Active material particles, electrochemical element, and electrochemical device

Abstract

An active material particle is provided with a composite particle containing a lithium silicate phase and a silicon phase dispersed in the lithium silicate phase, and with a first coating film that coats at least a portion of the surface of the composite particle. The first coating film contains a carbon material and an oxygen deficient oxide of a first element wherein the first element is an element other than a nonmetal element.

Description

[Technical Field]

[0001] The present disclosure is primarily concerned with improvements to active material particles. [Background technology]

[0002] As the applications of electrochemical devices become more diverse, improvements in various performances are being sought. In this regard, Patent Document 1 proposes coating the surfaces of positive and negative electrodes with metal oxides. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-97999 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the performance requirements for electrochemical devices is high capacity. For example, in lithium-ion secondary batteries, the use of silicon compounds as the negative electrode material is being considered. It is also known that silicon compounds are more susceptible to corrosion due to side reactions during battery operation than carbon materials used as the negative electrode material. Therefore, even when silicon compounds are used as active material particles, it is necessary to suppress the deterioration of the cycle characteristics of electrochemical devices. There is also a need for improved rate characteristics. [Means for solving the problem]

[0005] One aspect of the present disclosure relates to an active material particle comprising: a composite particle including a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase; and a first coating covering at least a portion of the surface of the composite particle, wherein the first coating includes an oxide of a first element having oxygen deficiencies and a carbon material, and the first element is an element other than a non-metal element.

[0006] Another aspect of the present disclosure relates to an electrochemical device including a current collector and an active material layer supported on the current collector, the active material layer including the above-described active material particles.

[0007] Yet another aspect of the present disclosure relates to an electrochemical device comprising a first electrode, a second electrode, and an electrolyte, wherein one of the first electrode and the second electrode is formed from the above-described electrochemical element. [Effects of the Invention]

[0008] According to the present disclosure, the cycle characteristics and rate characteristics of an electrochemical device can be improved.

[0009] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present application, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an active material particle according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged schematic cross-sectional view showing a main part of the active material particle shown in FIG. [Figure 3] 1 is a TEM image showing a main part of a cross section of an active material particle according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a schematic cross-sectional view showing in detail an active material particle according to an embodiment of the present disclosure. [Figure 5] 1 is a partially cutaway schematic perspective view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. [Figure 6] 1 is a flowchart illustrating a method for producing active material particles according to an embodiment of the present disclosure. [Figure 7] 1 is a flowchart illustrating a method for manufacturing an electrochemical device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] A. Active material particles Active material particles according to an embodiment of the present disclosure include composite particles and a first coating covering at least a portion of the surface of the composite particles. The composite particles include a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase. Hereinafter, the composite particles are also referred to as "lithium silicate composite particles." The first coating includes an oxide of a first element having oxygen deficiencies and a carbon material. The first element is an element other than non-metallic elements.

[0012] The first coating enhances the chemical stability of the lithium silicate composite particles while maintaining electrical conductivity. As a result, the cycle characteristics of the electrochemical device are improved. The oxide of the first element contained in the first coating contributes to suppressing corrosion of the lithium silicate composite particles. The carbon material contained in the first coating contributes to improving the electrical conductivity of the active material particles.

[0013] The oxide of the first element contained in the first coating has oxygen deficiencies, which enhances the ionic conductivity of the active material particles, allowing smooth absorption and desorption of lithium ions at the interface between the lithium silicate composite particles and the electrolyte. As a result, the rate characteristics of the electrochemical device are improved. The active material particles according to the present disclosure are preferably used as a negative electrode active material for lithium-ion secondary batteries.

[0014] Oxygen vacancies refer to a state in which no oxygen atoms are present in some of the oxygen sites in the crystal lattice of an oxide of the first element, forming vacancies. X-ray absorption near edge structure (XANES) analysis can be used to analyze oxygen vacancies in oxides of the first element.

[0015] The amount of oxygen deficiency in the oxide of the first element (for example, the x value in formula (1), the y value in formula (2), the z value in formula (3), and the u value in formula (4) described below) can be determined by the following method.

[0016] Disassemble the electrochemical device to remove the electrodes and obtain a thin sample (about 100 nm thick) of the active material layer for transmission electron microscope (TEM) observation. Observe the active material particles in the sample by TEM. Perform elemental mapping by TEM-EDS analysis (energy dispersive X-ray spectroscopy) on the active material particles to confirm that the surface of the lithium silicate composite particles is covered with the first coating. Perform XANES analysis on any plurality of points (for example, 10 points) of the first coating, obtain the average value of the valence of the first element, and determine the oxygen deficiency amount based on it. For example, in TiO 2-x when the average value of the valence of Ti is 3.8, the oxygen deficiency amount x is 0.1. In XANES analysis, check whether there are L-edge peaks of the metal (the first element) and K-edge shoulders of O, and determine whether it is the proper valence or oxygen deficiency.

[0017] The first element is an element other than a non-metal element, including a metal element and a so-called semi-metal element. Among them, in terms of having a high corrosion inhibition effect on the lithium silicate composite particles, the first element preferably contains at least one element selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements, and Group 6 elements of the periodic table. In particular, the first element preferably contains at least one selected from the group consisting of Al, Ti, Si, Zr, Mg, Nb, Ta, Sn, Ni, and Cr. Among them, from the viewpoint of being able to form an oxide that is a high dielectric and being easy to improve the rate characteristics, Ti is more preferable as the first element.

[0018] The oxide of the first element having oxygen deficiency may contain an oxide represented by the formula (1): MeO 2-x In the formula (1), Me is at least one selected from the group consisting of Ti, Si, Zr, and Sn, and satisfies 0 < x ≦ 1.95. The x in the formula (1) may be 0.1 or more and 1.9 or less, or may be 1.7 or more and 1.9 or less.

[0019] The oxide of the first element having oxygen deficiency is represented by the formula (2): MeO 1.5-yIt may contain an oxide represented by the formula. In formula (2), Me is Al, and 0 < y ≤ 1.47 is satisfied. In formula (2), y may be 0.1 or more and 1.45 or less, or may be 1.2 or more and 1.45 or less.

[0020] The oxide of the first element having oxygen deficiency may contain an oxide represented by the formula (3): MeO 1-z It may contain an oxide represented by the formula. In formula (3), Me is at least one selected from the group consisting of Mg and Ni, and 0 < z ≤ 0.9 is satisfied. In formula (3), z may be 0.1 or more and 0.89 or less, or may be 0.7 or more and 0.89 or less.

[0021] The oxide of the first element having oxygen deficiency may contain an oxide represented by the formula (4): MeO 3-u It may contain an oxide represented by the formula. In formula (4), Me is Cr, and 0 < u ≤ 2.1 is satisfied. In formula (4), u may be 0.1 or more and 2.05 or less, or may be 1.8 or more and 2.05 or less.

[0022] The oxide of the first element may contain two or more oxides. In this case, the respective oxides may be mixed or may be arranged in layers.

[0023] [Lithium silicate composite particles] The lithium silicate composite particles included in the active material particles according to the present embodiment include a lithium silicate phase and a silicon phase dispersed in the lithium silicate phase.

[0024] The lithium silicate composite particles usually exist as secondary particles in which a plurality of primary particles are aggregated. The first coating covers at least a part of the surface of the secondary particles. Each primary particle includes a lithium silicate phase and a silicon phase dispersed in the lithium silicate phase.

[0025] The particle size of the lithium silicate composite particles is not particularly limited. The average particle size of the lithium silicate composite particles may be, for example, 1 μm or more and 20 μm or less. The average particle size of the lithium silicate composite particles means the particle size (volume average particle size) at which the volume integration value is 50% in the volume particle size distribution measured by the laser diffraction scattering method.

[0026] (Lithium silicate phase) The lithium silicate phase (hereinafter sometimes simply referred to as the silicate phase) has few sites that can react with lithium, so it is difficult to cause a new irreversible reaction during charge and discharge. Therefore, excellent charge and discharge efficiency is exhibited at the initial stage of charge and discharge.

[0027] 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 is, for example, greater than 2 and less than 3. When O / Si is within this range, it is advantageous in terms of stability and lithium ion conductivity.

[0028] The silicate phase is, for example, Li 2v SiO 2+v (where v is 0 < v < 1). From the viewpoints of stability, ease of production, lithium ion conductivity, etc., v = 1 / 2 is more preferable.

[0029] The silicate phase may further contain the element M. Here, M can be, for example, 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 for improving the fluidity of the molten silicate. 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 is, for example, 10 mol% or less, and may be 5 mol% or less, based on the total amount of elements other than O contained in the silicate phase.

[0030] (Silicon phase) The silicon phase dispersed within the silicate phase has a particulate phase of simple silicon (Si) and is composed of a single crystallite or multiple crystallites. The crystallite size of the silicon phase is not particularly limited. The crystallite size of the silicon phase is more preferably 10 nm or more and 30 nm or less, and even more preferably 15 nm or more and 25 nm or less. When the crystallite size of the silicon phase is 10 nm or more, the surface area of ​​the silicon phase can be kept small, making it less likely for the silicon phase to deteriorate, which is accompanied by the generation of irreversible capacity. The crystallite size of the silicon phase is calculated using the Scherrer equation from the half-width of the diffraction peak assigned to the Si(111) plane in the X-ray diffraction (XRD) pattern of the silicon phase.

[0031] To increase capacity and improve cycle characteristics, the content of the silicon phase in the lithium silicate composite particles may be, for example, 30% by mass or more and 80% by mass or less. By setting the content of the silicon phase to 30% by mass or more, the proportion of the silicate phase decreases, making it easier to improve initial charge / discharge efficiency. By setting the content of the silicon phase to 80% by mass or less, it makes it easier to reduce the degree of expansion and contraction of the lithium silicate composite particles during charge / discharge.

[0032] (carbon phase) The lithium silicate composite particles may contain a carbon phase in addition to the silicate phase and the silicon phase. For example, the carbon phase covers at least a portion of the surface of the silicon phase and is present at at least a portion of the interface between adjacent primary particles.

[0033] The content of each element contained in the lithium silicate composite particles can be calculated, for example, by SEM-EDS analysis using a powder sample of the lithium silicate composite particles in a discharged state. The powder sample is analyzed to measure the spectral intensity of each element. Next, a calibration curve is created using commercially available standard samples of the elements, and the content of each element contained in the silicate phase is calculated.

[0034] Quantitative determination of each element in lithium silicate composite particles can also be performed using ICP-AES (inductively coupled plasma atomic emission spectroscopy), Auger electron spectroscopy (AES), laser ablation ICP mass spectroscopy (LA-ICP-MS), X-ray photoelectron spectroscopy (XPS), etc.

[0035] [First coating] The first coating covers at least a portion of the surface of the lithium silicate composite particles, which are secondary particles.

[0036] The first coating contains an oxide of a first element having an oxygen deficiency and a carbon material. Typically, the oxide of the first element having an oxygen deficiency and the carbon material are mixed in the first coating. The "mixing" mentioned above refers to, for example, a state in which the oxide of the first element is embedded in the gaps between the carbon materials. This allows sufficient conductive paths to be formed within the first coating while the first coating can suppress corrosion of the lithium silicate composite particles.

[0037] The first element may be present in a greater amount closer to the surface of the lithium silicate composite particle. This improves the effect of inhibiting corrosion of the lithium silicate composite particle. The average element ratio RA of the first element to the carbon material in the first coating is not particularly limited. The element ratio RA may be, for example, 0.01 or more and 99 or less.

[0038] Since the lithium silicate phase has poor electronic conductivity, the conductivity of the lithium silicate composite particles tends to be low. However, by coating the surface of the lithium silicate composite particles with a first coating containing a conductive carbon material, the conductivity of the lithium silicate composite particles can be dramatically increased.

[0039] Examples of carbon materials include amorphous carbon with low crystallinity, such as carbon black, coal, coke, charcoal, and activated carbon, and graphite with high crystallinity. Among these, amorphous carbon is preferred because of its low hardness and its strong buffering effect against the silicon phase, which changes in volume during charging and discharging. The amorphous carbon may be either easily graphitized carbon (soft carbon) or difficult to graphitize carbon (hard carbon). Examples of carbon black include acetylene black and ketjen black. Graphite refers to a material having a graphite-type crystalline structure, and examples include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0040] The thickness of the first coating is not particularly limited. From the viewpoint of corrosion inhibition, the thickness of the first coating may be 0.1 nm or more, 0.5 nm or more, or 1 nm or more. From the viewpoint of electrical conductivity and lithium ion diffusibility, the thickness of the first coating may be 50 nm or less, 10 nm or less, or 2 nm or less. The thickness of the first coating may be, for example, 0.1 nm or more and 50 nm or less, or 0.1 nm or more and 10 nm or less.

[0041] The thickness of the first coating can be measured by observing the cross section of the active material particles using an SEM or TEM. First, the electrochemical device is disassembled to remove the electrochemical element (e.g., electrode), and a cross section of the element is obtained using a cross-section polisher (CP). From the image of the cross section obtained using SEM or TEM, 10 active material particles with a maximum diameter of 5 μm or more are randomly selected. The thickness of the first coating is measured at any five points on each particle. The average thickness of these 50 points is calculated. After calculating this average, data that differs from the obtained average by 20% or more is excluded, and the average is calculated again. This corrected average is used as the thickness T1 of the first coating. A Let's say.

[0042] The starting point of the first coating is the interface between the first coating and a base particle (see below) formed by lithium silicate composite particles. For example, the starting point of the first coating can be determined as a point where the intensity of the peak attributed to Li obtained by SEM-EDS analysis is 1 / 10 or less of the peak attributed to the first element. The end point of the first coating can be determined as a point where the intensity of the peak attributed to the first element obtained by SEM-EDS analysis is 5% or less of its maximum value. If a second coating is formed, the end point of the first coating is the interface between the first coating and the second coating.

[0043] [Second coating] At least a portion of the first coating may be covered with a conductive second coating, which further improves the conductivity of the active material particles.

[0044] Unlike the first coating, the second coating is substantially free of oxides of the first element. The second coating being substantially free of oxides of the first element means that the intensity of the peak attributed to the first element obtained by SEM-EDS is below the detection limit.

[0045] The second coating contains a conductive material. The conductive material is preferably a conductive carbon material because it is electrochemically stable. Examples of the conductive carbon material include the carbon material contained in the first coating described above.

[0046] The thickness of the second coating is not particularly limited. The second coating is preferably thin enough that it does not substantially affect the average particle size of the lithium silicate composite particles. The thickness of the second coating may be 1 nm or more, or 5 nm or more. The thickness of the second coating may be 200 nm or less, or 100 nm or less. The thickness of the second coating, like the first coating, can be measured by observing the cross section of the lithium silicate composite particles using an SEM or TEM.

[0047] The starting point of the second coating is the interface with the first coating. The end point of the second coating is the outermost point of the active material particle that can be confirmed by SEM or TEM image. Alternatively, the end point of the second coating is the point where the intensity of the peak attributed to C obtained by SEM-EDS analysis is 5% or less of its maximum value.

[0048] First coating thickness T1 A and the thickness of the second coating T2 A That is, 0 <T2 A / T1 A It is preferable that the relationship of T2 <1500 is satisfied. This makes it easier to achieve both corrosion resistance, improved ion diffusibility, and improved electrical conductivity. A / T1 A is preferably 5 or more, more preferably 10 or more. A / T1 A is preferably 500 or less, and more preferably 100 or less.

[0049] Fig. 1 is a schematic cross-sectional view showing an active material particle according to an embodiment of the present disclosure, and Fig. 2 is a schematic cross-sectional view showing an enlarged view of a main part of the active material particle shown in Fig. 1.

[0050] The active material particle 20 includes a lithium silicate composite particle 23, a first coating 27 covering the surface of the lithium silicate composite particle 23, and a second coating 26 covering the first coating 27. Fig. 3 shows a TEM image of an example of an active material particle according to an embodiment of the present disclosure. The TEM image in Fig. 3 is a portion of a cross section of the active material particle, corresponding to Fig. 2.

[0051] 4 is a schematic cross-sectional view showing in detail a cross section of an example of an active material particle. The lithium silicate composite particle 23 is a secondary particle (parent particle) formed by agglomeration of a plurality of primary particles 24. Each primary particle 24 includes a silicate phase 21 and a silicon phase 22 dispersed within the silicate phase 21. The silicon phase 22 is dispersed approximately uniformly within the silicate phase 21.

[0052] A carbon phase (not shown) is disposed on at least a part of the interface S between adjacent primary particles 24. The carbon phase may cover at least a part of the surface of the silicon phase 22.

[0053] The surface of the lithium silicate composite particle (base particle) 23 is covered with a first coating 27. The first coating 27 is covered with a second coating 26.

[0054] B. Electrochemical element An electrochemical element according to an 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 above-described active material particles. Such an electrochemical element has excellent conductivity and is inhibited from deteriorating, making it possible to provide an electrochemical device with high capacity and long life.

[0055] The electrochemical element may be an electrode. The electrode may be, for example, at least one of a positive electrode and a negative electrode used in a secondary battery. The electrode according to an embodiment of the present disclosure is preferably used as a negative electrode for a lithium-ion secondary battery.

[0056] C. Electrochemical Devices An electrochemical device according to an embodiment of the present disclosure includes a first electrode, a second electrode, and a separator disposed therebetween. One of the first electrode and the second electrode is formed from the electrochemical element described above. Such an electrochemical device has a high capacity and a long life.

[0057] An electrochemical device is a device that transfers electrons between substances, causing a chemical reaction through this transfer of electrons. Examples of electrochemical devices include primary batteries, secondary batteries, capacitors, and electric double layer capacitors. The electrochemical device according to an embodiment of the present disclosure is preferably a lithium ion secondary battery that uses lithium silicate composite particles as a negative electrode active material.

[0058] Hereinafter, the configurations of an electrochemical element according to an embodiment of the present disclosure will be described using a negative electrode as an example and a lithium ion secondary battery as an example of an electrochemical device.

[0059] [Negative electrode] The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material contains at least the above-mentioned active material particles (hereinafter, sometimes referred to as a first active material). The negative electrode active material layer is formed as a layer containing a negative electrode mixture on the surface of a negative electrode current collector. The negative electrode active material layer may be formed on one surface or both surfaces of the negative electrode current collector. The negative electrode mixture contains the negative electrode active material as an essential component, and may contain a binder, a conductive agent, a thickener, etc. as optional components.

[0060] The negative electrode active material may further contain another active material (hereinafter, sometimes referred to as a second active material). Examples of the second active material include a conductive carbon material that electrochemically absorbs and releases lithium ions. By using the first active material and the conductive carbon material in combination, a further extension of the battery life can be expected.

[0061] Examples of conductive carbon materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). Of these, graphite is preferred because it has excellent charge / discharge stability and low irreversible capacity. Graphite refers to a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, and graphitized mesophase carbon particles. One type of conductive carbon material may be used alone, or two or more types may be used in combination.

[0062] The particle size of the conductive carbon material is not particularly limited, and the average particle size of the conductive carbon material may be, for example, 1 μm or more and 30 μm or less.

[0063] The proportion of the first active material in the total of the first and second active materials may be, for example, 3% by mass to 30% by mass, which makes it easier to achieve both high capacity and long life.

[0064] The negative electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of materials for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys. The thickness of the negative electrode current collector is not particularly limited, but is preferably 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 20 μm or less, from the viewpoint of balancing the strength and weight of the negative electrode.

[0065] The binder may be at least one selected from the group consisting of polyacrylic acid, polyacrylic acid salts, and derivatives thereof. As the polyacrylic acid salts, Li salts or Na salts are preferably used. Among them, cross-linked lithium polyacrylate is preferably used.

[0066] Examples of conductive agents include carbon blacks such as acetylene black, conductive fibers such as carbon fiber and metal fiber, carbon fluoride, 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. These may be used alone or in combination of two or more.

[0067] Examples of thickeners include carboxymethyl cellulose (CMC) and its modified products (including salts such as Na salt), cellulose derivatives such as methyl cellulose (cellulose ethers, etc.), saponified polymers having vinyl acetate units such as polyvinyl alcohol, polyethers (polyalkylene oxides such as polyethylene oxide, etc.), etc. These may be used alone or in combination of two or more.

[0068] [Positive electrode] The positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. The positive electrode active material layer may be formed on one surface or both surfaces of the positive electrode current collector.

[0069] The positive electrode active material layer is formed as a layer containing a positive electrode mixture on the surface of a positive electrode current collector. The positive electrode mixture contains a positive electrode active material as an essential component and may contain a binder, a conductive agent, and the like as optional components.

[0070] The positive electrode active material may be a lithium composite metal oxide. 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 Examples of suitable cations include Li2O4, LiMePO4, and Li2MePO4F. Here, M is at least one element 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 (e.g., at least one element selected from the group consisting of Mn, Fe, Co, and Ni). 0≦a≦1.2, 0≦b≦0.9, and 2.0≦c≦2.3.

[0071] The binder and conductive agent may be the same as those exemplified for the negative electrode. As the conductive agent, graphite such as natural graphite or artificial graphite may be used.

[0072] The shape and thickness of the positive electrode current collector can be selected from the shape and range corresponding to those of the negative electrode current collector. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0073] [Electrolyte] The electrochemical device according to the embodiment of the present disclosure further includes an electrolyte. The electrolyte includes, for example, 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 may contain known additives.

[0074] The solvent used may be an aqueous solvent or a non-aqueous solvent. Examples of non-aqueous solvents that may be used include cyclic carbonates, chain carbonates, and cyclic carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0075] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorine-containing acids (LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (LiN(SO2F)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.). One type of lithium salt may be used alone, or two or more types may be used in combination.

[0076] [Separator] A separator may be interposed between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. Examples of the separator include a microporous thin film, a woven fabric, and a nonwoven fabric. The separator is made of a polyolefin such as polypropylene or polyethylene.

[0077] An example of the structure of a secondary battery is a structure in which an electrode group formed by winding a positive electrode, a negative electrode, and a separator, and an electrolyte are housed in an exterior body. Instead of a wound-type electrode group, a stacked-type electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween may also be used. Other types of electrode groups may also be used. The secondary battery may be in any type, such as a cylindrical type, a prismatic type, a coin type, a button type, or a laminate type.

[0078] FIG. 5 is a schematic perspective view, with a portion cut away, of a prismatic secondary battery according to an embodiment of the present disclosure. The battery includes a bottomed prismatic battery case 4, an electrode group 1 and an electrolyte (not shown) housed within the battery case 4, and a sealing plate 5 that seals the opening of the battery case 4. The electrode group 1 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed therebetween. The negative electrode, positive electrode, and separator are wound around a flat winding core, and the electrode group 1 is formed by removing the winding core. The sealing plate 5 includes a liquid inlet closed with a sealing plug 8 and a negative electrode terminal 6 insulated from the sealing plate 5 by a gasket 7.

[0079] One end of a negative electrode lead 3 is attached to the negative electrode current collector of the negative electrode by welding or the like. One end of a 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 a negative electrode terminal 6. The other end of the positive electrode lead 2 is electrically connected to a sealing plate 5. A resin frame is disposed on top of the electrode group 1, separating the electrode group 1 from the sealing plate 5 and separating the negative electrode lead 3 from the battery case 4.

[0080] D. Method for manufacturing active material particles A method for producing active material particles according to an embodiment of the present disclosure includes a preparation step of preparing lithium silicate composite particles, the lithium silicate composite particles including a silicate phase and a silicon phase dispersed within the silicate phase, and at least a portion of the surface of which is coated with a carbon coating containing a carbon material, and a coating step of exposing the lithium silicate composite particles to a gas phase containing a first element other than a non-metallic element to introduce the first element into the carbon coating, thereby forming a first coating containing an oxide of the first element and the carbon material on at least a portion of the surface of the lithium silicate composite particles. According to this production method, the oxide of the first element is introduced into the carbon coating that coats the lithium silicate composite particles, thereby forming the first coating.

[0081] FIG. 6 is a flowchart showing a method for producing active material particles according to one embodiment of the present disclosure.

[0082] (i) Preparation step of lithium silicate composite particles (S11) (ii) Preparation of silicon particles First, silicon particles are prepared. Silicon particles can be obtained by chemical vapor deposition (CVD), thermal plasma, physical pulverization, etc. The following method can synthesize silicon nanoparticles with an average particle size of 10 nm or more and 200 nm or less. The average particle size of silicon particles refers to the particle size (volume average particle size) at which the volumetric integrated value is 50% in the volume particle size distribution measured by laser diffraction scattering.

[0083] (a) Chemical vapor deposition In the CVD method, silicon particles are generated by oxidizing or reducing a silane compound in a gas phase, for example. The reaction temperature may be set to, for example, 400°C or higher and 1300°C or lower.

[0084] Examples of silane compounds that can be used include silicon hydrides such as silane and disilane, halogenated silanes, and alkoxysilanes. Examples of halogenated silanes that can be used include dichlorosilane, trichlorosilane, and tetrachlorosilane. Examples of alkoxysilanes that can be used include tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane.

[0085] For example, contacting silicon hydride with an oxidizing gas in the gas phase produces a composite of silicon particles and silicon oxide particles. That is, the gas phase atmosphere can be an oxidizing gas atmosphere. The composite is washed with, for example, hydrofluoric acid to remove the silicon oxide and obtain silicon particles.

[0086] To reduce halogenated silanes, alkoxysilanes, etc., a silane compound can be contacted with molten metal atomized by atomization. Examples of the molten metal include Na, K, Mg, Ca, Zn, and Al. Examples of the atomization gas include an inert gas, halogenated silane, and hydrogen gas. The gaseous atmosphere can be an inert gas or reducing gas.

[0087] (b) Thermal plasma method The thermal plasma method is a method in which silicon raw material is introduced into generated thermal plasma and silicon particles are generated in the high-temperature plasma. Thermal plasma can be generated by arc discharge, high-frequency discharge, microwave discharge, laser light irradiation, etc. Among these, radio frequency (RF) discharge is preferable because it is a non-polarized discharge and impurities are less likely to be mixed into the silicon particles.

[0088] The raw material can be, for example, silicon oxide. When the raw material is introduced into the plasma, silicon and oxygen in atomic or ionic states are instantly generated, and during cooling, the silicon combines and solidifies to generate silicon particles.

[0089] (c) Physical crushing method The physical pulverization method (mechanical milling method) is a method in which coarse silicon particles are pulverized using a pulverizer such as a ball mill, a bead mill, etc. The interior of the pulverizer may be filled with, for example, an inert gas atmosphere.

[0090] (i-ii) Coating of silicon particles with carbon phase At least a portion of the surface of the silicon particles may be coated with a carbon phase.

[0091] Methods for coating silicon particles with a carbon phase include chemical vapor deposition (CVD), sputtering, atomic layer deposition (ALD), wet mixing, dry mixing, etc. Among these, CVD and wet mixing are preferred.

[0092] (a) Chemical vapor deposition In the CVD method, silicon particles are introduced into a hydrocarbon gas atmosphere, which is then heated. The carbon material produced by thermal decomposition of the hydrocarbon gas is deposited on the particle surface, forming a carbon phase. The temperature of the hydrocarbon gas atmosphere may be, for example, 500°C or higher and 1000°C or lower. Examples of hydrocarbon gases that can be used include chain hydrocarbon gases such as acetylene and methane, and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0093] (b) Wet mixing method In the wet mixing method, a carbon precursor such as coal pitch, petroleum pitch, or tar is dissolved in a solvent, the resulting solution is mixed with silicon particles, and the resulting solution is dried. The silicon particles coated with the carbon precursor are then heated in an inert gas atmosphere at temperatures of, for example, 600°C or less or 1000°C or less to carbonize the carbon precursor and form a carbon phase.

[0094] (i-iii) Synthesis of lithium silicate composite particles A raw material for the silicate phase is prepared.

[0095] The raw material for the silicate phase can be a raw material mixture containing a Si raw material and a Li raw material in a specified ratio. The raw material mixture can be melted and the molten liquid passed through a metal roll to form flakes, thereby obtaining silicate. Alternatively, the raw material mixture can be fired at a temperature below the melting point without being melted, and silicate can be synthesized by a solid-state reaction.

[0096] Silicon oxide (e.g., SiO2) can be used as the Si raw material. Carbonates, oxides, hydroxides, hydrides, nitrates, sulfates, etc. of lithium or element M can be used as the Li raw material or element M raw material, respectively. Of these, carbonates, oxides, hydroxides, etc. are preferred.

[0097] Next, silicon particles at least partly coated with a carbon phase (hereinafter also referred to as carbon-coated silicon particles) are blended with the silicate and mixed together. For example, lithium silicate composite particles are produced through the following steps.

[0098] First, carbon-coated silicon particles and silicate powder are mixed in a mass ratio of, for example, 20:80 to 95:5.

[0099] Next, the mixture of carbon-coated silicon particles and silicate is stirred using a device such as a ball mill. Preferably, an organic solvent is added to the mixture and wet-mixed. A predetermined amount of organic solvent may be added to the grinding vessel all at once at the beginning of grinding, or may be added intermittently in multiple batches during the grinding process. The organic solvent serves to prevent adhesion of the material to be ground to the inner wall of the grinding vessel. Examples of organic solvents that can be used include alcohols, ethers, fatty acids, alkanes, cycloalkanes, silicate esters, and metal alkoxides.

[0100] The mixture is then sintered by heating it to a temperature between 450°C and 1000°C under pressure in an inert gas atmosphere (e.g., argon, nitrogen, etc.). Sintering can be performed using a sintering device capable of applying pressure in an inert atmosphere, such as a hot press or spark plasma sintering. During sintering, the silicate melts and flows to fill the gaps between the silicon particles. As a result, a dense block-shaped sintered body can be obtained, with the silicate phase forming the sea and the particulate silicon phase forming the islands.

[0101] Finally, the sintered body is pulverized to obtain lithium silicate composite particles. By appropriately selecting the pulverization conditions, lithium silicate composite particles having a predetermined average particle size can be obtained.

[0102] (i-iv) Coating of lithium silicate composite particles with carbon film Next, at least a portion of the surface of the lithium silicate composite particles is coated with a carbon coating, and the carbon material contained in the first coating is derived from this carbon coating.

[0103] Examples of methods for forming a carbon coating on the surface of lithium silicate composite particles include chemical vapor deposition using a chain hydrocarbon gas such as acetylene or methane as a raw material, and a method in which coal pitch, petroleum pitch, phenolic resin, or the like is mixed with lithium silicate composite particles and heated to carbonize them. Carbon black may also be attached to the surface of the lithium silicate composite particles.

[0104] The carbon coating is preferably thin enough that it does not substantially affect the average particle size of the lithium silicate composite particles. On the other hand, considering that the carbon coating is the carbon source for the first coating, it is desirable that the thickness of the carbon coating be equal to or greater than the desired thickness of the first coating. The carbon coating may be 0.1 nm or more, or even 1 nm or more. Considering the diffusibility of lithium ions, the carbon coating is preferably 300 nm or less, more preferably 200 nm or less. The thickness of the carbon coating can be measured by observing the cross section of the lithium silicate composite particles using a SEM or TEM, similar to the first coating.

[0105] Finally, the lithium silicate composite particles having the carbon coating may be washed with an acid. For example, by washing the composite particles with an acidic aqueous solution, trace amounts of alkaline components that may be present on the surface of the lithium silicate composite particles can be dissolved and removed. Examples of the acidic aqueous solution include aqueous solutions of inorganic acids such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid, and carbonic acid, and aqueous solutions of organic acids such as citric acid and acetic acid.

[0106] (ii) First coating formation step (S12) The lithium silicate composite particles having a carbon coating are exposed to a gas phase containing a first element, whereby the first element is introduced into the carbon coating, and a first coating containing an oxide of the first element and a carbon material is formed on at least a portion of the surface of the lithium silicate composite particles.

[0107] Examples of vapor phase methods include CVD, ALD, and physical vapor deposition (PVD). In particular, ALD is preferred because it allows the first coating to be formed at a relatively low temperature. According to the ALD method, the first coating can be formed in an atmosphere of 200°C or less.

[0108] In the ALD method, an organometallic compound (precursor) containing a first element is used as the raw material for the first coating. 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 a target object is placed. This forms a layer containing an oxide of the first element on the surface of the target object.

[0109] At least a portion of the surface of the lithium silicate composite particles, which are the target, is covered with a carbon coating. The first element contained in the raw material gas can pass through this carbon coating and reach the surface of the lithium silicate composite particles. The first element is then deposited directly on the surface of the lithium silicate composite particles. Therefore, the first element is located more in the vicinity of the surface of the lithium silicate composite particles. The formed first coating contains an oxide of the first element as well as a carbon material derived from the carbon coating. Note that, in the portion of the surface of the lithium silicate composite particles, which is the target, that is not covered with the carbon coating, the first element contained in the raw material gas is deposited on the surface of the lithium silicate composite particles.

[0110] In the ALD method, a self-limiting mechanism functions, allowing the first element to deposit on the surface of the target object in atomic layers. In the ALD method, the thickness of the first coating is controlled by the number of cycles, each cycle consisting of: supply (pulse) of source gas → exhaust (purge) of source gas → supply (pulse) of oxidant → exhaust (purge) of oxidant. In the ALD method, one cycle may consist of: supply (pulse) of oxidant → exhaust (purge) of oxidant → supply (pulse) of source gas → exhaust (purge) of source gas. By controlling the thickness of the first coating to be approximately the same as that of the carbon coating, the oxide of the first element can be distributed throughout the entire carbon coating, although there is a concentration gradient. By controlling the thickness of the first coating to be thinner than that of the carbon coating, a first coating containing an oxide of the first element and a carbon material is formed on the surface side of the lithium silicate composite particle, and a second coating derived from the remainder of the carbon coating is formed at a position farther away from the surface of the lithium silicate composite particle than the first coating.

[0111] The precursor is an organometallic compound containing the first element, and various organometallic compounds that have been used in the ALD method can be used as the precursor.

[0112] Examples of precursors containing Ti include bis(t-butylcyclopentadienyl)titanium(IV) dichloride (C 18 H 26Examples of precursors that contain aluminum include titanium(IV) diisopropoxide-bis(2,2,6,6-tetramethyl-3,5-heptanedionate) (Ti[OCC(CH)CHCOC(CH)](OCH)), titanium tetrachloride (TiCl), titanium(IV) isopropoxide (Ti[OCH(CH)]), and titanium(IV) ethoxide (Ti[O(CH)]). Examples of precursors containing aluminum include trimethylaluminum ((CH)Al) (TMA).

[0113] The source gas may contain multiple types of precursors. Different types of precursors may be supplied to the reaction chamber simultaneously or sequentially. Alternatively, the type of precursor contained in the source gas may be changed for each cycle.

[0114] The oxidizing agent may be any oxidizing agent conventionally used in the ALD method. Examples of the oxidizing agent include water, oxygen, and ozone. The oxidizing agent may be supplied to the reaction chamber as plasma using the oxidizing agent as a raw material.

[0115] The conditions for the ALD method are not particularly limited. The oxygen deficiency in the oxide of the first element can be controlled, for example, by adjusting the temperature in the reaction chamber (the temperature of the atmosphere containing the precursor or the oxidizing agent), the pulse time of the oxidizing agent, etc.

[0116] The temperature of the atmosphere containing the precursor or oxidizing agent in the reaction chamber may be, for example, 25° C. or higher and 200° C. or lower, or 50° C. or higher and 150° C. or lower. From the same viewpoint, the pressure in the reaction chamber during the treatment may be, for example, 1×10 -5 Pa or more, 1×10 -2 Pa or less, and -4 Pa or more, 1×10 -3The pulse time of the source gas may be 0.01 seconds or more and 5 seconds or less, or 0.05 seconds or more and 3 seconds or less. The pulse time of the oxidizing agent may be 0.005 seconds and 3 seconds or less.

[0117] E. Manufacturing method of electrochemical element An electrochemical device according to an embodiment of the present disclosure includes the first active material described above. This electrochemical device can be obtained by supporting the first active material having a first coating on the surface of a current collector. This electrochemical device can also be obtained by supporting lithium silicate composite particles coated with a carbon coating on the surface of a current collector, and then forming the first coating by a vapor phase method.

[0118] FIG. 7 is a flowchart showing a method for manufacturing an electrochemical device according to an embodiment of the present disclosure.

[0119] The manufacturing method shown in FIG. 7 includes a preparation step of preparing lithium silicate composite particles that contain a silicate phase and a silicon phase dispersed within the silicate phase, and at least a portion of the surface of which is coated with a carbon coating containing a carbon material; a support step of supporting the lithium silicate composite particles on the surface of a current collector; and a coating step of exposing the lithium silicate composite particles to a gas phase containing a first element other than a non-metallic element to introduce the first element into the carbon coating, thereby forming an active material layer in which a first coating containing an oxide of the first element and a carbon material is formed on at least a portion of the surface of the lithium silicate composite particles.

[0120] (I) Preparation step of lithium silicate composite particles (S21) Lithium silicate composite particles coated with a carbon film are prepared in the same manner as the steps (ii) to (i-iv) of the lithium silicate composite particle preparation step in the active material particle production method.

[0121] (II) Lithium silicate composite particle supporting step (S22) A slurry in which the prepared negative electrode mixture containing the lithium silicate composite particles is dispersed in a dispersion medium is applied to the surface of the current collector, and the slurry is dried, thereby forming a precursor of the active material layer on the surface of the current collector.

[0122] The dispersion medium is not particularly limited, but examples thereof include water, alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0123] (III) First coating formation step (S23) A current collector including a precursor of the active material layer is exposed to a gas phase containing a first element. This introduces the first element into the carbon coating, and at least a portion of the surface of the lithium silicate composite particles contained in the precursor is covered with a first coating containing an oxide of the first element and a carbon material. This forms an active material layer. As described above, the gas phase method is preferably the ALD method.

[0124] The precursor and oxidant used in the ALD method can be the same as those used in the step (ii) of forming the first coating in the method for producing active material particles.

[0125] The conditions for the ALD method are not particularly limited. Examples of the temperature of the atmosphere containing the precursor or oxidant, the pressure in the reaction chamber during the treatment, and the pulse time of the source gas are the same as those of the temperature of the atmosphere containing the precursor or oxidant, the pressure in the reaction chamber during the treatment, and the pulse time of the source gas shown in the first coating formation step (ii) in the method for producing active material particles.

[0126] (IV) Rolling process (S24) After forming the first coating, the active material layer may be rolled. The conditions for rolling are not particularly limited and may be appropriately set so that the active material layer has a predetermined thickness or density. This increases the density of the active material layer, thereby increasing the capacity of the electrochemical device.

[0127] 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.

[0128] Example 1 [Preparation of negative electrode] (1) Preparation of silicon particles Coarse silicon particles (3N, average particle size 10 μm) were loaded into a pot (SUS, volume 500 mL) of a planetary ball mill (Fritsch, P-5), 24 SUS balls (diameter 20 mm) were placed in the pot, the lid was closed, and the mixture was ground at 200 rpm in an inert atmosphere until the average particle size reached 150 nm, thereby preparing silicon particles.

[0129] (2) Coating of silicon particles with carbon phase A carbon material was deposited on the surface of silicon particles by chemical vapor deposition. Specifically, silicon particles were introduced into an acetylene gas atmosphere and heated to 700°C to thermally decompose the acetylene gas, which was then deposited on the surface of the silicon particles to form a carbon phase. The amount of carbon material was 10 parts by mass per 100 parts by mass of silicon particles.

[0130] (3) Preparation of lithium silicate composite particles Silicon dioxide and lithium carbonate were mixed at an atomic ratio (Si / Li) of 1.05, and the mixture was calcined in air at 950°C for 10 hours to obtain lithium silicate represented by Li2Si2O5 (z=0.5). The obtained lithium silicate was then pulverized to an average particle size of 10 μm.

[0131] Lithium silicate (Li2Si2O5) with an average particle size of 10 μm and carbon-coated silicon were mixed in a mass ratio of 70:30. The mixture was placed in a 500 mL stainless steel pot (P-5, manufactured by Fritsch), 24 20 mm diameter stainless steel balls were placed in the pot, and the lid was closed. The mixture was stirred at 200 rpm for 50 hours in an inert atmosphere.

[0132] Next, the powder mixture was taken out in an inert atmosphere and sintered at 800°C for 4 hours under pressure from a hot press in an inert atmosphere to obtain a sintered body of the mixture, which was then crushed to obtain lithium silicate composite particles.

[0133] The crystallite size of the silicon phase calculated from the diffraction peak attributable to the Si(111) plane by XRD analysis using the Scherrer equation was 15 nm. In the silicate phase, the Si / Li ratio was 1.0, and the Li2Si2O5 content measured by Si-NMR was 70 mass% (the silicon phase content was 30 mass%).

[0134] (4) Coating of lithium silicate composite particles with carbon film The obtained lithium silicate composite particles were passed through a 40 μm mesh and then mixed with coal pitch (MCP250, manufactured by JFE Chemical Corporation). The mixture of lithium silicate composite particles and pitch was fired at 800°C for 5 hours in an inert atmosphere to form a carbon coating on the surface of the lithium silicate composite particles. The amount of carbon coating was 5 mass% based on the total mass of the lithium silicate composite particles and the carbon coating. Then, using a sieve, particles with an average particle size of 10 μm, which comprised lithium silicate composite particles and a carbon coating formed on their surfaces, were separated. The thickness of the carbon coating was 50 nm.

[0135] (5) Preparation of negative electrode precursor Lithium silicate composite particles with a carbon coating and a second active material (graphite) were mixed in a mass ratio of 5:95 and used as the negative electrode active material. Water was added to a negative electrode mixture containing the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), and lithium polyacrylate in a mass ratio of 96.5:1:1.5:1, and the mixture was then stirred using a mixer (TK Hibismix, manufactured by Primix Corporation) to prepare a negative electrode slurry. Next, a 1 m thick layer was applied to the surface of copper foil. 2 The negative electrode slurry was applied to both sides of the copper foil so that the mass of the negative electrode mixture was 190 g per sheet, and the coating was dried to form a negative electrode mixture with a density of 1.5 g / cm. 3The thickness of the negative electrode active material layer in the negative electrode precursor was 202 μm.

[0136] (6) Formation of the first and second coatings The negative electrode precursor was placed in a predetermined reaction chamber, and a first coating was formed on the surface of the negative electrode precursor by the ALD method according to the following procedure.

[0137] Vaporized oxidant (HO) was supplied to the reaction chamber containing the negative electrode precursor. The pulse time was 0.005 seconds. The temperature of the atmosphere containing the oxidant in the reaction chamber was controlled at 150°C, and the pressure was controlled at 260 Pa. After 30 seconds, excess oxidant was purged with nitrogen gas.

[0138] Next, a precursor (TDMAT) serving as a source of the first element (Ti) was vaporized and supplied to the reaction chamber containing the negative electrode precursor. The pulse time was 0.1 seconds. The temperature of the atmosphere containing the precursor in the reaction chamber was controlled at 150°C and the pressure at 260 Pa. After 30 seconds, the surface of the negative electrode precursor was covered with a monolayer of the precursor, and excess precursor was purged with nitrogen gas.

[0139] The first coating containing titanium was formed by repeating the process of supplying an oxidizing agent, purging, supplying a precursor, and purging 22 times. The thickness of the first coating was adjusted so that it was thinner than the carbon coating, and the first coating and the second coating covering the first coating were simultaneously formed.

[0140] The first and second coatings were analyzed by SEM, EDS, ICP, etc. The first coating contained Ti and C. The second coating contained C. The thickness of the first coating, T1 A The thickness of the second coating, T2, was 5 nm. A The thickness was 45 nm. XANES analysis confirmed that the Ti-containing oxide contained in the first coating had a crystalline structure with oxygen vacancies. TiO 2-x The x value was about 0.1.

[0141] After the first coating and the second coating were formed, the negative electrode active material layer was rolled to obtain a negative electrode.

[0142] [Preparation of positive electrode] N-methyl-2-pyrrolidone (NMP) was added to a positive electrode mixture containing lithium cobalt oxide, acetylene black, and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5, and the mixture was stirred using a mixer (TK Hibismix, manufactured by Primix Corporation) to prepare a positive electrode slurry. The positive electrode slurry was then applied to the surface of an aluminum foil, the coating was dried, and the foil was rolled to form a positive electrode slurry having a density of 3.6 g / cm on both sides of the aluminum foil. 3 A positive electrode having the positive electrode active material layer formed thereon was produced. The thickness of the positive electrode active material layer was 138 μm.

[0143] [Preparation of electrolyte] An electrolyte solution was prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7.

[0144] [Secondary battery production] A tab was attached to each electrode, and the positive and negative electrodes were spirally wound with the separator interposed therebetween so that the tabs were positioned at the outermost periphery to prepare an electrode assembly. The electrode assembly was inserted into an exterior case made of aluminum laminate film and vacuum dried at 105°C for 2 hours. After that, an electrolyte solution was poured into the exterior case, and the opening of the exterior case was sealed to obtain a secondary battery A1.

[0145] Example 2 In the formation of the first and second coatings (6), a series of operations consisting of supplying an oxidant, purging, supplying a precursor, and purging was repeated 44 times, except that a first active material was produced in the same manner as in Example 1, and a secondary battery A2 was fabricated.

[0146] The first coating contained Ti and C. Thickness T1 of the first coating A is 10 nm, the thickness of the second coating T2 AThe thickness was 40 nm. XANES analysis confirmed that the Ti-containing oxide contained in the first coating had a crystalline structure with oxygen vacancies. TiO 2-x The x value was about 0.1.

[0147] Example 3 In the formation of the first and second coating films (6), a first active material was produced in the same manner as in Example 1, except that trimethylaluminum was used as the precursor serving as the source of the first element (Al), and a secondary battery A3 was fabricated.

[0148] The first coating contained Al and C. Thickness T1 of the first coating A is 5 nm, the thickness of the second coating T2 A The thickness was 45 nm. XANES analysis confirmed that the Al-containing oxide contained in the first coating had a crystalline structure with oxygen vacancies. AlO 1.5-y The y value was about 0.1.

[0149] Example 4 In the formation of the first and second coatings (6), trimethylaluminum was used as the precursor, which was the supply source of the first element (Al). The temperature of the atmosphere containing the oxidizing agent in the reaction chamber was set to 120°C. The temperature of the atmosphere containing the precursor in the reaction chamber was set to 120°C. A series of operations consisting of supplying the oxidizing agent, purging, supplying the precursor, and purging was repeated 44 times. Except for the above, the first active material was produced in the same manner as in Example 1, and a secondary battery A4 was fabricated.

[0150] The first coating contained Al and C. Thickness T1 of the first coating A is 10 nm, the thickness of the second coating T2 A The thickness was 40 nm. XANES analysis confirmed that the Al-containing oxide contained in the first coating had a crystalline structure with oxygen vacancies. AlO 1.5-y The y value was about 0.1.

[0151] Comparative Example 1 Except for not performing the formation of the first coating and the second coating (6), an active material was produced in the same manner as in Example 1, and a secondary battery B1 was fabricated. The active material was coated with a carbon coating having a thickness of 50 nm.

[0152] Comparative Example 2 In the formation of the first and second coatings (6), the pulse time when vaporizing and supplying the oxidizing agent (HO) was 0.015 seconds. The temperature of the atmosphere containing the oxidizing agent in the reaction chamber was 200°C. The temperature of the atmosphere containing the precursor in the reaction chamber was 200°C. Except for the above, the first active material was produced in the same manner as in Example 1, and a secondary battery B2 was fabricated.

[0153] First coating thickness T1 A is 5 nm, the thickness of the second coating T2 A The thickness was 45 nm. XANES analysis confirmed that the Ti-containing oxide contained in the first coating had a crystalline structure without oxygen vacancies. TiO 2-x The x value was 0.

[0154] Comparative Example 3 In the formation of the first and second coatings (6), the pulse time when vaporizing and supplying the oxidizing agent (HO) was 0.015 seconds. The temperature of the atmosphere containing the oxidizing agent in the reaction chamber was 200°C. The temperature of the atmosphere containing the precursor in the reaction chamber was 200°C. A series of operations consisting of supplying the oxidizing agent, purging, supplying the precursor, and purging was repeated 44 times. Except for the above, the first active material was produced in the same manner as in Example 1, and a secondary battery B3 was fabricated.

[0155] First coating thickness T1 A is 10 nm, the thickness of the second coating T2 A The thickness was 40 nm. XANES analysis confirmed that the Ti-containing oxide contained in the first coating had a crystalline structure without oxygen vacancies. TiO 2-x The x value was 0.

[0156] The batteries prepared as above in the Examples and Comparative Examples were evaluated as follows.

[0157] [Evaluation of rate characteristics: (1C capacity / 0.1C capacity) measurement] The battery was charged at a constant current of 1 C at 25°C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 1 / 20 C. After a 10-minute break, the battery was discharged at a constant current of 1 C at 25°C until the voltage reached 2.5 V, and the discharge capacity at this point was calculated as the 1 C capacity.

[0158] The battery was charged at a constant current of 1 C at 25°C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current dropped to 1 / 20 C. After a 10-minute break, the battery was discharged at a constant current of 0.1 C at 25°C until the voltage reached 2.5 V, and the discharge capacity at this point was calculated as the 0.1 C capacity. The ratio of the 1 C capacity to the 0.1 C capacity (1 C capacity / 0.1 C capacity) was calculated.

[0159] [Evaluation of cycle characteristics: measurement of capacity retention rate] Charge and discharge were repeated under the following conditions. <Charging> At 25°C, constant current charging was performed at a current of 1 C until the voltage reached 4.2 V, and then constant voltage charging was performed at a voltage of 4.2 V until the current reached 1 / 20 C.

[0160] <Discharge> At 25°C, constant current discharge was carried out at a current of 1C until the voltage reached 2.5V.

[0161] The rest period between charge and discharge was 10 minutes. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle was calculated as the capacity retention rate.

[0162] The evaluation results are shown in Table 1.

[0163] [Table 1]

[0164] In batteries A1 to A4, lithium silicate composite particles were coated with a first coating containing an oxide of a first element having oxygen deficiency and a carbon material, resulting in a high capacity retention rate and (1C capacity / 0.1C capacity), as well as excellent cycle characteristics and rate characteristics.

[0165] On the other hand, in battery B1, the lithium silicate composite particles were not coated with a first coating containing an oxide of the first element having oxygen deficiency and a carbon material, so the cycle characteristics and rate characteristics were significantly reduced.

[0166] In batteries B2 and B3, the lithium silicate composite particles were coated with a first coating containing an oxide of the first element, and thus a higher capacity retention rate was obtained than in battery B1. However, because the oxide of the first element did not have oxygen deficiencies, the ionic conductivity of the active material particles was low, resulting in a decrease in rate characteristics. [Industrial Applicability]

[0167] According to the present disclosure, it is possible to provide an electrochemical device with high capacity and long life. The electrochemical device according to the present disclosure is useful as a main power source for mobile communication devices, portable electronic devices, and the like.

[0168] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Explanation of symbols]

[0169] 1 electrode group 2 positive leads 3 Negative lead 4 Battery case 5 Sealing plate 6 Negative terminal 7 Gasket 8. Seal 20 Active material particles 21 Silicate phase 22 Silicon phase 23 Lithium silicate composite particles 24 Primary particles 26 Second coating 27 First coating

Claims

1. Composite particles including a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase; a first coating that covers at least a portion of the surface of the composite particle; the first coating includes an oxide of a first element having oxygen deficiency and a carbon material; The active material particles, wherein the first element includes at least one element selected from the group consisting of Al, Ti, Si, Zr, Mg, Nb, Ta, Sn, Ni, and Cr.

2. The oxide of the first element is MeO ２－ｘ 2. The active material particles according to claim 1, comprising an oxide represented by the formula: wherein Me is at least one selected from the group consisting of Ti, Si, Zr, and Sn, and 0<x≦1.95 is satisfied.

3. The oxide of the first element is MeO １．５－ｙ 2. The active material particles according to claim 1, comprising an oxide represented by the formula: wherein Me is Al, and 0<y≦1.47 is satisfied.

4. The oxide of the first element is MeO １－ｚ 2. The active material particles according to claim 1, comprising an oxide represented by the formula: wherein Me is at least one element selected from the group consisting of Mg and Ni, and 0<z≦0.9 is satisfied.

5. The oxide of the first element is MeO ３－ｕ 2. The active material particles according to claim 1, comprising an oxide represented by the formula: wherein Me is Cr, and 0<u≦2.1 is satisfied.

6. Thickness T1 of the first coating Ａ The active material particles according to any one of claims 1 to 5, wherein the average particle diameter is 0.1 nm or more and 50 nm or less.

7. the active material particles further include a second coating film that covers at least a portion of the first coating film and has a different conductivity from the first coating film; 7. The active material particles according to claim 1, wherein the second coating is substantially free of an oxide of the first element.

8. The active material particles according to claim 7 , wherein the second coating contains a carbon material.

9. The active material particles according to claim 7 or 8, wherein the thickness T1 A of the first coating and the thickness T2 A of the second coating satisfy the relationship 10≦T2 A / T1 A ≦500.

10. a current collector; and an active material layer supported on the current collector; An electrochemical device, wherein the active material layer comprises the active material particles according to any one of claims 1 to 9.

11. a first electrode, a second electrode, and an electrolyte; An electrochemical device, wherein one of the first electrode and the second electrode is constituted by the electrochemical element according to claim 10 .

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