Ferric chloride solid-state battery and preparation method thereof

Abstract

This invention relates to a ferric chloride solid-state battery and its preparation method. The battery utilizes a ferric chloride composite cathode material modified with 2-phosphonobutane-1,2,4-tricarboxylic acid and incorporating lithium vanadium oxide functional additives. This composite cathode, together with a lithium metal anode and a gel polymer electrolyte membrane formed by in-situ polymerization, constitutes an integrated solid-state energy storage system. The composite cathode forms a stable coordination layer on the ferric chloride surface via PBTCA, and competitively anchors chloride ions at strong Lewis acid sites on the LVO particle surface, blocking the formation of polychloride intermediates. These two aspects synergistically inhibit the dissolution of the active material. The gel polymer electrolyte membrane uses a fibrous material as a framework and is formed by in-situ polymerization in a lithium salt-containing DOL solution and a Lewis acid-containing DME solution, creating a three-dimensional cross-linked network. Based on this design, the solid-state battery exhibits good interfacial contact, a lithium-ion transference number of no less than 0.416, and a long cycle life exceeding 990 cycles.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a solid-state battery based on a solvent-resistant ferric chloride composite cathode. In particular, it relates to a battery system that uses PBTCA (2-phosphonobutane-1,2,4-tricarboxylic acid) to coordinate and modify ferric chloride, and uses lithium vanadium oxide (LVO) to anchor the ferric chloride, and then combines it with an in-situ polymerized gel electrolyte membrane to jointly inhibit the dissolution and shuttle of active materials and achieve an ultra-long cycle life. Background Technology

[0002] With the increasing demands for energy density in lithium-ion batteries, conversion-type cathode materials have attracted widespread attention due to their high theoretical capacity. Among them, ferric chloride (FeCl3), as a representative of iron-based halide cathodes, has a high theoretical capacity (approximately 302 mAh·g). -1 FeCl3 possesses advantages such as abundant raw materials and low cost, showing promising application prospects. However, a fundamental problem exists when FeCl3 is used in traditional liquid electrolyte systems: soluble polychloride intermediates (such as FeCl4) are generated during charging and discharging. - ).

[0003] In traditional liquid electrolyte batteries, these soluble intermediates can migrate freely, pass through the separator, and reach the lithium anode surface to cause irreversible side reactions. This leads to continuous loss of positive electrode active material, electrolyte consumption, and interface deterioration, i.e., a severe dissolution shuttle effect, which causes rapid capacity decay and extremely short cycle life.

[0004] Using all-solid-state electrolytes (such as inorganic ceramics or ordinary solid polymers) to physically block polychloride migration is an intuitive solution. However, all-solid-state systems introduce new problems: the solid-solid interface between rigid solid electrolytes and electrodes has high contact impedance and poor interface stability, making it prone to contact failure during cycling, which limits ion transport efficiency and affects battery performance.

[0005] Using gel polymer electrolytes is a compromise approach involving physical barriers, but it fails to fundamentally address the problem of active material dissolution at the source. Existing research on cathode modification (such as polymer coating) largely focuses on physical barriers or simple chemical modifications, failing to fundamentally address the chemical nature of FeCl3 dissolution, i.e., the dissolution of Fe... 3+ (Lewis acids) and Cl - The coordination reaction between (Lewis bases). Therefore, if we can simultaneously address both ends of this reaction, we can design a method that stabilizes Fe. 3+ It can also effectively capture Cl -The combination of a complex chemical inhibition mechanism and a physical barrier network holds promise for fundamentally blocking the dissolution shuttle effect. However, designing and realizing such a material system with a clear chemical mechanism and synergistic effect, especially selecting materials that can specifically anchor Cl, remains a challenge. - Functional materials are a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies and provide a ferric chloride solid-state battery and its preparation method. The core idea of ​​this invention is to construct a triple synergistic protection system comprising chemical coordination, bulk anchoring, and gel network to block migration, starting from the chemical nature of the dissolution reaction. First, the surface coordination of ferric chloride is modified using the artificially synthesized multidentate ligand PBTCA (rich in carboxyl / phosphonate groups, a Lewis base), which directly reacts with Fe... 3+ (Lewis acid) binding forms a stable coordination layer, reducing the dissolution tendency of active substances from the source (first-level source inhibition). Secondly, innovatively, surface sites rich in strong Lewis acid sites (such as V) are introduced. 5+ Lithium vanadium oxide (LVO) is a lithium vanadium oxide. Its mechanism of action lies in the fact that the strong Lewis acid sites on the LVO surface can react with Cl- produced during the dissolution process. - (Lewis bases) exhibit specific and potent interactions, competitively anchoring chlorine species and thereby disrupting polychloride intermediates (such as FeCl4). - The generation and stabilization of ferric chloride effectively confine or anchor it within the positive electrode (secondary source suppression). Finally, this bifunctional modified positive electrode is matched with a gel polymer electrolyte membrane that can polymerize in situ under mild conditions. After polymerization, the membrane forms a dense three-dimensional network, providing final physical blocking (path blocking) for any residual dissolved species. These three mechanisms work synergistically to achieve comprehensive and multi-level suppression of the ferric chloride dissolution shuttle effect.

[0007] To achieve the above objectives, the technical solution adopted by this invention is as follows: a ferric chloride solid-state battery, the core of which lies in the use of a ferric chloride composite cathode material that has been coordinated and modified by PBTCA and composited with lithium vanadium oxide (LVO), which, together with a lithium metal anode and a gel polymer electrolyte membrane formed by in-situ polymerization, synergistically constructs an integrated solid-state energy storage system. The ferric chloride composite cathode undergoes surface treatment of ferric chloride with PBTCA ethanol-water solution to form a strong coordination protective layer, and then LVO is added as an additive to specifically anchor chloride ions (Cl...). -The process involves blocking the formation of polychlorinated compounds, followed by compounding with acetylene black conductive agent and PVDF binder. The gel polymer electrolyte membrane uses an existing membrane as a supporting framework, with a three-dimensional cross-linked network formed by in-situ polymerization of lithium-containing DOL solution and Lewis acid-containing DME solution within the framework. This dual design, combining a modified positive electrode with a barrier-type gel electrolyte, synergistically suppresses polychlorinated intermediates (such as FeCl4) during charging and discharging from both the source of active materials (chemical anchoring) and the migration path (physical barrier) levels. - The dissolution and shuttle effect of ).

[0008] Technical solution The technical solution of the present invention includes the following steps: (1) Preparation of ferric chloride composite cathode: Anhydrous ferric chloride powder is dispersed in a certain concentration of PBTCA ethanol-water solution (preferably volume ratio 1:1), and stirred at room temperature to react the phosphonic acid group and carboxylic acid group of PBTCA molecule with Fe 3+ After the reaction is complete, the solid is collected by centrifugation or filtration, and unreacted PBTCA is removed by washing with ethanol. After vacuum drying, PBTCA-modified ferric chloride complex is obtained. The complex, a certain mass of lithium vanadium oxide (LVO) powder, acetylene black, and PVDF are mixed in N-methylpyrrolidone (NMP) in a certain proportion to form a slurry, which is then coated onto an aluminum foil current collector and vacuum dried to obtain a ferric chloride composite positive electrode. (2) Preparation of precursor solution: Lithium salt was dissolved in 1,3-dioxolane (DOL) to obtain solution A; Lewis acid was dissolved in 1,2-dimethoxyethane (DME) to obtain solution B; solution A and solution B were mixed to obtain mixed precursor solution C; (3) Preparation of gel electrolyte membrane: The supporting skeleton is immersed in the mixed precursor solution C obtained in step (2), and then a polymerization reaction occurs at room temperature, so that DOL is ring-opened and polymerized in situ in the membrane skeleton to form a gel polymer electrolyte membrane. (4) Battery assembly: The ferric chloride positive electrode obtained in step (1), the gel polymer electrolyte membrane obtained in step (3), and the lithium metal negative electrode are assembled to obtain the solid-state battery.

[0009] Preferably, in step (1), the concentration of PBTCA ethanol-water solution is 0.01~0.1 M, the molar ratio of PBTCA to ferric chloride is (0.01~0.2):1, the stirring reaction time is 2~12 h, the mass percentage of LVO particles in the positive electrode active layer is 5%~30%, and the mass ratio of the resulting active material mixture (PBTCA-FeCl3+LVO) to acetylene black and PVDF is (6-8):(1-2):1.

[0010] Preferably, in step (2), the concentration of solution A is 0.5 M to 2 M, the concentration of solution B is 0.01 M to 0.05 M, and the volume ratio of solution A to solution B is 1:1 to 10:1.

[0011] Preferably, in step (3), the supporting frame is any one of glass fiber membrane, polyolefin membrane or polyacrylonitrile (PAN) membrane.

[0012] Compared with the prior art, the advantages and beneficial effects of the present invention are: (1) Mechanism innovation, precise and efficient source inhibition: For the first time, a mechanism based on Lewis base coordination center metal (PBTCA for Fe) was proposed. 3+ Lewis acid-anchored halide ions (LVO for Cl) - This mechanism employs a dual chemical source inhibition mechanism. It directly targets the chemical nature of FeCl3 dissolution, precisely intervening from both ends of the reactants. The mechanism is clear, and its synergistic effect far surpasses that of a single action or simple physical adsorption.

[0013] (2) Constructing a triple synergistic protection system to completely block shuttle: A synergistic protection system is formed by the surface coordination of PBTCA, the bulk chemical anchoring of LVO, and the dense barrier of gel electrolyte. These three mechanisms intervene from the source of dissolution, the process of occurrence, and the migration path, respectively, and together achieve effective and lasting inhibition of the shuttle effect.

[0014] (3) Stable interface, ensuring long-term cycling: Both the PBTCA coordination layer and LVO particles have good chemical stability and good compatibility with the gel electrolyte interface, which together ensure the long-term stability of the electrode / electrolyte interface and significantly reduce interfacial impedance and side reactions.

[0015] (4) Excellent performance and significantly extended cycle life: The triple synergistic effect enables a qualitative leap in battery cycle stability. Examples show that the battery using the positive electrode and gel electrolyte membrane of this invention can achieve more than 990 stable cycles, and the capacity retention rate is significantly better than that of the comparative example.

[0016] (5) The material combination exhibits remarkable non-obviousness: PBTCA, a commonly used synthetic multidentate ligand in industrial water treatment, is combined with lithium vanadium oxides (such as Li3VO4), which are mainly used in negative electrodes or solid electrolytes, to jointly solve the dissolution problem of ferric chloride cathodes. This material selection is far from the conventional thinking of those skilled in the art. This invention reveals and verifies for the first time the unique advantages and excellent synergistic effects of this specific combination in constructing a bifunctional interface (coordination + anchoring). Attached Figure Description

[0017] The invention will now be further described with reference to the accompanying drawings.

[0018] Figure 1 Optical photograph of the gel polymer electrolyte membrane prepared in Example 1.

[0019] Figure 2 Optical photograph of the gel polymer electrolyte prepared in Example 1.

[0020] Figure 3 Ion migration curve of the gel polymer electrolyte membrane prepared in Example 1.

[0021] Figure 4 Optical photographs of the gel polymer electrolyte prepared in Example 1 and after the ratio was changed: (a) after mixing and stirring; (b) after standing at room temperature for 20 min; (c) after standing at room temperature for 24 h.

[0022] Figure 5 Electrochemical performance graphs of Example 1: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0023] Figure 6 Electrochemical performance graphs of Example 2: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0024] Figure 7 Electrochemical performance graphs of Example 3: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0025] Figure 8 Electrochemical performance graphs of Example 4: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0026] Figure 9 Electrochemical performance graphs of Example 5: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0027] Figure 10 Electrochemical performance graphs of Example 6: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0028] Figure 11 Electrochemical performance graphs of Example 7: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0029] Figure 12 Electrochemical performance graphs of Example 8: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0030] Figure 13 Electrochemical performance graphs of Example 9: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0031] Figure 14Electrochemical performance graphs of Example 10: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0032] Figure 15 Electrochemical performance graphs of Example 11: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph.

[0033] Figure 16 Electrochemical performance graphs of Example 12: (a) Charge-discharge curves for the first three cycles; (b) Cycle efficiency graph. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments will be used in conjunction with the accompanying drawings to further illustrate the invention. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Rather, the invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined by the claims. Furthermore, to provide the public with a better understanding of the invention, some specific details are described in detail below. Those skilled in the art will fully understand the invention even without these detailed descriptions.

[0035] This invention utilizes a combination of PBTCA coordination modification and Lewis acid anchoring with lithium vanadium oxide (LVO) to prepare a dissolution-resistant ferric chloride cathode. This cathode is then synergistically combined with an in-situ polymerized gel electrolyte membrane to systematically address the dissolution shuttle problem of FeCl3 cathodes from both chemical source anchoring and physical pathway barrier perspectives. Compared to using only traditional liquid electrolytes (which cannot suppress dissolution) or ordinary all-solid electrolytes (which have poor solid-solid interface contact), this approach enhances intrinsic stability through cathode modification and ensures excellent interfacial contact through the fluidity of the gel. After solidification, a stable three-dimensional barrier network is formed, thus exhibiting good interfacial compatibility, high ionic conductivity (lithium-ion transference number ≥ 0.416), and significant polychloride barrier capability. The preparation process is mild and simple; the PBTCA modification and LVO composite process of the cathode is convenient and efficient, and the gel electrolyte can be polymerized in-situ at room temperature without the need for complex equipment. This collaborative design combines source suppression with path blocking, thereby reducing the formation of polychlorides at the source and blocking their migration along the path. This not only suppresses the shuttle effect and side reactions, but also indirectly promotes the formation of a stable electrode interface. Ultimately, this enables the full cell to achieve an ultra-long cycle life of over 990 cycles and high coulombic efficiency, providing a new technical path and practical solution for developing high-performance, long-life lithium metal batteries to address the challenges of dissolution failure of cathode materials such as iron-based halides.

[0036] Example 1 Preparation of ferric chloride composite cathode: First, prepare 10 mL of 0.05 M PBTCA ethanol-water solution (ethanol:water volume ratio = 1:1). Weigh 1.0 g of anhydrous ferric chloride (FeCl3) powder and slowly add it to the above solution with stirring. Continue stirring at room temperature for 6 hours. After the reaction is complete, centrifuge the mixture, collect the solid product, and wash it three times with anhydrous ethanol to remove residual PBTCA and solvent. Dry the washed solid in a vacuum oven at 60℃ for 12 h to obtain the PBTCA coordination-modified ferric chloride composite (PBTCA-FeCl3). Weigh 0.63 g of this composite, 0.07 g of Li3VO4 powder, 0.2 g of acetylene black, and 0.1 g of PVDF and mix them in an appropriate amount of NMP, then grind and prepare a slurry (where Li3VO4 accounts for 10% of the total mass of the active material). Coat the slurry evenly onto aluminum foil, dry it in a vacuum oven at 100℃ for 12 h, and cut it to obtain the cathode sheet.

[0037] Precursor solution preparation: In a glove box (H2O, O2 < 0.1 ppm), 287.1 mg of LiTFSI was weighed and dissolved in 1 mL of DOL to obtain solution A; 16.7 mg of Sn(OTf)2 was weighed and dissolved in 1 mL of DME to obtain solution B. Solution A and solution B were mixed at a volume ratio of 10:1 and stirred for 15 min to obtain precursor solution C.

[0038] Preparation of gel electrolyte membrane: Immerse a glass fiber membrane in precursor solution C to ensure complete wetting, and let it stand at room temperature for 30 min. DOL undergoes ring-opening polymerization to form a gel within the glass fiber skeleton, thus obtaining a gel polymer electrolyte membrane.

[0039] The materials were fabricated into batteries as follows: lithium foil was used as the negative / counter electrode, a gel polymer electrolyte membrane as the separator and electrolyte, and ferric chloride composite positive electrode. These were assembled into CR2025 type button cells in an argon-protected glove box. After all batteries were assembled, they were allowed to stand for 8 hours, and then cycle performance tests were conducted at 1 C using a LAND CT2001A battery testing system.

[0040] Example 2 This embodiment only changes the ferric chloride active material in Example 1. In step (1), 0.63 g of unmodified original FeCl3 powder and 0.07 g of Li3VO4 powder are mixed, and PBTCA treatment is not performed. The battery assembly and testing methods are the same as in Example 1.

[0041] Example 3 The difference between this embodiment and Embodiment 1 is that in step (1), Li3VO4 powder is not added; instead, 0.7 g of PBTCA-FeCl3 composite is used, mixed with 0.2 g of acetylene black and 0.1 g of PVDF to form a slurry. The battery assembly and testing methods are the same as in Embodiment 1.

[0042] Example 4 The only difference between this embodiment and Example 1 is that Li3VO4 is replaced with an equal mass of titanium dioxide (TiO2) powder, while the other steps and proportions are exactly the same.

[0043] Example 5 The difference between this embodiment and Example 1 is that in step (3), a gel electrolyte membrane is not prepared; instead, a Celgard 2400 polypropylene (PP) membrane is used, and 60 μL of conventional liquid electrolyte (1 M LiTFSI in DOL / DME (1:1 v / v) with 2% LiNO3) is added. The battery assembly and testing methods are the same as in Example 1.

[0044] Example 6 The difference between this embodiment and Example 1 is that in step (1), the modifier PBTCA is replaced with an equimolar amount of disodium ethylenediaminetetraacetate (EDTA-2Na), and the rest of the steps are exactly the same.

[0045] Example 7 The difference between this embodiment and embodiment 1 is that in step (1), the molar ratio of PBTCA to ferric chloride is changed to 0.005:1, while the rest of the steps are exactly the same.

[0046] Example 8 The difference between this embodiment and embodiment 1 is that in step (1), the amount of Li3VO4 added is changed to 2% of the total mass of the active substance (i.e., PBTCA-FeCl3 0.686 g, Li3VO4 0.014 g), and the rest of the steps are exactly the same.

[0047] Example 9 The difference between this embodiment and embodiment 1 is that in step (1), the amount of Li3VO4 added is changed to 35% of the total mass of the active substance (i.e., PBTCA-FeCl3 0.455 g, Li3VO4 0.245 g), and the rest of the steps are exactly the same.

[0048] Example 10 In this embodiment, the lithium salt in Example 1 is replaced with lithium hexafluorophosphate (LiPF6), while the preparation method of the polymer electrolyte membrane, battery assembly and testing method are exactly the same as in Example 1.

[0049] Example 11 In this embodiment, the only difference is that the supporting membrane in Example 1 is replaced with polyimide (PI) nonwoven fabric. The preparation method of the polymer electrolyte membrane, battery assembly and testing method are exactly the same as in Example 1.

[0050] Example 12 In this embodiment, the Lewis acid in the initiator solution of Example 1 is replaced with boron trifluoride diethyl ether complex (BF3·Et2O). The solution preparation, battery assembly and testing methods are exactly the same as in Example 1.

[0051] The precursor in Example 1 completely solidified at room temperature for 20 minutes, confirming that the polymerization reaction was fully completed. Figure 2 As shown; the gel polymer electrolyte membrane obtained after impregnation and curing with the precursor solution retains the appearance of glass fibers under optical conditions and inherits the flexibility of glass fibers, such as Figure 1 As shown. When this separator is used to assemble batteries, its lithium-ion transference number reaches 0.416 (…). Figure 3 It exhibits excellent ion transport properties. Furthermore, the ratio of solution A to solution B affects gel formation; in Example 1, after changing the ratio of the precursor solution, it still failed to solidify even after being left at room temperature for 24 hours. Figure 4 ).

[0052] Electrochemical performance analysis: Electrochemical performance was tested using the LAND CT2001A battery testing system. The charge-discharge curves of the batteries assembled in each embodiment at 1C rate for the first three cycles are shown below. Figure 5 As shown in figures a to 16a, analysis reveals that Example 1, employing the core solution of this invention, exhibits the clearest and most stable voltage plateau and the smallest polarization voltage in its charge-discharge curves, demonstrating a highly reversible and efficient electrochemical reaction process.

[0053] In contrast, the curve features of the comparative embodiments clearly reflect the importance of each technical element: The curve of Example 2 (with only LVO added and no PBTCA modification) shows large voltage polarization and plateau decay, indicating that the active material is severely dissolved when the PBTCA surface coordination layer is lacking, and the auxiliary effect of LVO alone is limited.

[0054] The plateau stability of Example 3 (PBTCA modification only, without LVO addition) was worse than that of Example 1, and the polarization voltage was higher. This directly proves the key role of introducing LVO in anchoring chloride ions in the bulk phase and improving the stability of the reaction plateau.

[0055] The charge-discharge curve plateau stability of Example 4 (with Li3VO4 replaced by TiO2) was significantly worse than that of Example 1. This indicates that although TiO2 is a common inorganic filler, its surface lacks properties such as V...5+ The presence of strong Lewis acid sites makes it impossible to effectively anchor chloride ions through chemical action, thus verifying the necessity of using LVO in this invention.

[0056] Example 5 (using liquid electrolyte instead of gel) exhibited poor charge-discharge voltage plateau stability, a sloping curve, and a significantly increased polarization voltage. This demonstrates that even with dual modification of the cathode, the shuttle effect of polychlorides cannot be effectively suppressed in a liquid medium without the physical barrier provided by the three-dimensional network of the gel electrolyte.

[0057] For the series of embodiments with parameter adjustments, their charge-discharge curves further confirm the precise requirements for system synergy: The plateau stability and voltage polarization of Example 6 (with the modifier replaced by EDTA-2Na) were inferior to those of Example 1, demonstrating that PBTCA, due to its specific phosphonic acid properties, exhibits these characteristics. The unique advantages of carboxylic acid hybrid molecular structures in constructing stable coordination layers.

[0058] The curves of Example 7 (PBTCA dosage too low) and Example 8 (LVO content 2%) both show that the voltage plateau stability is lower than that of Example 1, and the voltage polarization is increased, indicating that when the amount of modifier and functional additive is insufficient, it is difficult to form a complete and effective protective network.

[0059] The curve plateau of Example 9 (LVO content of 35%) was shortened and the capacity decreased, indicating that excessive LVO may affect the electron conductivity and active material ratio of the positive electrode, and there is an optimal addition range.

[0060] The curves of Example 10 (lithium salt replaced with LiPF6), Example 11 (skeleton replaced with PI) and Example 12 (initiator replaced with BF3·Et2O) all showed varying degrees of increased voltage polarization or decreased plateau persistence, indicating that the key components in the gel electrolyte system need to be optimized to ensure the best ion transport and interface stability.

[0061] From the cycle performance graph ( Figure 5 A more direct conclusion can be drawn from (b to 16b): The battery assembled in Example 1 exhibited excellent long-cycle stability, capable of stable cycling for over 990 cycles, with both capacity retention and coulombic efficiency maintained at extremely high levels.

[0062] For direct comparison: The battery cycle life of Example 2 (with only LVO added and no PBTCA modification) was significantly shortened and the capacity decayed rapidly, indicating that relying solely on gel electrolyte for physical barrier is insufficient.

[0063] Example 3 (PBTCA modification only, without LVO) showed faster battery capacity decay, indicating that without the bulk chemical anchoring effect of LVO, dissolved species cannot be effectively restricted, resulting in limited improvement in cycle performance.

[0064] Battery cycle performance of Example 4 (with Li3VO4 replaced by TiO2) Figure 8 (b) Significant degradation was observed, with its capacity retention and long-cycle stability being significantly lower than in Example 1. This result directly confirms that ordinary fillers lacking strong Lewis acid sites cannot replace LVO to achieve effective chloride ion anchoring, highlighting the irreplaceable nature of LVO materials in the system of this invention.

[0065] The battery capacity of Example 5 (liquid electrolyte) decayed rapidly in the early stages. This result demonstrates from the opposite perspective that even with dual modification of the positive electrode, without the three-dimensional network of the gel electrolyte for final physical barrier, it is impossible to effectively resist the violent shuttle of polychlorides in the liquid medium.

[0066] Although the performance of Example 6 (with the modifier replaced by EDTA-2Na) was better than that of the liquid system, it was significantly inferior to that of Example 1, indicating that not any strong complexing agent can achieve the same synergistic effect as PBTCA.

[0067] In Examples 7 to 12, any deviation of key parameters (PBTCA dosage, LVO content, lithium salt type, framework material, initiator type) from the preferred range led to accelerated capacity decay or reduced coulombic efficiency, systematically demonstrating that the realization of the superior performance of the present invention is highly dependent on the precise synergy of each component within the scope of the claims.

[0068] In summary, the complete experimental data demonstrate that this invention successfully constructs a novel, multi-layered protection system by combining the surface coordination modification of ferric chloride with PBTCA, the bulk chemical anchoring effect of LVO on chloride ions, and synergistically using an in-situ polymerized gel electrolyte membrane. This system effectively suppresses the dissolution shuttle effect of ferric chloride at three levels: surface chemical stabilization, bulk ion anchoring, and migration path blocking.

[0069] This integrated approach significantly surpasses the traditional approach of simply improving the cathode or replacing the electrolyte. The specific combination of PBTCA and LVO (especially Li3VO4) overcomes the limitations of single modification measures and achieves a synergistic effect of source protection; while the gel electrolyte prepared by specific formulation and process not only provides good interfacial contact and ion transport capabilities, but also acts as a reliable barrier to prevent the migration of dissolved species.

[0070] Therefore, this invention endows ferric chloride-based batteries with an ultra-long cycle life of over 990 cycles and high coulombic efficiency, fundamentally solving the core challenges in the commercial application of this system. Meanwhile, a series of comparative experiments show that any key component (such as the type and amount of PBTCA, the type and content of LVO, the selection of lithium salts, the framework, and the initiator in the gel electrolyte) deviates significantly from the preferred range described in this invention, resulting in a significant decrease in overall performance. This provides sufficient experimental evidence for the limitations on components, proportions, and structures specified in the claims.

Claims

1. A ferric chloride solid-state battery, characterized in that, It includes a ferric chloride composite positive electrode, a lithium metal negative electrode, and a gel polymer electrolyte membrane; The active material of the ferric chloride composite cathode is a ferric chloride complex with coordination modified by 2-phosphonobutane-1,2,4-tricarboxylic acid PBTCA and lithium vanadium oxide (LVO) particles, which are mixed with conductive agent acetylene black and binder polyvinylidene fluoride to prepare the cathode. The gel polymer electrolyte membrane is formed by in-situ polymerization on a supporting framework using a precursor solution formed by mixing a DOL solution containing lithium salt and a DME solution containing Lewis acid initiator.

2. The solid-state battery according to claim 1, characterized in that, In the PBTCA-coordination modified ferric chloride complex, the molar ratio of PBTCA to ferric chloride is (0.01~0.2):1; Its mass percentage in the ferric chloride composite positive electrode active layer is 5% to 30%.

3. The solid-state battery according to claim 1, characterized in that, The lithium vanadium oxide is at least one selected from Li3VO4, LiV3O8, LiVO2 and LiV2O5.

4. The solid-state battery according to claim 1, characterized in that, In the ferric chloride composite cathode, the mixing mass ratio of active material, acetylene black, and PVDF is (6-8):(1-2):1, wherein the mass ratio of PBTCA-modified ferric chloride composite to LVO in the active material is (70-95):(5-30).

5. The solid-state battery according to claim 1, characterized in that, In the DOL solution containing lithium salt, the lithium salt is any one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium difluorooxalateborate, and its concentration in DOL is from 0.5 M to 2 M.

6. The solid-state battery according to claim 1, characterized in that, In the DME solution containing the Lewis acid initiator, the Lewis acid is any one of stannous trifluoromethanesulfonate, aluminum trifluoromethanesulfonate, and ferric trifluoromethanesulfonate, and its concentration in the DME is from 0.01 M to 0.05 M.

7. The solid-state battery according to claim 1, characterized in that, In the preparation of the gel polymer electrolyte membrane, the mixing volume ratio of the DOL solution containing lithium salt to the DME solution containing Lewis acid is 1:1 to 10:

1.

8. The solid-state battery according to claim 1, characterized in that, The supporting frame is any one of glass fiber membrane, polyolefin membrane or polyacrylonitrile membrane.

9. A method for preparing a ferric chloride solid-state battery according to any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Preparation of ferric chloride composite cathode: Anhydrous ferric chloride powder was dispersed in an ethanol-water solution of PBTCA. After stirring, washing and drying, PBTCA coordination-modified ferric chloride composite was obtained. The composite, lithium vanadium oxide powder, acetylene black and PVDF were mixed in N-methylpyrrolidone to form a slurry, which was coated on an aluminum foil current collector and dried under vacuum to obtain ferric chloride composite cathode sheet. (2) Preparation of precursor solution: Lithium salt was dissolved in 1,3-dioxolane to obtain solution A; Lewis acid was dissolved in 1,2-dimethoxyethane to obtain solution B; solution A and solution B were mixed to obtain mixed precursor solution C; (3) Preparation of gel electrolyte membrane: The supporting skeleton is immersed in the mixed precursor solution C obtained in step (2), and then a polymerization reaction occurs at room temperature, so that DOL is ring-opened and polymerized in situ in the membrane skeleton to form a gel polymer electrolyte membrane. (4) Battery assembly: The ferric chloride positive electrode obtained in step (1), the gel polymer electrolyte membrane obtained in step (3), and the lithium metal negative electrode are assembled to obtain the solid-state battery.

10. The application of a ferric chloride solid-state battery as described in any one of claims 1 to 8 in an electrochemical energy storage device.

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