Composite pole piece, negative pole piece preparation method and solid-state battery

Abstract

This invention belongs to the field of solid-state battery technology, and particularly relates to a composite electrode, a method for preparing a negative electrode, and a solid-state battery. The method for preparing the composite electrode includes: spraying a modified ceramic electrolyte slurry onto the surface of a positive electrode, and then curing it to obtain the composite electrode; the preparation of the modified ceramic electrolyte slurry includes: dissolving a metal salt precursor of the ceramic electrolyte and the salt corresponding to the doped metal in an organic solvent, adding an additive, and stirring to obtain the modified ceramic electrolyte slurry; when the ceramic electrolyte is a garnet-type oxide solid-state electrolyte, the doped metal is selected from one or more of Al, Ga, and Nb; when the ceramic electrolyte is a perovskite-type oxide solid-state electrolyte, the doped metal is Sr and / or Ba. By constructing a dense modified ceramic electrolyte film on the surface of the positive electrode, the fast-charging performance and cycle life are simultaneously improved, and the process is simple and controllable, suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, and particularly relates to a composite electrode, a method for preparing a negative electrode, and a solid-state battery. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in power batteries, energy storage batteries, and other fields due to their advantages such as low cost, high safety, and long cycle life. However, LFP cathode materials have a low lithium-ion diffusion coefficient, and under high-rate fast charging conditions, the cathode / electrolyte interface is prone to electrolyte oxidation and decomposition. The resulting byproducts increase interfacial impedance, and the rapid insertion and extraction of lithium ions can easily lead to structural damage to the cathode material, resulting in problems such as rapid battery capacity decay and poor fast charging performance, which limits its application in high-rate fast charging scenarios.

[0003] To improve the fast-charging performance of lithium iron phosphate batteries, existing technologies mainly focus on modifying cathode materials, optimizing electrolytes, and designing electrode structures. For example, nano-sized lithium iron phosphate particles and doping with conductive elements enhance their electron and ion conductivity; adding film-forming additives optimizes the electrolyte and improves interface stability; and fabricating porous electrode structures shortens the lithium-ion transport path. However, these methods still have limitations: nano-sized particles are prone to aggregation, increasing the difficulty of fabrication; the effect of electrolyte additives is limited, making it difficult to maintain interface stability under high-rate fast charging; and porous electrode structures have lower mechanical strength, affecting the battery's cycle performance.

[0004] Solid-state electrolytes possess high ionic conductivity, a wide electrochemical window, and good interfacial stability, making their application in lithium-ion battery interface modification an effective way to improve fast-charging performance. Currently, existing technologies use solid-state electrolytes to mix with cathode materials to prepare composite electrodes. While this can improve interfacial performance to some extent, the addition of solid-state electrolytes reduces the electrode's energy density, and the mixing uniformity is difficult to control. Therefore, how to construct a stable cathode / electrolyte interface using solid-state electrolytes without reducing electrode energy density has become a key technical challenge for improving the fast-charging performance of lithium iron phosphate batteries. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a composite electrode, a method for preparing a negative electrode, and a solid-state battery. By spraying a modified ceramic electrolyte film layer onto the surface of the positive electrode, a highly efficient ion conduction channel and a stable interface protection barrier are constructed, thereby achieving a simultaneous improvement in battery fast-charging performance and cycle life.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect, this application provides a method for preparing a composite electrode, comprising: A modified ceramic electrolyte slurry is sprayed onto the surface of the positive electrode and cured to obtain a composite electrode. The preparation of the modified ceramic electrolyte slurry includes: dissolving the metal salt precursor of the ceramic electrolyte and the salt corresponding to the doped metal in an organic solvent, adding an additive, and stirring to obtain the modified ceramic electrolyte slurry; The active material of the positive electrode is lithium iron phosphate.

[0007] A dense modified ceramic electrolyte film can be constructed on the surface of the positive electrode by spraying and curing a modified ceramic electrolyte slurry. This film has high ionic conductivity, which can serve as a fast transport channel for lithium ions at the positive electrode / electrolyte interface, reducing interfacial impedance. At the same time, the dense structure can inhibit the oxidative decomposition of the electrolyte, thereby improving the fast charging performance of the battery.

[0008] Optionally, the ceramic electrolyte is a garnet-type oxide solid electrolyte or a perovskite-type oxide solid electrolyte; When the ceramic electrolyte is a garnet-type oxide solid electrolyte, the doped metal is selected from one or more of Al, Ga, and Nb; preferably Al. When the ceramic electrolyte is a perovskite-type oxide solid electrolyte, the doped metal is Sr and / or Ba; preferably Sr.

[0009] By doping and modifying the ceramic electrolyte with the aforementioned specific metals, the ionic conductivity and interfacial stability of the ceramic electrolyte can be further improved, the interfacial protection effect can be enhanced, and the cycle life of the battery can be extended.

[0010] Optionally, the amount of the doped metal added accounts for 0.5 to 5% of the total metal element content in the modified ceramic electrolyte slurry, by mass.

[0011] By controlling the amount of doped metal within this doping ratio range, ion transport efficiency can be optimized without damaging the crystal structure of the ceramic electrolyte, ensuring that the thin film has both high ionic conductivity and good interfacial compatibility.

[0012] Optionally, the curing process employs gradient temperature curing, comprising: First stage: Keep warm at 80~95℃ for 30~50 minutes; Second stage: 120~135℃, keep warm for 40~60 minutes; Third stage: 170~210℃, keep warm for 60~90 minutes.

[0013] By employing gradient temperature curing, solvent removal is achieved at the first temperature stage, film densification is achieved at the second temperature stage, and the formation of an ion-conducting phase is achieved at the third temperature stage. The curing temperature does not exceed 210℃ throughout the entire process, thus avoiding damage to the properties of the aluminum foil, PVDF, and conductive agent.

[0014] Optionally, the organic solvent is ethanol or isopropanol.

[0015] Optionally, the additives include dispersants and crosslinking agents; the amount of dispersant added accounts for 0.15~0.35 wt% of the modified ceramic electrolyte slurry; the amount of crosslinking agent added accounts for 0.4~0.7 wt% of the modified ceramic electrolyte slurry.

[0016] Optionally, the dispersant is polyvinylpyrrolidone, and the crosslinking agent is tetrabutyl titanate.

[0017] By optimizing the ratio of solvents and additives, the dispersion stability of the slurry and the uniformity of the coating film can be significantly improved.

[0018] Optionally, the spraying is performed using electrostatic spray deposition or atomic layer deposition. The conditions for electrostatic spray deposition include: spray voltage 15~25kV, distance between nozzle and electrode 15~25cm, slurry flow rate 0.6~1.5mL / h, and substrate temperature 80~110℃. The conditions for spraying using atomic layer deposition include: precursor pulse time of 0.3~0.7s, purging time of 5~8s, and deposition temperature of 100~160℃.

[0019] By employing electrostatic spray deposition or atomic layer deposition for spraying and controlling the range of process parameters, uniform, dense, and thickness-controllable spraying of ceramic electrolyte films can be achieved. The process parameters are easy to adjust and are suitable for large-scale industrial production.

[0020] Optionally, the preparation of the positive electrode includes: Raw materials including lithium iron phosphate, conductive agent, and binder are mixed and solvent is added to form a positive electrode slurry. This slurry is coated onto an aluminum foil current collector, dried at 100~120℃, and rolled to a surface density of 18~22 mg / cm² to obtain the positive electrode sheet.

[0021] Optionally, the mass ratio of lithium iron phosphate, conductive agent, and binder is (90~95):(3~7):(2~5).

[0022] By preparing positive electrode sheets according to a given ratio of raw materials, the positive electrode sheets can have good mechanical strength and conductive network, forming a stable interface bond with the ceramic electrolyte film sprayed on the surface, thus synergistically improving the fast charging performance and cycle life of the battery.

[0023] Secondly, this application provides a composite electrode sheet prepared by the method described in the first aspect.

[0024] Optionally, the composite electrode includes a positive electrode and a modified ceramic electrolyte film layer formed on the positive electrode, wherein the thickness of the modified ceramic electrolyte film layer is 50~500nm.

[0025] Composite electrodes within this thickness range can effectively leverage the ion transport and interface protection functions of the ceramic electrolyte film without significantly increasing the electrode thickness and mass, thereby improving electrochemical performance while ensuring that the battery's energy density is not reduced; this composite electrode achieves simultaneous improvement in fast charging performance and cycle life.

[0026] Thirdly, this application also provides a solid-state battery containing the composite electrode described in the second aspect.

[0027] The solid-state battery prepared using the composite electrode of the present invention can achieve a synergistic improvement in high-rate fast charging capability and long cycle life, and has excellent comprehensive electrochemical performance.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects: This invention achieves simultaneous improvements in fast-charging performance and cycle life by constructing a dense modified ceramic electrolyte film on the surface of the positive electrode. The process is simple and controllable, making it suitable for large-scale industrial production. Details are as follows: 1. Improved fast charging performance: The ceramic electrolyte film has high ionic conductivity, which can serve as a fast transport channel for lithium ions at the cathode / electrolyte interface and reduce interface impedance. At the same time, the dense structure of the film can suppress the oxidative decomposition of the electrolyte, reduce the generation of interface by-products, and ensure stable charging and discharging of the battery at 10C and above.

[0029] 2. Extended Cycle Life: The ceramic electrolyte film acts as an interfacial protective barrier, effectively preventing direct contact between the electrolyte and the positive electrode active material, avoiding structural damage to the positive electrode material under high-rate fast charging, and simultaneously inhibiting the growth of lithium dendrites, thus improving the battery's cycle stability. Tests show that the battery cell of this invention retains over 90% of its capacity after 1000 cycles under 10C fast charging conditions, far exceeding that of traditional lithium iron phosphate batteries.

[0030] 3. No reduction in energy density: The present invention uses surface spraying to prepare ceramic electrolyte film with a film thickness of only 50~500nm, which does not significantly increase the thickness and mass of the electrode, effectively ensuring the energy density of the battery.

[0031] 4. Simple and controllable process: The electrostatic spray deposition or atomic layer deposition process used in this invention can achieve uniform and dense spraying of ceramic electrolyte films. The process parameters are easy to control and are suitable for large-scale industrial production. Detailed Implementation

[0032] The present invention will now be described in further detail: Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0033] All reagents and materials used in this example can be purchased routinely. The quantitative experiments involved in the examples were all repeated at least three times, and the results were averaged.

[0034] Raw material source: Carbon nanotubes: purchased from Tiannai; Polyvinylidene fluoride: purchased from Finoline; Polyvinylpyrrolidone: Purchased from Yuang Technology.

[0035] Example 1

[0036] 1. Lithium iron phosphate (particle size 1μm, specific surface area 15m² / g), carbon nanotubes and polyvinylidene fluoride are mixed in a mass ratio of 92:3:3, NMP solvent is added to make a slurry, which is coated on aluminum foil, dried at 100℃, rolled to a surface density of 20mg / cm², and then cut to obtain positive electrode sheets. 2. Weigh LiNO3, La(NO3)3 and Zr(NO3)4 according to the stoichiometric ratio of the metal elements in the garnet-type oxide solid electrolyte, and weigh Al(NO3)3 (by molar amount, Al doping accounts for 1.2% of all metal elements (Li+La+Zr+Al)). Dissolve them in ethanol, add 0.3wt% polyvinylpyrrolidone and 0.7wt% tetrabutyl titanate, stir at room temperature for 3h to obtain a modified ceramic electrolyte slurry with a solid content of 10wt%. 3. An electrostatic spray deposition method was used to spray the modified ceramic electrolyte slurry onto the surface of the positive electrode. The process parameters were: spray voltage 20kV, nozzle-to-electrode distance 20cm, solution flow rate 1mL / h, and substrate temperature 90℃. After spraying, curing was performed under the following conditions: first, a single-stage curing at 90℃ for 40min; then a second-stage curing at 125℃ for 50min; and finally, curing at 190℃ for 70min. This resulted in a composite electrode with a modified ceramic electrolyte film layer thickness of 200nm and a room temperature ionic conductivity of 4.5×10⁻⁶. -4 S / cm, interfacial bonding strength is 15N / m.

[0037] 4. The composite electrode, graphite negative electrode, and polypropylene separator are wound together, packed into an aluminum-plastic film shell, and injected with electrolyte (1.1 mol / L LiPF6, EC:DMC:EMC=1:1:1, with 1 wt% fluoroethylene carbonate added). After encapsulation, formation, and capacity testing, a 10Ah soft-pack cell (i.e., solid-state battery) is obtained.

[0038] 5. Performance test: The battery cell was tested for 10C fast charging performance. The results showed that the battery cell took 12 minutes to charge to 3.65V at 10C constant current, and the discharge capacity retention rate was 95%; after 1000 cycles under 10C fast charging conditions, the capacity retention rate was 92%.

[0039] Example 2

[0040] 1. Preparation of positive electrode sheet: Same as in Example 1.

[0041] 2. Weigh LiNO3, La(NO3)3 and TiO2 according to the stoichiometric ratio of the metal elements in the perovskite oxide solid electrolyte, and weigh Sr(NO3)2 (by molar amount, Sr doping accounts for 0.7% of all metal elements (Li+La+Ti+Sr)). Dissolve them in isopropanol, add 0.2wt% polyvinylpyrrolidone and 0.6wt% tetrabutyl titanate, stir at room temperature for 2.5h to obtain a modified ceramic electrolyte slurry with a solid content of 8wt%. 3. Atomic layer deposition (ALD) was used to spray the modified ceramic electrolyte slurry onto the surface of the positive electrode. The process parameters were: precursor pulse time 0.5 s, purge time 8 s, and deposition temperature 130℃. After spraying, curing was performed under the following conditions: first, a single-stage curing process at 85℃ for 45 min; then a second-stage curing process at 130℃ for 40 min; and finally, curing at 200℃ for 80 min. This resulted in a composite electrode with a modified ceramic electrolyte film layer thickness of 160 nm and a room temperature ionic conductivity of 3.3 × 10⁻⁶. -4 The interfacial bonding strength is 12 N / m, with a strength of S / cm.

[0042] 4. Cell assembly (i.e. solid-state battery preparation): Same as in Example 1.

[0043] 5. Performance test: The battery cell takes 13 minutes to charge to 3.65V at 10C constant current, and the discharge capacity retention rate is 93%; after 1000 cycles under 10C fast charging conditions, the capacity retention rate is 90%.

[0044] Comparative Example 1 The difference between this comparative example and Example 1 is that step 2 is omitted; LiNO3, La(NO3)3, Zr(NO3)4, and Al(NO3)3 are directly mixed with the powders from step 1, and then a slurry is prepared. The specific steps are as follows: 1. Lithium iron phosphate (particle size 1μm, specific surface area 15m² / g), carbon nanotubes, and polyvinylidene fluoride were mixed in a mass ratio of 92:3:3, and NMP solvent was added to form a slurry. At the same time, LiNO3, La(NO3)3, Zr(NO3)4, and Al(NO3)3 corresponding to the garnet-type oxide solid electrolyte were directly added to the positive electrode slurry for physical blending (the amount of each raw material was converted according to the molar ratio of metal elements in the modified ceramic electrolyte slurry in Example 1, ensuring that the Al doping amount accounted for 1.2% of the total amount of metal elements (Li+La+Zr+Al), and that the solid content and total molar amount of the effective components of the solid electrolyte were completely equivalent to the total amount of modified ceramic electrolyte material coated on the positive electrode surface in Example 1). The mixed slurry was coated on aluminum foil, dried at 100°C, rolled to a surface density of 20mg / cm², and slit to obtain the positive electrode sheet.

[0045] 2. The above-mentioned positive electrode sheet, graphite negative electrode sheet, and polypropylene separator are wound together, packed into an aluminum-plastic film shell, and injected with the same electrolyte as in Example 1. After encapsulation, formation, and capacity testing, a 10Ah soft-pack battery cell is obtained.

[0046] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that in step 3, after spraying, the electrode is kept at 125°C for 160 minutes to obtain the composite electrode. The remaining steps are the same as in Embodiment 1.

[0047] Comparative Example 3 The difference between this comparative example and Example 1 is that Al(NO3)3 is not added in step 2.

[0048] The specific steps are as follows: 1. First, prepare the positive electrode sheet according to the method in Example 1; 2. Weigh LiNO3, La(NO3)3 and Zr(NO3)4 according to the stoichiometric ratio of the metal elements in the garnet-type oxide solid electrolyte, dissolve them in ethanol, add 0.3wt% polyvinylpyrrolidone and 0.7wt% tetrabutyl titanate, stir at room temperature for 3h to obtain unmodified ceramic electrolyte slurry. 3. Following the same method as step 3 in Example 1, spray the unmodified ceramic electrolyte slurry onto the surface of the positive electrode sheet and cure it to obtain the composite electrode sheet; 4. Prepare pouch cells according to the method in step 4 of Example 1.

[0049] The electrochemical performance of the battery cells prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 is shown in Table 1 below. It can be seen that, compared to Comparative Example 1, this application avoids direct physical mixing of the solid electrolyte and the positive electrode active material. Instead, it constructs a dense and continuous ion-conducting thin film through surface spraying, significantly shortening the lithium-ion transport path and reducing interfacial impedance without reducing electrode energy density. In Comparative Example 2, conventional single-temperature curing was used. Rapid initial heating easily led to rapid boiling and evaporation of the solvent inside the slurry, causing micropores, pinholes, and microcracks in the film layer, resulting in poor film density. Simultaneously, low temperatures failed to fully remove the solvent, and high temperatures failed to stably form a complete ion-conducting crystal phase, ultimately leading to discontinuous ion transport channels in the electrolyte film layer, weak interfacial bonding, easy penetration and corrosion of the positive electrode interface by the electrolyte, a significant increase in interfacial impedance, and a significant decrease in fast-charging capability and cycle stability. In contrast, this invention uses gradient temperature curing, achieving low-temperature solvent removal, medium-temperature dense film formation, and high-temperature crystallization and conduction in stages. The resulting film layer is uniform, dense, and defect-free, balancing film integrity and ion conductivity. Compared with Comparative Example 3, this application further improves the ionic conductivity and interfacial compatibility of the solid electrolyte by modifying the ceramic electrolyte with metal doping, making the film layer denser and the interfacial bonding stronger, thus achieving simultaneous improvement in fast charging performance and long cycle life.

[0050] Table 1 Electrochemical performance results of the battery cells

Claims

1. A method for preparing a composite electrode, characterized in that, include: A modified ceramic electrolyte slurry is sprayed onto the surface of the positive electrode and cured to obtain a composite electrode. The preparation of the modified ceramic electrolyte slurry includes: dissolving the metal salt precursor of the ceramic electrolyte and the salt corresponding to the doped metal in an organic solvent, adding an additive, and stirring to obtain the modified ceramic electrolyte slurry; The active material of the positive electrode is lithium iron phosphate.

2. The method for preparing the composite electrode according to claim 1, characterized in that, The ceramic electrolyte is a garnet-type oxide solid electrolyte or a perovskite-type oxide solid electrolyte. When the ceramic electrolyte is a garnet-type oxide solid electrolyte, the doped metal is selected from one or more of Al, Ga, and Nb; When the ceramic electrolyte is a perovskite-type oxide solid electrolyte, the doped metal is Sr and / or Ba.

3. The method for preparing the composite electrode according to claim 1, characterized in that, In terms of the amount of substance, the amount of the doped metal added accounts for 0.5 to 5% of the total amount of metal elements in the modified ceramic electrolyte slurry.

4. The method for preparing the composite electrode according to claim 1, characterized in that, The curing process employs a gradient temperature increase curing method, including: First stage: Keep warm at 80~95℃ for 30~50 minutes; Second stage: 120~135℃, keep warm for 40~60 minutes; Third stage: 170~210℃, keep warm for 60~90 minutes.

5. The method for preparing the composite electrode according to claim 1, characterized in that, The organic solvent is ethanol or isopropanol.

6. The method for preparing the composite electrode according to claim 1, characterized in that, The additives include dispersants and crosslinking agents; the amount of dispersant added accounts for 0.15~0.35 wt% of the modified ceramic electrolyte slurry; the amount of crosslinking agent added accounts for 0.4~0.7 wt% of the modified ceramic electrolyte slurry.

7. The method for preparing the composite electrode according to claim 6, characterized in that, The dispersant is polyvinylpyrrolidone, and the crosslinking agent is tetrabutyl titanate.

8. The method for preparing the composite electrode according to claim 1, characterized in that, The spraying method is electrostatic spray deposition or atomic layer deposition. The conditions for electrostatic spray deposition include: spray voltage 15~25kV, distance between nozzle and electrode 15~25cm, slurry flow rate 0.6~1.5mL / h, and substrate temperature 80~110℃. The conditions for spraying using atomic layer deposition include: precursor pulse time of 0.3~0.7s, purging time of 5~8s, and deposition temperature of 100~160℃.

9. The method for preparing the composite electrode according to claim 1, characterized in that, The preparation of the positive electrode includes: Raw materials including lithium iron phosphate, conductive agent, and binder are mixed and solvent is added to form a positive electrode slurry. This slurry is coated onto an aluminum foil current collector, dried at 100~120℃, and rolled to a surface density of 18~22 mg / cm² to obtain the positive electrode sheet.

10. A composite electrode, characterized in that, It is prepared by the method described in any one of claims 1-9.

11. The composite electrode according to claim 10, characterized in that, The composite electrode includes a positive electrode and a modified ceramic electrolyte film layer formed on the positive electrode, wherein the thickness of the modified ceramic electrolyte film layer is 50~500nm.

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