NaxMn1-yMyO2-coated MgAl2O4 composite material, preparation thereof and application of NaxMn1-yMyO2-coated MgAl2O4 composite material in sodium ion battery

Abstract

The invention belongs to the field of sodium ion batteries, and particularly relates to a NaxMn1-yMyO2-coated MgAl2O4 composite material, which has a core-shell structure, the core is NaxMn1-yMyO2 with a P2 / T composite phase or an O3 / P3 composite phase, x is 0.5-0.7, y is more than 0 and less than or equal to 0.6, M is at least one of Ca, Fe, Mg, Sr, Ta, Ti, Cu, Zn, V, Cr, Sn, Zr, Y, La, Ce, Nb, Mo, Ru and Ir, and the core is NaxMn1-yMyO2-coated MgAl2O4 composite material. And the shell is made of MgAl2O4. The invention also provides a preparation method and application of the material. According to the invention, the MgAl2O4 material is innovatively adopted as a coating material, and combined control of a special P2 / T composite phase or O3 / P3 composite phase of a nickel-free manganese-rich matrix is matched, so that synergy can be realized, the problems of dissolution of manganese and the like of the composite material can be remarkably improved, the structural stability and ion transmission performance of the composite material are improved, and the service life of the composite material is prolonged. Therefore, the long cycle performance of the material in high magnification and wide temperature range is improved.

Description

Technical Field

[0001] The present invention belongs to the field of cathode materials, and particularly relates to the field of manganese-rich nickel-free composite sodium-ion battery materials. Background Art

[0002] As an important component of sodium-ion batteries, transition metal oxides (Na x MeO2) stand out among many cathode materials due to their low cost, easy synthesis, high specific capacity, etc. Among them, manganese-rich transition metal oxide cathode materials have become one of the mainstream cathode materials today due to their outstanding cost advantages, diverse structures, non-toxicity and environmental friendliness. However, the Jahn-Teller effect caused by the increase in the manganese element content will lead to the distortion of the crystal structure, resulting in the instability of the material structure, and then affecting the cycle performance of the battery. At the same time, poor electronic conductivity and the problem of manganese dissolution under high voltage will limit the development of manganese-rich cathode materials. Based on this, modification measures for manganese-rich cathode materials of sodium-ion batteries are proposed, including element doping, surface coating and structure design, etc. Doping modification is a common strategy to improve the above problems and enhance the electrochemical performance of manganese-rich cathode materials. Cation doping such as Al, Cu, Ti, Ni, etc. can inhibit lattice distortion, reduce the Jahn-Teller effect of manganese, stabilize the crystal structure and then improve the cycle life of the battery. However, the synthesis process in the doping modification process is complex, the doping amount is difficult to accurately control, and inappropriate doping amount may not achieve the expected performance improvement effect, and even have a negative impact on the material performance.

[0003] Surface coating is expected to inhibit the structural distortion caused by the Jahn-Teller effect and improve the cycle stability. The coating layer can also inhibit the side reaction between the cathode material and the electrolyte. Many coating schemes have been reported in the prior art. For example, the Chinese patent document with the publication number CN116864651A discloses an O3-type quaternary single-crystal cathode material, including the following components: a core material and a carbon coating layer covering the outer surface of the core material; the core material is composed of a quaternary system main material and an auxiliary material doped in the quaternary system main material; the chemical formula of the quaternary system main material is NaNiMFeMnO, where M is one of Ca, Zr, Zn, Mg and Ti; the auxiliary material is two or more of Ca, Zr, Zn, Mg and Ti other than M. Another example is that the Chinese patent document with the publication number CN117219772A discloses a preparation method of a sodium-ion battery cathode material with a low-nickel shell structure. The cathode material includes: the inner core is a low-nickel iron-manganese-based ternary cathode material with an O3 phase, and its general formula: Na x Ni a Fe b Mn 1-a-b O2, where 0.9 < x ≤ 1.3, 0.01 ≤ a < 0.1, 0.3 < b < 0.5; the outer shell is a metal oxide, and the general formula: Na yMO₂, where 0 < y ≤ 1.0, and M is a transition metal element including one or more of Ti, Mn, Fe, Cu, and Zn. Chinese patent document with publication number CN117638051A discloses a coated O3-type manganese-based sodium-ion battery cathode material, including an O3-type manganese-based sodium-ion battery cathode material and sodium titanate phosphate coated on the surface of the O3-type manganese-based sodium-ion battery cathode material. Chinese patent document with publication number CN118073552A discloses a sodium-ion battery cathode material, which is prepared by doping metal Bi and metal Ni into a P2-phase layered manganese-based material, and the chemical general formula of the core is NaBiNiMnO, and the material of the shell is NaMnNiO.

[0004] Although there are many coating improvement schemes in the prior art, most of the matrix materials of the existing materials contain nickel, and there are few improved schemes adapted to the nickel-free and manganese-rich matrix. Summary of the Invention

[0005] Aiming at the problems of serious Jahn-Teller effect leading to lattice distortion, poor structural stability, unsatisfactory material performance, and dissolution of manganese in the nickel-free and manganese-rich matrix material, the first object of the present invention is to provide a Na x Mn 1-y M y O₂@MgAl₂O₄ composite material, aiming to provide a new material that adapts to the characteristics of the nickel-free and manganese-rich composite phase body, and takes into account surface structure stability, high electrical conductivity, excellent long cycle, rate performance, and wide temperature range performance.

[0006] The second object of the present invention is to provide a preparation method of the Na x Mn 1-y M y O₂@MgAl₂O₄ composite material and its application in sodium-ion batteries.

[0007] The third object of the present invention is to provide a sodium-ion battery containing the Na x Mn 1-y M y O₂@MgAl₂O₄ composite material, and its positive electrode and positive electrode material.

[0008] Aiming at the problems faced by the special physical and chemical characteristics of nickel-free and manganese-rich materials, such as difficulty in adapting to fast charging and wide temperature range use, etc., the present invention provides the following technical solutions:

[0009] A Na x Mn 1-y M y O₂@MgAl₂O₄ composite material, having a core-shell structure, and the core is Na x Mn 1-y My O₂, where x is 0.5 to 0.7, 0 < y ≤ 0.6, and M is at least one of Ca, Fe, Mg, Sr, Ta, Ti, Cu, Zn, V, Cr, Sn, Zr, Y, La, Ce, Nb, Mo, Ru, Ir;

[0010] The shell is MgAl₂O₄.

[0011] Aiming at the problems faced by nickel-free and manganese-rich sodium electrode materials, the present invention innovatively uses MgAl₂O₄ material as the coating material and combines it with the joint control of the special P2 / T composite phase or O3 / P3 composite phase of the nickel-free and manganese-rich matrix. In this way, synergy can be achieved, and problems such as the dissolution of manganese in the composite material can be significantly improved, its structural stability and ion transport performance can be improved, and further, the long-cycle performance of the material at high rates and wide temperature ranges can be improved.

[0012] In the present invention, x is 1 / 2 to 2 / 3; further, it can be 1 / 2 or 2 / 3.

[0013] M includes Fe and at least one of Nb, Ti, and Mg. y is 0.4 to 0.5. Further, the molar amount of Fe accounts for more than 50% of the molar amount of M. In the present invention, aiming at the migration difficulty caused by the superposition of manganese-rich and iron-containing materials, in the present invention, by using the combination of the P2 / T composite phase or O3 / P3 composite phase and the MgAl₂O₄, good effects can also be obtained, and the stability of the material at high voltages and high rates in a wide temperature range can also be improved.

[0014] In the present invention, the core is Na of the P2 / T composite phase 0.5 Fe 0.38 Nb 0.05 Mn 0.57 O₂, Na of the P3 / O3 composite phase 2 / 3Fe 1 / 5 Mn 3 / 5 Ti 1 / 5 O₂, Na of the P2 / T composite phase 0.5 Mg 0.1 Fe 0.3 Mn 0.6 At least one of O₂.

[0015] In the present invention, the Na x Mn 1-y M y In the Na

[0016] The present invention also provides a method for preparing the Na x Mn 1-y M y O2@MgAl2O4 composite material. React a Mn source, an M source, an auxiliary agent A and a precipitating agent, and wash and dry with deionized water to obtain a Mn-M precursor; the auxiliary agent A is at least one of ammonia water and organic polyacid;

[0017] Carry out liquid-phase compounding of the Mn-M precursor, a Mg source and an Al source, and then carry out spray pyrolysis, and then wash and dry to obtain a Mn-M@Mg-Al composite precursor coated with magnesium and aluminum; the molar ratio of Mg / Al in the Mg source and the Al source is 1:1.9 to 2.1; the temperature of the spray pyrolysis is above 800 °C;

[0018] Mix the Mn-M@Mg-Al composite precursor and a sodium source and then carry out roasting treatment to obtain the Na x Mn 1-y M y O2@MgAl2O4 composite material.

[0019] The present invention innovatively forms a Mn-M precursor of the elements and stoichiometric ratios, and then coats a Mg source and an Al source on the surface of the precursor to obtain a composite precursor, and further carries out sodium-doped roasting on the composite precursor. By adopting this process method, it is possible to successfully prepare the composite material with the special P2 / T or P3 / O3 composite phase matrix and in-situ coated MgAl2O4 of the present invention. The material prepared by the method of the present invention can effectively improve the core-shell synergy of the material and improve the electrochemical performance of the material.

[0020] In the present invention, the Mn source is one or more of manganese acetate, manganese oxalate, manganese nitrate, and manganese sulfate.

[0021] Preferably, the M source is one or more of the acetate, oxalate, nitrate, and sulfate of M.

[0022] Preferably, the precipitating agent is one or more of sodium hydroxide, sodium carbonate, sodium oxalate, and ammonium bicarbonate.

[0023] Preferably, the auxiliary agent A is at least one of ammonia water, citric acid, oxalic acid, and ethylenediaminetetraacetic acid.

[0024] Preferably, the auxiliary agent A is 1.2 to 2.5 times the total molar amount of the Mn source and the M source; the dosage of the precipitating agent is 1 to 2 times the theoretical molar amount of metal precipitation.

[0025] The pH at the end of the precipitation reaction is 8 to 12.

[0026] Preferably, the temperature of the precipitation reaction is 40 to 85 °C; the time of the precipitation reaction is 12 to 24 hours.

[0027] In the present invention, the Mg source is one or more of magnesium acetate, magnesium nitrate, magnesium sulfate, magnesium chloride, and magnesium isopropoxide; the Al source is one or more of aluminum sulfate, aluminum acetate, aluminum isopropoxide, and aluminum citrate.

[0028] In the present invention, the Mn-M precursor and the Mg source and the Al source can be pre-dispersed under ultrasound, and then spray pyrolysis is carried out to obtain the Mn-M@Mg-Al composite precursor.

[0029] In the present invention, MgAl2O4 is Na x Mn 1-y M y 0.5% to 10% of the total weight of O2; further, it can be 1 to 5 wt.%, and further 1 to 2 wt.%. Research shows that under the preferred coating amount, the wide-temperature performance of the material can be further synergistically optimized.

[0030] In the present invention, the carrier gas for spray pyrolysis is air or nitrogen;

[0031] Preferably, the temperature of spray pyrolysis is 800 to 1200 °C, and further 1000 to 1150 °C. Research shows that at the preferred spray temperature, the wide-temperature performance of the prepared material can be further synergistically optimized.

[0032] After spray pyrolysis, it is washed with deionized water and then dried. The temperature for drying after washing is 80 to 120 °C; the drying time is 12 to 24 hours.

[0033] In the present invention, the Mn-M@Mg-Al composite precursor and the sodium source are mixed and then calcined, wherein the sodium source can be at least one of sodium oxides, hydroxides, carbonates, and bicarbonates.

[0034] In the present invention, the dosage of the Na source is 1 to 1.05 times the theoretical molar amount.

[0035] In the present invention, the atmosphere in the calcination stage is an oxygen-containing atmosphere.

[0036] In the present invention, the calcination process includes two-stage heat preservation processes, wherein the temperature of the first-stage heat preservation stage is 300 to 550 °C (further, it can be 400 to 500 °C); the temperature of the second-stage heat preservation stage is 800 to 950 °C.

[0037] In the present invention, the time for the first-stage heat preservation is 3 to 6 hours; the time for the second-stage heat preservation is 12 to 15 hours.

[0038] The present invention also includes the Nax Mn 1-y M y A scheme for preparing a sodium-ion battery and its positive electrode and positive electrode material using the MyO2@MgAl2O4 composite material as the positive electrode active material.

[0039] The present invention also provides a positive electrode material for a sodium-ion battery, comprising the Na x Mn 1-y M y yO2@MgAl2O4 composite material described in the present invention.

[0040] For the positive electrode material described in the present invention, components that are allowed to be added within the positive electrode material are also allowed, such as conductive agents and binders, etc.

[0041] In the present invention, in the positive electrode material, in addition to comprising the Na x Mn 1-y M y yO2@MgAl2O4 composite material, other components and their contents can be well-known.

[0042] The present invention also provides a positive electrode for a sodium-ion battery, comprising a current collector and a positive electrode material compounded on its surface, and the positive electrode material is the positive electrode material described in the present invention and comprising the Na x Mn 1-y yO2@MgAl2O4 composite material.

[0043] The present invention also provides a sodium-ion battery, which comprises a positive electrode comprising the Na x Mn 1-y yO2@MgAl2O4 composite material.

[0044] For the sodium-ion battery, its positive electrode and positive electrode material described in the present invention, in addition to comprising the Na x Mn 1-y M y yO2@MgAl2O4 composite material, other components, component contents and structures can be conventional.

[0045] Beneficial effects:

[0046] Innovatively, the present invention coats the nickel-free manganese-rich matrix of the special composite phase with the MgAl2O4 material, so that synergy can be achieved, problems such as manganese dissolution of the composite material can be significantly improved, the structural distortion caused by the Jahn-Teller effect of the manganese-rich material can be improved, sodium-ion transport can be promoted, at the same time, electrolyte erosion can be isolated, the crystal structure can be stabilized, and the composite material can obtain excellent long-cycle performance and rate performance at both high and low temperatures.

[0047] The present invention innovatively prepares the composite precursor by spray pyrolysis of the Mn-M precursor, Mg source, and Al source, and further performs sodium-doped calcination on the composite precursor. By adopting this process method, the composite material with the special P2 / T or O3 / P3 composite phase matrix and in-situ coated MgAl2O4 described in the present invention can be successfully prepared. The material prepared by the method of the present invention can effectively improve the core-shell synergy of the material and improve the electrochemical performance of the material. Brief Description of the Drawings

[0048] Figure 1 It is the SEM image of the material finally obtained in Example 1.

[0049] Figure 2 It is the charge-discharge performance graph of the cathode material obtained in Example 1 in the first cycle at a rate of 0.1C and a voltage of 2.0 - 4.0V.

[0050] Figure 3 It is the charge-discharge performance graph of the cathode material obtained in Example 1 in the first cycle at a rate of 1.0C and a voltage of 2.0 - 4.0V.

[0051] Figure 4 It is the cycling performance graph of the cathode materials obtained in Example 1 and Comparative Example 1 at -40°C, a rate of 1.0C, and a voltage of 2.0 - 4.0V for 100 cycles; Detailed Description of the Invention

[0052] The following will clearly and completely describe the concept and technical effects of the present invention in combination with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

[0053] The preparation method of the optional material of the present invention includes the following steps:

[0054] Step S1, weigh the manganese source and M source according to the stoichiometric ratio, add deionized water and mix evenly to prepare a metal salt solution;

[0055] Step S2, add the metal salt solution, auxiliary agent A, and precipitating agent described in Step S1 to the bottom liquid in Step S1 for reaction; during the reaction process, control the pH to be 8 - 12, the reaction temperature to be 40 - 85°C; the aging time to be 12 - 24 hours; after aging, centrifuge the coprecipitate, wash it with deionized water, and vacuum dry it at 80 - 120°C for 12 - 24 hours to obtain Precursor I;

[0056] Step S3, disperse the precursor I in deionized water with ultrasonic dispersion, weigh a magnesium source and an aluminum source according to a molar ratio of Mg:Al of 1:2, dissolve them in deionized water, add them dropwise to the above solution and stir to obtain a suspension, and continue stirring for not less than 30 minutes; the total weight of the magnesium source and the aluminum source is MgAl2O4 Na x Mn 1-y M y Calculated as 0.5% to 10% of the total O2;

[0057] Step S4, pouring the mixed solution obtained in step S3 into a sprayer for spray pyrolysis treatment, then collecting the product, washing it with deionized water for multiple times, and vacuum drying it at 80-120° C. for 12-24 hours to obtain a precursor mixture powder II;

[0058] Step S5, the precursor powder II obtained in step S4 is mixed with the sodium source in a stoichiometric ratio and then fully ground. After being calcined at 300-550° C. in an air or oxygen atmosphere and kept warm for 3-6 hours, it is then calcined at 800-950° C. and kept warm for 12-15 hours. After cooling, the obtained product is ground and sieved to obtain a MgAl2O4-modified composite phase sodium ion battery manganese-rich layered oxide positive electrode material.

[0059] In step S1, the manganese source is one or more of manganese acetate, manganese oxalate, manganese nitrate, and manganese sulfate, and the M source is one or more of acetate, nitrate, oxalate, and sulfate of M.

[0060] In step S2, the precipitant is one or more of sodium hydroxide solution, sodium carbonate solution, sodium oxalate solution, and ammonium bicarbonate solution, and the concentration is 0.1-2 mol / L; the auxiliary agent A is one or more of ammonia solution, citric acid solution, oxalic acid solution, and ethylenediaminetetraacetic acid, and the concentration is 0.1-2 mol / L.

[0061] In step S3, the magnesium source is one or more of magnesium acetate, magnesium nitrate, magnesium sulfate, magnesium chloride, and magnesium isopropoxide; the aluminum source is one or more of aluminum acetate, aluminum isopropoxide, aluminum sulfate, and aluminum citrate.

[0062] In step S4, the temperature of the high temperature furnace (the temperature of spray pyrolysis) is 800-1200°C; more preferably, 1000-1150°C.

[0063] In step S5, the heating rate is 1-10°C / min, and the sintering atmosphere is air or oxygen, so as to obtain a MgAl2O4 coated and modified composite phase sodium ion battery manganese-rich layered oxide positive electrode material.

[0064] The present invention also provides a positive electrode sheet for a sodium ion battery, which comprises a current collector and a positive electrode material layer coated on the current collector, and the positive electrode material layer comprises the positive electrode material, a conductive additive and a binder.

[0065] Among them, the conductive additive is one or more of conductive carbon black, acetylene black, Ketjen black, and Super P; the binder is polyvinylidene fluoride.

[0066] Example 1

[0067] A manganese-rich positive electrode material for a P2 / T composite phase sodium ion battery modified by MgAl2O4 coating, and the chemical formula of the positive electrode material of the P2 / T composite phase sodium ion battery is Na 0.5 Fe 0.38 Nb 0.05 Mn 0.57 O2@MgAl2O4, and the mass of the MgAl2O4 coating layer is 1% of the mass of Na 0.5 Fe 0.38 Nb 0.05 Mn 0.57 O2.

[0068] A preparation method of a manganese-rich positive electrode material for a P2 / T composite type sodium ion battery modified by MgAl2O4 coating, comprising the following steps:

[0069] (1) Weigh manganese acetate, iron acetate and niobium acetate according to the molar ratio of Mn:Fe:Nb in the chemical formula Na 0.5 Fe 0.38 Nb 0.05 Mn 0.57 O2 being 0.57:0.38:0.05, uniformly mix them and configure them into a salt solution with 1 L of deionized water;

[0070] The precipitating agent is a sodium hydroxide solution with a concentration of 0.25 mol / L;

[0071] The auxiliary agent A is an ammonia water solution with a concentration of 0.5 mol / L;

[0072] (2) Add 50 ml of deionized water as the bottom liquid into the reaction vessel, and drop the auxiliary agent A (ammonia water, which is 1.5 to 2 times the total molar amount of Mn:Fe:Nb) and the precipitating agent (0.5 M sodium hydroxide solution; which is 1.1 to 1.3 times the theoretical molar amount of precipitating Mn:Fe:Nb) into the reaction vessel for reaction; finish dropping within 6 h, and then stir for 2 h; during the reaction process, control the pH to be 8 and the reaction temperature to be 60 °C; then age for 15 hours; after aging, centrifuge the coprecipitate, wash it with deionized water until the filtrate is neutral, and then vacuum dry it at 100 °C for 24 h to obtain the precursor Ⅰ;

[0073] (3) Weigh 4 g of precursor I, disperse it in 80 mL of deionized water, and ultrasonically disperse it for 20 minutes. Select magnesium sulfate as the magnesium source and aluminum sulfate as the aluminum source. Weigh magnesium acetate and aluminum acetate and dissolve them in 10 mL of deionized water. Add them dropwise to the mixed solution and stir to obtain a suspension. While adding dropwise, stir magnetically for 130 minutes to obtain a suspension. The rotation speed is selected to be 500 rpm. The molar ratio of Mg:Al in the magnesium source and the aluminum source is 1:2. The total weight of the magnesium source and the aluminum source is MgAl2O4:Na 0.5 Fe 0.38 Nb 0.05 Mn 0.57 Calculated as 1% of the total O2;

[0074] (4) subjecting the mixed solution obtained in step (3) to a spray pyrolysis treatment, wherein the temperature of the spray pyrolysis is 1100° C., washing the spray pyrolysis product with deionized water for multiple times until the filtrate is neutral, and then vacuum drying at 100° C. for 24 hours to obtain a precursor mixture dry powder II;

[0075] (5) The precursor mixture dry powder II obtained in step (4) is mixed with a sodium source (the molar ratio of the precursor mixture dry powder II to Mn:Fe:Nb:Na in sodium carbonate is 0.57:0.38:0.05:0.5), and then fully ground and placed in a calcination boat. In an air atmosphere, the mixture is calcined at 500°C (T1) for 5 hours and then calcined at 900°C (T2) for 12 hours. The mixture is naturally cooled to about 150°C, taken out, and fully ground to obtain a MgAl2O4-modified P2 / T composite phase sodium ion battery manganese-rich layered oxide positive electrode material.

[0076] Example 2

[0077] Compared with Example 1, the only difference is that the base material is changed, and the specific difference is:

[0078] Group A: The matrix material is a P3 / O3 composite phase sodium ion battery manganese-rich positive electrode material, a MgAl2O4 coated modified sodium ion battery positive electrode material with a chemical formula of Na 2 / 3 Fe 1 / 5 Mn 3 / 5 Ti 1 / 5 O2@MgAl2O4, other operations and parameters are the same as in Example 1.

[0079] Group B: The matrix material is a P2 / T composite phase sodium ion battery manganese-rich positive electrode material, a MgAl2O4 coated modified sodium ion battery positive electrode material with a chemical formula of Na 0.5 Mg 0.1 Fe 0.3 Mn 0.6 O2@MgAl2O4, other operations and parameters are the same as in Example 1.

[0080] Example 3

[0081] Compared with Example 1, the difference is only that in step (3), the dosage of MgAl2O4 is replaced by 4 wt.% of the P2 / T composite phase sodium ion battery rich-manganese cathode material, and other preparation conditions are the same as those in Example 1.

[0082] Example 4

[0083] Compared with Example 1, the difference is only that in step (4), the temperature of spray pyrolysis is 800 °C, and other preparation conditions are the same as those in Example 1.

[0084] Example 5

[0085] Compared with Example 1, the difference is only that in step (5), the temperature T1 is controlled at 400 °C for 4 h, the temperature T2 is 850 °C for 14 h; other preparation conditions are the same as those in Example 1.

[0086] Comparative Example 1

[0087] Compared with Example 1, the difference is only that in step (3), magnesium acetate and aluminum acetate are not added, and other operations and parameters are the same as those in Example 1.

[0088] Comparative Example 2

[0089] Compared with Example 1, the difference is only that in step (3), ferric acetate is used to replace the aluminum acetate in an equimolar amount, and other operations and parameters are the same as those in Example 1.

[0090] Comparative Example 3

[0091] Compared with Example 1, the difference is only that in step (3), the molar ratio of Mg / Al is controlled at 1:1.5, the total weight of magnesium and aluminum, and other operations and parameters are the same as those in Example 1.

[0092] Comparative Example 4

[0093] Compared with Example 1, the difference is only that in step (3), the temperature of spray pyrolysis is controlled at 700 °C, and other operations and parameters are the same as those in Example 1.

[0094] Comparative Example 5

[0095] Compared with Example 1, the difference is only that in step (3), the mixed solution is desolvated at a temperature of 200 °C to obtain a mixed material, and then the mixed material is heat-insulated at a temperature of 1100 °C. Other operations and parameters are the same as those in Example 1.

[0096] Comparative Example 6

[0097] Compared with Example 1, the difference is only that the matrix coated with MgAl2O4 is replaced with a P2 / O3 composite phase sodium-ion battery rich-manganese cathode material. That is, in step (5), the molar ratio of Mn:Fe:Nb:Na is 0.57:0.38:0.05:0.75, and P2 / O3 composite phase Na 0.75 Fe 0.38 Nb 0.05 Mn 0.57 O2 is prepared, and other operations and parameters are the same as those in Example 1.

[0098] Sodium secondary battery performance test:

[0099] The active substances, acetylene black (AB), and polyvinylidene fluoride (PVDF) finally prepared in the above cases were added to an N-methyl-2-pyrrolidone (NMP) solution in a molar ratio of 8:1:1. After grinding and dispersing, the slurry was evenly coated on an aluminum foil and dried in a vacuum oven at 80°C for more than 10 h to make a positive electrode plate. Acetylene black is a conductive additive, polyvinylidene fluoride is a binder, and aluminum foil is a current collector. The positive electrode surface loading is about 2.5 mg / cm 2 。

[0100] In a glove box filled with argon, where the concentrations of H2O and O2 are lower than 0.1 ppm, 2032 button cells were assembled. The electrolyte is a solution of 1 M NaPF6 in propylene carbonate (PC) and 5% fluoroethylene carbonate (PEC). A sodium metal foil is used as the negative electrode, and a glass fiber membrane is used as the separator of the half-cell.

[0101] Table 1

[0102]

[0103]

[0104] From the examples and comparative examples, it can be seen that innovatively using MgAl2O4 material as the coating material and cooperating with the joint control of the special P2 / T composite phase or O3 / P3 composite phase of the nickel-free rich-manganese matrix can achieve synergy, significantly improve problems such as the dissolution of manganese in the composite material, improve its structural stability and ion transport performance, and further improve the long-cycle performance of the material at high rates and wide temperature ranges.

Claims

1. A Na x Mn 1-y M y O2@MgAl2O4 composite material has a core-shell structure and is characterized by: The core is a Na2O3 having a P2 / T composite phase or an O3 / P3 composite phase. x Mn 1-y M y O2, wherein x is 0.5 to 0.7, 0 < y ≤ 0.6, and M is at least one of Ca, Fe, Mg, Sr, Ta, Ti, Cu, Zn, V, Cr, Sn, Zr, Y, La, Ce, Nb, Mo, Ru, and Ir; The shell is MgAl2O4.

2. Na as claimed in claim 1 x Mn 1-y M y O2@MgAl2O4 composite material, characterized in that The x is 1 / 2 to 2 / 3; Preferably, the M includes Fe and at least one of Nb, Ti and Mg, the y is 0.4 to 0.5, and further, the molar amount of Fe accounts for more than 50% of the molar amount of M; Preferably, the core is a P2 / T composite phase of Na 0.5 Fe 0.38 Nb 0.05 Mn 0.57 O2, P3 / O3 composite phase Na 2 / 3 Fe 1 / 5Mn 3 / 5 Ti 1 / 5 O2, P2 / T composite phase Na 0.5 Mg 0.1 Fe 0.3 Mn 0.6 At least one of O2; Preferably, the Na x Mn 1-y M y In the O2@MgAl2O4 composite material, the content of the shell material is 0.5-10wt.%.

3. A Na according to claim 1 or 2 x Mn 1-y M y The preparation method of O2@MgAl2O4 composite material is characterized in that: The Mn source, the M source, the auxiliary agent A and the precipitant are reacted, and the Mn-M precursor is prepared after being washed with deionized water and dried; the auxiliary agent A is at least one of ammonia water and an organic polyacid; The Mn-M precursor is composited with the Mg source and the Al source in liquid phase and then spray pyrolyzed, and then washed and dried to obtain the Mn-M@Mg-Al composite precursor coated with magnesium and aluminum; the molar ratio of Mg / Al in the Mg source and the Al source is 1:1.9-2.1; the temperature of the spray pyrolysis is above 800°C; The Mn-M@Mg-Al composite precursor and the sodium source are mixed and calcined to obtain the Na x Mn 1-y M y O2@MgAl2O4 composite materials.

4. Na as claimed in claim 3 x Mn 1-y M y The preparation method of O2@MgAl2O4 composite material is characterized in that: The Mn source is one or more of manganese acetate, manganese oxalate, manganese nitrate and manganese sulfate; Preferably, the M source is one or more of acetate, oxalate, nitrate and sulfate of M; Preferably, the precipitant is one or more of sodium hydroxide, sodium carbonate, sodium oxalate, and ammonium bicarbonate; Preferably, the auxiliary agent A is at least one of ammonia water, citric acid, oxalic acid, and ethylenediaminetetraacetic acid; Preferably, the auxiliary agent A is 1.2 to 2.5 times the total molar amount of the Mn source and the M source; the pH at the end point of the precipitation reaction is 8 to 12; Preferably, the precipitation reaction temperature is 40 to 85° C.; the precipitation reaction time is 12 to 24 hours.

5. Na as claimed in claim 3 x Mn 1-y M y The preparation method of O2@MgAl2O4 composite material is characterized in that: The Mg source is one or more of magnesium acetate, magnesium nitrate, magnesium sulfate, magnesium chloride, and magnesium isopropoxide; the Al source is one or more of aluminum sulfate, aluminum acetate, aluminum isopropoxide, and aluminum citrate; Preferably, MgAl2O4 is Na x Mn 1-y M y O2 0.5%-10% of the total weight.

6. Na as claimed in claim 3 x Mn 1-y M y The preparation method of O2@MgAl2O4 composite material is characterized in that: The carrier gas for spray pyrolysis is air or nitrogen; Preferably, the temperature of the spray pyrolysis is 800-1200°C.

7. Na as claimed in claim 3 x Mn 1-y M y The preparation method of O2@MgAl2O4 composite material is characterized in that: The atmosphere during the calcination stage is an oxygen-containing atmosphere; Preferably, the roasting process includes two stages of heat preservation, wherein the temperature of the first stage of heat preservation is 300-550°C; the temperature of the second stage of heat preservation is 800-950°C; Preferably, the first insulation period is 3 to 6 hours; the second insulation period is 12 to 15 hours.

8. A positive electrode material for a sodium ion battery, characterized in that: Containing the Na according to any one of claims 1 to 2 x Mn 1- y M y O2@MgAl2O4 composite material or Na2O4 prepared by the preparation method according to any one of claims 3 to 7 x Mn 1-y M y O2@MgAl2O4 composite materials.

9. A positive electrode of a sodium ion battery, comprising a current collector and a positive electrode material composited on the surface thereof, characterized in that: The positive electrode material is the positive electrode material according to claim 8.

10. A sodium ion battery, characterized in that: The positive electrode according to claim 9 is included.

Images