A high-entropy doped composite sodium iron pyrophosphate cathode material and its preparation method and battery

Abstract

This invention provides a high-entropy doped composite sodium iron pyrophosphate cathode material, its preparation method, and a battery. The preparation method includes: passing a mixed metal source solution, a phosphorus source mixture, an oxidant solution, and a complexing agent solution into a base liquid to perform a co-precipitation reaction to obtain a precursor material; the mixed metal source solution includes an ferrous source, a nickel source, a cobalt source, a manganese source, a chromium source, and additives, wherein the additives include sodium alginate and / or sodium carboxymethyl cellulose; the precursor material, the sodium source, and the carbon source are sequentially mixed, spray-dried, and sintered to obtain the high-entropy doped composite sodium iron pyrophosphate cathode material. The preparation method of this invention introduces multiple metal elements, additives, and complexing agents during the co-precipitation reaction, enabling multiple metal elements to be uniformly doped into the crystal structure of the material. This utilizes the synergistic effect of high-entropy multiple factors to enhance the structural stability of the material, optimize electron / ion transport dynamics, and improve cycle and high-rate performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a high-entropy doped composite sodium iron pyrophosphate cathode material, its preparation method, and a battery. Background Technology

[0002] With rising lithium and copper prices, the cost of lithium-ion batteries is gradually increasing. Sodium batteries, due to their abundant resources, exhibit a cost advantage, with the cost expected to drop below 0.4 yuan / Wh. Therefore, sodium batteries are poised for explosive growth in large-scale applications, with the first large-scale application markets, such as electric two-wheelers, low-speed electric vehicles, A00-class electric vehicles, and energy storage systems, projected to ship over 10-20 GWh. Currently, in existing technologies, sodium battery cathode materials mostly employ a dual-track strategy, simultaneously deploying layered oxide and polyanionic routes. Composite sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), with its low-cost advantage, has attracted particular attention and currently occupies a major market share.

[0003] Composite sodium iron pyrophosphate boasts an extremely long cycle life (theoretically exceeding 10,000 cycles, practically exceeding 4,000 cycles). Leveraging this long cycle life advantage will establish a competitive edge in specific technological routes or regional markets. Secondly, the demand for high-rate performance in certain fields also places higher requirements on sodium-ion batteries. However, in reality, the inherent advantages of composite sodium iron pyrophosphate in terms of long cycle life and high-rate performance have not been fully realized. Currently, there are shortcomings in cycle performance and high-rate performance, primarily due to the instability of the cathode material's crystal structure under long-term cycling or high-rate charge-discharge conditions.

[0004] Based on the above research, there is a need to provide a method for preparing composite sodium iron pyrophosphate cathode materials that simultaneously possess long cycle life and high rate performance. Summary of the Invention

[0005] The purpose of this invention is to provide a high-entropy doped composite sodium iron pyrophosphate cathode material, its preparation method, and a battery. The preparation method introduces multiple metal elements, additives, and complexing agents during the precursor preparation process, enabling these metal elements to be uniformly doped into the crystal structure of the material. By utilizing the multiple effects of high entropy to synergistically optimize the material's performance, enhance its structural stability, and optimize electron / ion transport dynamics, the sodium iron pyrophosphate cathode material exhibits advantages such as long cycle life and high rate performance due to its stable in-situ high-entropy phase structure.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material, the method comprising the following steps:

[0008] (1) A mixed metal source solution, a mixed phosphorus source solution, an oxidant solution and a complexing agent solution are passed into a bottom liquid to carry out a co-precipitation reaction to obtain a precursor material;

[0009] The mixed metal source solution includes ferrous source, nickel source, cobalt source, manganese source, chromium source and additives, the additives including sodium alginate and / or sodium carboxymethyl cellulose; the phosphorus source mixture includes a phosphorus source (referring to a phosphorus source containing phosphate ions) and a pyrophosphate source (referring to a pyrophosphate source containing pyrophosphate ions).

[0010] (2) The precursor material, sodium source and carbon source described in step (1) are mixed, spray-dried and sintered in sequence to obtain the high-entropy doped composite sodium iron pyrophosphate cathode material.

[0011] The preparation method described in this invention involves uniformly doping multiple elements during the precursor material preparation stage. During sintering, Ni, Co, Mn, and Cr elements enter the Fe atomic sites and form an in-situ high-entropy doped phase with the iron element in the matrix. The high-entropy multiple effects synergistically optimize the material performance, enhance the structural stability of the material, and optimize the electron / ion transport dynamics, thereby giving the high-entropy doped composite sodium iron pyrophosphate cathode material advantages such as long cycle life and high rate performance.

[0012] However, co-precipitation of multiple elements suffers from problems such as elemental segregation. To improve the uniformity of multi-element doping, this invention incorporates specific additives, such as sodium alginate and / or sodium carboxymethyl cellulose, during the preparation of the precursor material. These additives partially cross-link in an oxidizing environment, forming a stable three-dimensional network structure. Metal ions are anchored by carboxyl groups within the network, and the co-precipitation reaction occurs within the network. The resulting particles are encapsulated by the three-dimensional network, fundamentally eliminating ion migration and segregation. Furthermore, this invention simultaneously adds a complexing agent to the existing oxidant, thereby stabilizing ions in an oxidizing environment and preventing the instantaneous precipitation of certain ions due to excessive reactivity. This results in a more balanced precipitation rate for multiple ions, further enhancing the uniformity of multi-element co-precipitation.

[0013] Preferably, the mixed metal source solution and oxidant solution in step (1) are fed in a molar ratio of oxidant to ferrous source of (0.5~1.0):1, for example, it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1.0:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, in the mixed metal source solution of step (1), the molar ratio of the additive to the ferrous source is (2~6):100, for example, it can be 2:100, 3:100, 4:100, 5:100 or 6:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] The content of the additives described in this invention will affect the uniformity of element distribution. If the additive content is too low, the uniformity of element distribution will decrease. If the additive content is too high, it will affect the material's capacity and structural stability.

[0016] Preferably, the mixed metal source solution and complexing agent solution in step (1) are fed in a ratio of complexing agent to ferrous source of (3~10):100, for example, it can be 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the mixed metal source solution and phosphorus source mixture in step (1) are fed in a ratio of pyrophosphate source to ferrous source of (3~5):10, for example, it can be 3:10, 3.5:10, 4:10, 4.5:10 or 5:10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the ratio of the total molar amount of nickel, cobalt, manganese and chromium to the molar amount of iron in the mixed metal source solution in step (1) is (0.01~0.2):(2.70~2.89), for example, it can be 0.01:2.89, 0.05:2.85, 0.1:2.8, 0.15:2.75 or 0.2:2.70, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] The total content of doping elements in this invention affects the performance of the material. If the content of doping elements is too low, the high-entropy doping effect will decrease. If the content of doping elements is too high, an excessive high-entropy phase will be formed, causing lattice distortion and reducing cycle and rate performance.

[0020] Preferably, in the mixed metal source solution described in step (1), the molar ratio of nickel, cobalt, manganese and chromium is 1:(0.8~1.2):(0.8~1.2):(0.8~1.2), for example, it can be 1:0.8:1:1, 1:1:0.8:0.8 or 1:1.2:1.2:1.2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the pH of the phosphorus source mixture in step (1) is 4.0 to 7.0, for example, it can be 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 or 7.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the phosphorus source in the phosphorus source mixture in step (1) includes any one or a combination of at least two of sodium phosphate, sodium hydrogen phosphate, or sodium dihydrogen phosphate, and the pyrophosphate source includes any one or a combination of at least two of sodium pyrophosphate, trisodium monohydrogen pyrophosphate, or disodium dihydrogen pyrophosphate.

[0023] Preferably, in the phosphorus source mixture in step (1), the molar ratio of phosphorus atoms in the phosphorus source to phosphorus atoms in the pyrophosphate source is (1.5~2.2):1, for example, it can be 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1 or 2.2:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the complexing agent in the complexing agent solution in step (1) includes sodium potassium tartrate.

[0025] Because an oxidant is added during the coprecipitation reaction of this invention, the oxidant can oxidize metal ions into high-valence ions. The complexing agent of this invention is preferably sodium potassium tartrate, which has a special complexing ability for high-valence ions, can stabilize these ions in an oxidizing environment, prevent them from precipitating instantly due to excessive reactivity, and make the precipitation rates of various ions more matched.

[0026] Preferably, the oxidant in the oxidant solution in step (1) includes hydrogen peroxide and / or sodium persulfate.

[0027] Preferably, the base liquid in step (1) includes deionized water.

[0028] Preferably, the ratio of the volume of the bottom liquid in step (1) to the volume of the system solution at the end of the coprecipitation reaction is 1:(3~5), for example, it can be 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the temperature of the coprecipitation reaction in step (1) is 40℃~80℃, for example, 40℃, 50℃, 60℃, 70℃ or 80℃, and the time is 4h~10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, after the coprecipitation reaction in step (1), the precursor material is further subjected to filtration, washing and drying in sequence to obtain the precursor material.

[0031] Preferably, the mixing method in step (2) includes sand milling.

[0032] Preferably, the ratio of the total molar amount of metal elements in the precursor material to the molar amount of sodium elements in the sodium source in step (2) is 1:(1~2), for example, it can be 1:1, 1:1.25, 1:1.5, 1:1.75 or 1:2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the amount of carbon source added in step (2) is 2wt% to 5wt% of the precursor material mass, for example, it can be 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the carbon source in step (2) includes any one or a combination of at least two of carbon nanotubes, graphene, glucose, or citric acid.

[0035] Preferably, the sintering in step (2) includes pre-firing at 300℃-400℃, for example, 300℃, 325℃, 350℃, 375℃ or 400℃ for 2h-5h, for example, 2h, 3h, 4h or 5h, and then sintering at 550℃-600℃, for example, 550℃, 575℃ or 600℃ for 5h-15h, for example, 5h, 7.5h, 10h, 12.5h or 15h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the sintering atmosphere in step (2) includes an inert gas, such as a hydrogen-argon mixture or nitrogen.

[0037] In a second aspect, the present invention provides a high-entropy doped composite sodium iron pyrophosphate cathode material, which is prepared by the preparation method described in the first aspect.

[0038] The precursor material prepared by this invention has the chemical formula Na. x Fe 2.9-0.8y (CoNiCrMn) y (PO4)2P2O7, where 0≤x≤2.5, for example, it can be 0.1, 0.5, 1, 1.5, 2 or 2.5, and 0<y≤0.2, for example, it can be 0.1, 0.125, 0.15, 0.175 or 0.2. The chemical formula of the high-entropy doped composite sodium iron pyrophosphate cathode material is Na4Fe 2.9-0.8y (CoNiCrMn) y (PO4)2P2O7, where 0 < y ≤ 0.2, for example, it can be 0.1, 0.125, 0.15, 0.175 or 0.2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Thirdly, the present invention provides a battery comprising the high-entropy doped composite sodium iron pyrophosphate cathode material as described in the second aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention employs a co-precipitation method to uniformly dope multiple elements. During sintering, Ni, Co, Mn, and Cr elements enter the Fe atomic sites, forming an in-situ high-entropy doped phase with the Fe matrix. In other words, this invention introduces multiple elements to form a high-entropy solid solution FeCoNiCrMn, enhancing the material's structural stability, suppressing lattice distortion and irreversible phase transitions during charge and discharge, buffering volume stress caused by sodium ion insertion / extraction, and improving cycle stability. Furthermore, the high-entropy doping in this invention can construct a three-dimensional network of sodium ion diffusion channels, reducing the migration barrier, shortening the diffusion path, optimizing ion diffusion kinetics, and significantly improving electronic conductivity, thereby enhancing rate performance. Attached Figure Description

[0042] Figure 1 This is a scanning electron microscope image of the high-entropy doped composite sodium iron pyrophosphate cathode material obtained in Example 1 of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0044] Example 1

[0045] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material, the method comprising the following steps:

[0046] (1) Dissolve ferrous sulfate in water to form a ferrous sulfate solution. Add nickel sulfate, manganese sulfate, cobalt sulfate, chromium sulfate and sodium alginate to the ferrous sulfate solution in sequence. Mix and stir evenly to obtain a mixed metal source solution. In the mixed metal source solution, the total molar amount of nickel, cobalt, manganese and chromium is 0.04:2.86 to the molar amount of iron, the molar ratio of nickel, cobalt, manganese and chromium is 1:1:1:1, and the molar ratio of sodium alginate to ferrous sulfate is 4:100.

[0047] Sodium phosphate and sodium pyrophosphate were mixed in a 2:1 molar ratio of phosphorus atoms to obtain a phosphorus source solution. The pH of the mixture was then adjusted to 4.5 with dilute acid. Sodium persulfate solution and potassium sodium tartrate solution were also prepared separately.

[0048] (2) A certain amount of deionized water is used as the reaction base liquid. The ratio of the volume of deionized water to the volume of the mixed liquid at the end of the coprecipitation reaction is 1:4. The temperature of the reaction base liquid is 70℃.

[0049] (3) Using a co-current feeding method, the mixed metal source solution, phosphorus source mixture, sodium persulfate solution and potassium sodium tartrate solution are simultaneously added to the reaction base liquid. The temperature is maintained at 70℃, and the co-precipitation reaction is carried out for 6 hours to obtain a suspension. The suspension is then filtered, washed and dried to obtain the precursor material.

[0050] The mixed metal source solution and sodium persulfate solution are fed in a ratio of sodium persulfate to ferrous sulfate of 0.8:1; the mixed metal source solution and potassium tartrate solution are fed in a ratio of potassium tartrate to ferrous sulfate of 5:100; and the mixed metal source solution and phosphorus source mixture are fed in a ratio of pyrophosphate source to ferrous sulfate of 4:10.

[0051] (4) The precursor material, sodium carbonate and glucose described in step (3) are mixed, milled and then spray-dried to obtain mixed spherical powder, wherein the ratio of the total molar amount of metal elements in the precursor material to the molar amount of sodium elements in the sodium carbonate is 1:2, and the amount of glucose added is 5 wt% of the mass of the precursor material.

[0052] The mixed spherical powder was then pre-sintered at 350°C for 3 hours in a hydrogen-argon mixed atmosphere, followed by high-temperature sintering at 575°C for 12 hours to obtain the high-entropy doped composite sodium iron pyrophosphate cathode material. The scanning electron microscope image of the high-entropy doped composite sodium iron pyrophosphate cathode material is shown below. Figure 1 As shown.

[0053] Example 2

[0054] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material, the method comprising the following steps:

[0055] (1) Dissolve ferrous sulfate in water to form a ferrous sulfate solution. Add nickel sulfate, manganese sulfate, cobalt sulfate, chromium sulfate and sodium alginate to the ferrous sulfate solution in sequence. Mix and stir evenly to obtain a mixed metal source solution. In the mixed metal source solution, the total molar amount of nickel, cobalt, manganese and chromium is 0.2:2.70 to the molar amount of iron, the molar ratio of nickel, cobalt, manganese and chromium is 1:1.2:1.2:0.8, and the molar ratio of sodium alginate to ferrous sulfate is 6:100.

[0056] Sodium phosphate and sodium pyrophosphate were mixed in a molar ratio of 2.2:1 for phosphorus atoms, and the pH of the mixture was adjusted to 4.0 with dilute acid to obtain a phosphorus source mixture. Sodium persulfate solution and potassium sodium tartrate solution were also prepared separately.

[0057] (2) A certain amount of deionized water is used as the reaction base liquid. The ratio of the volume of deionized water to the volume of the mixed liquid at the end of the coprecipitation reaction is 1:5. The temperature of the reaction base liquid is 80℃.

[0058] (3) Using a co-current feeding method, the mixed metal source solution, phosphorus source mixture, sodium persulfate solution and potassium sodium tartrate solution are simultaneously added to the reaction base liquid. The temperature is maintained at 80℃, and the co-precipitation reaction is carried out for 4 hours to obtain a suspension. The suspension is then filtered, washed and dried to obtain the precursor material.

[0059] The mixed metal source solution and sodium persulfate solution are fed in a molar ratio of sodium persulfate to ferrous sulfate of 1.0:1; the mixed metal source solution and potassium tartrate solution are fed in a molar ratio of potassium tartrate to ferrous sulfate of 3:100; and the mixed metal source solution and phosphorus source mixture are fed in a molar ratio of sodium pyrophosphate to ferrous sulfate of 3.5:10.

[0060] (4) The precursor material, sodium carbonate and glucose described in step (3) are mixed, milled and then spray-dried to obtain mixed spherical powder, wherein the ratio of the total molar amount of metal elements in the precursor material to the molar amount of sodium elements in the sodium carbonate is 1:1.5, and the amount of glucose added is 3 wt% of the mass of the precursor material;

[0061] The mixed spherical powder was then pre-sintered at 300°C for 5 hours in a hydrogen-argon mixed atmosphere, and then sintered at 600°C for 5 hours to obtain the high-entropy doped composite sodium iron pyrophosphate cathode material.

[0062] Example 3

[0063] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material, the method comprising the following steps:

[0064] (1) Dissolve ferrous sulfate in water to form a ferrous sulfate solution. Add nickel sulfate, manganese sulfate, cobalt sulfate, chromium sulfate and sodium carboxymethyl cellulose in sequence to the ferrous sulfate solution. Mix and stir evenly to obtain a mixed metal source solution. In the mixed metal source solution, the total molar amount of nickel, cobalt, manganese and chromium is 0.01:2.89 to the molar amount of iron, the molar ratio of nickel, cobalt, manganese and chromium is 1:0.8:0.8:1.2, and the molar ratio of sodium carboxymethyl cellulose to ferrous sulfate is 2:100.

[0065] Sodium dihydrogen phosphate and sodium pyrophosphate were mixed in a molar ratio of 1.8:1 for phosphorus atoms, and the pH of the mixture was adjusted to 5.0 with dilute acid to obtain a phosphorus source mixture. Hydrogen peroxide solution and potassium sodium tartrate solution were also prepared separately.

[0066] (2) A certain amount of deionized water is used as the reaction base liquid. The ratio of the volume of deionized water to the volume of the mixed liquid at the end of the coprecipitation reaction is 1:3. The temperature of the reaction base liquid is 50℃.

[0067] (3) Using a co-flow feeding method, the mixed metal source solution, phosphorus source mixture, hydrogen peroxide solution and potassium sodium tartrate solution are simultaneously added to the reaction base liquid. The temperature is maintained at 50℃, and the co-precipitation reaction is carried out for 10 hours to obtain a suspension. The suspension is then filtered, washed and dried to obtain the precursor material.

[0068] The mixed metal source solution and hydrogen peroxide solution are fed in a ratio of 0.5:1 (hydrogen peroxide to ferrous sulfate molar ratio), the mixed metal source solution and potassium tartrate solution are fed in a ratio of 10:100 (potassium tartrate to ferrous sulfate molar ratio), and the mixed metal source solution and phosphorus source mixture are fed in a ratio of 4.5:10 (sodium pyrophosphate to ferrous sulfate molar ratio).

[0069] (4) The precursor material, sodium carbonate and glucose described in step (3) are mixed, milled and then spray-dried to obtain mixed spherical powder, wherein the ratio of the total molar amount of metal elements in the precursor material to the molar amount of sodium elements in the sodium carbonate is 1:2, and the amount of glucose added is 2 wt% of the mass of the precursor material.

[0070] The mixed spherical powder was then pre-sintered at 400°C for 2 hours in a hydrogen-argon mixed atmosphere, and then sintered at 550°C for 15 hours to obtain the high-entropy doped composite sodium iron pyrophosphate cathode material.

[0071] Example 4

[0072] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material. Except for step (1), in which the total molar amount of nickel, cobalt, manganese and chromium in the mixed metal source solution is 0.005:2.895 to the molar amount of iron, the preparation method is the same as in Example 1.

[0073] Example 5

[0074] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material. Except for step (1), in which the total molar ratio of nickel, cobalt, manganese and chromium to iron in the mixed metal source solution is 0.3:2.6, the preparation method is the same as in Example 1.

[0075] Example 6

[0076] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material. Except for step (1), in which the molar ratio of sodium alginate to ferrous sulfate in the mixed metal source solution is 0.5:100, the preparation method is the same as in Example 1.

[0077] Example 7

[0078] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material. Except for step (1), in which the molar ratio of sodium alginate to ferrous sulfate in the mixed metal source solution is 8:100, the preparation method is the same as in Example 1.

[0079] Example 8

[0080] This embodiment provides a method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material. The preparation method is the same as in Example 1, except that the potassium sodium tartrate solution is replaced with sodium citrate solution of equal concentration, and the metal source solution and sodium citrate solution are fed in a ratio of sodium citrate to ferrous sulfate of 5:100.

[0081] Comparative Example 1

[0082] This comparative example provides a method for preparing sodium iron pyrophosphate cathode material. Except for step (1) when preparing the mixed metal source solution, nickel sulfate, manganese sulfate, cobalt sulfate, chromium sulfate and sodium alginate are not added, and potassium sodium tartrate solution is not added during the co-precipitation reaction in step (3), the preparation method is the same as in Example 1.

[0083] Comparative Example 2

[0084] This comparative example provides a method for preparing sodium iron pyrophosphate cathode material. Except for step (1) when preparing the mixed metal source solution, sodium alginate is not added, the preparation method is the same as in Example 1.

[0085] Comparative Example 3

[0086] This comparative example provides a method for preparing sodium iron pyrophosphate cathode material. Except for step (3) coprecipitation reaction in which potassium sodium tartrate solution is not added, the preparation method is the same as in Example 1.

[0087] The positive electrode materials obtained in the above examples and comparative examples were used to prepare positive electrodes. Then, using a sodium metal sheet as the negative electrode, they were assembled into CR2032 coin cells with a separator and electrolyte under vacuum. Electrochemical performance tests were then conducted within a voltage range of 2.0-3.7V and a current density of 0.1-10C. The rate capacity retention (based on 0.1C) and cycle capacity retention after 8000 cycles at 5C are shown in Table 1 below.

[0088] Table 1

[0089]

[0090] As can be seen from Table 1 above:

[0091] As shown in Example 1 and Comparative Example 1, the present invention, through high-entropy doping combined with the introduction of additives and complexing agents, can simultaneously improve the cycling performance and rate performance of the material. As shown in Example 1 and Comparative Example 2, the additives added during the co-precipitation reaction of the present invention can prevent element segregation, promote uniform element precipitation, and enhance the effect of high-entropy doping. As shown in Example 1 and Comparative Example 3, the addition of the complexing agent of the present invention can further promote uniform element precipitation, thereby further improving the performance of the material. As shown in Example 1 and Examples 4-5, the present invention preferably uses a ratio of the total molar amount of doped elements to the molar amount of iron within a specific range to dope elements with verified content, promoting the multiple synergistic effects of high-entropy doping. As shown in Example 1 and Examples 6-7, the present invention preferably uses a molar ratio of the additives to the ferrous source within a specific range to promote the uniformity of element distribution, while avoiding excessive addition that could affect the performance of the material. As shown in Example 1 and Example 8, the specific type of complexing agent of the present invention can work in conjunction with the oxidant to better match the precipitation rates of various ions, further promoting the uniformity of precipitation of various elements.

[0092] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a high-entropy doped composite sodium iron pyrophosphate cathode material, characterized in that, The preparation method includes the following steps: (1) A mixed metal source solution, a mixed phosphorus source solution, an oxidant solution and a complexing agent solution are passed into a bottom liquid to carry out a co-precipitation reaction to obtain a precursor material; The mixed metal source solution includes ferrous source, nickel source, cobalt source, manganese source, chromium source and additives, the additives including sodium alginate and / or sodium carboxymethyl cellulose; the phosphorus source mixture includes phosphorus source and pyrophosphate source; (2) The precursor material, sodium source and carbon source described in step (1) are mixed, spray-dried and sintered in sequence to obtain the high-entropy doped composite sodium iron pyrophosphate cathode material.

2. The preparation method according to claim 1, characterized in that, In step (1), the mixed metal source solution and oxidant solution are fed in a ratio of oxidant to ferrous source of (0.5~1.0):

1. Preferably, in the mixed metal source solution of step (1), the molar ratio of the additive to the ferrous source is (2~6):100; Preferably, in step (1), the mixed metal source solution and the complexing agent solution are fed in a ratio of (3~10):100 of complexing agent to ferrous source; Preferably, the mixed metal source solution and phosphorus source mixture in step (1) are fed in a ratio of pyrophosphate source to ferrous source of (3~5):

10.

3. The preparation method according to claim 1 or 2, characterized in that, The ratio of the total molar amount of nickel, cobalt, manganese and chromium to the molar amount of iron in the mixed metal source solution in step (1) is (0.01~0.2):(2.70~2.89); Preferably, in the mixed metal source solution described in step (1), the molar ratio of nickel, cobalt, manganese and chromium is 1:(0.8~1.2):(0.8~1.2):(0.8~1.2).

4. The preparation method according to claim 1 or 2, characterized in that, The pH of the phosphorus source mixture in step (1) is 4.0~7.0; Preferably, the phosphorus source in the phosphorus source mixture in step (1) includes any one or a combination of at least two of sodium phosphate, sodium hydrogen phosphate, or sodium dihydrogen phosphate, and the pyrophosphate source includes any one or a combination of at least two of sodium pyrophosphate, trisodium monohydrogen pyrophosphate, or disodium dihydrogen pyrophosphate. Preferably, in the phosphorus source mixture in step (1), the molar ratio of phosphorus atoms in the phosphorus source to phosphorus atoms in the pyrophosphate source is (1.5~2.2):

1.

5. The preparation method according to claim 1 or 2, characterized in that, The complexing agent in the complexing agent solution in step (1) includes sodium potassium tartrate; Preferably, the oxidant in the oxidant solution in step (1) includes hydrogen peroxide and / or sodium persulfate.

6. The preparation method according to claim 1 or 2, characterized in that, The base solution in step (1) includes deionized water; Preferably, the ratio of the volume of the bottom liquid in step (1) to the volume of the system solution at the end of the coprecipitation reaction is 1:(3~5).

7. The preparation method according to claim 1 or 2, characterized in that, The temperature of the coprecipitation reaction in step (1) is 40℃~80℃, and the time is 4h~10h; Preferably, after the coprecipitation reaction in step (1), the precursor material is further subjected to filtration, washing and drying in sequence to obtain the precursor material.

8. The preparation method according to claim 1 or 2, characterized in that, The mixing method in step (2) includes sand milling; Preferably, the ratio of the total molar amount of metal elements in the precursor material in step (2) to the molar amount of sodium elements in the sodium source is 1:(1~2); Preferably, the amount of carbon source added in step (2) is 2wt% to 5wt% of the precursor material mass; Preferably, the carbon source in step (2) includes any one or a combination of at least two of carbon nanotubes, graphene, glucose, or citric acid; Preferably, the sintering in step (2) includes pre-firing at 300℃-400℃ for 2h-5h, and then sintering at 550℃-600℃ for 5h-15h.

9. A high-entropy doped composite sodium iron pyrophosphate cathode material, characterized in that, The high-entropy doped composite sodium iron pyrophosphate cathode material is prepared by the preparation method described in any one of claims 1-8.

10. A battery, characterized in that, The battery comprises the high-entropy doped composite sodium iron pyrophosphate cathode material as described in claim 9.

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