Lithium iron phosphate positive electrode material, preparation method and application thereof
By using a porous framework structure of nanofibers and aerogels and vanadium-doped lithium iron phosphate cathode materials, the problems of conductivity and lithium-ion diffusion in lithium iron phosphate cathode materials have been solved, thereby improving the electrochemical performance and cycle stability of lithium batteries.
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
- 2026-08-04
AI Technical Summary
Existing lithium iron phosphate cathode materials have low intrinsic conductivity and slow lithium-ion diffusion kinetics, resulting in low actual capacity, which hinders their further development and application.
By employing a porous framework structure built from both nanofibers and aerogels, and doping with vanadium, vanadium-doped graphene/carbon fiber aerogel composite materials were prepared to improve the diffusion rate and conductivity of lithium ions and electrolytes.
It significantly improves the conductivity and electrochemical performance of lithium iron phosphate cathode materials, enhances the electrochemical performance of lithium batteries, and improves the specific capacity and cycle stability of lithium-ion batteries.
Smart Images
Figure CN118479440B_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-ion batteries are currently the most widely used energy storage devices, and their cathode material, lithium iron phosphate (LFP), has attracted widespread attention due to its advantages such as high theoretical specific capacity, good charge-discharge cycle performance, high safety performance, and being environmentally friendly and pollution-free. However, limited by its crystal structure, LFP suffers from defects such as low intrinsic conductivity and slow lithium-ion diffusion kinetics, which results in its actual capacity being lower than its theoretical capacity and seriously hinders its further development and application. Currently, to address these issues, existing technologies often employ high-temperature solid-state or liquid-phase methods, along with modification techniques such as material nano-sizing, ion doping, morphology control, and carbon layer coating, to prepare LFP batteries, thereby improving the capacity retention and specific capacity of lithium-ion batteries.
[0003] CN117936749A discloses a method for preparing large-particle lithium iron phosphate / carbon composite materials and their applications. The preparation method includes grinding and pre-firing raw materials into precursor 1 and precursor 2 in one step, adding carbon source 1, grinding a second time, and sintering to obtain the large-particle lithium iron phosphate / carbon composite material.
[0004] CN117199345A discloses a lithium iron phosphate, its preparation method, and its application. The lithium iron phosphate has a bitter gourd-like structure. The preparation method includes: first mixing a phosphorus source solution, an iron source solution, and oleic acid; then adding a weak base for a second mixing; followed by a microwave hydrothermal reaction and a first sintering to obtain iron phosphate; and finally mixing the iron phosphate with a lithium source and performing a second sintering to obtain the lithium iron phosphate.
[0005] The products prepared by the above-mentioned methods using high-temperature solid-state methods have poor uniformity and impure phases, and the particles are prone to severe agglomeration, which is not conducive to the diffusion and transfer of lithium ions. On the other hand, some technologies such as vapor deposition and microwave hydrothermal methods have problems such as complex processes, difficult reaction process control, and high energy consumption, making it difficult to achieve industrial production.
[0006] Therefore, developing a simple and convenient method to prepare lithium iron phosphate cathode materials that facilitate lithium-ion diffusion and interfacial electrolyte penetration is of great significance for improving the overall electrochemical performance of lithium batteries and promoting their large-scale market application. 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. This invention constructs a porous framework structure with nanofibers and aerogel, which, combined with vanadium doping, achieves a synergistic effect, thereby improving the diffusion rate of lithium ions and electrolytes, increasing the conductivity of the lithium iron phosphate cathode material, and enhancing the overall electrochemical performance of lithium batteries.
[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) A vanadium source, cellulose nanofibers, graphene oxide dispersion and reducing agent are mixed and heated to react to obtain a composite hydrogel. The composite hydrogel is dried to form a composite aerogel and then sintered to obtain a precursor material.
[0011] (2) The precursor material is pretreated and then mixed with an iron source, a phosphorus source, a lithium source and a solvent, and then heat-treated to obtain a lithium iron phosphate precursor;
[0012] (3) The lithium iron phosphate precursor is calcined to obtain the lithium iron phosphate cathode material.
[0013] This invention first uniformly mixes a vanadium source, cellulose nanofibers, graphene oxide dispersion, and a reducing agent, then heats the mixture to obtain a composite hydrogel material, which is subsequently dried to form an aerogel. The aerogel is then carbonized at high temperature to obtain a graphene / vanadium pentoxide / carbon nanofiber composite aerogel material (precursor material). Under hydrothermal conditions, a lithium iron phosphate precursor is grown in situ within the pores of the aerogel material. After the reaction, the resulting precursor powder is ground and then calcined at high temperature under an inert atmosphere for a period of time to obtain a vanadium-doped graphene / carbon nanofiber aerogel composite lithium iron phosphate cathode material. The porous framework structure built by both nanofibers and aerogel, along with vanadium doping, synergistically improves the rapid diffusion of lithium ions and electrolytes, enhances the conductivity of the lithium iron phosphate cathode material, and improves the overall electrochemical performance of the lithium battery.
[0014] Preferably, the vanadium source in step (1) includes ammonium metavanadate.
[0015] Preferably, the reducing agent in step (1) includes ascorbic acid.
[0016] Preferably, the concentration of the graphene dispersion in step (1) is 0.3 to 0.5 g / L, for example: 0.3 g / L, 0.35 g / L, 0.4 g / L, 0.45 g / L or 0.5 g / L, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0017] Preferably, the mass ratio of vanadium source to cellulose nanofiber in step (1) is 1:(8-12), for example: 1:8, 1:9, 1:10, 1:11 or 1:12, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0018] Preferably, the mass ratio of the reducing agent in step (1) to the graphene oxide dispersion is (3-7):1, for example: 3:1, 4:1, 5:1, 6:1 or 7:1, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0019] Preferably, the heating reaction in step (1) includes a water bath heating reaction.
[0020] Preferably, the heating reaction temperature in step (1) is 80 to 100°C, for example: 80°C, 85°C, 90°C, 95°C or 100°C, etc., not limited to the listed values, and other unlisted values within this range are also applicable.
[0021] Preferably, the heating reaction time in step (1) is 0.5 to 1 hour, for example: 0.5 hours, 0.6 hours, 0.8 hours, 0.9 hours or 1 hour, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0022] Preferably, the drying in step (1) is vacuum freeze drying.
[0023] Preferably, the temperature for vacuum freeze drying is -40 to -60°C, for example: -40°C, -45°C, -50°C, -55°C, or -60°C, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0024] Preferably, the vacuum freeze-drying time is 12 to 36 hours, for example: 12 hours, 18 hours, 24 hours, 30 hours or 36 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 sintering process in step (1) includes oxygen-containing nitrogen gas.
[0026] Preferably, the volume percentage of oxygen in the oxygen-containing nitrogen gas is 0.2% to 1%.
[0027] Preferably, the sintering temperature in step (1) is 500 to 700°C, for example: 500°C, 550°C, 600°C, 650°C or 700°C, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0028] Preferably, the sintering time in step (1) is 2 to 3 hours, for example: 2 hours, 2.2 hours, 2.5 hours, 2.8 hours or 3 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0029] Preferably, the sintering process described in step (1) is followed by grinding.
[0030] Preferably, the pretreatment in step (2) includes immersing the precursor material in a hydrogen peroxide solution.
[0031] Preferably, the mass percentage concentration of the hydrogen peroxide solution is 2% to 10%, for example: 2%, 4%, 6%, 8% or 10%, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0032] Preferably, the soaking time is 0.2 to 1 hour, for example: 0.2 hours, 0.4 hours, 0.6 hours, 0.8 hours or 1 hour, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0033] Preferably, the impregnation is followed by washing and drying.
[0034] Preferably, the phosphorus source in step (2) includes any one or a combination of at least two of lithium phosphate, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate.
[0035] Preferably, the lithium source in step (2) includes any one or a combination of at least two of lithium carbonate, lithium acetate, or lithium phosphate.
[0036] Preferably, the solvent in step (2) includes ethanol.
[0037] Preferably, the iron source in step (2) includes ferrous oxalate and / or ferrous sulfate.
[0038] Preferably, the molar ratio of vanadium in the precursor material, lithium in the lithium source, and iron in the iron source in step (2) is (0.05~0.08):1:1, for example: 0.05:1:1, 0.055:1:1, 0.06:1:1, 0.07:1:1 or 0.08:1:1, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0039] Preferably, the heat treatment temperature in step (2) is 150 to 180°C, for example: 150°C, 155°C, 160°C, 170°C or 180°C, etc., not limited to the listed values, and other unlisted values within this range are also applicable.
[0040] Preferably, the heat treatment time in step (2) is 5 to 8 hours, for example: 5 hours, 5.5 hours, 6 hours, 7 hours or 8 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0041] Preferably, the atmosphere for the calcination treatment in step (3) includes nitrogen and / or argon.
[0042] Preferably, the calcination temperature in step (3) is 650 to 750°C, for example: 650°C, 680°C, 700°C, 720°C or 750°C, etc., not limited to the listed values, and other unlisted values within this range are also applicable.
[0043] Preferably, the calcination time in step (3) is 7 to 10 hours, for example: 7 hours, 7.5 hours, 8 hours, 9 hours or 10 hours, etc., and is not limited to the listed values. Other unlisted values within this range are also applicable.
[0044] 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.
[0045] The lithium iron phosphate cathode material described in this invention is a vanadium-doped graphene / carbon fiber aerogel composite lithium iron phosphate cathode material. Carbon nanofibers act as a three-dimensional nano-support framework during the formation of lithium iron phosphate particles, preventing their aggregation. Simultaneously, the porous structure formed by carbon nanofibers and aerogel increases the specific surface area of the cathode material and its contact area with the electrolyte, effectively shortening the lithium-ion transport path and providing more electrochemical reaction active sites, thereby improving the rate performance of the lithium iron phosphate battery. Furthermore, the carbon nanofiber-aerogel structure effectively buffers the volume and stress changes of the electrode material during charge and discharge, thus improving its cycle stability.
[0046] Thirdly, the present invention provides a positive electrode sheet comprising the lithium iron phosphate positive electrode material as described in the second aspect.
[0047] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the third aspect.
[0048] Compared with the prior art, the present invention has the following beneficial effects:
[0049] (1) This invention prepares a vanadium-doped graphene / carbon fiber aerogel composite lithium iron phosphate cathode material. The porous framework structure built by the nanofibers and aerogel and the vanadium doping are conducive to synergistically improving the rapid diffusion of lithium ions and electrolytes, improving the conductivity of lithium iron phosphate cathode material and enhancing the overall electrochemical performance of lithium battery.
[0050] (2) In this invention, vanadium is doped into lithium iron phosphate cathode material. The appropriate doping amount is beneficial to improving the specific capacity and rate performance of the electrode material. In addition, carbon materials graphene and carbon fiber can also be used as carbon reducing agents to inhibit the oxidation of divalent iron ions in the hydrothermal synthesis and high-temperature calcination process of the material, so as to ensure the synthesis of high-purity lithium iron phosphate.
[0051] (3) The lithium iron phosphate cathode material prepared by this invention has good performance indicators, with a specific surface area of up to 14.7 m². 2 The battery, with a capacity of over / g, exhibits superior electrochemical performance after being assembled into a lithium battery. Its 0.1C discharge specific capacity can reach over 158.1 mAh / g, and its 0.5C discharge specific capacity can reach over 152.2 mAh / g. The initial charge-discharge efficiency can reach over 98.28%. By controlling the preparation conditions and parameters, the battery was prepared with a maximum charge-discharge capacity of 159.2 mAh / g and 153.6 mAh / g at 0.1C and 0.5C, respectively, and a maximum initial charge-discharge efficiency of 99.12%. Attached Figure Description
[0052] Figure 1 This is a SEM image of the lithium iron phosphate cathode material prepared in Example 1.
[0053] Figure 2 This is a SEM image of the precursor material described in Example 1.
[0054] Figure 3 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1.
[0055] Figure 4 This is the XPS image of the lithium iron phosphate cathode material prepared in Example 1.
[0056] Figure 5 This is a comparison chart of the cycling performance of lithium-ion coin cells prepared with lithium iron phosphate cathode materials obtained in Example 1 and Comparative Example 3 at a current density of 0.1C. Detailed Implementation
[0057] 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.
[0058] Example 1
[0059] This embodiment provides a lithium iron phosphate cathode material, and the preparation method of the lithium iron phosphate cathode material is as follows:
[0060] (1) 0.1g ammonium metavanadate and 1g cellulose nanofibers were dispersed in 100mL of graphene oxide dispersion with a concentration of 0.5g / L. After mixing evenly, 250mg ascorbic acid was added and stirred for 0.5h. Then, the mixture was heated in a water bath at 90℃ for 0.5h to obtain graphene / vanadate compound (IV) / cellulose nanofiber composite hydrogel (i.e., composite hydrogel). The composite hydrogel was placed in a vacuum freeze dryer at -50℃ for 24h to obtain graphene / vanadate compound (IV) / cellulose nanofiber composite aerogel (i.e., composite aerogel). The aerogel was then placed in a muffle furnace and carbonized at 600℃ for 2h in an atmosphere containing oxygen nitrogen (oxygen volume percentage of 1%). After cooling to room temperature, the product was taken out and ground to obtain the precursor material.
[0061] (2) The precursor material was immersed in 50 mL of hydrogen peroxide solution (5%) for 0.5 h. The product was then taken out and washed with deionized water and anhydrous ethanol in sequence. It was then dried in a vacuum oven at 70 °C overnight. 0.017 mol ferrous sulfate and 0.0057 mol lithium phosphate were dispersed in 60 mL of anhydrous ethanol and mixed evenly. The pretreated precursor material was then added to the above solution (the molar ratio of V element in the precursor material, Li element in the lithium source and Fe element in the iron source was 0.05:1:1). After stirring for 0.5 h, it was poured into a 100 mL stainless steel autoclave and kept at 150 °C for 5 h in an oven. After cooling to room temperature, the product was washed and vacuum dried to obtain the lithium iron phosphate precursor.
[0062] (3) The lithium iron phosphate precursor is thoroughly ground and placed in a tube furnace under an argon atmosphere and calcined at 700°C for 8 hours to obtain a vanadium-doped graphene / carbon fiber aerogel composite lithium iron phosphate cathode material.
[0063] The SEM image of the lithium iron phosphate cathode material is as follows: Figure 1 As shown, by Figure 1 It can be seen that the lithium iron phosphate particles prepared by the method of the present invention are grown in situ in a porous framework constructed of nanofibers / aerogel, and are uniformly distributed.
[0064] The SEM image of the precursor material is as follows: Figure 2 As shown, by Figure 2 It can be seen that the precursor material has a network porous skeleton structure.
[0065] The XRD pattern of the lithium iron phosphate cathode material is as follows: Figure 3 As shown, by Figure 3 It can be seen that the lithium iron phosphate cathode material prepared by the method of the present invention exhibits sharp diffraction peaks and the Pnma space group of crystalline LiFePO4, indicating that the doping of V element has little effect on the structure of LiFePO4.
[0066] The XPS diagram of the lithium iron phosphate cathode material is as follows: Figure 4 As shown, by Figure 4 As can be seen, the XPS spectrum of the lithium iron phosphate cathode material prepared by the method of the present invention shows peaks corresponding to Fe, Li, P and V elements, further indicating that vanadium element has been successfully doped into the structure of lithium iron phosphate.
[0067] Example 2
[0068] This embodiment provides a lithium iron phosphate cathode material, and the preparation method of the lithium iron phosphate cathode material is as follows:
[0069] (1) 0.1g ammonium metavanadate and 0.8g cellulose nanofibers were dispersed in 100mL of graphene oxide dispersion with a concentration of 0.3g / L. After mixing evenly, 90mg ascorbic acid was added and stirred for 0.5h. Then, the mixture was heated in a water bath at 80℃ for 1h to obtain graphene / vanadate compound (IV) / cellulose nanofiber composite hydrogel (i.e., composite hydrogel). The composite hydrogel was placed in a vacuum freeze dryer at -40℃ for 36h to obtain graphene / vanadate compound (IV) / cellulose nanofiber composite aerogel (i.e., composite aerogel). The aerogel was then placed in a muffle furnace and carbonized at 500℃ for 3h in an atmosphere containing oxygen and nitrogen (oxygen volume percentage of 0.5%). After cooling to room temperature, the product was taken out and ground to obtain the precursor material.
[0070] (2) The precursor material was immersed in 50 mL of hydrogen peroxide solution (10%) for 0.2 h. The product was then taken out and washed with deionized water and anhydrous ethanol in sequence. It was then dried overnight in a vacuum oven at 70 °C. 0.0142 mol ferrous sulfate and 0.00472 mol lithium phosphate were dispersed in 60 mL of anhydrous ethanol and mixed evenly. The pretreated precursor material was then added to the above solution (the molar ratio of V element in the precursor material, Li element in the lithium source and Fe element in the iron source was 0.06:1:1). After stirring for 0.5 h, it was poured into a 100 mL stainless steel autoclave and kept at 170 °C for 6 h in an oven. After cooling to room temperature, the product was washed and vacuum dried to obtain the lithium iron phosphate precursor.
[0071] (3) The lithium iron phosphate precursor is thoroughly ground and calcined in a tube furnace under an argon atmosphere at 650°C for 10 hours to obtain a vanadium-doped graphene / carbon fiber aerogel composite lithium iron phosphate cathode material.
[0072] Example 3
[0073] This embodiment provides a lithium iron phosphate cathode material, and the preparation method of the lithium iron phosphate cathode material is as follows:
[0074] (1) 0.1g ammonium metavanadate and 1.2g cellulose nanofibers were dispersed in 100mL of graphene oxide dispersion with a concentration of 0.4g / L. After mixing evenly, 210mg ascorbic acid was added and stirred for 0.5h. Then, the mixture was heated in a water bath at 100℃ for 0.5h to obtain graphene / vanadate compound (IV) / cellulose nanofiber composite hydrogel (i.e., composite hydrogel). The composite hydrogel was placed in a vacuum freeze dryer at -60℃ for 12h to obtain graphene / vanadate compound (IV) / cellulose nanofiber composite aerogel (i.e., composite aerogel). The aerogel was then placed in a muffle furnace and carbonized at 700℃ for 2h in an atmosphere containing oxygen and nitrogen (oxygen volume percentage of 0.2%). After cooling to room temperature, the product was taken out and ground to obtain the precursor material.
[0075] (2) The precursor material was immersed in 50 mL of hydrogen peroxide solution (2%) for 1 h. The product was then taken out and washed with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum oven at 70 °C overnight. 0.0107 mol ferrous sulfate and 0.0036 mol lithium phosphate were dispersed in 60 mL of anhydrous ethanol and mixed evenly. The pretreated precursor material was then added to the above solution (the molar ratio of V element in the precursor material, Li element in the lithium source and Fe element in the iron source was 0.08:1:1). After stirring for 0.5 h, it was poured into a 100 mL stainless steel autoclave and kept at 180 °C for 5 h in an oven. After cooling to room temperature, the product was washed and vacuum dried to obtain the lithium iron phosphate precursor.
[0076] (3) The lithium iron phosphate precursor is thoroughly ground and placed in a tube furnace under an argon atmosphere and calcined at 750°C for 7 hours to obtain a vanadium-doped graphene / carbon fiber aerogel composite lithium iron phosphate cathode material.
[0077] Example 4
[0078] The only difference between this embodiment and Embodiment 1 is that the concentration of the hydrogen peroxide solution in step (2) is 1%, while the other conditions and parameters are exactly the same as in Embodiment 1.
[0079] Example 5
[0080] The only difference between this embodiment and Embodiment 1 is that the concentration of the hydrogen peroxide solution in step (2) is 15%, while the other conditions and parameters are exactly the same as in Embodiment 1.
[0081] Example 6
[0082] The only difference between this embodiment and embodiment 1 is that the molar ratio of vanadium in the precursor material, lithium in the lithium source, and iron in the iron source in step (2) is 0.02:1:1. All other conditions and parameters are exactly the same as in embodiment 1.
[0083] Example 7
[0084] The only difference between this embodiment and embodiment 1 is that the molar ratio of vanadium in the precursor material, lithium in the lithium source, and iron in the iron source in step (2) is 0.1:1:1. All other conditions and parameters are exactly the same as in embodiment 1.
[0085] Comparative Example 1
[0086] The only difference between this comparative example and Example 1 is that ammonium metavanadate is not added; all other conditions and parameters are exactly the same as in Example 1.
[0087] Comparative Example 2
[0088] The only difference between this comparative example and Example 1 is that vanadium-doped lithium iron phosphate cathode material is prepared instead of aerogel precursor material. The specific operation is as follows:
[0089] 0.017 mol ferrous sulfate and 0.0057 mol lithium phosphate were dispersed in 60 mL anhydrous ethanol and stirred for 0.5 h. The mixture was then poured into a 100 mL stainless steel autoclave and kept at 150 °C for 5 h in an oven. After cooling to room temperature, the product was washed and vacuum dried to obtain a lithium iron phosphate precursor. Subsequently, the precursor powder was thoroughly mixed and ground with 0.00085 mol ammonium metavanadate and calcined at 700 °C for 8 h in a tube furnace under an argon atmosphere to obtain vanadium-doped lithium iron phosphate cathode material (the molar ratio of V, Li, and Fe is 0.05:1:1).
[0090] Comparative Example 3
[0091] This comparative example directly uses a hydrothermal, high-temperature calcination method to prepare lithium iron phosphate cathode material. The specific operation is as follows:
[0092] 0.017 mol ferrous sulfate and 0.0057 mol lithium phosphate were dispersed in 60 mL anhydrous ethanol and stirred for 0.5 h. The mixture was then poured into a 100 mL stainless steel autoclave and kept at 150 °C for 5 h in an oven. After cooling to room temperature, the product was washed and vacuum dried to obtain a lithium iron phosphate precursor. Subsequently, the precursor powder was ground and calcined at 700 °C for 8 h in a tube furnace under an argon atmosphere to obtain the lithium iron phosphate cathode material.
[0093] Comparative Example 4
[0094] The only difference between this comparative example and Example 1 is that vacuum freeze-drying is not performed; all other conditions and parameters are exactly the same as in Example 1.
[0095] Performance testing:
[0096] The specific surface area of the lithium iron phosphate cathode materials prepared in the examples and comparative examples was tested by the BET method.
[0097] The lithium iron phosphate cathode materials prepared in the examples and comparative examples were used to fabricate coin cells for lithium-ion battery electrochemical performance testing (with charge / discharge voltage controlled between 2.5-4.5V). The test results are shown in Table 1.
[0098] Table 1
[0099]
[0100]
[0101] As shown in Table 1, and based on Examples 1-3, the specific surface area of the lithium iron phosphate cathode material prepared by the method of the present invention can reach 14.7 m². 2 The specific capacity at 0.1C discharge is above 158.1mAh / g, the specific capacity at 0.5C discharge is above 152.2mAh / g, and the initial charge / discharge efficiency is above 98.28%.
[0102] A comparison of Examples 1 and 4-5 shows that the concentration of the pretreated hydrogen peroxide solution affects the performance of the lithium iron phosphate cathode material prepared according to the present invention. Controlling the mass percentage concentration of hydrogen peroxide between 2% and 10% results in a better-performing lithium iron phosphate cathode material. If the concentration of the hydrogen peroxide solution is too high, its strong oxidizing properties may damage the pore structure of the precursor material, thereby affecting the electrical performance of the prepared cathode material. If the concentration of the hydrogen peroxide solution is too low, it may lead to incomplete exposure of oxygen-containing groups on the surface of the precursor material, reducing its ability to complex metal ions in the mixture, thus affecting the formation of the lithium iron phosphate material.
[0103] A comparison of Examples 1 and 6-7 shows that the amount of vanadium added during the preparation of the lithium iron phosphate cathode material of the present invention affects its performance. Controlling the molar ratio of vanadium in the precursor material, lithium in the lithium source, and iron in the iron source to 0.05–0.08:1:1 yields a lithium iron phosphate cathode material with better performance. Excessive vanadium addition leads to unstable cathode material structure, resulting in reduced electron and ion transport efficiency, and decreased battery capacity and charge / discharge efficiency. Conversely, insufficient vanadium addition is detrimental to improving the electronic conductivity and rate performance of the cathode material.
[0104] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention incorporates vanadium into the lithium iron phosphate cathode material. The appropriate doping amount is beneficial to improving the specific capacity and rate performance of the electrode material. At the same time, the porous framework structure built by both nanofibers and aerogel and the vanadium doping are beneficial to synergistically improving the rapid diffusion of lithium ions and electrolytes, improving the conductivity of the lithium iron phosphate cathode material, and enhancing the overall electrochemical performance of the lithium battery.
[0105] As can be seen from the comparison between Example 1 and Comparative Example 2, in the lithium iron phosphate cathode material of the present invention, carbon nanofibers can act as a three-dimensional nano-support framework during the formation of lithium iron phosphate particles, preventing their aggregation. At the same time, the porous structure formed by carbon nanofibers superimposed with aerogel can increase the specific surface area of the cathode material and the contact area with the electrolyte, effectively shortening the lithium ion transport path and providing more electrochemical reaction active sites, thereby improving the rate performance of lithium iron phosphate batteries. In addition, the carbon nanofiber superimposed with aerogel structure can effectively buffer the volume and stress changes of the electrode material during charging and discharging, thereby improving its cycle stability.
[0106] The comparison of the cycle performance of lithium-ion coin cells prepared with lithium iron phosphate cathode materials obtained in Example 1 and Comparative Example 3 at a current density of 0.1C is shown in the figure below. Figure 5 As shown, a comparison between Example 1 and Comparative Example 3 reveals that the lithium iron phosphate described in this invention is doped with metal elements and has a three-dimensional porous structure, which has the advantages of large specific surface area, short and fast lithium-ion diffusion path and low de-intercalation / de-intercalation resistance. Therefore, the lithium-ion battery exhibits superior electrochemical performance.
[0107] As can be seen from the comparison between Example 1 and Comparative Example 4, the precursor material prepared by sintering the hydrogel after vacuum freeze-drying has a porous structure, which enables the cathode material prepared from it to have better electrochemical performance; while the hydrogel that has not been vacuum-frozen exhibits an agglomerated morphology after sintering, which is not conducive to improving the electrical performance of the electrode material.
[0108] 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) A vanadium source, cellulose nanofibers, graphene oxide dispersion and reducing agent are mixed and heated to react to obtain a composite hydrogel. The composite hydrogel is dried to form a composite aerogel and then sintered to obtain a precursor material. The heating reaction includes a water bath heating reaction; The heating reaction is carried out at a temperature of 80~100℃ for a time of 0.5~1h; The atmosphere for the sintering process includes oxygen-containing nitrogen gas, wherein the volume percentage of oxygen in the oxygen-containing nitrogen gas is 0.2% to 1%. The sintering process is carried out at a temperature of 500~700℃ for 2~3 hours. (2) After pretreatment of the precursor material, it is mixed with iron source, phosphorus source, lithium source and solvent, and then heat-treated to obtain lithium iron phosphate precursor; The molar ratio of vanadium in the precursor material, lithium in the lithium source, and iron in the iron source is (0.05~0.08):1:1; The pretreatment includes immersing the precursor material in a hydrogen peroxide solution, wherein the hydrogen peroxide solution has a mass percentage concentration of 2-10%. The heat treatment is performed at a temperature of 150~180℃ for 5~8 hours. (3) The lithium iron phosphate precursor is calcined to obtain the lithium iron phosphate cathode material; The atmosphere for the calcination treatment includes nitrogen and / or argon; The calcination treatment is carried out at a temperature of 650~750℃ for 7~10 hours.
2. The preparation method according to claim 1, characterized in that, The vanadium source in step (1) includes ammonium metavanadate.
3. The preparation method according to claim 1, characterized in that, The reducing agent in step (1) includes ascorbic acid.
4. The preparation method according to claim 1, characterized in that, The concentration of the graphene oxide dispersion in step (1) is 0.3~0.5 g / L.
5. The preparation method according to claim 1, characterized in that, The mass ratio of vanadium source to cellulose nanofiber in step (1) is 1:(8~12).
6. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the reducing agent to the graphene oxide dispersion is (3~7):
1.
7. The preparation method according to claim 1, characterized in that, The drying process in step (1) includes vacuum freeze drying.
8. The preparation method according to claim 7, characterized in that, The vacuum freeze-drying temperature is -40~-60℃.
9. The preparation method according to claim 7, characterized in that, The vacuum freeze-drying time is 12~36 hours.
10. The preparation method according to claim 1, characterized in that, After the sintering process described in step (1), the material is ground.
11. The preparation method according to claim 1, characterized in that, The soaking time is 0.2 to 1 hour.
12. The preparation method according to claim 1, characterized in that, The soaking process is followed by washing and drying.
13. The preparation method according to claim 1, characterized in that, The phosphorus source in step (2) includes any one or a combination of at least two of lithium phosphate, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate.
14. The preparation method according to claim 1, characterized in that, The lithium source in step (2) includes any one or a combination of at least two of lithium carbonate, lithium acetate, or lithium phosphate.
15. The preparation method according to claim 1, characterized in that, The solvent in step (2) includes ethanol.
16. The preparation method according to claim 1, characterized in that, The iron source in step (2) includes ferrous oxalate and / or ferrous sulfate.
17. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is prepared by the method described in any one of claims 1-16.
18. A positive electrode plate, characterized in that, The positive electrode comprises the lithium iron phosphate positive electrode material as described in claim 17.
19. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 18.