Coated negative electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and provides a coated negative electrode material and a preparation method and application thereof.The coated negative electrode material comprises an inner core, a first coating layer is arranged on the surface of the inner core, and a second coating layer is arranged on the surface, away from the inner core, of the first coating layer; the inner core contains a silicon-based material; the first coating layer comprises a conductive polymer material, and the second coating layer comprises a fast ion conductor material. According to the invention, the organic-inorganic double-component coated silicon-based material is adopted, the double coating layers simulate the components of a real SEI film, and the conductive polymer is adopted as the organic component, so that the surface coating of the material is more compact; the fast ion conductor is used as an inorganic component, interface diffusion of the material can be improved, and fast charging performance is enhanced. The specific double coating layers can avoid excessive consumption of lithium ions in the first charging and discharging process, so that the first efficiency of the battery is improved; and the material interface stability is improved, so that the material cycle performance is remarkably enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to a coated negative electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid growth of the new energy vehicle market and the increasing demand for high-energy-density energy storage systems, power battery technology is facing unprecedented development opportunities and challenges. In this context, the performance optimization of lithium-ion batteries, as the most promising energy storage device, has become a research hotspot. Among them, the negative electrode material is one of the key components that determine the overall performance of the battery. Its material properties directly affect the battery's core indicators such as energy density, cycle life, rate performance and safety. Although traditional graphite-based carbon negative electrode materials have good cycle stability and low cost advantages, their theoretical specific capacity (about 372mAh / g) is close to the limit, which makes it difficult to meet the development needs of high-energy-density batteries in the future.

[0003] Silicon is considered to be an ideal component for the next generation of high-capacity negative electrode materials because of its extremely high theoretical specific capacity (up to 4200mAh / g). Compared with traditional carbon negative electrode materials, silicon is not only resource-rich and environmentally friendly, but also has a moderate lithium insertion potential and good thermodynamic stability. These advantages make silicon-based negative electrode materials (such as silicon alone, silicon-carbon composite materials, etc.) show great potential in improving battery energy density. However, in actual application, silicon-based negative electrode materials have also exposed many technical difficulties that need to be solved. For example, silicon undergoes drastic volume changes during charging and discharging, and the expansion rate can reach more than 300%. Repeated volume changes during the cycle will cause stress concentration inside the active material particles, which will cause structural rupture or even pulverization, seriously weakening the stability of the electrode. In addition, since silicon is a semiconductor material, its intrinsic electronic conductivity is low (about 10 -5 ~10 -3 S cm -1 ), which directly limits its electrochemical reaction kinetics and causes the material to exhibit poor rate performance under high current charge and discharge conditions.

[0004] Another key issue is the interfacial instability of silicon-based negative electrode materials in the electrolyte. When lithium is first inserted, its surface will undergo a side reaction with the electrolyte to form a solid electrolyte interface film (SEI film). Although this film can prevent further electrolyte decomposition to a certain extent, thereby protecting the electrode material, due to the continuous volume expansion and contraction of silicon during the cycle, the original SEI film is easily broken and continuously regenerated, resulting in additional lithium ion consumption, reducing the battery's initial coulombic efficiency, and exacerbating the capacity attenuation problem. At the same time, the SEI film also faces the problem of uniformity. An uneven SEI film will cause uneven local current distribution, thereby inducing the growth of lithium dendrites, posing a potential safety hazard. Therefore, how to effectively regulate the interfacial behavior of silicon-based negative electrode materials is one of the key technical issues to improve the stability of silicon-based negative electrode materials.

[0005] Surface coating technology has therefore attracted attention. Currently, commonly used coating materials mainly include carbon materials (such as amorphous carbon, graphene, carbon nanotubes) and metal oxides (such as Al2O3, TiO2). For example, carbon coating can effectively improve the electron transport capacity of silicon-based negative electrode materials and provide a certain buffer space to accommodate volume changes, but the improvement in the ion transport of the material is not large; while metal oxide coating can enhance the interface stability of the material while maintaining a certain mechanical strength, but the oxide itself expands greatly and has poor compatibility with the electrolyte. Moreover, some coating layers still have the risk of falling off or failing during long-term cycles, and some coating materials themselves may have a large mass share, thereby reducing the effective specific capacity of the overall electrode. More importantly, most of the current coating solutions focus mainly on the improvement of a single function, lacking the design concept of synergistic optimization of multiple properties (such as conductivity, structural stability and interface stability), making it difficult to fully meet the needs of high-energy-density battery systems.

[0006] Therefore, in order to address the above-mentioned problems of existing silicon-based negative electrode materials, it is urgent to develop a new surface coating strategy to facilitate its promotion and application in industrial production. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a coated negative electrode material and its preparation method and use, wherein the coated negative electrode material comprises an inner core, a first coating layer is provided on the surface of the inner core, and a second coating layer is provided on the surface of the first coating layer away from the inner core; the inner core contains a silicon-based material; the first coating layer comprises a conductive polymer material, and the second coating layer comprises a fast ion conductor material. The present invention adopts an organic-inorganic dual-component coating silicon-based material, and adopts a conductive polymer as the organic component, which can make the surface coating of the material more dense and is conducive to improving the rate performance; adopting a fast ion conductor as the inorganic component can improve the interface diffusion of the material and enhance the fast charging performance. The double coating layer simulates the composition of the real SEI film, which can avoid excessive consumption of lithium ions during the first charge and discharge process and improve the first efficiency of the battery; and the improved stability of the material interface significantly enhances the material cycle performance.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a coated negative electrode material, comprising an inner core, a first coating layer being provided on the surface of the inner core, and a second coating layer being provided on the surface of the first coating layer away from the inner core; the inner core contains a silicon-based material; the first coating layer comprises a conductive polymer material, and the second coating layer comprises a fast ion conductor material.

[0010] In order to solve the problem of poor conductivity and rate performance of traditional silicon-based materials, the present invention adopts a conductive polymer to coat the silicon-based material. On the one hand, it makes the coating denser, improves the elasticity and helps to alleviate the expansion of the core, and is more conducive to the subsequent inorganic components to form a uniform and stably combined second coating layer, and on the other hand, it helps to improve the conductivity of the negative electrode material; at the same time, it is matched with the inorganic component fast ion conductor to form a second coating layer, which further restrains the expansion of the core, and relies on the high ionic conductivity of the fast ion conductor itself and the better compatibility with the electrolyte. It is conducive to improving the diffusion ability of lithium ions through the SEI film, further improving the rate and fast charging performance of the negative electrode material. At the same time, in order to solve the problem of reduced first efficiency and repeated formation of SEI film caused by the exposure of traditional silicon-based materials, this organic-inorganic double coating method is used to simulate the components of SEI, and the silicon-based material is completely coated inside, avoiding direct contact with the electrolyte, which is conducive to reducing the capacity reduction caused by SEI formation during charging and discharging, while improving the interface stability and enhancing the cycle performance.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0012] As a preferred technical solution of the present invention, the silicon-based material includes a silicon-carbon composite material.

[0013] Preferably, the conductive polymer material includes PEDOT (poly 3,4-ethylenedioxythiophene).

[0014] Preferably, the fast ion conductor material includes Li3PO4 (lithium phosphate).

[0015] Preferably, the average particle size of the core is 3 to 8 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm or 8 μm.

[0016] Preferably, the thickness of the first coating layer is 50-500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm.

[0017] Preferably, the second coating layer has a thickness of 50 to 500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm.

[0018] In the present invention, since the conductive polymer material itself has no specific capacity, if the first coating layer is too thick, the impedance will increase. If the first coating layer is too thin, it cannot completely cover the core, resulting in gas production and limited reduction in material expansion. If the second coating layer is too thick, the specific capacity will also be reduced. If it is too thin, the expansion of the material, rate and fast charging performance will be limited.

[0019] In a second aspect, the present invention provides a method for preparing the coated negative electrode material according to the first aspect, the preparation method comprising:

[0020] Provide silicon-based materials as core, provide raw materials for preparing conductive polymer materials, and provide raw materials for preparing fast ion conductors;

[0021] Mixing the core with the raw material of the conductive polymer material in liquid phase, and then performing a first reaction to generate the conductive polymer material and form a first coating layer on the surface of the core to obtain an intermediate;

[0022] The intermediate is mixed with the raw material for preparing the fast ion conductor for liquid phase mixing, and then a second reaction is carried out to generate a fast ion conductor and form a second coating layer on the surface of the first coating layer to obtain a coated negative electrode material.

[0023] The preparation method of the present invention adopts liquid-phase in-situ coating technology, so that the first coating layer and the second coating layer can be more evenly and densely coated on the surface of the material, which is beneficial to ensure that the direct contact between the silicon-based material of the inner core and the electrolyte is reduced, and the occurrence of side reactions is fully avoided. The improvement in the interface stability of the double-layer coating further significantly enhances the cycle performance of the coated negative electrode material.

[0024] As a preferred technical solution of the present invention, when the silicon-based material includes a silicon-carbon composite material, the method for preparing the silicon-carbon composite material includes: mixing a porous carbon material with a gaseous silicon source, performing a deposition reaction, forming elemental nano-silicon and depositing it inside the porous carbon to obtain a silicon-carbon composite material.

[0025] In the present invention, the silicon-carbon composite material is preferably a gaseous silicon source cracked to generate nano-silicon which is deposited in the porous carbon. The expansion of the nano-silicon is effectively reduced by relying on the space reserved by the porous carbon.

[0026] Preferably, the deposition reaction is carried out in a fluidized bed apparatus.

[0027] Preferably, the gaseous silicon source includes silane; the gaseous silicon source and an inert gas form a mixed gas and then mixed with the porous carbon material, and the volume ratio of the gaseous silicon source to the inert gas is 1:(0.5~1.5), for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, etc., and the inert gas includes nitrogen.

[0028] Preferably, the flow rate of the silane gas is 1 to 3 L / min, for example, 1 L / min, 1.2 L / min, 1.4 L / min, 1.6 L / min, 1.8 L / min, 2 L / min, 2.2 L / min, 2.4 L / min, 2.6 L / min, 2.8 L / min or 3 L / min.

[0029] Preferably, the reaction pressure of the deposition reaction is 0.8-1.2 kPa, for example, 0.8 kPa, 0.83 kPa, 0.85 kPa, 0.88 kPa, 0.9 kPa, 0.93 kPa, 0.95 kPa, 0.98 kPa, 1 kPa, 1.03 kPa, 1.05 kPa, 1.08 kPa, 1.1 kPa, 1.13 kPa, 1.15 kPa, 1. 18kPa or 1.2kPa, etc.; the temperature is 500-600°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C, etc.; the time is 2-8h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, etc.

[0030] As a preferred technical solution of the present invention, the conductive polymer material raw materials include monomers and oxidants.

[0031] Preferably, when the conductive polymer material includes PEDOT, the monomer includes EDOT (3,4-ethylenedioxythiophene), and the oxidant includes K3Fe(CN)6 (potassium ferrocyanate).

[0032] Preferably, when the conductive polymer material includes PEDOT, the conductive polymer material raw material further includes a dopant, and the dopant includes PSS (polystyrene sulfonate).

[0033] As a preferred technical solution of the present invention, when the conductive polymer material includes PEDOT, the preparation method includes: first mixing the core and the monomer in water, then adjusting the pH, then adding the dopant and mixing, and then adding the oxidant to start the first reaction.

[0034] Preferably, the dosage is controlled according to the mass ratio of the core to the monomer of (8-20):1, for example, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, and the concentration of the monomer in the solution is controlled to be 0.5-1.5 mmol / L, for example, 0.5 mmol / L, 0.6 mmol / L, 0.7 mmol / L, 0.8 mmol / L, 0.9 mmol / L, 1 mmol / L, 1.1 mmol / L, 1.2 mmol / L, 1.3 mmol / L, 1.4 mmol / L or 1.5 mmol / L, etc.

[0035] In the present invention, the amount of monomer used should be appropriate. If the core content is relatively too high and the monomer amount is small, the coating integrity will be low, resulting in the exposure of the core, especially the exposure of the nano-silicon contained therein, which is easy to produce gas; if the core content is too low and the coating amount is too high, it will lead to increased impedance, which will reduce the fast charging performance.

[0036] Preferably, the regulator used to adjust the pH includes hydrochloric acid, and the pH range is 1 to 2, such as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0037] Preferably, the dosage is controlled according to the mass ratio of the dopant to the monomer of (1 to 6): 1, for example, 1: 1, 1.5: 1, 2: 1, 2.5: 1, 3: 1, 3.5: 1, 4: 1, 4.5: 1, 5: 1, 5.5: 1 or 6: 1, and the concentration of the dopant in the solution is controlled to be 1 to 3 mmol / L, for example, 1 mmol / L, 1.3 mmol / L, 1.5 mmol / L, 1.8 mmol / L, 2 mmol / L, 2.3 mmol / L, 2.5 mmol / L, 2.8 mmol / L or 3 mmol / L, etc.

[0038] Preferably, the concentration of the oxidant in the solution is controlled to be 1 to 3 mmol / L, for example, 1 mmol / L, 1.3 mmol / L, 1.5 mmol / L, 1.8 mmol / L, 2 mmol / L, 2.3 mmol / L, 2.5 mmol / L, 2.8 mmol / L or 3 mmol / L.

[0039] Preferably, the temperature of the first reaction is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, and the time is 6-18h, for example, 6h, 8h, 10h, 12h, 14h, 16h or 18h, etc.

[0040] Preferably, after the first reaction is completed, filtration, washing and drying are performed in sequence to obtain the intermediate.

[0041] As a preferred technical solution of the present invention, when the fast ion conductor includes Li3PO4, the fast ion conductor raw materials include a phosphorus source and a lithium source; the phosphorus source includes lithium dihydrogen phosphate, and the lithium source includes lithium hydroxide.

[0042] As a preferred technical solution of the present invention, when the fast ion conductor includes Li3PO4, the preparation method includes: pre-preparing the intermediate into a dispersion in water, adding lithium dihydrogen phosphate to the dispersion, and then adding the lithium hydroxide to start the second reaction.

[0043] Preferably, the amount is controlled according to the mass ratio of the intermediate to the lithium dihydrogen phosphate of (8-20):1, for example, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1.

[0044] Preferably, the lithium hydroxide is pre-prepared as a lithium hydroxide aqueous solution with a mass concentration of 15% to 25% before use, for example, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%.

[0045] Preferably, the amount is controlled according to a molar ratio of lithium dihydrogen phosphate to the lithium hydroxide of 1:(1-1.02), for example, 1:1, 1:1.01, 1:1.015 or 1:1.02.

[0046] Preferably, the second reaction time is 0.5 to 1.5 h, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h or 1.5 h.

[0047] Preferably, after the second reaction is completed, filtration and drying are performed in sequence to obtain the coated negative electrode material.

[0048] In a third aspect, the present invention provides a negative electrode plate comprising the coated negative electrode material described in the first aspect.

[0049] In a fourth aspect, the present invention provides a battery comprising the coated negative electrode material described in the first aspect or the negative electrode sheet described in the third aspect.

[0050] It should be noted that due to space limitations and to avoid redundancy, the present invention does not exhaustively list all point values ​​within the above numerical range, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0051] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0052] The coated anode material described in this invention utilizes an organic-inorganic dual-component coating on a silicon-based core. A conductive polymer, as the organic component, forms the first coating layer, improving coating uniformity, stability, and bonding. The conductive polymer also enhances the material's conductivity, thereby improving the rate capability of the coated anode material. A fast ion conductor, as the inorganic component, forms the second coating layer, improving the interfacial diffusion capacity and enhancing fast-charging performance. The dual coating layer mimics the composition of a real SEI film, preventing excessive lithium ion consumption during the initial charge and discharge process and improving the battery's initial efficiency.

[0053] The present invention adopts liquid-phase in-situ coating technology, conductive polymers are in-situ polymerized and evenly and densely coated on the surface of the core to form a first coating layer, and fast ion conductors are in-situ reacted and generated and evenly and densely coated on the surface of the first coating layer to form a second coating layer. The double coating layer can ensure that the direct contact between the silicon-based material core and the electrolyte is reduced, reducing the occurrence of side reactions, and the enhanced interface stability of the double coating layer further enhances the cycle performance of the negative electrode material. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0055] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0056] Example 1

[0057] This embodiment provides a coated negative electrode material, including a core, a first coating layer is provided on the surface of the core, and a second coating layer is provided on the surface of the first coating layer away from the core; the core contains a silicon-based material; the first coating layer is a conductive polymer material PEDOT and is doped with PSS, and the second coating layer is a fast ion conductor material Li3PO4; the average particle size of the core is 5μm; the thickness of the first coating layer is 250nm; the thickness of the second coating layer is 250nm.

[0058] The preparation method of the coated negative electrode material comprises:

[0059] S1. The porous carbon material was placed in a fluidized bed apparatus and a mixture of silicon source silane and nitrogen was introduced simultaneously. The silane flow rate was 2 L / min, the volume ratio of silane to nitrogen was 1:1, and the pressure in the reactor was 1 kPa. The deposition reaction was carried out at 550°C for 5 h. Under high temperature conditions, the silane was decomposed to form elemental silicon, which was deposited inside the porous carbon, resulting in an uncoated silicon-carbon composite material as the core.

[0060] S2. The core is mixed in water, and the monomer EDOT is added, and the amount of the monomer is controlled according to the mass ratio of the core to the monomer of 10:1, and the concentration of the monomer in the solution is controlled to be 1 mmol / L; after adjusting the pH to 1.4 with hydrochloric acid, the dopant is added, and the amount of the dopant is controlled according to the mass ratio of the dopant to the monomer of 2:1, and the concentration of the dopant in the solution is controlled to be 2 mmol / L, and stirred until completely dissolved; then the oxidant K3Fe(CN)6 is added, and the concentration of the oxidant in the solution is controlled to be 2 mmol / L, and the first reaction is carried out at 60°C for 12 hours. The color of the solution is observed to change from colorless to dark blue, indicating that PEDOT polymerization is complete, a conductive polymer material has been generated, and a first coating layer is formed on the surface of the core, and then filtered, washed and dried in sequence to obtain the intermediate (PEDOT-coated silicon-carbon composite material);

[0061] S3. Lithium hydroxide is prepared into a lithium hydroxide aqueous solution with a mass concentration of 20%, and then the intermediate is pre-prepared in water into a dispersion with a mass concentration of 15%, and then the lithium dihydrogen phosphate is added to the dispersion, and the amount of the lithium dihydrogen phosphate is controlled according to the mass ratio of the intermediate to the lithium dihydrogen phosphate of 10:1, and then the lithium hydroxide aqueous solution is added, and the amount of the lithium hydroxide aqueous solution is controlled according to the molar ratio of lithium dihydrogen phosphate to the lithium hydroxide of 1:1. After the second reaction is carried out for 1 hour, a fast ion conductor has been generated and a second coating layer is formed on the surface of the first coating layer, and then filtration and drying are carried out in sequence to obtain the coated negative electrode material.

[0062] Example 2

[0063] This embodiment provides a coated negative electrode material, and the amount of the monomer in step S2 of the preparation method is adjusted so that the mass ratio of the core to the monomer is adjusted from 10:1 to 2:1, resulting in the thickness of the first coating layer being changed from 250 nm to 1000 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0064] Example 3

[0065] This embodiment provides a coated negative electrode material, and the amount of the monomer in step S2 of the preparation method is adjusted so that the mass ratio of the core to the monomer is adjusted from 10:1 to 8:1, resulting in the thickness of the first coating layer being changed from 250 nm to 500 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0066] Example 4

[0067] This embodiment provides a coated negative electrode material, and the amount of the monomer in step S2 of the preparation method is adjusted so that the mass ratio of the core to the monomer is adjusted from 10:1 to 20:1, resulting in the thickness of the first coating layer being changed from 250 nm to 50 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0068] Example 5

[0069] This embodiment provides a coated negative electrode material, and the amount of the monomer in step S2 of the preparation method is adjusted so that the mass ratio of the core to the monomer is adjusted from 10:1 to 30:1, resulting in the thickness of the first coating layer being changed from 250 nm to 10 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0070] Example 6

[0071] This embodiment provides a coated negative electrode material. The amount of lithium dihydrogen phosphate in step S3 of the preparation method is adjusted so that the mass ratio of the intermediate to the lithium dihydrogen phosphate is adjusted from 10:1 to 2:1, resulting in the thickness of the second coating layer being changed from 250 nm to 1200 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0072] Example 7

[0073] This embodiment provides a coated negative electrode material. The amount of lithium dihydrogen phosphate in step S3 of the preparation method is adjusted so that the mass ratio of the intermediate to the lithium dihydrogen phosphate is adjusted from 10:1 to 8:1, resulting in the thickness of the second coating layer being changed from 250 nm to 500 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0074] Example 8

[0075] This embodiment provides a coated negative electrode material. The amount of lithium dihydrogen phosphate in step S3 of the preparation method is adjusted so that the mass ratio of the intermediate to the lithium dihydrogen phosphate is adjusted from 10:1 to 20:1, resulting in the thickness of the second coating layer being changed from 250 nm to 50 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0076] Example 9

[0077] This embodiment provides a coated negative electrode material. The amount of lithium dihydrogen phosphate in step S3 of the preparation method is adjusted so that the mass ratio of the intermediate to the lithium dihydrogen phosphate is adjusted from 10:1 to 30:1, resulting in the thickness of the second coating layer being changed from 250 nm to 20 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0078] Comparative Example 1

[0079] This comparative example provides a coated negative electrode material, the preparation method of which does not perform step S3 and only forms the first coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0080] Comparative Example 2

[0081] This comparative example provides a coated negative electrode material. The preparation method thereof does not perform step S2. The core obtained in step S1 is subjected to step S3 to form only a second coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0082] Comparative Example 3

[0083] This comparative example provides a coated negative electrode material, the preparation method of which includes:

[0084] 5 g of PEDOT and 5 g of lithium phosphate were added to 500 g of dimethyl carbonate solvent and dispersed evenly. Then, 100 g of the uncoated silicon-carbon composite material in step S1 of Example 1 was added and ultrasonically dispersed evenly. The mixture was spray-dried (inlet temperature 180°C, outlet temperature 80°C, flow rate 0.2 kg / h, 2 h) to obtain a PEDOT / lithium phosphate-coated silicon-carbon composite material, i.e., PEDOT / lithium phosphate formed a mixed coating layer.

[0085] Characterization and testing:

[0086] The coated negative electrode material prepared in the above examples and comparative examples was mixed and stirred evenly with the binder polyacrylic acid, conductive carbon black and dispersant sodium carboxymethyl cellulose, then coated on copper foil and dried, cut to obtain a negative electrode sheet, and then assembled with a positive electrode sheet (NCM811) to obtain a button battery.

[0087] 1) Cyclic performance test:

[0088] The prepared button battery (full battery) was cyclically charged and discharged at a rate of 0.1C, with a voltage range of 0.005 to 1.5V, and the capacity retention rate of the battery after 600 cycles was recorded.

[0089] 2) Rate performance test:

[0090] The first cycle: discharge at a rate of 0.33C to 5mV, stand for 10 minutes, and then charge at a rate of 0.1C to 1.5V, and record the discharge capacity; the second cycle: discharge at a rate of 0.5C to 5mV, stand for 10 minutes, and then charge at a rate of 0.1C to 1.5V, and record the discharge capacity; the third cycle: discharge at a rate of 1.0C to 5mV, stand for 10 minutes, and then charge at a rate of 0.1C to 1.5V, and record the discharge capacity; the fourth cycle: discharge at a rate of 2C to 5mV, stand for 10 minutes, and then charge at a rate of 0.1C to 1.5V, and record the discharge capacity; the fifth cycle: discharge at a rate of 3C to 5mV, stand for 10 minutes, and then charge at a rate of 0.1C to 1.5V, and record the discharge capacity; the sixth cycle: discharge at a rate of 4C to 5mV, stand for 10 minutes, and then charge at a rate of 0.1C to 1.5V, and record the discharge capacity.

[0091] 3) Diffusion coefficient test: Assemble the negative electrode and lithium sheet and discharge at 0.1C, with a single-step discharge time of 2 minutes. Let it rest for 30 minutes. Repeat the above steps until the voltage is less than 0.005V. Record the voltage at each step and calculate the lithium ion diffusion coefficient.

[0092] The above test results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1:

[0096] Comparing Example 1, Example 2 to Example 5 and Comparative Example 2, it can be seen that the reduction in the amount of PEDOT coating significantly reduces the first effect and cycle retention rate of the material, and the reduction in the amount of conductive polymer coating increases the powder resistivity of the material and reduces the rate performance of the material. Comparing Example 1, Example 6 to Example 9 and Comparative Example 1, it can be seen that the reduction in the amount of fast ion conductor coating reduces the lithium ion diffusion coefficient, deteriorates the rate performance of the material, and deteriorates the interface stability, resulting in accelerated cycle attenuation. In particular, when the negative electrode material changes from an inorganic-organic dual-component coating to a single coating, the absence of any one of the two components will deteriorate the cycle performance of the material, and the rate performance of the single-component coated material deteriorates significantly compared to other materials. Compared with Example 1, Comparative Example 3 adopts a non-in-situ polymerization method to form a coating layer, and only forms a mixed coating layer through liquid phase mixing, which makes the contact between the materials poor, the polarization is large, the impedance is relatively large, and its cycle performance is reduced.

[0097] As can be seen above, the present invention simulates SEI components and prepares a high-performance coated anode material through an organic-inorganic double-layer coating. The results show that the material has excellent rate and cycling stability. The dense double-layer coating significantly improves the initial efficiency of the material and effectively avoids side reactions between silicon and carbon and the electrolyte.

[0098] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0099] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0100] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A coated negative electrode material, characterized in that: It comprises an inner core, a first coating layer is provided on the surface of the inner core, and a second coating layer is provided on the surface of the first coating layer away from the inner core; the inner core contains a silicon-based material; the first coating layer comprises a conductive polymer material, and the second coating layer comprises a fast ion conductor material.

2. The coated negative electrode material according to claim 1, characterized in that The silicon-based material includes a silicon-carbon composite material; Preferably, the conductive polymer material includes PEDOT; Preferably, the fast ion conductor material comprises Li3PO4; Preferably, the average particle size of the core is 3 to 8 μm; Preferably, the thickness of the first coating layer is 50 to 500 nm; Preferably, the thickness of the second coating layer is 50-500 nm.

3. A method for preparing the coated negative electrode material according to claim 1 or 2, characterized in that: The preparation method comprises: Provide silicon-based materials as core, provide raw materials for preparing conductive polymer materials, and provide raw materials for preparing fast ion conductors; Mixing the core with the raw material of the conductive polymer material in liquid phase, and then performing a first reaction to generate the conductive polymer material and form a first coating layer on the surface of the core to obtain an intermediate; The intermediate is mixed with the raw material for preparing the fast ion conductor in liquid phase, and then a second reaction is carried out to generate a fast ion conductor and form a second coating layer on the surface of the first coating layer to obtain a coated negative electrode material.

4. The method for preparing a coated negative electrode material according to claim 3, wherein: When the silicon-based material includes a silicon-carbon composite material, the method for preparing the silicon-carbon composite material includes: mixing a porous carbon material with a gaseous silicon source, performing a deposition reaction, forming elemental silicon and depositing it inside the porous carbon, thereby obtaining the silicon-carbon composite material; Preferably, the deposition reaction is carried out in a fluidized bed apparatus; Preferably, the gaseous silicon source comprises silane; the gaseous silicon source and an inert gas form a mixed gas which is then mixed with the porous carbon material, the volume ratio of the gaseous silicon source to the inert gas being 1:(0.5-1.5), and the inert gas comprises nitrogen; Preferably, the flow rate of the silane gas is 1 to 3 L / min; Preferably, the deposition reaction is carried out at a pressure of 0.8 to 1.2 kPa, a temperature of 500 to 600° C., and a reaction time of 2 to 8 hours.

5. The method for preparing a coated negative electrode material according to claim 3 or 4, characterized in that: The conductive polymer material raw materials include monomers and oxidants; Preferably, when the conductive polymer material includes PEDOT, the monomer includes EDOT, and the oxidant includes K3Fe(CN)6; Preferably, when the conductive polymer material includes PEDOT, the conductive polymer material raw material further includes a dopant, and the dopant includes PSS.

6. The method for preparing a coated negative electrode material according to claim 5, wherein: When the conductive polymer material includes PEDOT, the preparation method includes: first mixing the core and the monomer in water, then adjusting the pH, then adding the dopant and mixing, and then adding the oxidant to start the first reaction; Preferably, the dosage is controlled according to the mass ratio of the core to the monomer being (8-20):1, and the concentration of the monomer in the solution is controlled to be 0.5-1.5 mmol / L; Preferably, the pH regulator used to adjust the pH includes hydrochloric acid, and the pH range is 1 to 2; Preferably, the dosage is controlled according to a mass ratio of the dopant to the monomer of (1-6):1, and the concentration of the dopant in the solution is controlled to be 1-3 mmol / L; Preferably, the concentration of the oxidant in the solution is controlled to be 1 to 3 mmol / L; Preferably, the temperature of the first reaction is 40-80°C and the time is 6-18h; Preferably, after the first reaction is completed, filtration, washing and drying are performed in sequence to obtain the intermediate.

7. The method for preparing a coated negative electrode material according to any one of claims 3 to 6, wherein: When the fast ion conductor includes Li3PO4, the fast ion conductor raw materials include a phosphorus source and a lithium source; the phosphorus source includes lithium dihydrogen phosphate, and the lithium source includes lithium hydroxide.

8. The method for preparing a coated negative electrode material according to claim 7, wherein: When the fast ion conductor comprises Li3PO4, the preparation method comprises: pre-preparing the intermediate into a dispersion in water, adding lithium dihydrogen phosphate to the dispersion, and then adding the lithium hydroxide to start the second reaction; Preferably, the amount is controlled according to the mass ratio of the intermediate to the lithium dihydrogen phosphate of (8-20):1; Preferably, the lithium hydroxide is pre-prepared as a lithium hydroxide aqueous solution with a mass concentration of 15% to 25% before use; Preferably, the amount is controlled according to a molar ratio of lithium dihydrogen phosphate to lithium hydroxide of 1:(1-1.02); Preferably, the second reaction time is 0.5 to 1.5 hours; Preferably, after the second reaction is completed, the filter agent is dried in sequence to obtain the coated negative electrode material.

9. A negative electrode plate, characterized in that: Contains the coated negative electrode material according to claim 1 or 2.

10. A battery, characterized in that: Contains the coated negative electrode material according to claim 1 or 2 or contains the negative electrode sheet according to claim 9.

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