A cathode material co-modified by fluorine-rare earth elements and a preparation method thereof

Abstract

The present application discloses a preparation method of a cathode material co-modified by fluorine and rare earth elements, comprising the following steps: adding the waste lithium-ion battery cathode material into 2-hydroxypropanoic acid solution and ascorbic acid solution successively for reaction to obtain a leaching solution of metal ions, then adjusting the molar ratio of metal ions and doped rare earth element R ions in the leaching solution, adding an organic fluorine source, adjusting the pH, heating and evaporating to concentrate to form a gel. Finally, the gel is subjected to stepwise calcination to obtain the cathode material co-modified by fluorine and rare earth elements. This preparation method realizes the uniform distribution of doped rare earth elements by adopting the sol-gel method combined with fluorine and rare earth element doping modification, and can effectively improve the electrochemical performance of the recycled cathode material. The present application also provides a cathode material co-modified by fluorine and rare earth elements.

Description

Technical Field

[0001] This application relates to the technical field of cathode materials for lithium-ion batteries, and particularly to a cathode material co-modified by fluorine-rare earth elements and a preparation method thereof. Background Art

[0002] Doping modification is one of the effective methods to improve the cycle stability, structural stability and safety of cathode materials. To a certain extent, it can inhibit the reversible phase change during the charge and discharge process of cathode materials, improve the structural stability inside the crystal lattice, buffer the change of the layered structure during lithium deintercalation and intercalation, and reduce the reaction between the material in the charged state and each component of the battery, thereby improving the cycle life and safety performance of the material. In the actual operation process, the doping effect is limited by doping elements and doping process conditions. On the one hand, different doping elements play different roles in the system. At present, most of the research focuses on the doping of metal cations. There has been a lot of research on conventional metal elements such as Al and Zr. However, the research on the synergistic in-situ doping of rare earth elements and anion fluorine by the sol-gel method is rarely seen. On the other hand, most of the existing doping processes use the co-precipitation method to dope the intercalation ions in the form of inorganic carriers, or doping during solid-phase sintering. However, it is difficult to ensure the uniform distribution of the doping ions in the bulk phase of the cathode material by these two methods. Impurities are easily generated during the synthesis process, resulting in disproportionate changes in the lattice parameters of the cathode material, causing lattice distortion, and it is difficult to ensure that the role of the doping phase in the system can be fully exerted.

[0003] In addition, the existing recycling methods for cathode materials of waste lithium-ion batteries mainly focus on wet processes and mainly recover the valuable metal elements therein. The valuable metals in the cathode material are transferred into the solution in the form of ions through acid leaching or alkali leaching, and then nickel sulfate, cobalt sulfate, manganese sulfate, lithium carbonate, cobalt oxide, nickel oxide and other salts or oxides are obtained through separation, purification and multi-step precipitation. However, this recycling process is complex, the high-efficiency separation technology of various metal ions in the leached solution is difficult, the separation index is poor, the process flow is relatively cumbersome, and the cost is high.

[0004] In summary, it is necessary to propose a simple preparation method to modify the recycled waste lithium-ion battery cathode material to improve its performance while recycling it. Summary of the Invention

[0005] To solve the above problems, this application provides a preparation method for a cathode material co-modified by fluorine-rare earth elements with simple operation and uniform doping.

[0006] Another object of this application is to provide a cathode material co-modified by fluorine-rare earth elements prepared by the above preparation method.

[0007] The present application provides a method for preparing a cathode material co-modified by fluorine-rare earth elements, comprising the following steps:

[0008] Add the cathode material of waste lithium-ion batteries into a 2-hydroxypropionic acid solution for the first reaction; then add an ascorbic acid solution to the reacted system for the second reaction, and filter to obtain a leaching solution of metal ions; adjust the molar ratio of metal ions and doped rare earth element R ions in the leaching solution, add an organic fluorine source, adjust the pH, and heat and evaporate to concentrate to form a gel; perform stepwise calcination on the gel to obtain a cathode material co-modified by fluorine-rare earth elements.

[0009] The present application also provides a cathode material co-modified by fluorine-rare earth elements prepared by the above preparation method.

[0010] Compared with the prior art, the preparation method provided by the present application has the following beneficial effects:

[0011] (1) By successively using 2-hydroxypropionic acid and ascorbic acid to leach the cathode material of waste lithium-ion batteries, a leaching solution rich in metal ions with high purity is recovered, and then a regenerated cathode material is prepared by a one-step sol-gel method. During this process, rare earth elements are introduced for in-situ doping to achieve uniform distribution of the doped rare earth elements, enabling the preferential growth of the cathode material synthesis towards a layered structure and making the material structure more stable.

[0012] (2) In order for rare earth elements to play their role stably in the internal lattice structure of the cathode material, fluorine with a stronger electronegativity than oxygen is introduced. The introduction of fluorine has the following three characteristics: First, the fluorine source uses organic fluorides and is introduced during the sol-gel process. This fluorine-containing organic carbon chain can complex metal ions, further ensuring the uniformity of ion doping; Second, fluorine replaces some oxygen in the layered structure and forms a fluorine-rare earth element bond with rare earth elements, making the material structure more stable, thereby effectively improving the electrochemical performance of the regenerated cathode material; Third, the introduction of fluorine can reduce the side reaction between the material and the electrolyte to a certain extent, reduce the corrosion of the material by trace HF in the battery system, and thus enable the lithium-ion battery to have better high-temperature safety performance and high-temperature rate performance. Description of the Drawings

[0013] Figure 1 XRD pattern of the cathode material co-modified by fluorine-rare earth elements prepared in Example 1.

[0014] Figure 2 Cycling curves of the lithium-ion batteries prepared in Example 1 and Comparative Examples 1-3 at a 5C rate and 45 °C. Detailed Embodiments

[0015] The present application will be further elaborated below in conjunction with embodiments. These embodiments are only used to illustrate the present application and not to limit the scope of the present application. For the experimental methods without specific conditions indicated in the following embodiments, they are generally in accordance with the conventional conditions in the art or the conditions recommended by the manufacturers; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as the conventional market. Any non-substantive changes and substitutions made by those skilled in the art based on the present application fall within the scope of protection required by the present application.

[0016] An embodiment of the present application provides a method for preparing a cathode material co-modified by fluorine-rare earth elements, comprising the following steps:

[0017] Adding the cathode material of waste lithium-ion batteries into a 2-hydroxypropanoic acid solution for the first reaction; then adding an ascorbic acid solution to the reaction system for the second reaction, and filtering to obtain a leaching solution of metal ions; adjusting the molar ratio of metal ions and doped rare earth element R ions in the leaching solution, adding an organic fluorine source, adjusting the pH, heating and evaporating to concentrate to form a gel; subjecting the gel to stepwise calcination to obtain the cathode material co-modified by fluorine-rare earth elements.

[0018] In the present application, the recycling of metals from waste lithium-ion batteries is organically combined with the preparation of cathode materials. The one-step sol-gel method is used to crosslink metal ions to regenerate a new cathode material, and in-situ doping and co-modification of fluorine-rare earth elements are carried out on the regenerated material during the regeneration process, so that the doped fluorine-rare earth elements are evenly distributed in the bulk phase of the cathode material, realizing an atomic-level uniform mixing. This not only omits the subsequent dry doping step, shortens the process, and saves costs, but also achieves the purpose of doping and modifying the regenerated material. This method is simple and easy to operate, does not require metal ion separation of the leaching solution, shortens the process flow, has low cost, and is easy to realize industrialization.

[0019] Due to their high electron charge, large ionic radius, and strong self-polarization ability, rare earth elements have become an important choice for doping and modification. The present application uses an in-situ doping method to introduce at least one rare earth element. In terms of structure, since the ionic radius of rare earth ions is larger than that of transition metal ions, the substitution of rare earth ions will cause lattice expansion, which to some extent changes the potential energy surface of the cathode, expands the three-dimensional diffusion channels in the cathode material, and increases the migration barrier or changes the migration path of Li + ; in terms of electronic structure, the system still basically maintains semi-conductivity, but the band gap becomes smaller, and some band edge states appear near the Fermi level. The smaller band gap and the appearance of impurity states or smaller polaron migration barriers will improve the electronic conductivity of the cathode material; in terms of Li + mobility, after the application of rare earth, the Li + layer thickness becomes larger, and Li +The migration barrier will be reduced. Along the migration path near the rare-earth ions, the migration barrier is relatively higher. The mutual competition caused by the increase in the Li layer thickness and the local potential energy change brought about by the rare-earth ions improves the electrochemical performance of the material. After rare-earth doping, the lithium deintercalation / insertion potential increases. At the same time, the volume change rate during the lithium deintercalation / insertion process decreases, indicating that rare-earth doping can improve the structural stability during the lithium deintercalation / insertion process and improve the cycling performance.

[0020] Meanwhile, in order for the doped rare-earth elements to play a more stable role in the cathode material, anion fluorine is introduced. In the cathode material structure, on the one hand, the electronegativity of fluorine is stronger than that of oxygen, and the fluorine-rare-earth element bond energy is more stable, which can inhibit the structural instability caused by the movement of transition metals and rare-earth elements in the lattice structure during the cycling process of the cathode material; on the other hand, F - can replace O 2- to change the electronic environment and prevent the migration of O 2- in the lithium-deintercalated material, or reduce the release of reactive oxygen species. The less reactive oxygen species are released, the fewer reactions occur between the reactive oxygen species and the electrolyte on the surface of the material, thereby further improving the electrochemical performance.

[0021] Moreover, through the pre-acidification treatment with an organic acid (2-hydroxypropanoic acid) and the continuous reduction leaching method with an organic reducing agent (ascorbic acid), the acidity, chelating property of the organic acid and the reducing property, chelating property of the organic reducing agent are fully utilized, avoiding problems such as the loss of part of the reducing property due to the one-time addition of the organic reducing agent and the insufficient utilization of the reducing property. It can realize the recycling of valuable metal elements in the cathode material of waste lithium-ion batteries, recover a leaching solution rich in valuable metals with high purity, the leaching process is mild and controllable, the residence time of heating is short, and finally the goal of high leaching rate is achieved with low energy consumption.

[0022] In some embodiments, the chemical general formula of the cathode material of the waste lithium-ion battery is LiNi x Co y Mn z O2, where x:y:z = (0 - 1):(0 - 1):(0 - 1), and x, y, z are not all 0 at the same time.

[0023] In some embodiments, the chemical general formula of the cathode material modified by the fluorine-rare-earth element synergy is Li k Ni x Co y Mn z R r F n O 2-n, where x:y:z:r = (0.10 - 0.85):(0 - 0.10):(0.10 - 0.35):(0.001 - 0.01), and x + y + z + r = 1, 0.95 ≤ k ≤ 1.15, 0.001 < n ≤ 0.05.

[0024] In some embodiments, the mass ratio of the 2-hydroxypropionic acid to the mass of the waste lithium-ion battery cathode material is (5 - 50):(50 - 95). The temperature of the first reaction is 30 - 70°C, the time is 0.1 - 1 h, and the stirring speed is 200 - 600 r / min.

[0025] In some embodiments, the mass ratio of the ascorbic acid to the mass of the waste lithium-ion battery cathode material is 5 - 500:1000. The temperature of the second reaction is 30 - 55°C, the time is 0.1 - 1 h, and the stirring speed is 300 - 800 r / min.

[0026] In the specific implementation process, the content of each metal ion in the leachate can be detected by conventional detection means such as inductively coupled plasma atomic emission spectrometry (ICP), and then by adding the corresponding metal elements, salts of rare earth element R (such as acetate, etc.) and organic fluorine sources, the elements in the leachate can be adjusted to the target ratio. Two ICP tests before and after the leachate can be used to determine whether the ion ratios meet the design requirements.

[0027] In some embodiments, the rare earth element R is at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu. The organic fluorine source is one or more of octafluoro-1,6-hexanediol, tetrabutylammonium fluoride, fluoroacetic acid, fluorocarboxylic acid.

[0028] In some embodiments, the pH is adjusted to 6.5 - 7.5, and the heating temperature is 40 - 90°C; the reagents for adjusting the pH are one or more of ammonia water, ammonium acetate, ammonium citrate.

[0029] In some embodiments, the stepwise calcination includes: performing three-step calcination on the gel in an oxygen or air atmosphere.

[0030] Among them, the temperature of the first-step calcination is 100 - 400°C, the residence time is 2 - 15 h, and the heating rate is 1 - 10°C / min; the temperature of the second-step calcination is 450 - 900°C, the residence time is 1 - 12 h, and the heating rate is 1 - 20°C / min; the temperature of the third-step calcination is 350 - 550°C, the residence time is 1 - 9 h, and the cooling rate is 5 - 20°C / min.

[0031] Among them, the equipment for stepwise calcination includes one of a rotary kiln, a tube furnace, a box furnace, a bell jar furnace, or a roller hearth kiln.

[0032] In this application, the sol-gel method combined with stepwise calcination is used to prepare the fluorine-rare earth element co-modified cathode material. In the first-step calcination, the organic substances or organic carbon chains in the sol-gel process are fully removed at a relatively low temperature to prepare for the crystallization of the material in the next step. The second-step calcination is a process of material crystallization at a relatively high temperature, that is, a process of constructing the material structure. The material prepared in this process basically reaches the applicable level. The third-step calcination is an optimization process of the material, which will repair and optimize problems such as lattice defects and crystallinity defects that occur in the previous synthesis process of the material. If stepwise calcination is not used, it may lead to insufficient removal of organic substances or organic carbon chains, rapid material crystallization, and residual organic impurities, seriously affecting the performance.

[0033] This application also provides a fluorine-rare earth element co-modified cathode material prepared by the above preparation method.

[0034] The following uses specific examples and comparative examples to illustrate the preparation method and performance of the regenerated cathode material.

[0035] Example 1

[0036] This example provides a preparation method for a fluorine-lanthanum co-modified cathode material. The chemical formula of the required fluorine-lanthanum co-modified cathode material is LiNi 0.499 Co 0.199 Mn 0.299 La 0.003 F 0.009 O 1.991 . The specific preparation method includes the following steps:

[0037] (1) Add 1000 g of 2-hydroxypropionic acid to 90 L of deionized water to prepare a 2-hydroxypropionic acid solution. Add 10 kg of the spent lithium-ion battery cathode material with the composition of LiNi 0.33 Co 0.33 Mn 0.33 O2 to the above solution, and react at 55 °C under heating conditions and 350 r / min under stirring conditions for 0.4 h.

[0038] (2) Add 200 g of ascorbic acid to 18 L of deionized water to prepare an ascorbic acid solution. Slowly pump the above ascorbic acid solution into the system after the reaction in step (1) at a flow rate of 18 L / h. The reaction conditions are a temperature of 50 °C and a stirring speed of 500 r / min. After 1 h, the pumping ends to obtain a black turbid liquid. Filter the black turbid liquid to remove the filter residue, and obtain the leaching solution of metal ions.

[0039] (3) Add lanthanum acetate (La 3+ ) to the leaching solution obtained in step (2), and adjust the molar ratios of Ni 2+ , Co 2+ , Mn 2+ , La 3+ , Li + to satisfy x:y:z:r:k = 0.499:0.199:0.299:0.003, k = 1.07. Add fluoro-carboxylic acid according to the stoichiometric ratio, and then adjust the pH to 7.0 with ammonium acetate and ammonium citrate solutions. Remove most of the water under heating at 50 °C to form a gel.

[0040] (4) Transfer the above gel to a rotary kiln furnace and carry out stepwise calcination in an air atmosphere. The temperature of the first calcination is 200 °C, the residence time is 4 h, and the heating rate is 5 °C / min; the temperature of the second calcination is 820 °C, the residence time is 8 h, and the heating rate is 10 °C / min; the temperature of the third calcination is 500 °C, the residence time is 6 h, and the cooling rate is 10 °C / min. After sieving the calcined material, the fluorine-lanthanum co-modified cathode material is obtained.

[0041] Figure 1 is the XRD pattern of the fluorine-lanthanum co-modified cathode material. It can be seen from the figure that the cathode material prepared in this example is LiNi 0.499 Co 0.199 Mn 0.299 La 0.003 F 0.009 O 1.991 . Each diffraction peak is sharp, with high crystallinity and no impurity peaks. Each main peak conforms to the structure of the nickel-cobalt-manganese cathode material, indicating that the doping elements have been completely incorporated into the lattice structure of the cathode material and no compounds are formed separately outside the main structure of the nickel-cobalt-manganese cathode material.

[0042] Example 2

[0043] This example provides a preparation method of a fluorine-cerium co-modified cathode material. The chemical formula of the prepared fluorine-cerium co-modified cathode material is LiNi 0.698 Co 0.1 Mn 0.197 Ce 0.005 F 0.015 O 1.985 . The preparation method specifically includes the following steps:

[0044] (1) Add 55 g of 2-hydroxypropanoic acid to 3 L of deionized water to prepare a 2-hydroxypropanoic acid solution. Add 500 g of a composition of LiNi 0.6 Co 0.2 Mn0.2 The spent cathode material of lithium-ion battery containing O2 is added to the above 2-hydroxypropanoic acid solution, and the reaction is carried out for 0.2 h under the heating condition of 58 °C and the stirring condition of 300 r / min.

[0045] (2) 20 g of ascorbic acid is added to 4.8 L of deionized water to prepare an ascorbic acid solution. The above ascorbic acid solution is slowly pumped into the system after the reaction in step (1) at a flow rate of 4.8 L / h. The reaction conditions are a temperature of 45 °C and a stirring speed of 350 r / min. After 1 h, the pumping ends, and a black turbid liquid is obtained. The black turbid liquid is filtered to remove the filter residue, and the leaching solution of metal ions is obtained.

[0046] (3) Ce is added to the leaching solution in step (2), 3+ and the molar ratios x:y:z:r:k of Ni, 2+ Co, 2+ Mn, 2+ Ce, 3+ Li + satisfy x:y:r:m = 0.698:0.1:0.197:0.005, k = 1.08, and octafluoro-1,6-hexanediol is added according to the stoichiometric ratio. Then, the pH is adjusted to 7.1 with ammonium acetate solution, and most of the water is removed under the heating condition of 50 °C to form a gel.

[0047] (4) The above gel is transferred to a rotary kiln and calcined step by step in an oxygen atmosphere. The temperature of the first calcination is 250 °C, the residence time is 3 h, and the heating rate is 5 °C / min; the temperature of the second calcination is 800 °C, the residence time is 10 h, and the heating rate is 10 °C / min; the temperature of the third calcination is 400 °C, the residence time is 3 h, and the cooling rate is 10 °C / min. After screening the calcined material, the cathode material modified by fluorine-cerium synergy is obtained.

[0048] Example 3

[0049] This example provides a preparation method of a cathode material modified by fluorine-scandium-yttrium synergy. The chemical formula of the cathode material modified by fluorine-scandium-yttrium synergy is LiNi, 0.59 Co, 0.19 Mn, 0.29 R, 0.008 F, 0.024 O, 1.976 where R is Sc and Y. The preparation method specifically includes the following steps:

[0050] (1) 510 g of 2-hydroxypropanoic acid is added to 30 L of deionized water to prepare a 2-hydroxypropanoic acid solution. 5200 g of the composition LiNi, 0.5 Co,0.2 Mn 0.3 The cathode material of waste lithium - ion batteries is added to the above 2 - hydroxypropanoic acid solution, and the reaction is carried out for 0.2 h under the heating condition of 50 °C and the stirring condition of 400 r / min.

[0051] (2) 130 g of ascorbic acid is added to 20 L of deionized water to prepare an ascorbic acid solution. The above ascorbic acid solution is slowly pumped into the system after the reaction in step (1) at a flow rate of 20 L / h. The reaction conditions are a temperature of 45 °C and a stirring speed of 450 r / min. After 1 h, the pumping ends, and a black turbid liquid is obtained. The black turbid liquid is filtered to remove the filter residue, and the leaching solution of metal ions is obtained.

[0052] (3) Rare earth element ions R 3+ (Sc 3+ 、Y 3+ ) are added to the leaching solution obtained in step (2), and the molar ratios x:y:z:r:k of Ni 2+ 、Co 2+ 、Mn 2+ 、R 3+ 、Li + are adjusted to satisfy x:y:z:r = 0.59:0.19:0.29:0.03, k = 1.05. Tetrabutylammonium fluoride is added according to the stoichiometric ratio, and the pH is adjusted to 7.0 with ammonium acetate solution. Most of the water is removed under the heating condition of 50 °C to form a gel.

[0053] (4) The above gel is transferred to a rotary kiln and calcined step - by - step in an oxygen atmosphere. The temperature of the first - step calcination is 300 °C, the residence time is 3 h, and the heating rate is 5 °C / min; the temperature of the second - step calcination is 850 °C, the residence time is 11 h, and the heating rate is 10 °C / min.

[0054] The temperature of the third - step calcination is 400 °C, the residence time is 5 h, and the cooling rate is 10 °C / min. After the calcined material is sieved, the cathode material modified by fluorine - scandium - yttrium synergy is obtained.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that no fluorine doping is carried out. The chemical formula of the prepared cathode material is LiNi 0.499 Co 0.199 Mn 0.299 La 0.003 O2. That is, in step (3), the molar ratios of Ni 2+ 、Co 2+ 、Mn 2+ 、La 3+ 、Li +The molar ratio x:y:z:r:k satisfies x:y:z:m = 0.499:0.199:0.299:0.003, and k = 1.07.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 1 is that no fluorine-rare earth element doping is carried out, and the chemical formula of the prepared cathode material is LiNi 0.5 Co 0.2 Mn 0.3 O2, that is, in step (3), the molar ratio x:y:z:k of Ni 2+ Co 2+ Mn 2+ Li + satisfies x:y:z:m = 0.5:0.2:0.3, and k = 1.07.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 1 is that during the leaching process, the waste cathode material is simultaneously added to the mixed solution of 2-hydroxypropionic acid and ascorbic acid, that is, the leaching solution is obtained by a one-step reaction:

[0061] 1000 g of 2-hydroxypropionic acid and 200 g of ascorbic acid were added to 108 L of deionized water to prepare a mixed solution. 10 kg of the waste lithium-ion battery cathode material with the composition of LiNi 0.33 Co 0.33 Mn 0.33 O2 was added to the above mixed solution for reaction. The reaction temperature was 55 °C, the reaction time was 1.4 h, and the stirring speed was 350 r / min to obtain a black turbid liquid. The black turbid liquid was filtered to remove the filter residue, and the leaching solution rich in valuable metal ions was obtained.

[0062] Other steps are the same as those in Example 1, and the chemical formula of the prepared fluorine-lanthanum co-modified cathode material is LiNi 0.499 Co 0.199 Mn 0.299 La 0.003 F 0.009 O 1.991 .

[0063] It was found that there were more filter residues in the black turbid liquid obtained in Comparative Example 3, indicating that more waste lithium-ion battery cathode materials were not dissolved, and the mass of the filter residue was 20 to 50 times that of Example 1.

[0064] The cathode materials co-modified by fluorine-rare earth elements prepared in Example 1 and Comparative Examples 1-3 were respectively added with acetylene black and polyvinylidene fluoride (PVDF). After being mixed evenly, they were ground into a uniform slurry, coated on an aluminum foil to make a cathode. A lithium metal sheet was used as the anode, and a LiPF6-based electrolyte was used to make a coin-type lithium-ion battery. The electrochemical test voltage was 4.3 V.

[0065] Figure 2 Figure 4 is the cycle curve diagram of the lithium-ion batteries prepared in Example 1 and Comparative Examples 1-3 at a 5C rate and 45 °C. As can be seen from Figure 2 it, the initial discharge specific capacity of the lithium-ion battery prepared in Example 1 reached 159.5 mAh / g, and the discharge specific capacity was still as high as 151.4 mAh / g after 100 cycles, with a capacity retention rate as high as 94.9%. However, the capacity retention rates of the lithium-ion batteries prepared in Comparative Example 1 and Comparative Example 2 were only 92.0% and 90.3% respectively, and the initial discharge specific capacity of the lithium-ion battery prepared in Comparative Example 3 was only 156.8 mAh / g, and the capacity retention rates were only 92.5% respectively.

[0066] In summary, in this application, the recovery of valuable metals from waste lithium-ion batteries is organically combined with the preparation of cathode materials. The one-step sol-gel method is used to crosslink metal ions to regenerate a new cathode material, and the regenerated material is co-modified by fluorine-rare earth elements during the regeneration process, so that the doped fluorine and rare earth elements are evenly distributed in the bulk phase of the cathode material, realizing uniform mixing at the atomic level. The prepared cathode material co-modified by fluorine-rare earth elements has high crystallinity, uniform doping and no impurity phase, and thus has excellent electrochemical performance.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A preparation method of a cathode material co-modified by fluorine-rare earth elements, characterized in that, It includes the following steps: Adding the spent lithium-ion battery cathode material into a 2-hydroxypropanoic acid solution for the first reaction; Adding an ascorbic acid solution into the system after the first reaction for the second reaction, and filtering to obtain a leaching solution of metal ions; Adjusting the molar ratio of metal ions and doped rare earth element R ions in the leaching solution, adding an organic fluorine source, adjusting the pH, heating, and evaporating and concentrating to form a gel; Performing stepwise calcination on the gel, where the stepwise calcination includes three steps of calcination. Among them, the temperature of the first step of calcination is 100-400 °C, the temperature of the second step of calcination is 450-900 °C, and the temperature of the third step of calcination is 350-550 °C, to obtain a cathode material co-modified by fluorine-rare earth elements; 2. The preparation method according to claim 1, characterized in that, The chemical general formula of the waste lithium-ion battery cathode material is LiNi x Co y Mn z O2, where x:y:z = (0~1):(0~1):(0~1), and x, y, and z are not all 0 at the same time.

3. The preparation method according to claim 1, characterized in that, The chemical general formula of the positive electrode material co-modified by fluorine-rare earth elements is Li k Ni x Co y Mn z R r F n O 2-n , where x:y:z:r = (0.10~0.85):(0~0.10):(0.10~0.35):(0.001~0.01), and x + y + z + r = 1, 0.95 ≤ k ≤ 1.15, 0.001 < n ≤ 0.

05.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the 2-hydroxypropanoic acid to the mass of the spent lithium-ion battery cathode material is (5-50):(50-95); The temperature of the first reaction is 30-70 °C, the time is 0.1-1 h, and the stirring speed is 200-600 r / min; 5. The preparation method according to claim 1, characterized in that, The mass ratio of the ascorbic acid to the mass of the spent lithium-ion battery cathode material is 5-500:1000; The temperature of the second reaction is 30-55 °C, the time is 0.1-1 h, and the stirring speed is 300-800 r / min; 6. The preparation method according to claim 1, characterized in that, The rare earth element R is at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu; 7. The preparation method according to claim 1, characterized in that, The organic fluorine source is at least one of octafluoro-1,6-hexanediol, tetrabutylammonium fluoride, fluoroacetic acid, or fluorocarboxylic acid; 8. The preparation method according to claim 1, wherein Adjusting the pH to 6.5-7.5, and the heating temperature is 40-90 °C; the reagent for adjusting the pH is one or more of ammonia water, ammonium acetate, and ammonium citrate; 9. The preparation method according to claim 1, characterized in that, The three-step calcination includes: performing three-step calcination on the gel in an oxygen or air atmosphere; Among them, the residence time of the first step of calcination is 2-15 h, the heating rate is 1-10 °C / min, the residence time of the second step of calcination is 1-12 h, the heating rate is 1-20 °C / min, the residence time of the third step of calcination is 1-9 h, and the cooling rate is 5-20 °C / min; 10. A cathode material co-modified by fluorine-rare earth elements, characterized in that, Prepared by using the preparation method described in any one of claims 1-9.

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