Negative electrode material, electrode sheet containing the material, electrochemical device, and electronic device

Abstract

The present invention provides a negative electrode material, a pole piece containing the material, an electrochemical device, and an electronic device. The negative electrode material includes silicon-based particles and SiOC present on the surface of the silicon-based particles, and the atomic ratio of Si, O, and C in the SiOC is 1:0.5-5:0.5-10. The present invention significantly improves the surface cycle stability of the negative electrode material during the volume expansion and contraction process, thereby reducing the accumulation of by-products. As a result, an electrochemical device using the negative electrode piece has good cycle stability and good volume expansion performance.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry, and specifically, to a negative electrode material, a pole piece containing the material, an electrochemical device, and an electronic device.

Background Art

[0002] Lithium-ion batteries have advantages such as high specific energy, high operating voltage, low self-discharge rate, small volume, and small weight, and are widely used in the consumer electronics field. With the rapid development of electric vehicles and portable electronic devices, the requirements for the energy density, safety, cycle performance, etc. of lithium-ion batteries are increasing. Among them, silicon-based negative electrode materials have a high capacity of 1500-4200 mAh / g per gram and are considered to be the most promising next-generation lithium-ion negative electrode materials.

[0003] However, silicon-based anode materials have a low conductivity of silicon of about 100 Ω·cm, have a volume expansion of about 300% during the charge and discharge process, and furthermore, there is an unstable SEI (Solid Electrolyte Interphase) film. These problems have hindered the further application of silicon-based anode materials. Currently, methods to improve the cycle stability performance and rate performance of silicon-based materials include the design of porous silicon-based materials, the reduction of the size of silicon oxygen materials, oxide coating, polymer coating, and carbon material coating. The methods of designing porous silicon-based materials and reducing the size of silicon oxygen materials can improve the rate performance to a certain extent, but with the progress of the cycle, the occurrence of side reactions and the growth of the uncontrollable SEI film further destroy the cycle stability of the silicon-based anode materials. Oxide coating and polymer coating can avoid coating the electrolyte and electrode materials, but due to the poor conductivity of the silicon-based anode materials, the electrochemical resistance increases, and the coating layer is easily broken during the lithium intercalation and deintercalation process, thereby reducing the cycle life of the anode materials. Carbon material coating can further provide excellent conductivity, but during the processing of the electrode sheets of lithium-ion batteries, the carbon-coated silicon-based materials may experience a decarbonization phenomenon due to the reciprocating shear force, which affects their Coulomb efficiency. On the other hand, during multiple cycles, due to the expansion, contraction, and rupture of silicon, the carbon coating layer is also easily peeled off from the substrate. Along with the growth of the SEI film and the inclusion of by-products, the electrochemical resistance and polarization increase, thus affecting the cycle life of lithium-ion batteries.

[0004] Therefore, there is a need for a silicon-based anode material that can further improve the cycle stability of lithium-ion batteries and further reduce the volume expansion of lithium-ion batteries.

Summary of the Invention

[0005] The present invention aims to provide a negative electrode material for improving the cycle stability of an electrochemical device and reducing the volume expansion of the electrochemical device, a pole piece containing the material, an electrochemical device, and an electronic device. The specific technical solutions are as follows.

[0006] In a first aspect of the present invention, there is provided a negative electrode material, wherein the negative electrode material includes silicon-based particles and a silicon oxycarbon ceramic material (SiOC) present on the surface of the silicon-based particles, the atomic ratio of Si, O, and C in the SiOC is 1:0.5 - 5:0.5 - 10, the Dv50 of the negative electrode material is 2.5 μm - 10 μm, and the mass of the SiOC is 0.1% - 20% of the mass of the negative electrode material.

[0007] In one embodiment of the present invention, the SiOC has an amorphous structure.

[0008] In one embodiment of the present invention, the particle size distribution of the silicon-based particles satisfies 0.3 ≤ Dn10 / Dv50 ≤ 0.6.

[0009] In one embodiment of the present invention, the silicon-based particles include at least one selected from the group consisting of nano-silicon particles, silicon monoxide particles, and carbon-silicon composite particles.

[0010] In one embodiment of the present invention, the silicon-based particles include at least one selected from the group consisting of Li element and Mg element.

[0011] In one embodiment of the present invention, the SiOC is formed by thermal decomposition of a siloxane raw material, and the siloxane raw material includes at least one selected from the group consisting of siloxane, hydrolysis products of siloxane, and silane resin.

[0012] In one embodiment of the present invention, the siloxane includes at least one selected from the group consisting of methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, diphenyltriethoxysilane, diethoxymethylphenylsilane, methyltrimethoxysilane, benzyltriethoxysilane, vinyltrimethoxysilane, isobutyltriethoxysilane, dimethoxy(methyl)phenylsilane, cyclohexylmethyldimethoxysilane, octyltrimethoxysilane, propyltrimethoxysilane, octadecyltriethoxysilane, hexyltriethoxysilane, octylmethyldimethoxysilane, dimethyldiethoxysilane, octadecyltrimethoxysilane, dodecyltriethoxysilane, allyltrimethoxysilane, cetyltrimethoxysilane, methylvinyldiethoxysilane, n-octyltriethoxysilane, diisobutyldimethoxysilane, (chloromethyl)diethoxy(methyl)silane, dimethoxymethylvinylsilane, γ-aminopropylmethyldiethoxysilane, and 1,4-bis(triethoxysilyl)benzene. The silane resin includes a silicone resin, and the silicone resin includes at least one selected from the group consisting of an aliphatic group silane resin and a phenylsilane resin.

[0013] In one embodiment of the present invention, on the surface of the silicon-based particles, there is further an oxide represented by the chemical formula MeO y wherein the Me element includes at least one selected from the group consisting of Al, Si, Ti, Mn, V, Cr, Co, and Zr, 0.5 ≦ y ≦ 3, and the oxide includes a carbon material, where the mass of the oxide is 0.1% to 5% of the mass of the negative electrode material, preferably 1% to 3%.

[0014] In one embodiment of the present invention, on the surface of the silicon-based particles, there is further a polymer, and the polymer includes a carbon material, where the mass of the polymer is 1% to 10% of the mass of the negative electrode material, preferably 3% to 6% of the mass of the negative electrode material.

[0015] In one embodiment of the present invention, the polymer includes at least one selected from the group consisting of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid, polystyrene-butadiene rubber, polyacrylamide, polyimide, polyamideimide, and derivatives thereof.

[0016] In one embodiment of the present invention, the carbon material includes at least one selected from the group consisting of carbon nanotubes, carbon nanoparticles, carbon fibers, and graphene.

[0017] In a second aspect of the present invention, a negative electrode sheet including the negative electrode material described in the first aspect is provided.

[0018] In a third aspect of the present invention, a positive electrode sheet, a negative electrode sheet, a separator positioned between the positive electrode sheet and the negative electrode sheet, and an electrolytic solution are included, and the negative electrode sheet is the negative electrode sheet described in the second aspect, to provide an electrochemical device.

[0019] In a fourth aspect of the present invention, an electronic device including the electrochemical device described in the third aspect is provided.

Advantages of the Invention

[0020] Since SiOC exists on the surface of the silicon-based particles in the negative electrode material provided by the present invention, SiOC and the silicon-based particles have good bonding strength, and can greatly improve the surface cycle stability of the negative electrode material during the process of volume expansion and contraction. Thereby, the accumulation of by-products can be reduced. Furthermore, the negative electrode sheet, the electrochemical device, and the electronic device including the negative electrode material of the present invention have good cycle stability and good volume expansion performance.

Brief Description of the Drawings

[0021] To more clearly illustrate the present invention and the technical solutions of the prior art, the following briefly describes the embodiments and the drawings required for the prior art. The drawings in the following description are only those of certain embodiments of the present invention, and it is obvious that those skilled in the art can obtain other technical solutions based on these drawings without creative labor.

[0022]

Figure 1

[0023]

Figure 2

Embodiments for Carrying out the Invention

[0024] To more clearly illustrate the object, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the drawings and embodiments. Of course, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other technical solutions that can be conceived by those skilled in the art without creative labor belong to the protection scope of the present invention.

[0025]

[0026] The present invention provides a negative electrode material, wherein the negative electrode material includes silicon-based particles and SiOC present on the surface of the silicon-based particles, the atomic ratio of Si, O, and C in the SiOC is 1:0.5-5:0.5-10, the Dv50 of the negative electrode material is 2.5 μm-10 μm, where the mass of SiOC is 0.1%-20% of the mass of the negative electrode material, preferably 0.3%-10% of the mass of the negative electrode material, and more preferably 0.5%-5% of the mass of the negative electrode material.

[0027] Note that the Dv50 is the particle diameter of the particles at which the cumulative volume calculated from the small particle diameter side in the volume-based particle size distribution is 50%.

[0028] As a result of investigations by the present inventors, SiOC exists on the surface of the silicon-based particles, and since SiOC and the silicon-based particles have good bonding strength, the negative electrode material is stabilized, and the surface cycle stability of the negative electrode material in the process of volume expansion and contraction is greatly improved, and the accumulation of by-products can be reduced. Thereby, it has been found that the volume expansion after cycling of the electrochemical device can be reduced. Note that the silicon-based particles may have SiOC present on at least a part of the surface, or may be entirely wrapped in SiOC.

[0029] In one embodiment of the present invention, the SiOC has an amorphous structure. Without being limited by any theory, the amorphous structure generally has higher mechanical stability, and thus the negative electrode material of the present invention has higher structural stability.

[0030] In one embodiment of the present invention, the particle size distribution of the silicon-based particles satisfies 0.3 ≦ Dn10 / Dv50 ≦ 0.6.

[0031] Here, the Dn10 is the particle diameter of the particles at which the cumulative number calculated from the small particle diameter side in the number-based particle size distribution is 10%.

[0032] In the present invention, the silicon-based particles are not particularly limited as long as the object of the present invention can be achieved. In one embodiment of the present invention, the silicon-based particles may include at least one selected from the group consisting of nanosilicon particles, silicon monoxide particles, and carbon-silicon composite particles.

[0033] In one embodiment of the present invention, the silicon-based particles contain at least one selected from the group consisting of Li element and Mg element. As a result of investigations by the present inventors, it has been found that the presence of SiOC on the surface of the silicon-based particles containing Li element and / or Mg element can effectively improve the cycle performance of the electrochemical device.

[0034] In one embodiment of the present invention, the SiOC is formed by subjecting a siloxane raw material to a thermal decomposition reaction, where the siloxane raw material contains at least one selected from the group consisting of siloxane, a hydrolysis product of siloxane, and a silane resin.

[0035] In one embodiment of the present invention, the siloxane may contain at least one selected from the group consisting of methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, diphenyltriethoxysilane, diethoxymethylphenylsilane, methyltrimethoxysilane, benzyltriethoxysilane, vinyltrimethoxysilane, isobutyltriethoxysilane, dimethoxy(methyl)phenylsilane, cyclohexylmethyldimethoxysilane, octyltrimethoxysilane, propyltrimethoxysilane, octadecyltriethoxysilane, hexyltriethoxysilane, octylmethyldimethoxysilane, dimethyldiethoxysilane, octadecyltrimethoxysilane, dodecyltriethoxysilane, allyltrimethoxysilane, cetyltrimethoxysilane, methylvinyldiethoxysilane, n-octyltriethoxysilane, diisobutyldimethoxysilane, (chloromethyl)diethoxy(methyl)silane, dimethoxymethylvinylsilane, γ-aminopropylmethyldiethoxysilane, and 1,4-bis(triethoxysilyl)benzene.

[0036] The silane resin contains a silicone resin, and the silicone resin contains at least one selected from the group consisting of an aliphatic group silane resin and a phenyl silane resin. Here, the aliphatic group silane resin may contain at least one selected from the group consisting of polydimethylsiloxane, methylhydrogen silicone resin, and vinylmethyl silicone resin, and the phenyl silane resin may contain at least one selected from the group consisting of polydiphenylsilicone resin, polymethylphenylsilicone resin, and vinylphenylsilicone resin.

[0037] In one embodiment of the present invention, an oxide represented by the chemical formula MeO y is present on the surface of the silicon-based particles. The Me element contains at least one selected from the group consisting of Al, Si, Ti, Mn, V, Cr, Co, and Zr, and 0.5 ≦ y ≦ 3. The silicon-based particles may have an oxide present on at least a part of the surface, or may be entirely encapsulated by the oxide. In the present invention, there is no particular limitation on the content of the oxide. For example, the mass of the oxide is 0.1% to 5% of the mass of the negative electrode material, preferably 1% to 3% of the mass of the negative electrode material.

[0038] As a result of the study by the present inventors, without being limited by any theory, when an oxide is present on the surface of the silicon-based particles containing SiOC, since the oxide itself has stability, further encapsulating SiOC with the oxide can bring better structural stability to the negative electrode material. Further, the oxide may contain a carbon material. Thereby, the conductivity of the negative electrode material can be improved.

[0039] In one embodiment of the present invention, a polymer is further present on the surface of the silicon-based particles, and the polymer contains a carbon material. Note that the silicon-based particles may, for example, have a polymer present on at least a part of their surface, or may be entirely encapsulated by the polymer. In the present invention, there is no particular limitation on the content of the polymer. For example, the mass of the polymer is 1% to 10% of the mass of the negative electrode material, preferably 3% to 6% of the mass of the negative electrode material.

[0040] As a result of investigations by the present inventors, without being limited by any theory, it has generally been found that the polymer itself has good structural stability and can also serve as a carrier for conductive substances such as carbon materials. In one embodiment of the present invention, in order to further improve the conductivity of the negative electrode material, a conductive polymer can further be present on the surface of the silicon-based particles containing SiOC.

[0041] In the present invention, there is no particular limitation on the carbon material, as long as the object of the present invention can be achieved. In one embodiment of the present invention, the carbon material may include at least one selected from the group consisting of carbon nanotubes, carbon nanoparticles, carbon fibers, and graphene. The amount of the carbon material used is not particularly limited and may be selected according to common general knowledge in this field. The carbon material may be used alone or in combination of two or more in any ratio.

[0042] In the present invention, the addition amount of the carbon material in the oxide or polymer is not particularly limited as long as the object of the present invention can be achieved. In one embodiment of the present invention, the range of the addition amount of the carbon material in the oxide is 10% to 90%. For example, the addition amount of the carbon material in the oxide is 10%, the addition amount of the carbon material in the oxide is 20%, the addition amount of the carbon material in the oxide is 30%, the addition amount of the carbon material in the oxide is 40%, the addition amount of the carbon material in the oxide is 50%, the addition amount of the carbon material in the oxide is 60%, the addition amount of the carbon material in the oxide is 70%, the addition amount of the carbon material in the oxide is 80%, and the addition amount of the carbon material in the oxide is 90%.

[0043] In one embodiment of the present invention, the range of the addition amount of the carbon material in the polymer is 20% to 80%. For example, the addition amount of the carbon material in the polymer is 20%, the addition amount of the carbon material in the polymer is 30%, the addition amount of the carbon material in the polymer is 40%, the addition amount of the carbon material in the polymer is 50%, the addition amount of the carbon material in the polymer is 60%, the addition amount of the carbon material in the polymer is 70%, and the addition amount of the carbon material in the polymer is 80%.

[0044] In one embodiment of the present invention, the polymer includes at least one selected from the group consisting of polyvinylidene fluoride, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid, styrene-butadiene rubber, polyacrylamide, polyimide, polyamideimide, and derivatives thereof.

[0045] Since SiOC exists on the surface of the silicon-based particles in the negative electrode material provided by the present invention, SiOC and the silicon-based particles have good bonding strength, greatly improving the surface cycle stability of the negative electrode material during the process of volume expansion and contraction, thereby reducing the accumulation of by-products.

[0046] The method for preparing the negative electrode material provided by the present invention is not particularly limited, and can be prepared, for example, by the following methods. 1. Dissolve the siloxane raw material in a water-containing organic solvent to obtain solution A. 2. Put the catalyst solution into solution A to obtain solution B. 3. Put the silicon-based particles into solution B, stir, remove the solvent, and dry to obtain a precursor. 4. Bake the precursor in an inert gas and keep it warm to obtain the negative electrode material.

[0047] Alternatively, it can be prepared by the following method. First, disperse the silicon-based particles in a water-containing organic solvent to obtain a mixed solution C. Then, put the siloxane raw material into the mixed solution C, further add a catalyst, stir, remove the solvent, and dry to obtain a precursor. Furthermore, bake the precursor in an inert gas and keep it warm to obtain the negative electrode material.

[0048] In the present invention, the organic solvent is not particularly limited as long as the object of the present invention can be achieved. In one embodiment of the present invention, the organic solvent may include at least one selected from the group consisting of n-hexane and ethanol.

[0049] In one embodiment of the present invention, the water content of the water-containing organic solvent is 5 to 10 Vol%.

[0050] In the present invention, the catalyst is not particularly limited as long as the object of the present invention can be achieved. In one embodiment of the present invention, the catalyst may be an organic acid solution such as an oxalic acid solution.

[0051] In one embodiment of the present invention, the stirring time is 0.5 to 24 h.

[0052] In one embodiment of the present invention, the removal of the solvent may be performed by at least one selected from the group consisting of rotary evaporation, spray drying, filtration, and freeze drying.

[0053] In one embodiment of the present invention, the firing temperature is 600 to 1000 °C, the heat preservation time is 2 to 12 h, and the heating rate is 3 to 20 °C / min.

[0054] In one embodiment of the present invention, at least one inert gas selected from the group consisting of nitrogen gas, argon gas, and helium gas may be used.

[0055] In the process of preparing the negative electrode material of the present invention, by mixing a siloxane raw material and silicon-based particles in an aqueous solvent, the surface of the silicon-based particles has activating groups such as abundant silanol groups, and the silica gel particles obtained by hydrolyzing the siloxane raw material also have abundant silanol groups. Therefore, the two are dehydrated and condensed in an aqueous solution to form a precursor having strong chemical bonds. As a result, after firing, SiOC and the silicon-based particles have good bonding strength. Thereby, the surface cycle stability of the negative electrode material in the process of volume expansion and contraction can be greatly improved, and the accumulation of by-products can be reduced, so that the volume expansion of the electrochemical device after cycling can be reduced. On the other hand, by adjusting the components of the precursor and the firing temperature, the lithium storage characteristics of SiOC can be effectively adjusted, so that the lithium storage rate can be effectively improved, the negative electrode polarization of the electrochemical device can be reduced, and thereby the resistance can be reduced.

[0056] The present invention further provides a negative electrode sheet including the negative electrode material described in any one of the above embodiments. Since the surface cycle stability of the negative electrode material is greatly improved in the process of volume expansion and contraction, the accumulation of by-products is reduced. Therefore, the negative electrode sheet of the present invention has good cycle stability and good volume expansion performance.

[0057] The present invention further provides an electrochemical device. The electrochemical device includes a positive electrode sheet, a negative electrode sheet described in the embodiments of the present invention, a separator located between the positive electrode sheet and the negative electrode sheet, and an electrolytic solution. Since the surface cycle stability of the negative electrode material in the negative electrode sheet is significantly improved during the processes of volume expansion and contraction, the accumulation of by-products is reduced. Therefore, the electrochemical device of the present invention has good cycle stability and good volume expansion performance.

[0058] The preparation process of the electrochemical device is not particularly limited and is a process well known to those skilled in the art. For example, a secondary battery can be manufactured by stacking a positive electrode and a negative electrode via a separator, and if necessary, winding, folding, etc., putting them into a battery container, and injecting an electrolytic solution into the battery container and sealing it. Here, the negative electrode used is the above-described negative electrode sheet provided by the present invention. Further, in order to prevent an increase in the pressure inside the battery and overcharge / discharge, an overcurrent prevention element, a lead plate, etc. may be put into the battery container if necessary.

[0059] The present invention further provides an electronic device including the electrochemical device described in the embodiments of the present invention. Since the electrochemical device included in the electronic device has good cycle stability and good volume expansion performance, the electronic device has a longer service life and higher safety.

[0060] The positive electrode sheet of the present invention is not particularly limited, and any positive electrode sheet known in the art may be used. For example, a positive electrode sheet containing lithium cobaltate, a positive electrode sheet containing lithium manganate, a positive electrode sheet containing lithium iron phosphate, or a positive electrode sheet containing lithium nickel cobalt manganate or lithium nickel cobalt aluminate can be mentioned.

[0061] In the present invention, the electrolytic solution is not particularly limited, and any electrolytic solution known in the art may be used. For example, it may be any one of a gel, a solid, and a liquid. For example, the liquid electrolytic solution may contain a lithium salt and a non-aqueous solvent.

[0062] The lithium salt is not particularly limited, and any lithium salt known in the art may be used as long as the object of the present invention can be achieved. For example, the lithium salt may be LiPF 6 、LiBF 4 、LiAsF 6 、LiClO 4 、LiB(C 6 H 5 ) 4 、LiCH 3 SO 3 、LiCF 3 SO 3 、LiN(SO 2 CF 3 ) 2 、LiC(SO 2 CF 3 ) 3 、and LiPO 2 F 2 and may include at least one selected from the group consisting of. For example, as the lithium salt, LiPF 6 can be selected.

[0063] The non-aqueous solvent is not particularly limited as long as the object of the present invention can be achieved. For example, the non-aqueous solvent may include at least one selected from the group consisting of carbonate ester compounds, carboxylic acid ester compounds, ether compounds, nitrile compounds, and other organic solvents.

[0064] For example, the carbonate compound may include at least one selected from the group consisting of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethyl ethylene carbonate.

[0065] The material of the current collector of the present invention is not particularly limited, and materials well known to those skilled in the art may be used. For example, the material of the current collector may include at least one selected from the group consisting of copper, nickel, titanium, molybdenum, aluminum, iron, zinc, and stainless steel, but is not limited thereto. Alternatively, a conductive inorganic material, for example, carbon or graphene, may be used. These materials may be used alone or in combination of two or more.

[0066] Hereinafter, embodiments of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.

[0067] Example 1 1. 100 g of a silicon oxygen material was dispersed in 500 mL of water-containing n-hexane and stirred uniformly. Here, the silicon oxygen material was SiO (silicon monoxide), and the water content of n-hexane was 5 Vol%. 2. 0.5 g of TPS (triethoxyvinylsilane) was dissolved in the mixed solution obtained in Step 1. 3. The catalyst was put into the mixed solution obtained in Step 2 so that the SiO addition amount was 1 / 10 of that in Example 1, the temperature was raised to 60 °C, and after stirring for 2 hours, the solvent was removed and dried to obtain a precursor. Here, the catalyst was an oxalic acid solution with a concentration of 2.5 mol / L. 4. The precursor obtained in Step 3 was calcined with argon gas at a calcination temperature of 600 °C, held for 2 h, and the heating rate was 3 °C / min to obtain a negative electrode material.

[0068] Example 2 The same procedure as in Example 1 was carried out, except that the calcination temperature was 800 °C.

[0069] Example 3 The same procedure as in Example 1 was carried out, except that the calcination temperature was 1000 °C.

[0070] Example 4 The same procedure as in Example 1 was carried out, except that TVS (triethoxyvinylsilane) was selected as the siloxane raw material.

[0071] Example 5 The same procedure as in Example 1 was carried out, except that DPS (diethoxydiphenylsilane) was selected as the siloxane raw material.

[0072] Example 6 The same procedure as in Example 1 was carried out, except that BSB (1,4-bis(triethoxysilyl)benzene) was selected as the siloxane raw material.

[0073] Example 7 The same procedure as in Example 1 was carried out, except that PDMS (dimethylsiloxane) was selected as the siloxane raw material and the addition amount of PDMS was 2 g.

[0074] Example 8 The same procedure as in Example 7 was carried out, except that the addition amount of PDMS was 1 g.

[0075] Example 9 The same procedure as in Example 7 was carried out, except that the addition amount of PDMS was 0.5 g.

[0076] Example 10 The silicon-oxygen material was a lithium-containing silicon-oxygen material, and it was carried out in the same manner as in Example 6 except that the mass of lithium was 8% of the mass of the lithium-containing silicon-oxygen material.

[0077] Example 11 The silicon-oxygen material was a magnesium-containing silicon-oxygen material, and it was carried out in the same manner as in Example 6 except that the mass of magnesium was 13% of the mass of the magnesium-containing silicon-oxygen material.

[0078] Comparative Example 1 1. 100 g of a silicon-oxygen material was dispersed in 500 mL of water-containing n-hexane and stirred uniformly. Here, the silicon-oxygen material was SiO (silicon monoxide), and the water content of n-hexane was 5 Vol%. 2. After removing the solvent from the mixed solution obtained in Step 1, drying, and then firing in an inert gas, the firing temperature was 600 °C, holding for 2 h, and the heating rate was 3 °C / min to obtain a negative electrode material.

[0079] Comparative Example 2 The silicon-oxygen material was a lithium-containing silicon-oxygen material, and it was carried out in the same manner as in Comparative Example 1 except that the mass of lithium was 8% of the mass of the lithium-containing silicon-oxygen material.

[0080] Comparative Example 3 The silicon-oxygen material was a magnesium-containing silicon-oxygen material, and it was carried out in the same manner as in Comparative Example 1 except that the mass of magnesium was 13% of the mass of the magnesium-containing silicon-oxygen material. Here, in each of the above Examples and Comparative Examples, the preparation process of SiO was as follows. Silicon dioxide and metal silicon powder were mixed at a molar ratio of 1:5 to 5:1 to obtain a mixed material. For the mixed material, under the conditions of 10 -4 ~10 -1 kPa, heated in the temperature range of 1200 to 1450 °C for 0.5 to 24 h to obtain a gas. The obtained gas was condensed to obtain a solid, and the obtained solid was pulverized and sieved to obtain SiO. The lithium-containing silicon oxygen material is a prelithium storage material of SiO, and the mass of lithium may be 6% - 12% of the mass of the lithium-containing silicon oxygen material. The magnesium-containing silicon oxygen material is a premagnesium storage material of SiO, and the mass of magnesium may be 5% - 20% of the mass of the magnesium-containing silicon oxygen material.

[0081] <Measurement of Performance>

[0082] Measurement of the powder properties of the anode material: Observation of the microscopic morphology of powder particles: Using a scanning electron microscope, the microscopic morphology of the anode material powder was observed to characterize the coating situation on the surface of the material. The measuring instrument was OXFORD EDS (X-max-20mm2), the acceleration voltage was 10 KV, the focal distance was adjusted, high-magnification observation was carried out at an observation magnification of 50 K, and the aggregation situation of particles was mainly observed at a low magnification of 500 - 2000.

[0083] Measurement of the specific surface area of the anode material: At a certain low temperature, after measuring the adsorption amount of gas on the solid surface at different relative pressures, based on the Brunauer-Emmett-Teller adsorption theory and its formula (BET formula), the specific surface area of the solid was calculated by obtaining the monolayer adsorption amount of the sample. When measuring, 1.5 - 3.5 g of the powder sample was weighed, put into the sample bottle for measurement of the specific surface area and pore size distribution analyzer (model: TriStar II 3020), degassed at 200 °C for 120 min, and then the measurement was carried out.

[0084] Measurement of the particle size of the anode material: Put 0.02 g of the powder sample into a 50 ml clean beaker, add 20 ml of deionized water, drop a few drops of 1% surfactant, and completely disperse the powder in water. Then, place it in a 120 W ultrasonic cleaner and apply ultrasonic waves for 5 minutes, and measure the particle size distribution with a laser particle size distribution analyzer (model: MasterSizer 2000).

[0085] Measurement of the tap density of the negative electrode material: It was carried out in accordance with GB / T 5162-2006 "Measurement of the tap density of metal powders".

[0086] Measurement of the carbon content of the negative electrode material: The negative electrode material sample was heated at high temperature in a high-frequency furnace under oxygen-rich conditions to burn, oxidizing carbon to carbon dioxide and sulfur to sulfur dioxide. After the obtained gas was treated, it was put into the corresponding cuvette, absorbed the corresponding infrared radiation, and was converted into the corresponding signal by a detector. This signal was sampled by a computer, linearly corrected, and then converted into a value proportional to the concentrations of carbon dioxide and sulfur dioxide. After accumulating the values of the entire analysis process, after the analysis was completed, the computer divided this accumulated value by the weight value, multiplied by the calibration coefficient, and subtracted the blank to obtain the percentages of carbon and sulfur in the sample. The sample was measured with a high-frequency infrared sulfur and carbon analyzer (model: Shanghai Dekai Instrument Co., Ltd. HCS-140).

[0087] Measurement of the atomic ratio on the surface of the negative electrode material: The negative electrode material was sprinkled on a copper foil with a conductive adhesive, and the cross-section obtained by cutting the copper foil was polished with a plasma polishing machine (Leica EM TIC 3X-Ion Beam Slope Cutter), and then placed in a scanning electron microscope (SEM). The cut silicon-based particles were searched for, and the above silicon-based particles were cut in a direction perpendicular to the cross-section with a focused ion beam (FIB). After obtaining a thin slice (about 50 nm) containing the cross-section of the silicon-based particles, using TEM measurement, a point 1-2 nm from the outer surface was selected and measured with an energy spectrometer (EDS) to obtain the ratio of Si:O:C. Figure 1 is a cross-sectional FIB-TEM structural diagram of the negative electrode material fabricated in Example 6. In the drawing, the SiOC layer structure can be clearly confirmed, and the thickness of the SiOC layer is about 4 nm. Figure 2 is a cross-sectional FIB-TEM structural diagram of the negative electrode material fabricated in Comparative Ratio 1. In the drawing, the SiOC layer structure cannot be confirmed.

[0088] Measurement of I2 / I1 of the negative electrode material: XRD measurement: Weighed 1.0 - 2.0 g of the anode material sample, placed it in the groove of a glass sample rack, compressed it with a glass piece to make it flat, and measured it using an X-ray diffractometer (model: Bruker, D8) according to JJS K 0131-1996 "General Principles of X-ray Diffraction Analysis". The measurement voltage was 40 kV, the current was 30 mA, the scanning angle range was 10 - 85°, the scanning step width was 0.0167°, the time per step was 0.24 s, obtained the XRD diffraction pattern, obtained the highest peak I1 attributed to 2θ = 28.4° and the highest peak I2 attributed to 21.0° from the pattern, and calculated the ratio of I2 / I1.

[0089] Measurement of the initial efficiency of the half-cell: The anode material prepared in each example and comparative example, conductive carbon black, and polymer were mixed at a ratio of 80:10:10, added to deionized water, stirred to form a slurry, a coating layer with a thickness of 100 μm was formed on the surface of the current collector by a doctor blade, dried in a vacuum drying oven at 85°C for 12 hours, cut out into a disc with a diameter of 1 cm using a punching machine in a dry environment, and in a glove box, a metal lithium plate was used as the counter electrode, a ceglard composite film was selected as the separator, filled with electrolyte, and assembled into a button-type battery. The charge and discharge of the battery were measured by a LAND series battery measurement system. The calculation method of the initial efficiency is the capacity with a discharge cut-off voltage of 2.0 V / the capacity with a charge cut-off voltage of 0.005 V. The measurement results are shown in Table 1.

[0090] Calculation method of the capacity per gram of the half-cell: The capacity per gram of the half-cell with a discharge cut-off voltage of 2.0 V.

[0091] Measurement of the performance of the full cell:

[0092] Measurement of the cycle performance: 25 o C or 45 oAt the measurement temperature of C, it was charged at a constant current until it reached 4.4 V at 0.7C, charged at a constant voltage until it reached 0.025C, left standing for 5 minutes, and then discharged at 0.5C until it reached 3.0 V. The capacity obtained in this step was taken as the initial capacity. Cycle measurements were performed at 0.7C charge / 0.5C discharge, and the capacity per cycle was compared with the initial capacity to obtain a capacity decay curve. The number of cycles at which the cycle cut-off capacity retention rate was 90% at 25°C was defined as the room temperature cycle performance of the battery, and the number of cycles at which the cycle cut-off capacity retention rate was 80% at 45°C was defined as the high temperature cycle performance of the battery. By comparing the number of cycles in the above two cases, the cycle performance of the materials was compared. The cycle performance of each example and comparative example is shown in Table 2.

[0093] Measurement of discharge rate: At 25°C, it was discharged at 0.2C until it reached 3.0 V, left standing for 5 minutes, charged at 0.5C until it reached 4.45 V, charged at a constant voltage until it reached 0.05C, left standing for 5 minutes, the discharge rate was adjusted, and discharge measurements were performed at 0.2C, 0.5C, 1C, 1.5C, and 2.0C respectively to obtain the respective discharge capacities. The ratio of the 2C discharge capacity to the 0.2C discharge capacity at each rate was defined as the rate performance.

[0094] Measurement of the full charge expansion rate of the lithium-ion battery: Using a spiral micrometer, the thickness of a new battery at half charge of the lithium-ion battery, i.e., at 50% state of charge (SOC), was measured. When the number of cycles reached 400 and the battery reached the full charge state, i.e., 100% SOC state, the thickness of the battery at this time was measured using a spiral micrometer. By comparing with the thickness of the new battery at the first half charge, the expansion rate of the fully charged lithium-ion battery at this time was obtained.

[0095] Preparation of the full cell:

[0096] Preparation of the lithium-ion battery:

[0097] Preparation of the positive electrode: LiCoO 2Conductive carbon black and polyvinylidene fluoride (PVDF) were sufficiently stirred in an N-methylpyrrolidone solvent system at a weight ratio of 95%:2.5%:2.5%, and uniformly mixed to prepare a positive electrode slurry with a solid content of 75 wt%. The prepared positive electrode slurry was applied to an aluminum foil serving as a positive electrode current collector, dried, and cold-pressed to obtain a positive electrode with a coding layer thickness of 110 μm.

[0098] Preparation of negative electrode: Graphite, the negative electrode materials prepared in the examples and comparative examples, a conductive agent, and a binder were mixed at a weight ratio of 70%:15%:5%:10%, an appropriate amount of water was added, kneaded with a solid content of 55 wt% - 70 wt%, and then an appropriate amount of water was added to adjust the viscosity of the slurry to 4000 - 6000 Pa·s to obtain a negative electrode slurry. The prepared negative electrode slurry was applied to a copper foil serving as a negative electrode current collector, dried, and cold-pressed to obtain a negative electrode with a coding layer thickness of 100 μm. Here, conductive carbon black was selected as the conductive agent, and polyacrylic acid (PAA) was selected as the binder.

[0099] Preparation of electrolyte: In a dry argon gas environment, LiPF 6 was added to a solvent formed by mixing propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC), uniformly mixed, and then 12.5 wt% of fluoroethylene carbonate (FEC) was added and uniformly mixed to obtain an electrolyte. Here, the weight ratio of propylene carbonate, ethylene carbonate, and diethyl carbonate was 1:1:1, and the concentration of LiPF 6 was 1.15 mol / L.

[0100] Preparation of separator: A polyvinyl (PE) porous polymer film with a thickness of 15 μm was used as the separator.

[0101] Preparation of lithium-ion battery: The separator was interposed between the positive electrode and the negative electrode to play a role of isolation. The positive electrode, the separator, and the negative electrode were laminated and wound in this order to obtain an electrode assembly. The electrode assembly was placed in an exterior package, electrolyte was injected, sealed, and subjected to processes such as formation, degassing, and trimming to obtain a lithium-ion battery.

[0102]

Table 1

[0103]

Table 2

[0104] As can be seen from the comparison between Examples 1 to 6, 8 to 9 and Comparative Example 1, if a negative electrode material with SiOC present on its surface is adopted compared to a negative electrode material without SiOC on its surface, the lithium-ion battery has significantly improved cycle performance at different temperatures, and the expansion rate and discharge rate performance are also improved. And as can be seen from Examples 1 to 3, as the firing temperature gradually increases, the carbon element on the surface of the negative electrode material gradually decreases, the cycle performance gradually decreases, and the expansion rate and discharge rate gradually increase. Therefore, if a lower temperature, preferably 600 °C, is selected, good results can be obtained.

[0105] As can be seen from the comparison between Example 7 and Comparative Example 1, Example 7 has slightly more cycle times at 25 °C than Comparative Example 1 and slightly fewer cycle times at 45 °C than Comparative Example 1, but both the expansion rate and the discharge rate are significantly improved. This is considered to be due to the large addition amount of PDMS. Since the spread of PDMS itself on the surface of the negative electrode material is poor, if the addition amount of PDMS is large, on the contrary, the surface is likely to become unstable, which has an adverse effect on the cycle performance of the lithium-ion battery, but both the expansion rate and the discharge rate of the lithium-ion battery can be improved.

[0106] As can be seen from the comparison between Example 10 and Comparative Example 2, in the case of the same Li element-containing siloxane material, if a negative electrode material with SiOC present on the surface is adopted, compared with a negative electrode material without SiOC present on the surface, the lithium-ion battery has significantly improved cycle performance at different temperatures, and the expansion rate and discharge rate performance are also improved.

[0107] As can be seen from the comparison between Example 11 and Comparative Example 3, in the case of the same Mg element-containing siloxane material, if a negative electrode material with SiOC present on the surface is adopted, compared with a negative electrode material without SiOC present on the surface, the lithium-ion battery has significantly improved cycle performance at different temperatures, and the expansion rate and discharge rate performance are also improved.

[0108] As can be seen from the comparison between Examples 7 to 9 and Comparative Example 1, when preparing a negative electrode material with SiOC present on the surface by adding different contents of siloxane materials, compared with a negative electrode material without SiOC present on the surface, the lithium-ion battery has significantly improved cycle performance, and the expansion rate and discharge rate performance are also improved.

[0109] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and principles of the present invention all belong to the protection scope of the present invention.

Claims

1. A negative electrode material, wherein the negative electrode material contains silicon-based particles and SiO C present on the surface of the silicon-based particles, wherein the atomic ratio of Si, O, and C in the SiO C is 1:0.5 to 5:0.5 to 10, wherein the Dv50 of the negative electrode material is 2.5 μm to 10 μm, and the mass of the SiO C is 0.1% to 20% of the mass of the negative electrode material, wherein the silicon-based particles include silicon monoxide (SiO) particles, wherein the silicon-based particles include at least one selected from the group consisting of Li element and Mg element, negative electrode material.

2. The SiO C has an amorphous structure, the negative electrode material according to Claim 1.

3. A negative electrode sheet including the negative electrode material according to Claim 1 or 2.

4. a positive electrode sheet, a negative electrode sheet, a separator positioned between the positive electrode sheet and the negative electrode sheet, and an electrolytic solution, wherein the negative electrode sheet is the negative electrode sheet according to Claim 3, electrochemical device.

5. An electronic device including the electrochemical device according to Claim 4.

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