Preparation method of a rate type bamboo-like based thin-layer graphite negative electrode, negative electrode sheet and lithium ion battery
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SICHUAN JINGLEI SCI & TECH CO LED
- Filing Date
- 2026-03-17
- Publication Date
- 2026-06-26
AI Technical Summary
Existing graphite anode materials have insufficient performance at high rates, and traditional preparation methods are energy-intensive and environmentally unfriendly.
Using renewable bamboo as raw material, a thin-layer graphite anode with a thickness of 10-20 nm, an interlayer spacing of 0.336-0.340 nm, and a specific surface area of 900-1200 m2/g is prepared by applying a DC voltage at 700°C-850°C through a low-energy molten salt electrolysis method. The anode sheet is then prepared by combining conductive agents and binders.
It achieves high rate performance and cycle stability, shortens the lithium-ion diffusion path, accelerates the interface reaction kinetics, is suitable for high-power applications, and has an environmentally friendly and low-energy-consumption process.
Smart Images
Figure CN122279620A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a method for preparing a rate-capable thin-layer graphite anode suitable for high-power lithium-ion batteries, an anode sheet, and a lithium-ion battery. The thin-layer graphite is prepared from biomass-derived charcoal from bamboo thorns via a molten salt electrochemical method. Background Technology
[0002] Graphite is currently the most mainstream anode material for lithium-ion batteries due to its stable electrochemical properties and high theoretical capacity. However, commercially available synthetic graphite and natural graphite have certain limitations. First, the highly ordered graphite crystal structure results in a long diffusion path for lithium ions between layers, and the interlayer spacing (typically about 0.335 nm) is relatively small. This leads to greater resistance to lithium ion insertion and extraction, especially under high-rate charge and discharge conditions, where the interfacial reaction kinetics are slow, causing rapid capacity decay and poor rate performance. Second, the specific surface area of traditional graphite materials is usually low, limiting their effective contact area with the electrolyte, further restricting the achievement of high-rate performance.
[0003] Traditional methods for preparing thin-layer graphite, such as chemical vapor deposition or the Hummers process for preparing graphene oxide followed by thermal reduction, often suffer from problems such as complex processes, high costs, or environmental pollution caused by the use of strong acids and oxidants. While conventional high-temperature graphitization technology (>2500℃) can improve the graphitization degree of materials, it consumes extremely high energy and is prone to causing graphite sheets to stack and fuse, which reduces the specific surface area and narrows the interlayer spacing, thus hindering the improvement of rate performance. Summary of the Invention
[0004] To address the shortcomings of existing graphite anode materials in terms of insufficient performance at high rates and the high energy consumption and environmental unfriendliness of traditional preparation methods, this invention provides a method for preparing a rate-capable thin-layer graphite anode, an anode sheet, and a lithium-ion battery using renewable bamboo as raw material and a green, low-energy molten salt electrolysis process.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] A method for preparing a rate-multiplying bamboo-based thin-layer graphite anode includes the preparation of thin-layer graphite and the fabrication of the anode sheet. The preparation of the thin-layer graphite includes: grinding bamboo-derived charcoal to a particle size of 1.0 µm-10.0 µm and pressing it into a sheet as the cathode; using graphite or a nickel-based alloy as the anode; electrolyzing at a temperature of 700°C-850°C for 8-12 hours under a DC voltage of 1.9V-2.2V; and washing and drying the electrolysis product to obtain the thin-layer graphite. By controlling the voltage and time parameters within this specific range, the complete and controllable conversion of bamboo-derived charcoal to a highly graphitized structure can be achieved. The anions in the molten salt electrolyte required for electrolysis include Cl-. - OH - CO3 2- One or more of the following, the anions and cations of the molten salt electrolyte required for electrolysis include Mg 2+ Ca 2 + Zn 2+ Na + K + Li + One or more of the following; wherein, electrolysis includes one or more of electrolysis after cathode immersion and electrolysis during cathode immersion; wherein, the thickness of the thin-layer graphite is 10nm-20nm, the interlayer spacing d(002) is 0.336nm-0.340nm, the degree of graphitization is 46.5%-93%, and the specific surface area is 900 m². 2 / g-1200 m 2 / g. The negative electrode sheet is made by mixing thin-layer graphite, conductive agent and binder to form a slurry, coating it on a copper foil current collector, drying and rolling it to obtain the negative electrode sheet, wherein the activity of the thin-layer graphite accounts for 80%-95% of the mass percentage of the negative electrode slurry.
[0007] Optionally, the molten salt electrolysis system required for electrolysis includes one or a combination of two of MgCO3, Na2CO3, K2CO3, MgCl2, CaCO3, and CaCl2.
[0008] Optionally, cathode immersion followed by electrolysis refers to immersing the cathode in an electrolyte solution for 2 to 10 hours before electrolysis.
[0009] Optionally, the thin-layer graphite activity accounts for 90% of the mass percentage of the negative electrode slurry.
[0010] Optionally, the conductive agent is conductive graphite, and the binder is polyvinylidene fluoride.
[0011] Optionally, the preparation of charcoal derived from thorny bamboo includes: first, heat-drying thorny bamboo and then carbonizing it, with the heat-drying temperature being 50°C - 250°C and the time being 12h - 48h; and the carbonization temperature being 400°C - 1100°C and the time being 2h - 48h.
[0012] Optionally, thorny bamboo includes one or more of bamboo leaves, bamboo branches, bamboo nodes, bamboo walls, and bamboo weaving.
[0013] In another aspect, this application also provides a negative electrode sheet obtained by any of the above preparation methods.
[0014] In another aspect, this application also provides a lithium-ion battery including the above-mentioned negative electrode.
[0015] The thin-layer graphite prepared in this application has a thickness of 10-20 nm and an expanded interlayer spacing, with the (002) crystal plane interlayer spacing d(002) being 0.336-0.340 nm, corresponding to a graphitization degree of 46.5%-93%; it also possesses a high specific surface area of 900-1200 m². 2 / g. A multi-scale graphite material with nano-thin layers, interlayer spacing, and high specific surface area was successfully prepared. The thin-layer structure can effectively shorten the diffusion path of lithium ions, while the increased specific surface area provides more active sites for lithium ions, which is conducive to the realization of rapid interfacial reaction kinetics.
[0016] The thin-layer graphite structure effectively shortens the lithium-ion diffusion path and promotes interfacial reaction kinetics, resulting in excellent high-rate performance. Specifically, when applied in battery anode sheets, it exhibits a reversible capacity ≥200 mAh / g at 1C and a capacity retention ≥90% at 2C. This anode maintains high reversible capacity while demonstrating outstanding high-rate performance and cycle stability, making it particularly suitable for high-power applications.
[0017] Secondly, the molten salt electrolysis method achieves graphitization of biomass carbon at relatively low temperatures (typically <1000℃, compared to traditional high-temperature graphitization) and low voltages (1.9-2.2V), significantly reducing energy consumption. By driving ions to embed between carbon layers under an electric field, bamboo-derived charcoal can be directly and efficiently converted into thin-layer graphite. This process is mild and controllable, and the molten salt can be recycled, avoiding the use of strong acids and strong oxidants, making it environmentally friendly.
[0018] Furthermore, using biomass such as thorny bamboo as a carbon source is widely available, inexpensive, and sustainable, which aligns with the green energy development strategy. Attached Figure Description
[0019] Figure 1 This is a graph showing the rate performance of the electrode in Example 1;
[0020] Figure 2 This is a graph showing the rate performance of the electrode in Example 3;
[0021] Figure 3 This is a graph showing the rate performance of the electrode in Example 6;
[0022] Figure 4 This is a graph showing the rate performance of the electrode in Example 9;
[0023] Figure 5 This is a graph showing the rate performance of the electrode in Example 12;
[0024] Figure 6 This is a SEM image of the product in Example 3. Detailed Implementation
[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but these are not intended to limit the scope of the invention.
[0026] This invention provides a method for preparing a rate-multiplying bamboo-based thin-layer graphite anode, the general process of which includes:
[0027] Preparation of charcoal derived from thorny bamboo: The thorny bamboo is first heat-dried and then carbonized. The heat-dried temperature is 50~250°C and the time is 12~48h; the carbonization temperature is 400~1100°C and the time is 2~48h.
[0028] Charcoal derived from thorny bamboo (including one or more of bamboo leaves, branches, nodes, walls, and weaving) is pre-treated by ball milling to a specific particle size range (1.0-10.0 µm), pressed into sheets to serve as the cathode, and high-purity graphite rods as the anode, placed in a molten salt electrolyte with a specific composition. The molten salt participates in the reaction and acts as the electrolyte medium, with Cl- as its anion. - OH - CO3 2- One or more of them, whose cation is Mg 2+ Ca 2+ Zn 2+ Na + K + Li + One or more of them.
[0029] Electrolysis was performed at 700-850°C with a DC voltage of 1.9-2.2V for 8-12 hours. The electrolysis product was repeatedly washed with deionized water and dried to obtain the target thin-layer graphite, with a thickness distribution of 10-20 nm.
[0030] Subsequently, the thin-layer graphite, conductive carbon black, and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 90:5:5 to form a slurry, which was then coated onto a copper foil current collector. After drying and rolling, a negative electrode sheet was obtained. Finally, using this electrode sheet as the working electrode and a lithium metal sheet as the counter / reference electrode, a CR2032 type button cell was assembled in an argon-protected glove box for electrochemical performance testing.
[0031] The following examples illustrate the process parameters and test results, which are summarized in Table 1 below:
[0032] Example 1
[0033] Carbon derived from bamboo leaves was ball-milled to a particle size of 1.0-2.3 μm and pressed into sheets at 10 MPa to serve as the cathode. High-purity graphite rods were used as the anode, and a molten salt mixture of MgCO3 and K2CO3 at 850°C was used as the electrolyte. Electrolysis was performed by immersion electrolysis at 1.9V for 10 hours. The electrolysis product was repeatedly washed with deionized water and dried to obtain a thin layer of graphite. This thin layer of graphite, conductive carbon black, and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 90:5:5 to form a slurry, which was then coated onto copper foil and dried to form a negative electrode. Using this electrode as the working electrode and lithium metal as the counter electrode, a CR2032 button cell was assembled in an argon-protected glove box for electrochemical testing. The battery was charged and discharged at 2C, 4C, 6C, and 8C rates, with discharge capacities of 125 mAh / g, 80 mAh / g, 55 mAh / g, and 49 mAh / g, respectively. Subsequent cycling at 1C and 2C rates yielded discharge capacities of 202 mAh / g and 121 mAh / g, respectively.
[0034] Example 2
[0035] Carbon derived from *Phyllostachys edulis* leaves was ball-milled to a particle size of 2.3-4.6 μm. The cathode preparation and electrolysis conditions were the same as in Example 1, but the electrolytic molten salt was changed to Na₂CO₃-K₂CO₃ at 800°C, and the electrolysis time was extended to 12 hours at 2.1V. The resulting batteries were tested, and the discharge capacities at 2C, 4C, 6C, and 8C rates were 121 mAh / g, 77 mAh / g, 71 mAh / g, and 51 mAh / g, respectively. The post-cycle capacities at 1C and 2C were 202 mAh / g and 119 mAh / g, respectively.
[0036] Example 3
[0037] Carbon derived from bamboo branches was ball-milled to a particle size of 4.6-6.4 μm and electrolyzed for 10 hours at 2.1V using Na₂CO₃-K₂CO₃ as the molten salt at 850°C. Battery test results showed that the capacities at 2C, 4C, 6C, and 8C were 130 mAh / g, 86 mAh / g, 60 mAh / g, and 42 mAh / g, respectively. After cycling, the capacities at 1C and 2C were 205 mAh / g and 120 mAh / g, respectively.
[0038] Example 4
[0039] The carbon derived from the branches of *Phyllostachys edulis* was ball-milled to a particle size of 6.4-10.0 μm. Electrolysis conditions were the same as in Example 3, but the electrolysis time was extended to 12 hours. Battery test results showed that the capacities at 2C, 4C, 6C, and 8C were 116 mAh / g, 73 mAh / g, 68 mAh / g, and 48 mAh / g, respectively. After cycling, the capacities at 1C and 2C were 195 mAh / g and 116 mAh / g, respectively.
[0040] Example 5
[0041] Carbon derived from bamboo nodes was ball-milled to a particle size of 1.0-2.3 μm, and MgCl2-K2CO3 was used as the molten salt at 750°C. A soaking-and-electrolysis method was employed: soaking for 2 hours, followed by electrolysis at 2.0V for 8 hours. Battery test results showed 2C, 4C, 6C, and 8C capacities of 122 mAh / g, 78 mAh / g, 73 mAh / g, and 53 mAh / g, respectively. After cycling, the 1C / 2C capacities were 208 mAh / g and 123 mAh / g, respectively.
[0042] Example 6
[0043] Carbon derived from bamboo nodes was ball-milled to a particle size of 2.3-4.6 μm, and molten salt of Na₂CO₃-K₂CO₃ was used at 850°C. The mixture was first soaked for 3 hours, followed by electrolysis at 2.0V for 10 hours. Battery test results showed capacities of 135 mAh / g, 90 mAh / g, 75 mAh / g, and 55 mAh / g at 2C, 4C, 6C, and 8C respectively. After cycling, the capacities at 1C and 2C were 220 and 130 mAh / g respectively.
[0044] Example 7
[0045] Carbon derived from bamboo nodes was ball-milled to a particle size of 4.6-6.4 μm and then treated with MgCl2-K2CO3 molten salt at 750°C. The mixture was first soaked for 5 hours, followed by electrolysis at 2.0V for 10 hours. Battery test results showed capacities of 117 mAh / g, 75 mAh / g, 69 mAh / g, and 49 mAh / g at 2C, 4C, 6C, and 8C respectively. After cycling, the capacities at 1C and 2C were 200 mAh / g and 119 mAh / g respectively.
[0046] Example 8
[0047] Carbon derived from bamboo nodes was ball-milled to a particle size of 6.4-10.0 μm and molten in MgCl2-K2CO3 at 750°C. The mixture was first soaked for 6 hours, followed by electrolysis at 2.1V for 10 hours. Battery test results showed capacities of 115 mAh / g, 72 mAh / g, 67 mAh / g, and 47 mAh / g at 2C, 4C, 6C, and 8C respectively. After cycling, the capacities at 1C and 2C were 192 mAh / g and 115 mAh / g respectively.
[0048] Example 9
[0049] Carbon derived from bamboo nodes was ball-milled to a particle size of 2.3-4.6 μm and molten in Na₂CO₃-K₂CO₃ at 800°C. The mixture was first soaked for 10 hours, followed by electrolysis at 2.1V for 10 hours. Battery test results showed capacities of 125 mAh / g at 2C, 101 mAh / g at 4C, 76 mAh / g at 6C, and 55 mAh / g at 8C. After cycling, the capacities at 1C and 2C were 220 mAh / g and 126 mAh / g, respectively.
[0050] Example 10
[0051] Carbon derived from bamboo nodes was ball-milled to a particle size of 4.6-6.4 μm and then treated with Na₂CO₃-CaCO₃ molten salt at 800°C. The mixture was first soaked for 5 hours, followed by electrolysis at 2.0V for 10 hours. Battery test results showed capacities of 123 mAh / g, 79 mAh / g, 74 mAh / g, and 54 mAh / g at 2C, 4C, 6C, and 8C respectively. After cycling, the capacities at 1C and 2C were 210 and 125 mAh / g respectively.
[0052] Example 11
[0053] Carbon derived from bamboo nodes was ball-milled to a particle size of 2.3-4.6 μm and molten in CaCl2-CaCO3 at 800°C. The mixture was first soaked for 4 hours, followed by electrolysis at 2.2V for 10 hours. Battery test results showed capacities of 118 mAh / g, 77 mAh / g, 71 mAh / g, and 51 mAh / g at 2C, 4C, 6C, and 8C respectively. After cycling, the capacities at 1C and 2C were 203 mAh / g and 121 mAh / g respectively.
[0054] Example 12
[0055] Carbon derived from bamboo nodes was ball-milled to a particle size of 2.3-4.6 μm and then treated with Na₂CO₃-CaCO₃ molten salt at 750°C. The mixture was first soaked for 2 hours, followed by electrolysis at 2.0V for 10 hours. Battery test results showed capacities of 112 mAh / g, 76 mAh / g, 60 mAh / g, and 51 mAh / g at 2C, 4C, 6C, and 8C respectively. After cycling, the capacities at 1C and 2C were 213 and 126 mAh / g respectively.
[0056] Comparative Example 1 (Traditional High-Temperature Graphitization):
[0057] Carbon derived from *Phyllostachys edulis* var. *sinensis* with the same source and particle size (2.3-4.6 µm) as in Example 6 was subjected to high-temperature graphitization treatment at 2800°C for 2 hours under argon protection. The resulting product was used to prepare a negative electrode sheet and assembled into a battery for testing, following the same method as in Example 6.
[0058] Results: Although the material has a high degree of graphitization (>95%), the interlayer spacing is reduced to 0.3354 nm, and the specific surface area is significantly reduced to <50 m². 2 Electrochemical testing showed that its 2C discharge capacity was only 85 mAh / g, and the capacity decreased sharply to 35 mAh / g at 4C. After cycling, the 1C capacity was 180 mAh / g, and the 2C capacity was 82 mAh / g. This indicates that although the traditional high-temperature method can increase the degree of graphitization, it leads to structural densification, which seriously impairs the rate performance of the material.
[0059] Comparative Example 2 (Commercial Artificial Graphite):
[0060] Commercially available synthetic thin-layer graphite was used directly as the negative electrode active material, and the same electrode formulation (active material: conductive agent: binder = 90:5:5) and battery assembly process as in the example were used for testing.
[0061] Results: The discharge capacities of this commercial graphite at 2C, 4C, 6C, and 8C rates were 105 mAh / g, 52 mAh / g, 28 mAh / g, and 15 mAh / g, respectively. After cycling, the 1C and 2C capacities were 185 mAh / g and 98 mAh / g, respectively. Its high-rate performance is significantly inferior to all embodiments of the present invention.
[0062] The above embodiments demonstrate that the bamboo-based thin-layer graphite anode prepared by this invention exhibits stable and excellent capacity at different high rates, and can rapidly recover most of its capacity after high-rate cycling, fully proving its superior rate performance and structural stability. Different parts of the bamboo have little impact on the final result. In the molten salt system, Na₂CO₃-K₂CO₃ performs better, especially when Na₂CO₃-K₂CO₃ is soaked before electrolysis, resulting in optimal rate performance and structural stability.
[0063] Comparing Examples 2 and 6, it can be seen that soaking for 3 hours before the electrolysis time is 10 hours has a significantly better effect than direct electrolysis for 12 hours. The capacity of 2C / 4C increased by 11.5% and 16.9% respectively, and the capacity increased by 9% and 9.2% after cycling 1C and 2C respectively.
[0064] By comparing Examples 2 and 9, it can be seen that soaking for 10 hours before the electrolysis time is 10 hours has a significantly better effect than direct electrolysis for 12 hours. The 4C capacity increased by 31%, and the capacity increased by 9% and 5% after cycling for 1C and 2C, respectively.
[0065] The inventors also experimented with other commercially available binders, such as cellulose-based binders and polyacrylic binders. The rate performance was significantly improved compared to both the traditional high-temperature graphite used in Comparative Example 1 and the commercially available synthetic thin-layer graphite used in Comparative Example 2.
[0066] The inventors also experimented with mixing thin-layer graphite, conductive carbon black, and polyvinylidene fluoride (PVDF) binder in a mass ratio of 85:10:5 or 95:2.5:2.5. The final results were similar to those obtained in the previous examples.
[0067] Table 1 Comparison of electrochemical performance of Examples 1-12
[0068]
[0069] Table 2 Comparison of thin-layer graphite parameters in Examples 1-12
[0070]
[0071] This invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications and improvements within the scope of the claims.
Claims
1. A method for preparing a rate-multiplying bamboo-based thin-layer graphite anode, characterized in that, include: Preparation of thin-layer graphite: Bamboo charcoal was ground to a particle size of 1.0 µm-10.0 µm and pressed into sheets to serve as the cathode. Graphite or a nickel-based alloy was used as the anode. Electrolysis was performed at 700°C-850°C for 8-12 hours under a DC voltage of 1.9V-2.2V. After washing and drying the electrolysis product, thin-layer graphite was obtained. The anions in the molten salt electrolyte required for electrolysis included Cl-. - OH - CO3 2- One or more of the following, the anions and cations of the molten salt electrolyte required for electrolysis include Mg 2+ Ca 2+ Zn 2+ Na + K + Li + One or more of the following; wherein the electrolysis includes one or more of electrolysis after cathode immersion and electrolysis during cathode immersion; wherein the thickness of the thin graphite layer is 10nm-20nm, the interlayer spacing d(002) is 0.336nm-0.340nm, the degree of graphitization is 46.5%-93%, and the specific surface area is 900 m². 2 / g-1200 m 2 / g; Negative electrode sheet preparation: The thin-layer graphite, conductive agent and binder are mixed to form a slurry, which is then coated onto a copper foil current collector. After drying and rolling, a negative electrode sheet is obtained. The thin-layer graphite accounts for 80%-95% of the mass percentage of the negative electrode slurry.
2. The method for preparing a rate-multiplying bamboo-based thin-layer graphite anode according to claim 1, characterized in that, The molten salt electrolysis system required for electrolysis includes one or a combination of two of MgCO3, Na2CO3, K2CO3, MgCl2, CaCO3, and CaCl2.
3. The method for preparing a rate-multiplying bamboo-based thin-layer graphite anode according to claim 1, characterized in that, The term "electrolysis after cathode immersion" refers to immersing the cathode in an electrolyte solution for 2 to 10 hours before electrolysis.
4. The method for preparing a rate-multiplying bamboo-based thin-layer graphite anode according to claim 1, characterized in that, The active thin-layer graphite accounts for 90% of the mass percentage of the negative electrode slurry.
5. The method for preparing a rate-multiplying bamboo-based thin-layer graphite anode according to claim 1, characterized in that, The conductive agent is conductive graphite, and the binder is polyvinylidene fluoride.
6. The method for preparing a rate-multiplying bamboo-based thin-layer graphite anode according to claim 1, characterized in that, The preparation of the charcoal derived from the thorny bamboo includes: first, heat-drying the thorny bamboo and then carbonizing it. The heat-drying temperature is 50°C-250°C and the time is 12h-48h; the carbonization temperature is 400°C-1100°C and the time is 2h-48h.
7. The method for preparing a rate-multiplying bamboo-based thin-layer graphite anode according to claim 6, characterized in that, The thorny bamboo includes one or more of the following: bamboo leaves, bamboo branches, bamboo nodes, bamboo walls, and bamboo weaving.
8. A negative electrode sheet, characterized in that, It is prepared by the method for preparing rate-multiplying bamboo-based thin-layer graphite anode as described in any one of claims 1-7.
9. A lithium-ion battery, characterized in that, It includes the negative electrode as described in claim 8.