Lithium ion battery artificial graphite negative material, preparation method thereof and lithium ion solid-state battery

Abstract

The application discloses a kind of lithium ion battery artificial graphite negative material and its preparation method and lithium ion solid battery, belong to lithium ion solid battery technical field, comprising: the pretreatment of carbon source material;Under inert atmosphere, the flash evaporation joule heating of pretreated carbon source material is carried out, then it is rapidly cooled, and the graphitization intermediate is obtained, and the screening, washing and drying of graphitization intermediate are carried out;Under ice bath condition, graphitization intermediate is mixed with strong acid and reacts, and graphitization intermediate is oxidized and expanded, and the expanded graphite is obtained;Expanded graphite is mixed with mercaptan acetic acid, ethyl acetate is mixed, catalyst is added, and after a certain time, lithium ion battery artificial graphite negative material is obtained.The application introduces flash evaporation joule pulse graphitization technology, sulfur-oxygen bifunctional synergistic modification and structure-performance integrated design, and systematically solves the three major technical bottlenecks of traditional artificial graphite negative material: rate performance is limited, interface stability is poor and volume expansion is significant.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion solid-state batteries, and more particularly, the present application relates to a lithium ion battery artificial graphite negative material, a preparation method thereof and a lithium ion solid-state battery. BACKGROUND

[0002] Lithium ion batteries have become the core energy storage devices in the fields of portable electronic devices and electric vehicles due to their high energy density, long cycle life and environmental friendly characteristics. As one of the key elements that determine the performance of the battery, artificial graphite occupies a dominant position due to its excellent physical and chemical stability and cycle performance. However, the existing artificial graphite negative material still faces three major technical bottlenecks: limited rate performance: limited by the slow diffusion kinetics of lithium ions (diffusion coefficient of about 10 -10 ~10 - 12 cm 2 / s), it is difficult to meet the demand of high power charging and discharging; insufficient interface compatibility: frequent chemical / electrochemical side reactions with sulfide electrolyte, leading to poor stability of solid electrolyte interface (SEI) film, causing capacity decay and safety hazards; significant volume expansion: during the lithium ion intercalation / deintercalation process, the volume change rate of graphite interlayer can reach 10%~13%, which easily causes electrode structure pulverization and mechanical failure.

[0003] To solve the above problems, the existing technology mainly optimizes through two strategies of chemical functionalization modification and structure regulation. For example: patent CN116062745A adopts a natural / artificial graphite composite strategy to improve the rate performance by polymerizing needle-shaped coke and spherical graphite, but the granulation process efficiency and particle uniformity are insufficient, resulting in poor batch stability of the material; patent CN114940495A reduces the resistance by densification treatment of the coating agent, but excessive densification inhibits the transmission of lithium ions, and the process parameters need to be repeatedly optimized to balance the conductivity and ion mobility.

[0004] The common limitations of current modification technologies are: single functional orientation: such as only introducing oxygen-containing functional groups (hydroxyl, epoxy, etc.) to widen the interlayer spacing, or relying on thiol groups to enhance the interface adhesion, which is difficult to simultaneously improve ion diffusion and interface stability; high process complexity, multi-step carbonization, coating and doping processes lead to a sharp increase in energy consumption and cost; performance compromise effect: although the micro-expansion effect alleviates the volume expansion, it may sacrifice the tap density and energy density of the material. SUMMARY

[0005] An object of the present application is to solve at least the above problems and / or deficiencies, and to provide at least the advantages described later.

[0006] To achieve these objects and other advantages and in accordance with the purpose of the application, as embodied and broadly described herein, the application provides a method for preparing a lithium-ion battery artificial graphite negative electrode material, comprising the following steps:

[0007] Step A, pretreating the carbon source material;

[0008] Step B, flash Joule heating the pretreated carbon source material under an inert atmosphere, followed by rapid cooling to obtain a graphitized intermediate, and then performing screening, washing, and drying treatment on the graphitized intermediate;

[0009] Step C, mixing and reacting the graphitized intermediate with a strong acid under ice bath conditions, and then obtaining expanded graphite through oxidation and expansion of the graphitized intermediate;

[0010] Step D, mixing the expanded graphite with mercaptoacetic acid and ethyl acetate, adding a catalyst, and then obtaining the lithium-ion battery artificial graphite negative electrode material after a certain period of reaction, wherein the reaction process of using mercaptoacetic acid to modify the expanded graphite in this step is as follows:

[0011] Graphite-O-Graphite+HS-CH2-COOH→Graphite-S-CH2-COOH+Graphite-OH

[0012] Graphite-OH+HS-CH2-COOH→Graphite-O-CO-CH2-SH;

[0013] Under the catalysis of the catalyst, the mercapto group (-SH) in the mercaptoacetic acid molecule acts as a nucleophile to attack active groups (such as hydroxyl groups and carboxyl groups) on the surface of the expanded graphite, and the mercapto group (-SH) of the mercaptoacetic acid molecule and the epoxy group (Graphite-O-Graphite) on the surface of the graphite undergo nucleophilic ring-opening reaction to generate a sulfide bond (C-S-C).

[0014] During the reaction, the carboxyl group of the mercaptoacetic acid may further react with other groups on the surface of the graphite to form a more stable ester bond (-O-CO-).

[0015] Preferably, in the step A, the method for pretreating the carbon source material specifically comprises: grinding the carbon source material into a powder with a D50 particle size controlled within the range of 4-15 μm; heating to 1000-1200 °C under an inert gas atmosphere, and maintaining the temperature for 4-6 h to remove impurities and improve the purity and reactivity of the carbon source material.

[0016] Preferably, in the step A, the grinding method specifically comprises: using high-energy ball milling to crush the carbon source material to a D50=4-8 μm, with a ball-to-material ratio of 10:1, a ball milling speed of 300-600 rpm, and a ball milling time of 2-6 h.

[0017] Preferably, in the step A, the carbon source material comprises one or more of petroleum coke, needle coke, pitch.

[0018] Preferably, in the step B, argon is used as the inert atmosphere, 5vol% hydrogen is added to the argon, and the purpose of adding hydrogen is to reduce the surface oxygen defects of the carbon source material and reduce the grain boundary resistance (<0.1Ω·cm).

[0019] The pre-processed carbon source material is subjected to flash Joule heating using a bipolar pulse current, the peak current of the bipolar pulse current is ≥8500A, the pulse width is 1~100ms, and the frequency is 1~100kHz; the temperature of the flash Joule heating is 2800~3200℃, and the holding time is 2~5min.

[0020] The rapid cooling method comprises one of liquid nitrogen jet quenching, supercritical CO2 cooling, forced air cooling, and radiation cooling; wherein the cooling rate of the liquid nitrogen jet quenching is >1000℃ / s; the graphite intermediate structure La is >100nm, and / or Lc is >50nm, and / or the lattice defect density is <0.3%.

[0021] The screening adopts a pneumatic sorting technology, and is sorted according to the particle size distribution D10=8μm, D50=10~14μm, and D90=15μm.

[0022] The drying adopts vacuum gradient drying, and the temperature is raised in stages, specifically, the temperature is raised to 50~60℃, and then held for 1~2h, then the temperature is raised to 100~120℃, and then held for 1~2h, and finally the temperature is raised to 160~200℃, and then held for 1~2h, and the dynamic vacuum is 10 -3 Pa, and the moisture content of the graphitized intermediate after drying is <0.1wt%.

[0023] Preferably, in the step C, the strong acid is one or more of nitric acid, concentrated sulfuric acid, perchloric acid, chromic acid, or chloric acid, the concentration of the nitric acid is 70~80%, and the mass ratio of the graphitized intermediate to the nitric acid is 1:5~10; the oxidation and expansion time is 5~20h.

[0024] Preferably, in the step D, the mass ratio of the expanded graphite, mercaptoacetic acid, and ethyl acetate is 1:10~20:3~10, and the amount of the catalyst is 0.1%~1% of the mass of the expanded graphite.

[0025] Preferably, in the step D, the expanded graphite is mixed with the mercaptoacetic acid, and the reaction temperature after adding the catalyst is 50~70℃, and the reaction time is 4~6h.

[0026] The catalyst is one or more of triethylamine, tributylamine, tripropylamine, or tetramethylammonium hydroxide.

[0027] A lithium ion battery artificial graphite negative electrode material prepared by the above-mentioned method for preparing a lithium ion battery artificial graphite negative electrode material.

[0028] A lithium ion solid-state battery, the negative electrode material of which is the above-mentioned lithium ion battery artificial graphite negative electrode material.

[0029] The present application at least includes the following beneficial effects:

[0030] The present application solves the three technical bottlenecks of the traditional artificial graphite negative electrode material: rate performance, interface stability and volume expansion by introducing flash Joule pulse graphitization technology, sulfur-oxygen bifunctional synergistic modification and structure-performance integrated design. Specifically, the present application completes efficient low-defect graphitization treatment within 2-5 min, the energy consumption is reduced to below 8 kWh / kg, the lithium ion diffusion coefficient is increased to 10 -9 cm 2 / s, and the high-rate charge and discharge capacity of the battery is significantly improved.

[0031] The thiol group forms a coordination bond with the metal center. During the sulfur-oxygen bifunctional modification process, the thiol group (-SH) in thiol acetic acid can form a stable coordination bond with metal ions (such as Li + , etc.) in the sulfide electrolyte. This chemical interaction greatly enhances the adhesion between the graphite surface and the electrolyte, making the electrode surface more stable and effectively preventing adverse reactions between the electrolyte and the electrode material, reducing the generation of by-products.

[0032] Moreover, the presence of the thiol group also plays a key role in stabilizing the solid electrolyte interface (SEI) film. The SEI layer is a very important component in lithium ion batteries, as it not only affects the first coulombic efficiency of the battery, but also directly determines the cycle life and safety of the battery. The thiol group can optimize the composition and structure of the SEI layer through interaction with electrolyte molecules, making it more uniform and dense, thereby improving its mechanical strength and chemical stability. Experimental data show that the capacity retention rate can still reach ≥92% after 1000 charge and discharge cycles, indicating that this method significantly improves the long-cycle stability of the battery.

[0033] In addition, the introduction of oxygen-containing functional groups can produce a small but controllable expansion between the graphite layers, which helps to alleviate the stress generated during lithium intercalation and reduce the damage to the electrode structure caused by volume change. At the same time, this also promotes the rapid transport of electrons and ions within the electrode, and the structural optimization reduces the volume expansion rate to ≤5%, ensuring high energy density and long cycle life. In addition, the green and efficient preparation process realizes the recycling of waste acid, reduces production costs and meets ESG standards, providing an innovative negative electrode solution for the next generation of high-performance lithium ion batteries.

[0034] Other advantages, objects, and features of the application will be apparent from the following specification and appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Figure 1 is a graph showing the rate performance of a lithium ion battery artificial graphite negative electrode material prepared in accordance with Example 1 of the present application;

[0036] Figure 2 Figure 2 is an SEM image of a lithium ion battery artificial graphite negative electrode material prepared in accordance with Example 1 of the present application. DETAILED DESCRIPTION

[0037] The present application will be further described with reference to the drawings, in which those skilled in the art will be able to implement the application according to the description as set forth herein.

[0038] It should be understood that the terms such as "have", "contain", and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0039] Example 1:

[0040] A method for preparing a lithium ion battery artificial graphite negative electrode material, comprising the following steps:

[0041] Step A, petroleum coke is selected as the carbon source, which is pulverized by high-energy ball milling (ball-to-material ratio of 10:1, rotation speed of 400 rpm, and time of 4 h) to D50=5 μm, and then heated to 1000 °C for 6 h for pretreatment.

[0042] Step B, under an argon atmosphere, 5 vol% hydrogen is doped, a bipolar pulse current (peak current of the bipolar pulse current is 10 kA, pulse width is 50 ms, and frequency is 10 Hz) is applied, the temperature of the carbon source is raised to 3000 °C, and the pretreated carbon source is subjected to flash Joule heating for 3 minutes to obtain a graphitized intermediate;

[0043] Subsequently, the graphitized intermediate is rapidly cooled (cooling rate >1000 °C / s) by a liquid nitrogen spraying quenching method, and the obtained graphitized intermediate has a lattice defect density <0.3%. After pneumatic sorting, the graphitized intermediate with D10=8 μm, D50=12 μm, and D90=15 μm is obtained;

[0044] After washing, the graphitized intermediate is first heated to 60 °C, and then kept at 60 °C for 2 h, and then heated to 120 °C, and kept at 120 °C for 1 h, and finally heated to 180 °C, and kept at 180 °C for 1 h for vacuum gradient drying under a dynamic vacuum degree of 10 -3 Pa, so as to reduce the moisture content of the graphitized intermediate to below 0.1 wt%.

[0045] Step C: Under ice bath conditions, the graphitization intermediate is mixed with 70% nitric acid at a mass ratio of 1:7, reacted for 10 hours, washed until neutral, and then dried to obtain expanded graphite.

[0046] Step D: Expanded graphite, thioacetic acid, and ethyl acetate are mixed in a mass ratio of 1:15:5. Triethylamine is added at 0.5% of the mass of the expanded graphite. The mixture is reacted at 50°C for 6 hours and then vacuum dried to obtain the artificial graphite anode material for lithium-ion batteries. The SEM image of the artificial graphite anode material prepared in this embodiment is shown below. Figure 2 As shown, Figure 2 The SEM images show that the artificial graphite anode material prepared in this embodiment has uniform micron-sized particles (D50=12μm) and a rough surface structure. The surface unevenness and local coating features indicate that the sulfur-oxygen bifunctional modification effectively improves the lithium-ion intercalation active sites. Combined with the low lattice defect density (<0.3%) and physical bridging structure, it jointly ensures the high rate performance and cycle stability of the material.

[0047] Example 2:

[0048] A method for preparing an artificial graphite anode material for lithium-ion batteries includes the following steps:

[0049] Step A: Select needle coke as the carbon source, pulverize it to D50=4μm by high-energy ball milling (ball-to-material ratio 10:1, speed 400rpm, time 4h), and then heat it to 1000℃ for pretreatment for 6h.

[0050] Step B: In an argon atmosphere, 5 vol% hydrogen is added, and a bipolar pulsed current (the peak current of the bipolar pulsed current is 10 kA, the pulse width is 50 ms, and the frequency is 10 Hz) is applied to raise the carbon source temperature to 2800℃. The temperature is held for 5 minutes, and the pretreated carbon source is subjected to flash evaporation and Joule heating to obtain a graphitized intermediate.

[0051] Subsequently, the graphitized intermediate was rapidly cooled by liquid nitrogen jet quenching (cooling rate > 1000℃ / s), and the resulting graphitized intermediate had a lattice defect density of < 0.3%; after pneumatic sorting, graphitized intermediates with D10 = 8μm, D50 = 10μm, and D90 = 15μm were obtained.

[0052] After washing, under a dynamic vacuum of 10 -3 Under Pa conditions, the graphitized intermediate was first heated to 60°C and held for 2 hours, then heated to 120°C and held for 1 hour, and finally heated to 180°C and held for 1 hour, and then vacuum gradient dried to reduce the moisture content of the graphitized intermediate to below 0.1 wt%.

[0053] Step C, under ice bath condition, mix the graphitized intermediate with 70% nitric acid according to mass ratio 1:5, react for 15h, wash to neutral and dry to obtain expanded graphite;

[0054] Step D, mix the expanded graphite, mercaptoacetic acid and ethyl acetate according to mass ratio 1:10:3.5, add 0.3% triethylamine based on the mass of expanded graphite, react for 6h at 50℃, and vacuum dry to obtain the artificial graphite negative electrode material for lithium ion battery.

[0055] Example 3:

[0056] A method for preparing an artificial graphite negative electrode material for lithium ion battery, comprising the following steps:

[0057] Step A, select pitch as carbon source, crush to D50=6μm by high-energy ball milling (ball-to-material ratio 10:1, rotation speed 400rpm, time 4h), and then heat to 1000℃ for pretreatment for 6h.

[0058] Step B, under argon atmosphere, add 5vol% hydrogen, apply bipolar pulse current (peak current of bipolar pulse current is 10kA, pulse width 50ms, frequency 10Hz), and raise the temperature of carbon source to 3200℃, keep for 2min, to perform flash Joule heating on the pretreated carbon source to obtain graphitized intermediate;

[0059] Subsequently, rapidly cool the graphitized intermediate by liquid nitrogen spraying method (cooling rate >1000℃ / s), and the obtained graphitized intermediate has lattice defect density <0.3%. After pneumatic sorting, the graphitized intermediate with D10=8μm, D50=14μm and D90=15μm is obtained;

[0060] After washing, under dynamic vacuum degree 10 -3 Pa, first raise the temperature of the graphitized intermediate to 60℃, keep for 2h, then raise the temperature to 120℃, keep for 1h, and finally raise the temperature to 180℃, keep for 1h, to perform vacuum gradient drying, and reduce the moisture of the graphitized intermediate to below 0.1wt%;

[0061] Step C, under ice bath condition, mix the graphitized intermediate with 70% nitric acid according to mass ratio 1:10, react for 20h, wash to neutral and dry to obtain expanded graphite;

[0062] Step D, mix the expanded graphite, mercaptoacetic acid and ethyl acetate according to mass ratio 1:20:7, add 1% triethylamine based on the mass of expanded graphite, react for 6h at 50℃, and vacuum dry to obtain the artificial graphite negative electrode material for lithium ion battery.

[0063] Example 4:

[0064] A preparation method of a lithium ion battery artificial graphite negative electrode material, comprising the following steps:

[0065] Step A, taking needle coke as a carbon source, crushing to D50=8 μm by high-energy ball milling (ball-to-material ratio 10:1, rotation speed 400 rpm, time 4 h), and then heating to 1000 ℃ for pretreatment for 6 h.

[0066] Step B, under an argon atmosphere, adding 5 vol% hydrogen, applying a bipolar pulse current (peak current of the bipolar pulse current is 10 kA, pulse width is 50 ms, and frequency is 10 Hz), increasing the temperature of the carbon source to 2900 ℃, and holding for 4 minutes to perform flash Joule heating on the pretreated carbon source to obtain a graphitized intermediate;

[0067] Then, the graphitized intermediate is rapidly cooled (cooling rate >1000 ℃ / s) by using a liquid nitrogen spraying quenching method, the obtained graphitized intermediate has a lattice defect density of 0.2%; and after pneumatic sorting, the graphitized intermediate has D10=8 μm, D50=13 μm, and D90=15 μm;

[0068] After washing, the graphitized intermediate is first heated to 60 ℃ under a dynamic vacuum degree of 10 -3 Pa, held for 2 h, then heated to 120 ℃, held for 1 h, finally heated to 180 ℃, held for 1 h, and vacuum gradient dried to reduce the moisture of the graphitized intermediate to below 0.1 wt%;

[0069] Step C, under ice bath conditions, the graphitized intermediate is mixed with 70% nitric acid at a mass ratio of 1:8, reacts for 8 h, washed to neutral, and dried to obtain expanded graphite;

[0070] Step D, the expanded graphite, mercaptoacetic acid and ethyl acetate are mixed at a mass ratio of 1:12:4, 0.8% of triethylamine based on the mass of the expanded graphite is added, and 50 ℃ is reacted for 6 h, and vacuum drying obtains a lithium ion battery artificial graphite negative electrode material.

[0071] Comparative Example 1:

[0072] A preparation method of a lithium ion battery artificial graphite negative electrode material, comprising the following steps:

[0073] Step A, taking needle coke as a carbon source, crushing to D50=8 μm by high-energy ball milling (ball-to-material ratio 10:1, rotation speed 400 rpm, time 4 h), and then heating to 1000 ℃ for pretreatment for 6 h.

[0074] Step B, under the atmosphere of argon with 5vol% hydrogen, the bipolar pulse current (peak current of 10kA, pulse width of 50ms, frequency of 10Hz) was applied to increase the temperature of the carbon source to 3200℃, and the pretreated carbon source was flash joule heated for 2 minutes to obtain the graphitized intermediate;

[0075] Subsequently, the graphitized intermediate was rapidly cooled (cooling rate >1000℃ / s) by liquid nitrogen spray quenching, and the obtained graphitized intermediate had a lattice defect density <0.3%. After pneumatic sorting, the graphitized intermediate with D10=8μm, D50=14μm, and D90=15μm was obtained;

[0076] After washing, the graphitized intermediate was first heated to 60℃ under a dynamic vacuum of 10 -3 Pa, and then vacuum gradient drying was performed by heating to 60℃ for 2h, heating to 120℃ for 1h, and finally heating to 180℃ for 1h to reduce the moisture content of the graphitized intermediate to below 0.1wt%;

[0077] Step C, under ice bath conditions, the graphitized intermediate was mixed with 70% nitric acid at a mass ratio of 1:10, and reacted for 20h. After washing to neutral, the expanded graphite was obtained by drying;

[0078] Step D, the expanded graphite, mercaptoacetic acid, and ethyl acetate were mixed at a mass ratio of 1:20:7, 1% of triethylamine based on the mass of the expanded graphite was added, and the mixture was reacted at 50℃ for 6h. Vacuum drying obtained the lithium ion battery artificial graphite negative electrode material.

[0079] Comparative Example 2:

[0080] A method for preparing a lithium ion battery artificial graphite negative electrode material, comprising the following steps:

[0081] Step A, select pitch as the carbon source, under the atmosphere of argon with 5vol% hydrogen, the bipolar pulse current (peak current of 5kA, pulse width of 50ms, frequency of 10Hz) was applied to increase the temperature of the carbon source to 2000℃, and the pretreated carbon source was flash joule heated for 2 minutes to obtain the graphitized intermediate;

[0082] Subsequently, the graphitized intermediate was rapidly cooled (cooling rate >1000℃ / s) by liquid nitrogen spray quenching, and the obtained graphitized intermediate had a lattice defect density <0.3%. After pneumatic sorting, the graphitized intermediate with D10=8μm, D50=14μm, and D90=15μm was obtained;

[0083] After washing, the graphitized intermediate was first heated to 60℃ under a dynamic vacuum of 10 -3The graphitization intermediate is first heated to 60°C under a pressure of 0.1 Pa, and then kept at 60°C for 2 hours, heated to 120°C for 1 hour, and finally heated to 180°C for 1 hour to perform vacuum gradient drying, so as to reduce the moisture content of the graphitization intermediate to less than 0.1 wt%.

[0084] Step B: The graphitization intermediate is mixed with 70% nitric acid at a mass ratio of 1:15 under ice bath conditions, and reacted for 20 hours. After washing to neutral, drying is performed to obtain expanded graphite.

[0085] Step C: The expanded graphite, mercaptoacetic acid and ethyl acetate are mixed at a mass ratio of 1:20:7, and 1% of triethylamine based on the mass of the expanded graphite is added. Reaction is performed at 50°C for 6 hours, and vacuum drying is performed to obtain a lithium ion battery artificial graphite negative electrode material.

[0086] Comparative Example 3:

[0087] A preparation method of a lithium ion battery artificial graphite negative electrode material, comprising the following steps:

[0088] Step A: Petroleum coke is selected as a carbon source, and is pulverized to D50=5 μm through high-energy ball milling (ball-to-material ratio of 10:1, rotation speed of 400 rpm, and time of 4 hours). Subsequently, the carbon source is heated to 1000°C for pretreatment for 6 hours.

[0089] Step B: Under an argon atmosphere, 5 vol% hydrogen is added, and a bipolar pulse current (peak current of the bipolar pulse current is 10 kA, pulse width is 50 ms, and frequency is 10 Hz) is applied to increase the temperature of the carbon source to 3000°C, and the pretreated carbon source is subjected to flash johar heating for 3 minutes to obtain a graphitization intermediate.

[0090] Subsequently, the graphitization intermediate is rapidly cooled (cooling rate >1000°C / s) by using a liquid nitrogen spraying quenching method. The obtained graphitization intermediate has a lattice defect density of <0.3%. After pneumatic sorting, the graphitization intermediate has D10=8 μm, D50=12 μm, and D90=15 μm.

[0091] After washing, the graphitization intermediate is dried under a dynamic vacuum degree of 10 -3 The graphitization intermediate is first heated to 60°C under a pressure of 0.1 Pa, and then kept at 60°C for 2 hours, heated to 120°C for 1 hour, and finally heated to 180°C for 1 hour to perform vacuum gradient drying, so as to reduce the moisture content of the graphitization intermediate to less than 0.1 wt%.

[0092] Step C: The graphitization intermediate is mixed with 70% nitric acid at a mass ratio of 1:7 under ice bath conditions, and reacted for 10 hours. After washing to neutral, drying is performed to obtain expanded graphite.

[0093] Step D: Mix expanded graphite, thioacetic acid, and ethyl acetate in a mass ratio of 1:5:1.6, add triethylamine at 0.5% of the mass of expanded graphite, react at 50°C for 2 hours, and then vacuum dry to obtain artificial graphite anode material for lithium-ion batteries.

[0094] Comparative Example 4

[0095] A method for preparing an artificial graphite anode material for lithium-ion batteries includes the following steps:

[0096] Step A: Select needle coke as the carbon source, pulverize it to D50=8μm by high-energy ball milling (ball-to-material ratio 10:1, speed 400rpm, time 4h), and then heat it to 1000℃ for pretreatment for 6h.

[0097] Step B: Heat the needle coke to 2500℃ and hold for 8 hours to obtain a graphitized intermediate;

[0098] Subsequently, the graphitized intermediate was rapidly cooled using liquid nitrogen jet quenching (cooling rate > 1000℃ / s), resulting in a lattice defect density > 1%. After pneumatic sorting, graphitized intermediates with D10 = 8μm, D50 = 12μm, and D90 = 15μm were obtained.

[0099] After washing, under a dynamic vacuum of 10 -3 Under Pa conditions, the graphitized intermediate was first heated to 60°C and held for 2 hours, then heated to 120°C and held for 1 hour, and finally heated to 180°C and held for 1 hour, and then vacuum gradient dried to reduce the moisture content of the graphitized intermediate to below 0.1 wt%.

[0100] Step C: Under ice bath conditions, the graphitization intermediate is mixed with 50% nitric acid at a mass ratio of 1:3, reacted for 8 hours, washed until neutral, and then dried to obtain expanded graphite.

[0101] The functionalized artificial graphite anode materials prepared in the above comparative examples and embodiments were subjected to the first coulombic efficiency and rate performance tests at different current densities.

[0102] The solid-state battery preparation method during testing was as follows: Functionalized negative electrode material, electrolyte LiP6S5Cl, and conductive agent were ball-milled together. Then, polyvinylidene chloride-hexafluoropropylene binder and N,N-dimethylacetamide solvent were added, and the mixture was coated onto copper foil to form an electrode sheet. After drying, the electrode sheet was cut into 10mm diameter discs, placed in a mold, and LiP6S5Cl electrolyte was added. The counter electrode was a Li-In alloy. The entire assembly was pressed at 450MPa to obtain the electrode sheet, which was then encapsulated to obtain a half-cell. The test pressure was 200MPa. The charge / discharge range was -0.61 to 1.5V. The first charge / discharge cycle was conducted at 0.05C. The test results are shown in Table 1 and... Figure 1shown.

[0103] Table 1 Performance data comparison of half-cell samples assembled from lithium-ion battery artificial graphite negative electrode materials

[0104]

[0105] Volume expansion rate test method: In-situ expansion tester, 0.05C constant current charge and discharge, voltage range -0.61 to 1.5V. Cycle 1000 times, use laser thickness gauge to measure the initial thickness (T0) of fresh electrode. Charge and discharge cycle under the above conditions, pause every 100 cycles, clean the electrode surface and measure the thickness (T n ). The volume expansion rate of the electrode is calculated as follows:

[0106]

[0107] Constant current intermittent titration technique (GITT): charge at 0.05C current for 10 minutes, stand for 2h until the voltage is stable. Record the voltage-time curve in the standing phase.

[0108] wherein the lithium ion diffusion rate is calculated as follows:

[0109]

[0110] wherein τ is the pulse time, Δ E s is the steady-state voltage change, Δ E t is the transient voltage change. Example 1 is the optimal scheme, and its core advantages are: high rate performance (3C capacity 320mAh / g, capacity retention rate 92%), flash johr graphitization technology (3000℃, 3min) significantly shortens the graphitization time, lattice defect density <0.3%, and improves the lithium ion diffusion rate (1.2×10 -9 cm² / s). Sulfur-oxygen dual-function synergistic modification (mass ratio of expanded graphite to mercaptoacetic acid 1:15) forms Li-S coordination bond with sulfide electrolyte through mercapto group (-SH), inhibits shuttle effect, reduces interface impedance by 40%, and stabilizes SEI film. Low volume expansion (volume expansion rate ≤5% after 1000 cycles):

[0111] Gradient particle size sorting (D50=12μm) and directional distribution of conductive agent, construct electron-ion double continuous transmission network, relieve interlayer stress during lithium intercalation. High efficiency and energy saving: pulse heating energy consumption is only 8kWh / kg, which is reduced by 100 times compared with traditional process. Comparative example 1 (traditional graphitization process), defects: without pulse heating, lattice defect density >1%, resulting in lithium ion diffusion coefficient (3.0×10-10 cm 2 / s) was only 25% of Example 1.

[0112] As shown, the specific capacity of Example 1 at 0.05C, 3C current density was significantly higher than that of Comparative Example 1. For example, under the condition of 3C high rate, the capacity retention of Example 1 was 320 mAh / g, while that of Comparative Example 1 was only 248 mAh / g. Figure 1

[0113] Results: The capacity retention (59%) and 3C capacity (248 mAh / g) of the artificial graphite negative electrode material prepared by Comparative Example 1 decreased significantly, and the volume expansion rate (12%) was much higher than that of Example 1, verifying the key role of pulse heating in defect control. Comparative Example 2 (carbon source without pretreatment), defects: directly using raw petroleum coke (particle size > 20 μm), uneven particles leading to blocked ion transmission path and increased interface impedance. Results: The first coulombic efficiency (85%) and 3C capacity (230 mAh / g) were extremely low, indicating that carbon source pretreatment (particle size control 4-15 μm) was the key to building a uniform structure. Comparative Example 3 (sulfur alcohol acetic acid ratio insufficient), defects: the mass ratio of expanded graphite to sulfur alcohol acetic acid was 1:5 (lower than the range of 1:10-20 of the mass ratio of expanded graphite to sulfur alcohol acetic acid), the reaction time was shortened to 2h, and the sulfur-oxygen synergistic modification was insufficient. Results: The SEI film stability was poor, and the capacity retention (57%) and ion diffusion coefficient (2.8×10 -10 cm 2 / s) were lower than those of Example 1-Example 4, highlighting the necessity of sulfur-oxygen dual functional modification.

[0114] In summary, the flash-jet impulse graphitization technology: through instantaneous high temperature (2800-3200℃) and rapid cooling (liquid nitrogen quenching), reduces the lattice defects (<0.3%), and improves the lithium ion diffusion rate, which is the core guarantee of high rate performance. Sulfur-oxygen dual functional synergistic modification: sulfur alcohol groups (-SH) anchor polysulfides, oxygen-containing functional groups induce interlayer micro-expansion (0.342-0.348 nm), and together optimize the interface stability and ion transmission efficiency. Structure-performance integrated design: particle size grading (4-15 μm) and directional distribution of conductive agent, realize the electronic-ion double continuous network, effectively inhibit the volume expansion (≤5%). Example 1-Example 4 integrates impulse graphitization, sulfur-oxygen modification and structure optimization, and systematically solves the three major bottlenecks (rate performance, interface stability, volume expansion) of traditional graphite negative electrode.

[0115] The number of devices and the scale of processing described herein are used to simplify the explanation of the present application. Applications, modifications and variations of the present application will be apparent to those skilled in the art.

[0116] ​While embodiments of the application have been disclosed in connection with the above specification and drawings this description is not intended to limit the scope of the application and many modifications, enhancements, alternatives, and variations will become apparent to those skilled in the art from this disclosure. Accordingly, it is intended that the application not be limited to the described embodiments, but that it include all variations falling within the scope of the claims, and their equivalents.

Claims

1. A method for preparing an artificial graphite anode material for lithium-ion batteries, characterized in that, Includes the following steps: Step A: Grind the carbon source material into powder, with the powder D50 particle size controlled within the range of 4~15μm; heat to 1000~1200℃ under an inert gas atmosphere and hold for 4~6h; Step B: Under an inert atmosphere, the pretreated carbon source material is subjected to flash Joule heating using a bipolar pulsed current. The peak current of the bipolar pulsed current is ≥8500A, the pulse width is 1~100ms, and the frequency is 1~100kHz. The temperature rise of the flash Joule heating is 2800~3200℃, the holding time is 2~5min, and then it is rapidly cooled to obtain a graphitized intermediate. The graphitized intermediate is then sieved, washed, and dried. Step C: Under ice bath conditions, the graphitization intermediate is mixed with a strong acid and reacted. The graphitization intermediate oxidizes and expands to obtain expanded graphite. Step D: Mix expanded graphite with thioacetic acid and ethyl acetate, add a catalyst, and react for a certain time to obtain artificial graphite anode material for lithium-ion batteries. In step C, the strong acid is one or more of nitric acid, concentrated sulfuric acid, perchloric acid, chromic acid, or chloric acid; the concentration of nitric acid is 70-80%; the mass ratio of graphitization intermediate to nitric acid is 1:5-10; and the oxidation expansion time is 5-20 hours. In step D, the mass ratio of expanded graphite, thioacetic acid, and ethyl acetate is 1:10~20:3~10, and the amount of catalyst used is 0.1%~1% of the mass of expanded graphite. In step D, expanded graphite is mixed with thioacetic acid, and the reaction temperature after adding the catalyst is 50~70℃, and the reaction time is 4~6h. The catalyst is one or more of triethylamine, tributylamine, tripropylamine, or tetramethylammonium hydroxide.

2. The method for preparing the artificial graphite anode material for lithium-ion batteries as described in claim 1, characterized in that, In step A, the grinding method specifically includes: using a high-energy ball mill to pulverize the carbon source material to D50=4~8μm, with a ball-to-material ratio of 10:1, a ball milling speed of 300~600rpm, and a ball milling time of 2~6h.

3. The method for preparing the artificial graphite anode material for lithium-ion batteries as described in claim 1, characterized in that, In step A, the carbon source material includes one or more of petroleum coke, needle coke, and pitch.

4. The method for preparing the artificial graphite anode material for lithium-ion batteries as described in claim 1, characterized in that, In step B, argon is used as an inert atmosphere, and 5 vol% hydrogen is added to the argon. The rapid cooling method includes one of liquid nitrogen jet quenching, supercritical CO2 cooling, forced air cooling, and radiation cooling; wherein the liquid nitrogen jet quenching cooling rate is >1000℃ / s; the graphitized intermediate structure has La>100nm, and / or Lc>50nm, and / or lattice defect density <0.3%; The sieving process uses pneumatic separation technology to separate particles according to their size distribution: D10=8μm, D50=10~14μm, and D90=15μm. The drying process employs a vacuum gradient drying method with staged temperature increases. Specifically, the temperature is raised to 50-60℃, held for 1-2 hours, then raised to 100-120℃, held for 1-2 hours, and finally raised to 160-200℃, held for 1-2 hours. The dynamic vacuum is 10... -3 Pa, the moisture content of the graphitized intermediate after drying is <0.1wt%.

5. A type of artificial graphite anode material for lithium-ion batteries, characterized in that, The artificial graphite anode material for lithium-ion batteries is prepared by the method for preparing artificial graphite anode materials for lithium-ion batteries according to any one of claims 1-4.

6. A lithium-ion solid-state battery, characterized in that, The negative electrode material of the lithium-ion solid-state battery is the artificial graphite negative electrode material of the lithium-ion battery as described in claim 5.

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