Mixed silane-modified WO3 photoanode, preparation method and its application in photoelectrochemical complexation and lithium extraction

Abstract

This invention discloses a mixed silane-modified WO3 photoanode, its preparation method, and its application in photoelectrochemical lithium extraction. The invention utilizes PTMS and MTMS to modify WO3, obtaining a mixed silane-modified WO3 photoanode. A dual-electrode series system is constructed using the mixed silane-modified WO3 photoanode and a FePO4 cathode. Battery waste liquid containing lithium-crown ether complexes is pumped into the reactor. Under illumination and bias voltage, the waste liquid flows through the dual electrodes. The photoanode oxidizes and degrades the crown ether in situ, releasing free lithium ions. Subsequently, the cathode performs highly selective solid-phase intercalation extraction of lithium ions, realizing lithium extraction from complex battery waste liquid systems, suitable for large-scale engineering application.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery waste liquid resource recycling technology, specifically involving a mixed silane modified WO3 photoanode, its preparation method, and its application in photoelectrochemical decomposition and lithium extraction. Background Technology

[0002] With the rapid increase in the number of retired lithium-ion batteries, the efficient extraction and recovery of lithium resources from complex battery waste liquids has significant strategic and environmental importance. In recent years, photoelectrochemical lithium extraction using the photoelectric effect of semiconductors has attracted much attention. Traditional technologies typically employ a semiconductor photoanode (such as WO3) to oxidize and de-complexing agents (such as 12-crown ether-4), prompting lithium ions to be released and migrate to the counter electrode (such as FePO4) for intercalation and recovery. However, the photoelectrode thin film material used in this system faces three major problems: (1) WO3 has hydrophilic oxygen-containing sites such as W-OH on its surface, which have a strong adsorption capacity for water molecules under aqueous reaction conditions. Water molecules may compete with the target complexing agent to occupy the surface active sites, resulting in severe water oxidation side reactions, consuming photogenerated holes, and thus reducing the oxidation decomposition and complexation efficiency of the complexing agent; (2) WO3 surface polar poisoning deadlock. After the crown ether molecule is oxidized and ring-opened on the WO3 surface (W-OH site), the highly polar organic small molecule intermediate product (such as glycolic acid) generated in situ will be irreversibly chemically adsorbed on the hydrophilic active sites, resulting in rapid poisoning of the catalyst and a cliff-like decrease in photocurrent in a short period of time; (3) WO3 has poor intrinsic structural stability. When working in complex waste electrolyte containing organic matter and ions for a long time, it is very easy to undergo photocorrosion and dissolution decay, which is difficult to meet the lifespan requirements of industrial long-cycle recycling.

[0003] Chinese patent CN105923694B discloses a method for preparing a WO3 / V2O5 composite photoelectrode, which improves the visible light response and photogenerated carrier transport performance of the material by forming a heterojunction, and is used for the photoelectrocatalytic degradation of methylene blue; however, this bulk engineering cannot fundamentally solve the problems of hydrophilic poisoning and intrinsic corrosion on the WO3 surface, resulting in poor cycle performance. Chinese patent CN110342833A discloses a method for introducing oxygen-containing groups such as carboxyl and aldehyde groups onto the surface of a WO3 film using ozone modification to improve hydrophilicity and interfacial reactivity; this method is beneficial for enhancing the contact between water molecules and the photoelectrode surface, but for reaction systems targeting the oxidation and decomposition of organic matter, too many polar sites not only promote competitive adsorption of water molecules but also enhance the surface retention of polar oxidation products.

[0004] The literature (https: / / doi.org / 10.1039 / C7RA03648E) uses methyltrimethoxysilane to composite with WO3 sol, utilizing the silicon-oxygen network formed by the hydrolysis of methyltrimethoxysilane to improve the film-forming properties, crack resistance, and gas-induced color stability of the film. However, its main applications are in gas-induced color thin films and optical control materials. Furthermore, the above methods typically use methyltrimethoxysilane as the network-forming component of the composite film, resulting in a film with a large thickness and high siloxane content. In photoelectrochemical reactions, a thicker or more highly cross-linked silicon-oxygen network may increase the resistance to mass transfer and interfacial charge transfer. Simultaneously, the single methyl group is mainly used to adjust the hydrophobicity of the material, making it difficult to simultaneously meet the requirements of crown ether substrate enrichment and polar product repulsion in photoelectrochemical lithium extraction applications. Summary of the Invention

[0005] The present invention aims to provide a mixed silane-modified WO3 photoanode that can resist polar product poisoning, improve the intrinsic stability of the electrode, and maintain efficient photocharge transport, as well as its preparation method and its application in photoelectrochemical decomposition and lithium extraction. The present invention utilizes two mixed silanes, phenyltrimethoxysilane (PTMS) and methyltrimethoxysilane (MTMS), to modify WO3. The resulting WO3 photoanode can specifically enrich crown ether substrates and sterically exclude polar poisoning products, significantly improving the efficiency and long-cycle stability of photoelectrochemical decomposition and lithium extraction. Furthermore, the lithium ions released after decomposition are further embedded in the FePO4 cathode, realizing the continuous separation and recovery of lithium resources from lithium battery waste liquid.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] The preparation method of WO3 photoanode modified with mixed silane includes the following steps:

[0008] A clean conductive substrate with WO3 nanosheet arrays was immersed in a mixed silane reaction solution and allowed to self-assemble at a constant temperature of 60-70°C. The substrate was then removed, washed with ethanol, dried, and heat-treated at 60-110°C to obtain a mixed silane-modified WO3 photoanode. The mixed silane reaction solution was an ethanol solution of PTMS and MTMS.

[0009] Furthermore, the conductive substrate is FTO conductive glass.

[0010] Furthermore, in the mixed silane reaction solution, the total volume concentration of the mixed silane is 0.02% to 0.1%, and the volume ratio of PTMS to MTMS is 1:1 to 3:1.

[0011] Furthermore, the constant temperature standing time is 3 to 10 hours.

[0012] Furthermore, the heat treatment time is 1 to 2 hours.

[0013] The present invention provides a mixed silane-modified WO3 photoanode prepared by the above preparation method, which is composed of a mixed silane modification layer, a light absorption layer and a conductive substrate. The mixed silane modification layer is a network constructed of phenyltrimethoxysilane and methyltrimethoxysilane, and the light absorption layer is an array of WO3 nanosheets.

[0014] The present invention also provides the application of the above-mentioned mixed silane modified WO3 photoanode in photoelectrochemical decomposition and lithium extraction.

[0015] Furthermore, the specific application method is as follows: a single-chamber membrane-free flow reactor is used, and a dual-electrode system is constructed using a mixed silane-modified WO3 photoanode and a FePO4 cathode. The two electrodes are placed in lithium battery waste liquid, and photoelectrocatalysis is carried out under light and bias conditions to oxidize and ring-open the crown ether complexing agent in the lithium battery waste liquid and gradually degrade it, thereby converting the complexed lithium into free lithium. + Free state Li + LiFePO4 is formed by embedding into the FePO4 lattice, thereby achieving solid-phase intercalation extraction of lithium.

[0016] Furthermore, the illumination condition is natural light; the bias condition is constant potential mode, with a potential of 0~1.23V.

[0017] This invention employs a silane-modified WO3 photoanode to construct a dual-electrode system for lithium extraction from lithium-ion battery waste. Under illumination and an applied bias voltage, the silane-modified WO3 photoanode absorbs light energy and generates photogenerated electron-hole pairs. These photogenerated holes migrate to the electrode surface, oxidizing and ring-opening the crown ether complex in the lithium-ion battery waste and gradually degrading it, thus breaking down the crown ether and Li-ion interaction. + The coordination structure between them allows the complexed lithium to be converted into free Li. + Photogenerated electrons are transferred to the FePO4 cathode via an external circuit, releasing Li₂. + Under the influence of an electric field and a concentration gradient, the lithium migrates to the cathode and embeds itself in the FePO4 lattice to form LiFePO4, thereby realizing a coupled recovery process of "anodic decomposition and cathode lithium extraction".

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) This invention utilizes a mixture of PTMS and MTMS silanes to modify WO3, constructing a specific molecular trapping network on the WO3 surface. The high-density benzene rings of PTMS in the modified layer have an electron-rich π system, which specifically enriches crown ether complexing agents (such as 12-crown ether-4 substrate) in lithium battery waste liquid at the nanoscale through CH-π interactions, significantly reducing the oxidation overpotential of crown ether complexing agents and accelerating interfacial catalytic kinetics.

[0020] (2) In this invention, PTMS and MTMS are used to modify WO3. Since PTMS and MTMS synergistically construct a local hydrophobic microenvironment, based on the principle of polar incompatibility, they generate a strong steric repulsion force on the highly polar byproducts (such as glycolic acid) generated by crown ether oxidation, completely blocking their adsorption and poisoning at the catalytic site, and maintaining extremely high long-cycle stability.

[0021] (3) This invention uses a single-chamber membrane-free flow reactor with the anode and cathode directly connected in series. After the lithium battery waste liquid is pumped into the reactor, the photoanode degrades and releases lithium ions in situ, and the cathode extracts them through highly selective solid-phase intercalation. This series-connected flow phase device, which first de-complexes and then extracts, completely eliminates the mass transfer dead zone, achieves a green, efficient and pollution-free process, and has the potential for large-scale engineering promotion. Attached Figure Description

[0022] Figure 1 This is a SEM image of a bare WO3 photoanode film.

[0023] Figure 2 The image shows a SEM image of the WO3 photoanode film modified with mixed silane prepared in Example 3.

[0024] Figure 3 SEM image of bare WO3 and WO3 photoanode film modified with mixed silane prepared in Example 3. XRD pattern of the crystal structure of the film.

[0025] Figure 4 Fourier transform infrared (FTIR) spectra of bare WO3 and the mixed silane-modified WO3 photoanode film prepared in Example 3.

[0026] Figure 5 Photocurrent density-potential curves of bare WO3 and the mixed silane-modified WO3 photoanode prepared in Example 3 under AM 1.5G illumination in solutions containing and without crown ether.

[0027] Figure 6 Photocurrent density-potential curves of bare WO3 and the mixed silane-modified WO3 photoanode prepared in Example 3 in dark state in solutions containing and without crown ether.

[0028] Figure 7 Photocurrent density-time curves of bare WO3 and the mixed silane-modified WO3 photoanode prepared in Example 3 under continuous droplet addition of 12-crown ether-4 and glycolic acid (GA).

[0029] Figure 8 The image shows the chromatogram of the products from the photoanodic degradation of 12-crown ether-4 by WO3 modified with mixed silanes prepared in Example 3.

[0030] Figure 9The long-cycle stability test curves of bare WO3 and the prepared mixed silane-modified WO3 photoanode at a bias voltage of 1.23 V are shown.

[0031] Figure 10 A schematic diagram of the photoelectric lithium extraction mechanism of a WO3 / FePO4 dual-electrode coupling system modified with mixed silane.

[0032] Figure 11 The curves showing the changes in cathode current and lithium-ion concentration under a 1V bias voltage are shown for the dual-electrode system consisting of a mixed silane-modified WO3 photoanode and a FePO4 cathode prepared in Example 3.

[0033] Figure 12 The image shows the X-ray photoelectron spectroscopy (XPS) spectra of the FePO4 cathode before and after the lithium extraction reaction.

[0034] Figure 13 Photocurrent density-potential curves of PTMS-modified WO3 photoanodes prepared in Comparative Example 1 and mixed silane-modified WO3 photoanodes prepared in Examples 1-3 under AM 1.5G illumination in crown ether-containing solutions. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific examples. It should be noted that the following examples are intended to facilitate further understanding of the present invention, and are not intended to limit the present invention in any way.

[0036] In the examples below, the conductive substrates on which WO3 nanosheet arrays are grown are prepared according to the reference [https: / / doi.org / 10.1002 / anie.202210804].

[0037] Example 1

[0038] (1) After cleaning the FTO conductive glass electrode with WO3 nanosheet array, let it stand in room temperature air for 30 minutes to allow the surface to naturally adsorb a trace amount of water molecules.

[0039] (2) Use a micropipette to mix PTMS and MTMS at a volume ratio of 1:1, then add an appropriate amount of the mixture to anhydrous ethanol to make the total silane concentration 0.05 vol%. Stir evenly to obtain a mixed silane reaction solution.

[0040] (3) The FTO conductive glass electrode with WO3 nanosheet array was completely immersed in the mixed silane reaction solution and left to stand for 4 hours at a constant temperature and atmospheric pressure of 60°C. The electrode was then removed and immediately rinsed three times with anhydrous ethanol to remove the physically stacked multilayer free silane. It was then quickly dried with nitrogen and placed in a vacuum drying oven for curing at a constant temperature of 60°C for 1 hour. After natural cooling to room temperature, the mixed silane modified WO3 photoanode was obtained.

[0041] Example 2

[0042] (1) After cleaning the FTO conductive glass electrode with WO3 nanosheet array, let it stand in room temperature air for 20 minutes to allow the surface to naturally adsorb a trace amount of water molecules.

[0043] (2) Use a micropipette to mix PTMS and MTMS at a volume ratio of 2:1, then add an appropriate amount of the mixture to anhydrous ethanol to make the total silane concentration 0.02 vol%. Stir evenly to obtain a mixed silane reaction solution.

[0044] (3) The FTO conductive glass electrode with WO3 nanosheet array was completely immersed in the mixed silane reaction solution and left to soak at a constant temperature and pressure of 65°C for 3 hours. The electrode was then removed and immediately rinsed three times with anhydrous ethanol to remove the physically stacked multilayer free silane. It was then quickly dried with nitrogen and placed in a vacuum drying oven for curing at a constant temperature of 80°C for 2 hours. After natural cooling to room temperature, the mixed silane modified WO3 photoanode was obtained.

[0045] Example 3

[0046] (1) After cleaning the FTO conductive glass electrode on which WO3 nanosheet array is to be grown, let it stand in room temperature air for 40 minutes to allow a trace amount of water molecules to be naturally adsorbed on its surface.

[0047] (2) Use a micropipette to mix PTMS and MTMS at a volume ratio of 3:1, then add an appropriate amount of the mixture to anhydrous ethanol to make the total silane concentration 0.1 vol%. Stir evenly to obtain a mixed silane reaction solution.

[0048] (3) The FTO conductive glass electrode with WO3 nanosheet array was completely immersed in the mixed silane reaction solution and left to stand for 4 hours at a constant temperature and pressure of 70°C. The electrode was then removed and immediately rinsed three times with anhydrous ethanol to remove the physically stacked multilayer free silane. It was then quickly dried with nitrogen and placed in a vacuum drying oven for curing at a constant temperature of 110°C for 1 hour. After natural cooling to room temperature, the mixed silane modified WO3 photoanode was obtained.

[0049] Figure 1The image shows a SEM image of the bare WO3 photoanode film, which appears to be a regular and uniform array of nanosheets.

[0050] Figure 2 The image shows the SEM image of the WO3 photoanode film modified with mixed silane prepared in Example 3. According to the comparison of the microstructure, it can be seen that after modification with ultra-low concentration mixed silane, the surface of the film still maintains the intact nanosheet array morphology and no agglomeration or pore blockage occurs.

[0051] Figure 3 The XRD patterns of bare WO3 and the mixed silane-modified WO3 photoanode film prepared in Example 3 are shown. Based on the characteristic diffraction peaks that match perfectly in the patterns (standard card JCPDS No. 20-1324), it can be determined that the modified crystal is still the intrinsic orthorhombic WO3, proving that the mild silane assembly process did not destroy the light absorption crystal form of the substrate.

[0052] Figure 4 The FTIR spectra of bare WO3 and the mixed silane-modified WO3 photoanode film prepared in Example 3 are shown. Based on the 1000–1100 cm⁻¹ region of the spectrum... -1 The distinct Si-O characteristic vibrational absorption bands appearing in the interval can conclusively confirm that the mixed silane molecules have been successfully and stably grafted onto the WO3 substrate surface through covalent bonding.

[0053] Figure 5 and Figure 6 Photocurrent density-potential curves of bare WO3 and the mixed silane-modified WO3 photoanode prepared in Example 3 under light and dark conditions in solutions containing and without crown ether, respectively. Figure 6 The dark-state curves show that the mixed silane-modified layer significantly delays the dark current onset potential in the crown-ether-free solution, confirming that it effectively suppresses the thermodynamic dark-state water oxidation side reaction by covering the active sites; according to Figure 5 The photocurrent of the modified WO3-S in the crown ether-containing solution was significantly increased and the turn-on potential was advanced by a large margin. This confirms that the large benzene ring in the hydrophobic modification layer has a specific adsorption and enrichment effect on the crown ether substrate, which greatly accelerates the oxidative degradation kinetics.

[0054] Figure 7 The photocurrent density-time curves are shown for bare WO3 and the mixed silane-modified WO3 photoanode prepared in Example 3 under continuous dropwise addition of 12-crown ether-4 and glycolic acid. The test results show that the bare WO3 electrode experiences an irreversible and severe current drop after the addition of highly polar glycolic acid, while the mixed silane-modified WO3 photoanode prepared in Example 3 maintains a stable linear plateau, confirming that the hydrophobic silane layer constructed based on the principle of polar repulsion successfully resists the adsorption and poisoning of organic byproducts. Figure 8The retention times of the characteristic peaks in the chromatogram can be further determined, and the macromolecule 12-crown ether-4 is effectively oxidized and degraded into small molecule organic compounds such as glycolic acid on the surface of the WO3 photoanode modified with mixed silane. Figure 9 The graphs show the long-cycle stability test curves of bare WO3 and the prepared mixed silane-modified WO3 photoanode at a bias voltage of 1.23 V. According to the graphs, the mixed silane-modified WO3 photoanode prepared in Example 3 showed almost no current decay during the 10-hour test, indicating that the mixed silane modification layer can reduce the adsorption of polar oxidation products on the electrode surface and reduce the direct contact between the electrolyte and the WO3 surface to a certain extent, thereby slowing down the electrode activity decay and improving the cycle stability of the WO3 photoanode.

[0055] Application examples

[0056] The mixed silane-modified WO3 photoanodes prepared in Examples 1-3 were used for activity and stability testing in photoelectrocatalytic lithium extraction. The specific operation process is as follows: A dual-electrode system (or a series continuous flow system) containing a mixed silane-modified WO3 photoanode and a FePO4 cathode was used for testing. The two electrodes were placed in a solution containing 0.01 mol L... -1 Photoelectrocatalysis was performed in a simulated waste liquid containing 12-crown ether-4 and lithium ions, with the electrolyte continuously pumped in and the illumination condition using a simulated solar intensity (AM1.5G).

[0057] Figure 10 This diagram illustrates the photoelectric lithium extraction mechanism based on a WO3 / FePO4 dual-electrode coupling system modified with mixed silanes. Under illumination and an applied bias voltage, the WO3 photoanode modified with mixed silanes absorbs light energy and generates photogenerated electron-hole pairs. The photogenerated holes migrate to the electrode surface, oxidizing and gradually degrading the crown ether complexing agent in the lithium battery waste liquid, thus disrupting the relationship between the crown ether and Li. + The coordination structure between them allows the complexed lithium to be converted into free Li. + Photogenerated electrons are transferred to the FePO4 cathode via an external circuit, releasing Li₂. + Under the influence of an electric field and concentration gradient, the lithium migrates to the cathode and embeds itself in the FePO4 lattice to form LiFePO4, thereby achieving the coupled recovery of "photoanodic decomposition degradation - cathode lithium extraction".

[0058] Figure 11 The cathode current versus lithium-ion concentration curves of the dual-electrode system consisting of a mixed silane-modified WO3 photoanode and a FePO4 cathode prepared in Example 3 under a 1V bias voltage demonstrate the lithium extraction process. Based on the significant and steady decrease in the solution lithium-ion concentration (broken line) and the stable maintenance of the photocurrent (solid line), it can be determined that the system can continuously and stably complete the closed-loop lithium extraction operation. Figure 12The images show XPS plots of the FePO4 cathode before and after the lithium extraction reaction. Based on the obvious peak of the Li 1s orbital, it can be conclusively confirmed that the free lithium ions released by the decomplexation of the photoanode have successfully shuttled and embedded into the cathode lattice.

[0059] Comparative Example 1

[0060] (1) After cleaning the FTO conductive glass electrode with WO3 nanosheet array, let it stand in room temperature air for 40 minutes to allow the surface to naturally adsorb a trace amount of water molecules.

[0061] (2) Use a micropipette to add PTMS to anhydrous ethanol to make the PTMS concentration 0.1 vol%. Stir well to obtain silane reaction solution.

[0062] (3) The FTO conductive glass electrode with WO3 nanosheet array was completely immersed in the silane reaction solution and left to stand for 4 hours at a constant temperature and atmospheric pressure of 70°C. The electrode was then removed and immediately rinsed three times with anhydrous ethanol to remove the physically stacked multilayer free silane. It was then quickly dried with nitrogen and placed in a vacuum drying oven for curing at a constant temperature of 110°C for 1 hour. After natural cooling to room temperature, a PTMS-modified WO3 photoanode was obtained.

[0063] Figure 13 The photocurrent density-potential curves of the PTMS-modified WO3 photoanode prepared in Comparative Example 1 and the mixed silane-modified WO3 photoanodes prepared in Examples 1-3 under AM 1.5G illumination in a crown ether-containing solution were presented. The results showed that, compared with the PTMS-modified WO3 photoanode, the mixed silane-modified WO3 photoanodes prepared in Examples 1-3 all exhibited higher photocurrent densities at the same test potential, with Example 3 showing the highest photocurrent density. These results indicate that the mixed silane modification layer constructed by PTMS and MTMS can, while retaining the enrichment effect of the benzene ring on the crown ether interface, adjust the coverage state of the modification layer and the interfacial microenvironment, reducing the mass transfer and charge transfer resistance that may be caused by single PTMS modification, thereby improving the photoelectrochemical oxidation activity of the WO3 photoanode for crown ethers.

[0064] Comparative Example 2

[0065] The test was conducted using a two-electrode system (or a series continuous flow system) consisting of a platinum anode and a FePO4 cathode. The two electrodes were placed in a solution containing 0.01 mol / L... -1 Electrocatalysis was performed in a simulated waste liquid containing 12-crown ether-4 and lithium ions, with the electrolyte continuously pumped in.

[0066] Table 1 shows the comparison of solution ICP tests before and after the lithium-rich cathodes of the Pt / FePO4 dual-electrode system (Pt||FP) and the mixed silane-modified WO3 / FePO4 dual-electrode system (WO3||FP) in Comparative Example 2 were subjected to constant potential oxidation to release lithium ions after the lithium extraction reaction.

[0067] Table 1

[0068]

[0069] As shown in Table 1, traditional pure electrocatalysis cannot effectively break the complex bond. The photoelectric-driven decomposition of the present invention is the key to realizing the extraction of complex waste liquid lithium.

Claims

1. A method for preparing a WO3 photoanode modified with mixed silanes, characterized in that, Includes the following steps: A clean conductive substrate with WO3 nanosheet arrays was immersed in a mixed silane reaction solution and allowed to self-assemble at a constant temperature of 60-70°C. The substrate was then removed, washed with ethanol, dried, and heat-treated at 60-110°C to obtain a mixed silane-modified WO3 photoanode. The mixed silane reaction solution was an ethanol solution of PTMS and MTMS.

2. The preparation method according to claim 1, characterized in that, The conductive substrate is FTO conductive glass.

3. The preparation method according to claim 1, characterized in that, In the mixed silane reaction solution, the total volume concentration of the mixed silanes is 0.02% to 0.1%.

4. The preparation method according to claim 1, characterized in that, The volume ratio of PTMS to MTMS is 1:1 to 3:

1.

5. The preparation method according to claim 1, characterized in that, The constant temperature standing time is 3 to 10 hours.

6. The preparation method according to claim 1, characterized in that, The heat treatment time is 1 to 2 hours.

7. A mixed silane-modified WO3 photoanode prepared by any one of the preparation methods according to claims 1 to 6.

8. The application of the mixed silane-modified WO3 photoanode as described in claim 7 in photoelectrochemical decomposition and lithium extraction.

9. The application according to claim 8, characterized in that, The specific application method is as follows: A single-chamber membraneless flow reactor is used, and a dual-electrode system is constructed using a WO3 photoanode modified with mixed silane and a FePO4 cathode. The two electrodes are placed in lithium battery waste liquid, and photoelectrocatalysis is carried out under light and bias conditions to oxidize and open the ring and gradually degrade the crown ether complexing agent in the lithium battery waste liquid, and to convert the complexed lithium into free lithium. + Free state Li + LiFePO4 is formed by embedding into the FePO4 lattice, thereby achieving solid-phase intercalation extraction of lithium.

10. The application according to claim 9, characterized in that, The illumination condition is natural light; the bias condition is constant potential mode, with a potential of 0~1.23V.

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