Phosphate-based positive electrode material, and preparation method therefor and use thereof

Abstract

A phosphate-based positive electrode material, and a preparation method therefor and a use thereof. The phosphate-based positive electrode material comprises matrix particles and a carbon coating layer coating the surface of the matrix particles. The chemical formula of the matrix particles is LixMyPO4, wherein 0.96≤x≤1.08, 0.96≤y≤1, and M comprises at least one of Fe and Mn; a first metal element is doped at the position of M, and the first metal element comprises at least one of Ti, V, Cr, Co, Ni, Nb, Mo, and W; and / or, a second metal element is doped at the position of Li, and the second metal element comprises at least one of Mg and Zr. The carbon coating layer comprises a carbon material, and the degree of disorder in the carbon material satisfies: ID / IG≤1.2.

Description

A phosphate-based positive electrode material, a preparation method and application thereof

[0001] The present application claims priority to the Chinese patent application No. 2024108679673 filed on June 28, 2024 with the China Patent Office, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium batteries, in particular to a phosphate-based positive electrode material, a preparation method and application thereof. BACKGROUND

[0003] Lithium ion batteries have the advantages of high energy density, small self-discharge, long cycle life, safety and environmental protection, and are widely used in consumer electronics, electric vehicles, power and communication energy storage and other fields. According to the different positive electrode materials, lithium ion batteries can be divided into lithium cobaltate batteries, lithium manganate batteries, ternary lithium batteries, lithium iron phosphate batteries, etc., which correspond to positive electrode materials lithium cobaltate (LCO), lithium manganate (LMO), ternary nickel-cobalt-manganese lithium acid (NMC) and ternary nickel-cobalt-aluminum lithium acid (NCA), etc. Among them, the preparation cost of lithium cobaltate LCO, ternary nickel-cobalt-manganese lithium acid NMC and ternary nickel-cobalt-aluminum lithium acid NCA is relatively high, which limits its application range to a certain extent. Although the price of spinel lithium manganate LMO is relatively low, its energy density and cycle life are slightly low, which is not conducive to the application of LMO in high-end products.

[0004] In order to reduce the preparation cost of lithium batteries and enable lithium batteries to maintain good application performance, research on phosphate-based active materials without precious metal elements (nickel, cobalt and manganese) has gradually attracted attention. The commonly used phosphate-based active materials at present mainly include lithium iron phosphate (LFP), lithium manganese phosphate (LMP) and lithium manganese iron phosphate (LMFP) etc.

[0005] Lithium iron phosphate LFP is widely used in passenger car power batteries, commercial vehicle power batteries and power communication energy storage batteries due to its structural stability, abundant reserves of main elements Fe and P, low price, super-long cycle life and high safety. However, due to the influence of its olivine structure (as shown in FIG. 1), the conductivity of LFP is low, the ion diffusion performance is poor, and the rate performance and low temperature performance are poor.

[0006] Lithium manganese phosphate LMP has basically the same crystal structure as lithium iron phosphate LFP, and there is a significant polarization phenomenon during charging. After being applied in lithium batteries, the capacity and power density of lithium batteries will be significantly reduced.

[0007] Lithium manganese iron phosphate LMFP is a product of mixing lithium manganese iron phosphate LFP and lithium manganese phosphate LMP, the crystal structure of lithium manganese iron phosphate LMFP is basically the same as that of lithium iron phosphate LFP, LMFP has the same advantages as LFP, and has a higher discharge voltage and a higher energy density under a similar discharge capacity. However, the constant voltage charging of lithium manganese iron phosphate LMFP is relatively large, so it is not suitable for energy storage batteries, and the cycle life is short and the capacity is difficult to develop. TECHNICAL PROBLEM

[0008] After the above several phosphate active materials are applied in lithium batteries, there is still the case of Fe and Mn dissolution, the dissolved iron ions or / and manganese ions can migrate to the negative electrode to form heterogeneous catalytic active centers, catalyze the decomposition of electrolyte and negative electrode SEI film, affect the self-discharge rate, cycle performance and storage performance of lithium ion battery, and is not conducive to the improvement of lithium ion battery ion conductivity and rate performance. TECHNICAL SOLUTION

[0009] In a first aspect, the present application provides a phosphate-based positive electrode material, which adopts the following technical scheme:

[0010] A phosphate-based positive electrode material, the phosphate-based positive electrode material comprises base particles and a carbon coating layer coated on the surface of the base particles; the chemical formula of the base particles is Li x M y PO4, 0.96≤x≤1.08, 0.96≤y≤1, M includes at least one of Fe and Mn;

[0011] Wherein, the M site is doped with a first metal element, the first metal element includes at least one of Ti, V, Cr, Co, Ni, Nb, Mo and W; and / or, the Li site is doped with a second metal element, the second metal element includes at least one of Mg and Zr;

[0012] The carbon coating layer includes a carbon material, and the carbon material has a disorder degree I D / I G ≤1.2.

[0013] The typical scattering peaks of the carbon material in Raman spectrum are two, one is D peak, located at 1350cm -1 nearby, and the other is G peak, located at 1580cm -1 nearby, I D is the peak intensity of D peak in Raman spectrum within 1300cm - 1 to 1400cm - 1 G - 1 ​​to 16300 cm - 1 Peak intensity of the inner G peak.

[0014] In a second aspect, the application provides a preparation method of a phosphate-based positive electrode material, which adopts the following technical scheme:

[0015] A preparation method of a phosphate-based positive electrode material, comprising the following steps:

[0016] S1, mixing an iron source, a manganese source, a lithium source and a doping source, grinding after adding water to obtain a premixed slurry;

[0017] S2, after spray drying and sintering of the premixed slurry, crushing to obtain a phosphate-based positive electrode material.

[0018] In a third aspect, the application provides a lithium ion battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises an active material layer, and the active material layer comprises the phosphate-based positive electrode material as described above. Beneficial effects

[0019] First, on the one hand, by doping high-valence metal elements at M sites, not only can local lithium vacancies be caused to improve the lithium diffusion coefficient, but also vacancy defects can be formed in the material lattice and a relatively narrow TDOS band gap can be generated, thereby improving the ionic conductivity of the positive electrode material and improving its rate performance and low-temperature performance; on the other hand, by doping Mg and Zr elements at Li sites, not only can local lithium vacancies be caused to improve the lithium diffusion coefficient, but also the lithium layer channel can be expanded and the de-intercalation resistance of lithium ions can be reduced, thereby improving the rate performance and ionic conductivity of the positive electrode material.

[0020] Second, since I D and I G correspond to sp 3 hybridization and sp 2 hybridization of carbon respectively, the smaller the ratio of the highest peak intensity of the D peak to the highest peak intensity of the G peak (I D / I G ), the lower the degree of disorder and the higher the degree of graphitization of the carbon material, and by using a carbon material with low degree of disorder and high degree of graphitization to coat the substrate, the electrochemical activity of the positive electrode material can be significantly improved, the degree of graphitization of the coating layer is higher, which can reduce the impedance of the material interface, thereby significantly reducing the charge transfer impedance of the material, and helping to further improve the rate performance and low-temperature performance of the positive electrode material.

[0021] Thirdly, the defects in the carbon coating layer will promote the side reaction of the phosphate-based positive electrode material in the electrolyte to a certain extent, and the doping of the first metal element and the second metal element can inhibit the promotion and also help to reduce the deterioration degree of the material in the carbon coating layer, avoid the increase of the disorder degree of the carbon coating layer in the lithium battery cycle process, and improve the stability of the carbon coating layer; and the stable carbon coating layer can also stabilize the coated substrate particles, reduce the dissolution of Mn and Fe in the substrate particles, thereby reducing the deposition amount of Fe / Mn ions from the positive electrode to the negative electrode by electro-migration, reducing the catalytic decomposition of the electrolyte and the negative electrode SEI film, and further improving the self-discharge rate and cycle performance of the lithium battery.

[0022] Fourthly, the doping of the high-valence metal element and the existence of the carbon coating layer can significantly reduce the dissolution of Fe / Mn in the positive electrode material, which will greatly avoid the negative influence of the dissolution of Fe / Mn ions on the electrolyte and the negative electrode SEI film, and improve the self-discharge rate, cycle performance and storage performance of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of the crystal structure of the phosphate-based positive electrode material.

[0024] Figure 2 is an XRD spectrum diagram of the phosphate-based positive electrode material prepared in Example 1 of the present application.

[0025] Figure 3 is an SEM diagram of the phosphate-based positive electrode material prepared in Example 1 of the present application (a) and an SEM diagram of the phosphate-based positive electrode material prepared in Example 4 (b).

[0026] Figure 4 is a charge-discharge curve test diagram of the LFP lithium battery in Example 1 (a) and a charge-discharge curve test diagram of the LMFP lithium battery in Example 4 (b). Embodiments of the present application

[0027] Unless otherwise indicated, all numerical values of the amount of components, reaction conditions, and the like used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the compositions and methods of the present application.

[0028] As used herein, "and / or" means one or all of the listed items.

[0029] As used herein, "comprises" and "comprising" encompass the presence of only the recited elements as well as the presence of additional elements not recited.

[0030] All percentages in the present application are weight percentages, unless otherwise specified.

[0031] As used in the specification, "a," "an," "one," and "the" are intended to include "at least one," or "one or more" unless specified otherwise. For example, "a component" means one or more components.

[0032] In some embodiments, the carbon content in the phosphate-based cathode material is 1wt%-2wt%.

[0033] By controlling the carbon content in the phosphate-based cathode material, the content of graphitized carbon in the phosphate-based cathode material is increased, and the electrochemical performance of the phosphate-based cathode material is significantly improved; when the mass percentage content of the carbon coating layer is too low, an effective conductive network structure cannot be constructed in the cathode active material layer formed by the phosphate-based cathode active material, the battery impedance and polarization are too large, and the battery performance is deteriorated; when the mass percentage content of the carbon coating layer is too high, the defects present in the carbon material will act as active sites to intensify the degree of side reactions of the cathode in the electrolyte, the side reaction products will block the lithium ion transmission channels of the carbon coating layer, and seriously even destroy the order degree of the carbon coating layer, thereby significantly increasing the battery impedance and consuming active lithium to rapidly attenuate the capacity of the lithium battery.

[0034] In some embodiments, the doping amount of the first metal element is ≤5000ppm.

[0035] In some embodiments, the doping amount of the second metal is ≤3000ppm.

[0036] By controlling the doping amount of the first metal element and the second metal element, the generation of impurity phases can be avoided, and the occurrence of the situation that residual lithium appears on the surface of the cathode and causes the initial capacity of the material to decrease can be avoided.

[0037] In some embodiments, the particle size D50 of the phosphate-based cathode material is 50-2000nm.

[0038] In some embodiments, the particle size D50 of the phosphate-based cathode material refers to the particle size D50 of the primary particles of the phosphate-based cathode material observed in SEM detection.

[0039] In some embodiments, the tap density of the phosphate-based cathode material is 2-2.7g / cm 3 .

[0040] By controlling the reasonable particle size distribution of the phosphate-based cathode material, the phosphate-based cathode material can obtain a relatively wide range of tap densities, so as to improve the application range of the cathode material of the present application.

[0041] In some embodiments, the iron source comprises at least one of FePO4, Fe2O3, FeC2O4; the manganese source comprises at least one of MnPO4, MnCO3, Mn3O4; the lithium source comprises at least one of Li2CO3, LiOH.H2O, LiCl, Li2SO4, Li2HPO4, LiH2PO4, Li3PO4, LiNO3;

[0042] The doping source comprises an M-site doping source and a Li-site doping source, the M-site doping source comprises at least one of a Ti salt and an oxide thereof, a V salt and an oxide thereof, a Cr salt and an oxide thereof, a Co salt and an oxide thereof, a Ni salt and an oxide thereof, a Nb salt and an oxide thereof, a Mo salt and an oxide thereof, a W salt and an oxide thereof, and the Li-site doping source comprises at least one of a Mg salt and an oxide thereof, a Zr salt and an oxide thereof.

[0043] The carbon source comprises a high-molecular carbon source and a small-molecular carbon source; wherein the high-molecular carbon source comprises at least one of polyethylene glycol, polyvinylpyrrolidone, graphene, and carbon nanotube; and the small-molecular carbon source comprises at least one of glucose, sucrose, and conductive carbon black.

[0044] In some embodiments, the mass proportion of the high-molecular carbon source in the carbon source is less than 50%.

[0045] The composite carbon source is formed by the cooperation of the high-molecular carbon source and the small-molecular carbon source. Since the C-C bonds in the small-molecular carbon source are disordered and the C-C bonds in the high-molecular carbon source are ordered, under the action of high temperature in the sintering process of the preparation of the positive electrode material, the small-molecular carbon source is more likely to form sp 3 hybrid carbon and the high-molecular carbon source is more likely to form sp 2 hybrid carbon; by adjusting the amount ratio of the high-molecular carbon source and the small-molecular carbon source, the content of sp 2 hybrid carbon is increased, so that the ratio of I D / I G is controlled within a suitable range.

[0046] In some embodiments, the S1 further comprises a phosphorus source, and the phosphorus source comprises at least one of Li2HPO4, LiH2PO4, Li3PO4, (NH4)2HPO4, NH4H2PO4, and H3PO4.

[0047] In some embodiments, in the S1, the solid content of the premixed slurry is 20wt%-60wt%;

[0048] In S2, the grinding slurry is ground by sand milling, the particle size of the sand milling beads is 0.2-0.5mm, and the sand milling time is 8-20h; the temperature of the spray drying is ≤300℃; the sintering temperature is 650-850℃, the sintering time is 5-20h, and the heating rate during the sintering process is 2-15℃ / min.

[0049] In some embodiments, the solid content of the premixed slurry is 35wt%-50wt%.

[0050] In some embodiments, during the sintering process, an organic molecule liquid is added to the sintering environment; the organic molecule liquid comprises at least one of ethanol, methanol, and acetone; and the rate at which the organic molecule is pumped into the sintering environment is 1-100mL / min.

[0051] By further regulating the heating rate during the sintering process and introducing an organic molecule liquid that can instantaneously vaporize at a high temperature during the sintering process, the graphitization degree of the carbon coating layer can be further regulated, and the content of sp 2 hybrid carbon in the positive electrode material can be increased.

[0052] Example 1

[0053] 1. Preparation of a phosphate-based positive electrode material

[0054] S1, Fe 0.97 PO4, Li2CO3, glucose, and polyethylene glycol with a mass ratio of 7:2 are mixed, TiO2 and MgCO3 are added, and deionized water is added to obtain a premixed slurry with a solid content of 40wt%;

[0055] S2, the premixed slurry is sand milled, sand milling beads (zirconia) with a particle size of 0.2-0.5mm are used during the sand milling process, and the sand milling time is 12h to obtain a ground slurry; the above ground slurry is spray dried at 200℃ to obtain a solid product, the above solid product is sintered at 750℃ for 10h, the heating rate during the sintering process is controlled to be 5℃ / min, and ethanol is pumped into the sintering environment at a pumping rate of 10mL / min during the sintering process; the obtained product is airflow crushed to obtain a phosphate-based positive electrode material; and finally, a phosphate-based positive electrode material with a chemical formula of Li 1.03 Fe 0.97 PO4 / C is prepared.

[0056] The SEM image of the phosphate-based positive electrode material prepared in this example is shown in FIG. 3(a).

[0057] 2. Preparation of a positive electrode sheet

[0058] The positive electrode slurry was prepared as follows: the above phosphate-based positive electrode material, conductive agent acetylene black, and binder PVDF were added into a vacuum stirrer in a mass ratio of 97.9:0.9:1.2 for mixing, then solvent NMP was added into the mixed slurry, and the mixed slurry was stirred to be uniform under the action of the vacuum stirrer, thereby obtaining the positive electrode slurry of the present example. The above positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil, and after air drying at room temperature, it was transferred to an oven for continuous drying. After drying in the oven, a positive electrode sheet semi-finished product was obtained, and then the positive electrode sheet semi-finished product was cold-pressed and cut to obtain a positive electrode sheet to be assembled.

[0059] 3. Assembling of button cell

[0060] A commercially available polyethylene film was used as the separator of the lithium battery, a commercially available electrolyte suitable for a 4.2V (upper limit of charging voltage) voltage system battery was used as the electrolyte, and a commercially available lithium sheet was used as the negative electrode. The above positive electrode sheet, negative electrode, and separator were assembled together, injected with electrolyte, and packaged to obtain a button cell.

[0061] The charge-discharge curve test diagram of the button cell prepared in the present example is shown in FIG. 4(a).

[0062] Example 2

[0063] 1. Preparation of phosphate-based positive electrode material

[0064] S1, Mn 0.6 Fe 0.37 PO4, Li2CO3, and glucose and polyethylene glycol in a mass ratio of 7:2 were mixed, and V2O5 was added. After adding deionized water, a premixed slurry with a solid content of 40wt% was obtained;

[0065] S2, the premixed slurry was sand milled, and sand milling beads (zirconium oxide) with a particle size of 0.2-0.5mm were used for sand milling for 20h during the sand milling process to obtain a ground slurry; the above ground slurry was spray dried at 300℃ to obtain a solid product, and the above solid product was sintered at 650℃ for 20h, with a controlled heating rate of 2℃ / min during the sintering process, and methanol was pumped into the sintering environment at a pump-in rate of 100mL / min during the sintering process. The obtained product was mechanically crushed to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0066] The remaining steps and parameter settings were consistent with those of Example 1.

[0067] Example 3

[0068] 1. Preparation of phosphate-based positive electrode material

[0069] S1, FePO4, MnCO3 (molar ratio of Fe / Mn 3.7:6), H4H2PO4 were mixed with glucose and polyethylene glycol with a mass ratio of 7:2, and Cr2O3 and ZrO2 were added, and after adding deionized water, a premixed slurry with a solid content of 40wt% was obtained;

[0070] S2, the premixed slurry was sand milled, and sand milling beads (zirconia) with a particle size of 0.2-0.5mm were used for sand milling for 8h, and a ground slurry was obtained; the above ground slurry was spray dried at 150°C to obtain a solid product, and the above solid product was sintered at 850°C for 5h, the heating rate was controlled at 15°C / min during sintering, and acetone was pumped into the sintering environment at a pumping rate of 80mL / min during sintering, and the obtained product was airflow crushed to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0071] The remaining steps and parameter settings are consistent with Example 1.

[0072] Example 4

[0073] 1. Preparation of a phosphate-based positive electrode material

[0074] S1, FePO4, Mn3CO4 (molar ratio of Fe / Mn 3.7:6), H4H2PO4 were mixed with glucose and polyethylene glycol with a mass ratio of 7:2, and Cr2O3 and ZrO2 were added, and after adding deionized water, a premixed slurry with a solid content of 40wt% was obtained;

[0075] S2, the premixed slurry was sand milled, and sand milling beads (zirconia) with a particle size of 0.2-0.5mm were used for sand milling for 8h, and a ground slurry was obtained; the above ground slurry was spray dried at 150°C to obtain a solid product, and the above solid product was sintered at 850°C for 5h, the heating rate was controlled at 15°C / min during sintering, and acetone was pumped into the sintering environment at a pumping rate of 80mL / min during sintering, and the obtained product was airflow crushed to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0076] The remaining steps and parameter settings are consistent with Example 1. The XRD pattern of the phosphate-based positive electrode material prepared in this example is shown in FIG. 2. The SEM pattern of the phosphate-based positive electrode material prepared in this example is shown in FIG. 3(b). The charge-discharge curve test diagram of the button cell prepared in this example is shown in FIG. 4(b).

[0077] Example 5

[0078] The difference between this example and Example 4 is that the phosphate-based positive electrode material is prepared;

[0079] 1. Preparation of the phosphate-based positive electrode material

[0080] S1, Fe2O3, MnCO3 (molar ratio of Fe / Mn 3.7:6), H4H2PO4 were mixed with glucose and polyethylene glycol in a mass ratio of 7:2, and CoO and MgO were added. After adding deionized water, a premixed slurry with a solid content of 40wt% was obtained;

[0081] S2, the premixed slurry was sand milled, and sand milling beads (zirconium oxide) with a particle size of 0.2-0.5mm were used for sand milling for 12h, and a ground slurry was obtained; the above ground slurry was spray dried at 200°C to obtain a solid product, and the above solid product was sintered at 700°C for 12h, and the sintering process was controlled at a heating rate of 10°C / min, and ethanol was pumped into the sintering environment at a pumping rate of 30mL / min during the sintering process, and the obtained product was air-jet milled to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0082] The remaining steps and parameter settings are consistent with Example 4.

[0083] Example 6

[0084] The difference between this example and Example 4 is that the phosphate-based positive electrode material is prepared;

[0085] 1. Preparation of the phosphate-based positive electrode material

[0086] S1, Fe2O3, Mn3O4 (molar ratio of Fe / Mn 3.7:6), H4H2PO4 were mixed with glucose and polyethylene glycol in a mass ratio of 7:2, and NiO and ZrO2 were added. After adding deionized water, a premixed slurry with a solid content of 40wt% was obtained;

[0087] S2, sand grinding the premixed slurry, using sand grinding beads (zirconium oxide) with a particle size of 0.2-0.5 mm to sand grind for 12 h, to obtain a ground slurry; spray drying the above ground slurry at 200 ℃ to obtain a solid product, sintering the above solid product at 700 ℃ for 12 h, controlling the heating rate to be 5 ℃ / min during the sintering process, and pumping ethanol into the sintering environment at a pumping rate of 60 mL / min during the sintering process, mechanically crushing the obtained product to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0088] The remaining steps and parameter settings are consistent with those of Example 4.

[0089] Example 7

[0090] The difference between this example and Example 4 is that the phosphate-based positive electrode material is prepared;

[0091] 1. Preparation of a phosphate-based positive electrode material

[0092] S1, mixing FeC2O4, MnCO3 (molar ratio of Fe / Mn 3.7:6), H4H2PO4, and glucose and polyethylene glycol with a mass ratio of 7:2, adding TiO2 and MgO, and adding deionized water to obtain a premixed slurry with a solid content of 40 wt%;

[0093] S2, sand grinding the premixed slurry, using sand grinding beads (zirconium oxide) with a particle size of 0.2-0.5 mm to sand grind for 12 h, to obtain a ground slurry; spray drying the above ground slurry at 200 ℃ to obtain a solid product, sintering the above solid product at 750 ℃ for 12 h, controlling the heating rate to be 10 ℃ / min during the sintering process, and pumping ethanol into the sintering environment at a pumping rate of 80 mL / min during the sintering process, air-jet crushing the obtained product to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0094] The remaining steps and parameter settings are consistent with those of Example 4.

[0095] Example 8

[0096] The difference between this example and Example 4 is that the phosphate-based positive electrode material is prepared;

[0097] 1. Preparation of a phosphate-based positive electrode material

[0098] S1, FeC2O4, Mn3O4 (molar ratio of Fe / Mn 3.7:6), H4H2PO4 were mixed with glucose and polyethylene glycol with a mass ratio of 7:2, and TiO2 and ZrO2 were added, and after adding deionized water, a premixed slurry with a solid content of 40wt% was obtained;

[0099] S2, the premixed slurry was sand milled, and sand milling beads (zirconium oxide) with a particle size of 0.2-0.5mm were used for sand milling for 12h, and a ground slurry was obtained; the above ground slurry was spray dried at 200°C to obtain a solid product, and the above solid product was sintered at 700°C for 12h, the heating rate was controlled at 5°C / min during sintering, and ethanol was pumped into the sintering environment at a pumping rate of 30mL / min during sintering, and the product was mechanically crushed to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0100] The remaining steps and parameter settings are consistent with Example 4.

[0101] Example 9

[0102] The difference between this example and Example 4 is that the carbon content in the phosphate-based positive electrode material is 0.2wt%, and the remaining steps and parameter settings are consistent with Example 4.

[0103] Example 10

[0104] The difference between this example and Example 4 is that the doping amount of the first metal element in the phosphate-based positive electrode material is 10000ppm, and the remaining steps and parameter settings are consistent with Example 4.

[0105] Example 11

[0106] The difference between this example and Example 4 is that the doping amount of the first metal element in the phosphate-based positive electrode material is 7000ppm, and the remaining steps and parameter settings are consistent with Example 4.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 4 is that the phosphate-based positive electrode material in this comparative example is not doped with M and Li, and the remaining steps and parameter settings are consistent with Example 4.

[0109] Comparative Example 2

[0110] The difference between this comparative example and Example 4 is that the carbon material used in this comparative example has a degree of disorder of 1.5;

[0111] 1. Preparation of phosphate-based positive electrode material

[0112] S1, FeC2O4, Mn3O4 (molar ratio of Fe / Mn 3.7:6), H4H2PO4 and glucose were mixed, and TiO2 and ZrO2 were added, and deionized water was added to obtain a premixed slurry with a solid content of 40wt%;

[0113] S2, the premixed slurry was sand milled, and sand milling beads (zirconium oxide) with a particle size of 0.2-0.5mm were used for sand milling for 12h, to obtain a grinding slurry; the grinding slurry was spray dried at 200°C to obtain a solid product, and the solid product was sintered at 700°C for 12h, with a controlled heating rate of 20°C / min during sintering, and the obtained product was mechanically crushed to obtain a phosphate-based positive electrode material; the chemical formula of the finally prepared phosphate-based positive electrode material is Li 1.03 Mn 0.60 Fe 0.37 PO4 / C.

[0114] The remaining steps and parameter settings are consistent with Example 4.

[0115] Test method

[0116] I D / I G Test

[0117] The phosphate-based positive electrode materials prepared in the above examples and comparative examples were subjected to Raman spectrum test, and the specific test steps were as follows: the I - 1 / I G of the carbon material was calculated by measuring the peak intensity (I - 1 ) of the D band (about 1350cm D D / I G . The measurement equipment / conditions are as follows:

[0118] (1) Raman spectrometer: inVia, Renishaw (UK);

[0119] (2) Argon ion laser wavelength: 532nm;

[0120] (3) Exposure time: 10 seconds, integration times: 10 times.

[0121] II. Carbon content test

[0122] ​The carbon content of the phosphate-based positive and negative materials prepared in the above examples and comparative examples was tested. Specifically, the test was performed by a high-frequency infrared carbon and sulfur analyzer HW2000.

[0123] III. Metal element doping content test

[0124] The carbon content of the phosphate-based positive and negative materials prepared in the above examples and comparative examples was tested. Specifically, the test was performed according to GB / T 30902-2014 Inorganic Chemical Products-Determination of Impurity Elements-Inductively Coupled Plasma Optical Emission Spectrometry. During the test, an ICP-OES device was used to test the content of the first metal element doped at the M site and the content of the second metal element doped at the Li site.

[0125] IV. Ion dissolution rate test

[0126] The Mn / Fe ion dissolution rate of the phosphate-based positive materials prepared in the above examples and comparative examples was tested. Specifically, 5 g of phosphate-based positive material powder was weighed into a beaker and 50 ml of ultrapure water was added. The beaker was sealed with plastic wrap and placed at room temperature for 70 h. The supernatant obtained after standing was introduced into three layers of medium-speed filter paper at a constant speed, and the filtrate was collected. The collected filtrate was filtered with three layers of filter membrane (pore size 0.22 um), 1 ml of filtrate was taken into a 50 / 100 ml volumetric flask for constant volume, and then ICP was used to test the Mn / Fe content. The Mn / Fe content in the solution was converted to the dissolution rate of 5 g of phosphate-based positive material powder.

[0127] V. Powder compaction density test

[0128] The compaction density of the phosphate-based positive materials prepared in the above examples and comparative examples was tested. Specifically, the test device was a powder compaction density instrument UTM7305 from Shenzhen Sansi Longxian, and the test condition was 30 kN pressure.

[0129] VI. Rct test

[0130] The EIS test of the coin cell prepared in the above examples and comparative examples was performed by an electrochemical workstation, and the Rct was obtained by fitting the measured EIS data. The specific test device was a VMP3 French Bio-Logic multi-channel electrochemical workstation.

[0131] Table 1

[0132]

[0133] In combination with Examples 1-4, Comparative Examples 1-2 and Table 1, it can be seen that by doping the first metal element at the M site and / or doping the second metal element at the Li site and controlling the order degree of the carbon material in the carbon coating layer, the Fe / Mn elution rate of the phosphate-based positive electrode material can be significantly reduced, thereby facilitating the improvement of the cycle performance of the positive electrode material; and at this time, the charge transfer impedance of the phosphate-based positive electrode material is small, so that the positive electrode material has excellent rate performance.

[0134] In combination with Examples 1-8 and Table 1, it can be seen that by preparing the non-strict stoichiometric ratio phosphate-based positive electrode material by the method in the present application, the phosphate-based positive electrode material has low charge transfer impedance and low Fe / Mn elution rate, has excellent rate performance and low-temperature cycle performance; and also has a wide range of powder compaction density, which can be applied to different application requirements of lithium batteries.

[0135] In combination with Examples 4, 9, and Table 1, it can be seen that when the carbon content in the phosphate-based positive electrode material is low, the Fe / Mn elution rate and the charge transfer impedance of the positive electrode material increase to some extent, because the carbon coating layer cannot construct an effective coated conductive network structure on the surface of the phosphate-based positive electrode active material, and the phosphate-based positive electrode material in Example 4 of the present application has low disorder degree and high graphitization degree of the carbon material in the carbon coating layer, which can form an efficient conductive network structure, thereby significantly reducing the charge transfer impedance of the phosphate-based positive electrode material.

[0136] In combination with Examples 4, 10-11, and Table 1, it can be seen that when the doping content of the first metal element is too high or the doping content of the second metal element is too high, impurity phases will be generated in the phosphate-based positive electrode material, which reduces the stability of the crystal structure, and the Fe / Mn elution rate and the charge transfer impedance of the phosphate-based positive electrode material increase to some extent; and in Example 4, since the doping of the first metal element and the second metal element is controlled within a reasonable range, not only can the generation of impurity phases be reduced, but also the promotion effect of the defects in the carbon coating layer on the side reaction of the phosphate-based positive electrode material in the electrolyte can be inhibited, which also helps to reduce the degree of deterioration of the carbon coating layer by the side reaction, thereby further stabilizing the structural stability of the phosphate-based positive electrode material, reducing the Fe / Mn elution rate, and helping to improve the cycle performance of the lithium battery.

[0137] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, but these modifications or replacements are within the protection scope of the present application.

Claims

1. A phosphate-based positive electrode material comprising a base particle and a carbon coating layer coated on a surface of the base particle; the base particle has a chemical formula of Li1-xMxPO4, 0.96≤x≤1.08, 0.96≤y≤1, M comprises at least one of Fe, Mn. x M y PO4, 0.96≤x≤1.08, 0.96≤y≤1, M comprises at least one of Fe, Mn. wherein The M site is doped with a first metal element, and the first metal element includes at least one of Ti, V, Cr, Co, Ni, Nb, Mo, and W; and / or, the Li site is doped with a second metal element, and the second metal element includes at least one of Mg and Zr. The carbon coating layer includes carbon material, and the carbon material has a disorder degree I D / I G ≤1.

2.

2. The phosphate-based cathode material of claim 1, wherein: The carbon content in the phosphate-based positive electrode material is 1wt%-2wt%.

3. The phosphate-based cathode material of claim 1, wherein: The doping amount of the first metal element is ≤5000ppm.

4. The phosphate-based cathode material of claim 1, wherein: The doping amount of the second metal is ≤3000ppm.

5. The phosphate-based cathode material of claim 1, wherein: The particle size D50 of the phosphate-based positive electrode material is 50-2000nm.

6. The phosphate-based cathode material according to any one of claims 1 to 5, wherein: The compaction density of the phosphate-based positive electrode material is 2-2.7 g / cm 3 .

7. The preparation method of the phosphate-based positive electrode material according to any one of claims 1-6, comprising the following steps: S1, mixing an iron source, a manganese source, a lithium source, and a carbon source, grinding after adding water to obtain a premixed slurry; S2, after spray drying and sintering the premixed slurry, crushing to obtain the phosphate-based positive electrode material.

8. The method for producing the phosphate-based positive electrode material according to claim 7, wherein: The iron source includes at least one of FePO4, Fe2O3, and FeC2O4; The manganese source includes at least one of MnPO4, MnCO3, and Mn3O4; The lithium source includes at least one of Li2CO3, LiOH.H2O, LiCl, Li2SO4, Li2HPO4, LiH2PO4, Li3PO4, and LiNO3; The doping source includes an M site doping source and a Li site doping source, the M site doping source includes at least one of a Ti salt and an oxide thereof, a V salt and an oxide thereof, a Cr salt and an oxide thereof, a Co salt and an oxide thereof, a Ni salt and an oxide thereof, a Nb salt and an oxide thereof, a Mo salt and an oxide thereof, and a W salt and an oxide thereof, and the Li site doping source includes at least one of a Mg salt and an oxide thereof and a Zr salt and an oxide thereof; The carbon source includes a high molecular carbon source and a small molecular carbon source; wherein the high molecular carbon source includes at least one of polyethylene glycol, polyvinylpyrrolidone, graphene, and carbon nanotubes; and the small molecular carbon source includes at least one of glucose, sucrose, and conductive carbon black.

9. The method of producing a phosphate-based cathode material according to claim 7, wherein: In S1, the solid content of the premixed slurry is 20wt%-60wt%; In S2, the grinding slurry is ground by sand milling, the sand milling time is 8-20h; the spray drying temperature is ≤300℃; the sintering temperature is 650-850℃, the sintering time is 5-20h, and the heating rate during sintering is 2-15℃ / min.

10. A lithium ion battery comprising a positive electrode sheet, the positive electrode sheet comprising an active material layer, and the active material layer comprising the phosphate-based positive electrode material according to any one of claims 1-6.

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