Ionic conductor coated modified lithium iron phosphate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of positive electrode active materials, and particularly relates to ion conductor coated modified lithium iron phosphate as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing lithium iron grafted graphene; reaction liquid is prepared and comprises a lithium source, an iron source, lithium iron grafted graphene and phosphoric acid, and the mass ratio of the lithium iron grafted graphene to the phosphoric acid is (1.15-3): 1; performing hydrothermal reaction on the reaction liquid, and roasting to obtain modified lithium iron phosphate; and carrying out ion conductor coating treatment on the modified lithium iron phosphate to obtain the ion conductor coated modified lithium iron phosphate. According to the preparation method, the ionic conductor is used for coating the modified lithium iron phosphate, so that the conductivity, the ion diffusion coefficient, the cycling stability and the service life of the lithium iron phosphate are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of positive electrode active material preparation, and specifically relates to an ion conductor coated modified 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] Existing methods for improving the cycle stability of lithium iron phosphate include optimizing battery materials (such as doping modification, surface coating, particle size control, etc.), optimizing electrolytes (such as selecting electrolytes with high chemical stability, optimizing electrolyte ratios, controlling electrolyte acidity and moisture content, etc.), and improving battery processes (such as optimizing electrode porosity and compaction density, using highly conductive current collectors, introducing conductive agents and binders, etc.). Among them, optimizing battery materials is a more common method. Although doping with metals (such as manganese, cobalt, nickel, aluminum, titanium, etc.) or non-metals (such as nitrogen, sulfur, fluorine, etc.) can effectively improve the conductivity and ion diffusion coefficient of lithium iron phosphate, thereby improving its rate performance, its cycle stability and service life will be reduced due to the doping of elements. Summary of the invention

[0004] The present invention provides an ion conductor coated modified lithium iron phosphate and a preparation method and application thereof. The preparation method adopts an ion conductor coated modified lithium iron phosphate to significantly improve the conductivity, ion diffusion coefficient, cycle stability and service life of the lithium iron phosphate.

[0005] The present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing an ion conductor coated modified lithium iron phosphate, comprising the following steps:

[0007] Preparation of lithium iron grafted graphene;

[0008] Prepare a reaction solution, the reaction solution contains a lithium source, an iron source, lithium iron grafted graphene and phosphoric acid, and the mass ratio of lithium iron grafted graphene to phosphoric acid is (1.15-3):1;

[0009] The reaction solution is subjected to a hydrothermal reaction and then calcined to obtain modified lithium iron phosphate;

[0010] The modified lithium iron phosphate is subjected to an ion conductor coating treatment to obtain ion conductor coated modified lithium iron phosphate.

[0011] In some possible implementations, the preparation of lithium iron grafted graphene includes the following steps:

[0012] The suspension is ultrasonically treated, filtered, washed and dried to obtain lithium iron grafted graphene; the suspension contains lithium aspartate, ferrous lysine, graphene oxide and water.

[0013] In some possible implementations, the atomic ratio of Li, Fe and C in the lithium aspartate, the ferrous lysine and the graphene oxide is 1:1:(120-300).

[0014] In some possible implementations, during the ultrasonic treatment, the temperature is 80° C. to 100° C., the ultrasonic frequency is 40 kHz to 50 kHz, and the ultrasonic time is 1 h to 2 h.

[0015] In some possible implementations, the temperature of the hydrothermal reaction is 150°C to 200°C.

[0016] In some possible implementations, the ion conductor coating process includes the following steps:

[0017] Lithium hydroxide, ammonium phosphate, citric acid and water are mixed, and then mixed with modified lithium iron phosphate for hydrothermal reaction, and calcined to obtain ion conductor coated modified lithium iron phosphate.

[0018] In some possible implementations, the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:(12-24):(16-30):(20-35).

[0019] In a second aspect, the present invention provides an ion conductor coated modified lithium iron phosphate prepared by the preparation method of the ion conductor coated modified lithium iron phosphate provided by the present invention.

[0020] In some possible implementations, the powder resistivity of the ion conductor coated modified lithium iron phosphate is 4Ω·cm to 10Ω·cm.

[0021] In a third aspect, the present invention provides an application of the ion conductor coated modified lithium iron phosphate provided by the present invention in household appliances, electric vehicles, ships, satellites or energy storage systems.

[0022] The ion conductor coated modified lithium iron phosphate and the preparation method thereof provided by the present invention have at least the following beneficial technical effects compared with the prior art:

[0023] (1) In the ion conductor coated modified lithium iron phosphate provided by the present invention, the selected ferrous cysteine ​​can also dope the lithium iron phosphate with sulfur and carbon elements, and the lithium iron phosphate is modified by combining with graphene, which not only improves the structural stability of the lithium iron phosphate, but also improves the conductivity of the lithium iron phosphate. The ion conductor coated modified lithium iron phosphate has excellent conductivity, cycle stability and rate performance.

[0024] (2) The preparation method of the ion conductor coated modified lithium iron phosphate provided by the present invention grafts lithium aspartate and ferrous lysine onto graphene oxide, which can not only promote the dispersion of graphene in water; but also during the hydrothermal reaction, lithium aspartate and ferrous lysine slowly release lithium ions and ferrous ions, respectively, to control the reaction rate. In addition, aspartic acid has a certain antioxidant property, which prevents the ferrous ions in the reaction solution from being oxidized into ferric ions and carbon elements from being oxidized, and reduces the ferrous ions in the reaction solution to ferrous ions, thereby reducing the occurrence of side reactions and improving the yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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.

[0026] Figure 1 The figure is a schematic flow chart of a method for preparing ion conductor-coated modified lithium iron phosphate according to an embodiment of the present invention;

[0027] Figure 2 This is a SEM image of the ion conductor coated with modified lithium iron phosphate in Example 1 of the present invention;

[0028] Figure 3 This is an EDS image of carbon element in the ion conductor-coated modified lithium iron phosphate in Example 1 of the present invention;

[0029] Figure 4 This is an EDS image of sulfur element in the ion conductor coated modified lithium iron phosphate in Example 1 of the present invention.

[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 invention more clearly understood, the present invention 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 invention and are not used to limit the present invention.

[0032] In the present invention, 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 represent: 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 before and after are in an "or" relationship.

[0033] In the present invention, "at least one" means one or more, and "plurality" 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 the present invention, 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 invention are only for the purpose of describing specific implementation rules, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the implementation rules of the present invention 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 various embodiments of the present invention, 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 one after the other, 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 the present invention.

[0037] The weight of the relevant components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also indicate the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the description of the embodiments of the present invention, it is within the scope disclosed in the description of the embodiments of the present invention. Specifically, the mass described in the description of the embodiments of the present invention may 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 the present invention can be purchased from the market or prepared by existing methods.

[0040] All phosphoric acids involved in the embodiments of the present invention are concentrated phosphoric acid with a concentration of about 85%.

[0041] The calcination step involved in the embodiment of the present invention is carried out in a reducing atmosphere of hydrogen to reduce the trivalent iron in the precursor and prevent the carbon element from being oxidized into carbon dioxide to affect the doping effect or the progress of the reaction.

[0042] 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.

[0043] Currently, the rate performance is improved by doping lithium iron phosphate with metal elements (such as manganese, cobalt, nickel, aluminum, titanium, etc.) and / or non-metals (such as nitrogen, sulfur, phosphorus, fluorine, etc.). However, the cycle stability and service life of lithium iron phosphate are reduced due to the doped heteroatoms.

[0044] To this end, an embodiment of the present invention provides an ion conductor coated modified lithium iron phosphate and a preparation method thereof. The ion conductor coated modified lithium iron phosphate prepared by the preparation method improves the structural stability and electrical conductivity of the lithium iron phosphate. The ion conductor coated modified lithium iron phosphate has excellent electrical conductivity, cycle stability and rate performance.

[0045] The following is a detailed description of an ion conductor coated modified lithium iron phosphate and a preparation method thereof according to an embodiment of the present invention.

[0046] The present invention provides a method for preparing an ion conductor coated modified lithium iron phosphate, such as Figure 1 As shown, the following steps are included:

[0047] S10. Preparation of lithium iron grafted graphene.

[0048] S20. Prepare a reaction solution, the reaction solution contains a lithium source, an iron source, lithium iron grafted graphene and phosphoric acid, and the mass ratio of lithium iron grafted graphene to phosphoric acid is (1.15~3):1.

[0049] S30. The reaction solution is subjected to a hydrothermal reaction and then calcined to obtain modified lithium iron phosphate.

[0050] S40. Performing an ion conductor coating treatment on the modified lithium iron phosphate to obtain ion conductor coated modified lithium iron phosphate.

[0051] The method for preparing the ion conductor coated modified lithium iron phosphate of the embodiment of the present invention first prepares lithium iron grafted graphene as the doping source of graphene, and can also be used as a "seed" to promote the directional reaction to generate modified lithium iron phosphate in the hydrothermal reaction, thereby improving the reaction rate and yield, and thus improving the structural stability and conductivity of lithium iron phosphate; the ion conductor coating can improve the good electronic and ion conduction path, which helps to improve the electronic and ion conduction between the lithium iron phosphate material particles, thereby improving the conductivity of the material. It should be noted that the ratio of lithium source, iron source, and phosphoric acid is a conventional ratio in the art, and there is no need to make special restrictions in the embodiment of the present invention, but as an example, the molar ratio of lithium source, iron source, and phosphoric acid can be (0.95-1.05):(0.95-1.05):1.

[0052] In the embodiment, the mass ratio of lithium iron grafted graphene to phosphoric acid is (1.15-3):1, which can be a typical but non-limiting mass ratio such as 1.15:1, 2.15:1, 3:1, or a range between any two mass ratios.

[0053] In some embodiments, in the above step S10, preparing lithium iron grafted graphene includes the following steps:

[0054] S101. After ultrasonic treatment of the suspension, the suspension is filtered, washed and dried to obtain lithium iron grafted graphene; the suspension contains lithium aspartate, ferrous lysine, graphene oxide and water.

[0055] In the above-mentioned step of preparing lithium iron grafted graphene, lithium aspartate and ferrous lysine are grafted onto graphene oxide, which can not only promote the dispersion of graphene in water; and during the hydrothermal reaction, lithium aspartate and ferrous lysine respectively release lithium ions and ferrous ions slowly to control the reaction speed, and aspartic acid has a certain antioxidant property, which prevents the ferrous ions in the reaction solution from being oxidized to iron ions and carbon elements, and reduces the iron ions in the reaction solution to ferrous ions, thereby reducing the occurrence of side reactions and improving the yield. Lithium aspartate and ferrous lysine both contain nitrogen and carbon elements. After roasting, sulfur and carbon elements can also be uniformly doped in lithium iron phosphate, thereby improving the lithium ion diffusion rate, and then improving the cycle performance and charge and discharge efficiency of the battery.

[0056] In some embodiments, in the above step S101, the step of preparing the suspension includes: mixing lithium aspartate, ferrous lysine, graphene oxide and water under stirring conditions of a temperature of 60°C to 80°C and a rotation speed of 100rpm to 200rpm to obtain a suspension.

[0057] In some embodiments, in the above step S101, the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide is 1: 1: (120-300). In this case, graphene oxide has enough space to graft lithium aspartate and ferrous lysine. It should be noted that the amount of water can be added as needed by those skilled in the art, and it is not necessary to be particularly limited in the embodiments of the present invention, but as an example, the amount of water added can be 1 to 2 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0058] In some embodiments, in the above step S101, during the ultrasonic treatment, the temperature is 80°C to 100°C, the ultrasonic frequency is 40kHz to 50kHz, and the ultrasonic time is 1h to 2h. In this case, low-temperature and low-frequency ultrasound for 1h to 2h can promote the collision and reaction between lithium aspartate, ferrous lysine and graphene oxide molecules, increase the contact area and frequency between the reactants, thereby reducing the generation of side reactions and improving the purity and yield of the product.

[0059] In some embodiments, in the above step S101, 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.

[0060] In some embodiments, in the above step S101, 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.

[0061] In some embodiments, in the above step S20, the iron source includes at least one of ferrous sulfate, ferrous chloride, and ferrous oxalate.

[0062] In some embodiments, in the above step S20, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0063] In some embodiments, in the above step S20, the step of preparing the reaction solution includes:

[0064] Under the stirring condition of a rotation speed of 50 rpm to 100 rpm, a lithium source, an iron source and lithium-iron grafted graphene are added to phosphoric acid to obtain a reaction solution.

[0065] In some embodiments, in the above step S30, the temperature of the hydrothermal reaction is 150°C to 200°C. In exemplary embodiments, it can be a typical but non-limiting temperature such as 150°C, 170°C, 180°C, 200°C, or a range between any two temperatures.

[0066] In some embodiments, in the above step S30, the hydrothermal reaction time is 1 h to 5 h. In exemplary embodiments, it can be 1 h, 2 h, 3 h, 4 h, 5 h, etc., typical but non-limiting time or a range between any two time periods.

[0067] In some embodiments, in the above step S30, the calcination temperature of the calcination step is 600°C to 700°C. In the exemplary embodiment, it can be a typical but non-limiting temperature such as 600°C, 680°C, 700°C, or a range between any two temperatures. It should be noted that it is well known in the art that the calcination is carried out under a hydrogen atmosphere to prevent ferrous iron from being oxidized, so it is not particularly limited in the embodiments of the present invention; the calcination time is related to the amount of the hydrothermal reaction product, and can be adjusted conventionally according to the well-known in the art, and is not particularly limited in the embodiments of the present invention.

[0068] In some embodiments, in the above step S40, the ion conductor coating process includes the following steps:

[0069] S401. Mix lithium hydroxide, ammonium phosphate, citric acid and water, and then mix with modified lithium iron phosphate to carry out hydrothermal reaction, and calcine to obtain ion conductor coated modified lithium iron phosphate.

[0070] In some embodiments, in the above step S401, the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:(12-24):(16-30):(20-35).

[0071] In some embodiments, in the above step S401, the temperature of the hydrothermal reaction is 120°C to 180°C. In exemplary embodiments, it can be a typical but non-limiting temperature such as 120°C, 150°C, 180°C, or a range between any two temperatures.

[0072] In some embodiments, in the above step S401, the hydrothermal reaction time is 1 h to 5 h. In exemplary embodiments, it can be 1 h, 2 h, 3 h, 4 h, 5 h, etc., typical but non-limiting time or a range between any two time periods.

[0073] In some embodiments, in the above step S401, the calcination temperature is 600°C to 700°C. In the exemplary embodiment, it can be a typical but non-limiting temperature such as 600°C, 680°C, 700°C, or a range between any two temperatures. It should be noted that it is well known in the art that calcination is carried out under a hydrogen atmosphere to prevent oxidation of carbon elements in organic matter, so it is not particularly limited in the embodiments of the present invention; the calcination time is related to the amount of the hydrothermal reaction product, and can be adjusted conventionally according to the knowledge in the art, and is not particularly limited in the embodiments of the present invention.

[0074] In some embodiments, a method for preparing an ion conductor coated modified lithium iron phosphate is provided, the steps being as follows:

[0075] S11. Preparation of lithium iron grafted graphene:

[0076] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:(120-300).

[0077] ② Under stirring conditions of a temperature of 60° C. to 80° C. and a rotation speed of 100 rpm to 200 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 to 2 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0078] ③ After ultrasonicating the suspension at a temperature of 80°C to 100°C and a frequency of 40kHz to 50kHz for 1h to 2h, the suspension 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.

[0079] S21. Preparation of reaction solution:

[0080] ① Obtain the reaction liquid raw materials according to the following ratios: the mass ratio of lithium iron grafted graphene and phosphoric acid is (1.15-3):1, and the molar ratio of lithium acetate, ferrous oxalate and phosphoric acid is (0.95-1.05):(0.95-1.05):1.

[0081] ② Under stirring conditions at a rotation speed of 50 rpm to 100 rpm, lithium acetate, ferrous oxalate, and lithium iron-grafted graphene are added to phosphoric acid to obtain a reaction solution.

[0082] S31. Preparation of modified lithium iron phosphate: The reaction solution is subjected to a hydrothermal reaction at 150°C to 200°C for 1h to 5h and then calcined at 600°C to 700°C to obtain modified lithium iron phosphate.

[0083] S41. Ion conductor coating:

[0084] ① Obtain raw materials in the following proportions: the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:(12-24):(16-30):(20-35).

[0085] ② After mixing lithium hydroxide, ammonium phosphate, citric acid and water, mix them with modified lithium iron phosphate and carry out hydrothermal reaction at 120°C to 180°C for 1h to 5h.

[0086] ③ The hydrothermal reaction product is calcined at 600°C to 700°C to obtain ion conductor coated modified lithium iron phosphate.

[0087] A second aspect of the embodiments of the present invention provides an ion conductor coated modified lithium iron phosphate prepared by the preparation method of the ion conductor coated modified lithium iron phosphate provided by the embodiments of the present invention.

[0088] The ion conductor-coated modified lithium iron phosphate in the embodiment of the present invention is doped with graphene and carbon, which improves the conductivity of the lithium iron phosphate. The ion conductor coating layer can provide a good electron and ion conduction path, which helps to improve the electron and ion conduction between the lithium iron phosphate material particles, thereby improving the conductivity, cycle stability and rate performance of the lithium iron phosphate.

[0089] In some embodiments, the powder resistivity of the ion conductor coated modified lithium iron phosphate is 4Ω·cm to 10Ω·cm. In an exemplary embodiment, it can be a typical but non-limiting powder resistivity such as 4Ω·cm, 6Ω·cm, 8Ω·cm, 10Ω·cm, or a range between any two powder resistivities. In this case, the ion conductor coated modified lithium iron phosphate has a very high lithium ion transfer rate, thereby improving the energy density, cycle stability and safety of the battery.

[0090] The following is a description of the specific examples. All phosphoric acids involved in the following examples are concentrated phosphoric acid with a concentration of about 85%; all calcinations involved in the following examples are carried out in a hydrogen atmosphere.

[0091] Example 1

[0092] Example 1 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps of which are as follows:

[0093] (1) Preparation of lithium iron grafted graphene:

[0094] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:200.

[0095] ② Under stirring conditions of a temperature of 70° C. and a rotation speed of 170 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0096] ③ After ultrasonicating the suspension at a temperature of 90°C and a frequency of 45kHz for 2h, the suspension was filtered and washed three times with pure water, and dried at 120°C to obtain lithium iron grafted graphene.

[0097] (2) Preparation of reaction solution:

[0098] ① Obtain the reaction liquid raw materials according to the following ratio: the mass ratio of lithium iron grafted graphene and phosphoric acid is 2:1, and the molar ratio of lithium acetate, ferrous oxalate and phosphoric acid can be 1:1:1.

[0099] ② Under the stirring condition of a rotation speed of 80 rpm, lithium acetate, ferrous oxalate, and lithium iron grafted graphene are added to phosphoric acid to obtain a reaction solution.

[0100] (3) Preparation of modified lithium iron phosphate: The reaction solution was subjected to hydrothermal reaction at 180° C. for 3 h and then calcined at 680° C. to obtain modified lithium iron phosphate.

[0101] (4) Ion conductor coating:

[0102] ① Obtain raw materials in the following proportions: the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:20:25:30.

[0103] ② Mix lithium hydroxide, ammonium phosphate, citric acid and water, then mix with modified lithium iron phosphate, and perform hydrothermal reaction at 150° C. for 2 hours.

[0104] ③ The hydrothermal reaction product is calcined at 700° C. to obtain ion conductor coated modified lithium iron phosphate.

[0105] Example 1 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 5Ω·cm.

[0106] Example 2

[0107] Example 2 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0108] (1) Preparation of lithium iron grafted graphene:

[0109] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:120.

[0110] ② Under stirring conditions of a temperature of 60° C. and a rotation speed of 200 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0111] ③ After ultrasonicating the suspension at a temperature of 80°C and a frequency of 50 kHz for 1 hour, the suspension was filtered and washed three times with pure water, and dried at 100°C to obtain lithium iron grafted graphene.

[0112] Example 2 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 4Ω·cm.

[0113] Example 3

[0114] Example 3 provides a method for preparing ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0115] (1) Preparation of lithium iron grafted graphene:

[0116] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:150.

[0117] ② Under stirring conditions of a temperature of 75° C. and a rotation speed of 180 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0118] ③ After ultrasonicating the suspension at a temperature of 85°C and a frequency of 47 kHz for 2 hours, the suspension was filtered and washed three times with pure water, and dried at 115°C to obtain lithium iron grafted graphene.

[0119] Example 3 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 8Ω·cm.

[0120] Example 4

[0121] Example 4 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0122] (1) Preparation of lithium iron grafted graphene:

[0123] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:230.

[0124] ② Under stirring conditions of a temperature of 80° C. and a rotation speed of 150 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0125] ③ After ultrasonicating the suspension at a temperature of 95°C and a frequency of 50 kHz for 1 hour, the suspension was filtered and washed three times with pure water, and dried at 125°C to obtain lithium iron grafted graphene.

[0126] Example 4 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 6Ω·cm.

[0127] Example 5

[0128] Example 5 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0129] (1) Preparation of lithium iron grafted graphene:

[0130] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:280.

[0131] ② Under stirring conditions of a temperature of 80° C. and a rotation speed of 130 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0132] ③ After ultrasonicating the suspension at a temperature of 100°C and a frequency of 48 kHz for 1 hour, the suspension was filtered and washed three times with pure water, and dried at 130°C to obtain lithium iron grafted graphene.

[0133] Example 5 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 9Ω·cm.

[0134] Example 6

[0135] Example 6 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0136] (1) Preparation of lithium iron grafted graphene:

[0137] ① Obtain lithium aspartate, ferrous lysine and graphene oxide according to the atomic ratio of Li, Fe and C in lithium aspartate, ferrous lysine and graphene oxide being 1:1:300.

[0138] ② Under stirring conditions of a temperature of 65° C. and a rotation speed of 100 rpm, lithium aspartate, ferrous lysine and graphene oxide are dissolved in water to prepare a suspension; the amount of water used is 1 times the total mass of lithium aspartate, ferrous lysine and graphene oxide.

[0139] ③ After ultrasonicating the suspension at a temperature of 95°C and a frequency of 40 kHz for 1 hour, the suspension was filtered and washed three times with pure water, and dried at 130°C to obtain lithium iron grafted graphene.

[0140] Example 6 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 10Ω·cm.

[0141] Example 7

[0142] Example 7 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0143] (2) Preparation of reaction solution:

[0144] ① Obtain the reaction liquid raw materials according to the following ratio: the mass ratio of lithium iron grafted graphene and phosphoric acid is 1.15:1, and the molar ratio of lithium acetate, ferrous oxalate and phosphoric acid can be 1:1:1.

[0145] ② Under the stirring condition of a rotation speed of 100 rpm, lithium acetate, ferrous oxalate, and lithium iron grafted graphene are added to phosphoric acid to obtain a reaction solution.

[0146] (4) Ion conductor coating:

[0147] ① Obtain raw materials in the following proportions: the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:12:16:20.

[0148] ② Mix lithium hydroxide, ammonium phosphate, citric acid and water, then mix with modified lithium iron phosphate, and perform hydrothermal reaction at 150°C for 2 hours.

[0149] ③ The hydrothermal reaction product is calcined at 700° C. to obtain ion conductor coated modified lithium iron phosphate.

[0150] Example 7 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 10Ω·cm.

[0151] Example 8

[0152] Example 8 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0153] (2) Preparation of reaction solution:

[0154] ① Obtain the reaction liquid raw materials according to the following ratios: the mass ratio of lithium iron grafted graphene and phosphoric acid is 3:1, and the molar ratio of lithium acetate, ferrous oxalate, and phosphoric acid can be 1:1:1.

[0155] ② Under the stirring condition of a rotation speed of 50 rpm, lithium acetate, ferrous oxalate, and lithium iron grafted graphene are added to phosphoric acid to obtain a reaction solution.

[0156] (4) Ion conductor coating:

[0157] ① Obtain raw materials in the following proportions: the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:24:25:35.

[0158] ② Mix lithium hydroxide, ammonium phosphate, citric acid and water, then mix with modified lithium iron phosphate, and perform hydrothermal reaction at 150°C for 2 hours.

[0159] ③ The hydrothermal reaction product is calcined at 700° C. to obtain ion conductor coated modified lithium iron phosphate.

[0160] Example 8 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 5Ω·cm.

[0161] Example 9

[0162] Example 9 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are basically the same as those of Example 1, except that:

[0163] (2) Preparation of reaction solution:

[0164] ① Obtain the reaction liquid raw materials according to the following ratios: the mass ratio of lithium iron grafted graphene and phosphoric acid is 2.5:1, and the molar ratio of lithium acetate, ferrous oxalate, and phosphoric acid can be 1:1:1.

[0165] ② Under the stirring condition of a rotation speed of 90 rpm, lithium acetate, ferrous oxalate, and lithium iron grafted graphene are added to phosphoric acid to obtain a reaction solution.

[0166] (4) Ion conductor coating:

[0167] ① Obtain raw materials in the following proportions: the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:18:20:35.

[0168] ② Mix lithium hydroxide, ammonium phosphate, citric acid and water, then mix with modified lithium iron phosphate, and perform hydrothermal reaction at 150°C for 2 hours.

[0169] ③ The hydrothermal reaction product is calcined at 700° C. to obtain ion conductor coated modified lithium iron phosphate.

[0170] Example 9 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 7Ω·cm.

[0171] Comparative Example 1

[0172] Comparative Example 1 provides a method for preparing an ion conductor coated modified lithium iron phosphate, the steps are as follows:

[0173] 1) Preparation of modified lithium iron phosphate:

[0174] ① Obtain the reaction liquid raw materials according to the following ratio:

[0175] The atomic ratio of Li, Fe, and C in lithium aspartate, ferrous lysine, and graphene oxide is 1:1:200;

[0176] The mass ratio of the total mass of lithium aspartate, ferrous lysine and graphene oxide to phosphoric acid is 2:1;

[0177] The molar ratio of lithium acetate, ferrous oxalate and phosphoric acid may be 1:1:1.

[0178] ② Under stirring conditions at a rotation speed of 80 rpm, lithium aspartate, ferrous lysine, graphene oxide, lithium acetate and ferrous oxalate were added to phosphoric acid to obtain a reaction solution.

[0179] ③ The reaction solution was hydrothermally reacted at 180° C. for 3 h and then calcined at 680° C. to obtain modified lithium iron phosphate.

[0180] 2) Ion conductor coating:

[0181] ① Obtain raw materials in the following proportions: the mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:20:25:30.

[0182] ② Mix lithium hydroxide, ammonium phosphate, citric acid and water, then mix with modified lithium iron phosphate, and perform hydrothermal reaction at 150°C for 2 hours.

[0183] ③ The hydrothermal reaction product is calcined at 700° C. to obtain ion conductor coated modified lithium iron phosphate.

[0184] Comparative Example 1 also provides an ion conductor coated modified lithium iron phosphate, which is prepared by the preparation method of this comparative example: the powder resistivity of the ion conductor coated modified lithium iron phosphate is 30Ω·cm.

[0185] Comparative Example 2

[0186] Comparative Example 2 provides a method for preparing modified lithium iron phosphate, and the steps are basically the same as those of Example 1, except that:

[0187] The ion conductor coating in step (4) is not performed, that is, graphene-doped modified lithium iron phosphate is prepared.

[0188] Comparative Example 2 also provides a modified lithium iron phosphate, which is prepared by the preparation method of this comparative example: the powder resistivity of the modified lithium iron phosphate is 40Ω·cm.

[0189] In order to verify the advancement of the ion conductor coated modified lithium iron phosphate and the preparation method thereof provided in the embodiment of the present invention, taking Example 1 as an example, a scanning electron microscope was used to scan the ion conductor coated modified lithium iron phosphate prepared in Example 1, and the corresponding Figure 2 SEM images shown; and according to Figure 2 The SEM images shown in Figure 3 The EDS patterns of carbon and Figure 4 The EDS graph of sulfur is shown. The ion conductors of the embodiment and the comparative example were coated with modified lithium iron phosphate / modified lithium iron phosphate to prepare button batteries, and then the button batteries were subjected to electrical performance tests including 0.1C discharge, initial charge and discharge efficiency, 5C discharge and 1C cycle 500 times capacity retention rate in the voltage range of 2.0V to 3.8V using a blue electric device. The test results are shown in Table 1 below.

[0190] in,

[0191] The preparation steps of button cells are as follows:

[0192] (1) Preparing positive electrode slurry: mixing modified lithium iron phosphate coated with ion conductor / modified lithium iron phosphate: conductive carbon black: polyvinylidene fluoride in a mass ratio of 90:5:5, adding solvent N-methylpyrrolidone (NMP) to adjust the viscosity to 4000 mPa·s to 8000 mPa·s, and preparing positive electrode slurry.

[0193] (2) The positive electrode slurry is evenly coated on one surface (perpendicular to the thickness direction) of the aluminum foil (positive electrode current collector) and dried, and then rolled and sliced ​​to obtain a positive electrode sheet containing a positive electrode film layer.

[0194] (5) Using lithium hexafluorophosphate-ethyl methyl carbonate as the electrolyte and polypropylene as the isolation membrane, the prepared positive electrode sheet and negative lithium sheet are combined to form a button half-cell.

[0195] Table 1

[0196]

[0197] According to Table 1 above and the instructions attached Figures 2 to 4 At least the following conclusions can be drawn:

[0198] 1) Instruction Manual Figures 2 to 4 It can be seen from Table 1 that the ion conductor coated modified lithium iron phosphate contains graphene. In the ion conductor coated modified lithium iron phosphate provided in the embodiment of the present invention, the ferrous cysteine ​​is used to dope the lithium iron phosphate with sulfur and carbon (such as Figure 3 and Figure 4As shown in the figure, the modification of lithium iron phosphate by combining graphene not only improves the structural stability of lithium iron phosphate, but also improves the conductivity of lithium iron phosphate. The ion conductor coated modified lithium iron phosphate has excellent conductivity, cycle stability and rate performance.

[0199] 2) The preparation method of the ion conductor coated modified lithium iron phosphate of the embodiment of the present invention, in which lithium aspartate and ferrous lysine are grafted onto graphene oxide, can not only promote the dispersion of graphene in water; but also during the hydrothermal reaction, lithium aspartate and ferrous lysine slowly release lithium ions and ferrous ions, respectively, to control the reaction rate, and aspartic acid has a certain antioxidant property, which prevents the ferrous ions in the reaction solution from being oxidized into ferric ions and carbon elements from being oxidized, and reduces the ferrous ions in the reaction solution to ferrous ions, thereby reducing the occurrence of side reactions and improving the yield.

[0200] It should be noted that the present invention 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 exerting the same effect within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the main purpose of the present invention, 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 invention.

Claims

1. A method for preparing ion conductor coated modified lithium iron phosphate, characterized in that: The steps include: Preparation of lithium iron grafted graphene; Prepare a reaction solution, the reaction solution contains a lithium source, an iron source, lithium iron grafted graphene and phosphoric acid, and the mass ratio of lithium iron grafted graphene to phosphoric acid is (1.15-3):1; The reaction solution is subjected to a hydrothermal reaction and then calcined to obtain modified lithium iron phosphate; The modified lithium iron phosphate is subjected to an ion conductor coating treatment to obtain ion conductor coated modified lithium iron phosphate.

2. The method for preparing the ion conductor coated modified lithium iron phosphate according to claim 1, characterized in that: The preparation of lithium iron grafted graphene comprises the following steps: The suspension is ultrasonically treated, filtered, washed and dried to obtain lithium iron grafted graphene; the suspension contains lithium aspartate, ferrous lysine, graphene oxide and water.

3. The method for preparing the ion conductor coated modified lithium iron phosphate according to claim 2, characterized in that: The atomic ratio of Li, Fe and C in the lithium aspartate, the ferrous lysine and the graphene oxide is 1:1:(120-300).

4. The method for preparing the ion conductor coated modified lithium iron phosphate according to claim 2, characterized in that: In the ultrasonic treatment, the temperature is 80° C. to 100° C., the ultrasonic frequency is 40 kHz to 50 kHz, and the ultrasonic time is 1 h to 2 h.

5. The method for preparing ion conductor coated modified lithium iron phosphate according to any one of claims 1 to 4, characterized in that: The temperature of the hydrothermal reaction is 150°C to 200°C.

6. The method for preparing ion conductor coated modified lithium iron phosphate according to any one of claims 1 to 4, characterized in that: The ion conductor coating process comprises the following steps: Lithium hydroxide, ammonium phosphate, citric acid and water are mixed, and then mixed with modified lithium iron phosphate for hydrothermal reaction, and calcined to obtain ion conductor coated modified lithium iron phosphate.

7. The method for preparing the ion conductor coated modified lithium iron phosphate according to claim 6, characterized in that: The mass ratio of lithium hydroxide, ammonium phosphate, citric acid and modified lithium iron phosphate is 1:(12-24):(16-30):(20-35).

8. An ion conductor coated modified lithium iron phosphate prepared by the method for preparing ion conductor coated modified lithium iron phosphate according to any one of claims 1 to 7.

9. The ion conductor coated modified lithium iron phosphate according to claim 8, characterized in that: The powder resistivity of the ion conductor coated modified lithium iron phosphate is 4Ω·cm to 10Ω·cm.

10. Use of the ion conductor coated modified lithium iron phosphate as claimed in claim 9 in household appliances, electric vehicles, ships, satellites or energy storage systems.

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