Doped and coated modified lithium-rich manganese-based positive electrode material, preparation method thereof and battery

Abstract

The invention provides a doped and coated modified lithium-rich manganese-based positive electrode material, a preparation method thereof and a battery, and the preparation method comprises the following steps: merging a manganese-rich mixed salt solution, an alkaline solution and an EDTA (Ethylene Diamine Tetraacetic Acid) solution, injecting into a base solution to prepare a precursor, mixing the precursor with a tantalum source, a tungsten source and a magnesium source, and carrying out solvothermal reaction to obtain a doped precursor; and mixing the doped precursor with a lithium source, carrying out sintering treatment to obtain a lithium-rich material, mixing the lithium-rich material with the lithium tantalate sol, evaporating a solvent, and carrying out calcination treatment to obtain the doped and coated modified lithium-rich manganese-based positive electrode material. According to the invention, the lithium-rich manganese-based positive electrode material is doped, coated and modified, so that the two core problems of unstable bulk phase structure and unstable surface interface of the lithium-rich manganese-based positive electrode material are solved, the surface conductivity of the material is improved, and the dissolution of transition metal ions is inhibited.

Description

TECHNICAL FIELD

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

[0002] In the field of new energy power batteries, with the continuous rise of the demand for high energy density, long cycle life and high safety of batteries in the industries of electric vehicles, energy storage power stations and the like, the technical iteration of positive electrode materials, as the core component determining the performance of lithium ion batteries, has attracted much attention. Lithium-rich manganese-based positive electrode materials are considered as one of the core candidates for the next generation of high-energy-density lithium ion battery positive electrode materials due to their ultra-high theoretical specific capacity, excellent cost advantage (abundant reserves and low price of manganese element) and low risk, and show broad application prospects in high-end power batteries and large-scale energy storage fields.

[0003] However, the current lithium-rich manganese-based positive electrode materials still face two core problems of unstable bulk structure and unstable surface interface in actual industrial application, accompanied by problems of poor surface electronic conductivity and manganese element dissolution, which seriously restrict the improvement of their cycle performance, rate performance and safety, and become the key bottleneck hindering their large-scale application.

[0004] CN120341253A discloses a surface-coated and doped lithium-rich manganese-based positive electrode material and a preparation method and application thereof. The material comprises an internal layered structure, a doped layer located on the surface of the internal layered structure, and a coating layer located on the surface of the doped layer.

[0005] CN120535029A discloses a preparation method and application of a fluorine-doped and carbon-coated synergistically modified lithium-rich manganese-based single-crystal positive electrode material based on PVDF. The preparation method comprises: S1, preparing a transition metal salt solution, a NaOH aqueous solution and an ammonia solution; S2, pumping the transition metal salt solution, the NaOH and the ammonia solution into a reaction kettle at the same time, controlling the pH value of the reaction to be kept at 11.0-11.2, to obtain a precursor; S3, pre-sintering the precursor at 500°C; S4, mixing the sintered precursor with a stoichiometric ratio of PVDF and a lithium source, and performing secondary calcination under a nitrogen atmosphere to obtain a loosely combined F-doped lithium-rich manganese-based polycrystal positive electrode material; and S5, crushing the prepared lithium-rich manganese-based polycrystal positive electrode material in an airflow crusher to obtain a lithium-rich manganese-based single-crystal positive electrode material with carbon coating and fluorine doping.

[0006] The lithium-rich manganese-based positive electrode material prepared by the above scheme has problems of unstable bulk structure, unstable surface interface and poor surface conductivity, which leads to poor effect in the actual discharge process. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide a doped and coated modified lithium-rich manganese-based positive electrode material, a preparation method thereof and a battery.

[0008] To achieve the object of the present application, the following technical solutions are adopted:

[0009] In a first aspect, the present application provides a preparation method of a doped and coated modified lithium-rich manganese-based positive electrode material, which comprises the following steps:

[0010] The manganese-rich mixed salt solution, the alkaline solution and the EDTA solution are injected into the bottom liquid in parallel to obtain a precursor, the precursor is mixed with a tantalum source, a tungsten source and a magnesium source, and a solvothermal reaction is performed to obtain a doped precursor;

[0011] The doped precursor is mixed with a lithium source and subjected to sintering treatment to obtain a sintered material, the sintered material is mixed with a lithium tantalate precursor sol and the solvent is evaporated, and then calcination treatment is performed to obtain the doped and coated modified lithium-rich manganese-based positive electrode material.

[0012] The present application first prepares a precursor, wherein the addition of EDTA can form a stable complex with metal ions in the solution, slow down the precipitation rate, make the crystal grains grow more slowly and regularly, avoid composition segregation and irregular morphology caused by rapid precipitation, and further improve the uniformity of the precursor, so that a precursor with highly uniform element distribution, good sphericity and narrow particle size distribution is obtained. Then, tantalum, tungsten and magnesium are gradient-doped in the precursor by a solvothermal method. Ta and W are high-charge and large-radius cations that can effectively stabilize the crystal lattice structure and inhibit phase transformation and oxygen loss during the cycle process. Mg 2+ Doping can widen the Li interlayer spacing and improve the Li + diffusion rate. The solvothermal method ensures that these elements are embedded in the material lattice to produce a synergistic effect. Finally, the doped precursor is lithiated and coated with lithium tantalate by a sol-gel method. Lithium tantalate is a fast ion conductor that can not only physically isolate the positive electrode material from direct contact with the electrolyte to reduce side reactions, but also provide a channel for Li + transport.

[0013] Preferably, the total molar amount of metal ions in the manganese-rich mixed salt solution is 100%, and the molar proportion of manganese is 60% to 90%, for example, 60%, 65%, 70%, 75%, 80% or 90%, etc. The range of values also applies to other values not listed.

[0014] Preferably, the metal ions in the manganese-rich mixed salt solution also include nickel and / or cobalt.

[0015] Preferably, the basic solution comprises a sodium hydroxide solution.

[0016] Preferably, the base solution comprises water.

[0017] Preferably, the molar ratio of total metal ions in the manganese-rich mixed salt solution, solute in the basic solution, and EDTA in the EDTA solution is (2.5-3.5):(1.5-2.5):1, such as 2.5:1.5:1, 2.8:1.5:1, 3:2:1, 3:2.5:1, or 3.5:2.5:1, etc., not limited to the listed values, other values not listed within the range of values are also applicable.

[0018] Preferably, the tantalum source comprises tantalum nitrate and / or tantalum ethoxide.

[0019] Preferably, the tungsten source comprises sodium tungstate and / or ammonium tungstate.

[0020] Preferably, the magnesium source comprises magnesium nitrate and / or magnesium acetate.

[0021] Preferably, the molar ratio of the precursor to the tantalum element in the tantalum source is 100:(0.2-0.4), such as 100:0.2, 100:0.25, 100:0.3, 100:0.35, or 100:0.4, etc., not limited to the listed values, other values not listed within the range of values are also applicable.

[0022] Preferably, the molar ratio of the precursor to the tungsten element in the tungsten source is 100:(0.2-0.4), such as 100:0.2, 100:0.25, 100:0.3, 100:0.35, or 100:0.4, etc., not limited to the listed values, other values not listed within the range of values are also applicable.

[0023] Preferably, the molar ratio of the precursor to the magnesium element in the magnesium source is 100:(0.1-0.2), such as 100:0.1, 100:0.12, 100:0.15, 100:0.18, or 100:0.2, etc., not limited to the listed values, other values not listed within the range of values are also applicable.

[0024] Preferably, the temperature of the solvothermal reaction is 160-200°C, such as 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, or 200°C, etc., not limited to the listed values, other values not listed within the range of values are also applicable.

[0025] Preferably, the time of the solvothermal reaction is 5h~12h, for example: 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0026] Preferably, the lithium source comprises lithium carbonate and / or lithium hydroxide.

[0027] Preferably, the molar ratio of the total moles of lithium element in the lithium source and metal element in the doping precursor is (1.2~1.6):1, for example: 1.2:1, 1.25:1, 1.3:1, 1.4:1, 1.5:1 or 1.6:1, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0028] Preferably, lithium fluoride is also added before the sintering treatment.

[0029] Preferably, the amount of lithium fluoride added is 0.5%~1.5% based on 100% of the mass of the doping precursor, for example: 0.5%, 0.8%, 1%, 1.2% or 1.5%, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0030] Preferably, the atmosphere of the sintering treatment comprises air and / or oxygen.

[0031] Preferably, the temperature of the sintering treatment is 750℃~1000℃, for example: 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 900℃ or 1000℃, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0032] Preferably, the holding time of the sintering treatment is 8h~24h, for example: 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0033] Preferably, the lithium tantalate precursor sol is prepared by the following method:

[0034] The lithium source solution is added dropwise to the tantalum source solution, and citric acid is added during stirring to react, to obtain the lithium tantalate precursor sol.

[0035] The present application coats the lithium-rich manganese-based positive electrode material with lithium tantalate precursor sol, which is composed of molecular-level tantalum source and lithium source. The sol can perfectly infiltrate and adhere to every surface of the sintered material particles through capillary force generated by solvent evaporation, thereby forming a nanoscale, continuous and dense LiTaO3 coating layer. This is far superior to the discontinuous and uneven-thickness coating layer obtained by simple mechanical mixing.

[0036] Preferably, the solute in the lithium source solution comprises lithium nitrate and / or lithium acetate.

[0037] Preferably, the solute in the tantalum source solution comprises tantalum ethoxide.

[0038] Preferably, the solvent in the lithium source solution and the tantalum source solution comprises water.

[0039] Preferably, the mass ratio of the sintered material to lithium tantalate in the precursor sol is 100:(1~2), such as 100:1, 100:1.2, 100:1.5, 100:1.8 or 100:2, etc. The values not listed in the range are also applicable.

[0040] In the lithium tantalate precursor sol of the present application, complete lithium tantalate is not generated. Therefore, the mass of lithium tantalate (LiTaO3) in the precursor sol is the mass of (Li+Ta+3×O) therein.

[0041] Preferably, the calcination process comprises a first calcination and a second calcination.

[0042] Preferably, the temperature of the first calcination is 150℃~300℃, such as 150℃, 200℃, 250℃ or 300℃, etc. The values not listed in the range are also applicable.

[0043] Preferably, the holding time of the first calcination is 5h~10h, such as 5h, 6h, 7h, 8h, 9h or 10h, etc. The values not listed in the range are also applicable.

[0044] Preferably, the temperature of the second calcination is 500℃~800℃, such as 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, etc. The values not listed in the range are also applicable.

[0045] Preferably, the holding time of the second calcination is 2h~6h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, etc. The values not listed in the range are also applicable.

[0046] In a second aspect, the present application provides a doped and coated modified lithium-rich manganese-based positive electrode material, which is prepared by the method as described in the first aspect.

[0047] In the doped and coated modified lithium-rich manganese-based positive electrode material, the pentavalent tantalum has a strong electrostatic shielding effect, can inhibit the transition metal migration, form a Ta-O-Mn bond, further stabilize the oxygen framework, reduce the oxygen release at high voltage and reduce the manganese dissolution. 3+ The hexavalent tungsten has a high polarization capacity, can more strongly stabilize the Mn

[0048] In a third aspect, the present application provides a lithium ion battery, which comprises the doped and coated modified lithium-rich manganese-based positive electrode material as described in the second aspect.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] (1) The present application improves the two core problems of the unstable bulk structure and the unstable surface interface of the lithium-rich manganese-based positive electrode material by doping and coating modification of the lithium-rich manganese-based positive electrode material, and also improves the surface conductivity of the material and avoids the manganese dissolution.

[0051] (2) By doping and coating the lithium-rich material, the surface structure stability is improved, the release of O2 is inhibited, the first coulombic efficiency of the material is improved, the corrosion of the electrolyte to the surface of the positive electrode material is hindered, and the dissolution of the transition metal ions is reduced, so the structural stability of the material is enhanced and the cycle performance of the lithium-rich material is improved.

[0052] (3) The highest discharge specific capacity of the battery made of the doped and coated modified lithium-rich manganese-based positive electrode material can reach 259.8 mAh / g or more, the 50th cycle specific capacity can reach 241.6 mAh / g or more, the cycle efficiency can reach 93% or more, the 100th cycle specific capacity can reach 236.7 mAh / g or more, and the cycle efficiency can reach 91.1% or more. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be further described in the following specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0054] "ranges" disclosed herein can be defined, for example, by the lower and upper values. Any lower limit can independently be combined with any upper limit to define a range of any value. For example, if a range of 60-120 and 80-110 is listed as exemplary, it is understood that a range of 60-110 and 80-120 is also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing all the individual real combinations of values within the range, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all the real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand way of describing these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to listing the parameter as, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a parameter is an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0055] In the present application, the phrase "combination of at least two" means, unless otherwise specified, greater than or equal to two in number. For example, "any one or a combination of at least two" means one or greater than or equal to two. It is understood that the phrase "combination of at least two" means a combination of any suitable number of items, i.e., a combination of "at least two" items in a manner that does not conflict with and enables the present application.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0057] In the present application, the phrase "embodiments" means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment or embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments.

[0058] In the present application, the open technical features or technical solutions described by the words such as "include" do not exclude additional members beyond the listed members, and can be regarded as providing both the closed features or technical solutions composed of the listed members and the open features or solutions including additional members beyond the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members, or it can not include additional members, and it can be regarded as providing the technical features or technical solutions of "A is composed of a1, a2 and a3" or "A is selected from a1, a2 and a3", and also providing the technical features or technical solutions of "A includes a1, a2 and a3, and also includes other members".

[0059] In the present application, unless otherwise specified, the "and / or" corresponding features or solutions include any one of two or more related listed items, and also include any and all combinations of the related listed items, including any two related listed items, any more related listed items, or all related listed items. For example, "A and / or B" represents a group composed of A, B and "the combination of A and B". Wherein, "including A and / or B" can represent "including A, including B, and including A and B", and also can represent "including A, including B, or including A and B", which can be understood according to the sentence.

[0060] In the present application, the terms "first", "second", "third", "fourth" and the like are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration description, and it should be understood that they do not constitute a closed limitation on the quantity.

[0061] The lithium tantalate precursor sol used in the examples and comparative examples of the present application is prepared by the following method:

[0062] The lithium acetate, ethanol solution is added dropwise to the tantalum ethoxide, ethanol solution, and citric acid is added during stirring to react, to obtain the lithium tantalate precursor sol.

[0063] Example 1

[0064] The present example provides a doped and coated modified lithium-rich manganese-based positive electrode material, which is prepared by the following method:

[0065] The manganese nickel salt solution (Mn:Ni=3:1), the sodium hydroxide solution, and the EDTA solution are injected into a reaction kettle containing an aqueous bottom liquid (total liquid injection amount 1 / 5) in a concurrent manner at a solute molar ratio of 3:2:1 under nitrogen, and a precursor is obtained by stirring; the precursor is mixed with tantalum ethoxide, ammonium tungstate, and magnesium acetate at a molar ratio of precursor:Ta:W:Mg of 100:0.3:0.3:0.2, and a solvothermal reaction is performed at 170°C for 10h to obtain a doped precursor by filtration;

[0066] The doped precursor is mixed with lithium carbonate at a molar ratio of Li:transition metal of 1.25:1, and 1% of lithium fluoride based on the mass of the doped precursor is added, and the mixture is ground for 30min, and then heat treatment is performed at 780°C for 10h under an air atmosphere to obtain a sintered material;

[0067] The sintered material is mixed with a lithium tantalate precursor sol at a mass ratio of sintered material: lithium tantalate of 100:1.5, and calcination is performed at 350°C for 3h, and then calcination is performed at 600°C for 5h to obtain the doped coated modified lithium-rich manganese-based positive electrode material.

[0068] Example 2

[0069] The present embodiment provides a doped coated modified lithium-rich manganese-based positive electrode material, which is prepared by the following method:

[0070] The manganese nickel salt solution (Mn:Ni=3:1), the sodium hydroxide solution, and the EDTA solution are injected into a reaction kettle containing an aqueous bottom liquid (total liquid injection amount 1 / 5) in a concurrent manner at a solute molar ratio of 3:2:1 under nitrogen, and a precursor is obtained by stirring; the precursor is mixed with tantalum ethoxide, ammonium tungstate, and magnesium acetate at a molar ratio of precursor:Ta:W:Mg of 100:0.3:0.3:0.2, and a solvothermal reaction is performed at 170°C for 10h to obtain a doped precursor by filtration;

[0071] The doped precursor is mixed with lithium carbonate at a molar ratio of Li:transition metal of 1.25:1, and 1% of lithium fluoride based on the mass of the doped precursor is added, and the mixture is ground for 30min, and then heat treatment is performed at 780°C for 10h under an air atmosphere to obtain a sintered material;

[0072] The sintered material is mixed with a lithium tantalate precursor sol at a mass ratio of sintered material: lithium tantalate of 100:1.5, and calcination is performed at 350°C for 3h, and then calcination is performed at 600°C for 5h to obtain the doped coated modified lithium-rich manganese-based positive electrode material.

[0073] Example 3

[0074] The present embodiment provides a doped coated modified lithium-rich manganese-based positive electrode material, which is prepared by the following method:

[0075] The manganese nickel salt solution (Mn:Ni=3:1), the sodium hydroxide solution, and the EDTA solution were injected into the reaction kettle containing the aqueous bottom liquid (total liquid injection amount 1 / 5) under nitrogen according to a solute molar ratio of 3.5:2.5:1 in a concurrent manner, and a precursor was obtained by stirring. The precursor was mixed with the tantalum ethoxide, the ammonium tungstate, and the magnesium acetate according to a molar ratio of precursor:Ta:W:Mg of 100:0.4:0.4:0.2, and a doped precursor was obtained by solvothermal reaction at 180°C for 8h and filtration.

[0076] The doped precursor was mixed with lithium carbonate according to a molar ratio of Li:transition metal of 1.5:1, and lithium fluoride was added in an amount of 0.5% of the mass of the doped precursor. After grinding for 30min, the sintering material was obtained by heat treatment at 800°C for 4h in an air atmosphere.

[0077] The sintering material was mixed with the lithium tantalate precursor sol according to a mass ratio of sintering material: lithium tantalate of 100:1, and the doped coated modified lithium-rich manganese-based positive electrode material was obtained by calcination at 300°C for 5h and then calcination at 500°C for 6h.

[0078] Example 4

[0079] The difference between this example and Example 1 is only that the precursor:Ta=100:0.1, and the other conditions and parameters are completely the same as those of Example 1.

[0080] Example 5

[0081] The difference between this example and Example 1 is only that the precursor:Ta=100:0.5, and the other conditions and parameters are completely the same as those of Example 1.

[0082] Example 6

[0083] The difference between this example and Example 1 is only that the precursor:W=100:0.1, and the other conditions and parameters are completely the same as those of Example 1.

[0084] Example 7

[0085] The difference between this example and Example 1 is only that the precursor:W=100:0.5, and the other conditions and parameters are completely the same as those of Example 1.

[0086] Example 8

[0087] The difference between this example and Example 1 is only that the precursor:Mg=100:0.05, and the other conditions and parameters are completely the same as those of Example 1.

[0088] Example 9

[0089] The difference between this example and Example 1 is only that the precursor:Mg=100:0.3, and the other conditions and parameters are completely the same as those of Example 1.

[0090] Example 10

[0091] The difference between this example and Example 1 is that the sintering material is mixed with the lithium tantalate precursor sol according to a mass ratio of sintering material: lithium tantalate = 100:0.5, and other conditions and parameters are exactly the same as in Example 1.

[0092] Example 11

[0093] The difference between this example and Example 1 is that the sintering material is mixed with the lithium tantalate precursor sol according to a mass ratio of sintering material: lithium tantalate = 100:3, and other conditions and parameters are exactly the same as in Example 1.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is that no tantalum ethoxide is added, and other conditions and parameters are exactly the same as in Example 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that no ammonium tungstate is added, and other conditions and parameters are exactly the same as in Example 1.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that no magnesium acetate is added, and other conditions and parameters are exactly the same as in Example 1.

[0100] Comparative Example 4

[0101] The difference between this comparative example and Example 1 is that no lithium tantalate is coated, and other conditions and parameters are exactly the same as in Example 1.

[0102] Performance test: First, the positive electrode material is made into a slurry, and then the positive electrode material, carbon black and PVDF are mixed uniformly according to a ratio of 8:1:1, and then coated on an aluminum foil, and then dried in a vacuum drying oven, and then cut into positive electrode sheets with a cutting machine, and then assembled into a 2032 button cell, with a metal lithium sheet as the negative electrode, a CR2032 separator, and a carbonate solution as the electrolyte, with LiPF6 as the solute, and EC: EMC: DMC = 1:1:1.

[0103] Battery charge and discharge test conditions: voltage test conditions: 2.0~4.8V, current is 0.1C (25mAh / g), 1C is 250mAh / g.

[0104] The test results are shown in Table 1:

[0105] Table 1

[0106]

[0107] As can be seen from Table 1, it can be obtained from Examples 1-11 that the maximum discharge specific capacity of the battery made of the doped and coated modified lithium-rich manganese-based positive electrode material according to the application can reach 259.8 mAh / g or more, the specific capacity after 50 cycles can reach 241.6 mAh / g or more, the cycle efficiency can reach 93% or more, the specific capacity after 100 cycles can reach 236.7 mAh / g or more, and the cycle efficiency can reach 91.1% or more. Due to the problems such as the release of O2 during the first charging of the lithium-rich positive electrode material due to the unstable surface structure, the first efficiency is low, and the cycle performance is poor. Through the surface metal element doping and coating, the corrosion of the electrolyte to the positive electrode material is inhibited, the metal-O bond on the surface is enhanced, the release of O2 on the surface is inhibited, and thus the structural stability and anion redox reversibility of the material are improved, and the cycle performance and the first charge-discharge efficiency of the material are improved.

[0108] As can be obtained from the comparison of Example 1 and Examples 4-5, in the preparation process of the doped and coated modified lithium-rich manganese-based positive electrode material according to the application, the addition amount of the tantalum source will affect the performance. The molar ratio of the precursor to Ta in the tantalum source is controlled at 100:0.2-0.4, and the performance of the doped and coated modified lithium-rich manganese-based positive electrode material prepared is better. If the addition amount of the tantalum source is too low, the ion migration and mixing of the transition metal layer during the cycle process cannot be effectively inhibited, and the improvement of the structural stability is limited. If the addition amount of the tantalum source is too high, the excessive Ta 5+ will occupy the active sites, which will reduce the amount of transition metal ions participating in the reaction and reduce the capacity.

[0109] As can be obtained from the comparison of Example 1 and Examples 6-7, in the preparation process of the doped and coated modified lithium-rich manganese-based positive electrode material according to the application, the addition amount of the tungsten source will affect the performance. The molar ratio of the precursor to W in the tungsten source is controlled at 100:0.2-0.4, and the performance of the doped and coated modified lithium-rich manganese-based positive electrode material prepared is better. If the addition amount of the tungsten source is too low, the effect of stabilizing the crystal lattice and inhibiting oxygen precipitation is insufficient. If the addition amount of the tungsten source is too high, the ion polarization ability of W 6+ is extremely strong, and the excessive introduction will seriously distort the transition metal oxygen octahedron and destroy the layered structure of the material.

[0110] As can be obtained from the comparison of Example 1 and Examples 8-9, in the preparation process of the doped and coated modified lithium-rich manganese-based positive electrode material according to the application, the molar ratio of the precursor to Mg in the magnesium source is controlled at 100:0.1-0.2, and the performance of the doped and coated modified lithium-rich manganese-based positive electrode material prepared is better. If the addition amount of the magnesium source is too low, the supporting effect on the Li layer is insufficient, which cannot effectively inhibit the lithium / nickel mixing phenomenon during the cycle process, and the improvement of the lithium ion diffusion kinetics is also limited. If the addition amount of the magnesium source is too high, the excessive Mg 2+ will occupy a large number of lithium ion active sites, which will directly lead to the decrease of the reversible capacity.

[0111] From the comparison of Example 1 and Examples 10-11, it can be seen that in the preparation process of the doped coated modified lithium-rich manganese-based positive electrode material, the coating amount of lithium tantalate will affect its performance. The sintering material and lithium tantalate precursor sol are mixed according to the mass ratio of sintering material: lithium tantalate = 100:1-2, and the performance of the doped coated modified lithium-rich manganese-based positive electrode material is better. If the coating amount of lithium tantalate is too low, a continuous and dense coating layer cannot be formed, and only island-shaped coating can be formed. The electrolyte can still easily penetrate the uncoated area to corrode the material surface, and cannot effectively inhibit the side reaction, transition metal dissolution and oxygen loss, and the coating effect is poor. If the coating amount of lithium tantalate is too high, the thick coating layer will hinder the diffusion of Li + From the electrolyte to the active material body, the interface diffusion impedance is increased.

[0112] From the comparison of Example 1 and Comparative Examples 1-3, it can be seen that the present application uniformly dopes tantalum, tungsten and magnesium in the positive electrode material. Ta and W are high-charge and large-radius cations, which can effectively stabilize the lattice structure and inhibit phase change and oxygen loss during the cycle process; Mg 2+ Doping can widen the Li layer spacing and improve the Li + diffusion rate.

[0113] From the comparison of Example 1 and Comparative Example 4, it can be seen that lithium tantalate is a fast ion conductor, which can not only physically isolate the direct contact between the positive electrode material and the electrolyte to reduce the side reaction, but also provide a channel for the transmission of Li + , and at the same time, lithium tantalate can stabilize the near-surface structure.

[0114] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a doped and modified lithium-rich manganese-based cathode material, characterized in that, The preparation method includes the following steps: A manganese-rich mixed salt solution, an alkaline solution, and an EDTA solution were injected concurrently into the base liquid to obtain a precursor. The precursor was then mixed with a tantalum source, a tungsten source, and a magnesium source, and subjected to a solvothermal reaction to obtain a doped precursor. The doped precursor is mixed with a lithium source and sintered to obtain a sintered material. The sintered material is then mixed with a lithium tantalate precursor sol and the solvent is evaporated before calcination to obtain the doped and modified lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The total molar amount of metal ions in the manganese-rich mixed salt solution is 100%, and the molar percentage of manganese is 60% to 90%. Preferably, the metal ions in the manganese-rich mixed salt solution also include nickel and / or cobalt; Preferably, the alkaline solution includes a sodium hydroxide solution; Preferably, the base liquid comprises water; Preferably, the molar ratio of the total molar amount of metal ions in the manganese-rich mixed salt solution, the molar ratio of the solute in the alkaline solution to the molar ratio of EDTA in the EDTA solution is (2.5~3.5):(1.5~2.5):

1.

3. The preparation method according to claim 1 or 2, characterized in that, The tantalum source includes tantalum nitrate and / or tantalum ethanol; Preferably, the tungsten source includes sodium tungstate and / or ammonium tungstate; Preferably, the magnesium source includes magnesium nitrate and / or magnesium acetate; Preferably, the molar ratio of the precursor to the tantalum element in the tantalum source is 100:(0.2~0.4); Preferably, the molar ratio of the precursor to the tungsten element in the tungsten source is 100:(0.2~0.4); Preferably, the molar ratio of the precursor to magnesium in the magnesium source is 100:(0.1~0.2).

4. The preparation method according to any one of claims 1-3, characterized in that, The temperature of the solvothermal reaction is 160℃~200℃; Preferably, the solvothermal reaction time is 5h to 12h.

5. The preparation method according to any one of claims 1-4, characterized in that, The lithium source includes lithium carbonate and / or lithium hydroxide; Preferably, the molar ratio of the total molar amount of lithium element in the lithium source to the total molar amount of metal element in the doped precursor is (1.2~1.6):1; Preferably, lithium fluoride is added before the sintering treatment; Preferably, the amount of lithium fluoride added is 0.5% to 1.5% based on the mass of the doped precursor being 100%.

6. The preparation method according to any one of claims 1-5, characterized in that, The atmosphere for the sintering process includes air and / or oxygen; Preferably, the sintering temperature is 750℃~1000℃; Preferably, the holding time for the sintering treatment is 8h to 24h.

7. The preparation method according to any one of claims 1-6, characterized in that, The lithium tantalate precursor sol was prepared by the following method: A lithium source solution was added dropwise to a tantalum source solution, and citric acid was added during stirring to react and obtain the lithium tantalate precursor sol. Preferably, the solute in the lithium source solution includes lithium nitrate and / or lithium acetate; Preferably, the solute in the tantalum source solution includes tantalum ethoxide; Preferably, the solvents for the lithium source solution and the tantalum source solution include water; Preferably, the mass ratio of the sintering material to the lithium tantalate precursor sol is 100:(1~2).

8. The preparation method according to any one of claims 1-7, characterized in that, The calcination process includes a first calcination and a second calcination; Preferably, the temperature of the first calcination is 150℃~300℃; Preferably, the heat preservation time for the first calcination is 5h to 10h; Preferably, the second calcination temperature is 500℃~800℃; Preferably, the heat preservation time for the second calcination is 2h to 6h.

9. A doped and modified lithium-rich manganese-based cathode material, characterized in that, The doped and coated modified lithium-rich manganese-based cathode material is prepared by the preparation method described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the doped and coated modified lithium-rich manganese-based cathode material as described in claim 9.

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