Full-concentration-gradient high-nickel positive electrode material precursor, preparation method and application thereof

Abstract

This invention provides a high-nickel cathode material precursor with a full concentration gradient, its preparation method, and its application. The preparation method includes: first, placing a portion of a first nickel-cobalt-manganese solution in a mixing tank; then, simultaneously introducing the first and second nickel-cobalt-manganese solutions into the mixing tank at a first and a second flow rate, respectively, to obtain a mixed salt solution; subsequently, simultaneously introducing the mixed salt solution, tungsten source solution, precipitant solution, and complexing agent solution into a reaction vessel containing a bottom liquid for a co-precipitation reaction; 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; and the nickel content in the first nickel-cobalt-manganese solution is higher than that in the second nickel-cobalt-manganese solution. This invention achieves a high-nickel cathode material precursor with a full concentration gradient nickel content distribution from the core to the surface and uniform W doping. The high-nickel cathode material prepared in this way exhibits both high discharge specific capacity and long 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 high-nickel cathode material precursor 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] CN109742377A discloses a surface modification method for high-nickel ternary cathode materials. The high-nickel ternary cathode material is placed in a plasma generator, and carbon dioxide gas is used as the arc-starting gas. The ternary cathode material is surface-treated in a carbon dioxide plasma atmosphere, and a layer of lithium carbonate and carbon coating is constructed in situ on its surface. This not only effectively isolates the active material from direct contact with the electrolyte and enhances the electronic conductivity of its surface interface, but also significantly improves the chemical stability after long-term exposure in humid air, which helps to improve the structural stability and post-processing properties of the material.

[0004] CN118198352A discloses a method for modifying high-nickel ternary cathode materials, comprising: mixing an organoboric acid functional factor with a solvent to obtain an organoboric acid solution; mixing the high-nickel ternary cathode material with the organoboric acid solution until the reaction is complete, to obtain the modified high-nickel ternary cathode material. This modification method can utilize the organoboric acid functional factor to react with the residual alkali on the surface of the high-nickel ternary cathode material, transforming it in situ into a new surface adhesion layer. The residual alkali content on the surface of the modified high-nickel ternary cathode material is greatly reduced, significantly improving the structural and interfacial stability of the high-nickel ternary cathode material, and improving the cycle performance and rate performance of lithium-ion batteries.

[0005] CN114538532A discloses a method for preparing a high-nickel ternary cathode material. The method involves uniformly mixing a precursor containing the ternary cathode material with a lithium source, then compacting the mixture. The compacted mixture is then sintered at a low temperature in an oxygen atmosphere to obtain a low-temperature sintered product. The low-temperature sintered product is then uniformly mixed with additives, followed by high-temperature sintering in an oxygen atmosphere. The mixture is then cooled, ground, and sieved to obtain the doped and modified high-nickel ternary cathode material. This invention, by first mixing and compacting the lithium salt and precursor, then pre-sintering, and finally adding additives and sintering, obtains a shallowly doped and coated high-nickel ternary cathode material, significantly improving the rate performance and cycle life of the material. Simultaneously, the obtained high-nickel ternary cathode material reduces residual alkali and improves the utilization rate of the lithium salt.

[0006] Therefore, it is of great significance to provide a high-nickel cathode material precursor 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 high-nickel cathode material precursor with a full concentration gradient, its preparation method, and its applications. This invention prepares a high-nickel cathode material precursor with a full concentration gradient exhibiting a decreasing slope of nickel content from the core to the surface, and uniform W doping from the core to the surface, by controlling the concentration of transition metal ions in a mixed salt solution and simultaneously introducing a tungsten source solution during co-precipitation. This allows for precise control of the full concentration gradient slope from the core to the surface, resulting in a high discharge specific capacity and long 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 high-nickel cathode material precursor with a full concentration gradient, the method comprising:

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Preferably, the concentration of the tungsten source in the tungsten source solution is 0.1 mol / L to 2 mol / L.

[0017] 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.

[0018] Preferably, the ratio of the third flow rate to the flow rate of the tungsten source solution is 1:(0.0025~0.05).

[0019] Preferably, the ratio of the third flow velocity to the sum of the first and second flow velocities is 1:(0.25~1).

[0020] 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.

[0021] Preferably, the volume of the reactor is V, and the third flow rate is 2%V / h to 4%V / h.

[0022] Preferably, the flow rate of the tungsten source solution is 0.01% V / h to 0.1% V / h.

[0023] 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.

[0024] 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.

[0025] Preferably, the solvent of the tungsten source solution includes sodium hydroxide solution and / or potassium hydroxide solution.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Preferably, the concentration of sodium hydroxide solution or potassium hydroxide solution in the tungsten source solution is 10wt% to 20wt%.

[0034] Preferably, the concentration of the precipitant solution is 20wt% to 40wt%.

[0035] Preferably, the concentration of the complexing agent solution is 10 wt% to 20 wt%.

[0036] Preferably, the base liquid includes water, NaOH solution, and ammonia solution.

[0037] Preferably, the pH of the base solution is 10.0 to 12.0.

[0038] Preferably, the ammonia concentration of the base liquid is 1.5 g / L to 3 g / L.

[0039] Preferably, the reaction vessel is in an inert atmosphere.

[0040] Preferably, the inert atmosphere includes nitrogen and / or an inert gas, wherein the inert gas includes argon and / or helium.

[0041] In a second aspect, the present invention provides a high-nickel cathode material precursor with a full concentration gradient, wherein the high-nickel cathode material precursor with a full concentration gradient is prepared by the preparation method described in the first aspect.

[0042] Preferably, the D50 particle size of the full-concentration gradient high-nickel cathode material precursor is 8 μm to 14 μm, and more preferably 9.5 μm to 10.5 μm.

[0043] Thirdly, the present invention provides a high-nickel cathode material with a full concentration gradient, wherein the high-nickel cathode material with a full concentration gradient is prepared from the high-nickel cathode material precursor with a full concentration gradient as described in the second aspect.

[0044] Fourthly, the present invention provides a method for preparing a high-nickel cathode material with a full concentration gradient as described in the third aspect, the method comprising:

[0045] The high-nickel cathode material with full concentration gradient is prepared by mixing the precursor with a lithium source and subjecting it to a first heat treatment and a second heat treatment.

[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 molar ratio of the full-concentration gradient high-nickel cathode material precursor to the lithium source is 1:(1.0 to 1.4), and more preferably 1:(1.02 to 1.1).

[0051] Fifthly, the present invention provides a lithium-ion battery comprising the high-nickel cathode material with full concentration gradient as described in the third aspect.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] This invention optimizes the co-precipitation process and simultaneously introduces a tungsten source solution during the co-precipitation process, thereby achieving a full concentration gradient distribution of nickel content from the core to the surface, and a high-nickel cathode material precursor with uniform W doping. The high-nickel cathode material prepared in this way has both high discharge specific capacity and long cycle life. Attached Figure Description

[0054] Figure 1 This is a SEM image of the high-nickel cathode material precursor prepared in Example 1 with full concentration gradient.

[0055] Figure 2 This is a SEM image of the high-nickel cathode material with full concentration gradient prepared in Example 1.

[0056] Figure 3 This is a SEM image of the high-nickel cathode material with full concentration gradient prepared in Comparative Example 1.

[0057] Figure 4 This is a SEM image of the high-nickel cathode material with full concentration gradient prepared in Comparative Example 2. 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 a first specific embodiment, the present invention provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient, the method comprising:

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] In some embodiments, the ratio of the third flow velocity to the sum of 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.

[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, 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 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.

[0073] 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%.

[0074] 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.

[0075] In some embodiments, the solvent of the tungsten source solution includes sodium hydroxide solution and / or potassium hydroxide solution.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] In some embodiments, the base liquid includes water, NaOH solution, and ammonia solution.

[0087] 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.

[0088] 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.

[0089] In some embodiments, the reaction vessel is in an inert atmosphere.

[0090] In some embodiments, the inert atmosphere includes nitrogen and / or an inert gas, wherein the inert gas includes argon and / or helium.

[0091] In a second specific embodiment, the present invention provides a high-nickel cathode material precursor with a full concentration gradient, which is prepared by the preparation method described in the first specific embodiment.

[0092] In some embodiments, the D50 particle size of the 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.

[0093] In a third embodiment, the present invention provides a high-nickel cathode material with a full concentration gradient, which is prepared from the high-nickel cathode material precursor with a full concentration gradient described in the second embodiment.

[0094] In a fourth embodiment, the present invention provides a method for preparing a high-nickel cathode material with a full concentration gradient as described in the third embodiment above, the method comprising:

[0095] The high-nickel cathode material with full concentration gradient is prepared by mixing the precursor with a lithium source and subjecting it to a first heat treatment and a second heat treatment.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

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

[0101] In a fifth embodiment, the present invention provides a lithium-ion battery comprising the high-nickel cathode material with full concentration gradient described in the third embodiment above.

[0102] Example 1

[0103] This embodiment provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient, the preparation method comprising:

[0104] (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.

[0105] (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 0.6% V / h and 0.65% 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 2.5% 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 nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution 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. Co-precipitation reaction was carried out to prepare a high-nickel cathode material precursor with a D50 particle size of 10 μm and a full concentration gradient.

[0106] This embodiment also provides a method for preparing a high-nickel cathode material with a full concentration gradient, the method comprising:

[0107] The high-nickel cathode material precursor with full concentration gradient prepared in this embodiment was mixed with lithium hydroxide at a molar ratio of 1:1.05. Then, under an oxygen atmosphere, it was subjected to a first heat treatment at a temperature of 480°C for 5 hours and a second heat treatment at a temperature of 800°C for 15 hours to prepare the high-nickel cathode material with full concentration gradient.

[0108] Example 2

[0109] This embodiment provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient, the preparation method comprising:

[0110] (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.

[0111] (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 high-nickel cathode material precursor with a D50 particle size of 8 μm and a full concentration gradient.

[0112] This embodiment also provides a method for preparing a high-nickel cathode material with a full concentration gradient, the method comprising:

[0113] The high-nickel cathode material precursor with full concentration gradient prepared in this embodiment was mixed with lithium hydroxide at a molar ratio of 1:1.02. Then, under an oxygen atmosphere, it was subjected to a first heat treatment at a temperature of 450°C for 2 hours and a second heat treatment at a temperature of 600°C for 5 hours to prepare the high-nickel cathode material with full concentration gradient.

[0114] Example 3

[0115] This embodiment provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient, the preparation method comprising:

[0116] (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.

[0117] (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 high-nickel cathode material precursor with a D50 particle size of 14 μm and a full concentration gradient.

[0118] This embodiment also provides a method for preparing a high-nickel cathode material with a full concentration gradient, the method comprising:

[0119] The high-nickel cathode material precursor with full concentration gradient prepared in this embodiment was mixed with lithium hydroxide at a molar ratio of 1:1.1, and then subjected to a first heat treatment at 600°C for 8 hours and a second heat treatment at 900°C for 20 hours under an argon atmosphere to prepare the high-nickel cathode material with full concentration gradient.

[0120] Example 4

[0121] This embodiment provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient. The preparation method is the same as in Example 1, except that the ammonia concentration in the base solution is 5 g / L.

[0122] This embodiment provides a method for preparing a high-nickel cathode material with a full concentration gradient. Except for using the high-nickel cathode material precursor prepared in this embodiment to prepare the high-nickel cathode material with a full concentration gradient, the rest is the same as in Example 1.

[0123] Example 5

[0124] This embodiment provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient. The preparation method is the same as in Example 1, 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.

[0125] This embodiment provides a method for preparing a high-nickel cathode material with a full concentration gradient. Except for using the high-nickel cathode material precursor prepared in this embodiment to prepare the high-nickel cathode material with a full concentration gradient, the rest is the same as in Example 1.

[0126] Example 6

[0127] This embodiment provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient. The preparation method is the same as in Example 1, except that 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.

[0128] This embodiment provides a method for preparing a high-nickel cathode material with a full concentration gradient. Except for using the high-nickel cathode material precursor prepared in this embodiment to prepare the high-nickel cathode material with a full concentration gradient, the rest is the same as in Example 1.

[0129] Comparative Example 1

[0130] This comparative example provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient. The preparation method is the same as in Example 1, except that a tungsten source solution is not introduced into the reactor.

[0131] This comparative example provides a method for preparing a high-nickel cathode material with a full concentration gradient. Except for using the high-nickel cathode material precursor prepared in this example to prepare the high-nickel cathode material with a full concentration gradient, the rest is the same as in Example 1.

[0132] Comparative Example 2

[0133] This comparative example provides a method for preparing a high-nickel cathode material precursor with a full concentration gradient. The preparation method is the same as in Example 1, except that a tungsten source solution is not introduced into the reactor.

[0134] This comparative example provides a method for preparing a high-nickel cathode material with a full concentration gradient. In addition to mixing the high-nickel cathode material precursor prepared in this example with a lithium source, (NH4)6H2W is added at a rate of 0.5% of the total molar amount of transition metal elements in the precursor. 12 O 40 Except for the above, everything else is the same as in Example 1.

[0135] Comparative Example 3

[0136] This comparative example provides a method for preparing a high-nickel cathode material precursor. The preparation method is the same as in Example 1, except that the first nickel-cobalt-manganese solution and the second nickel-cobalt-manganese solution are premixed to obtain a mixed salt solution and then flowed into the reactor in parallel.

[0137] This comparative example provides a method for preparing a high-nickel cathode material. Except for using the high-nickel cathode material precursor prepared in this example to prepare the high-nickel cathode material with full concentration gradient, the rest is the same as in Example 1.

[0138] Performance testing:

[0139] The high-nickel cathode material precursor and the high-nickel cathode material with full concentration gradient prepared in Example 1, as well as the high-nickel cathode materials with full concentration gradient prepared in Comparative Examples 1 and 2, were subjected to SEM tests. The test results are shown in the figures below. Figure 1 , Figure 2 , Figure 3 and Figure 4 .

[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, Comparative Example 1, and Comparative Example 2 in Table 1, if tungsten is not doped or if the tungsten source solution is not introduced concurrently during the co-precipitation process, it is impossible to achieve uniform doping of tungsten from the core to the surface in the full concentration 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 diffusion of transition metal ions. Consequently, the composition of the final full concentration gradient high nickel cathode material deviates significantly from the full concentration gradient slope design in the full concentration gradient high nickel cathode material precursor, resulting in unsatisfactory improvement in capacity and cycle life.

[0144] Based on the test results of Example 1 and Comparative Example 3, 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 this invention, the cycle life of the high-nickel cathode material cannot be effectively improved.

[0145] Based on the test results of Examples 1 and 4, a suitable ammonia concentration helps to alleviate the generation of microcracks in the high-nickel cathode precursor particles during the preparation process. This results in the high-nickel cathode material particles with a high concentration gradient that inherit some of the precursor characteristics having higher structural strength and better cycle performance during charge-discharge cycles. If the ammonia concentration is too high, the precursor particles are more prone to microcracks, which makes the prepared high-nickel cathode material more prone to structural collapse during charge-discharge cycles, resulting in rapid capacity decay.

[0146] According to the test results of Examples 1, 5 and 6, if the flow rate of the tungsten source 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 full concentration gradient high nickel cathode material will deviate from the concentration gradient slope design in the invention. This will lead to the inability to alleviate the heterogeneous stress generated inside during charge and 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.

[0147] 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 full-concentration-gradient high-nickel cathode material precursor, characterized in that, The preparation method 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.

2. The production method according to claim 1, wherein The concentration of the tungsten source in the tungsten source solution is 0.1 mol / L to 2 mol / L; And / or, 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; And / or, the ratio of the third flow rate to the flow rate of the tungsten source solution is 1:(0.0025~0.05); And / or, the ratio of the third flow velocity to the sum of the first and second flow velocities is 1:(0.25~1).

3. The preparation method according to claim 1 or 2, 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.

4. The preparation method according to claim 3, characterized in that, The solvent for the tungsten source solution includes sodium hydroxide solution and / or potassium hydroxide solution.

5. 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, 0≤z1≤0.1; And / or, 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, 0≤z2≤0.

4.

6. The preparation method according to claim 1, characterized in that, The base liquid includes water, NaOH solution, and ammonia solution; And / or, the pH of the substrate solution is 10.0~12.0; And / or, the ammonia concentration of the bottom solution is 1.5 g / L to 3 g / L; And / or, the reaction vessel is in an inert atmosphere.

7. A high-nickel cathode material precursor with a full concentration gradient, characterized in that, The high-nickel cathode material precursor with full concentration gradient is prepared by the preparation method described in any one of claims 1 to 6.

8. A high-nickel cathode material with a full concentration gradient, characterized in that, The full-concentration gradient high-nickel cathode material is prepared from the full-concentration gradient high-nickel cathode material precursor as described in claim 7.

9. A method for preparing a high-nickel cathode material with a full concentration gradient as described in claim 8, characterized in that, The preparation method includes: The high-nickel cathode material with full concentration gradient is prepared by mixing the precursor and a lithium source and then subjecting them to a first heat treatment and a second heat treatment.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the high-nickel cathode material with full concentration gradient as described in claim 8.

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