Negative electrode material and secondary battery

Abstract

The present application relates to the technical field of battery negative electrode materials. The present application discloses a negative electrode material and a secondary battery. The negative electrode material comprises a porous material and an active substance, wherein the active substance is at least partially distributed in pores of the porous material, and the active substance comprises a silicon material; the atomic percentage of Si at n depths is obtained by using X-ray photoelectron spectroscopy (XPS) in combination with argon ion sputtering to etch the negative electrode material, wherein the atomic percentage of Si on the surface of the negative electrode material and the atomic percentage of Si at the n depths satisfy: formula (I), wherein γ≤0.4. The negative electrode material according to embodiments of the present application has good overall performance.

Description

Anode materials and secondary batteries

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510554634.X, filed on April 29, 2025, entitled “Anode Material and Secondary Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application generally relates to the field of battery anode material technology. More specifically, this application relates to an anode material and a secondary battery. Background Technology

[0004] Lithium-ion batteries, with their advantages of high energy density, long lifespan, and no environmental pollution, are widely used in the 3C field (communication, computer, and consumer electronics) and large equipment such as electric vehicles and power tools. To improve battery energy density, silicon-based anode materials, due to their low voltage platform, environmental friendliness, and abundant resources, have become one of the most promising materials for achieving high-capacity lithium-ion batteries. However, existing ordinary silicon-based materials have many problems. During charge and discharge, their large volume expansion easily leads to pulverization and detachment from the current collector. Simultaneously, the repeated volume changes of silicon-based active materials during electrochemical cycling cause the surface-formed SEI film ("Solid Electrolyte Interphase") to continuously break down and regenerate, continuously consuming lithium ions, severely affecting battery stability, and leading to a rapid decline in battery capacity during long cycles.

[0005] In view of this, there is an urgent need to provide a solution for anode materials in order to improve the overall electrochemical performance of anode materials. Summary of the Invention

[0006] In order to at least solve one or more of the technical problems mentioned above, this application proposes a solution for a negative electrode material and a secondary battery in several aspects.

[0007] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a matrix material and an active material, wherein the active material is at least partially distributed within the matrix material, and the active material comprises silicon material; the negative electrode material is etched using X-ray photoelectron spectroscopy (XPS) combined with argon ion sputtering to obtain the percentage of Si atoms at n depths, wherein the percentage of Si atoms on the surface of the negative electrode material and the percentage of Si atoms at the n depths satisfy the following: γ≤0.4; where γ represents the uniformity parameter of Si atom distribution in the negative electrode material, A i% represents the percentage of Si atoms at the i-th depth from the surface of the negative electrode material into its interior. A i-1 % represents the percentage of Si atoms at the (i-1)th depth from the surface of the negative electrode material to its interior. A0% represents the percentage of Si atoms at the surface of the negative electrode material. D represents the depth interval between two adjacent test depths, in nm. D = 20; n = 8.

[0008] In a second aspect, this application provides a secondary battery, which includes the negative electrode material described in the first aspect of this application.

[0009] In the above-described anode material scheme, the anode material of this application embodiment includes a matrix material and an active material. XPS etching is performed from the surface of the anode material to multiple depths inside the anode material to obtain the percentage of Si atoms at multiple depths. The percentage of Si atoms on the surface of the anode material and the percentage of Si atoms at multiple depths satisfy the following: Furthermore, γ≤0.4 indicates that the percentage distribution of Si atoms from the surface to the interior of the negative electrode material is relatively uniform, which is beneficial to the stress distribution inside the negative electrode material. This enables the negative electrode material to maintain good cycle stability in the battery, thereby obtaining excellent cycle performance and exhibiting excellent first discharge specific capacity and first coulombic efficiency. Attached Figure Description

[0010] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:

[0011] Figure 1 shows a schematic diagram of a battery in a discharged state, i.e., during operation.

[0012] Figure 2 shows an exemplary flowchart of a method for preparing a negative electrode material according to some embodiments of this application.

[0013] The following reference numerals appear in the above figures: 110, positive electrode sheet; 120, negative electrode sheet; 130, separator membrane; 111, positive current collector; 112, positive active layer; 121, negative current collector; 122, negative active material layer; 140, metal ion. Detailed Implementation

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0015] It should be understood that the terms "comprising" and "including" as used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0016] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0017] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[0018] The specific embodiments of this application are described in detail below with reference to the accompanying drawings. Unless otherwise specified, the materials, reagents and equipment used in the embodiments of this application are obtained through conventional commercial channels.

[0019] Figure 1 shows a schematic diagram of a battery in a discharged state, i.e., during operation. As shown in Figure 1, the electrode assembly includes a positive electrode 110, a negative electrode 120, and a separator 130, with the separator 130 disposed between the positive electrode 110 and the negative electrode 120. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 110, the separator 130, and the negative electrode 120. 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.

[0020] Positive electrode tablets:

[0021] The positive electrode 110 includes a positive current collector 111 and a positive active layer 112 disposed on at least one surface of the positive current collector. The positive current collector 111 can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining a conductive foil and a polymer substrate. The positive active layer 112 contains a positive active material, which includes compounds that reversibly insert and extract metal ions. In some embodiments, the positive 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. 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 the following: O4 or lithium iron phosphate (LiFePO4).

[0022] Negative electrode plate:

[0023] The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector 121. The negative electrode current collector 121 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collectors, 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 122 includes a negative electrode material.

[0024] During battery operation, i.e. when the battery is in a discharge state, metal ions 140 (e.g., lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator 130, and are embedded in the lattice of the positive electrode material.

[0025] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the electrolyte / electrolyte through the separator 130, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing metal ions to be embedded in the lattice of the negative electrode material.

[0026] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve the discharge and charge process in thousands of cycles.

[0027] The inventors have discovered that the uniformity of active material (e.g., silicon) deposition within the negative electrode material significantly affects its performance. If the percentage distribution of Si atoms from the inside out of the negative electrode material is uneven, the stress in different parts of the material will become uneven during repeated charge-discharge cycles. This stress imbalance leads to stress concentration at certain points of high local stress, increasing the probability of breakage or pulverization at those points and resulting in deterioration of the negative electrode material's cycle performance. Therefore, the smaller the variation in the percentage distribution of Si atoms from the inside out of the negative electrode material, the better it is for maintaining the cycle stability of the negative electrode material, resulting in better cycle performance.

[0028] Based on the above findings, this application aims to provide a negative electrode material with a uniform Si atom percentage distribution, in order to improve the cycle performance of the negative electrode material. A detailed description follows.

[0029] In a first aspect, this application provides a negative electrode material, comprising a matrix material and an active material, wherein the active material is at least partially distributed within the matrix material, and the active material comprises silicon material; the negative electrode material is etched using X-ray photoelectron spectroscopy combined with argon ion sputtering to obtain a percentage of Si atoms at n depths, wherein the percentage of Si atoms on the surface of the negative electrode material and the percentage of Si atoms at the n depths satisfy the following:

[0030] And γ≤0.4;

[0031] Where γ represents the uniformity parameter of Si atoms in the negative electrode material, and A i % represents the percentage of Si atoms at the i-th depth from the surface of the negative electrode material into its interior. A i-1 % represents the percentage of Si atoms at the (i-1)th depth from the surface of the negative electrode material to its interior. A0% represents the percentage of Si atoms at the surface of the negative electrode material. D represents the depth interval between two adjacent test depths, in nm. D = 20; n = 8.

[0032] XPS etching from the surface of the negative electrode material to n depths inside the negative electrode material to obtain the percentage of Si atoms at n depths refers to using XPS etching technology to etch n depths from the surface of the negative electrode material to its interior, and measuring the percentage of Si atoms at each of the n depths.

[0033] X-ray photoelectron spectroscopy (XPS) is a surface analysis technique that combines XPS and ion etching. XPS works by irradiating the sample surface with X-rays, exciting electrons in the sample atoms to form photoelectrons. By measuring the energy and intensity of these photoelectrons, information such as the elemental composition and chemical state of the sample surface can be obtained. Ion etching, on the other hand, uses a high-energy ion beam (such as an argon ion beam) to bombard the sample surface, removing atoms layer by layer, thus enabling analysis at different depths of the sample. By alternating between ion etching and XPS measurements, information on the elemental distribution from the surface to different depths within the sample can be obtained.

[0034] A value of γ ≤ 0.4 indicates a relatively uniform distribution of Si atoms from the surface to the interior of the negative electrode material. This effectively avoids stress concentration caused by uneven Si atom distribution, thereby improving the stability of the negative electrode material during charge and discharge. Furthermore, the initial discharge specific capacity and initial coulombic efficiency of the negative electrode material are excellent. For example, γ can be 0.4, 0.3, 0.25, 0.2, 0.15, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or other values ​​not exceeding 0.4. In some preferred embodiments, γ ≤ 0.3. If γ > 0.4, it indicates a significant difference in the percentage of Si atoms at different depths within the negative electrode material. This suggests a relatively uneven distribution of Si atoms within the negative electrode material, potentially leading to stress imbalance and affecting the overall performance of the negative electrode material, including cycle stability, initial discharge specific capacity, and initial coulombic efficiency.

[0035] In this application, controlling D=20 can provide a more detailed distribution of the percentage of Si atoms, ensuring the accuracy of the evaluation results of the uniformity of Si atom distribution in the negative electrode material, and can also help control the testing cost.

[0036] In some implementations, 17≤A i ≤25, where i is any integer from 4 to 8. For example, A i It can be any value from 17, 18, 19, 20, 21, 22, 23, 24, 25, or other values ​​within the range of 17 to 25. The percentage content of Si atoms at different depths can be the same or different.

[0037] The percentage of Si atoms within the above range indicates that the silicon content inside the negative electrode material is moderate, which helps to improve the charge and discharge specific capacity of the negative electrode material, and also helps to reduce the volume expansion rate of the negative electrode material during cycling.

[0038] In some implementations, 5≤A i≤17, where i is any integer from 1 to 3. For example, A i It can be any value from 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or other values ​​within the range of 5 to 17. The percentage of Si atoms on the surface of the negative electrode material can be the same as or different from the percentage of Si atoms at different depths.

[0039] Within the above-mentioned range, the percentage of Si atoms ensures that silicon material provides high battery capacity as an active material, ensures the stability of the anode material during cycling, and further reflects the uniformity of the percentage of Si atoms at different depths of the anode material.

[0040] In other embodiments, the average value of A0–A3 is B1, and the average value of A4–A8 is B2, where B1 < B2. This distribution indicates that the percentage of Si atoms inside the negative electrode material is higher than the percentage of Si atoms on the surface, forming a gradient distribution. This gradient distribution helps improve the cycle performance of the negative electrode material. Specifically, a higher percentage of Si atoms inside the negative electrode material can provide higher capacity, while a lower percentage of Si atoms on the surface can reduce stress concentration on the surface of the negative electrode material, which is beneficial to improving the cycle stability of the material. Furthermore, if the percentage of Si atoms on the surface is too high, it may lead to the formation of a dense silicon shell on the pore surface of the negative electrode material (i.e., "pore sealing"), hindering the insertion and extraction of lithium ions, while increasing the risk of SEI film formation and lithium ion consumption. A lower percentage of surface Si atoms can avoid this problem and maintain the open structure of the material.

[0041] Porous materials can serve as the matrix material for anode materials, and the desired anode material can be obtained by depositing active substances in the porous material. In some embodiments, the porous material includes at least one of activated carbon, capacitor carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, porous TiO2, etc.

[0042] The active substance is at least partially distributed within the pores of the porous material; it may be a portion of the active substance distributed within the pores of the porous material, or it may be all of the active substance distributed within the pores of the porous material.

[0043] In other embodiments, the silicon material may include at least one of elemental silicon, silicon oxide, and silicon alloy.

[0044] When the silicon material includes elemental silicon, the elemental silicon includes one or more of amorphous silicon, crystalline silicon, and composites of crystalline and amorphous silicon. Preferably, the elemental silicon includes amorphous silicon, which expands isotropically during lithium intercalation, reducing the collapse of pores in the matrix, suppressing the rapid decay of the specific capacity of the battery including the negative electrode material, and further improving the lithium intercalation cycle performance of the negative electrode material.

[0045] When silicon materials include silicon oxides, the general formula for silicon oxides is SiO₂. x Where 0 < x ≤ 2, silicon oxide is a silicon-oxygen complex containing oxygen atoms and silicon atoms, with a molar ratio of oxygen atoms to silicon atoms of 0 to 2, excluding 0. It can be Si, SiO₂, etc. 0.2 SiO 0.5 SiO 0.8 SiO, SiO 1.2 SiO 1.5 SiO 1.8 It can be a substance composed of two or more of the above-mentioned materials, such as SiO2, or other values ​​within the above range. This application does not impose any restrictions on these values.

[0046] When silicon materials include silicon alloys, the silicon alloys can be silicon-lithium alloys, silicon-magnesium alloys, etc. Of course, it should be noted that in some cases, silicon alloys include elemental silicon particles and alloys.

[0047] In some embodiments, the silicon material further includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The silicon oxide layer includes silicon oxide, the general formula of which is SiO. x Where 0.5 ≤ x < 2. Specifically, SiO x Specifically, it could be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 etc. are not specified here.

[0048] In some embodiments, the silicon material further includes silicon particles and a silicon oxide layer on the surface of the silicon particles. Based on the mass of the silicon material, the mass percentage of oxygen atoms in the silicon material is between 1% and 18%. Specifically, the mass percentage of oxygen atoms in the silicon material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or any value within the range of any two of the above values. Controlling the mass percentage of oxygen atoms in the silicon material within the above range is beneficial for forming a stable silicon oxide layer on the surface of the silicon particles, reducing direct contact between the silicon particles and the electrolyte, thereby reducing side reactions between the silicon particles and the electrolyte, and improving the cycle stability of the negative electrode material; it can also maintain the stable activity of the silicon-based material and increase the specific capacity of the negative electrode material.

[0049] In some embodiments, the particle size distribution of the negative electrode material satisfies: 0.9 ≤ (Dv90 - Dv10) / Dv50 ≤ 5. Dv10 represents the particle size corresponding to a cumulative particle size distribution volume percentage of 10%. Dv90 represents the particle size corresponding to a cumulative particle size distribution volume percentage of 90%. Dv50 represents the particle size corresponding to a cumulative particle size distribution volume percentage of 50%. Exemplarily, (Dv90 - Dv10) / Dv50 of the negative electrode material can be 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, etc., or other values ​​within the range of 0.9 to 5.

[0050] The particle size distribution of the negative electrode material satisfies the condition: 0.9 ≤ (Dv90 - Dv10) / Dv50 ≤ 5, indicating that the particle size distribution of the negative electrode material is relatively uniform. This uniform particle size distribution helps to improve the electrochemical performance of the negative electrode material because materials with uniform particle size have a more uniform stress distribution during charge and discharge, thereby reducing the risk of particle breakage and improving the cycle stability of the battery.

[0051] In other embodiments, the volumetric median particle size Dv50 of the negative electrode material is 0.5 μm to 40 μm. Exemplarily, the Dv50 of the negative electrode material is 0.5 μm, 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 35 μm, 36 μm, 38 μm, 40 μm, etc., or other values ​​within the range of 0.5 μm to 40 μm. In some preferred embodiments, the volumetric median particle size Dv50 of the negative electrode material is 5 μm to 20 μm.

[0052] The median particle size (Dv50) of the negative electrode material within the aforementioned range indicates that the lithium ion insertion and extraction pathways within the negative electrode material are moderate, resulting in good charge-discharge performance. Furthermore, this negative electrode material exhibits good processability, facilitating the fabrication of flat positive electrode sheets, thereby contributing to improved overall electrochemical performance of the battery. In some embodiments, the compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 For example, the compaction density of the negative electrode material can be 0.8 g / cm³. 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 etc., or 0.8g / cm 3 ~1.3g / cm 3 Other values ​​within the range. Compacted density refers to the density of a material during the compaction process, and is commonly used to describe the compactness of battery materials. In the manufacturing process of lithium-ion batteries, compacted density has a significant impact on battery performance. The higher the compacted density, the higher the battery capacity is generally; therefore, compacted density is also considered one of the reference indicators for material energy density. Controlling the compacted density within the above-mentioned range is beneficial for improving the capacity of the negative electrode material.

[0053] In other embodiments, the tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 For example, the tap density of the negative electrode material can be 0.5 g / cm³. 3 0.6g / cm 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 etc., or 0.5g / cm 3 ~1.5g / cm 3 Other values ​​within the range. Tap density refers to the mass per unit volume of powder in a container after it has been tapped under specified conditions. Tap density reflects the compactness of the material particles; a high tap density is beneficial for improving the volumetric energy density of the battery.

[0054] In some other embodiments, the powder conductivity of the negative electrode material at a pressure of 20 kN is 0.1 S / cm to 2 S / cm. Exemplarily, the powder conductivity of the negative electrode material at a pressure of 20 kN can be 0.1 S / cm, 0.2 S / cm, 0.3 S / cm, 0.4 S / cm, 0.5 S / cm, 0.6 S / cm, 0.7 S / cm, 0.8 S / cm, 0.9 S / cm, 1 S / cm, 1.1 S / cm, 1.2 S / cm, 1.3 S / cm, 1.4 S / cm, 1.5 S / cm, 1.6 S / cm, 1.7 S / cm, 1.8 S / cm, 1.9 S / cm, 2 S / cm, etc., or other values ​​within the range of 0.1 S / cm to 2 S / cm.

[0055] When the powder conductivity of the negative electrode material under 20kN pressure is within the above range, it indicates that the negative electrode material has good conductivity, which can help improve the charging and discharging efficiency of the battery, reduce the charging and discharging impedance of the battery, and also help reduce the charge transfer impedance of the battery during cycling, thereby improving the cycle stability of the battery and extending the battery's service life.

[0056] In some implementations, the gas production rate of the negative electrode material is ≤1 mL / g / day. A lower gas production rate indicates that the negative electrode material has better chemical stability in the battery system, which can reduce problems such as battery bulging and short circuits caused by gas production, thereby improving battery safety and service life.

[0057] In other embodiments, the total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g. For example, the total pore volume of the negative electrode material can be 0.001 cm³. 3 / g, 0.005cm 3 / g, 0.01cm 3 / g, 0.015cm 3 / g, 0.02cm 3 / g, 0.025cm 3 / g, 0.03cm 3 / g, 0.035cm 3 / g, 0.04cm 3 / g, 0.045cm 3 / g, 0.05cm 3 / g, 0.055cm 3 / g, 0.06cm 3 / g, 0.065cm 3 / g, 0.07cm 3 / g, 0.075cm 3 / g, 0.08cm 3 / g, 0.085cm 3 / g, 0.09cm 3 / g, 0.095cm 3 / g, 0.1cm 3 / g, or 0.001cm 3 / g~0.1cm 3 Other values ​​within the range of / g. The total pore volume of the negative electrode material refers to the pore volume of all pores in the negative electrode material. A suitable total pore volume helps mitigate the volume changes of silicon materials during charging and discharging.

[0058] Generally speaking, pores with a diameter ≤ 2 nanometers (nm) are called micropores, pores with a diameter between 2 nanometers and 50 nanometers (nm) are called mesopores, and pores larger than 50 nanometers are called macropores. The total pore volume of the negative electrode material is the sum of the micropore volume, mesopore volume, and macropore volume.

[0059] In other embodiments, the volume ratio of the micropore volume of the negative electrode material to the total pore volume is ≤10%. For example, the volume ratio of the micropore volume of the negative electrode material to the total pore volume can be 10%, 9.5%, 9%, 8.5%, 8%, 7.5%, 7%, 6.5%, 6%, 5.5%, 5%, or other values ​​≤10%.

[0060] In some embodiments, the mesopore volume of the negative electrode material accounts for ≥80% of the total pore volume. Exemplarily, the mesopore volume of the negative electrode material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or other values ​​≥80%. This shows that mesopores are the predominant pore type among all the pores in the negative electrode material. A high proportion of mesopores is beneficial for electrolyte penetration and ion transport, thus improving the charge and discharge efficiency of the battery.

[0061] In some embodiments, the volume ratio of macropores in the negative electrode material to the total pore volume is ≤20%. Exemplarily, the volume ratio of macropores in the negative electrode material to the total pore volume can be 20%, 19.5%, 19%, 18.5%, 18%, 17.5%, 17%, 16.5%, 16%, 15.5%, 15%, 14.5%, 14%, 13.5%, 13%, 12.5%, 12%, 11.5%, 11%, 10.5%, 10%, 9%, 7%, 5%, 3%, 1%, or other values ​​≤20%.

[0062] In some other embodiments, the average pore size of the negative electrode material is 0.45 nm to 50 nm. Exemplarily, the average pore size of the negative electrode material can be 0.45 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or other values ​​within the range of 0.45 nm to 50 nm. An appropriate average pore size facilitates sufficient contact between the electrolyte and the negative electrode material, thereby improving the lithium-ion insertion / extraction kinetics and enhancing the rate performance of the battery.

[0063] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 0.5m². 2 / g, 1.0m 2 / g, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 9.0m 2 / g, 10m 2 / g, or 0.5m 2 / g~10m 2 Other values ​​within the / g range.

[0064] An appropriate specific surface area can balance the reactivity and irreversible capacity of a material. The specific surface area of ​​the negative electrode material affects the contact area between the negative electrode material and the electrolyte. When the specific surface area of ​​the negative electrode material is within the above-mentioned range, it can ensure that the negative electrode material and the electrolyte have a suitable contact area, thereby enhancing the reactivity and improving rate performance while controlling the irreversible capacity within an acceptable range.

[0065] In other embodiments, the negative electrode material after removing the silicon material is a silicon-removed negative electrode material, and the total pore volume of the silicon-removed negative electrode material is 0.2 cm³. 3 / g~1.5cm 3 / g. In some embodiments, the negative electrode material, after the silicon material is removed, becomes a porous material. For example, the total pore volume of the negative electrode material after removing the silicon material can be 0.2 cm³. 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, or 0.2cm 3 / g~1.5cm 3 Other values ​​within the / g range.

[0066] In some other embodiments, the volume percentage of micropores in the anode material without silicon is ≥15% of the total volume of all pores. For example, the volume percentage of micropores in the anode material without silicon can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or other values ​​≥15%. It can be seen that the volume percentage of micropores in the anode material without silicon is greater than the volume percentage of micropores in the anode material itself. When the volume of micropores in the anode material without silicon is large, the capillary effect of the micropores makes it easier for the active silicon material to preferentially deposit into the micropores, which is beneficial for controlling the growth of the active material into nanoscale silicon and for increasing the deposition amount of the active material.

[0067] In some implementations, the volume fraction of mesopores in the anode material, which removes silicon material, is ≤85% of the total volume fraction of all pores. Exemplarily, the volume fraction of mesopores in all pores can be 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, or other values ​​≤85%.

[0068] In other embodiments, the volume percentage of macropores in the silicon-removed anode material is ≤2% of the total volume of all pores. Exemplarily, the volume percentage of macropores in all pores can be 2%, 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, or other values ​​≤2%. Therefore, a smaller volume percentage of macropores in the silicon-removed anode material effectively avoids the problem of active material mainly depositing in macropores, potentially forming large-grained active material, which would hinder the control of active material expansion during battery charging and discharging.

[0069] In some other embodiments, the volume percentage of pores smaller than 5 nm in the silicon-removed anode material is ≥90% of all pores. For example, the volume percentage of pores smaller than 5 nm in all pores can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or other values ​​≥90%. In this embodiment, the presence of pores smaller than 5 nm as the majority of all pores in the silicon-removed anode material not only improves the deposition amount of active material but also helps control the growth of active material, thereby controlling the expansion volume of active material during battery charging and discharging.

[0070] In some embodiments, the specific surface area of ​​the anode material without silicon is 200 m². 2 / g~3000m 2 / g. For example, the specific surface area of ​​the anode material with silicon removed can be 200m². 2 / g、400m 2 / g、500m 2 / g、600m 2 / g、800m 2 / g, 1000m 2 / g、1200m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g、2400m 2 / g、2500m 2 / g、2600m 2 / g、2800m 2 / g、3000m 2 / g, or 200m 2 / g~3000m 2 Other values ​​within the / g range.

[0071] The removal of silicon from the anode material, i.e., porous materials, provides more active sites for subsequent silicon deposition due to their larger specific surface area. During silicon deposition, silicon atoms can be more uniformly dispersed within the pores of the porous material, forming a more stable structure. This helps improve the overall performance of the anode material; for example, during charge and discharge, uniformly dispersed silicon can participate more effectively in electrochemical reactions, reducing structural damage caused by localized stress concentration and improving battery cycle stability. Too small a specific surface area cannot provide sufficient sites for the growth of nano-silicon. Too large a specific surface area weakens the structural stability of the anode material, thus affecting subsequent processing performance.

[0072] In some embodiments, the average pore size of the anode material without silicon is 1.0 nm to 20 nm. Exemplarily, its average pore size can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, etc., or other values ​​within the range of 1.0 nm to 20 nm.

[0073] In other embodiments, the true density of the anode material without silicon is 1.6 g / cm³. 3 ~2.4g / cm 3 For example, the true density of the anode material without silicon can be 1.6 g / cm³. 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 etc., or 1.6g / cm 3 ~2.4g / cm 3 Other values ​​within the range.

[0074] In other embodiments, the negative electrode material includes a core and a coating layer covering at least a portion of the surface of the core, the core comprising a porous material and an active substance. In some embodiments, the coating layer covering at least a portion of the surface of the core includes a coating layer covering a portion of the surface of the core, or a coating layer covering the entire surface of the core.

[0075] In some embodiments, the coating layer includes a carbon material, which may be one or more of graphene, soft carbon, and hard carbon. The carbon material coating layer possesses good electrical conductivity, which can improve the conductivity of the negative electrode material. Furthermore, the coating layer located on the surface of the negative electrode material can protect the porous material on which the active material is deposited, reducing direct contact between the active material and the electrolyte, and improving the stability of the SEI film. This, in turn, is beneficial for further improving the cycle life and rate performance of the negative electrode material.

[0076] In some embodiments, the coating layer can be a single-layer coating layer formed from a single material, a coating layer formed from a combination of multiple materials, a multi-layer coating layer formed from a single material, or a multi-layer coating layer formed from multiple materials, etc., and the layer structure of the coating layer can be selected according to actual needs. Understandably, when the coating layer has a multi-layer coating structure, the density is higher.

[0077] In some embodiments, the silicon content in the negative electrode material is 20% to 60% by mass, based on the mass of the negative electrode material. Exemplarily, the silicon content in the negative electrode material can be 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, 50%, 52%, 54%, 55%, 56%, 58%, 60%, or other values ​​within the range of 20% to 60%. Maintaining a silicon content within this range allows for control of material volume changes while ensuring high battery capacity, thereby achieving stable cycle performance.

[0078] In other embodiments, the carbon content in the negative electrode material is 35% to 80% by mass, based on the mass of the negative electrode material. This carbon originates from the carbon coating layer and / or porous materials. Exemplarily, the carbon content in the negative electrode material can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or other values ​​within the range of 35% to 80%. Within this range, the carbon content serves both to improve conductivity and mitigate the volume expansion of the negative electrode material, thereby improving its cycle performance. If the carbon content is too low, it will reduce the conductivity and structural stability of the negative electrode material. If the carbon content is too high, it will lead to a reduction in the deposition of active material, thus decreasing the battery capacity.

[0079] It is understood that the negative electrode material in the embodiments of this application may include oxygen and / or other elements in addition to the silicon and carbon elements mentioned above. This application does not impose any limitations on this.

[0080] In another aspect, this application also provides a method for preparing a negative electrode material to obtain a negative electrode material having the aforementioned characteristics. An exemplary description will be provided below with reference to FIG2.

[0081] Figure 2 shows an exemplary flowchart of a method for preparing a negative electrode material according to some embodiments of this application. As shown in Figure 2, the preparation method 200 may include: in step S201, loading a porous material into a vapor deposition apparatus; in step S202, introducing a silicon-containing gas into the vapor deposition apparatus in a pulsed manner to deposit silicon material in the pores of the porous material to obtain a negative electrode material; wherein the pulse pressure during the deposition process is controlled to be -3kPa to 7kPa, the frequency of the pulse bias voltage is 200Hz to 1000Hz, and the duty cycle is 0.15 to 0.85.

[0082] In some embodiments, the preparation method 200 further includes step S204, in which a carbon source gas is introduced into a vapor deposition apparatus to coat the outer surface of the negative electrode material obtained in step S202 with a carbon material to obtain the final negative electrode material.

[0083] In some embodiments, the vapor deposition apparatus may include, for example, a vapor deposition furnace. In other embodiments, the amount of porous material loaded may be 1 kg to 5 kg, such as 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg, 3.5 kg, 4 kg, 4.5 kg, 5 kg, or other values ​​within the range of 1 kg to 5 kg.

[0084] In other embodiments, the porous material may include at least one of activated carbon, capacitive carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, porous TiO2, etc. In still other embodiments, in step S201, after loading the porous material into the vapor deposition equipment, a vacuum of 10... -4 Pa ~ 10 Pa.

[0085] In some embodiments, before step S202, the preparation method 200 may further include step S203, whereby, under a protective gas flow, the heating system of the vapor deposition apparatus is activated to heat the vapor deposition apparatus. In other embodiments, the heating rate is 1°C / min to 10°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or other values ​​within the range of 1°C / min to 10°C / min.

[0086] In some embodiments, the protective gas in step S203 can be an inert gas. In still other embodiments, the protective gas can include one or more of nitrogen, argon, and helium. In some embodiments, the flow rate of the protective gas is 0.5 L / min to 60 L / min, for example, it can be 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, 55 L / min, 60 L / min, etc., or other values ​​within the range of 0.5 L / min to 60 L / min. In some preferred embodiments, the flow rate of the protective gas can be 2 L / min to 50 L / min. In a further preferred embodiment, the flow rate of the protective gas can be 5 L / min to 20 L / min.

[0087] In some implementations, the oxygen content after the protective gas is introduced into the vapor deposition equipment is less than 50 ppm, at which point the introduction of the protective gas can be stopped.

[0088] Next, the temperature inside the vapor deposition apparatus can be raised to 300°C to 800°C and held at that temperature before proceeding to step S202. Exemplarily, the temperature inside the vapor deposition apparatus can be raised to 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or other values ​​within the range of 300°C to 800°C. In some preferred embodiments, the temperature inside the vapor deposition apparatus can be raised to 400°C to 600°C.

[0089] A suitable temperature range is beneficial for controlling the reaction rate and the growth of Si grains. If the temperature is too low, the silicon-containing gas may not be able to decompose to generate silicon atoms, which may result in the inability to deposit silicon material or an insufficient amount of silicon material deposited. If the temperature is too high, the reaction rate may be too fast, leading to an excessively rapid growth rate of Si grains, resulting in large crystalline silicon particles. It may even prevent the silicon-containing gas from diffusing into the porous material, forming a hard shell on the surface of the porous material, which affects the cycle performance of the anode material.

[0090] In step S202, silicon-containing gas is introduced into the vapor deposition equipment in a pulse manner. Due to the instantaneous high energy input of the pulse discharge, the deposition process can be completed rapidly in a short time, which makes it easier to prepare anode materials with the same Si content in a shorter time, thereby increasing the deposition rate.

[0091] In some embodiments, the silicon-containing gas introduced in step S202 may include one or more of the following: silane, dichlorosilane, propane, butane, monochlorosilane, dichlorosilane, trichlorosilane, methyltrichlorosilane, dimethyldichlorosilane, tetrachlorosilane, etc. In other embodiments, the pulse pressure during the deposition process is controlled to be between -3 kPa and 7 kPa. For example, the pulse pressure may be -3 kPa, -2 kPa, -1 kPa, 0 kPa, 3 kPa, 3.5 kPa, 4 kPa, 4.5 kPa, 5 kPa, 5.5 kPa, 6 kPa, 6.5 kPa, 7 kPa, etc., or other values ​​within the range of -3 kPa to 7 kPa. When the pulse pressure is negative, it indicates that the deposition process is carried out under conditions below atmospheric pressure (i.e., vacuum).

[0092] According to the embodiments of this application, the pulse pressure is controlled within a low range, which allows for a shorter charging time. This prevents the Si atoms from silane decomposition at high temperatures from agglomerating into large molecules. Furthermore, the higher gas flow rate prevents crust formation on the surface of the porous material, ensuring timely replenishment of Si atoms deposited within the porous material. This improves the uniformity of Si atom distribution in the negative electrode material. In particular, during the later stages of deposition (i.e., the later densification stage), the adsorption capacity of the porous material decreases because many pores within the particles are already filled with silicon material, making surface crust formation more likely. However, by using the pulsed method and controlling the pulse pressure within a low range, Si atoms can continue to deposit into the pores of the porous material, resulting in more uniform silicon filling within the porous material and increasing the amount of silicon deposited.

[0093] If the pulse pressure is too low, it affects the deposition rate of silicon material. If the pulse pressure is too high and the gas filling time is too long, the silicon-containing gas undergoes a more complete cracking reaction, generating intermediate products that are large molecular clusters, hindering the transport of silicon-containing gas. As the densification process proceeds, the densification front of the porous material gradually moves to the outer surface, and a large amount of Si is cracked and deposited on the outer surface of the porous material, blocking the transport channels of silicon-containing gas, resulting in a further increase in the difference in the percentage of Si atoms inside and outside the material particles.

[0094] In some other embodiments, the frequency of the controlled pulse bias voltage in step S202 is 200Hz to 1000Hz. For example, the frequency of the pulse bias voltage can be 200Hz, 300Hz, 400Hz, 500Hz, 600Hz, 700Hz, 800Hz, 900Hz, 1000Hz, or other values ​​within the range of 200Hz to 1000Hz.

[0095] The frequency of the pulse bias voltage refers to the number of times the pulse signal appears per unit time (per second) when the pulse power supply applies a bias voltage, and the unit is Hertz (Hz). In the preparation method of this application, the pulse bias voltage provides energy and driving force for the reaction and deposition of silicon-containing gas. The frequency of the pulse bias voltage determines the number of times the reaction and deposition processes occur per unit time. A higher pulse bias voltage frequency means more energy input and reaction opportunities per unit time, which will accelerate the reaction and deposition rate; a lower pulse bias voltage frequency results in a relatively slower reaction and deposition rate.

[0096] By controlling the frequency of the pulse bias voltage within the range of 200Hz to 1000Hz, the heat generated by the reaction can be fully diffused. Under conditions of higher overpotential and lower concentration polarization, the nucleation rate of Si grains is much greater than the growth rate of Si grains, thereby achieving a uniform Si distribution within the porous material and improving the deposition uniformity of silicon materials.

[0097] If the pulse bias frequency is too low, fewer pulses are released, resulting in slower reaction and deposition rates and a smaller amount of silicon material deposited. If the pulse bias frequency is too high, more pulses are released per unit time, and the pulse time interval is shortened, reducing heat dissipation efficiency and leading to heat accumulation. Under the action of adjacent pulses, Si tends to aggregate, accelerating the growth rate of Si grains and easily forming large Si grains, which is detrimental to the cycle performance of the anode material.

[0098] In some implementations, the duty cycle in step S202 can be controlled to be 0.15 to 0.85. For example, the duty cycle can be 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or other values ​​within the range of 0.15 to 0.85.

[0099] Duty cycle refers to the ratio of the time a pulse signal is at a high level within one pulse cycle to the total pulse cycle time. In this embodiment, the duty cycle is controlled within the aforementioned range, making the total discharge and total energy storage more suitable. This increases the continuity of the transition of silicon-containing gas to the porous material, allowing the silicon-containing gas to transition more quickly to the surface and interior of the porous material. This improves the continuity and uniformity of silicon material deposition, resulting in a gradual increase in the amount of silicon material deposited.

[0100] If the duty cycle is too small, the single-pulse discharge energy and average current density are low, resulting in a low Si particle generation rate and a low silicon-containing gas diffusion rate. This does not provide sufficient time for the porous material to adsorb Si, leading to a low Si deposition rate and poor deposition uniformity. If the duty cycle is too large, the total energy released in a single pulse cycle will be too high, causing violent reactions in the silicon-containing gas, overheating within the vapor deposition equipment, a large heat-affected zone, and even the eruption of a strong electric arc, resulting in poor Si deposition uniformity.

[0101] Based on the above analysis, it can be seen that the embodiments of this application introduce silicon-containing gas into the vapor deposition equipment in a pulse manner, and control the pulse pressure during the deposition process to be -3kPa to 7kPa, the pulse bias frequency to be 200Hz to 1000Hz, and the duty cycle to be 0.15 to 0.85, thereby comprehensively controlling the deposition process and thus being able to prepare a negative electrode material with uniform silicon material distribution, so that the γ value of the negative electrode material meets the characteristic of ≤0.4.

[0102] It is understandable that introducing silicon-containing gas into a vapor deposition apparatus in a pulsed manner to carry out the deposition reaction can also be called pulsed chemical vapor deposition (PCVD). This method utilizes a pulsed power supply to generate high-energy particles during gas discharge. These high-energy particles react chemically with reactants in the gas phase to form a solid deposit. The "pulsed" manner refers to the instantaneous injection of silicon-containing gas to the required pressure via a pulsed power supply, allowing the silicon-containing gas to diffuse throughout the porous material, achieving deposition in a short time, followed by rapid exhaust of the waste gas. This cycle significantly reduces the concentration gradient generated during the diffusion of silicon-containing gas within the porous material, effectively avoiding the problem of uneven silicon deposition.

[0103] Further, in step S202, the total duration of silicon-containing gas introduction can be controlled to be between 60 min and 1200 min. Exemplarily, the total introduction time can be 60 min, 100 min, 200 min, 300 min, 400 min, 500 min, 600 min, 700 min, 800 min, 900 min, 1000 min, 1100 min, 1200 min, etc., or other values ​​within the range of 60 min to 1200 min. In some preferred embodiments, the total introduction time of silicon-containing gas is between 90 min and 480 min. In other preferred embodiments, the total introduction time of silicon-containing gas is between 120 min and 360 min.

[0104] In some embodiments, the flow rate of the silicon-containing gas can be controlled to be from 0.5 L / min to 50 L / min, for example, it can be 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, etc., or other values ​​within the range of 0.5 L / min to 50 L / min. In some preferred embodiments, the flow rate of the silicon-containing gas can be from 1 L / min to 20 L / min. In a further preferred embodiment, the flow rate of the silicon-containing gas can be from 2 L / min to 10 L / min.

[0105] In some embodiments, in step S202, a dilution gas may be introduced simultaneously with the silicon-containing gas. In other embodiments, the dilution gas may include hydrogen or the like. In still other embodiments, the flow rate of the dilution gas can be controlled to be 0.5 L / min to 50 L / min, for example, 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, or other values ​​within the range of 0.5 L / min to 50 L / min. In some preferred embodiments, the flow rate of the dilution gas can be 2 L / min to 20 L / min. In a further preferred embodiment, the flow rate of the dilution gas can be 5 L / min to 10 L / min.

[0106] The deposition reaction rate can be controlled by introducing a dilution gas. By introducing hydrogen as a dilution gas, the rate at which silicon-containing gases decompose to generate Si atoms can be controlled. This avoids an excessively fast deposition reaction rate, thus preventing silicon material from depositing on the surface of porous materials and forming a hard shell, which would hinder further silicon deposition. In some embodiments, the negative electrode material obtained after the aforementioned deposition reaction can be carbon-coated. In other embodiments, the carbon coating treatment can include at least one of gas-phase coating, liquid-phase coating, and solid-phase coating. In still other embodiments, the carbon coating treatment can be gas-phase coating, and the carbon source in the carbon coating treatment can include one or more gaseous carbon sources such as methane, ethylene, and propane.

[0107] In some embodiments, the carbon coating treatment temperature is 500℃ to 650℃, the time is 1h to 6h, and the volume fraction of the carbon source gas is 6% to 60%. The carbon source gas can be diluted with an inert gas, including one or more of nitrogen, argon, and helium. Exemplarily, the carbon coating treatment temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, etc., or other values ​​within the range of 500℃ to 650℃. The carbon coating treatment time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, etc., or other values ​​within the range of 1h to 6h. The volume fraction of the carbon source gas can be 6%, 10%, 20%, 30%, 40%, 50%, 60%, or other values ​​within the range of 6% to 60%.

[0108] By carbon coating the anode material, one or more robust "shells" (i.e., carbon coating layers) can be added to the surface of the anode material to suppress the volume change that may occur during cycling. This can help improve the cycling performance of the anode material and also make the prepared anode material have better electronic conductivity and less overall gas production, thus obtaining anode materials with superior comprehensive performance.

[0109] Furthermore, in some embodiments, the preparation method 200 may further include, after the deposition reaction is completed, lowering the temperature inside the vapor deposition equipment to room temperature, removing the negative electrode material, and performing post-processing such as pulverization, sieving, and demagnetization. In some embodiments, pulverization may be performed using any one of an air jet mill, a ball mill, a turbine mill, etc. In other embodiments, sieving may be performed using any one of a vibrating screen, an air classifier, etc.

[0110] In another aspect, this application provides a secondary battery comprising the negative electrode material described in any of the first aspects of this application or the negative electrode material prepared according to the preparation method described above in conjunction with FIG. 2. One embodiment of this application provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.) comprising a casing, electrode components, and an electrolyte / electrolyte. Both the electrode components and the electrolyte / electrolyte are located within the casing. The casing can be a packaging bag encapsulated with an encapsulation film (such as an aluminum-plastic film), such as a pouch battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc. The secondary battery of this application embodiment also includes electrode components such as the positive electrode sheet and separator shown in FIG. 1, which will not be described further here.

[0111] Examples and comparative examples:

[0112] To better understand the performance of the negative electrode material and its preparation method according to the embodiments of this application, specific examples will be described below. Several comparative examples are also provided below to further illustrate the advantages of the negative electrode material according to the embodiments of this application.

[0113] Example 1:

[0114] Step 1) Load 2 kg of activated carbon into the vapor deposition furnace and evacuate to 10 °C. -2 Pa;

[0115] Step 2) Under the inert protective gas flow, start the furnace heating system to heat the vapor deposition furnace at a heating rate of 5℃ / min; the inert protective gas is argon with a flow rate of 10L / min; after the inert protective gas is introduced into the vapor deposition furnace, the oxygen content is lower than 50ppm; then stop the introduction of the inert protective gas.

[0116] Step 3) After heating to 500℃, maintain the temperature and introduce silane into the vapor deposition furnace for a total duration of 240 min at a flow rate of 5 L / min. Simultaneously, introduce dilution gas hydrogen at a flow rate of 10 L / min. The pulse pressure is controlled at 1.5 kPa, the pulse bias frequency is 500 Hz, and the duty cycle is 0.5.

[0117] Step 4) Raise the temperature to 575℃, introduce carbon source gas and inert gas, and keep it at this temperature for 3.5 hours. The volume fraction of the carbon source gas is 33%, the carbon source gas is acetylene, and the inert gas is nitrogen.

[0118] Step 5) After cooling the product obtained in Step 4) to room temperature, it is crushed, sieved and demagnetized to obtain the negative electrode material. The crushing is carried out by an air jet mill and the sieving is carried out by an air classifier.

[0119] Example 2: The only difference from Example 1 is that in step 3), the pulse pressure is -1.5 kPa.

[0120] Example 3: The only difference from Example 1 is that in step 3), the pulse pressure is 5 kPa.

[0121] Example 4: The only difference from Example 2 is that in step 3), the duty cycle is 0.15.

[0122] Example 5: The only difference from Example 2 is that in step 3), the duty cycle is 0.85.

[0123] Example 6: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 200Hz.

[0124] Example 7: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 1000Hz.

[0125] Example 8: The only difference from Example 1 is that step 4 is omitted.

[0126] Example 9: The only difference from Example 1 is that in step 3), the pulse pressure is -5 kPa.

[0127] Comparative Example 1: The only difference from Example 1 is that in step 3), the pulse pressure is 8.5 kPa.

[0128] Comparative Example 2: The only difference from Example 1 is that in step 3), the duty cycle is 0.1.

[0129] Comparative Example 3: The only difference from Example 1 is that in step 3), the duty cycle is 0.9.

[0130] Comparative Example 4: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 100Hz.

[0131] Comparative Example 5: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 2000Hz.

[0132] Comparative Example 6: The only difference from Example 1 is that in step 3), the total time for introducing silane is 30 min.

[0133] Comparative Example 7: The only difference from Example 1 is that in step 3), the total time for introducing silane is 2000 min.

[0134] Comparative Example 8: The only difference from Example 1 is that, in step 3), the flow rate of silane is 0.2 L / min.

[0135] Comparative Example 9: The only difference from Example 1 is that, in step 3), the flow rate of silane is 100 L / min.

[0136] Performance testing methods:

[0137] This application also conducted the following performance tests on the anode materials prepared in the above embodiments and comparative examples:

[0138] (1) Test method for particle size of negative electrode material:

[0139] The particle size distribution range of the negative electrode material was tested using a Malvern laser particle size analyzer (Mastersizer 3000). The volumetric cumulative particle size distribution for particle size distribution determination was obtained using laser diffraction, referring to GB / T 19077.1-2008 "Particle Size Analysis - Laser Diffraction - Part 1: General Rules" or the equipment manual, yielding Dv10, Dv50, and Dv90. During testing, 1 mL of a surfactant aqueous solution diluted 1:50 was first added to a beaker containing an appropriate amount of the negative electrode material sample and stirred. Then, pure water was added and stirred thoroughly before testing (the sample-to-water ratio should ensure that the light-blocking effect is between 8% and 15% during testing).

[0140] (2) Method for testing specific surface area:

[0141] The specific surface area / pore size distribution of the material was tested using a TriStar 3000 & 3020 surface area and pore size analyzer from the USA, in accordance with GB / T 19587-2017 "Determination of Specific Surface Area / Porosity of Solid Substances by Gas Adsorption BET Method". A dry specific surface area tube was taken, and 1 / 2 to 2 / 3 of the volume of material was weighed from the tube bulb. Degassing (removing moisture or impurities) was performed before testing using a vacuum heating method (vacuum heating method: set the degassing temperature to 300℃, degassing time to 1 hour; after degassing, place the tube in a cooling tank or on an external specific surface area tube rack for 20 minutes, then backfill with gas for 5-10 seconds (depending on the situation, to avoid sample ejection and adhesion to the sample tube sidewall). The sample tube was then disassembled, and a rubber stopper was quickly used to seal the sample tube before subsequent testing). The determination was performed according to the instruction manual of the specific surface area / pore size analyzer.

[0142] (3) True density test method:

[0143] The true density was measured using a Bestech 3H-2000TD true density meter. The true density of the material was tested according to GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries": Helium gas with a purity higher than 99.9% was used; the sample was placed in the sample cell to fill at least 2 / 3 of the sample cell volume, and the sample cell was gently vibrated until the inner surface of the sample cell was highly stable. The sample mass was then accurately weighed to an accuracy of 0.0001g; the measurement was performed according to the instruction manual of the true density meter.

[0144] (4) Test methods for pore volume and pore diameter:

[0145] The specific surface area / pore size distribution of materials was tested using a Micromeretics ASAP 2460 pore size analyzer according to GB / T 19587-2017 "Determination of Specific Surface Area / Porosity of Solids by Gas Adsorption BET Method": A dry specific surface area tube was taken, and 1 / 2 to 2 / 3 of the volume of material was weighed from the tube bulb. Degassing (removing moisture or impurities) was performed before testing using a vacuum heating method (vacuum heating method: set the degassing temperature to 300℃, degassing time to 1 hour; after degassing, place the tube in a cooling tank or on an external specific surface area tube holder for 20 minutes, then backfill with gas for 5-10 seconds (depending on the situation, to avoid sample ejection and adhesion to the sample tube sidewall). The sample tube was then disassembled, and a rubber stopper was quickly used to seal the sample tube before subsequent testing. The determination was performed according to the instruction manual of the specific surface area / pore size analyzer.

[0146] (5) Test method for powder conductivity:

[0147] The four-probe method was used to determine the volume resistivity of the sample. Using the MCP-PD51 powder conductivity meter from Mitsubishi Chemical (Japan), the conductivity of the powder at five pressure points (4kN, 8kN, 12kN, 16kN, and 20kN) can be measured, and then the resistivity of the powder is automatically calculated by computer.

[0148] (6) Test method for compaction density:

[0149] The compaction density of the material was tested using a CARVER 4350.22 powder compaction density tester from McNaught (USA) and in accordance with GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". A sample of a specified mass was placed in a mold and a pressure of 1.0T was applied. After holding the pressure for 30 seconds, the pressure was released and the thickness was measured. The compaction density was calculated as: ρ = 10 m / (S*H).

[0150] (7) Test method for tap density:

[0151] The tap density of the material was tested using a CANTA DAT-6-220 tap density meter, referring to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders". A 50g sample was placed in a 100mL graduated cylinder and vibrated for the specified number of times (3000 vibrations for routine testing, vibration frequency 260 times / min, vibration amplitude 3mm). The volume of the graduated cylinder after vibration was read and the tap density was calculated. The calculation formula is as follows: Tap density = Sample mass / Volume of graduated cylinder after vibration.

[0152] (8) Gas production test method:

[0153] ① Prepare the slurry at room temperature according to a certain ratio: Carboxymethyl cellulose (CMC) is glued at a ratio of 1.4 wt%, dispersed evenly, and then 10 g of glue solution is mixed with 10 g of sample to make the slurry. ② Pack the slurry into an aluminum-plastic film bag and record the slurry mass; then seal it to form a sealed aluminum-plastic film bag. ③ Measure the volume of gas produced: Fix the sealed aluminum-plastic film bag at the bottom of the container, completely immerse it in water, and record the volume of the aluminum-plastic film bag. ④ After 24 hours, record the volume of the aluminum-plastic film bag again. ⑤ Calculate the gas production of the negative electrode material based on the change in the volume of the aluminum-plastic film, unit: mL / g / day;

[0154] (9) Method for testing the mass content of carbon:

[0155] The carbon content of the material was tested using a Bruker+D20, G4 ICARUS HF infrared carbon-sulfur analyzer, referencing GB / T 20123-2006, Iron and Steel - Determination of Total Carbon and Sulfur Content - Infrared Absorption Method after Combustion in a High-Frequency Induction Furnace (Conventional Method) and GB / T 38823-2020, Determination of Carbon Content in Anode Materials for Lithium-ion Batteries. 0.35 g of pure iron flux was taken, followed by 0.1 ± 0.0010 g of the sample, and finally 1 g of tungsten-tin flux. The mixture was placed in a ceramic crucible and burned in a high-frequency furnace with oxygen. The CO2 concentration in the combustion gas was determined by infrared absorption, and the mass content of carbon in the sample was calculated.

[0156] (10) Test method for the mass content of silicon:

[0157] Weigh 1.0–1.2 g of sample into a corundum crucible (accurate to 0.1 mg), place it in a muffle furnace, and heat using the following program: initial temperature 30°C, increase to 400°C after 30 min, hold at 400°C for 60 min, increase to 900°C after 60 min, hold at 900°C for 120 min, increase to 1200°C after 30 min, and hold at 1200°C for 480 min; when the muffle furnace temperature drops below 400°C, open the furnace door, remove the crucible, let it cool slightly for 2–5 minutes, place the crucible in a desiccator, and cool to room temperature. Weigh the cooled crucible and product using a 0.01 g balance; then place the crucible and product back into the muffle furnace. In a muffle furnace, the heating program is set as follows: 30 min to 400℃, hold for 60 min; 90 min to 1200℃, hold for 120 min. After calcination, cool and weigh using a method similar to the previous step, record the total weight of the crucible and product, and compare it with the weight difference after the first calcination. If the difference does not exceed 0.3 mg, the test ends; otherwise, repeat this step until the weight difference after two calcinations does not exceed 0.3 mg. Calculate the silicon content using the formula Si% = (total weight of crucible and product after constant weight m3 - crucible weight m0) / sample weight m1 × (28.09 / 60.09) × 100%.

[0158] (11) Methods for removing silicon material from negative electrode materials:

[0159] Under stirring, a 20% HF acid solution was added dropwise to 10g of anode material. Yellow fumes (SiF4 and H2 gases) were generated and heat was released. After no more yellow fumes were generated in the solution, the supernatant acid solution was removed by centrifugation. Finally, 150mL of a 20% HF acid solution was added and stirred for 12h. The supernatant acid solution was then removed to dissolve the residue. The anode material was then washed with pure water until neutral and dried to obtain the anode material after removing the silicon material.

[0160] (12) Test method for the percentage of Si atoms at different depths in anode materials:

[0161] The negative electrode material was tested using a Thermo Scientific K-Alpha X-ray photoelectron spectrometer. Before testing, the following sample preparation was performed: an appropriate amount of negative electrode material sample was taken, evenly dispersed, and pressed onto the conductive adhesive surface of the sample stage, ensuring a smooth, dense, and agglomerated sample layer. The prepared sample stage was then placed in the instrument pretreatment chamber for vacuum degassing to remove surface adsorbed impurities, and subsequently transferred to the analysis chamber for testing. The entire testing process was completed within an argon-atmospheric glove box.

[0162] Ta2O5 was used as a sputtering standard to calibrate the sputtering rate and depth scale: a uniformly thick thermally oxidized Ta2O5 film with a thickness of 300 nm was prepared on a single-crystal Ta substrate; the Ta2O5 layer was stripped by argon ion sputtering, and the intensity changes of the Ta2O5 characteristic peak and the elemental Ta characteristic peak in the Ta4f fine spectrum were monitored to determine the time required for complete stripping of Ta2O5. The sputtering rate was calculated based on the known thickness (sputtering rate = thickness / sputtering time), and the sputtering time corresponding to the theoretical sputtering depth of 20 nm was determined based on the sputtering rate. The sputtering time was strictly controlled in subsequent tests.

[0163] Each spectral analysis was performed to obtain the fine spectra of C, O, and Si. The argon ion sputtering depth interval was D nm. In this test, D = 20. Depth profiling was performed using an equal-interval sputtering method. The test mode was: spectral acquisition - sputtering etching - spectral acquisition cycle.

[0164] The specific testing process is as follows: the surface of the unsputtered sample is directly tested to obtain the percentage of Si atoms on the surface of the negative electrode material, A0%; the spectrum is sampled once after each sputtering etching of 20nm, and the cycle is repeated 8 times to obtain the percentage of Si atoms at depths of 20nm, 40nm, 60nm, ..., 160nm from the surface, which are recorded as A1%, A2%, A3%...A8%, respectively.

[0165] Three parallel tests were performed at the same depth location of the negative electrode material, and the arithmetic mean was taken as the final result of the percentage content of Si atoms at that depth.

[0166] (13) Electrochemical performance testing methods:

[0167] Button cell testing method: A negative electrode slurry was prepared by mixing negative electrode material, conductive carbon black, and polyacrylic acid (PAA) in a mass ratio of 70:15:15. This slurry was coated onto copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the coin cells were assembled in a glove box filled with Ar gas. The coin cells were charged and discharged at a current density of 0.1C within a charge-discharge range of 0.01V to 5V to obtain the initial reversible specific capacity (or initial discharge specific capacity) and initial coulombic efficiency (ICE) of the coin cells.

[0168] Cyclic expansion performance test method: A negative electrode slurry was prepared by mixing the test material with conductive carbon black Super-P, expanded graphite KS-6, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR in a mass ratio of 92:2:2:2:2. This slurry was then coated onto copper foil and dried to form a negative electrode sheet. The test material included a mixture of negative electrode material and graphite; the proportions of the negative electrode material and graphite in the mixture were determined by their initial reversible specific capacity and the required combined capacity. A coin cell was assembled using a lithium metal sheet as the counter electrode in a glove box filled with Ar gas. The coin cell was subjected to 50 repeated charge-discharge cycles at a current density of 1C within a charge-discharge range of 0.01V to 5V to obtain the capacity retention rate and electrode thickness expansion rate after 50 cycles.

[0169] To facilitate the description of the differences between the above embodiments and comparative examples, as well as the test results of each embodiment and comparative example, further explanation will be provided below with reference to Tables 1 to 5. Tables 1 to 5 show the test results of the negative electrode material samples prepared in each embodiment and comparative example, with Table 4 showing the test results of the negative electrode material after removing the silicon material. Table 2 uses XPS etching at multiple depths with equal intervals of 20 nm as an example. A0 represents the percentage of Si atoms on the surface of the negative electrode material, A1 represents the percentage of Si atoms at a depth of 20 nm from the surface of the negative electrode material into the negative electrode material, A2 represents the percentage of Si atoms at a depth of 40 nm from the surface of the negative electrode material into the negative electrode material, A3 represents the percentage of Si atoms at a depth of 60 nm, A4 represents the percentage of Si atoms at a depth of 80 nm, A5 represents the percentage of Si atoms at a depth of 100 nm, A6 represents the percentage of Si atoms at a depth of 120 nm, A7 represents the percentage of Si atoms at a depth of 140 nm, and A8 represents the percentage of Si atoms at a depth of 160 nm. γ is calculated based on these nine percentages of Si atoms.

[0170] Table 1:

[0171] Table 2:

[0172] Table 3:

[0173] Table 4: Test results of anode material after removing silicon material

[0174] Table 5:

[0175] The data in Tables 1 to 5 above show that:

[0176] During the preparation of the negative electrode materials in Examples 1 to 8, different pulse pressures, duty cycles, and pulse bias frequencies were controlled. The negative electrode materials prepared all satisfied γ≤0.4, indicating that the Si element distribution in the prepared negative electrode materials was relatively uniform. Furthermore, the initial discharge specific capacity, initial coulombic efficiency, electrode thickness expansion rate after 50 cycles, and capacity retention rate all showed excellent performance.

[0177] The negative electrode material of Example 9 satisfies γ≤0.4, indicating that the Si element distribution in the negative electrode material is relatively uniform. This reduces the electrode thickness expansion rate after 50 cycles, improves the capacity retention rate, and enhances the cycling performance of the negative electrode material. However, compared to Example 1, the total pore volume of Example 9 is larger, and the volume ratio of micropores reaches 20%, indicating that the amount of silicon material deposited in the negative electrode material of Example 9 is relatively small, thus affecting its initial discharge specific capacity and initial coulombic efficiency.

[0178] In Comparative Example 1, a pulse pressure greater than 7 kPa was used to prepare the negative electrode material. Compared with Example 1, the negative electrode material of Comparative Example 1 had a higher gas production rate and γ > 0.4, indicating that the distribution of Si atoms in the negative electrode material was not uniform, which affected the capacity retention rate of the negative electrode material in long-term cycling and increased the electrode thickness expansion rate, which was not conducive to the cycle life and safety performance of the battery.

[0179] In Comparative Example 2, the duty cycle was controlled at 0.1 during the preparation of the negative electrode material. Compared to Example 1, the γ value of the negative electrode material in Comparative Example 2 was >0.4, indicating that the percentage distribution of Si atoms in the negative electrode material was not uniform, thus affecting the cycle performance of the negative electrode material. Furthermore, compared to Example 1, the total pore volume of the negative electrode material in Comparative Example 2 was larger, with micropores accounting for >10% and mesopores accounting for <80%. Given that the negative electrode materials of Comparative Example 2 and Example 1 had similar pore sizes and volumes after silicon removal, it indicates that the amount of silicon deposited in the negative electrode material of Comparative Example 2 was less, thus affecting its initial discharge specific capacity and initial coulombic efficiency.

[0180] In Comparative Example 3, the duty cycle was controlled at 0.9 during the preparation of the anode material. A higher duty cycle resulted in a higher Si content in the prepared anode material, thus improving its initial discharge specific capacity and initial coulombic efficiency. However, the anode material in Comparative Example 3 exhibited a γ > 0.4 and a gas production rate > 1 mL / g / day, indicating that an excessively high duty cycle led to poor uniformity of Si atom distribution in the anode material. This, in turn, affected the capacity retention rate after 50 cycles, increased the electrode thickness expansion rate, and was detrimental to improving the cycle performance and safety performance of the anode material.

[0181] In Comparative Example 4, the negative electrode material has a γ > 0.4. During the preparation of the negative electrode material in Comparative Example 4, a pulse bias frequency of 100 Hz was used. Compared to Example 1, the initial discharge specific capacity and initial coulombic efficiency of the negative electrode material in Comparative Example 4 are both lower. Therefore, compared to Comparative Example 4, the negative electrode material of Example 1 exhibits superior overall performance.

[0182] In Comparative Example 5, a pulse bias frequency of 2000 Hz was used during the preparation of the negative electrode material. Compared to Example 1, the higher pulse bias frequency resulted in a higher Si content in the prepared negative electrode material, thereby improving its initial discharge specific capacity and initial coulombic efficiency. However, the negative electrode material of Comparative Example 5 exhibited γ > 0.4 and gas production > 1 mL / g / day, indicating that the excessively high pulse bias frequency worsened the uniformity of Si atom distribution in the negative electrode material. This, in turn, affected the capacity retention rate after 50 cycles, increased the electrode thickness expansion rate, and reduced the cycle performance and safety performance of the negative electrode material.

[0183] In Comparative Example 6, the γ value of the negative electrode material is greater than 0.4. Since the total silane introduction time during the preparation of the negative electrode material in Comparative Example 6 was only 30 minutes, this excessively short total silicon-containing gas introduction time affected the total amount of silicon-containing gas introduced, resulting in a low Si content in the negative electrode material and a large total pore volume, with micropores accounting for as much as 49% of the volume. Given that the negative electrode materials of Comparative Example 6 and Example 1 have similar pore sizes and volumes after silicon removal, it indicates that compared to Example 1, the amount of silicon deposited in the negative electrode material of Comparative Example 6 is too small, leading to a significant decrease in its initial discharge specific capacity and initial coulombic efficiency. Therefore, compared to Comparative Example 6, the negative electrode material of this application exhibits superior overall performance.

[0184] In Comparative Example 7, the total time for introducing silane during the preparation of the anode material was 2000 min. Compared to Example 1, the higher total time for introducing silicon-containing gas resulted in a higher Si content in the prepared anode material. Although this significantly improved its initial discharge specific capacity and initial coulombic efficiency, the anode material in Comparative Example 7 had a γ > 0.4, indicating poor uniformity of Si atom deposition. This led to a gas production rate > 1 mL / g / day for the anode material in Comparative Example 7, resulting in poor capacity retention and electrode thickness expansion after 50 cycles, thus affecting the cycle performance and safety performance of the anode material. Therefore, compared to Comparative Example 7, the anode material in Example 1 exhibits superior overall performance.

[0185] In Comparative Example 8, the anode material has a γ > 0.4. During the preparation of the anode material in Comparative Example 8, the silane flow rate was only 0.2 L / min. This excessively low silicon-containing gas flow rate affected the total amount of silicon-containing gas introduced, resulting in a low Si content in the anode material and a large total pore volume, with micropores accounting for as much as 40% of the volume. Given that the anode materials of Comparative Example 8 and Example 1 have similar pore sizes and volumes after silicon removal, it indicates that the amount of silicon deposited in the anode material of Comparative Example 8 is too small compared to Example 1, leading to a significant decrease in its initial discharge specific capacity and initial coulombic efficiency. Therefore, compared to Comparative Example 8, the anode material of this application exhibits superior overall performance.

[0186] In Comparative Example 9, the silane flow rate was 100 L / min during the preparation of the anode material. This high silicon-containing gas flow rate resulted in a high Si content in the prepared anode material. While this significantly improved the initial discharge specific capacity and initial coulombic efficiency, the Si anode material in Comparative Example 9 had a Si atom content >0.4, indicating poor uniformity in Si atom distribution. This led to a gas production rate >1 mL / g / day for the anode material in Comparative Example 9, resulting in poor capacity retention and electrode thickness expansion after 50 cycles, thus affecting the cycle performance and safety performance of the anode material. Therefore, compared to Comparative Example 9, the anode material in Example 1 exhibits superior overall performance.

[0187] In summary, this application provides a negative electrode material, wherein XPS etching is performed from the surface of the negative electrode material to multiple depths inside the negative electrode material to obtain the percentage of Si atoms at multiple depths. The percentage of Si atoms on the surface of the negative electrode material and the percentage of Si atoms at n depths satisfy the following: Furthermore, γ ≤ 0.4 indicates a relatively uniform distribution of Si atoms in the negative electrode material. This results in a more dispersed stress distribution throughout the material during charging and discharging, preventing stress concentration points and leading to better cycle retention and lower expansion rate. On the other hand, the uniform distribution of Si atoms in the negative electrode material also reduces the likelihood of a sharp peak (0.45V–0.5V) on the dQ / dV curve due to the free growth of Si particles during charging and discharging. The presence of this peak corresponds to the presence of Li… 15 The Si4 phase is crystalline and involves an additional phase transformation during lithium insertion / extraction. Compared to other amorphous lithium-silicon alloys, this Li4 phase... 15 The insertion and extraction process of the Si4 phase is more difficult, which leads to the deterioration of its electrochemical performance. The negative electrode material provided in the embodiments of this application can effectively avoid this problem.

[0188] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A negative electrode material, characterized by, The negative electrode material includes a matrix material and an active substance, wherein the active substance is at least partially distributed within the matrix material, and the active substance includes silicon material; The X-ray photoelectron spectroscopy is combined with argon ion sputter etching of the negative electrode material to obtain the number percentage content of Si atoms at n depths, the number percentage content of Si atoms on the surface of the negative electrode material, and the number percentage content of Si atoms at the n depths satisfy: γ≤0.4; wherein γ represents a distribution uniformity parameter of Si atoms in the negative electrode material, A i represents a percentage content of the number of Si atoms at the i-th depth from the surface of the negative electrode material to the inside of the negative electrode material, A i-1 represents a percentage content of the number of Si atoms at the i-1-th depth from the surface of the negative electrode material to the inside of the negative electrode material, A0represents a percentage content of the number of Si atoms at the surface of the negative electrode material, D represents a depth interval between two adjacent test depths, in nm, D = 20; n = 8.

2. The negative electrode material according to claim 1, characterized in that, The value of γ is 0.4, 0.3, 0.25, 0.2, 0.15, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, or 0.02; or, the value of γ is ≤ 0.

3.

3. The negative electrode material of claim 1, wherein, 17≤A i ≤25, i is selected from any one of the integers from 4 to 8.

4. The negative electrode material of claim 1, wherein, 5≤A i ≤17, i is selected from any one of the integers from 1 to 3.

5. The negative electrode material of claim 1, wherein, The average value of A0 to A3 is B1, and the average value of A4 to A8 is B2, where B1 < B2.

6. The negative electrode material of claim 1, wherein, The negative electrode material also satisfies at least one of the following characteristics: (1) The volume ratio of the micropore volume to the total pore volume of the negative electrode material is ≤10%; (2) The volume of mesopores in the negative electrode material accounts for ≥80% of the total pore volume; (3) The volume ratio of macropores in the negative electrode material to the total pore volume is ≤20%; (4) the total pore volume of the negative electrode material is 0.001 cm 3 / g ~ 0.1 cm 3 / g; (5) The average pore size of the negative electrode material is 0.45 nm to 50 nm; (6) the specific surface area of the negative electrode material is 0.5 m 2 / g ~ 10 m 2 / g.

7. The negative electrode material of claim 1, wherein, After the silicon material is removed from the negative electrode material, it satisfies at least one of the following characteristics: (1) Total pore volume is 0.2 cm 3 / g ~ 1.5 cm 3 / g; (2) The volume percentage of micropores in all pores is ≥15%; (3) The volume fraction of mesopores in all pores is ≤85%; (4) The volume percentage of macropores in all pores is ≤2%; (5) The volume percentage of pores smaller than 5 nm in all pores is ≥90%; (6) a specific surface area of 200 m 2 / g to 3000 m 2 / g; (7) The average pore size is 1.0 nm to 20 nm; (8) true density of 1.6 g / cm 3 ~ 2.4 g / cm 3 .

8. The negative electrode material of claim 1, wherein, The negative electrode material also satisfies at least one of the following characteristics: (1) The particle size distribution of the negative electrode material satisfies: 0.9≤(Dv90-Dv10) / Dv50≤5; (2) The volume median particle size Dv50 of the negative electrode material is 0.5 μm to 40 μm; (3) The volume median particle size Dv50 of the negative electrode material is 5μm to 20μm.

9. The negative electrode material of claim 1, wherein, The negative electrode material also satisfies at least one of the following characteristics: (1) the compaction density of the negative electrode material is 0.8 g / cm 3 ~ 1.3 g / cm 3 ; (2) the tap density of the negative electrode material is 0.5 g / cm 3 ~ 1.5 g / cm 3 ; (3) The powder conductivity of the negative electrode material under a pressure of 20 kN is 0.1 S / cm to 2 S / cm; (4) The gas production of the negative electrode material is ≤1 mL / g / day.

10. The negative electrode material of claim 1, wherein, The negative electrode material also satisfies at least one of the following characteristics: (1) The matrix material includes porous materials, which include at least one of activated carbon, capacitive carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, and porous TiO2. (2) The matrix material includes a porous material, and at least a portion of the active substance is distributed in the pores of the porous material.

11. The negative electrode material of claim 1, wherein, The negative electrode material also satisfies at least one of the following characteristics: (1) The silicon material includes elemental silicon, which includes one or more of amorphous silicon, crystalline silicon, and composites of crystalline silicon and amorphous silicon; (2) the silicon material comprises a silicon oxide of the general formula SiO x wherein 0 < x < 2; (3) the silicon material includes silicon particles and a silicon oxide layer on the surface of the silicon particles, and the silicon oxide layer includes a silicon oxide of a general formula SiO x wherein 0 < x < 2.

12. The negative electrode material of claim 1, wherein, The negative electrode material includes a coating layer located on at least a portion of the surface of the matrix material and / or the active substance.

13. The negative electrode material of claim 12, wherein, The coating layer comprises a carbon material, which includes one or more of graphene, soft carbon, and hard carbon.

14. The negative electrode material of claim 1, wherein, The negative electrode material also satisfies at least one of the following characteristics: (1) Based on the mass of the negative electrode material, the mass content of silicon in the negative electrode material is 20% to 60%; (2) the mass content of carbon element in the negative electrode material is 35% to 80% based on the mass of the negative electrode material.

15. A secondary battery characterized by comprising: The secondary battery comprises the negative electrode material according to any one of claims 1-14.

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