Composite coating material as well as preparation method and application thereof

Abstract

The invention relates to a composite coating material and a preparation method and application thereof, the composite coating material comprises: an inner core having a core-shell structure; the shell structure of the inner core is made of carbon, and the core structure of the inner core is made of a silicon-based material; the shell is coated outside the inner core, the shell comprises a pore structure, and the shell contains a polymer and hydroxylated lithium lanthanum zirconium oxygen-based particles; the pore structure comprises macropores with the pore diameter of 200-1000 nm, mesopores with the pore diameter of 50-100 nm and micropores with the pore diameter of 2-5 nm. Through composite coating structure design and interface cooperative regulation, the electrochemical performance and mechanical stability of the silicon-carbon negative electrode material are remarkably improved, and dual adaptation of a liquid-state battery system and a solid-state battery system is realized.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and specifically relates to a composite coating material, a preparation method thereof, and an application thereof. Background Art

[0002] Silicon-based materials are regarded as the most promising anode system due to their theoretical specific capacity of up to 4200 mAh / g. However, the severe volume expansion (>300%) leading to electrode pulverization seriously restricts the practical application process. Although the traditional carbon coating technology can partially alleviate the volume effect, a single carbon layer coating is difficult to balance the synergistic requirements of ion transport and electron conduction, especially showing significant shortcomings in fast charging scenarios. In the prior art, tantalum-doped LLZO (Li 7-x La3Zr 2-y Ta y O 12 ) coating layer has an interfacial impedance > 180 Ω·cm 2 .

[0003] In the liquid electrolyte system, there is prior art that uses electrospinning to prepare a core-shell structure of PAN-coated silicon-based materials. Although physical coating of silicon particles is achieved, the ionic conductivity of its PAN-based coating layer only reaches the order of 10 -6 S / cm, which cannot meet the requirements of high-rate charge and discharge. More seriously, the suppression efficiency of this scheme for silicon volume expansion is less than 50%, resulting in the capacity retention rate decaying to 72.3% after 500 cycles, making it difficult to coordinate the mechanical buffering ability and electrochemical stability.

[0004] The prior art CN112467116A discloses a graphite coating material, a preparation method thereof, and a battery anode. The graphite coating material includes: a core, the core includes graphite; a shell coated outside the core, the shell includes tantalum-doped lithium lanthanum zirconium oxide, amorphous carbon, and a conductive material. Doping tantalum-doped lithium lanthanum zirconium oxide and a conductive material in the surface coating layer of graphite can effectively improve the lithium ion transport rate and diffusion coefficient, and the conductive material can effectively improve the electronic conductivity of the material; the tantalum-doped lithium lanthanum zirconium oxide, amorphous carbon, and conductive material in the shell synergistically exhibit good lithium ion conductivity and electronic conductivity, which is beneficial to improving the ion transport rate and conductivity of the graphite coating material, and can effectively improve the rate performance, safety performance, and cycle performance of the graphite anode material. However, this prior art is only applicable to a graphite core (theoretical capacity 372 mAh / g) and cannot be adapted to high-capacity silicon-based materials (theoretical capacity 4200 mAh / g); moreover, its expansion suppression is insufficient: it does not involve a volume expansion buffering mechanism and has no alleviating effect on the >300% expansion of silicon-based materials; the interfacial impedance is high: the unmodified LLZO has poor interfacial compatibility with graphite, and the interfacial impedance of the solid-state battery > 180 Ω·cm 2 .

[0005] The prior art CN111244410B discloses a lithium battery anode material and its preparation method, specifically relating to a silicon-based anode material with high stability and long cycle life and its preparation method. The silicon-based anode material has a core-shell structure, the inner core contains silicon oxide compounds and has a relatively high initial efficiency; the outer shell consists of 3 layers. The inner layer is a carbon coating layer, which can effectively buffer the volume expansion of the inner core and improve electron conductivity. The middle layer is an HF isolation layer, which can effectively prevent F - from passing through without hindering the transmission of Li + . The outermost layer is a Li + conductor layer with the function of an artificial SEI film, which can effectively improve the lithium ion conductivity and stabilize the SEI film. Using the above anode material, a lithium ion battery with high energy density and long life can be prepared. However, the multi-layer deposition process of this prior art is complex, and the ion conductivity of the SEI layer is insufficient. The interface between the SEI layer and the carbon layer is prone to delamination, and the capacity retention rate after 500 cycles is only 73.2%.

[0006] The prior art CN115241526A discloses an artificial graphite composite material coated with a boron-doped solid electrolyte composite material, presenting a core-shell structure. Its inner core is artificial graphite, and the outer shell is composed of 0.5 - 2% lithium borate, 1 - 5% solid electrolyte, 0.5 - 2% conductive agent, and amorphous carbon. The composite material of this invention utilizes the high ionic conductivity characteristics of the solid electrolyte and the electron conductivity characteristics of the conductive agent to improve the electron-ion conduction rate of the material. At the same time, lithium borate provides sufficient lithium ions for the material to improve its initial efficiency, and plays the coupling role of the coupling agent in the coating layer to form a conductive network, improving the structural stability and rate cycling performance of the material. However, this prior art is designed for graphite, and lithium borate (0.5 - 2wt%) cannot adapt to the expansion stress of silicon-based materials; there are defects in the conductive network, and the electron mobility of the conductive network constructed by relying on the coupling agent (aluminate / titanate) is only 10 -3 S / cm magnitude.

[0007] For the solid-state battery system, although the PVDF-HFP-based solid electrolyte has good interfacial flexibility, its room-temperature ionic conductivity is lower than 10 -5 S / cm, and the interfacial impedance with the silicon anode exceeds 200 Ω·cm ² , making it difficult to achieve efficient charge transfer. A deeper technical bottleneck lies in: there are significant interfacial incompatibility problems between traditional inorganic fillers (such as LLZO, LATP) and the polymer matrix, resulting in filler agglomeration (particle size > 500 nm) and stress concentration, seriously weakening the mechanical integrity of the composite electrolyte. At the same time, the interfacial contact between this organic solid electrolyte system and the silicon-based anode material is poor, resulting in poor electrochemical performance of the solid-state battery.

[0008] Common technical challenges are concentrated in two aspects: First, the existing coating structures cannot construct ion / electron dual-continuous transport channels, manifested as the difficulty in synchronously improving ionic conductivity and electron mobility; Second, the weak interfacial interaction between the inorganic and organic phases leads to interfacial delamination during the cycling process, triggering contact failure between the active material and the current collector. These defects jointly restrict the practical application of silicon-based anodes in high-performance batteries, and it is urgent to achieve breakthroughs through the collaborative innovation of material design and interfacial engineering. Summary of the Invention

[0009] The purpose of the present invention is to provide a composite coating material with high ionic conductivity and low volume expansion rate, its preparation method, and its application in silicon-carbon anode materials.

[0010] To achieve the above purpose, the present invention adopts the following technical solutions:

[0011] A composite coating material, comprising:

[0012] A core, the core having a core-shell structure; the material of the shell structure of the core is carbon, and the material of the core structure of the core is a silicon-based material; And a shell coated outside the core, the shell including a pore structure, and the shell containing a polymer and hydroxylated lithium lanthanum zirconate particles;

[0013] Wherein, the structural formula of the lithium lanthanum zirconate particles is Li 7-x La3Zr 2-y M y O 12 , M is at least one of the doping elements Ta, Al, Nb that equally replaces the Zr site, 0 ≤ x ≤ 1, 0 ≤ y ≤ 0.6;

[0014] The pore structure includes macropores with a pore diameter of 200 - 1000 nm, mesopores with a pore diameter of 50 - 100 nm, and micropores with a pore diameter of 2 - 5 nm.

[0015] In the pore structure, the macropores (200 - 1000 nm) preferentially absorb the macroscopic strain of the silicon core expansion; the mesopores (50 - 100 nm) disperse the shear stress to prevent crack propagation; the micropores (2 - 5 nm) stabilize the SEI film through surface adsorption effect. In Example 1, the integrity rate of the electrode after cycling is 92% with the three-pore system, while it is only 78% with the two-pore system.

[0016] The necessity and size effects of different pore diameters are as follows:

[0017] Macropores: Absorb the macroscopic strain of silicon expansion (ΔV > 200%), and need to match the size of the silicon particles in the core, which is 5 - 12 μm. Too small will lead to a reduction in the buffering efficiency.

[0018] Mesopores: Facilitate electrolyte penetration (liquid system) and ion transport (solid system). The size is adapted to the particle size of LLZO, which is 80 - 90 nm. If it is too large, the active sites will decrease; if it is too small, the ion migration path will be blocked.

[0019] Micropores: Provide high specific surface area active sites (Li + adsorption). The size is adapted to the graphitized carbon layer. If it is too large, the SEI film will be too thick or unstable; if it is too small, Li + diffusion will be blocked.

[0020] The effects of the pore number and type are as follows:

[0021] Only two scales of pores:

[0022] a) Lack of macropores: The volume expansion rate rebounds to >200%;

[0023] b) Lack of micropores: The 1C capacity attenuation rate increases by 30% (ion transport bottleneck).

[0024] Too many scales of pores (such as a four - level pore structure):

[0025] a) The mechanical strength decreases and the electrode processing breakage rate increases;

[0026] b) The interfacial impedance dispersion increases.

[0027] In one preferred embodiment, in the pore structure, the macropore proportion is 50 - 60% (volume ratio). In the embodiment, focused ion beam - scanning electron microscopy (FIB - SEM) three - dimensional reconstruction statistics are used, and the pore volume is extracted by threshold segmentation.

[0028] In one preferred embodiment, in the pore structure, the mesopore proportion is 30 - 40% (volume ratio). In the embodiment, based on the BJH model of nitrogen adsorption - desorption isotherms, LLZO nanoparticles (D50 = 80 - 90 nm) are stacked to form "sphere close - packing" - like pores (porosity ≈ 26%), and electron tomography (ET) is combined to verify the spatial distribution uniformity.

[0029] In one preferred embodiment, in the pore structure, the micropore proportion is 5 - 10% (volume ratio). In the embodiment, small - angle X - ray scattering (SAXS) is combined with density functional theory (DFT) model fitting to quantify the lattice - level pores caused by carbonization shrinkage (the micropore density saturates when the graphitization degree of the carbon layer is ≥80%).

[0030] In one preferred embodiment, macropores are mainly distributed on the outer surface of the coating layer; mesopores are distributed in the LLZO particle stacking area; micropores are concentrated in the carbonized polymer matrix.

[0031] The pore distribution basically conforms to the rule of sparse outside and dense inside.

[0032] In one preferred embodiment, the macroscopic pore density increases from the inside to the outside.

[0033] In one preferred embodiment, the polymer is one or more of polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyethylene oxide (PEO).

[0034] In one preferred embodiment, in the inner core, the mass proportion of the core structure is 15-50wt%.

[0035] In one preferred embodiment, the particle size D50 of the core is 5-12 μm, and the specific surface area is 1-3 m 2 / g, and the tap density is 0.8-1.2 g / cm 3 .

[0036] In one preferred embodiment, the silicon-based material includes elemental silicon, porous silicon, nano silicon, SiO x A combination of one or more silicon-oxygen materials (0<x<2).

[0037] In one preferred embodiment, the shell structure has a thickness of 50-200 nm and a crystallinity of ≥75%.

[0038] In one preferred embodiment, the shell structure is made of graphitized carbon.

[0039] In one preferred embodiment, the porosity of the inner core is ≤5%.

[0040] In one preferred embodiment, the core is G4S-C800 or G4S-C600, purchased from Shanghai Shanshan New Materials Co., Ltd.

[0041] In one preferred embodiment, the mass ratio of the polymer to the hydroxylated lithium lanthanum zirconium oxy-particles is 8-5:2-5.

[0042] In the present invention, LLZO nanoparticles (Li 7-x Ln3Z 2-y M y O 12 ) provides a fast migration path for lithium ions, and the polymer carbonization forms a continuous conductive network, realizing the decoupling and synergy of ion / electron transport, which is better than the traditional single carbon coating (10 -6The (S / cm) is increased by four orders of magnitude. The formed "macropores (200 - 1200 nm) - mesopores (50 - 100 nm) - micropores (5 - 15 nm)" structure dissipates stress hierarchically through the synergistic effect of multi-scale pores, avoiding the rupture, pulverization, and failure of the coating layer during long-term cycling. The hydroxylation of the LLZO surface (≥3 per nm 2 forms La - O - C covalent bonds with the polymer carbonization network, enhancing the interfacial bonding between the inorganic and organic phases. The high melting point of LLZO (>1500 °C) synergizes with the flame retardancy of the carbonized polymer to inhibit the thermal chain reaction; the porous structure delays heat accumulation. Its thermal runaway onset temperature reaches 200 °C, a 56% increase compared to the conventional core (128 °C).

[0043] In one preferred embodiment, the preparation method of the hydroxylated lithium lanthanum zirconate oxide particles includes the following steps: ball-milling and drying the lithium lanthanum zirconate oxide particles, and then adding them to an acid solution for ultrasonic treatment to obtain the hydroxylated lithium lanthanum zirconate oxide particles.

[0044] In one preferred embodiment, the ball-milling is carried out using a gradient dispersion process, and the gradient dispersion process is as follows: first, rough-mill at a speed of 300 - 400 rpm for 1 - 3 hours, and then fine-mill at a speed of 100 - 150 rpm for 3 - 5 hours.

[0045] In one preferred embodiment, the ball-milling medium used in the ball-milling is zirconia balls, and the diameter of the zirconia balls is 2 - 6 mm.

[0046] In one preferred embodiment, among the zirconia balls, the volume ratio of the zirconia balls with a diameter of 2 - 3 mm to the zirconia balls with a diameter of 5 - 6 mm is 1:2 - 3.

[0047] In one preferred embodiment, the D50 particle size of the hydroxylated lithium lanthanum zirconate oxide particles is 80 - 90 nm.

[0048] In one preferred embodiment, the acid solution is a nitric acid solution, and the concentration of the nitric acid solution is 1 - 5 wt%.

[0049] In one preferred embodiment, the temperature of the ultrasonic treatment is 40 - 90 °C, preferably 70 - 80 °C; the ultrasonic time is 30 - 180 min, preferably 60 - 120 min.

[0050] In one preferred embodiment, the frequency of the ultrasonic treatment is 40 - 60 kHz, the power is 300 - 350 W, and the pulse mode is 5 - 10 s on / 5 - 10 s off.

[0051] In one preferred embodiment, the drying is carried out by treating at 60 - 110 °C for 6 - 24 hours.

[0052] In one preferred embodiment, the surface of the hydroxylated lithium lanthanum zirconium oxide particles has active sites with a hydroxyl density greater than 3 per nm 2 .

[0053] The lithium lanthanum zirconium oxide particles are treated with a nitric acid solution, and selective etching occurs on the surface (hydrolysis of the La - O bond). At the same time, the Zr - O bond is partially broken to form surface hydroxyl groups (-OH). The hydroxylated lithium lanthanum zirconium oxide particles (with La - OH on the surface) undergo a condensation reaction with the polymer (such as PAN) during the carbonization process to form La - O - C bonds. The La - O - C bond makes the interfacial binding energy greater than the physical adsorption interfacial binding energy in the case of non - hydroxylated particles.

[0054] (1) Quantitative relationship between hydroxyl density and interfacial binding energy

[0055] Let the hydroxyl density on the surface of LLZO be ρ OH (unit: per nm 2 ), the binding energy of each hydroxyl group with the polymer carbonization network to form La - O - C bonds is εbond (the value needs to be determined experimentally, unit: eV / bond), and the effective contact area is (to be measured by AFM, nm 2 ). Then the interfacial binding energy E per unit area can be expressed as: E = ρOH * εbond * A contact ;

[0056] Assume ρOH ≥ 3 per nm², εbond = 0.8 eV, A contact = 80%; E ≥ 3 * 0.8 * 0.8 = 1.92 eV / nm 2 = 8.7 J / m 2 .

[0057] (2) Promotion of ion transport by La - O - C bonds

[0058] The polar effect of the La - O - C bond can reduce the migration activation energy E of Li + . According to the Arrhenius equation, a decrease in E can increase the ionic conductivity.

[0059] (3) Inhibition of volume expansion by interfacial stability

[0060] The breaking strength of the La - O - C bond is much greater than the silicon volume expansion stress, and the La - O - C at the silicon interface can effectively inhibit the volume expansion of silicon.

[0061] In one preferred embodiment, the polymer is uniformly distributed in the outer shell.

[0062] In one preferred embodiment, the hydroxylated lithium lanthanum zirconate particles are uniformly distributed in the shell.

[0063] Based on the same inventive concept, the present invention also claims the preparation method of the composite coating material, comprising the following steps:

[0064] S1. Mix the polymer and the hydroxylated lithium lanthanum zirconate particles according to a mass ratio of 8 - 5:2 - 5; after mixing evenly, add a pore-forming agent and perform ultrasonic treatment to obtain a mixture;

[0065] S2. Add a core to the mixture and mix evenly to obtain a pre-product;

[0066] S3. Perform gradient heat treatment on the pre-product to obtain the composite coating material;

[0067] The process of the gradient heat treatment is as follows: under argon protection, heat up at a rate of 2 - 3 °C / min to 200 - 250 °C for pre-oxidation for 1 - 2 h, then heat up at a rate of 5 - 10 °C / min to 700 - 800 °C for carbonization for 2 - 3 h, then cool down at a rate of 5 - 7 °C / min to 600 - 650 °C for heat preservation for 15 - 20 min, and finally cool slowly to room temperature.

[0068] During the gradient heat treatment process, under argon protection, the pre-oxidation of the polymer molecular chains is completed at 200 - 250 °C; subsequently, at the main carbonization temperature of 700 - 800 °C, constant-temperature carbonization is performed under a certain argon gas flow rate to form a continuous conductive network; finally, a gradient slow-cooling program is executed to optimize the carbon crystal structure.

[0069] In one preferred embodiment, in step S1, the addition amount of the pore-forming agent is 0.1 - 15 wt% of the polymer mass.

[0070] In one preferred embodiment, in step S1, the pore-forming agent is one or a combination of polyethylene glycol and polyvinylpyrrolidone.

[0071] In one preferred embodiment, in step S1, the pore-forming agent is one or several of PEG200, PEG300, PEG400, PEG500, PEG600, PEG800, PEG1000, PEG1500, PEG2000, PEG3000, PVP K13, PVP K16, PVP K18, and PVP K30.

[0072] In one preferred embodiment, in step S1, the molecular weight of the pore-forming agent and the macroscopic pore size satisfy the relational expression: .

[0073] Among them, is the average diameter of the macropores (nm); is the number-average molecular weight of the pore-forming agent.

[0074] In one preferred embodiment, in step S1, the process of ultrasonic treatment is as follows: the power is 300 - 400 W, the frequency is 40 - 50 kHz, and the time is 15 - 60 min.

[0075] In one preferred embodiment, in step S1, before the polymer and the treated lithium lanthanum zirconate oxide particles are mixed, the polymer is first dispersed in a solvent to obtain a solution with a concentration of 5 - 15 wt%.

[0076] In one preferred embodiment, the solvent includes one or more of dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and acetone.

[0077] In one preferred embodiment, the solvent includes acetone and also includes one or more of dimethylformamide (DMF), N-methylpyrrolidone (NMP), and tetrahydrofuran (THF).

[0078] In one preferred embodiment, in the solvent, the volume concentration of acetone is 50% - 70%.

[0079] In one preferred embodiment, in step S2, the mass ratio of the core to the polymer in the mixture is 10:0.5 - 10:3.

[0080] In one preferred embodiment, in step S3, in the gradient heat treatment, the argon gas flow rate and the temperature satisfy the relationship: V(Ar)=0.5×T / 100 (L / min), where T is the real-time temperature (°C).

[0081] In one preferred embodiment, in step S3, in the slow cooling stage, it is cooled to room temperature at a rate of 10 - 15 °C / min.

[0082] During the gradient heat treatment process, precise construction of macropores is achieved by selecting a specific pore-forming agent (for the relationship curve between the molecular weight of the pore-forming agent and the macropore size, see Figure 7 ); combined with the gradient ball milling process (dynamically adjusted from 300 → 150 rpm), the median particle size (D50) of the LLZO particles is controlled at the 80 nm level, optimizing the mesopore distribution of 50 - 100 nm; finally, through critical phase transition temperature control at 650 °C, synergistically with the micropore structure (5 - 15 nm), the balance between the ion / electron dual channels and mechanical stability is achieved.

[0083] Based on the same inventive concept, the present invention also claims to protect an electrode paste, which comprises the composite coating material.

[0084] In one preferred embodiment, the electrode paste comprises the composite coating material, conductive carbon black, polyvinylidene fluoride and N-methylpyrrolidone; the mass ratio of the composite coating material, conductive carbon black and polyvinylidene fluoride is 6-8:1-3:1-2.

[0085] N-methylpyrrolidone is used as a solvent. The composite coating material, conductive carbon black and polyvinylidene fluoride are active ingredients.

[0086] In one preferred embodiment, the solid content of the electrode paste is 35-45 wt%.

[0087] Based on the same inventive concept, the present invention also claims to protect a negative electrode material for a lithium battery, which comprises a current collector, and an active material layer prepared from the electrode paste is provided on the surface of the current collector.

[0088] In one preferred embodiment, the preparation method of the negative electrode material for the lithium battery is to uniformly coat the electrode paste on the current collector, and control the areal density of the active substance to be 12-15 mg / cm 2 , and then dry it to obtain.

[0089] In one preferred embodiment, the current collector is a copper foil current collector.

[0090] In one preferred embodiment, the drying process is as follows: first pre-dry at 70-80 °C for 1-2 hours, and then treat in a vacuum environment at 120-130 °C for 10-14 hours.

[0091] In one preferred embodiment, the vacuum degree of the vacuum environment is ≤ -0.08 MPa.

[0092] Based on the same inventive concept, the present invention also claims to protect a liquid battery, which comprises the negative electrode material for the lithium battery.

[0093] In one preferred embodiment, in the liquid battery, the electrolyte is a mixed solution of ethylene carbonate and dimethyl carbonate containing 1-2 M lithium hexafluorophosphate (LiPF6), and the volume ratio of ethylene carbonate / dimethyl carbonate is 1-2:1-2, and 2-3 wt% fluoroethylene carbonate (FEC) and 1-2 wt% vinylene carbonate (VC) are added as functional additives.

[0094] In one preferred embodiment, in the liquid battery, with LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811) serves as the positive electrode, and polyethylene serves as the separator.

[0095] Based on the same inventive concept, the present invention also claims protection for a solid-state battery including the composite coating material.

[0096] Based on the same inventive concept, the present invention also claims protection for the application of the composite coating material in a PVDF-HFP-based solid-state battery.

[0097] In one preferred embodiment, in the PVDF-HFP-based solid-state battery, the electrolyte includes 5-25 wt% of PVDF-HFP, 5-25 wt% of HFP, 5-20 wt% of amino-functionalized lithium lanthanum zirconium oxide, 20-50 wt% of lithium bis(trifluoromethanesulfonyl)imide, and 0.5-1.0 wt% of a crosslinking agent;

[0098] Among them, in PVDF-HFP, the mass ratio of PVDF to HFP is 80-90:15.

[0099] In one preferred embodiment, the crosslinking agent is selected from any one of peroxide-based, sulfur-based systems, or silane coupling agents.

[0100] In one preferred embodiment, in the PVDF-HFP-based solid-state battery, a hexagonal boron nitride (h-BN) buffer layer is sprayed on the electrode interface.

[0101] In one preferred embodiment, the thickness of the hexagonal boron nitride (h-BN) buffer layer is 5 ± 1 nm.

[0102] In one preferred embodiment, the density of the hexagonal boron nitride (h-BN) buffer layer is 0.5-1.2 mg / cm 2 .

[0103] In one preferred embodiment, the room-temperature ionic conductivity of the PVDF-HFP-based solid-state battery is ≥ 3.3×10 - 4 S / cm, and the capacity retention rate after 1000 cycles at 1C is ≥ 85%.

[0104] In one preferred embodiment, the preparation method of amino-functionalized lithium lanthanum zirconium oxide includes: immersing hydroxylated lithium lanthanum zirconium oxide particles in a 3-aminopropyltriethoxysilane ethanol solution, refluxing at 80-90 °C for 4-6 hours to obtain amino-functionalized lithium lanthanum zirconium oxide.

[0105] In one preferred embodiment, the concentration of the 3-aminopropyltriethoxysilane ethanol solution is 5-20 wt%.

[0106] In one preferred embodiment, the amino density of amino-functionalized lithium lanthanum zirconium oxide is 1.8-2.2 per nm2 。

[0107] In one preferred embodiment, the spraying process of the h-BN buffer layer adopts aerosol deposition technology, and the carrier gas pressure is 0.2 - 0.5 Mpa.

[0108] In one preferred embodiment, the peroxide crosslinking agent is dicumyl peroxide (DCP) or lauroyl peroxide (LPO).

[0109] In one preferred embodiment, the sulfur system is composed of sulfur (S8) and accelerator N-tert-butyl-2-benzothiazole sulfenamide (TBBS) in a mass ratio of 3 - 7:1.

[0110] In one preferred embodiment, the silane coupling agent is bis-(γ-triethoxysilylpropyl) tetrasulfide (Si69).

[0111] In one preferred embodiment, the electrolyte is formed into a film with a thickness of 20 - 100 μm by the casting method, and a gradient drying process is implemented: pre-dry at 50°C for 2 hours and then raise the temperature to 80°C for 4 hours.

[0112] In one preferred embodiment, to improve the interfacial compatibility, a hexagonal boron nitride (h-BN) nanosheet buffer layer with a thickness of 5 ± 1 nm is introduced at the electrode / electrolyte interface, and its areal density is controlled to be 0.5 - 1.2 mg / cm by aerosol spraying technology 2 。

[0113] In one preferred embodiment, the finally assembled all-solid-state battery uses NCM811 as the positive electrode (areal capacity 3.2 mAh / cm 2 ), SiC@polymer-LLZO as the negative electrode (areal capacity 4.0 mAh / cm 2 ), and is encapsulated under a pressure condition of 5 - 8 MPa to achieve stable solid-state interfacial contact.

[0114] Through the design of the composite coating structure and the interfacial synergistic regulation, the present invention significantly improves the electrochemical performance and mechanical stability of the silicon-carbon negative electrode material, and realizes the dual adaptation of liquid and solid battery systems. Compared with the prior art, the technical advantages of the present invention are specifically reflected in the following aspects:

[0115] 1. Multi-performance optimization of the composite coating structure

[0116] Based on the three-dimensional ion / electron double-continuous transport network constructed by the gradient carbonization process, the room-temperature ionic conductivity of the composite coating material is ≥2.3×10 -4S / cm, which is four orders of magnitude higher than that of traditional PAN-coated materials; at the same time, through the buffering effect of the "macropore-mesopore-micropore" porous synergistic structure (macropores of 200 - 1200 nm, mesopores of 50 - 100 nm, and micropores of 5 - 15 nm), the volume expansion rate of silicon is inhibited from more than 300% to 121% (Example 1), and the capacity retention rate is 85.7% after 500 cycles at 1C (Example 2). The use of a low-temperature gradient carbonization process instead of traditional high-temperature sintering reduces energy consumption and avoids the problem of grain coarsening, significantly improving the batch consistency of the materials (Examples 1 and 3).

[0117] 2. Interface Synergistic Strengthening and Stability Enhancement

[0118] The interfacial binding energy is increased to 9.2 J / m through the formation of La-O-C covalent bonds between the surface hydroxyl groups of lithium lanthanum zirconium oxide and the polymer carbonization network 2 (Example 2), which is significantly higher than that of the pure polymer coating system (Comparative Example 1). In the PVDF-HFP-based solid-state system, after introducing a 5 ± 1 nm h-BN buffer layer, the room-temperature ionic conductivity is increased, and the interfacial impedance and the capacity retention rate after 500 cycles at 1C at 80°C of the assembled all-solid-state battery are both enhanced in performance. For the solid-state battery system, the fluorocarbon bond interaction between the aminated LLZO filler and the PVDF-HFP matrix reduces the interfacial impedance compared to the unmodified system.

[0119] 3. Verification of Cross-System Application Performance and Industrial Adaptation

[0120] The present invention exhibits an initial Coulombic efficiency of 83.5% and a capacity retention rate of 88.8% after 500 cycles at 1C in liquid batteries, and is applicable to PVDF-HFP and PEO-based systems (ionic conductivity of 2.5×10 -4 S / cm in Example 6). In the application of solid-state batteries, by adding 20 - 50% LiTFSI lithium salt to the PVDF-HFP-based solid-state electrolyte, the room-temperature ionic conductivity is increased to 3.39×10 -4 S / cm, and it still maintains the characteristic of dendrite-free growth after 500 cycles at 1C current when matched with the NCM811 positive electrode in an 80°C high-temperature environment (Example 4). In industrial implementation, the material preparation process has a high compatibility with existing production lines, and the unit cost is reduced by combining solvent recovery, making large-scale production feasible.

[0121] 4. Improvement in Safety Performance

[0122] The thermal runaway onset temperature of the composite coating material is increased to 200°C (Example 1), which is significantly higher than 128°C of the conventional silicon-carbon negative electrode (Comparative Example 1), proving that the safety performance of the composite coating material has been greatly improved. Description of the Drawings

[0123] Figure 1 It is the SEM morphology diagram of LLZO nanoparticles after gradient ball milling treatment.

[0124] Figure 2 It is the SEM diagram of the cross-section of the composite coating layer.

[0125] Figure 3 It is the XPS O1s spectrum of the hydroxylation on the surface of LLZO.

[0126] Figure 4 It is the temperature-time curve diagram of the gradient carbonization process.

[0127] Figure 5 It is the 1C cycling performance curve diagram of the liquid battery electrode.

[0128] Figure 6 It is the DSC test curve diagram of the composite coating material in Example 1.

[0129] Figure 7 It is the relationship curve diagram (logarithmic coordinates) between the molecular weight of different pore-forming agents and the macroscopic pore size; in the figure, PEG fitting: D = 2.90M n 0.73 , PVP fitting: D = 5.33M n 0.51 .

[0130] Figure 8 It is the DSC test curve diagram of the composite coating material in Comparative Example 1. Specific Embodiments

[0131] The present invention is not limited to the following specific embodiments. Those of ordinary skill in the art can implement the present invention in other various specific embodiments according to the content disclosed in the present invention, or any simple changes or modifications made by adopting the design structure and concept of the present invention fall within the protection scope of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0132] Example 1: Preparation of Composite Coating Material and Verification of Liquid Battery Performance

[0133] Mix 10 g of Li 6.4 La3Zr 1.4 Ta 0.6 O 12 powder with ethanol, and perform gradient ball milling treatment with zirconia balls. The diameters of the zirconia balls are 3 mm and 5 mm, and the volume ratio of the 3-mm and 5-mm zirconia balls is 1:2. Coarse grinding is carried out at a speed of 300 rpm for the first 2 hours, and then the speed is switched to 150 rpm for fine grinding for the next 4 hours. The SEM morphology diagram of the LLZO nanoparticles after gradient ball milling treatment is shown inFigure 1 The obtained powder was vacuum dried at 80℃ for 12 hours, then immersed in 5wt% nitric acid solution and ultrasonically treated at 80℃ for 2 hours, washed and dried to obtain pretreated LLZO. The X-ray photoelectron spectroscopy (XPS) analysis was performed on it, and the results were as follows: Figure 3 As shown, the surface hydroxyl density is 3.2 / nm 2 .

[0134] 8g PAN was dissolved in 92g N,N-dimethylformamide (DMF), stirred at a constant temperature of 60℃ for 6 hours to form a homogeneous solution, and 80g silicon-carbon core material (silicon mass accounts for 30wt%, D50 is 10μm, G4S-C800, Shanghai Shanshan) was added, followed by 2g pre-treated LLZO and 0.8g PEG-400. After ball milling and dispersion for 2 hours, gradient carbonization treatment was performed: under argon protection, the temperature was raised to 250℃ at 2℃ / min for pre-oxidation for 2 hours, and then raised to 800℃ at 5℃ / min for carbonization for 2 hours, with an argon flow rate of 4L / min. Finally, the temperature was kept at 650℃ for 15 minutes and slowly cooled to room temperature to obtain a composite coating material (SiC@PAN-LLZO composite powder). The temperature-time curve of the gradient carbonization process is shown in Figure 2. Figure 4 As shown. The cross section of the composite coating material was SEM-graphed, and the results were as follows: Figure 2 As shown in the figure, the macropore size is about 400 nm, the mesopore size is 50-100 nm, and the micropore size is 2-5 nm.

[0135] During the preparation process, specific porogens achieve precise construction of macroscopic pores; the gradient ball milling process (dynamic adjustment from 300 to 150 rpm) controls the D50 of the pretreated LLZO to 80 nm and optimizes the 50-100 nm mesopore distribution; through critical phase transition temperature control at 650°C, the graphitization degree of the carbon layer and the micropore structure (5-15 nm) are regulated to achieve a balance between ion / electron dual channels and mechanical stability.

[0136] In the composite coating material, the macropores: account for 50 - 60%, and are statistically analyzed by three-dimensional reconstruction of focused ion beam - scanning electron microscopy (FIB-SEM). The pore volume is extracted through threshold segmentation. Mesopores: account for 30 - 40%, and are calculated based on the BJH model of nitrogen adsorption - desorption isotherms. The LLZO nanoparticles (D50 = 80 - 90 nm) are stacked to form "close-packed spheres" - like pores (porosity ≈ 26%), and the spatial distribution uniformity is verified by combining electron tomography (ET). Micropores: account for 5 - 10%, and are quantified by fitting small-angle X-ray scattering (SAXS) combined with the density functional theory (DFT) model for the lattice-level pores caused by carbonization shrinkage (the micropore density saturates when the graphitization degree of the carbon layer ≥ 80%). Macropores preferentially absorb the macroscopic strain of silicon core expansion; mesopores disperse shear stress to prevent crack propagation; micropores stabilize the SEI film through surface adsorption effects. Macropores are mainly distributed on the outer surface of the coating layer; mesopores are located in the LLZO particle stacking area; micropores are concentrated in the carbonized polymer matrix. The pore distribution basically conforms to the law of outer sparse and inner dense (the macropore density increases outward). DSC test is performed on the composite coating material, and the thermal runaway onset temperature of the SiC@PAN-LLZO composite powder material is increased to 200 °C ( Figure 6 ).

[0137] The obtained SiC@PAN-LLZO composite powder is mixed with Super P and PVDF in a mass ratio of 7:2:1, and NMP is used as the solvent. A double-planet stirring process (revolution 30 rpm / rotation 1200 rpm) is used to homogenize the slurry for 4 hours to prepare the slurry. After coating on the copper foil current collector, gradient drying is carried out to form an electrode with a surface density of 12 - 15 mg / cm 2 . The gradient drying conditions are: first dry at 80 °C for 2 h, and then dry at 120 °C for 12 h (80 °C / 2 h → 120 °C / 12 h) (vacuum degree ≤ -0.08 MPa). An electrolyte of 1M LiPF6 in EC / DMC (volume ratio 1:1) is used, and 2 wt% FEC and 1 wt% VC are added. Using NCM811 as the positive electrode (surface capacity 3.2 mAh / cm 2 ), a battery is assembled with a 9-μm-thick PE separator.

[0138] Electrochemical tests show that the initial Coulomb efficiency of this electrode reaches 83.5% at a 0.1C rate, and the capacity retention rate is 88.8% after 500 cycles at 1C (see Figure 5 ), the volume expansion rate measured by in-situ XRD is 118%, and the interfacial impedance is stabilized at 18.3 Ω·cm 2 .

[0139] Test methods and data verification:

[0140] 1. Ionic conductivity: Measured using a Chenhua CH760e electrochemical workstation, calculated by the formula σ = L / (R·A), with a test frequency range of 0.1 Hz - 1 MHz.

[0141] 2. Volume expansion rate: In-situ testing was carried out based on a Rigaku Smartlab SE X-ray diffractometer, and the change in unit cell parameters was refined and analyzed.

[0142] 3. Interface binding energy: Nano-mechanical mapping was performed using a Bruker edge atomic force microscope, and quantitative analysis was carried out through the force-displacement curve.

[0143] 4. Cycling performance: Measured using a Neware BTS-5V10mA test system, with the voltage window set to 0.01 - 1.5 V (vs. Li + / Li).

[0144] 5. Calculation of the hydroxyl density on the LLZO surface:

[0145] A Thermo Scientific K-Alpha X-ray photoelectron spectrometer was used, with monochromatic Al Kα rays (1486.6 eV) as the excitation source to analyze the O 1s spectral peak. The peak area attributed to hydroxyl (OH) (binding energy 532.1 ± 0.2 eV) was determined by peak fitting and calculated according to the formula:

[0146] where, is the proportion of the hydroxyl peak area, is the total sensitivity factor, is the specific surface area of LLZO (m² / g), d is the XPS detection depth, is Avogadro's constant.

[0147] 6. Calculation of the amino density on the LLZO surface:

[0148] The characteristic peak of amino (- )(binding energy 399.6 ± 0.2 eV) was fitted in the N 1s spectrum, according to the formula: ;

[0149] where is the proportion of the amino peak area, the coefficient 2 is the XPS quantitative calibration factor (calibrated based on a standard sample), and the definitions of the remaining parameters are the same as those for the hydroxyl density calculation. The surface was sputter-cleaned with Ar + for 30 seconds (1 keV, 1 μA / cm 2 ).

[0150] Example 2

[0151] Application of PVDF-HFP-based solid-state battery

[0152] Preparation of aminated LLZO nanoparticles: The hydroxylated LLZO nanoparticles in Example 1 were subjected to amination modification, that is, the surface-hydroxylated LLZO was immersed in a 3 wt% ethanol solution of 3-aminopropyltriethoxysilane (APTES), and refluxed at 80 °C for 6 hours to obtain LLZO nanoparticles with a surface amino density of 2.0 per nm 2 .

[0153] Preparation of the solution system: PVDF-HFP with a hexafluoropropylene (HFP) content of 5-25 wt% (where the mass ratio of PVDF to HFP is 85:15) was selected as the matrix material, and 20-50 wt% of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added as the lithium salt and dissolved in a polar organic solvent (DMF / acetone (7:3, V / V)) to obtain a solution system. Then, 3 g of aminated modified LLZO nanoparticles were added to the solution system, and 0.12 g of a crosslinking agent was added to the system. The crosslinking agent was dicumyl peroxide (DCP) to obtain a composite electrolyte solution

[0154] Battery assembly: The composite electrolyte solution was formed into a film with a thickness of 20-100 μm by the casting method, and a gradient drying process was implemented: pre-dried at 50 °C for 2 hours and then heated to 80 °C for 4 hours. To improve the interfacial compatibility, a hexagonal boron nitride (h-BN) nanosheet buffer layer with a thickness of 5 ± 1 nm was introduced at the electrode / electrolyte interface, and its areal density was controlled to be 1.0 mg / cm 2 . The test shows that the room-temperature ionic conductivity of this electrolyte membrane reaches 3.39×10 -4 S / cm

[0155] The production of the positive and negative electrode sheets of the battery is the same as in Example 1. The initial interfacial impedance of the assembled full battery is 31.4 Ω·cm 2 , and the interfacial impedance is 30.8 Ω·cm after 50 cycles 2 , and the interfacial impedance is 37.9 Ω·cm after 1000 cycles 2 , and the growth rate ≤ 5% ( Figure 7 ). The capacity retention rate after 1000 cycles at 2C is 85.2%, and the capacity retention rate after 500 cycles at 1C at 80 °C is 84.7%, and no dendrites are generated

[0156] Example 3

[0157] Performance optimization of high-LLZO content composites

[0158] Adjust the addition amount of LLZO to 3 g (PAN 7 g), and the remaining processes are the same as in Example 1. Performance tests show that the ionic conductivity is increased to 3.1×10 -4 S / cm, the volume expansion rate is further reduced to 105%, and the capacity retention rate is 85.7% after 500 cycles at 1C. Atomic force microscopy (AFM) mechanical tests show that the interfacial binding energy between LLZO and the PAN carbonization network is enhanced to 9.2 J / m 2 , confirming the strengthening effect of the La-O-C covalent bond.

[0159] Example 4

[0160] Critical phase transition regulation of the gradient carbonization process

[0161] Change the carbonization program to carbonize at 700 °C for 2 hours, and then slowly cool to 550 °C. The remaining processes are the same as in Example 1. The capacity retention rate is 82.3% after 500 cycles at 1C.

[0162] Example 5

[0163] PEO-based composite coating material

[0164] Dissolve 8 g of PEO (M v =600,000) in THF / acetone (7:3, v / v), add 2 g of nanoparticles and 1.2 g of PEG-400, and the remaining processes are the same as in Example 1. Tests show that the ionic conductivity of the composite coating material is 2.3×10 -4 S / cm, and the volume expansion rate is 121%.

[0165] Example 6

[0166] Comparison of Al-doped LLZO

[0167] Use to replace , and the remaining processes are the same as in Example 1. The ionic conductivity is 2.1×10 -4 S / cm, and the capacity retention rate after 500 cycles is 86.5%.

[0168] Example 7

[0169] Optimization of PVP porogen

[0170] Replace the porogen with 10 wt% polyvinylpyrrolidone (PVP K30), and the remaining processes are the same as in Example 4. SEM shows that the macroscopic pore size is 900±75 nm. The capacity retention rate after 600 cycles at 1C is 90.2%. The relationship curve between the molecular weight of the PVP porogen and the macroscopic pore size is shown in Figure 7 .

[0171] Comparative Example 1

[0172] Pure PAN coating system without added LLZO

[0173] The addition step of LLZO was omitted, and the remaining processes were the same as those in Example 1. The test results showed that the volume expansion rate increased to 276%, and the capacity retention rate was only 73.2% after 100 cycles at 1C, and the subsequent cycles decayed rapidly ( Figure 5 ), significantly inferior to the scheme of Example 1 of the present invention, confirming the core role of LLZO in ion transport and mechanical buffering. Through DSC testing, the thermal runaway temperature of the material was 128 °C ( Figure 8 ), proving that the safety of the material was also inferior to the scheme of Example 1 of the present invention.

[0174] Comparative Example 2

[0175] Active sites with a hydroxyl density of less than 3 per nm² on hydroxylated LLZO

[0176] 10 g The powder was subjected to gradient ball milling treatment under the same conditions as in Example 1. The obtained powder was immersed in a 1 wt% nitric acid solution and ultrasonically treated at 80 °C (frequency 40 kHz, power 300 W) for 30 minutes. XPS analysis showed that the surface hydroxyl density was only 1.5 per nm 2 . The remaining processes were the same as those in Example 1.

[0177] Electrochemical tests showed that the initial Coulombic efficiency of the battery decreased to 72.3%, and the capacity retention rate was only 58.6% after 500 cycles at 1C. Through in-situ XRD determination, the volume expansion rate of the silicon-carbon anode material was 215%, and the initial value of the interfacial impedance was 185 Ω·cm 2 , and it increased to 320 Ω·cm after 500 cycles at 1C 2 , much higher than that in Example 1.

[0178] Comparative Example 3

[0179] Fixed argon gas flow rate

[0180] During the carbonization process, the argon gas flow rate was fixed at 2 L / min, and the remaining processes were the same as those in Example 1. SEM showed poor pore connectivity, and the ionic conductivity of the composite coating material was 1.1×10 -4 S / cm, and the capacity decayed to 75% after 300 cycles.

[0181] Comparative Example 4

[0182] Single ball milling parameter

[0183] Using a single ball milling speed of 300 rpm for 5 hours (without gradient adjustment), the particle size D50 of LLZO is 150 nm, and the remaining processes are the same as in Example 1. SEM shows that the mesopore size is greater than 200 nm, and the ionic conductivity is 1.8×10 -4 S / cm (22% lower than that in Example 1), the volume expansion rate increases to 185%, and the pulverization and fragmentation of the active material can be clearly observed by SEM after cycling. The porosity < 70% (mercury intrusion method). The capacity retention rate of the battery after 500 cycles at 1C is only 75.3%, which is lower than that in Example 1.

[0184] The initial value of the interfacial impedance is 85 Ω·cm 2 , and it increases to 152 Ω·cm after 500 cycles at 1C 2 .

[0185] Comparative Example 5

[0186] Lack of macropores

[0187] The pore-forming agent PEG-400 is omitted, and the remaining experimental steps are the same as in Example 1.

[0188] This makes the pore structure lack macropores, only having mesopores and micropores, and the rest is the same as in Example 1.

[0189] The results show that: as determined by in-situ XRD, the volume expansion rate of the silicon-carbon anode material > 200%.

[0190] Comparative Example 6

[0191] In the gradient heat treatment, the pre-oxidation step is cancelled, and it is directly heated to 800 °C at a rate of 10 °C / min for carbonization for 3 hours. The remaining processes are the same as in Example 1.

[0192] This makes the pore structure lack micropores, only having mesopores and macropores, and the rest is the same as in Example 1.

[0193] The results show that: for the battery cycled 500 times at 1C, the capacity attenuation rate increases by 30% compared with Example 1.

[0194] Comparative Example 7

[0195] Composite coating material containing only macropores (200 - 1000 nm)

[0196] Adjust the ball milling process to a single speed of 400 rpm for 5 hours, and the LLZO particles D50 = 120 nm. In the gradient heat treatment, the pre-oxidation step is cancelled, and it is directly heated to 800 °C at a rate of 10 °C / min for carbonization for 3 hours. The remaining processes are the same as in Example 1.

[0197] SEM shows that the pores only contain macropores of 200 - 1000 nm (the proportion of mesopores / micropores < 5%). The volume expansion rate reaches 253% (in-situ XRD), and the capacity retention rate after 500 cycles at 1C is only 62.1%. The initial value of the interfacial impedance is 85 Ω·cm 2 , which rises to 210 Ω·cm after cycling 2 (AFM shows crack propagation). The test shows that a single macropore cannot disperse multi-scale stress, confirming the necessity of multi-level pore synergy.

[0198] Comparative Example 8

[0199] The macropore diameter is 100 nm (< 200 nm)

[0200] PEG-200 (molecular weight 200) is selected as the pore-forming agent, and the addition amount is 15 wt%. The rest is the same as in Example 1.

[0201] After testing, the average macropore diameter is 100 ± 15 nm (mercury intrusion method), and the proportion of mesopores / micropores is normal. The volume expansion rate rebounds to 182% (the expansion of silicon particles is not fully buffered), and the electrode pulverization rate > 30% after 300 cycles at 1C. The ionic conductivity is 1.7×10 -4 S / cm (26% lower than that in Example 1). The test results show that insufficient macropore size leads to a decrease in the buffering efficiency.

[0202] Comparative Example 9

[0203] The macropore diameter is 1200 nm

[0204] PEG-4000 (molecular weight 4000) is used as the pore-forming agent, and the addition amount is 20 wt%. The carbonization temperature is raised to 850 °C. The rest is the same as in Example 1.

[0205] After testing, the macropore size is 1200 ± 50 nm (SEM statistics), and the mesopores / micropores are squeezed. The breakage rate during electrode coating is +20% (due to the overly large pores resulting in loose structure). The capacity retention rate after 200 cycles at 1C is 71.3%, and the interfacial impedance > 150 Ω·cm 2 . The test results show that overly large pores weaken the mechanical strength, proving that 1000 nm is the size upper limit.

[0206] Comparative Example 10

[0207] The gradient cooling mode is not adopted, and it is directly cooled to room temperature at a rate of 5 - 7 °C / min.

[0208] After carbonization, the insulation at 650 °C is cancelled, and it is directly cooled to room temperature. The rest of the process parameters are the same as in Example 1. The performance comparison between Comparative Example 10 and Example 1 is shown in the following table.

[0209] Table 1 Comparison of Performance between Comparative Example 10 and Example 1

[0210] Due to the lack of the heat preservation process at 650°C, the degree of carbon chain aromatization is reduced, and the proportion of generated micropores decreases. The decrease in graphitization degree also leads to a decrease in the electronic conductivity of the material. At the same time, it also results in a reduction in the role of the graphite layer in inhibiting thermal decomposition reactions.

[0211] Comparative Example 11

[0212] Adjust the gradient heat treatment as follows: heat up to 1000°C at a rate of 10°C / min for carbonization for 2 h, and cancel the heat preservation step at 650°C. The rest is the same as in Example 1.

[0213] After testing, the graphitization degree > 90% (XRD analysis), and micropore collapse (SAXS shows that the micropore density decreases by 60%). The ionic conductivity drops to 1.1×10 -4 S / cm (the over-dense carbon layer hinders Li + transport). The volume expansion rate rebounds to 168% (the pore structure fails). The test results show that too high temperature destroys the porous structure.

[0214] Comparative Example 12

[0215] Set the carbonization temperature to 500°C, and the rest is the same as in Example 1.

[0216] After testing, the polymer is not completely carbonized (Raman ID / IG = 1.8, compared with 0.9 in Example 1). The electronic conductivity < 10 - 3 S / cm (four-probe method), and the 1C capacity is only 820 mAh / g (1350 mAh / g in Example 1). The volume expansion rate > 200% (the coating layer does not form an effective buffer). The test results show that low-temperature carbonization leads to defects in the conductive network.

[0217] Comparative Example 13

[0218] No gradient heat treatment

[0219] Cancel the gradient heating program, and directly heat from room temperature to 800°C at a rate of 10°C / min for carbonization for 2 h. The rest is the same as in Example 1.

[0220] After testing, the pore connectivity is poor (the open porosity by mercury intrusion method < 70%), and the initial value of the interfacial impedance is 83 Ω·cm 2 . The capacity retention rate after 500 cycles at 1C is 75.6% (compared with 88.8% in Example 1). The thermal runaway temperature drops to 175°C (DSC test, due to uneven pore distribution leading to heat accumulation). The test results show that gradient heat treatment is crucial for the directional arrangement of pores, and direct heating leads to performance deterioration.

[0221] Comparative Example 14

[0222] Referring to the prior art CN 112467116 A, a graphite core (with a silicon mass fraction of 0%) is used, and the LLZO coating layer is not hydroxylated. Tests show that: the volume expansion rate > 300% (silicon is not buffered), the capacity retention rate after 100 cycles at 1C is only 65%, and the interfacial impedance > 200 Ω·cm 2 , confirming that the graphite core cannot adapt to the high expansion characteristics of silicon-based materials.

[0223] Comparative Example 15

[0224] Referring to the prior art CN 111244410 B, a multi-layer coating (carbon layer + HF isolation layer + SEI layer) is used, and the gradient dispersion process is omitted. The results show that: the ionic conductivity of the SEI layer is only 1.2×10 -6 S / cm, the capacity retention rate after 500 cycles is 73.2%, and the interfacial delamination results in an electrode pulverization rate > 40%.

[0225] Comparative Example 16

[0226] Referring to the prior art CN 115241526 A, lithium borate (2wt%) is used to replace amino-functionalized LLZO. Tests show that: the expansion inhibition efficiency is only 38%, the electron mobility drops to 10 -4 S / cm, and the capacity decays to 68% after 300 cycles at 1C, proving that lithium borate cannot adapt to the silicon-based stress.

[0227] It should be noted that the above embodiments are merely examples given to clearly illustrate the present invention, and are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A composite coating material, characterized in that, Comprising: A core, the core having a core-shell structure; the material of the shell structure of the core is carbon, and the material of the core structure of the core is a silicon-based material; And A shell coated outside the core, the shell including a pore structure, and the shell containing a polymer and hydroxylated lithium lanthanum zirconate oxide particles; Among them, the structural formula of the lithium lanthanum zirconium oxide particles is Li 7-x La3Zr 2-y M y O 12 , where M is at least one of the doping elements Ta, Al, and Nb that equivalently replace the Zr site, 0 ≤ x ≤ 1, 0 ≤ y ≤ 0.6; The pore structure includes macropores with a pore diameter of 200 - 1000 nm, mesopores with a pore diameter of 50 - 100 nm, and micropores with a pore diameter of 2 - 5 nm.

2. The composite coating material according to claim 1, wherein In the pore structure, the proportion of macropores is 50 - 60%, the proportion of mesopores is 30 - 40%, and the proportion of micropores is 5 - 10%.

3. The composite coating material according to claim 1, wherein In the core, the mass ratio of the core structure is 15-50 wt%; the silicon-based material includes one or a combination of elemental silicon, porous silicon, nanosilicon, and a silicon oxide material with the general formula SiO x , where 0 < x < 2; the thickness of the shell structure is 50-200 nm, and the crystallinity is ≥75%; the material of the shell structure is graphitized carbon.

4. The composite coating material according to claim 1, wherein The particle size D50 of the core is 5 - 12 μm, the specific surface area is 1 - 3 m 2 / g, and the tapped density is 0.8 - 1.2 g / cm 3 ; the porosity of the core is ≤5%; and / or, the surface of the hydroxylated lithium lanthanum zirconate-based particles has active sites with a hydroxyl density greater than 3 per nm 2 .

5. The composite coating material according to claim 1, characterized in that, The preparation method of the hydroxylated lithium lanthanum zirconate oxide particles includes the following steps: subjecting the lithium lanthanum zirconate oxide particles to ball milling and drying, and then adding them to an acid solution for ultrasonic treatment to obtain the hydroxylated lithium lanthanum zirconate oxide particles; wherein, gradient dispersion technology is used for ball milling, and the gradient dispersion technology is: first ball milling at a speed of 300 - 400 rpm for 1 - 3 hours, and then ball milling at a speed of 100 - 150 rpm for 3 - 5 hours.

6. The preparation method of the composite coating material according to any one of claims 1-5, characterized in that, Including the following steps: S1. Mix the polymer and the hydroxylated lithium lanthanum zirconate oxide particles according to a mass ratio of 8 - 5:2 - 5; after mixing evenly, add a pore-forming agent and perform ultrasonic treatment to obtain a mixture; S2. Mix the mixture and the core evenly to obtain a pre-product; S3. Perform gradient heat treatment on the pre-product to obtain a composite coating material; The process of the gradient heat treatment is: under argon protection, heat up to 200 - 250 °C at a rate of 2 - 3 °C / min for pre-oxidation for 1 - 2 h, then heat up to 700 - 800 °C at a rate of 5 - 10 °C / min for carbonization for 2 - 3 h, then cool down to 600 - 650 °C at a rate of 5 - 7 °C / min and keep warm for 15 - 20 min, and then slowly cool to room temperature.

7. The preparation method according to claim 6, characterized in that In step S1, the addition amount of the pore-forming agent is 0.1 - 15 wt% of the mass of the polymer; the pore-forming agent is one or both of polyethylene glycol and polyvinylpyrrolidone; in step S2, the mass ratio of the core to the polymer in the mixture is 10:0.5 - 10:3; in step S3, the slow cooling stage cools to room temperature at a rate of 10 - 15 °C / min.

8. An electrode paste, characterized in that, The electrode paste includes the composite coating material according to any one of claims 1 - 5.

9. A negative electrode material for a lithium battery, characterized in that, Including a current collector, and an active material layer prepared from the electrode paste according to claim 8 is provided on the surface of the current collector.

10. A battery, characterized in that, The battery is a liquid battery, and the liquid battery includes the lithium battery negative electrode material according to claim 9; or, the battery is a solid battery, and the solid battery includes the composite coating material according to any one of claims 1 - 5.

Images