Modified LiFePO4 positive electrode material and preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

The present invention provides a modified LiFePO4 positive electrode material, a preparation method thereof, a positive electrode sheet, and a lithium-ion battery. The preparation method comprises: step S1, mixing raw materials including FePO4 / C, a lithium source, a carbon source, and water, and then sequentially grinding, dehydrating, and pre-sintering to obtain a pre-sintered product; step S2, in an inert atmosphere, injecting raw materials including a transition metal ion source into the surface of the pre-sintered product by ion implantation to obtain an implanted product; and step S3, sintering the implanted product to obtain a modified LiFePO4 positive electrode material. The preparation method of the present application solves the problem of uneven coating of LiFePO4 positive electrode materials in the prior art. Therefore, the LiFePO4 positive electrode material prepared by the preparation method of the present application has excellent rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a modified LiFePO4 positive electrode material and a preparation method thereof, a positive electrode sheet and a lithium ion battery. Background Art

[0002] Lithium iron phosphate (LiFePO4) has become one of the most widely commercialized materials due to its abundant raw materials, low cost, excellent safety performance, non-toxicity, low pollution, and stable and high operating voltage platform. However, its structural characteristics lead to poor electronic conductivity and ion diffusion rate, as well as low compaction density, which restricts its application and often requires modification.

[0003] Currently, the main methods for modifying lithium iron phosphate (LFP) to address its poor electronic conductivity and ion diffusion rate include element doping, morphology and size control, and surface modification. Methods for improving compaction density primarily include optimizing raw material types, adjusting the sintering schedule, matching particle size, and adding sintering aids. While element doping, surface modification, and sintering aids offer significant improvements and are widely used, they often suffer from uneven doping and coating, resulting in poor LFP production consistency. Therefore, identifying technologies suitable for doping and surface modification of LiFePO4 cathode materials is imperative. Summary of the Invention

[0004] The main purpose of the present invention is to provide a modified LiFePO4 positive electrode material and a preparation method thereof, a positive electrode sheet and a lithium ion battery, so as to solve the problem of uneven coating of LiFePO4 positive electrode materials in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a modified LiFePO4 positive electrode material is provided, which comprises: step S1, mixing raw materials including FePO4 / C, a lithium source, a carbon source and water, and then grinding, dehydrating and pre-sintering them in sequence to obtain a pre-sintered product; step S2, in an inert atmosphere, injecting a raw material including a transition metal ion source into the surface of the pre-sintered product by ion implantation to obtain an implanted product; and step S3, sintering the implanted product to obtain a modified LiFePO4 positive electrode material.

[0006] Furthermore, in the above step S2, the ion injection amount of the transition metal ion source is 1×10 18 ~8×10 18 ions / cm 2; and / or, the transition metal ion source is a titanium ion source, preferably the titanium ion source is selected from any one or more of titanium dioxide, titanium tetrachloride and barium metatitanate; and / or, the raw material further includes a boron ion source, and the ion injection amount of the boron ion source is 1×10 15 ~8×10 15 ions / cm 2 , preferably, the boron ion source is selected from any one or more of boric acid, diborane, triborane and tetraborane; and / or, the ion implantation temperature is 400-450°C; and / or, the ion implantation pressure is 10-30 Pa; and / or, the ion implantation voltage is 300-500 V; and / or, the ion implantation time is 30-60 min.

[0007] Furthermore, in the above step S3, the sintering temperature is 730-790° C.; and / or the sintering time is 8-12 hours.

[0008] Furthermore, in the above-mentioned step S1, the temperature of the pre-sintering treatment is 400-550°C; and / or the time of the pre-sintering treatment is 8-12h; and / or the molar ratio of the lithium element in the lithium source to the iron element in FePO4 / C is 1-1.2:1; and / or the lithium source is selected from any one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide, lithium nitrate, lithium oxalate and lithium acetate; and / or the carbon source is selected from any one or more of glucose, sucrose, starch, cyclodextrin, citric acid, polyethylene glycol, polyvinyl alcohol, polypropylene glycol, polyethylene oxide, polystyrene, styrene-butadiene-styrene block copolymer and carbon nanotubes; and / or the mass content of C in FePO4 / C is 0.8-1.2%; and / or the D50 of the mixture obtained after grinding treatment is 0.35-0.65μm.

[0009] Furthermore, in the above step S1, the preparation method of FePO4 / C includes: step S11, mixing raw materials including iron-carbon micro-electrolysis filler, acidic solution and impurity remover, and then performing impurity removal treatment, solid-liquid separation and drying treatment in sequence to obtain a Fe / C mixture; step S12, mixing raw materials including the Fe / C mixture and phosphoric acid solution, and then performing hydrothermal reaction, solid-liquid separation, drying treatment and calcination treatment in sequence to obtain FePO4 / C; wherein the mass ratio of iron-carbon micro-electrolysis filler, acidic solution and impurity remover is 1-3:100:1-5; and / or the pH value of the acidic solution is 2-4; and / or the acidic solution is selected from sulfuric acid, hydrochloric acid, Any one or more of nitric acid, formic acid and acetic acid; and / or, the impurity remover is selected from any one or more of biochar, montmorillonite, hydrotalcite, fungi and bacteria; and / or, the molar ratio of iron in the Fe / C mixture to phosphorus in the phosphoric acid solution is 1:4; and / or, the mass concentration of the phosphoric acid solution is 20-50%; and / or, the hydrothermal reaction is carried out in an oxygen-containing atmosphere; and / or, the temperature of the hydrothermal reaction is 60-90°C; and / or, the time of the hydrothermal reaction is 3-8 hours; and / or, the pressure of the hydrothermal reaction is 1-5 atm; and / or, the temperature of the calcination treatment is 400-700°C; and / or, the time of the calcination treatment is 2-6 hours.

[0010] According to another aspect of the present invention, a modified LiFePO4 positive electrode material prepared by the aforementioned preparation method is provided, wherein the modified LiFePO4 positive electrode material includes FePO4, a carbon element and a transition metal oxide layer, wherein the carbon element is distributed in the pores formed between different FePO4 particles, and the transition metal oxide layer is coated on the surface of the FePO4.

[0011] Furthermore, the above transition metal oxide is titanium dioxide; and / or the mass content of carbon in the modified LiFePO4 positive electrode material is 0.8-2.0%.

[0012] Furthermore, the compaction density of the modified LiFePO4 positive electrode material is 2.5 to 2.65 g / cm 3 and / or, the specific surface area of ​​the modified LiFePO4 cathode material is 11 to 14 m 2 / g; and / or, the D50 of the modified LiFePO4 positive electrode material is 1.5 to 3.0 μm.

[0013] According to another aspect of the present invention, a positive electrode sheet is provided, which contains the aforementioned modified LiFePO4 positive electrode material.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, an electrolyte, a separator and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0015] Applying the technical solution of the present application, the purpose of the grinding treatment in step S1 is to control the particle size of FePO4 / C, lithium source and carbon source within a certain range, which helps to promote sufficient mixing between FePO4 / C, lithium source and carbon source. The purpose of the pre-sintering treatment is to improve the interaction between FePO4 / C, lithium source and carbon source. In step S2, the pre-sintered product is treated with an ion implantation method by a transition metal element, which helps to make the surface of the pre-sintered product evenly distributed with transition metal elements. In step S3, the injected product is sintered to form a uniformly distributed transition metal oxide coating on the surface of the lithium iron phosphate. The coating formed is conducive to improving the embedding and extraction of lithium ions in the modified LiFePO4 positive electrode material, and is also conducive to isolating the electrolyte from the lithium iron phosphate, alleviating the side reaction of the electrolyte and the lithium iron phosphate, and thus helping to improve the cycle stability and rate performance of the modified LiFePO4 positive electrode material. DETAILED DESCRIPTION

[0016] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0017] As analyzed in the background technology of this application, the prior art has the problem of uneven coating of LiFePO4 positive electrode materials. In order to solve this problem, this application provides a modified LiFePO4 positive electrode material and a preparation method thereof, a positive electrode sheet and a lithium-ion battery.

[0018] It should be noted that the so-called ion implantation amount in this application refers to the number of ions contained on the surface of the pre-sintered product per square centimeter.

[0019] In a typical embodiment of the present application, a method for preparing a modified LiFePO4 positive electrode material is provided, which comprises: step S1, mixing raw materials including FePO4 / C, a lithium source, a carbon source and water, and then grinding, dehydrating and pre-sintering in sequence to obtain a pre-sintered product; step S2, in an inert atmosphere, injecting a raw material including a transition metal ion source into the surface of the pre-sintered product by ion implantation to obtain an implanted product; and step S3, sintering the implanted product to obtain a modified LiFePO4 positive electrode material.

[0020] The purpose of the grinding process in step S1 is to control the particle size of FePO4 / C, lithium source and carbon source within a certain range, which helps to promote the sufficient mixing between FePO4 / C, lithium source and carbon source. The purpose of the pre-sintering process is to improve the interaction between FePO4 / C, lithium source and carbon source. In step S2, the pre-sintered product is treated with an ion implantation method by a transition metal element, which helps to make the surface of the pre-sintered product evenly distributed with transition metal elements. In step S3, the injected product is sintered to form a uniformly distributed transition metal oxide coating on the surface of the lithium iron phosphate. The coating formed is conducive to improving the embedding and de-embedding of lithium ions in the modified LiFePO4 positive electrode material, and is also conducive to isolating the electrolyte from the lithium iron phosphate, alleviating the side reaction of the electrolyte and the lithium iron phosphate, and thus helping to improve the cycle stability and rate performance of the modified LiFePO4 positive electrode material.

[0021] Furthermore, the inert atmosphere is preferably controlled to argon, which helps improve the efficiency of ion implantation. The dehydration treatment is preferably spray drying, which helps remove moisture without destroying the structure of the ground mixture. The sintered product is preferably pulverized to help control the particle size of the modified LiFePO4 positive electrode material.

[0022] In one embodiment of the present application, in the above step S2, the ion injection amount of the transition metal ion source is 1×10 18 ~8×10 18 ions / cm 2 ; and / or, the transition metal ion source is a titanium ion source, preferably the titanium ion source is selected from any one or more of titanium dioxide, titanium tetrachloride and barium metatitanate; and / or the raw material further includes a boron ion source, the ion injection amount of the boron ion source is 1×10 15 ~8×10 15 ions / cm 2 , preferably, the boron ion source is selected from any one or more of boric acid, diborane, triborane and tetraborane; and / or, the ion implantation temperature is 400-450°C; and / or, the ion implantation pressure is 10-30 Pa; and / or, the ion implantation voltage is 300-500 V; and / or, the ion implantation time is 30-60 min.

[0023] The ion injection amount of the transition metal ion source is preferably controlled within the above range, which helps to control the mass ratio of the transition metal oxide finally formed to FePO4 / C, thereby helping to improve the embedding and extraction of lithium ions in the modified LiFePO4 positive electrode material, and is also beneficial for isolating the electrolyte from lithium iron phosphate, alleviating the side reaction between the electrolyte and lithium iron phosphate, and thus helping to improve the cycle stability and rate performance of the modified LiFePO4 positive electrode material. The type of transition metal ion source is preferably controlled within the above range, which helps to improve the efficiency of ion injection. Adding a boron ion source during the ion injection process can play a good sintering-aiding role when the subsequent material is sintered, so that the modified LiFePO4 positive electrode material can be obtained by calcining at a lower temperature. Boron oxide still remains in the obtained modified LiFePO4 positive electrode material, but a very small amount of boron oxide does not affect the cycle stability and rate performance of the modified LiFePO4 positive electrode material. The ion injection amount of the boron ion source is preferably controlled within the above range, which helps to further reduce the sintering temperature, thereby helping to reduce the production cost of the modified LiFePO4 positive electrode material. The type of boron ion source is preferably controlled within the above range, which helps to further reduce the production cost of the modified LiFePO4 positive electrode material. The temperature, pressure, voltage and time of ion implantation are preferably controlled within the above range, which helps to improve the uniformity of ion dispersion on the surface of the positive electrode material.

[0024] In one embodiment of the present application, in the above step S3, the sintering temperature is 730-790° C.; and / or the sintering time is 8-12 hours.

[0025] It is preferred to control the temperature and time of the sintering treatment within the above ranges, thereby improving the efficiency and effect of the sintering treatment, thereby helping to further promote the formation of the modified LiFePO4 positive electrode material, and ultimately obtaining a positive electrode material with a high compaction density.

[0026] In one embodiment of the present application, in the above-mentioned step S1, the temperature of the pre-sintering treatment is 400-550°C; and / or, the time of the pre-sintering treatment is 8-12 hours; and / or, the molar ratio of the lithium element in the lithium source to the iron element in FePO4 / C is 1-1.2:1; and / or, the lithium source is selected from any one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide, lithium nitrate, lithium oxalate and lithium acetate; and / or, the carbon source is selected from any one or more of glucose, sucrose, starch, cyclodextrin, citric acid, polyethylene glycol, polyvinyl alcohol, polypropylene glycol, polyethylene oxide, polystyrene, styrene-butadiene-styrene block copolymer and carbon nanotubes; and / or, the mass content of C in FePO4 / C is 0.8-1.2%; and / or, the D50 of the mixture obtained after grinding treatment is 0.35-0.65 μm.

[0027] The temperature and time of the pre-sintering treatment are preferably controlled within the above ranges to help enhance the interaction between the FePO4 / C, lithium source, and carbon source, thereby improving the structural stability of the mixture. The molar ratio of the lithium element in the lithium source, the carbon element in the carbon source, and the iron element in the FePO4 / C is preferably controlled within the above ranges to further enhance the rate performance of the modified LiFePO4 positive electrode material. The types of lithium source and carbon source are preferably controlled within the above ranges to enrich the selectivity of the material types.

[0028] In one embodiment of the present application, in the above step S1, the preparation method of FePO4 / C includes: step S11, mixing raw materials including iron-carbon micro-electrolysis filler, acidic solution and impurity remover, and then performing impurity removal treatment, solid-liquid separation and drying treatment in sequence to obtain a Fe / C mixture; step S12, mixing raw materials including the Fe / C mixture and phosphoric acid solution, and then performing hydrothermal reaction, solid-liquid separation, drying treatment and calcination treatment in sequence to obtain FePO4 / C; wherein the mass ratio of iron-carbon micro-electrolysis filler, acidic solution and impurity remover is 1-3:100:1-5; and / or the pH value of the acidic solution is 2-4; and / or the acidic solution is selected from sulfuric acid , any one or more of hydrochloric acid, nitric acid, formic acid and acetic acid; and / or, the impurity remover is selected from any one or more of biochar, montmorillonite, hydrotalcite, fungi and bacteria; and / or, the molar ratio of iron element in the Fe / C mixture to phosphorus element in the phosphoric acid solution is 1:4; and / or, the mass concentration of the phosphoric acid solution is 20-50%; and / or, the hydrothermal reaction is carried out in an oxygen-containing atmosphere; and / or, the temperature of the hydrothermal reaction is 60-90°C; and / or, the time of the hydrothermal reaction is 3-8h; and / or, the pressure of the hydrothermal reaction is 1-5atm; and / or, the temperature of the calcination treatment is 400-700°C; and / or, the time of the calcination treatment is 2-6h.

[0029] The use of iron-carbon micro-electrolysis filler as an iron source not only reduces production costs but also realizes the resource utilization of environmental pollutants. The iron-carbon micro-electrolysis filler serves as both an iron source and a carbon source, so that the prepared modified LiFePO4 positive electrode material has a higher specific surface area and a smaller size, which helps to reduce the charge transfer resistance, thereby improving the lithium ion diffusion performance, and making the modified LiFePO4 positive electrode material have better rate performance. In step S11, other impurities in the iron-carbon micro-electrolysis filler are removed by impurity removal treatment, and in step S12, Fe / C is reacted with phosphoric acid to obtain FePO4 / C through hydrothermal reaction, solid-liquid separation, drying treatment and calcination treatment. It is preferred to control the mass ratio of the iron-carbon micro-electrolysis filler, the acidic solution and the impurity remover within the above range, which helps to make the iron-carbon micro-electrolysis filler more fully impurity-removed, and it is preferred to control the pH value of the acidic solution within the above range, which helps to improve the efficiency of impurity removal. It is preferred to control the types of the acidic solution and the impurity remover within the above range, which helps to enrich the selectivity of the material. The molar ratio of the iron element in the Fe / C mixture to the phosphorus element in the phosphoric acid solution is preferably controlled within the above-mentioned values ​​to facilitate the formation of FePO4 / C. The concentration of the phosphoric acid solution is preferably controlled within the above-mentioned range to facilitate sufficient contact between the phosphate ions and the Fe / C. The temperature, time, and pressure of the hydrothermal reaction are preferably controlled within the above-mentioned ranges to facilitate enhanced interaction between the phosphate ions and the Fe / C. The temperature and time of the calcination treatment are preferably controlled within the above-mentioned ranges to facilitate the formation of FePO4 / C.

[0030] In another typical embodiment of the present application, a modified LiFePO4 positive electrode material prepared by the aforementioned preparation method is provided, wherein the modified LiFePO4 positive electrode material includes FePO4, a carbon element and a transition metal oxide layer, wherein the carbon element is distributed in the pores formed between different FePO4 particles, and the transition metal oxide layer is coated on the surface of the FePO4.

[0031] Because the modified LiFePO4 cathode material is prepared using the above-mentioned preparation method, a uniformly distributed transition metal oxide coating is formed on the surface of the lithium iron phosphate of the modified LiFePO4 cathode material. The formed coating is conducive to improving the embedding and extraction of lithium ions in the modified LiFePO4 cathode material, and is also conducive to isolating the electrolyte from the lithium iron phosphate, alleviating the side reaction between the electrolyte and the lithium iron phosphate, thereby helping to improve the cycle stability and rate performance of the modified LiFePO4 cathode material. The presence of carbon helps to improve the conductivity of the modified LiFePO4 cathode material, thereby further improving the rate performance of the modified LiFePO4 cathode material.

[0032] In one embodiment of the present application, the transition metal oxide is titanium dioxide; and / or the mass content of carbon in the modified LiFePO4 positive electrode material is 0.8-2.0%.

[0033] Preferably, controlling the type of transition metal oxide within the above range helps to further improve the efficiency of lithium ion insertion and extraction in the modified LiFePO4 positive electrode material, and alleviates the side reaction between the electrolyte and lithium iron phosphate, thereby helping to further improve the cycle stability and rate performance of the modified LiFePO4 positive electrode material. Preferably, controlling the carbon content in the modified LiFePO4 positive electrode material within the above range helps to further improve the conductivity of the modified LiFePO4 positive electrode material, thereby further improving the rate performance of the modified LiFePO4 positive electrode material.

[0034] In order to further improve the cycle stability and rate performance of the modified LiFePO4 cathode material, in one embodiment of the present application, the compaction density of the modified LiFePO4 cathode material is preferably 2.5 to 2.65 g / cm 3 and / or, the specific surface area of ​​the modified LiFePO4 cathode material is 11 to 14 m 2 / g; and / or, the D50 of the modified LiFePO4 positive electrode material is 1.5 to 3.0 μm.

[0035] In another typical embodiment of the present application, a positive electrode sheet is provided, which contains the aforementioned modified LiFePO4 positive electrode material.

[0036] Since the above-mentioned positive electrode sheet contains the modified LiFePO4 positive electrode material prepared by the preparation method of the present application, the positive electrode sheet has excellent cycle stability and rate performance.

[0037] In another typical embodiment of the present application, a lithium-ion battery is provided, comprising a positive electrode sheet, an electrolyte, a separator and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0038] Since the above-mentioned lithium-ion battery includes a positive electrode sheet containing the modified LiFePO4 positive electrode material prepared by the preparation method of the present application, the lithium-ion battery has excellent cycle stability and rate performance.

[0039] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0040] Example 1

[0041] S1: adding an excess of a dilute hydrochloric acid solution with a pH of 2 to the iron-carbon micro-electrolysis filler, stirring for 2 h, adding 2% (based on the mass of the solution) of biochar and continuing to stir, filtering and drying to obtain an Fe / C mixture, wherein the mass ratio of the iron-carbon micro-electrolysis filler to the dilute hydrochloric acid solution is 2:100;

[0042] S2: adding a 20% H3PO4 solution to the Fe / C mixture at a molar ratio of Fe:phosphoric acid of 1:4, and adding the mixed solution to a reactor for a hydrothermal reaction at a temperature of 60°C, introducing oxygen into the reactor, and maintaining a pressure of 2.5 atm. After reacting for 3 hours, the reaction product is washed and dried, and calcined at 400°C for 2 hours to obtain FePO4 / C, wherein the mass content of carbon in the FePO4 / C is 1.2%;

[0043] S3: FePO4 / C is uniformly mixed with lithium carbonate and glucose in water, and the molar ratio of Li:FePO4 is controlled to be 1:1, and the carbon content (calculated as the carbon in glucose) is 1.6% (the carbon content is 1.6% of the final lithium iron phosphate product). After uniform mixing, it is sand-milled to obtain a slurry with a D50 of 0.65μm, and the yellow material is obtained by spray drying.

[0044] S4: The yellow material was placed in a tube furnace and pre-sintered at 400 °C for 8 h to obtain a pre-sintered product. The pre-sintered product was then placed in an ion implantation furnace and titanium dioxide and boric acid were used as ion sources for particle implantation. The ion implantation amount of the titanium ion source was 8×10 18 ions / cm 2 The ion implantation volume of the boron ion source is 8×10 15 ions / cm 2 , the temperature was 400 ° C, the pressure environment was 10 Pa, the voltage was set to 300 V, the holding time was 30 minutes, and finally it was placed in a tube furnace and sintered at 730 ° C for 8 hours to obtain a sintered product;

[0045] S5: The sintered product is crushed to obtain a modified LiFePO4 positive electrode material, wherein the D50 of the modified LiFePO4 positive electrode material is 3 μm.

[0046] Example 2

[0047] S1: adding an excess amount of a dilute sulfuric acid solution with a pH of 2 to the iron-carbon micro-electrolysis filler, stirring for 2 hours, adding 2% (based on the mass of the solution) of montmorillonite and continuing to stir, filtering and drying to obtain an Fe / C mixture, wherein the mass ratio of the iron-carbon micro-electrolysis filler to the dilute sulfuric acid solution is 3:100;

[0048] S2: adding a 30% H3PO4 solution to the Fe / C mixture at a molar ratio of Fe:phosphoric acid of 1:4, and adding the mixed solution to a reactor for hydrothermal reaction at a temperature of 70°C, introducing oxygen into the reactor, and maintaining a pressure of 4 atm. After reacting for 4 hours, the reaction product is washed and dried, and calcined at 500°C for 2 hours to obtain FePO4 / C, wherein the mass content of carbon in the FePO4 / C is 1%;

[0049] S3: FePO4 / C is uniformly mixed with lithium carbonate and glucose in water, and the molar ratio of Li:FePO4 is controlled to be 1.05:1, and the carbon content (calculated as the carbon in glucose) is 1.4% (the carbon content is 1.4% of the final lithium iron phosphate product). After uniform mixing, the slurry with a D50 of 0.55 μm is obtained by sand grinding, and the yellow material is obtained by spray drying.

[0050] S4: The yellow material was placed in a tube furnace and pre-sintered at 450 ° C for 10 h to obtain a pre-sintered product. The pre-sintered product was then placed in an ion implantation furnace of an ion implantation device. Titanium dioxide and diborane were used as ion sources for particle implantation. The ion implantation amount of the titanium ion source was 5×10 18 ions / cm 2 The ion implantation volume of the boron ion source is 5×10 15 ions / cm 2 , the temperature is 410℃, the pressure environment is 15Pa, the voltage is set to 350V, the holding time is 40min, and finally it is placed in a tube furnace and sintered at 750℃ for 10h to obtain a sintered product;

[0051] S5: The sintered product is crushed to obtain a modified LiFePO4 positive electrode material, wherein the D50 of the modified LiFePO4 positive electrode material is 2.5 μm.

[0052] Example 3

[0053] S1: adding an excess of a dilute nitric acid solution with a pH of 2 to the iron-carbon micro-electrolysis filler, stirring for 2 hours, adding 2% (based on the mass of the solution) of montmorillonite and continuing to stir, filtering and drying to obtain an Fe / C mixture, wherein the mass ratio of the iron-carbon micro-electrolysis filler to the dilute hydrochloric acid solution is 1:100;

[0054] S2: adding a 40% H3PO4 solution to the Fe / C mixture at a molar ratio of Fe:phosphoric acid of 1:4, and adding the mixed solution to a reactor for hydrothermal reaction at a temperature of 80°C, introducing oxygen into the reactor, and maintaining a pressure of 2 atm. After reacting for 4 hours, the reaction product is washed and dried, and calcined at 500°C for 2 hours to obtain FePO4 / C, wherein the mass content of carbon in the FePO4 / C is 0.8%;

[0055] S3: FePO4 / C is uniformly mixed with lithium carbonate and glucose in water, and the molar ratio of Li:FePO4 is controlled to be 1.05:1, and the carbon content (calculated as the carbon in glucose) is 1.2% (the carbon content is 1.2% of the final lithium iron phosphate product). After uniform mixing, the slurry with a D50 of 0.45 μm is obtained by sand grinding, and the yellow material is obtained by spray drying.

[0056] S4: The yellow material was placed in a tube furnace and pre-sintered at 500°C for 12 hours to obtain a pre-sintered product. The pre-sintered product was then placed in an ion implantation furnace and titanium dioxide and boric acid were used as ion sources for particle implantation. The ion implantation amount of the titanium ion source was 3×10 18 ions / cm 2 The ion injection volume of the boron ion source is 3×10 15 ions / cm 2 , the temperature is 420℃, the pressure environment is 20Pa, the voltage is set to 400V, the holding time is 50min, and finally it is placed in a tube furnace and sintered at 770℃ for 12h to obtain a sintered product;

[0057] S5: The sintered product is crushed to obtain a modified LiFePO4 positive electrode material, wherein the D50 of the modified LiFePO4 positive electrode material is 2 μm.

[0058] Example 4

[0059] S1: adding an excess of a dilute nitric acid solution with a pH of 2 to the iron-carbon micro-electrolysis filler, stirring for 2 hours, adding 2% (based on the mass of the solution) of montmorillonite and continuing to stir, filtering and drying to obtain an Fe / C mixture, wherein the mass ratio of the iron-carbon micro-electrolysis filler to the dilute hydrochloric acid solution is 2:100;

[0060] S2: adding a 40% H3PO4 solution to the Fe / C mixture at a molar ratio of Fe:phosphoric acid of 1:4, and adding the mixed solution to a reactor for hydrothermal reaction at a temperature of 80°C. Oxygen is introduced into the reactor at a pressure of 1 atm. After reacting for 4 hours, the reaction product is washed and dried, and calcined at 500°C for 2 hours to obtain FePO4 / C, wherein the mass content of carbon in the FePO4 / C is 0.8%;

[0061] S3: FePO4 / C is uniformly mixed with lithium carbonate and glucose in water, and the molar ratio of Li:FePO4 is controlled to be 1.1:1, and the carbon content (calculated as the carbon in glucose) is 1.0% (the carbon content is 1.0% of the final lithium iron phosphate product). After uniform mixing, the slurry with a D50 of 0.40 μm is obtained by sand grinding, and the yellow material is obtained by spray drying.

[0062] S4: The yellow material was placed in a tube furnace and pre-sintered at 500 °C for 12 h to obtain a pre-sintered product. The pre-sintered product was then placed in an ion implantation furnace and titanium dioxide and diborane were used as ion sources for particle implantation. The ion implantation amount of the titanium ion source was 3×10 18 ions / cm 2 The ion injection volume of the boron ion source is 3×10 15 ions / cm 2 , the temperature is 430℃, the pressure environment is 25Pa, the voltage is set to 450V, the holding time is 50min, and finally it is placed in a tube furnace and sintered at 780℃ for 12h to obtain a sintered product;

[0063] S5: The sintered product is crushed to obtain a modified LiFePO4 positive electrode material, wherein the D50 of the modified LiFePO4 positive electrode material is 1.8 μm.

[0064] Example 5

[0065] S1: adding an excess of a dilute hydrochloric acid solution with a pH of 2 to the iron-carbon micro-electrolysis filler, stirring for 2 h, adding 2% (based on the mass of the solution) of biochar and continuing to stir, filtering and drying to obtain an Fe / C mixture, wherein the mass ratio of the iron-carbon micro-electrolysis filler to the dilute hydrochloric acid solution is 2:100;

[0066] S2: adding a 50% H3PO4 solution to the Fe / C mixture at a molar ratio of Fe:phosphoric acid of 1:4, and adding the mixed solution to a reactor for a hydrothermal reaction at a temperature of 90°C, introducing oxygen into the reactor, and maintaining a pressure of 5 atm. After reacting for 4 hours, the reaction product is washed and dried, and calcined at 500°C for 2 hours to obtain FePO4 / C, wherein the mass content of carbon in the FePO4 / C is 0.8%;

[0067] S3: FePO4 / C is uniformly mixed with lithium carbonate and glucose in water, and the molar ratio of Li:FePO4 is controlled to be 1.1:1, and the carbon content (calculated as the carbon in glucose) is 0.8% (the carbon content is 0.8% of the final lithium iron phosphate product). After uniform mixing, the slurry with a D50 of 0.35μm is obtained by sand grinding, and the yellow material is obtained by spray drying.

[0068] S4: The yellow material was placed in a tube furnace and pre-sintered at 500 °C for 12 h to obtain a pre-sintered product. The pre-sintered product was then placed in an ion implantation furnace and titanium dioxide and diborane were used as ion sources for particle implantation. The ion implantation amount of the titanium ion source was 3×10 18 ions / cm 2 The ion injection volume of the boron ion source is 3×10 15 ions / cm 2 , the temperature is 450 ° C, the pressure environment is 30 Pa, the voltage is set to 500 V, the holding time is 60 minutes, and finally it is placed in a tube furnace and sintered at 790 ° C for 12 hours to obtain a sintered product;

[0069] S5: The sintered product is crushed to obtain a modified LiFePO4 positive electrode material, wherein the D50 of the modified LiFePO4 positive electrode material is 1.5 μm.

[0070] Example 6

[0071] The difference from Example 3 is that the ion injection amount of the titanium ion source is 1×10 18 ions / cm 2 The ion implantation volume of the boron ion source is 1×10 15 ions / cm 2 , and finally the modified LiFePO4 positive electrode material was obtained.

[0072] Example 7

[0073] The difference from Example 3 is that the ion injection amount of the titanium ion source is 8×10 18 ions / cm 2 The ion implantation volume of the boron ion source is 8×10 15ions / cm 2 , and finally the modified LiFePO4 positive electrode material was obtained.

[0074] Example 8

[0075] The difference from Example 3 is that the ion injection amount of the titanium ion source is 5×10 17 ions / cm 2 The ion implantation volume of the boron ion source is 5×10 14 ions / cm 2 , and finally the modified LiFePO4 positive electrode material was obtained.

[0076] Example 9

[0077] The difference from Example 3 is that the ion injection temperature is 450° C., the ion injection pressure is 30 Pa, the ion injection voltage is 500, and the ion injection time is 60 min, and finally a modified LiFePO4 positive electrode material is obtained.

[0078] Example 10

[0079] The difference from Example 3 is that the ion injection temperature is 400° C., the ion injection pressure is 10 Pa, the ion injection voltage is 300 V, and the ion injection time is 30 min, and finally a modified LiFePO4 positive electrode material is obtained.

[0080] Example 11

[0081] The difference from Example 3 is that the ion injection temperature is 500° C., the ion injection pressure is 40 Pa, the ion injection voltage is 200 V, and the ion injection time is 20 min, and finally a modified LiFePO4 positive electrode material is obtained.

[0082] Example 12

[0083] The difference from Example 3 is that the sintering temperature is 730° C., the sintering time is 12 h, and a modified LiFePO 4 positive electrode material is finally obtained.

[0084] Example 13

[0085] The difference from Example 3 is that the sintering temperature is 790° C. and the sintering time is 8 h, and finally a modified LiFePO 4 positive electrode material is obtained.

[0086] Example 14

[0087] The difference from Example 3 is that the sintering temperature is 800° C.; and / or the sintering time is 14 h, and finally a modified LiFePO 4 positive electrode material is obtained.

[0088] Example 15

[0089] The difference from Example 3 is that the pre-sintering temperature is 550° C., the pre-sintering time is 8 h, and finally a modified LiFePO 4 positive electrode material is obtained.

[0090] Example 16

[0091] The difference from Example 3 is that the pre-sintering temperature is 400° C., the pre-sintering time is 12 h, and a modified LiFePO 4 positive electrode material is finally obtained.

[0092] Example 17

[0093] The difference from Example 3 is that the pre-sintering temperature is 600° C., the pre-sintering time is 14 h, and a modified LiFePO 4 positive electrode material is finally obtained.

[0094] Example 18

[0095] The difference from Example 3 is that the temperature of the hydrothermal reaction is 90° C., the time of the hydrothermal reaction is 8 h, the pressure of the hydrothermal reaction is 1 atm, and finally a modified LiFePO 4 positive electrode material is obtained.

[0096] Example 19

[0097] The difference from Example 3 is that the temperature of the hydrothermal reaction is 60° C., the time of the hydrothermal reaction is 3 h, the pressure of the hydrothermal reaction is 5 atm, and finally a modified LiFePO 4 positive electrode material is obtained.

[0098] Example 20

[0099] The difference from Example 3 is that the temperature of the hydrothermal reaction is 100° C., the time of the hydrothermal reaction is 2 h, the pressure of the hydrothermal reaction is 0.5 atm, and finally a modified LiFePO 4 positive electrode material is obtained.

[0100] Comparative Example 1

[0101] The difference from Example 3 is that in step S4, the pre-sintered product is mixed with titanium dioxide and boric acid by ball milling and then sintered to finally obtain a modified LiFePO4 positive electrode material.

[0102] Performance Testing

[0103] The modified LiFePO4 positive electrode materials prepared in the above examples and comparative examples were measured for specific surface area and powder compaction density. The modified LiFePO4 positive electrode materials prepared in the above examples and comparative examples were used as positive electrode materials in batteries. Lithium iron phosphate positive electrode sheets were prepared using a mass ratio of modified LiFePO4 positive electrode material: conductive agent SP: polyvinylidene fluoride = 8:1:1. These sheets were assembled into CR2016 button-type batteries and their rate performance was tested at a test temperature of 25°C and test rates of 0.2C and 1C, respectively. The specific surface area and powder compaction density of the modified LiFePO4 positive electrode materials, as well as the 0.2C gram capacity and 1C gram capacity of the batteries are shown in Table 1.

[0104] Table 1

[0105]

[0106] From the data in Table 1, it can be seen that the modified LiFePO4 positive electrode material prepared by the preparation method of the present application has relatively excellent rate performance.

[0107] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0108] The purpose of the grinding process in step S1 is to control the particle size of FePO4 / C, lithium source and carbon source within a certain range, which helps to promote the sufficient mixing between FePO4 / C, lithium source and carbon source. The purpose of the pre-sintering process is to improve the interaction between FePO4 / C, lithium source and carbon source. In step S2, the pre-sintered product is treated with an ion implantation method by a transition metal element, which helps to make the surface of the pre-sintered product evenly distributed with transition metal elements. In step S3, the injected product is sintered to form a uniformly distributed transition metal oxide coating on the surface of the lithium iron phosphate. The coating formed is conducive to improving the embedding and de-embedding of lithium ions in the modified LiFePO4 positive electrode material, and is also conducive to isolating the electrolyte from the lithium iron phosphate, alleviating the side reaction of the electrolyte and the lithium iron phosphate, and thus helping to improve the cycle stability and rate performance of the modified LiFePO4 positive electrode material.

[0109] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a modified LiFePO4 positive electrode material, characterized in that: The preparation method comprises: Step S1, mixing raw materials including FePO4 / C, a lithium source, a carbon source and water, and then sequentially grinding, dehydrating and pre-sintering to obtain a pre-sintered product; Step S2, in an inert atmosphere, injecting a raw material including a transition metal ion source into the surface of the pre-sintered product by ion implantation to obtain an implanted product; and Step S3, sintering the infiltration product to obtain the modified LiFePO4 positive electrode material, wherein the modified LiFePO4 positive electrode material includes a titanium dioxide layer; The transition metal ion source is a titanium ion source; The raw materials also include a source of boron ions.

2. The preparation method according to claim 1, characterized in that In step S2, the ion injection amount of the transition metal ion source is 1×10 18 ~8×10 18 ions / cm 2 ; and / or, the titanium ion source is selected from any one or more of titanium dioxide, titanium tetrachloride and barium metatitanate; and / or, the ion implantation amount of the boron ion source is 1×10 15 ~8×10 15 ions / cm 2 , and / or, the boron ion source is selected from any one or more of boric acid, diborane, triborane and tetraborane; and / or, the temperature of the ion implantation is 400~450°C; and / or, the pressure of the ion implantation is 10~30Pa; and / or, the voltage of the ion implantation is 300~500V; and / or, the time of the ion implantation is 30~60min.

3. The preparation method according to claim 1 or 2, characterized in that In step S3, the sintering temperature is 730-790° C.; and / or the sintering time is 8-12 hours.

4. The preparation method according to claim 1 or 2, characterized in that In step S1, the pre-sintering temperature is 400-550° C.; and / or the pre-sintering time is 8-12 hours; and / or the molar ratio of lithium in the lithium source to iron in the FePO4 / C is 1-1.2:1; And / or, the lithium source is selected from any one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide, lithium nitrate, lithium oxalate and lithium acetate; and / or, the carbon source is selected from any one or more of glucose, sucrose, starch, cyclodextrin, citric acid, polyethylene glycol, polyvinyl alcohol, polyglycerol, polyethylene oxide, polystyrene, styrene-butadiene-styrene block copolymer and carbon nanotubes; And / or, the mass content of C in the FePO4 / C is 0.8-1.2%; And / or, the D50 of the mixture obtained after the grinding treatment is 0.35-0.65 μm.

5. The preparation method according to claim 1 or 2, characterized in that In step S1, the preparation method of FePO4 / C includes: Step S11, mixing raw materials including iron-carbon micro-electrolysis filler, acidic solution and impurity remover, and then sequentially performing impurity removal treatment, solid-liquid separation and drying treatment to obtain an Fe / C mixture; Step S12, mixing the raw materials including the Fe / C mixture and the phosphoric acid solution, and then sequentially performing hydrothermal reaction, solid-liquid separation, drying treatment and calcination treatment to obtain the FePO4 / C; wherein, The mass ratio of the iron-carbon micro-electrolysis filler, the acidic solution and the impurity remover is 1-3:100:1-5.

6. The preparation method according to claim 5, characterized in that The pH value of the acidic solution is 2-4; and / or the acidic solution is selected from any one or more of sulfuric acid, hydrochloric acid, nitric acid, formic acid and acetic acid; And / or, the impurity remover is selected from any one or more of biochar, montmorillonite, hydrotalcite, fungi and bacteria; and / or, the molar ratio of the iron element in the Fe / C mixture to the phosphorus element in the phosphoric acid solution is 1:4; And / or, the mass concentration of the phosphoric acid solution is 20-50%; and / or, the hydrothermal reaction is carried out in an oxygen-containing atmosphere; and / or, the temperature of the hydrothermal reaction is 60-90° C.; and / or, the time of the hydrothermal reaction is 3-8 hours; and / or, the pressure of the hydrothermal reaction is 1-5 atm; And / or, the calcination temperature is 400-700° C.; and / or, the calcination time is 2-6 hours.

7. A modified LiFePO4 positive electrode material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The modified LiFePO4 positive electrode material includes FePO4, carbon and a titanium dioxide layer, wherein the carbon is distributed in the pores formed between different FePO4 particles, and the titanium dioxide layer is coated on the surface of the FePO4.

8. The modified LiFePO4 cathode material according to claim 7, characterized in that The mass content of the carbon element in the modified LiFePO4 positive electrode material is 0.8-2.0%.

9. The modified LiFePO4 cathode material according to claim 7 or 8, characterized in that The compaction density of the modified LiFePO4 positive electrode material is 2.5-2.65 g / cm 3 and / or, the specific surface area of ​​the modified LiFePO4 cathode material is 11~14m 2 / g; and / or, the D50 of the modified LiFePO4 positive electrode material is 1.5~3.0 μm.

10. A positive electrode sheet, characterized in that: The positive electrode sheet contains the modified LiFePO4 positive electrode material according to any one of claims 7 to 9.

11. A lithium-ion battery comprising a positive electrode, an electrolyte, a separator and a negative electrode, characterized in that: The positive electrode sheet is the positive electrode sheet according to claim 10.

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