Preparation method of polypyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano silicon negative electrode material

Abstract

The invention relates to a preparation method of a polypyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano silicon negative electrode material, and belongs to the technical field of lithium ion batteries. The material comprises nano silicon particles, and a lithium metaborate layer and a polypyrrole layer which are sequentially coated on the surfaces of the nano silicon particles, the material is prepared by combining a solution evaporation drying method and a liquid phase chemical oxidation polymerization method, the diffusion path of lithium ions can be shortened by selecting the nano silicon particles, and the lithium is more uniformly intercalated and deintercalated, so that the stress concentration is reduced, and LBO is used as a rigid coating layer, so that the stability of the material is improved. And the surface of the nano silicon particles is coated with the composite material, so that impact can be resisted, irreversible deformation and fracture are avoided, the integrity of the structure is kept, and the lithium ion conductivity of the material in the charging and discharging process is improved. PPy is used as a flexible coating layer, coats the surface of the LBO layer, has relatively high flexibility and viscosity, and can adapt to volume expansion of silicon particles; the synergistic effect of the two improves the lithium ion conductivity and electrochemical performance of the nano-silicon negative electrode material.

Description

Technical Field

[0001] This invention relates to a method for preparing a nano-silicon anode material co-coated with a polypyrrole / lithium metaborate composite flexible / rigid layer, belonging to the field of lithium-ion battery technology. Background Technology

[0002] In recent years, the development of lithium-ion battery (LIB) technology has placed multi-dimensional performance demands on electrode materials. Besides long cycle life and environmental friendliness, high energy / power density has become a key indicator. Currently, commercially available graphite anodes are limited to 372 mAh g⁻¹. -1 The theoretical specific capacity of batteries severely restricts breakthroughs in improving battery energy density, making it difficult to meet the ever-growing market demand. Against this backdrop, the development of novel anode materials that combine high specific capacity, excellent mechanical stability, and long cycle life is imperative.

[0003] Silicon-based materials are characterized by their ultra-high theoretical specific capacity (~3579 mAh g⁻¹). -1 Silicon (with a capacity nearly ten times that of graphite) has become the most promising anode material candidate. Its advantages also include high crustal abundance and low raw material costs. However, the dramatic volume expansion (~300%) that occurs during electrochemical lithium insertion / extraction in silicon triggers multiple failure mechanisms: including repeated rupture and dynamic reconstruction of the SEI film, microcrack propagation of active particles, and pulverization. These irreversible damages directly lead to a decrease in first-cycle coulombic efficiency (ICE), accelerated capacity decay, and deterioration of cycle stability. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing a nano-silicon anode material co-coated with a polypyrrole / lithium metaborate composite flexible / rigid layer. By using a solution evaporation method and a liquid-phase chemical oxidation polymerization method, a flexible-rigid coating layer is formed to improve the structural stability of the silicon anode material during cycling, thereby improving the first-cycle coulombic efficiency and long-cycle performance.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material, the material comprising nano-silicon particles and a lithium metaborate layer and a polypyrrole layer sequentially coated on the surface of the nano-silicon particles.

[0007] Preferably, the particle size of the silicon nanoparticles is 80–120 nm.

[0008] A method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material, the method steps include:

[0009] (1) using lithium metaborate (LBO) to coat nano-silicon particles (Si NPs) by solution evaporation method, to obtain lithium metaborate coated nano-silicon particles (NPs@LBO);

[0010] (2) using pyrrole as monomer, using liquid phase chemical oxidation polymerization method to coat the lithium metaborate coated nano-silicon particles, to obtain poly-pyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano-silicon negative electrode material (NPs@LBO@PPy).

[0011] Preferably, in step (1), the nano-silicon particles (Si NPs) and lithium metaborate (LBO) are mixed and dispersed in an acidic solution, stirred until the solution is evaporated, and the obtained powder is dried and heat treated in a protective gas atmosphere to obtain lithium metaborate coated nano-silicon particles (NPs@LBO).

[0012] Preferably, the mass ratio of the nano-silicon particles to lithium metaborate is 2-100:1, more preferably 2-10:1.

[0013] Preferably, the acidic solution is a formic acid aqueous solution, and the volume ratio of formic acid to water is 1-5:100.

[0014] Preferably, the evaporation temperature is 60-80℃.

[0015] Preferably, the heat treatment temperature is 300-500℃, the heating rate is 5-10℃·min -1 , and the heat treatment holding time is 3-6h.

[0016] Preferably, in step (2), the lithium metaborate coated nano-silicon particles are dispersed in an organic solvent, pyrrole, sodium p-toluenesulfonate and ferric chloride (FeCl3) are added, stirred in an ice water bath, centrifuged, dried, and the obtained powder is heat treated in a protective gas atmosphere to obtain poly-pyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano-silicon negative electrode material (NPs@LBO@PPy).

[0017] Preferably, the organic solvent is ethanol.

[0018] Preferably, the amount ratio of the lithium metaborate coated nano-silicon particles, pyrrole, sodium p-toluenesulfonate and ferric chloride is 0.3-0.7g:250-300μL:0.05-0.15g:0.5-1g.

[0019] Preferably, the stirring is performed in an ice water bath at 0-3℃ for 5-6h.

[0020] Preferably, the centrifugation is performed by alternately treating with deionized water and anhydrous ethanol for 4-5 times.

[0021] Preferably, the heat treatment temperature is 300-500 DEG C, the heating rate is 5-10 DEG C / min -1 , and the heat treatment holding time is 3-6 h.

[0022] A lithium ion battery, wherein the negative electrode material of the battery is the poly-pyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano-silicon negative electrode material.

[0023] Advantages

[0024] The material comprises nano-silicon particles and a lithium metaborate layer and a poly-pyrrole layer successively coated on the surface of the nano-silicon particles, the selected nano-silicon particles can shorten the diffusion path of lithium ions, more uniformly embed and extract lithium, thereby reducing stress concentration, the LBO as a rigid coating layer can resist impact, avoid irreversible deformation and fracture, maintain the integrity of the structure, and improve the lithium ion conduction capacity of the material in the charging and discharging process. The PPy as a flexible coating layer is coated on the surface of the LBO layer, has strong flexibility and adhesion, and can adapt to the volume expansion of the silicon particles; meanwhile, the high polymer adaptively expands the volume, buffers the risk of interface peeling, and the synergistic effect of the two improves the lithium ion conduction capacity and electrochemical performance of the nano-silicon negative electrode material.

[0025] The present application is prepared by combining the solution evaporation method and the liquid phase chemical oxidation polymerization method, a stable functional coating layer is constructed on the surface of the nano-silicon negative electrode, the coating layer comprises a rigid coating layer of lithium metaborate and a flexible coating layer of poly-pyrrole. The double-layer coating layer has the following core advantages: (1) stress buffering effect: effectively buffers the volume strain in the lithium intercalation and extraction process, and balances the rigidity and flexibility, thereby inhibiting the crack propagation caused by stress concentration in the particle; (2) SEI regulation function: promotes the formation of a dense and stable SEI film structure, and reduces the interface side reaction; (3) structure reinforcement effect: enhances the overall mechanical integrity of the electrode, and inhibits the peeling of the active material. The synergistic effect significantly improves the electrochemical performance, and provides a new path for the practicalization of high-specific-energy silicon-based negative electrodes. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 X-ray diffraction patterns of NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, NPs@LBO@PPy samples.

[0027] Figure 2 X-ray diffraction pattern of a LiBO2 standard sample.

[0028] Figure 3 FT-IR curves of NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, NPs@LBO@PPy samples.

[0029] Figure 4 The image shows the FT-IR curve of the LiBO2 standard sample.

[0030] Figure 5 For NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes, under a voltage window of 0.01–1.5V, a current density of 0.1C (2000 mA g) is applied. -1 The first-cycle charge-discharge curve obtained by current density cycling.

[0031] Figure 6 For NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes, under a voltage window of 0.01–1.5V, a current density of 0.1C (2000 mA g) is applied. -1 Charge-discharge cycle data obtained from current density cycling.

[0032] Figure 7 For NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes, under a voltage window of 0.01–1.5V, a current density of 0.3C (2000 mA at 1C) is applied. -1 Charge-discharge cycle data obtained from current density cycling.

[0033] Figure 8 For NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes, under a voltage window of 0.01–1.5V, a current density of 1C (2000 mA g) is applied. -1 Charge-discharge cycle data obtained from current density cycling. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments.

[0035] Comparative Example 1

[0036] 0.5 g of nano-silicon powder (100 nm) was dispersed in 40 mL of ethanol. 0.1 g of sodium p-toluenesulfonate (dopant 0.05–0.15 g) and 280 μL of pyrrole monomer were added, and the mixture was sonicated for 10 min. The mixture was stirred in an ice bath, and then FeCl3 ethanol solution (0.8 g FeCl3 dissolved in 20 mL of ethanol) was added. The mixture was stirred at 0 °C for 6 h. After alternating centrifugation with water and anhydrous ethanol, the powder was dried at 80 °C for 720 min to obtain a grayish-brown powder.

[0037] The resulting grayish-brown powder was transferred to a tube furnace and heated at a rate of 5 °C / min under an argon atmosphere. -1The temperature was raised to 400℃ and kept for 6h to obtain the polypyrrole-coated nano-silicon powder, denoted as NPs@PPy.

[0038] Comparative Example 2

[0039] 1g of nano-silicon powder (100nm) and 0.5g of lithium metaborate were weighed and mixed and dispersed in 101mL of formic acid solution (formic acid and deionized water in a volume ratio of 1:100), and magnetically stirred at 80℃ until the solution was evaporated to dryness. The solid product was collected and ground to obtain a dark brown powder.

[0040] The obtained dark brown powder was transferred to a tube furnace, and heated at a rate of 5℃·min-1 to 400℃ under an argon atmosphere, and kept for 6h to obtain the lithium metaborate-coated nano-silicon powder, denoted as NPs@LBO. -1 The temperature was raised to 400℃ and kept for 6h to obtain the polypyrrole-coated nano-silicon powder, denoted as NPs@PPy.

[0041] Comparative Example 3

[0042] The nano-silicon powder in Comparative Example 2 was replaced by NPs@PPy in Comparative Example 1, and the rest was the same as Comparative Example 2, to obtain a nano-silicon powder coated with a lithium metaborate / polypyrrole composite rigid layer / soft layer, denoted as NPs@PPy@LBO.

[0043] Example 1

[0044] The nano-silicon powder in Comparative Example 1 was replaced by NPs@LBO in Comparative Example 2, and the rest was the same as Comparative Example 1, to obtain a nano-silicon powder coated with a polypyrrole / lithium metaborate composite soft layer / rigid layer, denoted as NPs@LBO@PPy.

[0045] The X-ray diffraction patterns of the above NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, NPs@LBO@PPy samples are shown in Figure 1 The nano-Si bulk (NPs) was detected at 28.4°, 47.3°, 56.1°, 69.1° and 76.3°, which were the typical Si characteristic peaks belonging to the (111), (220), (311), (400) and (331) crystal planes of Si (PDF #27-1402). After coating with PPy, the peak shape of the sample did not change significantly, which may be due to the structure of PPy showing amorphous state and not producing obvious diffraction peaks. After coating with lithium metaborate (LBO), the NPs@LBO, NPs@PPy@LBO, NPs@LBO@PPy samples very obviously appeared the characteristic peaks of LBO at 27.9°, 30.4°, 37.1° and 41.5°, which belonged to the (-102), (002), (-211) and (020) crystal planes of LBO (PDF #51-0517). The X-ray diffraction pattern of the standard LBO sample is shown in Figure 2As shown, this indicates that LBO was successfully coated onto the sample. Further investigation was conducted using Fourier transform infrared spectroscopy (FT-IR) to study the molecular structure of the material, such as... Figure 3 As shown. The original sample and the modified sample were at 1100 cm. -1 Obvious absorption peaks were observed at all positions, corresponding to the stretching vibrations of the Si-O-Si bond, and a peak was also detected at 1552 cm⁻¹. -1 1471cm -1 and 1309cm -1 The characteristic vibrational absorption peaks of the pyrrole ring at the location represent the stretching vibrations of the C=C bond, the stretching vibrations of the C=N bond, and the bending vibrations of the C=N bond, respectively, indicating the successful encapsulation of PPy. The X-ray diffraction pattern of the standard LBO sample is shown below. Figure 4 As shown in the figure, at 1400cm -1 Significant BO stretching vibration was detected at [location name]. Figure 3 1400cm -1 BO stretching vibration was also detected at the site, further confirming the successful encapsulation of LBO.

[0046] The aforementioned NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy were used as negative electrode active materials, with Super P as the conductive agent and PAA-Li as the binder. These three materials were mixed in a 6:2:2 mass ratio and ground in an agate mortar for 30 minutes using water as the solvent to obtain the electrode slurry. Copper foil was used as the current collector, and the electrode slurry was coated onto the copper foil. The coated foil was then transferred to a vacuum drying oven and vacuum dried at 80°C for 12 hours. After drying, the foil was cut into 11mm diameter circular electrode sheets using a cutting machine and further dried at 120°C for 2 hours in a vacuum drying oven. The prepared electrode sheets were used as the negative electrode, lithium foil as the counter electrode, Celgard 2500 as the separator, and an organic solvent containing 1 mol / L LiPF6 in EC+DMC (volume ratio 1:1) with 5% FEC was used as the electrolyte. The cells were assembled into CR2032 button batteries in an argon-filled glove box.

[0047] Electrochemical performance tests were conducted on the assembled batteries using the LAND battery testing system. Figure 5 For comparative examples and embodiments, the NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were used at 0.1C (1C current density is 2000 mA g) within a voltage window of 0.01–1.5V. -1 The first-cycle charge-discharge curves obtained from current density cycling are shown in the figure. It can be seen from the figure that the discharge specific capacity and charge specific capacity of the NPs@PPy example in the first cycle are 3065.0 mAh g. -1 and 2616.1mAh g -1The first-week coulomb efficiency was 85.4%; the discharge specific capacity and charge specific capacity of NPs@LBO during the first-week cycle were 3024 mAh g and 1000 mAh g, respectively. -1 and 2559.5mAh g -1 The first-week coulombic efficiency was 84.6%; the discharge specific capacity and charge specific capacity of NPs@PPy@LBO during the first-week cycle were 3003.61 mAh g, respectively. -1 and 2649.41mAh g -1 The first-week coulomb efficiency was 88.2%; the discharge specific capacity and charge specific capacity of NPs@LBO@PPy during the first-week cycle were 3048.6 mAh g, respectively. -1 and 2728.9mAh g -1 The first-week coulombic efficiency was 89.5%. The NPs electrode exhibited a discharge specific capacity and a charge specific capacity of 2869.2 mAh g⁻¹ during the first-week cycle. -1 and 2291.2mAh g -1 In the first week, Cullen's efficiency was only 79.9%.

[0048] Figure 6 For comparative and example data, the NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were cycled for 120 cycles at 0.1C within a voltage window of 0.01–1.5V. After 120 stable cycles, the reversible specific capacities of the NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were 1702.0 mAh g. -1 1601.2mAh g -1 1759.2mAh g -1 1884.9mAh g -1 This is far higher than the reversible specific capacity of NPs electrodes (185.1 mAh g). -1 ).

[0049] Figure 7 For comparative and example data, the NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were cycled 100 times at 0.3C within a voltage window of 0.01–1.5V. After 100 stable cycles, the reversible specific capacities of the NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were 1218.2 mAh g. -1 1247.4mAh g -1 1445.6mAh g -1 1512.0mAh g -1The reversible specific capacity of the NPs electrode dropped to 1096.4 mAh g after the 6th cycle. -1 After 100 cycles, the reversible specific capacity almost approaches 0 (101.8 mAh g). -1 ).

[0050] Figure 8 For comparative and example data, the NPs, NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were cycled at 1C for 250 cycles within a voltage window of 0.01–1.5V. After 50 cycles, the reversible specific capacities of the NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were 1705.6 mAh g. -1 1792.8mAh g -1 1773.5mAh g -1 1988.2mAh g -1 After 250 stable cycles, the reversible specific capacities of the NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes were 1425.1 mAh g. -1 1500.1mAh g -1 1530.8mAh g -1 1790.7mAh g -1 The capacity retention rates of the NPs@PPy, NPs@LBO, NPs@PPy@LBO, and NPs@LBO@PPy electrodes from cycle 50 to 250 were 83.6%, 83.7%, 86.3%, and 90.1%, respectively. In contrast, the NPs electrode experienced rapid capacity decay almost immediately after cycle 7, with a reversible specific capacity of only 42.3 mAh g⁻¹ after 250 cycles. -1 .

[0051] Therefore, it can be seen that the double-layer coating structure of NPs@LBO@PPy, which first rigidly coats and then flexibly coats, helps to improve the first-cycle coulombic efficiency and long cycle life of nano-silicon solar cells.

[0052] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material, characterized in that: The material comprises silicon nanoparticles and a lithium metaborate layer and a polypyrrole layer sequentially coated on the surface of the silicon nanoparticles.

2. The polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 1, characterized in that: The particle size of the nano-silicon particles is 80–120 nm.

3. A method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 1 or 2, characterized in that: The method steps include: (1) The nano-silicon particles were coated with lithium metaborate by solution evaporation to obtain lithium metaborate coated nano-silicon particles. (2) Using pyrrole as a monomer, the nano-silicon particles coated with lithium metaborate were coated by liquid phase chemical oxidation polymerization to obtain a polypyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano-silicon anode material.

4. The method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 3, characterized in that: In step (1), nano-silicon particles and lithium metaborate are mixed and dispersed in an acidic solution and stirred until the solution evaporates to dryness. After the powder is dried, it is heat-treated under a protective gas atmosphere to obtain nano-silicon particles coated with lithium metaborate.

5. The method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 4, characterized in that: The mass ratio of the nano-silicon particles to lithium metaborate is 2 to 100:1, more preferably 2 to 10:1; The acidic solution is an aqueous solution of formic acid, with a volume ratio of formic acid to water of 1 to 5:

100.

6. The method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 4 or 5, characterized in that: The evaporation temperature is 60–80℃; The heat treatment temperature is 300–500℃, and the heating rate is 5–10℃·min. -1 The heat treatment holding time is 3 to 6 hours.

7. The method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 3, characterized in that: In step (2), the lithium metaborate-coated silicon nanoparticles are dispersed in an organic solvent, and pyrrole, sodium p-toluenesulfonate and ferric chloride are added and mixed. After stirring in an ice-water bath, the mixture is centrifuged and dried. The resulting powder is then heat-treated under a protective gas atmosphere to obtain a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated silicon nanoparticle anode material.

8. The method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 3, characterized in that: The organic solvent is ethanol; The ratio of lithium metaborate-coated silicon nanoparticles, pyrrole, sodium p-toluenesulfonate, and ferric chloride is 0.3–0.7 g: 250–300 μL: 0.05–0.15 g: 0.5–1 g.

9. The method for preparing a polypyrrole / lithium metaborate composite flexible / rigid layer co-coated nano-silicon anode material as described in claim 3, characterized in that: Stir for 5-6 hours in an ice-water bath at 0-3℃; During centrifugation, treat the centrifuge with deionized water and anhydrous ethanol alternately 4 to 5 times; The heat treatment temperature is 300–500℃, and the heating rate is 5–10℃·min. -1 The heat treatment holding time is 3 to 6 hours.

10. A lithium-ion battery, characterized in that: The negative electrode material of the battery is the polypyrrole / lithium metaborate composite flexible layer / rigid layer co-coated nano-silicon negative electrode material as described in claim 1 or 2.

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