Composite coated layered oxide positive electrode material for solid-state battery and preparation method of composite coated layered oxide positive electrode material

Abstract

The invention discloses a composite coated layered oxide positive electrode material for a solid-state battery and a preparation method, and the preparation method comprises the following steps: taking layered oxide and a dopamine monomer as raw materials to prepare an intermediate of which the surfaces of layered oxide particles are coated with polydopamine; taking the intermediate, a pyrrole monomer and an oxidizing agent as raw materials to prepare an emulsion composite precursor of which the surfaces of layered oxide particles are coated with a polydopamine / polypyrrole composite coating layer; and preparing the composite precursor into microsphere powder, and performing carbonization treatment to obtain the composite coated layered oxide positive electrode material. According to the gradient composite coating layer prepared through the in-situ sequential polymerization process, organic unification of interface anchoring and a conductive network is achieved, the interface contact resistance is reduced by 60% or above, phase interface mutation between PDA and PPy is eliminated, the volume stress in the charging and discharging process is effectively buffered, and falling and internal cracking of the coating layer are prevented. The comprehensive performance is good when the material is applied to solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and specifically to a composite coated layered oxide cathode material for solid-state batteries and its preparation method. Background Technology

[0002] Solid-state batteries are a new type of battery technology that uses solid electrodes and solid electrolytes. They have higher energy density, better safety and longer cycle life potential, while layered oxide cathodes can provide high capacity and high voltage, playing an important role in the field of solid-state batteries.

[0003] To address the interfacial side reactions in layered oxide cathodes of solid-state batteries and improve cycle stability and rate performance, surface coating of layered oxide materials is an efficient and scalable approach. However, in practical applications of layered oxide cathode coating in solid-state batteries, existing coating strategies still face significant challenges, making it difficult to coat layered oxides in solid-state batteries. The specific reasons are as follows: 1. Interface stability issues (1) Mismatch between thermodynamic and electrochemical stability: There is often a mismatch between the thermodynamic and electrochemical stability windows of layered oxide cathodes and solid electrolytes. For example, sulfide solid electrolytes are prone to decomposition under high voltage, while nickel-rich oxide cathodes (such as NMC811) will undergo interfacial side reactions with the electrolyte under high voltage, forming insulating decomposition products, which leads to increased interfacial resistance and affects battery performance.

[0004] (2) Formation of space charge layer (SCL): Due to the mismatch of electrochemical potential, a space charge layer will be formed between the positive electrode and the electrolyte, which will cause Li+ to redistribute near the interface, forming a high resistance layer and hindering the transport of lithium ions.

[0005] 2. Technical difficulties in preparing the coating layer (1) Coating uniformity: It is a technical challenge to uniformly and densely coat the surface of layered oxide particles with a protective material. The uniformity of the coating directly affects its effect. If the coating is not uniform, it may not be able to effectively suppress interfacial side reactions, or even introduce new performance problems.

[0006] (2) Control of coating thickness and morphology: The thickness and morphology of the coating have a significant impact on battery performance. An excessively thick coating will increase the battery's internal resistance and reduce energy density; while an excessively thin coating may not be able to effectively protect the cathode material. In addition, the morphology of the coating (such as porous, dense, etc.) will also affect lithium-ion transport and battery safety.

[0007] Currently, some researchers have attempted to use polydopamine to coat layered oxides as cathode materials for solid-state batteries to improve the interfacial compatibility between the layered oxide cathode and the solid electrolyte. For example, patent document CN 117438568 A discloses a layered oxide material and its preparation method, in which a coating layer is provided between the oxide matrix and the nitrogen-containing organic framework, the protective layer contains polydopamine, and metal particles are also doped on the surface of the coating layer. However, the coating process in this patent relies on simple oscillatory mixing, resulting in an excessively wide control range for the thickness of the dopamine coating layer (0.01-1 μm), making it difficult to ensure the formation of a uniform and dense coating layer on the matrix surface. This non-uniformity easily causes differences in interfacial properties between material particles, becoming a weak point in the cycling process. At the same time, although a polydopamine carbon layer and metal particle doping are introduced, the conductivity of polydopamine itself is generally poor, and the degree of graphitization of the formed carbon layer is unclear; the optimization of metal doping is insufficient, and an efficient and continuous three-dimensional conductive network has not been constructed. Finally, the volume resistivity of the material is still relatively high (10). 3 -10 5 The impedance (on the order of kΩ·cm) indicates that the ion and electron migration resistance has not been fundamentally resolved, limiting the full utilization of specific capacity and rapid charge / discharge capability. Therefore, the coating uniformity and conductivity in this patent are still insufficient.

[0008] In the field of polymer composites, research on surface functionalization and bonding improvement of biomaterials and nanomaterials has explored the combined use of polydopamine (PDA) and polypyrrole (PPy). Typically, dopamine and pyrrole monomers are simply mixed and copolymerized to form a composite coating on the oxide surface. This type of coating exhibits good surface hydrophilicity and a certain degree of conductivity in its original research area. However, when this composite coating based on simple mixing polymerization is directly applied to solid-state battery cathode materials with extremely high requirements for interfacial stability, electron-ion conduction efficiency, and long-term cycle reliability, its inherent defects in the preparation method become apparent: due to the competitive polymerization of dopamine and pyrrole monomers, polymer chains grow disorderedly on the surface of the active material. This not only weakens the strong chemical bonds that should form between polydopamine and the layered oxide matrix, resulting in weak interfacial bonding of the coating layer, but also causes a chaotic and discontinuous distribution of the polypyrrole conductive network, making it difficult to form efficient and orderly electron conduction pathways. Simultaneously, this disordered composite structure exhibits significant modulus abrupt changes, which can easily lead to interfacial instability under the volumetric stress of battery cycling. Therefore, the PDA / PPy coating obtained by directly applying the existing simple hybrid polymerization method cannot meet the stringent requirements of solid-state batteries for the interface stability, uniform electronic conduction, and long-term mechanical integrity of the cathode material.

[0009] Therefore, this patent application is filed. Summary of the Invention

[0010] To address the aforementioned technical issues, this invention provides a method for preparing a composite-coated layered oxide cathode material for solid-state batteries. The gradient composite coating layer prepared through an in-situ sequential polymerization process exhibits a significant synergistic effect. It not only achieves the organic unity of interface anchoring and conductive network, reducing interface contact resistance by more than 60%, but also eliminates the phase interface abrupt change between PDA and PPy through a gradient structure with molecular-level penetration. This effectively buffers volumetric stress during charging and discharging and prevents the coating layer from detaching. Applying the composite coating strategy of PDA and PPy to the field of solid-state batteries broadens its application scenarios.

[0011] The first objective of this invention is to provide a method for preparing a composite-coated layered oxide cathode material for solid-state batteries, comprising the following steps: (1) Using layered oxides and dopamine monomers as raw materials, an intermediate with polydopamine coated on the surface of layered oxide particles was prepared; (2) Using the intermediate, pyrrole monomer and oxidant as raw materials, an emulsion-like composite precursor with a polydopamine / polypyrrole composite coating layer on the surface of layered oxide particles is prepared; (3) The composite precursor is made into microsphere powder, and then the microsphere powder is carbonized to obtain a composite coated layered oxide cathode material.

[0012] The cathode material obtained by this invention is a functional composite material with a core-shell gradient structure. Its core is a layered oxide cathode particle, and its shell is a nitrogen-doped carbon-based coating layer with a continuous transition of composition from the inside to the outside, constructed by in-situ sequential polymerization.

[0013] In the preparation process, layered oxides and dopamine monomers are first used as raw materials. The dopamine monomers undergo an oxidative self-polymerization reaction to form a polydopamine (PDA) coating layer with strong affinity on the particle surface. In this stage, the abundant catechol and amine functional groups in the PDA molecule are utilized to tightly bind with the metal atoms and hydroxyl groups on the surface of the layered oxide through hydrogen bonds, coordination bonds, or covalent bonds, constructing a molecularly anchored base coating that provides active sites for the subsequent growth of the conductive layer.

[0014] Then, using intermediates, pyrrole monomers, and oxidants as raw materials, the porosity and wettability of the polydopamine layer are utilized to induce pyrrole monomers to penetrate into the surface and internal micropores of the PDA layer. With the slow initiation of hydrogen peroxide, pyrrole undergoes secondary polymerization in situ within the PDA framework, causing physical entanglement and chemical cross-linking between the polypyrrole (PPy) molecular chains and the polydopamine chains, thereby forming an "interpenetrating network" precursor without a clear phase interface. Finally, through carbonization and denitrification processes, a nitrogen-doped composite carbon layer with moderate crystallinity and electrochemical activity is formed.

[0015] Traditional composite coatings often consist of a simple stack of two or more components at the microscopic level, resulting in significant abrupt changes in physical properties (such as elastic modulus and coefficient of thermal expansion) at the interface. During long-term cycling of all-solid-state batteries, the layered oxide particles undergo volume expansion and contraction. This interfacial stress concentration easily leads to the coating peeling off from the substrate surface or internal cracking, thereby losing its inhibitory effect on side reactions and significantly increasing interfacial impedance. Furthermore, the oxidants used in the polymerization process in existing technologies can leave residual metal impurity ions in the coating, negatively interfering with the electrochemical stability of the solid electrolyte. Therefore, how to construct a gradient composite coating that can achieve both molecular-level firm anchoring and continuous component transition and efficient charge transport through process innovation has become an urgent need to solve the key interfacial challenges of solid-state batteries.

[0016] This invention innovatively designs this in-situ sequential polymerization process, and the resulting gradient composite coating layer produces a significant synergistic effect. It not only achieves the organic unity of interface anchoring and conductive network, reducing the interface contact resistance by more than 60%, but also eliminates the phase interface abrupt change between PDA and PPy through the gradient structure of molecular-level penetration. This effectively buffers the volume stress during the charging and discharging process and prevents the coating layer from falling off or cracking internally, reduces interface impedance, and enhances the inhibition of side reactions.

[0017] The gradient coating structure obtained by this invention improves the capacity retention of all-solid-state batteries to over 90% after 200 cycles at 1C rate, effectively suppresses interfacial side reactions at a high voltage of 4.3V, and ensures the high purity and electrochemical stability of the solid-state battery system. It also well balances conductivity, interfacial stability and coating uniformity, demonstrating the substantial progress of this invention in solving key interface problems of solid-state batteries.

[0018] The layered oxides mentioned in this invention refer to lithium transition metal oxides with an α-NaFeO2 type layered structure that can be used as positive electrode active materials for lithium-ion batteries. Their general formula can be represented as LiTMO2, where TM is one or more transition metal elements (such as Ni, Co, Mn, Al, etc.) that can be obtained commercially.

[0019] As a preferred technical solution, in step (1), the layered oxide powder is first dispersed in a Tris-HCl solution, then dopamine monomer is added to it, and an oxidative self-polymerization reaction is carried out at 60~85℃ to form a polydopamine coating layer on the surface of the layered oxide particles.

[0020] As a preferred technical solution, the pH value of the Tris-HCl solution is 8.0~9.0; After adding layered oxide powder to Tris-HCl solution, a suspension is obtained by stirring or sonication.

[0021] As a preferred technical solution, the mass ratio of dopamine monomer to pyrrole monomer is 1:(0.05~1).

[0022] As a preferred technical solution, in step (1), the mass ratio of the layered oxide to the dopamine monomer is 1:(0.01~0.1).

[0023] As a preferred technical solution, the oxidant is a hydrogen peroxide solution; And / or, the concentration of the hydrogen peroxide aqueous solution is 20-30%.

[0024] Existing technologies often use oxidants containing metal salts (such as ammonium persulfate). The residual metal impurity ions in the coating layer can negatively interfere with the electrochemical stability of the solid electrolyte. This invention uses hydrogen peroxide to initiate polymerization, avoiding the impurity residues caused by traditional metal salt oxidants, and ensuring the high purity and electrochemical stability of the solid-state battery system.

[0025] As a preferred technical solution, in step (2), the reaction temperature of the intermediate, pyrrole monomer and oxidant is 60~85℃.

[0026] As a preferred technical solution, in step (3), the emulsion-like composite precursor is prepared into microsphere powder by spray drying; The carbonization process is carried out in an inert atmosphere and is a segmented carbonization process.

[0027] As a preferred technical solution, the carbonization process is as follows: Phase 1: Keep warm at 300-450℃ for 1-3 hours; Second stage: Keep warm at 600-850℃ for 0.5-2 hours.

[0028] In this invention, the first stage of carbonization promotes preliminary thermal dehydration and structural rearrangement of the two polymer components, ensuring that the gradient interface is consolidated before high-temperature carbonization. The second stage of carbonization completes the final carbonization and denitrification process, forming a nitrogen-doped composite carbon layer with a thickness of approximately 25 nm, moderate crystallinity, and electrochemical activity. This segmented carbonization process ensures that the final product retains strong adhesion while possessing excellent electronic conductivity.

[0029] A second objective of the present invention is to provide a composite coated layered oxide cathode material for solid-state batteries, which is prepared by the preparation method described in any of the preceding claims.

[0030] Compared with the prior art, the present invention has the following advantages: 1. The gradient composite coating layer prepared by the in-situ sequential polymerization process of this invention produces a significant synergistic effect. It not only achieves the organic unity of interface anchoring and conductive network, reducing the interface contact resistance by more than 60%, but also eliminates the phase interface abrupt change between PDA and PPy through the gradient structure of molecular-level penetration. This effectively buffers the volume stress during the charging and discharging process and prevents the coating layer from falling off or cracking internally, reduces the interface impedance, and enhances the inhibition of side reactions.

[0031] 2. Experimental data show that the gradient coating structure obtained in this invention improves the capacity retention of the all-solid-state battery to over 90% after 200 cycles at 1C rate, and effectively suppresses interfacial side reactions at a high voltage of 4.3V. The improvement in cycle stability far exceeds that of single-component coating or disordered mixed coating schemes, effectively balancing conductivity, interfacial stability, and coating uniformity. Furthermore, the process of this invention does not use traditional metal salt oxidants, avoiding residual impurities and ensuring the high purity and electrochemical stability of the solid-state battery system. This demonstrates a substantial advancement in solving key interfacial challenges in solid-state batteries.

[0032] 3. The preparation method employed in this invention possesses both excellent process controllability and repeatability. In-situ sequential polymerization ensures the uniformity and continuity of the coating layer on the particle surface; by adjusting the monomer feed ratio and optimizing the carbonization regime, effective control over the coating layer thickness and microstructure is achieved. This overcomes the technical bottlenecks commonly found in traditional coating technologies, such as uneven coating and uncontrolled thickness, providing a reliable technical solution for the controllable preparation of high-performance solid-state battery cathode materials. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 The images show SEM images of the cathode material obtained in Example 1 at two different magnifications.

[0034] Figure 2 This is a comparison of the cyclic stability and capacity retention of sample AG.

[0035] Figure 3 This is the Raman spectrum of sample B in Example 1.

[0036] Figure 4The image shows the Raman spectrum of sample D in Comparative Example 2.

[0037] Figure 5 This is a scanning electron microscope image of sample D in Comparative Example 4. Detailed Implementation

[0038] The embodiments of this application will be described in further detail below with reference to the examples. The detailed description of the following embodiments is used to illustrate the principles of this application, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. The process is performed sequentially. For example, the method includes steps (a) and (b), indicating that the method may include step (a) performed sequentially. (b) may also include steps (b) and (a) performed sequentially. For example, the method may also include step (c). This indicates that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c). It may also include steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included. Example

[0044] A composite-coated layered oxide cathode material for solid-state batteries, the preparation process of which is as follows: (1) Weigh 20.0 g of NCM811 powder and disperse it in 400 mL of Tris-HCl buffer solution with pH 8.5. Sonicate the solution to form a homogeneous suspension. The NCM811 powder was commercially available LiNi powder purchased from Hefei Kejing Materials Technology Co., Ltd. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) cathode material powder.

[0045] (2) Add 1.0 g of dopamine hydrochloride, stir at 70°C for 8 hours, centrifuge, wash and dry to obtain an intermediate with polydopamine coated on the surface of layered oxide particles.

[0046] (3) Next, the above intermediate was redispersed in 300 ml of deionized water, 0.1 g of pyrrole monomer was added, and after stirring evenly in an ice-water bath, 0.12 g of hydrogen peroxide (concentration of 20%) was added dropwise, and the reaction was carried out at 65°C for 18 hours to obtain the composite precursor (PDA / PPy@NCM811 (DA:Py=1:0.1)).

[0047] (4) The composite precursor was made into a slurry and spray-dried to obtain dried microsphere powder; The specific process is as follows: The emulsion-like composite precursor obtained in step (3) is mixed in deionized water, and the solid content is controlled to be 5%~20%. It is then processed into a uniform slurry by high-speed shearing or ball milling. Subsequently, it is dried using a spray dryer: the inlet air temperature is set to 150℃~220℃ (preferably 180℃~200℃), the outlet air temperature is set to 80℃~120℃ (preferably 90℃~110℃), and the feed rate is adjusted according to the slurry viscosity to obtain dry microsphere powder with good flowability.

[0048] (5) The microsphere powder collected in step (4) is subjected to segmental carbonization in an argon atmosphere: first, the temperature is increased to 380°C at a rate of 2°C / min and held for 2 hours, then the temperature is increased to 700°C at a rate of 5°C / min and held for 1 hour, finally obtaining the gradient coating material G-NCM811 (where G represents the gradient coating material). This is used as sample B. Example

[0049] The difference between this embodiment and Example 1 is that the amount of pyrrole monomer added is adjusted to 0.5 grams, thus changing the mass ratio of dopamine monomer to pyrrole monomer to 1:0.5. Subsequent dispersion, oxidative polymerization, spray drying, and segmented carbonization processes are performed according to the exact same steps as in Example 1, ultimately yielding a composite-coated layered oxide cathode material, which is designated as Sample E. Example

[0050] The difference between this embodiment and Embodiment 1 is that the layered oxide matrix is ​​replaced with an equal mass of commercially available LiNi purchased from Shenzhen BTR. 0.8 Co 0.15 Al 0.05 O2 (NCA) powder. Following the exact same steps as in Example 1, polydopamine coating, polypyrrole composite coating, spray drying, and segmented carbonization were performed to finally prepare a composite coated cathode material with NCA as the matrix, which was used as sample F. Example

[0051] The difference between this embodiment and Embodiment 1 lies in the fine-tuning of the segmented carbonization process. Specifically, after obtaining the spray-dried microsphere powder, the temperature was first increased to 420°C at 2°C / min and held for 1.5 hours in an argon atmosphere; then, the temperature was increased to 750°C at 5°C / min and held for 1 hour, followed by natural cooling. The resulting composite-coated layered oxide cathode material was thus prepared as sample G. Example

[0052] The difference between this embodiment and Example 1 is that only the mass ratio of dopamine monomer (i.e., dopamine hydrochloride) to pyrrole monomer is changed to 1:1, which is used as sample C. Everything else is the same as in Example 1.

[0053] Comparative Example 1: The difference between this comparative example and Example 1 is that only the mass ratio of dopamine monomer (i.e., dopamine hydrochloride) to pyrrole monomer was changed to 1:0.02, which is used as sample A. Everything else is the same as in Example 1.

[0054] Comparative Example 2: In this comparative example, the composite precursor PPy / PDA@NCM811 (DA:Py=1:0.1) was used as the raw material. The difference from Example 1 is that a one-step carbonization process was adopted.

[0055] One-step carbonization: directly heat to 700℃ and hold for 2 hours. Everything else is the same as in Example 1. This is sample D.

[0056] Comparative Example 3: A composite-coated layered oxide cathode material for solid-state batteries, the preparation process of which is as follows: (1) First, 20.0 g of NCM811 powder was dispersed in 400 mL of Tris-HCl buffer solution with pH 8.5 and ultrasonically treated to form a uniform suspension.

[0057] (2) Add 0.1 g of pyrrole monomer and add 0.12 g of hydrogen peroxide (concentration of 20%) as an oxidant, and react at 65°C for 18 hours to obtain the intermediate of PPy coated layered oxide.

[0058] (3) The intermediate was then transferred to Tris-HCl buffer at pH 8.5, 1.0 g of dopamine hydrochloride was added, and the mixture was reacted at 70 °C for 8 hours to obtain the composite precursor.

[0059] (4) Segmented carbonization was performed under the same conditions as in Example 1. This was used as sample H.

[0060] Comparative Example 4: A composite-coated layered oxide cathode material for solid-state batteries, the preparation process of which is as follows: (1) Weigh 20.0 g of NCM811 powder and disperse it in Tris-HCl buffer solution with pH 8.5. At the same time, add 1.0 g of dopamine hydrochloride and 0.1 g of pyrrole monomer, and add hydrogen peroxide oxidant dropwise. Stir the reaction at room temperature for 24 hours to allow the two competing polymers to grow. A composite precursor is obtained.

[0061] (2) The composite precursor obtained above was made into a slurry and spray-dried, and then segmented carbonized in an argon atmosphere: first, the temperature was increased to 380°C at a rate of 2°C / min and held for 2 hours, and then the temperature was increased to 700°C at a rate of 5°C / min and held for 1 hour to obtain the cathode material. This was taken as sample I.

[0062] Meanwhile, uncoated NCM811 powder was used as a reference.

[0063] Test results: 1. The inventors performed SEM characterization on sample B, see... Figure 1 As shown, a complete, uniform, and gradient coating layer is formed on the surface of the material particles.

[0064] 2. The inventors assembled all-solid-state batteries using the cathode materials obtained in the various embodiments and comparative examples. Performance tests were conducted on the obtained all-solid-state batteries, and the results are shown in Table 1.

[0065] The testing procedure was as follows: Electrochemical tests were performed at 25°C. Charge-discharge tests were conducted within a voltage window of 2.8 V – 4.3 V (relative to Li+ / Li) to evaluate its performance at high voltages. Electrochemical impedance spectroscopy was performed at open-circuit potential after different cycles to analyze the evolution of interfacial impedance.

[0066] Figure 2 The diagram also shows a comparison of the cyclic stability and capacity retention of the AG samples.

[0067] Table 1 As shown in Table 1, the uncoated NCM811 exhibits the worst performance across all categories, with a capacitance retention of only 72.4% after 200 cycles and an interface impedance as high as 428 Ω·cm. 2 This demonstrates that the interface problem of uncoated matrix materials is serious.

[0068] When sample B obtained in Example 1 was used as a positive electrode material in a battery assembly, the initial discharge specific capacity reached 188.5 mAh / g, and after 200 cycles, the interfacial impedance decreased significantly from 428 Ω·cm² for the uncoated sample to 162 Ω·cm². 2 Furthermore, after 200 cycles at 1C, the capacity retention rate is 91.2%, indicating good performance.

[0069] Comparing samples B and C, it can be seen that the electronic conductivity of the material powder increases sequentially with the increase of the proportion of pyrrole monomer, with sample B having the highest conductivity, reaching 1.8 × 10⁻⁶. -2 S / cm. In terms of electrochemical performance, sample B exhibited the best rate capability, with a 5C discharge capacity of 178.2 mAh / g; while sample C showed a certain degree of performance degradation due to its excessively thick coating layer. Samples E, F, and G also showed good performance. Sample A in Comparative Example 1 exhibited severe polarization at high rates due to an imperfect conductive network. These examples and comparative examples demonstrate that a dopamine to pyrrole monomer mass ratio within the range of 1:0.05 to 1:1 achieves the best synergy between interfacial adhesion and electronic conductivity.

[0070] In Comparative Example 2, a one-step carbonization process was used. Raman spectroscopy tests were performed on the materials of sample B in Example 1 and sample D in Comparative Example 2, respectively. Figure 3 , 4As shown in the diagram, the analysis reveals that the ID / IG ratio of sample B (1.05) is lower than that of sample D (1.32), indicating that segmented carbonization contributes to the formation of a more ordered graphitized structure with fewer carbon layer defects. In full-cell testing, sample B exhibits a significantly higher capacity retention (91.2%) after 200 cycles at 1C compared to sample D (85.1%), and also demonstrates lower interfacial impedance. These results confirm the crucial role of segmented carbonization in forming a stable, highly conductive composite coating.

[0071] In Comparative Example 3, PPy was coated first, followed by PDA. Because the PPy surface lacks chemical bonding sites of the same strength as the oxide matrix, and the subsequently coated PDA struggles to penetrate the PPy layer and act on the matrix, the overall adhesion of the coating layer is poor. Electrochemical tests (Table 1) show that after 200 cycles at 1C, the capacity retention is only 81.6%, and the interfacial impedance after 200 cycles is as high as 310 Ω⋅cm. 2 , This demonstrates the necessity of wrapping PDA first and then PPy for constructing a stable interface.

[0072] In Comparative Example 4, dopamine monomer and pyrrole monomer were added simultaneously during the coating process. Figure 5 Scanning electron microscopy revealed that the components of the coating layer generated by the mixed polymerization were randomly distributed, resulting in a chaotic functional distribution within the coating layer. Polydopamine could not be precisely positioned in the innermost layer of the cathode particles to exert its "interface anchoring" effect, weakening the chemical bond between the coating layer and the active material, and failing to form an ordered functional gradient of "inner layer adhesion, outer layer conductivity." In battery testing (Table 1), its rate performance was significantly weaker than Example 1 (5C capacity was only 158.5 mAh / g), and its initial efficiency dropped to 88.2%. This indicates that only through sequential polymerization can effective anchoring of the PDA interface and continuous coverage of the PPy conductive network be achieved. In single mixed polymerization, polypyrrole cannot form a continuous and ordered electronic conduction network in the outermost layer, making it difficult to produce the synergistic effect of this invention.

[0073] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite-coated layered oxide cathode material for solid-state batteries, characterized in that, Includes the following steps: (1) Using layered oxides and dopamine monomers as raw materials, an intermediate with polydopamine coated on the surface of layered oxide particles was prepared; (2) Using the intermediate, pyrrole monomer and oxidant as raw materials, an emulsion-like composite precursor with a polydopamine / polypyrrole composite coating layer on the surface of layered oxide particles is prepared; (3) The composite precursor is made into microsphere powder, and then the microsphere powder is carbonized to obtain a composite coated layered oxide cathode material.

2. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 1, characterized in that, In step (1), the layered oxide powder is first dispersed in a Tris-HCl solution, then dopamine monomer is added to it, and an oxidative self-polymerization reaction is carried out at 60~85℃ to form a polydopamine coating layer on the surface of the layered oxide particles.

3. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 2, characterized in that, The pH value of the Tris-HCl solution is 8.0~9.0; After adding layered oxide powder to Tris-HCl solution, a suspension is obtained by stirring or sonication.

4. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 1, characterized in that, The mass ratio of dopamine monomer to pyrrole monomer is 1:(0.05~1).

5. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 1, characterized in that, In step (1), the mass ratio of the layered oxide to the dopamine monomer is 1:(0.01~0.1).

6. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 1, characterized in that, The oxidant is selected as a hydrogen peroxide aqueous solution; And / or, the concentration of the hydrogen peroxide aqueous solution is 20-30%.

7. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 1, characterized in that, In step (2), the reaction temperature of the intermediate, pyrrole monomer and oxidant is 60~85℃.

8. The method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to claim 1, characterized in that, In step (3), the emulsion-like composite precursor is prepared into microsphere powder by spray drying. The carbonization process is carried out in an inert atmosphere and is a segmented carbonization process.

9. A method for preparing a composite-coated layered oxide cathode material for solid-state batteries according to any one of claims 1 to 8, characterized in that, The carbonization process is as follows: Phase 1: Keep warm at 300-450℃ for 1-3 hours; Second stage: Keep warm at 600-850℃ for 0.5-2 hours.

10. A composite-coated layered oxide cathode material for solid-state batteries, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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