Negative electrode material, negative electrode plate and battery

Abstract

The invention provides a negative electrode material, a negative electrode plate and a battery, the negative electrode material comprises a substrate and an active substance, the substrate is provided with holes, at least a part of the active substance is located in the holes of the substrate, the conductivity of the negative electrode material is sigma S / cm, the content of the active substance in the negative electrode material is a1%, 16 < = a1 < = 65, M is set to be sigma / a1, and a1 < = sigma / a2. M is more than or equal to 0.015 and less than or equal to 5; the deposition parameter gamma of the active substance in the substrate is greater than or equal to 0.85; and the formed negative electrode material has excellent performances of high conductivity, high capacity, high first efficiency, long circulation and low expansion.

Description

Technical Field

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

[0002] Silicon-based anode materials possess advantages such as high specific capacity, environmental friendliness, and abundant resources, making them a promising alternative to graphite anode materials in next-generation high-energy-density lithium-ion batteries. However, the silicon material in silicon-based anode materials undergoes drastic volume changes during cycling, easily leading to pulverization and breakage of the anode material. Furthermore, the volume expansion of silicon material during electrochemical cycling causes the SEI film formed on the surface of the anode material to be continuously damaged and regenerated, resulting in continuous consumption of lithium ions and ultimately leading to rapid capacity decay of the battery made from the anode material.

[0003] Preparing silicon-carbon anode materials by depositing silicon materials in porous carbon can solve the problem of volume expansion of silicon materials. The resulting anode materials also have high capacity, high initial efficiency and long cycle life. However, silicon-carbon anode materials have low electrical conductivity, which affects the charge and discharge efficiency and cycle performance of the battery.

[0004] Therefore, there is an urgent need to develop a negative electrode material with high conductivity to improve the charge and discharge efficiency and cycle performance of batteries. Summary of the Invention

[0005] This application provides a negative electrode material, a negative electrode sheet, and a battery to solve the above-mentioned problems.

[0006] To achieve the above objectives, in a first aspect, this application provides a negative electrode material, comprising a matrix and an active material, wherein the matrix has pores, and at least a portion of the active material is located within the pores of the matrix. Based on the mass of the negative electrode material, the mass content of the active material in the negative electrode material is a1%, and the conductivity of the negative electrode material is σS / cm, wherein 16≤a1≤65, and M is set to σ / a1, wherein the value of M is 0.015≤M≤5; and the deposition parameter γ of the active material in the matrix is ​​≥0.85, wherein the deposition parameter γ represents the ratio of the volume of the active material located within the pores of the matrix to the total volume of the active material in the negative electrode material.

[0007] In some embodiments, the median particle size D50 of the negative electrode material is 1-15 μm, and the particle size distribution satisfies 0.1≤(D90-D10) / D50≤2.

[0008] In some embodiments, the specific pore volume of the negative electrode material is 0.001–0.1 cm³. 3 / g, with an average pore size of 0.45–50 nm.

[0009] In some embodiments, the negative electrode material has a micropore content of 10% to 30%, a mesopore content of 30% to 80%, and a macropore content of 0% to 10%.

[0010] In some embodiments, the specific surface area of ​​the negative electrode material is 0.1-5 m². 2 / g.

[0011] In some embodiments, the matrix includes a carbon matrix, which includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microspheres, activated carbon, carbon gel, etc.

[0012] In some embodiments, the carbon matrix has a micropore content of ≥70%.

[0013] In some embodiments, the average pore size in the carbon matrix is ​​0.1-5 nm.

[0014] In some embodiments, the pore volume of the carbon matrix is ​​≥0.4 cm³. 3 / g.

[0015] In some embodiments, the carbon matrix content is 30% to 75% based on the mass of the negative electrode material.

[0016] In some embodiments, the active material includes a silicon material, which includes at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloys, and mixtures of crystalline and amorphous silicon.

[0017] In some embodiments, the purity of the silicon material is greater than 99%.

[0018] In some embodiments, the average particle size of the silicon material is 1-500 nm.

[0019] In some embodiments, the negative electrode material further includes a coating material distributed on at least a portion of the surface of the substrate, the coating material including at least one of carbon materials, metal oxides, conductive polymers, fluorides, phosphates, and nitrides.

[0020] Secondly, this application provides a negative electrode sheet, comprising the aforementioned negative electrode material.

[0021] Thirdly, this application provides a battery that includes the aforementioned negative electrode plate.

[0022] The technical solution of this application has at least the following beneficial effects:

[0023] In the negative electrode material provided in this application, γ represents the deposition parameter of the active material inside the matrix, and M represents the distribution parameter of the active material in the negative electrode material. The γ value is limited to the aforementioned range, allowing more active material to be distributed inside the matrix, thereby constructing electron transport channels within the pores of the matrix, which is beneficial for improving the conductivity of the formed negative electrode material. The M value being limited to the aforementioned range indicates that the negative electrode material contains an appropriate mass proportion of active material and has high conductivity. Therefore, the combined effect of the M and γ values ​​greatly improves the conductivity of the negative electrode material. Simultaneously, this application limits 16 ≤ a1 ≤ 65, meaning that when the content of active material is within this range, it can fully fill the pores in the matrix. While improving the conductivity of the negative electrode material, it also ensures good other properties of the negative electrode material, such as good cycle performance and initial coulombic efficiency, ultimately forming a negative electrode material with excellent overall performance. Attached Figure Description

[0024] Figure 1 This is a flowchart of the preparation process of the negative electrode material provided in this application;

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the negative electrode material provided in Embodiment 1 of this application;

[0026] Figure 3 This is the XRD pattern of the negative electrode material provided in Embodiment 1 of this application;

[0027] Figure 4 This is the first charge-discharge curve of the negative electrode material provided in Embodiment 1 of this application;

[0028] Figure 5 This is a comparison chart of the conductivity of the negative electrode material provided in Example 1 of this application and the negative electrode material provided in Comparative Example 1. Detailed Implementation

[0029] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below.

[0030] One embodiment of this application provides a battery including a housing, a battery assembly, and an electrolyte (not shown), wherein the battery assembly and the electrolyte are both located inside the housing.

[0031] The casing can be a packaging bag made by encapsulating with a film, such as, but not limited to, aluminum-plastic film, meaning the battery can be a pouch battery. The casing can also be, but not limited to, casings disclosed in the prior art such as steel-cased batteries and aluminum-cased batteries.

[0032] The electrolyte can be one or more of the following: gel, solid, and liquid. In some embodiments, the liquid electrolyte includes a lithium salt and an organic solvent. The lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethanesulfonyl)methyllithium (LiC(SO2CF3)3), lithium dioxolaneborate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is selected as the lithium salt because it provides high ionic conductivity and improves cycling characteristics. The organic solvent may be a carbonate compound, a carboxylic acid ester compound, or an ether. Compounds, nitrile compounds, other organic solvents, or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0033] The battery assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The positive electrode, separator, and negative electrode can be stacked alternately in sequence to form a stacked electrode assembly. In other embodiments, the positive electrode, separator, and negative electrode are stacked in sequence and then wound to form a wound electrode assembly.

[0034] The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector. The positive current collector can be 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 and polymer substrate. The positive active layer contains a positive active material, which includes compounds that reversibly insert and extract lithium ions (i.e., lithiation intercalation compounds). In some embodiments, the positive active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive 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).

[0035] The positive electrode active layer also contains an adhesive to bond the positive electrode active material particles, thereby facilitating the formation of the film layer, and at the same time improving the bonding force between the positive electrode active layer and the positive electrode current collector.

[0036] In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, sodium carboxymethyl cellulose, sodium alginate, sodium polyacrylate, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0037] The positive electrode active layer may also comprise a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based material may include, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanotubes, or any combination thereof. In some embodiments, the metal-based material may include, but is not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0038] The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. The negative current collector can 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, a current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0039] The negative electrode active layer includes a negative electrode material. The negative electrode material of this application includes a matrix and an active substance. The matrix has pores, and at least a portion of the active substance is located within the pores of the matrix.

[0040] In some embodiments, the matrix is ​​a carbon matrix, more specifically a porous carbon-based material, and the porous carbon-based material includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microspheres, activated carbon, carbon gel, etc.

[0041] In some embodiments, the active material includes one or more of silicon-based materials, tin-based materials, phosphorus-based materials, sulfur-based materials, germanium-based materials, and lead-based materials. For example, using silicon-based materials as a component of the negative electrode active material can improve the specific capacity of the negative electrode material, thereby increasing the energy density of the secondary battery.

[0042] Silicon-based materials include silicon materials, which include at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloys, and mixtures of crystalline and amorphous silicon. Specifically, silicon alloys can be lithium silicon alloys, magnesium silicon alloys, etc. Of course, in some cases, silicon alloys include elemental silicon particles and alloys.

[0043] In some embodiments, the silicon material includes amorphous silicon. It is understood that amorphous silicon expands isotropically during lithium intercalation, which can reduce the collapse of the pore structure in the anode material, suppress the rapid decay of the specific capacity of the anode material, and improve the lithium intercalation cycle performance of the anode material.

[0044] In some embodiments, the purity of the silicon material is greater than 99%. High-purity silicon material is beneficial for Li-Si alloying with lithium, thereby improving the cycle performance of lithium-ion batteries.

[0045] In this application, the deposition parameter γ of the active material in the matrix of the negative electrode material is ≥0.85, and the distribution parameter M of the active material in the negative electrode material is 0.015≤M≤5. The distribution parameter M of the active material in the negative electrode material is obtained through the following formula I:

[0046] M = σ / a1;

[0047] Among them, based on the mass of the negative electrode material, the mass percentage of the active material in the negative electrode material is a1%, the conductivity of the negative electrode material is σS / cm, and it is limited to 16≤a1≤65. The final value of M is between 0.015 and 5.

[0048] The deposition parameter γ is obtained from the following formula II:

[0049]

[0050] Where m1 is the mass of the negative electrode material, based on m1, the mass percentage of the active material is a1, and the specific pore volume of the negative electrode material is p1; m2 is the mass of the negative electrode material after removing the active material, based on m2, the mass percentage of the active material is a2, and the specific pore volume of the negative electrode material after removing the active material is p2; ρ is the density of the active material.

[0051] In some embodiments, "removing active substances from the negative electrode material" includes: mixing the negative electrode material with an acid solution. The negative electrode material is mixed with an acid solution of sufficient concentration and stirred thoroughly. The acid solution is used to etch the negative electrode material, which can remove active substances from the substrate pores and substrate surface of the negative electrode material to a certain extent. After cleaning and drying the etched negative electrode material, the removal of active substances is completed.

[0052] In some embodiments, the acid solution includes one or more of hydrochloric acid, nitric acid, and hydrofluoric acid. More specifically, taking silicon-based material as an example, "removal of active material from negative electrode material" includes: preparing an acid solution using 70% hydrochloric acid and 50% hydrofluoric acid at a volume ratio of 2:1, placing the negative electrode material in the acid solution and stirring for at least 10 hours, and then cleaning and drying the negative electrode material.

[0053] In Formula II above, the polynomial m2×p2-m1×p1 represents the difference between the pore volume of the negative electrode material after active material removal and the pore volume of the provided negative electrode material, used to characterize the volume of the active material disposed within the pores of the substrate in the provided negative electrode material; the polynomial m2×p2-m1×p1 represents the difference between the mass of the active material in the provided negative electrode material and the mass of the active material in the negative electrode material after active material removal, used to characterize the total mass of the active material removed by acid in the provided negative electrode material (including all active materials disposed within the pores of the substrate and in other locations in the substrate), and the ratio of the polynomial m2×p2-m1×p1 to the density ρ of the active material corresponds to characterizing the total volume of the active material in the provided negative electrode material. Therefore, Formula II as a whole is used to characterize the proportion of the active material disposed within the pores of the substrate in the negative electrode material to the total active material. In some embodiments, taking silicon material as an example, ρ in Formula II can be taken as 2.34, and the deposition parameter γ of the silicon material can be calculated through Formula II, which can further characterize the proportion of silicon material deposited within the pores of the substrate.

[0054] This application characterizes the proportion of active material deposited in the matrix pores of the negative electrode material, i.e., the deposition parameter γ, by measuring the changes in pore volume and mass of the negative electrode material before and after the removal of active material. In this application, the active material deposition parameter γ is greater than or equal to 0.85, which ensures that most of the active material is attached to the pores of the matrix. This can reduce the side reactions between the negative electrode material and the electrolyte during charging and discharging, improve the cycle performance of the battery, and reduce the hydrolysis of active material during slurry preparation and battery use, i.e., reduce gas generation and improve the safety performance of the battery. In addition, when the active material content is constant, the increase of the active material content in the matrix pores can also improve the particle strength of the negative electrode material.

[0055] Specifically, the parameter γ can be any value between 0.85, 0.91, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, and 0.99, or other values ​​not lower than 0.85, and is not limited here. When γ ≥ 0.85, it indicates that a relatively large amount of active material is deposited in the pores inside the matrix.

[0056] The negative electrode material provided in this application is limited to 16≤a1≤65, and the value of M is limited to between 0.015 and 5. When the content of active material is within this range, it can fully fill the pores in the matrix. While improving the conductivity of the negative electrode material, it can also ensure other properties of the negative electrode material, such as good cycle performance and first coulombic efficiency, and finally form a negative electrode material with excellent performance in all aspects.

[0057] The negative electrode material includes an appropriate amount of active material and possesses suitable electrical conductivity. It should be noted that, taking silicon as an example, silicon, as a semiconductor material, inherently has poor conductivity, with a conductivity of only 10⁻⁶. -7With a density of approximately S / cm, when combined with the substrate, if the silicon content in the negative electrode material is too high or its distribution on the substrate surface is excessive, a thicker electron layer will form, reducing conductivity. When a1 < 16, it indicates that the silicon content in the negative electrode material is too low, resulting in a large number of pores distributed within the substrate. Some of these pores are not filled by active material, leading to a larger specific surface area of ​​the resulting negative electrode material. During the charging and discharging process of the battery prepared with this negative electrode material, the contact area between the negative electrode material and the electrolyte increases, leading to more side reactions between them. The SEI film on the surface of the negative electrode material continues to thicken, consuming excessive lithium salt. Furthermore, the volume effect easily causes electrodesorption between particles, resulting in a decrease in the reversible capacity and coulombic efficiency of the battery. When α > 65, the proportion of active material in the negative electrode material is too high, and some of the active material will begin to adhere to the surface of porous carbon, thereby significantly increasing the specific surface area of ​​the negative electrode material. This leads to increased contact between the composite material and the electrolyte during charging and discharging, increased side reactions, and difficulty in maintaining a stable SEI film. Furthermore, the silicon particles attached to the substrate surface are prone to hydrolysis during slurry preparation and battery use, generating a large amount of gas, which leads to decreased slurry stability and potential battery safety hazards.

[0058] Specifically, M can be any value between 0.015, 0.081, 0.16, 0.22, 0.36, 0.68, 1.24, 1.98, 2.25, 2.87, 3.33, 3.89, 4.41, 4.88, and 5, or other values ​​within the range of 0.015-5, without limitation. Therefore, it can be understood that when the value of M is within this range, it indicates that the negative electrode material contains an appropriate amount of active material, and that the active material is relatively well distributed within the matrix. Simultaneously, the deposition parameter γ is not less than 0.85, meaning that a relatively large amount of active material is distributed within the pores of the matrix. The two characteristics of M and γ within the numerical range complement each other, resulting in a relatively abundant and uniform deposition of active material within the matrix, creating unobstructed electron channels within the pores of the matrix, and improving the conductivity of the negative electrode material.

[0059] In some embodiments, the median particle size D50 of the negative electrode material is 1-15 μm, specifically 1 μm, 1.8 μm, 3 μm, 5 μm, 7.5 μm, 8 μm, 8.8 μm, 9.2 μm, and 10 μm, etc., and of course, other values ​​within the above range are also possible, without limitation. It is understood that a median particle size within the above range for the negative electrode material exhibits better mechanical strength and a higher specific surface area, which is beneficial for improving the cycle performance of the negative electrode material.

[0060] In some embodiments, the particle size distribution of the negative electrode material satisfies the following relationship: 0.1 ≤ (D90 - D10) / D50 ≤ 2. Specifically, it can be any value among 0.1, 0.3, 0.8, 1.4, 1.8, and 2, or other values ​​within the above range, which are not limited here. When the particle size of the negative electrode material is within the above range, different particle sizes can cooperate with each other, and smaller particles can be used to fill the gaps between larger particles, thereby improving the tap density of the negative electrode material.

[0061] It should be noted that the cumulative particle size distribution measured by laser diffraction method 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%.

[0062] In some embodiments, the specific pore volume p1 of the negative electrode material is 0.001–0.1 cm³. 3 / g. For example, the specific pore volume of the negative electrode material can be 0.001 cm³. 3 / g, 0.003cm 3 / g, 0.005cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g, 0.03cm 3 / g, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g or any value within the range of any two of the above values. Understandably, after the matrix is ​​filled with active material, the remaining pores in the matrix can reserve space for the volume expansion of the active material, mitigating the expansion effect of the negative electrode material and improving its cycle stability. The remaining pores in the matrix can also adsorb or contain a small amount of gas generated by the side reactions between the active material and the electrolyte, thereby improving the gas generation phenomenon of the negative electrode material.

[0063] In some embodiments, the average pore size of the negative electrode material is 0.45–50 nm. For example, the average pore size of the negative electrode material can be 0.45 nm, 0.65 nm, 0.85 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range of any two of the above values. Controlling the average pore size in the negative electrode material facilitates the passage of lithium ions through the pores, improving the charge / discharge rate performance of the negative electrode material while also helping to buffer the volume expansion of the active material and enhance the structural stability of the negative electrode material. In this embodiment, most of the active material is distributed within the pores of the matrix; therefore, the average pore size of the formed negative electrode material is increased.

[0064] In some embodiments, the micropore content of the negative electrode material is 10%–30%, the mesopore content is 30%–80%, and the macropore content is 0%–10%. Understandably, since the molecular size generated by the electrolyte is generally smaller than or equal to the pore size 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. For example, as the micropore volume increases, the adsorption capacity of the negative electrode material increases, thereby increasing the side reactions between the negative electrode material and the electrolyte. Therefore, controlling the volume ratio of micropores, mesopores, and macropores in the negative electrode material within this range can improve the uniformity of the silicon material distribution inside the negative electrode material. Specifically, the micropores are basically filled with active material, and the remaining majority of the pores are mesopores, which can effectively alleviate the volume expansion of the active material and reduce the excessive local expansion stress caused by the uneven volume change of the active material during cycling, thus preventing the negative electrode material from cracking or pulverizing.

[0065] In some embodiments, the specific surface area of ​​the negative electrode material is 0.1-5 m². 2 / g, specifically, the specific surface area can be a value of 0.1m³. 2 / g, 0.8m 2 / g, 1.4m 2 / g, 1.8m 2 / g, 2.5m 2 / g, 3.2m 2 / g, 4.1m 2 / g, 4.8m 2 / g and 5m 2 Any value in / g or other values ​​within the above range. It is understandable that the specific surface area of ​​the negative electrode material affects the contact area between the negative electrode material and the electrolyte. A specific surface area of ​​the negative electrode material within the above range can reduce the amount of lithium ions consumed by the SEI film formed during the first charge and discharge process of the lithium-ion battery, thereby reducing the irreversible capacity loss of the lithium-ion battery.

[0066] In some embodiments, the average gas production of the negative electrode material at 25°C over 24 hours is less than 0.15 mL / g. For example, the average gas production of the negative electrode material at 25°C over 24 hours can be 0.052 mL / g, 0.07 mL / g, 0.09 mL / g, 0.1 mL / g, 0.11 mL / g, 0.13 mL / g, or any value within the range of any two of the above values. Controlling the gas production value of the negative electrode material within the above range indicates that most of the active material can be relatively uniformly distributed within the pores of the matrix, reducing direct contact between the active material and the electrolyte, thereby reducing side reactions (such as silicon hydrolysis into silicates and hydrogen) between the dissolved active material and the electrolyte or during slurry preparation, effectively lowering the gas production value of the negative electrode material.

[0067] In some embodiments, the micropore content of the carbon matrix is ​​≥70%, and the pore size of the micropores is less than 2 nm. Preferably, it is ≥80%, more preferably ≥90%. Specifically, the micropore content can be any value or within the range of 70%, 75%, 80%, 86%, 89%, 92%, 96%, 98%, etc. Understandably, the pores of the carbon matrix are mainly micropores, which is beneficial for the deposition of active materials, such as silicon materials, on the micropores inside the carbon matrix. In addition, a high micropore content results in higher cycle performance and initial coulombic efficiency of the final battery.

[0068] In some embodiments, the average pore size of the carbon matrix is ​​0.1-5 nm, preferably 0.1-2 nm, and more preferably 0.1-1.8 nm. Specifically, it can be any value between 0.1 nm, 0.4 nm, 0.8 nm, 1.8 nm, 2 nm, 2.5 nm, 3.4 nm, 4.5 nm, and 5 nm, or other values ​​within the above range, and is not limited herein. This pore size distribution facilitates the deposition of active materials during the deposition process, thereby improving the compactness of the anode material.

[0069] In some embodiments, the pore volume of the carbon matrix is ​​≥0.4 cm³, based on the mass of the carbon matrix. 3 / g, preferably ≥0.5cm 3 / g, more preferably ≥0.7cm 3 / g. Specifically, it can be 0.4cm. 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3Any value in / g or other values ​​within the above range are not limited here. Understandably, when the carbon matrix has abundant pores, these pores can accommodate active materials and allow space for the volume expansion of the active materials. Furthermore, the higher the pore volume of the carbon matrix, the more active materials it can accommodate, allowing more active materials to deposit inside the carbon matrix, thus improving the conductivity and cycle performance of the anode material.

[0070] In some embodiments, the total pore volume of the negative electrode material is smaller than that of the carbon matrix. In this application, the total pore volume of the negative electrode material is significantly lower than that of the carbon matrix. This is because the active material can fill the pores within the porous framework of the carbon matrix relatively uniformly, causing most of the pores in the carbon matrix to shrink after being filled with the active material. This indicates that the pores of the carbon matrix are effectively and relatively uniformly filled by the active material, thereby improving the specific capacity of the negative electrode material.

[0071] In some embodiments, the average particle size of the carbon matrix is ​​1-50 μm, specifically any value between 1 μm, 8 μm, 12 μm, 25 μm, 32 μm, 43 μm and 50 μm or other values ​​within the above range.

[0072] In some embodiments, the carbon matrix content is 30% to 75% based on the mass of the negative electrode material. Specifically, the carbon matrix content can be any value among 30%, 38%, 45%, 51%, 60%, 70%, and 75%, or other values ​​within the above range.

[0073] In some embodiments, the average particle size of the silicon material is between 1 and 500 nm. Specifically, the average particle size of the silicon material can be other values ​​between 1 nm, 150 nm, 210 nm, 340 nm, 400 nm, 470 nm, and 500 nm, which can be selected according to actual needs. The mechanical stress during silicon material expansion decreases as the particle size decreases, allowing the secondary battery to maintain a good battery capacity and reducing irreversible capacity loss. Furthermore, the smaller size shortens the electron and ion transport paths. Simultaneously, as the particle size of the silicon material decreases, the gaps between adjacent silicon materials increase, reserving space for expansion. Preferably, the average particle size of the silicon material is 1 nm to 50 nm; more preferably, the average particle size of the silicon material is 1 nm to 10 nm.

[0074] In some embodiments, the morphology of the silicon material includes at least one of dot-like, spherical, ellipsoidal, and sheet-like shapes. The morphology of the silicon material can be selected according to actual needs and is not limited herein.

[0075] The negative electrode active layer also contains a binder to bond the negative electrode material particles, thereby facilitating the formation of the film layer, and also improving the bonding force between the negative electrode active layer and the negative electrode current collector.

[0076] In some embodiments, the adhesive may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, sodium carboxymethyl cellulose, sodium alginate, sodium polyacrylate, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0077] The separator membrane comprises a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator membrane may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane, etc.

[0078] The aforementioned battery is applied in electronic devices to power other electronic components within those devices. The use of the lithium-ion battery in this application is not particularly limited; it can be used in any electronic device known in the prior art. In some embodiments, the lithium-ion battery of this application can be used in, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0079] like Figure 1 As shown in the embodiments, this application describes a method for preparing a negative electrode material, which includes the following steps:

[0080] S100: An activator is added to the carbon-based raw material for activation. After activation, the raw material is acid-washed to obtain a carbon-based precursor. The carbon-based precursor is then dried to obtain a porous carbon precursor. The activator is a compound containing metal ions.

[0081] In some embodiments, the activator includes at least one of potassium ferrate, nickel nitrate, ferric chloride, ferric nitrate, cobalt nitrate, nickel chloride, cobalt chloride, ferric bromide, cobalt bromide, nickel bromide, ferric carbonate, cobalt carbonate, and nickel carbonate, and the amount of activator added is 0.2%-5% of the mass of the carbon-based raw material. The above-mentioned activators have strong activation capabilities, enabling the formation of numerous and uniformly distributed micropores in the porous carbon precursor, with a micropore ratio of not less than 70%, which is beneficial for subsequent active materials to fill the micropores. If the amount of activator added exceeds 5%, the pore size and number of pores in the porous carbon precursor will be larger, which can easily lead to structural collapse of the anode material during the insertion / extraction process, resulting in reduced cycle performance of the anode material. Simultaneously, the reduced micropore ratio in the porous carbon precursor and excessively high content of metal impurities can easily affect other properties of the anode material, such as reducing the initial coulombic efficiency. If the amount of activator added is too small, a suitable number and uniform distribution of activation pores cannot be formed inside the porous carbon precursor. This is detrimental to the subsequent deposition of silicon material within the pores of the porous carbon precursor, resulting in a large amount of silicon material deposited on the surface of the porous carbon precursor, causing significant volume expansion of the anode material. Furthermore, the increased contact area between the silicon material deposited on the surface of the porous carbon precursor and the electrolyte facilitates electrolyte contact, increasing the thickness of the SEI film on the surface of the anode material and extending the lithium-ion diffusion distance. This hinders the smooth insertion and extraction of lithium ions, ultimately leading to a loss of capacity in the anode material. Moreover, because silicon material cannot be deposited inside the porous carbon precursor, the M value and deposition coefficient γ of the anode material are both outside the preset range of this application, resulting in a conductivity of the formed anode material far below 1 S / cm.

[0082] In some embodiments, the activation temperature is 500–1200°C, and the activation time is 0.5–20 h.

[0083] At this activation temperature and time, the activator is embedded in the internal structure of the carbon-based raw material and undergoes cross-linking or polycondensation reactions with the carbon atoms and heteroatoms in the carbon-based raw material. Non-carbon atoms N and H are volatilized and removed, causing some carbon atoms to be etched away. Holes appear at the etched locations. The average pore size of the formed pores is small and the pore volume is high, which helps to accommodate more silicon material and allows silicon material to be deposited in the pores.

[0084] In some embodiments, the carbon-based material includes, but is not limited to, at least one of bamboo charcoal, coconut shell, graphite, peanut shell, fruit shell, and neutralizing resin. When the porous carbon-based raw material is amorphous hard carbon-based raw material such as coconut shell, bamboo charcoal, peanut shell, and fruit shell, it needs to be carbonized first. For shaped raw materials such as graphite, it only needs to be directly mixed with an activator for activation. It should be noted that the carbon inside amorphous carbon-based materials is in an amorphous state, so the cost is lower, and correspondingly, the electrical conductivity is also lower, generally 1-100 S / cm. Graphite, as a layered crystal structure, has a higher electrical conductivity, but its processing cost is higher. Therefore, in practical applications, amorphous carbon-based raw materials are generally used. Pre-treatment of the carbon-based raw material enables the active material to be uniformly deposited inside, thereby improving the electrical conductivity of the formed negative electrode material and compensating for the low conductivity of the active material itself.

[0085] In some embodiments, the activated carbon-based raw material is pickled with hydrochloric acid, wherein the concentration of hydrochloric acid is 12% to 25% and the pickling time is 5 to 6 hours to obtain a carbon-based precursor. The pickled carbon-based precursor is then dried to obtain a porous carbon precursor.

[0086] Hydrochloric acid is used to clean and activate the metallic impurities in the carbon-based raw materials, as well as the impurities in the carbon-based materials themselves, thereby opening up the pore structure of the carbon-based raw materials and increasing the specific surface area and micropore size of the activated carbon-based raw materials.

[0087] S200: Pretreatment of porous carbon precursors to obtain carbon matrix.

[0088] The specific pretreatment operation is as follows: the porous carbon precursor is mixed with a catalyst containing metal ions and an organic activator in an aqueous solution and dried. Then, it is heated and reduced under a reducing atmosphere to obtain a carbon material with metal elements attached. Finally, the carbon material is dispersed in an acid solution for dissolution to remove the metal element particles on the surface of the carbon material and obtain a carbon matrix.

[0089] In some embodiments, the catalyst containing metal ions is specifically a catalyst containing zinc ions, and the compound may be one or a mixture of zinc chloride, zinc nitrate, zinc acetate, and zinc sulfate.

[0090] In some embodiments, the organic surfactant is at least one of polyoxyethylene polyoxypropylene ether block copolymer (Pluronic F127), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP).

[0091] In some embodiments, the reducing atmosphere is at least one of a mixture of gases such as hydrogen, helium, and nitrogen.

[0092] In some embodiments, the acid solution is at least one of dilute hydrochloric acid and dilute nitric acid, the cleaning time of the acid solution is 1-12 hours, and the concentration is 0.5-1 mol / L. The acid solution is used to clean and remove elemental zinc adhering to the surface of the carbon material, while also reducing the reaction between elemental zinc inside the carbon material particles and the acid solution, resulting in a carbon matrix with elemental zinc adhering to the particles.

[0093] S300: A silicon source is used to perform vapor deposition on a carbon matrix to obtain the vapor deposition product.

[0094] In some embodiments, the silicon source includes at least one of silane, disilane, hexane, and propane. A silicon source is used to perform vapor deposition on the aforementioned carbon matrix with attached elemental zinc. The elemental zinc catalyzes the deposition of silicon material within the carbon matrix particles. In the prepared anode material, the silicon material is mainly distributed within the carbon matrix particles, thereby facilitating electron transport and improving the powder conductivity of the anode material.

[0095] In some embodiments, the silicon deposition conditions are as follows: the ambient vacuum pressure is set to p Pa, the silane gas concentration is N%, and the flow rate is V L / min, satisfying α = N * V. 2 / p, the value of α is: 0.1≤α≤50.

[0096] By controlling the vacuum pressure, silane gas concentration, and gas flow rate in the vapor deposition environment, uniform silicon deposition within the carbon matrix is ​​achieved. Specifically, silicon source precipitates as silicon nanoparticles dispersed within the pores of the porous carbon matrix. The resulting silicon-carbon material exhibits a uniform composition and relatively dense structure. The pores within the porous carbon matrix buffer volume expansion, resulting in a low expansion rate and excellent cycle performance in the formed anode material. Furthermore, the carbon matrix framework is not only inexpensive to manufacture but also possesses excellent lithium storage capacity. Its low density and light weight contribute to the high energy density of the formed anode material. Moreover, when the α value is between 0.1 and 50, a relatively large amount of silicon is uniformly deposited within the pores of the porous carbon matrix. Tests show that the deposition coefficient γ of the formed silicon-carbon anode material is no less than 0.85, and the M value is between 0.015 and 5. In practical applications, the conductivity is consistently no less than 0.7 S / cm, with some reaching as high as 80 S / cm.

[0097] In some embodiments, the silicon deposition reaction temperature is 400-800°C and the time is 1-13 hours.

[0098] When the silicon deposition time is less than 1 hour, the overall silicon content is low, making it difficult to deposit uniformly inside the carbon matrix. When the silicon deposition time exceeds 13 hours, some silicon overflows and deposits on the surface of the carbon matrix. As a result, the silicon on the surface of the carbon matrix is ​​more likely to come into contact with the electrolyte and react, increasing the gas production value of the negative electrode material. In addition, after the silicon material is deposited on the surface of the carbon matrix, it continues to grow and become larger, which will lead to particle pulverization and shedding, thereby reducing the electrochemical performance of the negative electrode material.

[0099] S400: The material obtained by vapor deposition and the coating material are mixed and heat-treated to obtain the negative electrode material.

[0100] In some embodiments, the coating material includes at least one of carbon materials, metal oxides, conductive polymers, fluorides, phosphates, and nitrides, without specific limitations herein.

[0101] In some embodiments, the coating material includes carbon material, which includes at least one of soft carbon and hard carbon, without being specifically limited herein.

[0102] In some embodiments, the coating material includes a metal oxide, which includes at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide, without being specifically limited herein.

[0103] In some embodiments, the coating material includes nitrides, which include at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride, without being specifically limited herein.

[0104] In some embodiments, the coating material includes a conductive polymer, which includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly-3-hexylthiophene, poly(p-phenylenevinylene), polypyridine, and polyphenylenevinylene, without being specifically limited herein.

[0105] In some embodiments, the coating material includes fluorides, which include at least one of vinyl fluoride, fluoropolymers, lithium fluoride, sodium fluoride, potassium fluoride, fluorocarbon polymers, fluorosilicone polymers, hexafluorobutyl acrylate, polytetrafluoroethylene, fluorinated ethylene-propylene copolymers, perfluoroalkoxy resins, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymers, polyvinylidene fluoride, and polyvinylidene fluoride, without specific limitation herein.

[0106] In some embodiments, the coating material includes phosphates, which include at least one of magnesium phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate, without being specifically limited herein.

[0107] In some embodiments, a coating material forms a coating layer on the surface of a carbon substrate, and the thickness of the coating layer is 1–500 nm. Specifically, the thickness of the coating layer can be 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, or 500 nm. Understandably, the coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas generated by the reaction of dissolved silicon material with the electrolyte. Controlling the thickness of the coating layer within the above range is beneficial for maintaining the stability of the particle structure of the negative electrode material during cycling, reducing the dissolution of silicon material, and improving the lithium-ion transport efficiency, thus enhancing the charge-discharge performance of the negative electrode material.

[0108] Those skilled in the art will understand that the methods for preparing lithium-ion batteries described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0109] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications can be made to the implementation without altering the main rights.

[0110] Example 1

[0111] (1) The coconut shell is placed in a carbonization furnace for carbonization. The specific carbonization temperature is 900℃ and the carbonization time is 3h. The carbon-based material after carbonization is mixed with potassium ferrate (K2FeO4). The mass of potassium ferrate added is 1% of the mass of the coconut shell. The mixture is activated at 800℃ for 10h. Then, hydrochloric acid is added for acid washing. The hydrochloric acid concentration is 20% and the washing time is 5h to obtain a carbon-based precursor. The acid-washed carbon-based precursor is dried to obtain a porous carbon precursor.

[0112] (2) Weigh 1.7 kg of zinc acetate and 360 g of Pluronic F127 and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 800 °C in a 10 vol% hydrogen / argon mixed atmosphere for 4 hours to obtain a black powder sample. Finally, put the obtained black powder sample into 10 L of 0.5 mol / L dilute hydrochloric acid and stir for 6 hours. Then wash the sample with pure water and dry it for later use to obtain a carbon matrix.

[0113] (3) Place the carbon matrix in a chemical vapor deposition (CVD) device, set the vacuum degree to 8000 Pa, then introduce silane into the CVD device, control the silane concentration to 50%, the gas rate to 50 L / min, raise the temperature to 600 °C, react for 4 h, and obtain the vapor-deposited product.

[0114] (4) The vapor phase deposition product and polyvinyl chloride were mixed at a mass ratio of 50:20. Then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 660°C for 2 hours. The obtained sample was crushed, sieved and graded to obtain the negative electrode material.

[0115] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0116] like Figure 2 The image shown is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1. As can be seen from the image, the particle shape is irregular.

[0117] like Figure 3 The figure shows the XRD pattern of the negative electrode material prepared in Example 1. It can be observed from the figure that the product is amorphous.

[0118] like Figure 4 The figure shows the first charge-discharge curve of the negative electrode material prepared in Example 1. As can be seen from the figure, the first charge-discharge capacity of the negative electrode material in Example 1 is 2098 mAh / g, and the first efficiency is 93.1%.

[0119] like Figure 5 As shown in the figure, the conductivity of the negative electrode material prepared in Example 1 is a graph. It can be seen from the figure that the conductivity of Example 1 increases with increasing pressure and is much higher than that of the sample in Comparative Example 1.

[0120] Example 2

[0121] (1) Bamboo charcoal was placed in a carbonization furnace for carbonization at a temperature of 1200℃ for 4 hours. A mixture of nickel nitrate and potassium hydroxide (mass ratio 1:89) was added to the treated carbon-based material, with the mass addition of the nickel nitrate and potassium hydroxide mixture being 2.5% of the mass of the bamboo charcoal. The mixture was activated at 800℃ for 10 hours. Then, hydrochloric acid was added for acid washing at a concentration of 12% for 5 hours to obtain a carbon-based precursor. The acid-washed carbon-based precursor was dried to obtain a porous carbon precursor.

[0122] (2) Weigh 1.7 kg of zinc chloride and 360 g of Pluronic PVA and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 800 °C in a 10 vol% hydrogen / argon mixed atmosphere for 4 hours to obtain a black powder sample. Put the obtained black powder sample into 10 L of 0.5 mol / L dilute hydrochloric acid and stir for 6 hours. Then wash the sample with pure water and dry it for later use to obtain a carbon matrix.

[0123] (3) Place the carbon matrix in a chemical vapor deposition (CVD) device, set the vacuum degree to 10130 Pa, then introduce silane into the CVD device, control the silane concentration to 80%, the gas rate to 72 L / min, raise the temperature to 400 °C, react for 4 h, and obtain the vapor-deposited product.

[0124] (4) The vapor phase deposition product and sucrose were mixed at a mass ratio of 50:45. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 920°C for 2 hours. The obtained sample was then crushed, sieved and graded to obtain the negative electrode material.

[0125] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0126] Example 3

[0127] (1) Graphite is mixed with potassium hydroxide (KOH) as an active agent, wherein the mass of KOH added is 4.4% of the mass of graphite. The mixture is activated at 1100℃ for 10h, and then hydrochloric acid is added for acid washing. The concentration of hydrochloric acid is 10% and the washing time is 6h to obtain a carbon-based precursor. The acid-washed carbon-based precursor is dried to obtain a porous carbon precursor.

[0128] (2) Weigh 1.7 kg of zinc sulfate and 360 g of F127 and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 800 °C in a 10 vol% hydrogen / argon mixed atmosphere for 4 hours. Then put the obtained black powder sample into 10 L of 0.5 mol / L dilute hydrochloric acid and stir for 6 hours. Then wash the sample with pure water and dry it for later use to obtain carbon matrix.

[0129] (3) Place the carbon matrix in a chemical vapor deposition (CVD) device, set the vacuum degree to 5000 Pa, then introduce silane into the CVD device with a silane concentration of 10% and a gas rate of 35 L / min, raise the temperature to 500 °C, and react for 3 h to obtain the vapor-deposited product.

[0130] (4) The vapor deposition product and epoxy resin were mixed at a mass ratio of 50:25. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 620°C for 2 hours. The obtained sample was then crushed, sieved and graded to obtain the negative electrode material.

[0131] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0132] Example 4

[0133] (1) Carbonize the coconut shell at 800℃ for 12 hours. Add a mixture of ferric chloride and KOH (mass ratio 5:95) to the treated carbon-based material, wherein the mass of the mixture of ferric chloride and KOH added is 3.9% of the mass of the coconut shell. Activate at 850℃ for 10 hours, then add hydrochloric acid for acid washing at a concentration of 25% for 5 hours to obtain a carbon-based precursor. Dry the acid-washed carbon-based precursor to obtain a porous carbon precursor.

[0134] (2) Weigh 1.7 kg of zinc acetate and 360 g of Pluronic F127 and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 900 °C in a 12 vol% hydrogen / argon mixed atmosphere for 4 hours. Then put the obtained black powder sample into 12 L of 0.5 mol / L dilute hydrochloric acid and stir for 6 hours. Finally, wash the sample with pure water and dry it for later use to obtain the carbon matrix.

[0135] (3) Place the carbon matrix in a chemical vapor deposition (CVD) device, set the vacuum degree to 500 Pa, then introduce silane into the CVD device, control the silane concentration to 20%, the gas rate to 30 L / min, raise the temperature to 600 °C, react for 1 h, and obtain the vapor-deposited product.

[0136] (4) The vapor deposition product and citric acid were mixed at a mass ratio of 50:20. The mixed material was then placed in a high-temperature box furnace, nitrogen was introduced, and the mixture was heat-treated at 760°C for 2 hours. The obtained sample was then crushed, sieved and graded to obtain the negative electrode material.

[0137] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, 2M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0138] Example 5

[0139] The difference from Example 1 is that step (1) is as follows: the coconut shell is placed in a carbonization furnace for carbonization, the specific carbonization temperature is 900℃, the carbonization time is 3h, the carbonized porous carbon-based material is mixed with potassium ferrate (K2FeO4), wherein the mass of potassium ferrate added is 0.2% of the mass of coconut shell, the mixture is activated at 800℃ for 10h, and then hydrochloric acid is added for acid washing, wherein the hydrochloric acid concentration is 20%, the washing time is 5h, and a carbon-based precursor is obtained. The acid-washed carbon-based precursor is dried to obtain a porous carbon precursor.

[0140] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0141] Example 6

[0142] The difference from Example 1 is that step (1) is as follows: the coconut shell is placed in a carbonization furnace for carbonization, the specific carbonization temperature is 900℃, the carbonization time is 3h, the carbon-based material after carbonization is mixed with potassium ferrate (K2FeO4), wherein the mass of potassium ferrate added is 3% of the mass of coconut shell, the activation is carried out at 800℃ for 10h, and then hydrochloric acid is added for acid washing, wherein the hydrochloric acid concentration is 20%, the washing time is 5h, and a carbon-based precursor is obtained. The acid-washed carbon-based precursor is dried to obtain a porous carbon precursor.

[0143] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0144] Example 7

[0145] The difference from Example 3 is that step (3) is as follows: the carbon substrate is placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 5000Pa, and then silane is introduced into the CVD device with a silane concentration of 10% and a gas rate of 35L / min. The temperature is raised to 500℃ and the reaction is carried out for 1.5h to obtain the vapor-deposited product.

[0146] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material located within the carbon matrix. The deposition coefficient γ, M value, conductivity, and silicon content of the negative electrode material are shown in Table 2.

[0147] Example 8

[0148] The difference from Example 1 is that step (3) is as follows: the carbon substrate is placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 1250 Pa, and then silane is introduced into the CVD device with a silane concentration of 50% and a gas rate of 16 L / min. The temperature is raised to 500 °C and the reaction is carried out for 1.5 h to obtain the vapor-deposited product.

[0149] Example 9

[0150] Unlike Example 1, in step (3), the carbon matrix is ​​placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 680 Pa, and then silane is introduced into the CVD device with a silane concentration of 50% and a gas rate of 26 L / min. The temperature is raised to 500 °C and the reaction is carried out for 1.5 h to obtain the vapor-deposited product.

[0151] Example 10

[0152] The difference from Example 1 is that step (1) is as follows: the coconut shell is placed in a carbonization furnace for carbonization, the specific carbonization temperature is 900℃, the carbonization time is 3h, the carbon-based raw material after carbonization is mixed with potassium ferrate (K2FeO4), wherein the mass of potassium ferrate added is 5% of the mass of coconut shell, the activation is carried out at 800℃ for 10h, and then hydrochloric acid is added for acid washing, wherein the hydrochloric acid concentration is 20%, the washing time is 5h, and a carbon-based precursor is obtained. The acid-washed carbon-based precursor is dried to obtain a carbon precursor.

[0153] Example 11

[0154] Unlike Example 1, a mixture of nickel nitrate and potassium hydroxide (mass ratio 1:89) was added to the treated carbon-based material, wherein the mass addition amount of the mixture of nickel nitrate and potassium hydroxide was 2.5% of the mass of bamboo charcoal, and the material was activated at 800°C for 16 hours.

[0155] Example 12

[0156] Unlike Example 1, a mixture of nickel nitrate and potassium hydroxide (mass ratio 1:89) was added to the treated carbon-based material, wherein the mass addition amount of the mixture of nickel nitrate and potassium hydroxide was 2.5% of the mass of bamboo charcoal, and the material was activated at 800°C for 20 hours.

[0157] Comparative Example 1

[0158] The difference from Example 1 is that step (1) involves carbonizing the coconut shell in a carbonization furnace at a temperature of 900°C for 3 hours, then acid-washing the carbon-based material after carbonization at a concentration of 20% for 5 hours, and finally drying the acid-washed carbon-based precursor to obtain a porous carbon precursor. In other words, only the coconut shell is carbonized and acid-washed without activation to obtain the carbon precursor.

[0159] Comparative Example 2

[0160] The difference from Example 1 is that step (1) is as follows: the coconut shell is placed in a carbonization furnace for carbonization, the specific carbonization temperature is 900℃, the carbonization time is 3h, the carbonized porous carbon-based material is mixed with potassium ferrate (K2FeO4), wherein the mass addition amount of potassium ferrate is 0.05% of the mass of the coconut shell, the mixture is activated at 800℃ for 10h, and then acid-washed, the acid concentration is 20%, the washing time is 5h, and the acid-washed carbon-based precursor is dried to obtain the porous carbon precursor.

[0161] Comparative Example 3

[0162] The difference from Example 1 is that step (1) is as follows: the coconut shell is placed in a carbonization furnace for carbonization, the specific carbonization temperature is 900℃, the carbonization time is 3h, the carbon-based material after carbonization is mixed with potassium ferrate (K2FeO4), wherein the mass addition amount of potassium ferrate is 5.2% of the coconut shell mass, the activation is carried out at 800℃ for 10h, and then acid washing is performed, the acid washing concentration is 20%, the washing time is 5h, and the acid-washed carbon-based precursor is dried to obtain a porous carbon precursor.

[0163] Comparative Example 4

[0164] Unlike Example 1, step (2) was not performed, i.e., the porous carbon precursor was not pretreated.

[0165] Comparative Example 5

[0166] The difference from Example 1 is that step (3) is as follows: the carbon substrate is placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 8000Pa, and then silane is introduced into the CVD device with a silane concentration of 50% and a gas rate of 50L / min. The temperature is raised to 600℃ and the reaction is carried out for 0.5h to obtain the vapor-deposited product.

[0167] Comparative Example 6

[0168] The difference from Example 1 is that step (3) is as follows: the carbon substrate is placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 700 Pa, and then silane is introduced into the CVD device with a silane concentration of 30% and a gas rate of 35 L / min. The temperature is raised to 500 °C and the reaction is carried out for 1 h to obtain the vapor-deposited product.

[0169] Comparative Example 7

[0170] The difference from Example 1 is that step (3) is as follows: the carbon substrate is placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 8000Pa, and then silane is introduced into the CVD device with a silane concentration of 50% and a gas rate of 50L / min. The temperature is raised to 600℃ and the reaction is carried out for 14h to obtain the vapor-deposited product.

[0171] Test method:

[0172] I. Parameter Testing Methods for Anode Materials

[0173] 1. Test method for average particle size of materials:

[0174] The material particles are observed using a field emission scanning electron microscope or a transmission electron microscope. The particle size of 5-10 material particles is randomly measured using a scale bar, and the average particle size is taken as the final average particle size of the material.

[0175] 2. Test method for the mass content of silicon in negative electrode materials:

[0176] Using the Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace: ignition in an oxygen atmosphere causes silicon and silicon suboxide in the sample to react to form silicon dioxide, and carbon is burned into carbon dioxide and discharged. The silicon content is then calculated by weighing.

[0177] 3. Test method for particle size of negative electrode material:

[0178] The D50, measured using a laser particle size analyzer, exhibits a symmetrical distribution resembling a normal distribution. In its volumetric baseline distribution, the cumulative 50% diameter is D50, and so on, with the cumulative 90% diameter being D90 and the cumulative 10% diameter being D10.

[0179] 4. Test method for conductivity of negative electrode material powder:

[0180] The conductivity at a pressure of 20 kN was tested using the MCP-PD51 powder resistance testing system from Mitsubishi Chemical Corporation of Japan, and the volume resistivity of the sample was determined using the four-probe method. This instrument can measure the resistance of the powder, and then the computer automatically calculates the conductivity and resistivity of the powder.

[0181] 5. Test methods for specific pore volume, average pore size, and volume ratio of micropores, mesopores, and macropores in negative electrode materials:

[0182] The material was tested using an ASAP2460 instrument from Microchip Technology, USA, to obtain the proportions of micropores and mesopores. The pore volume V was determined using the BJH Desorption Cumulative Volume of Pores model. Calculated within the aperture range.

[0183] Micropore and mesopore analyses were performed using 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 properties. By combining the relationship between adsorption amount and relative pressure during the adsorption process, various models can be fitted to calculate the pore size. The software report uses density functional theory (DFT) to calculate the pore size distribution, specific pore volume, and pore volume within a certain range.

[0184] 6. Test method for carbon content in negative electrode materials:

[0185] Using the Bruker G4 ICARUS HF infrared carbon-sulfur analyzer from Germany, the sample is burned in a high-temperature, oxygen-rich environment, where the carbon is oxidized into carbon dioxide. The generated gas enters the infrared detector along with the carrier gas, and the carbon content can be calculated by quantitatively analyzing the changes in the carbon dioxide signal.

[0186] 7. Test method for specific surface area of ​​negative electrode material:

[0187] The surface area and pore size were measured using a McTriStar3000 surface area and pore size analyzer from the USA.

[0188] 8. Test method for gas generation value of negative electrode material:

[0189] 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.

[0190] 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.

[0191] II. Electrochemical Performance Testing

[0192] 1. Test methods for reversible capacity and 7C capacity retention:

[0193] 1) Battery preparation: The prepared negative electrode material, conductive agent and binder are dissolved and mixed in a solvent at a mass percentage of 94:1:5, and the solid content is controlled at 50%. The mixture is coated on a copper foil current collector, vacuum dried, and a negative electrode sheet is obtained. Then, a ternary positive electrode sheet prepared by conventional mature process, a 1mol / L LiPF6 / ethyl cellulose + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte, a polypropylene separator (Celgard 2400) and a shell are assembled using conventional production processes to form an 18650 cylindrical single cell battery.

[0194] 2) Testing: The above-mentioned batteries were charged and discharged using the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd. Under normal temperature conditions, constant current charging and discharging at 0.2C was used, with the charging and discharging voltage limited to 2.75~4.2V, to obtain the first reversible capacity; then constant current charging and discharging at 7C was used, with the charging and discharging voltage limited to 2.75~4.2V, to obtain the reversible capacity. The ratio of the two was calculated to obtain the 7C capacity retention rate.

[0195] 2. Test method for initial coulomb efficiency (ICE):

[0196] 1) Preparation of coin cell batteries: A negative electrode slurry was prepared by mixing negative electrode material, conductive carbon black, and polyacrylic acid (PPA) in a mass ratio of 75:15:10. The slurry was coated on copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and coin cells were assembled in an argon-filled glove box.

[0197] 2) Testing: The coin cell was charged and discharged at a current density of 0.1C within the charge and discharge range of 0.01V-5V to obtain the initial coulombic efficiency (ICE) of the coin cell.

[0198] 3. Test method for electrode thickness expansion rate after 50 cycles:

[0199] 1) Preparation of coin cell batteries: A negative electrode slurry was prepared by mixing negative electrode active material, conductive 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 a negative electrode sheet. The negative electrode active material is a mixture of the negative electrode material and graphite described in this application. The ratio of the negative electrode material to graphite is determined by the initial reversible specific capacity of both materials and the desired combined capacity. A coin cell was assembled using a lithium metal sheet as the counter electrode in an argon-filled glove box.

[0200] 2) Testing: The button cell was subjected to 50 repeated charge-discharge cycles at a current density of 1C within the charge-discharge range of 0.01V-5V to obtain the electrode thickness expansion rate after 50 battery cycles.

[0201] Table 1: Results of relevant parameters for the negative electrode materials in Examples 1-12 and Comparative Examples 1-7

[0202]

[0203] Table 2: Relevant parameter results of the negative electrode materials of Examples 1-12 and Comparative Examples 1-7

[0204]

[0205] Table 3: Electrochemical performance characterization of the negative electrode materials of Examples 1-12 and Comparative Examples 1-7

[0206]

[0207]

[0208] Based on Examples 1-12 and Tables 1 and 2, the method for preparing the negative electrode material according to this application, by limiting the mass addition of the activator to 0.2%-5% of the carbon-based raw material mass, can form a large number of uniformly distributed micropores in the porous carbon precursor, with a micropore ratio of not less than 70%, which is beneficial for the subsequent filling of active materials into the micropores. During the deposition of active materials such as silicon, the deposition conditions are controlled, limiting 0.1≤α≤50, so that the deposition parameter γ of the final negative electrode material is not less than 0.85, that is, a relatively large amount of active material is deposited inside the matrix, reducing the direct contact between the negative electrode active material and the electrolyte during charging and discharging, and reducing the probability of active materials such as silicon hydrolyzing in water to form silicates, thereby effectively reducing the gas production value of the negative electrode material; at the same time, the value of M is greater than 0.015 and less than 5, ensuring that a relatively large amount of silicon material is uniformly deposited in the carbon matrix, and the negative electrode material has a relatively high conductivity. Importantly, the overall process does not introduce too many metal impurities, so the resulting negative electrode material has high conductivity, high charge and discharge efficiency, and good cycle performance.

[0209] Referring to Examples 1-12 and Tables 1 to 3, the content of mesopores in the negative electrode material is 30%-80%, and the proportion of micropores is 10%-30%. This indicates that the micropores in the negative electrode material are basically filled by active materials such as silicon. As a result, the deposition parameters of the negative electrode material are relatively high, thereby constructing electron transport channels in the pores of the carbon matrix. This is beneficial to improve the conductivity of the negative electrode material and further improve the M value. As a result, the cycle performance and initial coulombic efficiency of the battery are also higher.

[0210] Referring to Examples 1-12 and Tables 1 and 3, the specific pore volume p1 of the negative electrode material is between 0.001 and 0.1 cm⁻¹. 3 At / g, the expansion rate of the formed negative electrode material is low, all within 40%. This is because after the silicon material is filled into the carbon matrix, the remaining pores in the carbon matrix can reserve space for the volume expansion of the silicon material, thereby alleviating the expansion effect of the negative electrode material and improving the cycle stability of the negative electrode material. The remaining pores in the carbon matrix can also adsorb or contain some of the small amount of gas generated by the side reaction between the silicon material and the electrolyte, thereby reducing the gas production value of the negative electrode material.

[0211] In conjunction with Examples 1-12 and referring to Tables 1 and 3, when the average pore size of the negative electrode material is within the range of 0.45 to 50 nm, it can facilitate the transport channels of lithium ions, improve the conductivity of the negative electrode material, and increase the first coulombic efficiency.

[0212] Compared to Example 1, Comparative Example 1 did not add potassium ferrate, i.e., did not activate the carbon-based raw material. Therefore, it was impossible to form a suitable number and uniformly distributed activation pores inside the carbonized material. Active materials such as silicon materials were difficult to deposit inside the pores of the carbon matrix, but instead deposited on the surface of the carbon matrix. As a result, the anode material formed had a large volume expansion and low conductivity. In addition, the silicon material deposited on the surface of the carbon matrix increased the contact area with the electrolyte, increased the thickness of the SEI film, and increased the diffusion distance of lithium ions, hindering the smooth insertion and extraction of lithium ions. Ultimately, this resulted in a very low capacity retention rate of the anode material.

[0213] Compared with Example 1, Comparative Example 2 has a lower amount of potassium ferrate added, which makes it impossible to form a suitable number and uniformly distributed activation pores inside the carbonized material. Only part of the silicon material is deposited inside the carbon matrix, while more is deposited on the surface of the carbon matrix. As a result, the deposition coefficient γ and M value of the formed negative electrode material are lower than the preset values, the conductivity of the negative electrode material is poor, and the electrochemical performance, especially the capacity retention rate, is far lower than the capacity retention rate of Example 1.

[0214] Compared with Example 1, Comparative Example 3 has a higher amount of potassium ferrate added, which increases the pore size and number of pores formed during the activation process, thereby reducing the proportion of micropores in the carbon matrix and increasing the size of the deposited silicon. In addition, the formed negative electrode material introduces more metal impurities, which causes the structure of the negative electrode material to collapse during the insertion and extraction process, resulting in a decrease in the cycle performance of the negative electrode material.

[0215] Compared with Example 1, Comparative Example 4 did not pretreat the carbon substrate, so the silicon material was partially deposited on the surface of the carbon substrate, and the resulting M value was only 0.002, which is about 1 / 10 of the limit specified in this application. The deposition parameter γ was also lower than 0.85, and the conductivity of the generated negative electrode material was only 0.1 S / cm, which is far from meeting the usage standard required by this application.

[0216] Compared with Example 1, Comparative Example 5 reduced the silicon deposition time, so the mass percentage of silicon in the resulting anode material was only 15%. Although the M value, deposition coefficient γ and conductivity of the formed anode material were all within the set values, the specific capacity and initial coulombic efficiency of the anode material were both low.

[0217] Compared with Example 1, Comparative Example 6 changed the deposition conditions of silicon material, specifically by changing the vacuum degree of silicon material deposition, so that the deposition condition α of silicon material was 52.5%, which exceeded the preset range value. This resulted in a larger specific pore volume of the negative electrode material and more silicon material being deposited on the surface of the carbon matrix. Consequently, the gas generation value of the formed negative electrode material was larger, and the deposition coefficient γ and M value of the formed negative electrode material were both lower, resulting in poorer electrochemical performance of the formed battery.

[0218] Compared to Example 1, Comparative Example 7 increased the silicon deposition time, resulting in a silicon mass percentage exceeding 65%. However, some silicon overflowed and deposited on the substrate surface, making it easier for the silicon on the substrate surface to react with the electrolyte, increasing the gas generation value of the negative electrode material. Furthermore, after the silicon material deposited on the carbon substrate surface, it continued to grow, leading to particle pulverization and detachment, thereby reducing the electrochemical performance of the negative electrode material. For example, the resulting battery performance, especially the 7C capacity retention rate, was very low, at only 2.5%, failing to meet the standards for using superior battery materials.

[0219] Those skilled in the art will understand that the methods for preparing lithium-ion batteries described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes a matrix and an active material. The matrix has pores, and at least a portion of the active material is located within the pores of the matrix. Based on the mass of the negative electrode material, the mass percentage of the active material in the negative electrode material is a1%. The conductivity of the negative electrode material is σS / cm, where 16≤a1≤65. M is defined as σ / a1, and the value of M is 0.015≤M≤5. Furthermore, the deposition parameter γ of the active material within the matrix is ​​≥0.85, where the deposition parameter γ represents the ratio of the volume of the active material located within the pores of the matrix to the total volume of the active material.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following characteristics: (1) The median particle size D50 of the negative electrode material is 1-15 μm; (2) The particle size distribution of the negative electrode material satisfies 0.1≤(D90-D10) / D50≤2.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following characteristics: (1) The specific pore volume of the negative electrode material is 0.001–0.1 cm³. 3 / g; (2) The average pore size of the negative electrode material is 0.45–50 nm; (3) The specific surface area of ​​the negative electrode material is 0.1-5m². 2 / g.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following characteristics: (1) The micropore ratio of the negative electrode material is 10% to 30%; (2) The mesoporous content of the negative electrode material is 30% to 80%; (3) The macropore ratio of the negative electrode material is 0-10%.

5. The negative electrode material according to claim 1, characterized in that, The matrix includes a carbon matrix, which includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microspheres, activated carbon, and carbon gel.

6. The negative electrode material according to claim 5, characterized in that, The carbon matrix includes at least one of the following characteristics: (1) The carbon matrix has a micropore content of ≥70%; (2) The average pore size in the carbon matrix is ​​0.1-5 nm; (3) The pore volume of the carbon matrix is ​​≥0.4 cm³. 3 / g; (4) Based on the mass of the negative electrode material, the carbon content is 30% to 75%.

7. The negative electrode material according to claim 1, characterized in that, The active material includes silicon material, which includes at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloy, and a mixture of crystalline and amorphous silicon.

8. The negative electrode material according to claim 7, characterized in that, The silicon material includes at least one of the following characteristics: (1) The purity of the silicon material is greater than 99%; (2) The average particle size of the silicon material is 1-500 nm.

9. A negative electrode sheet, characterized in that, It includes the negative electrode material as described in any one of claims 1-8.

10. A battery, characterized in that, It includes the negative electrode sheet as described in claim 9.

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