Lithium iron phosphate positive electrode material and preparation method thereof, positive plate and secondary battery
By using additives to regulate particle size distribution and lithium oxide coating, the problems of complex and costly preparation of high-density lithium iron phosphate cathode materials in existing technologies have been solved, achieving efficient and low-cost material preparation and improving the energy density and electrical performance of secondary batteries.
Patent Information
- Application Number
- CN202511714732.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-02-10
AI Technical Summary
Existing methods for preparing high-density lithium iron phosphate cathode materials are complex and costly, making it difficult to achieve large-scale industrial production, and the improvement in material performance is limited.
A particle size distribution control method using additives X and Y is employed, and high-density lithium iron phosphate cathode material is formed through spray drying and sintering of large and small particles. This material is then combined with a lithium oxide coating layer to enhance its performance.
The preparation of high-density lithium iron phosphate cathode material has been achieved, which improves the volumetric energy density and electrical performance of secondary batteries, reduces production costs, and is suitable for large-scale industrial production.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of cathode material technology, specifically relating to a lithium iron phosphate cathode material and its preparation method, cathode sheet and secondary battery. Background Technology
[0002] To meet the evolving demands for high energy density and ultra-fast charging in rechargeable batteries, high-compact-density lithium iron phosphate (LiFePO4) cathode materials have become a core focus for technological breakthroughs in the industry. Increasing the compaction density of lithium iron phosphate materials can achieve a dual leap in both energy density and fast-charging performance of rechargeable batteries. Currently, the compaction density is 2.6 g / cm³. 3 ~2.7g / cm 3 The fourth-generation product has achieved large-scale commercial application, 2.7g / cm³. 3 The aforementioned fifth-generation technology has also entered the final stage of research and development, highlighting that there is still huge room for performance improvement in lithium iron phosphate cathode materials.
[0003] Most existing methods for preparing high-density lithium iron phosphate cathode materials employ a two-stage sintering process. This process is complex, involves numerous critical control steps, and has high production costs, hindering large-scale applications. Therefore, there is an urgent need to develop a more easily controllable method for preparing high-density lithium iron phosphate cathode materials to reduce production costs and improve production efficiency. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide a lithium iron phosphate cathode material, its preparation method, cathode sheet, and secondary battery. The preparation method provided by the present invention is simple, efficient, and low-cost, which is conducive to large-scale industrial production. Furthermore, the resulting lithium iron phosphate cathode material possesses both high compaction density and good cycle performance.
[0005] To achieve this objective, the present invention adopts the following technical solution:
[0006] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate cathode material, the method comprising the following steps:
[0007] S1. Prepare a precursor mixture slurry containing iron phosphate, lithium source, carbon source and doped ion source;
[0008] S2. A portion of the precursor mixture slurry is mixed with additive X and subjected to a first grinding process to obtain large-particle abrasive; another portion of the precursor mixture slurry is subjected to a second grinding process to obtain small-particle abrasive.
[0009] S3. The large-particle abrasive and the small-particle abrasive are each subjected to spray drying treatment to obtain large-particle spray yellow material and small-particle spray yellow material respectively;
[0010] S4. Mix the small-particle spray yellow material and additive Y to obtain a mixture; sinter the mixture together with the large-particle spray yellow material to obtain the lithium iron phosphate cathode material.
[0011] This invention utilizes additives X and Y in combination to regulate particle size distribution, thereby preparing lithium iron phosphate cathode materials with high compaction density, effectively improving the volumetric energy density and electrical performance of secondary batteries, as shown below:
[0012] (1) On the one hand, the present invention introduces additive X into the mixed slurry of large particle precursor, which can play a fluxing role and help the subsequent sintering and melting growth into large particle lithium iron phosphate material; on the other hand, the present invention mixes additive Y into small particle spray yellow material, so that the small particle spray yellow material is further coated by additive Y, which inhibits the further growth of small particle lithium iron phosphate material during sintering and can effectively avoid the melting phenomenon between large and small particles, thereby increasing the difference between the particle size of large and small particles and forming an effective gradation.
[0013] (2) The mixture provided by the present invention is sintered to obtain lithium iron phosphate cathode material with large and small particle gradation. The small particles fill the gaps between the large particles, reducing the porosity between particles, which ultimately helps to improve the compaction density of lithium iron phosphate cathode material and the migration efficiency of metal ions, thereby meeting the requirements of high energy density secondary batteries.
[0014] Preferably, in step S1, the precursor mixture further includes a solvent, which includes water.
[0015] Preferably, in the precursor mixture slurry, the mass ratio of the solvent, iron phosphate, lithium source, carbon source and doped ion source is (50~60):(28~35):(6.0~10.0):(3.0~5.0):(0.01~1.0), for example, it can be 50:28:6.0:3.0:0.01, 52:29:7.0:3.2:0.05, 55:30:8.0:3.5:0.1, 58:31:9.0:4.0:0.2, 59:32:10.0:4.5:0.5, 60:33:8.0:5.0:0.8 or 60:35:10.0:5.0:1.0, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0016] Preferably, in step S1, the doped ion source includes a compound containing any one or at least two elements selected from titanium, magnesium, aluminum, niobium, or vanadium.
[0017] Specifically, the doped ion source includes, but is not limited to, any one or a combination of at least two of titanium dioxide, magnesium oxide, aluminum oxide, niobium pentoxide, vanadium trioxide, or ammonium metavanadate.
[0018] Preferably, in step S1, based on the total mass of the lithium iron phosphate cathode material as 100%, the total content of doping elements in the doped ion source is no higher than 7000 ppm, for example, it can be 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm or 7000 ppm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0019] In this invention, by rationally controlling the type of doped ion source and the content of doped elements, it is beneficial to comprehensively improve the specific capacity and rate performance of lithium iron phosphate cathode materials.
[0020] In this invention, in step S1, the carbon source includes glucose and / or polyethylene glycol.
[0021] Preferably, in step S1, the solid content of the precursor mixture slurry is 35% to 45%, for example, it can be 35%, 38%, 40%, 42% or 45%, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0022] Preferably, in step S2, the additive X includes any one or a combination of at least two of citric acid, ascorbic acid, phthalic acid, phosphoric acid, or phosphates, thereby facilitating subsequent sintering and melting growth into large-particle lithium iron phosphate materials.
[0023] Preferably, in step S2, based on the total mass of the lithium iron phosphate cathode material as 100%, the mass percentage of additive X is 0.1% to 1.0%, preferably 0.4%, for example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8% or 1.0%, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0024] In this invention, by adjusting the content of additive X to a reasonable range, it helps to promote the further growth of large-particle lithium iron phosphate materials, thereby increasing the size difference between large and small particles and forming an effective gradation.
[0025] Preferably, in step S2, the mass ratio of one part of the precursor mixture slurry to the other part of the precursor mixture slurry is (20~50):(50~80), preferably 30:70. For example, it can be 20:80, 25:75, 30:70, 35:65, 40:60, 45:55 or 50:50, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0026] Preferably, in step S2, the particle size D of the large-particle abrasive is... 50 The particle size is 0.6μm to 1.8μm, for example, it can be 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm or 1.2μm, 1.4μm, 1.6μm or 1.8μm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0027] Preferably, in step S2, the particle size D of the small abrasive particles... 50 The particle size is 0.15μm to 0.35μm, for example, it can be 0.15μm, 0.18μm, 0.20μm, 0.25μm, 0.30μm or 0.35μm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0028] In this invention, the first grinding process and the second grinding process in step S2 can be exemplarily described as ball milling and / or sand milling, and this invention does not limit them.
[0029] Preferably, in step S3, the temperature of the spray drying process is 270℃~290℃, for example, it can be 270℃, 275℃, 280℃, 285℃ or 290℃, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0030] Preferably, in step S4, the additive Y includes a compound containing any one or at least two elements from Mg, Ca, Ti, Nb, V or Al, and more preferably a compound containing V and / or Al, which can play a doping and coating role, thereby effectively inhibiting the sintering and melting growth of small-particle lithium iron phosphate materials.
[0031] Preferably, in step S4, based on the total mass of the lithium iron phosphate cathode material as 100%, the total doping amount of metal elements in the additive Y is 500ppm to 6000ppm, preferably 3000ppm. For example, it can be 500ppm, 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, or 6000ppm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0032] In this invention, by adjusting the total amount of metal elements in additive Y to a reasonable range, it helps to suppress the further growth of small-particle lithium iron phosphate materials during sintering and can effectively avoid melting between large and small particles. At the same time, it can improve the cycle performance of lithium iron phosphate cathode materials to a certain extent.
[0033] In this invention, the small-particle spray yellow material and additive Y are mixed first, and then sintering is performed. This allows additive Y to fully coat the small-particle spray yellow material without affecting the large-particle spray yellow material.
[0034] Preferably, in step S4, the sintering temperature is 700℃~900℃, for example, 700℃, 750℃, 800℃, 850℃, or 900℃; the sintering time is 6h~12h, for example, 6h, 8h, 10h, or 12h, and is not limited to the listed values; other unlisted values within this range are also applicable. Because the high-density lithium iron phosphate cathode material has high crystallinity, the sintering temperature of this invention is adjusted to 700℃~900℃.
[0035] Secondly, the present invention provides a lithium iron phosphate cathode material, which is prepared by the method for preparing lithium iron phosphate cathode material as described in the first aspect, wherein the compaction density of the lithium iron phosphate cathode material is not less than 2.60 g / cm³. 3 For example, it can be 2.60 g / cm³. 3 2.62 g / cm 3 2.65g / cm 3 Or 2.68g / cm 3 The term "etc." is not limited to the listed values; it also applies to other unlisted values within the range.
[0036] Preferably, the lithium iron phosphate cathode material comprises a lithium iron phosphate material core and a lithium oxide coating layer covering at least a portion of the surface of the lithium iron phosphate material core.
[0037] In this invention, the lithium oxide coating layer is mainly formed by the reaction of lithium oxide produced from the decomposition of lithium source with surface-coated additive Y. Taking lithium carbonate as an example, the specific reaction formula is shown below. During battery charging and discharging, it can isolate the electrolyte and reduce side reactions, thereby improving the cycle performance of the secondary battery. In addition, this lithium oxide coating layer can lower the energy barrier for metal ion diffusion, thereby increasing the diffusion rate of metal ions.
[0038] Li2CO3→Li2O+CO2↑;
[0039] M x O y +Li₂O + Li₂CO₃ → LiM x O z +CO2↑.
[0040] Preferably, the thickness of the lithium oxide coating layer is <4nm, for example, it can be 0.5nm, 0.8nm, 1nm, 2nm or 3nm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0041] In this invention, by reasonably controlling the thickness range of the lithium oxide coating layer, it is beneficial to improve the diffusion rate of metal ions and reduce the charge transfer resistance, thereby improving the electrical performance of the lithium iron phosphate cathode material.
[0042] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the material of the positive active material layer comprising the lithium iron phosphate positive electrode material as described in the second aspect.
[0043] Fourthly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the positive electrode as described in the third aspect. The positive electrode made from the high-density lithium iron phosphate positive electrode material provided by the present invention can further improve the volumetric energy density and electrical performance of the secondary battery.
[0044] In this invention, the secondary battery exemplarily includes a lithium-ion battery or a sodium-ion battery.
[0045] In this invention, the electrolyte includes, but is not limited to, at least one of liquid electrolyte, gel electrolyte or solid electrolyte.
[0046] The numerical range described in this invention includes not only the point values listed above, but also any point values within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values included in the range.
[0047] Compared with the prior art, the present invention has the following beneficial effects:
[0048] This invention provides a method for preparing lithium iron phosphate cathode material. Specifically, by using additives X and Y in combination to regulate particle size distribution, a lithium iron phosphate cathode material with high compaction density is prepared, thereby effectively improving the volumetric energy density and electrical performance of the secondary battery. The specific results are as follows:
[0049] (1) On the one hand, the present invention mixes additive X in the large particle precursor mixture slurry, which can play a fluxing role and help the subsequent sintering and melting growth into large particle lithium iron phosphate material; on the other hand, the present invention mixes additive Y in the small particle spray yellow material, so that the small particle spray yellow material is further coated by additive Y, which inhibits the further growth of small particle lithium iron phosphate material during sintering and can effectively avoid the melting phenomenon between large and small particles, thereby increasing the difference in particle size between large and small particles and forming an effective gradation.
[0050] (2) The mixture provided by the present invention is sintered to obtain lithium iron phosphate cathode material with large and small particle gradation. The small particles fill the gaps between the large particles, reducing the porosity between particles, which ultimately helps to improve the compaction density of lithium iron phosphate cathode material and the migration efficiency of metal ions, thereby meeting the requirements of high energy density secondary batteries. Detailed Implementation
[0051] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0052] Example 1
[0053] This embodiment provides a lithium iron phosphate cathode material and its preparation method. The lithium iron phosphate cathode material includes a lithium iron phosphate core and a lithium oxide coating layer (2 nm thick) covering the surface of the lithium iron phosphate core. The preparation method includes the following steps:
[0054] S1. First, iron phosphate, lithium carbonate, glucose, polyethylene glycol, titanium dioxide dopant, and water are mixed to obtain a precursor mixture slurry. The mass ratio of water, iron phosphate, lithium carbonate, glucose, polyethylene glycol, and titanium dioxide dopant is 55:32:8.0:2.0:2.0:0.2. Based on the total mass of lithium iron phosphate cathode material as 100%, the titanium content is 3000 ppm, resulting in a precursor mixture slurry with a solid content of 40%.
[0055] S2. A portion of the precursor slurry is mixed with a phosphate additive (based on the total mass of lithium iron phosphate cathode material being 100%, the phosphate additive has a mass percentage of 0.4%), and subjected to a first grinding process to obtain particle D. 50 Large-particle abrasive with a particle size of 1.2 μm; another portion of the precursor mixture slurry undergoes a second grinding process to obtain particle D. 50 The small particle abrasive has a particle size of 0.30 μm, wherein the mass ratio of a portion of the precursor mixture slurry to another portion of the precursor mixture slurry is 30:70.
[0056] S3. The large-particle abrasive and the small-particle abrasive are spray-dried separately at 280°C to obtain large-particle spray-dried yellow material and small-particle spray-dried yellow material, respectively.
[0057] S4. First, mix the small-particle spray yellow material and the additive alumina evenly to obtain a mixture; sinter the mixture together with the large-particle spray yellow material at 790°C for 9 hours, and then pulverize to obtain the lithium iron phosphate cathode material, wherein, based on the total mass of the lithium iron phosphate cathode material as 100%, the total doping amount of metal elements in the additive alumina is 3000ppm.
[0058] Example 2
[0059] This embodiment provides a lithium iron phosphate cathode material and its preparation method. The lithium iron phosphate cathode material includes a lithium iron phosphate core and a lithium oxide coating layer (0.5 nm thick) covering the surface of the lithium iron phosphate core. The preparation method includes the following steps:
[0060] S1. First, iron phosphate, lithium carbonate, glucose, polyethylene glycol, titanium dioxide dopant, and water are mixed to obtain a precursor mixture slurry. The mass ratio of water, iron phosphate, lithium carbonate, glucose, polyethylene glycol, and titanium dioxide dopant is 50:28:6.0:1.0:2.0:0.02. Based on the total mass of lithium iron phosphate cathode material as 100%, the titanium content is 500 ppm, resulting in a precursor mixture slurry with a solid content of 43%.
[0061] S2. A portion of the precursor slurry is mixed with a phosphate additive (based on 100% of the total mass of lithium iron phosphate cathode material, the phosphate additive has a mass percentage of 0.05%), and subjected to a first grinding process to obtain particle D. 50 Large-particle abrasive with a particle size of 0.6 μm; another portion of the precursor mixture is subjected to a second grinding process to obtain particle D. 50 The small particle abrasive has a particle size of 0.15 μm, wherein the mass ratio of a portion of the precursor mixture to another portion of the precursor mixture is 20:80.
[0062] S3. The large-particle abrasive and the small-particle abrasive are spray-dried separately at 270°C to obtain large-particle spray-dried yellow material and small-particle spray-dried yellow material, respectively.
[0063] S4. First, mix the small-particle spray yellow material and the additive alumina evenly to obtain a mixture; sinter the mixture together with the large-particle spray yellow material at 700°C for 12 hours, and then pulverize to obtain the lithium iron phosphate cathode material, wherein, based on the total mass of the lithium iron phosphate cathode material as 100%, the total doping amount of metal elements in the additive alumina is 500 ppm.
[0064] Example 3
[0065] This embodiment provides a lithium iron phosphate cathode material and its preparation method. The lithium iron phosphate cathode material includes a lithium iron phosphate core and a lithium oxide coating layer (3.5 nm thick) covering the surface of the lithium iron phosphate core. The preparation method includes the following steps:
[0066] S1. First, iron phosphate, lithium carbonate, glucose, polyethylene glycol, titanium dioxide dopant, and water are mixed to obtain a precursor mixture slurry. The mass ratio of water, iron phosphate, lithium carbonate, glucose, polyethylene glycol, and titanium dioxide dopant is 60:35:10.0:3.0:2.0:1.0. Based on the total mass of lithium iron phosphate cathode material as 100%, the titanium content is 6000 ppm, resulting in a precursor mixture slurry with a solid content of 45%.
[0067] S2. A portion of the precursor mixture slurry is mixed with a phosphate additive (based on 100% of the total mass of lithium iron phosphate cathode material, the phosphate additive content is 1.0%), and subjected to a first grinding process to obtain particle D. 50 Large-particle abrasive with a particle size of 1.8 μm; another portion of the precursor mixture slurry undergoes a second grinding process to obtain particle D. 50 The small particle abrasive has a particle size of 0.35 μm, wherein the mass ratio of a portion of the precursor mixture slurry to another portion of the precursor mixture slurry is 50:50.
[0068] S3. The large-particle abrasive and the small-particle abrasive are spray-dried separately at 290°C to obtain large-particle spray-dried yellow material and small-particle spray-dried yellow material respectively.
[0069] S4. First, mix the small-particle spray yellow material and the additive alumina evenly to obtain a mixture; sinter the mixture together with the large-particle spray yellow material at 770°C for 9 hours, and then pulverize to obtain the lithium iron phosphate cathode material, wherein, based on the total mass of the lithium iron phosphate cathode material as 100%, the total doping amount of metal elements in the additive alumina is 5000ppm.
[0070] Example 4
[0071] The difference between this embodiment and Embodiment 1 is that in step S2, phosphoric acid is replaced with phthalic acid of equal mass percentage, and in step S4, the additive alumina is replaced with vanadium oxide of equal mass percentage. The thickness of the lithium oxide coating layer is 2 nm. All other aspects are the same as in Embodiment 1.
[0072] Example 5
[0073] The difference between this embodiment and Embodiment 1 is that in step S2, with the total mass of lithium iron phosphate cathode material being 100%, the mass percentage of phosphoric acid is 0.005%, while all other aspects are the same as in Embodiment 1.
[0074] Example 6
[0075] The difference between this embodiment and Embodiment 1 is that in step S2, with the total mass of lithium iron phosphate cathode material being 100%, the mass percentage of phosphoric acid is 1.2%, and everything else is the same as in Embodiment 1.
[0076] Example 7
[0077] The difference between this embodiment and Embodiment 1 is that in step S2, phosphoric acid is replaced with aluminum oxide of equal mass percentage, and the thickness of the lithium oxide coating layer is 2.5 nm. All other aspects are the same as in Embodiment 1.
[0078] Example 8
[0079] The difference between this embodiment and Embodiment 1 is that, in step S4, with the total mass of lithium iron phosphate cathode material being 100%, the total doping amount of metal elements in alumina is 300 ppm, and the thickness of the lithium oxide coating layer is 0.2 nm. All other aspects are the same as in Embodiment 1.
[0080] Example 9
[0081] The difference between this embodiment and Embodiment 1 is that, in step S4, with the total mass of lithium iron phosphate cathode material being 100%, the total doping amount of metal elements in alumina is 7000ppm, and the thickness of the lithium oxide coating layer is 5nm. All other aspects are the same as in Embodiment 1.
[0082] Example 10
[0083] The difference between this embodiment and Embodiment 1 is that in step S4, alumina is replaced with phosphoric acid of equal mass percentage, and the thickness of the lithium oxide coating layer is 0 nm. All other aspects are the same as in Embodiment 1.
[0084] Comparative Example 1
[0085] The difference between this comparative example and Example 1 is that in step S2, phosphate additive is not added, and a portion of the precursor mixture slurry is directly subjected to the first grinding process. Everything else is the same as in Example 1.
[0086] Comparative Example 2
[0087] The difference between this comparative example and Example 1 is that in step S4, alumina is not added, and the small-particle spray yellow material and large-particle spray yellow material are directly mixed to obtain a mixture. The thickness of the lithium oxide coating layer is 0 nm. All other aspects are the same as in Example 1.
[0088] Comparative Example 3
[0089] The difference between this comparative example and Example 1 is that phosphate additive is not added in step S2, and a portion of the precursor mixture slurry is directly subjected to the first grinding process; and alumina is not added in step S4, and small-particle spray yellow material and large-particle spray yellow material are directly mixed. All other aspects are the same as in Example 1.
[0090] Comparative Example 4
[0091] The difference between this comparative example and Example 1 is that glucose and polyethylene glycol are not added in step S1, and the phosphoric acid in step S2 is replaced with an equal mass percentage of glucose, and the alumina in step S4 is replaced with an equal mass percentage of glucose. All other aspects are the same as in Example 1.
[0092] Lithium-ion coin cells were prepared using the lithium iron phosphate cathode materials provided in the above embodiments and comparative examples. The preparation method is as follows:
[0093] Preparation of positive electrode sheet: The lithium iron phosphate positive electrode material, Super P conductive agent and polyvinylidene fluoride binder provided in the above examples and comparative examples are mixed in a mass ratio of 90:5:5. N-methylpyrrolidone is added and stirred thoroughly to form a uniform positive electrode slurry. The slurry is coated on an aluminum foil with a thickness of 6 μm, dried and rolled to obtain the positive electrode sheet.
[0094] Preparation of negative electrode: Lithium metal sheet is used as negative electrode.
[0095] Preparation of lithium-ion batteries: The positive electrode, separator and negative electrode are stacked in sequence and injected with electrolyte to obtain lithium-ion coin cells.
[0096] Test conditions
[0097] The lithium iron phosphate cathode materials and their lithium-ion coin cells prepared in the above embodiments and comparative examples were subjected to performance testing. The testing methods are as follows:
[0098] (1) Compaction density: Using the Sansi Zongheng equipment, weigh 0.8g of lithium iron phosphate sample and put it into the mold. Perform a compaction test with a force of 3N and record the compaction density.
[0099] (2) Electrochemical performance test: The prepared lithium-ion coin cells were subjected to electrochemical performance test. The test voltage was 2.0V to 3.75V. The capacity retention rate of the lithium-ion cells after 200 charge-discharge cycles at 25°C and 0.5C was tested. The discharge capacity of the lithium-ion cells was also tested after 3 cycles of constant voltage and constant current at 25°C and 0.1C, followed by 1 week of constant voltage and constant current charge-discharge at 1.0C.
[0100] The test results are shown in Table 1:
[0101] Table 1
[0102]
[0103] As can be seen from Table 1, compared with Comparative Examples 1 to 2, the lithium iron phosphate cathode materials prepared in Examples 1 to 4 of this invention have higher compaction density, which can further improve the discharge capacity and cycle performance of lithium-ion batteries.
[0104] Comparing Examples 1 and 5-6, it can be seen that by controlling the content of additive X within a reasonable range, the present invention helps to promote the further growth of large-particle lithium iron phosphate materials, thereby better controlling the size difference between large and small particles, forming an effective gradation, and thus comprehensively improving the volumetric energy density and electrical performance of lithium-ion batteries.
[0105] Comparing Examples 1 and 8-9, it can be seen that by adjusting the total amount of metal elements in additive Y to a reasonable range, the present invention helps to suppress the further growth of small-particle lithium iron phosphate materials during sintering and can effectively avoid the melting phenomenon between large and small particles. While ensuring that the prepared lithium iron phosphate cathode material has a high compaction density, it further improves its cycle performance.
[0106] Comparing Examples 1, 7 and 10, it can be seen that the present invention effectively improves the volumetric energy density and electrical performance of lithium-ion batteries by adding different types of additives at different stages.
[0107] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A method for preparing a lithium iron phosphate cathode material, characterized in that, The preparation method includes the following steps: S1. Prepare a precursor mixture slurry containing iron phosphate, lithium source, carbon source and doped ion source; S2. A portion of the precursor mixture slurry is mixed with additive X and subjected to a first grinding process to obtain large-particle abrasive; another portion of the precursor mixture slurry is subjected to a second grinding process to obtain small-particle abrasive. S3. The large-particle abrasive and the small-particle abrasive are each subjected to spray drying treatment to obtain large-particle spray yellow material and small-particle spray yellow material respectively; S4. Mix the small-particle spray yellow material and additive Y to obtain a mixture; sinter the mixture together with the large-particle spray yellow material to obtain the lithium iron phosphate cathode material.
2. The preparation method according to claim 1, characterized in that, In step S1, the precursor mixing slurry further includes a solvent, which includes water; Preferably, in the precursor mixture slurry, the mass ratio of the solvent, iron phosphate, lithium source, carbon source and doped ion source is (50~60):(28~35):(6.0~10.0):(3.0~5.0):(0.01~1.0); Preferably, in step S1, the doped ion source includes a compound containing any one or at least two elements selected from titanium, magnesium, aluminum, niobium, or vanadium. Preferably, in step S1, based on the total mass of the lithium iron phosphate cathode material as 100%, the total content of doping elements in the doped ion source is no higher than 7000 ppm; Preferably, in step S1, the solid content of the precursor mixture slurry is 35% to 45%.
3. The preparation method according to claim 1 or 2, characterized in that, In step S2, the additive X includes any one or a combination of at least two of citric acid, ascorbic acid, phthalic acid, phosphoric acid, or phosphates. Preferably, in step S2, based on the total mass of the lithium iron phosphate cathode material as 100%, the mass percentage of additive X is 0.01% to 1.0%, preferably 0.4%. Preferably, in step S2, the mass ratio of one part of the precursor mixture slurry to the other part of the precursor mixture slurry is (20~50):(50~80), more preferably 30:70; Preferably, in step S2, the particle size D of the large-particle abrasive is... 50 The particle size is 0.6μm~1.8μm; Preferably, in step S2, the particle size D of the small abrasive particles... 50 The particle size is 0.15μm~0.35μm.
4. The preparation method according to any one of claims 1-3, characterized in that, In step S3, the temperature of the spray drying process is 270℃~290℃.
5. The preparation method according to any one of claims 1-4, characterized in that, In step S4, the additive Y includes a compound containing any one or at least two elements selected from Mg, Ca, Ti, Nb, V or Al, preferably a compound containing V and / or Al. Preferably, in step S4, based on the total mass of the lithium iron phosphate cathode material as 100%, the total doping amount of metal elements in the additive Y is 500ppm~6000ppm, preferably 3000ppm.
6. The preparation method according to any one of claims 1-5, characterized in that, In step S4, the sintering temperature is 700℃~900℃, and the sintering time is 6h~12h.
7. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is prepared by the method for preparing lithium iron phosphate cathode material as described in any one of claims 1-6, and the compaction density of the lithium iron phosphate cathode material is not less than 2.60 g / cm³. 3 .
8. The lithium iron phosphate cathode material according to claim 7, characterized in that, The lithium iron phosphate cathode material includes a lithium iron phosphate core and a lithium oxide coating layer covering at least a portion of the surface of the lithium iron phosphate core. Preferably, the thickness of the lithium oxide coating layer is <4 nm.
9. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the material of the positive active material layer includes the lithium iron phosphate positive electrode material as described in claim 7 or 8.
10. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode as described in claim 9.