An ion-doped manganese-based sodium-ion cathode material, its preparation method and application

Abstract

The present invention provides an ion-doped manganese-based sodium-ion cathode material, a preparation method thereof and an application thereof. The preparation method comprises the following steps: under a protective atmosphere, an ion solution, a doping element solution, a complexing agent and a precipitating agent are mixed and introduced into a bottom solution. After the particle size D50 reaches the target particle size, the feeding is stopped, and solid-liquid separation is carried out to obtain an ion-doped manganese-based ternary precursor; a sodium source and the ion-doped manganese-based ternary precursor are mixed and sintered in an oxygen-containing atmosphere to obtain the ion-doped manganese-based sodium-ion cathode material; the ion solution includes soluble manganese salts, nickel salts and copper salts; the doping element solution includes any one or a combination of at least two of soluble aluminum salts, zirconium salts or titanium salts. The precursor obtained by the preparation method has a narrow particle size distribution, can be single-crystallized during sintering, and Ni, Cu and doping elements are used to improve the manganese-based sodium-ion cathode material, thereby improving the structural stability and air stability of the finally obtained cathode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a cathode material, in particular to an ion-doped manganese-based sodium-ion cathode material and its preparation method and application. Background Art

[0002] Lithium-ion batteries are widely used in energy storage devices and the electric vehicle industry due to their advantages such as high working voltage, high energy density, and long cycle life. However, lithium resources have disadvantages such as low reserves, uneven distribution, and low recovery rate. The rapidly growing lithium-ion battery market will surely increase the consumption of lithium resources and lead to continuous increase in lithium prices, making it difficult to meet the demand for large-scale low-cost energy storage.

[0003] Compared with lithium-ion batteries, sodium-ion batteries have a similar working principle, and the sodium element used in them is more widely distributed in the earth's crust and much cheaper. The abundant reserves and insertion mechanism of sodium make sodium-ion batteries an ideal substitute for lithium-ion batteries in large-scale applications. However, at present, sodium-ion batteries have problems of poor cycle stability and poor rate performance. Therefore, improving the cycle stability and rate performance of sodium-ion battery cathode materials has become the key to related research on sodium-ion batteries.

[0004] A large number of studies have shown that, without excessively reducing the electrochemical performance of sodium-ion cathode materials, doping transition metal ions can retain the O3 layered structure, increase the sodium layer spacing, promote the diffusion of Na + and the highly reversible phase transition process, inhibit the side reaction between the particle surface and the electrolyte, and ensure the structural stability and cycle stability of sodium-ion cathode materials.

[0005] CN113782735A discloses a sodium-ion battery cathode material, a sodium-ion battery and a preparation method thereof. The sodium-ion battery cathode active material provided by it includes NaTm 1-x Al x O2, where Tm is a transition element; its preparation method is: grinding metal oxides and 3-5 wt% excess sodium carbonate powder, and then pressing them into wafers; calcining the wafers at 800-1200 °C at a heating rate of 1-20 °C / min, keeping the temperature for 12-24 h, and obtaining the cathode active material NaTm 1- x Al x O2 after natural cooling.

[0006] CN111554920A discloses a sodium-ion-rich lithium manganese-based cathode material, its precursor and a preparation method thereof. Among them, the general formula of the sodium-ion-containing manganese-based precursor is Na x Mn y M 1-y O z(0 < x ≤ 1, 0.3 ≤ y ≤ 1, 1 ≤ z ≤ 3); The general formula of the sodium-rich lithium manganese-based cathode material is Li n Na x Mn y M 1-y O2 (0.5 ≤ n ≤ 2, 0 < x ≤ 1, 0.3 < y ≤ 1). In this technical solution, a three-step method is used to synthesize the sodium-rich lithium manganese-based cathode material containing sodium ions. During the synthesis process, sodium ions are first embedded into the manganese-based precursor to form a new type of manganese-based precursor containing sodium ions, and then the manganese-based precursor containing sodium ions is used as a raw material for high-temperature solid-phase synthesis of the sodium-rich lithium manganese-based cathode material containing sodium ions.

[0007] The existing technologies for doping transition metal ions in sodium-ion cathode materials include the solid-phase method and the co-precipitation method. Using the solid-phase method for doping has the defect of local enrichment of doped elements, which interferes with the particle uniformity of the sodium-ion cathode material, easily reduces the stability of the sodium-ion cathode material, and thus affects the capacitance to a certain extent. At the same time, there is little research on doping transition metal ions by the co-precipitation method in the existing technologies. It is necessary to provide a manganese-based sodium-ion cathode material with good electrochemical performance based on the co-precipitation method, its preparation method and application. Summary of the Invention

[0008] Aiming at the deficiencies of the existing technologies, the purpose of the present invention is to provide a manganese-based sodium-ion cathode material with ion doping, its preparation method and application. The preparation method improves the structural stability and thermal stability of the finally obtained cathode material by controlling the type ratio of doped elements.

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

[0010] In the first aspect, the present invention provides a preparation method of a manganese-based sodium-ion cathode material with ion doping. The preparation method includes the following steps:

[0011] (1) Under a protective atmosphere, a mixed ion solution, a doped element solution, a complexing agent and a precipitating agent are introduced into the bottom liquid. After the particle size D50 reaches the target particle size, the feeding is stopped, and solid-liquid separation is carried out to obtain an ion-doped manganese-based ternary precursor;

[0012] (2) A sodium source is mixed with the ion-doped manganese-based ternary precursor obtained in step (1), and sintering is carried out in an oxygen-containing atmosphere to obtain an ion-doped manganese-based sodium-ion cathode material;

[0013] The mixed ion solution in step (1) includes soluble manganese salts, nickel salts and copper salts;

[0014] The doped element solution in step (1) includes any one or at least two combinations of soluble aluminum salts, zirconium salts or titanium salts.

[0015] The addition amount of the sodium source in step (2) of the present invention is such that the molar amount of sodium ions in the sintered cathode material conforms to the chemical formula NaMnO2 of a conventional sodium manganese-based cathode material.

[0016] The preparation method provided by the present invention uses Ni, Cu and doping elements to improve the sodium manganese-based cathode material. Moreover, wet doping is carried out in the precursor preparation stage, so that the doping elements are evenly distributed in the obtained cathode material, improving the structural stability and air stability of the finally obtained cathode material.

[0017] The gas used in the protective atmosphere in step (1) includes but is not limited to nitrogen and / or inert gas.

[0018] The gas used in the oxygen-containing atmosphere in step (2) includes air and / or oxygen.

[0019] Preferably, the particle size D50 of the ion-doped manganese-based ternary precursor obtained in step (1) is 4-5 μm. For example, it can be 4 μm, 4.2 μm, 4.5 μm, 4.6 μm, 4.8 μm or 5 μm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0020] Preferably, the particle size of the ion-doped manganese-based ternary precursor obtained in step (1) satisfies: 0.6 ≤ ((D90 - D10) / D50) ≤ 0.7. For example, it can be 0.6, 0.62, 0.64, 0.66, 0.68 or 0.7, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0021] The control of the particle size of the ion-doped manganese-based ternary precursor prepared by the present invention is beneficial to the single crystallization of the ion-doped manganese-based ternary precursor during sintering, thereby ensuring the electrochemical properties such as the tap density, particle strength and voltage of the obtained cathode material.

[0022] Preferably, the bottom liquid in step (1) is composed of water, ammonia water and sodium hydroxide.

[0023] Preferably, the pH value of the bottom liquid in step (1) is 11-13. For example, it can be 11, 11.5, 12, 12.5 or 13, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0024] Preferably, the ammonia concentration in the bottom liquid in step (1) is 5-20 g / L. For example, it can be 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 18 g / L or 20 g / L, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0025] Preferably, the temperature of the bottom liquid in step (1) is 40 - 80°C. For example, it can be 40°C, 45°C, 50°C, 60°C, 70°C, or 80°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0026] Preferably, during the introduction process in step (1), the pH value, ammonia concentration, and temperature of the mixed solution are kept constant.

[0027] Preferably, during the introduction process in step (1), stirring is carried out, and the stirring speed is 200 - 500 rpm. For example, it can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0028] Preferably, the flow rate of the mixed ion solution in step (1) is 8 - 100 L / h. For example, it can be 8 L / h, 20 L / h, 30 L / h, 40 L / h, 50 L / h, 60 L / h, 80 L / h, or 100 L / h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0029] Preferably, the flow rate of the doped element solution in step (1) is 1.5 - 20 L / h. For example, it can be 1.5 L / h, 4 L / h, 5 L / h, 8 L / h, 10 L / h, 15 L / h, or 20 L / h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0030] Preferably, the manganese salt in the mixed ion solution in step (1) includes any one or a combination of at least two of manganese sulfate, manganese chloride, or manganese nitrate. Typical but non - restrictive combinations include the combination of manganese sulfate and manganese chloride, the combination of manganese sulfate and manganese nitrate, the combination of manganese chloride and manganese nitrate, or the combination of manganese sulfate, manganese chloride, and manganese nitrate.

[0031] Preferably, the nickel salt in the mixed ion solution in step (1) includes any one or a combination of at least two of nickel sulfate, nickel chloride, or nickel nitrate. Typical but non - restrictive combinations include the combination of nickel sulfate and nickel chloride, the combination of nickel sulfate and nickel nitrate, the combination of nickel chloride and nickel nitrate, or the combination of nickel sulfate, nickel chloride, and nickel nitrate.

[0032] Preferably, the copper salt in the mixed ion solution in step (1) includes any one or a combination of at least two of copper sulfate, copper chloride, or copper nitrate. Typical but non - restrictive combinations include the combination of copper sulfate and copper chloride, the combination of copper sulfate and copper nitrate, the combination of copper chloride and copper nitrate, or the combination of copper sulfate, copper chloride, and copper nitrate.

[0033] Preferably, in the mixed ionic solution in step (1), the molar ratio of manganese ions, nickel ions to copper ions is (6.5 - 7.5):(1.8 - 2.2):1.

[0034] In the mixed ionic solution in step (1), the molar ratio of manganese ions to copper ions is 6.5 - 7.5:1. For example, it can be 6.5:1, 6.8:1, 7:1, 7.2:1 or 7.5:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0035] In the mixed ionic solution in step (1), the molar ratio of nickel ions to copper ions is 1.8 - 2.2:1. For example, it can be 1.8:1, 1.9:1, 2:1, 2.1:1 or 2.2:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0036] Preferably, in the mixed ionic solution in step (1), the total molar concentration of manganese ions, nickel ions and copper ions is 1.6 - 2.4 mol / L. For example, it can be 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L or 2.4 mol / L, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0037] Preferably, the aluminum salt in the doping element solution in step (1) includes any one or a combination of at least two of aluminum sulfate, aluminum chloride or aluminum nitrate. Typical but non - restrictive combinations include the combination of aluminum sulfate and aluminum chloride, the combination of aluminum sulfate and aluminum nitrate, the combination of aluminum chloride and aluminum nitrate, or the combination of aluminum sulfate, aluminum chloride and aluminum nitrate.

[0038] Preferably, the zirconium salt in the doping element solution in step (1) includes any one or a combination of at least two of zirconium sulfate, zirconium chloride or zirconium nitrate. Typical but non - restrictive combinations include the combination of zirconium sulfate and zirconium chloride, the combination of zirconium sulfate and zirconium nitrate, the combination of zirconium chloride and zirconium nitrate, or the combination of zirconium sulfate, zirconium chloride and zirconium nitrate.

[0039] Preferably, the titanium salt in the doping element solution in step (1) includes titanium chloride and / or titanium nitrate.

[0040] Preferably, the molar concentration of the doping ions in the doping element solution in step (1) is 0.08 - 0.12 mol / L. For example, it can be 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.11 mol / L or 0.12 mol / L, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0041] Preferably, the precipitant in step (1) includes a NaOH solution.

[0042] Preferably, the concentration of the NaOH solution is 30-35 wt%, for example, it can be 30 wt%, 32 wt%, 33 wt%, 34 wt% or 35 wt%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0043] Preferably, the complexing agent in step (1) includes ammonia water with a concentration of 12-16 wt%, for example, it can be 12 wt%, 13 wt%, 14 wt%, 15 wt% or 16 wt%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0044] Preferably, the sintering temperature in step (2) is 900-1100 °C, for example, it can be 900 °C, 950 °C, 1000 °C, 1050 °C or 1100 °C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0045] Preferably, the sintering time in step (2) is 10-16 h, for example, it can be 10 h, 12 h, 14 h, 15 h or 16 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0046] In a second aspect, the present invention provides an ion-doped manganese-based sodium-ion cathode material, and the ion-doped manganese-based sodium-ion cathode material is prepared by the preparation method described in the first aspect.

[0047] In a third aspect, the present invention provides a cathode, and the cathode includes the ion-doped manganese-based sodium-ion cathode material described in the second aspect.

[0048] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] (1) The preparation method provided by the present invention uses Ni, Cu and doping elements to improve the manganese-based sodium-ion cathode material. Moreover, wet doping is carried out in the precursor preparation stage, so that the doping elements are evenly distributed in the obtained cathode material, improving the structural stability and air stability of the finally obtained cathode material;

[0051] (2) The control of the particle size of the ion-doped manganese-based ternary precursor prepared by the present invention is beneficial to the single crystallization of the ion-doped manganese-based ternary precursor during sintering, thereby ensuring the electrochemical properties such as the tap density, particle strength and voltage of the obtained cathode material. Detailed implementation manners

[0052] The technical solution of the present invention will be further described below through specific embodiments.

[0053] Example 1

[0054] This example provides a preparation method of an ion-doped manganese-based sodium ion cathode material, and the preparation method includes the following steps:

[0055] (1) Under a nitrogen atmosphere, an ion solution, a doping element solution, 15 wt% ammonia water and 32 wt% NaOH solution are mixed and fed into a bottom liquid under stirring at a rotation speed of 350 rpm. After the particle size D50 reaches 4.0 μm, the feeding is stopped, and solid-liquid separation is performed to obtain an ion-doped manganese-based ternary precursor; the particle size of the obtained ion-doped manganese-based ternary precursor satisfies ((D90 - D10) / D50) of 0.67; during the feeding process, the pH value, ammonia concentration and temperature of the mixed solution are kept constant;

[0056] (2) A sodium source is mixed with the ion-doped manganese-based ternary precursor obtained in step (1) and sintered in an oxygen atmosphere to obtain an ion-doped manganese-based sodium ion cathode material; the sintering temperature is 1000 °C and the time is 14 h;

[0057] The mixed ion solution in step (1) includes manganese sulfate, nickel sulfate and copper sulfate, where the total molar concentration of manganese ions, nickel ions and copper ions is 2 mol / L, and the molar ratio of manganese ions, nickel ions and copper ions is 7:2:1;

[0058] The doping element solution in step (1) includes zirconium sulfate, where the molar concentration of zirconium ions is 0.1 mol / L;

[0059] The pH value of the bottom liquid in step (1) is 12, the ammonia concentration is 10 g / L, and the temperature is 40 °C;

[0060] The flow rate of the mixed ion solution in step (1) is 40 L / h, and the flow rate of the doping element solution is 2 L / h.

[0061] Example 2

[0062] This example provides a preparation method of an ion-doped manganese-based sodium ion cathode material, and the preparation method includes the following steps:

[0063] (1) Under a nitrogen atmosphere, a mixed ion solution, a doping element solution, 12 wt% ammonia water, and 30 wt% NaOH solution are introduced into the bottom liquid under stirring at a rotation speed of 200 rpm. After the particle size D50 reaches 4.5 μm, the feeding is stopped, and solid-liquid separation is carried out to obtain an ion-doped manganese-based ternary precursor; the particle size of the obtained ion-doped manganese-based ternary precursor satisfies ((D90 - D10) / D50) of 0.64; during the introduction process, the pH value, ammonia concentration, and temperature of the mixed solution are kept constant;

[0064] (2) A sodium source is mixed with the ion-doped manganese-based ternary precursor obtained in step (1) and sintered in an oxygen atmosphere to obtain an ion-doped manganese-based sodium-ion cathode material; the sintering temperature is 900 °C and the time is 16 h;

[0065] The mixed ion solution in step (1) includes manganese chloride, nickel chloride, and copper chloride, where the total molar concentration of manganese ions, nickel ions, and copper ions is 1.6 mol / L, and the molar ratio of manganese ions, nickel ions, and copper ions is 6.5:2.2:1;

[0066] The doping element solution in step (1) includes zirconium chloride, where the molar concentration of zirconium ions is 0.08 mol / L;

[0067] The pH value of the bottom liquid in step (1) is 11, the ammonia concentration is 5.5 g / L, and the temperature is 42 °C;

[0068] The flow rate of the mixed ion solution in step (1) is 20 L / h, and the flow rate of the doping element solution is 1.5 L / h.

[0069] Example 3

[0070] This example provides a preparation method of an ion-doped manganese-based sodium-ion cathode material, and the preparation method includes the following steps:

[0071] (1) Under a nitrogen atmosphere, a mixed ion solution, a doping element solution, 16 wt% ammonia water, and 35 wt% NaOH solution are introduced into the bottom liquid under stirring at a rotation speed of 500 rpm. After the particle size D50 reaches 5 μm, the feeding is stopped, and solid-liquid separation is carried out to obtain an ion-doped manganese-based ternary precursor; the particle size of the obtained ion-doped manganese-based ternary precursor satisfies ((D90 - D10) / D50) of 0.65; during the introduction process, the pH value, ammonia concentration, and temperature of the mixed solution are kept constant;

[0072] (2) A sodium source is mixed with the ion-doped manganese-based ternary precursor obtained in step (1) and sintered in an oxygen atmosphere to obtain an ion-doped manganese-based sodium-ion cathode material; the sintering temperature is 1100 °C and the time is 10 h;

[0073] The mixed ionic solution in step (1) includes manganese nitrate, nickel nitrate and copper nitrate. The total molar concentration of manganese ions, nickel ions and copper ions is 2.4 mol / L, and the molar ratio of manganese ions, nickel ions and copper ions is 7.5:1.8:1;

[0074] The doping element solution in step (1) includes zirconium nitrate, and the molar concentration of zirconium ions is 0.12 mol / L;

[0075] The pH value of the bottom solution in step (1) is 13, the ammonia concentration is 20 g / L, and the temperature is 58 °C;

[0076] The flow rate of the mixed ionic solution in step (1) is 100 L / h, and the flow rate of the doping element solution is 10 L / h.

[0077] Example 4

[0078] This example provides a preparation method of an ion-doped manganese-based sodium-ion cathode material. Except that zirconium sulfate in the doping element solution is replaced with aluminum sulfate, and zirconium ions are replaced with aluminum ions in an equimolar amount, the rest are the same as in Example 1.

[0079] Example 5

[0080] This example provides a preparation method of an ion-doped manganese-based sodium-ion cathode material. Except that zirconium sulfate in the doping element solution is replaced with titanium chloride, and zirconium ions are replaced with titanium ions in an equimolar amount, the rest are the same as in Example 1.

[0081] Example 6

[0082] This example provides a preparation method of an ion-doped manganese-based sodium-ion cathode material. Except that the feeding is stopped after the particle size D50 in step (1) reaches 3.5 μm, the rest are the same as in Example 1.

[0083] Example 7

[0084] This example provides a preparation method of an ion-doped manganese-based sodium-ion cathode material. Except that the feeding is stopped after the particle size D50 in step (1) reaches 5.5 μm, the rest are the same as in Example 1.

[0085] Example 8

[0086] This example provides a preparation method of an ion-doped manganese-based sodium-ion cathode material. Except that the molar concentration of the doping ions in the doping element solution in step (1) is 0.05 mol / L, the rest are the same as in Example 1.

[0087] Example 9

[0088] This embodiment provides a method for preparing an ion-doped manganese-based sodium-ion cathode material. Except that the molar concentration of the doped ions in the doped element solution described in step (1) is 0.15 mol / L, the rest are the same as in Example 1.

[0089] Comparative Example 1

[0090] This comparative example provides a method for preparing an ion-doped manganese-based sodium-ion cathode material. Except that ferric chloride is used and Cu in the mixed ion solution is replaced by Fe in an equimolar amount 2+ , the rest are the same as in Example 1. 3+

[0091] Comparative Example 2

[0092] This comparative example provides a method for preparing a manganese-based sodium-ion cathode material. The preparation method includes the following steps:

[0093] (1) Under a nitrogen atmosphere, a mixed ion solution, 15 wt% ammonia water, and 32 wt% NaOH solution are fed into the bottom liquid under stirring at a rotation speed of 350 rpm. After the particle size D50 reaches 4.5 μm, the feeding is stopped, and solid-liquid separation is carried out to obtain a manganese-based ternary precursor; the particle size of the obtained manganese-based ternary precursor satisfies ((D90 - D10) / D50) of 0.68; during the feeding process, the pH value, ammonia concentration, and temperature of the mixed solution are kept constant;

[0094] (2) A sodium source is mixed with the manganese-based ternary precursor obtained in step (1), and sintering is carried out in an oxygen atmosphere to obtain a manganese-based sodium-ion cathode material; the sintering temperature is 1000 °C and the time is 14 h;

[0095] The mixed ion solution described in step (1) includes manganese sulfate and nickel sulfate, where the total molar concentration of manganese ions and nickel ions is 2 mol / L, and the molar ratio of manganese ions to nickel ions is 7:3;

[0096] The pH value of the bottom liquid described in step (1) is 12, the ammonia concentration is 10 g / L, and the temperature is 45 °C;

[0097] The flow rate of the mixed ion solution described in step (1) is 40 L / h.

[0098] Performance Test

[0099] The particle sizes of the ion-doped manganese-based ternary precursors obtained in Examples 1-9 and Comparative Example 1, and the manganese-based ternary precursor obtained in Comparative Example 2 are tested using a Malvern laser particle size analyzer, and the values of the particle size ((D90 - D10) / D50) are calculated. The obtained results are shown in Table 1.

[0100] ​The ion-doped manganese-based sodium-ion cathode materials obtained in Examples 1-9 and Comparative Example 1, as well as the manganese-based sodium-ion cathode materials obtained in Comparative Example 2, were fabricated into lithium-ion batteries. The fabrication method is as follows:

[0101] The cathode material, binder polyvinylidene fluoride, and conductive agent Super P were added to N-methylpyrrolidone at a mass ratio of 97:1.5:1.5 and stirred to form a first cathode slurry. Then, the first cathode slurry was uniformly coated on the cathode current collector aluminum foil, dried, and rolled to obtain a cathode electrode sheet.

[0102] Graphite, conductive agent acetylene black, thickener CMC, and binder SBR were mixed at a mass ratio of 96:1:1.5:1.5, and deionized water as the solvent was added and stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil, dried, cold-pressed, and slit to obtain a negative electrode sheet.

[0103] Ethylene carbonate EC, ethyl methyl carbonate EMC, and diethyl carbonate DEC were mixed at a volume ratio of 1:1:1. Then, the thoroughly dried lithium salt LiPF6 was dissolved in the mixed solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0104] The cathode electrode sheet, separator, and negative electrode sheet were stacked in sequence, then wrapped with an aluminum-plastic film, dried, injected with the electrolyte, and subjected to processes such as encapsulation, standing, and formation to obtain a lithium-ion battery. The separator is a PE porous membrane with a thickness of 11 μm, a gas permeability of 280 s / 100 mL, and a porosity of 40%.

[0105] The specific capacity, air stability, cycle capacity retention rate, and rate performance of the obtained lithium-ion batteries were tested, and the results are shown in Table 1.

[0106] The testing method for specific capacity is as follows: Using a Blue Power battery testing system, at 25 °C, the lithium-ion battery was charged and discharged at a rate of 0.04 A / g (calculated based on the mass of the cathode material) in the voltage range of 2 V to 4.3 V for 3 cycles to measure the specific capacity of the battery.

[0107] The testing method for air stability is as follows: The doped manganese-based sodium-ion cathode material was taken out after being placed in an air atmosphere at 25 °C for 15 days, fabricated into a sodium-ion battery, and then the specific capacity was measured by charge and discharge testing on a Blue Power battery testing system.

[0108] The testing method for cycle capacity retention rate is as follows: At 25 °C, cycling was carried out at a charge and discharge rate of 0.19 A / g (calculated based on the mass of the cathode material). After cycling to 500 cycles, the discharge capacity of the battery at this time was divided by the discharge capacity of the first cycle to obtain the 500-cycle capacity retention rate of the battery.

[0109] The test method for rate performance is as follows: Under the condition of 25 °C, with a charge-discharge regime of 0.04 A / g (calculated based on the mass of the positive electrode material), within the voltage range of 2 V to 4.3 V, three charge-discharge cycles are performed to obtain the discharge capacity C0 of the last cycle; then, with a charging regime of 0.04 A / g (calculated based on the mass of the positive electrode material), the battery is charged to 4.3 V, and with a discharge regime of 0.12 A / g (calculated based on the mass of the positive electrode material), the battery is discharged to 2 V to obtain the discharge capacity C2 of the last cycle; the ratio of C2 / C0 is the rate performance.

[0110] Table 1

[0111]

[0112] As can be seen from Table 1, the ion-doped manganese-based sodium-ion positive electrode materials obtained in Examples 1-5 have a specific capacity of more than 116.4 mAh / g, an air specific capacity of 107.2 mAh / g, a cycle capacity retention rate of more than 59.8%, and a rate performance of more than 90.2%.

[0113] From the comparison between Examples 6 and 7 and Example 1, it can be seen that when the feeding is stopped when the target particle size D50 does not reach 4 μm, the specific capacity of the obtained positive electrode material decreases from 119.2 mAh / g to 106.3 mAh / g, the air specific capacity decreases from 118.3 mAh / g to 100.7 mAh / g, the cycle capacity retention rate decreases from 61.2% to 60.1%, and the rate performance decreases from 91.4% to 78.9%. When the feeding is stopped when the target particle size D50 exceeds 5 μm, the specific capacity of the obtained positive electrode material decreases from 119.2 mAh / g to 108.2 mAh / g, the air specific capacity decreases from 118.3 mAh / g to 100.7 mAh / g, the cycle capacity retention rate decreases from 61.2% to 59.6%, and the rate performance decreases from 91.4% to 80.1%.

[0114] From the comparison between Examples 8 and 9 and Example 1, it can be seen that when the doping ion concentration in the doping element solution is low, the specific capacity of the obtained positive electrode material decreases from 119.2 mAh / g to 110.8 mAh / g, the air specific capacity decreases from 118.3 mAh / g to 105.9 mAh / g, the cycle capacity retention rate decreases from 61.2% to 51.2%, and the rate performance decreases from 91.4% to 79.5%; when the doping ion concentration in the doping element solution is high, the specific capacity of the obtained positive electrode material decreases from 119.2 mAh / g to 96.7 mAh / g, the air specific capacity decreases from 118.3 mAh / g to 95.8 mAh / g, the cycle capacity retention rate decreases from 61.2% to 53.4%, and the rate performance decreases from 91.4% to 82.7%.

[0115] It can be seen from the comparison of Comparative Examples 1 and 2 with Example 1 that when an equimolar amount of Cu 2+ is replaced with Fe 3+ , or when no element doping is carried out, the performance of the obtained cathode material significantly deteriorates.

[0116] In summary, the preparation method provided by the present invention uses Ni, Cu and doping elements to improve the manganese-based sodium-ion cathode material. Moreover, wet doping is carried out in the precursor preparation stage, so that the doping elements are evenly distributed in the obtained cathode material, improving the structural stability and thermal stability of the finally obtained cathode material; the control of the particle size of the ion-doped manganese-based ternary precursor prepared by the present invention is beneficial to the single crystallization of the ion-doped manganese-based ternary precursor during sintering, thereby ensuring the electrochemical properties such as the tap density, particle strength and voltage of the obtained cathode material.

[0117] The specific embodiments described above have further elaborated on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of an ion-doped manganese-based sodium-ion cathode material, characterized in that, The preparation method includes the following steps: (1) Under a protective atmosphere, a mixed ion solution, a doping element solution, a complexing agent, and a precipitating agent are introduced into a bottom solution. After the particle size D50 reaches the target particle size of 4 - 5 μm, the feeding is stopped, and solid-liquid separation is performed to obtain an ion-doped manganese-based ternary precursor; the particle size of the obtained ion-doped manganese-based ternary precursor satisfies: 0.64 ≤ ((D90 - D10) / D50) ≤ 0.67; The pH value of the bottom solution is 11 - 12, the ammonia concentration in the bottom solution is 5 - 10 g / L, the temperature of the bottom solution is 40 - 80 °C, and during the introduction process, the pH value, ammonia concentration, and temperature of the mixed solution are kept constant; The flow rate of the mixed ion solution is 20 - 40 L / h, the flow rate of the doping element solution is 1.5 - 2 L / h, and the molar concentration of the doping ions in the doping element solution is 0.08 - 0.12 mol / L; (2) A sodium source and the ion-doped manganese-based ternary precursor obtained in step (1) are mixed and sintered in an oxygen-containing atmosphere to obtain an ion-doped manganese-based sodium-ion cathode material; The mixed ion solution in step (1) includes soluble manganese salts, nickel salts, and copper salts; The doping element solution in step (1) includes soluble zirconium salts; 2. The preparation method according to claim 1, characterized in that, The bottom solution in step (1) is composed of water, ammonia water, and sodium hydroxide; 3. The preparation method according to claim 1, characterized in that, During the introduction process in step (1), stirring is carried out, and the stirring speed is 200 - 500 rpm; 4. The preparation method according to claim 1, characterized in that, The manganese salt in the mixed ion solution in step (1) includes any one or a combination of at least two of manganese sulfate, manganese chloride, or manganese nitrate; 5. The preparation method according to claim 1, characterized in that, The nickel salt in the mixed ion solution in step (1) includes any one or a combination of at least two of nickel sulfate, nickel chloride, or nickel nitrate; 6. The preparation method according to claim 1, wherein The copper salt in the mixed ion solution in step (1) includes any one or a combination of at least two of copper sulfate, copper chloride, or copper nitrate; 7. The preparation method according to claim 1, characterized in that, In the mixed ion solution in step (1), the molar ratio of manganese ions, nickel ions, and copper ions is (6.5 - 7.5):(1.8 - 2.2):1; 8. The preparation method according to claim 1, characterized in that, In the mixed ion solution in step (1), the total molar concentration of manganese ions, nickel ions, and copper ions is 1.6 - 2.4 mol / L; 9. The preparation method according to claim 1, characterized in that, The zirconium salt in the doping element solution in step (1) includes any one or a combination of at least two of zirconium sulfate, zirconium chloride, or zirconium nitrate; 10. The preparation method according to claim 1, characterized in that, The precipitating agent in step (1) includes a NaOH solution; 11. The preparation method according to claim 10, characterized in that, The concentration of the NaOH solution is 30 - 35 wt%; 12. The preparation method according to claim 1, characterized in that, The complexing agent in step (1) includes ammonia water with a concentration of 12 - 16 wt%; 13. The preparation method according to claim 1, characterized in that, The sintering temperature in step (2) is 900 - 1100 °C; 14. The preparation method according to claim 1, characterized in that, The sintering time in step (2) is 10 - 16 h; 15. An ion-doped manganese-based sodium-ion cathode material, characterized in that, The ion-doped manganese-based sodium-ion cathode material is prepared by the preparation method described in any one of claims 1 - 14; 16. A positive electrode, characterized in that, The cathode includes the ion-doped manganese-based sodium-ion cathode material described in claim 15.

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