Lithium iron phosphate with high compacted density and preparation method thereof

Abstract

The application belongs to the technical field of lithium battery positive electrode materials, and provides a high-pressing-density lithium iron phosphate and a preparation method thereof, the preparation method comprising the following steps: step 1, adding pretreated polyvinyl alcohol into deionized water, heating to 80-85 DEG C, stirring, adjusting the pH value to 10.5-11.0, adding epichlorohydrin to react, adding aniline to continue to react, cooling, adjusting the pH value to 1-2, adding ammonium persulfate to react, and obtaining modified polyvinyl alcohol after dialysis and impurity removal; step 2, adding a lithium source, an iron source and a phosphorus source into deionized water to mix, drying after ball milling to obtain a lithium iron phosphate precursor; step 3, placing the lithium iron phosphate precursor into a tube furnace, adding an inorganic carbon source, heating to react, cooling and crushing to obtain primary sintered lithium iron phosphate; and step 4, mixing the primary sintered lithium iron phosphate and the modified polyvinyl alcohol, and placing them into a tube furnace to heat to react, cool and crush to obtain lithium iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery cathode material technology, specifically relating to a high-density lithium iron phosphate and its preparation method. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is one of the mainstream cathode materials for lithium-ion batteries on the market. Compared with other cathode materials, such as lithium cobalt oxide and ternary cathode materials, lithium iron phosphate cathode materials have advantages such as low price, non-toxicity, and environmental friendliness. Moreover, they have excellent safety performance and cycle stability, and have great application prospects in the fields of power and energy storage.

[0003] However, current battery systems composed of lithium iron phosphate (LFP) have relatively low energy density, resulting in short driving range and limiting their application in power batteries. To improve the energy density of LFP batteries, it is necessary to increase the capacity, voltage plateau, or compaction density of LFP. The compaction density of LFP directly affects the battery's energy density and volumetric energy density. Compaction density is not only affected by the material's microstructure but also closely related to the particle size and gradation. Therefore, improving its compaction density is key to improving battery performance. Generally, the smaller the particle size of a material, the higher its packing density. However, for LFP, smaller particle sizes result in a larger specific surface area, making processing more difficult and often requiring secondary granulation to reduce the specific surface area. Furthermore, when slightly larger, uniformly sized spheres are stacked, there are numerous voids between the spheres. If suitable small-diameter particles are not used to fill these voids, the packing density will be very low.

[0004] Therefore, it is of great significance to develop a lithium iron phosphate with high compaction density, simple preparation method, and good performance, as well as its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a high-density lithium iron phosphate and its preparation method, so as to solve the technical problem of low energy density of lithium iron phosphate cathode materials in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] The first aspect of this invention provides a method for preparing high-density lithium iron phosphate, comprising the following steps:

[0008] Step 1: Add polyvinyl alcohol, urea and dicyandiamide to dimethyl sulfoxide, raise the temperature to 95-100℃, stir until completely dissolved, add phytic acid solution, continue to raise the temperature to 105-110℃, continue stirring for 3-5 hours, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol.

[0009] Pretreated polyvinyl alcohol was added to deionized water, heated to 80-85℃, stirred until completely dissolved, and the pH was adjusted to 10.5-11.0. Epichlorohydrin was added and reacted for 1.0-1.5 h. Aniline was added and the reaction continued for 1.5-2 h. The mixture was cooled to 0℃, the pH was adjusted to 1-2, and ammonium persulfate was added and reacted for 24-28 h. After dialysis to remove impurities, modified polyvinyl alcohol was obtained.

[0010] Step 2: Add lithium source, iron source and phosphorus source to deionized water and mix. After ball milling and drying, lithium iron phosphate precursor is obtained.

[0011] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add an inorganic carbon source, heat up to react, cool, crush to obtain primary sintered lithium iron phosphate.

[0012] Step 4: After mixing the once-sintered lithium iron phosphate and modified polyvinyl alcohol, place them in a tube furnace under a nitrogen protective atmosphere, heat up to react, cool, and crush to obtain lithium iron phosphate.

[0013] As a further embodiment of the present invention, the ratio of pretreatment polyvinyl alcohol, deionized water, epichlorohydrin, aniline and ammonium persulfate is 9.8-10.2g:100mL:0.5-1.0g:3.0-3.2g:2.4-3.0g.

[0014] As a further embodiment of the present invention, the ratio of polyvinyl alcohol, urea, dicyandiamide, dimethyl sulfoxide and phytic acid solution is 3.0-3.2g: 1.78-1.80g: 0.70-0.72g: 100mL: 5.0-5.5mL; the phytic acid solution is 50wt%.

[0015] As a further embodiment of the present invention, the molar ratio of lithium source, iron source and phosphorus source in step 2 is 1:1:1; the lithium source in step 2 is one of lithium carbonate, lithium hydroxide, lithium sulfate and lithium nitrate; the iron source is one of ferrous sulfate, ferrous nitrate and ferrous chloride; and the phosphorus source is one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate and potassium dihydrogen phosphate.

[0016] As a further aspect of the present invention, the amount of inorganic carbon source used in step 3 is 2-5 wt% of the lithium iron phosphate precursor; the inorganic carbon source is at least one of graphene and carbon nanotubes. During high-temperature calcination, the inorganic carbon source can directly contact lithium iron phosphate to form a conductive network, thereby significantly improving the material's conductivity. Simultaneously, during sintering, it can inhibit the excessive growth and agglomeration of lithium iron phosphate particles, thus maintaining the material's uniformity and small particle size, which helps reduce the length of the lithium-ion diffusion path and improve the battery's charge-discharge performance.

[0017] As a further embodiment of the present invention, in step 3, the temperature is raised to 660-680°C and the reaction is maintained for 12-14 hours; the heating rate is 8-10°C / min.

[0018] As a further embodiment of the present invention, in step 4, the temperature is raised to 700-730°C and the reaction is maintained for 15-18 hours; the heating rate is 16-20°C / min.

[0019] As a further embodiment of the present invention, the amount of modified polyvinyl alcohol used in step 4 is 2 to 5 wt% of the lithium iron phosphate sintered in one step.

[0020] The second aspect of the present invention provides a high-density lithium iron phosphate obtained by the preparation method described in the first aspect above.

[0021] The beneficial effects of this invention are:

[0022] This invention provides a method for preparing high-density lithium iron phosphate. By improving the carbon source and sintering process, an inorganic carbon source is used as the primary coating carbon source, and modified polyvinyl alcohol is used as the secondary coating carbon source, combined with a secondary sintering method to synthesize a high-density lithium manganese iron phosphate cathode material. Specifically, the method includes the following steps: First, a lithium iron phosphate precursor is prepared and then sintered with an inorganic carbon source. The introduction of the inorganic carbon source can significantly improve the conductivity of the lithium iron phosphate material, but its coating uniformity is poor, resulting in uneven particle size. Although this non-uniform coating is beneficial to improving the compaction density, small particles are prone to agglomeration. Agglomeration reduces the effective contact area between the cathode material and the electrolyte, thus leading to poor electrochemical performance. Therefore, this invention further adds modified polyvinyl alcohol for secondary sintering. Secondary sintering allows for secondary grain growth, and the formed film-like coating carbon layer can maintain uniform coating while having a low specific surface area, reducing the agglomeration of small particles and thus improving the compaction density of the lithium iron phosphate material. Meanwhile, modified polyvinyl alcohol, as a secondary carbon source, can effectively coat the surface of lithium iron phosphate material, thereby effectively suppressing side reactions between the material and the electrolyte, improving cycle performance, and finally preparing lithium iron phosphate material with high compaction density.

[0023] Polyvinyl alcohol (PVA) exhibits excellent film-forming properties. When used as a carbon source, its film-like carbon coating can ensure uniform coating on the material surface while possessing a low specific surface area, thus effectively improving the compaction density of lithium iron phosphate materials. However, PVA itself has poor electrical conductivity. Therefore, this invention uses phytic acid and polyaniline to modify PVA to improve its conductivity. First, PVA is reacted with phytic acid, utilizing the strong hydrogen bonds between the C-OH groups on the PVA molecular chain and the P=O groups on the phytic acid molecules to prepare pretreated PVA. Then, polyaniline is grafted onto the pretreated PVA using epichlorohydrin, effectively improving its conductivity. Furthermore, the modified PVA contains P and N elements, with P having a higher electron-donating ability, thereby promoting electronic conductivity and improving bonding stability. Simultaneously, the high specific surface area generated by the PC bonds formed after P doping the carbon layer helps to improve the graphitization level of the carbon layer, resulting in excellent electrochemical performance. N can effectively inhibit the growth and aggregation of lithium iron phosphate nanoparticles, thereby improving cycle stability.

[0024] The preparation method provided by this invention is simple and highly operable, and can effectively improve the compaction density of lithium iron phosphate cathode material, thereby effectively improving the energy density of lithium iron phosphate cathode material and broadening the application range of lithium iron phosphate material. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, modifications to design, manufacturing, or production based on the disclosed technical content are merely conventional technical means and should not be construed as insufficient disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Moreover, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0027] Example 1

[0028] This embodiment provides a method for preparing high-density lithium iron phosphate, including the following steps:

[0029] Step 1: Add 3.0g polyvinyl alcohol, 1.78g urea and 0.70g dicyandiamide to 100mL dimethyl sulfoxide, raise the temperature to 100℃, stir until completely dissolved, add 5.0mL phytic acid solution (50wt%), continue to raise the temperature to 110℃, continue to stir for 3-5h, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol;

[0030] Add 9.8g of pretreated polyvinyl alcohol to 100mL of deionized water, heat to 80℃, stir until completely dissolved, adjust the pH to 11.0, add 0.5g of epichlorohydrin and react for 1.0h, add 3.0g of aniline and continue the reaction for 1.5h, cool to 0℃, adjust the pH to 1, add 2.4g of ammonium persulfate and react for 24h, and obtain modified polyvinyl alcohol after dialysis to remove impurities;

[0031] Step 2: Lithium carbonate, ferrous sulfate and ammonium dihydrogen phosphate are added to deionized water in a molar ratio of 1:1:1 and mixed. After ball milling and drying, lithium iron phosphate precursor is obtained.

[0032] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add graphene (2 wt% of the lithium iron phosphate precursor), heat to 660℃ at 8℃ / min, hold for 14h, cool naturally to room temperature, and crush to obtain primary sintered lithium iron phosphate.

[0033] Step 4: Mix the primary sintered lithium iron phosphate and modified polyvinyl alcohol (2 wt% of the primary sintered lithium iron phosphate), place them in a tube furnace under a nitrogen protective atmosphere, heat to 700℃ at 16℃ / min, hold for 18h, cool naturally to room temperature, and crush to obtain lithium iron phosphate.

[0034] The high-density lithium iron phosphate is prepared through the above steps.

[0035] Example 2

[0036] The only difference from Example 1 is step 1:

[0037] Step 1: Add 3.2g polyvinyl alcohol, 1.80g urea and 0.72g dicyandiamide to 100mL dimethyl sulfoxide, raise the temperature to 100℃, stir until completely dissolved, add 5.5mL phytic acid solution (50wt%), continue to raise the temperature to 110℃, continue stirring for 3-5h, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol;

[0038] Add 9.8g of pretreated polyvinyl alcohol to 100mL of deionized water, heat to 80℃, stir until completely dissolved, adjust the pH to 11.0, add 0.5g of epichlorohydrin and react for 1.0h, add 3.0g of aniline and continue the reaction for 1.5h, cool to 0℃, adjust the pH to 1, add 2.4g of ammonium persulfate and react for 24h, and obtain modified polyvinyl alcohol after dialysis to remove impurities;

[0039] Example 3

[0040] The only difference from Example 1 is step 1:

[0041] Step 1: Add 3.0g polyvinyl alcohol, 1.78g urea and 0.70g dicyandiamide to 100mL dimethyl sulfoxide, raise the temperature to 100℃, stir until completely dissolved, add 5.0mL phytic acid solution (50wt%), continue to raise the temperature to 110℃, continue to stir for 3-5h, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol;

[0042] 10.2 g of pretreated polyvinyl alcohol was added to 100 mL of deionized water, heated to 80 °C, stirred until completely dissolved, the pH was adjusted to 11.0, 1.0 g of epichlorohydrin was added and reacted for 1.0 h, 3.2 g of aniline was added and the reaction continued for 1.5 h, cooled to 0 °C, the pH was adjusted to 1, 3.0 g of ammonium persulfate was added and reacted for 24 h, and after dialysis to remove impurities, modified polyvinyl alcohol was obtained.

[0043] Example 4

[0044] The only difference from Example 1 is step 1:

[0045] Step 1: Add 3.0g polyvinyl alcohol, 1.79g urea and 0.71g dicyandiamide to 100mL dimethyl sulfoxide, raise the temperature to 100℃, stir until completely dissolved, add 5.3mL phytic acid solution (50wt%), continue to raise the temperature to 110℃, continue to stir for 3-5h, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol;

[0046] Add 10.0g of pretreated polyvinyl alcohol to 100mL of deionized water, heat to 80℃, stir until completely dissolved, adjust the pH to 11.0, add 0.75g of epichlorohydrin and react for 1.0h, add 3.1g of aniline and continue the reaction for 1.5h, cool to 0℃, adjust the pH to 1, add 2.7g of ammonium persulfate and react for 24h, and obtain modified polyvinyl alcohol after dialysis to remove impurities;

[0047] Example 5

[0048] The only difference from Example 1 is step 3:

[0049] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add graphene (4.5 wt% of the lithium iron phosphate precursor), heat to 660°C at 8°C / min, hold for 14 hours, self-cool to room temperature, and crush to obtain primary sintered lithium iron phosphate.

[0050] Example 6

[0051] The only difference from Example 1 is step 3:

[0052] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add graphene (2wt% of the lithium iron phosphate precursor), heat to 680℃ at 10℃ / min, hold for 12h, self-cool to room temperature, and crush to obtain primary sintered lithium iron phosphate.

[0053] Example 7

[0054] The only difference from Example 1 is step 4:

[0055] Step 4: Mix the primary sintered lithium iron phosphate and modified polyvinyl alcohol (4.8 wt% of the primary sintered lithium iron phosphate), place them in a tube furnace under a nitrogen protective atmosphere, heat to 700℃ at 16℃ / min, hold for 18h, cool naturally to room temperature, and crush to obtain lithium iron phosphate.

[0056] Example 8

[0057] The only difference from Example 1 is step 4:

[0058] Step 4: Mix the primary sintered lithium iron phosphate and modified polyvinyl alcohol (2 wt% of the primary sintered lithium iron phosphate), place them in a tube furnace under a nitrogen protective atmosphere, heat to 730℃ at 20℃ / min, hold for 15h, cool naturally to room temperature, and crush to obtain lithium iron phosphate.

[0059] Comparative Example 1

[0060] The only difference from Example 1 is that graphene is not added in step 3:

[0061] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, heat it to 660℃ at 8℃ / min, hold it at that temperature for 14h, cool it naturally to room temperature, and crush it to obtain primary sintered lithium iron phosphate.

[0062] Comparative Example 2

[0063] The only difference from Example 1 is that modified polyvinyl alcohol is not added in step 4:

[0064] Step 4: Place the once-sintered lithium iron phosphate in a tube furnace under a nitrogen protective atmosphere, heat it to 700℃ at a rate of 16℃ / min, hold it at that temperature for 18 hours, let it cool naturally to room temperature, and then crush it to obtain lithium iron phosphate.

[0065] Comparative Example 3

[0066] The only difference from Example 1 is that the modified polyvinyl alcohol obtained in step 1 is replaced with polyvinyl alcohol:

[0067] Step 1: Lithium carbonate, ferrous sulfate and ammonium dihydrogen phosphate are added to deionized water in a molar ratio of 1:1:1 and mixed. After ball milling and drying, lithium iron phosphate precursor is obtained.

[0068] Step 2: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add graphene (2 wt% of the lithium iron phosphate precursor), heat to 660℃ at 8℃ / min, hold for 14h, cool naturally to room temperature, and crush to obtain primary sintered lithium iron phosphate.

[0069] Step 3: Mix the primary sintered lithium iron phosphate and polyvinyl alcohol (2 wt% of the primary sintered lithium iron phosphate), place them in a tube furnace under a nitrogen protective atmosphere, heat to 700℃ at 16℃ / min, hold for 18h, cool naturally to room temperature, and crush to obtain lithium iron phosphate.

[0070] Comparative Example 4

[0071] The only difference from Example 1 is step 1:

[0072] Step 1: Add 2.8g polyvinyl alcohol, 1.78g urea and 0.70g dicyandiamide to 100mL dimethyl sulfoxide, raise the temperature to 100℃, stir until completely dissolved, add 5.0mL phytic acid solution (50wt%), continue to raise the temperature to 110℃, continue stirring for 3-5h, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol;

[0073] Add 9.8g of pretreated polyvinyl alcohol to 100mL of deionized water, heat to 80℃, stir until completely dissolved, adjust the pH to 11.0, add 0.5g of epichlorohydrin and react for 1.0h, add 3.0g of aniline and continue the reaction for 1.5h, cool to 0℃, adjust the pH to 1, add 2.4g of ammonium persulfate and react for 24h, and obtain modified polyvinyl alcohol after dialysis to remove impurities.

[0074] Comparative Example 5

[0075] The only difference from Example 1 is step 1:

[0076] Step 1: Add 3.0g polyvinyl alcohol, 1.78g urea and 0.70g dicyandiamide to 100mL dimethyl sulfoxide, raise the temperature to 100℃, stir until completely dissolved, add 5.0mL phytic acid solution (50wt%), continue to raise the temperature to 110℃, continue to stir for 3-5h, precipitate, filter and wash, and vacuum dry to obtain pretreated polyvinyl alcohol;

[0077] Add 9.5g of pretreated polyvinyl alcohol to 100mL of deionized water, heat to 80℃, stir until completely dissolved, adjust the pH to 11.0, add 0.5g of epichlorohydrin and react for 1.0h, add 3.0g of aniline and continue the reaction for 1.5h, cool to 0℃, adjust the pH to 1, add 2.4g of ammonium persulfate and react for 24h, and obtain modified polyvinyl alcohol after dialysis to remove impurities.

[0078] Comparative Example 6

[0079] The only difference from Example 1 is step 2:

[0080] Step 2: Lithium carbonate, ferrous sulfate and ammonium dihydrogen phosphate are added to deionized water in a molar ratio of 1.1:1:1 and mixed. After ball milling and drying, lithium iron phosphate precursor is obtained.

[0081] Comparative Example 7

[0082] The only difference from Example 1 is step 3:

[0083] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add graphene (1 wt% of the lithium iron phosphate precursor), heat to 660℃ at 8℃ / min, hold for 14h, cool naturally to room temperature, and crush to obtain primary sintered lithium iron phosphate.

[0084] Comparative Example 8

[0085] The only difference from Example 1 is step 3:

[0086] Step 3: Place the lithium iron phosphate precursor in a tube furnace under a nitrogen protective atmosphere, add graphene (2 wt% of the lithium iron phosphate precursor), heat to 630℃ at 8℃ / min, hold for 14h, cool naturally to room temperature, and crush to obtain primary sintered lithium iron phosphate.

[0087] Comparative Example 9

[0088] The only difference from Example 1 is step 4:

[0089] Step 4: Mix the primary sintered lithium iron phosphate and modified polyvinyl alcohol (1 wt% of the primary sintered lithium iron phosphate), place them in a tube furnace under a nitrogen protective atmosphere, heat to 700℃ at 16℃ / min, hold for 18h, cool naturally to room temperature, and crush to obtain lithium iron phosphate.

[0090] Comparative Example 10

[0091] The only difference from Example 1 is step 4:

[0092] Step 4: Mix the primary sintered lithium iron phosphate and modified polyvinyl alcohol (2 wt% of the primary sintered lithium iron phosphate), place them in a tube furnace under a nitrogen protective atmosphere, heat to 680℃ at 16℃ / min, hold for 18h, cool naturally to room temperature, and crush to obtain lithium iron phosphate.

[0093] The following application performance tests were conducted on Examples 1-8 and Comparative Examples 1-10:

[0094] The lithium iron phosphate obtained in the examples and comparative examples was used to prepare lithium-ion batteries. Specifically, 800g of lithium iron phosphate obtained in the examples or comparative examples, 100g of conductive agent acetylene black, and 100g of binder polyvinylidene fluoride (PVDF) were added to 800g of N-methylpyrrolidone solution (NMP solution), and stirred in a vacuum mixer for 2 hours to obtain a positive electrode slurry. The slurry was uniformly coated on aluminum foil, then dried in a vacuum drying oven at 120°C for 12 hours, and then cut into 14mm diameter discs as positive electrode sheets. The positive electrode sheet, negative electrode sheet (14.5mm diameter lithium metal sheet), separator (Celgard 2400 microporous polypropylene membrane), and electrolyte (1mol / L LiPF6 / EC+DMC (volume ratio 1:1)) were assembled into CR2025 type coin-type lithium-ion batteries in a hydrogen-filled glove box. The electrochemical performance of the prepared lithium-ion batteries was tested; the test results are shown in Table 1.

[0095] Table 1

[0096]

[0097] As can be seen from Table 1, compared with the lithium iron phosphate prepared in Comparative Examples 1-10, the lithium iron phosphate prepared in Examples 1-8 of this invention has a higher compaction density, a larger initial discharge specific capacity, and better battery cycle performance. This shows that the method for preparing high compaction density lithium iron phosphate provided in this invention produces lithium iron phosphate with excellent compaction density and electrochemical performance. Moreover, the preparation method is simple, easy to operate, and broadens the application range of lithium iron phosphate materials.

[0098] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0099] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. 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 rules of this application.

[0100] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0101] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions, and all technical features and optional technical features of this application can be combined to form new technical solutions.

[0102] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing a high-density lithium iron phosphate, characterized by, Comprising the following steps: Step 1, polyvinyl alcohol, urea and dicyandiamide are added into dimethyl sulfoxide, raised to 95-100℃, stirred until completely dissolved, add phytic acid solution, continue to warm to 105-110℃, continue to stir for 3-5h, precipitate, suction filtration and washing, vacuum drying to obtain pretreated polyvinyl alcohol; wherein the amount ratio of polyvinyl alcohol, urea, dicyandiamide, dimethyl sulfoxide and phytic acid solution is 3.0-3.2g:1.78-1.80g:0.70-0.72g:100mL:5.0-5.5mL; the phytic acid solution is 50wt%; The pretreated polyvinyl alcohol is added into deionized water, heated to 80-85℃, stirred, the pH value is adjusted to 10.5-11.0, epoxy chloropropane is added for reaction, aniline is added for further reaction, cooled, the pH value is adjusted to 1-2, ammonium persulfate is added for reaction, after dialysis and impurity removal, the modified polyvinyl alcohol is obtained; wherein the amount ratio of pretreated polyvinyl alcohol, deionized water, epoxy chloropropane, aniline and ammonium persulfate is 9.8-10.2g:100mL:0.5-1.0g:3.0-3.2g:2.4-3.0g Step 2, lithium source, iron source and phosphorus source are added into deionized water for mixing, after ball milling and drying, the lithium iron phosphate precursor is obtained; Step 3, the lithium iron phosphate precursor is placed in a tube furnace, inorganic carbon source is added, the amount of inorganic carbon source is 2-5wt% of the lithium iron phosphate precursor, heated for reaction, cooled, broken to obtain primary sintered lithium iron phosphate; wherein the inorganic carbon source is at least one of graphene and carbon nanotube; Step 4, the primary sintered lithium iron phosphate and the modified polyvinyl alcohol are mixed, the amount of modified polyvinyl alcohol is 2-5wt% of the primary sintered lithium iron phosphate, placed in a tube furnace, heated for reaction, cooled, broken to obtain lithium iron phosphate.

2. The method of claim 1, wherein the lithium iron phosphate has a high tap density. The amount ratio of lithium source, iron source and phosphorus source in step 2 is 1:1:1; the lithium source in step 2 is one of lithium carbonate, lithium hydroxide, lithium sulfate and lithium nitrate; the iron source is one of ferrous sulfate, ferrous nitrate and ferrous chloride; the phosphorus source is one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate and potassium dihydrogen phosphate.

3. The method of claim 1, wherein the lithium iron phosphate has a high tap density. In step 3, the temperature is raised to 660-680℃, and the reaction is kept for 12-14h; the heating rate is 8-10℃ / min.

4. The method of claim 1, wherein the lithium iron phosphate has a high tap density. In step 4, the temperature is raised to 700-730℃, and the reaction is kept for 15-18h; the heating rate is 16-20℃ / min.

5. A high tap density lithium iron phosphate characterized in that, A high compaction density lithium iron phosphate is prepared by the preparation method of any one of claims 1-4. A high compaction density lithium iron phosphate is prepared by the preparation method of any one of claims 1-4.

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