Modified lithium iron phosphate, preparation method thereof, positive electrode material, battery and application

Abstract

The application relates to the technical field of lithium iron phosphate materials, in particular to modified lithium iron phosphate, a preparation method thereof, a positive electrode material, a battery and application. The raw materials of the modified lithium iron phosphate include a lithium source, an iron source, a phosphorus source and a zinc halide; in the raw materials, the atomic percentage content of zinc is 1% to 5% of that of iron. The modified lithium iron phosphate provided by the application has very high electronic conductivity and lithium ion diffusion rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium iron phosphate material, and particularly relates to modified lithium iron phosphate, a preparation method thereof, a positive electrode material, a battery and application. BACKGROUND

[0002] At present, the methods for pore-forming modification of lithium iron phosphate (LiFePO4, LFP) material mainly include template method, sol-gel method, biological template method, spray drying method, freeze drying method and etching method. Although these methods can improve the ion / electron transmission performance to some extent, thereby improving the rate performance and energy density of the battery, there are still the following main technical problems: (1) the template method has complex process, high cost, and the pore structure prepared thereby is easy to collapse and difficult to scale; (2) the pore diameter distribution of the lithium iron phosphate prepared by the sol-gel method and the biological template method is uneven and the pore diameter is uncontrollable; (3) the spray drying method and the freeze drying method have high energy consumption, low particle strength and difficult control of pore diameter gradient (the solvent volatilization speed is uneven in the drying process, and closed pores or pores with poor connectivity are easy to form); (4) the etching method will cause material loss of LFP due to the use of acid / alkali etching, resulting in loss of active material. SUMMARY

[0003] To solve the above problems, the present application provides a modified lithium iron phosphate, a preparation method thereof, a positive electrode material, a battery and application. At least one aspect of the above technical problems is solved.

[0004] The present application is realized by the following technical solutions:

[0005] In a first aspect, the present application provides a modified lithium iron phosphate, and the raw materials include lithium iron phosphate and zinc halide.

[0006] In the raw materials, the atomic percentage content of zinc is 1% to 5% of the atomic percentage of iron.

[0007] In some possible implementation manners, the zinc halide is:

[0008] R1-Zn-R2;

[0009] wherein R1 is Cl, Br, alkyl, alkenyl, phenyl, haloalkyl, haloalkenyl or halophenyl; and R2 is Cl, Br, haloalkyl, haloalkenyl or halophenyl.

[0010] In some possible implementation manners, in the R1, the alkyl is C 1~6 alkyl.

[0011] In some possible implementation manners, in the R1, the alkenyl is C 2~6 alkenyl.

[0012] In some possible implementation manners, in the R1, the halogenated alkyl group is a C 1~6 haloalkyl group or a C 1~6 dihaloalkyl group.

[0013] In some possible implementation manners, in the R1, the halogenated alkenyl group is a C 2~6 haloalkenyl group.

[0014] In some possible implementation manners, in the R1, the halogenated phenyl group is a monohalogenated phenyl group or a dihalogenated phenyl group.

[0015] In some possible implementation manners, in the R2, the halogenated alkyl group is a C 1~6 haloalkyl group or a dihaloalkyl group.

[0016] In some possible implementation manners, in the R2, the halogenated alkenyl group is a C 2~6 haloalkenyl group.

[0017] In some possible implementation manners, in the R2, the halogenated phenyl group is a monohalogenated phenyl group, an ortho-dihalogenated phenyl group, a meta-dihalogenated phenyl group or a para-dihalogenated phenyl group.

[0018] In a second aspect, the present application provides a preparation method of the modified lithium iron phosphate, and the preparation method comprises the following steps:

[0019] The lithium iron phosphate and the zinc halide are mixed and sintered to obtain the modified lithium iron phosphate.

[0020] In some possible implementation manners, the sintering step comprises:

[0021] The temperature is raised to 750-800 DEG C at a temperature raising rate of 8-15 DEG C / min, and then the temperature is kept constant.

[0022] In some possible implementation manners, the time for keeping the temperature constant is 2-6 h.

[0023] In a third aspect, the present application provides a positive electrode material, which comprises the modified lithium iron phosphate prepared by the preparation method.

[0024] In a fourth aspect, the present application provides a battery comprising the positive electrode material.

[0025] In a fifth aspect, the present application provides an application of the modified lithium iron phosphate prepared by the preparation method in the field of battery materials.

[0026] Compared with the prior art, the modified lithium iron phosphate and the preparation method thereof provided by the present application have at least the following beneficial technical effects:

[0027] (1) The modified lithium iron phosphate provided by the present application has high electronic conductivity and lithium ion diffusion rate.

[0028] (2) The preparation method of the modified lithium iron phosphate provided by the application can prepare the modified lithium iron phosphate with a porous structure, thereby shortening the diffusion path of Li + and improving the rate performance and cycle stability of the material. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort based on the drawings shown.

[0030] Figure 1 SEM image of the modified lithium iron phosphate in Embodiment 1 of the present application;

[0031] Figure 2 EDS image of the oxygen element in the modified lithium iron phosphate in Embodiment 1 of the present application;

[0032] Figure 3 EDS image of the iron element in the modified lithium iron phosphate in Embodiment 1 of the present application;

[0033] Figure 4 EDS image of the phosphorus element in the modified lithium iron phosphate in Embodiment 1 of the present application;

[0034] Figure 5 EDS image of the zinc element in the modified lithium iron phosphate in Embodiment 1 of the present application;

[0035] Figure 6 SEM image of the modified lithium iron phosphate in Embodiment 2 of the present application.

[0036] The implementation, functional features and advantages of the present application will be further described with reference to the drawings in combination with the embodiments. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be described and explained in combination with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. Based on the embodiments provided by the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application.

[0038] It is apparent that the following description is merely some examples or embodiments of the present application, and for those skilled in the art, the present application can also be applied to other similar situations without creative labor. In addition, it can be understood that although the efforts made in this development process can be complex and lengthy, some design, manufacture or production changes made on the basis of the disclosed technology of the present application are only routine technical means for those skilled in the art related to the disclosed content of the present application, and should not be understood as insufficient disclosure of the present application.

[0039] However, there will be cases of omission of unnecessary detailed description. For example, there are cases of omitting detailed description of well-known matters, repeated description of actually identical structures. This is to avoid the following description unnecessarily becoming lengthy, facilitating understanding by those skilled in the art. In addition, the following description is provided in order for those skilled in the art to fully understand the present application, and is not intended to limit the subject matter recited in the claims.

[0040] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0041] The first aspect of the embodiment of the present application provides a modified lithium iron phosphate, and the raw materials include lithium iron phosphate and zinc halide.

[0042] In the raw materials, the atomic percentage of zinc is 1% to 5% of the atomic percentage of iron.

[0043] The modified lithium iron phosphate provided by the embodiment of the present application contains zinc elements, which can improve the electronic conductivity of the modified lithium iron phosphate, enhance the lithium ion diffusion rate, and thus improve the rate performance of the material. It should be noted that in the lithium iron phosphate, the atomic ratio of lithium, iron and phosphorus is conventional in the art, and is not particularly limited in the embodiment of the present application, but as an example, the atomic ratio of lithium, iron and phosphorus is (1.05-2):1:1.

[0044] In some embodiments, the zinc halide is:

[0045] R1-Zn-R2;

[0046] Wherein, R1 is Cl, Br, alkyl, alkenyl, phenyl, halogenated alkyl, halogenated alkenyl or halogenated phenyl; R2 is Cl, Br, halogenated alkyl, halogenated alkenyl or halogenated phenyl.

[0047] In some embodiments, in R1, the alkyl is C 1~6 alkyl.

[0048] In some embodiments, C1~6 The alkyl groups are CH3-, CH3CH2-, CH3CH2CH2-, , CH3CH2CH2CH2- , One of them.

[0049] In some embodiments, in R1, the alkenyl group is C. 2~6 The alkenyl group.

[0050] In some embodiments, C 2~6 The alkenyl group is one of CH2=CH-, CH3CH=CH-, CH3CH2CH=CH-, CH3CH2CH2CH=CH-, CH3CH2CH2CH2CH=CH-, and CH3CH=CHCH2CH=CH-.

[0051] In some embodiments, in R1, the haloalkyl group is C1. 1~6 Monohaloalkyl or C 1~6 Dihaloalkyl.

[0052] In some embodiments, C 1~6 The monohalogenated alkyl groups are ClCH2-, ClCH2CH2-, ClCH2CH2CH2-, CH3CHClCH2-, , ClCH2CH2CH2CH2- , One of them.

[0053] In some embodiments, C 1~6 The dihaloalkyl is , , , , , , , , , One of them.

[0054] In some embodiments, the haloalkenyl group in R1 is C 2~6 Monohaloalkenyl.

[0055] In some embodiments, C 2~6 The monohaloalkenyl group is , , , One of them.

[0056] In some embodiments, in R1, the haloalkyl is a C1-C6 haloalkyl.

[0057] In some embodiments, in R2, the haloalkyl is a C1-C6 haloalkyl. 1~6 In some embodiments, in R2, the haloalkyl is a C1-C6 haloalkyl.

[0058] In some embodiments, in R2, the haloalkenyl is a C1-C6 haloalkenyl. 2~6 In some embodiments, in R2, the haloalkenyl is a C1-C6 haloalkenyl.

[0059] In some embodiments, in R2, the haloalkyl is a C1-C6 haloalkyl.

[0060] In some specific embodiments, the zinc halide is at least one of zinc chloride, zinc bromide, CH3-Zn-Cl, (CH3)2CHCH2ZnCl, C7H7ZnCl.

[0061] The second aspect of the embodiments of the present application provides a preparation method of the modified lithium iron phosphate as described above, comprising the following steps:

[0062] S10. Sintering the lithium iron phosphate and the zinc halide after mixing to obtain the modified lithium iron phosphate.

[0063] The preparation method of the modified lithium iron phosphate provided by the embodiments of the present application can prepare the modified lithium iron phosphate with a porous structure by sintering the lithium iron phosphate and the zinc halide after mixing, thereby shortening the diffusion path of Li + , improving the rate performance and cycle stability of the material. In addition, when the zinc halide contains a carbon element, the modified lithium iron phosphate obtained after sintering also contains carbon element doping.

[0064] In some embodiments, in the step S10 as described above, the preparation of the lithium iron phosphate comprises the following steps:

[0065] S101. Removing water after hydrothermal reaction of a lithium source, an iron source and a phosphorus source.

[0066] In some embodiments, in the step S101 as described above, the lithium source comprises at least one of lithium hydroxide, lithium chloride, lithium carbonate and lithium acetate.

[0067] In some embodiments, in the step S101 as described above, the iron source comprises at least one of ferrous sulfate, ferrous chloride, ferrous oxalate and ferrous phosphate.

[0068] In some embodiments, in the step S101 as described above, the phosphorus source comprises at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid and ferrous phosphate.

[0069] In some embodiments, in the step S101, the temperature of the hydrothermal reaction is 120-160°C.

[0070] In some embodiments, in the step S101, the time of the hydrothermal reaction is 12-24h.

[0071] In some embodiments, in the step S101, the step of removing water comprises: drying the product obtained from the hydrothermal reaction after filtration, and the drying temperature is 80-110°C.

[0072] In some embodiments, in the step S10, the step of sintering comprises:

[0073] After the temperature is raised to 750-800°C at a temperature raising rate of 8-15°C / min, the temperature is kept constant.

[0074] In the step of sintering, the temperature is raised at a temperature raising rate of 8-15°C / min, at low temperature, zinc is inserted (or further inserted) into the lithium iron phosphate crystal structure to form zinc doping; when the temperature is raised to 750-800°C and kept constant, the remaining free zinc halide sublimates from the system at high temperature, and the system is subjected to pore forming to form the pores of the system, thereby obtaining the porous modified lithium iron phosphate, and further shortening the diffusion path of Li + , improving the rate performance and cycle stability of the material.

[0075] In some embodiments, in the step of sintering, the time of keeping constant at 750-800°C is 2-6h.

[0076] In some other embodiments, a method for preparing the modified lithium iron phosphate is provided, comprising the following steps:

[0077] S11. After the lithium iron phosphate is subjected to surface treatment, the lithium iron phosphate is mixed with zinc halide and then sintered to obtain the modified lithium iron phosphate.

[0078] In the method for preparing the modified lithium iron phosphate, the surface treatment of the lithium iron phosphate can improve the compatibility between the lithium iron phosphate precursor and the carbon-containing zinc halide, thereby further improving the electrical conductivity and cycle stability of the modified lithium iron phosphate.

[0079] In some embodiments, in the step S11, the step of surface treatment comprises:

[0080] S111. The lithium iron phosphate is subjected to carbon coating treatment to obtain a first product.

[0081] S112. The first product is mixed with a silane coupling agent.

[0082] In the surface treatment step, the lithium iron phosphate is subjected to carbon coating treatment to obtain a first product, and then mixed with a silane coupling agent to activate the carbon-coated lithium iron phosphate. The compatibility between the surface-treated lithium iron phosphate and the organic zinc halide is improved, so that the modified lithium iron phosphate has higher conductivity and rate performance. It should be noted that the carbon coating is a conventional technology in the art, and in the embodiments of the present application, it is not particularly limited, but as an example, the chemical vapor deposition method can be used for carbon coating, and the carbon source is at least one of methane, ethane and propane.

[0083] In some embodiments, in the step S112, the mass ratio of the second product to the silane coupling agent is 1: (0.2-0.8).

[0084] In some embodiments, in the step S112, the silane coupling agent is KH-550.

[0085] The third aspect of the embodiments of the present application provides a positive electrode material, which comprises the modified lithium iron phosphate prepared by the preparation method provided by the embodiments of the present application.

[0086] The fourth aspect of the embodiments of the present application provides a battery comprising the positive electrode material provided by the embodiments of the present application.

[0087] The following will be further described with reference to specific embodiments.

[0088] In Example 2, the CAS number of CH3-Zn-Cl is 5158-46-3.

[0089] In Example 3, the CAS number of (CH3)2CHCH2ZnCl is 82510-93-8.

[0090] In Example 4, the CAS number of C7H7ZnCl is 90252-89-4.

[0091] Example 1

[0092] Example 1 provides a modified lithium iron phosphate, and the raw materials include lithium iron phosphate and zinc chloride.

[0093] In the raw materials, the atomic percentage of zinc is 1% of the atomic percentage of iron.

[0094] The present embodiment also provides a preparation method of the modified lithium iron phosphate, and the steps are as follows:

[0095] E11. mixing lithium chloride, ferrous chloride and phosphoric acid, and then performing hydrothermal reaction, filtering and drying to obtain lithium iron phosphate;

[0096] In the lithium chloride, ferrous chloride and phosphoric acid, the atomic ratio of lithium, iron and phosphorus is 1.05:1:1; the temperature of the hydrothermal reaction is 150°C, and the reaction time is 18h; and the drying temperature is 100°C.

[0097] E21. Lithium iron phosphate and zinc chloride are mixed to obtain a modified lithium iron phosphate precursor.

[0098] E31. The modified lithium iron phosphate precursor is heated to 750℃ at a heating rate of 10℃ / min under an argon atmosphere and then held for 6h to obtain a modified lithium iron phosphate.

[0099] Example 2

[0100] Example 2 provides a modified lithium iron phosphate, and the raw materials include lithium iron phosphate and CH3ZnCl.

[0101] In the raw materials, the atomic percentage of zinc is 3% of the atomic percentage of iron.

[0102] The example also provides a preparation method of the modified lithium iron phosphate, and the steps are as follows:

[0103] E12. Lithium acetate, ferrous oxalate and phosphoric acid are mixed and then subjected to a hydrothermal reaction, and then filtered and dried to obtain lithium iron phosphate.

[0104] Among the lithium acetate, ferrous oxalate and phosphoric acid, the atomic ratio of lithium, iron and phosphorus is 2:1:1; the temperature of the hydrothermal reaction is 190℃, and the reaction time is 16h; and the drying temperature is 80℃.

[0105] E22. The lithium iron phosphate is carbon-coated by a chemical vapor deposition method to obtain a first product.

[0106] Among them, the carbon source is methane.

[0107] E32. The first product is mixed with silane coupling agent KH-550 to obtain surface-treated lithium iron phosphate.

[0108] Among them, the mass ratio of the first product to KH-550 is 1:0.5.

[0109] E42. The surface-treated lithium iron phosphate is mixed with CH3CH2-Zn-Cl to obtain a modified lithium iron phosphate precursor.

[0110] E52. The modified lithium iron phosphate precursor is heated to 780℃ at a heating rate of 15℃ / min under an argon atmosphere and then held for 6h to obtain a modified lithium iron phosphate.

[0111] Example 3

[0112] Example 3 provides a modified lithium iron phosphate, and the raw materials include lithium iron phosphate and (CH3)2CHCH2ZnCl.

[0113] In the raw materials, the atomic percentage of zinc is 5% of the atomic percentage of iron.

[0114] The embodiment also provides a preparation method of the modified lithium iron phosphate, and the steps are as follows:

[0115] E13. Lithium acetate, ferrous oxalate and phosphoric acid are mixed and subjected to a hydrothermal reaction, and then filtered and dried to obtain lithium iron phosphate;

[0116] In the lithium acetate, ferrous oxalate and phosphoric acid, the atomic ratio of lithium, iron and phosphorus is 2:1:1; the temperature of the hydrothermal reaction is 200 DEG C, and the reaction time is 12 h; and the drying temperature is 110 DEG C.

[0117] E23. The lithium iron phosphate is coated with carbon by using a chemical vapor deposition method to obtain a first product;

[0118] In the method, the carbon source is ethane.

[0119] E33. The first product is mixed with silane coupling agent KH-550 to obtain the surface-treated lithium iron phosphate;

[0120] In the method, the mass ratio of the first product to KH-550 is 1:0.8.

[0121] E43. The surface-treated lithium iron phosphate is mixed with CH3CH2-Zn-CH2CH2Cl to obtain a modified lithium iron phosphate precursor.

[0122] E53. Under an argon atmosphere, the modified lithium iron phosphate precursor is heated to 800 DEG C at a heating rate of 8 DEG C / min and then kept for 2 h to obtain the modified lithium iron phosphate.

[0123] Example 4

[0124] Example 4 provides a modified lithium iron phosphate and a preparation method thereof, which are basically the same as those of Example 2, except that:

[0125] The zinc halide is C7H7ZnCl.

[0126] Comparative Example 1

[0127] Comparative Example 1 provides a preparation method of lithium iron phosphate, which comprises the following steps:

[0128] D11. The mixed solution is subjected to a hydrothermal reaction at 190 DEG C for 18 h;

[0129] In the method, the mixed solution contains lithium chloride, ferrous chloride, phosphoric acid and cetyltrimethylammonium bromide (CTAB), the mass fraction of CTAB is 1%, and the atomic ratio of lithium, iron and phosphorus is 1.5:1:1.

[0130] D21. The precipitate obtained by the hydrothermal reaction is collected by centrifugation, and the precipitate is washed with ethanol and water alternately for 3 times to remove residual CTAB.

[0131] D31. The washed precipitate was sintered at 750℃ for 6h to obtain lithium iron phosphate.

[0132] Comparative Example 2

[0133] Comparative Example 2 provides a preparation method of the modified lithium iron phosphate provided in Example 2, and the steps are basically the same as those in Example 2, except that:

[0134] In step E52, the modified lithium iron phosphate precursor is directly sintered at 780℃ for 6h.

[0135] In order to verify the progressiveness of the modified lithium iron phosphate and the preparation method thereof provided in the embodiments of the present application, taking Example 1 and Example 2 as examples, the modified lithium iron phosphate prepared in Example 1 and Example 2 was scanned by a scanning electron microscope, and the corresponding SEM images as shown in Figure 1 and Figure 6 were obtained, and the EDS element analysis of the modified lithium iron phosphate of Example 1 was performed to obtain the EDS element spectrum as shown in Figures 2-5 . The content of each element is shown in Table 1.

[0136] Table 1

[0137]

[0138] The modified lithium iron phosphate or lithium iron phosphate provided in the examples and comparative examples was then detected after being made into button cells. Among them,

[0139] 1. The assembly steps of the button cell are as follows:

[0140] (1) Positive electrode sheet: lithium iron phosphate / modified lithium iron phosphate, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:5:5, N-methyl pyrrolidone (NMP) was used as the solvent, and the slurry was uniformly coated on an aluminum foil. After drying, it was compacted and vacuum dried at 120℃ for 12h to obtain a positive electrode sheet, and the active material mass of the positive electrode sheet was 12mg.

[0141] (2) Negative electrode sheet: the negative electrode was a metal lithium sheet.

[0142] (3) The separator was a polypropylene porous membrane, and the electrolyte was lmol / L LiPF6 / EC+DEC+DMC (EC:DEC:DMC=1:1:1 by volume).

[0143] EC: Ethylene Carbonate, carbonic acid ethylene ester;

[0144] DEC: Diethyl Carbonate, carbonic acid diethyl ester;

[0145] DMC: Dimethyl Carbonate, dimethyl carbonate.

[0146] Table 2

[0147]

[0148] From the above table and the description of the drawings, at least the following conclusions can be drawn:

[0149] (1) In Table 2, Examples 1-4 and Comparative Example 1 can be compared to see that the modified lithium iron phosphate provided by the examples of the present application has excellent electrical conductivity, cycle stability and rate performance, with zinc halide acting as both a zinc source for doping and a pore-forming agent.

[0150] (2) In Table 2, Example 1 and Comparative Example 2 can be compared to see that the preparation method of the modified lithium iron phosphate provided by the examples of the present application can make zinc chloride at low temperature zinc-embedded into the lithium iron phosphate crystal structure to form zinc doping, and the remaining free zinc halide is removed from the system at high temperature of 750-800°C, thereby shortening the diffusion path of Li + , improving the rate performance and cycle stability of the material.

[0151] (3) In Table 2, Example 1 can be compared with Examples 2-4 to see that the selection of zinc halide containing carbon-containing organic matter can further improve the electrical conductivity, cycle stability and rate performance of the modified lithium iron phosphate.

[0152] (4) From the description of the drawings and Table 1, it can be seen that the modified lithium iron phosphate provided by the examples of the present application has a rich porous structure and is doped with zinc elements.

[0153] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A modified lithium iron phosphate characterized in that, The raw material includes lithium iron phosphate and zinc halide; In the raw material, the atomic percentage of zinc is 1% to 5% of the atomic percentage of iron; The preparation method of the modified lithium iron phosphate includes the following steps: After the lithium iron phosphate is surface treated, the lithium iron phosphate is mixed with the zinc halide and then sintered to obtain the modified lithium iron phosphate; The step of surface treatment includes: after the lithium iron phosphate is carbon-coated, a first product is obtained; and the first product is mixed with a silane coupling agent; The mass ratio of the first product to the silane coupling agent is 1:0.2 to 0.8; The step of sintering includes: heating at a heating rate of 8°C / min to 15°C / min to 750°C to 800°C and then holding; The zinc halide is: R1-Zn-R2; wherein R1 is alkyl, alkenyl, phenyl, haloalkyl, haloalkenyl or halophenyl; and R2 is Cl, Br, haloalkyl, haloalkenyl or halophenyl.

2. The modified lithium iron phosphate of claim 1, wherein, The R1 satisfies any one of the following characteristics (1) to (5): (1) alkyl is C 1~6 alkyl; (2) the alkenyl group is a C 2~6 alkenyl group of C (3) haloalkyl is C 1~6 haloalkyl or C 1~6 haloalkyl; (4) haloalkenyl is C 2~6 haloalkenyl; (5) the halophenyl is monohalophenyl, ortho-dihalophenyl, meta-dihalophenyl or para-dihalophenyl.

3. The modified lithium iron phosphate of claim 1 or 2, wherein, The R2 satisfies any one of the following characteristics (1) to (3): (1) haloalkyl is C 1~6 haloalkyl or dihaloalkyl; (2) haloalkenyl is C 2~6 haloalkenyl; (3) the halophenyl is monohalophenyl, ortho-dihalophenyl, meta-dihalophenyl or para-dihalophenyl.

4. A method for preparing modified lithium iron phosphate, characterized by, A preparation method of the modified lithium iron phosphate as claimed in any one of claims 1 to 3 includes the following steps: After the lithium iron phosphate is surface treated, the lithium iron phosphate is mixed with the zinc halide and then sintered to obtain the modified lithium iron phosphate; The step of surface treatment includes: after the lithium iron phosphate is carbon-coated, a first product is obtained; and the first product is mixed with a silane coupling agent; The mass ratio of the first product to the silane coupling agent is 1:0.2 to 0.8; The step of sintering includes: heating at a heating rate of 8°C / min to 15°C / min to 750°C to 800°C and then holding.

5. The method of claim 4, wherein the modified lithium iron phosphate is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphoric acid; and heating the mixture at a temperature of 600 to 800°C for 6 to 24 hours. The holding time is 2h to 6h.

6. A positive electrode material, characterized by, The modified lithium iron phosphate prepared by the preparation method as claimed in any one of claims 4 to 5.

7. A battery, characterized by The positive electrode material as claimed in claim 6.

8. Use of the modified lithium iron phosphate prepared by the preparation method as claimed in any one of claims 4 to 5 in the field of battery materials.

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