Preparation method of lithium hydroxide

Abstract

The invention provides a preparation method of lithium hydroxide, and belongs to the technical field of preparation of lithium hydroxide. The preparation method at least comprises the following steps: providing lithium chloride crude salt; dissolving the lithium chloride crude salt with ethanol, and then carrying out solid-liquid separation to obtain an ethanol solution of lithium chloride; taking an ethanol solution of lithium chloride as an anode solution; an ethanol aqueous solution is used as a cathode solution, and the mass content of ethanol is x% based on the mass of the cathode solution; determining the value range of x based on the solubility and current density of lithium hydroxide; and the anode solution and the cathode solution are subjected to electrolytic treatment, and a lithium hydroxide hydrate is separated out at the cathode. Ethanol is adopted for impurity removal, a liquid system after impurity removal can be directly used for electrolysis, the separation of lithium hydroxide is promoted by regulating and controlling the ethanol content of a cathode solution, the step of evaporative crystallization of lithium chloride and lithium hydroxide is omitted, and the method has the advantages of simple and convenient process and high production efficiency.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium hydroxide preparation, and specifically relates to a method for preparing lithium hydroxide. Background Art

[0002] As one of the important primary processed lithium products among lithium and its compounds, lithium hydroxide can be further used to produce products such as lithium acetate, lithium fluoride, lithium bromide, lithium nitrate and lithium benzoate. In the battery industry, adding lithium hydroxide to the electrolyte of alkaline batteries and nickel-hydrogen batteries can extend the battery life and increase the storage capacity. In addition, lithium hydroxide is also used in organic synthesis and pharmaceuticals, reagents, heat carriers of nuclear reactors and protective agents for metal surfaces, materials used in breathing gas purification systems in spacecraft, submarines and underwater breathing apparatuses, etc. Therefore, it is necessary to research and develop a preparation method with high product purity, simple process and environmental friendliness for lithium hydroxide.

[0003] Brine lithium ore (hereinafter referred to as brine, containing lithium chloride) has the advantage of rich mineral resources. The existing technology proposes to use brine as raw material to prepare lithium hydroxide by ion exchange membrane electrolysis. The main production process includes: first, remove impurities from the brine, then evaporate and crystallize, collect lithium chloride; then electrolyze the lithium chloride into a solution to obtain lithium hydroxide solution; finally, the lithium hydroxide solution is concentrated, crystallized, separated, washed and dried to obtain lithium hydroxide products. This method has the problems of complex process, low yield and high cost. Summary of the invention

[0004] In view of this, the present application provides a method for preparing lithium hydroxide, which uses ethanol for impurity removal. The liquid system after impurity removal can be directly used for electrolysis, and the ethanol content of the cathode solution is adjusted to promote the precipitation of lithium hydroxide, thereby eliminating the evaporation and crystallization steps of lithium chloride and lithium hydroxide, and has the advantages of simple process and high production efficiency.

[0005] Specifically, the present application provides a method for preparing lithium hydroxide, which comprises at least the following steps:

[0006] Step 100, providing lithium chloride crude salt; dissolving the lithium chloride crude salt with ethanol, and then performing solid-liquid separation to obtain an ethanol solution of lithium chloride; using the ethanol solution of lithium chloride as an anode solution; Step 200, using an ethanol aqueous solution as a cathode solution, wherein the mass content of ethanol is x% based on the mass of the cathode solution; wherein the value range of x is determined by a method comprising the following steps: Step 210, recording the solubility of lithium hydroxide as yg / 100mL, and determining a regression model of y and x as y=f(x); Step 220, recording the current density of the electrolysis treatment as z mA / cm 2, determine the regression model z=j(x) of z and x; step 230, based on the solubility and current density of lithium hydroxide, determine the value range of x; step 300, electrolyze the anode solution and the cathode solution to precipitate lithium hydroxide hydrate at the cathode.

[0007] The present application adopts ethanol to dissolve lithium chloride crude salt, which can selectively dissolve lithium chloride. Most of the sodium and potassium impurities in lithium chloride crude salt are insoluble in ethanol and can be removed by solid-liquid separation. After solid-liquid separation, the ethanol solution of lithium chloride is obtained, which is directly used as the anode solution for electrolysis treatment. There is no need to carry out the evaporation and crystallization process of lithium chloride, which reduces the process operation of removing impurities from lithium chloride and then evaporating and crystallizing it in the industrial production process, and reduces the cost of evaporation and crystallization. On the other hand, ethanol can be recycled, which reduces the use of water and reduces the cost of raw materials. In combination with ethanol-water solution as the cathode solution, during the electrolysis process, lithium ions pass through the cationic membrane and react with water in the cathode chamber to generate lithium hydroxide. The present application utilizes the lithium hydroxide solubility yg / 100mL corresponding to different ethanol contents in the cathode solution and the electrolysis treatment current density z mA / cm 2 By constructing regression models of y, z and x respectively, the mass content of ethanol in the cathode solution is determined and regulated, so as to increase the current density while reducing the solubility of lithium hydroxide in the cathode solution, thereby improving the electrolysis efficiency and promoting the continuous precipitation of lithium hydroxide hydrate at the cathode, directly obtaining the solid product of lithium hydroxide hydrate, eliminating the need for the traditional industrial production process of evaporating and crystallizing lithium hydroxide, thereby greatly saving time and energy costs and improving production efficiency. And the lithium hydroxide hydrate obtained in this application has high purity and high economic value and industrial application value.

[0008] In this application, the reaction equation during the electrolytic treatment is:

[0009] Overall reaction: 2LiCl + 4H2O = 2LiOH·H2O↓ + H2↑ + Cl2↑;

[0010] Anode: 2Cl － -2e － =Cl2↑;

[0011] Cathode: 2Li + +4H2O+2e － =2LiOH·H2O↓+H2↑.

[0012] In the present application, lithium chloride crude salt can be obtained by methods known in the art, such as evaporating and concentrating brine to obtain lithium chloride crude salt. Depending on the source of the brine, based on the quality of the lithium chloride crude salt, the mass content of lithium chloride is 40% to 60%, such as 40%, 41%, 42%, 44%, 45%, 47%, 49%, 51%, 54%, 55%, 57%, 59%, 60% or a value within the range of any two thereof. In some embodiments, lithium chloride crude salt includes sodium chloride and potassium chloride, and the present application uses ethanol to selectively extract lithium chloride and remove sodium chloride and potassium chloride impurities therein.

[0013] In some embodiments, in step 210, determining the regression model y=f(x) of y and x includes the following steps:

[0014] Step 211, obtaining m ethanol aqueous solutions with different ethanol mass contents;

[0015] Step 212: Test the solubility of lithium hydroxide in the ethanol aqueous solution in step 211 to obtain x-y regression data, which are arranged in ascending order according to the x value as (x 11 ,y1)、(x 12 ,y2),…,(x m ,y m );

[0016] Step 213, performing fitting processing on the regression data of x-y in step 212, and determining the regression model y=f(x) of y and x; and / or,

[0017] In step 220, the regression model z=j(x) of z and x is determined, including the following steps:

[0018] Step 221, obtaining n ethanol aqueous solutions with different ethanol mass contents;

[0019] Step 222: electrolyze the ethanol aqueous solution in step 221, detect the current density, and obtain the regression data of x-z, which are arranged in ascending order according to the x value as (x 21 、z1)、(x 22 ,z2),…,(x n 、z n );

[0020] Step 223: Perform fitting processing on the regression data of x-z in step 222 to determine the regression model z=j(x) of z and x.

[0021] Through the above method, the present application can respectively construct a regression model of the solubility of lithium hydroxide in an ethanol-water solution and the ethanol concentration, as well as a regression model of the current density and the ethanol concentration in the electrolysis treatment, so as to determine the appropriate ethanol mass content in the ethanol-water solution (that is, the cathode solution) according to the required target lithium hydroxide solubility and current density, balance the electrolysis rate and the precipitation rate of lithium hydroxide hydrate in the electrolysis treatment, avoid the electrolysis rate being too low to affect the preparation efficiency, or the electrolysis rate being too high but the lithium hydroxide hydrate being dissolved too much and unable to be precipitated from the cathode solution in time, thereby improving the production efficiency of the preparation process.

[0022] In the present application, the above-mentioned ethanol aqueous solution with different ethanol mass content can be obtained by methods known in the art, such as preparing by using ethanol and water in different proportions. The present application has no special limitation on the ethanol mass content of the ethanol aqueous solution used for solubility test and current density test, as long as the purpose of the present application can be achieved, for example, the ethanol mass content can be 0%, 4%, 10%, 17%, 24%, 34%, 43%, 50%, 59%, 64%, 76%, 78%, 92%, 100% or a value within the range composed of any two of them. It is understandable that when the ethanol mass content is 0%, the "ethanol aqueous solution" is actually water, and when the ethanol mass content is 100%, the "ethanol aqueous solution" is actually ethanol.

[0023] In some embodiments, in step 211, m ethanol aqueous solutions with different ethanol mass contents are obtained, and in step 221, n ethanol aqueous solutions with different ethanol mass contents are obtained. They can be prepared separately or from the same batch of ethanol aqueous solutions.

[0024] In some embodiments, when the same batch of ethanol aqueous solution is used, it can be understood that m=n, x 11 =x 21 , …, x m =x n At this time, in step 210, the regression model y=f(x) of y and x is determined, including the following steps:

[0025] Step 211, obtaining m ethanol aqueous solutions with different ethanol mass contents;

[0026] Step 212: Test the solubility of lithium hydroxide in the ethanol aqueous solution in step 211 to obtain x-y regression data, which are arranged in ascending order according to the x value as (x 11 ,y1)、(x 12 ,y2),…,(x m ,y m );

[0027] Step 213, performing fitting processing on the regression data of x-y in step 212, and determining the regression model y=f(x) of y and x; and / or,

[0028] In step 220, the regression model z=j(x) of z and x is determined, including the following steps:

[0029] Step 221, obtaining n ethanol aqueous solutions with different ethanol mass contents;

[0030] Step 222: electrolyze the ethanol aqueous solution in step 221, detect the current density, and obtain the regression data of x-z, which are arranged in ascending order according to the x value as (x 21 、z1)、(x 22 ,z2),…,(x n 、z n );

[0031] Step 223: Perform fitting processing on the regression data of x-z in step 222 to determine the regression model z=j(x) of z and x.

[0032] In some embodiments, m≥5, x m -x 11 ≥40; and / or, n≥5, x n -x 21 ≥40. The values ​​of m and n can be the same or different. By controlling the number of data m and the x value interval (x m -x 11 ), as well as the number of data n and the x value interval (x n -x 21 ), so that the regression models of the two can be fitted with sufficient and representative data, which is conducive to improving the accuracy and precision of the regression models.

[0033] Preferably, the value of m can be selected from 5, 6, 7, 8, 9, 10, 13, 17, 25 or a value in the range of any two thereof, and x m -x 11 The value of may be selected from 40, 46, 50, 57, 64, 69, 75, 81, 88, 96, 100 or a value in the range of any two thereof. On the other hand, preferably, the value of n may be selected from 5, 6, 7, 8, 9, 10, 13, 17, 25 or a value in the range of any two thereof, and x n -x 21 The value of can be selected from 40, 45, 50, 59, 64, 69, 75, 81, 86, 91, 100 or a value in the range consisting of any two thereof.

[0034] In some embodiments, the regression model of y and x, y=f(x), and the regression model of z and x, z=j(x), are independently selected from a linear regression model or a polynomial regression model; optionally, the polynomial regression model comprises a binomial regression model.

[0035] In some preferred embodiments, the regression model y=f(x) of y and x and the regression model z=j(x) of z and x are both binomial regression models. In the electrolytic treatment system of the present application, this model can more accurately reflect the solubility of lithium hydroxide and the changing relationship between current density and ethanol mass content, which is conducive to determining the appropriate ethanol mass content range.

[0036] In some embodiments, in step 230, based on the solubility and current density of lithium hydroxide, determining the value range of x includes: substituting the value ranges of y and z into the regression model y=f(x) and z=j(x) respectively to obtain the value range of x. In the present application, substituting the value ranges of y and z into the regression model respectively can obtain the corresponding range of the ethanol mass content x in the cathode solution respectively, and finding the intersection of the two value ranges can determine the value range of x, which is conducive to providing guidance for the subsequent control of the ethanol mass content.

[0037] In some embodiments, the value ranges of y and z are: y≤6, z≥40; when the solubility and current density of lithium hydroxide in the ethanol aqueous solution are controlled to meet the above ranges, the electrolysis process and the lithium hydroxide precipitation process can be coordinated to obtain a suitable range of ethanol mass content, taking into account a higher current density and precipitation rate. Preferably, the value ranges of y and z are: y≤5, z≥60.

[0038] In some embodiments, step 300 further includes: in the electrolysis process of step 300 , adding supplementary water to the cathode solution to control the mass content of ethanol in the cathode solution to satisfy the value range of x in step 200 .

[0039] In some embodiments, the quality of the supplementary water is determined by the following method: in the electrolysis process of step 300, the volume reduction of the cathode solution is monitored, and the quality of the supplementary water is determined based on the volume reduction of the cathode solution; or, the mass H g of water consumed in the electrolysis process of step 300 is obtained, and the quality of the supplementary water is determined based on the mass of water consumed. Determining the quality of the supplementary water by the mass of water consumed can avoid the volume interference of the cathode precipitated product, and more accurately control the ethanol mass content of the cathode solution.

[0040] In some embodiments, obtaining the mass of water consumed in the electrolysis process of step 300 includes: detecting the electrolysis capacity Q Ah of the electrolysis process of step 300, and determining the mass of water consumed based on H=Q / 0.74.

[0041] According to the total chemical reaction equation in the electrolytic treatment process: 2LiCl+4H2O=2LiOH·H2O↓+H2↑+Cl2↑, it can be known that when 1 mol of water is consumed, 0.5 mol of electrons are transferred, and the amount of electricity per mol of electrons is 96500 coulombs (1Ah=3600 coulombs). Then the amount of electricity corresponding to the consumption of 1g of water is (0.5 / 18×96500) / 3600Ah=0.74Ah, where 0.74Ah / g is regarded as the gram capacity of water, which is a constant. By monitoring the electrolytic capacity through electrolytic treatment equipment, the quality of water consumption can be easily and intuitively obtained, thereby achieving real-time water replenishment of the cathode solution, controlling the mass content of ethanol in the cathode solution to meet the requirements, and improving the efficiency of electrolytic treatment and product precipitation efficiency.

[0042] The present application does not specifically limit the method for replenishing water, and it can be carried out by methods known in the art, as long as the purpose of the present application can be achieved. For example, instructions can be transmitted from a monitoring device to a control device, and the control device can control a water pump to replenish water into the cathode solution. Water replenishment can also be carried out manually.

[0043] In some embodiments, step 300 further includes: drying the lithium hydroxide hydrate to obtain lithium hydroxide.

[0044] Based on the above-mentioned method for preparing lithium hydroxide provided in the present application, the beneficial effects are at least:

[0045] The present application extracts lithium chloride crude salt with ethanol to obtain an ethanol solution of lithium chloride, which can remove most of the sodium and potassium impurities and improve the purity of the lithium hydroxide product. The above-mentioned ethanol solution of lithium chloride can be directly used for electrolytic treatment, reducing the operation of evaporation and crystallization after impurity removal, which is conducive to saving time, energy and other costs. On the other hand, by constructing the solubility of lithium hydroxide in ethanol aqueous solution and the regression model of the current density and ethanol mass content in the electrolytic treatment, the appropriate ethanol mass content range is determined, so as to achieve the improvement of the electrolytic treatment efficiency and the precipitation rate of lithium hydroxide, so that lithium hydroxide hydrate is continuously saturated and precipitated in the cathode chamber, and a relatively pure lithium hydroxide product is obtained. This method eliminates the need to evaporate and crystallize the electrolytic raw material and the electrolytic product after the impurity removal and electrolytic treatment in the traditional electrolytic process, and can improve the purity of the lithium hydroxide product, with the advantages of simple process, high production efficiency and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The regression model y=f(x) of y and x and the regression model z=j(x) of z and x in the method for preparing lithium hydroxide provided in Example 1;

[0047] Figure 2Schematic diagram of the electrolysis device used in the method for preparing lithium hydroxide provided in the specific embodiment of the present application; wherein, 1-anode electrode, 2-anode solution, 3-cation membrane, 4-cathode electrode, 5-cathode solution. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0049] The scheme of the present application is described below in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0050] Example 1

[0051] This embodiment provides a method for preparing lithium hydroxide, comprising the following steps:

[0052] Step 100, take 50g of lithium chloride crude salt (wherein the mass content of each substance is LiCl: 49.7%, NaCl: 47.7% and KCl: 2.6%), then add 130ml of ethanol to dissolve the lithium chloride crude salt, then filter to remove insoluble impurities, obtain an ethanol solution of lithium chloride after ethanol extraction, and then use the ethanol solution of lithium chloride as an anode solution. This step can remove sodium ions and potassium ions in the lithium chloride crude salt.

[0053] Step 200: Using ethanol aqueous solution as the cathode solution, based on the mass of the cathode solution, the mass content of ethanol is x%, wherein the value range of x is determined by a method comprising the following steps:

[0054] Step 210, record the solubility of lithium hydroxide as yg / 100mL, and determine the regression model y=f(x) of y and x, including:

[0055] Step 211, preparing 6 ethanol aqueous solutions with ethanol mass contents of 0%, 20%, 40%, 60%, 80%, and 100% respectively;

[0056] Step 212: Test the solubility of lithium hydroxide in the ethanol aqueous solution in step 211 to obtain regression data of xy, which are arranged in ascending order according to the x value as (x 11 ,y1)、(x 12 ,y2),…,(x m ,y m ), as shown in Table 1 below;

[0057] Step 213: Fit the regression data of xy in step 212 to determine the regression model of y and x: y=f(x)=0.00201x 2 -0.30704x+12.43571;

[0058] Step 220: record the current density of the electrolysis treatment as z mA / cm 2 , determine the regression model z=j(x) of z and x, including:

[0059] Step 221, using the ethanol aqueous solution prepared in step 211;

[0060] Step 222: electrolyze the ethanol aqueous solution in step 221. The schematic diagram of the electrolysis device is as follows: Figure 2 Take 100mL of lithium chloride ethanol solution as anode solution 2, 100mL of ethanol aqueous solution in step 221 as cathode solution 5, titanium plate as anode electrode 1, platinum sheet as cathode electrode 4, cationic membrane 3 is Shandong Dongyue cationic membrane, model DF2807, membrane area 20cm 2 After the electrolysis device is assembled, power is turned on for electrolysis. The voltage is set to 4V. During the electrolysis process, the current density is detected and the regression data of xz is obtained. The data is recorded in order from the smallest to the largest value of x as (x 21 、z1)、(x 22 ,z2),…,(x n 、z n ), as shown in Table 1 below;

[0061] Step 223: Fit the regression data of xz in step 222 to determine the regression model of z and x: z=j(x)=0.00469x 2 -1.53161x+109.39286. The regression model of y and x is y=f(x) and the regression model of z and x is z=j(x). Figure 1 shown.

[0062] Table 1

[0063] Ethanol mass content x (%) 0 20 40 60 80 100 <![CDATA[Current density (mA / cm 2 )]]> 105 85 65 24 14 7 Solubility (g / 100mL) 12.8 6.5 3.3 1.4 1.2 1.5

[0064] Step 230 , based on the value ranges of the solubility y of lithium hydroxide and the current density z: y≤6, z≥40, determine the value range of x: 25≤x≤54.

[0065] Step 300, using the electrolysis device in step 222, the voltage is set to 4V, and the anode solution and the cathode solution are electrolyzed. During the electrolysis, the electrolysis capacity Q Ah of the electrolysis device is detected, and the mass Hg of water consumption is determined based on H=Q / 0.74. Supplementary water is added to the cathode solution to control the mass content of ethanol in the cathode solution to meet 25≤x≤54. After 2.6 hours, lithium hydroxide precipitation is observed in the cathode chamber. After 10 hours of electrolysis, the lithium hydroxide hydrate crystals are taken out by the suction filtration device, and 8.0g of lithium hydroxide powder is obtained after drying. The total impurity content in the lithium hydroxide product is tested by ICP analysis to be less than 110ppm, and the impurities are mainly NaOH, and a small amount of K, Ca, and Mg impurity ions.

[0066] The preparation method of lithium hydroxide in Example 2 is different from that in Example 1 only in that: in step 230, based on the value ranges of the solubility y of lithium hydroxide and the current density z: y≤5, z≥60, the value range of x is determined: 30≤x≤36.

[0067] Step 300, 2.7 hours later, lithium hydroxide was observed to precipitate in the cathode chamber. After 8 hours of electrolysis, the obtained lithium hydroxide hydrate crystals were dried to obtain 8.2 g of lithium hydroxide powder. The total impurity content in the lithium hydroxide product was less than 100 ppm by analysis and testing, and the impurities were mainly NaOH, and a small amount of K, Ca, and Mg impurity ions.

[0068] The preparation method of lithium hydroxide in Example 3 is different from that in Example 1 only in that: in step 230, based on the value ranges of the solubility y of lithium hydroxide and the current density z: y≤8, z≥30, the value range of x is determined: 16≤x≤64.

[0069] Step 300, 6.2 hours later, lithium hydroxide was observed to precipitate in the cathode chamber. After 10 hours of electrolysis, the obtained lithium hydroxide hydrate crystals were dried to obtain 4.3 g of lithium hydroxide powder. The total impurity content in the lithium hydroxide product was less than 100 ppm by analysis and testing, and the impurities were mainly NaOH, and a small amount of K, Ca, and Mg impurity ions.

[0070] According to the above embodiments, when the solubility and current density of lithium hydroxide in the ethanol aqueous solution are controlled to satisfy y≤6 and z≥40, the electrolytic treatment process and the lithium hydroxide precipitation process can be coordinated to obtain a suitable range of ethanol mass content, taking into account a higher current density and precipitation rate, thereby improving the production efficiency of lithium hydroxide. In particular, when y≤5 and z≥60 are controlled, the production efficiency of lithium hydroxide can be further improved.

[0071] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing lithium hydroxide, characterized in that: At least the following steps are included: Step 100, providing crude lithium chloride salt; dissolving the crude lithium chloride salt with ethanol, and then performing solid-liquid separation to obtain an ethanol solution of lithium chloride; and using the ethanol solution of lithium chloride as an anode solution; Step 200, using an ethanol aqueous solution as a cathode solution, wherein the mass content of the ethanol is x% based on the mass of the cathode solution; The value range of x is determined by a method comprising the following steps: Step 210, record the solubility of lithium hydroxide as yg / 100mL, and determine the regression model of y and x: y=f(x); Step 220: record the current density of the electrolysis treatment as z mA / cm 2 , determine the regression model z=j(x) of z and x; Step 230: determining a value range of x based on the solubility of the lithium hydroxide and the current density; Step 300: electrolyze the anode solution and the cathode solution to precipitate lithium hydroxide hydrate at the cathode.

2. The preparation method according to claim 1, characterized in that: In step 210, determining the regression model y=f(x) of y and x includes the following steps: Step 211, obtaining m ethanol aqueous solutions with different ethanol mass contents; Step 212: Test the solubility of lithium hydroxide in the ethanol aqueous solution in step 211 to obtain x-y regression data, which are arranged in ascending order according to the x value as (x 11 ,y1)、(x 12 ,y2),…,(x m ,y m ); Step 213, performing fitting processing on the regression data of x-y in step 212, and determining a regression model y=f(x) of y and x; and / or, In step 220, determining the regression model z=j(x) of z and x includes the following steps: Step 221, obtaining n ethanol aqueous solutions with different ethanol mass contents; Step 222: electrolyze the ethanol aqueous solution in step 221, detect the current density, and obtain the regression data of x-z, which are arranged in ascending order according to the x value as (x 21 、z1)、(x 22 ,z2),…,(x n 、z n ); Step 223: Fit the regression data of x-z in step 222 to determine the regression model z=j(x) of z and x.

3. The preparation method according to claim 2, characterized in that: m≥5,x m -x 11 ≥40; and / or, n≥5,x n -x 21 ≥40。 4. The preparation method according to claim 1, characterized in that: The regression model of y and x, y=f(x), and the regression model of z and x, z=j(x), are independently selected from a linear regression model or a polynomial regression model; Optionally, the polynomial regression model comprises a binomial regression model.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In the step 230, the value range of x is determined based on the solubility of the lithium hydroxide and the current density, including: substituting the value ranges of y and z into the regression models y=f(x) and z=j(x) respectively to obtain the value range of x.

6. The preparation method according to claim 5, characterized in that: The value range of y and z is: y≤6, z≥40; Preferably, the value ranges of y and z are: y≤5, z≥60.

7. The preparation method according to any one of claims 1 to 4, characterized in that: The step 300 also includes: in the electrolysis process of the step 300 , adding supplementary water to the cathode solution, and controlling the mass content of the ethanol in the cathode solution to satisfy the value range of x in the step 200 .

8. The preparation method according to claim 7, characterized in that: The quality of the supplementary water is determined by the following method: in the electrolysis process of step 300, the volume reduction of the cathode solution is monitored, and the quality of the supplementary water is determined based on the volume reduction of the cathode solution; or, The consumed mass Hg of water in the electrolysis process of step 300 is obtained, and the mass of the supplementary water is determined based on the consumed mass of water.

9. The preparation method according to claim 8, characterized in that: The obtaining of the mass of water consumed in the electrolysis treatment of step 300 includes: detecting the electrolysis capacity Q Ah of the electrolysis treatment of step 300, and determining the mass of water consumed based on H=Q / 0.

74.

10. The preparation method according to any one of claims 1 to 4, characterized in that: Step 300 also includes: drying the lithium hydroxide hydrate to obtain the lithium hydroxide.

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