A multi-level pore regular square high-density lithium iron phosphate cathode material, a preparation method and application thereof

Abstract

This invention relates to the field of battery materials technology, specifically to a hierarchical porous, regularly square-shaped, high-compact lithium iron phosphate cathode material, its preparation method, and its applications. The cathode material comprises micron-sized secondary particles with a regularly square morphology, containing continuously interconnected mesoporous channels formed by primary nanocrystal aggregation, and the olivine lattice is doped with metal ions. This material is prepared by inducing liquid-phase co-precipitation with a composite crystal-directing agent combined with a three-stage sintering process and simultaneous carbon coating, achieving a powder compaction density > 3.0 g / cm³. 3 Furthermore, a dual-mode synergistic vibration coating and segmented high-pressure compaction rolling process were used to fabricate the positive electrode sheet, achieving a compaction density > 3.1 g / cm³. 3 The breakage rate is ≤0.15%. This invention achieves high compaction, high rate capability, and low breakage rate through synergistic innovation of regular square morphology, multi-level porous structure, lattice doping, and electrode forming process, significantly improving the volumetric energy density and processing performance of lithium iron phosphate materials, making them suitable for power lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a multi-level porous regular square high-pressure lithium iron phosphate cathode material, its preparation method, and its application. Background Technology

[0002] Lithium iron phosphate (LFP) has become the mainstream cathode material for power / energy storage lithium batteries due to its long cycle life, low cost, and good safety. However, its low compaction density is a core bottleneck in improving its volumetric energy density. Conventional LFP is mostly spherical or irregular in shape, with a powder compaction density of only 2.4~2.7 g / cm³. 3 The compaction density of the electrode sheets is difficult to exceed 3.0 g / cm³. 3 Its volumetric energy density is much lower than that of ternary materials.

[0003] The existing technology has the following core defects: 1. Conventional nanocrystalline agglomerated spherical LFP technology: Although the rate performance problem is solved by constructing micron-sized secondary particles with nanocrystals, the spherical particles are point-contact stacked, resulting in high interparticle porosity, low upper limit of intrinsic compaction density of the powder, and difficulty in exceeding 3.0 g / cm³ in electrode compaction density. 3 The increase in volumetric energy density is limited; and under high pressure, the spherical secondary particles are easily broken, the internal pore structure collapses, and the cycle life is greatly reduced.

[0004] 2. Micron-level large single crystal LFP technology: Dense single crystal particles are prepared by high-temperature sintering to improve compaction density. However, the lithium-ion solid-phase diffusion path of single crystal particles is long, resulting in a severe degradation of rate performance. It can only be adapted to low-rate energy storage scenarios of 0.2C~0.5C and cannot meet power requirements. Moreover, single crystal particles are brittle and are easily broken under high-pressure compaction rollers, causing the conductive network to break.

[0005] 3. High-pressure rolling process optimization technology: Simply increasing the rolling pressure and reducing the roll gap to achieve high compaction results in an initial compaction density of only 1.8~2.0 g / cm³ for conventionally coated dry electrode sheets. 3 During the rolling process, the electrode deformation exceeded 40%, the internal stress increased sharply, and the compaction density exceeded 2.7 g / cm³. 3 The breakage rate after the breakage rate soared, and the mass production processing yield was less than 80%. At the same time, excessive rolling can cause active particles to break and conductive / ion transport channels to collapse, resulting in a significant reduction in battery cycle life.

[0006] 4. Particle size gradation modification technology: The bulk density is increased by combining large and small particles, but small particles tend to fill the gaps between large particles, resulting in an overall low porosity of the electrode, which hinders electrolyte wetting and reduces rate performance. Moreover, it cannot solve the core problem of electrode breakage under high pressure.

[0007] In summary, existing technologies have failed to systematically resolve the contradiction between high compaction and high rate capability, long cycle life, low breakage rate, and mass production feasibility of lithium iron phosphate materials. There is an urgent need to develop a completely new technical solution that innovates the entire chain from the intrinsic structural design of the material to the electrode processing technology, so as to achieve a comprehensive breakthrough in the overall performance of lithium iron phosphate materials. Summary of the Invention

[0008] Against this backdrop, the present invention aims to provide a multi-level porous, regular square-shaped, high-compact lithium iron phosphate cathode material, its preparation method, and its application. Through a synergistic technology of precise control of the regular square morphology and construction of internal ion transport channels, an integrated solution is formed, combining intrinsic high compaction of the material, rapid internal ion transport, and a novel electrode forming process. Simultaneously, it achieves: ① Powder compaction > 3.0 g / cm³. 3 Electrode compaction > 3.1 g / cm³ 3 ② It is still suitable for medium-to-high rate scenarios of 1~3C even with micron-sized particles; ③ The electrode structure is intact and the electrochemical performance decays little under high pressure.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a hierarchical, regular square-shaped high-pressure lithium iron phosphate cathode material, the cathode material comprising micron-sized secondary particles with a regular square morphology, the micron-sized secondary particles having a hierarchical porous structure, the hierarchical porous structure comprising continuous through-hole mesoporous channels formed by primary nanocrystal aggregation; the olivine lattice of the cathode material is doped with metal ions.

[0010] As a preferred embodiment of the present invention, the positive electrode material has at least one of the following characteristics a1) to a5): a1) The metal ion is selected from at least one of Mg ions and Zr ions; a2) The particle size of the micron-sized secondary particles is 2-5 μm; where, particle size <2 μm: the packing porosity increases and the compaction density cannot meet the standard; >5 μm: the particle mechanical strength decreases and the particles are easily broken under high compaction; a3) The pore size of the continuous through-hole mesoporous channel is 2-10 nm; mesopores <2 nm: electrolyte wetting is hindered; >10 nm: particle density decreases, compaction density decreases; a4) The particle size of the primary nanocrystals is 50-100 nm; a5) The compacted density of the cathode material powder is >3.0 g / cm³. 3 Lithium-ion diffusion coefficient ≥10 -12 cm 2 / s.

[0011] Secondly, the present invention provides a method for preparing the aforementioned hierarchical porous regular square high-pressure lithium iron phosphate cathode material, comprising the following steps: Preparation of composite crystal-type directing agent solution; A mixed solution is prepared by mixing lithium source, iron source and phosphorus source in stoichiometric ratio, and the composite crystal type guiding agent solution and mesoporous pore-forming agent are added. The liquid phase co-precipitation reaction is carried out under constant temperature conditions to obtain precursor slurry. A metal ion dopant is added to the precursor slurry, dispersed evenly, and then spray-dried to obtain precursor powder; The precursor powder was sintered in three stages under an inert atmosphere, while a carbon-containing gas source was introduced for in-situ carbon coating, and then cooled in the furnace to obtain lithium iron phosphate cathode material.

[0012] As a preferred embodiment of the present invention, the composite crystal-directing agent is a mixture of sodium citrate and EDTA-2Na, with a mass ratio of 1:(0.5-0.8), and the concentration of the composite crystal-directing agent solution is 0.5-1 mol / L; wherein, the parameters affect the following: EDTA-2Na content < 0.5: insufficient control effect on prismatic morphology; EDTA-2Na content > 0.8: particles are prone to agglomeration, and monodispersity decreases.

[0013] And / or, the Li:Fe:P molar ratio of the lithium source, iron source, and phosphorus source is (1.01-1.05):1:1, and the total metal ion concentration of the mixed solution is 1.5-2 mol / L; the amount of the composite crystal form guiding agent added is 3-5% of the total mass of the precursor, and the amount of the mesoporous pore-forming agent is a cationic surfactant added is 1-2% of the total mass of the precursor; the temperature of the liquid phase co-precipitation reaction is 60-80℃, and the reaction time is 4-6h; wherein, the parameters affect: composite crystal form guiding agent addition <3%: unable to form a regular square morphology; >5%: particle size is too small, and the compaction density decreases; pore-forming agent <1%: unable to form continuous mesopores; >2%: insufficient particle density, and the compaction density decreases; reaction temperature <60℃: incomplete crystal growth; >80℃: particles are prone to agglomeration.

[0014] And / or, the doping amount of the metal ions is 0.2-0.5% of the molar amount of iron; the inlet temperature of the spray dryer is 180-200℃, and the outlet temperature is 80-90℃; wherein, the parameters have the following effects: inlet temperature <180℃: insufficient powder drying; >200℃: powder morphology damage and severe agglomeration.

[0015] And / or, the three-stage sintering specifically comprises: a first stage of low-temperature pre-sintering at 300-350℃ for 1-3 hours; a second stage of medium-temperature sintering at 600-650℃ for 3-5 hours; and a third stage of high-temperature sintering at 750-800℃ for 5-7 hours; the carbon-containing gas source is acetylene gas, with a volume fraction of 0.5-1%. The parameters affecting the process are as follows: pre-sintering temperature <300℃: incomplete removal of the pore-forming agent, preventing mesopore formation; >350℃: mesopores easily collapse; high-temperature sintering <750℃: inability to form a regular square morphology; >800℃: abnormal grain growth, leading to a decrease in rate performance.

[0016] In the above scheme, the morphology control and intrinsic high-pressure compaction mechanism are as follows: the sodium citrate + EDTA-2Na composite directing agent is selectively adsorbed on specific crystal faces of lithium iron phosphate crystals, inducing the crystals to grow isotropically into regular square morphologies; when square particles are stacked, there is surface contact, which reduces the packing porosity by more than 30% compared to the point contact of conventional spherical particles, thus achieving ultra-high pressure compaction density from the intrinsic material properties.

[0017] Multi-level structure and ion transport mechanism: The multi-level structure of micron particles is constructed using nanocrystals, which not only retains the high compaction advantage of micron particles, but also shortens the lithium ion solid-phase diffusion path from the micron level to the nano level through 50~100nm single nanocrystals + continuous through-hole mesoporous channels, and improves the diffusion coefficient by more than one order of magnitude, thus achieving compatibility between high compaction and high rate.

[0018] Doping Modification and Anti-Fragmentation Mechanism: Mg 2+ / Zr 4+ Uniform doping into the olivine lattice enhances the rigidity of the lattice framework, increasing the compressive strength of the particles by more than 40%, ensuring that secondary particles do not break and mesoporous channels do not collapse under ultra-high pressure compaction; at the same time, it suppresses Li / Fe cation mixing, widens lithium-ion diffusion channels, and improves intrinsic electronic conductivity, thus balancing structural stability and electrochemical performance.

[0019] Thirdly, the present invention provides a high-compact lithium iron phosphate cathode sheet, comprising the cathode material as described in claim 1; the compaction density of the cathode sheet is >3.1 g / cm³. 3 The breakage rate is ≤0.15%.

[0020] Fourthly, the present invention provides a method for preparing the high-pressure lithium iron phosphate positive electrode sheet, comprising the following steps: A cathode slurry is prepared by mixing cathode material, composite conductive agent, binder and organic solvent and dispersing under vacuum. The positive electrode slurry is coated onto the surface of the current collector using a dual-mode synergistic vibration coating process, and then dried under vacuum to obtain a dry electrode sheet. The dry electrode sheet is subjected to segmented high-pressure compaction rolling to obtain a positive electrode sheet with a compaction density.

[0021] As a preferred embodiment of the present invention, the mass ratio of the positive electrode material, the composite conductive agent, and the binder is (95-98):(0.2-3):(1.2-3); the solid content of the positive electrode slurry is 55-70%, and the viscosity is 5000-8000 mPa·s.

[0022] And / or, the dual-mode synergistic vibration coating adopts a slot extrusion coating method; the dual-mode vibration includes low-frequency vibration and high-frequency vibration, the low-frequency vibration frequency is 10-20Hz, the high-frequency vibration frequency is 50-80Hz, and the amplitude is 0.1-0.3mm; the vacuum drying temperature is 120℃, and the drying time is 10-14h; wherein, the parameters have the following effects: low frequency < 10Hz / high frequency < 50Hz: insufficient particle orientation and arrangement effect; low frequency > 20Hz / high frequency > 80Hz: leveling defects are prone to occur in the wet film; amplitude < 0.1mm: insufficient densification effect; > 0.3mm: uneven wet film thickness.

[0023] And / or, the segmented high-pressure compaction rolling process specifically involves: first, low-pressure pre-compression at 200-300 MPa to achieve preliminary densification, followed by high-pressure fine compaction at 800-1000 MPa to obtain a high-pressure compacted positive electrode sheet. Regarding parameter influence: single high-pressure rolling can easily cause electrode sheet cracking, powder shedding, and collapse of mesopore channels; segmented rolling can protect the internal structure of the material.

[0024] As a preferred embodiment of the present invention, the initial compaction density of the dried electrode sheet before segmented roller pressing is 2.4-2.6 g / cm³. 3 Roll forming deformation ≤25%, mass production yield ≥99%.

[0025] In the above scheme, the electrode processability optimization and band breakage suppression mechanism are as follows: dual-mode vibration coating induces the directional and compact arrangement of regular square particles, achieving an initial compaction density of dry electrode from the conventional 1.8-2.0 g / cm³. 3 Increased to 2.4-2.6 g / cm³ 3 The accompanying mass-production universal gradient drying process eliminates internal stress in the electrode sheets, and the rolling process only requires a deformation of ≤25% to achieve 3.1 g / cm³. 3 The target compaction significantly reduces deformation by more than 40% compared to conventional processes, resulting in a substantial reduction in internal stress in the electrode sheet. This fundamentally solves the industry pain point of electrode sheet cracking and strip breakage under high-pressure compaction. At the same time, low-deformation rolling can prevent the breakage of active particles and protect the integrity of the internal mesoporous channels and conductive network.

[0026] The synergistic mechanism of densification and conductivity: Three-stage sintering eliminates large pores inside the particles, bulk doping stabilizes the olivine lattice and improves the mechanical strength of the particles; simultaneous carbon coating on the surface and mesoporous inner walls constructs a three-dimensional continuous conductive network, which maintains the integrity of the electronic pathway even after high-pressure compaction, thus balancing material density and electronic conduction efficiency.

[0027] Fifthly, the present invention provides a lithium-ion battery comprising the aforementioned high-pressure lithium iron phosphate positive electrode sheet.

[0028] Sixthly, the present invention provides a system for preparing the aforementioned high-pressure lithium iron phosphate positive electrode sheet, comprising: A coating apparatus, wherein the coating apparatus integrates a vibration system for applying vibrations comprising at least two different frequencies to the wet film to be coated during the coating process; Drying device, used to dry coated electrode sheets; A roller pressing device configured to perform a segmented roller pressing process, the segmented roller pressing process including at least a low-pressure pre-pressing station and a high-pressure fine pressing station.

[0029] Compared with existing technologies, this invention pioneers a nanocrystalline structure for LFP materials, which consists of multi-level porous, regularly shaped square micron-sized particles. Combined with a full-chain electrode processing technology encompassing lattice doping for anti-breakage, dual-mode vibration coating for pre-densification, mass-production-ready low-stress gradient drying, and segmented low-stress rolling, this invention achieves comprehensive material-process synergistic innovation. The specific advantages and beneficial effects include: On the materials side: First, this invention utilizes a sodium citrate and EDTA-2Na composite crystal-directing agent to selectively adsorb specific crystal faces, inducing isotropic growth of lithium iron phosphate into regular square micron-sized secondary particles of 2-5 μm. These square particles are tightly packed in a surface-contact manner, resulting in a porosity reduction of over 30% compared to the point-contact packing of conventional spherical particles, thus breaking through the upper limit of compaction density at the intrinsic material level. The compaction density of the powder in this invention is >3.0 g / cm³. 3 This technology achieves a more than 10% improvement over conventional commercial spherical LFPs, laying the foundation for ultra-high compaction of the electrode. Secondly, this invention employs a multi-level structural design that uses 50-100nm primary nanocrystal clusters to construct micron-sized secondary particles, while simultaneously using a cationic surfactant pore-forming agent to form continuous, interconnected mesoporous channels of 2-10nm within the particles. This structure retains the high compaction advantages of micron-sized particles while shortening the lithium-ion solid-phase diffusion path from the micron level to the nanometer level, resulting in a lithium-ion diffusion coefficient ≥10. -12 cm 2 / s, which is more than an order of magnitude higher than that of conventional LFP. The final result is 3.1 g / cm³. 3Under ultra-high pressure conditions, the capacity retention rate is ≥88% at 1C and ≥82% at 2C, making it suitable for medium-to-high rate power scenarios at 1-3C, completely breaking through the limitation that large single-crystal LFPs can only be adapted to low rate scenarios at 0.2-0.5C. Finally, this invention utilizes Mg... 2+ / Zr 4+ Uniform doping into the olivine lattice enhances the rigidity of the lattice framework, increasing the compressive strength of the particles by over 40%, preventing secondary particles from breaking and internal mesoporous channels from collapsing under ultra-high pressure compaction. Furthermore, it suppresses Li / Fe cation mixing, further widening lithium-ion diffusion channels and improving intrinsic electronic conductivity. Compared to the undoped Comparative Example 3, the electrode bandgap rate of the material of this invention is reduced from 0.35% to below 0.15%, and the capacity retention rate after 1000 cycles at 0.5C is increased from 88.9% to over 92%, achieving a balance between structural stability and electrochemical performance.

[0030] On the process side: First, this invention employs a dual-mode vibration slit extrusion coating process with low frequency (10-20Hz) and high frequency (50-80Hz) to induce regularly shaped square particles to be oriented and tightly arranged in the wet film, thereby reducing the initial compaction density of the electrode after drying from 1.8-2.0 g / cm³ to that of conventional processes. 3 Significantly increased to 2.4-2.6 g / cm³ 3 This process reduces the deformation requirements of the rolling process from the source, achieving a result of 3.1 g / cm³. 3 The required rolling deformation for target compaction is ≤25%, far lower than the conventional process's deformation of over 40%, significantly reducing the internal stress of the electrode and fundamentally solving the problems of electrode cracking and strip breakage under high compaction. Secondly, this invention innovatively employs a segmented rolling process of 200-300MPa low-pressure pre-pressing + 800-1000MPa high-pressure fine pressing. Low-pressure pre-pressing first achieves initial densification of the electrode and releases internal stress, followed by high-pressure fine pressing to achieve the target compaction density. Compared to Comparative Example 4, which involves a single high-pressure rolling process, the electrode strip breakage rate of this invention is reduced from 0.68% to below 0.15%, with a mass production yield ≥99%. Simultaneously, it avoids active particle breakage, mesoporous channel collapse, and conductive network breakage, ensuring the electrochemical performance of the battery after high compaction. Finally, this invention simultaneously introduces acetylene gas during the three-stage sintering process, achieving simultaneous carbon coating on the surface of lithium iron phosphate particles and the inner walls of the internal mesopores, constructing a three-dimensional continuous conductive network. The network remains intact after ultra-high pressure compaction, solving the problem that traditional carbon coating only covers the particle surface and the internal electron conduction is blocked after high pressure compaction, thus balancing material density and electron conduction efficiency. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0032] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0033] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0034] Example 1 This embodiment provides a method for preparing a multi-level porous, regular square high-pressure lithium iron phosphate cathode material, including: 1. Preparation of Crystal Directing Agent Solution Sodium citrate and EDTA-2Na were mixed at a mass ratio of 1:0.65, and deionized water was added to prepare a 0.8 mol / L solution. The solution was stirred at room temperature for 30 minutes until completely dissolved.

[0035] 2. Preparation of liquid-phase coprecipitation precursors Ammonium dihydrogen phosphate, ferrous sulfate heptahydrate, and lithium nitrate were mixed in a molar ratio of Li:Fe:P = 1.03:1:1, and deionized water was added to prepare a mixed solution with a total metal ion concentration of 1.8 mol / L. A crystal-directing agent solution accounting for 4% of the total mass of the precursor was added, and CTAB mesoporous pore-forming agent accounting for 1.5% of the total mass of the precursor was added. The mixture was stirred at a constant temperature of 70°C for 5 hours to obtain the precursor slurry.

[0036] 3. Doping modification and spray drying Magnesium nitrate dopant at a molar ratio of 0.35% of Fe was added to the precursor slurry and stirred and dispersed for 30 min; the precursor powder was obtained by spray drying at an inlet temperature of 190℃ and an outlet temperature of 85℃.

[0037] 4. Three-stage sintering and simultaneous carbon coating The precursor powder was sintered in a three-stage process under a high-purity nitrogen atmosphere, with 0.8% acetylene gas introduced throughout the process to achieve simultaneous carbon coating. The finished material was obtained by furnace cooling. First stage low-temperature pre-firing: heat at 320℃ for 2 hours to remove pore-forming agent and organic impurities and construct mesoporous channels; The second stage of medium-temperature sintering: holding at 620℃ for 4 hours to achieve preliminary crystal nucleation and growth; The third stage of high-temperature sintering: holding at 780℃ for 6 hours to achieve regularized grain growth and form a regular square morphology.

[0038] The preparation method for the matching high-voltage real positive electrode includes: 1. Preparation of positive electrode slurry The LFP material, composite conductive agent (SP:CNT=7:3 mass ratio), and binder (PVDF) were mixed at a mass ratio of 96.5:1.5:2. NMP solvent was added to adjust the solid content to 62%, and the mixture was dispersed at high speed in a vacuum double planetary mixer for 2 hours to prepare a bubble-free slurry with a viscosity of 6500 mPa·s.

[0039] 2. Dual-mode coordinated vibration coating The slurry was coated onto a 14μm double-sided carbon-coated aluminum foil using slit extrusion coating. During the coating process, a low-frequency-high-frequency dual-mode vibration system was activated, with a low-frequency vibration of 15Hz and a high-frequency vibration of 65Hz, with an amplitude of 0.2mm. After coating, the substrate was vacuum dried at 120℃ for 12h.

[0040] 3. Segmented high-pressure compacted roller pressing The dried electrode sheet is first pre-densified by low pressure of 250MPa, and then finely pressed by high pressure of 9000MPa to finally obtain a high-pressure compacted LFP positive electrode sheet.

[0041] Example 2 The results are basically the same as in Example 1, except that the mass ratio of sodium citrate to EDTA-2Na in the composite crystal directing agent is 1:0.5, the three-stage sintering temperatures are 300℃, 600℃, and 750℃, the dopant ion is Zr, and the doping amount is 0.2%.

[0042] Example 3 The results are basically the same as in Example 1, except that: the mass ratio of sodium citrate to EDTA-2Na in the composite crystal guiding agent is 1:0.8, the three-stage sintering temperatures are 350℃, 650℃, and 800℃, the doping ion is Mg, the doping amount is 0.5%, and the amount of mesoporous pore-forming agent added is 2%.

[0043] Comparative Example 1 (Conventional Spherical LFP) Spherical nano-agglomerated LFP materials were prepared by conventional co-precipitation method without the addition of crystal directing agents, mesoporous pore-forming agents, or doping. After spray drying, conventional one-stage sintering (750℃) was performed. Electrode preparation was carried out by conventional coating and single rolling (800MPa).

[0044] Comparative Example 2 (Square LFP without hierarchical porous structure) The process is basically the same as in Example 1, except that no mesoporous pore-forming agent was added, and the three-stage sintering only involves two steps: medium temperature and high temperature (without a pre-sintering stage).

[0045] Comparative Example 3 (Undoped square hierarchical porous LFP) It is basically the same as Example 1, except that no metal ion dopant is added.

[0046] Comparative Example 4 (Vibrationless Coating + Single Roll Press) The LFP material prepared in Example 1 was used, but the electrode preparation was carried out using conventional coating (no vibration) and single rolling (900MPa).

[0047] The performance testing method is as follows: Powder compaction density: Tested using a powder compaction density meter, referring to standard GB / T 44330-2024.

[0048] Electrode compaction density: Calculated by the mass per unit area of ​​the electrode after roll pressing / thickness.

[0049] Breakage rate: Number of breakages / total length when continuously rolling 1000m of electrode sheet.

[0050] Lithium-ion diffusion coefficient: tested using galvanostatic intermittent titration (GITT).

[0051] Rate performance: After assembling CR2032 coin cells and activating at 0.1C, the capacity retention rates at 1C / 0.1C and 2C / 0.1C are as follows.

[0052] Cycling performance: 500 cycles of 0.5C charge-discharge with capacity retention.

[0053] The test results are shown in Tables 1 and 2.

[0054] Table 1 Table 2 The performance comparison between the above embodiments and comparative examples shows that: The regular square morphology and hierarchical porous structure of Examples 1-3 significantly improved the compacted density of the powder (>3.0 g / cm³). 3 ) and electrode compaction density (>3.1 g / cm³) 3 The density of the powder was significantly higher than that of conventional spherical LFP (Comparative Example 1). Example 3 achieved the highest compaction density (3.10 g / cm³ powder) by optimizing the proportion of the crystal guide agent, sintering temperature, and doping amount. 3 Electrode 3.20g / cm 3 The optimal rate capability and cycle performance demonstrate the synergistic advantages of integrated material-process design.

[0055] Comparative Example 2, lacking mesoporous channels, showed a significant decrease in rate performance despite some compaction, indicating that continuous mesoporous channels are crucial for ion transport. Comparative Example 3, without metal ion doping, exhibited a significantly increased band breakage rate (0.35%) and a decreased cycle retention rate to 88.9%, demonstrating that Mg / Zr doping effectively improved particle compressibility and lattice stability. Comparative Example 4, using conventional coating followed by a single high-pressure roll pressing, achieved a band breakage rate as high as 0.68%, far exceeding that of Example 1 (0.12%). This indicates that dual-mode vibration coating combined with segmented roll pressing can effectively pre-densify and reduce roll pressing deformation, thereby suppressing electrode cracking.

[0056] In summary, the multi-level porous regular square high-pressure lithium iron phosphate cathode material, its preparation method, and electrode preparation process provided by this invention can effectively overcome the contradiction between high pressure, high rate, and low breakage rate of existing LFP materials, and has significant industrial application value and mass production compatibility.

[0057] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multi-level porous, regular square high-pressure lithium iron phosphate cathode material, characterized in that, The cathode material comprises micron-sized secondary particles with a regular square morphology. The micron-sized secondary particles have a multi-level porous structure, which includes continuous through-hole mesoporous channels formed by the aggregation of primary nanocrystals. The olivine lattice of the cathode material is doped with metal ions.

2. The multi-level porous regular square high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, The cathode material has at least one of the following characteristics a1) to a5): a1) The metal ion is selected from at least one of Mg ions and Zr ions; a2) The particle size of the micron-sized secondary particles is 2-5 μm; a3) The pore size of the continuous through-hole channel is 2-10 nm; a4) The particle size of the primary nanocrystals is 50-100 nm; a5) The compacted density of the cathode material powder is >3.0 g / cm³. 3 Lithium-ion diffusion coefficient ≥10 -12 cm 2 / s.

3. A method for preparing the multi-level porous regular square high-pressure lithium iron phosphate cathode material as described in claim 1, characterized in that, Includes the following steps: Preparation of composite crystal-type directing agent solution; A mixed solution is prepared by mixing lithium source, iron source and phosphorus source in stoichiometric ratio, and the composite crystal type guiding agent solution and mesoporous pore-forming agent are added. The liquid phase co-precipitation reaction is carried out under constant temperature conditions to obtain precursor slurry. A metal ion dopant is added to the precursor slurry, dispersed evenly, and then spray-dried to obtain precursor powder; The precursor powder was sintered in three stages under an inert atmosphere, while a carbon-containing gas source was introduced for in-situ carbon coating, and then cooled in the furnace to obtain lithium iron phosphate cathode material.

4. The preparation method according to claim 3, characterized in that, The composite crystal directing agent is a mixture of sodium citrate and EDTA-2Na, with a mass ratio of 1:(0.5-0.8), and the concentration of the composite crystal directing agent solution is 0.5-1 mol / L; And / or, the Li:Fe:P molar ratio of the lithium source, iron source, and phosphorus source is (1.01-1.05):1:1, and the total metal ion concentration of the mixed solution is 1.5-2 mol / L; the amount of the composite crystal-directing agent added is 3-5% of the total mass of the precursor, and the mesoporous pore-forming agent is a cationic surfactant added at 1-2% of the total mass of the precursor; the temperature of the liquid-phase coprecipitation reaction is 60-80℃, and the reaction time is 4-6 h; And / or, the doping amount of the metal ions is 0.2-0.5% of the molar amount of iron; the inlet temperature of the spray dryer is 180-200℃, and the outlet temperature is 80-90℃; And / or, the three-stage sintering specifically comprises: a first stage of low-temperature pre-firing at 300-350℃ for 1-3 hours; a second stage of medium-temperature sintering at 600-650℃ for 3-5 hours; and a third stage of high-temperature sintering at 750-800℃ for 5-7 hours; wherein the carbon-containing gas source is acetylene gas, with a volume fraction of 0.5-1%.

5. A high-pressure lithium iron phosphate positive electrode sheet, characterized in that, The cathode material comprises that described in claim 1; the compacted density of the cathode sheet is >3.1 g / cm³. 3 The breakage rate is ≤0.15%.

6. A method for preparing a high-pressure lithium iron phosphate positive electrode sheet as described in claim 5, characterized in that, Includes the following steps: A cathode slurry is prepared by mixing cathode material, composite conductive agent, binder and organic solvent and dispersing under vacuum. The positive electrode slurry is coated onto the surface of the current collector using a dual-mode synergistic vibration coating process, and then dried under vacuum to obtain a dry electrode sheet. The dry electrode sheet is subjected to segmented high-pressure compaction rolling to obtain a positive electrode sheet with a compaction density.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the positive electrode material, composite conductive agent, and binder is (95-98):(0.2-3):(1.2-3); the solid content of the positive electrode slurry is 55-70%, and the viscosity is 5000-8000 mPa·s. And / or, the dual-mode coordinated vibration coating adopts a slot extrusion coating method; the dual-mode vibration includes low-frequency vibration and high-frequency vibration, the low-frequency vibration frequency is 10-20Hz, the high-frequency vibration frequency is 50-80Hz, and the amplitude is 0.1-0.3mm; the vacuum drying temperature is 120℃, and the drying time is 10-14h. And / or, the segmented high-pressure compaction roller pressing specifically involves: first, low-pressure pre-pressing at 200-300MPa to achieve preliminary densification, and then high-pressure fine pressing at 800-1000MPa to obtain a high-pressure compacted positive electrode sheet.

8. The preparation method according to claim 7, characterized in that, The initial compaction density of the dried electrode sheet before segmented roller pressing is 2.4-2.6 g / cm³. 3 Roll forming deformation ≤25%, mass production yield ≥99%.

9. A lithium-ion battery, characterized in that, It includes the high-pressure lithium iron phosphate positive electrode sheet as described in claim 5.

10. A system for preparing the high-pressure lithium iron phosphate positive electrode sheet of claim 5, characterized in that, include: A coating apparatus, wherein the coating apparatus integrates a vibration system for applying vibrations comprising at least two different frequencies to the wet film to be coated during the coating process; Drying device, used to dry coated electrode sheets; A roller pressing device configured to perform a segmented roller pressing process, the segmented roller pressing process including at least a low-pressure pre-pressing station and a high-pressure fine pressing station.

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