A method for preparing a solid-state anode sheet with high stability and low interfacial impedance

Abstract

The application discloses a kind of high stability, low interface impedance solid anode sheet preparation method, comprising the following steps: S1, nitrogen pretreatment LATP: LATP powder is annealed under nitrogen protection at high temperature;After annealing, it is transferred to glove box and is stored;S2, dry mixing process: silicon carbon negative pole Si / C, conductive agent, carbon nanotube, pretreated LATP, according to mass ratio 90~98%:1~5%:1~5%:1~10% after dry mixing, under inert atmosphere Mechanical ball milling is carried out, and 1~5 wt% PTFE binder is added simultaneously, to obtain mixture;S3, dry pressing forming: the mixture in S2 is formed into anode film by multiple rolling or hot pressing;The anode film is rolled and covered on the surface of current collector to obtain anode sheet.The application improves the environmental stability of LATP by nitrogen pretreatment LATP, and realizes the efficient compounding of LATP and silicon carbon negative pole by dry process;At the same time, the combination problem of low expansion, high interface stability and environmental protection process is realized.

Description

Technical Field

[0001] This invention relates to the field of solid-state lithium-ion battery technology, and more specifically to a method for preparing a solid-state anode sheet with high stability and low interfacial impedance. Background Technology

[0002] Currently, anode materials for rechargeable batteries serve as carriers of metal ions and electrons during charging, playing a crucial role in energy storage and release. Therefore, as a major factor influencing battery energy density, future research and development of anode materials will focus on breakthroughs in high capacity, high energy density, and high cycle performance.

[0003] Limitations of silicon-carbon anodes: The significant volume expansion of silicon materials can lead to electrode structural collapse, and solvent residues in traditional wet processes exacerbate side reactions, affecting initial efficiency and cycle stability. Spherical or near-spherical silicon-carbon particles, due to their higher compaction density and excellent cycle life, are often used as anode materials in high-energy-density cells. However, their unique spherical structure results in a small contact area with the current collector. During battery charging and discharging, these particles experience significant volume expansion stress, making them prone to detaching from the current collector. This increases the battery's internal resistance, leading to a substantial decrease in battery capacity and shortening the rechargeable battery's lifespan. Therefore, reducing the impact of volume expansion stress on spherical or near-spherical silicon-carbon particles and lowering contact resistance are urgent technical problems to be solved. Traditional wet electrode preparation requires solvents, which easily leave residues leading to interfacial side reactions, and is also costly and environmentally unfriendly. LATP (Lithium aluminum titanium phosphate (Li 1+x Al Ti 2-x (PO4)3) and the negative electrode interface problem: Ti in LATP 4+ It is easily reduced, leading to increased interfacial impedance; existing composite methods (such as wet coating) compromise material stability due to the introduction of solvents. LATP (lithium aluminum titanium phosphate) solid electrolyte is hygroscopic, resulting in decreased ionic conductivity, and has poor interfacial contact with silicon-carbon anodes, leading to significant cyclic expansion problems.

[0004] Challenges of dry process: Traditional dry electrode preparations use high amounts of binders (e.g., PTFE ≥ 5%), affecting energy density. Uneven dispersion of LATP and active materials, and discontinuous conductive networks, result in high electrode impedance during dry preparation. Summary of the Invention

[0005] To address the problems and shortcomings of existing technologies, the present invention aims to provide a method for preparing a solid anode sheet with high stability and low interfacial impedance. This method improves the environmental stability of LATP by pretreating it with nitrogen, and combines it with a dry process to achieve efficient composite of LATP and silicon-carbon anode. At the same time, it achieves a combination of low expansion, high interfacial stability, and environmentally friendly process.

[0006] The technical solution adopted by this invention to solve the technical problem is: a method for preparing a solid anode sheet with high stability and low interfacial impedance, the preparation method mainly includes the following steps: S1. Nitrogen pretreatment of LATP: The LATP powder is annealed at high temperature under nitrogen protection; after annealing, it is transferred to a glove box for storage. S2. Dry mixing process: The silicon-carbon anode Si / C, conductive agent, carbon nanotubes, and pretreated LATP are dry-mixed in a mass ratio of 90~98% : 1~5% : 1~5% : 1~10%, and then mechanically ball-milled under an inert atmosphere, while 1~5wt% PTFE binder is added simultaneously to obtain the mixture. S3, Dry pressing: The mixture in S2 is rolled or hot-pressed multiple times to form an anode film; the anode film is rolled and pressed onto the surface of the current collector to obtain an anode sheet.

[0007] Nitrogen pretreatment, through high-temperature annealing in an inert atmosphere, decomposes adsorbed impurities and desorbs water of crystallization, improving material purity and structural stability. Simultaneously, a nitrogen-doped passivation layer is formed on the LATP surface, inhibiting the formation of Ti. 4+ The process reduces chemical bonding with silicon-carbon, thereby minimizing subsequent interfacial side reactions with the silicon-carbon anode. Furthermore, the pretreated LATP exhibits superior storage performance due to the protective effect of the passivation layer.

[0008] Furthermore, in step S1, the annealing temperature is 400~600℃, the heating rate is 2℃ / min, and the annealing time is 1~30 hours.

[0009] Further, in step S1, the particle size D50 of the LATP powder is 100~500nm.

[0010] Furthermore, in step S2, the ball milling speed is 200~600 rpm, and the ball milling time is 1~4 hours.

[0011] Furthermore, in step S2, the mixing and ball milling specifically includes the following: S21, firstly, the silicon-carbon anode, conductive agent, and carbon nanotubes are ball-milled at a speed of 400-500 rpm for 20-40 min to obtain a first mixture; S22, then pretreated LATP is added to the first mixture and ball-milled at a speed of 400-500 rpm for 50-70 min to obtain a second mixture; S23, PTFE and the second mixture are ball-milled in steps, with the first step at a speed of 250-350 rpm for 50-70 min and the second step at a speed of 500-600 rpm for 50-70 min to perform fibrosis treatment, resulting in a fibrous mixture.

[0012] The core challenge of the dry process lies in achieving a uniform mixture of LATP, silicon-carbon anode, and conductive agent (such as Super P) to construct an efficient conductive network and form a high-density electrode structure. Mechanical ball milling must be carried out under an inert atmosphere to avoid material oxidation; the binder PTFE needs to be fiberized through shear force to enhance the mechanical strength of the electrode while avoiding excessive compression that would lead to excessively low porosity; the interface design must balance the ionic conduction of LATP with the electronic conduction of silicon-carbon, and the electrochemical performance can be optimized by adjusting the LATP blending ratio.

[0013] Furthermore, in step S3, the pressure of the roller pressing or hot pressing is 10~30 MPa, and the temperature is 50~200℃.

[0014] Furthermore, in step S3, the thickness of the anode film is 80~150μm and the porosity is 15~35%.

[0015] The beneficial effects of this invention are as follows: Compared with the prior art, the method for preparing a solid anode sheet with high stability and low interfacial impedance provided by this invention has the following advantages: 1) Interface stability: A nitrogen-doped passivation layer is formed on the LATP surface through high-temperature treatment in a nitrogen atmosphere, which inhibits Ti... 4+ Reduction, while enhancing chemical bonding with silicon and carbon, and reducing interfacial resistance; 2) Structural stability: The modified LATP particles are embedded in the silicon-carbon matrix as an ion-conducting network, which alleviates volume expansion and provides lithium-ion transport channels; it gives the system excellent cycle life and significantly improves capacity retention. 3) Environmental friendliness of the process: Step-by-step ball milling, rolling or hot pressing processes are used to prepare high-density electrode sheets with no solvent and low binder (≤3%), avoiding pollution. Attached Figure Description

[0016] Figure 1A schematic diagram of the structure of a nitrogen-pretreated LATP-doped silicon-carbon solid anode.

[0017] Figure 2 This is a schematic diagram of the structure of LATP after nitrogen pretreatment in this invention. Detailed Implementation

[0018] The present invention will be further illustrated below with specific embodiments. However, these examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] Example 1 This embodiment provides a method for preparing a solid anode sheet with high stability and low interfacial impedance. The preparation method mainly includes the following steps: S1. Nitrogen pretreatment of LATP: 100g of LATP (D50 is 300nm, ionic conductivity is 10 at 25℃) is pretreated with nitrogen. -4 The S / cm) was placed in a rotary furnace and heated to 450℃ at a heating rate of 2℃ / min. It was then heat-treated in a nitrogen atmosphere for 8 hours to obtain LATP with nitrogen-doped surface. S2, Dry mixing process: Silicon-carbon anode Si / C, conductive agent, carbon nanotubes, pretreated LATP, PTEE, sampled at a mass ratio of 98% : 1% : 1% : 2% : 2%; S21. The silicon-carbon anode, Super P, and carbon nanotubes are ball-milled at 500 rpm for 30 minutes to obtain a first mixture; S22. LATP and the first mixture are ball-milled at 500 rpm for 60 minutes to obtain a second mixture; S23. PTEE and the second mixture are ball-milled in steps, with the first step at 300 rpm for 60 minutes and the second step at 600 rpm for 60 minutes, to perform fibrosis treatment, resulting in a fibrous mixture; S3. Dry pressing process: The fibrous mixture is rolled multiple times on a differential roller press at a roller temperature of 80°C to obtain an anode film of the target thickness; 5) The obtained anode film is rolled and covered on the surface of the current collector (copper foil) to obtain an anode sheet.

[0020] Corresponding battery manufacturing: The fabricated anode sheet is used as the working electrode, the lithium metal sheet is used as the counter electrode, a polyethylene diaphragm (PE) is placed between the counter electrode and the working electrode, and electrolyte is injected. The CR2032 button cell casing is used for button cell assembly.

[0021] Example 2 The difference between this embodiment and Embodiment 1 is that the LATP particle size D50 is 100 nm; the other parameters are the same as those in Embodiment 1.

[0022] Example 3 The difference between this embodiment and Embodiment 1 is that the LATP particle size D50 is 500 nm; the other parameters are the same as those in Embodiment 1.

[0023] Example 4 The difference between this embodiment and Embodiment 1 is that, during the annealing process in step S1, the temperature is increased to 400°C at a rate of 2°C / min, while the other parameters remain the same as in Embodiment 1.

[0024] Example 5 The difference between this embodiment and Embodiment 1 is that, during the annealing process in step S1, the temperature is increased to 500°C at a rate of 2°C / min, while the other parameters remain the same as in Embodiment 1.

[0025] Example 6 The difference between this embodiment and Embodiment 1 is that the annealing in step S1 is performed in nitrogen for 4 hours, while the other parameters remain the same as in Embodiment 1.

[0026] Example 7 The difference between this embodiment and Embodiment 1 is that the annealing in step S1 is carried out in nitrogen for 12 hours, while the other parameters remain the same as in Embodiment 1.

[0027] Example 8 The difference between this embodiment and Embodiment 1 is that the mass ratio of pretreated LATP is adjusted to 1%; the remaining parameters remain the same as in Embodiment 1.

[0028] Example 9 The difference between this embodiment and Embodiment 1 is that the mass ratio of pretreated LATP is adjusted to 4%; the remaining parameters are the same as those in Embodiment 1.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that LATP is not added; the other parameters remain the same as in Example 1.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that LATP was not pretreated with nitrogen; the other parameters are the same as those in Example 1.

[0031] The electrochemical performance tests of the materials obtained in the examples and comparative examples are shown in Table 1. Button cell test conditions: constant temperature 25℃, CR2032, initial charge / discharge I=0.1C, using a battery testing system at room temperature from 0.001 to 2.0V (vsLi / Li). + Constant current charge and discharge test between )

[0032]

[0033] The data from Examples 1-3 show that if the LATP particle size is too large, the number of reactive sites in LATP will decrease, which is not conducive to promoting the positive chemical reaction inside the electrode and will reduce the battery capacity retention rate. If the LATP particle size is too small, particle agglomeration is likely to occur during the mixing process, resulting in uneven dispersion of the overall material and a decrease in the final battery capacity retention rate.

[0034] As can be seen from the data results of Examples 1 and 4-7, if the heat preservation time and temperature are insufficient during the LATP pretreatment process, the passivation layer on the LATP surface will not be fully formed, which will lead to a decrease in battery capacity.

[0035] As can be seen from the data results of Examples 1 and 8-9, the amount of pretreatment LATP has a significant impact on the charge and discharge capacity of the battery, and the performance is optimal when the amount of pretreatment LATP is 2%.

[0036] A comparison of the data results of Example 1 and Comparative Example 1 shows that the cycling stability of LATP in Example 1 was improved after adding nitrogen for pretreatment (the capacity retention rate was as high as 85.6% after 50 cycles).

[0037] A comparison of the data results from Example 1 and Comparative Example 2 shows that LATP pretreated with nitrogen can increase its interfacial bonding with silicon and carbon.

[0038] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing a solid anode sheet with high stability and low interfacial impedance, characterized in that, The preparation method mainly includes the following steps: S1. Nitrogen pretreatment of LATP: LATP powder is annealed at high temperature under nitrogen protection; after annealing, it is transferred to a glove box for storage; the annealing temperature is 400~600℃, the heating rate is 2℃ / min; the annealing time is 1~30 hours. S2. Dry mixing process: The silicon-carbon anode Si / C, conductive agent, carbon nanotubes, and pretreated LATP are dry mixed in a mass ratio of 90~98% : 1~5% : 1~5% : 1~10%, and then mechanically ball-milled under an inert atmosphere, while 1~5 wt% PTFE binder is added simultaneously to obtain the mixture. The ball milling speed is 200-600 rpm, and the ball milling time is 1-4 hours. The mixing and ball milling specifically includes the following: S21, firstly, the silicon-carbon anode, conductive agent, and carbon nanotubes are ball milled at a speed of 400-500 rpm for 20-40 minutes to obtain a first mixture; S22, then pretreated LATP is added to the first mixture and ball milled at a speed of 400-500 rpm for 50-70 minutes to obtain a second mixture; S23, PTFE and the second mixture are ball milled in steps, with the first step at a speed of 250-350 rpm for 50-70 minutes and the second step at a speed of 500-600 rpm for 50-70 minutes to perform fibrosis treatment, and a fibrous mixture is obtained after completion. S3, Dry pressing: The mixture in S2 is rolled or hot-pressed multiple times to form an anode film; the anode film is rolled and pressed onto the surface of the current collector to obtain an anode sheet.

2. The method for preparing a high-stability, low-interfacial-resistance solid anode sheet as described in claim 1, characterized in that: In step S1, the particle size D50 of the LATP powder is 100~500nm.

3. The method for preparing a high-stability, low-interfacial-resistance solid anode sheet as described in claim 1, characterized in that: In step S3, the pressure of the roller pressing or hot pressing is 10~30 MPa, and the temperature is 50~200℃.

4. The method for preparing a high-stability, low-interfacial-resistance solid anode sheet as described in claim 1, characterized in that: In step S3, the thickness of the anode film is 80~150μm and the porosity is 15~35%.

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