Coated active material, electrode, battery, and method for producing coated active material

Abstract

This coated active material (130) is provided with an active material (110) and a coating layer (120) that coats at least a part of the surface of the active material (110), the coating layer (120) having a first layer (111) that contains a first solid electrolyte and a second layer (112) that contains a second solid electrolyte, the first layer (111) being located between the second layer (112) and the active material (110), the first solid electrolyte containing Li, Ti, and F, the second solid electrolyte containing Li, Ti, F, and O, and the first layer (111) being located between the active material (110) and the second layer (112). The ratio of Ti-O bonds in the bond group of Ti contained in the second solid electrolyte is higher than the ratio of Ti-O bonds in the bond group of Ti contained in the first solid electrolyte.

Description

Technical Field

[0001] This disclosure relates to coated active materials, electrodes, batteries, and methods for manufacturing coated active materials. Background Technology

[0002] It is known that coating the active material with a solid electrolyte improves battery durability. For example, the fluoride solid electrolyte disclosed in Patent Document 1 exhibits high ionic conductivity, giving the battery excellent output characteristics.

[0003] Prior art literature

[0004] Patent Document 1: International Publication No. 2021 / 186809 Summary of the Invention

[0005] The problem that the invention aims to solve

[0006] Patent Document 1 describes a solid electrolyte that exhibits reactivity with oxygen. Therefore, if a solvent with a high oxygen content is used in the electrolyte, it may react with the electrolyte during battery charging and discharging. If the solid electrolyte coated with the active material reacts with the electrolyte, the battery resistance increases and the output characteristics decrease. Therefore, there is a need for materials that are not easily degraded during battery charging and discharging.

[0007] Methods for solving problems

[0008] This disclosure provides a coated active material having an active material and a coating layer covering at least a portion of the surface of the active material.

[0009] The coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte.

[0010] The first layer is located between the second layer and the active substance.

[0011] The first solid electrolyte contains Ti and F.

[0012] The second solid electrolyte contains Ti, F, and O.

[0013] The proportion of Ti-O bonds in the Ti bond group of the second solid electrolyte is higher than the proportion of Ti-O bonds in the Ti bond group of the first solid electrolyte.

[0014] The effects of the invention

[0015] The coated active material disclosed herein is not easily degraded during battery charging and discharging, thereby improving the battery's output characteristics. Attached Figure Description

[0016] Figure 1This is a cross-sectional view showing the general structure of the coated active material of Embodiment 1 of this disclosure.

[0017] Figure 2 This is a process diagram illustrating the manufacturing method of the coated active material.

[0018] Figure 3 This is a schematic cross-sectional view of a lithium secondary battery according to Embodiment 2 of this disclosure.

[0019] Figure 4 These are the XPS spectra of the outermost surface of the coated active material in Example 1 and Comparative Example 1.

[0020] Figure 5 These are the XPS spectra of LTAF immediately after synthesis, used to prepare coated active materials, and the XPS spectra after 7 days of atmospheric exposure. Detailed Implementation

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0022] (Implementation Method 1)

[0023] Figure 1 This is a cross-sectional view showing the general structure of the coated active material according to Embodiment 1 of this disclosure. The coated active material 130 includes an active material 110 and a coating layer 120. The active material 110 is, for example, granular. The coating layer 120 coats at least a portion of the surface of the active material 110. The coating layer 120 includes a first layer 111 and a second layer 112. The first layer 111 is located between the second layer 112 and the active material 110. The first layer 111 is a layer containing a first solid electrolyte. The second layer 112 is a layer containing a second solid electrolyte.

[0024] The first solid electrolyte is a solid electrolyte containing Li, Ti, and F. The second solid electrolyte is a solid electrolyte containing Li, Ti, F, and O. The proportion of Ti-O bonds in the Ti bond set of the second solid electrolyte is higher than that in the first solid electrolyte.

[0025] The first and second solid electrolytes are fluoride solid electrolytes, which exhibit excellent oxidation resistance due to the high electronegativity of fluorine. If the active material 110 is coated by the coating layer 120, direct contact between the active material 110 and the electrolyte can be prevented. In particular, according to this embodiment, the second solid electrolyte contained in the second layer 112 contains more Ti-O bonds than the first solid electrolyte contained in the first layer 111. That is, the ratio of Ti atoms bonded to oxygen atoms is higher in the surface portion of the coating layer 120. By containing more Ti-O bonds, the activity of the second solid electrolyte relative to the electrolyte is suppressed. Therefore, even in the case of a solvent with a high oxygen content in the electrolyte, the coating layer 120 is less prone to deterioration during battery charging and discharging. As a result, the output characteristics of the battery using the coated active material 130 are improved. In particular, the retention rate of discharge capacity at high rates is improved.

[0026] The bond set of Ti refers to the group of bonds formed between anions and Ti. Titanium (Ti), fluorine (F), and oxygen (O) typically form compounds such as TiF4, TiOF2, and TiO2. Therefore, the bond set of Ti is represented by Ti-F bonds, Ti-OF bonds, and Ti-O bonds. By adjusting the proportion of Ti-O bonds in these bond sets, a coated active material 130 with a coating layer 120 that is not easily altered can be obtained.

[0027] The ratios of Ti-F, Ti-OF, and Ti-O bonds can be calculated using the following method. First, XPS (X-ray Photoelectron Spectroscopy) measurements are performed on the coated active material 130. The Ti2p spectrum observed in the binding energy range of 448 eV to 486 eV is separated into peaks for TiF4, TiOF2, and TiO2. The TiF4 peak is located near 462.0 eV. The TiOF2 peak is located near 460.2 eV. The TiO2 peak is located near 458.3 eV. The ratio of the area of ​​the TiF4 peak to the total area of ​​the separated peaks is calculated as the Ti-F bond ratio (in %). The ratio of the TiOF2 peak area to the total area of ​​the separated peaks is calculated as the Ti-OF bond ratio (in %). The ratio of the area of ​​the peak attributable to TiO2 to the total area of ​​the separated peaks is calculated as the Ti-O bond ratio (in %).

[0028] XPS measurements of the coated active material 130 without special processing allow for the investigation of the bond ratios in the second solid electrolyte. XPS measurements performed by removing a portion of the coating layer 120 by sputtering allow for the investigation of the bond ratios in the first solid electrolyte.

[0029] In the second solid electrolyte contained in the second layer 112, the proportion of Ti-O bonds is, for example, greater than 5%. In other words, the combined proportion of Ti-F bonds and Ti-OF bonds is less than 95%. By making the proportion of Ti-O bonds in the second solid electrolyte greater than 5%, a coated active material 130 with a coating layer 120 that is not easily deteriorated can be obtained.

[0030] The proportion of Ti-O bonds in the second solid electrolyte can be above 40%, above 50%, or above 80%. In other words, the combined proportion of Ti-F bonds and Ti-OF bonds can be below 60%, below 50%, or below 20%. By sufficiently increasing the proportion of Ti-O bonds in the second solid electrolyte, the effect of suppressing the deterioration of the coating layer 120 is improved.

[0031] There is no particular upper limit to the ratio of Ti-O bonds in the second solid electrolyte, for example, it is 95%.

[0032] In the first solid electrolyte contained in the first layer 111, the combined ratio of Ti-F bonds and Ti-OF bonds is, for example, 63% or more. In other words, the ratio of Ti-O bonds is 37% or less. The high combined ratio of Ti-F bonds and Ti-OF bonds in the first solid electrolyte indicates a low ratio of Ti atoms bonded to oxygen atoms. Based on this structure, the coating layer 120 tends to exhibit high ionic conductivity.

[0033] The combined ratio of Ti-F bonds and Ti-OF bonds in the first solid electrolyte can be 85% or more. In other words, the ratio of Ti-O bonds can be less than 15%. By increasing the combined ratio of Ti-F bonds and Ti-OF bonds, the coating layer 120 tends to exhibit high ionic conductivity.

[0034] There is no particular upper limit to the combined ratio of Ti-F bonds and Ti-OF bonds in the first solid electrolyte, but it can be, for example, 98%.

[0035] In this embodiment, the second layer 112 is the outermost layer containing the coated active material 130. That is, the second layer 112 forms at least a portion of the outermost surface of the coated active material 130. With this structure, it is possible to effectively suppress the deterioration of the coating layer 120 due to reaction with the electrolyte during battery charging and discharging.

[0036] In this embodiment, the first layer 111 is a layer existing in a region at a distance of 1 nm or more from the outermost surface of the coated active material 130. With this structure, the deterioration of the coating layer 120 due to reaction with the electrolyte during battery charging and discharging can be effectively suppressed. The thickness of the second layer 112 can be 1 nm or more, or it can be less than 1 nm.

[0037] The aforementioned relationship between the first solid electrolyte contained in the first layer 111 and the second solid electrolyte contained in the second layer 112 can also be established between the outermost surface of the coated active material 130 and the midpoint in the thickness direction of the coated layer 120. That is, the proportion of Ti-O bonds in the Ti bond sets contained in the outermost surface of the coated active material 130 is higher than the proportion of Ti-O bonds in the Ti bond sets contained in the coated layer 120 at the midpoint from the outermost surface of the coated active material 130 to the surface of the active material 110. The proportion of Ti-O bonds in the Ti bond sets contained in the outermost surface of the coated active material 130 is equal to the proportion of Ti-O bonds in the Ti bond sets contained in the second solid electrolyte. The proportion of Ti-O bonds in the Ti bond group contained in the coating layer 120 at the intermediate position from the outermost surface of the coated active material 130 to the surface of the active material 110 is equal to the proportion of Ti-O bonds in the Ti bond group contained in the first solid electrolyte.

[0038] The coating layer 120 can be positioned relative to the midpoint of its thickness direction, having a surface portion and a portion constituting the interface between the coating layer and the active material. The surface portion contains a higher proportion of Ti-O bonds in its Ti bond sets compared to the interface portion. This structure makes the coating layer 120 less prone to degradation during battery charging and discharging.

[0039] exist Figure 1 In the structure shown, the outermost part can be consistent with the second layer 112, and the part that forms the interface between the coating layer 120 and the active substance 110 can be consistent with the first layer 111.

[0040] On the outermost surface of the coated active material 130, the ratio of Ti-O bonds is, for example, greater than 5%. In other words, the combined ratio of Ti-F bonds and Ti-OF bonds is less than 95%. By making the ratio of Ti-O bonds on the outermost surface greater than 5%, a coated active material 130 with a coating layer 120 that is not easily deteriorated can be obtained.

[0041] On the outermost surface of the coated active material 130, the ratio of Ti-O bonds can be above 40%, above 50%, or above 80%. In other words, the combined ratio of Ti-F bonds and Ti-OF bonds can be below 60%, below 50%, or below 20%. By sufficiently increasing the ratio of Ti-O bonds on the outermost surface, the effect of inhibiting the deterioration of the coating layer 120 is improved.

[0042] There is no particular upper limit to the ratio of the outermost Ti-O bonds, for example, 95%.

[0043] At the midpoint of coating layer 120, the combined ratio of Ti-F bonds and Ti-OF bonds is, for example, 63% or more. In other words, the ratio of Ti-O bonds is 37% or less. The high combined ratio of Ti-F bonds and Ti-OF bonds at the midpoint indicates a low ratio of Ti atoms bonded to oxygen atoms. Based on this structure, coating layer 120 tends to exhibit high ionic conductivity.

[0044] At the middle position of the coating layer 120, the combined ratio of Ti-F bonds and Ti-OF bonds can be above 85%. In other words, the ratio of Ti-O bonds can be below 15%. By increasing the combined ratio of Ti-F bonds and Ti-OF bonds, the coating layer 120 tends to exhibit high ionic conductivity.

[0045] There is no particular upper limit to the combined ratio of Ti-F bonds and Ti-OF bonds in the middle position of the coating layer 120, for example, it is 98%.

[0046] The first solid electrolyte and the second solid electrolyte are described in detail.

[0047] The first and second solid electrolytes each possess lithium-ion conductivity. The coated active material 130 is suitable for lithium-ion secondary batteries.

[0048] The first solid electrolyte can be substantially composed of Li, Ti, and F. "The first solid electrolyte is substantially composed of Li, Ti, and F" means that the molar ratio (i.e., mole fraction) of the total mass of Li, Ti, and F relative to the total mass of all elements constituting the first solid electrolyte is 90% or more. In one example, this molar ratio can be 95% or more. The first solid electrolyte can also be composed solely of Li, Ti, and F.

[0049] The first solid electrolyte may also contain at least one element selected from Ca, Mg, Al, Y, and Zr. Including these elements improves the ionic conductivity of the first solid electrolyte. Al is preferred from the viewpoint of cost and ionic conductivity.

[0050] The first solid electrolyte may substantially consist of Li, Ti, M, and F. M is at least one selected from Ca, Mg, Al, Y, and Zr. "The first solid electrolyte substantially consists of Li, Ti, M, and F" means that the molar ratio (i.e., mole fraction) of the total mass of Li, Ti, M, and F relative to the total mass of all elements constituting the first solid electrolyte is 90% or more. In one example, this molar ratio may be 95% or more. The first solid electrolyte may consist only of Li, Ti, M, and F.

[0051] The first solid electrolyte may contain elements that are unavoidably mixed in. Examples of such elements include hydrogen, oxygen, and nitrogen. These elements are contained in the raw material powder of the first solid electrolyte or are present in the atmosphere used to manufacture and store the first solid electrolyte.

[0052] To further improve the ionic conductivity of the first solid electrolyte, the ratio of the mass of Li to the total mass of Ti and M can be greater than 1.7 and less than 4.2.

[0053] The first solid electrolyte, for example, has a composition represented by the following formula (1). Formula (1) satisfies 0 ≤ x < 1 and 0 < b ≤ 2. When the first solid electrolyte has a composition represented by the following formula (1), the first solid electrolyte exhibits good ionic conductivity.

[0054] Li 6-(4-x)b (Ti 1-x M x ) b Formula F6 (1)

[0055] In order to improve the ionic conductivity of the first solid electrolyte, equation (1) can satisfy 0.1≤x≤0.9.

[0056] In order to improve the ionic conductivity of the first solid electrolyte, equation (1) can satisfy 0.8≤b≤1.2.

[0057] The first solid electrolyte may have a crystalline phase. The first solid electrolyte may contain an amorphous phase.

[0058] To improve ionic conductivity, the first solid electrolyte may contain anions other than F. The anions other than F are selected from at least one of Cl, Br, I, and Se.

[0059] The second solid electrolyte can be substantially composed of Li, Ti, F, and O. "The second solid electrolyte is substantially composed of Li, Ti, F, and O" means that the molar ratio (i.e., mole fraction) of the total mass of Li, Ti, F, and O relative to the total mass of all elements constituting the second solid electrolyte is 90% or more. In one example, this molar ratio can be 95% or more. The second solid electrolyte can also be composed solely of Li, Ti, F, and O.

[0060] The second solid electrolyte may also contain at least one element selected from Ca, Mg, Al, Y, and Zr. Including these elements improves the ionic conductivity of the second solid electrolyte. Al is preferred from the viewpoint of cost and ionic conductivity.

[0061] The second solid electrolyte may substantially consist of Li, Ti, M, F, and O. M is at least one selected from Ca, Mg, Al, Y, and Zr. "The second solid electrolyte substantially consists of Li, Ti, M, F, and O" means that the molar ratio (i.e., mole fraction) of the total mass of Li, Ti, M, F, and O relative to the total mass of all elements constituting the second solid electrolyte is 90% or more. In one example, this molar ratio may be 95% or more. The second solid electrolyte may consist only of Li, Ti, M, F, and O.

[0062] The second solid electrolyte may contain elements that are inevitably mixed in. Examples of such elements include hydrogen and nitrogen.

[0063] The second solid electrolyte is obtained by oxidizing a portion of the first solid electrolyte after coating the active material 110 with the first solid electrolyte. In this case, the composition of the second solid electrolyte is the same as that of the first solid electrolyte, except for oxygen. According to this method, the process of coating the active material 110 with the solid electrolyte is completed in one step.

[0064] However, the composition of the second solid electrolyte when oxygen is ignored can also differ from that of the first solid electrolyte when oxygen is ignored. The constituent elements of the second solid electrolyte other than oxygen can differ from those of the first solid electrolyte other than oxygen. For example, after the active material 110 is coated with a first solid electrolyte with a low Ti-O bond ratio, the active material 110 can be coated with a second solid electrolyte with a high Ti-O bond ratio, thereby sequentially forming a first layer 111 containing the first solid electrolyte and a second layer 112 containing the second solid electrolyte on the active material 110.

[0065] The first and second solid electrolytes are preferably sulfur-free. Sulfur-free solid electrolytes do not produce hydrogen sulfide even when exposed to the atmosphere, thus providing excellent safety.

[0066] The coating layer 120 may only coat a portion of the surface of the particles of the active material 110. In this case, the particles of the active material 110 are in direct contact through the portion not covered by the coating layer 120, thereby ensuring the electronic conductivity between the particles of the active material 110. However, the coating layer 120 may also uniformly coat the surface of the particles of the active material 110.

[0067] The first layer 111 of the coating layer 120 may contain the first solid electrolyte as a main component, or it may contain only the first solid electrolyte. "Main component" refers to the component that is contained the most by mass. "Contains only the first solid electrolyte" means that no material other than the first solid electrolyte has been intentionally added, except for unavoidable impurities.

[0068] The second layer 112 of the coating layer 120 may contain the second solid electrolyte as a main component, or it may contain only the second solid electrolyte. "Main component" refers to the component that is contained the most by mass. "Contains only the second solid electrolyte" means that no material other than the second solid electrolyte has been intentionally added, except for unavoidable impurities.

[0069] The thickness of the coating layer 120 is preferably 1 nm or more and 500 nm or less, more preferably 1 nm or more and 100 nm or less, and even more preferably 1 nm or more and 20 nm or less. By appropriately adjusting the thickness of the coating layer 120, the contact between the active material 110 and the electrolyte can be sufficiently suppressed. The thickness of the coating layer 120 can be determined by thinning the coated active material 130 using methods such as ion milling and observing the cross-section of the coated active material 130 using a transmission electron microscope. The average thickness measured at any number of locations (e.g., 5 points) can be considered as the thickness of the coating layer 120. By observing with a transmission electron microscope, the position of the interface between the coating layer 120 and the active material 110 in the coated active material 130 can be determined.

[0070] The active material 110 contains a material that has the property of absorbing and releasing metal ions such as lithium ions.

[0071] In this embodiment, the active material 110 can be an oxide. The active material 110 can be an oxide that does not contain Ti, except in cases where it is unavoidably mixed in.

[0072] When the active material 110 is the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides can be used as the active material 110. In particular, using lithium-containing transition metal oxides or lithium-containing transition metal phosphates as the active material 110 can reduce the battery manufacturing cost and increase the average discharge voltage. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0073] The active material 110 can be a negative electrode active material. Examples of negative electrode active materials include lithium titanate, graphite, silicon, silicon compounds, and NiBi alloys.

[0074] There are no particular limitations on the shape of the particles of active substance 110. The particles of active substance 110 can be spherical, ellipsoidal, scaly, or fibrous.

[0075] Figure 2 This is a process diagram illustrating a method for manufacturing the coated active material 130. According to the manufacturing method of this embodiment, the coated active material 130 can be manufactured efficiently.

[0076] In step S1, the active material 110 is coated with a solid electrolyte containing Li, Ti, and F. The solid electrolyte containing Li, Ti, and F is the first solid electrolyte.

[0077] Solid electrolytes containing Li, Ti, and F can be synthesized, for example, by the following method. First, raw material powders are mixed in a manner that yields a solid electrolyte with the desired composition. The raw material powders are, for example, fluorides of each element. The target composition is Li... 2.7 Ti 0.3 Al 0.7 In the case of F6, LiF, TiF4, and AlF3 are mixed in a molar ratio of 2.7:0.3:0.7. Then, the raw material powders are reacted with each other using a mixing device such as a planetary ball mill. That is, the raw material powders are reacted with each other by a mechanochemical milling method. This yields a solid electrolyte with the target composition.

[0078] The process of coating the active material 110 with a solid electrolyte is described below. The powder of the active material 110 and the powder of the solid electrolyte are mixed in an appropriate ratio to obtain a mixture. The mixture is then milled to impart mechanical energy. Thus, the active material 110 is coated with the solid electrolyte. The milling process can be performed using a mixing device such as a ball mill. To suppress oxidation of the material, the milling process can be performed in a dry and inert atmosphere.

[0079] In step S2, an oxygen-containing liquid is applied to the active material 110 coated with a solid electrolyte. The oxygen-containing liquid is used to oxidize a portion of the solid electrolyte layer to increase Ti-O bonds. If heat treatment is performed while the oxygen-containing liquid is applied, the portion of the solid electrolyte layer can be effectively oxidized.

[0080] Oxygen-containing liquids include, for example, water. Water can bond with Ti and, through heat treatment, effectively oxidize the solid electrolyte. Oxygen-containing liquids can also be ethanol, N-methylpyrrolidone, etc. Oxygen-containing liquids can contain a variety of components.

[0081] In step S3, the active material 110 coated with the solid electrolyte is heat-treated to remove the oxygen-containing liquid. Thus, the coated active material 130 of this embodiment is obtained.

[0082] The ambient temperature during heat treatment is, for example, 180°C or higher. At such temperatures, a portion of the solid electrolyte layer can be effectively oxidized. There is no particular upper limit to the ambient temperature during heat treatment; for example, it is 300°C.

[0083] (Implementation Method 2)

[0084] Figure 3 This is a schematic cross-sectional view of a lithium secondary battery according to Embodiment 2 of this disclosure. The lithium secondary battery 100 includes a positive electrode 53, a negative electrode 56, an electrolyte layer 57, an outer casing 58, and a non-aqueous electrolyte 59. The positive electrode 53 has a positive current collector 51 and a positive active material layer 52. The positive active material layer 52 is disposed on the positive current collector 51. The negative electrode 56 has a negative current collector 54 and a negative active material layer 55. The negative active material layer 55 is disposed on the negative current collector 54. An electrolyte layer 57 is disposed between the positive electrode 53 and the negative electrode 56. The electrolyte layer 57 is a separator. The positive electrode 53, the negative electrode 56, the electrolyte layer 57, and the non-aqueous electrolyte 59 are housed in the outer casing 58.

[0085] The positive electrode 53 or negative electrode 56 contains the coated active material 130 of Embodiment 1. Specifically, the positive electrode active material layer 52 or the negative electrode active material layer 55 contains the coated active material 130 of Embodiment 1. The coated active material 130 has excellent durability relative to the non-aqueous electrolyte 59, thus improving the output characteristics of the lithium secondary battery 100.

[0086] The coated active material 130 is typically contained in the positive electrode 53.

[0087] The positive current collector 51 is, for example, a foil made of metallic materials such as aluminum, stainless steel, titanium, or their alloys. The negative current collector 54 is, for example, a foil made of metallic materials such as stainless steel, nickel, copper, or their alloys.

[0088] The positive electrode active material layer 52 and the negative electrode active material layer 55 may contain conductive additives, ion conductors, binders, etc.

[0089] The non-aqueous electrolyte 59 permeates the positive electrode 53, the negative electrode 56, and the electrolyte layer 57. The non-aqueous electrolyte 59 can fill the internal space of the outer casing 58.

[0090] The non-aqueous electrolyte 59 contains a non-aqueous solvent and a lithium salt.

[0091] Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles, amides, and lactones. One solvent selected from these can be used, or a combination of two or more can be used. Examples of solvents with a high oxygen content include lactones. γ-Butyrolactone is a specific example of a lactone. When the electrolyte contains lactones, the coated active material 130 of this disclosure can achieve even greater effects. "Lactones" refers to compounds having a lactone ring. A lactone ring is a heterocycle containing an ester group within the ring.

[0092] Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethanesulfonyl)imide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalate)borate. One or more of these electrolyte salts can be used.

[0093] The electrolyte layer 57 is lithium-ion conductive. The material of the electrolyte layer 57 is not particularly limited as long as lithium ions can pass through. The material of the electrolyte layer 57 can be at least one selected from solid electrolytes, gel electrolytes, lithium cation exchange resin membranes, semi-permeable membranes, and porous membranes. Using these materials to make the electrolyte layer 57 ensures sufficient safety for the lithium secondary battery 100. Examples of solid electrolytes include sulfide solid electrolytes such as Li₂S-P₂S₅ and Li₇La₃Zr₂O. 12(LLZ) and other oxide solid electrolytes, etc. Examples of gel electrolytes include gel electrolytes containing fluorinated resins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resins and porous membranes made of cellophane obtained by weaving glass fibers into nonwoven fabric. The electrolyte layer 57 has, for example, a thickness of 0.001 μm or more and 500 μm or less.

[0094] There is no particular limitation on the shape of the lithium secondary battery 100. The lithium secondary battery 100 can be in various shapes such as coin-shaped, cylindrical, square, sheet-shaped, button-shaped, flat, and stacked.

[0095] The lithium secondary battery 100 can be a solid-state battery that does not use a non-aqueous electrolyte. In solid-state batteries, there is also a possibility that the coated active material 130 may deteriorate due to the solid electrolyte or other materials. If the deterioration of the coated active material 130 is suppressed, the output characteristics of the lithium secondary battery are improved.

[0096] (Other implementation methods)

[0097] (Postscript)

[0098] Based on the above description of the embodiments, the following technical solution is disclosed.

[0099] (Technical Solution 1)

[0100] A coated active material having an active material and a coating layer covering at least a portion of the surface of the active material.

[0101] The coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte.

[0102] The first layer is located between the second layer and the active substance.

[0103] The first solid electrolyte contains Li, Ti, and F.

[0104] The second solid electrolyte contains Li, Ti, F, and O.

[0105] The proportion of Ti-O bonds in the Ti bond group of the second solid electrolyte is higher than the proportion of Ti-O bonds in the Ti bond group of the first solid electrolyte.

[0106] The coated active material disclosed herein is not easily degraded during battery charging and discharging, thereby improving the battery's output characteristics.

[0107] (Technical Solution 2)

[0108] According to the coated active material of technical solution 1, the ratio of Ti-O bonds in the second solid electrolyte is greater than 5%. By making the ratio of Ti-O bonds in the second solid electrolyte greater than 5%, a coated active material with a coating layer that is not easily deteriorated can be obtained.

[0109] (Technical Solution 3)

[0110] According to the coated active material described in technical solution 1 or 2, the combined ratio of Ti-F bonds and Ti-OF bonds in the first solid electrolyte is 63% or more. With this configuration, the coating layer tends to have high ionic conductivity.

[0111] (Technical Solution 4)

[0112] According to any one of technical solutions 1 to 3, the coated active material, the first solid electrolyte and the second solid electrolyte further contain at least one element selected from Ca, Mg, Al, Y and Zr. By including these elements, the ionic conductivity of the first solid electrolyte can be improved.

[0113] (Technical Solution 5)

[0114] According to any one of technical solutions 1 to 4, the second layer is the outermost layer containing the coated active material. With this configuration, it is possible to effectively suppress the coating layer from reacting with the electrolyte and deteriorating during battery charging and discharging.

[0115] (Technical Solution 6)

[0116] According to any one of technical solutions 1 to 5, the first layer is a layer existing in a region at a distance of 1 nm or more from the outermost surface of the coated active material. With this configuration, it is possible to effectively suppress the coating layer from reacting with the electrolyte and deteriorating during battery charging and discharging.

[0117] (Technical Solution 7)

[0118] According to any one of technical solutions 1 to 6, the thickness of the coating layer is 1 nm or more and 500 nm or less. By appropriately adjusting the thickness of the coating layer, the contact between the active material and the electrolyte can be sufficiently suppressed.

[0119] (Technical Solution 8)

[0120] A coated active material having an active material and a coating layer covering at least a portion of the surface of the active material.

[0121] The proportion of Ti-O bonds in the Ti bond group contained on the outermost surface of the coated active material is higher than the proportion of Ti-O bonds in the Ti bond group contained in the coating layer at the intermediate position from the outermost surface to the surface of the active material.

[0122] The coated active material disclosed herein is not easily degraded during battery charging and discharging, thereby improving the battery's output characteristics.

[0123] (Technical Solution 9)

[0124] According to the coated active material described in technical solution 8, the coating layer, with the intermediate position as a reference, has a portion on the outermost surface and a portion constituting the interface between the coating layer and the active material. The proportion of Ti-O bonds in the Ti bond sets contained in the outermost surface portion is higher than the proportion of Ti-O bonds in the Ti bond sets contained in the portion constituting the interface. With this configuration, the coating layer is less prone to deterioration during battery charging and discharging.

[0125] (Technical Solution 10)

[0126] According to the coated active material of technical solution 8 or 9, the ratio of Ti-O bonds on the outermost surface is greater than 5%. By making the ratio of Ti-O bonds on the outermost surface greater than 5%, a coated active material with a coating layer that is not easily deteriorated can be obtained.

[0127] (Technical Solution 11)

[0128] According to any one of technical solutions 8 to 10, in the coated active material at the intermediate position, the combined ratio of Ti-F bonds and Ti-OF bonds is 63% or more. With this configuration, the coating layer tends to have high ionic conductivity.

[0129] (Technical Solution 12)

[0130] According to any one of technical solutions 8 to 11, the coating active material further comprises at least one element selected from Ca, Mg, Al, Y, and Zr. By including these elements, the ionic conductivity of the coating layer can be improved.

[0131] (Technical Solution 13)

[0132] An electrode comprising the coated active material as described in any one of technical solutions 1 to 12. The coated active material exhibits excellent durability against the electrolyte, thereby improving the output characteristics of the battery.

[0133] (Technical Solution 14)

[0134] A battery comprising the electrodes described in technical solution 13. The coated active material exhibits excellent durability against the electrolyte, thereby improving the battery's output characteristics.

[0135] (Technical Solution 15)

[0136] The battery according to technical solution 14 further comprises an electrolyte containing lactones. When the electrolyte contains lactones, the coated active material of this disclosure can achieve higher performance.

[0137] (Technical Solution 16)

[0138] A method for manufacturing a coated active material, comprising:

[0139] The active material is coated with a solid electrolyte containing Li, Ti and F;

[0140] To allow an oxygen-containing liquid to adhere to the active material coated with the solid electrolyte; and

[0141] The active material coated with the solid electrolyte is subjected to heat treatment to remove the liquid.

[0142] According to the manufacturing method disclosed herein, coated active materials can be manufactured effectively.

[0143] (Technical Solution 17)

[0144] According to the method for manufacturing the coated active material described in technical solution 16, the liquid contains water. Water forms bonds with Ti and F, and heat treatment enables the solid electrolyte to be effectively oxidized.

[0145] (Technical Solution 18)

[0146] According to the manufacturing method of the coated active material described in technical solution 16 or 17, the ambient temperature during the heat treatment is above 180°C. At such a temperature, a portion of the solid electrolyte layer can be effectively oxidized.

[0147] Example

[0148] The present disclosure will now be described in detail with reference to embodiments and comparative examples. However, the present disclosure is not limited to the embodiments described below.

[0149] (Example 1)

[0150] [Preparation of fluoride solid electrolytes]

[0151] In an argon atmosphere with a dew point below -60°C, LiF, TiF4, and AlF3, as raw material powders, were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. They were placed together with 25g of 0.5mm φ balls into a container for a 45cc planetary ball mill. γ-Butyrolactone (GBL) as an organic solvent was added dropwise to the container, resulting in a solid content ratio of 50% by mass. The solid content ratio was calculated by {(mass of raw materials) / (mass of raw materials + mass of solvent)} × 100. The mixture was milled for 12 hours at 500 rpm using a planetary ball mill. After milling, the balls were separated to obtain a slurry. The slurry was dried using a jacketed heater under a nitrogen flow at 200°C for 1 hour. The resulting solid was pulverized in a mortar to obtain a powder of fluoride solid electrolyte. The fluoride solid electrolyte has the following composition: Li... 2.7 Ti 0.3 Al 0.7 F6 (hereinafter referred to as "LTAF") represents the composition.

[0152] [Preparation of the coated active substance]

[0153] LiCoO2 powder (hereinafter referred to as "LCO") was prepared as the positive electrode active material. Next, a coating layer formed of LTAF was formed on the surface of the LCO. The coating layer was formed by compression shearing using a particle composite device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, LCO and LTAF were weighed at a volume ratio of 100:3 and processed under the conditions of blade gap: 2 mm, rotation speed: 6000 rpm, and processing time: 30 min. Thus, LCO coated with LTAF was obtained. The thickness of the coating layer was measured using the above method. The thickness of the coating layer was 25 nm.

[0154] The LTAF-coated LCO was mixed with water and kneaded for 1 hour. The mass ratio of LTAF-coated LCO to water was (LTAF-coated LCO):water = 10:1. Then, the LTAF-coated LCO was heat-treated at an ambient temperature of 200°C for 24 hours. Thus, the coated active material of Example 1 was obtained.

[0155] (Comparative Example 1)

[0156] Except for omitting the steps of mixing with water and heat treatment, the coated active material of Comparative Example 1 was prepared using the same method as in Example 1.

[0157] [XPS determination of coated active substances]

[0158] XPS measurements of the coated active substances of Example 1 and Comparative Example 1 were performed under the following conditions. The XPS measurements were performed using a Quantera SXM (manufactured by ULVAC PHI). The measurement conditions are described below.

[0159] X-ray source: Al monochromatic (25W, 15kV)

[0160] Electron-ion neutralization gun: ON

[0161] Photoelectron extraction angle: 45 degrees

[0162] Ti was selected as the element to be measured, and the binding energy scan range was set to 450 eV–480 eV (Ti 2p orbitals). Peak separation was performed on XPS spectra in the range of 455 eV–486 eV, and the area of ​​each peak was calculated. Specifically, the spectrum was separated into peaks attributed to Ti-F bonds, Ti-OF bonds, and Ti-O bonds, and the area of ​​each peak (integrated peak area) was calculated. The ratio of the area of ​​the Ti-O bond peak to the total area of ​​the peaks was calculated (in %). The ratio of the area of ​​the Ti-OF bond peak to the total area of ​​the peaks was calculated (in %). The ratio of the area of ​​the Ti-F bond peak to the total area of ​​the peaks was calculated (in %). Peak fitting was performed using the Gauss-Lorentz function in the XPS spectral analysis.

[0163] Figure 4 These are the XPS spectra of the outermost surface of the coated active material in Example 1 and Comparative Example 1.

[0164] After XPS measurements of the outermost surface of the coated active materials in Examples 1 and Comparative Example 1 were performed, the surface layer of the coated active materials was removed by argon sputtering. Then, XPS measurements were performed again. By repeatedly performing argon sputtering and XPS measurements, XPS measurements were performed at depths of 1 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, and 25 nm from the outermost surface. The results are shown in Table 1.

[0165] Table 1

[0166]

[0167] As shown in Table 1, the surface Ti-O bond ratio of the coated active material in Example 1 is very high, at 80%. The surface Ti-O bond ratio of the coated active material in Comparative Example 1 is as low as 5%. It is speculated that the surface Ti-O bonds of the coated active material in Comparative Example 1 are caused by natural oxidation.

[0168] Since the active material is an oxide, Ti-O bonds were observed at depths of 1 nm to 25 nm in both Example 1 and Comparative Example 1. This suggests that during the fabrication of the coated active material, LTAF particles were forcefully pressed onto the surface of LCO particles, thereby forming Ti-O bonds. The ratio of Ti-O bonds on the outermost surface of the coated active material in Comparative Example 1 was lower than the ratio of Ti-O bonds at depths of 1 nm, 3 nm, and 5 nm. In contrast, the ratio of Ti-O bonds on the outermost surface of the coated active material in Example 1 significantly exceeded the ratio of Ti-O bonds at depths of 1 nm, 3 nm, and 5 nm. The ratio of Ti-O bonds on the outermost surface of the coated active material in Example 1 was more than twice the ratio of Ti-O bonds at a depth of 1 nm. Therefore, in Example 1, the interface between the first and second layers exists in a region less than 1 nm from the outermost surface of the coated active material, and the thickness of the second layer in Example 1 is less than 1 nm. The ratio of Ti-O bonds at depths of 1 nm, 3 nm, and 5 nm in Example 1 is greater than that in Comparative Example 1. Furthermore, 25 nm refers to the result observed near the interface between the coating layer and the active material.

[0169] [The manufacture of lithium secondary batteries]

[0170] The coating active material from Example 1, acetylene black as a conductive additive, polytetrafluoroethylene (PTFE) as a binder, and a solvent were mixed to obtain a positive electrode slurry. The ratio of the coating active material, acetylene black, and PTFE, based on mass, was 90:5:5. The positive electrode slurry was dried to obtain the positive electrode mixture.

[0171] By applying 100 mg of positive electrode mixture at 10 kN / cm 2 The particles (diameter: 10 mm) were obtained by pressure molding. The positive electrode of Example 1 was obtained by drying the particles at 200°C.

[0172] The positive electrode, polypropylene nonwoven fabric, and negative electrode from Example 1 were arranged in this order within a coin casing. 90 mg of electrolyte was injected into the coin casing. The coin casing was sealed with a cap to obtain the lithium secondary battery of Example 1. The electrolyte was prepared by dissolving lithium fluoride borate (LiBF4) in γ-butyrolactone. The concentration of lithium fluoride borate in the electrolyte was 1.0 mol / L. Metallic Li was used as the negative electrode.

[0173] The lithium secondary battery of Comparative Example 1 was manufactured using the same method as that of Example 1, except that the coated active material of Comparative Example 1 was used instead of the coated active material of Example 1.

[0174] [Charge and discharge test]

[0175] The charge-discharge tests of the lithium secondary batteries of Example 1 and Comparative Example 1 were conducted in the following order. Constant current charging was performed at an ambient temperature of 25°C with a current of 0.02C until the voltage reached 4.5V. After a 1-hour pause, constant current discharging was performed at a current of 2C until the voltage reached 3.0V, and the initial discharge capacity was measured. The 2C discharge capacities of the lithium secondary batteries of Example 1 and Comparative Example 1 are shown in Table 1. The 2C discharge capacities shown in Table 1 are the discharge capacities per unit mass of coated active material.

[0176] Table 2

[0177]

[0178] As shown in Table 2, the discharge capacity of the lithium secondary battery of Example 1 at a 2C rate is significantly greater than that of the lithium secondary battery of Comparative Example 1 at a 2C rate.

[0179] (Example for reference)

[0180] XPS measurements were performed on the LTAF used in the preparation of the coated active material immediately after synthesis, and after 7 days of atmospheric exposure. Results are as follows: Figure 5 As shown.

[0181] Depend on Figure 5 As shown in the two spectra, the spectral changes of LTAF before and after 7 days of atmospheric exposure are minimal. That is, as in Example 1, the changes caused by oxidation treatment using water and heat are significantly different from those caused by atmospheric exposure. It is predicted that even if the coated active material of Comparative Example 1 is exposed to the atmosphere for a prolonged period, the Ti-O bond ratio will not change significantly from the values ​​shown in Table 1 (5%).

[0182] Industry availability

[0183] The technology disclosed herein can be used for coating active materials used in batteries.

Claims

1. A coated active material, comprising the active material and a coating layer covering at least a portion of the surface of the active material. The coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte. The first layer is located between the second layer and the active substance. The first solid electrolyte contains Li, Ti, and F. The second solid electrolyte contains Li, Ti, F, and O. The proportion of Ti-O bonds in the Ti bond group of the second solid electrolyte is higher than the proportion of Ti-O bonds in the Ti bond group of the first solid electrolyte.

2. The coated active material according to claim 1, In the second solid electrolyte, the ratio of Ti-O bonds is greater than 5%.

3. The coated active material according to claim 1, In the first solid electrolyte, the combined ratio of Ti-F bonds and Ti-OF bonds is 63% or more.

4. The coated active material according to claim 1, The first solid electrolyte and the second solid electrolyte further contain at least one element selected from Ca, Mg, Al, Y and Zr.

5. The coated active material according to claim 1, The second layer is the outermost layer containing the coated active material.

6. The coated active material according to claim 1, The first layer is a layer that exists in a region at a distance of more than 1 nm from the outermost surface of the coated active material.

7. The coated active material according to claim 1, The thickness of the coating layer is greater than 1 nm and less than 500 nm.

8. A coated active material having an active material and a coating layer covering at least a portion of the surface of the active material. The proportion of Ti-O bonds in the Ti bond group contained on the outermost surface of the coated active material is higher than the proportion of Ti-O bonds in the Ti bond group contained in the coating layer at the intermediate position from the outermost surface to the surface of the active material.

9. The coated active material according to claim 8, The coating layer, with the intermediate position as a reference, has a portion on the outermost side and a portion constituting the interface between the coating layer and the active substance. The proportion of Ti-O bonds in the Ti bond set contained in the outermost surface portion is higher than the proportion of Ti-O bonds in the Ti bond set contained in the portion constituting the interface.

10. The coated active material according to claim 8, On the outermost surface, the ratio of Ti-O bonds is greater than 5%.

11. The coated active material according to claim 8, At the aforementioned intermediate position, the combined ratio of Ti-F bonds and Ti-OF bonds is over 63%.

12. The coated active material according to claim 8, The coating layer also contains at least one element selected from Ca, Mg, Al, Y and Zr.

13. An electrode comprising the coated active material according to any one of claims 1 to 12.

14. A battery comprising the electrode of claim 13.

15. The battery according to claim 14, further comprising an electrolyte containing lactones.

16. A method for manufacturing a coated active substance, comprising: The active material is coated with a solid electrolyte containing Li, Ti and F; The oxygen-containing liquid adheres to the active material coated with the solid electrolyte; as well as The active material coated with the solid electrolyte is subjected to heat treatment to remove the liquid.

17. The method for manufacturing the coated active material according to claim 16, The liquid contains water.

18. The method for manufacturing the coated active material according to claim 16, The ambient temperature during the heat treatment is above 180°C.

Images