Preparation method of sodium ion battery positive electrode composite material

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a preparation method of a sodium-ion battery positive electrode composite material, which comprises the following steps: selecting and pretreating phosphate, vanadate, sodium salt and a carbon fiber precursor material, preparing a precursor solution at an initial mixing speed, and adsorbing the precursor solution to a fiber precursor to obtain a compound; detecting the actual adsorption integrity to determine the adsorption duration, drying and sintering the compound to obtain the positive electrode composite material, determining a heating curve according to target sintering parameters, obtaining an actual heating rate, then adjusting the heating power by comparing with a threshold value, detecting the dispersion uniformity of surface gaps and internal crystals of the material, and adjusting the initial mixing speed and the actual heating rate. The sintering temperature and the mixing speed are adjusted by detecting the surface gap arrangement uniformity and the internal crystal particle dispersion uniformity of the battery positive electrode composite material, so that the internal and external uniformity of the composite material is improved, and the sodium ion capacity and the cycling stability of the sodium ion battery positive electrode composite material are improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a method for preparing a sodium-ion battery cathode composite material. Background Technology

[0002] Sodium-ion batteries hold great potential as energy storage power sources due to their adaptability, low cost, and environmental acceptability. Among rechargeable batteries, sodium-ion batteries are considered the most advantageous solution for large-scale energy storage because of the abundance and low cost of sodium resources and their similarity in operating principle to lithium-ion batteries. In sodium-ion batteries, sodium ions can reversibly move between the positive and negative electrodes, creating a potential difference that releases and stores electrical energy. However, the ionic radius of sodium ions is larger than that of lithium ions, resulting in lower capacity, poorer rate of change, and lower cycle stability in sodium-ion batteries. Therefore, to address these issues with sodium-ion batteries, it is necessary to seek suitable positive electrode materials or other high-energy-density electrode materials.

[0003] Chinese Patent Publication No. CN117673295A discloses a sodium-ion battery cathode composite material, its preparation method, and a sodium-ion battery. The sodium-ion battery cathode composite material comprises a layered oxide and a sodium orthophosphate ion material layer coating the surface of the layered oxide. In this invention, the surface of the layered oxide is coated with a sodium-rich sodium orthophosphate ion material layer, which protects the surface of the layered material, reduces the capacity decay rate of the sodium-ion battery cathode during cycling, and improves the cycle stability of the sodium-ion battery.

[0004] It is evident that the existing technology has the following problems: In the preparation process of sodium-ion battery cathode composite materials, the lack of a process to adjust the sintering temperature and mixing rate by detecting the uniformity of the surface gap arrangement and the uniformity of the internal crystal particle dispersion of the battery cathode composite material leads to inconsistent uniformity of particle distribution inside and outside the sodium-ion battery cathode composite material, which reduces the sodium-ion capacity of the sodium-ion battery cathode composite material and affects the battery capacity, rate and cycle stability. Summary of the Invention

[0005] Therefore, this invention provides a method for preparing sodium-ion battery cathode composite materials to overcome the problem in the prior art where the preparation process of sodium-ion battery cathode composite materials lacks a process for adjusting the sintering temperature and mixing rate by detecting the uniformity of surface gap arrangement and internal crystal particle dispersion of the battery cathode composite material. This results in inconsistent particle distribution uniformity between the inner and outer parts of the sodium-ion battery cathode composite material, reducing the sodium-ion capacity of the sodium-ion battery cathode composite material and affecting the battery capacity, rate, and cycle stability.

[0006] To achieve the above objectives, the present invention provides a method for preparing a sodium-ion battery cathode composite material, comprising: Raw materials for sodium-ion battery cathode composite materials were selected and pretreated to obtain phosphate, vanadate, sodium salt and carbon fiber precursor materials; Phosphate, vanadate, sodium salt, reducing agent and solution are mixed at an initial mixing rate to obtain a precursor solution. The precursor solution is adsorbed onto a fiber precursor material to obtain a fiber precursor complex. The actual adsorption integrity of the fiber precursor complex is detected, and the adsorption time is determined based on the actual adsorption integrity and the integrity threshold. The fiber precursor composite is dried and sintered to obtain a battery cathode composite material. The sintering heating rate curve is determined based on the target sintering temperature and sintering time. The actual heating rate is obtained based on the sintering heating rate curve. The heating power is adjusted based on the actual heating rate and the heating rate threshold range. The uniformity of surface gap arrangement and internal crystal particle dispersion of the battery cathode composite material are detected, and the initial mixing rate is adjusted based on the uniformity of surface gap arrangement and internal crystal particle dispersion, or the actual heating rate is adjusted. The uniformity of the surface gap arrangement is determined based on the distance between the carbon fiber and the crystal particles, and the uniformity of the internal crystal particle dispersion is determined based on the distance between the crystal particles.

[0007] Furthermore, the process of detecting the actual adsorption integrity of the fiber precursor complex includes: The fiber precursor complex is weighed to obtain the actual weight of the fiber precursor complex, and the actual adsorption integrity is determined based on the ratio of the actual weight of the fiber precursor complex to the maximum weight of the fiber precursor complex. The maximum weight of the fiber precursor composite is the weight of the precursor solution adsorbed onto the fiber precursor material within a preset adsorption time.

[0008] Furthermore, the process of determining the adsorption time based on the actual adsorption integrity and the integrity threshold includes: If the actual adsorption integrity is less than the integrity threshold, the adsorption time is extended based on the difference between the integrity threshold and the actual adsorption integrity. If the actual adsorption integrity is greater than or equal to the integrity threshold, the current adsorption duration is maintained.

[0009] Furthermore, the process of obtaining the actual heating rate based on the sintering heating rate curve includes: The sintering heating rate curve is segmented based on the inflection point to obtain a segmented sintering heating rate curve. The actual heating rate of the corresponding segmented curve is then determined based on the segmented sintering heating rate curve.

[0010] Furthermore, the process of adjusting the heating power based on the actual heating rate and the heating rate threshold range includes: If the actual heating rate is less than the minimum value of the heating rate threshold range, the heating power is increased based on the difference between the minimum value of the heating rate threshold range and the actual heating rate. If the actual heating rate is within the heating rate threshold range, then maintain the current heating power; If the actual heating rate is greater than the maximum value of the heating rate threshold range, then the heating power is reduced based on the difference between the actual heating rate and the maximum value of the heating rate threshold range. Only when the actual heating rate is determined to be outside the heating rate threshold range, the actual heating rate of the continuous sintering heating rate segmented curve is selected for comparison to obtain the actual increase in heating rate. Based on the comparison result between the actual increase in heating rate and the heating rate increase threshold range, the adjustment value of heating power is determined.

[0011] Furthermore, the process of determining the adjustment value of the heating power based on the comparison between the actual increase in the heating rate and the threshold range of the increase in the heating rate includes: Based on the fact that the actual increase in the heating rate is within the threshold range of the increase in the heating rate, the adjustment value is adjusted according to the initial value. Based on the fact that the actual increase in heating rate is less than the minimum value of the heating rate increase threshold range, the heating power is adjusted according to the difference between the minimum value of the heating rate increase threshold range and the actual increase in heating rate. Based on the fact that the actual increase in heating rate is greater than the maximum value of the heating rate increase threshold range, the adjustment value of heating power is reduced according to the difference between the actual increase in heating rate and the maximum value of the heating rate increase threshold range. The adjustment value is a reference value for each change in heating power.

[0012] Furthermore, the process of detecting the uniformity of surface gap arrangement in the battery cathode composite material includes: The distance between carbon fibers and crystal particles on the surface of the battery cathode composite material is detected to obtain several carbon crystal distances. The uniformity of surface gap arrangement is determined based on the comparison results between the carbon crystal distances and the standard carbon crystal distances. The number of carbon crystal distances is determined based on the comparison between the carbon crystal distance and the standard carbon crystal distance, and the uniformity of surface gap arrangement is determined based on the number of carbon crystal distances and the carbon crystal distance threshold. If the number of carbon crystal distances is less than or equal to the threshold number of carbon crystal distances, then the surface gap arrangement uniformity is determined based on the preset standard. If the number of carbon crystal distances is greater than the carbon crystal distance threshold, the uniformity of the standard surface gap arrangement is reduced based on the difference between the number of carbon crystal distances and the carbon crystal distance threshold.

[0013] Furthermore, the process of detecting the uniformity of internal crystal particle dispersion in the battery cathode composite material includes: The battery cathode composite material is sliced ​​to obtain composite material slices. The dispersion distance between crystal particles is determined based on the composite material slices to determine the particle distance. The number of particle distances is determined based on the comparison result of the particle distance and the particle distance threshold. The dispersion uniformity of internal crystal particles is determined based on the number of particle distances and the particle distance number threshold. If the particle distance is less than or equal to the particle distance threshold, the internal crystal particle dispersion uniformity is determined based on the preset standard. If the number of particle distances is greater than the particle distance threshold, the uniformity of internal crystal particle dispersion is determined based on the number of particle distances and the particle distance threshold.

[0014] Furthermore, the process of adjusting the heating rate includes: The reduction in the actual heating rate is determined based on the fact that the surface gap uniformity is less than the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is greater than or equal to the internal crystal particle dispersion uniformity threshold. Based on the fact that the surface gap uniformity is greater than or equal to the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is less than the internal crystal particle dispersion uniformity threshold, the reduction in the actual heating rate is determined by the difference between the internal crystal particle dispersion uniformity threshold and the internal crystal particle dispersion uniformity. Based on the fact that the surface gap uniformity is less than the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is less than the internal crystal particle dispersion uniformity threshold, the reduction in the actual heating rate is determined according to the difference between the surface gap uniformity and the internal crystal particle dispersion uniformity. Wherein, the difference in the uniformity of surface gap arrangement is the difference between the uniformity threshold of surface gap arrangement and the uniformity of surface gap arrangement, and the difference in the uniformity of internal crystal particle dispersion is the difference between the uniformity threshold of internal crystal particle dispersion and the uniformity of internal crystal particle dispersion.

[0015] Furthermore, the process of adjusting the initial mixing speed includes: Based on the fact that the internal uniformity difference is greater than the surface uniformity difference, the increment of the initial mixing rate is determined according to the difference level between the internal uniformity difference and the surface uniformity difference. Based on the fact that the internal uniformity difference is less than the surface uniformity difference, the adjustment range of the actual heating rate is determined according to the difference level between the surface uniformity difference and the internal uniformity difference.

[0016] Compared with existing technologies, the advantages of this invention are as follows: In implementation, the raw materials selected cover a variety of natural fibers and conventional chemical reagents, with wide availability and environmental friendliness; the pretreatment process is simple and efficient; and the purity of the raw materials is ensured by screening out impurities, laying the foundation for the subsequent preparation of high-quality composite materials. The precursor solution preparation and adsorption process employs a combination of precise temperature control, vacuum assistance, and liquid-solid ratio optimization to ensure uniform penetration of the solution into the internal pores of the fiber, achieving a tight bond between the active component and the carbon fiber precursor, avoiding performance defects caused by uneven adsorption. The sintering process uses nitrogen protection and a segmented heating strategy, ensuring the smooth conversion of the carbon fiber precursor and promoting the uniform growth of sodium vanadium phosphate crystals, effectively improving the material's crystallinity and structural stability. By precisely adjusting the mixing speed and heating rate, the surface gaps and internal particle dispersion of the material are simultaneously improved, significantly enhancing ion transport efficiency and interfacial bonding.

[0017] Furthermore, in implementation, the adsorption integrity is tested using a gravimetric method, with the saturated adsorption weight of the same batch of fibers as the benchmark. This avoids detection errors caused by differences between different batches of fibers, ensuring the accuracy and reliability of the test results. The adsorption time is extended only when the actual integrity does not reach the integrity threshold, with priority given to extending the atmospheric pressure adsorption stage. This ensures sufficient penetration into the internal pores of the fibers while avoiding excessive time consumption in the vacuum stage, thus improving adsorption efficiency. By controlling the integrity threshold, insufficient or excessive adsorption is avoided. Insufficient adsorption will lead to insufficient loading and performance degradation of the subsequent sintered products, while excessive adsorption will increase drying energy consumption and solution waste. This allows the process to adapt to the fluctuations in the state of different batches of fibers and solutions, enhancing the stability and consistency of mass production.

[0018] Furthermore, during implementation, the drying process utilizes precise temperature control to achieve gradient evaporation of moisture, effectively avoiding fiber cracking and precursor precipitation issues, thus laying a high-quality raw material foundation for subsequent sintering and phase formation. A segmented strategy based on inflection points at key reaction nodes ensures that the heating rate at each stage adapts to the reaction requirements. Combined with real-time temperature acquisition and rate calculation, this ensures the heating process is controllable and traceable. A power regulation mechanism with dual rate threshold judgments is established. In normal scenarios, power is maintained to ensure stability, while in abnormal scenarios, precise adjustment is achieved through continuous segmented increment comparison, avoiding the limitations of a single rate judgment. Differentiated adjustment logic is designed for different increment intervals, combining initial adjustment values ​​and compensation parameters to ensure adjustment accuracy while preventing over-adjustment. This significantly improves the anti-interference capability and stability of the sintering process, ultimately obtaining a battery cathode composite material with high crystallinity and uniform dispersion, balancing product performance and production reliability.

[0019] Furthermore, in implementation, surface inspection employs a multi-field, multi-point statistical approach, combined with standard carbon crystal distance range determination, to accurately quantify the uniformity of surface gap arrangement, providing a direct basis for interface performance optimization; internal inspection utilizes focused ion beam slicing and transmission electron microscopy observation to overcome the limitations of surface inspection and achieve accurate characterization of the internal crystal dispersion state; for single non-compliance scenarios on the surface or internally, the heating rate or mixing speed is optimized respectively; when both are non-compliance, the difference-dominant factor is adjusted as the core to ensure targeted process optimization.

[0020] Furthermore, during implementation, liquid nitrogen cryogenic-assisted focused ion beam slicing technology was employed, combined with ultrathin slicing preparation processes. This effectively avoided damage and detachment of internal crystal particles, achieving precise exposure of the material's deep structure. This breakthrough overcomes the limitations of traditional surface-level detection, ensuring the authenticity and comprehensiveness of the test results. Through multi-depth, multi-field particle distance acquisition and statistical analysis, coupled with clearly defined threshold ranges and deduction rules, the internal particle dispersion state was quantified into a uniformity index, making the test results intuitive and comparable, providing precise data support for process optimization. Targeting the root causes of abnormal particle dispersion, the precursor mixing or sintering parameters were precisely optimized, effectively solving the problems of particle agglomeration or excessively sparse dispersion.

[0021] Furthermore, during implementation, for single or double non-compliance scenarios involving surface gaps and internal particle dispersion, the two core parameters of heating rate and mixing speed are locked respectively to avoid process fluctuations caused by blind adjustments and improve the targeting of optimization. By quantifying the adjustment range through differential levels, a clear correlation is established between uniformity deviation and parameter adjustment amount, making the adjustment process quantifiable and repeatable. This ensures the accuracy of parameter optimization while reducing the difficulty of operation and adapting to the needs of industrial production. In double non-compliance scenarios, the dominant defect is addressed first, and the effect is verified by retesting after adjustment to ensure that both uniformity indicators meet the standards, effectively improving the stability of material performance. Attached Figure Description

[0022] Figure 1 This is a flowchart of the sodium-ion battery cathode composite material preparation method described in this embodiment; Figure 2 This is a flowchart illustrating the process of determining the adsorption time as described in this embodiment; Figure 3 This is a flowchart illustrating the process of adjusting the heating power as described in this embodiment; Figure 4 This is a flowchart illustrating the process of determining the adjustment value of the heating power as described in this embodiment. Detailed Implementation

[0023] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0024] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0025] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0026] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] Please see Figure 1 As shown, it is a flowchart of the sodium-ion battery cathode composite material preparation method described in this embodiment; This embodiment provides a method for preparing a sodium-ion battery cathode composite material, including: Step S1: Select and pre-treat the raw materials of sodium-ion battery cathode composite material to obtain phosphate, vanadate, sodium salt and carbon fiber precursor materials; Step S2: Mix phosphate, vanadate, sodium salt, reducing agent and solution at an initial mixing rate to obtain a precursor solution. Adsorb the precursor solution onto the fiber precursor material to obtain a fiber precursor complex. Detect the actual adsorption integrity of the fiber precursor complex and determine the adsorption time based on the actual adsorption integrity and integrity threshold. Step S3: The fiber precursor composite is dried and sintered to obtain the battery cathode composite material. Step S4: Determine the sintering heating rate curve based on the target sintering temperature and sintering time, obtain the actual heating rate based on the sintering heating rate curve, and adjust the heating power based on the actual heating rate and the heating rate threshold range. Step S5: Detect the uniformity of surface gap arrangement and internal crystal particle dispersion of the battery cathode composite material; adjust the heating rate based on the surface gap arrangement uniformity and internal crystal particle dispersion uniformity; if the adjusted heating rate still does not meet the standard, adjust the initial mixing rate. The uniformity of the surface gap arrangement is determined based on the distance between the carbon fiber and the crystal particles, and the uniformity of the internal crystal particle dispersion is determined based on the distance between the crystal particles.

[0028] In step S1, one or more phosphates are selected from natural materials such as degreased cotton, flax, and bamboo fiber, including ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid. The carbon fiber precursor material is selected from one or more degreased cotton, flax, and bamboo fiber. The sodium salt is selected from one or more sodium carbonate, sodium acetate, sodium dihydrogen phosphate, and sodium hydroxide. In this embodiment, the pretreatment of the raw materials for the sodium-ion battery cathode composite material is to remove impurities by screening through a 200-mesh standard sieve. In this embodiment, a preparation process for preparing NVP carbon fiber composite material is provided. Sodium dihydrogen phosphate dihydrate (42.8% by mass), ammonium metavanadate (21.4% by mass), and oxalic acid dihydrate (34.6% by mass) are weighed according to the chemical ratio and added to a predetermined proportion of deionized water. The mixture is heated to 80°C and stirred uniformly to form a homogeneous dark blue solution. The dark blue solution is added to a certain amount of degreased cotton and mixed uniformly with the cotton. The mixture is vacuum-baked at 80°C. After complete drying, the mixture is transferred to a vacuum tube furnace. First, the air in the tube furnace is completely removed with nitrogen. Then, under nitrogen protection, the temperature is raised to 350°C at a rate of 5°C / min and held for 3 hours to allow the degreased cotton to first form a carbon fiber precursor. The temperature is then raised to 750°C at the same rate and held for 10 hours. Finally, the temperature is allowed to cool naturally to obtain the NVP carbon fiber composite material, which is the cathode composite material for sodium-ion batteries. NVP is sodium vanadium phosphate. In step S2, the solution is water and anhydrous ethanol, and the reducing agents are citric acid and oxalic acid. Take 20g of pretreated flax fiber, cut it into 3cm short fibers, spread it evenly on a quartz sieve with a size of 10cm×10cm, and place it in a 60℃ forced-air drying oven for 30min to improve the temperature consistency between the flax and the precursor solution and reduce solution condensation during adsorption. After preheating, quickly transfer it to the adsorption device, place the quartz sieve carrying the flax fiber into the sealed adsorption tank, ensuring that the fiber is spread evenly with a thickness of about 2mm and without stacking, tighten the tank lid, start the vacuum pump to evacuate to -0.09MPa, turn off the vacuum pump and let it stand for 10min to confirm that the device is well sealed. 150g of preheated precursor solution (60℃) was slowly injected into the sealed adsorption tank under vacuum, ensuring the precursor solution completely submerged the flax fibers (liquid-solid ratio 7.5:1). The inlet was closed, and the tank was left to stand under vacuum for 30 minutes for initial adsorption. The vacuum in the sealed adsorption tank was then slowly released to atmospheric pressure, and the temperature control jacket was opened to maintain the tank temperature at 60℃. The adsorption tank was gently shaken at 50r / min to prevent fiber entanglement. Adsorption continued for 60 minutes, with the solution level observed every 20 minutes to ensure the fibers remained submerged. After adsorption was complete, the sealed adsorption tank was opened, and the quartz sieve and fibers were gently removed with tweezers. The quartz sieve was tilted to drain excess solution for 30 seconds. The free liquid was then gently blotted along the surface of the flax fibers with qualitative filter paper. The dried flax fibers were transferred to a clean petri dish and labeled as fiber precursor complex. Adsorption integrity was immediately tested.

[0029] In implementation, the raw materials selected cover a variety of natural fibers and conventional chemical reagents, with wide-ranging and environmentally friendly sources. The pretreatment process is simple and efficient, and the purity of the raw materials is ensured by screening out impurities, laying the foundation for the subsequent preparation of high-quality composite materials. The precursor solution preparation and adsorption process adopts a combination of precise temperature control, vacuum assistance, and liquid-solid ratio optimization to ensure that the solution penetrates the internal pores of the fiber uniformly, achieving a tight bond between the active component and the carbon fiber precursor, and avoiding performance defects caused by uneven adsorption. The sintering process adopts a nitrogen protection and segmented heating strategy, which not only ensures the smooth conversion of the carbon fiber precursor, but also promotes the uniform growth of sodium vanadium phosphate crystals, effectively improving the crystallinity and structural stability of the material. By precisely adjusting the mixing speed and heating rate, the surface gaps and internal particle dispersion of the material are improved simultaneously, significantly improving ion transport efficiency and interfacial bonding.

[0030] Specifically, the process of detecting the actual adsorption integrity of the fiber precursor complex includes: The fiber precursor complex is weighed to obtain the actual weight of the fiber precursor complex, and the actual adsorption integrity is determined based on the ratio of the actual weight of the fiber precursor complex to the maximum weight of the fiber precursor complex. The maximum weight of the fiber precursor composite is the weight of the precursor solution adsorbed onto the fiber precursor material within a preset adsorption time.

[0031] Please see Figure 2 As shown, it is a flowchart of the process for determining the adsorption time described in this embodiment; Specifically, the process of determining the adsorption time based on the actual adsorption integrity and the integrity threshold includes: If the actual adsorption integrity is less than the integrity threshold, the adsorption time is extended based on the difference between the integrity threshold and the actual adsorption integrity. If the actual adsorption integrity is greater than or equal to the integrity threshold, the current adsorption duration is maintained.

[0032] Take 20g of pretreated and preheated flax fiber from the same batch, which is exactly the same as the fiber used in the adsorption operation, weigh it with an electronic balance, and record it as the initial fiber weight m0=20.000g; To measure the maximum weight of the fiber precursor complex, 5g of pretreated flax fiber from the same batch was taken and adsorbed for 30min under vacuum and 60min under normal pressure. After the adsorption was completed, the surface free liquid was dried and the weight of the fiber precursor complex under saturation was immediately measured to be 17.5g. The maximum weight of the fiber precursor complex was calculated, that is, the weight of the complex under saturation was 17.5g. The corresponding maximum adsorption capacity per unit fiber was (17.5g-5g) / 5g=2.5g / g. The fiber precursor complex after adsorption in this embodiment was immediately weighed on an electronic balance, and the actual weight of the fiber precursor complex was 65.2g. Actual adsorption integrity = (actual weight of fiber precursor complex / maximum weight of fiber precursor complex) × 100%. Wherein, the maximum weight of the fiber precursor complex corresponding to 20g of initial fiber is m0 + (m0 × maximum adsorption capacity per unit fiber) = 20g + (20.000g × 2.5g / g) = 70.000g; actual adsorption integrity = (65.2g / 70g) × 100% = 93.14%; In this embodiment, the integrity threshold is set to 90%. The integrity threshold is determined based on the requirements of the drying and sintering process for the amount of adsorption. The integrity threshold helps the precursor solution to fill the pores of the fiber precursor composite uniformly. The 90% integrity threshold can ensure that there are no obvious voids in the precursor solution in the pores, avoid the formation of voids or local component loss after sintering, and ensure uniform crystal phase formation. If the actual adsorption integrity is greater than or equal to the integrity threshold, then maintain the current adsorption duration; If the actual adsorption integrity is 88% in a certain parallel experiment, the difference between the integrity threshold and the actual adsorption integrity is 2%. In this embodiment, the adsorption time is extended by 5 minutes for every 1% decrease in adsorption integrity. The adsorption time to be extended is 2 × 5 = 10 minutes. The total adsorption time after adjustment is 90 + 10 = 100 minutes. In this embodiment, the atmospheric pressure adsorption stage is extended and the vacuum settling stage is maintained for 30 minutes to ensure the permeation effect.

[0033] In implementation, the adsorption integrity was tested using a gravimetric method, with the saturated adsorption weight of the same batch of fibers as the benchmark. This avoided detection errors caused by differences between different batches of fibers, ensuring the accuracy and reliability of the test results. The adsorption time was extended only when the actual integrity did not reach the integrity threshold, with priority given to extending the atmospheric pressure adsorption stage. This ensured sufficient penetration into the internal pores of the fibers while avoiding excessive time consumption in the vacuum stage, thus improving adsorption efficiency. The integrity threshold control prevented under- or over-adsorption. Under-adsorption would lead to insufficient loading and performance degradation in subsequent sintered products, while over-adsorption would increase drying energy consumption and solution waste. This process adapted to the fluctuations in the state of different batches of fibers and solutions, enhancing the stability and consistency of mass production.

[0034] Specifically, the process of obtaining the actual heating rate based on the sintering heating rate curve includes: The sintering heating rate curve is segmented based on the inflection point to obtain a segmented sintering heating rate curve. The actual heating rate of the corresponding segmented curve is then determined based on the segmented sintering heating rate curve.

[0035] Please see Figure 3 As shown, it is a flowchart of the process of adjusting the heating power described in this embodiment; Specifically, the process of adjusting the heating power based on the actual heating rate and the heating rate threshold range includes: If the actual heating rate is less than the minimum value of the heating rate threshold range, the heating power is increased based on the difference between the minimum value of the heating rate threshold range and the actual heating rate. If the actual heating rate is within the heating rate threshold range, then maintain the current heating power; If the actual heating rate is greater than the maximum value of the heating rate threshold range, then the heating power is reduced based on the difference between the actual heating rate and the maximum value of the heating rate threshold range. Only when the actual heating rate is determined to be outside the heating rate threshold range, the actual heating rate of the continuous sintering heating rate segmented curve is selected for comparison to obtain the actual increase in heating rate. Based on the comparison result between the actual increase in heating rate and the heating rate increase threshold range, the adjustment value of heating power is determined.

[0036] Please see Figure 4 The diagram shown is a flowchart illustrating the process of determining the adjustment value of the heating power as described in this embodiment. Specifically, the process of determining the adjustment value of the heating power based on the comparison between the actual increase in the heating rate and the threshold range of the increase in the heating rate includes: Based on the fact that the actual increase in the heating rate is within the threshold range of the increase in the heating rate, the adjustment value is adjusted according to the initial value. Based on the fact that the actual increase in heating rate is less than the minimum value of the heating rate increase threshold range, the heating power is adjusted according to the difference between the minimum value of the heating rate increase threshold range and the actual increase in heating rate. Based on the fact that the actual increase in heating rate is greater than the maximum value of the heating rate increase threshold range, the adjustment value of heating power is reduced according to the difference between the actual increase in heating rate and the maximum value of the heating rate increase threshold range. The adjustment value is a reference value for each change in heating power.

[0037] In this embodiment, the target sintering temperature is set to 800°C, and the equipment used in the sintering process is all existing technology, which will not be described in detail here; Analyzing the sintering heating rate curve, the inflection point temperatures were determined based on key reaction nodes: 200℃ for drying residual moisture and removing oxalic acid decomposition products, and 500℃ for initial pre-crystallization of sodium vanadium phosphate. The entire curve was divided into three segments, forming a segmented sintering heating rate curve: Segment 1: Impurity removal stage from room temperature 25℃ to 200℃; Segment 2: Pre-crystallization stage at 200℃→500℃; Segment 3: Phase formation stage from 500℃ to 800℃; 10g of the dried battery positive electrode composite material was spread evenly on an alumina crucible with a thickness of 4mm and placed in the constant temperature zone of a tube furnace. The equipment was started and the temperature was increased according to the preset segmented curve. The temperature at each time point was recorded in real time by a data acquisition instrument. When each inflection point was reached, the heating was stopped and the temperature was held for 10 minutes to stabilize the thermocouple reading and eliminate temperature lag. The start and end temperatures and time of each segment were recorded. Segment 1: Starting temperature 25.3℃, ending temperature 200.1℃, time taken 176 minutes; Segment 2: Starting temperature 200.1℃, ending temperature 500.2℃, time taken 378 minutes; Segment 3: Starting temperature 500.2℃, ending temperature 800.1℃, time taken 602min; The actual heating rate of each segment is calculated as follows: actual heating rate = (final temperature - starting temperature) / segment time. Segment 1: (200.1-25.3) / 176≈0.99℃ / min; Segment 2: (500.2-200.1) / 378≈0.79℃ / min; Segment 3: (800.1-500.2) / 602≈0.49℃ / min; In this embodiment, the heating rate threshold range corresponding to segment 1 is set to 0.9-1.1℃ / min. This range is set based on the reaction characteristics of the impurity removal stage, the thermal stability of the fiber precursor, and the volatile matter removal efficiency. The core of this stage is to remove residual moisture, oxalic acid decomposition products, and other volatiles from the battery cathode composite material. The heating rate must match the volatile matter removal rate. If it is too fast, it will easily cause the volatiles to boil over, resulting in cracking or surface defects in the carbon fiber precursor composite. If it is too slow, it will prolong the impurity removal time and reduce production efficiency. It is usually set between 0.8-1.2℃ / min. In this embodiment, it is set to 0.9-1.1℃ / min, which can ensure that the volatiles are fully removed while avoiding damage to the carbon fiber structure due to drastic heating. This provides a complete carbon fiber skeleton for subsequent crystal growth and takes into account both production efficiency and process stability. The heating rate threshold range for segment 2 is set to 0.7-0.9℃ / min. This range is determined based on the pre-crystallization characteristics of sodium vanadium phosphate and the requirements for interfacial bonding. This stage is crucial for the initial formation of sodium vanadium phosphate crystals. The heating rate needs to be controlled within the equilibrium range between crystal nucleation and growth. Too fast a rate will lead to uneven crystal nucleation and grain agglomeration, affecting the quality of subsequent phase formation. Too slow a rate will lead to excessive crystal growth, reducing the interfacial bonding force with carbon fibers. The rate is usually set between 0.6-1.0℃ / min. In this embodiment, it is set to 0.7-0.9℃ / min, which can promote uniform nucleation of sodium vanadium phosphate crystals, avoid grain agglomeration or growth defects, and ensure the initial bonding between the crystal and the carbon fiber surface, laying a good foundation for high-temperature phase formation. The heating rate threshold range for segment 3 is set to 0.4-0.6℃ / min. This is based on the requirement for complete phase formation of sodium vanadium phosphate and the interface fusion efficiency between carbon fiber and sodium vanadium phosphate crystal. In this stage, the complete growth and structural densification of sodium vanadium phosphate crystal must be completed. The heating rate must be slow enough to ensure that the atoms of sodium vanadium phosphate crystal are arranged in an orderly manner. Too fast a rate will lead to an increase in crystal defects, a decrease in crystallinity, and insufficient interface fusion; too slow a rate will lead to an excessively long production cycle, increased energy consumption and cost. It is usually set between 0.3-0.7℃ / min. In this embodiment, it is set to 0.4-0.6℃ / min, which can achieve high crystallinity growth of sodium vanadium phosphate crystal, control the uniformity and regularity of crystal morphology, and promote the tight interface fusion between crystal and carbon fiber, significantly improving the conductivity and structural stability of composite material. The heating rate increment threshold is set to 0.2-0.6℃ / min, which is set according to the connection requirements of adjacent reaction segments. The heating rate increment is the difference between the actual heating rates of adjacent segments. The threshold needs to be controlled within the range that the equipment can stably adjust and the material can withstand thermal shock. Too small a threshold will lead to too frequent adjustments, affecting process stability; too large a threshold will cause drastic temperature fluctuations, damaging the formed sodium vanadium phosphate crystal structure or carbon fiber skeleton. It is usually set between 0.1-0.7℃ / min. In this embodiment, it is set to 0.2-0.6℃ / min, which can avoid thermal shock caused by sudden changes in the heating rate of adjacent segments, ensure the stability of the temperature field during sintering, achieve smooth adjustment of heating power, reduce crystal defects and interface peeling caused by temperature fluctuations, and further improve the consistency of product performance. After heating for 100 minutes in segment 2, the actual temperature was 279.8℃, corresponding to an actual heating rate of (279.8-200.1) / 100≈0.797℃ / min; after heating for another 50 minutes, the temperature reached 319.7℃, with an actual heating rate of (319.7-279.8) / 50≈0.798℃ / min; finally, at the end of the segment, the actual rate of 0.68℃ / min was less than the minimum value of the corresponding heating rate threshold range of 0.7℃ / min, and was therefore judged as abnormal. Since the actual heating rate is not within the corresponding heating rate threshold range, continuous segment 1 and segment 2 are selected for comparison of the actual heating rate. The actual increase in heating rate is 0.68 - 0.99 = -0.31℃ / min. Taking the absolute value of 0.31℃ / min, the actual increase in heating rate of 0.31℃ / min is within the threshold range of 0.2-0.6℃ / min. The actual heating rate of 0.68℃ / min is less than the minimum value of the heating rate threshold range of 0.7℃ / min, so the heating power needs to be increased. The difference is 0.7 - 0.68 = 0.02℃ / min. Based on the fact that the actual increase in heating rate is within the threshold range of heating rate increase, and calculated according to the initial adjustment value of 0.3kW / 0.01℃·min, the adjustment value = 0.02×0.3 = 0.006kW; The heating power of segment 2 was increased from 5kW to 5.006kW; If the actual increase in heating rate is 0.15℃ / min < the minimum value of the heating rate increase threshold range of 0.2℃ / min, the difference in increase = 0.2 - 0.15 = 0.05℃ / min; Basic adjustment value = rate difference × initial adjustment value = 0.05 × 0.3 = 0.015 kW; Additional adjustment value = increment difference × initial adjustment value × 0.5 = 0.05 × 0.3 × 0.5 = 0.0075 kW; where 0.5 is the compensation parameter for the impact of increment difference on adjustment value, and total adjustment value = 0.015 + 0.0075 = 0.0225 kW; If the actual heating rate increment of 0.70℃ / min is greater than the maximum value of the increment threshold range of 0.6℃ / min, the increment difference = 0.70 - 0.60 = 0.10℃ / min; Basic adjustment value = rate difference × initial adjustment value = 0.10 × 0.3 = 0.03 kW; The reduced regulation value = increment difference × initial regulation value × 0.3 = 0.10 × 0.3 × 0.3 = 0.009 kW; where 0.3 is the compensation parameter for the influence of increment difference on the reduced regulation value, and the total regulation value = 0.03 - 0.009 = 0.021 kW.

[0038] In implementation, the drying process utilizes precise temperature control to achieve gradient evaporation of moisture, effectively avoiding fiber cracking and precursor precipitation, thus laying a high-quality raw material foundation for subsequent sintering and phase formation. A segmented strategy based on inflection points at key reaction nodes ensures that the heating rate at each stage adapts to the reaction requirements. Combined with real-time temperature acquisition and rate calculation, this ensures the heating process is controllable and traceable. A power regulation mechanism with dual rate threshold judgments is established. In normal scenarios, it maintains stable power, while in abnormal scenarios, it achieves precise adjustment through continuous segmented increment comparison, avoiding the limitations of a single rate judgment. Differentiated adjustment logic is designed for different increment intervals, combining initial adjustment values ​​and compensation parameters to ensure adjustment accuracy while preventing over-adjustment. This significantly improves the anti-interference capability and stability of the sintering process, ultimately obtaining a battery cathode composite material with high crystallinity and uniform dispersion, balancing product performance and production reliability.

[0039] Specifically, the process of detecting the uniformity of surface gap arrangement in the battery cathode composite material includes: The distance between carbon fibers and crystal particles on the surface of the battery cathode composite material is detected to obtain several carbon crystal distances. The uniformity of surface gap arrangement is determined based on the comparison results between the carbon crystal distances and the standard carbon crystal distances. The number of carbon crystal distances is determined based on the comparison between the carbon crystal distance and the standard carbon crystal distance, and the uniformity of surface gap arrangement is determined based on the number of carbon crystal distances and the carbon crystal distance threshold. If the number of carbon crystal distances is less than or equal to the threshold number of carbon crystal distances, then the surface gap arrangement uniformity is determined based on the preset standard. If the number of carbon crystal distances is greater than the carbon crystal distance threshold, the uniformity of the standard surface gap arrangement is reduced based on the difference between the number of carbon crystal distances and the carbon crystal distance threshold.

[0040] In this embodiment, the surface gap uniformity is defined as the regularity of the carbon crystal distance between carbon fibers and sodium vanadium phosphate crystal particles on the material surface. It is quantified by statistically analyzing the proportion of effective carbon crystal distances within the standard range and their distribution dispersion. The internal crystal particle dispersion uniformity is defined as the consistency of the center-to-center distance between adjacent sodium vanadium phosphate crystal particles within the composite material. The core evaluation index is the distribution density and deviation of the crystal particle distance within the acceptable threshold range. The surface gap uniformity is detected using Image-Pro Plus. The 6.0 software, using 5000x magnification surface images acquired by scanning electron microscopy, employs a process of particle-fiber interface segmentation, automatic shortest distance measurement, outlier removal, and statistical distribution analysis to calculate the number of carbon crystal distances, which is then converted into a uniformity score. For internal crystal particle dispersion uniformity detection, ImageJ software is used. Targeting transmission electron microscopy images of ultrathin slices prepared by focused ion beam slicing, the software identifies crystal particle outlines, marks center coordinates, calculates the distance between adjacent particles, and performs multi-field data fusion. The dispersion uniformity is quantified by the proportion of qualified particle distances. These software and analytical methods are standard techniques in the field of material microstructure characterization, ensuring the objectivity and repeatability of the uniformity evaluation. Since the crystal distribution inside the composite material may have local agglomeration or uneven dispersion, only detecting a single field of view, such as only measuring the surface layer or a certain local area, will lead to biased data. Therefore, in this embodiment, slices are prepared at different positions of the same slice and at the surface, middle and bottom layers of the same material. Three random fields of view are then collected for each slice to form a multi-dimensional and wide-coverage field of view matrix. The surface gaps of the battery cathode composite material were detected using a scanning electron microscope. Image analysis software was used to analyze the surface gaps of the battery cathode composite material. Image analysis is an existing technology and will not be elaborated upon here. The standard carbon crystal distance range was set at 400-500 nm, within which ion transport resistance is minimal and the bonding force between carbon fiber and NVP crystal is ≥20 MPa. The threshold for the number of carbon crystal distances was set at 12, determined based on historical data. The standard surface gap uniformity was set at 90%. The surface gap uniformity adjustment coefficient was set at 1.5 points per gap, meaning that for each unqualified distance exceeding the standard, 1.5 points were deducted from the uniformity. After sintering, the composite material product was taken, and a 10mm × 10mm × 1mm sample block was cut using high-precision tweezers. The sample block was magnified 5000 times to ensure clear differentiation of the carbon crystal interface. After focusing, an electronic image was acquired. Four acquired images were opened, and 25 measurement points were selected in each image according to the principle of uniform distribution, for a total of 100 points. At each measurement point, the shortest distance between the carbon fiber surface and the surface of the adjacent NVP crystal particle was measured, i.e., the carbon crystal distance. All data were recorded, and abnormal data were removed. For example, significant deviations caused by image blurring were excluded. In this embodiment, 98 valid carbon crystal distances were retained. The data was compared with the standard carbon crystal distance range of 98 effective carbon crystal distances. The number of carbon crystal distances, i.e. the number of distances exceeding the standard carbon crystal distance range, was counted. The number of distances exceeding the standard carbon crystal distance range in the four images were 9, 10, 8, and 11, respectively. The total average number of distances exceeding the standard carbon crystal distance range was 9.5, which was rounded to 10. If the number of particle distances is less than or equal to the number of particle distances threshold, the internal crystal particle dispersion uniformity is determined based on the preset standard. The uniformity of the gap arrangement on the sample surface is 90. For samples with abnormal surface gap uniformity due to insufficient sintering and holding time, after repeating the above steps, the number of gaps exceeding the standard carbon crystal distance range was 15 > 12, with a difference of 3. The surface gap uniformity was 90 - 3 × 1.5 = 85.5.

[0041] In implementation, surface inspection employs a multi-field, multi-point statistical approach, combined with standard carbon crystal distance range determination, to accurately quantify the uniformity of surface gap arrangement, providing a direct basis for interface performance optimization. Internal inspection utilizes focused ion beam slicing and transmission electron microscopy observation to overcome the limitations of surface inspection and achieve accurate characterization of the internal crystal dispersion state. For single non-compliance scenarios on the surface or internal surface, the heating rate or mixing speed is optimized respectively. When both non-compliance is not met, the difference-dominant factor is used as the core adjustment to ensure targeted process optimization.

[0042] Specifically, the process of detecting the uniformity of internal crystal particle dispersion in the battery cathode composite material includes: The battery cathode composite material is sliced ​​to obtain composite material slices. The dispersion distance between crystal particles is determined based on the composite material slices to determine the particle distance. The number of particle distances is determined based on the comparison result of the particle distance and the particle distance threshold. The dispersion uniformity of internal crystal particles is determined based on the number of particle distances and the particle distance number threshold. If the particle distance is less than or equal to the particle distance threshold, the internal crystal particle dispersion uniformity is determined based on the preset standard. If the number of particle distances is greater than the particle distance threshold, the uniformity of internal crystal particle dispersion is determined based on the number of particle distances and the particle distance threshold.

[0043] In this embodiment, the particle distance threshold range is set to 300-800nm. Within this range, the particles do not agglomerate and the volume density meets the standard. A distance <300nm is considered agglomeration, and a distance >800nm ​​is considered too sparse. The particle distance number threshold is set to 15. The standard internal crystal particle dispersion uniformity is 95. The internal crystal particle dispersion uniformity deduction coefficient is 1 point / particle, that is, for every particle distance exceeding the threshold, the internal crystal particle dispersion uniformity is deducted by 1 point. The sintered composite material, measuring 10mm × 10mm × 5mm, was frozen in liquid nitrogen at -196℃ for 30 minutes to enhance its brittleness and facilitate slicing. After removal, it was quickly placed on the sample stage, and the central area was selected as the slicing region. A 2μm thick protective layer was formed by platinum ion deposition to prevent crystal particles from detaching during slicing. Ultrathin slices, 100nm thick and 2μm × 2μm in size, were prepared. Crystal particles were automatically identified and their center positions marked using particle analysis software. The distance between the centers of all adjacent crystal particles, i.e., the particle distance, was measured. Thirty measurements were taken for each image. To avoid local structural deviations in the slices, ultrathin slices were prepared at different depths of the same composite material sample, including the surface, middle, and bottom layers. Three images with different fields of view were acquired for each slice, resulting in a total of 270 particle distance data points. These 270 particle distances were compared with a particle distance threshold, and the number of particle distances exceeding the acceptable range was counted. The unacceptable distances in the nine images were 12, 10, 11, 13, 14, 12, 11, 13, and 12, respectively, with an average of 12.2 unacceptable distances. The number of unacceptable distances was rounded to 12. For the abnormal dispersion of samples caused by uneven concentration of precursor solution, after repeating the above steps, the number of particle distances was found to be 20 > 15, with a difference of 5. The dispersion uniformity of the internal crystal particles was 95 - 5 × 1 = 90.

[0044] In implementation, liquid nitrogen cryogenic-assisted focused ion beam slicing technology, combined with ultrathin slicing preparation process, was adopted to effectively avoid damage and detachment of internal crystal particles, achieving precise exposure of the deep structure of the material. This broke through the limitations of traditional surface detection and ensured the authenticity and comprehensiveness of the test results. Through multi-depth and multi-field particle distance acquisition and statistical analysis, coupled with clear threshold ranges and deduction rules, the internal particle dispersion state was quantified into a uniformity index, making the test results intuitive and comparable, and providing precise data support for process optimization. Targeting the root cause of abnormal particle dispersion, the precursor mixing or sintering parameters were precisely optimized, effectively solving the problems of particle agglomeration or excessively sparse dispersion.

[0045] Specifically, the process of adjusting the heating rate includes: The reduction in the actual heating rate is determined based on the fact that the surface gap uniformity is less than the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is greater than or equal to the internal crystal particle dispersion uniformity threshold. Based on the fact that the surface gap uniformity is greater than or equal to the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is less than the internal crystal particle dispersion uniformity threshold, the reduction in the actual heating rate is determined by the difference between the internal crystal particle dispersion uniformity threshold and the internal crystal particle dispersion uniformity. Based on the fact that the surface gap uniformity is less than the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is less than the internal crystal particle dispersion uniformity threshold, the reduction in the actual heating rate is determined according to the difference between the surface gap uniformity and the internal crystal particle dispersion uniformity. Wherein, the difference in the uniformity of surface gap arrangement is the difference between the uniformity threshold of surface gap arrangement and the uniformity of surface gap arrangement, and the difference in the uniformity of internal crystal particle dispersion is the difference between the uniformity threshold of internal crystal particle dispersion and the uniformity of internal crystal particle dispersion.

[0046] Specifically, the process of adjusting the initial mixing speed includes: Based on the fact that the internal uniformity difference is greater than the surface uniformity difference, the increment of the initial mixing rate is determined according to the difference level between the internal uniformity difference and the surface uniformity difference. Based on the fact that the internal uniformity difference is less than the surface uniformity difference, the adjustment range of the actual heating rate is determined according to the difference level between the surface uniformity difference and the internal uniformity difference.

[0047] In this embodiment, the threshold for uniformity of surface gap arrangement is set to 85; the threshold for uniformity of internal crystal particle dispersion is set to 90; the initial mixing speed is 300 r / min; the baseline actual heating rate in segment 2 is 0.8℃ / min; the difference level is divided into level 1 (1-3 points), level 2 (4-6 points), and level 3 (≥7 points). The surface gap uniformity of a certain batch of NVP carbon fiber composite material samples was 88 points < 85, the internal crystal particle dispersion uniformity was 92 points ≥ 90, the surface gap uniformity difference was 3 points, corresponding to level 1, and the internal crystal particle dispersion uniformity was 2 points. The cooling rate rules were set as follows: level 1, 0.05℃ / min; level 2, 0.1℃ / min; level 3, 0.15℃ / min. This time, a reduction of 0.1℃ / min is required. The actual heating rate of segment 2 was reduced from 0.8℃ / min to 0.7℃ / min, while the heating rates of other segments remained unchanged. After adjustment, the surface uniformity was retested and found to be 86 points ≥ 85, and the internal uniformity was 91 points, which met the requirements. Another batch of NVP carbon fiber composite material samples showed an internal crystal particle dispersion uniformity of 87 < 90 points, a surface gap arrangement uniformity of 88 points ≥ 85 points, and an internal uniformity difference of 3 points, corresponding to a difference level of 1. Based on the level 1 difference, the speed increase rules were set: level 1 increase by 50 r / min, level 2 increase by 100 r / min, and level 3 increase by 150 r / min. This time, the speed needs to be increased by 50 r / min, increasing the initial mixing speed of the precursor solution and carbon fiber from 300 r / min to 350 r / min, maintaining the mixing time at 30 min. After adjustment, the internal crystal particle dispersion uniformity was retested and found to be 91 points ≥ 90 points, and the surface gap arrangement uniformity was 87 points, meeting the requirements. The NVP carbon fiber composite sample showed an internal crystal particle dispersion uniformity of 84 points and a surface gap arrangement uniformity of 83 points. The internal uniformity difference was calculated to be 90-84=6 points, and the surface uniformity difference was 85-83=2 points. Since the internal uniformity difference was greater than the surface uniformity difference, the total difference between the internal and surface uniformity differences was 6-2=4 points. According to the two-level difference rule, the initial mixing speed should be increased by 100 r / min. The initial mixing speed was increased from 300 r / min to 400 r / min. After adjustment, the internal crystal particle dispersion uniformity was retested and the surface gap arrangement uniformity was 92 points and 84 points, both of which met the standards. The NVP carbon fiber composite sample showed an internal crystal particle dispersion uniformity of 88 points and a surface gap arrangement uniformity of 79 points. The internal uniformity difference was calculated as 90-88=2 points, and the surface uniformity difference was calculated as 85-79=6 points. The difference between the surface uniformity difference and the internal uniformity difference was 6-2=4 points. According to the level 2 difference rule, the actual heating rate was reduced by 0.1℃ / min. The actual heating rate of segment 2 was reduced from 0.8℃ / min to 0.7℃ / min. After adjustment, the surface gap arrangement uniformity was retested and the internal crystal particle dispersion uniformity was 89 points, both of which met the standards.

[0048] In implementation, for single or double non-compliance scenarios involving surface gaps and internal particle dispersion, the two core parameters of heating rate and mixing speed are locked respectively to avoid process fluctuations caused by blind adjustment and improve the targeting of optimization. By quantifying the adjustment range through differential levels, a clear correlation is established between uniformity deviation and parameter adjustment amount, making the adjustment process quantifiable and repeatable. This ensures the accuracy of parameter optimization, reduces the difficulty of operation, and adapts to the needs of industrial production. In double non-compliance scenarios, the dominant defect is addressed first, and the effect is verified by retesting after adjustment to ensure that both uniformity indicators meet the standards, effectively improving the stability of material performance.

[0049] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 sodium-ion battery cathode composite material, characterized in that, include: Raw materials for sodium-ion battery cathode composite materials were selected and pretreated to obtain phosphate, vanadate, sodium salt and carbon fiber precursor materials; Phosphate, vanadate, sodium salt, reducing agent and solution are mixed at an initial mixing rate to obtain a precursor solution. The precursor solution is adsorbed onto a fiber precursor material to obtain a fiber precursor complex. The actual adsorption integrity of the fiber precursor complex is detected, and the adsorption time is determined based on the actual adsorption integrity and the integrity threshold. The fiber precursor composite is dried and sintered to obtain a battery cathode composite material. The sintering heating rate curve is determined based on the target sintering temperature and sintering time. The actual heating rate is obtained based on the sintering heating rate curve. The heating power is adjusted based on the actual heating rate and the heating rate threshold range. The uniformity of surface gap arrangement and internal crystal particle dispersion of the battery cathode composite material are detected. The heating rate is adjusted based on the uniformity of surface gap arrangement and internal crystal particle dispersion. If the adjusted heating rate still does not meet the standard, the initial mixing rate is adjusted. The uniformity of the surface gap arrangement is determined based on the distance between the carbon fiber and the crystal particles, and the uniformity of the internal crystal particle dispersion is determined based on the distance between the crystal particles.

2. The method for preparing sodium-ion battery cathode composite material according to claim 1, characterized in that, The process for detecting the actual adsorption integrity of the fiber precursor complex includes: The fiber precursor complex is weighed to obtain the actual weight of the fiber precursor complex, and the actual adsorption integrity is determined based on the ratio of the actual weight of the fiber precursor complex to the maximum weight of the fiber precursor complex. The maximum weight of the fiber precursor composite is the weight of the precursor solution adsorbed onto the fiber precursor material within a preset adsorption time.

3. The method for preparing sodium-ion battery cathode composite material according to claim 2, characterized in that, The process of determining the adsorption time based on the actual adsorption integrity and the integrity threshold includes: If the actual adsorption integrity is less than the integrity threshold, the adsorption time is extended based on the difference between the integrity threshold and the actual adsorption integrity. If the actual adsorption integrity is greater than or equal to the integrity threshold, the current adsorption duration is maintained.

4. The method for preparing sodium-ion battery cathode composite material according to claim 3, characterized in that, The process of obtaining the actual heating rate based on the sintering heating rate curve includes: The sintering heating rate curve is segmented based on the inflection point to obtain a segmented sintering heating rate curve. The actual heating rate of the corresponding segmented curve is then determined based on the segmented sintering heating rate curve.

5. The method for preparing sodium-ion battery cathode composite material according to claim 4, characterized in that, The process of adjusting the heating power based on the actual heating rate and the heating rate threshold range includes: If the actual heating rate is less than the minimum value of the heating rate threshold range, the heating power is increased based on the difference between the minimum value of the heating rate threshold range and the actual heating rate. If the actual heating rate is within the heating rate threshold range, then maintain the current heating power; If the actual heating rate is greater than the maximum value of the heating rate threshold range, then the heating power is reduced based on the difference between the actual heating rate and the maximum value of the heating rate threshold range. Only when the actual heating rate is determined to be outside the heating rate threshold range, the actual heating rate of the continuous sintering heating rate segmented curve is selected for comparison to obtain the actual increase in heating rate. Based on the comparison result between the actual increase in heating rate and the heating rate increase threshold range, the adjustment value of heating power is determined.

6. The method for preparing sodium-ion battery cathode composite material according to claim 5, characterized in that, The process of determining the adjustment value of heating power based on the comparison between the actual increase in heating rate and the threshold range of the increase in heating rate includes: Based on the fact that the actual increase in the heating rate is within the threshold range of the increase in the heating rate, the adjustment value is adjusted according to the initial value. The heating power is adjusted based on the difference between the actual increase in heating rate and the actual increase in heating rate, since the actual increase in heating rate is less than the minimum value of the threshold range for increase in heating rate. Based on the fact that the actual increase in heating rate is greater than the maximum value of the heating rate increase threshold range, the adjustment value of heating power is reduced according to the difference between the actual increase in heating rate and the maximum value of the heating rate increase threshold range. The adjustment value is a reference value for each change in heating power.

7. The method for preparing sodium-ion battery cathode composite material according to claim 6, characterized in that, The process of detecting the uniformity of surface gap arrangement in battery positive electrode composite materials includes: The distance between carbon fibers and crystal particles on the surface of the battery cathode composite material is detected to obtain several carbon crystal distances. The uniformity of surface gap arrangement is determined based on the comparison results between the carbon crystal distances and the standard carbon crystal distances. The number of carbon crystal distances is determined based on the comparison between the carbon crystal distance and the standard carbon crystal distance, and the uniformity of surface gap arrangement is determined based on the number of carbon crystal distances and the carbon crystal distance threshold. If the number of carbon crystal distances is less than or equal to the threshold number of carbon crystal distances, then the surface gap arrangement uniformity is determined based on the preset standard. If the number of carbon crystal distances is greater than the carbon crystal distance threshold, the uniformity of the standard surface gap arrangement is reduced based on the difference between the number of carbon crystal distances and the carbon crystal distance threshold.

8. The method for preparing sodium-ion battery cathode composite material according to claim 7, characterized in that, The process of detecting the uniformity of internal crystal particle dispersion in battery cathode composite materials includes: The battery cathode composite material is sliced ​​to obtain composite material slices. The dispersion distance between crystal particles is determined based on the composite material slices to determine the particle distance. The number of particle distances is determined based on the comparison result between the particle distances and the particle distance threshold. The uniformity of internal crystal particle dispersion is determined based on the number of particle distances and the particle distance number threshold. If the particle distance is less than or equal to the particle distance threshold, the internal crystal particle dispersion uniformity is determined based on the preset standard. If the number of particle distances is greater than the particle distance threshold, the uniformity of internal crystal particle dispersion is determined based on the number of particle distances and the particle distance threshold.

9. The method for preparing sodium-ion battery cathode composite material according to claim 8, characterized in that, The process of adjusting the heating rate includes: The reduction in the actual heating rate is determined based on the fact that the surface gap uniformity is less than the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is greater than or equal to the internal crystal particle dispersion uniformity threshold. Based on the fact that the surface gap uniformity is greater than or equal to the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is less than the internal crystal particle dispersion uniformity threshold, the reduction in the actual heating rate is determined by the difference between the internal crystal particle dispersion uniformity threshold and the internal crystal particle dispersion uniformity. Based on the fact that the surface gap uniformity is less than the surface gap uniformity threshold and the internal crystal particle dispersion uniformity is less than the internal crystal particle dispersion uniformity threshold, the reduction in the actual heating rate is determined according to the difference between the surface gap uniformity and the internal crystal particle dispersion uniformity. Wherein, the difference in surface gap uniformity is the difference between the surface gap uniformity threshold and the surface gap uniformity, and the difference in internal crystal particle dispersion uniformity is the difference between the internal crystal particle dispersion uniformity threshold and the internal crystal particle dispersion uniformity.

10. The method for preparing sodium-ion battery cathode composite material according to claim 9, characterized in that, The process of adjusting the initial mixing speed includes: Based on the fact that the internal uniformity difference is greater than the surface uniformity difference, the increment of the initial mixing rate is determined according to the difference level between the internal uniformity difference and the surface uniformity difference. Based on the fact that the internal uniformity difference is less than the surface uniformity difference, the adjustment range of the actual heating rate is determined according to the difference level between the surface uniformity difference and the internal uniformity difference.

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