Doped coated lithium-rich manganese-based precursors, cathode materials, methods of making, and batteries
By preparing gradient doping and coating layers on the surface of lithium-rich manganese-based precursors, the cycling and kinetic problems of lithium-rich manganese-based cathode materials were solved, the structural stability and ion conduction performance of the materials were improved, and the energy density and rate performance were improved simultaneously.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JINGMEN GEM NEW MATERIAL CO LTD
- Filing Date
- 2026-04-07
- Publication Date
- 2026-06-05
AI Technical Summary
Existing lithium-rich manganese-based cathode materials suffer from problems such as low initial efficiency, poor kinetic performance, voltage decay, and structural collapse during cycling, and bulk doping may reduce the number of active sites.
Gradient doped and gradient coated layers were prepared in situ on the surface of lithium-rich manganese-based precursors by co-precipitation. The concentrations and flow rates of nickel-cobalt-manganese mixed salts, aluminum salts, and magnesium salts were controlled to form Al-Mg co-doped and Al2O3-MgO composite coated layers, thereby optimizing the lithium-ion transport path and interface stability.
It improves the cycle stability and rate performance of lithium-rich manganese-based cathode materials, ensures energy density and interface compatibility, inhibits Mn dissolution and electrolyte corrosion, and achieves simultaneous improvement in cycle performance and rate performance.
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, specifically to lithium-rich manganese-based precursors, and more particularly to a doped and coated lithium-rich manganese-based precursor, cathode material, preparation method, and battery. Background Technology
[0002] With the development of new energy vehicles and large-scale energy storage industries, the requirements for energy density, cycle stability, and cost of lithium-ion batteries are becoming increasingly stringent. Lithium-rich manganese-based cathode materials, with a theoretical specific capacity exceeding 250 mAh / g and manganese and lithium as the main components, are low in cost and abundant in resources, making them a core candidate material for next-generation lithium-ion batteries.
[0003] Although the unique cation-anion synergistic reaction mechanism of lithium-rich manganese-based cathode materials provides high capacity, the anion reaction mechanism also leads to problems such as low initial efficiency, poor kinetic performance, voltage decay, and voltage hysteresis. At the same time, the high operating voltage can also easily promote side reactions between lithium-rich manganese-based cathode materials and electrolytes, which in turn causes the collapse of the material interface to the bulk structure, resulting in a continuous decline in the electrochemical performance of lithium-rich manganese-based cathode materials.
[0004] CN119349666A discloses a micro / nano-sized magnesium-doped indium-coated lithium-rich manganese-based cathode material, its precursor, and preparation method. This invention couples multiple modification methods, using bulk magnesium doping, interfacial indium coating, and particle nano-sizing strategies to synergistically reduce the lithium-ion mass transfer pathway, improve the bulk-interface kinetics of the lithium-rich manganese-based cathode material, and maintain the bulk-interface structural stability of the lithium-rich manganese-based cathode material, ultimately improving its electrochemical performance.
[0005] CN121546044A discloses a lithium-rich manganese-based cathode material with a fast-ion conductor coating layer and bulk doping, and its preparation method. The invention process achieves the doping of other elements such as P and Al while completing the coating, that is, it realizes the coating and doping process in one step. Through surface phosphate modification and bulk doping, the first coulombic efficiency of the lithium-rich manganese-based cathode material is improved, and its cycle stability and rate performance are also improved.
[0006] CN118315568A discloses a cerium-doped lithium-rich manganese-based cathode material coated with nano-cerium oxide. By using cerium to dope the bulk phase of the lithium-rich manganese-based cathode material, and coating the cathode material with nano-cerium oxide, the lithium-rich manganese-based cathode material is modified and synergistically modified through dual modification of ion doping and metal oxide coating. This overcomes the problems of severe capacity decay and poor rate performance of existing cathode materials during cycling.
[0007] In existing technologies, lithium-rich manganese-based cathode materials are usually modified by bulk doping. However, excessive bulk doping may reduce the number of active sites, which is detrimental to the capacity of lithium-rich manganese-based cathode materials.
[0008] Therefore, it is of great significance to provide a lithium-rich manganese-based precursor with good structural and interfacial stability, as well as excellent rate performance and cycle performance, and its preparation method. Summary of the Invention
[0009] To address the shortcomings of existing technologies, the present invention aims to provide a doped and coated lithium-rich manganese-based precursor, a cathode material, a preparation method, and a battery. The present invention prepares the doped and coated lithium-rich manganese-based precursor via co-precipitation, and obtains a gradient doping layer and a gradient coating layer in situ on the surface of the lithium-rich manganese-based precursor substrate. By controlling the concentration, addition timing, and flow rate of the nickel-cobalt-manganese mixed salt solution, aluminum salt, and magnesium salt, precise control of the composition of the lithium-rich manganese-based precursor is achieved.
[0010] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing a doped and coated lithium-rich manganese-based precursor, the method comprising: (1) A nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution are fed into the bottom liquid of the reactor in a co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix. (2) The nickel-cobalt-manganese mixed salt solution, precipitant solution and complexing agent solution are continuously introduced, the aluminum salt solution and magnesium salt solution are introduced, and the flow rate of the aluminum salt solution and magnesium salt solution is continuously increased linearly to form a co-precipitation reaction and a gradient doped layer is formed on the surface of the lithium-rich manganese-based precursor substrate. (3) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, linearly increase the flow rate of the aluminum salt solution, and / or linearly decrease the flow rate of the magnesium salt solution to co-precipitate the solution and form a gradient coating layer on the surface of the gradient doped layer.
[0011] This invention forms a gradient doping layer and a gradient coating layer in situ on the surface of a lithium-rich manganese-based precursor matrix through co-precipitation. By controlling the concentration, addition timing, and flow rate of the nickel-cobalt-manganese mixed salt solution, aluminum salt, and magnesium salt, the composition of the lithium-rich manganese-based precursor is precisely controlled.
[0012] This invention prepares a bulk-doped lithium-rich manganese-based precursor layer with an increased doping concentration gradient on the surface of an undoped lithium-rich manganese-based precursor substrate in situ. This improves the compatibility between the lithium-rich manganese-based precursor substrate and the gradient doped layer, avoids structural damage caused by volume expansion during charge and discharge of the cathode material, and enhances structural stability, which is beneficial to improving the cycle stability of the lithium-rich manganese-based cathode material. At the same time, the undoped lithium-rich manganese-based precursor substrate provides sufficient active sites to ensure the energy density of the lithium-rich manganese-based cathode material, and the gradient doped layer optimizes the lithium-ion transport path, improves ion conductivity, and is beneficial to improving the rate performance of the lithium-rich manganese-based cathode material. It can also effectively suppress the dissolution of Mn. Furthermore, the gradient coating layer and the gradient doped layer work together to improve interface stability and suppress electrolyte corrosion of the cathode material. The introduction of Mg(OH)2 effectively improves the ion conductivity of the gradient coating layer, further enhancing the cycle performance and rate performance of the lithium-rich manganese-based cathode material.
[0013] Preferably, in the aluminum salt solution and magnesium salt solution introduced in step (2), the molar ratio of Al to Mg is 1:(0.5~1).
[0014] Preferably, the total molar amount of Al and Mg in the aluminum salt solution and magnesium salt solution introduced in step (2) is 1 mol% to 3 mol% of the total molar amount of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution introduced in step (2).
[0015] Preferably, at the end of the coprecipitation reaction in step (3), the molar ratio of Al to Mg in the aluminum salt solution and the magnesium salt solution is 1:(0.1~0.3).
[0016] Preferably, the concentration of the nickel-cobalt-manganese mixed salt solution in step (1) is 1 mol / L to 2.5 mol / L.
[0017] Preferably, the concentrations of the aluminum salt solution and the magnesium salt solution in step (2) are each independently 0.05 mol / L to 0.3 mol / L.
[0018] Preferably, the flow rate of the nickel-cobalt-manganese mixed salt solution in step (1) is 0.5 L / min to 2 L / min.
[0019] Preferably, the flow rates of the magnesium salt solution and the aluminum salt solution in step (2) are each independently 0.025 L / min to 0.5 L / min.
[0020] Preferably, the D50 particle size of the lithium-rich manganese-based precursor matrix doped and coated in step (1) is 2 μm to 10 μm.
[0021] Preferably, the thickness of the gradient doped layer in step (2) is 200 nm to 500 nm.
[0022] Preferably, the thickness of the gradient coating layer in step (3) is 100nm~300nm.
[0023] Preferably, in the precipitant solution of step (1), the precipitant includes any one or a combination of at least two of NaOH, KOH, Na2CO3 or NaHCO3.
[0024] Preferably, in the complexing agent solution of step (1), the complexing agent includes ammonia.
[0025] Preferably, the concentration of the precipitant solution in step (1) is 20wt%~50wt%.
[0026] Preferably, the concentration of the complexing agent solution in step (1) is 10wt%~30wt%.
[0027] Preferably, the base liquid comprises deionized water.
[0028] Preferably, the reaction vessel is filled with an inert atmosphere.
[0029] Preferably, the temperature of the coprecipitation reaction in steps (1) to (3) is 40°C to 60°C.
[0030] Preferably, the pH of the coprecipitation reaction in step (1) is 10-11.
[0031] Preferably, the pH of the coprecipitation reaction in steps (2) and (3) is independently 7.5 to 8.5.
[0032] Secondly, the present invention provides a doped and coated lithium-rich manganese-based precursor, wherein the doped and coated lithium-rich manganese-based precursor is prepared by the preparation method described in the first aspect.
[0033] The lithium-rich manganese-based precursor prepared by this invention includes a lithium-rich manganese-based precursor matrix, and a gradient doping layer and a gradient coating layer formed in situ on the surface of the lithium-rich manganese-based precursor matrix. The gradient doping layer is made of Al-Mg co-doped lithium-rich manganese-based precursor, and the total doping concentration gradient of Al and Mg increases along the direction away from the lithium-rich manganese-based precursor matrix. The gradient coating layer is made of Al(OH)3 and Mg(OH)2, and the content gradient of Al(OH)3 increases and the content gradient of Mg(OH)2 decreases along the direction away from the gradient doping layer.
[0034] In the gradient-doped lithium-rich manganese-based precursor prepared by this invention, by setting a gradient doping layer and a gradient coating layer on the surface of the lithium-rich manganese-based precursor matrix, the two functional layer structures work together to ensure that the active sites in the lithium-rich manganese-based precursor matrix can be fully utilized, that is, to ensure the energy density of the cathode material. At the same time, the interface compatibility, interface structure stability and ion conduction performance of the lithium-rich manganese-based cathode material are optimized, and the cycle performance and rate performance are improved simultaneously.
[0035] Thirdly, the present invention provides a cathode material, which is prepared from the lithium-rich manganese-based precursor doped and coated as described in the second aspect.
[0036] The cathode material provided by the present invention includes a lithium-rich manganese substrate, and an Al-Al gradient co-doped layer and an Al2O3-MgO gradient composite coating layer formed in situ on the surface of the lithium-rich manganese substrate; the total doping concentration gradient of Al and Mg in the Al-Al gradient co-doped layer increases along the direction away from the lithium-rich manganese substrate; and the Al2O3 content gradient and the MgO content gradient decrease in the Al2O3-MgO gradient composite coating layer along the direction away from the Al-Al gradient co-doped layer.
[0037] Fourthly, the present invention provides a battery comprising the positive electrode material as described in the third aspect.
[0038] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention prepares the doped and coated lithium-rich manganese-based precursor by co-precipitation. The gradient doped layer and the gradient coated layer are prepared in situ on the surface of the lithium-rich manganese-based precursor matrix. By controlling the concentration, addition time and flow rate of the nickel-cobalt-manganese mixed salt solution, aluminum salt and magnesium salt, the composition of the lithium-rich manganese-based precursor is precisely controlled.
[0039] (2) The lithium-rich manganese-based precursor substrate prepared by the present invention forms a gradient doping layer and a gradient coating layer in situ on the surface. The two functional layer structures work together to ensure that the active sites in the lithium-rich manganese-based precursor substrate can be fully utilized, that is, to ensure the energy density of the prepared lithium-rich manganese-based cathode material. At the same time, it also optimizes the interface compatibility, interface structure stability and ion conduction performance of the lithium-rich manganese-based cathode material, and achieves simultaneous improvement of cycle performance and rate performance.
[0040] (3) The cathode material provided by the present invention achieves simultaneous improvement in cycle performance and rate performance while ensuring energy density. Detailed Implementation
[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0042] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values 1 and 2 are listed, and maximum range values 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.
[0043] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.
[0044] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.
[0045] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.
[0046] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means 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), meaning that step (c) can 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.
[0047] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."
[0048] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.
[0049] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.
[0050] In one specific embodiment, the present invention provides a method for preparing a doped and coated lithium-rich manganese-based precursor, the method comprising: (1) A nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution are fed into the bottom liquid of the reactor in a co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix. (2) The nickel-cobalt-manganese mixed salt solution, precipitant solution and complexing agent solution are continuously introduced, the aluminum salt solution and magnesium salt solution are introduced, and the flow rate of the aluminum salt solution and magnesium salt solution is continuously increased linearly to form a co-precipitation reaction and a gradient doped layer is formed on the surface of the lithium-rich manganese-based precursor substrate. (3) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, linearly increase the flow rate of the aluminum salt solution, and / or linearly decrease the flow rate of the magnesium salt solution to co-precipitate the solution and form a gradient coating layer on the surface of the gradient doped layer.
[0051] This invention forms a gradient doping layer and a gradient coating layer in situ on the surface of a lithium-rich manganese-based precursor matrix through co-precipitation. By controlling the concentration, addition timing, and flow rate of the nickel-cobalt-manganese mixed salt solution, aluminum salt, and magnesium salt, the composition of the lithium-rich manganese-based precursor is precisely controlled.
[0052] This invention prepares a bulk-doped lithium-rich manganese-based precursor layer with an increased doping concentration gradient on the surface of an undoped lithium-rich manganese-based precursor substrate in situ. This improves the compatibility between the lithium-rich manganese-based precursor substrate and the gradient doped layer, avoids structural damage caused by volume expansion during charge and discharge of the cathode material, and enhances structural stability, which is beneficial to improving the cycle stability of the lithium-rich manganese-based cathode material. At the same time, the undoped lithium-rich manganese-based precursor substrate provides sufficient active sites to ensure the energy density of the lithium-rich manganese-based cathode material, and the gradient doped layer optimizes the lithium-ion transport path, improves ion conductivity, and is beneficial to improving the rate performance of the lithium-rich manganese-based cathode material. It can also effectively suppress the dissolution of Mn. Furthermore, the gradient coating layer and the gradient doped layer work together to improve interface stability and suppress electrolyte corrosion of the cathode material. The introduction of Mg(OH)2 effectively improves the ion conductivity of the gradient coating layer, further enhancing the cycle performance and rate performance of the lithium-rich manganese-based cathode material.
[0053] In some embodiments, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution introduced in step (2) is 1:(0.5~1), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1.
[0054] In gradient doped layers, Al doping enhances the structural stability of lithium-rich manganese-based precursors, stabilizes the layered structure, suppresses phase transitions, and improves thermal stability. Mg effectively suppresses lithium-nickel mixing and optimizes ion transport channels. This invention, by controlling the molar ratio of Al and Mg, achieves synergistic effects, jointly improving the structural stability and ion transport performance of the gradient doped layer.
[0055] In some embodiments, the total molar amount of Al and Mg in the aluminum salt solution and magnesium salt solution introduced in step (2) is 1 mol% to 3 mol% of the total molar amount of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution introduced in step (2).
[0056] In some embodiments, at the end of the coprecipitation reaction in step (3), the molar ratio of Al to Mg in the aluminum salt solution and the magnesium salt solution is 1:(0.1~0.3), for example, it can be 1:0.1, 1:0.15, 1:0.2, 1:0.25 or 1:0.3.
[0057] In the gradient coating layer, on the side adjacent to the gradient doped layer, the molar ratio of Al(OH)3 to Mg(OH)2 is the same as that of Al to Mg in the gradient doped layer, and it has a relatively high Mg(OH)2 content. 2+ The radius is close to Li + The ability to dope a small amount of crystal lattice is beneficial for improving the interfacial compatibility between the gradient doped layer and the gradient coating layer, stabilizing the layered structure, and improving cycle life. At the same time, the higher proportion of Mg(OH)2 is beneficial for improving the ion conduction performance of the gradient coating layer. Furthermore, along the direction away from the gradient doped layer, the content of Al(OH)3 increases, which can form a dense coating layer structure, which is beneficial for resisting electrolyte corrosion.
[0058] In some embodiments, the concentration of the nickel-cobalt-manganese mixed salt solution in step (1) is 1 mol / L to 2.5 mol / L, for example, it can be 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.75 mol / L, 2 mol / L, 2.25 mol / L or 2.5 mol / L.
[0059] In some embodiments, the concentrations of the aluminum salt solution and the magnesium salt solution in step (2) are each independently 0.05 mol / L to 0.3 mol / L, for example, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L.
[0060] In some embodiments, the flow rate of the nickel-cobalt-manganese mixed salt solution in step (1) is 0.5 L / min to 2 L / min, for example, it can be 0.5 L / min, 0.75 L / min, 1 L / min, 1.25 L / min, 1.5 L / min, 1.75 L / min or 2 L / min.
[0061] In some embodiments, the flow rates of the magnesium salt solution and the aluminum salt solution in step (2) are each independently 0.025 L / min to 0.5 L / min, for example, 0.025 L / min, 0.05 L / min, 0.075 L / min, 0.1 L / min, 0.15 L / min, 0.2 L / min, 0.25 L / min, 0.3 L / min, 0.35 L / min, 0.4 L / min, 0.45 L / min or 0.5 L / min.
[0062] In some embodiments, the D50 particle size of the lithium-rich manganese-based precursor matrix doped and coated in step (1) is 2 μm to 10 μm, for example, it can be 2 μm, 4 μm, 6 μm, 8 μm or 10 μm.
[0063] In some implementations, the thickness of the gradient doped layer in step (2) is 200nm~500nm, for example, it can be 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm.
[0064] In some implementations, the thickness of the gradient coating layer in step (3) is 100nm~300nm, for example, it can be 100nm, 150nm, 200nm, 250nm or 300nm.
[0065] In some embodiments, the precipitant solution in step (1) includes any one or a combination of at least two of NaOH, KOH, Na2CO3 or NaHCO3.
[0066] In some embodiments, the complexing agent in the complexing agent solution of step (1) includes ammonia.
[0067] In some embodiments, the concentration of the precipitant solution in step (1) is 20wt% to 50wt%, for example, it can be 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% or 50wt%.
[0068] In some embodiments, the concentration of the complexing agent solution in step (1) is 10wt% to 30wt%, for example, it can be 10wt%, 15wt%, 20wt%, 25wt% or 30wt%.
[0069] In some embodiments, the base liquid includes deionized water.
[0070] In some embodiments, the reactor is filled with an inert atmosphere.
[0071] In some embodiments, the temperature of the coprecipitation reaction in steps (1) to (3) is 40°C to 60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.
[0072] In some embodiments, the pH of the coprecipitation reaction in step (1) is 10 to 11, for example, it can be 10, 10.2, 10.4, 10.6, 10.8 or 11.
[0073] In some embodiments, the pH of the coprecipitation reaction described in steps (2) and (3) is independently 7.5 to 8.5, for example, it can be 7.5, 7.7, 7.9, 8, 8.1, 8.3 or 8.5.
[0074] In another specific embodiment, the present invention provides a doped and coated lithium-rich manganese-based precursor, which is prepared by the preparation method described in one of the preceding specific embodiments.
[0075] The lithium-rich manganese-based precursor prepared by this invention includes a lithium-rich manganese-based precursor matrix, and a gradient doping layer and a gradient coating layer formed in situ on the surface of the lithium-rich manganese-based precursor matrix. The gradient doping layer is made of Al-Mg co-doped lithium-rich manganese-based precursor, and the total doping concentration gradient of Al and Mg increases along the direction away from the lithium-rich manganese-based precursor matrix. The gradient coating layer is made of Al(OH)3 and Mg(OH)2, and the content gradient of Al(OH)3 increases and the content gradient of Mg(OH)2 decreases along the direction away from the gradient doping layer.
[0076] In the gradient-doped lithium-rich manganese-based precursor prepared by this invention, by setting a gradient doping layer and a gradient coating layer on the surface of the lithium-rich manganese-based precursor matrix, the two functional layer structures work together to ensure that the active sites in the lithium-rich manganese-based precursor matrix can be fully utilized, that is, to ensure the energy density of the cathode material. At the same time, the interface compatibility, interface structure stability and ion conduction performance of the lithium-rich manganese-based cathode material are optimized, and the cycle performance and rate performance are improved simultaneously.
[0077] In yet another embodiment, the present invention provides a cathode material prepared from the lithium-rich manganese-based precursor doped and coated as described in another embodiment above.
[0078] The cathode material provided by the present invention includes a lithium-rich manganese substrate, and an Al-Al gradient co-doped layer and an Al2O3-MgO gradient composite coating layer formed in situ on the surface of the lithium-rich manganese substrate; the total doping concentration gradient of Al and Mg in the Al-Al gradient co-doped layer increases along the direction away from the lithium-rich manganese substrate; and the Al2O3 content gradient and the MgO content gradient decrease in the Al2O3-MgO gradient composite coating layer along the direction away from the Al-Al gradient co-doped layer.
[0079] In yet another embodiment, the present invention provides a battery comprising a positive electrode material as described in yet another embodiment above.
[0080] The numerical range described in this invention includes not only the point values listed above, but also any point values within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values included in the range.
[0081] Example 1 This embodiment provides a method for preparing a doped and coated lithium-rich manganese-based precursor, the method comprising the following steps: (1) Nickel nitrate, cobalt nitrate and manganese nitrate are dissolved in water to prepare a nickel-cobalt-manganese mixed salt solution with a concentration of 2 mol / L; magnesium nitrate and aluminum nitrate are dissolved in water to prepare aluminum salt solution and magnesium salt solution with a concentration of 0.2 mol / L respectively; a 30 wt% NaOH solution is prepared as a precipitant and a 20 wt% ammonia solution is prepared as a complexing agent; deionized water is added to the reaction vessel as a bottom liquid and nitrogen gas is introduced into the reaction vessel.
[0082] (2) According to the stoichiometric ratio, the nickel-cobalt-manganese mixed salt solution, NaOH solution and ammonia solution were fed into the bottom liquid of the reactor in parallel. The flow rate of the nickel-cobalt-manganese mixed salt solution was 1.45 L / min. The flow rates of the NaOH solution and ammonia solution were controlled and the pH was adjusted to 10.6. The co-precipitation reaction was carried out at 50℃ to obtain a lithium-rich manganese-based precursor matrix with a D50 particle size of 6 μm. (3) While maintaining the continuous flow of nickel-cobalt-manganese mixed salt solution, NaOH solution, and ammonia solution, increase the flow of aluminum salt solution and magnesium salt solution, both with an initial flow rate of 0.025 L / min, adjust the pH to 8, and conduct the co-precipitation reaction at 50 °C. Continuously and linearly increase the flow rates of aluminum salt solution and magnesium salt solution to 0.3 L / min and 0.235 L / min, respectively, to form a 300 nm thick gradient doped layer on the surface of the lithium-rich manganese-based precursor substrate. In this step, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:0.8, and the total molar amount of Al and Mg is 2 mol% of the total molar amount of nickel-cobalt-manganese in the nickel-cobalt-manganese mixed salt solution. (4) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, adjust the pH to 8.1, and continue the co-precipitation reaction at 50°C. Continuously increase the flow rate of the aluminum salt solution to 0.5 L / min and simultaneously decrease the flow rate of the magnesium salt solution to 0.1 L / min. At this time, the molar ratio of Al to Mg in the fed aluminum salt solution and magnesium salt solution is 1:0.2, forming a 200 nm thick gradient coating layer on the surface of the gradient doped layer.
[0083] Example 2 This embodiment provides a method for preparing a doped and coated lithium-rich manganese-based precursor, the method comprising the following steps: (1) Nickel nitrate, cobalt nitrate and manganese nitrate were dissolved in water to prepare a nickel-cobalt-manganese mixed salt solution with a concentration of 1 mol / L; magnesium nitrate and aluminum nitrate were dissolved in water to prepare aluminum salt solution with a concentration of 0.1 mol / L and magnesium salt solution with a concentration of 0.05 mol / L, respectively; a 50 wt% NaOH solution was prepared as a precipitant and a 30 wt% ammonia solution was prepared as a complexing agent; deionized water was added to the reactor as a bottom liquid and nitrogen gas was introduced into the reactor.
[0084] (2) According to the stoichiometric ratio, the nickel-cobalt-manganese mixed salt solution, NaOH solution and ammonia solution were fed into the bottom liquid of the reactor in parallel. The flow rate of the nickel-cobalt-manganese mixed salt solution was 0.5 L / min. The flow rates of the NaOH solution and ammonia solution were controlled and the pH was adjusted to 10. The co-precipitation reaction was carried out at 40℃ to obtain a lithium-rich manganese-based precursor matrix with a D50 particle size of 2 μm. (3) The nickel-cobalt-manganese mixed salt solution, NaOH solution, and ammonia solution are continuously introduced. The flow rates of aluminum salt solution and magnesium salt solution, with initial concentrations of 0.03 L / min and 0.025 L / min respectively, are increased. The pH is adjusted to 7.5, and the co-precipitation reaction is carried out at 40 °C. The flow rates of aluminum salt solution and magnesium salt solution are continuously increased linearly to 0.036 L / min and 0.042 L / min respectively, forming a 200 nm thick gradient doped layer on the surface of the lithium-rich manganese-based precursor substrate. In this step, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:0.51, and the total molar amount of Al and Mg is 1 mol% of the total molar amount of nickel-cobalt-manganese in the nickel-cobalt-manganese mixed salt solution. (4) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, adjust the pH to 7.6, continue the co-precipitation reaction at 40°C, keep the flow rate of the magnesium salt solution constant, and continuously increase the flow rate of the aluminum salt solution to 0.21 L / min. At this time, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:0.1, and a 100 nm thick gradient coating layer is formed on the surface of the gradient doped layer.
[0085] Example 3 This embodiment provides a method for preparing a doped and coated lithium-rich manganese-based precursor, the method comprising the following steps: (1) Nickel nitrate, cobalt nitrate and manganese nitrate are dissolved in water to prepare a nickel-cobalt-manganese mixed salt solution with a concentration of 2.5 mol / L; magnesium nitrate and aluminum nitrate are dissolved in water to prepare aluminum salt solution and magnesium salt solution with a concentration of 0.3 mol / L respectively; a 20 wt% NaOH solution is prepared as a precipitant and a 10 wt% ammonia solution is prepared as a complexing agent; deionized water is added to the reactor as a bottom liquid and nitrogen gas is introduced into the reactor.
[0086] (2) According to the stoichiometric ratio, the nickel-cobalt-manganese mixed salt solution, NaOH solution and ammonia solution were fed into the bottom liquid of the reactor in parallel. The flow rate of the nickel-cobalt-manganese mixed salt solution was 2 L / min. The flow rates of the NaOH solution and ammonia solution were controlled and the pH was adjusted to 11. The co-precipitation reaction was carried out at 60℃ to obtain a lithium-rich manganese-based precursor matrix with a D50 particle size of 10 μm. (3) Maintain a continuous flow of nickel-cobalt-manganese mixed salt solution, NaOH solution, and ammonia solution. Increase the flow of aluminum salt solution and magnesium salt solution, both with an initial flow rate of 0.025 L / min. Adjust the pH to 8.5 and perform a co-precipitation reaction at 60 °C. Continuously and linearly increase the flow rates of aluminum salt solution and magnesium salt solution to 0.475 L / min to form a 300 nm thick gradient doped layer on the surface of the lithium-rich manganese-based precursor substrate. In this step, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:1, and the total molar amount of Al and Mg is 3 mol% of the total molar amount of nickel-cobalt-manganese in the nickel-cobalt-manganese mixed salt solution. (4) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, adjust the pH to 8.3, continue the co-precipitation reaction at 60°C, continuously increase the flow rate of the aluminum salt solution to 0.4 L / min, and simultaneously decrease the flow rate of the magnesium salt solution to 0.12 L / min. At this time, the molar ratio of Al to Mg in the fed aluminum salt solution and magnesium salt solution is 1:0.3, forming a gradient coating layer with a thickness of 200 nm on the surface of the gradient doped layer.
[0087] Example 4 This embodiment provides a method for preparing a lithium-rich manganese-based precursor with doping coating. The preparation method is the same as in Example 1 except that in step (3), the flow rates of the aluminum salt solution and the magnesium salt solution are continuously and linearly increased to 0.375 L / min and 0.154 L / min, respectively, so that the molar ratio of Al to Mg in the aluminum salt solution and the magnesium salt solution is 1:0.45, and in step (4), the flow rate of the aluminum salt solution and the magnesium salt solution is adjusted to 0.3 L / min and 0.235 L / min, respectively, while stopping the flow of the nickel-cobalt-manganese mixed salt solution into the reactor.
[0088] Example 5 This embodiment provides a method for preparing a lithium-rich manganese-based precursor with doping coating. Except for step (3), in which the flow rates of the aluminum salt solution and the magnesium salt solution are continuously and linearly increased to 0.258 L / min and 0.273 L / min respectively, so that the molar ratio of Al to Mg in the aluminum salt solution and the magnesium salt solution is 1:1.05, and in step (4), in which the flow of the nickel-cobalt-manganese mixed salt solution into the reactor is stopped while the flow rates of the aluminum salt solution and the magnesium salt solution are adjusted to 0.3 L / min and 0.235 L / min respectively, the rest of the method is the same as in Example 1.
[0089] Example 6 This embodiment provides a method for preparing a lithium-rich manganese-based precursor with doping coating. Except in step (4), the flow rate of the aluminum salt solution is continuously and linearly increased to 0.5 L / min, while the flow rate of the magnesium salt solution is simultaneously reduced to 0.04 L / min, so that at the end of co-precipitation, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:0.08. All other steps are the same as in Example 1.
[0090] Example 7 This embodiment provides a method for preparing a lithium-rich manganese-based precursor with doping coating. Except for step (4), in which the flow rate of the aluminum salt solution is continuously increased linearly to 0.5 L / min and the flow rate of the magnesium salt solution is simultaneously decreased to 0.175 L / min, so that when the co-precipitation is completed, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:0.35, the rest is the same as in Example 1.
[0091] Comparative Example 1 This comparative example provides a method for preparing a doped and coated lithium-rich manganese-based precursor, wherein the D50 particle size of the doped and coated lithium-rich manganese-based precursor is 6 μm, and the doped and coated lithium-rich manganese-based precursor includes an Al-Mg co-doped lithium-rich manganese-based precursor matrix and a gradient coating layer.
[0092] In the Al-Mg co-doped lithium-rich manganese-based precursor matrix, the molar ratio of Al to Mg is 1:0.8, and the total molar percentage of Al and Mg is 2 mol%. The gradient coating layer is made of Al(OH)3 and Mg(OH)2. On the side of the gradient coating layer adjacent to the gradient doping layer, the molar ratio of Al(OH)3 to Mg(OH)2 is 1:0.8. Along the direction away from the gradient doping layer, the molar ratio gradient of Al(OH)3 increases, and the molar ratio gradient of Mg(OH)2 decreases. On the side of the gradient coating layer away from the gradient doping layer, the molar ratio of Al(OH)3 to Mg(OH)2 is 1:0.2. The mass of the gradient coating layer is 1.5 wt% of the mass of the doped lithium-rich manganese-based precursor.
[0093] The preparation method of the doped and coated lithium-rich manganese-based precursor includes the following steps: (1) Nickel nitrate, cobalt nitrate and manganese nitrate are dissolved in water to prepare a nickel-cobalt-manganese mixed salt solution with a concentration of 2 mol / L; magnesium nitrate and aluminum nitrate are dissolved in water to prepare aluminum salt solution and magnesium salt solution with a concentration of 0.2 mol / L respectively; a 30 wt% NaOH solution is prepared as a precipitant and a 20 wt% ammonia solution is prepared as a complexing agent; deionized water is added to the reaction vessel as a bottom liquid and nitrogen gas is introduced into the reaction vessel.
[0094] (2) According to the stoichiometric ratio, a nickel-cobalt-manganese mixed salt solution, an aluminum salt solution, a magnesium salt solution, a NaOH solution, and an ammonia solution were simultaneously introduced into the bottom liquid of the reactor. The flow rate of the nickel-cobalt-manganese mixed salt solution was 1.45 L / min, the flow rate of the aluminum salt solution was 0.322 L / min, and the flow rate of the magnesium salt solution was 0.258 L / min. The flow rates of the NaOH solution and the ammonia solution were controlled, and the pH was adjusted to 10.6. The co-precipitation reaction was carried out at 50 °C to obtain an Al-Mg co-doped lithium-rich manganese-based precursor matrix, wherein the molar ratio of Al to Mg was 1:0.8, and the total molar percentage of Al and Mg was 2 mol%. (3) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, adjust the pH to 8.1, and continue the co-precipitation reaction at 50°C. Continuously increase the flow rate of the aluminum salt solution to 0.5 L / min and simultaneously decrease the flow rate of the magnesium salt solution to 0.1 L / min. At this time, the molar ratio of Al to Mg in the fed aluminum salt solution and magnesium salt solution is 1:0.2, forming a 200 nm thick gradient coating layer on the surface of the gradient doped layer.
[0095] Performance testing: The electrical properties of the cathode materials prepared from the doped and coated lithium-rich manganese-based precursors provided in all the above embodiments and comparative examples were tested. The test methods included: (a) Preparation of cathode material: The doped and coated lithium-rich manganese-based precursor materials provided in all the above examples and comparative examples are mixed with lithium hydroxide at a molar ratio of Li / (Ni+Co+Mn)=1.25 and sintered in air atmosphere. The sintering process includes sintering at 300°C for 2 hours at a heating rate of 5°C / min, then heating to 500°C for 2 hours, and finally heating to 850°C for 8 hours. The cathode material is then naturally cooled to room temperature to obtain the cathode material.
[0096] (b) Preparation of positive electrode sheet: The prepared positive electrode material is dispersed in NMP with polyvinylidene fluoride and conductive carbon black in a mass ratio of 94:3:3 to prepare a positive electrode slurry, which is then coated on the surface of aluminum foil and dried to obtain a positive electrode sheet.
[0097] (c) Assemble lithium-ion batteries: Match the positive electrode with the graphite negative electrode, use a polyethylene separator, and use a 1 mol / L LiPF6 EC:DEC:DMC=1:1:1 solution as the electrolyte to assemble lithium-ion batteries.
[0098] (d) At 25℃, within a voltage range of 2.5V to 4.3V, perform charge and discharge at 0.1C to test the 0.1C discharge specific capacity and first-time efficiency (first-time efficiency = first-time discharge specific capacity / first-time charge specific capacity × 100%); then test the battery's rate performance, including sequentially performing one 0.5C charge and discharge cycle, one 1C charge and discharge cycle, and one 3C charge and discharge cycle to test the battery's rate capacity retention rate at 0.5C, 1C, and 3C (rate capacity retention rate = nC discharge specific capacity / 0.1C discharge specific capacity × 100%); finally, at a 0.5C rate, perform 500 charge and discharge cycles to test the cycle capacity retention rate (cycle capacity retention rate = 500th discharge capacity / 1st discharge capacity × 100%).
[0099] The test results are shown in Table 1.
[0100] Table 1 In summary, compared with Examples 1 to 7 and the test results of Comparative Example 1, and compared with the traditional bulk doping combined with coating layer technical solution, the present invention, by setting a gradient doping layer and a gradient coating layer on the surface of the lithium-rich manganese-based precursor matrix, with the two functional layer structures working together, ensures that the active sites in the lithium-rich manganese-based precursor matrix can be fully utilized, that is, ensures the energy density of the prepared lithium-rich manganese-based cathode material, while also optimizing the interface compatibility, interface structure stability and ion conduction performance of the lithium-rich manganese-based cathode material, and achieving simultaneous improvement in cycle performance and rate performance.
[0101] According to the test results of Examples 1, 4 and 5, if the molar ratio of Al and Mg in the aluminum salt solution and magnesium salt solution introduced in step (3) is unbalanced, it will not be conducive to the gradient doping layer playing a role in stabilizing the structure and optimizing ion conductivity, resulting in unsatisfactory improvement in the cycle performance and rate performance of the battery.
[0102] According to the test results of Examples 1, 6 and 7, if the molar ratio of Al and Mg in the aluminum salt solution and magnesium salt solution introduced at the end of co-precipitation is unbalanced, the gradient coating layer cannot effectively inhibit the corrosion of the electrolyte and the dissolution of Mn, and cannot effectively improve the ion conduction performance of the coating layer, resulting in unsatisfactory improvement in the cycle performance and rate performance of the battery.
[0103] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A method for preparing a doped and coated lithium-rich manganese-based precursor, characterized in that, The preparation method includes: (1) A nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution are fed into the bottom liquid of the reactor in a co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix. (2) The nickel-cobalt-manganese mixed salt solution, precipitant solution and complexing agent solution are continuously introduced, the aluminum salt solution and magnesium salt solution are introduced, and the flow rate of the aluminum salt solution and magnesium salt solution is continuously increased linearly to form a co-precipitation reaction and a gradient doped layer is formed on the surface of the lithium-rich manganese-based precursor substrate. (3) Stop feeding the nickel-cobalt-manganese mixed salt solution into the reactor, linearly increase the flow rate of the aluminum salt solution, and / or linearly decrease the flow rate of the magnesium salt solution to co-precipitate the solution and form a gradient coating layer on the surface of the gradient doped layer.
2. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution is 1:(0.5~1); And / or, the total molar amount of Al and Mg in the aluminum salt solution and magnesium salt solution introduced in step (2) is 1 mol% to 3 mol% of the total molar amount of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution introduced in step (2).
3. The preparation method according to claim 1 or 2, characterized in that, When the coprecipitation reaction in step (3) ends, the molar ratio of Al to Mg in the aluminum salt solution and magnesium salt solution that are passed through is 1:(0.1~0.3).
4. The preparation method according to any one of claims 1 to 3, characterized in that, The concentration of the nickel-cobalt-manganese mixed salt solution in step (1) is 1 mol / L to 2.5 mol / L; And / or, the concentrations of the aluminum salt solution and the magnesium salt solution in step (2) are each independently 0.05 mol / L to 0.3 mol / L; And / or, the flow rate of the nickel-cobalt-manganese mixed salt solution in step (1) is 0.5 L / min to 2 L / min; And / or, the flow rates of the magnesium salt solution and the aluminum salt solution in step (2) are each independently 0.025 L / min to 0.5 L / min.
5. The preparation method according to any one of claims 1 to 4, characterized in that, The D50 particle size of the lithium-rich manganese-based precursor matrix doped and coated in step (1) is 2 μm to 10 μm; And / or, the thickness of the gradient doped layer in step (2) is 200 nm to 500 nm; And / or, the thickness of the gradient coating layer in step (3) is 100nm~300nm.
6. The preparation method according to any one of claims 1 to 5, characterized in that, In the precipitant solution described in step (1), the precipitant includes any one or a combination of at least two of NaOH, KOH, Na2CO3 or NaHCO3; And / or, in the complexing agent solution of step (1), the complexing agent includes ammonia; And / or, the concentration of the precipitant solution in step (1) is 20wt%~50wt%; And / or, the concentration of the complexing agent solution in step (1) is 10wt%~30wt%.
7. The preparation method according to any one of claims 1 to 6, characterized in that, The base liquid includes deionized water; And / or, the reactor is inert; And / or, the temperature of the coprecipitation reaction described in steps (1) to (3) is 40℃~60℃; And / or, the pH of the coprecipitation reaction described in step (1) is 10-11; And / or, the pH of the coprecipitation reaction described in steps (2) and (3) is independently 7.5 to 8.
5.
8. A doped and coated lithium-rich manganese-based precursor, characterized in that, The doped and coated lithium-rich manganese-based precursor is prepared by the preparation method according to any one of claims 1 to 7.
9. A positive electrode material, characterized in that, The cathode material is prepared from the lithium-rich manganese-based precursor doped and coated according to claim 8.
10. A battery, characterized in that, The battery includes the positive electrode material as described in claim 9.