Composite modified cobalt-free lithium-rich manganese-based precursors, their preparation methods and cathode materials

Abstract

This invention relates to a composite-modified cobalt-free lithium-rich manganese-based precursor, its preparation method, and a cathode material. The cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, possessing a core and a shell layer; the shell layer is doped with Nb with a +5 valence. This invention, by making the precursor a flower-like core-shell structure, provides a better substrate for subsequent Li-containing cathode materials during sintering. + The storage provides more sites, which is beneficial to improving its reversible capacity; it can also buffer part of the structural strain and effectively improve the tap density; the doping of Nb element reduces the disordered insertion of primary particles in secondary particles, while the primary particle wafers expand in a flower-like shape, which effectively increases the specific surface area of ​​the precursor, helps to increase the reaction contact area between the cathode material and the electrolyte, and has better electrochemical performance; the higher specific surface area allows the Na and S elements inside the precursor to deviate as much as possible, reducing the Na and S impurity content in the precursor, which is beneficial to the subsequent preparation of cathode materials.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a core-shell structure precursor, particularly to a composite modified cobalt-free lithium-rich manganese-based precursor, its preparation method, and cathode material. Background Technology

[0002] Rechargeable lithium-ion batteries possess superior energy storage capacity and environmentally friendly characteristics, leading to their widespread application in portable devices, plug-in hybrid electric vehicles, and electric vehicles. Most of these lithium-ion batteries utilize cobalt as a raw material. However, cobalt resources are scarce and expensive, resulting in high costs for cobalt-containing lithium-ion battery cathode materials. Cobalt-free, lithium-rich manganese-based materials, with their extremely high discharge specific capacity, relatively low price, and minimal toxicity, are considered one of the ideal cathode materials for power lithium-ion batteries.

[0003] However, cobalt-free lithium-rich manganese-based materials have some inherent drawbacks: during charge and discharge processes, Li... + The slow diffusion rate of cobalt-free lithium-rich manganese-based materials leads to poor electrochemical performance. Furthermore, these materials experience rapid capacity decay under high-current operating conditions, significant layered structure collapse, and secondary particles are prone to structural strain-induced fractures. These drawbacks limit their practical application in power batteries. In practical applications, cobalt-free lithium-rich manganese-based precursors are typically modified to optimize their performance. Therefore, selecting appropriate modification methods to prepare cobalt-free lithium-rich manganese-based precursors can improve their structure and electrochemical properties.

[0004] Therefore, there is a need to provide a composite modified cobalt-free lithium-rich manganese-based precursor with good particle uniformity, ordered layered structure, high specific surface area and tap density, as well as its preparation method and cathode material. Summary of the Invention

[0005] The purpose of this invention is to provide a composite modified cobalt-free lithium-rich manganese-based precursor, its preparation method, and a cathode material. The composite modified cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, which improves the electrochemical performance of the composite modified cobalt-free lithium-rich manganese-based precursor, thereby enhancing the electrochemical performance of the cathode material prepared from it.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite modified cobalt-free lithium-rich manganese-based precursor, wherein the cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, having a core and a shell.

[0008] The general formula of the kernel is Ni a Mn b(OH)2, where the value of a ranges from 0.2 to 0.4, the value of b ranges from 0.6 to 0.8, and the sum of a and b is 1;

[0009] The general formula of the shell is Ni. x Mn y Nb z (OH)2, where x ranges from 0.2 to 0.4, y ranges from 0.6 to 0.8, z ranges from 0.01 to 0.1, and the sum of x and y is 1;

[0010] In the general formula of the shell, Nb has a valence of +5.

[0011] The first aspect of this invention provides a composite-modified cobalt-free lithium-rich manganese-based precursor with a flower-like core-shell structure, which is beneficial for the subsequent sintering process of Li... + The storage provides more sites, which is beneficial to improving its reversible capacity; it can also buffer part of the structural strain and effectively improve the tap density; the doping of Nb element reduces the disordered insertion of primary particles in secondary particles, while the primary particle wafers expand in a flower-like shape, which effectively increases the specific surface area of ​​the precursor, helps to increase the reaction contact area between the cathode material and the electrolyte, and has better electrochemical performance; the higher specific surface area allows the Na and S elements inside the precursor to deviate as much as possible, reducing the Na and S impurity content in the precursor, which is beneficial to the subsequent preparation of cathode materials.

[0012] Secondly, the present invention provides a method for preparing a composite-modified cobalt-free lithium-rich manganese-based precursor, the preparation method comprising the following steps:

[0013] (1) Mix the first precipitant solution, the first complexing agent solution and the first metal salt solution in the base liquid to carry out a co-precipitation reaction to obtain a seed suspension;

[0014] (2) Adjust the pH value and ammonia concentration of the seed suspension, and then mix the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution in parallel to carry out an intermittent co-precipitation reaction to obtain a modified cobalt-free lithium-rich manganese-based suspension.

[0015] The doping compound in the doping solution is Nb₂O₅ and / or NaNb₂O₄;

[0016] (3) The modified cobalt-free lithium-rich manganese-based suspension was washed and dried to obtain the composite modified cobalt-free lithium-rich manganese-based precursor;

[0017] The obtained cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, with a core and a shell.

[0018] The general formula of the kernel is Ni a Mn b(OH)2, where the value of a ranges from 0.2 to 0.4, the value of b ranges from 0.6 to 0.8, and the sum of a and b is 1;

[0019] The general formula of the shell is Ni. x Mn y Nb z (OH)2, where x ranges from 0.2 to 0.4, y ranges from 0.6 to 0.8, z ranges from 0.01 to 0.1, and the sum of x and y is 1;

[0020] In the general formula of the shell, Nb has a valence of +5.

[0021] The second aspect of this invention provides a method for preparing a cobalt-free, lithium-rich manganese-based precursor with a flower-like core-shell structure, which is beneficial for subsequent sintering processes involving Li. + The storage provides more sites, which is beneficial to improving its reversible capacity; it can also buffer part of the structural strain and effectively improve the tap density; the doping of Nb element reduces the disordered insertion of primary particles in secondary particles, while the primary particle wafers expand in a flower-like shape, which effectively increases the specific surface area of ​​the precursor, helps to increase the reaction contact area between the cathode material and the electrolyte, and has better electrochemical performance; the higher specific surface area allows the Na and S elements inside the precursor to deviate as much as possible, reducing the Na and S impurity content in the precursor, which is beneficial to the subsequent preparation of cathode materials.

[0022] Preferably, in step (1), the metal salt in the first metal salt solution includes a first nickel salt and a first manganese salt;

[0023] In the first metal salt solution, the molar ratio of nickel to manganese is a:b.

[0024] Preferably, in step (2), the metal salt in the second metal salt solution includes a second nickel salt and a second manganese salt;

[0025] In the second metal salt solution, the molar ratio of nickel to manganese is x:y.

[0026] Preferably, the temperature of the coprecipitation reaction in step (1) is 45°C to 55°C.

[0027] Preferably, the pH value of the coprecipitation reaction in step (1) is 10.8 to 11.1.

[0028] Preferably, the ammonia concentration in the co-precipitation reaction in step (1) is 0.8 g / L to 1.2 g / L.

[0029] Preferably, the endpoint of the co-precipitation reaction in step (1) is to ensure that the seed crystals in the seed suspension meet the following requirements: a particle size Dv50 of 2.8 μm to 3.2 μm and a specific surface area of ​​10 m². 2 / g to 15m 2 / g, tap density is 0.8g / cm³ 2 Up to 1g / cm 2 .

[0030] Preferably, the temperature of the intermittent coprecipitation reaction in step (2) is 45°C to 55°C.

[0031] Preferably, the pH value of the intermittent coprecipitation in step (2) starts from a first pH value, decreases to a second pH value at a rate of 0.025 / h to 0.035 / h, and is maintained until the intermittent coprecipitation reaction ends.

[0032] Preferably, the ammonia concentration in the intermittent coprecipitation in step (2) is 2.7 g / L to 3.3 g / L.

[0033] Preferably, the endpoint of the intermittent coprecipitation in step (2) is to make the material in the modified cobalt-free lithium-rich manganese-based suspension meet the following requirements: particle size Dv50 is 5.8 μm to 6.2 μm.

[0034] Preferably, the elution rate of the intermittent coprecipitation reaction in step (2) is 7 L / h to 10 L / h.

[0035] Preferably, the washing in step (3) includes an alkaline wash and a water wash performed sequentially.

[0036] Preferably, the concentration of the alkaline solution used for alkaline washing is 0.01 wt% to 0.015 wt%.

[0037] Preferably, the temperature of the alkaline washing is 75°C to 85°C.

[0038] Preferably, the temperature of the water wash is 75°C to 85°C.

[0039] Preferably, the coprecipitation reaction in step (1) is carried out under stirring conditions.

[0040] Preferably, the intermittent coprecipitation reaction in step (2) is carried out under stirring conditions.

[0041] Preferably, the first precipitant solution is a sodium hydroxide solution.

[0042] Preferably, the second precipitant solution is a sodium hydroxide solution.

[0043] Preferably, the first complexing agent solution is ammonia.

[0044] Preferably, the second precipitant solution is ammonia.

[0045] Thirdly, the present invention provides a cathode material, wherein the raw materials for preparing the cathode material include the composite modified cobalt-free lithium-rich manganese-based precursor described in the first aspect, or the composite modified cobalt-free lithium-rich manganese-based precursor obtained by the preparation method described in the second aspect.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The composite-modified cobalt-free lithium-rich manganese-based precursor provided by this invention has a flower-like core-shell structure, which is beneficial for the subsequent sintering process of Li + The storage provides more sites, which is beneficial to improving its reversible capacity; it can also buffer part of the structural strain and effectively improve the tap density; the doping of Nb element reduces the disordered insertion of primary particles in secondary particles, while the primary particle wafers expand in a flower-like shape, which effectively increases the specific surface area of ​​the precursor, helps to increase the reaction contact area between the cathode material and the electrolyte, and has better electrochemical performance; the higher specific surface area allows the Na and S elements inside the precursor to deviate as much as possible, reducing the Na and S impurity content in the precursor, which is beneficial to the subsequent preparation of cathode materials. Attached Figure Description

[0048] Figure 1 The image shows a scanning electron microscope (SEM) image of the cobalt-free lithium-rich manganese-based precursor obtained in Example 1.

[0049] Figure 2 The image shows the SEM image of the cobalt-free lithium-rich manganese-based precursor obtained in Example 1 after CP (Cross-section Polisher) processing.

[0050] Figure 3 Here is a SEM image of the cobalt-free lithium-rich manganese-based precursor obtained in Comparative Example 1.

[0051] Figure 4 The images show X-ray diffraction (XRD) images of the cobalt-free lithium-rich manganese-based precursors obtained in Example 1 and Comparative Example 1. Detailed Implementation

[0052] 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.

[0053] An embodiment of the present invention provides a composite modified cobalt-free lithium-rich manganese-based precursor, wherein the cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, having a core and a shell.

[0054] The general formula of the kernel is Ni a Mnb (OH)2, where the value of a ranges from 0.2 to 0.4, the value of b ranges from 0.6 to 0.8, and the sum of a and b is 1;

[0055] The general formula of the shell is Ni. x Mn y Nb z (OH)2, where x ranges from 0.2 to 0.4, y ranges from 0.6 to 0.8, z ranges from 0.01 to 0.1, and the sum of x and y is 1;

[0056] In the general formula of the shell, Nb has a valence of +5.

[0057] The composite-modified cobalt-free lithium-rich manganese-based precursor provided by this invention has a flower-like core-shell structure, which is beneficial for the subsequent sintering process of Li + The storage provides more sites, which is beneficial to improving its reversible capacity; it can also buffer part of the structural strain and effectively improve the tap density; the doping of Nb element reduces the disordered insertion of primary particles in secondary particles, while the primary particle wafers expand in a flower-like shape, which effectively increases the specific surface area of ​​the precursor, helps to increase the reaction contact area between the cathode material and the electrolyte, and has better electrochemical performance; the higher specific surface area allows the Na and S elements inside the precursor to deviate as much as possible, reducing the Na and S impurity content in the precursor, which is beneficial to the subsequent preparation of cathode materials.

[0058] In the composite-modified cobalt-free lithium-rich manganese-based precursor provided by this invention, the core has the general formula Ni. a Mn b (OH)2, where the value of a ranges from 0.2 to 0.4, for example, it can be 0.2, 0.25, 0.3, 0.35 or 0.4, but is not limited to the listed values, and other unlisted values ​​within the range also apply; the value of b ranges from 0.6 to 0.8, for example, it can be 0.6, 0.65, 0.7, 0.75 or 0.8, but is not limited to the listed values, and other unlisted values ​​within the range also apply; and the sum of a and b is 1.

[0059] In some embodiments, the values ​​of a and b indicate the content of Ni and Mn elements in the core. For example, the ratio of a to b indicates the molar ratio of Ni and Mn elements in the core.

[0060] In the composite modified cobalt-free lithium-rich manganese-based precursor provided by this invention, the shell has the general formula Ni. x Mn y Nb z(OH)₂, where x ranges from 0.2 to 0.4, for example, 0.2, 0.25, 0.3, 0.35, or 0.4, but is not limited to the listed values; any other unlisted values ​​within the range also apply. y ranges from 0.6 to 0.8, for example, 0.6, 0.65, 0.7, 0.75, or 0.8, but is not limited to the listed values; any other unlisted values ​​within the range also apply. z ranges from 0.01 to 0.1, for example, 0.01, 0.03, 0.05, 0.08, or 0.1, but is not limited to the listed values; any other unlisted values ​​within the range also apply. The sum of x and y is 1.

[0061] In some embodiments, the values ​​of x, y, and z indicate the content of Ni, Mn, and Nb elements in the shell. For example, the ratio of x, y, and z indicates the molar ratio of Ni, Mn, and Nb elements in the shell.

[0062] In some embodiments, the sulfur content of the composite modified cobalt-free lithium-rich manganese-based precursor is less than 1032 ppm and the sodium content is less than 80 ppm; wherein ppm (parts per million) is the mass content.

[0063] An embodiment of the present invention provides a method for preparing a composite-modified cobalt-free lithium-rich manganese-based precursor, the method comprising the following steps:

[0064] (1) Mix the first precipitant solution, the first complexing agent solution and the first metal salt solution in the base liquid to carry out a co-precipitation reaction to obtain a seed suspension;

[0065] (2) Adjust the pH value and ammonia concentration of the seed suspension, and then mix the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution in parallel to carry out an intermittent co-precipitation reaction to obtain a modified cobalt-free lithium-rich manganese-based suspension.

[0066] The doping compound in the doping solution is Nb₂O₅ and / or NaNb₂O₄;

[0067] (3) The modified cobalt-free lithium-rich manganese-based suspension was washed and dried to obtain the composite modified cobalt-free lithium-rich manganese-based precursor;

[0068] The obtained cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, with a core and a shell.

[0069] The general formula of the kernel is Ni a Mn b(OH)₂, where a ranges from 0.2 to 0.4, b ranges from 0.6 to 0.8, and the sum of a and b is 1; where a ranges from 0.2 to 0.4, for example, it can be 0.2, 0.25, 0.3, 0.35, or 0.4, but is not limited to the listed values, and other unlisted values ​​within the range also apply; b ranges from 0.6 to 0.8, for example, it can be 0.6, 0.65, 0.7, 0.75, or 0.8, but is not limited to the listed values, and other unlisted values ​​within the range also apply; the ratio of a to b indicates the molar ratio of Ni to Mn elements in the core;

[0070] The general formula of the shell is Ni. x Mn y Nb z (OH)₂, where x ranges from 0.2 to 0.4, y ranges from 0.6 to 0.8, and z ranges from 0.01 to 0.1, and the sum of x and y is 1; where x ranges from 0.2 to 0.4, for example, it can be 0.2, 0.25, 0.3, 0.35, or 0.4, but is not limited to the listed values, and other unlisted values ​​within the range also apply; y ranges from 0.6 to 0.8, for example, it can be... 0.6, 0.65, 0.7, 0.75, or 0.8, but not limited to the listed values; any other unlisted values ​​within the range also apply. The value of z ranges from 0.01 to 0.1, for example, it can be 0.01, 0.03, 0.05, 0.08, or 0.1, but not limited to the listed values; any other unlisted values ​​within the range also apply. The ratio of x, y, to z indicates the molar ratio of Ni, Mn, and Nb elements in the shell.

[0071] In the general formula of the shell, Nb has a valence of +5.

[0072] The cobalt-free lithium-rich manganese-based precursor prepared by the method provided in this invention has a flower-like core-shell structure, which is beneficial for the subsequent Li sintering process. + The storage provides more sites, which is beneficial to improving its reversible capacity; it can also buffer part of the structural strain and effectively improve the tap density; the doping of Nb element reduces the disordered insertion of primary particles in secondary particles, while the primary particle wafers expand in a flower-like shape, which effectively increases the specific surface area of ​​the precursor, helps to increase the reaction contact area between the cathode material and the electrolyte, and has better electrochemical performance; the higher specific surface area allows the Na and S elements inside the precursor to deviate as much as possible, reducing the Na and S impurity content in the precursor, which is beneficial to the subsequent preparation of cathode materials.

[0073] The doping solution in this invention uses Nb2O5 and / or NaNb2O4 as doping compounds, which do not undergo redox reactions during the doping process, thereby stabilizing the crystal structure of the shell.

[0074] In some embodiments, the preparation method provided by the present invention is carried out in a protective atmosphere, wherein the gas used in the protective atmosphere includes nitrogen and / or an inert gas.

[0075] In some embodiments, the metal salt in the first metal salt solution in step (1) includes a first nickel salt and a first manganese salt;

[0076] In the first metal salt solution, the molar ratio of nickel to manganese is a:b.

[0077] For example, the first nickel salt includes any one or a combination of at least two of nickel sulfate, nickel chloride, nickel nitrate, or nickel acetate. Typical but non-limiting combinations include combinations of nickel sulfate and nickel chloride, nickel chloride and nickel nitrate, nickel nitrate and nickel acetate, nickel sulfate, nickel chloride and nickel nitrate, nickel chloride, nickel nitrate and nickel acetate, or nickel sulfate, nickel chloride, nickel nitrate and nickel acetate.

[0078] For example, the first manganese salt includes any one or a combination of at least two of manganese sulfate, manganese chloride, manganese nitrate, or manganese acetate. Typical but non-limiting combinations include combinations of manganese sulfate and manganese chloride, manganese chloride and manganese nitrate, manganese nitrate and manganese acetate, manganese sulfate, manganese chloride and manganese nitrate, manganese chloride, manganese nitrate and manganese acetate, or manganese sulfate, manganese chloride, manganese nitrate and manganese acetate.

[0079] In some embodiments, the temperature of the base liquid in step (1) is 45°C to 55°C, for example, it can be 45°C, 48°C, 50°C, 52°C or 55°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] In some embodiments, the pH value of the substrate solution in step (1) is 10.8 to 11.1, for example, it may be 10.8, 10.9, 11 or 11.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] In some embodiments, the ammonia concentration of the base liquid in step (1) is from 0.8 g / L to 1.2 g / L, for example, it can be 0.8 g / L, 0.9 g / L, 1 g / L, 1.1 g / L or 1.2 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] In some embodiments, the temperature of the coprecipitation reaction in step (1) is 45°C to 55°C, for example, 45°C, 48°C, 50°C, 52°C or 55°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0083] In some embodiments, the pH value of the coprecipitation reaction in step (1) is 10.8 to 11.1, for example, it can be 10.8, 10.9, 11 or 11.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0084] In some embodiments, the ammonia concentration in the coprecipitation reaction of step (1) is from 0.8 g / L to 1.2 g / L, for example, it can be 0.8 g / L, 0.9 g / L, 1 g / L, 1.1 g / L or 1.2 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0085] In some embodiments, the endpoint of the coprecipitation reaction in step (1) is to make the seeds in the seed suspension meet the following conditions: a particle size Dv50 of 2.8 μm to 3.2 μm and a specific surface area of ​​10 m². 2 / g to 15m 2 / g, tap density is 0.8g / cm³ 2 Up to 1g / cm 2 .

[0086] The present invention does not specifically limit the flow rates of the first precipitant solution, the first complexing agent solution and the first metal salt solution in step (1), as long as the co-precipitation reaction in step (1) meets the requirements of pH value and ammonia concentration.

[0087] In some embodiments, the metal salt in the second metal salt solution in step (2) includes a second nickel salt and a second manganese salt;

[0088] In the second metal salt solution, the molar ratio of nickel to manganese is x:y.

[0089] For example, the second nickel salt includes any one or a combination of at least two of nickel sulfate, nickel chloride, nickel nitrate, or nickel acetate. Typical but non-limiting combinations include combinations of nickel sulfate and nickel chloride, nickel chloride and nickel nitrate, nickel nitrate and nickel acetate, nickel sulfate, nickel chloride and nickel nitrate, nickel chloride, nickel nitrate and nickel acetate, or nickel sulfate, nickel chloride, nickel nitrate and nickel acetate.

[0090] For example, the second manganese salt includes any one or a combination of at least two of manganese sulfate, manganese chloride, manganese nitrate, or manganese acetate. Typical but non-limiting combinations include combinations of manganese sulfate and manganese chloride, manganese chloride and manganese nitrate, manganese nitrate and manganese acetate, manganese sulfate, manganese chloride and manganese nitrate, manganese chloride, manganese nitrate and manganese acetate, or manganese sulfate, manganese chloride, manganese nitrate and manganese acetate.

[0091] In some embodiments, step (2) of adjusting the pH and ammonia concentration of the seed suspension means adjusting the pH to 10.5 to 10.7 and the ammonia concentration to 2.7 g / L to 3.3 g / L.

[0092] For example, sodium hydroxide solution is used to adjust the pH value of the seed crystal suspension; ammonia water is used to adjust the ammonia concentration of the seed crystal suspension.

[0093] In some embodiments, the temperature of the intermittent coprecipitation reaction in step (2) is 45°C to 55°C, for example, 45°C, 48°C, 50°C, 52°C or 55°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0094] In some embodiments, the pH value of the intermittent coprecipitation in step (2) starts from a first pH value, decreases to a second pH value at a rate of 0.025 / h to 0.035 / h, and is maintained until the intermittent coprecipitation reaction ends.

[0095] In some embodiments, the first pH value is 10.5 to 10.7, for example, it may be 10.5, 10.6 or 10.7, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0096] In some embodiments, the second pH value is 9.8 to 10, for example, it may be 9.8, 9.9 or 10, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0097] In this invention, the rate at which the pH value decreases from the first pH value to the second pH value is 0.025 / h to 0.035 / h, for example, it can be 0.025 / h, 0.028 / h, 0.03 / h, 0.032 / h or 0.035 / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0098] In some embodiments, the ammonia concentration of the intermittent coprecipitation in step (2) is 2.7 g / L to 3.3 g / L, for example, it can be 2.7 g / L, 2.8 g / L, 3 g / L, 3.2 g / L or 3.3 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0099] In some embodiments, the endpoint of the intermittent coprecipitation in step (2) is to make the material in the modified cobalt-free lithium-rich manganese-based suspension meet the following requirements: particle size Dv50 is 5.8 μm to 6.2 μm.

[0100] In some embodiments, during the intermittent coprecipitation reaction, an external concentration device is connected to the reaction apparatus. When the feed rate of the second metal salt solution is 5 L / h, the rinsing rate of the intermittent coprecipitation reaction is 7 L / h to 10 L / h, for example, 7 L / h, 8 L / h, 9 L / h or 10 L / h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0101] The present invention does not specifically limit the flow rates of the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution in step (2), as long as the intermittent coprecipitation reaction in step (2) meets the requirements of pH value, ammonia concentration and shell formula.

[0102] In some embodiments, the washing in step (3) includes a sequential alkaline wash and a water wash.

[0103] In some embodiments, the concentration of the alkaline solution used for alkaline washing is from 0.01 wt% to 0.015 wt%, for example, it may be 0.01 wt%, 0.012 wt%, 0.014 wt% or 0.015 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0104] For example, the alkaline solution is a sodium hydroxide solution.

[0105] In some embodiments, the alkaline washing temperature is 75°C to 85°C, for example, 75°C, 78°C, 80°C, 82°C or 85°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0106] In some embodiments, the temperature of the water wash is 75°C to 85°C, for example, 75°C, 78°C, 80°C, 82°C or 85°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0107] In some embodiments, the coprecipitation reaction in step (1) is carried out under stirring conditions.

[0108] In some embodiments, the intermittent coprecipitation reaction described in step (2) is carried out under stirring conditions.

[0109] The coprecipitation reaction and the batch coprecipitation reaction described in this invention are carried out independently under stirring conditions. The stirring speed is 300 rpm to 400 rpm, for example, 300 rpm, 320 rpm, 350 rpm, 380 rpm or 400 rpm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0110] In some embodiments, the first precipitant solution is a sodium hydroxide solution.

[0111] In some embodiments, the second precipitant solution is a sodium hydroxide solution.

[0112] In some embodiments, the first complexing agent solution is ammonia.

[0113] In some embodiments, the second precipitant solution is ammonia.

[0114] An embodiment of the present invention provides a cathode material, wherein the raw materials for preparing the cathode material include the composite modified cobalt-free lithium-rich manganese-based precursor described in any embodiment, or the composite modified cobalt-free lithium-rich manganese-based precursor obtained by the preparation method described in any embodiment.

[0115] In some embodiments, the cathode material includes a sodium-ion cathode material or a lithium-ion cathode material.

[0116] For example, when the cathode material is a lithium-ion cathode material, the cathode material is obtained by sintering a mixed lithium source with a composite modified cobalt-free lithium-rich manganese-based precursor.

[0117] The lithium sources include lithium hydroxide and / or lithium carbonate.

[0118] Example 1

[0119] This embodiment provides a composite modified cobalt-free lithium-rich manganese-based precursor, which has a flower-like core-shell structure with a core and a shell.

[0120] The general formula of the kernel is Ni 0.25 Mn 0.75 (OH)2;

[0121] The general formula of the shell is Ni. 0.25 Mn 0.75 Nb 0.05 (OH)2, in which Nb has a oxidation state of +5;

[0122] The preparation method of the composite-modified cobalt-free lithium-rich manganese-based precursor includes the following steps:

[0123] (1) Prepare a base solution with a temperature of 50℃, an ammonia concentration of 1.2g / L and a pH of 10.98. Under nitrogen atmosphere and stirring at a stirring rate of 311rpm, mix the first precipitant solution, the first complexing agent solution and the first metal salt solution in parallel flow in the base solution to carry out a co-precipitation reaction and obtain a seed suspension.

[0124] The first precipitant solution is a sodium hydroxide solution with a concentration of 32 wt%; the first complexing agent solution is ammonia water with a concentration of 60 g / L; the first metal salt solution is a mixed solution of nickel sulfate and manganese sulfate, with a molar ratio of nickel to manganese of 0.25:0.75.

[0125] During the coprecipitation reaction, the pH value was 10.98, the ammonia concentration was maintained at 1.2 g / L, and the flow rate of the first metal salt solution was 5 L / h.

[0126] The seed crystals in the seed suspension meet the following requirements: particle size Dv50 is 3.18 μm, and specific surface area is 113.2 m². 2 / g, tap density is 0.82g / cm³ 2 ;

[0127] (2) The pH of the seed suspension was adjusted to 10.7 and the ammonia concentration to 3.3 g / L using a 32 wt% sodium hydroxide solution and a 60 g / L ammonia solution; then, under a nitrogen atmosphere and with stirring at a stirring rate of 311 rpm, the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution were mixed in a co-current flow to carry out an intermittent co-precipitation reaction to obtain a modified cobalt-free lithium-rich manganese-based suspension.

[0128] The second precipitant solution is a 32 wt% sodium hydroxide solution; the second complexing agent solution is a 60 g / L ammonia solution; the doping solution is an aqueous solution of Nb₂O₅; the second metal salt solution is a mixed solution of nickel sulfate and manganese sulfate, with a molar ratio of nickel to manganese of 0.25:0.75.

[0129] During the intermittent coprecipitation reaction, an external concentration device was connected. The flow rate of the second metal salt solution was 5 L / h, the effluent rate of the concentration device was 7.8 L / h, and the pH value decreased from 10.7 to 9.9 at a rate of 0.03 / h and was maintained until the particle size Dv50 of the material was 6 μm.

[0130] (3) The modified cobalt-free lithium-rich manganese-based suspension was washed with alkali and water, centrifuged to dry, and then dried in an oven at 120℃ for 12 hours to obtain the following... Figure 1 and Figure 2 The XRD pattern of the composite-modified cobalt-free lithium-rich manganese-based precursor shown is as follows. Figure 4 As shown; where Figure 2The image is a SEM image after processing with CP (Cross-section Polisher).

[0131] The alkaline washing was carried out at a temperature of 80°C using a 0.012 wt% sodium hydroxide solution.

[0132] The water washing temperature is 80℃.

[0133] Example 2

[0134] This embodiment provides a composite modified cobalt-free lithium-rich manganese-based precursor, which has a flower-like core-shell structure with a core and a shell.

[0135] The general formula of the kernel is Ni 0.25 Mn 0.75 (OH)2;

[0136] The general formula of the shell is Ni. 0.25 Mn 0.75 Nb 0.05 (OH)2, in which Nb has a oxidation state of +5;

[0137] The preparation method of the composite-modified cobalt-free lithium-rich manganese-based precursor includes the following steps:

[0138] (1) Prepare a base solution with a temperature of 45℃, an ammonia concentration of 0.8g / L and a pH of 10.8. Under a nitrogen atmosphere and a stirring rate of 311rpm, mix the first precipitant solution, the first complexing agent solution and the first metal salt solution in parallel in the base solution to carry out a co-precipitation reaction and obtain a seed suspension.

[0139] The first precipitant solution is a sodium hydroxide solution with a concentration of 32 wt%; the first complexing agent solution is ammonia water with a concentration of 60 g / L; the first metal salt solution is a mixed solution of nickel sulfate and manganese sulfate, with a molar ratio of nickel to manganese of 0.25:0.75.

[0140] During the coprecipitation reaction, the pH value was 10.8, the ammonia concentration was maintained at 0.8 g / L, and the flow rate of the first metal salt solution was 5 L / h.

[0141] The seed crystals in the seed suspension meet the following requirements: a particle size Dv50 of 3.12 μm and a specific surface area of ​​11.3 m². 2 / g, tap density is 0.86g / cm³ 2 ;

[0142] (2) The pH of the seed suspension was adjusted to 10.5 and the ammonia concentration to 2.7 g / L using a 32 wt% sodium hydroxide solution and a 60 g / L ammonia solution; then, under a nitrogen atmosphere and with stirring at a stirring rate of 311 rpm, the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution were mixed in a co-current flow to carry out an intermittent co-precipitation reaction to obtain a modified cobalt-free lithium-rich manganese-based suspension.

[0143] The second precipitant solution is a 32 wt% sodium hydroxide solution; the second complexing agent solution is a 60 g / L ammonia solution; the doping solution is an aqueous solution of NaNb2O4; the second metal salt solution is a mixed solution of nickel sulfate and manganese sulfate, with a molar ratio of nickel to manganese of 0.25:0.75.

[0144] During the intermittent coprecipitation reaction, an external concentration device was connected. The flow rate of the second metal salt solution was 5 L / h, the effluent rate of the concentration device was 7 L / h, and the pH value decreased from 10.5 to 9.8 at a rate of 0.025 / h and was maintained until the particle size Dv50 of the material was 5.8 μm.

[0145] (3) The modified cobalt-free lithium-rich manganese-based suspension was washed with alkali and water, centrifuged and dried, and then dried in an oven at 120°C for 12 hours to obtain the composite modified cobalt-free lithium-rich manganese-based precursor.

[0146] The alkaline washing was carried out at a temperature of 75°C using a 0.01 wt% sodium hydroxide solution.

[0147] The water washing temperature is 75°C.

[0148] Example 3

[0149] This embodiment provides a composite modified cobalt-free lithium-rich manganese-based precursor, which has a flower-like core-shell structure with a core and a shell.

[0150] The general formula of the kernel is Ni 0.25 Mn 0.75 (OH)2;

[0151] The general formula of the shell is Ni. 0.25 Mn 0.75 Nb 0.05 (OH)2, in which Nb has a oxidation state of +5;

[0152] The preparation method of the composite-modified cobalt-free lithium-rich manganese-based precursor includes the following steps:

[0153] (1) Prepare a base solution with a temperature of 55℃, an ammonia concentration of 1g / L and a pH of 11.1. Under nitrogen atmosphere and stirring at a stirring rate of 311rpm, mix the first precipitant solution, the first complexing agent solution and the first metal salt solution in parallel flow in the base solution to carry out a co-precipitation reaction and obtain a seed suspension.

[0154] The first precipitant solution is a sodium hydroxide solution with a concentration of 32 wt%; the first complexing agent solution is ammonia water with a concentration of 60 g / L; the first metal salt solution is a mixed solution of nickel sulfate and manganese sulfate, with a molar ratio of nickel to manganese of 0.25:0.75.

[0155] During the coprecipitation reaction, the pH value was 11.1, the ammonia concentration was maintained at 1 g / L, and the flow rate of the first metal salt solution was 5 L / h.

[0156] The seed crystals in the seed suspension meet the following requirements: a particle size Dv50 of 2.95 μm and a specific surface area of ​​12.3 m². 2 / g, tap density is 0.81g / cm³ 2 ;

[0157] (2) The pH of the seed suspension was adjusted to 10.7 and the ammonia concentration to 3g / L using a 32wt% sodium hydroxide solution and a 60g / L ammonia solution; then, under a nitrogen atmosphere and with stirring at a stirring rate of 311rpm, the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution were mixed in a co-precipitation reaction to obtain a modified cobalt-free lithium-rich manganese-based suspension.

[0158] The second precipitant solution is a 32 wt% sodium hydroxide solution; the second complexing agent solution is a 60 g / L ammonia solution; the doping solution is an aqueous solution of Nb₂O₅; the second metal salt solution is a mixed solution of nickel sulfate and manganese sulfate, with a molar ratio of nickel to manganese of 0.25:0.75.

[0159] During the intermittent coprecipitation reaction, an external concentration device is connected. The flow rate of the second metal salt solution is 5 L / h, the effluent rate of the concentration device is 10 L / h, and the pH value decreases from 10.7 to 10 at a rate of 0.035 / h and is maintained until the particle size Dv50 of the material is 6.2 μm.

[0160] (3) The modified cobalt-free lithium-rich manganese-based suspension was washed with alkali and water, centrifuged and dried, and then dried in an oven at 120°C for 12 hours to obtain the composite modified cobalt-free lithium-rich manganese-based precursor.

[0161] The alkaline washing was carried out at a temperature of 85°C using a 0.015 wt% sodium hydroxide solution.

[0162] The water washing temperature is 85℃.

[0163] Example 4

[0164] This embodiment provides a composite-modified cobalt-free lithium-rich manganese-based precursor, which, in addition to changing the flow rate of the doping solution during the intermittent co-precipitation reaction, makes the shell of the general formula Ni 0.25 Mn 0.75 Nb 0.01 Except for (OH)2, everything else is the same as in Example 1.

[0165] Example 5

[0166] This embodiment provides a composite-modified cobalt-free lithium-rich manganese-based precursor, which, in addition to changing the flow rate of the doping solution during the intermittent co-precipitation reaction, makes the shell of the general formula Ni 0.25 Mn 0.75 Nb 0.1 Except for (OH)2, everything else is the same as in Example 1.

[0167] Example 6

[0168] This embodiment provides a composite modified cobalt-free lithium-rich manganese-based precursor, which, in addition to changing the nickel and manganese content in the first and second metal salt solutions, makes the core have the general formula Ni. 0.2 Mn 0.8 (OH)2, the general formula of the shell is Ni 0.2 Mn 0.8 Nb 0.05 (OH)2, the rest are the same as in Example 1.

[0169] Example 7

[0170] This embodiment provides a composite modified cobalt-free lithium-rich manganese-based precursor, which, in addition to changing the nickel and manganese content in the first and second metal salt solutions, makes the core have the general formula Ni. 0.4 Mn 0.6 (OH)2, the general formula of the shell is Ni 0.4 Mn 0.6 Nb 0.05 (OH)2, the rest are the same as in Example 1.

[0171] Comparative Example 1

[0172] This comparative example provides a cobalt-free lithium-rich manganese-based precursor, which is identical to Example 1 except that no doping solution was used.

[0173] The SEM image of the cobalt-free lithium-rich manganese-based precursor obtained in this comparative example is shown below. Figure 3 As shown, the XRD pattern is as follows Figure 4 As shown.

[0174] Comparative Example 2

[0175] This comparative example provides a cobalt-free lithium-rich manganese-based precursor, except that a doping solution is used during core preparation to make the core have the general formula Ni. 0.2 Mn 0.8 Nb 0.05 (OH)2, the general formula of the shell is Ni 0.2 Mn 0.8 Nb 0.05 (OH)2, the rest are the same as in Example 1.

[0176] The cobalt-free lithium-rich manganese-based precursor provided in this comparative example has Nb doping in its core, which can improve the tap density, but the specific surface area decreases significantly, failing to meet the requirements of a cobalt-free lithium-rich manganese-based precursor with both high tap density and high specific surface area.

[0177] Comparative Example 3

[0178] This embodiment provides a composite-modified cobalt-free lithium-rich manganese-based precursor, which, in addition to changing the flow rate of the doping solution during the intermittent co-precipitation reaction, makes the shell of the general formula Ni 0.25 Mn 0.75 Nb 0.15 Except for (OH)2, everything else is the same as in Example 1.

[0179] Performance Characterization

[0180] The specific surface area, Na content, S content, particle size distribution, and tap density of the precursors obtained in the above embodiments and comparative examples were measured, and the results are shown in Table 1.

[0181] Table 1

[0182]

[0183]

[0184] In summary, this invention provides a cobalt-free, lithium-rich manganese-based precursor with a flower-like core-shell structure, which serves as the Li-based precursor for subsequent sintering processes. +The core-shell structure provides more storage sites, which is beneficial to improving its reversible capacity. Moreover, the core-shell structure can buffer some structural strain and effectively improve the tap density, so that the precursor can have both high specific surface area and tap density. The addition of Nb in the shell can reduce the disordered insertion of primary particles in the secondary particles. At the same time, the primary particle wafers are arranged in a flower-like pattern, which effectively increases the specific surface area of ​​the precursor and helps to increase the reaction contact area between the cathode material and the electrode liquid, resulting in better electrochemical performance. Meanwhile, the orderly flower-like radial pattern of the external primary particles helps to remove impurities such as Na and S inside the precursor as much as possible, reducing the Na and S impurity content in the precursor. In addition, the shell can act as a protective layer to reduce the erosion of the material during subsequent sintering, improve the lithium-ion transport channel, enhance electronic conductivity, and ensure the structural integrity during charging and discharging.

[0185] 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 composite-modified cobalt-free lithium-rich manganese-based precursor, characterized in that, The cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, with a core and a shell. The general formula of the kernel is Ni a Mn b (OH)2, where the value of a ranges from 0.2 to 0.4, the value of b ranges from 0.6 to 0.8, and the sum of a and b is 1; The general formula of the shell is Ni. x Mn y Nb z (OH)2, where x ranges from 0.2 to 0.4, y ranges from 0.6 to 0.8, z ranges from 0.01 to 0.1, and the sum of x and y is 1; In the general formula of the shell, Nb has a oxidation state of +5; The preparation method of the composite-modified cobalt-free lithium-rich manganese-based precursor includes the following steps: (1) The first precipitant solution, the first complexing agent solution and the first metal salt solution are mixed in the bottom liquid to carry out a co-precipitation reaction to obtain a seed suspension; (2) Adjust the pH value and ammonia concentration of the seed suspension, and then mix the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution in parallel to carry out an intermittent co-precipitation reaction to obtain the modified cobalt-free lithium-rich manganese-based suspension. The doping compound in the doping solution is Nb₂O₅ and / or NaNb₂O₄; (3) The modified cobalt-free lithium-rich manganese-based suspension was washed and dried to obtain the composite modified cobalt-free lithium-rich manganese-based precursor.

2. A method for preparing a composite-modified cobalt-free lithium-rich manganese-based precursor, characterized in that, The preparation method includes the following steps: (1) The first precipitant solution, the first complexing agent solution and the first metal salt solution are mixed in the bottom liquid to carry out a co-precipitation reaction to obtain a seed suspension; (2) Adjust the pH value and ammonia concentration of the seed suspension, and then mix the second precipitant solution, the second complexing agent solution, the doping solution and the second metal salt solution in parallel to carry out an intermittent co-precipitation reaction to obtain the modified cobalt-free lithium-rich manganese-based suspension. The doping compound in the doping solution is Nb₂O₅ and / or NaNb₂O₄; (3) The modified cobalt-free lithium-rich manganese-based suspension was washed and dried to obtain the composite modified cobalt-free lithium-rich manganese-based precursor; The obtained cobalt-free lithium-rich manganese-based precursor has a flower-like core-shell structure, with a core and a shell. The general formula of the kernel is Ni a Mn b (OH)2, where the value of a ranges from 0.2 to 0.4, the value of b ranges from 0.6 to 0.8, and the sum of a and b is 1; The general formula of the shell is Ni. x Mn y Nb z (OH)2, where x ranges from 0.2 to 0.4, y ranges from 0.6 to 0.8, z ranges from 0.01 to 0.1, and the sum of x and y is 1; In the general formula of the shell, Nb has a valence of +5.

3. The preparation method according to claim 2, characterized in that, Step (1) The metal salts in the first metal salt solution include a first nickel salt and a first manganese salt; In the first metal salt solution, the molar ratio of nickel to manganese is a:b.

4. The preparation method according to claim 2, characterized in that, Step (2) The metal salts in the second metal salt solution include a second nickel salt and a second manganese salt; In the second metal salt solution, the molar ratio of nickel to manganese is x:y.

5. The preparation method according to claim 2, characterized in that, The temperature of the coprecipitation reaction in step (1) is 45°C to 55°C.

6. The preparation method according to claim 2, characterized in that, The pH value of the coprecipitation reaction in step (1) is 10.8 to 11.

1.

7. The preparation method according to claim 2, characterized in that, The ammonia concentration in the coprecipitation reaction in step (1) is 0.8 g / L to 1.2 g / L.

8. The preparation method according to claim 2, characterized in that, The endpoint of the coprecipitation reaction in step (1) is to ensure that the seed crystals in the seed suspension meet the following requirements: a particle size Dv50 of 2.8 μm to 3.2 μm and a specific surface area of ​​10 m². 2 / g to 15m 2 / g, tap density is 0.8g / cm³ 2 Up to 1g / cm 2 .

9. The preparation method according to claim 2, characterized in that, The temperature of the intermittent coprecipitation reaction in step (2) is 45°C to 55°C.

10. The preparation method according to claim 2, characterized in that, In step (2), the pH value of the intermittent coprecipitation starts from the first pH value, decreases to the second pH value at a rate of 0.025 / h to 0.035 / h, and is maintained until the intermittent coprecipitation reaction ends.

11. The preparation method according to claim 10, characterized in that, The first pH value is 10.5 to 10.7, and the second pH value is 9.8 to 10.

12. The preparation method according to claim 2, characterized in that, The ammonia concentration in the intermittent coprecipitation in step (2) is 2.7 g / L to 3.3 g / L.

13. The preparation method according to claim 2, characterized in that, The endpoint of the intermittent coprecipitation in step (2) is to ensure that the material in the modified cobalt-free lithium-rich manganese-based suspension meets the following requirements: particle size Dv50 is 5.8 μm to 6.2 μm.

14. The preparation method according to any one of claims 9 to 13, characterized in that, The elution rate of the intermittent coprecipitation reaction in step (2) is 7 L / h to 10 L / h.

15. The preparation method according to claim 2, characterized in that, The washing process in step (3) includes an alkaline wash followed by a water wash.

16. The preparation method according to claim 15, characterized in that, The concentration of the alkaline solution used in the alkaline washing is from 0.01wt% to 0.015wt%.

17. The preparation method according to claim 15, characterized in that, The alkaline washing temperature is 75°C to 85°C.

18. The preparation method according to claim 15, characterized in that, The temperature of the water wash is 75°C to 85°C.

19. The preparation method according to claim 2, characterized in that, The coprecipitation reaction described in step (1) is carried out under stirring conditions.

20. The preparation method according to claim 2, characterized in that, The intermittent coprecipitation reaction described in step (2) is carried out under stirring conditions.

21. The preparation method according to claim 2, characterized in that, The first precipitant solution is a sodium hydroxide solution.

22. The preparation method according to claim 2, characterized in that, The second precipitant solution is a sodium hydroxide solution.

23. The preparation method according to claim 2, characterized in that, The first complexing agent solution is ammonia.

24. The preparation method according to claim 2, characterized in that, The second precipitant solution is ammonia.

25. A positive electrode material, characterized in that, The raw materials for preparing the cathode material include the composite modified cobalt-free lithium-rich manganese-based precursor as described in claim 1, or the composite modified cobalt-free lithium-rich manganese-based precursor obtained by any one of the preparation methods described in claims 2 to 24.

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