A negative electrode material, its preparation method, and a battery

Abstract

This invention discloses an anode material, its preparation method, and a battery, relating to the field of battery material preparation technology. The anode material includes a core and a coating layer that at least partially covers the core. The core material is a conductive material, and the coating layer includes a carbon layer doped with heteroatoms and at least two types of lithium metal salt particles dispersed in the carbon layer. The core material is a conductive material, serving as a conductive matrix and capacity host, providing high specific capacity and responsible for high-capacity lithium storage. The coating layer on the core is responsible for interface regulation and performance enhancement. The coating layer is a carbon layer doped with heteroatoms, which improves its conductivity and lithium-ion diffusion capability. Furthermore, at least two types of lithium metal salt particles are doped in the carbon layer to exert a synergistic effect, which is beneficial for improving the initial efficiency, compensating for the performance shortcomings of a single material, improving the battery's diffusion rate, reducing expansion, and improving cycle life, initial efficiency, and rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation technology, and in particular to a negative electrode material, its preparation method, and a battery. Background Technology

[0002] The increasing market demand for fast-charging lithium-ion batteries makes the anode material a key factor influencing its fast-charging performance. Currently, anodes are primarily made of artificial graphite, with soft or hard carbon coatings applied to improve fast-charging and low-temperature performance. However, while coatings can increase the diffusion coefficient, simply optimizing the carbon coating layer offers limited improvement in fast-charging performance. Lithium-ion compounds, with their advantages of fast ion diffusion, high reversible capacity, and strong solvation ability, can enhance lithium-ion transport rates during charging and discharging when coated onto the material surface. Examples include coating with organic or inorganic lithium compounds. Currently, some products use single inorganic lithium compounds, such as lithium titanate, but the improvement in performance is limited. Summary of the Invention

[0003] The main objective of this invention is to propose a negative electrode material, its preparation method, and a battery, aiming to solve the problem that the use of ordinary coating for negative electrode materials in the prior art has limited effect on improving battery performance.

[0004] To achieve the above objectives, the present invention proposes a negative electrode material comprising a core, wherein the core material comprises a conductive material; and, A coating layer, at least partially covering the core, the coating layer comprising a carbon layer doped with heteroatoms and at least two kinds of lithium salt particles dispersed in the carbon layer.

[0005] In one embodiment, the conductive material comprises one of artificial graphite, natural graphite, and mesophase carbon microspheres; and / or, The heteroatom includes at least one of nitrogen, boron, sulfur, and phosphorus; and / or, The two lithium metal salts include lithium titanate and lithium aluminate.

[0006] In one embodiment, the mass ratio of the coating layer to the negative electrode material is (5-15):100; and / or, The lithium salts in the two types of lithium salt particles include lithium titanate and lithium aluminate, wherein the mass ratio of lithium titanate to lithium aluminate is 1-5:1-5; and / or The lithium salt particles have a particle size of 0.5-2µm.

[0007] The present invention also provides a method for preparing a negative electrode material, the method comprising: S1. Mix polyol, polyisocyanate, catalyst and conductive material, perform first heat treatment under inert atmosphere, filter, vacuum dry to obtain composite material; S2. The composite material, alkaline solution, titanium source, aluminum source and lithium salt are mixed, spray dried and subjected to a second heat treatment to obtain the negative electrode material.

[0008] In one embodiment, in step S1: The polyol includes one of glycerol, glycerol, sorbitol, mannitol, pentaerythritol, and xylitol; and / or, The polyisocyanate includes at least one of toluene diisocyanate, trifluoro-p-toluene isocyanate, phenyl isocyanate, trifluoromethoxyphenyl isocyanate, and polymethylene polyphenyl polyisocyanate.

[0009] In one embodiment, the alkaline solution comprises at least one selected from 2-hydroxyethylamine, diethanolamine, tetramethylammonium hydroxide, and dimethylamine; and / or, The lithium salt includes at least one selected from lithium carbonate, lithium nitrate, lithium hydroxide, lithium dihydrogen phosphate, and lithium acetate; and / or, The titanium source includes at least one of tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropyl titanate, titanium acetylacetonate, and titanium citrate; and / or, The aluminum source includes at least one of basic aluminum acetate, basic aluminum acetate, basic aluminum diacetate, and basic aluminum stearate.

[0010] In one embodiment, the mass ratio of the polyol, the polyisocyanate, the catalyst, and the conductive material is 100-300:100-300:10-30:1000; and / or, The mass ratio of the composite material, the alkaline solution, the titanium source, the aluminum source, and the lithium salt is 100:50-200:1-5:1-5:5-10.

[0011] In one embodiment, the temperature of the first heat treatment is 80-100°C, and the duration of the first heat treatment is 12-48 hours; and / or, The temperature of the second heat treatment is 600-1000℃, and the time of the second heat treatment is 1-3 hours.

[0012] The present invention also provides a battery comprising the aforementioned negative electrode material or a negative electrode material prepared by the aforementioned method for preparing negative electrode material.

[0013] The present invention proposes a negative electrode material comprising a core and a coating layer. The core is made of a conductive material, serving as a conductive substrate and capacity carrier, providing high specific capacity and responsible for high-capacity lithium storage. The coating layer on the core is responsible for interface regulation and performance enhancement. The coating layer is a carbon layer doped with heteroatoms. The doping of heteroatoms improves its conductivity and lithium-ion diffusion capability. Furthermore, at least two types of lithium metal salt particles are doped into the carbon layer to exert a synergistic effect, compensating for the performance shortcomings of a single material, improving the diffusion rate of the battery, reducing expansion, and improving cycle and rate performance. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0015] Figure 1 This is a scanning electron microscope image of the negative electrode material in Example 1 of the present invention.

[0016] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The increasing market demand for fast-charging lithium-ion batteries makes the anode material a key factor influencing its fast-charging performance. Currently, anodes are primarily made of artificial graphite, with soft or hard carbon coatings applied to improve fast-charging and low-temperature performance. However, while coatings can increase the diffusion coefficient, simply optimizing the carbon coating layer offers limited improvement in fast-charging performance. Lithium-ion compounds, with their advantages of fast ion diffusion, high reversible capacity, and strong solvation ability, can enhance lithium-ion transport rates during charging and discharging when coated onto the material surface. Examples include coating with organic or inorganic lithium compounds. Currently, some products use single inorganic lithium compounds, such as lithium titanate, but the improvement in performance is limited.

[0019] In view of this, the present invention provides a negative electrode material comprising a core, wherein the core is made of a conductive material; and, A coating layer, at least partially covering the core, the coating layer comprising a carbon layer doped with heteroatoms and at least two kinds of lithium salt particles dispersed in the carbon layer.

[0020] The present invention proposes a negative electrode material comprising a core and a coating layer. The core is made of a conductive material, serving as a conductive substrate and capacity carrier, providing high specific capacity and responsible for high-capacity lithium storage. The coating layer on the core is responsible for interface regulation and performance enhancement. The coating layer is a carbon layer doped with heteroatoms. The doping of heteroatoms improves its conductivity and lithium-ion diffusion capability. Furthermore, at least two types of lithium metal salt particles are doped into the carbon layer to exert a synergistic effect, compensating for the performance shortcomings of a single material, improving the diffusion rate of the battery, reducing expansion, and improving cycle and rate performance.

[0021] In one embodiment, the conductive material includes one of artificial graphite, natural graphite, and mesophase carbon microspheres. For example, graphite is the mainstream negative electrode material on the market. It has high theoretical capacity and low cost, making it suitable as the main body for lithium storage. Carbon nanotubes or carbon fibers have excellent conductivity and mechanical strength and can be used as a conductive framework to improve the overall electrode conductive network. They are especially suitable for high-rate scenarios. The appropriate material can be selected according to the actual situation.

[0022] In any embodiment, the heteroatom includes at least one of nitrogen, boron, sulfur, and phosphorus, because the doping of heteroatoms can alter the electronic structure of carbon, thereby improving its conductivity and lithium-ion diffusion capability.

[0023] In any embodiment, the at least two lithium metal salts include lithium titanate and lithium aluminate, which can be used to provide an additional lithium source. During the high-temperature carbonization process of the prepared battery, they react with the introduced metal oxide to generate the target lithium salt compound. Lithium titanate has a large interlayer spacing and low expansion. Lithium titanate is a zero-strain material with excellent cycle stability, good rate performance, and a high voltage platform, avoiding lithium plating. Lithium aluminate has weak activity, strong high-temperature stability, stable structure, good safety, and can suppress thermal runaway, which is beneficial to the initial efficiency improvement. The combined effect of the two can achieve the synergistic optimization of "fast charging + safety".

[0024] In any embodiment, the mass ratio of the coating layer to the negative electrode material is (5-15):100. Within the above reasonable range, it can ensure that the coating layer can cover the core surface sufficiently while also effectively realizing functionalization. When the coating layer is too thick, it will increase the mass of inactive substances and reduce the overall energy density. When the coating layer is too thin, it cannot effectively play a modifying role and the interface protection is insufficient.

[0025] In any embodiment, the lithium salts in the two types of lithium metal salt particles include lithium titanate and lithium aluminate, and the mass ratio of lithium titanate to lithium aluminate is 1-5:1-5. The specific ratio can be 1:1, 1:5, or 5:1. If there is too much lithium titanate, the voltage plateau will increase and the energy density will decrease. If there is too much LiAlO2, the ion diffusion rate will decrease and the rate performance will be limited.

[0026] It should be noted that the amount (moles or mass) of lithium titanate and lithium aluminate in the final product is directly determined by the amount of tetraethyl titanate and basic aluminum acetate added to the raw materials. This is because lithium titanate is the only source of titanium, and lithium aluminate is the only source of aluminum. Taking Example 1 as an example, the carbonization of the material obtained in Example 1 at 800°C is a reaction process in which the temperature is slowly increased from room temperature to 800°C. In Example 1, 3g of tetraethyl titanate and 3g of basic aluminum acetate were used. The specific reaction process is as follows: ① The structural formula of tetraethyl titanate is Ti(OC2H5)4. It first undergoes a condensation reaction at low temperature (200-300℃) to generate TiO2; the structural formula of basic aluminum acetate is Al(OH)(CH3COO)2; it typically decomposes thermally at temperatures between 400-500℃ to generate Al2O3; subsequently, at a high temperature of 800℃, excess lithium carbonate reacts with TiO2 and Al2O3 respectively, as shown in the following equations: TiO2 + LiICO3 → Li2TiO4 + CO2↑; Li2CO3 + Al2O3 → 2LiAlO2 + CO2↑; ultimately, LI2TIO4 and LIALO2 are generated respectively.

[0027] Secondly: Ti(OC2H5)4 has a molecular weight of 228, and TI has a molecular weight of 47; the molar amount of Ti is 3 / 228 × 47 = 0.618 mol; the theoretical mass of Li2TiO4 is calculated to be 0.618 × 81.75 = 50.52 g; under normal conditions, the reaction efficiency and yield of the materials in this experiment are about 70%, that is, the mass of Li2TiO4 obtained is 50.52 × 0.70 = 35.36 g; Al(OH)(CH3COO)2 has a molecular weight of 142, and AL has a molecular weight of 27; the molar amount of Al is 3 / 142 × 27 = 0.57 mol; the mass of LiAlO2 is calculated to be 0.57 × 65.92 = 37.57 g; under normal conditions, the reaction efficiency and yield of the materials are 95%, that is, the mass of LiAlO2 obtained is 37.57 × 0.95 = 35.69 g; The final mass ratio of Li2TiO4 to LiAlO2 is approximately 1:1.

[0028] The present invention also provides a method for preparing a negative electrode material, the method comprising: S1. Mix polyol, polyisocyanate, catalyst and conductive material, perform first heat treatment, filter, vacuum dry to obtain composite material; S2. The composite material, alkaline solution, titanium source, aluminum source and lithium salt are mixed, spray dried and subjected to a second heat treatment to obtain the negative electrode material.

[0029] In the technical solution of this invention, in step S1: the conductive material serves as both the conductive matrix and the capacity host, providing high specific capacity. A polyurethane or polyurea precursor is generated through an addition polymerization reaction between a polyol and a polyisocyanate. This polyurethane layer contains a large number of polar groups (such as -NH- and C=O in urethane bonds). These groups possess lone pairs of electrons, which can act as Lewis base sites, effectively coordinating and adsorbing metal cations such as titanium and aluminum, achieving uniform anchoring of the metal source on the surface of the conductive material. In step S2: during the second heat treatment, the polyurethane coating undergoes pyrolysis and carbon conversion. Due to the introduction of nitrogen elements by the polyisocyanate, such as toluene diisocyanate (TDI), the polyurethane layer is in-situ transformed into a nitrogen-doped amorphous carbon layer. Simultaneously, the titanium and aluminum sources pre-adsorbed in the polymer network undergo a solid-phase reaction with lithium salts at high temperature, generating lithium titanate and lithium aluminate nanoparticles in situ. These particles are firmly embedded in the nitrogen-doped carbon layer, forming a synergistic protective layer of 'carbon skeleton + double lithium salt', providing both mechanical buffering and improved interfacial ion conduction rate.

[0030] In any embodiment, the polyol includes one of glycerol, glycerol, sorbitol, mannitol, pentaerythritol, and xylitol.

[0031] In the technical solution of this invention, these polyols have moderate molecular weight, good water solubility, and are easy to disperse uniformly. More importantly, they all contain multiple hydroxyl groups, which can undergo condensation reaction with polyisocyanates to generate polyurethane / polyurea, and further transform into polyurethane structures. For example, glycerol, sorbitol, etc. are green and renewable resources, which are environmentally friendly and conducive to the formation of a uniform and continuous organic coating layer, providing abundant coordination sites for subsequent metal ion adsorption.

[0032] In any embodiment, the polyisocyanate includes one of toluene diisocyanate, trifluoro-p-toluene isocyanate, phenyl isocyanate, trifluoromethoxyphenyl isocyanate, and polymethylene polyphenyl polyisocyanate. Since the polyisocyanate contains multiple -NCO groups, it can react with polyols to generate a cross-linking network, forming a dense polyurethane coating layer with a high degree of cross-linking. This not only has strong adhesion but also facilitates subsequent high-temperature carbonization to form high-quality nitrogen-doped carbon.

[0033] In any embodiment, in step S2, the alkaline solution includes at least one of 2-hydroxyethylamine, diethanolamine, tetramethylammonium hydroxide, and dimethylamine; this is because an alkaline environment can deprotonate the -NH- in the obtained polyurethane coating layer, enhancing its coordination ability to metal cations, and the organic base has good volatility, making it easy to remove during spray drying and reducing impurities.

[0034] In any embodiment, the lithium salt is at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium dihydrogen phosphate, and lithium acetate. The above-mentioned lithium salt is used to provide a lithium source, which reacts with the metal precursor during the high-temperature carbonization process to generate the target lithium salt, thereby promoting the in-situ generation of bimetallic lithium salt. Different lithium salts can be used in combination to regulate the reaction kinetics and product morphology.

[0035] In any embodiment, the titanium source is at least one selected from tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropyl titanate, titanium acetylacetonate, and titanium citrate; these are common titanium source precursors that can be hydrolyzed to generate Ti. 4+ Used to synthesize Li4Ti5O 12 For example, titanium acetylacetonate is a complex with high stability, making it suitable for uniform doping and enabling the uniform introduction and nano-distribution of titanium.

[0036] In any embodiment, the aluminum source is at least one of basic aluminum acetate, basic aluminum acetate, basic aluminum diacetate, and basic aluminum stearate. These are common aluminum source precursors that can release Al³⁺ during heating. + It is used to generate LiAlO2, which can achieve controlled release and uniform distribution of aluminum, and is conducive to the formation of high-purity, high-thermal-stability LiAlO2 phase.

[0037] In any embodiment, the mass ratio of the polyol, the polyisocyanate, the catalyst, and the conductive material is 100-300:100-300:10-30:1000. Within the above range, it is ensured that the reactants are in full contact, which is conducive to the formation of a uniform, thin, and continuous polyurethane coating, and avoids excessive coating that may hinder ion transport or insufficient coating that may affect the modification effect.

[0038] In any embodiment, the mass ratio of the composite material, the alkaline solution, the titanium source, the aluminum source, and the lithium salt is 100:50-200:1-5:1-5:5-10. Within the above range, controlling the metal ion loading can achieve nanoscale and uniform dispersion of the lithium salt and avoid agglomeration.

[0039] In any embodiment, the temperature of the first heat treatment is 80-100°C and the time of the first heat treatment is 12-48h. Within the above range, sufficient activation time can be provided to promote the complete polycondensation reaction. Too high a temperature may lead to side reactions or graphite oxidation, while too low a temperature will result in incomplete reaction. Long reaction time ensures that the coating layer is dense and uniform.

[0040] The second heat treatment is performed at a temperature of 600-1000℃ for 1-3 hours. Within this range, the polyurethane layer of the present invention is carbonized into a nitrogen-doped amorphous carbon layer. If the temperature is too low, the reaction will be incomplete; if the temperature is too high, it will lead to excessive graphitization of graphite or lithium volatilization.

[0041] The present invention also provides a battery, the lithium-ion battery comprising the aforementioned negative electrode material or the negative electrode material prepared by the aforementioned method for preparing the negative electrode material. Therefore, it possesses all the beneficial effects of the aforementioned negative electrode material or the aforementioned method for preparing the negative electrode material.

[0042] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0043] Example 1 A negative electrode material includes a core and a coating layer. The core is made of a conductive material, and the coating layer at least partially covers the core. The coating layer includes a carbon layer doped with heteroatoms and at least two kinds of lithium metal salt particles dispersed in the carbon layer. The specific preparation steps are as follows: Step S1: 200g of glycerol solution and 200g of toluene diisocyanate were mixed evenly, and 100g of graphite and 20g of aluminum trichloride catalyst were added and dispersed evenly. The mixture was reacted at 90℃ under a nitrogen atmosphere for 24 hours. After filtration, the mixture was vacuum dried at 80℃ for 24 hours to obtain the composite material, namely polyurethane-coated graphite material. Step S2: 100g of the composite material was added to 100g of a 20wt% 2-hydroxyethylamine ethanol solution (20g of 2-hydroxyethylamine (also called ethanolamine) was weighed, poured into a beaker, and then 80g of anhydrous ethanol was added. The mixture was stirred and mixed evenly to obtain 100g of a 20wt% 2-hydroxyethylamine ethanol solution). Then, 3g of tetraethyl titanate, 3g of basic aluminum acetate, and 8g of lithium carbonate were added and mixed evenly. The mixture was spray-dried, and the resulting material was carbonized at 800℃ for 2h to obtain the negative electrode material, namely, the bimetallic lithium salt modified negative electrode material. The lithium salts in the two lithium salt particles include lithium titanate and lithium aluminate, and the mass ratio of lithium titanate to lithium aluminate is approximately 1:1.

[0044] Example 2 A negative electrode material includes a core and a coating layer. The core is made of a conductive material, and the coating layer at least partially covers the core. The coating layer includes a carbon layer doped with heteroatoms and at least two kinds of lithium metal salt particles dispersed in the carbon layer. The specific preparation steps are as follows: Step S1: 100g of glycerol and 100g of trifluoro-p-toluene isocyanate were mixed evenly, and 1000g of artificial graphite and 10g of aluminum trichloride catalyst were added and dispersed evenly. The mixture was reacted at 80℃ under a nitrogen atmosphere for 48 hours, filtered, and vacuum dried at 80℃ for 24 hours to obtain the composite material, namely polyurethane-coated graphite material. Step S2: 100g of the composite material was added to 50g of an ethanol solution containing 30wt% diethanolamine, followed by the addition of 1g of tetrapropyl titanate, 5g of basic aluminum acetate, and 5g of lithium nitrate. The mixture was then spray-dried and carbonized at 600℃ for 3h to obtain a bimetallic lithium salt modified anode material. The lithium salts in the two lithium salt particles included lithium titanate and lithium aluminate, with a mass ratio of approximately 1:5 between the lithium titanate and the lithium aluminate.

[0045] Example 3 A negative electrode material includes a core and a coating layer. The core is made of a conductive material, and the coating layer at least partially covers the core. The coating layer includes a carbon layer doped with heteroatoms and at least two kinds of lithium metal salt particles dispersed in the carbon layer. The specific preparation steps are as follows: Step S1: 300g mannitol solution and 300g phenyl isocyanate were mixed evenly, and 1000g graphite and 30g aluminum trichloride catalyst were added and mixed evenly. The mixture was then reacted at 100℃ under a nitrogen atmosphere for 12 hours. After filtration, the filter residue was vacuum dried at 80℃ for 24 hours to obtain the composite material, namely polyurethane-coated graphite material. Step S2: 100g of the composite material was added to 200g of an ethanol solution of 10wt% tetramethylammonium hydroxide, followed by 5g of tetrabutyl titanate, 1g of basic aluminum diacetate, and 10g of lithium acetate. The mixture was then spray-dried and carbonized at 1000℃ for 1h to obtain a bimetallic lithium salt modified anode material. The lithium salts in the two lithium salt particles included lithium titanate and lithium aluminate, and the mass ratio of lithium titanate to lithium aluminate was approximately 5:1. Comparative Example 1 Unlike Example 1, tetraethyl titanate is not added in step S2, but otherwise it is the same as in Example 1.

[0046] Comparative Example 2 Unlike Example 1, basic aluminum acetate is not added in step S2; otherwise, it is the same as Example 1.

[0047] Comparative Example 3 Unlike Example 1, in step S1, polyurethane is not coated on the graphite surface; instead, graphite material is used to replace polyurethane coating on the graphite material. Otherwise, it is the same as Example 1.

[0048] Comparative Example 4 Unlike Example 1, the lithium salts in the two types of lithium salt particles include lithium titanate and lithium aluminate, and the mass ratio of lithium titanate to lithium aluminate is 1:9. The rest is the same as in Example 1.

[0049] Performance testing 1. SEM testing The bimetallic lithium salt-modified anode material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the above, the negative electrode material prepared in Example 1 is granular with a uniform size distribution and slight adhesion on the surface. Its particle size D50 is between 10-15 μm.

[0050] (2) Physical and chemical properties and button cell testing The degree of graphitization, OI value, and specific surface area of ​​the anode materials prepared in Examples 1-3 and Comparative Examples 1-4 were measured. The tests were conducted according to the methods outlined in the national standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The diffusion coefficient of the materials was tested using GITT, and the powder resistivity was measured using a four-probe analyzer. The test results are shown in Table 1.

[0051] The negative electrode materials from Examples 1-3 and Comparative Examples 1-4 were used as negative electrode materials for lithium-ion batteries to assemble coin cells. The specific preparation method of the negative electrode material was as follows: a negative electrode sheet was prepared by mixing negative electrode material:CMC:SBR:SP:H2O in a mass ratio of 95:2.5:1.5:1:150; a lithium sheet was used as the positive electrode; the electrolyte was LiPF6 / EC+DEC, in which LiPF6 was the electrolyte, and a mixture of EC and DEC with a volume ratio of 1:1 was used as the solvent, with an electrolyte concentration of 1.1 mol / L; the separator was a composite membrane of polyethylene (PE) and polypropylene (PP) (1:1). The coin cells were assembled in an argon-filled glove box. Electrochemical performance was performed on a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The initial discharge capacity and initial efficiency of the coin cells, as well as their charge DCR (50% SOC), were tested. The test results are shown in Table 1.

[0052]

[0053] As shown in Table 1, the anode materials of Examples 1-3 outperformed Comparative Examples 1-4 in terms of diffusion coefficient, specific surface area, initial efficiency, and OI value. This is because: compared to Comparative Example 1 (lacking titanium source) and Comparative Example 2 (lacking aluminum source), the DCR of Examples (bimetallic lithium salt) was lower, and the initial discharge capacity and initial efficiency were superior to those of the comparative examples modified with a single lithium metal salt. This indicates that the coexistence of lithium titanate and lithium aluminate particles produced a synergistic effect, which optimized electrochemical performance better than using either one alone. Compared to Comparative Example 3 (without coating), the DCR (DC internal resistance) of Example 1 was significantly reduced (21.3 Ω vs 26.4 Ω), and the specific surface area and diffusion coefficient were also higher. This indicates that the polyurethane-derived carbon coating effectively improved the interfacial conductivity and lithium-ion diffusion capability of the material. Compared to Comparative Example 4 (Ti:Al = 1:9), when the mass ratio of lithium titanate to lithium aluminate in Example 1 was 1:1, all indicators (especially DCR 21.3 Ω vs 27.1 Ω, diffusion coefficient 6.12 vs 27.1 Ω, and diffusion coefficient 6.12 vs 27.1 Ω) were significantly improved. The 1.96 ratio was significantly better than the comparative example 4 with a ratio of 1:9. The severe volume expansion effect caused by the high aluminum content damaged the mechanical integrity of the electrode, leading to the pulverization of the active material and the failure of the interface contact, thus greatly weakening the overall electrochemical performance of the battery. Therefore, lithium aluminate and lithium titanate can form a more complete ion transport channel or a more stable SEI film under appropriate ratio range.

[0054] (3) Soft-pack battery test: The negative electrode materials from Examples 1-3 and Comparative Examples 1-4 were slurried and coated to prepare negative electrode sheets. LFP was used as the positive electrode, and EC / DEC / PC (volume ratio EC:DEC:PC=1:1:1) was used as the solvent and LiPF6 with a concentration of 1.2 mol / L was used as the solute. Celgard 2400 membrane was used as the separator to prepare a 5Ah soft-pack battery. The liquid absorption capacity of the electrode sheet, the OI value of the electrode sheet, and the cycle performance and constant current ratio of the battery were tested.

[0055] Liquid absorption capacity of the negative electrode: Using a 1mL burette, take 1mL of electrolyte, add one drop to the surface of the negative electrode, and time the process until the electrolyte is completely absorbed. Record the time t.

[0056] Cycling performance: Charge / discharge current 2.0C / 2.0C, voltage range 2.5-3.65V, number of cycles 500.

[0057] Rate performance: constant current ratio under 2C charging conditions, i.e. 2C constant current capacity / (2C constant current capacity + 0.1C constant voltage capacity).

[0058] The test results are shown in Table 2.

[0059] Table 2

[0060] As shown in Table 2, the liquid absorption capacity, electrode OI value, cycle performance and rate performance of the electrodes in Examples 1-3 are significantly better than those of Comparative Examples 1-3. Compared with Comparative Examples 1 and 2, the liquid absorption speed of Example 1 is significantly faster (87s vs 133s / 145s), the electrode OI value is significantly lower (9.12 vs 11.97 / 12.15), and the cycle retention rate and 2C constant current ratio are better than those of the comparative examples with a single high orientation structure. The synergistic introduction of titanium source (tetraethyl titanate) and aluminum source (basic aluminum acetate) in step S2 is crucial. The co-modification of bimetallic lithium salts (lithium titanate and lithium aluminate) not only optimizes the chemical properties of the material surface and reduces the orientation degree (OI value) of the electrode, but also creates a more hydrophilic interface, thus significantly improving the electrolyte wetting speed and the rate charging performance of the battery compared to using one of the metal salts alone. Compared to Comparative Example 3, which does not coat the graphite surface with polyurethane, Example 1 has a faster liquid absorption speed and a higher 2C constant current ratio. This indicates that the coating layer not only provides a good conductive network but also effectively regulates the physical structure of the active material surface, reducing the orientation degree after electrode rolling, thereby providing a smoother transport channel for the electrolyte and significantly improving wettability and fast charging capability. Compared with Comparative Example 4, Example 1 is superior to Comparative Example 4 in all indicators (liquid absorption speed 87s vs 123s, OI value 9.12 vs 11.73), especially with a significant advantage in 2C constant current ratio. This shows that the mass ratio of lithium titanate to lithium aluminate has an important impact on the electrode interface characteristics. Although Comparative Example 4 also introduced bimetallic salts, the excessively high aluminum content (1:9) may lead to a decrease in surface hydrophilicity or dense particle accumulation, hindering electrolyte penetration. Example 1 uses the optimal ratio within the above range, which maximizes the surface wettability while reducing the electrode OI value, thereby achieving excellent liquid absorption speed and electrochemical performance.

[0061] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material, characterized in that, The method for preparing the negative electrode material includes: S1. Mix polyol, polyisocyanate, catalyst and conductive material, perform first heat treatment under inert atmosphere, filter, vacuum dry to obtain composite material; S2. The composite material, alkaline solution, titanium source, aluminum source, and lithium salt are mixed, spray-dried, and subjected to a second heat treatment to obtain the negative electrode material. The conductive material includes one of artificial graphite, natural graphite, and mesophase carbon microspheres; The temperature of the first heat treatment is 80-100℃, and the time of the first heat treatment is 12-48h; The temperature of the second heat treatment is 600-1000℃, and the time of the second heat treatment is 1-3 hours; The mass ratio of the composite material, the alkaline solution, the titanium source, the aluminum source, and the lithium salt is 100:50-200:1-5:1-5:5-10; The negative electrode material includes a core, and the core material includes a conductive material; and... A coating layer, at least partially covering the core, the coating layer comprising a carbon layer doped with heteroatoms and at least two kinds of lithium salt particles dispersed in the carbon layer.

2. The method for preparing the negative electrode material as described in claim 1, characterized in that, In step S1: The polyol includes one of glycerol, sorbitol, mannitol, pentaerythritol, and xylitol; and / or, The polyisocyanate includes at least one of toluene diisocyanate, trifluoro-p-toluene isocyanate, phenyl isocyanate, trifluoromethoxyphenyl isocyanate, and polymethylene polyphenyl polyisocyanate.

3. The method for preparing the negative electrode material as described in claim 1, characterized in that, In step S2: The alkaline solution comprises at least one of 2-hydroxyethylamine, diethanolamine, tetramethylammonium hydroxide, and dimethylamine; and / or, The lithium salt includes at least one selected from lithium carbonate, lithium nitrate, lithium hydroxide, lithium dihydrogen phosphate, and lithium acetate; and / or, The titanium source includes at least one of tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropyl titanate, titanium acetylacetonate, and titanium citrate; and / or, The aluminum source includes at least one of basic aluminum diacetate and basic aluminum stearate.

4. The method for preparing the negative electrode material as described in claim 1, characterized in that, The mass ratio of the polyol, the polyisocyanate, the catalyst, and the conductive material is 100-300:100-300:10-30:1000.

5. The method for preparing the negative electrode material as described in claim 1, characterized in that, The heteroatom includes at least one of nitrogen, boron, sulfur, and phosphorus; and / or, The at least two types of lithium metal salt particles include lithium titanate and lithium aluminate.

6. The method for preparing the negative electrode material as described in claim 1, characterized in that, In the negative electrode material, the mass ratio of the coating layer to the negative electrode material is (5-15):100; and / or, The lithium salt particles have a particle size of 0.5-2µm.

7. A battery, characterized in that, The battery includes a negative electrode material prepared by the method for preparing a negative electrode material as described in any one of claims 1 to 6.

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