Fluorine and tungsten co-doped full-concentration-gradient high-nickel positive electrode material and preparation method and application thereof

Abstract

This invention provides a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, its preparation method, and its application. The preparation method includes: mixing a tungsten-doped high-nickel cathode material precursor, a lithium source, and a fluorine source, followed by a first heat treatment and a second heat treatment to obtain the fluorine-tungsten co-doped high-nickel cathode material. This invention uses a tungsten-doped high-nickel cathode material precursor as raw material and introduces a fluorine source for surface doping during heat treatment to prepare the fluorine-tungsten co-doped high-nickel cathode material, achieving a simultaneous improvement in discharge specific capacity and cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to cathode materials, and more particularly to a fluorine-tungsten co-doped high-nickel cathode material with full concentration gradient, its preparation method, and its application. Background Technology

[0002] Layered lithium nickel cobalt manganese oxide (LiCO) ternary materials are among the most promising cathode materials. Currently, the main approaches to improving the capacity of LiCO ternary materials are usually to increase the nickel content or increase the operating voltage. However, in the deep delithiation state of LiCO ternary materials, Ni elements will form highly catalytically active Ni on the cathode surface. 4+ During this process, a side reaction occurs, reducing the oxygen to electrochemically inert NiO-like impurities. Simultaneously, this side reaction induces the release of oxygen from the bulk structure, accompanied by a dramatic release of heat, which can lead to thermal runaway in severe cases. Therefore, improving the structural stability of high-nickel content cathode materials is a crucial issue that urgently needs to be addressed.

[0003] CN108467070A discloses a chromium-doped high-voltage, high-nickel ternary lithium-ion battery cathode material and its preparation method. An inorganic salt containing tetravalent chromium is immersed in molten sodium hydroxide for reaction. After separating magnesium oxide, an ammonium complex containing nickel and chromium is obtained. Then, an oxidizing agent, a cobalt source, and a manganese source are added, followed by ball milling. A chromium-doped NCM precursor is then prepared using a co-precipitation method. After pre-calcination and grinding, it is mixed with powdered lithium source and subjected to oxygen-enriched solid-state sintering to obtain the chromium-doped high-nickel ternary lithium-ion battery cathode material. This method forms a stable nickel layer structure through the interaction of tetravalent chromium and trivalent nickel, while simultaneously allowing the tetravalent chromium to undergo disproportionation and mixed valence states during sintering. This effectively suppresses the problem of nickel ions detaching from the crystal lattice due to over-oxidation. The resulting high-nickel ternary cathode material exhibits good cycle performance, excellent high-temperature performance, minimal capacity loss in lithium-ion batteries during use, and good safety and stability.

[0004] CN114906884A discloses a method for preparing a fluorine-niobium dual-doped lithium niobate-coated ternary material, comprising the following steps: (1) preparing a nickel-cobalt-manganese hydroxide precursor by co-precipitation reaction; (2) uniformly stirring the fluorine-niobate acid and the nickel-cobalt-manganese hydroxide precursor, then adding ammonia water or introducing ammonia gas to generate niobium hydroxide and ammonium fluoride, thereby obtaining a composite material of the modified precursor; (3) mixing the composite material in step (2) with lithium hydroxide, and calcining it at high temperature under an oxygen atmosphere to obtain a fluorine-niobium dual-doped lithium niobate-coated ternary material; and crushing, classifying, and sieving the fluorine-niobium dual-doped lithium niobate-coated ternary material generated in step (3) using an air jet mill to obtain the finished ternary material. This invention utilizes in-situ fluorine-niobium dual-doped ternary material to generate lithium niobate on the surface, forming a fluorine-niobium dual-doped and lithium niobate-coated ternary material, improving the interface stability and cycle performance of the ternary material, and solving the residual alkali problem using a waterless washing process to reduce the loss of electrical performance.

[0005] CN113293441A discloses a method for preparing a strontium titanate-coated single-crystal nickel-rich ternary cathode material. This invention is based on the sol-gel method combined with ultrasonic external field treatment. It uses SrTiO3 as the core coating on the surface of a single-crystal high-nickel ternary material, introducing film-forming additives and complexing agents to capture active ions to ensure the formation of a uniform SrTiO3 coating layer. This reduces the loss of active material due to severe side reactions, improving the material's cycle life. Simultaneously, the large specific surface area and pseudocapacitive effect of nanoscale SrTiO3 accelerate the lithium-ion insertion / extraction process, improving the material's rate performance. This achieves the goal of simultaneously solving the problems of short cycle life and poor high-rate performance of single-crystal high-nickel materials.

[0006] Therefore, it is of great significance to provide a high-nickel cathode material with high capacity, good structural stability, and long cycle life, as well as its preparation method. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, its preparation method, and its applications. This invention uses a tungsten-doped high-nickel cathode material precursor as raw material and introduces a fluorine source for surface doping during heat treatment to prepare a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, achieving a simultaneous improvement in discharge specific capacity and cycle life.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, the method comprising:

[0010] The fluorine-tungsten co-doped high-nickel cathode material is prepared by sequentially subjecting a mixed tungsten-doped full-concentration gradient high-nickel cathode material precursor, a lithium source, and a fluorine source to a first heat treatment and a second heat treatment.

[0011] This invention uses a tungsten-doped high-nickel cathode material precursor with a full concentration gradient as raw material. Tungsten doping can suppress grain boundary fusion during subsequent heat treatment, and to a certain extent avoid the weakening of the concentration gradient caused by the diffusion of transition metal ions. This maintains a composition closer to the design of the full concentration gradient slope in the precursor, ensuring that the composition of the prepared tungsten-fluorine co-doped high-nickel cathode material matrix is ​​controllable, improving the structural stability of the material, and reducing intergranular microcracks caused by side reactions during charge and discharge, thereby achieving simultaneous improvement in capacity and cycle performance.

[0012] By introducing a fluorine source for surface doping, fluorine elements form extremely strong F-TM bonds with transition metal elements in the tungsten-doped high-nickel cathode material matrix at full concentration gradients, forming a rock salt phase fluorine-doped layer on the material surface. This further enhances the structural stability of the material, reduces oxygen loss during charge-discharge cycles, and further improves the cycle life of the material.

[0013] In this invention, the "full concentration gradient" refers to the continuous change in the transition metal concentration from the core to the surface of the prepared high-nickel cathode material precursor.

[0014] Preferably, the D50 particle size of the tungsten-doped full-concentration gradient high-nickel cathode material precursor is 8 μm to 14 μm, and more preferably 9.5 μm to 10.5 μm.

[0015] Preferably, the method for preparing the tungsten-doped high-nickel cathode material precursor with full concentration gradient includes:

[0016] First, a portion of a first nickel-cobalt-manganese solution is placed in a mixing tank. Then, the first and second nickel-cobalt-manganese solutions are introduced into the mixing tank in parallel at a first flow rate and a second flow rate, respectively, to obtain a mixed salt solution. The mixed salt solution, tungsten source solution, precipitant solution, and complexing agent solution are introduced into a reaction vessel containing a bottom liquid in parallel to carry out a co-precipitation reaction to prepare the high-nickel cathode material precursor with a full concentration gradient. The mixed salt solution is introduced into the reaction vessel at a third flow rate. The third flow rate is greater than the sum of the first and second flow rates. Based on the proportion of nickel in nickel-cobalt-manganese, the proportion of nickel in the first nickel-cobalt-manganese solution is higher than the proportion of nickel in the second nickel-cobalt-manganese solution.

[0017] In the co-precipitation process provided by this invention, a portion of the first nickel-cobalt-manganese solution is first introduced into the mixing tank, and then the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution are introduced into the mixing tank in parallel. The flow rate of the mixed salt solution is greater than the total flow rate of the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution. The second nickel-cobalt-manganese solution, which has a lower nickel content, can reduce the nickel content gradient in the mixed salt solution. At the same time, the introduction of the first nickel-cobalt-manganese solution can slow down the rate of decrease in the nickel content in the mixed salt solution, thus achieving controllable slope of the nickel concentration gradient in the prepared high-nickel cathode material precursor with full concentration gradient.

[0018] This invention simultaneously introduces a tungsten source solution during the co-precipitation process to prepare a high-nickel cathode material precursor with a full concentration gradient, where the nickel content decreases along the full concentration gradient from the core to the surface, while W is uniformly doped from the core to the surface. The uniformly doped W can suppress grain boundary fusion during subsequent heat treatment and, to a certain extent, block the concentration gradient weakening caused by the diffusion of transition metal ions. This maintains a composition closer to the designed full concentration gradient slope in the precursor, ensuring precise control of the full concentration gradient slope of the prepared high-nickel cathode material from the core to the surface. While improving capacity, the low-nickel surface component effectively avoids the problems of poor structural stability of high-nickel materials and easy side reactions with the electrolyte. The full concentration gradient slope alleviates the stress between the high-nickel and low-nickel components, improves the cycle stability of the precursor, and reduces intergranular microcracks caused by side reactions during charge and discharge, thereby achieving a simultaneous improvement in cycle performance.

[0019] Preferably, the coprecipitation reaction is carried out by overflow method to ensure that the volume of the reaction liquid in the reactor is always kept within the optimal range.

[0020] Preferably, with the volume of the reactor as V, the total volume of the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution is 300%V to 600%V.

[0021] Preferably, with the volume of the reactor as V, the sum of the first flow rate and the second flow rate is 0.5%V / h to 2%V / h.

[0022] Preferably, the volume of the reactor is V, and the third flow rate is 2%V / h to 4%V / h.

[0023] Preferably, the flow rate of the tungsten source solution is 0.01% V / h to 0.1% V / h.

[0024] Preferably, the ratio of the third flow rate to the flow rate of the tungsten source solution is 1:(0.0025~0.05).

[0025] Preferably, the ratio of the third flow velocity to the sum of the first and second flow velocities is 1:(0.25~1).

[0026] Preferably, the W in the tungsten source solution is 0.1 mol% to 5 mol% of the total amount of Ni, Co, and Mn in the mixed salt solution.

[0027] Preferably, in the first nickel-cobalt-manganese solution, the molar ratio of Ni:Co:Mn is x1:y1:z1, x1+y1+z1=1, 0.90≤x1≤1, 0≤y1≤0.1, and 0≤z1≤0.1.

[0028] Preferably, in the second nickel-cobalt-manganese solution, the molar ratio of Ni:Co:Mn is x2:y2:z2, x2+y2+z2=1, 0.6≤x2≤0.89, 0≤y2≤0.4, and 0≤z2≤0.4.

[0029] Preferably, in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution, the Ni source includes any one or a combination of at least two of nickel sulfate, nickel nitrate, or nickel acetate.

[0030] Preferably, in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution, the Co source includes any one or a combination of at least two of cobalt sulfate, cobalt nitrate, or cobalt acetate.

[0031] Preferably, in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution, the Mn source includes any one or a combination of at least two of manganese sulfate, manganese nitrate, or manganese acetate.

[0032] Preferably, the tungsten source in the tungsten source solution includes any one or a combination of at least two of tungsten trioxide, sodium tungstate, and tungsten dioxide.

[0033] Preferably, the solvent of the tungsten source solution includes sodium hydroxide solution and / or potassium hydroxide solution.

[0034] Preferably, the precipitant in the precipitant solution includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or sodium bicarbonate.

[0035] Preferably, the complexing agent in the complexing agent solution includes any one or a combination of at least two of ammonia, oxalic acid, citric acid, sodium carbonate, or ammonium bicarbonate.

[0036] Preferably, the concentration of the tungsten source in the tungsten source solution is 0.1 mol / L to 2 mol / L.

[0037] Preferably, the total concentration of Ni, Co and Mn in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution is 1.0 mol / L to 3.0 mol / L.

[0038] Preferably, the concentration of sodium hydroxide solution or potassium hydroxide solution in the tungsten source solution is 10wt% to 20wt%.

[0039] Preferably, the concentration of the precipitant solution is 20 wt% to 40 wt%.

[0040] Preferably, the concentration of the complexing agent solution is 10 wt% to 20 wt%.

[0041] Preferably, the base liquid includes water, NaOH solution, and ammonia solution.

[0042] Preferably, the pH of the base solution is 10.0 to 12.0.

[0043] Preferably, the ammonia concentration of the base liquid is 1.5 g / L to 3 g / L.

[0044] Preferably, the reaction vessel is in an inert atmosphere.

[0045] Preferably, the inert atmosphere includes nitrogen and / or an inert gas, wherein the inert gas includes argon and / or helium.

[0046] Preferably, the temperature of the first heat treatment is 450℃~600℃, and the time is 2h~8h.

[0047] Preferably, the temperature of the second heat treatment is 600℃~900℃, and the time is 5h~20h.

[0048] Preferably, the atmosphere for the first and second heat treatments includes any one or a combination of at least two of argon, nitrogen, helium, or oxygen, with oxygen being the most preferred.

[0049] Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium nitrate, with lithium hydroxide being the most preferred.

[0050] Preferably, the fluorine source includes any one or a combination of at least two of lithium fluoride, sodium fluoride, or ammonium fluoride.

[0051] Preferably, the molar ratio of the tungsten-doped full-concentration gradient high-nickel cathode material precursor, the lithium source, and the fluorine source is 1:(1.0~1.4):(0.003~0.015), and more preferably 1:(1.02~1.1):(0.003~0.015).

[0052] In a second aspect, the present invention provides a fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material prepared by the preparation method described in the first aspect, wherein the fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material includes a tungsten-doped gradient high-nickel cathode substrate and a rock salt phase fluorine-doped layer formed in situ on the surface of the tungsten-doped gradient high-nickel cathode substrate.

[0053] Thirdly, the present invention provides a lithium-ion battery comprising the fluorine-tungsten co-doped high-nickel cathode material with full concentration gradient as described in the second aspect.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] This invention uses tungsten-doped high-nickel cathode material precursors with full concentration gradient as raw materials and introduces a fluorine source for surface doping during heat treatment to prepare fluorine-tungsten co-doped high-nickel cathode materials with full concentration gradient, achieving simultaneous improvement in discharge specific capacity and cycle life. Attached Figure Description

[0056] Figure 1 This is a SEM image of the tungsten-doped high-nickel cathode material precursor with full concentration gradient in Example 1 of the present invention.

[0057] Figure 2 This is a SEM image of the fluorine-tungsten co-doped high-nickel cathode material with full concentration gradient in Example 1 of the present invention. Detailed Implementation

[0058] 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.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having” and any variations thereof in this invention are intended to cover non-exclusive inclusion.

[0060] In the description of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0061] In one specific embodiment, the present invention provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, the method comprising:

[0062] The fluorine-tungsten co-doped high-nickel cathode material is prepared by sequentially subjecting a mixed tungsten-doped full-concentration gradient high-nickel cathode material precursor, a lithium source, and a fluorine source to a first heat treatment and a second heat treatment.

[0063] This invention uses a tungsten-doped high-nickel cathode material precursor with a full concentration gradient as raw material. Tungsten doping suppresses grain boundary fusion during subsequent heat treatment, mitigating the weakening of the concentration gradient caused by transition metal ion diffusion. This maintains a composition closer to the designed full concentration gradient slope in the precursor, ensuring controllable composition of the prepared tungsten-doped high-nickel cathode material matrix, improving structural stability, and reducing intergranular microcracks caused by side reactions during charge-discharge cycles. This results in simultaneous improvements in capacity and cycle performance. A fluorine source is introduced for surface doping. Fluorine forms strong F-TM bonds with the transition metal elements in the tungsten-doped high-nickel cathode material matrix, forming a rock-salt phase fluorine-doped layer on the material surface. This further enhances structural stability, reduces oxygen loss during charge-discharge cycles, and further improves cycle life.

[0064] In some embodiments, the D50 particle size of the tungsten-doped full-concentration gradient high-nickel cathode material precursor is 8 μm to 14 μm, for example, it can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or 14 μm, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 9.5 μm to 10.5 μm.

[0065] In some embodiments, the preparation method of the tungsten-doped full-concentration gradient high-nickel cathode material precursor includes:

[0066] First, a portion of a first nickel-cobalt-manganese solution is placed in a mixing tank. Then, the first and second nickel-cobalt-manganese solutions are introduced into the mixing tank in parallel at a first flow rate and a second flow rate, respectively, to obtain a mixed salt solution. The mixed salt solution, tungsten source solution, precipitant solution, and complexing agent solution are introduced into a reaction vessel containing a bottom liquid in parallel to carry out a co-precipitation reaction to prepare the high-nickel cathode material precursor with a full concentration gradient. The mixed salt solution is introduced into the reaction vessel at a third flow rate. The third flow rate is greater than the sum of the first and second flow rates. Based on the proportion of nickel in nickel-cobalt-manganese, the proportion of nickel in the first nickel-cobalt-manganese solution is higher than the proportion of nickel in the second nickel-cobalt-manganese solution.

[0067] In some embodiments, the co-precipitation reaction employs an overflow method to ensure that the volume of the reaction solution in the reactor remains within an optimal range. Taking the volume of the reactor as V, the total volume of the first and second nickel-cobalt-manganese solutions is 300%V to 600%V, for example, 300%V, 350%V, 400%V, 450%V, 500%V, 550%V, or 600%V, including but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] In some embodiments, with the volume of the reactor as V, the third flow rate is 2%V / h to 4%V / h, for example, it can be 2%V / h, 2.25%V / h, 2.5%V / h, 2.75%V / h, 3%V / h, 3.25%V / h, 3.5%V / h, 3.75%V / h or 4%V / h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0069] In some embodiments, with the volume of the reactor as V, the sum of the first flow rate and the second flow rate is 0.5%V / h to 2%V / h, for example, it can be 0.5%V / h, 1%V / h, 1.1%V / h, 1.2%V / h, 1.3%V / h, 1.4%V / h, 1.5%V / h, 1.6%V / h, 1.7%V / h, 1.8%V / h, 1.9%V / h or 2%V / h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0070] In this invention, the flow rates of the first flow rate and the second flow rate are no longer specifically limited, and can be selected according to the slope of the nickel concentration gradient.

[0071] In some embodiments, with the volume of the reactor as V, the flow rate of the tungsten source solution is 0.01%V / h to 0.1%V / h, for example, it can be 0.01%V / h, 0.03%V / h, 0.05%V / h, 0.07%V / h, 0.09%V / h or 5%V / h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0072] In some embodiments, the ratio of the third flow rate to the flow rate of the tungsten source solution is 1:(0.0025 to 0.05), for example, it can be 1:0.0025, 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.04 or 1:0.05, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0073] In some implementations, the sum of the third flow velocity and the first and second flow velocities is 1:(0.25 to 1), for example, it can be 1:0.25, 1:0.5, 1:0.75 or 1:1, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0074] In this invention, the flow rates of the precipitant and complexing agent solutions are no longer specifically limited. It is sufficient to maintain the pH of the co-precipitation reaction at 10.0 to 12.0 and the ammonia concentration at 1.5 g / L to 3 g / L.

[0075] In some embodiments, the W in the tungsten source solution is 0.1 mol% to 5 mol% of the total amount of Ni, Co, and Mn in the mixed salt solution, for example, it can be 0.1 mol%, 0.25 mol%, 0.5 mol%, 0.75 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, or 5 mol%, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.25 mol% to 2.5 mol%.

[0076] In some embodiments, the molar ratio of Ni:Co:Mn in the first nickel-cobalt-manganese solution is x1:y1:z1, x1+y1+z1=1, 0.90≤x1≤1, for example, x1 can be 0.9, 0.92, 0.94, 0.96, 0.98 or 1, 0≤y1≤0.1, for example, y1 can be 0, 0.02, 0.04, 0.06, 0.08 or 0.1, 0≤z1≤0.1, for example, z1 can be 0, 0.02, 0.04, 0.06, 0.08 or 0.1, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0077] In some embodiments, the molar ratio of Ni:Co:Mn in the second nickel-cobalt-manganese solution is x2:y2:z2, where x2+y2+z2=1, and 0.6≤x2≤0.89. For example, x2 can be 0.6, 0.62, 0.64, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0... 0.86, 0.88, or 0.89, 0 ≤ y2 ≤ 0.4, for example, y2 can be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4, 0 ≤ z2 ≤ 0.4, for example, z2 can be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4, including but not limited to the listed values, and other unlisted values ​​within the range also apply.

[0078] In some embodiments, the Ni source in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution includes any one or a combination of at least two of nickel sulfate, nickel nitrate, or nickel acetate.

[0079] In some embodiments, the Co source in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution includes any one or a combination of at least two of cobalt sulfate, cobalt nitrate, or cobalt acetate.

[0080] In some embodiments, the Mn source in the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution includes any one or a combination of at least two of manganese sulfate, manganese nitrate, or manganese acetate.

[0081] In some embodiments, the tungsten source in the tungsten source solution includes any one or a combination of at least two of tungsten trioxide, sodium tungstate, and tungsten dioxide. Typical but non-limiting combinations include a combination of tungsten trioxide and sodium tungstate, a combination of tungsten dioxide and tungsten trioxide, or a combination of sodium tungstate and tungsten dioxide.

[0082] In some embodiments, the solvent of the tungsten source solution includes sodium hydroxide solution and / or potassium hydroxide solution.

[0083] In some embodiments, the precipitant in the precipitant solution includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or sodium bicarbonate.

[0084] In some embodiments, the complexing agent in the complexing agent solution includes any one or a combination of at least two of ammonia, oxalic acid, citric acid, sodium carbonate, or ammonium bicarbonate.

[0085] In some embodiments, the concentration of the tungsten source in the tungsten source solution is 0.1 mol / L to 2 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0086] In some embodiments, the concentration of sodium hydroxide solution or potassium hydroxide solution in the tungsten source solution is 10wt% to 20wt%, for example, it can be 10wt%, 12wt%, 14wt%, 16wt%, 18wt% or 20wt%, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0087] In some embodiments, the total concentration of Ni, Co, and Mn in the first and second nickel-cobalt-manganese solutions is 1.0 mol / L to 3.0 mol / L, for example, it can be 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, or 3 mol / L, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0088] In some embodiments, the concentration of the precipitant solution is 20wt% to 40wt%, for example, it can be 20wt%, 25wt%, 30wt%, 35wt% or 40wt%, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0089] In some embodiments, the concentration of the complexing agent solution is 10wt% to 20wt%, for example, it can be 10wt%, 12wt%, 14wt%, 16wt%, 18wt% or 20wt%, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0090] In some embodiments, the base liquid includes water, NaOH solution, and ammonia solution.

[0091] In some embodiments, the pH of the base solution is 10.0 to 12.0, for example, the pH can be 10.0, 10.5, 11, 11.2, 11.4, 11.6, 11.8 or 12, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0092] In some embodiments, the ammonia concentration of the base liquid is 1.5 g / L to 3 g / L, for example, it can be 1.5 g / L, 1.75 g / L, 2 g / L, 2.25 g / L, 2.5 g / L, 2.75 g / L or 3 g / L, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0093] In some embodiments, the reaction vessel is in an inert atmosphere.

[0094] In some embodiments, the inert atmosphere includes nitrogen and / or an inert gas, wherein the inert gas includes argon and / or helium.

[0095] In some embodiments, the temperature of the first heat treatment is 450°C to 600°C, for example, it can be 450°C, 500°C, 550°C or 600°C, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable. The time is 2h to 8h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0096] In some embodiments, the temperature of the second heat treatment is 600℃ to 900℃, for example, it can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable. The time is 5h to 20h, for example, it can be 5h, 7h, 9h, 11h, 13h, 15h, 17h, 19h or 20h, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0097] In some embodiments, the atmosphere for the first and second heat treatments includes any one or a combination of at least two of argon, nitrogen, helium, or oxygen, preferably oxygen.

[0098] In some embodiments, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium nitrate, preferably lithium hydroxide.

[0099] In some embodiments, the fluorine source includes any one or a combination of at least two of lithium fluoride, sodium fluoride, or ammonium fluoride.

[0100] In some embodiments, the molar ratio of the tungsten-doped full-concentration gradient high-nickel cathode material precursor, the lithium source, and the fluorine source is 1:(1.0-1.4):(0.003-0.015), for example, it can be 1:1:0.003, 1:1.05:0.005, 1:1.1:0.006, 1:1.15:0.007, 1:1.2:0.008, 1:1.25:0.009, 1:1.3:0.01, 1:1.35:0.012, or 1:1.4:0.015, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1:(1.02-1.1):(0.003-0.015).

[0101] In another specific embodiment, the present invention provides a fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material prepared by the preparation method described in the foregoing specific embodiment. The fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material includes a tungsten-doped gradient high-nickel cathode substrate and a rock salt phase fluorine-doped layer formed in situ on the surface of the tungsten-doped gradient high-nickel cathode substrate.

[0102] In yet another embodiment, the present invention provides a lithium-ion battery comprising the fluorine-tungsten co-doped high-nickel cathode material with full concentration gradient described in another preceding embodiment.

[0103] Example 1

[0104] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, the preparation method comprising:

[0105] A tungsten-doped full-concentration gradient high-nickel cathode material precursor was mixed with lithium hydroxide and ammonium fluoride at a molar ratio of 1:1.05:0.005. Then, under an oxygen atmosphere, the mixture underwent a first heat treatment at 480°C for 5 hours and a second heat treatment at 800°C for 15 hours to prepare the fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material. SEM images of the fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material are shown below. Figure 1 .

[0106] The method for preparing the tungsten-doped high-nickel cathode material precursor with full concentration gradient includes:

[0107] (1) Nickel sulfate, manganese sulfate and cobalt sulfate were mixed in molar ratios of 0.96:0.02:0.02 and 0.8:0.1:0.1 to prepare a first nickel cobalt manganese solution and a second nickel cobalt manganese solution. The total concentrations of Ni, Co and Mn in the first nickel cobalt manganese solution and the second nickel cobalt manganese solution were both 2 mol / L. Tungsten trioxide was dissolved in a 16 wt% sodium hydroxide solution to prepare a 1 mol / L tungsten source solution. A 32 wt% sodium hydroxide solution was prepared as a precipitant and a 16 wt% ammonia solution was prepared as a complexing agent. Pure water, NaOH solution and ammonia solution were added to the reaction vessel to control the pH at 11.8 and the ammonia concentration at 2 g / L.

[0108] (2) A portion of the first nickel-cobalt-manganese solution was introduced into the mixing tank, and then the first and second nickel-cobalt-manganese solutions were introduced into the mixing tank at flow rates of 0.6% V / h and 0.65% V / h, respectively, to obtain a mixed salt solution. Simultaneously, under a nitrogen atmosphere, the mixed salt solution, tungsten source solution, precipitant solution, and complexing agent solution were introduced into the reactor in parallel. The flow rate of the mixed salt solution was 2.5% V / h, the flow rate of the tungsten source solution was 0.025% V / h, the ratio of the flow rate of the mixed salt solution to the flow rate of the first and second nickel-cobalt-manganese solutions introduced into the mixing tank was 1:0.5, and the flow rate ratio of the mixed salt solution to the tungsten source solution was 1:0.01. A co-precipitation reaction was carried out to prepare a tungsten-doped full-concentration gradient high-nickel cathode material precursor with a D50 particle size of 10 μm. The SEM of the tungsten-doped full-concentration gradient high-nickel cathode material precursor is shown in [Image]. Figure 2 .

[0109] Example 2

[0110] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, the preparation method comprising:

[0111] A tungsten-doped full-concentration gradient high-nickel cathode material precursor was mixed with lithium hydroxide and lithium fluoride in a molar ratio of 1:1.02:0.003. Then, under an oxygen atmosphere, the mixture was subjected to a first heat treatment at 450°C for 2 hours and a second heat treatment at 600°C for 5 hours to prepare the fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material.

[0112] The preparation methods for tungsten-doped high-nickel cathode material precursors with full concentration gradients include:

[0113] (1) Nickel sulfate, manganese sulfate and cobalt sulfate were mixed in molar ratios of 0.92:0.04:0.04 and 0.6:0.2:0.2 to prepare a first nickel cobalt manganese solution and a second nickel cobalt manganese solution. The total concentration of Ni, Co and Mn in the first nickel cobalt manganese solution and the second nickel cobalt manganese solution was 1.0 mol / L. Tungsten trioxide was dissolved in 10 wt% sodium hydroxide solution to prepare a 2 mol / L tungsten source solution. A 20 wt% sodium hydroxide solution was prepared as a precipitant and a 10 wt% ammonia solution was prepared as a complexing agent. Pure water, NaOH solution and ammonia solution were added to the reaction vessel to control the pH to 11.5 and the ammonia concentration to 1.5 g / L.

[0114] (2) A portion of the first nickel-cobalt-manganese solution was introduced into the mixing tank, and then the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution were introduced into the mixing tank at flow rates of 0.5% V / h and 0.5% V / h, respectively, to obtain a mixed salt solution; at the same time, under a nitrogen atmosphere, the mixed salt solution, tungsten source solution, precipitant solution and complexing agent solution were introduced into the reactor in parallel. The flow rate of the mixed salt solution was 4% V / h, the flow rate of the tungsten source solution was 0.05% V / h, the ratio of the flow rate of the mixed salt solution to the flow rate of the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution introduced into the mixing tank was 1:0.25, and the flow rate ratio of the mixed salt solution to the tungsten source solution was 1:0.0025. Co-precipitation reaction was carried out to prepare a tungsten-doped full-concentration gradient high-nickel cathode material precursor with a D50 particle size of 8 μm.

[0115] Example 3

[0116] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, the preparation method comprising:

[0117] The tungsten-doped full-concentration gradient high-nickel cathode material precursor was mixed with lithium hydroxide and ammonium fluoride in a molar ratio of 1:1.1:0.01. Then, under an argon atmosphere, the mixture was subjected to a first heat treatment at 600°C for 8 hours and a second heat treatment at 900°C for 20 hours to prepare the fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material.

[0118] The method for preparing the tungsten-doped high-nickel cathode material precursor with full concentration gradient includes:

[0119] (1) Nickel sulfate, manganese sulfate and cobalt sulfate were mixed in molar ratios of 0.98:0.01:0.01 and 0.88:0.06:0.06 to prepare a first nickel cobalt manganese solution and a second nickel cobalt manganese solution. The total concentration of Ni, Co and Mn in the first nickel cobalt manganese solution and the second nickel cobalt manganese solution was 3.0 mol / L. Tungsten trioxide was dissolved in 20 wt% sodium hydroxide solution to prepare a 0.1 mol / L tungsten source solution. A 40 wt% sodium hydroxide solution was prepared as a precipitant and a 20 wt% ammonia solution was prepared as a complexing agent. Pure water, NaOH solution and ammonia solution were added to the reaction vessel to control the pH to 12.0 and the ammonia concentration to 3 g / L.

[0120] (2) A portion of the first nickel-cobalt-manganese solution was introduced into the mixing tank, and then the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution were introduced into the mixing tank at flow rates of 0.8% V / h and 0.8% V / h, respectively, to obtain a mixed salt solution; at the same time, under a nitrogen atmosphere, the mixed salt solution, tungsten source solution, precipitant solution and complexing agent solution were introduced into the reactor in parallel. The flow rate of the mixed salt solution was 2% V / h, the flow rate of the tungsten source solution was 0.1% V / h, the ratio of the flow rate of the mixed salt solution to the flow rate of the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution introduced into the mixing tank was 1:0.8, and the flow rate ratio of the mixed salt solution to the tungsten source solution was 1:0.05. Co-precipitation reaction was carried out to prepare a tungsten-doped full-concentration gradient high-nickel cathode material precursor with a D50 particle size of 14 μm.

[0121] Example 4

[0122] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with full concentration gradient. Except for the tungsten-doped high-nickel cathode material precursor being mixed with lithium hydroxide and ammonium fluoride in a molar ratio of 1:1.05:0.002, the rest is the same as in Example 1.

[0123] Example 5

[0124] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient. Except for the tungsten-doped high-nickel cathode material precursor being mixed with lithium hydroxide and ammonium fluoride in a molar ratio of 1:1.05:0.02, the rest is the same as in Example 1.

[0125] Example 6

[0126] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient. Except that the flow rate of the tungsten source solution is adjusted to 0.25% V / h and the ratio of the third flow rate to the flow rate of the tungsten source solution is 1:0.1 during the preparation of the tungsten-doped high-nickel cathode material precursor, the rest is the same as in Example 1.

[0127] Example 7

[0128] This embodiment provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient. Except that during the preparation of the tungsten-doped high-nickel cathode material precursor, the flow rate of the tungsten source solution is adjusted to 0.005% V / h, and the ratio of the third flow rate to the flow rate of the tungsten source solution is 1:0.002, the rest are the same as in Example 1.

[0129] Comparative Example 1

[0130] This comparative example provides a method for preparing a gradient high-nickel cathode material. Except that no tungsten source solution is introduced into the reactor during the preparation of the gradient high-nickel cathode material precursor, and no ammonium fluoride is added during the heat treatment, the rest is the same as in Example 1.

[0131] Comparative Example 2

[0132] This comparative example provides a method for preparing a tungsten-doped high-nickel cathode material with a full concentration gradient. Except for the absence of ammonium fluoride during the heat treatment process, the method is the same as in Example 1.

[0133] Comparative Example 3

[0134] This comparative example provides a method for preparing a fluorine-doped high-nickel cathode material with a full concentration gradient. Except for the fact that no tungsten source solution is introduced into the reactor during the preparation of the high-nickel cathode material precursor, the rest is the same as in Example 1.

[0135] Comparative Example 4

[0136] This comparative example provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient. The method differs from the method of not introducing a tungsten source solution into the reactor during the preparation of the high-nickel cathode material precursor. Instead, when mixing the high-nickel cathode material precursor with a lithium source and ammonium fluoride, (NH4)6H2W is added at a concentration of W equal to 0.5% of the total molar amount of transition metal elements in the precursor. 12 O 40 Then, except for the first heat treatment and the second heat treatment, everything else is the same as in Example 1.

[0137] Comparative Example 5

[0138] This comparative example provides a method for preparing a fluorine-tungsten co-doped high-nickel cathode material. Except for the preparation process of the tungsten-doped high-nickel cathode material precursor, in which the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution are pre-mixed to obtain a mixed salt solution and then flowed into the reactor in parallel, the rest is the same as in Example 1.

[0139] Performance testing:

[0140] The high-nickel cathode materials prepared in all the above examples and comparative examples were mixed with SP and PVDF at a mass ratio of 97:1.5:1.5 to prepare a cathode sheet. The cathode sheet was then matched with lithium metal to assemble a lithium-ion battery. The battery was tested at 25°C and within a voltage range of 2.7V to 4.3V. First, it was charged and discharged for 3 cycles at a rate of 0.1C, and then charged and discharged for 100 cycles at 1C. The electrochemical performance was then tested, and the test results are shown in Table 1.

[0141] Table 1

[0142]

[0143] According to the test results of Example 1 and Comparative Examples 1 to 3 in Table 1, if tungsten doping and fluorine doping are not carried out simultaneously, it is impossible to ensure that the composition of the prepared tungsten-doped high-nickel cathode material matrix with full concentration gradient is controllable, avoid intergranular microcracks caused by side reactions during charging and discharging, and reduce oxygen loss during charging and discharging cycles. Therefore, it is impossible to effectively improve the structural stability of the high-nickel cathode material and achieve simultaneous improvement in capacity and cycle life.

[0144] According to the test results of Example 1 and Comparative Example 4, if the tungsten source solution is not introduced concurrently during the co-precipitation process, but instead solid-phase mixing is carried out during the heat treatment process, it is impossible to achieve uniform doping of tungsten elements from the core to the surface in the gradient high-nickel cathode material. This makes it impossible to effectively suppress grain boundary fusion and avoid the weakening of the concentration gradient caused by the concentration diffusion of transition metal ions. Consequently, the composition of the tungsten-doped full-concentration gradient high-nickel cathode material matrix prepared in the end deviates greatly from the full concentration gradient slope design in the tungsten-doped full-concentration gradient high-nickel cathode material precursor, resulting in unsatisfactory improvement in capacity and cycle life.

[0145] Based on the test results of Example 1 and Comparative Example 5, if only uniform tungsten doping is performed on the high-nickel cathode material from the core to the surface, without the specific full concentration gradient slope design in the invention, the cycle life of the high-nickel cathode material cannot be effectively improved.

[0146] Based on the test results of Examples 1, 4, and 5, if the doping amount of fluorine is too high, the charge and discharge capacity of the cathode material will be reduced; if the doping amount of fluorine is too low, the cycle stability of the cathode material cannot be effectively improved.

[0147] According to the test results of Examples 1, 6 and 7, if the flow rate of the mixed salt solution is too fast or too slow, that is, if the amount of tungsten doping is too much or too little, the concentration gradient slope in the prepared gradient high-nickel cathode material will deviate from the concentration gradient slope design of the present invention. This will lead to the inability to alleviate the heterogeneous stress generated inside during charge-discharge cycles, which will continue to accumulate and make it easier for microcracks or even structural collapse to occur, thus failing to achieve simultaneous improvement in capacity and cycle life.

[0148] 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 fluorine-tungsten co-doped high-nickel cathode material with a full concentration gradient, characterized in that, The preparation method includes: The fluorine-tungsten co-doped high-nickel cathode material is prepared by sequentially subjecting a mixed tungsten-doped full-concentration gradient high-nickel cathode material precursor, a lithium source, and a fluorine source to a first heat treatment and a second heat treatment. The method for preparing the tungsten-doped high-nickel cathode material precursor with full concentration gradient includes: First, a portion of the first nickel-cobalt-manganese solution is placed in the mixing tank. Then, the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution are introduced into the mixing tank in parallel at the first flow rate and the second flow rate, respectively, to obtain a mixed salt solution. A co-precipitation reaction is carried out by introducing a mixed salt solution, a tungsten source solution, a precipitant solution, and a complexing agent solution into a reaction vessel containing a bottom liquid, thereby preparing the high-nickel cathode material precursor with full concentration gradient. The mixed salt solution is introduced into the reaction vessel at a third flow rate; the third flow rate is greater than the sum of the first and second flow rates. Based on the proportion of nickel in nickel-cobalt-manganese, the proportion of nickel in the first nickel-cobalt-manganese solution is higher than that in the second nickel-cobalt-manganese solution; With the volume of the reactor as V, the sum of the first flow rate and the second flow rate is 0.5%V / h~2%V / h; With the volume of the reactor as V, the third flow rate is 2%V / h~4%V / h; With the volume of the reactor as V, the flow rate of the tungsten source solution is 0.01%V / h~0.1%V / h.

2. The preparation method according to claim 1, characterized in that, In the first nickel-cobalt-manganese solution, the molar ratio of Ni:Co:Mn is x1:y1:z1, x1+y1+z1=1, 0.90≤x1≤1, 0≤y1≤0.1, and 0≤z1≤0.

1.

3. The preparation method according to claim 1, characterized in that, In the second nickel-cobalt-manganese solution, the molar ratio of Ni:Co:Mn is x2:y2:z2, x2+y2+z2=1, 0.6≤x2≤0.89, 0≤y2≤0.4, and 0≤z2≤0.

4.

4. The preparation method according to claim 1, characterized in that, The tungsten source in the tungsten source solution includes any one or a combination of at least two of tungsten trioxide, sodium tungstate, and tungsten dioxide.

5. The preparation method according to claim 1, characterized in that, The solvent for the tungsten source solution includes sodium hydroxide solution and / or potassium hydroxide solution.

6. The preparation method according to claim 1, characterized in that, The concentration of the tungsten source in the tungsten source solution is 0.1 mol / L to 2 mol / L.

7. The preparation method according to claim 1, characterized in that, In the first and second nickel-cobalt-manganese solutions, the total concentrations of Ni, Co, and Mn are 1.0 mol / L to 3.0 mol / L.

8. The preparation method according to claim 1, characterized in that, The base liquid includes water, NaOH solution, and ammonia solution.

9. The preparation method according to claim 1, characterized in that, The pH of the base solution is 10.0~12.

0.

10. The preparation method according to claim 1, characterized in that, The ammonia concentration of the base solution is 1.5 g / L to 3 g / L.

11. The preparation method according to claim 1, characterized in that, The reaction vessel is filled with an inert atmosphere.

12. The preparation method according to claim 1, characterized in that, The temperature of the first heat treatment is 450℃~600℃, and the time is 2h~8h.

13. The preparation method according to claim 1, characterized in that, The second heat treatment is performed at a temperature of 600℃ to 900℃ for a time of 5 hours to 20 hours.

14. The preparation method according to claim 1, characterized in that, The atmosphere for the first and second heat treatments includes any one or a combination of at least two of argon, nitrogen, helium, or oxygen.

15. The preparation method according to claim 1, characterized in that, The lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium nitrate.

16. The preparation method according to claim 1, characterized in that, The fluorine source includes any one or a combination of at least two of lithium fluoride, sodium fluoride, or ammonium fluoride.

17. The preparation method according to claim 1, characterized in that, The molar ratio of the tungsten-doped full-concentration gradient high-nickel cathode material precursor, lithium source, and fluorine source is 1:(1.0~1.4):(0.003~0.015).

18. A fluorine-tungsten co-doped high-nickel cathode material prepared by the preparation method according to any one of claims 1 to 17, characterized in that, The fluorine-tungsten co-doped full-concentration gradient high-nickel cathode material includes a tungsten-doped gradient high-nickel cathode substrate and a rock salt phase fluorine-doped layer formed in situ on the surface of the tungsten-doped gradient high-nickel cathode substrate.

19. A lithium-ion battery, characterized in that, The lithium-ion battery includes the fluorine-tungsten co-doped high-nickel cathode material as described in claim 18.

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