Negative electrode material and battery

Abstract

The application relates to a negative electrode material and a battery. The negative electrode material comprises a silicon-based material and a carbon material, and at least part of the carbon material is located on the surface of the silicon-based material. The negative electrode material has an open pore, and the micropore activation degree of the negative electrode material satisfies 0.001 < y <= 1.5. The negative electrode material has a proper amount of micropore structure, which is beneficial to the infiltration of electrolyte into the negative electrode material and the transmission of lithium ions in the micropore of the negative electrode material, improves the ion diffusion rate of the negative electrode material, and improves the rate performance of the negative electrode material. On the other hand, the catalytic effect of the micropore on the side reaction of the negative electrode material is reduced, the consumption of excessive electrolyte and the active substance of the silicon-based material is reduced, the first coulomb efficiency and the cycle life of the negative electrode material are improved. The negative electrode material can balance the rate performance, the first coulomb efficiency and the cycle life, and finally improve the comprehensive electrochemical performance of the negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of negative electrode materials technology, and more particularly to negative electrode materials and batteries. Background Technology

[0002] As the application of lithium-ion batteries continues to expand and deepen, the requirements for their performance are also increasing, especially in terms of energy density. Traditional graphite anode materials are no longer sufficient to meet the growing market demand. As a high-specific-capacity anode material, silicon-based anode materials have attracted much attention in recent years. The theoretical specific capacity of silicon-based anode materials is as high as 4200 mAh / g. However, compared with other anode materials, silicon-based anode materials have limited their practical applications due to their lower initial coulombic efficiency, poorer conductivity, and poorer cycle and rate performance. Summary of the Invention

[0003] This application provides a negative electrode material and a battery. The negative electrode material has a suitable micropore activation degree, which can achieve a balance between improving rate performance, coulombic efficiency and cycle life, thereby improving the overall electrochemical performance of the negative electrode material.

[0004] In a first aspect, embodiments of this application provide a negative electrode material, the negative electrode material comprising a silicon-based material and a carbon material, wherein at least a portion of the carbon material is located on the surface of the silicon-based material; The negative electrode material has openings, wherein the total specific surface area of ​​the openings with a pore size ≥ 2 nm in the negative electrode material is x 1 m². 2 / g, the total specific surface area of ​​all openings in the negative electrode material is x2m 2 / g; Add 5g of the negative electrode material to the mixed acid solution for etching until the etching gas generation ends, and record the etching time as H hours; wherein, the mixed acid solution is obtained by mixing 300mL of hydrofluoric acid with a mass fraction of 40%±2% and 100mL of concentrated nitric acid with a mass fraction of 68%; The micropore activation degree of the negative electrode material Furthermore, the negative electrode material satisfies the condition: 0.001 < y ≤ 1.5.

[0005] In some implementations, 0.1 ≤ x1 ≤ 25.

[0006] In some implementations, 0.3 ≤ x2 ≤ 35.

[0007] In some implementations, 0.5 ≤ H ≤ 72.

[0008] In some embodiments, the oil absorption value of the negative electrode material is 35 mL / 100g to 65 mL / 100g.

[0009] In some embodiments, the silicon-based material includes silicon and oxygen, and the atomic ratio of oxygen to silicon in the negative electrode material is x, where 0 < x < 2.2.

[0010] In some embodiments, the silicon-based material comprises silicon oxide, the silicon oxide having the general formula SiO. x , 0 < x ≤ 2.

[0011] In some embodiments, the silicon-based material comprises a silicon oxide and a compound of a metal element M, wherein the metal element M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr, Ca, Al, Na, Mn, and Zn.

[0012] In some embodiments, the compound of the metal element M includes at least one of the silicates of the metal element M and the oxides of the metal element M.

[0013] In some embodiments, the carbon material includes at least one of amorphous carbon, graphitized carbon, graphite, graphene, carbon nanotubes, and carbon fibers.

[0014] In some embodiments, the cumulative particle size distribution of the negative electrode material satisfies D20-D10≤4μm and D90-D80≤8μm.

[0015] In some embodiments, the volumetric particle size D50 of the negative electrode material is 1 μm ≤ D50 ≤ 15 μm.

[0016] In some embodiments, the carbon content in the negative electrode material is 1% to 97% by mass.

[0017] In some embodiments, the silicon content in the negative electrode material is 3% to 99% by mass.

[0018] In some embodiments, the pH of the negative electrode material is 5 to 12.

[0019] In some embodiments, the true density of the negative electrode material is 2.0 g / cm³. 3 ~3.4g / cm 3 .

[0020] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5 g / cm 3 .

[0021] Secondly, embodiments of this application provide a battery, the battery comprising the negative electrode material described in the first aspect.

[0022] Compared with the prior art, the technical solution of this application has at least the following beneficial effects: The negative electrode material provided in this application comprises a silicon-based material and a carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The negative electrode material has openings, which provide space for the volume expansion of the silicon-based material, reducing cracks and fractures caused by volume changes and improving the structural stability of the negative electrode material. When the proportion of pores with a diameter less than 2 nm (i.e., micropores) in the openings is too high, it leads to an increase in the specific surface area of ​​the negative electrode material, resulting in more active sites in contact with the electrolyte and an increase in side reactions on the surface of the negative electrode material. When the proportion of micropores in the openings is too low, the effective contact area between the negative electrode material and the electrolyte is reduced, the capillary effect of the electrolyte wetting the negative electrode material on the electrolyte is weakened, resulting in obstructed lithium-ion transport, a slower lithium-ion diffusion rate, and affecting the rate performance of the negative electrode material. In this application, x1 represents the total specific surface area of ​​pores with an aperture greater than or equal to 2 nm in the negative electrode material, x2 represents the total specific surface area of ​​all pores in the negative electrode material, and x2 - x1 represents the specific surface area of ​​the negative electrode material entirely contributed by micropores. The micropore activation degree of the negative electrode material is defined as... Wherein, H represents the gas generation time value of the negative electrode material during etching in a mixed acid solution. A longer gas generation time value indicates lower carbon material coating integrity and more pores on the surface of the negative electrode material, leading to more silicon-based material reacting with the mixed acid solution. Conversely, a shorter gas generation time value indicates better carbon material coating integrity on the surface of the negative electrode material, resulting in decreased electrolyte wetting ability and hindering lithium-ion transport. In this application, the micropore activation degree y of the negative electrode material is controlled between 0.001 and 1.5, excluding 0.001. The negative electrode material possesses an appropriate number of micropores, which on the one hand facilitates electrolyte wetting of the negative electrode material, promotes lithium-ion transport within the micropores, improves the ion diffusion rate of the negative electrode material, and enhances its rate performance; on the other hand, it reduces the catalytic effect of micropores on side reactions of the negative electrode material, reducing the consumption of excess electrolyte and active material by side reactions, thereby improving the coulombic efficiency and cycle life of the negative electrode material. The anode material of this application can achieve a balance between improving rate performance, coulombic efficiency and cycle life, ultimately improving the overall electrochemical performance of the anode material. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 A schematic diagram of the discharge state of a battery provided in an embodiment of this application; Figure 2 This is a scanning electron microscope (SEM) image of the negative electrode material of Embodiment 1 of this application. Detailed Implementation

[0025] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0028] 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.

[0029] In a first aspect, this application provides a negative electrode material, which includes a silicon-based material and a carbon material, wherein at least a portion of the carbon material is located on the surface of the silicon-based material; The negative electrode material has openings, wherein the total specific surface area of ​​the openings with a pore size ≥ 2 nm in the negative electrode material is x 1 m². 2 / g, the total specific surface area of ​​all openings in the negative electrode material is x2m 2 / g; Add 5g of the negative electrode material to the mixed acid solution for etching until the etching gas generation ends, and record the etching time as H hours; wherein, the mixed acid solution is obtained by mixing 300mL of hydrofluoric acid with a mass fraction of 40%±2% and 100mL of concentrated nitric acid with a mass fraction of 68%; The micropore activation degree of the negative electrode material Furthermore, the negative electrode material satisfies the condition: 0.001 < y ≤ 1.5.

[0030] The negative electrode material provided in this application comprises a silicon-based material and a carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The negative electrode material has openings, which provide space for the volume expansion of the silicon-based material, reducing cracks and fractures caused by volume changes and improving the structural stability of the negative electrode material. When the proportion of pores with a diameter less than 2 nm (i.e., micropores) in the openings is too high, it leads to an increase in the specific surface area of ​​the negative electrode material, resulting in more active sites in contact with the electrolyte and an increase in side reactions on the surface of the negative electrode material. When the proportion of micropores in the openings is too low, the effective contact area between the negative electrode material and the electrolyte is reduced, the capillary effect of the electrolyte wetting the negative electrode material on the electrolyte is weakened, resulting in obstructed lithium-ion transport, a slower lithium-ion diffusion rate, and affecting the rate performance of the negative electrode material. In this application, x1 represents the total specific surface area of ​​pores with an aperture greater than or equal to 2 nm in the negative electrode material, x2 represents the total specific surface area of ​​all pores in the negative electrode material, and x2 - x1 represents the specific surface area of ​​the negative electrode material entirely contributed by micropores. The micropore activation degree of the negative electrode material is defined as... Wherein, H represents the gas generation time value of the negative electrode material during etching in a mixed acid solution. A longer gas generation time value indicates lower carbon material coating integrity and more pores on the surface of the negative electrode material, leading to more silicon-based material reacting with the mixed acid solution. Conversely, a shorter gas generation time value indicates better carbon material coating integrity on the surface of the negative electrode material, resulting in decreased electrolyte wetting ability and hindering lithium-ion transport. In this application, the micropore activation degree y of the negative electrode material is controlled between 0.001 and 1.5, excluding 0.001. The negative electrode material possesses an appropriate number of micropores, which on the one hand facilitates electrolyte wetting of the negative electrode material, promotes lithium-ion transport within the micropores, improves the ion diffusion rate of the negative electrode material, and enhances its rate performance; on the other hand, it reduces the catalytic effect of micropores on side reactions of the negative electrode material, reducing the consumption of excess electrolyte and active material by side reactions, thereby improving the coulombic efficiency and cycle life of the negative electrode material. The anode material of this application can achieve a balance between improving rate performance, coulombic efficiency and cycle life, ultimately improving the overall electrochemical performance of the anode material.

[0031] In some embodiments, the micropore activation degree y of the negative electrode material is 0.001~1.5, excluding 0.001. Specifically, it can be 0.002, 0.008, 0.01, 0.05, 0.1, 0.3, 0.5, 0.8, 1.0, 1.3, or 1.5, etc., and of course, other values ​​within the above range are also possible, without limitation. When y is greater than 1.5, it indicates that there are too many micropores in the openings of the negative electrode material, resulting in too many reaction sites on the surface of the negative electrode material, exacerbating the side reactions between the negative electrode material and the electrolyte, and reducing the coulombic efficiency and cycle life of the negative electrode material. When y is less than or equal to 0.001, it indicates that there are too few micropores in the openings of the negative electrode material, which is not conducive to the transport of lithium ions in the micropores of the negative electrode material, resulting in a decrease in the ion diffusion rate of the negative electrode material and a deterioration in the rate performance of the negative electrode material.

[0032] This application controls the value of 0.001 < y ≤ 1.5, resulting in a suitable number of micropores in the negative electrode material. This effectively improves the wetting effect of the electrolyte on the negative electrode material, leading to better rate performance. Simultaneously, side reactions in the negative electrode material are controlled, reducing the consumption of silicon-based materials and electrolyte during charge and discharge, and improving the initial coulombic efficiency and cycle life of the negative electrode material.

[0033] In some implementations, 0.1 ≤ x1 ≤ 25, and the total specific surface area x1 of pores with a diameter ≥ 2 nm in the negative electrode material can specifically be 0.1 m. 2 / g, 0.5 m 2 / g、1 m 2 / g、3 m 2 / g、8 m 2 / g、10 m 2 / g、15 m 2 / g、18 m 2 / g、20 m 2 / g、23 m 2 / g or 25 m 2 / g, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Preferably, the value range of x1 is 0.5 m. 2 / g ~15 m 2 / g.

[0034] In some implementations, 0.3 ≤ x2 ≤ 35, and the total specific surface area x2 of all openings in the negative electrode material ranges from 0.3 m². 2 / g ~35 m 2 / g, specifically 0.3 m 2 / g, 0.7 m 2 / g、1 m 2 / g、5 m 2 / g、10 m2 / g、15 m 2 / g、18m 2 / g、23 m 2 / g、25 m 2 / g、30 m 2 / g or 35 m 2 / g, etc., and of course, other values ​​within the above range are also possible, and are not limited here. If the total specific surface area of ​​the pores in the negative electrode material is too large, the side reactions between the negative electrode material and the electrolyte will be aggravated, and the first-time coulombic efficiency of the negative electrode material will decrease. If the total specific surface area of ​​the pores in the negative electrode material is too small, the electrolyte will have difficulty effectively wetting the negative electrode material, and the lithium-ion transport performance of the negative electrode material will decrease. This application controls the total specific surface area of ​​the pores in the negative electrode material within the above range, which is beneficial for the negative electrode material to obtain a higher first-time coulombic efficiency and excellent rate performance. Preferably, the range of x2 is 0.7 m. 2 / g ~25 m 2 / g.

[0035] In some embodiments, the etching reaction time H of the negative electrode material in a mixed solution of hydrofluoric acid and concentrated nitric acid with a mass fraction of 35%~45% is 0.5h~72h, specifically 0.5h, 1h, 3h, 6h, 12h, 18h, 24h, 36h, 48h, or 72h, etc., and of course, other values ​​within the above range are also possible, and are not limited here. In this application, the negative electrode material is etched using a mixed solution of hydrofluoric acid and concentrated nitric acid to determine the micropore activity index in the negative electrode material.

[0036] In some embodiments, the negative electrode material also includes at least one of the following elements: oxygen, lithium, magnesium, copper, nickel, iron, chromium, calcium, aluminum, sodium, manganese, boron, nitrogen, and zinc.

[0037] In some embodiments, the silicon-based material includes silicon oxide and a compound of a metal element M, wherein the metal element M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr, and Zn. The compound of the metal element M can be a silicon-lithium alloy, a silicon-magnesium alloy, etc., and is not limited thereto.

[0038] In some embodiments, the atomic ratio of oxygen to silicon in the negative electrode material is x, where 0 < x < 2.2. Specifically, it can be 0.1, 0.2, 0.5, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 1.9, 2.1, 2.185, etc., or other values ​​within the above range.

[0039] In some embodiments, the oxygen-containing and silicon-containing components in the negative electrode material include, but are not limited to, at least one of silicon oxide and silicate.

[0040] In some implementations, silicon oxide can be represented by the general formula: (0 < x ≤ 2). Specifically, SiO x Specifically, it can be SiO 0.5 SiO 0.8 SiO 0.9 SiO, SiO 1.1 SiO 1.2 SiO 1.5 Alternatively, it can be SiO2, without limitation. Silicon oxide can be a material formed by dispersing silicon particles in SiO2, or it can be a material with tetrahedral structural units, where silicon atoms are located at the center of the tetrahedral structural units, and oxygen atoms and / or silicon atoms are located at the four vertices of the tetrahedral structural units.

[0041] In some embodiments, the silicon-containing component in the negative electrode material can be elemental silicon, silicon oxide, or silicate. Elemental silicon can be amorphous silicon and / or crystalline silicon, and silicate can be magnesium silicate, lithium silicate, etc.

[0042] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon. The amorphous carbon can be soft carbon and / or hard carbon. Understandably, carbon materials can improve the conductivity of silicon-based active materials.

[0043] In some embodiments, at least a portion of the surface of the negative electrode material has a carbon layer. Understandably, the carbon layer on the surface of the negative electrode material can reduce particle breakage caused by repeated SEI film formation, thereby improving the cycle performance of the negative electrode material and reducing volume expansion due to SEI film formation.

[0044] In some embodiments, the median particle size of the negative electrode material is 1 μm to 15 μm, specifically 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, or 15 μm, etc., and of course, other values ​​within the above range are also possible, without limitation here. 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.

[0045] In some implementations, the pH of the negative electrode material is 5 to 12, specifically 5, 6, 7, 8, 9, 10, 11 or 12, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0046] In some embodiments, the oil absorption value of the negative electrode material is 35 mL / 100g to 65 mL / 100g, specifically 35 mL / 100g, 40 mL / 100g, 45 mL / 100g, 50 mL / 100g, 55 mL / 100g, 60 mL / 100g, or 65 mL / 100g, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Controlling the oil absorption value of the negative electrode material within the above range indicates that there are fewer defects and pores on the surface of the negative electrode material, which can ensure the wetting ability of the negative electrode material and the electrolyte, improve the lithium-ion conduction efficiency, and improve the electrochemical performance of the negative electrode material.

[0047] In some embodiments, the true density of the negative electrode material is 2.0 g / cm³. 3 ~3.4g / cm 3 Specifically, it could be 2.0 g / cm³. 3 2.3 g / cm 3 2.5 g / cm 3 2.8 g / cm 3 3.0 g / cm 3 3.2 g / cm 3 Or 3.4 g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. A true density of the negative electrode material within the above range is beneficial for improving the energy density of batteries made from that material.

[0048] 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 0.6 g / cm 3 0.7 g / cm 3 0.8 g / cm 3 0.9 g / cm 3 1.0 g / cm 3 1.1 g / cm 3 1.2 g / cm 3 1.3g / cm 3 1.4 g / cm 3 Or 1.5 g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. Controlling the tap density of the negative electrode material within the above range indicates that the negative electrode material has good processing performance, which can reduce the difficulty in electrode coating and battery manufacturing processes. It also helps to maintain the structural stability of the electrode during cycling, thereby improving the cycle performance of the material and the energy density of the battery.

[0049] In some embodiments, the negative electrode material satisfies D20-D10≤4μm and D90-D80≤8μm. Specifically, D20-D10 can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, or 4μm, or other values ​​within the above range, which are not limited here. Similarly, D90-D80 can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, or 8μm, or other values ​​within the above range, which are not limited here. D90 represents the particle size at which the material's cumulative particle distribution reaches 90%, D80 represents the particle size at which the material's cumulative particle distribution reaches 80%, D20 represents the particle size at which the material's cumulative particle distribution reaches 20%, and D10 represents the particle size at which the material's cumulative particle distribution reaches 10%. D20-D10 are used to characterize the distribution of smaller particles in the negative electrode material, and D90-D80 are used to characterize the distribution of larger particles. This application controls D20-D10 ≤ 4 μm and D90-D80 ≤ 8 μm to indicate that the particle size distribution of the negative electrode material is suitable. The matching of smaller and larger particles results in a higher compaction density and a relatively uniform particle size distribution, which is beneficial for improving the ion conduction efficiency, rate performance, and cycle performance of the negative electrode material. If D20-D10≤4μm and D90-D80>8μm, it indicates that the particle size distribution of the negative electrode material is generally shifted towards larger particle sizes. If D20-D10>4μm and D90-D80≤8μm, it indicates that the particle size distribution of the negative electrode material is generally shifted towards smaller particle sizes. Both of these situations will lead to an increase in the particle size range of the negative electrode material. The lithium-ion diffusion path of small particles is shorter, while the diffusion path of large particles is longer. The difference in the lithium-ion diffusion path of the negative electrode material particles increases, and the rate performance and cycle performance of the negative electrode material decrease.

[0050] In some implementations, 0.4μm≤D10≤5.0μm, specifically 0.4μm, 0.8μm, 1.5μm, 2μm, 2.8μm, 3.5μm, 4.5μm or 5.0μm, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0051] In some implementations, 0.5μm≤D20≤7.0μm, specifically 0.5μm, 1.0μm, 1.8μm, 2.3μm, 3.0μm, 3.8μm, 4.5μm, 5.5μm, 6.5μm or 7.0μm, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0052] In some implementations, 1.5μm≤D80≤22.0μm, specifically 1.5μm, 2.5μm, 5.5μm, 8.0μm, 9.5μm, 13.0μm, 18.5μm, 20.0μm or 22.0μm, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0053] In some implementations, 2.5μm≤D90≤25.0μm, specifically 2.5μm, 6μm, 8.5μm, 10μm, 13.5μm, 18.5μm, 20.0μm, 22.5μm or 25.0μm, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0054] In some embodiments, the carbon content in the anode material is 1% to 97% by mass, specifically 1%, 3%, 5%, 10%, 20%, 35%, 50%, 65%, 73%, 83%, 90%, or 97%, etc., and other values ​​within the above range are also possible and are not limited here. Controlling the carbon content in the anode material within the above range can reduce the structural damage to the anode material caused by the volume expansion of silicon, improve the cycle performance of the anode material, facilitate the formation of a stable and thin solid electrolyte interphase (SEI) film, reduce the consumption of active lithium ions, improve the first coulombic efficiency of the anode material, and also contribute to the improvement of the cycle performance of the anode material.

[0055] In some embodiments, the silicon content in the anode material is 3% to 99% by mass, specifically 3%, 10%, 20%, 35%, 50%, 65%, 73%, 80%, 90%, 95%, or 99%, or other values ​​within the above range, which are not limited here. When the silicon content is too low, the specific capacity of the anode material is low, making it difficult to meet the requirements of high-energy-density batteries; when the silicon content is too high, the volume expansion of the anode material is too large, leading to severe degradation of the material's cycle performance.

[0056] Secondly, this application provides a method for preparing a negative electrode material, the method comprising the following steps: S100 involves heat-treating silicon-based raw materials under electrical conditions in a protective gas atmosphere, thereby exciting the protective gas into a plasma state and obtaining surface-modified silicon-based raw materials. S200, using a carbon source gas to coat the surface-modified silicon-based raw material to obtain a precursor.

[0057] S300 involves heating the precursor under vacuum conditions to obtain the negative electrode material.

[0058] The method for preparing the anode material provided in this application first involves heat-treating a silicon-based raw material in a protective gas atmosphere. Under the influence of the protective gas atmosphere, the silicon-based raw material changes from a solid state to a fluidized state. Simultaneously, the protective gas is excited into a plasma state under energized conditions. The plasma-state protective gas contains a large number of charged particles, such as ions, electrons, free radicals, and partially ionized gases. The high-energy plasma-state protective gas bombards the surface of the silicon-based raw material, thereby forming a microporous structure with specific pore sizes and distributions on and inside the silicon-based raw material. Further, a carbon source gas is used to coat the surface-modified silicon-based raw material. The carbon source gas absorbs energy in the plasma-state protective gas atmosphere, causing its electrons to jump to higher energy levels and form excited-state molecules. These excited-state molecules are unstable and release energy through dissociation, causing the reactant gas to decompose into atoms, which adhere to the surface of the silicon-based raw material to form a carbon layer of suitable density. The resulting precursor includes both silicon-based and carbon materials. Finally, the precursor is heat-treated to further adjust the micropore content of the anode material. Anode materials with suitable micropore activation can achieve a balance between improving rate performance, coulombic efficiency and cycle life, thereby improving the overall electrochemical performance of anode materials.

[0059] The preparation method provided in this scheme is described in detail below: S100 involves heat-treating silicon-based raw materials under electrical conditions in a protective gas atmosphere, thereby exciting the protective gas into a plasma state and obtaining surface-modified silicon-based raw materials.

[0060] In this step, the silicon-based material raw material is heat-treated under electric current in a protective gas atmosphere, which excites the protective gas into a plasma state, also known as plasma. The plasma state of the protective gas has energy.

[0061] In some embodiments, the particle size of the silicon-based raw material satisfies D20-D10 ≤ 4 μm and D90-D80 ≤ 8 μm. D20-D10 can specifically be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or 4 μm, etc., and other values ​​within the above range are also acceptable; no limitation is made here. D90-D80 can specifically be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm, etc., and other values ​​within the above range are also acceptable; no limitation is made here. This application demonstrates that the particle size distribution of the silicon-based material raw materials is suitable by controlling D20-D10≤4μm and D90-D80≤8μm. By matching smaller and larger particles, the preparation of anode materials using the above-mentioned raw materials is beneficial for obtaining a suitable specific surface area, electrolyte wetting, and improving the ion conduction efficiency of the anode material. At the same time, the anode material has good structural stability and is not easy to break during long-term cycling, thereby improving the capacity and cycle performance of the anode material.

[0062] It is understandable that before step S100, the silicon-based raw material can be crushed and sieved to ensure that the silicon-based raw material meets the above particle size requirements.

[0063] In some embodiments, the crushing includes at least one of air jet milling, ball milling, sand milling, roller milling, disc milling, and cryogenic crushing.

[0064] In some embodiments, the silicon-based raw material contains at least one of the following elements: oxygen, lithium, magnesium, copper, nickel, iron, chromium, calcium, aluminum, sodium, manganese, boron, nitrogen, and zinc. It is understood that the raw material for the silicon-based material of this application can be elemental silicon, silicon compounds, or silicon complexes, etc.

[0065] In some embodiments, the protective gas includes at least one of argon, helium, nitrogen, and neon, which has a moderate ionization energy and is capable of generating plasma under certain energized conditions.

[0066] In some embodiments, the flow rate of the protective gas is 0.5 L / min to 15 L / min, specifically 0.5 L / min, 1 L / min, 3 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, or 15 L / min, etc., and of course, other values ​​within the above range are also possible, without limitation. It is understood that controlling the flow rate of the protective gas within the above range ensures that sufficient protective gas is excited into a plasma state under heat treatment and electrical conditions, thereby ensuring that the plasma state has sufficient energy to cause the subsequent reaction gas to dissociate and generate sufficient carbon atoms, and controlling the morphology of carbon atom accumulation on the silicon-based material surface.

[0067] In some embodiments, the radio frequency power under energized conditions is 10 kW to 100 kW, specifically 10 kW, 20 kW, 30 kW, 40 kW, 50 kW, 60 kW, 70 kW, 80 kW, 90 kW, or 100 kW, etc., and of course, other values ​​within the above range are also possible, without limitation. It is understood that controlling the radio frequency power under energized conditions within the above range allows the plasma to obtain sufficient energy to enter the excited state, facilitating the accelerated reaction of the subsequently introduced reactive gas, thereby controlling the pore structure and pore size distribution of the material.

[0068] In some embodiments, the heat treatment temperature is 300℃~800℃, specifically 300℃, 400℃, 500℃, 600℃, 700℃ or 800℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0069] In some embodiments, the heating rate of the heat treatment is 1℃ / min to 20℃ / min, specifically 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, 13℃ / min, 16℃ / min, or 20℃ / min, etc., and other values ​​within the above range are also possible, without limitation. Preferably, the heating rate of the heat treatment is 5℃ / min to 15℃ / min, and other values ​​within the above range are also possible, without limitation.

[0070] In some embodiments, the heat treatment equipment may be, for example, a high-temperature reactor, specifically a fluidized bed high-temperature reactor. For example, the fluidized bed high-temperature reactor employs a quartz chamber with coils wound around it. By energizing the coils, the protective gas introduced into the high-temperature reactor is converted into a plasma state.

[0071] S200, using a carbon source gas to coat the surface-modified silicon-based raw material to obtain a precursor.

[0072] In this step, the carbon source gas can dissociate in a protective gas atmosphere in a plasma state to form corresponding carbon atoms and / or carbon free radicals. The carbon atoms and / or carbon free radicals are mixed with the raw materials of the fluidized silicon-based material. According to the free path and valence state of the carbon atoms and / or carbon free radicals that are cleaved, they are combined into specific basic structures. A coating layer is formed by stacking a large number of basic structures, thereby realizing the control of the microporous structure in the negative electrode material.

[0073] In some embodiments, the flow rate of the carbon source gas is 0.5 L / min to 10 L / min, specifically 0.5 L / min, 1 L / min, 3 L / min, 5 L / min, 8 L / min, or 10 L / min, etc., and other values ​​within the above range are also possible and are not limited here. Controlling the flow rate of the carbon source gas within the above range ensures that the carbon source gas has a suitable dissociation rate and controls the growth morphology of the carbon source gas dissociating into atoms deposited on the fluidized silicon-based material. This results in the formation of a suitable number of micropores on the surface and / or inside the silicon-based material, giving the active material a suitable specific surface area. On the one hand, this is beneficial for the electrolyte to wet the negative electrode material, which is conducive to the transport of lithium ions in the micropores of the negative electrode material, improves the ion diffusion rate of the negative electrode material, and enhances the rate performance of the negative electrode material. On the other hand, it reduces the catalytic effect of micropores on the side reactions of the negative electrode material, reduces the consumption of excess electrolyte and silicon-based active material by side reactions, and improves the coulombic efficiency and cycle life of the negative electrode material.

[0074] In some implementations, the coating time is 1h to 15h, specifically 1h, 3h, 5h, 8h, 10h, 12h or 15h, etc. Of course, other values ​​within the above range are also possible, and no limitation is made here.

[0075] S300 involves heating the precursor under vacuum conditions to obtain the negative electrode material.

[0076] In some embodiments, the heat treatment temperature is 400℃~1000℃, specifically 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, or 1000℃, etc., and of course, other values ​​within the above range are also possible, without limitation. Controlling the heating temperature within the above-mentioned range promotes the complete reaction of carbon. Larger pores in some carbon materials further break down and collapse during the thermal reaction, forming microporous structures, thereby adjusting the micropore content in the negative electrode material, increasing the graphitization degree of the carbon material, and reducing defects and impurities in the negative electrode material.

[0077] In some embodiments, the vacuum pressure for heat treatment is less than or equal to 100 Pa, specifically 10 Pa, 30 Pa, 50 Pa, 80 Pa, 90 Pa, or 100 Pa, or other values ​​within the above range, which are not limited here. Controlling the vacuum pressure for heat treatment within the above-mentioned range can reduce the oxidation of the active material and the possibility of side reactions between the active material and other substances, thereby improving the overall performance of the negative electrode material.

[0078] In some implementations, the heat treatment time is 1h to 16h, specifically 1h, 3h, 5h, 8h, 10h, 12h or 16h, etc. Of course, other values ​​within the above range are also possible, and no limitation is made here.

[0079] In some embodiments, the heating process employs a vacuum rotary heating device. Exemplarily, the vacuum rotary heating device employs a nested structure, wherein the precursor is placed in the inner cavity, and the inner cavity is equipped with a rotating mechanism to enable rotation; the outer cavity encloses the inner cavity, and both the inner and outer cavities are simultaneously evacuated to ensure that the vacuum level within the vacuum rotary heating device is within the range defined in this application. In some embodiments, a screw pump, a Roots pump, or the like can be used to achieve the vacuum process.

[0080] Thirdly, this application provides a battery comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the method described in the second aspect.

[0081] The battery provided in this application can be a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, electrode assembly, and electrolyte. Both the electrode assembly and electrolyte are located inside the casing. The casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), such as a pouch battery for secondary batteries.

[0082] In other embodiments, the secondary battery may also be a steel-cased battery, an aluminum-cased battery, etc.

[0083] Figure 1 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 1 As 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.

[0084] 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.

[0085] In some embodiments, the positive electrode 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 electrode active layer 102 contains a positive electrode active material, which includes compounds that can reversibly insert and deintercalate metal ions.

[0086] 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.

[0087] 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), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0088] 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.

[0089] 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.

[0090] Example 1 (1) Weigh an appropriate amount of SiO material and pulverize it using an air jet mill. The pulverized SiO material should meet the following requirements: D20-D10≤4μm, D90-D80≤8μm.

[0091] (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced into the vertical furnace at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0092] (3) The precursor is placed in a vacuum rotary heating device, the vacuum degree is evacuated to 70 Pa and heat-treated for 10 h at a temperature of 700 °C to obtain the negative electrode material.

[0093] The scanning electron microscope (SEM) image of the negative electrode material prepared in this embodiment is shown below. Figure 2 As shown, the negative electrode material includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material.

[0094] Example 2 (1) Weigh an appropriate amount of pre-lithiated silicon oxide (using the composite prepared in Example 1 of CN106816594A) and pulverize it using a ball mill. The pulverized pre-lithiated silicon oxide satisfies D20-D10≤4μm and D90-D80≤8μm.

[0095] (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 9L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 500℃. The coil is turned on and the radio frequency power is adjusted to 40kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0096] (3) The precursor is placed in a vacuum rotary heating device, the vacuum degree is evacuated to 100Pa and heat-treated for 10h at a temperature of 500℃ to obtain the negative electrode material.

[0097] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material is a pre-lithiated silicon oxide.

[0098] Example 3 (1) Weigh out an appropriate amount of magnesium silicate and SiO2. 1.5 The mixture was then pulverized using a mechanical mill. The pulverized Si-OC-Li composite material satisfied the following: D20-D10≤4μm, D90-D80≤8μm.

[0099] (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 9L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 500℃. The coil is turned on and the radio frequency power is adjusted to 40kW to excite the argon gas into a plasma state. Then, 3L / min of propane gas is introduced to carry out the reaction. After the reaction is carried out for 5 hours, the propane gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0100] (3) The precursor is placed in a vacuum rotary heating device, the vacuum degree is evacuated to 80 Pa and heat-treated for 10 h at a temperature of 500 °C to obtain the negative electrode material.

[0101] The negative electrode material prepared in this embodiment includes a silicon-based material and a carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes magnesium silicate and SiO2. 1.5 .

[0102] Example 4 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, 5L / min of methane gas is introduced to carry out the reaction. After the reaction is carried out for 7 hours, the methane gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0103] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0104] Example 5 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, 5L / min of methane gas is introduced to carry out the reaction. After the reaction is carried out for 10h, the methane gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. The equipment is allowed to cool down naturally and the material is discharged to obtain the precursor.

[0105] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0106] Example 6 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, 0.5L / min of acetylene gas is introduced to carry out the reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0107] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0108] Example 7 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 8L / min for reaction. After the reaction is 2h, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0109] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0110] Example 8 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 10L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0111] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0112] Example 9 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 10kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0113] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0114] Example 10 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 50kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0115] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0116] Example 11 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 70kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0117] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0118] Example 12 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. The coil is turned on and the radio frequency power is adjusted to 100kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0119] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0120] Example 13 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 300℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0121] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0122] Example 14 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a fluidized bed high-temperature reactor with a quartz cavity wound with a coil. The reactor diameter is 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 800℃. The coil is turned on and the radio frequency power is adjusted to 80kW to excite the argon gas into a plasma state. Then, acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while the argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0123] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0124] Example 15 Unlike Example 1: (1) Weigh an appropriate amount of SiO material and pulverize it using an air jet mill. The pulverized SiO material should meet the following requirements: D20-D10 is 4.3 μm and D90-D80 is 6.1 μm.

[0125] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0126] Example 16 Unlike Example 1: (1) Weigh an appropriate amount of SiO material and pulverize it using an air jet mill. The pulverized SiO material meets the following requirements: D20-D10 is 3.18μm and D90-D80 is 8.59μm.

[0127] The negative electrode material prepared in this embodiment includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes SiO material.

[0128] Comparative Example 1 Unlike Example 1: (2) Weigh 2kg of the material obtained in step (1) and put it into a quartz cavity fluidized bed high-temperature reactor with a reactor diameter of 30cm. Argon gas is introduced at a flow rate of 8L / min. After the material obtained in step (1) enters the fluidized state, the temperature is raised to 600℃. Acetylene gas is introduced at a flow rate of 3L / min for reaction. After the reaction is carried out for 2 hours, the acetylene gas and the coil are turned off. The heating is stopped while argon gas is continuously introduced. After the equipment cools down naturally, the material is discharged to obtain the precursor.

[0129] Comparative Example 2 Unlike Example 1, step (3) is not performed.

[0130] Test methods (1) Method for determining the total specific surface area of ​​pores with an aperture greater than or equal to 2 nm in the negative electrode material: According to GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method", the specific operation steps are as follows: Weigh a certain amount of negative electrode material sample and put it into a special bubble tube for specific surface area. Degas the special bubble tube containing the negative electrode material by purging it with nitrogen at 300℃ in a degassing station. After degassing is completed, cool it to room temperature. Weigh the actual mass of the negative electrode material sample. Then, install the special bubble tube containing the negative electrode material sample into a specific surface area and pore size analyzer (e.g., any one of Micromeritics TriStar 3000, Micromeritics TriStar 3020, or Micromeritics TriStar 3030). After inputting the actual mass of the negative electrode material sample, start measuring the specific surface area of ​​the negative electrode material with an aperture greater than or equal to 2 nm. The sampling range is 0.05 g / cm³. 3 ~0.3g / cm 3 Taking a point every 0.05cm, it can be understood that the total specific surface area of ​​the pores with an opening diameter greater than or equal to 2nm in the above negative electrode material is the sum of the specific surface areas of the intermediate pores and macropores in the negative electrode material.

[0131] (2) Method for determining the total specific surface area of ​​all pores in the negative electrode material: According to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method", the specific operating steps are as follows: Weigh a certain amount of the negative electrode material sample and place it into a special bubble tube for specific surface area determination. Degas the special bubble tube containing the negative electrode material at 300℃ using nitrogen in a degassing station. After degassing, cool to room temperature. Weigh the actual mass of the negative electrode material sample. Install the special bubble tube containing the negative electrode material sample into a specific surface area and pore size analyzer (e.g., ASAP2460). Input the actual mass of the negative electrode material sample and begin determining the specific surface area of ​​all pores in the negative electrode material. The sampling range is 0.05 g / cm³. 3 ~0.10g / cm 3 Taking a point every 0.01cm, it can be understood that the total specific surface area of ​​all openings in the above negative electrode material is the sum of the specific surface areas of micropores + mesopores + macropores in the openings of the negative electrode material.

[0132] (3) Determination of etching reaction time of negative electrode material: Weigh 300 mL of GR pure hydrofluoric acid with a mass fraction of 40% and 200 mL of concentrated nitric acid respectively, and mix them to obtain mixed acid. Add the mixed acid to the separatory funnel. Place 5 g of negative electrode material in a flask, and stopper the separatory funnel containing the mixed acid and the gas delivery tube in the flask. Insert the other end of the gas delivery tube into a bottle containing excess sodium hydroxide solution. The outlet of the gas delivery tube is submerged below the sodium hydroxide solution. Place the bottle containing sodium hydroxide solution on an electronic scale. Start timing while opening the liquid discharge switch of the separatory funnel. After the mixed acid solution has completely flowed into the flask, close the liquid discharge switch of the separatory funnel. Stop timing when the reading of the electronic scale no longer increases. The etching gas generation is considered to be over. This timing time is recorded as the etching reaction time.

[0133] (4) pH measurement method: pH meter of water system is used for testing.

[0134] (5) Test method for oil absorption value: Refer to GB / T 3780.2-2017 "Carbon Black Part 2: Determination of Oil Absorption Value" or the equipment instruction manual for measurement. Use an oil absorption value tester (ASAHI S-500) for measurement. The absorbent liquid used is dibutyl phthalate.

[0135] (6) Test method for true density: Refer to Appendix D of GB / T 24533-2019 "Test method for true density". Measured using a true density tester.

[0136] (7) Test method for tap density: Refer to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders" or the equipment instruction manual for measurement. Use a tap density meter (Kunta DAT-4-220) for measurement. The number of vibrations is 3000.

[0137] (8) Particle size testing method: Refer to GB / T 19077.1-2006 "Particle size analysis by laser diffraction - Part 1: General rules" or the equipment instruction manual for measurement. A laser particle size analyzer (Malvin Panaco MS3000) is used for measurement.

[0138] (9) Test method for carbon content: Refer to Appendix A of GB / T 38823-2020 "Test method for carbon content". Measured using an infrared carbon-sulfur analyzer.

[0139] (10) Test method for silicon mass content: The carbon content C of the material is tested by infrared carbon-sulfur analyzer, the oxygen content O of the material is tested by oxygen-nitrogen-hydrogen element analyzer, the total metal content M of the material is measured by total dissolution ICP method, and the Si element content of the material is 1-C%-O%-M.

[0140] (11) Electrochemical performance testing method: The negative electrode materials prepared in the above examples and comparative examples are mixed with graphite (artificial graphite S360 series) at a ratio of 10:90, and then mixed with sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder, Super-P conductive agent, and KS-6 conductive agent at a mass ratio of 92:2:2:4 to form a slurry. The slurry is coated on copper foil and then vacuum dried and rolled to prepare a negative electrode sheet. The counter electrode is a lithium sheet. A 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v=1:1:1) electrolyte and Celgard 2400 separator are assembled into a coin cell.

[0141] Cyclic performance testing employed a constant current charge-discharge experiment at 30mA, with the charge-discharge voltage limited to 0–1.5V. The LAND battery testing system from Wuhan Jinno Electronics Co., Ltd. was used for testing. At room temperature, the coin cells were cycled once each at 0.1C, 0.2C, and 0.5C, followed by 47 cycles at 1C. The 50-cycle capacity retention rate was obtained by dividing the capacity at week 50 by the capacity at week 1. The 0.1C capacity divided by the 1C capacity was used to evaluate rate performance.

[0142] The test results are detailed in Tables 1 and 2.

[0143] Table 1 Performance test results of each embodiment and comparative example

[0144] Table 2 Performance test results of each embodiment and comparative example

[0145] According to the test data in Tables 1 and 2, the micropore activation degree y of the negative electrode material provided in this application is 0.001~1.5 (excluding 0.001), indicating that the negative electrode material has a suitable number of micropores. On the one hand, this is beneficial for electrolyte wetting of the negative electrode material, which facilitates the transport of lithium ions in the micropores of the negative electrode material, improves the ion diffusion rate of the negative electrode material, and enhances the rate performance of the negative electrode material. On the other hand, it reduces the catalytic effect of micropores on the side reactions of the negative electrode material, reduces the consumption of excess electrolyte and silicon-based active material by side reactions, and improves the coulombic efficiency and cycle life of the negative electrode material. The negative electrode material of this application can achieve a balance between improving rate performance, coulombic efficiency, and cycle life, ultimately improving the overall electrochemical performance of the negative electrode material.

[0146] According to the test data of Examples 1 and 6 to 8, when the flow rate of the carbon source gas in this application is controlled within a suitable range, the carbon deposition rate increases with the increase of the carbon source gas flow rate, and the carbon content gradually increases. The faster carbon deposition rate makes it easier to generate more activated micropores, so that the micropore activation degree y of the negative electrode material increases with the increase of the carbon source gas flow rate.

[0147] According to the test data of Examples 1, 9 to 12, within the limit range of the coil RF power of this application, as the coil RF power increases, the micropore volume in the deposition tends to increase, which causes the micropore activation degree y of the negative electrode material to first decrease and then increase.

[0148] According to the test data of Examples 1, 13 to 14, within the heat treatment temperature range of this application, the carbon deposition rate increases with the increase of heat treatment temperature. At the same time, the higher the temperature, the easier it is to generate carbon structures with higher graphitization and fewer micropores, which makes the micropore activation degree y of the negative electrode material gradually decrease.

[0149] According to the test data of Examples 1, 15 and 16, the D20-D10 values ​​of the negative electrode material provided in Example 15 increased, indicating that the overall particle size distribution of the negative electrode material shifted towards smaller particle sizes. The D90-D80 of the negative electrode material provided in Example 16 was greater than 8 μm, indicating that the overall particle size distribution of the negative electrode material shifted towards larger particle sizes. Both of these situations will lead to an increase in the particle size range of the negative electrode material. The lithium-ion diffusion path of small particles is shorter, while the diffusion path of large particles is longer. The difference in the lithium-ion diffusion path of the negative electrode material particles increases, and the rate performance and cycle performance of the negative electrode material decrease.

[0150] According to the test data of Example 1 and Comparative Example 1, without using a coil to excite the protective gas, the desired pore structure cannot be effectively generated, resulting in an excessively high micropore activation degree y of the negative electrode material. This leads to an excessive number of micropores in the opening of the negative electrode material, an excessive number of reaction sites on the surface of the negative electrode material, and an aggravation of the side reactions between the negative electrode material and the electrolyte, resulting in a decrease in the coulombic efficiency and cycle life of the negative electrode material.

[0151] According to the test data of Example 1 and Comparative Example 2, if the precursor is not subjected to the vacuum heat treatment in step (3), the residual impurities in the material cannot be volatilized, the microporous structure is blocked, the micropore activation degree y of the negative electrode material is too small, the negative electrode material cannot be fully wetted by the electrolyte, lithium ions cannot be transported smoothly, and thus the electrochemical performance of the negative electrode material is deteriorated.

[0152] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material; The negative electrode material has openings, wherein the total specific surface area of ​​the openings with a pore size ≥ 2 nm in the negative electrode material is x 1 m². 2 / g, the total specific surface area of ​​all openings in the negative electrode material is x2 m 2 / g; Add 5g of the negative electrode material to the mixed acid solution for etching until etching gas generation is completed, and record the etching time as H hours; wherein, the mixed acid solution consists of a mass fraction of It is obtained by mixing 300 mL of hydrofluoric acid and 100 mL of concentrated nitric acid with a mass fraction of 68%; The micropore activation degree of the negative electrode material Furthermore, the negative electrode material satisfies the condition: 0.001 < y ≤ 1.

5.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following characteristics: （1）0.1≤x1≤25； （2）0.3≤x2≤35； （3）0.5≤H≤72。 3. The negative electrode material according to claim 1, characterized in that, The oil absorption value of the negative electrode material is 35 mL / 100g to 65 mL / 100g.

4. The negative electrode material according to claim 1, characterized in that, The silicon-based material comprises silicon and oxygen, wherein the atomic ratio of oxygen to silicon in the negative electrode material is x, where 0 < x < 2.2; and / or, the silicon-based material comprises silicon oxide, wherein the general formula of the silicon oxide is... , 0 < x ≤ 2.

5. The negative electrode material according to claim 1, characterized in that, The silicon-based material includes silicon oxide and a compound of metal element M, wherein the metal element M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr, Ca, Al, Na, Mn and Zn.

6. The negative electrode material according to claim 5, characterized in that, The compound of the metal element M includes at least one of the silicates of the metal element M and the oxides of the metal element M.

7. The negative electrode material according to claim 1, characterized in that, The carbon material includes at least one of amorphous carbon, graphitized carbon, graphite, graphene, carbon nanotubes, and carbon fibers.

8. The negative electrode material according to claim 1, characterized in that, The cumulative particle size distribution of the negative electrode material satisfies D20-D10≤4μm and D90-D80≤8μm; and / or, the volume distribution particle size D50 of the negative electrode material is 1μm≤D50≤15μm.

9. The negative electrode material according to any one of claims 1 to 8, characterized in that, (1) The carbon content in the negative electrode material is 1%~97% by mass; (2) The mass content of silicon in the negative electrode material is 3%~99%; (3) The pH of the negative electrode material is 5~12; (4) The true density of the negative electrode material is 2.0 g / cm³. 3 ~3.4g / cm 3 ; (5) The tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5 g / cm 3 .

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

Images