Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The following specifically describes a preparation method for improving the consistency of primary particles of a positive electrode material precursor and the precursor.
In a first aspect, the embodiment of the invention provides a preparation method for improving the consistency of primary particles of a precursor of a positive electrode material, which comprises the steps of suspending all feeding when the primary particles in a solution are different in size when the precursor of the positive electrode material is prepared by adopting a coprecipitation method, then increasing the rotating speed to inhibit the abnormal growth of the primary particles, and then introducing a low-concentration salt solution and a hydrogen peroxide solution to guide the primary particles to grow in the same direction, so that nucleation sites are reduced, and the consistency of the primary particles of the precursor of the positive electrode material is improved.
In the process of preparing the precursor, primary particles with inconsistent sizes are easy to form when the pH of the reaction system is adjusted or inert gas with high flow rate is introduced due to the characteristics of the reaction system or the product, obvious difference can be seen from a scanning electron microscope, the primary particle diameter width difference is larger than 100nm, the diameter length difference is larger than 200nm, and the performance of the positive electrode material or the battery is further reduced due to the poor consistency of the primary particles.
Therefore, the embodiment of the invention provides the preparation method for improving the consistency of the primary particles of the precursor of the positive electrode material, which can avoid the problem of poor consistency of the primary particles caused by adjustment of process conditions, and can reduce the number of nucleation sites on the surface of the secondary sphere under each process condition, so that the primary particle diameter wide difference of the precursor is less than 20nm, the diameter length difference is less than 50nm, the uniformity and consistency of the particles of the product are ensured, and the electrical performance of the product is stabilized. The method is completed through physical adjustment and a proper amount of additives, does not need to increase equipment, is simple, and is suitable for preparing the full-series precursor with the problems.
In an alternative embodiment, the method comprises the following steps of introducing mixed salt solution, precipitant solution and complexing agent solution into base solution in parallel under the protection of inert gas, reducing the pH value of a system to perform primary particle growth after crystal nucleus generation, suspending all feeding when the primary particle sizes are different in the solution, then increasing the rotating speed to inhibit the abnormal growth of the primary particles, maintaining the rotating speed to stir, introducing low-concentration salt solution and hydrogen peroxide solution with the same molar ratio to guide the primary particles to grow in the same direction when the precipitation tends to be suspended, reducing nucleation sites, improving the consistency of the primary particles of a precursor of a positive electrode material, and restoring the primary particles to the original feeding mode when the diameter width and diameter length difference value after re-feeding meet the design requirement until the materialization index of the primary particles is qualified.
In an alternative embodiment, the pH value of the reaction system is controlled to be 10.0-12.5, the pH value is lower than the lower limit, the growth rate is too fast, the growth and the size of precursor particles of the positive electrode material cannot be controlled, micro powder particles are easy to appear when the pH value exceeds the upper limit, the reaction cannot be normally carried out, the ammonia value is 2-20 g/L, ammonia is regulated along with the pH change and presents positive correlation, the ammonia value mismatch influences the coprecipitation efficiency, the temperature is 40-80 ℃, the mass transfer rate of the system is easy to be reduced when the temperature is lower than the lower limit, the particle crystallization is influenced, the precursor oxidation is caused when the upper limit is exceeded, the precursor performance is influenced, the rotating speed is 100-1000 rpm, the particles cannot be effectively dispersed and are seriously agglomerated when the lower than the lower limit, the electrical property of the precursor is reduced, the particles in the system cannot normally precipitate and crystallize, and the precursor cannot be synthesized when the upper limit is exceeded.
In an alternative embodiment, the pH value of the system is reduced after the crystal nucleus is generated, the feeding is stopped after the reaction is continued for 5-10 hours, if the feeding is stopped for less than the preset time, the state of the reaction system is inconsistent due to uneven mixing, and if the feeding is stopped for more than the preset time, the particles grow due to continuous feeding, so that the original crystal nucleus particle size is increased, and the regulation and control of the structure are affected.
In an alternative embodiment, the mixed salt solution has a concentration of 1.0mol/L to 2.5mol/L, the precipitant solution has a mass concentration of 20% to 25%, and the complexing agent solution has a mass concentration of 7% to 30%. And liquid alkali (sodium hydroxide solution) is used as a precipitator, and ammonia water is used as a complexing agent.
In an alternative embodiment, the rotational speed is increased to 1.2-2 times the original rotational speed, abnormal particle growth is restrained by increasing the rotational speed, the particle size growth rate is slowed down, the particle size range of the affected particles is weakened, the crystallization state of the system is changed by using high-rotational-speed stirring, and the pause time is maintained for 0.5-10 hours, so that the crystallization state is adjusted, the particle growth continuity is influenced by the time-out range, and the independent nucleation of the system is easily caused.
In an alternative embodiment, the low concentration salt solution concentration is 0.3 to 0.8 times that of the original mixed salt solution concentration, and the growth rate of the low concentration salt solution can be slowed down by the flow rate of the low concentration salt solution, so that the particles can be recrystallized in a uniform manner under a growth system.
In an alternative embodiment, the hydrogen peroxide solution has a mass fraction of 5% to 40%.
In an alternative embodiment, the method further comprises the steps of ageing the materials qualified in reaction, filtering, slurrying a filter cake obtained by filtering with dilute alkali, filtering and washing until the pH value of the filtrate is less than 9, and drying, screening and demagnetizing to obtain a precursor product with uniform primary particles.
In a second aspect, an embodiment of the present invention provides a positive electrode material precursor, where the positive electrode material precursor is prepared by using the method described above.
The above is apparent that the embodiment of the invention provides a preparation method for improving the consistency of primary particles of a positive electrode material precursor, which has the following characteristics and advantages:
(1) By adopting the scheme provided by the embodiment of the invention, the ternary precursor with uniform primary particles can be prepared, the primary particle difference caused by process adjustment or product self-characteristics can be avoided, and the electrical property of the positive electrode material is stabilized.
(2) The scheme provided by the embodiment of the invention is simple, convenient and effective, no new element is introduced, and the method is suitable for preparing the NCM (lithium nickel cobalt manganese oxide, liNiCoMnO 2) and NCA (lithium nickel cobalt aluminum oxide, liNiCoAlO 2) full-series precursors.
(3) The scheme provided by the embodiment of the invention can be applied to each stage of the precursor, the problem of particle consistency is solved in a targeted manner, no application taboo exists, and the scheme can be expanded to quaternary precursor equivalent type products.
(4) The scheme provided by the embodiment of the invention has low application cost and excellent reaction control, and the existing equipment is not required to be modified.
The invention is further described below with reference to examples.
Example 1
Preparing a reaction kettle base solution, wherein the temperature is 50 ℃, the ammonia value is 14g/L, the pH value is 11.4, simultaneously introducing nickel cobalt manganese sulfate solution, ammonia water and sodium hydroxide into the reaction kettle, introducing nitrogen for protection, setting the stirring rotating speed of the reaction kettle to be 550rpm, wherein the molar ratio of nickel to cobalt manganese in the mixed salt solution is 6:1:3, the concentration of the mixed salt solution is 1.6mol/L, the mass percentage concentration of the sodium hydroxide solution is 22%, and the mass percentage concentration of the ammonia water is 15%.
After the preparation of the crystal nucleus is finished, the pH value of a reaction system is adjusted to 10.9, particles are in a growth state, feeding is stopped after the reaction is continued for 8 hours, the rotating speed is increased to 750rpm, the current process is kept for 5 hours, then 0.8mol/L saline solution with the same proportion is introduced, 30% hydrogen peroxide solution by mass fraction is introduced, electron microscopy monitoring is continuously carried out during the process, when the diameter width and the diameter length difference value meet the design requirements after the feeding is carried out again for 10 hours, the feeding process before stopping is resumed until the materialization index is qualified.
Placing the kettle material in an ageing kettle for ageing, filtering, adding dilute alkali with a certain concentration into a filter cake for pulping, filtering and washing until the pH value of the filtrate is less than 9, and drying, screening and demagnetizing to obtain a precursor material with uniform primary particles. The SEM of the precursor materials is shown in fig. 1, and it can be seen that the precursor primary particles are uniform and have good consistency.
Example 2
Preparing a reaction kettle base solution, wherein the temperature is 45 ℃, the ammonia value is 6.5g/L, the pH value is 11.1, simultaneously introducing nickel cobalt manganese sulfate solution, ammonia water and sodium hydroxide into the reaction kettle, introducing nitrogen for protection, setting the stirring rotating speed of the reaction kettle to 360rpm, wherein the molar ratio of nickel to cobalt manganese in the mixed salt solution is 5:2:3, the concentration of the mixed salt solution is 1.6mol/L, the mass percentage concentration of the sodium hydroxide solution is 22%, and the mass percentage concentration of the ammonia water is 15%.
After the preparation of the crystal nucleus is finished, the pH value of a reaction system is adjusted to 10.8, particles are in a growth state, feeding is stopped after the reaction is continued for 6 hours, the rotating speed is increased to 504rpm, the current process is kept for 8 hours, then 0.8mol/L saline solution with the same proportion is introduced, 30% hydrogen peroxide solution by mass fraction is introduced, electron microscopy monitoring is continuously carried out during the process, when the diameter width and the diameter length difference value meet the design requirements after the feeding is carried out again for 6 hours, the feeding process before stopping is resumed until the materialization index is qualified.
Placing the kettle material in an ageing kettle for ageing, filtering, adding dilute alkali with a certain concentration into a filter cake for pulping, filtering and washing until the pH value of the filtrate is less than 9, and drying, screening and demagnetizing to obtain a precursor material with uniform primary particles. The SEM of the precursor materials is shown in fig. 2, and it can be seen that the precursor primary particles are uniform and have better consistency.
Comparative example 1 (comparative example 1, no rotation speed adjustment, no pause in feeding, no low concentration salt solution, no hydrogen peroxide solution)
Preparing a reaction kettle base solution, wherein the temperature is 50 ℃, the ammonia value is 14g/L, the pH value is 11.4, simultaneously introducing nickel cobalt manganese sulfate solution, ammonia water and sodium hydroxide into the reaction kettle, introducing nitrogen for protection, setting the stirring rotating speed of the reaction kettle to be 550rpm, wherein the molar ratio of nickel to cobalt manganese in the mixed salt solution is 6:1:3, the concentration of the mixed salt solution is 1.6mol/L, the mass percentage concentration of the sodium hydroxide solution is 22%, and the mass percentage concentration of the ammonia water is 15%.
After the preparation of the crystal nucleus is finished, the pH value of a reaction system is adjusted to 10.9, particles are in a growth state, the current process is kept to continuously feed, and the morphology change of an electron microscope is monitored in the process until the physical and chemical indexes are qualified.
Placing the kettle material in an ageing kettle for ageing, filtering, adding dilute alkali with a certain concentration into a filter cake for pulping, filtering and washing until the pH value of the filtrate is less than 9, and drying, screening and demagnetizing to obtain a precursor material, wherein SEM (scanning electron microscope) of the precursor material is shown in figure 3, and the primary particle size of the prepared precursor is large in width-diameter-length difference and does not meet the design requirement.
Comparative example 2 (comparative example was free of rotational speed adjustment compared to example 1)
Preparing a reaction kettle base solution, wherein the temperature is 50 ℃, the ammonia value is 14g/L, the pH value is 11.4, simultaneously introducing nickel cobalt manganese sulfate solution, ammonia water and sodium hydroxide into the reaction kettle, introducing nitrogen for protection, setting the stirring rotating speed of the reaction kettle to be 550rpm, wherein the molar ratio of nickel to cobalt manganese in the mixed salt solution is 6:1:3, the concentration of the mixed salt solution is 1.6mol/L, the mass percentage concentration of the sodium hydroxide solution is 22%, and the mass percentage concentration of the ammonia water is 15%.
After the preparation of the crystal nucleus is finished, the pH value of a reaction system is adjusted to 10.9, particles are in a growth state, feeding is stopped after the reaction is continued for 8 hours, the rotating speed is not improved, then 0.8mol/L saline solution with the same proportion is introduced, 30% hydrogen peroxide solution with mass fraction is introduced, and electron microscope monitoring is continuously carried out during the process, and the feeding process is resumed before stopping after the feeding is resumed for 10 hours until the physical and chemical indexes are qualified.
Placing the kettle material in an ageing kettle for ageing, filtering, adding dilute alkali with a certain concentration into a filter cake for pulping, filtering and washing until the pH value of the filtrate is less than 9, drying, screening and demagnetizing to obtain a precursor material, wherein the crystallization state is not obviously changed when primary particles with different sizes appear, and the uniformity of all particles in a system is not sufficiently changed when a low-concentration salt solution and a hydrogen peroxide solution are further used, so that the primary particle size width-diameter-length difference of the prepared precursor is larger and does not meet the design requirement.
Comparative example 3 (compared with example 1, there is no hold time after the rotational speed is raised in this comparative example)
Preparing a reaction kettle base solution, wherein the temperature is 50 ℃, the ammonia value is 14g/L, the pH value is 11.4, simultaneously introducing nickel cobalt manganese sulfate solution, ammonia water and sodium hydroxide into the reaction kettle, introducing nitrogen for protection, setting the stirring rotating speed of the reaction kettle to be 550rpm, wherein the molar ratio of nickel to cobalt manganese in the mixed salt solution is 6:1:3, the concentration of the mixed salt solution is 1.6mol/L, the mass percentage concentration of the sodium hydroxide solution is 22%, and the mass percentage concentration of the ammonia water is 15%.
After the preparation of the crystal nucleus is finished, the pH value of a reaction system is adjusted to 10.9, particles are in a growth state, feeding is stopped after the reaction is continued for 8 hours, the rotating speed is increased to 750rpm, no holding time is required, then 0.8mol/L saline solution with the same proportion is introduced, 30% hydrogen peroxide solution by mass fraction is introduced, electron microscope monitoring is continuously carried out during the process, and when feeding is resumed for 10 hours until the feeding process is stopped, the physicochemical index is qualified.
Placing the kettle material in an ageing kettle for ageing, filtering, adding dilute alkali with a certain concentration into a filter cake for pulping, filtering and washing until the pH value of the filtrate is less than 9, drying, screening and demagnetizing to obtain a precursor material, wherein the crystallization state is not changed due to no holding time after the rotation speed is increased, the subsequent process is insufficient to enable primary particles to uniformly grow, and the primary particle diameter of the prepared precursor is large in width-diameter-length difference and does not meet the design requirement.
Comparative example 4 (compared with example 1, the concentration of the mixed salt solution in this comparative example was not adjusted)
Preparing a reaction kettle base solution, wherein the temperature is 50 ℃, the ammonia value is 14g/L, the pH value is 11.4, simultaneously introducing nickel cobalt manganese sulfate solution, ammonia water and sodium hydroxide into the reaction kettle, introducing nitrogen for protection, setting the stirring rotating speed of the reaction kettle to be 550rpm, wherein the molar ratio of nickel to cobalt manganese in the mixed salt solution is 6:1:3, the concentration of the mixed salt solution is 1.6mol/L, the mass percentage concentration of the sodium hydroxide solution is 22%, and the mass percentage concentration of the ammonia water is 15%.
After the preparation of the crystal nucleus is finished, the pH value of a reaction system is adjusted to 10.9, particles are in a growth state, the feeding is stopped after the reaction is continued for 8 hours, the rotating speed is increased to 750rpm, the current process is kept for 5 hours, then 1.6mol/L of salt solution with the same proportion is introduced, 30% of hydrogen peroxide solution by mass fraction is introduced, the electron microscope monitoring is continuously carried out during the period, the width and the length of the primary particle diameter are not improved, and by contrast, the low-concentration salt solution plays a role of continuously reducing the growth power of the reaction system in the crystal form adjusting stage, and meanwhile, the raw materials and the time required by the crystal form conversion of the system are given. After the rotating speed is increased, if the original concentration mixed salt solution is adopted, the growth power is maintained at a higher level, the growth rate cannot be effectively reduced, abnormal particles continue to grow abnormally due to the power, and the diameter-width difference value of the finally prepared product is larger than 20nm and does not meet the design requirement.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.