An electrochemical device and an electronic device

Abstract

The application relates to an electrochemical device and an electronic device, the electrochemical device comprising a negative electrode sheet and a solid-state electrolyte; the negative electrode sheet comprises a negative electrode material layer, and the solid-state electrolyte is in contact with the negative electrode material layer; the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material is composed of micrometer silicon and double-layer graphene material coating the micrometer silicon; wherein a first graphene material forms a first mixed phase with the micrometer silicon, the first mixed phase is subjected to heat treatment to form a second mixed phase, and then the second mixed phase forms a third mixed phase with a second graphene material, and the third mixed phase is subjected to heat treatment to form the negative electrode active material; the first graphene material accounts for 10%-30% of the mass percentage of the first mixed phase; and the second graphene material accounts for 5%-20% of the mass percentage of the third mixed phase.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and more particularly to an electrochemical device and an electronic device. Background Technology

[0002] Currently, commercially available liquid lithium-ion batteries contain flammable liquid organic electrolytes. When a liquid lithium-ion battery is subjected to severe impact or the battery temperature is too high, the electrolyte is highly flammable, causing the battery to catch fire and even more serious safety accidents.

[0003] Solid-state batteries are batteries that use solid electrodes and solid electrolytes. The positive electrode material of solid-state batteries is not significantly different from that of liquid electrolyte batteries, while the negative electrode material is mainly lithium metal, lithium alloys, or graphene. The channel for transporting lithium ions is the solid electrolyte material. Using solid electrolytes instead of existing liquid organic electrolytes can effectively improve the safety performance of lithium batteries, while also increasing the energy density of lithium-ion batteries, among other advantages.

[0004] Silicon-based anodes are currently among the most popular anode materials due to their extremely high theoretical specific capacity, with micron-sized silicon being a particularly noteworthy material. However, the low ionic and electronic conductivity of silicon-based anodes affects the rapid insertion and extraction performance of lithium ions, thus limiting their widespread application in solid-state batteries. Furthermore, micron-sized silicon exhibits significant volume expansion and is easily broken and pulverized, further restricting its application. If these technical shortcomings can be overcome, the application of silicon-based anodes will undoubtedly bring another boost to the performance of solid-state batteries. Summary of the Invention

[0005] This invention provides an electrochemical device and an electronic device. In the electrochemical device, micron-sized silicon bilayer graphene permeation coating effectively alleviates material volume expansion. At the same time, the good ductility of the graphene thin layer improves the interface problem with the solid electrolyte, effectively improving the first cycle efficiency and cycle performance.

[0006] In a first aspect, embodiments of the present invention provide an electrochemical device, including a negative electrode and a solid electrolyte;

[0007] The negative electrode sheet includes a negative electrode material layer, and the solid electrolyte is in contact with the negative electrode material layer;

[0008] The negative electrode material layer includes a negative electrode active material, which is composed of micron-sized silicon and a bilayer graphene material coated with micron-sized silicon. The first graphene material forms a first mixed phase with the micron-sized silicon. This first mixed phase is then heat-treated to form a second mixed phase, which in turn forms a third mixed phase with the second graphene material. The third mixed phase is then heat-treated to form the negative electrode active material. The first graphene material accounts for 10%-30% of the mass percentage of the first mixed phase, and the second graphene material accounts for 5%-20% of the mass percentage of the third mixed phase.

[0009] Preferably, the electrochemical device is a solid-state battery or a capacitor.

[0010] Preferably, the first graphene material has 2-10 layers, and the size of the first graphene material layer is ≤45μm;

[0011] The second graphene material has 1-9 layers, and the size of each layer is ≤65μm.

[0012] The Dv50 of the micron-sized silicon is 1μm≤Dv50≤5μm;

[0013] The solid electrolyte has the general chemical formula: Li 1+x A x B 2-x (PO4)3, where x is between 0.01 and 0.5, A includes one or more of Al, Y, Ga, Cr, In, Fe, Se, or La, and B includes one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, hafnium (Hf), and their derivatives; or, Li x A y Zr 2-y Si x-y-1 P 4-x+y O 12 1≤x≤5, 0<y≤1, A includes one or more of Al, Cr, Fe, Ga, Se, Y, In or La; or, Na x A y Zr 2-y Si x-y-1 P 4-x+y O 12 2.5≤x≤3.5, 0<y≤1, A includes one or more of Al, Cr, Fe, Ga, Se, Y, In, and La; or, Li 3x La 2 / 3-x TiO3, where x is between 0.01 and 0.5.

[0014] Preferably, the number of layers in the second graphene material is less than the number of layers in the first graphene material; and the sheet size of the second graphene material is greater than the sheet size of the first graphene material.

[0015] Preferably, the negative electrode material layer further includes a dispersant and a binder.

[0016] In a second aspect, embodiments of the present invention provide an electronic device including the electrochemical device described in the first aspect above.

[0017] The electrochemical device of this invention can be an all-solid-state battery, effectively avoiding the formation of a solid electrolyte interphase (SEI) film and electrolyte leakage problems, thus improving the safety performance and service life of the electrochemical device. By combining micron-sized silicon with a solid electrolyte, a highly thermally stable solid electrolyte replaces the flammable conventional organic solvent electrolyte, solving the problem of easy combustion of lithium-ion batteries. Moreover, since the electrolyte is non-fluid, it can be easily assembled into high-voltage cells through internal series connection, which is beneficial to improving the assembly efficiency and energy density of the power battery system. Furthermore, the micron-sized silicon bilayer graphene permeation coating effectively alleviates the material volume expansion, while the good ductility of the graphene thin layer improves the interface problem with the solid electrolyte, effectively improving the first-cycle efficiency and cycle performance. This invention, by combining graphene, micron-sized silicon, and solid electrolyte in a specific manner, can obtain lithium batteries with excellent performance, especially solid-state lithium batteries. Attached Figure Description

[0018] The technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0019] Figure 1 This is a flowchart illustrating the preparation method of the electrochemical device according to an embodiment of the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0021] The electrochemical device of the present invention includes a negative electrode and a solid electrolyte;

[0022] The negative electrode sheet includes a material layer, and the solid electrolyte is in contact with the negative electrode material layer;

[0023] The negative electrode material layer includes a negative electrode active material, which is composed of micron-sized silicon and a bilayer graphene material coated with micron-sized silicon; wherein, the first graphene material forms a first mixed phase with micron-sized silicon, the first mixed phase is heat-treated to form a second mixed phase, and then forms a third mixed phase with the second graphene material, and the third mixed phase is heat-treated to form the negative electrode active material.

[0024] The first graphene material accounts for 10%-30% of the mass percentage of the first mixed phase; the second graphene material accounts for 5%-20% of the mass percentage of the third mixed phase; the number of layers of the second graphene material is less than the number of layers of the first graphene material; and the sheet size of the second graphene material is greater than the sheet size of the first graphene material.

[0025] The Dv50 of micron-sized silicon is 1μm≤Dv50≤5μm;

[0026] The general chemical formula for solid electrolytes is: Li 1+x A x B 2-x (PO4)3, where x is between 0.01 and 0.5, A includes one or more of Al, Y, Ga, Cr, In, Fe, Se, or La, and B includes one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, hafnium (Hf), and their derivatives; or, Li x A y Zr 2-y Si x-y-1 P 4-x+y O 12 1≤x≤5, 0<y≤1, A includes one or more of Al, Cr, Fe, Ga, Se, Y, In or La; or, Na x A y Zr 2-y Si x-y-1 P 4-x+y O 12 2.5≤x≤3.5, 0<y≤1, A includes one or more of Al, Cr, Fe, Ga, Se, Y, In, and La; or, Li 3x La 2 / 3-x TiO3, where x is between 0.01 and 0.5.

[0027] The Dv50 of the micron-sized silicon described above is 1μm ≤ Dv50 ≤ 5μm; this value was obtained through rigorous theoretical analysis and practical testing during the invention process. When the Dv50 of the micron-sized silicon is too small (less than 1μm), its specific surface area increases, the material activity increases, and the contact between the negative electrode active material and the electrolyte increases, leading to increased side reactions and electrolyte consumption, thus affecting the cycle performance and safety performance of the electrochemical device. When the Dv50 of the micron-sized silicon is too large (greater than 5μm), the Dv50 after secondary granulation is too large, the contact between the negative electrode active materials deteriorates, affecting the cycle stability of the electrochemical device.

[0028] Furthermore, in a preferred embodiment of this application, the first graphene material comprises 2-10 layers, and the size of each layer is ≤45μm. For example, the number of layers can be 2, 3, 4, 5, 6, 7, 8, 9, or 10. The layer size described here refers to the particle size of the layer, which is a dimensional characteristic of the layer on the xy-plane in a three-dimensional coordinate system, and can be understood as particle size; while the number of layers is a parameter of the graphene thickness, located in the z-direction. The applicant has found that when the number of graphene layers exceeds 10, its overall performance decreases; if the size of the graphene material layer is greater than 45μm, the particle size of the secondary granulation is too large, resulting in poor contact between the negative electrode active materials and affecting the cycle stability of the electrochemical device. The first graphene material accounts for 10%-30% of the mass percentage of the first mixed phase, and can be 10%, 15%, 20%, 25%, 30%, or any value within this range. The applicant discovered that when the content is below 10%, the integrity of the micron-sized silicon coating is poor, and when it is above 30%, it affects the coating of secondary graphene.

[0029] In a preferred embodiment of this application, the second graphene material has 1-9 layers, and the size of the second graphene material layer is ≤65μm. For example, the number of layers can be 1, 2, 3, 4, 5, 6, 7, 8, or 9. The applicant has found that if the size of the second graphene material layer is greater than 65μm, the particle size of the secondary granulation is too large, resulting in poor contact between the negative electrode active materials and affecting the cycle stability of the electrochemical device. The second graphene material accounts for 5%-20% of the mass percentage of the third mixed phase. For example, it can be 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any value within this range. The applicant has found that when it is below 5%, the integrity of the micron-sized silicon coating is poor; when it is above 20%, it affects the yield and pulping performance of the final product. Simultaneously, a high graphite content in the negative electrode material affects the energy density of the lithium-ion battery.

[0030] The second graphene material has fewer layers than the first graphene material. For example, if the first graphene material has 5 layers, the second graphene material can have any number of layers: 1, 2, 3, or 4. The applicant has found that when using two graphene layers of different thicknesses, a combination of a small, thick inner graphene layer and a thin, large outer graphene layer is more effective. This is because using small-particle graphene as the inner coating layer allows for effective adhesion to micron-sized silicon, increasing interfacial bonding. If large-particle graphene is used as the inner coating layer, there are numerous gaps between the inner layer and the micron-sized silicon, resulting in weak bonding and a lower tap density, which affects the material's energy density. Using thin, large graphene as the outer coating layer ensures complete coating of the primary particles, guaranteeing coating integrity, and the fewer the bonding points between the thin graphene sheets, the lower the contact resistance. Moreover, the outer layer uses thin-layer graphene, which has better conductivity and mechanical properties, and is beneficial for lithium ion insertion / extraction and rate performance improvement.

[0031] The negative electrode material layer of the present invention also includes a dispersant and a binder, both of which can be commonly used dispersants and binders for negative electrodes.

[0032] The negative electrode sheet of the present invention also includes a negative electrode current collector. The present invention does not have any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of the present invention. For example, it may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, foamed nickel, foamed copper or composite current collector, etc.

[0033] In this invention, the electrochemical device further includes a positive electrode sheet, which typically includes a positive current collector and a positive electrode material layer disposed on the surface of the positive current collector. In this invention, the positive current collector is not particularly limited, as long as it can achieve the purpose of this invention, such as including but not limited to aluminum foil, aluminum alloy foil, or composite current collector.

[0034] The electrochemical device of this invention is not particularly limited and can include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries or capacitors, wherein the secondary battery may specifically be a solid-state battery. This electrochemical device can be applied in electronic devices. The electrochemical device proposed in this invention has good cycle performance and safety performance, thereby enabling electronic devices to have a long service life.

[0035] In the aforementioned electrochemical device, it has been stated that the active layer of the negative electrode material is composed of micron-sized silicon and a bilayer graphene material coating micron-sized silicon. The electrochemical device of this invention can be prepared by the following method, specifically as follows: Figure 1 As shown, the main steps include:

[0036] Step 110: Prepare the negative electrode sheet;

[0037] The method includes: weighing the negative electrode active material, conductive additives, and binder according to the required proportions, and preparing a slurry in a pulping machine at room temperature. The prepared slurry is then uniformly coated onto the negative electrode and the fluid, dried in a forced-air drying oven, cut into electrode sheets, and vacuum-dried in a vacuum drying oven. The dried electrode sheets are then immediately transferred to a glove box for later use in battery assembly.

[0038] The preparation of the negative electrode active material specifically includes:

[0039] Step 111: Micron-sized silicon and the first graphene material are mixed in a certain proportion and spray-dried to obtain the first mixed phase;

[0040] Step 112: Heat-treat the first mixed phase at 600℃-1000℃ for 2-12 hours under a nitrogen atmosphere to obtain the second mixed phase;

[0041] Step 113: The second mixed phase and the second graphene material are mixed in a certain proportion and spray-dried to obtain the third mixed phase;

[0042] Step 114: The third mixed phase is heat-treated at 600℃-1000℃ for 2-12 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0043] Step 120: Prepare the positive electrode sheet;

[0044] The positive electrode active material, conductive agent, and binder are mixed in the required proportions, a solvent is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode current collector and dried to obtain a positive electrode sheet with a positive electrode material layer.

[0045] Step 130: Prepare a solid electrolyte sheet;

[0046] The solid electrolyte used is pressed into an electrode sheet.

[0047] Step 140: Assemble the electrochemical device;

[0048] A solid-state battery is assembled by sequentially assembling a positive electrode, a solid electrolyte sheet, and a negative electrode, wherein the solid electrolyte is in contact with the negative electrode material layer of the negative electrode sheet.

[0049] To better understand the technical solutions provided by this invention, the following describes the specific processes for preparing electrochemical devices using the methods provided in the above embodiments of this invention, and the electrochemical characteristics obtained by testing them, using several specific examples. In the following specific examples, the electrochemical device is specifically a solid-state battery.

[0050] In this embodiment, the method used to prepare the solid-state battery is as follows:

[0051] Preparation of negative electrode sheet:

[0052] The negative electrode active material, conductive additive carbon black, and binder (sodium cellulate and styrene-butadiene rubber in a 1:1 ratio) were weighed according to a ratio of 95:2:3. A slurry was prepared in a pulping machine at room temperature. The prepared slurry was then evenly coated onto copper foil. After drying in a forced-air drying oven at 50°C for 2 hours, the foil was cut into 8×8mm electrode sheets and vacuum-dried in a vacuum drying oven at 100°C for 10 hours. The dried electrode sheets were then immediately transferred to a glove box for use in battery assembly.

[0053] Preparation of the positive electrode sheet:

[0054] Lithium cobalt oxide (LiCoO2), acetylene black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil current collector and dried to obtain a positive electrode sheet with a single-sided coating of the positive electrode material. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material.

[0055] Preparation of solid electrolyte sheets:

[0056] The solid electrolyte used is pressed into an electrode sheet.

[0057] Solid-state lithium battery fabrication:

[0058] The positive electrode shell, positive electrode plate, solid electrolyte plate, negative electrode plate, gasket, spring, and negative electrode shell are assembled into a solid-state battery in sequence.

[0059] The following examples illustrate the preparation of the negative electrode active material, the selection of the solid electrolyte, and the assembly of the solid-state battery using the above methods.

[0060] Example 1

[0061] Micron-sized silicon with a Dv50 of 3.6 μm and a first graphene material with a sheet size of 32 μm and a number of layers of 6 were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 22% of the mass percentage of the first mixed phase;

[0062] The first mixed phase was treated at 650°C under a nitrogen atmosphere for 4 hours to obtain the second mixed phase;

[0063] The second mixed phase and a second graphene material with a sheet size of 55 μm and a number of layers of 3 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 12% of the mass percentage of the third mixed phase;

[0064] The third mixed phase was heat-treated at 850°C for 6 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0065] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.1 Al 0.1 Ti 1.9 (PO4)3 is assembled into a solid-state battery according to the above method.

[0066] Constant current charge-discharge mode tests were performed using a charge-discharge meter, with a discharge cutoff voltage of 0.005V and a charge cutoff voltage of 1.5V. The first week of charge-discharge testing was conducted at a current density of C / 10, and the second week of discharge testing was conducted at a current density of C / 10. Under these conditions, cycle tests were performed, and the capacity retention rate was 95% after 100 cycles.

[0067] Example 2

[0068] Micron-sized silicon with a Dv50 of 2.5 μm and a first graphene material with a sheet size of 33 μm and a number of layers of 5 were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 22% of the mass percentage of the first mixed phase.

[0069] The first mixed phase was treated at 700°C under a nitrogen atmosphere for 5 hours to obtain the second mixed phase;

[0070] The second mixed phase and a second graphene material with a sheet size of 53 μm and a number of layers of 3 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 8% of the mass percentage of the third mixed phase;

[0071] The third mixed phase was heat-treated at 850°C for 8 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0072] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li4Y. 0.2 Zr 1.8 Si 2.8 P 0.2 O 12 Assemble solid-state batteries using the methods described above.

[0073] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 92%.

[0074] Example 3

[0075] Micron-sized silicon with a Dv50 of 3.4 μm and a first graphene material with a sheet size of 36 μm and 6 layers were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 27% of the mass percentage of the first mixed phase.

[0076] The first mixed phase was treated at 600°C under a nitrogen atmosphere for 11 hours to obtain the second mixed phase;

[0077] The second mixed phase and a second graphene material with a sheet size of 57 μm and a number of layers were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 17% of the mass percentage of the third mixed phase;

[0078] The third mixed phase was heat-treated at 900°C for 7 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0079] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. Na3Se is selected as the solid electrolyte. 0.5 Zr 1.5 Si 1.5 P 1.5 O 12 Assemble solid-state batteries using the methods described above.

[0080] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 94%.

[0081] Example 4

[0082] Micron-sized silicon with a Dv50 of 4.2 μm and a first graphene material with a sheet size of 29 μm and a number of layers of 7 were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 18% of the mass percentage of the first mixed phase.

[0083] The first mixed phase was treated at 850°C under a nitrogen atmosphere for 5 hours to obtain the second mixed phase;

[0084] The second mixed phase and a second graphene material with a sheet size of 45 μm and a number of layers of 3 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 14% of the mass percentage of the third mixed phase;

[0085] The third mixed phase was heat-treated at 1000℃ for 8 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0086] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.42Al 0.42 Ta 1.58 (PO4)3 is assembled into a solid-state battery according to the above method.

[0087] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate was 95% after 100 cycles.

[0088] Example 5

[0089] Micron-sized silicon with a Dv50 of 4.7 μm and a first graphene material with a sheet size of 36 μm and 8 layers were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 12% of the mass percentage of the first mixed phase.

[0090] The first mixed phase was treated under a nitrogen atmosphere at 900°C for 4 hours to obtain the second mixed phase;

[0091] The second mixed phase and a second graphene material with a sheet size of 48 μm and a number of layers were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 12% of the mass percentage of the third mixed phase;

[0092] The third mixed phase was heat-treated at 850°C for 10 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0093] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 0.45 La 0.52 TiO3 was assembled into a solid-state battery using the method described above.

[0094] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 94%.

[0095] Example 6

[0096] Micron-sized silicon with a Dv50 of 2.2 μm and a first graphene material with a sheet size of 36 μm and a number of layers of 4 are mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounts for 16% of the mass percentage of the first mixed phase;

[0097] The first mixed phase was treated under a nitrogen atmosphere at 800°C for 10 hours to obtain the second mixed phase;

[0098] The second mixed phase and a second graphene material with a sheet size of 56 μm and a number of layers of 2 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 13% of the mass percentage of the third mixed phase;

[0099] The third mixed phase was heat-treated at 1000℃ for 4 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0100] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.2 Al 0.2 Ti 1.8 (PO4)3 is assembled into a solid-state battery according to the above method.

[0101] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 96%.

[0102] Example 7

[0103] Micron-sized silicon with a Dv50 of 1.9 μm and a first graphene material with a sheet size of 40 μm and a number of layers were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 24% of the mass percentage of the first mixed phase.

[0104] The first mixed phase was treated at 950°C under a nitrogen atmosphere for 6 hours to obtain the second mixed phase;

[0105] The second mixed phase and a second graphene material with a sheet size of 60 μm and a number of layers of 2 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 15% of the mass percentage of the third mixed phase;

[0106] The third mixed phase was heat-treated at 950°C for 6 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0107] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 0.27 La 0.58 TiO3 was assembled into a solid-state battery using the method described above.

[0108] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate was 95% after 100 cycles.

[0109] Example 8

[0110] Micron-sized silicon with a Dv50 of 3.5 μm and a first graphene material with a sheet size of 42 μm and 9 layers were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 20% of the mass percentage of the first mixed phase.

[0111] The first mixed phase was treated under a nitrogen atmosphere at 1000°C for 4 hours to obtain the second mixed phase;

[0112] The second mixed phase and a second graphene material with a sheet size of 49 μm and a number of layers of 6 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 16% of the mass percentage of the third mixed phase;

[0113] The third mixed phase was heat-treated at 850°C for 9 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0114] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.2 Al 0.2 Ti 1.8 (PO4)3 is assembled into a solid-state battery using the method described above.

[0115] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 93%.

[0116] The present invention also provides some comparative examples for comparison with the above embodiments.

[0117] Comparative Example 1

[0118] Micron-sized silicon with a Dv50 of 3.2 μm and a first graphene material with a sheet size of 42 μm and 12 layers were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 22% of the mass percentage of the first mixed phase.

[0119] The first mixed phase was treated at 650°C under a nitrogen atmosphere for 4 hours to obtain the second mixed phase;

[0120] The second mixed phase and a second graphene material with a sheet size of 55 μm and 26 layers were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 12% of the mass percentage of the third mixed phase.

[0121] The third mixed phase was heat-treated at 850°C for 6 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0122] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.1 Al 0.1 Zr 1.9 (PO4)3 is assembled into a solid-state battery using the method described above.

[0123] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 68%.

[0124] Comparative Example 2

[0125] Micron-sized silicon with a Dv50 of 3.2 μm and a first graphene material with a sheet size of 29 μm and a number of layers of 3 were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 22% of the mass percentage of the first mixed phase.

[0126] The first mixed phase was treated at 650°C under a nitrogen atmosphere for 4 hours to obtain the second mixed phase;

[0127] The second mixed phase and a second graphene material with a sheet size of 57 μm and 8 layers were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 12% of the mass percentage of the third mixed phase;

[0128] The third mixed phase was heat-treated at 850°C for 6 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0129] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.1 Al 0.1 Zr 1.9 (PO4)3 is assembled into a solid-state battery using the method described above.

[0130] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate was 70% after 100 cycles.

[0131] Comparative Example 3

[0132] Micron-sized silicon with a Dv50 of 3.2 μm and a first graphene material with a sheet size of 56 μm and 6 layers were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 22% of the mass percentage of the first mixed phase.

[0133] The first mixed phase was treated at 650°C under a nitrogen atmosphere for 4 hours to obtain the second mixed phase;

[0134] The second mixed phase and a second graphene material with a sheet size of 36 μm and a number of layers were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 12% of the mass percentage of the third mixed phase;

[0135] The third mixed phase was heat-treated at 850°C for 6 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0136] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. The solid electrolyte is Li. 1.1 Al 0.1 Zr 1.9 (PO4)3 is assembled into a solid-state battery using the method described above.

[0137] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 66%.

[0138] Comparative Example 4

[0139] Micron-sized silicon with a Dv50 of 3.6 μm and a first graphene material with a sheet size of 32 μm and a number of layers of 6 were mixed uniformly in a certain proportion to obtain a first mixed phase; wherein the first graphene material accounted for 22% of the mass percentage of the first mixed phase;

[0140] The first mixed phase was treated at 650°C under a nitrogen atmosphere for 4 hours to obtain the second mixed phase;

[0141] The second mixed phase and a second graphene material with a sheet size of 55 μm and a number of layers of 3 were mixed in a certain proportion and spray-dried to obtain a third mixed phase; wherein the second graphene material accounted for 12% of the mass percentage of the third mixed phase;

[0142] The third mixed phase was heat-treated at 850°C for 6 hours in a nitrogen atmosphere, and then demagnetized in stages to obtain the negative electrode active material.

[0143] After obtaining the negative electrode active material, the preparation methods for the negative electrode sheet and the positive electrode sheet are as described above. LiPF6 (EC:DMC = 1:1) is selected as the electrolyte for assembling the liquid battery.

[0144] According to the test conditions of Example 1 above, a cyclic test was conducted, and the capacity retention rate after 100 cycles was 84%.

[0145] As can be seen from Examples 1-8, the capacity retention rate of silicon-based batteries is significantly improved by designing all-solid-state batteries. Comparative Example 1 shows that when using a thicker graphene double-layer coating, the mechanical properties of the graphene are insufficient to support long-term volume expansion, resulting in rapid cycle degradation. Comparative Example 2 shows that coating with a thin layer followed by a thick layer of graphene does not significantly improve the material's cycle performance. Comparative Example 3 shows that using a small-layer graphene coating on the outer layer results in an unsatisfactory coating effect, with some exposed silicon remaining uncoated, thus leading to a relatively lower lifespan. Comparative Example 4 shows that when using a conventional liquid electrolyte, the continuous expansion of silicon particles after the formation of the SEI film causes continuous rupture of the SEI film, resulting in unsatisfactory battery cycle performance.

[0146] The electrochemical device of this invention uses micron-sized silicon as the raw material, with in-situ coating of a tough alloy, which increases the electronic conductivity of the silicon-based material. Simultaneously, the toughness of the alloy layer confines the volume expansion caused by lithium-ion insertion / extraction. The outer soft carbon coating improves charge / discharge capacity and efficiency, and enhances cycle performance.

[0147] In electrochemical devices, micron-sized silicon bilayer graphene permeation coating effectively alleviates material volume expansion, while the good ductility of the graphene thin layer improves the interface problem with the solid electrolyte, effectively improving the first cycle efficiency and cycle performance.

[0148] The electrochemical device of this invention can be an all-solid-state battery, effectively avoiding the formation of a solid electrolyte interphase (SEI) film and electrolyte leakage problems, thus improving the safety performance and service life of the electrochemical device. By combining micron-sized silicon with a solid electrolyte, a highly thermally stable solid electrolyte replaces the flammable conventional organic solvent electrolyte, solving the problem of easy combustion of lithium-ion batteries. Moreover, since the electrolyte is non-fluid, it can be easily assembled into high-voltage cells through internal series connection, which is beneficial to improving the assembly efficiency and energy density of the power battery system. Furthermore, the micron-sized silicon bilayer graphene permeation coating effectively alleviates the material volume expansion, while the good ductility of the graphene thin layer improves the interface problem with the solid electrolyte, effectively improving the first-cycle efficiency and cycle performance. This invention, by combining graphene, micron-sized silicon, and solid electrolyte in a specific manner, can obtain lithium batteries with excellent performance, especially solid-state lithium batteries.

[0149] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a negative electrode and a solid electrolyte; The negative electrode sheet includes a negative electrode material layer, and the solid electrolyte is in contact with the negative electrode material layer; The negative electrode material layer includes a negative electrode active material, which is composed of micron-sized silicon and a bilayer graphene material coated with micron-sized silicon. Specifically, a first graphene material forms a first mixed phase with the micron-sized silicon; this first mixed phase is heat-treated to form a second mixed phase, which is then heat-treated to form a third mixed phase with the second graphene material. The third mixed phase is then heat-treated to form the negative electrode active material. The first graphene material accounts for 10%-30% of the mass percentage of the first mixed phase; the second graphene material accounts for 5%-20% of the mass percentage of the third mixed phase. The first graphene material has 2-10 layers, and the size of each layer is ≤45μm. The second graphene material has 1-9 layers, and the size of each layer is ≤65μm. The second graphene material has fewer layers than the first graphene material; the sheet size of the second graphene material is larger than the sheet size of the first graphene material. The Dv50 of the micron-sized silicon is 1μm≤Dv50≤5μm.

2. The electrochemical device according to claim 1, characterized in that, The electrochemical device is a solid-state battery or a capacitor.

3. The electrochemical device according to claim 1, characterized in that, The solid electrolyte has the general chemical formula: Li 1+ x A x B 2-x (PO4)3, where x is between 0.01 and 0.5, A includes one or more of Al, Y, Ga, Cr, In, Fe, Se, or La, and B includes one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, hafnium (Hf), and their derivatives; or, Li x A y Zr 2- y Si x-y-1 P 4-x+y O 12 1≤x≤5, 0<y≤1, A includes one or more of Al, Cr, Fe, Ga, Se, Y, In or La; or, Na x A y Zr 2-y Si x-y-1 P 4-x+y O 12 2.5≤x≤3.5, 0<y≤1, A includes one or more of Al, Cr, Fe, Ga, Se, Y, In, and La; or, Li 3x La 2 / 3-x TiO3, where x is between 0.01 and 0.

5.

4. The electrochemical device according to claim 1, characterized in that, The negative electrode material layer also includes a dispersant and a binder.

5. An electronic device, characterized in that, The electronic device includes the electrochemical device according to any one of claims 1 to 4.

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