WO2025002174A1 - 负极材料、负极极片、电化学装置、用电设备 - Google Patents

负极材料、负极极片、电化学装置、用电设备 Download PDF

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WO2025002174A1
WO2025002174A1 PCT/CN2024/101601 CN2024101601W WO2025002174A1 WO 2025002174 A1 WO2025002174 A1 WO 2025002174A1 CN 2024101601 W CN2024101601 W CN 2024101601W WO 2025002174 A1 WO2025002174 A1 WO 2025002174A1
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Prior art keywords
negative electrode
electrode material
lithium
porous carbon
pores
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French (fr)
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谭福金
易政
郑子桂
谢远森
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to EP24830813.2A priority Critical patent/EP4738455A1/en
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to a negative electrode material, a negative electrode sheet, an electrochemical device, and an electrical equipment.
  • lithium-ion batteries Since Sony Corporation of Japan commercialized lithium-ion batteries in 1991, lithium-ion batteries have been rapidly used in mobile phones, miniature cameras, PDAs, laptop computers and other fields due to their high energy density, high operating voltage, good load characteristics and fast charging speed.
  • the negative electrode of commercial lithium-ion batteries is mainly graphite materials.
  • its theoretical specific capacity is only 372mAh/g, and the room for improvement is very limited.
  • the lithium diffusion between graphite layers also restricts its rate performance. Therefore, the research and preparation of new high-capacity, long-cycle lithium-ion batteries and negative electrode materials are the key to the continued development of lithium-ion batteries.
  • the existing technology constructs a porous carbon skeleton on the anode pole piece.
  • the lithium metal is stripped from the anode and embedded in the cathode material.
  • the porous carbon skeleton can maintain its own shape; during the battery charging process, the lithium metal is stripped from the cathode and deposited on the anode pole piece.
  • the porous carbon skeleton can also disperse the current and reduce the local current density, thereby reducing lithium dendrites and increasing the lithium deposition density, thereby achieving the purpose of improving the performance of lithium-ion batteries.
  • the porous carbon skeleton itself has a large binding energy for lithium, the deposition position is uncontrollable during the lithium metal deposition process, resulting in uneven lithium metal deposition, which makes the anode pole piece change greatly in volume and decay quickly in capacity during the cycle.
  • the purpose of the present application is to provide a negative electrode material, a negative electrode plate, an electrochemical device, and an electrical equipment.
  • an embodiment of the present application provides a negative electrode material, the negative electrode material comprising a core and a shell;
  • the core is porous carbon, and the core has pores;
  • the pore walls contain silicon material
  • the shell layer is made of carbon material, which wraps around the surface of the core and closes the pores.
  • the porous carbon and the carbon material of the shell are disordered structures and store less lithium.
  • the pores are the main area for lithium storage, and the pore walls contain silicon materials.
  • silicon materials can induce lithium to enter the pores of the core from the shell layer outside the negative electrode material, making the deposition position of lithium metal controllable during the deposition process, reducing the unevenness of lithium metal deposition, and thus helping to improve the specific capacity and cycle performance of lithium-ion batteries.
  • the shell layer wraps around the core surface, sealing the pores, turning the pores into closed pores, so that the external electrolyte cannot enter the internal pores, and lithium enters the pores after desolvation.
  • the pores can reserve a portion of space while storing metallic lithium in order to buffer the volume expansion caused by the lithium metal, thereby improving the cycle performance.
  • the thickness of the silicon material is 0.5 nm to 4 nm.
  • the silicon material accounts for 0.01% to 20% of the total mass of the negative electrode material by mass percentage.
  • the silicon material accounts for 0.01% to 4% of the total mass of the negative electrode material by mass percentage.
  • setting the silicon material to the total mass of the negative electrode material within the above range can not only effectively induce lithium to enter the pores of the core from the outer shell of the negative electrode material, but also make the entire negative electrode material have good cycle stability.
  • the area ratio of the silicon material to the porous carbon is 0.01 to 0.3.
  • the area ratio of silicon material to porous carbon reflects the lithium affinity of silicon material. This area ratio cannot be too high, otherwise it may reduce the overall energy density or cycle performance of the material.
  • the area ratio of silicon material to porous carbon is set to 0.01 to 0.3, which is beneficial to the overall energy density or cycle performance of the material.
  • the area ratio of the pores to the porous carbon is 0.3-3.
  • the area ratio of pores to porous carbon indirectly reflects the internal porosity of the material.
  • the area ratio of pores directly affects the capacity and energy density of the material. The larger the area ratio, the higher the material capacity.
  • the area ratio is too high, the compaction density of the material will be too low, which is not conducive to the improvement of energy density. Therefore, in the above technical solution, setting the area ratio of pores to porous carbon to 0.3 to 3 can improve the energy density.
  • the area ratio test method is: photograph and observe the negative electrode material through a transmission electron microscope, and then use the image analysis software Image J to randomly select 10 negative electrode material particles from the photo, distinguish and classify each particle into region 1, region 2 and region 3, calculate the area of region 1, region 2 and region 3 through the software, and calculate the area ratio of region 2 to region 1, recorded as A1; or calculate the area ratio of region 3 to region 1, recorded as A2; then take the average of 10 A1 corresponding to the 10 negative electrode material particles, which is the area ratio of silicon material to carbon material;
  • the average value of 10 A2 corresponding to 10 negative electrode material particles is the area ratio of pores to carbon material
  • region 1 is carbon material
  • region 2 is silicon material
  • region 3 is pores.
  • the silicon material includes at least one of silicon or silicon carbide.
  • Silicon carbide can be used as a lithiophilic substance, which can effectively induce lithium to enter the pores of the core from the shell of the negative electrode material, thereby helping to improve the specific capacity and cycle performance of lithium-ion batteries.
  • Silicon as a lithiophilic substance, can also be used as a lithium storage material. It can not only effectively induce lithium from the shell of the negative electrode material into the pores of the core, but also further improve the specific capacity of lithium-ion batteries.
  • the shell layer has a thickness of 2 nm to 20 nm.
  • the thickness of the shell cannot be too large, otherwise the energy barrier for lithium to diffuse through the shell is too high, causing lithium to nucleate and grow directly on the surface of the negative electrode material, which may increase the probability of thermal runaway; and if the thickness of the shell is too small, effective coating cannot be achieved.
  • the thickness of the silicon material is set to 0.5nm to 4nm, which can allow lithium to diffuse through the shell and effectively coat the core and close the pores.
  • the core satisfies at least one of the following characteristics:
  • the specific surface area of porous carbon is 500m 2 /g to 3000m 2 /g;
  • the average pore size of porous carbon is 1nm to 30nm;
  • the pore volume of the porous carbon is 0.1 cm 3 /g to 1.5 cm 3 /g;
  • D V 50 of porous carbon is 1 ⁇ m to 20 ⁇ m;
  • the pore size of porous carbon is 2nm ⁇ 40nm.
  • Porous carbon materials can be divided into crack pores, conical pores, cylindrical pores, spherical pores, etc. based on the pore shape. Some pores are irregular.
  • the pore diameter in the above technical solution is defined as the distance between the two points on the pore wall that are farthest apart. Too small pore diameters can allow silicon materials to better induce lithium diffusion, but will reduce the overall lithium storage capacity. When the pores are too large, the distance to the pores will be too large. The inductive effect of silicon materials farther away from the mouth is weakened.
  • the lithium metal is not deposited in the pores but on the surface of the particles, which will lead to uneven lithium deposition, rapid capacity decay, and even an increased probability of thermal runaway.
  • the average pore size of the porous carbon should not be too large or too small. If it is too large, it will be difficult to introduce silicon materials. In the above technical solution, setting the average pore size of the porous carbon within the above range makes it easy to introduce silicon materials.
  • the d002 of the porous carbon represents the interlayer spacing of the carbon layer.
  • a large interlayer spacing is beneficial to the transmission and diffusion of lithium ions, and is beneficial to the rate and low temperature performance of the final battery.
  • setting the d002 of the porous carbon within the above range is beneficial to the rate and low temperature performance of the battery.
  • the above negative electrode material meets the following characteristics:
  • the pore size of the negative electrode material is 3nm to 30nm;
  • the pore volume of the negative electrode material is 0.005 cm 3 /g to 0.06 cm 3 /g;
  • the average pore size of the negative electrode material is 0.01 nm to 5 nm;
  • the D V 50 of the negative electrode material is 1 ⁇ m to 20 ⁇ m.
  • the pore diameter of the negative electrode material is set to 3nm to 30nm, which can effectively increase the overall lithium storage capacity of the negative electrode material; and is conducive to uniform lithium metal deposition and cycle stability.
  • an embodiment of the present application provides a negative electrode plate, wherein the negative electrode plate comprises the negative electrode material provided in the first aspect.
  • an embodiment of the present application provides an electrochemical device, which includes the negative electrode plate provided in the second aspect.
  • an embodiment of the present application provides an electrical device, which includes the electrochemical device provided in the third aspect.
  • FIG1 schematically shows a cross-sectional structure diagram of a negative electrode material
  • FIG2 schematically shows a TEM image of a negative electrode material according to Example 1 of the present application
  • FIG3 schematically shows a nitrogen adsorption-desorption curve diagram of the negative electrode material according to Example 1 of the present application
  • FIG4 schematically shows a schematic diagram of the pore size distribution of the negative electrode material according to Example 1 of the present application
  • FIG5 schematically shows a schematic diagram of the pore size distribution of porous carbon-1 used in an embodiment of the present application
  • FIG6 schematically shows a specific capacity curve of a lithium-ion battery according to Example 1 of the present application
  • FIG. 7 schematically shows a cycle performance diagram of a lithium-ion battery according to Example 1 of the present application.
  • orientations or positional relationships indicated by the technical terms “inside” and “outside” are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.
  • some embodiments of the present application provide a negative electrode material, the negative electrode material comprising a core and a shell layer;
  • the core is porous carbon, and the core has pores;
  • the pore walls contain silicon material
  • the shell layer is made of carbon material, which wraps around the surface of the core and closes the pores.
  • the porous carbon and the carbon materials of the shell layer are disordered structures and store less lithium.
  • the pores are the main area for lithium storage, and the pore walls contain silicon materials.
  • the silicon material can induce lithium to enter the pores of the core from the shell layer outside the negative electrode material, so that the deposition position of lithium metal during deposition can be controlled, and the unevenness of lithium metal deposition is reduced, which is beneficial to improve the specific capacity and cycle performance of lithium-ion batteries.
  • the shell layer is wrapped around the core surface, closing the pores, making the pores into closed pores, so that the external electrolyte cannot enter the internal pores, so that lithium enters the pores after desolvation.
  • the silicon material is on the pore wall, and the pores can reserve a part of the space while storing metallic lithium, so as to buffer the volume expansion caused by lithium metal, thereby improving the cycle performance.
  • the pore walls contain silicon material, that is, silicon material only exists on the walls of the pores, and the remaining space of the pores can be used as lithium storage space; in the above technical solution, the surface of the core has pores; or both the surface of the core and the inside of the core have pores.
  • the negative electrode material of the present application can also be referred to as forming a core-shell structure, and the above-mentioned shell layer is the shell.
  • the thickness of the silicon material is 0.5 nm to 4 nm.
  • the thickness of the silicon material is the maximum thickness of the silicon material at all places on the pore wall as the thickness of the silicon material.
  • the thickness of the silicon material is tested by embedding and curing the negative electrode active material with epoxy resin, and then using ultrathin sectioning to cut the material into a size of 50nm to 70nm to prepare the sample.
  • a high-power transmission electron microscope is used to select a section of the particle sample for observation, and the pore area and the disordered carbon layer area are observed.
  • the area between the pore area and the disordered carbon layer area is the silicon material, and the outermost disordered part of the entire particle is the carbon shell.
  • the software Image J is used for processing.
  • the material is photographed and observed by TEM, and then the image analysis software Image J is used to randomly select 10 negative electrode material particles from the photo to obtain the thickness of the silicon material contained in the inner wall of the pores of these negative electrode material particles, and then the maximum thickness of the 10 material particles is taken as the thickness of the silicon material.
  • the thickness of the silicon material is 0.6 nm to 3.9 nm.
  • the thickness of the silicon material is 0.8 nm, 1.0 nm, 1.2 nm, 1.5 nm, 1.8 nm, 2.0 nm, 2.5 nm, 2.8 nm, 3.0 nm, 3.5 nm or 3.8 nm.
  • the silicon material accounts for 0.01% to 20% of the total mass of the negative electrode material by mass percentage.
  • setting the silicon material to account for 0.01% to 20% of the total mass of the negative electrode material can effectively induce lithium to enter the pores of the core from the outer shell of the negative electrode material, and can also make the entire negative electrode material have good cycle stability.
  • the silicon material accounts for 0.01% to 4% of the total mass of the negative electrode material in terms of mass percentage.
  • the silicon material accounts for 0.03%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 5%, 8%, 10%, 15% or 18% of the total mass of the negative electrode material, by mass percentage.
  • the area ratio of the silicon material to the porous carbon is 0.01 to 0.3.
  • the area ratio of the silicon material to the porous carbon reflects the lithium affinity of the silicon material.
  • the area ratio cannot be too high, as it may reduce the overall energy density or cycle performance of the material.
  • setting the area ratio of the silicon material to the porous carbon to 0.01 to 0.3 is beneficial to the overall energy density or cycle performance of the material.
  • the test method of the area ratio of the above silicon material to porous carbon is: embed and solidify the negative electrode active material with epoxy resin, and then use ultrathin sectioning to cut the material into a size of 50nm to 70nm to prepare the sample.
  • Use software Image J for processing The negative electrode material was photographed and observed using a transmission electron microscope. Then, 10 negative electrode material particles were randomly selected from the photograph using image analysis software Image J.
  • Each particle was identified and classified as region 1, region 2, and region 3.
  • the areas of region 1, region 2, and region 3 were calculated using the software, and the area ratio of region 2 to region 1 was also calculated, recorded as A1.
  • the 10 A1 values corresponding to the 10 negative electrode material particles were averaged, which was the area ratio of silicon material to carbon material. Region 1 was carbon material, region 2 was silicon material, and region 3 was pores.
  • the area ratio of the silicon material to the porous carbon is 0.01 to 0.29.
  • the area ratio of the silicon material to the porous carbon is 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.20, 0.25 or 0.28.
  • the area ratio of pores to porous carbon is 0.3 to 3.
  • the area ratio of pores to porous carbon indirectly reflects the internal porosity of the material. As the main area for lithium storage, the area ratio directly affects the capacity and energy density of the material. The larger the area ratio, the higher the material capacity. On the other hand, if the area ratio is too high, the compaction density of the material will be too low, which is not conducive to the improvement of energy density. Therefore, in the above technical solution, setting the area ratio of pores to porous carbon to 0.3 to 3 can improve the energy density.
  • the test method of the above-mentioned pore to porous carbon area ratio is: embed and solidify the negative electrode active material with epoxy resin, and then use ultrathin sectioning to cut the material into a size of 50nm to 70nm to prepare the sample.
  • the negative electrode material was photographed and observed using a transmission electron microscope. Then, 10 negative electrode material particles were randomly selected from the photograph using image analysis software Image J. Each particle was identified and classified as region 1, region 2, and region 3.
  • region 1, region 2, and region 3 were calculated using the software.
  • the area ratio of region 3 to region 1 was calculated and recorded as A2.
  • the 10 A2s corresponding to the 10 negative electrode material particles were averaged, which was the area ratio of pores to carbon materials.
  • Region 1 was carbon material
  • region 2 was silicon material
  • region 3 was pores.
  • the area ratio of pores to porous carbon is 0.31 to 3.
  • the area ratio of pores to porous carbon is 0.31, 0.35, 0.38, 0.40, 0.45, 0.50, 0.80, 1.00, 1.50, 2.00, 2.50 or 2.80.
  • the D V 50 of the silicon material is 0.1 nm to 10 nm.
  • Dv50 indicates that particles smaller than this particle size in the silicon material account for 50% of the total volume of the silicon material.
  • the D V 50 of the silicon material is set to 0.1 nm to 10 nm, the particle size is moderate, and the specific surface area is moderate, which is beneficial to the specific capacity and cycle performance of the lithium-ion battery.
  • the test method of D V 50 of the above silicon material is: refer to GB/T19077-2016.
  • the specific process is to weigh 1g of the sample and mix it evenly with 20mL of deionized water and a trace amount of dispersant, place it in an ultrasonic device for 5 minutes, and then pour the solution into the sampling system Hydro 2000SM for testing.
  • the test equipment used is the Mastersizer 3000 produced by Malvern.
  • the particle size measurement is completed by measuring the intensity of the scattered light.
  • the data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum.
  • the refractive index of the particles used in the test is 1.8.
  • One sample is tested three times, and the particle size is finally measured by taking the average value of the three tests to measure Dv50.
  • Dv50 means that particles smaller than this particle size value in the sample account for 50% of the total volume of the total sample.
  • D V 50 of the silicon material is 0.11 nm to 9.9 nm.
  • D V 50 of the silicon material is 0.15 nm, 0.2 nm, 0.5 nm, 1.0 nm, 2.0 nm, 3.0 nm, 4.0 nm, 5.0 nm, 6.0 nm, 7.0 nm or 8.0 nm.
  • the silicon material includes at least one of elemental silicon or silicon carbide.
  • Silicon carbide can be used as a lithium-philic substance, which can effectively induce lithium to enter the pores of the core from the shell of the negative electrode material, thereby facilitating the improvement of lithium ionization.
  • Silicon, as a lithium-philic material can also be used as a lithium storage material, which can not only effectively induce lithium from the shell of the negative electrode material into the pores of the core, but also further improve the specific capacity of lithium-ion batteries.
  • the shell thickness is 2nm to 20nm.
  • the thickness of the shell cannot be too large, otherwise the energy barrier for lithium to diffuse through the shell is too high, causing lithium to nucleate and grow directly on the surface of the negative electrode material, which may increase the probability of thermal runaway; and if the thickness of the shell is too small, effective coating cannot be achieved.
  • the thickness of the silicon material is set to 0.5nm to 4nm, which can allow lithium to diffuse through the shell and effectively coat the core and close the pores.
  • the shell thickness is tested by embedding and curing the negative electrode active material with epoxy resin, and then using ultrathin sectioning to cut the material into a size of 50nm to 70nm to prepare the sample.
  • a high-power transmission electron microscope is used to select a section of the particle sample for observation, and the pore area and the disordered carbon layer area are observed.
  • the pore area and the disordered carbon layer area are the core, and the outermost disordered part of the entire core is the carbon shell.
  • the material is photographed and observed by TEM, and then the image analysis software Image J is used to randomly select 10 negative electrode material particles from the photo to obtain the thickness of the outermost disordered part (shell) of these negative electrode material particles, and then the average thickness of the 10 negative electrode material particles is taken as the shell thickness.
  • the shell layer has a thickness of 2.1 nm to 19 nm.
  • the shell layer has a thickness of 2.5 nm, 3 nm, 5 nm, 10 nm, 12 nm, 15 nm or 18 nm.
  • the core may be selected from at least one of: activated carbon, template porous carbon, carbon molecular sieve, carbon nanofiber, carbon nanotube, etc. and expanded graphite.
  • the pore diameter of the core (porous carbon) is 2nm to 40nm; further optionally, the pore diameter of the core (porous carbon) is 5nm to 35nm; exemplarily, the pore diameter of the core (porous carbon) is 10nm, 15nm, 20nm, 25nm, 30nm or 32nm.
  • Porous carbon materials can be divided into crack holes, conical holes, cylindrical holes, spheres, etc. based on the shape of the pores. Some holes are irregular, so the pore size here is defined as the distance between the two farthest points in the pore wall. Too small pore size can allow silicon or silicon carbide particles to play a better inductive role in lithium diffusion, but it will reduce the overall lithium storage capacity. When the pores are too large, the inductive effect of silicon or silicon carbide particles far away from the pore mouth will be weakened.
  • the pore size of the core is within the above range, which is conducive to increasing the lithium storage capacity and facilitating uniform lithium deposition.
  • the specific surface area of the core (porous carbon) is 500m2 /g to 3000m2 /g; further optionally, the specific surface area of the core (porous carbon) is 550m2 /g to 2500m2 /g; illustratively, the specific surface area of the core (porous carbon) is 600m2 /g, 800m2 /g, 1000m2 /g, 1500m2 /g, 2000m2 /g or 2300m2 /g.
  • the specific surface area of the core (porous carbon) is within the above range, which is beneficial to the specific capacity and cycle performance of the lithium ion battery.
  • the pore volume of the core (porous carbon) is 0.1cm 3 /g to 1.5cm 3 /g; further optionally, the pore volume of the core (porous carbon) is 0.2cm 3 /g to 1.4cm 3 /g; illustratively, the pore volume of the core (porous carbon) is 0.5cm 3 /g, 0.8cm 3 /g, 1.0cm 3 /g, 1.2cm 3 /g or 1.3cm 3 /g.
  • the pore volume of the core (porous carbon) is set within the above range, which is beneficial to the specific capacity and cycle performance of the lithium ion battery. Further, in some embodiments of the present application, the pore volume of the core (porous carbon) is obtained by nitrogen testing at 77K.
  • the D V 50 of the core (porous carbon) is 1 ⁇ m to 20 ⁇ m; further optionally, the D V 50 of the core (porous carbon) is 2 ⁇ m to 19 ⁇ m; illustratively, the D V 50 of the core (porous carbon) is 5 ⁇ m, 10 ⁇ m, 12 ⁇ m, 15 ⁇ m or 18 ⁇ m.
  • the D V 50 of the core (porous carbon) is within the above range, the particle size is moderate, the specific surface area is moderate, and it is beneficial to the specific capacity and cycle performance of the lithium-ion battery.
  • test method for D V 50 of the core is the same as the test method for D V 50 of the aforementioned silicon material.
  • the d002 of the core (porous carbon) is 0.38nm to 0.41nm.
  • the d002 of the core (porous carbon) represents the interlayer spacing of the carbon layer, which affects the transmission and diffusion of lithium ions and ultimately affects the rate and capacity of the battery.
  • setting the d002 of the core (porous carbon) to 0.38nm-0.41nm is beneficial to the rate and low temperature performance of the battery.
  • the d002 of the core (porous carbon) is 0.39 nm to 0.40 nm.
  • the d002 of the core (porous carbon) is 0.39 nm, 0.40 nm or 0.41 nm.
  • the pore size of the negative electrode material is 3nm to 30nm.
  • Porous carbon materials can be divided into crack pores, conical pores, cylindrical pores, spheres, etc. based on the pore shape, and some pores are irregular.
  • the pore size in the above technical solution is defined as the distance between the two points farthest apart in the pore wall. Too small pore size can allow silicon materials to play a better inductive role in lithium diffusion, but it will reduce the overall lithium storage capacity. When the pores are too large, the inductive effect of silicon materials far from the pore mouth will be weakened.
  • the energy barrier for lithium diffusion through the shell of the negative electrode material is higher than the energy barrier for nucleation and growth on the surface of the particles, lithium metal is not deposited in the pores but on the surface of the particles, which will lead to uneven lithium deposition, fast capacity decay, and even increase the probability of thermal runaway.
  • Setting the pore size of the negative electrode material to 3nm to 30nm can effectively increase the overall lithium storage capacity of the negative electrode material; and it is conducive to uniform deposition of lithium metal and cycle stability.
  • the pore size of the negative electrode material is 4 nm to 29 nm.
  • the pore size of the negative electrode material is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm or 28 nm.
  • the pore volume of the negative electrode material is 0.005cm 3 /g to 0.06cm 3 /g. Further optionally, the pore volume of the negative electrode material is 0.006cm 3 / g to 0.06cm 3 /g. Exemplarily, the pore volume of the negative electrode material is 0.01cm 3 / g , 0.02cm 3 /g, 0.03cm 3 /g, 0.04cm 3 /g, 0.05cm 3 /g or 0.06cm 3 /g.
  • the pore volume of the negative electrode material is set within the above range, which is beneficial to the specific capacity and cycle performance of the lithium ion battery. Further, in some embodiments of the present application, the pore volume of the negative electrode material is obtained by nitrogen testing at 77K.
  • the average pore size of the negative electrode material is 0.01nm to 5nm. Further optionally, the average pore size of the negative electrode material is 0.02nm to 4.8nm. Exemplarily, the average pore size of the negative electrode material is 0.05nm, 1nm, 2nm, 3nm or 4nm. The average pore size of the negative electrode material is set within the above range, which is beneficial to the specific capacity and cycle performance of the lithium-ion battery. In some embodiments of the present application, the average pore size of the above-mentioned negative electrode material is obtained by testing nitrogen at 77K, and the average pore size is taken from the BJH desorption average pore size.
  • the D V 50 of the negative electrode material is 1 ⁇ m to 20 ⁇ m. Further optionally, the D V 50 of the negative electrode material is 1.5 ⁇ m to 19 ⁇ m. Exemplarily, the D V 50 of the negative electrode material is 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 10 ⁇ m, 12 ⁇ m, 15 ⁇ m or 18 ⁇ m.
  • the D V 50 of the negative electrode material is within the above range, the particle size is moderate, the specific surface area is moderate, and it is beneficial to the specific capacity and cycle performance of the lithium ion battery.
  • test method for D V 50 of the negative electrode material is the same as the test method for D V 50 of the aforementioned silicon material.
  • the negative electrode material can be prepared according to the following method:
  • Step S1 placing porous carbon powder into a CVD device, introducing protective gas, and heating to a target temperature T1 at a certain heating rate.
  • the heating rate in step S1 may be 1 to 20°C/min, and the target temperature T1 may be 300 to 600°C.
  • Step S2 introduce silicon element gas, perform chemical vapor deposition at the target temperature T1, perform chemical vapor deposition for 0.1h to 1h, then introduce nitrogen to purge the furnace for 0.2h, and then introduce silicon element gas again. Repeat chemical vapor deposition and purge 1 to 20 times in a periodic manner to obtain a precursor of the negative electrode material.
  • the silicon element gas in step S2 may be a mixed gas of silane and argon, and the mass concentration of silane may be 0.2% to 10%.
  • the silicon element gas source in step S2 may be monosilane or disilane; and the flow rate of the silicon element gas source may be 10 to 300 mL/min.
  • Step S3 close the silicon-containing gas source, introduce the carbon-containing gas source, heat up to the target temperature T2 at a certain heating rate, and keep the temperature constant for t; then close the carbon-containing gas source and cool down naturally to room temperature.
  • the carbon-containing gas source may be at least one of methane, ethane, propane, ethylene, acetylene or propyne.
  • the heating rate may be 1 to 20°C/min
  • the target temperature T2 may be 800 to 1200°C
  • the constant temperature time t may be 0 to 5h.
  • Some embodiments of the present application provide a negative electrode plate, which includes the negative electrode material provided by any of the aforementioned embodiments.
  • the negative electrode plate includes a current collector and a negative electrode active material layer located on the surface of the current collector, and the negative electrode active material layer includes the negative electrode material provided by any of the above embodiments.
  • the current collector includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.
  • the negative electrode active material layer also includes a binder, which includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.
  • a binder which includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene
  • the negative electrode active material layer further includes a conductive agent, which includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof.
  • a conductive agent which includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof.
  • the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver.
  • the conductive polymer is a polyphenylene derivative.
  • the negative electrode sheet of the present application can be prepared by a method known in the art. Generally, the negative electrode material and optional conductive agent (such as carbon black and other carbon materials and metal particles), binder (such as SBR), other optional additives (such as PTC thermistor materials) and other materials are mixed together and dispersed in a solvent (such as deionized water), stirred evenly and evenly coated on the negative electrode current collector, and dried to obtain the negative electrode sheet. Materials such as metal foil or porous metal plate can be used as the negative electrode current collector.
  • a solvent such as deionized water
  • Some embodiments of the present application provide an electrochemical device, which includes the negative electrode sheet provided by any of the aforementioned embodiments.
  • the electrochemical device includes, but is not limited to: all kinds of primary batteries, secondary batteries or capacitors.
  • the electrochemical device is a lithium secondary battery.
  • the electronic device has excellent electrochemical performance: the discharge capacity can be 700 mAh/g to 3000 mAh/g at a current density of 0.5 C, and the energy retention rate can be as high as 85% to 94% at a current density of 1 C.
  • the electrochemical device includes the negative electrode sheet provided by any of the aforementioned embodiments; and a positive electrode sheet, an electrolyte and a separator.
  • the positive electrode plate includes a current collector and a positive electrode active material layer located on the current collector.
  • the positive electrode active material includes a positive electrode material that can absorb and release lithium.
  • the positive electrode material that releases lithium includes but is not limited to lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium iron phosphate, lithium titanate and lithium-rich manganese-based materials.
  • the current collector may include, but is not limited to: aluminum foil.
  • the positive electrode active material layer further includes a binder, and optionally includes a conductive material.
  • the binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.
  • the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.
  • the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof.
  • the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver.
  • the conductive polymer is a polyphenylene derivative.
  • the positive electrode sheet can be prepared by a preparation method known in the art.
  • the positive electrode sheet can be obtained by the following method: mixing an active material, a conductive material and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector.
  • the solvent may include, but is not limited to: N-methylpyrrolidone.
  • the electrochemical device of the present application has higher energy density and cycle performance, and can meet application requirements.
  • the isolation membrane may include a substrate layer and a surface treatment layer.
  • the substrate layer is a non-woven fabric, a film or a composite film having a porous structure
  • the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected.
  • a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance.
  • the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinyl pyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinyl pyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).
  • the electrolyte may further include a non-aqueous solvent, which may be a carbonate compound, a carboxylate compound, an ether compound, or a combination thereof.
  • a non-aqueous solvent which may be a carbonate compound, a carboxylate compound, an ether compound, or a combination thereof.
  • the carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof.
  • linear carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) and a combination thereof.
  • Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC) or a combination thereof.
  • fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate or a combination thereof.
  • FEC fluoroethylene carbonate
  • 1,2-difluoroethylene carbonate 1,1-difluoroethylene carbonate
  • 1,1,2-trifluoroethylene carbonate 1,1,2,2-tetrafluoroethylene carbonate
  • 1-fluoro-2-methylethylene carbonate 1-fluoro-1-methylethylene carbonate
  • 1,2-difluoro-1-methylethylene carbonate 1,1,2-trifluoro-2-methylethylene carbonate
  • trifluoromethylethylene carbonate trifluoromethylethylene
  • carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, methyl formate or a combination thereof.
  • the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
  • Some embodiments of the present application provide an electrical device, which includes the electrochemical device provided by any of the aforementioned embodiments.
  • a negative electrode material is provided, which is prepared according to the following steps:
  • the pore size distribution curve of the porous carbon-1 used in step (1) of Example 1 is shown in FIG4 . It can be seen that the porous carbon-1 has micropores and mesopores, with an average pore size of 3.69 nm, a pore volume of 0.63 cm 3 /g, and a specific surface area of 1730 m 2 /g.
  • the nitrogen adsorption-desorption curve of the negative electrode material obtained in Example 1 is shown in FIG3 . It can be seen that the adsorption amount of porous carbon-1 becomes extremely small after the above steps, indicating that nitrogen cannot enter the pores and most of the pores have become closed pores.
  • the pore size distribution curve of the negative electrode material obtained in Example 1 is shown in Figure 5. It can be seen that the negative electrode material has both micropores and mesopores, with an average pore size of 5.8nm, a pore volume of 0.046cm3 /g, and a specific surface area of 33.3m2/g. Therefore, the BET and pore volume of porous carbon-1 after CVD coating become extremely small, indicating that most of the internal pores have become closed pores.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 455°C;
  • step (2) chemical vapor deposition and purge are repeated 4 times in a periodic alternating manner.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 485°C;
  • step (2) chemical vapor deposition and purge are repeated 5 times in a periodic alternating manner.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 485°C;
  • step (2) chemical vapor deposition and purge are repeated 5 times in a periodic alternating manner.
  • step (3) the constant temperature time is 1.5 h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 485°C;
  • step (2) chemical vapor deposition and purge are repeated 5 times in a periodic and alternating manner
  • step (3) the constant temperature time is 2 h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 455°C;
  • step (2) chemical vapor deposition and purge are repeated 4 times in a periodic and alternating manner
  • step (3) the temperature is increased to 1050° C. at a heating rate of 5° C./min.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 455°C;
  • step (2) chemical vapor deposition and purge are repeated 4 times in a periodic and alternating manner
  • step (3) the temperature is increased to 1050°C at a heating rate of 5°C/min and the constant temperature time is 2h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the porous carbon used is porous carbon-2, and the temperature is raised to 485° C.;
  • step (2) 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 5 times in a periodic alternating manner;
  • step (3) the constant temperature time is 2 h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the porous carbon used is porous carbon-2, and the temperature is raised to 485° C.;
  • step (2) 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 5 times in a periodic alternating manner;
  • step (3) the temperature is increased to 1050°C at a heating rate of 5°C/min and the constant temperature time is 2h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the porous carbon used is porous carbon-2, and the temperature is raised to 485° C.;
  • step (2) 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 6 times in a periodic alternating manner;
  • step (3) the temperature is increased to 1050°C at a heating rate of 5°C/min and the constant temperature time is 2h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the porous carbon used is porous carbon-3, and the temperature is raised to 485°C;
  • step (2) chemical vapor deposition and purge are repeated 5 times in a periodic and alternating manner
  • step (3) the constant temperature time is 2 h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the temperature is raised to 485°C;
  • step (2) chemical vapor deposition and purge are repeated 35 times in a periodic and alternating manner
  • step (3) the constant temperature time is 2 h.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:
  • step (1) the porous carbon used is porous carbon-2, and the temperature is raised to 485° C.;
  • step (2) 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 5 times in a periodic alternating manner;
  • step (3) the constant temperature time is 8 hours.
  • a negative electrode material is provided, which is the porous carbon-1 in Example 1.
  • a negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that there is no step (3).
  • the negative electrode active material was embedded and cured with epoxy resin, and then the material was cut into 50nm to 70nm size by ultrathin sectioning method to prepare the sample.
  • the particle sample section was selected for observation using a high-power transmission electron microscope to observe the pore area and the disordered carbon layer area.
  • the area between the pore area and the disordered carbon layer area is the silicon material, and the outermost disordered part of the entire particle is the carbon shell.
  • the software Image J was used for processing.
  • FIG2 shows a TEM image of the negative electrode material of Example 1 as an example.
  • the material was photographed and observed using TEM, and then 10 negative electrode material particles were randomly selected from the photograph using image analysis software Image J.
  • the thickness of the silicon material contained in the inner wall of the pores of these negative electrode material particles was obtained, and the maximum thickness of the 10 material particles was taken as the thickness of the silicon material.
  • the negative electrode material is photographed and observed by a transmission electron microscope, and then 10 negative electrode material particles are randomly selected from the photo using the image analysis software Image J. Each particle is distinguished and classified into region 1, region 2 and region 3.
  • the area of region 1, region 2 and region 3 is calculated by the software, and the area ratio of region 2 to region 1 is calculated, which is recorded as A1; or the area ratio of region 3 to region 1 is calculated, which is recorded as A2; then the average value of 10 A1 corresponding to the 10 negative electrode material particles is taken, which is the area ratio of silicon material to carbon material;
  • the average value of 10 A2 corresponding to 10 negative electrode material particles is the area ratio of pores to carbon material
  • region 1 is carbon material
  • region 2 is silicon material
  • region 3 is pores.
  • Negative electrode ion grinding (Cross-section) sample preparation process Cut the negative electrode piece into 0.5cm ⁇ 1cm size, use conductive glue to stick the cut negative electrode on a 1cm ⁇ 1.5cm silicon wafer carrier, and then use argon ion polishing (parameters: 8KV acceleration voltage, 4h for each sample) to process one end of the negative electrode piece.
  • Argon ion polishing uses a high-voltage electric field to ionize argon gas to produce an ion state. The generated argon ions bombard the negative electrode surface at high speed under the action of the acceleration voltage, and erode the negative electrode piece layer by layer to achieve the polishing effect.
  • Pore diameter The material is photographed and observed using FESEM. Ten material particles are randomly selected from the photographs, the size of the pores inside the particles is measured, and the distance between the two farthest points on the inner wall of the pore is measured. Finally, the average value of the distances measured inside the ten material particles is taken as the pore diameter.
  • the particle size test method refers to GB/T 19077-2016.
  • the specific process is to weigh 1g of the sample and mix it evenly with 20mL of deionized water and a trace amount of dispersant. After placing it in an ultrasonic device for 5 minutes, the solution is poured into the sampling system Hydro 2000SM for testing.
  • the test equipment used is the Mastersizer 3000 produced by Malvern.
  • the particle size measurement is completed by measuring the intensity of the scattered light.
  • the data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum.
  • the refractive index of the particles used in the test is 1.8.
  • One sample is tested three times, and the particle size is finally measured as the average of the three tests Dv50.
  • Dv50 means that particles smaller than this particle size value in the sample account for 50% of the total volume of the total sample.
  • the test instrument is ASAP2460-physical adsorption analyzer.
  • the dried and degassed samples are placed in liquid nitrogen, and different test pressures are adjusted to measure the adsorption of nitrogen, and the adsorption and desorption isotherms are plotted.
  • the shape of the pores is determined according to the shape of the hysteresis loop, and the pore distribution and pore volume are calculated according to different pore models.
  • the BJH model is used to fit the pore size distribution curves of mesopores and macropores
  • the DFT model is used to fit the pore size distribution curve of micropores.
  • a lithium sheet with a diameter of 18 mm and a thickness of 0.6 mm, a separator, and the negative electrode sheets in each embodiment and comparative example (cut into a diameter of 18 mm and used) are assembled and stacked in sequence, and an electrolyte is added.
  • the positive and negative electrodes are packaged in button-type stainless steel shells to obtain a button-type battery.
  • Lithium-ion button cell test The button cell is discharged at a current density of 50 mA/g for 10 to 80 hours, and then charged to 2.0 V at a current density of 50 mA/g. The capacity of the button cell at this time is recorded as the battery specific capacity.
  • FIG. 6 is a graph showing the specific capacity curve of the lithium ion battery of Example 1.
  • the positive electrode sheets, separators and negative electrode sheets are stacked in order, and they are wound, folded and the like as needed to obtain an electrode assembly with a wound structure, the electrode assembly is placed in a packaging bag, the electrolyte is injected into the packaging bag and the bag is sealed to obtain a full lithium-ion battery; alternatively, the positive electrode sheets, separators and negative electrode sheets are stacked in order, and the four corners of the entire stacked structure are fixed with tape to obtain an electrode assembly with a stacked structure, the electrode assembly is placed in a packaging bag, the electrolyte is injected into the packaging bag and the bag is sealed to obtain a full lithium-ion battery.
  • lithium-ion full batteries prepared in all comparative examples and embodiments were taken and the average value was calculated.
  • the lithium-ion full battery was repeatedly charged and discharged by the following steps, and the discharge capacity retention rate of the lithium-ion full battery was calculated.
  • the first charge and discharge are performed. Constant current charging is performed at a charging current of 1C until the upper limit voltage of 4.55V is reached, then constant voltage charging is performed, and then constant current discharge is performed at a discharge current of 1C until the final voltage is 2V, which is recorded as one cycle.
  • the data of the first cycle and the 500th cycle are recorded. From the first cycle to the 450th cycle, a capacity test is performed at a current of 0.2C every 50 cycles.
  • the specific operation is as follows: constant current charging is performed at a charging current of 0.2C until the upper limit voltage of 4.55V is reached, then constant voltage charging is performed, and then constant current discharge is performed at a discharge current of 0.2C until the final voltage is 2V.
  • cycle capacity retention rate (discharge capacity at the 500th cycle/discharge capacity at the first cycle) ⁇ 100%.
  • FIG. 7 is a graph showing the cycle performance of the lithium ion battery of Example 1.
  • the negative electrode materials prepared in the above-mentioned embodiments can enable lithium-ion batteries to have higher specific capacity and cycle performance.
  • the negative electrode material provided in Comparative Example 1 has low specific capacity and cycle performance of the lithium ion battery.
  • Example 3 has a higher Si content and A1 and A2 values, it can allow more lithium to pass through the carbon shell into the closed pores without allowing lithium to precipitate on the surface of the particles. Therefore, the negative electrode material prepared in Example 3 has a higher specific capacity of 2015 mAh/g, and has a capacity retention rate of 89.3%.
  • the carbon shell thicknesses of Examples 3 to 5 are 5.2 nm, 8.6 nm, and 15.1 nm, respectively, and the capacity retention rates are 89.3%, 90.1%, and 91.2%, respectively. It can be seen from Examples 3 to 5 that, within a limited range, the shell thickness has a smaller effect on the specific capacity and a greater effect on the cycle performance. Within a limited range, the larger the shell thickness, the more obvious the expansion inhibition during the lithium insertion process, and the material can better maintain the integrity of the core-shell structure during the cycle.
  • Example 6 and Example 7 Comparing Example 2, Example 6 and Example 7, the main difference is that the silicon material is different.
  • the generation of Si or silicon carbide can be controlled by regulating the temperature in the CVD coating process. Silicon carbide does not act as a lithium-embedded active material during the charge and discharge process, so it does not provide capacity, so the specific capacity of Example 6 and Example 7 is lower than that of Example 2, but because of the lack of expansion caused by silicon-embedded lithium, Example 6 and Example 7 have higher capacity retention rates, which are 92.8% and 93.6% respectively.
  • the porous carbon used is porous carbon-2, which has a larger BET, pore volume and pore diameter than porous carbon-1. It can be found that compared with Examples 1 to 7, the negative electrode materials of Examples 8 to 10 have a higher specific capacity, which is because the larger pore volume can accommodate more lithium while ensuring a higher capacity retention rate.
  • the porous carbon used is porous carbon-3, and its pore diameter is 52nm. Although it has a specific capacity of 1706, the capacity retention rate is only 66.3%. This is because the pore diameter is too large, resulting in lithium gradually failing to enter the deep pores during the cycle, causing excess lithium to precipitate on the surface of the particles, resulting in accelerated capacity decay. This shows that when the pore diameter of the porous carbon is 2nm to 40nm, the lithium-ion battery has a better specific capacity and cycle performance.
  • Example 12 Comparing Examples 1 to 7 with Example 12, the thickness of the silicon material in Example 12 is relatively large, 4.8nm. Although it also has a relatively high specific capacity of 1876mAh/g, due to the excessively high Si content, the A1 value is too high, the A2 value is too low, and the expansion space left by the pores is too small, resulting in the destruction of the structural stability during the cycle and the deterioration of the cycle performance.
  • the lithium-ion battery has a better specific capacity and cycle performance.
  • Example 13 Comparing Examples 8 to 10 with Example 13, the negative electrode material of Example 13 has a larger shell thickness of 50nm; Example 13 causes a higher energy barrier for lithium diffusion through the carbon shell in the late cycle, resulting in gradual precipitation outside the pores, thereby causing capacity decay. This shows that a shell thickness of 2nm to 20nm has better specific capacity and cycle performance.

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Abstract

一种负极材料、负极极片、电化学装置、用电设备。所述负极材料包括核和壳层；核为多孔碳，核具有孔隙；孔隙壁面上含有硅材料；壳层为碳材料，壳层包裹在核表面，封闭孔隙。所述负极材料中，多孔碳和壳层的碳材料为无序结构，储锂较少。孔隙作为储锂的主要区域，孔隙壁面上含有硅材料，硅材料作为亲锂性物质，可以诱导锂从负极材料外部的壳层进入核的孔隙，使锂金属沉积过程中沉积位置可控，降低锂金属沉积不均匀性，从而有利于提高锂离子电池的比容量和循环性能。

Description

负极材料、负极极片、电化学装置、用电设备
交叉引用
本申请要求2023年06月29日提交的申请号为202310791499.1、发明名称为“负极材料、负极极片、电化学装置、用电设备”的中国发明专利申请的优先权，其内容结合在此作为参考。
技术领域
本申请涉及一种负极材料、负极极片、电化学装置、用电设备。
背景技术
自1991年日本Sony公司将锂离子电池商品化以来，锂离子电池由于其能量密度高、工作电压高、负载特性好、充电速度快等优点，迅速在移动电话、微型相机、掌上电脑、笔记本电脑等领域得到了广泛的应用。
然而，随着下游应用对电池能量和功率性能的需求不断提升，目前商用的锂离子电池容量已显得捉襟见肘。
发明内容
目前，商用锂离子电池负极以石墨类材料为主，根据石墨层间LiC 6的储锂机制，其理论比容量仅为372mAh/g，提升空间十分有限，且石墨层间的锂扩散也制约了其倍率性能。因此，研究和制备新型的高容量、长循环的锂离子电池，负极材料是继续发展锂离子电池的关键。
为了提高锂离子电池的容量，现有技术通过在阳极极片上构建多孔碳骨架，在电池放电过程中，锂金属从阳极剥离并嵌入到阴极材料中，多孔碳骨架能够维持本身的形状；在电池充电过程中，锂金属从阴极剥离并沉积到阳极极片上，多孔碳骨架还可以分散电流，降低局部电流密度，从而减少锂枝晶，提高锂沉积密度，达到提高锂离子电池性能的目的。但是，由于多孔碳骨架本身对锂的结合能较大，在锂金属沉积过程中沉积位置不可控，导致锂金属沉积不均匀，使得阳极极片在循环过程中体积变化大和容量衰减快。
基于以上考虑，本申请的目的在于提供一种负极材料、负极极片、电化学装置、用电设备。
本申请的实施例是这样实现的：
第一方面，本申请实施例提供一种负极材料，负极材料包括核和壳层；
核为多孔碳，核具有孔隙；
孔隙壁面上含有硅材料；
壳层为碳材料，壳层包裹在核表面，封闭孔隙。
上述负极材料中，多孔碳和壳层的碳材料为无序结构，储锂较少。孔隙作为储锂的主要区域，孔隙壁面上含有硅材料，硅材料作为亲锂性物质，可以诱导锂从负极材料外部的壳层进入核的孔隙，使锂金属沉积过程中沉积位置可控，降低锂金属沉积不均匀性，从而有利于提高锂离子电池的比容量和循环性能。
进一步地，上述负极材料中，壳层包裹在核表面，封闭孔隙，使孔隙变为闭孔，使得外部电解液进入不到内部孔隙，使得锂在去溶剂化之后进入孔隙。
进一步地，硅材料在孔隙壁面上，孔隙储存金属锂的同时可预留一部分空间，以便缓冲由锂金属带来的体积膨胀，从而提高循环性能。
在一些可选的实施方案中，上述硅材料的厚度为0.5nm～4nm。
上述技术方案中，设置硅材料的厚度在上述范围内，有利于使得更多的锂穿过壳层进入到 孔隙里，同时有利于降低锂析出在负极材料表面，从而可以获得更高的比容量。
在一些可选的实施方案中，以质量百分比计，硅材料占负极材料总质量的0.01％～20％。可选地，以质量百分比计，硅材料占负极材料总质量的0.01％～4％。
上述技术方案中，设置硅材料占负极材料总质量在上述范围内，既可以有效地诱导锂从负极材料外部的壳层进入核的孔隙，又可以使得整个负极材料具有良好的循环稳定性。
在一些可选的实施方案中，上述硅材料与多孔碳的面积比为0.01～0.3。
硅材料与多孔碳的面积比反映了硅材料亲锂性的大小。该面积比值不能太高，过高可能会导致材料整体的能量密度或者循环性能降低。上述技术方案中，设置硅材料与多孔碳的面积比为0.01～0.3，有利于材料整体的能量密度或者循环性能。
在一些可选的实施方案中，上述孔隙与多孔碳的面积比为0.3～3。
孔隙与多孔碳的面积比间接反映了材料内部孔隙率，孔隙作为储锂的主要区域，该面积比值直接影响了材料的容量以及能量密度，该面积比值越大，材料容量越高。另一方面，该面积比值太高的话，材料的压实密度会过低，不利于能量密度的提升。因而，上述技术方案中，设置孔隙与多孔碳的面积比为0.3～3，可以使得能量密度提升。
在一些可选的实施方案中，面积比的测试方法为：通过透射电子显微镜对负极材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，对每个颗粒进行区域1、区域2和区域3的辩别以及分类识别，通过软件计算区域1、区域2和区域3的面积，并计算区域2和区域1的面积比，记为A1；或者计算区域3的和区域1的面积比，记为A2；然后对10个负极材料颗粒对应的10个A1取平均值，即为硅材料与碳材料的面积比；
对10个负极材料颗粒对应的10个A2取平均值，即为孔隙与碳材料的面积比；
其中，区域1为碳材料；区域2为硅材料；区域3为孔隙。
在一些可选的实施方案中，上述硅材料包括硅或碳化硅中的至少一种。
碳化硅可作为亲锂性物质，可以有效地诱导锂从负极材料的壳层进入核的孔隙，从而有利于提高锂离子电池的比容量和循环性能。
硅作为亲锂性物质的同时也可以作为储锂材料，不仅可以有效地诱导锂从负极材料的壳层进入核的孔隙，并且可以进一步提高锂离子电池的比容量。
在一些可选的实施方案中，上述壳层厚度2nm～20nm。
壳层的厚度不能过大，否则由于锂扩散穿过壳层的能垒过高导致锂直接在负极材料表面形核长大，可能会增加热失控的概率；而壳层的厚度过小，无法实现有效包覆。上述技术方案中，设置硅材料的厚度为0.5nm～4nm，即可以使得锂扩散穿过壳层，又能够有效地包覆核，封闭孔隙。
在一些可选的实施方案中，上述核满足以下特征中的至少一项：
(a)多孔碳的比表面积为500m2/g～3000m2/g；
(b)多孔碳的平均孔径为1nm～30nm；
(c)多孔碳的孔容为0.1cm3/g～1.5cm3/g；
(d)多孔碳的DV50为1μm～20μm；
(e)多孔碳的d002为0.38nm～0.41nm；
(f)多孔碳的孔隙孔径为2nm～40nm。
多孔碳材料从孔隙形状上可以分为裂缝孔、锥形孔、筒形孔、球形等，有些孔是不规则的。上述技术方案中的孔隙孔径定义为孔壁面内相距最远的两点之间的距离。过小的孔隙孔径可以让硅材料对锂扩散发挥更好的诱导作用，但是会降低整体的储锂量。当孔隙过大时，会导致距离孔 口较远的硅材料的诱导作用被削弱，当锂扩散穿过负极材料的壳层的能垒高于在颗粒表面形核长大的能垒时，锂金属不在孔隙内沉积而沉积在颗粒表面，就会导致锂沉积的不均匀，容量衰减快，甚者可能会增加热失控的概率。
多孔碳的平均孔径不宜过大或过小，过大不利于引入硅材料；上述技术方案中，设置多孔碳的平均孔径在上述范围内易于引入硅材料。
多孔碳的d002代表碳层的层间距，层间距大有利于锂离子的传输扩散，有利于最终电池的倍率以及低温性能。上述技术方案中，设置多孔碳的d002在上述范围内，有利于电池的倍率以及低温性能。
在一些可选的实施方案中，上述负极材料满足以下特征：
(g)负极材料的孔隙孔径为3nm～30nm；
(h)负极材料的孔容为0.005cm3/g～0.06cm3/g；
(i)负极材料的平均孔径为0.01nm～5nm；
(j)负极材料的DV50为1μm～20μm。
上述技术方案中，设置负极材料的孔隙孔径为3nm～30nm，可以有效地提高负极材料整体储锂量；且有利于锂金属沉积均匀，有利于循环稳定性。
第二方面，本申请实施例提供负极极片，上述负极极片前述第一方面提供的负极材料。
第三方面，本申请实施例提供一种电化学装置，该电化学装置包括第二方面提供的负极极片。
第四方面，本申请实施例提供一种用电设备，用电设备包括前述第三方面提供的电化学装置。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对实施例中所需要使用的附图作简单地介绍，应当理解，以下附图仅示出了本申请的某些实施例，因此不应被看作是对范围的限定，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他相关的附图。
图1示意性示出了负极材料的截面结构示意图；
图2示意性示出了根据本申请实施例1的负极材料的TEM图；
图3示意性示出了根据本申请实施例1的负极材料的氮气吸附-脱附曲线图；
图4示意性示出了根据本申请实施例1的负极材料的孔径分布的示意图；
图5示意性示出了根据本申请的实施例所用的多孔碳-1的孔径分布的示意图；
图6示意性示出了根据本申请实施例1的锂离子电池的比容量曲线图；
图7示意性示出了根据本申请实施例1的锂离子电池的循环性能图。
具体实施方式
下面将结合附图对本申请技术方案的实施例进行详细的描述。以下实施例仅用于更加清楚地说明本申请的技术方案，因此只作为示例，而不能以此来限制本申请的保护范围。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同；本文中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请；本申请的说明书和权利要求书及上述附图说明中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的包含。
在本申请实施例的描述中，技术术语“第一”、“第二”等仅用于区别不同对象，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量、特定顺序或主次关系。
在本申请实施例的描述中，技术术语“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本申请实施例和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本申请实施例的限制。
在本申请实施例的描述中，除非另有明确的规定和限定，技术术语“安装”“相连”“连接”“固定”等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或成一体；可以是直接相连，也可以通过中间媒介间接相连。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本申请实施例中的具体含义。
在本文中提及“实施例”意味着，结合实施例描述的特定特征、结构或特性可以包含在本申请的至少一个实施例中。在说明书中的各个位置出现该短语并不一定均是指相同的实施例，也不是与其它实施例互斥的独立的或备选的实施例。本领域技术人员显式地和隐式地理解的是，本文所描述的实施例可以与其它实施例相结合。
在本申请的实施例中，相同的附图标记表示相同的部件，并且为了简洁，在不同实施例中，省略对相同部件的详细说明。应理解，附图示出的本申请实施例中的各种部件的高度、长宽等尺寸，以及集成装置的整体高度、长宽等尺寸仅为示例性说明，而不应对本申请构成任何限定。
参照图1和图2，本申请一些实施方式提供一种负极材料，负极材料包括核和壳层；
核为多孔碳，核具有孔隙；
孔隙壁面上含有硅材料；
壳层为碳材料，壳层包裹在核表面，封闭孔隙。
上述负极材料中，多孔碳和壳层的碳材料为无序结构，储锂较少。孔隙作为储锂的主要区域，孔隙壁面上含有硅材料，硅材料作为亲锂性物质，可以诱导锂从负极材料外部的壳层进入核的孔隙，使锂金属沉积过程中沉积位置可控，降低锂金属沉积不均匀性，从而有利于提高锂离子电池的比容量和循环性能。同时，上述负极材料中，壳层包裹在核表面，封闭孔隙，使孔隙变为闭孔，使得外部电解液进入不到内部孔隙，使得锂在去溶剂化之后进入孔隙。进一步地，硅材料在孔隙壁面上，孔隙储存金属锂的同时可预留一部分空间，以便缓冲由锂金属带来的体积膨胀，从而提高循环性能。
应理解，上述技术方案中，孔隙壁面上含有硅材料，即孔隙中仅壁面上存在硅材料，孔隙的剩余空间可作为储锂空间；上述技术方案中，核的表面具有孔隙；或者核的表面和核的内部均具有孔隙。
在本申请一些实施方式中，本申请的负极材料也可以称之为形成核壳结构，上述的壳层即为壳。
进一步地，在本申请一些实施方式中，上述硅材料的厚度为0.5nm～4nm。上述硅材料的厚度以孔隙壁面所有地方的硅材料的最大厚度作为硅材料的厚度。上述技术方案中，设置硅材料的厚度在上述范围内，有利于使得更多的锂穿过壳层进入到孔隙里，同时有利于降低锂析出在负极材料表面，从而可以获得更高的比容量。
进一步地，在本申请一些实施方式中，上述硅材料的厚度的测试方法为：对负极活性材料进行环氧树脂的包埋固化，然后利用超薄切片法，将材料切成50nm至70nm的尺寸，备好样品。利用高倍透射电镜选取颗粒样品切面进行观察，观察孔隙区域以及无序碳层区域，孔隙区域和无序碳层区域之间的区域即为硅材料，整个颗粒的最外层无序部分即为碳壳。采用软件Image J进行处理。通过TEM对材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，得出这些负极材料颗粒孔隙内壁含有的硅材料的厚度，然后以10个材料颗粒的最大厚度为硅材料的厚度。
进一步地，在本申请一些实施方式中，上述硅材料的厚度为0.6nm～3.9nm。示例性地，在本申请一些实施方式中，上述硅材料的厚度为0.8nm、1.0nm、1.2nm、1.5nm、1.8nm、2.0nm、2.5nm、2.8nm、3.0nm、3.5nm或者3.8nm。
进一步地，在本申请一些实施方式中，以质量百分比计，硅材料占负极材料总质量的0.01％～20％。上述技术方案中，设置硅材料占负极材料总质量的0.01％～20％，既可以有效地诱导锂从负极材料外部的壳层进入核的孔隙，又可以使得整个负极材料具有良好的循环稳定性。
进一步可选地，在本申请一些实施方式中，以质量百分比计，硅材料占负极材料总质量的0.01％～4％。
示例性地，在本申请一些实施方式中，以质量百分比计，硅材料占负极材料总质量的0.03％、0.05％、0.1％、0.5％、1％、2％、3％、5％、8％、10％、15％或者18％。
进一步地，在本申请一些实施方式中，硅材料与多孔碳的面积比为0.01～0.3。硅材料与多孔碳的面积比反映了硅材料亲锂性的大小。该面积比值不能太高，过高可能会导致材料整体的能量密度或者循环性能降低。上述技术方案中，设置硅材料与多孔碳的面积比为0.01～0.3，有利于材料整体的能量密度或者循环性能。
进一步地，在本申请一些实施方式中，上述的硅材料与多孔碳的面积比的测试方法为：对负极活性材料进行环氧树脂的包埋固化，然后利用超薄切片法，将材料切成50nm至70nm的尺寸，备好样品。利用高倍透射电镜选取颗粒样品切面进行观察，观察孔隙区域以及无序碳层区域，孔隙区域和无序碳层区域为核，整个核的最外层无序部分即为碳壳。采用软件Image J进行处理。通过透射电子显微镜对负极材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，对每个颗粒进行区域1、区域2和区域3的辩别以及分类识别，通过软件计算区域1、区域2和区域3的面积，并计算区域2和区域1的面积比，记为A1；然后对10个负极材料颗粒对应的10个A1取平均值，即为硅材料与碳材料的面积比；其中，区域1为碳材料；区域2为硅材料；区域3为孔隙。
进一步可选地，在本申请一些实施方式中，硅材料与多孔碳的面积比为0.01～0.29。示例性地，在本申请一些实施方式中，硅材料与多孔碳的面积比为0.02、0.05、0.08、0.10、0.12、0.15、0.20、0.25或者0.28。
进一步地，在本申请一些实施方式中，孔隙与多孔碳的面积比为0.3～3。孔隙与多孔碳的面积比间接反映了材料内部孔隙率，孔隙作为储锂的主要区域，该面积比值直接影响了材料的容量以及能量密度，该面积比值越大，材料容量越高。另一方面，该面积比值太高的话，材料的压实密度会过低，不利于能量密度的提升。因而，上述技术方案中，设置孔隙与多孔碳的面积比为0.3～3，可以使得能量密度提升。
进一步地，在本申请一些实施方式中，上述的孔隙与多孔碳的面积比的测试方法为：对负极活性材料进行环氧树脂的包埋固化，然后利用超薄切片法，将材料切成50nm至70nm的尺寸，备好样品。利用高倍透射电镜选取颗粒样品切面进行观察，观察孔隙区域以及无序碳层区域，孔隙区域和无序碳层区域为核，整个核的最外层无序部分即为碳壳。通过透射电子显微镜对负极材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，对每个颗粒进行区域1、区域2和区域3的辩别以及分类识别，通过软件计算区域1、区域2和区域3的面积，计算区域3的和区域1的面积比，记为A2；然后对10个负极材料颗粒对应的10个A2取平均值，即为孔隙与碳材料的面积比；其中，区域1为碳材料；区域2为硅材料；区域3为孔隙。
进一步可选地，在本申请一些实施方式中，孔隙与多孔碳的面积比为0.31～3。示例性地，在本申请一些实施方式中，孔隙与多孔碳的面积比为0.31、0.35、0.38、0.40、0.45、0.50、0.80、1.00、1.50、2.00、2.50或者2.80。
进一步地，在本申请一些实施方式中，硅材料的DV50为0.1nm～10nm。Dv50表示硅材料中小于该粒径值的颗粒占硅材料总体积的50％。上述技术方案中，设置硅材料的DV50为0.1nm～10nm，颗粒大小适中，比表面积适中，有利于锂离子电池的比容量和循环性能。
进一步地，在本申请一些实施方式中，上述硅材料的DV50的测试方法为：参照GB/T19077-2016。具体流程为称量样品1g与20mL去离子水和微量分散剂混合均匀，置于超声设备中超声5min后将溶液倒入进样系统Hydro 2000SM中进行测试，所用测试设备为马尔文公司生产的Mastersizer 3000。测试过程中当激光束穿过分散的颗粒样品时，通过测量散射光的强度来完成粒度测量。然后数据用于分析计算形成该散射光谱图的颗粒粒度分布。测试所用颗粒折射率为1.8，一个样品测试三次，颗粒粒度最终取三次测试的平均值测得Dv50。Dv50表示样品中小于该粒径值的颗粒占总样品总体积的50％。
进一步可选地，在本申请一些实施方式中，硅材料的DV50为0.11nm～9.9nm。示例性地，在本申请一些实施方式中，硅材料的DV50为0.15nm、0.2nm、0.5nm、1.0nm、2.0nm、3.0nm、4.0nm、5.0nm、6.0nm、7.0nm或者8.0nm。
进一步地，在本申请一些实施方式中，硅材料包括单质硅或碳化硅中的至少一种。碳化硅可作为亲锂性物质，可以有效地诱导锂从负极材料的壳层进入核的孔隙，从而有利于提高锂离 子电池的比容量和循环性能。硅作为亲锂性物质的同时也可以作为储锂材料，不仅可以有效地诱导锂从负极材料的壳层进入核的孔隙，并且可以进一步提高锂离子电池的比容量。
进一步地，在本申请一些实施方式中，壳层厚度2nm～20nm。壳层的厚度不能过大，否则由于锂扩散穿过壳层的能垒过高导致锂直接在负极材料表面形核长大，可能会增加热失控的概率；而壳层的厚度过小，无法实现有效包覆。上述技术方案中，设置硅材料的厚度为0.5nm～4nm，即可以使得锂扩散穿过壳层，又能够有效地包覆核，封闭孔隙。
在本申请一些实施方式中，壳层厚度的测试方法为：对负极活性材料进行环氧树脂的包埋固化，然后利用超薄切片法，将材料切成50nm至70nm的尺寸，备好样品。利用高倍透射电镜选取颗粒样品切面进行观察，观察孔隙区域以及无序碳层区域，孔隙区域和无序碳层区域为核，整个核的最外层无序部分即为碳壳。通过TEM对材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，得出这些负极材料颗粒最外层无序部分(壳层)的厚度，然后以10个负极材料颗粒的平均厚度为壳层厚度。
进一步可选地，在本申请一些实施方式中，壳层厚度2.1nm～19nm。示例性地，在本申请一些实施方式中，上述的壳层的厚度为2.5nm、3nm、5nm、10nm、12nm、15nm或者18nm。
进一步地，在本申请一些实施方式中，核(多孔碳)可以选择：活性炭、模板多孔碳、炭分子筛、炭纳米纤维、碳纳米管等和膨胀石墨等中的至少一种。
进一步地，在本申请一些实施方式中，核(多孔碳)的孔隙孔径为2nm～40nm；进一步可选地，核(多孔碳)的孔隙孔径为5nm～35nm；示例性地，核(多孔碳)的孔隙孔径为10nm、15nm、20nm、25nm、30nm或者32nm。
多孔碳材料从孔隙形状上可以分为裂缝孔、锥形孔、筒形孔、球形等，有些孔是不规则的，所以这里的孔隙孔径定义为孔壁面内相距最远的两点之间的距离。过小的孔隙孔径可以让硅或碳化硅颗粒对锂扩散发挥更好的诱导作用，但是会降低整体的储锂量。当孔隙过大时，会导致距离孔口较远的硅或碳化硅颗粒的诱导作用被削弱，当锂扩散穿过颗粒的壳的能垒高于在颗粒表面形核长大的能垒时，锂金属不在孔隙内沉积而沉积在颗粒表面，就会导致锂沉积的不均匀，容量衰减快，增大热失效的概率。因而，上述技术方案中，核(多孔碳)的孔隙孔径在上述范围内，有利于提高储锂量、有利于锂沉积均匀。
进一步地，在本申请一些实施方式中，核(多孔碳)的比表面积为500m2/g～3000m2/g；进一步可选地，核(多孔碳)的比表面积为550m2/g～2500m2/g；示例性地，核(多孔碳)的比表面积为600m2/g、800m2/g、1000m2/g、1500m2/g、2000m2/g或者2300m2/g。核(多孔碳)的比表面积在上述范围内，有利于锂离子电池的比容量和循环性能。
进一步地，在本申请一些实施方式中，核(多孔碳)的平均孔径为1nm～30nm；进一步可选地，核(多孔碳)的平均孔径为2nm～29nm；示例性地，核(多孔碳)的平均孔径为3nm、5nm、10nm、15nm、20nm、25nm或者28nm。多孔碳的平均孔径不宜过大或过小，过大不利于引入硅材料；上述技术方案中，设置多孔碳的平均孔径在上述范围内易于引入硅材料。进一步地，在本申请一些实施方式中，上述的核(多孔碳)的平均孔径由氮气在77K下测试所得，平均孔径取自BJH解吸平均孔径。
进一步地，在本申请一些实施方式中，核(多孔碳)的孔容为0.1cm3/g～1.5cm3/g；进一步可选地，核(多孔碳)的孔容为0.2cm3/g～1.4cm3/g；示例性地，核(多孔碳)的孔容为0.5cm3/g、0.8cm3/g、1.0cm3/g、1.2cm3/g或者1.3cm3/g。核(多孔碳)的孔容设置在上述范围内，有利于锂离子电池的比容量和循环性能。进一步地，在本申请一些实施方式中，核(多孔碳)的孔容由氮气在77K下测试所得。
进一步地，在本申请一些实施方式中，核(多孔碳)的DV50为1μm～20μm；进一步可选地，核(多孔碳)的DV50为2μm～19μm；示例性地，核(多孔碳)的DV50为5μm、10μm、12μm、15μm或者18μm。核(多孔碳)的DV50在上述范围内，颗粒大小适中，比表面积适中，有利于锂离子电池的比容量和循环性能。
需要说明的是，此处核(多孔碳)的DV50的测试方法与前述硅材料的DV50的测试方法相同。
进一步地，在本申请一些实施方式中，核(多孔碳)的d002为0.38nm～0.41nm。上述核(多孔碳)的d002代表碳层的层间距，层间距影响锂离子的传输扩散，最终影响电池的倍率以 及低温性能。上述技术方案中，设置核(多孔碳)的d002为0.38nm～0.41nm，有利于电池的倍率以及低温性能。
进一步可选地，在本申请一些实施方式中，核(多孔碳)的d002为0.39nm～0.40nm。示例性地，在本申请一些实施方式中，核(多孔碳)的d002为0.39nm、0.40nm或者0.41nm。
进一步地，在本申请一些实施方式中，负极材料的孔隙孔径为3nm～30nm。多孔碳材料从孔隙形状上可以分为裂缝孔、锥形孔、筒形孔、球形等，有些孔是不规则的。上述技术方案中的孔隙孔径定义为孔壁面内相距最远的两点之间的距离。过小的孔隙孔径可以让硅材料对锂扩散发挥更好的诱导作用，但是会降低整体的储锂量。当孔隙过大时，会导致距离孔口较远的硅材料的诱导作用被削弱，当锂扩散穿过负极材料的壳层的能垒高于在颗粒表面形核长大的能垒时，锂金属不在孔隙内沉积而沉积在颗粒表面，就会导致锂沉积的不均匀，容量衰减快，甚者可能会增加热失控的概率。设置负极材料的孔隙孔径为3nm～30nm，可以有效地提高负极材料整体储锂量；且有利于锂金属沉积均匀，有利于循环稳定性。
进一步可选地，在本申请一些实施方式中，负极材料的孔隙孔径为4nm～29nm。示例性地，在本申请一些实施方式中，负极材料的孔隙孔径为5nm、10nm、15nm、20nm、25nm或者28nm。
进一步地，在本申请一些实施方式中，负极材料的孔容为0.005cm3/g～0.06cm3/g。进一步可选地，负极材料的孔容为0.006cm3/g～0.06cm3/g。示例性地，负极材料的孔容为0.01cm3/g、0.02cm3/g、0.03cm3/g、0.04cm3/g、0.05cm3/g或者0.06cm3/g。负极材料的孔容设置在上述范围内，有利于锂离子电池的比容量和循环性能。进一步地，在本申请一些实施方式中，负极材料的孔容由氮气在77K下测试所得。
进一步地，在本申请一些实施方式中，负极材料的平均孔径为0.01nm～5nm。进一步可选地，负极材料的平均孔径为0.02nm～4.8nm。示例性地，负极材料的平均孔径为0.05nm、1nm、2nm、3nm或者4nm。负极材料的平均孔径设置在上述范围内，有利于锂离子电池的比容量和循环性能。在本申请一些实施方式中，上述的负极材料的平均孔径由氮气在77K下测试所得，平均孔径取自BJH解吸平均孔径。
进一步地，在本申请一些实施方式中，负极材料的DV50为1μm～20μm。进一步可选地，负极材料的DV50为1.5μm～19μm。示例性地，负极材料的DV50为2μm、3μm、4μm、5μm、10μm、12μm、15μm或者18μm。负极材料的DV50在上述范围内，颗粒大小适中，比表面积适中，有利于锂离子电池的比容量和循环性能。
需要说明的是，此处负极材料的DV50的测试方法与前述硅材料的DV50的测试方法相同。
进一步地，在本申请一些实施方式中，上述负极材料可以按照以下方法制备：
步骤S1、将多孔碳粉末放入CVD设备中，通入保护气体，以一定的升温速率升温至目标温度T1。
进一步地，在本申请一些实施方式中，步骤S1中升温速率可以为1至20℃/min，目标温度T1可以为300至600℃。
步骤S2、通入硅元素气体，在目标温度T1下进行化学气相沉积，进行化学气相沉积0.1h至1h后，再通入氮气对炉内进行洗气0.2h，然后，再次通入硅元素气体，如此周期性交替重复进行化学气相沉积和洗气1至20次，获得负极材料的前驱体。
进一步地，在本申请一些实施方式中，步骤S2中硅元素气体可以为硅烷与氩气的混合气体，硅烷的质量浓度可以为0.2％至10％。
进一步地，在本申请一些实施方式中，步骤S2中硅元素气源可以为甲硅烷或者乙硅烷；硅元素气源流量可以为10至300mL/min。
步骤S3、关闭含硅元素气源，通入含碳元素气源，以一定的升温速率升温至目标温度T2，恒温时间为t；然后关闭含碳元素气源，自然降温至室温。
进一步地，在本申请一些实施方式中，步骤S3中，含碳元素气源可以为甲烷、乙烷、丙烷、乙烯、乙炔或者丙炔的至少一种。
进一步地，在本申请一些实施方式中，步骤S3中，升温速率可以为1至20℃/min，目标温度T2可以为800至1200℃，恒温时间t可以为0至5h。
本申请一些实施方式提供一种负极极片，该负极极片包括前述任一实施方式提供的负极材料。
进一步地，在本申请一些实施方式中，负极极片包括集流体和位于集流体表面的负极活性物质层，该负极活性物质层包括前述任一实施方式提供的负极材料。在一些实施例中，集流体包括：铜箔、铝箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜、覆有导电金属的聚合物基底或其任意组合。
在一些实施例中，负极活性物质层还包括粘结剂，粘结剂包括，但不限于：聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1，1二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等。
在一些实施例中，负极活性物质层还包括导电剂，导电剂包括，但不限于：基于碳的材料、基于金属的材料、导电聚合物和它们的混合物。在一些实施例中，基于碳的材料选自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料选自金属粉、金属纤维、铜、镍、铝或银。在一些实施例中，导电聚合物为聚亚苯基衍生物。
本申请的负极极片可以采用本领域的公知方法进行制备。通常，将负极材料以及可选的导电剂(例如碳黑等碳素材料和金属颗粒等)、粘结剂(例如SBR)、其他可选添加剂(例如PTC热敏电阻材料)等材料混合在一起分散于溶剂(例如去离子水)中，搅拌均匀后均匀涂覆在负极集流体上，烘干后即得到负极极片。可以使用金属箔或多孔金属板等材料作为负极集流体。
本申请一些实施方式提供一种电化学装置，该电化学装置包括前述任一实施方式提供的负极极片。
在本申请一些实施方式中，上述电化学装置包括，但不限于：所有种类的一次电池、二次电池或电容器。
在本申请一些实施方式中，上述电化学装置是锂二次电池。
在本申请一些实施方式中，上述电子装置具有优异的电化学性能：在0.5C的电流密度下放电比容量可以为700mAh/g至3000mAh/g,在1C的电流密度下能量保持率可以高达85％至94％。
进一步地，在本申请一些实施方式中，该电化学装置包括前述任一实施方式提供的负极极片；以及正极极片、电解液和隔离膜。
其中，正极极片包括集流体和位于该集流体上的正极活性材料层。在本申请一些实施方式中，正极活性材料包括能够吸收和释放锂的正极材料。释放锂的正极材料包括但不限于钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、磷酸铁锂、钛酸锂和富锂锰基材料。在本申请一些实施方式中，集流体可以包括，但不限于：铝箔。
在本申请一些实施方式中，正极活性材料层还包括粘合剂，并且可选地包括导电材料。粘合剂提高正极活性材料颗粒彼此间的结合，并且还提高正极活性材料与集流体的结合。
在本申请一些实施方式中，粘合剂包括，但不限于：聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1，1二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等。
在本申请一些实施方式中，导电材料包括，但不限于：基于碳的材料、基于金属的材料、导电聚合物和它们的混合物。在一些实施例中，基于碳的材料选自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料选自金属粉、金属纤维、铜、镍、铝或银。在一些实施例中，导电聚合物为聚亚苯基衍生物。
正极极片可以通过本领域公知的制备方法制备。例如，正极极片可以通过如下方法获得：在溶剂中将活性材料、导电材料和粘合剂混合，以制备活性材料组合物，并将该活性材料组合物涂覆在集流体上。在一些实施例中，溶剂可以包括，但不限于：N甲基吡咯烷酮。本申请的电化学装置具有更高的能量密度、循环性能，能够满足应用要求。
进一步地，在本申请一些实施方式中，隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚乙烯烷氧、聚偏氟乙烯和聚(偏氟乙烯-六氟丙烯)中的至少一种。
进一步地，在本申请一些实施方式中，电解液还可以包括非水溶剂。非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物或它们的组合。
碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。链状碳酸酯化合物的实例为碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸甲乙酯(MEC)及其组合。所述环状碳酸酯化合物的实例为碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)或者其组合。所述氟代碳酸酯化合物的实例为碳酸氟代亚乙酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯或者其组合。羧酸酯化合物的实例为乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯、甲酸甲酯或者其组合。醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃或者其组合。
本申请一些实施方式提供一种用电设备，该用电设备包括前述任一实施方式提供的电化学装置。
下面列举了一些具体实施例以更好地对本申请进行说明。
【负极材料的制备】
实施例1
提供一种负极材料，按照以下步骤制备：
(1)、将商购的多孔碳-1放入CVD设备中，通入氮气，以5℃/min的升温速率升温至435℃；
(2)、关闭氮气，通入含硅元素气源进行化学气相沉积，通入0.3h后，再通入氮气对炉内进行洗气0.2h，然后，再次通入0.7％的硅源气体，如此周期性交替重复进行化学气相沉积和洗气3次，获得负极材料的前驱体；
(3)、关闭硅源气体，通入含碳元素气源，以5℃/min的升温速率升温至850℃，恒温时间为1h；然后关闭含碳元素气源，自然降温至室温得到负极材料。
实施例1第(1)步骤中使用的多孔碳-1的孔径分布曲线如图4所示，可以看出，多孔碳-1存在微孔和介孔，平均孔径为3.69nm，孔容为0.63cm3/g，具有1730m2/g的比表面积。
实施例1得到的负极材料的氮气吸附-脱附曲线图如图3所示，可以看出多孔碳-1经过以上步骤以后吸附量变得极小，说明氮气进入不到孔里面，大部分孔已经变为闭孔。
实施例1得到的负极材料的孔径分布曲线如图5所示，可以看出，负极材料兼具微孔和中孔，平均孔径为5.8nm，孔容为0.046cm3/g，具有33.3m2/g的比表面积。所以经过CVD包覆之后的多孔碳-1的BET和孔容变得极小，说明内部大部分孔隙已经变为闭孔。
实施例2
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至455℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气4次。
实施例3
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至485℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气5次。
实施例4
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至485℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气5次。
在第(3)步骤中，恒温时间为1.5h。
实施例5
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至485℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气5次；
在第(3)步骤中，恒温时间为2h。
实施例6
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至455℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气4次；
在第(3)步骤中，以5℃/min的升温速率升温至1050℃。
实施例7
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至455℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气4次；
在第(3)步骤中，以5℃/min的升温速率升温至1050℃，恒温时间为2h。
实施例8
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，使用的多孔碳为多孔碳-2，升温至485℃；
在第(2)步骤中，通入1.5％的硅源气体，且周期性交替重复进行化学气相沉积和洗气5次；
在第(3)步骤中，恒温时间为2h。
实施例9
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，使用的多孔碳为多孔碳-2，升温至485℃；
在第(2)步骤中，通入1.5％的硅源气体，且周期性交替重复进行化学气相沉积和洗气5次；
在第(3)步骤中，以5℃/min的升温速率升温至1050℃，恒温时间为2h。
实施例10
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，使用的多孔碳为多孔碳-2，升温至485℃；
在第(2)步骤中，通入1.5％的硅源气体，且周期性交替重复进行化学气相沉积和洗气6次；
在第(3)步骤中，以5℃/min的升温速率升温至1050℃，恒温时间为2h。
实施例11
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，使用的多孔碳为多孔碳-3，升温至485℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气5次；
在第(3)步骤中，恒温时间为2h。
实施例12
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，升温至485℃；
在第(2)步骤中，周期性交替重复进行化学气相沉积和洗气35次；
在第(3)步骤中，恒温时间为2h。
实施例13
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：
在第(1)步骤中，使用的多孔碳为多孔碳-2，升温至485℃；
在第(2)步骤中，通入1.5％的硅源气体，且周期性交替重复进行化学气相沉积和洗气5次；
在第(3)步骤中，恒温时间为8h。
对比例1
提供一种负极材料，为实施例1中的多孔碳-1。
对比例2
提供一种负极材料，制备步骤与实施例1基本相同，所不同之处在于：没有第(3)步骤。
【性能测试】
对各个实施例和对比例制得的负极材料的性能进行测试。
1、TEM测试
对负极活性材料进行环氧树脂的包埋固化，然后利用超薄切片法，将材料切成50nm至70nm的尺寸，备好样品。利用高倍透射电镜选取颗粒样品切面进行观察，观察孔隙区域以及无序碳层区域，孔隙区域和无序碳层区域之间的区域即为硅材料，整个颗粒的最外层无序部分即为碳壳。采用软件Image J进行处理。
图2示出了实施例1的负极材料的TEM图，以此做为示例。
(1)硅材料的厚度
通过TEM对材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，得出这些负极材料颗粒孔隙内壁含有的硅材料的厚度，然后以10个材料颗粒的最大厚度为硅材料的厚度。
(2)面积比
通过透射电子显微镜对负极材料进行拍摄观察，然后使用图像解析软件Image J，从照片中随机地选出10个负极材料颗粒，对每个颗粒进行区域1、区域2和区域3的辩别以及分类识别，通过软件计算区域1、区域2和区域3的面积，并计算区域2和区域1的面积比，记为A1；或者计算区域3的和区域1的面积比，记为A2；然后对10个负极材料颗粒对应的10个A1取平均值，即为硅材料与碳材料的面积比；
对10个负极材料颗粒对应的10个A2取平均值，即为孔隙与碳材料的面积比；
其中，区域1为碳材料；区域2为硅材料；区域3为孔隙。
2、孔隙孔径
负极离子研磨(Cross-section)样品制备流程：将负极极片裁剪为0.5cm×1cm大小，使用导电胶将裁剪好的负极黏贴在1cm×1.5cm大小的硅片载体上，然后使用氩离子抛光(参数：8KV的加速电压，每个样品4h)对负极极片的一端进行处理，氩离子抛光是利用高压电场使氩气电离产生离子态，产生的氩离子在加速电压的作用下，高速轰击负极表面，对负极极片进行逐层剥蚀而达到抛光的效果。
孔隙孔径：通过FESEM对材料进行拍摄观察，从照片中随机地选出10个材料颗粒，对颗粒内部的孔隙进行尺寸量取，量取孔隙内壁相距最远的两点之间的距离，最后以10个材料颗粒内部量取的距离的平均值为孔隙孔径。
4、负极活性材料颗粒的粒径测试
颗粒粒度测试方法参照GB/T 19077-2016。具体流程为称量样品1g与20mL去离子水和微量分散剂混合均匀，置于超声设备中超声5min后将溶液倒入进样系统Hydro 2000SM中进行测试，所用测试设备为马尔文公司生产的Mastersizer 3000。测试过程中当激光束穿过分散的颗粒样品时，通过测量散射光的强度来完成粒度测量。然后数据用于分析计算形成该散射光谱图的颗粒粒度分布。测试所用颗粒折射率为1.8，一个样品测试三次，颗粒粒度最终取三次测试的平均值测得Dv50。Dv50表示样品中小于该粒径值的颗粒占总样品总体积的50％。
5、负极活性材料孔径分布测试
测试仪器为ASAP2460-物理吸附分析仪，将烘干脱气处理后的样品置于液氮中，调节不同试验压力，分别测出对氮气的吸附量，并绘出吸附和脱附等温线。根据滞后环的形状确定孔的形状，按不同的孔模型计算孔分布、孔容积，使用BJH模型拟合介孔及大孔的孔径分布曲线，使用DFT模型拟合微孔的孔径分布曲线。
6、半电池(扣式电池)的制备：
以金属锂为对电极，将直径18mm厚度0.6mm的锂片、隔膜、各实施例和对比例中的负极极片(裁切成直径18mm后采用)按顺序组装叠在一起，并加入电解液，装入正负极扣式不锈钢壳中封装，获得扣式电池。
锂离子扣式测试：扣式电池以50mA/g的电流密度放电，放电时间为10h至80h，以50mA/g的电流密度充电至2.0V，记录此时扣式电池的容量，记为电池比容量。
图6示出了实施例1的锂离子电池的比容量曲线图。
表2中的放电定容容量＝50mA/g×放电时间。
7、锂离子全电池循环性能测试：
将正极极片、隔膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入包装袋内，将电解液注入包装袋并封口，得到锂离子全电池；或者，将正极极片、隔膜和负极极片按顺序堆叠，然后用胶带将整个叠片结构的四个角固定好得到叠片结构的电极组件，将电极组件置入包装袋内，将电解液注入包装袋并封口，得到锂离子全电池。
将采用所有对比例和实施例制备的锂离子全电池各取5个，取平均值。通过以下步骤对锂离子全电池重复进行充电和放电，并计算锂离子全电池的放电容量保持率。
首先，在25℃的环境中，进行第一次充电和放电，在1C的充电电流下进行恒流充电，直到达到上限电压4.55V后转为恒压充电，然后在1C的放电电流下进行恒流放电，直到最终电压为2V，此记为一个循环。记录首次循环和第500次循环的数据。从首次循环到第450圈内，每跑完50个循环采用0.2C的电流进行容量测试，具体操作如下：在0.2C的充电电流下进行恒流充电，直到达到上限电压4.55V后转为恒压充电，然后在0.2C的放电电流下进行恒流放电，直到最终电压为2V。
表2中循环容量保持率＝(第500次循环的放电容量/首次循环的放电容量)×100％。
图7示出了实施例1的锂离子电池的循环性能图。
【结果】
各实施例和对比例的特征参数和性能参数如表1、表2所示。
表1

表2

从上述表格可以看出：
上述各个实施例制备的负极材料，可以使锂离子电池具有较高的比容量和循环性能。
相对于实施例，对比例1提供的负极材料，锂离子电池的比容量和循环性能均低。
进一步地，从实施例1到实施例3可以看出，硅材料的厚度分别为0.52nm、0.86nm和1.25nm，Si的质量百分数为0.8％、0.9％和1.52％，实施例3因为具有更高的Si含量以及A1和A2值，能让更多的锂穿过碳壳进入到闭孔里，同时又不会让锂析出在颗粒表面，所以实施例3制备的负极材料更有更高的比容量，为2015mAh/g，同时具有89.3％的容量保持率。
实施例3到实施例5的碳壳厚度分别为5.2nm、8.6nm和15.1nm，容量保持率分别为89.3％、90.1％和91.2％。从实施例3到实施例5可以看出，在限定范围内的情况下，壳层厚度对比容量的影响较小，对循环性能的影响更大。壳层厚度在限定范围内的情况下，越大对嵌锂过程中产生的膨胀抑制越明显，材料在循环过程中更能保持核壳结构的完整性。
对比实施例2、实施例6和实施例7，主要是区别在于硅材料的物质不同。可以根据调控在CVD包覆过程的温度来控制生成Si或者碳化硅。碳化硅在充放电过程中不作为嵌锂活性物质，所以不提供容量，所以实施例6和实施例7的比容量要比实施例2更低，但是因为缺少了硅嵌锂带来的膨胀，所以实施例6和实施例7具有更高的容量保持率，分别为92.8％和93.6％。
对比实施例8到实施例10，分别采用的多孔碳为多孔碳-2，相对于多孔碳-1，多孔碳-2具有更大的BET、孔容和孔隙孔径。可以发现对比实施例1到实施例7，实施例8到实施例10的负极材料具有更高的比容量，这是由于更大孔容可以容纳更多的锂，同时保证较高的容量保持率。
对于实施例11，采用的多孔碳为多孔碳-3，其孔隙孔径为52nm。虽然具有1706的比容量，但是容量保持率仅为66.3％。这是因为由于孔隙孔径过大，导致在循环过程中锂会逐渐进入不到深层次的孔中，导致多余的锂在颗粒表面析出，导致容量衰减加速。由此说明，多孔碳的孔隙孔径为2nm～40nm时，锂离子电池具有更优的比容量和循环性能。
对比实施例1到实施例7和实施例12，实施例12中硅材料厚度较大，为4.8nm，虽然也具有较高的比容量1876mAh/g，但是由于Si含量过高，导致A1值过高，A2值过低，孔隙留下的膨胀空间过小，导致在循环过程中结构稳定性受到破坏，循环性能变差。由此可见，硅材料的厚度为0.5nm～4nm；或者硅材料占负极材料总质量的0.01％～4％；或者硅材料与多孔碳的面积比为0.01～0.3；或者孔隙与所述多孔碳的面积比为0.3～3时，锂离子电池具有更优的比容量和循环性能。
对比实施例8到实施例10和实施例13，实施例13的负极材料具有较大的壳层厚度，为50nm；实施例13在循环后期会导致锂扩散穿过碳壳的能垒较高，导致逐渐在孔隙外面析出，从而导致容量的衰减。由此说明，壳层厚度2nm～20nm，具有更优的比容量和循环性能。
以上所描述的实施例是本申请一部分实施例，而不是全部的实施例。本申请的实施例的详细描述并非旨在限制要求保护的本申请的范围，而是仅仅表示本申请的选定实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。

Claims (12)

  1. 一种负极材料，其特征在于，所述负极材料包括核和壳层；
    所述核为多孔碳，所述核具有孔隙；
    所述孔隙壁面上含有硅材料；
    所述壳层为碳材料。
  2. 根据权利要求1所述的负极材料，其特征在于，
    以质量百分比计，所述硅材料占所述负极材料总质量的0.01％～20％。
  3. 根据权利要求1所述的负极材料，其特征在于，
    以质量百分比计，所述硅材料占所述负极材料总质量的0.01％～4％。
  4. 根据权利要求1所述的负极材料，其特征在于，
    所述硅材料与所述多孔碳的面积比为0.01～0.3。
  5. 根据权利要求1所述的负极材料，其特征在于，
    所述孔隙与所述多孔碳的面积比为0.3～3。
  6. 根据权利要求1-5任一项所述的负极材料，其特征在于，
    所述硅材料包括单质硅或碳化硅中的至少一种。
  7. 根据权利要求1-6任一项所述的负极材料，其特征在于，
    所述硅材料的厚度为0.5nm～4nm，和/或所述壳层的厚度2nm～20nm。
  8. 根据权利要求1-7任一项所述的负极材料，其特征在于，
    所述核满足以下特征中的至少一项：
    (a)所述多孔碳的比表面积为500m2/g～3000m2/g；
    (b)所述多孔碳的平均孔径为1nm～30nm；
    (c)所述多孔碳的孔容为0.1cm3/g～1.5cm3/g；
    (d)所述多孔碳的DV50为1μm～20μm；
    (e)所述多孔碳的d002为0.38nm～0.41nm；
    (f)所述多孔碳的孔隙孔径为2nm～40nm。
  9. 根据权利要求1-8任一项所述的负极材料，其特征在于，
    所述负极材料满足以下特征：
    (g)所述负极材料的孔隙孔径为3nm～30nm；
    (h)所述负极材料的孔容为0.005cm3/g～0.06cm3/g；
    (i)所述负极材料的平均孔径为0.01nm～5nm；
    (j)所述负极材料的DV50为1μm～20μm。
  10. 一种负极极片，其特征在于，
    所述负极极片包括权利要求1-9任一项所述的负极材料。
  11. 一种电化学装置，其特征在于，所述电化学装置包括权利要求10所述的负极极片。
  12. 一种用电设备，其特征在于，所述用电设备包括权利要求11所述的电化学装置。
PCT/CN2024/101601 2023-06-29 2024-06-26 负极材料、负极极片、电化学装置、用电设备 Ceased WO2025002174A1 (zh)

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