A sodium-ion battery layered oxide cathode material and a preparation method thereof
By constructing a three-dimensional interpenetrating buffer-conductive network in the layered oxide cathode material of sodium-ion batteries, the structural and interface failure problems of O3-type layered oxide cathode materials during charge and discharge processes were solved. This achieved mechanical and charge self-adaptation, improved the cycle stability, rate performance, and low-temperature performance of the battery, and provided technical support for the industrial application of sodium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QINGDAO QIANYUN HIGH TECH NEW MATERIAL
- Filing Date
- 2026-03-11
- Publication Date
- 2026-06-12
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Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery technology, specifically to a layered oxide cathode material for sodium-ion batteries and its preparation method. Background Technology
[0002] Sodium-ion batteries have become a promising electrochemical energy storage system for large-scale energy storage and low-speed transportation due to the natural advantages of abundant, widely distributed, and inexpensive sodium resources. Layered oxide cathode materials are one of the core research directions for sodium-ion battery cathode materials due to their high specific capacity, simple preparation process, and excellent electrochemical performance. Among them, O3-type layered oxides have become a key candidate material for commercial applications due to their regular layered structure and efficient sodium ion insertion / extraction kinetics.
[0003] However, O3-type layered oxide cathode materials face the dual problems of structural and interface failure during actual charge-discharge cycles, severely restricting their cycle life, rate performance, and low-temperature adaptability, becoming a core technological bottleneck for their industrial application. During deep charge-discharge, O3-type layered oxides undergo irreversible phase transformations such as O3-P3, accompanied by abrupt changes in lattice parameters and significant anisotropic volume changes, with expansion / contraction rates exceeding 5%. This non-uniform volume deformation generates a large amount of accumulated stress within the secondary particles, gradually initiating and propagating microcracks in the particles, ultimately leading to particle cracking and pulverization, causing structural collapse of the material itself. The large amount of fresh surface area generated by particle cracking will undergo violent side reactions with the electrolyte, generating an unstable solid electrolyte interphase (SEI) film, while simultaneously disrupting the electrical contact between the active material and the conductive agent and binder, causing a sharp increase in the charge transfer impedance of the battery, resulting in irreversible capacity decay, and even causing complete battery performance failure.
[0004] To address the aforementioned issues, various modification strategies have been developed in the prior art, mainly including three categories: bulk doping, rigid surface coating, and the introduction of flexible polymers. However, all of these have significant limitations and cannot fundamentally solve the problem of cyclic degradation of layered oxides. Bulk doping, by introducing heterogeneous metal ions to regulate the crystal structure, can stabilize the crystal lattice and suppress some irreversible phase transitions to a certain extent. However, it can only alleviate lattice distortion and cannot adapt to the macroscopic volume change stress of the material. It is still difficult to avoid stress accumulation and microcrack generation inside the particles. Rigid surface coatings, such as metal oxides and phosphate coatings, can effectively isolate the direct contact between the electrolyte and the surface of the active material and reduce the occurrence of side reactions. However, rigid coatings themselves do not have deformation capabilities. During the repeated expansion and contraction of the active material, the coating is prone to cracking and peeling, losing its protective function. In some cases, the cracked coating fragments can even become impurities inside the battery, further deteriorating the battery performance. The introduction of flexible polymers is mostly used as an electrode-level binder. It can only play a bonding and buffering role at the macroscopic level of the electrode sheet. It cannot penetrate into the interior of the active particles and the microscale space between particles, and cannot solve the problems of stress cracking inside the particles and electrical contact failure between particles.
[0005] In summary, the core deficiency of existing modification technologies lies in their failure to construct an adaptive structure for layered oxide cathode materials at the micro-nano scale that can "co-deform" with the active material. This structure must simultaneously possess mechanical buffering capabilities and continuous conductivity, absorbing dynamic volumetric stress during cycling to suppress particle cracking, while maintaining a continuous electron conduction path during material deformation to avoid loss of electrical contact. Therefore, developing a dual-functional modification structure that can penetrate into the interior and interparticles of active particles and possesses both mechanical and charge-adaptive capabilities, along with its corresponding preparation method, is of paramount importance for solving the cycle degradation problem of O3-type layered oxide cathode materials and promoting the industrial application of sodium-ion batteries. Summary of the Invention
[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a layered oxide cathode material for sodium-ion batteries and its preparation method. It constructs a three-dimensional interpenetrating buffer-conductive network, realizes mechanical and charge self-adaptation, significantly improves cycle stability, rate capability and low-temperature performance, and has strong process universality, making it suitable for the industrialization of sodium-ion batteries.
[0007] The technical solution of this invention is as follows: On one hand, the present invention provides a method for preparing a layered oxide cathode material for sodium-ion batteries, comprising the following steps: S1 is used to prepare precursors; S2 Gel Encapsulation of Precursor: The precursor is immersed in an acidic suspension containing aniline monomer, crosslinking agent, silver source and carbon nanotubes, and vacuum assistance is used to fully penetrate the precursor; an oxidant is added to initiate aniline polymerization, and at the same time, silver ions are reduced to silver nanoparticles by intermediate products generated during the polymerization process, forming a composite gel of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes to encapsulate the precursor. S3 Sintering and Crystallization: Under an inert atmosphere, the product of step S2 is treated at 280-320℃ for 1.5-2.5h to crosslink and solidify the polymer. Then, it is mixed with a sodium source and sintered at 750-800℃ for 8-10h under an oxygen atmosphere to crystallize the oxide and obtain the layered oxide cathode material for sodium-ion batteries.
[0008] Preferably, in step S1, the precursor is (Ni 0.33 Mn 0.33 Fe 0.33 CO3 or (Ni 0.33 Mn 0.67 CO3.
[0009] Preferably, in step S2, the crosslinking agent is polyethylene glycol diacrylate, the silver source is silver nitrate, and the oxidizing agent is ammonium persulfate.
[0010] Preferably, step S2 specifically includes the following steps: S21 Preparation of acidic aniline solution: Add hydrochloric acid solution to deionized water to adjust the pH to 1.8-2.2; add aniline monomer and stir until completely dissolved; S22 Add crosslinking agent: Add crosslinking agent to the solution obtained in step S21 and continue stirring; S23 Adding the silver source: Dissolve the silver source in deionized water and add it dropwise to the solution obtained in step S22, stirring in the dark; S24 Add carbon nanotubes: Add carbon nanotubes to the solution obtained in step S23 and disperse them by ultrasonication in an ice-water bath to obtain an acidic suspension; S25 Vacuum-assisted impregnation: The precursor is completely immersed in the acidic suspension prepared in step S24, and a vacuum is drawn to -0.095~-0.085MPa at room temperature and maintained for 30-60 minutes to fully expel the air from the pores of the precursor particles; then the air is released and the pressure is restored to normal, allowing the acidic suspension to naturally penetrate into the pores inside the particles; then ultrasonic treatment is performed to promote the uniform distribution and deep penetration of the acidic suspension inside the particles; after ultrasonication, stirring is continued at room temperature; S26 In-situ polymerization and composite: Prepare an oxidant solution, and add it dropwise to the mixture obtained in step S25 under ice-water bath cooling and continuous stirring; after the addition is complete, raise the temperature to 3-7℃ and continue stirring for 7-9 hours; after the reaction is complete, filter, wash, and vacuum dry the filter cake to obtain a composite of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes encapsulating the precursor.
[0011] Preferably, the mass ratio of the precursor, aniline monomer, crosslinking agent, silver source, carbon nanotubes and oxidant is 50:(1.8-2.2):(0.4-0.6):(0.25-0.35):(0.08-0.12):(2.8-3.2).
[0012] Preferably, the sodium source is sodium hydroxide, and the molar ratio of the sodium source to the metal element in the precursor is (1-1.1):1.
[0013] On the other hand, the present invention also provides a layered oxide cathode material for sodium-ion batteries, which is prepared by the above-described method for preparing layered oxide cathode materials for sodium-ion batteries.
[0014] The sodium-ion battery layered oxide cathode material and its preparation method of the present invention achieve a dual synergistic effect of mechanical self-adaptation and charge self-adaptation by constructing a three-dimensional interpenetrating buffer-conductive composite network of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes inside and between active particles. This fundamentally solves the core problems of particle cracking, interface failure, and impedance surge during cycling of traditional O3-type layered oxide cathode materials. Compared with the prior art, it has the following significant advantages: 1. This invention utilizes vacuum-assisted impregnation to allow the composite gel precursor liquid to fully penetrate into the interior of the primary precursor particles and the pores between particles. The resulting three-dimensional elastic network, formed after in-situ polymerization and sintering, can achieve "synergistic deformation" with the active particles. When the active particles expand / contract due to sodium ion intercalation / deintercalation, the elastic polymer skeleton can simultaneously stretch / contract, uniformly dispersing locally concentrated high stress into low stress that the network as a whole can withstand. This inhibits the initiation and propagation of microcracks from the source, preventing the pulverization of secondary particles.
[0015] 2. In the composite network, in-situ generated silver nanoparticles and carbon nanotubes form a "metal-carbon" binary high-conductivity phase, which, together with the polyaniline-based polymer framework, constructs a continuous ternary conductive pathway. During material volume deformation, this pathway maintains electronic conduction continuity through the physical overlap of silver nanoparticles and the high aspect ratio tunneling effect of carbon nanotubes, solving the problem of easy breakage in traditional rigid conductive networks. Simultaneously, the three-dimensional interpenetrating structure significantly shortens the diffusion path of sodium ions and improves the charge transfer rate, enabling the material to retain approximately 80% of its capacity at ultra-high rates of 10C, and over 83% at low temperatures of -20℃ and 0.5C rates, meeting the application requirements of high-rate discharge and low-temperature conditions in batteries.
[0016] 3. In this invention, the three-dimensional composite network not only coats the surface of the active particles but also fills the pores between the particles, forming a dense protective barrier. This effectively isolates the active material from direct contact with the electrolyte, significantly reducing side reactions and transition metal dissolution caused by fresh surface exposure, and lowering the probability of unstable solid electrolyte interphase (SEI) film formation. Simultaneously, continuous electron conduction ensures uniform current distribution on the electrode surface, avoiding interface degradation caused by localized overcharging / overdischarging. This results in a charge transfer impedance of only 30-35Ω after 500 cycles, achieving long-term stability of the battery impedance.
[0017] 4. The three-dimensional composite network constructed in this invention has both mechanical buffering and conductive functions. It can simultaneously replace traditional inert conductive agents (such as carbon black) and some binders in the electrode formulation. It can achieve structural stability and charge conduction of materials without adding a large amount of inactive components, which greatly increases the effective proportion of active materials in the electrode. It solves the problem of reduced energy density caused by adding a large amount of inert components in traditional modification strategies, and significantly improves the overall energy density of sodium-ion batteries.
[0018] 5. The preparation method of this invention uses carbonate precursors prepared by conventional co-precipitation methods as raw materials. A multi-step process involving vacuum-assisted impregnation, in-situ polymerization, low-temperature curing, and high-temperature crystallization is employed to construct the composite network. The process parameters for each step are mild and controllable. The aniline monomer, polyethylene glycol diacrylate, silver nitrate, and other raw materials used are all commonly used industrial reagents, requiring no special or expensive equipment. Furthermore, this modification strategy is independent of the specific chemical composition of the layered oxide and can be widely applied to NaNi... 0.33 Mn 0.33 Fe 0.33 O2, NaNi 0.33 Mn 0.67 O2 and other O3-type layered oxides possess strong process versatility and promising prospects for industrial application.
[0019] 6. Compared with traditional modified materials, the cathode material prepared by this invention does not exhibit obvious particle cracking or electrode peeling during cycling. The elastic constraint of the composite network allows the overall volume expansion rate of the electrode to be controlled within 6%, effectively ensuring the integrity of the electrode structure during long-term cycling and avoiding safety hazards such as battery electrode deformation and cell short circuits caused by volume expansion. At the same time, it improves the assembly compatibility of the battery.
[0020] In summary, through innovative structural design, this invention achieves simultaneous improvement in the mechanical stability, conductivity continuity, and interface integrity of layered oxide cathode materials for sodium-ion batteries, while also considering the battery's cycle life, rate performance, low-temperature performance, and energy density. It solves the core technical bottlenecks of existing technologies and provides an efficient and feasible technical solution for the industrial application of layered oxide cathode materials for sodium-ion batteries. Detailed Implementation
[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] Example 1 The method for preparing the sodium-ion battery layered oxide cathode material in this embodiment includes the following steps: Synthesis of S1 precursor: Prepared by co-precipitation method (Ni 0.33 Mn 0.33 Fe 0.33 CO3 precursor Preparation of metal salt solution: Weigh out 86.7g of nickel sulfate (NiSO4·6H2O), 55.8g of manganese sulfate (MnSO4·H2O), and 91.7g of ferrous sulfate (FeSO4·7H2O) according to the molar ratio of Ni, Mn, and Fe of 0.33:0.33:0.33. Dissolve them in deionized water and bring the volume up to 1L to obtain a mixed salt solution with a total metal ion concentration of 2mol / L.
[0023] Preparation of precipitant solution: Weigh 265g of sodium carbonate, dissolve it in deionized water, and add concentrated ammonia (25wt.%) to reduce the NH4+ concentration in the solution. + The concentration was maintained at 0.5 mol / L, and the volume was adjusted to 1 L to obtain a 2.5 mol / L sodium carbonate-ammonia water composite precipitant solution.
[0024] Coprecipitation reaction: Under continuous argon gas protection, the mixed salt solution and the precipitant solution were pumped concurrently into a 5L reactor at the same flow rate (5 mL / min each). The reaction temperature was controlled at 55℃, the stirring speed at 600 rpm, and the pH of the reaction system was maintained at 10.5 ± 0.2 by adjusting the feed rate.
[0025] Aging and Washing: After feeding, continue stirring and aging for 12 hours. Filter the precipitate, wash it three times with deionized water, and then twice with anhydrous ethanol. Each time, the washing solution should be five times the volume of the precipitate, until the filtrate is neutral and free of SO4. 2- Detected (using BaCl2 solution).
[0026] Drying: The filter cake was placed in a vacuum oven and dried at 100°C for 24 hours to obtain (Ni) 0.33 Mn 0.33 Fe 0.33 CO3 precursor powder.
[0027] S2 gel-encapsulated precursor To prepare an acidic aniline solution: Add 2.5 mL of concentrated hydrochloric acid (37 wt.%) to 100 mL of deionized water and adjust the pH to 2. Add 2 g of aniline monomer and stir magnetically until completely dissolved.
[0028] Add crosslinking agent: Add 0.5g of polyethylene glycol diacrylate to the solution obtained above and continue stirring for 20min.
[0029] Add silver source: Weigh 0.3g of silver nitrate, dissolve it in 10mL of deionized water, add it dropwise to the solution obtained above, and stir for 15min in the dark.
[0030] Add carbon nanotubes: Weigh 0.1g of carboxylated multi-walled carbon nanotubes and add them to the solution obtained above. Disperse the solution by ultrasonication in an ice-water bath (power 300W) for 30min to ensure uniform dispersion of the carboxylated multi-walled carbon nanotubes and obtain a black, uniform acidic suspension.
[0031] Vacuum-assisted impregnation: Take the (Ni) prepared in step S1 0.33 Mn 0.33 Fe 0.3350g of CO3 precursor powder was placed in a 500mL round-bottom flask. The acidic suspension was poured into the flask to completely submerge the powder. The flask was connected to a vacuum device, and a vacuum was drawn to -0.09MPa at room temperature and maintained for 60 minutes to fully expel air from the pores of the precursor particles. The pressure was then released, and the pressure was restored to normal, allowing the acidic suspension to naturally penetrate the pores of the particles using the pressure difference. The flask was then placed in an ultrasonic cleaner and sonicated at 300W for 2 hours to promote uniform distribution and deep penetration of the acidic suspension within the particles. After sonication, the flask was placed on a magnetic stirrer and stirred for another 2 hours at room temperature to ensure sufficient contact between the suspension and the particles.
[0032] Preparation of the oxidant solution: Weigh 3g of ammonium persulfate and dissolve it in 20mL of deionized water to obtain the oxidant solution. Under ice-water bath cooling and continuous stirring, add the oxidant solution dropwise to the mixture obtained above. After the addition is complete, raise the temperature of the reaction system to 5℃ and continue stirring for 8 hours to allow aniline to undergo in-situ oxidative polymerization. During this process, silver ions are reduced to silver nanoparticles by the intermediate products generated during polymerization, which are uniformly dispersed in the generated polyaniline network. After the reaction is complete, filter the mixture and wash it three times alternately with deionized water and ethanol to remove unreacted monomers and oxidant. Dry the filter cake under vacuum at 60℃ for 12 hours to obtain a composite of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes encapsulating the precursor.
[0033] S3 Sintering and Crystallization Low-temperature curing: The product obtained in step S2 is placed in a tube furnace and heated to 300°C at a heating rate of 2°C / min under an argon atmosphere (flow rate 100 sccm), and held at that temperature for 2 hours. During this process, polyaniline and polyethylene glycol diacrylate undergo cross-linking and curing to form a stable three-dimensional polymer network skeleton.
[0034] Sodium mixing: The product obtained above and sodium hydroxide powder are placed in an agate mortar at a molar ratio of Na to (Ni+Mn+Fe) of 1.05:1 and ground until they are evenly mixed.
[0035] High-temperature crystallization: The resulting mixture was placed in a corundum boat and then placed in a muffle furnace. Under a flowing oxygen atmosphere (50 sccm), it was heated to 780°C at a heating rate of 5°C / min and held for 9 hours to crystallize the layered oxide NaNi. 0.33 Mn 0.33 Fe 0.33 O2 crystallizes fully and, together with silver nanoparticles and carboxylated multi-walled carbon nanotubes, forms the final conductive-buffered network.
[0036] Post-processing: After cooling to room temperature in the furnace, the sintered product is taken out, ground in an agate mortar, and passed through a 400-mesh sieve to obtain the final cathode material.
[0037] Example 2 The method for preparing the sodium-ion battery layered oxide cathode material in this embodiment includes the following steps: Synthesis of S1 precursor: Prepared by co-precipitation method (Ni 0.33 Mn 0.67 CO3 precursor Preparation of metal salt solution: Weigh 86.7 g of nickel sulfate (NiSO4·6H2O) and 113.2 g of manganese sulfate (MnSO4·H2O) according to a Ni:Mn molar ratio of 0.33:0.67, dissolve them in deionized water, and bring the volume to 1 L to obtain a mixed salt solution with a total metal ion concentration of 2 mol / L. The remaining steps are the same as in Example 1, yielding (Ni... 0.33 Mn 0.67 CO3 precursor powder.
[0038] S2 gel-encapsulated precursor Preparation of acidic aniline solution: Add 2.5 mL of concentrated hydrochloric acid (37 wt.%) to 100 mL of deionized water and adjust the pH to 2. Add 1.8 g of aniline monomer and stir magnetically until completely dissolved.
[0039] Add crosslinking agent: Add 0.4 g of polyethylene glycol diacrylate to the solution obtained above and continue stirring for 20 min.
[0040] Add silver source: Weigh 0.25g of silver nitrate, dissolve it in 10mL of deionized water, add it dropwise to the solution obtained above, and stir for 15min in the dark.
[0041] Add carbon nanotubes: Weigh 0.08 g of carboxylated multi-walled carbon nanotubes and add them to the solution obtained above. Disperse the solution by ultrasonication in an ice-water bath (power 300 W) for 30 min to ensure uniform dispersion of the carboxylated multi-walled carbon nanotubes and obtain a black, uniform acidic suspension.
[0042] Vacuum-assisted impregnation: Take the (Ni) prepared in step S1 0.33 Mn 0.67 50g of CO3 precursor powder was placed in a 500mL round-bottom flask. The acidic suspension was poured into the flask to completely submerge the powder. The flask was connected to a vacuum device, and a vacuum was drawn to -0.095MPa at room temperature and maintained for 40 minutes to fully expel air from the pores of the precursor particles. The pressure was then released, and the pressure was restored to normal, allowing the acidic suspension to naturally penetrate the pores of the particles using the pressure difference. The flask was then placed in an ultrasonic cleaner and sonicated at 300W for 2 hours to promote uniform distribution and deep penetration of the acidic suspension within the particles. After sonication, the flask was placed on a magnetic stirrer and stirred for another 2 hours at room temperature to ensure sufficient contact between the suspension and the particles.
[0043] Preparation of the oxidant solution: Weigh 2.8 g of ammonium persulfate and dissolve it in 20 mL of deionized water to obtain the oxidant solution. Under ice-water bath cooling and continuous stirring, add the oxidant solution dropwise to the mixture obtained above. After the addition is complete, raise the temperature of the reaction system to 3 °C and continue stirring for 9 h to allow aniline to undergo in-situ oxidative polymerization. During this process, silver ions are reduced to silver nanoparticles by the intermediate products generated during polymerization, which are uniformly dispersed in the generated polyaniline network. After the reaction is complete, filter the mixture and wash it three times alternately with deionized water and ethanol to remove unreacted monomers and oxidant. Dry the filter cake under vacuum at 60 °C for 12 h to obtain a composite of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes encapsulating the precursor.
[0044] S3 Sintering and Crystallization Low-temperature curing: The product obtained in step S2 is placed in a tube furnace and heated to 280°C at a heating rate of 2°C / min under an argon atmosphere (flow rate 100 sccm), and held at that temperature for 2.5 h. During this process, polyaniline and polyethylene glycol diacrylate undergo cross-linking and curing to form a stable three-dimensional polymer network skeleton.
[0045] Sodium mixing: The product obtained above and sodium hydroxide powder are placed in an agate mortar at a molar ratio of Na to (Ni+Mn) of 1.07:1 and ground until they are evenly mixed.
[0046] High-temperature crystallization: The resulting mixture was placed in a corundum boat and then placed in a muffle furnace. Under a flowing oxygen atmosphere (flow rate 50 sccm), it was heated to 800℃ at a heating rate of 5℃ / min and held for 10 hours to form layered oxides NaNi. 0.33 Mn 0.67 O2 crystallizes fully and, together with silver nanoparticles and carboxylated multi-walled carbon nanotubes, forms the final conductive-buffered network.
[0047] Post-processing: After cooling to room temperature in the furnace, the sintered product is taken out, ground in an agate mortar, and passed through a 400-mesh sieve to obtain the final cathode material.
[0048] Example 3 The method for preparing the sodium-ion battery layered oxide cathode material in this embodiment includes the following steps: S1 was prepared using the same method as in Example 1 (Ni 0.33 Mn 0.33 Fe 0.33 CO3 precursor.
[0049] S2 gel-encapsulated precursor Preparation of acidic aniline solution: Add 2.5 mL of concentrated hydrochloric acid (37 wt.%) to 100 mL of deionized water and adjust the pH to 2. Add 2.2 g of aniline monomer and stir magnetically until completely dissolved.
[0050] Add crosslinking agent: Add 0.6 g of polyethylene glycol diacrylate to the solution obtained above and continue stirring for 20 min.
[0051] Add silver source: Weigh 0.35g of silver nitrate, dissolve it in 10mL of deionized water, add it dropwise to the solution obtained above, and stir for 15min in the dark.
[0052] Add carbon nanotubes: Weigh 0.12g of carboxylated multi-walled carbon nanotubes and add them to the solution obtained above. Disperse the solution by ultrasonication in an ice-water bath (power 300W) for 30min to ensure uniform dispersion of the carboxylated multi-walled carbon nanotubes and obtain a black, uniform acidic suspension.
[0053] Vacuum-assisted impregnation: Take the (Ni) prepared in step S1 0.33 Mn 0.33 Fe 0.33 50g of CO3 precursor powder was placed in a 500mL round-bottom flask. The acidic suspension was poured into the flask to completely submerge the powder. The flask was connected to a vacuum device, and a vacuum was drawn to -0.085MPa at room temperature and maintained for 30 minutes to fully expel air from the pores of the precursor particles. The pressure was then released, and the pressure was restored to normal, allowing the acidic suspension to naturally penetrate the pores of the particles using the pressure difference. The flask was then placed in an ultrasonic cleaner and sonicated at 300W for 2 hours to promote uniform distribution and deep penetration of the acidic suspension within the particles. After sonication, the flask was placed on a magnetic stirrer and stirred for another 2 hours at room temperature to ensure sufficient contact between the suspension and the particles.
[0054] Preparation of the oxidant solution: Weigh 3.2 g of ammonium persulfate and dissolve it in 20 mL of deionized water to obtain the oxidant solution. Under ice-water bath cooling and continuous stirring, add the oxidant solution dropwise to the mixture obtained above. After the addition is complete, raise the temperature of the reaction system to 7 °C and continue stirring for 7 h to allow aniline to undergo in-situ oxidative polymerization. During this process, silver ions are reduced to silver nanoparticles by the intermediate products generated during polymerization, which are uniformly dispersed in the generated polyaniline network. After the reaction is complete, filter the mixture and wash it three times alternately with deionized water and ethanol to remove unreacted monomers and oxidant. Dry the filter cake under vacuum at 60 °C for 12 h to obtain a composite of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes encapsulating the precursor.
[0055] S3 Sintering and Crystallization Low-temperature curing: The product obtained in step S2 is placed in a tube furnace and heated to 320°C at a heating rate of 2°C / min under an argon atmosphere (flow rate 100 sccm), and held at that temperature for 1.5 h. During this process, polyaniline and polyethylene glycol diacrylate undergo cross-linking and curing to form a stable three-dimensional polymer network framework.
[0056] Sodium mixing: The product obtained above and sodium hydroxide powder are placed in an agate mortar at a molar ratio of Na to (Ni+Mn+Fe) of 1.05:1 and ground until they are evenly mixed.
[0057] High-temperature crystallization: The resulting mixture was placed in a corundum boat and then placed in a muffle furnace. Under a flowing oxygen atmosphere (flow rate 50 sccm), it was heated to 800℃ at a heating rate of 5℃ / min and held for 8 hours to form layered oxides NaNi. 0.33 Mn 0.33 Fe 0.33 O2 crystallizes fully and, together with silver nanoparticles and carboxylated multi-walled carbon nanotubes, forms the final conductive-buffered network.
[0058] Post-processing: After cooling to room temperature in the furnace, the sintered product is taken out, ground in an agate mortar, and passed through a 400-mesh sieve to obtain the final cathode material.
[0059] Comparative Example 1 Following step S1 of Example 1, (Ni) was prepared. 0.33 Mn 0.33 Fe 0.33 CO3 precursor; the precursor and sodium hydroxide powder were placed in an agate mortar at a Na to (Ni+Mn+Fe) molar ratio of 1.05:1 and ground until homogeneous. The resulting mixture was placed in a corundum ark and then placed in a muffle furnace. Under a flowing oxygen atmosphere (flow rate 50 sccm), the temperature was increased to 750℃ at a heating rate of 5℃ / min and held for 8 hours. After cooling to room temperature with the furnace, the sintered product was removed, ground in an agate mortar, and passed through a 400-mesh sieve to obtain the final NaNi. 0.33 Mn 0.33 Fe 0.33 O2 materials.
[0060] Comparative Example 2 Take the NaNi prepared in Comparative Example 1 0.33 Mn 0.33 Fe 0.33 50g of O2 material was mixed with 2.5g of sucrose, and water was added to dissolve and moisten the sucrose. The mixture was stirred and evaporated to dryness at 80℃. The mixture was placed in a tube furnace and heated to 500℃ at a rate of 5℃ / min under an argon atmosphere, and held at that temperature for 3 hours to allow the sucrose to pyrolyze and carbonize, forming a carbon coating layer on the surface of the material. After natural cooling to room temperature, the sintered product was removed, ground in an agate mortar, and passed through a 400-mesh sieve to obtain the carbon-coated cathode material.
[0061] Comparative Example 3 Thermoplastic polyurethane particles were dissolved in DMF to prepare a 5 wt.% solution. The solution was poured into a petri dish and dried under vacuum at 60 °C for 24 h to form a film. The film was then cut into micron-sized fragments (approximately 100 μm in length) to obtain elastomer sheets. The elastomer sheets were compared with NaNi prepared in Comparative Example 1. 0.33 Mn 0.33 Fe 0.33 O2 materials are mixed to obtain positive electrode materials.
[0062] The cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were assembled into coin cells: Electrode preparation: Prepared according to a mass ratio of 8:1:1 (Comparative Example 3 was prepared using NaNi). 0.33 Mn 0.33 Fe 0.33 Weigh out the positive electrode material, conductive carbon black (SuperP), and polyvinylidene fluoride (PVDF) from Examples 1-3 and Comparative Examples 1-3 (mass ratio 78:10:10:2). Add NMP and stir on a magnetic stirrer until a uniform slurry is formed. Use a spatula to evenly coat the slurry onto aluminum foil, controlling the wet film thickness to 150 μm. Place the coated electrode in an 80°C vacuum oven to dry for 12 hours to remove the solvent. Use a die-cutting machine to cut the electrode into circular sheets with a diameter of 12 mm.
[0063] Battery assembly: The process was carried out in an argon-filled glove box (water and oxygen content both <0.1ppm). Using a CR2032 coin cell case, the positive electrode shell, positive electrode plate (active material side up), and glass fiber separator (Whatman GF / D, 16mm diameter) were placed in sequence. 80μL of electrolyte (1mol / L NaPF6 dissolved in ethylene carbonate / dimethyl carbonate, EC / DMC volume ratio 1:1) was added. A sodium metal sheet (14mm diameter, 0.5mm thickness) was placed as the counter electrode, followed by the gasket and spring contact. The negative electrode shell was then placed on top, and the assembly was completed using a coin cell sealing machine under 50MPa pressure.
[0064] The assembled battery was placed in a glove box for 12 hours to allow the electrolyte to fully wet the electrodes. The battery was then transferred to the battery testing system, and its electrochemical performance was tested under a constant temperature of 25°C. The voltage test range was 2-4.2V (vs. Na). + / Na). Two activation cycles were first performed at a rate of 0.05C, followed by subsequent rate and cycle performance tests. The test results are shown in Table 1: Table 1. Performance test results of batteries in Examples 1-3 and Comparative Examples 1-3 Comparative Example 1 is unmodified NaNi 0.33 Mn 0.33 Fe0.33 O2 pure-phase material is the basic sample for layered oxide cathodes in sodium-ion batteries. Its performance was the worst among all tested samples, with the core problems being the lack of structural protection and conductivity enhancement, resulting in severe structural and interface failures. While it exhibited the highest discharge specific capacity at 0.1C, its cycle / rate / low-temperature performance was extremely poor. This is because the pure-phase material lacks inert modifying components, with 100% active material. Therefore, its discharge specific capacity at 0.1C reaches 148 mAh / g, the highest among all samples. However, during charge-discharge cycles, an irreversible O3-P3 phase transformation occurs, causing a sudden change in lattice parameters that leads to an electrode expansion rate exceeding 25%. Extensive cracking and pulverization of secondary particles result in a capacity retention rate of only 68% after 2000 cycles at 1C, the lowest among all samples. Furthermore, without additional conductive pathways, the electron and sodium-ion diffusion paths rely solely on the material itself, resulting in low charge transfer efficiency. At an ultra-high rate of 10C, the capacity retention rate is only 25%, far lower than the over 78% of the previous example, making it unsuitable for high-rate discharge conditions. At low temperatures, the ion / electron conduction rate further decreases, and the intrinsic interfacial impedance of the pure-phase material is relatively high. At -20°C and 0.5°C, the capacity retention is only 45%, making it unsuitable for low-temperature applications. Particle cracking generates a large amount of fresh surface area, which undergoes violent side reactions with the electrolyte, forming an unstable SEI film that disrupts electrical contacts. After 500 cycles, the charge transfer impedance reaches as high as 200Ω, 6.7 times that of Example 1, becoming the core cause of irreversible capacity decay.
[0065] Comparative Example 2, based on a pure-phase material, underwent a surface rigid carbon coating treatment. Although its performance was significantly improved compared to Comparative Example 1, it was still far inferior to the Example. The core problem was that it only achieved surface interface protection, lacking mechanical buffering capability, and the conductivity enhancement effect was limited, failing to solve the problem of internal stress cracking within the particles. The 0.1C discharge specific capacity decreased slightly because the surface carbon coating introduced a small amount of inert carbon component, slightly reducing the proportion of active material. Therefore, the 0.1C discharge specific capacity decreased to 142 mAh / g, slightly lower than that of the pure relative Example 1. The carbon coating layer can isolate the electrolyte from direct contact with the material surface and reduce surface side reactions. Therefore, the capacity retention rate increased to 82% after 2000 cycles at 1C, and the impedance decreased to 80Ω after 500 cycles. However, the carbon coating is a rigid structure with no deformation capability. When the material expands / contracts during charge and discharge (electrode expansion rate > 15%), the coating is prone to cracking and peeling, failing to inhibit stress accumulation and microcrack initiation within the particles. The cycle stability is still far lower than that of the Example. The surface carbon layer can only optimize electron conduction on the material surface and cannot penetrate into the interior and between particles. It does not shorten the sodium ion diffusion path, nor does it construct a continuous three-dimensional conductive pathway. Therefore, the capacity retention rate at 10C is only 55%, and the low-temperature capacity retention rate at -20℃ is only 60%. Although this is an improvement over Comparative Example 1, the charge transfer rate is significantly lower than that of the three-dimensional conductive network in the embodiment. Without an elastic buffer structure to disperse volumetric stress, the electrode expansion rate is still >15%, far higher than <6% in the embodiment. Long-term cycling will still result in electrode structure damage.
[0066] Comparative Example 3 involved physically mixing thermoplastic polyurethane elastomer sheets into a pure-phase material, attempting to achieve mechanical buffering through the elastomer. The performance was improved compared to Comparative Example 1 but lower than Comparative Example 2. The core issue was that the elastomer only provided macroscopic mechanical buffering, lacking interfacial protection and conductivity enhancement effects, and its poor dispersibility prevented it from penetrating to the micro-nano scale. The 0.1C discharge specific capacity was comparable to Example 1. This is because the elastomer was only physically mixed without coating or modifying the material itself, and the proportion of active material was not significantly reduced. Therefore, the 0.1C discharge specific capacity remained at 145 mAh / g, the same as Example 1. The elastomer sheets are micrometer-scale, only providing adhesion and buffering at the macroscopic level of the electrode. They cannot penetrate into the interior of active particles or the microscale spaces between particles, and cannot suppress the initiation of microcracks within the particles (electrode expansion rate >18%). Furthermore, the elastomer is an insulating material, and physical mixing did not improve the material's conductivity. Therefore, the capacity retention rate after 2000 cycles at 1C was only 75%, lower than Comparative Example 2. The introduction of the insulating elastomer did not create any conductive pathways. Instead, the insulating phase between particles increased the charge transfer resistance to some extent. Therefore, the capacity retention rate at 10C was only 40%, and the low-temperature capacity retention rate at -20℃ was only 52%, both lower than Comparative Example 2 with carbon coating, and far inferior to the ternary conductive pathway effect of the embodiment. Without a surface protection structure, the fresh surface of the particles after cracking will still undergo side reactions with the electrolyte, and the elastomer cannot improve electrical contact. After 500 cycles, the charge transfer impedance reached 120Ω, higher than Comparative Example 2, and only much lower than the unmodified Comparative Example 1, indicating poor interface stability.
Claims
1. A method for preparing a layered oxide cathode material for sodium-ion batteries, characterized in that, Includes the following steps: S1 is used to prepare precursors; S2 Gel Encapsulation of Precursor: The precursor is immersed in an acidic suspension containing aniline monomer, crosslinking agent, silver source and carbon nanotubes, and vacuum assistance is used to fully penetrate the precursor; an oxidant is added to initiate aniline polymerization, and at the same time, silver ions are reduced to silver nanoparticles by intermediate products generated during the polymerization process, forming a composite gel of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes to encapsulate the precursor. S3 Sintering and Crystallization: Under an inert atmosphere, the product of step S2 is treated at 280-320℃ for 1.5-2.5h to crosslink and solidify the polymer. Then, it is mixed with a sodium source and sintered at 750-800℃ for 8-10h under an oxygen atmosphere to crystallize the oxide and obtain the layered oxide cathode material for sodium-ion batteries.
2. The method for preparing the layered oxide cathode material for sodium-ion batteries as described in claim 1, characterized in that, In step S1, the precursor is (Ni 0.33 Mn 0.33 Fe 0.33 CO3 or (Ni 0.33 Mn 0.67 CO3.
3. The method for preparing the layered oxide cathode material for sodium-ion batteries as described in claim 1, characterized in that, In step S2, the crosslinking agent is polyethylene glycol diacrylate, the silver source is silver nitrate, and the oxidizing agent is ammonium persulfate.
4. The method for preparing the layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, Step S2 specifically includes the following steps: S21 Preparation of acidic aniline solution: Add hydrochloric acid solution to deionized water to adjust the pH to 1.8-2.2; add aniline monomer and stir until completely dissolved; S22 Add crosslinking agent: Add crosslinking agent to the solution obtained in step S21 and continue stirring; S23 Adding the silver source: Dissolve the silver source in deionized water and add it dropwise to the solution obtained in step S22, stirring in the dark; S24 Add carbon nanotubes: Add carbon nanotubes to the solution obtained in step S23 and disperse them by ultrasonication in an ice-water bath to obtain an acidic suspension; S25 Vacuum-assisted impregnation: The precursor is completely immersed in the acidic suspension prepared in step S24, and a vacuum is drawn to -0.095~-0.085MPa at room temperature and maintained for 30-60 minutes to fully expel the air from the pores of the precursor particles; then the air is released and the pressure is restored to normal, allowing the acidic suspension to naturally penetrate into the pores inside the particles; then ultrasonic treatment is performed to promote the uniform distribution and deep penetration of the acidic suspension inside the particles; after ultrasonication, stirring is continued at room temperature; S26 In-situ polymerization and composite: Prepare an oxidant solution, and add it dropwise to the mixture obtained in step S25 under ice-water bath cooling and continuous stirring; after the addition is complete, raise the temperature to 3-7℃ and continue stirring for 7-9 hours; after the reaction is complete, filter, wash, and vacuum dry the filter cake to obtain a composite of polyaniline / crosslinking agent / silver nanoparticles / carbon nanotubes encapsulating the precursor.
5. The method for preparing the layered oxide cathode material for sodium-ion batteries as described in claim 4, characterized in that, The mass ratio of precursor, aniline monomer, crosslinking agent, silver source, carbon nanotubes and oxidant is 50:(1.8-2.2):(0.4-0.6):(0.25-0.35):(0.08-0.12):(2.8-3.2).
6. The method for preparing the layered oxide cathode material for sodium-ion batteries as described in claim 1, characterized in that, The sodium source is sodium hydroxide, and the molar ratio of the sodium source to the metal element in the precursor is (1-1.1):
1.
7. A layered oxide cathode material for sodium-ion batteries, characterized in that, It is prepared by the method for preparing sodium-ion battery layered oxide cathode material as described in any one of claims 1-6.