Coated active material, positive electrode material, positive electrode, and battery

Abstract

A coated active material 100 according to the present disclosure comprises: a positive electrode active material 101; and a coating layer 102 that contains a first solid electrolyte and covers at least a part of a surface of the positive electrode active material 101. The first solid electrolyte contains Li, Ti, M, and X. M is at least one element that is selected from the group consisting of metalloid elements and metal elements other than Li and Ti. X is at least one element that is selected from the group consisting of F, Cl, Br, and I. The value obtained by formula (A) below, specifically, the quotient obtained by dividing the ratio (%) of the mass of the first solid electrolyte to the total mass of the positive electrode active material 101 and the first solid electrolyte by the specific surface area (m2 / g) of the positive electrode active material 102 is 1.9 to 6.9 inclusive.　formula (A): \{(mass of first solid electrolyte) / (total mass of positive electrode active material and first solid electrolyte)\} × 100 / (specific surface area of positive electrode active material)

Description

Coated active material, positive electrode material, positive electrode, and battery

[0001] The present disclosure relates to coated active materials, positive electrode materials, positive electrodes, and batteries.

[0002] Patent Document 1 describes a method for producing a composite active material by coating a positive electrode active material with an oxide solid electrolyte and then coating it with a sulfide solid electrolyte.

[0003] JP 2016-18735 A

[0004] In the prior art, it is desirable to reduce the internal resistance of the battery.

[0005] The present disclosure provides a cathode active material comprising: a cathode active material; and a coating layer including a first solid electrolyte and coating at least a portion of a surface of the cathode active material, wherein the first solid electrolyte includes Li, Ti, M, and X, wherein M is at least one element selected from the group consisting of metal elements and semi-metal elements other than Li and Ti, and X is at least one element selected from the group consisting of F, Cl, Br, and I, and wherein the ratio (%) of the mass of the first solid electrolyte to the total mass of the cathode active material and the first solid electrolyte, calculated by the following mathematical formula (A), is calculated as a specific surface area (m 2 The present invention provides a coated active material, wherein the quotient obtained when the coated active material is divided by the mass of the first solid electrolyte (g / g) is 1.9 or more and 6.9 or less. Formula (A): {(mass of the first solid electrolyte) / (total mass of the positive electrode active material and the first solid electrolyte)}×100 / (specific surface area of ​​the positive electrode active material)

[0006] According to the technology of the present disclosure, the internal resistance of the battery can be reduced.

[0007] Fig. 1 is a cross-sectional view showing a schematic configuration of a coated active material according to embodiment 1. Fig. 2 is a cross-sectional view showing a schematic configuration of a positive electrode material according to embodiment 2. Fig. 3 is a cross-sectional view showing a schematic configuration of a battery according to embodiment 3.

[0008] (Findings that form the basis of the present disclosure) In batteries using solid electrolytes, oxygen may be generated from the positive electrode active material due to a side reaction between the positive electrode active material and the solid electrolyte, for example, at the end of charging. The generated oxygen oxidizes the solid electrolyte and increases the internal resistance of the battery. The increase in internal resistance causes various problems, such as a decrease in output voltage, heat generation in the battery, and a decrease in discharge capacity. Therefore, a technology suitable for reducing the internal resistance of batteries using solid electrolytes is desired.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0010] (Embodiment 1) Fig. 1 is a cross-sectional view showing a schematic configuration of a coated active material according to embodiment 1. The coated active material 100 includes a positive electrode active material 101 and a coating layer 102. The coating layer 102 contains a first solid electrolyte. The coating layer 102 coats at least a portion of the surface of the positive electrode active material 101. The coating layer 102 may coat only a portion of the surface of the positive electrode active material 101, or may uniformly coat the surface of the positive electrode active material 101.

[0011] In the coating layer 102, the first solid electrolyte contains Li, Ti, M, and X. M is at least one element selected from the group consisting of metal elements and semimetal elements other than Li and Ti. X is at least one element selected from the group consisting of F, Cl, Br, and I. In the coated active material 100, the ratio (%) of the mass of the first solid electrolyte to the total mass of the positive electrode active material 101 and the first solid electrolyte, which is calculated by the following formula (A), is calculated as the specific surface area (m 2 / g), the quotient obtained is 1.9 or more and 6.9 or less.

[0012] Formula (A): {(mass of first solid electrolyte) / (total mass of positive electrode active material and first solid electrolyte)}×100 / (specific surface area of ​​positive electrode active material)

[0013] Hereinafter, the ratio of the mass of the first solid electrolyte to the total mass of the positive electrode active material 101 and the first solid electrolyte may be referred to as "ratio MA1 / MAt." The specific surface area of ​​the positive electrode active material 101 may be referred to as "Sm." The quotient obtained by dividing the ratio of the mass of the first solid electrolyte to the total mass of the positive electrode active material 101 and the first solid electrolyte by the specific surface area of ​​the positive electrode active material 101 may be referred to as "ratio MA1 / MAt / specific surface area Sm."

[0014] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0015] The term "metal element" includes all elements included in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements included in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halogen elements.

[0016] The first solid electrolyte may be a solid electrolyte containing a halogen, a so-called halide solid electrolyte. Halide solid electrolytes have excellent oxidation resistance. Therefore, by coating the cathode active material 101 with the first solid electrolyte, oxidation of another solid electrolyte (e.g., the second solid electrolyte in the cathode material according to the second embodiment described below) contained in the cathode containing the coated active material 100 can be suppressed. This reduces the internal resistance of a battery using a cathode material containing the coated active material 100.

[0017] When the ratio MA1 / MAt / specific surface area Sm satisfies the above range, the cathode active material 101 is coated with the first solid electrolyte to a sufficient thickness, and the above-described effect is sufficiently obtained. Furthermore, when the ratio MA1 / MAt / specific surface area Sm satisfies the above range, the cathode active material 101 is coated with the first solid electrolyte to a sufficient thickness to obtain the above-described effect, i.e., to suppress oxidation of the other solid electrolyte, and the cathode material including the coated active material 100 has sufficient electronic conductivity. The ratio MA1 / MAt / specific surface area Sm may be 2.7 or more and 6.2 or less, or 3.5 or more and 5.0 or less.

[0018] The total mass MAt of the positive electrode active material 101 and the first solid electrolyte is the sum of the mass MA2 of the positive electrode active material 101 and the mass MA1 of the first solid electrolyte. The mass MA1 of the first solid electrolyte is the total mass of the first solid electrolyte in the powder of the coated active material 100. The mass MA2 of the positive electrode active material 101 is the total mass of the positive electrode active material 101 in the powder of the coated active material 100. In other words, the ratio MA1 / MAt is a value determined from the entire powder of a certain amount of the coated active material 100. Furthermore, if the coated active material 100 is mixed with, for example, another solid electrolyte to form a positive electrode material (e.g., the positive electrode material according to the second embodiment described below), the ratio MA1 / MAt can be determined using that positive electrode material. In this case, the mass MA1 of the first solid electrolyte is the total mass of the first solid electrolyte in the powder of the positive electrode material, and the mass MA2 of the positive electrode active material 101 is the total mass of the positive electrode active material 101 in the powder of the positive electrode material. Therefore, when the coated active material 100 constitutes a positive electrode material, the ratio MA1 / MAt can be determined from the entire powder of a certain amount of the positive electrode material.

[0019] The ratio MA1 / MAt can be calculated from the amount of material charged, or by the method described below. A positive electrode using the coated active material 100 is analyzed by high-frequency inductively coupled plasma atomic emission spectroscopy, and elements contained in the positive electrode active material 101 but not contained in the first solid electrolyte and elements contained in the first solid electrolyte but not contained in the positive electrode active material 101 are quantitatively analyzed to analyze the mass ratio of the positive electrode active material 101 and the first solid electrolyte, thereby enabling calculation of the ratio MA1 / MAt. The ratio MA1 / MAt can also be calculated from the composition ratio of particle cross sections analyzed by energy dispersive X-ray spectroscopy using a scanning electron microscope.

[0020] <Positive Electrode Active Material> The positive electrode active material 101 includes a material capable of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material 101 include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide as the positive electrode active material 101 can reduce the manufacturing cost of the battery and increase the average discharge voltage. Examples of lithium-containing transition metal oxides include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2.

[0021] The positive electrode active material 101 has, for example, a particle shape. There are no particular limitations on the shape of the particles of the positive electrode active material 101. The shape of the particles of the positive electrode active material 101 may be spherical, oval, scaly, or fibrous.

[0022] The specific surface area Sm of the positive electrode active material 101 is 0.4 m 2 / g or more and 0.8m 2 / g or less, and 2 / g or more and 0.7m 2 In this specification, the specific surface area is a BET specific surface area that can be measured by the BET method.

[0023] When determining the specific surface area Sm of the positive electrode active material 101 coated with the coating layer 102, the specific surface area Sm of the positive electrode active material 101 can be determined by removing the coating layer 102 from the surface of the positive electrode active material 101 and measuring the BET specific surface area of ​​the resulting positive electrode active material 101. The coating layer 102 can be removed by selecting an appropriate method taking into consideration the characteristics of the first solid electrolyte contained in the coating layer 102. For example, the coating layer 102 may be removed by dissolving the first solid electrolyte using an acid. Even when the coated active material 100 is contained in the positive electrode of a battery, the specific surface area Sm of the positive electrode active material 101 can be determined by selecting an appropriate method to remove the positive electrode active material 101 from the positive electrode and measuring the BET specific surface area of ​​the resulting positive electrode active material 101.

[0024] When the positive electrode active material used as the positive electrode active material 101 of the coated active material 100 is available, the BET specific surface area of ​​the obtained positive electrode active material may be measured and regarded as the specific surface area Sm of the positive electrode active material 101. Note that the case where the positive electrode active material used is available means a case where the positive electrode active material used is a commercially available product and can be obtained, or a case where the manufacturing method of the positive electrode active material used is clear and the same can be manufactured, etc.

[0025] When it is difficult to remove coating layer 102 from the surface of positive electrode active material 101 and further when it is difficult to obtain the positive electrode active material, it is also possible to determine the specific surface area of ​​positive electrode active material 101 from a scanning electron microscope (SEM) image of a cross section of coated active material 100, and regard the value as the specific surface area Sm of positive electrode active material 101. In this case, for example, a calibration curve may be created in advance by determining the relationship between the BET specific surface area of ​​the positive electrode active material and the specific surface area determined from the cross-sectional SEM image, and the BET specific surface area may be determined based on the specific surface area determined from the cross-sectional SEM image.

[0026] The median diameter of the coated active material 100 may be 0.1 μm or more and 100 μm or less. When the median diameter of the coated active material 100 is 0.1 μm or more, the coated active material 100 and the second solid electrolyte 201 can form a well-dispersed state in the positive electrode material 200. As a result, the charge / discharge characteristics of the battery are improved. When the median diameter of the coated active material 100 is 100 μm or less, the diffusion rate of lithium inside the coated active material 100 is sufficiently ensured. Therefore, the battery can operate at high power.

[0027] In this specification, the term "median diameter" refers to the particle size when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device or an image analysis device.

[0028] The specific surface area of ​​the coated active material 100 is 0.6 m 2 / g or more and 1.4m 2 / g or less, and 2 / g or more and 1.3m 2 / g or less.

[0029] <Coating Layer> The coating layer 102 includes a first solid electrolyte. The first solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity. The coating layer 102 is provided on the surface of the positive electrode active material 101. The coating layer 102 may include the first solid electrolyte as a main component, or may include only the first solid electrolyte. "Main component" refers to the component that is most abundant by mass. "Includes only the first solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the first solid electrolyte are intentionally added. For example, the inevitable impurities include raw materials for the first solid electrolyte and by-products generated during the production of the first solid electrolyte. The mass ratio of the inevitable impurities to the total mass of the coating layer 102 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0030] The first solid electrolyte is a material containing Li, Ti, M, and X. M and X are as described above. Such a material has excellent ionic conductivity and oxidation resistance. Therefore, the positive electrode material 200 having the coating layer 102 containing the first solid electrolyte improves the charge / discharge efficiency and thermal stability of the battery.

[0031] M may include at least one selected from the group consisting of Ca, Mg, Al, Y, Ni, Fe, Cr, and Zr. M may include at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. According to this configuration, the halide solid electrolyte as the first solid electrolyte exhibits high ionic conductivity.

[0032] M may contain Al (=aluminum). That is, the halide solid electrolyte as the first solid electrolyte may contain Al as a metal element. When M contains Al, the halide solid electrolyte as the first solid electrolyte exhibits high ionic conductivity.

[0033] The halide solid electrolyte as the first solid electrolyte is represented, for example, by the following composition formula (1): In composition formula (1), α, β, γ, and δ are each independently a value greater than 0. Li α Tiβ M γ X δ ...Compositional formula (1)

[0034] The halide solid electrolyte represented by composition formula (1) has higher ionic conductivity than halide solid electrolytes such as LiI, which are composed only of Li and halogen elements. Therefore, when the halide solid electrolyte represented by composition formula (1) is used in a battery, the charge / discharge efficiency of the battery can be improved.

[0035] In order to further increase the ionic conductivity of the first solid electrolyte, M in composition formula (1) may be Al.

[0036] The halide solid electrolyte as the first solid electrolyte may be represented by the following composition formula (2): In composition formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M2, and 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.2 are satisfied. Li6-(4-x-4y+my)b(Ti 1-x-y Al x M2 y ) b F 6-2z O z ...Compositional formula (2)

[0037] In the composition formula (2), when M2 contains a plurality of elements, m is the sum of the products of the composition ratios of the respective elements and the valences of the elements. For example, when M2 contains an element Me1 and an element Me2, and the composition ratio of the element Me1 is a1 and the valence is m1, and the composition ratio of the element Me2 is a2 and the valence of the element Me2 is m2, m is expressed as m1a1+m2a2.

[0038] The halide solid electrolyte as the first solid electrolyte may consist essentially of Li, Ti, Al, and X. Here, "the halide solid electrolyte consists essentially of Li, Ti, Al, and X" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, Ti, Al, and X to the total amount of substance of all elements constituting the halide solid electrolyte is 90% or more. As an example, the molar ratio (i.e., molar fraction) may be 95% or more. The halide solid electrolyte may consist only of Li, Ti, Al, and X.

[0039] To further increase the ionic conductivity of the first solid electrolyte, the ratio of the amount of substance of Li to the total amount of substance of Ti and Al in the halide solid electrolyte may be 1.12 or more and 5.07 or less.

[0040] The halide solid electrolyte as the first solid electrolyte may be represented by the following composition formula (3): In composition formula (3), 0<x<1 and 0<b≦1.5 are satisfied. 6-(4-x)b (Ti 1-x Al x ) b F6...composition formula (3)

[0041] A halide solid electrolyte having such a composition has high ionic conductivity.

[0042] In order to increase the ionic conductivity of the first solid electrolyte, 0.1≦x≦0.9 may be satisfied in composition formula (3).

[0043] In the composition formula (3), 0.1≦x≦0.7 may be satisfied.

[0044] The upper and lower limits of the range of x in composition formula (3) can be defined by any combination selected from the following numerical values: 0.1, 0.3, 0.4, 0.5, 0.6, 0.67, 0.7, 0.8, and 0.9.

[0045] In order to increase the ionic conductivity of the first solid electrolyte, the relationship 0.8≦b≦1.2 may be satisfied in composition formula (3).

[0046] The upper and lower limits of the range of b in composition formula (3) can be defined by any combination selected from the following numerical values: 0.8, 0.9, 0.94, 1.0, 1.06, 1.1, and 1.2.

[0047] The halide solid electrolyte as the first solid electrolyte may be crystalline or amorphous.

[0048] The shape of the halide solid electrolyte as the first solid electrolyte is not limited. Examples of the shape include needle-like, spherical, and oval-spherical. The halide solid electrolyte may be in the form of particles.

[0049] When the halide solid electrolyte as the first solid electrolyte has a particulate (e.g., spherical) shape, the solid electrolyte may have a median diameter of 0.01 μm or more and 100 μm or less.

[0050] The halide solid electrolyte as the first solid electrolyte may be a sulfur-free solid electrolyte. In this case, generation of sulfur-containing gases such as hydrogen sulfide gas from the solid electrolyte can be avoided. A sulfur-free solid electrolyte refers to a solid electrolyte represented by a composition formula that does not contain elemental sulfur. Therefore, a solid electrolyte containing a very small amount of sulfur, for example, a solid electrolyte having a sulfur content of 0.1 mass% or less, is classified as a sulfur-free solid electrolyte. The halide solid electrolyte as the first solid electrolyte may further contain oxygen as an anion other than the halogen element.

[0051] The thickness of the coating layer 102 is, for example, 1 nm or more and 500 nm or less. When the thickness of the coating layer 102 is appropriately adjusted, contact between the positive electrode active material 101 and the second solid electrolyte 201 can be sufficiently suppressed. The thickness of the coating layer 102 can be determined by slicing the coated active material by a method such as ion milling and observing the cross section of the coated active material with a transmission electron microscope. The average value of thicknesses measured at any multiple positions (e.g., five points) can be considered to be the thickness of the coating layer 102.

[0052] The coating layer 102 may contain a conductive additive to enhance electronic conductivity. Examples of the conductive additive include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0053] <Method for producing halide solid electrolyte as first solid electrolyte> The halide solid electrolyte as the first solid electrolyte can be produced, for example, by the following method. Here, a method for producing a halide solid electrolyte represented by composition formula (1) will be exemplified.

[0054] Raw material powders are prepared and mixed to obtain a desired composition. The raw material powders may be, for example, halides.

[0055] As an example, if the target composition is Li 2.7 Ti 0.3 Al 0.7 In the case of F, LiF, TiF, and AlF are mixed in a molar ratio of about 2.7:0.3:0.7. The raw material powders may be mixed in a pre-adjusted molar ratio to offset composition changes that may occur in the synthesis process.

[0056] The raw material powders are reacted with each other mechanochemically (i.e., using a mechanochemical milling method) in a mixing device such as a planetary ball mill to obtain a reactant. The reactant may be fired in a vacuum or in an inert atmosphere. Alternatively, a mixture of the raw material powders may be fired in a vacuum or in an inert atmosphere to obtain a reactant. The firing is carried out, for example, at a temperature of 100°C or higher and 400°C or lower for one hour or longer. To suppress compositional changes during firing, the raw material powders may be fired in a sealed container such as a quartz tube.

[0057] These methods provide a halide solid electrolyte.

[0058] <Method for Producing Coated Active Material> The coated active material 100 can be produced by the following method.

[0059] A powder of the positive electrode active material 101 and a powder of the first solid electrolyte are mixed in an appropriate ratio to obtain a mixture. The mixture is then milled to impart mechanical energy to the mixture. A mixing device such as a ball mill can be used for the milling process. The milling process may be performed in a dry and inert atmosphere to prevent oxidation of the materials.

[0060] The coated active material 100 may be manufactured by a dry particle compositing method. The treatment by the dry particle compositing method includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the positive electrode active material 101 and the first solid electrolyte. The positive electrode active material 101 and the first solid electrolyte are mixed in an appropriate ratio.

[0061] The apparatus used in producing the coated active material 100 is not particularly limited and may be an apparatus capable of applying impact, compression, and shear mechanical energy to a mixture of the positive electrode active material 101 and the first solid electrolyte. Examples of apparatus capable of applying mechanical energy include a ball mill, and a compression shear processing apparatus (particle composite apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation), "Nobilta" (manufactured by Hosokawa Micron Corporation), and "BALANCE GRAN" (manufactured by Freund Turbo Corporation).

[0062] "Mechanofusion" is a particle compounding device that uses a dry mechanical compounding technology by applying strong mechanical energy to multiple different raw material powders. In mechanofusion, raw material powders are placed between a rotating container and a press head, and mechanical energy of compression, shear, and friction is applied to them. This causes the particles to compound.

[0063] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced form of particle compounding technology, to compound nanoparticles as raw materials. Nobilta produces composite particles by applying mechanical energy of impact, compression, and shear to multiple types of raw material powders.

[0064] The BALANCE GRAN is a particle compositing device that uses dry mechanical compositing technology, an advanced form of particle compositing technology, to mix and composite particles as raw materials. The BALANCE GRAN produces composite particles by applying impact energy to multiple types of raw material powders.

[0065] In the "BALANCE GRAN," a chopper that stirs and circulates the powder is rotated in a horizontal cylindrical mixing vessel, causing the raw material powders to collide with each other multiple times. This applies an impact force to the mixture, allowing composite particles of the positive electrode active material 101 and the first solid electrolyte to be produced. By adjusting conditions such as the chopper rotation speed, processing time, and feed amount, the thickness of the coating layer 102 and the coverage rate of the positive electrode active material 101 with the first solid electrolyte can be controlled.

[0066] However, the treatment using the above-mentioned apparatus is not essential. The coated active material 100 may be produced by mixing the positive electrode active material 101 and the first solid electrolyte using a mortar, a mixer, or the like. The first solid electrolyte may be deposited on the surface of the positive electrode active material 101 by various methods such as a spray method, a spray-dry coating method, an electrodeposition method, an immersion method, or a mechanical mixing method using a disperser.

[0067] (Embodiment 2) Fig. 2 is a cross-sectional view showing a schematic configuration of a cathode material according to embodiment 2. The cathode material 200 includes a coated active material 100 and a second solid electrolyte 201. The coated active material 100 is the coated active material 100 described in embodiment 1. As described in embodiment 1, the coated active material 100 can suppress oxidation of the second solid electrolyte 201. This allows the cathode material 200 to reduce the internal resistance of the battery.

[0068] In the positive electrode material 200, the second solid electrolyte 201 and the coated active material 100 may be in contact with each other. In this case, the coating layer 102 and the second solid electrolyte 201 are in contact with each other. The positive electrode material 200 may include a plurality of particles of the second solid electrolyte 201 and a plurality of particles of the coated active material 100.

[0069] The median diameter of the coated active material 100 may be larger than the median diameter of the second solid electrolyte 201. This allows the positive electrode active material 101 and the second solid electrolyte 201 to be well dispersed.

[0070] Note that the coated active material 100, the cathode active material 101, the coating layer 102, and the first solid electrolyte are as described in Embodiment 1, and therefore detailed description thereof will be omitted here. The second solid electrolyte 201, other materials contained in the cathode material 200, and the method for manufacturing the cathode material 20 will be described below.

[0071] <Second Solid Electrolyte> The second solid electrolyte 201 may include at least one selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0072] Examples of the halide solid electrolyte include the materials described above as the first solid electrolyte. That is, the composition of the second solid electrolyte 201 may be the same as or different from the composition of the first solid electrolyte.

[0073] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These include LiX, LiO, and M'O. q , Li p MO q In this case, X in "LiX" is at least one selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q " The element M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q In the above formula, p and q are independent natural numbers.

[0074] The oxide solid electrolyte is a solid electrolyte containing oxygen. The oxide solid electrolyte may further contain anions other than sulfur and halogen elements as anions other than oxygen.

[0075] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element substitution products, LiSiCON type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those substituted with these elements, LiPO and its N-substituted compounds, and glass or glass ceramics containing a base material containing a Li-B-O compound such as LiBO or LiBO to which a material such as LiSO or LiCO is added can be used.

[0076] The polymer solid electrolyte may be, for example, a compound of a polymer compound and a lithium salt. The polymer compound may have an ethylene oxide structure. A polymer compound having an ethylene oxide structure may contain a large amount of lithium salt. This can further increase ionic conductivity. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF2F5)2, LiN(SO2CF3)(SO2CF4F9), and LiC(SO2CF3)3. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used.

[0077] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0078] The second solid electrolyte 201 may have a lithium ion conductivity higher than the lithium ion conductivity of the first solid electrolyte.

[0079] The second solid electrolyte 201 may contain, for example, Li and S. In other words, the second solid electrolyte 201 may contain a sulfide solid electrolyte. The sulfide solid electrolyte has high ionic conductivity and can improve the charge / discharge efficiency of the battery. On the other hand, although the sulfide solid electrolyte has poor oxidation resistance, applying the technology of the present disclosure can provide a high effect.

[0080] The second solid electrolyte 201 may be in contact with the positive electrode active material 101 via the coating layer 102 .

[0081] The second solid electrolyte 201 may contain inevitable impurities such as starting materials, by-products, decomposition products, etc. used in synthesizing the solid electrolyte. This also applies to the first solid electrolyte.

[0082] <Other Materials> The positive electrode material 200 may contain a binder to improve adhesion between particles. The binder is used to improve the binding of the materials that make up the positive electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polycarbonate, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, and ethyl cellulose. Also usable are copolymers of two or more monomers selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, butadiene, styrene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid ester, acrylic acid, and hexadiene. One selected from these may be used alone, or two or more may be used in combination.

[0083] The binder may be an elastomer because it has excellent binding properties. An elastomer is a polymer having rubber elasticity. The elastomer used as the binder may be a thermoplastic elastomer or a thermosetting elastomer. The binder may contain a thermoplastic elastomer. Examples of thermoplastic elastomers include styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-ethylene-propylene-styrene (SEEPS), butylene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), styrene-butylene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), hydrogenated isoprene rubber (HIR), hydrogenated butyl rubber (HIIR), hydrogenated nitrile rubber (HNBR), hydrogenated styrene-butylene rubber (HSBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), etc. One selected from these may be used alone, or two or more may be used in combination.

[0084] The positive electrode material 200 may contain a conductive additive for the purpose of enhancing electronic conductivity. Examples of the conductive additive include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0085] <Method for manufacturing the positive electrode material> The positive electrode material 200 is obtained by mixing the coated active material 100 and the second solid electrolyte 201. The method for mixing the coated active material 100 and the second solid electrolyte 201 is not particularly limited. The coated active material 100 and the second solid electrolyte 201 may be mixed using a tool such as a mortar, or the coated active material 100 and the second solid electrolyte 201 may be mixed using a mixing device such as a ball mill.

[0086] 3 is a cross-sectional view showing a schematic configuration of a battery according to Embodiment 3. Battery 300 includes a positive electrode 301, a separator layer 302, and a negative electrode 303. Separator layer 302 is disposed between positive electrode 301 and negative electrode 303. Positive electrode 301 includes positive electrode material 200 described in Embodiment 2. With this configuration, the internal resistance of battery 300 can be reduced.

[0087] The thickness of each of the positive electrode 301 and the negative electrode 303 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 301 and the negative electrode 303 is 10 μm or more, a sufficient energy density of the battery can be ensured. When the thickness of the positive electrode 301 and the negative electrode 303 is 500 μm or less, high-power operation of the battery 300 can be realized.

[0088] The separator layer 302 is a layer containing an electrolyte material. The separator layer 302 may contain at least one solid electrolyte selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. Details of each solid electrolyte are as described in the first embodiment.

[0089] The thickness of the separator layer 302 may be 1 μm or more and 300 μm or less. When the thickness of the separator layer 302 is 1 μm or more, the positive electrode 301 and the negative electrode 303 can be more reliably separated. When the thickness of the separator layer 302 is 300 μm or less, the battery 300 can operate at high power.

[0090] The negative electrode 303 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0091] Examples of the negative electrode active material that can be used include metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. The metal material may be a single metal. Alternatively, the metal material may be an alloy. Examples of the metal material include lithium metal and lithium alloys. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be preferably used.

[0092] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0093] The negative electrode 303 may contain other materials such as a solid electrolyte. As the solid electrolyte, the materials described in the first embodiment can be used.

[0094] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0095] (Technology 1) A cathode active material includes: a cathode active material; and a coating layer including a first solid electrolyte and coating at least a portion of a surface of the cathode active material, wherein the first solid electrolyte includes Li, Ti, M, and X, wherein M is at least one element selected from the group consisting of metal elements and semi-metal elements other than Li and Ti, and X is at least one element selected from the group consisting of F, Cl, Br, and I, and wherein the ratio (%) of the mass of the first solid electrolyte to the total mass of the cathode active material and the first solid electrolyte, calculated by the following mathematical formula (A), is calculated as a specific surface area (m 2 / g), the quotient obtained when divided by the % wt. / g is 1.9 or more and 6.9 or less.

[0096] This configuration can reduce the internal resistance of the battery.

[0097] (Technology 2) The coated active material according to Technology 1, wherein the quotient is 2.7 or more and 6.2 or less. With this configuration, the internal resistance of the battery can be further reduced.

[0098] (Technology 3) The coated active material according to Technology 2, wherein the quotient is 3.5 or more and 5.0 or less. With this configuration, the internal resistance of the battery can be reduced.

[0099] (Technology 4) The coated active material according to any one of Technologies 1 to 3, wherein M includes at least one selected from the group consisting of Ca, Mg, Al, Y, Ni, Fe, Cr, and Zr. With this configuration, the first solid electrolyte exhibits high ionic conductivity.

[0100] (Technology 5) The coated active material according to any one of Technologies 1 to 4, wherein M contains Al. With this configuration, the first solid electrolyte exhibits high ionic conductivity.

[0101] (Technology 6) The first solid electrolyte is represented by the following composition formula (1): Li α Ti β M γ X δ ...Composition Formula (1) Here, in the composition formula (1), α, β, γ, and δ are each independently a value greater than 0. When the first solid electrolyte represented by composition formula (1) is used in a battery, the output characteristics of the battery can be improved.

[0102] (Technology 7) The first solid electrolyte is represented by the following composition formula (2): Li6-(4-x-4y+my)b(Ti 1-x-y Al x M2 y ) b F 6-2z O z ...Composition formula (2) In the composition formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M2, and 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.2 are satisfied. The coated active material according to any one of techniques 1 to 6 can improve the output characteristics of a battery.

[0103] (Technology 8) A positive electrode material comprising the coated active material according to any one of Technologies 1 to 7 and a second solid electrolyte. With this configuration, the internal resistance of the battery can be reduced.

[0104] (Technology 9) The positive electrode material according to Technology 8, wherein the second solid electrolyte contains Li and S. With this configuration, the charge / discharge efficiency of the battery can be improved.

[0105] (Technology 10) A positive electrode comprising the positive electrode material according to Technology 8. Such a configuration can reduce the internal resistance of the battery.

[0106] (Technology 11) A battery comprising the positive electrode according to Technology 10. With such a configuration, the internal resistance of the battery can be reduced.

[0107] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. Note that the electrodes and batteries of the present disclosure are not limited to the following examples.

[0108] Example 1 Preparation of First Solid Electrolyte In an argon glove box with a dew point of -60°C or less, raw material powders of LiF, TiF4, and AlF3 were weighed out in a molar ratio of LiF:TiF4:AlF3 = 2.5:0.5:0.5. These were pulverized and mixed in a mortar to obtain a mixture. The obtained mixed powder was milled for 12 hours at 500 rpm using a planetary ball mill. In this way, a halide solid electrolyte powder was obtained as the first solid electrolyte of Example 1. The first solid electrolyte of Example 1 was made of Li, 2.5 Ti 0.5 Al 0.5 F6 (hereinafter referred to as "LTAF").

[0109] [Preparation of Coated Active Material] Powder of Li(NiCoAl)O (hereinafter referred to as "NCA") was prepared as a positive electrode active material. The BET specific surface area of ​​NCA was 0.58 m 2 / g. A coating layer made of LTAF was formed on the surface of the NCA. The coating layer was formed by shearing using a particle mixer (BALANCE GRAN, manufactured by Freund Turbo). Specifically, the NCA and LTAF were weighed out to a mass ratio of 98.39:1.61, and treated at a rotation speed of 3100 rpm for 1 hour. This resulted in the production of the coated active material of Example 1.

[0110] [Preparation of Second Solid Electrolyte] In an argon glove box with a dew point of −60°C or less, raw material powders LiS and PS were weighed out to a molar ratio of LiS:PS = 75:25. These were pulverized and mixed in a mortar to obtain a mixture. The mixture was then milled for 10 hours at 510 rpm using a planetary ball mill (Fritsch, P-7). This resulted in a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 2 hours. This resulted in a glass-ceramic sulfide solid electrolyte, LiS-PS (hereinafter referred to as "LPS"), being obtained as the second solid electrolyte.

[0111] [Preparation of Positive Electrode Material] In an argon glove box, the coated active material of Example 1 and LPS were weighed out so that the volume ratio of the coated active material to the sulfide solid electrolyte was 70:30. These were mixed in an agate mortar to prepare the positive electrode material of Example 1.

[0112] Example 2 A coated active material of Example 2 was obtained in the same manner as Example 1, except that the mass ratio of NCA to LTAF was changed to 97.55:2.45. The BET specific surface area of ​​the NCA was 0.58 m, the same as in Example 1. 2 / g.

[0113] The coated active material of Example 2 was used to obtain a positive electrode material of Example 2 in the same manner as in Example 1.

[0114] Example 3 A coated active material of Example 3 was obtained in the same manner as in Example 1, except that the mass ratio of NCA to LTAF was changed to 96.42:3.58. The BET specific surface area of ​​the NCA was 0.58 m, the same as in Example 1. 2 / g.

[0115] The coated active material of Example 3 was used to obtain a positive electrode material of Example 3 in the same manner as in Example 1.

[0116] Example 4: BET specific surface area: 0.68 m 2 A coated active material of Example 4 was obtained in the same manner as in Example 1, except that NCA having a molecular weight of 1 / g was used and the mass ratio of NCA to LTAF was changed to 97.55:2.45.

[0117] The coated active material of Example 4 was used to obtain a positive electrode material of Example 4 in the same manner as in Example 1.

[0118] Comparative Example 1 A coated active material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the mass ratio of NCA to LTAF was changed to 98.9:1.1. The BET specific surface area of ​​the NCA was 0.58 m, the same as in Example 1. 2 / g.

[0119] The coated active material of Comparative Example 1 was used to obtain a positive electrode material of Comparative Example 1 in the same manner as in Example 1.

[0120] Comparative Example 2 A coated active material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the mass ratio of NCA to LTAF was changed to 95.99:4.01. The BET specific surface area of ​​the NCA was 0.58 m, the same as in Example 1. 2 / g.

[0121] A positive electrode material of Comparative Example 2 was obtained in the same manner as in Example 1 using the coated active material of Comparative Example 2.

[0122] In the coated active materials of Examples 1 to 4, Comparative Example 1, and Comparative Example 2, the ratio (%) of the mass of LTAF to the total mass of NCA and LTAF was calculated based on the specific surface area (m 2 / g), the quotient obtained is as shown in Table 1. In Table 1, this quotient is represented as "LTAF mass / (LTAF mass+NCA mass) / (NCA specific surface area)". The ratio of the mass of LTAF to the total mass of NCA and LTAF was determined from the amounts of NCA and LTAF charged during production of the coated active material. The inventors also determined the ratio of the mass of LTAF to the total mass of NCA and LTAF by analyzing a positive electrode using the coated active material by high-frequency inductively coupled plasma atomic emission spectroscopy, and the value of this ratio was approximately the same as the value determined from the charged amounts.

[0123] [Battery Fabrication] The positive electrode material was weighed so that it contained 14 mg of NCA. LPS and the positive electrode material were stacked in this order inside an insulating outer cylinder. The resulting laminate was press-molded at a pressure of 720 MPa. Next, metallic lithium was placed in contact with the LPS layer, and the laminate was again press-molded at a pressure of 40 MPa. This produced a laminate consisting of a positive electrode, a solid electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed on the top and bottom of the laminate. Current collector leads were attached to each current collector. Next, the outer cylinder was sealed using an insulating ferrule to isolate the interior of the outer cylinder from the outside atmosphere. Through these processes, the batteries of Examples 1 to 5 and Comparative Example 1 were fabricated. The battery was restrained from above and below with four bolts, and a surface pressure of 150 MPa was applied to the battery.

[0124] [Evaluation of Battery Characteristics] The battery was placed in a thermostatic chamber at 25°C. The battery was charged at a constant current of 147 μA, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, until the voltage reached 4.3 V. The battery was then discharged at a constant current of 147 μA, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, until the voltage reached 3.6 V. After discharging to 3.6 V, the battery was discharged at a constant current of 0.136 A for 0.1 seconds, which corresponds to a 46.4 C rate relative to the theoretical capacity of the battery, and the battery resistance was calculated from the voltage drop at that time. The results are shown in Table 1.

[0125]

[0126] <Discussion> As shown in Table 1, the batteries of Examples 1 to 4, in which the cathode active material was coated with an optimal amount of the first solid electrolyte, which was a halide solid electrolyte, had reduced resistance. The batteries of Examples 1 to 4 had lower resistance than the battery of Comparative Example 1. This suggests that the coating of the cathode active material with the first solid electrolyte was insufficient in Comparative Example 1. Furthermore, the batteries of Examples 1 to 4 had lower resistance than the battery of Comparative Example 2. This is presumably because the coating of the cathode active material with the first solid electrolyte was thick in Comparative Example 2, resulting in increased electronic resistance.

[0127] It has been confirmed that even when at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Ti, such as Ca, Mg, Y, Ni, Fe, Cr, or Zr, is used instead of Al, the halide solid electrolyte exhibits the same level of ionic conductivity (see, for example, Japanese Patent Application No. 2020-048461 by the present applicant). Therefore, a halide solid electrolyte containing at least one element selected from the group consisting of these elements can be used in place of Al or in addition to Al. Even in this case, the battery is capable of charging and discharging, and the effect of suppressing the oxidation reaction of the second solid electrolyte (e.g., sulfide solid electrolyte) and suppressing an increase in resistance is achieved. Furthermore, oxidation of the sulfide solid electrolyte occurs primarily when the sulfide solid electrolyte comes into contact with the positive electrode active material, causing electrons to be extracted from the sulfide solid electrolyte. Therefore, according to the technology disclosed herein, the effect of suppressing oxidation of the second solid electrolyte (e.g., sulfide solid electrolyte) can be achieved even when an active material other than NCA is used.

[0128] The technology of the present disclosure is useful, for example, in all-solid-state lithium secondary batteries.

Claims

1. It includes a positive electrode active material and a coating layer that contains a first solid electrolyte and covers at least a part of the surface of the positive electrode active material. The first solid electrolyte contains Li, Ti, M, and X. M is at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Ti. X is at least one selected from the group consisting of F, Cl, Br, and I. The ratio (%) of the mass of the first solid electrolyte to the total mass of the positive electrode active material and the first solid electrolyte, as determined by the following formula (A), when divided by the specific surface area (m 2 / g) of the positive electrode active material, the quotient obtained is 1.9 or more and 6.9 or less. Coated active material. Formula (A): {(mass of the first solid electrolyte) / (total mass of the positive electrode active material and the first solid electrolyte)} × 100 / (specific surface area of the positive electrode active material) 2. The quotient is 2.7 or more and 6.2 or less, and the coating active material according to claim 1.

3. The quotient is 3.5 or more and 5.0 or less, and the coating active material according to claim 2.

4. The M includes at least one selected from the group consisting of Ca, Mg, Al, Y, Ni, Fe, Cr, and Zr, and the coating active material according to claim 1.

5. The M includes Al, and the coating active material according to claim 4.

6. The first solid electrolyte is represented by the following compositional formula (1): Li α Ti β M γ X δ ... Compositional formula (1) Here, in the above compositional formula (1), α, β, γ, and δ are each independently a value greater than 0. The coated active material according to claim 1.

7. The first solid electrolyte is represented by the following compositional formula (2): Li6-(4-x-4y+my)b(Ti 1-x-y Al x M2 y ) b F 6-2z O z ... Compositional formula (2) Here, in the above compositional formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of the M2, and 0.1 < x < 0.9, 0 ≦ y < 0.1, 0 ≦ z < 0.1, and 0.8 < b ≦ 1.2 are satisfied. The coated active material according to claim 1.

8. A positive electrode material comprising the coating active material according to any one of claims 1 to 7 and a second solid electrolyte.

9. The second solid electrolyte includes Li and S, and the positive electrode material according to claim 8.

10. A positive electrode comprising the positive electrode material according to claim 8.

11. A battery comprising the positive electrode according to claim 10.