Modified lithium-rich manganese-based material, preparation method thereof, positive electrode sheet and battery

Abstract

The application relates to a modified lithium-rich manganese-based material, a preparation method thereof, a positive plate and a battery. The modified lithium-rich manganese-based material comprises a double-alkali-metal manganese-rich matrix, and the expression of the double-alkali-metal manganese-rich matrix is as follows: Li 1+x Na z Mn a Co b Ni c M 1‑a‑b‑c O 2+x+z‑y D y ; wherein, 0

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a modified lithium-rich manganese-based material, a preparation method thereof, a positive plate and a battery. BACKGROUND

[0002] Lithium ion batteries are widely used in 3C products, energy storage systems and power batteries due to their high energy density, long cycle life and good rate performance. How to further improve the energy density and cycle life of lithium ion batteries has become a research hotspot in the field of lithium ion batteries. As the core part of lithium ion batteries, the positive electrode material plays a crucial role in the preparation of high-performance lithium ion batteries.

[0003] Currently commonly used positive electrode materials include lithium cobalt oxide (LiCoO2, LCO), nickel cobalt manganese ternary material (LiNi x Co y Mn 1-x- y O2, NCM), nickel cobalt aluminum ternary material (LiNi x Co y Al 1-x-y O2, NCA), lithium iron phosphate (LiFePO4, LFP) and lithium manganate (LiMn2O4, LMO) and the like. Among them, the lithium-rich manganese-based material (Li-rich NCM) has high manganese content and low nickel and cobalt content, and has two charge compensation mechanisms of anion and cation, and has higher specific capacity and lower cost compared with cobalt-based materials and nickel-based materials. However, the traditional lithium-rich manganese-based material still has the problems of low first coulomb efficiency, poor rate performance, poor cycle stability and high cost, which limits the commercial application of the lithium-rich manganese-based material. SUMMARY

[0004] Therefore, it is necessary to provide a modified lithium-rich manganese-based material, a preparation method thereof, a positive plate and a battery to solve the problems of low first coulomb efficiency, poor rate performance, poor cycle stability and high cost of the traditional lithium-rich manganese-based material.

[0005] The above-mentioned purpose of the application is realized by the following technical scheme:

[0006] In a first aspect of the application, a modified lithium-rich manganese-based material is provided, which comprises a double-alkali metal manganese-rich matrix.

[0007] The expression of the double-alkali metal manganese-rich matrix is: Li 1+x Na z Mn a Co b Ni c M 1-a-b-c O 2+x+z-y Dy ;

[0008] wherein 0 < x < 0.5, 0 < z < 0.2, 0 ≤ y ≤ 0.1;

[0009] 0.6 ≤ a ≤ 0.75, 0 ≤ b ≤ 0.1, 0.25 ≤ c ≤ 0.4, 0 < 1-a-b-c ≤ 0.05;

[0010] The M element includes one or more of Ca, Al, Ba, Ce, Cr, Cu, Fe, K, La, Mg, Mo, Te, Nb, Sb, Sm, Ta, Ti, V, W, Y, Sn, Zn and Zr;

[0011] The D element includes one or more of F, Cl and S;

[0012] The double alkali metal and manganese-rich matrix has an O3 layered phase, a P2 layered phase and a spinel phase, and the total mass fraction of the P2 layered phase and the spinel phase in the double alkali metal and manganese-rich matrix is 1% to 15%.

[0013] In one of the embodiments, the P2 layered phase is uniformly dispersed in the double alkali metal and manganese-rich matrix and is in close contact with the O3 layered phase;

[0014] The distribution concentration of the spinel phase gradually decreases in the direction from the surface of the double alkali metal and manganese-rich matrix to the inside.

[0015] In one of the embodiments, the X-ray diffraction pattern of the double alkali metal and manganese-rich matrix satisfies the following conditions:

[0016] (1) has a (003) crystal face diffraction peak belonging to the O3 layered phase at 2θ = 18° to 19°;

[0017] (2) has a (104) crystal face diffraction peak belonging to the O3 layered phase at 2θ = 43° to 46°, and has a shoulder peak or broadening belonging to the spinel phase on the left side of the (104) crystal face diffraction peak;

[0018] (3) has a diffraction peak belonging to the P2 layered phase at 2θ = 15.2° to 16.2°;

[0019] (4) has a superlattice diffraction peak belonging to Li2MnO3 at 2θ = 20° to 23°.

[0020] In one of the embodiments, the M element includes one or more of Nb, W, Mo, Sb, Cr and Zr.

[0021] In one embodiment, the modified lithium-rich manganese-based material further comprises a coating layer loaded on the double alkali metal manganese-rich matrix, the coating layer comprising one or more of phosphate, fluoride and oxide containing an R element, the R element comprising one or more of Li, Na, K, V, Cr, Mn, Co, Ni, Mg, Al, Zr, W, Mo, Ce, La and Y.

[0022] In a second aspect, the application provides a method for preparing the modified lithium-rich manganese-based material as described above, comprising the following steps:

[0023] mixing a manganese-rich precursor, a lithium source, a sodium source and a dopant to perform a first sintering treatment to obtain a first intermediate;

[0024] dispersing the first intermediate in a lithium salt solution to perform an ion exchange treatment, and performing a solid-liquid separation treatment and a drying treatment to obtain a second intermediate;

[0025] performing a second sintering treatment on the second intermediate to obtain a double alkali metal manganese-rich matrix;

[0026] wherein the dopant comprises an M source, or the dopant comprises an M source and a D source;

[0027] a mass ratio of lithium elements in the lithium salt solution to the first intermediate is (0.05-0.2):100;

[0028] a sintering temperature of the second sintering treatment is 300-700°C.

[0029] In one embodiment, the lithium salt in the lithium salt solution comprises one or more of lithium hydroxide, lithium nitrate, lithium acetate, lithium oxalate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide and lithium bis(oxalato)borate.

[0030] In one embodiment, a mass ratio of water in the lithium salt solution to the first intermediate is (1-5):1.

[0031] In one embodiment, conditions of the ion exchange treatment comprise a temperature of 0-25°C and a time of 1-10 min.

[0032] In one embodiment, the second sintering treatment on the second intermediate comprises the following steps:

[0033] holding the second intermediate at 300-700°C for 3-15 h to obtain the double alkali metal manganese-rich matrix; or

[0034] mixing the second intermediate and a coating agent, and holding at 300-700°C for 3-15 h to form a coating layer on the double alkali metal manganese-rich matrix.

[0035] The coating agent includes one or more of phosphates, fluorides and oxides containing R elements, the R elements including one or more of Li, Na, K, V, Cr, Mn, Co, Ni, Mg, Al, Zr, W, Mo, Ce, La and Y.

[0036] In one of the embodiments, the manganese-rich precursor includes one or more of oxides, hydroxides, salt compounds containing nickel elements, cobalt elements and manganese elements.

[0037] In one of the embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium acetate, lithium oxalate, lithium chloride and lithium fluoride.

[0038] In one of the embodiments, the sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium sulfate, sodium oxalate, sodium acetate, sodium chloride and sodium fluoride.

[0039] In one of the embodiments, the M source includes one or more of oxides, hydroxides and salt compounds containing M elements, the M elements including one or more of Ca, Al, Ba, Ce, Cr, Cu, Fe, K, La, Mg, Mo, Te, Nb, Sb, Sm, Ta, Ti, V, W, Y, Sn, Zn and Zr.

[0040] In one of the embodiments, the D source includes one or more of fluorides, chlorides and sulfides.

[0041] In one of the embodiments, the first sintering treatment includes the following steps:

[0042] holding at 300-800℃ for 0-10h and holding at 800-1000℃ for 4-20h.

[0043] In a third aspect, the present application provides a positive electrode sheet, which comprises the positive electrode material as described above.

[0044] In a fourth aspect, the present application provides a secondary battery, which comprises the positive electrode sheet as described above.

[0045] The present application has at least the following beneficial effects:

[0046] The modified lithium-rich manganese-based material provided by the present application includes a double-alkali manganese-based matrix, which introduces Na + replacing part of Li + , so that part of the O3 layered phase of the matrix is converted into a unique P2 layered phase, thereby reducing the cost while improving the initial coulombic efficiency of the material. Meanwhile, through the sodium-lithium exchange reaction, part of the Na in the P2 layered phase is+ substituted by Li + and alkali metal vacancies, so as to form a spinel phase with more stable structure, and the Na + content in the material is reduced, and residual alkali is reduced. Compared with a spinel coating layer constructed in situ on the surface of the material, the P2 layered phase and the spinel phase are gradually introduced into the substrate by ion exchange reaction in the present application, the interface compatibility between different crystal phases is good, the damage to the surface morphology and internal crystal structure of the substrate is small, and the lithium ion transmission kinetics is accelerated, so as to effectively improve the rate performance, structural stability and cycle stability. Therefore, the dual alkali metal manganese-rich substrate of the present application has a three-phase composite structure of O3 layered phase-P2 layered phase-spinel phase, and cooperates with appropriate M elements and D elements, so that the modified lithium-rich manganese-based material has the advantages of high first coulomb efficiency, high discharge capacity, good rate performance, excellent cycle stability and low cost, and is very suitable as a positive electrode material of a secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application, more completely understand the present application and its beneficial effects, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0048] Figure 1 It is a flowchart of the preparation method of the modified lithium-rich manganese-based material in an embodiment;

[0049] Figure 2 It is an XRD graph of the modified lithium-rich manganese-based material of Example 2;

[0050] Figure 3 It is an XRD graph of the modified lithium-rich manganese-based material of Comparative Example 3;

[0051] Figure 4 It is an XRD graph of the modified lithium-rich manganese-based material of Comparative Example 6;

[0052] Figure 5 It is a first circle charge-discharge curve graph of the coin-type half battery of Example 2;

[0053] Figure 6 It is a first circle charge-discharge curve graph of the coin-type half battery of Comparative Example 3;

[0054] Figure 7 It is a cycle discharge capacity change graph of the coin-type half batteries of Example 2 and Comparative Example 3. DETAILED DESCRIPTION

[0055] To facilitate understanding of this application, the following detailed description is provided in conjunction with specific embodiments. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0057] In this application, "and / or" means any and all combinations of one or more of the related listed items. "At least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two, three, etc., unless otherwise expressly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0058] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all subranges to which they are included.

[0059] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0061] The temperature parameters in the present application, unless otherwise specified, allow for constant temperature treatment and also allow for variations within a certain temperature range. It should be understood that the constant temperature treatment allows for fluctuations within the accuracy range controlled by the instrument. Fluctuations within a range of, for example, ±5°C, ±4°C, ±3°C, ±2°C, ±1°C are allowed.

[0062] In the present application, room temperature refers to indoor temperature, normal temperature or general temperature. Generally, the range of room temperature can be any one of the following temperature ranges: 23°C ± 2°C, 25°C ± 5°C or 20°C ± 5°C.

[0063] In the present application, the layered transition metal oxide is a layered structure formed by alternating arrangement of transition metal layers and alkali metal layers, and can be divided into P2 layered phase and O3 layered phase according to the stacking order of oxygen atoms. Among them, P and O respectively represent the alkali metal coordination environment is a prism and an octahedron, and the numbers 2 and 3 represent the stacking number of the minimum repeating unit of the oxygen layer. Compared with the O3 layered phase, the P2 layered phase has a lower diffusion barrier and a higher ionic conductivity, which is beneficial to improve the first coulombic efficiency and rate performance of the material, and the electrical performance is more excellent. In addition, the P2 layered phase has a high theoretical capacity of 250 mAh / g and a high operating voltage, and is considered as an ideal choice for the next generation of lithium ion battery cathode materials. However, the P2 layered phase also has the problems of high cost due to large amount of lithium, low first coulombic efficiency, poor cycle performance and the like. + No oxygen layer slip phenomenon occurs during the deintercalation process, and the structure is more stable.

[0064] The lithium-rich manganese-based material can be regarded as a continuous solid solution composed of Li2MnO3 and LiMO2 in different proportions, where M is Ni, Co or Mn. The lithium-rich manganese-based material has high manganese content and low nickel and cobalt content, and has lower cost compared with cobalt-based materials (such as lithium cobaltate) and high-nickel-based materials; the lithium-rich manganese-based material has two charge compensation mechanisms of anion and cation, the theoretical specific capacity reaches more than 250 mAh / g, and has advantages of high operating voltage, high safety and small pollution, and is considered as an ideal choice for the next generation of lithium ion battery cathode materials. However, the lithium-rich manganese-based material also has the problems of high cost due to large amount of lithium, low first coulombic efficiency, poor cycle performance and the like.

[0065] In terms of cost, the lithium content in the lithium-rich manganese-based material is 20%~50% higher than that in the conventional nickel-cobalt-manganese ternary material, and the cost advantage brought by low-price manganese is gradually weakened due to the increase in the price of lithium salt. In terms of material performance, the lithium-rich manganese-based material will release lattice oxygen during charging and discharging, and its layered structure will change to spinel structure and then to rock salt structure, resulting in a decrease in structural stability. These changes in crystal structure result in many problems in the electrochemical performance of the lithium-rich manganese-based material, such as large first irreversible capacity loss (i.e. low first coulombic efficiency), serious capacity and voltage attenuation due to structural degradation during the cycle process, poor rate performance due to poor kinetics, and poor high-temperature storage performance, which hinders the commercialization application process.

[0066] Based on this, the first aspect of the present application provides a modified lithium-rich manganese-based material to overcome the problems of low initial coulombic efficiency, poor rate performance, poor cycle performance and high cost of traditional lithium-rich manganese-based materials.

[0067] In some embodiments, the modified lithium-rich manganese-based material comprises a double-alkali metal manganese-rich matrix;

[0068] The expression of the double-alkali metal manganese-rich matrix is: Li 1+x Na z Mn a Co b Ni c M 1-a-b-c O 2+x+z-y D y ;

[0069] Wherein, 0 < x < 0.5, 0 < z < 0.2, 0 ≤ y ≤ 0.1;

[0070] 0.6 ≤ a ≤ 0.75, 0 ≤ b ≤ 0.1, 0.25 ≤ c ≤ 0.4, 0 < 1-a-b-c ≤ 0.05;

[0071] The M element includes one or more of Ca, Al, Ba, Ce, Cr, Cu, Fe, K, La, Mg, Mo, Te, Nb, Sb, Sm, Ta, Ti, V, W, Y, Sn, Zn and Zr;

[0072] The D element includes one or more of F, Cl and S;

[0073] The double-alkali metal manganese-rich matrix has an O3 layered phase, a P2 layered phase and a spinel phase, and the total mass fraction of the P2 layered phase and the spinel phase in the double-alkali metal manganese-rich matrix is 1% to 15%.

[0074] The modified lithium-rich manganese-based material provided by the present application includes a double-alkali metal manganese-rich matrix, which introduces Na + into the traditional lithium-rich manganese-based material to replace part of Li + , so that the O3 layered phase part of the matrix is converted into a unique P2 layered phase, thereby reducing the cost while improving the initial coulombic efficiency of the material. At the same time, through the sodium-lithium exchange reaction, part of Na + in the P2 layered phase is replaced by Li + and an alkali metal vacancy, thereby forming a spinel phase with more stable structure, and the Na +The content of the residual alkali is reduced. Compared with the spinel coating layer constructed in situ on the surface of the material, the application gradually introduces an appropriate amount of P2 layered phase and spinel phase in the matrix through ion exchange reaction, the interface compatibility between different crystal phases is good, the damage to the surface morphology and internal crystal structure of the matrix is small, and the lithium ion transmission kinetics is accelerated, thereby effectively improving the rate performance, structural stability and cycle stability. Therefore, the double alkali metal manganese-rich matrix has a three-phase composite structure of O3 layered phase-P2 layered phase-spinel phase, and is doped with an appropriate amount of M elements and D elements, so that the modified lithium-rich manganese-based material has the advantages of high first coulomb efficiency, high discharge capacity, good rate performance, excellent cycle stability and low cost, and is very suitable as a positive electrode material for secondary batteries.

[0075] Understandably, x, y, z, a, b and c respectively represent the stoichiometric ratio of the corresponding element in the double alkali metal manganese-rich matrix. Limiting the content of each element is beneficial to reducing the negative effects of introducing Na + , avoiding problems such as too high residual alkali in the material, poor structural stability, and decreased kinetics.

[0076] As an example, the value of x includes but is not limited to 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 or 0.49. Further optionally, 0.2≤x≤0.3.

[0077] As an example, the value of z includes but is not limited to 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18 or 0.20. Further optionally, 0.05≤z≤0.15.

[0078] In the application, by limiting the values of x and z, the molar ratio of Li + and Na + in the matrix can be controlled, which is beneficial to adjusting the mass ratio of the three crystal phases and avoiding the defects of too much Li + Na + and being unable to achieve the purpose of reducing the cost, and too little Li + Na + and causing the defects of low discharge capacity and too high surface residual alkali.

[0079] As an example, the value of y includes but is not limited to 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10. Further optionally, 0≤y≤0.05.

[0080] In the present application, the appropriate amount of D element is doped, which is conducive to promoting the anion redox reversibility and improving the initial coulombic efficiency.

[0081] As an example, the value of a includes but is not limited to 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.71, 0.72, 0.73, 0.74 or 0.75. Further optionally, 0.63≤a≤0.7.

[0082] As an example, the value of b includes but is not limited to 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1. Further optionally, 0.01≤b≤0.08.

[0083] As an example, the value of c includes but is not limited to 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.32, 0.34, 0.36, 0.38 or 0.40. Further optionally, 0.28≤x≤0.35.

[0084] In the present application, by limiting the values of a and c, the molar ratio of Ni and Mn in the double alkali metal manganese-rich oxide can be limited, on the one hand, it can avoid the influence of more Ni and less Mn on the embedding of Na + , thereby playing a role in reducing surface residual alkali and improving structural stability, on the other hand, it can reduce the defects caused by the kinetic decline of less Ni and more Mn.

[0085] As an example, the value of 1-a-b-c includes but is not limited to 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045 or 0.05. Further optionally, 0.005≤1-a-b-c≤0.025.

[0086] In the present application, the M element is doped, which is conducive to improving the structural stability of the double alkali metal manganese-rich matrix and promoting the capacity. Limiting 1-a-b-c to below 0.05 can ensure that the transition metal ions have a suitable doping amount, and avoid the defects of producing impurities and causing the discharge capacity to decline due to too high doping amount.

[0087] It can be understood that the M element can be selected from any one of Ca, Al, Ba, Ce, Cr, Cu, Fe, K, La, Mg, Mo, Te, Nb, Sb, Sm, Ta, Ti, V, W, Y, Sn, Zn and Zr, and can also be selected from a combination of two or more of the above elements. Further optionally, the M element includes one or more of Nb, W, Mo, Sb, Cr and Zr. On the one hand, the above elements doped at the surface interface can play a role in refining the grain, and on the other hand, the above elements doped in the bulk phase can play a role in stabilizing the stability of the bulk phase structure. Further optionally, the further optional Nb is further optionally.

[0088] It can be understood that the D element can be further optionally selected from F, Cl and S, and can also be selected from a combination of two or more of the above non-metallic elements. Further optionally, the D element is F.

[0089] Optionally, the P2 layered phase is uniformly dispersed in the double-alkali manganese-rich matrix and is in close contact with the O3 layered phase; along a direction from the surface of the double-alkali manganese-rich matrix to the inside, the distribution concentration of the spinel phase gradually decreases.

[0090] It can be understood that in the double-alkali manganese-rich matrix, the mass fraction of the O3 layered phase reaches 85% or more, which is the main crystal structure of the matrix. The P2 layered phase is formed by the introduction of sodium elements, can be uniformly dispersed in the matrix, and is in close contact with the O3 layered phase. The spinel phase is converted from part of the P2 layered phase through a surface-to-interior sodium-lithium exchange reaction, and its distribution concentration decreases in a gradient from the surface of the matrix to the inside of the matrix. The spinel phase has a very high distribution concentration on the surface of the matrix, and it can be approximately considered that the surface of the matrix has a continuous or discontinuous spinel coating layer.

[0091] As an example, the total mass fraction of the P2 layered phase and the spinel phase in the double-alkali manganese-rich matrix includes but is not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, and is further optionally 8% to 12%.

[0092] In this application, according to the formation mechanism of the three-phase composite structure, the spinel phase is converted from part of the P2 layered phase through a sodium-lithium exchange reaction, and the P2 layered phase is formed by replacing part of Li + with Na + from part of the O3 layered phase, so the total mass fraction of the P2 layered phase and the spinel phase in the double-alkali manganese-rich matrix can be estimated according to the Na + content before the sodium-lithium exchange reaction.

[0093] The total mass fraction of the P2 layered phase and the spinel phase is too low to achieve the effect of reducing cost and increasing efficiency. The higher the total mass fraction of the P2 layered phase and the spinel phase, the less the amount of lithium ions, but it will affect the capacity of the modified lithium-rich manganese-based material. Limiting the total mass fraction of the P2 layered phase and the spinel phase to 1% to 15% can well balance the cost, the first coulombic efficiency, the rate performance and the cycle performance, and greatly improve the comprehensive performance of the modified lithium-rich manganese-based material.

[0094] Optionally, the X-ray diffraction pattern (XRD pattern) of the double-alkali manganese-rich matrix satisfies the following conditions:

[0095] (1) having a (003) crystal face diffraction peak attributed to the O3 layered phase at 2θ = 18° to 19°;

[0096] (2) having a (104) crystal face diffraction peak attributed to the O3 layered phase at 2θ = 43° to 46°, and having a shoulder peak or broadening attributed to the spinel phase on the left side of the (104) crystal face diffraction peak;

[0097] (3) having a diffraction peak attributed to the P2 layered phase at 2θ = 15.2° to 16.2°;

[0098] (4) having a superlattice diffraction peak attributed to Li2MnO3 at 2θ = 20° to 23°.

[0099] From the XRD pattern of the double-alkali manganese-rich matrix, it can be known that the double-alkali manganese-rich matrix has a three-phase composite of the O3 layered phase, the P2 layered phase and the spinel phase.

[0100] Optionally, the modified lithium-rich manganese-based material further comprises a coating layer loaded on the double-alkali manganese-rich matrix, and the coating layer comprises one or more of phosphates, fluorides and oxides containing R elements, and the R elements comprise one or more of Li, Na, K, V, Cr, Mn, Co, Ni, Mg, Al, Zr, W, Mo, Ce, La and Y.

[0101] Selecting phosphates as the coating agent can construct an ion conductor coating layer on the double-alkali manganese-rich matrix, which not only has good structural stability, can reduce interface side reactions, inhibit the release of material lattice oxygen, improve the structural stability and long cycle performance of the material, but also has three-dimensional ion diffusion channels, which can not only conduct Li + but also conduct Na + , has excellent kinetics, ensures the rapid transmission of Li + and Na + , plays a role in increasing the discharge capacity, improving the ion diffusion rate and improving the rate performance. At the same time, fluorides and oxides as coating agents help to inhibit interface side reactions and improve long cycle performance.

[0102] Optionally, the coating layer is further optionally one or more of aluminum phosphate, aluminum oxide and zirconium fluoride.

[0103] Optionally, the mass ratio of the double-alkali manganese-rich matrix and the coating layer is 100:(0.05-2).

[0104] For example, the mass ratio of the double-alkali manganese-rich matrix and the coating layer includes but is not limited to 100:0.05, 100:0.08, 100:0.1, 100:0.2, 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8 or 100:2, and is further optionally 100:(0.5-1.5).

[0105] Understandably, the coating of the coating layer on the matrix can be partial coating or complete coating. The partial coating of the coating layer on the matrix means that the coating layer is loaded on part of the surface of the matrix to form a dispersed island structure. The complete coating of the coating layer on the core means that the coating layer is loaded on all surfaces of the matrix to form a continuous film layer structure, and the effect of improving the structural stability and long cycle performance is more significant. By limiting the mass ratio of the double-alkali manganese-rich matrix and the coating layer, the coating layer can form a good coating effect on the surface of the matrix, thereby improving the electrochemical performance of the material.

[0106] Optionally, the thickness of the coating layer is 5-20 nm.

[0107] For example, the thickness of the coating layer includes but is not limited to 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm.

[0108] Optionally, the D50 particle size of the modified lithium-rich manganese-based material is 2-15 μm.

[0109] For example, the D50 particle size of the modified lithium-rich manganese-based material includes but is not limited to 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0110] In a second aspect, the application provides a preparation method of a modified lithium-rich manganese-based material, which is used to prepare the modified lithium-rich manganese-based material as described above.

[0111] Please refer to Figure 1 which is a flowchart of the preparation method of the modified lithium-rich manganese-based material in an embodiment. As shown in Figure 1 the preparation method of the modified lithium-rich manganese-based material includes the following steps:

[0112] S100: mixing the manganese-rich precursor, the lithium source, the sodium source and the dopant, performing a first sintering treatment to obtain a first intermediate;

[0113] S200: dispersing the first intermediate in a lithium salt solution to perform an ion exchange treatment, and performing a solid-liquid separation treatment and a drying treatment to obtain a second intermediate;

[0114] S300: performing a second sintering treatment on the second intermediate to obtain a double-alkali manganese-rich matrix;

[0115] The dopant comprises an M source, or the dopant comprises an M source and a D source;

[0116] The mass ratio of lithium elements in the lithium salt solution to the first intermediate is (0.05-0.2):100;

[0117] The sintering temperature of the second sintering treatment is 300-700 DEG C.

[0118] It has been reported that a layer of spinel structure with more stable structure is constructed in situ on the surface of a traditional lithium-rich manganese-based material to improve the rate performance and slow down the voltage decay. The in-situ construction method mainly includes solid-phase coating, wet coating and gas-phase coating. However, the solid-phase coating cannot guarantee the uniformity of the spinel structure coating and the interface compatibility. The wet coating and the gas-phase coating often need to be performed in a redox environment or an acidic environment, which has a serious destructive effect on the material surface, causing problems such as a decrease in the energy density, a deterioration of the high-temperature performance and the like.

[0119] Compared with the in-situ construction method for forming a coating layer with a spinel structure, the present application is to mix the manganese-rich precursor, the lithium source, the sodium source and the dopant, and then perform a first sintering treatment. In this way, the M elements and the D elements are doped, and an appropriate amount of Na + is introduced at the same time, which promotes the first intermediate to form a double-phase composite structure with an O3 layered phase-P2 layered phase. Then, the ion exchange reaction is performed on the first intermediate in a lithium salt solution. By controlling the mass ratio of lithium elements in the lithium salt solution to the first intermediate, and through the solid-liquid separation treatment, the drying treatment and the second sintering treatment at a suitable temperature, part of the P2 layered phase can be converted into a spinel phase, so as to form a triple-phase composite structure of an O3 layered phase-P2 layered phase-spinel phase. The preparation method provided by the present application can guarantee good interface compatibility between different crystal phases, and does not need to be performed in a redox environment or an acidic environment, which has little destructive effect on the surface morphology and the internal crystal structure of the material. Therefore, the modified lithium-rich manganese-based material with high initial coulombic efficiency, high discharge capacity, good rate performance, excellent cycle stability and low cost can be prepared, which is very suitable for large-scale production and commercial application.

[0120] The preparation method of the modified lithium-rich manganese-based material is described in detail below in a step-by-step manner.

[0121] S100: mixing the manganese-rich precursor, the lithium source, the sodium source and the dopant, performing a first sintering treatment to obtain a first intermediate.

[0122] Optionally, the manganese-rich precursor includes one or more of oxides, hydroxides, and salt compounds containing nickel elements, cobalt elements and manganese elements, wherein the salt compounds include one or more of carbonates, oxalates, acetates, acetates and fluorinated salts. Further optionally, the manganese-rich precursor is a hydroxide containing nickel elements, cobalt elements and manganese elements.

[0123] Optionally, the molar ratio of manganese elements, cobalt elements and nickel elements in the manganese-rich precursor is (0.6-0.75):(0-0.1):(0.25-0.4), i.e. the molar ratio of manganese elements, cobalt elements and nickel elements in the manganese-rich precursor is the same as that in the double-alkali manganese-rich matrix.

[0124] Optionally, the lithium source includes one or more of lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium nitrate (LiNO3), lithium sulfate (Li2SO4), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium chloride (LiCl) and lithium fluoride (LiF), and further optionally lithium carbonate (Li2CO3). The raw material of the lithium source can contain combined water, such as lithium hydroxide monohydrate (LiOH•H2O) and lithium acetate monohydrate (CH3COOLi•H2O), or can not contain combined water, such as anhydrous lithium carbonate, anhydrous lithium hydroxide, anhydrous lithium acetate, etc.

[0125] Optionally, the sodium source includes one or more of sodium carbonate (Na2CO3), sodium hydroxide (NaOH), sodium sulfate (Na2SO4), sodium oxalate (Na2C2O4), sodium acetate (CH3COONa), sodium chloride (NaCl) and sodium fluoride (NaF), and further optionally sodium carbonate (Na2CO3). The raw material of the sodium source can also contain combined water, such as sodium carbonate monohydrate or sodium carbonate decahydrate, or can not contain combined water, such as anhydrous sodium carbonate.

[0126] Optionally, the M source includes one or more of oxides, hydroxides and salt compounds containing the M element, wherein the salt compounds include one or more of carbonates, oxalates, acetates, acetates and fluorinated salts. Further optionally, the M source is an oxide containing the M element, such as one or more of CaO, Al2O3, BaO, CeO2, Cr2O3, CuO, Fe2O3, K2O, La2O3, MgO, MoO3, TeO2, Nb2O5, Sb2O5, Sm2O3, Ta2O5, TiO2, V2O5, WO3, Y2O5, SnO2, ZnO and ZrO2. Still further optionally, the M source is one or more of Nb2O5, WO3, MoO3, Sb2O5, Cr2O3and ZrO2.

[0127] Optionally, the D source includes one or more of fluorides, chlorides and sulfides. Among them, the fluoride includes one or more of NaF, LiF, KF and NH4F; the chloride includes one or more of NaCl, LiCl, KCl and NH4Cl; and the sulfide includes one or more of Li2S, Na2S and CH4N2S. Further optionally, the D source is a fluoride. Still further optionally, the D source is NH4F.

[0128] Optionally, the molar ratio of lithium element in the lithium source to transition metal element in the manganese-rich precursor is d / (a+b+c)=1.1~1.5; the molar ratio of sodium element in the sodium source to transition metal element in the manganese-rich precursor is e / (a+b+c)=0.03~0.3; the molar ratio of M element in the M source to transition metal element in the manganese-rich precursor is (1-a-b-c) / (a+b+c)=0~0.05; and the molar ratio of D element in the D source to transition metal element in the manganese-rich precursor is y / (a+b+c)=0~0.1.

[0129] Na in the first intermediate + The content is a key factor to determine the total mass fraction of P2 layered phase and spinel phase. Since the ionic radius of Na + is larger than that of Li + , it is more difficult for Na + to enter the alkali metal site during the synthesis of the first intermediate than for Li + , and an additional concentration difference is needed to provide a diffusion driving force. At the same time, Li + and Na + in the first intermediate will react with Li + and H +The ion exchange is performed to reduce the alkali metal content in the second intermediate and finally affect the content of the three crystal phases in the double alkali metal-rich manganese substrate. Therefore, the sodium source should be appropriately excessive so that the alkali metal content of the second intermediate tends to be consistent with the alkali metal content of the target expression, and the total mass fraction of the P2 layered phase and the spinel phase in the double alkali metal-rich manganese substrate is 1%~15%.

[0130] Optionally, the first sintering treatment adopts a segmented sintering treatment, which includes the following steps: holding at 300℃~800℃ for 0h~10h, and holding at 800℃~1000℃ for 4h~20h.

[0131] The sintering temperature of the first sintering treatment should not be too high, because at a too high sintering temperature, the sintering product will grow excessively, resulting in an increase in the particle size of the first intermediate and an excessively high density, which is not conducive to the subsequent ion exchange treatment and the formation of the spinel phase, thereby negatively affecting the electrochemical performance.

[0132] As an example, the first sintering temperature of the first sintering treatment includes but is not limited to 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, further optionally 350℃~750℃, and more further optionally 450℃~550℃.

[0133] As an example, the holding time of the first sintering treatment at the first sintering temperature includes but is not limited to 0h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, further optionally 4h~8h.

[0134] As an example, the second sintering temperature of the first sintering treatment includes but is not limited to 800℃, 820℃, 850℃, 880℃, 900℃, 920℃, 950℃, 980℃ or 1000℃, further optionally 900℃~1000℃, and more further optionally 940℃~960℃.

[0135] As an example, the holding time of the first sintering treatment at the second sintering temperature includes but is not limited to 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, further optionally 8h~15h.

[0136] Optionally, the heating rate from room temperature to the first sintering temperature, and the heating rate from the first sintering temperature to the second sintering temperature in the first sintering process are each independently 1 °C / min to 10 °C / min, including but not limited to 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min.

[0137] Optionally, the first sintering process is performed in an oxygen-containing atmosphere, such as an air atmosphere and an oxygen atmosphere.

[0138] S200: performing ion exchange treatment by dispersing the first intermediate in a lithium salt solution, and performing solid-liquid separation treatment and drying treatment to obtain a second intermediate.

[0139] Na + The ionic radius of Li + The Na + in the surface layer of the P2 layered phase of the first intermediate can directly undergo sodium-lithium exchange. As the ion exchange reaction proceeds, the Na + in the interior of the first intermediate will also participate in sodium-lithium exchange, and the amount of ion exchange gradually decreases from the surface layer to the interior. Through ion exchange treatment, on the one hand, the content of Na + in the material can be reduced to reduce residual alkali, and on the other hand, Li + occupies the Na + site, and after the second sintering treatment, the part of the P2 layered phase that has undergone ion exchange is finally converted into spinel phase, which is beneficial to improve the interface stability and structural stability and accelerate the lithium ion transport kinetics. In addition, the ion exchange treatment is performed in a neutral or alkaline lithium salt solution, which will not cause any structural damage to the material.

[0140] Optionally, the lithium salt in the lithium salt solution includes one or more of lithium hydroxide (LiOH), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), and lithium bis(oxalato)borate (LiBC4O8, LiBOB), further optionally one or more of lithium hydroxide (LiOH), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), and lithium chloride (LiCl), and more further optionally lithium hydroxide (LiOH).

[0141] It can be understood that the raw material of lithium salt in the lithium salt solution can contain combined water, such as lithium hydroxide monohydrate (LiOH H2O) and lithium acetate monohydrate (CH3COOLi H2O), etc., or can not contain combined water, such as anhydrous lithium carbonate, anhydrous lithium hydroxide, anhydrous lithium acetate, etc. The lithium salt in the lithium salt solution has good water solubility and can be ionized in the aqueous solution to form a suitable concentration of Li + , which is conducive to the sufficient ion exchange reaction with the first intermediate.

[0142] Optionally, the pH value of the lithium salt solution is 7-13.

[0143] As an example, the pH value of the lithium salt solution includes but is not limited to 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or 13, and is further optionally 7-10.

[0144] Optionally, the mass ratio of lithium element in the lithium salt solution to the first intermediate is (0.05-0.2):100.

[0145] By controlling the mass ratio of lithium element in the lithium salt solution to the first intermediate, it can be ensured that the lithium salt solution contains a suitable concentration of Li + , which is conducive to controlling the ion exchange rate of Li + and Na + , so that the material contains an appropriate amount of alkali metal vacancies, and promotes the formation of spinel phase, thereby forming a modified lithium-rich manganese-based material with a three-phase composite structure.

[0146] As an example, the mass ratio of lithium element in the lithium salt solution to the intermediate includes but is not limited to 0.05:100, 0.06:100, 0.07:100, 0.08:100, 0.09:100, 0.10:100, 0.11:100, 0.12:100, 0.13:100, 0.14:100, 0.15:100, 0.16:100, 0.17:100, 0.18:100, 0.19:100 or 0.2:100, and is further optionally (0.08-0.12):100.

[0147] Optionally, the mass ratio of water in the lithium salt solution to the first intermediate is (1-5):1.

[0148] By controlling the mass ratio of solvent in the lithium salt solution to the first intermediate, it can be ensured that the lithium salt solution contains a suitable concentration of Li + and H + , which is conducive to controlling the ion exchange rate, thereby ensuring that the material has excellent structural stability and cycle stability.

[0149] As an example, the water in the lithium salt solution can be tap water, deionized water, pure water, ultrapure water, distilled water, or reverse osmosis water, and further can be deionized water or pure water to reduce the introduction of impurities.

[0150] As an example, the mass ratio of the water in the lithium salt solution to the first intermediate includes but is not limited to 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1, and further can be (1-2):1.

[0151] Optionally, the conditions of the ion exchange treatment include a temperature of 0°C to 25°C and a time of 1 min to 10 min.

[0152] The temperature of the ion exchange treatment should not be too high, because if the temperature is too high, the exchange degree of the alkali metal ions and Li + and H + in the lithium salt solution is too high, especially the sodium hydrogen exchange is excessive, which reduces the cycle stability; at the same time, the ion exchange treatment time is too long, which reduces the actual production efficiency and causes the spinel phase content to be too high; and the ion exchange treatment time is too short, and the lithium-sodium exchange effect is not obvious.

[0153] As an example, the temperature of the ion exchange treatment can be 0°C, 2°C, 5°C, 8°C, 10°C, 12°C, 15°C, 18°C, 20°C, 22°C, 24°C, or 25°C, and further can be 5°C to 15°C.

[0154] As an example, the time of the ion exchange treatment can be 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min, and further can be 2 min to 8 min.

[0155] Optionally, the method of the solid-liquid separation treatment includes one or more of suction filtration, pressure filtration, and centrifugation, and further can be suction filtration.

[0156] Optionally, the drying treatment includes the following steps: drying at 90°C to 200°C for 10 h to 24 h.

[0157] As an example, the method of the drying treatment includes one or more of air drying and vacuum drying.

[0158] As an example, the temperature of the drying treatment can be 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C, and further can be 90°C to 150°C.

[0159] As an example, the drying treatment can be performed for 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, or 22 h, 24 h, further optionally 12 h-18 h.

[0160] S300: performing a second sintering treatment on the second intermediate to obtain a double-alkali manganese-rich matrix;

[0161] Optionally, the sintering temperature of the second sintering treatment is 300-700 °C.

[0162] If the sintering temperature of the second sintering treatment is too low, the alkali metal vacancies and oxygen vacancies cannot be repaired, and it is difficult to form spinel phase. If the sintering temperature of the second sintering treatment is too high, the alkali metal vacancies in the material will be converted into inert rock salt phase at the high sintering temperature, thereby causing the discharge capacity to decrease. By controlling the sintering temperature of the second sintering treatment, the modified lithium-rich manganese-based material can be prompted to form a three-phase composite structure with O3 layered phase-P2 layered phase-spinel phase.

[0163] Optionally, the second sintering treatment on the second intermediate includes the following steps: heating the second intermediate at 300-700 °C for 3-15 h to obtain a double-alkali manganese-rich matrix.

[0164] As an example, the sintering temperature of the second sintering treatment can be 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, or 800 °C, further optionally 350-750 °C, and more further optionally 450-550 °C.

[0165] As an example, the holding time of the second sintering treatment can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, further optionally 8-12 h.

[0166] Optionally, in the second sintering treatment, the heating rate from room temperature to the sintering temperature is 1-10 °C / min, for example, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min, further optionally 2-6 °C / min.

[0167] Optionally, the second sintering treatment is performed in an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere.

[0168] Optionally, the second intermediate is subjected to a second sintering process, including the following steps: mixing the second intermediate and a coating agent, and keeping at 300-700℃ for 3-15h to form a coating layer on the double-alkali manganese-rich substrate; wherein the coating agent includes one or more of phosphate, fluoride and oxide containing an R element, the R element including one or more of Li, Na, K, V, Cr, Mn, Co, Ni, Mg, Al, Zr, W, Mo, Ce, La and Y.

[0169] Optionally, the coating agent includes one or more of aluminum phosphate, aluminum oxide and zirconium fluoride.

[0170] In a third aspect, the present application provides a positive electrode sheet, including the positive electrode material as described above.

[0171] Optionally, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer covering the positive electrode current collector.

[0172] It can be understood that the positive electrode active layer covers at least one surface of the positive electrode current collector, which can cover only one surface, or cover two opposite surfaces at the same time, to form a structure in which the positive electrode active layer, the positive electrode current collector and the positive electrode active layer are sequentially stacked.

[0173] Optionally, the positive electrode current collector includes a metal foil or a composite current collector. The metal foil can be an aluminum foil. The composite current collector includes a polymer substrate and a metal layer formed on the polymer substrate. The polymer substrate can be made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE). The metal layer can be made of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0174] Optionally, the positive electrode active layer includes a positive electrode material, a binder and a conductive agent. The positive electrode material is used for deintercalation of Li + and Na + , the binder is used to improve the bonding strength between the positive electrode active layer and the positive electrode current collector, and the conductive agent is used to improve the conductivity of the positive electrode active layer.

[0175] Optionally, the positive electrode material includes the modified lithium-rich manganese-based material as described above, or the modified lithium-rich manganese-based material prepared by the preparation method of the modified lithium-rich manganese-based material as described above.

[0176] It is appreciated that the positive electrode material in the positive electrode active layer can be used alone, i.e., the modified lithium-rich manganese-based material described above is used alone, or two or more of them are used in combination, i.e., the modified lithium-rich manganese-based material described above is used in combination with at least one of the positive electrode materials known in the art. As an example, the positive electrode materials known in the art include, but are not limited to, lithium transition metal oxides, lithium-containing phosphates of olivine structure, and modified compounds of each of them. Among them, the lithium transition metal oxides include, but are not limited to, lithium cobalt oxides such as LiCoO2; lithium nickel oxides such as LiNiO2; lithium manganese oxides such as LiMnO2or LiMn2O4; lithium nickel cobalt oxides; lithium manganese cobalt oxides; lithium nickel manganese oxides; lithium nickel cobalt manganese oxides such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2(NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ); lithium nickel cobalt aluminum oxides such as LiNi 0.85 Co 0.15 Al 0.05 O2; and modified compounds of the above lithium transition metal oxides. The lithium-containing phosphates of olivine structure include, but are not limited to, lithium iron phosphate (LiFePO4, LFP), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, and the like.

[0177] Optionally, the binder includes at least one of polyvinylidene fluoride (PVDF), sodium alginate (SA), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), hydrogenated nitrile rubber (HNBR), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA).

[0178] Optionally, the conductive agent includes at least one of conductive carbon, super conductive carbon, acetylene black, carbon black, ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers.

[0179] Optionally, the method for preparing the positive electrode sheet comprises the following steps: dispersing the positive electrode material, the conductive agent and the binder in an organic solvent to prepare a positive electrode slurry; covering the positive electrode slurry on at least one surface of the positive electrode current collector, and then performing drying, rolling and cutting to obtain the positive electrode sheet. The organic solvent is selected from N-methyl pyrrolidone (NMP); the solid content of the positive electrode slurry is 20% to 50%; the temperature for drying is 100°C to 150°C, and the time for drying is 60 minutes to 120 minutes, and further optionally, the drying is performed at 120°C for 80 minutes.

[0180] In a fourth aspect, the application provides a secondary battery comprising the positive electrode sheet as described above.

[0181] It can be understood that the secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the charging and discharging of the battery, active ions (such as Li + , Na + ) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the short circuit of the positive electrode and the negative electrode, and at the same time to allow the active ions to pass through. The electrolyte is arranged between the positive electrode sheet and the negative electrode sheet, mainly to conduct the active ions.

[0182] Optionally, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer covering at least one surface of the negative electrode current collector. The negative electrode current collector comprises a metal foil or a composite current collector. The metal foil in the negative electrode current collector can be a copper foil. The composite current collector in the negative electrode current collector is basically the same as the composite current collector selected for the positive electrode current collector, and will not be described herein.

[0183] Optionally, the negative electrode active layer comprises a negative electrode material, a binder and a conductive agent. The negative electrode material comprises at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy material. The binder comprises at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). The conductive agent comprises at least one of conductive carbon, superconducting carbon, acetylene black, carbon black, ketjen black, carbon quantum dots, carbon nanotubes, graphene and carbon nanofibers.

[0184] It can be understood that the electrolyte in the secondary battery can be in a liquid state, a gel state or a full solid state.

[0185] Optionally, the electrolyte adopts an electrolyte solution, which includes a lithium salt and an organic solvent. The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium difluoroboric bisoxalate, lithium difluorophosphoric bisoxalate, and lithium tetrafluorophosphoric oxalate; and the organic solvent includes at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0186] Optionally, the electrolyte solution further includes an additive, such as a negative electrode film-forming additive, a positive electrode film-forming additive, an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature or low-temperature performance of the battery, and the like.

[0187] It can be understood that the separator can be a porous separator with good chemical stability and mechanical stability; at the same time, the separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, without particular limitation.

[0188] Optionally, the material of the separator includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0189] It can be understood that the secondary battery of the present application includes a battery monomer form, a battery module form, and a battery pack form. The shape of the secondary battery can be cylindrical, square, or any other shape.

[0190] Optionally, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0191] Optionally, the secondary battery can include an outer package for packaging the above-mentioned electrode assembly and electrolyte. The outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate, and the like.

[0192] Optionally, the battery monomer can be assembled into a battery module, and the number of battery monomers contained in the battery module can be one or more. The battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more.

[0193] Optionally, the battery cell, the battery module, the battery pack can be used as the power supply of the electric device, and can also be used as the energy storage unit of the electric device. The electric device includes but is not limited to: mobile devices such as mobile phones, tablets, laptops, etc.; electric vehicles such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.; electric trains; ships; satellites; energy storage systems.

[0194] The following is further illustrated in combination with specific examples and comparative examples. The raw materials involved in the following specific examples and comparative examples, if not specifically stated, can be sourced from the market. The instruments used, if not specifically stated, can be sourced from the market. The processes involved, if not specifically stated, are routinely selected by those skilled in the art.

[0195] Example 1

[0196] Please refer to Table 1. The preparation method of the modified lithium-rich manganese-based material in this embodiment is as follows:

[0197] (1) Mix the manganese-rich precursor, lithium source, sodium source and dopant uniformly to obtain a mixture;

[0198] Manganese-rich precursor: nickel-cobalt-manganese hydroxide Ni 0.33 Co 0.01 Mn 0.66 (OH)2;

[0199] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.25;

[0200] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.25;

[0201] Dopant: Nb2O5 and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.005, F / (Ni+Co+Mn)=0.02.

[0202] (2) Place the mixture in an atmosphere box furnace for first sintering treatment: increase the temperature from room temperature to 500°C at a rate of 5°C / min, keep for 5h; increase the temperature from 500°C to 950°C at a rate of 5°C / min, keep for 15h; naturally cool down to room temperature with the furnace, to obtain a first intermediate, whose expression is:

[0203] Li 1.25 Na 0.25 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O2.48 F 0.02 .

[0204] (3) mixing the first intermediate and a lithium salt solution, the lithium salt solution is composed of LiOH and deionized water, the mass ratio of lithium element, deionized water and the first intermediate in the lithium salt solution is 0.05:200:100; ion exchange treatment is carried out under stirring, the temperature is 10℃, the time is 5min; solid-liquid separation treatment is carried out by suction filtration method, vacuum drying at 120℃ for 12h, and crushing treatment, to obtain the second intermediate with D50=10μm.

[0205] (4) the second intermediate is heated from room temperature to 500℃ at a heating rate of 5℃ / min, and second sintering treatment is carried out for 10h; the furnace is naturally cooled to room temperature, and the modified lithium-rich manganese-based material is obtained by passing through a 300-mesh sieve, and the expression is Li 1.244 Na 0.064 (Ni 0.33 Co 0.01 Mn 0.66 ) 0.995 Nb 0.005 O 2.288 F 0.02 (For the convenience of chemical formula writing, the approximate value is taken after rounding off the last three digits after the decimal point).

[0206] Example 2

[0207] The difference between this embodiment and example 1 is that the mass ratio of lithium element, deionized water and the first intermediate in the lithium salt solution is 0.1:200:100.

[0208] Example 3

[0209] The difference between this embodiment and example 1 is that the mass ratio of lithium element, deionized water and the first intermediate in the lithium salt solution is 0.2:200:100.

[0210] Examples 4-8

[0211] Examples 4-8 are basically the same as example 2, the difference is that:

[0212] Example 4: the sintering temperature in step (4) is 700℃.

[0213] Example 5: the sintering temperature in step (4) is 400℃.

[0214] Example 6: the lithium salt in step (3) is LiCl.

[0215] Example 7: the lithium salt in step (3) is CH3COOLi.

[0216] Example 8: The lithium salt in step (3) is LiNO3.

[0217] Example 9

[0218] This example differs from Example 2 in that the starting material of step (1) is different.

[0219] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.34 Mn 0.66 (OH)2;

[0220] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.24;

[0221] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.24;

[0222] Dopant: WO3 and NH4F, the molar ratio of each element satisfies: W / (Ni+Co+Mn)=0.01, F / (Ni+Co+Mn)=0.02.

[0223] Example 10

[0224] This example differs from Example 2 in that the starting material of step (1) is different.

[0225] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.25 Mn 0.75 (OH)2;

[0226] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.40;

[0227] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.28;

[0228] Dopant: MoO3 and NH4F, the molar ratio of each element satisfies: Mo / (Ni+Co+Mn)=0.02, F / (Ni+Co+Mn)=0.02.

[0229] Example 11

[0230] This example differs from Example 2 in that the starting material of step (1) is different.

[0231] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.3 Mn 0.7 (OH)2;

[0232] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.30;

[0233] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.26;

[0234] Dopant: Sb2O5 and NH4F, the molar ratio of each element satisfies: Sb / (Ni+Co+Mn)=0.02, F / (Ni+Co+Mn)=0.02.

[0235] Example 12

[0236] The difference between this embodiment and embodiment 2 is that the raw material of step (1) is different.

[0237] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.37 Mn 0.63 (OH)2;

[0238] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.18;

[0239] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.22;

[0240] Dopant: Cr2O3 and NH4F, the molar ratio of each element satisfies: Cr / (Ni+Co+Mn)=0.05, F / (Ni+Co+Mn)=0.02.

[0241] Example 13

[0242] The difference between this embodiment and embodiment 2 is that the raw material of step (1) is different.

[0243] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.4 Mn 0.6 (OH)2;

[0244] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.13;

[0245] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.2;

[0246] Dopant: ZrO2 and NH4F, the molar ratio of each element satisfies: Zr / (Ni+Co+Mn)=0.005, F / (Ni+Co+Mn)=0.02.

[0247] Example 14

[0248] The difference between this example and Example 2 is that the raw material of step (1) is different.

[0249] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.3 Co 0.1 Mn 0.6 (OH)2;

[0250] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.22;

[0251] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.23;

[0252] Dopant: Nb2O5 and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.01, F / (Ni+Co+Mn)=0.02.

[0253] Example 15

[0254] The difference between this example and Example 2 is that the raw material of step (1) is different.

[0255] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.33 Co 0.01 Mn 0.66 (OH)2;

[0256] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.25;

[0257] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.25;

[0258] Dopant: Nb2O5 and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.005.

[0259] Example 16

[0260] The difference between this example and Example 2 is that the water washing time is 10 min.

[0261] Example 17

[0262] The difference between this example and Example 2 is that the water washing time is 15 min.

[0263] Example 18

[0264] The embodiment differs from example 2 in that step (4) adds a coating agent, as follows:

[0265] The aluminum phosphate is used as the coating agent, and the mass ratio of the second intermediate and the coating agent is controlled to be 100:0.5. After mixing the second intermediate and the coating agent, the second sintering treatment is performed at a temperature rising rate of 5 ℃ / min from room temperature to 500 ℃ and with a holding time of 10 h. The furnace is naturally cooled to room temperature, and the modified lithium-rich manganese-based material is obtained by passing through a 300-mesh sieve.

[0266] Comparative Example 1

[0267] The comparative example differs from example 2 in that the lithium salt solution in step (3) is replaced by a sulfuric acid solution, and the mass ratio of sulfuric acid, deionized water and the first intermediate in the sulfuric acid solution is 0.1:200:100.

[0268] Comparative Example 2

[0269] The comparative example differs from example 2 in that the lithium salt solution in step (3) is replaced by hydrogen peroxide, and the mass ratio of H2O2, deionized water and the first intermediate in the hydrogen peroxide is 0.1:200:100.

[0270] Comparative Example 3

[0271] The comparative example differs from example 2 in that the lithium salt solution in step (3) is replaced by deionized water, and the mass ratio of deionized water and the first intermediate is 200:100.

[0272] Comparative Example 4

[0273] The comparative example differs from example 2 in that the mass ratio of lithium element, deionized water and the first intermediate in the lithium salt solution in step (3) is 0.3:200:100.

[0274] Comparative Example 5

[0275] The comparative example differs from example 2 in that the sintering temperature in step (4) is 250 ℃.

[0276] Comparative Example 6

[0277] The comparative example differs from example 2 in that the sintering temperature in step (4) is 800 ℃.

[0278] Comparative Example 7

[0279] The difference between this comparative example and Example 2 is that the raw material of step (1) is different.

[0280] Manganese-rich precursor: hydroxide of nickel cobalt manganese Ni 0.2 Mn 0.8 (OH)2;

[0281] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.49;

[0282] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.3;

[0283] Dopant: Nb2O5 and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.005, F / (Ni+Co+Mn)=0.02.

[0284] Comparative Example 8

[0285] The difference between this comparative example and Example 2 is that the raw material of step (1) is different.

[0286] Manganese-rich precursor: hydroxide of nickel cobalt manganese Ni 0.45 Mn 0.55 (OH)2;

[0287] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.09;

[0288] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.19;

[0289] Dopant: Nb2O5 and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.005, F / (Ni+Co+Mn)=0.02.

[0290] Comparative Example 9

[0291] The difference between this comparative example and Example 2 is that the raw material of step (1) is different.

[0292] Manganese-rich precursor: hydroxide of nickel cobalt manganese Ni 0.33 Co 0.01 Mn 0.66 (OH)2;

[0293] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.25;

[0294] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.25;

[0295] Dopant: Nb2O5and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.06, F / (Ni+Co+Mn)=0.02.

[0296] Comparative Example 10

[0297] The difference between the present comparative example and Example 2 is that no M source is added in step (1), and other raw materials remain the same, i.e. there are:

[0298] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.33 Co 0.01 Mn 0.66 (OH)2;

[0299] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.25;

[0300] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.25;

[0301] Dopant: NH4F, the molar ratio of each element satisfies: F / (Ni+Co+Mn)=0.02.

[0302] Comparative Example 11

[0303] The difference between the present comparative example and Example 2 is that no M source is added in step (1), and other raw materials remain the same, i.e. there are:

[0304] Manganese-rich precursor: nickel cobalt manganese hydroxide Ni 0.33 Co 0.01 Mn 0.66 (OH)2;

[0305] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.25;

[0306] Dopant: Nb2O5and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.06, F / (Ni+Co+Mn)=0.02.

[0307] Comparative Example 12

[0308] The difference between the present comparative example and Example 2 is that no M source is added in step (1), and other raw materials remain the same, i.e. there are:

[0309] Manganese-rich precursor: hydroxide of nickel-cobalt-manganese Ni 0.33 Co 0.01 Mn 0.66 (OH)2;

[0310] Lithium source: lithium carbonate, the molar ratio of each element satisfies: Li / (Ni+Co+Mn)=1.25;

[0311] Sodium source: sodium carbonate, the molar ratio of each element satisfies: Na / (Ni+Co+Mn)=0.35;

[0312] Dopant: Nb2O5 and NH4F, the molar ratio of each element satisfies: Nb / (Ni+Co+Mn)=0.06, F / (Ni+Co+Mn)=0.02.

[0313] Test Example

[0314] The modified lithium-rich manganese-based material was tested as follows:

[0315] 1. Morphology test: The scanning electron microscope (SEM) of model SU 8010 of Japan Hitachi Company was used for measurement, and the results are shown in Figure 1 .

[0316] 2. Composition test: The X-ray powder diffractometer (XRD) test was used for measurement, and the results are shown in Figure 2 .

[0317] 3. Na element content: The inductively coupled plasma atomic emission spectrometer (ICP-AES) of model Optima 7000 of the United States Perkin Elmer Company was used for measurement.

[0318] 4. Free lithium content: The potentiometric titration test of the automatic potentiometric titrator of model 905 of the Swiss Wanhong Company was used for measurement.

[0319] 5. Total mass fraction of P2 layered phase and spinel phase: The Na element content in the first intermediate was tested by ICP-AES, so as to estimate the total mass fraction of P2 layered phase and spinel phase in the double alkali manganese-rich matrix.

[0320] 6. Electrochemical performance test: The modified lithium-rich manganese-based material was used as a positive electrode material to make a positive electrode sheet, and was assembled into a 2032 type button cell for electrochemical performance test.

[0321] (1) Preparation of positive electrode sheet: the modified lithium-rich manganese-based material was uniformly dispersed with the binder PVDF and the carbon black conductive agent Super-P in a mass ratio of 90:5:5 in an appropriate amount of N-methyl pyrrolidone to obtain a positive electrode slurry; the positive electrode slurry was coated on an aluminum foil, dried at 120°C, rolled, punched and cut to prepare a positive electrode sheet with a diameter of 13 mm, and the loading amount of the modified lithium-rich manganese-based material in the positive electrode sheet was about 12 mg / cm 2 .

[0322] (2) Assembly of battery: in an argon-filled glove box, lithium sheet was used as the negative electrode, polypropylene microporous membrane (Celgard 2400) was used as the separator, and 1M LiPF6 / ethylene carbonate (EC) + dimethyl carbonate (DMC) was used as the electrolyte to assemble a 2032 type button cell.

[0323] (3) Electrochemical performance test: at 25°C, the 2032 type button cell was subjected to the following electrochemical performance test by using a new battery test system: ① charge-discharge test at 0.2C to evaluate the initial charge-discharge specific capacity and the initial coulombic efficiency of the positive electrode material; ② 100 cycles (100T) at 1C to evaluate the cycle performance of the material; ③ charge-discharge test at 0.2C, 0.33C, 0.5C and 1C respectively to evaluate the rate performance of the material. Among them, the charge-discharge voltage window of the battery was 2.5V~4.55V, and the charge-discharge current density at 1C (1 times rated capacity) was 230mA / g.

[0324] 6. Result analysis:

[0325] The above test results are shown in Table 3 and Figures 2-7 . Among them, Figure 2 is the XRD pattern of the modified lithium-rich manganese-based material of Example 2, Figure 3 is the XRD pattern of the modified lithium-rich manganese-based material of Comparative Example 3, Figure 4 is the XRD pattern of the modified lithium-rich manganese-based material of Comparative Example 6, Figure 5 is the first cycle charge-discharge curve of the button cell of Example 2; Figure 6 is the first cycle charge-discharge curve of the button cell of Comparative Example 3; Figure 7 is the cycle discharge capacity change graph of the button cells of Example 2 and Comparative Example 3.

[0326] From Figure 2It can be seen that in the XRD pattern of the modified lithium-rich manganese-based material in Example 2, the main strong peak (2θ=18°~19°) belongs to the (003) crystal plane diffraction peak of the O3 layered phase, the second strong peak (2θ=43°-46°) belongs to the (104) crystal plane diffraction peak of the O3 layered phase, and there is a shoulder peak or broadening belonging to the spinel phase to the left of the second strong peak. There is a diffraction peak belonging to the P2 layered phase at 2θ=15.2°~16.2°, and a lithium-rich superlattice diffraction peak belonging to Li2MnO3 near 2θ=21°. This proves that the modified lithium-rich manganese-based material in Example 2 has a three-phase composite structure of O3 layered phase-P2 layered phase-spinel phase.

[0327] Depend on Figure 3 As can be seen, in the XRD pattern of the modified lithium-rich manganese-based material of Comparative Example 3, the diffraction peaks of the P2 layered phase (2θ=15.2°~16.2°) are clearly visible, while no shoulder peak or broadening is observed to the left of the second strongest peak (2θ=43°-46°), indicating the absence of a spinel phase. This suggests that the modified lithium-rich manganese-based material of Comparative Example 1 possesses a two-phase composite structure of O3 layered phase and P2 layered phase. Figure 2 and Figure 3 The comparison shows that after the modified lithium-rich manganese-based material in Example 2 was treated with lithium salt solution by ion exchange, the characteristic peak intensity of the P2 layered phase decreased significantly, while the lithium-rich superlattice diffraction peak (Li2MnO3) near 2θ=21° was still well preserved, indicating that the spinel phase was transformed from part of the P2 layered phase.

[0328] Depend on Figure 4 As can be seen, in the XRD pattern of the modified lithium-rich manganese-based material in Comparative Example 6, the diffraction peaks of the P2 layered phase (2θ = 15.2°~16.2°) basically disappeared, and an inert rock salt phase was generated. This resulted in a significant decrease in the initial coulombic efficiency and further deterioration of the cycle performance in the electrical performance test. This indicates that performing a second sintering treatment at a suitable temperature can promote the formation of a three-phase composite structure of the modified lithium-rich manganese-based material with O3 layered phase, P2 layered phase, and spinel phase.

[0329] Taking Example 2 and Comparative Example 3 as examples, the mass fractions of the P2 layered phase and spinel phase in the modified lithium-rich manganese-based material were estimated using the following method: the P2 phase content was designed based on Li / (Ni+Co+Mn), and both Example 2 and Comparative Example 3 used Ni 0.33 Co 0.01 Mn 0.66The Li / (Ni+Co+Mn) = 1.25 both correspond to 10% of the P2 layered phase by mass (compared to the lithium content of the pure lithium-rich manganese-based material without Na is reduced by 10%); Comparative Example 3 uses deionized water for water washing, and the synthesized material is a two-phase composite structure of P2 layered phase-O3 layered phase, and the Na content contained therein corresponds to 10% of the P2 layered phase by mass; Example 2 uses a lithium salt solution for ion exchange to replace part of the sodium ions, and a three-phase composite structure is formed after secondary heat treatment, wherein the proportion of the P2 layered phase is determined by the ratio of the sodium content of Example 2 in Table 3 to the sodium content of Comparative Example 3, and the proportion of the spinel phase is determined by the ratio of the reduced sodium content of Example 2 to the sodium content of Comparative Example 3. The mass fraction of the P2 layered phase and the spinel phase in other examples and comparative examples is estimated in a similar manner, which is not described here.

[0330] As can be seen from Table 3, compared with Comparative Example 3 using deionized water for water washing, the sodium content and free lithium of the modified lithium-rich manganese-based material of Examples 1-18 are significantly reduced, indicating that the residual alkali on the surface of the material is significantly reduced, which is beneficial to the inhibition of gas production and the reduction of interface impedance of the material during long cycle.

[0331] Example 2 and Comparative Examples 1-2 compare the effects of lithium salt solution, sulfuric acid solution and hydrogen peroxide solution on ion exchange treatment. It can be found by comparison that after washing with dilute strong acid and strong oxidizing agent, the sodium ion content of the modified lithium-rich manganese-based material is significantly reduced, but the capacity, first coulombic efficiency, rate performance and cycle performance are severely deteriorated, which is due to excessive sodium / hydrogen exchange, resulting in excessive sodium release, collapse of the alkali metal layer structure, and formation of an inert rock salt phase during secondary sintering, which ultimately hinders the diffusion and migration of lithium ions.

[0332] Examples 1-3 and Comparative Examples 3-4 compare the effects of different concentrations of lithium salt solution on ion exchange treatment. Comparative Example 3 does not use a lithium salt solution, but uses deionized water for water washing, and the product forms a two-phase composite structure of O3 layered phase-P2 layered phase, and the sodium content of the P2 layered phase is high, although the first coulombic efficiency is high, but the cycle stability is relatively poor; the lithium salt dosage of Comparative Example 4 is too high, although the sodium content is further reduced, but the charge and discharge capacity is decreased and the free lithium is increased, which is due to the presence of excess lithium ions in the form of residual lithium on the surface, resulting in an increase in initial impedance, and the lack of alkali metal vacancies in the material is not conducive to the generation of spinel phase, and the excessive use of lithium is contrary to the original intention of reducing costs.

[0333] The comparison of Examples 2, 4-5 and Comparative Examples 5-6 shows that the temperature of the second sintering treatment is crucial for forming the three-phase composite structure. If the temperature of the second sintering treatment is too low, the alkali metal vacancies and oxygen vacancies cannot be repaired, and the three-phase composite structure cannot be formed, which cannot achieve the effect of improving the rate and cycle. If the temperature of the second sintering treatment is too high, the spinel phase will continue to transform into the inert rock salt phase, hindering the diffusion of lithium ions, resulting in deterioration of capacity, rate and cycle performance.

[0334] Examples 2, 6-8 use different soluble lithium salts, respectively, and can achieve similar modification effects, which shows that the modification reason comes from the lithium / sodium exchange reaction between lithium ions in the lithium salt solution and sodium ions of the first intermediate, and the influence of anions in the lithium salt solution is smaller.

[0335] The comparison of Examples 2, 9-14 and Comparative Examples 7-8 finds that if the Mn content is too high, it will lead to a decrease in kinetics, and thus the capacity and rate performance will decrease significantly; and if the Mn content is too low, although the kinetics is improved, the lithium-rich phase and sodium-rich phase are insufficient, which leads to a decrease in the initial coulombic efficiency, a decrease in capacity, and a deterioration in cycle stability.

[0336] The comparison of Example 15 and Example 2 shows that the introduction of F element reduces the valence state of Mn, promotes the capacity, but at the same time, the TM-F bond (chemical bond between transition metal element and fluorine element) has higher bond energy than the TM-O bond (chemical bond between transition metal element and oxygen element), so the cycle stability is not significantly affected.

[0337] The electrical performance tests of Examples 16-17 and Example 2 are close, which shows that the extension of ion exchange time at low temperature has little effect on the material performance, but considering the actual production efficiency, it is not recommended.

[0338] The comparison of Example 18 and Example 2 shows that after forming a coating layer on the surface of the double alkali metal manganese-rich matrix, the cycle stability is further enhanced due to the improvement of the material interface stability.

[0339] The comparison of Comparative Examples 9-10 and Example 2 shows that the electrical performance will decrease if the doping amount is too high or too low. Comparative Example 11 cannot form a layered phase due to serious lithium deficiency of the material. Comparative Example 12 has a high residual alkali due to the addition of a large amount of sodium element, which affects the long cycle performance of the material; and Comparative Example 13 has a P2 layered phase and spinel phase ratio of 16%, which leads to a decrease in capacity, an increase in residual alkali, and a decrease in cycle.

[0340] Table 1. Raw materials of the first intermediate

[0341]

[0342] Note: The molar ratio of NCM refers to the molar ratio of Ni element, Co element and Mn element; TM refers to transition metal element, for example, Li / TM represents Li / (Ni+Co+Mn).

[0343] Table 2. Ion exchange treatment and second sintering treatment

[0344]

[0345] Table 3. Performance of modified lithium-rich manganese-based material

[0346]

[0347] Note: " / " represents that it cannot be estimated; among them, Comparative Examples 1-2 cannot be estimated because of excessive sodium hydrogen exchange, and an inert rock salt phase is formed after secondary sintering; Comparative Example 6 cannot be estimated because the spinel phase is converted into an inert rock salt phase due to too high sintering temperature; Comparative Example 11 cannot be estimated because P2 layered phase cannot be generated and the spinel phase cannot be converted due to the absence of Na.

[0348] Any technical features in the above-described embodiments can be combined, and for the sake of brevity, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not contradict each other, they should be considered within the scope of the present disclosure.

[0349] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the protection scope of the present application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A modified lithium-rich manganese-based material, characterized in that, Including dual-alkali metal manganese-rich matrices; The expression for the dual-alkali metal manganese-rich matrix is: Li 1+x Na z Mn a Co b Ni c M 1-a-b-c O 2+x+z-y D y ; Among them, 0 <x<0.5,0<z<0.2,0≤y≤0.1; 0.6≤a≤0.75, 0≤b≤0.1, 0.25≤c≤0.4, 0<1-abc≤0.05; The element M includes one or more of the following: Ca, Al, Ba, Ce, Cr, Cu, Fe, K, La, Mg, Mo, Te, Nb, Sb, Sm, Ta, Ti, V, W, Y, Sn, Zn, and Zr. The element D includes one or more of F, Cl, and S; The dual alkali metal manganese-rich matrix has an O3 layered phase, a P2 layered phase, and a spinel phase; The P2 layered phase is uniformly dispersed in the dual alkali metal manganese-rich matrix and is in close contact with the O3 layered phase; Through a sodium-lithium exchange reaction, some of the Na in the P2 layered phase is removed. + Replace with Li + With alkali metal vacancies, a spinel phase is formed; Along the surface of the dual alkali metal manganese-rich matrix, pointing inward, the concentration of the spinel phase gradually decreases. The total mass fraction of the P2 layered phase and the spinel phase in the dual alkali metal manganese-rich matrix is ​​8% to 12%.

2. The modified lithium-rich manganese-based material as described in claim 1, characterized in that, The total mass fraction of the P2 layered phase and the spinel phase in the dual alkali metal manganese-rich matrix is ​​10%.

3. The modified lithium-rich manganese-based material as described in claim 1, characterized in that, The X-ray diffraction pattern of the dual-alkali metal manganese-rich matrix satisfies the following conditions: (1) It has a (003) crystal plane diffraction peak belonging to the O3 layered phase at 2θ = 18° to 19°; (2) There is a (104) crystal plane diffraction peak belonging to the O3 layered phase at 2θ=43°~46°, and the left side of the (104) crystal plane diffraction peak has a shoulder peak or broadening belonging to the spinel phase. (3) It has a diffraction peak at 2θ = 15.2° to 16.2° that belongs to the P2 layered phase; (4) It has superlattice diffraction peaks belonging to Li2MnO3 at 2θ=20°~23°.

4. The modified lithium-rich manganese-based material according to any one of claims 1 to 3, characterized in that, The M element includes one or more of Nb, W, Mo, Sb, Cr, and Zr.

5. The modified lithium-rich manganese-based material according to any one of claims 1 to 3, characterized in that, The modified lithium-rich manganese-based material further includes a coating layer supported on the dual alkali metal-rich manganese matrix. The coating layer includes one or more of phosphates, fluorides, and oxides containing element R. The element R includes one or more of Li, Na, K, V, Cr, Mn, Co, Ni, Mg, Al, Zr, W, Mo, Ce, La, and Y.

6. A method for preparing a modified lithium-rich manganese-based material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A first intermediate is obtained by mixing a manganese-rich precursor, a lithium source, a sodium source, and a dopant and performing a first sintering process. The first intermediate is dispersed in a lithium salt solution or a lithium hydroxide solution for ion exchange treatment, followed by solid-liquid separation and drying to obtain the second intermediate. The second intermediate is subjected to a second sintering treatment to obtain a dual alkali metal manganese-rich matrix; Wherein, the dopant includes an M source, or the dopant includes both an M source and a D source; The mass ratio of lithium element in the lithium salt solution to the first intermediate is (0.05~0.2):100; The sintering temperature for the second sintering treatment is 300℃~700℃.

7. The method for preparing the modified lithium-rich manganese-based material as described in claim 6, characterized in that, One or more of the following conditions must be met: (1) The lithium salt in the lithium salt solution includes one or more of lithium nitrate, lithium acetate, lithium oxalate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide and lithium dioxalate borate; (2) The mass ratio of water to the first intermediate in the lithium salt solution is (1-5):1; (3) The conditions for the ion exchange treatment include: temperature of 0℃~25℃ and time of 1min~10min.

8. The method for preparing the modified lithium-rich manganese-based material according to any one of claims 6 to 7, characterized in that, The second intermediate is subjected to a second sintering treatment, including the following steps: The second intermediate and the coating agent are mixed and kept at 300℃~700℃ for 3h~15h to form a coating layer on the dual alkali metal manganese-rich matrix; The coating agent comprises one or more of phosphates, fluorides, and oxides containing element R, wherein element R comprises one or more of Li, Na, K, V, Cr, Mn, Co, Ni, Mg, Al, Zr, W, Mo, Ce, La, and Y.

9. The method for preparing the modified lithium-rich manganese-based material as described in claim 6, characterized in that, One or more of the following conditions must be met: (1) The manganese-rich precursor includes one or more of oxides, hydroxides, and salt compounds containing nickel, cobalt, and manganese. (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium acetate, lithium oxalate, lithium chloride and lithium fluoride; (3) The sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium sulfate, sodium oxalate, sodium acetate, sodium chloride, and sodium fluoride; (4) The M source includes one or more of oxides, hydroxides and salts containing the M element, and the M element includes one or more of Ca, Al, Ba, Ce, Cr, Cu, Fe, K, La, Mg, Mo, Te, Nb, Sb, Sm, Ta, Ti, V, W, Y, Sn, Zn and Zr; (5) The D source includes one or more of fluorides, chlorides and sulfides.

10. The method for preparing the modified lithium-rich manganese-based material as described in claim 6, characterized in that, The first sintering process includes the following steps: Keep warm at 300℃~800℃ for 0h~10h, and then keep warm at 800℃~1000℃ for 4h~20h.

11. A positive electrode plate, characterized in that, The modified lithium-rich manganese-based material includes any one of the modified lithium-rich manganese-based materials as described in any one of claims 1 to 5, or the modified lithium-rich manganese-based material prepared by any one of the preparation methods of the modified lithium-rich manganese-based material as described in any one of claims 6 to 10.

12. A secondary battery, characterized in that, Including the positive electrode as described in claim 11.

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