An electrochemical device and a negative electrode sheet

Abstract

The present application relates to an electrochemical device and a negative electrode sheet. The electrochemical device includes an electrolyte, a positive electrode sheet, and a negative electrode sheet, the negative electrode sheet including a negative electrode active material, the negative electrode active material including a silicon-carbon material, the silicon-carbon material including a porous carbon material and nano-silicon-based particles, wherein the porous carbon material has a pore structure inside, the nano-silicon-based particles are distributed at least within the pore structure, and the nano-silicon-based particles have a particle size dsi of 3 nm to 15 nm. The electrochemical device has a high energy density while also having an improved initial coulomb efficiency.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to an electrochemical device and a negative electrode plate. Background Technology

[0002] New energy vehicles have seen significant development in recent years as an important means of achieving carbon emission reduction globally. Lithium-ion batteries, as a common electrochemical device, have become the most popular energy storage system due to their high operating voltage, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields.

[0003] With people's increasing demands for new energy vehicles, electrochemical devices need to have high energy density. Silicon-carbon materials, due to their high specific capacity, are widely used to improve the energy density of electrochemical devices.

[0004] The initial coulombic efficiency of silicon-carbon materials is generally lower than that of commercial graphite. Therefore, improving the initial coulombic efficiency of electrochemical devices while ensuring high energy density has become an urgent technical problem to be solved. Summary of the Invention

[0005] In view of this, the main objective of the present invention is to provide an electrochemical device and a negative electrode. This electrochemical device possesses both high energy density and improved initial coulombic efficiency.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] The present invention provides an electrochemical device, including an electrolyte, a positive electrode, and a negative electrode. The negative electrode includes a negative electrode active material, which includes a silicon-carbon material. The silicon-carbon material includes a porous carbon material and nano-silicon-based particles. The porous carbon material has a pore structure inside, and the nano-silicon-based particles are at least distributed within the pore structure. The particle size (dsi) of the nano-silicon-based particles is 3 nm to 15 nm.

[0008] In some embodiments, the particle size (dsi) of the nano-silicon-based particles is 7 nm to 15 nm.

[0009] In some embodiments, the negative electrode active material further includes a coating layer that coats a porous carbon material.

[0010] In some embodiments, the coating layer is a carbon coating layer.

[0011] In some embodiments, the coating layer accounts for 0.5% to 2.3% of the mass of the negative electrode active material.

[0012] In some embodiments, the volume average particle size Dv50 of the porous carbon material is 3 μm to 15 μm.

[0013] In some embodiments, the volume average particle size Dv50 of the porous carbon material is 7 μm to 10 μm.

[0014] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g to 54m 2 / g.

[0015] In some embodiments, the volume average particle size Dv50 of the porous carbon material and the particle size dsi of the nano-silicon-based particles satisfy: 5*10 -3 ≥dsi / Dv50≥0.2*10 -3 .

[0016] Compared with the prior art, the beneficial effects of this application are as follows:

[0017] In the electrochemical device disclosed in this application, by controlling the particle size of the nano-silicon-based particles to be between 3 nm and 15 nm, the specific surface area of ​​the nano-silicon-based particles is appropriately controlled, which helps to reduce the surface area of ​​the nano-silicon-based particles in contact with the electrolyte, thereby reducing the consumption of active lithium ions. Simultaneously, the volume expansion of nano-silicon-based particles within this particle size range is relatively small during lithium intercalation; therefore, the probability of cracking in the negative electrode is low, which further helps to reduce the consumption of active lithium ions. The reduced consumption of active lithium ions thus improves the initial coulombic efficiency of the electrochemical device. Furthermore, the negative electrode active material used in the electrochemical device includes silicon-carbon materials. Silicon-carbon materials include porous carbon materials and nano-silicon-based particles distributed within the pore structure of the porous carbon materials. The nano-silicon-based particles have a high theoretical specific capacity, thus the electrochemical device has a high energy density. Attached Figure Description

[0018] Figure 1 A schematic diagram of the negative electrode active material according to one embodiment of this application is shown.

[0019] Explanation of reference numerals in the attached figures:

[0020] 100 Anode active material; 10 Silicon-carbon material; 20 Carbon coating layer; 1 Nano silicon-based particle; 2 Porous carbon material. Detailed Implementation

[0021] The technical solution of this application will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0022] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0023] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0024] Unless otherwise specified, in this application, "one or more" or "at least one" refers to any one, two, or more of the listed items. "Several" refers to any two or more.

[0025] Typically, an electrochemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte. During battery charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between them while allowing ions to pass through.

[0026] With increasing demands for new energy vehicles, electrochemical devices require high energy density. Silicon-carbon materials, due to their high specific capacity, are widely used to improve the energy density of electrochemical devices. However, the increased volume expansion rate after lithium intercalation in silicon-carbon materials can lead to cracking of the negative electrode, consuming active lithium ions and consequently deteriorating the initial coulombic efficiency of the electrochemical device. Therefore, improving the initial coulombic efficiency of electrochemical devices while ensuring high energy density has become a pressing technical problem.

[0027] Based on this, this application provides an electrochemical device, including an electrolyte, a positive electrode, and a negative electrode. The negative electrode includes a negative electrode active material, which includes a silicon-carbon material. The silicon-carbon material includes a porous carbon material and nano-silicon-based particles. The porous carbon material has a pore structure inside, and the nano-silicon-based particles are at least distributed within the pore structure. The particle size (dsi) of the nano-silicon-based particles is 3 nm to 15 nm.

[0028] In their research, the inventors discovered through extensive experimental analysis that if the particle size of the nano-silicon-based particles is too small, it will lead to a significant increase in their specific surface area, thereby forming more SEI films on the surface of the nano-silicon-based particles. This will consume a large number of active lithium ions, directly resulting in a decrease in the initial coulombic efficiency of the electrochemical device.

[0029] If the particle size of the nano-silicon particles is too large, a large volume expansion will occur during lithium ion insertion. The stress generated by this expansion may cause the negative electrode to crack and pulverize, which will consume a large number of active lithium ions, directly resulting in a decrease in the initial coulombic efficiency of the electrochemical device.

[0030] Based on the above findings, the electrochemical device of this application, by controlling the particle size of the silicon nanoparticles to be between 3 nm and 15 nm, achieves appropriate control over the specific surface area of ​​the silicon nanoparticles. This helps reduce the surface area of ​​the silicon nanoparticles in contact with the electrolyte, thereby reducing the consumption of active lithium ions. Simultaneously, the volume expansion of silicon nanoparticles within this particle size range is relatively small during lithium intercalation, thus reducing the probability of cracking in the negative electrode and further contributing to reduced consumption of active lithium ions. The reduced consumption of active lithium ions thereby improves the initial coulombic efficiency of the electrochemical device.

[0031] Furthermore, the negative electrode active material used in the electrochemical device includes silicon-carbon materials. Silicon-carbon materials comprise porous carbon materials and nano-silicon-based particles distributed within the pore structure of the porous carbon materials. These nano-silicon-based particles possess a high theoretical specific capacity, thereby enabling the electrochemical device to achieve a high energy density.

[0032] In this application, "porous carbon material" refers to a type of carbon material with a highly developed pore structure. Porous carbon materials possess a large number of uniformly distributed pore structures that can be used to accommodate nano-silicon-based particles. Porous carbon materials typically exhibit good electrical conductivity, and their combination with nano-silicon-based particles can enhance the electron transport capability of the entire composite material (silicon-carbon material), thereby accelerating charge transport speed and improving the fast-charging performance of electrochemical devices.

[0033] In this application, "nano-silicon-based particles" refers to silicon material particles with a particle size between 3 nm and 15 nm. Nano-silicon-based particles are typically composed of silicon and possess high specific capacity. Nano-silicon-based particles can be at least one of spherical, near-spherical, or polyhedral shapes. Exemplarily, nano-silicon-based particles are at least one of spherical, oblate, elongated ellipsoidal, nanoflower-like, or nanosheet-like shapes. Exemplarily, the particle size (dsi) of the nano-silicon-based particles can be any value within the range of 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or any combination thereof.

[0034] In this application, the particle size "dsi" of the silicon nanoparticles is defined as the projected diameter or equivalent diameter of the silicon nanoparticles as observed under a microscope.

[0035] In this application, the dsi (diameter of silicon) can be tested in the following way. The nano-silicon particles to be tested (can be prepared nano-silicon particles or obtained by disassembling a battery) are used. The latter is used as an example to illustrate the testing process. Specifically, the battery is disassembled to obtain the negative electrode sheet, the negative electrode film is peeled off, and then the negative electrode film is dissolved using a digesting agent to obtain the negative electrode active material (silicon-carbon material). The cross-sectional morphology (CP) of the negative electrode active material is tested using a cross-sectional polishing instrument to obtain a cross-sectional scanning electron microscope (SEM) image of the negative electrode active material. The cross-sectional SEM image can distinguish between porous carbon material and nano-silicon particles distributed within the pore structure of the porous carbon material. Finally, the particle size (dsi) of the nano-silicon particles is measured according to the scale bar in the cross-sectional SEM image. If the cross-section of the silicon nanoparticle is a regular circle, then dsi is the diameter of the silicon nanoparticle. If the cross-section of the silicon nanoparticle is not a regular circle, then dsi refers to the length of the longest line segment (i.e., the equivalent diameter) where the straight line passing through the geometric center of the cross-section intersects the edge of the cross-section.

[0036] In some embodiments, the particle size (dsi) of the silicon nanoparticles is between 7 nm and 15 nm. A particle size within this range can further reduce the consumption of active lithium ions, thereby further improving the initial coulombic efficiency of the electrochemical device.

[0037] In some embodiments, the negative electrode active material further includes a coating layer that coats a porous carbon material. The coating layer mitigates the volume expansion of the silicon-carbon material during lithium intercalation, reducing mechanical stress and breakage, allowing more silicon-carbon material to participate in the initial discharge and thus improving the initial coulombic efficiency of the electrochemical device. Furthermore, the coating layer isolates the porous carbon material from direct contact with the electrolyte, reducing unnecessary side reactions between the electrolyte and the porous carbon material or nano-silicon particles, thereby minimizing the loss of active material and further improving the initial coulombic efficiency.

[0038] In some embodiments, the coating layer is a carbon coating layer. Choosing carbon as the coating layer not only provides a coating effect and improves the initial coulombic efficiency of the electrochemical device, but also combines a variety of excellent properties such as high strength, toughness, adhesion, resistance to stress concentration, lightweight, fatigue resistance, and wear resistance. This helps to mitigate the volume expansion of silicon-carbon materials during charge and discharge, reducing the resulting mechanical stress and silicon-carbon material cracking, allowing more silicon-carbon material to participate in the discharge during the first discharge, thereby improving the initial coulombic efficiency of the electrochemical device.

[0039] Figure 1 This is a schematic diagram of the negative electrode active material according to an embodiment of this application, as shown below. Figure 1 As shown, the negative electrode active material 100 includes a silicon-carbon material 10, which comprises a porous carbon material 2 and nano-silicon-based particles 1, with the nano-silicon-based particles 1 distributed within the pore structure of the porous carbon material 2. The negative electrode active material 100 also includes a carbon coating layer 20, which coats the outer surface of the silicon-carbon material 10.

[0040] In some embodiments, the mass percentage of the coating layer relative to the negative electrode active material is between 0.5% and 2.3%. A coating layer percentage within this range is beneficial in two ways: firstly, it ensures uniform coating of the silicon-carbon material surface, thereby mitigating volume expansion of the silicon-carbon material during charge and discharge, and further improving the initial high coulombic efficiency of the electrochemical device. Secondly, it helps to increase the energy density of the electrochemical device. Exemplarily, the mass percentage of the coating layer relative to the negative electrode active material is any value within the range of 0.5%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.3%, or any combination thereof.

[0041] In some embodiments, the volume average particle size (Dv50) of the porous carbon material is between 3 μm and 15 μm. By controlling the volume average particle size of the porous carbon material within this range, the particle size of the resulting silicon-carbon material can be kept within a suitable range, reducing the consumption of active lithium ions. In particular, in embodiments where the negative electrode active material includes a coating layer, having the volume average particle size of the porous carbon material within this range can further improve the uniformity of the coating, thereby further reducing the consumption of active lithium ions and improving the first coulombic efficiency.

[0042] In this application, the term "volume average particle size" "Dv50" refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the material, which can be measured using a scanning electron microscope. The porous carbon material to be tested can be either a prepared porous carbon material or a porous carbon material obtained by disassembling a battery. The latter will be used as an example to illustrate the testing process. Specifically, the negative electrode sheet is obtained by disassembling the battery, the negative electrode film layer is peeled off, and then the negative electrode film layer is dissolved using a digesting agent to obtain the negative electrode active material (silicon-carbon material). The cross-sectional morphology (CP) of the negative electrode active material is tested using a cross-sectional polisher to obtain a cross-sectional SEM image of the negative electrode active material. The cross-sectional SEM image can distinguish between the porous carbon material and the nano-silicon-based particles distributed within the pore structure of the porous carbon material. Finally, the particle size of the porous carbon material is measured according to the scale bar in the cross-sectional SEM image. The particle size distribution of the porous carbon material is statistically analyzed to obtain the volume average particle size Dv50 of the porous carbon material.

[0043] In some embodiments, the volume average particle size Dv50 of the porous carbon material is 7 μm to 10 μm. This is beneficial for further improving the first coulombic efficiency. Exemplarily, the volume average particle size Dv50 of the porous carbon material can be any value within the range of 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or any combination thereof.

[0044] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g to 54m 2 / g. In this application, by controlling the specific surface area of ​​the negative electrode active material within the above-mentioned range, the contact between the negative electrode active material and the electrolyte can be limited, reducing the consumption of active lithium ions, thereby improving the first coulombic efficiency within the above-mentioned range. For example, the specific surface area of ​​the negative electrode active material can be 1m². 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g、2m 2 / g, 2.2m 2 / g, 2.4m 2 / g, 2.5m 2 / g、5m 2 / g, 10m 2 / g、20m 2 / g、30m 2 / g、40m 2 / g、54m 2 / g or any value within a range of either / g or any combination of both.

[0045] In embodiments where the negative electrode active material includes a coating layer, the specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g to 8m 2 / g. The introduction of the coating layer helps to reduce the specific surface area of ​​the negative electrode active material, thereby reducing the consumption of active lithium ions, and thus further improving the first coulombic efficiency of the electrochemical device.

[0046] In this application, specific surface area has a meaning known in the art, and it can be obtained by testing using instruments or methods known in the art. Specifically, the negative electrode active material is taken as the sample to be tested, and then the specific surface area of ​​the sample is tested using the gas adsorption method, specifically referring to the standard test of GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0047] In some embodiments, the volume average particle size Dv50 of the porous carbon material and the particle size dsi of the nano-silicon-based particles satisfy: 5*10 -3 ≥dsi / Dv50≥0.2*10 -3 In this application, by controlling the dsi / Dv50 within the aforementioned range, the particle size ratio of porous carbon material to nano-silicon-based particles is appropriately balanced. This facilitates the uniform dispersion of nano-silicon-based particles within the pore structure of the porous carbon material, reduces agglomeration of nano-silicon-based particles, and allows more nano-silicon-based particles to participate in the discharge during the first discharge, thereby further improving the first coulombic efficiency of the electrochemical device. For example, the dsi / Dv50 can be 0.2*10⁻⁶. -3 0.5*10 -3 1*10 -3 1.5*10 -3 2*10 -3 2.5*10 -3 3*10 -3 3.5*10 -3 4*10 -3 4.5*10-3 5*10 -3 Or any value within a range consisting of any two of them.

[0048] The following is a further explanation of the components of the electrochemical device:

[0049] The negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material. In this application, the negative electrode active material includes silicon-carbon material, and the silicon-carbon material includes porous carbon material and nano-silicon-based particles.

[0050] In some embodiments, the mass fraction of silicon in the silicon-carbon material in the negative electrode active material is between 1% and 30%. By controlling the mass fraction of silicon in the silicon-carbon material in the negative electrode active material within the above range, it is beneficial to improve the energy density of the electrochemical device and to balance the volume expansion of the negative electrode active material, thereby improving the first coulombic efficiency of the electrochemical device. Exemplarily, the mass fraction of silicon in the silicon-carbon material in the negative electrode active material can be any value within the range of 1%, 5%, 10%, 15%, 20%, 25%, 30%, or any combination thereof.

[0051] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0052] In some embodiments, the negative electrode may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0053] In some embodiments, the negative electrode may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0054] In some embodiments, the negative electrode may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0055] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0056] Electrolytes

[0057] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0058] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0059] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethylsulfonyl)methyl, or lithium bis(trifluoromethylsulfonyl)imide.

[0060] In some embodiments, the solvent comprises a carbonate, wherein the carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). The solvent may also comprise a carboxylic acid ester, wherein the carboxylic acid ester includes one or more of propyl propionate (PP), ethyl propionate (EP), propyl acetate (PA), and ethyl acetate (EA).

[0061] Positive electrode sheet

[0062] In this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0063] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0064] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0065] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0066] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0067] Separating membrane

[0068] In this application, the electrochemical device also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0069] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0070] In some implementations, the positive electrode, negative electrode, and separator are fabricated into an electrode assembly using a stacking process.

[0071] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0072] A second aspect of this application provides a negative electrode sheet, comprising a negative electrode active material, which includes a silicon-carbon material. The silicon-carbon material comprises a porous carbon material and nano-silicon-based particles. The porous carbon material has an internal pore structure, and the nano-silicon-based particles are at least distributed within the pore structure. The particle size (dsi) of the nano-silicon-based particles is 3 nm to 15 nm. The 3 nm to 15 nm particle size of the nano-silicon-based particles in this negative electrode sheet allows for appropriate control of the specific surface area of ​​the nano-silicon-based particles, which helps reduce the surface area of ​​the nano-silicon-based particles in contact with the electrolyte, thereby reducing the consumption of active lithium ions. Simultaneously, the volume expansion of nano-silicon-based particles within this particle size range is relatively small during lithium intercalation. Therefore, the probability of crack formation in the negative electrode sheet is low, which further helps reduce the consumption of active lithium ions. Further, the negative electrode sheet uses a silicon-carbon material as the negative electrode active material. The silicon-carbon material comprises a porous carbon material and nano-silicon-based particles distributed within the pore structure of the porous carbon material. The nano-silicon-based particles have a high theoretical specific capacity, and the electrochemical device containing this negative electrode has a high energy density.

[0073] Example

[0074] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0075] Example 1

[0076] (1) Preparation of negative electrode sheet:

[0077] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 3 μm) was placed in a fluidized bed apparatus at a temperature of 460 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material. The silicon-carbon material comprises porous carbon material and nano-silicon-based particles deposited within the pore structure of the porous carbon material.

[0078] The fluidized bed equipment temperature was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas flow for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material. The negative electrode active material includes silicon-carbon material and a carbon coating layer.

[0079] The negative electrode active material, conductive carbon (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in deionized water at a weight ratio of 85%:5%:6%:4%, stirred at 1200 rpm / min for 2 hours, and then stirred at 500 rpm / min until the negative electrode slurry was obtained.

[0080] Copper foil was used as the negative electrode current collector. Negative electrode slurry was coated onto both surfaces of the current collector, and the mixture was baked at 100°C for 3 hours to form a negative electrode film. Subsequently, cold pressing, cutting, and slitting were performed to prepare the negative electrode sheet. The areal density of the single-sided negative electrode active material in the negative electrode sheet was 200 g / m³. 2 .

[0081] (2) Preparation of positive electrode sheet

[0082] A 250μm lithium sheet is used as the positive electrode.

[0083] (3) Preparation of electrolytes

[0084] In an argon atmosphere, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC) are mixed in a weight ratio of 0.3:0.3:0.3:0.07:0.03 to form an organic solvent. LiPF6 is then dissolved in the organic solvent to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0085] (4) Preparation of the separating membrane

[0086] A polyethylene film with a thickness of 12μm was used as the separator.

[0087] (5) Assembly of electrochemical devices

[0088] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked electrode assembly is then placed in an aluminum-plastic film, dried at 80°C, and injected with the prepared electrolyte. After vacuum sealing, settling, formation, and shaping, the electrochemical device is obtained.

[0089] Testing of negative electrode active materials:

[0090] (1) Test of particle size dsi of nano-silicon-based particles.

[0091] The silicon-carbon material prepared in Example 1 was subjected to ion-polished cross-sectional morphology (CP) measurements using a Fischione 1061 SEM Mill and a scanning electron microscope (Hitachi SU 1510, with magnification parameters ranging from 1000x to 10000x) to obtain cross-sectional SEM images of the anode active material. These images allowed for the differentiation between porous carbon materials and the nano-silicon-based particles distributed within the pore structure of the porous carbon material. Finally, the particle size distribution (dsi) of the nano-silicon-based particles was measured using the scale bar in the cross-sectional SEM images. The test results are recorded in Table 1.

[0092] (2) Test of the specific surface area of ​​the negative electrode active material.

[0093] The nitrogen adsorption specific surface area was measured according to GB / T 19587-2017, and the result was calculated using the BET (Brunauer Emmett Teller) method. The testing instrument was a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA. The test results are recorded in Table 1.

[0094] (3) Testing the mass ratio of the coating layer.

[0095] Referring to GB / T38823-2020, the carbon content of the materials before and after carbon coating was tested using a DEKRA HCS-140 carbon-sulfur analyzer to obtain the mass percentage of the coating layer. The test results are recorded in Table 1.

[0096] Performance testing of electrochemical devices

[0097] (1) Initial Coulomb efficiency test

[0098] ① Charge the battery to 1.5V at a constant current of 0.05C and record the initial charge capacity C1.

[0099] ② Let stand for 5 minutes.

[0100] ③ Discharge at a constant current of 0.05C to 0.05V and record the first discharge capacity D1.

[0101] Initial coulomb efficiency = D1 / C1. The test results are recorded in Table 1.

[0102] Example 2

[0103] Example 2 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0104] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 15 μm) was placed in a fluidized bed apparatus with the temperature set to 460 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0105] The temperature of the fluidized bed equipment was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0106] Example 3

[0107] Example 3 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0108] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 9 μm) was placed in a fluidized bed apparatus with the temperature set to 520 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0109] The temperature of the fluidized bed equipment was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0110] Example 4

[0111] Example 4 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0112] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 9 μm) was placed in a fluidized bed apparatus with the temperature set to 580 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0113] The temperature of the fluidized bed equipment was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0114] Example 5

[0115] Example 5 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0116] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 3 μm) was placed in a fluidized bed apparatus at a temperature of 580 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material. The silicon-carbon material comprises porous carbon material and nano-silicon-based particles deposited within the pore structure of the porous carbon material.

[0117] The fluidized bed equipment temperature was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas flow for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material. The negative electrode active material includes silicon-carbon material and a carbon coating layer.

[0118] Example 6

[0119] Example 6 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0120] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 10 μm) was placed in a fluidized bed apparatus with the temperature set to 550 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0121] The fluidized bed equipment temperature was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas flow for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material. The negative electrode active material includes silicon-carbon material and a carbon coating layer.

[0122] Example 7

[0123] Example 7 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0124] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 7 μm) was placed in a fluidized bed apparatus with the temperature set to 580 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0125] The fluidized bed equipment temperature was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas flow for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material. The negative electrode active material includes silicon-carbon material and a carbon coating layer.

[0126] Example 8

[0127] Example 8 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0128] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 7 μm) was placed in a fluidized bed apparatus with the temperature set to 500 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0129] The temperature of the fluidized bed equipment was adjusted to 500℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0130] Example 9

[0131] Example 9 and Example 1 use the same method to prepare the electrical device, the only difference being:

[0132] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 7 μm) was placed in a fluidized bed apparatus with the temperature set to 500 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0133] The temperature of the fluidized bed equipment was adjusted to 550℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0134] Example 10

[0135] Example 10 and Example 1 were prepared using the same method, with the only difference being:

[0136] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 7 μm) was placed in a fluidized bed apparatus with the temperature set to 500 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material.

[0137] The temperature of the fluidized bed equipment was adjusted to 600℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0138] Example 11

[0139] Example 11 and Example 1 were prepared using the same method, with the only difference being:

[0140] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 7 μm) was placed in a fluidized bed apparatus at a temperature of 500 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 hours to obtain silicon-carbon material. This silicon-carbon material was then used as the negative electrode active material.

[0141] Comparative Example 1

[0142] Comparative Example 1 and Example 1 were prepared using the same method, with the only difference being:

[0143] Under an argon atmosphere, 5 kg of porous carbon material (Dv50 = 3 μm) was placed in a fluidized bed apparatus with the temperature set to 440 °C. Silane gas was introduced into the fluidized bed apparatus at a total flow rate of 10 L / min for 6 h to obtain silicon-carbon material.

[0144] The temperature of the fluidized bed equipment was adjusted to 580℃, and then acetylene gas was introduced at a flow rate of 6L / min for high-temperature carbon coating. After continuous gas supply for 3 hours, the temperature was lowered to room temperature. The material was then dispersed, sieved, and demagnetized to obtain the negative electrode active material.

[0145] The silicon-carbon materials and electrochemical devices obtained in Examples 2 to 11 and Comparative Example 1 were tested using the same test methods as in Example 1. The test results are shown in Table 1 below.

[0146] Table 1

[0147]

[0148]

[0149] As shown in Table 1, the electrochemical devices of Examples 1 to 11 exhibit improved initial coulombic efficiency compared to Comparative Example 1. In particular, the initial coulombic efficiency of the electrochemical devices is further improved when the particle size (dsi) of the nano-silicon-based particles is between 7 nm and 15 nm.

[0150] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrochemical device, characterized in that, The device includes an electrolyte, a positive electrode, and a negative electrode. The negative electrode includes a negative electrode active material, which includes a silicon-carbon material. The silicon-carbon material includes a porous carbon material and nano-silicon-based particles. The porous carbon material has a pore structure inside, and the nano-silicon-based particles are at least distributed within the pore structure. The particle size (dsi) of the nano-silicon-based particles is 3 nm to 15 nm.

2. The electrochemical device according to claim 1, characterized in that, The particle size (dsi) of the nano-silicon-based particles is 7 nm to 15 nm.

3. The electrochemical device according to claim 1 or 2, characterized in that, The negative electrode active material further includes a coating layer, which coats the porous carbon material.

4. The electrochemical device according to claim 3, characterized in that, The coating layer is a carbon coating layer.

5. The electrochemical device according to claim 3 or 4, characterized in that, The coating layer accounts for 0.5% to 2.3% of the mass relative to the negative electrode active material.

6. The electrochemical device according to any one of claims 1 to 5, characterized in that, The volume average particle size Dv50 of the porous carbon material is 3 μm to 15 μm.

7. The electrochemical device according to any one of claims 1 to 6, characterized in that, The volume average particle size Dv50 of the porous carbon material is 7 μm to 10 μm.

8. The electrochemical device according to any one of claims 1 to 7, characterized in that, The specific surface area of ​​the negative electrode active material is 1.5 m². 2 / g to 54m 2 / g.

9. The electrochemical device according to any one of claims 1 to 8, characterized in that, The volume average particle size Dv50 of the porous carbon material and the particle size dsi of the nano-silicon-based particles satisfy: 5*10 -3 ≥dsi / Dv50≥0.2*10 -3 .

10. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes a silicon-carbon material. The silicon-carbon material includes a porous carbon material and nano-silicon-based particles. The porous carbon material has a pore structure inside, and the nano-silicon-based particles are at least distributed within the pore structure. The particle size (dsi) of the nano-silicon-based particles is 3 nm to 15 nm.

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