A method and apparatus for extracting lithium from solution using bipolar electrodes

Abstract

This invention belongs to the field of electrochemical lithium extraction, and relates to an electrochemical lithium extraction method and apparatus using bipolar electrodes. The apparatus uses electrodes coated with lithium-rich and lithium-deficient electroactive materials as end plates; several bipolar electrodes, each coated with lithium-rich and lithium-deficient electroactive materials on both sides, are used as separators in the middle, with the side facing the lithium-rich end plate being the lithium-deficient electroactive material and the opposite side being the lithium-rich end plate; the electrodes are further separated by an anion exchange membrane. The lithium extraction solution is introduced into the lithium-deficient side, and the supporting electrolyte is introduced into the lithium-rich side. The end plates are connected to the positive and negative terminals of a power supply. Due to electrostatic induction, the two sides of the bipolar electrodes generate different polarities, achieving the purpose of delithiation of the lithium-rich electroactive material and lithium extraction of the lithium-deficient electroactive material. This apparatus uses conventional voltage, has a small total current, simplifies power supply, and significantly reduces busbar consumption; the process is easy to control and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction metallurgy, specifically relating to an electrochemical lithium extraction method and apparatus using bipolar electrodes. Background Technology

[0002] Lithium is an important new energy metal. With the development of the new energy industry, global demand for lithium has surged. Currently, about 70% of the world's lithium is found in salt lake brines. How to extract lithium from salt lake brines in a green and economical way is receiving increasing attention.

[0003] In recent years, lithium extraction methods based on electrochemical deintercalation and intercalation have attracted widespread attention. For example, Chinese patent CN102382984A discloses a method and apparatus for separating and enriching lithium from magnesium in salt lake brine. This method uses an anion exchange membrane to divide an electrodialysis device into a lithium salt chamber and a brine chamber. The brine chamber is filled with salt lake brine, and the lithium salt chamber is filled with magnesium-free brine. 2+ Supporting the electrolyte solution, a conductive substrate coated with an ion sieve is placed in the brine chamber as the cathode; a conductive substrate coated with a lithium-intercalated ion sieve is placed in the lithium salt chamber as the anode; under the drive of an external potential, Li in the brine... + Lithium-intercalated ion sieves are formed by embedding lithium into ion sieves. The lithium-intercalated ion sieves in the lithium salt chamber will... + It is released into the electrolyte and reverts to an ion sieve.

[0004] This method has advantages such as a short process and simple operation, but it also has problems such as complicated device assembly, difficult maintenance, complex power supply system, and difficult process control. Summary of the Invention

[0005] The inventors continued their research and discovered that to extract more lithium at once, multiple anodes and cathodes need to be circulated and alternately arranged within an electrolyzer, with each anode and cathode connected to the positive and negative terminals of an external power source, thus forming an industrial-scale membrane stack electrolyzer. This operating method has a very low cell voltage (0.5–2V), but a very high total operating current for the membrane stack.

[0006] When a large current flows through the conductive busbar of the electrolytic cell, it causes a gradual decrease in voltage; the cell voltage decreases the further away from the power supply terminals (positive and negative). Simple calculations show that, taking the LiFePO4 / FePO4 electrode pair as an example, assuming the working area of ​​the electrode plate is 1m²... 2 A single pair of positive and negative electrodes generates 20 amperes of current; 50 pairs of electrodes would generate 2000 amperes of current. If a cross-sectional area of ​​200 mm² is used... 2 (Thickness × Width: 5 × 40 mm) 2 A 1-meter-long copper busbar was used as the conductor (copper resistivity is 0.072 Ω·mm). 2 / m), the voltage difference across the copper busbar reaches 0.72 volts (2000 × 0.072 / 200V = 0.72 volts). However, the cell voltage for lithium extraction using the LiFePO4 / FePO4 electrode is only around 0.2–0.3 volts. If the cell voltage of the last pair of positive and negative electrodes is to be controlled at 0.2–0.3 volts, then the cell voltage of the electrode closest to the power supply connection must reach 0.9–1 volts, far exceeding the 0.2–0.3 volts required for lithium extraction selectivity.

[0007] To ensure the selectivity of the electrode material for lithium, the cell voltage across each pair of positive and negative working electrodes must be strictly limited in actual operation. Therefore, the traditional method leads to differences in reaction performance on electrode plates at different locations within the electrolyzer, resulting in unstable electrolyzer operation, poor lithium selectivity, and reduced reaction rate and cycle life.

[0008] While increasing the amount of busbars can reduce busbar voltage drop to some extent, the investment cost of busbars also increases dramatically. Furthermore, the low-voltage, high-current operating conditions place extremely high demands on the power supply system, resulting in significant energy consumption not only on the conductive busbars but also high reactive power consumption within the power supply system itself. Additionally, the small anode-cathode distance within the electrolytic cell (industrial electrolytic cells often require a distance of around 5mm) makes connecting each electrode to the busbar extremely cumbersome, hindering industrial assembly and production.

[0009] Based on this, the present invention provides an electrochemical lithium extraction method and apparatus using bipolar electrodes, which enables the electrolytic cell to operate in a high-voltage-low-current mode, simplifying the power supply system, significantly reducing the amount of conductive busbars, and making process control extremely simple.

[0010] In a first aspect, the present invention provides an apparatus for extracting lithium from a solution using a bipolar electrode, comprising a tank, an end electrode, at least one conductive separator, and an anion exchange membrane having one more conductive separator than the number of conductive separators.

[0011] The end electrodes include a first end electrode for connecting to a first electrode and a second end electrode for connecting to a second electrode, respectively disposed at both ends of the tank; the surface of the first end electrode facing the second end electrode is coated with a lithium-deficient electroactive material, and the surface of the second end electrode facing the first end electrode is coated with a lithium-rich electroactive material.

[0012] A conductive separator is disposed inside the tank, physically dividing the tank into two or more independent chambers, and located between the first end electrode and the second end electrode; the surface of the conductive separator facing the first end electrode is coated with a lithium-rich electroactive material, and the surface of the conductive separator facing the second end electrode is coated with a lithium-deficient electroactive material.

[0013] An anion exchange membrane is installed in each independent chamber, dividing each independent chamber into two working areas. The side with the lithium-deficient electroactive material is used to introduce the lithium extraction raw material solution, which is called the first working area, and the side with the lithium-rich electroactive material is used to introduce the supporting electrolyte, which is called the second working area.

[0014] Lithium-rich and lithium-deficient electroactive materials are coated onto both sides of a separator material that is electronically conductive but ionicly non-conductive, forming bipolar electrodes. Several of these coated bipolar electrodes are inserted into an electrolytic cell, with a first end electrode and a second end electrode placed at each end of the cell, and connected to the positive and negative terminals of a power source, respectively. When the power is turned on, the bipolar electrodes generate an induced electric field, producing a positive charge on the lithium-rich electroactive material coating side, causing the transition metal in the lithium-rich electroactive material to oxidize and delithiate. Simultaneously, a negative charge is generated on the lithium-deficient electroactive material coating layer, causing the transition metal in the lithium-deficient electroactive material to be reduced, thus embedding lithium from the lithium-containing solution into the material.

[0015] Since only the two ends of the electrolytic cell are connected to the positive and negative terminals of the power supply, the bipolar electrodes operate by inducing different surface charges or induced electric fields on both sides of the electrode through an induced electric field. Therefore, the current passing through each piece of under-lithium electroactive material is consistent, and the reaction progress and degree of the entire electrode are synchronized, making the process extremely easy to control. In addition, the electrolytic cell operates in a conventional voltage-low current mode, simplifying the power supply system, significantly reducing the number of conductive busbars, and making voltage wiring extremely simple.

[0016] Preferably, the first end electrode, the second end electrode, the conductive separator, and the anion exchange membrane are arranged in parallel to each other.

[0017] Preferably, the spacing between the multiple conductive partitions is the same.

[0018] Furthermore, anion exchange membranes with different impurity ion rejection capabilities can be selected based on production needs and price.

[0019] Furthermore, depending on the viscosity of the lithium-containing solution and the water inlet rate, water distribution nets or baffles can be set on both sides of the anion exchange membrane to enhance the uniform distribution of the solution in the cavity.

[0020] Furthermore, the tank is equipped with slots for installing conductive partitions.

[0021] Furthermore, the lithium-rich electroactive material is one or a mixture of several of LiFePO4, LiMn2O4, LiMeO2, and their doped derivatives, wherein Me is one or more of Ni, Co, and Mn. The aforementioned electrode active materials possess characteristics such as lithium-ion transport and migration channels, redox reaction sites, and chemically stable crystal structures, and should have a stable electrochemical operating window in aqueous solution. By controlling the redox potential on the electrode surface, lithium ions can be selectively inserted and extracted into the material.

[0022] Furthermore, the lithium-deficient electroactive material is prepared by oxidizing the lithium-rich electroactive material to remove some or all of the lithium.

[0023] Specifically, conventional chemical oxidation and electrochemical oxidation methods can be used to oxidize low-valence transition metals in LiFePO4, LiMn2O4, and LiMeO2 (Me = one or more of Ni, Co, and Mn) to high-valence metals. At this point, Li... + Ions are extracted from the crystal lattice, forming a lithium-deficient material. During this process, the original crystal structure of LiFePO4, LiMn2O4, and LiMeO2 (Me = one or more of Ni, Co, and Mn) remains basically unchanged, exhibiting the characteristic of reduction-selective lithium intercalation.

[0024] Furthermore, the conductive separator is made of dense carbon paper, dense carbon fiber sintered cloth, graphite plate, corrosion-resistant intermetallic compound plate, ruthenium-coated titanium sheet, gold, platinum group metals and / or their alloy plates, or titanium, zirconium, hafnium, tantalum, niobium and / or their alloy plates.

[0025] Because the conductive separator exhibits different polarities (positive and negative) on both sides during the lithium extraction process in this patented method, the separator is required to not only be electronically conductive, but also resistant to corrosion from electro-oxidation and electrochemical reduction.

[0026] Secondly, the present invention also provides a method for extracting lithium from solution using a bipolar electrode, comprising the following steps:

[0027] Step 1: Take the above-mentioned bipolar electrode apparatus for extracting lithium from solution, introduce the lithium extraction raw material solution into the first working area, and introduce the supporting electrolyte into the second working area;

[0028] Step 2: Connect the first end electrode to the negative terminal of the power supply, connect the second end electrode to the negative terminal of the power supply, turn on the power supply, and current flows in from the second end electrode and is output from the first end electrode. At the same time, the following changes occur:

[0029] In the first working area, lithium ions in the raw material solution are embedded in the adjacent lithium-deficient electroactive material, and the lithium-deficient electroactive material gradually becomes lithium-rich electroactive material.

[0030] In the second working area, lithium ions in the lithium-rich electroactive material are released into the supporting electrolyte, and the lithium-rich electroactive material gradually becomes a lithium-deficient electroactive material.

[0031] Step 3: The reaction is terminated, the power is disconnected, and the raw material solution is converted into lithium-deficient liquid, the supporting electrolyte is converted into lithium-rich liquid, the lithium-deficient liquid is discharged, and the lithium-rich liquid is collected.

[0032] Step 4: Clean the tank, connect the first end electrode to the positive terminal of the power supply, and connect the second end electrode to the negative terminal of the power supply. Repeat steps 1-3.

[0033] Furthermore, the lithium-rich solution from the previous cycle can be used as the supporting electrolyte for the next cycle to continue lithium extraction and increase the lithium concentration in the solution; the lithium-poor solution from the previous cycle can be used as the lithium extraction feed solution for the next cycle to improve the lithium recovery rate.

[0034] Furthermore, the lithium extraction raw material solution can be any one or a mixture of several of the following: salt lake brine, brine obtained from any stage of brine treatment, old brine, underground brine, oilfield brine, lithium-containing solution obtained from ore decomposition and secondary resource recovery, and lithium precipitation mother liquor.

[0035] Furthermore, due to the differences in the lithium insertion / extraction potentials of the electrode active materials used (LiFePO4 approximately 0.4–0.6 V vs. SHE, LiMn2O4 approximately 0.7–1.0 V vs. SHE, and ternary material LiMeO2 0.7–1.0 V vs. SHE), the voltage required for lithium extraction varies depending on the coating materials on both sides of the bipolar electrode. Moreover, the required voltage can be adjusted within a certain range depending on the lithium concentration of the lithium-containing solution. Understandably, for low lithium concentration and high impurity content, a slightly lower cell voltage can be used to ensure material selectivity; for high lithium concentration and low impurity content lithium solutions, a higher cell voltage can be used to increase the lithium extraction rate while ensuring lithium extraction selectivity.

[0036] Specifically, the power supply voltage is (0.1-1.0)×n volts, where n is the number of independent cavities.

[0037] Preferably, when the electroactive material is LiFePO4 or its derivatives, the applied voltage is (0.1-0.5) × n volts;

[0038] When the electroactive material is LiMn2O4 or its derivatives, the applied voltage is (0.3-0.6) × n volts.

[0039] When the electroactive material is LiMeO2 or its derivative, the applied voltage is (0.4-0.8) × n volts;

[0040] When the electroactive material is LiMn2O4 and LiFePO4 and their derivatives, the applied voltage is (0.3-0.7) × n volts;

[0041] When the electroactive material is LiMn2O4 and LiMeO2 and their derivatives, the applied voltage is (0.4-0.9) × n volts;

[0042] When the electroactive material is LiFePO4 and LiMeO2 and their derivatives, the applied voltage is (0.4-1.0)×n volts.

[0043] The beneficial effects of this invention are as follows:

[0044] 1. By connecting the electrodes at both ends to the power supply, the induced electric field generated drives the bipolar electrodes inside the entire electrolytic cell to work, realizing the synchronous and simultaneous reaction of electroactive materials inside the electrolytic cell, and improving the stability and cycle performance of the electrode materials in the electrolytic cell.

[0045] 2. The current in the electrolytic cell passes through each bipolar electrode in sequence, and the current is small, which reduces the control precision and manufacturing requirements of the power supply, resulting in low reactive power consumption and low cost.

[0046] 3. It eliminates the need for a large number of conductive copper busbars required for electrode connections inside the electrolytic cell, fundamentally solving the cumbersome operation of connecting each electrode to the positive and negative terminals of the power supply in the traditional way.

[0047] 4. Lithium desorption and adsorption occur simultaneously on both sides of the adsorption electrode, enabling extraction and enrichment to proceed in a synchronized manner with high efficiency. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a simplified schematic diagram of the apparatus for extracting lithium from solution using bipolar electrodes provided by the present invention;

[0050] Figure 2A It is Figure 1 A simplified schematic diagram of the first structure of the device for series integration of the middle device;

[0051] Figure 2B It is Figure 1 A second simplified structural diagram of a device for series integration of the two devices;

[0052] Figure 3 This refers to the change in lithium concentration over time in the lithium-rich solution under different cell voltages in Example 1.

[0053] Figure 4 The change of lithium concentration in salt lake brine over time under different tank voltages in Example 1;

[0054] Figure 5 The adsorption capacity and cycling performance of the material under different cell voltages in Example 1;

[0055] Figure 6 The changes in lithium concentration in the brine over time during lithium extraction in Examples 2-6;

[0056] Figure 7 Examples 2-6 support changes in lithium concentration during electrolyte recycling;

[0057] Figure 8 Examples 2-6: Adsorption capacity changes with cycling;

[0058] Figure 9 Example 7: Changes in lithium concentration in brine and supporting electrolyte during lithium extraction process

[0059] Figure 10 Example 7 supports changes in lithium concentration during electrolyte recycling.

[0060] Figure 11 The lithium concentration in the supporting electrolyte changes over time during the lithium extraction process in Comparative Examples 1–3;

[0061] Figure 12 The changes in lithium concentration in the brine over time during the lithium extraction process of Comparative Examples 1-3.

[0062] Icons: 1-Tank, 2-End electrode, 3-Lithium-deficient active material, 4-Lithium-rich active material, 5-Anion exchange membrane, 6-Power supply, 7-Conductive separator. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0064] Figure 1 This is a simplified schematic diagram of the apparatus for extracting lithium from solution using bipolar electrodes provided by the present invention; Figure 2A-2B It is Figure 1 A simplified structural diagram of the front view of the device in which the devices are integrated in series.

[0065] Please see Figure 1 , Figure 2A and Figure 2B The device includes a tank 1, an end electrode 2, at least one conductive separator 7, and an anion exchange membrane 5, which is one more than the number of conductive separators 7.

[0066] The end electrode 2 includes a first end electrode for connecting to the first electrode and a second end electrode for connecting to the second electrode, respectively disposed at both ends of the tank body 1; the surface of the first end electrode facing the second end electrode is coated with a lithium-deficient electroactive material 3, and the surface of the second end electrode facing the first end electrode is coated with a lithium-rich electroactive material 4.

[0067] The conductive separator 7 is disposed inside the tank 1, physically dividing the tank 1 into two or more independent chambers, and is located between the first end electrode and the second end electrode; the surface of the conductive separator 7 facing the first end electrode is coated with a lithium-rich electroactive material 4, and the surface of the conductive separator 7 facing the second end electrode is coated with a lithium-deficient electroactive material 3.

[0068] An anion exchange membrane 5 is installed in each independent chamber, dividing each independent chamber into two working areas. The side with the lithium-deficient electroactive material 3 is used to introduce the lithium extraction raw material solution, which is called the first working area. The side with the lithium-rich electroactive material 4 is used to introduce the supporting electrolyte, which is called the second working area.

[0069] like Figure 1 As shown, there are six conductive separators 7 and seven anion exchange membranes 5. The conductive separators 7 divide the tank 1 into seven independent chambers, and the seven anion exchange membranes 5 are disposed in the seven independent chambers. The material of the conductive separators 7 can be the same as or different from the material of the first end electrode and the second end electrode; this application does not impose any limitation. It should be noted that the number of conductive separators 7 is not limited to six and can be set according to specific lithium extraction requirements.

[0070] Figure 2A It is Figure 1 A simplified structural diagram of a device that integrates multiple devices in series, whereby when the number of bipolar electrodes in a single electrolytic cell is too large, the device can be controlled in modules according to the power output. Figure 2B It is Figure 1 The second simplified structural diagram shows a device for series integration of multiple electrolytic cells, where the power supply systems of these cells are connected in series. Please refer to... Figure 2A and Figure 2B The apparatus provided in this application can also be integrated in series to extract lithium from more lithium-producing solutions. Furthermore, the solution transport within the electrolyzer can be configured with independent water channels connected in series or parallel as needed.

[0071] The present invention will be further described in detail below with reference to the embodiments.

[0072] Example 1

[0073] (1) The lithium-rich electroactive material lithium iron phosphate was added to a 0.1 mol / L sodium persulfate solution, and the molar ratio of lithium iron phosphate to sodium persulfate was controlled to be 2:1. After reacting at room temperature for 6 hours, the mixture was filtered, washed and dried to obtain pre-delithiated lithium iron phosphate.

[0074] (2) Lithium iron phosphate, acetylene black, and PVDF are mixed in an 8:1:1 ratio in N-methylpyrrolidone solvent and stirred thoroughly for 8 hours using a double planetary mixer to obtain lithium iron phosphate slurry; the lithium-deficient iron phosphate obtained in (1) is mixed in an 8:1:1 ratio in N-methylpyrrolidone solvent and stirred thoroughly for 8 hours using a double planetary mixer to obtain iron phosphate slurry.

[0075] (3) Coat the lithium iron phosphate slurry and iron phosphate slurry from (2) onto two 60×60cm sheets respectively. 2 On the titanium sheet (coating area is the middle 50×50cm) 2 Partially, the lithium iron phosphate slurry and iron phosphate slurry in (2) were coated onto a 60×60cm plate. 2 The titanium sheet has two sides (the coated area is the middle 50×50cm). 2 Partial), single-sided coating density is 150 mg / cm³ 2 The coated electrodes were then vacuum dried at 90°C for 12 hours to obtain two end electrodes and a bipolar electrode.

[0076] (4) Using the above-mentioned 2 end electrodes, 9 bipolar plates, and 10 anion exchange membranes, according to... Figure 1 The lithium extraction electrolytic cell is assembled as shown, wherein the end electrode coated with lithium iron phosphate material is connected to the positive terminal of the power supply, and the end electrode coated with iron phosphate material is connected to the negative terminal of the power supply.

[0077] (5) 300L of brine (composition shown in Table 1) was continuously circulated into the first working area (i.e., the electrode side coated with iron phosphate material), and 20L of 5g / L NaCl was added as the supporting electrolyte to the second working area (i.e., the electrode side coated with lithium iron phosphate material). Lithium extraction experiments were conducted with applied voltages of 1.0V, 3.0V, and 4.5V and a solution temperature of approximately 5℃. The composition of the brine in Example 1 is shown in Table 1. The lithium extraction process was terminated when the current decreased to 10% of the initial current. The changes in brine concentration during the lithium extraction process are shown in Table 2 and... Figure 3 As shown, the lithium concentration change in lithium-rich liquid is as follows: Figure 4 As shown, the cycle performance is as follows Figure 5 As shown.

[0078] As shown in Table 2, when the cell voltage is 1.0V, 3.0V, and 4.5V, the lithium concentration in the brine can be reduced from the initial 0.41g / L to 0.09g / L, 0.05g / L, and 0.1g / L, respectively. The lithium extraction rates can reach 78%, 87.8%, and 75.6%, respectively, and the lithium concentrations in the lithium-rich solutions can reach 4.74g / L, 5.34g / L, and 4.63g / L, respectively. Not only is the lithium concentration increased tenfold, but the resulting lithium-rich solutions also have low levels of other impurities, significantly simplifying subsequent purification processes.

[0079] from Figure 3-5 It can be seen that the time required for the lithium extraction process and the adsorption capacity of the material vary slightly depending on the cell voltage. A higher cell voltage can increase the lithium extraction rate, but the adsorption capacity will decrease slightly. When the cell voltage is 1.0V, 3.0V, and 4.5V, the average current of the process is 5.2A, 8.1A, and 8.9A, respectively, and the adsorption capacity is approximately 25mg(Li) / g, 28.5mg(Li) / g, and 24.5mg(Li) / g, respectively, and the system exhibits excellent cycling performance.

[0080] Table 1. Main ionic components of salt lake brine (g / L)

[0081] element Li Na Mg K B <![CDATA[SO4 2- ]]> Salt lake brine 0.41 62.10 52.30 3.46 1.67 16.45

[0082] Table 2. Main components (g / L) of brine and lithium-rich anode solution after lithium extraction

[0083]

[0084] Example 2

[0085] The difference between this embodiment and Example 1 is that the lithium-rich electroactive material used is LiMn2O4, and the lithium-deficient Li is prepared using step (1) in Example 1. 1-x Mn2O4 (x = 0.5~0.95, x is 0.8 in this example) material, and using the method in Example 1, respectively with Li 0.2 Mn₂O₄ and LiMn₂O₄ were used as lithium extraction materials to prepare terminal electrodes and bipolar electrodes, which were then assembled into a lithium extraction device. The volume of brine from the salt lake was 250L, the volume of the supporting electrolyte solution was 50L, and the process tank voltage was 5.0V.

[0086] Example 3

[0087] The difference between this embodiment and Embodiment 1 is that the lithium-rich electroactive material used is LiNi. 0.5 Co 0.2 Mn 0.3 O2, prepared as a lithium-deficient Li using step (1) in Example 1. 1-xNi 0.5 Co 0.2 Mn 0.3 O2 (x = 0.5~0.95, x is 0.85 in this embodiment) material; and dense carbon paper as a conductive separator, using the method in Example 1, respectively with Li 0.15 Ni 0.5 Co 0.2 Mn 0.3 O2 and LiNi 0.5 Co 0.2 Mn 0.3 O2 was used to prepare terminal electrodes and bipolar electrodes for lithium extraction, and then assembled into a lithium extraction device. The volume of brine in the salt lake was 200L, the volume of the supporting electrolyte solution was 50L, and the tank voltage was controlled at 6.0V.

[0088] Example 4

[0089] The difference between this embodiment and Example 1 is that LiFePO4 and LiMn2O4 are used as active materials, wherein LiFePO4 is prepared into a lithium-deficient state Li using step (1) in Example 1. 1-x FePO4 (x = 0.8–0.95, x is 0.9 in this example) material; and using a graphite plate as a conductive separator, the method described in Example 1 was used to separately apply Li 0.1 FePO4 and LiMn2O4 were used as lithium extraction materials to prepare terminal electrodes and bipolar electrodes, which were then assembled into a lithium extraction device. The volume of brine in the salt lake was 250L, the volume of the supporting electrolyte solution was 50L, and the cell voltage was controlled at 4.5V during the lithium extraction process.

[0090] Example 5

[0091] The difference between this embodiment and Embodiment 1 is that LiFePO4 and LiNi are used. 0.5 Co 0.2 Mn 0.3 O2 and two other materials were used as active materials, with LiFePO4 prepared into lithium-state Li using step (1) in Example 1. 1-x FePO4 (x = 0.8–0.95, x is 0.9 in this example) material; and using a ruthenium-coated titanium plate as a conductive separator, the method described in Example 1 was used to separately apply Li 0.1 FePO4 and LiNi 0.5 Co 0.2 Mn 0.3 O2 was used as the lithium extraction material to prepare terminal electrodes and bipolar electrodes, which were then assembled into a lithium extraction device. The volume of brine from the salt lake was 250L, the volume of the supporting electrolyte solution was 50L, and the cell voltage was controlled at 6.0V during the lithium extraction process.

[0092] Example 6

[0093] The difference between this embodiment and Embodiment 1 is that LiMn2O4 and LiNi are used. 0.5 Co 0.2 Mn 0.3 O2 and two other materials are used as active materials, with LiMn2O4 prepared as a lithium-deficient Li using step (1) in Example 1. 0.3 Mn2O4 material, and using the method in Example 1, respectively with Li 0.3 Mn2O4 and LiNi 0.5 Co 0.2 Mn 0.3 O2 was used as the lithium extraction material to prepare terminal electrodes and bipolar electrodes, which were then assembled into a lithium extraction device. The volume of brine from the salt lake was 250L, the volume of the supporting electrolyte solution was 50L, and the process tank voltage was controlled at 7.0V.

[0094] The composition of the lithium-rich solutions obtained from the lithium extraction processes in Examples 2-6 is shown in Table 3, and the changes in lithium concentration in the brine are shown in Table 3. Figure 6 As shown; supports multiple electrolyte (lithium-rich solution) cycles, with fresh brine added after lithium extraction from the brine. The changes in lithium content in the lithium-rich solution are as follows. Figure 7 As shown; the adsorption capacity and cycling performance of Examples 2-6 are as follows. Figure 8 As shown.

[0095] From Table 3 and Figure 6 It can be seen that although the lithium extraction performance of lithium extraction systems composed of different lithium battery active materials varies slightly, the overall selectivity is good. From Figure 7 It can be seen that by circulating the lithium-rich solution, the lithium concentration can be continuously accumulated, achieving further enrichment of lithium. From Figure 8 It can be seen that although the lithium extraction capacity of lithium extraction systems composed of different active materials varies slightly, their cycle performance is also very excellent, with an average process current of 7-8A.

[0096] Table 3. Concentration (g / L) of lithium in the lithium-rich solutions and brine obtained in Examples 2-6

[0097]

[0098] Example 7

[0099] The difference between this embodiment and Embodiment 1 is that the brine used is a carbonate-type brine with a solution pH of 9.5. Electrolytic lithium extraction was performed at 3.5V. The volume of the brine was 200L, and the volume of the supporting electrolyte solution was 50L. The composition of the brine and supporting electrolyte before and after lithium extraction is shown in Table 4. The changes in lithium concentration in the brine and supporting electrolyte over time are shown in Table 4. Figure 9 As shown.

[0100] From Table 4 and Figure 9It can be seen that the patented method is also well adapted to carbonate-type brine. After treating 0.67 g / L brine, the lithium concentration in the brine can be reduced to 0.08 g / L after 5 hours (brine circulation can achieve further lithium extraction), and the direct lithium extraction rate can reach 88%. One cycle continues until the lithium concentration in the electrolyte reaches 2.38 g / L, and the rejection rate of other impurity ions reaches over 99%.

[0101] from Figure 10 It can be seen that by cyclically enriching the supporting electrolyte, the lithium concentration can be further enriched, reaching 11.5 g / L after 6 cycles.

[0102] Table 4. Composition of carbonate lake brine (g / L)

[0103] element <![CDATA[Li + ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[SO4 2- ]]> <![CDATA[CO3 2- ]]> <![CDATA[B2O3]]> initial brine 0.67 97.2 15.3 10.3 21.8 4.5 Lithium-extracting brine 0.08 96.9 15.25 10.26 21.7 4.48 lithium-rich liquid 2.38 3.16 0.18 0.14 0.3 0.06

[0104] Comparative Example 1

[0105] (1) Using lithium iron phosphate as the lithium-rich active material, lithium iron phosphate slurry and lithium-intercalated iron phosphate slurry were prepared using the same method as in Example 1. The lithium iron phosphate slurry and lithium-intercalated iron phosphate slurry were respectively coated on both sides of a titanium sheet (titanium sheet size 50×50cm). 2 (both sides are made of the same material), and lithium iron phosphate electrode and lithium-intercalated iron phosphate electrode were prepared using the same coating density and drying conditions as in the example;

[0106] (2) The electrolytic cell is divided into 10 independent chambers by using 9 anion exchange membranes. 5 lithium iron phosphate electrodes and 5 lithium-intercalated iron phosphate electrodes are alternately placed in the independent chambers. Each lithium iron phosphate electrode is connected to the positive terminal of the power supply through a wire, and each lithium-intercalated iron phosphate electrode is connected to the enrichment of the power supply. The membrane stack lithium extraction electrolytic cell with traditional connection method and working mode is formed.

[0107] (3) Inject 300L of the same salt lake brine as in Example 1 into the cavity containing the lithium iron phosphate electrode (the injection and outflow of solutions in each cavity can be connected through external pipes), and inject 20L of 5g / L NaCl supporting electrolyte into the lithium-intercalated lithium iron phosphate electrode. Electrolyze and extract lithium at a voltage of 0.35V, and end the lithium extraction process when the lithium extraction current drops to 10% of the initial current.

[0108] Comparative Example 2

[0109] The only difference between this comparative example and comparative example (1) is that in this comparative example, lithium iron phosphate in step (1) of comparative example 1 is replaced with LiMn2O4, and the lithium extraction process is carried out by electrolysis at a voltage of 0.65V.

[0110] Comparative Example 3

[0111] The only difference between this comparative example and comparative example (1) is that in this comparative example, lithium iron phosphate in step (1) of comparative example 1 is replaced with LiNi. 0.5 Co 0.2 Mn 0.3 O2, and at the same time, the lithium extraction process is carried out by electrolysis at a voltage of 0.7V.

[0112] Table 5 shows the main ion concentrations in the brine and lithium-rich solution before and after lithium extraction in Comparative Examples 1–3. The changes in lithium concentration over time during the process are also shown in Table 5. Figure 11 , Figure 12 As shown.

[0113] Table 5. Concentrations of major ions in brine and lithium-rich solution before and after lithium extraction.

[0114]

[0115]

[0116] Compared to the lithium extraction modes of Examples 1-3, the lithium extraction effects of Comparative Examples 1-3 are comparable, with adsorption capacities reaching 26.5 mg / g, 16.6 mg / g, and 18.3 mg / g, respectively. However, a comparison of the process current clearly shows that, using the same number of electrodes, the current in the comparative examples is as high as approximately 70 A, about 10 times that of Examples 1-3. In actual production, to ensure the lithium extraction quantity of each membrane stack electrolyzer, 100-200 electrode plates need to be installed in one electrolyzer. Therefore, using the operating mode of Comparative Examples 1-3 would result in a current 100-200 times that of this patent, leading to excessively high current in the lithium extraction system. This not only increases the cost of power supply manufacturing but also causes a significant impact on the operating conditions of the electrolyzer electrodes due to the busbar voltage drop caused by the high current operation. The bipolar electrode lithium extraction mode of this patent fundamentally solves these problems.

[0117] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An apparatus for extracting lithium from solution using a bipolar electrode, characterized in that, It includes a tank, end electrodes, at least one conductive separator, and an anion exchange membrane, which is one more than the number of the conductive separators. The end electrode includes a first end electrode for connecting to a first electrode and a second end electrode for connecting to a second electrode, respectively disposed at both ends of the tank; the surface of the first end electrode facing the second end electrode is coated with a lithium-deficient electroactive material, and the surface of the second end electrode facing the first end electrode is coated with a lithium-rich electroactive material. The conductive separator is disposed inside the tank, physically dividing the tank into two or more independent chambers, and is located between the first end electrode and the second end electrode; the surface of the conductive separator facing the first end electrode is coated with a lithium-rich electroactive material, and the surface of the conductive separator facing the second end electrode is coated with a lithium-deficient electroactive material. An anion exchange membrane is provided in each of the independent chambers, dividing each independent chamber into two working areas. The side containing the lithium-deficient electroactive material is used to introduce the lithium extraction raw material solution, which is called the first working area, and the side containing the lithium-rich electroactive material is used to introduce the supporting electrolyte, which is called the second working area.

2. The apparatus for extracting lithium from solution using a bipolar electrode according to claim 1, characterized in that, The first end electrode, the second end electrode, the conductive separator, and the anion exchange membrane are arranged in parallel to each other, and the multiple conductive separators are spaced at the same distance.

3. The apparatus for extracting lithium from solution using a bipolar electrode according to claim 1, characterized in that, The groove is provided with a slot for installing the conductive partition.

4. The apparatus for extracting lithium from solution using a bipolar electrode according to claim 1, characterized in that, The lithium-rich electroactive material is one or a mixture of several of LiFePO4, LiMn2O4, LiMeO2 and their doped derivatives, wherein Me is one or more of Ni, Co and Mn; the lithium-deficient electroactive material is prepared by oxidizing the lithium-rich electroactive material to remove part or all of the lithium.

5. The apparatus for extracting lithium from solution using a bipolar electrode according to claim 1, characterized in that, The conductive separator is made of dense carbon paper, dense carbon fiber sintered cloth, graphite plate, corrosion-resistant intermetallic compound plate, ruthenium-coated titanium sheet, gold, platinum group metals and / or their alloy plates, or titanium, zirconium, hafnium, tantalum, niobium and / or their alloy plates.

6. A method for extracting lithium from solution using a bipolar electrode, characterized in that, Includes the following steps: Step 1: Take the apparatus for extracting lithium from solution using a bipolar electrode as described in any one of claims 1-5, introduce a lithium extraction raw material solution into the first working area, and introduce a supporting electrolyte into the second working area; Step 2: Connect the first end electrode to the negative terminal of the power supply, connect the second end electrode to the negative terminal of the power supply, turn on the power supply, and current flows in from the second end electrode and is output from the first end electrode. At the same time, the following changes occur: In the first working area, lithium ions in the raw material solution are embedded in the adjacent lithium-deficient electroactive material, and the lithium-deficient electroactive material gradually becomes lithium-rich electroactive material. In the second working area, lithium ions in the lithium-rich electroactive material are released into the supporting electrolyte, and the lithium-rich electroactive material gradually becomes a lithium-deficient electroactive material. Step 3: The reaction is terminated, the power is disconnected, and the raw material solution is converted into lithium-deficient liquid, the supporting electrolyte is converted into lithium-rich liquid, the lithium-deficient liquid is discharged, and the lithium-rich liquid is collected. Step 4: Clean the tank, connect the first end electrode to the positive terminal of the power supply, and connect the second end electrode to the negative terminal of the power supply. Repeat steps 1-3.

7. The method for extracting lithium from solution using a bipolar electrode according to claim 6, characterized in that, The lithium-rich solution from the previous cycle can be used as the supporting electrolyte for the next cycle to continue lithium extraction and increase the lithium concentration in the solution; the lithium-poor solution from the previous cycle can be used as the lithium extraction feed solution for the next cycle to improve the lithium recovery rate.

8. The method for extracting lithium from solution using a bipolar electrode according to claim 6, characterized in that, The lithium extraction raw material solution is any one or a mixture of several of the following: salt lake brine, brine obtained from any stage of brine treatment, old brine, underground brine, oilfield brine, lithium-containing solution obtained from ore decomposition and secondary resource recovery, and lithium precipitation mother liquor.

9. The method for extracting lithium from solution using a bipolar electrode according to claim 6, characterized in that, The power supply voltage is (0.1-1.0)×n volts, where n is the number of independent cavities.

10. The method for extracting lithium from solution using a bipolar electrode according to claim 9, characterized in that, When the electroactive material is LiFePO4 or its derivatives, the applied voltage is (0.1-0.5) × n volts. When the electroactive material is LiMn2O4 or its derivatives, the applied voltage is (0.3-0.6) × n volts. When the electroactive material is LiMeO2 or its derivative, the applied voltage is (0.4-0.8) × n volts; When the electroactive material is LiMn2O4 and LiFePO4 and their derivatives, the applied voltage is (0.3-0.7) × n volts; When the electroactive material is LiMn2O4 and LiMeO2 and their derivatives, the applied voltage is (0.4-0.9) × n volts; When the electroactive material is LiFePO4 and LiMeO2 and their derivatives, the applied voltage is (0.4-1.0)×n volts.

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