Positive electrode materials and their preparation methods, positive electrode sheets and batteries
By synthesizing lithium iron manganese phosphate cathode material using Fe-MOF precursor and high-temperature solid-state method, and introducing N and F co-doping technology, the problems of insufficient Li+ diffusion kinetics and electronic conductivity were solved, thereby improving the rate performance and cycle stability of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 中汽新能(天津)电池科技有限公司
- Filing Date
- 2026-03-19
- Publication Date
- 2026-06-02
AI Technical Summary
Existing lithium manganese iron phosphate materials suffer from insufficient Li+ diffusion kinetics and electronic conductivity during electrochemical processes, which hinders their commercial application, especially their poor rate performance and cycle performance.
Fe-MOF precursor was used as the iron source, and cathode material was synthesized by high-temperature solid-state method. N and F co-doping technology was introduced to improve lithium-ion diffusion channels and electronic conductivity through three-dimensional topology and doping.
It significantly improves the diffusion rate and electronic conductivity of lithium ions, enhances the rate performance and cycle life of the battery, reduces damage to the material structure, and extends the battery's lifespan.
Smart Images
Figure CN122136354A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and in particular to a positive electrode material and its preparation method, a positive electrode sheet, and a battery. Background Technology
[0002] Lithium manganese iron phosphate (LMFP), as an upgraded material of lithium iron phosphate (LFP), has become a preferred cathode material for emerging lithium-ion batteries due to its advantages of low cost, high safety, and high energy density. However, the lack of an effective synthesis process to address the challenges in the electrochemical process of Li... + Due to their low diffusion kinetics, poor electronic conductivity, and the problem of Mn dissolution, their commercial application remains challenging. Lithium manganese iron phosphate (LMP) exhibits extremely poor conductivity. According to first principles, the electron energy for electron transitions in LMP is 0.3 eV, classifying it as a semiconductor, while the energy for electron transitions in LMP is 2 eV, classifying it as an insulator. This makes it very difficult to prepare LMP materials capable of reversible charge-discharge, which limits its commercial application. To improve the intrinsic electronic conductivity of LMP materials and the Li... + Improving the ion diffusion coefficient, and further enhancing its rate capability, low-temperature performance, and cycling performance, is a technical problem that urgently needs to be solved at this stage. Summary of the Invention
[0003] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a positive electrode material, its preparation method, a positive electrode sheet, and a battery.
[0004] To achieve the above objectives, this application adopts the following solution: A cathode material includes an iron source, a carbon source, a phosphorus source, a manganese source, and a lithium source, wherein the iron source is an Fe-MOF precursor.
[0005] The Fe-MOF precursor is prepared by mixing a ferric salt and a fumaric acid ligand and then subjecting the mixture to a hydrothermal reaction in a sealed container. Preferably, the molar ratio of the ferric salt to the fumaric acid ligand is (1-1.2):1; more preferably, it is 1.1:1; preferably, the hydrothermal reaction temperature is 40-90℃; more preferably, it is 80℃.
[0006] The molar ratio of lithium source, iron source, manganese source and phosphorus source is (0.55~0.51):(0.43~0.2):(0.65~0.8):(1.1~1.0); preferably 0.55:0.43:0.65:1.1.
[0007] Preferably, the amount of carbon source added is 0.5-2% of the total amount of lithium source, iron source, manganese source, and phosphorus source; more preferably, it is 1.5%. Preferably, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; Preferably, the lithium source includes one or more of lithium carbonate and lithium dihydrogen phosphate; Preferably, the manganese source includes one or more of manganese carbonate, manganese sulfate, manganese oxalate, manganese acetate, and manganese oxide; Preferably, the carbon source includes one or more of sucrose, starch, glucose, phenolic resin, and citric acid.
[0008] The cathode material further includes a dopant NH4F; the amount of NH4F added is 0.05-0.15% of the total amount of lithium source, iron source, manganese source and phosphorus source; preferably 0.08%.
[0009] The cathode material is prepared by sintering lithium source, manganese source, iron source, phosphorus source, carbon source, and dopants, if applicable, using a high-temperature solid-state sintering method.
[0010] Specifically, the following steps are included: (1) Lithium source, manganese source, iron source, phosphorus source, carbon source, dopant and water are added to a sand mill and ground to obtain lithium manganese iron phosphate precursor slurry; preferably, the viscosity of the lithium manganese iron phosphate precursor slurry is controlled at 3000-4000 mPa s. (2) The lithium manganese iron phosphate precursor slurry is spray-dried in a spray tower to obtain lithium manganese iron phosphate precursor particles; preferably, the inlet temperature of the spray tower is set to 250-340℃, the outlet air temperature is set to 80-110℃, and the compressed air pressure is 0.4-0.5Mpa. (3) The spray-dried particles are annealed in an H2 / Ar atmosphere to obtain the desired cathode material.
[0011] In step (3), the annealing temperature is 650℃-750℃; preferably 700℃.
[0012] The present invention also includes a positive electrode sheet, comprising the aforementioned positive electrode material, positive electrode conductive agent, positive electrode binder, and dispersant; Preferably, the mass ratio of the positive electrode material, positive electrode conductive agent, positive electrode binder, and dispersant is 96.2:1.6:2:0.2; Preferably, the positive electrode conductive agent is conductive carbon black and / or single-arm carbon nanotubes; Preferably, the positive electrode binder is polyvinylidene fluoride.
[0013] The present invention also includes a battery comprising the aforementioned positive electrode, negative electrode, separator, and electrolyte.
[0014] The negative electrode sheet includes a negative electrode material, a negative electrode conductive agent, and a negative electrode binder; Preferably, the mass ratio of the negative electrode material, the negative electrode conductive agent, and the negative electrode binder is 96.5:1:2.5; The negative electrode material is graphite; preferably, the negative electrode conductive agent is conductive carbon black; preferably, the negative electrode binder is one or a mixture of sodium carboxymethyl cellulose, SBR, and lithium polyacrylate binder PPA.
[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By synthesizing the organometallic framework Fe-MOF precursor, a three-dimensional topological coordination network structure material is obtained, which has a large specific surface area, high porosity and abundant active sites. As an iron source, the cathode material is synthesized by high temperature solid-state method, which can significantly shorten the lithium-ion diffusion path and improve the rate performance of the battery. At the same time, the original morphological characteristics of the Fe-MOF precursor are maintained, which can better adapt to the volume expansion / contraction during the charging and discharging process, reduce the damage to the material structure, and extend the cycle life of the battery to a certain extent.
[0016] (2) Introducing N and F co-doping technology to improve ionic and electronic conductivity. F doping creates vacancies in metallic iron, widening the Li+ diffusion channel and thus increasing the lithium-ion diffusion rate. Furthermore, F has a stronger electronegativity than O, and F- reacts with Fe... 2+ The bond energy formed is relatively high compared to O. 2- with Fe 2+ It is stronger, enhancing PO4 3- The stability of the functional groups inhibits metal dissolution, thereby improving cycle life. Introducing nitrogen doping creates defects in the carbon layer, inducing more lithium-ion active sites and improving electronic conductivity. Attached Figure Description
[0017] Figure 1 This corresponds to the 0.33C charge / discharge curve of LFMP / NFC / / Gr in Example 1; Figure 2 This corresponds to the 1C-1C cycle curve of LFMP / NFC / / Gr in Example 1. Detailed Implementation
[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0019] Example 1: 1. Synthesis of Fe-MOF precursor: 9.6 mmol of fumaric acid was dissolved in 200 mL of deionized water and stirred at 500 rpm for 10 min at 70 °C to obtain homogeneous solution A. 10.4 mmol of Fe(NO3)3·9H2O was added to 40 mL of deionized water and stirred for 10 min to obtain solution B. Solution A and solution B were then mixed and stirred at 500 rpm for 10 min at 70 °C. The mixture was poured into a polytetrafluoroethylene-lined autoclave and hydrothermally reacted at 80 °C for 2 h. After the reaction, the autoclave was cooled to room temperature, removed, and washed repeatedly by centrifugation with deionized water and ethanol. Then, it was vacuum dried at 100 °C for 6 h to obtain the Fe-MOF precursor.
[0020] 2. A method for preparing the cathode material, comprising the following steps: using ammonium dihydrogen phosphate (NH4H2PO4) as the phosphorus source, lithium carbonate (Li2CO3) as the lithium source, Fe-MOF precursor as the Fe source, and manganese oxalate (MnC2O4) as the Mn source; the molar ratio of the starting materials Li:Fe:Mn:P is 0.55:0.43:0.65:1.1; and introducing 1.5% C sucrose as the carbon source. 12 H 22 O 11 LFMP / NFC was synthesized by high-temperature solid-state synthesis with dopant NH4F 0.08%.
[0021] Specific experimental procedure: (1) Weigh the lithium source, manganese source, iron source, phosphorus source, carbon source and doping additives according to the specified ratio, and slowly add them to the sand mill in a certain order. At the same time, add an appropriate amount of water to control the viscosity of the slurry at 3000-4000 mPa s. After grinding for 3-4 hours, the lithium manganese iron phosphate precursor slurry is obtained; (2) The lithium manganese iron phosphate precursor slurry is conveyed to the spray drying tower through a conduit. Under the compression of compressed air, the slurry is broken into droplets. In a hot environment, the water in the droplets is rapidly evaporated, eventually forming dry particles with uniform particle size distribution. The inlet temperature of the spray tower is set to 250-340℃, the outlet air temperature is set to 80-110℃, and the compressed air pressure is 0.5Mpa. (3) The spray-dried particles were annealed at 700℃ for 10h in H2 / Ar (5:95, volume) atmosphere to obtain LFMP / NFC samples.
[0022] Example 2: The difference between Example 2 and Example 1 is that the annealing temperature in step (3) of the positive electrode material preparation process is 650℃.
[0023] Example 3: The difference between Example 3 and Example 1 is that the annealing temperature in step (3) of the positive electrode material preparation process is 750℃.
[0024] Example 4: The difference between Example 4 and Example 1 is that in the preparation process of the positive electrode material, the compressed air pressure in step (2) is 0.4 MPa.
[0025] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that a conventional iron source (specific material) is used instead of Fe-MOF, and no dopant is added as a comparative example.
[0026] Comparative Example 2: Fe-MOF was replaced with a traditional iron source (specific material), and a dopant was added as Comparative Example 2.
[0027] Comparative Example 3: The iron source is Fe-MOF, and no dopant is added.
[0028] The cathode materials obtained in the examples and comparative examples are used to prepare batteries, including the following steps: (1) Preparation of positive electrode: The positive electrode material obtained in the examples and comparative examples has a content of 96.2%, conductive carbon black content of 1.5%, single-arm carbon nanotube content of 0.1%, binder content of 2.0%, and dispersant content of 0.2%. It is mixed with NMP to prepare a lithium manganese iron phosphate slurry with a solid content of 55-60%. It is coated on a carbon-coated aluminum foil with a thickness of 12 μm and a carbon layer thickness of 1 μm on both sides. The positive electrode is obtained by rolling and die cutting. (2) Preparation of negative electrode sheet: 96.5% graphite active material, 1.0% conductive carbon black, 0.5% sodium carboxymethyl cellulose, 0.5% SBR, and 1.5% lithium polyacrylate binder PPA are mixed with water to prepare a mixed slurry with a solid content of 50-55%. This slurry is then coated onto copper foil, rolled, and die-cut to obtain the negative electrode sheet. (3) Membrane: A polyethylene (PE) base membrane with a porosity of 40±2% and a thickness of 7μm is used. The A side is coated with boehmite (γ-AlOOH) and the B side is coated with an adhesive layer (PVDF). (4) Electrolyte: Lithium hexafluorophosphate (LiPF6) 12.0%, lithium bis(fluorosulfonyl)imide (LiFSI) 3.0%, lithium difluorooxalate borate (LiDFOB) 0.8%, ethylene carbonate (EC) 30.7%, ethyl methyl carbonate (EMC) 41%, ethyl acetate (EA) 10%, fluoroethylene carbonate (FEC) 1.0%, vinylene carbonate (VC) 1.0%, methanedisulfonate (MMDS) 0.5%; (5) Preparation of soft-pack battery: Assemble the above positive and negative electrode sheets, separator and electrolyte into a lithium-ion battery.
[0029] The discharge capacity variation data of the pouch cell prepared in Example 1 at different discharge rates are shown in Figure 1. Table 2 shows a comparison of the data of the battery assembled in Example 1 with other examples and comparative examples.
[0030] Table 1 is a comparison table of the battery rate performance of Example 1 LFMP / NFC / / Gr and Comparative Example 2.
[0031] Table 1
[0032] Figure 1 Example 1: 0.33C charge / discharge curve of LFMP / NFC / / Gr; Figure 2 Table 1 shows the 1C-1C cycling curves of LFMP / NFC / / Gr in Example 1. Table 1 also shows the capacity retention of the LFMP / NFC / / Gr full cell at different rate settings. With increasing rate, the capacity retention is 100.9%, 100.2%, 100%, 99.7%, 99.1%, 98.6%, 97.7%, and 96.7%, respectively. After 100 cycles at 0.1C, the capacity retention is 99.3%. The rate performance test of LFMP / NFC / / Gr demonstrates that LFMP / NFC material can be used as a cathode material for lithium-ion batteries.
[0033] Table 2 Comparison of data from Example 1 with other examples and comparative examples
[0034] As can be seen from Table 2, the pouch cells assembled with the cathode materials of Examples 1-4 have better retention rate, DCR, and discharge specific capacity at 0.33C after 700 cycles than those of Comparative Examples 1-3. This indicates that the cathode materials prepared in this application have a more stable structure during long-term charge and discharge, and have better ionic and electronic conductivity and faster lithium-ion diffusion kinetics, which can effectively improve the cycle stability, rate performance and discharge specific capacity.
[0035] In summary, it can be seen that (1) by synthesizing the organometallic framework Fe-MOF precursor, a three-dimensional topological coordination network structure material is obtained, which has a large specific surface area, high porosity and abundant active sites. As an iron source, the cathode material is synthesized by high temperature solid-state method, which can significantly shorten the lithium-ion diffusion path and improve the rate performance of the battery. At the same time, the original morphological characteristics of the Fe-MOF precursor are maintained, which can better adapt to the volume expansion / contraction during the charging and discharging process, reduce the damage to the material structure, and extend the cycle life of the battery to a certain extent.
[0036] (2) Introducing N and F co-doping technology to improve ionic and electronic conductivity. F doping creates vacancies in metallic iron, widening the Li+ diffusion channel and thus increasing the lithium-ion diffusion rate. Furthermore, F has a stronger electronegativity than O, and F- reacts with Fe... 2+ The bond energy formed is relatively high compared to O. 2- with Fe 2+It is stronger, enhancing PO4 3- The stability of the functional groups inhibits metal dissolution, thereby improving cycle life. Introducing nitrogen doping creates defects in the carbon layer, inducing more lithium-ion active sites and improving electronic conductivity.
[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.
[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A positive electrode material, characterized in that, It includes iron sources, carbon sources, phosphorus sources, manganese sources, and lithium sources, wherein the iron source is an Fe-MOF precursor.
2. The cathode material according to claim 1, characterized in that, The Fe-MOF precursor is prepared by mixing a ferric salt and a fumaric acid ligand and then subjecting the mixture to a hydrothermal reaction in a sealed container. Preferably, the molar ratio of the ferric salt to the fumaric acid ligand is (1-1.2):1; more preferably, it is 1.1:1; preferably, the hydrothermal reaction temperature is 40-90℃; more preferably, it is 80℃.
3. The cathode material according to claim 1, characterized in that, The molar ratio of lithium source, iron source, manganese source, and phosphorus source is (0.55~0.51):(0.43~0.2):(0.65~0.8):(1.1~1.0); preferably 0.55:0.43:0.65:1.
1. Preferably, the amount of carbon source added is 0.5-2% of the total amount of lithium source, iron source, manganese source, and phosphorus source; more preferably, it is 1.5%. Preferably, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; Preferably, the lithium source includes one or more of lithium carbonate and lithium dihydrogen phosphate; Preferably, the manganese source includes one or more of manganese carbonate, manganese sulfate, manganese oxalate, manganese acetate, and manganese oxide; Preferably, the carbon source includes one or more of sucrose, starch, glucose, phenolic resin, and citric acid.
4. The cathode material according to claim 1, characterized in that, It also includes the dopant NH4F; the amount of the dopant NH4F added is 0.05-0.15% of the total amount of lithium source, iron source, manganese source and phosphorus source; preferably 0.08%.
5. A method for preparing the cathode material according to any one of claims 1-4, characterized in that, The lithium source, manganese source, iron source, phosphorus source, carbon source, and dopants are prepared by high-temperature solid-state sintering.
6. The preparation method according to claim 5, characterized in that, Specifically, the following steps are included: (1) Lithium source, manganese source, iron source, phosphorus source, carbon source, dopant (if any) and water are added to a sand mill for grinding to obtain lithium manganese iron phosphate precursor slurry; preferably, the viscosity of the lithium manganese iron phosphate precursor slurry is controlled at 3000-4000 mPa s. (2) The lithium manganese iron phosphate precursor slurry is spray-dried in a spray tower to obtain lithium manganese iron phosphate precursor particles; preferably, the inlet temperature of the spray tower is set to 250-340℃, the outlet air temperature is set to 80-110℃, and the compressed air pressure is 0.4-0.5Mpa. (3) The spray-dried particles are annealed in an H2 / Ar atmosphere to obtain the desired cathode material.
7. The method for preparing the cathode material according to claim 6, characterized in that, In step (3), the annealing temperature is 650℃-750℃; preferably 700℃.
8. A positive electrode plate, characterized in that, Includes the positive electrode material, positive electrode conductive agent, positive electrode binder, and dispersant as described in any one of claims 1-4; Preferably, the mass ratio of the positive electrode material, positive electrode conductive agent, positive electrode binder, and dispersant is 96.2:1.6:2:0.2; Preferably, the positive electrode conductive agent is conductive carbon black and / or single-arm carbon nanotubes; Preferably, the positive electrode binder is polyvinylidene fluoride.
9. A battery, characterized in that, It includes the positive electrode, negative electrode, separator, and electrolyte as described in claim 8.
10. The battery according to claim 9, characterized in that, The negative electrode sheet includes a negative electrode material, a negative electrode conductive agent, and a negative electrode binder; Preferably, the mass ratio of the negative electrode material, the negative electrode conductive agent, and the negative electrode binder is 96.5:1:2.5; The negative electrode material is graphite; preferably, the negative electrode conductive agent is conductive carbon black; preferably, the negative electrode binder is one or a mixture of sodium carboxymethyl cellulose, SBR, and lithium polyacrylate binder PPA.