Lmfp composite cathode material and preparation method

Abstract

The application relates to the technical field of lithium batteries, in particular to an LMFP composite positive electrode material and a preparation method thereof. The method is used for preparing the LMFP composite positive electrode material by using a composite carbon source, and the composite carbon source comprises sucrose, polyvinyl alcohol and polystyrene microspheres. The method can obtain the LMFP composite positive electrode material with suitable carbon content, uniform particle size distribution, porosity and good electrochemical performance; the method has simple steps, mild conditions, low cost, does not need to introduce toxic chemicals, and has good environmental protection characteristics; the LMFP composite positive electrode material has high energy density, small electrochemical polarization, good rate performance and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to an LMFP composite cathode material and its preparation method. Background Technology

[0002] Society's demand for the development of sustainable energy storage and conversion technologies is increasing. Lithium-ion batteries (LIBs) have gradually become the leader in power solutions for portable electronic devices over the past few decades due to their excellent energy density, long cycle life and low environmental impact. They have also received widespread attention and application due to their stable structure, good cycle performance, environmental friendliness and high safety.

[0003] However, its low energy density, insufficient battery life, and slow charging speed limit its large-scale application in the transportation sector. Compared to LiFePO4, lithium manganese phosphate (LiMnPO4) has a theoretically higher energy density (21% higher) due to its higher operating voltage and similar theoretical capacity, and is considered a next-generation cathode material that can replace LiFePO4 for commercialization.

[0004] Similar to LiFePO4, lithium manganese phosphate has stable phosphate oxygen bonds and an olivine structure, thus releasing almost no oxygen during high-temperature charge and discharge, exhibiting high safety performance. LiFe... x Mn 1-x PO4 (LMFP) is considered a promising replacement for traditional LiFePO4. This is due to the high operating voltage of LMFP (4.1V vs. LiFePO4). + / L i) and a similar theoretical capacity (170mAh·g -1 Furthermore, LMFP possesses a higher energy density than LiFePO4, resulting in superior battery life. Simultaneously, since LMFP does not contain harmful heavy metals such as nickel and cobalt, it reduces negative environmental impact.

[0005] Ideal LiFe x Mn 1-x PO4 electrode materials should possess a porous, aggregated structure at the micrometer scale, which is beneficial for electrode fabrication and improving volumetric energy density. However, existing preparation methods often result in low crystallinity due to variations in carbon sources and preparation parameters, making it difficult to obtain a uniformly distributed porous aggregated structure. This limits the formation of a three-dimensional interconnected conductive network, leading to low electron and ion conduction efficiency, low volumetric energy density of the composite material, and poor specific capacity and rate performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an LMFP composite cathode material and a preparation method thereof.

[0007] The technical scheme for solving the above technical problems is as follows:

[0008] The application provides a preparation method of an LMFP composite positive electrode material.

[0009] Based on the above technical scheme, the application can be further improved as follows.

[0010] Further, the LMFP composite positive electrode material is LiMn 1-x Fe x PO4 / C, and the value of x is 0.2-0.5.

[0011] Further, the method comprises the following steps:

[0012] S1. A manganese source, an iron source and a phosphate salt are weighed according to a proportion, and are mixed with sucrose and polystyrene microspheres by ball milling, and polyvinyl alcohol solution and anhydrous ethanol are added to obtain a precursor slurry;

[0013] S2. The precursor slurry is centrifuged to obtain a solid mixture;

[0014] S3. The solid mixture is dried, calcined, heated and cooled to obtain the LMFP composite positive electrode material.

[0015] Further, the mass ratio of sucrose, polyvinyl alcohol and polystyrene microspheres is 6-10:4-6:4-6.

[0016] Further, the manganese source is manganese oxalate, the iron source is ferrous oxalate, and the phosphate salt is lithium dihydrogen phosphate.

[0017] Further, in the step S1, the manganese source, the iron source and the phosphate salt are first mixed with sucrose and ball milled, then the polystyrene microspheres are added to continue ball milling, and finally the polyvinyl alcohol solution and the anhydrous ethanol are added to continue ball milling.

[0018] Further, in the step S3, the calcination is performed in an argon atmosphere, the temperature of the calcination is 400-440 DEG C, the time of the calcination is 4-6 hours, the temperature of the heating is 630-670 DEG C, and the time of the heating is 6-10 hours.

[0019] Further, the preparation method of the polystyrene microspheres comprises the following steps:

[0020] Mixing polyvinylpyrrolidone and water to obtain a prepolymer mixture; adding styrene monomer into the prepolymer mixture, heating to obtain an emulsion; adding an initiator into the emulsion to make the emulsion undergo a polymerization reaction; after the polymerization reaction is completed, washing, precipitating, and drying to obtain the polystyrene microspheres.

[0021] The application also provides a LMFP composite cathode material prepared by the method.

[0022] The application also provides a lithium battery prepared by the LMFP composite cathode material.

[0023] The application has the following beneficial effects:

[0024] (1) The preparation method of the LMFP composite cathode material can obtain the LMFP composite cathode material with suitable carbon content, uniform particle size distribution, porosity, and good electrochemical performance by using the composite carbon source (sucrose, PVA, and a certain amount of polystyrene microspheres);

[0025] (2) The preparation method of the LMFP composite cathode material is simple, mild, and low in cost, does not need to introduce toxic chemicals, and has good environmental protection characteristics;

[0026] (3) The preparation method of the LMFP composite cathode material provides a reasonable way for designing and preparing other high-energy / power density olivine-based cathode materials;

[0027] (4) The LMFP composite cathode material has high energy density, small electrochemical polarization, good rate performance, and good cycle stability, high reversible capacity at 0.1C and 5C, and high capacity retention rate after 200 cycles at room temperature 0.5C rate;

[0028] (5) The LMFP composite cathode material can effectively shorten the diffusion distance of lithium ions and increase the specific surface area due to the optimized pore structure and small primary particle size, can improve the electron transport capacity and reduce the electrochemical polarization due to the uniform carbon coating, and can ensure the stability of the structure in a long period due to the good crystalline particles and high purity. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The preparation method of the LMFP composite cathode material is porous LiMn 0.8 Fe 0.2 PO4 / C micro-agglomeration preparation process schematic diagram;

[0030] Figure 2In Example 2, 'a' describes the preparation method of the LMFP composite cathode material of the present invention. Different carbon sources, LiMn, are used. 0.8 Fe 0.2 Raman spectra of PO4 / C materials; Figure 2 In Example 2, b represents different carbon sources, Li and Mn. 0.8 Fe 0.2 XRD pattern of PO4 / C sample;

[0031] Figure 3 In Example 3, for the preparation method of the LMFP composite cathode material of the present invention, different carbon sources LiMn were used. 0.8 Fe 0.2 SEM images of PO4 / C materials. Figure 3 In the middle, 'a' represents LMFP-82. Figure 3 In the middle, b represents LMFP-PVA. Figure 3 c stands for LMFP-PS. Figure 3 In the middle, d represents LMFP-PVA-PS;

[0032] Figure 4 In Example 4, a transmission electron microscope image of LMFP-PVA-PS is shown as part of the preparation method of the LMFP composite cathode material of the present invention. Figure 4 The scale bar for 'a' is 100 nm. Figure 4 The scale bar for b is 5 nm;

[0033] Figure 5 In Example 5, for the preparation method of the LMFP composite cathode material of the present invention, different carbon sources LiMn were used. 0.8 Fe 0.2 TG curve of PO4 / C material;

[0034] Figure 6 The XPS analysis chromatogram of Example 6 shows the preparation method of the LMFP composite cathode material of the present invention. Figure 6 In the middle, 'a' represents the full spectrum of LMFP-PVA-PS. Figure 6 In the image, b is the high-resolution XPS spectrum of Mn2p ions. Figure 6 In the image, c represents the high-resolution XPS spectrum of Fe2p ions. Figure 6 In the image, d represents the high-resolution XPS spectrum of C1 s ions. Figure 6 The high-resolution XPS spectrum of O1 s is shown in the image.

[0035] Figure 7 In Example 7, for the preparation method of the LMFP composite cathode material of the present invention, different carbon sources LiMn were used. 0.8 Fe 0.2 Electrochemical performance analysis diagram of PO4 / C material, Figure 7a is the cycle performance at different rates of 0.1C to 5C, Figure 7 b is the performance of 200 cycles at 0.5C rate, Figure 7 c is the charge-discharge curve at 0.1C, Figure 7 d is the charge-discharge curve at different rates of 0.1C to 5C;

[0036] Figure 8 a is the preparation method of the LMFP composite cathode material of the application, in Example 7, different carbon sources LiMn 0.8 Fe 0.2 EIS diagram of the LiFePO4 / C material, Figure 8 b is the different carbon sources LiMn 0.8 Fe 0.2 CV diagram of the LiFePO4 / C material at 0.1mV·s -1 scan rate. DETAILED DESCRIPTION

[0037] The principles and features of the application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the application and are not used to limit the scope of the application.

[0038] The preparation method of the LMFP composite cathode material of the application uses a composite carbon source to prepare the LMFP composite cathode material, and the composite carbon source includes sucrose, polyvinyl alcohol and polystyrene microspheres.

[0039] The preparation method of the LMFP composite cathode material of the application can obtain the LMFP composite cathode material with suitable carbon content, uniform particle size distribution, porosity and good electrochemical performance. The thermal decomposition characteristics of sucrose and polyvinyl alcohol provide uniform carbon coating for each primary particle, and the decomposition of polystyrene microspheres provides necessary pores for the particles. These pores not only facilitate the distribution of electrolyte, but also shorten the diffusion path of lithium ions, laying a foundation for improving the electrochemical performance of the material.

[0040] Preferably, the LMFP composite cathode material is LiMn 1-x Fe x PO4 / C, and the value of x is 0.2-0.5.

[0041] Further preferably, the value of x is 0.2, and the LMFP composite cathode material is LiMn 0.8 Fe 0.2 PO4 / C, and the micro-agglomeration preparation process is as shown in Figure 1 .

[0042] In the synthesis of lithium manganese iron phosphate, the manganese iron ratio, i.e. the molar ratio of manganese and iron, has an important influence on the structure, crystal morphology, electrochemical activity and the like of the material, and further influences the battery performance; when the manganese iron ratio is 8:2, the structure of the prepared material is the most stable, the particles present a micro-agglomeration state, and the material has the optimal electrochemical performance.

[0043] Preferably, the ratio of the total mass of the composite carbon source, the manganese source, the iron source and the phosphate salt is 0.06-0.13:1.

[0044] The preparation method of the LMFP composite cathode material of the application specifically comprises the following steps:

[0045] S1. The manganese source, the iron source and the phosphate salt are weighed according to the ratio, mixed with sucrose and polystyrene microspheres by ball milling, and polyvinyl alcohol solution and anhydrous ethanol are added to obtain a precursor slurry.

[0046] Preferably, the mass ratio of sucrose, polyvinyl alcohol and polystyrene microspheres is 6-10:4-6:4-6.

[0047] Preferably, the manganese source is manganese oxalate (Mn(CH3COO)2), the iron source is ferrous oxalate (Fe(CH3COO)2), and the phosphate salt is lithium dihydrogen phosphate (LiH2PO4).

[0048] Further preferably, when the LMFP composite cathode material is Li Mn 0.8 Fe 0.2 PO4 / C, Mn:Fe:PO is 0.8:0.2:1, specifically, manganese oxalate (Mn(CH3COO)2) is 0.032 mol, ferrous oxalate (Fe(CH3COO)2) is 0.008 mol, and lithium dihydrogen phosphate (LiH2PO4) is 0.04 mol.

[0049] Preferably, the manganese source, the iron source and the phosphate salt are first mixed with sucrose and ball milled, then polystyrene microspheres are added for further ball milling, and finally polyvinyl alcohol solution and anhydrous ethanol are added for further ball milling.

[0050] Further preferably, the manganese source, the iron source and the phosphate salt are first ball milled with sucrose for 5 hours, then polystyrene microspheres are added for ball milling for 3 hours, and finally polyvinyl alcohol is added for ball milling for 2 hours.

[0051] S2. The precursor slurry is centrifuged to obtain a solid mixture.

[0052] S3. The solid mixture is dried, calcined, heated and cooled to obtain the LMFP composite cathode material.

[0053] Preferably, the calcination is carried out in an argon atmosphere, the calcination temperature is 400-440 DEG C, the calcination time is 4-6 hours; the heating temperature is 630-670 DEG C, and the heating time is 6-10 hours.

[0054] In the method of the present application, the polystyrene microspheres used can be commercially available or prepared.

[0055] The method for preparing the polystyrene microspheres comprises the following steps:

[0056] The polystyrene microspheres are prepared by mixing polyvinylpyrrolidone and water to obtain a prepolymer mixture, adding styrene monomers to the prepolymer mixture, heating to obtain an emulsion, adding an initiator to the emulsion to cause polymerization of the emulsion, and washing, precipitating and drying the polystyrene microspheres after the polymerization is completed.

[0057] Preferably, the initiator is V-50, the heating temperature is 70 DEG C, and the heating mode is oil bath. Meanwhile, the polymerization conditions are also 70 DEG C oil bath, and the polymerization is carried out in a nitrogen atmosphere, and the reaction environment needs to be stable and free of oxygen.

[0058] The specific processing steps after the polymerization are completed are as follows: the unreacted monomers and initiators in the reaction system are removed by washing and precipitating with a large amount of water, and the washing is continued until the solution is neutral to ensure the purity of the nanospheres. Finally, the collected polystyrene nanospheres are washed with ethanol, and then dried in a vacuum environment at 60 DEG C overnight to obtain dry nanosphere products.

[0059] The LMFP composite positive electrode material of the present application is prepared by the above method.

[0060] The LMFP composite positive electrode material has high energy density, small electrochemical polarization, good rate performance and good cycle stability. 0.8 Fe 0.2 PO4 / C has reversible capacities of 151.3 mAh·g -1 and 106.2 mAh·g -1 at 0.1C and 5C, respectively, and a capacity retention rate of 96.6% after 200 cycles at a rate of 0.5C at room temperature.

[0061] The method of the present application can effectively shorten the diffusion distance of lithium ions and increase the specific surface area due to the optimized pore structure and small primary particle size, and can improve the electron transport capacity and reduce the electrochemical polarization due to the uniform carbon coating, and the good crystalline particles and high purity ensure the stability of the structure in a long period. This provides a reasonable way for designing and preparing other high energy / power density olivine-based positive electrode materials.

[0062] The lithium battery of the present application is prepared by using the LMFP composite cathode material as described above.

[0063] The present application is illustrated by specific examples as follows.

[0064] Example 1 Preparation of LMFP composite material

[0065] In this example, the LMFP composite material is prepared by the method of the present application, and the specific process is as follows:

[0066] (1) Preparation of polystyrene microspheres.

[0067] Take 0.16 grams of polyvinylpyrrolidone (PVP) and dissolve it in 100 milliliters of deionized water, and stir vigorously to ensure uniform dispersion. Maintain the stirring of the solution for 30 minutes under a nitrogen atmosphere to form a prepolymer mixture.

[0068] Add 10 milliliters of styrene monomer to the above mixture and place it in a 70°C oil bath for further heating for 30 minutes, during which the mixture turns into a white emulsion. This process is the initial stage of emulsion polymerization, preparing for the polymerization reaction. Then slowly add 1.3 mol of an aqueous solution containing 0.2 grams of V-50 initiator to the emulsion, and the entire polymerization reaction is carried out at 70°C under a nitrogen atmosphere to ensure a stable reaction environment and no oxygen participation, for 24 hours. After the polymerization is completed, the precipitate is washed with a large amount of water to remove the unreacted monomers and initiators in the reaction system, and the washing continues until the solution is neutral to ensure the purity of the nanospheres. Finally, the collected polystyrene nanospheres are washed with ethanol, and then dried in a vacuum environment at 60°C overnight to obtain the dry nanosphere product.

[0069] (2) Preparation of LiMn 0.8 Fe 0.2 PO4 / C composite cathode material

[0070] First, 0.3 grams of polyvinyl alcohol is dissolved in 5 milliliters of deionized water, and according to the stoichiometric ratio: manganese source: iron source: phosphate (Mn: Fe: PO4) = 0.8: 0.2: 1, 0.032 mol of manganese oxalate (Mn(CH3COO)2), 0.008 mol of ferrous oxalate (Fe(CH3COO)2), and 0.04 mol of lithium dihydrogen phosphate (LiH2PO4) are weighed.

[0071] The above substances and sucrose are added to a zirconium oxide ball mill jar for ball milling. After 5 hours of ball milling, polystyrene microspheres are added to the ball mill jar for continuous ball milling for 3 hours, and the prepared polyvinyl alcohol solution and 25 milliliters of anhydrous ethanol are added, and then the ball milling is continued for another 2 hours.

[0072] After centrifugation of the precursor slurry, the solid mixture was dried in vacuum at 80 °C for 1 h. After complete grinding of the precursor, it was calcined in a tube furnace under argon atmosphere at 420 °C for 5 h, then heated to 650 °C for 8 h, and then naturally cooled to room temperature to obtain the lithium manganese phosphate sample, which was labeled as LMFP-PVA-PS.

[0073] In this example, sucrose was 0.16 g, polyvinyl alcohol was 0.1 g, and polystyrene microspheres were 0.1 g.

[0074] In addition, as a comparison, LMFP-82, LMFP-PVA, and LMFP-PS were prepared using the same procedure and parameters, except that LMFP-82 used only sucrose as the carbon source, the amount of sucrose was 0.36 g, LMFP-PVA used only polyvinyl alcohol as the carbon source, the amount of polyvinyl alcohol was 0.22 g, and LMFP-PS used only polystyrene microspheres as the carbon source, the amount of polystyrene microspheres was 0.25 g.

[0075] XRD and Raman analysis of the composite material of Example 2

[0076] Figure 2 Table a is the lithium manganese phosphate synthesized using different carbon sources prepared in the examples 0.8 Fe 0.2 Raman spectra of the PO4 / C samples. Raman spectroscopy revealed that the Li Mn 0.8 Fe 0.2 PO4 / C composite material exhibited significant characteristic vibration peaks at 1330 cm -1 and 1590 cm -1 , which corresponded to the defect-dense region of amorphous carbon (D band) and the planar vibration of graphitic carbon (G band), respectively. The intensity ratio of the D band and the G band (I D / I G ) was used as a quantitative indicator to evaluate the degree of graphitization of the carbon material, where a lower I D / I G ratio reflected a relatively higher content of sp2 hybridized carbon, which was associated with higher electrical conductivity and degree of graphitization.

[0077] The I D / I G ratio of LMFP-PVA-PS, LMFP-PVA, LMFP-PS, and LMFP-82 was 0.89, 0.90, 0.97, and 1.08, respectively, indicating that LMFP-PVA-PS exhibited the highest degree of graphitization, which was indicative of excellent electrical conductivity. In addition, the Raman scattering peak near 950 cm -1 was weak, which was attributed to PO4 3-Anionic vibration features peaks, indicating the uniform distribution of the anion in the composite material. Considering the close mass fraction of carbon in the four samples, the low I D / I G The ratio also can explain the more uniform carbon distribution.

[0078] Figure 2 b is the X-ray diffraction (XRD) pattern of each sample. According to the pattern, it can be seen that the above-mentioned composite material has a single orthorhombic olivine structure, and each main diffraction peak is highly consistent with the standard PDF card 74-0375, and no other impurity phase is observed. The sharpness and high intensity of the diffraction peak characterize the high crystallinity of the sample. The lack of identifiable carbon diffraction peaks indicates that the carbon introduced during synthesis exists in a disordered state, which can be obtained through the carbonization process. From the entire XRD spectrum, it can be seen that the added carbon has no effect on the lattice structure of LiMn 0.8 Fe 0.2 PO4 / C.

[0079] SEM analysis of the composite material of Example 3

[0080] Figure 3 FESEM images of LiMn 0.8 Fe 0.2 PO4 / C composite materials synthesized using different carbon sources.

[0081] In LMFP-82, the aggregation of non-uniform spherical nanoparticles shows a potential disordered growth mechanism during the synthesis process, which can affect the penetration of the electrolyte and the transmission path of lithium ions.

[0082] In LMFP-PS, the fusion of particles and the appearance of porous structure indicate a more dynamic interaction between the decomposition of carbon source and the solid precursor during the synthesis process.

[0083] In LMFP-PVA, the particles exhibit more distinct boundaries, indicating potential differences in the use of carbon sources during the synthesis process in terms of thermal decomposition and material morphology control.

[0084] The uniform particle size and pore structure shown by the LMFP-PVA-PS sample are the result of highly ordered crystalline growth and precise thermal treatment control, which is beneficial to the full penetration of the electrolyte and the rapid diffusion of lithium ions in the electrode material. These structural differences, including particle size, porosity, and the continuity of the carbon layer, have a profound impact on the electrochemical performance of the material. The thermal decomposition characteristics of sucrose and polyvinyl alcohol provide a uniform carbon coating for each primary particle, while the decomposition of polystyrene microspheres provides the necessary pores for the particles. These pores not only facilitate the distribution of the electrolyte, but also shorten the diffusion path of lithium ions, laying the foundation for improving the electrochemical performance of the material.

[0085] Example 4: TEM analysis of composite materials

[0086] To further investigate the microstructure of LMFP-PVA-PS nanoparticles, a detailed microscopic characterization was performed using transmission electron microscopy (TEM), specifically as follows: Figure 4 As shown, the LMFP-PVA-PS particles are uniformly distributed at a size of approximately 100 nm and are tightly connected by a bridging structure of conductive carbon layers. This in-situ carbon coating not only connects the surface but also penetrates deep into the particle interior, forming a continuous conductive network. This carbon network provides an efficient electron transport path, ensuring immediate contact with the battery's reactive active sites, effectively reducing the migration distance of lithium ions within the electrode, reducing electrochemical polarization, and increasing the number of available active sites. Detailed observation also reveals that the composite material exhibits a small particle size and slight agglomeration. The carbon layer on the particle surface shows good integrity and continuity, with uniform layer thickness, consistent with the aforementioned scanning electron microscopy (SEM) analysis.

[0087] Example 5: TG Analysis of Composite Materials

[0088] Thermogravimetric analysis (TGA) was performed on the samples in an air atmosphere to determine the carbon content of the materials. Figure 5 In the TGA curves shown, the temperature was increased from room temperature to 800℃ (heating rate of 10℃ / min). The analytical results showed that the carbon contents of the LMFP-PVA-PS, LMFP-PVA, LMFP-PS, and LMFP-82 samples were 4.77%, 4.53%, 4.86%, and 4.36%, respectively.

[0089] XPS Analysis of Composite Materials in Example 6

[0090] Figure 6 This is the XPS spectrum of the LMFP-PVA-PS sample. By analyzing the peaks in the spectrum, the chemical environment of each element in the sample can be determined. With the C1s peak set as a reference energy of 284.8 eV, Li 1s, P2p, and O 1s appear at 55.5 eV, 133.9 eV, and 531.0 eV, respectively. These energy positions correspond to the characteristic energy states of lithium, phosphorus, and oxygen in the composite material. In particular, the P2p position indicates that phosphorus exists in the form of phosphate, which is consistent with the chemical composition of LiFePO4. The LMFP-PVA-PS sample exhibits Mn2p at 653.6 eV. 1 / 2 The spin-orbit splitting component and spin-orbit splitting.

[0091] Example 7 Electrochemical Performance Analysis of Composite Materials

[0092] The electrochemical properties of the LMFP / C series materials were systematically characterized to investigate the influence of different carbon sources on their performance.

[0093] Figure 7 Figure a is the rate performance of the materials synthesized with different carbon sources. As can be seen from the figure, the LMFP-PVA-PS material exhibits excellent performance under high-rate discharge conditions, with less energy attenuation and rapid recovery of the initial capacity when the rate is reduced. This phenomenon indicates that the LMFP-PVA-PS material has excellent electronic conductivity and ionic conductivity. In contrast, LMFP-82 and LFMP-PVA exhibit a sharp capacity drop when the current density is increased, indicating that their performance under high-rate discharge conditions is insufficient.

[0094] Figure 7 Figure b is the cycle stability of the materials synthesized with different carbon sources. After 200 charge-discharge cycles at a rate of 0.5C, the capacity retention rate of the LMFP-PVA-PS reached 97.6%, which is significantly higher than that of the other materials.

[0095] Figure 7 Figure c is the charge-discharge curve of the materials synthesized with different carbon sources at a rate of 0.1C. All materials exhibit characteristic redox peaks at 3.6 / 3.5V and 4.1 / 4.0V, corresponding to the electrochemical activity of Mn. LMFP and LMFP-PS exhibit lower specific capacity and significant potential polarization, indicating poor conductivity and lithium ion transport ability caused by a single carbon source.

[0096] Figure 7 Figure d shows the charge-discharge curves recorded at different rates for LMFP-PVA-PS. The reversible discharge capacity of LMFP-PVA-PS is 151.3, 134.5, 130.6, 124.7, 115.8 and 105.9 mAh·g -1 , respectively, at rates of 0.1, 0.2, 0.5, 1, 2 and 5C. In the charge-discharge curve at a rate of 0.1C, the LMFP-PVA-PS sample exhibits a high discharge capacity of 151.3 mAh·g -1 , and the performance at different rates is stable. After high-rate charge-discharge cycling, the specific capacity can be well recovered when the current density falls to a low rate, confirming that the material has excellent structural stability even at high current density. From the perspective of material synthesis, the use of a composite carbon source in the LMFP-PVA-PS sample is crucial for the formation of its microstructure, especially the electronic and lithium ion transport pathways. This composite strategy achieves precise microstructure control by controlling the decomposition of the carbon source, thereby optimizing the electrochemical performance.

[0097] Figure 8 Figure a is the EIS graph of the composite material,Figure 7 The middle b is the composite material at 0.1 mV·s -1 The cyclic voltammetry curves at the scan rate of 0.1 mV·s-1. EIS analyzes the impedance characteristics of LMFP-82, LMFP-PS, LFMP-PVA and LMFP-PVA-PS in the frequency range of 0.01 Hz to 100 kHz. The fitted charge transfer resistance (R CT ) values are 335.4 Ω, 347.1 Ω, 423.8 Ω and 597.1 Ω, respectively corresponding to the above four composites. LFMP-PVA-PS exhibits the optimal charge transfer performance, indicating a lower impedance in the electrochemical reaction, which is consistent with its high reversibility and excellent rate response.

[0098] This reduced impedance can be traced back to the micro-agglomerate structure formed under the addition and regulation of the organic carbon source, which provides a more convenient migration channel for lithium ions. The microstructure characteristics are positively correlated with the electrochemical performance advantages of the LFMP-PVA-PS electrode, confirming the importance of microstructure regulation in material design.

[0099] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a LMFP composite cathode material, characterized in that, The LMFP composite cathode material is prepared by using a composite carbon source, and the composite carbon source comprises sucrose, polyvinyl alcohol and polystyrene microspheres. The LMFP composite positive electrode material is LiMn 1-x Fe x PO4 / C, the value of x is 0.2-0.5; The preparation method comprises the following steps: S1, manganese source, iron source and phosphate salt are weighed according to a proportion, the manganese source, the iron source and the phosphate salt are first mixed with sucrose and then ball milled, the polystyrene microspheres are then added and ball milled, finally, polyvinyl alcohol solution and anhydrous ethanol are added and ball milled, thereby obtaining a precursor slurry; The mass ratio of sucrose, polyvinyl alcohol and polystyrene microspheres is 6-10:4-6:4-6; S2, the precursor slurry is centrifuged to obtain a solid mixture; S3, the solid mixture is dried, calcined, heated and cooled to obtain the LMFP composite cathode material; The calcination is performed in an argon atmosphere, the temperature of the calcination is 400-440 DEG C, and the time of the calcination is 4-6 hours; the temperature of the heating is 630-670 DEG C, and the time of the heating is 6-10 hours.

2. The method of claim 1, wherein the LMFP composite cathode material is prepared by the following steps: The manganese source is manganese oxalate, the iron source is ferrous oxalate, and the phosphate salt is lithium dihydrogen phosphate. ​ 3. A method for preparing an LMFP composite cathode material according to claim 1 or 2, characterized in that, The preparation method of the polystyrene microspheres comprises the following steps: Polyvinylpyrrolidone and water are mixed to obtain a prepolymer mixture, styrene monomers are added to the prepolymer mixture and heated to obtain an emulsion, an initiator is added to the emulsion to make the emulsion undergo a polymerization reaction, and after the polymerization reaction is completed, the polystyrene microspheres are obtained by washing, precipitating and drying.

4. A LMFP composite cathode material, characterized in that, The LMFP composite cathode material is prepared by using the method according to any one of claims 1-3.

5. A lithium battery, characterized by The LMFP composite cathode material is prepared by using the method according to any one of claims 1-3.

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