Negative electrode material, method for preparing the same, and battery

Abstract

The application provides a negative electrode material and a preparation method and a battery, and relates to the field of battery materials. The negative electrode material comprises graphite, a lithium carbonate layer coated on the surface of the graphite, and a lithium azide layer coated on the surface of the lithium carbonate layer. The lithium carbonate layer can effectively inhibit thermal stress damage of the material, significantly enhance the crystallization quality and purity of the material, and the lithium azide layer can further optimize the lithium ion transmission channel and reduce the interface resistance. The graphite, the lithium carbonate layer and the lithium azide layer of the application can cooperate with each other, so that the negative electrode material has high rate performance and excellent cycle stability, and the problem that the rate performance and cycle performance of the existing graphite-based negative electrode material are poor is improved.

Description

Technical Field

[0001] This application relates to the field of battery materials, and more particularly to a negative electrode material, its preparation method, and a battery. Background Technology

[0002] Driven by the urgent needs of global energy transition and environmental protection, innovation in energy storage technology has become a cutting-edge focus of technological development. Solid-state batteries, as the leader in future energy storage technology, are gradually leading a profound transformation in the energy storage field due to their superior energy density, inherent safety characteristics, and potential long-term cycle life. However, the widespread adoption and application of solid-state battery technology still faces many challenges. Among these, the performance optimization of electrode materials, especially anode materials, has become a key factor restricting the overall performance improvement of solid-state batteries.

[0003] Currently, most mainstream lithium-ion batteries on the market use graphite as the anode material. Although graphite exhibits good performance under normal conditions, its structure is prone to degradation during high-power charge and discharge processes, leading to a sharp decline in capacity and a significant reduction in cycle stability. Furthermore, the flammability and potential explosion risks of traditional liquid electrolyte systems further limit the expansion of lithium-ion batteries in high-energy-efficiency applications. To address these issues, researchers have conducted extensive research on modifying graphite anodes, such as coating them with metal oxides or carbon-based materials. However, these methods generally suffer from uneven coating, high process complexity, and high costs, making it difficult to ensure long-term cycle stability while improving high-rate performance, thus becoming a significant obstacle to the advancement of solid-state battery technology. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material, a method for preparing the same, and a battery to solve the above-mentioned problems.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A negative electrode material includes: graphite, a lithium carbonate layer coated on the surface of the graphite, and a lithium azide layer coated on the surface of the lithium carbonate layer.

[0007] According to an embodiment of this application, the mass ratio of the graphite to the lithium carbonate layer and the lithium azide layer is 1:(0.01-0.1):(0.01-0.08).

[0008] This application also provides a method for preparing the negative electrode material as described above, including:

[0009] A lithium carbonate layer is formed on the surface of graphite to obtain a graphite-lithium carbonate material;

[0010] A lithium azide layer is formed on the surface of the graphite-lithium carbonate material to obtain the negative electrode material.

[0011] According to embodiments of this application, the preparation of the graphite-lithium carbonate material includes:

[0012] Preparation of lithium hydroxide-coated graphite materials;

[0013] The lithium hydroxide-coated graphite material is heat-treated to convert the lithium hydroxide into lithium carbonate.

[0014] According to an embodiment of this application, the material for preparing lithium hydroxide-coated graphite includes: mixing graphite, a lithium source, and a solvent to obtain a lithium source-coated graphite material;

[0015] The lithium source-coated graphite material is mixed with an alkaline solution and dried to obtain a lithium hydroxide-coated graphite material.

[0016] According to embodiments of this application, the graphite includes flake graphite;

[0017] And / or, the lithium source includes at least one of lithium chloride, lithium hydride, lithium bromide, and lithium iodide, and the mass of the lithium source accounts for 2.5% to 10% of the mass of the graphite;

[0018] And / or, during the mixing of graphite, lithium source, and solvent, the method further includes adding a surfactant, wherein the surfactant includes at least one of tetraethyl orthosilicate, polyethylene glycol, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, polyoxyethylene sorbitan fatty acid ester, and silane coupling agent;

[0019] And / or, the alkaline solution includes a sodium hydroxide solution;

[0020] And / or, the concentration of the alkaline solution is 0.5-1 mol / L;

[0021] And / or, the amount of alkaline solution added is controlled such that the pH value of the system after mixing the lithium source-coated graphite material with the alkaline solution is in the range of 10 to 12.

[0022] According to an embodiment of this application, heat treatment of the lithium hydroxide-coated graphite material includes: heating the lithium hydroxide-coated graphite material to a first temperature at a first heating rate, then heating it to a second temperature at a second heating rate, and holding it at the second temperature; wherein the first heating rate is greater than the second heating rate, the process of heating to the first temperature and the process of heating to the second temperature are carried out under inert gas protection, and the process of holding it at the second temperature is carried out in a carbon dioxide-containing atmosphere.

[0023] According to an embodiment of this application, the first heating rate is 10-20℃ / min, and the second heating rate is 1-5℃ / min;

[0024] And / or, the first temperature is 80-250℃, the second temperature is 350-650℃, and the heat preservation time is 1-2 hours.

[0025] According to an embodiment of this application, forming a lithium azide layer on the surface of the graphite-lithium carbonate material includes: depositing an organic lithium compound and an azide source on the surface of the graphite-lithium carbonate material using atomic layer deposition.

[0026] According to an embodiment of this application, the deposition temperature is 130-160°C;

[0027] And / or, the deposition pressure is 0.08-0.12 Pa;

[0028] And / or, the organolithium compound includes at least one of butyllithium, phenyllithium, and lithium amino compounds, wherein the lithium amino compound includes hexamethyldisilazine lithium;

[0029] And / or, the azide source includes at least one of sodium azide, potassium azide, and ammonia;

[0030] And / or, the pulse time ratio of the organolithium compound to the azide source is 1:20 to 1:50;

[0031] And / or, the atomic layer deposition method has 100-1000 cycles;

[0032] And / or, after the deposition is completed, the method further includes: annealing the deposited material to obtain a negative electrode material; wherein the annealing temperature is 100-200℃ and the annealing time is 1-2h.

[0033] This application also provides a battery, including the negative electrode material described above or the negative electrode material prepared by the preparation method described above.

[0034] Compared with the prior art, the beneficial effects of this application include:

[0035] The anode material of this application includes graphite, and a lithium carbonate layer and a lithium azide layer coated on the surface of the graphite. The lithium carbonate layer can effectively suppress thermal stress damage to the material and significantly enhance the crystallinity and purity of the material. The lithium azide layer can further optimize the lithium-ion transport channel and reduce the interfacial resistance. The graphite, lithium carbonate layer, and lithium azide layer work together to enable the anode material to have high rate performance and excellent cycle stability, improving the poor rate performance and cycle performance of existing graphite-based anode materials.

[0036] This application forms a lithium carbonate layer on the surface of graphite, which effectively blocks the erosion of harmful substances in the electrolyte, reduces the occurrence of side reactions, and enhances the connection strength between graphite particles through chemical bonding, preventing structural fragmentation and collapse during cycling. This fundamentally improves the cycle durability of the anode material, ensuring that the battery maintains a high capacity retention rate after multiple charge-discharge cycles. This application also forms a lithium azide layer on the surface of the lithium carbonate layer, which reduces the mass transfer resistance of lithium ions at the interface, promotes rapid diffusion of lithium ions, and reduces energy loss during charge transfer. Furthermore, the lithium azide layer effectively regulates the formation of the SEI film, preventing the formation of large particles, thereby maintaining good electrochemical response during high-rate charge-discharge and improving the instantaneous power output of the battery. The anode material prepared by the method of this application exhibits high rate performance and excellent cycle stability. Moreover, the method of this application does not require the use of harmful solvents, making it environmentally friendly. In addition, the method of this application also has the advantage of low production cost, which is conducive to large-scale promotion and application. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0038] Figure 1 This is a SEM image of the negative electrode material prepared in Example 1 of this application;

[0039] Figure 2 This is a comparison chart of the cycle performance of the negative electrode materials prepared in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0040] As used in this article:

[0041] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0042] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0043] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0044] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0045] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0046] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0047] To better illustrate the technical solution provided in this application, the technical solution will be described in its entirety before the embodiments, as follows:

[0048] A negative electrode material includes: graphite, a lithium carbonate layer coated on the surface of the graphite, and a lithium azide layer coated on the surface of the lithium carbonate layer.

[0049] The lithium carbonate layer in the anode material of this application can effectively suppress thermal stress damage to the material and significantly enhance the crystal quality and purity of the material. The lithium azide layer can further optimize the lithium-ion transport channel and reduce the interfacial resistance. The graphite, lithium carbonate layer and lithium azide layer work together to enable the anode material to have high rate performance and excellent cycle stability, which is beneficial to improving the electrochemical performance and overall safety of the anode material.

[0050] Specifically, the lithium carbonate layer constructs a chemically stable and highly adhesive protective barrier on the graphite surface. This not only effectively blocks the erosion of harmful substances in the electrolyte and reduces side reactions, but also enhances the bonding strength between graphite particles through chemical bonding, preventing structural breakage and collapse during cycling. This fundamentally improves the cycle durability of the anode material, ensuring that the battery maintains a high capacity retention rate after multiple charge-discharge cycles. The lithium azide layer enables precise control of the ion transport path. The introduction of the lithium azide layer significantly reduces the mass transfer resistance of lithium ions at the interface. Its highly uniform and dense structure promotes rapid diffusion of lithium ions and reduces energy loss during charge transfer. Furthermore, the lithium azide layer effectively regulates the formation of the SEI film, preventing the formation of large particles, thus maintaining good electrochemical response during high-rate charge-discharge and improving the battery's instantaneous power output. The combined effect of the lithium carbonate and lithium azide layers enhances battery safety at both the intrinsic material level and the interfacial level. The lithium carbonate layer exhibits good thermal stability, maintaining structural integrity even at high temperatures and reducing the risk of thermal runaway. Simultaneously, the lithium azide layer can suppress side reactions between the electrolyte and electrodes, reducing gas generation and the possibility of internal short circuits, thereby enhancing the overall safety performance of the battery.

[0051] According to embodiments of this application, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:(0.01-0.1):(0.01-0.08). When the contents of the three components are within the above range, the anode material can have high rate performance and excellent cycle stability.

[0052] For example, the mass ratio of graphite to lithium carbonate layer and lithium azide layer can be any value between 1:0.01:0.01, 1:0.015:0.045, 1:0.055:0.019, 1:0.055:0.045, 1:0.055:0.075, 1:0.075:0.045, 1:0.1:0.08 or 1:(0.01-0.1):(0.01-0.08).

[0053] This application also provides a method for preparing the negative electrode material as described above, including:

[0054] A lithium carbonate layer is formed on the surface of graphite to obtain a graphite-lithium carbonate material;

[0055] A lithium azide layer is formed on the surface of the graphite-lithium carbonate material to obtain the negative electrode material.

[0056] According to embodiments of this application, the preparation of the graphite-lithium carbonate material includes:

[0057] Preparation of lithium hydroxide-coated graphite materials;

[0058] The lithium hydroxide-coated graphite material is heat-treated to convert the lithium hydroxide into lithium carbonate.

[0059] According to an embodiment of this application, the material for preparing lithium hydroxide-coated graphite includes: mixing graphite, a lithium source, and a solvent to obtain a lithium source-coated graphite material;

[0060] The lithium source-coated graphite material is mixed with an alkaline solution and dried to obtain a lithium hydroxide-coated graphite material.

[0061] According to embodiments of this application, the graphite includes flake graphite;

[0062] And / or, the lithium source includes at least one of lithium chloride, lithium hydride, lithium bromide, and lithium iodide, and the mass of the lithium source accounts for 2.5% to 10% of the mass of the graphite; for example, the mass of the lithium source accounts for any value between 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or 2.5% to 10% of the mass of the graphite.

[0063] And / or, during the mixing of graphite, lithium source, and solvent, the method further includes adding a surfactant, wherein the surfactant includes at least one of tetraethyl orthosilicate, polyethylene glycol, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, polyoxyethylene sorbitan fatty acid ester, and silane coupling agent; the above-mentioned surfactants can effectively reduce the surface tension of the dispersion, promote the lithium source to adhere more tightly to the graphite surface, and improve the coating effect.

[0064] In some embodiments, the surfactant accounts for 1%-3% of the mass of the graphite; for example, the surfactant may account for any value between 1%, 2%, 3% or 1%-3% of the mass of the graphite.

[0065] In some embodiments, the concentration of the surfactant is 0.1-15 mol / L; for example, the concentration of the surfactant can be 0.1 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L, 13 mol / L, 14 mol / L, 15 mol / L, or any value between 0.1-15 mol / L.

[0066] And / or, the alkaline solution includes a sodium hydroxide solution; by adding the alkaline solution, the Li content of the lithium source can be reduced. + With alkaline solution OH - The in-situ reaction generates LiOH, which immediately coats the surface of the graphite particles. This design strengthens the graphite particle structure and significantly improves the migration rate of lithium ions, which is beneficial for achieving high-speed charging and discharging of the battery.

[0067] And / or, the concentration of the alkaline solution is 0.5-1 mol / L; for example, the concentration of the alkaline solution can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L or any value between 0.5-1 mol / L.

[0068] And / or, the amount of alkaline solution added is controlled such that the pH value of the system after mixing the lithium source-coated graphite material with the alkaline solution is in the range of 10 to 12.

[0069] For example, the pH value of the system after mixing lithium-based graphite-coated materials with an alkaline solution can be 10, 11, 12, or any value between 10 and 12.

[0070] According to some embodiments of this application, after mixing the lithium source-coated graphite material with an alkaline solution, the method further includes: washing the obtained product with water until it becomes neutral, and then drying it.

[0071] According to some embodiments of this application, drying is carried out under vacuum conditions, the drying temperature is 50-80°C, and the drying time is 10-14 hours.

[0072] For example, the drying temperature can be any value between 50°C, 60°C, 70°C, 80°C or 50-80°C, and the drying time can be any value between 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 10-14 hours.

[0073] According to an embodiment of this application, heat treatment of the lithium hydroxide-coated graphite material includes: heating the lithium hydroxide-coated graphite material to a first temperature at a first heating rate, then heating it to a second temperature at a second heating rate, and holding it at the second temperature; wherein the first heating rate is greater than the second heating rate, the heating to the first temperature and the heating to the second temperature are carried out under inert gas protection, and the holding process at the second temperature is carried out in a carbon dioxide-containing atmosphere. This application employs a gradient heating strategy, which can reduce thermal stress, prevent material structure damage, and promote a more uniform conversion process. The initial stage of the gradient heating in this application is carried out in a nitrogen atmosphere, which can avoid premature formation of lithium carbonate, and the later stage of the gradient heating is carried out in a carbon dioxide-containing atmosphere, which helps to improve the purity and crystallinity of lithium carbonate.

[0074] This application does not impose a particular limitation on the carbon dioxide content in the aforementioned carbon dioxide-containing atmosphere, as long as it can react to produce lithium carbonate. In some embodiments, the carbon dioxide-containing atmosphere includes an air atmosphere, which can save production costs, reduce operational difficulty, and facilitate the widespread application of the method of this application.

[0075] According to some embodiments of this application, the generated product is treated with a rapid cooling method after heat treatment, including air cooling or water cooling. This design helps to fix the transformed structure, reduce grain growth, improve the cycling stability of the material, and convert lithium hydroxide into a stable lithium carbonate layer that coats the graphite surface.

[0076] According to an embodiment of this application, the first heating rate is 10-20℃ / min, and the second heating rate is 1-5℃ / min; for example, the first heating rate can be any value between 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, 20℃ / min or 10-20℃ / min, and the second heating rate can be any value between 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or 1-5℃ / min.

[0077] And / or, the first temperature is 80-250℃, the second temperature is 350-650℃, and the heat preservation time is 1-2 hours.

[0078] For example, the first temperature can be any value between 80℃, 100℃, 120℃, 150℃, 170℃, 200℃, 220℃, 250℃, or 80-250℃; the second temperature can be any value between 350℃, 370℃, 400℃, 420℃, 450℃, 470℃, 500℃, 520℃, 550℃, 570℃, 600℃, 620℃, 650℃, or 350-650℃; and the holding time can be any value between 1 hour, 1.5 hours, 2 hours, or 1-2 hours.

[0079] According to an embodiment of this application, forming a lithium azide layer on the surface of the graphite-lithium carbonate material includes: depositing an organic lithium compound and an azide source on the surface of the graphite-lithium carbonate material using atomic layer deposition.

[0080] According to embodiments of this application, the deposition temperature is 130-160°C. Within this temperature range, high-quality growth of the lithium azide layer can be ensured, which is beneficial for improving the rate performance and cycle stability of the battery. If the deposition temperature is too high, it may lead to uneven growth of the lithium azide layer, or even damage to the microstructure of the material, increasing interface defects and ultimately resulting in poor electrochemical performance of the battery. If the deposition temperature is too low, the reaction rate between the organic lithium compound and the azide source will be significantly slowed down, which may lead to incomplete reaction or the reactants adsorbed on the material surface but failing to be effectively converted into lithium azide. This will not only affect the formation rate of the lithium azide layer, but may also result in the lithium azide layer being insufficiently dense and uniform, thereby reducing its effectiveness as an ion transport channel optimizer.

[0081] For example, the deposition temperature can be any value between 130°C, 140°C, 150°C, 160°C, or 130°C-160°C.

[0082] And / or, the deposition pressure is 0.08-0.12 Pa; within the pressure range of 0.08-0.12 Pa, uniform and dense growth of the lithium azide layer can be ensured, ion transport can be optimized, and electrochemical performance can be enhanced. Too low a deposition pressure will result in a slow deposition rate and incomplete film formation; too high a deposition pressure will easily cause excessive adsorption of precursors, affecting film quality and structural stability.

[0083] For example, the deposition pressure can be any value between 0.08 Pa, 0.09 Pa, 0.1 Pa, 0.11 Pa, 0.12 Pa, or 0.08-0.12 Pa.

[0084] And / or, the organolithium compound includes at least one of butyllithium, phenyllithium, and lithium amino compounds, wherein the lithium amino compound includes hexamethyldisilamine lithium (LiN(Si(CH3)3)2), which has the advantages of good stability and ease of handling.

[0085] And / or, the azide source includes at least one of sodium azide, potassium azide, and ammonia;

[0086] And / or, the pulse time ratio of the organolithium compound to the azide source is 1:20 to 1:50; at a pulse time ratio of 1:20 to 1:50, uniform deposition of the lithium azide layer can be ensured, and the lithium-ion conduction pathway can be optimized. A pulse time ratio that is too small will lead to incomplete reaction and poor film quality; a pulse time ratio that is too large will cause precursor waste and uneven film thickness, thus reducing electrochemical performance.

[0087] For example, the pulse time ratio of the organolithium compound to the azide source can be 1:20, 1:25, 1:30, 1:35, 1:40, 1:50, or any value between 1:20 and 1:50.

[0088] And / or, the atomic layer deposition method involves 100-1000 cycles; under 100-1000 cycles, atomic layer deposition can form a uniform and dense lithium azide layer, effectively improving electrochemical performance. Too few cycles will result in a thin and discontinuous film; too many cycles will increase process costs and may cause stress problems, affecting material properties.

[0089] For example, the number of cycles in atomic layer deposition (ALD) can be 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or any value between 100 and 1000. Atomic layer deposition (ALD) technology has the advantages of high precision and high material utilization, significantly reducing waste generation and lowering long-term production costs.

[0090] And / or, after the deposition is completed, the method further includes: annealing the deposited material to obtain a negative electrode material; wherein the annealing temperature is 100-200℃ and the annealing time is 1-2 hours. Annealing can enhance the crystallinity and stability of the lithium azide layer, which is beneficial for obtaining a negative electrode material with high rate capability and long cycle life.

[0091] For example, the annealing temperature can be any value between 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or 100-200℃, and the annealing time can be any value between 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h or 1-2h.

[0092] The method described in this application can form a highly uniform lithium azide layer, which is beneficial for optimizing lithium-ion transport channels, reducing interfacial resistance, enhancing the electrochemical stability and overall safety of the material, and improving the performance of the anode material.

[0093] According to some embodiments of this application, the thickness of the lithium azide layer is 5-10 nm. For example, it can be 5 nm, 10 nm, or any value between 5-10 nm.

[0094] This application also provides a battery comprising the negative electrode material described above or the negative electrode material prepared by the preparation method described above. The aforementioned battery includes electrolyte batteries, semi-solid-state batteries, and all-solid-state batteries; that is, the negative electrode material of this application can be used in electrolyte batteries, semi-solid-state batteries, and all-solid-state batteries.

[0095] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0096] Example 1

[0097] Example 1 provides a negative electrode material, the preparation method of which includes:

[0098] Step 1: In-situ generation of lithium hydroxide-coated graphite

[0099] Raw material preparation: 10g of flake graphite was selected as the main material, and lithium chloride was selected as the lithium source, accounting for 5% of the graphite mass. 0.1g of polyethylene glycol and 0.1g of tetraethyl orthosilicate were also prepared as surfactants. Additionally, 50mL of deionized water and a sodium hydroxide solution with a sodium hydroxide concentration of 0.75mol / L were prepared.

[0100] Preparation process: First, graphite powder was uniformly dispersed in deionized water containing lithium source and ultrasonically dispersed for 30 minutes. During this period, tetraethyl orthosilicate and polyethylene glycol were added to improve the dispersion effect and promote LiOH coating. Then, sodium hydroxide solution was slowly added dropwise to adjust the pH of the system to 11, and stirring was continued for 2 hours to ensure that LiOH was generated in situ and coated on the surface of graphite particles.

[0101] Post-processing: After centrifugation, the material was washed with deionized water until neutral, and then vacuum dried at 60°C for 12 hours.

[0102] Step 2: Heat treatment to form a lithium carbonate layer

[0103] The dried coating material was placed in a tube furnace and first heated to 200°C at a rapid heating rate of 15°C / min, followed by a slow heating rate of 3°C / min to 450°C, and held at 450°C for 2 hours. The rapid heating to 200°C and the slow heating to 450°C were carried out in a nitrogen atmosphere, while the 2-hour holding at 450°C was carried out in an air atmosphere. Finally, air cooling was used for rapid cooling.

[0104] Step 3: ALD coating of lithium azidopside

[0105] Using ALD technology, hexamethyldisilazine lithium (LiN(Si(CH3)3)2) was selected as the organolithium compound precursor, and NH3 was used as the azide source. The deposition temperature was set at 140℃, the pressure in the reaction chamber was maintained at 0.1 Pa, the precursor pulse-time ratio was 1:30, and 500 deposition cycles were performed. The deposition amount was 3% of the graphite mass to obtain a uniform lithium azide coating with a thickness of 5 nm.

[0106] To enhance the structural stability of the lithium azide layer, the deposited material was annealed at 150°C for 1.5 hours to obtain the anode material.

[0107] SEM image of the negative electrode material prepared in Example 1 is shown below. Figure 1 As shown.

[0108] In the negative electrode material prepared in Example 1, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.055:0.045.

[0109] Example 2

[0110] The negative electrode material was prepared according to the method of Example 1. The difference from Example 1 is that the mass of lithium chloride in Example 2 accounts for 10% of the mass of graphite, and the vacuum drying temperature in step 1 of Example 2 is increased to 70°C, while other conditions remain unchanged.

[0111] In the negative electrode material prepared in Example 2, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.075:0.045.

[0112] Example 3

[0113] The negative electrode material was prepared according to the method of Example 1. The difference from Example 1 is that in Example 3, the temperature was reduced to 130°C and the deposition cycle was reduced to 100 cycles when lithium azide was deposited in ALD.

[0114] In the negative electrode material prepared in Example 3, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.055:0.019.

[0115] Example 4

[0116] The negative electrode material was prepared according to the method of Example 1. The difference between Example 4 and Example 1 is that the conditions for air heat treatment in step 2 are different from those in Example 1. In Example 1, the air heat treatment was carried out at a temperature of 450°C for 2 hours, while in Example 4, the air heat treatment was carried out at a temperature of 450°C for 1 hour.

[0117] In the negative electrode material prepared in Example 4, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.055:0.045.

[0118] Example 5

[0119] The negative electrode material was prepared according to the method of Example 1, except that the lithium azide precursor was modified to butyllithium and sodium azide.

[0120] In the negative electrode material prepared in Example 5, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.055:0.045.

[0121] Example 6

[0122] The negative electrode material was prepared according to the method of Example 1, except that the thickness of the lithium azide layer deposited by ALD was changed to 10 nm.

[0123] In the negative electrode material prepared in Example 6, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.055:0.075.

[0124] Example 7

[0125] The negative electrode material was prepared according to the method of Example 1, except that in Example 7, the mass of lithium chloride accounted for 2.5% of the mass of graphite, and the processing time and temperature remained unchanged.

[0126] In the negative electrode material prepared in Example 7, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.015:0.045.

[0127] Example 8

[0128] The negative electrode material was prepared according to the method of Example 1. The difference from Example 1 is that an additional pretreatment step was added, namely, cleaning the graphite with dilute hydrochloric acid to remove impurities. Then the original process was followed to explore the effect of purity improvement on the performance of the final product.

[0129] In the negative electrode material prepared in Example 8, the mass ratio of graphite to lithium carbonate layer and lithium azide layer is 1:0.055:0.045.

[0130] Comparative Example 1

[0131] The negative electrode material was prepared according to the method of Example 1. The difference between Comparative Example 1 and Example 1 is that the ALD lithium azide layer was not deposited. Only the lithium hydroxide coating and heat treatment to lithium carbonate were completed to compare the performance of the negative electrode material without the lithium azide layer.

[0132] Comparative Example 2

[0133] The negative electrode material was prepared according to the method of Example 1. The difference from Example 1 is that: Comparative Example 2 skipped the lithium hydroxide coating step and directly deposited a lithium azide layer on the surface of natural graphite to investigate the effect of the lack of a lithium carbonate layer on the performance of the negative electrode material.

[0134] Comparative Example 3

[0135] The negative electrode material was prepared according to the method of Example 1. The difference from Example 1 is that the ALD deposition temperature of Comparative Example 3 was increased to 200°C, and the negative impact of high temperature on the quality of lithium azide layer and battery performance was observed.

[0136] The electrochemical performance of the negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-3 was tested under the same conditions, and the test results are shown in Table 1.

[0137] Table 1. Electrochemical test results of Examples 1-8 and Comparative Examples 1-3

[0138]

[0139]

[0140] As can be seen from Table 1, Examples 1-8 have better specific capacity and long-cycle performance at different rates than Comparative Examples 1-3.

[0141] In Example 8, the graphite was purified, and the electrochemical performance of Example 8 was worse than that of Example 1. Although purification can improve the purity of graphite, it may also introduce adverse factors. Specifically, this may be due to the dilute hydrochloric acid treatment during the purification process altering the surface structure of the graphite and affecting the kinetics of lithium ion insertion / extraction; changes in the surface properties of the purified graphite affecting the quality and uniformity of the coating layers (lithium carbonate and lithium azide); and a thicker or higher resistivity of the formed SEI film, increasing the interfacial impedance.

[0142] The negative electrode materials of Examples 1-8 contain a lithium azide layer. Comparative Example 1 omits the ALD lithium azide layer deposition step; the negative electrode material of Comparative Example 1 only includes graphite and a lithium carbonate layer on the graphite surface. The negative electrode material of Comparative Example 1 lacks a lithium azide layer, as shown in Table 1. Figure 2 It can be seen that the material of Comparative Example 1 is inferior to that of Examples 1-8 in terms of ion conductivity, interface stability and cycle stability. Especially under high-rate charge and discharge conditions, the capacity decay of Comparative Example 1 is faster and the cycle life is shorter.

[0143] The anode materials in Examples 1-8 have a lithium carbonate layer within the graphite and lithium azide layers, which significantly improves the basic structural strength and lithium-ion diffusion efficiency. They exhibit excellent electrochemical performance in high-rate charge-discharge tests and have a high cycle life. Comparative Example 2, on the other hand, directly deposits lithium azide on the graphite surface. Since the anode material in Comparative Example 2 does not include a lithium carbonate layer, this results in insufficient structural stability, high interfacial impedance, and hinders rapid lithium-ion transport, thereby reducing rate performance and cycle stability.

[0144] Examples 1-8 used a relatively mild ALD deposition temperature to prepare the anode material, which ensured high-quality growth of the lithium azide layer and was beneficial to improving the rate performance and cycle stability of the battery. Comparative Example 3 increased the ALD deposition temperature to 200℃. The anode material prepared in Comparative Example 3 had poor electrochemical performance. This may be because the higher ALD deposition temperature leads to uneven growth of the lithium azide layer and may even cause microstructural damage to the material, increasing interface defects and thus resulting in poor electrochemical performance of the battery.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 therein. Such 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 this application.

[0146] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for producing a negative electrode material, characterized by, The negative electrode material comprises: graphite, a lithium carbonate layer coated on the surface of the graphite, and a lithium azide layer coated on the surface of the lithium carbonate layer; the mass ratio of the graphite to the lithium carbonate layer to the lithium azide layer is 1:(0.01-0.1):(0.01-0.08); The preparation method of the negative electrode material comprises: forming a lithium carbonate layer on the surface of graphite to obtain a graphite-lithium carbonate material; and forming a lithium azide layer on the surface of the graphite-lithium carbonate material to obtain the negative electrode material; The preparation of the graphite-lithium carbonate material comprises: preparing a lithium hydroxide-coated graphite material; and performing heat treatment on the lithium hydroxide-coated graphite material to convert the lithium hydroxide into lithium carbonate; The heat treatment on the lithium hydroxide-coated graphite material comprises: heating the lithium hydroxide-coated graphite material to a first temperature at a first heating rate, then heating to a second temperature at a second heating rate, and performing heat preservation at the second temperature; wherein the first heating rate is greater than the second heating rate, the heating to the first temperature and the heating to the second temperature are performed under the protection of inert gas, and the heat preservation at the second temperature is performed in an atmosphere containing carbon dioxide; The formation of the lithium azide layer on the surface of the graphite-lithium carbonate material comprises: using an atomic layer deposition method to deposit an organic lithium compound and an azide source on the surface of the graphite-lithium carbonate material, the deposition temperature is 130-160℃, the deposition pressure is 0.08-0.12Pa, and the cycle number of the atomic layer deposition method is 100-1000 times.

2. The method of producing a negative electrode material according to claim 1, characterized by, The preparation of the lithium hydroxide-coated graphite material comprises: mixing graphite, a lithium source and a solvent to obtain a lithium source-coated graphite material; Mixing the lithium source-coated graphite material with an alkaline solution and drying to obtain the lithium hydroxide-coated graphite material.

3. The method of producing a negative electrode material according to claim 2, characterized by, The graphite comprises flaky graphite; And / or, the lithium source comprises at least one of lithium chloride, lithium hydride, lithium bromide and lithium iodide, and the mass of the lithium source accounts for 2.5%-10% of the mass of the graphite; And / or, during the mixing of the graphite, the lithium source and the solvent, the method further comprises adding a surfactant, and the surfactant comprises at least one of tetraethyl orthosilicate, polyethylene glycol, sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide, polyoxyethylene sorbitan fatty acid ester and silane coupling agent; And / or, the alkaline solution comprises a sodium hydroxide solution; And / or, the concentration of the alkaline solution is 0.5-1 mol / L; And / or, the amount of the alkaline solution added is controlled so that the pH value of the system after mixing the lithium source-coated graphite material with the alkaline solution is in the range of 10-12.

4. The method of claim 1, wherein the method is characterized by: The first heating rate is 10-20℃ / min, and the second heating rate is 1-5℃ / min; The first temperature is 80-250℃, the second temperature is 350-650℃, and the heat preservation time is 1-2 hours.

5. The method of claim 1, wherein the method is characterized by: The organic lithium compound comprises at least one of butyl lithium, phenyl lithium and lithium amide compound, and the lithium amide compound comprises hexamethyldisilylamide lithium. And / or, the azide source comprises at least one of sodium azide, potassium azide, ammonia gas; And / or, the pulse time ratio of the organic lithium compound to the azide source is 1:20 to 1:

50. And / or, after the deposition is completed, the method further comprises: performing annealing treatment on the deposited material to obtain the negative electrode material; wherein the annealing temperature is 100-200 DEG C, and the annealing time is 1-2h.

6. A battery, characterized by The negative electrode material prepared by the preparation method in any one of claims 1-5. The negative electrode material prepared by the preparation method in any one of claims 1-5.

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