Lithium nickel manganese oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium nickel manganese oxide positive electrode material and a preparation method and application thereof. The lithium nickel manganese oxide positive electrode material comprises a lithium-deficient lithium nickel manganese oxide inner core and a lithium-rich lithium nickel manganese oxide shell layer located on the surface of the lithium-deficient lithium nickel manganese oxide inner core; the lithium-deficient lithium nickel manganese oxide inner core contains doped metal elements; and the phase proportion of the Fd-3m space group structure of the lithium nickel manganese oxide positive electrode material is 4.0-10.0%. According to the lithium nickel manganese oxide positive electrode material with the core-shell structure provided by the invention, the lithium element content in the shell layer is higher than that in the core material, and the phase proportion of the Fd-3m space group structure is 4.0-10.0%, so that the lithium nickel manganese oxide positive electrode material has lower transition metal oxide impurity phase content and higher stability; and lithium ions can be rapidly deintercalated in the charge-discharge cycle process, so that the discharge capacity, rate capability and cycle stability of the lithium nickel manganese oxide positive electrode material are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a lithium nickel manganese oxide positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used and developed in many fields due to their advantages such as high discharge voltage, high energy density, low self-discharge, long cycle life and low environmental pollution. Among them, the positive electrode material is the decisive factor in the electrochemical performance of lithium-ion batteries. It plays a leading role in the capacity, energy density and cycle performance of the battery. At present, LiCoO2, LiMn2O4, LiFePO4 and nickel-cobalt-manganese ternary materials (LiNi x Co y Mn z There are many types of positive electrode materials for lithium-ion batteries, represented by various materials such as 2,4-dioxide (2,4-dioxide), etc. However, due to certain defects in energy density, stable performance, and safety in commercial batteries, the rapid development of energy storage devices, electric vehicles, electronic products and other industries has gradually been restricted. There is an urgent need for a high-energy-density, safe, low-cost, and non-toxic positive electrode material. According to the working principle of lithium-ion batteries, the specification capacity and operating voltage of the positive electrode material directly affect the energy density of the lithium-ion battery. Therefore, introducing a positive electrode material with high specification capacity or high operating voltage to improve the energy density of lithium-ion batteries is an effective way to overcome this limitation.

[0003] In the above background, spinel LiNi 0.5 Mn 1.5 O4(LNMO) has abundant raw materials, reasonable cost and is suitable for commercial preparation. It also has an ultra-high discharge platform of 4.7V and an energy density of up to 650Wh·kg. -1 , respectively LiMn2O4(400Wh·kg -1 ) and LiFePO4 (495Wh·kg -1 ) are 1.63 times and 1.31 times higher than those of lithium-ion batteries. Therefore, high-voltage LNMO with a spinel structure is considered to be one of the most promising high-energy-density cathode candidate materials for the next generation of lithium-ion batteries. Despite these advantages, the high lithium-ion deintercalation potential of the lithium nickel manganese oxide cathode material during cyclic operation under high-voltage conditions makes it very easy for it to undergo serious side reactions with the electrolyte, resulting in electrolyte decomposition, Jahn-Teller effect causing structural damage, and Mn 3+ Transition metal dissolution and Li x Ni 1-x Problems such as the formation of O impurity phases cause its structural and chemical instability, resulting in a sharp decline in capacity, rate and cycle performance, which are the most critical issues in the application of LNMO.

[0004] Therefore, how to improve the capacity, rate performance and cycle stability of lithium nickel manganese oxide positive electrode materials is an urgent problem to be studied and solved in this field. Summary of the Invention

[0005] The purpose of the present invention is to address the problem that the capacity, rate and cycle performance of the lithium nickel manganese oxide materials prepared by the existing technology are significantly reduced due to structural and chemical instability, and to provide a lithium nickel manganese oxide positive electrode material with excellent capacity performance, rate performance and cycle stability, which can well meet the industry's expectations for high energy density and stable performance lithium batteries.

[0006] In a first aspect, the present invention provides a lithium nickel manganese oxide positive electrode material. The lithium nickel manganese oxide positive electrode material comprises a lithium-deficient lithium nickel manganese oxide core and a lithium-rich lithium nickel manganese oxide shell located on the surface of the lithium-deficient lithium nickel manganese oxide core; the lithium-deficient lithium nickel manganese oxide core contains a doped metal element, and the doped metal element is selected from at least one transition metal element other than lithium, nickel, and manganese; the ratio of the molar content of lithium to the molar content of nickel and manganese in the lithium-rich lithium nickel manganese oxide shell is greater than the ratio of the molar content of lithium to the molar content of nickel and manganese in the lithium-deficient lithium nickel manganese oxide core; and the lithium nickel manganese oxide positive electrode material has an Fd-3m space group structure phase ratio of 4.0 to 10.0%.

[0007] In a preferred embodiment, the molar ratio of the sum of the lithium content in the lithium-rich lithium nickel manganese oxide shell and the lithium content in the lithium-deficient lithium nickel manganese oxide core to the nickel and manganese content in the lithium nickel manganese oxide positive electrode material is 0.5:1.

[0008] In a preferred embodiment, the molar ratio of the lithium content in the lithium-deficient lithium nickel manganese oxide core, the lithium content in the lithium-rich lithium nickel manganese oxide shell, and the nickel and manganese content in the lithium nickel manganese oxide positive electrode material is m:n:1, wherein m+n=0.5, 0.4≦m<0.5, 0 <n≦0.1。

[0009] In a preferred embodiment, the lithium nickel manganese oxide positive electrode material comprises a chemical formula of Li y [Li 1- y Ni 0.5-x / 2 M x Mn 1.5-x / 2 O4] compound, wherein y represents the molar content of lithium in the lithium-rich lithium nickel manganese oxide shell, M is a doping metal element, <y≦0.1,0<x≦0.2。

[0010] In a preferred embodiment, the content of the doped metal element M in the lithium nickel manganese oxide positive electrode material is 0.1-1.0 wt %.

[0011] In a preferred embodiment, the doping metal element is selected from at least one of tungsten, yttrium, niobium, strontium, titanium, molybdenum, aluminum, magnesium, zinc, and zirconium.

[0012] In a preferred embodiment, the thickness of the lithium-rich lithium nickel manganese oxide shell is H and 0 <H≦100nm。

[0013] In a second aspect, the present invention provides a method for preparing a lithium nickel manganese oxide positive electrode material. The preparation method comprises the following steps: S1. mixing a nickel manganese compound precursor, a first lithium source, and an additive, and sintering the resulting first mixture to obtain a lithium-deficient lithium nickel manganese oxide core material; S2. mixing the resulting lithium-deficient lithium nickel manganese oxide core material and a second lithium source for a second time, and sintering the resulting second mixture for a second time, so that lithium is doped onto the surface of the lithium-deficient lithium nickel manganese oxide core and forms a lithium-rich lithium nickel manganese oxide shell, thereby obtaining a lithium nickel manganese oxide positive electrode material; the additive contains at least one transition metal element other than lithium, nickel, and manganese; and the lithium nickel manganese oxide positive electrode material has an Fd-3m space group structure phase ratio of 4.0 to 10.0%.

[0014] In a preferred embodiment, the molar ratio of the sum of the lithium content in the first lithium source and the second lithium source to the sum of the nickel and manganese content in the nickel-manganese compound precursor is 0.5:1;

[0015] In a preferred embodiment, in step S1, the molar ratio of the sum of the lithium content in the first lithium source and the nickel and manganese content in the nickel-manganese compound precursor is mˋ:1, wherein 0.4≦mˋ<0.5.

[0016] In a preferred embodiment, in step S1, the amount of the additive is 0.1-1.0 wt% of the mass of the nickel-manganese compound precursor.

[0017] In a preferred embodiment, in step S2, the molar ratio of the sum of the lithium content in the second lithium source and the nickel and manganese content in the nickel and manganese compound precursor is n:1, wherein 0 <nˋ≦0.1。

[0018] In a preferred embodiment, the nickel-manganese compound precursor is obtained by co-precipitation reaction of a nickel source and a manganese source under the action of a precipitant.

[0019] In a preferred embodiment, the first lithium source and the second lithium source are each independently selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium bromide, lithium fluoride, lithium iodide, and lithium sulfate.

[0020] In a preferred embodiment, the additive contains at least one of tungsten, yttrium, niobium, strontium, titanium, molybdenum, aluminum, magnesium, zinc, and zirconium.

[0021] In a preferred embodiment, the additive is selected from at least one of tungsten oxide, yttrium oxide, niobium oxide, strontium oxide, titanium oxide, molybdenum oxide, aluminum oxide, magnesium oxide, zinc oxide, and zirconium oxide.

[0022] In a preferred embodiment, in step S1, the primary mixing process is a first ball milling mixing process and / or a first high-speed mixing process.

[0023] In a preferred embodiment, in step S1, the rotation speed of the first ball milling mixing treatment is 100 to 500 rpm, and the time is 1 to 8 hours.

[0024] In a preferred embodiment, in step S1, the first high-speed mixing process includes at least a first mixing process section and a second mixing process section performed sequentially, and the rotation speed of the first mixing process section is lower than the rotation speed of the second mixing process section.

[0025] In a preferred embodiment, in step S1, the primary sintering process includes being performed at a first platform temperature and a second platform temperature.

[0026] In a preferred embodiment, in step S1, the temperature of the first platform is 700-850° C., and the holding time is 2-10 hours.

[0027] In a preferred embodiment, in step S1, the temperature of the second platform is 850-1000° C., and the holding time is 10-18 hours.

[0028] In a preferred embodiment, in step S2, the secondary mixing process is a second ball milling mixing process and / or a second high-speed mixing process.

[0029] In a preferred embodiment, in step S2, the rotation speed of the second ball milling mixing treatment is 100 to 400 rpm, and the time is 1 to 6 hours.

[0030] In a preferred embodiment, in step S2, the second high-speed mixing process includes at least a third mixing process section and a fourth mixing process section performed sequentially, and the rotation speed of the first mixing process section is lower than the rotation speed of the second mixing process section.

[0031] In a preferred embodiment, in step S2, the temperature of the secondary sintering treatment is 400-700°C, and the holding time is 2-10 hours.

[0032] In a third aspect, the present invention provides a lithium nickel manganese oxide positive electrode material prepared by the above method.

[0033] In a fourth aspect, the present invention also provides the use of the above-mentioned lithium nickel manganese oxide positive electrode material in lithium ion batteries.

[0034] Beneficial effect: The present invention provides a lithium nickel manganese oxide positive electrode material with a core-shell structure, wherein the molar ratio of lithium element to nickel manganese element in the shell layer is higher than the molar ratio of lithium element to nickel manganese element in the core material, that is, a lithium-rich shell layer and a lithium-deficient core layer are formed, and the core layer contains doped metal elements and the Fd-3m space group structure phase ratio is 4.0-10.0%. At this time, the lithium nickel manganese oxide positive electrode material has a lower transition metal oxide impurity content and higher stability. On the one hand, it is beneficial to reduce the surface energy of the positive electrode material under high voltage system and the core-shell structure plays the role of isolating the electrolyte, thereby maintaining the interface stability of the positive electrode material and reducing the dissolution of transition metals during battery charging and discharging, thereby improving the cycle performance. On the other hand, the positive electrode material structure has a higher Li + The diffusion coefficient and low impedance enable the lithium ions in the core-shell structure to be rapidly deintercalated during the charge-discharge cycle while preventing the collapse of the crystal structure, thereby improving the discharge capacity, rate performance, and cycle stability of the lithium nickel manganese oxide positive electrode material. Furthermore, the preparation method of the lithium nickel manganese oxide positive electrode material provided by the present invention has the advantages of simple process, few steps, high product purity, low production cost, excellent electrochemical properties of the prepared material, and suitability for large-scale production, thus having good promotion and application value. DETAILED DESCRIPTION

[0035] The lithium nickel manganese oxide positive electrode material provided by the present invention includes a lithium-deficient lithium nickel manganese oxide core and a lithium-rich lithium nickel manganese oxide shell located on the surface of the lithium-deficient lithium nickel manganese oxide core. The lithium nickel manganese oxide positive electrode material has an Fd-3m space group structure phase ratio of 4.0% to 10.0%, such as 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.0%, or any value therebetween, and more preferably 4.0% to 8.0%, such as 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, or any value therebetween.

[0036] In the present invention, the Fd-3m space group structural phase ratio of the lithium nickel manganese oxide positive electrode material can be obtained by the following methods: Method 1, based on the original XRD spectrum measured by the lithium nickel manganese oxide positive electrode material, the original XRD spectrum is refined by the Rietveld full spectrum fitting method to obtain the ratio; Method 2, the obtained lithium nickel manganese oxide positive electrode material is prepared into a button battery, and after charge and discharge tests are carried out under normal temperature battery laboratory conditions, the ratio is calculated based on the obtained charge and discharge data.

[0037] Furthermore, the specific steps of the Rietveld full spectrum fitting method include: using TOPAS software, importing an initial crystal structure model containing the main phase P4332 and the impurity phase Fd-3m space group, and correcting it through the least squares method combined with structural parameters, peak shape functions, background functions, etc., point-by-point fitting calculation of the polycrystalline diffraction spectrum, and continuously optimizing the structural model so that the calculated values and the measured values are gradually close, thereby obtaining unit cell parameters, phase composition, etc.

[0038] Furthermore, the specific steps of the method 2 include: (1) preparing a button battery with the obtained lithium nickel manganese oxide positive electrode material, charging the button battery at a constant current of 0.1C to a voltage of 4.9V under normal temperature battery laboratory conditions, and then charging at a constant voltage of 4.9V to a current of 0.05C. After standing for 5 minutes, the button battery is discharged at a constant current of 0.1C to a voltage of 3.5V, and obtaining its discharge capacity (Q1) and total discharge capacity (Q) in the voltage range of 4.5-3.5V and 4.9-3.5V from the original charge and discharge data curve obtained after the charge and discharge test of the button battery, and calculating its capacity proportion x=Q1 / Q of the 4V platform; (2) calculating the Mn content in the lithium nickel manganese oxide positive electrode material 3+ The formula is y≈0.45x / 1.5, where 0.45 is the mass content of Mn in the lithium nickel manganese oxide material and 1.5 is the stoichiometric ratio of Mn to Li in the lithium nickel manganese oxide material; (3) The content of the Fd-3m space group z (the content of the transition metal nickel manganese composite oxide) in the lithium nickel manganese oxide spinel material is calculated as z≈x / 0.375, where the coefficient 0.375 is assumed to be in a completely disordered state, and theoretically 3 / 4 of Ni will be Ni 3+ , which corresponds to the charge and discharge curve is Ni 3+ / Ni 2+ 3 / 4 of the platform becomes a 4V platform, and Ni 3+ / Ni 2+ The platform capacity accounts for half of the total capacity, so 1 / 2×3 / 4=0.375.

[0039] In the present invention, the lithium-deficient nickel manganese lithium oxide core contains a doped metal element, and the doped metal element is selected from at least one of transition metal elements other than lithium, nickel, and manganese, preferably selected from at least one of tungsten, yttrium, niobium, strontium, titanium, molybdenum, aluminum, magnesium, zinc, and zirconium, and more preferably at least one of tungsten, yttrium, aluminum, zinc, and zirconium. When the lithium-deficient nickel manganese lithium oxide core contains at least one of tungsten, yttrium, aluminum, zinc, and zirconium, it is more conducive to improving the stability of the spinel structure of nickel manganese lithium oxide and reducing the generation of impurity phases, suppressing interfacial side reactions and the decomposition of the electrolyte at high voltages, thereby improving the capacity, cycle performance, and rate performance of the positive electrode material. The reason is that by doping at least one of tungsten, yttrium, aluminum, zinc, and zirconium elements, effective lattice regulation of the spinel system structure and improvement of the inherent defect engineering of the material can be carried out, optimizing its electronic structure and interface, suppressing system phase change and manganese dissolution, thereby improving the comprehensive performance of the positive electrode material.

[0040] In the present invention, the molar ratio of the lithium element content in the lithium-rich nickel manganese lithium oxide shell to the molar content of nickel and manganese elements is greater than the molar ratio of the lithium element content in the lithium-deficient nickel manganese lithium oxide core to the molar content of nickel and manganese elements. At this time, it is beneficial to improve the Li + diffusion coefficient and reduce the impedance of the positive electrode material, thereby improving the discharge capacity, rate performance, and cycle stability performance of the lithium battery containing the positive electrode material.

[0041] In the present invention, the molar ratio of the lithium element content in the lithium-deficient nickel manganese lithium oxide core, the lithium element content in the lithium-rich nickel manganese lithium oxide shell, and the nickel and manganese element content in the nickel manganese lithium oxide positive electrode material is m:n:1. Preferably, m + n = 0.5, that is, the molar ratio of the sum of the lithium element content in the lithium-deficient nickel manganese lithium oxide core and the lithium-rich nickel manganese lithium oxide shell to the nickel and manganese element content in the nickel manganese lithium oxide positive electrode material is 0.5:1. Preferably, 0.4 ≤ m < 0.5, that is, m can be 0.4, 0.41, 0.42, 0.45, 4.48, 0.49, 0.495, or any value between them. Preferably, 0 < n ≤ 0.1, that is, n can be 0.005, 0.01, 0.02, 0.05, 0.08, 0.09, 0.1, or any value between them.

[0042] In the present invention, the nickel manganese lithium oxide positive electrode material preferably includes a chemical general formula of Li y [Li 1-y Ni 0.5-x / 2M x Mn 1.5-x / 2A compound of [O4], where y represents the molar content of lithium element in the lithium-rich nickel manganese lithium oxide shell layer, M is a doped metal element, 0 < y ≤ 0.1, that is, y can be 0.005, 0.01, 0.02, 0.05, 0.08, 0.09, 0.1 or any value between them, 0 < x ≤ 0.2, that is, x can be 0.005, 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2 or any value between them.

[0043] In the present invention, the content of the doped metal element M in the nickel manganese lithium oxide cathode material is preferably 0.1 - 1.0 wt%, such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt% or any value between them.

[0044] In the present invention, the thickness of the lithium-rich nickel manganese lithium oxide shell layer is H and 0 < H ≤ 100 nm, such as 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm or any value between them.

[0045] The preparation method of the nickel manganese lithium oxide cathode material provided by the present invention includes the following steps: S1. The nickel manganese compound precursor, the first lithium source, and the additive are subjected to a primary mixing treatment. After the obtained first mixture is subjected to a primary sintering treatment, a lithium-deficient nickel manganese lithium oxide core material is obtained; S2. The obtained lithium-deficient nickel manganese lithium oxide core material and the second lithium source are subjected to a secondary mixing treatment, and the obtained second mixture is subjected to a secondary sintering treatment so that lithium elements are doped onto the surface of the lithium-deficient nickel manganese lithium oxide core to form a lithium-rich nickel manganese lithium oxide shell layer, that is, the nickel manganese lithium oxide cathode material is obtained. Among them, both the lithium-deficient nickel manganese lithium oxide core material and the nickel manganese lithium oxide cathode material have a spinel structure and are mainly in the P4332 space group structure. The proportion of the Fd-3m space group structure phase of the nickel manganese lithium oxide cathode material is 4.0 - 10.0%, such as 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.0% or any value between them, and more preferably 4.0 - 8.0%, such as 4.0%, 5.0%, 6.0%, 7.0%, 8.0% or any value between them. The additive contains at least one of transition metal elements other than lithium, nickel, and manganese.

[0046] In the preparation process of the above nickel manganese lithium oxide cathode material, the molar ratio of the sum of the lithium element contents in the first lithium source and the second lithium source to the sum of the nickel and manganese element contents in the nickel manganese compound precursor is preferably 0.5:1.

[0047] In the present invention, in step S1, the molar ratio of the lithium element content in the first lithium source to the sum of the nickel and manganese element contents in the nickel-manganese compound precursor is preferably m':1, where 0.4 ≤ m' < 0.5, and m' can be 0.4, 0.41, 0.42, 0.45, 0.48, 0.49, 0.495 or any value between them.

[0048] In the present invention, in step S1, the dosage of the additive is preferably 0.1 - 1.0 wt% of the mass of the nickel-manganese compound precursor, such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt% or any value between them. Adding the additive in step S1, the introduced doped metal elements help to inhibit the oxygen evolution reaction during the sintering treatment in the process of preparing the lithium nickel manganese oxide material, reduce the formation of nickel-manganese oxides with the Fd-3m space group structure phase, and reduce the generation probability of impurity phases in the lithium nickel manganese oxide cathode material (the impurity phase can refer to one of metal oxides, such as manganese oxide, nickel oxide, lithium oxide, lithium nickel oxide, lithium manganese oxide, nickel manganese oxide, etc.). When the dosage of the additive is controlled within the above preferred range, it is more conducive to exerting and improving the capacity and rate performance of the material and stabilizing its cycle performance. [[ID=Z4]]

[0049] In the present invention, in step S2, the molar ratio of the lithium element content in the second lithium source to the sum of the nickel and manganese element contents in the nickel-manganese compound precursor is preferably n':1, where 0 < n' ≤ 0.1, and n' can be 0.005, 0.01, 0.02, 0.05, 0.08, 0.09, 0.1 or any value between them.

[0050] In the present invention, the molar ratio of nickel element to manganese element in the nickel-manganese compound precursor is preferably 1:(2.0 - 3.5), such as 1:2.0, 1:2.5, 1:2.7, 1:2.8, 1:2.9, 1:3.0, 1:3.2, 1:3.4, 1:3.5 or any value between them.

[0051] In the present invention, the nickel-manganese compound precursor can be nickel-manganese oxide or nickel-manganese hydroxide, and can be synthesized by conventional methods in the prior art, such as solid-phase method, co-precipitation method, sol-gel method, hydrothermal method, etc. The nickel-manganese compound precursor is preferably prepared by the co-precipitation method, specifically including: adding a precipitant to a mixed metal ion solution containing a nickel source and a manganese source, reacting under stirring, and the obtained precipitate product is the nickel-manganese compound precursor.

[0052] Furthermore, the nickel source is a type of reagent commonly used in the existing methods for preparing lithium nickel manganese oxide cathode materials, and the present invention does not make special limitations on it. Specifically, it can be selected from at least one of nickel carbonate, nickel nitrate, nickel sulfate, nickel chloride, nickel acetate.

[0053] Furthermore, the manganese source is a type of reagent commonly used in the existing method for preparing lithium nickel manganese oxide positive electrode materials. The present invention does not specifically limit it, and specifically can be selected from at least one of manganese carbonate, manganese nitrate, manganese sulfate, manganese chloride, and manganese acetate.

[0054] Furthermore, the precipitant is used to provide OH - The nickel ions and manganese ions are coprecipitated to obtain a nickel-manganese compound precursor, specific examples of which include but are not limited to at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate.

[0055] In the above-mentioned process of preparing the nickel-manganese compound precursor by coprecipitation, the sum of the nickel element in the nickel source and the manganese element in the manganese source and the OH group of the precipitant - The molar ratio of the nickel source and the manganese source is preferably 1: (2.5 to 3.5). Based on the total content of nickel in the nickel source and manganese in the manganese source as 1 mol, the OH of the precipitant is - The content of is preferably 2.5 to 3.5 mol, such as 2.5 mol, 2.8 mol, 3 mol, 3.2 mol, 3.5 mol or any value therebetween. The conditions for the coprecipitation reaction preferably include: a temperature of 25 to 50°C, such as 25°C, 30°C, 35°C, 40°C, 45°C, 50°C or any value therebetween; and a stirring speed of 25 to 35 Hz, such as 25 Hz, 28 Hz, 30 Hz, 32 Hz, 35 Hz or any value therebetween.

[0056] In the present invention, the lithium source is a reagent commonly used in existing methods for preparing lithium nickel manganese oxide positive electrode materials, and the present invention is not particularly limited thereto. The first lithium source and the second lithium source are each independently selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium bromide, lithium fluoride, lithium iodide, and lithium sulfate.

[0057] In the present invention, the additive preferably contains at least one of tungsten, yttrium, niobium, strontium, titanium, molybdenum, aluminum, magnesium, zinc, and zirconium, and more preferably contains at least one of tungsten, yttrium, aluminum, zinc, and zirconium.

[0058] In the present invention, specific examples of the additive include, but are not limited to, at least one of tungsten oxide, yttrium oxide, niobium oxide, strontium oxide, titanium oxide, molybdenum oxide, aluminum oxide, magnesium oxide, zinc oxide, and zirconium oxide. More preferably, the additive is selected from at least one of tungsten oxide, yttrium oxide, aluminum oxide, zinc oxide, and zirconium oxide. This has the advantage of further improving the capacity, rate capability, and cycle performance of the positive electrode material. This is because it improves the structural and interfacial stability of the positive electrode material, optimizes the electronic and ionic conductivity of the material, significantly inhibits interfacial side reactions and electrolyte decomposition, and reduces the formation of impurities, resulting in excellent electrochemical performance.

[0059] In the present invention, in step S1, the primary mixing process is a conventional technique employed in the prior art to uniformly mix the nickel-manganese compound precursor, the first lithium source, and the additive, preferably a first ball milling mixing process and / or a first high-speed mixing process. The present invention more preferably employs the first high-speed mixing process, which is more conducive to improving mixing efficiency and uniformity.

[0060] Furthermore, the rotation speed of the first ball milling mixing treatment is preferably 100-500 rpm, such as 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm or any value therebetween; the time is preferably 1-8 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or any value therebetween.

[0061] Furthermore, the first high-speed mixing process includes at least a first mixing process segment and a second mixing process segment performed in sequence, and the rotation speed of the first mixing process segment is lower than the rotation speed of the second mixing process segment. At this time, it has the advantages of high mixing efficiency and good mixing uniformity. The reason is that the segmented mixing is conducive to improving the dispersibility of the additive and the binding force on the precursor, thereby improving the uniformity of the mixture. At the same time, compared with the ball milling mixing process, the mixing process time is greatly shortened and the mixing efficiency is improved.

[0062] In a specific embodiment, the first high-speed mixing process includes a first mixing process section and a second mixing process section performed sequentially. The rotation speed of the first mixing process section is preferably 200-300 rpm, such as 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, or any value therebetween; the time is preferably 5-10 minutes, such as 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, or any value therebetween. The rotation speed of the second mixing process section is preferably 600-900 rpm, such as 600 rpm, 700 rpm, 800 rpm, 900 rpm, or any value therebetween; the time is preferably 20-40 minutes, such as 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or any value therebetween.

[0063] In the present invention, the primary sintering process is preferably carried out at a first platform temperature and a second platform temperature. The primary sintering process is preferably carried out in an oxygen-containing gas environment, such as air or a mixture of oxygen and an inert gas.

[0064] Furthermore, the first platform temperature is preferably 700-850°C, such as 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C or any value therebetween; the holding time is preferably 2-10h, such as 2h, 4h, 5h, 8h, 10h or any value therebetween.

[0065] Furthermore, the second platform temperature is preferably 850-1000°C, such as 850°C, 880°C, 900°C, 920°C, 950°C, 980°C, 1000°C or any value therebetween; the holding time is preferably 10-18h, such as 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h or any value therebetween.

[0066] In the present invention, in step S2, the secondary mixing treatment is a technical means conventionally adopted in the prior art, which is limited to uniformly mixing the lithium-deficient lithium nickel manganese oxide core material and the second lithium source, and is preferably a second ball milling mixing treatment and / or a second high-speed mixing treatment.

[0067] Furthermore, the rotation speed of the second ball milling mixing treatment is preferably 100-400 rpm, such as 100 rpm, 200 rpm, 300 rpm, 400 rpm or any value therebetween; and the time is preferably 1-6 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h or any value therebetween.

[0068] Furthermore, the second high-speed mixing process includes at least a third mixing process section and a fourth mixing process section which are performed sequentially, and the rotation speed of the third mixing process section is lower than the rotation speed of the fourth mixing process section.

[0069] In a specific embodiment, the second high-speed mixing process includes a third mixing process segment and a fourth mixing process segment performed sequentially. The rotation speed of the third mixing process segment is preferably 200-400 rpm, such as 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, 350 rpm, 400 rpm or any value therebetween; the time is preferably 5-15 min, such as 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 12 min, 15 min or any value therebetween. The rotation speed of the second mixing process segment is preferably 700-900 rpm, such as 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm or any value therebetween; the time is preferably 15-30 min. Such as 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min or any value therebetween.

[0070] In the present invention, the temperature of the secondary sintering treatment is preferably 400-700°C, such as 400°C, 500°C, 600°C, 700°C or any value therebetween; the holding time is preferably 2-10h, such as 2h, 3h, 5h, 7h, 8h, 10h or any value therebetween.

[0071] The present invention also provides a lithium nickel manganese oxide positive electrode material prepared by the above-mentioned method for preparing the lithium nickel manganese oxide positive electrode material.

[0072] The present invention also provides the use of the lithium nickel manganese oxide positive electrode material in a lithium ion battery.

[0073] The present invention will be described in detail below through specific examples. The examples of the embodiments are intended to explain the present invention and are not to be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0074] Preparation Example 1

[0075] This preparation example is used to illustrate the preparation of a nickel-manganese compound precursor, which specifically includes:

[0076] 147.29 g of nickel sulfate and 285.54 g of manganese sulfate were weighed and dissolved in deionized water in a molar ratio of nickel to manganese of 1:2 to obtain a metal ion solution; 280 mL of a 30 mol / L sodium hydroxide solution was prepared as a precipitant in a molar ratio of the total amount of metal ions to hydroxide ions in the metal ion solution of 1:3, and the sodium hydroxide solution was slowly added to the metal ion solution within 10 minutes at a temperature of 35°C, a pH of 10.8 and a stirring speed of 28 Hz. The temperature was raised to 35°C for a coprecipitation reaction for 12 hours to obtain a suspension, and the suspension was filtered, washed and dried to obtain a nickel-manganese compound precursor.

[0077] Preparation Example 2

[0078] This preparation example is used to illustrate the preparation of a nickel-manganese compound precursor, which specifically includes:

[0079] 77.4 g of nickel sulfate and 226.5 g of manganese sulfate were weighed and dissolved in deionized water in a molar ratio of nickel to manganese of 1:3 to obtain a metal ion solution; 300 mL of a 20 mol / L sodium hydroxide solution was prepared as a precipitant in a molar ratio of the total amount of metal ions to hydroxide ions in the metal ion solution of 1:3, and the sodium hydroxide solution was slowly added to the metal ion solution within 10 minutes at a temperature of 35° C., a pH of 10.8, and a stirring speed of 28 Hz. The temperature was raised to 35° C. for a coprecipitation reaction for 12 hours to obtain a suspension, and the suspension was filtered, washed, and dried to obtain a nickel-manganese compound precursor.

[0080] Example 1

[0081] This embodiment is used to illustrate the preparation of a lithium nickel manganese oxide positive electrode material, which specifically includes:

[0082] S1. Lithium carbonate, tungsten oxide, and the nickel-manganese compound precursor obtained in Preparation Example 1 were placed in a high-speed mixer, first mixed at a speed of 250 rpm for 10 min, and then mixed at a speed of 700 rpm for 30 min to obtain a mixture; the obtained mixture was then sintered at a first platform temperature of 750° C. for 6 h, directly heated to a second platform temperature of 930° C. and continued to sinter for 12 h, and then cooled to room temperature at a cooling rate of about 58° C. / h within 16 h to obtain a lithium-deficient lithium nickel manganese oxide core material;

[0083] S2, taking lithium carbonate and the lithium-deficient lithium nickel manganese oxide core material prepared in S1, mixing them in a high-speed mixer at 300 rpm for 10 minutes, and then mixing them at 750 rpm for 25 minutes to obtain a mixture; then taking the obtained mixture and sintering it at 600° C. for 6 hours, cooling it naturally to room temperature, and then gas-breaking and sieving it to obtain the lithium nickel manganese oxide positive electrode material with the core-shell structure;

[0084] Among them, the molar ratio of lithium ions in lithium carbonate in S1 to the total amount of metal ions in the nickel-manganese compound precursor is 0.45:1; based on the mass of the nickel-manganese compound precursor, the amount of tungsten oxide used is 0.2wt%; and the molar ratio of the total amount of lithium ions in lithium carbonate in S2 to the total amount of metal ions in the nickel-manganese compound precursor is 0.05:1.

[0085] Example 2

[0086] This embodiment is used to illustrate the preparation of a lithium nickel manganese oxide positive electrode material, which specifically includes:

[0087] S1. Lithium chloride, aluminum oxide, and the nickel-manganese compound precursor obtained in Preparation Example 2 were placed in a high-speed mixer and mixed at 300 rpm for 5 min and then at 900 rpm for 20 min to obtain a mixture. The mixture was then sintered at a first platform temperature of 700° C. for 8 h, directly heated to a second platform temperature of 880° C. and continued to sinter for 16 h. The temperature was then cooled to room temperature at a cooling rate of approximately 58° C. / h within 16 h to obtain a lithium-deficient lithium nickel manganese oxide core material.

[0088] S2. Take lithium chloride and the lithium-deficient lithium nickel manganese oxide core material prepared in S1 and put them into a high-speed mixer. First, mix them at 400 rpm for 5 minutes, and then mix them at 850 rpm for 15 minutes to obtain a mixture. Then, take the obtained mixture and sinter it at 700°C for 4 hours. After naturally cooling to room temperature, it is gas-broken and sieved to obtain the lithium nickel manganese oxide positive electrode material with the core-shell structure.

[0089] Among them, the molar ratio of lithium ions in lithium chloride to the total amount of metal ions in the nickel-manganese compound precursor is 0.49:1; based on the mass of the nickel-manganese compound precursor, the amount of aluminum oxide used is 0.5wt%; and the molar ratio of the total amount of lithium ions in lithium chloride in S2 to the total amount of metal ions in the nickel-manganese compound precursor is 0.01:1.

[0090] Example 3

[0091] This embodiment is used to illustrate the preparation of a lithium nickel manganese oxide positive electrode material, which specifically includes:

[0092] S1. Lithium hydroxide, yttrium oxide, and the nickel-manganese compound precursor obtained in Preparation Example 1 are placed in a high-speed mixer, first mixed at a speed of 200 rpm for 10 minutes, and then mixed at a speed of 600 rpm for 40 minutes to obtain a mixture; the obtained mixture is then sintered at a first platform temperature of 850° C. for 4 hours, directly heated to a second platform temperature of 1000° C. and continued to sinter for 10 hours, and then cooled to room temperature at a cooling rate of about 58° C. / h within 16 hours to obtain a lithium-deficient lithium nickel manganese oxide core material;

[0093] S2. Take lithium hydroxide and the lithium-deficient lithium nickel manganese oxide core material prepared in S1 and put them into a high-speed mixer. First, mix them at 400 rpm for 15 minutes, and then mix them at 700 rpm for 30 minutes to obtain a mixture; then, take the obtained mixture and sinter it at 500°C for 8 hours. After naturally cooling to room temperature, it is gas-broken and sieved to obtain the lithium nickel manganese oxide positive electrode material with the core-shell structure.

[0094] Among them, the molar ratio of lithium ions in lithium hydroxide to the total amount of metal ions in the nickel manganese compound precursor is 0.4:1; based on the mass of the nickel manganese compound precursor, the amount of yttrium oxide is 1.0wt%; the molar ratio of the total amount of lithium ions in lithium hydroxide in S2 to the total amount of metal ions in the nickel manganese compound precursor is 0.1:1.

[0095] Example 4

[0096] This embodiment is used to illustrate the preparation of a lithium nickel manganese oxide positive electrode material, which specifically includes:

[0097] S1. Lithium carbonate, tungsten oxide, and the nickel-manganese compound precursor obtained in Preparation Example 1 were placed in a ball mill and mixed at 300 rpm for 5 hours to obtain a mixture; the mixture was then sintered at a first platform temperature of 750° C. for 6 hours, directly heated to a second platform temperature of 930° C. and continued to sinter for 12 hours, and then cooled to room temperature at a cooling rate of approximately 58° C. / h within 16 hours to obtain a lithium-deficient lithium nickel manganese oxide core material;

[0098] S2. Take lithium carbonate and the lithium-deficient lithium nickel manganese oxide core material prepared in S1 and put them into a ball mill. Mix them at 250 rpm for 3.5 hours to obtain a mixture. Then, take the obtained mixture and sinter it at 600°C for 6 hours. After naturally cooling to room temperature, it is gas-broken and sieved to obtain the lithium nickel manganese oxide positive electrode material with the core-shell structure.

[0099] Among them, the molar ratio of lithium ions in lithium carbonate in S1 to the total amount of metal ions in the nickel-manganese compound precursor is 0.45:1; based on the mass of the nickel-manganese compound precursor, the amount of tungsten oxide used is 0.2wt%; and the molar ratio of the total amount of lithium ions in lithium carbonate in S2 to the total amount of metal ions in the nickel-manganese compound precursor is 0.05:1.

[0100] Example 5

[0101] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that the amount of tungsten oxide used in step S1 was 2.0 wt %. The other conditions were the same as those of Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material with a core-shell structure.

[0102] Example 6

[0103] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that in step S2, the molar ratio of lithium ions of lithium carbonate to the total amount of metal ions of the nickel manganese compound precursor was 0.03:1, and the other conditions were the same as in Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material.

[0104] Example 7

[0105] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that in step S2, the molar ratio of lithium ions of lithium carbonate to the total amount of metal ions of the nickel manganese compound precursor was 0.08:1, and the other conditions were the same as in Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material.

[0106] Example 8

[0107] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that the same amount of zirconium oxide was used instead of tungsten oxide in step S1, and the other conditions were the same as those of Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material.

[0108] Example 9

[0109] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that the same amount of zinc oxide was used instead of tungsten oxide in step S1, and the other conditions were the same as those of Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material.

[0110] Example 10

[0111] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that the same amount of titanium oxide was used instead of tungsten oxide in step S1, and the other conditions were the same as those of Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material.

[0112] Example 11

[0113] A lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that the same amount of strontium oxide was used instead of tungsten oxide in step S1. The other conditions were the same as those of Example 1, thereby preparing a lithium nickel manganese oxide positive electrode material.

[0114] Comparative Example 1

[0115] A reference lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that step S2 was not performed. The other conditions were the same as those of Example 1, thereby preparing a reference lithium nickel manganese oxide positive electrode material.

[0116] Comparative Example 2

[0117] A reference lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that the molar ratio of lithium ions of lithium carbonate to the total amount of metal ions of the nickel manganese compound precursor in step S1 was 0.5:1, and step S2 was not performed. The remaining conditions were the same as in Example 1, thereby preparing a reference lithium nickel manganese oxide positive electrode material.

[0118] Comparative Example 3

[0119] A reference lithium nickel manganese oxide positive electrode material was prepared according to the method of Example 1, except that tungsten oxide was not added when preparing the mixture in step S1. The other conditions were the same as those in Example 1, thereby preparing a reference lithium nickel manganese oxide positive electrode material.

[0120] Test Case

[0121] This test example is used to illustrate the relevant performance of the lithium nickel manganese oxide positive electrode materials provided in the above embodiments and comparative examples. The test specifically includes:

[0122] 1. Preparation of button-type full battery: lithium nickel manganese oxide positive electrode material, conductive agent Super P and binder PVDF were mixed in a mass ratio of 94:3:3, and the slurry was adjusted in a degassing machine to control the viscosity of the slurry to 8000mPa·s. Then, an automatic coating machine was used to evenly coat the slurry on aluminum foil to form an original electrode sheet, which was placed in a vacuum oven at 130°C for 4 hours, and then placed in a blast oven at 80°C for 12 hours to obtain a test piece; a punching die with a diameter of 14mm was used to cut out several small electrode sheets at different positions of the above test piece, and the small electrode sheets with regular morphology, smooth surface and edges were selected and weighed with a 1 / 10,000 balance. The small electrode sheet was placed in a vacuum drying oven and evacuated to 0.1 MPa to obtain a positive electrode sheet, which was stored for future use. In an inert gas glove box with a water and oxygen mass content of less than or equal to 0.0005%, a button battery was assembled according to the battery specifications of CR2023, wherein the negative electrode was a lithium sheet, the separator was a polypropylene film, the high-voltage electrolyte solvent was a mixed solution of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, and the conductive salt was 1M lithium hexafluorophosphate. After the assembly was completed, it was packaged at 800 Pa for 5 seconds to obtain a button battery.

[0123] 2. Microstructure Testing: Coin-type batteries prepared from the lithium nickel manganese oxide positive electrode materials prepared in the Examples and Comparative Examples were used as test subjects. The content z value of the metal oxide with an Fd-3m space group structure phase (e.g., manganese oxide, nickel oxide, lithium oxide, lithium nickel oxide, lithium manganese oxide, nickel manganese oxide, etc.) in the lithium nickel manganese oxide spinel material was calculated using the Fd-3m space group structure phase ratio calculation method described in Method 2 above. The results are shown in Table 1.

[0124] Table 1

[0125] cathode materials 4V platform proportion x <![CDATA[Mn 3+ Content y]]> Fd-3m space group structure phase ratio z Example 1 1.85％ 0.56％ 4.93％ Example 2 2.20％ 0.66％ 5.87％ Example 3 2.41％ 0.72％ 6.43％ Example 4 1.93％ 0.58％ 5.15％ Example 5 3.53％ 1.06％ 9.41％ Example 6 3.74％ 1.12％ 9.97％ Example 7 3.34％ 1.00％ 8.91％ Example 8 2.77％ 0.83％ 7.39％ Example 9 2.85％ 0.86％ 7.60％ Example 10 3.28％ 0.98％ 8.75％ Example 11 3.40％ 1.02％ 9.07％ Comparative Example 1 12.19％ 3.66％ 32.51％ Comparative Example 2 9.16％ 2.75％ 24.43％ Comparative Example 3 18.60％ 5.58％ 49.60％

[0126] 3. Test of electrochemical performance:

[0127] A button cell battery testing system was used to conduct constant current charge and discharge tests at different current densities. The test temperature was 25°C, the charge and discharge range was 3.5 to 4.9V, and the rate performance was tested in the 0.1 to 5C rate range and the 0.1C cycle performance was tested. The test results are shown in Table 2.

[0128] (1) Charge and discharge performance test: The button-type full battery assembled according to the method in 1 was charged at a constant current of 0.1C to a voltage of 4.9V under normal temperature battery laboratory conditions, and then charged at a constant voltage of 4.9V to a current of 0.05C. The battery was left to stand for 5 minutes, and the charge capacity was recorded. The button-type full battery was then discharged at a constant current of 0.1C to a voltage of 3.5V, and the discharge capacity was recorded. The first discharge capacity in grams at 0.1C was calculated.

[0129] (2) Rate performance test: The button-type full battery assembled according to the method in 1 was charged at a constant current of 5C to a voltage of 4.9V under normal temperature battery laboratory conditions, and then charged at a constant voltage of 4.9V to a current of 0.05C. The battery was left to stand for 5 minutes, and the charge capacity was recorded. The button-type full battery was then discharged at a constant current of 5C to a voltage of 3.5V, and the discharge capacity was recorded. The discharge capacity in grams at 5C was calculated, and the ratio of the discharge capacity in grams at 5C to the first discharge capacity in grams at 0.1C was calculated.

[0130] (3) Cycling performance test: The button-type full battery assembled according to the method in 1 was charged and discharged 50 times at a constant current of 0.1C in the voltage range of 3.5 to 4.9V under normal temperature battery laboratory conditions, and the capacity retention rate of the battery before and after the cycle was calculated.

[0131] Table 2

[0132]

[0133]

[0134] It can be seen from the results in Table 1 that, compared with Comparative Examples 1 to 3, the lithium nickel manganese oxide positive electrode materials provided by Examples 1 to 11 of the present invention not only maintain good discharge gram capacity, but also have better discharge gram capacity retention rate and better cycle capacity retention rate under high rate conditions, and have good rate performance and stability.

[0135] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A lithium nickel manganese oxide positive electrode material, characterized in that The lithium nickel manganese oxide positive electrode material includes a lithium-deficient lithium nickel manganese oxide core and a lithium-rich lithium nickel manganese oxide shell located on the surface of the lithium-deficient lithium nickel manganese oxide core; the lithium-deficient lithium nickel manganese oxide core contains doped metal elements, and the doped metal elements are selected from at least one transition metal element other than lithium, nickel and manganese; the ratio of the molar content of lithium element to the molar content of nickel and manganese element in the lithium-rich lithium nickel manganese oxide shell is greater than the ratio of the molar content of lithium element to the molar content of nickel and manganese element in the lithium-deficient lithium nickel manganese oxide core; the Fd-3m space group structure phase ratio of the lithium nickel manganese oxide positive electrode material is 4.0 to 10.0%.

2. The lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that The molar ratio of the sum of the lithium content in the lithium-rich lithium nickel manganese oxide shell and the lithium content in the lithium-deficient lithium nickel manganese oxide core to the nickel and manganese content in the lithium nickel manganese oxide positive electrode material is 0.5:1; Preferably, the molar ratio of the lithium content in the lithium-deficient lithium nickel manganese oxide core, the lithium content in the lithium-rich lithium nickel manganese oxide shell, and the nickel and manganese content in the lithium nickel manganese oxide positive electrode material is m:n:1, wherein m+n=0.5, 0.4≦m<0.5, 0 <n≦0.1。 3. The lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that The lithium nickel manganese oxide positive electrode material includes a chemical formula of Li y [Li 1-y Ni 0.5-x / 2 M x Mn 1.5-x / 2 O4] compound, wherein y represents the molar content of lithium in the lithium-rich lithium nickel manganese oxide shell, M is a doping metal element, <y≦0.1,0<x≦0.2; Preferably, the content of the doped metal element M in the lithium nickel manganese oxide positive electrode material is 0.1-1.0 wt%.

4. The lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that The doping metal element is selected from at least one of tungsten, yttrium, niobium, strontium, titanium, molybdenum, aluminum, magnesium, zinc, and zirconium; preferably, the thickness of the lithium-rich nickel manganese oxide shell is H and 0 <H≦100nm。 5. A method for preparing a lithium nickel manganese oxide positive electrode material, characterized in that: The preparation method comprises the following steps: S1. The nickel-manganese compound precursor, the first lithium source, and the additive are mixed once, and the resulting first mixture is sintered once to obtain a lithium-deficient lithium nickel manganese oxide core material; S2. The obtained lithium-deficient lithium nickel manganese oxide core material and the second lithium source are subjected to a secondary mixing process, and the obtained second mixture is subjected to a secondary sintering process to allow lithium to be doped into the surface of the lithium-deficient lithium nickel manganese oxide core and to form a lithium-rich lithium nickel manganese oxide shell layer, thereby obtaining a lithium nickel manganese oxide positive electrode material; The additive contains at least one transition metal element except lithium, nickel and manganese; the Fd-3m space group structure phase ratio of the lithium nickel manganese oxide positive electrode material is 4.0-10.0%.

6. The method for preparing the lithium nickel manganese oxide positive electrode material according to claim 5, characterized in that: The molar ratio of the sum of the lithium content in the first lithium source and the second lithium source to the sum of the nickel and manganese content in the nickel-manganese compound precursor is 0.5:1; Preferably, in step S1, the molar ratio of the lithium content in the first lithium source to the sum of the nickel and manganese content in the nickel-manganese compound precursor is mˋ:1, wherein 0.4≦mˋ<0.5; Preferably, in step S1, the amount of the additive is 0.1 to 1.0 wt% of the mass of the nickel-manganese compound precursor; Preferably, in step S2, the molar ratio of the sum of the lithium content in the second lithium source and the nickel and manganese content in the nickel and manganese compound precursor is n:1, wherein 0 <nˋ≦0.1。 7. The method for preparing the lithium nickel manganese oxide positive electrode material according to claim 5, characterized in that: The nickel-manganese compound precursor is obtained by co-precipitation reaction of nickel source and manganese source under the action of precipitant; Preferably, the first lithium source and the second lithium source are each independently selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium bromide, lithium fluoride, lithium iodide, and lithium sulfate; Preferably, the additive contains at least one of tungsten, yttrium, niobium, strontium, titanium, molybdenum, aluminum, magnesium, zinc, and zirconium; Preferably, the additive is selected from at least one of tungsten oxide, yttrium oxide, niobium oxide, strontium oxide, titanium oxide, molybdenum oxide, aluminum oxide, magnesium oxide, zinc oxide, and zirconium oxide.

8. The method for preparing the lithium nickel manganese oxide positive electrode material according to claim 5, characterized in that: In step S1, the primary mixing process is a first ball milling mixing process and / or a first high-speed mixing process; Preferably, the first ball milling mixing treatment is performed at a rotation speed of 100 to 500 rpm and for a time of 1 to 8 hours; Preferably, the first high-speed mixing process comprises at least a first mixing process section and a second mixing process section which are performed sequentially, and the rotation speed of the first mixing process section is lower than the rotation speed of the second mixing process section; Preferably, the primary sintering process includes being performed at a first platform temperature and a second platform temperature; Preferably, the temperature of the first platform is 700-850°C, and the holding time is 2-10 hours; Preferably, the temperature of the second platform is 850-1000° C., and the holding time is 10-18 hours.

9. The method for preparing a lithium nickel manganese oxide positive electrode material according to claim 5, wherein: In step S2, the secondary mixing process is a second ball milling mixing process and / or a second high-speed mixing process; Preferably, the second ball milling mixing treatment is performed at a speed of 100 to 400 rpm and for a time of 1 to 6 hours; Preferably, the second high-speed mixing process comprises at least a third mixing process section and a fourth mixing process section which are performed sequentially, and the rotation speed of the first mixing process section is lower than the rotation speed of the second mixing process section; Preferably, the temperature of the secondary sintering treatment is 400-700° C., and the holding time is 2-10 hours.

10. A lithium nickel manganese oxide positive electrode material prepared by the method for preparing a lithium nickel manganese oxide positive electrode material according to any one of claims 5 to 9.

11. Use of the lithium nickel manganese oxide positive electrode material according to any one of claims 1 to 4 and 9 in lithium ion batteries.

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