A lithium-rich manganese-based positive electrode material and preparation method thereof

Abstract

The present invention belongs to the technical field of lithium-ion batteries and specifically relates to a lithium-rich manganese-based positive electrode material and a preparation method thereof, comprising the following steps: (1) preparing a Mg-doped precursor; (2) synthesizing a Mg-doped positive electrode material; (3) synthesizing a Mg- and Na-doped positive electrode material; and (4) synthesizing a Mg-, Na-, and Se-doped positive electrode material. The present invention uses the non-electrochemically active elements Mg, Na, and Se to replace some elements of the positive electrode material. After sintering, the positive electrode material is less susceptible to structural transformation during the charge and discharge process, thereby stabilizing performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a lithium-rich manganese-based positive electrode material and a preparation method thereof. Background Art

[0002] At present, the cathode electrode materials of mainstream power batteries, such as lithium iron phosphate batteries, nickel-cobalt-manganese ternary lithium batteries, and lithium cobalt oxide batteries, have relatively low specific capacity and their performance is approaching a bottleneck. It is urgent to develop new power battery cathode materials to meet the requirements. In recent years, the emergence of lithium-rich manganese-based cathode materials is expected to solve the pain point of low capacity of current cathode materials. The lithium-rich manganese-based cathode material xLi2MnO3·(1-x)LiMO2 (M=Mn, Co, Ni, etc.) has become the focus of scientific researchers due to its high specific capacity, low price, and environmental friendliness.

[0003] Lithium-rich manganese-based cathode materials are relatively cheap to produce, safe, and environmentally friendly because they contain more manganese elements. The monoclinic Li2MnO3 phase in the material not only stabilizes the structure, but also provides additional capacity, which further improves the discharge capacity of the overall material. Although the performance of lithium-rich manganese-based cathode materials is relatively superior, their first coulombic efficiency is low. During the charge and discharge cycle, the material gradually transforms from a layered structure to a spinel-like structure, resulting in an unstable overall structure of the material, as well as capacity decay, voltage decay, and poor rate capability, which to a certain extent affect its practicality. Therefore, in recent years, many researchers have conducted a large number of modification studies on lithium-rich manganese-based materials, such as bulk doping, surface coating, and new structure design and construction. Traditional element doping and surface coating have a certain effect on improving the electrochemical performance of the material, but different modification methods have different improvement effects. At present, a single modification method cannot fundamentally solve the problems faced by the material. Therefore, it is necessary to adopt a combination of multiple modification methods and develop new structures (such as single crystal structure, composite structure, composition regulation and gradient structure, etc.) to solve the problems faced by the material. In addition, the structure and composition design of the lithium-rich manganese-based positive electrode material precursor is also very important. It is necessary to consider the high capacity of the material and pay attention to density improvement to achieve a relative balance between capacity and density.

[0004] Patent No. CN202011100886.9 proposes a dual-system co-precipitation method to prepare a lithium-rich manganese-based precursor co-doped with fluorine and magnesium. The cathode material prepared from this precursor effectively improves the material's crystal stability and suppresses voltage decay, resulting in excellent electrochemical performance. However, the simultaneous doping of fluorine and magnesium into the precursor material increases uncontrollable factors in the preparation process, making it more difficult to control the precursor morphology and precipitated components.

[0005] A doctoral dissertation from Central South University studied the effects of Se dopants on the electrochemical properties, morphology, and structural characteristics of ternary cathode materials. The results showed that Se doped into ternary cathode materials had a first-cycle discharge capacity of 293.5 mAh / g and a coulombic efficiency of 94.3%. At a current density of 1 C, the capacity retention rate was 88.4% after 400 cycles, outperforming undoped cathode materials.

[0006] Starting from the structure of lithium-rich manganese-based materials, the present invention explores a preparation method that can stabilize its structure, thereby improving its charge and discharge cycle performance and rate capability, and providing ideas for industrialization. Summary of the Invention

[0007] In order to solve the problem in the prior art that the structure of lithium-rich manganese-based positive electrode materials changes during the charge and discharge process, resulting in a decrease in discharge specific capacity, and to further improve the rate performance and cycle performance of the material, the present invention provides a lithium-rich manganese-based positive electrode material and a preparation method thereof.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for preparing a lithium-rich manganese-based positive electrode material comprises the following steps:

[0010] (1) nickel salt, cobalt salt, manganese salt and magnesium salt are prepared into a mixed salt solution; NH3HCO3 is used as a buffer solution, a precipitant, a complexing agent and the mixed salt solution are added to react, and after the reaction is completed, an aging treatment is performed to obtain a Mg-doped precursor;

[0011] (2) taking the Mg-doped precursor of step (1), adding lithium salt and sodium salt, mixing thoroughly and sintering in an air atmosphere to obtain a Mg-doped and Na-doped positive electrode material;

[0012] (3) The Mg and Na-doped positive electrode material of step (2) is crushed, Se powder is added, mixed evenly, and sintered in an inert atmosphere to obtain a Na, Mg, and Se-doped lithium-rich manganese-based positive electrode material.

[0013] Furthermore, in step (1), in the mixed salt solution, the molar ratio of nickel, cobalt, manganese and magnesium is 0.13:0.13:0.52:0.02.

[0014] Furthermore, in step (1), the nickel salt is selected from one or more of water-soluble NiSO4, Ni(NO3)2, and Ni(CH3COO)2; the cobalt salt is selected from one or more of water-soluble CoSO4, Co(NO3)2, and Co(CH3COO)2; the manganese salt is selected from one or more of MnSO4, Mn(NO3)2, and Mn(CH3COO)2; and the magnesium salt is selected from one or more of MgSO4, Mg(NO3)2, and Mg(CH3COO)2.

[0015] Furthermore, in step (1), the complexing agent is aqueous ammonia; and the precipitating agent is selected from one or more of Na2CO3, NaHCO3, NH4HCO3, (NH4)2CO3, and K2CO3.

[0016] Furthermore, in step (1), during the reaction process, the pH is controlled between 8.5-9.5 and the temperature is controlled between 55°C and 65°C.

[0017] Preferably, in step (2), the lithium salt is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate; the sodium salt is selected from one or more of sodium carbonate, sodium nitrate, and sodium bicarbonate; and the sintering is carried out in an air atmosphere, with a first stage at 400-600°C and a second stage at 900-980°C and a heating rate of 3°C / min.

[0018] Preferably, in step (3), the sintering is carried out in an inert atmosphere at a sintering temperature of 550-650° C. for 4-7 hours.

[0019] A lithium-rich manganese-based positive electrode material is prepared by the above-mentioned method for preparing the lithium-rich manganese-based positive electrode material.

[0020] The process of the present invention is as follows Figure 1 shown.

[0021] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0022] (1) The production of precursors using the more traditional co-precipitation method in a small reactor can be scaled up and applied to actual production to achieve industrialization;

[0023] (2) Using weakly alkaline carbonate as a precipitant is safer than other hydroxide precipitants, and the low pH solution is easy to neutralize and is environmentally friendly;

[0024] (3) Using non-electrochemically active elements Mg, Na, and Se to replace some elements of the positive electrode material, the sintered positive electrode material is less likely to undergo structural transformation during the charge and discharge process, thus stabilizing performance;

[0025] (4) The high-temperature solid-phase method is used for sintering, and the sintering operation can be completed without adding special equipment or devices, thus reducing investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow chart of the present invention;

[0027] Figure 2 Figure 1 is a scanning electron microscope image of the precursor; Figure a is the undoped precursor of Comparative Example 1, and Figure b is the Mg-doped precursor of Example 1;

[0028] Figure 3 This is the XRD pattern of Example 1. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] Example 1

[0031] (1) nickel salt, cobalt salt, manganese salt and magnesium salt are prepared into a 2 mol / L mixed salt solution, wherein the molar ratio of nickel, cobalt, manganese and magnesium in the mixed salt solution is 0.13:0.13:0.52:0.02; 0.2 mol / L NH3HCO3 is used as a buffer base liquid, and a precipitant, a complexing agent and the mixed salt solution are pumped in for reaction, and the pumping flow rates are as follows: mixed salt solution 1 ml / min, complexing agent 0.75 ml / min, and the precipitant flow rate is automatically adjusted according to the pH change of the equipment, and nitrogen is introduced for protection to prevent oxidation, and the pH is controlled at 9.0, the temperature is 60°C, the stirring speed is 50 rpm / min, the reaction time is 15 h, and the aging is carried out for 20 h, and then filtered, washed with deionized water several times, and dried at 110°C for 15 h to obtain a Mg-doped precursor; wherein sodium carbonate is used as the precipitant, and the solution concentration is 2 mol / L, and ammonia water is used as the complexing agent, and the solution concentration is 0.5 mol / L;

[0032] (2) Take the Mg-doped precursor of step (1), add lithium carbonate and sodium carbonate, mix thoroughly and then sinter. The sintering atmosphere is air. The first stage is kept at 500℃ for 4h, and the second stage is kept at 950℃ for 12h. The heating rate is 3℃ / min. The sintered product is ground and sieved to obtain Mg-doped and Na-doped positive electrode materials. The amount of lithium carbonate and sodium carbonate is based on the Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.52 Mg 0.02 O2 chemical formula calculation, wherein lithium carbonate is added according to 105% of the theoretical amount;

[0033] (3) Take the Mg and Na-doped positive electrode material of step (2), crush it, add Se powder (the amount of Se powder added is based on the Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.52 Mg 0.02 O1.975 Se 0.025 Chemical formula calculation), mixed evenly, sintered in an argon atmosphere at a temperature of 600 ° C for 5 h; the sintered selenized lithium-rich manganese-based positive electrode material was washed several times with CS2 and anhydrous ethanol solution, vacuum dried at 120 ° C for 10 h, ground into powder, and sieved to obtain Na, Mg, Se-doped lithium-rich manganese-based positive electrode material Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.5 2Mg 0.02 O 1.975 Se 0.025 .

[0034] Example 2

[0035] The steps of Example 2 are basically the same as those of Example 1, except that: in step (1), during the reaction, the pH is controlled between 8.5 and the temperature is 55°C; in step (2), the sintering is carried out in an air atmosphere, with the first stage being kept at 400°C for 5 hours and the second stage being kept at 900°C for 10 hours, with a heating rate of 3°C / min; in step (3), the sintering is carried out in an argon atmosphere, with a sintering temperature of 550°C, and selenization sintering is carried out for 4 hours.

[0036] Example 3

[0037] The steps of Example 2 are basically the same as those of Example 1, except that: in step (1), during the reaction, the pH is controlled between 9.5 and the temperature is 65°C; in step (2), the sintering is carried out in an air atmosphere, with the first stage being kept at 600°C for 6 hours and the second stage being kept at 980°C for 15 hours, with a heating rate of 3°C / min; in step (3), the sintering is carried out in an argon atmosphere, with a sintering temperature of 650°C, and selenization sintering is carried out for 7 hours.

[0038] Comparative Example 1

[0039] The difference from Example 1 is that the comparative example 1 prepared the undoped Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based positive electrode material.

[0040] The preparation steps are as follows:

[0041] (1) nickel salt, cobalt salt and manganese salt were prepared into a 2 mol / L mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese in the mixed salt solution was 0.13:0.13:0.54; 0.2 mol / L NH3HCO3 was used as a buffer solution, and a precipitant, a complexing agent and the mixed salt solution were pumped in for reaction, and the pumping flow rates were as follows: mixed salt solution 1 ml / min, complexing agent 0.75 ml / min, and the precipitant flow rate was automatically adjusted according to the pH change of the equipment, and nitrogen was introduced for protection to prevent oxidation, and the pH was controlled at 9.0, the temperature was 60°C, the stirring speed was 50 rpm / min, the reaction time was 15 h, and the product was aged for 20 h, then filtered, washed with deionized water several times, and dried at 110°C for 15 h to obtain a precursor; wherein the precipitant was sodium carbonate with a solution concentration of 2 mol / L, and ammonia water was used as the complexing agent with a solution concentration of 0.5 mol / L;

[0042] (2) Take the precursor of step (1), add lithium carbonate, mix thoroughly and sinter. The sintering atmosphere is air. The first stage is kept at 500℃ for 4h, the second stage is kept at 950℃ for 12h, and the heating rate is 3℃ / min. The sintered product is ground and sieved to obtain undoped Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based positive electrode material; the amount of lithium carbonate used is based on Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O2 chemical formula calculation, wherein lithium carbonate is added according to 105% of the theoretical amount.

[0043] Comparative Example 2

[0044] The difference from Example 1 is that the Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based positive electrode material.

[0045] The specific steps are as follows:

[0046] (1) nickel salt, cobalt salt and manganese salt were prepared into a 2 mol / L mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese in the mixed salt solution was 0.13:0.13:0.54; 0.2 mol / L NH3HCO3 was used as a buffer solution, and a precipitant, a complexing agent and the mixed salt solution were pumped in for reaction, and the pumping flow rates were as follows: mixed salt solution 1 ml / min, complexing agent 0.75 ml / min, and the precipitant flow rate was automatically adjusted according to the pH change of the equipment, and nitrogen was introduced for protection to prevent oxidation, and the pH was controlled at 9.0, the temperature was 60°C, the stirring speed was 50 rpm / min, the reaction time was 15 h, and the product was aged for 20 h, then filtered, washed with deionized water several times, and dried at 110°C for 15 h to obtain a precursor; wherein the precipitant was sodium carbonate with a solution concentration of 2 mol / L, and ammonia water was used as the complexing agent with a solution concentration of 0.5 mol / L;

[0047] (2) Take the precursor of step (1), add lithium carbonate and sodium carbonate, mix thoroughly and then sinter. The sintering atmosphere is air. The first stage is kept at 500℃ for 4h, and the second stage is kept at 950℃ for 12h. The heating rate is 3℃ / min. The sintered product is ground and sieved to obtain Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based positive electrode material; the amount of lithium carbonate and sodium carbonate is based on Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O2 chemical formula calculation, wherein lithium carbonate is added according to 105% of the theoretical amount.

[0048] Comparative Example 3

[0049] The difference from Example 1 is that the Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O 1.975 Se 0.025 Lithium-rich manganese-based positive electrode materials.

[0050] The specific steps are as follows:

[0051] (1) nickel salt, cobalt salt and manganese salt were prepared into a 2 mol / L mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese in the mixed salt solution was 0.13:0.13:0.54; 0.2 mol / L NH3HCO3 was used as a buffer solution, and a precipitant, a complexing agent and the mixed salt solution were pumped in for reaction, and the pumping flow rates were as follows: mixed salt solution 1 ml / min, complexing agent 0.75 ml / min, and the precipitant flow rate was automatically adjusted according to the pH change of the equipment, and nitrogen was introduced for protection to prevent oxidation, and the pH was controlled at 9.0, the temperature was 60°C, the stirring speed was 50 rpm / min, the reaction time was 15 h, and the product was aged for 20 h, then filtered, washed with deionized water several times, and dried at 110°C for 15 h to obtain a precursor; wherein the precipitant was sodium carbonate with a solution concentration of 2 mol / L, and ammonia water was used as the complexing agent with a solution concentration of 0.5 mol / L;

[0052] (2) Take the precursor of step (1), add lithium carbonate and sodium carbonate, mix thoroughly and then sinter. The sintering atmosphere is air. The first stage is kept at 500℃ for 4h, and the second stage is kept at 950℃ for 12h. The heating rate is 3℃ / min. The sintered product is ground and sieved to obtain Mg-doped and Na-doped positive electrode materials. The amount of lithium carbonate and sodium carbonate is based on the Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O2 chemical formula calculation, wherein lithium carbonate is added according to 105% of the theoretical amount;

[0053] (3) Take the Mg and Na-doped positive electrode material of step (2), crush it, add Se powder (the amount of Se powder added is based on the Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.54 O 1.975 Se 0.025 Chemical formula calculation), mixed evenly, sintered in an argon atmosphere at a temperature of 600 ° C for 5 h; the sintered selenized lithium-rich manganese-based positive electrode material was washed several times with CS2 and anhydrous ethanol solution, vacuum dried at 120 ° C for 10 h, ground into powder, and sieved to obtain Na, Mg, Se-doped lithium-rich manganese-based positive electrode material Li 1.18 Na 0.02 Ni 0.13 Co 0.13 Mn 0.5 4O 1.975 Se 0.025 .

[0054] Electrochemical performance test:

[0055] The lithium-rich manganese-based positive electrode materials of Examples 1-3 and Comparative Examples 1-3 were prepared into button batteries to test their electrochemical performance. The battery preparation and testing methods are as follows: the lithium-rich manganese-based positive electrode material, acetylene black, and PVDF dissolved in NMP were accurately weighed in a mass ratio of 8:1:1, mixed into a slurry, and coated on an aluminum current collector foil. Subsequently, the aluminum foil was placed in a vacuum oven at 110°C and dried for 30 minutes to vaporize the NMP. The dried aluminum foil was rolled, and the aluminum foil punch was placed in a vacuum oven and dried at 110°C for 12 hours to prepare the positive electrode sheet. A lithium metal sheet was used as the negative electrode. PP / PE polymer was used as a separator to separate the positive and negative electrodes. A 1 mol / L LiPF6 solution of EC / EMC / DMC was used as the electrolyte. CR2032 button half-cells were assembled in an argon-filled glove box. The battery charge-discharge cycle was analyzed using a battery testing system. Cycling tests were conducted in a 25°C temperature-controlled chamber. All batteries rested for 2 hours before testing and were subsequently activated at a rate of 0.1C (1C = 220 mA / g) in the 2.0-4.7V voltage range. The final cycle was performed at a rate of 0.1C for 100 cycles.

[0056] Table 1 shows the electrochemical properties of various embodiments and comparative examples:

[0057] Table 1

[0058]

[0059] From Table 1 we can see that:

[0060] (1) As can be seen from Examples 1-3, the 0.1C first-cycle discharge specific capacity is relatively high, indicating that Mg has been doped into the transition metal layer of the material, which plays a role in stabilizing the structure of the material during the charge and discharge process. The capacity retention rate after 100 cycles is also maintained at a high level.

[0061] (2) Compared with Example 1, Comparative Examples 1 and 2, the first cycle discharge specific capacity is reduced because Na is electrochemically inactive and replaces part of the Li site, which reduces the capacity. However, it plays a supporting role in the Li layer during the charge and discharge process, allowing Li to be smoothly removed and embedded. The capacity retention rate of 100 cycles increases with the incorporation of Na.

[0062] (3) Comparative Example 1 and Comparative Examples 2-3, as Se is doped into the oxygen site, the capacity retention rate of 100 cycles is further improved. This is because during the charge and discharge process, lattice oxygen in the Li2MnO3 phase will be released to form oxygen release. This process is irreversible. Se doping can effectively reduce this process, thereby improving the structural stability of the material and improving the capacity retention rate.

[0063] (4) Comparing Examples 1-3, the second-stage sintering temperature has an impact on the first-cycle discharge capacity and the 100-cycle capacity retention rate. When the sintering temperature is low, the structure of the positive electrode material is less stable, and the first-cycle discharge capacity and the 100-cycle capacity retention rate are relatively low; when the sintering temperature is higher, the structure is more stable, and the 100-cycle capacity retention rate is relatively high, but the electrochemical active substance becomes more difficult to be removed and embedded in the material, and the discharge capacity is relatively reduced.

[0064] Scanning electron microscope (SEM)

[0065] Figure 2 It is a scanning electron microscope image of the precursor; Figure a is the undoped precursor of comparative example 1, and Figure b is the Mg-doped precursor of embodiment 1. It can be seen from the figure that the surface of the Mg-doped sphere is loose, and the Li element can diffuse more quickly inside the sphere during the sintering process and is evenly distributed inside the material, so that the material has good electrochemical properties.

[0066] Figure 3 The XRD pattern of Example 1 shows that the (006) / (012) peak and the (018) / (110) peak split significantly, indicating that the material has a good layered structure, which is beneficial to Li + Extraction and embedding. The typical Li2MnO3 diffraction peak is between 2θ=20°-25°, belonging to the C2 / m space group, which is the main characteristic of lithium-rich manganese-based materials.

[0067] In the above embodiments and comparative examples, the nickel salt is selected from NiSO4. Those skilled in the art may also choose one or more of water-soluble Ni(NO3)2 and Ni(CH3COO)2 according to common sense; the cobalt salt is selected from CoSO4. Those skilled in the art may also choose one or more of water-soluble Co(NO3)2 and Co(CH3COO)2 according to common sense; the manganese salt is selected from MnSO4. Those skilled in the art may also choose one or more of Mn(NO3)2 and Mn(CH3COO)2 according to common sense; the magnesium salt is selected from MgSO4. Those skilled in the art may also choose one or more of Mg(NO3)2 and Mg(CH3COO)2 according to common sense.

[0068] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based positive electrode material, characterized in that The steps include: (1) nickel salt, cobalt salt, manganese salt and magnesium salt are prepared into a mixed salt solution; NH3HCO3 is used as a buffer base liquid, and a precipitant, a complexing agent and the mixed salt solution are added to react, and after the reaction is completed, an aging treatment is performed to obtain a Mg-doped precursor; in the mixed salt solution, the molar ratio of nickel, cobalt, manganese and magnesium is 0.13:0.13:0.52:0.02; the precipitant is selected from one or more of Na2CO3, NaHCO3, NH4HCO3, (NH4)2CO3 and K2CO3; during the reaction process, the pH is controlled between 8.5 and 9.5, and the temperature is controlled between 55°C and 65°C; (2) Take the Mg-doped precursor of step (1), add lithium salt and sodium salt, mix thoroughly and then sinter. The sintering atmosphere is air. The first stage is kept at 400-600℃ for 4-6 hours. The second stage is kept at 900-980℃ for 10-15 hours. The heating rate is 3℃ / min to obtain Mg-doped and Na-doped positive electrode materials. (3) Take the Mg and Na doped positive electrode material of step (2), crush it, add Se powder, mix it evenly, sinter it in an inert atmosphere at a sintering temperature of 550-650°C, and perform selenization sintering for 4-7h to obtain a Na, Mg, and Se doped lithium manganese-based positive electrode material.

2. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, wherein: In step (1), the nickel salt is selected from one or more of water-soluble NiSO4, Ni(NO3)2, and Ni(CH3COO)2; the cobalt salt is selected from one or more of water-soluble CoSO4, Co(NO3)2, and Co(CH3COO)2; the manganese salt is selected from one or more of MnSO4, Mn(NO3)2, and Mn(CH3COO)2; and the magnesium salt is selected from one or more of MgSO4, Mg(NO3)2, and Mg(CH3COO)2.

3. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, wherein: In step (1), the complexing agent is aqueous ammonia.

4. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, wherein: In step (2), the lithium salt is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate; and the sodium salt is selected from one or more of sodium carbonate, sodium nitrate, and sodium bicarbonate.

5. A lithium-rich manganese-based positive electrode material, characterized in that The lithium-rich manganese-based positive electrode material is prepared by the preparation method of any one of claims 1 to 4.

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