Active material particles, electrochemical element, and manufacturing method thereof, and electrochemical device

Abstract

Each one of the active material particles according to the present invention is provided with: a lithium silicate composite particle that contains a lithium silicate phase and silicon particles dispersed in the lithium silicate phase; and a first coating film that covers at least a part of the surface of the lithium silicate composite particle. The first coating film contains carbon atoms and an oxide of a first element that is other than a non-metallic element; and if T1A is the thickness of the first coating film, the element ratio Rb of the first element to the carbon atoms of the first coating film at the position of 0.25T1A from the surface of the lithium silicate composite particle and the element ratio Rt of the first element to the carbon atoms of the first coating film at the position of 0.75T1A from the surface of the lithium silicate composite particle satisfy Rb > Rt.

Description

[Technical field]

[0001] The present disclosure relates primarily to improvements in active material particles. [Background technology]

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

[0003] [Patent Document 1] JP 2017-97999 A Summary of the Invention

[0004] One of the performance requirements for electrochemical devices is to increase capacity. For example, in lithium-ion secondary batteries, the use of silicon compounds as negative electrode materials has been 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 negative electrode materials. Therefore, even when silicon compounds are used as active material particles, it is necessary to suppress the decrease in the capacity retention rate of electrochemical devices.

[0005] One aspect of the present disclosure is a lithium silicate composite particle including a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and a first coating covering at least a portion of a surface of the lithium silicate composite particle, the first coating including an oxide of a first element other than a nonmetallic element and carbon atoms, and a thickness of the first coating being T1 A When the first coating is formed on the surface of the lithium silicate composite particle, the first coating is formed on the surface of the lithium silicate composite particle. A and the element ratio Rb of the first element to the carbon atom at the position of 0.75T1 from the surface of the lithium silicate composite particle of the first coating. AThe element ratio Rt of the first element to the carbon atom at the position satisfies Rb>Rt.

[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 a separator interposed therebetween, wherein one of the first electrode and the second electrode is constituted by the above-described electrochemical element.

[0008] Yet another aspect of the present disclosure relates to a method for producing active material particles, the method comprising: a preparation step of preparing lithium silicate composite particles which contain a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and at least a portion of the surface of which is covered with a carbon coating containing carbon atoms; and a coating formation 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 atoms on at least a portion of the surface of the lithium silicate composite particles.

[0009] Yet another aspect of the present disclosure relates to a method for manufacturing an electrochemical element, comprising: a preparation step of preparing lithium silicate composite particles which contain a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and at least a portion of a surface of which is covered with a carbon coating containing carbon atoms; a supporting step of supporting the lithium silicate composite particles on a surface of a current collector; and a coating formation 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 an oxide of the first element and a first coating containing the carbon atoms are formed on at least a portion of the surface of the lithium silicate composite particles.

[0010] According to the present disclosure, it is possible to increase the capacity retention rate of an electrochemical device. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an active material particle according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is an enlarged schematic cross-sectional view showing a main part of the active material particle shown in FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing in detail an active material particle according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic perspective view, with a portion cut away, of a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure. [Diagram 5] FIG. 5 is a flowchart showing a method for producing active material particles according to one embodiment of the present disclosure. [Figure 6] FIG. 6 is a flow chart showing a method for manufacturing an electrochemical device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A. Active material particles The active material particle according to the embodiment of the present disclosure includes a lithium silicate composite particle containing lithium and a first coating that coats at least a part of the surface of the lithium silicate composite particle. The first coating of the lithium silicate composite particle contains carbon atoms together with an oxide of a first element other than nonmetallic elements. The first coating can improve the chemical stability of the lithium silicate composite particle while maintaining electrical conductivity. The active material particle according to the embodiment of the present disclosure is preferably used as a negative electrode active material for a lithium ion secondary battery.

[0013] The first element is present in a greater amount closer to the surface of the lithium silicate composite particle. This improves the effect of suppressing corrosion of the lithium silicate composite particle. Since the first coating further contains carbon atoms, the electrical conductivity of the active material particles is improved.

[0014] Specifically, the thickness of the first coating is T1 A When the first coating is formed, the lithium silicate composite particle is 0.25T1 A The element ratio Rb (=first element / carbon atom) of the first element to the carbon atom at the position of 0.75T1 from the surface of the lithium silicate composite particle of the first coating A The element ratio Rt (=first element / carbon atom) of the first element to the carbon atom at the position satisfies Rb>Rt. A The position of the first coating is 0.25T1 from the interface between the first coating and the lithium silicate composite particle. A The position is equivalent to the position of 0.75T1 from the surface of the lithium silicate composite particle of the first coating. A The position of the first coating is 0.75T1 from the interface between the first coating and the lithium silicate composite particle. A is synonymous with the position of.

[0015] The element ratio Rb and the element ratio Rt may satisfy Rb / Rt>1.3, Rb / Rt>2, or Rb / Rt>3.

[0016] The element ratio (=first element / carbon atom, hereinafter referred to as element ratio R) inside the first coating can be obtained by evaluating the element distribution state (depth profile) using energy dispersive X-ray spectroscopy (EDS). A Divide it into 4 equal parts and remove 0.25T1 from the surface of the lithium silicate composite particle. A and the surface of the lithium silicate composite particle. A This evaluation is performed for a number of lithium silicate composite particles (for example, five particles) and the element ratio at each point can be determined by averaging.

[0017] The elemental ratio may be determined by evaluating the distribution of the first element and the carbon atoms using a combination of X-ray photoelectron spectroscopy (XPS (X-ray Photoelectron Spectroscopy), also known as electron energy-loss spectroscopy (EELS) or Electron Spectroscopy for Chemical Analysis (ESCA)) and ion etching.

[0018] The molar fraction of carbon atoms and the first element in the first coating may be taken as the element ratio R. The molar fraction can be calculated from the volume fraction (%) of the first element and carbon atoms using EDS or the like. The volume fraction (%) is calculated by multiplying the specific gravity (g / cm3) of each atom by the volume fraction (%). 3 ) and the molecular weight of each atom (g / mol), it can be converted to a mole fraction (%).

[0019] The element ratio R changes so as to become smaller from the surface of the lithium silicate composite particle toward the outside. This change may be continuous or stepwise, and may be sufficient as long as it can be understood as an overall trend.

[0020] For example, the depth profile at multiple locations (e.g., five locations) at different distances from the surface of the lithium silicate composite particle on a straight line in the thickness direction of the first coating is evaluated by EDS, and the element ratio R at each location is calculated. The element ratio R calculated in this manner is plotted on a graph with the horizontal axis representing the distance from the surface of the lithium silicate composite particle and the vertical axis representing the element ratio R. From this graph, if the approximation line or approximation curve obtained by the least squares method slopes downward to the right, it can be determined that, as a whole, the element ratio R decreases from the surface of the lithium silicate composite particle toward the outside.

[0021] [Lithium silicate composite particles] The lithium silicate composite particles according to this embodiment include a lithium silicate phase and silicon particles dispersed in the lithium silicate phase. The lithium silicate composite particles have a lithium silicate phase, which is the sea part of the sea-island structure, and silicon particles, which are the island parts.

[0022] 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 silicon particles dispersed in the lithium silicate phase.

[0023] 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.

[0024] (Lithium silicate phase) Since the lithium silicate phase (hereinafter, may be simply referred to as the silicate phase) has few sites that can react with lithium, 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.

[0025] 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.

[0026] The silicate phase is Li 2z SiO 2+z (z is 0 < z < 1). From the viewpoints of stability, ease of production, lithium ion conductivity, etc., z = 1 / 2 is more preferable.

[0027] The silicate phase may further include element M. Here, M may 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 silicate in a molten state. In addition, Al, Zr, Nb, Ta and La can improve the Vickers hardness while maintaining the ionic conductivity of the silicate phase. The content of element M may be, for example, 10 mol% or less, or 5 mol% or less, based on the total amount of elements other than O contained in the silicate phase.

[0028] (silicon particles) The silicon particles dispersed in the silicate phase have a particulate phase of simple silicon (Si) and are composed of single or multiple crystallites. The crystallite size of the silicon particles is not particularly limited. The crystallite size of the silicon particles 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 particles is 10 nm or more, the surface area of ​​the silicon particles can be kept small, so that the deterioration of the silicon particles accompanied by the generation of irreversible capacity is unlikely to occur. The crystallite size of the silicon particles is calculated by Scherrer's formula from the half-width of the diffraction peak assigned to the Si (111) plane in the X-ray diffraction (XRD) pattern of the silicon particles.

[0029] In order to increase the capacity and improve the cycle characteristics, the content of silicon particles in the lithium silicate composite particles may be, for example, 30% by mass or more and 80% by mass or less. By making the content of silicon particles 30% by mass or more, the proportion of the silicate phase is reduced, and the initial charge / discharge efficiency is likely to be improved. By making the content of silicon particles 80% by mass or less, the degree of expansion and contraction of the lithium silicate composite particles during charge and discharge is likely to be reduced.

[0030] (carbon phase) The lithium silicate composite particles may contain a carbon phase together with the silicate phase and the silicon particles, for example, the carbon phase covering at least a portion of the surface of the silicon particles and present at at least a portion of the interface between adjacent primary particles.

[0031] 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. Then, a calibration curve is created using a commercially available standard sample of the element, and the content of each element contained in the silicate phase is calculated.

[0032] Quantitative determination of each element in lithium silicate composite particles is also possible using ICP-AES analysis (inductively coupled plasma atomic emission spectroscopy), Auger electron spectroscopy (AES), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray photoelectron spectroscopy (XPS), etc.

[0033] [First coating] The first coating covers at least a portion of the surface of the lithium silicate composite particles, which are secondary particles.

[0034] The first coating contains an oxide of a first element other than a nonmetallic element and carbon atoms. The oxide and the carbon atoms are mixed in the first coating. However, as described above, the first element is present in greater amounts closer to the surface of the lithium silicate composite particle.

[0035] The average elemental ratio R of the first element to carbon atoms in the first coating A is not particularly limited. A may be, for example, 0.01 or more and 99 or less. In other words, the element ratio R A When is equal to or greater than 0.01 and equal to or less than 99, the coating is a first coating that includes a first element and carbon atoms.

[0036] 0.25T1 from the surface of the lithium silicate composite particle of the first coating AThe element ratio Rb of the first element to the carbon atom at the position is not particularly limited. The element ratio Rb may be, for example, 5 or more and 99 or less, 10 or more and 99 or less, or 20 or more and 99 or less.

[0037] 0.75T1 from the surface of the lithium silicate composite particle of the first coating A The element ratio Rt of the first element to the carbon atom at the position is not particularly limited. The element ratio Rt may be, for example, 0.01 or more and 10 or less, or 0.01 or more and 5 or less.

[0038] The first element is an element other than a nonmetallic element, and includes a metal element and a so-called metalloid element. In particular, in terms of the high corrosion inhibition effect of the lithium silicate composite particles, it is preferable that the first element includes 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, it is preferable that 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.

[0039] When two or more kinds of oxides are contained, the oxides may be mixed together or may be arranged in layers.

[0040] Examples of carbon include amorphous carbon with low crystallinity such as carbon black, coal, coke, charcoal, and activated carbon, and graphite with high crystallinity. Among them, amorphous carbon is preferred because it has low hardness and a large buffering effect on silicon particles that change 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 crystal structure, and examples of the graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0041] 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.

[0042] The thickness of the first coating can be measured by observing the cross section of the active material particles using an SEM or TEM.

[0043] 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 5 points on each particle. The average value of the thicknesses at these 50 points is calculated. After calculating this average value, data that differs from the obtained average value by 20% or more is excluded, and the average value is calculated again. This corrected average value is used as the thickness of the first coating, T1 A Let us assume that.

[0044] The starting point of the first coating is the interface between the mother particle (see below) formed by the lithium silicate composite particle and the first coating. For example, the starting point of the first coating can be regarded 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 regarded 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. When the second coating is formed, the end point of the first coating is the interface between the first coating and the second coating.

[0045] [Second Coating] At least a portion of the first coating may be covered with a conductive second coating, thereby further improving the conductivity of the active material particles.

[0046] The second coating is different from the first coating in that it does not contain an oxide of the first element. The fact that the second coating does not contain an oxide of the first element means that the intensity of the peak attributed to the first element obtained by SEM-EDS is equal to or lower than the detection limit.

[0047] 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 contained in the first coating.

[0048] The thickness of the second coating is not particularly limited. The second coating is preferably thin enough not to 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 can be measured by observing the cross section of the lithium silicate composite particles using a SEM or TEM, similar to the first coating.

[0049] The start 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.

[0050] Thickness of the first coating T1 A and the thickness of the second coating T2 A What 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 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.

[0051] Fig. 1 is a schematic cross-sectional view showing an active material particle according to an embodiment of the present disclosure, Fig. 2 is a schematic cross-sectional view showing an enlarged main part of the active material particle shown in Fig. 1.

[0052] The active material particle 20 includes a lithium silicate composite particle 23 , a first coating 27 covering the surface thereof, and a second coating 26 covering the first coating 27 .

[0053] 3 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 silicon particles 22 dispersed in the silicate phase 21. The silicon particles 22 are dispersed approximately uniformly in the silicate phase 21.

[0054] A carbon phase 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 particle 22.

[0055] 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.

[0056] B. Electrochemical element 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 includes the above-mentioned active material particles. Such an electrochemical element has excellent electrical conductivity and is inhibited from deteriorating, so that it is possible to provide an electrochemical device with high capacity and long life.

[0057] 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 the embodiment of the present disclosure is preferably used as a negative electrode for a lithium ion secondary battery.

[0058] C. Electrochemical Devices The electrochemical device according to the embodiment of the present disclosure includes a first electrode, a second electrode, and a separator interposed therebetween. One of the first electrode and the second electrode is formed of the electrochemical element described above. Such an electrochemical device has a high capacity and a long life.

[0059] An electrochemical device is a device that transfers electrons between substances to cause a chemical reaction. Examples of electrochemical devices include primary batteries, secondary batteries, capacitors, and air double layer capacitors. The electrochemical device according to the embodiment of the present disclosure is preferably a lithium ion secondary battery that uses lithium silicate composite particles as a negative electrode active material.

[0060] Hereinafter, the configurations of the negative electrode as the electrochemical element according to the embodiment of the present disclosure and the lithium ion secondary battery as the electrochemical device will be described.

[0061] [Negative electrode] The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer.

[0062] The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes at least the above-mentioned active material particles (hereinafter, may be referred to as a first active material). The negative electrode active material layer is formed as a layer including 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 includes the negative electrode active material as an essential component, and may include a binder, a conductive agent, a thickener, and the like as optional components.

[0063] The negative electrode active material may further include another active material (hereinafter, sometimes referred to as a second active material). An example of the second active material is 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 longer life can be expected.

[0064] Examples of conductive carbon materials include graphite, graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). Among them, graphite is preferred because of its excellent charge / discharge stability and low irreversible capacity. Graphite means a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, and graphitized mesophase carbon particles. The conductive carbon materials may be used alone or in combination of two or more.

[0065] The particle size of the conductive carbon material is not particularly limited. The average particle size of the conductive carbon material may be, for example, 1 μm or more and 30 μm or less.

[0066] 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.

[0067] As the negative electrode current collector, a non-porous conductive substrate (metal foil, etc.) or a porous conductive substrate (mesh, net, punched sheet, etc.) is used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, copper alloy, etc. The thickness of the negative electrode current collector is not particularly limited, but is preferably 1 μm or more and 50 μm or less, more preferably 5 μm or more and 20 μm or less, from the viewpoint of the balance between the strength and weight reduction of the negative electrode.

[0068] The binder may be, for example, 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, it is preferable to use crosslinked lithium polyacrylate.

[0069] Examples of conductive agents include carbon blacks such as acetylene black, conductive fibers such as carbon fibers and metal fibers, 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.

[0070] Examples of thickeners include carboxymethylcellulose (CMC) and its modified products (including salts such as Na salt), cellulose derivatives such as methylcellulose (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.

[0071] [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.

[0072] 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.

[0073] The positive electrode active material may be a lithium composite metal oxide. For example, 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 , Lia Mn2O4, Li a Mn 2-b M b O 4、 LiMePO 4、 Li2MePO4F is an example. 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 (e.g., at least one 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.

[0074] 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.

[0075] 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.

[0076] [Separator] The separator is interposed between the positive electrode and the negative electrode. The separator has high ion permeability and has appropriate mechanical strength and insulation 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] [Electrolyte] The electrochemical device according to 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 may contain a known additive.

[0078] The solvent used may be an aqueous solvent or a non-aqueous solvent. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, and cyclic carboxylates. Examples of the cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of the cyclic carboxylates include γ-butyrolactone (GBL) and γ-valerolactone (GVL). The non-aqueous solvents may be used alone or in combination of two or more.

[0079] 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.), etc. The lithium salts may be used alone or in combination of two or more.

[0080] An example of the structure of the 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 laminated type electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween may be used. In addition, an electrode group of another form may be applied. The secondary battery may be in any form, such as a cylindrical type, a square type, a coin type, a button type, or a laminate type.

[0081] FIG. 4 is a schematic perspective view of a partially cutaway 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 housed in 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, the positive electrode, and the 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 injection port blocked by a plug 8 and a negative electrode terminal 6 insulated from the sealing plate 5 by a gasket 7.

[0082] 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 the upper part of the electrode group 1 to separate the electrode group 1 from the sealing plate 5 and to separate the negative electrode lead 3 from the battery case 4.

[0083] D. Method for producing 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 that contain a silicate phase and silicon particles dispersed in the silicate phase and at least a portion of the surface of which is covered with a carbon coating containing carbon atoms, and a coating formation step of exposing the lithium silicate composite particles to a gas phase containing a first element other than nonmetallic elements to introduce the first element into the carbon coating and form a first coating containing an oxide of the first element and carbon atoms 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 covers the lithium silicate composite particles, forming the first coating.

[0084] FIG. 5 is a flowchart showing a method for producing active material particles according to one embodiment of the present disclosure.

[0085] (i) Preparation step of lithium silicate composite particles (S11) (ii) Preparation of silicon particles First, silicon particles are prepared.

[0086] Silicon particles can be obtained by chemical vapor deposition (CVD), thermal plasma, physical pulverization, etc. In the following method, for example, silicon nanoparticles with an average particle size of 10 nm to 200 nm can be synthesized. The average particle size of silicon particles means the particle size (volume average particle size) at which the volumetric integrated value is 50% in the volume particle size distribution measured by the laser diffraction scattering method.

[0087] (a) Chemical vapor deposition In the CVD method, for example, a silane compound is oxidized or reduced in a gas phase to generate silicon particles. The reaction temperature may be set to, for example, 400° C. or higher and 1300° C. or lower.

[0088] Examples of the silane compound include silicon hydrides such as silane and disilane, halogenated silanes, and alkoxysilanes. Examples of the halogenated silanes include dichlorosilane, trichlorosilane, and tetrachlorosilane. Examples of the alkoxysilanes include tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane.

[0089] For example, when silicon hydride is contacted with an oxidizing gas in the gas phase, a composite of silicon particles and silicon oxide particles is obtained. That is, the gas phase atmosphere may be an oxidizing gas atmosphere. The composite is washed with, for example, hydrofluoric acid to remove the silicon oxide and obtain silicon particles.

[0090] When reducing halogenated silanes, alkoxysilanes, etc., it is sufficient to contact a silane compound with molten metal that has been finely atomized by an atomization method. Na, K, Mg, Ca, Zn, Al, etc. can be used as the molten metal. An inert gas, halogenated silane, hydrogen gas, etc. can be used as the atomization gas. That is, the gas phase atmosphere can be an inert gas or reducing gas atmosphere.

[0091] (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 desirable because it is a non-polarized discharge and impurities are less likely to become mixed into the silicon particles.

[0092] The raw material may 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 the silicon bonds and solidifies during cooling to generate silicon particles.

[0093] (c) Physical crushing method The physical pulverization method (mechanical milling method) is a method in which coarse silicon particles are pulverized by a pulverizer such as a ball mill, a bead mill, etc. The inside of the pulverizer may be, for example, an inert gas atmosphere.

[0094] (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.

[0095] 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.

[0096] (a) Chemical vapor deposition In the CVD method, silicon particles are introduced into a hydrocarbon gas atmosphere, which is then heated to deposit the carbon material produced by pyrolysis of the hydrocarbon gas on the particle surface, forming a carbon phase. The temperature of the hydrocarbon gas atmosphere may be, for example, 500°C to 1000°C. As the hydrocarbon gas, chain hydrocarbon gases such as acetylene and methane, and aromatic hydrocarbons such as benzene, toluene, and xylene may be used.

[0097] (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, and the resulting solution is mixed with silicon particles and dried. The silicon particles coated with the carbon precursor are then heated in an inert gas atmosphere at a temperature of, for example, 600° C. to 1000° C. to carbonize the carbon precursor and form a carbon phase.

[0098] (i-iii) Synthesis of lithium silicate composite particles A silicate phase raw material is prepared.

[0099] The raw material for the silicate phase may be a raw material mixture containing a Si raw material and a Li raw material in a specified ratio. The raw material mixture is melted and the molten liquid is passed through a metal roll to form flakes, to obtain silicate. Alternatively, the raw material mixture may not be melted, but may be fired at a temperature below the melting point to synthesize silicate through a solid-phase reaction.

[0100] 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. Among them, carbonates, oxides, hydroxides, etc. are preferred.

[0101] Next, silicon particles at least part of whose surface is coated with a carbon phase (hereinafter also referred to as carbon-coated silicon particles) are blended with the silicate and the two are mixed. For example, lithium silicate composite particles are produced through the following steps.

[0102] First, carbon-coated silicon particles and silicate powder are mixed in a mass ratio of, for example, 20:80 to 95:5.

[0103] Next, the mixture of carbon-coated silicon particles and 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 wet mix it. A predetermined amount of organic solvent may be charged into the grinding vessel all at once at the beginning of grinding, or may be charged into the grinding vessel intermittently in multiple batches during the grinding process. The organic solvent serves to prevent the material to be ground from adhering to the inner wall of the grinding vessel. As the organic solvent, alcohol, ether, fatty acid, alkane, cycloalkane, silicate ester, metal alkoxide, etc. can be used.

[0104] The mixture is then sintered by heating at 450°C to 1000°C under pressure in an inert gas atmosphere (e.g., argon, nitrogen, etc.). For sintering, a sintering device capable of applying pressure in an inert atmosphere, such as a hot press or spark plasma sintering, can be used. 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 as the sea portion and the silicon particles as the islands.

[0105] 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.

[0106] (i-iv) Coating of lithium silicate composite particles with carbon films Next, at least a portion of the surface of the lithium silicate composite particles is coated with a carbon coating, and the carbon atoms contained in the first coating are derived from the carbon coating.

[0107] Examples of methods for forming a carbon coating on the surface of lithium silicate composite particles include a chemical vapor deposition method using a chain hydrocarbon gas such as acetylene or methane as a raw material, and a method in which coal pitch, petroleum pitch, phenol resin, or the like is mixed with lithium silicate composite particles and heated to carbonize them. Carbon black may be attached to the surface of the lithium silicate composite particles.

[0108] 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 a carbon source for the first coating, the thickness of the carbon coating is desirably equal to or greater than the desired first coating. The carbon coating may be 0.1 nm or more, or may be 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.

[0109] Finally, a step of washing the lithium silicate composite particles having the carbon coating with an acid may be performed. For example, by washing the composite particles with an acidic aqueous solution, it is possible to dissolve and remove trace amounts of alkaline components that may be present on the surface of the lithium silicate composite particles. As the acidic aqueous solution, an aqueous solution of an inorganic acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid, or carbonic acid, or an aqueous solution of an organic acid such as citric acid or acetic acid can be used.

[0110] (ii) Step of forming a first coating (S12) The lithium silicate composite particles having the 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 carbon atoms is formed on at least a portion of the surface of the lithium silicate composite particles.

[0111] Examples of the gas phase method include CVD, ALD, and physical vapor deposition (PVD). In particular, the ALD method is preferred because it can form the first coating at a relatively low temperature. According to the ALD method, the first coating can be formed in an atmosphere of 200° C. or less.

[0112] In the ALD method, an organometallic compound (precursor) containing a first element is used as a raw material for the first coating. In the ALD method, a raw material gas containing a vaporized precursor and an oxidizing agent are alternately supplied to a reaction chamber in which a target object is placed. As a result, a layer containing an oxide of the first element is formed on the surface of the target object.

[0113] At least a part of the surface of the lithium silicate composite particle, which is the object, 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 particle. The first element is then deposited as is on the surface of the lithium silicate composite particle. Therefore, the first element is arranged more in the vicinity of the surface of the lithium silicate composite particle. The formed first coating contains carbon atoms derived from the carbon coating as well as an oxide of the first element.

[0114] In the ALD method, the first element is deposited on the surface of the target object in atomic layers due to the self-limiting effect. In the ALD method, the thickness of the first coating is controlled by the number of cycles, which is one cycle consisting of supply of source gas (pulse) → exhaust of source gas (purge) → supply of oxidizing agent (pulse) → exhaust of oxidizing agent (purge). If the thickness of the first coating is controlled to be approximately the same as that of the carbon coating, the oxide of the first element can be arranged throughout the carbon coating, although there is a concentration gradient. If the thickness of the first coating is controlled to be thinner than that of the carbon coating, a first coating containing an oxide of the first element and carbon atoms 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 to cover the first coating.

[0115] The precursor is an organometallic compound containing the first element. As the precursor, various organometallic compounds that have been conventionally used in the ALD method can be used.

[0116] An example of a precursor containing Ti is bis(t-butylcyclopentadienyl)titanium(IV) dichloride (C 18 H 26 C l2Examples of the precursors containing Al include trimethylaluminum ((CH3)3Al, TMA).

[0117] The source gas may contain a plurality of 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.

[0118] The oxidizing agent may be any oxidizing agent that has been used in the ALD method. Examples of the oxidizing agent include water, oxygen, ozone, etc. The oxidizing agent may be supplied to the reaction chamber as plasma using the oxidizing agent as a raw material.

[0119] The conditions of the ALD method are not particularly limited. In order to facilitate the arrangement of the first element in the vicinity of the surface of the lithium silicate composite particles, the temperature of the atmosphere containing the precursor or the oxidizing agent in the reaction chamber may be 10° C. or more and 200° C. or less, or 25° C. or more and 100° C. or less. From the same viewpoint, the pressure in the reaction chamber during the treatment is 1×10 -5 Pa or more 1×10 5 Pa or less, and -4 Pa or more 1×10 4 Pa or less.

[0120] In order to facilitate the arrangement of the first element 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 in the reaction chamber during the treatment is 1×10 -5 Pa or more 1×10 5 When the pressure is less than or equal to Pa, the pulse time of the source gas may be 0.01 seconds or more, and may be 0.05 seconds or more. The pulse time of the source gas may be 5 seconds or less, and may be 3 seconds or less.

[0121] E. Manufacturing method of electrochemical element The electrochemical element according to the embodiment of the present disclosure includes the first active material. The electrochemical element is obtained by supporting the first active material having the first coating on the surface of a current collector. The electrochemical element can also be obtained by supporting lithium silicate composite particles covered with a carbon coating on the surface of a current collector, and then forming the first coating by a gas phase method.

[0122] FIG. 6 is a flow chart showing a method for manufacturing an electrochemical device according to an embodiment of the present disclosure.

[0123] The latter manufacturing method includes a preparation step of preparing lithium silicate composite particles which contain a silicate phase and silicon particles dispersed in the silicate phase, and at least a portion of the surface of which is covered with a carbon coating containing carbon atoms; a supporting step of supporting the lithium silicate composite particles on the surface of a current collector; and a coating formation step of exposing the lithium silicate composite particles to a gas phase containing a first element other than non-metallic elements 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 carbon atoms is formed on at least a portion of the surface of the lithium silicate composite particles.

[0124] (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 in the steps (ii) to (i-iv) of preparing the lithium silicate composite particles in the method for producing active material particles.

[0125] (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.

[0126] 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.

[0127] (III) Step of forming first coating (S23) A current collector having a precursor of an active material layer is exposed to a gas phase containing a first element. As a result, the first element is introduced into the carbon coating, and at least a part of the surface of the lithium silicate composite particle contained in the precursor is covered with a first coating containing an oxide of the first element and carbon atoms. As a result, an active material layer is formed. As described above, the ALD method is preferably used as the gas phase method.

[0128] Examples of the precursor and oxidant used in the ALD method include the same ones as those shown as the steps (ii) to (i-iv) of forming the first coating film in the method for producing active material particles.

[0129] The conditions of the ALD method are not particularly limited. In order to facilitate the arrangement of the first element in the vicinity of the surface of the lithium silicate composite particles, the temperature of the atmosphere containing the precursor or the oxidizing agent may be 10° C. or higher and 200° C. or lower, or 25° C. or higher and 100° C. or lower. From the same viewpoint, the pressure in the reaction chamber during the treatment is 1×10 -5 Pa or more 1×10 5 Pa or less, and -4 Pa or more 1×10 4 Pa or less.

[0130] In order to facilitate the arrangement of the first element 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 in the reaction chamber during the treatment is 1×10 -5 Pa or more 1×10 5 When the pressure is less than or equal to Pa, the pulse time of the source gas may be 0.01 seconds or more, and may be 0.05 seconds or more. The pulse time of the source gas may be 5 seconds or less.

[0131] (IV) Rolling process (S24) After the first coating is formed, 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.

[0132] 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.

[0133] 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 (made of SUS, volume 500 mL) of a planetary ball mill (manufactured by 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 became 150 nm, to prepare silicon particles.

[0134] (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 at 700°C to pyrolyze the acetylene gas and deposit it on the surface of the silicon particles, forming a carbon phase. The amount of carbon material per 100 parts by mass of silicon particles was 10 parts by mass.

[0135] (3) Preparation of lithium silicate composite particles Silicon dioxide and lithium carbonate were mixed so that the atomic ratio (=Si / Li) was 1.05, and the mixture was fired in air at 950°C for 10 hours to obtain lithium silicate represented by Li2Si2O5 (z=0.5). The obtained lithium silicate was pulverized to an average particle size of 10 μm.

[0136] 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 charged into a pot (made of SUS, volume 500 mL) of a planetary ball mill (manufactured by Fritsch, P-5), 24 SUS balls (diameter 20 mm) were placed in the pot, the lid was closed, and the mixture was stirred at 200 rpm for 50 hours in an inert atmosphere.

[0137] Next, the powder mixture was taken out in an inert atmosphere, and sintered at 800°C for 4 hours in an inert atmosphere while applying pressure with a hot press machine to obtain a sintered body of the mixture. The sintered body was then pulverized to obtain lithium silicate composite particles.

[0138] The crystallite size of the silicon particles was calculated to be 15 nm using the Scherrer formula from the diffraction peaks assigned to the Si(111) plane by XRD analysis. In the silicate phase, the Si / Li ratio was 1.0, and the content of Li2Si2O5 measured by Si-NMR was 70 mass% (the content of silicon particles was 30 mass%).

[0139] (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 the 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 the 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 having an average particle size of 10 μm and comprising the lithium silicate composite particles and the carbon coating formed on the surface thereof were separated. The thickness of the carbon coating was 50 nm.

[0140] (5) Preparation of negative electrode precursor The lithium silicate composite particles with a carbon coating and a second active material (graphite) were mixed in a mass ratio of 5:95 to be used as the negative electrode active material. Water was added to a negative electrode mixture containing the negative electrode active material, sodium carboxymethylcellulose (CMC-Na), styrene butadiene rubber (SBR), and lithium polyacrylate in a mass ratio of 96.5:1:1.5:1, and then the mixture was stirred using a mixer (TK Hivismix, manufactured by Primix Corporation) to prepare a negative electrode slurry. Next, a 1 m thick layer was applied to the surface of the 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 unit area, and the coating was dried to obtain a density of 1.5 g / cm. 3 The thickness of the negative electrode active material layer in the negative electrode precursor was 202 μm.

[0141] (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 an ALD method according to the following procedure.

[0142] The precursor (TDMAT) serving as the 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 200°C, and the pressure was controlled 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.

[0143] Next, an oxidant (HO) was vaporized and supplied to the reaction chamber containing the negative electrode precursor. The pulse time was 0.015 seconds. The temperature of the atmosphere containing the oxidant was controlled at 200°C, and the pressure was controlled at 260 Pa. After 30 seconds, the excess oxidant was purged with nitrogen gas.

[0144] A series of operations consisting of supplying a precursor, purging, supplying an oxidizing agent, and purging was repeated 22 times to form a first coating containing titanium. The first coating was adjusted to be thinner than the carbon coating, and the first coating and a second coating covering the first coating were formed simultaneously.

[0145] The first coating was analyzed by SEM, EDS, ICP, etc. The first coating contained Ti and C. The minimum value of the element ratio R of the first element to the carbon atom was 0.03, and the maximum value was 8. The thickness T1 of the first coating A The thickness of the first coating was 0.25T1 A The element ratio Rb of the first element to the carbon atom at the position was 6.2. A The element ratio Rt of the first element to the carbon atom at the position was 0.08.

[0146] The composition of the second coating was analyzed in the same manner and found to contain C. The thickness of the second coating T2 A was 49 nm, and the sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0147] After the first coating and the second coating were formed, the negative electrode active material layer was rolled to obtain a negative electrode.

[0148] [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 Hivismix, 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 aluminum 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 of the above formula was formed. The thickness of the positive electrode active material layer was 138 μm.

[0149] [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.

[0150] [Preparation of secondary battery] A tab was attached to each electrode, and the positive and negative electrodes were spirally wound with a separator interposed therebetween so that the tabs were located at the outermost periphery to prepare an electrode group. The electrode group was inserted into an exterior body made of an aluminum laminate film and vacuum dried at 105°C for 2 hours, after which an electrolyte solution was poured in and the opening of the exterior body was sealed to obtain a secondary battery A1.

[0151] Example 2 In the formation of the first and second coatings (6), a series of operations consisting of supplying a precursor, purging, supplying an oxidizing agent, and purging was repeated 44 times, and the same procedure as in Example 1 was used to produce a first active material and a secondary battery A2. A is 2 nm, the thickness of the second coating T2 A was 48 nm, and the sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0152] The minimum value of the element ratio R of the first element to the carbon atoms was 0.03, and the maximum value was 7.4.A The element ratio Rb of the first element to the carbon atom at the position was 6.1. A The element ratio Rt of the first element to the carbon atom at the position was 0.1.

[0153] Example 3 In the formation of the first and second coatings (6), a series of operations consisting of supplying a precursor, purging, supplying an oxidizing agent, and purging was repeated 100 times, and the same procedure as in Example 1 was used to produce a first active material, and a secondary battery A3 was fabricated. A is 5 nm, the thickness of the second coating T2 A was 45 nm, and the sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0154] The minimum value of the element ratio R of the first element to the carbon atoms was 0.03, and the maximum value was 7.2. A The element ratio Rb of the first element to the carbon atom at the position was 5.7. A The element ratio Rt of the first element to the carbon atom at the position was 0.11.

[0155] Example 4 In the formation of the first and second coatings (6), a series of operations consisting of supplying a precursor, purging, supplying an oxidizing agent, and purging was repeated 200 times, and the same procedure as in Example 1 was used to produce a first active material, and a secondary battery A4 was fabricated. A is 10 nm, the thickness of the second coating T2 A was 40 nm, and the sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0156] The minimum value of the element ratio R of the first element to the carbon atoms was 0.03, and the maximum value was 6.8. AThe element ratio Rb of the first element to the carbon atom at the position was 5.0. A The element ratio Rt of the first element to the carbon atom at the position was 0.12.

[0157] Comparative Example 1 An active material was produced in the same manner as in Example 1, except that the coating of the lithium silicate composite particles with a carbon film (4) and the formation of the first film and the second film (6) were not performed, and a secondary battery B1 was fabricated.

[0158] Comparative Example 2 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 B2 was fabricated. The active material was covered with a carbon coating having a thickness of 50 nm.

[0159] Comparative Example 3 Except for not coating the lithium silicate composite particles with a carbon coating (4), an active material was produced in the same manner as in Example 4, and a secondary battery B3 was fabricated. The lithium silicate composite particles were covered with a coating containing titanium oxide, and the thickness of the coating was 10 nm.

[0160] [First charge / discharge] Each battery was charged at 25°C at a constant current of 1 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 rest period, the battery was discharged at a constant current of 1 C until the voltage reached 2.75 V.

[0161] [Charge / discharge cycle test] The battery was repeatedly charged and discharged under the following conditions.

[0162] <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.

[0163] <Discharge> At 25° C., constant current discharge was performed at a current of 1 C until the voltage reached 2.75 V.

[0164] The rest period between charging and discharging was 10 minutes. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was defined as the capacity retention rate. Furthermore, the direct current internal resistance (DCIR) was calculated from the voltage change before and after the first cycle discharge and the discharge current value. The evaluation results are shown in Table 1.

[0165] [Table 1]

[0166] It is apparent from Table 1 that in the batteries A1 to A4, the capacity retention rate was significantly improved while the increase in internal resistance was suppressed.

[0167] Example 5 A first active material was produced in the same manner as in Example 1, except that TMA was used as the precursor, and a secondary battery A5 was produced. The first coating and the second coating were analyzed by SEM, EDS, ICP, etc. The first coating contained Al and C. It was also confirmed that the element ratio Rb and the element ratio Rt satisfied Rb>Rt. The composition of the second coating was analyzed in the same manner and found to contain C. The sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0168] Example 6 A first active material was produced in the same manner as in Example 2, except that TMA was used as the precursor, and a secondary battery A6 was produced. The first coating and the second coating were analyzed by SEM, EDS, ICP, etc. The first coating contained Al and C. It was also confirmed that the element ratio Rb and the element ratio Rt satisfied Rb>Rt. The composition of the second coating was analyzed in the same manner and found to contain C. The sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0169] Example 7 A first active material was produced in the same manner as in Example 3, except that TMA was used as the precursor, and a secondary battery A7 was produced. The first coating and the second coating were analyzed by SEM, EDS, ICP, etc. The first coating contained Al and C. It was also confirmed that the element ratio Rb and the element ratio Rt satisfied Rb>Rt. The composition of the second coating was analyzed in the same manner and found to contain C. The sum of the thickness of the first coating and the thickness of the second coating was 50 nm.

[0170] The capacity retention rate and DCIR of the fabricated secondary batteries A5 to A7 were determined in the same manner as for the secondary battery A1 etc. Table 2 shows the evaluation results.

[0171] [Table 2]

[0172] From Table 2, it can be seen that in the batteries A5 to A7, the capacity retention rate was significantly improved while the increase in internal resistance was suppressed. [Industrial Applicability]

[0173] According to the present disclosure, it is possible to provide an electrochemical device having a high capacity and a 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. [Explanation of symbols]

[0174] 1 electrode group 2 Positive Lead 3 Negative lead 4 Battery case 5 Sealing plate 6 Negative terminal 7 Gasket 8. Sealing 20 Active material particles 21 Silicate phase 22 Silicon particles 23 Lithium silicate composite particles 24 Primary particles 26 Second Coat 27 First Coat

Claims

1. lithium silicate composite particles comprising a lithium silicate phase and silicon particles dispersed within the lithium silicate phase; A first coating film that covers at least a portion of the surface of the lithium silicate composite particle, the first coating contains an oxide of a first element other than a nonmetallic element and carbon atoms; The first element includes at least one of Ti and Al, The thickness of the first coating is T1 Ａ When 0.25T1 from the surface of the lithium silicate composite particle of the first coating Ａ an element ratio Rb of the first element to the carbon atom at the position 0.75T1 from the surface of the lithium silicate composite particle of the first coating Ａ The element ratio Rt of the first element to the carbon atom at the position Active material particles satisfying Rb>Rt.

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

3.

3. The active material particle according to claim 1 , wherein the element ratio Rb is 5 or more and 99 or less.

4. The active material particles according to any one of claims 1 to 3, wherein the element ratio Rt is 0.01 or more and 10 or less.

5. The thickness T1 of the first coating Ａ The active material particles according to any one of claims 1 to 4, wherein the average particle diameter is 0.1 nm or more and 50 nm or less.

6. The active material particles according to any one of claims 1 to 5, further comprising a second coating having a different conductivity from the first coating, the second coating covering at least a portion of the first coating.

7. The active material particle according to claim 6 , wherein the second coating comprises carbon atoms.

8. The thickness T1 of the first coating Ａ and the thickness T2 of the second coating Ａ What is that? 0<T2 Ａ / T1 Ａ The active material particles according to claim 6 or 7, which satisfy the relationship:

9. 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 8.

10. The battery includes a first electrode, a second electrode, and a separator disposed therebetween; An electrochemical device, wherein one of the first electrode and the second electrode is constituted by the electrochemical element according to claim 9 .

11. A preparation step of preparing lithium silicate composite particles including a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and at least a portion of a surface of the lithium silicate composite particle is coated with a carbon coating containing carbon atoms; a coating formation step of exposing the lithium silicate composite particles to a gas phase containing a first element other than nonmetallic elements to introduce 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 part of the surface of the lithium silicate composite particles, The method for producing active material particles, wherein the first element includes at least one of Ti and Al.

12. The method for producing active material particles according to claim 11 , wherein the coating step is performed by atomic deposition.

13. A preparation step of preparing lithium silicate composite particles including a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and at least a portion of a surface of the lithium silicate composite particle is coated with a carbon coating containing carbon atoms; a supporting step of supporting the lithium silicate composite particles on a surface of a current collector; a coating formation step of exposing the lithium silicate composite particles to a gas phase containing a first element other than nonmetallic elements to introduce the first element into the carbon coating, and forming an active material layer in which a first coating 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 particles, The method for manufacturing an electrochemical element, wherein the first element includes at least one of Ti and Al.

14. The method for producing an electrochemical device according to claim 13 , wherein the film forming step is performed by atomic layer deposition.

15. The method for producing an electrochemical device according to claim 13 or 14, further comprising a rolling step of rolling the active material layer after the coating step.

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