Composite negative electrode material, preparation method therefor, and lithium-ion battery

Abstract

The present application provides a composite negative electrode material, a preparation method therefor, and a lithium-ion battery. The preparation method comprises: step S1: preparing a first slurry from a carbon source and graphite particles, and subjecting the first slurry to first drying and first calcination to obtain a first precursor; step S2: preparing a second slurry from a titanium source and the first precursor, and subjecting the second slurry to a first reaction and second drying to obtain a second precursor; and step S3: preparing a third slurry from a niobium source, a lithium source, and the second precursor, and subjecting the third slurry to a second reaction and second calcination to obtain a composite negative electrode material. In the present application, the structure of the prepared composite negative electrode material is designed by means of specific process conditions, so that the composite negative electrode material has a graphite core, and a carbon layer and an inorganic electrically conductive layer are sequentially formed on the surface of the graphite core. The obtained structure can significantly improve the cycle stability and electrochemical performance of the composite negative electrode material, thereby prolonging the service life of a battery.

Description

Composite anode materials, their preparation methods and lithium-ion batteries

[0001] This application claims priority to Chinese Patent Application No. 2024116378095, filed on November 15, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion batteries, and more specifically, to a composite anode material, its preparation method, and a lithium-ion battery. Background Technology

[0003] Currently, the stable voltage window of conventional electrolytes is 1–5V. However, in actual operation, the negative electrode voltage of a battery cell is generally between 0–1V, and the electrolyte is unstable at this potential. Simultaneously, the volume expansion of the negative electrode continuously forms an electrolyte interphase (SEI), leading to a decline in battery performance. Numerous studies have shown that current cell failures are primarily caused by the continuous formation of the SEI film and its consumption of active lithium. Furthermore, with increasing user demands for charging speeds, current user requirements are generally between 3C and 6C. However, the main limitation for fast charging lies on the graphite negative electrode side, where conventional graphite can only achieve a charging rate of 2C. Under these conditions, using a higher charging rate will result in severe lithium plating, posing significant safety hazards. Therefore, it is necessary to modify the negative electrode material to improve its rate performance.

[0004] To improve the stability of the SEI film in graphite anodes, Chinese patents CN114655951A, CN105140501A, CN109888229A, and CN115842122A all involve the preparation of composite anode materials of lithium titanate coated with graphite. However, due to the significant difference between the lithium intercalation potential of lithium titanate and that of graphite, the graphite anode faces a high risk of lithium plating under high-rate charge-discharge conditions due to its large charge transfer impedance. Furthermore, the aforementioned patents CN114655951A, CN105140501A, and CN115842122A all utilize a sol-gel method involving the hydrolysis and condensation of metal alkoxides, which is costly. CN109888229A employs atomic layer deposition technology, which also suffers from high cost, low yield, and inability to achieve mass production.

[0005] Currently, the main approach to modifying the rate performance of graphite is through a combination of secondary granulation and carbon coating. However, the graphite prepared by this method has a large specific surface area, and the surface has poor crystallinity and density of its carbon layer. Under high temperature conditions, the SEI film becomes unstable and decomposes continuously, ultimately accelerating the cycle failure of the battery cell.

[0006] In summary, suppressing the formation of the SEI film on the negative electrode side and improving the rate performance of the negative electrode material can significantly enhance the long-term cycle performance, rate performance, and low-temperature performance of the battery cell. However, existing single graphite composite negative electrode materials coated with lithium titanate or carbon layers are insufficient to meet the requirements of battery cells for long cycle life, high rate performance, and high-temperature stability.

[0007] Therefore, how to provide a composite anode material with better electrochemical performance, which can suppress the rise of anode potential and reduce the formation of SEI film, thereby enabling the lithium-ion battery in which it is located to exhibit better long cycle performance, rate performance and high and low temperature storage performance, is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0008] The main objective of this application is to provide a composite anode material, its preparation method, and a lithium-ion battery, in order to solve the problem that existing lithium-ion battery anode materials are difficult to suppress the rise of anode potential and reduce the formation of SEI film, which leads to poor performance of the lithium-ion battery.

[0009] To achieve the above objectives, the first aspect of this application provides a method for preparing a composite anode material, comprising: step S1, preparing a first slurry by mixing a carbon source and graphite particles, wherein the first slurry is subjected to a first drying and a first calcination to obtain a first precursor; the first precursor includes graphite particles and an organic carbon layer coated on the surface of the graphite particles; step S2, preparing a second slurry by mixing a titanium source and the first precursor, wherein the second slurry is subjected to a first reaction and a second drying to obtain a second precursor; the second precursor includes the first precursor and a titanium dioxide layer coated on the surface of the first precursor; and step S3, preparing a third slurry by mixing a niobium source, a lithium source, and the second precursor, wherein the third slurry is subjected to a second reaction and a second calcination to obtain a composite anode material.

[0010] Further, in step S1, the first drying is spray drying, and the outlet temperature of the spray drying is 80℃~250℃; and / or, the temperature of the first calcination is 500℃~1000℃, and the time is 3h~9h.

[0011] Further, in step S1, the weight ratio of carbon source to graphite particles is (0.015~0.035):1, preferably (0.015~0.020):1; preferably, the carbon source is selected from one or more of polydopamine, phenolic resin, glucose, fructose, sucrose, cellulose, starch, polyvinylpyrrolidone, polyvinyl alcohol, polypyrrole, polyethylene glycol, pitch, anthracene, aniline, tannic acid and citric acid.

[0012] Further, in step S2, the temperature of the second reaction is 100℃~160℃, and the time is 2h~20h; and / or, the temperature of the second drying is 100℃~160℃.

[0013] Further, in step S2, the weight ratio of the titanium source to the first precursor is (0.001-0.2):1, preferably (0.012-0.002):1; preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium oxysulfate, titanium sulfate, tetrabutyl titanate and isopropyl titanate.

[0014] Furthermore, in step S3, the reaction temperature of the second reaction is 150℃~200℃, and the time is 5h~15h; the reaction temperature of the second calcination is 900℃~1200℃, and the time is 1h~6h.

[0015] Further, in step S3, the weight ratio of lithium source to second precursor is (0.001 to 0.050):1, and the weight ratio of lithium source to niobium source is 1:(2 to 5); preferably, the niobium source is selected from one or more of niobium monoxide, niobium dioxide and niobium pentoxide; and / or, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate.

[0016] The second aspect of this application provides a composite anode material, which is prepared by the above-described method for preparing composite anode materials. The composite anode material includes a graphite core and a composite layer coated on the surface of the graphite core. The composite layer includes an organic carbon layer and an inorganic conductive layer. The organic carbon layer and the inorganic conductive layer are arranged sequentially in a direction away from the graphite core. The inorganic conductive layer includes one or more of lithium titanate, lithium niobate, and niobium titanium oxide.

[0017] Furthermore, based on the total weight of the composite negative electrode material (100%), the content of the organic carbon layer is 0.01% to 10.0%, preferably 0.2% to 0.5%; and the content of the inorganic conductive layer is 0.01% to 10.0%, preferably 1.0% to 1.5%.

[0018] A third aspect of this application provides a lithium-ion battery, including a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the negative electrode includes the aforementioned composite negative electrode material.

[0019] By applying the technical solution of this application and through specific process conditions, the structure of the composite anode material is designed to have a graphite core, and a carbon layer and an inorganic conductive layer are formed on its surface in sequence. The resulting structure can significantly improve the cycle stability and electrochemical performance of the composite anode material, thereby effectively alleviating the problem of anode potential rise and SEI film formation in the lithium-ion battery during charging and discharging, and extending the battery's service life. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 is a scanning electron microscope image of the composite negative electrode material obtained in Example 1;

[0022] Figure 2 is a scanning electron microscope image of the negative electrode material obtained in Comparative Example 1;

[0023] Figure 3 shows a scanning electron microscope image of the negative electrode material obtained in Comparative Example 2. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0025] As described in the background art, the stable voltage range of the electrolyte in existing lithium-ion batteries is 1-5V, while the negative electrode material is generally between 0-1V, leading to the continuous and excessive formation of the SEI film, which in turn causes poor performance of the lithium-ion battery. To solve the above technical problem, the first aspect of this application provides a method for preparing a composite negative electrode material, comprising: step S1, preparing a first slurry by mixing a carbon source and graphite particles, subjecting the first slurry to a first drying and a first calcination to obtain a first precursor; the first precursor includes graphite particles and an organic carbon layer coated on the surface of the graphite particles; step S2, preparing a second slurry by mixing a titanium source and the first precursor, subjecting the second slurry to a first reaction and a second drying to obtain a second precursor; the second precursor includes the first precursor and a titanium dioxide layer coated on the surface of the first precursor; step S3, preparing a third slurry by mixing a niobium source, a lithium source, and the second precursor, subjecting the third slurry to a second reaction and a second calcination to obtain the composite negative electrode material.

[0026] Currently, graphite-based anode materials are primarily used in lithium-ion batteries. These materials form a solid electrolyte interphase (SEI) film on their surface during battery formation, hindering continuous side reactions between active lithium and the electrolyte. However, during storage at low state of charge (SOC), including 0% SOC, graphite is at a high potential. The instability of the graphite interface leads to continuous reduction reactions between the active lithium in the graphite and the electrolyte, resulting in a decrease in active lithium and a rapid rise in the anode potential. When the anode potential reaches 1.8V, the SEI film decomposes, generating a large amount of gas, causing battery bulging and performance degradation. The main solution to this problem is to coat the graphite material with a carbon layer.

[0027] However, as mentioned in the background section, carbon coating alone cannot effectively suppress the continuous formation of the SEI film on the graphite anode surface. Therefore, this application further coats the carbon-coated graphite anode material with a dense inorganic fast-ion conductor layer containing titanium, niobium, and lithium. This structural design significantly reduces SEI film formation, thereby effectively suppressing the decomposition and gas generation of the SEI film under unstable conditions and the continuous consumption of electrolyte, thus reducing SEI film impedance. Furthermore, it significantly reduces the charge transfer impedance on the graphite anode surface, improves the fast-charging performance of the graphite anode material, significantly reduces lithium plating, and enhances the cycle performance of the corresponding lithium-ion battery.

[0028] Specifically, the preparation method provided in this application first involves mixing, drying, and calcining to form a dense and uniform carbon coating layer on the surface of graphite particles (its morphological changes are shown in Figures 2 and 3). Pre-forming a carbon coating layer on the graphite surface helps to cover the intrinsic active sites on the graphite surface, reduce the occurrence of irreversible side reactions, decrease the specific surface area of ​​the graphite core particles, inhibit the formation of the SEI film, isolate the graphite particles from the electrolyte, prevent solvent co-intercalation leading to capacity reduction, and also restrict and buffer the volume expansion of graphite, increasing cycle stability. Then, a titanium dioxide coating layer is formed on the surface of the first precursor with the carbon coating layer through a reaction, thus obtaining the second precursor. Finally, the obtained second precursor is mixed with a niobium source and a lithium source and reacted, allowing the titanium dioxide coating layer to react with niobium and lithium to obtain lithium titanate, lithium niobate, and niobium titanium oxides (such as TiNb2O7, NbTiO3, Nb2Ti5O). 15 At least one of the following (etc.) is used to form a dense and uniform inorganic fast ion conductor layer on the outermost surface. The possible reaction equations during the above reaction process are shown below. The resulting bilayer structure can significantly optimize the ion transport path of the composite anode material, improve its electrochemical performance and cycle stability, effectively suppress SEI film formation and anode potential rise during charge and discharge, and ultimately enable the lithium-ion battery to exhibit superior performance. 2Li2CO3+5TiO2→Li4Ti5O 12 +2CO2 (1) Li2O+Nb2O5→2LiNbO3, Li2O+Nb2O3+O2→2LiNbO3 (2) TiO2+Nb2O5→TiNb2O7 (3)

[0029] In the bilayer coating structure formed by the above preparation method, the outermost layer includes at least one of lithium titanate, lithium niobate, and niobium titanium oxide. Lithium niobate and lithium titanate possess good ionic conductivity and high chemical stability, thus improving the stability of the anode material in which they are located. Niobium titanium oxide possesses a unique crystal structure and electronic properties. When the lithium-ion battery is charged, lithium ions are extracted from the positive electrode and migrate to the negative electrode through the electrolyte. When niobium titanium oxide is present in the anode material, the insertion of lithium ions can form Li... x NbTiO3. The unique layered or tunnel-like structure of niobium titanium oxide allows lithium ions to stably intercalate and deintercalate within the layers or tunnels of the niobium titanium oxide, without significantly altering the numerous lithium ion intercalation and deintercalation sites provided by the material's crystal structure. This results in high-capacity lithium-ion storage and a stable discharge process. In particular, when these three components exist in pairs or together, lithium titanate, lithium niobate, and niobium titanium oxide exhibit a synergistic effect, significantly enhancing their structural stability and high conductivity. Simultaneously, they form a good synergy with the intermediate carbon layer, comprehensively improving the electrochemical performance of the resulting composite anode material, especially its long-cycle stability.

[0030] In practical applications, the graphite particles are natural graphite and / or artificial graphite. Furthermore, the solvents used to prepare the above slurry are water and / or organic solvents, which may be selected from one or more of methanol, ethanol, isopropanol, polyethylene glycol, ethylene glycol, glycerol, propylene glycol, benzyl alcohol, phenethyl alcohol, dimethylformamide, acetonitrile, dimethyl sulfoxide, oleic acid, and oleylamine.

[0031] In several typical embodiments, the solvents used in preparing the above-mentioned slurries are all water or ethanol, and do not include any other organic solvents. This avoids environmental pollution caused by organic solvents, resulting in greater environmental friendliness. Furthermore, surfactants can be added during the preparation of the above-mentioned slurries to improve the dispersion uniformity of the resulting slurry system. The surfactants used are selected from one or more of hexadecyltrimethylammonium bromide, hydroxyethyl cellulose, sodium hexadecylbenzene sulfonate, polyvinylpyrrolidone, sodium dodecyl sulfate, polyvinyl alcohol, and sodium oleate.

[0032] Furthermore, in step S1, the first drying is spray drying, and the outlet temperature of the spray dryer is 80℃~250℃ to effectively remove moisture from the first slurry, while improving the structural integrity and uniformity of the formed organic carbon layer, creating favorable prerequisites for the subsequent calcination step. Preferably, the first calcination temperature is 500℃~1000℃, and the time is 3h~9h, thereby allowing the organic carbon layer to be more fully carbonized, forming a more stable carbon-coated framework structure, while inhibiting structural damage to graphite particles and improving the high-capacity characteristics of the resulting anode material.

[0033] In several typical embodiments, the weight ratio of carbon source to graphite particles in step S1 is (0.015–0.035):1, preferably (0.015–0.020):1. This control and optimization of the carbon source to graphite particle ratio can adjust the thickness and quality of the organic carbon layer, thereby optimizing the electrochemical and structural properties of the composite anode material and enabling it to exhibit superior cycle stability. Preferably, the carbon source is selected from one or more of polydopamine, phenolic resin, glucose, fructose, sucrose, cellulose, starch, polyvinylpyrrolidone, polyvinyl alcohol, polypyrrole, polyethylene glycol, pitch, anthracene, aniline, tannic acid, and citric acid.

[0034] In step S2, which forms the titanium dioxide layer, the preferred temperature for the second reaction is 100℃–160℃, and the preferred time is 2h–20h. This promotes the crystallization of the titanium source and the formation of a more uniform and stable titanium dioxide layer. This, in turn, leads to the formation of a higher-performance inorganic conductive layer in subsequent preparation processes, further enhancing the lithium-ion storage performance and structural stability of the resulting composite anode material. The preferred temperature for the second drying is also 100℃–160℃. This ensures that while maintaining the structural integrity and uniformity of the titanium dioxide layer, it effectively removes moisture from its structure, reduces impurity formation, and optimizes the electrochemical performance and stability of the resulting anode material.

[0035] In several typical embodiments, the weight ratio of the titanium source to the first precursor in step S2 is (0.001–0.2):1, preferably (0.012–0.002). This weight ratio enables the formation of a titanium dioxide layer with a more suitable thickness and higher uniformity, optimizes the reaction kinetics of the subsequent titanium dioxide with the niobium and lithium sources, forms a denser, more uniform, and structurally more stable outermost inorganic conductive coating layer, and ultimately optimizes the storage resistance and long-cycle stability of the resulting composite anode material. Simultaneously, this ratio also allows the titanium dioxide layer formed by the titanium source to tightly bond with the organic carbon layer during calcination, further improving the structural stability of the composite anode material. More preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium oxysulfate, titanium sulfate, tetrabutyl titanate, and isopropyl titanate.

[0036] In particular, through extensive experimentation, the inventors have preferred to further add urea in step S2, and more preferably, the weight ratio of urea to titanium source is 1:(1.2-1.5). Because urea slowly releases OH- at a certain temperature, it can uniformly precipitate with titanium sulfate solution to obtain hydrated titanium dioxide, thereby controlling the hydrolysis rate and thus controlling the thickness and density of the TiO2 layer coating.

[0037] Furthermore, the preferred reaction temperature for the second reaction in step S3 is 150℃~200℃, and the reaction time is 5h~15h; the preferred reaction temperature for the second calcination is 900℃~1200℃, and the reaction time is 1h~6h. This is to promote the full reaction between the niobium source and the lithium source and the titanium dioxide layer on the surface of the second precursor, forming a more uniform, more complete, and structurally more stable inorganic conductive layer, thereby further optimizing the electrochemical performance and cycle stability of the composite anode material.

[0038] To better coordinate the lithium titanate, lithium niobate, and niobium titanium oxide generated after the second reaction, thereby further improving the overall performance of the resulting composite anode material, especially its cycle stability, it is preferred that in step S3, the weight ratio of the lithium source to the second precursor is (0.001–0.050):1, and the weight ratio of the lithium source to the niobium source is 1:(2–5). In several typical embodiments, the niobium source is preferably selected from one or more of niobium monoxide, niobium dioxide, and niobium pentoxide; and / or, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate. Theoretically, both the niobium source and the lithium source can be of commonly used types in the art. The types selected by the inventors through extensive experiments, especially niobium dioxide and lithium carbonate, not only have high reactivity and readily form lithium titanate, lithium niobate, and niobium titanium oxide, but also promote a tighter bond between the generated conductive inorganic compound layer and the carbon layer during the reaction, thereby significantly improving the structural stability and long cycle life of the resulting composite anode material.

[0039] The second aspect of this application provides a composite anode material prepared by the aforementioned method. The composite anode material includes a graphite core and a composite layer coated on the surface of the graphite core. The composite layer includes an organic carbon layer and an inorganic conductive layer. The organic carbon layer and the inorganic conductive layer are sequentially arranged away from the graphite core. The inorganic conductive layer includes one or more of lithium titanate, lithium niobate, and niobium titanium oxide. The composite anode material prepared by the method provided in this application has a double-layer structure, with the intermediate organic carbon layer and the outermost inorganic conductive layer working synergistically to significantly improve the cycle stability and electrochemical performance of the anode material.

[0040] In several preferred embodiments, based on the total weight of the composite anode material (100%), the content of the organic carbon layer is 0.01% to 10.0%, preferably 0.2% to 0.5%; the content of the inorganic conductive layer is 0.01% to 10.0%, preferably 1.0% to 1.5%. Through extensive experiments, the inventors optimized the content of the two coating layers in the obtained anode material and found that when they are within the above-mentioned ranges, they can better coordinate and improve conductivity, promote ion transport, enhance safety, and increase cycle life during the charging and discharging process of lithium-ion batteries, thereby enabling the obtained composite anode material to exhibit superior overall electrical performance.

[0041] A third aspect of this application provides a lithium-ion battery, including a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the negative electrode includes the aforementioned composite negative electrode material. Because the composite negative electrode material provided in this application not only exhibits excellent conductivity but also, thanks to its unique double-layer structure, effectively suppresses SEI film formation and anode potential rise during lithium-ion battery use, it significantly improves the cycle stability of the lithium-ion battery during use, optimizes its constant current charge ratio, and thus better balances high charging speed and long battery life.

[0042] During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, placed between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0043] Specifically, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material, a conductive agent, a binder, etc. The positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0044] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, positive electrode binder, and any other components (e.g., dispersant, anti-cracking agent), in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then performing processes such as drying, rolling, slitting, and die-cutting to obtain the positive electrode sheet. The positive electrode active material can be any battery-grade positive electrode active material known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811)LiNi 0.9 Co 0.05 Mn 0.05 O2 (also known as NCM900505), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also abbreviated as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode binder may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0045] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, a conductive agent, a binder, etc. The negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0046] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned composite negative electrode material, conductive agent, negative electrode binder, and any other components (e.g., thickener, dispersant, anti-cracking agent) in a solvent (deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then performing processes such as drying, rolling, slitting, and die-cutting to obtain the negative electrode sheet. The negative electrode binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (PAA-Li), sodium polyacrylate (PAAS), sodium alginate (SA), and carboxymethyl chitosan (CMCS). The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0047] The electrolyte comprises an electrolyte salt, a solvent, and additives. The electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), and lithium difluorophosphate (LiPO2F2). Additives may include negative electrode film-forming additives, positive electrode film-forming additives, additives to improve the dissolution of transition metal elements in the positive electrode, additives to improve battery overcharge performance, additives to improve battery high-temperature performance, and additives to improve battery low-temperature performance.

[0048] Lithium-ion batteries also include a battery casing. The main materials for the battery casing include aluminum-plastic film, aluminum casing, and steel casing. In the actual manufacturing process, the positive electrode, negative electrode, and separator are assembled into a bare battery by winding or stacking, placed in the battery casing, and then filled with electrolyte and sealed to obtain a lithium-ion secondary battery.

[0049] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0050] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0051] Example 1

[0052] A method for preparing a composite anode material:

[0053] (1) Dissolve 15.75g of carbon source glucose in 2500mL of deionized water, then add 1000g of artificial graphite (i.e., the weight ratio of carbon source to graphite particles is 0.01575:1), stir for 2h to obtain a suspension, i.e., the first slurry; perform a first spray drying on the suspension to obtain glucose-coated graphite powder, the outlet temperature of the first spray drying is 175℃, and the inlet pump speed is 4L / min; calcine the obtained powder at a first calcination temperature of 600℃ and in an inert nitrogen atmosphere for 8h to obtain a graphite particle composite material coated with an organic carbon layer, i.e., the first precursor;

[0054] (2) Dissolve 3.36g of titanium source and titanium oxysulfate in 100mL of deionized water, then add 400g of the first precursor (the weight ratio of titanium source to first precursor is 0.0084:1), and then add 2.52g of urea (the weight ratio of urea to titanium source is 1:1.33). Stir for 2h to obtain a suspension, i.e., the second slurry. Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene lining, place the reactor in a hydrothermal box, and heat at 120℃ for 2h. Dry the heated second slurry at 150℃, wash with water, filter, and dry to obtain the first precursor coated with a titanium dioxide layer, i.e., the second precursor.

[0055] (3) Disperse 0.6g of niobium source Nb2O5 and 40g of the second precursor in 100mL of deionized water and stir for 10min. Then add 0.25g of lithium source Li2CO3 and mix evenly (i.e., the weight ratio of lithium source to second precursor is 0.00625:1 and the weight ratio of lithium source to niobium source is 1:2.4). Then, perform hydrothermal reaction at 160℃ for 10h. After centrifugation, washing, drying, and calcination at 1000℃ for 2h, a double-layer coated composite anode material is obtained.

[0056] The resulting composite anode material comprises a graphite core and, from the inside out, sequentially coated with an organic carbon layer and an inorganic conductive layer. Based on the total weight of the resulting material (100%), the content of the organic carbon layer is 0.5%, and the content of the inorganic conductive layer is 1.5%.

[0057] The scanning electron microscope image of the obtained composite anode material is shown in Figure 1.

[0058] Example 2

[0059] A method for preparing a composite anode material:

[0060] The only difference between this embodiment and Embodiment 1 is that the amount of glucose added in step (1) is changed to 18.9g, and the weight ratio of carbon source to graphite particles is changed to 0.01890:1.

[0061] Example 3

[0062] A method for preparing a composite anode material:

[0063] The only difference between this embodiment and embodiment 1 is that the amount of glucose added in step (1) is changed to 22.05g, and the weight ratio of carbon source to graphite particles is changed to 0.02205:1.

[0064] Example 4

[0065] A method for preparing a composite anode material:

[0066] The only difference between this embodiment and Embodiment 1 is that the amount of glucose added in step (1) is changed to 25.2g, and the weight ratio of carbon source to graphite particles is changed to 0.02520:1.

[0067] Example 5

[0068] A method for preparing a composite anode material:

[0069] The only difference between this embodiment and embodiment 1 is that the amount of glucose added in step (1) is changed to 28.35g, and the weight ratio of carbon source to graphite particles is changed to 0.02835:1.

[0070] Example 6

[0071] A method for preparing a composite anode material:

[0072] The only difference between this embodiment and embodiment 1 is that the amount of glucose added in step (1) is changed to 31.5g, and the weight ratio of carbon source to graphite particles is changed to 0.03150:1.

[0073] Example 7

[0074] A method for preparing a composite anode material:

[0075] The only difference between this embodiment and embodiment 1 is that the amount of titanium oxysulfate added in step (2) is changed to 4.032g, and the weight ratio of titanium source to first precursor is changed to 0.01008:1.

[0076] Example 8

[0077] A method for preparing a composite anode material:

[0078] The only difference between this embodiment and embodiment 1 is that the amount of titanium oxysulfate added in step (2) is changed to 4.704g, and the weight ratio of titanium source to first precursor is changed to 0.01176:1.

[0079] Example 9

[0080] A method for preparing a composite anode material:

[0081] The only difference between this embodiment and embodiment 1 is that the amount of titanium oxysulfate added in step (2) is changed to 5.376g, and the weight ratio of titanium source to first precursor is changed to 0.01344:1.

[0082] Example 10

[0083] A method for preparing a composite anode material:

[0084] The only difference between this embodiment and embodiment 1 is that the amount of titanium oxysulfate added in step (2) is changed to 6.048g, and the weight ratio of titanium source to first precursor is changed to 0.01512:1.

[0085] Example 11

[0086] A method for preparing a composite anode material:

[0087] The only difference between this embodiment and embodiment 1 is that the amount of titanium oxysulfate added in step (2) is changed to 6.720g, and the weight ratio of titanium source to first precursor is changed to 0.0168:1.

[0088] Example 12

[0089] A method for preparing a composite anode material:

[0090] (1) Dissolve 15.75g of carbon source glucose in 2500mL of deionized water, then add 1000g of artificial graphite (i.e., the weight ratio of carbon source to graphite particles is 0.01575:1), stir for 2h to obtain a suspension, i.e., the first slurry; perform a first spray drying on the suspension to obtain glucose-coated graphite powder, the outlet temperature of the first spray drying is 120℃, and the inlet pump speed is 4L / min; calcine the obtained powder in a nitrogen inert atmosphere at 550℃ for 9h to obtain a graphite particle composite material coated with an organic carbon layer, i.e., the first precursor.

[0091] (2) Dissolve 3.36g of titanium source and titanium oxysulfate in 100mL of deionized water, then add 400g of the first precursor (the weight ratio of titanium source to first precursor is 0.0084:1), and then add 2.52g of urea (the weight ratio of urea to titanium source is 1:1.33). Stir for 2h to obtain a suspension, i.e., the second slurry. Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene lining, place the reactor in a hydrothermal box, and heat at 140℃ for 1h. Dry the heated second slurry at 100℃, wash with water, filter, and dry to obtain the first precursor coated with a titanium dioxide layer, i.e., the second precursor.

[0092] (3) Disperse 0.6g of niobium source Nb2O5 and 40g of the second precursor in 100mL of deionized water and stir for 10min. Then add 0.25g of lithium source Li2CO3 and mix evenly (i.e., the weight ratio of lithium source to second precursor is 0.00625:1 and the weight ratio of lithium source to niobium source is 1:2.4). Then, perform hydrothermal reaction at 200℃ for 5h. After centrifugation, washing, drying, and calcination at 900℃ for 6h, a double-layer coated composite anode material is obtained.

[0093] Example 13

[0094] A method for preparing a composite anode material:

[0095] (1) Dissolve 15.75g of carbon source glucose in 2500mL of deionized water, then add 1000g of artificial graphite (i.e., the weight ratio of carbon source to graphite particles is 0.01575:1), stir for 2h to obtain a suspension, i.e., the first slurry; perform a first spray drying on the suspension to obtain glucose-coated graphite powder, the outlet temperature of the first spray drying is 250℃, and the inlet pump speed is 4L / min; calcine the obtained powder in a nitrogen inert atmosphere at 700℃ for 6h to obtain a graphite particle composite material coated with an organic carbon layer, i.e., the first precursor.

[0096] (2) Dissolve 3.36g of titanium source and titanium oxysulfate in 100mL of deionized water, then add 400g of the first precursor (the weight ratio of titanium source to first precursor is 0.0084:1), and then add 2.52g of urea (the weight ratio of urea to titanium source is 1:1.33). Stir for 2h to obtain a suspension, i.e., the second slurry. Transfer the suspension to a stainless steel reactor with a polytetrafluoroethylene lining, place the reactor in a hydrothermal box, and heat at 100℃ for 3h. Dry the heated second slurry at 160℃, wash with water, filter, and dry to obtain the first precursor coated with a titanium dioxide layer, i.e., the second precursor.

[0097] (3) Disperse 0.6g of niobium source Nb2O5 and 40g of the second precursor in 100mL of deionized water and stir for 10min. Then add 0.25g of lithium source Li2CO3 and mix evenly (i.e., the weight ratio of lithium source to second precursor is 0.00625:1 and the weight ratio of lithium source to niobium source is 1:2.4). Then, perform hydrothermal reaction at 150℃ for 15h. After centrifugation, washing, drying, and calcination at 1200℃ for 1h, a double-layer coated composite anode material is obtained.

[0098] Example 14

[0099] A method for preparing a composite anode material:

[0100] The only difference between this embodiment and Embodiment 1 is that the outlet temperature of the first spray drying in step (1) is changed to 60°C; and the first calcination temperature of the obtained powder is changed to 450°C, and the calcination time is changed to 10h.

[0101] Example 15

[0102] A method for preparing a composite anode material:

[0103] The only difference between this embodiment and Embodiment 1 is that the outlet temperature of the first spray drying in step (1) is changed to 280°C; at the same time, the first calcination temperature of the obtained powder is changed to 850°C and the calcination time is changed to 3h.

[0104] Example 16

[0105] A method for preparing a composite anode material:

[0106] The only difference between this embodiment and embodiment 1 is that the reaction temperature of the reactor in step (2) in the hydrothermal box is changed to 80°C and the reaction time is changed to 4h; at the same time, the temperature of the second drying is changed to 80°C.

[0107] Example 17

[0108] A method for preparing a composite anode material:

[0109] The only difference between this embodiment and embodiment 1 is that the reaction temperature of the reactor in step (2) in the hydrothermal box is changed to 160°C and the reaction time is changed to 0.5h; at the same time, the temperature of the second drying is changed to 180°C.

[0110] Example 18

[0111] A method for preparing a composite anode material:

[0112] The only difference between this embodiment and Embodiment 1 is that urea was not added in step (2).

[0113] Example 19

[0114] A method for preparing a composite anode material:

[0115] The only difference between this embodiment and Embodiment 1 is that the hydrothermal reaction temperature in step (3) is changed to 140°C and the reaction time is changed to 18h; at the same time, the second calcination temperature is changed to 800°C and the time is changed to 8h.

[0116] Example 20

[0117] A method for preparing a composite anode material:

[0118] The only difference between this embodiment and Embodiment 1 is that the hydrothermal reaction temperature in step (3) is changed to 220°C and the reaction time is changed to 4h; at the same time, the second calcination temperature is changed to 1400°C and the time is changed to 0.5h.

[0119] Comparative Example 1

[0120] The artificial graphite core was used directly as the negative electrode material, and its scanning electron microscope image is shown in Figure 2.

[0121] Comparative Example 2

[0122] The first precursor obtained in step (1) of Example 1, namely the graphite particle composite material coated with organic carbon layer, is directly used as the negative electrode material.

[0123] The scanning electron microscope image of the obtained negative electrode material is shown in Figure 3.

[0124] Comparative Example 3

[0125] A method for preparing a composite anode material:

[0126] That is, the only difference between this comparative example and Example 1 is that step (2) was not performed, that is, the resulting composite negative electrode material does not include an organic carbon layer.

[0127] Comparative Example 4

[0128] A method for preparing a composite anode material:

[0129] The only difference between this comparative example and Example 1 is that no niobium source was added in step (3).

[0130] Comparative Example 5

[0131] A method for preparing a composite anode material:

[0132] 15.75 g of glucose (carbon source), 84 g of titanium oxysulfate (titanium source), 1.5 g of niobium (NbO2) and 0.625 g of lithium (Li2CO3) were dissolved together in 2500 mL of deionized water. Then, 1000 g of artificial graphite was added and the mixture was stirred for 2 h to obtain a suspension. The suspension was spray-dried to obtain powder. The outlet temperature of the spray dryer was 175 °C and the inlet pump speed was 4 L / min. The obtained powder was calcined at 600 °C in a nitrogen inert atmosphere for 8 h to obtain a composite anode material.

[0133] That is, all raw materials are directly mixed according to the weight ratio in Example 1 to prepare the composite anode material.

[0134] Battery sample preparation:

[0135] (a) Preparation of positive electrode sheet: LiMn 0.6 Fe 0.4 PO4 and LiNi 0.78 Co 0.12 Mn 0.1 O2 was mixed with polyvinylidene fluoride (PVDF), conductive agent Super P carbon black, and conductive agent single-walled carbon nanotubes (SWCNTs) in a weight ratio of 97.35:1.8:0.8:0.05 to form a slurry. The prepared slurry was then coated onto an aluminum foil current collector, with a double-sided surface density of 395 g / m². 2 After drying in an oven, it is hot-pressed, and the compacted density is 2.55 g / cm³. 3 The electrode sheets are die-cut into 123*93mm size;

[0136] (b) Preparation of negative electrode sheet: The negative electrode materials obtained in each example and comparative example were mixed with styrene-butadiene rubber (SBR), conductive agent Super P carbon black, and sodium methyl cellulose (CMC) in a weight ratio of 96.5:1.8:0.5:1.2 to prepare a slurry. The prepared slurry was coated onto a copper foil current collector, with a double-sided areal density of 194 g / m². 2 After drying in an oven, it is hot-cold pressed, and the compacted density is 1.65 g / cm³. 3 The electrode sheets are die-cut into 126*96mm size;

[0137] (c) Preparation of electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain the electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0138] (d) Separator: Polyethylene (PE) film is used as the separator, with a porosity of 40%, a thickness of 15μm, and a width of 130mm.

[0139] (e) Preparation of secondary batteries: The positive electrode, negative electrode and separator are stacked and then processed through casing, baking, liquid injection, formation and capacity testing to prepare 10Ah cells.

[0140] (f) Preparation of button cells: The negative electrode sheet is wiped into a single-sided film and punched into a small round piece of 12mm. Using lithium metal as the counter electrode, it is assembled into a 2025 type button cell.

[0141] Battery sample performance testing:

[0142] (a) First-cycle coulombic efficiency: Each battery sample was subjected to two charge-discharge cycles at 0.05C (charging cut-off voltage 1.5V, discharging cut-off voltage 0.005V) to obtain the first-cycle efficiency;

[0143] (b) High-temperature cycling performance: At 45°C, each battery sample was charged at a constant current rate of 1C to the charging termination voltage of 4.25V, then charged at a constant voltage rate to a current of 0.05C; then discharged at a constant current rate of 1C to the discharge termination voltage of 2.75V, and then allowed to stand for 10 minutes. This constitutes one cycle of charge and discharge. The discharge capacity at this point is recorded as the discharge capacity of the first cycle. When the cycle capacity retention reaches 80% EOL, the number of cycles is recorded.

[0144] (c) Cell Charge Cycle Test: At 25℃, the battery was first charged at constant current rates of 0.5C, 1C, and 2C until the charging termination voltage of 4.25V, then charged at constant voltage until the current was 0.05C; next, it was discharged at constant current rate of 1C until the discharge termination voltage of 2.75V, and then allowed to stand for 10 minutes. This constitutes one charge-discharge cycle. The constant current charging capacity and constant current charge ratio (CC capacity / (CC capacity+CV capacity), where CC refers to the cell capacity in the constant current stage and CV refers to the cell capacity in the constant voltage stage) were recorded, which represents the 0.5C rate charging performance. The battery was then tested at 2C rate using the same method to obtain the constant current charge ratio at 2C. This value represents the rate performance of the material; the higher the value, the better the rate performance of the material, and the greater the reduction in polarization.

[0145] The test results are shown in Table 1.

[0146] Table 1

[0147] As can be seen from the above description, the embodiments of this application achieve a significantly higher first-cycle coulombic efficiency in lithium-ion batteries prepared using these materials as the negative electrode active material compared to the graphite negative electrode material prepared in the comparative example, and the rate performance is also effectively improved. Simultaneously, the reduction in the SEI film significantly improves the high-temperature cycling stability of the battery samples.

[0148] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0149] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a composite negative electrode material, characterized in that, include: Step S1: The carbon source and graphite particles are mixed to form a first slurry. The first slurry is then dried and calcined to obtain a first precursor. The first precursor includes graphite particles and an organic carbon layer coating the surface of the graphite particles. Step S2: The titanium source and the first precursor are formulated into a second slurry. The second slurry undergoes a first reaction and a second drying to obtain a second precursor. The second precursor includes the first precursor and a titanium dioxide layer coated on the surface of the first precursor. Step S3: The niobium source, lithium source and the second precursor are formulated into a third slurry, and the third slurry is subjected to a second reaction and a second calcination to obtain the composite anode material.

2. The method for preparing the composite negative electrode material according to claim 1, characterized in that, In step S1, The first drying is spray drying, and the outlet temperature of the spray dryer is 80℃~250℃; and / or, The first calcination temperature is 500℃~1000℃, and the time is 3h~9h.

3. The method for preparing the composite negative electrode material according to claim 1 or 2, characterized in that, In step S1, the weight ratio of the carbon source to the graphite particles is (0.015~0.035):1, preferably (0.015~0.020):1; Preferably, the carbon source is selected from one or more of polydopamine, phenolic resin, glucose, fructose, sucrose, cellulose, starch, polyvinylpyrrolidone, polyvinyl alcohol, polypyrrole, polyethylene glycol, pitch, anthracene, aniline, tannic acid, and citric acid.

4. The method for preparing the composite negative electrode material according to any one of claims 1 to 3, characterized in that, In step S2, The first reaction is carried out at a temperature of 100℃ to 160℃ for a time of 2 hours to 20 hours; and / or, The second drying temperature is 100℃~160℃.

5. The method for preparing the composite negative electrode material according to any one of claims 1 to 4, characterized in that, In step S2, the weight ratio of the titanium source to the first precursor is (0.001-0.2):1, preferably (0.012-0.002):1; Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium oxysulfate, titanium sulfate, tetrabutyl titanate, and isopropyl titanate.

6. The method for preparing the composite negative electrode material according to any one of claims 1 to 5, characterized in that, In step S3, The reaction temperature for the second reaction is 150℃~200℃, and the reaction time is 5h~15h; The reaction temperature for the second calcination is 900℃~1200℃, and the time is 1h~6h.

7. The method for preparing the composite negative electrode material according to any one of claims 1 to 6, characterized in that, In step S3, the weight ratio of the lithium source to the second precursor is (0.001 to 0.050):1, and the weight ratio of the lithium source to the niobium source is 1:(2 to 5). Preferably, the niobium source is selected from one or more of niobium monoxide, niobium dioxide, and niobium pentoxide; and / or, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate.

8. A composite negative electrode material, characterized in that, The composite anode material is prepared by the method for preparing composite anode material according to any one of claims 1 to 7, and the composite anode material includes a graphite core and a composite layer covering the surface of the graphite core, wherein the composite layer includes an organic carbon layer and an inorganic conductive layer. The organic carbon layer and the inorganic conductive layer are arranged sequentially in a direction away from the graphite core; The inorganic conductive layer includes one or more of lithium titanate, lithium niobate, and niobium titanium oxide.

9. The composite negative electrode material according to claim 8, characterized in that, Based on the total weight of the composite negative electrode material being 100%, The content of the organic carbon layer is 0.1% to 10.0%, preferably 0.2% to 0.5%; The content of the inorganic conductive layer is 0.1% to 10.0%, preferably 1.0% to 1.5%.

10. A lithium-ion battery, comprising a negative electrode, a positive electrode, a separator, and an electrolyte, characterized in that, The negative electrode sheet includes the composite negative electrode material as described in claim 8 or 9.

Images