Iron manganese lithium phosphate cathode material, preparation method thereof, cathode sheet and lithium ion battery

Abstract

The application provides a lithium iron manganese phosphate positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. x Mn y M z PO4 particles, wherein 0 The application performs medium-entropy doping on the lithium iron manganese phosphate positive electrode material, and four different metal elements are doped in the lithium iron manganese phosphate positive electrode material, which helps to avoid the problems of side reactions and high material production cost caused by high-temperature sintering required by high-entropy doping, and the types of the four different metal elements are controlled within the above range, which helps to improve the cycle performance and rate performance of the lithium iron manganese phosphate positive electrode material. Therefore, the lithium iron manganese phosphate positive electrode material has excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a lithium iron manganese phosphate cathode material, its preparation method, cathode sheet, and lithium-ion battery. Background Technology

[0002] With the widespread adoption of mobile internet devices such as smartphones and laptops, the promotion of electric vehicles such as electric cars, and the development of aerospace technologies such as drones and space probes, lithium-ion batteries have become a widely used key energy storage device due to their many advantages, such as high volumetric and mass energy density, long cycle life, and no memory effect.

[0003] Lithium iron phosphate (LFP) cathode material has a very stable olivine crystal structure and boasts advantages such as good charge-discharge cycle stability, high safety, and low cost and availability, making it the most widely used commercial lithium-ion battery cathode material. However, LFP cathode material has a relatively low discharge voltage plateau (3.4V), resulting in a lower energy density. Lithium manganese iron phosphate (LMP), on the other hand, has a similar structure to LFP, with a theoretical specific capacity close to 170 mAh / g and a higher discharge voltage plateau (approximately 4.1V). Therefore, LMP's theoretical energy density is about 20% higher than that of LFP, making it a promising next-generation high-energy-density cathode material. However, LMP contains Mn during charge-discharge processes. 3+ The Jahn-Teller effect causes lattice distortion in lithium manganese iron phosphate (LFP), leading to poor cycle performance. Furthermore, LFP's low electronic and ionic conductivity also contributes to its poor rate performance. Although researchers have made significant modifications to LFP cathode materials, such as doping with metals or non-metals in the bulk phase and carbon coating the surface, its structural stability still needs improvement. Summary of the Invention

[0004] The main objective of this invention is to provide a lithium iron manganese phosphate cathode material, its preparation method, cathode sheet, and lithium-ion battery, in order to solve the problems of poor structural stability and low rate performance of lithium iron manganese phosphate cathode materials in the prior art.

[0005] To achieve the above objectives, according to one aspect of the present invention, a lithium iron manganese phosphate cathode material is provided, the lithium iron manganese phosphate cathode material comprising LiFe x Mn y M zPO4 particles, wherein 0 < x < 1, 0 < y < 1, 0.01 ≤ z ≤ 0.1, x + y + z = 1, and M is selected from any four metallic elements from Al, Mg, Ti, V, Nb, and Ag. The variety of these four different metallic elements helps to increase the cell parameters of the lithium iron manganese phosphate cathode material, which is beneficial for the extraction and insertion of lithium ions during charging and discharging, thereby improving the cycle performance and rate performance of the lithium iron manganese phosphate cathode material. The aforementioned z range helps to form a uniform medium-entropy doped crystal structure, thus disrupting the original stable crystal structure.

[0006] Furthermore, the molar ratio of the four metal elements is 0.8–1.2:0.8–1.2:0.8–1.2:0.8–1.2, preferably 1:1:1:1. This molar ratio helps to further improve the structural stability of the lithium iron manganese phosphate cathode material.

[0007] Furthermore, the aforementioned lithium iron manganese phosphate cathode material includes elemental carbon, which is distributed across different LiFe... x Mn y M z In the pores formed between PO4 particles, elemental carbon and LiFe... x Mn y M z The mass ratio of PO4 particles is 0.2 to 5:100. This mass ratio helps to further improve the efficiency of lithium-ion extraction and insertion.

[0008] Furthermore, in the aforementioned lithium iron manganese phosphate cathode material, the cell parameters a are 1.0412–1.0510 nm, b are 0.6070–0.6197 nm, and c are 0.4727–0.4814 nm; and / or, the D50 particle size of the lithium iron manganese phosphate cathode material is 0.2–0.5 μm. Lithium iron manganese phosphate cathode materials with the above-mentioned cell parameter range are beneficial for the extraction and insertion of lithium ions during charging and discharging.

[0009] According to another aspect of the present invention, a method for preparing the aforementioned lithium iron manganese phosphate cathode material is provided. The method includes: step S1, sequentially grinding and dehydrating a mixture of raw materials comprising a lithium source, an iron source, a manganese source, a phosphorus source, and water to obtain a precursor compound; step S2, sequentially ball milling, drying, pre-sintering, and sintering a mixture of the precursor compound, an M metal source, a dispersant, and water to obtain the lithium iron manganese phosphate cathode material; wherein the pre-sintering and sintering are each carried out independently in nitrogen and / or argon atmospheres; the M metal source is selected from any four of Al, Mg, Ti, V, Nb, and Ag sources. The aforementioned M metal source results in the formation of a lithium iron manganese phosphate cathode material doped with the aforementioned four metal elements, thereby helping to increase the cell parameters of the lithium iron manganese phosphate cathode material and facilitating the extraction and insertion of lithium ions during charging and discharging.

[0010] Further, in step S2 above, the pre-sintering temperature is 200–350°C; and / or, the pre-sintering time is 1–12 h; and / or, the sintering temperature is 600–800°C; and / or, the sintering time is 6–24 h; and / or, the ball milling is wet ball milling at a speed of 300–800 r / min; and / or, the wet ball milling time is 1–12 h; and / or, the drying temperature is 80–105°C; and / or, the drying time is 6–12 h. The above-mentioned sintering temperatures and times help promote the formation of lithium iron manganese phosphate cathode material, thereby improving the structural integrity and stability of the lithium iron manganese phosphate cathode material. The above-mentioned ball milling helps to further improve the dispersion uniformity of the M metal source in the precursor compound. The above-mentioned drying process helps to more thoroughly remove dispersants and water from the mixed material.

[0011] Further, in step S2 above, the Mg source is selected from any one or more of magnesium oxide, magnesium hydroxide, magnesium chloride, magnesium sulfate, and magnesium nitrate; and / or, the Al source is selected from any one or more of aluminum oxide, aluminum hydroxide, aluminum chloride, aluminum sulfate, and aluminum nitrate; the Ti source is TiO2; the V source is V2O5; the Nb source is Nb2O5; the Ag source is AgCl; and / or, the dispersant is selected from any one or more of polyethylene glycol, sodium dodecylbenzenesulfonate, acrylic acid, and tetraethylethylenediamine. The types of Mg, Al, Ti, V, Nb, and Ag sources mentioned above help to further improve the structural stability of the lithium iron manganese phosphate cathode material. The types of dispersants mentioned above help to further improve the dispersibility of the M metal source in the precursor compound.

[0012] Further, in step S1 above, the grinding process includes: performing a first grinding process on the raw material mixture to obtain first-ground particles; performing a second grinding process on the first-ground particles to obtain second-ground particles; wherein the D50 particle size of the first-ground particles is 0.8–1 μm, and / or the D50 particle size of the second-ground particles is 0.3–0.5 μm; and / or, the dehydration process is spray drying, and the spray drying atmosphere is an inert atmosphere; and / or, the spray drying temperature is 100–120°C; and / or, the spray drying time is 10–30 s; and / or, the raw material mixture further includes a carbon source, and the mass ratio of the carbon source to the precursor compound is 0.5–6:100; and / or, the carbon source The source is selected from any one or more of glucose, sucrose, starch, cellulose, acetylene black, graphite, carbon nanotubes, and ascorbic acid; and / or, the lithium source is selected from any one or more of lithium phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, and lithium nitrate; and / or, the iron source is selected from any one or more of ferric phosphate, ferric oxide, ferrous oxalate, ferric nitrate, ferric oxalate, ferric acetate, ferrous acetate, ferrous sulfate, and ferrous chloride; and / or, the manganese source is selected from any one or more of manganese phosphate, manganese acetate, manganese sulfate, manganese nitrate, and manganese carbonate; and / or, the phosphorus source is selected from any one or more of phosphoric acid, manganese phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ferric phosphate, and lithium dihydrogen phosphate. The above grinding process helps improve the interaction and mixing uniformity between the lithium, iron, manganese, and phosphorus sources. The above spray drying helps to fully remove moisture without damaging the structural uniformity of the mixture of lithium, iron, manganese, and phosphorus sources. The aforementioned carbon source helps to improve the conductivity of the final lithium iron manganese phosphate cathode material, and the mass ratio of the aforementioned carbon source to the precursor compound helps to further improve the conductivity of the final lithium iron manganese phosphate cathode material.

[0013] According to another aspect of the present invention, a positive electrode is provided, which contains the aforementioned lithium iron manganese phosphate positive electrode material. This positive electrode exhibits excellent cycle stability and rate performance.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode. This lithium-ion battery exhibits excellent cycle stability and rate performance.

[0015] By applying the technical solution of this invention, this application performs medium-entropy doping on lithium iron manganese phosphate cathode materials. Doping the lithium iron manganese phosphate cathode material with four different metal elements helps avoid the side reactions and high production costs associated with high-entropy doping requiring high-temperature sintering. Preferably, the types of the four different metal elements are controlled within the aforementioned range. Al doping helps reduce the cell volume and particle size, thereby shortening the lithium-ion transport path and improving the rate performance of the cathode material. Ti doping helps reduce the interplanar spacing and particle size, thus improving the rate performance of the cathode material. Doping with Mg, V, Ni, and Ag helps induce lattice distortion, thereby widening the lithium-ion transport channels and suppressing the JT distortion effect of Mn ions, thus improving the rate and cycle performance of the material. Simultaneously, the four different metal element atoms occupy transition metal atom sites in the lithium iron manganese phosphate cathode material, thereby increasing the cell parameters of the lithium iron manganese phosphate cathode material, which is beneficial for the extraction and insertion of lithium ions during charging and discharging, further improving the cycle and rate performance of the lithium iron manganese phosphate cathode material. Furthermore, preferably controlling z within the aforementioned range helps to form a uniform medium-entropy doped crystal structure. If z is too small, the improvement effect of medium-entropy doping is not significant; if z is too large, too many transition metal atomic sites are replaced by doped metal elements, thus destroying the original stable crystal structure. Therefore, the lithium iron manganese phosphate cathode material of this application has excellent cycle stability and rate performance. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 The LiFe shown in Embodiment 1 of this application is illustrated. 0.28 Mn 0.68 M 0.04 SEM image of PO4;

[0018] Figure 2 The LiFe shown in Embodiment 1 of this application is illustrated. 0.28 Mn 0.68 M 0.04 XRD pattern of PO4. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] As analyzed in the background section of this application, the existing technology has problems such as poor structural stability and low rate performance of lithium iron manganese phosphate cathode materials. In order to solve the above problems, this application provides a lithium iron manganese phosphate cathode material, its preparation method, cathode sheet and lithium-ion battery.

[0021] In a typical embodiment of this application, a lithium iron manganese phosphate cathode material is provided, which includes LiFe x Mn y M z PO4 particles, wherein 0 < x < 1, 0 < y < 1, 0.01 ≤ z ≤ 0.1, x + y + z = 1, and M is selected from any four metallic elements from Al, Mg, Ti, V, Nb, and Ag.

[0022] This application describes medium-entropy doping of lithium iron manganese phosphate (LMP) cathode materials. Doping with four different metal elements helps avoid the side reactions and high production costs associated with high-entropy doping, which requires high-temperature sintering. Preferably, the types of the four different metal elements are controlled within the aforementioned range. Al doping helps reduce the cell volume and particle size, thereby shortening the lithium-ion transport path and improving the rate performance of the cathode material. Ti doping helps reduce the interplanar spacing and particle size, further improving the rate performance. Doping with Mg, V, Ni, and Ag induces lattice distortion, widening the lithium-ion transport channels and suppressing the JT distortion effect of Mn ions, thus improving the rate and cycle performance. Furthermore, the four different metal element atoms occupy transition metal atom sites in the LMP cathode material, increasing the cell parameters and facilitating lithium-ion extraction and insertion during charging and discharging, further enhancing the cycle and rate performance. Furthermore, preferably controlling z within the aforementioned range helps to form a uniform medium-entropy doped crystal structure. If z is too small, the improvement effect of medium-entropy doping is not significant; if z is too large, too many transition metal atomic sites are replaced by doped metal elements, thus destroying the original stable crystal structure. Therefore, the lithium iron manganese phosphate cathode material of this application has excellent cycle stability and rate performance.

[0023] In one embodiment of this application, the molar ratio of the four metal elements is 0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2, and preferably the molar ratio of the four metal elements is 1:1:1:1.

[0024] An excessively large or small molar ratio of the four metal elements is detrimental to improving the stability of the crystal structure. It is preferable to control the molar ratio of the four metal elements within the above-mentioned range, which helps to further improve the structural stability of lithium iron manganese phosphate cathode materials.

[0025] In one embodiment of this application, the above-mentioned lithium iron manganese phosphate cathode material includes elemental carbon, which is distributed in different LiFe... x Mn y M z In the pores formed between PO4 particles, elemental carbon and LiFe... x Mn y M z The mass ratio of PO4 particles is 0.2 to 5:100.

[0026] The presence of elemental carbon provides excellent conductivity to lithium iron manganese phosphate cathode materials, contributing to improved efficiency in lithium-ion extraction and insertion. Preferably, the interaction between elemental carbon and LiFe... x Mn y M z The mass ratio of PO4 particles within the above range helps to further improve the efficiency of lithium-ion extraction and insertion.

[0027] In one embodiment of this application, the cell parameters of the lithium iron manganese phosphate cathode material are a = 1.0412–1.0510 nm, b = 0.6070–0.6197 nm, and c = 0.4727–0.4814 nm; and / or, the D50 particle size of the lithium iron manganese phosphate cathode material is 0.2–0.5 μm.

[0028] Lithium iron manganese phosphate cathode materials with the aforementioned cell parameter range are beneficial for the extraction and insertion of lithium ions during charging and discharging, thereby helping to improve the cycle performance and rate performance of lithium iron manganese phosphate cathode materials. Preferably, controlling the D50 particle size of lithium iron manganese phosphate cathode materials within the above range helps to give lithium iron manganese phosphate cathode materials higher surface activity and structural stability.

[0029] In another typical embodiment of this application, a method for preparing the aforementioned lithium iron manganese phosphate cathode material is provided. The method includes: step S1, sequentially grinding and dehydrating a mixture of raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, and water to obtain a precursor compound; step S2, sequentially ball milling, drying, pre-sintering, and sintering a mixture of the precursor compound, an M metal source, a dispersant, and water to obtain the lithium iron manganese phosphate cathode material; wherein the pre-sintering and sintering are each carried out independently in nitrogen and / or argon; the M metal source is selected from any four of Al, Mg, Ti, V, Nb, and Ag sources.

[0030] In step S1, the lithium, iron, manganese, and phosphorus sources are thoroughly mixed through grinding and dehydration to obtain a precursor compound. In step S2, ball milling ensures that the M metal source is more uniformly dispersed in the precursor compound. Pre-sintering and sintering processes then yield a lithium iron manganese phosphate cathode material doped with the four metal elements. Preferably, the pre-sintering and sintering processes are carried out independently in the aforementioned atmosphere to avoid oxidation of the metals due to the presence of oxygen. Preferably, the M metal source is within the aforementioned range, ensuring that the formed lithium iron manganese phosphate cathode material is doped with the four metal elements mentioned above. The four different doped metal atoms occupy transition metal atom sites in the lithium iron manganese phosphate cathode material, thereby increasing the cell parameters of the lithium iron manganese phosphate cathode material. This facilitates the extraction and insertion of lithium ions during charging and discharging, thus improving the cycle performance and rate performance of the lithium iron manganese phosphate cathode material.

[0031] In addition, it is preferable to directly heat the material for sintering after the pre-sintering treatment is completed. It is also preferable to pulverize the sintered product using an air jet mill, wherein the air jet for pulverizing is high-pressure nitrogen gas, the high-pressure nitrogen gas is heated to a temperature of 110-130°C, and the material is pulverized to a D50 particle size of 0.2-0.5μm. It is also preferable to obtain lithium iron manganese phosphate cathode material after graded demagnetization.

[0032] In one embodiment of this application, in step S2 above, the pre-sintering temperature is 200–350°C; and / or, the pre-sintering time is 1–12 h; and / or, the sintering temperature is 600–800°C; and / or, the sintering time is 6–24 h; and / or, the ball milling is wet ball milling, and the wet ball milling speed is 300–800 r / min; and / or, the wet ball milling time is 1–12 h; and / or, the drying temperature is 80–105°C; and / or, the drying time is 6–12 h.

[0033] Preferably, the temperature and time of the pre-sintering treatment are controlled within the above-mentioned range. The purpose of pre-sintering is to remove moisture and impurities from the precursor in advance, avoiding any impact on the crystallization process during sintering. Preferably controlling the temperature and time of the sintering treatment within the above-mentioned range helps to promote the formation of lithium iron manganese phosphate cathode material, thereby improving the integrity and stability of the lithium iron manganese phosphate cathode material structure. The sintering treatment in the preparation method of this application does not require excessively high sintering temperatures, thus helping to avoid side reactions and high material production costs caused by excessively high sintering temperatures. Preferably controlling the ball milling conditions within the above-mentioned range helps to further improve the dispersion uniformity of the M metal source in the precursor compound. Preferably controlling the temperature and time of the drying treatment within the above-mentioned range helps to more thoroughly remove dispersants and water from the mixed material.

[0034] In one embodiment of this application, in step S2 above, the Mg source is selected from any one or more of magnesium oxide, magnesium hydroxide, magnesium chloride, magnesium sulfate, and magnesium nitrate; and / or, the Al source is selected from any one or more of aluminum oxide, aluminum hydroxide, aluminum chloride, aluminum sulfate, and aluminum nitrate; the Ti source is TiO2; the V source is V2O5; the Nb source is Nb2O5; the Ag source is AgCl; and / or, the dispersant is selected from any one or more of polyethylene glycol, sodium dodecylbenzenesulfonate, acrylic acid, and tetraethylethylenediamine.

[0035] Preferably controlling the types of Mg, Al, Ti, V, Nb, and Ag sources within the aforementioned ranges helps improve the synergistic effect between the metal sources, thereby further enhancing the structural stability of the lithium iron manganese phosphate cathode material. Preferably controlling the types of dispersants within the aforementioned ranges also helps further improve the dispersibility of the M metal source in the precursor compound.

[0036] In one embodiment of this application, step S1 above includes the grinding process comprising: performing a first grinding process on the raw material mixture to obtain first ground particles; performing a second grinding process on the first ground particles to obtain second ground particles; wherein the D50 particle size of the first ground particles is 0.8–1 μm, and / or the D50 particle size of the second ground particles is 0.3–0.5 μm; and / or, the dehydration process is spray drying, and the spray drying atmosphere is an inert atmosphere; and / or, the spray drying temperature is 100–120°C; and / or, the spray drying time is 10–30 s; and / or, the raw material mixture further includes a carbon source, and the mass ratio of the carbon source to the precursor compound is 0.5–6:100; and / or The carbon source is selected from any one or more of glucose, sucrose, starch, cellulose, acetylene black, graphite, carbon nanotubes, and ascorbic acid; and / or, the lithium source is selected from any one or more of lithium phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, and lithium nitrate; and / or, the iron source is selected from any one or more of ferric phosphate, ferric oxide, ferrous oxalate, ferric nitrate, ferric oxalate, ferric acetate, ferrous acetate, ferrous sulfate, and ferrous chloride; and / or, the manganese source is selected from any one or more of manganese phosphate, manganese acetate, manganese sulfate, manganese nitrate, and manganese carbonate; and / or, the phosphorus source is selected from any one or more of phosphoric acid, manganese phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ferric phosphate, and lithium dihydrogen phosphate.

[0037] Preferably controlling the grinding conditions within the aforementioned range helps to increase the contact area between the lithium, iron, manganese, and phosphorus sources, thereby improving their interaction and mixing uniformity. Preferably controlling the dehydration process as spray drying, and preferably controlling the spray drying atmosphere within the aforementioned range, more preferably using nitrogen, with an outlet temperature <80°C, helps to fully remove moisture without compromising the structural uniformity of the lithium, iron, manganese, and phosphorus source mixture. Adding a carbon source to the raw material mixture helps to improve the conductivity of the final lithium iron manganese phosphate cathode material. Preferably controlling the mass ratio of carbon source to precursor compound within the aforementioned range helps to further improve the conductivity of the final lithium iron manganese phosphate cathode material. Preferably controlling the carbon, lithium, iron, manganese, and phosphorus sources within the aforementioned range helps to enrich the material's selectivity.

[0038] In another typical embodiment of this application, a positive electrode sheet is provided, which contains the aforementioned lithium iron manganese phosphate positive electrode material.

[0039] Since the above-mentioned cathode contains the lithium iron manganese phosphate cathode material of this application, the cathode has excellent cycle stability and rate performance.

[0040] In another typical embodiment of this application, a lithium-ion battery is provided, including a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0041] Since the above-mentioned lithium-ion battery includes a cathode sheet containing the lithium iron manganese phosphate cathode material of this application, the lithium-ion battery has excellent cycle stability and rate performance.

[0042] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0043] Example 1

[0044] S1: Lithium carbonate, ferrous oxalate, manganese sulfate, ammonium dihydrogen phosphate, and glucose were dissolved in water in sequence. The atomic molar ratio of feed was Li:Fe:Mn:P = 1:0.28:0.68:1, and glucose accounted for 3% of the total feed mass. The precursor compound was obtained by coarse grinding (D50 = 0.87 μm), sand milling (D50 = 0.41 μm), and spray drying. The spray drying conditions were hot nitrogen drying at 110℃, droplet residence time of 20s, and discharge temperature of 70℃.

[0045] S2: The precursor compound and four metal source compounds, Al2O3, MgO, TiO2 and V2O5, are poured into a high-speed ball mill. The molar ratio of the four metal atoms, Al, Mg, Ti and V are the same, and the molar ratio of the four metals to the lithium metal in the precursor compound after mixing is M:Li = 0.04:1. Water is used as solvent and polyethylene glycol is used as dispersant. The ball milling speed is 450 rpm. After wet ball milling for 6 hours, the material is dried. The drying conditions are baking in a 90℃ oven for 8 hours.

[0046] S3: The dried material is placed in a heating furnace and pre-sintered at 250°C for 3 hours under a nitrogen atmosphere. The temperature is then raised to 700°C for sintering for 10 hours. After cooling, the material is pulverized using an air jet mill with high-pressure nitrogen gas. The high-pressure nitrogen gas is heated to 110°C, and the material is pulverized until the particle size D50 is 0.3 μm. After sieving and demagnetization, LiFe is obtained. 0.28 Mn 0.68 M 0.04 PO4 cathode material. This includes elemental carbon and LiFe. x Mn y M z The mass ratio of PO4 particles is 2.5:100.

[0047] Example 2

[0048] The difference from Example 1 is that in step S2, the precursor compound and four metal source compounds, Al2O3, Nb2O5, AgCl, and V2O5, are poured into a high-speed ball mill, and the molar ratio of the four metals Al, Nb, Ag, and V is the same, finally obtaining the cathode material.

[0049] Example 3

[0050] S1: Lithium carbonate, iron phosphate, manganese phosphate, ammonium dihydrogen phosphate, and sucrose were dissolved in water in sequence. The atomic molar ratio of the feed was Li:Fe:Mn:P = 1:0.3:0.69:1, and the sucrose accounted for 5% of the total feed mass. The precursor compound was obtained by coarse grinding (D50 = 0.91 μm), sand milling (D50 = 0.35 μm), and spray drying. The spray drying conditions were hot nitrogen drying at a drying temperature of 110℃, a droplet residence time of 20s, and a discharge temperature of 60℃.

[0051] S2: The precursor compound and four metal source compounds, Al2O3, MgO, TiO2 and V2O5, are poured into a high-speed ball mill. The molar ratio of the four metal atoms, Al, Mg, Ti and V are the same, and the molar ratio of the four metals to the lithium metal in the precursor compound after mixing is M:Li = 0.04:1. Water is used as solvent and polyethylene glycol is used as dispersant. The ball milling speed is 600 rpm. After ball milling for 12 hours, the material is dried. The drying conditions are baking in a 90℃ oven for 8 hours.

[0052] S3: The dried material is placed in a heating furnace and pre-sintered at 250°C for 3 hours under a nitrogen atmosphere. The temperature is then raised to 700°C for sintering for 10 hours. After cooling, the material is pulverized using an air jet mill with high-pressure nitrogen gas. The high-pressure nitrogen gas is heated to 110°C, and the material is pulverized until the particle size D50 is 0.3 μm. After sieving and demagnetization, LiFe is obtained. 0.3 Mn 0.69 M 0.01 PO4 cathode material.

[0053] Example 4

[0054] S1: Lithium carbonate, ferrous oxalate, manganese sulfate, ammonium dihydrogen phosphate, and glucose were dissolved in water in sequence. The atomic molar ratio of the feed was Li:Fe:Mn:P = 1:0.45:0.45:1, and glucose accounted for 3% of the total feed mass. The precursor compound was obtained by coarse grinding (D50 = 0.85 μm), sand milling (D50 = 0.38 μm), and spray drying. The spray drying conditions were hot nitrogen drying at a temperature of 110℃, a droplet residence time of 20s, and a discharge temperature of 70℃.

[0055] S2: The precursor compound and four metal source compounds, Al2O3, MgO, TiO2 and V2O5, are poured into a high-speed ball mill. The molar ratio of the four metal atoms, Al, Mg, Ti and V are the same, and the molar ratio of the four metals to the lithium metal in the precursor compound after mixing is M:Li = 0.1:1. Water is used as solvent and polyethylene glycol is used as dispersant. After wet ball milling for 6 hours, the material is dried. The drying conditions are baking in an oven at 110℃ for 4 hours.

[0056] S3: The dried material is placed in a heating furnace and pre-fired at 250°C for 3 hours under a nitrogen atmosphere. The temperature is then raised to 700°C for sintering for 10 hours. After cooling, the material is pulverized using an air jet mill with high-pressure nitrogen gas. The high-pressure nitrogen gas is heated to 110°C, and the material is pulverized until the particle size D50 is 0.3 μm. After sieving and demagnetization, LiFe is obtained. 45 Mn 0.45 M 0.1 PO4 cathode material.

[0057] Example 5

[0058] S1: Lithium carbonate, iron phosphate, manganese phosphate, ammonium dihydrogen phosphate, and sucrose were dissolved in water in sequence. The atomic molar ratio of feed was Li:Fe:Mn:P = 1:0.68:0.28:1, and sucrose accounted for 5% of the total feed mass. The precursor compound was obtained by coarse grinding (D50 = 0.84 μm), sand milling (D50 = 0.45 μm), and spray drying. The spray drying conditions were hot nitrogen drying at 110℃, droplet residence time of 20s, and discharge temperature of 60℃.

[0059] S2: The precursor compound and four metal source compounds, Al2O3, MgO, TiO2 and V2O5, are poured into a high-speed ball mill. The molar ratio of the four metal atoms, Al, Mg, Ti and V are the same, and the molar ratio of the four metals to the lithium metal in the precursor compound after mixing is M:Li = 0.04:1. Water is used as solvent and polyethylene glycol is used as dispersant. After wet ball milling for 6 hours, the material is dried. The drying conditions are baking in an oven at 110℃ for 4 hours.

[0060] S3: The dried material is placed in a heating furnace and pre-fired at 300℃ for 2 hours under a nitrogen atmosphere. The temperature is then raised to 800℃ for sintering for 8 hours. After cooling, the material is pulverized using an air jet mill with high-pressure nitrogen gas. The high-pressure nitrogen gas is heated to 110℃, and the material is pulverized until the particle size D50 is 0.4μm. After sieving and demagnetization, LiFe is obtained. 0.68 Mn 0.28 M 0.04 PO4 cathode material.

[0061] Example 6

[0062] The difference from Example 1 is that in step S2, the atomic molar ratio of the four metals to lithium metal in the precursor compound after mixing is M:Li = 0.1:1, and the cathode material is finally obtained.

[0063] Example 7

[0064] The difference from Example 1 is that in step S2, the atomic molar ratio of the four metals to lithium metal in the precursor compound after mixing is M:Li = 0.01:1, and the cathode material is finally obtained.

[0065] Example 8

[0066] The difference from Example 1 is that in step S2, glucose accounts for 0.5% of the total feed mass, ultimately yielding the cathode material, wherein elemental carbon and LiFe... x Mn y M zThe mass ratio of PO4 particles is 0.2:100.

[0067] Example 9

[0068] The difference from Example 1 is that in step S2, glucose accounts for 6% of the total feed mass, ultimately yielding the cathode material, wherein elemental carbon and LiFe... x Mn y M z The mass ratio of PO4 particles is 5:100.

[0069] Example 10

[0070] The difference from Example 1 is that in step S2, glucose accounts for 7% of the total feed mass, ultimately yielding the cathode material, wherein elemental carbon and LiFe... x Mn y M z The mass ratio of PO4 particles is 5.5:100.

[0071] Example 11

[0072] The difference from Example 1 is that in step S3, the material is pulverized to a particle size D50 of 0.2 μm, and the positive electrode material is finally obtained.

[0073] Example 12

[0074] The difference from Example 1 is that in step S3, the material is pulverized to a particle size D50 of 0.5 μm, and the positive electrode material is finally obtained.

[0075] Example 13

[0076] The difference from Example 1 is that in step S3, the material is pulverized to a particle size D50 of 0.6 μm, and the positive electrode material is finally obtained.

[0077] Example 14

[0078] The difference from Example 1 is that in step S3, the pre-sintering temperature is 200°C, the pre-sintering time is 12h, the sintering temperature is 800°C, the sintering time is 6h, and finally the cathode material is obtained.

[0079] Example 15

[0080] The difference from Example 1 is that in step S3, the pre-sintering temperature is 350°C, the pre-sintering time is 1 hour, the sintering temperature is 600°C, and the sintering time is 24 hours, finally obtaining the cathode material.

[0081] Example 16

[0082] The difference from Example 1 is that in step S3, the pre-sintering temperature is 400°C, the pre-sintering time is 0.5h, the sintering temperature is 500°C, the sintering time is 5h, and finally the cathode material is obtained.

[0083] Comparative Example 1

[0084] S1: Lithium carbonate, ferrous oxalate, manganese sulfate, ammonium dihydrogen phosphate, and glucose were dissolved in water in sequence. The atomic molar ratio of the feed was Li:Fe:Mn:P = 1:0.3:0.7:1, and glucose accounted for 3% of the total feed mass. The precursor compound was obtained by coarse grinding (D50 = 0.85 μm), sand milling (D50 = 0.45 μm), and spray drying. The spray drying conditions were hot nitrogen drying at 110℃, droplet residence time of 20s, and discharge temperature of 70℃.

[0085] S2: The above material is placed in a heating furnace and pre-calcined at 250°C for 3 hours under a nitrogen atmosphere. The temperature is then raised to 700°C for sintering for 10 hours. After cooling, it is pulverized using an air jet mill with high-pressure nitrogen gas. The high-pressure nitrogen gas is heated to 110°C, and the material is pulverized until the particle size D50 is 0.3 μm. After sieving and demagnetization, LiFe is obtained. 0.3 Mn 0.7 PO4 cathode material.

[0086] Comparative Example 2

[0087] The difference from Comparative Example 1 is that in step S1, Li:Fe:Mn:P = 1:0.5:0.5:1, ultimately yielding LiFe. 0.5 Mn 0.5 PO4 cathode material.

[0088] Comparative Example 3

[0089] The difference from Comparative Example 1 is that in step S1, Li:Fe:Mn:P = 1:0.7:0.3:1, ultimately yielding LiFe. 0.7 Mn 0.3 PO4 cathode material.

[0090] Comparative Example 4

[0091] The difference from Example 1 is that in step S2, the precursor compound and five metal source compounds, Al2O3, MgO, TiO2, V2O5 and Nb2O5, are poured into a high-speed ball mill to finally obtain the cathode material.

[0092] Comparative Example 5

[0093] The difference from Example 1 is that in step S2, the atomic molar ratio of the four metals to lithium metal in the precursor compound after mixing is M:Li = 0.15:1, and the cathode material is finally obtained.

[0094] Comparative Example 6

[0095] The difference from Example 1 is that in step S2, the precursor compound and three metal source compounds, Al2O3, MgO and TiO2, are poured into a high-speed ball mill to finally obtain the cathode material.

[0096] Performance testing

[0097] The cathode materials used in the comparative examples and embodiments above were respectively fabricated into lithium-ion batteries. The specific preparation steps are as follows:

[0098] Preparation of positive electrode sheet: The positive electrode material active material, conductive agent super conductive carbon (SP), and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methyl-2-pyrrolidone solvent system at a mass ratio of 97:1:2. The slurry is then coated onto the current collector Al foil, and the positive electrode sheet is obtained by slitting, die cutting, and rolling.

[0099] Preparation of negative electrode:

[0100] Artificial graphite, superconducting carbon (SP) as a conductive agent, styrene-butadiene rubber (SBR) as a binder, and sodium carboxymethyl cellulose (CMC) as a thickener were thoroughly mixed in a deionized water solvent system at a mass ratio of 95:1:2:2. The slurry was then coated onto a Cu foil current collector, and after slitting, rolling, and die-cutting, a negative electrode sheet was obtained. A 4μm nano-alumina coating was applied to a 12μm polypropylene (PP) base film as a separator. The positive electrode sheet, separator, and negative electrode sheet were sequentially stacked to obtain a bare cell using a stacked battery process. The bare cell was then pre-encapsulated in an aluminum-plastic film, injected with the prepared electrolyte, and then fully encapsulated to obtain the desired soft-pack battery.

[0101] The aforementioned pouch batteries were formed and capacity-graded using a battery testing cabinet. The formation process involved charging at a constant current of 0.1C to 3.7V, followed by aging at 45℃ for 12 hours. The capacity-graded process involved charging at a constant current and voltage of 0.33C to 4.2V, with a cutoff current of 0.05C, followed by discharging at a constant current of 0.33C to 2.7V, repeated three times. The initial capacity C0 was recorded. For cycle performance testing, the capacity-graded batteries were cycled 500 times at room temperature using a constant current and voltage of 1C / 1C, within a voltage range of 2.5–4.2V. The discharge capacity C at the end of the cycle was recorded. 500 Then the cycle capacity retention rate = C 500 / C0*100%; Rate performance test: Charge the battery at room temperature with 1C constant current and constant voltage to 4.2V, and then discharge it at 4C constant current to 2.7V. Record the discharge capacity C4. Then the 4C rate discharge capacity retention rate = (C4 / C0)*100%.

[0102] The cathode materials in the above embodiments and comparative examples were subjected to XRD tests, and the cell parameters were calculated. The calculation results are shown in Table 1. The test results of the battery capacity retention efficiency after 500 cycles and the 4C rate discharge capacity retention rate of the cathode materials in the above embodiments and comparative examples are shown in Table 2.

[0103] Table 1

[0104]

[0105]

[0106] Table 2

[0107]

[0108]

[0109] As can be seen from the comparison of the test results of the embodiments and comparative examples in Table 1, the cathode material prepared in this application successfully achieved the entropy doping crystal structure of four metal elements, and the cell parameters became larger after doping, which is more conducive to improving the lithium ion insertion and extraction rate, thereby improving the rate performance of lithium ion batteries.

[0110] As can be seen from the comparison of the test results of the embodiments and comparative examples in Table 2, the medium-entropy doped lithium iron manganese phosphate cathode material prepared in this application significantly improves the cycle and rate performance of the cathode material. This indicates that the technical solution of this invention uses four different metal element atoms to dope and occupy some transition metal atom sites in the lithium iron manganese phosphate cathode material, thereby forming a higher mixed entropy, which can improve the structural stability of the lithium iron manganese phosphate cathode material, and thus improve the charge and discharge cycle and rate performance of the lithium-ion battery.

[0111] Figure 1 LiFe in Embodiment 1 of this application 0.28 Mn 0.68 M 0.04 SEM image of PO4, from Figure 1 As can be seen, the material exhibits a spherical, granular nanostructure.

[0112] Figure 2 LiFe in Embodiment 1 of this application 0.28 Mn 0.68 M 0.04 XRD pattern of PO4, from Figure 2The results show that the material has an olivine-type crystal structure and no impurity phase peaks related to Al2O3, MgO, TiO2, and V2O5 are observed, indicating that the metal elements have been successfully doped into the crystal structure of the lithium iron manganese phosphate cathode material.

[0113] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0114] This application describes medium-entropy doping of lithium iron manganese phosphate (LMP) cathode materials. Doping with four different metal elements helps avoid the side reactions and high production costs associated with high-entropy doping, which requires high-temperature sintering. Preferably, the types of the four different metal elements are controlled within the aforementioned range. Al doping helps reduce the cell volume and particle size, thereby shortening the lithium-ion transport path and improving the rate performance of the cathode material. Ti doping helps reduce the interplanar spacing and particle size, further improving the rate performance. Doping with Mg, V, Ni, and Ag induces lattice distortion, widening the lithium-ion transport channels and suppressing the JT distortion effect of Mn ions, thus improving the rate and cycle performance. Furthermore, the four different metal element atoms occupy transition metal atom sites in the LMP cathode material, increasing the cell parameters and facilitating lithium-ion extraction and insertion during charging and discharging, further enhancing the cycle and rate performance. Furthermore, preferably controlling z within the aforementioned range helps to form a uniform medium-entropy doped crystal structure. If z is too small, the improvement effect of medium-entropy doping is not significant; if z is too large, too many transition metal atomic sites are replaced by doped metal elements, thus destroying the original stable crystal structure. Therefore, the lithium iron manganese phosphate cathode material of this application has excellent cycle stability and rate performance.

[0115] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium iron manganese phosphate cathode material, characterized in that, The lithium iron manganese phosphate cathode material includes LiFe x Mn y M z PO4 particles, wherein 0 < x < 1, 0 < y < 1, 0.01 ≤ z ≤ 0.1, x + y + z = 1, and M is selected from four metallic elements: Al, Mg, Ti, and V, and the molar ratio of the four metallic elements is 1:1:1:1; In the cell parameters of the lithium iron manganese phosphate cathode material, a is 1.0412~1.0510 nm, b is 0.6070~0.6197 nm, and c is 0.4727~0.4814 nm. The lithium iron manganese phosphate cathode material includes elemental carbon, which is distributed in different LiFe... x Mn y M z Within the pores formed between the PO4 particles, the elemental carbon and the LiFe x Mn y M z The mass ratio of PO4 particles is 0.2~5:100; the D50 particle size of the lithium iron manganese phosphate cathode material is 0.2~0.5μm; The preparation method of the lithium iron manganese phosphate cathode material includes: Step S1 involves sequentially grinding and dehydrating a raw material mixture comprising a lithium source, an iron source, a manganese source, a phosphorus source, and water to obtain a precursor compound; the raw material mixture also includes a carbon source, and the mass ratio of the carbon source to the precursor compound is 0.5~6:

100. Step S2 involves mixing the raw materials, including the precursor compound, the M metal source, the dispersant, and water, and then sequentially subjecting them to ball milling, drying, pre-sintering, and sintering to obtain the lithium iron manganese phosphate cathode material; wherein, The pre-sintering treatment and the sintering treatment are each carried out independently in nitrogen and / or argon gas; the temperature of the pre-sintering treatment is 200~350℃; the time of the pre-sintering treatment is 1~12h; the temperature of the sintering treatment is 600~800℃; the time of the sintering treatment is 6~24h. The M metal source is selected from Al source, Mg source, Ti source and V source.

2. The lithium iron manganese phosphate cathode material according to claim 1, characterized in that, The ball milling process is a wet ball milling process, wherein the rotation speed of the wet ball milling process is 300~800 r / min; and / or, the wet ball milling time is 1~12 h; and / or, the drying temperature is 80~105℃; and / or, the drying time is 6~12 h.

3. The lithium iron manganese phosphate cathode material according to claim 1, characterized in that, In step S2, the Mg source is selected from any one or more of magnesium oxide, magnesium hydroxide, magnesium chloride, magnesium sulfate, and magnesium nitrate; and / or, the Al source is selected from any one or more of aluminum oxide, aluminum hydroxide, aluminum chloride, aluminum sulfate, and aluminum nitrate; the Ti source is TiO2; the V source is V2O5; and / or, the dispersant is selected from any one or more of polyethylene glycol, sodium dodecylbenzenesulfonate, acrylic acid, and tetraethylethylenediamine.

4. The lithium iron manganese phosphate cathode material according to any one of claims 1 to 3, characterized in that, In step S1, the grinding process includes: performing a first grinding process on the raw material mixture to obtain first ground particles; The first ground particles are subjected to a second grinding process to obtain the second ground particles. Wherein, the D50 particle size of the first ground particles is 0.8~1μm, and / or the D50 particle size of the second ground particles is 0.3~0.5μm; And / or, the dehydration treatment is spray drying, and the spray drying atmosphere is an inert atmosphere; and / or, the spray drying temperature is 100~120℃; and / or, the spray drying time is 10~30s; And / or, the carbon source is selected from any one or more of glucose, sucrose, starch, cellulose, acetylene black, graphite, carbon nanotubes, and ascorbic acid; And / or, the lithium source is selected from any one or more of lithium phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, and lithium nitrate; And / or, the iron source is selected from any one or more of ferric phosphate, ferric oxide, ferrous oxalate, ferric nitrate, ferric oxalate, ferric acetate, ferrous sulfate, and ferrous chloride; And / or, the manganese source is selected from any one or more of manganese phosphate, manganese acetate, manganese sulfate, manganese nitrate, and manganese carbonate; And / or, the phosphorus source is selected from any one or more of phosphoric acid, manganese phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, and lithium dihydrogen phosphate.

5. A positive electrode plate, characterized in that, The positive electrode sheet contains lithium iron manganese phosphate positive electrode material as described in any one of claims 1 to 4.

6. A lithium-ion battery, comprising a positive electrode, an electrolyte, a separator, and a negative electrode, characterized in that, The positive electrode is the positive electrode as described in claim 5.

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