Negative active material, pole piece, and electrochemical device and electric device comprising same

Abstract

The invention relates to a negative electrode active material, a pole piece and an electrochemical device and an electric device comprising the same, and belongs to the technical field of electrochemical energy storage. The negative electrode active material comprises an inner core, a first coating layer and a second coating layer, the first coating layer and the second coating layer sequentially coat at least part of the surface of the inner core, the inner core comprises a silicon material, the first coating layer comprises polydopamine, and the second coating layer comprises silver. According to the negative electrode active material, the silicon material is adopted as an inner core, the surface of the inner core is sequentially coated with the polydopamine layer and the silver, the polydopamine layer has excellent reducibility and adhesion, so that the silver coating layer can be uniformly reduced and deposited in situ, the silver coating layer and lithium can be subjected to alloying reaction to generate Ag-Li alloy, the interfacial ion transport kinetics is improved, and the conductivity of the lithium ion battery is improved. And the ductility of the silver coating layer can buffer the volume expansion of silver and stabilize the interface, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application belongs to the field of electrochemical energy storage technology, specifically relating to negative electrode active materials, electrode sheets, and electrochemical devices and electrical devices including them. Background Technology

[0002] Sulfide-based all-solid-state batteries have become a research hotspot for next-generation energy storage technologies due to their high safety and high energy density. Silicon is considered an ideal anode material due to its ultra-high theoretical specific capacity; however, its large volume expansion and poor interfacial stability, especially when in contact with sulfide solid electrolytes (such as LPSCl and LGPS), can lead to severe interfacial side reactions and mechanical failures, resulting in rapid capacity decay and shortened cycle life. Current technologies for improving silicon anodes primarily target liquid electrolyte systems (such as carbon coating), but these strategies often have limited effectiveness in sulfide-based all-solid-state systems. Therefore, developing anode active materials that can improve the performance of sulfide-based all-solid-state batteries is of great significance. Summary of the Invention

[0003] The purpose of this application is to overcome the problems existing in the prior art and provide a negative electrode active material, an electrode sheet, and an electrochemical device and an electrical device including the same.

[0004] This application is implemented through the following technical solution: This application provides a negative electrode active material, including a core and a first coating layer and a second coating layer sequentially covering the outer surface of the core. The core includes silicon material, the first coating layer includes polydopamine, and the second coating layer includes silver.

[0005] In some embodiments, the mass fraction of silver in the negative electrode active material is W%, satisfying 2% ≤ W% ≤ 15%.

[0006] In some embodiments, the mass fraction of polydopamine in the negative electrode active material is V%, satisfying 0.5% ≤ V% ≤ 5%.

[0007] In some embodiments, the thickness of the second coating layer is T nm, satisfying 10 nm ≤ T nm ≤ 100 nm.

[0008] In some embodiments, the D50 particle size of the silicon material is D μm, satisfying 0.5μm≤Dμm≤10μm.

[0009] In some implementations, T and D satisfy 1 ≤ T / D ≤ 20.

[0010] In another aspect, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material described in this application.

[0011] In some embodiments, the negative electrode active material layer satisfies: 0.01 ≤ I Ag / I Si ≤0.2, where I Ag I represents the peak intensity of the silver (111) diffraction peak in the XRD pattern of the negative electrode active material layer. Si The peak intensity of the silicon (111) diffraction peak in the XRD pattern of the negative electrode active material layer is given.

[0012] In another aspect, this application provides an electrochemical device, comprising a positive electrode and a negative electrode as described in this application, wherein the positive electrode comprises a positive electrode material, and the areal capacity of the positive electrode material is C mAh / cm². 2 The relationship between C and the mass fraction W% of Ag in the negative electrode active material is: 1 ≤ W / C ≤ 10.

[0013] In some embodiments, the electrochemical device includes a solid electrolyte, which includes a sulfide solid electrolyte.

[0014] This application further provides an electrical device, including the electrochemical device described in this application.

[0015] This application has the following beneficial effects: This application uses silicon as the core of the negative electrode active material, with a polydopamine layer and a silver layer sequentially coated on its surface. The polydopamine layer has excellent reducing and adhesive properties, enabling in-situ and uniform reduction and deposition of the silver coating layer. This results in a continuous, dense, and uniform silver coating layer, with the silver existing in a metallic state. During battery charging and discharging, the silver in the coating layer undergoes an alloying reaction with lithium to form Ag-Li alloys (such as LiAg, Li2Ag, etc.). This alloy phase has extremely high mixed ionic and electronic conductivity, which significantly enhances the transport capacity of lithium ions at the interface between the negative electrode material and the sulfide solid electrolyte, effectively reducing interface impedance and thus significantly improving the rate performance of the all-solid-state battery. In addition, metallic silver has good ductility and mechanical strength. This silver coating layer can effectively constrain and buffer the large volume changes of silicon particles during cycling, reducing particle breakage. At the same time, it acts as a physical barrier, reducing direct contact between silicon and the sulfide solid electrolyte, suppressing unfavorable interfacial side reactions between the two, and together significantly improving the cycle stability of the all-solid-state battery. Attached Figure Description

[0016] Figure 1The XRD pattern of the negative electrode active material layer in the all-solid-state battery is shown in Example 1. Detailed Implementation

[0017] In the description of this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0018] In the description of this application, the use of terms such as "first," "second," etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0019] Throughout the description of this application, references to "some embodiments," "partial embodiments," "one embodiment," "another embodiment," "a specific embodiment," or "partial embodiment" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example.

[0020] In the description of this application, a list of items connected by the terms “one of,” “one of,” “a kind of,” or other similar terms may mean any one of the listed items; a list of items connected by the term “at least one of” may mean any combination of the listed items.

[0021] In the description of this application, numerical ranges are referred to. Unless otherwise specified, such numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0023] This application provides a negative electrode active material, including a core and a first coating layer and a second coating layer sequentially coating at least a portion of the surface of the core, wherein the core comprises silicon material, the first coating layer comprises polydopamine, and the second coating layer comprises silver.

[0024] This application uses silicon as the core of the negative electrode active material, with a polydopamine layer and silver sequentially coated on its surface. The polydopamine layer has excellent reducing and adhesive properties, enabling in-situ and uniform reduction and deposition of the silver coating layer. This results in a continuous, dense, and uniform silver coating layer, with the silver existing in a metallic state. During battery charging and discharging, the silver in the coating layer undergoes an alloying reaction with lithium to form Ag-Li alloys (such as LiAg, Li2Ag, etc.). This alloy phase has extremely high mixed ionic and electronic conductivity, which significantly enhances the transport capacity of lithium ions at the interface between the negative electrode material and the sulfide solid electrolyte, effectively reducing interface impedance and thus significantly improving the rate performance of the all-solid-state battery. In addition, metallic silver has good ductility and mechanical strength. This silver coating layer can effectively constrain and buffer the large volume changes of silicon particles during cycling, reducing particle breakage. At the same time, it acts as a physical barrier, reducing direct contact between silicon and the sulfide solid electrolyte, suppressing unfavorable interfacial side reactions between the two, and together significantly improving the cycle stability of the all-solid-state battery.

[0025] It should be noted that the coating described in this application can be full coating or partial coating (such as island-shaped or mesh-shaped coating).

[0026] In some embodiments, the mass fraction of silver in the negative electrode active material is W%, satisfying 2% ≤ W% ≤ 15%.

[0027] Specifically, the method for testing and calculating the mass fraction of silver in the negative electrode active material can be as follows: the molar content of silver in the negative electrode active material is tested by ICP, and then converted into the mass and mass fraction of silver. The mass fraction of silver in the negative electrode active material = the mass of silver in the negative electrode active material / the mass of the negative electrode active material.

[0028] For example, the mass fraction W% of silver in the negative electrode active material can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, or fall within the range of any two of the above values.

[0029] In some embodiments, the mass fraction of polydopamine in the negative electrode active material is V%, satisfying 0.5% ≤ V% ≤ 5%.

[0030] It should be noted that the test and calculation method for the mass fraction V% of polydopamine in the negative electrode active material is as follows: In an air atmosphere, polydopamine will oxidize and decompose between 250℃ and 500℃, and silicon will oxidize to SiO2 at >600℃. Taking the mass at 300℃ as the baseline (at this point, physically adsorbed water has been removed, and polydopamine (PDA) has not decomposed in large quantities), the mass loss up to 500℃ is observed. This loss is mainly attributed to the decomposition of PDA. The mass fraction of polydopamine in the negative electrode active material is V% = (m 300℃ -m 500℃ ) / m 300℃ ×100%.

[0031] For example, the mass fraction of silicon material in the negative electrode active material can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or fall within the range of any two of the above values.

[0032] In some embodiments, the thickness of the second coating layer is T nm, satisfying 10 nm ≤ T nm ≤ 100 nm.

[0033] Specifically, the thickness of the second coating layer was obtained by TEM transmission electron microscopy.

[0034] For example, the thickness of the second coating layer may be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, or within the range of any two of the above values.

[0035] In some embodiments, the silicon material includes micron-sized silicon.

[0036] In some embodiments, the D50 particle size of the silicon material is D μm, satisfying 0.5μm≤Dμm≤10μm.

[0037] D50 refers to the particle size corresponding to a cumulative particle distribution of 50%. For example, the D50 particle size of the silicon material is 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm or 10μm, or within the range of any two of the above values.

[0038] In some implementations, T and D satisfy 1 ≤ T / D ≤ 20.

[0039] For example, the T / D can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, or be within the range of any two of the above values.

[0040] This study found that when T / D is within the above range, it ensures that the functional layer can construct continuous ion / electron pathways at the microscale, effectively manage the huge mechanical stress of the silicon anode, and also act as a stable interface buffer layer at the macroscale.

[0041] In some implementations, T and D satisfy 5 ≤ T / D ≤ 16.

[0042] In some embodiments, the average grain size d of the silver is 10 nm to 100 nm.

[0043] The silver particles in the silver coating obtained in this application are at the nanoscale. Specifically, the average size of the silver grains was observed by SEM and TEM transmission electron microscopy.

[0044] For example, the average grain size d of the silver can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, or fall within the range of any two of the above values.

[0045] In another aspect, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material described in this application.

[0046] In some embodiments, the negative electrode active material layer satisfies: 0.01 ≤ I Ag / I Si ≤0.2, where I Ag I represents the peak intensity of the silver (111) diffraction peak in the XRD pattern of the negative electrode active material layer. SiThe peak intensity of the silicon (111) diffraction peak in the XRD pattern of the negative electrode active material layer is given.

[0047] This study found that when the intensity of the (111) diffraction peak of silver in the negative electrode active material layer and the (111) diffraction peak of silicon material meet the above range, the relative content of silver and the degree of silicon crystallization can be better matched, forming an effective conductive network and ensuring ion transport, so that the battery has better conductivity and interface stability, thereby effectively improving the performance of the battery.

[0048] For example, the I Ag / I Si It can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.04, 0.15, 0.16, 0.17, 0.18, 0.19 or 0.2, or fall within the range of any two of the above values.

[0049] It should be noted that the XRD pattern of the negative electrode active material layer was tested under the following conditions: Cu Kα radiation source, scanning speed 2° / min, step size 0.02°, where the diffraction peak of the silver (111) plane is (2θ≈38.1°) and the diffraction peak of the silicon (111) plane is (2θ≈28.4°), and the peak intensity refers to the integrated intensity.

[0050] In some embodiments, the negative electrode active material layer satisfies: 0.04 ≤ I Ag / I Si ≤0.1, where I Ag I represents the peak intensity of the silver (111) diffraction peak in the XRD pattern of the negative electrode active material layer. Si The peak intensity of the silicon (111) diffraction peak in the XRD pattern of the negative electrode active material layer is given.

[0051] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate. In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon.

[0052] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent.

[0053] In some embodiments, the negative electrode binder may include at least one of the following: polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0054] In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0055] This application also provides an electrochemical device, including any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, including, but not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0056] In some embodiments, the electrochemical device includes a positive electrode and a negative electrode as described in this application, wherein the positive electrode includes a positive electrode material with an areal capacity of C mAh / cm². 2 The relationship between C and the mass fraction W% of Ag in the negative electrode active material is: 1 ≤ W / C ≤ 10.

[0057] This application research found that when the areal capacity of the positive electrode material and the mass fraction of Ag in the negative electrode active material are within the above range, the negative electrode has sufficient silver to construct a stable and efficient hybrid conductive network and buffer layer to meet the electrochemical and mechanical stress requirements determined by the positive electrode capacity, thereby ensuring the battery's excellent rate performance and cycle life; and that excessive use of the precious metal silver leads to energy density loss and cost spikes.

[0058] Specifically, the method for testing and calculating the areal capacity of the positive electrode material is as follows: after the battery under test is completely discharged to the cutoff voltage with a small current (such as 0.1C), the positive electrode sheet is disassembled and removed. The positive electrode sheet is soaked in dimethyl carbonate for 2 hours and then dried. The treated positive electrode sheet is used as the working electrode and the lithium metal sheet is used as the counter electrode / reference electrode. The two electrodes are assembled into a coin cell (CR2032 type) in a glove box for electrochemical testing.

[0059] In some embodiments, the areal capacity of the positive electrode material is 2 mAh / cm². 2 ~5mAh / cm 2 For example, it could be 2mAh / cm³. 2 2.5mAh / cm 2 2.8mAh / cm 2 3mAh / cm 2 3.5mAh / cm 2 4mAh / cm 2 4.5mAh / cm 2 5mAh / cm 2 Or it falls within the range of any two of the above values.

[0060] In some embodiments, the positive electrode sheet may include a positive current collector and a positive electrode material layer disposed on at least one side of the positive current collector.

[0061] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0062] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0063] In some embodiments, the positive electrode material layer may include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0064] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al zThe group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0065] In some embodiments, the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0066] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof. In some embodiments, the dopant is not Fe, Ni, Mn, Mg, Zn, Ti, La, Ce, Ru, Si, or Ge. In some embodiments, the dopant is not Al, Sn, or Zr.

[0067] In some embodiments, the positive electrode active material may include LiNi. 0.33 Mn 0.33 Co 0.33 O2, LiNiO2, LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0068] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), polyisobutylene (PIB), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0069] In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0070] In some embodiments, the electrochemical device includes a solid electrolyte, which includes a sulfide solid electrolyte.

[0071] In some embodiments, the sulfide solid electrolyte includes Li 10 GeP2S 12 At least one of (LGPS) and Li6PS5Cl (LPSCl).

[0072] This application further provides an electrical device, including the electrochemical device described in this application.

[0073] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. According to some embodiments of this application, the electrical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and embodied intelligent robots.

[0074] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description will be provided in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0075] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0076] Example 1 A negative electrode active material is prepared by the following method: (1) Disperse 1.0 g of micron-sized silica powder (D50=5μm) in 200 mL of Tris buffer (10 mM, pH=8.5) and sonicate for 30 minutes; (2) Add 0.1 g of dopamine hydrochloride and stir the reaction at room temperature for 4 hours; (3) Add 30 mL of 0.01 M silver nitrate solution dropwise and continue stirring in the dark for 6 hours; (4) After the reaction is complete, the product is collected by centrifugation, washed three times with deionized water and three times with ethanol, and dried under vacuum at 60°C for 12 hours to obtain the negative electrode active material.

[0077] In this embodiment, the mass fraction of silver in the negative electrode active material was 3.2% as determined by ICP testing.

[0078] Examples 2-6 This embodiment provides a negative electrode active material. The difference from Embodiment 1 is that the amount of silver nitrate solution added in step (3) and dopamine hydrochloride added in step (2) of this embodiment is different from that in Embodiment 1 to achieve the parameters in Table 1 and Table 2, which are specifically shown in Table 1 and Table 2.

[0079] Examples 7-10 This embodiment provides a negative electrode active material. The difference from Embodiment 1 is that the D50 particle size of the micron-sized silicon powder used in step (1) of this embodiment is different from that in Embodiment 1 to achieve the parameters in Table 1, which are shown in Table 1.

[0080] Examples 11-12 This embodiment provides a negative electrode active material. The difference from Embodiment 1 is that the D50 particle size of the micron-sized silicon powder used in step (1) and the amount of silver nitrate solution added in step (2) are different from those in Embodiment 1 to achieve the parameters in Table 1, which are shown in Table 1.

[0081] The negative electrode active materials of the examples were respectively used to prepare all-solid-state batteries for electrochemical devices. The preparation method of the all-solid-state batteries is as follows: (1) Preparation of the positive electrode: The positive electrode active material LiCoO2, sulfide solid electrolyte (lithium-sulfur-phosphorus-chloride fast ion conductor, Li6PS5Cl), positive electrode conductive agent (vapor-grown carbon fiber, VGCF), and positive electrode binder (polyisobutylene, PIB) were mixed in a mass ratio of 75:21:2:2. Pxylene (PX) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 45 wt%. A 9 µm aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was uniformly coated onto one surface of the current collector. After drying, cold pressing, and cutting, a positive electrode with a single-sided layer of positive electrode active material was obtained. The areal capacity C of the positive electrode material in the positive electrode sheet was 2.8 mAh / cm². 2 .

[0082] (2) Preparation of negative electrode: The negative electrode active material, conductive agent (vapor-grown carbon fiber, VGCF), and binder (polyacrylic acid, PAA) of each embodiment are mixed in a mass ratio of 90:3:7 to form a slurry, coated and dried to obtain a negative electrode sheet. (3) Assembly of all-solid-state batteries 150 μm thick LPSCl powder was cold-pressed into a dense separator at 300 MPa to obtain an electrolyte layer. The electrolyte layer and the negative electrode were stacked in a mold in the order of positive electrode, electrolyte layer and negative electrode. The whole assembly was isostatically pressed at 500 MPa for 5 minutes to obtain an all-solid-state battery.

[0083] Examples 13-16 This embodiment provides an all-solid-state battery. The difference between this embodiment and the all-solid-state battery obtained in Embodiment 1 is that the crystallinity of the micron-sized silicon powder used in step (1) of the preparation of the negative electrode active material is increased by calcining at 700°C or by mechanical ball milling to reduce the crystallinity. The calcination time and ball milling time are controlled to achieve the parameters in Table 2, which are shown in Table 2.

[0084] Examples 17-19 This embodiment provides an all-solid-state battery. The difference between this embodiment and the all-solid-state battery obtained in Embodiment 1 is that the areal capacity of the positive electrode material is adjusted by adjusting the mass ratio of LCO, LPSCl and VGCF in the positive electrode sheet, as shown in Table 1.

[0085] The XRD pattern of the negative electrode active material layer in the all-solid-state battery obtained in Example 1 is as follows: Figure 1 As shown, from Figure 1 The characteristic peak positions of Ag can be seen as: 38.1° (111), 44.3° (200), 64.4° (220), and 77.5° (311), indicating that silver ions are reduced to metallic silver. The peak intensity of the silver (111) diffraction peak is I. Ag And the peak intensity I of the diffraction peak of silicon material (111). SiIt is shown in Table 2.

[0086] In the examples, the D50 particle size Dμm of micron-sized silicon, the thickness T nm of the second coating layer, the mass fraction W% of silver in the negative electrode active material, and the areal capacity C mAh / cm² of the positive electrode material in the all-solid-state battery are also specified. 2 The mass fraction V% of polydopamine in the negative electrode active material and the peak intensity I of the silver (111) diffraction peak. Ag And the peak intensity I of the (111) diffraction peak of silicon material Si The results are shown in Tables 1 and 2.

[0087] Table 1. Parameters of the negative electrode active material and all-solid-state battery in the embodiments. Table 2. Parameters of the negative electrode active material and all-solid-state battery in the embodiments. Comparative Example 1 This comparative example provides a negative electrode active material, the preparation method of which is as follows: (1) Disperse 1.0 g of micron-sized silica powder (D50=5μm) in 200 mL of Tris buffer (10 mM, pH=8.5) and sonicate for 30 minutes; (2) Add 30 mL of 0.01 M silver nitrate solution dropwise, add the reducing agent L-ascorbic acid, and continue to stir the reaction in the dark for 6 hours; (3) After the reaction is complete, the product is collected by centrifugation, washed three times with deionized water and ethanol, and dried under vacuum at 60°C for 12 hours to obtain the negative electrode active material.

[0088] That is, the difference between this comparative example and Example 1 is that dopamine hydrochloride is not added, and the final negative electrode active material does not contain a polydopamine layer.

[0089] Comparative Example 2 This comparative example provides a negative electrode active material, which is prepared by ball milling micron-sized silicon powder (D50=5μm) and silver powder at a mass ratio of 96.8:3.2 to obtain the negative electrode active material of this comparative example.

[0090] Comparative Example 3 This comparative example uses micron-sized silicon powder with a D50 of 5 μm as the negative electrode active material.

[0091] The negative electrode active material of the comparative example was prepared into an all-solid-state battery according to the aforementioned preparation method. The all-solid-state batteries obtained in the examples and the comparative example were subjected to the following performance tests: 1. Cyclic performance: Constant current and constant voltage charging was performed at a charging current of 0.1C until the upper limit voltage was 4.5V, and then constant current discharging was performed at a discharging current of 0.1C until the final voltage was 3V. The charge and discharge capacity of the first cycle was recorded to calculate the 0.1C first efficiency. Then, 100 charge and discharge cycles were performed, and the discharge capacity of the 100th cycle was recorded to calculate the cycle capacity retention rate. 2. Interface Impedance Test: The assembled battery is subjected to a small AC voltage disturbance of 10mV in a frequency range of 0.01 Hz to 1 MHz under a specific state of charge by EIS test. Its impedance response is measured. The interface impedance is obtained by analyzing the obtained Nyquist spectrum and fitting it with an equivalent circuit.

[0092] The test results are shown in Table 3 below.

[0093] Table 3. Performance test results of all-solid-state batteries in the examples and comparative examples. As can be seen from the test results in Table 3, compared with the comparative example, the all-solid-state battery of the embodiment has excellent electrochemical performance, indicating that the structure of the negative electrode active material of this application can effectively improve the conductivity of silicon material, enhance interfacial ion transport by utilizing the Ag-Li alloying reaction, and buffer volume expansion through the ductility of the silver coating layer, thus significantly improving the electrochemical performance of silicon-based negative electrode active material.

[0094] The negative electrode active material in Comparative Example 1 lacks a polydopamine coating layer, resulting in uneven silver particle distribution and easy aggregation in the silver coating layer, thus reducing battery performance. In Comparative Example 2, the negative electrode active material obtained through simple physical mixing leads to uneven silver distribution and low conductivity, resulting in high interfacial impedance and poor cycle performance. In Comparative Example 3, ordinary micron-sized silicon is used as the negative electrode active material, which exhibits extremely poor activity, very high interfacial impedance, and a significant decrease in cycle performance in an all-solid-state battery.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A negative electrode active material, characterized by, The core comprises a silicon material, the first coating layer comprises polydopamine, and the second coating layer comprises silver.

2. The negative electrode active material according to claim 1, characterized by The mass fraction of the silver in the negative electrode active material is W%, and 2%≤W%≤15%.

3. The negative electrode active material according to claim 1, characterized by The thickness of the second coating layer is T nm, and 10nm≤T nm≤100nm.

4. The negative electrode active material according to claim 3, characterized by The D50 particle size of the silicon material is D μm, and 0.5μm≤D μm≤10μm.

5. The negative electrode active material according to claim 4, characterized by The T and the D satisfy 1≤T / D≤20.

6. The negative electrode active material according to claim 1, characterized by The mass fraction of the polydopamine in the negative electrode active material is V%, and 0.5%≤V%≤5%.

7. A negative electrode sheet characterized by comprising: The electrochemical device comprises a solid-state electrolyte, and the solid-state electrolyte comprises a sulfide solid-state electrolyte.

8. The negative electrode sheet according to claim 7, characterized by The negative electrode active material layer satisfies: 0.01 ≤ I Ag / I Si ≤ 0.2, where I Ag is the peak intensity of a silver (111) diffraction peak in an XRD pattern of the negative electrode active material layer, and I Si is the peak intensity of a silicon material (111) diffraction peak in the XRD pattern of the negative electrode active material layer.

9. An electrochemical device, characterized by, The secondary battery includes the positive electrode sheet and the negative electrode sheet according to claim 7 or 8, the positive electrode sheet includes a positive electrode material, a surface capacity of the positive electrode material is C mAh / cm 2 , and the C and a mass fraction W% of Ag in the negative electrode active material satisfy a relationship: 1 ≤ W / C ≤ 10.

10. The electrochemical device of claim 9, wherein, The electrochemical device comprises a solid-state electrolyte, and the solid-state electrolyte comprises a sulfide solid-state electrolyte.

11. An electrical device, characterized by The electrochemical device comprises a solid-state electrolyte, and the solid-state electrolyte comprises a sulfide solid-state electrolyte.

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