Negative electrode material, negative electrode sheet, electrochemical apparatus, and electric device

Abstract

A negative electrode material, a negative electrode sheet, an electrochemical apparatus, and an electric device. The negative electrode material comprises a core and a shell layer; the core is porous carbon and has pores; the wall surfaces of the pores contain a silicon material; the shell layer is a carbon material and wraps the surface of the core to seal pores. In the negative electrode material, the porous carbon and the carbon material of the shell layer are of a disordered structure, and the stored lithium is less. The pores are used as main lithium storage areas, the wall surfaces of the pores contain the silicon material, and the silicon material, as a lithium-philic substance, can induce lithium to enter the pores of the core from the outer shell layer of the negative electrode material, so that the deposition position of lithium metal during deposition can be controlled, and the non-uniformity of lithium metal deposition can be reduced, thereby improving the specific capacity and cycle performance of lithium ion batteries.

Description

Negative electrode materials, negative electrode sheets, electrochemical devices, and electrical equipment

[0001] Cross-references

[0002] This application claims priority to the Chinese invention patent application with application number 202310791499.1 filed on June 29, 2023, and invention name “Negative electrode material, negative electrode sheet, electrochemical device, and electrical equipment,” the contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to a negative electrode material, a negative electrode plate, an electrochemical device, and an electrical device. Background Art

[0004] Since Sony Corporation of Japan commercialized lithium-ion batteries in 1991, lithium-ion batteries have been widely 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.

[0005] However, as downstream applications continue to increase their demands for battery energy and power performance, the capacity of current commercial lithium-ion batteries has become insufficient.

[0006] Summary of the Invention

[0007] Currently, commercial lithium-ion battery anodes are primarily graphite-based. Based on the lithium storage mechanism of LiC6 between graphite layers, their theoretical specific capacity is only 372 mAh / g, leaving limited room for improvement. Furthermore, lithium diffusion between graphite layers also restricts their rate performance. Therefore, researching and preparing new high-capacity, long-cycle lithium-ion battery anode materials is key to the continued development of lithium-ion batteries.

[0008] To increase the capacity of lithium-ion batteries, existing technologies construct a porous carbon skeleton on the anode electrode. During battery discharge, lithium metal is stripped from the anode and embedded in the cathode material, allowing the porous carbon skeleton to maintain its shape. During battery charging, lithium metal is stripped from the cathode and deposited on the anode electrode. The porous carbon skeleton also disperses the current, reducing local current density, thereby reducing lithium dendrites and increasing lithium deposition density, thereby improving lithium-ion battery performance. However, due to the porous carbon skeleton's high binding energy for lithium, the deposition position of lithium metal during the deposition process is uncontrollable, resulting in uneven lithium metal deposition, large volume changes in the anode electrode during cycling, and rapid capacity decay.

[0009] Based on the above considerations, the purpose of this application is to provide a negative electrode material, a negative electrode plate, an electrochemical device, and an electrical equipment.

[0010] The embodiment of the present application is implemented as follows:

[0011] In a first aspect, an embodiment of the present application provides a negative electrode material, the negative electrode material comprising a core and a shell;

[0012] The core is porous carbon, and the core has pores;

[0013] The pore walls contain silicon material;

[0014] The shell is made of carbon material, which wraps around the core surface and closes the pores.

[0015] Among the aforementioned negative electrode materials, the porous carbon and the carbon shell have disordered structures and store less lithium. The pores, the primary area for lithium storage, contain silicon on the pore walls. As a lithiophilic substance, silicon can induce lithium to flow from the outer shell of the negative electrode material into the pores of the core. This allows for controllable lithium metal deposition and reduces uneven lithium metal deposition, thereby improving the specific capacity and cycling performance of lithium-ion batteries.

[0016] Furthermore, in the above-mentioned negative electrode material, the shell layer wraps around the core surface, sealing the pores and turning the pores into closed pores, so that the external electrolyte cannot enter the internal pores, and lithium enters the pores after desolvation.

[0017] Furthermore, on the pore walls of the silicon material, the pores can reserve a portion of space while storing metallic lithium to buffer the volume expansion caused by lithium metal, thereby improving the cycle performance.

[0018] In some optional embodiments, the thickness of the silicon material is 0.5 nm to 4 nm.

[0019] In the above technical solution, setting the thickness of the silicon material within the above range is conducive to allowing more lithium to pass through the shell and enter the pores, while also helping to reduce lithium precipitation on the surface of the negative electrode material, thereby obtaining a higher specific capacity.

[0020] In some optional embodiments, the silicon material accounts for 0.01% to 20% of the total mass of the negative electrode material by mass percentage. Alternatively, the silicon material accounts for 0.01% to 4% of the total mass of the negative electrode material by mass percentage.

[0021] In the above technical solution, 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.

[0022] In some optional embodiments, the area ratio of the silicon material to the porous carbon is 0.01 to 0.3.

[0023] The area ratio of the silicon material to the porous carbon reflects the lithium affinity of the silicon material. This ratio should not be too high, as it may reduce the overall energy density or cycling performance of the material. In the above technical solution, 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 and cycling performance of the material.

[0024] In some optional embodiments, the area ratio of the pores to the porous carbon is 0.3-3.

[0025] 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 of pores 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.

[0026] In some optional embodiments, the area ratio test method is: photographing and observing the negative electrode material through a transmission electron microscope, and then using image analysis software Image J to randomly select 10 negative electrode material particles from the photograph, and distinguish and classify each particle into region 1, region 2, and region 3. The software calculates the areas of region 1, region 2, and region 3, and calculates the area ratio of region 2 to region 1, recorded as A1; or calculates the area ratio of region 3 to region 1, recorded as A2; then the average of the 10 A1s corresponding to the 10 negative electrode material particles is taken, which is the area ratio of the silicon material to the carbon material;

[0027] The average value of 10 A2 corresponding to 10 negative electrode material particles is the area ratio of pores to carbon material;

[0028] Among them, region 1 is carbon material; region 2 is silicon material; and region 3 is pores.

[0029] In some optional embodiments, the silicon material includes at least one of silicon or silicon carbide.

[0030] 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 improving the specific capacity and cycle performance of lithium-ion batteries.

[0031] 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.

[0032] In some optional embodiments, the shell layer has a thickness of 2 nm to 20 nm.

[0033] The shell thickness cannot be too large, otherwise the high energy barrier for lithium to diffuse through the shell will cause lithium to nucleate and grow directly on the surface of the negative electrode material, potentially increasing the probability of thermal runaway. If the shell thickness is too small, effective coating will not be achieved. In the above technical solution, the silicon material thickness is set to 0.5nm to 4nm, which allows lithium to diffuse through the shell while effectively coating the core and sealing the pores.

[0034] In some optional embodiments, the core satisfies at least one of the following characteristics:

[0035] (a) The specific surface area of ​​porous carbon is 500 m 2 / g~3000m 2 / g;

[0036] (b) The average pore size of porous carbon is 1 nm to 30 nm;

[0037] (c) The pore volume of porous carbon is 0.1 cm 3 / g~1.5cm 3 / g;

[0038] (d) D of porous carbon V 50 is 1μm~20μm;

[0039] (e) d002 of porous carbon is 0.38nm~0.41nm;

[0040] (f) The pore size of porous carbon is 2nm~40nm.

[0041] 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 diameter in the above technical solution is defined as the distance between the two points farthest apart on the pore wall. Too small a pore diameter 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 away from the pore mouth will be weakened. When the energy barrier for lithium to diffuse through the shell of the negative electrode material is higher than the energy barrier for nucleation and growth on the surface of the particles, the lithium metal will not be 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.

[0042] 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.

[0043] The d002 of the porous carbon represents the interlayer spacing of the carbon layers. A large interlayer spacing is beneficial to the transport and diffusion of lithium ions, which is beneficial to the rate and low-temperature performance of the final battery. In the above technical solution, setting the d002 of the porous carbon within the above range is beneficial to the rate and low-temperature performance of the battery.

[0044] In some optional embodiments, the above-mentioned negative electrode material meets the following characteristics:

[0045] (g) The pore size of the negative electrode material is 3 nm to 30 nm;

[0046] (h) The pore volume of the negative electrode material is 0.005 cm 3 / g~0.06cm 3 / g;

[0047] (i) The average pore size of the negative electrode material is 0.01 nm to 5 nm;

[0048] (j) D of negative electrode material V 50 is 1μm~20μm.

[0049] In the above technical solution, 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 deposition of lithium metal and cycle stability.

[0050] In a second aspect, 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.

[0051] In a third aspect, an embodiment of the present application provides an electrochemical device, which includes the negative electrode sheet provided in the second aspect.

[0052] In a fourth aspect, an embodiment of the present application provides an electrical device, which includes the electrochemical device provided in the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0054] FIG1 schematically shows a cross-sectional structure diagram of a negative electrode material;

[0055] FIG2 schematically shows a TEM image of the negative electrode material according to Example 1 of the present application;

[0056] FIG3 schematically shows a nitrogen adsorption-desorption curve of the negative electrode material according to Example 1 of the present application;

[0057] FIG4 schematically shows a schematic diagram of the pore size distribution of the negative electrode material according to Example 1 of the present application;

[0058] FIG5 schematically shows a schematic diagram of the pore size distribution of porous carbon-1 used in an embodiment of the present application;

[0059] FIG6 schematically shows a specific capacity curve of a lithium-ion battery according to Example 1 of the present application;

[0060] FIG7 schematically shows a cycle performance diagram of the lithium-ion battery according to Example 1 of the present application. DETAILED DESCRIPTION

[0061] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0063] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0064] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "inside" and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0065] In the description of the embodiments of this application, unless otherwise specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0066] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0067] In the embodiments of this application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components in different embodiments are omitted. It should be understood that the heights, lengths, widths, and other dimensions of the various components in the embodiments of this application, as well as the overall heights, lengths, widths, and other dimensions of the integrated device shown in the drawings are merely illustrative and do not constitute any limitation on this application.

[0068] 1 and 2 , some embodiments of the present application provide a negative electrode material, the negative electrode material including a core and a shell;

[0069] The core is porous carbon, and the core has pores;

[0070] The pore walls contain silicon material;

[0071] The shell is made of carbon material, which wraps around the core surface and closes the pores.

[0072] In the above-mentioned negative electrode materials, the porous carbon and the carbon materials 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, as lithium-philic substances, can induce lithium to enter the pores of the core from the shell layer outside the negative electrode material, making the deposition position controllable during the lithium metal deposition process and reducing the unevenness of lithium metal deposition, which is beneficial to improving the specific capacity and cycle performance of lithium-ion batteries. At the same time, in the above-mentioned negative electrode materials, the shell layer is wrapped around the core surface, closing the pores and turning the pores into closed pores, so that the external electrolyte cannot enter the internal pores, allowing lithium to enter the pores after desolvation. Furthermore, the silicon material is on the pore wall, and while the pores store metallic lithium, a portion of space can be reserved to buffer the volume expansion caused by lithium metal, thereby improving the cycle performance.

[0073] It should be understood that in the above technical solution, the pore walls contain silicon material, that is, silicon material exists only 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 interior of the core have pores.

[0074] In some embodiments of the present application, 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.

[0075] Furthermore, in some embodiments of the present application, the thickness of the silicon material is 0.5 nm to 4 nm. The thickness of the silicon material is determined by taking the maximum thickness of the silicon material at all locations on the pore wall as the thickness of the silicon material. In the above technical solution, setting the thickness of the silicon material within the above range is conducive to allowing more lithium to pass through the shell and enter the pores, while also helping to reduce lithium precipitation on the surface of the negative electrode material, thereby achieving a higher specific capacity.

[0076] Furthermore, in some embodiments of the present application, the thickness of the silicon material is tested as follows: the negative electrode active material is embedded and cured with epoxy resin, and then the material is cut into a size of 50nm to 70nm using an ultrathin sectioning method to prepare a sample. A high-power transmission electron microscope is used to select a cross-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 photograph 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.

[0077] Furthermore, in some embodiments of the present application, the thickness of the silicon material is 0.6 nm to 3.9 nm. For example, in some embodiments of the present application, 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.

[0078] Furthermore, in some embodiments of the present application, the silicon material accounts for 0.01% to 20% of the total mass of the negative electrode material, calculated as a percentage by mass. In the above technical solution, setting the silicon material to account for 0.01% to 20% of the total mass of the negative electrode material can effectively induce lithium from the outer shell of the negative electrode material to enter the pores of the core, while also ensuring that the entire negative electrode material has good cycle stability.

[0079] Further optionally, in some embodiments of the present application, the silicon material accounts for 0.01% to 4% of the total mass of the negative electrode material in terms of mass percentage.

[0080] Illustratively, in some embodiments of the present application, 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, as a percentage by mass.

[0081] Furthermore, in some embodiments of the present application, 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. This area ratio cannot be too high, as it may lead to a decrease in the overall energy density or cycle performance of the material. In the above technical solution, 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.

[0082] Furthermore, in some embodiments of the present application, the area ratio of the silicon material to the porous carbon is measured by encapsulating and curing the negative electrode active material with epoxy resin, then ultrathinly sectioning the material into samples of 50 to 70 nm. A high-magnification transmission electron microscope is used to observe the cross-section of the particle sample, focusing on the pore region and the disordered carbon layer. The pore region and the disordered carbon layer are the core, and the outermost disordered portion of the core is the carbon shell. Image J software is used 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 calculated, recorded as A1. The average of the 10 Al's corresponding to the 10 negative electrode material particles was then taken, which was the area ratio of silicon material to carbon material. Among them, region 1 was carbon material; region 2 was silicon material; and region 3 was pores.

[0083] Further optionally, in some embodiments of the present application, the area ratio of the silicon material to the porous carbon is 0.01 to 0.29. For example, in some embodiments of the present application, 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.

[0084] Furthermore, in some embodiments of the present application, the area ratio of the pores to the porous carbon is 0.3 to 3. The area ratio of the pores to the 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 the pores to the porous carbon to 0.3 to 3 can improve the energy density.

[0085] Furthermore, in some embodiments of the present application, the above-mentioned pore-to-porous carbon area ratio is tested by: embedding and curing the negative electrode active material with epoxy resin, then using ultrathin sectioning to cut the material into pieces of 50 nm to 70 nm in size, preparing a sample. A cross-section of the particle sample is observed using a high-magnification transmission electron microscope to observe the pore region and the disordered carbon layer region. The pore region and the disordered carbon layer region are the core, and the outermost disordered portion of the entire core is the carbon shell. 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 the 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 3 to region 1 was calculated and recorded as A2. The average of the 10 A2 values ​​corresponding to the 10 negative electrode material particles was then taken, which was the area ratio of the pores to the carbon material. Among them, region 1 was the carbon material; region 2 was the silicon material; and region 3 was the pores.

[0086] Further optionally, in some embodiments of the present application, the area ratio of the pores to the porous carbon is 0.31 to 3. For example, in some embodiments of the present application, the area ratio of the pores to the 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.

[0087] Furthermore, in some embodiments of the present application, the D of the silicon material V 50 is 0.1nm~10nm. Dv50 means that the particles smaller than this particle size in the silicon material account for 50% of the total volume of the silicon material. V 50 is 0.1nm~10nm, the particle size is moderate, and the specific surface area is moderate, which is beneficial to the specific capacity and cycle performance of lithium-ion batteries.

[0088] Furthermore, in some embodiments of the present application, the D of the silicon material VThe test method for Dv50 is: refer to GB / T19077-2016. The specific process is to weigh 1g of 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. During the test, when the laser beam passes through the dispersed particle sample, 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 to obtain 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.

[0089] Further optionally, in some embodiments of the present application, the D of the silicon material V 50 is 0.11nm~9.9nm. For example, in some embodiments of the present application, D of the silicon material V 50 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.

[0090] Furthermore, in some embodiments of the present application, the silicon material includes at least one of elemental silicon or silicon carbide. Silicon carbide can act as a lithiophilic substance, effectively inducing lithium from the shell of the negative electrode material into the pores of the core, thereby facilitating improved specific capacity and cycle performance of lithium-ion batteries. Silicon, while being a lithiophilic substance, can also act as a lithium storage material, effectively inducing lithium from the shell of the negative electrode material into the pores of the core and further improving the specific capacity of the lithium-ion battery.

[0091] Furthermore, in some embodiments of the present application, the shell thickness is 2nm to 20nm. The shell thickness 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. If the shell thickness is too small, effective coating cannot be achieved. In the above technical solution, the thickness of the silicon material is set to 0.5nm to 4nm, which allows lithium to diffuse through the shell while effectively coating the core and sealing the pores.

[0092] In some embodiments of the present application, the shell thickness is tested as follows: the negative electrode active material is embedded and cured with epoxy resin, and then the material is cut into a size of 50nm to 70nm by ultrathin sectioning to prepare a sample. A high-power transmission electron microscope is used to select a cross-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 10 negative electrode material particles are randomly selected from the photo using the image analysis software Image J 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.

[0093] Further optionally, in some embodiments of the present application, the shell layer has a thickness of 2.1 nm to 19 nm. For example, in some embodiments of the present application, the shell layer has a thickness of 2.5 nm, 3 nm, 5 nm, 10 nm, 12 nm, 15 nm, or 18 nm.

[0094] Furthermore, in some embodiments of the present application, the core (porous carbon) may be selected from at least one of activated carbon, template porous carbon, carbon molecular sieve, carbon nanofiber, carbon nanotube, expanded graphite, and the like.

[0095] Furthermore, in some embodiments of the present application, 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.

[0096] Porous carbon materials can be divided into crack pores, conical pores, cylindrical pores, spheres, etc. based on the pore shape. Some pores are irregular, so the pore diameter here is defined as the distance between the two farthest points in the pore wall. Too small a pore diameter 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 that are far away from the pore mouth will be weakened. When the energy barrier for lithium to diffuse through the shell of the particle is higher than the energy barrier for nucleation and growth on the surface of the particle, lithium metal is not deposited in the pores but on the surface of the particle, which will lead to uneven lithium deposition, rapid capacity decay, and increased probability of thermal failure. Therefore, in the above technical solution, the pore diameter of the core (porous carbon) is within the above range, which is conducive to increasing the lithium storage capacity and facilitating uniform lithium deposition.

[0097] Furthermore, in some embodiments of the present application, the specific surface area of ​​the core (porous carbon) is 500m 2 / g~3000m 2 / g; further optionally, the specific surface area of ​​the core (porous carbon) is 550m 2 / g~2500m 2 / g; For example, the specific surface area of ​​the core (porous carbon) is 600m 2 / g、800m 2 / g、1000m 2 / g、1500m 2 / g、2000m 2 / g or 2300m 2 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.

[0098] Furthermore, in some embodiments of the present application, the average pore size of the core (porous carbon) is 1nm to 30nm; further optionally, the average pore size of the core (porous carbon) is 2nm to 29nm; illustratively, the average pore size of the core (porous carbon) is 3nm, 5nm, 10nm, 15nm, 20nm, 25nm or 28nm. The average pore size of the porous carbon should not be too large or too small, as too large a size is not conducive to the introduction of silicon materials; in the above technical solution, setting the average pore size of the porous carbon within the above range facilitates the introduction of silicon materials. Further, in some embodiments of the present application, the average pore size of the core (porous carbon) is obtained by testing with nitrogen at 77K, and the average pore size is taken from the BJH desorption average pore size.

[0099] Furthermore, in some embodiments of the present application, the pore volume of the core (porous carbon) is 0.1 cm 3 / g~1.5cm 3 / g; further optionally, the pore volume of the core (porous carbon) is 0.2cm 3 / g~1.4cm 3 / g; For example, 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.

[0100] Furthermore, in some embodiments of the present application, the D of the core (porous carbon) V 50 is 1 μm to 20 μm; further optionally, the D of the core (porous carbon) V 50 is 2 μm to 19 μm; for example, the D of the core (porous carbon) V50 is 5 μm, 10 μm, 12 μm, 15 μm or 18 μm. D of the core (porous carbon) V 50 Within the above range, the particle size and specific surface area are moderate, which is beneficial to the specific capacity and cycle performance of lithium-ion batteries.

[0101] It should be noted that the D of the core (porous carbon) V The test method of 50 is the same as that of the aforementioned silicon material D V 50 is tested in the same way.

[0102] Furthermore, in some embodiments of the present application, 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 layers, which affects the transport and diffusion of lithium ions, ultimately affecting the battery's rate and low-temperature performance. In the above technical solution, setting the d002 of the core (porous carbon) to 0.38nm to 0.41nm is beneficial to the battery's rate and low-temperature performance.

[0103] Further optionally, in some embodiments of the present application, the d002 of the core (porous carbon) is 0.39 nm to 0.40 nm. For example, in some embodiments of the present application, the d002 of the core (porous carbon) is 0.39 nm, 0.40 nm, or 0.41 nm.

[0104] Furthermore, in some embodiments of the present application, the pore diameter 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 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 a pore diameter can allow the silicon material 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 the silicon material far away from the pore mouth will be weakened. When the energy barrier for lithium to diffuse through the shell of the negative electrode material is higher than the energy barrier for nucleation and growth on the particle surface, the lithium metal will not be deposited in the pores but on the particle surface, which will lead to uneven lithium deposition, rapid capacity decay, and even an increased probability of thermal runaway. Setting the pore diameter of the negative electrode material to 3nm to 30nm can effectively increase the overall lithium storage capacity of the negative electrode material; it is also conducive to uniform lithium metal deposition and cycle stability.

[0105] Further optionally, in some embodiments of the present application, the pore size of the negative electrode material is 4 nm to 29 nm. For example, in some embodiments of the present application, the pore size of the negative electrode material is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm or 28 nm.

[0106] Furthermore, in some embodiments of the present application, the pore volume of the negative electrode material is 0.005 cm 3 / g~0.06cm 3 / g. Further optionally, the pore volume of the negative electrode material is 0.006cm 3 / g~0.06cm 3 / g. For example, 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.

[0107] Furthermore, in some embodiments of the present application, 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 nitrogen testing at 77K, and the average pore size is taken from the BJH desorption average pore size.

[0108] Furthermore, in some embodiments of the present application, the D of the negative electrode material V 50 is 1 μm to 20 μm. Further optionally, the D V 50 is 1.5 μm to 19 μm. For example, the D V 50 is 2μm, 3μm, 4μm, 5μm, 10μm, 12μm, 15μm or 18μm. V 50 Within the above range, the particle size and specific surface area are moderate, which is beneficial to the specific capacity and cycle performance of lithium-ion batteries.

[0109] It should be noted that the D of the negative electrode material here V The test method of 50 is the same as that of the aforementioned silicon material D V 50 is tested in the same way.

[0110] Furthermore, in some embodiments of the present application, the above-mentioned negative electrode material can be prepared according to the following method:

[0111] Step S1: placing porous carbon powder into a CVD device, introducing a protective gas, and heating the device to a target temperature T1 at a certain heating rate.

[0112] Furthermore, in some embodiments of the present application, the heating rate in step S1 may be 1 to 20°C / min, and the target temperature T1 may be 300 to 600°C.

[0113] Step S2: introduce silicon element gas and perform chemical vapor deposition at the target temperature T1. After performing chemical vapor deposition for 0.1 to 1 hour, introduce nitrogen gas to purge the furnace for 0.2 hours. Then, introduce silicon element gas again. Repeat chemical vapor deposition and purge 1 to 20 times in this manner to obtain a precursor of the negative electrode material.

[0114] Furthermore, in some embodiments of the present application, the silicon element gas in step S2 may be a mixture of silane and argon, and the mass concentration of silane may be 0.2% to 10%.

[0115] Furthermore, in some embodiments of the present application, 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.

[0116] Step S3: turn off the silicon-containing gas source, introduce the carbon-containing gas source, and heat the temperature to the target temperature T2 at a certain heating rate, and keep the temperature constant for t; then turn off the carbon-containing gas source and cool naturally to room temperature.

[0117] Furthermore, in some embodiments of the present application, in step S3, the carbon-containing gas source may be at least one of methane, ethane, propane, ethylene, acetylene or propyne.

[0118] Furthermore, in some embodiments of the present application, in step S3, the heating rate may be 1 to 20°C / min, the target temperature T2 may be 800 to 1200°C, and the constant temperature time t may be 0 to 5h.

[0119] Some embodiments of the present application provide a negative electrode plate, which includes the negative electrode material provided by any of the aforementioned embodiments.

[0120] Furthermore, in some embodiments of the present application, the negative electrode plate includes a current collector and a negative electrode active material layer located on the surface of the current collector, wherein the negative electrode active material layer includes the negative electrode material provided in any of the aforementioned embodiments. In some 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.

[0121] In some embodiments, the negative electrode active material layer further includes a binder, which 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.

[0122] In some embodiments, the negative electrode active material layer further comprises a conductive agent, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0123] The negative electrode sheet of the present application can be prepared using methods known in the art. Typically, the negative electrode material, optional conductive agent (e.g., carbon black and other carbon materials and metal particles), binder (e.g., SBR), and other optional additives (e.g., PTC thermistor material) are mixed together and dispersed in a solvent (e.g., deionized water). After stirring, the mixture is 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.

[0124] Some embodiments of the present application provide an electrochemical device, which includes the negative electrode sheet provided by any of the aforementioned embodiments.

[0125] In some embodiments of the present application, the electrochemical device includes, but is not limited to: all types of primary batteries, secondary batteries or capacitors.

[0126] In some embodiments of the present application, the electrochemical device is a lithium secondary battery.

[0127] In some embodiments of the present application, 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.

[0128] Furthermore, in some embodiments of the present application, 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.

[0129] The positive electrode plate includes a current collector and a positive electrode active material layer located on the current collector. In some embodiments of the present application, the positive electrode active material includes a positive electrode material that can absorb and release lithium. Positive electrode materials that release lithium include but are 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 oxyphosphate, lithium iron phosphate, lithium titanate and lithium-rich manganese-based materials. In some embodiments of the present application, the current collector may include, but is not limited to: aluminum foil.

[0130] In some embodiments of the present application, the positive electrode active material layer further includes a binder and optionally 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.

[0131] In some embodiments of the present application, 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.

[0132] In some embodiments of the present application, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0133] The positive electrode sheet can be prepared using methods known in the art. For example, the positive electrode sheet can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition on a current collector. In some embodiments, 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, meeting application requirements.

[0134] Furthermore, in some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0135] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. 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 and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinyl pyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinyl pyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0136] Furthermore, in some embodiments of the present application, 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.

[0137] The carbonate compound can be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof. Examples of linear carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC) and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC) or combinations thereof. Examples of the fluorinated carbonate compound 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. Examples of the carboxylate compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof. Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0138] Some embodiments of the present application provide an electrical device, which includes the electrochemical device provided by any of the aforementioned embodiments.

[0139] Some specific embodiments are listed below to better illustrate the present application.

[0140]

Preparation of negative electrode materials

[0141] Example 1

[0142] Provide a negative electrode material, which is prepared according to the following steps:

[0143] (1) Place the commercially available porous carbon-1 into a CVD device, introduce nitrogen, and heat it to 435°C at a heating rate of 5°C / min;

[0144] (2) Turn off the nitrogen, introduce a silicon-containing gas source for chemical vapor deposition, introduce nitrogen for 0.3 h, then introduce nitrogen to purge the furnace for 0.2 h, then introduce 0.7% silicon source gas again, and repeat chemical vapor deposition and purge three times in this cycle to obtain a precursor of the negative electrode material;

[0145] (3) Turn off the silicon source gas, introduce a carbon-containing gas source, and heat it to 850°C at a heating rate of 5°C / min, and keep it at this temperature for 1 hour; then turn off the carbon-containing gas source and cool it naturally to room temperature to obtain the negative electrode material.

[0146] 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 and a pore volume of 0.63 cm 3 / g, with 1730m 2 / g specific surface area.

[0147] 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.

[0148] The pore size distribution curve of the negative electrode material obtained in Example 1 is shown in FIG5 . It can be seen that the negative electrode material has both micropores and mesopores, with an average pore size of 5.8 nm and a pore volume of 0.046 cm 3 / g, with 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.

[0149] Example 2

[0150] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0151] In step (1), the temperature is raised to 455°C;

[0152] In step (2), chemical vapor deposition and purge are repeated 4 times in a periodic alternating manner.

[0153] Example 3

[0154] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0155] In step (1), the temperature is raised to 485°C;

[0156] In step (2), chemical vapor deposition and purge are repeated 5 times in a periodic alternating manner.

[0157] Example 4

[0158] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0159] In step (1), the temperature is raised to 485°C;

[0160] In step (2), chemical vapor deposition and purge are repeated 5 times in a periodic alternating manner.

[0161] In step (3), the constant temperature time is 1.5 h.

[0162] Example 5

[0163] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0164] In step (1), the temperature is raised to 485°C;

[0165] In step (2), chemical vapor deposition and purge are repeated 5 times in a periodic alternating manner;

[0166] In step (3), the constant temperature time is 2 h.

[0167] Example 6

[0168] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0169] In step (1), the temperature is raised to 455°C;

[0170] In step (2), chemical vapor deposition and purge are repeated 4 times in a periodic alternating manner;

[0171] In step (3), the temperature is increased to 1050°C at a heating rate of 5°C / min.

[0172] Example 7

[0173] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0174] In step (1), the temperature is raised to 455°C;

[0175] In step (2), chemical vapor deposition and purge are repeated 4 times in a periodic alternating manner;

[0176] In step (3), the temperature is raised to 1050°C at a heating rate of 5°C / min and the holding time is 2h.

[0177] Example 8

[0178] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0179] In step (1), the porous carbon used is porous carbon-2, and the temperature is raised to 485°C;

[0180] In step (2), 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 5 times in a periodic alternating manner;

[0181] In step (3), the constant temperature time is 2 h.

[0182] Example 9

[0183] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0184] In step (1), the porous carbon used is porous carbon-2, and the temperature is raised to 485°C;

[0185] In step (2), 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 5 times in a periodic alternating manner;

[0186] In step (3), the temperature is raised to 1050°C at a heating rate of 5°C / min and the holding time is 2h.

[0187] Example 10

[0188] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0189] In step (1), the porous carbon used is porous carbon-2, and the temperature is raised to 485°C;

[0190] In step (2), 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 6 times in a periodic alternating manner;

[0191] In step (3), the temperature is raised to 1050°C at a heating rate of 5°C / min and the holding time is 2h.

[0192] Example 11

[0193] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0194] In step (1), the porous carbon used is porous carbon-3, and the temperature is raised to 485°C;

[0195] In step (2), chemical vapor deposition and purge are repeated 5 times in a periodic alternating manner;

[0196] In step (3), the constant temperature time is 2 h.

[0197] Example 12

[0198] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0199] In step (1), the temperature is raised to 485°C;

[0200] In step (2), chemical vapor deposition and purge are repeated 35 times in a periodic alternating manner;

[0201] In step (3), the constant temperature time is 2 h.

[0202] Example 13

[0203] A negative electrode material is provided, and the preparation steps are basically the same as those in Example 1, except that:

[0204] In step (1), the porous carbon used is porous carbon-2, and the temperature is raised to 485°C;

[0205] In step (2), 1.5% silicon source gas was introduced, and chemical vapor deposition and purge were repeated 5 times in a periodic alternating manner;

[0206] In step (3), the constant temperature time is 8 hours.

[0207] Comparative Example 1

[0208] A negative electrode material is provided, which is the porous carbon-1 in Example 1.

[0209] Comparative Example 2

[0210] 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).

[0211]

Performance test

[0212] The performance of the negative electrode materials prepared in various embodiments and comparative examples was tested.

[0213] 1. TEM test

[0214] The negative electrode active material was embedded and cured in epoxy resin. Ultrathin sections were then cut into 50-70 nm sections to prepare the sample. High-magnification transmission electron microscopy was used to examine the cross-section of the particle sample, focusing on the pores and disordered carbon layer. The region between the pores and the disordered carbon layer constituted the silicon material, while the outermost disordered portion of the particle constituted the carbon shell. Image J software was used for processing.

[0215] FIG2 shows a TEM image of the negative electrode material of Example 1, as an example.

[0216] (1) Thickness of silicon material

[0217] The material was photographed and observed using TEM, and then 10 negative electrode material particles were randomly selected from the photo using the 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 then taken as the thickness of the silicon material.

[0218] (2) Area ratio

[0219] 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 the image analysis software Image J. Each particle was identified and classified as region 1, region 2, and region 3. The software was used to calculate the areas of region 1, region 2, and region 3, and the area ratio of region 2 to region 1 was calculated, recorded as A1; or the area ratio of region 3 to region 1 was calculated, recorded as A2. The average of the 10 Al's corresponding to the 10 negative electrode material particles was then taken, which was the area ratio of the silicon material to the carbon material.

[0220] The average value of 10 A2 corresponding to 10 negative electrode material particles is the area ratio of pores to carbon material;

[0221] Among them, region 1 is carbon material; region 2 is silicon material; and region 3 is pores.

[0222] 2. Pore diameter

[0223] Negative electrode ion milling (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 per 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.

[0224] Pore ​​diameter: The material is photographed and observed using FESEM. Ten material particles are randomly selected from the photographs, and the size of the pores inside the particles is measured. The distance between the two farthest points on the inner wall of the pore is measured, and the average value of the distances measured inside the ten material particles is taken as the pore diameter.

[0225] 4. Particle size test of negative electrode active material particles

[0226] The particle size test method refers to GB / T 19077-2016. The specific process is to weigh 1g of 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. During the test, when the laser beam passes through the dispersed particle sample, 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.

[0227] 5. Pore size distribution test of negative electrode active materials

[0228] The test instrument, an ASAP2460 physical adsorption analyzer, placed the dried and degassed sample in liquid nitrogen. The nitrogen adsorption was measured at different test pressures, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the hysteresis loop, and the pore distribution and pore volume were calculated using different pore models. The BJH model was used to fit the pore size distribution curves for mesopores and macropores, while the DFT model was used to fit the pore size distribution curve for micropores.

[0229] 6. Preparation of half-cell (button cell):

[0230] Using metallic lithium as the counter electrode, 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) were assembled and stacked together in sequence, and an electrolyte was added. The positive and negative electrodes were placed in a button-type stainless steel shell and sealed to obtain a button-type battery.

[0231] 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.

[0232] FIG6 shows a specific capacity curve of the lithium-ion battery of Example 1. FIG.

[0233] The discharge constant capacity in Table 2 = 50 mA / g × discharge time.

[0234] 7. Lithium-ion full battery cycle performance test:

[0235] The positive electrode sheets, separators and negative electrode sheets are stacked in sequence, and they are wound, folded and other operations are performed 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 lithium-ion full battery; alternatively, the positive electrode sheets, separators and negative electrode sheets are stacked in sequence, 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 lithium-ion full battery.

[0236] Five lithium-ion full batteries prepared using all comparative examples and examples were taken and the average value was calculated. The lithium-ion full batteries were repeatedly charged and discharged using the following steps, and the discharge capacity retention rate of the lithium-ion full batteries was calculated.

[0237] First, in an environment of 25°C, perform the first charge and discharge. Perform constant current charging at a charging current of 1C until the upper limit voltage of 4.55V is reached, then switch to constant voltage charging. Then, perform constant current discharge at a discharge current of 1C until the final voltage is 2V. This is recorded as one cycle. Record the data of the first cycle and the 500th cycle. From the first cycle to the 450th cycle, a capacity test is performed with a current of 0.2C every 50 cycles. The specific operation is as follows: perform constant current charging at a charging current of 0.2C until the upper limit voltage of 4.55V is reached, then switch to constant voltage charging. Then, perform constant current discharge at a discharge current of 0.2C until the final voltage is 2V.

[0238] In Table 2, cycle capacity retention rate=(discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0239] FIG. 7 is a graph showing the cycle performance of the lithium-ion battery of Example 1. FIG.

[0240]

result

[0241] The characteristic parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0242] Table 1

[0243] Table 2

[0244] From the above table we can see that:

[0245] The negative electrode materials prepared in the above embodiments can enable lithium-ion batteries to have higher specific capacity and cycle performance.

[0246] Compared with the examples, the negative electrode material provided in Comparative Example 1 has low specific capacity and cycle performance of the lithium ion battery.

[0247] Furthermore, it can be seen from Examples 1 to 3 that the thickness of the silicon material is 0.52 nm, 0.86 nm and 1.25 nm, respectively, and the mass percentages of Si are 0.8%, 0.9% and 1.52%. Because 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 a capacity retention rate of 89.3%.

[0248] The carbon shell thicknesses of Examples 3 to 5 are 5.2nm, 8.6nm, and 15.1nm, 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 impact on the cycling performance. Within a limited range, the larger the shell thickness, the more significant the suppression of expansion during lithium insertion, and the better the material maintains the integrity of the core-shell structure during cycling.

[0249] 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 of the CVD coating process. Silicon carbide does not serve as a lithium-intercalation active material during the charge and discharge process, so it does not provide capacity. Therefore, the specific capacity of Example 6 and Example 7 is lower than that of Example 2. However, due to the lack of expansion caused by silicon intercalation of lithium, Example 6 and Example 7 have higher capacity retention rates, which are 92.8% and 93.6% respectively.

[0250] Comparative Examples 8 to 10, the porous carbon used was Porous Carbon-2. Compared to Porous Carbon-1, Porous Carbon-2 has a larger BET, pore volume, and pore diameter. It can be found that the negative electrode materials of Comparative Examples 1 to 7 and Examples 8 to 10 have higher specific capacities. This is because the larger pore volume can accommodate more lithium while ensuring a higher capacity retention rate.

[0251] For Example 11, 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 better specific capacity and cycle performance.

[0252] Comparing Examples 1 to 7 with Example 12, the silicon material in Example 12 is thicker, at 4.8nm. Although it also has a high specific capacity of 1876mAh / g, the excessively high Si content results in an excessively high A1 value and an excessively low A2 value, leaving too little room for expansion in the pores. This damages the structural stability during cycling and deteriorates the cycling performance. This shows that lithium-ion batteries have better specific capacity and cycling performance when the silicon material thickness is 0.5nm to 4nm; or when the silicon material accounts for 0.01% to 4% of the total mass of the negative electrode material; or when the area ratio of the silicon material to the porous carbon is 0.01 to 0.3; or when the area ratio of the pores to the porous carbon is 0.3 to 3.

[0253] Comparing Examples 8 to 10 with Example 13, the negative electrode material of Example 13 has a thicker shell, 50 nm. In the later stages of cycling, Example 13 results in a higher energy barrier for lithium diffusion through the carbon shell, leading to gradual lithium precipitation outside the pores and consequent capacity decay. This suggests that a shell thickness of 2 nm to 20 nm exhibits superior specific capacity and cycling performance.

[0254] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises 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.

2. The negative electrode material according to claim 1, characterized in that In terms of mass percentage, the silicon material accounts for 0.01% to 20% of the total mass of the negative electrode material.

3. The negative electrode material according to claim 1, characterized in that In terms of mass percentage, the silicon material accounts for 0.01% to 4% of the total mass of the negative electrode material.

4. The negative electrode material according to claim 1, characterized in that The area ratio of the silicon material to the porous carbon is 0.01 to 0.

3.

5. The negative electrode material according to claim 1, characterized in that The area ratio of the pores to the porous carbon is 0.3-3.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that: The silicon material includes at least one of elemental silicon or silicon carbide.

7. The negative electrode material according to any one of claims 1 to 6, characterized in that: The thickness of the silicon material is 0.5 nm to 4 nm, and / or the thickness of the shell layer is 2 nm to 20 nm.

8. The negative electrode material according to any one of claims 1 to 7, characterized in that: The core satisfies at least one of the following characteristics: (a) The specific surface area of ​​the porous carbon is 500 m 2 / g~3000m 2 / g; (b) The average pore size of the porous carbon is 1 nm to 30 nm; (c) The pore volume of the porous carbon is 0.1 cm 3 / g~1.5cm 3 / g; (d) D of the porous carbon V 50: 1μm~20μm; (e) d002 of the porous carbon is 0.38 nm to 0.41 nm; (f) The pore diameter of the porous carbon is 2nm to 40nm.

9. The negative electrode material according to any one of claims 1 to 8, characterized in that: The negative electrode material meets the following characteristics: (g) the pore diameter of the negative electrode material is 3nm to 30nm; (h) The pore volume of the negative electrode material is 0.005 cm 3 / g~0.06cm 3 / g; (i) the average pore size of the negative electrode material is 0.01 nm to 5 nm; (j) D of the negative electrode material V 50 is 1μm~20μm.

10. A negative electrode plate, characterized in that: The negative electrode plate comprises the negative electrode material according to any one of claims 1 to 9.

11. An electrochemical device, characterized in that: The electrochemical device comprises the negative electrode sheet according to claim 10.

12. An electrical equipment, characterized in that: The electrical equipment comprises the electrochemical device according to claim 11.

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