Nitrogen indium gallium doped lithium iron phosphate and its preparation method and application

Abstract

The present application belongs to the technical field of positive electrode active materials, and specifically relates to a nitrogen-indium-gallium doped lithium iron phosphate and its preparation method and application. The preparation method comprises the following steps: ball milling the ball milling solution in supercritical water and then calcining to obtain nitrogen-indium-gallium doped lithium iron phosphate; the ball milling solution contains a lithium source, an iron source, a phosphorus source, an indium source, a gallium source, phosphoric acid-grafted graphene oxide and lithium iron-grafted graphene oxide; in the calcining step, calcining is carried out in a nitrogen-hydrogen mixed gas atmosphere, and the calcining temperature is 680°C to 800°C. In the preparation method, calcining is carried out in a nitrogen-hydrogen mixed gas atmosphere, and the nitrogen element in the mixed gas can be doped into the lithium iron phosphate in the form of gas. The nitrogen-indium-gallium doped lithium iron phosphate obtained by calcining has excellent conductivity, cycle stability and rate performance.

Description

Technical Field

[0001] The present application belongs to the technical field of positive electrode active materials, and specifically relates to a nitrogen-indium-gallium doped lithium iron phosphate and a preparation method and application thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4), the cathode active material of lithium batteries, has the characteristics of high thermal stability and long cycle life, but low rate performance. For lithium iron phosphate, improving its rate performance is certainly the key direction of improvement, but as a cathode active material, its cycle stability is also particularly important for batteries.

[0003] The existing preparation methods of lithium iron phosphate mainly include solid phase method and liquid phase method. However, the synthesis reaction of lithium iron phosphate is a complex multiphase reaction involving phosphate, iron salt (or oxide), lithium salt, carbon precursor and reducing gas phase; therefore, the conductivity, cycle stability and rate performance of the prepared lithium iron phosphate are poor. Summary of the invention

[0004] The present application provides a nitrogen-indium-gallium doped lithium iron phosphate and a preparation method and application thereof, so as to solve at least one aspect of the above technical problems.

[0005] This application is implemented through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, comprising the following steps:

[0007] The ball milling liquid is ball milled in supercritical water and then calcined to obtain nitrogen-indium-gallium-doped lithium iron phosphate;

[0008] The ball milling solution contains a lithium source, an iron source, a phosphorus source, an indium source, a gallium source, phosphoric acid-grafted graphene oxide, and lithium-iron-grafted graphene oxide;

[0009] In the calcination step, the calcination is carried out in a nitrogen-hydrogen mixed gas atmosphere at a calcination temperature of 680°C to 800°C.

[0010] In some possible implementations, preparing phosphoric acid grafted graphene oxide comprises the following steps:

[0011] The first graphene oxide is mixed with phosphoric acid and subjected to a first microwave ultrasound treatment, and then washed and dried to obtain phosphoric acid-grafted graphene oxide.

[0012] In some possible implementations, the mass ratio of the first graphene oxide to phosphoric acid is (0.03-0.08):1.

[0013] In some possible implementations, preparing the lithium iron grafted graphene oxide comprises the following steps:

[0014] The first solution is subjected to a second microwave ultrasound treatment, filtered, washed and dried to obtain lithium-grafted graphene oxide; the first solution contains second graphene oxide and lithium chloride;

[0015] The second solution is subjected to a third microwave ultrasound, filtered, washed and dried to obtain lithium iron grafted graphene oxide; the second solution contains lithium grafted graphene oxide and ethylenediaminetetraacetic acid ferrous complex.

[0016] In some possible implementations, the step of preparing the second solution includes:

[0017] Under an argon atmosphere and a stirring condition of 100 rpm to 200 rpm, ethylenediaminetetraacetic acid is added to the ferrous chloride aqueous solution to obtain an ethylenediaminetetraacetic acid ferrous complex solution, wherein the pH value of the ferrous chloride aqueous solution is 3 to 5;

[0018] Under the stirring condition of a rotation speed of 80 rpm to 150 rpm, lithium-grafted graphene oxide is added to the ethylenediaminetetraacetic acid ferrous complex solution to obtain a second solution.

[0019] In some possible implementations, in the preparation of the lithium iron grafted graphene oxide, the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and the second graphene oxide is (2.9-5.8):(35-55):(2.5-5):1.

[0020] In some possible implementations, in the nitrogen-indium-gallium doped lithium iron phosphate, the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen is (0.95-1.05):(0.95-1.05):1:(0.1-0.3):(0.1-0.3):(0.1-0.3).

[0021] In some possible implementations, the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphorus source is (0.1-0.2):(0.7-0.9):1.

[0022] In some possible implementations, in the nitrogen-hydrogen mixed gas atmosphere, the volume ratio of nitrogen to hydrogen is (0.1-0.2):1.

[0023] In a second aspect, the present application provides nitrogen-indium-gallium-doped lithium iron phosphate prepared by the preparation method of nitrogen-indium-gallium-doped lithium iron phosphate of the present application.

[0024] In a third aspect, the present application provides an application of the nitrogen-indium-gallium-doped lithium iron phosphate provided in the present application in the field of lithium battery preparation.

[0025] The present application provides a nitrogen-indium-gallium-doped lithium iron phosphate and a preparation method thereof, which has at least the following beneficial technical effects compared with the prior art:

[0026] The preparation method of nitrogen-indium-gallium doped lithium iron phosphate of the present application comprises the following steps: ball milling a ball milling liquid containing a lithium source, an iron source, a phosphorus source, an indium source, a gallium source, phosphoric acid-grafted graphene oxide and lithium iron-grafted graphene oxide in supercritical water. The phosphoric acid-grafted graphene oxide and the lithium iron-grafted graphene oxide are not only used as raw materials for graphene, but also as "seeds" during ball milling to promote the directional reaction of the lithium source, the iron source and phosphoric acid to generate lithium iron phosphate, thereby improving the reaction rate and yield; supercritical water has excellent solubility and good mass transfer characteristics, which promotes the ball milling liquid to fully disperse and dissolve in supercritical water to form a precursor; the indium source and the gallium source provide indium and gallium doping elements of the lithium iron phosphate to improve the conductivity of the lithium iron phosphate; and the mixture is calcined in a nitrogen-hydrogen mixed gas atmosphere, and the nitrogen element in the mixed gas can be doped into the lithium iron phosphate in the form of gas to increase the specific surface area of ​​the lithium iron phosphate. The calcined nitrogen-indium-gallium doped lithium iron phosphate has excellent conductivity, cycle stability and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0028] Figure 1 It is a schematic flow chart of a method for preparing indium gallium nitrogen-doped lithium iron phosphate according to an embodiment of the present invention;

[0029] Figure 2 This is a SEM image of InGaN-doped lithium iron phosphate in Example 1 of the present application.

[0030] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0033] In the present application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, a~b (i.e. a and b), a~c, b~c, or a~b~c, where a, b, c can be single or multiple, respectively.

[0034] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. For example, without departing from the scope of the implementation regulations of this application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0035] The terms used in the embodiments of the present application are only for the purpose of describing specific implementation rules, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the implementation rules of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0036] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0037] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0038] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0039] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0040] The cycle stability of lithium iron phosphate is an important indicator of high capacity, long life and safety of batteries, and the cycle stability is closely related to the structural stability of lithium iron phosphate.

[0041] In order to improve the cycle stability of lithium iron phosphate batteries, the present application embodiment proposes a nitrogen-indium-gallium-doped lithium iron phosphate and a preparation method thereof. The nitrogen-indium-gallium-doped lithium iron phosphate prepared by the preparation method improves the conductivity of lithium iron phosphate, thereby increasing the discharge capacity density of the battery, improving the rate performance of the battery, enhancing the electrochemical stability of the battery, and thus improving the cycle stability of the battery.

[0042] The following is a detailed description of an indium gallium nitrogen-doped lithium iron phosphate and a preparation method thereof according to an embodiment of the present invention.

[0043] The present application provides a method for preparing indium gallium nitrogen doped lithium iron phosphate, such as Figure 1 As shown, the following steps are included:

[0044] S1. The ball milling liquid is ball milled in supercritical water and then calcined to obtain nitrogen-indium-gallium-doped lithium iron phosphate.

[0045] The ball milling solution contains a lithium source, an iron source, a phosphorus source, an indium source, a gallium source, phosphoric acid-grafted graphene oxide, and lithium-iron-grafted graphene oxide;

[0046] In the calcination step, the calcination is carried out in a nitrogen-hydrogen mixed gas atmosphere at a calcination temperature of 680°C to 800°C.

[0047] The preparation method of nitrogen-indium-gallium doped lithium iron phosphate in the embodiment of the present application is to ball-mill a ball-milling liquid containing a lithium source, an iron source, a phosphorus source, an indium source, a gallium source, phosphoric acid-grafted graphene oxide and lithium iron-grafted graphene oxide in supercritical water. Phosphoric acid-grafted graphene oxide and lithium iron-grafted graphene oxide are not only used as raw materials for graphene, but also can promote the directional reaction of lithium source, iron source and phosphoric acid to generate lithium iron phosphate during ball milling, thereby improving the reaction rate and the yield of lithium iron phosphate; supercritical water has excellent solubility and good mass transfer characteristics, which promotes the ball-milling liquid to fully disperse and dissolve in supercritical water to form a precursor; indium source and gallium source provide indium and gallium doping elements of lithium iron phosphate to improve the conductivity of lithium iron phosphate; and calcining in a nitrogen-hydrogen mixed gas atmosphere, the nitrogen element in the mixed gas can be doped into the lithium iron phosphate in the form of gas. The calcined nitrogen-indium-gallium doped lithium iron phosphate has excellent conductivity, cycle stability and rate performance. It should be noted that the ratio of lithium source, iron source and phosphoric acid is a conventional technology in the field and does not need to be specifically limited in the embodiments of the present application. However, as an example, the atomic ratio of lithium, iron and phosphorus in the lithium source, iron source and phosphorus source can be (0.95~1.05):(0.95~1.05):1.

[0048] In some embodiments, in the above step S1, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0049] In some embodiments, in the above step S1, the iron source includes at least one of ferrous sulfate, ferrous chloride, and ferrous oxalate.

[0050] In some embodiments, in the above step S1, the phosphorus source includes at least one of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0051] In some embodiments, in the above step S1, the indium source is indium acetate. In some embodiments, in the above step S1, the gallium source is gallium acetate. In this case, during ball milling, indium acetate and gallium acetate can slow down the reaction rate, so that the reaction is directed to generate indium gallium-doped lithium iron phosphate, reducing the occurrence of side reactions.

[0052] In some embodiments, in the above step S1, preparing phosphoric acid grafted graphene oxide comprises the following steps:

[0053] S101. Mix the first graphene oxide and phosphoric acid, perform a first microwave ultrasound treatment, wash and dry to obtain phosphoric acid-grafted graphene oxide.

[0054] In the above step of preparing phosphoric acid grafted graphene oxide, the first graphene oxide and phosphoric acid are mixed by microwave ultrasound to make the phosphate group easy to graft with the first graphene oxide; washing is performed to remove excess phosphoric acid, and the phosphoric acid grafted graphene oxide is obtained after drying. It should be noted that the amount of phosphoric acid used here is not included in the amount of phosphoric acid used in the ball milling solution.

[0055] In some embodiments, in the above step S101, the mass ratio of the first graphene oxide to the phosphoric acid is (0.03-0.08):1. In the exemplary embodiment, it can be a typical but non-limiting mass ratio such as 0.03:1, 0.054:1, 0.073:1, 0.08:1, or a range between any two mass ratios.

[0056] In some embodiments, in the above step S101, the mass concentration of phosphoric acid is 75% to 85%.

[0057] In some embodiments, in the above step S101, the microwave power of the first microwave ultrasound is 150W to 300W, the ultrasound frequency is 60kHz to 80kHz, and the microwave ultrasound time is 30min to 1h. In this case, microwave ultrasound accelerates the graphene oxide to fully contact and graft with phosphoric acid to obtain phosphoric acid-grafted graphene oxide.

[0058] In some embodiments, in the above step S101, the temperature of the first microwave ultrasound is 30°C to 70°C, and in the exemplary embodiment, it can be a typical but non-limiting temperature such as 30°C, 50°C, 70°C, or a range between any two temperatures. In this temperature range, the grafting reaction rate can be accelerated without causing side reactions due to overheating.

[0059] In some embodiments, in the above step S101, in the washing step, pure water suction filtration washing is used until the filtrate is neutral. In this case, the use of pure water suction filtration washing can remove excess impurities such as phosphoric acid to prevent the impurities from affecting the subsequent reaction.

[0060] In some embodiments, in the above step S101, the drying temperature is 100°C to 130°C. In the exemplary embodiment, it can be a typical but non-limiting temperature such as 100°C, 110°C, 120°C, 130°C, or a range between any two temperatures. In this case, low-temperature drying removes moisture without destroying the structure of the phosphoric acid-grafted graphene oxide. It should be noted that the drying time can be determined according to the actual production volume and is not particularly limited in the embodiments of the present application.

[0061] In some embodiments, in the above step S1, preparing lithium iron grafted graphene oxide comprises the following steps:

[0062] S102. After subjecting the first solution to a second microwave ultrasound, the solution is filtered, washed and dried to obtain lithium-grafted graphene oxide; the first solution contains second graphene oxide and lithium chloride.

[0063] S103. After subjecting the second solution to a third microwave ultrasound, the solution is filtered, washed and dried to obtain lithium iron grafted graphene oxide; the second solution contains lithium grafted graphene oxide and ethylenediaminetetraacetic acid ferrous complex.

[0064] In some embodiments, in the above step S102, the step of preparing the first solution includes: adding the second graphene oxide to the lithium chloride solution under stirring conditions of a rotation speed of 80 rpm to 150 rpm to obtain the first solution.

[0065] In some specific embodiments, the mass fraction of lithium chloride in the lithium chloride solution is 30% to 45%.

[0066] In some embodiments, in the above step S102, the microwave power of the second microwave ultrasound is 150W to 300W, the ultrasonic frequency is 60kHz to 80kHz; the microwave ultrasound time is 30min to 1h. In some embodiments, in the above step S102, the temperature of the second microwave ultrasound is 50°C to 100°C, and in the exemplary embodiment, it can be a typical but non-limiting temperature such as 50°C, 80°C, 100°C, or a range between any two temperatures. In this case, the grafting reaction rate can be accelerated without causing side reactions due to overheating.

[0067] In some embodiments, in the above step S102, after the second microwave ultrasound, pure water is used for suction filtration and washing, and the number of suction filtration and washing is 3 to 5 times. In this case, the use of pure water can remove excess reaction impurities and prevent impurities from affecting the subsequent reaction.

[0068] In some embodiments, in the above step S102, the drying temperature is 100° C. to 130° C., and in exemplary embodiments, it can be a typical but non-limiting temperature such as 100° C., 110° C., 120° C., 130° C., or a range between any two temperatures. In this case, low-temperature drying removes moisture without destroying the structure of the lithium-grafted graphene oxide.

[0069] In some embodiments, in the above step S102, the step of preparing the second solution includes:

[0070] S1020. Under an argon atmosphere and stirring conditions at a rotation speed of 100 rpm to 200 rpm, ethylenediaminetetraacetic acid is added to the ferrous chloride aqueous solution to obtain an ethylenediaminetetraacetic acid ferrous complex solution, wherein the pH value of the ferrous chloride aqueous solution is 3 to 5.

[0071] S1021. Under stirring conditions of 80 rpm to 150 rpm, add lithium-grafted graphene oxide to the ethylenediaminetetraacetic acid ferrous complex solution to obtain a second solution.

[0072] In some embodiments, in the above step S1020, the mass fraction of ferrous chloride in the ferrous chloride aqueous solution is 20% to 35%. At this concentration, the concentration of ferrous chloride is relatively high and is easy to form a complex with ethylenediaminetetraacetic acid.

[0073] In some embodiments, in the preparation of lithium iron grafted graphene oxide, the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and the second graphene oxide is (2.9-5.8): (35-55): (2.5-5): 1. In the exemplary embodiment, it can be a typical but non-limiting mass ratio such as 2.9: 35: 2.5: 1, 4: 45: 3.45: 1, 5.8: 55: 5: 1 or a range between any two mass ratios. In this case, the excess ethylenediaminetetraacetic acid can fully complex with ferrous chloride to form a complex, and lithium chloride is fully grafted with the second graphene oxide to improve the grafting yield. It should be noted that the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and the second graphene oxide is the original mass ratio, and their loss is not considered and cannot be accurately detected during the preparation of the first solution and the second solution.

[0074] In some embodiments, in the above step S103, the microwave power of the third microwave ultrasound is 150W to 300W, the ultrasonic frequency is 60kHz to 80kHz; the microwave ultrasound time is 30min to 1h. In some embodiments, in the above step S1, the temperature of the third microwave ultrasound is 50°C to 100°C, and in the exemplary embodiment, it can be a typical but non-limiting temperature such as 50°C, 80°C, 100°C, or a range between any two temperatures. In this case, the grafting reaction rate can be accelerated without causing side reactions due to overheating.

[0075] In some embodiments, in the above step S103, pure water is used for suction filtration and washing, and the number of suction filtration and washing is 3 to 5 times. In this case, the use of pure water can remove excess reaction impurities and prevent the impurities from affecting the subsequent reaction.

[0076] In some embodiments, in the above step S103, the drying temperature is 100° C. to 130° C., and in the exemplary embodiment, it can be a typical but non-limiting temperature such as 100° C., 110° C., 120° C., 130° C., or a range between any two temperatures. In this case, low-temperature drying removes moisture without destroying the structure of the lithium iron grafted graphene oxide.

[0077] In some embodiments, the total mass of the first graphene oxide and the second graphene oxide is the mass of graphene doped in indium gallium nitrogen-doped lithium iron phosphate.

[0078] In some embodiments, in the above step S1, in the nitrogen-indium-gallium doped lithium iron phosphate, the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen is (0.95~1.05):(0.95~1.05):1:(0.1~0.3):(0.1~0.3):(0.1~0.3).

[0079] In some embodiments, in the above step S1, the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphorus source is (0.1-0.2):(0.7-0.9):1, which can be typical but non-limiting mass ratios such as 0.1:0.8:1, 0.2:0.7:1, 0.2:0.8:1, 0.15:0.85:1, 0.1:0.9:1, or a range between any two mass ratios.

[0080] In some embodiments, in the above step S1, the step of preparing the ball milling solution comprises:

[0081] S104. According to the set raw material ratio, under the stirring condition of a rotation speed of 100rpm to 200rpm, lithium source, iron source, indium source, gallium source, phosphoric acid grafted graphene oxide and lithium iron grafted graphene oxide are respectively added to the phosphorus source aqueous solution to obtain a ball milling solution.

[0082] In some embodiments, in the above step S1, during ball milling, the ball-to-material ratio (volume ratio) is 1:(3-6), the ball milling time is 8h-20h, and the ball milling speed is 200rpm-400rpm. In this case, the yield of the lithium iron phosphate precursor is improved in synergy with supercritical water and the particle size of the lithium iron phosphate particles is refined.

[0083] In some specific embodiments, the grinding balls are at least one of zirconium oxide grinding balls, stainless steel grinding balls, and agate.

[0084] In some embodiments, the grinding balls include large-diameter grinding balls, medium-diameter grinding balls, and small-diameter grinding balls, and the number ratio is 2:(10-12):(20-25). In this case, the large-diameter grinding balls, medium-diameter grinding balls, and small-diameter grinding balls fully cooperate to promote the generation and refinement of lithium iron phosphate particles.

[0085] In some embodiments, the diameter of the large-diameter grinding ball is 80 mm to 100 mm, the diameter of the medium-diameter grinding ball is 50 mm to 70 mm, and the diameter of the small-diameter grinding ball is 20 mm to 25 mm.

[0086] In some embodiments, in the above step S1, the calcination temperature is 680°C to 800°C, and in the exemplary embodiment, it can be a typical but non-limiting temperature such as 680°C, 700°C, 720°C, or a range between any two temperatures. It should be noted that the calcination time is related to the amount of the reaction product, and can be adjusted conventionally according to the common knowledge in the art, and is not particularly limited in the embodiments of the present application.

[0087] In some embodiments, in the above step S1, the volume ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas atmosphere is (0.1-0.2): 1. In this case, the nitrogen in the nitrogen-hydrogen mixed gas atmosphere can be doped into the lithium iron phosphate material as one of the nitrogen sources, and the hydrogen provides a reducing atmosphere to prevent oxidation of ferrous iron and organic carbon elements.

[0088] In some embodiments, a method for preparing indium gallium nitrogen doped lithium iron phosphate is provided, the steps of which are as follows:

[0089] S201. Preparation of phosphoric acid grafted graphene oxide

[0090] ① The first graphene oxide and phosphoric acid are mixed in a mass ratio of (0.03-0.08):1, and after the first microwave ultrasound, pure water is filtered and washed until the filtrate is neutral; wherein the temperature of the first microwave ultrasound is 30°C-70°C, the microwave power is 150W-300W, the ultrasonic frequency is 60kHz-80kHz; and the microwave ultrasound time is 30min-1h.

[0091] ② Dry the filter residue at 100° C. to 130° C. until the water is completely removed to obtain phosphoric acid-grafted graphene oxide.

[0092] S202. Preparation of LiFe-grafted Graphene Oxide

[0093] ① Prepare raw materials according to the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and second graphene oxide of (2.9-5.8):(20-48):(2.5-5):1.

[0094] ② Prepare 20% to 35% by mass ferrous chloride solution and 30% to 45% by mass lithium chloride solution.

[0095] ③ Under the stirring condition of a rotation speed of 80rpm to 150rpm, add the second graphene oxide to the lithium chloride solution to obtain a first solution; after subjecting the first solution to a second microwave ultrasound for 30min to 1h, filter and wash it with pure water for 3 to 5 times, and dry it at 100°C to 130°C to obtain lithium-grafted graphene oxide; wherein the temperature of the second microwave ultrasound is 50°C to 100°C, the microwave power is 150W to 300W, and the ultrasonic frequency is 60kHz to 80kHz.

[0096] ④ adjusting the pH value of the ferrous chloride solution to 3-5 with hydrochloric acid; adding ethylenediaminetetraacetic acid to the ferrous chloride aqueous solution under an argon atmosphere and a stirring condition of 100rpm-200rpm to obtain an ethylenediaminetetraacetic acid ferrous complex solution;

[0097] Under the stirring condition of a rotation speed of 80 rpm to 150 rpm, lithium-grafted graphene oxide is added to the ethylenediaminetetraacetic acid ferrous complex solution to obtain a second solution.

[0098] ⑤ After subjecting the second solution to a third microwave ultrasound for 30 minutes to 1 hour, the solution is filtered and washed with pure water for 3 to 5 times, and dried at 100°C to 130°C to obtain lithium iron grafted graphene oxide; wherein the temperature of the third microwave ultrasound is 50°C to 100°C, the microwave power is 150W to 300W, and the ultrasonic frequency is 60kHz to 80kHz.

[0099] S203. Preparation of ball milling solution

[0100] ① According to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid of 0.2:0.7:1, the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen indium gallium doped lithium iron phosphate is (0.95-1.05):(0.95-1.05):1:(0.1-0.3):(0.1-0.3):(0.1-0.3) to prepare the ball milling liquid raw materials.

[0101] ② According to the set raw material ratio, under the stirring condition of a rotation speed of 100rpm to 200rpm, phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium source, iron source, phosphorus source, indium source and gallium source are mixed, and water is added as a ball milling medium to obtain a ball milling liquid.

[0102] S204.Ball mill

[0103] ① Add stainless steel grinding balls to the ball milling liquid at a ratio of 1:(3-6) between balls and materials; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:(10-12):(20-25), the diameter of the large-diameter grinding balls is 80mm-100mm, the diameter of the medium-diameter grinding balls is 50mm-70mm, and the diameter of the small-diameter grinding balls is 20mm-25mm.

[0104] ② In supercritical water, ball mill the ball milling liquid (including stainless steel grinding balls) at a ball milling rate of 200 rpm to 400 rpm for 8 h to 20 h.

[0105] S205. Calcinate at 620°C to 700°C in a nitrogen-hydrogen mixed gas atmosphere with a volume ratio of nitrogen to hydrogen of (0.1 to 0.2):1 to obtain nitrogen-indium-gallium-doped lithium iron phosphate.

[0106] A second aspect of an embodiment of the present application provides nitrogen-indium-gallium-doped lithium iron phosphate prepared by the preparation method of nitrogen-indium-gallium-doped lithium iron phosphate provided in an embodiment of the present application.

[0107] A third aspect of the embodiments of the present application provides an application of the nitrogen-indium-gallium-doped lithium iron phosphate provided by the embodiments of the present application in the field of lithium battery preparation.

[0108] The following is a description of the specific embodiments, wherein the mass concentration of phosphoric acid involved is 85%.

[0109] Example 1

[0110] Example 1 provides a method for preparing indium gallium nitrogen doped lithium iron phosphate, the steps are as follows:

[0111] (1) Preparation of phosphoric acid grafted graphene oxide

[0112] ① The first graphene oxide and phosphoric acid are mixed in a mass ratio of 0.054:1, and after the first microwave ultrasound, pure water is filtered and washed until the filtrate is neutral; wherein the temperature of the first microwave ultrasound is 40° C., the microwave power is 150 W, the ultrasonic frequency is 60 kHz; and the microwave ultrasound time is 1 hour.

[0113] ② Dry the filter residue at 110° C. until the water is completely removed to obtain phosphoric acid-grafted graphene oxide.

[0114] (2) Preparation of LiFe-grafted Graphene Oxide

[0115] ① Prepare raw materials according to the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and second graphene oxide of 4:45:3.45:1.

[0116] ②Using water as solvent, prepare 30% by mass ferrous chloride solution and 32% by mass lithium chloride solution.

[0117] ③ Under the stirring condition of a rotation speed of 100 rpm, add the second graphene oxide to the lithium chloride solution to obtain a first solution; after subjecting the first solution to a second microwave ultrasound for 1 hour, filter and wash it with pure water for 3 times, and dry it at 120°C to obtain lithium-grafted graphene oxide; wherein the temperature of the second microwave ultrasound is 80°C, the microwave power is 200 W, and the ultrasonic frequency is 70 kHz.

[0118] ④ Adjust the pH value of the ferrous chloride solution to 3-5 with hydrochloric acid; add ethylenediaminetetraacetic acid to the ferrous chloride aqueous solution under an argon atmosphere and a stirring condition of 150 rpm to obtain an ethylenediaminetetraacetic acid ferrous complex solution;

[0119] Under the stirring condition of a rotation speed of 80 rpm, lithium-grafted graphene oxide was added to the ethylenediaminetetraacetic acid ferrous complex solution to obtain a second solution.

[0120] ⑤ After subjecting the second solution to the third microwave ultrasound for 1 hour, the solution was filtered and washed three times with pure water, and dried at 100°C to obtain lithium iron grafted graphene oxide; wherein the temperature of the third microwave ultrasound was 80°C, the microwave power was 200W, and the ultrasonic frequency was 70kHz.

[0121] (3) Preparation of ball milling solution:

[0122] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.2:0.7:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.3:0.3:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate respectively.

[0123] ② According to the set raw material ratio, under the stirring condition of a rotation speed of 180 rpm, phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling liquid.

[0124] (4) Ball milling:

[0125] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:5; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:12:22, the diameter of the large-diameter grinding balls is 90 mm, the diameter of the medium-diameter grinding balls is 60 mm, and the diameter of the small-diameter grinding balls is 20 mm.

[0126] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 300 rpm for 15 h.

[0127] (5) Sintering at 680° C. in a nitrogen-hydrogen mixed gas atmosphere with a volume ratio of nitrogen to hydrogen of 0.1:1 to obtain nitrogen-indium-gallium doped lithium iron phosphate.

[0128] Example 1 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0129] Example 2

[0130] Example 2 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0131] (3) Preparation of ball milling solution:

[0132] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.1:0.8:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.2:0.2:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate respectively.

[0133] ② Phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling solution.

[0134] (4) Ball milling:

[0135] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:5; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:11:22, the diameter of the large-diameter grinding balls is 90 mm, the diameter of the medium-diameter grinding balls is 60 mm, and the diameter of the small-diameter grinding balls is 20 mm.

[0136] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 300 rpm for 15 h.

[0137] Example 2 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0138] Example 3

[0139] Example 3 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those in Example 1, except that:

[0140] (3) Preparation of ball milling solution:

[0141] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.1:0.9:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.1:0.1:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate, respectively.

[0142] ② Phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling solution.

[0143] (4) Ball milling:

[0144] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:6; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:12:25, the diameter of the large-diameter grinding balls is 100 mm, the diameter of the medium-diameter grinding balls is 70 mm, and the diameter of the small-diameter grinding balls is 25 mm.

[0145] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 200 rpm for 20 hours.

[0146] Example 3 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0147] Example 4

[0148] Example 4 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0149] (3) Preparation of ball milling solution:

[0150] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.1:0.9:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.3:0.3:0.3. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, phosphoric acid, indium acetate and gallium acetate respectively.

[0151] ② Phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, phosphoric acid, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling solution.

[0152] (4) Ball milling:

[0153] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:6; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:10:20, the diameter of the large-diameter grinding balls is 80 mm, the diameter of the medium-diameter grinding balls is 50 mm, and the diameter of the small-diameter grinding balls is 20 mm.

[0154] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 400 rpm for 18 h.

[0155] Example 4 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0156] Example 5

[0157] Example 5 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those in Example 1, except that:

[0158] (3) Preparation of ball milling solution:

[0159] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.2:0.9:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.3:0.2:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate respectively.

[0160] ② Phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling solution.

[0161] (4) Ball milling:

[0162] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:3; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:10:20, the diameter of the large-diameter grinding balls is 80 mm, the diameter of the medium-diameter grinding balls is 50 mm, and the diameter of the small-diameter grinding balls is 20 mm.

[0163] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 400 rpm for 18 h.

[0164] Example 5 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0165] Example 6

[0166] Example 6 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those in Example 1, except that:

[0167] (3) Preparation of ball milling solution:

[0168] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.15:0.85:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.3:0.2:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate respectively.

[0169] ② Phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium hydroxide, ferrous chloride, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling solution.

[0170] (4) Ball milling:

[0171] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:4; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:12:25, the diameter of the large-diameter grinding balls is 100 mm, the diameter of the medium-diameter grinding balls is 70 mm, and the diameter of the small-diameter grinding balls is 25 mm.

[0172] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 400 rpm for 20 h.

[0173] Example 6 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0174] Example 7

[0175] Example 7 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those in Example 1, except that:

[0176] (3) Preparation of ball milling solution:

[0177] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphoric acid being 0.2:0.8:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.2:0.3:0.3. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, phosphoric acid, indium acetate and gallium acetate respectively.

[0178] ② Phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium hydroxide, ferrous chloride, phosphoric acid, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling solution.

[0179] (4) Ball milling:

[0180] ① Add stainless steel grinding balls to the ball milling liquid at a ball-to-material ratio of 1:3; among the grinding balls, the ratio of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:12:25, the diameter of the large-diameter grinding balls is 80 mm, the diameter of the medium-diameter grinding balls is 70 mm, and the diameter of the small-diameter grinding balls is 25 mm.

[0181] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 400 rpm for 20 h.

[0182] Example 7 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0183] Example 8

[0184] Example 8 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those in Example 1, except that:

[0185] (2) Preparation of lithium iron grafted graphene oxide:

[0186] ① Prepare raw materials according to the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and second graphene oxide of 2.9:20:2.5:1.

[0187] ②Using water as solvent, prepare 30% by mass ferrous chloride solution and 35% by mass lithium chloride solution.

[0188] ③ Under the stirring condition of a rotation speed of 150 rpm, add the second graphene oxide to the lithium chloride solution to obtain a first solution; after subjecting the first solution to a second microwave ultrasound for 30 minutes, filter and wash it with pure water for 5 times, and dry it at 120°C to obtain lithium-grafted graphene oxide; wherein the temperature of the second microwave ultrasound is 100°C, the microwave power is 300 W, and the ultrasonic frequency is 80 kHz.

[0189] ④ Adjust the pH value of the aqueous solution of ferrous chloride with hydrochloric acid to 3-5; add ethylenediaminetetraacetic acid to the aqueous solution of ferrous chloride under an argon atmosphere and a stirring condition of 200 rpm to obtain an ethylenediaminetetraacetic acid ferrous complex solution;

[0190] Under the stirring condition of a rotation speed of 150 rpm, lithium-grafted graphene oxide was added to the ethylenediaminetetraacetic acid ferrous complex solution to obtain a second solution.

[0191] ⑤ After subjecting the second solution to the third microwave ultrasound for 1 hour, the solution was filtered and washed three times with pure water, and dried at 130° C. to obtain lithium iron grafted graphene oxide; wherein the temperature of the third microwave ultrasound was 80° C., the microwave power was 150 W, and the ultrasonic frequency was 70 kHz.

[0192] Example 8 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0193] Example 9

[0194] Example 9 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0195] (1) Preparation of lithium iron grafted graphene oxide:

[0196] ① According to the mass ratio of ferrous chloride, phenylalanine, lithium carbonate and first graphene oxide of 5.8:48:5:1, a 30% by mass fraction ferrous chloride solution and a 35% by mass fraction lithium chloride solution were prepared.

[0197] ② Under the stirring condition of a rotation speed of 80 rpm, add the first graphene oxide to the lithium chloride solution to obtain a first solution.

[0198] ③ After subjecting the first solution to the first microwave ultrasound for 1 hour, the solution was filtered and washed 5 times with pure water, and dried at 120° C. to obtain lithium-grafted graphene oxide; wherein the temperature of the first microwave ultrasound was 80° C., the microwave power was 300 W, and the ultrasonic frequency was 80 kHz.

[0199] ④ Adjusting the pH value of the aqueous solution of ferrous chloride to 3-5 with hydrochloric acid; adding phenylalanine to the aqueous solution of ferrous chloride under an argon atmosphere and a stirring condition of 100 rpm to obtain a phenylalanine ferrous complex solution;

[0200] Under stirring conditions at a rotation speed of 80 rpm, the lithium-grafted graphene oxide obtained in step ③ was added to the phenylalanine ferrous complex solution to obtain a second solution.

[0201] ⑤ After subjecting the second solution to a second microwave ultrasound for 1 hour, the solution was filtered and washed 5 times with pure water, and dried at 100° C. to obtain lithium iron grafted graphene oxide; wherein the temperature of the second microwave ultrasound was 100° C., the microwave power was 300 W, and the ultrasonic frequency was 80 kHz.

[0202] Example 9 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this example.

[0203] Comparative Example 1

[0204] Comparative Example 1 provides a method for preparing graphene-doped lithium iron phosphate, the steps are as follows:

[0205] (1) lithium acetate, ferrous oxalate and phosphoric acid are obtained as reaction raw materials with a molar ratio of lithium acetate, ferrous oxalate and phosphoric acid of 0.95:0.95:1 and a graphene oxide doping amount of 10% of the mass of lithium iron phosphate;

[0206] (2) Mix lithium acetate, ferrous oxalate, phosphoric acid and water to form a ball milling solution.

[0207] (3) Stainless steel grinding balls are added to the ball milling liquid at a ratio of 1:5; among the grinding balls, the ratio of the number of large-diameter grinding balls, medium-diameter grinding balls and small-diameter grinding balls is 2:11:22, the diameter of the large-diameter grinding balls is 90 mm, the diameter of the medium-diameter grinding balls is 60 mm, and the diameter of the small-diameter grinding balls is 20 mm.

[0208] ② In supercritical water, ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 400 rpm for 8 h.

[0209] (5) After ball milling, the mixture was calcined at 650°C for 12 h to obtain graphene-doped lithium iron phosphate.

[0210] Comparative Example 1 also provides a graphene-doped lithium iron phosphate, which is prepared using the preparation method of this comparative example.

[0211] Comparative Example 2

[0212] Comparative Example 2 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0213] The method does not include step (1), i.e., phosphoric acid grafted graphene oxide is not prepared.

[0214] (3) Preparation of ball milling solution

[0215] ① The ball milling liquid raw materials are prepared according to the mass ratio of lithium iron grafted graphene oxide and phosphoric acid being 0.8:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen indium gallium doped lithium iron phosphate being 1:1:1:0.3:0.3:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source are lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate respectively.

[0216] ② According to the set raw material ratio, under the stirring condition of a rotation speed of 100 rpm, phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling liquid.

[0217] Comparative Example 2 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this comparative example.

[0218] Comparative Example 3

[0219] Comparative Example 3 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those in Example 1, except that:

[0220] The step (2) is not included, i.e., lithium iron grafted graphene oxide is not prepared.

[0221] (3) Preparation of ball milling solution:

[0222] ① The ball milling liquid raw materials were prepared according to the mass ratio of phosphoric acid grafted graphene oxide and phosphoric acid being 0.2:1, and the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen in nitrogen-indium-gallium doped lithium iron phosphate being 1:1:1:0.3:0.3:0.1. The lithium source, iron source, phosphorus source, indium source and gallium source were lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate respectively.

[0223] ② According to the set raw material ratio, under the stirring condition of a rotation speed of 100 rpm, phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide, lithium carbonate, ferrous oxalate, diammonium hydrogen phosphate, indium acetate and gallium acetate are mixed, and water is added as a ball milling medium to obtain a ball milling liquid.

[0224] Comparative Example 3 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this comparative example.

[0225] Comparative Example 4

[0226] Comparative Example 4 provides a method for preparing indium gallium nitrogen-doped lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0227] (4) Ball milling:

[0228] ① Add stainless steel grinding balls into the ball milling liquid at a ratio of 1:5; the grinding balls are small-diameter grinding balls with a diameter of 20 mm.

[0229] ② Ball mill the ball milling liquid (containing stainless steel grinding balls) at a ball milling rate of 400 rpm for 8 h.

[0230] Comparative Example 4 also provides a nitrogen-indium-gallium doped lithium iron phosphate, which is prepared using the preparation method of this comparative example.

[0231] In order to verify the advancement of the indium gallium doped lithium iron phosphate and the preparation method thereof provided in the embodiments of the present application, taking embodiment 1 as an example, the indium gallium doped lithium iron phosphate prepared in embodiment 1 was scanned by a scanning electron microscope to obtain the corresponding Figure 2 The SEM image shown. Then, the lithium iron phosphate doped with indium gallium nitride provided in the embodiment and the comparative example was made into a 2032-type button battery to test the discharge specific capacity (mAh / g) of the obtained lithium battery at different rates (0.1C, 1C and 10C). The test results are shown in Table 1 below.

[0232] Among them, the 2032 button battery uses metal lithium sheet as the negative electrode and reference electrode, polypropylene microporous membrane as the separator, and LiPF6 / EC+DMC as the electrolyte.

[0233] EC: Ethylene Carbonate;

[0234] DMC: Dimethyl Carbonate.

[0235] Table 1

[0236]

[0237]

[0238] According to Table 1 above and the instructions attached Figure 2 At least the following conclusions can be drawn:

[0239] 1) In the nitrogen-indium-gallium doped lithium iron phosphate provided in the embodiment of the present application, the selected ethylenediaminetetraacetic acid complex can dope the lithium iron phosphate with N and C elements, and combined with graphene, indium source and gallium source doping, not only the structural stability of the lithium iron phosphate is improved, but also the conductivity of the lithium iron phosphate is improved. The prepared nitrogen-indium-gallium doped lithium iron phosphate has excellent conductivity, cycle stability and rate performance.

[0240] 2) The preparation method of the nitrogen-indium-gallium doped lithium iron phosphate of the embodiment of the present application is to react the ball-milling liquid containing lithium source, iron source, phosphorus source, indium source, gallium source, phosphoric acid grafted graphene oxide and lithium iron grafted graphene oxide in supercritical water. Phosphoric acid grafted graphene oxide and lithium iron grafted graphene oxide are not only used as raw materials for graphene, but also can promote the directional reaction of lithium source, iron source and phosphoric acid to generate lithium iron phosphate during ball milling, thereby improving the reaction rate and the yield of lithium iron phosphate; supercritical water has excellent solubility and good mass transfer characteristics, which promotes the ball-milling liquid to fully disperse and dissolve in supercritical water to form a precursor; indium source and gallium source provide indium and gallium doping elements of lithium iron phosphate to improve the conductivity of lithium iron phosphate; calcined in a nitrogen-hydrogen mixed gas atmosphere, the nitrogen element in the mixed gas can be doped into the lithium iron phosphate in the form of gas. The calcined nitrogen-indium-gallium doped lithium iron phosphate has excellent conductivity, cycle stability and rate performance.

[0241] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing indium gallium nitrogen doped lithium iron phosphate, characterized in that: The steps include: The ball milling liquid is ball milled in supercritical water and then calcined to obtain nitrogen-indium-gallium-doped lithium iron phosphate; The ball milling solution contains a lithium source, an iron source, a phosphorus source, an indium source, a gallium source, phosphoric acid-grafted graphene oxide, and lithium-iron-grafted graphene oxide; In the calcination step, the calcination is carried out in a nitrogen-hydrogen mixed gas atmosphere at a calcination temperature of 680°C to 800°C.

2. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to claim 1, characterized in that: The preparation of phosphoric acid grafted graphene oxide comprises the following steps: The first graphene oxide is mixed with phosphoric acid and subjected to a first microwave ultrasound treatment, and then washed and dried to obtain phosphoric acid-grafted graphene oxide.

3. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to claim 2, characterized in that: The mass ratio of the first graphene oxide to phosphoric acid is 0.03-0.08:

1.

4. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to claim 1, characterized in that: The preparation of the lithium iron grafted graphene oxide comprises the following steps: The first solution is subjected to a second microwave ultrasound treatment, filtered, washed and dried to obtain lithium-grafted graphene oxide; the first solution contains second graphene oxide and lithium chloride; The second solution is subjected to a third microwave ultrasound, filtered, washed and dried to obtain lithium iron grafted graphene oxide; the second solution contains lithium grafted graphene oxide and ethylenediaminetetraacetic acid ferrous complex.

5. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to claim 4, characterized in that: The steps of preparing the second solution include: Under an argon atmosphere and a stirring condition of 100 rpm to 200 rpm, ethylenediaminetetraacetic acid is added to the ferrous chloride aqueous solution to obtain an ethylenediaminetetraacetic acid ferrous complex solution, wherein the pH value of the ferrous chloride aqueous solution is 3 to 5; Under the stirring condition of a rotation speed of 80 rpm to 150 rpm, lithium-grafted graphene oxide is added to the ethylenediaminetetraacetic acid ferrous complex solution to obtain a second solution.

6. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to claim 5, characterized in that: In the preparation of the lithium iron grafted graphene oxide, the mass ratio of ferrous chloride, ethylenediaminetetraacetic acid, lithium chloride and the second graphene oxide is 2.9-5.8:35-55:2.5-5:

1.

7. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to claim 1, characterized in that: In the nitrogen-indium-gallium doped lithium iron phosphate, the atomic ratio of lithium, iron, phosphorus, indium, gallium and nitrogen is 0.95-1.05:0.95-1.05:1:0.1-0.3:0.1-0.3:0.1-0.

3.

8. The method for preparing indium gallium nitrogen doped lithium iron phosphate according to any one of claims 1 to 7, characterized in that: The mass ratio of phosphoric acid grafted graphene oxide, lithium iron grafted graphene oxide and phosphorus source is 0.1-0.2:0.7-0.9:1; And / or, in the nitrogen-hydrogen mixed gas atmosphere, the volume ratio of nitrogen to hydrogen is 0.1-0.2:

1.

9. Nitride-indium-gallium-doped lithium iron phosphate prepared by the method for preparing nitrogen-indium-gallium-doped lithium iron phosphate as claimed in any one of claims 1 to 8.

10. An application of the indium gallium nitrogen doped lithium iron phosphate as claimed in claim 9 in the field of lithium battery preparation.

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