Anode materials and their preparation methods, battery cells and electrical devices

Abstract

This invention relates to negative electrode materials and their preparation methods, battery cells, and electrical devices. The negative electrode materials include porous carbon materials coated with carbon nanospheres, and the I of the negative electrode material... D / I G Value ≤ 0.8, where I D It is the peak intensity of the D band in the Raman spectrum of the negative electrode material, I G This refers to the peak intensity of the G band in the Raman spectrum of the anode material. The carbon nanosphere coating structure not only effectively buffers the volume expansion of the internal porous carbon material but also inhibits the excessive growth of the solid electrolyte interface film. The anode material forms a highly graphitized structure, thereby significantly improving its electronic conductivity. Simultaneously, the porous structure of the porous carbon material provides more lithium-ion storage active sites. Furthermore, the porous structure of the anode material can shorten the lithium-ion diffusion path. The anode material of this application has a stable structure and simultaneously improves the specific capacity of the carbon anode material, as well as the rate performance and cycle performance of the battery cell.

Description

Technical Field

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

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in portable electronic devices, new energy vehicles, and large-scale energy storage systems. The anode material, as a key component of lithium-ion batteries, directly affects the overall performance of the battery.

[0003] Currently, commercially available lithium-ion battery anode materials mainly employ graphite-based carbon materials. While these materials exhibit a low lithium intercalation potential, their theoretical specific capacity is also low (approximately 372 mAh / g), making it difficult to meet the ever-increasing demand for high energy density. Furthermore, the layered, ordered structure of graphite carbon exhibits strong anisotropy, limiting its ion transport capabilities at high rates. Simultaneously, due to the limitations imposed by the interlayer spacing, graphite carbon materials undergo volume expansion and structural fragmentation during repeated lithium intercalation and deintercalation processes, resulting in poor cycle life. Therefore, developing carbon anode materials that simultaneously possess high specific capacity, excellent rate performance, and long cycle life remains a challenge in the field of lithium-ion battery anode materials. Summary of the Invention

[0004] Based on this, in order to simultaneously improve the specific capacity of carbon anode materials as well as the rate performance and cycle performance of battery cells, this application provides an anode material and its preparation method, a battery cell and an electrical device.

[0005] In a first aspect, this application provides a negative electrode material comprising a porous carbon material coated with carbon nanospheres, wherein the negative electrode material I... D / I G Value ≤ 0.8, where I D It is the peak intensity of the D band in the Raman spectrum of the negative electrode material, I G It is the peak intensity of the G band in the Raman spectrum of the negative electrode material.

[0006] According to embodiments of this application, the diameter of the carbon nanospheres is ≤500nm; and / or, the thickness of the coating layer formed by the carbon nanospheres is 100nm~500nm.

[0007] According to the embodiments of this application, the specific surface area of ​​the negative electrode material is 500m². 2 / g~2000m 2 / g; and / or, the proportion of mesopores with an internal pore size of 2nm~5nm in porous carbon materials is ≥50%.

[0008] Secondly, this application provides a method for preparing a negative electrode material, which includes first solvent-displacing a biomass precursor to obtain a solvent-displaced biomass solid, then freeze-drying the biomass solid to obtain a biomass aerogel, and then heat-treating the biomass aerogel to obtain a porous carbon material coated with carbon nanospheres; wherein, the biomass precursor includes biomass material containing macromolecular sugars, and the macromolecular sugars include natural polymers composed of more than 10 monosaccharide molecules linked by glycosidic bonds; the heat treatment includes heating to 2000℃~3000℃ within 60s.

[0009] According to embodiments of this application, the biomass precursor has a water content ≥60%; and / or, the biomass precursor includes at least one of watermelon rind, banana peel, orange peel, grapefruit peel, straw core, and sugarcane.

[0010] According to embodiments of this application, the heat treatment includes flash Joule heating carbonization, which employs a capacitor discharge device; and / or, the heat treatment includes flash Joule heating carbonization, which involves placing biomass aerogel in a flash Joule heating reaction quartz tube, and under an inert atmosphere, setting the voltage of the flash Joule heating carbonization to 50V~300V, the discharge time to 0.1s~10s, and the number of discharges to 1~5 times.

[0011] According to the embodiments of this application, solvent replacement includes immersing the biomass precursor in an organic solution, ultrasonically vibrating it for 1 to 3 hours, and repeating the replacement 2 to 5 times; wherein the organic solution includes an organic solvent, and the surface tension of the organic solvent is less than that of water.

[0012] According to embodiments of this application, the organic solvent includes at least one of ethanol, isoalkanes, isohexyl glycol, and isopropanol; and / or, the volume fraction of the organic solvent in the organic solution is 70% to 99.99%; and / or, before solvent replacement, the biomass precursor is pretreated, the pretreatment including washing the biomass precursor and then pre-freezing it at a temperature of -10°C to -20°C for 4 to 8 hours.

[0013] According to the embodiments of this application, the pre-freezing temperature for freeze drying is -20℃ to -80℃, the pre-freezing time is 2h to 10h, the cold trap temperature is < -50℃, the vacuum degree is 5Pa to 30Pa, and the drying time is 12h to 24h.

[0014] Thirdly, this application provides a battery cell that includes the negative electrode material in the above embodiments or the negative electrode material prepared according to the preparation method of the negative electrode material in the above embodiments.

[0015] Compared with the prior art, this application has the following beneficial effects: The negative electrode material of this application improves the cycle performance of the prepared battery cell by coating porous carbon material with carbon nanospheres. The coating structure of the carbon nanospheres not only effectively buffers the volume expansion of the internal porous carbon material but also inhibits the excessive growth of the solid electrolyte interface film. D / I G When the above conditions are met, a highly graphitized structure is formed, thereby significantly improving the electronic conductivity of the anode material. Simultaneously, the porous structure of the porous carbon material effectively increases the specific surface area, providing more lithium-ion storage active sites and improving the capacity of the anode material. Furthermore, the porous structure of the anode material shortens the lithium-ion diffusion path and increases the reaction interface area, thereby significantly reducing solid-phase diffusion resistance and concentration polarization, and ultimately improving the rate performance of the prepared battery cell. The anode material of this application has a stable structure and simultaneously improves the specific capacity of the carbon anode material as well as the rate performance and cycle performance of the battery cell.

[0016] In the preparation method of the negative electrode material of this application, the biomass precursor is first solvent-replaced to obtain a solvent-replaced biomass solid. This can reduce the irreversible structural damage to the biomass precursor caused by water crystal volume expansion and ice crystal growth during direct freeze-drying, and at the same time, it can form a denser porous structure, avoiding or improving the problem of biomass precursor collapse. This application uses biomass aerogel as a precursor. Aerogel has a stable high porosity structure, which can achieve simultaneous control of high graphitization degree and porous structure. Using biomass materials containing macromolecular sugars as biomass precursors is conducive to the in-situ growth of carbon nanospheres on the surface of porous carbon framework, which can form a carbon nanosphere coating structure. Heating to above 2000℃ in a short time can achieve rapid graphitization of biomass precursor, obtaining carbon materials with high graphitization degree. The negative electrode material prepared in this application has high specific capacity, high rate performance and high cycle performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a scanning electron microscope image of the negative electrode material provided in Embodiment 1 of this application; Figure 2 The Raman spectrum of the negative electrode material provided in Example 1 of this application; Figure 3 A scanning electron microscope image of the negative electrode material provided in Comparative Example 1 of this application; Figure 4The Raman spectrum of the negative electrode material provided in Comparative Example 1 of this application; Figure 5 Discharge curve of a button cell made of the negative electrode material provided in Example 1 of this application at 100 mA / g; Figure 6 The discharge curve of a button cell made of the negative electrode material provided in Comparative Example 1 of this application at 100 mA / g. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] This application provides a negative electrode material, which includes a porous carbon material coated with carbon nanospheres, wherein the negative electrode material I... D / I G Value ≤ 0.8.

[0021] Among them, I D It is the peak intensity of the D band in the Raman spectrum (Raman test wavelength is 532 nm) of the negative electrode material. The D band (usually located at ~1350 cm⁻¹) -1 The activation mechanism of D bands is very special; theoretically, a perfect, infinitely large graphite crystal has no D peak. D bands only appear and are enhanced when the structure exhibits the following conditions: 1. Structural defects (vacancies, dislocations, grain boundaries); 2. Edge effects (graphite sheet boundaries, broken bonds); 3. Heteroatoms / functional groups (nitrogen / sulfur doping, oxygen-containing functional groups disrupting sp). 2 4. Disordered regions (amorphous carbon, smaller crystallite size), therefore, The enhancement directly corresponds to the increase of "imperfect" areas in the material, I D The stronger it is, the more "chaotic" the material is and the more defects it has.

[0022] I G It is the peak intensity of the G band in the Raman spectrum of the negative electrode material (Raman test wavelength is 532 nm). The G band (usually located at ~1580 cm⁻¹) -1 ) originates from carbon atoms sp 2 The in-plane stretching vibration of the six-membered ring formed by hybridization directly corresponds to the abundance of the carbon network with long-range ordered electron delocalization structure in the material.

[0023] For example, the I of the negative electrode material D / I GThe value can be any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or any value within the range of any two of the above values.

[0024] Optionally, the I of the negative electrode material D / I G Value ≤ 0.7.

[0025] Optionally, the I of the negative electrode material D / I G Value ≤ 0.6.

[0026] Optionally, the I of the negative electrode material D / I G Value ≤ 0.5.

[0027] In some specific embodiments, the diameter of the carbon nanospheres is ≤500nm.

[0028] The diameter of carbon nanospheres was measured by the following method: a scanning electron microscope (SEM) image of the surface of the negative electrode material was obtained. The carbon nanospheres were identified as the approximately circular or spherical coating particles that could be clearly identified in the SEM image. Starting from one corner of the image, the diameters of 20 independent carbon nanospheres with clear outlines, no overlap, and no cuts were measured. The diameter range of the carbon nanospheres was obtained by statistically analyzing five SEM images from different positions.

[0029] By keeping the diameter of the carbon nanospheres within the aforementioned range, this application facilitates control over the thickness of the carbon nanosphere coating layer, thereby guiding the electrolyte to penetrate into the interior of the porous carbon material and improving the material's reversible capacity.

[0030] In some specific embodiments, the coating thickness formed by the carbon nanospheres is 100 nm to 500 nm.

[0031] The thickness of the coating layer formed by carbon nanospheres was measured by the following method: obtaining scanning electron microscope (SEM) images of the cross-section of the anode material, in which the complete coating layer and part of the core can be clearly seen. In the cross-section SEM images, the vertical distance from the outer surface of the porous carbon core to the outermost edge of the carbon nanosphere coating layer is the thickness of the coating layer formed by the carbon nanospheres. The thickness of the coating layer formed by the carbon nanospheres was measured in the cross-section SEM images of 20 independent anode material particles, and the average value was calculated to obtain the thickness of the coating layer formed by the carbon nanospheres.

[0032] This application, by ensuring that the thickness of the coating layer formed by the carbon nanospheres is within the aforementioned range, can guide the electrolyte to wet into the interior of the porous carbon material, which is beneficial to the utilization of the material's reversible capacity.

[0033] In some specific embodiments, the specific surface area of ​​the negative electrode material is 500 m². 2 / g~2000m 2 / g.

[0034] The specific surface area of ​​the negative electrode material was measured by the BET test method.

[0035] By ensuring that the specific surface area of ​​the anode material is within the aforementioned range, this application not only helps to control the SEI film area on the material surface and improve the initial coulombic efficiency of the prepared battery cell, but also provides more lithium storage active sites, thereby increasing the capacity of the anode material.

[0036] In some specific embodiments, the proportion of mesopores with a pore size of 2nm to 5nm in the porous carbon material is ≥50%.

[0037] The proportion of mesopores with an internal pore size of 2nm to 5nm in porous carbon materials was measured by nitrogen adsorption method.

[0038] This application achieves a higher proportion of mesopores with pore sizes of 2nm to 5nm within the porous carbon material. This makes the mesopores with pore sizes of 2nm to 5nm dominant within the porous carbon material, which not only helps to increase the specific surface area of ​​the anode material, thereby increasing the lithium storage active sites and the capacity of the anode material, but also provides more lithium ion migration paths, thereby reducing polarization and improving the rate performance of the prepared battery cells.

[0039] It should be noted that, apart from mesopores with a pore size of 2nm to 5nm, the porous carbon material has a uniform distribution of other pore structures and a hierarchical porous structure inside.

[0040] The negative electrode material of this application improves the cycle performance of the prepared battery cell by coating porous carbon material with carbon nanospheres. The coating structure of the carbon nanospheres not only effectively buffers the volume expansion of the internal porous carbon material but also inhibits the excessive growth of the solid electrolyte interface film. D / I G When the above conditions are met, a highly graphitized structure is formed, thereby significantly improving the electronic conductivity of the anode material. Simultaneously, the porous structure of the porous carbon material effectively increases the specific surface area, providing more lithium-ion storage active sites and improving the capacity of the anode material. Furthermore, the porous structure of the anode material shortens the lithium-ion diffusion path and increases the reaction interface area, thereby significantly reducing solid-phase diffusion resistance and concentration polarization, and ultimately improving the rate performance of the prepared battery cell. The anode material of this application has a stable structure and simultaneously improves the specific capacity of the carbon anode material as well as the rate performance and cycle performance of the battery cell.

[0041] This application also provides a method for preparing a negative electrode material, which includes the following steps: S1, solvent displacement The biomass precursor is first pretreated, and then the pretreated biomass precursor is solvent-displaced to obtain solvent-displaced biomass solid.

[0042] Among them, biomass precursors include biomass materials containing macromolecular sugars, which are natural high-molecular polymers composed of more than 10 monosaccharide molecules linked by glycosidic bonds.

[0043] Optionally, the water content of the biomass precursor is ≥60%. High water content biomass can utilize its naturally abundant three-dimensional network structure and numerous pore channels to provide a structural basis for the subsequent construction of high-porosity, low-density aerogel precursors, and ensure full solvent exchange during the solvent replacement process.

[0044] For example, the water content of the biomass precursor can be any value among 60%, 70%, 80%, 90%, 99.9% or any value within the range of any two of the above values.

[0045] Optionally, the biomass precursor has a water content of ≥70%.

[0046] Optionally, the biomass precursor has a water content of ≥80%.

[0047] Optionally, the biomass precursor has a water content of ≥90%.

[0048] Optionally, the biomass precursor includes at least one of watermelon rind, banana peel, orange peel, grapefruit peel, straw core, and sugarcane.

[0049] For example, the biomass precursor can be a single watermelon rind, banana peel, orange peel, grapefruit peel, straw core, or sugarcane, or it can be a mixture of watermelon rind and banana peel, or a mixture of watermelon rind and orange peel, or a mixture of watermelon rind, banana peel, and grapefruit peel.

[0050] Optionally, the pretreatment includes first cleaning the biomass precursor, and then pre-freezing it at a temperature of -10℃ to -20℃ for 4 to 8 hours. Cleaning helps remove impurities from the surface of the biomass precursor, and pre-freezing facilitates sufficient solvent replacement in the subsequent process.

[0051] For example, the pre-freezing temperature can be any value among -10℃, -12℃, -15℃, -18℃, and -20℃, or any value within the range of any two of the above values, and the pre-freezing time can be any value among 4h, 5h, 6h, 7h, and 8h, or any value within the range of any two of the above values.

[0052] Solvent replacement involves immersing the biomass precursor in an organic solution, followed by ultrasonic agitation for 1-3 hours, repeating this process 2-5 times to thoroughly displace the water from the biomass. The organic solution comprises an organic solvent, the surface tension of which is lower than that of water. Utilizing an organic solvent with low surface tension to replace water in the biomass precursor reduces the shrinkage stress generated in the micropores, minimizing irreversible structural damage to the three-dimensional network framework caused by water crystal expansion and ice crystal growth during direct freeze-drying, while simultaneously creating a denser porous structure.

[0053] For example, the ultrasonic oscillation time during solvent displacement can be any value among 1h, 1.5h, 2h, 2.5h, 3h, or any value within the range of any two of the above values, and the displacement can be repeated 2 times, 3 times, 4 times, or 5 times.

[0054] Optionally, the organic solvent includes at least one of ethanol, isoalkanes, isohexyl glycol, and isopropanol.

[0055] For example, the organic solvent may be ethanol, isoalkane, isohexanediol or isopropanol alone, or may be a mixture of ethanol and isopropanol, or may be a mixture of isoalkane and isohexanediol, or may be a mixture of ethanol, isohexanediol and isopropanol.

[0056] Optionally, the volume fraction of the organic solvent in the organic solution is 70% to 99.99%.

[0057] For example, the volume fraction of the organic solvent in the organic solution can be any value among 70%, 80%, 90%, 99.99%, or any value within the range of any two of the above values.

[0058] S2, Preparation of biomass aerogels Biomass aerogels with a dense porous structure on the surface are obtained by freeze-drying solid biomass.

[0059] Optionally, the pre-freezing temperature for freeze drying is -20℃ to -80℃, the pre-freezing time is 2h to 10h, the cold trap temperature is < -50℃, the vacuum degree is 5Pa to 30Pa, and the drying time is 12h to 24h.

[0060] For example, the pre-freezing temperature for freeze drying can be any value from -20℃, -30℃, -40℃, -50℃, -60℃, -70℃, -80℃ or any value within the range of any two of the above values; the pre-freezing time can be any value from 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or any value within the range of any two of the above values; the cold trap temperature can be any value from -49.9℃, -40℃, -30℃, -20℃ or any value within the range of any two of the above values; the vacuum degree can be any value from 5Pa, 10Pa, 20Pa, 25Pa, 30Pa or any value within the range of any two of the above values; and the drying time can be any value from 12h, 15h, 18h, 21h, 24h or any value within the range of any two of the above values.

[0061] S3, Heat Treatment Biomass aerogels were thermally treated to obtain porous carbon materials coated with carbon nanospheres. Under the influence of the porous structure and surface tension, the surface of the high-water-content biomass aerogels underwent shrinkage and cross-linking during pyrolysis, gradually forming nanosphere-shaped carbon particles on the material surface, resulting in highly graphitized porous carbon materials coated with carbon nanospheres.

[0062] The heat treatment includes heating to 2000℃~3000℃ within 60 seconds.

[0063] For example, the heat treatment temperature can be any value among 2000℃, 2200℃, 2500℃, 2800℃, and 3000℃, or any value within the range of any two of the above values.

[0064] Optionally, the heat treatment includes flash Joule heating carbonization, which employs a capacitive discharge device. This application uses a high-voltage pulse to instantaneously heat the biomass aerogel; this carbonization method achieves rapid temperature rise in a short time, resulting in high graphitization efficiency and low energy consumption.

[0065] The flash Joule heating carbonization process involves placing biomass aerogel in a flash Joule heating quartz tube, and under an inert atmosphere, setting the voltage of the flash Joule heating carbonization process to 50V~300V, the discharge time to 0.1s~10s, and the number of discharges to 1~5 times.

[0066] Optionally, the inert gas includes at least one of nitrogen, helium, argon and xenon.

[0067] In the preparation method of the negative electrode material of this application, the biomass precursor is first solvent-replaced to obtain a solvent-replaced biomass solid. This can reduce the irreversible structural damage to the biomass precursor caused by water crystal volume expansion and ice crystal growth during direct freeze-drying, and at the same time, it can form a denser porous structure, avoiding or improving the problem of biomass precursor collapse. This application uses biomass aerogel as a precursor. Aerogel has a stable high porosity structure, which can achieve simultaneous control of high graphitization degree and porous structure. Using biomass materials containing macromolecular sugars as biomass precursors is conducive to the in-situ growth of carbon nanospheres on the surface of porous carbon framework, which can form a carbon nanosphere coating structure. Heating to above 2000℃ in a short time can achieve rapid graphitization of biomass precursor, obtaining carbon materials with high graphitization degree. The negative electrode material prepared in this application has high specific capacity, high rate performance and high cycle performance.

[0068] This application also provides an electrical device comprising the above-described negative electrode material or a negative electrode material prepared according to the above-described method for preparing the negative electrode material.

[0069] This application also provides an electrical device, which includes the aforementioned battery or battery cells as described above. It is capable of receiving electrical energy from the aforementioned battery or battery cells. The aforementioned electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, power tool, energy storage device, amusement equipment, elevator, and lifting equipment, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, or electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc.; energy storage devices can be energy storage walls, base station energy storage, container energy storage, etc.; amusement equipment can be a carousel, a drop tower, etc.

[0070] The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended vehicles, etc. For new energy vehicles, the aforementioned battery can serve as a driving power source, thereby replacing fossil fuels to provide propulsion. This application does not impose any special restrictions on the aforementioned electrical devices.

[0071] The technical solution of this application will be described below with reference to specific embodiments.

[0072] Example 1 This application provides a negative electrode material and its preparation method, which includes the following steps: S1, solvent displacement Fresh watermelon rind was selected as a biomass precursor. The watermelon rind was first cut into pieces and rinsed repeatedly with deionized water to remove surface impurities. The washed watermelon rind was then pre-frozen at -18℃ for 5 hours to obtain frozen watermelon rind pieces. Next, the frozen watermelon rind pieces were soaked in a 99% ethanol aqueous solution and ultrasonically vibrated for 2 hours to perform ethanol replacement. This replacement was repeated 3 times to obtain ethanol-based watermelon rind.

[0073] S2, Preparation of biomass aerogels The ethanol-based watermelon rind obtained above was placed in a freeze dryer, with a pre-freezing temperature of -40℃ and a pre-freezing time of 4 hours; the cold trap temperature was -55℃, the vacuum degree was 10 Pa, and the drying time was 20 hours to obtain watermelon rind aerogel.

[0074] S3, Heat Treatment The watermelon rind aerogel obtained above was placed in a flash Joule heating quartz tube reactor and pyrolyzed under a nitrogen atmosphere. The voltage was set to 60V, the current to 55A, the discharge time to 6 seconds, the carbonization temperature to 2200℃, and the number of discharges to 2 times. Finally, black carbon solid was obtained. The obtained carbon solid was ball-milled to obtain a negative electrode material with uniform particle size.

[0075] Scanning electron microscope images of the obtained negative electrode material, such as... Figure 1 As shown, the scanning electron microscope (SEM) image reveals that the negative electrode material is a porous carbon material coated with carbon nanospheres. The average diameter of the carbon nanospheres was measured to be 120.5 nm, and the thickness of the coating layer formed by the carbon nanospheres was 217.3 nm.

[0076] The peak intensities of the D band and G band in the Raman spectrum of the negative electrode material were measured. The Raman spectrum of the negative electrode material is as follows: Figure 2 As shown, the I of the negative electrode material D / I G The value is 0.48.

[0077] The specific surface area of ​​the negative electrode material was measured to be 1350 m² using the BET test method. 2 / g, the proportion of mesopores with a pore size of 2nm~5nm in the porous carbon material was measured by nitrogen adsorption method to be 72.5%.

[0078] Example 2 This application provides an anode material and its preparation method, which is based on Example 1, but with the biomass precursor changed to fresh banana peel, while other aspects remain unchanged.

[0079] Example 3 This application provides a negative electrode material and its preparation method, which is based on Example 1, except that in S1 and solvent replacement, the 99% volume concentration of the ethanol aqueous solution is replaced with an 85% volume concentration of the ethanol aqueous solution, while other aspects remain unchanged.

[0080] Example 4 This application provides a negative electrode material and its preparation method, which is based on Example 1, except that in S1 and solvent replacement, the 99% volume concentration of the ethanol aqueous solution is replaced with a 70% volume concentration of the ethanol aqueous solution, while other aspects remain unchanged.

[0081] Example 5 This application provides a negative electrode material and its preparation method, which is based on Example 1, except that the 99% volume concentration ethanol aqueous solution in step S1 and solvent replacement step is replaced with a 99% volume concentration isopropanol aqueous solution, while the others remain unchanged.

[0082] Example 6 This application provides a negative electrode material and its preparation method, which is based on Example 1, except that the pre-freezing temperature of freeze-drying in step S2 and the preparation of biomass aerogel is changed to -20°C, while the others remain unchanged.

[0083] Example 7 This application provides a negative electrode material and its preparation method, which is based on Example 1, except that the pre-freezing temperature of freeze-drying in step S2 and the preparation of biomass aerogel is changed to -80°C, while the others remain unchanged.

[0084] Example 8 This application provides a negative electrode material and its preparation method, which is based on Example 1, except that the discharge time of flash Joule thermal pyrolysis in step S3 and the heat treatment step is changed to 3s, while the others remain unchanged.

[0085] Example 9 This application provides a negative electrode material and its preparation method. Based on Example 1, the voltage of flash Joule thermal pyrolysis in step S3 and the heat treatment step is changed to 50V, the carbonization temperature is 2000℃, and the others remain unchanged.

[0086] Example 10 This application provides a negative electrode material and its preparation method. Based on Example 1, the voltage of flash Joule thermal pyrolysis in step S3 and the heat treatment step is changed to 300V, the carbonization temperature is 3000℃, and other parameters remain unchanged.

[0087] Comparative Example 1 This application provides a comparative example of an anode material and its preparation method, which includes the following steps: S1, solvent displacement Fresh watermelon rind was selected as a biomass precursor. The watermelon rind was first cut into pieces and rinsed repeatedly with deionized water to remove surface impurities. The washed watermelon rind was then dried at 90℃ for 12 hours to obtain dried watermelon rind.

[0088] S2, Heat Treatment The dried watermelon rind obtained above was placed in a flash Joule heating quartz tube reactor and pyrolyzed under a nitrogen atmosphere. The voltage was set to 60V, the current to 55A, the discharge time to 6 seconds, the carbonization temperature to 2200℃, and the number of discharges to 2 times. Finally, black carbon solid was obtained. The obtained carbon solid was ball-milled to obtain a negative electrode material with uniform particle size.

[0089] Scanning electron microscope images of the obtained negative electrode material, such as... Figure 3 As shown, the scanning electron microscope image reveals that the surface of the negative electrode material is smooth and lacks a carbon nanosphere coating layer, while the interior has a porous structure.

[0090] The peak intensities of the D band and G band in the Raman spectrum of the negative electrode material were measured. The Raman spectrum of the negative electrode material is as follows: Figure 4 As shown, the I of the negative electrode material D / I G The value is 0.78.

[0091] The specific surface area of ​​the negative electrode material was measured to be 852 m² using the BET test method. 2 / g, the proportion of mesopores with a pore size of 2nm~5nm in the porous carbon material was 46.2% as determined by nitrogen adsorption method.

[0092] Comparative Example 2 This application provides a comparative example of an anode material and its preparation method, which includes the following steps: S1, solvent displacement Fresh watermelon rind was selected as a biomass precursor. The watermelon rind was first cut into pieces and rinsed repeatedly with deionized water to remove surface impurities. The washed watermelon rind was then pre-frozen at -18℃ for 5 hours to obtain frozen watermelon rind pieces. Next, the frozen watermelon rind pieces were soaked in a 99% ethanol aqueous solution and ultrasonically vibrated for 2 hours to perform ethanol replacement. This replacement was repeated 3 times to obtain ethanol-based watermelon rind.

[0093] S2, Preparation of biomass aerogels The ethanol-based watermelon rind obtained above was placed in a freeze dryer, with a pre-freezing temperature of -40℃ and a pre-freezing time of 4 hours; the cold trap temperature was -55℃, the vacuum degree was 10 Pa, and the drying time was 20 hours to obtain watermelon rind aerogel.

[0094] S3, Heat Treatment Watermelon rind aerogel was placed in a vacuum tube furnace, then transferred to a ceramic boat and placed inside the furnace. The furnace was then heated at 10°C / min under a nitrogen atmosphere. -1 The temperature was increased to 900℃ and held for 30 minutes. After cooling, a black carbon solid was obtained. The obtained carbon solid was ball-milled to obtain a negative electrode material with uniform particle size.

[0095] The scanning electron microscope (SEM) image of the obtained negative electrode material shows that the surface of the negative electrode material has a carbon nanosphere coating structure. The average diameter of the carbon nanospheres is 267.2 nm, the thickness of the coating layer formed by the carbon nanospheres is 60.7 nm, and the surface has a porous structure.

[0096] The peak intensities of the D band and G band in the Raman spectrum of the negative electrode material were measured, and the I of the negative electrode material was... D / I G The value is 0.98.

[0097] The specific surface area of ​​the negative electrode material was measured to be 1026 m² using the BET test method. 2 / g, the proportion of mesopores with a pore size of 2nm~5nm in the porous carbon material was measured by nitrogen adsorption method to be 73.6%.

[0098] Comparative Example 3 This application provides a comparative example of an anode material and its preparation method, which includes the following steps: S1, Preprocessing Fresh watermelon rind is selected as a biomass precursor. The watermelon rind is first cut into pieces and rinsed repeatedly with deionized water to remove surface impurities.

[0099] S2, Preparation of biomass aerogels The pretreated watermelon rind was placed in a freeze dryer at a pre-freezing temperature of -40°C for 4 hours; the cold trap temperature was -55°C, the vacuum degree was 10 Pa, and the drying time was 20 hours to obtain watermelon rind aerogel.

[0100] S3, Heat Treatment The watermelon rind aerogel obtained above was placed in a flash Joule heating quartz tube reactor and pyrolyzed under a nitrogen atmosphere. The voltage was set to 60V, the current to 55A, the discharge time to 6 seconds, the carbonization temperature to 2200℃, and the number of discharges to 2 times. Finally, black carbon solid was obtained. The obtained carbon solid was ball-milled to obtain a negative electrode material with uniform particle size.

[0101] The scanning electron microscope (SEM) image of the obtained negative electrode material shows that the surface of the negative electrode material has a layer of carbon nanospheres that are unevenly distributed.

[0102] The peak intensities of the D band and G band in the Raman spectrum of the negative electrode material were measured, and the I of the negative electrode material was... D / I G The value is 0.64.

[0103] The specific surface area of ​​the negative electrode material was measured to be 1265 m² using the BET test method. 2 / g, the proportion of mesopores with a pore size of 2nm~5nm in the porous carbon material was 50.3% as measured by nitrogen adsorption method, the average diameter of carbon nanospheres was 150.4nm, and the thickness of the coating layer formed by carbon nanospheres was 45.1nm.

[0104] Comparative Example 4 This application provides a comparative example of an anode material and its preparation method, which includes the following steps: S1, solvent displacement Dehaired pigskin was selected as a biomass precursor. First, the dehaired pigskin was cut into pieces and rinsed repeatedly with deionized water to remove surface impurities. Then, the cleaned dehaired pigskin was pre-frozen at -18℃ for 5 hours to obtain frozen pieces of dehaired pigskin. Next, the frozen pieces of dehaired pigskin were soaked in a 99% ethanol aqueous solution and ultrasonically vibrated for 2 hours to perform ethanol replacement. This replacement was repeated 3 times to obtain ethanol-based pigskin.

[0105] S2, Preparation of biomass aerogels The ethanol-based pigskin obtained above was placed in a freeze dryer, with a pre-freezing temperature of -40℃ and a pre-freezing time of 4 hours; the cold trap temperature was -55℃, the vacuum degree was 10 Pa, and the drying time was 20 hours to obtain pigskin aerogel.

[0106] S3, Heat Treatment The pigskin aerogel obtained above was placed in a flash Joule heating quartz tube reactor and pyrolyzed under a nitrogen atmosphere. The voltage was set to 60V, the current to 55A, the discharge time to 6 seconds, the carbonization temperature to 2200℃, and the number of discharges to 2 times. Finally, black carbon solid was obtained. The obtained carbon solid was ball-milled to obtain a negative electrode material with uniform particle size.

[0107] The scanning electron microscope (SEM) image of the obtained negative electrode material shows that the surface of the negative electrode material is not covered with carbon nanospheres, but exhibits an open macroporous structure.

[0108] The peak intensities of the D band and G band in the Raman spectrum of the negative electrode material were measured, and the I of the negative electrode material was... D / I G The value is 0.87.

[0109] The specific surface area of ​​the negative electrode material was measured to be 1103 m² using the BET test method. 2 / g, the proportion of mesopores with a pore size of 2nm~5nm in the porous carbon material was 31.2% as determined by nitrogen adsorption method.

[0110] Comparative Example 5 This application provides a conventional graphene material as a negative electrode material in a comparative example.

[0111] The graphite carbon material was rinsed multiple times with deionized water to remove surface impurities, and then dried in an oven at 110℃ for 12 hours after being cleaned.

[0112] The obtained dried graphite carbon solid was ball-milled to obtain graphite carbon powder with uniform particle size.

[0113] The peak intensities of the D and G bands in the Raman spectrum of graphite carbon powder were measured, and the I of the anode material was... D / I G The value is 0.31.

[0114] The specific surface area of ​​the negative electrode material was measured to be 3.21 m² using the BET test method. 2 / g.

[0115] The parameters of the negative electrode materials of Examples 1-10 and Comparative Examples 1-5 are shown in Table 1.

[0116] Table 1 The negative electrode materials of Examples 1-10 and Comparative Examples 1-5 were used to make button cells. The specific capacity of the button cells at a current density of 100 mA / g (1C), the capacity retention rate at a high rate of 5C, and the capacity retention rate after 500 cycles were measured. The results are shown in Table 2.

[0117] The preparation method is as follows: Preparation of the negative electrode sheet: The negative electrode material, acetylene black conductive agent, and PVDF binder were mixed evenly at a mass ratio of 8:1:1. NMP was added and the mixture was ground in an agate mortar until the PVDF was completely dissolved, forming a uniform and fine negative electrode slurry. The negative electrode slurry was evenly coated onto copper foil using a four-sided coating tool, and then placed in a vacuum drying oven and vacuum dried at 110°C for 10 hours.

[0118] The dried negative electrode sheet was cut into 12mm diameter discs using a die-cutting machine. Lithium foil was used as the positive electrode sheet, polypropylene as the separator, and LiPF6 as the electrolyte (solvent being EC and DMC in a 1:1 volume ratio, and solute being 1mol / L LiPF6). The prepared electrodes were then assembled into button cells in an argon-filled glove box.

[0119] Test conditions: Constant current charge-discharge tests were conducted at room temperature using a Blue Battery testing system, with a voltage window of 0.01V ~ 3.0V (vs. Li / Li). + ).

[0120] At a current density of 100 mA / g (1C), the battery was activated by three cycles, and the capacity of the third cycle was taken as the specific capacity data. The battery was charged and discharged at a constant current of 5C, and the capacity of this 5C charge and discharge was recorded. The capacity retention rate at the 5C high rate was calculated by comparing it with the 1C discharge capacity. The cycle performance was obtained by 500 charge and discharge cycles at a current density of 0.5C.

[0121] The discharge curves of the button cells made from the negative electrode materials of Example 1 and Comparative Example 1 at 100 mA / g are shown below. Figure 5 and 6 As shown.

[0122] Table 2 As can be seen from Examples 1 to 10, the batteries made from the negative electrode materials prepared by the method of this application have high specific capacity, good rate performance and cycle performance.

[0123] A comparison of Example 2 and Example 1 shows that Example 2, which uses banana peel instead of watermelon peel as the biomass precursor, slightly increases the ID / IG ratio of the negative electrode material, indicating a decrease in the graphitization degree of the negative electrode material. The specific surface area also decreases slightly. The rate performance and cycle performance of the battery in Example 2 are comparable to those in Example 1, but the specific capacity is slightly lower. This is because banana peel has a lower water content than watermelon peel, and the biomass precursor structure is different.

[0124] A comparison of Examples 3-4 and Example 1 shows that Example 3 used an 85% (v / v) ethanol aqueous solution as the replacement solvent, while Example 4 used a 70% (v / v) ethanol aqueous solution. The ID / IG ratio of the negative electrode material slightly increased, indicating a decrease in the graphitization degree of the negative electrode material. The specific capacity, rate performance, and cycle performance of the batteries from Examples 3-4 were all worse than those from Example 1. This is because the concentration of the organic solvent in the replacement solvent decreased, the water content increased, and the precursor structure was more prone to collapse.

[0125] As can be seen from the comparison between Example 5 and Example 1, Example 5 uses an isopropanol aqueous solution with a volume concentration of 99% as the replacement solvent, and the ID / IG ratio of the negative electrode material is basically the same as that of Example 1. Moreover, the specific capacity, rate performance and cycle performance of the battery in Example 5 are not much different from those in Example 1.

[0126] A comparison of Examples 6-7 and Example 1 shows that the pre-freezing temperature for freeze-drying in Example 6 was -20℃, and in Example 7 it was -80℃. The ID / IG ratios of the negative electrode materials were higher in Example 6 than in Example 1, indicating a decrease in the graphitization degree and a lower specific surface area. The specific capacity, rate performance, and cycle performance of the batteries from Examples 6-7 were slightly worse than those from Example 1. This is because increasing the pre-freezing temperature increases the structural disorder of the highly graphitized porous carbon material coated with carbon nanospheres, resulting in insufficient freezing and destruction of the pore structure during vaporization, leading to fewer mesopores. Conversely, extremely low pre-freezing temperatures disrupt biological structures, increasing the structural order of the highly graphitized porous carbon material coated with carbon nanospheres.

[0127] A comparison of Example 8 and Example 1 shows that the discharge time of flash Joule pyrolysis in Example 8 is 3 seconds, and the ID / IG ratio of the negative electrode material is higher than that in Example 1, indicating a decrease in the graphitization degree of the negative electrode material. The specific capacity, rate performance, and cycle performance of the battery in Example 8 are slightly worse than those in Example 1. This is because the degree of flash Joule pyrolysis is not sufficient.

[0128] A comparison of Examples 9-10 and Example 1 shows that in Example 9, the flash Joule pyrolysis voltage was 50V and the carbonization temperature was 2000℃. The ID / IG ratio of the negative electrode material was higher than that in Example 1, indicating a decrease in the graphitization degree of the negative electrode material. The specific capacity, rate performance, and cycle performance of the battery in Example 9 were slightly worse than those in Example 1. In Example 10, the flash Joule pyrolysis voltage was 300V and the carbonization temperature was 3000℃. The ID / IG ratio of the negative electrode material was lower than that in Example 1, indicating an increase in the graphitization degree of the negative electrode material. The specific capacity, rate performance, and cycle performance of the battery in Example 10 were slightly worse than those in Example 1. This indicates that a lower flash Joule pyrolysis voltage leads to a lower carbonization temperature, which results in a lower degree of graphitization in the prepared negative electrode material. Conversely, a higher flash Joule pyrolysis voltage leads to a higher carbonization temperature, which results in an increase in the degree of graphitization in the prepared negative electrode material.

[0129] A comparison of Comparative Example 1 and Example 1 shows that Comparative Example 1, which did not undergo aerogelation treatment of the biomass precursor, has a higher ID / IG ratio in its negative electrode material than Example 1. This indicates a decrease in the graphitization degree of the negative electrode material. Consequently, the specific capacity, rate performance, and cycle performance of the battery in Comparative Example 1 are significantly worse than those in Example 1. This is because aerogelation treatment of the biomass precursor is necessary to form a dense porous structure on the material surface. During carbonization, the surface material can aggregate and cross-link to form a spherical structure. The carbon material formed after carbonization of the biomass precursor without aerogelation treatment has a porous structure, a smooth surface, and lacks carbon nanosphere coating.

[0130] A comparison of Comparative Example 2 and Example 1 reveals that Comparative Example 2, which did not employ flash Joule thermal carbonization but instead used conventional tubular furnace carbonization, showed a significantly higher ID / IG ratio for its anode material compared to Example 1. This indicates a decrease in the graphitization degree of the anode material. Consequently, the specific capacity, rate performance, and cycle performance of the battery in Comparative Example 2 were all far inferior to those in Example 1. This is because the graphitization degree of carbon materials prepared by conventional pyrolysis is much lower than that obtained through flash Joule thermal carbonization.

[0131] Comparing Comparative Example 3 with Example 1, it can be seen that Comparative Example 3, without solvent replacement, has an unevenly distributed carbon nanosphere layer on the surface of the negative electrode material. The ID / IG ratio of the negative electrode material is higher than that of Example 1. The specific capacity, rate performance, and cycle performance of the battery in Comparative Example 3 are significantly worse than those in Example 1. This is because solvent replacement can reduce the irreversible structural damage to the biomass precursor caused by water crystal volume expansion and ice crystal growth during direct freeze-drying. Simultaneously, it can form a denser porous structure, avoiding or improving the problem of biomass precursor collapse. The precursor structure will collapse without solvent replacement.

[0132] A comparison of Comparative Example 4 and Example 1 shows that Comparative Example 4 uses dehaired pigskin as a biomass precursor. Since dehaired pigskin does not contain macromolecular sugars, the ID / IG ratio of the negative electrode material is higher than that of Example 1. The specific capacity, rate performance, and cycle performance of the battery in Comparative Example 4 are significantly worse than those in Example 1. This is because biomass materials containing macromolecular sugars are crucial for forming the carbon nanosphere coating structure; dehaired pigskin, which does not contain macromolecular sugars, cannot form this carbon nanosphere coating structure.

[0133] A comparison between Comparative Example 5 and Example 1 shows that Comparative Example 5 uses conventional graphene as the negative electrode material. The specific surface area of ​​conventional graphene is much lower than that of the negative electrode material in Example 1 of this application. Consequently, the specific capacity, rate performance, and cycle performance of the battery in Comparative Example 5 are significantly worse than those in Example 1. This demonstrates that the porous carbon material coated with carbon nanospheres of this application, as a negative electrode, can possess both high specific capacity and good rate performance and cycle performance.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A negative electrode material, characterized in that, The negative electrode material comprises porous carbon material coated with carbon nanospheres, and the I of the negative electrode material D / I G Value ≤ 0.8, where I D I is the peak intensity of the D band in the Raman spectrum of the negative electrode material. G It is the peak intensity of the G band in the Raman spectrum of the negative electrode material.

2. The negative electrode material according to claim 1, characterized in that, The diameter of the carbon nanospheres is ≤500nm; And / or, the thickness of the coating layer formed by the carbon nanospheres is 100nm~500nm.

3. The negative electrode material according to claim 1 or 2, characterized in that, The specific surface area of ​​the negative electrode material is 500 m². 2 / g~2000m 2 / g; And / or, the proportion of mesopores with an internal pore size of 2nm~5nm in the porous carbon material is ≥50%.

4. A method for preparing a negative electrode material, characterized in that, The preparation method of the negative electrode material includes: first, solvent replacement of the biomass precursor to obtain solvent-replaced biomass solid, then freeze-drying the biomass solid to obtain biomass aerogel, and then heat-treating the biomass aerogel to obtain porous carbon material coated with carbon nanospheres. The biomass precursor includes biomass materials containing macromolecular sugars, wherein the macromolecular sugars include natural high molecular polymers consisting of more than 10 monosaccharide molecules linked by glycosidic bonds. The heat treatment involves heating to 2000℃~3000℃ within 60 seconds.

5. The method for preparing the negative electrode material according to claim 4, characterized in that, The biomass precursor has a water content of ≥60%; And / or, the biomass precursor includes at least one of watermelon rind, banana peel, orange peel, grapefruit peel, straw core, and sugarcane.

6. The method for preparing the negative electrode material according to claim 4, characterized in that, The heat treatment includes flash Joule heating carbonization, which employs a capacitor discharge device. And / or, the heat treatment includes flash Joule heating carbonization, which involves placing the biomass aerogel in a flash Joule heating quartz tube, under an inert atmosphere, setting the voltage of the flash Joule heating carbonization to 50V~300V, the discharge time to 0.1s~10s, and the number of discharges to 1~5 times.

7. The method for preparing the negative electrode material according to any one of claims 4 to 6, characterized in that, The solvent replacement includes immersing the biomass precursor in an organic solution, ultrasonically vibrating it for 1 to 3 hours, and repeating the replacement 2 to 5 times. The organic solution includes an organic solvent, and the surface tension of the organic solvent is less than that of water.

8. The method for preparing the negative electrode material according to claim 7, characterized in that, The organic solvent includes at least one of ethanol, isoalkanes, isohexyl glycol, and isopropanol; And / or, the volume fraction of the organic solvent in the organic solution is 70%~99.99%; And / or, before the solvent replacement, the biomass precursor is pretreated, the pretreatment including first washing the biomass precursor, and then pre-freezing it at a temperature of -10℃ to -20℃ for 4h to 8h.

9. The method for preparing the negative electrode material according to any one of claims 4 to 6, characterized in that, The freeze-drying process involves a pre-freezing temperature of -20℃ to -80℃, a pre-freezing time of 2h to 10h, a cold trap temperature of < -50℃, a vacuum degree of 5Pa to 30Pa, and a drying time of 12h to 24h.

10. A single battery cell, characterized in that, The battery cell includes the negative electrode material according to any one of claims 1 to 3 or the negative electrode material prepared by the method according to any one of claims 4 to 9.

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