Ternary positive electrode material precursor and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and provides a ternary positive electrode material precursor and a preparation method and application thereof.The preparation method comprises the steps that a mixed salt solution, a precipitator, a complexing agent and a surfactant are subjected to a generation reaction, seed crystals are obtained, then an overflow reaction and a thickening reaction are sequentially conducted on the seed crystals, and the ternary positive electrode material precursor is obtained. The ternary positive electrode material precursor with a loose and porous interior and a compact and compact exterior structure is prepared by controlling the process parameters of the three-stage reaction, such as the pH value and the feeding flow; the internal loose and porous structure is beneficial to reducing the internal resistance of the obtained ternary positive electrode material, shortening the Li < + > transmission path and improving the electrochemical performance of the ternary positive electrode material; and the compact external structure is beneficial to enhancing the structural stability, so that the ternary positive electrode material is not easy to crack in the charge-discharge process, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials and relates to a ternary positive electrode material precursor and a preparation method and use thereof. Background Art

[0002] As an efficient and environmentally friendly energy storage device, lithium-ion batteries have been widely used in electric vehicles, portable electronic devices, energy storage systems and other fields. One of the core components of lithium-ion batteries is the positive electrode material, and its performance directly affects the overall performance of the battery. Therefore, the development of high-performance positive electrode materials is of great significance to promote the development of lithium-ion battery technology.

[0003] At present, the commonly used positive electrode materials for lithium-ion batteries mainly include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and ternary positive electrode materials, etc. Combining the advantages of nickel, cobalt and manganese, it has the characteristics of high specific capacity, high discharge voltage, low toxicity and low cost, and is considered to be one of the ideal positive electrode materials in power batteries.

[0004] There are many methods for preparing ternary cathode materials, and common methods include solid phase reaction method, sol-gel method, hydrothermal method and co-precipitation method. Among them, co-precipitation method is a simple and efficient common preparation method. By mixing a metal salt solution with a precipitant, the metal ions are precipitated at the same time, and then the precursor is obtained by washing and drying. The precursor is further calcined with a lithium source to obtain the target ternary cathode material. The process flow of the co-precipitation method is relatively simple, does not require complex equipment and harsh reaction conditions, and is suitable for large-scale industrial production. And it is easy to achieve effective regulation of the product particle size distribution by adjusting the reaction conditions, such as pH value, temperature, stirring speed, etc. However, in practical applications, the morphology of the precursor obtained by the co-precipitation method is relatively simple, mostly spherical particles. According to existing research, the regulation of the particle structure and morphology of the cathode material, such as the formation of a hollow structure or a porous structure, or the change of the internal structure is conducive to further improving the electrochemical performance of the material.

[0005] Therefore, further research and development of the co-precipitation method of ternary positive electrode materials to achieve the adjustment of particle structure and / or morphology is of great practical significance for further improving the electrochemical properties of materials and promoting the development of lithium-ion battery technology. Summary of the invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide a ternary cathode material precursor and a preparation method and use thereof, wherein the preparation method comprises performing a generation reaction by mixing a salt solution, a precipitant, a complexing agent and a surfactant to obtain a seed crystal, and then performing an overflow reaction and a concentration reaction on the seed crystal in sequence, and preparing a ternary cathode material precursor having a loose and porous interior and a compact and dense structure outside by controlling the process parameters of the three-stage reaction, such as pH value and feed flow rate; the loose and porous structure inside is conducive to reducing the internal resistance of the obtained ternary cathode material, shortening the Li + The transmission path improves the electrochemical performance of the ternary positive electrode material; the compact and dense external structure is conducive to enhancing the structural stability, making the ternary positive electrode material less likely to crack during the charging and discharging process, thereby increasing the battery life.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a ternary cathode material precursor, the preparation method comprising:

[0009] (1) providing a mixed salt solution, a precipitant, a complexing agent and a surfactant; preparing an initial base solution with an initial pH value, wherein the initial base solution includes the precipitant and the complexing agent;

[0010] (2) adding the mixed salt solution, precipitant, complexing agent and surfactant to the initial base solution in parallel, maintaining the solution at a first pH value, and performing a formation reaction to obtain seed crystals having a first particle size;

[0011] (3) preparing a growth base solution, wherein the growth base solution contains the seed crystal; adding the mixed salt solution, the precipitant and the complexing agent to the growth base solution in parallel to perform an overflow reaction; during the overflow reaction, maintaining the second pH value and continuously increasing the flow rate of the mixed salt solution; when the particle size of the seed crystal increases to the second particle size, starting to continuously reduce the flow rate of the mixed salt solution, maintaining the third pH value, and performing a concentration reaction until the particle size of the seed crystal increases to the third particle size, thereby obtaining a ternary positive electrode material precursor;

[0012] In steps (1) to (3), the initial pH value>the third pH value>the second pH value≥the first pH value.

[0013] In the preparation method of the present invention, the introduction of a surfactant in the formation reaction can effectively prevent the adhesion of the primary particles, make the primary particles grow in the direction of slender strips, increase the pores between the primary particles, and help form a loose and porous structure, thereby shortening the Li +The transmission path of the precursor is reduced to reduce the internal resistance of the material. Furthermore, by dividing the growth of the precursor into an overflow stage and a dense stage, and by changing the pH value and feed flow rate in the reaction process of each stage, the growth rate in the overflow reaction is faster and the transformation of the precursor structure is not obvious. In the dense reaction process, the increase in solid content will slow down the growth of particles, which is conducive to achieving structural transformation. Ultimately, it can change the growth mode of primary particles and control the growth rate of secondary particles, so that on the basis of the seed with a loose and porous structure inside, a dense structure is gradually grown, and the particle size is controlled while the internal structure is controllable, and finally a ternary positive electrode precursor that changes from loose to dense from the inside to the outside is obtained.

[0014] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, in step (1), the mixed salt solution includes at least two of nickel salt, cobalt salt and manganese salt, preferably sulfate.

[0016] Preferably, the total concentration of metal ions in the mixed salt solution is 1 to 2.5 mol / L, for example, 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L or 2.5 mol / L.

[0017] Preferably, the precipitating agent comprises sodium hydroxide solution.

[0018] Preferably, the mass concentration of the precipitant is 30% to 35%, for example, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5% or 35%, etc.

[0019] Preferably, the complexing agent comprises aqueous ammonia.

[0020] Preferably, the mass concentration of the complexing agent is 10% to 20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.

[0021] Preferably, the surfactant comprises sodium lauryl sulfate.

[0022] Preferably, the concentration of the surfactant is 0.1-0.4 mol / L, for example, 0.1 mol / L, 0.15 mol / L, 0.18 mol / L, 0.23 mol / L, 0.25 mol / L, 0.3 mol / L, 0.32 mol / L, 0.36 mol / L or 0.4 mol / L.

[0023] As a preferred technical solution of the present invention, the initial pH is 11.2-12, such as 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9 or 12; the first pH is 9.5-10.5, such as 9.5, 9.6, 9.7, 9.8, 9.9, 10, 10.1, 10.2, 10.3, 10.4 or 10.5; the second pH The H value is 10-10.5, for example, 10, 10.05, 10.1, 10.15, 10.2, 10.25, 10.3, 10.35, 1.4, 1.45 or 10.5, etc.; the third pH value is 10.5-11, for example, 10.5, 10.55, 10.6, 10.65, 10.7, 10.75, 10.8, 10.85, 10.9, 10.95 or 11, etc.

[0024] The present invention finds that compared with other parameters, pH value has the greatest impact on the morphology of primary particles. By simply changing the feed flow rate, the change in morphology and structure can be made more obvious, achieving the target morphology and size regulation effect.

[0025] Preferably, the ammonia concentration in the initial base solution is 3-8 g / L, for example, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L or 8 g / L; the ammonia concentration in the reaction system of the generation reaction is 3-4 g / L, for example, 3 g / L, 3.1 g / L, 3.2 g / L, 3.3 g / L, 3.4 g / L, 3.5 g / L, 3.6 g / L, 3.7 g / L, 3.8 g / L, 3.9 g / L or 4 g / L; the ammonia concentration in the growth base solution is 4-6 g / L, for example, 4 g / L, 4.2 g / L, 4.5 g / L, 4.8 g / L / L, 5g / L, 5.3g / L, 5.5g / L, 5.8g / L or 6g / L, etc.; the ammonia concentration in the reaction system of the overflow reaction is 4-5g / L, for example, 4g / L, 4.1g / L, 4.2g / L, 4.3g / L, 4.4g / L, 4.5g / L, 4.6g / L, 4.7g / L, 4.8g / L, 4.9g / L or 5g / L, etc.; the ammonia concentration in the reaction system of the dense reaction is 5-6g / L, for example, 5g / L, 5.1g / L, 5.2g / L, 5.3g / L, 5.4g / L, 5.5g / L, 5.6g / L, 5.7g / L, 5.8g / L, 5.9g / L or 6g / L, etc.

[0026] In the present invention, generally speaking, after the primary particles are formed, in the subsequent growth reaction process (overflow reaction and dense reaction), the ammonia concentration of the system is slightly greater than the ammonia concentration of the system during the generation reaction, and the ammonia concentration gradually increases during the entire reaction process. Maintaining a high ammonia concentration in the initial bottom liquid is conducive to the primary particles becoming coarser and forming a dense structure.

[0027] Preferably, the stirring speed in the generation reaction is 300-400 rpm, for example, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm, etc., the initial stirring speed of the overflow reaction is the same as the stirring speed in the generation reaction, and the stirring speed continues to decrease during the overflow reaction, and further continues to decrease during the concentrated reaction.

[0028] Preferably, the reaction temperature of the generating reaction is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C; the reaction temperature of the overflow reaction is 50-70°C, for example, 50°C, 55°C, 60°C, 65°C or 70°C; the reaction temperature of the dense reaction is 50-70°C, for example, 50°C, 55°C, 60°C, 65°C or 70°C.

[0029] As a preferred technical solution of the present invention, in the generation reaction, the flow rate of the mixed salt solution is 10 to 80 L / h, for example, 10 L / h, 15 L / h, 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h, 50 L / h, 55 L / h, 60 L / h, 65 L / h, 70 L / h, 75 L / h or 80 L / h, etc.; the flow rate of the precipitant is 2 to 20 L / h, for example, 2 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 14 L / h, 16 L / h, 18 L / h or 20 L / h, etc.; The flow rate of the complexing agent is 2 to 10 L / h, for example, 2 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 14 L / h, 16 L / h, 18 L / h or 20 L / h, etc.; the flow rate of the surfactant makes the concentration of the surfactant in the reaction system of the generating reaction be 0.02 to 0.1 mol / L, for example, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L or 1 mol / L, etc.

[0030] Preferably, in the overflow reaction, the initial flow rate of the mixed salt solution is the same as the flow rate of the mixed salt solution in the generation reaction, and in the overflow reaction, the flow rate is adjusted by increasing 10 L / h for every 1 μm increase in the particle size of the seed crystal, and the feed flow rates of the precipitant and the complexing agent are adaptively adjusted so that the second pH value remains stable.

[0031] Preferably, in the concentrated reaction, the flow rate of the mixed salt solution is adjusted by reducing the flow rate by 5 L / h for every 2 μm increase in the particle size of the seed crystal, keeping the final flow rate greater than the initial flow rate of the mixed salt solution obtained in the overflow reaction, and adaptively adjusting the feed flow rates of the precipitant and the complexing agent so that the second pH value remains stable.

[0032] As a preferred technical solution of the present invention, the solid content of the seed crystals in the growth base solution is 20-80 g / L, for example, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L or 80 g / L, etc.

[0033] Preferably, the overflow reaction is achieved by setting and opening an overflow valve in the reaction system.

[0034] Preferably, the thickening reaction is achieved by setting and closing an overflow valve in the reaction system and setting and starting a thickener.

[0035] Preferably, the primary particle D50 size value of the first particle size is 2 to 5 μm, for example, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm or 5 μm, etc.; the primary particle D50 size value of the second particle size is 5 to 9 μm, for example, 5 μm, 5.5 μm , 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm or 9μm, etc.; the D50 particle size value of the primary particles of the third particle size is 8-14μm, for example, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm or 14μm, etc.

[0036] In a second aspect, the present invention provides a ternary positive electrode material precursor obtained according to the preparation method described in the first aspect.

[0037] In a third aspect, the present invention provides a method for synthesizing a ternary positive electrode material, the method comprising: mixing the ternary positive electrode material precursor described in the second aspect with a lithium source, and performing a sintering process to obtain the ternary positive electrode material.

[0038] As a preferred technical solution of the present invention, the lithium source includes lithium hydroxide;

[0039] Preferably, the primary sintering temperature is 500-800°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, and the time is 6-10h, for example, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h.

[0040] Preferably, the synthesis method further comprises mixing the obtained ternary positive electrode material with a boron source and performing secondary sintering to obtain a boron-coated ternary positive electrode material.

[0041] Preferably, the boron source comprises boric acid.

[0042] Preferably, the secondary sintering temperature is 200-500°C, for example 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C, and the time is 2-6h, for example 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h.

[0043] The present invention preferably sintering and coating the obtained ternary positive electrode material to obtain a lithium ion battery positive electrode material with a coating layer, which further effectively improves the electrochemical performance of the lithium battery positive electrode material.

[0044] In a fourth aspect, the present invention provides a ternary positive electrode material obtained using the synthesis method described in the third aspect.

[0045] In a fifth aspect, the present invention provides a lithium-ion battery comprising the ternary positive electrode material described in the fourth aspect.

[0046] It should be noted that due to space limitations and to avoid redundancy, the present invention does not list all point values ​​within the above numerical range one by one, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0047] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0048] The preparation method of the ternary cathode material precursor of the present invention comprises the following steps: a mixed salt solution, a precipitant, a complexing agent and a surfactant are subjected to a generation reaction to obtain a seed crystal, and then an overflow reaction and a concentration reaction are sequentially performed on the seed crystal. By controlling the process parameters of the three-stage reaction, such as pH value and feed flow rate, a ternary cathode material precursor with a loose and porous interior and a compact and dense exterior structure is prepared; the ternary cathode material prepared using the obtained precursor inherits the structural characteristics, and its loose and porous interior structure is conducive to reducing the internal resistance of the obtained ternary cathode material and shortening the Li +The transmission path improves the electrochemical performance of the ternary positive electrode material; the compact and dense external structure is conducive to enhancing the structural stability, making the ternary positive electrode material less likely to crack during the charging and discharging process, thereby increasing the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is the SEM image of the ternary precursor obtained in Example 1.

[0050] Figure 2 This is a cross-sectional SEM image of the ternary precursor obtained in Example 1. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0052] It should be clear to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0053] Example 1

[0054] This embodiment provides a method for synthesizing a ternary positive electrode material. Steps (1) to (3) in the synthesis method are a method for preparing a ternary positive electrode material precursor. The synthesis method specifically includes:

[0055] (1) preparing nickel sulfate, cobalt sulfate and manganese sulfate solutions into a mixed salt solution with a metal ion concentration of 2 mol / L in a molar ratio of nickel:cobalt:manganese=95:3:2; providing a sodium hydroxide solution with a mass concentration of 32% as a precipitant; providing ammonia water with a mass concentration of 16% as a complexing agent; and providing an aqueous solution of sodium lauryl sulfate with a concentration of 0.2 mol / L as a surfactant;

[0056] Add pure water, precipitant and complexing agent to a 1 cubic reactor to prepare the initial bottom solution, and pass N 2 As the protective gas, the initial pH of the initial bottom solution was adjusted to 11.4, the ammonia concentration was adjusted to 5.6 g / L, and the temperature was controlled at 60 °C.

[0057] (2) Adding the mixed salt solution, precipitant and complexing agent to the reactor in parallel, with flow rates of 20 L / h, 6 L / h and 3 L / h respectively; continuously adding surfactant during the reaction to ensure that the concentration of the surfactant in the reactor is 0.04 mol / L, the reaction pH is maintained between the first pH value of 9.5 and 10.4, the ammonia concentration is maintained at 3 to 4 g / L, the reaction temperature is maintained at 50°C, the stirring speed is adjusted to 380 rpm, and the generation reaction is carried out until the D50 particle size value of the primary particles reaches the first particle size of 3 μm, then stopping the feeding, washing and dehydrating, and obtaining seed crystals.

[0058] (3) adding the obtained seed crystals and water to the reactor at a solid content of 26 g / L, adding a complexing agent to adjust the ammonia concentration to 5.2 g / L, controlling the temperature at 60°C, and then allowing the mixed salt solution, precipitant and complexing agent to flow into the reactor at the same flow rate as in step (2) as the initial speed, opening the overflow valve, and conducting an overflow reaction. During this period, the initial stirring speed is set to be the same as in step (2), and the rotation speed is continuously reduced. For every increase of 1 μm in particle size, the flow rate of the mixed salt solution is increased by 10 L / h, and the flow rates of the corresponding precipitant and complexing agent are matched to ensure that the pH of the reaction system during the reaction is maintained between the second pH value of 10.0 and 10.4, and the ammonia concentration is maintained at 4 to 5 g / L. When the D50 particle size value of the primary particles of the seed crystals reaches the second particle size of 6 μm, the overflow valve is closed.

[0059] Starting from the second particle size (including the second particle size), the rotation speed continues to be reduced, and for every 2μm increase in the particle size, the flow rate of the mixed salt solution is reduced by 5L / h, and the flow rates of the corresponding precipitant and complexing agent are matched to maintain the reaction pH at a third pH value of 10.5-11, and the ammonia concentration is maintained at 5-6g / L, so that the slurry of the reaction system enters the thickener for a thickening reaction, until the D50 particle size value of the primary particles of the seed crystal reaches the third particle size of 10μm, the reaction is terminated, and after washing and drying, a ternary precursor is obtained.

[0060] (4) The obtained ternary cathode material precursor is mixed with lithium hydroxide as a lithium source at a molar ratio of 1:1.05, and the mixture is taken out after sintering at 650°C for 8 hours to obtain a ternary cathode material. The obtained ternary cathode material is then mixed with boric acid as a boron source, and sintered at 250°C for 5 hours to obtain a boron-coated ternary precursor, in which the boron element accounts for 0.01wt%.

[0061] Example 2

[0062] This embodiment provides a method for synthesizing a ternary positive electrode material, wherein the first particle size is adjusted from 3 μm to 4 μm, the second particle size is adjusted from 6 μm to 8 μm, and the third particle size is adjusted from 10 μm to 14 μm. Except for the above, other conditions are exactly the same as those in Example 1.

[0063] Example 3

[0064] This embodiment provides a method for synthesizing a ternary positive electrode material. In the synthesis method, the concentration of the surfactant in the kettle in step (2) is adjusted from 0.04 mol / L to 0.01 mol / L. Except for the above, other conditions are exactly the same as those in Example 1.

[0065] Example 4

[0066] This embodiment provides a method for synthesizing a ternary positive electrode material. In the synthesis method, the concentration of the surfactant in the kettle in step (2) is adjusted from 0.04 mol / L to 0.02 mol / L. Except for the above, other conditions are exactly the same as those in Example 1.

[0067] Example 5

[0068] This embodiment provides a method for synthesizing a ternary positive electrode material. In the synthesis method, the concentration of the surfactant in the kettle in step (2) is adjusted from 0.04 mol / L to 0.06 mol / L. Except for the above, other conditions are exactly the same as those in Example 1.

[0069] Example 6

[0070] This embodiment provides a method for synthesizing a ternary positive electrode material. In the synthesis method, the concentration of the surfactant in the kettle in step (2) is adjusted from 0.04 mol / L to 0.1 mol / L. Except for the above, other conditions are exactly the same as those in Example 1.

[0071] Comparative Example 1

[0072] This comparative example provides a method for synthesizing a ternary positive electrode material. In the synthesis method, no surfactant is used in step (1) and step (2). Except for the above, other conditions are the same as those in Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a method for synthesizing a ternary positive electrode material. In the synthesis method, in step (2) and step (3), the second pH value is adjusted from 10 to 10.4 to 10.5 to 11, and the third pH value is adjusted from 10.5 to 11 to 10 to 10.4, that is, the third pH value is kept lower than the second pH value. Except for the above, other conditions are the same as those in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a method for synthesizing a ternary positive electrode material. In the synthesis method, in step (2) and step (3), the first pH value is adjusted from 9.5 to 10 to 10 to 10.5, and the third pH value is adjusted from 10.5 to 11 to 10 to 10.5, that is, the first pH value, the second pH value, and the third pH value are kept the same. Except for the above, other conditions are the same as those in Example 1.

[0077] Comparative Example 4

[0078] This comparative example provides a method for synthesizing a ternary positive electrode material. During the overflow reaction in step (2) of the synthesis method, the flow rate of the mixed salt solution is maintained unchanged. Except for the above, other conditions are the same as those in Example 1.

[0079] Comparative Example 5

[0080] This comparative example provides a method for synthesizing a ternary positive electrode material. During the concentrated reaction in step (2) of the synthesis method, the flow rate of the mixed salt solution is maintained unchanged. Except for the above, other conditions are the same as those in Example 1.

[0081] Comparative Example 6

[0082] This comparative example provides a method for synthesizing a ternary positive electrode material. In step (4) of the synthesis method, no secondary sintering and boron coating is performed. Except for the above, other conditions are the same as those in Example 1.

[0083] Characterization and Testing:

[0084] Ⅰ. Use SEM to test the morphology of the material. Figure 1 is a SEM image of the ternary precursor obtained in Example 1, Figure 2 This is a cross-sectional SEM image of the ternary precursor obtained in Example 1. It can be seen from the figure that the ternary positive electrode material precursor obtained by the preparation method of the present invention has the characteristics of being loose and porous inside and compact and dense outside, and the particles are complete, the particle size distribution is uniform, the dispersion is good, and the sphericity is high, which is conducive to the subsequent ternary positive electrode material inheriting these structural characteristics, thereby achieving improved electrochemical performance.

[0085] Ⅱ. The obtained positive electrode material, conductive carbon black SP (TIMCAL) and polyvinylidene fluoride PVDF (HSV900) were mixed in a mass ratio of 90:5:5, and N-methylpyrrolidone was used as the solvent. The mixture was stirred into a slurry, and the obtained slurry was evenly coated on an aluminum foil with a scraper with a coating gap of 100 μm; after coating, it was first blown dry, then rolled and cut into circular electrode sheets, and then vacuum dried at 120°C and weighed to obtain a button half-cell positive electrode sheet; a metal lithium sheet was used as the negative electrode, a PP microporous membrane was used as the separator, and a lithium battery basic electrolyte was used as the electrolyte. The positive electrode sheet, the metal lithium sheet, the separator and the electrolyte were assembled to obtain a button cell; the electrochemical properties of the positive electrode material were tested at a voltage range of 2.8 to 4.3 V and a rate of 0.1C, and the results are shown in Table 1.

[0086] Table 1

[0087] Precursor Initial discharge capacity (mAh / g) magnification Cycle times Cycle retention rate (%) Example 1 199.3 0.1C 100 94.8 Example 2 198.1 0.1C 100 93.9 Example 3 188.4 0.1C 100 91.2 Example 4 190.4 0.1C 100 90.6 Example 5 191.5 0.1C 100 90.0 Example 6 186.8 0.1C 100 89.3 Comparative Example 1 172.7 0.1C 100 84.7 Comparative Example 2 176.5 0.1C 100 85.2 Comparative Example 3 178.8 0.1C 100 83.3 Comparative Example 4 179.2 0.1C 100 84.2 Comparative Example 5 180.1 0.1C 100 86.1 Comparative Example 6 170.3 0.1C 100 82.1

[0088] It can be seen from Table 1 that:

[0089] By comparing Example 1 with Examples 3-6, it can be seen that the concentration of the surfactant in the preparation method of the precursor of the present invention affects the performance of the lithium-ion battery. In the present invention, adding a surfactant in step (2) is conducive to forming a loose and porous precursor structure, thereby shortening the transmission path of lithium ions in the positive electrode material prepared from the precursor and reducing the internal resistance; when the concentration of the surfactant is low, the material cannot form a loose and porous structure well, which is not conducive to the transmission of lithium ions; when the concentration of the surfactant is high, it will affect the orderly arrangement of the primary particles, thereby reducing the electrochemical performance of the material.

[0090] By comparing Example 1 with Comparative Example 1, it can be seen that the participation of surfactants affects the electrochemical performance. The role of surfactants is to reduce the adhesion of primary particles, increase the gap between primary particles, and is more conducive to forming a loose and porous structure. Without the participation of surfactants, the porosity inside the precursor will be greatly reduced, thereby increasing the internal resistance of the material and reducing the battery performance.

[0091] By comparing Example 1 with Comparative Examples 2-3, it can be seen that the pH value of the reaction system affects the battery performance. This is because the pH affects the primary particle morphology of the precursor. When the pH value (third pH value) increases, the primary particles tend to become coarser, and the precursor is more likely to form a dense structure, which is beneficial to improving the structural stability of the precursor, thereby improving the cycle performance of the battery.

[0092] By comparing Example 1 with Comparative Examples 4-5, it can be seen that the feed flow rate of the reaction system will affect the battery performance. This is because the feed flow rate will affect the growth rate of the precursor. When the feed flow rate is increased, the growth rate of the precursor is accelerated, and the primary particles tend to grow radially, which is conducive to increasing the internal porosity; when the feed flow rate is reduced, the effect is the opposite. Therefore, it is necessary to appropriately adjust the feed flow rate to form a precursor with a loose internal and dense external structure.

[0093] By comparing Example 1 with Comparative Example 6, it can be seen that the boron coating layer can effectively prevent the electrolyte from corroding the positive electrode material, thereby improving the cycle performance of the battery containing the positive electrode material.

[0094] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0095] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0096] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a ternary cathode material precursor, characterized in that: The preparation method comprises: (1) providing a mixed salt solution, a precipitant, a complexing agent and a surfactant; preparing an initial base solution with an initial pH value, wherein the initial base solution includes the precipitant and the complexing agent; (2) adding the mixed salt solution, precipitant, complexing agent and surfactant to the initial base solution in parallel, maintaining the solution at a first pH value, and performing a formation reaction to obtain seed crystals having a first particle size; (3) preparing a growth base solution, wherein the growth base solution contains the seed crystal; adding the mixed salt solution, the precipitant and the complexing agent to the growth base solution in parallel to perform an overflow reaction; during the overflow reaction, maintaining the second pH value and continuously increasing the flow rate of the mixed salt solution; when the particle size of the seed crystal increases to the second particle size, starting to continuously reduce the flow rate of the mixed salt solution, maintaining the third pH value, and performing a concentration reaction until the particle size of the seed crystal increases to the third particle size, thereby obtaining a ternary positive electrode material precursor; In steps (1) to (3), the initial pH value>the third pH value>the second pH value≥the first pH value.

2. The method for preparing a ternary cathode material precursor according to claim 1, characterized in that: In step (1), the mixed salt solution includes at least two of nickel salt, cobalt salt and manganese salt, preferably sulfate; Preferably, the total concentration of metal ions in the mixed salt solution is 1 to 2.5 mol / L; Preferably, the precipitant comprises sodium hydroxide solution; Preferably, the mass concentration of the precipitant is 30% to 35%; Preferably, the complexing agent comprises aqueous ammonia; Preferably, the mass concentration of the complexing agent is 10% to 20%; Preferably, the surfactant comprises sodium lauryl sulfate; Preferably, the concentration of the surfactant is 0.1-0.4 mol / L.

3. The method for preparing a ternary cathode material precursor according to claim 1 or 2, characterized in that: The initial pH is 11.2 to 12; the first pH is 9.5 to 10.5; the second pH is 10 to 10.5; the third pH is 10.5 to 11; Preferably, the ammonia concentration in the initial base solution is 3-8 g / L; the ammonia concentration in the reaction system of the generation reaction is 3-4 g / L; the ammonia concentration in the growth base solution is 4-6 g / L; the ammonia concentration in the reaction system of the overflow reaction is 4-5 g / L; the ammonia concentration in the reaction system of the concentration reaction is 5-6 g / L; Preferably, the stirring speed in the generation reaction is 300-400 rpm; the initial stirring speed of the overflow reaction is the same as the stirring speed in the generation reaction, and the stirring speed is continuously reduced during the overflow reaction, and further continuously reduced during the concentration reaction; Preferably, the reaction temperature of the forming reaction is 40-80°C; the reaction temperature of the overflow reaction is 50-70°C; and the reaction temperature of the dense reaction is 50-70°C.

4. The method for preparing a ternary cathode material precursor according to any one of claims 1 to 3, characterized in that: In the generation reaction, the flow rate of the mixed salt solution is 10 to 80 L / h, the flow rate of the precipitant is 2 to 20 L / h, the flow rate of the complexing agent is 2 to 10 L / h, and the flow rate of the surfactant is such that the concentration of the surfactant in the reaction system of the generation reaction is 0.02 to 0.1 mol / L; Preferably, in the overflow reaction, the initial flow rate of the mixed salt solution is the same as the flow rate of the mixed salt solution in the generation reaction, and in the overflow reaction, the flow rate is adjusted by increasing by 10 to 15 L / h for every 1 μm increase in the particle size of the seed crystal, and the feed flow rates of the precipitant and the complexing agent are adaptively adjusted so that the second pH value remains stable; Preferably, in the concentrated reaction, the flow rate of the mixed salt solution is adjusted by reducing the flow rate by 5 to 10 L / h for every 2 μm increase in the particle size of the seed crystal, keeping the final flow rate greater than the initial flow rate of the mixed salt solution obtained in the overflow reaction, and adaptively adjusting the feed flow rates of the precipitant and the complexing agent so that the second pH value remains stable.

5. The method for preparing a ternary cathode material precursor according to any one of claims 1 to 4, characterized in that: The solid content of the seed crystal in the growth base solution is 20 to 80 g / L; Preferably, the overflow reaction is achieved by setting and opening an overflow valve in the reaction system; Preferably, the thickening reaction is achieved by setting and closing an overflow valve in the reaction system and setting and starting a thickener; Preferably, the D50 particle size value of the primary particles of the first particle size is 2 to 5 μm; the D50 particle size value of the primary particles of the second particle size is 5 to 9 μm; and the D50 particle size value of the primary particles of the third particle size is 8 to 14 μm.

6. A ternary cathode material precursor, characterized in that: Obtained according to the preparation method according to any one of claims 1 to 5.

7. A method for synthesizing a ternary cathode material, characterized in that: The synthesis method comprises: mixing the ternary positive electrode material precursor according to claim 6 with a lithium source, and performing a sintering process to obtain the ternary positive electrode material.

8. The method for synthesizing the ternary cathode material according to claim 7, characterized in that: The lithium source includes lithium hydroxide; Preferably, the primary sintering temperature is 500-800°C and the time is 6-10h; Preferably, the synthesis method further comprises mixing the obtained ternary cathode material with a boron source and performing secondary sintering to obtain a boron-coated ternary cathode material; Preferably, the boron source comprises boric acid; Preferably, the secondary sintering is carried out at a temperature of 200 to 500° C. and for a time of 2 to 6 hours.

9. A ternary positive electrode material, characterized in that: Obtained using the synthesis method described in claim 7 or 8.

10. A lithium ion battery, characterized in that: Contains the ternary positive electrode material according to claim 9.

Images