A core-shell structure sodium-ion battery manganese-based layered positive electrode material and a preparation method thereof

Abstract

The application discloses a core-shell structure sodium ion battery manganese-based layered positive electrode material and a preparation method thereof. x [M 1‑y Mn y ] α [T a M 1‑a‑b Mn b ] 1‑α O2, wherein 0.50

Description

TECHNICAL FIELD

[0001] The application belongs to the field of new energy batteries, and particularly relates to a core-shell structure high-specific-capacity long-cycle sodium-ion battery manganese-based layered positive electrode material and a preparation method thereof. BACKGROUND

[0002] Sodium-ion batteries have broad application prospects in large-scale energy storage due to abundant sodium resources and low cost. As a key component of sodium-ion batteries, positive electrode materials play a crucial role in reducing battery cost and improving battery performance in practical applications. Among various positive electrode materials, layered manganese-based transition metal oxides (Na x TMO2, 0 < x < 1) have great development prospects in the field of large-scale energy storage of sodium-ion batteries due to their high energy density, relatively simple synthesis process, flexible composition and low cost. However, this type of material also faces many challenges, such as phase transition (P2→O2 / OP4) at high voltage region (>4V vs. Na + / Na), Mn 3+ Structural distortion caused by the Jahn-Teller effect, etc. This often leads to irreversible damage to the material structure, hinders the transmission of sodium ions, and thus causes performance degradation.

[0003] In terms of improving the structural stability of the material, one of the effective methods for the phase transition problem at the high voltage region is non-active element doping, that is, using non-electrochemically active elements to replace transition metal ions in layered oxides, which can leave more sodium ions in the alkali metal layer when charging to the high voltage region (>4V vs. Na + / Na), thereby generating more static shielding and reducing the possibility of layer slipping, thereby inhibiting the occurrence of phase transition. However, for layered oxides, although a large amount of non-electrochemically active element doping can effectively inhibit phase transition and improve structural stability, it inevitably causes a large loss of capacity. Therefore, how to achieve high specific capacity and ensure structural stability in the technology of sodium-ion battery layered oxide positive electrode materials, even to overturn this balance, that is, to achieve the dual goals of high capacity and low strain at the same time, is undoubtedly a great challenge. SUMMARY

[0004] Based on the above problems, the application provides a core-shell structure high-specific-capacity long-cycle sodium-ion battery manganese-based layered positive electrode material and a preparation method thereof. The core-shell structure sodium-ion battery manganese-based layered positive electrode material provided by the application has high specific capacity and long cycle life, and also exhibits excellent stability to air and water, which is suitable for large-scale industrial production.

[0005] The technical scheme provided by the application is as follows:

[0006] A high specific capacity long cycle sodium ion battery manganese-based layered positive electrode material with a core-shell structure has a molecular formula of Na x [M 1-y Mn y ] α [T a M 1-a-b Mn b ] 1-α O2, wherein 0.50 < x < 1.0, 0.50 < y < 1.0, 0.50 < b < 0.99, 0.01 < a < 0.20, 0 < alpha < 1, M is one or more of Fe, Ni and Cu electrochemically active elements, T is one or more of Mg, Zn, Al, Ti and Ca non-electrochemically active elements, wherein the M elements are uniformly distributed in the secondary particles of the material, and the T elements are uniformly or gradiently distributed in the shell layer of the secondary particles.

[0007] The sodium ion battery positive electrode material is a manganese-based layered oxide with a core-shell structure.

[0008] The preferred high specific capacity long cycle positive electrode material has a chemical formula of Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2.

[0009] In the high specific capacity long cycle positive electrode material with a core-shell structure, the non-electrochemically active Mg ions only exist in the shell layer of the material, the shell layer stability is achieved, the P2 to O2 phase transition of the material in the core region is inhibited by confinement, the structural stability of the material is greatly improved, and the capacity retention rate is improved. Meanwhile, since the non-active elements only exist in the shell layer, the specific capacity is greatly improved compared with the material in which the non-active elements exist in the whole material.

[0010] To achieve the above object, the application further provides a preparation method of the high specific capacity long cycle sodium ion battery manganese-based layered positive electrode material with a core-shell structure.

[0011] Step one, under a rotating speed of 300-800 r / min, a metal carbonate or hydroxide precipitate precursor with a core-shell structure is prepared by using a co-precipitation post-feeding or series feeding method;

[0012] Step two, the precursor and a sodium source are ground and uniformly mixed, and then pre-sintered at 400-550 DEG C for 1-6 h, and then calcined at 500-1200 DEG C for 5-14 h, and the final product is obtained after natural cooling.

[0013] Further, the co-precipitation is divided into two stages, the first stage prepares the inner core with high specific energy, which is a carbonate precipitate or hydroxide precipitate with coexistence of M metal ions and Mn ions, and the second stage continues to precipitate outside the inner core to form a stable outer shell, which is a carbonate precipitate or hydroxide precipitate with coexistence of T metal ions, M metal ions and Mn ions.

[0014] The preferred synthesis step of the application is Na x [M 1-y Mn y ] α [T a M 1-a-b Mn b ] 1-α O2, when the molar percentage of a certain metal in the M source is 0% to 15%, the M source is added in stoichiometric ratio in step two to obtain the product by calcination.

[0015] Further, the specific preparation method of step one is:

[0016] (1) According to the stoichiometric ratio of transition metals in the inner core and the outer shell of the core-shell structure positive electrode material, first pump the manganese source aqueous solution, the M source aqueous solution, the precipitant and the complexing agent into the reactor at the same time to prepare the inner core of the material by co-precipitation reaction;

[0017] (2) After a period of reaction, continue to pump the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution, the precipitant and the complexing agent into the reactor at the same time to coat the outer shell on the inner core of the material by co-precipitation reaction, and after the reaction is completed, the co-precipitation product is filtered, washed with water and dried to obtain the core-shell structure precursor.

[0018] Further, the manganese source in the manganese source aqueous solution in reaction (1) of step one is one or more of manganese monoxide, dimanganese trioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate and manganese nitrate, and the manganese content in the manganese source aqueous solution is 50% to 100% of the molar percentage of metal ions in the manganese source aqueous solution and the M source aqueous solution.

[0019] Further, the manganese source in the manganese source aqueous solution in reaction (2) of step one is one or more of manganese monoxide, dimanganese trioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate and manganese nitrate, and the manganese content in the manganese source aqueous solution is 50% to 99% of the molar percentage of metal ions in the manganese source aqueous solution, the M source aqueous solution and the T source aqueous solution.

[0020] Further, the M source in the M source aqueous solution in reaction (1) in step one is one or more of Fe source, Ni source, and Cu source, the Fe source is one or more of iron sulfate, magnetite, ferrous oxide, ferrous acetate tetrahydrate, ferroferric oxide, ferrous carbonate, and iron nitrate nonahydrate; the Ni source is one or more of nickel sulfate, nickel oxide, and nickel acetate; the Cu source is one or more of copper nitrate, copper oxide, copper acetate, and copper carbonate, and the content of M in the M source aqueous solution is 0% to 50% of the molar proportion of metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution.

[0021] Further, the M source in the M source aqueous solution in reaction (2) in step one is one or more of Fe source, Ni source, and Cu source, the Fe source is one or more of iron sulfate, magnetite, ferrous oxide, ferrous acetate tetrahydrate, ferroferric oxide, ferrous carbonate, and iron nitrate nonahydrate; the Ni source is one or more of nickel sulfate, nickel oxide, and nickel acetate; the Cu source is one or more of copper nitrate, copper oxide, copper acetate, and copper carbonate, and the content of M in the M source aqueous solution is 0% to 49% of the molar proportion of metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution.

[0022] Further, the T source in the T source aqueous solution is one or more of Mg source, Zn source, Al source, Ti source, and Ca source; the Mg source is one or more of magnesium acetate, magnesium oxide, and magnesium carbonate; the Zn source is one or more of zinc sulfate, zinc oxide, zinc acetate, and zinc carbonate; the Al source is one or more of aluminum oxide, aluminum sulfate, aluminum nitrate nonahydrate, and aluminum acetate; the Ti source is one or more of titanium monoxide, titanium dioxide, and titanium oxide; and the Ca source is one or more of calcium carbonate, calcium chloride, calcium oxide, and calcium hydroxide.

[0023] Further, the precipitant is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium oxide, the concentration of sodium hydroxide in step (1) is the sum of the molar concentrations of metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution multiplied by the total valence, and in step (2) is the sum of the molar concentrations of all metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution multiplied by the total valence, the concentration of sodium carbonate or sodium bicarbonate in step (1) is the sum of the molar concentrations of all metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution, and in step (2) is the sum of the molar concentrations of all metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution.

[0024] Further, the complexing agent is one or more of ammonia, ethylenediaminetetraacetic acid, citric acid, malic acid, malonic acid, succinic acid, succinic acid, lactic acid, and the amount of the complexing agent added is 0.05-1.0 mol / L in step (1) and 0.05-1.0 mol / L in step (2).

[0025] Further, the sodium source is one or more of sodium acetate, sodium chloride, sodium carbonate, sodium fluoride, and sodium nitrate.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] The core-shell structure Na x [M 1-y Mn y ] α [T a M 1-a-b Mn b ] 1-α The O2 positive electrode material has less capacity loss because only the shell region has non-active elements, but still has excellent cycle stability, and under the condition that the initial specific capacity is not less than 75 mAh g -1 , the capacity retention rate after 500 cycles is not less than 90%. It has good stability to air and water. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2 synthesized in Example 1.

[0029] Figure 2 SEM image of Na 0.67 [Ni 0.25 Mn 0.75 ]O2 synthesized in Comparative Example 1.

[0030] Figure 3 SEM image of Na 0.67 [Ni 0.21 Mn 0.71 Mg 0.08 ]O2 synthesized in Comparative Example 2.

[0031] Figure 4 SEM image of Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg0.08 Ni 0.21 Mn 0.71 ] 0.5 XRD pattern of O2.

[0032] Figure 5 Na synthesized for Comparative Example 1 0.67 [Ni 0.25 Mn 0.75 ]O2.

[0033] Figure 6 Na synthesized for Comparative Example 2 0.67 [Ni 0.21 Mn 0.71 Mg 0.08 ]O2.

[0034] Figure 7 Na synthesized for Example 1 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 Elemental line scan in FIB-SEM cross-section of O2.

[0035] Figure 8 Na synthesized for Example 1 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 Cycle performance plot (rate: 5C, voltage window: 2.0-4.2V) of O2 and Na synthesized for Comparative Example 1 0.67 [Ni 0.25 Mn 0.75 ]O2.

[0036] Figure 9 Na synthesized for Example 1 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 XRD pattern of O2 charged to 4.2V.

[0037] Figure 10 Na synthesized for Comparative Example 1 0.67 [Ni 0.25 Mn 0.75XRD pattern of Na

[0038] Figure 11 Na synthesized for example 1 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 XRD pattern of Na after air exposure. DETAILED DESCRIPTION

[0039] The specific embodiments of the present application are further described in conjunction with the specific examples below, so that the technical solutions of the present application are easier to understand and master, but the present application is not limited thereto.

[0040] Example 1

[0041] In this example 1, a core-shell structure positive electrode material Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2 was synthesized by co-precipitation post-feeding combined with solid sintering method, its structure was explored, its sodium ion battery performance was investigated, and its phase change in the charging and discharging process was explored.

[0042] First, according to the stoichiometric ratio of transition metals in the molecular formula of the core-shell structure positive electrode material in the core and the shell, and combined with the K sp value of the precipitate corresponding to each metal ion. Using deionized water, 1000 mL of 2 mol / L manganese sulfate and nickel sulfate mixed solution (molar ratio Ni:Mn = 1:3) A, 1000 mL of 2 mol / L manganese sulfate, nickel sulfate and magnesium sulfate mixed solution (molar ratio Ni:Mn:Mg = 7:2:1) B, 2000 mL of 2 mol / L sodium carbonate solution and 0.3 mol / L ammonia water mixed solution C. At 55℃, the stirring rate is 500r / min, A and C solutions are pumped in at the same time to prepare the core of the precursor, and after A is reacted, B and C solutions are continuously pumped in to continue to build the shell outside the core. After the reaction is completed, the co-precipitation product is filtered and washed with water and dried to obtain the core-shell structure precursor. Next, sintering is carried out, 1.0g of the precursor and anhydrous sodium acetate 0.52g are weighed and mixed and ground uniformly according to the stoichiometric ratio in the molecular formula. Then sinter in a muffle furnace at 500℃ for 1h, continue to heat to 900℃ and calcine for 10h. After natural cooling to room temperature, the core-shell structure sodium ion battery positive electrode material Na0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2.

[0043] The sample from Example 1 was characterized as follows:

[0044] As attached Figure 1 SEM results showed that the material in Example 1 was a secondary particle formed by the agglomeration of primary particles, wherein the primary particles were hexagonal flakes and the secondary particles were spherical with an average particle size of 20 μm.

[0045] As attached Figure 4 XRD results showed that the prepared Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2 is a pure P2 phase, belonging to the hexagonal crystal system, with space group P63 / mmc.

[0046] As attached Figure 7 Na was determined by elemental line scanning using FIB-SEM. 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2 has a core-shell structure. Metallic elements (T) exist in the shell region of the core-shell structure.

[0047] The sample from Example 1 was assembled into a sodium-ion battery using the following method, and the battery performance was tested:

[0048] (1) Preparation of positive electrode material electrode

[0049] Will Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5O2 cathode material, conductive carbon black (Super P) and binder polyvinylidene fluoride (PVDF) were grinded in a mass ratio of 7:2:1, uniformly dispersed in N-methyl pyrrolidone (NMP) solvent to obtain a mixed slurry of the cathode material. The mixed slurry was uniformly coated on the positive current collector aluminum foil, vacuum dried overnight, and then cut into a circular positive electrode sheet with a diameter of 10 mm.

[0050] (2) Assembly of sodium ion battery

[0051] The above positive electrode sheet was used as the positive electrode, the sodium sheet was used as the negative electrode, 1M sodium perchlorate (NaClO4) + propylene carbonate (PC) + 5wt% fluoroethylene carbonate (FEC) was used as the electrolyte, and other necessary battery components (separator and shell, etc.) were assembled into a CR2032 type button cell in an argon-filled glove box.

[0052] (3) Performance test of the battery

[0053] The battery assembled by the above method was tested for charge and discharge performance in a Neware battery test system, and the test temperature was 25℃ and the voltage window was 2.0-4.2V. The test results showed that the Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 The O2 cathode material had an initial capacity of up to 76mAh g -1 at a rate of 5C, and the capacity retention rate was 94% after 500 cycles, showing excellent cycle stability, as shown in the accompanying Figure 8 .

[0054] (4) XRD test of the charged state of the cathode material

[0055] The sodium ion half-cell charged to 4.2V at 25℃ and a rate of 0.2C was disassembled, and the positive electrode sheet was taken out for XRD test. The test results are shown in the accompanying Figure 9 , Na 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 The O2 cathode material remained in the P2 phase throughout the charge and discharge process, confirming the structural stability of the core-shell structure material.

[0056] (5) Stability test of the cathode material to air and to water

[0057] Na after exposure to air for 90 and 180 days 0.67 [Ni 0.25 Mn 0.75 ] 0.5 [Mg 0.08 Ni 0.21 Mn 0.71 ] 0.5 O2 was subjected to XRD testing, and the results are attached. Figure 11 The test results show that the P2 phase can be well preserved, demonstrating its good stability to air and water.

[0058] Comparative Example 1:

[0059] This comparative example synthesizes a cathode material Na using a co-precipitation combined with solid-state sintering method. 0.67 [Ni 0.25 Mn 0.75 The performance of sodium-ion batteries was investigated, and the phase changes during the charging and discharging process were explored.

[0060] First, according to the stoichiometric ratio of transition metals in the chemical formula of the cathode material, and combined with the K of the corresponding precipitates of each metal ion, sp Value. Using deionized water, prepare 2000 mL of a mixed solution A of 2 mol / L manganese sulfate and nickel sulfate (molar ratio Ni:Mn = 1:3), and 2000 mL of a mixed solution B of 2 mol / L sodium carbonate and 0.3 mol / L ammonia. Simultaneously pump solutions A and B into the solution at 55℃ and a stirring rate of 500 r / min. After the reaction is complete, filter, wash with water, and dry the co-precipitated product to obtain the precursor. Next, sintering is performed. Weigh 1.0 g of the precursor according to the stoichiometric ratio in the molecular formula and 0.48 g of anhydrous sodium acetate (5% excess), mix and grind for 30 min until homogeneous. Then sinter in a muffle furnace at 500℃ for 1 h, and continue heating to 900℃ for calcination for 10 h. After naturally cooling to room temperature, the sodium-ion battery cathode material Na is obtained. 0.67 [Ni 0.25 Mn 0.75 O2.

[0061] The sample of Comparative Example 1 was characterized as follows:

[0062] As attached Figure 2 SEM results show that the material in Comparative Example 1 consists of spherical secondary particles. (See attached image.) Figure 5 XRD results showed that the prepared Na 0.67 [Ni 0.25 Mn 0.75 O2 is a pure P2 phase, belonging to the hexagonal crystal system, with space group P63 / mmc.

[0063] The sample of Comparative Example 1 was assembled into a sodium ion battery according to the following method and battery performance test was conducted:

[0064] (1) Preparation of positive electrode material tab

[0065] Na 0.67 [Ni 0.25 Mn 0.75 ]O2 positive electrode material, conductive carbon black (Super P) and binder polyvinylidene fluoride (PVDF) were ground in a mass ratio of 7:2:1, uniformly dispersed in N-methyl pyrrolidone (NMP) solvent to obtain a mixed slurry of the positive electrode material. The mixed slurry was uniformly coated on the positive electrode current collector aluminum foil, and after overnight vacuum drying, it was cut into a circular positive electrode tab with a diameter of 10 mm.

[0066] (2) Assembly of sodium ion battery

[0067] The above positive electrode tab was used as the positive electrode, a sodium sheet was used as the negative electrode, 1M sodium perchlorate (NaClO4) + propylene carbonate (PC) + 5wt% fluoroethylene carbonate (FEC) was used as the electrolyte, and other necessary battery components (separator and shell, etc.) were assembled into a CR2032 type button cell in an argon-filled glove box.

[0068] (3) Performance test of battery

[0069] The battery assembled by the above method was subjected to charge-discharge performance test in a new battery test system, the test temperature was 25°C, the voltage window was 2.0-4.2V, and the capacity retention rate of Na 0.67 [Ni 0.25 Mn 0.75 ]O2 positive electrode material was 40% after 500 cycles at a rate of 5C, as shown in the attached Figure 8 .

[0070] (4) Charge state XRD test of positive electrode material

[0071] The sodium ion half-cell charged to 4.2V at 25°C and a rate of 0.2C was disassembled, and the positive electrode tab was taken out for XRD test. The test results are shown in the attached Figure 10 , Na 0.67 [Ni 0.25 Mn 0.75 ]O2 positive electrode material undergoes P2→O2 phase transition when charged to 4.2V, which greatly damages the material structure, explaining the reason for the rapid capacity decay.

[0072] Comparative Example 2:

[0073] This comparative example used a co-precipitation combined with solid state sintering method to synthesize a positive electrode material Na 0.67 [Ni 0.21 Mn0.71 Mg 0.08 The performance of sodium-ion batteries was investigated, and the phase changes during the charging and discharging process were explored.

[0074] First, according to the stoichiometric ratio of transition metals in the chemical formula of the cathode material, and combined with the K of the corresponding precipitates of each metal ion, sp Value. Using deionized water, prepare 1000 mL of a mixed solution A of 2 mol / L manganese sulfate, nickel sulfate, and magnesium sulfate (Ni:Mn:Mg = 7:2:1), and 2000 mL of a mixed solution B of 2 mol / L sodium carbonate and 0.3 mol / L ammonia. Simultaneously pump solutions A and B into the mixture at 55℃ and a stirring rate of 500 r / min. After the reaction is complete, filter, wash with water, and dry the co-precipitated product to obtain the precursor. Next, sintering is performed. Weigh 1.0 g of the precursor according to the stoichiometric ratio in the molecular formula and 0.50 g of anhydrous sodium acetate (5% excess), mix and grind for 30 min until homogeneous. Then sinter in a muffle furnace at 500℃ for 1 h, and continue calcining at 900℃ for 10 h. After naturally cooling to room temperature, the sodium-ion battery cathode material Na is obtained. 0.67 [Ni 0.21 Mn 0.71 Mg 0.08 O2.

[0075] The sample of Comparative Example 2 was characterized as follows:

[0076] As attached Figure 3 SEM results show that the material in Comparative Example 2 consists of spherical secondary particles. (See attached image.) Figure 6 XRD results showed that the prepared Na 0.67 [Ni 0.21 Mn 0.71 Mg 0.08 O2 is a pure P2 phase, belonging to the hexagonal crystal system, with space group P63 / mmc.

[0077] The sample from Comparative Example 2 was assembled into a sodium-ion battery using the following method, and the battery performance was tested:

[0078] (1) Preparation of positive electrode material electrode

[0079] Will Na 0.67 [Ni 0.21 Mn 0.71 Mg 0.08The O2 cathode material, conductive carbon black (Super P) and binder polyvinylidene fluoride (PVDF) are ground in a mass ratio of 7:2:1, uniformly dispersed in N-methyl pyrrolidone (NMP) solvent to obtain a mixed slurry of the cathode material. The mixed slurry is uniformly coated on the cathode current collector aluminum foil, vacuum dried overnight, and then cut into a circular cathode sheet with a diameter of 10 mm.

[0080] (2) Assembly of sodium ion battery

[0081] The above-mentioned cathode sheet is used as the positive electrode, the sodium sheet is used as the negative electrode, 1M sodium perchlorate (NaClO4) + propylene carbonate (PC) + 5wt% fluoroethylene carbonate (FEC) is used as the electrolyte, and other necessary battery components (diaphragm and shell, etc.) are assembled into a CR2032 type button cell in a glove box filled with high-purity argon.

[0082] (3) Performance test of battery

[0083] The battery assembled by the above-mentioned method is subjected to charge-discharge performance test in a new battery test system, the test temperature is 25°C, and the voltage window is 2.0-4.2V. The test results show that the Na 0.67 [Ni 0.21 Mn 0.71 Mg 0.08 ]O2 cathode material has a capacity retention rate of 92% at a 5C rate after 500 cycles, showing good cycle stability, but because the material as a whole contains non-active element magnesium, a lot of specific capacity is lost, so the initial capacity is only 67mAh g -1 Compared with the core-shell structure, there is a larger capacity loss, as shown in the accompanying Figure 8 .

[0084] The above examples are only exemplary embodiments of the present application and are not used to limit the present application, the protection scope of the present application is defined by the claims. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A core-shell structured sodium-ion battery manganese-based layered cathode material, characterized in that, The material secondary particles are core-shell structure, and the molecular formula is Na x [M 1-y Mn y ] α [T a M 1-a-b Mn b ] 1-α O2, wherein 0.50 < x ≤ 1.0, 0.50 ≤ y < 1.0, 0.50 ≤ b < 0.99, 0.01 ≤ a ≤ 0.20, 0 < α < 1, M is one or more of the electrochemically active elements Fe, Ni, Cu, T is one or more of the non-electrochemically active elements Mg, Zn, Al, Ti, Ca, wherein the M elements are uniformly distributed in the material secondary particles, and the T elements are only in the shell layer of the secondary particles, and the concentration is uniformly or gradiently distributed.

2. The method of claim 1, wherein the core-shell structured sodium-ion battery manganese-based layered cathode material is prepared by the following steps: 1) preparing a precursor of a sodium-ion battery manganese-based layered cathode material; 2) coating the precursor with a coating layer; and 3) annealing the precursor coated with the coating layer. Step one, first use co-precipitation post-feeding or series feeding method to prepare metal carbonate or hydroxide precipitate precursor with core-shell structure at 300-800r / min; Step two, grind the precursor and sodium source, mix uniformly, first pre-sinter at 400-550℃ for 1-6h, then continue to sinter at 500-1200℃ for 5-14h, and then cool naturally to obtain the final product.

3. The method of producing a core-shell structured sodium-ion battery manganese-based layered cathode material according to claim 2, characterized in that, The co-precipitation is divided into two stages, the first stage prepares the inner core with high specific energy, which is a carbonate precipitate or hydroxide precipitate co-existing with M metal ions and Mn ions, and the second stage continues to precipitate outside the inner core to form a stable outer shell, which is a carbonate precipitate or hydroxide precipitate co-existing with T metal ions, M metal ions and Mn ions.

4. The method of claim 3, wherein the method further comprises a step of calcining the mixture at a temperature of 600-800 °C for 10-20 hours. The specific preparation method of step one is: (1) according to the stoichiometric ratio of transition metals in the inner core and the outer shell of the molecular formula of the core-shell structure positive electrode material, first pump manganese source aqueous solution, M source aqueous solution, precipitant and complexing agent into the reactor at the same time to prepare the inner core of the material; (2) after a period of reaction, continue to pump manganese source aqueous solution, M source aqueous solution, and T source aqueous solution, precipitant and complexing agent into the reactor at the same time to coat the outer shell on the inner core of the material, and then after the reaction is completed, the co-precipitation product is filtered, washed and dried to obtain the core-shell structure precursor.

5. The method of producing a core-shell structured sodium-ion battery manganese-based layered cathode material according to claim 4, characterized in that, The manganese source in the manganese source aqueous solution is one or more of manganese monoxide, manganese sesquioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate and manganese nitrate, the content of manganese in the manganese source aqueous solution in reaction stage (1) accounts for 50%-100% of the total metal content of the manganese source aqueous solution and the M source aqueous solution; the content of manganese in the manganese source aqueous solution in reaction stage (2) accounts for 50%-99% of the total metal content of the manganese source aqueous solution, the M source aqueous solution and the T source aqueous solution.

6. The method of producing a core-shell structured sodium-ion battery Mn-based layered cathode material according to claim 4, characterized in that, The M source in the M source aqueous solution is one or more of Fe source, Ni source and Cu source, the Fe source is one or more of iron sulfate, magnetite, ferrous oxide, ferrous acetate, ferrous oxide, ferrous carbonate, and ferric nitrate; the Ni source is one or more of nickel sulfate, nickel oxide and nickel acetate; the Cu source is one or more of copper nitrate, copper oxide, copper acetate and copper carbonate; the content of M in the M source aqueous solution in reaction stage (1) accounts for 0%-50% of the total metal content of the manganese source aqueous solution and the M source aqueous solution; the content of M in the M source aqueous solution in reaction stage (2) accounts for 0%-49% of the total metal content of the manganese source aqueous solution, the M source aqueous solution and the T source aqueous solution.

7. The method of producing a core-shell structured sodium-ion battery Mn-based layered cathode material according to claim 4, characterized in that, The T source in the T source aqueous solution is one or more of a Mg source, a Zn source, an Al source, a Ti source, and a Ca source; wherein the Mg source is one or more of magnesium acetate, magnesium oxide, and magnesium carbonate; the Zn source is one or more of zinc sulfate, zinc oxide, zinc acetate, and zinc carbonate; the Al source is one or more of aluminum oxide, aluminum sulfate, aluminum nitrate nonahydrate, and aluminum acetate; the Ti source is one or more of titanium monoxide, titanium sesquioxide, and titanium dioxide; and the Ca source is one or more of calcium carbonate, calcium chloride, calcium oxide, and calcium hydroxide.

8. The method of producing a core-shell structured sodium-ion battery Mn-based layered cathode material according to claim 4, characterized in that, The precipitant is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium oxide; the concentration of sodium hydroxide in step (1) is the sum of the molar concentrations of the metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution multiplied by the sum of the valence states, and in step (2) is the sum of the molar concentrations of all the metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution multiplied by the sum of the valence states; the concentration of sodium carbonate or sodium bicarbonate in step (1) is the sum of the molar concentrations of all the metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution, and in step (2) is the sum of the molar concentrations of all the metal ions in the manganese source aqueous solution, the M source aqueous solution, and the T source aqueous solution.

9. The method of producing a core-shell structured sodium-ion battery Mn-based layered cathode material according to claim 4, characterized in that, The complexing agent is one or more of ammonia, ethylenediaminetetraacetic acid, citric acid, malic acid, malonic acid, succinic acid, and lactic acid; the amount of the complexing agent added in step (1) is 0.05-1.0 mol / L, and in step (2) is 0.05-1.0 mol / L.

10. The method of producing a core-shell structured sodium-ion battery Mn-based layered cathode material according to claim 2, characterized in that, The sodium source is one or more of sodium acetate, sodium chloride, sodium carbonate, sodium fluoride, and sodium nitrate.

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