Flow battery device for recovering li+, and recovery method

Abstract

Disclosed in the present application are a flow battery device for recovering Li+ and a recovery method. In the present invention, a waste LiFePO4 solid wrapped by a porous PTFE filter membrane is placed on one side of a positive electrode electrolyte of a flow battery, such that the positive electrode electrolyte in an oxidized state can penetrate through the filter membrane to be in full contact and react with LiFePO4. The electrolyte of the positive electrode oxidizes LiFePO4 into Li+ and FePO4 by means of an oxidation reaction, and the generated Li+ enters the electrolyte and penetrates through the membrane to reach one side of the negative electrode in the form of a supporting electrolyte; in addition, the membrane material has strong selectivity for Li+, ensuring that the other ions cannot penetrate through the membrane. The electrode surface of the negative electrode of the flow battery is coated with a hydrogen evolution catalyst to perform a hydrogen evolution reaction and recover hydrogen, thereby achieving the dual purpose of recovering Li+ and producing hydrogen by means of electrolysis. A new LiFePO4 electrode material is re-obtained by means of calcination, etc., from the FePO4 produced at the positive electrode and the Li+ product obtained at the negative electrode, and is used in a lithium-ion battery.

Description

A flow battery device and method for Li+ recovery Technical Field

[0001] This application relates to a flow battery device that can be used for the simultaneous electrolysis of lithium elements in waste LiFePO4 cathode materials to produce hydrogen, belonging to the fields of flow batteries, lithium-ion batteries, and water electrolysis for hydrogen production. Background Technology

[0002] Achieving carbon peaking and carbon neutrality is a crucial strategic goal for my country, making the development of an energy structure dominated by new energy sources essential. However, the intermittent nature of renewable energy means it cannot continuously and stably output electricity for extended periods, necessitating energy storage technologies to ensure its continuous and stable operation. The storage and release of renewable energy can be achieved through various means, such as physical and chemical energy storage, where renewable energy is stored and released as electricity. A representative example is the lithium-ion battery, with the LiFePO4 battery system capable of stable operation exceeding 10,000 cycles. Its high energy density and low cost make it one of the most important energy storage technologies. In contrast to "electricity storage," using renewable energy to electrolyze water to produce and store hydrogen can overcome battery capacity limitations, enabling long-term energy storage across different seasons. Furthermore, hydrogen has a high calorific value, and its combustion product is only water, making it clean and environmentally friendly.

[0003] Lithium-ion batteries that have been in operation for a long time often face the problem of material structure collapse, resulting in a gradual decrease in battery capacity. + Resources are limited, therefore, it is necessary to recycle and reuse lithium resources from spent lithium-ion batteries. However, in the process of producing hydrogen through water electrolysis, oxygen is usually generated at the positive electrode. As a byproduct, oxygen not only wastes electrical energy, but high concentrations of oxygen also harm the environment. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for Li + This invention relates to a novel lithium recovery and hydrogen production device based on a flow battery. The device generates hydrogen through a hydrogen evolution reaction on the negative electrode side, while on the positive electrode side, the electrolyte oxidizes waste LiFePO4 to generate Li. + And it produces FePO4, in which Li + The electrolyte passes through the membrane material to the negative electrode side and is then re-sintered with FePO4 to obtain a new LiFePO4 electrode material. Therefore, this device combines hydrogen production and lithium resource recovery, significantly improving energy utilization while avoiding a series of environmental problems caused by the oxygen byproducts generated during hydrogen electrolysis.

[0005] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0006] In a first aspect, the present invention provides a method for Li + Recycled flow battery devices, including flow batteries;

[0007] The flow battery includes a flow battery stack consisting of one or more flow single cells connected in series and / or parallel, positive and negative electrolyte storage tanks containing positive and negative electrolytes respectively, and a liquid pump; the positive electrolyte storage tank containing the positive electrolyte is connected to the positive electrolyte inlet and outlet of the flow battery through pipelines, and a liquid pump is installed on the pipelines; the negative electrolyte storage tank containing the negative electrolyte is connected to the negative electrolyte inlet and outlet of the flow battery through pipelines, and a liquid pump is installed on the pipelines.

[0008] The filter membrane encapsulates the Li to be recovered. + The LiFePO4 electrode material is placed in the positive electrolyte of the positive electrolyte storage tank, or the internal chamber of the positive electrolyte storage tank is divided into two regions by a filter membrane, with the positive electrolyte outlet of the positive electrolyte storage tank located in one of the regions, from which Li is to be recovered. + The LiFePO4 electrode material is placed in the positive electrolyte in another region, and the positive electrolyte outlet is located in one of the regions from which Li is to be recovered. + The LiFePO4 electrode material is divided into regions;

[0009] The electrode on the negative electrode side is coated with a hydrogen evolution catalyst, and the electrolyte at the negative electrode contains a proton source.

[0010] Furthermore, the filter membrane is a hydrophilic PTFE filter membrane, which is used to encapsulate the solid LiFePO4 electrode material to prevent solid particles from scattering into the electrolyte; or, a hydrophilic PTFE filter membrane is used to separate the LiFePO4 electrode material from the positive electrolyte outlet to prevent solid particles from flowing out of the positive electrolyte outlet.

[0011] The filter membrane can prevent LiFePO4 solid particles from entering the electrolyte, while not preventing the electrolyte from permeating and reacting with LiFePO4.

[0012] The hydrophilic PTFE filter membrane has a pore size between 5μm and 15μm, with a preferred pore size of 10μm to 12μm. This can both block LiFePO4 solid from entering the electrolyte and ensure that the electrolyte can easily pass through and react with LiFePO4.

[0013] The single cell comprises a positive electrode plate, a positive electrode current collector, a positive electrode, a membrane, a negative electrode, a negative electrode current collector, and a negative electrode plate stacked sequentially. Its positive electrode electrolyte undergoes an oxidation reaction during charging. The oxidized electrolyte can chemically react with the LiFePO4 electrode material wrapped in the filter membrane, reducing the Li in the LiFePO4 to a higher concentration. + FePO4 is formed by extraction, and Li is generated at the positive electrode. + It enters the negative electrode side through an ion-selective membrane material in the form of a supporting electrolyte.

[0014] Furthermore, relative to the oxidation process at the positive electrode, the reduction process at the negative electrode is a hydrogen evolution reaction; the active component of the hydrogen evolution catalyst coated on the electrode on the negative electrode side includes one or more of the following: carbon materials, transition metal elements (the transition metal elements include noble metals such as Rh and Pt, or non-noble metals such as Ni), transition metal nitrides, phosphides, sulfides, selenides, and carbides, with platinum / carbon catalysts preferred as the hydrogen evolution catalyst at the negative electrode;

[0015] The positive electrode material is one or more of carbon felt, carbon paper, or carbon cloth; the negative electrode material is one or more of carbon felt, carbon paper, or carbon cloth; the loading of the hydrogen evolution catalyst on the negative electrode is 1–3 mg cm⁻¹. -2 Preferred dosage: 1-1.2 mg cm -2 .

[0016] Furthermore, the pH of the positive electrode electrolyte of the flow battery is near neutral, wherein near neutral is pH = 4-8, preferably pH = 6-7.

[0017] The oxidation state of the positive electrode electrolyte in the aforementioned flow battery can oxidize LiFePO4 to release Li. + And it generates FePO4; since LiFePO4 decomposes into Fe in strong acid. 2+ and Li + In strong alkali, Fe(OH)3 will be generated. Therefore, a near-neutral positive electrolyte is required for lithium recovery (pH=4-8, preferably pH=6-7) to ensure that LiFePO4 will not decompose due to acid or alkali.

[0018] Furthermore, the positive electrode electrolyte must be an oxidizing and nearly neutral solution; additionally, the active material of the positive electrode electrolyte in the flow battery must not undergo side reactions with LiFePO4, such as Fe(CN)6. 3- / Fe(CN)6 4- It may react with LiFePO4 to form Fe4[Fe(CN)6]3 precipitate, so it cannot be selected.

[0019] The positive electrode electrolyte contains I. - / I3 - ,Br- / Br2、Cl - An aqueous solution of one or more active substance redox couples in Cl2, preferably Br - / Br2、I - / I3 - The redox couple serves as the active material in the electrolyte, wherein the concentration of the active material in the electrolyte is 0.1-4 mol / L. -1 Preferred concentration: 2.0-3.0 mol / L -1 More preferably I - / I3 - The redox couple serves as the active material in the electrolyte, 0.1-4 mol / L. -1 Preferred concentration: 2.0-3.0 mol / L -1 .

[0020] Furthermore, the negative electrode electrolyte is a weak acid with a pH value of 1-3;

[0021] Furthermore, the negative electrode electrolyte is an aqueous solution of one or more of citric acid, phosphoric acid, formic acid, acetic acid, propionic acid, and gluconic acid, preferably a citric acid solution;

[0022] The concentration of the solute in the negative electrode electrolyte is 0.1-0.5M, preferably 0.4-0.5M.

[0023] Furthermore, the positive and negative electrodes of the single cell are separated by a membrane material, which is capable of conducting Li... + Furthermore, the selected membrane material must not undergo side reactions with the electrolyte. The membrane material includes one or more of SPEEK, Nafion, PBI, or PVDF, with Nafion 212 membrane being preferred.

[0024] The Li to be recovered from + The LiFePO4 electrode material is a waste LiFePO4 electrode positive material; the waste LiFePO4 electrode positive material includes one or more of LiFePO4 or binders and conductive agents combined with LiFePO4 to form an electrode material.

[0025] The binder comprises PVDF, and the conductive agent comprises conductive carbon.

[0026] Secondly, the present invention provides a method for recovering Li using the aforementioned flow battery device. + The method includes the following steps:

[0027] 1) The filter membrane-coated material from which Li is to be recovered +The LiFePO4 electrode material is placed in the positive electrolyte of the positive electrolyte storage tank; or the internal chamber of the positive electrolyte storage tank is divided into two regions by a filter membrane, with the positive electrolyte outlet of the positive electrolyte storage tank located in one of the regions, from which Li is to be recovered. + The LiFePO4 electrode material is placed in the positive electrolyte in another region, and the positive electrolyte outlet is located in one of the regions from which Li is to be recovered. + The LiFePO4 electrode material is divided into regions;

[0028] 2) The reduced electrolyte at the positive electrode is electrochemically oxidized to form an oxidized solution, and the Li at the positive electrode... + The electrolyte is conducted to the negative electrode in the form of a supporting electrolyte; the negative electrode electrolyte undergoes a hydrogen evolution side reaction on the catalyst layer to generate H2;

[0029] Simultaneously, the oxidized electrolyte at the positive electrode can react with LiFePO4 in the storage tank to generate FePO4 while releasing Li. + .

[0030] During the charging process of a flow battery, the positive electrode electrolyte undergoes an oxidation reaction and can also chemically react with the electrode material wrapped in the filter membrane, converting lithium in LiFePO4 into Li. + The form is released and forms the corresponding FePO4, producing Li + It enters the negative electrode electrolyte in the form of a supporting electrolyte through an ion-selective membrane material and is enriched.

[0031] The current density during the charging process of a flow battery is 100-400 mA / cm². 2 The charging voltage is 0.7-2.5V; the charging cut-off condition is a voltage rise of 0.3-0.5V.

[0032] Furthermore, reference indicators for judging the lithium recovery effect of flow batteries include lithium recovery rate, lithium recovery speed, and lithium recovery energy consumption.

[0033] Lithium recovery rate (R) is the ratio of the actual amount of lithium recovered (P, kg) to the theoretical amount of lithium recovered (I, kg).

[0034] R = P / I * 100%

[0035] Lithium recovery rate (S, kg / (h*cm)) 2 That is, unit time (T, h) and unit area (A, cm²) 2 The amount of lithium (kg) that the electrode material (positive or negative electrode of a single cell) can recover depends on the battery's operating current density (C; mA cm⁻¹). -2 ) and lithium recovery rate (R);

[0036] S = 0.000258C / R

[0037] Lithium recovery energy consumption (E, Wh / kg) is the energy required to recover a unit mass of lithium (kg), which is directly related to the battery's operating voltage (V) and lithium recovery rate (R).

[0038] E=1000 / 6.94*26.8*V*R=3861.67*V / R.

[0039] The beneficial effects that this application can produce include:

[0040] 1. This application proposes a novel lithium recovery device capable of simultaneously recovering Li from LiFePO4. + The system innovatively combines lithium recovery and hydrogen production through recycling and electrolysis.

[0041] 2. Compared with the traditional direct oxidation method, this design can realize the continuous and long-term operation of the lithium recovery process. After the positive electrode electrolyte reacts with LiFePO4, it can be reused repeatedly through the charging oxidation process.

[0042] 3. Compared with the traditional water electrolysis hydrogen production process, the positive electrode no longer undergoes the oxygen evolution side reaction, avoiding a series of environmental problems caused by oxygen evolution, while significantly improving the utilization rate of electrical energy. Attached Figure Description

[0043] Figure 1 shows the XRD characterization of the FePO4 product generated from the positive electrode LiFePO4 in Example 1.

[0044] Figure 2 shows the voltage curve for lithium recovery in Example 1.

[0045] Figure 3 shows the lithium recovery rate test conducted by ICP in Example 1.

[0046] Figure 4 shows the XRD detection of the LiFePO4 product prepared by sintering the positive and negative electrode recovered products in Example 1.

[0047] Figure 5 shows the performance test of the lithium-ion battery using the LiFePO4 product prepared by sintering in Example 1.

[0048] Figure 6 shows the voltage curve of the lithium recovery process in Example 5.

[0049] Figure 7 shows the lithium recovery rate test conducted by ICP in Comparative Example 1.

[0050] Figure 8 shows the lithium recovery rate test conducted by ICP in Comparative Example 2.

[0051] Figure 9 shows the voltage curve of the lithium recovery process in Comparative Example 3.

[0052] Figure 10 shows the XRD characterization of the oxidation products of LiFePO4 in Comparative Example 3.

[0053] Figure 11 shows the voltage curve of the lithium recovery process in Comparative Example 4.

[0054] Figure 12 shows the XRD characterization of the oxidation products of LiFePO4 in Comparative Example 4.

[0055] Figure 13 shows the application of the present invention for Li + Recycled flow battery devices. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Example 1

[0058] As shown in Figure 13, it is used for Li + The recovered flow battery device includes a flow battery, which is a single cell containing positive and negative electrolytes in separate positive and negative electrolyte tanks and a pump. The positive electrolyte tank is connected to the positive electrolyte inlet and outlet of the flow battery via pipelines, and a pump is installed on the pipeline connecting the tank to the positive electrolyte inlet. Similarly, the negative electrolyte tank is connected to the negative electrolyte inlet and outlet of the flow battery via pipelines, and a pump is installed on the pipeline connecting the tank to the negative electrolyte inlet. A filter membrane is used to recover Li. + The LiFePO4 electrode material was placed in the positive electrolyte in the positive electrolyte storage tank;

[0059] The filter membrane is a hydrophilic PTFE filter membrane (Nantong Longjin Membrane Industry Co., Ltd.), with a pore size of 10μm;

[0060] The single cell comprises a positive electrode plate, a positive electrode current collector, a positive electrode, a membrane, a negative electrode, a negative electrode current collector, and a negative electrode plate stacked in sequence.

[0061] The positive electrode is a carbon felt electrode with a thickness of 4.3 mm;

[0062] The negative electrode is a carbon felt electrode with a thickness of 4.3 mm.

[0063] The negative electrode uses a platinum / carbon catalyst with a platinum loading of 5% as the active material (i.e., the negative electrode catalyst), and the platinum / carbon loading is 1.2 mg cm⁻¹. -2The positive and negative electrodes have an area of ​​3cm x 3cm (length x width); the positive electrode electrolyte uses LiCl, LiI, or LiBr as the active material at a concentration of 2M, and the positive electrode electrolyte has a pH of ~7; the negative electrode electrolyte is 0.5M citric acid (from which Li is recovered). + The LiFePO4 electrode material is recycled lithium iron phosphate battery material (Chuanheng Group; impurities: PVDF, conductive carbon).

[0064] In the embodiments and comparative examples of the present invention, the volumes of the positive and negative electrolytes are both 200 mL.

[0065] Apply different currents (1.8A-2.7A, current density 200mA / cm²) between the positive and negative electrodes. -2 up to 300mA cm -2 The charging cutoff condition is a voltage rise of 0.3-0.5V.

[0066] The specific process for lithium recovery is as follows:

[0067] (1) Examples 1-4: 200 mL of 2M LiI was used as the positive electrode electrolyte, 200 mL of 0.5M citric acid (H3Cit) was used as the negative electrode electrolyte, Nafion 212 or Nafion 115 membranes were used as membrane materials, and the platinum / carbon loading was 1.2 mg / cm³. -2 A platinum / carbon catalyst with a platinum mass fraction of 5% was used as the active material (i.e., the negative electrode catalyst); a current density of 200 mA cm⁻¹ was applied between the positive and negative electrodes. -2 or 300mA cm -2 The current is such that the charging cutoff condition is 50% of the theoretical capacity of the positive electrode electrolyte.

[0068] Positive electrode electrolysis generates I3 - It can react with LiFePO4 to produce Li + And FePO4, to generate Li + It can be conducted to the negative electrode through the Nafion 212 / 115 film; in addition, the positive electrode I3 - / I -The electrode potential (0.54V vs. SHE) is slightly higher than that of LiFePO4 / FePO4 (0.4V vs. SHE), which enables rapid oxidation of lithium iron phosphate. Citric acid, the negative electrode electrolyte, is a weak acid that can provide protons to generate H2 on the Pt / C catalyst. As shown in Figures 1-5 in Example 1, the lithium recovery rate can reach nearly 100%, and the lithium salt recovered from the negative electrode can be combined with the FePO4 generated at the positive electrode to synthesize LiFePO4 and exhibit excellent performance in lithium-ion batteries. (2) Examples 5-8: 200mL of 2M LiBr was used as the positive electrode electrolyte, 200mL of 0.5M citric acid (H3Cit) was used as the negative electrode electrolyte, Nafion 212 or Nafion 115 membrane was used as the membrane material, and the platinum / carbon loading was 1.2mg cm⁻¹. -2 A platinum / carbon catalyst with a platinum mass fraction of 5% was used as the active material (i.e., the negative electrode catalyst); a current density of 200 mA cm⁻¹ was applied between the positive and negative electrodes. -2 or 300mA cm -2 The current is such that the charging cutoff condition is 50% of the theoretical capacity of the positive electrode electrolyte.

[0069] Br2 generated during battery charging can react with LiFePO4 to form Li + and FePO4 (positive electrode Br2 / Br) - The electrode potential of the electrode (1.08V vs. SHE) is much higher than that of LiFePO4 / FePO4 (0.4V vs. SHE), resulting in the formation of Li + It can be conducted to the negative electrode through the Nafion 212 / 115 membrane. The negative electrode electrolyte, citric acid, is a weak acid that can provide protons to generate H2 on the Pt / C catalyst. Figure 6 shows the charge-discharge curves of Example 5 using LiBr as the lithium recovery medium; its lithium recovery rate can also reach 100%, but due to the Br... - / Br 2 The electrode voltage is relatively high, resulting in increased energy consumption.

[0070] (3) Examples 9-10

[0071] Examples 9-10: 200 mL of 0.5 M LiI or LiBr was used as the positive electrode electrolyte, and 200 mL of 0.5 M citric acid (H3Cit) was used as the negative electrode electrolyte. Nafion 212 or Nafion 115 membranes were used as the membrane material, with a platinum / carbon loading of 1.2 mg / cm³. -2 A platinum / carbon catalyst with a platinum mass fraction of 5% was used as the active material (i.e., the negative electrode catalyst); a current density of 200 mA cm⁻¹ was applied between the positive and negative electrodes. -2The charging current was set at 50% of the theoretical capacity of the positive electrolyte. Due to the slightly lower electrolyte concentration, the polarization of the battery during charging was still higher compared to the 2M electrolyte, resulting in increased energy consumption. Although Li + The recovery rate remains close to 100%.

[0072] (4) Examples 11-12

[0073] Examples 11-12: 200 mL of 2M LiCl was used as the positive electrode electrolyte, and 200 mL of 0.5M citric acid (H3Cit) was used as the negative electrode electrolyte. Nafion 212 or Nafion 115 membranes were used as membrane materials, with a platinum / carbon loading of 1.2 mg / cm³. -2 A platinum / carbon catalyst with a platinum mass fraction of 5% was used as the active material (i.e., the negative electrode catalyst); a current density of 200 mA cm⁻¹ was applied between the positive and negative electrodes. -2 The charging current is set at 50% of the theoretical capacity of the positive electrolyte. Similar to Examples 5-8, the lithium recovery voltage using the Cl- / Cl2 redox couple is higher, but the battery energy consumption is greater. However, Li + The recovery rate can still reach ~100%.

[0074] (5) Examples 13-14

[0075] Examples 13-14: 200 mL of 2M LiI was used as the positive electrode electrolyte, and 200 mL of 0.5M citric acid (H3Cit) was used as the negative electrode electrolyte. SPEEK or PBI membranes were used as the membrane material, with a platinum / carbon loading of 1.2 mg / cm³. -2 A platinum / carbon catalyst with a platinum mass fraction of 5% was used as the active material (i.e., the negative electrode catalyst); a current density of 200 mA cm⁻¹ was applied between the positive and negative electrodes. -2 The charging current is set at 50% of the theoretical capacity of the positive electrolyte. Due to the slightly higher sheet resistance of the SPEEK or PBI membrane, the energy consumption for lithium recovery is slightly higher.

[0076] Reference indicators for judging the lithium recovery effect of flow batteries include lithium recovery rate, lithium recovery speed, and lithium recovery energy consumption.

[0077] Lithium recovery rate (R) is the ratio of the actual amount of lithium recovered (P, kg) to the theoretical amount of lithium recovered (I, kg).

[0078] R = P / I * 100%

[0079] Lithium recovery rate (S, kg / (h*cm)) 2 That is, unit time (T, h) and unit area (A, cm²) 2The amount of lithium (kg) that the electrode material (positive or negative electrode of a single cell) can recover depends on the battery's operating current density (C; mA cm⁻¹). -2 The level of lithium recovery (R) is related to its recovery rate.

[0080] S = 0.000258C / R

[0081] Lithium recovery energy consumption (E, Wh / kg) is the energy required to recover a unit mass of lithium (kg), which is directly related to the battery's operating voltage (V) and lithium recovery rate (R).

[0082] E=1000 / 6.94*26.8*V*R=3861.67*V / R.

[0083] The processes and conditions of Examples 2-14 and Comparative Examples 1-7 are the same as those of Example 1 above, except that: see Tables 1 and 2 for details.

[0084] Table 1. Lithium recovery rate, operating voltage, and energy consumption under different conditions in Examples 1-14.

[0085] Table 2 shows the lithium recovery rate, operating voltage, and energy consumption under different conditions in Comparative Examples 1-7.

[0086] Based on Tables 1 and 2, the following conclusions can be drawn:

[0087] Examples 1-4: Using LiI as the positive electrode electrolyte, I3 is generated by positive electrode electrolysis. - It can react with LiFePO4 to produce Li + And FePO4, to generate Li + It can be conducted to the negative electrode through the Nafion 212 / Nafion 115 film; in addition, the positive electrode I3 - / I - The electrode potential (0.54V vs. SHE) is similar to that of LiFePO4 / FePO4 (0.4V vs. SHE), which can reduce the energy consumption of electrolysis. The negative electrode electrolyte, citric acid, is a weak acid that can provide protons to generate H2 on the Pt / C catalyst, keeping the negative electrode electrolyte in a near-neutral state and preventing OH- from forming at the negative electrode. - Generation, crosstalk, and influence of Li + Recovery rate.

[0088] Examples 5-8: Using LiBr as the electrolyte, the Br2 generated during battery charging can react with LiFePO4 to generate Li + and FePO4 (positive electrode Br2 / Br) -The electrode potential of the electrode (1.08V vs. SHE) is much higher than that of LiFePO4 / FePO4 (0.4V vs. SHE), resulting in the formation of Li + It can be conducted to the negative electrode through the Nafion 212 / Nafion 115 membrane; the lithium-ion recovery rate is close to 100%. Compared with LiI as the positive electrode electrolyte, using LiBr as the electrolyte, although the lithium recovery rate is still close to 100%, the electrolysis voltage is increased and the energy consumption is increased.

[0089] Examples 9-10: Using LiI / LiBr with a lower concentration as the electrolyte, the concentration of active material is lower, and due to the relatively low conductivity, the polarization of the battery is slightly greater.

[0090] Examples 11-12: Using LiCl as the electrolyte, the electrode potential of the active material is relatively high (~1.38V), which increases the energy consumption of the battery.

[0091] Examples 13-14: Using SPEEK or PBI membranes, the lithium ion recovery rate can also be close to 100%, but due to the slightly higher sheet resistance, the energy consumption for lithium recovery is slightly higher.

[0092] Comparative Examples 1-2: Compared to using citric acid as the electrolyte at the negative electrode, using deionized water or LiOH solution at the negative electrode will generate a large amount of OH- during the hydrogen evolution process. - And migrate toward the positive electrode, affecting Li + mobility and Li + Recovery rate. As shown in Figure 7-8, the actual Li + The recovered concentration was far lower than the theoretical value.

[0093] Comparative Example 3: Compared to using LiI as the active material, the positive electrode uses Li4Fe(CN)6 as the active material Fe(CN)6. 4- It can react with LiFePO4 to form Prussian blue precipitate, affecting the purity of the FePO4 product at the cathode. As shown in Figure 9-10, the actual product at the cathode is not pure phase FePO4.

[0094] Comparative Example 4: The positive electrode uses MnSO4 as the active material, Mn 2+ It will also react with LiFePO4 to form a precipitate, affecting the purity of the product. As shown in Figure 11-12, the actual product of the positive electrode is not pure phase FePO4.

[0095] Comparative Example 5: The negative electrode uses IrO2 catalyst for O2 reduction reaction, which generates a large amount of OH. - And it passes through the membrane, resulting in a significant decrease in lithium recovery rate.

[0096] Comparative Examples 6-7: The positive electrode uses LiI electrolyte with too low or too high concentration. Too low electrolyte concentration will limit mass transfer inside the battery, while too high concentration will result in too high electrolyte viscosity, which will also affect mass transfer. Therefore, the lithium recovery voltage is too high and the energy consumption is large.

[0097] In summary, the positive electrode couple selected for lithium recovery experiments needs to comprehensively consider whether the electrode potential of the positive electrolyte can oxidize LiFePO4 to FePO4 without generating other byproducts. Furthermore, the levels of the positive and negative electrode potentials determine the energy consumption of lithium recovery. The concentration and kinetics of the positive and negative electrode couples also affect the operating current density, i.e., the recovery rate, of the lithium recovery device. Finally, the selectivity of the membrane material, i.e., limiting the migration of other ions, ensures the recovery of LiFePO4. + High mobility is essential for achieving 100% Li recovery. + This is an important guarantee.

Claims

1. A method for Li + The recovered flow battery device is characterized by: Including flow batteries; The flow battery includes a flow battery stack consisting of one or more flow single cells connected in series and / or parallel, positive and negative electrolyte storage tanks containing positive and negative electrolytes respectively, and a liquid pump; the positive electrolyte storage tank containing the positive electrolyte is connected to the positive electrolyte inlet and outlet of the flow battery through pipelines, and a liquid pump is installed on the pipelines; the negative electrolyte storage tank containing the negative electrolyte is connected to the negative electrolyte inlet and outlet of the flow battery through pipelines, and a liquid pump is installed on the pipelines. The filter membrane encapsulates the Li to be recovered. + The LiFePO4 electrode material is placed in the positive electrolyte of the positive electrolyte storage tank, or the internal chamber of the positive electrolyte storage tank is divided into two regions by a filter membrane, with the positive electrolyte outlet of the positive electrolyte storage tank located in one of the regions, from which Li is to be recovered. + The LiFePO4 electrode material is placed in the positive electrolyte in another region, and the positive electrolyte outlet is located in one of the regions from which Li is to be recovered. + The LiFePO4 electrode material is divided into regions; The electrode on the negative electrode side is coated with a hydrogen evolution catalyst, and the electrolyte at the negative electrode contains a proton source.

2. The flow battery device according to claim 1, characterized in that: The filter membrane is a hydrophilic PTFE filter membrane. The hydrophilic PTFE filter membrane is used to encapsulate the solid LiFePO4 electrode material to prevent solid particles from scattering into the electrolyte; or, the hydrophilic PTFE filter membrane is used to separate the LiFePO4 electrode material from the positive electrolyte outlet to prevent solid particles from flowing out of the positive electrolyte outlet. The pore size of the hydrophilic PTFE filter membrane is between 5μm and 15μm, preferably a filter membrane with a pore size of 10μm to 12μm. The single cell comprises a positive electrode plate, a positive electrode current collector, a positive electrode, a membrane, a negative electrode, a negative electrode current collector, and a negative electrode plate stacked sequentially. Its positive electrode electrolyte undergoes an oxidation reaction during charging. The oxidized electrolyte can chemically react with the LiFePO4 electrode material wrapped in the filter membrane, reducing the Li in the LiFePO4 to a higher concentration. + FePO4 is formed by extraction, and Li is generated at the positive electrode. + It enters the negative electrode side through an ion-selective membrane material in the form of a supporting electrolyte.

3. The flow battery device according to claim 1 or 2, characterized in that: Compared to the oxidation process at the positive electrode, the reduction process at the negative electrode is a hydrogen evolution reaction; the active components of the hydrogen evolution catalyst coated on the electrode on the negative electrode side include one or more of carbon materials, transition metal elements, transition metal nitrides, phosphides, sulfides, selenides, and carbides, with platinum / carbon catalysts preferred as the hydrogen evolution catalyst at the negative electrode. The positive electrode material is one or more of carbon felt, carbon paper, or carbon cloth; the negative electrode material is one or more of carbon felt, carbon paper, or carbon cloth; the loading of the hydrogen evolution catalyst on the negative electrode is 1–3 mg cm⁻¹. -2 Preferred dosage: 1-1.2 mg cm -2 .

4. The flow battery device according to claim 1, characterized in that: The pH of the positive electrode electrolyte of the flow battery is near neutral, specifically pH = 4-8, preferably pH = 6-7.

5. The flow battery device according to claim 4, characterized in that: The positive electrode electrolyte contains I. - / I3 - ,Br - / Br2、Cl - An aqueous solution of one or more active substance redox couples in Cl2, preferably Br - / Br2、I - / I3 - The redox couple serves as the active material in the electrolyte, wherein the concentration of the active material in the electrolyte is 0.1-4 M, preferably 2.0-3.0 M; more preferably 1 M. - / I3 - The redox couple serves as the active material in the electrolyte, with a concentration of 0.1-4 M, preferably 2.0-3.0 M.

6. The flow battery device according to claim 1, 4, or 5, characterized in that: The pH value of the negative electrode electrolyte is 1-3.

7. The flow battery device according to claim 6, characterized in that: The negative electrode electrolyte is an aqueous solution of one or more of the following: citric acid, phosphoric acid, formic acid, acetic acid, propionic acid, and gluconic acid, preferably a citric acid solution. The concentration of the solute in the negative electrode electrolyte is 0.1-0.5M, preferably 0.4-0.5M.

8. The flow battery device according to claim 1, characterized in that: The positive and negative electrodes of a single cell are separated by a membrane material, which includes one or more of SPEEK, Nafion, PBI or PVDF, with Nafion membrane being preferred. The Li to be recovered from + The LiFePO4 electrode material is a waste LiFePO4 electrode positive material; the waste LiFePO4 electrode positive material includes one or more of LiFePO4 or binders and conductive agents combined with LiFePO4 to form an electrode material.

9. A flow battery device according to any one of claims 1-8 for recovering Li + The method is characterized by: Includes the following steps: 1) The filter membrane-coated material from which Li is to be recovered + The LiFePO4 electrode material is placed in the positive electrolyte of the positive electrolyte storage tank; or the internal chamber of the positive electrolyte storage tank is divided into two regions by a filter membrane, with the positive electrolyte outlet of the positive electrolyte storage tank located in one of the regions, from which Li is to be recovered. + The LiFePO4 electrode material is placed in the positive electrolyte in another region, and the positive electrolyte outlet is located in one of the regions from which Li is to be recovered. + The LiFePO4 electrode material is divided into regions; 2) The reduced electrolyte at the positive electrode is electrochemically oxidized to form an oxidized solution, and the Li at the positive electrode... + The electrolyte is conducted to the negative electrode in the form of a supporting electrolyte; the negative electrode electrolyte undergoes a hydrogen evolution side reaction on the catalyst layer to generate H2; Simultaneously, the oxidized electrolyte at the positive electrode can react with LiFePO4 in the storage tank to generate FePO4 while releasing Li. + .

10. The method according to claim 9, characterized in that: Reference indicators for judging the lithium recovery effect of flow batteries include lithium recovery rate, lithium recovery speed, and lithium recovery energy consumption. Lithium recovery rate (R) is the ratio of the actual amount of lithium recovered (P, kg) to the theoretical amount of lithium recovered (I, kg). R = P / I * 100% Lithium recovery rate (S, kg / (h*cm)) 2 That is, unit time (T, h) and unit area (A, cm²) 2 The amount of lithium (kg) that the electrode material (positive or negative electrode of a single cell) can recover depends on the battery's operating current density (C; mA cm⁻¹). -2 ) and lithium recovery rate (R); S = 0.000258C / R Lithium recovery energy consumption (E, Wh / kg) is the energy required to recover a unit mass of lithium (kg), which is related to the battery's operating voltage (V) and lithium recovery rate (R). E=1000 / 6.94*26.8*V*R=3861.67*V / R.

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