithium-ion secondary battery and suppressing the increase in internal resistance caused by repeated charge-discharge cycles.

[0036] For example, if the electrolyte absorber particles of the present invention are incorporated into at least one of the positive and negative electrodes, heat generation can be suppressed even at high rates, resulting in long-life and stable battery performance.

[0037] Furthermore, the electrolyte absorber particles of the present invention have a resin layer on their surface, thus reducing the amount of binder used when incorporated into at least one of the positive and negative electrodes. As a result, the decrease in monomer energy density can be suppressed.

[0038] Furthermore, if the layer containing the electrolyte absorber particles of the present invention is disposed between at least one of the positive electrode layer and the negative electrode layer and the separator, electrolyte insufficiency can be particularly suppressed. Electrolyte insufficiency occurs due to the high reaction force caused by the expansion and contraction of the electrodes during charging and discharging, which forces the electrolyte between the electrode surface and the separator to be squeezed out. As a result, lithium deposition can also be suppressed by rapid charging, improving not only the previously problematic short-circuit toughness but also the battery's durability.

[0039] Furthermore, the electrolyte absorber particles of the present invention have a resin layer on their surface, thus exhibiting adhesive properties. Therefore, if a layer containing the electrolyte absorber particles of the present invention is disposed between at least one of the positive electrode layer and the negative electrode layer and the separator, gaps can be prevented between the electrode and the separator due to the expansion and contraction of the electrode accompanying charging and discharging. Attached Figure Description

[0040] Figure 1 This is a graph illustrating the discharge rate of the lithium-ion secondary batteries manufactured in the embodiments and comparative examples.

[0041] Figure 2 This is a graph illustrating the charging rate of the lithium-ion secondary batteries manufactured in the embodiments and comparative examples.

[0042] Figure 3 It is a graph illustrating the endurance capacity of the lithium-ion secondary batteries manufactured in the embodiments and comparative examples. Detailed Implementation

[0043] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments.

[0044] <Electrolyte Absorbing Particles>

[0045] The electrolyte-absorbing particles of the present invention are particles having a resin layer on the surface of a high-dielectric oxide solid capable of absorbing electrolyte.

[0046] [Highly dielectric oxide solid]

[0047] There are no particular limitations as long as it is a solid composed of a highly dielectric oxide. Various particles can be used.

[0048] (Lithium-ion conductivity)

[0049] Preferably, the oxide is a lithium-ion conductive oxide. If the high-dielectric oxide solid constituting the electrolyte absorber particles of the present invention is a lithium-ion conductive oxide, the lithium ions within the particles are easily mobile and will effectively exhibit dielectric properties. Therefore, the degree of dissociation of the electrolyte becomes easier to increase.

[0050] Furthermore, it is preferable that the high-dielectric oxide solid constituting the electrolyte absorber particles of the present invention has a dielectric constant of 10 at 25°C. -7 Oxides with lithium-ion conductivity of S / cm or higher. Lithium-ion conductivity is preferably 10 at 25°C. -5 S / cm or higher, with 10 being particularly preferred. -4 S / cm or higher.

[0051] As a high-dielectric oxide solid constituting the electrolyte absorber particles of the present invention, it has a dielectric constant of 10 at 25°C. -7 In the case of lithium-ion conductive oxides with a S / cm or higher, lithium ions within the particles become more mobile, thus exhibiting dielectric properties more effectively.

[0052] (Relative permittivity of powder)

[0053] The high-dielectric oxide solid constituting the electrolyte absorber particles of the present invention is preferably a strong dielectric oxide with a relative permittivity of 10 or more. More preferably, it is a strong dielectric oxide with a relative permittivity of 15 or more, and particularly preferably, it is a strong dielectric oxide with a relative permittivity of 20 or more.

[0054] Here, the relative permittivity of the powder in this specification refers to the value obtained using the following method.

[0055] {Methods for determining the relative permittivity of powder}

[0056] Powder was introduced into a tablet forming machine with a diameter (R) of 38 mm for testing, and compressed using a hydraulic press to achieve a thickness (d) of 1–2 mm, forming compressed powder. The forming conditions for the compressed powder were set to 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 1kHz was measured using an inductance-capacitance-resistance (LCR) meter and an automatic balancing bridge method. total The relative permittivity ε of the pressed powder was calculated. total In order to determine the dielectric constant ε of the actual volume portion from the obtained relative dielectric constant of the pressed powder. power The dielectric constant ε0 of vacuum can be set to 8.854 × 10⁻⁶. -12 The relative permittivity ε of air air Let ε be 1, and use the following formulas (1) to (3) to calculate the relative permittivity ε of the powder. power ".

[0057] The contact area between the pressed powder and the electrode is A = (R / 2). 2 *π (1)

[0058] C total =ε total ×ε0×(A / d) (2)

[0059] ε total =ε powder ×D powder +ε air ×(1-D powder (3)

[0060] As a high-dielectric oxide solid constituting the electrolyte absorber particles of the present invention, when a strong dielectric oxide with a relative permittivity of 10 or more is used, the degree of dissociation of the electrolyte can be improved and the resistance of the electrolyte can be reduced.

[0061] As a strongly dielectric oxide with a relative permittivity of 10 or higher, there are no particular limitations; examples include BaTiO3 and Ba... x Sr 1-x TiO3 (X = 0.4–0.8), BaZr x Ti 1-x Composite metal oxides with perovskite-type crystal structures such as O3 (X = 0.2–0.5) and KNbO3, and composite metal oxides with layered perovskite-type crystal structures containing bismuth such as SrBi2Ta2O9 and SrBi2Nb2O9, etc., are preferred in this invention. In this invention, at least one selected from the group consisting of these is preferably used.

[0062] Additionally, as a product with a temperature of 25°C and a strength of 10... -7 Oxides with lithium-ion conductivity of S / cm or higher are not particularly limited; for example, those with the chemical formula Li can be listed. 7-y La 3-x A x Zr 2-y M y O 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 garnet-type composite metal oxide.

[0063] Or you can list examples containing the chemical formula Li. 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 The composite metal oxide with a sodium superionic conductor (NASICON) crystal structure is represented by (where 0≦x≦1, 0≦y≦1).

[0064] More specifically, examples of high-dielectric oxide solids constituting the electrolyte absorber particles of the present invention include Li7La3Zr2O. 12 (LLZO), Li 6.75 La3Zr 1.75 Ta 0.25 O 12 (LLZTO), Li 0.33 La 0.56 TiO3(LLTO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP) and Li 1.6 Al 0.6 Ge1.4 (PO4)3(LAGP). In this invention, it is preferred to use at least one selected from the group consisting of these.

[0065] (Particle size)

[0066] The particle size of the high-dielectric oxide solid constituting the electrolyte absorber particles of the present invention is not particularly limited, but is preferably 0.1 μm or more and the particle size of the active material is less than or equal to 10 μm or less.

[0067] If the particle size becomes too small, for example, when the electrolyte absorber particles of the present invention are formulated into at least one of the positive and negative electrodes, they will adhere to the surface of the electrode active material and hinder electron conductivity, thus increasing the monomer resistance. On the other hand, if the particle size is too large, it will hinder the improvement of the filling rate of the active material in the electrode.

[0068] [Resin Layer]

[0069] In this invention, a resin layer is formed on the surface of a high-dielectric oxide solid in the electrolyte-absorbing particles. In this invention, the resin layer functions to absorb and retain the electrolyte, thus preventing electrolyte loss from the particle surface. As a result, the lithium-ion transport characteristics are improved, thereby reducing the initial resistance of the lithium-ion secondary battery and suppressing the increase in internal resistance caused by repeated charge-discharge cycles.

[0070] In the electrolyte absorber particles of the present invention, the resin layer preferably has fine pores. The fine pores are filled with and absorb the electrolyte. By filling the fine pores with electrolyte, electrolyte movement caused by gravity and electrolyte extrusion caused by electrode expansion and contraction during charging and discharging can be suppressed, thereby preventing electrolyte deficiency. As a result, battery performance can be maintained at a sufficient level, achieving long-life and stable battery performance.

[0071] In the electrolyte absorber particles of the present invention, when the resin layer has fine pores, the manufacturing method is not particularly limited. For example, methods that use plasticizers or the like to form a fine pore structure inside the resin layer can be listed.

[0072] In the electrolyte absorber particles of the present invention, when the resin layer has fine pores, the volume of the fine pores is preferably 30 vol% or more relative to the volume of the resin layer. More preferably, it is 50 vol% or more relative to the volume of the resin layer, and particularly preferably 60 vol% or more.

[0073] When the volume of the pores relative to the volume of the resin layer is less than 30 vol%, it is impossible to exhibit a good retention effect on the electrolyte. By making it 30 vol% or more, sufficient electrolyte retention can be ensured, thus further improving the degree of electrolyte dissociation.

[0074] <Self-standing tablets containing electrolyte absorber particles>

[0075] The self-standing sheet of the present invention is a sheet containing the electrolyte absorbing particles of the present invention described above, and it possesses independent self-standing properties. Its size, thickness, etc., are not particularly limited. Furthermore, in addition to the electrolyte absorbing particles of the present invention, the self-standing sheet may arbitrarily contain other components.

[0076] The self-standing sheet containing the electrolyte absorber particles of the present invention is preferably disposed between the positive electrode layer and / or the negative electrode layer and the separator of a lithium-ion secondary battery during the formation of a lithium-ion secondary battery.

[0077] By distributing a self-standing sheet containing the electrolyte-absorbing particles of the present invention on the surface of the electrode layer, the internal short-circuit toughness of the monomer can be improved. In particular, since the self-standing sheet containing the electrolyte-absorbing particles of the present invention has sufficient electrolyte retention function, it can suppress electrolyte extrusion caused by the expansion and contraction of the electrode during charging and discharging, thereby suppressing electrolyte deficiency. Therefore, in addition to improving short-circuit toughness, it can also improve durability.

[0078] <Electrodes for Lithium-ion Secondary Batteries>

[0079] [First Form: Mixing Type]

[0080] The first form of the electrode for lithium-ion secondary batteries of the present invention is an electrode for lithium-ion secondary batteries comprising an electrode active material and the electrolyte absorption particles of the present invention described above.

[0081] The structure of the electrode for the lithium-ion secondary battery of the present invention in the first embodiment is not particularly limited. For example, a structure in which an electrode layer composed of an electrode composite material is stacked on a current collector, wherein the electrode composite material includes an electrode active material and the electrolyte absorber particles of the present invention described above. The electrode layer may arbitrarily contain known components such as conductive additives and binders.

[0082] According to the first embodiment of the present invention, the electrode for lithium-ion secondary batteries can suppress heat generation even at high rates by incorporating the electrolyte absorber particles of the present invention into the electrode, resulting in long-life and stable battery performance.

[0083] In addition, the resin layer present on the surface of the electrolyte absorber particles can reduce the amount of adhesive used at the same time, thereby suppressing the decrease in monomer energy density.

[0084] (Distribution quantity)

[0085] When an electrode of the first form comprising the electrode active material and the electrolyte absorber particles of the present invention described above is manufactured, the amount of electrolyte absorber particles of the present invention is preferably 0.1 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the total composition of the electrode composite material constituting the electrode. More preferably, it is in the range of 0.5 parts by mass or more and 5.0 parts by mass or less, and particularly preferably, it is in the range of 0.5 parts by mass or more and 2.0 parts by mass or less.

[0086] When the amount of electrolyte absorber particles is less than 0.1 parts by mass relative to 100 parts by mass of the total composition of the electrode composite material constituting the electrode, the degree of dissociation of the electrolyte penetrating into the electrode becomes insufficient. On the other hand, when it is more than 5 parts by mass, the amount of electrolyte penetrating into the electrode becomes insufficient, and the movement path of lithium ions inside the electrode is restricted.

[0087] The electrode for a lithium-ion secondary battery according to the first embodiment of the present invention can be either a positive electrode or a negative electrode for a lithium-ion secondary battery. That is, the electrode active material contained in the electrode for a lithium-ion secondary battery of the present invention can be either a positive electrode active material or a negative electrode active material. The effects of the present invention can be obtained in either the positive or negative electrode configuration.

[0088] (Clottery Collector)

[0089] When fabricating an electrode comprising the electrode active material and the electrolyte absorber particles of the present invention as described above, there are no particular limitations on the current collector that can be used. Known current collectors applicable to lithium-ion secondary batteries can be used.

[0090] 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. 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.

[0091] Furthermore, the shape of the electrode current collector can be, for example, foil, plate, or mesh. There are no particular limitations on its thickness; for example, 1–20 μm can be used, and it can be selected appropriately as needed.

[0092] (Active substances)

[0093] 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 any known material that can be used as an electrode active material for lithium-ion secondary batteries can be used.

[0094] When the electrode for the lithium-ion secondary battery of the present invention is a positive electrode for a lithium-ion secondary battery, examples of positive electrode active material layers include LiCoO2, LiCoO4, LiMn2O4, LiNiO2, LiFePO4, lithium sulfide, and sulfur. As the positive electrode active material, a material exhibiting a higher potential than the negative electrode can be selected from the materials capable of constituting the electrode.

[0095] When the electrode for a lithium-ion secondary battery of the present invention is a negative electrode for a lithium-ion secondary battery, examples of negative electrode active materials 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 exhibiting a lower potential compared to the positive electrode can be selected from the materials capable of constituting the electrode.

[0096] (Electrode layer configuration)

[0097] In the first embodiment of the electrode for a lithium-ion secondary battery of the present invention, the electrode layer, composed of an electrode composite material containing electrode active material and electrolyte absorber particles of the present invention as essential components, may be formed on at least one side of the current collector, or on both sides. It can be appropriately selected according to the type and structure of the target lithium-ion secondary battery.

[0098] (thickness)

[0099] The thickness of the electrode for lithium-ion secondary batteries according to the first embodiment of the present invention is not particularly limited, but is preferably 40 μm or more. When the thickness is 40 μm or more and the volumetric fill rate of the electrode active material is 60% or more, the obtained electrode for lithium-ion secondary batteries will become a high-density electrode. Furthermore, the volumetric energy density of the manufactured battery cell can reach 500 Wh / L or more.

[0100] (Manufacturing method of electrodes for lithium-ion secondary batteries)

[0101] In the case where the electrode for the lithium-ion secondary battery of the present invention is an electrode comprising an electrode active material and the electrolyte absorber particles of the present invention described above, the manufacturing method is not particularly limited. General methods in this technical field can be applied.

[0102] For example, a method can be described as coating an electrode slurry onto a current collector, drying it, and then rolling it, wherein the electrode slurry is an electrode composite material containing an electrode active material and the electrolyte absorber particles of the present invention as essential components.

[0103] As a method for coating electrode paste onto a current collector, known methods can be used. Examples include roller coating, screen coating, doctor blade coating, spin coating, and bar coating.

[0104] [Second Form: Layered Type]

[0105] The second form of the electrode for a lithium-ion secondary battery of the present invention includes a current collector and an electrode active material layer formed on at least one side of the current collector and comprising an electrode active material. Furthermore, an electrolyte absorption layer is formed on the electrode active material layer, the electrolyte absorption layer comprising the electrolyte absorption particles of the present invention described above.

[0106] In the second embodiment of the lithium-ion secondary battery electrode of the present invention, the electrolyte absorption layer formed on the electrode active material layer is preferably in contact with the separator when the lithium-ion secondary battery is formed.

[0107] In the second embodiment of the lithium-ion secondary battery electrode of the present invention, by having an electrolyte absorption layer containing the electrolyte absorption particles of the present invention present at the contact interface between the electrode active material layer and the separator, the internal short-circuit toughness of the cell can be improved.

[0108] Furthermore, the ample electrolyte retention function provided by the electrolyte absorber particles of the present invention suppresses electrolyte extrusion caused by the expansion and contraction of the electrodes during charging and discharging, thereby preventing electrolyte deficiency. As a result, smooth movement of lithium ions between the electrode active material layer and the separator can be achieved, thereby further improving charge-discharge characteristics and cycle life.

[0109] The second embodiment of the electrode for a lithium-ion secondary battery of the present invention can be either a positive electrode or a negative electrode for a lithium-ion secondary battery. That is, the electrode active material constituting the electrode active material layer in the electrode for a lithium-ion secondary battery can be either a positive electrode active material or a negative electrode active material. The effects of the present invention can be obtained in either the positive or negative electrode configuration.

[0110] (Active substances)

[0111] The positive and negative active materials that can be used in the electrode of the second type of lithium-ion secondary battery are the same as those that can be used in the electrode of the first type of lithium-ion secondary battery.

[0112] (Configuration of the electrolyte absorption layer)

[0113] In the second embodiment of the lithium-ion secondary battery electrode, an electrolyte absorption layer comprising the electrolyte absorption particles of the present invention is formed on the electrode active material layer. When the electrode active material layer is formed on both sides of the current collector, it is formed at least on the side that contacts the separator when the lithium-ion secondary battery is formed.

[0114] (thickness)

[0115] In the second embodiment of the electrode for lithium-ion secondary batteries of the present invention, the thickness of the electrolyte absorption layer containing the electrolyte absorption particles of the present invention is not particularly limited. For example, it is preferably in the range of 1 / 100 to the average particle size (D50) of the solid dielectric oxide.

[0116] Furthermore, there is no particular limitation on the overall thickness of the lithium-ion secondary battery electrode of the second embodiment of the present invention. Similar to the lithium-ion secondary battery electrode of the first embodiment of the present invention, for example, a thickness of 40 μm or more and a volume fill rate of 60% or more of the electrode active material can be set to produce a high-density lithium-ion secondary battery electrode.

[0117] (Manufacturing method of electrodes for lithium-ion secondary batteries)

[0118] In the case where the electrode for the lithium-ion secondary battery of the present invention is a second-type electrode in which an electrolyte absorption layer comprising the electrolyte absorption particles of the present invention is formed on the electrode active material layer, the manufacturing method is not particularly limited. General methods in this technical field can be applied.

[0119] For example, the following method can be used: similar to the electrode for a lithium-ion secondary battery of the first form, an electrode slurry as an electrode composite material containing electrode active material is coated on a current collector, dried, and then rolled to form an electrode active material layer. After that, a particle dispersion slurry containing electrolyte absorber particles of the present invention is applied externally.

[0120] As a method for externally applying a particle dispersion slurry containing electrolyte-absorbing particles, known methods can be used. Examples include roller coating, screen coating, doctor blade coating, spin coating, and bar coating.

[0121] <Septum>

[0122] The separator of the present invention is a separator for lithium-ion secondary batteries, which has an electrolyte absorption layer on at least one side of a substrate, the electrolyte absorption layer comprising the electrolyte absorption particles of the present invention described above. Its size, thickness, etc., are not particularly limited.

[0123] The separator of the present invention is disposed between the positive electrode layer and the negative electrode layer of a lithium-ion secondary battery when forming a lithium-ion secondary battery.

[0124] There are no particular limitations on the substrate used as a separator; any known substrate used as a separator for lithium-ion secondary batteries can be used.

[0125] (Method for manufacturing the diaphragm)

[0126] The method for manufacturing the diaphragm of the present invention is not particularly limited. For example, a method of coating a particle dispersion slurry containing the electrolyte absorber particles of the present invention and any other components onto a substrate can be cited.

[0127] As a method for externally applying a particle dispersion slurry containing electrolyte absorbent particles, known methods can be used. Examples include roller coating, screen coating, doctor blade coating, spin coating, and bar coating.

[0128] Lithium-ion secondary batteries

[0129] The lithium-ion secondary battery of the present invention comprises: a positive electrode layer for a lithium-ion secondary battery, having a positive active material layer comprising a positive active material; a negative electrode layer for a lithium-ion secondary battery, having a negative active material layer comprising a negative active material; a separator disposed between the positive electrode layer and the negative electrode layer; and an electrolyte. Furthermore, it is characterized in that an electrolyte absorption layer is provided between the positive electrode layer and / or the negative electrode layer and the separator, the electrolyte absorption layer comprising the electrolyte absorption particles described above in the present invention.

[0130] [Positive electrode layer for lithium-ion secondary batteries]

[0131] The positive electrode layer for a lithium-ion secondary battery, which is a component of the lithium-ion secondary battery of the present invention, includes a positive electrode active material layer comprising a positive electrode active material. As long as a positive electrode active material layer is included, other structures are not particularly limited, and any known positive electrode layer used in lithium-ion secondary batteries can be used.

[0132] In this invention, the preferred electrode is either the first or second type described above. Specifically, it is preferably a positive electrode layer for a lithium-ion secondary battery formed by stacking an electrode layer comprising an electrode composite material containing a positive electrode active material and electrolyte absorber particles of the present invention onto a current collector, or a positive electrode layer for a lithium-ion secondary battery formed by stacking an electrolyte absorber layer comprising electrolyte absorber particles of the present invention onto an electrode active material layer formed on a current collector.

[0133] Negative electrode layer for lithium-ion secondary batteries

[0134] The negative electrode layer for a lithium-ion secondary battery, which is a component of the lithium-ion secondary battery of the present invention, includes a negative electrode active material layer comprising a negative electrode active material. As long as a negative electrode active material layer is included, other structures are not particularly limited, and any known negative electrode layer used in lithium-ion secondary batteries can be used.

[0135] In this invention, the preferred electrode is either the first or second type described above. Specifically, it is preferably a negative electrode layer for a lithium-ion secondary battery formed by stacking an electrode layer, consisting of an electrode composite material containing a negative electrode active material and electrolyte absorber particles of the present invention, onto a current collector; or a negative electrode layer for a lithium-ion secondary battery formed by stacking an electrolyte absorber layer containing electrolyte absorber particles of the present invention onto an electrode active material layer formed on a current collector.

[0136] [Septum]

[0137] The separator used as a component of the lithium-ion secondary battery of the present invention is not particularly limited, and any known separator that can be used in lithium-ion secondary batteries can be used.

[0138] In this invention, the diaphragm described above is preferred. That is, a diaphragm having an electrolyte absorption layer comprising the electrolyte absorption particles of this invention formed on at least one side of a substrate.

[0139] Electrolyte

[0140] The electrolyte used in the lithium-ion secondary battery of the present invention is not particularly limited, and any known electrolyte used as an electrolyte in a lithium-ion secondary battery can be used.

[0141] (solvent)

[0142] As a solvent used in the electrolyte, solvents that form general non-aqueous electrolytes can be used. Examples include solvents with cyclic structures such as ethylene carbonate (EC) and propylene carbonate (PC), and solvents with chain structures such as dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diethylcarbonate (DEC). Additionally, partially fluorinated fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) can also be used.

[0143] In addition, known additives can be incorporated into the electrolyte. Examples of additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and propanesultone (PS).

[0144] In addition, ionic liquids may also be included as electrolytes. Examples of such ionic liquids include pyrrolidineonium, piperidinium, and imidazolonium, which are composed of quaternary ammonium salt cations.

[0145] In this invention, it is ideal to use a combination of solvents with high relative permittivity, such as EC or PC, and solvents with low viscosity, such as DMC or EMC. By using a solvent with a high relative permittivity, the dissociation degree of the lithium salt is increased, allowing the lithium salt to be used at a high concentration. Furthermore, if only a solvent with a high relative permittivity is used, the viscosity will increase and the ionic conductivity will decrease; therefore, it is necessary to moderately mix in a solvent with low viscosity to adjust the viscosity. As a component of the electrolyte, the amount of solvent with a high relative permittivity, such as EC or PC, is preferably 20% by volume or more and 40% by volume or less. More ideally, it is 25% by volume or more and 35% by volume or less.

[0146] (Lithium salt)

[0147] The lithium salt contained in the electrolyte used in the lithium-ion secondary battery of the present invention is not particularly limited. Examples include LiPF6, LiBF4, LiClO4, LiN(SO2CF3), LiN(SO2C2F5)2, and LiCF3SO3. Among these, LiPF6, LiBF4, or mixtures thereof are preferred due to their high ionic conductivity and high degree of dissociation.

[0148] (Manufacturing method of lithium-ion secondary batteries)

[0149] The manufacturing method of the lithium-ion secondary battery of the present invention is not particularly limited, and general methods in this technical field can be applied.

[0150] Example

[0151] The invention will now be described in more detail based on embodiments, but the invention is not limited thereto. Furthermore, the materials used in the embodiments and comparative examples are shown below.

[0152] (1) Electrode active material

[0153] • Positive electrode active material: LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622)

[0154] D50 = 12μm

[0155] • Negative electrode active material: natural graphite (NG)

[0156] D50 = 12μm

[0157] (2) Lithium-ion conductive oxides

[0158] ·Li 1.3 Al 0.3 Ti 1.7 P3O 12 (LATP)

[0159] D50 = 0.5 μm, overall lithium-ion conductivity: 5 × 10⁻⁶ -4 S / cm

[0160] Powder relative permittivity: 30

[0161] ·Li7La3Zr2O 12 (LLZO)

[0162] D50 = 0.15 μm, overall lithium-ion conductivity: 5 × 10⁻⁶ -4 S / cm

[0163] Relative permittivity of the powder: 48.7

[0164] (3) Strong dielectric oxides

[0165] ·BaTiO3(BTO)

[0166] D50 = 0.6 μm, relative permittivity of powder: 67

[0167] (4) Oxides

[0168] Al2O3

[0169] D50 = 0.3 μm, relative permittivity of powder: 8.7

[0170] (5) Materials forming the resin layer

[0171] • Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)

[0172] Polyvinyl chloride (PVC)

[0173] <Preparation of Electrolyte Absorbing Particles>

[0174] [Electrolyte absorbing particles 1 to 4]

[0175] PVDF-HFP was used as the material to form the resin layer. PVDF-HFP was dissolved in acetone, and then ethylene carbonate (EC) as a plasticizer and LATP (relative permittivity of the powder: 30) as a lithium-ion conductive oxide were mixed and dispersed to obtain a dispersion. The dispersion was then stirred continuously using a mixer until the solvent, acetone, evaporated, resulting in a powder. The obtained powder was impregnated in dimethyl carbonate (DMC) to remove the EC as a plasticizer, thus forming micropores in the resin layer, obtaining electrolyte-absorbing particles.

[0176] The composition of the obtained electrolyte absorber particles 1 to 4 and the porosity of the resin layer are shown in Table 1.

[0177] [Electrolyte Absorbing Particles 5]

[0178] Polyvinyl chloride (PVC) was used as the material to form the resin layer. PVC was dissolved in tetrahydrofuran (THF), and then EC (eclogic acid) as a plasticizer and LLZO (relative permittivity of the powder: 48.7) as a lithium-ion conductive oxide were mixed and dispersed to obtain a dispersion. The dispersion was then stirred continuously using a mixer until the solvent, THF, evaporated, resulting in a powder. The obtained powder was impregnated in DMC to remove the EC as a plasticizer, thus forming micropores in the resin layer, obtaining electrolyte-absorbing particles.

[0179] The composition of the obtained electrolyte absorber particles 5 and the porosity of the resin layer are shown in Table 1.

[0180] [Electrolyte Absorbing Particles 6]

[0181] PVDF-HFP was used as the material to form the resin layer. PVDF-HFP was dissolved in acetone, and then EC (as a plasticizer) and BTO (powder relative permittivity: 67) as a dielectric oxide were mixed and dispersed to obtain a dispersion. The dispersion was then stirred continuously using a mixer until the solvent, acetone, evaporated, resulting in a powder. The obtained powder was impregnated in DMC to remove the EC as a plasticizer, thus forming micropores in the resin layer, obtaining electrolyte-absorbing particles.

[0182] The composition of the obtained electrolyte absorber particles 6 and the porosity of the resin layer are shown in Table 1.

[0183] [Electrolyte Absorbing Particles 7]

[0184] PVDF-HFP was used as the material to form the resin layer. PVDF-HFP was dissolved in acetone, and then EC (as a plasticizer) and Al2O3 (relative permittivity of the powder: 8.7) were mixed and dispersed to obtain a dispersion. The dispersion was then stirred continuously using a mixer until the solvent, acetone, evaporated, resulting in a powder. The obtained powder was impregnated in DMC to remove the EC as a plasticizer, thus forming micropores in the resin layer, obtaining electrolyte-absorbing particles.

[0185] The composition of the obtained electrolyte absorber particles 7 and the porosity of the resin layer are shown in Table 1.

[0186] [Table 1]

[0187]

[0188] <Examples 1 to 7, Comparative Examples 1 to 2>

[0189] [The production of the positive electrode]

[0190] Using the compositions shown in Tables 2 and 3, electrolyte absorber particles, acetylene black (AB) as a conductive additive, PVDF as a binder, and N-methyl-N-pyrrolidinone (NMP) as a solvent were wet-mixed using a rotary mixer to obtain a premixed slurry. Then, NCM622, as the positive electrode active material, was mixed with the premixed slurry in the manner shown in Tables 2 and 3, and dispersed using a planetary mixer to obtain the positive electrode slurry. Furthermore, if the electrolyte absorber particles are not added, only that step is omitted.

[0191] The obtained positive electrode slurry was coated onto one side of an Al current collector with a thickness of 12 μm. After drying at 120°C for 10 minutes, it was pressed using a roller with a linear pressure of 1 t / cm, and then dried in a vacuum at 120°C to produce a positive electrode for lithium-ion secondary batteries. Furthermore, the produced positive electrode was stamped into a size of 30 mm × 40 mm before use.

[0192] [Making the negative electrode]

[0193] Using the compositions shown in Tables 2 and 3, electrolyte absorber particles, acetylene black (AB) as a conductive additive, and an aqueous solution of carboxymethyl cellulose (CMC) as a binder were mixed and dispersed using a planetary mixer to obtain a mixture. Natural graphite (NG) as the negative electrode active material was then mixed into the obtained mixture and dispersed again using a planetary mixer. Subsequently, water as a dispersion solvent and styrene-butadiene rubber (SBR) as a binder were added and dispersed as shown in Table 2 to prepare a negative electrode slurry. Alternatively, the process of adding electrolyte absorber particles is omitted.

[0194] The obtained negative electrode slurry was coated onto a Cu current collector with a thickness of 8 μm, dried at 100°C for 10 minutes, then pressed with a linear pressure of 1 t / cm using a roller press, and subsequently dried in a vacuum at 100°C to produce a negative electrode for lithium-ion secondary batteries. Furthermore, the produced negative electrode was stamped to a size of 34 mm × 44 mm before use.

[0195] [Table 2]

[0196]

[0197] [Table 3]

[0198]

[0199] <Examples 8 to 11, Comparative Example 3>

[0200] [The production of the positive electrode]

[0201] Acetylene black (AB) as a conductive additive, PVDF as a binder, and N-methyl-N-pyrrolidone (NMP) as a solvent were wet-mixed using a rotary mixer to obtain a premixed slurry. Then, NCM622, as the positive electrode active material, was mixed with the obtained premixed slurry and dispersed using a planetary mixer to obtain the positive electrode slurry.

[0202] The mass ratio of each component in the positive electrode slurry of Examples 8 to 11 and Comparative Example 3 was set as NCM622:AB:PVDF = 94.0:4.1:1.9.

[0203] The obtained positive electrode slurry was coated onto one side of an Al current collector with a thickness of 12 μm. After drying at 120°C for 10 minutes, it was pressed using a roller with a linear pressure of 1 t / cm, and then dried in a vacuum at 120°C to produce a positive electrode for lithium-ion secondary batteries. Furthermore, the produced positive electrode was stamped into a size of 30 mm × 40 mm before use.

[0204] [Making the negative electrode]

[0205] Using a planetary mixer, acetylene black (AB) as a conductive additive and an aqueous solution of carboxymethyl cellulose (CMC) as a binder were premixed. Then, natural graphite (NG) as the negative electrode active material was mixed into the resulting mixture, and the mixture was further premixed using a planetary mixer. Subsequently, 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 the negative electrode slurry.

[0206] The mass ratio of each component in the negative electrode slurry of Examples 8 to 11 and Comparative Example 3 was set as NG:AB:SBR:CMC = 96.5:1.0:1.5:1.0.

[0207] [Fabrication of the electrolyte absorber layer]

[0208] The electrolyte absorber particles shown in Table 4 were mixed with CMC at a mass ratio of 95:5 to prepare a dispersion slurry with water as the dispersing solvent. The obtained dispersion slurry, as shown in Table 4, was applied to the surface of the electrode active material layer of the above-formed positive or negative electrode and dried at 100°C to prepare an electrolyte absorber layer of the thickness shown in Table 4.

[0209] [The fabrication of lithium-ion secondary batteries]

[0210] The lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the positive or negative electrode with the electrolyte absorption layer obtained above and the positive or negative electrode without the electrolyte absorption layer were used in the combinations shown in Table 4.

[0211] [Table 4]

[0212]

[0213]

[0214] <Evaluation>

[0215] The following evaluation is performed on the lithium-ion secondary batteries obtained in the embodiments and comparative examples.

[0216] [Initial discharge capacity]

[0217] The fabricated lithium-ion secondary battery was placed at the measured temperature (25°C) for 1 hour, then charged with a constant current of 8.4 mA to 4.2V, followed by a constant voltage charge at 4.2V for 1 hour. After being placed for 30 minutes, it was discharged with a constant current of 8.4 mA to 2.5V. This process was repeated 5 times, and the discharge capacity at the 5th discharge was taken as the initial discharge capacity. The results are shown in Tables 2 to 4. Furthermore, the current value that can complete the discharge in 1 hour (H) for the obtained discharge capacity was defined as 1C.

[0218] [Initial cell resistance]

[0219] 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 0.2C to adjust the state of charge (SOC) to 50% and placed for 10 minutes. Next, a pulse discharge was performed at a rate of 0.5C for 10 seconds, and the voltage at 10 seconds of discharge was measured. Then, the voltage at 10 seconds of discharge was plotted relative to the current value at 0.5C, with the horizontal axis representing current and the vertical axis representing voltage. After placing for 10 minutes, a recharge was performed to restore the SOC to 50%, and then the battery was placed for another 10 minutes.

[0220] The above operations were performed for each C-rate: 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. The voltage after 10 seconds of discharge was plotted relative to the current value at each C-rate. Then, the slope of the approximate straight line obtained from each plotted graph based on the least squares method was taken as the internal resistance of the lithium-ion secondary battery. The results are shown in Tables 2 to 4.

[0221] [Discharge capacity after durability]

[0222] For the charge-discharge cycle durability test, one cycle was defined as charging to 4.2V at a constant current rate of 1C and discharging to 2.5V at a constant current rate of 2C in a constant temperature bath at 45°C. This operation was repeated for 1000 cycles. After 1000 cycles, the constant temperature bath was changed to 25°C and left for 24 hours. Then, it was charged to 4.2V at a constant current rate of 0.2C, followed by constant voltage charging at 4.2V for 1 hour. After being left for 30 minutes, it was discharged to 2.5V at a constant current rate of 0.2C, and the discharge capacity after durability was measured. The results are shown in Tables 2 to 4.

[0223] [Single-cell resistor after durability]

[0224] Similar to the initial cell resistance determination, the lithium-ion secondary battery was charged to 50% (State of Charge, SOC) after the endurance discharge capacity was measured, and the endurance cell resistance was determined using the same method as the initial cell resistance determination. The results are shown in Tables 2 to 4.

[0225] [Capacity Maintenance Rate]

[0226] The ratio of the post-durability discharge capacity to the initial discharge capacity measured above was determined and used as the post-durability capacity retention rate. The results are shown in Tables 2 to 4.

[0227] [Single-cell resistance rise rate]

[0228] The ratio of the resistance of a single cell after durability testing to the initial resistance of the single cell measured above is used as the rate of increase in single cell resistance. The results are shown in Tables 2 to 4.

Claims

1. An electrolyte-absorbing particle for a lithium-ion secondary battery, comprising an electrolyte, wherein the particle has a resin layer on the surface of a high-dielectric oxide solid capable of absorbing the electrolyte. The aforementioned resin layer has fine pores, which are filled with and absorb electrolyte. The volume of the aforementioned pores relative to the volume of the aforementioned resin layer is 30 vol% or more. in, The aforementioned high-dielectric oxide solids are strong dielectric oxides with a relative permittivity of 10 or higher in powder form. The aforementioned high-dielectric oxide solids are oxides with lithium-ion conductivity. The aforementioned resin layer contains poly(vinylidene fluoride-co-hexafluoropropylene) or polyvinyl chloride.

2. The electrolyte absorber particles according to claim 1, wherein, The aforementioned high-dielectric oxide solid has a dielectric constant of 10 at 25°C. -7 Oxides with lithium-ion conductivity above S / cm.

3. The electrolyte absorber particles according to claim 1, wherein, The aforementioned high-dielectric oxide solid is composed of the chemical formula Li 7-y La 3-x A x Zr 2-y M y O 12 The garnet-type composite metal oxide is represented by the formula, where A is any metal selected from the group consisting of Y, Nd, Sm, and Gd, x is in the range of 0 ≤ x < 3, M is Nb or Ta, and y is in the range of 0 ≤ y < 2.

4. The electrolyte absorber particles according to claim 1, wherein, The aforementioned high-dielectric oxide solid contains Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 The crystal is a composite metal oxide, where 0≦x≦1 and 0≦y≦1.

5. A self-standing sheet comprising electrolyte-absorbing particles according to claim 1.

6. An electrode for a lithium-ion secondary battery, comprising an electrode active material and electrolyte absorber particles according to claim 1.

7. The electrode for a lithium-ion secondary battery according to claim 6, wherein, Compared to 100 parts by mass of the aforementioned electrode for lithium-ion secondary batteries, the amount of the aforementioned electrolyte absorbent particles is 0.1 parts by mass or more and 5 parts by mass or less.

8. The electrode for a lithium-ion secondary battery according to claim 6, wherein, The aforementioned electrode active material is a positive electrode active material.

9. The electrode for a lithium-ion secondary battery according to claim 6, wherein, The aforementioned electrode active material is a negative electrode active material.

10. An electrode for a lithium-ion secondary battery, comprising: a current collector; an electrode active material layer formed on at least one side of the current collector and comprising the electrode active material; and an electrolyte; and, An electrolyte absorption layer is provided on the aforementioned electrode active material layer, the electrolyte absorption layer comprising electrolyte absorption particles according to claim 1.

11. The electrode for a lithium-ion secondary battery according to claim 10, wherein, The aforementioned electrolyte absorption layer comes into contact with the separator when a lithium-ion secondary battery is formed.

12. The electrode for a lithium-ion secondary battery according to claim 10, wherein, The aforementioned electrode active material is a positive electrode active material.

13. The electrode for a lithium-ion secondary battery according to claim 10, wherein, The aforementioned electrode active material is a negative electrode active material.

14. A separator for a lithium-ion secondary battery, having an electrolyte absorption layer on at least one side of a substrate, the electrolyte absorption layer comprising electrolyte absorption particles according to claim 1.

15. A lithium-ion secondary battery, comprising: A positive electrode layer for lithium-ion secondary batteries, which has a positive electrode active material layer containing positive electrode active material; A negative electrode layer for lithium-ion secondary batteries, which has a negative electrode active material layer containing negative electrode active material. A separator, disposed between the aforementioned positive electrode layer and the aforementioned negative electrode layer for a lithium-ion secondary battery; and, Electrolyte; and, An electrolyte absorption layer is provided between the aforementioned positive electrode layer and / or the aforementioned negative electrode layer for lithium-ion secondary batteries and the aforementioned separator, wherein the electrolyte absorption layer comprises electrolyte absorption particles according to claim 1.

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