Positive electrode material, preparation method thereof and lithium ion battery
By modifying lithium manganese iron phosphate materials with medium entropy doping and carbon coating, the problem of poor cycle life of lithium manganese iron phosphate batteries was solved, the battery conductivity and structural stability were improved, and longer cycle life and better rate performance were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EVE ENERGY CO LTD
- Filing Date
- 2025-12-26
- Publication Date
- 2026-05-01
AI Technical Summary
Lithium iron manganese phosphate batteries suffer from manganese leaching during charging and discharging, resulting in poor cell cycle life and failing to meet market demands.
The lithium manganese iron phosphate material was modified using medium-entropy doping technology. By introducing three transition metal elements and magnesium or aluminum doping into the material, combined with a carbon material coating layer, the lithium ion insertion/extraction path was optimized and the conductivity was improved.
It improves the conductivity and structural stability of lithium manganese iron phosphate batteries, enhances the rate performance and cycle life of the batteries, and achieves a capacity retention rate of 90%~93% after 2000 cycles.
Smart Images
Figure CN121964632A_ABST
Abstract
Description
Cathode materials and their preparation methods, lithium-ion batteries Technical Field
[0001] This application relates to the field of lithium-ion battery technology, specifically to a cathode material and its preparation method, and a lithium-ion battery. Background Technology
[0002] Driven by both the "dual-carbon" strategy and industrial transformation, the electrification of commercial vehicles is accelerating rapidly. However, the energy density of lithium iron phosphate (LFP) cells is currently low, and LFP battery packs suffer from drawbacks such as short driving range and heavy weight, hindering the penetration of commercial vehicles in the long-haul logistics sector. Lithium manganese iron phosphate (LFP) batteries, with their high energy density and high safety, are gradually becoming a significant force driving this transformation.
[0003] However, lithium manganese iron phosphate, as a cathode material, suffers from a large amount of manganese leaching during charging and discharging, resulting in poor cell cycle life and an inability to meet market demand for the number of cycles.
[0004] Therefore, how to develop methods to modify lithium manganese iron phosphate cathode materials to improve the cycle life of lithium manganese iron phosphate batteries is a problem that needs to be solved. Summary of the Invention
[0005] The purpose of this application is to provide a cathode material and its preparation method, as well as a lithium-ion battery, in order to solve the problem of poor cycle life of existing lithium manganese iron phosphate batteries.
[0006] The first embodiment of this application provides a cathode material, comprising: a core, wherein the core comprises a material with the chemical formula LiMn x Fe 1-x-y M y The active material of PO4, wherein 0.4≤x≤0.7, 0.05≤y≤0.2, and M is selected from at least three elements selected from transition metal elements, magnesium, and aluminum; a coating layer covering the surface of the core, the coating layer comprising a carbon material.
[0007] In some embodiments, M includes a first dopant element M1, a second dopant element M2, and a third dopant element M3. M1, M2, and M3 are each independently selected from any one of Ir, Co, Ni, Cu, Zn, Mg, Al, Ti, Zr, Nb, and Mo, and M1, M2, and M3 are different from each other. The molar percentages of M1, M2, and M3 in the active material are not exactly the same.
[0008] In some embodiments, the molar ratio of M1, M2 and M3 satisfies (0.01~0.1):(0.01~0.1):(0.01~0.1).
[0009] In some embodiments, the mass ratio of the kernel to the overlay is (48.25~244.5):1.
[0010] In some embodiments, the ratio between the thickness of the coating layer and the particle size of the core is (0.00008~0.01):1.
[0011] In some embodiments, the thickness of the coating layer is 2~20 nm.
[0012] In some embodiments, the kernel has a particle size of 2~25μm.
[0013] The second embodiment of this application provides a method for preparing a cathode material, which is used to prepare the cathode material in any of the above embodiments, including the following steps: providing a lithium source, a manganese source, an iron source, an M source, a phosphorus source and a carbon source, adding an organic solvent to mix, ball milling and drying to obtain a cathode material precursor; mixing the cathode material precursor with a conductive agent solution, evaporating the organic solvent, pre-calcining, heating, and high-temperature sintering to obtain the cathode material.
[0014] In some embodiments, the molar ratio of the lithium source, the manganese source, the iron source, the M source, the phosphorus source and the carbon source is (0.095~0.105):(0.045~0.055):(0.045~0.055):(0.002~0.008):0.1:(0.005~0.05).
[0015] In some embodiments, the mass ratio of the positive electrode material precursor to the conductive agent is 1:(0.002~0.022).
[0016] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate.
[0017] In some embodiments, the manganese source includes at least one of manganese acetate, manganese carbonate, and manganese sulfate.
[0018] In some embodiments, the iron source includes at least one of ferric nitrate, ferric oxide, and ferric sulfate.
[0019] In some embodiments, the M source includes at least three of the following: cobalt nitrate, cobalt carbonate, cobalt tetroxide, nickel sulfate, nickel hydroxide, nickel oxide, nickel nitrate, zinc nitrate, zinc oxide, zinc sulfate, and dimethyl zinc.
[0020] In some embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate and phosphoric acid.
[0021] In some embodiments, the carbon source includes at least one of citric acid, glucose, and polyvinylpyrrolidone.
[0022] In some embodiments, the organic solvent includes at least one of ethanol, tetrahydrofuran, and acetone.
[0023] In some embodiments, the conductive agent includes at least one of graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, and Super P.
[0024] In some embodiments, the pre-calcination temperature is 150~400℃ and the time is 2~8h.
[0025] In some embodiments, the high-temperature sintering temperature is 500~900℃ and the time is 5~10h.
[0026] The third embodiment of this application provides a lithium-ion battery, including a positive electrode sheet, wherein the positive electrode sheet includes the positive electrode material in any of the above embodiments or the positive electrode material prepared by the preparation method in any of the above embodiments; the capacity retention rate of the lithium-ion battery after 2000 cycles is 90%~93%.
[0027] This application provides a cathode material, comprising: a core, the core comprising a material with the chemical formula LiMn x Fe 1-x-y M y The active material is PO4, wherein 0.4 ≤ x ≤ 0.7, 0.05 ≤ y ≤ 0.2, and M is selected from at least three elements selected from transition metals, magnesium, and aluminum; a coating layer is applied to the surface of the core, and the coating layer includes carbon material. This application optimizes the lithium-ion insertion / extraction pathway and reduces the activation energy of lithium sites by performing medium-entropy doping on the material, thereby enabling rapid insertion / extraction of lithium ions within the material. Simultaneously, the outer carbon coating layer provides favorable reaction conditions for the interfacial chemical reaction of lithium ions on the cathode material surface, thereby improving the conductivity and structural stability of the cathode material, and ultimately improving the rate performance and cycle life of the battery. Attached Figure Description
[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0029] Figure 1 is an electron micrograph of the cathode material in Embodiment 1 of this application. Detailed Implementation
[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0031] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection, an indirect connection through an intermediate medium, or an indirect connection through a pipe or conduit; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.
[0032] Lithium manganese iron phosphate (LiMn) x Fe 1-x PO4 (LMFP) as a cathode material suffers from low conductivity and difficulty in lithium-ion insertion / extraction, resulting in poor rate performance of the battery cell and failing to meet market demands; LiMn x Fe 1-x PO4 has an olivine crystal structure, which is unstable and results in a large amount of manganese dissolution, leading to poor cell cycle life and an inability to achieve 4,000 cycles.
[0033] Conventional lithium manganese iron phosphate cathode materials can be prepared by simultaneously mixing soluble lithium, iron, manganese, phosphorus, and carbon sources to prepare a precursor, followed by high-temperature calcination. However, this method suffers from problems such as large and uneven particle size, high manufacturing costs, low conductivity, and localized manganese enrichment in the material.
[0034] The applicant discovered through research that by modifying lithium manganese iron phosphate materials with medium-entropy doping (i.e., introducing 3 to 4 doping elements into lithium manganese iron phosphate materials to make the mixed entropy of the materials at a medium level), the crystal structure can be effectively optimized, thereby improving its conductivity and structural stability, and achieving an improvement in the rate performance and cycle life of lithium manganese iron phosphate batteries.
[0035] The first embodiment of this application provides a cathode material, comprising: a core, the core comprising a material with the chemical formula LiMn x Fe 1-x-y M y The active material of PO4, wherein 0.4≤x≤0.7, 0.05≤y≤0.2, and M is selected from at least three elements selected from transition metal elements, magnesium, and aluminum; a coating layer, which coats the surface of the core, and the coating layer includes carbon materials.
[0036] It is understandable that, since element M includes at least three doping elements, it can perform medium-entropy doping on lithium manganese iron phosphate materials, slightly distorting the initial olivine crystal structure of lithium manganese iron phosphate, thereby optimizing the lithium-ion insertion / extraction path and reducing the activation energy of lithium sites, allowing lithium ions to rapidly insert / extract within the material. Simultaneously, the outer carbon coating layer provides favorable reaction conditions for the interfacial chemical reaction of lithium ions on the cathode material surface, thereby improving the conductivity and structural stability of the cathode material, and ultimately improving the rate performance and cycle life of the battery. The value of x can be any value from 0.4, 0.5, 0.6, 0.7 or any value within the range of any two values, and the value of y can be any value from 0.05, 0.08, 0.11, 0.14, 0.17, 0.2 or any value within the range of any two values. When the value of y meets the above range, it can ensure the effective improvement of the crystal structure of lithium manganese iron phosphate, while avoiding excessive doping that leads to excessive occupation of active sites in the crystal lattice, resulting in a reduction in the number of lithium ions that can participate in insertion and extraction, leading to a decrease in cell capacity and consequently a deterioration in the rate performance of the battery.
[0037] In some embodiments, M includes a first dopant element M1, a second dopant element M2, and a third dopant element M3. M1, M2, and M3 are each independently selected from any one of Ir, Co, Ni, Cu, Zn, Mg, Al, Ti, Zr, Nb, and Mo, and M1, M2, and M3 are different from each other. The molar percentages of M1, M2, and M3 in the active material are not exactly the same.
[0038] It is understandable that when an active material contains three doping elements, its chemical formula can also be written as LiMn. x Fe 1-x-y M 1y1 M 2y2 M 3y3 PO4, where 0.05 ≤ y1 + y2 + y3 ≤ 0.2, and at most two parameters of y1, y2, and y3 have the same value. By controlling the doping elements in the active material to three types, on the one hand, it is possible to increase the entropy of the system by mixing multiple doping elements, thereby promoting the formation of a stable single solid solution lattice in the material; on the other hand, it is possible to avoid the reduction of the specific capacity of the battery due to excessive doping elements.
[0039] In some embodiments, the molar ratio of M1, M2, and M3 satisfies (0.01~0.1):(0.01~0.1):(0.01~0.1).
[0040] Based on the above embodiments, 0 < y1 ≤ 0.1, 0 < y2 ≤ 0.1, 0 < y3 ≤ 0.1. It can be understood that the value of y1 can be any value among 0.02, 0.04, 0.06, 0.08, 0.1 or a value within the range between any two of these values. The value of y2 can be any value among 0.02, 0.04, 0.06, 0.08, 0.1 or a value within the range between any two of these values. The value of y3 can be any value among 0.02, 0.04, 0.06, 0.08, 0.1 or a value within the range between any two of these values. When y1, y2, and y3 satisfy the above value ranges, the distortion effect of M1, M2, and M3 on the crystal lattice can be fully exerted, forming a lithium-ion diffusion path with a low diffusion barrier, while avoiding excessive lattice distortion caused by too high content of a certain element and preventing the hindrance of lithium-ion migration.
[0041] In some embodiments, the mass ratio of the core to the coating layer is (48.25~244.5):1.
[0042] It can be understood that the value of the mass ratio of the core to the coating layer can be any value among 48.25:1, 97.4:1, 146.55:1, 195.7:1, 244.5:1 or a value within the range between any two of these values. When the mass ratio of the core to the coating layer satisfies the above value range, it can ensure that the coating layer formed by the carbon material can fully cover the surface of the core, providing a continuous conductive network and effectively improving the conductivity of the material; at the same time, it can avoid the reduction of the active material content caused by too high proportion of the coating layer, achieving the balance between the conductive performance and the capacity performance of the cathode material.
[0043] In some embodiments, the ratio of the thickness of the coating layer to the particle size of the core is (0.00008~0.01):1.
[0044] It can be understood that when calculating the ratio of the thickness of the coating layer to the particle size of the core, the dimensions of the thickness of the coating layer and the particle size of the core are the same. The value of the ratio of the thickness of the coating layer to the particle size of the core can be any value among 0.00008:1, 0.0025:1, 0.005:1, 0.0075:1, 0.01:1 or a value within the range between any two of these values. By controlling the ratio of the thickness of the coating layer to the particle size of the core to satisfy the above value range, it can ensure that the cathode material has a relatively stable structure, and at the same time, it will not increase the lithium-ion interface transfer resistance due to the coating layer being too thick relative to the core.
[0045] In some embodiments, the thickness of the coating layer is 2~20 nm.
[0046] It is understandable that the thickness of the coating layer can be any value from 2nm, 6nm, 10nm, 14nm, 18nm, and 20nm, or any value within a range of any two values. When the thickness of the coating layer meets the above range, it can further ensure that the cathode material has a relatively stable structure, while not increasing the lithium-ion interface transport resistance due to the coating layer being too thick relative to the core.
[0047] In some embodiments, the kernel size is 2~25μm.
[0048] It is understandable that the core particle size can be any value from 2μm, 6μm, 10μm, 14μm, 18μm, 22μm, and 25μm, or any value within a range of two such values. When the core particle size meets the above-mentioned range, it can further ensure that the core particle size achieves a balance between specific surface area and structural stability, thereby improving the lithium-ion reactivity while reducing the pulverization of cathode particles during battery cycling.
[0049] The second embodiment of this application provides a method for preparing a cathode material, which is used to prepare the cathode material in any of the above embodiments, including the following steps: providing a lithium source, a manganese source, an iron source, an M source, a phosphorus source and a carbon source, adding an organic solvent to mix, ball milling and drying to obtain a cathode material precursor; mixing the cathode material precursor with a conductive agent solution, evaporating the organic solvent, pre-calcining, heating, and high-temperature sintering to obtain the cathode material.
[0050] It is understandable that by adding source M during the preparation of the precursor, the dopant element is uniformly mixed with other elements. Subsequent pre-calcination and high-temperature sintering then form a hierarchical porous structure modified lithium manganese iron phosphate cathode material coated with a three-dimensional porous carbon network. Specifically, the source M includes at least sources M1, M2, and M3, and sources M1, M2, and M3 are distinct from each other. The above preparation method employs a solid-state process, which is simple and suitable for industrial production.
[0051] In some embodiments, the molar ratio of lithium source, manganese source, iron source, M source, phosphorus source and carbon source is (0.095~0.105):(0.045~0.055):(0.045~0.055):(0.002~0.008):0.1:(0.005~0.05).
[0052] It is understandable that when the added proportions of lithium, manganese, iron, M, phosphorus, and carbon sources meet the above-mentioned ranges, it can ensure that each element reacts fully in stoichiometric proportions to form the ideal LiMn. x Fe 1-x-y M y PO4 is an active substance that prevents the formation of impurity phases.
[0053] Furthermore, the molar ratio of source M1, source M2 and source M3 is (0.01~0.1):(0.01~0.1):(0.01~0.1).
[0054] It is understandable that when the molar ratio of sources M1, M2, and M3 meets the above-mentioned range, it can ensure that each doping element has an ideal doping ratio during the process of medium-entropy doping of the active material, thereby forming a lithium-ion diffusion path with low diffusion energy barrier.
[0055] In some embodiments, the mass ratio of the positive electrode material precursor to the conductive agent is 1:(0.002~0.022).
[0056] It is understandable that the mass ratio of the cathode material precursor to the conductive agent can be any value from 1:0.002, 1:0.006, 1:0.01, 1:0.014, 1:0.018, 1:0.022, or any value within a range of any two values. By controlling the mass ratio of the cathode material precursor to the conductive agent to meet the above-mentioned range, the conductive agent can fully coat the surface of the cathode material precursor and form a continuous conductive network, ensuring that the formed core particle size and coating layer thickness have an ideal ratio.
[0057] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate.
[0058] In some embodiments, the manganese source includes at least one of manganese acetate, manganese carbonate, and manganese sulfate.
[0059] In some embodiments, the iron source includes at least one of ferric nitrate, ferric oxide, and ferric sulfate.
[0060] In some embodiments, the M source includes at least three of the following: cobalt nitrate, cobalt carbonate, cobalt tetroxide, nickel sulfate, nickel hydroxide, nickel oxide, nickel nitrate, zinc nitrate, zinc oxide, zinc sulfate, and dimethyl zinc.
[0061] In some embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate and phosphoric acid.
[0062] In some embodiments, the carbon source includes at least one of citric acid, glucose, and polyvinylpyrrolidone.
[0063] Furthermore, citric acid is preferred as the carbon source, as it can better dissolve metal compounds and help disperse metal atoms.
[0064] In some embodiments, the organic solvent includes at least one of ethanol, tetrahydrofuran, and acetone.
[0065] In some embodiments, the conductive agent includes at least one of graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, and Super P.
[0066] In some embodiments, the pre-calcination temperature is 150~400℃ and the time is 2~8h.
[0067] Understandably, the pre-calcination temperature can be any value from 150℃, 200℃, 250℃, 300℃, 350℃, and 400℃, or any value within a range of any two values. The pre-calcination time can be any value from 2h, 3h, 4h, 5h, 6h, 7h, and 8h, or any value within a range of any two values. When the pre-calcination temperature and time meet the above ranges, volatile impurities in the precursor can be effectively removed, high-temperature sintering defects can be avoided, and violent reactions at high temperatures can be suppressed, ensuring ordered crystal lattice formation.
[0068] In some embodiments, the high-temperature sintering temperature is 500~900℃ and the time is 5~10h.
[0069] Understandably, the high-temperature sintering temperature can be any value from 500℃, 600℃, 700℃, 800℃, and 900℃, or any value within a range of any two values. The high-temperature sintering time can be any value from 5h, 6h, 7h, 8h, 9h, and 10h, or any value within a range of any two values. When the high-temperature sintering temperature and time meet the above ranges, sufficient crystal growth can be ensured, and the cathode material exhibits good structural stability and an ideal specific surface area.
[0070] The third embodiment of this application provides a lithium-ion battery, including a positive electrode sheet, which includes the positive electrode material in any of the above embodiments or the positive electrode material prepared by the preparation method in any of the above embodiments; the lithium-ion battery has a capacity retention rate of 90% to 93% after 2000 cycles.
[0071] The following specific embodiments illustrate the cathode material, its preparation method, and the lithium-ion battery provided in this application: Embodiment 1 This embodiment provides a cathode material, prepared in the following manner: according to the chemical formula LiMn 0.46 Fe 0.47 M 0.070.1 mol of PO4 (M1=Co, M2=Ni, M3=Zn, and y1=0.02, y2=0.02, y3=0.03) was weighed. 0.1 mol of lithium carbonate, 0.046 mol of manganese acetate, 0.047 mol of iron nitrate, 0.002 mol of cobalt nitrate, 0.002 mol of nickel nitrate, 0.003 mol of zinc nitrate, and 0.1 mol of ammonium dihydrogen phosphate were mixed with citric acid and an ethanol-tetrahydrofuran complex solvent, ball-milled for 8 hours, and dried to obtain the cathode material precursor.
[0072] The cathode material precursor was mixed with a graphene solution (30g, solid content 0.5%), the organic solvent was evaporated, and the mixture was pre-calcined at 350℃ for 5h, and then sintered at 700℃ for 8h to form the cathode material.
[0073] The prepared cathode material was characterized by electron microscopy, and the characterization image is shown in Figure 1. As can be seen from Figure 1, the cathode material prepared by the method provided in this application has a relatively uniform core-shell structure.
[0074] Examples 2-6 are prepared in the same way as Example 1, except for the adjustment of the reactants.
[0075] Comparative Example 1: The preparation method of Comparative Example 1 is the same as that of Example 1, except for the adjustment of the reactants.
[0076] Table 1
[0077] Comparative Example 3 This comparative example provides a cathode material prepared by the following method: according to the chemical formula LiMn 0.5 Fe 0.5 Weigh 0.1 mol of raw material: Mix the raw material lithium source (0.1 mol lithium carbonate), manganese source (0.046 mol manganese acetate), iron source (0.047 mol ferric nitrate), phosphorus source (0.1 mol ammonium dihydrogen phosphate), carbon source (citric acid), and ethanol-tetrahydrofuran compound solvent, ball mill for 8 hours, and dry to obtain the cathode material precursor.
[0078] The cathode material precursor was mixed with a graphene solution (30g, solid content 0.5%), the organic solvent was evaporated, and the mixture was pre-calcined at 350℃ for 5h, and then sintered at 700℃ for 8h to form the cathode material.
[0079] Comparative Example 4 provides a cathode material prepared in the following manner: according to the chemical formula LiMn 0.46 Fe 0.46 Mg 0.08Weigh 0.1 mol of raw material: Mix the raw material lithium source (0.1 mol lithium carbonate), manganese source (0.046 mol manganese acetate), iron source (0.046 mol ferric nitrate), magnesium source (0.008 mol magnesium carbonate), phosphorus source (0.1 mol ammonium dihydrogen phosphate) with carbon source (citric acid) and ethanol-tetrahydrofuran complex solvent, ball mill for 8 hours, and dry to obtain the cathode material precursor.
[0080] The cathode material precursor was mixed with a graphene solution (30g, solid content 0.5%), the organic solvent was evaporated, and the mixture was pre-calcined at 350℃ for 5h, and then sintered at 700℃ for 8h to form the cathode material.
[0081] The conductivity of the above-mentioned cathode material was tested using the four-probe method.
[0082] The above positive electrode material is used to prepare a lithium-ion battery. The steps are as follows: 1. Preparation of raw materials for positive electrode sheet preparation: Weigh 85% lithium iron phosphate (LiFePO4) as positive electrode active material, 7% polyvinylidene fluoride (PVDF) as binder, and 8% conductive carbon black (SuperP) as conductive agent according to the mass fraction. Place them in a dry container for later use and control the ambient humidity to below 30%.
[0083] Slurry preparation: PVDF is added to N-methylpyrrolidone (NMP) and stirred until dissolved. Conductive carbon black is added and stirred to disperse. Finally, lithium iron phosphate is added and stirred at low speed first and then at high speed to form a uniform positive electrode slurry.
[0084] Electrode coating and drying: The slurry was coated onto 20μm aluminum foil using an automatic coating machine, with the coating speed controlled at 0.5m / min and the thickness at 150μm. After coating, the foil was placed in a vacuum drying oven at 120℃ for 12h.
[0085] Electrode rolling: The electrode is rolled at a pressure of 100MPa using a roller press to achieve a compaction density of approximately 2.3g / cm³.
[0086] 2. Preparation of negative electrode sheet (using graphite as negative electrode active material) Raw material preparation: Weigh 92% artificial graphite as negative electrode active material, 4% sodium carboxymethyl cellulose (CMC) as thickener, and 4% styrene-butadiene rubber (SBR) as binder.
[0087] Slurry preparation: CMC is added to deionized water and stirred to dissolve, SBR is added and stirred to disperse, and finally artificial graphite is added. The mixture is stirred at low speed first and then at high speed to form a negative electrode slurry.
[0088] Electrode coating and drying: The slurry was coated onto a 12μm copper foil using an automatic coating machine, with the coating speed controlled at 0.6m / min and the thickness at 100μm. After coating, the foil was placed in a vacuum drying oven at 80℃ for 8 hours.
[0089] 3. Preparation of battery assembly separator: Select 25μm polypropylene (PP) microporous separator and cut it to the appropriate size.
[0090] Electrolyte injection: In a dry argon glove box (water and oxygen content less than 0.1 ppm), inject a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 mol / L lithium hexafluorophosphate (LiPF6) (volume ratio 1:1) into the battery case to wet the positive and negative electrode plates and the separator.
[0091] Battery packaging: The positive electrode, separator and negative electrode are stacked in sequence, put into the battery case, and the battery cover and case are sealed and welded together with a laser welding machine.
[0092] The above-mentioned lithium-ion batteries were subjected to cycle performance and rate performance tests. The test methods included: 1. Cycle test: Initial charge and discharge: At a specific temperature (e.g., 25°C), the battery was charged with a constant current until the set charging cutoff voltage was reached. Subsequently, it was discharged with a constant current until the discharge cutoff voltage was reached. The initial charge and discharge capacity was recorded.
[0093] Cyclic charge and discharge: Repeat the above charge and discharge process, and record the battery capacity after each cycle.
[0094] Termination condition: Stop the test when the battery capacity decays to 80% of the initial capacity, and record the number of cycles as the battery's cycle life.
[0095] 2. Rate testing: Select the rate: Choose different charge / discharge rates according to the test requirements, such as 0.2C, 0.5C, 1C, 2C, etc.
[0096] Constant current charge / discharge: At a specific temperature, the battery is charged at a selected rate using a constant current until the charging cutoff voltage is reached. Subsequently, it is discharged at the same rate using a constant current until the discharging cutoff voltage is reached. The charge / discharge capacity and voltage changes are recorded.
[0097] Repeated testing: Repeat the above charge and discharge process at different rates and record the data for each test.
[0098] The results are shown in Table 2.
[0099] Table 2
[0100] As shown in Table 2, the cathode material obtained by the scheme provided in this application exhibits good performance in terms of conductivity, rate capability, and cycle stability. Comparative Example 1 shows that when the total molar percentage of doped elements y > 0.2, it affects the conductivity of the cathode material. Comparative Example 2 shows that when the molar ratio of M1, M2, and M3 does not meet the condition (0.01~0.1):(0.01~0.1):(0.01~0.1), it also affects the conductivity of the cathode material. Comparative Example 3 shows that the LMFP cathode material without M doping has low conductivity and a significant decrease in capacity retention after cycling. Comparative Example 4 shows that the conductivity of the LMFP cathode material with single Mg doping is improved, but the rate capability is low, and the cycle stability is not ideal.
[0101] The above provides a detailed description of the cathode material and its preparation method, as well as the lithium-ion battery, provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A positive electrode material, characterized in that, include: The core, comprising the chemical formula LiMn x Fe 1-x-y M y The active substance of PO4, wherein 0.4≤x≤0.7, 0.05≤y≤0.2, and M is selected from at least three elements selected from transition metal elements, magnesium and aluminum; A coating layer, covering the surface of the core, the coating layer comprising a carbon material.
2. The cathode material according to claim 1, characterized in that, M includes a first dopant element M1, a second dopant element M2, and a third dopant element M3. M1, M2, and M3 are each independently selected from any one of Ir, Co, Ni, Cu, Zn, Mg, Al, Ti, Zr, Nb, and Mo. M1, M2, and M3 are all different from each other, and the molar percentages of M1, M2, and M3 in the active material are not exactly the same.
3. The cathode material according to claim 2, characterized in that, The molar ratio of M1, M2 and M3 satisfies (0.01~0.1):(0.01~0.1):(0.01~0.1).
4. The cathode material according to claim 1, characterized in that, The mass ratio of the core to the coating layer is (48.25~244.5):
1.
5. The cathode material according to claim 1, characterized in that, The ratio between the thickness of the coating layer and the particle size of the core is (0.00008~0.01):
1.
6. The cathode material according to claim 1, characterized in that, The thickness of the coating layer is 2~20nm; and / or the particle size of the core is 2~25μm.
7. A method for preparing a cathode material as described in any one of claims 1 to 6, characterized in that, The process includes the following steps: providing a lithium source, a manganese source, an iron source, an M source, a phosphorus source, and a carbon source; mixing them with an organic solvent; ball milling and drying to obtain a cathode material precursor; mixing the cathode material precursor with a conductive agent solution; evaporating the organic solvent; pre-calcining; heating; and high-temperature sintering to obtain the cathode material.
8. The method for preparing the cathode material according to claim 7, characterized in that, The molar ratio of the lithium source, the manganese source, the iron source, the M source, the phosphorus source, and the carbon source is (0.095~0.105):(0.045~0.055):(0.045~0.055):(0.002~0.008):0.1:(0.005~0.05); and / or, the mass ratio of the cathode material precursor to the conductive agent is 1:(0.002~0.022).
9. The method for preparing the cathode material according to claim 7, characterized in that, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate; and / or, the manganese source includes at least one of manganese acetate, manganese carbonate, and manganese sulfate; and / or, the iron source includes at least one of ferric nitrate, ferric oxide, and ferric sulfate; and / or, the M source includes at least three of cobalt nitrate, cobalt carbonate, cobalt tetroxide, nickel sulfate, nickel hydroxide, nickel oxide, nickel nitrate, zinc nitrate, zinc oxide, zinc sulfate, and dimethyl zinc; and / or, the phosphorus source includes at least one of ammonium dihydrogen phosphate and phosphoric acid; and / or, the carbon source includes at least one of citric acid, glucose, and polyvinylpyrrolidone; and / or, the organic solvent includes at least one of ethanol, tetrahydrofuran, and acetone; and / or, the conductive agent includes at least one of graphene, single-walled carbon nanotubes, and multi-walled carbon nanotubes.
10. The method for preparing the cathode material according to claim 7, characterized in that, The pre-calcination temperature is 150~400℃ and the time is 2~8h; and / or the high-temperature sintering temperature is 500~900℃ and the time is 5~10h.
11. A lithium-ion battery, comprising a positive electrode, characterized in that, The positive electrode sheet comprises the positive electrode material as described in any one of claims 1 to 6 or the positive electrode material prepared by the preparation method as described in any one of claims 7 to 10; the capacity retention rate of the lithium-ion battery after 2000 cycles is 90% to 93%.