A poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material and its preparation method

Abstract

The present invention relates to a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material and a preparation method thereof, belonging to the technical field of electrochemical energy storage. Micron silicon particles and lithium phosphate are mixed and dispersed in an acidic solution, heated and stirred until the solution is evaporated to dryness, the solid product is collected and ground to obtain a dark brown powder; the above dark brown powder is transferred to a tube furnace and heat-treated under a protective atmosphere to obtain Si@LPO powder; the Si@LPO powder is dispersed in a Tris solution and subjected to ultrasonic oscillation to obtain a Si@LPO / Tris dispersion solution; dopamine hydrochloride powder is added to the Si@LPO / Tris dispersion solution to obtain a mixture; the above mixture is filtered and washed, the insoluble matter is collected and dried in vacuo to obtain a Si@LPO / PDA anode material. By combining the solution evaporation method and the in-situ polymerization method, a lithium phosphate inorganic coating layer and a poly-dopamine organic coating layer are sequentially constructed on the surface of the micron silicon particles to stabilize the material / electrolyte interface and achieve the performance improvement of the micron silicon-based anode.

Description

Technical Field

[0001] The present invention relates to a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micro-silicon material and a preparation method thereof, belonging to the technical field of electrochemical energy storage. Background Art

[0002] With the rapid development of the social and economic level and people's attention to environmental protection, the use of various clean energies and electric vehicles has been popularized, and the trend of replacing traditional fuel vehicles with new energy vehicles has gradually been accepted by people. As the most advantageous and commercially developed energy storage system at present, lithium-ion batteries have been widely used in electric vehicles. In the context of the increasing demand for long driving ranges of electric vehicles, the research and development of lithium-ion power batteries with high energy density has become a key task in related fields.

[0003] Silicon reacts with lithium ions to form a lithium-silicon alloy, which has an ultra-high theoretical capacity of 3579 mAh·g -1 and is nearly ten times that of traditional graphite anodes. Moreover, it widely exists in nature, has rich reserves and low costs, and is considered to be one of the most competitive anode materials for the next generation of high-energy-density lithium-ion batteries. However, silicon-based anodes have serious volume effects during charge and discharge processes. The volume change exceeding 300% easily causes the repeated rupture and regeneration of the solid electrolyte interface (SEI) film on the surface of the anode material, as well as the pulverization and exfoliation of active substances, ultimately affecting the cycle life of the electrode and leading to battery failure.

[0004] Currently, the modification strategies for silicon-based anode materials mainly focus on the nanosizing of particle size and the construction of surface coating layers. However, the preparation cost of nano-silicon particles is expensive and the technical difficulty is high, which is not conducive to the commercial production and promotion of materials. Moreover, the mechanical strength of the commonly used carbon material coating layer is insufficient to withstand the stress generated during the volume change of silicon particles. Therefore, based on the micro-scale silicon materials with cost advantages, it is of great significance to develop a surface modification technology for silicon anodes with high mechanical strength and excellent electrochemical performance. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micro-silicon material and a preparation method thereof. The method combines solution evaporation method and in-situ polymerization method to sequentially construct a lithium phosphate inorganic coating layer and a poly-dopamine organic coating layer on the surface of micro-silicon particles, stabilize the material / electrolyte interface, and realize the performance improvement of the micro-silicon-based anode.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A preparation method of a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micro-silicon material, the method steps include:

[0008] (1) Mix micron-sized silicon particles (Si) and lithium phosphate (LPO) and disperse them in an acidic solution. Heat and stir until the solution is evaporated to dryness. Collect the solid product and grind it to obtain a dark brown powder.

[0009] (2) Transfer the above dark brown powder to a tube furnace and perform heat treatment under a protective atmosphere to obtain Si@LPO powder.

[0010] (3) Disperse the Si@LPO powder in a tris(hydroxymethyl)aminomethane (Tris) solution and perform ultrasonic oscillation to obtain a Si@LPO / Tris dispersion solution.

[0011] (4) Add dopamine hydrochloride (DA) powder to the Si@LPO / Tris dispersion solution and stir to polymerize DA to obtain a mixture.

[0012] (5) Filter and wash the above mixture, collect the insoluble matter and dry it under vacuum to obtain a Si@LPO / PDA anode material.

[0013] Among them, in step (1), the mass ratio of the micron-sized silicon to lithium phosphate is 100:1 to 10:1.

[0014] In step (3), the ultrasonic oscillation time is 20 - 30 min. The purpose of the ultrasonic treatment step is to uniformly disperse the Si@LPO particles in the solution, which is beneficial to the subsequent in-situ polymerization of dopamine. When the ultrasonic time is too long, the LPO coating layer is likely to fall off, and the modification purpose cannot be achieved; when the ultrasonic time is too short, the Si@LPO particles are likely to agglomerate, affecting the uniformity and integrity of the subsequent in-situ polymerization and coating of dopamine on the surface of single particles, and the best modification effect cannot be achieved. Therefore, a certain limit must be set for the ultrasonic oscillation time.

[0015] In step (4), the mass ratio of dopamine hydrochloride to Si@LPO is 1:100 to 5:100.

[0016] Preferably, in step (1), the particle size of the micron-sized silicon is 1 - 5 microns.

[0017] Preferably, the solute of the acidic solution in step (1) is formic acid or acetic acid. More preferably, the acidic solution in (1) is a formic acid solution, and the volume ratio of formic acid to water is 1:100.

[0018] Preferably, the temperature for heating to dryness in step (1) is 60 - 80 °C.

[0019] Preferably, the protective atmosphere in step (2) is nitrogen or an inert gas.

[0020] Preferably, in step (2), the heat treatment temperature is 300 - 500 °C, the heating rate is 5 - 10 °C / min, and the heat treatment holding time is 3 - 6 h. More preferably, in step (2), the heat treatment temperature is 400 °C, the heating rate is 5 °C / min, and the heat treatment holding time is 6 h.

[0021] Preferably, in step (3), the concentration of the Tris solution is 5 - 15 mmol / L.

[0022] Preferably, in step (4), the magnetic stirring time is 24 - 48 h.

[0023] Preferably, in step (5), the vacuum drying temperature is 60 - 80 °C, and the drying time is 6 - 12 h.

[0024] A poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material is prepared by the above method.

[0025] A lithium-ion battery, wherein the negative electrode of the battery uses the poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material described in the present invention.

[0026] Beneficial effects

[0027] (1) The present invention provides a method for preparing an organic layer / inorganic layer co-coated micron silicon negative electrode material. The lithium phosphate inorganic coating layer has a high Young's modulus and high mechanical strength to resist the stress generated by the volume effect of silicon particles during charge and discharge. In addition, lithium phosphate is a lithium ion conductor, which can improve the lithium ion conduction ability of the material during charge and discharge. The poly-dopamine organic coating layer has strong adhesion and mechanical toughness, which can inhibit the pulverization failure of silicon particles. The organic / inorganic co-coating layer combines the characteristics of high strength and high toughness, while ensuring the lithium ion conduction ability of the negative electrode material, and can effectively improve the electrochemical performance of the micron silicon negative electrode.

[0028] (2) The raw material selected in the present invention is silicon particles at the micron scale. Compared with the currently commonly used nano-silicon, it has the characteristics of simple preparation process and low cost. In addition, the organic layer / inorganic layer co-coated micron silicon negative electrode material prepared in the present invention has the characteristics of high tap density and high capacity, and has the prospect of industrial application. Description of the drawings

[0029] Figure 1 It is the X-ray diffraction (XRD) pattern of Si@LPO / PDA in Example 1.

[0030] Figure 2 It is the scanning electron microscope (SEM) image of the Si@LPO / PDA sample prepared in Example 1.

[0031] Figure 3 The first charge-discharge curve of the Si@LPO / PDA electrode in Example 1 cycled at a current density of 0.1C (1C current density is 2000 mA / g) in the voltage window of 0.01 - 1.5V.

[0032] Figure 4 Charge-discharge cycle data of the Si@LPO / PDA electrode in Example 1 tested at a current density of 1 / 3C in the voltage window of 0.01 - 1.5V.

[0033] Figure 5 Charge-discharge cycle data of the Si@LPO / PDA electrode in Example 1 tested at a current density of 1C in the voltage window of 0.01 - 1.5V.

[0034] Figure 6 The first charge-discharge curve of the Si@1LPO / PDA electrode in Example 2 cycled at a current density of 0.1C in the voltage window of 0.01 - 1.5V.

[0035] Figure 7 Charge-discharge cycle data of the Si@1LPO / PDA electrode in Example 2 tested at a current density of 1C in the voltage window of 0.01 - 1.5V.

[0036] Figure 8 The first charge-discharge curve of the Si@10LPO / PDA electrode in Example 3 cycled at a current density of 0.1C in the voltage window of 0.01 - 1.5V.

[0037] Figure 9 Charge-discharge cycle data of the Si@10LPO / PDA electrode in Example 3 tested at a current density of 1C in the voltage window of 0.01 - 1.5V.

[0038] Figure 10 X-ray diffraction (XRD) pattern of the original micron silicon in Comparative Example 1.

[0039] Figure 11 Scanning electron microscope (SEM) image of the original micron silicon in Comparative Example 1.

[0040] Figure 12 The first charge-discharge curve of the original micron silicon electrode in Comparative Example 1 cycled at a current density of 0.1C in the voltage window of 0.01 - 1.5V.

[0041] Figure 13 Charge-discharge cycle data of the micron silicon electrode in Comparative Example 1 tested at a current density of 1 / 3C in the voltage window of 0.01 - 1.5V.

[0042] Figure 14The charge-discharge cycle data of the micron silicon electrode in Comparative Example 1 were tested at a current density of 1C within a voltage window of 0.01 - 1.5V.

[0043] Figure 15 The first charge-discharge curve of the Si@PDA electrode in Comparative Example 2 cycled at a current density of 0.1C within a voltage window of 0.01 - 1.5V.

[0044] Figure 16 The charge-discharge cycle data of the Si@PDA electrode in Comparative Example 2 were tested at a current density of 1C within a voltage window of 0.01 - 1.5V.

[0045] Figure 17 The first charge-discharge curve of the Si@LPO electrode in Comparative Example 3 cycled at a current density of 0.1C within a voltage window of 0.01 - 1.5V.

[0046] Figure 18 The charge-discharge cycle data of the Si@LPO electrode in Comparative Example 3 were tested at a current density of 1C within a voltage window of 0.01 - 1.5V. Detailed implementation manners

[0047] The present invention will be further described in detail below in conjunction with specific embodiments.

[0048] Example 1

[0049] (1) Weigh 2g of micron silicon powder and 0.1g of lithium phosphate, mix and disperse them in a formic acid solution (the volume ratio of formic acid to deionized water is 1:100), and magnetically stir at 80°C until the solution is evaporated to dryness. Collect the solid product and grind it to obtain a dark brown powder.

[0050] (2) Transfer the above dark brown powder to a tube furnace, keep it at 400°C for 6h under an argon atmosphere, and the heating rate is 5°C / min to obtain Si@LPO powder.

[0051] (3) Disperse the Si@LPO powder in 100 mL of a 10 mmol / L tris(hydroxymethyl)aminomethane (Tris) solution and ultrasonically oscillate for 30 min to obtain a Si@LPO / Tris dispersion solution.

[0052] (4) Weigh 0.1g of dopamine hydrochloride (DA) powder, add it to the above Si@LPO / Tris dispersion solution, and magnetically stir at room temperature for 24h to polymerize DA.

[0053] (5) Filter and wash the above solution, collect the insoluble matter, transfer it to a vacuum oven, and vacuum dry it at 60°C for 6h to obtain the Si@LPO / PDA negative electrode material.

[0054] The XRD test results of Si@LPO / PDA are as follows Figure 1 shown. The strong diffraction peaks at 2Theta of 28.45°, 47.30° and 56.12° correspond to the (111), (220) and (311) crystal planes of crystalline silicon respectively, indicating that the modification process does not change the crystal structure of micron silicon. In addition, a series of characteristic peaks of lithium phosphate appear in the range of 2Theta from 21.10° to 25.50° and near 34.10°, indicating the presence of lithium phosphate. The relatively weak diffraction peak intensity may be due to the poor crystallinity of the inorganic layer of lithium phosphate on the surface.

[0055] The SEM test results of Si@LPO / PDA are as follows Figure 2 shown. It can be observed that after co - coating with lithium phosphate and polydopamine, the surface of the material particles becomes dense.

[0056] Using the above Si@LPO / PDA as the negative electrode active material, Super P as the conductive agent, and PAALi as the binder, the three are mixed in a mass ratio of 8:1:1. Using water as the solvent, grind them in an agate mortar for 30 min to obtain the electrode slurry. Using copper foil as the current collector, coat the electrode slurry on the copper foil, transfer it to a vacuum drying oven, take it out after vacuum drying at 80 °C for 12 h, use a cutter to punch out circular electrodes with a diameter of 11 mm, and continue to dry them in a vacuum drying oven at 120 °C for 2 h. Using the prepared electrode as the negative electrode, a lithium sheet as the counter electrode, celgard2500 as the separator, and an organic solvent solution of 1 mol / L LiPF6 in EC + DMC (volume ratio 1:1) with 5% FEC as the electrolyte, assemble a CR2032 button battery in a glove box filled with an argon atmosphere.

[0057] Perform electrochemical performance tests on the assembled battery on a LAND battery test system. Figure 3 is the first - cycle charge - discharge curve of the Si@LPO / PDA electrode in Example 1 at a current density of 0.1C (1C current density is 2000 mA / g) in the voltage window of 0.01 - 1.5V, indicating that the discharge specific capacity and charge specific capacity of Si@LPO / PDA in the first - cycle are 3452.6 mAh / g and 3122.1 mAh / g respectively, and the first - cycle Coulomb efficiency is 90.4%. Figure 4 is the charge - discharge cycle data of the Si@LPO / PDA electrode in Example 1 at a current density of 1 / 3C in the voltage window of 0.01 - 1.5V. After 40 stable cycles, it still has a reversible specific capacity of 1324.9 mAh / g, and the capacity retention rate is 69.24%. Figure 5For the Si@LPO / PDA electrode in Example 1, charge-discharge cycle data was tested at a current density of 1C within a voltage window of 0.01 - 1.5V. After 100 cycles, it still had a reversible specific capacity of 1187.5 mAh / g, and the capacity retention rate was 59.15%.

[0058] Example 2

[0059] (1) Weigh 2 g of micron-sized silicon powder and 0.2 g of lithium phosphate and disperse them in a formic acid solution (the volume ratio of formic acid to deionized water is 1:100). Stir magnetically at 80°C until the solution is evaporated to dryness. Collect the solid product and grind it to obtain a dark brown powder.

[0060] (2) Transfer the above dark brown powder to a tube furnace, keep it at 400°C for 6 h under an argon atmosphere, and the heating rate is 5°C / min to obtain Si@LPO powder.

[0061] (3) Disperse the Si@LPO powder in 100 mL of a 10 mmol / L tris(hydroxymethyl)aminomethane (Tris) solution and ultrasonically oscillate for 30 min to obtain a Si@LPO / Tris dispersion solution.

[0062] (4) Weigh 0.1 g of hydrochloric acid dopamine (DA) powder and add it to the above Si@LPO / Tris dispersion solution. Stir magnetically at room temperature for 24 h to polymerize DA.

[0063] (5) Filter and wash the above solution, collect the insoluble matter and transfer it to a vacuum oven, and vacuum dry it at 60°C for 6 h to obtain the Si@10LPO / PDA negative electrode material.

[0064] The XRD test results of Si@LPO / PDA indicate the presence of lithium phosphate.

[0065] The SEM test results of Si@LPO / PDA show that after co - coating with lithium phosphate and polydopamine, the surface of the material particles becomes dense.

[0066] Using the above Si@10LPO / PDA as the negative electrode active material, Super P as the conductive agent, and PAALi as the binder, the three were mixed at a mass ratio of 8:1:1. Using water as the solvent, they were ground in an agate mortar for 30 min to obtain an electrode slurry. Using copper foil as the current collector, the electrode slurry was coated on the copper foil, transferred to a vacuum drying oven, taken out after vacuum drying at 80 °C for 12 h, and a circular pole piece with a diameter of 11 mm was obtained using a cutting machine, and it was further dried in a vacuum drying oven at 120 °C for 2 h. Using the prepared pole piece as the negative electrode, a lithium piece as the counter electrode, celgard2500 as the separator, and an organic solvent with 1 mol / L LiPF6 dissolved in EC+DMC (volume ratio 1:1) added with 5% FEC as the electrolyte, a CR2032 button battery was assembled in a glove box filled with an argon atmosphere.

[0067] The assembled battery was subjected to electrochemical performance testing on a LAND battery test system. Figure 6 It is the first-cycle charge-discharge curve obtained by cycling the Si@10LPO / PDA electrode in Example 2 at a current density of 0.1C (1C current density is 2000 mA / g) in a voltage window of 0.01 - 1.5V, indicating that the discharge specific capacity and charge specific capacity of Si@10LPO / PDA in the first-cycle are 3336.8 mAh / g and 3009.2 mAh / g respectively, and the first-cycle Coulombic efficiency is 90.2%. Figure 7 It is the charge-discharge cycle data obtained by testing the Si@10LPO / PDA electrode in Example 2 at a current density of 1C in a voltage window of 0.01 - 1.5V. After 100 cycles, it still has a reversible specific capacity of 1098.2 mAh / g, and the capacity retention rate is 57.80%.

[0068] Example 3

[0069] (1) Weigh 2 g of micron-sized silicon powder and 0.02 g of lithium phosphate and disperse them in a formic acid solution (the volume ratio of formic acid to deionized water is 1:100), and stir magnetically at 80 °C until the solution evaporates to dryness. Collect the solid product and grind it to obtain a dark brown powder.

[0070] (2) Transfer the above dark brown powder to a tubular furnace, keep it at 400 °C for 6 h under an argon atmosphere, and the heating rate is 5 °C / min to obtain Si@LPO powder.

[0071] (3) Disperse the Si@LPO powder in 100 mL of a 10 mmol / L tris(hydroxymethyl)aminomethane (Tris) solution and ultrasonically oscillate for 30 min to obtain a Si@LPO / Tris dispersion solution.

[0072] (4) Weigh 0.1 g of dopamine hydrochloride (DA) powder and add it to the above Si@LPO / Tris dispersion solution. Stir magnetically at room temperature for 24 h to polymerize DA.

[0073] (5) Filter and wash the above solution, collect the insoluble matter and transfer it to a vacuum oven. Dry it under vacuum at 60 °C for 6 h to obtain the Si@1LPO / PDA anode material.

[0074] The XRD test results of Si@LPO / PDA indicate the presence of lithium phosphate.

[0075] The SEM test results of Si@LPO / PDA show that after co - coating with lithium phosphate and polydopamine, the surface of the material particles becomes dense.

[0076] Take the above Si@1LPO / PDA as the anode active material, Super P as the conductive agent, and PAALi as the binder. Mix the three in a mass ratio of 8:1:1, use water as the solvent, and grind in an agate mortar for 30 min to obtain the electrode slurry. Use copper foil as the current collector, coat the electrode slurry on the copper foil, transfer it to a vacuum drying oven, take it out after drying under vacuum at 80 °C for 12 h, use a cutter to punch out a circular pole piece with a diameter of 11 mm, and continue to dry it in the vacuum drying oven at 120 °C for 2 h. Take the prepared pole piece as the anode, a lithium piece as the counter electrode, celgard2500 as the separator, and an organic solvent solution of 1 mol / L LiPF6 in EC + DMC (volume ratio 1:1) with 5% FEC added as the electrolyte, and assemble it into a CR2032 button battery in a glove box filled with argon atmosphere.

[0077] Conduct electrochemical performance tests on the assembled battery on the LAND battery test system. Figure 8 The first - cycle charge - discharge curve of the Si@1LPO / PDA electrode in Example 3 at a current density of 0.1C (1C current density is 2000 mA / g) in the voltage window of 0.01 - 1.5V shows that the discharge specific capacity and charge specific capacity of Si@1LPO / PDA in the first - cycle are 3572.1 and 3198.7 mAh / g respectively, and the first - cycle Coulomb efficiency is 89.5%. Figure 9 The charge - discharge cycle data of the Si@1LPO / PDA electrode in Example 3 at a current density of 1C in the voltage window of 0.01 - 1.5V. After 100 cycles, it still has a reversible specific capacity of 1226.4 mAh / g, and the capacity retention rate is 58.43%.

[0078] Comparative Example 1

[0079] (1) Transfer 2 g of micron-sized silicon powder into a tube furnace, pass high-purity argon gas, heat it to 400 °C at a heating rate of 5 °C / min under the protection of an argon atmosphere, hold for 6 h, and then cool it with the furnace to obtain a heat-treated micron-sized silicon sample.

[0080] The XRD test results of the micron-sized silicon are as Figure 10 shown. The strong diffraction peaks at 2Theta of 28.45°, 47.30°, and 56.12° correspond to the (111), (220), and (311) crystal planes of crystalline silicon respectively. After comparing with the PDF card, there are no other impurity peaks except the characteristic peaks of crystalline silicon.

[0081] The SEM test results of the micron-sized silicon are as Figure 11 shown. It can be observed that the silicon particle sizes are mainly distributed in the range of 1 - 5 μm, the particle surfaces are rough, and there is a certain degree of agglomeration.

[0082] (2) Use the above-mentioned micron-sized silicon directly as the active material, Super P as the conductive agent, and PAALi as the binder. Mix the three at a mass ratio of 8:1:1, use water as the solvent, and grind them in an agate mortar for 30 min to obtain the electrode slurry. Use a copper foil as the current collector, coat the electrode slurry on the copper foil, transfer it to a vacuum drying oven, take it out after vacuum drying at 80 °C for 12 h, use a cutting machine to punch out a circular pole piece with a diameter of 11 mm, and continue to dry it in the vacuum drying oven at 120 °C for 2 h. Use the prepared pole piece as the negative electrode, a lithium piece as the counter electrode, celgard2500 as the separator, and an organic solvent solution of 1 mol / L LiPF6 in EC + DMC (volume ratio 1:1) with 5% FEC added as the electrolyte to assemble a CR2032 button battery in a glove box filled with an argon atmosphere.

[0083] Carry out electrochemical performance tests on the assembled battery on a LAND battery test system. Figure 12 This is the first-cycle charge-discharge curve of the micron-sized silicon electrode in Comparative Example 1 obtained by cycling at a current density of 0.1C in a voltage window of 0.01 - 1.5V. It can be seen from the figure that the first-cycle discharge specific capacity and charge specific capacity of the Si electrode are 3668.5 and 2900.5 mAh / g respectively, and the first-cycle Coulombic efficiency is 79.1%. Figure 13 This is the charge-discharge cycle data of the micron-sized silicon electrode tested at a current density of 1 / 3C in a voltage window of 0.01 - 1.5V. After 40 cycles, the reversible specific capacity is 1002.9 mAh / g, and the capacity retention rate is 57.82%. Figure 14 This is the charge-discharge cycle data of the micron-sized silicon electrode tested at a current density of 1C in a voltage window of 0.01 - 1.5V. After 100 cycles, it has a reversible specific capacity of 607.4 mAh / g, and the capacity retention rate is 46.03%.

[0084] Comparative Example 2

[0085] (1) Take 2 g of micron-sized silicon powder and disperse it in 100 mL of a 10 mmol / L tris(hydroxymethyl)aminomethane (Tris) solution, and ultrasonically oscillate for 30 min to obtain a Si / Tris dispersion solution.

[0086] (2) Weigh 0.1 g of dopamine hydrochloride (DA) powder, add it to the above dispersion solution, and magnetically stir at room temperature for 24 h to polymerize DA.

[0087] (4) Filter and wash the above solution, collect the insoluble matter, transfer it to a vacuum oven, and vacuum dry it at 60 °C for 6 h to obtain the Si@PDA anode material.

[0088] Using the above Si@PDA as the active material, Super P as the conductive agent, and PAALi as the binder, mix the three at a mass ratio of 8:1:1, use water as the solvent, and grind in an agate mortar for 30 min to obtain an electrode slurry. Using a copper foil as the current collector, coat the electrode slurry on the copper foil, transfer it to a vacuum drying oven, take it out after vacuum drying at 80 °C for 12 h, use a cutter to punch out a circular electrode sheet with a diameter of 11 mm, and continue to dry it in the vacuum drying oven at 120 °C for 2 h. Use the prepared electrode sheet as the anode, a lithium sheet as the counter electrode, celgard2500 as the separator, and an organic solvent containing 1 mol / L LiPF6 in EC+DMC (volume ratio 1:1) with 5% FEC added as the electrolyte, and assemble it into a CR2032 coin cell in a glove box filled with an argon atmosphere.

[0089] Perform electrochemical performance tests on the assembled battery on a LAND battery test system. Figure 15 Figure is the first-cycle charge-discharge curve of the Si@PDA electrode in Comparative Example 2 cycled at a current density of 0.1C in the voltage window of 0.01 - 1.5V. It can be seen from the figure that the first-cycle discharge specific capacity and charge specific capacity of the Si@PDA electrode are 3566.7 and 2827.6 mAh / g respectively, and the first-cycle Coulombic efficiency is 79.3%. Figure 16 Figure shows the charge-discharge cycle data of the Si@PDA electrode tested at a current density of 1C within the voltage window of 0.01 - 1.5V. After 100 cycles, it has a reversible specific capacity of 562 mAh / g and a capacity retention rate of 42.49%.

[0090] Comparative Example 3

[0091] (1) Weigh 2 g of micron-sized silicon powder and 0.1 g of lithium phosphate, mix and disperse them in a formic acid solution (the volume ratio of formic acid to deionized water is 1:100), magnetically stir at 80 °C until the solution evaporates to dryness, collect the solid product and grind it to obtain a dark brown powder.

[0092] (2) Transfer the above-mentioned dark brown powder into a tubular furnace, keep it at 400 °C for 6 h under an argon atmosphere, with a heating rate of 5 °C / min, to obtain Si@LPO powder.

[0093] Using the above Si@LPO as the active material, Super P as the conductive agent, and PAALi as the binder, mix the three according to a mass ratio of 8:1:1, use water as the solvent, and grind in an agate mortar for 30 min to obtain the electrode slurry. Using a copper foil as the current collector, coat the electrode slurry on the copper foil, transfer it to a vacuum drying oven, take it out after vacuum drying at 80 °C for 12 h, use a cutter to punch out a circular pole piece with a diameter of 11 mm, and continue to dry it in the vacuum drying oven at 120 °C for 2 h. Use the prepared pole piece as the negative electrode, a lithium piece as the counter electrode, celgard2500 as the separator, and an organic solvent solution of 1 mol / L LiPF6 in EC+DMC (volume ratio 1:1) added with 5% FEC as the electrolyte, and assemble it into a CR2032 button battery in a glove box filled with an argon atmosphere.

[0094] Perform electrochemical performance tests on the assembled battery on a LAND battery test system. Figure 15 Figure [X] is the first-cycle charge-discharge curve of the Si@LPO electrode in Comparative Example 2 cycled at a current density of 0.1C in the voltage window of 0.01 - 1.5V. As can be seen from the figure, the first-cycle discharge specific capacity and charge specific capacity of the Si@LPO electrode are 3570.9 and 3092.1 mAh / g respectively, and the first-cycle Coulombic efficiency is 86.6%. Figure 16 Figure [X] shows the charge-discharge cycle data of the Si@LPO electrode tested at a current density of 1C in the voltage window of 0.01 - 1.5V. After 100 cycles, it has a reversible specific capacity of 969.2 mAh / g and a capacity retention rate of 53.72%.

[0095] Table 1 Comparison of Electrochemical Performance of Different Samples

[0096]

[0097]

[0098] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention will be regarded as within the protection scope of the present invention.

Claims

1. A preparation method of a polydopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material, characterized in that: The method steps include: (1) Mix and disperse micron-sized silicon (Si) particles and lithium phosphate (LPO) in an acidic solution, and stir magnetically and heat until the solution is evaporated to dryness. Collect the solid product and grind it to obtain a dark brown powder; (2) Transfer the above dark brown powder to a tube furnace and perform heat treatment under a protective atmosphere to obtain Si@LPO powder; (3) Disperse the Si@LPO powder in a tris(hydroxymethyl)aminomethane (Tris) solution and perform ultrasonic oscillation to obtain a Si@LPO / Tris dispersion solution; (4) Add dopamine hydrochloride (DA) powder to the Si@LPO / Tris dispersion solution, and stir magnetically at room temperature to polymerize DA to form polydopamine (PDA) to obtain a mixture; (5) Filter and wash the above mixture, collect the insoluble matter and dry it under vacuum to obtain a Si@LPO / PDA anode material; Among them, in step (1), the mass ratio of the micron-sized silicon to lithium phosphate is 100:1 to 10:1; In step (3), the ultrasonic oscillation time is 20 to 30 min; In step (4), the mass ratio of dopamine hydrochloride to Si@LPO is 1:100 to 5:

100.

2. The preparation method of a polydopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material as described in claim 1, characterized in that: In step (1), the particle size of the micron-sized silicon is 1 to 5 microns.

3. The preparation method of a polydopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material as described in claim 1, wherein: In step (1), the solute of the acidic solution is formic acid or acetic acid; the temperature for heating to dryness is 60 to 80 °C.

4. The preparation method of a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material according to claim 1, wherein: The protective atmosphere in step (2) is nitrogen or an inert gas.

5. The preparation method of a polydopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material according to claim 1, characterized in that: In step (2), the heat treatment temperature is 300 to 500 °C, the heating rate is 5 to 10 °C / min, and the heat treatment holding time is 3 to 6 h.

6. The preparation method of a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material as described in claim 1, wherein: In step (3), the concentration of the Tris solution is 5 to 15 mmol / L.

7. The preparation method of a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material as described in claim 1, characterized in that: In step (4), the magnetic stirring time is 24 to 48 h.

8. The preparation method of a poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron silicon material according to claim 1, characterized in that: In step (5), the vacuum drying temperature is 60 to 80 °C, and the drying time is 6 to 12 h.

9. A poly-dopamine / lithium phosphate composite organic layer / inorganic layer co-coated micro-silicon material, characterized in that: The material is prepared by the method according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that: The anode material of the battery is a polydopamine / lithium phosphate composite organic layer / inorganic layer co-coated micron-sized silicon material according to claim 9.

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