Active material particles, electrochemical element and method for manufacturing the same, and electrochemical device

Abstract

The active material particle has: lithium silicate composite particles including a lithium silicate phase and silicon particles dispersed in the lithium silicate phase; and a first coating film covering at least a portion of a surface of the lithium silicate composite particles, the first coating film including an oxide of a first element other than a metal element and a carbon atom, the thickness of the first coating film being T1 A When T1 A Rb, an element ratio of the first element to the carbon atom at a position where the first coating film is 0.25T1 A from the surface of the lithium silicate composite particles, and Rt, an element ratio of the first element to the carbon atom at a position where the first coating film is 0.75T1 A from the surface of the lithium silicate composite particles, satisfy Rb > Rt.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to improvements in active material particles. BACKGROUND

[0002] As the use of electrochemical devices diversifies, improvements in various properties are required. In this regard, Patent Literature 1 proposes a scheme in which the surfaces of positive and negative electrodes are covered with a metal oxide.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2017-97999 SUMMARY

[0006] As one of the properties of electrochemical devices, high capacity is required. In lithium ion secondary batteries, for example, the use of a silicon compound as a negative electrode material has been studied. It is also known that a silicon compound is easily corroded due to a side reaction during battery operation, as compared with the case where a carbon material is used as a negative electrode material. Therefore, even in the case where a silicon compound is used as an active material particle, it is required to suppress the decrease in the capacity retention rate of an electrochemical device.

[0007] One aspect of the present disclosure relates to an active material particle including: a lithium silicate composite particle including a lithium silicate phase and a silicon particle dispersed in the lithium silicate phase; and a first coating film covering at least a portion of a surface of the lithium silicate composite particle, the first coating film including an oxide of a first element other than a metal element and a carbon atom, wherein when a thickness of the first coating film is set to T1 A , the first element at a position of 0.25T1 A from the surface of the lithium silicate composite particle is in an element ratio Rb to the carbon atom, and the first element at a position of 0.75T1 A from the surface of the lithium silicate composite particle is in an element ratio Rt to the carbon atom, Rb > Rt is satisfied.

[0008] Another aspect of the present disclosure relates to an electrochemical element including: a current collector; and an active material layer supported on the current collector, the active material layer including the active material particle.

[0009] A further aspect of the present disclosure relates to an electrochemical device including: a first electrode; a second electrode; and a separator interposed between the first and second electrodes, one of the first and second electrodes being composed of the electrochemical element.

[0010] Still another aspect of the present disclosure relates to a manufacturing method of a manufacturing method of an active material particle, including: a preparation step of preparing a lithium silicate composite particle including a lithium silicate phase and a silicon particle dispersed in the lithium silicate phase, and having at least a part of a surface covered with a carbon coating film containing a carbon atom; and a coating film formation step of exposing the lithium silicate composite particle to a gas phase containing a first element other than a non-metallic element, introducing the first element into the carbon coating film, and forming a first coating film containing an oxide of the first element and the carbon atom on at least a part of the surface of the lithium silicate composite particle.

[0011] Still another aspect of the present disclosure relates to a manufacturing method of an electrochemical device, including: a preparation step of preparing a lithium silicate composite particle including a lithium silicate phase and a silicon particle dispersed in the lithium silicate phase, and having at least a part of a surface covered with a carbon coating film containing a carbon atom; a loading step of loading the lithium silicate composite particle on a surface of a current collector; and a coating film formation step of exposing the lithium silicate composite particle to a gas phase containing a first element other than a non-metallic element, introducing the first element into the carbon coating film, and forming an active material layer in which a first coating film containing an oxide of the first element and the carbon atom is formed on at least a part of the surface of the lithium silicate composite particle.

[0012] According to the present disclosure, it is possible to improve the capacity maintenance rate of an electrochemical device. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A schematic cross-sectional view of an active material particle according to an embodiment of the present disclosure.

[0014] Figure 2 Enlarged Figure 1 A schematic cross-sectional view of a main part of the active material particle shown.

[0015] Figure 3 A schematic cross-sectional view of an active material particle according to an embodiment of the present disclosure.

[0016] Figure 4 A perspective view of a part of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0017] Figure 5 A flowchart of a manufacturing method of an active material particle according to an embodiment of the present disclosure.

[0018] Figure 6 A flowchart of a manufacturing method of an electrochemical device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] A. Active material particle

[0020] The active material particle of the embodiment of the present disclosure has: a lithium silicate composite particle containing lithium, and a first coating film covering at least a part of a surface of the lithium silicate composite particle. The first coating film of the lithium silicate composite particle contains an oxide of a first element other than a metal element and contains a carbon atom. By the first coating, it is possible to improve the chemical stability of the lithium silicate composite particle while maintaining the electrical conductivity. The active material particle of the embodiment of the present disclosure is preferably used as a negative active material for a lithium ion secondary battery.

[0021] The first element is present in a larger amount as it is closer to the surface of the lithium silicate composite particle. Thereby, the effect of suppressing corrosion of the lithium silicate composite particle is improved. The first coating film also contains a carbon atom, and thus the electrical conductivity of the active material particle is improved.

[0022] Specifically, when the thickness of the first coating film is set to T1 A , the element ratio Rb (= first element / carbon atom) of the first element at a position of the first coating film that is 0.25T1 A from the surface of the lithium silicate composite particle satisfies Rb > Rt (= first element / carbon atom) of the first element at a position of the first coating film that is 0.75T1 A from the surface of the lithium silicate composite particle. The position of 0.25T1 A from the surface of the lithium silicate composite particle means the same as the position of 0.25T1 A from the interface of the first coating film and the lithium silicate composite particle. The position of 0.75T1 A from the surface of the lithium silicate composite particle means the same as the position of 0.75T1 A from the interface of the first coating film and the lithium silicate composite particle.

[0023] The element ratio Rb and the element ratio Rt can satisfy Rb / Rt > 1.3, can satisfy Rb / Rt > 2, and can satisfy Rb / Rt > 3.

[0024] The element ratio (= first element / carbon atom. Hereinafter, referred to as element ratio R) of the inside of the first coating film can be calculated as follows: using an energy dispersive X-ray spectroscopy (EDS), evaluating the element distribution state (depth profile), and thereby it can be calculated. The thickness T1 A of the first coating film is divided into 4, and the position of 0.25T1 A from the surface of the lithium silicate composite particle and the position of 0.75T1 AThe evaluation is performed on a plurality of lithium silicate composite particles (for example, 5) and averaged, whereby the element ratio at each site can be obtained.

[0025] The distribution of the first element and carbon atoms is evaluated by X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS), or ESCA (also referred to as Electron Spectroscopy for Chemical Analysis) in combination with ion etching, whereby the element ratio can also be obtained.

[0026] The mole fraction of carbon atoms in the first coating film and the first element can be taken as the element ratio R. The mole fraction can be calculated from the volume fraction (%) of the first element and carbon atoms using EDS or the like. The volume fraction (%) can be converted into the mole fraction (%) using the specific gravity (g / cm 3 ) of each atom and the molecular weight (g / mole) of each atom.

[0027] The element ratio R changes in such a manner that it gradually decreases from the surface of the lithium silicate composite particle outward. The change can be continuous or in stages, as long as it is to the extent that the overall tendency can be grasped.

[0028] For example, the depth profile in a plurality of sites (for example, 5 sites) located on a straight line in the thickness direction of the first coating film and different in distance from the surface of the lithium silicate composite particle is evaluated by EDS, and the element ratio R at each site is calculated. The element ratio R thus calculated is plotted on a graph with the horizontal axis being the distance from the surface of the lithium silicate composite particle and the vertical axis being the element ratio R. In the case where the approximate straight line or the approximate curve obtained by the least squares method is downward to the right, it can be judged as a tendency that the element ratio R decreases from the surface of the lithium silicate composite particle outward as a whole.

[0029] [Lithium silicate composite particle]

[0030] The lithium silicate composite particle of the present embodiment contains a lithium silicate phase and silicon particles dispersed in the lithium silicate phase. The lithium silicate composite particle has the lithium silicate phase as a sea portion of an island-in-sea structure and the silicon particles as island portions.

[0031] The lithium silicate composite particle generally exists in the form of secondary particles in which a plurality of primary particles are aggregated. The first coating film covers at least a portion of the surface of the secondary particle. Each primary particle has a lithium silicate phase and silicon particles dispersed in the lithium silicate phase.

[0032] The particle diameter of the lithium silicate composite particle is not particularly limited. The average particle diameter of the lithium silicate composite particle may, for example, be 1 μm or more and 20 μm or less. The average particle diameter of the lithium silicate composite particle refers to the particle diameter at which the volume cumulative value becomes 50% in the volume particle size distribution measured by the laser diffraction scattering method (volume average particle diameter).

[0033] (lithium silicate phase)

[0034] The lithium silicate phase (hereinafter, sometimes simply referred to as the silicate phase) has no large number of sites capable of reacting with lithium, and thus, is less likely to cause a new irreversible reaction at the time of charge and discharge. Thus, at the initial of charge and discharge, excellent charge and discharge efficiency is exhibited.

[0035] The silicate phase is an oxide phase containing Li, Si, and O. The atomic ratio of O to Si (= O / Si) in the silicate phase may, for example, be greater than 2 and less than 3. If O / Si is in this range, it is advantageous in terms of stability, lithium ion conductivity.

[0036] The silicate phase contains Li 2z SiO 2+z (z is 0 < z < 1) is represented. From the viewpoints of stability, ease of production, lithium ion conductivity, and the like, z = 1 / 2 is more preferable.

[0037] The silicate phase can further contain an element M. Here, M may, for example, be at least one selected from the group consisting of Be, Mg, Al, B, Zr, Nb, Ta, La, V, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W. Among them, B has a low melting point, and is advantageous in improving the flowability of the silicate in the molten state. In addition, Al, Zr, Nb, Ta, and La can improve the Vickers hardness while maintaining the ion conductivity of the silicate phase. The content of the element M may, for example, be 10 mol% or less, and can be 5 mol% or less, with respect to the total amount of the elements other than O contained in the silicate phase.

[0038] (silicon particle)

[0039] The silicon particle dispersed in the silicate phase has a particle shape of silicon (Si) simple substance, alone or composed of a plurality of crystallites. The crystallite size of the silicon particle is not particularly limited. The crystallite size of the silicon particle is more preferably 10 nm or more and 30 nm or less, and further preferably 15 nm or more and 25 nm or less. In the case where the crystallite size of the silicon particle is 10 nm or more, the surface area of the silicon particle can be suppressed to be small, and thus, the degradation of the silicon particle accompanied by the generation of irreversible capacity is less likely to occur. The crystallite size of the silicon particle is calculated from the half-value width of the diffraction peak attributable to the Si (111) plane in the X-ray diffraction (XRD) spectrum of the silicon particle according to the Scherrer formula.

[0040] The content of the silicon particles in the lithium silicate composite particles can be, for example, 30 mass% or more and 80 mass% or less, in order to increase the capacity and improve the cycle characteristics. By having the content of the silicon particles be 30 mass% or more, the proportion of the silicate phase becomes small, and the initial charge-discharge efficiency becomes easy to improve. By having the content of the silicon particles be 80 mass% or less, the degree of expansion and contraction of the lithium silicate composite particles at the time of charge and discharge becomes easy to reduce.

[0041] (Carbon phase)

[0042] The lithium silicate composite particles can contain both the silicate phase and the silicon particles and the carbon phase. The carbon phase, for example, covers at least a portion of the surface of the silicon particles and is present at least a portion of the interface of adjacent primary particles.

[0043] The content of each element contained in the lithium silicate composite particles can be calculated, for example, from the results of SEM-EDS analysis of a powder sample of the lithium silicate composite particles in a discharged state. The powder sample is analyzed, and the spectral intensity of each element is measured. Then, a standard curve is prepared using a commercially available elemental standard sample, and the content of each element contained in the silicate phase is calculated.

[0044] The quantification of each element in the lithium silicate composite particles can be performed using ICP-AES analysis (inductively coupled plasma emission spectrometry), Auger electron spectroscopy (AES), laser ablation ICP mass spectrometry (LA-ICP-MS), X-ray photoelectron spectroscopy (XPS), or the like.

[0045] [First coating film]

[0046] The first coating film covers at least a portion of the surface of the lithium silicate composite particles as secondary particles.

[0047] The first coating film contains an oxide of the first element other than a non-metallic element and carbon atoms. The oxide and the carbon atoms are mixed in the first coating film. Among them, as described above, the first element is present in a larger amount as it is closer to the surface of the lithium silicate composite particles.

[0048] The average elemental ratio R of the first element to carbon atoms in the first coating film A There is no particular limitation. The elemental ratio R A For example, it can be 0.01 or more and 99 or less. In other words, the elemental ratio R A In the case where the elemental ratio R is 0.01 or more and 99 or less, the coating film is the first coating film containing the first element and carbon atoms.

[0049] The first coating film is 0.25T1 or less from the surface of the lithium silicate composite particles AThe element ratio Rb of the first element at the position of the lithium silicate composite particle with respect to carbon atoms is not particularly limited. The element ratio Rb can be, for example, 5 or more and 99 or less, can be 10 or more and 99 or less, or can be 20 or more and 99 or less.

[0050] The first coating film is 0.75T1 A The element ratio Rt of the first element at the position of the lithium silicate composite particle with respect to carbon atoms is not particularly limited. The element ratio Rt can be, for example, 0.01 or more and 10 or less, or can be 0.01 or more and 5 or less.

[0051] The first element is an element other than a metalloid element, and includes a metal element and a so-called semimetal element. Among these, in terms of high corrosion inhibition effect of the lithium silicate composite particle, the first element preferably contains at least one element selected from the group consisting of a Group 3 element, a Group 4 element, a Group 5 element, and a Group 6 element of the periodic table. The first element particularly preferably contains at least one element selected from the group consisting of Al, Ti, Si, Zr, Mg, Nb, Ta, Sn, Ni, and Cr.

[0052] In the case where two or more oxides are contained, each oxide can be present in a mixed state, or can be arranged in a layered state.

[0053] As the carbon, there can be mentioned amorphous carbon such as carbon black, coal, coke, charcoal, and activated carbon, and graphite having high crystallinity. Among these, amorphous carbon is preferable in terms of low hardness and large buffering effect on the volume change of the silicon particles occurring during charge and discharge. The amorphous carbon can be easy graphitizable carbon (soft carbon), or can be hard graphitizable carbon (hard carbon). As the carbon black, there can be mentioned acetylene black and Ketjen black. Graphite refers to a material having a graphite-type crystal structure, and there can be mentioned, for example, natural graphite, artificial graphite, and graphitized mesocarbon microbeads.

[0054] The thickness of the first coating film is not particularly limited. In terms of corrosion inhibition, the thickness of the first coating film can be 0.1 nm or more, can be 0.5 nm or more, or can be 1 nm or more. In terms of conductivity and lithium ion diffusivity, the thickness of the first coating film can be 50 nm or less, can be 10 nm or less, or can be 2 nm or less. The thickness of the first coating film can be, for example, 0.1 nm or more and 50 nm or less, or can be 0.1 nm or more and 10 nm or less.

[0055] The thickness of the first coating film can be measured from cross-sectional observation of the active material particles using SEM or TEM.

[0056] First, the electrochemical device is disassembled, and an electrochemical element (for example, an electrode) is taken out, and a cross-section of the element is obtained using a cross-section polisher (CP). From an image of the cross-section obtained using SEM or TEM, 10 active material particles having a maximum diameter of 5 μm or more are randomly selected. For each particle, the thickness of the first coating film is measured at 5 arbitrary points. The average of the thicknesses at the total of 50 points is calculated. After the average is calculated, data deviating by 20% or more from the average obtained is removed, and the average is calculated again. The average after the correction is taken as the thickness T1 of the first coating film A .

[0057] The starting point of the first coating film is the interface between the base particle (described later) formed of the lithium silicate composite particle and the first coating film. For example, a site where the intensity of the peak attributed to Li obtained by SEM-EDS analysis is 10% or less of the intensity of the peak attributed to the first element can be regarded as the starting point of the first coating film. The end point of the first coating film can be regarded as, for example, a site where the intensity of the peak attributed to the first element obtained by SEM-EDS analysis becomes 5% or less of the maximum value thereof. In the case where the second coating film is formed, the end point of the first coating film is the interface between the first coating film and the second coating film.

[0058] [Second Coating Film]

[0059] At least a part of the first coating film can be covered with the electrically conductive second coating film. Thereby, the electrical conductivity of the active material particle is further improved.

[0060] The second coating film is different from the first coating film, and does not contain the oxide of the first element. The second coating film not containing the oxide of the first element means the same as the intensity of the peak attributed to the first element obtained by SEM-EDS being below the detection limit.

[0061] The second coating film contains an electrically conductive material. In terms of electrochemical stability, the electrically conductive material is preferably an electrically conductive carbon material. As the electrically conductive carbon material, the carbon contained in the first coating film described above can be given.

[0062] The thickness of the second coating film is not particularly limited. The second coating film is preferably thin to the extent that it does not substantially affect the average particle diameter of the lithium silicate composite particle. The thickness of the second coating film can be 1 nm or more, and can be 5 nm or more. The thickness of the second coating film can be 200 nm or less, and can be 100 nm or less. The thickness of the second coating film can be measured in the same manner as the first coating film, from the cross-sectional observation of the lithium silicate composite particle using SEM or TEM.

[0063] The start point of the second coating film is the interface with the first coating film. The end point of the second coating film is the outermost point of the active material particle that can be confirmed from the SEM or TEM image. Alternatively, the end point of the second coating film is the point at which the intensity of the peak attributed to C becomes 5% or less of the maximum value by SEM-EDS analysis.

[0064] The thickness T1 of the first coating film A The thickness T2 of the second coating film A It is preferable to satisfy 0 < T2 A / T1 A <1500. Thereby, it becomes easy to balance the corrosion resistance and the improvement of the electrical conductivity. T2 A / T1 A It is preferable to be 5 or more, preferably 10 or more. T2 A / T1 A It is preferable to be 500 or less, preferably 100 or less.

[0065] Figure 1 A schematic cross-sectional view of an active material particle according to an embodiment of the present disclosure. Figure 2 A schematic cross-sectional view of a main portion of the active material particle shown in Figure 1 A schematic cross-sectional view of a main portion of the active material particle shown in

[0066] The active material particle 20 includes a lithium silicate composite particle 23, a first coating film 27 covering the surface thereof, and a second coating film 26 covering the first coating film 27.

[0067] Figure 3 A schematic cross-sectional view of an example of the active material particle. The lithium silicate composite particle 23 is a secondary particle (base particle) in which a plurality of primary particles 24 are aggregated. Each primary particle 24 includes a silicate phase 21 and a silicon particle 22 dispersed in the silicate phase 21. The silicon particles 22 are substantially uniformly dispersed in the silicate phase 21.

[0068] A carbon phase is disposed at least at a portion of the interface S of the adjacent primary particles 24. The carbon phase can cover at least a portion of the surface of the silicon particle 22.

[0069] The surface of the lithium silicate composite particle (base particle) 23 is covered with the first coating film 27. The first coating film 27 is covered with the second coating film 26.

[0070] B. Electrochemical element

[0071] The electrochemical element according to the embodiment of the present disclosure includes a current collector and an active material layer supported on the current collector. The active material layer contains the active material particle described above. Such an electrochemical element is excellent in the electrical conductivity and the deterioration is suppressed, and thus, it is possible to provide an electrochemical device that is high in capacity and long in life.

[0072] As the electrochemical element, an electrode can be given. The electrode is, for example, at least one of a positive electrode and a negative electrode used in a secondary battery. The electrode of the embodiment of the present disclosure is preferably used as a negative electrode for a lithium ion secondary battery.

[0073] C. Electrochemical device

[0074] The electrochemical device of the embodiment of the present disclosure has a first electrode, a second electrode, and a separator interposed therebetween. One of the first electrode and the second electrode is composed of the above-described electrochemical element. Such an electrochemical device is high in capacity and long in life.

[0075] The electrochemical device is a device in which electron donation and acceptance between substances occur, and a chemical reaction is generated by the electron donation and acceptance. As the electrochemical device, for example, a primary battery, a secondary battery, a capacitor, and an air double-layer capacitor can be given. The electrochemical device of the embodiment of the present disclosure is preferably a lithium ion secondary battery using lithium silicate composite particles as a negative electrode active material.

[0076] Hereinafter, a negative electrode as the electrochemical element of the embodiment of the present disclosure and a lithium ion secondary battery as the electrochemical device will be described as examples, and the configurations thereof will be described.

[0077] [Negative electrode]

[0078] The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer.

[0079] The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes at least the above-described active material particle (hereinafter, sometimes referred to as a first active material). The negative electrode active material layer is formed as a layer including a negative electrode composite material on the surface of the negative electrode current collector. The negative electrode active material layer can be formed on one surface of the negative electrode current collector, or can be formed on both surfaces. The negative electrode composite includes the negative electrode active material as a necessary component, and can include a binder, a conductive agent, a thickening agent, and the like as arbitrary components.

[0080] The negative electrode active material can further include another active material (hereinafter, sometimes referred to as a second active material). As the second active material, for example, a conductive carbon material that electrochemically occludes and releases lithium can be given. By using the first active material in combination with the conductive carbon material, further high life can be expected.

[0081] As the conductive carbon material, for example, graphite, easily graphitizable carbon (soft carbon), and difficultly graphitizable carbon (hard carbon) can be given. Among them, graphite is preferred in which stability at the time of charge and discharge is excellent and an irreversible capacity is also small. Graphite refers to a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, graphitized mesocarbon microbeads, and the like. The conductive carbon material can be used alone in one kind, or can be used in combination of two or more kinds.

[0082] There is no particular limitation on the particle size of conductive carbon materials. The average particle size of conductive carbon materials can be, for example, greater than 1 μm and less than 30 μm.

[0083] The proportion of the first active ingredient in the total of the first and second active ingredients is, for example, 3% by mass or more and 30% by mass or less. This makes it easier to achieve both high capacity and long lifespan.

[0084] As the negative current collector, a non-porous conductive substrate (such as metal foil) or a porous conductive substrate (such as a mesh, wire mesh, or perforated sheet) can be used. Examples of materials for the negative current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys. The thickness of the negative current collector is not particularly limited, but from the viewpoint of balancing the strength and lightweight of the negative electrode, a thickness of 1 μm or more and 50 μm or less is preferred, and more preferably 5 μm or more and 20 μm or less.

[0085] Examples of binders include at least one selected from the group consisting of polyacrylic acid, polyacrylates, and their derivatives. Li or Na salts are preferred as polyacrylates. Cross-linked lithium polyacrylate is particularly preferred.

[0086] Examples of conductive agents include carbon blacks such as acetylene black; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon; metal powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and organic conductive materials such as phenylene derivatives. They can be used individually or in combination of two or more.

[0087] Examples of thickeners include carboxymethyl cellulose (CMC) and its modified forms (including salts such as Na salts), cellulose derivatives such as methyl cellulose (cellulose ethers, etc.); saponifications of polymers containing vinyl acetate units such as polyvinyl alcohol; and polyethers (polyethylene oxides, polyoxyethylene ethers, etc.). They can be used individually or in combination of two or more.

[0088] [positive electrode]

[0089] The positive electrode, for example, comprises: a positive current collector and a positive active material layer formed on the surface of the positive current collector. The positive active material layer may be formed on one surface of the positive current collector or on both surfaces.

[0090] The positive electrode active material layer is formed on the surface of the positive electrode current collector as a layer containing the positive electrode composite material. The positive electrode mixture contains the positive electrode active material as an essential component and may contain binders, conductive agents, etc. as optional components.

[0091] Lithium-based composite metal oxides can be used as positive electrode active materials. Examples of lithium-based composite metal oxides include Li.a CoO2, Li a NiO2, Li a MnO2, Li a Co b Ni 1-b O2, Li a Co b M 1-b O c , Li a Ni 1-b M b O c , Li a Mn2O4, Li a Mn 2- b M b O4, LiMePO4, Li2MePO4F. Here, M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Me contains at least a transition element (for example, at least one selected from the group consisting of Mn, Fe, Co, Ni). a is 0≤a≤1.2, b is 0≤b≤0.9, and c is 2.0≤c≤2.3.

[0092] As the binder and the conductive agent, the same substances as those for the negative electrode example can be used. As the conductive agent, natural graphite, artificial graphite, or the like can also be used.

[0093] The shape and the thickness of the positive electrode current collector can be selected from those of the negative electrode current collector, respectively. As the material of the positive electrode current collector, for example, stainless steel, aluminum, aluminum alloy, titanium, or the like can be exemplified.

[0094] [Separator]

[0095] The separator is interposed between the positive electrode and the negative electrode. The separator has a high ion permeability, and has a moderate mechanical strength and an insulating property. As the separator, for example, a microporous film, a woven fabric, a nonwoven fabric, or the like can be given. As the material of the separator, for example, polyolefin such as polypropylene or polyethylene can be used.

[0096] [Electrolyte]

[0097] The electrochemical device of the embodiment of the present disclosure further includes an electrolyte. The electrolyte includes a solvent and a lithium salt dissolved in the solvent. The concentration of the lithium salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte can contain a publicly known additive.

[0098] As the non-aqueous solvent, for example, a cyclic carbonate, a chain carbonate, a cyclic carboxylate, or the like is used. As the cyclic carbonate, propylene carbonate (PC), ethylene carbonate (EC), or the like can be given. As the chain carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or the like can be given. As the cyclic carboxylate, γ-butyrolactone (GBL), γ-valerolactone (GVL), or the like can be given. The non-aqueous solvent can be used alone or in combination of two or more kinds.

[0099] As the lithium salt, for example, a lithium salt of a chlorine-containing acid (LiClO4, LiAlCl4, LiB 10 Cl 10 LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, or the like), a lithium salt of a fluorine-containing acid imide (LiN(SO2F)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, or the like), a lithium halide (LiCl, LiBr, LiI, or the like), or the like can be given. The lithium salt can be used alone or in combination of two or more kinds.

[0100] As an example of the structure of the secondary battery, a structure in which an electrode group in which a positive electrode, a negative electrode, and a separator are wound is housed in an outer case with an electrolyte can be given. Instead of the wound-type electrode group, a laminated-type electrode group in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween can be used. In addition, other forms of the electrode group can be applicable. The secondary battery can be in any form such as a cylindrical type, a square type, a coin type, a button type, a laminated type, or the like.

[0101] Figure 4 A perspective view of a part of a square-type secondary battery of an embodiment of the present disclosure is cut away. The battery has a bottomed square battery case 4, an electrode group 1 and an electrolyte housed in the battery case 4, and a sealing plate 5 that seals an opening portion of the battery case 4. The electrode group 1 has an elongated band-shaped negative electrode, an elongated band-shaped positive electrode, and a separator interposed therebetween. The negative electrode, the positive electrode, and the separator are wound around a flat plate-shaped jelly roll, and the jelly roll is pulled out to form the electrode group 1. The sealing plate 5 has a liquid injection port plugged by a sealing plug 8, and a negative electrode terminal 6 insulated from the sealing plate 5 by a gasket 7.

[0102] One end of the negative electrode lead 3 is attached to the negative electrode current collector of the negative electrode by welding or the like. One end of the positive electrode lead 2 is attached to the positive electrode current collector of the positive electrode by welding or the like. The other end of the negative electrode lead 3 is electrically connected to the negative electrode terminal 6. The other end of the positive electrode lead 2 is electrically connected to the sealing plate 5. A resin-made frame that separates the electrode group 1 from the sealing plate 5 and separates the negative electrode lead 3 from the battery case 4 is disposed at the upper portion of the electrode group 1.

[0103] D. Method for manufacturing active material particle

[0104] The method for manufacturing an active material particle of an embodiment of the present disclosure includes a preparation step of preparing lithium silicate composite particles including a silicate phase and silicon particles dispersed in the silicate phase, and at least a part of a surface of which is covered with a carbon coating film including a carbon atom; and a coating film formation step of exposing the lithium silicate composite particles to a gas phase including a first element other than a nonmetal element, introducing the first element into the carbon coating film, and forming a first coating film including an oxide of the first element and the carbon atom on at least a part of the surface of the lithium silicate composite particles. According to the manufacturing method, the first coating film is formed by introducing the oxide of the first element into the inside of the carbon coating film covering the lithium silicate composite particles.

[0105] Figure 5 A flowchart of the method for manufacturing an active material particle of an embodiment of the present disclosure is shown.

[0106] (i) Preparation step of lithium silicate composite particles (S11)

[0107] (i-i) Preparation of silicon particles

[0108] First, silicon particles are prepared.

[0109] The silicon particles can be obtained by a chemical vapor deposition method (CVD method), a thermal plasma method, a physical pulverization method, or the like. In the following methods, for example, silicon nanoparticles having an average particle diameter of 10 nm or more and 200 nm or less can be synthesized. The average particle diameter of the silicon particles refers to a particle diameter at which a volume cumulative value becomes 50% in a volume particle size distribution measured by a laser diffraction scattering method (volume average particle diameter).

[0110] (a) Chemical vapor deposition method

[0111] In the CVD method, for example, a method in which a silane compound is oxidized or reduced to generate silicon particles in a gas phase is used. The reaction temperature can be set to 400°C or more and 1300°C or less, for example.

[0112] As the silane compound, a hydridosilane such as silane, disilane, a halogenated silane, an alkoxysilane, or the like can be used. As the halogenated silane, dichlorosilane, trichlorosilane, tetrachlorosilane, or the like can be used. As the alkoxysilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, or the like can be used.

[0113] For example, if a hydridosilane is brought into contact with an oxidizing gas in a gas phase, a composite of silicon particles and silicon oxide particles is obtained. That is, the atmosphere of the gas phase can be an oxidizing gas atmosphere. The composite is washed with, for example, hydrofluoric acid, and thus the silicon oxide is removed, and silicon particles are obtained.

[0114] In the case of reduction of halosilane, alkoxysilane, etc., for example, it is sufficient to contact molten metal micronized by an atomization method with a silane compound. As the molten metal, Na, K, Mg, Ca, Zn, Al, etc. can be used. As the atomization gas, non-active gas, halosilane, hydrogen, etc. can be used. That is, the atmosphere in the gas phase can be non-active gas, reducing gas atmosphere.

[0115] (b) Thermal plasma method

[0116] The thermal plasma method is a method in which a raw material of silicon is introduced into generated thermal plasma, and silicon particles are generated in the high-temperature plasma. The thermal plasma can be generated by arc discharge, high-frequency discharge, microwave discharge, laser irradiation, etc. Among them, the discharge based on high frequency (RF) is non-polar discharge, and is ideal in terms of not easily mixing impurities in the silicon particles.

[0117] As the raw material, for example, silicon oxide can be used. If the raw material is introduced into the plasma, silicon in the state of instantaneously generated atoms or ions and oxygen are combined and solidified during the cooling process, and silicon particles are generated.

[0118] (c) Physical pulverization method

[0119] The physical pulverization method (mechanical grinding method) is a method in which a coarse particle of silicon is pulverized by a pulverizer such as a ball mill, a bead mill, etc. The inside of the pulverizer can be, for example, set to a non-active gas atmosphere.

[0120] (i-ii) Covering of silicon particles based on carbon phase

[0121] At least a part of the surface of the silicon particles can be covered by a carbon phase.

[0122] As the method of covering the silicon particles by a carbon phase, a chemical vapor deposition method (CVD method), sputtering, an atomic layer deposition method (ALD method: Atomic Layer Deposition), a wet mixing method, a dry mixing method, etc. can be given. Among them, the CVD method, the wet mixing method, etc. are preferred.

[0123] (a) Chemical vapor deposition method

[0124] The CVD method is as follows: the silicon particles are introduced into a hydrocarbon gas atmosphere and heated, and a carbon material generated by thermal cracking of the hydrocarbon gas is deposited on the surface of the particles to form a carbon phase. The temperature of the hydrocarbon gas atmosphere can be, for example, 500°C or higher and 1000°C or lower. As the hydrocarbon gas, acetylene, chain hydrocarbon gas such as methane, aromatic hydrocarbon such as benzene, toluene, xylene, etc. can be used.

[0125] (b) Wet mixing method

[0126] In the wet mixing method, for example, a carbon precursor such as coal pitch, petroleum pitch, tar, or the like is dissolved in a solvent, and the resulting solution is mixed with silicon particles and dried. Thereafter, the silicon particles covered with the carbon precursor are heated at, for example, 600°C or lower and 1000°C or lower in a non-reactive gas atmosphere to carbonize the carbon precursor, forming a carbon phase.

[0127] (i-iii) Synthesis of lithium silicate composite particles

[0128] A raw material of the silicate phase is prepared.

[0129] A raw material mixture containing a Si raw material and a Li raw material in a prescribed ratio can be used as the raw material of the silicate phase. If the raw material mixture is dissolved and the melt is flaked by passing through a metal roll, a silicate can be obtained. A silicate can also be synthesized by a solid phase reaction by performing a firing at a temperature below the melting point without dissolving the raw material mixture.

[0130] Silicon oxide (e.g., Si02) can be used as the Si raw material. Carbonates, oxides, hydroxides, hydrides, nitrates, sulfates, or the like of lithium or the element M can be used as the Li raw material or the raw material of the element M, respectively. Among these, carbonates, oxides, hydroxides, or the like are preferred.

[0131] Next, silicon particles having at least a portion of the surface thereof covered with a carbon phase (hereinafter, also referred to as carbon-coated silicon particles) are mixed with the silicate. For example, the lithium silicate composite particles are produced by the following procedures.

[0132] First, the carbon-coated silicon particles are mixed with the powder of the silicate at a mass ratio of, for example, 20:80 to 95:5.

[0133] Next, the mixture of the carbon-coated silicon particles and the silicate is stirred using a device such as a ball mill. At this time, it is preferable to add an organic solvent to the mixture and perform wet mixing. A prescribed amount of the organic solvent can be added to the pulverization container all at once at the start of pulverization, or can be added to the pulverization container intermittently in multiple portions during the pulverization process. The organic solvent functions to prevent the pulverization target from adhering to the inner wall of the pulverization container. As the organic solvent, alcohols, ethers, fatty acids, alkanes, cycloalkanes, silicates, metal alkoxides, or the like can be used.

[0134] Then, the mixture is heated and sintered at 450°C or higher and 1000°C or lower while being pressurized in a non-reactive gas atmosphere (e.g., an atmosphere of argon, nitrogen, or the like). A sintering device capable of pressurization in a non-reactive atmosphere, such as hot pressing, discharge plasma sintering, or the like, can be used in the sintering. During the sintering, the silicate melts and flows in a manner that fills the gaps between the silicon particles. As a result, a dense block-shaped sintered body having a sea of the silicate phase and islands of the silicon particles can be obtained.

[0135] Finally, if the sintered body obtained is pulverized, lithium silicate composite particles are obtained. By appropriately selecting the pulverization conditions, lithium silicate composite particles having a prescribed average particle diameter can be obtained.

[0136] (i-iv) Carbon-coated lithium silicate composite particles

[0137] Next, at least a part of the surface of the lithium silicate composite particles is covered with a carbon coating film. The carbon atoms contained in the first coating film are derived from this carbon coating film.

[0138] As a method of forming a carbon coating film on the surface of the lithium silicate composite particles, for example, a chemical vapor deposition method using acetylene, a chain hydrocarbon gas such as methane, a method of mixing and heating coal pitch, petroleum pitch, phenol resin, or the like with the lithium silicate composite particles to carbonize them, or the like can be exemplified. Carbon black can be attached to the surface of the lithium silicate composite particles.

[0139] The carbon coating film is preferably thin to the extent that it does not substantially affect the average particle diameter of the lithium silicate composite particles. On the other hand, if the carbon source for the first coating film is taken into account, the thickness of the carbon coating film desirably is the same as or more than the desired first coating film. The carbon coating film can be 0.1 nm or more, and can be 1 nm or more. If the diffusivity of lithium ions is taken into account, the carbon coating film is preferably 300 nm or less, and more preferably 200 nm or less. The thickness of the carbon coating film, like the first coating film, can be measured by cross-sectional observation of the lithium silicate composite particles using SEM or TEM.

[0140] Finally, a step of cleaning the lithium silicate composite particles having the carbon coating film with an acid can also be performed. For example, by cleaning the composite particles with an acidic aqueous solution, a trace amount of alkali components that can be present on the surface of the lithium silicate composite particles can be dissolved and removed. As the acidic aqueous solution, an aqueous solution of an inorganic acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, or an aqueous solution of an organic acid such as citric acid, acetic acid can be used.

[0141] (ii) Step of forming the first coating film (S12)

[0142] The lithium silicate composite particles having the carbon coating film are exposed to a gas phase containing the first element. Thereby, the first element is introduced into the carbon coating film, and a first coating film containing the first element and carbon atoms is formed on at least a part of the surface of the lithium silicate composite particles.

[0143] As the gas phase method, for example, a CVD method, an ALD method, a physical vapor deposition method (PVD), or the like can be exemplified. The ALD method is particularly preferable in terms of being able to form the first coating film at a lower temperature. According to the ALD method, the first coating film can be formed in an atmosphere of 200°C or lower.

[0144] In the ALD method, as a raw material for the first coating film, an organic metal compound (precursor) containing the first element is used. In the ALD method, a raw material gas containing the vaporized precursor and an oxidizing agent are alternately supplied to a reaction chamber in which the object is disposed. Thereby, a layer containing an oxide of the first element is formed on the surface of the object.

[0145] At least a part of the surface of the lithium silicate composite particle as the object is covered with the carbon coating film. The first element contained in the raw material gas can pass through the carbon coating film and reach the surface of the lithium silicate composite particle. Also, the first element is directly deposited on the surface of the lithium silicate composite particle. Therefore, the first element is more disposed in the vicinity of the surface of the lithium silicate composite particle. The first coating film formed contains an oxide of the first element and carbon atoms derived from the carbon coating film.

[0146] In the ALD method, the self-limiting action functions, and therefore, the first element is deposited on the surface of the object in an atomic layer unit. In the ALD method, the thickness of the first coating film is controlled depending on the number of cycles of the supply (pulse) of the raw material gas → the exhaust (purge) of the raw material gas → the supply (pulse) of the oxidizing agent → the exhaust (purge) of the oxidizing agent as one cycle. If the thickness of the first coating film is controlled so as to become the same degree as the carbon coating film, the oxide of the first element can be disposed in the entire carbon coating film although there is a concentration gradient. If the thickness of the first coating film is controlled so as to become thinner than the carbon coating film, the first coating film containing the oxide of the first element and carbon atoms is formed on the surface side of the lithium silicate composite particle, and the second coating film derived from the excess of the carbon coating film is formed so as to cover the first coating film.

[0147] The precursor is an organic metal compound containing the first element. As the precursor, various organic metal compounds used in the conventional ALD method can be used.

[0148] As the precursor containing Ti, for example, bis (tert-butylcyclopentadienyl) titanium (IV) dichloride (C 18 H 26chloride (TiCl4), titanium (IV) isopropoxide (Ti[OCH(CH3)2]4), titanium (IV) ethoxide (Ti[O(C2H5)]4). As the precursor containing Al, for example, trimethylaluminum ((CH3)3Al, TMA) can be given.

[0149] The source gas can contain a plurality of precursors. To the reaction chamber, different kinds of precursors can be supplied at the same time or sequentially. Alternatively, the kind of the precursor contained in the source gas can be changed every cycle.

[0150] As the oxidizing agent, an oxidizing agent used in the conventional ALD method can be used. As the oxidizing agent, for example, water, oxygen, ozone, and the like can be given. The oxidizing agent can be supplied to the reaction chamber in the form of plasma in which the oxidizing agent is a raw material.

[0151] The condition of the ALD method is not particularly limited. In terms of the first element becoming easy to be more disposed in the vicinity of the surface of the lithium silicate composite particle, the temperature of the atmosphere containing the precursor or the oxidizing agent in the reaction chamber can be 10°C or higher and 200°C or lower, and can be 25°C or higher and 100°C or lower. From the same viewpoint, the pressure of the reaction chamber during the treatment can be 1 x 10 -5 Pa or more and 1 x 10 5 Pa or less, and can be 1 x 10 -4 Pa or more and 1 x 10 4 Pa or less.

[0152] In terms of the first element becoming easy to be more disposed in the vicinity of the surface of the lithium silicate composite particle, the temperature of the atmosphere containing the precursor or the oxidizing agent in the reaction chamber is 10°C or higher and 200°C or lower, and the pressure of the reaction chamber during the treatment is 1 x 10 -5 Pa or more and 1 x 10 5 Pa or less, and can be 1 x 10

[0153] E. Method for manufacturing electrochemical element

[0154] The electrochemical element of the embodiment of the present disclosure has the above-mentioned first active material. The electrochemical element can be obtained by loading the first active material having the first coating film on the surface of the current collector. The electrochemical element can also be obtained by loading the lithium silicate composite particles covered with the carbon coating film on the surface of the current collector, and then forming the first coating film by a vapor phase method.

[0155] Figure 6 A flowchart of a method for manufacturing an electrochemical element of an embodiment of the present disclosure is shown.

[0156] The latter manufacturing method includes the following steps: a preparation step of preparing lithium silicate composite particles including a silicate phase, and silicon particles dispersed in the silicate phase, and having at least a part of the surface covered with a carbon coating film including carbon atoms; a loading step of loading the lithium silicate composite particles on the surface of the current collector; and a coating film formation step of exposing the lithium silicate composite particles to a gas phase including a first element other than a non-metallic element, introducing the first element into the carbon coating film, and forming an active material layer having a first coating film including an oxide of the first element and carbon atoms formed on at least a part of the surface of the lithium silicate composite particles.

[0157] (I) Preparation step of lithium silicate composite particles (S21)

[0158] The lithium silicate composite particles covered with the carbon coating film are prepared in the same manner as the steps (i-i) to (i-iv) of the preparation step of the lithium silicate composite particles in the method for manufacturing the active material particles.

[0159] (II) Loading step of lithium silicate composite particles (S22)

[0160] A slurry of a negative electrode material including the prepared lithium silicate composite particles dispersed in a dispersion medium is applied to the surface of the current collector, and the slurry is dried. Thus, a precursor of the active material layer is formed on the surface of the current collector.

[0161] The dispersion medium is not particularly limited, and examples thereof include water, alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.

[0162] (III) Formation step of first coating film (S23)

[0163] The current collector having the precursor of the active material layer is exposed to a gas phase including the first element. Thus, the first element is introduced into the carbon coating film, and at least a part of the surface of the lithium silicate composite particles contained in the precursor is covered with the first coating film including an oxide of the first element and carbon atoms. Thus, the active material layer is formed. As the vapor phase method, the ALD method can be preferably used, as described above.

[0164] The precursors and oxidizing agents used in the ALD method can exemplify the same substances as those shown in the formation process (ii) to (i-iv) of the first coating film as the manufacturing method of active material particles.

[0165] The conditions of the ALD method are not particularly limited. In terms of the first element becoming more easily disposed in the vicinity of the surface of the lithium silicate composite particle, the temperature of the atmosphere containing the precursor or the oxidizing agent can be 10°C or higher and 200°C or lower, can be 25°C or higher and 100°C or lower. From the same viewpoint, the pressure of the reaction chamber during the processing can be 1 x 10 -5 Pa or higher and 1 x 10 5 Pa or lower, can be 1 x 10 -4 Pa or higher and 1 x 10 4 Pa or lower.

[0166] In terms of the first element becoming more easily disposed in the vicinity of the surface of the lithium silicate composite particle, the temperature of the atmosphere containing the precursor or the oxidizing agent in the reaction chamber is 10°C or higher and 200°C or lower, and the pressure of the reaction chamber during the processing is 1 x 10 -5 Pa or higher and 1 x 10 5 Pa or lower, the pulse time of the raw material gas can be 0.01 seconds or longer, can be 0.05 seconds or longer. The pulse time of the raw material gas can be 5 seconds or shorter.

[0167] (IV) Calendering process (S24)

[0168] After the first coating film is formed, the active material layer can be subjected to calendering. The conditions of the calendering are not particularly limited, and can be appropriately set in such a manner that the active material layer becomes a prescribed thickness or density. Thereby, the density of the active material layer is increased, and the capacity of the electrochemical device can be increased.

[0169] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0170] Example 1

[0171] [Production of negative electrode]

[0172] (1) Preparation of silicon particles

[0173] A coarse particle of silicon (3N, average particle diameter 10 pm) was filled into a tank (SUS, volume 500 mL) of a planetary ball mill (manufactured by FRITSCH Co., Ltd., P-5), 24 SUS balls (diameter 20 mm) were put in the tank, the lid was closed, and the crushing was performed in an inactive atmosphere at 200 rpm until the average particle diameter became 150 nm, and silicon particles were prepared.

[0174] (2) Covering of silicon particles based on carbon phase

[0175] The carbon material was deposited on the surface of the silicon particles by a chemical vapor deposition method. Specifically, the silicon particles were introduced into an atmosphere of acetylene gas, heated at 700°C, and the acetylene gas was thermally cracked and deposited on the surface of the silicon particles to form a carbon phase. The amount of the carbon material was set to 10 parts by mass relative to 100 parts by mass of the silicon particles.

[0176] (3) Preparation of lithium silicate composite particles

[0177] Silicon dioxide and lithium carbonate were mixed at an atomic ratio (= Si / Li) of 1.05, and the mixture was calcined at 950°C for 10 hours in air to obtain lithium silicate represented by Li2Si2O5 (z = 0.5). The obtained lithium silicate was pulverized to have an average particle diameter of 10 μm.

[0178] The lithium silicate (Li2Si2O5) having an average particle diameter of 10 μm was mixed with carbon-coated silicon at a mass ratio of 70:30. The mixture was filled into a pot (SUS, volume 500 mL) of a planetary ball mill (P-5, manufactured by FRITSCH Co.), 24 SUS balls (diameter 20 mm) were put in the pot, the lid was closed, and the mixture was stirred at 200 rpm for 50 hours in an inactive atmosphere.

[0179] Next, the powder-like mixture was taken out in an inactive atmosphere, and was calcined at 800°C for 4 hours in an inactive atmosphere under application of pressure based on a hot press to obtain a sintered body of the mixture. Thereafter, the sintered body was pulverized to obtain lithium silicate composite particles.

[0180] The crystallite size of the silicon particles calculated by the Scherrer method from the diffraction peak attributed to the Si (111) plane was 15 nm. In the silicate phase, the Si / Li ratio was 1.0, and the content of Li2Si2O5 measured by Si-NMR was 70% by mass (the content of the silicon particles was 30% by mass).

[0181] (4) Coating of lithium silicate composite particles based on carbon coating film

[0182] The obtained lithium silicate composite particles were passed through a 40-μm mesh, mixed with coal pitch (MCP250, manufactured by JFE Chemical Corporation), and the mixture of the lithium silicate composite particles and the pitch was calcined at 800°C for 5 hours in an inactive atmosphere to form a carbon coating film on the surface of the lithium silicate composite particles. The amount of coating based on the carbon coating film was set to 5% by mass relative to the total mass of the lithium silicate composite particles and the carbon coating film. Thereafter, the particles having an average particle diameter of 10 μm, which had the lithium silicate composite particles and the carbon coating film formed on the surface thereof, were classified using a sieve. The thickness of the carbon coating film was 50 nm.

[0183] (5) Production of the negative electrode precursor

[0184] The lithium silicate composite particles with the carbon coating film were mixed with the second active material (graphite) at a mass ratio of 5:95, and used as the negative electrode active material. The negative electrode slurry was prepared by adding water to the negative electrode active material and a negative electrode binder including carboxymethylcellulose sodium (CMC-Na), styrene butadiene rubber (SBR), and polyacrylate lithium salt at a mass ratio of 96.5:1:1.5:1, and stirring the mixture using a mixer (T.K. HIVIS MIX manufactured by Primex Corporation). Subsequently, the negative electrode slurry was applied to the surface of a copper foil at a rate of 190 g per 1 m2of the mass of the negative electrode binder, and the coating film was dried, thereby producing a negative electrode precursor in which the negative electrode active material layer having a density of 1.5 g / cm2was formed on both surfaces of the copper foil. The thickness of the negative electrode active material layer in the negative electrode precursor was 202 μm. 2 3

[0185] (6) Formation of the first and second coating films

[0186] The negative electrode precursor was housed in a prescribed reaction chamber, and the first coating film was formed on the surface of the negative electrode precursor by the ALD method according to the following procedure.

[0187] In the reaction chamber in which the negative electrode precursor was housed, the precursor (TDMAT) that was the supply source of the first element (Ti) was vaporized and supplied. The pulse time was set to 0.1 seconds. The temperature of the atmosphere containing the precursor in the reaction chamber was controlled to 200°C, and the pressure was controlled to 260 Pa. After 30 seconds, the surface of the negative electrode precursor was covered with a monomolecular layer of the precursor, and the excess precursor was purged with nitrogen.

[0188] Subsequently, in the reaction chamber in which the negative electrode precursor was housed, the oxidizing agent (H2O) was vaporized and supplied. The pulse time was set to 0.015 seconds. The temperature of the atmosphere containing the oxidizing agent was controlled to 200°C, and the pressure was controlled to 260 Pa. After 30 seconds, the excess oxidizing agent was purged with nitrogen.

[0189] The series of operations of the supply of the precursor, the purging, the supply of the oxidizing agent, and the purging were repeated 22 times, thereby forming the first coating film containing titanium. The first coating film was adjusted to be thinner than the carbon coating film, and the first coating film and the second coating film that covered the first coating film were formed simultaneously.

[0190] The first coating film was analyzed using SEM, EDS, ICP, and the like. The first coating film contained Ti and C. The minimum value of the element ratio R of the first element with respect to carbon atoms was 0.03, and the maximum value was 8. The thickness T1 of the first coating film was 1 nm. The first coating film was 0.25 T1 A A ​​​The element ratio Rt of the 1st element at the position of the 1st element to carbon atom is 0.08. A The element ratio Rt of the 1st element at the position of the 1st element to carbon atom is 0.08.

[0191] The composition of the 2nd coating film was also analyzed, and the result contained C. The thickness T2 of the 2nd coating film was 49 nm, and the sum of the thickness of the 1st coating film and the thickness of the 2nd coating film was 50 nm. A The element ratio Rt of the 1st element at the position of the 1st element to carbon atom is 0.08.

[0192] After the 1st coating film and the 2nd coating film were formed, the negative electrode active material layer was calendered to obtain a negative electrode.

[0193] [Manufacture of the positive electrode]

[0194] A positive electrode slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) to a positive electrode mixture containing lithium cobaltate, acetylene black, and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5, and then stirring the mixture with a mixer (T.K. HIVIS MIX manufactured by Primex Corporation). Next, the positive electrode slurry was applied to the surface of an aluminum foil, and the coating film was dried and calendered to manufacture a positive electrode having positive electrode active material layers with a density of 3.6 g / cm 3 The thickness of the positive electrode active material layer was 138 μm.

[0195] [Preparation of the electrolyte]

[0196] An electrolyte was prepared by dissolving LiPF6 in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7 at a concentration of 1.0 mol / L.

[0197] [Manufacture of the secondary battery]

[0198] The positive electrode and the negative electrode were wound in a spiral shape with the tabs located at the outermost periphery, with the separator interposed therebetween, to manufacture an electrode group. The electrode group was inserted into an outer case made of an aluminum laminate film, and vacuum-dried at 105°C for 2 hours. Then, the electrolyte was injected, the opening of the outer case was sealed, and a secondary battery Al was obtained.

[0199] [Example 2]

[0200] In the formation of the 1st and 2nd coating films (6), the series of operations of supplying the precursor, purging, supplying the oxidizing agent, and purging were repeated 44 times, and otherwise, the 1st active material was manufactured in the same manner as in Example 1 to manufacture a secondary battery A2. The thickness T1 of the 1st coating film was 2 nm, the thickness T2 of the 2nd coating film was 48 nm, and the sum of the thickness of the 1st coating film and the thickness of the 2nd coating film was 50 nm. A The element ratio Rt of the 1st element at the position of the 1st element to carbon atom is 0.08. A The element ratio Rt of the 1st element at the position of the 1st element to carbon atom is 0.08.

[0201] The minimum value of the element ratio R of the first element to carbon atom is 0.03, and the maximum value is 7.4. The first coating film is located at a position of 0.25T1from the surface of the lithium silicate composite particle A The element ratio Rb of the first element to carbon atom at a position of 0.75T1from the surface of the lithium silicate composite particle is 6.1. The first coating film is located at a position of 0.75T1from the surface of the lithium silicate composite particle A The element ratio Rt of the first element to carbon atom at a position of T1from the surface of the lithium silicate composite particle is 0.1.

[0202] Example 3

[0203] In the formation of the first and second coating films (6), the series of operations of the supply of the precursor, the purging, the supply of the oxidizing agent, and the purging were repeated 100 times, and otherwise, the first active material was produced in the same manner as in Example 1, and the secondary battery A3 was produced. The thickness T1of the first coating film was 5 nm, the thickness T2of the second coating film was 45 nm, and the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm. A A In the formation of the first and second coating films (6), the series of operations of the supply of the precursor, the purging, the supply of the oxidizing agent, and the purging were repeated 100 times, and otherwise, the first active material was produced in the same manner as in Example 1, and the secondary battery A3 was produced. The thickness T1of the first coating film was 5 nm, the thickness T2of the second coating film was 45 nm, and the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.

[0204] The minimum value of the element ratio R of the first element to carbon atom is 0.03, and the maximum value is 7.4. The first coating film is located at a position of 0.25T1from the surface of the lithium silicate composite particle A The element ratio Rb of the first element to carbon atom at a position of 0.75T1from the surface of the lithium silicate composite particle is 5.7. The first coating film is located at a position of 0.75T1from the surface of the lithium silicate composite particle A The element ratio Rt of the first element to carbon atom at a position of T1from the surface of the lithium silicate composite particle is 0.11.

[0205] Example 4

[0206] In the formation of the first and second coating films (6), the series of operations of the supply of the precursor, the purging, the supply of the oxidizing agent, and the purging were repeated 200 times, and otherwise, the first active material was produced in the same manner as in Example 1, and the secondary battery A4 was produced. The thickness T1of the first coating film was 10 nm, the thickness T2of the second coating film was 40 nm, and the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm. A A In the formation of the first and second coating films (6), the series of operations of the supply of the precursor, the purging, the supply of the oxidizing agent, and the purging were repeated 200 times, and otherwise, the first active material was produced in the same manner as in Example 1, and the secondary battery A4 was produced. The thickness T1of the first coating film was 10 nm, the thickness T2of the second coating film was 40 nm, and the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.

[0207] The minimum value of the element ratio R of the first element to carbon atom is 0.03, and the maximum value is 7.4. The first coating film is located at a position of 0.25T1from the surface of the lithium silicate composite particle A The element ratio Rb of the first element to carbon atom at a position of 0.75T1from the surface of the lithium silicate composite particle is 5.0. The first coating film is located at a position of 0.75T1from the surface of the lithium silicate composite particle A The element ratio Rt of the first element to carbon atom at a position of T1from the surface of the lithium silicate composite particle is 0.12. ​​

[0208] Comparative Example 1

[0209] The active material was produced in the same manner as in Example 1 except that the covering of the lithium silicate composite particles with the carbon coating film (4) and the formation of the first coating film and the second coating film (6) were not performed, and the secondary battery B1 was produced.

[0210] Comparative Example 2

[0211] The active material was produced in the same manner as in Example 1 except that the formation of the first coating film and the second coating film (6) was not performed, and the secondary battery B2 was produced. The active material was covered with a carbon coating film having a thickness of 50 nm.

[0212] Comparative Example 3

[0213] The active material was produced in the same manner as in Example 4 except that the covering of the lithium silicate composite particles with the carbon coating film (4) was not performed, and the secondary battery B3 was produced. The lithium silicate composite particles were covered with a coating film containing titanium oxide, and the coating film had a thickness of 10 nm.

[0214] [Primary charge-discharge]

[0215] For each battery, constant current charging was performed at 25°C until the voltage became 4.2 V at a current of 1 C, and then constant voltage charging was performed at a voltage of 4.2 V until the current became 1 / 20 C. After a pause of 10 minutes, constant current discharging was performed at a current of 1 C until the voltage became 2.75 V.

[0216] [Charge-discharge cycle test]

[0217] The charge-discharge was repeatedly performed under the following conditions.

[0218] <Charge>

[0219] Constant current charging was performed at 25°C until the voltage became 4.2 V at a current of 1 C, and then constant voltage charging was performed at a voltage of 4.2 V until the current became 1 / 20 C.

[0220] <Discharge>

[0221] Constant current discharging was performed at 25°C until the voltage became 2.75 V at a current of 1 C.

[0222] The pause period between the charge and the discharge was set to 10 minutes. The proportion of the discharge capacity at the 100th cycle with respect to the discharge capacity at the 1st cycle was taken as the capacity retention rate. Further, the direct current internal resistance (DCIR) was calculated from the voltage change and the discharge current value before and after the discharge at the 1st cycle. The evaluation results are shown in Table 1.

[0223] [Table 1]

[0224]

[0225] As is apparent from Table 1, in the batteries Al to A4, the increase in internal resistance was suppressed, and the capacity maintenance rate was greatly improved.

[0226] Example 5

[0227] The first active material was produced in the same manner as in Example 1, except that TMA was used as the precursor, and the secondary battery A5 was produced. The first coating film and the second coating film were analyzed by SEM, EDS, ICP, and the like. The first coating film contained Al and C. In addition, it was confirmed that the element ratio Rb and the element ratio Rt satisfied Rb > Rt. The composition of the second coating film was analyzed in the same manner, and as a result, C was contained. The sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.

[0228] Example 6

[0229] The first active material was produced in the same manner as in Example 2, except that TMA was used as the precursor, and the secondary battery A6 was produced. The first coating film and the second coating film were analyzed by SEM, EDS, ICP, and the like. The first coating film contained Al and C. In addition, it was confirmed that the element ratio Rb and the element ratio Rt satisfied Rb > Rt. The composition of the second coating film was analyzed in the same manner, and as a result, C was contained. The sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.

[0230] Example 7

[0231] The first active material was produced in the same manner as in Example 3, except that TMA was used as the precursor, and the secondary battery A7 was produced. The first coating film and the second coating film were analyzed by SEM, EDS, ICP, and the like. The first coating film contained Al and C. In addition, it was confirmed that the element ratio Rb and the element ratio Rt satisfied Rb > Rt. The composition of the second coating film was analyzed in the same manner, and as a result, C was contained. The sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.

[0232] The capacity maintenance rate and the DCIR were calculated in the same manner as in the secondary battery Al for the produced secondary batteries A5 to A7. The evaluation results are shown in Table 2.

[0233] [Table 2]

[0234]

[0235] As is apparent from Table 2, in the batteries A5 to A7, the increase in internal resistance was suppressed, and the capacity maintenance rate was greatly improved.

[0236] Industrial Applicability

[0237] According to the present disclosure, an electrochemical device with high capacity and long life can be provided. The electrochemical device of the present disclosure is useful as a main power source for a mobile body communication device, a portable electronic device, or the like.

[0238] Explanation of Reference Signs

[0239] 1 Electrode Group

[0240] 2 Positive Electrode Lead

[0241] 3 Negative Electrode Lead

[0242] 4 Battery Case

[0243] 5 Sealing Plate

[0244] 6 Negative Electrode Terminal

[0245] 7 Gasket

[0246] 8 Sealing Plug

[0247] 20 Active Material Particles

[0248] 21 Silicate Phase

[0249] 22 Silicon Particles

[0250] 23 Lithium Silicate Composite Particles

[0251] 24 Primary Particles

[0252] 26 Second Coating Film

[0253] 27 First Coating Film

Claims

1. An active substance particle, comprising: Lithium silicate composite particles comprising a lithium silicate phase and silicon particles dispersed within the lithium silicate phase; and, A first coating covering at least a portion of the surface of the lithium silicate composite particles. The first coating comprises: an oxide of a first element other than a metal and carbon atoms. The thickness of the first coating film is set to T1 A when, The first coating is 0.25T1 from the surface of the lithium silicate composite particles A The element ratio Rb of the first element at the position of 0.25T1 from the surface of the lithium silicate composite particles with respect to the carbon atom is 0.5 or more and less than 1. The first film is located at a distance of 0.75T1 from the surface of the lithium silicate composite particles A The element ratio Rt of the first element at the position of 0.75T1 from the surface of the lithium silicate composite particles with respect to the carbon atom satisfies Rb > Rt. in, The element ratio Rb is 5 or higher and 99 or lower, and the element ratio Rt is 0.01 or higher and 5 or lower. The first element comprises at least one element selected from the group consisting of Al, Ti, Si, Zr, Mg, Nb, Ta, Sn, Ni, and Cr.

2. The active substance particles according to claim 1, wherein, The element ratio Rb and the element ratio Rt satisfy Rb / Rt>1.

3.

3. The active substance particles according to claim 1 or 2, wherein, The thickness T1 of the first coating A is 0.1 nm or more and 50 nm or less.

4. The active substance particles according to claim 1 or 2, wherein, The active material particles further comprise a second coating that covers at least a portion of the first coating and has a different conductivity than the first coating.

5. The active substance particles according to claim 4, wherein, The second coating contains carbon atoms.

6. The active substance particles according to claim 4, wherein, the thickness T1 of the first coating A the thickness T2 of the second coating A satisfies the relationship 0 < T2 A / T1 A <1500.

7. An electrochemical element comprising: a current collector and an active material layer loaded on said current collector, The active substance layer comprises: active substance particles as described in any one of claims 1 to 6.

8. An electrochemical device comprising: a first electrode, a second electrode, and a spacer sandwiched between them. One of the first electrode and the second electrode is constituted by the electrochemical element as described in claim 7.

9. A method for manufacturing active substance particles according to claim 1, comprising the following steps; Preparation step: Prepare lithium silicate composite particles, wherein the lithium silicate composite particles comprise a lithium silicate phase, silicon particles dispersed within the lithium silicate phase, and at least a portion of the surface is covered by a carbon coating containing carbon atoms; and, The coating formation process involves exposing the lithium silicate composite particles to a gas phase containing a first element other than a non-metallic element, introducing the first element into the carbon coating, and forming a first coating containing an oxide of the first element and the carbon atoms on at least a portion of the surface of the lithium silicate composite particles.

10. The method for manufacturing active substance particles according to claim 9, wherein, The coating formation process is performed using atomic deposition.

11. A method for manufacturing an electrochemical element according to claim 7, comprising the following steps: The preparation process involves preparing lithium silicate composite particles, wherein the lithium silicate composite particles comprise a lithium silicate phase and silicon particles dispersed within the lithium silicate phase, and at least a portion of the surface is covered by a carbon coating containing carbon atoms. The loading process involves loading the lithium silicate composite particles onto the surface of the current collector; and, In the coating formation process, the lithium silicate composite particles are exposed to a gas phase containing a first element other than a non-metallic element, the first element is introduced into the carbon coating, and an active material layer containing an oxide of the first element and the carbon atoms is formed on at least a portion of the surface of the lithium silicate composite particles.

12. The method for manufacturing an electrochemical element according to claim 11, wherein, The coating formation process is performed using atomic layer deposition.

13. The method for manufacturing an electrochemical element according to claim 11 or 12, wherein, After the coating formation process, a calendering process is performed to calender the active material layer.

Images