Silicon-carbon composite electrode and preparation method thereof
By preparing carbon-coated lithium-silicon alloy composite electrode sheets, the battery performance attenuation problem caused by volume expansion in lithium-ion batteries is solved, and efficient electrochemical and mechanical properties are achieved.
Patent Information
- Application Number
- CN202510377273.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-07-25
AI Technical Summary
In the charging and discharging process of existing lithium-ion batteries, the battery capacity attenuation and the SEI film repeatedly rupture due to volume expansion during charging and discharging, affecting battery performance.
A silicon-carbon composite electrode is prepared by using a method of preparing a silicon-carbon composite electrode, including soaking the current collector in a silicate solution and heating it, reducing the magnesium heat to generate loaded silicon particles, then alloying with lithium hydride, and finally carbonizing in a phenolic resin solution to form a carbon-coated lithium silicon alloy composite electrode sheet.
It effectively suppresses the volume expansion of the silicon-carbon composite electrode during charging and discharging, and improves the cycle stability and rate performance of the battery.
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Figure CN120376581A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a silicon-carbon composite electrode and a preparation method thereof. Background Art
[0002] Lithium-ion batteries have become one of the most concerned energy storage systems due to their long service life, high specific capacity, and environmental friendliness, and are widely used in small electronic devices, aerospace and other fields. Commercial lithium-ion batteries usually use layered transition metal oxides as the positive electrode and graphite as the negative electrode. Although the specific capacity of the current graphite negative electrode can already be close to the theoretical value, with the rapid development of electric vehicles such as new energy vehicles, the power and energy density of traditional lithium-ion batteries are gradually unable to meet the needs of consumers. Crystalline silicon is a potential negative electrode material, which can provide a theoretical lithium intercalation capacity of up to 3579 mA h g -1 at room temperature, which is much higher than that of graphite (372 mA h g -1 ) which is currently the most widely used. In addition, silicon also has the advantages of high reserves, environmental friendliness, and low production cost. However, there is a serious problem with silicon negative electrodes: when lithium ions are fully embedded in the silicon matrix, the silicon matrix will undergo serious volume expansion (>300%), which will cause the silicon negative electrode to pulverize after multiple charge and discharge cycles, and then cause the silicon to lose electrical contact with the current collector, resulting in a rapid decline in battery capacity. At the same time, the volume effect generated by the silicon negative electrode during the cycling process will cause the SEI film to rupture and regenerate repeatedly, resulting in a decrease in the Coulomb efficiency of the battery and an increase in the ion transport resistance.
[0003] Therefore, in order to realize the commercial application of silicon negative electrodes, solving their volume effect is the primary problem. Researchers have found that in order to solve the problems of expansion and failure faced by silicon-based negative electrodes, academia and industry have developed a variety of silicon-based negative electrode modification methods, mainly including silicon oxidation, nanosizing, compounding, porosification, alloying, prelithiation, premagnesiation, etc., which are mainly divided into silicon oxide and silicon carbon categories in general. Among the detailed technical routes, there are currently three routes that have been industrially applied. The first is the grinding method for nano-silicon carbon route, the second is the silicon oxide route (first-generation silicon oxide and prelithiated silicon oxide), and the third is the CVD chemical vapor deposition silicon carbon route. Now, on the basis that the other two silicon negative electrode technical routes face certain bottlenecks, with the breakthrough of CVD chemical vapor deposition silicon carbon products and the verification of the performance of full batteries, downstream cell factories have gradually started to shift the focus of attention to CVD chemical vapor deposition silicon carbon. However, there are many technical barriers and industrialization difficulties in CVD chemical vapor deposition silicon carbon, such as the selection of porous carbon, deposition equipment and deposition process, etc., and the preparation process has strict requirements for equipment and requires the use of dangerous gases such as silane, so it restricts the rapid promotion of its new silicon carbon negative electrode in the market. Summary of the Invention
[0004] Based on the technical problems existing in the background art, the present invention proposes a silicon-carbon composite electrode and a preparation method thereof.
[0005] A preparation method of a silicon-carbon composite electrode proposed by the present invention includes the following steps:
[0006] S1. Immerse the current collector in a silicate solution, take it out, and perform heat treatment to obtain a current collector loaded with silicon dioxide;
[0007] S2. Perform a magnesiothermic reduction reaction on the current collector loaded with silicon dioxide, and perform pickling to obtain a current collector loaded with silicon particles;
[0008] S3. Add lithium hydride to the current collector loaded with silicon particles, and perform heat treatment to obtain a current collector loaded with a lithium-silicon alloy;
[0009] S4. Immerse the current collector loaded with the lithium-silicon alloy in a phenolic resin solution, take it out, and perform carbonization treatment to obtain a silicon-carbon composite electrode.
[0010] The preparation process of the present invention is simple, low in cost, and suitable for mass production, solving the problems of high requirements for CVD chemical vapor deposition silicon-carbon production equipment, difficult raw material storage and transportation, and complex deposition process.
[0011] Preferably, in the S1, the current collector is a porous conductive material, and the porous conductive material is selected from one or more of copper foam and carbon foam.
[0012] More preferably, the porosity of the porous conductive material is 70-80%, and the average pore diameter is 0.1-5 μm.
[0013] More preferably, the thickness of the porous conductive material is 6-10 μm.
[0014] The specification parameters of the porous conductive material within a certain range are helpful for preparing a pole piece and applying it to an electric core.
[0015] Preferably, in the S1, before taking it out, it further includes adjusting the pH of the silicate solution to 5-6 and continuing to stand still.
[0016] Preferably, in the S1, the silicate solution is selected from one or more of sodium silicate aqueous solution, lithium silicate aqueous solution, and potassium silicate aqueous solution.
[0017] There are differences in the solubility of different silicates. The silicate solution selected by the present invention helps the uniform loading of silicon dioxide on the current collector.
[0018] Preferably, in the S1, the content of silicic acid in the silicate solution is 5-15%; the pH range of the silicate solution is 8-10.
[0019] The effect of the content of silicic acid in the silicate solution within a certain range is to ensure that the silicic acid is evenly distributed in the solution and will not settle.
[0020] Preferably, in the above-mentioned S1, the soaking time is 0.5 - 3 h.
[0021] Preferably, in the above-mentioned S1, the heat treatment includes treating at 300 - 500 °C for 0.5 - 2 h under a protective gas atmosphere.
[0022] More preferably, the protective gas is selected from one or more of argon and nitrogen.
[0023] The effect of the heat treatment is that under this condition, the silicate decomposes into silicon dioxide, enabling the in-situ loading of silicon dioxide on the current collector.
[0024] Preferably, in the above-mentioned S2, the magnesium thermal reduction reaction includes reacting the current collector loaded with silicon dioxide with metallic magnesium under an argon / hydrogen mixed atmosphere at 600 - 800 °C and 50 - 200 Pa for 2 - 4 h.
[0025] More preferably, the mass ratio of silicon dioxide to metallic magnesium in the current collector loaded with silicon dioxide is (2 - 3):3.
[0026] More preferably, the volume ratio of argon to hydrogen in the argon / hydrogen mixed atmosphere is (92 - 97):(3 - 8).
[0027] The present invention controls the conditions of the magnesium thermal reduction reaction, and by sublimating metallic magnesium under low pressure, reduces silicon dioxide in the carbon matrix to silicon particles, obtaining a current collector loaded with silicon particles.
[0028] Preferably, in the above-mentioned S2, the state of the metallic magnesium is in powder form or granular form.
[0029] Preferably, in the above-mentioned S2, the acidic solution for pickling is selected from one of hydrochloric acid and sulfuric acid.
[0030] More preferably, the concentration of the acidic solution is 1 - 2 mol / L, and the pickling time is 0.5 - 4 h.
[0031] The effect of pickling is to remove impurities such as magnesium oxide and magnesium silicate generated during the magnesium thermal reduction process.
[0032] Preferably, in the above-mentioned S3, the mass ratio of silicon particles to lithium hydride in the current collector loaded with silicon particles is (5 - 8):1.
[0033] Controlling the mass ratio of silicon particles to lithium hydride in the current collector loaded with silicon particles within a certain range helps to ensure the completion of alloying on the surface of the silicon particles.
[0034] Preferably, in the step S3, the heat treatment includes treating at 400 - 600 °C for 1 - 3 h.
[0035] Controlling the temperature and time of the heat treatment within a certain range helps the decomposition of lithium hydride to form lithium vapor, enabling the deposition of lithium metal on the current collector to form a lithium-silicon alloy, and obtaining a current collector loaded with the lithium-silicon alloy.
[0036] Preferably, in the step S4, the phenolic resin solution is a mixed solution of phenolic resin and absolute ethanol, and the mass of phenolic resin in the phenolic resin solution accounts for 5% - 10% of the total mass of the phenolic resin solution.
[0037] The concentration of the phenolic resin within a certain range is beneficial to the formation of a complete carbon coating layer.
[0038] Preferably, in the step S4, the soaking time is 0.5 - 1 h.
[0039] Preferably, in the step S4, the carbonization treatment includes introducing a protective gas, first treating at 300 - 500 °C for 0.1 - 1 h, and then treating at 500 - 1000 °C for 1 - 5 h.
[0040] The function of first treating at 300 - 500 °C is to complete the solvent volatilization, enabling the preliminary curing and carbonization of the phenolic resin, forming a dense carbon layer, removing the oxygen-containing functional groups on the carbon surface, and enhancing the conductivity of the current collector. The function of the carbonization treatment is to perform carbon coating to obtain a carbon-coated lithium-silicon alloy composite electrode with the current collector as the substrate.
[0041] More preferably, the protective gas is selected from one or more of argon and nitrogen.
[0042] Preferably, in the step S4, the mass ratio of the lithium-silicon alloy in the current collector loaded with the lithium-silicon alloy to the phenolic resin in the phenolic resin solution is (80 - 85):(15 - 20).
[0043] The present invention also provides a silicon-carbon composite electrode prepared by the above preparation method.
[0044] The beneficial effects of the present invention are as follows:
[0045] The present invention changes the combination mode of the silicon-carbon material and the current collector. The carbon-coated lithium-silicon alloy particles are evenly distributed in the current collector. By forming a new type of silicon-carbon composite electrode material, the material expansion is effectively inhibited.
[0046] The preparation method of the present invention has a simple process. The obtained composite electrode has excellent electrochemical performance and mechanical properties, and is suitable for the manufacture of high-performance lithium-ion batteries.
[0047] In the present invention, phenolic resin is used as the carbon source, sodium silicate as the silicon source, and lithium hydride as the lithium source. With a current collector as the substrate, a lithium-silicon alloy is loaded on the current collector, and finally carbon coating is carried out to obtain a carbon-coated lithium-silicon alloy composite electrode sheet with the current collector as the substrate, namely a novel silicon-carbon composite electrode sheet material. Through carbon coating and the restriction of the current collector metal framework, the volume expansion of the active material during charge and discharge cycles can be effectively inhibited. Description of the Drawings
[0048] Figure 1 The charge-discharge curve of the silicon-carbon composite electrode prepared in Example 6 at a current density of 0.1C.
[0049] Figure 2 The room-temperature cycle of the silicon-carbon composite electrode prepared in Example 6 at 25°C and a current density of 1C.
[0050] Figure 3 The high-temperature cycle of the silicon-carbon composite electrode prepared in Example 6 at 45°C and a current density of 1C. Detailed Description of the Invention
[0051] The technical solution of the present invention will be described in detail through specific examples.
[0052] The materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources unless otherwise specified.
[0053] Example 1
[0054] A preparation method of a silicon-carbon composite electrode includes the following steps:
[0055] S1. Place a foam copper electrode sheet with a thickness of 8μm in a 5% sodium silicate solution (solvent is water) and let it stand for 0.5h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and let it stand for 0.5h; then take it out and quickly dry it at 300°C in a nitrogen atmosphere for 1h to in-situ generate silicon dioxide inside the 75% high-porosity foam copper, obtaining foam copper loaded with silicon dioxide.
[0056] S2. Place the foam copper loaded with silicon dioxide and metallic magnesium (powder or granular) in a reaction vessel. The mass ratio of silicon dioxide to metallic magnesium in the foam copper loaded with silicon dioxide is 2:3. Heat it to 650°C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100Pa, and keep it warm for 2h. Sublime metallic magnesium under low pressure to reduce the silicon dioxide in the foam copper, and then pickle it with 1mol / L hydrochloric acid for 2h to obtain foam copper loaded with silicon particles.
[0057] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of the silicon particles to lithium hydride in the copper foam loaded with silicon particles is 5:1. Keep it warm for 2 h under an argon atmosphere at 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, thus obtaining the copper foam loaded with the lithium-silicon alloy.
[0058] S4. Immerse the copper foam electrode loaded with the lithium-silicon alloy in a phenolic resin solution for 1 h. The mass concentration of the phenolic resin solution is 5%, and the solvent is anhydrous ethanol. Take out the electrode and quickly dry it for 1 h at 300 °C in an argon atmosphere, and then keep it warm at 700 °C for 2 h to obtain the silicon-carbon composite electrode.
[0059] Example 2
[0060] A method for preparing a silicon-carbon composite electrode, comprising the following steps:
[0061] S1. Place the copper foam electrode with a thickness of 8 μm in a 6% sodium silicate solution (the solvent is water) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and then let it stand for 0.5 h. Then take it out and quickly dry it for 1 h under a nitrogen atmosphere at 300 °C to in-situ generate silicon dioxide inside the 75% high-porosity copper foam, thus obtaining the copper foam loaded with silicon dioxide.
[0062] S2. Place the copper foam loaded with silicon dioxide and metallic magnesium (in powder or granular form) in a reaction vessel. The mass ratio of the silicon dioxide to metallic magnesium in the copper foam loaded with silicon dioxide is 2:3. Heat it up to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silicon dioxide in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain the copper foam loaded with silicon particles.
[0063] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of the silicon particles to lithium hydride in the copper foam loaded with silicon particles is 5:1. Keep it warm for 2 h under an argon atmosphere at 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, thus obtaining the copper foam loaded with the lithium-silicon alloy.
[0064] S4. Immerse the copper foam electrode loaded with the lithium-silicon alloy in a phenolic resin solution for 1 h. The mass concentration of the phenolic resin solution is 0.05%, and the solvent is anhydrous ethanol. Take out the electrode and quickly dry it for 1 h at 300 °C in an argon atmosphere, and then keep it warm at 700 °C for 2 h to obtain the silicon-carbon composite electrode.
[0065] Example 3
[0066] A method for preparing a silicon-carbon composite electrode, comprising the following steps:
[0067] S1. Place the 8-μm-thick copper foam electrode in a 7% sodium silicate solution (with water as the solvent) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and then let it stand for 0.5 h. Then take it out and quickly dry it in a nitrogen atmosphere at 300 °C for 1 h to in-situ generate silica inside the 75% high-porosity copper foam, obtaining copper foam loaded with silica.
[0068] S2. Place the copper foam loaded with silica and metallic magnesium (in powder or granular form) in a reaction vessel. The mass ratio of silica to metallic magnesium in the copper foam loaded with silica is 2:3. Heat it to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silica in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain copper foam loaded with silicon particles.
[0069] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the copper foam loaded with silicon particles is 5:1. Keep it warm for 2 h in an argon atmosphere at 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, obtaining copper foam loaded with a lithium-silicon alloy.
[0070] S4. Place the copper foam electrode loaded with a lithium-silicon alloy in a phenolic resin solution for 1 h. The mass concentration of the phenolic resin solution is 5%, and the solvent is absolute ethanol. Take out the electrode and quickly dry it in an argon atmosphere at 300 °C for 1 h, and keep it warm at 700 °C for 2 h to obtain a silicon-carbon composite electrode.
[0071] Example 4
[0072] A preparation method of a silicon-carbon composite electrode, comprising the following steps:
[0073] S1. Place the 8-μm-thick copper foam electrode in a 6% sodium silicate solution (with water as the solvent) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and then let it stand for 0.5 h. Then take it out and quickly dry it in a nitrogen atmosphere at 300 °C for 1 h to in-situ generate silica inside the 75% high-porosity copper foam, obtaining copper foam loaded with silica.
[0074] S2. Place the copper foam loaded with silica and metallic magnesium (in powder or granular form) in a reaction vessel. The mass ratio of silica to metallic magnesium in the copper foam loaded with silica is 2:3. Heat it to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silica in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain copper foam loaded with silicon particles;
[0075] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the copper foam loaded with silicon particles is 6:1. Keep it warm for 2 h under an argon atmosphere at 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, obtaining copper foam loaded with a lithium-silicon alloy;
[0076] S4. Immerse the copper foam electrode loaded with a lithium-silicon alloy in a phenolic resin solution for 1 h, where the mass concentration of the phenolic resin solution is 5% and the solvent is anhydrous ethanol. Take out the electrode and quickly dry it at 300 °C for 1 h in an argon atmosphere, and keep it warm at 700 °C for 2 h to obtain a silicon-carbon composite electrode.
[0077] Example 5
[0078] A method for preparing a silicon-carbon composite electrode, comprising the following steps:
[0079] S1. Place the copper foam electrode with a thickness of 8 μm in a 6% sodium silicate solution (the solvent is water) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and let it stand for 0.5 h; then take it out and quickly dry it at 300 °C for 1 h in a nitrogen atmosphere to in-situ generate silica inside the 75% high-porosity copper foam, obtaining copper foam loaded with silica;
[0080] S2. Place the copper foam loaded with silica and metallic magnesium (in powder or granular form) in a reaction vessel. The mass ratio of silica to metallic magnesium in the copper foam loaded with silica is 2:3. Heat it to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silica in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain copper foam loaded with silicon particles;
[0081] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the copper foam loaded with silicon particles is 7:1. Keep it warm for 2 h under an argon atmosphere at 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, obtaining copper foam loaded with a lithium-silicon alloy;
[0082] S4. Place the copper foam electrode loaded with lithium silicon alloy in a phenolic resin solution for 1 h. The mass concentration of the phenolic resin solution is 5%, and the solvent is absolute ethanol. Take out the electrode and quickly dry it at 300 °C for 1 h in an argon atmosphere, and keep it at 700 °C for 2 h to obtain a silicon-carbon composite electrode.
[0083] Example 6
[0084] A method for preparing a silicon-carbon composite electrode, comprising the following steps:
[0085] S1. Place the copper foam electrode with a thickness of 8 μm in a 6% sodium silicate solution (solvent is water) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and let it stand for 0.5 h. Then take it out and quickly dry it at 300 °C for 1 h under a nitrogen atmosphere to in-situ generate silica inside the 75% high-porosity copper foam, obtaining a copper foam loaded with silica.
[0086] S2. Place the copper foam loaded with silica and metallic magnesium (in powder or granular form) in a reaction vessel. The mass ratio of silica to metallic magnesium in the copper foam loaded with silica is 2:3. Heat it to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silica in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain a copper foam loaded with silicon particles.
[0087] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the copper foam loaded with silicon particles is 6:1. Keep it warm at 500 °C for 2 h in an argon atmosphere to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium silicon alloy, obtaining a copper foam loaded with lithium silicon alloy.
[0088] S4. Place the copper foam electrode loaded with lithium silicon alloy in a phenolic resin solution for 1 h. The mass concentration of the phenolic resin solution is 8%, and the solvent is absolute ethanol. Take out the electrode and quickly dry it at 300 °C for 1 h in an argon atmosphere, and keep it at 700 °C for 2 h to obtain a silicon-carbon composite electrode.
[0089] Example 7
[0090] A method for preparing a silicon-carbon composite electrode, comprising the following steps:
[0091] S1. Place the copper foam electrode with a thickness of 8 μm into a 6% sodium silicate solution (solvent is water) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and then let it stand for 0.5 h. Then take it out and quickly dry it in a nitrogen atmosphere at 300 °C for 1 h, and in-situ generate silica inside the 75% high-porosity copper foam to obtain copper foam loaded with silica;
[0092] S2. Place the copper foam loaded with silica and metallic magnesium (powder or granular) in a reaction vessel. The mass ratio of silica to metallic magnesium in the copper foam loaded with silica is 2:3. Heat it up to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silica in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain copper foam loaded with silicon particles;
[0093] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the copper foam loaded with silicon particles is 6:1. Keep it warm for 2 h in an argon atmosphere at 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, obtaining copper foam loaded with a lithium-silicon alloy;
[0094] S4. Place the copper foam electrode loaded with a lithium-silicon alloy in a phenolic resin solution for 1 h, where the mass concentration of the phenolic resin solution is 10% and the solvent is anhydrous ethanol. Take out the electrode and quickly dry it in an argon atmosphere at 300 °C for 1 h, and keep it warm at 700 °C for 2 h to obtain a silicon-carbon composite electrode.
[0095] Comparative Example 1
[0096] A preparation method of a silicon-carbon composite electrode includes the following steps:
[0097] S1. Place the copper foam electrode with a thickness of 8 μm into a 6% sodium silicate solution (solvent is water) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and then let it stand for 0.5 h. Then take it out and quickly dry it in a nitrogen atmosphere at 300 °C for 1 h, and in-situ generate silica inside the 75% high-porosity copper foam to obtain copper foam loaded with silica;
[0098] S2. Place the copper foam loaded with silica and metallic magnesium (powder or granular) in a reaction vessel. The mass ratio of silica to metallic magnesium in the copper foam loaded with silica is 2:3. Heat it up to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silica in the copper foam, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain copper foam loaded with silicon particles;
[0099] S3. Place the copper foam loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the copper foam loaded with silicon particles is 6:1. Keep it warm for 2 h under the condition of an argon atmosphere and 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the copper foam to form a lithium-silicon alloy, thus obtaining copper foam loaded with a lithium-silicon alloy.
[0100] S4. Place the copper foam electrode loaded with the lithium-silicon alloy in a tube furnace, heat it up to 570 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), introduce 99.99% acetylene gas, and keep it warm for 2 h to obtain a silicon-carbon composite electrode.
[0101] Comparative Example 2
[0102] A preparation method of a silicon-carbon composite electrode includes the following steps:
[0103] S1. Place the foam carbon electrode with a thickness of 8 μm in a 6% sodium silicate solution (the solvent is water) and let it stand for 0.5 h. Gradually add hydrochloric acid to the sodium silicate solution to adjust the pH to 6, and then let it stand for 0.5 h. Then take it out and quickly dry it for 1 h under the condition of a nitrogen atmosphere and 300 °C to in-situ generate silicon dioxide inside the 75% high-porosity foam carbon, thus obtaining foam carbon loaded with silicon dioxide.
[0104] S2. Place the foam carbon loaded with silicon dioxide and metallic magnesium (powder or granular) in a reaction vessel. The mass ratio of silicon dioxide to metallic magnesium in the foam carbon loaded with silicon dioxide is 2:3. Heat it up to 650 °C in an argon / hydrogen mixed atmosphere (95% argon + 5% hydrogen), maintain the reaction pressure at 100 Pa, and keep it warm for 2 h. Sublime metallic magnesium under low pressure to reduce the silicon dioxide in the foam carbon, and then pickle it with 1 mol / L hydrochloric acid for 2 h to obtain foam carbon loaded with silicon particles.
[0105] S3. Place the foam carbon loaded with silicon particles and lithium hydride in a reaction vessel. The mass ratio of silicon particles to lithium hydride in the foam carbon loaded with silicon particles is 6:1. Keep it warm for 2 h under the condition of an argon atmosphere and 500 °C to decompose lithium hydride to form lithium vapor, and deposit lithium metal on the foam carbon to form a lithium-silicon alloy, thus obtaining foam carbon loaded with a lithium-silicon alloy.
[0106] S4. Place the copper foam electrode loaded with the lithium-silicon alloy in a phenolic resin solution for 1 h, where the mass concentration of the phenolic resin solution is 8% and the solvent is absolute ethanol. Take out the electrode and quickly dry it for 1 h in an argon atmosphere at 300 °C, and keep it warm at 700 °C for 2 h to obtain a silicon-carbon composite electrode.
[0107] Use the prepared electrode as the working electrode, a lithium metal sheet as the counter electrode, and a polypropylene film as the separator, 1 mol L -1A lithium hexafluorophosphate solution (wherein the solvent is a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1) was used as the electrolyte, and a CR2025 button cell was assembled in a glove box filled with argon for electrochemical performance testing. The discharge cut-off voltage was 0.005V, the charge cut-off voltage was 1.5V, and the charge-discharge test was carried out at a current density of C / 10. The results are shown in Table 1.
[0108] Table 1
[0109]
[0110] It can be seen from the data in Table 1 that the silicon-carbon composite electrode prepared by the present invention has a high specific capacity and initial efficiency, and Example 6 shows better performance effects. That is, when the sodium silicate solution is 6%, the mass ratio of silicon particles to lithium hydride is 6:1, and the mass concentration of the phenolic resin solution is 8%, the prepared electrode material has the highest specific capacity, the best cycle stability and rate performance.
[0111] It can be seen from the data of Comparative Example 1 and Example 6 that after changing the carbon source, the capacity and initial efficiency are slightly lower than those of Example 6, and the electrode expansion rate increases slightly. It can be seen from the data of Comparative Example 2 and Example 6 that after changing the substrate porous material, due to the difference in its material strength, the electrode expansion rate has a larger increase. In the present invention, copper foam is used as a framework confinement material to confine the volume expansion during the cycle.
[0112] As Figure 1 shown, Figure 1 The charge-discharge curve of the silicon-carbon composite electrode prepared in Example 6 at a current density of 0.1C is shown. It can be seen that there is no obvious polarization phenomenon in the battery, which is beneficial to cycling. Figure 2 The room temperature cycle of the silicon-carbon composite electrode prepared in Example 6 at 25°C and a current density of 1C is shown. It can be seen that under room temperature conditions, the capacity retention rate of Example 6 is good and there is no cycle diving phenomenon. Figure 3 The high temperature cycle of the silicon-carbon composite electrode prepared in Example 6 at 45°C and a current density of 1C is shown. It can be seen that high temperature affects its capacity retention rate, which is a normal phenomenon, and there is also no cycle diving phenomenon.
[0113] In summary, the silicon-carbon composite electrode provided by the present invention can effectively inhibit the volume expansion of the active material during charge-discharge cycling, and has excellent cycle stability, rate performance and high specific capacity.
[0114] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.
Claims
1. A method for preparing a silicon-carbon composite electrode, characterized in that, It includes the following steps: S1. Immerse the current collector in a silicate solution, take it out, and perform heat treatment to obtain a current collector loaded with silicon dioxide; S2. Perform a magnesiothermic reduction reaction on the current collector loaded with silicon dioxide, and perform pickling to obtain a current collector loaded with silicon particles; S3. Add lithium hydride to the current collector loaded with silicon particles, and perform heat treatment to obtain a current collector loaded with a lithium-silicon alloy; S4. Immerse the current collector loaded with the lithium-silicon alloy in a phenolic resin solution, take it out, and perform carbonization treatment to obtain a silicon-carbon composite electrode.
2. The preparation method according to claim 1, characterized in that, In the above S1, the silicate solution is selected from one or more of aqueous sodium silicate solution, aqueous lithium silicate solution, and aqueous potassium silicate solution; the content of silicic acid in the silicate solution is 5-15%.
3. The preparation method according to claim 1, characterized in that, In the above S1, the current collector is a porous conductive material, and the porous conductive material is selected from one or more of copper foam and carbon foam; the porosity of the porous conductive material is 70-80%, the average pore diameter is 0.1-5 μm; the thickness of the porous conductive material is 6-10 μm.
4. The preparation method according to claim 1, wherein In the above S1, the heat treatment includes treating at 300-500 °C for 1-3 h under a protective gas atmosphere; the protective gas is selected from one or more of argon and nitrogen.
5. The preparation method according to claim 1, characterized in that, In the above S2, the magnesiothermic reduction reaction includes reacting the current collector loaded with silicon dioxide with metallic magnesium under an argon / hydrogen mixed atmosphere, at 600-800 °C, and 50-200 Pa for 2-4 h; the mass ratio of silicon dioxide to metallic magnesium in the current collector loaded with silicon dioxide is (2-3):3; the volume ratio of argon to hydrogen in the argon / hydrogen mixed atmosphere is (92-97):(3-8).
6. The preparation method according to claim 1, characterized in that, In the above S2, the pickling acidic solution is selected from one of hydrochloric acid and sulfuric acid; the concentration of the acidic solution is 1-2 mol / L, and the pickling time is 0.5-4 h.
7. The preparation method according to claim 1, wherein In the above S3, the mass ratio of silicon particles to lithium hydride in the current collector loaded with silicon particles is (5-8):1; the heat treatment includes treating at 400-600 °C for 1-3 h.
8. The preparation method according to claim 1, wherein In the above S4, the phenolic resin solution is a mixed solution of phenolic resin and absolute ethanol, and the mass of phenolic resin in the phenolic resin solution accounts for 5%-10% of the total mass of the phenolic resin solution.
9. The preparation method according to claim 1, characterized in that, In the above S4, the carbonization treatment includes introducing a protective gas, first treating at 300-500 °C for 0.1-1 h, and then treating at 500-1000 °C for 1-5 h.
10. A silicon-carbon composite electrode, characterized in that, Prepared by the preparation method according to any one of claims 1-9.