Iron phosphide precursor and preparation method therefor, sodium iron phosphate pyrophosphate, electrode sheet, battery, and electric device

Abstract

Provided are an iron phosphide precursor and a preparation method therefor, sodium iron phosphate pyrophosphate, an electrode sheet, a battery, and an electric device. The iron phosphide precursor comprises a component having a chemical composition of Fex(PO4)y(HPO4)z·aH2O, where 0.6 < x / (y+z) < 0.8, and 0 < a / (y+z) < 2.5. The iron-phosphorus molar ratio in the iron phosphide precursor provided by the present application is excellent, and after the prepared sodium iron phosphate pyrophosphate is used in a battery, the specific capacity of the battery can be significantly improved.

Description

A phosphorus iron oxide precursor and its preparation method, sodium iron pyrophosphate, electrode sheet, battery, and electrical equipment.

[0001] This application claims priority to Chinese Patent Application No. 202510121293.7, filed on January 24, 2025, entitled "A Phosphoric Iron Precursor and its Preparation Method, Sodium Iron Pyrophosphate, Electrode Sheet, Battery, and Electrical Equipment", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to a ferric phosphate precursor, as well as a method for preparing the ferric phosphate precursor, sodium iron pyrophosphate, electrode sheets, batteries, and electrical devices, belonging to the field of secondary batteries. Background Technology

[0003] Sodium-ion batteries hold great promise for large-scale electrochemical energy storage due to their low cost. Polyanionic iron-based phosphate sodium-ion batteries, in particular, perfectly meet the demands of large-scale energy storage for low cost and long lifespan, thanks to the excellent structural stability of polyanionic materials and the low cost based on Fe. For example, sodium iron pyrophosphate (Na4Fe3(PO4)2(P2O7), NFPP) cathode material, which has been widely studied in recent years, possesses a high theoretical specific capacity of 129 mAh / g, an average discharge voltage of ~3.0 V, and excellent cycle stability, making it one of the most competitive materials for sodium-ion battery cathodes used in energy storage.

[0004] Currently, the large-scale preparation of NFPP mainly uses FePO4 precursor as the Fe and P source. However, since the theoretical Fe / P ratio of NFPP is 0.75, which is significantly different from the approximately 1:1 ratio of the FePO4 precursor, the local Fe / P ratio after mixing deviates from the theoretical value of NFPP, thereby reducing the actual specific capacity of NFPP. Summary of the Invention

[0005] This application provides a phosphide precursor with an iron-phosphorus molar ratio close to the theoretical value, which results in high purity of the NFPP prepared from the precursor, thereby ensuring the specific capacity of the NFPP.

[0006] This application also provides a method for preparing an iron phosphate precursor, which is simple to operate and can prepare the above-mentioned iron phosphate precursor.

[0007] This application also provides a sodium iron pyrophosphate, which is prepared from the above-mentioned iron phosphate precursor and has high purity and excellent specific capacity.

[0008] This application also provides an electrode sheet comprising the aforementioned sodium iron pyrophosphate, which exhibits excellent electrochemical performance.

[0009] This application also provides a battery that includes the aforementioned electrode plates and has excellent performance.

[0010] This application also provides an electrical device that includes the aforementioned battery and has good performance.

[0011] This application provides a ferrophosphorus precursor, wherein the ferrophosphorus precursor comprises a chemical composition of Fe. x (PO4) y (HPO4) z ·a H2O components;

[0012] Among them, 0.6 <x / (y+z)<0.8,0<a / (y+z)<2.5。

[0013] The ferrophosphide precursor described above has an amorphous structure.

[0014] This application further provides a method for preparing the ferrophosphide precursor as described above, comprising the following steps:

[0015] 1) A co-precipitation reaction is carried out on a mixture containing an iron source and a phosphorus source to obtain the first precursor;

[0016] 2) The first precursor is dried at 80℃-200℃ to obtain the iron phosphate precursor;

[0017] In the ferrophosphide precursor, the molar ratio of iron to phosphorus is A, satisfying 0.6. <A<0.8。

[0018] The preparation method described above, wherein the coprecipitation reaction includes the following steps:

[0019] The iron source solution and the phosphorus source solution were mixed, and then the pH was adjusted to 1.5-7.0. The mixture was aged for 1-24 hours, filtered and washed to obtain the first precursor.

[0020] In the preparation method described above, the iron source comprises divalent iron;

[0021] The mixture also includes an oxidant, the number of electrons required for the oxidant to reduce is A, and the number of electrons lost by the ferrous iron to ferric iron is B, satisfying A:B = (1~3):1.

[0022] In the preparation method described above, the oxidant includes at least one of hydrogen peroxide, oxygen, ozone, nitric acid, potassium permanganate, and potassium chlorate.

[0023] In the preparation method described above, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and tripotassium phosphate.

[0024] And / or, the iron source includes at least one of ferric nitrate, ferrous nitrate, ferrous sulfate, ferric sulfate, ferric chloride, ferrous chloride, ferrous acetate, and ferrous phosphate.

[0025] In another aspect, this application provides sodium iron pyrophosphate, which is prepared using the iron phosphate precursor described above.

[0026] The preparation process of sodium ferric pyrophosphate as described above includes the following steps:

[0027] 1) The phosphite precursor is mixed with supplementary phosphorus source, supplementary iron source, sodium source and carbon source in the liquid phase to obtain a slurry;

[0028] 2) The slurry is dried to obtain the second precursor;

[0029] 3) The second precursor is sintered in an inert or reducing atmosphere to obtain the sodium iron pyrophosphate.

[0030] In another aspect, this application provides an electrode sheet comprising sodium iron pyrophosphate as described above.

[0031] In another aspect, this application provides a battery including the electrode sheets described above.

[0032] This application also provides an electrical device, including the battery described above.

[0033] The Fe / P ratio in the phosphide precursor provided in this application ranges from 0.60 to 0.80, which is closer to the theoretical iron-phosphorus molar ratio of 0.75 for NFPP materials than FePO4. Therefore, it is more advantageous for the synthesis of NFPP materials. When this precursor is used as a raw material to prepare NFPP, the resulting material has higher phase purity, reduces the content of impurity phases such as NaFePO4 and Na2FeP2O7, increases the proportion of high specific capacity component NFPP, and ensures that NFPP has a higher specific capacity. Attached Figure Description

[0034] Figure 1 shows the XRD patterns of the iron phosphate precursors provided in Examples 1-3 of this application;

[0035] Figure 2 is a SEM image of the iron phosphate precursor provided in Example 1 of this application;

[0036] Figure 3 shows the XRD patterns of NFPP materials prepared from the phosphine precursors provided in Examples 1-4 and Comparative Examples 1-2 of this application;

[0037] Figure 4 shows the charge-discharge curves of NFPP prepared from the phosphine precursors provided in Examples 1-4 and Comparative Examples 1-2 of this application.

[0038] Figure 5 is a schematic diagram of the structure of an electrode sheet provided in this application;

[0039] Figure 6 is a structural schematic diagram of an electrical device provided in this application.

[0040] Reference numerals: 100-Electrode sheet; 110-Positive current collector; 120-Positive active layer; 2-Battery; 3-Electrical device. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0042] Currently, FePO4 is mainly used as the main raw material for the large-scale preparation of NFPP. However, the Fe / P ratio in FePO4 is 1:1, which is significantly different from the theoretical Fe / P ratio of 0.75:1 in NFPP. This results in the NFPP being prepared with uneven distribution of iron and phosphorus, producing other inactive or low-activity impurity phases, leading to a low specific capacity of NFPP.

[0043] Therefore, it is necessary to develop precursors that are similar to the iron-phosphorus molar ratio in NFPP as raw materials, so as to make the iron and phosphorus elements in NFPP more uniformly distributed and ensure the specific capacity of NFPP.

[0044] This application provides a ferrophosphorus precursor, which comprises a chemical composition of Fe. x (PO4) y (HPO4) z ·a H2O components;

[0045] Among them, 0.6 <x / (y+z)<0.8,0<a / (y+z)<2.5。

[0046] In the iron phosphide precursor provided by the present application, the molar ratio of iron to phosphorus includes, but is not limited to, 0.61, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, 0.74, 0.76, 0.78, 0.79, or any range greater than 0.6 and less than 0.8, while the water to phosphorus ratio includes, but is not limited to, 0.1, 0.5, 1.0, 1.5, 2.0, 2.4, or any range greater than 0 and less than 2.5.

[0047] Among them, common methods in the art can be used to test the contents of iron element, phosphorus element, and water content, such as measuring using inductively coupled plasma method (ICP). Among them, when using the ICP method for testing, the content of phosphorus element in the sample can be measured and calculated through processes such as calibration curve, instrument setting, measurement, and data analysis in sequence, and phosphorus element may exist in phosphate ion or monohydrogen phosphate ion.

[0048] In a specific embodiment, 0.65 < x / (y + z) < 0.75. When the molar ratio of iron to phosphorus is within this range, using the iron phosphide precursor to prepare NFPP can more effectively avoid the formation of the impurity phase NaFePO4 and reduce the influence of the impurity phase on the specific capacity of NFPP. <00,00133>

[0049] The NFPP prepared using the iron phosphide precursor provided by the present application has a high specific capacity. The Fe / P ratio range in the iron phosphide precursor provided by the present application is 0.60 - 0.80, which is closer to the theoretical iron to phosphorus molar ratio of 0.75 of the NFPP material than FePO4. Therefore, this characteristic makes the distribution of iron and phosphorus elements in the material before sintering more uniform, reduces or eliminates the diffusion difficulty of iron and phosphorus elements during the sintering process, and is more conducive to the synthesis of NFPP materials. When using this precursor as the raw material to prepare NFPP, the obtained material has a higher phase purity, reduces the content of impurity phases such as NaFePO4 and Na2FeP2O7, increases the proportion of the target product NFPP, and ensures that NFPP has a higher specific capacity.

[0050] In a specific embodiment, the iron phosphide precursor has an amorphous structure.

[0051] Among them, it is found through XRD testing that the iron phosphide precursor of the present application has no obvious characteristic peaks, indicating that the iron phosphide precursor lacks a long-range ordered crystal structure. This disorder can provide more structural defects and voids, contribute to the rapid migration of ions, provide a transmission path, and thus contribute to the uniform dispersion of elements, resulting in a high-purity NFPP material. <0000,139>

[0052] On the other hand, the present application provides a preparation method for the iron phosphide precursor as described above, including the following steps:

[0053] 1) Co-precipitation reaction is carried out on the mixed solution including an iron source and a phosphorus source to obtain a first precursor;

[0054] 2) The first precursor is dried at 80°C - 200°C to obtain an iron phosphate precursor;

[0055] Among them, the molar ratio of iron element to phosphorus element in the iron phosphate precursor is A, satisfying 0.6 < A < 0.8.

[0056] The preparation method provided by this application can prepare an iron phosphate precursor with a chemical composition of Fe x (PO4) y (HPO4) z ·a H2O, 0.6 < x / (y + z) < 0.8, 0 < a / (y + z) < 2.5.

[0057] Specifically, in step 1), the mixed solution including an iron source and a phosphorus source is subjected to co-precipitation reaction to form a precipitate, the molar ratio of the iron source to the phosphorus source in the mixed solution is controlled, and then separation and drying are carried out to obtain the iron phosphate precursor.

[0058] Considering that the iron source and the phosphorus source may have residues, insufficient reaction, etc. during the reaction process, the molar ratio of the iron source to the phosphorus source can be adjusted according to the actual operation conditions. For example, in a specific embodiment, the molar ratio of the iron source to the phosphorus source is (0.3 - 1.0):1.

[0059] Among them, separation methods commonly used in the art can be selected, such as filtration, centrifugal separation, etc.

[0060] It can be understood that the precipitate obtained after separation may have some iron ions, phosphorus atoms or other heteroatoms remaining on its surface, and washing can be used to avoid the influence of heteroatoms on subsequent reactions.

[0061] In a specific embodiment, the first precursor obtained by separation is dispersed in deionized water for washing, and then separation treatment is carried out again. After repeating several times, the first precursor is obtained.

[0062] [[ID=3)) In step 2), the first precursor is dried, and impurities and excess moisture in the precursor are removed by drying to obtain an iron phosphate precursor with 0 < a / (y + z) < 2.5.

[0063] This application does not limit the specific operation mode of drying either, such as oven blowing drying, vacuum drying, spray drying, flash evaporation or rotary evaporation, etc.

[0064] The preparation method provided in this application is simple to operate. By controlling the molar ratio of iron source and phosphorus source and the drying temperature, the iron-phosphorus molar ratio and the water-phosphorus ratio in the iron-phosphorus precursor can be adjusted to obtain an iron-phosphorus precursor with an iron-phosphorus molar ratio within a suitable range.

[0065] In one specific embodiment, the coprecipitation reaction includes the following steps:

[0066] The iron source solution and the phosphorus source solution were added dropwise and mixed, then the pH was adjusted to 1.5-7.0, aged for 1-24 hours, filtered and washed to obtain the first precursor.

[0067] In detail, an iron source is dissolved in a solvent to obtain an iron source solution, a phosphorus source is dissolved in a solvent to obtain a phosphorus source solution, the iron source solution and the phosphorus source solution are mixed, and then the pH is adjusted to 1.5-7.0 using an alkaline solution. The mixture is aged for 1-24 hours under stirring, and then filtered and washed to obtain the first precursor.

[0068] This application does not limit the type of solvent, and solvents commonly used in the art, such as water, ethanol, acetonitrile, etc., can be selected.

[0069] Common alkaline solutions can be used for pH adjustment, such as ammonia, sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, and potassium bicarbonate.

[0070] The coprecipitation reaction steps described above ensure the purity and homogeneity of the first precursor, laying the foundation for the performance of the subsequent final iron phosphate precursor.

[0071] In one specific embodiment, the iron source includes ferrous iron; the mixture also includes an oxidant, the number of electrons required for the oxidant to reduce is A, and the number of electrons lost by ferrous iron to ferric iron is B, satisfying A:B = (1~3):1.

[0072] When the iron source includes ferrous iron, in order to make the preparation process of ferric phosphate precursor stable and controllable, the oxidant in the mixture plays the role of oxidizing ferrous iron to ferric iron.

[0073] The ratio of A to B includes, but is not limited to, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any combination thereof.

[0074] When the number of electrons required for the reduction of the oxidant and the number of electrons lost when ferrous iron is oxidized to ferric iron meet the above range, not only can the reaction conditions be optimized so that the redox reaction can proceed within a controllable range and the reaction efficiency can be improved, but also unnecessary side reactions and waste of resources can be avoided.

[0075] Furthermore, in one specific embodiment, the oxidant includes at least one selected from hydrogen peroxide, oxygen, ozone, nitric acid, potassium permanganate, and potassium chlorate.

[0076] When the above-mentioned types of oxidants are selected, the oxidation of ferrous iron can be effectively achieved.

[0077] In one specific embodiment, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and tripotassium phosphate.

[0078] In another specific embodiment, the iron source includes at least one of ferric nitrate, ferrous nitrate, ferrous sulfate, ferric sulfate, ferric chloride, ferrous chloride, ferrous acetate, and ferrous phosphate.

[0079] The aforementioned types of phosphorus and iron sources are suitable for different application scenarios, providing diversity in the selection of raw materials for iron phosphate precursors.

[0080] In another aspect, this application provides sodium iron pyrophosphate, which is prepared using the iron phosphate precursor as described above.

[0081] Since this sodium ferric pyrophosphate is prepared using the aforementioned ferric phosphate precursor, it exhibits excellent specific capacity.

[0082] This application does not limit the preparation method of sodium iron pyrophosphate; it can be prepared using common methods in the art.

[0083] In one specific embodiment, the method for preparing sodium iron pyrophosphate includes the following steps:

[0084] 1) The above-mentioned phosphine iron precursor is thoroughly mixed with supplementary phosphorus source, supplementary iron source, sodium source and carbon source in the liquid phase;

[0085] 2) The mixed slurry is dried to obtain the second precursor;

[0086] 3) The second precursor is sintered in an inert or reducing atmosphere to obtain the NFPP product.

[0087] In step 1), an appropriate ratio can be selected to mix with the supplementary phosphorus source, supplementary iron source, and sodium source according to the situation of sodium ferric pyrophosphate. For example, in a specific embodiment, the phosphorus iron precursor, supplementary phosphorus source, supplementary iron source, and sodium source are supplemented according to the final Na, Fe, P molar ratio of 1:0.73:1 in sodium ferric pyrophosphate.

[0088] Among them, common raw materials can be selected according to actual conditions. For example, the phosphorus source includes one or more combinations of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and triammonium phosphate. As an optional implementation, ammonium dihydrogen phosphate and sodium dihydrogen phosphate can be used. The iron source includes one or more combinations of iron powder, ferrous oxalate, ferric oxide, ferrous oxide, ferrous sulfate, ferric nitrate, ferrous nitrate, and ferrous acetate. Ferrous oxalate and ferric nitrate are preferred. The sodium source includes one or more combinations of sodium acetate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium oxalate, and sodium citrate. As an optional implementation, sodium acetate and sodium carbonate can be used. The carbon source includes one or more combinations of organic carbon sources such as citric acid, glucose, sucrose, fructose, ascorbic acid, and polyethylene glycol, as well as one or more combinations of inorganic carbon sources such as carbon black, graphite powder, carbon nanotubes, and graphene. As an optional implementation, glucose can be used.

[0089] In one specific embodiment, in step 1), the mixing method is selected from at least one of sand milling and ball milling, and the particle size range after mixing is 0.1-2μm.

[0090] In another specific embodiment, step 2) includes drying treatment including spray drying and evaporative drying. As an optional embodiment, spray drying may be used.

[0091] Common inert or reducing gases can be selected, such as at least one of nitrogen, argon, and hydrogen.

[0092] In one specific embodiment, sintering is performed using an atmosphere tube furnace or an atmosphere box furnace, with a sintering temperature range of 450-600℃, or 500-550℃ as an optional embodiment; the sintering time is 4-18h, or 6-12h as an optional embodiment.

[0093] In another aspect, this application provides an electrode sheet 100 comprising sodium iron pyrophosphate as described above.

[0094] Because the electrode 100 includes the aforementioned sodium pyrophosphate, it has excellent specific capacity.

[0095] As shown in Figure 5, the electrode sheet 100 of this application specifically includes a positive current collector 110 and a positive active layer 120 formed of a positive active material disposed on the surface of the positive current collector 110, wherein the positive active layer 120 includes sodium iron pyrophosphate.

[0096] Specifically, in preparing the electrode sheet 100, for example, the sodium iron pyrophosphate of this application can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated onto the positive electrode current collector 110, and after drying, rolling and slitting, the electrode sheet 100 is obtained. In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder, and further comprises 80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0097] The positive current collector 110 can be made of aluminum foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from one of PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and PAN (polyacrylonitrile).

[0098] In another aspect, this application provides a battery 2, including the electrode sheet 100 as described above.

[0099] It is conceivable that, in addition to the aforementioned electrode sheet 100, the battery 2 of this application also includes a negative electrode sheet, an electrolyte, and a separator.

[0100] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in sodium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (mainly including tin and tin alloys).

[0101] This application does not strictly limit the choice of electrolyte, which may include one or more of the solvents commonly used in sodium-ion battery electrolytes, as well as the electrolyte sodium salts commonly used in sodium-ion electrolytes. For example, the solvent may be one or more of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, difluoroethylene carbonate, dipropyl carbonate, and methyl ethyl carbonate; the sodium salt may be one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0102] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in sodium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0103] In the preparation of sodium-ion batteries, electrode sheets 100, separators, and negative electrode sheets are wound or stacked to obtain bare cells, which are then packaged into pre-stamped aluminum-plastic film bags. After the packaged batteries are dried at 85°C, electrolyte is injected into the dried batteries. After the batteries are left to stand, formed, and resealed, the preparation of the sodium-ion battery is completed.

[0104] In another aspect, this application provides an electrical device 3, as shown in FIG6, which includes the battery 2 as described above.

[0105] This application does not limit the specific type of electrical equipment 3, and may include any device that requires a battery to power it, such as electric vehicles, mobile phones, smart home devices, robots, drones, e-cigarettes, and speakers.

[0106] The electrical device 3 provided in this application includes the aforementioned battery 2, and therefore has good electrochemical performance.

[0107] The following detailed description of the phosphide precursor provided in this application is provided through specific embodiments.

[0108] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0109] Example 1

[0110] The method for preparing the ferrophosphide precursor provided in this embodiment includes the following steps:

[0111] 1. Ferrous sulfate and ammonium dihydrogen phosphate were selected as the iron and phosphorus sources, respectively, and hydrogen peroxide was used as the oxidant. 25% ammonia was used to adjust the pH. 0.3 mol of ferrous sulfate was added to 200 g of deionized water to obtain solution A; 0.18 mol of hydrogen peroxide was added to 50 mL of water to obtain solution B; 0.5 mol of ammonium dihydrogen phosphate was dissolved in 150 g of water to obtain solution C; solutions B and C were simultaneously added to solution A using a peristaltic pump to obtain mixture D; ammonia was added dropwise to mixture D to adjust the pH to 2.0. After stirring and aging for 2 hours, the slurry was centrifuged to obtain a solid precipitate. The precipitate was redispersed and washed with deionized water, followed by centrifugation. After washing three times, the precipitate was dried at 120℃ for 12 hours to obtain the ferric phosphate precursor.

[0112] The elemental composition of the iron phosphate precursor provided in this embodiment was determined by ICP testing. The iron phosphate precursor contains components with a chemical composition of Fe. x (PO4) y (HPO4) z The composition of ·a H2O is as follows: x is 2.93, y+z is 4, and a is 3.86. Specifically, the Fe and P element contents and the corresponding Fe / P ratios are shown in Table 1, and the iron-phosphorus molar ratio is 0.733.

[0113] The obtained material was characterized by XRD, and the results are shown in Figure 1. It can be seen that the iron phosphate precursor has no obvious diffraction peaks. The material was morphologically tested by SEM, as shown in Figure 2. The iron phosphate precursor is a coral-like or keel-like material with a diameter of 500 nm to 5 μm.

[0114] Example 2

[0115] The preparation method of the ferrophosphide precursor provided in this embodiment is basically the same as that in Example 1, except that:

[0116] 1. Ferric nitrate and ammonium dihydrogen phosphate were selected as the iron and phosphorus sources, respectively, and the pH value was adjusted with 25% ammonia solution. 0.3 mol of ferric nitrate was added to 200 g of deionized water to obtain solution A; 0.6 mol of ammonium dihydrogen phosphate was dissolved in 150 g of water to obtain solution B; solution B was added to solution A using a peristaltic pump to obtain mixture C.

[0117] The same post-treatment as in Example 1 was used to prepare the ferrophosphide precursor.

[0118] ICP testing of the elemental composition of the material revealed that the iron phosphate precursor contained Fe. x (PO4) y (HPO4) z The composition of ·a H2O is x = 2.76, y+z = 4, a = 5.09, and the results are shown in Table 1. The iron-phosphorus molar ratio is 0.689.

[0119] The obtained material was characterized by XRD, and the results are shown in Figure 1. The obtained iron phosphate precursor had no obvious diffraction peaks.

[0120] Example 3

[0121] The method for preparing the ferrophosphide precursor provided in this embodiment includes the following steps:

[0122] 1. Ferric nitrate and sodium dihydrogen phosphate were selected as the iron and phosphorus sources, respectively. A 10% NaOH solution was prepared to adjust the pH value. 0.3 mol of ferric nitrate was added to 200 g of deionized water to obtain solution A; 0.5 mol of sodium dihydrogen phosphate was dissolved in 150 g of water to obtain solution B; solution B was added to solution A via a peristaltic pump to obtain mixture C; 10% NaOH solution was added dropwise to solution C to adjust the pH value to 2.8, and the mixture was stirred and aged for 10 h. The slurry was then centrifuged to obtain a solid precipitate; the solid precipitate was redispersed and washed with deionized water, followed by centrifugation. After washing three times, the precipitate was dried in a forced-air oven at 120℃ for 12 h to obtain the ferric phosphate precursor.

[0123] ICP testing of the elemental composition of the material revealed that the iron phosphate precursor contained Fe. x (PO4) y (HPO4) z The composition of ·a H2O is x = 2.89, y+z = 4, a = 5.21, and the results are shown in Table 1. The iron-phosphorus molar ratio is 0.722.

[0124] Example 4

[0125] The method for preparing the ferrophosphide precursor provided in this embodiment includes the following steps:

[0126] 1. Ferric nitrate and ammonium dihydrogen phosphate were selected as the iron and phosphorus sources, respectively, and 25% ammonia water was used to adjust the pH value. 0.5 mol of ferric nitrate was added to 300 g of deionized water to obtain solution A; 1.5 mol of sodium dihydrogen phosphate was dissolved in 500 g of water to obtain solution B; solution B was added to solution A via a peristaltic pump to obtain mixture C; 25% ammonia water was added dropwise to solution C to adjust the pH value to 2.2, and the mixture was stirred and aged for 2 hours. The slurry was then centrifuged to obtain a solid precipitate; the solid precipitate was redispersed and washed with deionized water, followed by centrifugation. After washing three times, the precipitate was dried in a forced-air oven at 100℃ for 12 hours to obtain the ferric phosphate precursor.

[0127] ICP testing of the elemental composition of the material revealed that the iron phosphate precursor contained Fe. x (PO4) y (HPO4)z The composition of ·a H2O, x is 2.58, y+z is 4, a is 6.0, and the results are shown in Table 1. The iron-phosphorus molar ratio is 0.633.

[0128] Example 5

[0129] The preparation method of the ferrophosphide precursor provided in this embodiment is basically the same as that in Example 1, except that:

[0130] In step 1) of this embodiment, the amount of hydrogen peroxide is 0.3 mol. ICP analysis of the elemental composition of the obtained iron phosphate precursor reveals that the iron phosphate precursor contains Fe... x (PO4) y (HPO4) z The composition of ·a H2O is x = 3.08, y+z = 4, a = 5.76, and the results are shown in Table 1. The iron-phosphorus molar ratio is 0.758.

[0131] Example 6

[0132] The preparation method of the ferrophosphide precursor provided in this embodiment is basically the same as that in Example 1, except that:

[0133] In step 2) of this embodiment, the drying temperature is 150°C. ICP analysis of the elemental composition of the obtained iron phosphate precursor reveals that the iron phosphate precursor comprises substances with a chemical composition of Fe. x (PO4) y (HPO4) z The composition of ·a H2O is x = 2.89, y+z = 4, a = 5.21, and the results are shown in Table 1. The iron-phosphorus molar ratio is 0.722.

[0134] Comparative Example 1

[0135] The precursor provided in this comparative example is commercially available anhydrous iron phosphate FePO4.

[0136] Comparative Example 2

[0137] The method for preparing the iron phosphate precursor provided in this comparative example includes the following steps:

[0138] 1. Ferric chloride and ammonium dihydrogen phosphate were selected as the iron and phosphorus sources, respectively, and 25% ammonia water was used to adjust the pH value. 0.5 mol of ferric chloride was added to 300 g of deionized water to obtain solution A; 0.8 mol of sodium dihydrogen phosphate was dissolved in 300 g of water to obtain solution B; solution B was added to solution A via a peristaltic pump to obtain mixture C; 25% ammonia water was added dropwise to solution C to adjust the pH value to 3.0, and the mixture was stirred and aged for 10 h. The slurry was then centrifuged to obtain a solid precipitate; the solid precipitate was redispersed and washed with deionized water, followed by centrifugation. After washing three times, the first precursor was obtained.

[0139] 2. The first precursor was calcined in a forced-air oven at 120°C for 12 hours to obtain the ferrophosphide precursor.

[0140] ICP testing of the elemental composition of the material revealed that the iron phosphate precursor contained Fe. x (PO4) y (HPO4) z The composition of ·a H2O is x = 3.41, y+z = 4, a = 8.84, and the results are shown in Table 1. The iron-phosphorus molar ratio is 0.855.

[0141] Test case

[0142] 1. Iron-phosphorus molar ratio test

[0143] All phosphide precursors provided in the examples and comparative examples were tested according to industry standard HG / T 4701-2021, and the specific test results are shown in Table 1.

[0144] Table 1

[0145] 2. Electrochemical performance testing

[0146] NFPP was prepared sequentially using the ferrophosphide precursors provided in all examples and comparative examples, including the following steps:

[0147] Weigh out the ferric phosphate precursor, and supplement with ammonium dihydrogen phosphate, ferrous oxalate, and sodium acetate according to a Na / Fe / P molar ratio of 1:0.73:1. Weigh out an appropriate amount of glucose as a carbon source and reducing agent. Add water to the ferric phosphate precursor, supplemented phosphorus source, iron source, sodium source, and glucose, and then ball mill the mixture for 60 minutes in a high-energy ball mill to obtain a mixed slurry. Spray dry the mixed slurry to obtain powder. Place the powder in an argon-protected tube furnace and hold at 500℃ for 12 hours to obtain carbon-coated NFPP material.

[0148] The prepared NFPP materials were subjected to XRD phase testing. The XRD patterns of Examples 1-6 and Comparative Examples 1-2 are shown in Figure 3. It can be seen that the NFPP phase prepared by the iron phosphate compound provided in Examples 1-6 has high purity. There is no obvious (011) diffraction peak belonging to Na2FeP2O7 near about 10.5 degrees, and (220) and (121) diffraction peaks belonging to NaFePO4 impurity phase near 33 degrees.

[0149] The battery prepared using the NFPP material described above was subjected to electrochemical performance testing, including the following steps:

[0150] The above-mentioned NFPP, Super P, and polyvinylidene fluoride (PVDF) were mixed in a ratio of 8:1:1, and an appropriate amount of NMP solvent was added. A slurry was obtained by grinding or stirring. The prepared slurry was then coated onto an aluminum foil current collector, controlling the areal density to be 1-2 mg / cm³. 2 The aluminum foil coated with the positive electrode material was dried in a vacuum oven at 110°C for 6 hours, and then cut into circular electrode sheets with a diameter of 1.2 cm.

[0151] Using a sodium sheet as the counter electrode, glass fiber as the separator, and 1 mL of NaClO4 dissolved in a mixed solvent with an EC:DEC ratio of 50:50 (volume ratio) as the electrolyte, a coin cell was assembled using a 2032 battery case for electrochemical performance testing.

[0152] The above-mentioned button cells were subjected to charge and discharge tests within a voltage range of 2.0-4.0V, with a charge and discharge current of 0.1C (1C = 129mA / g). The specific test results are shown in Table 2.

[0153] Figure 4 shows the charge-discharge curves of the batteries provided in Examples 1-6 and Comparative Examples 1-2. As can be seen from Figure 4, the charge-discharge specific capacity of the batteries provided in Examples 1-6 is significantly better than that of the batteries provided in Comparative Examples 1-2.

[0154] Table 2

[0155] As shown in Table 2, the batteries prepared from the phosphine iron oxide precursors provided in Examples 1-6 of this application have a 0.1C charging specific capacity of not less than 104.6 mAh / g and a 0.1C discharging specific capacity of not less than 93.3 mAh / g, which are much higher than those prepared from the precursors provided in Comparative Examples 1 and 2. It can be seen that the technical solution provided in this application can significantly improve the charging and discharging performance of the battery.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A phosphorus iron oxide precursor, characterized in that, The ferrophosphide precursor comprises a chemical composition of Fe. x (PO4) y (HPO4) z ·a H2O components; Among them, 0.6 <x / (y+z)<0.8,0<a / (y+z)<2.5。 2. The phosphine iron oxide precursor according to claim 1, characterized in that, The phosphite precursor has an amorphous structure.

3. A method for preparing the ferrophosphide precursor according to claim 1 or 2, characterized in that, Includes the following steps: 1) A co-precipitation reaction is carried out on a mixture containing an iron source and a phosphorus source to obtain the first precursor; 2) The first precursor is dried at 80℃-200℃ to obtain the iron phosphate precursor; In the ferrophosphide precursor, the molar ratio of iron to phosphorus is A, satisfying 0.

6. <A<0.8。 4. The preparation method according to claim 3, characterized in that, The coprecipitation reaction includes the following steps: The iron source solution and the phosphorus source solution were mixed, and then the pH was adjusted to 1.5-7.

0. The mixture was aged for 1-24 hours, filtered and washed to obtain the first precursor.

5. The preparation method according to claim 3 or 4, characterized in that, The iron source includes divalent iron; The mixture also includes an oxidant, the number of electrons required for the oxidant to reduce is A, and the number of electrons lost by the ferrous iron to ferric iron is B, satisfying A:B = (1~3):

1.

6. The preparation method according to claim 5, characterized in that, The oxidant includes at least one of hydrogen peroxide, oxygen, ozone, nitric acid, potassium permanganate, and potassium chlorate.

7. The preparation method according to any one of claims 3-6, characterized in that, The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and tripotassium phosphate. And / or, the iron source includes at least one of ferric nitrate, ferrous nitrate, ferrous sulfate, ferric sulfate, ferric chloride, ferrous chloride, ferrous acetate, and ferrous phosphate.

8. A sodium ferric pyrophosphate, characterized in that, It is prepared using the ferrophosphide precursor as described in claim 1 or 2.

9. The sodium ferric pyrophosphate according to claim 8, characterized in that, The preparation process includes the following steps: 1) The phosphite precursor is mixed with supplementary phosphorus source, supplementary iron source, sodium source and carbon source in the liquid phase to obtain a slurry; 2) The slurry is dried to obtain the second precursor; 3) The second precursor is sintered in an inert or reducing atmosphere to obtain the sodium iron pyrophosphate.

10. An electrode sheet (100), characterized in that, Includes sodium iron pyrophosphate as described in claim 9.

11. A battery (2), characterized in that, Includes the electrode sheet (100) as described in claim 10.

12. An electrical appliance (3), characterized in that, Includes the battery (2) as described in claim 11.

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