Two-phase dispersed lithium-rich manganese-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a two-phase dispersed lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of preparation of battery positive electrode materials. According to the lithium-rich manganese-based positive electrode material, in a diffraction pattern obtained by adopting an XRD (X-Ray Diffraction) instrument taking Cu-K alpha as an incident light source, the value range of the half-peak width ratio A of a LiMn6 peak of which 2 theta is positioned at 20.6 + / -0.1 degrees to a (003) peak of which 2 theta is positioned at 18.6 + / -0.1 degrees is more than or equal to 0.5 and less than or equal to 1.8. By optimizing the sintering process of the lithium-rich manganese-based material, the dynamics of the solid-phase sintering reaction of the lithium-rich manganese-based material is greatly improved, the reaction is promoted to be more thorough, the two phases of the lithium-rich manganese-based material are distributed more uniformly, the layered structure is more ordered and stable, and the lithium-rich manganese-based material shows higher specific capacity and longer cycle life.

Description

Technical Field

[0001] The present invention relates to the technical field of battery positive electrode material preparation, and in particular to a two-phase dispersed lithium-rich manganese-based positive electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The mass and cost of positive electrode materials in lithium-ion batteries account for up to 40-50%, and their performance and cost largely determine the key performance indicators of the battery, such as energy density, safety, and cost. Lithium-rich manganese-based materials have the advantages of high capacity, low cost, and high thermal stability, and are considered to be the most promising new positive electrode materials. The special structure of the monoclinic phase of Li2MnO3 and the hexagonal phase of LiMO2 is the main reason for its high capacity. High-resolution transmission electron microscopy shows that the monoclinic phase and the hexagonal phase exist in the form of nano-microregions (which can be considered as grains). For lithium-rich materials of the same particle size, the smaller the nano-microregion, the more uniform the distribution of the two phases, and the higher the capacity and longer the life. It has very important practical significance for the application of lithium-rich manganese-based materials in lithium-ion batteries. The Debye-Scherrer formula D=Kλ / Bcosθ based on the principle of X-ray diffraction can be used to estimate the grain size. When calculating, the grains are approximately assumed to be nearly spherical, and the D value obtained by the diffraction peak corresponding to a specific crystal orientation is considered to be the grain size. For example, in a lithium-rich manganese-based two-phase structure, the grain size of the hexagonal phase structure can be estimated by the (003) peak with a diffraction angle of about 18.6°, while the grain size of the monoclinic phase can be estimated by the LiMn6 superlattice peak of about 20.6°.

[0003] Solid phase sintering is the most commonly used method for preparing positive electrode materials for lithium-ion batteries. The precursor and the lithium source (usually lithium carbonate or lithium hydroxide) are uniformly mixed in a certain proportion and then sintered at high temperature to cause solid phase reaction and crystal growth. The solid phase reaction is the process in which the precursor is gradually lithiated, exhaust gas is discharged, and a layered structure is formed under the participation of oxygen. Crystal growth is the process in which the layered structure tends to be perfect and defects are dissipated. The sintering process parameters must be strictly controlled to finally obtain a lithium-rich manganese-based positive electrode material with a specific crystal structure and excellent performance. In actual production, due to the particularity of the two-phase structure, the consistency of lithium-rich manganese-based materials is usually difficult to control, especially the bottom of the material layer has problems such as low reaction degree and difficulty in timely exhaust gas discharge. The electrochemical performance is far inferior to that of the surface material. The stability problem can be improved to a certain extent by regulating and optimizing the sintering process. For example, Chinese patent CN18206162A discloses a method for improving the consistency and stability of lithium-rich manganese-based materials. After the precursor is pre-sintered, the mixed material is subjected to a second sintering, which reduces the formation of spinel phase. Chinese patent CN118136832A discloses a method for preparing a low-voltage, high-capacity lithium-rich manganese-based material. The precursor is first thermally transformed in an oxygen-containing atmosphere or under negative pressure, and then lithium is added and calcined in an oxygen-deficient atmosphere, which helps to make it still have high capacity, voltage stability and long-range cycle performance at low voltage. However, the above technical solutions all require pretreatment of the precursor, which increases its manufacturing cost, and does not consider the impact of the sintering process on the crystal structure of the lithium-rich manganese-based material. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a lithium-rich manganese-based positive electrode material with uniform two-phase structure distribution, low specific surface area and long cycle life and a preparation method thereof, so as to solve the problems of poor batch stability and consistency during the sintering process. Based on the XRD diffraction principle and the Scherrer formula, the present invention uses the hexagonal (003) diffraction peak and the monoclinic LiMn6 diffraction peak to estimate the grain size of the hexagonal phase and the monoclinic phase respectively, and uses the ratio of the two to evaluate the uniformity of the two-phase distribution.

[0005] One of the purposes of the present invention is to provide a lithium-rich manganese-based positive electrode material with two-phase dispersed distribution.

[0006] The second object of the present invention is to provide a method for preparing the two-phase dispersed lithium-rich manganese-based positive electrode material.

[0007] The third object of the present invention is to provide a lithium-ion battery, comprising the two-phase dispersed lithium-rich manganese-based positive electrode material.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] In a first aspect, the present invention provides a two-phase dispersed lithium-rich manganese-based positive electrode material, wherein the chemical formula of the lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiMO2, wherein M is at least one element of Mn, Ni, and Co, and 0.1≤x≤0.9;

[0010] In the diffraction pattern of the lithium-rich manganese-based positive electrode material obtained by an XRD instrument with Cu-Kα as the incident light source, the half-peak width ratio A of the LiMn6 peak with 2θ located at 20.6±0.1° and the (003) peak with 2θ located at 18.6±0.1° is in the range of 0.5≤A≤1.8, preferably 1≤A≤1.5.

[0011] In some embodiments, the specific surface area of ​​the lithium-rich manganese-based positive electrode material is ≤1.2 m 2 / g.

[0012] In a second aspect, the present invention provides a method for preparing a two-phase dispersed lithium-rich manganese-based positive electrode material, comprising the following steps:

[0013] The lithium-rich manganese-based precursor is uniformly mixed with a lithium source, and sintered under an oxygen-containing atmosphere and a slightly negative pressure to obtain the lithium-rich manganese-based positive electrode material.

[0014] In some embodiments, the lithium-rich manganese-based precursor is prepared by the following method:

[0015] A metal salt aqueous solution of a soluble nickel salt, a soluble manganese salt and a soluble cobalt salt in corresponding proportions is prepared according to a chemical formula, and a lithium-rich manganese-based precursor is prepared through a precipitation reaction.

[0016] Preferably, the soluble nickel salt includes any one of nickel sulfate, nickel acetate, nickel oxalate or nickel nitrate, or a combination of at least two of them; the soluble manganese salt includes any one of manganese sulfate, manganese acetate, manganese oxalate or manganese nitrate, or a combination of at least two of them; and the soluble cobalt salt includes any one of cobalt sulfate, cobalt acetate, cobalt oxalate or cobalt nitrate, or a combination of at least two of them.

[0017] In some embodiments, the lithium source includes any one of lithium acetate, lithium nitrate, lithium carbonate, and lithium hydroxide, or a combination of at least two thereof; and the molar ratio of the lithium-rich manganese-based precursor to the lithium source (in terms of Li) is greater than 1 and less than 1.3.

[0018] In some embodiments, the oxygen-containing atmosphere includes air or oxygen, or a mixture of the two in any proportion; slightly negative pressure refers to a pressure in the sintering furnace of -100 to -1 Pa, preferably -20 to -5 Pa.

[0019] In some embodiments, the sintering conditions are: first increase the temperature to 400-700°C at a heating rate of 0.1-10°C / min, keep warm for 1-8 hours, then increase the temperature to 800-1100°C at a heating rate of 0.1-10°C / min, and keep warm for 10-20 hours.

[0020] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the above-mentioned two-phase dispersed lithium-manganese-rich positive electrode material.

[0021] Beneficial effects:

[0022] (1) The present invention optimizes the sintering process of lithium-rich manganese-based materials, greatly improves the kinetics of the solid-phase sintering reaction of lithium-rich manganese-based materials, promotes a more thorough reaction, makes the two-phase distribution of lithium-rich manganese-based materials more uniform, and makes the layered structure more orderly and stable, showing a higher specific capacity and a longer cycle life.

[0023] (2) The method for preparing low specific surface area and long cycle lithium-rich manganese-based materials proposed in the present invention breaks through the problem of unstable batch sintering and poor consistency of lithium-rich manganese-based materials. The method is simple, the conditions are mild and controllable, and large-scale, industrialized preparation can be achieved.

[0024] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM picture of Example 1;

[0026] Figure 2 This is the SEM picture of Example 2;

[0027] Figure 3 This is the SEM picture of Comparative Example 1;

[0028] Figure 4 The XRD patterns of Example 1 and Comparative Example 1 are shown in FIG.

[0029] Figure 5 The first charge and discharge curves of Example 1 and Comparative Example 1 (2.0-4.6V, 0.1C);

[0030] Figure 6 The normal temperature cycle curves (25°C) of Example 1 and Comparative Example 1;

[0031] Figure 7 The high temperature cycle curves (45°C) of Example 1 and Comparative Example 1;

[0032] Figure 8 The first charge and discharge curve of Example 2 (2.0-4.6V, 0.1C);

[0033] Fig. 9 is the normal temperature cycle curve (25°C) of Example 2;

[0034] Fig.10 This is the high temperature cycle curve (45°C) of Example 2. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0036] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0037] Example 1

[0038] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to -10Pa to obtain a lithium-rich manganese-based material. SEM Figure 1 shown.

[0039] Example 2

[0040] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2(OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to -5Pa to obtain a lithium-rich manganese-based material. SEM Figure 2 shown.

[0041] Example 3

[0042] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to -25Pa to obtain a lithium-rich manganese-based material.

[0043] Example 4

[0044] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to -3Pa to obtain a lithium-rich manganese-based material.

[0045] Example 5

[0046] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 300g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to -10Pa to obtain a lithium-rich manganese-based material.

[0047] For saggers of the same size, the material layer will become thicker if the sintering amount is large. In this way, the material at the bottom of the sagger will be affected in structure and performance because the reaction exhaust gas cannot be removed in time. Sintering micro-negative pressure can solve this problem.

[0048] Comparative Example 1

[0049] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to 10Pa to obtain a lithium-rich manganese-based material. SEM Figure 3 shown.

[0050] Comparative Example 2

[0051] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2(OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 300g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to 10Pa to obtain a lithium-rich manganese-based material.

[0052] Comparative Example 3

[0053] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to -110Pa to obtain a lithium-rich manganese-based material.

[0054] Comparative Example 4

[0055] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace and heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process and the pressure in the muffle furnace was adjusted to 0Pa to obtain a lithium-rich manganese-based material.

[0056] Comparative Example 5

[0057] According to the molar ratio of Mn:Ni:Co of 0.4:0.4:0.2, corresponding masses of manganese sulfate monohydrate, nickel sulfate hexahydrate and cobalt sulfate heptahydrate were weighed to prepare a metal salt solution, which was subjected to precipitation reaction with a sodium hydroxide aqueous solution, and then washed, filtered and dried to obtain a metal salt solution with a composition of Mn 0.4 Ni 0.4 Co 0.2 (OH)2 lithium-rich manganese-based precursor. The precursor was mixed with lithium carbonate (in terms of Li) at a molar ratio of 1:1.15, 50g of the mixed sample was placed in a 20cm*20cm sagger, placed in an atmosphere furnace, heated to 550℃ at a heating rate of 3℃ / min and kept warm for 4h, and then continued to heat to 900℃ at a heating rate of 3℃ / min, sintered for 20h, and air atmosphere was introduced throughout the sintering process. The pressure in the muffle furnace was adjusted to -10Pa in the first insulation stage, and the pressure in the furnace was adjusted to 10Pa in the second insulation stage to obtain a lithium-rich manganese-based material.

[0058] XRD test:

[0059] The crystal structures of all samples were investigated by powder X-ray diffraction on a Smart Lab 9KW under Cu-Kα radiation in the range of 10–90° with a scan rate of 10° / min.

[0060] Electrochemical performance test:

[0061] The positive electrode active material, acetylene black, polyvinylidene fluoride and N-methylpyrrolidone are mixed to form a slurry, which is evenly coated on the surface of an aluminum foil to obtain a positive electrode plate; then, a lithium plate is used as a negative electrode plate, and a 1 mol / L lithium hexafluorophosphate ethylene carbonate (EC) and dimethyl carbonate (DMC) solution (the volume ratio of EC to DMC is 1:1) is used as an electrolyte, and assembled in a glove box to obtain a lithium-ion battery.

[0062] The lithium-ion battery was tested for cycle performance using an electrochemical tester at a temperature of 25°C and a current density of 0.1C (1C = 200 mAg -1 ), charge and discharge voltage range 4.6-2.0V, test the battery's initial charge and discharge performance. Normal temperature cycle performance: 25±2℃, 2.0-4.6V, 0.1C charge and discharge in the first week, 2.0-4.4V, 1C / 1C charge and discharge system for subsequent cycles to test cycle performance. High temperature cycle performance: 60±2℃, 2.0-4.6V, 0.1C charge and discharge in the first week, 2.0-4.4V, 1C / 1C charge and discharge system for subsequent cycles to test cycle performance.

[0063] A LiMn6 / (003) : The ratio of the half-width of the LiMn6 peak at 20.6° and the half-width of the (003) peak at 18.6° in the XRD spectrum.

[0064] Specific surface area: The specific surface area is tested according to the national standard GB / T 19587-2017 / ISO 9277:2010.

[0065] The XRD patterns of Example 1 and Comparative Example 1 are as follows: Figure 4 As shown, the first charge and discharge curves (2.0-4.6V, 0.1C) of Example 1 and Comparative Example 1 are as follows Figure 5 As shown, the normal temperature cycle curve and high temperature cycle curve of Example 1 and Comparative Example 1 are respectively as shown in Figure 6 and Figure 7 As shown, the first charge and discharge curve, normal temperature cycle curve and high temperature cycle curve of Example 2 are as follows Figure 8 , Fig. 9 and Fig.10 The results are shown in Table 1.

[0066] Table 1

[0067]

[0068] Comparative Example 5 shows that segmented micro-negative pressure cannot solve the problem of lithium-rich sintering.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A two-phase dispersed lithium-rich manganese-based positive electrode material, characterized in that: The chemical formula of the lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiMO2, wherein M is at least two elements of Mn, Ni, and Co, and 0.1≤x≤0.9; In the diffraction pattern of the lithium-rich manganese-based positive electrode material obtained by an XRD instrument with Cu-Kα as the incident light source, the half-peak width ratio A of the LiMn6 peak with 2θ located at 20.6±0.1° and the (003) peak with 2θ located at 18.6±0.1° has a value range of 0.5≤A≤1.

8.

2. The two-phase dispersed lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The value range of A is 1≤A≤1.

5.

3. The two-phase dispersed lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The specific surface area of ​​the lithium-rich manganese-based positive electrode material is ≤1.2m 2 / g.

4. A method for preparing a two-phase dispersed lithium-rich manganese-based positive electrode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: The lithium-rich manganese-based precursor is uniformly mixed with a lithium source, and sintered under an oxygen-containing atmosphere and a slightly negative pressure to obtain the lithium-rich manganese-based positive electrode material.

5. The preparation method according to claim 4, characterized in that: The lithium-rich manganese-based precursor is prepared by the following method: A metal salt aqueous solution of a soluble nickel salt, a soluble manganese salt and a soluble cobalt salt in corresponding proportions is prepared according to a chemical formula, and a lithium-rich manganese-based precursor is prepared through a precipitation reaction.

6. The preparation method according to claim 5, characterized in that: The soluble nickel salt includes any one of nickel sulfate, nickel acetate, nickel oxalate or nickel nitrate, or a combination of at least two of them; the soluble manganese salt includes any one of manganese sulfate, manganese acetate, manganese oxalate or manganese nitrate, or a combination of at least two of them; and the soluble cobalt salt includes any one of cobalt sulfate, cobalt acetate, cobalt oxalate or cobalt nitrate, or a combination of at least two of them.

7. The preparation method according to claim 4, characterized in that: The lithium source includes any one of lithium acetate, lithium nitrate, lithium carbonate, and lithium hydroxide, or a combination of at least two thereof; the molar ratio of the lithium-rich manganese-based precursor to the lithium source in terms of Li is greater than 1 and less than 1.

3.

8. The preparation method according to claim 4, characterized in that: The oxygen-containing atmosphere includes air or oxygen, or a mixed gas of the two in any proportion; the slightly negative pressure refers to the pressure in the sintering furnace being -100 to -1Pa, preferably -20 to -5Pa.

9. The preparation method according to claim 4, characterized in that: The sintering conditions are: firstly increase the temperature to 400-700°C at a heating rate of 0.1-10°C / min, keep the temperature for 1-8 hours, then increase the temperature to 800-1100°C at a heating rate of 0.1-10°C / min, keep the temperature for 10-20 hours.

10. A lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the two-phase dispersed lithium-manganese-rich positive electrode material according to any one of claims 1 to 3 or the two-phase dispersed lithium-manganese-rich positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

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