Lithium-sodium composite lithium-rich manganese-based positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to a lithium-sodium composite lithium-rich manganese-based positive electrode material and a preparation method and application thereof.The lithium-sodium composite lithium-rich manganese-based positive electrode material comprises a base material and a coating layer coating at least part of the surface of the base material, the coating layer is formed by mixing sodium ferric sulfate and carbon, and the mass ratio of the sodium ferric sulfate to the carbon is (15: 1)-(35: 1). The lithium-sodium composite lithium-rich manganese-based positive electrode material has excellent cycling stability and rate capability.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a lithium-sodium composite lithium-rich manganese-based positive electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Among the positive electrode materials for lithium-ion batteries, lithium-rich manganese-based positive electrode materials have obvious capacity and cost advantages over other ternary materials due to their low nickel and cobalt content and the existence of two charge compensation mechanisms of anions and cations. However, their lithium content is 20%-50% higher than that of other ternary positive electrode materials, which increases the cost.

[0003] In order to further reduce costs, the existing technology introduces cheaper sodium ions to replace a portion of lithium ions to obtain a lithium-sodium composite lithium-rich manganese-based positive electrode material composed of a Na-containing P2 phase and a Li-containing O3 phase. However, since the ionic radius of sodium ions (0.113nm) is larger than the ionic radius of lithium ions (0.076nm), during the solid-phase sintering process, sodium ions are difficult to diffuse into the interior of the material and accumulate on the surface of the material, resulting in excessive residual alkali on the surface of the material and reduced reversible specific capacity; at the same time, the Na-containing P2 phase cannot match the operating voltage of the Li-containing O3 phase, resulting in the Na-containing P2 phase being structurally unstable at high voltages and prone to structural degradation from the surface of the material to the bulk phase, affecting the transmission of lithium ions, thereby affecting the cycle stability and rate performance of the material. Summary of the Invention

[0004] Based on this, it is necessary to provide a lithium-sodium composite lithium-rich manganese-based positive electrode material and its preparation method and application to address the above problems. The lithium-sodium composite lithium-rich manganese-based positive electrode material has both excellent cycle stability and rate performance.

[0005] A lithium-sodium composite lithium-rich manganese-based positive electrode material, comprising a base material and a coating layer coated on at least a portion of the surface of the base material, wherein the base material is a lithium-sodium composite lithium-rich manganese-based oxide, the coating layer is composed of a mixture of sodium ferric sulfate and carbon, and the mass ratio of the sodium ferric sulfate to the carbon is 15:1-35:1.

[0006] In one embodiment, the molecular formula of the sodium ferric sulfate is Na 6-2x Fe x (SO4)3, where 1.5≤x≤2.5.

[0007] In one embodiment, the mass of the coating layer is 0.5%-2% of the mass of the base material.

[0008] In one embodiment, the mass of the carbon is 0.015%-0.125% of the mass of the matrix material.

[0009] In one embodiment, the molecular general formula of the lithium-sodium composite lithium-rich manganese-based oxide is Li a Na b Ni x Co y Mn z M c O 1+a+b-e-f (SO4) e D f , where 1.1 < a < 1.5, 0.03 < b ≤ 0.15, 0.25 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.1, 0.6 ≤ z ≤ 0.75, 0 < c ≤ 0.05, x + y + z + c = 1, 0 ≤ e ≤ 0.01, 0 ≤ f ≤ 0.05, M is selected from at least one of K, Mg, Ca, Cu, Zn, Sr, Ba, Al, Y, Ce, Cr, La, Sm, Fe, Te, Sn, Zr, Ti, Nb, Sb, Ta, V, W, Mo, and D is selected from at least one of F, Cl, S. <00​​​​​​​​​​

[0014] In one embodiment, in the step of preparing the base material, at least one of the following conditions is met:

[0015] (1) In the step of mixing the manganese-rich precursor, the lithium salt, and the sodium salt, a dopant is further added, wherein the dopant is selected from a compound containing an M element, or the dopant is selected from a compound containing an M element and a compound containing an D element, wherein M is selected from at least one of K, Mg, Ca, Cu, Zn, Sr, Ba, Al, Y, Ce, Cr, La, Sm, Fe, Te, Sn, Zr, Ti, Nb, Sb, Ta, V, W, and Mo, and D is selected from at least one of F, Cl, and S;

[0016] (2) The manganese-rich precursor is selected from at least one of nickel-cobalt-manganese oxide, nickel-cobalt-manganese carbonate, nickel-cobalt-manganese hydroxide, and nickel-cobalt-manganese oxalate;

[0017] (3) The lithium salt is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium sulfate, and lithium fluoride;

[0018] (4) The sodium salt is at least one selected from sodium carbonate, sodium hydroxide, sodium sulfate, sodium oxalate, sodium acetate, sodium chloride, and sodium fluoride;

[0019] (5) The first sintering process includes: in an oxygen-containing atmosphere, increasing the temperature to 300°C-800°C at a heating rate of 1°C / min-10°C / min and holding the temperature for 0-10 hours, then increasing the temperature to 800°C-1000°C at a heating rate of 1°C / min-10°C / min and holding the temperature for 4-20 hours;

[0020] (6) The washing process includes: a washing temperature of 0°C to 25°C, a mass ratio of the washing liquid to the intermediate of 1:1 to 5:1, and a washing time of 1 min to 10 min;

[0021] (7) Drying process includes: drying temperature of 90℃-150℃, drying time of 10h-24h.

[0022] In one embodiment, in the step of mixing the base material, ferrous sulfate, ammonium sulfate salt and organic carbon source and then performing a second sintering in an inert atmosphere to form the coating layer in situ, at least one of the following conditions is met:

[0023] (1) The mass ratio of the ferrous sulfate to the matrix material is 0.15:100-1:100;

[0024] (2) the molar ratio of the ferrous sulfate to the ammonium sulfate salt is 1:1-4:1;

[0025] (3) the ammonium sulfate salt is selected from ammonium sulfate and / or ammonium bisulfate;

[0026] (4) The organic carbon source is selected from at least one of ascorbic acid, glucose, sucrose, and citric acid;

[0027] (5) The second sintering time is 6h-15h, and the heating rate is 1℃ / min-10℃ / min.

[0028] In the preparation method of the lithium-sodium composite lithium-rich manganese-based positive electrode material of the present invention, by controlling the temperature of the second sintering and the sintering atmosphere, on the one hand, ferrous ions and sulfate ions are caused to diffuse and migrate to the surface of the base material, and combine with the residual sodium on the surface of the base material to form sodium ferric sulfate in situ, thereby reducing the amount of residual alkali on the surface of the material and reducing the side reactions and gas production problems caused by excessive residual alkali; at the same time, the organic carbon source is carbonized to form carbon in situ on the surface of the base material, and is mixed with the sodium ferric sulfate to form a coating layer, and the carbon has reducing properties, which can inhibit the oxidation of iron ions and improve the performance stability of the sodium ferric sulfate; on the other hand, it can avoid the depletion of oxygen on the surface of the positive electrode material to form an inert rock salt phase due to excessively high sintering temperature, thereby preventing performance deterioration; at the same time, by controlling the mass ratio of ferrous sulfate and the organic carbon source, the mass ratio of sodium ferric sulfate and carbon in the coating layer can be effectively controlled, so that the coating layer has good electron and lithium ion conductivity, thereby obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material with both excellent cycle stability and rate performance.

[0029] A positive electrode sheet prepared using the lithium-sodium composite lithium-rich manganese-based positive electrode material.

[0030] A lithium ion battery prepared using the positive electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 X-ray diffractometer spectra of the lithium-sodium composite lithium-rich manganese-based positive electrode materials of Example 2 and Comparative Example 1 provided by the present invention;

[0033] Figure 2 A scanning electron microscope image of the lithium-sodium composite lithium-rich manganese-based positive electrode material of Example 2 provided by the present invention;

[0034] Figure 3 A scanning electron microscope image of the lithium-sodium composite lithium-rich manganese-based positive electrode material of Comparative Example 1 provided by the present invention;

[0035] Figure 4 This is the first cycle charge and discharge curve of a button-type half-cell prepared using the lithium-sodium composite lithium-rich manganese-based positive electrode material of Example 2 of the present invention at 0.2C;

[0036] Figure 5 This is the first cycle charge and discharge curve of a button-type half-cell prepared using the lithium-sodium composite lithium-rich manganese-based positive electrode material of Comparative Example 1 of the present invention at 0.2C;

[0037] Figure 6 The cyclic discharge capacity change diagrams of the corresponding button half-cells prepared using the lithium-sodium composite lithium-rich manganese-based positive electrode materials of Example 2 and Comparative Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention.

[0040] The present invention provides a lithium-sodium composite lithium-rich manganese-based positive electrode material, which includes a base material and a coating layer coated on at least a portion of the surface of the base material, wherein the base material is a lithium-sodium composite lithium-rich manganese-based oxide, and the coating layer is composed of a mixture of sodium ferric sulfate and carbon, and the mass ratio of the sodium ferric sulfate to the carbon is 15:1-35:1.

[0041] In the lithium sodium composite lithium-rich manganese-based positive electrode material of the present invention, a lithium sodium composite lithium-rich manganese-based oxide is used as a matrix material, and a coating layer is formed by mixing sodium ferric sulfate and carbon, wherein sodium ferric sulfate, as a sodium-electric positive electrode active material, not only has the ability to reversibly deintercalate sodium ions, but also has better structural stability at high voltages (such as 4.5V) compared to sodium-electric layered oxides, i.e., the P2 phase (that is, sodium phase) containing Na in the matrix material, and its operating voltage is matched with the matrix material, so that the coating layer matches the voltage window of the matrix material, which can not only improve the stability of the sodium phase on the surface of the material, but also improve the cycle stability and rate performance of the positive electrode material, and can give full play to the ability of sodium ferric sulfate to deintercalate sodium, reduce sodium from still entering the matrix material during the first discharge and grabbing sites with lithium ions, provide more active sites for lithium ions, and further improve the rate performance of the positive electrode material. In addition, the sodium source in the sodium ferric sulfate in the coating layer comes from the residual sodium on the surface of the matrix material, thereby effectively reducing the amount of residual alkali on the surface of the matrix material, which is conducive to improving the reversible specific capacity of the positive electrode material.

[0042] Although sodium ferric sulfate has the ability to reversibly deintercalate sodium ions and good structural stability, its conductivity is poor, while carbon has good conductivity. In the present invention, the conductivity of carbon is utilized to compensate for the poor conductivity of sodium ferric sulfate, thereby improving the overall conductivity of the coating layer, reducing polarization, and improving the rate performance of the positive electrode material.

[0043] At the same time, considering that when the carbon content is too high and the sodium ferric sulfate content is too low, the ion transmission efficiency on the coating layer will be affected, and when the carbon content is too low and the sodium ferric sulfate content is too high, the electron transmission efficiency on the coating layer will be affected, for this reason, in the present invention, by controlling the mass ratio of sodium ferric sulfate and carbon, the electronic conductivity and the ionic conductivity on the coating layer are in a balanced state, so that the coating layer as a whole has good electron and ion conductivity, constructs electron transmission channels and ion transmission channels, thereby improving the electronic conductivity and ionic conductivity of the positive electrode material, and effectively improving the rate performance of the positive electrode material.

[0044] Therefore, the lithium-sodium composite lithium-rich manganese-based positive electrode material of the present invention has both excellent cycle stability and rate performance.

[0045] It should be noted that the coating layer in the present invention is composed of a mixture of sodium ferric sulfate and carbon, and is not composed of a stack of sodium ferric sulfate layers and carbon layers. Moreover, compared with the coating layer composed of a stack of sodium ferric sulfate layers and carbon layers, the sodium ferric sulfate and carbon in the coating layer of the present invention complement each other, and can fully utilize the characteristics of the two themselves. Under the synergistic effect of the two, the voltage window of the coating layer is matched with that of the base material, and at the same time, it has good electron and ion conductivity, thereby improving the cycle stability and rate performance of the positive electrode material.

[0046] In the present invention, the molecular formula of sodium iron sulfate is Na 6-2x Fe x (SO4)3, where 1.5 ≤ x ≤ 2.5, preferably Na 6-2x Fe x (SO4)3, where 1.5 < x < 2.5, more preferably Na 2.4 Fe 1.8 (SO4)3. By setting it like this, the ratio of iron ions to sodium ions can be regulated within a suitable range by adjusting the value of the parameter x in the molecular formula, effectively avoiding the formation of impurity phases during the synthesis process, which is beneficial to improving the ion transport efficiency, and further improving the rate performance of the positive electrode material.

[0047] It should be noted that in the present invention, when x is 1.5, the molecular formula of sodium iron sulfate is Na3Fe 1.5 (SO4)3 or Na2Fe(SO4)2.

[0048] Optionally, the mass of the coating layer is 0.5% - 2% of the mass of the matrix material. By setting it like this, it is beneficial to protect the matrix material from being corroded by the electrolyte while not hindering the diffusion of lithium ions, enabling lithium ions to easily pass through the coating layer and enter the electrolyte, improving the ion conductivity of the positive electrode material, thereby improving the rate performance of the positive electrode material, and at the same time, the specific capacity of the positive electrode material will not decrease.

[0049] Furthermore, the mass of the carbon is 0.015% - 0.125% of the mass of the matrix material. By setting it like this, the content of sodium iron sulfate and the content of the coating layer can be regulated by controlling the carbon content, which is beneficial to enabling the coating layer to have better ion-conducting and electron-conducting abilities, further improving the rate performance and cycle stability of the positive electrode material.

[0050] In the present invention, there are many general molecular formulas of the lithium-sodium composite rich-lithium manganese-based oxide, preferably the general molecular formula of the lithium-sodium composite rich-lithium manganese-based oxide is Li a Na b Ni x Co y Mn z M c O 1+a+b-e-f (SO4) e D f, where 1.1 < a < 1.5, 0.03 < b ≤ 0.15, 0.25 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.1, 0.6 ≤ z ≤ 0.75, 0 < c ≤ 0.05, x + y + z + c = 1, 0 ≤ e ≤ 0.01, 0 ≤ f ≤ 0.05, M is selected from at least one of K, Mg, Ca, Cu, Zn, Sr, Ba, Al, Y, Ce, Cr, La, Sm, Fe, Te, Sn, Zr, Ti, Nb, Sb, Ta, V, W, Mo, and D is selected from at least one of F, Cl, S.

[0051] It can be understood that in the present invention, in the molecular general formula of the lithium-sodium composite lithium-rich manganese-based oxide, a, b, c, x, y, z, e, and f respectively represent the stoichiometric ratios of the corresponding elements in the lithium-sodium composite lithium-rich manganese-based oxide (matrix material), and the overall molecular general formula of the lithium-sodium composite lithium-rich manganese-based oxide satisfies charge balance.

[0052] According to the molecular general formula, in the present invention, by introducing sodium ions to replace part of the lithium ions, part of the O3 layered phase of the matrix material is transformed into the P2 layered phase, obtaining a matrix material with a composite composition of a Li-containing O3 phase and a Na-containing P2 phase. Compared with the traditional lithium-rich manganese-based material, it can reduce costs while improving the first Coulomb efficiency of the material; at the same time, by doping an appropriate amount of element M, it is beneficial to improve the structural stability of the matrix material and promote capacity utilization, and by doping an appropriate amount of element D, it is beneficial to promote the reversibility of anion redox and improve the first Coulomb efficiency of the cathode material.

[0053] It should be noted that in the above molecular general formula, when e = 0, it means that during the synthesis of sodium iron sulfate, no sulfate ions enter the matrix material; when 0 < e ≤ 0.01, it means that during the synthesis of sodium iron sulfate, part of the sulfate ions enter the matrix material, making the matrix material contain a small amount of polyanion (sulfate ion) doping. Such a setting can effectively reduce the over-oxidation of lattice oxygen in the matrix material, reduce the precipitation of oxygen, and is beneficial to further improving the structural stability.

[0054] At the same time, the present invention also provides a preparation method for the lithium-sodium composite lithium-rich manganese-based cathode material described above, including the following steps:

[0055] S1, mixing a manganese-rich precursor, a lithium salt, and a sodium salt and then performing a first sintering to obtain an intermediate, and then washing and drying the intermediate to obtain a matrix material. It can be understood that in step S1, by mixing a manganese-rich precursor, a lithium salt, and a sodium salt and then performing a first sintering, an appropriate amount of sodium ions are introduced to replace part of the lithium ions, promoting the intermediate to form a dual-phase composite structure with an O3 layered phase and a P2 layered phase.

[0056] In step S1, a dopant is further added, and the dopant is selected from a compound containing element M, or the dopant is selected from a compound containing element M and a compound containing element D, wherein M is selected from at least one of K, Mg, Ca, Cu, Zn, Sr, Ba, Al, Y, Ce, Cr, La, Sm, Fe, Te, Sn, Zr, Ti, Nb, Sb, Ta, V, W, and Mo, and D is selected from at least one of F, Cl, and S.

[0057] Specifically, a manganese-rich precursor, a lithium salt, a sodium salt and a dopant are mixed and then sintered for the first time to obtain an intermediate. This arrangement allows for the introduction of sodium ions to replace part of the lithium ions while achieving doping with M and D elements, thereby improving the structural stability and capacity of the matrix material and the first coulombic efficiency of the positive electrode material.

[0058] In one embodiment, the compound containing element M is selected from at least one of an oxide containing element M, a hydroxide containing element M, and a salt compound containing element M, preferably an oxide containing element M, and further preferably at least one of CaO, Al2O3, BaO, CeO2, Cr2O3, CuO, Fe2O3, K2O, La2O3, MgO, MoO3, TeO2, Nb2O5, Sb2O5, Sm2O3, Ta2O5, TiO2, V2O5, WO3, Y2O5, SnO2, ZnO, and ZrO2.

[0059] In one embodiment, the compound containing element D is at least one selected from fluoride, chloride and sulfide, preferably fluoride.

[0060] Furthermore, the fluoride is selected from at least one of NaF, LiF, KF and NH4F; the chloride is selected from at least one of NaCl, LiCl, KCl and NH4Cl; and the sulfide is selected from at least one of Li2S, Na2S and CH4N2S.

[0061] Optionally, the manganese-rich precursor is selected from at least one of nickel-cobalt-manganese oxide, nickel-cobalt-manganese carbonate, nickel-cobalt-manganese hydroxide, and nickel-cobalt-manganese oxalate, preferably nickel-cobalt-manganese hydroxide.

[0062] In one embodiment, the molar ratio of nickel, cobalt and manganese in the manganese-rich precursor is (0.25-0.4):(0-0.1):(0.6-0.75), that is, the molar ratio of manganese, cobalt and nickel in the manganese-rich precursor is the same as that in the matrix material.

[0063] It should be noted that, in the present invention, the preparation method of the manganese-rich precursor is prepared by a conventional method, such as a co-precipitation method, and therefore will not be described in detail here.

[0064] In one embodiment, the molar ratio of the lithium element in the lithium salt to the transition metal element in the manganese-rich precursor is: a / (x+y+z)=1.1-1.5; the molar ratio of the sodium element in the sodium salt to the transition metal element in the manganese-rich precursor is b / (x+y+z)=0.05-0.3; the molar ratio of the M element in the dopant to the transition metal element in the manganese-rich precursor is c / (x+y+z)=0.0001-0.05; and the molar ratio of the D element in the D source to the transition metal element in the manganese-rich precursor is f / (x+y+z)=0-0.05.

[0065] Optionally, the lithium salt is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium sulfate, and lithium fluoride.

[0066] Optionally, the sodium salt is selected from at least one of sodium carbonate, sodium hydroxide, sodium sulfate, sodium oxalate, sodium acetate, sodium chloride, and sodium fluoride.

[0067] Optionally, the first sintering process includes: in an oxygen-containing atmosphere, increasing the temperature to 300°C-800°C at a heating rate of 1°C / min-10°C / min and keeping it for 0h-10h, then increasing the temperature to 800°C-1000°C at a heating rate of 1°C / min-10°C / min and keeping it for 4h-20h.

[0068] In one embodiment, the oxygen-containing atmosphere may be an air atmosphere or an oxygen atmosphere.

[0069] In the present invention, the washing process comprises the following steps: placing a washing liquid in a stirring tank, adding an intermediate for washing under stirring, and then removing the washing liquid, wherein the washing temperature is 0°C-25°C, the mass ratio of the washing liquid to the intermediate is 1:1-5:1, and the washing time is 1 min-10 min; such an arrangement is conducive to removing impurities.

[0070] In one embodiment, the washing liquid is selected from at least one of deionized water and ethanol, preferably deionized water.

[0071] In one embodiment, the method for removing the washing liquid is selected from any one of suction filtration, centrifugation, and filter press.

[0072] Optionally, the drying process includes: a drying temperature of 90° C.-150° C., and a drying time of 10 h-24 h.

[0073] In one embodiment, the drying method is air drying and / or vacuum drying.

[0074] S2, mixing the base material, ferrous sulfate, ammonium sulfate and organic carbon source, and then performing a second sintering in an inert atmosphere to form a coating layer in situ to obtain a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the mass ratio of the ferrous sulfate to the organic carbon source is 1:1-5:1, and the second sintering temperature is 300°C-400°C.

[0075] In step S2, after mixing the base material, ferrous sulfate, ammonium sulfate and an organic carbon source, a second sintering is carried out in an inert atmosphere, and the second sintering temperature is controlled. During the sintering process, ferrous ions and sulfate ions diffuse and migrate to the surface of the material, combine with sodium ions on the surface of the base material, and form sodium ferric sulfate in situ on the surface of the base material, that is, the residual sodium on the surface of the base material is used as the sodium source, the residual alkali amount on the surface of the base material is reduced, and the side reactions and gas production problems caused by excessive residual alkali amount are reduced; at the same time, during the synthesis process of sodium ferric sulfate, the organic carbon source is carbonized to form carbon in situ on the surface of the base material, and is mixed with sodium ferric sulfate to form a coating layer. Moreover, carbon has reducing properties, which can inhibit the oxidation of iron ions and improve the performance stability of sodium ferric sulfate; at the same time, by controlling the second sintering temperature within an appropriate range, it is possible to avoid the depletion of oxygen on the surface of the positive electrode material to form an inert rock salt phase due to excessive sintering temperature.

[0076] Furthermore, by controlling the mass ratio of ferrous sulfate and the organic carbon source, the mass ratio of sodium ferric sulfate and carbon in the coating layer can be effectively controlled to 15:1-35:1, so that the coating layer has good electron and lithium ion conductivity, thereby obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material with excellent cycle stability and rate performance.

[0077] It should be noted that in step S2, during the in-situ formation of sodium ferric sulfate on the surface of the matrix material, some sulfate ions are likely to enter the interior of the matrix material during the sintering process to form polyanion doping, reducing the excessive oxidation of lattice oxygen in the matrix material and reducing oxygen precipitation, which is conducive to further improving structural stability.

[0078] Optionally, the mass ratio of the ferrous sulfate to the matrix material is 0.15:100-1:100; the molar ratio of the ferrous sulfate to the ammonium sulfate salt is 1:1-4:1; such a setting is conducive to regulating the iron-sodium ratio within a suitable range during the synthesis of sodium ferric sulfate, so that the molecular formula of sodium ferric sulfate is Na 6-2x Fe x (SO4)3, where 1.5≤x≤2.5, is beneficial to improving the rate performance of the positive electrode material.

[0079] Furthermore, the ammonium sulfate salt is selected from ammonium sulfate and / or ammonium bisulfate; and the organic carbon source is selected from at least one of ascorbic acid, glucose, sucrose, and citric acid.

[0080] In step S2, the second sintering time is 6 hours to 15 hours, and the heating rate is 1°C / min to 10°C / min. Such an arrangement is conducive to the simultaneous formation of uniformly mixed sodium ferrous sulfate and carbon, and better in-situ formation of a uniform coating layer.

[0081] In one embodiment, the inert atmosphere is selected from a nitrogen atmosphere and / or an inert gas atmosphere.

[0082] In one embodiment, after the second sintering is completed, the material is cooled and sieved to obtain a lithium-sodium composite lithium-rich manganese-based positive electrode material.

[0083] In addition, the present invention also provides a positive electrode sheet prepared using the lithium-sodium composite lithium-rich manganese-based positive electrode material.

[0084] And, a lithium ion battery prepared using the positive electrode sheet.

[0085] Hereinafter, the lithium sodium composite lithium-rich manganese-based positive electrode material and its preparation method and application will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If the specific conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are all conventional products that can be obtained commercially if the manufacturer is not specified.

[0086] Example 1

[0087] Nickel cobalt manganese hydroxide (Ni 0.33 Co 0.01 Mn 0.66(OH)2), sodium carbonate, lithium carbonate and niobium pentoxide (Nb2O5) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel cobalt manganese hydroxide is Li / (Ni+Co+Mn)=1.25, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel cobalt manganese hydroxide is Na / (Ni+Co+Mn)=0.25, and the molar ratio of niobium element in niobium pentoxide to transition metal element in nickel cobalt manganese hydroxide is Nb / (Ni+Co+Mn)=0.005; and then the mixture is placed in an atmosphere furnace. The first sintering is performed, wherein the first sintering conditions are: heating from room temperature to 500°C at a heating rate of 5°C / min, keeping warm for 5 hours, then heating from 500°C to 950°C at a heating rate of 5°C / min, keeping warm for 15 hours, and then naturally cooling to room temperature with the furnace to obtain an intermediate; the intermediate is mixed with deionized water and washed with stirring, wherein the water temperature is 10°C, the mass ratio of deionized water to the intermediate is 2:1, and the washing time is 5 minutes; then solid-liquid separation and drying are performed, wherein the drying temperature is 100°C and the drying time is 18 hours, to obtain Li 1.25 Na 0.08 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.33 base material.

[0088] The above-obtained base material, ferrous sulfate, ammonium sulfate and ascorbic acid are mixed, wherein the mass ratio of ferrous sulfate to the base material is 0.3:100, the molar ratio of ferrous sulfate to ammonium sulfate is 1.5:1, and the mass ratio of ferrous sulfate to ascorbic acid is 2:1; then the mixture is placed in a nitrogen atmosphere for a second sintering in situ to form a coating layer, wherein the second sintering conditions are: heating from room temperature to 360°C at a heating rate of 5°C / min and keeping warm for 10 hours; then naturally cooling to room temperature with the furnace, passing through a 300-mesh sieve, and obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 24:1, the mass of the coating layer is 0.5% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0089] Example 2

[0090] The only difference between Example 2 and Example 1 is that, in the step of preparing the mixture, lithium fluoride (LiF) is further contained, wherein the molar ratio of the fluorine element in the lithium fluoride to the transition metal element in the nickel cobalt manganese hydroxide is F / (Ni+Co+Mn)=0.02; the mass ratio of ferrous sulfate to the matrix material is 0.7:100; and the other conditions are the same, and the molecular formula is Li 1.25 Na 0.07 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.3 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0091] Example 3

[0092] The only difference between Example 3 and Example 2 is that the mass ratio of ferrous sulfate to matrix material is 1:100; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.0.06 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.29 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 22:1, the mass of the coating layer is 1.7% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0093] Example 4

[0094] The only difference between Example 4 and Example 2 is that the mass ratio of ferrous sulfate to matrix material is 1.5:100; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.05 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.28 F 0.02The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 2.5% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0095] Example 5

[0096] The only difference between Example 5 and Example 2 is that the mass ratio of ferrous sulfate to matrix material is 0.1:100; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.1 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.33 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 0.3% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0097] Example 6

[0098] The only difference between Example 6 and Example 2 is that the molar ratio of ferrous sulfate to ammonium sulfate is 1.1:1; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.07 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.3 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 25:1, the mass of the coating layer is 1.3% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.8 Fe 1.6 (SO4)3.

[0099] Example 7

[0100] The only difference between Example 7 and Example 2 is that the molar ratio of ferrous sulfate to ammonium sulfate is 3.3:1; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.08 (Ni0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.31 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 18:1, the mass of the coating layer is 1% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 1.4 Fe 2.3 (SO4)3.

[0101] Example 8

[0102] The only difference between Example 8 and Example 2 is that the molar ratio of ferrous sulfate to ammonium sulfate is 5:1; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.08 (Ni 0.33 Co 00.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.31 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 17:1, the mass of the coating layer is 0.9% of the mass of the base material, and the molecular formula of sodium ferric sulfate is NaFe 2.5 (SO4)3.

[0103] Example 9

[0104] The only difference between Example 9 and Example 2 is that the molar ratio of ferrous sulfate to ammonium sulfate is 1:1.5; the other conditions are the same, and the molecular formula is Li 1.25 Na 0.06 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.29 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 33:1, the mass of the coating layer is 1.7% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 3.6 Fe 1.2 (SO4)3.

[0105] Example 10

[0106] Nickel manganese hydroxide (Ni 0.34 Mn 0.66 (OH)2), sodium carbonate, lithium carbonate, tungsten trioxide (WO3) and lithium chloride (LiCl) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel manganese hydroxide is Li / (Ni+Mn)=1.24, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel manganese hydroxide is Na / (Ni+Mn)=0.24, the molar ratio of tungsten element in tungsten trioxide to transition metal element in nickel manganese hydroxide is W / (Ni+Mn)=0.01, and the molar ratio of chlorine element in lithium chloride to transition metal element in nickel manganese hydroxide is Cl / (Ni+Mn)=0.0 1; then the mixture is placed in an atmosphere furnace for a first sintering, wherein the first sintering conditions are: heating from room temperature to 500°C at a heating rate of 5°C / min, keeping warm for 5 hours, then heating from 500°C to 940°C at a heating rate of 5°C / min, keeping warm for 15 hours, and then naturally cooling to room temperature with the furnace to obtain an intermediate; the intermediate is mixed with deionized water and washed with stirring, wherein the water temperature is 10°C, the mass ratio of deionized water to the intermediate is 2:1, and the washing time is 5 minutes; then solid-liquid separation and drying are performed, wherein the drying temperature is 130°C and the drying time is 15 hours, to obtain a product with a molecular formula of Li 1.25 Na 0.09 (Ni 0.34 Mn 0.66 ) 0.99 W 0.01 O 2.29 Cl 0.01 base material.

[0107] The above-obtained matrix material, ferrous sulfate, ammonium sulfate and glucose are mixed, wherein the mass ratio of ferrous sulfate to the matrix material is 0.7:100, the molar ratio of ferrous sulfate to ammonium sulfate is 1.5:1, and the mass ratio of ferrous sulfate to glucose is 2:1; then the mixture is placed in a nitrogen atmosphere for a second sintering in situ to form a coating layer, wherein the second sintering conditions are: heating from room temperature to 350°C at a heating rate of 6°C / min and keeping warm for 10 hours; then naturally cooling to room temperature with the furnace, passing through a 300-mesh sieve, and obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the matrix material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0108] Example 11

[0109] Nickel manganese hydroxide (Ni 0.25 Mn 0.75(OH)2), sodium carbonate, lithium carbonate, molybdenum trioxide (MoO3) and lithium fluoride (LiF) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel manganese hydroxide is Li / (Ni+Mn)=1.4, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel manganese hydroxide is Na / (Ni+Mn)=0.28, the molar ratio of molybdenum element in molybdenum trioxide to transition metal element in nickel manganese hydroxide is Mo / (Ni+Mn)=0.02, and the molar ratio of fluorine element in lithium fluoride to transition metal element in nickel manganese hydroxide is F / (Ni+Mn)=0.02 ; The mixture is then placed in an atmosphere furnace for a first sintering, wherein the first sintering conditions are: heating from room temperature to 500°C at a heating rate of 5°C / min, keeping warm for 5 hours, then heating from 500°C to 960°C at a heating rate of 5°C / min, keeping warm for 15 hours, and then naturally cooling to room temperature with the furnace to obtain an intermediate; the intermediate is mixed with deionized water and washed with stirring, wherein the water temperature is 10°C, the mass ratio of deionized water to the intermediate is 2:1, and the washing time is 5 minutes; then solid-liquid separation and drying are carried out, wherein the drying temperature is 100°C and the drying time is 18 hours, to obtain Li 1.4 Na 0.12 (Ni 0.25 Mn 0.75 ) 0.98 Mo 0.02 O 2.5 F 0.02 base material.

[0110] The above-obtained matrix material, ferrous sulfate, ammonium sulfate and sucrose are mixed, wherein the mass ratio of ferrous sulfate to the matrix material is 0.7:100, the molar ratio of ferrous sulfate to ammonium sulfate is 1.5:1, and the mass ratio of ferrous sulfate to sucrose is 2:1; then the mixture is placed in a nitrogen atmosphere for a second sintering in situ to form a coating layer, wherein the second sintering conditions are: heating from room temperature to 380°C at a heating rate of 5°C / min and keeping warm for 10 hours; then naturally cooling to room temperature with the furnace, passing through a 300-mesh sieve, and obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the matrix material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0111] Example 12

[0112] Nickel manganese hydroxide (Ni 0.3 Mn 0.7(OH)2), sodium carbonate, lithium carbonate, antimony pentoxide (Sb2O5) and lithium fluoride (LiF) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel manganese hydroxide is Li / (Ni+Mn)=1.3, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel manganese hydroxide is Na / (Ni+Mn)=0.26, the molar ratio of antimony element in antimony pentoxide to transition metal element in nickel manganese hydroxide is Sb / (Ni+Mn)=0.02, and the molar ratio of fluorine element in lithium fluoride to transition metal element in nickel manganese hydroxide is F / (Ni+Mn)=0. 02; then the mixture is placed in an atmosphere furnace for the first sintering, wherein the first sintering conditions are: heating from room temperature to 500°C at a heating rate of 5°C / min, keeping warm for 5 hours, then heating from 500°C to 960°C at a heating rate of 5°C / min, keeping warm for 15 hours, and then naturally cooling to room temperature with the furnace to obtain an intermediate; the intermediate is mixed with deionized water and washed with stirring, wherein the water temperature is 10°C, the mass ratio of deionized water to the intermediate is 2:1, and the washing time is 5 minutes; then solid-liquid separation and drying are carried out, wherein the drying temperature is 100°C and the drying time is 18 hours, to obtain a product with the molecular formula Li 1.3 Na 0.1 (Ni 0.3 Mn 0.7 ) 0.98 Sb 0.02 O 2.38 F 0.02 base material.

[0113] The above-obtained matrix material, ferrous sulfate, ammonium sulfate and sucrose are mixed, wherein the mass ratio of ferrous sulfate to the matrix material is 0.7:100, the molar ratio of ferrous sulfate to ammonium sulfate is 1.5:1, and the mass ratio of ferrous sulfate to sucrose is 2:1; then the mixture is placed in a nitrogen atmosphere for a second sintering in situ to form a coating layer, wherein the second sintering conditions are: heating from room temperature to 380°C at a heating rate of 5°C / min and keeping warm for 10 hours; then naturally cooling to room temperature with the furnace, passing through a 300-mesh sieve, and obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the matrix material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0114] Example 13

[0115] Nickel manganese hydroxide (Ni 0.37 Mn 0.63(OH)2), sodium carbonate, lithium carbonate, chromium trioxide (Cr2O3) and lithium fluoride (LiF) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel manganese hydroxide is Li / (Ni+Mn)=1.18, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel manganese hydroxide is Na / (Ni+Mn)=0.22, the molar ratio of chromium element in chromium trioxide to transition metal element in nickel manganese hydroxide is Cr / (Ni+Mn)=0.05, and the molar ratio of fluorine element in lithium fluoride to transition metal element in nickel manganese hydroxide is F / (Ni+Mn)=0. 02; then the mixture is placed in an atmosphere furnace for the first sintering, wherein the first sintering conditions are: heating from room temperature to 500°C at a heating rate of 5°C / min, keeping warm for 5 hours, then heating from 500°C to 940°C at a heating rate of 5°C / min, keeping warm for 15 hours, and then naturally cooling to room temperature with the furnace to obtain an intermediate; the intermediate is mixed with deionized water and washed with stirring, wherein the water temperature is 10°C, the mass ratio of deionized water to the intermediate is 2:1, and the washing time is 5 minutes; then solid-liquid separation and drying are carried out, wherein the drying temperature is 100°C, and the drying time is 18 hours, to obtain a product with the molecular formula Li 1.18 Na 0.07 (Ni 0.37 Mn 0.63 ) 0.95 Cr 0.05 O 2.23 F 0.02 base material.

[0116] The above-obtained base material, ferrous sulfate, ammonium sulfate and sucrose are mixed, wherein the mass ratio of ferrous sulfate to the base material is 0.7:100, the molar ratio of ferrous sulfate to ammonium sulfate is 1.5:1, and the mass ratio of ferrous sulfate to sucrose is 2:1; then the mixture is placed in a nitrogen atmosphere for a second sintering in situ to form a coating layer, wherein the second sintering conditions are: heating from room temperature to 360°C at a heating rate of 5°C / min and keeping warm for 10 hours; then naturally cooling to room temperature with the furnace, passing through a 300-mesh sieve, and obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0117] Example 14

[0118] The only difference between Example 14 and Example 13 is that nickel manganese hydroxide (Ni 0.4 Mn 0.6(OH)2), sodium carbonate, lithium carbonate, zirconium dioxide (ZrO2) and lithium fluoride (LiF) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel manganese hydroxide is Li / (Ni+Mn)=1.13, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel manganese hydroxide is Na / (Ni+Mn)=0.2, the molar ratio of zirconium element in zirconium dioxide to transition metal element in nickel manganese hydroxide is Zr / (Ni+Mn)=0.005, and the molar ratio of fluorine element in lithium fluoride to transition metal element in nickel manganese hydroxide is F / (Ni+Mn)=0.02; other conditions are the same, and the molecular formula is Li 1.13 Na 0.06 (Ni 0.4 Mn 0.6 ) 0.995 Zr 0.005 O 2.17 F 0.02 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0119] Example 15

[0120] The only difference between Example 15 and Example 2 is that nickel cobalt manganese hydroxide (Ni 0.3 Co 0.1 Mn 0.6 (OH)2), sodium carbonate, lithium carbonate, niobium pentoxide (Nb2O5) and lithium fluoride (LiF) are mixed to obtain a mixture, wherein the molar ratio of lithium element in lithium carbonate to transition metal element in nickel cobalt manganese hydroxide is Li / (Ni+Co+Mn)=1.22, the molar ratio of sodium element in sodium carbonate to transition metal element in nickel cobalt manganese hydroxide is Na / (Ni+Co+Mn)=0.23, the molar ratio of niobium element in niobium pentoxide to transition metal element in nickel cobalt manganese hydroxide is Nb / (Ni+Co+Mn)=0.01, and the molar ratio of fluorine element in lithium fluoride to transition metal element in nickel cobalt manganese hydroxide is F / (Ni+Co+Mn)=0.02; other conditions are the same, and the molecular formula is obtained. 1.22 Na 0.08 (Ni 0.3 Co 0.1 Mn 0.6 ) 0.99 Nb 0.01 O 2.28 F 0.02The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0121] Example 16

[0122] The only difference between Example 16 and Example 2 is that in the step of preparing the mixture, niobium pentoxide (Nb2O5) and lithium fluoride (LiF) are not contained; the other conditions are the same, and the molecular formula is Li 1.25 Na 07 (Ni 0.33 Co 0.01 Mn 0.66 )O 2.32 The base material and the lithium sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 23:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0123] Example 17

[0124] Example 17 is different from Example 2 only in that the second sintering condition is: heating from room temperature to 400°C at a heating rate of 5°C / min and keeping warm for 15h; the other conditions are the same, and a lithium sodium composite lithium-rich manganese-based positive electrode material is obtained, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 20:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3, and the molecular formula of the matrix material in the lithium-sodium composite lithium-rich manganese-based positive electrode material is Li 1.22 Na 0.0.07( Ni 0.3 Co 0.1 Mn 0.6 ) 0.99 Nb 0.01 O 2.27 (SO4) 0.01 F 0.02 .

[0125] Detection by infrared spectrometer shows that the base material of the lithium-sodium composite lithium-rich manganese-based positive electrode material prepared in this embodiment is doped with a small amount of sulfate ions.

[0126] Comparative Example 1

[0127] The only difference between Comparative Example 1 and Example 2 is that the step of mixing the base material, ferrous sulfate, ammonium sulfate and ascorbic acid is not included, that is, the base material is directly placed in a nitrogen atmosphere for the second sintering; the other conditions are the same, and a lithium-sodium composite lithium-rich manganese-based positive electrode material is obtained.

[0128] Comparative Example 2

[0129] Comparative Example 2 is different from Example 2 only in that ascorbic acid is not contained, that is, the base material, ferrous sulfate and ammonium sulfate are mixed, wherein the mass ratio of ferrous sulfate to the base material is 0.7:100; the other conditions are the same, and a lithium sodium composite lithium-rich manganese-based positive electrode material is obtained, wherein the coating layer is a sodium ferrous sulfate layer, the mass of the coating layer is 1.05% of the mass of the base material, and the molecular formula of sodium ferrous sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0130] Comparative Example 3

[0131] Compared with Example 2, Comparative Example 3 differs only in that it does not contain ferrous sulfate and ammonium sulfate, that is, the base material and ascorbic acid are mixed, wherein the mass ratio of the base material to the ascorbic acid is 100:0.35; the other conditions are the same, and a lithium-sodium composite lithium-rich manganese-based positive electrode material is obtained, wherein the coating layer is a carbon layer, and the mass of the coating layer is 0.05% of the mass of the base material.

[0132] Comparative Example 4

[0133] Comparative Example 4 is different from Example 2 only in that the mass ratio of ferrous sulfate to ascorbic acid is 0.5:1; the other conditions are the same, and a lithium sodium composite lithium-rich manganese-based positive electrode material is obtained, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 6:1, the mass of the coating layer is 1.35% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0134] Comparative Example 5

[0135] Comparative Example 5 is different from Example 2 only in that the mass ratio of ferrous sulfate to ascorbic acid is 6:1; the other conditions are the same, and a lithium sodium composite lithium-rich manganese-based positive electrode material is obtained, wherein the coating layer is composed of a mixture of sodium ferric sulfate and carbon, the mass ratio of sodium ferric sulfate to the carbon is 70:1, the mass of the coating layer is 1.15% of the mass of the base material, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0136] Comparative Example 6

[0137] Comparative Example 6 differs from Example 2 only in that the second sintering condition is: heating from room temperature to 250°C at a rate of 5°C / min and holding for 10 hours; all other conditions remain the same, resulting in a lithium-sodium composite lithium-rich manganese-based positive electrode material. In this comparative example, sodium ferric sulfate cannot be formed because the second sintering temperature is too low.

[0138] Comparative Example 7

[0139] Comparative Example 7 differs from Example 2 only in that the second sintering condition is: heating from room temperature to 500°C at a rate of 5°C / min and holding for 10 hours; all other conditions remain the same, resulting in a lithium-sodium composite lithium-rich manganese-based positive electrode material. In Comparative Example 7, due to the excessively high sintering temperature, the formed sodium ferric sulfate decomposes, resulting in the absence of sodium ferric sulfate in the coating layer of the lithium-sodium composite lithium-rich manganese-based positive electrode material.

[0140] Comparative Example 8

[0141] Comparative Example 8 is different from Example 2 only in that the base material, ferrous sulfate, and ammonium sulfate are mixed and placed in a nitrogen atmosphere for a second sintering to obtain a composite product, wherein the second sintering condition is: heating from room temperature to 360°C at a heating rate of 5°C / min and keeping warm for 10 hours; then the composite product is mixed with ascorbic acid and placed in a nitrogen atmosphere for a third sintering, wherein the third sintering condition is: heating from room temperature to 360°C at a heating rate of 5°C / min and keeping warm for 10 hours; the other conditions are the same to obtain a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer includes a sodium ferrous sulfate layer and a carbon layer sequentially stacked on the surface of the base material, the mass ratio of the sodium ferrous sulfate layer to the carbon layer is 23:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferrous sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0142] Comparative Example 9

[0143] Comparative Example 9 is different from Example 2 only in that the base material and anti-cycloheximide are mixed and placed in a nitrogen atmosphere for a second sintering to obtain a composite product, wherein the second sintering condition is: heating from room temperature to 360°C at a heating rate of 5°C / min and keeping warm for 10 hours; then the composite product is mixed with ferrous sulfate and ammonium sulfate and placed in a nitrogen atmosphere for a third sintering, wherein the third sintering condition is: heating from room temperature to 360°C at a heating rate of 5°C / min and keeping warm for 10 hours; the other conditions are the same to obtain a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the coating layer includes a carbon layer and a sodium ferrous sulfate layer sequentially stacked on the surface of the base material, the mass ratio of the sodium ferrous sulfate layer to the carbon layer is 20:1, the mass of the coating layer is 1.2% of the mass of the base material, and the molecular formula of sodium ferrous sulfate is Na 2.4 Fe 1.8 (SO4)3.

[0144] The lithium-sodium composite lithium-rich manganese-based positive electrode materials prepared in Example 2 and Comparative Example 1 were tested using X-ray diffractometer (XRD). The test results are as follows: Figure 1 As shown, from Figure 1 It can be seen that the lithium-sodium composite lithium-rich manganese-based positive electrode materials prepared in Example 2 and Comparative Example 1 both have obvious P2 characteristic peaks and O3 lithium-rich manganese characteristic peaks, that is, they have obvious P2 layered phases and O3 layered phases, and there is no obvious difference between the two. The reason may be that the coating layer content in Example 2 is low or the coating layer is an amorphous phase.

[0145] The morphology of the lithium-sodium composite lithium-rich manganese-based positive electrode materials prepared in Example 2 and Comparative Example 1 was tested using a scanning electron microscope. The test results are as follows: Figure 2-3 As shown, from Figure 2-3 It can be seen that compared with Comparative Example 1, the surface of the lithium-sodium composite lithium-rich manganese-based positive electrode material prepared in Example 2 has obvious amorphous coating, that is, a coating layer is formed.

[0146] Surface etching technology was used to perform elemental analysis on the coating layers in the lithium-sodium composite lithium-rich manganese-based positive electrode materials of Example 2, Comparative Examples 8, and Comparative Examples 9. The analysis showed that as the etching depth increased, Example 2 showed that the trends of changes in the concentrations of Fe and C elements were basically the same, while Comparative Examples 8 and Comparative Examples 9 showed that the concentrations of Fe and C elements alternately increased or decreased. At the same time, transmission electron microscopy was used to detect and analyze the coating layers in the lithium-sodium composite lithium-rich manganese-based positive electrode materials of Example 2, Comparative Examples 8, and Comparative Examples 9. The detection and analysis showed that Comparative Examples 8 and Comparative Example 9 had double-layer coating characteristics outside the interface of the base material, while Example 2 had a single-layer coating characteristic.

[0147] The element content and surface residual alkali content of the lithium-sodium composite lithium-rich manganese-based positive electrode materials prepared in Examples 1-17 and Comparative Examples 1-9 were tested respectively. The test results are shown in Table 1. The specific test method is as follows:

[0148] (1) Element content: Na, Fe, and S were measured by inductively coupled plasma emission spectrometry; C was measured by a high-frequency infrared carbon-sulfur analyzer.

[0149] (2) Residual alkali test: obtained by potentiometric titration test using an automatic potentiometric titrator, in which the residual alkali mainly appears in the form of carbonate and hydroxide.

[0150] Table 1

[0151]

[0152] From the S and Fe contents in Table 1, it can be seen that the composition and content of the coating layer of the lithium sodium composite lithium-rich manganese-based positive electrode material prepared in the embodiment of the present invention are consistent with the content and composition matrix of the designed coating layer, indicating that the coating layer is successfully synthesized on the surface of the base material, and the coating layer is composed of a mixture of sodium ferric sulfate and carbon; specifically, the coating layer designed in Example 2 is composed of a mixture of sodium ferric sulfate and carbon, and the molecular formula of sodium ferric sulfate is Na 2.4 Fe 1.8 (SO4)3, the content of the coating layer is 1.2%. Theoretically, the theoretical contents of Fe and S elements in the coating layer in the lithium-sodium composite lithium-rich manganese-based positive electrode material are approximately 2551ppm and 2441ppm, respectively. The actual tested Fe content is 2422ppm, which is close to the theory. According to the test results of Comparative Examples 1 and 3, when the coating layer does not contain sodium ferric sulfate, the S content in the lithium-sodium composite lithium-rich manganese-based positive electrode material is approximately 1700ppm, indicating that the S content of the matrix material itself is approximately 1700ppm. The theoretical S content in the lithium-sodium composite lithium-rich manganese-based positive electrode material of Example 2 is 1700+2441=4141ppm, which is basically consistent with the actually measured 4162ppm. According to the C element content in the coating layer of Example 2 shown in Table 1, it can be inferred that the carbon conversion rate of the organic carbon source is approximately 15%, which is within the normal range. At the same time, according to the Na content in Table 1, the Na content in all embodiments and comparative examples is basically the same. This is because no new sodium source is introduced during the coating process. This also shows that there are sufficient sodium ions in the matrix material to combine with the added sulfate to form sodium ferric sulfate.

[0153] In addition, from the data of the surface residual alkali amount shown in Table 1, it can be seen that compared with Comparative Examples 1 and 3, the residual alkali in Examples 1-17 is significantly reduced because the coating layers all contain sodium ferric sulfate, indicating that a large amount of sodium ions exist in the form of residual alkali before coating, and after coating, these sodium ions participate in the formation of sodium ferric sulfate in situ, which significantly reduces the residual alkali amount; compared with Examples 1-4, it can be seen that as the content of the coating layer increases, the residual alkali amount also maintains a decreasing trend, indicating that there are sufficient sodium ions to meet the synthesis needs of sodium ferric sulfate during the coating process.

[0154] At the same time, the lithium-sodium composite lithium-rich manganese-based positive electrode materials prepared in Examples 1-17 and Comparative Examples 1-9 were used as positive electrode materials to prepare corresponding positive electrode sheets, and assembled into corresponding 2032-type button batteries, which were then subjected to electrical performance tests. The test results are shown in Table 2.

[0155] The method for assembling the 2032 button battery is as follows: the positive electrode material, the carbon black conductive agent Super-P, the polyvinylidene fluoride binder PVDF are mixed with an appropriate amount of N-methylpyrrolidone in a mass ratio of 90:5:5 to form a uniform slurry, which is then coated on aluminum foil and dried at 120°C, rolled, and punched to form a positive electrode sheet with a diameter of 13 mm. The positive electrode material loading is approximately 12 mg / cm 2 ; Then, in an argon-filled glove box, a 2032-type button battery was assembled with a lithium sheet as the negative electrode, a polypropylene microporous membrane as the separator (Celgard2400), and 1M LiPF6 / EC+DMC as the electrolyte.

[0156] Subsequently, at 25°C, the electrochemical performance of the 2032 button battery was tested using the Xinwei battery testing system, where the charge and discharge current density of 1C was 230mA / g. The specific testing methods were as follows: a. The prepared button battery was subjected to charge and discharge tests at 2.5-4.55V and 0.2C to evaluate the initial charge and discharge specific capacity and initial efficiency of the material; b. The prepared button battery was cycled 100 times at 2.5-4.55V and 1C to evaluate the cycle performance of the material; c. The prepared button battery was subjected to charge and discharge tests at 2.5-4.55V, 0.2C, 0.33C, and 1C, respectively, to evaluate the rate performance of the material.

[0157] Table 2

[0158]

[0159] As can be seen from the data in Table 2, compared with Example 1 and Example 2, in Example 2, anions are also doped on the basis of doping cations, thereby improving the rate performance and cycle stability of the positive electrode material and the battery; compared with Example 2 and Examples 4-5, it can be seen that controlling the content of the coating layer within a suitable range is beneficial to improving the rate performance and cycle stability of the positive electrode material and the battery; compared with Example 2 and Examples 8-9, it can be seen that controlling the molar ratio of ferrous sulfate to ammonium sulfate within a suitable range is beneficial to avoiding the generation of heterogeneous phases, which is beneficial to improving the rate performance and cycle stability of the positive electrode material and the battery; compared with Example 2 and Example 17, it can be seen that the matrix material is doped with polyanions (sulfate radicals), which is beneficial to improving the cycle stability of the positive electrode material and the battery.

[0160] At the same time, combined Figure 4-6 Compared with Example 2 and Comparative Example 1, it can be seen that the setting of the coating layer in the present invention can significantly improve the rate performance and cycle stability of the positive electrode material and the battery. Compared with Example 2 and Comparative Examples 2-3, it can be seen that there is a synergistic relationship between sodium ferric sulfate and carbon in the coating layer of the present invention, and under the synergistic effect of the two, the cycle stability of the positive electrode material and the battery can be significantly improved. This is because sodium ferric sulfate has poor conductivity. Although the use of a sodium ferric sulfate layer as a coating layer is beneficial to the stability of the Na-containing phase and the interface, it will lead to a serious increase in polarization. Although the use of a carbon layer as a coating layer can reduce polarization, it does not improve the stability of the interface and the bulk phase. In addition, during the carbonization process, the transition metal ions in the substrate will be reduced to form oxygen defects, thereby deteriorating the structural stability. Compared with Example 2 and Comparative Examples 4-7, it can be seen that by controlling the sintering temperature and the mass ratio of ferrous sulfate and the organic carbon source, a coating layer composed of a mixture of sodium ferric sulfate and carbon can be formed in situ on the surface of the base material, effectively controlling the mass ratio of sodium ferric sulfate and carbon in the coating layer, and obtaining a lithium-sodium composite lithium-rich manganese-based positive electrode material with excellent cycle stability and rate performance. Compared with Example 2 and Comparative Examples 8-9, it can be seen that compared with the coating layer including a stacked sodium ferric sulfate layer and a carbon layer, the coating layer in the present invention is composed of a mixture of sodium ferric sulfate and carbon, which can give full play to the characteristics and synergistic effects of sodium ferric sulfate and carbon themselves, and significantly improve the rate performance and cycle stability of the positive electrode material.

[0161] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0162] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A lithium-sodium composite lithium-rich manganese-based positive electrode material, characterized in that: The lithium-sodium composite lithium-rich manganese-based positive electrode material includes a base material and a coating layer coated on at least a portion of the surface of the base material, wherein the base material is a lithium-sodium composite lithium-rich manganese-based oxide, and the coating layer is composed of a mixture of sodium ferric sulfate and carbon, and the mass ratio of the sodium ferric sulfate to the carbon is 15:1-35:

1.

2. The lithium-sodium composite lithium-rich manganese-based positive electrode material according to claim 1, characterized in that The molecular formula of the sodium ferric sulfate is Na 6-2x Fe x (SO4)3, where 1.5≤x≤2.

5.

3. The lithium-sodium composite lithium-rich manganese-based positive electrode material according to claim 1, characterized in that The mass of the coating layer is 0.5%-2% of the mass of the base material.

4. The lithium-sodium composite lithium-rich manganese-based positive electrode material according to claim 3, characterized in that The mass of the carbon is 0.015%-0.125% of the mass of the matrix material.

5. The lithium-sodium composite lithium-rich manganese-based positive electrode material according to any one of claims 1 to 4, characterized in that The molecular general formula of the lithium-sodium composite lithium-rich manganese-based oxide is Li a Na b Ni x Co y Mn z M c O 1+a+b-e-f (SO4) e D f , where 1.1 < a < 1.5, 0.03 < b ≤ 0.15, 0.25 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.1, 0.6 ≤ z ≤ 0.75, 0 < c ≤ 0.05, x + y + z + c = 1, 0 ≤ e ≤ 0.01, 0 ≤ f ≤ 0.05, M is selected from at least one of K, Mg, Ca, Cu, Zn, Sr, Ba, Al, Y, Ce, Cr, La, Sm, Fe, Te, Sn, Zr, Ti, Nb, Sb, Ta, V, W, Mo, and D is selected from at least one of F, Cl, S.

6. A method for preparing the lithium-sodium composite lithium-rich manganese-based positive electrode material according to any one of claims 1 to 5, characterized in that: The steps include: A manganese-rich precursor, a lithium salt, and a sodium salt are mixed and first sintered to obtain an intermediate, and then the intermediate is washed and dried to obtain a base material; The matrix material, ferrous sulfate, ammonium sulfate and an organic carbon source are mixed, and then a second sintering is performed in an inert atmosphere to form a coating layer in situ to obtain a lithium-sodium composite lithium-rich manganese-based positive electrode material, wherein the mass ratio of the ferrous sulfate to the organic carbon source is 1:1-5:1, and the second sintering temperature is 300°C-400°C.

7. The method for preparing the lithium-sodium composite lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: In the step of preparing the base material, at least one of the following conditions is met: (1) In the step of mixing the manganese-rich precursor, the lithium salt, and the sodium salt, a dopant is further added, wherein the dopant is selected from a compound containing an M element, or the dopant is selected from a compound containing an M element and a compound containing an D element, wherein M is selected from at least one of K, Mg, Ca, Cu, Zn, Sr, Ba, Al, Y, Ce, Cr, La, Sm, Fe, Te, Sn, Zr, Ti, Nb, Sb, Ta, V, W, and Mo, and D is selected from at least one of F, Cl, and S; (2) The manganese-rich precursor is selected from at least one of nickel-cobalt-manganese oxide, nickel-cobalt-manganese carbonate, nickel-cobalt-manganese hydroxide, and nickel-cobalt-manganese oxalate; (3) The lithium salt is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium sulfate, and lithium fluoride; (4) The sodium salt is at least one selected from sodium carbonate, sodium hydroxide, sodium sulfate, sodium oxalate, sodium acetate, sodium chloride, and sodium fluoride; (5) The first sintering process includes: in an oxygen-containing atmosphere, increasing the temperature to 300°C-800°C at a heating rate of 1°C / min-10°C / min and holding the temperature for 0-10 hours, then increasing the temperature to 800°C-1000°C at a heating rate of 1°C / min-10°C / min and holding the temperature for 4-20 hours; (6) The washing process includes: a washing temperature of 0°C to 25°C, a mass ratio of the washing liquid to the intermediate of 1:1 to 5:1, and a washing time of 1 min to 10 min; (7) Drying process includes: drying temperature of 90℃-150℃, drying time of 10h-24h.

8. The method for preparing the lithium-sodium composite lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: In the step of mixing the base material, ferrous sulfate, ammonium sulfate salt and organic carbon source and then performing a second sintering in an inert atmosphere to form the coating layer in situ, at least one of the following conditions is met: (1) The mass ratio of the ferrous sulfate to the matrix material is 0.15:100-1:100; (2) the molar ratio of the ferrous sulfate to the ammonium sulfate salt is 1:1-4:1; (3) the ammonium sulfate salt is selected from ammonium sulfate and / or ammonium bisulfate; (4) The organic carbon source is selected from at least one of ascorbic acid, glucose, sucrose, and citric acid; (5) The second sintering time is 6h-15h, and the heating rate is 1℃ / min-10℃ / min.

9. A positive electrode sheet prepared using the lithium-sodium composite lithium-rich manganese-based positive electrode material according to any one of claims 1 to 5.

10. A lithium-ion battery prepared using the positive electrode sheet according to claim 9.

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