A negative electrode material, a preparation method therefor, and an application thereof

Abstract

This invention provides an anode material, its preparation method, and its application. The anode material includes a core and a shell layer located on at least a portion of the surface of the core. The core comprises silicon and lithium compounds. The shell layer comprises oxides of iron-based elements. The silicon grain size is less than or equal to 5 nm. The residual active lithium content in the anode material is less than or equal to 2700 ppm by mass. The iron-based element content in the anode material is 50 ppm to 2000 ppm by mass. The anode material provided by this invention can improve the first-cycle coulombic efficiency of lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode active materials, and particularly relates to a negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Developing high-energy-density lithium-ion batteries is an important direction in the new energy field, and the performance breakthrough of negative electrode materials is the key to achieving this goal. The silicon-oxygen negative electrode material (SiO x , 0 < x < 2) has become a research hotspot in the field of negative electrodes for high-energy-density lithium-ion batteries due to its theoretical specific capacity of up to 2600 mAh / g and relatively excellent cycle stability. However, this material generally has the problem of low initial Coulomb efficiency during the first charge-discharge process, and its value is usually only 65% to 78%. This is mainly because inert lithium silicate and lithium oxide and other irreversible products are generated during initial lithium intercalation, consuming a large amount of active lithium from the positive electrode, seriously restricting its actual application process. In addition, the silicon-oxygen material will undergo severe volume expansion (>100%) during the charge-discharge process, easily leading to electrode structure pulverization and interface failure, further exacerbating capacity attenuation.

[0003] To compensate for the first irreversible capacity loss and improve the initial Coulomb efficiency, researchers have developed a variety of silicon-oxygen negative electrode materials. However, existing silicon-oxygen negative electrode materials still have many limitations in actual applications. On the one hand, in the materials obtained by high-temperature prelithiation treatment, silicon grains often grow excessively, resulting in increased volume expansion and easy pulverization of the structure during subsequent charge-discharge processes, and the cycle stability and capacity performance are thus significantly affected. On the other hand, high-reactivity unreacted lithium species (such as lithium hydride, etc.) often remain in existing prelithiated materials. These residual active lithium will continuously consume the electrolyte during battery operation; even if the residual lithium content is reduced by post-treatment methods, it often sacrifices some pre-embedded active lithium, resulting in the weakening of the improvement effect of the initial Coulomb efficiency of the material.

[0004] Therefore, developing a prelithiation technology that can efficiently solve the first irreversible capacity loss and at the same time take into account the structural stability and safety of the material has become the key to enhancing the actual application value of negative electrode materials. Summary of the Invention

[0005] The present invention provides a negative electrode material, a preparation method thereof, and an application thereof. The negative electrode material is suitable for lithium-ion batteries and can effectively improve the initial Coulomb efficiency of lithium-ion batteries.

[0006] In a first aspect, the present invention provides a negative electrode material comprising a core and a shell layer located on at least a portion of the surface of the core; the phase of the core comprising silicon and lithium compounds; the shell layer comprising oxides of iron-based elements; wherein the grain size of the silicon is less than or equal to 5 nm; the mass percentage of residual active lithium in the negative electrode material is less than or equal to 2700 ppm; and the content of iron-based elements in the negative electrode material is 50 ppm to 2000 ppm based on the mass of the negative electrode material.

[0007] Optionally, the iron-based element includes at least one of cobalt and nickel; and / or, the oxide of the iron-based element includes at least one of cobalt oxide and nickel oxide, preferably, the cobalt oxide includes Co3O4 and the nickel oxide includes NiO; and / or, the grain size of the silicon is 1.5 nm to 3.7 nm.

[0008] Optionally, the shell layer further includes lithium carbonate; preferably, the lithium carbonate in the negative electrode material has a mass percentage content of 1.9% to 3.3%.

[0009] Optionally, the lithium compound includes lithium silicate.

[0010] Secondly, the present invention provides a method for preparing a negative electrode material, comprising the steps of: pre-lithiation reaction of a raw material system including silicon-oxygen raw material, lithium hydride and iron-based catalyst in an inert atmosphere; after the pre-lithiation reaction, removing the residual iron-based catalyst and residual lithium hydride in the reaction system to obtain the negative electrode material; wherein the temperature of the pre-lithiation reaction is 450℃~500℃, and the mass ratio of the iron-based element in the iron-based catalyst to the mass of the silicon-oxygen raw material is (0.01~0.06):1.

[0011] Optionally, the iron-based catalyst includes at least one of elemental cobalt and elemental nickel.

[0012] Optionally, the process of removing residual iron-based catalyst from the reaction system includes: magnetically separating the product of the pre-lithiation reaction to remove the residual iron-based catalyst from the reaction system; preferably, the magnetic separation process includes: passing the product of the pre-lithiation reaction through a high-gradient magnetic separator at a flow rate of 5 L / min to 15 L / min, wherein the magnetic field strength of the magnetic separation is 0.5 T to 1.5 T, and the magnetic separation is performed in 2 to 4 cycles.

[0013] Optionally, the process of removing residual lithium hydride from the reaction system includes: introducing carbon dioxide gas into the product of the pre-lithiation reaction and reacting at 450°C to 500°C for 45 min to 90 min to remove the residual lithium hydride from the reaction system; the pressure of the carbon dioxide gas is 0.02 atm to 0.05 atm.

[0014] Optionally, the silicon-oxygen raw material includes SiO2. x , 0.9≤x≤1.1; and / or, the lithium hydride and the SiO x The mass ratio is (0.5~1):1; and / or the pre-lithiation reaction time is 3h~6h.

[0015] Thirdly, the present invention provides a lithium-ion battery comprising the above-described negative electrode material or a negative electrode material obtained by the above-described method for preparing the negative electrode material.

[0016] This invention provides an anode material, its preparation method, and its applications, which have at least the following beneficial effects: The anode material of this invention achieves significant improvements in electrochemical performance and safety through multiple synergistic designs of its microstructure. Specifically, by controlling the silicon grain size to less than or equal to 5 nm, the smaller silicon grains effectively suppress the volume expansion of the anode material during charge and discharge, achieving excellent cycle stability of the lithium-ion battery. The shell structure formed on the surface of the anode material acts as a physical barrier, reducing direct contact between the active material and the electrolyte, suppressing side reactions, and compensating for the lithium consumed in the formation of the solid electrolyte interphase (SEI) film, thus contributing to improved initial coulombic efficiency. The iron-based element components introduced into the shell effectively reduce the electrode impedance of the lithium-ion battery and decrease battery polarization. This, combined with the above structural features, further improves the initial coulombic efficiency. Furthermore, the material has extremely low residual active lithium content, eliminating safety hazards caused by residual lithium and ensuring consistent material performance and reliable use. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a comparison chart of the first charge-discharge curves of Example 1 and Comparative Example 1 in a lithium-ion battery.

[0019] Figure 2 This is a scanning electron microscope image provided in Embodiment 1 of the present invention;

[0020] Figure 3 The X-ray diffraction pattern provided in Embodiment 5 of the present invention;

[0021] Figure 4 The images shown are scanning electron microscope images and energy-dispersive X-ray spectra provided in Embodiment 5 of the present invention, wherein a is a scanning electron microscope image provided in Embodiment 5, b is an energy-dispersive X-ray spectra of carbon provided in Embodiment 5, and c is an energy-dispersive X-ray spectra of cobalt provided in Embodiment 5. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In a first aspect, embodiments of the present invention provide a negative electrode material, the negative electrode material comprising a core and a shell layer located on at least a portion of the surface of the core; the phase of the core comprises silicon and lithium compounds; the shell layer comprises oxides of iron-based elements; wherein the grain size of silicon is less than or equal to 5 nm; the mass percentage of residual active lithium in the negative electrode material is less than or equal to 2700 ppm; and the content of iron-based elements in the negative electrode material is 50 ppm to 2000 ppm based on the mass of the negative electrode material.

[0024] According to research and analysis, the anode material of this invention achieves significant improvements in electrochemical performance and safety through a multi-layered synergistic design of its microstructure. Specifically, by controlling the silicon grain size to less than or equal to 5 nm, the smaller silicon grains effectively suppress the volume expansion of the anode material during charge and discharge, achieving excellent cycle stability of the lithium-ion battery. The shell structure formed on the surface of the anode material acts as a physical barrier, reducing direct contact between the active material and the electrolyte, suppressing side reactions, and compensating for the lithium consumed in the formation of the solid electrolyte interphase (SEI) film, thus contributing to improved initial coulombic efficiency. The iron-based element components introduced into the shell effectively reduce the electrode impedance of the lithium-ion battery and reduce battery polarization. This, combined with the above structural features, further improves the initial coulombic efficiency. In addition, the material has extremely low residual active lithium content, eliminating safety hazards caused by residual lithium and ensuring the consistency of material performance and reliability in use.

[0025] The shell (surface decoration layer) on the kernel surface can cover part or all of the kernel surface.

[0026] The core phases include silicon and lithium compounds; specifically, the lithium compounds may include lithium silicate (Li₂SiO₃) and lithium silicon alloys (Li₂SiO₃). x At least one of Si and lithium disilicate (Li2Si2O5).

[0027] Silicon, as the electrochemically active component, undergoes an alloying reaction with lithium ions during charge and discharge, providing the material with charge and discharge capacity. Simultaneously, the active lithium stored in Li₂SiO₃ can compensate for the lithium ions consumed during the formation of the SEI film during the first charge and discharge cycle, thereby effectively improving the material's first coulombic efficiency.

[0028] The silicon grain size is less than or equal to 5 nm, for example, 1, 1.5, 1.57, 1.69, 1.89, 2, 2.13, 2.33, 3, 3.52, 3.64, 3.7, 4, 5 nm or any combination thereof, preferably 1.5 nm to 3.7 nm.

[0029] When the grain size of silicon meets the above range, it can effectively suppress the volume expansion of the anode material (silicon-oxygen anode material) during the charging and discharging process, which is beneficial to improving the cycle stability and first-cycle coulombic efficiency of lithium-ion batteries.

[0030] The shell may include oxides of iron-based elements. Specifically, the iron-based elements may include at least one of cobalt and nickel. Further, the oxides of the iron-based elements may include at least one of cobalt oxide and nickel oxide, wherein the cobalt oxide may include Co3O4 and the nickel oxide may include NiO.

[0031] The oxides of the aforementioned iron-based elements are p-type semiconductor materials, with electrical conductivity far exceeding that of insulating silica-based oxides. Using them as a shell layer to coat the surface of the negative electrode material can significantly improve the material's electronic conductivity, reduce powder impedance, thereby decreasing battery polarization and further enhancing the initial coulombic efficiency.

[0032] Based on the mass of the negative electrode material, the content of iron-based elements in the negative electrode material can be from 50ppm to 2000ppm, for example, 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000ppm or any combination thereof. The iron-based element content meeting the above range is beneficial to improving the first-cycle coulombic efficiency of lithium-ion batteries.

[0033] The mass percentage of residual active lithium in the anode material can be less than or equal to 2700 ppm, such as 2700 ppm, 2500 ppm, 2000 ppm, 1500 ppm, 1000 ppm, 500 ppm or any combination thereof. Residual active lithium refers to active lithium that reacts with water to produce hydrogen gas. Excessive content of this material will bring significant safety hazards to production.

[0034] In some embodiments, the shell further includes lithium carbonate; further, the mass percentage of lithium carbonate in the negative electrode material is 1.9% to 3.3%, for example, 1.9%, 1.97%, 2.03%, 2.04%, 2.30%, 2.56%, 3.21%, 3.3%, or any combination thereof.

[0035] Lithium carbonate (Li₂CO₃) possesses relatively good chemical stability and can act as a physical barrier for anode materials, effectively reducing direct contact between the anode material and the electrolyte, thereby suppressing ongoing side reactions and reducing electrolyte decomposition and consumption. Furthermore, lithium carbonate is a crucial component of the SEI film in anode materials. When the mass percentage of lithium carbonate meets the aforementioned range, it introduces lithium-containing compounds onto the material surface, compensating for lithium losses caused by SEI film formation and improving the material's charge / discharge capacity.

[0036] Secondly, the present invention provides a method for preparing a negative electrode material, the steps of which include: in an inert atmosphere, a raw material system comprising silicon-oxygen raw materials, lithium hydride and an iron-based catalyst undergoing a pre-lithiation reaction; after the pre-lithiation reaction, the residual iron-based catalyst and residual lithium hydride in the reaction system are removed to obtain the negative electrode material.

[0037] The anode material prepared by the above method has high safety and is simple to process and easy to mass-produce.

[0038] For example, the above steps may specifically include: in an inert atmosphere, thoroughly mixing a raw material system including silicon-oxygen raw materials, lithium hydride and iron-based catalyst, and carrying out a pre-lithiation reaction in a high-temperature reaction vessel at a certain temperature; after the pre-lithiation reaction, removing the residual iron-based catalyst and residual lithium hydride in the reaction system to obtain the negative electrode material.

[0039] The electronic configurations of Co and Ni are 3d and 3d, respectively. 7 4s 2 and 3D 8 4s 2 Its incompletely filled d orbitals give it excellent surface adsorption and activation capabilities for small molecules (such as H2 and -H). Surface atoms can adsorb -H atoms in LiH and interact with them, effectively polarizing and weakening the Li-H bond, significantly reducing the activation energy of LiH decomposition, thereby achieving low-temperature pre-lithiation.

[0040] An inert atmosphere may include an argon atmosphere (e.g., a high-purity argon atmosphere).

[0041] Silicon-oxygen raw materials may include SiO x , 0.9≤x≤1.1, for example, a range consisting of 0.9, 1, 1.1 or any two of them.

[0042] Silicon-oxygen raw materials that meet the above criteria can achieve a balance in terms of lithium-ion battery capacity, cycle stability, initial coulombic efficiency, and volume expansion suppression.

[0043] The mass ratio of lithium hydride (LiH) to silicon oxide raw material can be (0.5~1):1, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1 or any combination thereof, preferably 0.7:1.

[0044] On the one hand, it can provide sufficient active lithium to achieve full pre-lithiation and significantly improve the first coulombic efficiency of the material; on the other hand, it can effectively suppress the introduction of excess lithium and reduce the generation of residual active lithium after the reaction, thereby ensuring the pre-lithiation effect while eliminating the safety hazards caused by residual lithium and achieving synergistic optimization of electrochemical performance and safety.

[0045] After a pre-lithiation reaction, silicon-oxygen raw materials and lithium hydride are reacted to produce silicon and lithium compounds. The lithium compounds may include lithium silicate (Li₂SiO₃) and lithium silicon alloys (Li₂SiO₃). x The core phase may include at least one of Si and lithium disilicate (Li2Si2O5), and may also include unreacted silicon-oxygen raw materials.

[0046] In this embodiment of the invention, the temperature of the pre-lithiation reaction is 450°C to 500°C, for example, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, or any combination thereof.

[0047] If the pre-lithiation reaction temperature meets the above-mentioned range, low-temperature pre-lithiation of silicon-oxygen raw materials can be achieved. The lower sintering temperature avoids excessive growth of silicon grains in the silicon-oxygen core due to high temperature. Smaller silicon grains can effectively alleviate volume changes during charge and discharge, thus improving the cycle stability of the anode material. If the pre-lithiation reaction temperature is below 450℃, the reaction kinetics are insufficient, the lithiation reaction is incomplete, resulting in a low degree of pre-lithiation, a high content of residual active oxygen in the material, and limited improvement in the first coulombic efficiency. If the pre-lithiation reaction temperature is above 500℃, the silicon grains in the silicon-oxygen core are prone to agglomeration and excessive growth at high temperatures. Larger silicon grains expand significantly in volume during charge and discharge, which can easily lead to pulverization of the electrode material and a decrease in cycle stability.

[0048] The heating rate of the pre-lithiation reaction can be 2℃ / min to 5℃ / min, for example, 2, 3, 4, 5℃ / min or any combination thereof.

[0049] The pre-lithiation reaction time can be 3h to 6h, for example, 3, 4, 5, 6h or any combination thereof.

[0050] Meeting the above-mentioned time range for the pre-lithiation reaction ensures sufficient pre-lithiation of silicon-oxygen raw materials, effectively improving the initial coulombic efficiency. On the other hand, it avoids excessive silicon grain growth and residual active lithium caused by excessive reaction time, thereby eliminating safety hazards while ensuring the electrochemical performance of the material and synergistically improving the initial coulombic efficiency, cycle stability, and safety of lithium-ion batteries.

[0051] The mass ratio of iron-based elements to silicon-oxygen raw materials in iron-based catalysts can be (0.01~0.06):1, for example, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1 or any combination thereof.

[0052] When the quality of the iron-based catalyst meets the above-mentioned range, it can promote the generation of more electrochemically active silicon, thereby improving the charge and discharge capacity of the material. On the other hand, through solid-solid contact reaction, the iron oxides of the iron-based catalyst reaction products can be concentrated and distributed on the surface of the silicon-oxygen material to form a functional shell structure.

[0053] Furthermore, the iron-based catalyst may include at least one of elemental cobalt and elemental nickel, with a purity of not less than 99.8%.

[0054] When the iron-based catalyst is elemental cobalt, elemental cobalt (such as cobalt powder) reacts with SiO₂. x (0.9≤x≤1.1) can undergo a redox reaction to obtain Co3O4. Taking x=1 as an example, the reaction equation can be expressed as 4SiO+3Co=4Si+Co3O4.

[0055] In some specific embodiments, the process of removing residual iron-based catalyst from the reaction system includes: magnetically separating the products of the pre-lithiation reaction to remove residual iron-based catalyst from the reaction system.

[0056] Specifically, the magnetic separation process includes: passing the pre-lithiation reaction product through a high gradient magnetic separator at a flow rate of 5 L / min to 15 L / min, with a magnetic field strength of 0.5 T to 1.5 T, and performing magnetic separation 2 to 4 cycles.

[0057] The above-mentioned iron-based catalyst removal process avoids the side reactions between active lithium and water that may be caused by water washing, significantly improving process safety. At the same time, the process can more thoroughly remove unreacted iron-based catalysts, achieving efficient separation of iron-based catalysts and precise control of the iron content in the material.

[0058] Specifically, before magnetic separation, the products of the pre-lithiation reaction can be cooled and appropriately dispersed.

[0059] The flow rate of the product from the pre-lithiation reaction can be 5 L / min to 15 L / min, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 L / min or any combination thereof.

[0060] The magnetic field strength for magnetic separation can be 0.5T to 1.5T, for example, 0.5, 1.0, 1.5T or any combination thereof.

[0061] The magnetic separation cycle can be 2 to 4 times, for example, 2, 3, 4 times or any combination thereof.

[0062] When the conditions for magnetic separation meet the above range, excess iron-based catalysts can be removed more effectively, enabling precise control of the iron content in the material and thus improving the first-cycle coulombic efficiency of lithium-ion batteries.

[0063] Furthermore, the process of removing residual lithium hydride from the reaction system includes: introducing carbon dioxide gas into the product of the pre-lithiation reaction and reacting at 450°C to 500°C for 45 min to 90 min to remove residual lithium hydride from the reaction system.

[0064] Compared to the traditional process of removing lithium hydride by washing with water, this invention uses carbon dioxide to treat the surface lithium hydride, reducing the amount of residual active lithium on the surface of the negative electrode material, effectively avoiding the violent reaction between water and active lithium, significantly improving process safety, and at the same time retaining more pre-intercalated active lithium, improving the pre-lithiation effect, thereby improving the first-cycle coulombic efficiency and capacity stability of lithium-ion batteries.

[0065] Specifically, the process of removing residual lithium hydride from the reaction system (CO2 post-treatment) can be carried out in a reactor with a controlled atmosphere.

[0066] Furthermore, after the reaction is complete, the material is cooled to room temperature (<40℃) to obtain the negative electrode material.

[0067] The reaction temperature for lithium hydride removal can be 450℃~500℃, for example, 450, 460, 470, 480, 490, 500℃ or any combination thereof; the time can be 45min~90min, for example, 45, 50, 60, 70, 80, 90min or any combination thereof.

[0068] When the temperature or time of the lithium hydride removal reaction meets the above range, the residual trace amount of LiH can react with CO2 to generate stable Li2CO3, reducing the residual active lithium content and generating a lithium carbonate shell, which further improves the first-cycle coulombic efficiency and cycle stability of the anode material.

[0069] The pressure of carbon dioxide gas can be 0.02 atm to 0.05 atm, for example, 0.02, 0.03, 0.04, 0.05 atm or any combination thereof.

[0070] When the gas pressure of carbon dioxide meets the above range, it can accelerate the reaction and form a uniform and dense lithium carbonate shell.

[0071] Thirdly, embodiments of the present invention provide a lithium-ion battery, comprising the above-mentioned negative electrode material or a negative electrode material prepared by the above-mentioned method for preparing the negative electrode material.

[0072] The aforementioned lithium-ion batteries exhibit excellent electrochemical performance, with an initial coulombic efficiency of ≥90%, and also possess high charge / discharge capacity, good cycle stability, and high safety.

[0073] The aforementioned negative electrode material is disposed on the negative electrode sheet. Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer formed of the negative electrode material disposed on the surface of the negative electrode current collector.

[0074] In the specific preparation of the negative electrode, the negative electrode material, conductive agent, and binder can be dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained. In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of negative electrode material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0075] The negative electrode current collector layer can be made of at least one of copper foil, nickel foam, and copper foam; the conductive agent can be selected from at least one of acetylene black, Ketjen black, and carbon fiber; and the binder can be selected from at least one of carboxymethyl cellulose and styrene-butadiene rubber.

[0076] In addition to the aforementioned negative electrode, the lithium-ion battery of the present invention also includes a positive electrode, a separator, and an electrolyte.

[0077] This invention does not strictly limit the positive electrode active material in the positive electrode sheet. It can be any positive electrode active material commonly used in lithium-ion batteries, such as at least one composite oxide of lithium with cobalt, manganese, nickel, or combinations thereof. More specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, lithium-rich manganese-based materials, etc., or it can be just metallic lithium.

[0078] The embodiments of the present invention do not strictly limit the selection of electrolyte, and may include one or more of the solvents commonly used in lithium-ion battery electrolytes, as well as the electrolyte lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate (EC), propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), preferably 1M LiPF6 in EC / DEC (1:1 v / v).

[0079] The embodiments of the present invention do not strictly limit the choice of separator material. It can be a separator material commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PPPEPP), cellulose nonwoven separator, and separator with ceramic coating.

[0080] In the preparation of lithium-ion batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0081] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0082] Example 1

[0083] This embodiment provides a method for preparing a negative electrode material, the specific steps of which are as follows:

[0084] In an argon atmosphere (inert atmosphere), 1000g of SiO will be included. 0.98 (Silicon-oxygen raw materials, D) 50 The raw material system consisting of approximately 7μm), lithium hydride (added at 70wt% of the silicon-oxygen raw material) and cobalt powder (iron-based catalyst, elemental cobalt, purity 99.9%, nano-sized, mass ratio of its mass to silicon-oxygen raw material is 0.03:1) was subjected to a pre-lithiation reaction at 450℃ for 6h.

[0085] After the pre-lithiation reaction, the product of the pre-lithiation reaction is separated by magnetic separation. The flow rate of the product of the pre-lithiation reaction is 5 L / min, the magnetic field strength is 1.0 T, and the number of magnetic separation cycles is 3 to remove the residual iron-based catalyst in the reaction system.

[0086] Carbon dioxide gas was introduced into the product of the pre-lithiation reaction, and the reaction was carried out at 450°C for 60 min at a pressure of 0.04 atm to remove residual lithium hydride from the reaction system, thereby obtaining the negative electrode material.

[0087] Example 2

[0088] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cobalt powder to silicon oxide raw material is 0.015:1.

[0089] Example 3

[0090] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cobalt powder to silicon oxide raw material is 0.045:1.

[0091] Example 4

[0092] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cobalt powder to silicon oxide raw material is 0.055:1.

[0093] Example 5

[0094] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cobalt powder to silicon oxide raw material is 0.06:1.

[0095] Example 6

[0096] This embodiment provides a method for preparing a negative electrode material, the specific steps of which are as follows:

[0097] In an argon atmosphere (inert atmosphere), 1000g of SiO will be included.1.1 (Silicon-oxygen raw materials, D) 50 The raw material system of lithium hydride (approximately 7 μm), lithium hydride (added at 100 wt% of silicon-oxygen raw material), and nickel powder (iron-based catalyst, elemental nickel, purity 99.9%, nano-sized, mass ratio of its mass to silicon-oxygen raw material is 0.01:1) was subjected to a pre-lithiation reaction at 500℃ for 3 h.

[0098] After the pre-lithiation reaction, the product of the pre-lithiation reaction is separated by magnetic separation. The flow rate of the product of the pre-lithiation reaction is 15 L / min, the magnetic field strength is 1.5 T, and the number of magnetic separation cycles is 4 to remove the residual iron-based catalyst in the reaction system.

[0099] Carbon dioxide gas was introduced into the product of the pre-lithiation reaction, and the reaction was carried out at 500°C for 45 min at a pressure of 0.02 atm to remove residual lithium hydride in the reaction system, thereby obtaining the negative electrode material.

[0100] Example 7

[0101] This embodiment provides a method for preparing a negative electrode material, the specific steps of which are as follows:

[0102] In an argon atmosphere (inert atmosphere), 1000g of SiO will be included. 0.9 (Silicon-oxygen raw materials, D) 50 The raw material system consisting of approximately 7μm), lithium hydride (added at 50wt% of the silicon-oxygen raw material), and cobalt powder (iron-based catalyst, elemental cobalt, purity 99.9%, nano-sized, mass ratio of its mass to silicon-oxygen raw material is 0.03:1) was subjected to a pre-lithiation reaction at 480℃ for 5h.

[0103] After the pre-lithiation reaction, the product of the pre-lithiation reaction is separated by magnetic separation. The flow rate of the product of the pre-lithiation reaction is 10 L / min, the magnetic field strength is 1.0 T, and the magnetic separation cycle is 2 times to remove the residual iron-based catalyst in the reaction system.

[0104] Carbon dioxide gas was introduced into the product of the pre-lithiation reaction, and the reaction was carried out at 480°C for 90 min with a carbon dioxide gas pressure of 0.05 atm to remove residual lithium hydride in the reaction system, thereby obtaining the negative electrode material.

[0105] Comparative Example 1

[0106] It is basically the same as Example 1, except that no iron-based catalyst is added, and the rest of the steps are the same as in Example 1.

[0107] Comparative Example 2

[0108] In an argon atmosphere (inert atmosphere), 1000g of SiO will be included. 0.98(Silicon-oxygen raw materials, D) 50 The raw material system of ≈7μm) and lithium hydride (added at 70wt% of silicon oxide raw material) was subjected to a pre-lithiation reaction at 450℃ for 6h.

[0109] After the pre-lithiation reaction, the product of the pre-lithiation reaction is cooled naturally and soaked in deionized water for 2 hours to remove residual lithium hydride in the reaction system. After filtration and drying, the negative electrode material is obtained.

[0110] Comparative Example 3

[0111] It is basically the same as Comparative Example 2, except that the temperature of the pre-lithiation reaction is 500℃, and the rest of the steps are the same as Comparative Example 2.

[0112] Comparative Example 4

[0113] It is basically the same as Comparative Example 2, except that the temperature of the pre-lithiation reaction is 550℃, and the rest of the steps are the same as Comparative Example 2.

[0114] Comparative Example 5

[0115] It is basically the same as Comparative Example 2, except that the temperature of the pre-lithiation reaction is 600℃, and the rest of the steps are the same as Comparative Example 2.

[0116] Comparative Example 6

[0117] It is basically the same as Comparative Example 2, except that the temperature of the pre-lithiation reaction is 650℃, and the rest of the steps are the same as Comparative Example 2.

[0118] Comparative Example 7

[0119] It is basically the same as Comparative Example 2, except that the temperature of the pre-lithiation reaction is 700℃, and the rest of the steps are the same as Comparative Example 2.

[0120] Comparative Example 8

[0121] The procedure is basically the same as in Example 1, except that the mass ratio of cobalt powder to silicon oxide raw material is 0.065:1, and the remaining steps are the same as in Example 1.

[0122] Comparative Example 9

[0123] The procedure is basically the same as in Example 1, except that the mass ratio of cobalt powder to silicon oxide raw material is 0.005:1, and the remaining steps are the same as in Example 1.

[0124] Comparative Example 10

[0125] The process is basically the same as in Example 1, except that the temperature of the pre-lithiation reaction is 550°C, and the remaining steps are the same as in Example 1.

[0126] Test case

[0127] 1. Silicon grain size testing

[0128] X-ray diffraction (XRD) was used to fit and determine the silicon grain size of the anode materials in the examples and comparative examples. The measurement method is as follows: First, high-quality diffraction data was acquired using slow step scanning (step size ≤ 0.01°); then, background subtraction was performed on the original spectra, and the characteristic peaks of silicon were fitted using the Pseudo-Voigt function to effectively separate the silicon peaks from other phase peaks such as Li2SiO3 and Co3O4; finally, the physical half-width at half-maximum (HWHM) after instrument broadening was extracted and substituted into the Scherrer formula (D = Kλ / (βcosθ)) to calculate the grain size, where D is the grain size, K is a constant (taken as 0.89), λ is the X-ray wavelength, β is the HWHM of the diffraction peak, and θ is the diffraction angle. The test results are shown in Table 1, where the XRD pattern of Example 5 is shown in Table 1. Figure 3 As shown.

[0129] Depend on Figure 3 It can be seen that the negative electrode material prepared in Example 5 contains silicon, lithium silicate (Li2SiO3) and Co3O4 (oxide of iron-based elements).

[0130] 2. Residual lithium content test

[0131] The residual lithium content was tested by a gas collection method. The specific method was as follows: 5g of the negative electrode material prepared in the example or comparative example was accurately weighed, 100mL of deionized water was added, and the mixture was stirred for 30mins. During this process, the amount of gas generated was collected and then converted into the residual lithium content. The results are shown in Table 1.

[0132] 3. Iron group element content test

[0133] The iron group element content was tested by inductively coupled plasma mass spectrometry (ICP-MS), and the results are shown in Table 1.

[0134] 4. Lithium carbonate content test

[0135] The mass percentage of lithium carbonate in the shell of the negative electrode material was determined and calculated by titration. The calculation method was as follows: 3g of the negative electrode material prepared in the example or comparative example was accurately weighed and placed in 100mL of deionized water. After stirring for 30 minutes, insoluble substances were filtered off, and 10mL of the solution was transferred for acid-base titration to measure the CO content. 3- The content was calculated, then converted into the lithium carbonate content, and then the mass percentage of lithium carbonate in the anode material was calculated. The results are shown in Table 1.

[0136] Table 1

[0137]

[0138] As shown in Table 1, under conventional high-temperature pre-lithiation processes (Comparative Examples 3-7), the silicon grain size in the anode material increases with increasing reaction temperature. In contrast, the method of this invention can achieve effective pre-lithiation at lower temperatures, and the silicon grain size of the material obtained at 450°C is much smaller than that obtained by conventional high-temperature processes. For the sample without an iron-based catalyst (Comparative Example 2), effective pre-lithiation could not be achieved even at 450°C, therefore its silicon grain size was not included in the statistics.

[0139] Further analysis revealed that the residual lithium content in materials obtained by traditional high-temperature pre-lithiation processes is generally higher than that obtained by the method of this invention. This is because, in the absence of a catalyst, the reactivity of LiH with silicon-oxygen materials is low, and a large amount of LiH fails to fully participate in the reaction, adhering to the material surface as residual lithium. Residual LiH easily undergoes side reactions with the electrolyte in the battery, thereby deteriorating battery performance. The method of this invention, however, utilizes the catalytic effect of iron-based elements to significantly improve the thoroughness of the pre-lithiation reaction, thus effectively reducing the residual lithium content.

[0140] 5. Lithium-ion battery performance testing

[0141] The initial charge capacity, initial coulombic efficiency, and capacity retention of the lithium-ion battery were tested using a charge-discharge tester, and the powder impedance of the lithium-ion battery was tested using a powder impedance meter (PD-51). The results are shown in Table 2. A comparison of the first-cycle charge-discharge curves of Example 1 and Comparative Example 1 is shown in the figure below. Figure 1 As shown.

[0142] Table 2

[0143]

[0144] Combine Table 2 and Figure 3 It can be seen that, within a defined range, the powder impedance of the material decreases with increasing residual cobalt content (Examples 1-5). This is because oxides of iron-based elements possess certain semiconductor properties, with cobalt oxide exhibiting a conductivity of up to 1.12 × 10⁻⁶. -2 The S / cm ratio is significantly higher than that of lithium carbonate and silicon suboxide (both of which are close to insulating materials). Introducing this type of conductive component into the shell effectively reduces the powder impedance of the material, decreases battery polarization, and improves the initial coulombic efficiency and capacity stability of lithium-ion batteries.

[0145] When the cobalt content was greater than 2000 ppm (Comparative Example 8) or less than 50 ppm (Comparative Example 9), the initial coulombic efficiency decreased significantly. This is mainly because when the cobalt content is too low, there are insufficient catalytic active sites, LiH decomposition is incomplete, and the pre-lithiation effect is limited; while when the cobalt content is too high, due to the very low diffusion coefficient of lithium ions in Co3O4, excessive cobalt oxide increases the resistance of lithium ions through the surface modification layer, offsetting the advantages brought by its conductivity.

[0146] In the presence of an iron-based catalyst, when the temperature exceeds 500℃ (Comparative Example 10), the silicon grain size, although smaller than that of the traditional high-temperature pre-lithiation process at the same temperature (Comparative Example 4), is still significantly larger than the grain size corresponding to the 450℃~500℃ range. This indicates that the silicon grain size cannot be effectively controlled under this temperature condition, leading to significant volume expansion during the charging and discharging of lithium-ion batteries, which in turn affects the battery's initial coulombic efficiency and capacity stability.

[0147] 6. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) testing

[0148] SEM tests were performed on the negative electrode materials of Examples 1 and 5, respectively, and the results are as follows: Figure 2 and Figure 4 As shown in Figure a, EDS testing was also performed on Example 5, and the results are as follows. Figure 4 b、 Figure 4 As shown in c.

[0149] Combination Figure 2 and Figure 4 The analysis results of a show that the negative electrode material prepared by the present invention has a single-particle block morphology, and its particle size D is... 50 It is approximately 7 μm. Figure 4 b further shows that the surface of the anode material particles is coated with a carbon-containing substance, namely Li2CO3. Li2CO3 can form a physical barrier on the surface of the active material, effectively reducing the direct contact between the anode material and the electrolyte, thereby inhibiting continuous side reactions between them and reducing electrolyte decomposition and consumption. In addition, cobalt was also detected on the surface of the anode material. Figure 4 The presence of c) combined with XRD analysis results confirms that Co exists on the particle surface in the form of Co3O4.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a core and a shell located on at least a portion of the surface of the core; the phase of the core includes silicon and lithium compounds; the shell includes oxides of iron-based elements; wherein the grain size of the silicon is less than or equal to 5 nm; The mass percentage of residual active lithium in the negative electrode material is less than or equal to 2700 ppm; Based on the mass of the negative electrode material, the content of iron-based elements in the negative electrode material is 50 ppm to 2000 ppm.

2. The negative electrode material according to claim 1, characterized in that, The iron-group elements include at least one of cobalt and nickel; And / or, the oxides of the iron-group elements include at least one of cobalt oxide and nickel oxide, preferably, the cobalt oxide includes Co3O4 and the nickel oxide includes NiO; And / or, the silicon grain size is 1.5 nm to 3.7 nm.

3. The negative electrode material according to claim 1 or 2, characterized in that, The shell layer further includes lithium carbonate; preferably, the lithium carbonate in the negative electrode material has a mass percentage content of 1.9% to 3.3%.

4. The negative electrode material according to any one of claims 1-3, characterized in that, The lithium compound includes lithium silicate.

5. A method for preparing the negative electrode material according to any one of claims 1-4, characterized in that the step include: In an inert atmosphere, a raw material system comprising silicon-oxygen raw materials, lithium hydride, and an iron-based catalyst is subjected to a pre-lithiation reaction. After the pre-lithiation reaction, the residual iron-based catalyst and residual lithium hydride in the reaction system are removed to obtain the negative electrode material. The temperature of the pre-lithiation reaction is 450℃~500℃, and the mass ratio of the iron-based element in the iron-based catalyst to the mass of the silicon-oxygen raw material is (0.01~0.06):

1.

6. The method for preparing the negative electrode material according to claim 5, characterized in that, The iron-based catalyst includes at least one of elemental cobalt and elemental nickel.

7. The method for preparing the negative electrode material according to claim 5 or 6, characterized in that, The process of removing residual iron-based catalyst from the reaction system includes: magnetically separating the products of the pre-lithiation reaction to remove the residual iron-based catalyst from the reaction system; Preferably, the magnetic separation process includes: passing the product of the pre-lithiation reaction through a high-gradient magnetic separator at a flow rate of 5 L / min to 15 L / min, wherein the magnetic field strength of the magnetic separation is 0.5 T to 1.5 T, and the magnetic separation is performed in 2 to 4 cycles.

8. The method for preparing the negative electrode material according to any one of claims 5-7, characterized in that, The process of removing residual lithium hydride from the reaction system includes: Carbon dioxide gas is introduced into the product of the pre-lithiation reaction, and the reaction is carried out at 450°C to 500°C for 45 min to 90 min to remove the residual lithium hydride in the reaction system; the pressure of the carbon dioxide gas is 0.02 atm to 0.05 atm.

9. The method for preparing the negative electrode material according to any one of claims 5-7, characterized in that, The silicon-oxygen raw material includes SiO₂ x , 0.9≤x≤1.1; And / or, the mass ratio of the lithium hydride to the silicon oxide raw material is (0.5~1):1; And / or, the pre-lithiation reaction time is 3h to 6h.

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

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