Negative electrode material and preparation method thereof, and lithium ion battery

Abstract

The application relates to a negative electrode material and a preparation method thereof and a lithium ion battery, the negative electrode material comprising a core and a coating layer arranged on at least part of the surface of the core, the core comprising porous carbon and an active substance filled in the pore structure of the porous carbon, the porous carbon having a first pore structure with a pore diameter less than or equal to 2 nm and a second pore structure with a pore diameter greater than 2 nm, the ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon being greater than or equal to 40%, and the filling rate of the second pore structure being greater than or equal to 95%. The negative electrode material of the application can effectively inhibit volume expansion, has the advantages of high rate capability, high capacity and good cycle performance.

Description

Technical Field

[0001] This application relates to the field of anode material technology, and more specifically, to anode materials and their preparation methods, and lithium-ion batteries. Background Technology

[0002] Silicon, the second most abundant element in the Earth's crust, is a common semiconductor material and has become an indispensable technological foundation for modern high-tech society. Elemental silicon has wide and important applications in energy, semiconductors, organosilicon, and metallurgy. Currently, the main anode material for mature commercial lithium-ion batteries is graphite-based carbon materials, but the theoretical lithium storage capacity of carbon materials is only 372 mAh / g, which cannot meet the demand for high-energy-density materials. Silicon, as an anode material for lithium-ion batteries, has a very high theoretical capacity (approximately 4200 mAh / g), ten times higher than that of commercially available graphite, and has great potential in energy storage.

[0003] Currently, silicon anodes exhibit severe volume expansion during cycling, leading to material pulverization and breakage, and rapid battery degradation. Therefore, developing an anode material with high capacity and good cycle performance is a key technical challenge in the lithium-ion battery field. Summary of the Invention

[0004] Based on this, it is necessary to provide a negative electrode material and its preparation method, as well as a lithium-ion battery. The negative electrode material of this application has high conductivity, can effectively suppress volume expansion, and improve the capacity performance and cycle performance of the negative electrode material.

[0005] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a core and a coating layer disposed on at least a portion of the surface of the core, the core comprising porous carbon and an active substance filled in the porous carbon pore structure, the porous carbon having a first pore structure with a pore size less than or equal to 2 nm and a second pore structure with a pore size greater than 2 nm, the ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon being greater than or equal to 40%, and the filling rate of the second pore structure being greater than or equal to 95%.

[0006] In some alternative embodiments, the negative electrode material also includes active material distributed between the porous carbon.

[0007] In some alternative embodiments, the median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.4 ≤ D1 / D2 ≤ 6.

[0008] In some alternative embodiments, the median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy the following condition: 0.5 ≤ D1 / D2 ≤ 4.5.

[0009] In some alternative embodiments, the median particle size of the active material is 1 nm to 300 nm.

[0010] In some alternative embodiments, the morphology of the active substance includes at least one of the following: dot-like, spherical, ellipsoidal, and sheet-like.

[0011] In some alternative embodiments, the active material includes Li, Na, K, Sn, Ge, Si, and SiO. x At least one of Fe, Mg, Ti, Zn, Al, Ni, P and Cu, wherein 0 < x < 2.

[0012] In some alternative embodiments, the porous carbon includes at least one of carbon black, ordered mesoporous carbon materials, and nanoporous carbon materials.

[0013] In some alternative embodiments, the median particle size of the porous carbon is 1 nm to 500 nm.

[0014] In some alternative implementations, the median particle size of the kernel is 0.8 μm to 10 μm.

[0015] In some alternative embodiments, the coating layer includes at least one of a carbon layer, a metal oxide layer, a polymer layer, and a nitride layer.

[0016] In some alternative embodiments, the carbon layer is made of at least one of soft carbon, crystalline carbon, amorphous carbon, and hard carbon.

[0017] In some alternative embodiments, the metal oxide layer is made of at least one of oxides of Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0018] In some alternative embodiments, the material of the nitride layer includes at least one of silicon nitride, aluminum nitride, titanium nitride, and tantalum nitride.

[0019] In some alternative embodiments, the thickness of the coating layer is 10 nm to 500 nm.

[0020] In some alternative embodiments, the polymer layer is made of at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide, and polyvinyl alcohol.

[0021] In some alternative embodiments, the specific surface area of ​​the negative electrode material is less than or equal to 10 m². 2 / g.

[0022] In some alternative embodiments, the median particle size of the negative electrode material is 0.5 μm to 20 μm.

[0023] In some alternative embodiments, the porosity of the negative electrode material is less than or equal to 10%.

[0024] Secondly, embodiments of this application provide a method for preparing a negative electrode material, comprising the following steps:

[0025] A precursor is obtained by vacuum mixing raw materials containing porous carbon and active substances. The porous carbon has a first pore structure with a pore size less than or equal to 2 nm and a second pore structure with a pore size greater than 2 nm. The ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon is greater than or equal to 40%. The vacuum degree of the vacuum mixing is 10. -7 Pa ~ 10 Pa;

[0026] The precursor is coated to obtain the negative electrode material.

[0027] In some alternative embodiments, the median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.4 ≤ D1 / D2 ≤ 6.

[0028] In some alternative embodiments, the median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy the following condition: 0.5 ≤ D1 / D2 ≤ 4.5.

[0029] In some alternative embodiments, the median particle size of the active material is 1 nm to 300 nm.

[0030] In some alternative embodiments, the active material includes Li, Na, K, Sn, Ge, Si, and SiO. x At least one of Fe, Mg, Ti, Zn, Al, Ni, P and Cu, wherein 0 < x < 2.

[0031] In some alternative embodiments, the porous carbon includes at least one of carbon black, ordered mesoporous carbon materials, and nanoporous carbon.

[0032] In some alternative embodiments, the median particle size of the porous carbon is 1 nm to 500 nm.

[0033] In some alternative embodiments, the mass ratio of the porous carbon to the active material is 40:(10-80).

[0034] In some alternative embodiments, the vacuum mixing equipment includes at least one of a dual-star vacuum mixer, a planetary vacuum mixer, a planetary vacuum disperser, a grate vacuum mixer, a multi-functional vacuum mixer, a vacuum disperser, and a vacuum emulsifier.

[0035] In some alternative embodiments, the vacuum mixing is followed by a drying process, and the vacuum mixing time is 0.5 h to 15 h.

[0036] In some alternative embodiments, the vacuum mixing is followed by a drying process at a temperature of -50°C to 500°C.

[0037] In some alternative embodiments, the vacuum mixing is followed by a drying process for 0.5 to 15 hours.

[0038] In some alternative embodiments, the vacuum mixing is followed by a drying process, and the drying equipment includes at least one of a rotary evaporator, a vacuum oven, a spray dryer, a heat treatment furnace, and a freeze dryer.

[0039] In some alternative embodiments, the process of adding additives and solvents is further included before vacuum mixing the raw materials containing porous carbon and active substances.

[0040] In some alternative embodiments, the additives include at least one selected from polyvinyl alcohol, octadecanoic acid, lauric acid, polyacrylic acid, sodium dodecylbenzenesulfonate, icosanoic acid, palmitic acid, tetradecanoic acid, undecanoic acid, fatty acids, hexadecyltrimethylammonium bromide, and polyvinylpyrrolidone.

[0041] In some alternative embodiments, the solvent includes at least one selected from phenol, methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, n-hexane, cyclohexane, ethyl acetate, chloroform, carbon tetrachloride, methyl acetate, acetone, and pentanol.

[0042] In some alternative embodiments, the mass ratio of the additive to the porous carbon is (0.05–3):100.

[0043] In some alternative embodiments, the mass ratio of the solvent to the porous carbon is 100:(15-55).

[0044] In some optional implementations, the step of coating the precursor to obtain the negative electrode material specifically involves mixing the precursor and the coating material and then performing heat treatment.

[0045] In some alternative embodiments, the coating material includes at least one of carbon materials, metal oxide materials, polymer materials, and nitride materials.

[0046] In some alternative embodiments, the carbon material includes at least one of soft carbon, hard carbon, crystalline carbon, and amorphous carbon.

[0047] In some alternative embodiments, the metal oxide material includes at least one oxide selected from Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0048] In some alternative embodiments, the nitride material includes at least one of silicon nitride, aluminum nitride, titanium nitride, and tantalum nitride.

[0049] In some alternative embodiments, the coating material includes at least one of carbon materials, metal oxide materials, polymer materials, and nitride materials, wherein the polymer material includes at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide, and polyvinyl alcohol.

[0050] In some alternative embodiments, the mass ratio of the negative electrode material to the coating material is 100:(5-100).

[0051] In some alternative embodiments, the heat treatment temperature is 400°C to 900°C.

[0052] In some optional embodiments, the heat treatment holding time is 1 hour to 12 hours.

[0053] In some alternative embodiments, the heating rate of the heat treatment is 1°C / min to 15°C / min.

[0054] In some alternative embodiments, the heat treatment is performed in a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, and krypton.

[0055] In some alternative embodiments, the negative electrode material is mixed with the coating material and then subjected to heat treatment, followed by a step of crushing and sieving the resulting material.

[0056] In some alternative embodiments, the pulverizing equipment includes at least one of a mechanical pulverizer, an air jet mill, and a crusher.

[0057] In some alternative implementations, the sieve size for screening is 10 mesh to 800 mesh.

[0058] Thirdly, embodiments of this application provide a lithium-ion battery, including the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect.

[0059] The technical solution of this application has at least the following beneficial effects:

[0060] The core of the anode material in this application comprises porous carbon and active material. The first pore structure of the porous carbon is micropores (average pore size less than or equal to 2 nm). Micropores with a volume ratio greater than or equal to 40% provide additional space for the expansion of the active material, effectively mitigating volume expansion and thus avoiding or reducing pulverization of the anode material due to large volume changes and stress during lithium insertion / extraction. The second pore structure 112 of the porous carbon 11 consists of pores with a pore size greater than 2 nm. The active material fills the second pore structure of the porous carbon, making the filling rate of the second pore structure greater than or equal to 95%. This can improve the material capacity while avoiding stress concentration and electrolyte penetration caused by the material. The anode material retains an appropriate number of small pores to avoid pores with excessively large pore sizes. The two pore structures work together to enable the anode material of this application to effectively suppress volume expansion and possess the advantages of high rate performance, high capacity, and good cycle performance. Attached Figure Description

[0061] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0062] Figure 1 This is a schematic diagram of the structure of the negative electrode material in this application. Figure 1 ;

[0063] Figure 2 This is a schematic diagram of the porous carbon structure in which active substances are distributed within the second pore structure of this application.

[0064] Figure 3 This is a schematic diagram of the structure of the negative electrode material in this application. Figure 2 ;

[0065] Figure 4 This is a flowchart illustrating the preparation process of the negative electrode material in this application;

[0066] Figure 5 This is a SEM image of the negative electrode material prepared in Example 1 of this application;

[0067] Figure 6 The image shows the XRD pattern of the negative electrode material prepared in Example 1 of this application.

[0068] Figure 7 The first charge-discharge curve of the negative electrode material prepared in Example 1 of this application;

[0069] Figure 8 The cycling performance curve of the negative electrode material prepared in Example 1 of this application.

[0070] Figure 1 , Figure 2 and Figure 3 middle:

[0071] 1-Kernel;

[0072] 11-Porous carbon;

[0073] 111 - First hole structure;

[0074] 112 - Second hole structure;

[0075] 12-Active substances;

[0076] 2-Covering layer. Detailed Implementation

[0077] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0078] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0079] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0080] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0081] This application provides a negative electrode material, such as... Figure 1 As shown, the negative electrode material includes a core 1 and a coating layer 2 disposed on at least a portion of the surface of the core 1, such as... Figure 2 As shown, the core 1 includes porous carbon 11 and active material 12 filled in the pore structure of porous carbon 11. The porous carbon 11 has a first pore structure 111 with a pore size of less than or equal to 2 nm and a second pore structure 112 with a pore size of greater than 2 nm. The ratio of the pore volume of the first pore structure 111 to the total pore volume of the porous carbon 11 is greater than or equal to 40%, and the filling rate of the second pore structure 112 is greater than or equal to 95%.

[0082] In the above scheme, the core 1 of the negative electrode material of this application includes porous carbon 11 and active material 12. The porous carbon 11 includes two pore structures with different pore sizes. The first pore structure 111 of the porous carbon 11 is a micropore (pore size less than or equal to 2 nm). The micropores with a volume ratio greater than or equal to 40% can provide additional space for the expansion of the active material 12, effectively alleviate the volume expansion, and thus avoid or reduce the pulverization of the negative electrode material due to huge volume changes and stress during the lithium insertion and extraction process. The second pore structure 112 of the porous carbon 11 has pores with a diameter greater than 2 nm. The second pore structure is prone to stress concentration and electrolyte penetration. Therefore, it is necessary to fill the second pore structure as much as possible. The second pore structure 112 of the porous carbon 11 is filled with active material 12, and the filling rate of the active material in the second pore structure 112 is greater than or equal to 95%. This can improve the material capacity while avoiding stress concentration and electrolyte penetration caused by the second pore structure. The anode material retains an appropriate number of small pores to avoid pores with excessively large diameters. The two pore structures work together to enable the anode material of this application to effectively suppress volume expansion and has the advantages of high rate performance, high capacity and good cycle performance.

[0083] Specifically, the aperture of the first pore structure 111 can be 0.05nm, 0.07nm, 0.1nm, 0.3nm, 0.5nm, 0.8nm, 1nm, 1.5nm, and 2nm, or other values ​​within the above range, which are not limited here. The aperture of the second pore structure 112 can be 2.5nm, 5nm, 10nm, 20nm, 100nm, 150nm, 200nm, 250nm, and 300nm, or other values ​​within the above range, which are not limited here.

[0084] In the porous carbon of this application, the first pore structure 111 has pores with a diameter of less than or equal to 2 nm, and the second pore structure 112 has pores with a diameter greater than 2 nm. The smaller pore size of the first pore structure 111 can effectively alleviate the volume expansion of the active material 12, while reducing the expansion of the electrode film and improving the safety of the battery. Compared with the first pore structure 111, the second pore structure 112 has a larger pore size. The larger pore size of the second pore structure 112 is filled with active material, which can avoid stress concentration and electrolyte penetration caused by the second pore structure, while improving the capacity of the negative electrode material.

[0085] The ratio of the pore volume of the first pore structure 111 to the total pore volume of the porous carbon 11 can specifically be 40%, 45%, 50%, 55%, 60%, 65%, and 70%, etc., or other values ​​within the above range, which are not limited here. If the pore volume ratio of the first pore structure 111 is less than 40%, it cannot effectively alleviate the volume expansion of silicon. Preferably, the ratio of the pore volume of the first pore structure 111 to the total pore volume of the porous carbon 11 is greater than or equal to 45%.

[0086] The filling rate of the second pore structure 112 can be 95%, 96%, 97%, 98%, and 99%, or other values ​​within the above range, which are not limited here. If the filling rate of the second pore structure 112 is less than 95%, it will easily lead to stress concentration and electrolyte penetration problems in the material. It should be noted that the filling rate of the second pore structure 112 can refer to the filling rate of the active material 12 in the pore, or the filling rate of the coating material and the active material together in the pore. Preferably, it refers to the filling rate of the active material in the pore, which is beneficial to improving the capacity of the negative electrode material.

[0087] In some implementations, such as Figure 3 As shown, the negative electrode material also includes an active material 12 distributed between the porous carbon 11, that is, the active material 12 fills the pore structure of the porous carbon 11 and is also distributed between the porous carbon 11.

[0088] In some embodiments, the median particle size D1 of porous carbon 11 and the median particle size D2 of active material 12 satisfy: 0.4≤D1 / D2≤6. For example, D1 / D2 can be 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 and 6, etc. Of course, it can also be other values ​​within the above range, which are not limited here. By satisfying the median particle size D1 of porous carbon 11 and the median particle size D2 of active material 12 as 0.4≤D1 / D2≤6, a core structure in which active material 12 and porous carbon 11 are well bonded can be obtained. In the core structure, active material 12 and porous carbon 11 are uniformly distributed, and there is no or only a small amount of direct contact between active materials 12. Most of the contact is indirect, with porous carbon 11 acting as a buffer layer. The high porosity of the porous carbon can buffer the volume expansion of active material 12 and prevent the material from pulverizing. In the elemental distribution spectrum obtained by scanning the SEM section of the core of the negative electrode material with X-rays, the distribution of C and active material elements is uniformly dispersed. When D1 / D2 is greater than 6, meaning the size of the porous carbon 11 is much larger than the size of the active material 12 distributed between the porous carbon 11, on the one hand, the bonding between the porous carbon 11 and the active material 12 distributed between the porous carbon 11 becomes worse; on the other hand, the volume of the porous carbon 11 in the core 1 exceeds the volume of the active material 12, resulting in increased porosity within the material and preventing an increase in the material's capacity. When D1 / D2 is less than 0.4, meaning the size of the active material 12 distributed between the porous carbon 11 is much larger than the size of the porous carbon 11, direct contact will occur between the active materials 12, forming a "hard contact" between the active materials. During the lithium insertion / extraction process, the resulting large deformation can easily cause the active material 12 to pulverize and deform, thereby reducing the structural stability of the anode material. Preferably, the median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.5 ≤ D1 / D2 ≤ 4.5.

[0089] In some embodiments, the morphology of the active substance 12 includes at least one of the following: dot-like, spherical, ellipsoidal, and sheet-like.

[0090] In some embodiments, the median particle size of the active material 12 is 1 nm to 300 nm, specifically 1 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, and 300 nm, etc., and of course, other values ​​within the above range are also possible, which are not limited here. Preferably, the average particle size of the active material 12 is 5 nm to 200 nm, and more preferably, the average particle size of the active material 12 is 5 nm to 80 nm.

[0091] In some embodiments, the active substance 12 includes Li, Na, K, Sn, Ge, Si, and SiO. x At least one of Fe, Mg, Ti, Zn, Al, Ni, P, and Cu, wherein 0 < x < 2. It is understood that the active material distributed between the porous carbon 11 particles and the active material located in the second pore structure of the porous carbon 11 particles can be the same, different, or partially the same and partially different.

[0092] For example, when the active material located between the porous carbon 11 and the active material located in the second pore structure of the porous carbon 11 are both silicon particles, the core 1 includes porous carbon 11 and silicon particles. The silicon particles on the surface and the porous carbon together form the core, and the silicon particles and porous carbon are uniformly distributed. The silicon particles provide lithium storage capacity, and the porous carbon 11 can both buffer the volume change of the silicon anode during charging and discharging and improve the conductivity of the silicon particles, thereby improving the rate performance of the battery. The porous carbon 11 has a first pore structure 111 and a second pore structure 112, wherein the pore size of the first pore structure 111 is smaller than the pore size of the second pore structure 112. The second pore structure 112 is filled with silicon particles. The silicon particles are wrapped with porous carbon, which can improve the conductivity of silicon on the one hand and prevent the silicon particles from agglomerating on the other hand. In the anode material of this embodiment, the silicon particles are located between and inside the porous carbon 11, which can improve the conductivity of the anode material, further improve the rate performance of the anode material, and alleviate the volume expansion of nano-silicon.

[0093] In some embodiments, porous carbon 11 includes at least one of carbon black, ordered mesoporous carbon material (CMK), and nanoporous carbon material (NCP).

[0094] In some embodiments, the median particle size of porous carbon 11 is 1 nm to 500 nm, specifically 1 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, etc., and of course, other values ​​within the above range are also possible, without limitation. Preferably, the median particle size of porous carbon 11 is 5 nm to 200 nm, and more preferably, the median particle size of porous carbon 11 is 5 nm to 150 nm.

[0095] In some implementations, the median particle size of kernel 1 is 0.8 μm to 10 μm, specifically 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm and 10 μm, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0096] In some embodiments, the coating layer 2 includes at least one of a carbon layer, a metal oxide layer, a polymer layer, and a nitride layer. The coating layer 2 serves two purposes: firstly, it prevents the electrolyte from entering the negative electrode material and causing side reactions that could reduce initial efficiency and capacity; secondly, it mitigates the volume expansion of silicon, reduces the overall volume expansion of the composite material, and minimizes electrode sheet swelling.

[0097] In some embodiments, the carbon layer is made of at least one of soft carbon, hard carbon, crystalline carbon, and amorphous carbon.

[0098] In some embodiments, the metal oxide layer is made of at least one of oxides of Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0099] In some embodiments, the nitride layer is made of at least one of silicon nitride, aluminum nitride (AlN), titanium nitride (TiN), and tantalum nitride (TaN).

[0100] In some embodiments, the polymer layer is made of at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide, and polyvinyl alcohol.

[0101] In some embodiments, the thickness of the coating layer 2 is 10nm to 500nm, specifically 1nm, 10nm, 20nm, 50nm, 80nm, 100nm, 200nm, 300nm, 400nm, and 500nm, or other values ​​within the above range, which are not limited here. It is understood that the coating layer 2 can reduce the contact between silicon and the electrolyte, reduce the formation of passivation film, and improve the reversible capacity of the battery. If the thickness of the coating layer 2 is greater than 500nm, the lithium-ion transport efficiency decreases, which is not conducive to high-rate charge and discharge of the negative electrode material and reduces the overall performance of the negative electrode material. If the thickness of the coating layer is less than 10nm, it is not conducive to increasing the conductivity of the negative electrode material and has weak suppression performance on the volume expansion of the negative electrode material, resulting in poor cycle performance.

[0102] In some embodiments, the specific surface area of ​​the negative electrode material is less than or equal to 10 m². 2 / g, specifically 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g and 10m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Understandably, controlling the specific surface area of ​​the negative electrode material within the above range can suppress the volume expansion of the negative electrode material, which is beneficial to improving the cycle performance of the negative electrode material.

[0103] In some embodiments, the median particle size of the negative electrode material is 0.5 μm to 20 μm, specifically 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, and 20 μm, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Preferably, the median particle size of the negative electrode material is 0.8 μm to 12 μm, and more preferably, the median particle size of the negative electrode material is 1 μm to 8 μm. It can be understood that controlling the median particle size of the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0104] In some embodiments, the porosity of the negative electrode material is less than or equal to 10%, specifically it can be 1%, 2%, 2.5%, 5%, 7%, 8.5%, and 10%, etc., and of course, other values ​​within the above range are also possible, without limitation. Preferably, the porosity of the negative electrode material is less than or equal to 5%, and more preferably, the porosity of the negative electrode material is less than or equal to 2.5%. If the porosity of the negative electrode material is too high, it leads to a decrease in the tap density of the material, which in turn leads to a decrease in the energy density of the material.

[0105] Secondly, this application provides a method for preparing the aforementioned negative electrode material, such as... Figure 4 As shown, it includes the following steps:

[0106] A precursor is obtained by vacuum mixing a raw material containing porous carbon and an active substance. The porous carbon has a first pore structure with a pore size less than or equal to 2 nm and a second pore structure with a pore size greater than 2 nm. The ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon is greater than or equal to 40%. The vacuum degree of the vacuum mixing is 10. -7 Pa ~ 10 Pa;

[0107] The precursor is coated to obtain the negative electrode material.

[0108] In the above scheme, the porous carbon raw material of this application includes two pore structures with different pore sizes. The first pore structure 111 of the porous carbon 11 is micropores (pore size less than or equal to 2 nm). Micropores with a volume ratio greater than or equal to 40% can effectively alleviate volume expansion, thereby avoiding or reducing pulverization of the negative electrode material due to huge volume changes and stress during lithium insertion / extraction. The second pore structure 112 of the porous carbon 11 has pores with a pore size greater than 2 nm. The second pore structure 112 is prone to stress concentration and electrolyte penetration. This application uses vacuum mixing to fill the active material into the larger second pore structure 112 of the porous carbon, and then... -7 Under a vacuum pressure of Pa to 10 Pa, the filling rate of the second pore structure 112 is greater than or equal to 95%, avoiding stress concentration and electrolyte penetration problems caused by the presence of the second pore structure 112. Finally, the precursor is coated to prevent the electrolyte from entering the negative electrode material and causing side reactions that would reduce the initial efficiency and capacity. It also mitigates the volume expansion of the active material, reduces the overall volume expansion of the composite material, and minimizes electrode swelling. The preparation method of this application is simple. By selecting porous carbon with a specific pore structure and size, the active material is filled into the second pore structure 112 inside the porous carbon 11, which effectively suppresses volume expansion and further improves the rate performance, capacity, and cycle performance of the negative electrode material.

[0109] The preparation method of this application is described in detail below with reference to the embodiments:

[0110] Step S100: Vacuum mixing of raw materials containing porous carbon and active substances yields a precursor. The porous carbon has a first pore structure and a second pore structure. The average pore diameter of the first pore structure is less than or equal to 2 nm, and the average pore diameter of the second pore structure is greater than 2 nm. The ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon is greater than or equal to 40%. The vacuum degree of the vacuum mixing is 10. -7 Pa ~ 10 Pa.

[0111] In some embodiments, the average aperture of the first pore structure 111 can be 0.05nm, 0.07nm, 0.1nm, 0.3nm, 0.5nm, 0.8nm, 1nm, 1.5nm and 2nm, etc., or other values ​​within the above range, which are not limited here.

[0112] In some embodiments, the average pore size of the second pore structure 112 can be 2.5nm, 5nm, 10nm, 20nm, 100nm, 150nm, 200nm, 250nm and 300nm, etc., or other values ​​within the above range, which are not limited here.

[0113] In the porous carbon of this application, the first pore structure 111 has pores with a diameter of less than or equal to 2 nm, and the second pore structure 112 has pores with a diameter of greater than 2 nm. The smaller pore size of the first pore structure 111 can effectively alleviate the volume expansion of the active material 12, while reducing the expansion of the electrode film and improving the safety of the battery. Compared with the first pore structure 111, the second pore structure 112 has a larger pore size. The larger pore size of the second pore structure 112 is filled with active material, which can avoid stress concentration and electrolyte penetration caused by the second pore structure 112.

[0114] In some embodiments, the ratio of the pore volume of the first pore structure 111 to the total pore volume of the porous carbon 11 can be 40%, 45%, 50%, 55%, 60%, 65%, and 70%, etc., or other values ​​within the above range, which are not limited here. If the pore volume ratio of the first pore structure 111 is less than 40%, it cannot effectively alleviate the volume expansion of silicon. Preferably, the ratio of the pore volume of the first pore structure 111 to the total pore volume of the porous carbon 11 is greater than or equal to 45%.

[0115] In some embodiments, this application controls the vacuum level of vacuum mixing to be 10. -7 Pa to 10 Pa ensures that the filling rate of the second pore structure 112 is greater than or equal to 95%. Specifically, the vacuum degree of vacuum mixing in this application can be 10 Pa. -7 Pa, 10 -6 Pa, 10 -5 Pa, 10 -4 Pa, 10 -3 Pa, 10 -2 Pa and 10 Pa, etc., are also possible values ​​within the above range, and are not limited here. This application controls the filling rate of active material in porous carbon through vacuum mixing treatment, so that the active material fills the secondary pore structure of the porous carbon as much as possible. If the vacuum degree is greater than 10 Pa, the vacuum degree is too low, and the force generated is not enough to fill the corresponding pores with active material, and the filling rate of the secondary pore structure will decrease; if the vacuum degree is less than 10 Pa, the filling rate of the secondary pore structure will decrease. -7If the pressure is 10 Pa, an additional molecular pump needs to be configured, which will increase the cost.

[0116] In some embodiments, the active material includes Li, Na, K, Sn, Ge, Si, and SiO. x At least one of Fe, Mg, Ti, Zn, Al, Ni, P and Cu, wherein 0 < x < 2.

[0117] In some embodiments, the median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy 0.4 ≤ D1 / D2 ≤ 6, for example, 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, and 6, etc., and of course, other values ​​within the above range are also possible, which are not limited here. It can be understood that by limiting the ratio of the median particle size D1 of the porous carbon to the median particle size D2 of the active material to the above range, the resulting precursor structure includes porous carbon 11 and active material 12 distributed between the porous carbon 11. The porous carbon 11 can be well and uniformly dispersed with the active material 12 to form a well-dispersed structure. There is no or only a small amount of direct contact between the active materials. Most of the contact is indirect, with the porous carbon acting as a buffer layer. The high porosity of the porous carbon particle layer can buffer the volume expansion of the active material while avoiding the pulverization of the material. When D1 / D2 is greater than 6, meaning the size of porous carbon 11 is much larger than the size of active material 12, on the one hand, the bonding between porous carbon 11 and active material 12 becomes poor; on the other hand, the volume of porous carbon 11 exceeds the volume of active material 12, resulting in increased internal porosity and preventing an increase in material capacity. When D1 / D2 is less than 0.4, meaning the size of active material 12 is much larger than the size of porous carbon 11, direct contact will occur between the active materials 12, forming a "hard contact" between them. During lithium insertion / extraction, the resulting large deformation can easily cause pulverization and deformation of the active material, thereby reducing the structural stability of the anode material. Preferably, the median particle size D1 of porous carbon and the median particle size D2 of active material satisfy: 0.5 ≤ D1 / D2 ≤ 4.5.

[0118] In some embodiments, the median particle size of the active material is 1 nm to 300 nm, specifically 1 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, and 300 nm, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Preferably, the median particle size of the active material is 5 nm to 200 nm, and more preferably, the median particle size of the active material is 5 nm to 80 nm.

[0119] In some embodiments, porous carbon includes at least one of carbon black, ordered mesoporous carbon materials, and nanoporous carbon materials.

[0120] In some embodiments, the median particle size of the porous carbon is 10 nm to 500 nm, specifically 1 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm and 500 nm, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0121] In some embodiments, the mass ratio of porous carbon to active material is 40:(10-80). Specifically, the mass ratio of porous carbon to active material to silicon material can be 40:10, 40:20, 40:30, 40:40, 40:50, 40:60, 40:70, and 40:80, etc., and other values ​​within the above range are also possible and are not limited here. Controlling the mass ratio of porous carbon to active material within the above range is beneficial for obtaining a uniformly dispersed core material and for improving the material's cycle performance and structural stability.

[0122] In some embodiments, the vacuum mixing equipment includes at least one of a dual-star vacuum mixer, a planetary vacuum mixer, a planetary vacuum disperser, a screw vacuum mixer, a multi-functional vacuum mixer, a vacuum disperser, and a vacuum emulsifier;

[0123] In some embodiments, the vacuum mixing time is 0.5h to 15h, specifically 0.5h, 1h, 3h, 5h, 7h, 9h, 10h, 12h, 14h and 15h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0124] In some embodiments, the raw materials containing porous carbon and active substances are vacuum-mixed and then dried.

[0125] In some embodiments, the drying temperature is -50℃ to 500℃, specifically -50℃, -40℃, -30℃, -20℃, 50℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, and 500℃, etc., or other values ​​within the above range, which are not limited here. It is understood that the drying process can be low-temperature freeze-drying or high-temperature drying.

[0126] In some embodiments, the drying time is 0.5h to 15h, specifically 0.5h, 1h, 3h, 5h, 7h, 9h, 10h, 12h, 14h and 15h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0127] In some embodiments, the drying equipment includes at least one of a rotary evaporator, a vacuum oven, a spray dryer, a heat treatment furnace, and a freeze dryer.

[0128] In some embodiments, before vacuum mixing the raw materials containing porous carbon and active substances, the step of adding additives and solvents is included. That is, step S100 includes: placing porous carbon, active substances and additives in a solvent for vacuum mixing and drying to obtain a precursor.

[0129] In some embodiments, the additives include at least one selected from polyvinyl alcohol, octadecanoic acid, lauric acid, polyacrylic acid, sodium dodecylbenzenesulfonate, icosanoic acid, palmitic acid, tetradecanoic acid, undecanoic acid, fatty acids, hexadecyltrimethylammonium bromide, and polyvinylpyrrolidone. These additives can modify the pore structure surface of the active material and porous carbon, thereby facilitating the penetration of active material particles into the pores of the porous carbon.

[0130] In some embodiments, the solvent includes at least one of organic solvents and non-organic solvents. The organic solvents include at least one of phenol, methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, n-hexane, cyclohexane, ethyl acetate, chloroform, carbon tetrachloride, methyl acetate, acetone, and pentanol. The non-organic solvents include at least one of water, liquid ammonia, liquid carbon dioxide and liquid sulfur dioxide, and superacids.

[0131] In some embodiments, the mass ratio of the additive to porous carbon is (0.05 to 3):100, specifically 0.05:100, 0.01:100, 0.1:100, 1:100, 2:100 and 3:100, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0132] In some embodiments, the mass ratio of solvent to porous carbon is 100:(15-55), specifically 100:15, 100:20, 100:25, 100:30, 100:35, 100:40, 100:50 and 100:55, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0133] In some embodiments, coating the precursor specifically includes: mixing the precursor with a coating material and then heat-treating to obtain the negative electrode material. By coating with the coating material, on the one hand, it can prevent the electrolyte from entering the interior of the negative electrode material and causing side reactions that would reduce initial efficiency and capacity; on the other hand, it can alleviate the volume expansion of silicon, reduce the overall volume expansion of the composite material, and minimize electrode sheet swelling.

[0134] In some embodiments, the coating material includes at least one of carbon materials, metal oxide materials, polymer materials, and nitride materials;

[0135] In some embodiments, the carbon material includes at least one of soft carbon, hard carbon, crystalline carbon, and amorphous carbon.

[0136] In some embodiments, the metal oxide material includes at least one oxide selected from Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0137] In some embodiments, the nitride material includes at least one of silicon nitride, aluminum nitride, titanium nitride, and tantalum nitride.

[0138] In some embodiments, the polymer material includes at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide, and polyvinyl alcohol.

[0139] In some embodiments, the mass ratio of the precursor to the coating material is 100:(5-100), specifically 100:5, 100:10, 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, and 100:100, etc., or other values ​​within the above range, which are not limited here. A mass ratio of precursor to coating material less than 100:100 results in a coating layer that is too thin, which is not conducive to increasing the conductivity of the negative electrode material and has weak suppression performance on the volume expansion of the negative electrode material, leading to poor cycle performance. A mass ratio of precursor to coating material greater than 100:5 results in a coating layer that is too thick, reducing lithium-ion transport efficiency and lowering the overall performance of the negative electrode material.

[0140] In some embodiments, the heat treatment temperature is 400℃ to 900℃, specifically 400, 500, 600, 700, 800 and 900, etc., or other values ​​within the above range, which are not limited here.

[0141] In some embodiments, the heat treatment holding time is 1h to 12h, specifically 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h and 12h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0142] In some embodiments, the heating rate of the heat treatment is 1℃ / min to 15℃ / min, specifically 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 8℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min and 15℃ / min, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0143] In some embodiments, the heat treatment is carried out in a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, and krypton.

[0144] In some embodiments, the heat treatment is followed by a step of crushing and sieving the resulting material.

[0145] In some embodiments, the pulverizing equipment includes at least one of a mechanical pulverizer, an air jet mill, and a crusher.

[0146] In some embodiments, the sieve size for screening is 10 mesh to 800 mesh, specifically 10 mesh, 50 mesh, 100 mesh, 200 mesh, 300 mesh, 400 mesh, 500 mesh, 600 mesh, 700 mesh and 800 mesh.

[0147] Thirdly, this application provides a lithium-ion battery comprising the above-described negative electrode material or the negative electrode material prepared by the above-described preparation method.

[0148] Those skilled in the art will understand that the methods for preparing lithium-ion batteries described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0149] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the main claims.

[0150] Example 1

[0151] (1) Nano-silicon particles and porous carbon particles were screened by BET tester and Malvern particle size analyzer to obtain nano-silicon with a median particle size of 17nm and porous carbon particles with a median particle size of 20nm. The porous carbon particles were specifically carbon black, and the volume ratio of pores with a diameter of less than or equal to 2nm (micropores) in the porous carbon particles was 60%.

[0152] (2) The selected nano-silicon particles, porous carbon particles and polyvinyl alcohol were placed in phenol at a mass ratio of 50:25:25. Then, the vacuum degree was controlled at 0.1 Pa in a planetary vacuum ball mill and the ball milling was carried out for 2 hours. The precursor was obtained by rotary evaporation at 120°C.

[0153] (3) The precursor and phenolic resin were mixed at a mass ratio of 50:45. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 820°C for 4 hours.

[0154] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0155] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon and nano-silicon particles distributed in the porous carbon pore structure, and the outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0156] Example 2

[0157] (1) Nano-silicon particles and porous carbon particles were screened by BET tester and Malvern particle size analyzer to obtain nano-silicon with a median particle size of 50nm and porous carbon particles with a median particle size of 40nm. The porous carbon particles were specifically carbon black, and the volume ratio of pores with a diameter of less than or equal to 2nm (micropores) in the porous carbon particles was 45%.

[0158] (2) The selected nano-silicon particles, porous carbon particles and polyvinyl alcohol were placed in phenol at a mass ratio of 50:25:25. Then, the vacuum degree was controlled at 0.1 Pa in a planetary vacuum ball mill and the ball milling was carried out for 2 hours. The precursor was obtained by rotary evaporation at 120°C.

[0159] (3) The precursor and phenolic resin were mixed at a mass ratio of 50:45. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 820°C for 4 hours.

[0160] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0161] like Figure 5 The image shown is a SEM image of the negative electrode material prepared in this embodiment. The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The second pore structure is filled with nano-silicon. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0162] like Figure 6 The image shown is the XRD pattern of the negative electrode material prepared in Example 1. Figure 6 It is evident that silicon peaks are present in the product.

[0163] like Figure 7 The figure shows the first charge-discharge curve of the negative electrode material prepared in Example 1. Figure 7 It is evident that this material exhibits high initial charge / discharge capacity and high initial efficiency.

[0164] like Figure 8The figure shown is a cycle performance curve of the negative electrode material prepared in Example 1. Figure 8 As can be seen, the negative electrode material prepared in this embodiment has excellent cycling performance, with a capacity retention rate of 92.1% after 100 cycles.

[0165] Example 3

[0166] (1) Nano-silicon particles and porous carbon particles were screened using a BET analyzer and a Malvern particle size analyzer to obtain nano-silicon particles with a median particle size of 30 nm and porous carbon particles with a median particle size of 50 nm. The porous carbon particles were specifically Ketjen Black. The volume percentage of the porous carbon particles with a pore size of 2 nm or less (micropores) was 49%.

[0167] (2) The selected nano-silicon particles, porous carbon particles and polyvinyl alcohol were placed in isopropanol at a mass ratio of 50:35:22. The mixture was then mixed for 4 hours with a vacuum degree controlled at 0.01 Pa in a double-star vacuum mixer and then evaporated at 150 degrees to obtain the precursor.

[0168] (3) The precursor and sucrose were mixed at a mass ratio of 50:55. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 920°C for 3 hours.

[0169] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0170] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The second pore structure is filled with nano-silicon. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0171] Example 4

[0172] (1) Nano-silicon particles and porous carbon particles were screened using a BET analyzer and a Malvern particle size analyzer to obtain nano-silicon particles with a median particle size of 20 nm and porous carbon particles with a median particle size of 30 nm. The porous carbon particles were specifically MCM-41, and the volume percentage of the porous carbon particles with a pore size of less than or equal to 2 nm (micropores) was 55%.

[0173] (2) The screened nano-silicon particles, porous carbon particles, and polyvinyl alcohol were placed in butanol at a mass ratio of 50:31:18, and then the vacuum degree was controlled at 10 in a vacuum disperser. -5 Pa, mixed for 5 hours, and then evaporated at 220 degrees Celsius to obtain the precursor.

[0174] (3) The precursor and glucose were mixed at a mass ratio of 50:45. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 780°C for 5 hours.

[0175] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0176] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0177] Example 5

[0178] (1) Nano-silicon particles and porous carbon particles were screened using a BET analyzer and a Malvern particle size analyzer to obtain nano-silicon particles with a median particle size of 60 nm and porous carbon particles with a median particle size of 80 nm. The porous carbon particles were specifically CMK-3, and the volume percentage of the porous carbon particles with a pore size of less than or equal to 2 nm (micropores) was 62%.

[0179] (2) The selected nano-silicon particles, porous carbon particles and polyvinyl alcohol were placed in phenol at a mass ratio of 40:25:25. The vacuum degree was controlled at 1.5 Pa in a screw vacuum mixer and mixed for 2 hours. The precursor was obtained by rotary evaporation at 120 degrees.

[0180] (3) Mix the precursor with polyethyleneamine and heat treat it at 350°C.

[0181] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0182] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon. The outer shell is a polymer coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0183] Example 6

[0184] (1) SiO particles and porous carbon particles were screened using a BET analyzer and a Malvern particle size analyzer to obtain SiO particles with a median particle size of 25 nm and porous carbon particles with a median particle size of 20 nm. The porous carbon particles were specifically NCP. The micropore volume ratio of the porous carbon particles was 70%.

[0185] (2) The selected SiO particles, porous carbon particles and polyvinyl alcohol were placed in phenol at a mass ratio of 30:25:15. The vacuum degree was controlled at 3Pa in a vacuum mixer and mixed for 8 hours. The precursor was obtained by rotary evaporation at 150 degrees.

[0186] (3) The precursor and asphalt were mixed at a mass ratio of 30:25. Then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 980°C for 3 hours.

[0187] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0188] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, SiO particles distributed in the porous carbon pore structure, and SiO particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the SiO particles are shown in Table 1.

[0189] Example 7

[0190] (1) Nano-silicon particles and porous carbon particles were screened by BET tester and Malvern particle size analyzer to obtain nano-silicon with a median particle size of 50nm and porous carbon particles with a median particle size of 40nm. The porous carbon particles were specifically carbon black, and the volume ratio of pores with a pore size of less than or equal to 2nm (micropores) in the porous carbon particles was 45%.

[0191] (2) The selected nano-silicon particles, porous carbon particles and polyvinyl alcohol were placed in phenol at a mass ratio of 30:25:15. The mixture was then mixed in a vacuum mixer with a vacuum degree of 5 Pa for 8 hours and then evaporated at 150 degrees to obtain the precursor.

[0192] (3) The precursor and asphalt were mixed at a mass ratio of 30:25. Then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 980°C for 3 hours.

[0193] (4) The obtained sample is crushed, sieved, and then classified to obtain the negative electrode material.

[0194] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nanoparticles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0195] Example 8

[0196] Unlike Example 2, step (2) replaces the vacuum degree with 10. -7 Pa.

[0197] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0198] Example 9

[0199] Unlike Example 2, step (2) replaces the vacuum level with 10 Pa.

[0200] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0201] Example 10

[0202] Unlike Example 2, the precursor and titanium oxide were mixed at a mass ratio of 50:35.

[0203] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon. The outer shell is a titanium oxide coating layer. The porous carbon forms a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0204] Example 11

[0205] Unlike Example 2, the precursor and silicon nitride were mixed at a mass ratio of 50:35.

[0206] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles in the porous carbon pore structure, and nano-silicon particles distributed in the pores of the porous carbon. The outer shell is a silicon nitride coating layer. The porous carbon forms a first pore structure and a second pore structure. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0207] Example 12

[0208] Unlike Example 2, the median particle size of the nano-silicon is 50 nm, and the median particle size of the porous carbon particles is 250 nm.

[0209] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The second pore structure is filled with nano-silicon. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0210] Example 13

[0211] Unlike Example 2, the median particle size of the nano-silicon is 50 nm, and the median particle size of the porous carbon particles is 20 nm.

[0212] The negative electrode material prepared in this embodiment has a core-shell structure. The core includes porous carbon, nano-silicon particles distributed in the porous carbon pore structure, and nano-silicon particles distributed between the porous carbon particles. The outer shell is a carbon coating layer. The porous carbon has a first pore structure and a second pore structure. The second pore structure is filled with nano-silicon. The volume ratio of the first pore structure, the filling rate of the second pore structure, the median particle size of the porous carbon, and the median particle size of the nano-silicon particles are shown in Table 1.

[0213] Comparative Example 1

[0214] Unlike Example 1, the volume percentage of porous carbon particles with pore sizes of 2 nm or less (micropores) is 30%.

[0215] Comparative Example 2

[0216] Unlike Example 1, step (2) replaces the vacuum degree with 10. -8 Pa.

[0217] Comparative Example 3

[0218] Unlike Example 1, step (2) replaces the vacuum level with 15 Pa.

[0219] Comparative Example 4

[0220] Unlike Example 1, in step (2), nano-silicon, porous carbon particles and polyvinyl alcohol are mixed using a planetary mixer.

[0221] Performance testing

[0222] 1. The silicon in the core of the negative electrode material is etched away using HF solution. The pore volume of the pore structure is tested using BET pore distribution. The ratio of the pore volume of the first and second pore structures in the porous carbon to the total pore volume of the porous carbon is calculated.

[0223] 2. Before etching the active material in the negative electrode material, test the volume V1 of the second pore structure of the material. After etching the silicon, test the volume V2 of the second pore structure. (V2-V1) / V2 is the filling rate of the active material in the second pore structure.

[0224] 3. Use a Malvern particle size analyzer to test the median particle size of the material.

[0225] 4. Observe 200 carbon material and active substance particles under a scanning electron microscope, and use the Nano Measure to determine the median particle size of the two substances.

[0226] 5. The specific surface area of ​​the negative electrode material was tested using a Microt Tristar 3020 specific surface area and pore size analyzer. A certain mass of powder was weighed and completely degassed under vacuum heating to remove surface adsorbates. Then, the specific surface area of ​​the particles was calculated by using the nitrogen adsorption method based on the amount of nitrogen adsorbed.

[0227] 6. The pore volume of the negative electrode material is tested using the micropore size distribution method, and the pore volume is ΔV; the true density P of the negative electrode material is tested, and the porosity of the negative electrode material is calculated as ΔV / (ΔV+1 / P).

[0228] 7. The following methods were used to test the electrochemical performance:

[0229] The negative electrode material, conductive agent, and binder were dissolved in a solvent at a mass ratio of 94:1:5, with the solid content controlled at 50%. This mixture was then coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. Next, a ternary positive electrode sheet prepared using conventional mature processes, a 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing were assembled into an 18650 cylindrical cell using conventional manufacturing processes. Charge-discharge testing of the cylindrical cells was conducted on the LAND battery testing system at Wuhan Jinno Electronics Co., Ltd., under room temperature conditions, with a constant current charge-discharge of 0.2C and a charge-discharge voltage limited to 2.75–4.2V. The initial reversible capacity, first charge capacity, and first discharge capacity were obtained. The initial coulombic efficiency was calculated as: first discharge capacity / first charge capacity.

[0230] Repeat the cycle 100 times and record the discharge capacity as the remaining capacity of the lithium-ion battery; capacity retention rate = remaining capacity / initial capacity * 100%.

[0231] Electrode expansion rate (%) determination after 30 cycles: The negative electrode material was mixed with graphite to form a fixed capacity (450mAh / g), coated into an electrode sheet, and the electrode sheet thickness d1 was measured. Then, it was assembled into a coin cell for testing. After 30 cycles, the battery was disassembled, and the electrode sheet thickness d2 was measured again. Electrode expansion rate = (d2-d1) / d1*100%.

[0232] The test results are shown in Table 1.

[0233] Table 1. Performance test data for each embodiment and comparative example

[0234]

[0235] According to the data in Table 1, in the negative electrode materials prepared in Examples 1-13 of this application, the active material is uniformly dispersed in the pores of porous carbon, forming a well-dispersed structure. There is little or no direct contact between the active materials; most of the contact is indirect, with porous carbon acting as a buffer layer. This allows the high volume ratio of the first pore structure of the porous carbon to buffer the volume expansion of the active material, which is beneficial for improving the rate performance of the negative electrode material while mitigating the volume expansion of nano-silicon. Furthermore, the active material filling the porous carbon results in a second pore structure filling rate of greater than or equal to 95%, which can improve the material capacity while avoiding stress concentration and electrolyte penetration. The negative electrode material of this application can effectively suppress volume expansion while exhibiting good structural stability, possessing advantages such as high rate performance, high capacity, and good cycle performance.

[0236] According to Comparative Example 1, the volume ratio of the first pore structure in porous carbon is too small, which means that the anode material cannot completely alleviate the volume expansion.

[0237] According to Comparative Examples 2 and 3, the vacuum degree of vacuum treatment is greater than 10 Pa or less than 10 Pa. -7 Pa, both lead to a decrease in the filling rate of the second pore structure, thereby reducing the structural stability and capacity retention of the anode material.

[0238] According to Comparative Example 4, when the negative electrode material is prepared using a conventional mixing method, the filling rate of the second pore structure is 45%, which is much lower than 95% in Example 1. This leads to stress concentration in the negative electrode material, resulting in reduced cycle performance and a larger expansion rate.

[0239] The applicant declares that the detailed process equipment and process flow of this invention are illustrated through the above embodiments, but this invention is not limited to the above detailed process equipment and process flow, that is, it does not mean that this invention must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the products of this invention, additions of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a core and a coating layer disposed on at least a portion of the surface of the core. The core includes porous carbon and an active material filling the porous carbon pore structure. The active material includes Si and SiO. x At least one of the following, wherein 0 < x < 2, the porous carbon has a first pore structure with a pore size less than or equal to 2 nm and a second pore structure with a pore size greater than 2 nm, the ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon is greater than or equal to 40%, the filling rate of the second pore structure is greater than or equal to 95%, the negative electrode material further comprises an active material distributed between the porous carbon, and the thickness of the coating layer is 10 nm to 500 nm.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following features (1) to (7): (1) The median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.4≤D1 / D2≤6; (2) The median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.5≤D1 / D2≤4.5; (3) The median particle size of the active material is 1 nm to 300 nm; (4) The morphology of the active substance includes at least one of spherical, ellipsoidal and flake-like shapes; (5) The porous carbon material includes at least one of carbon black, ordered mesoporous carbon material and nanoporous carbon material; (6) The median particle size of the porous carbon is 1 nm to 500 nm; (7) The median particle size of the kernel is 0.8 μm ~ 10 μm.

3. The negative electrode material according to claim 1, characterized in that, The coating layer comprises at least one of a carbon layer, a metal oxide layer, a polymer layer, and a nitride layer, and the coating layer comprises at least one of the following features (1) to (4): (1) The material of the carbon layer includes at least one of soft carbon, crystalline carbon, and amorphous carbon; (2) The material of the metal oxide layer includes at least one of the oxides of Sn, Ge, Fe, Cu, Ti, Na, Mg, Al, Ca and Zn; (3) The material of the nitride layer includes at least one of silicon nitride, aluminum nitride, titanium nitride and tantalum nitride; (4) The polymer layer is made of at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide and polyvinyl alcohol.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following features (1) to (3): (1) The specific surface area of ​​the negative electrode material is less than or equal to 10 m². 2 / g; (2) The median particle size of the negative electrode material is 0.5 μm to 20 μm; (3) The porosity of the negative electrode material is less than or equal to 10%.

5. A method for preparing the negative electrode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: A precursor is obtained by vacuum mixing raw materials containing porous carbon and active materials, wherein the active materials include Si and SiO. x At least one of the following, wherein 0 < x < 2, the porous carbon has a first pore structure with a pore size less than or equal to 2 nm and a second pore structure with a pore size greater than 2 nm, the ratio of the pore volume of the first pore structure to the total pore volume of the porous carbon is greater than or equal to 40%, and the vacuum degree of the vacuum mixing is 10. -7 Pa ~10Pa; The precursor is coated to obtain the negative electrode material.

6. The preparation method according to claim 5, characterized in that, The method includes at least one of the following features (1) to (6): (1) The median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.4≤D1 / D2≤6; (2) The median particle size D1 of the porous carbon and the median particle size D2 of the active material satisfy: 0.5≤D1 / D2≤4.5; (3) The median particle size of the active material is 1 nm to 300 nm; (4) The porous carbon includes at least one of carbon black, ordered mesoporous carbon materials and nanoporous carbon materials; (5) The median particle size of the porous carbon is 1 nm to 500 nm; (6) The mass ratio of the porous carbon to the active material is 40: (10~80).

7. The preparation method according to claim 5, characterized in that, The method includes at least one of the following features (1) to (5): (1) The vacuum mixing equipment includes at least one of the following: a dual-star vacuum mixer, a planetary vacuum mixer, a screw vacuum mixer, a multi-functional vacuum mixer, a vacuum disperser, and a vacuum emulsifier; (2) The vacuum mixing time is 0.5 h ~ 15 h; (3) After vacuum mixing, the mixture is further dried at a temperature of -50℃ to 500℃. (4) After vacuum mixing, a drying process is performed for 0.5 to 15 hours; (5) After vacuum mixing, the mixture is further dried. The equipment for drying includes at least one of rotary evaporator, vacuum oven, spray dryer, heat treatment furnace and freeze dryer.

8. The preparation method according to claim 5, characterized in that, The raw material comprising porous carbon and active substances also includes additives and solvents, and the method includes at least one of the following features (1) to (4): (1) The additives include at least one of polyvinyl alcohol, octadecanoic acid, lauric acid, polyacrylic acid, sodium dodecylbenzenesulfonate, icosanoic acid, palmitic acid, tetradecanoic acid, undecanoic acid, fatty acids, hexadecyltrimethylammonium bromide and polyvinylpyrrolidone; (2) The solvent includes at least one of phenol, methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, n-hexane, cyclohexane, ethyl acetate, chloroform, carbon tetrachloride, methyl acetate, acetone and pentanol; (3) The mass ratio of the additive to the porous carbon is (0.05~3):100; (4) The mass ratio of the solvent to the porous carbon is 100: (15~55).

9. The preparation method according to claim 5, characterized in that, The step of coating the precursor to obtain the negative electrode material specifically involves: mixing the precursor and the coating material and then heat-treating them. The method includes at least one of the following features (1) to (13): (1) The coating material includes at least one of carbon materials, metal oxides, polymer materials and nitrides; (2) The coating material includes at least one of carbon materials, metal oxide materials, polymer materials and nitride materials, wherein the carbon material includes at least one of soft carbon, crystalline carbon and amorphous carbon; (3) The coating material includes at least one of carbon materials, metal oxide materials, polymer materials and nitride materials, and the metal oxide material includes at least one of oxides of Sn, Ge, Fe, Cu, Ti, Na, Mg, Al, Ca and Zn; (4) The coating material includes at least one of carbon materials, metal oxide materials, polymer materials and nitride materials, wherein the polymer material includes at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide and polyvinyl alcohol; (5) The coating material includes at least one of carbon materials, metal oxide materials and nitride materials, and the nitride material includes at least one of silicon nitride, aluminum nitride, titanium nitride and tantalum nitride; (6) The mass ratio of the precursor to the coating material is 100:(5~100); (7) The temperature of the heat treatment is 400℃~900℃; (8) The heat treatment holding time is 1 h to 12 h; (9) The heating rate of the heat treatment is 1℃ / min to 15℃ / min; (10) The heat treatment is carried out in a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon and krypton; (11) The process of heat treatment after mixing the precursor and the coating material further includes the steps of crushing and sieving the resulting material; (12) After the precursor and the coating material are mixed and heat-treated, the process further includes the steps of crushing and screening the resulting material. The crushing equipment includes at least one of a mechanical crusher, an air jet mill, and a crusher. (13) After the precursor and the coating material are mixed and heat-treated, the process further includes the steps of crushing and sieving the resulting material, wherein the sieve size is 10 mesh to 800 mesh.

10. A lithium-ion battery, characterized in that, Includes the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the preparation method according to any one of claims 5 to 9.

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