Lithium iron phosphate composite material and preparation method thereof, lithium ion battery positive electrode material and lithium ion battery
By coating the surface of lithium iron phosphate with pyrophosphate to form an amorphous film, the problems of insufficient electronic conductivity and kinetic performance of lithium iron phosphate cathode materials are solved, and efficient charging and discharging and low-temperature performance of lithium-ion batteries are improved.
Patent Information
- Application Number
- CN202511125706.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-12
- Publication Date
- 2025-11-21
AI Technical Summary
The low electronic conductivity, poor kinetic performance, and poor low-temperature performance of lithium iron phosphate cathode materials limit their application in lithium-ion batteries.
By coating the surface of lithium iron phosphate with pyrophosphate, an amorphous film layer with good lithium-ion conductivity is formed, which enhances the migration ability of Li+ in the crystal and suppresses the side reactions between lithium iron phosphate and electrolyte, thereby improving cycle stability.
It significantly improves the kinetic performance and cycle stability of lithium iron phosphate materials, and enhances the charge-discharge efficiency and low-temperature performance of lithium-ion batteries.
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Figure CN120998960A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium iron phosphate composite material, a preparation method thereof, a lithium ion battery cathode material and a lithium ion battery. BACKGROUND
[0002] A lithium ion battery mainly comprises a positive electrode, an electrolyte and a negative electrode. Among them, the lithium ion battery cathode material is the key factor to determine the electrochemical performance, safety performance, energy density and price cost of the battery. At present, there are many lithium ion battery cathode materials, such as cobalt-based cathode materials, nickel-based cathode materials, manganese-based cathode materials, lithium iron phosphate cathode materials, etc.
[0003] Among them, lithium iron phosphate as a lithium ion battery cathode material has the advantages of high theoretical specific capacity, flat discharge platform, excellent cycle performance, good structural stability and thermal stability, etc., and the raw materials are widely available, the price is low, and it is friendly to the environment, so it has great market prospect in various mobile power fields, especially in the field of large-scale power sources required by electric vehicles, and becomes a new generation of lithium ion battery cathode material with the greatest development and application potential. However, its electronic conductivity is low, and its kinetic performance and low-temperature performance are poor. SUMMARY
[0004] In view of the above problems of the prior art, the present application provides a lithium iron phosphate composite material and a preparation method thereof, and a lithium ion battery cathode material and a lithium ion battery. By coating lithium iron phosphate with pyrophosphate, the chemical diffusion coefficient of Li+ is improved, and the kinetic performance is improved.
[0005] In a first aspect, the present application provides a lithium iron phosphate composite material, which is composed of a matrix and a coating layer; the matrix is LiFePO4 / C (carbon-coated lithium iron phosphate); the composition of the coating layer is M2P2O7 or M4(P2O7)3; wherein M is a metal element selected from one of Fe, Zn, Cu, Mn, Ti, V, Nb, Ni, Co, Zr and Mg; the composition of the coating layer is M2P2O7 or M4(P2O7)3; wherein M is a metal element selected from one of Fe, Zn, Cu, Mn, Ti, V, Nb, Ni, Co, Zr and Mg.
[0006] As a preferred technical solution, the mass ratio of the matrix to the coating layer is 97.8-99.99:0.01-2.2.
[0007] In a second aspect, the present application provides a preparation method of the lithium iron phosphate composite material, comprising the following steps: S1, mixing raw materials containing a lithium source compound, an iron source compound, a phosphorus source compound and a carbon source compound, and then calcining I to obtain LiFePO4 / C; S2, mixing pyrophosphoric acid, a M salt and the LiFePO4 / C, and then calcining II to obtain the lithium iron phosphate composite material.
[0008] As a preferred technical solution, the ratio of the lithium source compound, the iron source compound, the phosphorus source compound and the carbon source compound is (1-2.2):(1-1.5):1:(0.4-1.5), preferably (1-2):(1-1):1:(1-1.5), and more preferably 1:1:1:1, in terms of the molar ratio of lithium element, iron element, phosphorus element and carbon element.
[0009] As a preferred technical solution, the lithium source compound is at least one selected from lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate, lithium nitrate and lithium dihydrogen phosphate.
[0010] As a preferred technical solution, the iron source compound is at least one selected from ferrous oxide, triiron tetroxide, diiron trioxide, iron nitrate, iron phosphate, ferrous nitrate and ferrous oxalate.
[0011] As a preferred technical solution, the phosphorus source compound is at least one selected from phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate and iron phosphate.
[0012] As a preferred technical solution, the carbon source is at least one selected from glucose, sucrose, lactose, phenolic resin, graphene, carbon nanotube and graphite.
[0013] The M salt is one or more of nitrate, oxalate, acetate, sulfate and phosphate of M.
[0014] The synthesis of the LiFePO4 / C material can be performed by two-step calcination or one-step calcination: the one-step calcination method, i.e. carbonthermal reduction method, involves adding an excess amount of carbon source, so as to reduce Fe 3+ to Fe 2+ .
[0015] As a preferred technical solution, the calcining I is performed by one-step method or two-step method; the conditions of the one-step method include: inert atmosphere, temperature of 600-800℃, and time of 12-24h; the conditions of the two-step method include: inert atmosphere, first calcining at 300-400℃ for 5-6h, and then calcining at 600-800℃ for 8-12h; the inert atmosphere is preferably nitrogen or argon.
[0016] As a preferred technical scheme, before the calcining I, the method further comprises a mixing treatment I, wherein the lithium source compound, the iron source compound, the phosphorus source compound, the carbon source compound and a dispersing agent are mixed and ball milled, and then dried at 45-85℃.
[0017] As a preferred technical scheme, the calcining II is performed at 400-650℃ for 5-12h, preferably at 450-600℃.
[0018] As a preferred technical scheme, the mass ratio of the pyrophosphoric acid, the M salt and the LiFePO4 / C is (2-5):(3-15):(80-95).
[0019] In a third aspect, the present application provides a lithium ion battery cathode material, which comprises the lithium iron phosphate composite material of any one of the first aspect or the lithium iron phosphate composite material obtained by the preparation method of any one of the second aspect.
[0020] In a fourth aspect, the present application provides a lithium ion battery, which comprises the lithium ion battery cathode material of the third aspect.
[0021] In theory, Li + can be deintercalated by the electrolyte on any surface of the lithium iron phosphate crystal, however, Li + can only migrate into the crystal through the (010) surface of the lithium iron phosphate crystal. The present application generates an amorphous film layer with good lithium ion conduction ability on the surface of the material, so that Li + is easily conducted to the surface of the crystal grain, and meanwhile the amorphous film layer eliminates the anisotropy of the crystal surface, enhances the migration ability of Li + on the (010) surface, and can greatly improve the kinetic performance of the lithium iron phosphate material.
[0022] The lithium ion battery cathode material provided by the present application uses pyrophosphate as the coating layer, which does not participate in the electrochemical reaction, can inhibit the side reaction of the lithium iron phosphate with the electrolyte, reduce the structural deformation in the charging and discharging process, and thus improves the cycle stability. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1 is the SEM image of the Zn2P2O7-coated LiFePO4 / C cathode material obtained in Example 1;
[0024] Figure 2 is the specific capacity graph of the Zn2P2O7-coated LiFePO4 / C cathode material obtained in Example 1 and the LiFePO4 / C cathode material obtained in Comparative Example 1 under different current densities. DETAILED DESCRIPTION
[0025] The present application is further described below in conjunction with specific embodiments, but does not constitute any limitation to the present application.
[0026] Example 1
[0027] Lithium carbonate, ferrous oxalate, ammonium dihydrogen phosphate and graphite were mixed in a molar ratio of 1:1:1:0.8, and ball-milled with anhydrous ethanol as a dispersant. The mixed material was dried at 60°C under vacuum to remove the dispersant, and a dry precursor was obtained.
[0028] The dry precursor was calcined at 350°C for 10h under nitrogen atmosphere to completely decompose the raw materials, and then calcined at 750°C for 10h to obtain LiFePO4 / C material.
[0029] Pyrophosphoric acid and zinc nitrate were ground in anhydrous ethanol for 30min (the amount of anhydrous ethanol was just enough to soak the materials), and then LiFePO4 / C material was added and ground for another 1h. The mass ratio of pyrophosphoric acid, zinc nitrate and LiFePO4 / C was 3:6:91. The dry precursor was then dried at 70°C, and calcined at 450°C for 10h under nitrogen atmosphere to obtain Zn2P2O7-coated LiFePO4 / C.
[0030] The SEM image of Zn2P2O7-coated LiFePO4 / C composite material is shown in Figure 1 , which shows that the particles have good dispersibility, smooth surface, clear boundaries between particles, and no obvious agglomeration phenomenon. The particle size is about 0.5-1.2μm.
[0031] Test Example
[0032] Zn2P2O7-coated LiFePO4 / C was used as a positive electrode material to assemble a lithium ion battery, and the test results are shown in Table 1 and Figure 2 .
[0033] The positive electrode material, conductive carbon black, dispersant and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97.4:0.7:0.2:1.7, and then N-methyl pyrrolidone (NMP) was added in a high-speed mixer and uniformly mixed to obtain a positive electrode slurry with a solid content of 64%. The slurry was coated on one side of an aluminum foil with a thickness of 12μm using a transfer coater, and dried to maintain the dry weight of the coating per unit area at 21.5mg / cm 2 . Then the same process was used to coat and dry the other side of the aluminum foil to obtain a positive electrode sheet semi-finished product.
[0034] The artificial graphite powder, conductive carbon black, CMC, PAA and SBR were mixed in a mass ratio of 96.5:1:0.4:1.7:0.4, and then deionized water was added in a high-speed blender and uniformly mixed into a negative electrode slurry with a solid content of 52%. The slurry was coated on one side of a copper foil with a thickness of 8 μm using a transfer coater and dried, keeping the dry coating weight per unit area at 9.8 mg / cm 2 . Then the other side of the copper foil was coated and dried using the same procedure to obtain a negative electrode tab half-finished product.
[0035] The exposed metal foil part of the above positive electrode tab half-finished product and negative electrode tab half-finished product was processed and welded into a tab, and then wound with a separator film to form a core. The core was wrapped with an aluminum plastic film to form a semi-finished battery core, which was dried and then injected with an electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a lithium ion battery was obtained.
[0036] Rate discharge test method and parameters: at 25±1℃, the battery was charged to 3.65V at 0.33C, then charged at 3.65V, the cutoff current was 0.05C, then rested for 30min, and discharged at 0.33C, 0.5C, 1C and 2C to 2.50V respectively. The capacity during discharge was recorded, and the discharge capacity at 0.33C was taken as the initial capacity, and the ratio of other rate discharge capacities to it was taken as the discharge capacity retention rate.
[0037] Low-temperature discharge test method and parameters: at 25±1℃, the battery was charged to 3.65V at 0.33C, then charged at 3.65V, the cutoff current was 0.05C, rested for 30min, and discharged at 0.33C to 2.50V. The capacity during discharge was recorded. The battery was charged to 3.65V at 0.33C, then charged at 3.65V, the cutoff current was 0.05C, and the fully charged battery was placed at -20℃ for 24h to ensure uniform and constant temperature of the whole battery, and then discharged at 0.33C to 2.50V. The discharge capacity was recorded. The low-temperature discharge capacity retention rate was the ratio of the discharge capacity measured at -20℃ to the discharge capacity measured at room temperature.
[0038] 25℃ cycle test method and parameters: at 25±1℃, the battery was charged to 3.65V at 1C, then charged at 3.65V, the cutoff current was 0.05C, rested for 30min, and discharged at 1C to 2.50V. This process was repeated for cycle test, and the cycle capacity retention rate was the ratio of the discharge capacity of the last cycle to the discharge capacity of the first cycle.
[0039] SEM test method and parameters: the test sample is coated on the test sample table, the acceleration voltage is set to 10 kV, the beam current is 6.0, the T2 probe is used, and the SEM test is carried out at a resolution of 10000X. The relevant data are observed and recorded, such as Figure 1 as shown.
[0040] Cycling rate test method and parameters: at 25±1℃, the battery is charged to 3.65V at 0.1C, then charged at 3.65V, the cutoff current is 0.05C, and the battery is rested for 30min, then discharged to 2.50V at 0.1C, repeated 10 times, which is the 10 times cycle gram capacity at 0.1C, and so on, the 10 times cycle gram capacity at 0.2C, 0.5C, 1C, 0.1C can be obtained, such as Figure 2 as shown.
[0041] Comparative Example 1
[0042] Lithium carbonate, ferrous oxalate, ammonium dihydrogen phosphate and graphite are mixed in a molar ratio of 1:1:1:0.8, ball milled with anhydrous ethanol as a dispersant, and the mixed material is dried at 60℃ under vacuum after uniform mixing to remove the dispersant, and a dried precursor is obtained.
[0043] The dried precursor is heated at 350℃ for 10h under nitrogen atmosphere to completely decompose the raw materials, and then heated at 750℃ for 10h to obtain LiFePO4 / C material.
[0044] According to the method of the test example, LiFePO4 / C is used as the positive electrode material, and a lithium ion battery is assembled to test its performance, and the test results are shown in Table 1 and Figure 2 .
[0045] Figure 2 It is shown that the discharge capacity of Example 1 at 0.1C, 0.2C, 0.5C and 1C is 160.5mAh / g, 156.0mAh / g, 148.2mAh / g and 141.3mAh / g respectively, and the discharge capacity returns to 159.1mAh / g when the rate returns to 0.1C; the discharge capacity of Comparative Example 1 at 0.1C, 0.2C, 0.5C and 1C is 150.3mAh / g, 142.1mAh / g, 132.4mAh / g and 121.7mAh / g respectively, and the discharge capacity returns to 147.5mAh / g when the rate returns to 0.1C. It can be seen that the Zn2P2O7-coated LiFePO4 / C positive electrode material of Example 1 significantly improves the rate performance.
[0046] Example 2
[0047] Iron oxide, lithium dihydrogen phosphate and glucose were mixed in a molar ratio of 1:1:1.5 of lithium, iron, phosphorus and carbon elements, and ball-milled with anhydrous ethanol as a dispersant. The mixed material was dried at 60°C under vacuum to remove the dispersant, and a dried precursor was obtained.
[0048] The dried precursor was calcined at 650°C for 24h under a nitrogen atmosphere to obtain a LiFePO4 / C material.
[0049] Pyrophosphoric acid and manganese sulfate were ground in anhydrous ethanol for 30min, and then LiFePO4 / C material was added (in a mass ratio of pyrophosphoric acid:manganese sulfate:LiFePO4 / C material = 3:6:91) and ground for another 1h. The dried precursor was calcined at 500°C for 10h under a nitrogen atmosphere, and a Mn2P2O7-coated LiFePO4 / C material was obtained after cooling.
[0050] According to the method of the test example, the Mn2P2O7-coated LiFePO4 / C material was used as a positive electrode material, and a lithium ion battery was assembled to test its performance. The test results are shown in Table 1.
[0051] Comparative Example 2
[0052] Iron oxide, lithium dihydrogen phosphate and glucose were mixed in a molar ratio of 1:1:1.5 of lithium, iron, phosphorus and carbon elements, and ball-milled with anhydrous ethanol as a dispersant. The mixed material was dried at 60°C under vacuum to remove the dispersant, and a dried precursor was obtained.
[0053] The dried precursor was calcined at 650°C for 24h under a nitrogen atmosphere to obtain a LiFePO4 / C material.
[0054] According to the method of the test example, the LiFePO4 / C material was used as a positive electrode material, and a lithium ion battery was assembled to test its performance. The test results are shown in Table 1.
[0055] Example 3
[0056] Lithium carbonate, iron phosphate and sucrose were mixed in a molar ratio of 1:1:1 of lithium, iron and phosphorus elements, and ball-milled with anhydrous ethanol as a dispersant. The mixed material was dried at 60°C under vacuum to remove the dispersant, and a dried precursor was obtained.
[0057] The dried precursor was incubated at 350°C for 6h under a nitrogen atmosphere to completely decompose the raw materials, and then incubated at 700°C for 15h to obtain a LiFePO4 / C material.
[0058] Pyrophosphoric acid and copper sulfate were ground in anhydrous ethanol for 30 min, then LiFePO4 / C material was added (mass ratio: pyrophosphoric acid: manganese sulfate: LiFePO4 / C material = 3:6:91) and ground for 1 h, then dried at 70°C, and the dried precursor was calcined at 550°C for 10 h under nitrogen atmosphere, and Cu2P2O7-coated LiFePO4 / C was obtained after cooling.
[0059] According to the method of the test example, Cu2P2O7-coated LiFePO4 / C was used as the positive electrode material, and a lithium ion battery was assembled to test its performance, and the test results are shown in Table 1.
[0060] Example 4
[0061] Lithium acetate, diiron trioxide, diammonium hydrogen phosphate and glucose were mixed in a molar ratio of 1:1:1:1.5, and ball-milled with anhydrous ethanol as a dispersant. The mixed material was dried at 60°C under vacuum to remove the dispersant, and a dried precursor was obtained.
[0062] The dried precursor was heated at 300°C for 5 h under nitrogen atmosphere to completely decompose the raw materials, and then heated at 800°C for 10 h to obtain LiFePO4 / C material.
[0063] Pyrophosphoric acid and iron oxalate were ground in anhydrous ethanol for 30 min, then LiFePO4 / C material was added (mass ratio: pyrophosphoric acid: manganese sulfate: LiFePO4 / C material = 3:6:91) and ground for 1 h, then dried at 70°C, and the dried precursor was calcined at 600°C for 10 h under nitrogen atmosphere, and Fe4(P2O7)3-coated LiFePO4 / C was obtained after cooling.
[0064] According to the method of the test example, Fe4(P2O7)3-coated LiFePO4 / C was used as the positive electrode material, and a lithium ion battery was assembled to test its performance, and the test results are shown in Table 1.
[0065] Table 1
[0066] Group 2C rate discharge capacity retention rate (%) -20°C discharge capacity retention rate (%) 25°C @ 1C cycle 800 cls after capacity retention rate (%) Example 1 89.80％ 37.12％ 98.13％ Example 2 89.94％ 41.23％ 94.11％ Example 3 88.66％ 40.23％ 98.42％ Example 4 88.61％ 36.20％ 98.86％ Comparative Example 1 85.63％ 32.60％ 92.20％ Comparative Example 2 84.38％ 33.37％ 89.94％
[0067] Any numerical values recited herein include all values from the lower value and up to the upper value. Values that are recited herein include intermediate values unless the context clearly indicates otherwise. Thus, to illustrate, a range of " 50% to 90%" is intended to include, in addition to the recited range, values such as 51 to 89, 52 to 88, 53 to 87, etc. Likewise, other ranges can be expressed to include integers and non-integers as appropriate. In the application, similar principles apply to other numerical values recited herein as would normally be understood by one skilled in the art.
[0068] It should be noted that the foregoing examples have been provided merely for the purposes of illustration and are not intended to limit the application. The application has been described in reference to exemplary embodiments thereof. It should be understood that the words which have been used herein are words of description, and that they are being utilized under the description and definition with regard to the application rather than under a strict literal interpretation. Discretions have been made herein as to what has been disclosed for the sake of providing a concise description. Modifications of the disclosed embodiments incorporating the essential characteristics thereof can be made without departing from the spirit and scope thereof. Although the present application has been described in detail with reference to the examples described above, it should be understood that various modifications can be made without departing from the spirit of the application. Accordingly, other embodiments are within the scope of the following claims.
Claims
1. A lithium iron phosphate composite material, characterized in that, The lithium iron phosphate composite material consists of a matrix and a coating layer; The matrix is LiFePO4 / C; The coating layer is composed of M2P2O7 or M4(P2O7)3; wherein M is a metallic element selected from Fe, Zn, Cu, Mn, Ti, V, Nb, Ni, Co, Zr, and Mg.
2. The lithium iron phosphate composite material according to claim 1, characterized in that, The mass ratio of the substrate to the coating layer is 97.8–99.99:0.01–2.
2.
3. The method for preparing the lithium iron phosphate composite material according to claim 1 or 2, characterized in that, Including the following steps: S1 contains raw materials containing lithium source compounds, iron source compounds, phosphorus source compounds and carbon source compounds, which are then calcined to obtain LiFePO4 / C; S2 pyrophosphate, M salt and the LiFePO4 / C are mixed and calcined (II) to obtain the lithium iron phosphate composite material.
4. The preparation method according to claim 3, characterized in that, The ratio of the lithium source compound, iron source compound, phosphorus source compound, and carbon source compound, based on the molar ratio of lithium, iron, phosphorus, and carbon, is (1-2.2):(1-1.5):1:(0.4-1.5). And / or, the lithium source compound is selected from at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate, lithium nitrate and lithium dihydrogen phosphate; And / or, the iron source compound is selected from at least one of ferrous oxide, magnetite, ferric oxide, ferric nitrate, ferrous nitrate and ferrous oxalate; And / or, the phosphorus source compound is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, and ammonium phosphate; And / or, the carbon source is selected from at least one of glucose, sucrose, lactose, phenolic resin, graphene, carbon nanotubes and graphite.
5. The preparation method according to claim 3 or 4, characterized in that, The calcination I is performed using a one-step or two-step method; The conditions for the one-step method include: inert atmosphere, temperature 600-800℃, and time 12-24h; The conditions for the two-step method include: an inert atmosphere, calcination at 300-500℃ for 4-8 hours, and then calcination at 600-800℃ for 8-12 hours; Preferably, the inert atmosphere is nitrogen or argon; And / or, before the calcination I, the mixture treatment I is further included: the lithium source compound, iron source compound, phosphorus source compound, carbon source compound and dispersant are mixed and ball-milled, and then dried at 45-85°C.
6. The method for preparing the lithium iron phosphate composite material according to any one of claims 3-5, characterized in that, The M salt is one or more of the nitrate, oxalate, acetate, sulfate, and phosphate of M.
7. The method for preparing the lithium iron phosphate composite material according to any one of claims 3-6, characterized in that, The conditions for calcination II include: 400℃~650℃, 5~12h.
8. The method for preparing the lithium iron phosphate composite material according to any one of claims 3-7, characterized in that, The mass ratio of the pyrophosphate, M salt and LiFePO4 / C is (2-5):(3-15):(80-95).
9. A lithium-ion battery cathode material, characterized in that, The lithium iron phosphate composite material containing any one of claims 1 or 2, or the lithium iron phosphate composite material obtained by any one of claims 3-8.
10. A lithium-ion battery, characterized in that, It contains the lithium-ion battery cathode material as described in claim 9.