Interface modified high-rate lithium iron phosphate cathode material and preparation method thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a preparation method of an interface-modified high-rate lithium iron phosphate positive electrode material, which is used for solving the problems of interface impedance, rate performance and low energy density of existing lithium iron phosphate; the preparation method uses zirconium-niobium co-doped iron phosphate as a precursor of the lithium iron phosphate positive electrode material, widens lithium ion diffusion channels, improves a lithium ion diffusion coefficient, simultaneously has an olivine structure framework, provides a wider tunnel space for lithium ion migration, provides extra electrons through zirconium-niobium, and cooperatively improves electronic conductivity; Li2ZrCl6-LiCl interface modification can isolate sulfide electrolyte from direct contact with the positive electrode material, and inhibit interface side reactions; carbon nanotube coating can enhance conductivity, reduce corrosion, and improve Li + diffusion coefficient and material structure stability, and improve charge-discharge rate.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion batteries, in particular to an interface-modified high-rate lithium iron phosphate positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of electric vehicles and portable electronic devices, the demand for lithium ion batteries is also increasing, especially the high-rate performance of the positive electrode material, which has become the key to improving the performance of the battery. Lithium iron phosphate has become one of the preferred positive electrode materials due to its good safety, low cost and long cycle life.

[0003] However, the lithium iron phosphate positive electrode material exhibits poor energy density and cycle stability during high-rate charging and discharging, which limits its application in high-performance batteries. Therefore, modifying lithium iron phosphate through various methods to improve its rate performance has become one of the current research hotspots, and has important research and application value.

[0004] Therefore, it is of great significance to develop an interface-modified high-rate lithium iron phosphate positive electrode material and a preparation method thereof in the field of lithium ion batteries. SUMMARY

[0005] In order to overcome the above technical problems, the purpose of the application is to provide an interface-modified high-rate lithium iron phosphate positive electrode material and a preparation method thereof. By doping zirconium-niobium in the synthesis process of lithium iron phosphate, a double-doped lithium iron phosphate powder is obtained, and then mixed with Li2ZrCl6-LiCl and carbon nanotubes respectively, stirred and sintered to obtain an interface-modified high-rate lithium iron phosphate positive electrode material, which solves the problems of interface impedance, rate performance and low energy density of the existing lithium iron phosphate.

[0006] The purpose of the application can be achieved by the following technical solutions:

[0007] In a first aspect, the application provides a preparation method of an interface-modified high-rate lithium iron phosphate positive electrode material, comprising the following steps:

[0008] Step a1: FeCl3·H2O, NH4H2PO4 and deionized water were added into a three-necked flask equipped with a stirrer and a thermometer, mixed and stirred for 15-20 min to obtain a first solution; ZrOCl2·8H2O, C2H5NNbO4 and hydrochloric acid solution were added into a beaker, mixed and stirred for 20-30 min to obtain a second solution; cetyltrimethylammonium bromide solution was added into the first solution, nitrogen was introduced for protection, the first solution was heated to 85℃, and was stirred at a speed of 1200 r / min for 1-2 h, the second solution was added, NaOH solution was synchronously added to maintain pH at 1.8-2, and reaction was carried out for 12 h, then centrifugation was carried out, the precipitate was placed in a vacuum drying box and dried at a temperature of 50-55℃ for 2-3 h to obtain zirconium-niobium co-doped FePO4;

[0009] Step a2: zirconium-niobium co-doped FePO4, Li2CO3 and sucrose were mixed and added into a planetary ball mill, anhydrous ethanol was added as a dispersion solvent, the ball-to-material ratio was 5:1 (the ball-to-material ratio refers to the mass ratio of grinding bodies to materials in the mill), and ball milling was carried out at 350 r / min for 4 h, then the sample was placed in a 80℃ air drying oven and dried for 12 h, after crushing and grinding, a vacuum tube furnace was used, and the sample was first pre-fired at 350℃ for 4 h and then sintered at 750℃ for 12 h under a nitrogen atmosphere to obtain modified lithium iron phosphate;

[0010] Step a3: LiCl, ZrCl4 and NbCl5 with a molar ratio of 10 / 13 were vacuum dried at 120℃ for 24 h, then were loaded into a ball mill tank, the ball-to-material ratio was 10:1, and ball milling was carried out at 500 r / min for 10 h under argon protection, the remaining LiCl with a molar ratio of 3 / 13 was dissolved in anhydrous ethanol, was sprayed into liquid nitrogen, and was vacuum dried to obtain nano LiCl, which was added into the above ball mill tank and ball milled at a speed of 200 r / min for 1 h to obtain Li2ZrCl6 modified by Nb-LiCl complex;

[0011] Step a4: the modified lithium iron phosphate and the modified Li2ZrCl6 were loaded into a high-speed mixer, nitrogen was introduced for protection, and mixing was carried out at a speed of 2000 r / min for 15-30 min, then a hot roller press was used, the roller temperature was 150℃, and the pressure was 5 MPa to obtain lithium iron phosphate coated with Li2ZrCl6-LiCl;

[0012] Step a5: the lithium iron phosphate coated with Li2ZrCl6-LiCl, C6H 12O6·H2O, carbon nanotubes are added into a ball milling tank, the ball-to-material ratio is 10:1, the milling ball is nano zirconium ball, anhydrous ethanol is added as a dispersion solvent, and the ball milling is carried out at 600 r / min for 10-12 h in a ball mill, the ball milling tank is taken out, the ball and the material are separated, the material is dried and ground, is laid flat on a porcelain boat, and is placed into a tube furnace for sintering, 25℃ is kept for 4 h, then the temperature is increased to 680℃, and the temperature is kept constant for 10 h, and finally the temperature is naturally cooled to 25℃, after the sintering is completed, the interface modified high-rate lithium iron phosphate positive electrode material is obtained.

[0013] As a further scheme of the application, the amount ratio of FeCl3·H2O, NH4H2PO4, deionized water, ZrOCl2·8H2O, C2H5NNbO4, hydrochloric acid solution and cetyltrimethylammonium bromide solution in step a1 is 0.985 mol:1 mol:600 mL:0.01 mol:0.005 mol:400 mL:200 mL.

[0014] As a further scheme of the application, the molar concentration of the hydrochloric acid solution in step a1 is 0.5 mol / L; the molar concentration of the cetyltrimethylammonium bromide solution is 0.1 mol / L; and the molar concentration of the NaOH solution is 4 mol / L.

[0015] As a further scheme of the application, the amount ratio of the zirconium-niobium co-doped FePO4, Li2CO3, sucrose and anhydrous ethanol in step a2 is 158.3 g:1.03 mol:0.1 mol:200-300 mL.

[0016] As a further scheme of the application, the amount ratio of the LiCl, ZrCl4, NbCl5 and anhydrous ethanol in step a3 is 2.34 mol:0.8 mol:0.2 mol:540 mL.

[0017] As a further scheme of the application, the amount ratio of the modified lithium iron phosphate and the modified Li2ZrCl6 in step a4 is 90 g:10 g.

[0018] As a further scheme of the application, the amount ratio of the Li2ZrCl6-LiCl coated lithium iron phosphate, C6H 12 The amount ratio of O6·H2O, carbon nanotubes and anhydrous ethanol is 175.9 g:1.23 g:5.28 g:200-300 mL.

[0019] In a second aspect, the application provides an interface modified high-rate lithium iron phosphate positive electrode material, which is prepared according to the above-mentioned preparation method of the interface modified high-rate lithium iron phosphate positive electrode material.

[0020] The beneficial effects of the present application are:

[0021] The interface modified high-rate lithium iron phosphate positive electrode material and the preparation method thereof, the first solution is obtained by mixing FeCl3·H2O, NH4H2PO4 and deionized water and stirring, the second solution is obtained by mixing ZrOCl2·8H2O, C2H5NNbO4 and hydrochloric acid solution in a beaker and stirring, the cetyltrimethylammonium bromide solution is added to the first solution and stirred, the second solution is added for reaction, and then centrifugal drying is carried out to obtain zirconium-niobium co-doped FePO4; the zirconium-niobium co-doped FePO4, Li2CO3 and sucrose are mixed and ball milled, dried, broken and ground, and then sintered to obtain modified lithium iron phosphate; the zirconium-niobium co-doped iron phosphate is used as the precursor of the lithium iron phosphate positive electrode material, wherein Zr 4+ substitutes Li + site, Nb 5+ substitutes Fe 2+ site, forms cation vacancies and lattice distortion in the crystal lattice, effectively widens the lithium ion diffusion channel, improves the lithium ion diffusion coefficient, maintains the stable olivine structure framework at the same time, provides a wider tunnel space for lithium ion migration, zirconium-niobium provides additional electrons, and both of them synergistically improve the electronic conductivity; the LiCl, ZrCl4 and NbCl5 are dry ball milled, the remaining LiCl is dissolved in anhydrous ethanol, sprayed to liquid nitrogen freezing, and then vacuum dried to obtain nano LiCl, which is added to the ball mill tank for ball milling to obtain Li2ZrCl6 modified by niobium-doped-LiCl compounding; the modified lithium iron phosphate and the modified Li2ZrCl6 are mixed and roll pressed to obtain lithium iron phosphate coated by Li2ZrCl6-LiCl; Li2ZrCl6 provides a three-dimensional lithium ion channel, niobium element doping can promote cationic disordering and induce lattice distortion, so that Li + is more easily transmitted in the crystal lattice, the ion conductivity is improved, LiCl as an interface wetting agent fills the crystal boundary gap, the interface lubrication effect of LiCl reduces the energy barrier of Li + from the lattice binding to reduce the activation energy, meanwhile, it isolates the direct contact between the sulfide electrolyte and the positive electrode material, inhibits the interface side reaction, and provides a high lithium-conducting interface at the same time; the lithium iron phosphate coated by Li2ZrCl6-LiCl, C6H 12 O6·H2O and carbon nanotubes are mixed and ball milled, and sintered to obtain the interface modified high-rate lithium iron phosphate positive electrode material; the carbon nanotubes are coated on the surface of the lithium iron phosphate, which enhances the conductivity and is conducive to the embedding and extraction of Li + ; in the sintering process, the growth of the lithium iron phosphate particles is inhibited, and the Li + migration path is shortened; the carbon nanotube coating reduces the erosion of the electrolyte to the lithium iron phosphate positive electrode material, and reduces the Li +migration barrier, improving Li + diffusion coefficient and stability of material structure, improving charge-discharge rate. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present application.

[0023] Embodiment 1

[0024] The present embodiment is a preparation method of an interface-modified high-rate lithium iron phosphate positive electrode material, comprising the following steps:

[0025] Step S1: 0.985 mol of FeCl3·H2O, 1 mol of NH4H2PO4 and 600 mL of deionized water are added into a three-necked flask equipped with a stirrer and a thermometer, mixed and stirred for 15 min to obtain a first solution; 0.01 mol of ZrOCl2·8H2O, 0.005 mol of C2H5NNbO4 and 400 mL of a hydrochloric acid solution with a molar concentration of 0.5 mol / L are added into a beaker, mixed and stirred for 20 min to obtain a second solution; 200 mL of a cetyltrimethylammonium bromide solution with a molar concentration of 0.1 mol / L is added into the first solution, nitrogen gas is introduced for protection, the first solution is heated to 85℃, and constant stirring is performed at a rotating speed of 1200 r / min for 1 h; the second solution is added, a NaOH solution with a molar concentration of 4 mol / L is synchronously added to maintain a pH of 1.8, and reaction is performed for 12 h; then centrifugation is performed, the precipitate is placed in a vacuum drying box, and drying is performed at a temperature of 50℃ for 2 h to obtain zirconium-niobium co-doped FePO4;

[0026] Step S2: 158.3 g of the zirconium-niobium co-doped FePO4, 1.03 mol of Li2CO3 and 0.1 mol of sucrose are mixed and added into a planetary ball mill, 200 mL of anhydrous ethanol is added as a dispersion solvent, the ball-to-material ratio is 5:1, and ball milling is performed at a speed of 350 r / min for 4 h; after ball milling, the mixture is placed in a 80℃ air-drying box for drying for 12 h; after crushing and grinding, a vacuum tube furnace is used, and pre-sintering is performed at 350℃ for 4 h, and then sintering is performed at 750℃ for 12 h under a nitrogen atmosphere to obtain modified lithium iron phosphate;

[0027] Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, 0.2 mol NbCl5 were vacuum dried at 120℃ for 24h, then loaded into a ball mill tank, the ball-to-material ratio was 10:1, ball milling at 500r / min for 10h under argon protection, the remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed into liquid nitrogen, and then vacuum dried to obtain nano LiCl, which was added to the above ball mill tank and ball-milled at 200r / min for 1h to obtain Nb-doped LiCl composite modified Li2ZrCl6;

[0028] Step S4: 90g modified lithium iron phosphate, 10g modified Li2ZrCl6 were loaded into a high-speed mixer, the rotation speed was 2000r / min, nitrogen was introduced for protection, and mixed for 15min, then treated by a hot roller press with a roller temperature of 150℃ and a pressure of 5MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate;

[0029] Step S5: 175.9g Li2ZrCl6-LiCl coated lithium iron phosphate, 1.23g C6H 12 O6·H2O, 5.28g carbon nanotubes were added into a ball mill tank, the ball-to-material ratio was 10:1, the grinding ball was nano zirconium ball, 200mL of anhydrous ethanol was added as a dispersion solvent, and ball milling was carried out at 600r / min for 10h in a ball mill, the ball mill tank was taken out, the ball and material were separated, the material was dried and ground, laid on a porcelain boat, put into a tube furnace for sintering, 25℃ for 4h, then heated to 680℃, and sintered at constant temperature for 10h, finally naturally cooled to 25℃, after sintering, Li2ZrCl6-LiCl interface modified high-rate lithium iron phosphate positive electrode material was obtained.

[0030] Example 2:

[0031] The present embodiment is a preparation method of an interface modified high-rate lithium iron phosphate positive electrode material, comprising the following steps:

[0032] Step S1: 0.985 mol FeCl3·H2O, 1 mol NH4H2PO4 and 600 mL deionized water were added into a three-necked flask equipped with a stirrer and a thermometer, and mixed and stirred for 18 min to obtain a first solution; 0.01 mol ZrOCl2·8H2O, 0.005 mol C2H5NNbO4 and 400 mL hydrochloric acid solution with a molar concentration of 0.5 mol / L were added into a beaker, mixed and stirred for 25 min to obtain a second solution; 200 mL cetyltrimethylammonium bromide solution with a molar concentration of 0.1 mol / L was added into the first solution, nitrogen was introduced for protection, the first solution was heated to 85°C, and was stirred at a constant speed of 1200 r / min for 1.5 h, then the second solution was added, a NaOH solution with a molar concentration of 4 mol / L was synchronously added to maintain the pH value at 1.9, and reaction was performed for 12 h, after which centrifugation was performed, the precipitate was placed in a vacuum drying box and dried at a temperature of 55°C for 2.5 h to obtain zirconium-niobium co-doped FePO4;

[0033] Step S2: 158.3 g zirconium-niobium co-doped FePO4, 1.03 mol Li2CO3 and 0.1 mol sucrose were mixed and added into a planetary ball mill, 250 mL anhydrous ethanol was added as a dispersion solvent, the ball-to-material ratio was 5:1, and ball milling was performed at 350 r / min for 4 h, after ball milling, the sample was placed in a 80°C air-drying oven and dried for 12 h, after crushing and grinding, a vacuum tube furnace was used, and the sample was pre-fired at 350°C for 4 h and then sintered at 750°C for 12 h in a nitrogen atmosphere to obtain modified lithium iron phosphate;

[0034] Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4 and 0.2 mol NbCl5 were vacuum dried at 120°C for 24 h, then were loaded into a ball mill tank, the ball-to-material ratio was 10:1, ball milling was performed at 500 r / min for 10 h under argon protection, 0.54 mol LiCl remaining was dissolved in 540 mL anhydrous ethanol, was sprayed into liquid nitrogen, and was vacuum dried to obtain nano LiCl, which was added into the ball mill tank and ball milled at a speed of 200 r / min for 1 h to obtain Li2ZrCl6 modified by Nb-LiCl compounding;

[0035] Step a4: 90 g modified lithium iron phosphate and 10 g modified Li2ZrCl6 were loaded into a high-speed mixer, nitrogen was introduced for protection, the rotating speed was 2000 r / min, and mixing was performed for 25 min, then a hot roller press was used, the roller temperature was 150°C, and the pressure was 5 MPa to obtain lithium iron phosphate coated with Li2ZrCl6-LiCl;

[0036] Step S5: 175.9 g lithium iron phosphate coated with Li2ZrCl6-LiCl, 1.23 g C6H 12O6·H2O, 5.28 g carbon nanotubes were added into a ball mill tank, the ball-to-material ratio was 10:1, the milling ball was nano-zirconium ball, 250 mL anhydrous ethanol was added as a dispersion solvent, and the ball mill was operated at 600 r / min for 11 h. The ball mill tank was taken out, the ball and material were separated, the material was dried and ground, and then was laid on a porcelain boat and placed in a tube furnace for sintering. The temperature was kept at 25℃ for 4 h, then was increased to 680℃, and was kept at the constant temperature for 10 h. Finally, the temperature was naturally cooled to 25℃. After sintering, the Li2ZrCl6-LiCl interfacial modified high-rate lithium iron phosphate positive electrode material was obtained.

[0037] Example 3

[0038] The embodiment is a preparation method of an interfacial modified high-rate lithium iron phosphate positive electrode material, which comprises the following steps:

[0039] Step S1: 0.985 mol FeCl3·H2O, 1 mol NH4H2PO4 and 600 mL deionized water were added into a three-necked flask equipped with a stirrer and a thermometer, and were mixed and stirred for 20 min to obtain a first solution. 0.01 mol ZrOCl2·8H2O, 0.005 mol C2H5NNbO4 and 400 mL hydrochloric acid solution with a molar concentration of 0.5 mol / L were added into a beaker, and were mixed and stirred for 30 min to obtain a second solution. 200 mL cetyltrimethylammonium bromide solution with a molar concentration of 0.1 mol / L was added into the first solution, and nitrogen was introduced for protection. The first solution was heated to 85℃, and was stirred at a constant speed of 1200 r / min for 2 h. The second solution was added, and a 4 mol / L NaOH solution was synchronously added to maintain the pH value at 2. The reaction was carried out for 12 h, and then centrifugation was performed. The precipitate was placed in a vacuum drying box and was dried at a temperature of 55℃ for 3 h to obtain zirconium-niobium co-doped FePO4.

[0040] Step S2: 158.3 g zirconium-niobium co-doped FePO4, 1.03 mol Li2CO3 and 0.1 mol sucrose were mixed and added into a planetary ball mill, 300 mL anhydrous ethanol was added as a dispersion solvent, and the ball-to-material ratio was 5:1. The ball mill was operated at 350 r / min for 4 h. After ball milling, the mixture was placed in a 80℃ air drying box and was dried for 12 h. After crushing and grinding, a vacuum tube furnace was used, and the mixture was pre-sintered at 350℃ for 4 h and then was sintered at 750℃ for 12 h under a nitrogen atmosphere to obtain modified lithium iron phosphate.

[0041] Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, 0.2 mol NbCl5 were vacuum dried at 120°C for 24 h, then loaded into a ball mill tank, the ball-to-material ratio was 10:1, ball milling was carried out at 500 r / min for 10 h under argon protection, and the remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed into liquid nitrogen, and vacuum dried to obtain nano LiCl, which was added to the above ball mill tank and ball milled at 200 r / min for 1 h to obtain Li2ZrCl6 modified by Nb-doped LiCl composite;

[0042] Step S4: 90 g of modified lithium iron phosphate and 10 g of modified Li2ZrCl6 were loaded into a high-speed mixer, nitrogen was introduced at a rotation speed of 2000 r / min, and mixed for 30 min, followed by treatment by a hot roller press at a roller temperature of 150°C and a pressure of 5 MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate;

[0043] Step S5: 175.9 g of Li2ZrCl6-LiCl coated lithium iron phosphate, 1.23 g of C6H 12 O6·H2O, and 5.28 g of carbon nanotubes were added to a ball mill tank, the ball-to-material ratio was 10:1, the grinding balls were nano zirconium balls, 300 mL of anhydrous ethanol was added as a dispersion solvent, and ball milling was carried out at 600 r / min for 12 h in a ball mill. The ball mill tank was removed, the ball and material were separated, the material was dried and ground, spread on a porcelain boat, and placed in a tube furnace for sintering. The temperature was kept at 25°C for 4 h, then increased to 680°C, and kept at this temperature for 10 h. Finally, the temperature was naturally cooled to 25°C. After sintering, Li2ZrCl6-LiCl interfacial modified high-rate lithium iron phosphate positive electrode material was obtained.

[0044] Comparative Example 1:

[0045] The present comparative example is a preparation method of an interfacial modified high-rate lithium iron phosphate positive electrode material, comprising the following steps:

[0046] Step S1: 1.8 mol LiCl, 0.8 mol ZrCl4, 0.2 mol NbCl5 were vacuum dried at 120°C for 24 h, then loaded into a ball mill tank, the ball-to-material ratio was 10:1, ball milling was carried out at 500 r / min for 10 h under argon protection, and the remaining 0.54 mol LiCl was dissolved in 540 mL of anhydrous ethanol, sprayed into liquid nitrogen, and vacuum dried to obtain nano LiCl, which was added to the above ball mill tank and ball milled at 200 r / min for 1 h to obtain Li2ZrCl6 modified by Nb-doped LiCl composite;

[0047] Step S2: 90 g of lithium iron phosphate and 10 g of modified Li2ZrCl6 were loaded into a high-speed mixer, nitrogen was introduced at a rotating speed of 2000 r / min, and mixed for 25 min. Then, the mixture was processed by a hot roller press at a roller temperature of 150 ℃ and a pressure of 5 MPa to obtain a high-rate lithium iron phosphate cathode material modified by a Li2ZrCl6-LiCl interface.

[0048] Comparative Example 2:

[0049] The present comparative example is a preparation method of an interface-modified high-rate lithium iron phosphate cathode material, comprising the following steps:

[0050] Step S1: 0.985 mol of FeCl3·H2O, 1 mol of NH4H2PO4, and 600 mL of deionized water were added to a three-necked flask equipped with a stirrer and a thermometer, and mixed and stirred for 18 min to obtain a first solution. Separately, 0.01 mol of ZrOCl2·8H2O, 0.005 mol of C2H5NNbO4, and 400 mL of a 0.5 mol / L hydrochloric acid solution were added to a beaker and mixed and stirred for 25 min to obtain a second solution. 200 mL of a 0.1 mol / L cetyltrimethylammonium bromide solution was added to the first solution, nitrogen was introduced, the first solution was heated to 85 ℃, and stirred at a constant speed of 1200 r / min for 1.5 h. The second solution was added, and a 4 mol / L NaOH solution was added simultaneously to maintain a pH of 1.9. The reaction was carried out for 12 h, and then centrifugation was performed. The precipitate was placed in a vacuum drying oven and dried at a temperature of 55 ℃ for 2.5 h to obtain zirconium-niobium co-doped FePO4;

[0051] Step S2: 158.3 g of zirconium-niobium co-doped FePO4, 1.03 mol of Li2CO3, and 0.1 mol of sucrose were mixed and added to a planetary ball mill. 250 mL of anhydrous ethanol was added as a dispersion solvent, the ball-to-material ratio was 5:1, and the ball milling was carried out at 350 r / min for 4 h. After ball milling, the mixture was placed in a 80 ℃ air-drying oven and dried for 12 h. After crushing and grinding, a vacuum tube furnace was used to pre-burn at 350 ℃ for 4 h and then sinter at 750 ℃ for 12 h under a nitrogen atmosphere to obtain modified lithium iron phosphate.

[0052] Step S3: 1.8 mol LiCl, 0.8 mol ZrCl4, 0.2 mol NbCl5 were vacuum dried at 120°C for 24 h, then loaded into a ball mill tank, the ball-to-material ratio was 10:1, ball milling was carried out at 500 r / min for 10 h under argon protection, the remaining 0.54 mol LiCl was dissolved in 540 mL anhydrous ethanol, sprayed into liquid nitrogen freezing, and then vacuum dried to obtain nano LiCl, which was added to the above ball mill tank and ball milling was carried out at 200 r / min for 1 h to obtain Li2ZrCl6 modified by Nb-doped LiCl;

[0053] Step S4: 90 g of the modified lithium iron phosphate and 10 g of the modified Li2ZrCl6 were loaded into a high-speed mixer, mixed at a speed of 2000 r / min for 25 min under nitrogen protection, and then treated by a hot roller mill at a roller temperature of 150°C and a pressure of 5 MPa to obtain the Li2ZrCl6-LiCl interfacial modified high-rate lithium iron phosphate positive electrode material.

[0054] Comparative Example 3:

[0055] The present comparative example is a preparation method of an interfacial modified high-rate lithium iron phosphate positive electrode material, comprising the following steps:

[0056] Step S1: 1.8 mol LiCl, 0.8 mol ZrCl4, 0.2 mol NbCl5 were vacuum dried at 120°C for 24 h, then loaded into a ball mill tank, the ball-to-material ratio was 10:1, ball milling was carried out at 500 r / min for 10 h under argon protection, the remaining 0.54 mol LiCl was dissolved in 540 mL anhydrous ethanol, sprayed into liquid nitrogen freezing, and then vacuum dried to obtain nano LiCl, which was added to the above ball mill tank and ball milling was carried out at 200 r / min for 1 h to obtain Li2ZrCl6 modified by Nb-doped LiCl;

[0057] Step S2: 90 g of lithium iron phosphate and 10 g of the modified Li2ZrCl6 were loaded into a high-speed mixer, mixed at a speed of 2000 r / min for 25 min under nitrogen protection, and then treated by a hot roller mill at a roller temperature of 150°C and a pressure of 5 MPa to obtain Li2ZrCl6-LiCl coated lithium iron phosphate;

[0058] Step S3: 175.9 g of the Li2ZrCl6-LiCl coated lithium iron phosphate, 1.23 g of C6H 12O6·H2O, 5.28 g carbon nanotubes were added to the ball mill jar, the ball-to-material ratio was 10:1, the milling ball was nano zirconium ball, 250 mL anhydrous ethanol was added as a dispersion solvent, and the ball mill was operated at 600 r / min for 11 h. The ball mill jar was taken out, the ball and material were separated, the material was dried and ground, and then was laid flat on a porcelain boat and placed in a tube furnace for sintering. The temperature was kept at 25 °C for 4 h, then increased to 680 °C, and kept at this temperature for 10 h. Finally, the temperature was naturally cooled to 25 °C. After sintering, the Li2ZrCl6-LiCl interfacially modified high-rate lithium iron phosphate positive electrode material was obtained.

[0059] The interfacially modified high-rate lithium iron phosphate positive electrode materials of examples 1-3 and comparative examples 1-3, graphite, polyethylene UTEC 4041 produced by Yuetai, and lithium iodide were prepared into batteries, and the electrochemical performance of the batteries was tested. The interface impedance of the batteries was tested by EIS. The energy density and electrochemical performance of the batteries were tested according to GB / T 31486-2024. The test results are shown in the following table:

[0060]

[0061] Referring to the above table, comparative example 1 is a blank control group only subjected to Li2ZrCl6-LiCl interfacial modification. Compared with examples 1-3, it can be concluded that the battery performance prepared by the interfacially modified high-rate lithium iron phosphate positive electrode material of the present application is significantly better than that of comparative example 1. According to the comparison between examples 1-3 and comparative example 2, it can be concluded that the coating of lithium iron phosphate with carbon nanotubes in combination with Li2ZrCl6-LiCl interfacial modification can significantly reduce the interface impedance, improve the rate performance of the material at 10C, and increase the energy density. According to the comparison between examples 1-3 and comparative example 3, it can be concluded that the doping of zirconium-niobium can significantly reduce the interface impedance, improve the rate performance of the battery at 0.2C, 5C and 10C, improve the conductivity of the material, and increase the volume energy density.

[0062] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0063] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the invention or exceed the scope defined in the present application.

Claims

1. A method for preparing an interfacially modified high-rate lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: Step a1: mixing FeCl3·H2O, NH4H2PO4 and deionized water to obtain a first solution; mixing ZrOCl2·8H2O, C2H5NNbO4 and a hydrochloric acid solution to obtain a second solution; mixing the first solution, a cetyltrimethylammonium bromide solution and the second solution, adding a NaOH solution to maintain pH, centrifuging and drying to obtain zirconium-niobium co-doped FePO4; Step a2: mixing zirconium-niobium co-doped FePO4, Li2CO3 and sucrose, adding anhydrous ethanol for ball milling, and then sintering to obtain modified lithium iron phosphate; Step a3: vacuum drying LiCl, ZrCl4 and NbCl5 in a molar ratio of 10 / 13, then loading into a ball milling tank for ball milling, dissolving the remaining LiCl in anhydrous ethanol, then spraying and drying to obtain nano LiCl, and adding to the ball milling tank for ball milling to obtain niobium-doped Li2ZrCl6 composite modified Li2ZrCl6; Step a4: mixing the modified lithium iron phosphate and the modified Li2ZrCl6 and rolling through a hot roller to obtain Li2ZrCl6-LiCl coated lithium iron phosphate; Step a5: Li2ZrCl6-LiCl coated lithium iron phosphate, C6H 12 O6·H2O, carbon nanotubes are mixed, anhydrous ethanol is added for ball milling, dried, ground, sintered, and naturally cooled to obtain Li2ZrCl6-LiCl interfacial modified high-rate lithium iron phosphate positive electrode material.

2. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The use amount ratio of the FeCl3·H2O, NH4H2PO4, deionized water, ZrOCl2·8H2O, C2H5NNbO4, the hydrochloric acid solution and the cetyltrimethylammonium bromide solution in step a1 is 0.985 mol: 1 mol: 600 mL: 0.01 mol: 0.005 mol: 400 mL: 200 mL.

3. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The molar concentration of the hydrochloric acid solution in step a1 is 0.5 mol / L; the molar concentration of the cetyltrimethylammonium bromide solution is 0.1 mol / L; and the molar concentration of the NaOH solution is 4 mol / L.

4. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The use amount ratio of the zirconium-niobium co-doped FePO4, Li2CO3, sucrose and anhydrous ethanol in step a2 is 158.3 g: 1.03 mol: 0.1 mol: 200-300 mL.

5. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The use amount ratio of the LiCl, ZrCl4, NbCl5 and anhydrous ethanol in step a3 is 2.34 mol: 0.8 mol: 0.2 mol: 540 mL.

6. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, The use amount ratio of the modified lithium iron phosphate and the modified Li2ZrCl6 in step a4 is 90 g: 10 g.

7. The method for preparing an interface-modified high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, Li2ZrCl6-LiCl coated lithium iron phosphate, C6H 12 O6-H2O, carbon nanotubes and anhydrous ethanol in a ratio of 175.9 g: 1.23 g: 5.28 g: 200-300 mL.

8. An interfacially modified high rate lithium iron phosphate cathode material, characterized in that, The interface-modified high-rate lithium iron phosphate positive electrode material is prepared according to the preparation method of the interface-modified high-rate lithium iron phosphate positive electrode material in any one of claims 1-7.

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