Negative electrode material and battery

Abstract

The invention relates to the technical field of negative electrode materials, in particular to a negative electrode material and a battery, the negative electrode material comprises a base material and a silicon material, at least part of the silicon material is located in the base material, and the silicon material comprises a first phase and a second phase; wherein the negative electrode material is measured by a precession electron diffraction method: based on the region where the silicon material is located, the area proportion of the region where the silicon material of the first phase is located is A which is greater than or equal to 70%, and the area proportion of the region where the silicon material of the second phase is located is B which is greater than 0 and less than or equal to 30%. The negative electrode material provided by the invention has low expansion, high capacity and excellent cycle performance.

Description

Technical Field

[0001] This application relates to the field of negative electrode materials technology, and in particular to negative electrode materials and batteries. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long lifespan, and no environmental pollution, are widely used in the 3C (computer, communication, and consumer electronics) field. With market development, lithium-ion batteries are not only widely used in mobile devices such as smartphones and laptops, but also in large equipment such as electric vehicles and power tools. To improve battery energy density, the research and development of silicon-based anode materials has become increasingly mature. However, silicon-based materials experience significant volume expansion during charge and discharge, which can easily lead to particle pulverization and subsequent detachment from the current collector. Furthermore, the repeated volume changes of silicon-based materials during electrochemical cycling cause the solid electrolyte film formed on the silicon-based material surface to continuously break down and regenerate, resulting in continuous consumption of lithium ions and affecting the stability of the silicon-based material. During long cycles, the battery capacity will rapidly decline.

[0003] Therefore, how to improve the volume expansion of silicon-based anode materials and enhance their structural and cycle stability is an urgent problem to be solved. Summary of the Invention

[0004] This application provides a negative electrode material and a battery, which can improve the volume expansion of the negative electrode material and enhance its structural stability and cycle stability.

[0005] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a matrix material and a silicon material, wherein at least a portion of the silicon material is located within the matrix material, and the silicon material comprises a first phase and a second phase;

[0006] The negative electrode material was measured by precession electron diffraction:

[0007] Based on the region where the silicon material is located, the area ratio of the region where the silicon material of the first phase is located is A, where A ≥ 70%, and the area ratio of the region where the silicon material of the second phase is located is B, where 0 < B ≤ 30%.

[0008] In some embodiments, the substrate material has pores, and at least a portion of the silicon material is located within the pores of the substrate material.

[0009] In some embodiments, the anode material with removed silicon material has micropores, and the pore volume of the micropores accounts for ≥80%.

[0010] In some embodiments, the anode material from which silicon material is removed has mesopores, with the pore volume ratio of the mesopores being ≤20%.

[0011] In some embodiments, the anode material with removed silicon has macropores, and the volume percentage of the macropores is ≤1%.

[0012] In some embodiments, the total pore volume of the anode material after removing the silicon material is 0.4 cm. 3 / g~1.5cm 3 / g.

[0013] In some embodiments, the specific surface area of ​​the anode material without silicon is 200 m². 2 / g~3000m 2 / g.

[0014] In some embodiments, in the anode material where silicon material is removed, the pore volume ratio of pores with a diameter of less than 5 nm is ≥90%.

[0015] In some embodiments, the matrix material includes a carbon matrix, which includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

[0016] In some embodiments, the matrix material comprises a non-carbon matrix, which includes at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates.

[0017] In some embodiments, the negative electrode material has a dome-shaped diffuse peak in the XRD pattern of the negative electrode material within the range of 28.4°±0.5°, and the grain size of the silicon material is c≤1nm.

[0018] In some embodiments, the total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g.

[0019] In some embodiments, the average pore size of the negative electrode material is 0.4 nm to 50 nm.

[0020] In some embodiments, the negative electrode material includes micropores, and the pore volume ratio of the micropores is ≤10%.

[0021] In some embodiments, the negative electrode material includes mesopores, with the pore volume accounting for ≥80%.

[0022] In some embodiments, the negative electrode material includes macropores, with the macropore volume accounting for ≤20%.

[0023] In some embodiments, the average gas production of the negative electrode slurry prepared from the negative electrode material is ≤1 mL / g per day when placed in an environment of 25°C.

[0024] In some embodiments, the median particle size D of the negative electrode material 50 The size ranges from 5μm to 20μm.

[0025] In some embodiments, the particle size distribution of the negative electrode material satisfies: 0.9 ≤ (D 90 -D 10 ) / D 50 ≤5.

[0026] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g.

[0027] In some embodiments, the compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 .

[0028] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 .

[0029] In some embodiments, the powder conductivity of the negative electrode material at a pressure of 20 kN is 0.1 S / cm to 2 S / cm.

[0030] In some embodiments, the silicon content in the negative electrode material is 20% to 60% by mass.

[0031] Secondly, this application provides a battery comprising the negative electrode material described in the first aspect.

[0032] The technical solution of this application has at least the following beneficial effects:

[0033] The negative electrode material provided in this application combines silicon material with a matrix material. The matrix material can buffer the volume change of the silicon material and also act as a conductive network to maintain good electronic conductivity within the negative electrode material. In this application, based on the region containing the silicon material, the area proportion of the first phase silicon material is A, where A ≥ 70%, and the area proportion of the second phase silicon material is B, where 0 < B ≤ 30%. Because the first phase silicon material has a low volume expansion effect during charge and discharge, its volume expansion is isotropic during lithium insertion / extraction, while the second phase silicon material exhibits anisotropic volume expansion. Therefore, the first phase silicon material has better structural reversibility and mechanical stability. Furthermore, the critical fracture size of the first phase silicon material is much larger than that of the second phase silicon material. The first phase silicon material contains dangling bonds and voids, allowing it to withstand crushing during cycling and resulting in a lower lithiation barrier than the second phase silicon material. Therefore, by controlling the area ratio of the first phase silicon material to the second phase silicon material, the silicon material in the anode material is mainly in the first phase state. This allows for greater utilization of the structural stability brought by the first phase silicon material, resulting in a more stable capacity and lower expansion effect for the anode material. Furthermore, the use of a porous matrix material further mitigates the volume expansion of the silicon material, effectively reducing volume expansion during cycling, minimizing particle breakage of the anode material, and comprehensively improving the cycling performance of the anode material. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the discharge state of a battery provided in an embodiment of this application.

[0035] Figure 2a This is a prevolute electron diffraction pattern of the negative electrode material provided in Embodiment 3 of this application.

[0036] Figure 2b The image is a processed version of the precession electron diffraction pattern of the negative electrode material provided in Embodiment 3 of this application. Detailed Implementation

[0037] The following examples illustrate this solution. These examples are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0038] In a first aspect, this application provides a negative electrode material, including a matrix material and a silicon material, wherein at least a portion of the silicon material is located within the matrix material, and the silicon material includes a first phase and a second phase;

[0039] The negative electrode material was measured by precession electron diffraction:

[0040] Based on the region where the silicon material is located, the area ratio of the region where the silicon material of the first phase is located is A, where A ≥ 70%, and the area ratio of the region where the silicon material of the second phase is located is B, where 0 < B ≤ 30%.

[0041] The first phase corresponds to the region in the XRD test where the Si(111) grain size is ≤0.5nm and cannot be matched with the CIF (Crystallographic Information File) file of crystalline Si; the second phase corresponds to the region in the XRD test where the Si(111) grain size is >0.5nm and can be matched with the CIF file of crystalline Si.

[0042] The negative electrode material provided in this application combines silicon material with a matrix material. The matrix material can buffer the volume change of the silicon material and also act as a conductive network to maintain good electronic conductivity within the negative electrode material. In this application, based on the region containing the silicon material, the area proportion of the first phase silicon material is A, where A ≥ 70%, and the area proportion of the second phase silicon material is B, where 0 < B ≤ 30%. Because the first phase silicon material has a low volume expansion effect during charge and discharge, its volume expansion is isotropic during lithium insertion / extraction, while the second phase silicon material exhibits anisotropic volume expansion. Therefore, the first phase silicon material has better structural reversibility and mechanical stability. Furthermore, the critical fracture size of the first phase silicon material is much larger than that of the second phase silicon material. The first phase silicon material contains dangling bonds and voids, allowing it to withstand crushing during cycling and resulting in a lower lithiation barrier than the second phase silicon material. Therefore, by controlling the area ratio of the first phase silicon material to the second phase silicon material, the silicon material in the anode material is mainly in the first phase state. This allows for greater utilization of the structural stability brought by the first phase silicon material, resulting in a more stable capacity and lower expansion effect for the anode material. Furthermore, the use of a porous matrix material further mitigates the volume expansion of the silicon material, effectively reducing volume expansion during cycling, minimizing particle breakage of the anode material, and comprehensively improving the cycling performance of the anode material.

[0043] In some embodiments, the substrate material has pores, and at least a portion of the silicon material is located within the pores of the substrate material. Composites of silicon material with a porous substrate material can utilize the substrate material to buffer volume changes in the silicon material, and the substrate material can also act as a conductive network to maintain good electronic conductivity within the negative electrode material.

[0044] In some embodiments, the matrix material includes a carbon matrix, which includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

[0045] Understandably, the carbon matrix chosen from the above materials can all serve as a supporting framework and also have good electrical conductivity, ensuring the conductivity of the negative electrode material.

[0046] In this application, taking carbon matrix as an example, under stirring, 150 mL of 20% HF acid solution is added dropwise to 10 g of negative electrode material. This will generate SiF4 and H2 gases and release heat. After no more gas is generated, the supernatant acid solution is removed by centrifugation. Another 150 mL of 20% HF acid solution is added to the negative electrode material, and the mixture is stirred for 12 h. The supernatant acid solution is removed by centrifugation again. Then, the negative electrode material is washed with pure water until neutral and dried to obtain the negative electrode material after removing silicon material, i.e., carbon matrix.

[0047] In some embodiments, the carbon matrix has at least one of micropores, mesopores, and macropores. According to internationally accepted pore size ranges, micropores refer to pores with a diameter of less than 2 nm, mesopores refer to pores with a diameter of 2 to 50 nm, and macropores refer to pores with a diameter of greater than 50 nm.

[0048] In some embodiments, the anode material, i.e., the carbon matrix, is removed from the silicon material. The carbon matrix has a micropore volume ratio of ≥80%, a mesopore volume ratio of ≤20%, and a macropore volume ratio of ≤1%.

[0049] Specifically, the pore volume percentage of micropores can be 80%, 85%, 89%, 90%, 92%, 95%, or 98%, the pore volume percentage of mesopores can be 20%, 18%, 17%, 15%, 14%, 12%, 10%, 8%, 6%, 5%, 2%, or 1%, and the pore volume percentage of macropores can be 1%, 0.8%, 0.7%, 0.5%, 0.3%, 0.2%, or 0%. Understandably, the volume percentages of micropores, mesopores, and macropores in the carbon matrix are controlled within the above ranges. Since most of the pores in the carbon matrix are micropores, the size of the deposited silicon material can be adjusted, the dispersion uniformity of the carbon matrix and silicon material can be improved, the volume expansion of the silicon material can be reduced, and the cycle stability of the anode material can be enhanced.

[0050] In some embodiments, the total pore volume of the anode material after removing the silicon material is 0.4 cm. 3 / g~1.5cm 3 / g, specifically 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm3 / g, 1.0cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., can also be specific values ​​within the above range, without limitation. The anode material, i.e., the carbon matrix, is used to remove the silicon material. The carbon matrix has abundant pores that can accommodate the silicon material and reserve space for the volume expansion of the accommodated silicon material. Understandably, when the carbon matrix and silicon material form a composite material, at least some of the silicon material is deposited within the pores of the carbon matrix; therefore, the total pore volume of the resulting composite material will be smaller than the total pore volume of the initial carbon matrix.

[0051] In some embodiments, the average pore size of the silicon-removed anode material is from 0.1 nm to 8 nm. For example, the average pore size of the silicon-removed anode material can be 0.1 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, or any value within the range of any two of the above values. Controlling the average pore size of the silicon-removed anode material within the above range indicates that the pores in the carbon matrix include micropores with a relatively large volume proportion, and also include at least one or more of mesopores and macropores. Micropores in the carbon matrix can reduce the aggregation of silicon material in the carbon matrix, increase the silicon content in the carbon matrix and the uniformity of silicon material distribution, thereby improving the specific capacity and mechanical properties of the obtained anode material. Relatively large mesopores or macropores can provide sufficient buffer space for the volume expansion of silicon material, effectively alleviating the volume expansion of silicon material, reducing the risk of excessive local expansion stress caused by uneven volume changes of silicon material during cycling, leading to cracking and pulverization of the anode material, and thus improving the particle structure stability and cycle stability of the anode material.

[0052] In some embodiments, in the anode material without silicon, the volume percentage of pores with a diameter of less than 5 nm is ≥90%. Specifically, the volume percentage of pores with a diameter of less than 5 nm in all pores can be 90%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, etc., and is not limited here. Understandably, the pores in the carbon matrix are mainly pores with a diameter of less than 5 nm, with almost no large mesopores (>5 nm) and macropores. This is beneficial for the filling of silicon material, and the anode material after silicon filling is mainly composed of mesopores and macropores. Since the proportion of mesopores (>5 nm) and macropores in carbon material is already small, the pore volume occupied by mesopores and macropores in the anode material after filling is also very small. An appropriate total pore volume can buffer the volume expansion of silicon during the cycling of the negative electrode material. However, an excessively large total pore volume will result in insufficient density inside the particles, creating stress weak points. Moreover, if these intermediate pores (>5nm) and macropores are exposed on the particle surface, it is difficult to fill them through subsequent coating methods, increasing the probability of electrolyte immersion.

[0053] The aforementioned methods for testing pore size and pore volume ratios can be summarized as follows: The pore volume of a carbon matrix refers to the total pore volume per unit mass of carbon matrix material, which can be measured through gas adsorption. Nitrogen adsorption is a technique that characterizes the porosity and pore size distribution of a material by condensing gas within the pores of a solid. As pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure continues to rise until a saturation point is reached, at which point all pores are filled with liquid. The nitrogen pressure is then gradually decreased to allow the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms allows for the determination of pore volume and pore size distribution, as well as the respective proportions of micropores, mesopores, and macropores in the total pore volume.

[0054] In some embodiments, the specific surface area of ​​the anode material without silicon is 200 m². 2 / g~3000m 2 / g, the specific surface area of ​​the negative electrode material can be 300m² 2 / g、500m 2 / g、800m 2 / g, 1000m 2 / g, 1500m 2 / g、2000m 2 / g、2500m 2 / g or 3000m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Removing silicon material from the anode material, i.e. the substrate, and controlling the specific surface area of ​​the substrate within the above range is beneficial to the uniform dispersion and stable adhesion of silicon material on the substrate, thereby reducing the risk of silicon material falling off the substrate and improving the stability and durability of the anode material.

[0055] In some embodiments, the matrix material includes a non-carbon matrix, which includes at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates.

[0056] In some embodiments, the metal oxide includes at least one of aluminum oxide, zirconium oxide, germanium dioxide, and manganese dioxide.

[0057] In some embodiments, the silicide includes at least one of silicon carbide and silicon nitride.

[0058] In some embodiments, the silicate includes at least one of cordierite, mullite, and zeolite.

[0059] In some embodiments, the phosphate includes at least one selected from aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate.

[0060] In some embodiments, the titanate includes at least one of calcium titanate, iron titanate, lithium titanate, and barium titanate.

[0061] In some embodiments, the XRD pattern of the negative electrode material shows a dome-shaped diffuse peak within the range of 28.4° ± 0.5°, and the grain size of the silicon material is c ≤ 1 nm. In this application, the grain size of the silicon material is controlled below 1 nm, which can alleviate the volume expansion of the silicon material during charge and discharge. The dome-shaped diffuse peak is the scattering peak of amorphous silicon. The expansion effect of amorphous silicon during lithium intercalation is isotropic, and it can have better structural reversibility during charge and discharge. Furthermore, amorphous silicon has better mechanical stability and can withstand crushing during cycling. The negative electrode material of this application can have a more stable capacity and a better stress relief mechanism.

[0062] In some embodiments, the total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g, specifically 0.001cm 3 / g, 0.005cm 3 / g, 0.006cm 3 / g, 0.007cm 3 / g, 0.01cm 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.08cm 3 / g or 0.1cm3 / g, etc., can also be other values ​​within the above range, and are not limited here. After the matrix material is filled with silicon material, the remaining pores can reserve space for the volume expansion of silicon material, alleviate the expansion effect of negative electrode material, improve the cycle stability of negative electrode material, and can also adsorb or contain a small amount of gas generated by the side reaction between silicon material and electrolyte, thus improving the gas generation phenomenon of negative electrode material.

[0063] In some embodiments, the average pore size of the negative electrode material is 0.4 nm to 50 nm; specifically, it can be 0.4 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm, etc., and of course, other values ​​within the above range are also possible, which are not limited here. The pores of the negative electrode material can provide sufficient expansion buffer space for the silicon material, which is beneficial to reducing the particle fragmentation phenomenon caused by the volume expansion of the silicon material.

[0064] In some embodiments, the pores of the negative electrode material include micropores, mesopores, and macropores, wherein the ratio of the pore volume of micropores to the pore volume of mesopores is (1-50):(50-99), specifically 1:99, 5:95, 10:90, 20:80, 30:65, 40:50, or 50:50, etc., and is not limited thereto. In this application, the proportion of mesopore volume is increased, and the proportion of micropore volume is decreased. Since the molecular size generated by the electrolyte is generally smaller than or equal to the pore diameter of the micropores, under the strong capillary adsorption capacity of the micropores, the adsorption capacity of the negative electrode material is largely proportional to the pore volume of the micropores. That is, as the micropore volume increases, the adsorption capacity of the negative electrode material increases, and therefore the side reactions between the negative electrode material and the electrolyte will increase. Therefore, controlling the pore volume ratio of the micropores in the negative electrode material can reduce the active sites for side reactions between the negative electrode material and the electrolyte, thereby reducing the thickening of the solid electrolyte film caused by the continuous intrusion of the electrolyte, which is beneficial to improving the cycle performance of the negative electrode material. In addition, the increased volume ratio of mesopores can reserve sufficient buffer space for the volume expansion of silicon material, which is beneficial to improving the particle structure stability of the negative electrode material.

[0065] In some embodiments, the total volume of pores in the negative electrode material is taken as 100%. The negative electrode material includes micropores, and the pore volume percentage of the micropores is ≤10%, specifically 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, or 2%, etc., or other values ​​within the above range, which are not limited here. A pore volume percentage within the above range indicates that a large number of micropores in the matrix material have been effectively filled by the silicon material, resulting in fewer micropores remaining in the obtained negative electrode material. The silicon material filling the micropores in the matrix material ensures the structural compactness of the matrix material, preventing structural collapse during the compaction process of electrode fabrication. Because the micropores in the matrix material are relatively uniformly distributed and effectively filled, almost no micropores remain inside the negative electrode material, while the micropores on the surface of the negative electrode material are effectively filled by the coating material. This makes the interior of the negative electrode material denser, increasing its compressive strength (compacted density), which helps the negative electrode material remain stable during cycling. At the same time, the micropores on the surface of the negative electrode material are filled, reducing the specific surface area of ​​the negative electrode material, which helps reduce side reactions of the negative electrode material.

[0066] In some embodiments, the total pore volume in the negative electrode material is taken as 100%, wherein the negative electrode material includes mesopores, and the pore volume ratio of mesopores is ≥80%; specifically, it can be 80%, 82%, 85%, 87%, 90%, 93%, 95%, or 99%, etc., and of course, other values ​​within the above range are also possible, which are not limited here. In the embodiments of this application, the pore volume ratio of mesopores is determined by nitrogen desorption. Limiting the pore volume ratio of mesopores in the negative electrode material to the above range indicates that after the carbon matrix is ​​filled with silicon material, the micropores of the negative electrode material are partially or completely filled, resulting in a change in its pore structure from micropore-dominated to mesopore-dominated. This change in pore structure is formed by the large amount of filling of micropores by silicon material, which improves the conductivity, capacity, and structural stability of the negative electrode material.

[0067] In some embodiments, the total volume of pores in the negative electrode material is taken as 100%. The negative electrode material includes macropores, and the volume percentage of macropores is ≤20%, specifically 20%, 18%, 15%, 12%, 10%, 8%, 7%, 5%, 4%, 3%, or 2%, etc., and other values ​​within the above range are also possible and are not limited here. A smaller proportion of macropores in the negative electrode material can increase its tap density and compaction density, reducing problems such as breakage and cracking during the pressing process when the negative electrode material is made into an electrode sheet, thus improving the processing performance of the negative electrode material. Furthermore, a smaller proportion of macropores in the negative electrode material indicates lower porosity. A negative electrode material with lower porosity has a higher carbon content (using a carbon matrix as an example here), resulting in good electronic conductivity and providing a well-developed conductive network, thus improving the conductivity of the negative electrode material.

[0068] Understandably, controlling the volume ratio of micropores, mesopores, and macropores in the negative electrode material within the above-mentioned range can improve the uniformity of silicon material distribution inside the negative electrode material. Since most of the pores are mesopores, they can effectively alleviate the volume expansion of silicon material, reduce the excessive local expansion stress caused by uneven volume changes of silicon material during cycling, which can lead to cracking and pulverization of the negative electrode material, and improve the cycling stability of the negative electrode material.

[0069] In some embodiments, the average pore size of the pores in the negative electrode material can be 0.45 nm to 50 nm, more specifically 0.5 nm to 30 nm, or even 1 nm to 15 nm. Exemplary values ​​include 0.45 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 8 nm, 10 nm, 15 nm, 25 nm, 30 nm, 40 nm, or 50 nm. It is understood that the average pore size of the negative electrode material is related to its surface density. Generally, a decrease in surface density, indicating an excessive number of micropores on the surface of the negative electrode material, will lead to a decrease in the average pore size. An average pore size within the above range indicates that the negative electrode material has a high surface density, which is beneficial for reducing the reaction between dissolved silicon particles and the electrolyte, and lowering the gas production value.

[0070] In some embodiments, the mass percentage of silicon in the negative electrode material is 20% to 60%. Specifically, the mass percentage of silicon in the negative electrode material is 20%, 25%, 30%, 40%, 45%, 50%, 55%, or 60%, and is not limited thereto. In this application, controlling the mass percentage of silicon in the negative electrode material within the above range can improve the specific capacity of the negative electrode material. Considering the particle stability and specific capacity of the negative electrode material, the mass percentage of silicon in the negative electrode material is preferably 40% to 55%.

[0071] In some embodiments, the average gas production of the negative electrode slurry prepared from the negative electrode material, placed in an environment of 25°C for one day, is ≤1 mL / g. Specifically, it can be 1 mL / g, 0.8 mL / g, 0.6 mL / g, 0.5 mL / g, 0.4 mL / g, 0.3 mL / g, 0.2 mL / g, or 0.1 mL / g, etc., and of course, other values ​​within the above range are also possible, without limitation. The gas production value of the negative electrode material in this application is controlled within the above range, indicating that most of the silicon material can be relatively uniformly distributed within the pores of the matrix material. Direct contact between the silicon material and the electrolyte is reduced, thereby reducing the side reactions of the dissolved silicon material with the electrolyte (i.e., silicon hydrolysis into silicates and hydrogen gas), and effectively reducing the gas production value of the negative electrode material. When the surface density of the negative electrode material is insufficient, the gas production value of the negative electrode material will increase significantly.

[0072] In some embodiments, the median particle size of the negative electrode material is 5 μm to 20 μm, specifically 5 μm, 8 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 18 μm, or 20 μm, etc., and of course, other values ​​within the above range are also possible, without limitation. It is understood that a median particle size of the negative electrode material within the above range can ensure the time for lithium-ion insertion and extraction, allowing the negative electrode material to achieve a rapid and sufficient lithium insertion state, thereby ensuring the charge and discharge performance of the lithium-ion battery.

[0073] In some embodiments, the particle size distribution of the negative electrode material satisfies: 0.9 ≤ (D 90 -D 10 ) / D 50 ≤5; specifically, it can be 0.9, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4, 4.5, or 5, etc., and of course, other values ​​within the above range are also possible, without limitation. The particle size distribution of the negative electrode material is within the above range. The larger particles and smaller particles of the negative electrode material can cooperate with each other, and the smaller particles fill the pores between the larger particles, which can improve the tap density of the negative electrode material.

[0074] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g, specifically 10m 2 / g, 8.9m 2 / g, 6.8m 2 / g, 5.5m 2 / g, 4.2m 2 / g、4m 2 / g、3m 2 / g, 2.5m 2 / g、2m 2 / g、1m 2 / g or 0.5m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Understandably, the specific surface area of ​​the negative electrode material affects the contact area between the negative electrode material and the electrolyte. When the specific surface area of ​​the negative electrode material is within the above range, the amount of lithium ions consumed by the SEI film formed during the first charge and discharge process of the lithium-ion battery can be reduced, thereby reducing the irreversible capacity loss of the lithium-ion battery.

[0075] In some embodiments, the compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 Specifically, it could be 0.8 g / cm³. 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm3 1.2g / cm 3 Or 1.3g / cm 3 "etc." can also be other values ​​within the above range, and no restrictions are imposed here.

[0076] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 Specifically, it can be 0.5g / cm 3 0.6g / cm 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 Or 1.5g / cm 3 "etc." can also be other values ​​within the above range, and no restrictions are imposed here.

[0077] In some embodiments, the powder conductivity of the negative electrode material at a pressure of 20 kN is 0.1 S / cm to 2 S / cm, specifically 0.1 S / cm, 0.5 S / cm, 0.8 S / cm, 1.0 S / cm, 1.2 S / cm, 1.5 S / cm, 2 S / cm, etc., or other values ​​within the above range, which are not limited here. With the powder conductivity of the negative electrode material controlled within the above range, very little silicon material is exposed on the surface of the negative electrode material. The silicon material is embedded within the matrix material particles, which can effectively improve the electrochemical performance of the negative electrode material.

[0078] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps:

[0079] Step S10: The substrate material is heated to a deposition temperature of 200℃~400℃ using plasma-enhanced chemical vapor deposition (PECVD), and a reaction gas is introduced, including a silicon source gas and a dilution gas. The deposition gas pressure is controlled at 10Pa~200Pa, the plasma excitation power is 20W~30W, and the vacuum degree is 3.0*10⁻⁶. -4 Pa ~ 4.0 * 10 -4 Pa, deposition time of 40 min to 60 min, to obtain the negative electrode material.

[0080] In some embodiments, the matrix material includes a carbon matrix, which includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

[0081] Understandably, the carbon matrix chosen from the above materials can all serve as a supporting framework and also have good electrical conductivity, ensuring the conductivity of the negative electrode material.

[0082] In some embodiments, the volume percentage of micropores in the carbon matrix is ​​≥80%, the volume percentage of mesopores is ≤20%, and the volume percentage of macropores is ≤1%. Specifically, the volume percentage of micropores can be 80%, 85%, 89%, 90%, 92%, 95%, or 98%, the volume percentage of mesopores can be 20%, 18%, 17%, 15%, 14%, 12%, 10%, 8%, 6%, 5%, 2%, or 1%, and the volume percentage of macropores can be 1%, 0.8%, 0.7%, 0.5%, 0.3%, 0.2%, or 0%. Understandably, the volume percentages of micropores, mesopores, and macropores in the carbon matrix are controlled within the above ranges. Since most of the pores in the carbon matrix are micropores, the size of the deposited silicon material can be adjusted, the dispersion uniformity of the carbon matrix and silicon material can be improved, the volume expansion of the silicon material can be reduced, and the cycle stability of the anode material can be enhanced.

[0083] In some embodiments, the total pore volume of the carbon matrix is ​​0.4 cm³. 3 / g~1.5cm 3 / g, specifically 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., can also be any of the special values ​​within the above range, without limitation.

[0084] In some embodiments, the specific surface area of ​​the carbon matrix is ​​200 m². 2 / g~3000m 2 / g, the specific surface area of ​​the negative electrode material can be 300m² 2 / g、500m 2 / g、800m 2 / g, 1000m 2 / g, 1500m 2 / g、2000m 2 / g、2500m 2 / g or 3000m2 / g, etc., can also be other values ​​within the above range, and are not limited here.

[0085] In some embodiments, the volume percentage of pores with a diameter of 5 nm or less in the carbon matrix is ​​≥90%. Specifically, the volume percentage of pores with a diameter of 5 nm or less in all pores can be 90%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, etc., and is not limited thereto. Understandably, the pores in the carbon matrix are mainly composed of pores with a diameter of 5 nm or less. This pore size distribution helps to regulate the size of the silicon material formed during the deposition process, improve the dispersion uniformity of the carbon matrix and silicon material, and reduce the segregation of silicon material.

[0086] In some embodiments, the matrix material includes a non-carbon matrix, which includes at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates.

[0087] In some embodiments, the metal oxide includes at least one of aluminum oxide, zirconium oxide, germanium dioxide, and manganese dioxide.

[0088] In some embodiments, the silicide includes at least one of silicon carbide and silicon nitride.

[0089] In some embodiments, the silicate includes at least one of cordierite, mullite, and zeolite.

[0090] In some embodiments, the phosphate includes at least one selected from aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate.

[0091] In some embodiments, the titanate includes at least one of calcium titanate, iron titanate, lithium titanate, and barium titanate.

[0092] In some embodiments, the total pore volume, specific surface area, and pore size distribution of the non-carbon matrix are similar to those of the carbon matrix, and will not be described in detail here.

[0093] In some implementations, using a non-carbon matrix to contain silicon materials can improve the overall strength of the anode material particles. In particular, during the coating and molding process of the anode material, it can improve the rolling resistance of the anode material, reduce particle breakage, and improve the cycle capacity retention rate of the anode material.

[0094] In some embodiments, the reaction gas includes a silicon source gas and a dilution gas. The silicon source gas includes at least one of silane, disilane, trisilane and tetrasilane, which can be selected according to actual needs and are not limited here.

[0095] In some embodiments, the radio frequency power supply frequency of the plasma is 13.56MHz. It should be noted that the radio frequency power supply frequency of the plasma is generally a fixed value, which is a frequency parameter built into the device. In other embodiments, the radio frequency power supply frequency of the plasma can also be 27.12MHz, 40.68MHz, etc., and is not limited here.

[0096] In some embodiments, the diluent gas includes at least one of hydrogen, argon, nitrogen, and helium. Preferably, the diluent gas includes hydrogen and argon.

[0097] In some implementations, the flow rate of the silicon source gas is 5 sccm to 50 sccm, specifically 50 sccm, 45 sccm, 30 sccm, 25 sccm, 20 sccm, 15 sccm, 10 sccm or 5 sccm, etc., or other values ​​within the above range, which are not limited here.

[0098] In some embodiments, the dilution gas includes hydrogen, and the flow rate of hydrogen is 20 to 200 sccm, specifically 20 sccm, 50 sccm, 60 sccm, 80 sccm, 100 sccm, 120 sccm, 150 sccm, 180 sccm or 200 sccm, etc. Of course, other values ​​within the above range are also possible, and no limitation is made here.

[0099] In some embodiments, the volume ratio of silicon source gas to dilution gas is 100:(50-500), specifically 100:50, 100:100, 100:150, 100:200, 100:250, 100:300, 100:350, 100:400, or 100:500, etc., which are not limited here. When the volume ratio of dilution gas is small, the silicon source gas can quickly decompose and form stable Si-Si bonds during the deposition process. The deposition rate is too fast, and the large number of Si-Si bonds formed are dispersed on the surface of the substrate material, blocking the pore structure of the substrate material surface, which is not conducive to inward deposition, resulting in most of the silicon material being deposited on the surface. When the volume ratio of dilution gas is large, the silicon material easily transforms from the first phase to the second phase. The volume expansion of the second phase silicon material exhibits anisotropy, exacerbating the expansion effect of the anode material.

[0100] Taking hydrogen as the dilution gas and silane SiH4 as the silicon source gas as an example, the reaction mechanism during the vapor deposition process is shown in equation (1):

[0101]

[0102] During vapor deposition, H atoms bombard the surface of the substrate material, causing more Si-H bonds to react with hydrogen, breaking the Si-H bonds to form Si-Si bonds. Alternatively, H atoms can cause weaker Si-Si bonds to break and recombine into strong, regular Si-Si bonds, which is a transformation from the first phase to the second phase or crystalline phase.

[0103] As the SiH4 concentration increases, the forward reaction rate r1 increases, resulting in an excessively fast deposition rate. The deposited Si atoms do not have enough time to form strong, stable bonds, and the silicon material primarily exists in the first phase. Conversely, as the SiH4 concentration decreases, the H2 concentration increases. Hydrogen decomposes under plasma conditions to generate more [H] atoms. The presence of [H] atoms increases the reverse reaction rate r2, thereby improving crystallinity and reducing the deposition rate.

[0104] When the diluent gas includes argon, and the silicon source gas is silane SiH4, the reaction mechanism during the vapor deposition process is shown in equations (2) to (5) below:

[0105] Ar+SiH4→SiH3+H+Ar(k=1.4*10 -10 cm 3 / s) Equation (2)

[0106] Ar+SiH3→SiH2+H+Ar(k=1.0*10 -10 cm 3 / s) Equation (3)

[0107] Ar + SiH₂ → SiH + H + Ar (k = 1.0 * 10⁻⁶) -10 cm 3 / s) Equation (4)

[0108] Ar + SiH → Si + H + Ar (k = 1.0 * 10⁻⁶) -10 cm 3 / s) Equation (5).

[0109] Specifically, at higher argon concentrations, the low-hydrogen silicon atoms generated by plasma excitation are easier to nucleate than SiH3. On the other hand, the collision between metastable argon atoms and the matrix material will cause a quenching reaction, which can transfer energy to the matrix material, which is conducive to the formation of the second phase silicon material. This can slightly increase the deposition rate of silicon material. However, the increase in argon concentration will reduce the concentration of silicon source gas in the reaction gas. A large number of metastable argon atoms will undergo secondary reactions with the silicon source gas as shown in equations (3)-(5) to generate low-hydrogen silicon atoms (SiH2, SiH, Si, mainly SiH2), which are easy to nucleate in the gas phase and form large dust particles that are lost, thereby reducing the deposition rate. When the argon concentration is too low, the deposition rate increases slightly as the argon dilution concentration decreases. This is because the metastable argon atoms undergo a quenching reaction with silane molecules as shown in equation (2), which promotes the decomposition of silane to produce SiH3, which slightly increases the growth rate of Si and increases the tap density of the negative electrode material. Therefore, argon, as a dilution gas, is beneficial to the formation of silicon materials in the second phase, but it is difficult to replace hydrogen as a dilution gas.

[0110] In one embodiment, the deposition temperature is 200–400°C, specifically 200°C, 250°C, 280°C, 300°C, 350°C, 380°C, or 400°C, etc., and of course, other values ​​within the above range are also acceptable, without limitation. When the deposition temperature is too low, the ionized Si atoms or atomic groups have low surface activity and are not easy to find low-energy sites to form bonds and crystallize, resulting in poor deposition efficiency. When the deposition temperature is too high, the Si atoms in the matrix material at higher temperatures have larger diffusion free energy, enabling them to form stable bonds. Higher temperatures also facilitate the release of [H] atoms and the decomposition of the active groups in the above formula (1), thereby increasing the deposition rate of silicon materials. However, excessively high deposition temperatures will cause the first phase of silicon material to transform into the second phase of silicon material, resulting in a higher crystallinity of silicon material in the anode material, which is not conducive to improving the cycle stability of the anode material.

[0111] In some embodiments, the deposition pressure is 10 Pa to 200 Pa, specifically 10 Pa, 20 Pa, 30 Pa, 50 Pa, 80 Pa, 100 Pa, 120 Pa, 150 Pa or 200 Pa, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0112] In some embodiments, the plasma power is 20W to 30W or 90W to 100W. Specifically, the plasma power can be 20W, 25W, 30W, 90W, 92W, 95W, or 100W, or other values ​​within the above range, which are not limited here.

[0113] When the deposition pressure is in the range of 10 Pa to 200 Pa, the degree of crystallinity of silicon material first increases and then decreases with the increase of plasma power. Understandably, as shown in equation (1), when the plasma power is in the range of 20 W to 30 W, as the plasma power increases, there are more high-energy electrons in the reaction chamber, and more SiH4 decomposes to generate [SiHm], which in turn generates more high-energy hydrogen. The etching ability of [H] plasma on silicon material is also enhanced, and weak Si-Si bonds break and recombine to form strong and regular Si-Si. As the amount of decomposed [SiHm] increases, the energy increases, which will promote the crystallization of silicon material. Excessive crystallization of silicon material will lead to an aggravated expansion effect of the negative electrode material, and the particle breakage of the negative electrode material will be aggravated during cycling. When the plasma power is further increased to 90W-100W, more SiH4 decomposes, resulting in an excessively fast deposition rate. The ionized Si atoms or atomic groups do not have enough time to find the lowest energy positions to form bonds, which is detrimental to crystallization. High-energy hydrogen atoms will etch away the already attached silicon atoms, reforming them as vaporized [SiHm] groups, which is also unfavorable for silicon material crystallization. Therefore, the degree of crystallinity of the silicon material decreases again. Thus, by controlling the plasma power within the aforementioned range, this application can control the area ratio of the first and second phases of silicon material in the deposited silicon material, enabling the anode material to possess both high cycle stability and high capacity.

[0114] In some implementations, the deposition time is 40 min to 60 min, and the specific time can be 40 min, 45 min, 50 min, 55 min and 60 min, or other values ​​within the range. It can be selected according to actual needs and is not limited here.

[0115] Furthermore, the method may also include: step S20, coating the deposited product with a coating material to obtain a negative electrode material.

[0116] In some embodiments, the coating material includes carbon material, and the thickness of the carbon layer formed by the carbon material is 1 nm to 300 nm. It is understood that the carbon layer can reduce the dissolution of silicon material, thereby reducing the amount of gas generated by the reaction of the dissolved silicon material with the electrolyte. This is beneficial for the negative electrode material to maintain the stability of the particle structure during cycling and improve the charge and discharge performance of the negative electrode material.

[0117] Thirdly, embodiments of the present invention also provide a battery. Figure 1 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 1As shown, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0118] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0119] In some embodiments, the positive current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0120] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0121] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), and lithium manganese oxide (LiMn2O3). 4) Lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0122] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector 201 may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the aforementioned preparation method.

[0124] The battery provided in this application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid-state electrolyte battery, etc., and is not limited thereto.

[0125] Those skilled in the art will understand that the battery preparation methods described above are merely embodiments. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0126] The present application will be further described below with reference to several embodiments. However, the embodiments of the present application are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the main claims.

[0127] Test method:

[0128] 1. Precession electron diffraction test of negative electrode material:

[0129] A WWFI-T105 precession electron diffractometer from NanoMEGAS (Belgium) mounted on a double-spherical-aberration-corrected transmission electron microscope (TEM) was used to rapidly acquire PED patterns point-by-point across the region of interest (600*600nm) with an electron beam precession angle of 0.6° and a spot diameter of 5nm, using a step size of 4nm. The results were then calibrated offline. Further surface analysis and visualization were performed automatically using ASTAR MapViewer software and Channel 5 software package to identify and index the electron diffraction patterns, and to automatically generate crystal orientation maps and phase distribution maps.

[0130] 2. XRD testing of negative electrode materials:

[0131] The negative electrode material was fabricated into a sheet and tested using an X-ray diffraction analyzer. The fitting range was 26–30°. The sample was scanned and fitted to obtain the FWHM (half-width at half maximum) and half-angle of the negative electrode material within the range of 28.4° ± 0.5°. The grain size of the silicon material was calculated using the following formula:

[0132] c = 0.89λ / FWHM*cosθ, where c is the grain size of silicon material in nm; λ is the wavelength of radiation, which is 0.154056 nm for copper target used in this application; FWHM is the full width at half maximum (FWHM); and θ is the half diffraction angle.

[0133] 3. Test methods for pore diameter and pore volume ratio:

[0134] The tests were conducted using an ASAP2460 instrument from Microtek (USA). The pore volume V was determined using the BJH Desorption Cumulative Volume of Pores model. Calculated within the aperture range.

[0135] Micropore and mesopore analysis was performed using a Micromeretics ASAP 2460. At liquid nitrogen temperature, the equilibrium adsorption amount of nitrogen on an object's surface is related to its pore size and other characteristics. By combining the law of adsorption amount changing with relative pressure during the adsorption process, various models can be fitted to calculate the pore size. Measurements can be taken using nitrogen adsorption (micropore and mesopore) or mercury porosimeter (macropore). Nitrogen adsorption and mercury porosimeter methods can also obtain information such as pore size distribution and average pore size. Specifically, a certain amount of sample is weighed and placed into a special bubble tube for specific surface area analysis. The sample is purged with nitrogen at 300°C for a certain period of time in a degassing station. After degassing, the sample is cooled to room temperature, and the actual mass of the sample is weighed. The special bubble tube containing the sample is then installed into the specific surface area and pore size analyzer. After inputting the sample mass, the specific surface area and pore size of the sample are measured. For concentrations below 0.01, quantitative gas injection is performed at 20 mL / g. For concentrations above 0.01, fixed-point gas injection is performed at intervals of 0.01 to 0.10, with intervals of 0.01; at intervals of 0.02, with intervals of 0.02; and at intervals of 0.05, with intervals of 0.20 to 1.0. Degassing is then performed at intervals of 0.05, from 1.00 to 0.15.

[0136] 4. Method for testing the specific surface area of ​​the negative electrode material and the negative electrode material after removing silicon:

[0137] The specific surface area was measured using a McTriStar3000 specific surface area and pore size analyzer from the USA.

[0138] 5. Gas production test:

[0139] Carboxymethyl cellulose (CMC) was dispersed in water at a mass ratio of 1.4% and then glued. After uniform dispersion, 10g of glue solution was mixed with 10g of negative electrode material to obtain a slurry. The slurry was then placed in an aluminum-plastic film bag, and the mass of the slurry was recorded. The bag was then sealed to form a sealed aluminum-plastic film bag.

[0140] The sealed aluminum-plastic film bag was fixed to the bottom of the container and completely submerged in water. The volume of the aluminum-plastic film bag was recorded. After a fixed time (24h), the volume of the aluminum-plastic film bag was recorded again. The gas production of the silicon anode material was calculated based on the change in the volume of the aluminum-plastic film, in mL / g.

[0141] 6. Test of silicon mass percentage in anode materials:

[0142] Taking carbon as the matrix material as an example, a box-type atmosphere furnace (model: SA2-9-17TP) is used to ignite the sample in an oxygen atmosphere, causing silicon and silicon suboxide in the sample to react to form silicon dioxide. The carbon is then burned and released as carbon dioxide. The mass percentage of silicon in the negative electrode material is calculated by weighing. Specific operating procedures:

[0143] Weigh 1.0000g to 1.2000g of negative electrode material into an alumina crucible, accurate to 0.1mg. Weigh two parallel samples for each sample. Set the muffle furnace heating program: initial temperature 30℃, rise to 400℃ in 30 minutes, and hold at 400℃ for 60 minutes. This step is to thoroughly remove moisture and low-boiling-point volatiles. Then continue for 60 minutes to rise to 900℃ and hold at 900℃ for 120 minutes to remove carbon and other volatile impurities. Then continue for 30 minutes to rise to 1100℃ and hold at 1100℃ for 480 minutes to fully oxidize silicon or silicon suboxide to silicon dioxide. Finally, set the stop, i.e., turn off the heating and begin cooling.

[0144] 7. Test of carbon mass percentage in negative electrode materials:

[0145] Taking carbon as the matrix material as an example, the sample was burned in a high-temperature oxygen-rich state using the German Bruker / Elt infrared carbon-sulfur analyzer G4ICARUS HF / CS-i. The carbon element contained in the sample was oxidized into carbon dioxide, and the generated gas entered the infrared detector with the carrier gas. The carbon content was quantitatively calculated by statistically analyzing the change in the intensity of the infrared absorption wavelength of the carbon dioxide signal.

[0146] 8. Powder conductivity test:

[0147] The MCP-PD51 powder conductivity meter from Mitsubishi Chemicals of Japan can measure the conductivity of powder at five pressure points: 4, 8, 12, 16, and 20 kN. The computer then automatically calculates the resistivity of the powder. The specific testing method involves placing the sample into a circular mold cavity. Four equally spaced probes, numbered 1, 2, 3, and 4, are fixed to a ceramic disc at the bottom center of the cavity. Pressure is applied to the sample using a cylindrical top post with the same diameter as the cavity, causing the four probe electrodes on the ceramic disc at the bottom of the sample to come into close contact and be gradually compressed. A current I flows between probes numbered 1 and 4, resulting in a potential difference V between probes numbered 2 and 3. By using the dynamic four-probe method to test the resistance of circular block materials under different pressures, the resistivity and conductivity of the powder sample under different pressures can be accurately calculated, and the relationship curve between pressure and conductivity can be obtained. This instrument can be used to measure the resistance of powder, and then the computer can automatically calculate the conductivity and resistivity of the powder.

[0148] 9. Tap density test of negative electrode material:

[0149] Using the Meconta DAT-6-220 tap density meter, place the sample of the specified mass in the graduated cylinder, vibrate it for the specified number of times (3000 times for routine testing), read the volume of the graduated cylinder after tapping, and calculate the tap density.

[0150] 10. Compaction density test of negative electrode material:

[0151] Using a CARVER 4350.22 powder compaction density tester from the USA, a sample of a specified mass m was placed in a mold and a pressure of 1.0T was applied. After holding the pressure for 30 seconds, the pressure was released and the thickness was measured. The compaction density was then calculated.

[0152] 11. Test methods for particle size and particle size distribution:

[0153] The volumetric cumulative particle size distribution was determined using a Malvern laser particle size analyzer (Mastersizer 3000) and laser diffraction method. D10 represents the particle size corresponding to a cumulative particle size distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative particle size distribution percentage of 90%.

[0154] 12. Electrical performance testing:

[0155] The following method was used to test the coin cell: A negative electrode slurry was prepared by mixing negative electrode material, conductive carbon black, and polyacrylic acid copolymer (PPA) in a mass ratio of 70:15:15. This slurry was then coated onto copper foil and dried to form the negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the coin cell was assembled in a glove box filled with Ar gas. The coin cell was then charged and discharged at a current density of 0.1C within a charge-discharge range of 0.01V-5V to obtain the initial reversible specific capacity and initial coulombic efficiency.

[0156] A negative electrode slurry was prepared by mixing negative electrode material with graphite, carbon black Super-P, conductive graphite KS-6, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR in a mass ratio of 92:2:2:2:2. This slurry was coated onto copper foil and dried to form the negative electrode sheet. The proportions of Si-C and graphite in the Si-C composite material and graphite mixture were determined by their initial reversible specific capacity and the required combined capacity. A coin cell was assembled using a lithium metal sheet as the counter electrode in an Ar-filled glove box. The coin cell was subjected to 50 repeated charge-discharge cycles at a current density of 1C within a charge-discharge range of 0.01V-5V to obtain the capacity retention rate and electrode thickness expansion rate after 50 cycles.

[0157] Example 1:

[0158] (1) The porous carbon matrix is ​​placed in the reaction chamber of a plasma-enhanced chemical vapor deposition furnace, and the porous carbon matrix is ​​heated to the deposition temperature of 300℃. The vacuum degree P0 in the reaction chamber is controlled to be 3.5*10. -4Pa, RF power supply frequency is 13.56MHz, plasma power is 25W;

[0159] (2) Silane and hydrogen are introduced for vapor phase deposition, wherein the silane flow rate is 20 sccm, the hydrogen flow rate is 100 sccm, the deposition pressure is controlled at 133.3 Pa, and the deposition time is 50 min to obtain the negative electrode material.

[0160] The relevant test data of the examples and comparative examples were obtained according to the above test methods. The specific process parameters are detailed in Table 1, and the test results are shown in Tables 2 to 5 below:

[0161] Table 1. Preparation process parameters of negative electrode materials

[0162]

[0163] Table 2. Parameters of the negative electrode material

[0164]

[0165]

[0166] Table 3. Parameters of Anode Materials

[0167]

[0168]

[0169] Table 4. Anode materials after Si particle removal

[0170]

[0171] Table 5. Performance test results of examples and comparative examples

[0172]

[0173]

[0174] According to the test data of Examples 1 to 18, the area ratio A of the region where the first phase silicon material is located is ≥70%, and the area ratio B of the region where the second phase silicon material is located is 0 < B ≤ 30%. The silicon material in the negative electrode material is mainly in the first phase state, which can make greater use of the structural stability brought by the first phase silicon material, so that the negative electrode material has a more stable capacity and a lower expansion effect. Furthermore, the use of a porous matrix material can further alleviate the volume expansion of the silicon material, effectively alleviate the volume expansion of the silicon material during cycling, reduce particle breakage of the negative electrode material, and comprehensively improve the cycling performance of the negative electrode material.

[0175] Based on the test data of Comparative Example 1, it can be seen that when the deposition temperature rises to 500℃, a large portion of the first phase silicon material is transformed into the second phase silicon material. The area ratio A of the region where the first phase silicon material is located is 40%, and the area ratio B of the region where the second phase silicon material is located is 60%. The area ratios of the first and second phase silicon materials in the negative electrode material of Comparative Example 1 are not within the above range, which is not conducive to improving the cycle stability of the negative electrode material. The expansion rate of the negative electrode material in Comparative Example 1 is significantly higher than that of the negative electrode material in Example 1.

[0176] Based on the test data of Comparative Example 2, it can be seen that when the silane flow rate is too low, the area ratio A of the region where the silicon material of the first phase is located is 55%, and the area ratio B of the region where the silicon material of the second phase is located is 45%. The area ratios of the regions where the silicon material of the first phase and the silicon material of the second phase are located in the negative electrode material of Comparative Example 2 are not within the above ranges. Compared with the negative electrode material in Example 1, the expansion rate of the negative electrode material in Comparative Example 2 is significantly increased, and the capacity retention rate of the negative electrode material is significantly decreased.

[0177] Based on the test data of Comparative Example 3, it can be seen that when the plasma power is 60W, due to the etching of silicon material by a large amount of [H] plasma, part of the first phase silicon material is transformed into the second phase silicon material. The area ratio of the first phase silicon material in the negative electrode material is 60%, and the area ratio of the second phase silicon material is 40%. The area ratio of the first phase silicon material and the second phase silicon material in the negative electrode material of Comparative Example 3 is not within the above range. Compared with the negative electrode material in Example 1, the expansion rate of the negative electrode material in Comparative Example 3 is significantly increased, and the capacity retention rate of the negative electrode material is significantly decreased.

[0178] According to the test data of Examples 1, 11 and 12, adjusting the deposition pressure and deposition time during silicon deposition can adjust the area ratio of the silicon material in the first phase of the anode material. As long as the area ratio of the silicon material in the first phase to the silicon material in the second phase is controlled within the above range, the anode material can have a more stable capacity and a lower expansion effect.

[0179] According to the test data of Examples 1 and 12-17, different substrate materials have little effect on the deposited silicon material. However, different substrate materials have different conductivity, so they have a slight effect on the powder conductivity of the negative electrode material and the specific capacity of the negative electrode material.

[0180] According to the test data of Example 1 and Comparative Example 4, when the diluent gas is argon, the flow rate of argon is 50 sccm. Due to the presence of argon, some of the first phase silicon material in the negative electrode material is easily transformed into the second phase silicon material. The area ratio of the first phase silicon material in the negative electrode material is 62%, and the area ratio of the second phase silicon material is 38%. The area ratio of the first phase silicon material and the second phase silicon material in the negative electrode material of Comparative Example 4 is not within the above range, which is not conducive to improving the cycle stability of the negative electrode material.

[0181] The above description, based on the embodiments shown in the drawings, details the structure, features, and effects of this application. The above description is only a preferred embodiment of this application, but this application does not limit the scope of implementation to what is shown in the drawings. Any changes made in accordance with the concept of this application, or modifications to equivalent embodiments, that do not exceed the spirit covered by the specification and drawings, should be within the protection scope of this application.

Claims

1. A negative electrode material, characterized in that, It includes a matrix material and a silicon material, with at least a portion of the silicon material located within the matrix material, wherein the silicon material comprises a first phase and a second phase; The negative electrode material was measured by precession electron diffraction: Based on the region where the silicon material is located, the area ratio of the region where the silicon material of the first phase is located is A, where A ≥ 70%, and the area ratio of the region where the silicon material of the second phase is located is B, where 0 < B ≤ 30%.

2. The negative electrode material as described in claim 1, characterized in that, The substrate material has pores, and at least a portion of the silicon material is located within the pores of the substrate material.

3. The negative electrode material according to claim 2, characterized in that, The anode material that removes silicon material satisfies at least one of the following characteristics: (1) The anode material with removed silicon material has micropores, and the pore volume ratio of the micropores is ≥80%; (2) The negative electrode material with silicon removed has mesopores, and the pore volume ratio of mesopores is ≤20%; (3) The anode material with removed silicon material has large pores, and the pore volume ratio of the large pores is ≤1%; (4) The total pore volume of the anode material after removing the silicon material is 0.4 cm³. 3 / g~1.5cm 3 / g; (5) The specific surface area of ​​the anode material with removed silicon material is 200m². 2 / g~3000m 2 / g; (6) In the anode material with silicon removed, the pore volume ratio of pores with a pore size of less than 5 nm is ≥90%.

4. The negative electrode material as described in claim 1, characterized in that, The matrix material includes a carbon matrix, which includes one or more of the following: artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microspheres, carbon nanotubes, carbon nanofibers, and graphene.

5. The negative electrode material according to claim 1, characterized in that, The matrix material includes a non-carbon matrix, which includes at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that, In the XRD pattern of the negative electrode material, the negative electrode material has a dome-shaped diffuse peak in the range of 28.4°±0.5°, and the grain size of the silicon material is c≤1nm.

7. The negative electrode material according to any one of claims 1 to 5, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g; (2) The average pore size of the negative electrode material is 0.4 nm to 50 nm; (3) The negative electrode material includes micropores, and the pore volume ratio of the micropores is ≤10%; (4) The negative electrode material includes mesopores, and the pore volume of the mesopores accounts for ≥80%; (5) The negative electrode material includes macropores, and the volume ratio of macropores is ≤20%.

8. The negative electrode material according to any one of claims 1 to 5, characterized in that, The negative electrode slurry prepared from the negative electrode material has an average gas production of ≤1 mL / g per day when placed in an environment of 25°C.

9. The negative electrode material according to any one of claims 1 to 5, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The median particle size D of the negative electrode material 50 The thickness ranges from 5μm to 20μm. (2) The particle size distribution of the negative electrode material satisfies: 0.9 ≤ (D 90 -D 10 ) / D 50 ≤5; (3) The specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g; (4) The compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 ; (5) The tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 ; (6) The powder conductivity of the negative electrode material under a pressure of 20 kN is 0.1 S / cm to 2 S / cm; (7) The mass percentage of silicon in the negative electrode material is 20% to 60%.

10. A battery, characterized in that, The battery includes the negative electrode material as described in any one of claims 1 to 9.

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