Lithium ion battery negative electrode material for start-stop power supply and preparation method of lithium ion battery negative electrode material

Abstract

The invention discloses a lithium ion battery negative electrode material for a start-stop power supply and a preparation method of the lithium ion battery negative electrode material, and belongs to the field of battery materials. The lithium ion battery negative electrode material for the start-stop power supply is formed by compounding artificial graphite secondary particles and hard carbon, the compounding mass ratio of the artificial graphite secondary particles to the hard carbon is (1-10): (10-1); the problems that an existing material is low in rate capability and high in cost are solved.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a lithium-ion battery anode material for start-stop power supplies and its preparation method. Background Technology

[0002] Currently, lead-acid batteries still have some use in traditional electric vehicles in certain specific applications (such as some start-stop systems and low-speed electric vehicles) due to their low cost, mature technology, and high current discharge capability. However, lead-acid batteries have drawbacks such as low energy density leading to short driving range, short cycle life requiring frequent replacements and increasing operating costs, high self-discharge rate resulting in significant power loss after long-term parking, poor low-temperature performance (especially in severe cold environments where capacity drops sharply and starting becomes difficult), and high environmental pollution risks. Therefore, seeking a better and more environmentally friendly alternative is imperative. Lithium-ion batteries, with their significant advantages such as high energy density, long cycle life, low self-discharge rate, and relative environmental friendliness, have become the mainstream choice to replace lead-acid batteries and are widely used in modern electric vehicles. However, its large-scale promotion still faces challenges: on the one hand, although the power output and capacity retention of traditional lithium-ion batteries based on graphite anodes are generally better than those of lead-acid batteries in low-temperature environments, there is still room for improvement in extreme low temperatures; on the other hand, and more importantly, high-rate charge and discharge capability is a traditional advantage of lead-acid batteries, while conventional graphite anode lithium-ion batteries are relatively inferior in this performance, making it difficult to meet certain application scenarios with instantaneous high power demands (such as cold start and rapid acceleration).

[0003] Currently, commercially available lithium-ion battery anode materials primarily use graphite, with artificial graphite being more widely used than natural graphite due to its more stable structure and consistent performance. The preparation of artificial graphite typically involves key processes such as crushing, shaping, and graphitization. The relatively small interlayer spacing (~0.335 nm) of the crystal structure of traditional graphite materials limits the rapid insertion and extraction kinetics of lithium ions during charging and discharging, especially under high-rate conditions, resulting in relatively poor rate performance and becoming a bottleneck for improving the fast charging and discharging capabilities of lithium-ion batteries. Hard carbon materials, due to their larger interlayer spacing and more disordered structure, provide faster and smoother diffusion channels for lithium ions, exhibiting excellent rate performance and outstanding low-temperature performance (low resistance to lithium-ion insertion / extraction). Therefore, hard carbon is considered one of the key anode materials for addressing the shortcomings in rate performance and low-temperature performance of lithium-ion batteries. In the production process of artificial graphite, the crushing / shaping process is a crucial step, aiming to obtain particles with specific sizes and morphologies to meet battery performance requirements. However, this process inevitably generates approximately 15-30% of fine powder or substandard morphology "tailings" from the total raw material output. These tailings, unable to be directly used to prepare high-performance graphite anodes, are typically treated as industrial waste for low-cost disposal or landfilling. This not only results in a severe waste of valuable carbon resources and increases production costs but also creates environmental pressure. Therefore, effectively improving the rate performance of lithium-ion battery anodes to compensate for their lower discharge current compared to lead-acid batteries, while simultaneously reducing the cost of high-rate / low-temperature anode materials and addressing the waste problem in artificial graphite production, is of significant technical and economic importance. Summary of the Invention

[0004] To alleviate or partially alleviate the above-mentioned technical problems, the solution of the present invention is as follows:

[0005] A lithium-ion battery negative electrode material for start-stop power supplies is composed of artificial graphite secondary particles and hard carbon composite.

[0006] The mass ratio of the compound is artificial graphite secondary particles: hard carbon = (1-10): (10-1).

[0007] Preferably, the artificial graphite secondary particles are obtained from the artificial graphite production tailings through granulation, pre-carbonization, and graphitization; the artificial graphite production tailings include at least one of petroleum coke, needle coke, and pitch coke.

[0008] Preferably, the median particle size D of the artificial graphite production tailings v 50 is 3-5μm; the mass fraction of volatile matter in the tailings of artificial graphite production is 6-12%, and the mass content of sulfur is 0.2-3%.

[0009] Preferably, the artificial graphite secondary particles also include asphalt, and the mixing mass ratio of artificial graphite production tailings and asphalt before granulation is 100:4.

[0010] Preferably, the asphalt softening point is 130-250ºC, the quinoline insoluble content is ≤1%, and the coking value is ≥70%.

[0011] This solution also provides a method for preparing the above-mentioned lithium-ion battery negative electrode material for start-stop power supplies, including the following steps:

[0012] S1. Preparation of secondary artificial graphite particles:

[0013] The tailings from artificial graphite production are granulated in a reactor, stirred with nitrogen gas, and the reactor is heated in two stages.

[0014] The granulated material undergoes pre-carbonization and graphitization treatment;

[0015] S2, Compounding: Mix the product from step S1 with hard carbon in a certain proportion, controlling the rotation speed at 50-100 rpm and the time at 10-30 min.

[0016] Preferably, the reaction vessel in step S1 is heated in two stages: the first stage heating rate is ≤10ºC / min, the maximum temperature is ≤450ºC, and the holding time is 1-3h; the second stage heating rate is ≤5ºC / min, the maximum temperature is ≤700ºC, and the holding time is 2-4h.

[0017] The stirring speed of the reactor is 15-30 rpm, and the nitrogen flow rate is controlled at 1-5 L / min.

[0018] Preferably, the median particle size D of the granulated material is... v 50 has a thickness of 6-9 μm and a tap density ≥0.50 g / cm³. 3 Specific surface area ≤8m² 2 / g, volatile matter ≤8%.

[0019] Preferably, the pre-carbonization temperature is 1000-1200ºC, and the heating rate is ≤10ºC / min;

[0020] Preferably, the median particle size D of the pre-carbonized semi-finished product is... v 50 has a thickness of 5-8 μm and a tap density ≥0.60 g / cm³. 3 Specific surface area ≤ 5m² 2 / g, volatile matter ≤1%.

[0021] Preferably, the graphitization is carried out in an Atchison graphitization furnace, with a power supply time of 45-60 hours, a maximum power of 27000kW, a constant power time of 10-20 hours, a cooling period of about 20-30 days, and a crucible temperature ≤200ºC.

[0022] Preferably, the median particle size D of the graphitized semi-finished product is... v 50 has a thickness of 5-7 μm and a tap density ≥0.80 g / cm³. 3 Specific surface area ≤3m² 2 / g, powder compaction (5T) ≥1.5g / cm 3 Graphitization degree ≥90%, irreversible specific capacity ≥335mAh / g, first coulombic efficiency ≥90%.

[0023] Preferably, after the graphitization treatment in step S1, a coating carbonization treatment is further included; the coating carbonization treatment step is as follows: adding coating pitch to the graphitization product; mixing and then carbonizing.

[0024] Preferably, the amount of coated bitumen added is 1-3% of the mass of the graphitized semi-finished product;

[0025] The softening point of the coated asphalt is 180-250ºC, the quinoline insoluble content is ≤1%, and the coking value is ≥60%.

[0026] The mixing process involves mixing the graphitized semi-finished product with the coated asphalt at a mixing speed of 100-200 rpm and a mixing time of 20-30 min.

[0027] The carbonization temperature is 1150-1200ºC, the heating rate is ≤10ºC / min, and the oxygen content is ≤1ppm.

[0028] Preferably, the median particle size D of the carbonized finished product is... v 50 has a thickness of 6-8 μm and a tap density ≥0.75 g / cm³. 3 Specific surface area ≤2m² 2 / g, powder compaction (5T) ≥1.5g / cm 3 Graphitization degree ≥90%, irreversible specific capacity ≥338mAh / g, first coulombic efficiency ≥91%.

[0029] The technical solution of this invention has one or more of the following beneficial technical effects:

[0030] By combining specific small-diameter secondary graphite particles prepared from the tailings of artificial graphite production with hard carbon materials, synergistic performance was achieved. The inherent wide interlayer spacing and open structure of hard carbon provide rapid lithium-ion diffusion channels, compensating for the shortcomings of traditional graphite anodes in ion diffusion kinetics under high-rate discharge (high current) and low-temperature environments; while the processed graphite tailings particles provide a stable lithium storage structure and conductive network. The combination of the two enables the composite anode material to maintain high energy density while significantly improving the battery's fast charge and discharge capability (rate performance) and capacity retention and power output at low temperatures, making it more suitable for scenarios with instantaneous high power demands such as start-stop power supplies.

[0031] This invention solves the long-standing problem of waste material (fine powder / material with substandard morphology) disposal in artificial graphite production. It transforms waste materials that could previously only be disposed of at low cost into functional components that can be directly used in the anodes of high-performance lithium-ion batteries. This not only achieves the recycling of valuable carbon resources, avoiding resource waste and environmental pressure from landfills, but also improves the economic efficiency and sustainability of the entire graphite production line, achieving the goals of "turning waste into treasure" and green manufacturing.

[0032] Furthermore, other beneficial effects of the present invention will be mentioned in the specific embodiments. Attached Figure Description

[0033] Figure 1 This is a SEM image of PCP in Embodiment 1 of the present invention;

[0034] Figure 2 This is a SEM image of the LHC in Embodiment 1 of the present invention;

[0035] Figure 3 This is a charge-discharge curve diagram of PCP and LHC in Embodiment 1 of the present invention;

[0036] Figure 4 This is a full-rate test chart of PCP, LHC, and A-PCP@A / LHC-55 in Embodiment 1 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] This solution first provides a lithium-ion battery negative electrode material for start-stop power supply, which is composed of artificial graphite secondary particles and hard carbon; the mass ratio of the composite is artificial graphite secondary particles: hard carbon = (1-10):(10-1). In the embodiment shown, the ratio of artificial graphite secondary particles to hard carbon is 3:7, 7:3, 5:5, or it can be 1:10, 10:1.

[0039] The secondary artificial graphite particles are obtained from artificial graphite production tailings through granulation, pre-carbonization, and graphitization. In the illustrated embodiment, the artificial graphite production tailings include petroleum coke, needle coke, or pitch coke. The median particle size D of the artificial graphite production tailings is... v 50 represents 3-5 μm; the median particle size D of the waste material from artificial graphite production. vThe volatile matter content in the waste material from the production of 50-type artificial graphite is 6-12% by mass, and the sulfur content is 0.2-3% by mass.

[0040] In some embodiments, the artificial graphite secondary particles also include asphalt, and the mass ratio of the artificial graphite production tailings before granulation to the asphalt is 100:4, the asphalt softening point is 130-250ºC, the quinoline insoluble matter is ≤1%, and the coking value is ≥70%.

[0041] The above-mentioned method for preparing the lithium-ion battery negative electrode material for start-stop power supplies includes the following steps:

[0042] S1. Preparation of secondary artificial graphite particles:

[0043] The tailings from artificial graphite production are granulated in a reactor under nitrogen aeration and stirring at a speed of 15-30 rpm and a nitrogen flow rate of 1-5 L / min. The reactor is heated in two stages: the first stage has a heating rate ≤10ºC / min, a maximum temperature ≤450ºC, and a holding time of 1-3 hours; the second stage has a heating rate ≤5ºC / min, a maximum temperature ≤700ºC, and a holding time of 2-4 hours. The median particle size D of the granulated material is... v 50 has a thickness of 6-9 μm and a tap density ≥0.50 g / cm³. 3 Specific surface area ≤8m² 2 / g, volatile matter ≤8%.

[0044] The granulated material undergoes pre-carbonization and graphitization treatment;

[0045] The pre-carbonization temperature is 1000-1200ºC, and the heating rate is ≤10ºC / min; the median particle size D of the semi-finished product after pre-carbonization v 50 has a thickness of 5-8 μm and a tap density ≥0.60 g / cm³. 3 Specific surface area ≤ 5m² 2 / g, volatile matter ≤1%.

[0046] Graphitization was performed using an Atchison graphitization furnace, with a power supply time of 45-60 hours, a maximum power of 27000 kW, a constant power time of 10-20 hours, and a cooling period of approximately 20-30 days. The crucible outlet temperature was ≤200ºC. The median particle size D of the semi-finished product after graphitization was... v 50 has a thickness of 5-7 μm and a tap density ≥0.80 g / cm³. 3 Specific surface area ≤3m² 2 / g, powder compaction (5T) ≥1.5g / cm 3 Graphitization degree ≥90%, irreversible specific capacity ≥335mAh / g, first coulombic efficiency ≥90%.

[0047] S2, Compounding: Mix the product from step S1 with hard carbon in a certain proportion, controlling the rotation speed at 50-100 rpm and the time at 10-30 min.

[0048] In some embodiments, step S1, after graphitization, further includes a coating carbonization process; the coating carbonization process comprises: adding coating pitch to the graphitized product; mixing the graphitized semi-finished product with the coating pitch at a mixing speed of 100-200 rpm for 20-30 min; carbonizing after mixing at a carbonization temperature of 1150-1200ºC, a heating rate ≤10ºC / min, and an oxygen content ≤1ppm; the amount of coating pitch added is 1-3% of the mass of the graphitized semi-finished product; the softening point of the coating pitch is 180-250ºC, the quinoline insoluble matter is ≤1%, and the coking value is ≥60%;

[0049] Median particle size D of the carbonized finished product v 50 has a thickness of 6-8 μm and a tap density ≥0.75 g / cm³. 3 Specific surface area ≤2m² 2 / g, powder compaction (5T) ≥1.5g / cm 3 Graphitization degree ≥90%, irreversible specific capacity ≥338mAh / g, first coulombic efficiency ≥91%.

[0050] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0051] Example 1

[0052] A method for preparing a negative electrode material for a start-stop power supply, comprising the following steps:

[0053] S1: First, take 20kg of the tailings (particle size D) produced from the crushed and shaped petroleum coke. vThe material (3.5 μm, sulfur content 0.4%, volatile matter 11.5%) was directly granulated without asphalt. The stirring frequency in the reactor was 30 rpm, the nitrogen flow rate was 2 L / min, and the temperature was increased from room temperature to 450°C at 6°C / min and held for 1 hour, then increased to 600°C at 3°C / min and held for 2 hours. After cooling, the material was placed in a silicon carbide crucible and heated to 1100°C at 10°C / min and held for 2 hours. After natural cooling, it was removed and placed in a graphite crucible in an Atchison graphitization furnace to complete graphitization. The power supply time was 50 hours, the maximum power was 26500kW, and the constant power time was 20 hours. Feeding began within 72 hours after power supply was completed, and the material was discharged when the crucible temperature reached 200°C. Finally, the finished product, denoted as PCP, was obtained after sieving.

[0054] S2: Take the PCP prepared in step S1 and mix it with commercially available hard carbon (LHC) at a mass ratio of 5:5. Mix at 100 rpm for 20 min. This mixture is denoted as A-PCP / LHC-55.

[0055] Example 2

[0056] A method for preparing a negative electrode material for a start-stop power supply, comprising the following steps:

[0057] S1: First, take 20kg of the tailings (particle size D) produced from the crushed and shaped petroleum coke. v The material (3.5 μm, sulfur content 0.4%, volatile matter 11.5%) was directly granulated without asphalt. The stirring frequency in the reactor was 30 rpm, the nitrogen flow rate was 2 L / min, and the temperature was increased from room temperature to 450°C at 6°C / min and held for 1 hour, then increased to 600°C at 3°C / min and held for 2 hours. After cooling, the material was placed in a silicon carbide crucible and heated to 1100°C at 10°C / min and held for 2 hours. After natural cooling, it was removed and placed in a graphite crucible in an Atchison graphitization furnace to complete graphitization. The power supply time was 50 hours, the maximum power was 26500kW, and the constant power time was 20 hours. Feeding began within 72 hours after power supply was completed, and the material was discharged when the crucible temperature reached 200°C. Next, add 2% asphalt (softening point 200ºC, coking value 60.8%, quinoline insolubles 0.10%) and mix at 200 rpm for 20 min. Then, increase the temperature to 1150ºC at 10ºC / min and keep it constant for 2 h. Finally, after sieving, the finished product is obtained and is denoted as PCP@A.

[0058] S2: Take the PCP prepared in step S1 and mix it with commercially available hard carbon at a mass ratio of 5:5. Mix at 100 rpm for 20 min and record as A-PCP@A / LHC-55.

[0059] Example 3

[0060] A method for preparing a negative electrode material for a start-stop power supply, comprising the following steps:

[0061] S1: First, take 20 kg of petroleum coke tailings (particle size Dv50 is 3.5 μm, sulfur content is 0.4%, volatile matter is 11.5%) after crushing and shaping. Do not mix with asphalt and directly granulate. The stirring frequency of the reactor is 30 rpm, the nitrogen flow rate is 2 L / min, the temperature is increased to 450ºC at room temperature at 6ºC / min and held for 1 h, and then increased to 600ºC at 3ºC / min and held for 2 h. After cooling, the material was placed in a silicon carbide crucible and heated to 1100ºC at 10ºC / min and held at that temperature for 2 hours. After natural cooling, it was removed and then placed in a graphite crucible in an Atchison graphitization furnace to complete graphitization. The power supply time was 50 hours, the maximum power was 26500kW, and the constant power time was 20 hours. After the power supply was completed, the material was started to be sucked up within 72 hours. The material was discharged when the crucible temperature reached 200ºC. Then, 2% pitch (softening point 200ºC, coking value 60.8%, quinoline insolubles 0.10%) was added and mixed at 200rpm for 20 minutes. The temperature was then increased to 1150ºC at 10ºC / min and held at that temperature for 2 hours. Finally, the finished product was obtained after sieving, which was denoted as PCP@A.

[0062] S2: Take the PCP prepared in step S1 and mix it with commercially available hard carbon at a mass ratio of 3:7. Mix at 100 rpm for 20 min and record as A-PCP@A / LHC-37.

[0063] Example 4

[0064] A method for preparing a negative electrode material for a start-stop power supply, comprising the following steps:

[0065] S1: First, take 20 kg of petroleum coke tailings (particle size Dv50 is 3.5 μm, sulfur content is 0.4%, volatile matter is 11.5%) after crushing and shaping. Do not mix with asphalt and directly granulate. The stirring frequency of the reactor is 30 rpm, the nitrogen flow rate is 2 L / min, the temperature is increased to 450ºC at room temperature at 6ºC / min and held for 1 h, and then increased to 600ºC at 3ºC / min and held for 2 h. After cooling, the material was placed in a silicon carbide crucible and heated to 1100ºC at 10ºC / min and held at that temperature for 2 hours. After natural cooling, it was removed and then placed in a graphite crucible in an Atchison graphitization furnace to complete graphitization. The power supply time was 50 hours, the maximum power was 26500kW, and the constant power time was 20 hours. After the power supply was completed, the material was started to be sucked up within 72 hours. The material was discharged when the crucible temperature reached 200ºC. Then, 2% pitch (softening point 200ºC, coking value 60.8%, quinoline insolubles 0.10%) was added and mixed at 200rpm for 20 minutes. The temperature was then increased to 1150ºC at 10ºC / min and held at that temperature for 2 hours. Finally, the finished product was obtained after sieving, which was denoted as PCP@A.

[0066] S2: Take the PCP prepared in step S1 and mix it with commercially available hard carbon at a mass ratio of 7:3. Mix at 100 rpm for 20 min and record as A-PCP@A / LHC-73.

[0067] Example 5

[0068] A method for preparing a negative electrode material for a start-stop power supply, comprising the following steps:

[0069] S1: First, take 20kg of tailings (particle size D) from the oil-based needle coke after crushing and shaping. v The sample was 4.0 μm thick, with a sulfur content of 0.4% and a volatile content of 6.7%. It was then mixed with 4% asphalt (softening point 250ºC, coking value 71.4%, quinoline insolubles 0.12%) and granulated. The stirring frequency of the reactor was 25 rpm, the nitrogen flow rate was 3 L / min, the temperature was increased to 450ºC at room temperature at 6ºC / min and held for 2 h, and then increased to 650ºC at 3ºC / min and held for 3 h. After cooling, the material was placed in a silicon carbide crucible and heated to 1150ºC at 10ºC / min and held at that temperature for 2 hours. After natural cooling, it was removed and then placed in a graphite crucible in an Atchison graphitization furnace to complete graphitization. The power supply time was 45 hours, the maximum power was 26000kW, and the constant power time was 22 hours. After the power supply was completed, the material was started to be sucked up within 72 hours. The material was discharged when the crucible temperature reached 200ºC. Then, 2.5% pitch (softening point 200ºC, coking value 60.8%, quinoline insolubles 0.10%) was added and mixed at 100rpm for 30 minutes. The temperature was then increased to 1150ºC at 10ºC / min and held at that temperature for 2 hours. Finally, the product was obtained after sieving and was denoted as NCP@A.

[0070] S2: Take the PCP prepared in step S1 and mix it with commercially available hard carbon at a mass ratio of 5:5. Mix at 100 rpm for 20 min and record as A-NCP@A / LHC-55.

[0071] Example 6

[0072] A negative electrode material for start-stop power supplies and its preparation method, comprising the following steps:

[0073] S1: First, take 20 kg of tailings from the asphalt coke after crushing and shaping (particle size Dv50 is 5 μm, sulfur content is 0.35%, volatile matter is 6.9%), mix with 4% asphalt (softening point 250ºC, coking value 71.4%, quinoline insoluble matter 0.12%) and granulate. The stirring frequency of the reactor is 30 rpm, the nitrogen flow rate is 2 L / min, the temperature is increased to 450ºC at room temperature at 6ºC / min and held for 1 h, and then increased to 650ºC at 2ºC / min and held for 2 h. After cooling, the material was placed in a silicon carbide crucible and heated to 1150ºC at 10ºC / min and held at that temperature for 2 hours. After natural cooling, it was removed and then placed in a graphite crucible in an Atchison graphitization furnace to complete graphitization. The power supply time was 45 hours, the maximum power was 25500kW, and the constant power time was 25 hours. After the power supply was completed, the material was started to be sucked up within 72 hours. The material was discharged when the crucible temperature was 200ºC. Then, 2% pitch (softening point 200ºC, coking value 60.8%, quinoline insoluble matter 0.10%) was added and mixed at 200rpm for 20 minutes. The temperature was then increased to 1150ºC at 10ºC / min and held at that temperature for 2 hours. Finally, the finished product was obtained after sieving, denoted as AP@A.

[0074] S2: Take the PCP prepared in step S1 and mix it with commercially available hard carbon at a mass ratio of 5:5. Mix at 100 rpm for 20 min and record as A-AP@A / LHC-55.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that the maximum power is 27000kW and the constant power time is 20h.

[0077] Comparative Example 2

[0078] The difference from Example 2 is that the asphalt softening point is 250ºC, the coking value is 71.4%, the quinoline insolubles are 0.12%, and the addition ratio is 1.5%.

[0079] The PCP and LHC prepared in Example 1 were subjected to SEM testing, and the test results are as follows: Figure 1 , Figure 2 As shown, PCP contains many fine particles that are bonded together, which is beneficial for improving the rate performance of the cell. LHC has a more uniform particle size distribution and no obvious pores on its surface, which improves the initial efficiency to some extent.

[0080] The silicon-carbon anodes obtained in Examples 1-3 and Comparative Examples 1-2 were uniformly mixed with styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), and carbon black (SP) in a mass ratio of 95.5:1.7:1.5:1.3 to form a slurry. This slurry was then coated onto a 6μm copper current collector, and then transferred to an 80ºC forced-air drying oven for 2 hours. After drying in a 90ºC vacuum drying oven overnight, the slurry was finally compacted by a roller mill and then sliced.

[0081] Assembly was carried out in an argon-filled glove box. The counter electrode of the battery was a lithium sheet (1 mm thick), the electrolyte was 1.3 M LiPF6 / (VEC:VDEC=3:7), and the separator was 20 μm microporous polyethylene.

[0082] The half-cell was first allowed to stand for 12 hours, then discharged to 5mV at 0.05C. After standing for 5 minutes, it was discharged to 5mV at 0.05mA, then discharged to 5mV at 0.01mA after another 5 minutes. Finally, after standing for 5 minutes, it was charged to 2.0V at 0.1C. The tests were performed on a Blue Electric CT3002A. The charge / discharge curves for PCP and LHC are shown below. Figure 3 The test results of the physicochemical properties of all samples are shown in Table 1.

[0083] Table 1

[0084] Test Item Sample Name <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Tap density (g / cm 3 )]]> Initial charge capacity (mAh / g) First-time efficiency (%) PCP 2.86 0.90 337.8 91.2 PCP@A 2.18 0.80 339.8 92.6 Example 1 2.78 0.79 331.2 85.6 Example 2 2.35 0.75 332.5 87.1 Example 3 2.51 0.71 329.4 84.2 Example 4 2.26 0.77 333.5 89.3 Example 5 2.14 0.82 336.8 87.4 Example 6 2.47 0.76 330.5 86.8 Comparative Example 1 2.75 0.80 333.7 85.9 Comparative Example 2 2.39 0.77 333.6 86.9 LHC 2.81 0.67 320.1 80.4

[0085] By analyzing the charge-discharge curves of PCP and LHC, it can be seen that the graphite anode forms a clear voltage plateau after the initial potential drops to 0.2V; while the hard carbon anode shows a sloped voltage curve that gradually decreases from 0.8V to 0V. The high potential region of the sloped voltage curve is related to the storage of lithium ions in the micropores of hard carbon, while the low potential region is attributed to the embedding of lithium ions in the interlayer gaps of carbon.

[0086] The combination of graphite and hard carbon yields the best results from each ingredient. The addition of graphite not only improves the overall specific capacity of the sample but also compensates for the insufficient initial efficiency of hard carbon. Furthermore, the sample with a 5:5 ratio of graphite to hard carbon exhibits superior overall physicochemical properties.

[0087] To explore the practical applicability of the compounded samples, the samples prepared in Examples 2-4 were assembled into pouch cells with NCM811 positive electrode sheets, and their cycle performance was tested. The N / P ratio of the full cell was designed to be 1.10, with a voltage range of 2.75-4.2V. The cells were first formed at 0.1C, followed by charging at 1C, 3C, 5C, 10C, and 1C, and then cycled 5 times at 1C discharge. The test results are shown in [Figure number missing]. Figure 4 .

[0088] Test results show that the capacity retention rate of graphite and hard carbon composites is lower than that of hard carbon monomers at the same rate, but still exceeds 90% of the capacity retention rate. The composite graphite and hard carbon strategy effectively breaks the inherent trade-off between energy density and power density, achieving synergistic improvement of both. The hybrid anode design opens up a new path for efficient and rapid charging and discharging of start-stop batteries for electric vehicles.

[0089] To better illustrate the present invention, numerous specific details have been provided in the detailed embodiments described above. Those skilled in the art should understand that the present invention can be practiced even without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of the present invention.

[0090] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A lithium-ion battery negative electrode material for use in start-stop power supplies, characterized in that, It is made from a mixture of artificial graphite secondary particles and hard carbon; The mass ratio of the compound is artificial graphite secondary particles: hard carbon = (1-10): (10-1).

2. The negative electrode material according to claim 1, characterized in that, The artificial graphite secondary particles are obtained from the artificial graphite production tailings through granulation, pre-carbonization, and graphitization; the artificial graphite production tailings include at least one of petroleum coke, needle coke, and pitch coke.

3. The negative electrode material according to claim 1 or 2, characterized in that, Median particle size D of artificial graphite production waste v 50 is 3-5μm; the mass fraction of volatile matter in the tailings of artificial graphite production is 6-12%, and the mass content of sulfur is 0.2-3%.

4. The negative electrode material according to claim 2, characterized in that, The artificial graphite secondary particles also include asphalt, and the mass ratio of the artificial graphite production tailings before granulation to asphalt is 100:

4.

5. A method for preparing a lithium-ion battery negative electrode material for a start-stop power supply as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of secondary artificial graphite particles: The tailings from the production of artificial graphite are granulated in a reactor, stirred with nitrogen gas, and the reactor is heated in two stages; after granulation, the material undergoes pre-carbonization and graphitization treatment. S2, Compounding: Mix the product from step S1 with hard carbon in a certain proportion, controlling the rotation speed at 50-100 rpm and the time at 10-30 min.

6. The preparation method according to claim 5, characterized in that, The reaction vessel described in step S1 is heated in two stages: the first stage has a heating rate of ≤10ºC / min, a maximum temperature of ≤450ºC, and a holding time of 1-3h; the second stage has a heating rate of ≤5ºC / min, a maximum temperature of ≤700ºC, and a holding time of 2-4h. The stirring speed of the reactor is 15-30 rpm, and the nitrogen flow rate is controlled at 1-5 L / min.

7. The preparation method according to claim 5, characterized in that, The pre-carbonization temperature is 1000-1200ºC, and the heating rate is ≤10ºC / min.

8. The preparation method according to claim 5, characterized in that, The graphitization process uses an Atchison graphitization furnace with a power supply time of 45-60 hours, a maximum power of 27,000 kW, a constant power time of 10-20 hours, and a cooling period of approximately 20-30 days. The crucible temperature is ≤200ºC.

9. The preparation method according to claim 5, characterized in that: Step S1, after graphitization, also includes a coating carbonization process; the coating carbonization process is as follows: adding coating pitch to the graphitization product; mixing and then carbonizing.

10. The preparation method according to claim 9, characterized in that, The amount of coated bitumen added is 1-3% of the mass of the graphitized semi-finished product; The mixing process involves mixing the graphitized semi-finished product with the coated asphalt at a mixing speed of 100-200 rpm and a mixing time of 20-30 min. The carbonization temperature is 1150-1200ºC, the heating rate is ≤10ºC / min, and the oxygen content is ≤1ppm.

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