Iron phosphate material, and preparation method therefor and use thereof

Abstract

The present disclosure provides an iron phosphate material, and a preparation method therefor and a use thereof. The method comprises the following steps: mixing a solution of a temperature-sensitive polymer having an upper critical solution temperature, a solution containing an iron source, and a solution containing a phosphorus source to obtain a mixed solution; carrying out gelation treatment on the mixed solution, then adding an alkali liquid, adjusting the pH value until the solution is acidic, and heating to obtain a precipitate; carrying out aging reaction on the precipitate together with a phosphoric acid solution to obtain a precursor material; and carrying out calcination treatment on the precursor material to obtain the iron phosphate material. In the present disclosure, by introducing the temperature-sensitive polymer, a thermo-responsive reversible sol-gel is prepared as a medium to fractionate and distribute the alkaline precipitant, so as to achieve uniform diffusion of the precipitant, avoid the problems of excess local concentration and poor product uniformity, and suppress movement of nanoparticles, thereby preventing agglomeration of iron phosphate particles.

Description

A kind of iron phosphate material and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of iron phosphate materials, and particularly relates to an iron phosphate material and a preparation method and application thereof. Background Art

[0002] As a type of energy storage device, lithium-ion secondary batteries offer advantages such as high capacity, high voltage, high cycle performance, and high energy density, making them widely used in electric vehicles, smart grids, and portable electronics. In the past two years, lithium iron phosphate (LiFePO4) cathode materials have experienced rapid development and rapid upgrades, leading to a corresponding increase in the price of the raw material used in their production. As one of the precursor materials for preparing LiFePO4 cathode materials, the morphology and quality of the synthesized iron phosphate affect the electrochemical performance of LiFePO4 battery systems.

[0003] At present, the commonly used preparation method of iron phosphate is coprecipitation, which belongs to the liquid phase method. The coprecipitation method not only has a short reaction time, but also has a uniform mixing of raw materials. The specific principle is to add a precipitant to completely precipitate the product precursor required in the mixed solution. Most of the iron phosphate preparation processes disclosed in the prior art use alkali solution as a precipitant to adjust the pH value of the system. However, when the alkali solution is added dropwise, it often causes excessive local concentration and instantaneous nucleation, resulting in excessive crystal growth rate. At the same time, the surrounding impurity ions will be wrapped in it for precipitation, which in turn causes the problem of poor product uniformity.

[0004] To address these issues, CN116216677A discloses a saturated β-cyclodextrin / NaOH solution. This solution utilizes the slow and stable release of hydroxide ions, effectively avoiding transient localized overconcentrations and poor product uniformity. However, this preparation process still requires freshly prepared saturated solution each time the pH is adjusted, increasing process time and costs.

[0005] Therefore, in this field, there is an urgent need to develop a sustainable regeneration method to solve the problem of excessive local concentration of precipitant in the co-precipitation method.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] In response to the shortcomings of the prior art, the present disclosure aims to provide an iron phosphate material, a preparation method, and an application thereof. The present disclosure provides a method for resolving the problem of excessive local concentration caused by the addition of a precipitant during the co-precipitation process for preparing the iron phosphate material. By introducing a temperature-sensitive polymer, a heat-responsive reversible sol-gel is prepared as a medium to subdivide and divert the alkaline precipitant, thereby achieving uniform diffusion of the precipitant, avoiding the problems of excessive local concentration and poor product uniformity, and inhibiting the movement of nanoparticles, thereby preventing the agglomeration of the iron phosphate particles.

[0009] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, the present disclosure provides a method for preparing an iron phosphate material, the method comprising the following steps:

[0011] mixing a solution of a thermosensitive polymer having an upper critical solution temperature, a solution containing an iron source, and a solution containing a phosphorus source to obtain a mixed solution;

[0012] The mixed solution is subjected to gelation treatment, and then an alkali solution is added to adjust the pH value to acidic, and a precipitate is obtained after heating;

[0013] The precipitate and the phosphoric acid solution are subjected to an aging reaction to obtain a precursor material; and the precursor material is subjected to a calcination treatment to obtain the iron phosphate material.

[0014] The present invention combines sol-gel and coprecipitation methods to quickly prepare highly dispersible iron phosphate materials by introducing a thermosensitive polymer with an upper critical solution temperature (UCST). UCST-type thermosensitive polymers can achieve reversible transformations of sol and gel at different temperatures. When the temperature is lower than the UCST temperature, it is a semisolid gel, and when the temperature is higher than the UCST temperature, it is a sol liquid with strong fluidity. When the raw materials for the preparation of iron phosphate and the thermosensitive polymer are uniformly mixed into a gel at a temperature lower than the UCST temperature, the polymer has a porous structure and framework characteristics. The added alkali solution precipitant can be subdivided and shunted by the pores on the surface of the gel, thereby achieving uniform diffusion of the precipitant, avoiding the situation in which impurity precipitation is generated due to excessive local concentration caused by the addition of a precipitant in the traditional sense. When the temperature is then raised again, the gel will become a sol liquid, and the iron phosphate begins to coprecipitate.

[0015] In addition, after the temperature is raised, the swelling rate of the thermosensitive polymer due to polymer disassociation increases, and the polymer after becoming a sol liquid can inhibit the movement of nanoparticles, thereby preventing the agglomeration of iron phosphate particles. The sol-gel method disclosed in the prior art can prepare highly dispersed iron phosphate, but it requires a long time of gel drying and calcination, so the process time is prolonged; the coprecipitation method disclosed in the prior art can obtain the iron phosphate product quickly but it is easy to agglomerate, and the alkali solution is easy to cause excessive local concentration when added, resulting in uneven distribution problems, thereby affecting the consistency and stability of the product morphology. Based on the above situation, the present disclosure combines the above two methods to learn from each other's strengths and weaknesses, and the thermosensitive polymer can be recycled and reused due to the reversibility of the sol-gel itself, thereby reducing production costs.

[0016] In one embodiment, the temperature-sensitive polymer having an upper critical solution temperature comprises an acrylic acid-acrylamide copolymer.

[0017] In one embodiment, the molar percentage of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is 40%-45%, for example, 40%, 41%, 42%, 43%, 44%, 45%, etc.

[0018] In the present disclosure, the molar percentage of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is controlled to ensure that the acrylic acid-acrylamide copolymer has a suitable UCST temperature range. If the molar percentage is too low, the UCST temperature of the acrylic acid-acrylamide copolymer will be low, thereby increasing the difficulty of the gelation process, for example, requiring the copolymer to be maintained at a low temperature for a long time, and vice versa.

[0019] In one embodiment, the number average molecular weight of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is 2×10 4 -10×10 6 g / mol, for example, 2×10 4 g / mol, 3×10 4 g / mol, 4×10 4 g / mol, 5×10 4 g / mol, 6×10 4 g / mol, 7×10 4 g / mol, 8×10 4 g / mol, 9×10 4 g / mol, 1×10 5 g / mol, 2×10 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 2×106 g / mol, 5×10 6 g / mol, 8×10 6 g / mol, 10×10 6 g / mol, etc.; further optional 5×10 5 -5×10 6 g / mol,.

[0020] In the present disclosure, the number average molecular weight of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is controlled to ensure that the copolymer has suitable solubility and reversible sol-gel transition temperature. A too low number average molecular weight will result in a low reversible sol-gel transition temperature, while a too high number average molecular weight will make the acrylic acid-acrylamide copolymer difficult to dissolve.

[0021] In one embodiment, the preparation method of the acrylic acid-acrylamide copolymer comprises mixing acrylic acid, acrylamide and water, and then adding an initiator to react to obtain the acrylic acid-acrylamide copolymer.

[0022] In one embodiment, the molar ratio of acrylic acid to acrylamide is (1-1.5):1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0023] In one embodiment, the initiator includes a combination of 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid and 4,4'-azobis(4-cyanovaleric acid).

[0024] In one embodiment, the molar ratio of the 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid, 4,4'-azobis(4-cyanovaleric acid) and acrylic acid-acrylamide copolymer is (10-12):(0.2-0.3):(400-450), for example, it can be 10:0.2:400, 10:0.25:450, 10:0.3:450, 10.2:0.22:410, 10.5:0.25:415, 10.8:0.28:420, 11:0.3:430, 11.2:0.2:440, 11.5:0.25:450, 12:0.2:450, 12:0.3:400, etc.

[0025] In the present disclosure, the molar ratio of 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid, 4,4'-azobis(4-cyanovaleric acid) and acrylic acid-acrylamide copolymer is regulated to allow the initiator to play a moderate cross-linking role. If the molar ratio is too low, fewer cross-linking points and a small degree of cross-linking will result, and the formed network structure will be larger, which will not play the role of precipitant diversion; otherwise, a large degree of cross-linking will result, and the formed spatial network will be small and the strength of the gel will be high, which is not conducive to conversion into a dilute sol for co-precipitation reaction.

[0026] In one embodiment, the reaction further comprises bubbling with nitrogen.

[0027] In the present disclosure, the time for bubbling treatment with nitrogen is 2-5 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0028] In one embodiment, the reaction temperature is 70-85°C, for example, 70°C, 75°C, 80°C, 85°C, etc.; the reaction time is 60-80h, for example, 60h, 65h, 70h, 75h, 80h, etc.

[0029] In one embodiment, the upper critical solution temperature of the thermosensitive polymer having an upper critical solution temperature is 30-40°C, for example, 30°C, 33°C, 36°C, 38°C, 40°C, etc.

[0030] In one embodiment, the mass concentration of the solution of the thermosensitive polymer having an upper critical solution temperature is 8wt%-15wt%, for example, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, etc.

[0031] In the present disclosure, by regulating the mass concentration of a solution of a thermosensitive polymer having an upper critical solution temperature, the reversible sol-gel generated thereby can respond quickly to temperature stimulation. If the mass concentration is too low, gelation will not occur, and conversely, conversion to a dilute sol will not occur.

[0032] In one embodiment, the iron source includes any one or a combination of at least two of ferrous chloride, ferrous sulfate, ferric chloride, ferric nitrate or ferric perchlorate.

[0033] In one embodiment, when the iron source includes ferrous chloride and / or ferrous sulfate, an oxidizing agent is required to oxidize the ferrous chloride and / or ferrous sulfate to convert the divalent iron into trivalent iron.

[0034] In the present disclosure, the oxidizing agent includes but is not limited to hydrogen peroxide.

[0035] In one embodiment, the phosphorus source includes any one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, or disodium hydrogen phosphate, or a combination of at least two thereof.

[0036] In one embodiment, the molar ratio of the iron source to the phosphorus source is 1:(1-1.1), for example, it can be 1:1, 1:1.02, 1:1.05, 1:1.08, 1:1.1, etc.

[0037] In one embodiment, the concentration of the solution containing the iron source is 0.1-1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, etc.

[0038] In one embodiment, the concentration of the solution containing the phosphorus source is 0.1-1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, etc.

[0039] In one embodiment, the mass concentration of the temperature-sensitive polymer in the mixed solution is not less than 3wt%, and can be optionally 3wt%-6wt%, for example, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, etc.

[0040] In the present disclosure, by regulating the mass concentration of the thermosensitive polymer in the mixed solution, the generated reversible sol-gel can respond quickly under temperature stimulation. If the mass concentration is too low, gelation will not occur, and vice versa, solubility will not occur.

[0041] In one embodiment, the gelation treatment comprises natural cooling.

[0042] In one embodiment, the pH value is 1.7-2.2, for example, it can be 1.7, 1.8, 2, 2.1, 2.2, etc.

[0043] In one embodiment, the heating temperature is 60-85°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, etc.

[0044] In one embodiment, the concentration of the phosphoric acid solution is 0.2-2 mol / L, for example, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, etc.

[0045] In one embodiment, the aging reaction temperature is 80-100°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the aging reaction time is 2-5h, for example, 2h, 3h, 4h, 5h, etc.

[0046] In one embodiment, the aging reaction further includes filtering, washing and drying treatments in sequence.

[0047] In the present disclosure, the washing is performed using deionized water and ethanol respectively until the upper layer of liquid is in a clear state.

[0048] In the present disclosure, the drying process may exemplarily be a drying process at 70-110° C. in a drying oven.

[0049] In one embodiment, the calcination temperature is 500-650°C, for example, 500°C, 550°C, 600°C, 650°C, etc.; the calcination time is 3-5h, for example, 3h, 4h, 5h, etc.

[0050] In the present disclosure, the equipment for the calcination treatment includes but is not limited to a muffle furnace, and the calcination treatment is performed to remove the crystal water in the crystal structure.

[0051] In a second aspect, the present disclosure provides an iron phosphate material, which is prepared by the method for preparing an iron phosphate material according to the first aspect.

[0052] In a third aspect, the present disclosure provides a lithium iron phosphate positive electrode material, wherein the raw materials for preparing the lithium iron phosphate positive electrode material include the iron phosphate material according to the second aspect.

[0053] In a fourth aspect, the present disclosure provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the material of the positive electrode comprises the lithium iron phosphate positive electrode material according to the third aspect.

[0054] Compared with the prior art, the present disclosure has the following beneficial effects:

[0055] The present disclosure provides a method for preparing an iron phosphate material, which combines a sol-gel and a coprecipitation method to quickly prepare a highly dispersible iron phosphate material by introducing a thermosensitive polymer with an upper critical solution temperature (UCST) type. The UCST type thermosensitive polymer can achieve reversible transformation of sol and gel at different temperatures. When it is lower than the UCST temperature, it is a semisolid gel, and when it is higher than the UCST temperature, it is a sol liquid with strong fluidity. When the raw materials for preparing iron phosphate and the thermosensitive polymer are uniformly mixed into a gel at a temperature lower than the UCST temperature, the polymer has a porous structure and framework characteristics. The added alkali solution precipitant can be subdivided and shunted by the pores on the surface of the gel, thereby achieving uniform diffusion of the precipitant, avoiding the situation in which the impurity precipitation caused by the excessive local concentration of the precipitant added in the traditional sense is generated, and then when the temperature is raised again, the gel will become a sol liquid, and the iron phosphate begins to coprecipitate.

[0056] In addition, after the temperature is raised, the swelling rate of the thermosensitive polymer due to polymer disassociation increases, and the polymer after becoming a sol liquid can inhibit the movement of nanoparticles, thereby preventing the agglomeration of iron phosphate particles. The sol-gel method disclosed in the prior art can prepare highly dispersed iron phosphate, but it requires a long time of gel drying and calcination, so the process time is prolonged; the coprecipitation method disclosed in the prior art can obtain the iron phosphate product quickly but it is easy to agglomerate, and the alkali solution is easy to cause the problem of excessive local concentration and uneven distribution when added, thereby affecting the consistency and stability of the product morphology. Based on the above situation, the present disclosure combines the above two methods to learn from each other's strengths and weaknesses, and the thermosensitive polymer can be recycled and reused due to the reversibility of the sol-gel itself, thereby reducing production costs.

[0057] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0059] FIG1 is a SEM image of the iron phosphate prepared in Example 1. DETAILED DESCRIPTION

[0060] The technical solution of the present disclosure is further described below with reference to the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0061] Example 1

[0062] This embodiment provides an iron phosphate material (FePO4) and a preparation method thereof as shown in FIG1 . The preparation method comprises the following steps:

[0063] Acrylamide and acrylic acid were dissolved in deionized water at a molar ratio of 0.42:0.58 to form a monomer solution. A 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid initiator and a 4,4'-azobis(4-cyanovaleric acid) free radical initiator were then added to the monomer solution to obtain a reaction solution, wherein the molar ratio of the 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid initiator, the 4,4'-azobis(4-cyanovaleric acid) free radical initiator, and the acrylamide-acrylic acid copolymer was 11:0.2:420. The reaction solution was bubbled with nitrogen for 3 hours and then soaked in a distilled water bath (75°C) for 3 days to obtain an acrylamide-acrylic acid copolymer.

[0064] Ferric chloride and ammonium dihydrogen phosphate were prepared into a 0.5 mol / L solution in water as solvent. A certain amount of acrylamide-acrylic acid copolymer (abbreviated as P(AA-co-AM)s, with a molar percentage of acrylamide structural unit of 42% and a number average molecular weight of acrylamide structural unit of 1.3×10 5 g / mol, upper critical solution temperature is 37 ° C) and water, heated in a water bath to above 35 ° C and stirred to dissolve, and prepared into a 10wt% acrylamide-acrylic acid copolymer solution. 3+ :PO4 3- =1:1 molar ratio is added to the acrylamide-acrylic acid copolymer solution, so that the mass concentration of P(AA-co-AM)s in the acrylamide-acrylic acid copolymer solution in the mixed solution is 4wt%, and after mixing evenly, a mixed solution is obtained;

[0065] The mixture was cooled to below 35°C for gelation, and a 30% ammonia solution was slowly added to allow for uniform diffusion. After adjusting the pH to 1.7, the mixture was heated to 65°C until the semi-gel state of the mixture became a sol liquid and iron phosphate precipitate began to appear. After 30 minutes, the mixture was filtered and removed.

[0066] The ferric phosphate precipitate was placed in a phosphoric acid solution (concentration: 1 mol / L) and aged at 80°C for 4 hours. The precursor material was filtered and the supernatant was washed with deionized water and ethanol until clear. The washed precursor material was dried in a drying oven at 70°C to obtain FePO4·xH2O material. The prepared FePO4·xH2O material was then placed in a muffle furnace and heated to 600°C at a rate of 4°C for 4 hours to remove crystal water and other impurities, thereby obtaining anhydrous FePO4 material.

[0067] Example 2

[0068] The difference between this embodiment and embodiment 1 is that the molar ratio of 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid initiator, 4,4'-azobis(4-cyanovaleric acid) free radical initiator and acrylamide-acrylic acid copolymer is 10:0.2:420, and other conditions are exactly the same as those in embodiment 1.

[0069] Example 3

[0070] The difference between this embodiment and embodiment 1 is that the molar ratio of 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid initiator, 4,4'-azobis(4-cyanovaleric acid) free radical initiator and acrylamide-acrylic acid copolymer is 12:0.2:420, and other conditions are exactly the same as those in embodiment 1.

[0071] Example 4

[0072] The difference between this embodiment and embodiment 1 is that the molar ratio of 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid initiator, 4,4'-azobis(4-cyanovaleric acid) free radical initiator and acrylamide-acrylic acid copolymer is 10:0.25:450, and other conditions are exactly the same as those in embodiment 1.

[0073] Example 5

[0074] The difference between this embodiment and embodiment 1 is that the molar ratio of 2-((butylthio)-carbonylthio)thio-2-methylpropionic acid initiator, 4,4'-azobis(4-cyanovaleric acid) free radical initiator and acrylamide-acrylic acid copolymer is 12:0.3:400, and other conditions are exactly the same as in embodiment 1.

[0075] Example 6

[0076] The difference between this embodiment and embodiment 1 is that the molar percentage of the acrylamide structural unit in the acrylamide-acrylic acid copolymer is 40%, and the number average molecular weight of the acrylamide structural unit is 2×10 4 g / mol, and other conditions are exactly the same as in Example 1.

[0077] Example 7

[0078] The difference between this embodiment and embodiment 1 is that the molar percentage of the acrylamide structural unit in the acrylamide-acrylic acid copolymer is 45%, and the number average molecular weight of the acrylamide structural unit is 7.9×10 4 g / mol, and other conditions are exactly the same as in Example 1.

[0079] Example 8

[0080] The difference between this embodiment and embodiment 1 is that the molar percentage of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is 35%. Other aspects are the same as those in embodiment 1.

[0081] Example 9

[0082] The difference between this embodiment and embodiment 1 is that the molar percentage of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is 50%. Other aspects are the same as those in embodiment 1.

[0083] Example 10

[0084] The difference between this embodiment and embodiment 1 is that the concentration of the acrylamide-acrylic acid copolymer solution in the mixed solution is 3 wt %. The other aspects are the same as those in embodiment 1.

[0085] Example 11

[0086] The difference between this embodiment and embodiment 1 is that the concentration of the acrylamide-acrylic acid copolymer solution in the mixed solution is 6 wt %. The other aspects are the same as those in embodiment 1.

[0087] Example 12

[0088] The difference between this embodiment and embodiment 1 is that the mass concentration of the acrylamide-acrylic acid copolymer in the mixed solution is 1 wt %. The other aspects are the same as those in embodiment 1.

[0089] Example 13

[0090] The difference between this embodiment and embodiment 1 is that the acrylamide-acrylic acid copolymer is replaced by polyacrylamide, and the rest is the same as embodiment 1.

[0091] Comparative Example 1

[0092] This comparative example provides a method for preparing an iron phosphate material, which comprises the following steps:

[0093] (1) Ferric chloride and ammonium dihydrogen phosphate were prepared into 0.5 mol / L Fe 3+ Solution and PO4 3- Solution, the two solutions were mixed according to Fe 3+ :[PO4] 3- =1 molar ratio, heated to 65°C in a water bath, and then added with aqueous ammonia to adjust the pH to 1.7 to form a precipitate. After 30 minutes, filter and remove the resulting precipitate. Place it in a 1 mol / L phosphoric acid solution and age it at 80°C for 4 hours. Filter the FePO4·xH2O precipitate, and clarify the supernatant by washing with deionized water and ethanol.

[0094] (3) The washed precipitate was dried in a drying oven at 70°C to obtain FePO4·xH2O material. The prepared FePO4·xH2O was then placed in a muffle furnace and heated to 600°C at a heating rate of 4°C and kept warm for 4 h to remove crystallization water and other impurities, thereby obtaining anhydrous FePO4 material.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that after the ferric chloride solution and the ammonium dihydrogen phosphate solution were added to the acrylamide-acrylic acid copolymer solution and mixed uniformly, the temperature of the mixed solution was not lowered to below 35°C for gelation treatment. Instead, the temperature of the mixed solution was maintained at 35°C, and an ammonia solution was added dropwise to adjust the pH value to 1.7. All other conditions were the same as in Example 1.

[0097] Preparation Example

[0098] The anhydrous FePO4 material, lithium carbonate, and glucose provided in Examples 1 to 13 and Comparative Examples 1 to 2 were uniformly dispersed in water and mixed in a stoichiometric ratio of 1:1.02:0.06 for the iron, lithium, and carbon elements. The mixture was ball-milled at 700 rpm for 4 hours until uniform, and then spray-dried to obtain a precursor powder. The precursor powder was heated to 300°C at a heating rate of 3°C / min under a nitrogen atmosphere and held for 2 hours. The temperature was then raised to 750°C and calcined for 7 hours to obtain the LiFePO4 / C positive electrode material.

[0099] The resulting LiFePO4 / C cathode material was assembled into a button-type battery for electrochemical performance testing of the lithium-ion battery. The specific steps were as follows: the cathode material LiFePO4 / C active material, the conductive agent acetylene black, and the adhesive polyvinylidene fluoride were uniformly mixed in a mass ratio of 90:5:5 in N-methylpyrrolidone. The mixture was ground into a slurry, coated onto aluminum foil, and dried in a vacuum drying oven. After drying, the battery was assembled in an argon glove box. A 12mm positive electrode sheet was pressed using a tablet press. The negative electrode was a metallic lithium sheet. The electrolyte composition was 1 mol / L lithium hexafluorophosphate (LiPF6) lithium salt, and the solvent was a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. A polypropylene porous membrane was used as the separator to obtain the button-type battery.

[0100] Test conditions

[0101] The button batteries provided by Preparation Examples 1 to 13 and Comparative Preparation Examples 1 to 2 were tested, wherein the test voltage range was 2.4-4.6V, and the test rates were 0.1C and 1C, respectively, with 1C=170mA / g.

[0102] The test results are shown in Table 1:

[0103] Table 1

[0104] As can be seen from Table 1, the preparation methods of the iron phosphate materials provided in Preparation Examples 1-7 of the present disclosure introduce an acrylamide-acrylic acid copolymer with an upper critical solution temperature (UCST) type, combine the sol-gel method with the co-precipitation method to quickly prepare highly dispersed iron phosphate materials, and further optimize the content relationship of the components to avoid the problems of excessive local concentration and poor product uniformity.

[0105] From the comparison of Preparation Example 1, Preparation Example 8 and Preparation Example 9, it can be seen that by adjusting the molar percentage of the acrylamide structural unit in the acrylic acid-acrylamide copolymer, the acrylic acid-acrylamide copolymer has a higher and more suitable UCST temperature range.

[0106] From the comparison of Preparation Examples 1, 10 and 11, it can be seen that by regulating the preferred concentration of the acrylamide-acrylic acid copolymer solution, the generated reversible sol-gel can respond quickly under temperature stimulation.

[0107] From the comparison between Preparation Example 1 and Preparation Example 12, it can be seen that by regulating the mass concentration of the temperature-sensitive polymer in the mixed solution, the reversible sol-gel produced can respond quickly under temperature stimulation.

[0108] From the comparison between Preparation Example 1 and Preparation Example 13, it can be seen that replacing the acrylamide-acrylic acid copolymer with other types in the prior art cannot achieve all the technical effects of the present disclosure.

[0109] From the comparison between Preparation Example 1 and Comparative Preparation Example 1, it can be seen that the battery prepared from the iron phosphate material prepared by the conventional co-precipitation method has poor electrochemical performance.

[0110] It can be seen from Preparation Example 1 and Comparative Preparation Example 2 that if the temperature of the mixed solution is not lowered to below 35° C. for gelation treatment, uniform diffusion of the precipitant cannot be achieved, resulting in poor performance of the prepared battery.

Claims

1. A method for preparing iron phosphate material, comprising the following steps: Mix a solution of a thermosensitive polymer having an upper critical solution temperature, a solution containing an iron source, and a solution containing a phosphorus source to obtain a mixed solution; Subject the mixed solution to gelation treatment, then add an alkali solution, adjust the pH value to acidic, and obtain a precipitate after heating; Carry out an aging reaction on the precipitate and phosphoric acid solution to obtain a precursor material; Calcine the precursor material to obtain the iron phosphate material.

2. The method according to claim 1, wherein, The thermosensitive polymer having an upper critical solution temperature includes an acrylic acid - acrylamide copolymer.

3. The method according to claim 2, wherein The molar percentage content of acrylamide structural units in the acrylic acid - acrylamide copolymer is 40% - 45%.

4. The method according to claim 2 or 3, wherein The number-average molecular weight of the acrylamide structural unit in the acrylic acid-acrylamide copolymer is 2×10 4 -10×10 6 g / mol, and further preferably 5×10 5 -5×10 6 g / mol.

5. The method according to any one of claims 2-4, wherein The preparation method of the acrylic acid - acrylamide copolymer includes mixing acrylic acid, acrylamide, and water, then adding an initiator, and reacting to obtain the acrylic acid - acrylamide copolymer; The molar ratio of acrylic acid to acrylamide is (1 - 1.5):

1.

6. The method according to claim 5, wherein, The initiator includes a combination of 2 - ((butylthio)-carbonylthio)thio - 2 - methylpropanoic acid and 4,4'-azobis(4 - cyanovaleric acid); The molar ratio of 2 - ((butylthio)-carbonylthio)thio - 2 - methylpropanoic acid, 4,4'-azobis(4 - cyanovaleric acid), and acrylic acid - acrylamide copolymer is (10 - 12):(0.2 - 0.3):(400 - 450); Before the reaction, it further includes foaming treatment with nitrogen; The temperature of the reaction is 70 - 85°C, and the time is 60 - 80 h.

7. The method according to any one of claims 1-6, wherein, The upper critical solution temperature of the thermosensitive polymer having an upper critical solution temperature is 30 - 40°C.

8. The method according to any one of claims 1-7, wherein, The mass concentration of the solution of the thermosensitive polymer having an upper critical solution temperature is 8wt% - 15wt%.

9. The method according to any one of claims 1-8, wherein, The iron source includes any one or a combination of at least two of ferrous chloride, ferrous sulfate, ferric chloride, iron nitrate, or iron perchlorate; The phosphorus source includes any one or a combination of at least two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphamide, sodium dihydrogen phosphate, or disodium hydrogen phosphate; The molar ratio of the iron source to the phosphorus source is 1:(1 - 1.1).

10. The method according to any one of claims 1 - 9, wherein when the iron source includes ferrous chloride and / or ferrous sulfate, an oxidant is used to oxidize ferrous chloride and / or ferrous sulfate.

11. According to the method described in any one of claims 1-10, wherein The concentration of the solution containing the iron source is 0.1 - 1 mol / L; The concentration of the solution containing the phosphorus source is 0.1 - 1 mol / L; The mass concentration of the thermosensitive polymer in the mixed solution is not less than 3wt%, and further optionally 3wt% - 6wt%.

12. The method according to any one of claims 1-11, wherein, The gelation treatment method includes natural cooling; The pH value is 1.7 - 2.2; The heating temperature is 60 - 85°C.

13. The method according to any one of claims 1-12, wherein, The concentration of the phosphoric acid solution is 0.2 - 2 mol / L; The temperature of the aging reaction is 80 - 100°C, and the time is 2 - 5 h; After the aging reaction, it further includes filtration, washing, and drying treatments in sequence; The calcination treatment temperature is 500 - 650°C, and the time is 3 - 5 h.

14. A ferric phosphate material prepared by the method for preparing a ferric phosphate material according to any one of claims 1-13.

15. A lithium iron phosphate cathode material comprising the ferric phosphate material according to claim 14.

16. A secondary battery comprising the lithium iron phosphate cathode material according to claim 15, including a positive electrode, a negative electrode, an electrolyte, and a separator.

Images