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

Abstract

The application relates to a nickel-iron-manganese ternary layered positive electrode material and a preparation method thereof, and the expression of the positive electrode material is Na[Ni x Fe y Mn z M b ]O2@(a‑b)Na p MO k @Na q NO k . Through a concentration-induced method, W, Mo, Ru, Si, Sb, Nb or Ta elements doped in the nickel-iron-manganese ternary layered positive electrode material are self-segregated on the surface of primary particles to form a self-coating layer of the positive electrode material, and then a coating layer is further formed on the surface of secondary particles through a traditional coating method, so that the cycle stability of the material is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of synthesis of sodium ion battery positive electrode materials, in particular to a nickel-iron-manganese ternary layered positive electrode material which is doped in a bulk phase and coated on surfaces of primary particles and secondary particles and a preparation method thereof. BACKGROUND

[0002] Compared with lithium ion batteries which are limited in resources and expensive in raw materials, sodium ion batteries are considered as one of the supplements suitable for energy storage battery systems due to their abundant resources and wide distribution. Generally, the positive electrode materials of sodium ion batteries are divided into three types of transition metal oxides, prussian blue analogues and polyanion compounds. Among them, the transition metal oxides are considered as the most potential sodium ion battery positive electrode materials in large scale due to their abundant resources, simple synthesis method and environmental friendliness. The nickel-iron-manganese ternary positive electrode material, as a typical transition metal oxide, has a high theoretical capacity and is a relatively suitable positive electrode material for industrial development. In the current large-scale synthesis of materials, the most common method is to synthesize a precursor of a target product by co-precipitation and then perform high-temperature sodium sintering to obtain positive electrode particles of micron-sized secondary particles which are formed by agglomeration of fine primary particles, and the positive electrode particles have the characteristics of simple preparation process, uniform particle size distribution, high energy density and excellent electrochemical performance.

[0003] With the migration of Na+ from the crystal structure in the process of electrochemical cycling, the nickel-iron-manganese ternary positive electrode material will undergo a series of structural evolution and severe expansion and contraction of the lattice volume, which inevitably leads to kinetic hysteresis. In addition, Na+ has a low charge density and redox potential, which leads to poor air stability and easy reaction with H2O and CO2 in the air, thereby affecting the structural stability and electrochemical performance. On the other hand, the side reaction between the electrolyte and the electrode leads to decomposition of the electrolyte, corrosion of the positive electrode material and gas production.

[0004] In view of the above problems, the modification strategies adopted by researchers mainly include ion doping, structure / composition design, surface coating, positive electrode pre-sodium and the like, which improve the performance of the nickel-iron-manganese ternary positive electrode material to a certain extent. However, the above modification strategies are still insufficient to support the application of sodium ion layered oxide positive electrode materials in sodium ion batteries. Therefore, there is an urgent need for a modified method which has a simple preparation process and excellent electrochemical performance. SUMMARY

[0005] The purpose of the present application is to provide a nickel-iron-manganese ternary layered positive electrode material and a preparation method thereof, in which a coating layer is formed on the surfaces of primary particles and secondary particles of the material, so as to improve the cycle stability of the material.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a nickel-iron-manganese ternary layered positive electrode material is provided, which has the expression Na[Nix Fe y Mn z M b ]O2@(a-b) Na p MO k @ Na q NO k , M is one of W, Mo, Ru, Si, Sb, Nb or Ta, N is one of Al, Ti, Nb or Ta, wherein 0 < a, b, x, y, z < 1, p, q = 1 or 2, k = 2, 3 or 4, Na p MO k is a coating layer formed by primary particle surface segregation, Na q NO k is a coating layer formed by secondary particle surface.

[0007] According to another aspect of the present application, there is provided a preparation method of the above-mentioned nickel-iron-manganese ternary layered positive electrode material, comprising the steps of:

[0008] Step one, simultaneously adding solution I containing Ni, Fe, Mn salts and solution II containing M salts into a reaction kettle during co-precipitation, adding lye to control pH to 8-12 and performing heating reflux and stirring, filtering, washing and drying the precipitate in the reaction kettle after the reaction is completed to obtain the precursor Ni e Fe f Mn g M h (OH)2;

[0009] Step two, mixing the precursor obtained in step one with sodium salt according to stoichiometric ratio, and calcining at 700-1000℃ for 10-15 hours to obtain the nickel-iron-manganese ternary layered positive electrode material Na[Ni x Fe y Mn z M b ]O2@(a-b) Na p MO k ;

[0010] Step three, mixing the positive electrode material obtained in step two with coating material according to stoichiometric ratio in alcohol, and calcining in oxygen atmosphere at 400-700℃ for 5-10 hours to obtain the nickel-iron-manganese ternary layered positive electrode material Na[Ni x Fe y Mn z M b ]O2@(a-b) Na p MO k @ Na qNO k .

[0011] Furthermore, in step one, the molar ratio of Ni, Fe, Mn, and M is n 总 (Ni, Fe, Mn): nM is (4~99):1.

[0012] Further, in step one, the nickel salt is selected from NiSO4·6H2O; the iron salt is selected from FeSO4·7H2O; and the manganese salt is selected from MnSO4·H2O.

[0013] Furthermore, in step one, the tungsten salt is selected from NaWO4, NH4WO4, W(CH3COO)6, H 28 N6O 41 W 12 [(NH4)46W7O] 24 At least one of [·6H2O]; the molybdenum salt is selected from MoO3, C 48 H 90 MoO 12 At least one of (NH4)2MoO4 and Na2MoO4; the ruthenium salt is selected from C l2 H 18 At least one of N6Ru, Ru(C2O4)2, C6Cl4O6Ru2, and (C5H5)2Ru; the antimony salt is selected from at least one of Na.O3Sb, SbOCl, Sb(CH3COO)3, (SbO)2SO4, Sb(C6H5)3, and Sb2(C6H5)4; the niobium salt is selected from C 10 H 25 NbO5, C 10 H5NbO 20 At least one of the following; the tantalum salt is selected from C 10 H 25 At least one of O5Ta, TaF5, TaCl5, and TaBr5.

[0014] Furthermore, in step one, the alkaline solution is selected from sodium hydroxide (NaOH), ammonia (NH3H2O), and hexamethylenetetramine (HMT) (C6H2O). 12 One or more of N4).

[0015] Furthermore, the concentration of the alkaline solution is 1-15 mol / L.

[0016] Furthermore, in step one, the reflux temperature is 40-60℃, the stirring speed is 400-700 r / min, and the reaction time is 30-50 h.

[0017] Furthermore, in step two, the molar ratio of the precursor to the sodium salt is 1:(1~1.5).

[0018] Further, in step three, the positive electrode material Na[Ni x Fe y Mn z M b ]O2@(a-b)Na p MO k After mixing with the coating material in alcohol, it is stirred and evaporated at 60℃.

[0019] The present application induces the doped W, Mo, Ru, Si, Sb, Nb or Ta elements in the nickel-iron-manganese ternary layered positive electrode material to self-segregate on the surface of primary particles by concentration induction, to form a self-coating layer for the positive electrode material, and then a coating layer is further formed on the surface of secondary particles by a traditional coating method, to improve the cycle stability of the material. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 XRD data graph of the positive electrode material prepared in Example 1 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0021] Figure 2 SEM graph of the positive electrode material prepared in Example 1 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0022] Figure 3 XRD graph of the positive electrode material prepared in Example 2 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0023] Figure 4 SEM graph of the positive electrode material prepared in Example 2 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0024] Figure 5 TEM graph of the positive electrode material prepared in Example 2 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0025] Figure 6 XRD graph of the positive electrode material prepared in Example 3 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0026] Figure 7 XRD graph of the positive electrode material prepared in Example 4 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0027] Figure 8 XRD graph of the positive electrode material prepared in Example 5 of the present application, which is doped in bulk phase and double-coated on the surface of primary particles and secondary particles.

[0028] Figure 9 Electrochemical cycling graph of the bulk doped and primary particle, secondary particle surface double-coated cathode material prepared for the embodiment 6 of the present application.

[0029] Figure 10 XRD graph of the bulk doped and primary particle, secondary particle surface double-coated cathode material prepared for the embodiment 7 of the present application.

[0030] Figure 11 XRD graph of the bulk doped and primary particle, secondary particle surface double-coated cathode material prepared for the embodiment 8 of the present application.

[0031] Figure 12 XRD graph of the bulk doped and primary particle, secondary particle surface double-coated cathode material prepared for the embodiment 9 of the present application.

[0032] Figure 13 XRD graph of the bulk doped and primary particle, secondary particle surface double-coated cathode material prepared for the embodiment 10 of the present application. DETAILED DESCRIPTION

[0033] A typical embodiment of the present application provides a nickel-iron-manganese ternary layered cathode material, which is expressed as Na[Ni x Fe y Mn z M b ]O2@(a-b) Na p MO k @ Na q NO k , M is one of W, Mo, Ru, Si, Sb, Nb or Ta, N is one of Al, Ti, Nb or Ta, wherein 0 < a, b, x, y, z < 1, p, q = 1 or 2, k = 2, 3 or 4, Na p MO k is a coating layer formed by primary particle surface segregation, Na q NO k is a coating layer formed by secondary particle surface.

[0034] In the above embodiments, by doping metal elements W, Mo, Ru, Si, Sb, Nb or Ta into the nickel-iron-manganese ternary cathode material, and because these elements have lower surface energy and larger ion radius, they can be segregated in situ on the primary particles of the cathode material by concentration-induced method to form a protective layer for the cathode material, and then a protective layer is coated on the surface of the secondary particles, so that a coating layer is formed on the surface of the primary particles and the secondary particles of the material, and the cycle stability of the material is improved.

[0035] Another typical embodiment of the present invention provides a method for preparing a nickel-iron-manganese ternary layered cathode material, comprising the following steps:

[0036] Step 1: During co-precipitation, solution I containing Ni, Fe, and Mn salts and solution II containing M salt are simultaneously added to the reaction vessel. Alkali solution is added to control the pH to 8-12, and the mixture is heated under reflux and stirred. After the reaction is complete, the precipitate in the reaction vessel is filtered, washed, and dried to obtain the precursor Ni. e Fe f Mn g M h (OH)2.

[0037] The nickel salt is selected from NiSO4·6H2O; the iron salt is selected from FeSO4·7H2O; and the manganese salt is selected from MnSO4·H2O.

[0038] Among them, M salt is one of W salt, Mo salt, Ru salt, Si salt, Sb salt, Nb salt, or Ta salt. Tungsten salt is selected from NaWO4, NH4WO4, W(CH3COO)6, [(NH4)46W7O 24 At least one of [·6H2O]; the molybdenum salt is selected from MoO3, C 48 H 90 MoO 12 At least one of (NH4)2MoO4 and Na2MoO4; ruthenium salts are selected from C l2 H 18 At least one of N6Ru, Ru(C2O4)2, C6Cl4O6Ru2, and (C5H5)2Ru; the antimony salt is selected from at least one of Na.O3Sb, SbOCl, Sb(CH3COO)3, (SbO)2SO4, Sb(C6H5)3, and Sb2(C6H5)4; the niobium salt is selected from C 10 H 25 NbO5, C 10 H5NbO 20 At least one of the following; the tantalum salt is selected from C 10 H 25 At least one of O5Ta, TaF5, TaCl5, and TaBr5.

[0039] The molar ratio of Ni, Fe, Mn, and M is n 总 (Ni, Fe, Mn): nM is (4~99):1.

[0040] The alkaline solution is selected from sodium hydroxide (NaOH), ammonia (NH3H2O), and hexamethylenetetramine (HMT) (C6H2O). 12 One or more of N4), preferably, the concentration of the alkaline solution is 1-15 mol / L.

[0041] More specifically, the temperature of the heating reflux is 40-60℃; the speed of the stirring is 400-700 r / min; and the time of the reaction is 30-50 h.

[0042] The washing process is repeated washing, suction filtration and the like to remove various impurities present in the solution, and the drying is drying the washed precursor in an oven at 90-120℃.

[0043] Step two, the precursor obtained in step one is mixed with sodium salt in stoichiometric ratio, and is calcined at 700-1000℃ for 10-15 hours to obtain the nickel-iron-manganese ternary layered cathode material Na[Ni x Fe y Mn z M b ]O2@(a-b) Na p MO k .

[0044] The sodium salt is selected from one or both of Na2CO3 or NaOH; the molar ratio of the precursor and sodium salt is 1: (1-1.5), and the sodium-mixing calcination process is calcining at 700-1000℃ for 10-15 hours in an oxygen atmosphere, and then naturally cooling to room temperature.

[0045] Step three, the cathode material obtained in step two is mixed with coating material in stoichiometric ratio in alcohol, and is calcined at 400-700℃ for 5-10 hours in an oxygen atmosphere to obtain the nickel-iron-manganese ternary layered cathode material Na[Ni x Fe y Mn z M b ]O2@(a-b) Na p MO k @ Na q NO k .

[0046] The coating material is selected from one of C 10 H 25 NbO5, C9H 21 AlO3, C 10 H 25 O5Ta, C 16 H 36 O4Ti, and the mixing process in alcohol is mixing Na[Ni x Fe y Mn z M b ]O2@(a-b) Na p MOk The calcination process is roasting at 400-700℃ for 5-10h in oxygen atmosphere, and then naturally cooling to room temperature.

[0047] Both ion doping and surface coating improve the performance of sodium ion layered oxide cathode material to some extent. However, these two modification methods are difficult to support the application of sodium ion layered oxide cathode material in sodium ion batteries. Studies have shown that certain metal elements within a certain concentration range tend to precipitate on the surface of the primary grains and spontaneously form a coating layer after being doped into the precursor of the ternary material during the sintering process, while some ions are doped into the grain interior.

[0048] According to theoretical calculations and experimental verification, metal elements W, Mo, Ru, Si, Sb, Nb or Ta, etc. after being doped into the precursor of nickel-iron-manganese ternary cathode material, due to the low surface energy and large ion radius of these elements, through the method of concentration induction, can spontaneously segregate on the surface of the primary grains of the cathode material, forming a protective layer for the cathode material, and then a protective layer is coated on the surface of the secondary particles through traditional coating method, thereby forming a cathode material with bulk doping and double-coating on the surface of primary and secondary particles. The use of multiple modification methods has a positive effect on the cycle stability, thermal stability and structural stability of the cathode material.

[0049] Example 1

[0050] An appropriate amount of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O was weighed and added to deionized water in a molar ratio of 1:1:1 to prepare a salt solution with a total metal ion concentration of 2 mol / L in 3L. A solution of C6Cl4O6Ru2 was prepared, in which the total amount of Ni, Fe, and Mn was 0.99:0.01 compared to the amount of Ru.

[0051] Subsequently, deionized water was mixed with sodium hydroxide to prepare a 10 mol / L sodium hydroxide solution, and deionized water was mixed with ammonia water to prepare a 13.5 mol / L ammonia water solution, obtaining the required lye and ammonia solution for the experiment, in which sodium hydroxide is the precipitating agent and ammonia is the complexing agent for the reaction.

[0052] In the reaction kettle, under the protection of inert gas N2, the above salt solution, base solution, ammonia solution and solution containing C6Cl4O6Ru2 were added dropwise. The feeding speed was controlled so that the salt solution and C6Cl4O6Ru2 solution were completely added at the same time, and the concentration of C6Cl4O6Ru2 in the reaction kettle was strictly controlled at 0.0075 mol / L. The pH value in the reaction kettle was controlled to be constant at 11, the temperature of the circulating reflux water was 55°C, and the stirring paddle speed was 500 rpm / min, and other conditions were controlled. 33 Fe 0.33 Mn0. 33 )0. 99 Ru 0.01 ](OH) 2.04 After washing with deionized water for several times and drying at 120°C, the precursor powder was obtained.

[0053] The precursor was mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+Ru)=1.05, and sintered in an oxygen atmosphere at a sintering temperature of 900°C for 15h, and then cooled to room temperature to obtain the concentration-induced bulk phase-doped and primary particle surface self-coated positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x Ru x ]O2@(0.01-x) Na2RuO3.

[0054] The above positive electrode material and C9H 21 AlO3 were mixed in a mass ratio of 1:0.01 in alcohol, then stirred and evaporated to dryness at 60°C, and then calcined in an oxygen atmosphere at 700°C for 10h, and then naturally cooled to room temperature to obtain the bulk phase-doped and primary particle and secondary particle surface double-coated nickel-iron-manganese ternary layered positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x Ru x ]O2@(0.01-x) Na2RuO3@0.01 NaAlO2.

[0055] Figure 1 The XRD pattern of the prepared positive electrode material shows 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-coated layer, which cannot be identified in the XRD spectrum. The coated NaAlO3 cannot be identified in the XRD spectrum due to its low concentration. Figure 2 The SEM image of the prepared material is shown in Figure 2.

[0056] Example 2

[0057] An appropriate amount of NiSO4-6H2O, MnSO4-H2O and FeSO4-7H2O were weighed and added into deionized water in a molar ratio of 1:1:1 to prepare a salt solution with a total concentration of 2 mol / L of metal ions in 3 L of deionized water. A solution of C6Cl4O6Ru2 was prepared, in which the total amount of substance of Ni, Fe and Mn was in a ratio of 0.9:0.1 to the amount of substance of Ru.

[0058] Subsequently, deionized water was mixed with sodium hydroxide to prepare a 10 mol / L sodium hydroxide solution, and deionized water was mixed with ammonia water to prepare a 13.5 mol / L ammonia water solution, thereby obtaining the required alkali solution and ammonia water solution, in which sodium hydroxide was used as a precipitant and ammonia water was used as a complexing agent for the reaction.

[0059] The above salt solution, alkali solution, ammonia water solution and solution containing C6Cl4O6Ru2 were added dropwise into a reaction kettle under the protection of inert gas N2. The feeding speed was controlled so that the salt solution and the C6Cl4O6Ru2 solution were completely added at the same time, and the concentration of C6Cl4O6Ru2 in the reaction kettle was strictly controlled at 0.075 mol / L. The pH value in the reaction kettle was controlled to be constant at 11, the temperature of the circulating reflux water was 55°C, and the stirring paddle speed was 500 rpm / min, and other conditions were controlled to synthesize the hydroxide precursor [(Ni0. 33 Fe 0.33 Mn0. 33 )0.9Ru 0. 1 ](OH) 2. 2 After being washed with deionized water several times and dried at 120°C, the precursor powder was obtained.

[0060] The precursor was mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+Ru)=1.05, and then sintered in an oxygen atmosphere at a sintering temperature of 900°C for 15 h, and then cooled to room temperature, thereby obtaining the positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x Ru x ]O2@(0.1-x) Na2RuO3.

[0061] The above positive electrode material and C9H 21 AlO3 were mixed in a mass ratio of 1:0.01 in alcohol, and then stirred and evaporated to dryness at 60°C, and then calcined in an oxygen atmosphere at 700°C for 10 h, and then naturally cooled to room temperature, thereby obtaining the nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.33 Fe 0.33 Mn0. 33 ) 1-x Ru x ]O2@(0. 1-x) Na2RuO3@0.01 NaAlO2。

[0062] Figure 3 The XRD pattern of the prepared positive electrode material shows that the crystal structure is consistent with the composite phase structure of R-3m hexagonal system and Na2RuO3, indicating that the bulk doping is induced and the primary particles are self-coated under this doping concentration. The coated NaAlO2 cannot be identified in the XRD spectrum due to its low concentration. Figure 4 The SEM image of the prepared material. Figure 5 The TEM image of the prepared material shows that the secondary particles are coated with a layer of NaAlO2.

[0063] Example 3

[0064] An appropriate amount of NiSO4·6H2O, MnSO4·H2O, and FeSO4·7H2O was weighed and added to deionized water in a molar ratio of 1:1:1 to prepare a salt solution with a total concentration of 2 mol / L of metal ions in 3 L of deionized water. A solution of C6Cl4O6Ru2 was prepared, in which the total amount of Ni, Fe, and Mn was 0.9:0.1 of the amount of Ru.

[0065] Subsequently, deionized water was mixed with sodium hydroxide to prepare a 10 mol / L sodium hydroxide solution, and deionized water was mixed with ammonia to prepare a 13.5 mol / L ammonia solution, obtaining the required lye and ammonia solution. Sodium hydroxide is the precipitating agent, and ammonia is the complexing agent for the reaction.

[0066] In the reaction kettle, the above salt solution, base solution, ammonia solution, and solution containing C6Cl4O6Ru2 were added dropwise under the protection of inert gas N2. The feeding speed was controlled to ensure that the salt solution and C6Cl4O6Ru2 solution were completely added at the same time, and the concentration of C6Cl4O6Ru2 in the reaction kettle was strictly controlled at 0.075 mol / L. The pH value in the reaction kettle was controlled at 11, the temperature of the circulating reflux water was 55°C, and the stirring paddle speed was 500 rpm / min, and other conditions were controlled to synthesize the hydroxide precursor [(Ni0. 33 Fe 0.33 Mn0. 33 )0.9Ru 0. 1 ](OH) 2. 2 After washing with deionized water several times and drying at 120°C, the precursor powder was obtained.

[0067] The precursor is mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+Ru)=1.05, and the sintering temperature is 900°C in an oxygen atmosphere, and the sintering time is 15h, and then the temperature is lowered to room temperature, so that the concentration-induced bulk phase doped and primary particle surface self-coated positive electrode material Na[(Ni0. 33 Fe 0.33 Mn0. 33 ) 1-x Ru x ]O2@(0.01-x) Na2RuO3.

[0068] The above positive electrode material and C9H 21 AlO3 are uniformly stirred in alcohol, and then the alcohol is evaporated by stirring at 60°C, and then the mixture is calcined at 700°C for 10h in an oxygen atmosphere, and then the mixture is naturally cooled to room temperature, so that the bulk phase doped and primary particle and secondary particle surface double-coated nickel-iron-manganese ternary layered positive electrode material Na[(Ni0. 0.33 Fe 0.33 Mn0. 33 ) 1-x Ru x ]O2@(0. 1-x) Na2RuO3@0. 1 NaAlO2.

[0069] Figure 6 The XRD pattern of the positive electrode material prepared by the amplification method shows that the crystal structure conforms to the composite phase structure of R-3m hexagonal system and Na2RuO3 and NaAlO2, which indicates that the secondary particle surface coating does exist, that is, the NaAlO2 coating layer.

[0070] Example 4

[0071] A certain amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O is weighed, and then added to deionized water in a molar ratio of 4:4:2 to prepare a salt solution with a total concentration of 2mol / L of metal ions in 3L. 28 N6O 41 W 12 The total amount of substance of Ni, Fe and Mn is in a ratio of 0.995:0.005 to the amount of substance of H 28 N6O 41 W 12 .

[0072] Subsequently, deionized water is mixed with sodium hydroxide to prepare a 10mol / L sodium hydroxide solution, and deionized water is mixed with ammonia water to prepare 13.5mol / L ammonia water, so as to obtain the required lye and ammonia water solution, wherein the sodium hydroxide is a precipitating agent, and the ammonia water is a complexing agent for the reaction.

[0073] In the reaction kettle, under the protection of inert gas N2, the above-mentioned salt solution, base solution, ammonia solution and H 28 N6O 41 W 12 Solution are added drop by drop. The feeding speed is controlled so that the salt solution and H 28 N6O 41 W 12 Solution are completely added at the same time, and the concentration of H 28 N6O 41 W 12 In the reaction kettle is strictly controlled at 0.00375 mol / L. The pH value in the reaction kettle is controlled to be constant at 11, the temperature of the circulating reflux water is 55℃, and the stirring paddle speed is 500 rpm / min, and other conditions. The hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0. 995 W 0.005 ](OH) 2.02 Is synthesized. After washing with deionized water several times and drying in an oven at 120℃, the precursor powder is obtained.

[0074] The precursor is mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+W)=1.05, and sintered in an oxygen atmosphere at a sintering temperature of 900℃ for 15h, and then cooled to room temperature. The concentration-induced bulk phase doped and primary particle surface self-coated positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x W x ]O2@(0.005-x) Na2WO4 is obtained.

[0075] The above-mentioned positive electrode material and C 10 H 25 NbO5 are uniformly stirred in alcohol, then evaporated to dryness at 60℃, and then calcined at 600℃ for 10h in an oxygen atmosphere, and then naturally cooled to room temperature. The nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x W x ]O2@(0.005-x) Na2WO4@ 0.01 NaNbO3 with bulk phase doping and primary particle and secondary particle surface double-coating is obtained.

[0076] Figure 7 The XRD pattern of the prepared positive electrode material is shown in the figure. The crystal structure conforms to the R-3m structure, indicating that the doping concentration is too low to induce the formation of a self-coated layer, and it cannot be identified in the XRD spectrum.

[0077] Example 5

[0078] A certain amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O were weighed and added into deionized water in a molar ratio of 4:4:2 to prepare a salt solution with a total concentration of 2 mol / L of metal ions in 3 L of deionized water. A solution of H 28 N6O 41 W 12 was prepared, wherein the total amount of substance of Ni, Fe and Mn was in a ratio of 0.99:0.01 to the amount of substance of H 28 N6O 41 W 12 .

[0079] Subsequently, deionized water was mixed with sodium hydroxide to prepare a 10 mol / L sodium hydroxide solution, and deionized water was mixed with ammonia water to prepare 13.5 mol / L ammonia water, thereby obtaining the required alkaline solution and ammonia water solution, wherein the sodium hydroxide was a precipitating agent and the ammonia water was a complexing agent for the reaction.

[0080] In a reaction kettle, the above-mentioned salt solution, alkaline solution, ammonia water solution and a solution containing H 28 N6O 41 W 12 were added dropwise under the protection of inert gas N2. The feeding speed was controlled so that the salt solution and the H 28 N6O 41 W 12 solution were completely added at the same time, and the concentration of H 28 N6O 41 W 12 in the reaction kettle was strictly controlled to be 0.0075 mol / L. The conditions were controlled to be that the pH value in the reaction kettle was constant at 11, the temperature of the circulating reflux water was 55°C, and the stirring paddle speed was 500 rpm / min, and the like, so as to synthesize the hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0. 99 W 0.01 ](OH) 2.04 . After being washed with deionized water for multiple times and dried in an oven at 120°C, the precursor powder was obtained.

[0081] The precursor was mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+W)=1.05, and then sintered in an oxygen atmosphere at a sintering temperature of 900°C for 15 h, and then cooled to room temperature, thereby obtaining the concentration-induced bulk-phase-doped and primary particle surface self-coated positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x W x ]O2@(0.01-x)Na2WO4.

[0082] The above positive electrode material and C 10 H 25 NbO5 is stirred uniformly in alcohol, then is stirred and evaporated dry at 60°C, and then is baked in an oxygen atmosphere at 700°C for 10h, and then is naturally cooled to room temperature to obtain the body-doped and primary particle and secondary particle surface double-coated nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x W x ]O2@(0.01-x) Na2WO4@0.01 NaNbO3.

[0083] Figure 8 The XRD pattern of the prepared positive electrode material shows that the crystal structure conforms to the composite phase structure of R-3m hexagonal system and Na2WO4, indicating that a self-coating layer is induced to form at this doping concentration.

[0084] Example 6

[0085] An appropriate amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O is weighed, and deionized water is added according to a molar ratio of 4:4:2 to prepare a salt solution with a total concentration of 2mol / L of metal ions in 3L. An H 28 N6O 41 W 12 solution is prepared, and the total amount of substance of Ni, Fe and Mn is in a ratio of 0.95:0.05 to the amount of substance of H 28 N6O 41 W 12 .

[0086] Then, a 10mol / L sodium hydroxide solution and a 13.5mol / L ammonia water are prepared to obtain the required lye and ammonia solution, wherein the ammonia water is used as a complexing agent for the reaction, and the sodium hydroxide is used as a precipitating agent.

[0087] In the reaction kettle, the above salt solution, alkali solution, ammonia solution and H 28 N6O 41 W 12 solution are added dropwise under inert gas protection. The feeding speed is controlled to make the salt solution and H 28 N6O 41 W 12 solution completely added to control the concentration of W ions in the reaction kettle to be 0.0375mol / L. The pH value in the reaction kettle is controlled to be constant at 11, the temperature is controlled to be 50°C, and the stirring paddle speed is controlled to be 450rpm / min, and other conditions are controlled to synthesize the hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4).99 W 0.05 ](OH) 2.1 . After washing with deionized water for several times and drying at 120℃, the precursor powder is obtained.

[0088] The precursor is mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+W)=1.05, and sintered in an oxygen atmosphere at a sintering temperature of 900℃ for 15h, and then cooled to room temperature to obtain the positive electrode material of the present application with concentration-induced bulk phase doping and one-time particle surface self-coating, Na[(Ni0.4Fe 0.2 Mn0.4) 1-x W x ]O2@(0.05-x)Na2WO4.

[0089] The above positive electrode material and C 10 H 25 NbO5 are uniformly stirred in alcohol, and then evaporated to dryness by stirring at 60℃, and then calcined in an oxygen atmosphere at 700℃ for 10h, and then naturally cooled to room temperature to obtain the nickel-iron-manganese ternary layered positive electrode material of the present application with bulk phase doping and double-coating on the surface of one-time particles and secondary particles, Na[(Ni0.4Fe 0.2 Mn0.4) 1-x W x ]O2@(0.05-x) Na2WO4@0.01 NaNbO3.

[0090] Figure 9 The electrochemical cycle diagram of the prepared self-coated material and the original material shows that the cycle stability of the self-coated material is obviously better than that of the original material.

[0091] Example 7

[0092] An appropriate amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O is weighed and added to deionized water to prepare a salt solution with a total metal ion concentration of 2mol / L in 3L, in a molar ratio of 4:4:2. A(NH4)2MoO4 solution is prepared, and the ratio of the total amount of substance of Ni, Fe and Mn to the amount of substance of(NH4)2MoO4 is 0.85:0.15.

[0093] Subsequently, a 10mol / L sodium hydroxide solution and a 13.5mol / L ammonia solution are prepared to obtain the required lye and ammonia solution, wherein the ammonia is used as a complexing agent for the reaction, and the sodium hydroxide is used as a precipitating agent.

[0094] In a reaction kettle, the above salt solution, base solution, ammonia solution and (NH4)2MoO4 solution were added dropwise under inert gas protection. The feeding speed was controlled so that the salt solution and (NH4)2MoO4 solution were completely added at the same time to control the concentration of Mo ions in the reaction kettle to be 0.13725 mol / L. The pH value in the reaction kettle was controlled to be constant at 11, the temperature was 50°C, and the stirring paddle speed was 450 rpm / min, and other conditions were controlled to synthesize the hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0. 85 Mo 0.15 ](OH) 2.6 . After washing with deionized water for several times and drying at 120°C, the precursor powder was obtained.

[0095] The precursor was mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+Mo)=1.05, and then sintered in an oxygen atmosphere at a sintering temperature of 900°C for 15h, and then cooled to room temperature to obtain the positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Mo x ]O2@(0.05-x) Na2MoO4 of the present application with concentration-induced bulk doping and one-time particle surface self-coating.

[0096] The above positive electrode material and C 10 H 25 NbO5 were uniformly stirred in alcohol, then evaporated and dried by stirring at 60°C, and then calcined in an oxygen atmosphere at 700°C for 10h, and then naturally cooled to room temperature to obtain the nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Mo x ]O2@(0.15-x) Na2MoO4@0.1 NaNbO3 of the present application with bulk doping and double-coating of one-time particles and secondary particles on the surface.

[0097] Figure 10 The XRD pattern of the prepared positive electrode material shows that its crystal structure conforms to the composite phase structure of R-3m hexagonal system and Na2MoO4 and NaNbO3, indicating that the secondary particle surface coating does exist NaNbO3 coating layer.

[0098] Example 8

[0099] An appropriate amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O is weighed, and a salt solution with a total concentration of 2 mol / L of metal ions in 3 L of deionized water is prepared according to a molar ratio of 4:4:2. A Sb(CH3COO)3 solution is prepared, and the ratio of the total amount of substance of Ni, Fe and Mn to the amount of substance of Sb(CH3COO)3 is 0.8:0.2.

[0100] Subsequently, a 10 mol / L sodium hydroxide solution and a 13.5 mol / L ammonia solution are prepared to obtain the required alkaline solution and ammonia solution, wherein the ammonia serves as a complexing agent for the reaction, and the sodium hydroxide serves as a precipitating agent.

[0101] The above salt solution, alkaline solution, ammonia solution and Sb(CH3COO)3 solution are added dropwise into the reaction kettle under inert gas protection. The feeding speed is controlled so that the salt solution and the Sb(CH3COO)3 solution are completely added at the same time to control the concentration of Sb ions in the reaction kettle to be 0.15712 mol / L. The pH value in the reaction kettle is controlled to be constant at 11, the temperature is controlled to be 50°C, and the stirring paddle speed is controlled to be 450 rpm / min, and other conditions are controlled to synthesize the hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0.8Sb 0.2 ](OH) 2.6 After being washed with deionized water for multiple times and being dried at 120°C, the precursor powder is obtained.

[0102] The precursor is mixed with sodium carbonate according to a molar ratio of Na:(Ni+Fe+Mn+Sb)=1.05, and the mixture is uniformly mixed. In an oxygen atmosphere, the sintering temperature is 900°C, the sintering time is 15 h, and the temperature is cooled to room temperature, so that the concentration-induced bulk phase-doped and primary particle surface self-coated positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Sb x ]O2@(0.2-x)Na2SbO3 is obtained.

[0103] The above positive electrode material and C 10 H 25 NbO5 are uniformly stirred in alcohol, and then the mixture is stirred and evaporated at 60°C. Then, the mixture is calcined at 700°C for 10 h in an oxygen atmosphere, and then the mixture is naturally cooled to room temperature, so that the bulk phase-doped and primary particle and secondary particle surface double-coated nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Sb x ]O2@(0.2-x) Na2SbO3@0.1NaNbO3 is obtained.

[0104] Figure 11 The XRD pattern of the prepared positive electrode material shows that the crystal structure is consistent with the composite phase structure of R-3m hexagonal system and Na2SbO3 and NaNbO3, which indicates that the NaNbO3 coating layer indeed exists on the surface of the secondary particles.

[0105] Example 9

[0106] An appropriate amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O is weighed, and deionized water is added according to a molar ratio of 4:4:2 to prepare a salt solution with a total concentration of 2 mol / L of metal ions in 3 L of deionized water. C 10 H 25 NbO5 solution, and the total amount of substance of Ni, Fe and Mn is in a ratio of 0.8:0.2 to C 10 H 25 NbO5.

[0107] Subsequently, a 10 mol / L sodium hydroxide solution and a 13.5 mol / L ammonia solution are prepared to obtain the required alkaline solution and ammonia solution, wherein the ammonia water is used as a complexing agent for the reaction, and the sodium hydroxide is used as a precipitating agent.

[0108] In the reaction kettle, the above-mentioned salt solution, alkaline solution, ammonia solution and C 10 H 25 NbO5 solution are added dropwise under inert gas protection. The feeding speed is controlled to ensure that the salt solution and C 10 H 25 NbO5 solution are completely added at the same time to control the concentration of Nb ions in the reaction kettle to be 0.15712 mol / L. The pH value in the reaction kettle is controlled to be constant at 11, the temperature is controlled to be 50°C, and the stirring paddle speed is controlled to be 450 rpm / min, and other conditions are controlled to synthesize the hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0.8Nb 0.2 ](OH) 2.6 After being washed with deionized water for multiple times and dried at 120°C, the precursor powder is obtained.

[0109] The precursor is mixed with sodium carbonate according to a molar ratio of Na:(Ni+Fe+Mn+Nb)=1.05, and then uniformly mixed. In an oxygen atmosphere, the sintering temperature is 900°C, the sintering time is 15h, and the temperature is lowered to room temperature, so that the positive electrode material with concentration-induced bulk phase doping and primary particle surface self-coating Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Nb x ]O2@(0.05-x) NaNbO3 is obtained.

[0110] The above positive electrode material and C9H 21 AlO3 is stirred uniformly in alcohol, then evaporated to dryness at 60℃ under stirring, and then baked in an oxygen atmosphere at 700℃ for 10h, and then naturally cooled to room temperature to obtain the body-doped and primary particle and secondary particle surface double-coated nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Nb x ]O2@(0.2-x) NaNbO3@0.1 NaAlO2.

[0111] Figure 12 The XRD pattern of the prepared positive electrode material shows that the crystal structure conforms to the composite phase structure of R-3m hexagonal system and NaNbO3 and NaAlO2, indicating that the secondary particle surface coating does exist.

[0112] Example 10

[0113] An appropriate amount of NiSO4·6H2O, MnSO4·H2O and FeSO4·7H2O is weighed, and deionized water is added according to a molar ratio of 4:4:2 to prepare a salt solution with a total concentration of 2 mol / L of metal ions in 3L. C 10 H 25 O5Ta solution, and the total amount of substance of Ni, Fe and Mn is in a ratio of 0.8:0.2 to the amount of substance of C 10 H 25 O5Ta.

[0114] Subsequently, a 10 mol / L sodium hydroxide solution and a 13.5 mol / L ammonia solution are prepared to obtain the required lye and ammonia solution, wherein the ammonia is used as a complexing agent for the reaction, and the sodium hydroxide is used as a precipitating agent.

[0115] In the reaction kettle, the above salt solution, lye solution, ammonia solution and C 10 H 25 O5Ta solution are added dropwise under inert gas protection. The feeding speed is controlled to make the salt solution and C 10 H 25 O5Ta solution completely added at the same time, so that the concentration of Ta ions in the reaction kettle is 0.15712 mol / L. The pH value in the reaction kettle is controlled to be constant at 11, the temperature is controlled to be 50℃, and the stirring paddle speed is controlled to be 450 rpm / min, and other conditions are controlled to synthesize the hydroxide precursor [(Ni0.4Fe 0.2 Mn0.4)0.8Ta 0.2 ](OH) 2.1 . After being washed with deionized water for multiple times and dried at 120℃, the precursor powder is obtained.

[0116] The precursor is mixed with sodium carbonate in a molar ratio of Na:(Ni+Fe+Mn+Ta)=1.05, and then sintered in an oxygen atmosphere at a sintering temperature of 900°C for 15h, and then cooled to room temperature to obtain the concentration-induced bulk phase doped and primary particle surface self-coated positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Ta x ]O2@(0.2-x)NaTaO3.

[0117] The above positive electrode material and C9H 21 AlO3 are uniformly stirred in alcohol, and then evaporated to dryness by stirring at 60°C, and then calcined in an oxygen atmosphere at 700°C for 10h, and then naturally cooled to room temperature to obtain the bulk phase doped and primary particle and secondary particle surface double-coated nickel-iron-manganese ternary layered positive electrode material Na[(Ni0.4Fe 0.2 Mn0.4) 1-x Ta x ]O2@(0.2-x) NaTaO3@0.1 NaAlO2.

[0118] Figure 13 The XRD pattern of the prepared positive electrode material shows that the crystal structure conforms to the composite phase structure of R-3m hexagonal system and NaTaO3 and NaAlO2, indicating that the secondary particle surface coating does exist NaAlO2 coating layer.

Claims

1. A method for preparing a nickel-iron-manganese ternary layered cathode material, the formula of which is Na[Ni x Fe y Mn z M b ]O2@(ab)Na p MO k @ Na q NO k M is one of W, Mo, Ru, Si, Sb, Nb, or Ta, and N is one of Al, Ti, Nb, or Ta. 0< a, b, x, y, z < 1, p, q=1 or 2, k=2, 3 or 4, Na p MO k This is a sodium-containing composite oxide coating layer formed by concentration-induced segregation of dopant element M to the surface of primary particles; Na q NO k The coating layer formed on the surface of secondary particles; its preparation method includes the following steps: Step 1: During co-precipitation, solution I containing Ni, Fe, and Mn salts and solution II containing M salt are simultaneously added to the reaction vessel. Alkali solution is added to control the pH to 8-12, and the mixture is heated under reflux and stirred. After the reaction is complete, the precipitate in the reaction vessel is filtered, washed, and dried to obtain the precursor Ni. e Fe f Mn g M h (OH)2; Step two: The precursor obtained in step one is mixed with sodium salt in a stoichiometric ratio and calcined at 700-1000℃ for 10-15 hours to obtain a bulk-doped and primary particle-surface-coated nickel-iron-manganese ternary layered cathode material Na[Ni x Fe y Mn z M b O2@(ab) NapMO k ; Step 3: The cathode material obtained in Step 2 is mixed with coating material in alcohol according to stoichiometric ratio. The mixture is then calcined in an oxygen atmosphere at 400-700℃ for 5-10 hours to obtain a bulk-doped nickel-iron-manganese ternary layered cathode material, Na[Ni], with double coating on the surfaces of primary and secondary particles. x Fe y Mn z M b ]O2@(ab) Na p MO k @ Na q NO k ; In the M salt, the tungsten salt is selected from NaWO4, NH4WO4, W(CH3COO)6, H 28 N6O 41 W 12 [(NH4)4 6W7O 24 At least one of [·6H2O]; the molybdenum salt is selected from MoO3, C 48 H 90 MoO 12 At least one of (NH4)2MoO4 and Na2MoO4; ruthenium salts are selected from C l2 H 18 At least one of N6Ru, Ru(C2O4)2, C6Cl4O6Ru2, and (C5H5)2Ru; antimony salts are selected from at least one of Na2O3Sb, SbOCl, Sb(CH3COO)3, (SbO)2SO4, Sb(C6H5)3, and Sb2(C6H5)4; niobium salts are selected from C 10 H 25 NbO5, C 10 H5NbO 20 At least one of the following; tantalum salts are selected from C 10 H 25 At least one of O5Ta, TaF5, TaCl5, and TaBr5.

2. The method according to claim 1, characterized in that: In step one, the molar ratio of Ni, Fe, Mn, and M is n 总 (Ni, Fe, Mn): nM is (4~99):

1.

3. The method according to claim 1 or 2, characterized in that: In step one, the nickel salt is selected from NiSO4·6H2O; the iron salt is selected from FeSO4·7H2O; and the manganese salt is selected from MnSO4·H2O.

4. The method according to claim 3, characterized in that: In step one, the alkaline solution is selected from sodium hydroxide (NaOH), ammonia (NH3H2O), and hexamethylenetetramine (HMT) (C6H2O). 12 One or more of N4).

5. The method according to claim 4, characterized in that: The concentration of the alkaline solution is 1-15 mol / L.

6. The method according to claim 1 or 5, characterized in that: In step one, the reflux temperature is 40-60℃, the stirring speed is 400-700 r / min, and the reaction time is 30-50 h.

7. The method according to claim 6, characterized in that: In step two, the molar ratio of the precursor to the sodium salt is 1:(1~1.5).

8. The method according to claim 1 or 7, characterized in that: In step three, the positive electrode material Na[Ni] obtained in step two is... x Fe y Mn z M b ]O2@(ab)Na p MO k After mixing with the coating material in alcohol, the mixture is stirred and evaporated to dryness at 60°C.

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