A method for preparing a spherical graphite and negative electrode material composite

Abstract

This invention discloses a method for preparing a composite of spherical graphite and anode material, specifically relating to the field of lithium-ion battery anode material technology. The method first disperses spherical graphite in N-methylpyrrolidone, then adds a silane coupling agent and an initiator under nitrogen protection, reacting at 70-85°C for 1-4 hours to obtain a surface-activated spherical graphite suspension. Subsequently, pretreated anode active material and glycidyl methacrylate are added to the suspension, undergoing a gradient temperature polymerization reaction to form a primary composite system. Finally, 3-aminophenylboronic acid is added to adjust the pH to 8-9, and a crosslinking reaction is carried out at 55-70°C for 3-6 hours. After ethanol precipitation, washing, and vacuum drying, the composite anode material is obtained. This method enhances interfacial bonding through covalent bonding and a dynamic crosslinking network, effectively buffering volume expansion and improving the material's structural stability and cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a method for preparing a composite of spherical graphite and anode material. Background Technology

[0002] The field of lithium-ion battery anode material technology includes the design, synthesis, and structural performance regulation of anode active materials. The core of this technology is the construction of the microstructure of anode materials and the optimization of their electrochemical performance. It involves various anode material systems, such as carbon-based materials represented by artificial graphite and natural graphite, alloy materials represented by silicon-based materials, and lithium-intercalated materials represented by lithium titanate, as well as the preparation techniques, modification methods, and composite strategies of the above materials.

[0003] Patent CN118099402B addresses the shortcomings of existing graphite anode materials by developing a novel spherical graphite / silicon anode material. Through steps such as sol-gel reaction, graphene oxide coating, magnesia reduction, and Ti doping, an anode material with high energy and power density, excellent conductivity, chemical stability, and mechanical strength is obtained, effectively improving the charge-discharge efficiency and cycle life of the battery.

[0004] The theoretical specific capacity limit of spherical graphite in existing technologies is relatively low. Improvements in its capacity through physical purification and morphology optimization have reached their limits. Its surface chemistry is stable and inert, lacking functional groups that can strongly interact with other active substances, resulting in insufficient reactivity and interfacial compatibility as a composite matrix. Attempts to combine these two materials using conventional methods such as mechanical mixing or ordinary coating fail to achieve complementary advantages and instead introduce new and more complex systemic failures.

[0005] The smooth, inert surface of spherical graphite makes it difficult to form a strong chemical bond or physical anchor between it and silicon. During cycling, the volume change of the silicon phase can rapidly lead to the delamination of the two-phase interface, causing the composite structure to fail and its performance to deteriorate sharply. Non-uniform and undesigned composite structures cannot effectively buffer and disperse the huge stress of the silicon phase. The stress is concentrated at local contact points, which may cause the structure of the spherical graphite carrier itself to be destroyed, losing its advantage as a stable framework.

[0006] Therefore, this invention proposes a method for preparing a composite of spherical graphite and negative electrode material. Summary of the Invention

[0007] The main objective of this invention is to provide a method for preparing a composite of spherical graphite and anode material, which can effectively solve the problems of weak interfacial bonding, large volume expansion stress, and poor structural stability of graphite anode materials.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a composite of spherical graphite and a negative electrode material includes the following steps: S1. Spherical graphite is placed in a mixed acid of concentrated nitric acid and concentrated sulfuric acid for oxidation treatment. After washing and drying, spherical graphite with surface oxidation is obtained. The spherical graphite with surface oxidation is dispersed in a first organic solvent. A silane coupling agent is added under an inert atmosphere to react and obtain an activated spherical graphite suspension. S2. Add pretreated negative electrode active material, glycidyl methacrylate and initiator to activated spherical graphite suspension to carry out polymerization reaction to obtain primary composite system; S3. Add 3-aminophenylboronic acid to the primary composite system, adjust the pH of the system, control the temperature for reaction, and after the reaction is completed, separate, wash and dry to obtain the composite anode material.

[0009] Preferably, in step S1, the volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed acid is 1:(1-3), the oxidation treatment temperature is 60-90℃, the time is 2-6h, the silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane, the reaction temperature is 70-85℃, and the reaction time is 1-4h.

[0010] Preferably, the pretreatment of the negative electrode active material in step S2 specifically includes: dispersing the negative electrode active material in a buffer solution with a pH of 8.0-8.5, adding dopamine hydrochloride, stirring at room temperature for 12-24 hours, and obtaining the pretreated negative electrode material after centrifugation, washing, and drying.

[0011] Preferably, the negative electrode active material in step S2 is selected from one of elemental silicon, silicon oxide, silicon alloy, elemental tin, tin oxide or tin alloy, and its average particle size is 50-200 nm.

[0012] Preferably, the conditions for the free radical polymerization reaction in step S2 include: reacting at 40-50°C for 1-2 hours, and then raising the temperature to 60-70°C to continue the reaction for 3-6 hours.

[0013] Preferably, the first organic solvent in step S1 is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide.

[0014] Preferably, in step S3, the pH of the system is adjusted to 8-9, the target temperature of the temperature-controlled reaction is 55-70℃, and the total reaction time is 3-6h.

[0015] Preferably, the mass ratio of spherical graphite to silane coupling agent in step S1 is 10:(0.5-1.5).

[0016] Preferably, in step S2, the mass ratio of the amount of pretreated negative electrode material, glycidyl methacrylate, and initiator added relative to spherical graphite is 10:(1-8):(0.1-2.5):(0.05-0.3); the initiator is azobisisobutyronitrile.

[0017] More preferably, the amount of dopamine hydrochloride added in step S2 is 0.5 parts.

[0018] Preferably, in step S3, the addition ratio of 3-aminophenylboronic acid to the spherical graphite is 10:(0.1-2).

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention introduces oxygen-containing functional groups controllably into the surface of spherical graphite through mixed acid oxidation treatment, transforming it from a relatively inert conductor into a chemically reactive substrate. Subsequently, a silane coupling agent is firmly grafted onto the graphite surface via covalent bonds, successfully introducing polymerizable double bonds. After dopamine pretreatment, the surface of the negative electrode active material forms a polydopamine network with strong adhesion and abundant functional groups. Under the action of an initiator, glycidyl methacrylate is activated, and its polymerization reaction not only occurs in solution but also preferentially begins and grows from the anchoring points on the graphite surface and around the polydopamine coating, forming a polymer network bound by covalent bonds and strong physical forces. As a buffer interface, its flexible properties provide a certain deformation space for the volume changes of the active material during charging and discharging, helping to alleviate the direct mechanical stress caused by the drastic volume expansion.

[0020] 2. The 3-aminophenylboronic acid introduced into the polymerization system in this invention reacts with the epoxy groups on the polymer chain, introducing phenylboronic acid groups into the composite material system. Under suitable pH conditions, the phenylboronic acid groups can form dynamically reversible borate ester bonds with ortho-hydroxyl groups and other groups in the system. When local stress is too high, some borate ester bonds can break to dissipate energy; when stress is released or conditions change, they can recombine, helping to maintain the integrity of the overall structure of the composite material and reducing crack accumulation and structural pulverization caused by repeated expansion and contraction during long-term cycling.

[0021] 3. The present invention reduces the direct and large-area contact between the negative electrode material and the electrolyte to a certain extent through a dense polymer-crosslinked network composite coating layer. This helps to suppress the continuous and excessive growth of the solid electrolyte interface film during cycling, reduce irreversible capacity loss in the first cycle, and form a stable connection between the graphite core and the active particles through chemical bonding. The electron transport pathway is better maintained during cycling, which helps to alleviate the capacity decay caused by the failure of electrical contact of the active material. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation process of the present invention; Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise range thresholds, and these range thresholds should be understood to include values ​​close to these range thresholds. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0024] In the following preparation examples and embodiments, spherical graphite (average particle size 20 μm, purity ≥99.9%, battery grade) was purchased from Shenzhen BTR New Energy Materials Co., Ltd.; elemental silicon nanoparticles (average particle size 50 nm, purity ≥99.9%) were purchased from Beijing Deco Shimadzu Technology Co., Ltd.; N-methylpyrrolidone (NMP, purity ≥99.9%, battery grade) was purchased from BASF (China) Co., Ltd.; vinyltrimethoxysilane (purity ≥98%) was purchased from Aladdin Reagent (Shanghai) Co., Ltd.; dopamine hydrochloride (purity ≥98%) and 3-aminophenylboronic acid (purity ≥98%) were purchased from... The following reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.: glycidyl methacrylate (GMA, purity ≥96%) and azobisisobutyronitrile (AIBN, purity ≥98%, analytical grade); Tris-HCl buffer (pH=8.0, 0.01M, biochemically pure), concentrated nitric acid (purity 65-68%, analytical grade), concentrated sulfuric acid (purity 95-98%, analytical grade), ammonia (analytical grade), and anhydrous ethanol (analytical grade).

[0025] The following describes in detail, with reference to the accompanying drawings, a method for preparing a composite of spherical graphite and a negative electrode material provided in the embodiments of this specification.

[0026] like Figure 1 The diagram shows a process for preparing a composite of spherical graphite and a negative electrode material. The specific operations are as follows.

[0027] Example 1 S1: Weigh 10 parts of spherical graphite (average particle size 20μm), place them in a flask, add concentrated nitric acid and concentrated sulfuric acid in a 1:1 volume ratio mixed acid, stir and oxidize at 60℃ for 2 hours, after the reaction is completed, cool and wash with deionized water until neutral, and dry in a vacuum oven at 80℃ for 12 hours.

[0028] The dried spherical graphite oxide was dispersed in N-methylpyrrolidone and placed in a three-necked flask equipped with a condenser and a magnetic stirrer. High-purity nitrogen was purged for 30 minutes to replace the air in the system, and the nitrogen atmosphere was maintained. Then, vinyltrimethoxysilane (at a mass ratio of 10:1) was slowly added dropwise using a constant-pressure dropping funnel. After the addition was complete, the system was heated to 80°C and stirred at this temperature for 3 hours. After the reaction was complete, an activated spherical graphite suspension was obtained.

[0029] S2: Weigh one part of elemental silicon nanoparticles with an average particle size of approximately 50 nm and disperse them in a Tris-HCl buffer solution with pH=8.0. Add 0.5 parts of dopamine hydrochloride, stir magnetically for 12 h at room temperature, and after the reaction is complete, centrifuge and wash three times each with deionized water and anhydrous ethanol. Dry under vacuum at 60 °C for 6 h to obtain polydopamine-coated silicon nanoparticles.

[0030] Polydopamine-coated silicon nanoparticles, 0.1 parts glycidyl methacrylate, and 0.05 parts azobisisobutyronitrile were added sequentially to the activated spherical graphite suspension prepared in S1. Under nitrogen protection, the reaction system was first stirred at 40°C for 1 hour, then the temperature was raised to 60°C and the reaction continued for 3 hours. During the reaction, the viscosity of the system gradually increased, resulting in a viscous primary composite system.

[0031] S3: Add 0.1 parts of 3-aminophenylboronic acid to the above primary composite system, adjust the pH of the system to 8 using dilute ammonia solution, then control the system temperature at 55℃ and continue stirring for 3 hours. After the reaction is complete, slowly add the reaction solution dropwise to a large amount of anhydrous ethanol, with a volume ratio of ethanol to reaction solution of approximately 10:1, while stirring. A dark flocculent precipitate is observed to form. After standing, discard the supernatant and collect the precipitate. Wash the precipitate three times each with anhydrous ethanol and deionized water to remove unreacted raw materials and byproducts. Finally, vacuum dry the washed product at 80℃ for 24 hours, grind it through a 400-mesh sieve, and obtain the final dark brown powdery composite negative electrode material.

[0032] The negative electrode active material used in the examples is selected from elemental silicon with an average particle size of 50 nm.

[0033] Example 2 S1: Weigh 10 parts of spherical graphite (average particle size 20μm), place them in a flask, add concentrated nitric acid and concentrated sulfuric acid in a mixed acid with a volume ratio of 1:3, stir and oxidize at 90℃ for 2-6 hours, after the reaction is completed, cool and wash with deionized water until neutral, and dry in a vacuum oven at 80℃ for 12 hours.

[0034] The dried spherical graphite oxide was dispersed in N-methylpyrrolidone and placed in a three-necked flask equipped with a condenser and a magnetic stirrer. High-purity nitrogen was introduced for 30 minutes to displace the air in the system, and the nitrogen atmosphere was maintained. Subsequently, vinyltrimethoxysilane (at a mass ratio of 10:1) was slowly added dropwise using a constant-pressure dropping funnel. After the addition was complete, the system was heated to 80°C and stirred at this temperature for 3 hours. After the reaction was complete, an activated spherical graphite suspension was obtained.

[0035] S2: Weigh 8 portions of elemental silicon nanoparticles with an average particle size of approximately 50-200 nm and disperse them in a Tris-HCl buffer solution with pH=8.5. Add 0.5 portions of dopamine hydrochloride, and stir magnetically for 24 h at room temperature. After the reaction is complete, centrifuge and wash three times each with deionized water and anhydrous ethanol. Dry under vacuum at 60 °C for 6 h to obtain polydopamine-coated silicon nanoparticles.

[0036] Polydopamine-coated silicon nanoparticles, 2.5 parts glycidyl methacrylate, and 0.3 parts azobisisobutyronitrile were added sequentially to the activated spherical graphite suspension prepared in S1. Under nitrogen protection, the reaction system was first stirred at 50°C for 2 hours, then the temperature was raised to 70°C and the reaction continued for 6 hours. During the reaction, the viscosity of the system gradually increased, resulting in a viscous primary composite system.

[0037] S3: Add 2 parts of 3-aminophenylboronic acid to the above primary composite system, adjust the pH of the system to 9 using dilute ammonia solution, then control the system temperature at 70℃ and continue stirring for 6 hours. After the reaction is complete, slowly add the reaction solution dropwise to a large amount of anhydrous ethanol, with a volume ratio of ethanol to reaction solution of approximately 10:1, while stirring. A dark flocculent precipitate is observed to form. After standing, discard the supernatant and collect the precipitate. Wash the precipitate three times each with anhydrous ethanol and deionized water to remove unreacted raw materials and byproducts. Finally, vacuum dry the washed product at 80℃ for 24 hours, grind it through a 400-mesh sieve, and obtain the final dark brown powdery composite negative electrode material.

[0038] The negative electrode active material used in the examples is selected from elemental silicon, with an average particle size of 200 nm.

[0039] Example 3 S1: Weigh 10 parts of spherical graphite (average particle size 20μm), place them in a flask, add concentrated nitric acid and concentrated sulfuric acid in a mixed acid with a volume ratio of 1:2, stir and oxidize at 60-90℃ for 4 hours, after the reaction is completed, cool and wash with deionized water until neutral, and dry in a vacuum oven at 80℃ for 12 hours.

[0040] The dried spherical graphite oxide was dispersed in N-methylpyrrolidone and placed in a three-necked flask equipped with a condenser and a magnetic stirrer. High-purity nitrogen was introduced for 30 minutes to displace the air in the system, and the nitrogen atmosphere was maintained. Subsequently, vinyltrimethoxysilane (at a mass ratio of 10:1) was slowly added dropwise using a constant-pressure dropping funnel. After the addition was complete, the system was heated to 80°C and stirred at this temperature for 3 hours. After the reaction was complete, an activated spherical graphite suspension was obtained.

[0041] S2: Weigh 4 portions of elemental silicon nanoparticles with an average particle size of approximately 125 nm and disperse them in a Tris-HCl buffer solution with a pH of 8.0-8.5. Add 0.5 portions of dopamine hydrochloride and stir magnetically for 18 h at room temperature. After the reaction is complete, centrifuge and wash three times each with deionized water and anhydrous ethanol. Dry under vacuum at 60 °C for 6 h to obtain polydopamine-coated silicon nanoparticles.

[0042] Polydopamine-coated silicon nanoparticles, 1.2 parts glycidyl methacrylate, and 0.15 parts azobisisobutyronitrile were added sequentially to the activated spherical graphite suspension prepared in S1. Under nitrogen protection, the reaction system was first stirred at 40-50℃ for 1-2 hours, then the temperature was raised to 65℃ and the reaction continued for 4.5 hours. During the reaction, the viscosity of the system gradually increased, resulting in a viscous primary composite system.

[0043] S3: Add 1 part of 3-aminophenylboronic acid to the above primary composite system, and adjust the pH of the system to 8.5 using a dilute ammonia solution. Then, maintain the system temperature at 65℃ and continue stirring for 4.5 hours. After the reaction is complete, slowly add the reaction solution dropwise to a large amount of anhydrous ethanol, with a volume ratio of ethanol to reaction solution of approximately 10:1, while stirring. A dark flocculent precipitate is observed to form. After standing, discard the supernatant and collect the precipitate. Wash the precipitate three times each with anhydrous ethanol and deionized water to remove unreacted raw materials and byproducts. Finally, vacuum dry the washed product at 80℃ for 24 hours, grind it through a 400-mesh sieve, and obtain the final dark brown powdery composite anode material.

[0044] The negative electrode active material used in the examples is selected from elemental tin, with an average particle size of 100 nm.

[0045] Comparative Example 1 Without performing the oxidation and silane coupling activation in step S1, the untreated spherical graphite was directly dispersed in 200 mL of NMP, and the remaining steps were exactly the same as in Example 1.

[0046] Comparative Example 2 Without performing the boric acid crosslinking reaction in step S3, without adding 3-aminophenylboronic acid and adjusting the pH, the primary composite system obtained in step S2 was directly subjected to ethanol precipitation, washing and drying to obtain the comparative material. The remaining steps were exactly the same as in Example 1.

[0047] Comparative Example 3 Spherical graphite and pretreated silicon nanoparticles were simply physically mixed. 5.0 g of the PDA-coated silicon nanoparticles prepared in Example 1 and 5.0 g of untreated raw spherical graphite were weighed and placed in a ball mill jar. An appropriate amount of anhydrous ethanol was added as a dispersion medium, and the mixture was ball-milled at 300 rpm for 6 hours. Subsequently, the mixture was dried at 80°C, ground, and sieved to obtain the physically mixed comparative material.

[0048] Comparative Example 4 The pretreatment step of the negative electrode active material is omitted, and it is directly mixed with the activated spherical graphite suspension for polymerization reaction. The remaining steps are the same as in Example 1.

[0049] Comparative Example 5 After the polymerization reaction was completed, 3-aminophenylboronic acid was not added for crosslinking reaction. The primary composite system was directly precipitated with ethanol, washed and dried. The remaining steps were the same as in Example 1.

[0050] The composite negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-5, the conductive agent (Super P), and the binder (CMC / SBR) were mixed at a mass ratio of 8:1:1, using deionized water as a solvent, and stirred in a vacuum mixer for 4 hours to form a uniform slurry. The slurry was then uniformly coated onto copper foil using a coating machine, with a wet film thickness of 150 μm. The coated foil was then initially dried in an 80°C forced-air oven for 2 hours, followed by drying in a 120°C vacuum oven for 12 hours to completely remove moisture. The dried electrode sheet was pressed to a compaction density of approximately 1.0 g / cm³ using a roller mill. It was then punched into 12 mm diameter discs using a punching machine to serve as the working electrode. CR2032 button cells were assembled in an argon-atmosphere glove box. The cell configuration consisted of the prepared negative electrode sheet, a Celgard 2400 separator lithium metal sheet (counter electrode / reference electrode). The electrolyte used was 1.0 M LiPF6 in EC / DEC (1:1 vol%) with 10% FEC.

[0051] 1. Electrochemical Performance Testing: All batteries were tested under a constant temperature environment of 25℃. Charge and discharge were performed at a rate of 0.1C (1C = 1600 mA / g), with a voltage range of 0.01-1.5V vs. Li⁺ / Li. The initial discharge specific capacity and initial coulombic efficiency were recorded. After the first cycle, constant current charge-discharge cycling tests were performed at a rate of 0.5C. The discharge capacity at the 100th and 200th cycles was recorded, and the capacity retention rate relative to the discharge capacity of the second cycle was calculated. After two cycles of activation at 0.1C, the batteries were cycled for 5 cycles each at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C, and finally returned to 0.1C for 5 cycles. The stable discharge specific capacity at each rate was recorded (usually the capacity of the last cycle at that rate), and the capacity recovery rate after returning from 5C to 0.1C was calculated. The results are shown in Table 1-2. Table 1. Partial Constant Current Charge-Discharge Test Results Table 2. Partial Constant Current Charge-Discharge Test Results As shown in Figure 1, the initial discharge specific capacity of Examples 1-3 is between 1575-1590 mAh / g, and the initial coulombic efficiency is between 86.8-87.5%. This indicates that the examples prepared composite anode materials with high initial discharge specific capacity and coulombic efficiency.

[0052] Comparative Example 1, without the oxidation and silane coupling activation in step S1, showed a significant decrease in initial discharge specific capacity to 1335 mAh / g and an initial coulombic efficiency to 81.5%. This is because oxidation and silane coupling activation increase the surface active sites of spherical graphite, enhancing its binding ability with the negative electrode active material and thus improving the material's electrochemical performance. Without these treatments, the material's structure is unfavorable for lithium-ion insertion and extraction, leading to a decrease in capacity and efficiency.

[0053] Comparative Example 2, which omits the boric acid crosslinking reaction in step S3, exhibits lower initial discharge specific capacity and coulombic efficiency compared to Examples 1-3. The boric acid crosslinking reaction enhances the chemical bonding between components in the composite material, improving its structural stability and facilitating lithium-ion transport and storage. The absence of this step results in decreased structural stability and negatively impacts initial charge-discharge performance.

[0054] Comparative Example 3 involved simple physical mixing of spherical graphite and pretreated silicon nanoparticles, resulting in the lowest initial discharge specific capacity and the lowest initial coulombic efficiency. Physical mixing fails to establish effective chemical bonds between the components, leading to an inhomogeneous material structure and problems such as inconsistent volume changes during charge and discharge, resulting in a significant decrease in capacity and efficiency.

[0055] Comparative Example 4 omitted the pretreatment step for the negative electrode active material, resulting in lower initial discharge specific capacity and coulombic efficiency compared to the Example. Pretreatment can improve the surface properties of the negative electrode active material, enhance its compatibility and binding ability with the polymer, and facilitate the formation of a stable composite structure. Without pretreatment, the material properties are affected.

[0056] Comparative Example 5, which did not include 3-aminophenylboronic acid for crosslinking after the polymerization reaction, also exhibited lower performance than the Example. Similar to Comparative Example 2, the lack of a crosslinking step resulted in insufficient structural stability of the material, affecting its initial charge-discharge performance.

[0057] The capacity retention rates of Examples 1-3 were between 89.2% and 89.8% after 100 cycles and between 81.8% and 82.6% after 200 cycles, demonstrating good cycle stability. This is because the composite material formed through multi-step processing has a stable structure, effectively buffering volume changes during charge and discharge, reducing electrode material pulverization and shedding, thereby maintaining a high capacity.

[0058] The cycle capacity retention rates of Comparative Examples 1-5 were significantly lower than those of the Example. Comparative Example 1 lacked oxidation and silane coupling activation, resulting in a material structure unfavorable for buffering lithium-ion transport and volume changes. Comparative Examples 2 and 5 lacked cross-linking reactions, leading to poor material structural stability. Comparative Example 3's physical mixing resulted in structural inhomogeneity. Comparative Example 4's anode active material was not pretreated, resulting in weak bonding with the polymer. These factors all contributed to the rapid degradation of material performance and reduced capacity retention during cycling.

[0059] As shown in Table 2, Examples 1-3 all exhibited high discharge specific capacity at 0.1C, 1C, and 5C rates, and the capacity decrease was relatively gradual with increasing rate. For example, Example 1 had a capacity of 1588 mAh / g at 0.1C, 1125 mAh / g at 1C, and 940 mAh / g at 5C. This indicates that the composite material has good rate performance and can adapt to charge and discharge requirements at different rates.

[0060] The discharge specific capacity of Comparative Examples 1-5 at different discharge rates was lower than that of the Examples, and the capacity decrease was more pronounced with increasing discharge rate. For example, Comparative Example 1 had a capacity of 1330 mAh / g at 0.1C, which dropped to 795 mAh / g at 1C, and only 695 mAh / g at 5C. This is because the materials in these comparative examples have structural defects, such as a lack of effective chemical bonding and structural instability, which hinders lithium-ion transport and prevents rapid insertion and extraction reactions at high discharge rates, thus resulting in a significant decrease in capacity.

[0061] The capacity recovery rates of Examples 1-3 were between 95.8% and 96.3%, indicating that the material can recover its capacity well to that at low rates after high-rate charge-discharge, demonstrating good reversibility. This further proves the stability of the material structure and its good lithium-ion transport performance.

[0062] The capacity recovery rates of Comparative Examples 1-5 were all lower than those of the Example, ranging from 72.0% to 87.8%. This indicates that the materials in these comparative examples underwent irreversible structural changes or side reactions during high-rate charge-discharge processes, resulting in significant capacity loss and poor reversibility.

[0063] In summary, the preparation process described in the embodiments can form a composite anode material with stable structure and good chemical bonding between components, which is beneficial for the rapid insertion and extraction of lithium ions, can effectively buffer volume changes during charge and discharge, reduce pulverization and shedding of electrode materials, thereby improving the initial charge and discharge performance, cycle stability and rate performance of the material.

[0064] In the description of this specification, the reference to terms such as "embodiment," "various embodiments," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or preparation example is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite of spherical graphite and a negative electrode material, characterized in that, Includes the following steps: S1. Spherical graphite is placed in a mixed acid of concentrated nitric acid and concentrated sulfuric acid for oxidation treatment. After washing and drying, spherical graphite with surface oxidation is obtained. The spherical graphite with surface oxidation is dispersed in a first organic solvent. A silane coupling agent is added under an inert atmosphere to react and obtain an activated spherical graphite suspension. S2. Add pretreated negative electrode active material, glycidyl methacrylate and initiator to activated spherical graphite suspension to carry out polymerization reaction to obtain primary composite system; S3. Add 3-aminophenylboronic acid to the primary composite system, adjust the pH of the system, control the temperature for reaction, and after the reaction is completed, separate, wash and dry to obtain the composite anode material.

2. The preparation method according to claim 1, characterized in that, In step S1, the volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed acid is 1:(1-3), the oxidation treatment temperature is 60-90℃, the time is 2-6h, the silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane, the reaction temperature is 70-85℃, and the reaction time is 1-4h.

3. The preparation method according to claim 1, characterized in that, The pretreatment of the negative electrode active material in step S2 specifically includes: dispersing the negative electrode active material in a buffer solution with a pH of 8.0-8.5, adding dopamine hydrochloride, stirring at room temperature for 12-24 hours, and obtaining the pretreated negative electrode material after centrifugation, washing, and drying.

4. The preparation method according to claim 3, characterized in that, The negative electrode active material in step S2 is selected from one of elemental silicon, silicon oxide, silicon alloy, elemental tin, tin oxide, or tin alloy, and its average particle size is 50-200 nm.

5. The preparation method according to claim 1, characterized in that, The conditions for the free radical polymerization reaction in step S2 include: reacting at 40-50℃ for 1-2 hours, and then raising the temperature to 60-70℃ to continue the reaction for 3-6 hours.

6. The preparation method according to claim 1, characterized in that, The first organic solvent in step S1 is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide.

7. The preparation method according to claim 1, characterized in that, In step S3, the pH of the system is adjusted to 8-9, the target temperature for the temperature-controlled reaction is 55-70℃, and the total reaction time is 3-6 hours.

8. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of spherical graphite to silane coupling agent is 10:(0.5-1.5).

9. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of the amount of pretreated negative electrode material, glycidyl methacrylate, and initiator added relative to spherical graphite is 10:(1-8):(0.1-2.5):(0.05-0.3); the initiator is azobisisobutyronitrile.

10. The preparation method according to claim 1, characterized in that, In step S3, the ratio of 3-aminophenylboronic acid added to spherical graphite is 10:(0.1-2).

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