Method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive electrode sheets

Abstract

A method for preparing a lithium hydroxide and nickel-cobalt-manganese solution from spent ternary battery positive electrodes, belonging to the field of waste battery recycling technology, comprises: oxidizing and sintering the spent ternary battery positive electrodes, followed by sieving and separating to obtain a sieve undersize; washing the sieve undersize with water, followed by a first filtration to obtain a slurry and a lithium hydroxide-containing solution; and acid-washing the slurry, followed by a second filtration to obtain a first nickel-cobalt-manganese solution. The present invention utilizes an "oxidation-sintering-water-washing-acid-washing" process to recover nickel, cobalt, manganese, and lithium from spent ternary battery positive electrodes. This method features excellent lithium, nickel-cobalt-manganese separation, simple procedures, low cost, and a high metal element dissolution rate.

Description

Technical Field

[0001] The present invention relates to the technical field of waste battery recycling, and in particular to a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive electrode sheets. Background Art

[0002] Ternary battery, full name ternary polymer lithium battery, refers to a lithium battery whose positive electrode material uses nickel cobalt manganese oxide ternary positive electrode material. The ternary composite positive electrode material precursor product is made of nickel salt, cobalt salt and manganese salt as raw materials, and is safer than lithium cobalt oxide batteries.

[0003] With the widespread use of ternary batteries, a large amount of waste ternary battery materials are generated, and there is an urgent need to recycle and process these waste ternary battery materials. The current recycling method for ternary battery waste mainly uses the method of dissolving all four metal elements of lithium, nickel, cobalt, and manganese simultaneously. This increases the difficulty of element separation and extraction, making the recycling process cumbersome, increasing costs, and reducing the metal element dissolution rate. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive plates, so as to solve the technical problems of complicated steps, high cost and low metal element dissolution rate in the existing method of recovering nickel-cobalt-manganese-lithium from waste ternary battery positive plates.

[0005] The present invention provides a method for preparing a lithium hydroxide and nickel-cobalt-manganese solution from a waste ternary battery positive electrode sheet, the method comprising:

[0006] The waste ternary battery positive electrode sheets are oxidized and sintered, and then sieved to obtain the undersize;

[0007] The sieve underfill is washed with water, and then subjected to a first filtration to obtain a slurry and a lithium hydroxide-containing solution;

[0008] The slurry is acid-washed and then subjected to a second filtration to obtain a first nickel-cobalt-manganese solution.

[0009] Furthermore, the working parameters of the oxidation sintering include: a temperature of 500° C. to 800° C. and a time of 1 to 5 hours.

[0010] Furthermore, the specific process of washing the undersize material with water and then performing a first filtration to obtain a slurry and a lithium hydroxide-containing solution includes:

[0011] The sieve underflow is subjected to a first water washing and then to a third filtration to obtain a first slurry and a lithium hydroxide-containing solution;

[0012] The first slurry is subjected to a second water washing and then to a fourth filtration to obtain a slurry.

[0013] Furthermore, the solid-to-liquid ratio of the first water wash and the second water wash is 1:(1-3) by weight;

[0014] The first filtrate obtained after the fourth filtration is used as the washing liquid for the first water washing of the next batch of screen material, so as to achieve the effect of recycling the washing filtrate and increasing the concentration of the lithium hydroxide-containing solution.

[0015] Furthermore, the molar concentration of hydrogen ions in the pickling is 2 to 4 mol / L.

[0016] Furthermore, the acid used in the pickling process includes at least one of hydrochloric acid, sulfuric acid and nitric acid.

[0017] Furthermore, the valence states of the nickel ions, cobalt ions and manganese ions in the first nickel-cobalt-manganese solution are at least one of positive trivalence and positive tetravalence.

[0018] Furthermore, the method further comprises:

[0019] Under an inert atmosphere, reducing the first nickel-cobalt-manganese solution with a metal element to obtain a second nickel-cobalt-manganese solution;

[0020] Wherein, the metal element is at least one of metal nickel, metal cobalt and metal manganese.

[0021] Furthermore, the valence states of nickel ions, cobalt ions and manganese ions in the second nickel-cobalt-manganese solution are all positive divalent.

[0022] Furthermore, the ratio of the metal element to the total amount of nickel ions, cobalt ions and manganese ions contained in the first nickel-cobalt-manganese solution is ≥2 on a molar basis.

[0023] Compared with the prior art, the above solution provided by the embodiment of the present application has at least the following beneficial effects:

[0024] An embodiment of the present application provides a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive electrodes. The method uses an "oxidation sintering-water washing-acid washing" process to recover the four elements of nickel, cobalt, manganese, and lithium from the waste ternary battery positive electrodes. The method has the characteristics of good separation effect of lithium and nickel-cobalt-manganese, simple steps, low cost, and high dissolution rate of metal elements. The specific principle of the above-mentioned "oxidation sintering-water washing-acid washing" process includes: in an oxidizing atmosphere, the waste ternary battery positive electrode sheet is oxidized and sintered, so that the powder in the waste ternary battery positive electrode sheet falls off from the current collector aluminum foil, while ensuring that the elements in the powder are oxidized to a high valence state, forcing the powder inside the particles to fall out on the surface of the particles, and then sieving and separating to obtain the undersize (the undersize is the powder, and the oversize is the current collector aluminum foil), and then washing and dissolving the lithium on the surface of the powder with water, thereby achieving efficient separation of lithium from nickel, cobalt and manganese and preparation of lithium hydroxide, while partially replacing "acid washing and erosion" with "water washing and erosion", reducing the amount of acid used in the entire recovery step; then acid washing and dissolving the slurry obtained by washing with acid to obtain a nickel, cobalt and manganese solution. The various steps of the whole process cooperate with each other and are indispensable, so that the lithium element is preferentially separated from the ternary battery waste, which not only greatly simplifies the recovery steps and reduces the recovery cost, but also has the characteristics of high metal element dissolution rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 A schematic flow chart of a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive electrode sheets provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0029] The overall idea of the technical solution provided by the embodiment of the present invention is as follows:

[0030] In the first aspect, the present invention provides a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive electrode sheets, such as Figure 1 As shown, the method includes:

[0031] The waste ternary battery positive electrode sheets are oxidized and sintered, and then sieved to obtain the undersize;

[0032] The sieve underfill is washed with water, and then subjected to a first filtration to obtain a slurry and a lithium hydroxide-containing solution;

[0033] The slurry is acid-washed and then subjected to a second filtration to obtain a first nickel-cobalt-manganese solution.

[0034] An embodiment of the present application provides a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive electrodes. The method uses an "oxidation sintering-water washing-acid washing" process to recover the four elements of nickel, cobalt, manganese, and lithium from the waste ternary battery positive electrodes. The method has the characteristics of good separation effect of lithium and nickel-cobalt-manganese, simple steps, low cost, and high dissolution rate of metal elements. The specific principle of the above-mentioned "oxidation sintering-water washing-acid washing" process includes: in an oxidizing atmosphere, the waste ternary battery positive electrode sheet is oxidized and sintered, so that the powder in the waste ternary battery positive electrode sheet falls off from the current collector aluminum foil, while ensuring that the elements in the powder are oxidized to a high valence state, forcing the powder inside the particles to fall out on the surface of the particles, and then sieving and separating to obtain the undersize (the undersize is the powder, and the oversize is the current collector aluminum foil), and then washing and dissolving the lithium on the surface of the powder with water, thereby achieving efficient separation of lithium from nickel, cobalt and manganese and preparation of lithium hydroxide, while partially replacing "acid washing and erosion" with "water washing and erosion", reducing the amount of acid used in the entire recovery step; then acid washing and dissolving the slurry obtained by washing with acid to obtain a nickel, cobalt and manganese solution. The various steps of the whole process cooperate with each other and are indispensable, so that the lithium element is preferentially separated from the ternary battery waste, which not only greatly simplifies the recovery steps and reduces the recovery cost, but also has the characteristics of high metal element dissolution rate.

[0035] Compared with existing technologies such as Chinese patent CN 201711338941.6, which discloses a method for recovering valuable metals from waste nickel-cobalt-manganese oxide lithium ternary battery cathode materials, the above technical solution provided in the embodiments of the present application has at least the following differences:

[0036] 1) In the roasting or sintering step, the embodiment of the present application adopts an oxidizing atmosphere such as oxygen, air (oxygen content is greater than 10% by volume) to perform oxidative sintering treatment on the waste ternary battery positive electrode sheet. The purpose is that oxygen oxidizes the divalent ions such as nickel, cobalt, and manganese in the waste ternary positive electrode material at high temperature, so that its internal layered structure is destroyed, thereby achieving the effect of lithium migrating from the inside of the powder particles to the surface of the powder, which is conducive to the efficient separation of lithium and nickel, cobalt and manganese in the subsequent water washing process and the dissolution of metal elements in the acid washing process, thereby increasing the dissolution rate of metal elements; the existing technology adopts the "reduction roasting" method, the main purpose of which is to roast and decompose the binder, and shorten the subsequent acid leaching time while reducing the metal elements.

[0037] 2) During the metal element intrusion process, the embodiment of the present application adopts the method of "water washing first and then acid washing" to perform intrusion treatment on the powder obtained by oxidation sintering, and uses water to efficiently separate lithium from the powder. This is because during oxidation sintering, lithium migrates from the interior of the particles to the surface of the particles (because nickel, cobalt, and manganese are oxidized and their structures change in an oxidizing atmosphere, lithium forms lithium oxide with oxygen and then migrates out of the structure, and subsequently further reacts with water to form lithium hydroxide that is easily soluble in water. Even if nickel, cobalt, and manganese change in structure, their oxides will not dissolve in water, so they can be separated from lithium (lithium hydroxide)). Moreover, since there are no other anions in the oxidizing atmosphere, the lithium oxide that migrates to the surface of the powder subsequently reacts with water to form lithium hydroxide that is easily soluble in water, thereby achieving the effect of water-soluble and particle separation. By separating lithium from the remaining nickel, cobalt and manganese in steps, the need for multiple extraction and back-extraction steps is eliminated, simplifying the entire recovery process and reducing the recovery cost. At the same time, the "acid washing and leaching" is partially replaced by the "water washing and leaching" process, reducing the amount of acid used in the entire recovery process and further reducing the recovery cost.

[0038] 3) From the above, it can be seen that the embodiment of the present application provides a new method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive plates. The method adopts the "oxidation sintering-water washing-acid washing" process to recover the four elements of nickel, cobalt, manganese and lithium in the waste ternary battery positive plates. The various steps are interrelated, coordinated with each other and indispensable, and together play a role in improving the separation effect of lithium and nickel-cobalt-manganese, simplifying the recovery steps, reducing the recovery cost and increasing the dissolution rate of metal elements.

[0039] In this application, the term "oxidative sintering," which may also be referred to as "oxidative roasting," "sintering oxidation," or "roasting oxidation," specifically refers to sintering the cathode sheets of used ternary batteries in an oxidizing atmosphere. In some specific embodiments, the oxidizing atmosphere may be provided by gases such as oxygen or air.

[0040] In some specific embodiments, the waste ternary battery positive electrode sheets can be crushed before being oxidized and sintered, such as crushing the waste ternary battery positive electrode sheets into fragments with a size of 1 cm×1 cm to 10 cm×10 cm.

[0041] In some specific embodiments, the sieving separation may be performed using a sieve with a mesh size of 18-200, wherein the material on the sieve is the current collector aluminum foil, and the material under the sieve is powder.

[0042] In some specific embodiments, the water used in the water wash can be deionized water to further improve the purity of the obtained product.

[0043] In some specific embodiments, the obtained lithium hydroxide-containing solution can be concentrated and purified by methods disclosed in the prior art, such as evaporation and crystallization, to obtain a lithium hydroxide solid product, which will not be described in detail in this application document.

[0044] As an implementation method of the embodiment of the present application, the working parameters of the oxidation sintering include: a temperature of 500° C. to 800° C. and a time of 1 to 5 hours.

[0045] In the present application, the temperature of the oxidation sintering is controlled to be 500℃~800℃ and the time is 1~5 hours. The purpose is to oxidize and sinter nickel, cobalt and manganese. Since nickel, cobalt and manganese are oxidized and their structures change in an oxidizing atmosphere, lithium and oxygen form lithium oxide and then migrate out of the structure. Later, they are dissolved in water to form lithium hydroxide. Even if nickel, cobalt and manganese change in their structures, their oxides will not dissolve in water, so they can be separated from lithium (lithium hydroxide). If the temperature of the oxidation sintering is too low or the time is too short, the adverse effect is that the oxidation sintering is not sufficient, part of the ternary material maintains its original structure, lithium cannot fully form lithium oxide, and the subsequent process is not fully separated from nickel, cobalt and manganese when dissolved in water; if the temperature of the oxidation sintering is too high or the time is too long, the adverse effect is that the sintering time is long, resulting in energy waste. In some specific embodiments, the temperature of oxidation sintering may be 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, etc.; the time of oxidation sintering may be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0046] As an implementation method of the present application, the specific process of washing the undersize material with water and then performing a first filtration to obtain a slurry and a lithium hydroxide-containing solution includes:

[0047] The sieve underflow is subjected to a first water washing and then to a third filtration to obtain a first slurry and a lithium hydroxide-containing solution;

[0048] The first slurry is subjected to a second water washing and then to a fourth filtration to obtain a slurry.

[0049] In the present application, washing the undersize material twice can further reduce the lithium content in the resulting slurry, thereby further improving the purity of the nickel-cobalt-manganese mixed solution obtained by subsequent acid washing. In some specific embodiments, the first slurry can be subjected to a second water wash and then a fourth filtration to obtain a secondary water-washed lithium (lithium hydroxide)-containing washing solution (with a lower lithium content) as the wash water in the first water wash.

[0050] In some specific embodiments, the slurry may be acid-washed twice or more to further increase the concentration of the obtained nickel-cobalt-manganese solution and the dissolution rate of the corresponding metal elements.

[0051] As an implementation method of the present application, the solid-to-liquid ratio of the first water washing and the second water washing is 1: (1-3) by weight;

[0052] The first filtrate obtained after the fourth filtration is used as the washing liquid for the first water washing of the next batch of screen material, so as to achieve the effect of recycling the washing filtrate and increasing the concentration of the lithium hydroxide-containing solution.

[0053] In the present application, the purpose of controlling the solid-liquid ratio of the first water wash and the second water wash to be 1: (1 to 3) by weight is to ensure that the water wash can dissolve the lithium in the solid at an appropriate concentration for lithium extraction in the subsequent process. If the solid-liquid ratio is too small, the adverse effect is that there is too much liquid, resulting in a low lithium concentration, which is not conducive to subsequent lithium recovery. At the same time, the amount of wastewater is large, which increases the cost of lithium recovery. If the solid-liquid ratio is too large, the adverse effect is that the solid-liquid ratio is large, that is, there is too much solid, and a high-concentration liquid is washed out. Lithium hydroxide is an alkaline compound, and the slurry viscosity is high during washing and filtration, making it difficult to filter and the washing yield is low.

[0054] As an implementation method of the embodiment of the present application, the molar concentration of hydrogen ions in the pickling is 2 to 4 mol / L.

[0055] In this application, the purpose of controlling the molar concentration of hydrogen ions during pickling to 2-4 mol / L is to dissolve nickel oxide, cobalt, and manganese into water-soluble ionic compounds. If the molar concentration of hydrogen ions is too low, the adverse effects are slow reaction speed and low dissolution efficiency. Although this does not affect the yield, the low hydrogen ion concentration means that the concentration of the dissolved nickel, cobalt, and manganese solution is low, and the subsequent wastewater volume increases. If the molar concentration of hydrogen ions is too high, the adverse effect is that the concentration is high, and the carbon slag contains a large amount of nickel, cobalt, and manganese, which affects the yield.

[0056] As an implementation of an embodiment of the present application, the acid used in the pickling process includes at least one of hydrochloric acid, sulfuric acid and nitric acid.

[0057] In some specific embodiments, the mass concentrations of the hydrochloric acid, sulfuric acid and nitric acid can be 20%, 30%, etc.

[0058] As an implementation method of an embodiment of the present application, the valence states of the nickel ions, cobalt ions and manganese ions in the first nickel-cobalt-manganese solution are at least one of positive trivalence and positive tetravalence.

[0059] In this application, the first nickel-cobalt-manganese solution contains Me 3+ / Me 4+ Nickel-cobalt-manganese solution with high-valent ions (Me is nickel, cobalt, or manganese metal).

[0060] As an implementation of the embodiment of the present application, the method further includes:

[0061] Under an inert atmosphere, reducing the first nickel-cobalt-manganese solution with a metal element to obtain a second nickel-cobalt-manganese solution;

[0062] Wherein, the metal element is at least one of metal nickel, metal cobalt and metal manganese.

[0063] This application is obtained by 3+ / Me 4+ A nickel-cobalt-manganese solution containing high-valent ions (Me is nickel, cobalt, or manganese) is prepared by adding reducing metal powder (at least one of nickel, cobalt, and manganese) to the first nickel-cobalt-manganese solution. The purpose is that the nickel, cobalt, and manganese can reduce the high-valent metal ions to obtain a low-valent (divalent) second nickel-cobalt-manganese solution. Since no other impurities are introduced during the entire reduction process, the low-valent (divalent) second nickel-cobalt-manganese solution does not need to be separated and purified and can be directly used to prepare the ternary precursor. The specific reaction process is as follows:

[0064] Me+Me 3+ =2Me 2+ ;

[0065] 2Me+Me 4+ =3Me 2+ ;

[0066] Among them, Me is nickel, cobalt, or manganese metal; Me 2+ It is a low-valent ion; Me 3+ / Me 4+ High-valent ions.

[0067] As an implementation method of an embodiment of the present application, the valence states of nickel ions, cobalt ions and manganese ions in the second nickel-cobalt-manganese solution are all positive divalent.

[0068] The second nickel-cobalt-manganese solution obtained in the present application is a low-valent (divalent) nickel-cobalt-manganese solution. The valuable elements of nickel, cobalt and manganese do not need to be separated and can be directly used for ternary precursor synthesis, which has broad application prospects.

[0069] As an implementation manner of an embodiment of the present application, the ratio of the metal element to the total amount of nickel ions, cobalt ions and manganese ions contained in the first nickel-cobalt-manganese solution is ≥2 on a molar basis.

[0070] In the present application, the molar ratio of the metal element to the total amount of nickel ions, cobalt ions and manganese ions contained in the first nickel-cobalt-manganese solution is controlled to be ≥2 in order to ensure that the high-valent metal ions can be fully reduced to the low-valent (divalent) second nickel-cobalt-manganese solution.

[0071] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0072] Example 1-9 and Comparative Example 1-5 provide a method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive plates, the method comprising:

[0073] Cut the waste ternary battery positive electrode sheets into waste ternary battery positive electrode fragments with a size of 1 cm×10 cm;

[0074] Weighing 1500 g of the waste ternary battery positive electrode fragments, performing oxidation sintering, and then sieving (100-150 mesh) to separate the sieve material - powder;

[0075] The undersize material was subjected to a first water wash (1245.3 g of undersize material-powder, 3735.9 g of deionized water, and stirred at room temperature for 60 min), and then subjected to a third filtration to obtain a first slurry and a lithium hydroxide-containing solution;

[0076] The first slurry is subjected to a second water washing, and then subjected to a fourth filtration to obtain a slurry;

[0077] The slurry is pickled with dilute sulfuric acid, and then subjected to a second filtration to obtain a first nickel-cobalt-manganese solution;

[0078] Under an inert atmosphere, reducing the first nickel-cobalt-manganese solution with a metal element to obtain a second nickel-cobalt-manganese solution; the molar ratio of the metal element to the total amount of nickel ions, cobalt ions, and manganese ions in the first nickel-cobalt-manganese solution is 3.0;

[0079] The mass content of the undersize material detected was: lithium 6.69%, nickel 28.31%, cobalt 12.13%, manganese 17.02%, and the rest were oxygen, carbon and other components.

[0080] The specific parameters of each step in the above examples are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] By detecting the lithium content in the lithium hydroxide-containing solution (obtained by one water wash) obtained in each of Examples 1-9 and Comparative Examples 1-5 and the nickel, cobalt and manganese contents in the first nickel-cobalt-manganese solution (obtained by one acid wash), the dissolution rates of lithium, nickel, cobalt and manganese were calculated according to the ratio of the content of the metal element in the leached solution to the content of the same metal element in the sieve undersize. The specific results are shown in Table 2.

[0085] Table 2

[0086]

[0087] In summary, the embodiments of the present application provide a new method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive plates. This method uses an "oxidation sintering-water washing-acid washing" process to recover the four elements of nickel, cobalt, manganese, and lithium from waste ternary battery positive plates. The various steps are interrelated, coordinated and indispensable, and together they improve the separation effect of lithium and nickel-cobalt-manganese, simplify the recovery steps, reduce the recovery cost, and increase the dissolution rate of metal elements. At the same time, the valuable elements of nickel, cobalt, and manganese do not need to be separated again, and the resulting low-valent nickel-cobalt-manganese solution can be directly used for ternary precursor synthesis, which has broad application prospects.

[0088] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0089] In addition, in the description of this application, the terms "including", "comprising", etc. mean "including but not limited to". In this document, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0090] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A method for preparing lithium hydroxide and nickel-cobalt-manganese solution from waste ternary battery positive plates, characterized in that: The method comprises: The waste ternary battery positive electrode sheets are oxidized and sintered, and then sieved to obtain the undersize; The sieve underfill is washed with water, and then subjected to a first filtration to obtain a slurry and a lithium hydroxide-containing solution; The slurry is acid-washed and then filtered for a second time to obtain a first nickel-cobalt-manganese solution; Under an inert atmosphere, reducing the first nickel-cobalt-manganese solution with a metal element to obtain a second nickel-cobalt-manganese solution; The working parameters of the oxidation sintering include: a temperature of 500°C to 800°C and a time of 1 to 5 hours; The specific process of washing the undersize material with water and then performing a first filtration to obtain a slurry and a lithium hydroxide-containing solution includes: The sieve underflow is subjected to a first water washing and then to a third filtration to obtain a first slurry and a lithium hydroxide-containing solution; The first slurry is subjected to a second water washing, and then subjected to a fourth filtration to obtain a slurry; The molar concentration of hydrogen ions in the pickling process is 2 to 4 mol / L; The solid-to-liquid ratio of the first water wash and the second water wash is 1:(1-3) by weight; The first filtrate obtained after the fourth filtration is used as the washing liquid for the first water washing of the next batch of undersize material, so as to achieve the effect of recycling the washing filtrate and increasing the concentration of the lithium hydroxide-containing solution; The valence states of the nickel ions, cobalt ions and manganese ions in the first nickel-cobalt-manganese solution are at least one of positive trivalence and positive tetravalence; The metal element is at least one of metal nickel, metal cobalt and metal manganese; The valence states of nickel ions, cobalt ions and manganese ions in the second nickel-cobalt-manganese solution are all positive divalent; In terms of molar amount, the ratio of the metal element to the total amount of nickel ions, cobalt ions and manganese ions contained in the first nickel-cobalt-manganese solution is ≥2.

2. The method according to claim 1, characterized in that The acid used in the pickling process includes at least one of hydrochloric acid, sulfuric acid and nitric acid.

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