Nickel-iron-manganese layered oxide positive electrode material and preparation method thereof

Abstract

The present invention relates to a nickel-iron-manganese layered oxide positive electrode material and a preparation method thereof. The nickel-iron-manganese layered oxide positive electrode material is expressed as Na[Ni x Fe y Mn z M b ]O2@(a‑b)Na i MO k The first solution containing Ni, Fe, and Mn salts and the second solution containing M salts are added to the reactor, and the precursor Ni is obtained after the reaction is completed. e Fe f Mn g M d (OH) 2+d The precursors were mixed with sodium salts according to a stoichiometric ratio, calcined at 700-1000°C for 10-15 hours, and cooled naturally to room temperature to obtain the nickel-iron-manganese layered oxide positive electrode material Na[Ni x Fe y Mn z M b ]O2@(a‑b)Na i MO k By doping W, Mo, Ru, Sb, Nb or Ta elements in the nickel-iron-manganese layered oxide cathode material, a one-step bulk doping and concentration-induced surface segregation self-coating layer are achieved to improve the cycling stability of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery positive electrode materials, and in particular to a nickel-iron-manganese ternary layered positive electrode material with surface segregation in-situ coating of primary particle size and bulk doping of high-valent metal ions, and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in new energy vehicles and energy storage systems, significantly transforming our daily lives. However, the uneven distribution of global resources, coupled with rising lithium and cobalt prices, has limited their further development. Sodium-ion batteries, due to their similar operating principles and the abundance of sodium in the Earth's crust, significantly reduce production costs, making them a promising complementary option to lithium-ion batteries.

[0003] The cathode material is the key to prepare high performance sodium ion batteries, and layered transition metal oxides Na x MO2 (M represents a transition metal element) has become a research hotspot due to its simple synthesis and relatively excellent performance. Nickel-iron-manganese ternary materials, as a typical sodium-ion layered oxide cathode, exhibit high theoretical specific capacity and are considered to be a very promising cathode material. During the material preparation process, the most suitable scalable synthesis method is to synthesize the target material precursor through co-precipitation, followed by high-temperature sodium sintering to obtain a micron-sized secondary particle material formed by the agglomeration of primary grains. This material has high tap density, uniform particle size distribution, and excellent electrochemical performance.

[0004] Na x The performance degradation mechanism of MO2 layered oxide cathode materials mainly focuses on the following three aspects: (1) The transition metal layer is prone to slip during charge and discharge, triggering multiple phase transitions of O3-P3 or P2-O2, resulting in a decrease in the diffusion rate of sodium ions and poor cycle stability; (2) The low charge density and redox potential of sodium ions lead to poor air stability of the material. External H2O and CO2 react with sodium ions on the particle surface, causing an increase in the amount of residual alkali on the surface of the material and gelation of the slurry, resulting in a sharp increase in the storage cost of the material; (3) In view of the fact that Na + Due to the larger ion radius, the volume change of the material during the charge and discharge cycle is more obvious than that of lithium-containing materials, and greater stress is generated inside the particles, inducing the formation of microcracks, blocking the electron and ion transmission channels, and making it easier to destroy the long-term cycle stability of the material.

[0005] Ion doping and surface coating are both effective means of improving material structure and interfacial stability, enhancing the electrochemical performance of sodium-ion layered cathode materials to a certain extent. However, due to the inherent intrinsic properties of sodium ions, the results of these two methods for modifying sodium-ion layered materials are still insufficient to support their application in sodium-ion batteries. Therefore, developing a material modification method with simpler processes and superior electrochemical performance is a highly worthy research direction. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a nickel-iron-manganese layered oxide positive electrode material and a preparation method thereof, so as to achieve the purpose of improving the cycle stability of the material.

[0007] In order to solve the above technical problems, according to one aspect of the present invention, a nickel-iron-manganese layered oxide positive electrode material is provided, which is expressed as Na[Ni x Fe y Mn z M b ]O2@(ab) Na i MO k ; Wherein, M is one or more of W, Mo, Ru, Sb, Nb or Ta; 0.1 < x, y, z, a, b < 1; Na i MO k is the self-cladding layer formed, i=1 or 2, k=3 or 4.

[0008] According to another aspect of the present invention, provided is a method for preparing the above-mentioned nickel-iron-manganese layered oxide positive electrode material, comprising:

[0009] Step 1: Add the first solution containing Ni, Fe, and Mn salts and the second solution containing M salts into the reactor, add alkali solution to control the pH value to 9-13, heat and reflux at 40-70 ° C and stir, and filter, wash and dry the precipitate in the reactor after the reaction to obtain the precursor Ni e Fe f Mn g M d (OH) 2+d , d>0;

[0010] Step 2: The precursor obtained in step 1 is mixed with sodium salt according to a stoichiometric ratio, calcined at 700-1000°C for 10-15 hours, and cooled naturally to room temperature to obtain the nickel-iron-manganese layered oxide positive electrode material Na[Ni x Fe y Mn z M b ]O2@(ab) Na i MO k.

[0011] Furthermore, in step 1, the stirring speed is 500-800 r / min, and the reaction time is 25-48 h.

[0012] Furthermore, in step 1, the washing process is to repeatedly wash with deionized water, filter, etc. to remove impurities in the solution; and the drying process is to dry the washed precursor at 90-120°C.

[0013] Furthermore, in step 1, the nickel salt is selected from NiSO4·6H2O; the manganese salt is selected from MnSO4·H2O; and the iron salt is selected from FeSO4·7H2O.

[0014] Furthermore, in step 1, the tungsten salt in the M salt is selected from W(CH3COO)6, NaWO4, NH4WO4, [(NH4)46W7O 24 ·6H2O]、H 28 N6O 41 W 12 At least one of; Molybdenum salt is selected from C 48 H 90 MoO 12 , MoO3, Na2MoO4, (NH4)2MoO4 at least one; ruthenium salt is selected from Ru(C2O4)2, C l2 H 18 At least one of N6Ru, (C5H5)2Ru, C6Cl4O6Ru2; antimony salt is selected from at least one of Sb(CH3COO)3, NaO3Sb, SbOCl and (SbO)2SO4, Sb(C6H5)3, Sb2(C6H5)4; niobium salt is selected from C 10 H5NbO 20 、C 10 H 25 At least one of NbO5, the tantalum salt is selected from TaF5, TaCl5, TaBr5, C 10 H 25 At least one of O5Ta.

[0015] Furthermore, in step 1, n 总 (Ni, Fe, Mn): nM is (4~99):1.

[0016] Furthermore, in step 1, the alkali solution is selected from sodium hydroxide (NaOH), ammonia (NH3H2O), hexamethylenetetramine HMT (C6H 12 N4) one or more.

[0017] Furthermore, the concentration of the alkali solution is 0.5-15 mol / L.

[0018] Furthermore, in step 2, the sodium salt is selected from Na2CO3; and the molar ratio of the precursor to the sodium salt is 1:(1-1.2).

[0019] The present invention dopes metal elements such as W, Mo, Ru, Sb, Nb and Ta into the nickel-iron-manganese ternary precursor. In addition, since these elements have low surface energy and large ionic radius, they can be in-situ segregated on the surface of the primary particles of the positive electrode material through concentration induction, forming a protective layer for the positive electrode particles, thereby improving the cycle stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 1 of the present invention.

[0021] Figure 2 This is an SEM image of the bulk-doped and surface-self-coated positive electrode material prepared in Example 1 of the present invention.

[0022] Figure 3 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 2 of the present invention.

[0023] Figure 4 This is an SEM image of the bulk-doped and surface-self-coated positive electrode material prepared in Example 2 of the present invention.

[0024] Figure 5 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 3 of the present invention.

[0025] Figure 6 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 4 of the present invention.

[0026] Figure 7 This is a TEM image of the bulk-doped and surface-self-coated positive electrode material prepared in Example 4 of the present invention.

[0027] Figure 8 This is the electrochemical cycle diagram of the bulk-doped and surface-self-coated positive electrode material prepared in Example 5 of the present invention.

[0028] Figure 9 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 6 of the present invention.

[0029] Figure 10 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 7 of the present invention.

[0030] Figure 11 This is the XRD pattern of the bulk-doped and surface-self-coated positive electrode material prepared in Example 8 of the present invention. DETAILED DESCRIPTION

[0031] Ion doping and surface coating can, to a certain extent, improve the material structure and interface stability, and enhance the electrochemical performance of sodium-ion layered cathode materials. However, due to the inherent intrinsic defect characteristics of sodium ions, the results of the modification research on sodium-ion layered materials using these two methods are still insufficient to support their application in sodium-ion batteries. Studies have shown that after certain metal elements within a certain concentration range are doped into the material precursor, during the sintering process, the energy barrier for the formation of sodium-containing composite oxides on the surface of the primary grains is smaller than that for the formation of sodium-containing composite oxides in the interior of the particles. Therefore, they tend to precipitate on the surface of the primary grains and spontaneously form a coating layer.

[0032] The basic concept of the present invention is to dope W, Mo, Ru, Sb, Nb or Ta elements in the nickel-iron-manganese layered oxide positive electrode material, and form a self-segregation coating layer on the particle surface through concentration induction, thereby improving the cycle stability of the material.

[0033] Based on this, a typical embodiment of the present invention provides a nickel-iron-manganese layered oxide positive electrode material, the expression of which is Na[Ni x Fe y Mn z M b ]O2@(ab) Na i MO k ; Wherein, M is one or more of W, Mo, Ru, Sb, Nb or Ta; 0.1< x, y, z, a, b < 1; Na i MO k is the self-cladding layer formed, i=1 or 2, k=3 or 4.

[0034] Another typical embodiment of the present invention provides a method for preparing the above-mentioned nickel-iron-manganese layered oxide positive electrode material, which adopts the concentration induction method to obtain the product by roasting the nickel-iron-manganese layered oxide positive electrode material precursor doped with a certain concentration of elements such as W, Mo, Ru, Sb, Nb or Ta and sodium salt, including the following steps.

[0035] Step 1: Add the first solution containing Ni, Fe, and Mn salts and the second solution containing M salts into the reactor, add alkali solution to control the pH value to 9-13, heat and reflux at 40-70 ° C and stir, and filter, wash and dry the precipitate in the reactor after the reaction to obtain the precursor Ni e Fe f Mn g M d (OH) 2+d , d>0.

[0036] The preferred stirring speed is 500-800 r / min, and the reaction time is 25-48 h.

[0037] The washing process is to repeatedly wash with deionized water, filter and remove impurities in the solution; the drying process is to dry the washed precursor at 90-120°C.

[0038] The nickel salt is selected from NiSO4·6H2O; the manganese salt is selected from MnSO4·H2O; and the iron salt is selected from FeSO4·7H2O.

[0039] In the M salt, the tungsten salt is selected from W (CH3COO) 6, NaWO4, NH4WO4, [(NH4)4 6W7O 24 ·6H2O]、H 28 N6O 41 W 12 At least one of; Molybdenum salt is selected from C 48 H 90 MoO 12 , MoO3, Na2MoO4, (NH4)2MoO4 at least one; ruthenium salt is selected from Ru(C2O4)2, C l2 H 18 At least one of N6Ru, (C5H5)2Ru, C6Cl4O6Ru2; antimony salt is selected from at least one of Sb(CH3COO)3, NaO3Sb, SbOCl and (SbO)2SO4, Sb(C6H5)3, Sb2(C6H5)4; niobium salt is selected from C 10 H5NbO 20 、C 10 H 25 At least one of NbO5, the tantalum salt is selected from TaF5, TaCl5, TaBr5, C 10 H 25 At least one of O5Ta.

[0040] The total amount of Ni, Fe and Mn and C 10 H 25 The molar ratio of NbO5 is (4~99):1.

[0041] The alkali solution is selected from sodium hydroxide (NaOH), ammonia (NH3H2O), hexamethylenetetramine HMT (C6H 12 N4) one or more. The concentration of the alkali solution is preferably 0.5-15 mol / L.

[0042] Step 2: The precursor obtained in step 1 is mixed with sodium salt in a stoichiometric ratio, calcined at 700-1000°C for 10-15 hours under an oxygen atmosphere, and cooled naturally to room temperature to obtain a nickel-iron-manganese ternary layered positive electrode material Na[Ni x Fe y Mn z M b ]O2@(ab) Na i MO k .

[0043] Wherein, the sodium salt is selected from Na2CO3; the molar ratio of the precursor to the sodium salt is 1: (1~1.2).

[0044] According to theoretical calculations and experimental verification, after metal elements such as W, Mo, Ru, Sb, Nb and Ta are doped into the cathode material precursor, due to the low surface energy of these elements and the concentration-induced mechanism, they spontaneously segregate and coat the surface of the primary grains of the cathode particles to form a protective layer.

[0045] The above method realizes one-step bulk doping and surface in-situ segregation of secondary phase to coat the primary particle size. The coating layer has the characteristics of thin thickness, uniform distribution, and in-situ coating, which can reduce the corrosion effect of the electrolyte on the positive electrode material and improve its air stability. At the same time, bulk doping can effectively reduce the structural phase change during the charging and discharging process, reduce stress and strain, and reduce the generation of microcracks between grains. The two have a positive effect on the cyclic stability, thermal stability and structural stability of the material.

[0046] The technical solutions claimed in the present invention are further illustrated below by means of some examples. However, the examples and comparative examples are intended to illustrate embodiments of the present invention and do not exceed the scope of the subject matter of the present invention. The scope of protection of the present invention is not limited by the examples. Unless otherwise specified, the materials and reagents used in the present invention can be obtained from commercial products in the art. Example 1

[0047] Weigh appropriate amounts of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add deionized water at a molar ratio of 4:4:2 to prepare 3 L of salt solution with a total metal ion concentration of 2 mol / L. 10 H 25 The total amount of Ni, Fe and Mn in NbO5 aqueous solution and C 10 H 25 The molar ratio of NbO5 is 0.99:0.01.

[0048] Then, 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia water were prepared to obtain the alkaline solution and ammonia solution required for the experiment, wherein the ammonia water was used as a complexing agent for the reaction and the sodium hydroxide was used as a precipitant.

[0049] In the reactor, under the protection of inert gas, the above salt solution, alkaline solution, ammonia solution and C 10 H 25 NbO5 aqueous solution. Control the feed rate to make the salt solution and C 10 H 25 NbO5 solution was added to the control reactor at the same time 10 H 25 The concentration of NbO5 was 0.007856 mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature was 50°C, and the stirring speed was 450 rpm / min. The hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0. 99 Nb 0.01 ](OH) 2.03 The precursor powder was obtained after washing with deionized water for several times and drying at 120°C.

[0050] The precursor was mixed with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+Nb) = 1.05, sintered at 950 ° C in an oxygen atmosphere for 12 h, and cooled to room temperature to obtain the positive electrode material Na[(Ni]) prepared by the one-step bulk doping and concentration-induced surface segregation self-coating method of the present invention. 0.4 Fe 0.2 Mn0.4) 1-x Nb x ]O2@(0.01-x) NaNbO3.

[0051] Figure 1 This is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the R-3m structure, indicating that the doping concentration is too low to induce the formation of a self-coating layer, which cannot be identified in the XRD spectrum. Figure 2 is the SEM image of the prepared material. Example 2

[0052] Weigh appropriate amounts of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and mix them in a ratio of 4:4:2.

[0053] Add deionized water at a molar ratio to prepare 3L of salt solution with a total metal ion concentration of 2mol / L. 10 H 25 The total amount of Ni, Fe and Mn in NbO5 aqueous solution and C 10 H25 The molar ratio of NbO5 is 0.9:0.1.

[0054] Then, 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia water were prepared to obtain the alkaline solution and ammonia solution required for the experiment, wherein the ammonia water was used as a complexing agent for the reaction and the sodium hydroxide was used as a precipitant.

[0055] In the reactor, under the protection of inert gas, the above salt solution, alkaline solution, ammonia solution and C 10 H 25 NbO5 aqueous solution. Control the feed rate to make the salt solution and C 10 H 25 NbO5 solution was added to the control reactor at the same time 10 H 25 The concentration of NbO5 was 0.07856 mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature was 50°C, and the stirring speed was 450 rpm / min. The hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0.9Nb 0. 1 ](OH) 2. 3 The precursor powder was obtained after washing with deionized water for several times and drying at 120°C.

[0056] The precursor was mixed with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+Nb) = 1.05, sintered at 950 ° C in an oxygen atmosphere for 12 h, and cooled to room temperature to obtain the positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Nb x ]O2@(0. 1-x) NaNbO3.

[0057] Figure 3 Figure 2 is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the composite phase structure of R-3m hexagonal crystal system and NaNbO3, indicating that a self-coating layer is induced at this doping concentration. Figure 4 is the SEM image of the prepared material. Example 3

[0058] Weigh appropriate amounts of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add deionized water at a molar ratio of 1:1:1 to prepare 3 L of salt solution with a total metal ion concentration of 2 mol / L. 28 N6O 41 W 12 The total amount of Ni, Fe and Mn in the solution is related to H28 N6O 41 W 12 The amount of substance ratio is 0.995:0.005.

[0059] Then, 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia water were prepared to obtain the alkaline solution and ammonia solution required for the experiment, wherein the ammonia water was used as a complexing agent for the reaction and the sodium hydroxide was used as a precipitant.

[0060] In the reactor, the above salt solution, alkali solution, ammonia solution and H 28 N6O 41 W 12 Solution. Control the feed rate to make the salt solution and H 28 N6O 41 W 12 The solution was added to the reactor to control the concentration of W ions to 0.00375 mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature was 50°C, and the stirring speed was 450 rpm / min. The hydroxide precursor [(Ni0. 33 Fe 0.33 Mn0. 33 )0. 995 W 0.005 ](OH) 2.02 , washed with deionized water several times and dried at 120 °C to obtain the precursor powder.

[0061] The precursor was mixed evenly with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+W) = 1.05, sintered in an oxygen atmosphere at 900°C for 15 h, and then cooled to room temperature to obtain the positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x W x ]O2@(0.005-x) Na2WO4.

[0062] Figure 5 This is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the R-3m structure, indicating that the doping concentration is too low to induce the formation of a self-coating layer, which cannot be identified in the XRD spectrum. Example 4

[0063] Weigh appropriate amounts of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add deionized water at a molar ratio of 1:1:1 to prepare 3 L of salt solution with a total metal ion concentration of 2 mol / L.28 N6O 41 W 12 The total amount of Ni, Fe and Mn in the solution is related to H 28 N6O 41 W 12 The amount of substance ratio is 0.99:0.01.

[0064] Then, 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia water were prepared to obtain the alkaline solution and ammonia solution required for the experiment, wherein the ammonia water was used as a complexing agent for the reaction and the sodium hydroxide was used as a precipitant.

[0065] In the reactor, the above salt solution, alkali solution, ammonia solution and H 28 N6O 41 W 12 Solution. Control the feed rate to make the salt solution and H 28 N6O 41 W 12 The solution was added completely at the same time to control the concentration of W ions in the reactor to 0.0075 mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature was 50°C, and the stirring speed was 450 rpm / min. The hydroxide precursor [(Ni0. 33 Fe 0.33 Mn0. 33 )0. 99 W 0.01 ](OH) 2.04 , washed with deionized water several times and dried at 120 °C to obtain the precursor powder.

[0066] The precursor was mixed evenly with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+W) = 1.05, sintered in an oxygen atmosphere at 900°C for 15 h, and then cooled to room temperature to obtain the positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x W x ]O2@(0.01-x) Na2WO4.

[0067] Figure 6 Figure 2 is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the composite phase structure of R-3m hexagonal crystal system and Na2WO4, indicating that a self-coating layer is induced at this doping concentration. Figure 7 TEM image of the prepared material. Example 5

[0068] Weigh appropriate amounts of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add deionized water at a molar ratio of 1:1:1 to prepare 3 L of salt solution with a total metal ion concentration of 2 mol / L. 28 N6O 41 W 12 The total amount of Ni, Fe and Mn in the solution is related to H 28 N6O 41 W 12 The amount of substance ratio is 0.95:0.05.

[0069] Then, 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia water were prepared to obtain the alkaline solution and ammonia solution required for the experiment, wherein the ammonia water was used as a complexing agent for the reaction and the sodium hydroxide was used as a precipitant.

[0070] In the reactor, the above salt solution, alkali solution, ammonia solution and H 28 N6O 41 W 12 Solution. Control the feed rate to make the salt solution and H 28 N6O 41 W 12 The solution was added to the reactor to control the concentration of W ions to 0.0375 mol / L. The pH value in the reactor was kept constant at 11, the temperature was 50°C, and the stirring speed was 450 rpm / min. The hydroxide precursor [(Ni0. 33 Fe 0.33 Mn0. 33 )0. 99 W 0.05 ](OH) 2.1 The precursor powder was obtained after washing with deionized water for several times and drying at 120°C.

[0071] The precursor was mixed evenly with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+W) = 1.05, sintered in an oxygen atmosphere at 900°C for 15 h, and then cooled to room temperature to obtain the positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x W x ]O2@(0.05-x) Na2WO4.

[0072] Figure 8The electrochemical cycle diagram of the one-step bulk doping and concentration-induced surface segregation self-coating material and the original material. It can be seen that the cycle stability of the one-step bulk doping and concentration-induced surface segregation self-coating material is significantly better than that of the original material. Example 6

[0073] Weigh a certain amount of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add them to deionized water at a molar ratio of 4:4:2 to prepare 3 L of a salt solution with a total metal ion concentration of 2 mol / L. Prepare a (NH4)2MoO4 solution in which the molar ratio of the total amount of Ni, Fe, and Mn to the molar ratio of (NH4)2MoO4 is 0.85:0.15.

[0074] Subsequently, deionized water and sodium hydroxide were mixed to prepare a 10 mol / L sodium hydroxide solution, and deionized water and ammonia water were mixed to prepare a 13.5 mol / L ammonia water to obtain the alkaline solution and ammonia solution required for the experiment, wherein sodium hydroxide was a precipitant and ammonia water was a complexing agent for the reaction.

[0075] In the reactor, under the protection of inert gas N2, the above-mentioned salt solution, alkaline solution, ammonia solution and solution containing (NH4)2MoO4 were added dropwise. The feed rate was controlled so that the salt solution and (NH4)2MoO4 solution were added completely at the same time, and the concentration of (NH4)2MoO4 in the reactor was strictly controlled to be 0.13725mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature of the circulating reflux water was 55℃, and the stirring blade speed was 500rpm / min. The hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0. 85 Mo 0.15 ](OH) 2.6 The precursor powder was obtained after washing with deionized water for several times and drying in an oven at 120°C.

[0076] The precursor was mixed with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+Mo) = 1.05, sintered at 900 ° C for 15 h in an oxygen atmosphere, and cooled to room temperature to obtain the concentration-induced bulk doping and primary particle surface self-coating positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Mo x ]O2@(0.15-x) Na2MoO4.

[0077] Figure 9This is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the composite phase structure of R-3m hexagonal crystal system and Na2MoO4, indicating that a self-coating layer is induced at this doping concentration. Example 7

[0078] Weigh a certain amount of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add them to deionized water at a molar ratio of 4:4:2 to prepare 3L of salt solution with a total metal ion concentration of 2mol / L. l2 H 18 The total amount of Ni, Fe and Mn in N6Ru solution is l2 H 18 The molar ratio of N6Ru is 0.82:0.18.

[0079] Subsequently, deionized water and sodium hydroxide were mixed to prepare a 10 mol / L sodium hydroxide solution, and deionized water and ammonia water were mixed to prepare a 13.5 mol / L ammonia water to obtain the alkaline solution and ammonia solution required for the experiment, wherein sodium hydroxide was a precipitant and ammonia water was a complexing agent for the reaction.

[0080] In the reactor, under the protection of inert gas N2, the above salt solution, alkaline solution, ammonia solution and C l2 H 18 N6Ru solution. Control the feed rate to make the salt solution and C l2 H 18 N6Ru solution was added completely at the same time, and the C l2 H 18 The concentration of N6Ru was 0.1707 mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature of the circulating reflux water was 55°C, and the stirring speed was 500 rpm / min. The hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0. 82 Ru 0.18 ](OH) 2.72 The precursor powder was obtained after washing with deionized water for several times and drying in an oven at 120°C.

[0081] The precursor was mixed with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+Ru) = 1.05, sintered at 900 ° C for 15 h in an oxygen atmosphere, and cooled to room temperature to obtain the concentration-induced bulk doping and primary particle surface self-coating positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Ru x]O2@(0.18-x) Na2RuO4.

[0082] Figure 10 Figure 2 is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the composite phase structure of R-3m hexagonal crystal system and Na2RuO4, indicating that a self-coating layer is induced at this doping concentration. Example 8

[0083] Weigh a certain amount of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O and add them to deionized water at a molar ratio of 4:4:2 to prepare 3 L of a salt solution with a total metal ion concentration of 2 mol / L. Prepare a Sb(CH3COO)3 solution, where the molar ratio of the total amount of Ni, Fe, and Mn to the molar ratio of Sb(CH3COO)3 is 0.8:0.2.

[0084] Subsequently, deionized water and sodium hydroxide were mixed to prepare a 10 mol / L sodium hydroxide solution, and deionized water and ammonia water were mixed to prepare a 13.5 mol / L ammonia water to obtain the alkaline solution and ammonia solution required for the experiment, wherein sodium hydroxide was a precipitant and ammonia water was a complexing agent for the reaction.

[0085] In the reactor, under the protection of inert gas N2, the above-mentioned salt solution, alkaline solution, ammonia solution and solution containing Sb(CH3COO)3 were added dropwise. The feed rate was controlled so that the salt solution and Sb(CH3COO)3 solution were added completely at the same time, and the concentration of Sb(CH3COO)3 in the reactor was strictly controlled to be 0.19444 mol / L. The pH value in the reactor was controlled to be constant at 11, the temperature of the circulating reflux water was 55°C, and the stirring blade speed was 500 rpm / min. The hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0.8Sb 0.2 ](OH) 2.6 The precursor powder was obtained after washing with deionized water for several times and drying in an oven at 120°C.

[0086] The precursor was mixed with sodium carbonate in a molar ratio of Na: (Ni+Fe+Mn+Sb) = 1.05, sintered at 900 ° C for 15 h in an oxygen atmosphere, and cooled to room temperature to obtain the concentration-induced bulk doping and primary particle surface self-coating positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Sb x ]O2@(0.2-x) NaSbO3.

[0087] Figure 11Figure 2 is the XRD pattern of the prepared positive electrode material. It can be seen that its crystal structure conforms to the composite phase structure of R-3m hexagonal crystal system and NaSbO3, indicating that a self-coating layer is induced at this doping concentration.

Claims

1. A method for preparing a nickel-iron-manganese layered oxide positive electrode material, characterized in that: The expression of nickel-iron-manganese layered oxide cathode material is Na[Ni x Fe y Mn z M b ]O2@(ab) Na i MO k ; Wherein, M is one or more of W, Mo, Ru, Sb, Nb or Ta; 0.1 < x, y, z, a, b < 1; Na i MO k The sodium-containing composite oxide coating layer is formed by concentration-induced segregation of the doping element M to the surface of the primary particle, i=1 or 2, k=3 or 4; the preparation method thereof comprises: Step 1: Add the first solution containing Ni, Fe, and Mn salts and the second solution containing M salts into the reactor, add alkali solution to control the pH value to 9-13, heat and reflux at 40-70 ° C and stir, and filter, wash and dry the precipitate in the reactor after the reaction to obtain the precursor Ni e Fe f Mn g M d (OH) 2+d , d>0; In the M salt, the tungsten salt is selected from W (CH3COO) 6, NaWO4, NH4WO4, [(NH4)4 6W7O 24 6H2O]; the molybdenum salt is selected from C 48 H 90 MoO 12 , MoO3, Na2MoO4, (NH4)2MoO4 at least one; ruthenium salt is selected from Ru(C2O4)2, C l2 H 18 At least one of N6Ru, (C5H5)2Ru, C6Cl4O6Ru2; antimony salt is selected from at least one of Sb(CH3COO)3, NaO3Sb, SbOCl and (SbO)2SO4, Sb(C6H5)3, Sb2(C6H5)4; niobium salt is selected from C 10 H5NbO 20 、C 10 H 25 At least one of NbO5, tantalum salt is selected from TaF5, TaCl5, TaBr5, C 10 H 25 At least one of O5Ta; Step 2: The precursor obtained in step 1 is mixed with sodium salt according to a stoichiometric ratio, calcined at 700-1000°C for 10-15 hours, and cooled naturally to room temperature to obtain the nickel-iron-manganese layered oxide positive electrode material Na[Ni x Fe y Mn z M b ]O2@(ab) Na i MO k .

2. The method according to claim 1, wherein: In step 1, the stirring speed is 500-800 r / min and the reaction time is 25-48 h.

3. The method according to claim 2, wherein: In step 1, the washing process is to repeatedly wash with deionized water and filter to remove impurities in the solution; the drying process is to dry the washed precursor at 90-120°C.

4. The method according to claim 1 or 3, characterized in that: In step 1, the nickel salt is selected from NiSO4·6H2O; the manganese salt is selected from MnSO4·H2O; and the iron salt is selected from FeSO4·7H2O.

5. The method according to claim 4, characterized in that: In step 1, n 总 (Ni, Fe, Mn): nM is (4~99):

1.

6. The method according to claim 1 or 5, characterized in that: In step 1, the alkali solution is selected from sodium hydroxide (NaOH), ammonia (NH3H2O), hexamethylenetetramine HMT (C6H 12 N4) one or more.

7. The method according to claim 6, characterized in that: The concentration of the alkali solution is 0.5-15 mol / L.

8. The method according to claim 1 or 7, characterized in that: In step 2, the sodium salt is selected from Na2CO3; the molar ratio of the precursor to the sodium salt is 1: (1-1.2).

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