阅读说明：本技术 一种废旧三元正极材料单晶化再生方法 (Single crystallization regeneration method for waste ternary positive electrode material ) 是由 孟奇 刘磊 张英杰 董鹏 林艳 曾晓苑 费子桐 李晨晨 赵妍 于 2021-06-15 设计创作，主要内容包括：本发明提供了一种废旧三元正极材料单晶化再生方法,可以包括以下步骤：将废旧三元正极材料的二次颗粒沿晶界裂开为一次颗粒；对裂开为一次颗粒的三元正极材料进行熔盐煅烧,使一次颗粒形核生长为单晶颗粒；去除熔盐,对生长为单晶颗粒的三元正极材料进行退火处理,得到单晶三元正极材料。本发明以废旧的三元正极材料为原料,成功的制备了单晶三元正极材料,制备方法简单、成本低、操作条件易控制,产物纯度高,为废旧锂电池三元正极材料回收再生提供了新的思路。(The invention provides a single crystallization regeneration method of a waste ternary cathode material, which comprises the following steps: cracking secondary particles of the waste ternary cathode material into primary particles along a grain boundary; carrying out fused salt calcination on the ternary cathode material cracked into primary particles to ensure that the primary particles nucleate and grow into single crystal particles; and removing the molten salt, and annealing the ternary cathode material growing into single crystal particles to obtain the single crystal ternary cathode material. The method successfully prepares the single crystal ternary cathode material by taking the waste ternary cathode material as the raw material, has the advantages of simple preparation method, low cost, easily controlled operation conditions and high product purity, and provides a new thought for recycling the waste lithium battery ternary cathode material.)

1. A single crystallization regeneration method of a waste ternary positive electrode material is characterized by comprising the following steps:

cracking secondary particles of the waste ternary cathode material into primary particles along a grain boundary;

carrying out fused salt calcination on the ternary cathode material cracked into primary particles to ensure that the primary particles nucleate and grow into single crystal particles;

and removing the molten salt, and annealing the ternary cathode material growing into single crystal particles to obtain the single crystal ternary cathode material.

2. The waste ternary cathode material single-crystallization regeneration method according to claim 1, wherein the temperature of molten salt calcination is 500-850 ℃, and the molten salt calcination time is 6-24 hours.

3. The waste ternary positive electrode material single-crystallization regeneration method according to claim 1 or 2, wherein the annealing treatment comprises annealing treatment for 5-7 hours at a temperature rise speed of 2-5 ℃/min and at a temperature rise speed of 600-800 ℃.

4. The method for single-crystallization regeneration of the waste ternary cathode material as claimed in claim 1 or 2, wherein the step of cracking the secondary particles of the waste ternary cathode material into primary particles along grain boundaries comprises the following steps:

mixing the waste ternary positive electrode material with absolute ethyl alcohol, and then carrying out wet grinding to obtain a primary particle ternary positive electrode material, wherein the liquid-solid ratio in the wet grinding process is 5-30 ml/g, the ball-material ratio is (5-50): 1, the rotating speed is 100-500 r/min, and the wet grinding time is 5-60 min; or the like, or, alternatively,

mixing the waste ternary positive electrode material with an aqueous solution or a first lithium salt solution, carrying out a hydrothermal reaction for 10-30 h at 180-280 ℃, and obtaining a primary particle ternary positive electrode material after the reaction is finished, wherein the liquid-solid ratio of the waste ternary positive electrode material to the solution is 10-25 ml/g; or the like, or, alternatively,

the waste ternary positive electrode material is used as a negative electrode, the second lithium salt solution is used as an electrolyte, and the current density is 5mA^-2~50mA.cm^-2And electrolyzing under the condition to obtain the primary particle ternary cathode material after the electrolysis is finished, wherein the concentration of lithium ions in the electrolyte is 1-3 mol/L.

5. The single crystallization regeneration method of the waste ternary cathode material as claimed in claim 4, wherein the molten salt calcination of the ternary cathode material cracked into primary particles comprises:

mixing the primary particle ternary cathode material obtained after wet grinding, the primary particle ternary cathode material obtained after hydrothermal reaction or the primary particle ternary cathode material obtained after electrolysis with molten salt and a lithium supplement agent, grinding, and then calcining the molten salt, wherein the molar ratio of the waste ternary cathode material to the lithium supplement agent is (50-2): 1.

6. The single crystallization regeneration method of the waste ternary cathode material as claimed in claim 4, wherein the first lithium salt comprises one or more of lithium hydroxide, lithium hydroxide hydrate, lithium sulfate hydrate, lithium chloride hydrate, lithium nitrate, lithium acetate and lithium acetate hydrate; the second lithium salt includes one or more of lithium sulfate, lithium chloride, and lithium nitrate in combination.

7. The method for single-crystallization regeneration of the waste ternary cathode material as claimed in claim 1 or 2, wherein the step of cracking the secondary particles of the waste ternary cathode material into primary particles along grain boundaries comprises the following steps:

mixing the waste ternary cathode material with molten salt and a lithium supplement agent, grinding, calcining at 850-1050 ℃, and calcining at high temperature to obtain the primary particle ternary cathode material.

8. The single crystallization regeneration method of the waste ternary cathode material as claimed in claim 7, wherein the molten salt calcination of the ternary cathode material cracked into primary particles comprises: and after high-temperature calcination, carrying out cooling treatment so as to enable the temperature to reach 500-850 ℃, and then carrying out molten salt calcination.

9. The single crystallization regeneration method of the waste ternary cathode material as claimed in claim 5 or 8, wherein the molten salt comprises one or more of lithium sulfate, lithium sulfate hydrate, lithium chloride hydrate, sodium sulfate hydrate, sodium chloride and potassium chloride; the lithium supplement agent comprises one or more of lithium hydroxide, lithium hydroxide hydrate, lithium carbonate, lithium acetate and lithium acetate hydrate.

10. The single crystallization regeneration method of the waste ternary cathode material as claimed in claim 1, 2, 5, 6 or 8, wherein the waste ternary cathode material is polycrystallineA ternary cathode material with the chemical formula of LiNi_xCo_yMn_zO₂Or LiNi_xCo_yAl_zO₂Wherein x + y + z =1, 1>x≥0.5。

Technical Field

The invention relates to the field of recovery and preparation of ternary cathode materials of batteries, in particular to a single crystallization regeneration method of a waste ternary cathode material.

Background

At present, the method for regenerating and recycling the anode of the waste lithium ion battery mainly comprises the following steps: coprecipitation, sol-gel and solid phase methods. The coprecipitation method mainly uses hydroxide or carbonate as precipitant and ammonia water (NH)₃•H₂O) is a chelating agent, the maximum metal ion content in the leachate is detected, a proper amount of precipitator and chelating agent is added, the proper precipitation condition is adjusted to prepare a precursor of the ternary cathode material, and then lithium mixing and calcination are carried out to finally realize the regeneration of the ternary cathode material. The coprecipitation method for preparing the ternary cathode material has the advantages of simple required equipment, industrialization, good precursor purity and the like, but has the defects of easy impurity of a regeneration material, difficult control of precipitation conditions and the like.

The sol-gel method is to use a compound containing high chemical activity components as a precursor, to form a stable transparent sol system in a solution by adding a chelating agent and controlling proper sol conditions, to prepare a dry gel by evaporation, and to prepare the ternary cathode material by high-temperature calcination. The ternary cathode material synthesized by the sol-gel method has the advantages of uniform molecular mixing, less impurities, small structural granularity and the like, but has the defects of long time, higher cost, difficult process, difficult operation and the like.

The solid phase method is mainly realized by coating or doping. Coating is a widely used method to improve the stability of the positive electrode, and it can work in conjunction with other positive electrode modification strategies. The surface coating of the anode material can reduce stress, increase the wettability of the liquid electrolyte, reduce the interface charge transfer resistance and reduce side reactions, thereby effectively optimizing the anode material. Doping is generally common to doping cations, anions, and co-doping, among others. Different effects can be achieved by replacing lithium, transition metals and oxygen. The doping can effectively improve the structural stability of the anode material, reduce the capacity loss of the electrode material in the charging and discharging process, stabilize the valence of nickel ions, reduce the mixed arrangement of lithium and nickel, and inhibit the phase change in the charging and discharging process to a certain extent, thereby improving the structural stability, the electrochemical performance and the like. Although the coating and doping have the advantages, the coating and doping are difficult to repair the damaged positive electrode material structure, and the coating and doping usually use rare earth metal oxides and are high in cost.

In addition, the performance of the current ternary cathode material is continuously improved mainly by the microstructure and the morphology. The conventional polycrystalline ternary positive electrode material is generally composed of secondary spherical polycrystalline particles formed by aggregating a plurality of primary nano-scale particles. Grain cracking in polycrystalline ternary positive electrode materials is one of the more common failure mechanisms, and the cracking can result in active material isolation and increased surface area, thereby increasing surface reaction with electrolyte to cause capacity loss. Meanwhile, a large number of primary nano-scale particles generate severe microstrain at the boundary when expanding and contracting, and the long cycle performance of the ternary cathode material is reduced. Compared with the polycrystalline ternary cathode material with the defects, the monocrystalline ternary cathode material has the following advantages:

1) the compaction density is high, and the high compaction density is beneficial to reducing the internal resistance of the electrode and increasing the volume energy density of the battery;

2) the specific surface area of the single crystal particles is small, so that the surface reaction with the electrolyte is effectively reduced;

3) the integral structure of the primary single crystal particles is relatively stable, and the service life of the battery is long;

4) the surfaces of the single crystal particles are smooth, so that the single crystal particles are beneficial to fully contacting and coating the conductive carbon material;

5) the single crystal structure is more beneficial to the transmission of lithium ions in the material.

For the above reasons, more and more people begin to research the preparation of single crystal ternary cathode materials, but the process is more complex and the cost is higher than that of the traditional polycrystalline ternary cathode materials.

Aiming at the defects of the existing technology for regenerating and recycling the cathode material of the waste ternary lithium battery, in particular to the defects of the process preparation process for regenerating the single crystal ternary cathode material by using the cathode material of the waste ternary lithium battery, a new regeneration and recycling method is urgently needed to prepare the single crystal ternary cathode material.

Disclosure of Invention

In view of the deficiencies in the prior art, it is an object of the present invention to address one or more of the problems in the prior art as set forth above. For example, one of the purposes of the invention is to provide a simple and low-cost method for single-crystallization regeneration of waste ternary cathode materials.

The invention provides a single crystallization regeneration method of a waste ternary cathode material, which comprises the following steps: cracking secondary particles of the waste ternary cathode material into primary particles along a grain boundary; mixing the ternary positive electrode material cracked into primary particles with molten salt to perform molten salt calcination, and nucleating and growing the primary particles into single crystal particles; and removing the molten salt, and annealing the ternary cathode material growing into single crystal particles to obtain the single crystal ternary cathode material.

Compared with the prior art, the beneficial effects of the invention at least comprise at least one of the following:

(1) the method successfully prepares the single crystal ternary cathode material by taking the waste ternary cathode material as the raw material, has the advantages of simple preparation method, low cost, easily controlled operation conditions and high product purity, and provides a new thought for recycling the waste lithium battery ternary cathode material.

(2) The method can repair the anode material with the damaged structure, realizes the repair and regeneration of the structure by converting the structure type of the anode material, and the prepared single crystal ternary anode material has high capacity retention rate and more stable capacity.

(3) The method can realize fused salt calcination at a lower temperature to ensure that the secondary particle nucleation grows into the single crystal particle without damaging the self structure of the primary particle, and the prepared single crystal ternary cathode material has a highly ordered layered structure, good activity and excellent electrochemical performance.

Drawings

The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

fig. 1 is a graph showing a discharge specific capacity of a raw material of a waste ternary positive electrode material used in each of examples 1 to 4 as a function of cycle number;

FIG. 2 is a graph showing discharge specific capacity of single crystal ternary positive electrode material products prepared in examples 1 to 4 respectively as a function of cycle number;

FIG. 3 shows XRD patterns of single-crystal ternary cathode material products respectively prepared in examples 1-4;

FIG. 4 shows SEM images of raw materials of waste ternary cathode materials used in examples 1 and 2;

fig. 5 shows an SEM image of the positive electrode material after ball milling of example 1;

FIG. 6 shows an SEM image of a single crystal ternary cathode material product prepared in example 1;

fig. 7 shows an SEM image of the cathode material after hydrothermal reaction of example 2;

FIG. 8 shows an SEM image of a single crystal ternary cathode material product prepared in example 2;

fig. 9 shows an SEM image of a used ternary cathode material feedstock used in example 3;

fig. 10 shows an SEM image of the cathode material after the electrolysis reaction of example 3;

fig. 11 shows an SEM image of a single crystal ternary cathode material product prepared in example 3;

fig. 12 shows an SEM image of a used ternary cathode material feedstock used in example 4;

fig. 13 shows an SEM image of the single crystal ternary cathode material product prepared in example 4.

Detailed Description

Hereinafter, a single-crystallization regeneration method of a waste ternary cathode material according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

In particular, the process of the inventionFirstly, splitting secondary particles of the waste ternary cathode material into primary particles along a grain boundary. By cracking the secondary particles in the anode material into primary particles, the method can realize that the primary particles are nucleated and grown into single crystal particles in a molten salt environment by calcining molten salt at a lower temperature of 500-850 ℃ in a shorter time. At the low-temperature calcination temperature, the layered structure of the ternary cathode material can be maintained, the problems that the internal structure of the ternary cathode material is damaged due to calcination at a high temperature and the cathode material is aged and inactivated and has serious lithium-nickel mixed discharge are avoided, and the activity of the ternary cathode material can be maintained to the maximum extent. Then through annealing, the crystal grains of the anode material are refined, the tissue defect is improved, and the anode material has better alpha-NaFeO through further oxidation₂Layered rock salt structure and better crystallinity.

The invention provides a single crystallization regeneration method of a waste ternary cathode material. In an exemplary embodiment of the method for single-crystallization regeneration of waste ternary cathode materials, the method may include the following steps:

and step S01, splitting the secondary particles of the waste ternary cathode material into primary particles along the grain boundary.

Step S02, carrying out fused salt calcination on the ternary cathode material cracked into primary particles to ensure that the primary particles nucleate and grow into single crystal particles;

and step S03, removing the molten salt, and annealing the ternary cathode material growing into single crystal particles to obtain the single crystal ternary cathode material.

Further, in step S01, the conventional polycrystalline ternary positive electrode material is a secondary spheroidal large particle composed of primary particles. Meanwhile, due to different processes, the sizes of the ternary cathode material particles are different, and the size of the secondary particles can be between 4 and 20 micrometers generally; the primary particle size may typically be between 0.2 μm and 3 μm. And splitting along grain boundaries, which herein means the contact interface between primary particles.

Further, splitting the secondary particles of the waste ternary cathode material into primary particles along the grain boundary can use a ball milling method, and specifically, the method can comprise the following steps:

wet grinding is carried out on the waste ternary cathode material in absolute ethyl alcohol so as to crack the secondary particles into primary particles, and the primary particle ternary cathode material is obtained. The parameters of wet milling may include, among others: the liquid-solid ratio can be 5 ml/g-30 ml/g, the ball-material ratio can be (5-50): 1, the rotating speed can be 100 r/min-500r/min, and the wet grinding time is 5 min-60 min. During ball milling, the ball milling parameters should be set to ensure that the structure of the primary particles is not destroyed on the premise that as many secondary particles as possible are broken into primary particles. Through setting up liquid-solid ratio, ball material ratio, rotational speed and wet-milling time in above-mentioned within range, mutually support between each setting parameter, can maximize with secondary particle fracture and can not destroy the structure of splitting back primary particle, can ensure that the ternary cathode material who obtains has better activity. At a higher rotation speed, the wet grinding time can be correspondingly reduced; at lower rotational speeds, wet milling times can be correspondingly extended. For the ball milling process, for example, the liquid-solid ratio may be 15ml/g, the ball-to-material ratio may be 30:1, the rotation speed may be 350r/min, and the wet milling time may be 15 min. Preferably, the liquid-solid ratio can be 10ml/g, the ball-to-material ratio can be 20:1, the rotation speed can be 200r/min, the wet milling time can be 20min, and under the preferred parameters, the primary particles are cracked much. The cracked primary particles are more, the temperature and the time for calcining the molten salt can be correspondingly reduced, the internal structure of the primary particles can be well preserved, and the damage to the internal structure can be reduced to the maximum extent. In addition, because the ternary cathode material has water absorption, the internal structure of the ternary cathode material cannot be damaged by wet grinding of anhydrous ethanol and the waste ternary cathode material.

Further, cracking the secondary particles of the waste ternary cathode material into primary particles along the grain boundary can use a hydrothermal method, and specifically the method can comprise the following steps:

mixing the aqueous solution or the first lithium salt solution with the waste ternary cathode material, carrying out hydrothermal reaction for 10-30 h at 180-280 ℃, and obtaining the primary particle ternary cathode material after the reaction is finished. Similarly, parameters set in the hydrothermal process ensure that the structure of the primary particles cannot be damaged on the premise of cracking more secondary particles into the primary particles as much as possible, so the reaction is carried out for 10 to 30 hours at the hydrothermal temperature of 180 to 280 ℃.

In the above, the first lithium salt solution may be a solution formed by lithium salts, and the lithium salts may be one or a combination of more of lithium hydroxide, lithium hydroxide hydrate, lithium sulfate hydrate, lithium chloride hydrate, lithium nitrate, lithium acetate and lithium acetate hydrate.

Preferably, the solubility of lithium ions in the first lithium salt solution is not more than 10 mol/L. The excessive concentration of the lithium ions can cause the boiling point of a reaction system to be increased, and incomplete reaction can be caused within the set temperature of 180-280 ℃. Therefore, the concentration of the lithium ion solution is not more than 10 mol/L at the reaction temperature of 180-280 ℃. For example, the concentration of lithium ions may be 4 mol/L or 7 mol/L.

Preferably, the hydrothermal reaction may be carried out in a hydrothermal reactor. In order to enable the hydrothermal kettle to have better pressure so as to enable the secondary particles to be cracked into primary particles better and faster, the material filling ratio of the inner container of the hydrothermal kettle can be 1/4-5/6. Preferably, the filling ratio may be 3/4 to 5/6 in order to ensure sufficient pressure in the reaction kettle to further reduce the time required for the secondary particles to break into primary particles.

Preferably, the liquid-solid ratio of the aqueous solution or the first lithium salt solution to the waste ternary cathode material can be 10 ml/g-25 ml/g. For example, the liquid-solid ratio may be 15 ml/g.

Above, more preferably, the hydrothermal reaction process may include: mixing a lithium hydroxide solution with the concentration of 5mol/L with a waste ternary cathode material, selecting the liquid-solid ratio of the added solution to the waste ternary cathode material to be 15ml/L, controlling the hydrothermal reaction temperature to be 260 ℃, controlling the reaction time to be 20h, and selecting 3/4 the ratio of the volume of the inner container of the reaction kettle to the volume of the added material. Through the preferable hydrothermal reaction conditions, the pressure in the reaction kettle can be matched with the reaction temperature, the liquid-solid ratio and the reaction time, and secondary particles can be better cracked into primary particles.

Further, the method for cracking the secondary particles of the waste ternary cathode material into the primary particles along the grain boundary can use an electrolytic method, and specifically comprises the following steps:

to wasteThe used ternary cathode material is used as a cathode, the second lithium salt solution is used as an electrolyte, and the current density can be 5mA^-2~50mA.cm^-2And electrolyzing to obtain the primary particle ternary cathode material after the electrolysis is finished, wherein the concentration of lithium ions in the electrolyte can be 1-3 mol/L. The concentration of lithium ions affects the conductivity of the electrolyte, thereby changing the current density and ultimately affecting the degree of primary particle detachment. Therefore, the concentration of lithium ions in the electrolyte is set to 1mol/L to 3 mol/L. For example, the current density may be 20 mA.cm^-2The lithium ion concentration in the electrolyte may be 2 mol/L.

The second lithium salt solution may be lithium sulfate (Li)₂SO₄) Solution, lithium chloride (LiCl) solution, lithium nitrate (LiNO)₃) One or more combinations in solution.

Preferably, in order to make the secondary particles break apart into primary particles better, stirring may be applied to the negative electrode. The stirring speed can be controlled within 200r/min-500 r/min. For example, the stirring speed may be 300 r/min. The electrolytic cell can be a three-opening H-shaped electrolytic cell, and at the moment, the mixture of the waste ternary anode material and the electrolyte is used as a negative electrode, and the negative electrode is stirred at the rotating speed of 200r/min-500 r/min. And placing a second lithium salt solution at the positive electrode port and the reference electrode port. The three-opening H-shaped electrolytic cell is used, and the sponge is placed between the anode and the cathode, so that the ternary anode material can be prevented from diffusing to the anode end in the stirring process, and the electrolysis is facilitated.

Preferably, the liquid-solid ratio of the electrolyte to the waste ternary cathode material can be set to be 20-100 ml/g. For example, the liquid-solid ratio may be 50 ml/g.

More preferably, the rotation speed of the negative electrode may be 400r/min, and lithium ions (Li) in the electrolyte⁺) The concentration can be 1.6mol/L, the liquid-solid ratio of the electrolyte to the added waste anode material can be 50ml/g, and the current density is 10mA.cm^-2The electrolytic reaction time can be 40 min. By the above-described more preferable electrolysis parameters, the secondary particles can be split into the primary particles as much as possible, and the temperature and time for the molten salt calcination can be further reduced.

Further, splitting secondary particles of the waste ternary cathode material into primary particles along a grain boundary can use a high-temperature molten salt method, and specifically, the method can comprise the following steps:

mixing the waste ternary cathode material with molten salt and a lithium supplement agent, grinding, calcining at 850-1050 ℃, and calcining at high temperature to obtain the primary particle ternary cathode material.

The molten salt can be selected to be in a molten state at 850-1050 ℃ and not to chemically react with the cathode material and the lithium supplement agent. For example, an alkali metal halide salt, an alkali metal sulfate salt, or the like may be mentioned. Preferably, the molten salt may be one or a combination of more of lithium sulfate, lithium sulfate hydrate, lithium chloride hydrate, sodium sulfate hydrate, sodium chloride, and potassium chloride.

The lithium supplement agent can comprise one or more of lithium hydroxide, lithium hydroxide hydrate, lithium carbonate, lithium acetate and lithium acetate hydrate.

Preferably, in order to make the reaction more sufficient and to further facilitate the cracking of the secondary particles into the primary particles, the molar ratio of the waste ternary cathode material to the molten salt may be set between 1:6 and 10: 1. For example, the molar ratio of the waste ternary cathode material to the molten salt is 4: 1. The growth process of the single crystal is influenced by the amount of the molten salt, and the single crystal can grow within the range of the molar ratio.

Preferably, in order to ensure that a sufficient amount of lithium is replenished into the waste ternary cathode material and no waste of the lithium replenishing agent is caused, the molar ratio of the waste ternary cathode material to the lithium replenishing agent can be set to (50-2): 1. For example, the molar ratio may be 5: 1.

Preferably, the temperature rise process of the high-temperature calcination can include rising the temperature from room temperature to 850-1050 ℃ at a speed of 2-10 ℃/min, and the time of the high-temperature calcination is 1-5 h. For example, the temperature may be raised at a temperature raising rate of 7 ℃/min.

More preferably, the molar ratio of the waste ternary cathode material to the molten salt is set to be 4:1, the molar ratio of the waste ternary cathode material to the lithium supplement agent is set to be 5:1, and the temperature rise speed is set to be 5 ℃/min.

Further, after the secondary particles of the waste ternary cathode material are cracked into primary particles along the grain boundary by the ball milling method, the hydrothermal method and the electrolytic method, fused salt calcination can be carried out by the following method to nucleate and grow the primary particles into single crystal particles:

mixing a primary particle ternary cathode material obtained after wet grinding (ball milling), a primary particle ternary cathode material obtained after hydrothermal reaction or a primary particle ternary cathode material obtained after electrolysis with molten salt and a lithium supplement agent, and calcining the mixture at 500-850 ℃ for 3-24 h to nucleate primary particles in the cathode material to grow the particles into single crystal particles. For example, calcination may be carried out at 650 ℃ for 5 h.

Specifically, the ternary positive electrode material cracked into primary particles can be washed by deionized water, then placed into an oven for drying, then added with molten salt and a lithium supplement agent for grinding for 15-30 min, and calcined for 3-24 h at 500-850 ℃. The molten salt may include one or more combinations of lithium sulfate, lithium sulfate hydrate, lithium chloride hydrate, sodium sulfate hydrate, sodium chloride, and potassium chloride. The lithium supplement agent can comprise one or more of lithium hydroxide, lithium hydroxide hydrate, lithium carbonate, lithium acetate and lithium acetate hydrate.

Wherein the molar ratio of the waste ternary cathode material to the molten salt can be 10:1 to 1: 6. For example, the molar ratio of the waste ternary cathode material to the molten salt may be 4: 1. Of course, the molar ratio of the waste ternary cathode material to the molten salt is not limited to this, and the molten salt may be added in an amount larger than that. On one hand, the adding amount of the lithium supplement agent is related to the lithium shortage of the waste ternary cathode material, the waste ternary cathode material has more lithium shortage, and the added lithium supplement agent is more; on the other hand, the lithium supplement agent and the molten salt can form co-melting, so that the melting temperature of the molten salt can be reduced after the lithium supplement agent is added, and a certain amount of the lithium supplement agent can be added for reducing the melting temperature of the molten salt. Based on the comprehensive consideration of the two reasons, the molar ratio of the waste ternary cathode material to the lithium supplement agent can be set to (50-2): 1. Preferably, the molar ratio of the waste ternary cathode material to the lithium supplement agent can be set to be 5: 1.

The molten salt calcination process may include: the temperature is raised to 500-850 ℃ at the temperature raising speed of 2-10 ℃/min and calcined for 3-24 h. The temperature rise speed of calcination is controlled at 10 ℃/min, the structure of the ternary cathode material cannot be influenced due to the excessively high temperature rise speed, and meanwhile, sufficient lithium supplement time can be reserved to avoid insufficient lithium supplement. The temperature rise speed, the calcination temperature and the calcination time are matched with each other, so that the internal structure of the prepared single crystal ternary cathode material can be ensured not to be damaged, and the single crystal ternary cathode material can keep good activity. For example, the temperature may be raised to 750 ℃ at a rate of 5 ℃/min and the calcination may be carried out for 15 hours. Certainly, the molten salt calcination can also be performed with sectional heating, for example, the temperature can be kept for 4 to 6 hours when the temperature is between 180 and 220 ℃, and then the temperature is raised to the temperature required by the molten salt calcination.

Further, ball milling. The hydrothermal method and the electrolytic method are different, and if the high-temperature molten salt method is used for cracking the secondary particles of the waste ternary cathode material into the primary particles along the grain boundary, the nucleation and growth of the primary particles into the single crystal particles may include:

and after the high-temperature calcination is finished, cooling, and reducing the temperature to 500-850 ℃ for molten salt calcination.

Further, performing the annealing process may include:

and (2) washing the ternary cathode material which grows into single crystal particles after the molten salt is calcined by using deionized water to wash away the molten salt and the unreacted lithium supplement agent, and then carrying out annealing treatment, wherein the annealing treatment can comprise the step of heating to 600-800 ℃ at the heating speed of 2-5 ℃/min for 5-7 h. And grinding after annealing to obtain the regenerated single crystal ternary cathode powder. Preferably, before the annealing treatment, the ternary cathode material after the molten salt calcination can be dried, and the drying process comprises the following steps: heating to 80-150 ℃ at a heating rate of 2-10 ℃/min, and drying for 2-5 h. For example, the mixture is dried for 3.5 hours by heating to 120 ℃ at a heating rate of 4 ℃/min.

Further, the waste ternary cathode material can be a polycrystalline ternary cathode material, and the chemical formula of the waste ternary cathode material can be LiNi_xCo_yMn_zO₂Or LiNi_xCo_yAl_zO₂Wherein x + y + z =1, 1>x is more than or equal to 0.5. Of course, the present inventionThe method can be used for recovering the waste ternary cathode material with any nickel content. For the high-nickel waste ternary cathode material with x being more than or equal to 0.5, the traditional method can damage the internal structure of the material to cause material inactivation, so that the recovery method can effectively treat the high-nickel-content ternary cathode material. For raw materials with different nickel contents, the corresponding preferred parameters in the process of calcining the molten salt are different. When 0.8>When x is more than or equal to 0.5, the preferred calcining temperature is 820 ℃, and the calcining time is 8 h; when 1 is>When x is more than or equal to 0.8, the preferred calcining temperature is 700 ℃ and the calcining time is 20 h. Preferably, when 1>When x is more than or equal to 0.8, the raw materials contain a large amount of nickel, and sufficient oxygen is needed under high-temperature reaction, so oxygen can be introduced in the processes of molten salt calcination and high-temperature calcination, and the anode material is sintered in the atmosphere of oxygen.

In order that the above-described exemplary embodiments of the invention may be better understood, further description thereof with reference to specific examples is provided below.

Example 1

Step 1, weighing 5g of waste NCM622 (LiNi) recovered from the market_0.6Co_0.2Mn_0.2O₂) Adding the ternary anode material powder into a ball milling tank, adding 100g of zirconia balls, adding 50ml of absolute ethyl alcohol, and carrying out wet milling, wherein the rotating speed is set to be 200r/min, and the ball milling time is 20 min.

Step 2, cleaning the ball-milled positive electrode powder with deionized water, drying the ball-milled positive electrode powder in a 120 ℃ drying oven for 4 hours, weighing 2g of ball-milled positive electrode powder and 0.433g of LiOH & H₂O and 0.6217g Li₂SO₄·H₂And O, putting the materials into a mortar, mixing and grinding for 25 min. After grinding, the mixture is put into a crucible and calcined in a box furnace. The temperature rising step is set as follows: the first-stage heating rate is as follows: heating from room temperature to 200 deg.C at 5 deg.C/min, maintaining for 5h, heating at 3 deg.C/min to 820 deg.C, maintaining for 10h, and naturally cooling.

And 3, taking out the material calcined by the molten salt, putting the material into a beaker, and adding 40 ml of deionized water for static soaking for 3 hours. Pouring out the supernatant, adding deionized water, stirring for 5 minutes, then placing into a centrifuge tube, placing into a centrifuge at a speed of 2000r/min, centrifuging for 3 minutes, pouring out the supernatant after the centrifugation is finished, adding deionized water, washing, and repeating the steps for 3 times. Then, drying and annealing the washed anode material, firstly, drying at low temperature, setting the temperature rise speed to be 5 ℃/min, the drying temperature to be 100 ℃, and the drying time to be 4 h; then high-temperature annealing is carried out, the temperature rise speed is set to be 3 ℃/min, the annealing temperature is set to be 700 ℃, and the annealing time is set to be 6 h. Finally, the regenerated single crystal ternary cathode material is obtained and named as 1-SC-622.

Example 2

Step 1, weighing 2g of waste NCM622 (LiNi) recovered from the market_0.6Co_0.2Mn_0.2O₂) Ternary positive electrode powder. 3.5g of lithium hydroxide monohydrate (LiOH) was added to a 50ml hydrothermal kettle^.H₂O), then adding 32ml of deionized water, adding 2g of weighed cathode powder after dissolution, and carrying out hydrothermal reaction. Setting the hydrothermal reaction temperature at 260 ℃ and the reaction time at 16h, wherein the ratio of the volume of the inner container of the reaction kettle to the volume of the added materials is about 3: 4.

And 2, washing excessive lithium hydroxide after the reaction is finished, drying in a 120 ℃ oven for 4 hours, adding 0.62g of lithium sulfate monohydrate and 0.21g of lithium hydroxide monohydrate after drying, mixing, grinding for 20min, putting into a crucible, and calcining in a box-type furnace. The temperature rising step is set as follows: the temperature of the first section is raised from room temperature to 200 ℃ at the speed of 5 ℃/min, the temperature is kept for 2h, then the temperature is raised to 820 ℃ at the speed of 3 ℃/min, and the temperature is kept for 10h and then the product is naturally cooled.

And 3, taking out the material calcined by the molten salt, putting the material into a beaker, and adding 40 ml of deionized water for static soaking for 3 hours. Pouring out the supernatant, adding deionized water, stirring for 5 minutes, then placing into a centrifuge tube, placing into a centrifuge at a speed of 2000r/min, centrifuging for 3 minutes, pouring out the supernatant after the centrifugation is finished, adding deionized water, washing, and repeating the steps for 3 times. Then, drying and annealing the washed anode material, firstly, drying at low temperature, setting the temperature rise speed to be 5 ℃/min, the drying temperature to be 100 ℃, and the drying time to be 4 h; then high-temperature annealing is carried out, the temperature rise speed is set to be 3 ℃/min, the annealing temperature is set to be 700 ℃, and the annealing time is set to be 6 h. Finally, the regenerated single crystal ternary cathode material is obtained and named as 2-SC-622.

Example 3

Step 1, connecting the electrode into a 200ml three-port H-shaped electrolytic cell, and weighing 2g of waste NCM523 (LiNi) recovered from the market_0.5Co_0.2Mn_0.3O₂) Adding the ternary cathode powder into one end of a cathode, and adding 100ml of 1.6mol/L lithium sulfate (Li)₂SO₄) In the solution and electrolytic cell, the rotating speed of a rotor is set to be 400 r/min; using a current density of 10mA^.cm^-2(ii) a The electrolytic reaction time was 40 min.

And 2, washing the lithium sulfate residual liquid on the surface of the anode material after the reaction is finished, drying the lithium sulfate residual liquid in a 120 ℃ drying oven for 4 hours, adding 0.64g of lithium sulfate monohydrate and 0.22g of lithium hydroxide monohydrate after drying, mixing, grinding for 20min, putting the mixture into a crucible, and calcining in a box type furnace. The temperature rising step is set as follows: the temperature of the first stage is raised from room temperature to 200 ℃ at the speed of 5 ℃/min, the temperature is kept for 2h, then the temperature is raised to 840 ℃ at the speed of 3 ℃/min, and the temperature is kept for 8h and then the product is naturally cooled.

And 3, taking out the material calcined by the molten salt, putting the material into a beaker, and adding 40 ml of deionized water for static soaking for 3 hours. Pouring out supernatant, adding deionized water, stirring for 5min, naturally settling for 5min, separating precipitate, pouring out supernatant, adding deionized water, washing, and repeating the above steps for 3 times. And then, drying and annealing the washed anode material, firstly drying at low temperature, and setting the temperature rise speed as follows: 5 ℃/min, the drying temperature is 100 ℃, and the drying time is 4 h; then high-temperature annealing is carried out, the temperature rise speed is set to be 3 ℃/min, and the annealing temperature is as follows: the annealing time is 6h at 700 ℃. Finally, the regenerated single crystal ternary cathode material is obtained and named as SC-523.

Example 4

Step 1, weighing 2g of commercially recovered NA90 (LiNi) with structural defects_0.9Al_0.1O₂) The positive electrode powder was mixed with 0.676g of lithium sulfate monohydrate and 0.22g of lithium hydroxide monohydrate, ground for 20min, placed in a crucible, and calcined in a tube furnace, which required the total process of introducing oxygen. The temperature rising step is set as follows: the temperature of the first section is raised from room temperature to 450 ℃ at the speed of 5 ℃/min, the temperature is kept for 6h, then the temperature is raised to 900 ℃ at the speed of 3 ℃/min, and the temperature is kept for 3 h.

And 2, after the high-temperature molten salt reaction is finished, cooling to 750 ℃ at the speed of 3 ℃/min, preserving heat for 20h, and then naturally cooling.

And 3, taking out the material calcined by the molten salt, putting the material into a beaker, and adding 40 ml of deionized water for static soaking for 3 hours. Pouring out supernatant, adding deionized water, stirring for 5min, naturally settling for 5min, separating precipitate, pouring out supernatant, adding deionized water, washing, and repeating the above steps for 3 times. Then, drying and annealing the washed anode material, firstly, drying at low temperature, setting the temperature rise speed to be 5 ℃/min, the drying temperature to be 100 ℃, and the drying time to be 4 h; then high-temperature annealing is carried out, the temperature rise speed is set to be 3 ℃/min, the annealing temperature is set to be 700 ℃, and the calcination time is set to be 6 h. Finally, the regenerated single crystal ternary cathode material is obtained and named as SC-NA 90.

The ternary positive electrode materials of 1-SC-622, 2-SC-622, SC-523 and SC-NA90 obtained in the above examples 1 to 4, respectively, were mixed with conductive carbon and PVDF (polyvinylidene fluoride) binder in a mass ratio of 8:1:1 in NMP (N-methyl pyrrolidone) and then coated on an aluminum foil to obtain a pole piece, which was dried in a forced air oven at 80 ℃ and then dried in a vacuum oven at 120 ℃ overnight. The dried pole piece is used as a battery anode, lithium metal is used as a battery cathode, a single-layer polyethylene film is used as a diaphragm, 1M LiPF6EC-EMC (namely the concentration of LiPF6 in an EC-EMC solvent is 1M, EC is ethylene carbonate, EMC is methyl ethyl carbonate, and the volume ratio of EC to EMC is 3:7) is used as electrolyte, and a 2025 half battery is assembled for electrochemical test. And (3) testing conditions are as follows: the voltage range is 2.8-4.3V, and the current is circulated for 100 times at 1C multiplying power.

Fig. 1 is a graph showing changes of charge and discharge specific capacities of the waste ternary cathode material used in each of examples 1 to 4 with respect to cycle times at 25 ℃, 2.8V to 4.3V, and a magnification of 1C, where a curve a is a change curve of the discharge specific capacity of the raw material used in examples 1 and 2 with respect to cycle times, a curve B is a change curve of the discharge specific capacity of the raw material used in example 3 with respect to cycle times, and a curve C is a change curve of the discharge specific capacity of the raw material used in example 4 with respect to cycle times. As can be seen from the figure, the first turn capacity of the raw material 1C used in examples 1 and 2 was 143.4 mAh/g. Example 3 used starting material 1C with a head-circle capacity of 116.1 mAh/g. Example 4 starting material 1C used a head-turn capacity of 150.7 mAh/g. The capacity retention rate of the raw materials used in examples 1 and 2 after 100 cycles is only 18.2%; the capacity retention rate of the raw material used in the example 3 is only 69.5%; the capacity retention of the feedstock used in example 4 was only 7.3%. Under the same test parameters, the product performances obtained in examples 1 to 4 are tested, as shown in fig. 2, wherein a curve a is the change of the specific discharge capacity of the product obtained in example 1 with the cycle number, a curve B is the change of the specific discharge capacity of the product obtained in example 2 with the cycle number, a curve C is the change of the specific discharge capacity of the product obtained in example 3 with the cycle number, and a curve D is the change of the specific discharge capacity of the product obtained in example 4 with the cycle number. As can be seen from FIG. 2, the first-turn capacity of the regenerated single-crystal positive electrode material (1-SC-622)1C obtained in example 1 is 167.1 mAh/g; the first-turn capacity of the regenerated single-crystal cathode material (2-SC-622)1C obtained in example 2 is 164.9 mAh/g; the first-turn capacity of the regenerated single-crystal positive electrode material (SC-523)1C obtained in example 3 is 145.0 mAh/g; example 4 the first cycle capacity of the resulting regenerated single crystal positive electrode material (SC-NA90)1C was 186.7 mAh/g. The capacity retention rate of 1-SC-622 after 100 cycles is 87.7%; the capacity retention rate of 2-SC-622 is 90.7%; the capacity retention rate of SC-523 is 90.6%; the capacity retention rate of SC-NA90 was 81.9%. Compared with fig. 1 and fig. 2, the capacity retention rate of the regenerated single crystal ternary cathode material prepared by the method of the invention is remarkably improved, and the capacity retention rate of the regenerated single crystal ternary cathode material is higher.

XRD tests were performed on the products obtained in examples 1 to 4, and the results are shown in FIG. 3. As can be seen from FIG. 3, the ternary cathode materials obtained in examples 1 to 4 have high purity and typical alpha-NaFeO₂The layered rock salt has a structure and good crystallinity.

Fig. 4 shows SEM images of raw materials of waste ternary cathode materials used in examples 1 and 2. Fig. 5 shows an SEM image of the cathode material after ball milling of example 1. Comparing fig. 4 and 5, many primary small particles were separated along the grain boundary after ball milling, indicating that ball milling has a significant effect on breaking secondary large particles into primary small particles.

Fig. 7 shows an SEM image of the cathode material after hydrothermal reaction of example 2. Comparing fig. 4 and fig. 7, after the hydrothermal reaction, a large amount of primary particles have been dispersed along the grain boundaries, and the effect of the hydrothermal reaction to split the secondary particles into the primary particles is significant.

Fig. 9 shows an SEM image of the used raw ternary cathode material used in example 3. Fig. 10 shows an SEM image of the cathode material after the electrolytic reaction of example 3. Comparing fig. 9 and fig. 10, after the waste ternary cathode material is electrolyzed, the secondary particles are crushed, and a plurality of primary particles are separated, which shows that the electrolysis can realize that the secondary particles are cracked into the primary particles along the grain boundary.

Figure 6 shows an SEM image of the product obtained in example 1. Fig. 8 shows an SEM image of the product obtained in example 2. Figure 11 shows an SEM image of the product obtained in example 3. As can be seen from FIGS. 6, 8 and 11, the prepared product has smooth particle surface and particle size of 1-3 μm.

Fig. 12 shows an SEM image of the used raw ternary cathode material used in example 4. Fig. 13 shows an SEM image of the single crystal ternary cathode material product prepared in example 4. As shown in fig. 12, the waste cathode material NA90 has irregular particle shape and many fine particles on the surface. As shown in FIG. 13, the prepared SC-NA90 cathode material has smooth particle surface and nonuniform particle size, and the particle size is about 0.5-2 μm.

Although the present invention has been described above in connection with exemplary embodiments, it will be apparent to those skilled in the art that various modifications and changes may be made to the exemplary embodiments of the present invention without departing from the spirit and scope of the invention as defined in the appended claims.