Lithium iron phosphate positive electrode material, preparation method and application thereof
By constructing carbon nanotubes and silk fibroin networks in lithium iron phosphate cathode materials, which self-assemble into spherical structures and form carbon networks, the problem of poor uniformity of carbon coating layers is solved, the sphericity and conductivity of the material are improved, and the rate performance and discharge capacity of the battery are enhanced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG BRUNP RECYCLING TECH CO LTD
- Filing Date
- 2024-05-07
- Publication Date
- 2026-06-09
Smart Images
Figure CN118495492B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a lithium iron phosphate cathode material, its preparation method and application. Background Technology
[0002] Lithium iron phosphate (LiFePO4) cathode materials with an olivine structure have attracted widespread attention in lithium-ion batteries due to their environmental friendliness, safety, and long cycle life. Compared to layered materials, its most prominent advantage is that the phosphate ions in LiFePO4 are highly stable anions, preventing oxygen desorption during charge and discharge, and the material itself exhibits relatively small volume strain.
[0003] The large-scale application of lithium iron phosphate cathode materials is hampered by low electronic conductivity and low ion diffusion rate (10). -17 ~10 - 14 cm 2 The low tap density and other properties limit the lithium-ion insertion / extraction distance. Therefore, current research focuses on improving the lithium-ion insertion / extraction distance by fabricating porous or nanomaterials. However, porous materials reduce the volumetric energy density of the battery, while nanomaterials reduce its tap density. Carbon coating is another efficient way to improve electronic conductivity, but the uniformity of carbon coating remains a challenge for researchers.
[0004] CN117819509A discloses a method for preparing a porous carbon-coated lithium iron phosphate cathode active material, comprising the following steps: mixing lithium source material, iron source material, phosphorus source material with a first carbon source and pre-sintering to prepare a precursor, then adding polymethyl methacrylate and heating to 400-700℃ and holding for 9-25 hours, thereby obtaining a porous carbon-coated lithium iron phosphate cathode active material.
[0005] CN117832427A discloses a method for preparing and applying lithium iron phosphate composite materials, using lithium hydroxide as the lithium source and polyvinyl alcohol microspheres as the carbon source. The carbon-coated microspherical lithium iron phosphate composite material is obtained through a carbothermal reduction method.
[0006] The lithium iron phosphate cathode material prepared by the above method has poor controllability of the uniformity of the carbon coating layer, resulting in low sphericity, poor tap density and rate performance. Summary of the Invention
[0007] The purpose of this invention is to provide a lithium iron phosphate cathode material, its preparation method, and its application. The lithium iron phosphate cathode material of this invention has a carbon nanotube and carbon network structure. The network structure can not only improve the conductivity of the material, but also utilize the capillary action of the carbon nanotubes to wet the electrolyte into the lithium iron phosphate spheres, thereby increasing the electrolyte wetting and shortening the lithium ion transport path, thus improving the rate performance.
[0008] To achieve this objective, the present invention adopts the following technical solution:
[0009] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate cathode material, the method comprising the following steps:
[0010] (1) Mix silk fibroin, carbon nanotubes and solvent to obtain a mixed solution, adjust the pH of the mixed solution, add ferrous source and phosphate source to carry out a one-step reaction to obtain a precursor suspension;
[0011] (2) The precursor suspension was mixed with a polyethylene glycol aqueous solution to carry out a two-step reaction to obtain spherical ferrous phosphate;
[0012] (3) Mix spherical iron phosphate with lithium phosphate and sinter to obtain the lithium iron phosphate cathode material.
[0013] In this invention, silk fibroin and carbon nanotubes are first prepared into a mixed solution. The amino acid residues in the silk fibroin interact with the carbon nanotubes through π-π bonds, making the carbon nanotubes uniformly dispersed in water and possessing a certain degree of stability. After adding ferrous ions and a phosphate source, ferrous phosphate nanocrystals grow on the network composed of carbon nanotubes and silk fibroin. After growing to a certain extent, a precursor suspension is obtained. By adding polyethylene glycol to the precursor suspension, its interaction with silk fibroin is utilized. Specifically, polyethylene glycol absorbs water molecules (free water and bound water in silk fibroin), increasing the interaction of the hydrophobic part in silk fibroin and inducing the formation of β-sheets in the hydrophobic region of silk fibroin. This induces the self-assembly of the hydrophobic region of silk fibroin into a microsphere structure (the outside of the microsphere is the hydrophobic part of polyethylene glycol and silk fibroin after β-sheet). The ferrous phosphate nanocrystals in the microsphere continue to grow, eventually forming a highly spherical ferrous phosphate precursor. A high-sphericity lithium iron phosphate material was prepared by mixing ferrous phosphate precursor with lithium phosphate and then using solid-state sintering. During the sintering process, carbon nanotubes and silk fibroin carbonized and formed a carbon network inside and outside the lithium iron phosphate, which improved the conductivity of the material.
[0014] Preferably, the solvent in step (1) includes water.
[0015] Preferably, the inner diameter of the carbon nanotube in step (1) is 10 to 20 nm, for example: 10 nm, 12 nm, 15 nm, 18 nm or 20 nm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0016] Preferably, the mass percentage concentration of silk fibroin in the mixed solution in step (1) is 10% to 15%, for example: 10%, 11%, 12%, 13%, 14% or 15%, etc., not limited to the listed values, and other unlisted values within this range are also applicable.
[0017] Preferably, the mass percentage concentration of carbon nanotubes in the mixed solution in step (1) is 0.3% to 0.5%, for example: 0.3%, 0.35%, 0.4%, 0.45% or 0.5%, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0018] Preferably, the pH in step (1) is 5 to 6, for example: 5, 5.2, 5.5, 5.8 or 6, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0019] Preferably, the ferrous source in step (1) includes any one or a combination of at least two of ferrous sulfate, ferrous chloride, or ferrous nitrate. Typical but non-limiting combinations include combinations of ferrous sulfate and ferrous chloride, ferrous sulfate and ferrous nitrate, or ferrous chloride and ferrous nitrate.
[0020] Preferably, the phosphoric acid source in step (1) includes any one or a combination of at least two of H3PO4, NaH2PO4 or Na2HPO4. Typical but non-limiting combinations include combinations of H3PO4 and NaH2PO4, combinations of NaH2PO4 and Na2HPO4, or combinations of H3PO4 and Na2HPO4, etc.
[0021] Preferably, the molar volume ratio of the ferrous source to the mixed solution in step (1) is 0.5 to 2 mol / L, for example: 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, etc.
[0022] Preferably, the molar ratio of iron in the ferrous source to phosphorus in the phosphate source is (1.45 to 1.5):1, for example: 1.45:1, 1.46:1, 1.47:1, 1.48:1, 1.49:1 or 1.5:1, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0023] Preferably, the stirring speed of the one-step reaction in step (1) is 100 to 300 rpm, for example: 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0024] Preferably, the reaction time in step (1) is 1 to 1.5 hours, for example: 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours or 1.5 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0025] Preferably, the atmosphere of the one-step reaction in step (1) includes a protective atmosphere.
[0026] Preferably, the protective atmosphere includes nitrogen and / or argon.
[0027] Preferably, the molecular weight of polyethylene glycol in the polyethylene glycol aqueous solution in step (2) is 4 to 10 kDa, for example: 4 kDa, 5 kDa, 6 kDa, 8 kDa or 10 kDa, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0028] Preferably, the mass percentage concentration of the polyethylene glycol aqueous solution in step (2) is 20% to 30%, for example: 20%, 22%, 25%, 28% or 30%, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0029] Preferably, the volume ratio of the polyethylene glycol aqueous solution and the precursor suspension in step (2) is (0.15 to 0.25):1, for example: 0.15:1, 0.18:1, 0.2:1, 0.22:1 or 0.25:1, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0030] Preferably, the reaction time of the two steps in step (2) is 2 to 6 hours, for example: 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0031] Preferably, the atmosphere of the two-step reaction in step (2) includes a protective atmosphere.
[0032] Preferably, the protective atmosphere includes nitrogen and / or argon.
[0033] Preferably, the two-step reaction described in step (2) is followed by filtration, washing, and vacuum drying.
[0034] Preferably, the vacuum drying temperature is 70-80°C, for example: 70°C, 72°C, 75°C, 78°C or 80°C, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0035] Preferably, the vacuum drying time is 80 to 90 minutes, for example: 80 minutes, 82 minutes, 85 minutes, 88 minutes or 90 minutes.
[0036] Preferably, in step (3), the molar ratio of iron to lithium in the mixture obtained by mixing spherical ferrous phosphate and lithium phosphate is 1:(1.05~1.1), for example: 1:1.05, 1:1.06, 1:1.07, 1:1.08 or 1:1.1, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0037] Preferably, the mixing method in step (3) includes ball milling.
[0038] Preferably, the ball milling time is 8 to 12 hours, for example: 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0039] Preferably, the dispersant used in the ball milling includes ethanol.
[0040] Preferably, the atmosphere for the sintering process in step (3) includes a protective atmosphere.
[0041] Preferably, the protective atmosphere includes nitrogen and / or argon.
[0042] Preferably, the sintering temperature in step (3) is 650 to 750°C, for example: 650°C, 680°C, 700°C, 720°C or 750°C, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0043] Preferably, the sintering time in step (3) is 8 to 10 hours, for example: 8 hours, 8.5 hours, 9 hours, 9.5 hours or 10 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0044] Preferably, the sintering process described in step (3) is followed by grinding.
[0045] In a second aspect, the present invention provides a lithium iron phosphate cathode material, which is prepared by the method described in the first aspect.
[0046] The method described in this invention produces lithium iron phosphate cathode materials with high sphericity, resulting in higher tap density. The carbon nanotubes in the lithium iron phosphate cathode material have capillary action, which allows the electrolyte to wet the lithium iron phosphate spheres, increasing the wetting effect of the electrolyte, shortening the lithium ion transport path, and improving rate performance.
[0047] Thirdly, the present invention provides a positive electrode sheet comprising the lithium iron phosphate positive electrode material as described in the second aspect.
[0048] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the third aspect.
[0049] Compared with the prior art, the present invention has the following beneficial effects:
[0050] (1) This invention uses carbon nanotubes and silk fibroin to form a network. After growing ferrous phosphate nanocrystals on the network, polyethylene glycol is used to induce the formation of a ferrous phosphate precursor with high sphericity. In the subsequent mixing and sintering process with lithium source, carbon nanotubes and silk fibroin are carbonized to form a carbon network inside and outside the lithium iron phosphate to improve the conductivity of the material. At the same time, the capillary action of carbon nanotubes can be used to wet the electrolyte into the lithium iron phosphate spheres, increasing the wetting effect of the electrolyte, shortening the lithium ion transport path, and improving the rate performance of the battery. By improving the sphericity of the lithium iron phosphate material, the tap density of the lithium iron phosphate material is improved.
[0051] (2) The tap density of the lithium iron phosphate cathode material prepared by the method of the present invention can reach 1.29 g / cm³. 3 The resulting batteries have a discharge capacity of over 162 mAh / g at 0.2C, over 156 mAh / g at 1C, over 150 mAh / g at 2C, over 142 mAh / g at 5C, and over 130 mAh / g at 10C. Attached Figure Description
[0052] Figure 1 This is a SEM image of the lithium iron phosphate cathode material prepared in Example 1 of the present invention. Detailed Implementation
[0053] 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.
[0054] Example 1
[0055] This embodiment provides a lithium iron phosphate cathode material, and the preparation method of the lithium iron phosphate cathode material is as follows:
[0056] (1) Silk fibroin was placed in water and stirred until completely dissolved. Then carbon nanotubes with an inner diameter of 10-20 nm were added and ultrasonically treated for 30 min to fully disperse the mixture to obtain a mixed solution (the mass percentage concentration of silk fibroin in the mixed solution was 13%, and the mass percentage concentration of carbon nanotubes in the mixed solution was 0.4%). The pH of the mixed solution was adjusted to 5.2. Ferrous sulfate was added under a nitrogen atmosphere and stirred evenly. Then disodium hydrogen phosphate was added. The solution temperature was controlled at 20℃ and the reaction was stirred at a constant speed of 200 rpm for 1.2 h to obtain a precursor suspension. The amount of ferrous sulfate added (i.e., the molar volume ratio of ferrous sulfate to the mixed solution) was 1 mol / L, and the molar ratio of ferrous sulfate to disodium hydrogen phosphate was 1.5:1.
[0057] (2) Add a 25wt% polyethylene glycol aqueous solution to the precursor suspension formed above. The polyethylene glycol has a molecular weight of 6kDa. The volume ratio of the polyethylene glycol aqueous solution to the precursor suspension is 0.2:1. Continue the reaction for 4 hours to allow it to fully self-assemble into spherical ferrous phosphate. Then, filter, wash, and vacuum dry at 75°C for 90 minutes to obtain spherical ferrous phosphate.
[0058] (3) The spherical iron phosphate and lithium phosphate are ball-milled for 10 hours with ethanol as a dispersant at a Fe / Li molar ratio of 1:1.08. After vacuum drying at 70°C for 8 hours, the mixture is calcined at 700°C under a nitrogen atmosphere for 9 hours. After cooling and grinding to obtain the lithium iron phosphate cathode material.
[0059] SEM images of the prepared lithium iron phosphate cathode material are shown below. Figure 1 As shown, by Figure 1 It can be seen that the lithium iron phosphate cathode material prepared by this invention has a high sphericity.
[0060] Example 2
[0061] This embodiment provides a lithium iron phosphate cathode material, and the preparation method of the lithium iron phosphate cathode material is as follows:
[0062] (1) Silk fibroin was placed in water and stirred until completely dissolved. Then carbon nanotubes with an inner diameter of 10-20 nm were added and ultrasonically treated for 30 min to fully disperse the mixture to obtain a mixed solution (the mass percentage concentration of silk fibroin in the mixed solution was 10%, and the mass percentage concentration of carbon nanotubes in the mixed solution was 0.3%). The pH of the mixed solution was adjusted to 5, and ferrous chloride was added under a nitrogen atmosphere. After stirring evenly, phosphoric acid was added, and the solution temperature was controlled at 20℃. The mixture was stirred at a constant speed of 100 rpm for 1.5 h to obtain a precursor suspension. The amount of ferrous chloride added (i.e., the molar volume ratio of ferrous chloride to the mixed solution) was 1 mol / L, and the molar ratio of ferrous chloride to phosphoric acid was 1.45:1.
[0063] (2) Add a 20wt% polyethylene glycol aqueous solution to the precursor suspension formed above. The polyethylene glycol has a molecular weight of 4kDa and the volume ratio of the polyethylene glycol aqueous solution to the precursor suspension is 0.25:1. Continue the reaction for 6 hours to allow it to fully self-assemble into spherical ferrous phosphate. Then filter, wash, and vacuum dry at 80°C for 80 minutes to obtain spherical ferrous phosphate.
[0064] (3) The spherical iron phosphate and lithium phosphate are ball-milled for 10 hours with ethanol as a dispersant at a Fe / Li molar ratio of 1:1.05. After vacuum drying at 70°C for 8 hours, the mixture is calcined at 650°C under a nitrogen atmosphere for 10 hours and then cooled and ground until uniform to obtain the lithium iron phosphate cathode material.
[0065] Example 3
[0066] This embodiment provides a lithium iron phosphate cathode material, and the preparation method of the lithium iron phosphate cathode material is as follows:
[0067] (1) Silk fibroin was placed in water and stirred until completely dissolved. Then carbon nanotubes with an inner diameter of 10-20 nm were added and ultrasonically treated for 30 min to fully disperse the mixture to obtain a mixed solution (the mass percentage concentration of silk fibroin in the mixed solution was 15%, and the mass percentage concentration of carbon nanotubes in the mixed solution was 0.5%). The pH of the mixed solution was adjusted to 6, and ferrous chloride was added under an argon atmosphere. After stirring evenly, phosphoric acid was added, and the solution temperature was controlled at 20℃. The mixture was stirred at a constant speed of 300 rpm for 1 h to obtain a precursor suspension. The amount of ferrous chloride added (i.e., the molar volume ratio of ferrous chloride to the mixed solution) was 1 mol / L, and the molar ratio of ferrous chloride to phosphoric acid was 1.5:1.
[0068] (2) Add a 30wt% polyethylene glycol aqueous solution to the precursor suspension formed above. The polyethylene glycol has a molecular weight of 10kDa and the volume ratio of the polyethylene glycol aqueous solution to the precursor suspension is 0.15:1. Continue the reaction for 2 hours to allow it to fully self-assemble into spherical ferrous phosphate. Then filter, wash, and vacuum dry at 70°C for 90 minutes to obtain spherical ferrous phosphate.
[0069] (3) The spherical iron phosphate and lithium phosphate are ball-milled for 10 hours with ethanol as a dispersant at a Fe / Li molar ratio of 1:1.1. Then, the mixture is vacuum-dried at 70°C for 8 hours and calcined at 750°C in a nitrogen atmosphere for 8 hours. After cooling and grinding, the lithium iron phosphate cathode material is obtained.
[0070] Example 4
[0071] The only difference between this embodiment and Example 1 is that the mass percentage concentration of silk fibroin in the mixed solution is 8%, while the other conditions and parameters are exactly the same as in Example 1.
[0072] Example 5
[0073] The only difference between this embodiment and Example 1 is that the mass percentage concentration of silk fibroin in the mixed solution is 18%, while the other conditions and parameters are exactly the same as in Example 1.
[0074] Example 6
[0075] The only difference between this embodiment and Example 1 is that the mass percentage concentration of carbon nanotubes in the mixed solution is 0.2%, while the other conditions and parameters are exactly the same as in Example 1.
[0076] Example 7
[0077] The only difference between this embodiment and Example 1 is that the mass percentage concentration of carbon nanotubes in the mixed solution is 0.6%, while the other conditions and parameters are exactly the same as in Example 1.
[0078] Example 8
[0079] The only difference between this embodiment and Example 1 is that the volume ratio of the polyethylene glycol aqueous solution (25% by mass) to the precursor suspension is 0.1:1. All other conditions and parameters are exactly the same as in Example 1.
[0080] Example 9
[0081] The only difference between this embodiment and Example 1 is that the volume ratio of the polyethylene glycol aqueous solution (25% by mass) to the precursor suspension is 0.3:1. All other conditions and parameters are exactly the same as in Example 1.
[0082] Comparative Example 1
[0083] The only difference between this comparative example and Example 1 is that silk fibroin is not added; all other conditions and parameters are exactly the same as in Example 1.
[0084] Comparative Example 2
[0085] The only difference between this comparative example and Example 1 is that an aqueous solution of polyethylene glycol is not added; all other conditions and parameters are exactly the same as in Example 1.
[0086] Performance testing:
[0087] The tap density of the lithium iron phosphate cathode materials obtained in the examples and comparative examples was tested using the fixed mass method of GB / T 31057.2-2018.
[0088] The lithium iron phosphate cathode material, acetylene black, and PVDF prepared in the examples and comparative examples were mixed into a uniform slurry at a mass ratio of 75:15:10 and uniformly coated onto an aluminum foil substrate to serve as the cathode of the simulated battery. The cathode of the simulated battery used a lithium sheet, a polypropylene porous membrane as the separator, and the electrolyte was 1 mol LiPF6 dissolved in 1 L of a mixed solvent of EC and DMC (volume ratio 1:1). The cathode, cathode, electrolyte, and separator were assembled into a battery in an argon-protected glove box.
[0089] Simulated battery rate and cycle testing procedures:
[0090] First, the battery is charged to 4.2V using a constant current, then discharged to 2.0V using a higher rate current. The capacity discharged is the discharge capacity at that rate. After discharging, the battery is discharged again to 2.0V using a constant current. Then, the next rate test is performed, and the results are shown in Table 1.
[0091] Table 1
[0092]
[0093] As shown in Table 1, based on Examples 1-3, the tap density of the lithium iron phosphate cathode material prepared by the method of the present invention can reach 1.29 g / cm³. 3 The resulting batteries have a discharge capacity of over 162 mAh / g at 0.2C, over 156 mAh / g at 1C, over 150 mAh / g at 2C, over 142 mAh / g at 5C, and over 130 mAh / g at 10C.
[0094] A comparison of Examples 1 and 4-5 shows that the mass percentage concentration of silk fibroin affects the performance of the lithium iron phosphate cathode material prepared according to the present invention. Controlling the mass percentage concentration of silk fibroin in the mixed solution to 10%–15% results in a lithium iron phosphate cathode material with better performance. If the mass percentage concentration of silk fibroin is too low, the driving force is insufficient to allow it to self-assemble into spheres, ultimately affecting the sphericity of ferrous phosphate, which in turn affects its tap density, effectively reducing carbon content and carbon network distribution, thus affecting electronic conductivity and lowering rate performance. Conversely, if the mass percentage concentration of silk fibroin is too high, it leads to an increase in carbon content, affecting the battery's specific capacity, reducing active material, and lowering specific capacity.
[0095] A comparison of Examples 1 and 6-7 shows that the mass percentage concentration of carbon nanotubes affects the performance of the lithium iron phosphate cathode material prepared according to the present invention. Controlling the mass percentage concentration of carbon nanotubes in the mixed solution to 0.3%–0.5% results in a lithium iron phosphate cathode material with better performance. If the mass percentage concentration of carbon nanotubes is too low, it will reduce the lithium-ion transport rate, thus reducing the rate performance of the battery. It will also affect the sphericity of the final material, possibly because the addition of carbon nanotubes causes some silk fibroin to form β-sheets, increasing the stability of the ferrous phosphate nanocrystal growth network. If the mass percentage concentration of carbon nanotubes is too high, it will reduce the volumetric capacity and specific capacity of the battery, and will also affect the self-assembly of silk fibroin, affecting the sphericity of ferrous phosphate, thereby reducing the tap density and rate performance.
[0096] A comparison of Examples 1 and 8-9 shows that the amount of polyethylene glycol aqueous solution added during the preparation of the lithium iron phosphate cathode material of the present invention affects its performance. Controlling the volume ratio of polyethylene glycol aqueous solution to precursor suspension at 0.15–0.25:1 yields a lithium iron phosphate cathode material with better performance. If the amount of polyethylene glycol aqueous solution added is too low, it will prevent sufficient β-sheet formation of silk fibroin, affecting its sphericity, tap density, and rate performance. If the amount of polyethylene glycol aqueous solution added is too high, there is no substantial improvement in performance, but the preparation cost will increase.
[0097] As can be seen from the comparison between Example 1 and Comparative Example 1, the absence of silk fibroin will result in the carbon nanotubes not being evenly distributed and the material not being able to form spheres, which will significantly reduce the rate performance and tap density of the prepared lithium iron phosphate cathode material.
[0098] As can be seen from the comparison between Example 1 and Comparative Example 2, without the addition of polyethylene glycol, the material cannot be spherically formed, which will significantly reduce the rate performance and tap density of the prepared lithium iron phosphate cathode material.
[0099] 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: (1) Mix silk fibroin, carbon nanotubes and solvent to obtain a mixed solution, adjust the pH of the mixed solution, add ferrous source and phosphate source to carry out a one-step reaction to obtain a precursor suspension; (2) The precursor suspension was mixed with a polyethylene glycol aqueous solution to carry out a two-step reaction to obtain spherical ferrous phosphate; (3) Mix spherical ferrous phosphate with lithium phosphate and sinter to obtain the lithium iron phosphate cathode material; In step (1), the mass percentage concentration of silk fibroin in the mixed solution is 10%~15%, and the mass percentage concentration of carbon nanotubes in the mixed solution is 0.3%~0.5%. In step (2), the mass percentage concentration of the polyethylene glycol aqueous solution is 20%~30%, and the volume ratio of the polyethylene glycol aqueous solution to the precursor suspension is (0.15~0.25):
1.
2. The preparation method according to claim 1, characterized in that, The solvent in step (1) includes water.
3. The preparation method according to claim 1, characterized in that, The inner diameter of the carbon nanotubes in step (1) is 10~20nm.
4. The preparation method according to claim 1, characterized in that, The pH value in step (1) is 5-6.
5. The preparation method according to claim 1, characterized in that, The ferrous source in step (1) includes any one or a combination of at least two of ferrous sulfate, ferrous chloride, or ferrous nitrate.
6. The preparation method according to claim 1, characterized in that, The phosphoric acid source in step (1) includes any one or a combination of at least two of H3PO4, NaH2PO4 or Na2HPO4.
7. The preparation method according to claim 1, characterized in that, The molar volume ratio of the ferrous source to the mixed solution in step (1) is 0.5~2 mol / L.
8. The preparation method according to claim 1, characterized in that, The molar ratio of iron in the ferrous source to phosphorus in the phosphate source is (1.45~1.5):
1.
9. The preparation method according to claim 1, characterized in that, The stirring speed for the one-step reaction in step (1) is 100~300 rpm.
10. The preparation method according to claim 1, characterized in that, The reaction time in step (1) is 1 to 1.5 hours.
11. The preparation method according to claim 1, characterized in that, The atmosphere for the one-step reaction in step (1) includes a protective atmosphere.
12. The preparation method according to claim 11, characterized in that, The protective atmosphere includes nitrogen and / or argon.
13. The preparation method according to claim 1, characterized in that, The molecular weight of polyethylene glycol in the polyethylene glycol aqueous solution in step (2) is 4~10 kDa.
14. The preparation method according to claim 1, characterized in that, The reaction time for the two steps in step (2) is 2 to 6 hours.
15. The preparation method according to claim 1, characterized in that, The atmosphere for the two-step reaction in step (2) includes a protective atmosphere.
16. The preparation method according to claim 15, characterized in that, The protective atmosphere includes nitrogen and / or argon.
17. The preparation method according to claim 1, characterized in that, After the two-step reaction described in step (2), the mixture is filtered, washed, and vacuum dried.
18. The preparation method according to claim 17, characterized in that, The vacuum drying temperature is 70~80℃.
19. The preparation method according to claim 17, characterized in that, The vacuum drying time is 80-90 minutes.
20. The preparation method according to claim 1, characterized in that, In step (3), the spherical ferrous phosphate and lithium phosphate are mixed to obtain a mixture in which the molar ratio of iron to lithium is 1:(1.05~1.1).
21. The preparation method according to claim 1, characterized in that, The mixing method described in step (3) includes ball milling.
22. The preparation method according to claim 21, characterized in that, The ball milling time is 8-12 hours.
23. The preparation method according to claim 21, characterized in that, The dispersant used in the ball milling includes ethanol.
24. The preparation method according to claim 1, characterized in that, The atmosphere for the sintering process in step (3) includes a protective atmosphere.
25. The preparation method according to claim 24, characterized in that, The protective atmosphere includes nitrogen and / or argon.
26. The preparation method according to claim 1, characterized in that, The sintering temperature in step (3) is 650~750℃.
27. The preparation method according to claim 1, characterized in that, The sintering process in step (3) takes 8 to 10 hours.
28. The preparation method according to claim 1, characterized in that, After the sintering process described in step (3), the material is ground.