Preparation method of lithium hydroxide

Abstract

The invention belongs to the technical field of lithium hydroxide preparation, and particularly relates to a preparation method of lithium hydroxide. The method at least comprises the following steps: providing a lithium source; mixing a lithium source with a fluxing agent to obtain a mixed system; taking the mixed system as an anode raw material; taking an ethanol aqueous solution as a cathode raw material, and based on the mass of the cathode raw material, the mass content of ethanol is x%; determining the value range of x based on the solubility and current density of lithium hydroxide; and then heating to enable the anode raw material to be in a molten state, carrying out electrolytic treatment on the anode raw material and the cathode raw material, and separating out a lithium hydroxide hydrate at the cathode. The lithium source in the molten state is electrolyzed, lithium hydroxide with high purity can be efficiently separated out by controlling the content of ethanol in the cathode raw material, the requirement for the purity of the raw material is low, and the method has the advantages of being simple and convenient in process, low in cost and high in 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] In recent years, with the expansion of the new energy vehicle market, the demand for lithium-ion batteries has continued to grow. As one of the important raw materials for lithium-ion batteries, the demand for lithium hydroxide has also shown a significant growth trend.

[0003] At present, the main methods for preparing lithium hydroxide include lithium carbonate causticizing method, lithium sulfate conversion method and lithium chloride electrolysis method. Among them, the lithium carbonate causticizing method uses sodium carbonate to precipitate lithium, and then uses slaked lime conversion method to prepare lithium hydroxide. This method will introduce calcium impurities in slaked lime into the lithium hydroxide product, resulting in the latter having low purity and requiring further purification. It has problems such as long process, high energy consumption, low conversion rate and impure product. The lithium sulfate conversion method requires the use of freezing to separate LiOH from the impurity Na2SO4·10H2O, and subsequent leaching and purification are required, which has problems such as high energy consumption, more steps and low final product yield; the conventional lithium chloride electrolysis method produces lithium hydroxide monohydrate with low purity, which requires preliminary impurity removal to ensure a high purity of lithium chloride, and has high requirements for the initial impurity concentration in the electrolysis chamber. Summary of the invention

[0004] In view of this, the present application provides a method for preparing lithium hydroxide, in which a molten lithium source is electrolyzed, and by controlling the ethanol content in the cathode raw material, lithium hydroxide with high purity can be efficiently precipitated, and the requirements for raw material purity are low. It has the advantages of simple process, low cost and high efficiency.

[0005] Specifically, the preparation method of lithium hydroxide provided in the present application comprises at least the following steps: step 100, providing a lithium source; mixing the lithium source with a flux to obtain a mixed system; using the mixed system as an anode raw material; step 200, using an ethanol aqueous solution as a cathode raw material, and based on the mass of the cathode raw material, the mass content of ethanol is x%; wherein the value range of x is determined by a method comprising the following steps: step 210, recording the solubility of lithium hydroxide in the ethanol aqueous solution at T°C as yg / 100mL, and determining a regression model y=f(x) of y and x; step 220, recording the current density of the electrolysis treatment at T°C as z mA / cm 2 , determine the regression model z=j(x) of z and x; step 230, based on the solubility of lithium hydroxide and the current density, determine the value range of x; step 300, raise the temperature to T℃ to make the anode raw material in a molten state, electrolyze the anode raw material and the cathode raw material, and precipitate lithium hydroxide hydrate at the cathode.

[0006] The present invention uses a molten lithium source as the anode raw material and an ethanol aqueous solution as the cathode raw material. During the electrolysis process, under the action of an external electric field, the chloride ions in the anode raw material lose electrons on the inert electrode to generate Cl2, and at the same time, the lithium ions in the anode raw material move to the cathode side; the water molecules obtain electrons from the cathode inert electrode and are reduced to H2, leaving OH - Combined with lithium ions and water molecules to form high-purity lithium hydroxide hydrate. This application constructs the mass content of ethanol in ethanol aqueous solution and the solubility of lithium hydroxide yg / 100mL, as well as the electrolysis treatment current density z mA / cm 2 The regression model is used to determine and regulate the mass content of ethanol in the cathode solution within a certain range of proportions, so that the cathode system exhibits a lower solubility for lithium hydroxide and improves the electrolysis efficiency, thereby increasing the solid precipitation amount and precipitation efficiency of lithium hydroxide. Subsequently, high-purity lithium hydroxide monohydrate can be obtained by simple treatments such as filtration and low-temperature drying, without the need for evaporation and concentration steps in traditional electrolysis processes, thereby greatly saving time and energy costs and improving production efficiency. In addition, this method does not require high raw material purity. Using a lower-purity lithium source as an anode raw material can also prepare high-purity lithium hydroxide with high economic value, omitting the raw material purification process, and has the advantages of simple process and high efficiency.

[0007] In this application, the reaction equation during the electrolytic treatment is:

[0008] Overall reaction: 2LiCl + 4H2O = 2LiOH·H2O↓ + H2↑ + Cl2↑;

[0009] Anode: 2Cl － -2e － =Cl2↑;

[0010] Cathode: 2Li + +4H2O+2e － =2LiOH·H2O↓+H2↑.

[0011] In some embodiments, in step 210, determining the regression model y=f(x) of y and x includes the following steps:

[0012] Step 211, obtaining m ethanol aqueous solutions with different ethanol mass contents;

[0013] Step 212: Test the solubility of lithium hydroxide in the ethanol aqueous solution in step 211 at T°C to obtain regression data of xy, which are recorded in ascending order according to the x value as (x 11 ,y1)、(x 12 ,y2),…,(x m ,y m );

[0014] Step 213, performing fitting processing on the regression data of xy in step 212, and determining the regression model y=f(x) of y and x; and / or,

[0015] In step 220, the regression model z=j(x) of z and x is determined, including the following steps:

[0016] Step 221, obtaining n ethanol aqueous solutions with different ethanol mass contents;

[0017] Step 222: electrolyze the ethanol aqueous solution in step 221 at T°C, detect the current density, and obtain the regression data of xz, which are arranged in ascending order according to the x value as (x 21 、z1)、(x 22 ,z2),…,(x n 、z n );

[0018] Step 223: Perform fitting processing on the regression data of xz in step 222 to determine the regression model z=j(x) of z and x.

[0019] The present application uses the above method to construct regression models of the solubility of lithium hydroxide in ethanol aqueous solution and the ethanol concentration, as well as the regression model of the current density in the electrolysis treatment and the ethanol concentration, respectively, so as to determine the appropriate ethanol mass content in the ethanol aqueous 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 too dissolved and unable to be precipitated from the cathode solution in time, thereby improving the production efficiency of the preparation process.

[0020] 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.

[0021] In some embodiments, when the ethanol mass content of the ethanol aqueous solution is 95.6%, ethanol and water are in an azeotropic state with a boiling point of about 78.2°C. At this ratio, ethanol and water evaporate and reflux together, and there is no need to consider the different volatilization rates of ethanol and water. The process can be further simplified, and the stability of the ethanol mass content in the ethanol aqueous solution during the electrolysis process is maintained, which is beneficial to improving the electrolysis efficiency and precipitation rate.

[0022] 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, which can be prepared separately or from the same batch of ethanol aqueous solutions. In some embodiments, when the same batch of ethanol aqueous solutions is used, it can be understood that m=n, x=n. 11 =x 21 , …, x m =x n .

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] In some embodiments, the lithium source includes a lithium salt; the lithium salt includes lithium chloride; based on the mass of the lithium source, the mass content of lithium chloride is m%, 20≤m≤100. Compared with the traditional electrolysis process, the preparation method provided in the present application can adapt to lithium source raw materials with lower purity, thereby simplifying the impurity removal process of the raw materials, reducing the cost of the raw materials, and improving the economic value of the preparation process. In addition, when the preparation method of the present application uses a high-purity lithium source raw material, it is beneficial to improve the lithium ion migration rate, thereby promoting the improvement of production efficiency. Exemplarily, the value of m can be 20, 31, 36, 40, 48, 55, 62, 66, 71, 80, 84, 90, 96, 99 or a value within the range composed of any two of them.

[0030] In some specific embodiments, 20≤m≤90. Compared with the traditional electrolysis process, the lithium hydroxide obtained by the present application using the above-mentioned lower purity lithium source raw material has higher purity.

[0031] In some embodiments, the flux includes at least one of aluminum chloride (AlCl3) and lithium aluminum chloride (LiAlCl4); the mass ratio of the lithium source to the flux is (0.8-1.5): 1, preferably (1-1.3): 1. The present application regulates the mass ratio of the lithium source to the flux to meet the above range, which can change the electronic structure or lattice structure of the lithium source, reduce the melting point of the lithium salt, promote the lithium source to quickly reach a molten state, and improve production efficiency.

[0032] In some embodiments, a lithium ion solid electrolyte is arranged between the anode material and the cathode material of the electrolysis device. The lithium ion solid electrolyte only allows lithium ions to pass through but does not allow other atoms to pass through. Its materials include but are not limited to lithium lanthanum zirconium tantalum oxide (LLZTO), lithium aluminum titanium phosphate (LATP), lithium lanthanum titanium oxide (LLTO), etc. The present application arranges a lithium ion solid electrolyte between the anode and the cathode of the electrolysis device, and utilizes the lithium ion solid electrolyte to only allow lithium ions to pass through. + Through the property that other impurity ions cannot pass through, rapid extraction of lithium elements is achieved, and the purity requirements of the lithium source are low.

[0033] In some embodiments, 150°C≤T≤250°C, for example, T can be selected from 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or any two thereof. At the above temperature, the anode raw material can be in a molten state, and the ionic conductivity of the lithium ion solid electrolyte is relatively high compared to room temperature. For example, the ionic conductivity of the LLZTO electrolyte at 200°C is 6.8×10 -2 S / cm. Therefore, regulating the electrolysis temperature to the above temperature can also help to increase the lithium ion transfer rate and thus improve production efficiency.

[0034] Optionally, the electrolysis voltage of the electrolysis treatment is between 1.5V and 4V.

[0035] In some specific embodiments, in order to avoid volatilization of ethanol and water during the electrolysis process, the cathode is provided with a reflux device, and a large electrolysis current density is maintained by adjusting the ethanol mass content of the ethanol-water solution.

[0036] In some embodiments, step 300 further includes: in the electrolysis treatment of step 300, adding supplementary water to the cathode raw material, and controlling the mass content of ethanol in the cathode raw material to meet the value range of x in step 200. The higher the mass content of ethanol in the ethanol aqueous solution, the smaller the electrolysis current and the smaller the solubility of lithium hydroxide. By adjusting the ratio of ethanol and water, faster solid precipitation of lithium hydroxide and a larger electrolysis current can be achieved. During the electrolysis process, water will be gradually consumed by reaction, and the concentration of lithium ions at the anode will gradually decrease, and the electrolysis current will gradually decrease. At this time, by replenishing water to the cathode in an appropriate amount, that is, by adjusting the ratio of ethanol and water, the current reduction caused by the above two reasons can be offset. Therefore, before replenishing the anode, the electrolysis device can maintain a larger current density by replenishing water to the cathode, thereby improving the electrolysis efficiency and precipitation rate.

[0037] 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 raw material is monitored, and the quality of the supplementary water is determined based on the volume reduction of the cathode raw material; 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. Among them, 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.

[0038] In some embodiments, obtaining the mass of water consumed in the electrolytic treatment of step 300 includes: detecting the electrolytic capacity Q Ah of the electrolytic treatment of step 300, and determining the mass of water consumed based on H=Q / 0.74. 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 value. By monitoring the electrolytic capacity through the electrolytic treatment equipment, the mass of water consumption can be conveniently 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 the electrolytic treatment and the product precipitation efficiency.

[0039] 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.

[0040] In some embodiments, step 300 further includes: drying the lithium hydroxide hydrate at ≥100° C. to obtain lithium hydroxide.

[0041] The preparation method of lithium hydroxide provided in the present application has at least the following beneficial effects compared with the traditional process:

[0042] A. The preparation method provided in the present application uses a molten lithium source as the anode raw material, has low requirements on the purity of the raw material, and can extract lithium from low-purity raw materials to produce high-purity lithium hydroxide, eliminating the need for raw material purification processes, which is conducive to simplifying the process and reducing time and raw material costs.

[0043] B. The present application regulates the mass content of ethanol in the cathode raw material so that the cathode system exhibits a lower solubility for lithium hydroxide to achieve the maximum and rapid solid precipitation of lithium hydroxide, and subsequent filtration and drying can obtain high-purity lithium hydroxide monohydrate without the need for evaporation and concentration. At the same time, regulating the mass content of ethanol in the cathode raw material can also maintain a larger current density of the electrolysis device, thereby taking into account the improvement of the electrolysis treatment efficiency and the precipitation rate of lithium hydroxide, so that lithium hydroxide hydrates are continuously saturated and precipitated in the cathode chamber to obtain a relatively pure lithium hydroxide product.

[0044] C. The lithium hydroxide monohydrate prepared by the method provided in the present application has a high purity and meets the national standard requirements for battery-grade lithium hydroxide monohydrate, without the need for further purification of the prepared lithium hydroxide monohydrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the electrolysis device used in the preparation method of lithium hydroxide provided in the specific embodiment of the present application; wherein, 1-lithium ion solid electrolyte; 2-anode inert electrode; 3-anode raw material; 4-chlorine gas outlet pipe; 5-anode feed port; 6-cathode water supply port; 7-cathode reflux device; 8-hydrogen gas outlet pipe; 9-cathode raw material; 10-cathode inert electrode; 11-lithium hydroxide monohydrate solid;

[0046] Figure 2 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 of the present application are: DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] Example 1

[0050] This embodiment provides a method for preparing lithium hydroxide, comprising the following steps:

[0051] Step 100, using 50g of lithium chloride-containing crude salt as a lithium source, wherein the content of LiCl is 30wt%. Using AlCl3 as a flux, the lithium source and the flux are mixed in a mass ratio of 1.2:1 to obtain a mixed system; using the mixed system as an anode raw material;

[0052] Step 200: 100 mL of ethanol aqueous solution is used as a cathode solution. Based on the mass of the cathode solution, the mass content of ethanol is x%. The value range of x is determined by a method comprising the following steps:

[0053] Step 210, record the solubility of lithium hydroxide as yg / 100mL, and determine the regression model y=f(x) of y and x, including:

[0054] Step 211, preparing ethanol aqueous solutions with ethanol contents of 0%, 20%, 40%, 60%, 80%, 95%, and 100% respectively;

[0055] Step 212: Test the solubility of lithium hydroxide in the ethanol aqueous solution in step 211 at 200° C. 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;

[0056] Step 213: Fit the regression data of xy in step 212 to determine the regression model of y and x: y=f(x)=14.144-0.223x+0.000898x 2 ;

[0057] 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:

[0058] Step 221, using the ethanol aqueous solution prepared in step 211;

[0059] Step 222: electrolyze the ethanol aqueous solution in step 221 in batches. The schematic diagram of the electrolysis device is as follows: Figure 1 As shown. The lithium-ion solid electrolyte 1 uses an LLZTO ceramic electrolyte sheet with a diameter of 50mm and a thickness of 1.5mm; the lithium source LiCl content of the anode raw material 3 is 30wt%, and the mass ratio of the lithium source to the flux AlCl3 is 1.2:1. The temperature is raised to 200°C to make the lithium source in a molten state. The ethanol aqueous solution prepared in step 211 is used as the cathode raw material 9 according to different batches, and the electrolysis temperature is 200°C and the electrolysis is performed at a constant voltage of 3.5V. The anode chamber uses a graphite electrode as the anode inert electrode 2. During the electrolysis process, the chloride ions lose electrons on the graphite electrode 2 to generate chlorine gas and are discharged through the chlorine gas outlet pipe 4, while the lithium ions enter the cathode chamber through the LLZTO ceramic electrolyte sheet driven by an external power supply. The cathode chamber uses a stainless steel electrode as the cathode inert electrode 10, and the lithium ions react with water molecules to form 2Li + +4H2O+2e - =2LiOH·H2O+H2, generating lithium hydroxide monohydrate and hydrogen, the generated hydrogen is discharged through the hydrogen outlet pipe 8, and lithium hydroxide monohydrate 11 is precipitated in the cathode chamber. During the electrolysis process, water is slowly and continuously added to the cathode chamber through the cathode water supply port 6 to maintain a constant ratio of ethanol and water. During the electrolysis process, the current density is detected and the regression data of xz is obtained, which is recorded in order from small to large x values ​​as (x 21 、z1)、(x 22 ,z2),…,(x n 、z n ), as shown in Table 1 below;

[0060] Table 1

[0061] Ethanol mass content x (%) 0 20 40 60 80 95 100 <![CDATA[Current density (mA / cm 2 )]]> 112 108 95 73 66 48 30 Solubility (g / 100mL) 14.5 9.0 7.5 4.2 1.5 1.2 0.9

[0062] Step 223: Fit the regression data of xz in step 222 to determine the regression model of z and x: z=j(x)=112.625-0.2323x-0.00531x 2 The regression model of y and x is y = f(x) and the regression model of z and x is z = j(x). Figure 2 shown.

[0063] 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: 44≤x≤97.

[0064] Step 300, using the electrolysis device in step 222 to electrolyze the anode raw material and the cathode raw material, the initial mass content of ethanol in the ethanol aqueous solution is 80%, the electrolysis temperature is 200°C, and the constant voltage electrolysis is 3.5V. During the electrolysis treatment, the electrolysis capacity Q Ah of the electrolysis device is detected, and the mass H g 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 44≤x≤97. After 1.5 hours, lithium hydroxide precipitation is observed in the cathode chamber. After 11 hours of electrolysis treatment, the lithium hydroxide hydrate crystals are taken out by the suction filtration device, and 7.3g of lithium hydroxide powder is obtained after drying. The purity of lithium hydroxide is detected by ICP analysis and testing to be 99.2%, and other impurity requirements meet the national standards.

[0065] 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: 60≤x≤80.

[0066] Step 300, 1.6 hours later, lithium hydroxide was observed to precipitate in the cathode chamber, and after 7.5 hours of electrolysis, the obtained lithium hydroxide hydrate crystals were dried to obtain 7.8g of lithium hydroxide powder. The purity of lithium hydroxide was 99.3% through analytical testing, and other impurity requirements met the national standards.

[0067] 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≤7, z≥50, the value range of x is determined: 38≤x≤88.

[0068] Step 300, 4.7 hours later, lithium hydroxide was observed to precipitate in the cathode chamber, and after 11 hours of electrolysis, the obtained lithium hydroxide hydrate crystals were dried to obtain 3.5 g of lithium hydroxide powder. The purity of lithium hydroxide was 99.3% through analytical testing, and other impurity requirements met the national standards.

[0069] 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.

[0070] 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 a lithium source; mixing the lithium source with a flux to obtain a mixed system; and using the mixed system as an anode raw material; Step 200, using ethanol aqueous solution as a cathode raw material, based on the mass of the cathode raw material, the mass content of ethanol is x%; The value range of x is determined by a method comprising the following steps: Step 210, record the solubility of lithium hydroxide in ethanol aqueous solution at T°C as yg / 100mL, and determine the regression model y=f(x) of y and x; Step 220: record the current density of the electrolysis treatment at T°C 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, raising the temperature to T°C to make the anode raw material in a molten state, electrolyzing the anode raw material and the cathode raw material 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 at T°C in step 211 to obtain regression data of xy, which are recorded 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 xy in step 212 to determine the 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 at T°C, detect the current density, and obtain regression data of xz, 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 xz 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 lithium source includes a lithium salt; the lithium salt includes lithium chloride; based on the mass of the lithium source, the mass content of the lithium chloride is m%, 20≤m≤100.

8. The preparation method according to claim 7, characterized in that: The flux includes at least one of aluminum chloride and lithium aluminum chloride; the mass ratio of the lithium source to the flux is (0.8-1.5):1, preferably (1-1.3):

1.

9. 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 raw material, and controlling the mass content of the ethanol in the cathode raw material to meet the value range of x in the step 200 .

10. The preparation method according to claim 9, 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 raw material is monitored, and the quality of the supplementary water is determined based on the volume reduction of the cathode raw material; 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.

11. The preparation method according to claim 10, 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.

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