An Fe-free prussian blue analogue, a preparation method thereof and a solid energy storage material

Abstract

The application relates to the technical field of liquid flow batteries, in particular to a Fe-free Prussian blue analogue, a preparation method thereof and a solid energy storage material. a [M(CN) b ] c ; wherein: V exists in one of V 2+ , V 3+ , VO 2+ or VO2 + or a mixed form of two or more thereof; wherein M is one of Co, Ni or a mixture of Co and Ni, when M is the mixture of Co and Ni, the molar ratio of Co to Ni is 3:1-1:3, the molar ratio of M to V is 1:2-1:5; the trivalent cobalt is partially reduced, the molar ratio of trivalent nickel to divalent nickel is <=0.3:1, and V, M and cyanide ions form a three-dimensional network crystal through coordination bonds. The Fe-free Prussian blue analogue of the application is prepared by directly coordinating hexacyanocobaltate and / or tetracyanonickelate with a vanadium ion salt solution after valence state regulation, and can solve the technical problems of poor reversibility and low voltage efficiency of the existing solid energy storage material.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, and in particular to an Fe-free Prussian blue analogue, its preparation method, and a solid energy storage material. Background Technology

[0002] Solid-state energy storage materials used in vanadium redox flow batteries (VRFB) refer to functional materials that exist in solid form within the vanadium redox flow battery system and can participate in energy storage and conversion through physical / chemical processes such as vanadium ion adsorption-desorption, storage-release, or redox reactions (oxidation-reduction reactions). Solid-state energy storage materials can improve the volumetric capacity of vanadium electrolytes without sacrificing electrolyte stability. However, existing solid-phase energy storage materials have some drawbacks, such as poor reversibility and electron transfer imbalance affecting voltage efficiency during the charge and discharge process of flow batteries. Furthermore, the preparation cycle of existing solid-state energy storage materials is long, and the ion exchange method often used is prone to impurities and particle agglomeration, resulting in low utilization of active sites.

[0003] One commonly used solid-state energy storage material for flow batteries is Prussian blue / Prussian white (PB / PW). Its core function relies on single-molecule redox-targeted (SMRT) reactions to achieve energy storage, overcoming the capacity limitations of traditional electrolytes. Its working principle involves energy storage through a synergistic reaction with redox mediator molecules in the electrolyte. A commonly used material is ferrocyanide / ferricyanide (Fe(CN)6). 4- / 3- Taking the mediator molecule as an example, during charging and discharging, the mediator molecule completes electron exchange at the electrode and then undergoes a SMRT reaction with PB / PW in the storage tank. During discharge, the (Fe(CN)6) on the electrode... 3- It was reduced to (Fe(CN)6) 4- After flowing into the energy storage tank with the electrolyte, PB is reduced to PW, and it is re-oxidized to (Fe(CN)6). 3- And it flows back to the electrode for cyclic reaction; during charging, the opposite occurs, PW is oxidized to PB, and the mediator molecules simultaneously complete the reverse conversion, Na + K + The insertion and extraction of cations occur throughout the entire reaction process, ensuring charge balance.

[0004] For example, CN118645668A discloses a vanadium redox flow battery based on solid energy storage materials. It uses Prussian blue analogue energy storage particles prepared by reacting ferrocyanide / ferricyanide with vanadium oxysulfate and acids, or composite materials on carbon felt loaded with Prussian blue analogues via electrodeposition, as the solid energy storage material. The latter is mixed with a vanadium electrolyte at a specific ratio, and assembled with a carbon felt single electrode and a graphite bipolar plate to obtain a vanadium redox flow battery containing solid energy storage materials. This approach using solid energy storage materials can reduce the vanadium electrolyte concentration and expand the operating temperature range of the vanadium redox flow battery.

[0005] CN118299630B discloses a high-capacity vanadium redox flow battery positive electrode electrolyte. The electrolyte contains a solid energy storage material at a concentration of 0.02-1 g / mL, primarily composed of a targeted redox solid energy storage material containing ammonium-rich iron / copper ferrocyanide. This material reacts with the positive electrode redox medium VOCs in a supporting electrolyte containing ammonium ions. 2+ / VO2 + Having similar equilibrium potentials, they can undergo reversible redox reactions to prolong the charging and discharging process. This scheme uses low-cost solid-state energy storage materials as the main energy storage medium, while employing a lower positive electrode redox medium VO. 2+ / VO2 + High capacity and energy can be achieved at lower concentrations, and the pentavalent vanadium VO2 is also reduced. + Concentration can enhance the temperature adaptability of vanadium redox flow battery systems and reduce electrolyte costs.

[0006] However, existing technologies do focus on Prussian blue analogues (PBA) in the "vanadium cation-ferrocyanide / ferricyanide" system, without fully considering other anions in the electrolyte (such as SO42-). 2- Cl - ,Br - I - The influence of (etc.) on the structural stability of PBA; and the irreversible dissolution of iron ions in the strongly acidic electrolyte of vanadium redox flow batteries. Irreversible dissolution of iron ions includes the skeletal iron ions (Fe) in Prussian blue analogue (PBA) solid energy storage materials. 2+ / Fe 3+ In the strongly acidic electrolyte environment of vanadium redox flow batteries (such as H2SO4, HCl system, pH usually < 2), it detaches from the coordination polymer backbone of PBA and releases as free Fe. 2+ / Fe 3+ The form dissolves into the electrolyte and cannot be reintegrated into the PBA framework through redox reactions during charge-discharge cycles, leading to irreversible destruction of the PBA structure. This is because the core structure of PBA is composed of metal ions (such as Fe). 2+ / Fe 3+ )-Cyanide (-CN)- The stability of the three-dimensional coordination network formed by vanadium electrolyte (such as Fe4[Fe(CN)6]3) depends on the integrity of the coordination bonds under strongly acidic conditions; while the high concentration of H2 in vanadium electrolytes... + It will protonate cyanide (-CN) - +H + →HCN), weakening the interaction between Fe and -CN. - Coordination between them leads to the shedding of Fe ions from the framework; vanadium ions (such as VO2) in the electrolyte + It also has strong oxidizing properties and may also oxidize Fe in PBA. 2+ Oxidized to Fe 3+ And Fe 3+ Its solubility is even higher in acidic electrolytes, further accelerating iron dissolution; the dissolved Fe... 2+ / Fe 3+ It will react with SO4 in the electrolyte 2- Cl - Anions can form stable complexes (such as [FeCl4)). - (e.g., Fe2(SO4)3), which cannot reconstruct the PBA framework through reversible reactions, ultimately leading to a continuous decline in PBA energy storage capacity and a deterioration in cycle stability.

[0007] The irreversible dissolution of iron ions in iron-based Prussian blue analogues (PBA) is a key issue restricting the cycling stability of PBA. However, existing technologies have not addressed this issue or provided effective solutions. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides an Fe-free Prussian blue analogue, its preparation method and a solid energy storage material. The solid energy storage material has high reaction reversibility and high kinetic performance, which helps to solve the technical problems of poor reversibility and low voltage efficiency of existing solid energy storage materials.

[0010] (II) Technical Solution

[0011] Firstly, an Fe-free Prussian blue analogue with the chemical composition V a [M(CN) b ] c A three-dimensional network crystal formed by V, M and cyanide ions through coordination bonds;

[0012] Among them, V is V 2+ V 3+ VO 2+ or VO2 +It exists in one or more mixed forms; wherein M is one or two of Co and Ni, and when M is a mixture of Co and Ni, the molar ratio of Co to Ni is 3:1-1:3; the molar ratio of M to V is 1:2-1:5;

[0013] The Co element is a mixture of divalent and trivalent cobalt, and the molar ratio of divalent cobalt to the total molar amount of Co is less than 100%; the Ni element is divalent nickel or a mixture of divalent and trivalent nickel, and the molar ratio of trivalent nickel to divalent nickel is ≤0.3:1.

[0014] The Fe-free Prussian blue analogue is prepared by direct coordination of a solution of hexacyanocobalaminate and / or tetracyanonitrile with or without valence adjustment to a salt solution of vanadium ions.

[0015] Secondly, the present invention provides a method for preparing an Fe-free Prussian blue analogue, comprising:

[0016] S1. Preparation of precursor solution

[0017] Preparation of solution A: Dissolve one or both of hexacyanocobalaminate and tetracyanonitrile completely in water to prepare a solution with a concentration of 0.02-0.5M;

[0018] Preparation of solution B: Dissolve the vanadium salt in sulfuric acid solution or a mixed solution of sulfuric acid and hydrochloric acid to prepare a solution with a vanadium ion concentration of 0.08-2M;

[0019] S2. While stirring, pour solution A (volume ratio 1:1) into solution B, continue stirring rapidly for 20-40 minutes, then let it stand for aging for 12-24 hours. Centrifuge to separate the precipitate, wash, and vacuum dry to obtain the Fe-free Prussian blue analog powder.

[0020] The Fe-free Prussian blue analog powder of this invention is prepared by direct coordination method. Subsequent experiments have shown that, compared with Prussian blue analog materials prepared by ion exchange method, the direct coordination method of this invention does not require an ion exchange step, and the resulting product has a lower impurity content and controllable cyanide valence state, resulting in better redox reversibility and compatibilization ability of PBA materials.

[0021] Preferably, in S1, after solution A is prepared, the valence state of M in solution A is then adjusted; the valence state adjustment includes using a reducing agent or an oxidizing agent or an external chemical workstation to lower or raise the valence state of the ions of M in solution A; the reducing agent is at least one of sodium thiosulfate, potassium thiosulfate, sodium sulfite, potassium sulfite, sodium metabisulfite, potassium metabisulfite, ascorbic acid, and hydrazine hydrate; the oxidizing agent is at least one of hydrogen peroxide and potassium permanganate.

[0022] Preferably, in S1, when M contains Co, the valence state regulation includes [Co(CN)6] 3- The trivalent cobalt in M ​​is partially reduced, and the reduction rate of trivalent cobalt is controlled to be less than 100%. When M contains Ni, the valence state control includes controlling Ni to remain at +2 valence or the molar ratio of trivalent nickel to divalent nickel ≤ 0.3:1, more preferably Ni. 3+ :Ni 2+ The molar ratio is ≤0.1:1. When Ni is in the +2 oxidation state, Ni is in the unoxidized state (stable state). 2+ It has a stronger coordination effect with cyanide ions, which makes the constructed PBA three-dimensional network crystalline material structure more stable.

[0023] Preferably, in S1, the total concentration of cyanide ions in solution A is ≤0.3M; and,

[0024] When the metal M in solution A is Co, the valence state control includes adding sodium sulfite or potassium sulfite to solution A to [Co(CN)6]. 3- The trivalent cobalt is partially reduced, with a reduction rate of 1 / 3 to 2 / 3.

[0025] When the metal M in solution A is Ni, maintain Ni at +2 valence or add an oxidant to solution A, and control the amount of oxidant added so that the molar ratio of trivalent nickel to divalent nickel in tetracyanonitrile is ≤0.3:1;

[0026] When the metal M in A is a combination of Co and Ni, the valence state control includes adding a reducing agent to solution A to partially reduce the trivalent cobalt in hexacyanocobalamate to divalent cobalt, and keeping the nickel in tetracyanonitrile at a +2 valence.

[0027] The above scheme, by controlling the concentration of cyanide ions in solution A, avoids the problems of excessive cyanide aggregation caused by high ionic strength, which leads to increased PBA particle agglomeration, decreased electrolyte wettability, encapsulation of active sites, and reduced product compatibilization efficiency. Experiments show that when the cyanide concentration > 0.30 M, the agglomeration effect dominates, and the various properties of PBA will significantly decrease.

[0028] Preferably, in S1, when the metal M in the solution is Co or Ni, its concentration is 0.06-0.20 M; when solution A contains both hexacyanocobalaate and tetracyanonate, the molar ratio of hexacyanocobalaate to tetracyanonate is 3:1 to 1:3, and the total cyanide concentration is ≤0.12 M. Experiments have also shown that PBA materials prepared by bimetallic synergy can achieve high capacity expansion performance even at lower cyanide concentrations (0.06-0.1 M).

[0029] Preferably, after solution B is prepared, the valence state of vanadium ions in solution B is further controlled; the control methods include: adding an oxidant or a reducing agent to solution B to increase or decrease the valence state of vanadium ions, or using electrolysis to increase or decrease the valence state of vanadium ions.

[0030] Preferably, when preparing solution B, the vanadium salt is dissolved in a mixed solution of sulfuric acid and hydrochloric acid with a total concentration of 1.8-2.2M, and the hydrochloric acid concentration in the mixed solution is ≥0; the vanadium salt is selected from vanadium oxysulfate and vanadium ion salts of divalent, trivalent, or pentavalent vanadium obtained by reduction or oxidation treatment of vanadium oxysulfate solution, and vanadium ion salts of divalent, trivalent, or tetravalent vanadium ions prepared by reduction of vanadium pentoxide, ammonium metavanadate, vanadium oxychloride, or vanadium chloride.

[0031] Preferably, in the mixed system composed of solution A and solution B obtained in S2, the molar ratio of Co:V is 1:2-1:3 or the molar ratio of Ni:V is 1:2.5-1:5, or the total molar amount of cobalt and nickel is 1:3 with respect to V.

[0032] The Fe-free Prussian blue analogue PBA prepared in this invention is an intermediate for the subsequent preparation of bulk PBA solid energy storage materials.

[0033] Thirdly, the present invention provides a solid energy storage material comprising a bulk material formed by pressing together Fe-free Prussian blue analog powder prepared from any of the above embodiments, a conductive agent, and a binder. Preferably, the conductive agent is at least one selected from carbon black, Ketjen black, acetylene black, or carbon nanotubes; the binder is a binder used in electrode active materials such as PVDF, PAA, SBR, and CMC.

[0034] Preferably, the blocky PBA solid energy storage material has a diameter of 10 mm and a thickness of 3-5 mm. Experiments have shown that it achieves a reversible battery reaction efficiency of ≥95% in flow battery systems and a capacity retention rate of ≥90% after 100 cycles.

[0035] Fourthly, this invention provides a block-shaped PBA solid energy storage material, comprising: dispersing Fe-free Prussian blue analogue PBA powder, a conductive agent, and a binder prepared in any of the above embodiments in a solvent, ultrasonically homogenizing, vacuum drying, and pressing into a block material with a diameter of 10 mm and a thickness of 3-5 mm. The solvent is a commonly used solvent for electrode active materials, such as DMF, acetone, DMSO, or NMP, and the binder is a binder used in electrode active materials such as PVDF, PAA, SBR, and CMC.

[0036] Preferably, the blocky PBA solid energy storage material is used as a solid capacity enhancer for the electrolyte in a flow battery to improve the energy storage capacity and reaction reversibility of the electrolyte.

[0037] Preferably, the flow battery is a vanadium redox flow battery with an operating temperature range of -20℃ to 50℃ and a current density of 110 mA / cm².

[0038] (III) Beneficial Effects

[0039] The technical solution of the present invention has the following technical effects:

[0040] (1) This invention abandons the traditional ion exchange method for preparing Fe-free PBA, and directly uses potassium cobalt cyanide or potassium nickel cyanide to prepare Fe-free PBA through direct coordination, eliminating the ion exchange step and achieving precise control of cyanide valence state and concentration. The preparation process of this invention can effectively reduce the impurity content in PBA materials, while avoiding the particle agglomeration problem easily caused by the ion exchange method. Compared with the comparative ion exchange method, the preparation process of this invention can improve the redox reversibility of PBA by more than 20%, and the capacity increase per unit mass can reach up to 23.3 mAh / g, which is significantly better than the materials prepared by the ion exchange method, shortens the preparation cycle of solid-phase energy storage materials, and solves the disadvantage of long preparation cycle of traditional processes. The Fe-free PBA provided by this invention uses Ni or Co to replace Fe, although due to the cyanide group (CN) in NiCo-PBA - The intrinsic problem of protonation to form HCN in strong acids persists. Under long-term cycling, issues such as ion dissolution and continuous decay of PBA energy storage capacity still occur, and the problem of metal dissolution in the traditional Fe-PBA framework cannot be completely avoided. However, due to Ni… 2+ -N≡C- and Coi 2+ The coordination bond between -N≡C- is more stable than that between Fe. 2+ -N≡C- (i.e., Coi) 2+ Ni 2+ (Stronger coordination with cyanide ions), more thermodynamically stable, and more resistant to H+. + Attacks, and Ni 2+ \Co 3+ Fe 2+ It has stronger antioxidant properties, which also increases the stability of the Ni / Co-based PBA framework.

[0041] (2) In some embodiments of the preparation of Fe-free PBA, the present invention performs differentiated and precise valence state control on Co / Ni, and implements valence state control for Co and Ni in the bimetallic system respectively, using "Co 3+ Partial reduction + Ni 2+ A combined regulatory strategy of "unoxidized or minimally oxidized" is used to avoid Co 3+ Over-reduction, while eliminating Ni 2+Partial oxidation of Co solves the technical problem of electron transfer imbalance caused by the imbalance of metal valence states. Compared with the scheme where Co is completely unreduced or over-reduced (completely reduced), "Co..." 3+ Partial reduction + Ni 2+ The "unoxidized or minimally oxidized" nature of PBA materials ensures the effective utilization of active sites, and the constructed PBA can improve the voltage efficiency of batteries by 3%-5%, avoiding the problems associated with Ni. 2+ The technical problem of decreased utilization of active sites due to oxidation lays the foundation for the high reversibility of solid energy storage materials.

[0042] (3) In a preferred method for preparing Fe-free PBA, precise control of cyanide concentration is achieved by limiting the optimal concentration range of cyanide complexes, such as controlling the concentration of cyanide complexes to ≤0.3M, to avoid the problem of increased PBA particle agglomeration caused by excessively high cyanide concentration (>0.3M); more preferably, the total cyanide concentration is more preferably in the range of 0.06-0.2M, to avoid structural defects in PBA caused by excessively low total concentrations of cyanide and M, thereby achieving a balance between the redox reversibility and structural stability of PBA materials. Limiting the cyanide concentration to the range of 0.06-0.2M solves the problems of PBA particle agglomeration and decreased electrolyte wettability caused by excessively high cyanide concentration, avoids the problem of low capacity expansion efficiency of energy storage materials and electron transfer imbalance caused by improper cyanide concentration, and ensures the voltage efficiency of energy storage materials during charging and discharging. The capacity expansion per unit mass of PBA materials prepared within this concentration range can reach more than 18mAh / g, and the product has excellent capacity expansion performance.

[0043] (4) In some embodiments, the present invention uses a Co-Ni bimetallic synergistic system to replace a single metal system, and specifies that the feed ratio of Co to Ni is in the range of 3:1 to 1:3. This scheme breaks through the limitations of single Co-based or Ni-based PBA materials; by constructing a Co-Ni bimetallic synergistic Fe-free PBA system, the performance complementarity of the bimetals is achieved. Compared with single metal PBA, the bimetallic synergistic effect can significantly improve the battery capacity and reaction reversibility of the PBA energy storage material, while further optimizing the kinetic performance of the material, making it more suitable for the capacity expansion requirements of vanadium redox flow battery electrolytes.

[0044] (5) Further, this invention uses ultrasonic homogenization, vacuum drying, and pressing to form a blocky energy storage material of a specific size (10 mm in diameter and 3-5 mm in thickness) by combining PBA / carbon-based conductive material with a binder. This imparts high conductivity and mechanical stability to the material, solving the problems of pure PBA powder being non-conductive and easily dissolved and pulverized. This makes the PBA material suitable for vanadium redox flow battery electrolyte capacity enhancement scenarios, possessing both high reversibility and high kinetic performance, and achieving stable and efficient capacity enhancement of solid-phase energy storage materials in electrolytes. Compared with composite materials of PBA loaded on carbon felt by electrodeposition, the blocky Fe-free PBA blocky material prepared by this invention is not easy to fall off during charging and discharging. Furthermore, the mechanical stability of the blocky material is ensured by the bonding effect of the binder. This solves the drawbacks of pure PBA powder being non-conductive and easily dissolved and pulverized, as well as the technical problems of carbon felt electrodeposited PBA composite materials being limited by the loading method, having low utilization of active sites, rapid capacity decay at high rates, and insufficient kinetic performance.

[0045] (6) This invention obtains a multi-dimensional control system by systematically regulating the concentration of cyanometalate precursor solution, the valence state of Co / Ni / V metal ions and the Co-Ni ratio, and prepares cyanometal complexes composed of different anions and vanadium cations, thereby achieving a significant improvement in the utilization rate of active sites and a dynamic balance of electron transfer. The prepared solid-phase energy storage material can significantly increase the volume capacity of vanadium electrolyte without sacrificing electrolyte stability, effectively reducing the electrolyte cost of vanadium redox flow batteries, and solving the drawbacks of poor reversibility and low utilization rate of traditional solid-phase energy storage materials. Detailed Implementation

[0046] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0047] Example 1

[0048] This embodiment provides a method for preparing an Fe-free Prussian blue analogue (PBA) solid energy storage material, the steps of which are as follows:

[0049] (1) Preparation of PBA powder

[0050] 0.02 mol potassium hexacyanocobalaminate (K3[Co(CN)6]) was dissolved in 500 mL of deionized water to prepare a 0.04 M solution, denoted as solution A. 0.04 mol vanadium oxysulfate was dissolved in 500 mL of 2 M sulfuric acid to prepare a 0.08 M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (the molar ratio of Co to V was 1:2), and vigorous stirring was maintained for 30 min. After that, the mixture was allowed to stand for 12 h for aging. After centrifugation, washing, and vacuum drying at 60 °C, PBA powder was obtained.

[0051] (2) Preparation of PBA block solid energy storage material

[0052] PBA powder, carbon black, and PVDF were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. After ultrasonic homogenization for 30 min, the mixture was vacuum dried at 70℃ for 8 h and then pressed into block PBA solid energy storage material with a diameter of 10 mm and a thickness of 4 mm.

[0053] Example 2

[0054] This embodiment is based on Example 1, but the molar concentration of potassium hexacyanocobalamin in solution A is increased to 0.06 M. The specific steps are as follows:

[0055] 0.03 mol potassium hexacyanocobalaminate (K3[Co(CN)6]) was dissolved in 500 mL of deionized water to prepare a 0.06 M solution, denoted as solution A. 0.075 mol NH4VO3 was dissolved in 500 mL of 2 M sulfuric acid, reduced with Na2SO3, and then dissolved to prepare a 0.15 M tetravalent vanadium solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Co to V molar ratio of 1:2.5), and vigorous stirring was maintained for 30 min. The mixture was then allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0056] Example 3

[0057] This embodiment is based on Example 1, but the molar concentration of potassium hexacyanocobalaminate in solution A is increased to 0.1 M, and a reducing agent is used to adjust the valence state of cobalt. The specific steps are as follows:

[0058] Dissolve 0.05 mol potassium hexacyanocobalaminide in 500 mL of deionized water to prepare a 0.1 M solution, then add sodium disulfite (to dilute the Co). 3+ The reduction rate was 50%, denoted as solution A; 0.15 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.3M solution, denoted as solution B; under vigorous stirring, solution A was slowly poured into solution B (Co to V molar ratio of 1:3), and vigorous stirring was maintained for 30 min, followed by standing and aging for 12 h, centrifugation, washing, and vacuum drying at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0059] Example 4

[0060] This embodiment is based on Example 1, but the molar concentration of potassium hexacyanocobalamin in solution A is increased to 0.15 M. The specific steps are as follows:

[0061] Dissolve 0.075 mol potassium hexacyanocobalaminide in 500 mL of deionized water, then add solid Na2SO3 (to make Co... 3+ A 0.15M solution (with a reduction rate of 50%) was prepared by dissolving 0.2 mol VCl3 in 500 mL of 2M sulfuric acid to prepare a 0.4M solution (referred to as solution B). Under vigorous stirring, solution A was slowly poured into solution B (Co to V molar ratio of 1:2.67), and vigorous stirring was maintained for 30 min. The mixture was then allowed to stand for 12 h to age, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0062] Example 5

[0063] This embodiment is based on Example 1, but the molar concentration of potassium hexacyanocobalamin in solution A is increased to 0.2 M. The specific steps are as follows:

[0064] Dissolve 0.1 mol potassium hexacyanocobalaminide in 500 mL of deionized water to prepare a 0.2 M solution, then add sodium disulfite (to dilute the Co). 3+ The reduction rate was 2 / 3, denoted as solution A; 0.25 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.5M solution, denoted as solution B; under vigorous stirring, solution A was slowly poured into solution B (Co to V molar ratio of 1:2.5), and vigorous stirring was maintained for 30 min, followed by standing and aging for 12 h, centrifugation, washing, and vacuum drying at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0065] Example 6

[0066] This embodiment is based on Example 1, but the molar concentration of potassium hexacyanocobalaminate in solution A is increased to 0.3 M, and a reducing agent is used to adjust the valence state of cobalt. The specific steps are as follows:

[0067] Dissolve 0.15 mol potassium hexacyanocobalaminide in 500 mL of deionized water to prepare a 0.3 M solution, then add sodium disulfite (to dilute the Co). 3+ The reduction rate was 2 / 3, denoted as solution A; 0.45 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.9M solution, denoted as solution B; under vigorous stirring, solution A was slowly poured into solution B (Co to V molar ratio of 1:3), and vigorous stirring was maintained for 30 min, followed by standing and aging for 12 h, centrifugation, washing, and vacuum drying at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0068] Example 7

[0069] This embodiment provides a method for preparing an Fe-free Prussian blue analogue (PBA) solid energy storage material, the steps of which are as follows:

[0070] Dissolve 0.01 mol of potassium tetracyanide (K₂[Ni(CN)₄]) in 500 mL of deionized water to prepare a 0.02 M solution, denoted as solution A. Dissolve 0.03 mol of vanadium pentoxide (V₂O₅) in 500 mL of a 2 M mixture of sulfuric acid and hydrochloric acid (volume ratio of sulfuric acid to hydrochloric acid 1:1) to prepare a 0.12 M solution. Then add hydrazine hydrate to reduce the solution to a solution containing VO₂O₅. 2+ A tetravalent vanadium solution, denoted as solution B, was prepared. Solution A was slowly poured into solution B (Ni to V molar ratio 1:3) under vigorous stirring. Vigorous stirring was maintained for 30 minutes, followed by aging for 12 hours. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA bulk solid energy storage material is described in Example 1.

[0071] Example 8

[0072] This embodiment is based on Example 7, but the molar concentration of potassium tetracyanobenzene nickel in solution A is increased to 0.06M. The specific steps are as follows: 0.03 mol of potassium tetracyanobenzene nickel is dissolved in 500 mL of deionized water to prepare a 0.06M solution, denoted as solution A; 0.075 mol of vanadium oxysulfate is dissolved in 500 L of 2M sulfuric acid to prepare a 0.15M solution, denoted as solution B. Under vigorous stirring, solution A is slowly poured into solution B (Ni to V molar ratio of 1:2.5), and vigorous stirring is maintained for 30 min. Afterwards, it is allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0073] Example 9

[0074] This embodiment is based on Example 7, but the molar concentration of potassium tetracyanidate in solution A is increased to 0.1M. The specific steps are as follows: 0.05 mol of potassium tetracyanidate is dissolved in 500 mL of deionized water to prepare a 0.1M solution. Then, a certain amount of hydrogen peroxide is added to partially dissolve Ni in the solution. 2+ Oxidized, and Ni 3+ :Ni 2+The ratio of Ni to V was 0.3:1, denoted as solution A. 0.15 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.3M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Ni to V molar ratio 1:3), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0075] Example 10

[0076] This embodiment is based on Example 7, but the molar concentration of potassium tetracyanidate in solution A is increased to 0.2M. The specific steps are as follows: 0.1 mol of potassium tetracyanidate is dissolved in 500 mL of deionized water to prepare a 0.2M solution. Then, a certain amount of hydrogen peroxide is added to increase the Ni concentration in the solution. 3+ :Ni 2+ The ratio of Ni to V was 0.3:1, denoted as solution A. 0.5 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 1M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Ni to V molar ratio 1:5), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0077] Example 11

[0078] This embodiment is based on Example 7, but the molar concentration of potassium tetracyanidate in solution A is increased to 0.4 M. The specific steps are as follows: 0.2 mol of potassium tetracyanidate is dissolved in 500 mL of deionized water to prepare a 0.4 M solution. Then, a certain amount of hydrogen peroxide is added to increase the molar concentration of potassium tetracyanidate in the solution.

[0079] Ni 3+ :Ni 2+ The ratio of Ni to V was 0.1:1, denoted as solution A. 0.5 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 1M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Ni to V molar ratio 1:2.5), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of the PBA bulk solid energy storage material is described in Example 1.

[0080] Example 12

[0081] This embodiment is based on Example 7, but the molar concentration of potassium tetracyanidate in solution A is increased to 0.5M. The specific steps are as follows: 0.25 mol of potassium tetracyanidate is dissolved in 500 mL of deionized water to prepare a 0.5M solution. Then, a certain amount of hydrogen peroxide is added to increase the Ni concentration in the solution. 3+ :Ni 2+ The ratio of Ni to V was 0.1:1, denoted as solution A. 0.75 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 1.5M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Ni to V molar ratio 1:3), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of the PBA bulk solid energy storage material is described in Example 1.

[0082] Example 13

[0083] This embodiment provides a method for preparing an Fe-free Prussian blue analogue (PBA) solid energy storage material, the steps of which are as follows:

[0084] Potassium hexacyanocobaltide and potassium tetracyanide nickelate were dissolved in 500 mL of deionized water at a molar ratio of 3:1 to prepare a 0.06 M solution. Sodium disulfite was added simultaneously to dilute the Co... 3+ The reduction rate was 2 / 3, denoted as solution A; 0.09 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.18M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (M to V molar ratio of 1:3), and vigorous stirring was maintained for 30 min. Afterwards, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0085] Example 14

[0086] This embodiment is based on Example 13, with the molar ratio of potassium hexacyanocobaltide and potassium tetracyanide nickelate in solution A adjusted to 1:1. The specific steps are as follows:

[0087] Potassium hexacyanocobalamin and potassium tetracyanide nickelate were dissolved in 500 mL of deionized water at a molar ratio of 1:1 to prepare a 0.06 M solution. Sodium disulfite was added simultaneously to dilute the Co... 3+The reduction rate was 2 / 3, denoted as solution A; 0.09 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.18M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (M to V molar ratio of 1:3), and vigorous stirring was maintained for 30 min. Afterwards, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0088] Example 15

[0089] This embodiment is based on Example 13, with the molar ratio of potassium hexacyanocobaltide and potassium tetracyanide nickelate in solution A adjusted to 1:3. The specific steps are as follows:

[0090] Potassium hexacyanocobalamin and potassium tetracyanide nickelate were dissolved in 500 mL of deionized water at a molar ratio of 1:3 to prepare a 0.1 M solution. Sodium disulfite was added simultaneously to dilute the Co. 3+ The reduction rate was 1 / 3, denoted as solution A. 0.15 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.3M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (M to V molar ratio of 1:3), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0091] Example 16

[0092] This embodiment is based on Example 1, but the molar concentration of potassium hexacyanocobalamin in solution A is adjusted to 0.3M, and a reducing agent is used to adjust the valence state of cobalt. The specific steps are as follows:

[0093] Dissolve 0.15 mol potassium hexacyanocobalaminide in 500 mL of deionized water to prepare a 0.3 M solution, then add sodium disulfite (Co). 3+ The reduction rate was 100%, denoted as solution A. 0.45 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 0.9M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Co to V molar ratio of 1:3), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of PBA block solid energy storage material is described in Example 1.

[0094] Example 17

[0095] This embodiment is based on Example 7, but the molar concentration of potassium tetracyanidate in solution A is increased to 0.3M. The specific steps are as follows: 0.15 mol of potassium tetracyanidate is dissolved in 500 mL of deionized water to prepare a 0.3M solution. Then, a certain amount of hydrogen peroxide is added to increase the Ni concentration in the solution. 3+ :Ni 2+ The ratio of Ni to V was 0.3:1, denoted as solution A. 0.75 mol of vanadium oxysulfate was dissolved in 500 mL of 2M sulfuric acid to prepare a 1.5M solution, denoted as solution B. Under vigorous stirring, solution A was slowly poured into solution B (Ni to V molar ratio 1:5), and vigorous stirring was maintained for 30 min. Afterward, the mixture was allowed to stand for 12 h for aging, centrifuged, washed, and vacuum dried at 60 °C to obtain PBA powder. The preparation method of the PBA bulk solid energy storage material is described in Example 1.

[0096] Example 18

[0097] The main difference between this embodiment and Example 11 is that the concentration of potassium tetracyanidate in solution A is adjusted to 0.2M, and the valence state is controlled by adjusting Ni. 3+ :Ni 2+ =0.1:1; Solution B is the same as in Example 11; The preparation process of PVA material is the same as in Example 11. In this example, the molar ratio of Ni to V is 1:5.

[0098] Comparative Example 1

[0099] This comparative example uses the ion exchange method to prepare PBA bulk solid energy storage material. The preparation method is as follows:

[0100] Dissolve 0.05 mol of potassium ferrocyanide (K₄Fe(CN)₆) in 500 ml of deionized water to prepare a 0.1 M solution, denoted as solution X. Dissolve 0.05 mol of cobalt sulfate (CoSO₄) in 500 ml of 4 M sulfuric acid solution to prepare a 0.1 M solution, denoted as solution Y. Mix solutions X and Y and stir for 2 h to perform ion exchange, obtaining solution A (containing 0.05 M Co). 2+ and 0.05M of (CN)6 6- 0.3 mol of vanadium oxysulfate was dissolved in 1000 mL of 2M sulfuric acid solution to prepare a 0.3M solution, denoted as solution B. Solution A was slowly poured into solution B under vigorous stirring for 30 min, followed by aging for 12 h. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA block solid energy storage material is described in Example 1.

[0101] Comparative Example 2

[0102] This comparative example uses the ion exchange method to prepare PBA bulk solid energy storage material. The preparation method is as follows:

[0103] Dissolve 0.05 mol of potassium ferrocyanide (K₄Fe(CN)₆) in 500 ml of deionized water to prepare a 0.1 M solution, denoted as solution X. Dissolve nickel sulfate (NiSO₄) in 500 ml of a mixed solution of 4 M sulfuric acid and hydrochloric acid (volume ratio of sulfuric acid to hydrochloric acid 1:1) to prepare a 0.12 M solution, denoted as solution Y. Mix solution X and solution Y and stir for 2 h to perform ion exchange, obtaining solution A (containing 0.06 M NiSO₄). 2+ and 0.05M of (CN)6 6- 0.3 mol of vanadium oxysulfate was dissolved in 1000 mL of 2M sulfuric acid solution to prepare a 0.3M solution, denoted as solution B. Solution A was slowly poured into solution B under vigorous stirring for 30 min, followed by aging for 12 h. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA block solid energy storage material is described in Example 1.

[0104] Comparative Example 3

[0105] This comparative example uses the ion exchange method to prepare PBA bulk solid energy storage material. The preparation method is as follows:

[0106] Dissolve 0.05 mol of potassium ferrocyanide (K₄Fe(CN)₆) in 500 ml of deionized water to prepare a 0.1 M solution, denoted as solution X. Dissolve cobalt chloride (CoCl₂) and nickel sulfate (NiSO₄) in a molar ratio of 1:3 in 500 ml of a mixed solution of 4 M sulfuric acid and hydrochloric acid (volume ratio of sulfuric acid to hydrochloric acid 1:1) to prepare a 0.12 M solution, denoted as solution Y. Mix solution X and solution Y and stir for 2 h to perform ion exchange, obtaining solution A (containing 0.015 M CoCl₂). 2+ and 0.045M Ni 2+ 0.05M of (CN)6 6- 0.3 mol of vanadium oxysulfate was dissolved in 1000 mL of 2M sulfuric acid solution to prepare a 0.3M solution, denoted as solution B. Solution A was slowly poured into solution B under vigorous stirring for 30 min, followed by aging for 12 h. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA block solid energy storage material is described in Example 1.

[0107] Comparative Example 4

[0108] This comparative example uses the ion exchange method to prepare PBA bulk solid energy storage material. The preparation method is as follows:

[0109] 0.075 mol of potassium ferrocyanide (K₄Fe(CN)₆) was dissolved in 500 ml of deionized water to prepare a 0.15 M solution, denoted as solution X. Cobalt chloride (CoCl₂) was dissolved in 500 ml of 4 M sulfuric acid solution to prepare a 0.2 M solution, denoted as solution Y. Solutions X and Y were mixed and stirred for 2 h to perform ion exchange, yielding solution A (containing 0.1 M CoCl₂). 2+ and 0.075M of (CN)6 6- 0.3 mol of vanadium oxysulfate was dissolved in 1000 mL of 2M sulfuric acid solution to prepare a 0.3M solution, denoted as solution B. Solution A was slowly poured into solution B under vigorous stirring for 30 min, followed by aging for 12 h. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA block solid energy storage material is described in Example 1.

[0110] Comparative Example 5

[0111] This comparative example uses the ion exchange method to prepare PBA bulk solid energy storage material. The preparation method is as follows:

[0112] Dissolve 0.05 mol of potassium ferrocyanide (K₄Fe(CN)₆) in 500 ml of deionized water to prepare a 0.1 M solution, denoted as solution X. Dissolve nickel chloride (NiCl₂) in 500 ml of a mixed solution of 4 M sulfuric acid and hydrochloric acid (volume ratio of sulfuric acid to hydrochloric acid 1:1) to prepare a 0.12 M solution, denoted as solution Y. Mix solution X and solution Y and stir for 2 h to perform ion exchange, obtaining solution A (containing 0.06 M NiCl₂). 2+ and 0.05M of (CN)6 6- 0.3 mol of vanadium oxysulfate was dissolved in 1000 mL of 2M sulfuric acid solution to prepare a 0.3M solution, denoted as solution B. Solution A was slowly poured into solution B under vigorous stirring for 30 min, followed by aging for 12 h. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA block solid energy storage material is described in Example 1.

[0113] Comparative Example 6

[0114] This comparative example uses the ion exchange method to prepare PBA bulk solid energy storage material. The preparation method is as follows:

[0115] Dissolve 0.05 mol of potassium ferrocyanide (K₄Fe(CN)₆) in 500 ml of deionized water to prepare a 0.1 M solution, denoted as solution X. Dissolve cobalt chloride and nickel sulfate in a 1:1 molar ratio in 500 ml of a mixed solution of 4 M sulfuric acid and hydrochloric acid (volume ratio of sulfuric acid to hydrochloric acid 1:2) to prepare a 0.15 M solution, denoted as solution Y. Mix solution X and solution Y and stir for 2 h to perform ion exchange, obtaining solution A (containing 0.0375 M Ni). 2+ and 0.0375M Co 2+ 0.05M of (CN)6 6- 0.3 mol of vanadium oxysulfate was dissolved in 1000 mL of 2M sulfuric acid solution to prepare a 0.3M solution, denoted as solution B. Solution A was slowly poured into solution B under vigorous stirring for 30 min, followed by aging for 12 h. The mixture was then centrifuged, washed, and vacuum dried at 60°C to obtain PBA powder. The preparation method of the PBA block solid energy storage material is described in Example 1.

[0116] The composition of solutions A and B and their valence states in Examples 1-18 above is summarized in Table 1. The composition of solutions A and B and their valence states in Comparative Examples 1-6 is summarized in Table 2.

[0117] Table 1: Composition and valence state control of solutions A and B in each embodiment

[0118]

[0119] Table 2: Composition and valence state regulation of solutions A and B in Comparative Examples 1-6

[0120]

[0121] The PBA block solid energy storage materials of the above embodiments and comparative examples were tested as single cells using the following method: 48cm... 2 A single cell was used as the power unit for charging and discharging. The positive electrode electrolyte consisted of a 1.65M tetravalent vanadium sulfate-based electrolyte and a vanadium electrolyte in a mixed acid system of sulfuric acid and hydrochloric acid. The negative electrode used an electrolyte with the same concentration as the positive electrode, but with the vanadium species' valence state changed to trivalent. Initially, 70ml of electrolyte was added to the positive electrode and 100ml to the negative electrode. After 5 cycles, 10g of PBA block solid energy storage material was added. Charge-discharge cycle tests were conducted at a constant current density of 110mA / cm², and the voltage efficiency (VE) and capacity increase per unit mass (mAh / g) were recorded. The test results are shown in Table 3-4.

[0122] Table 3: Statistics on single-cell voltage efficiency data and capacity increase in Examples 1-18

[0123]

[0124] Table 4: Statistics on single-cell voltage efficiency and capacity increase of Comparative Examples 1-6

[0125]

[0126] The comparison of the results of the examples and comparative examples in Tables 3-4 shows that the capacity increase per unit mass (15.8-23.3 mAh / g) and voltage efficiency (59.2%-66.0%) of the Fe-free PBA materials prepared in Examples 1-18 are significantly higher than those of Comparative Examples 1-6 (capacity increase per unit mass 12.9-15.5 mAh / g, efficiency 55.3%-58.1%). This indicates that the energy storage performance of the Fe-free PBA materials prepared by the direct coordination method is superior to that prepared by the ion exchange method, showing significant advantages in both capacity increase per unit mass and voltage efficiency compared to the products prepared by the ion exchange method in the comparative examples. This may be because the direct coordination method does not require an ion exchange step, has low impurity content, and allows for controllable cyanide valence state, thereby improving the redox reversibility of the prepared PBA materials by more than 20%, with a maximum capacity increase per unit mass of 23.3 mAh / g (Example 15), which is 50.3% higher than the highest value of the comparative examples (15.5 mAh / g, Comparative Example 6).

[0127] From the perspective of cyanide concentration, for all samples, when the cyanide concentration was too low, especially less than 0.06 M (Examples 1 and 7), the concentration of cyanide complex was insufficient, resulting in more defects in the three-dimensional network crystal structure of PBA, fewer active sites, and poor compatibilization and voltage efficiency of the product. However, when the cyanide concentration was within the suitable range of 0.06-0.2 M (Examples 3-5, 8-10, and 13-15), the cyanide ions could fully participate in the coordination reaction, forming a more complete and uniformly dispersed three-dimensional network crystal structure. This avoided the structural defects of low concentrations and the agglomeration problems of high concentrations, thus resulting in PBA materials with higher compatibilization and voltage efficiency. While the cyanide ion concentration in Example 2 was within the suitable range, its Co content was insufficient. 3+ Without valence state modulation, the capacity enhancement and voltage efficiency of PBA materials were not significantly improved. However, excessively high cyanide concentrations are also detrimental to obtaining high-performance PBA materials. For example, when the cyanide concentration is ≥0.3M (Examples 6, 11-12, 16-17), the performance of PBA materials significantly deteriorates again. This is mainly due to excessive aggregation of cyanide ions at high concentrations, which intensifies PBA particle agglomeration, reduces electrolyte wettability, and encapsulates active sites, leading to a decrease in the capacity enhancement efficiency of the PBA product. All examples show that when the total cyanide concentration in solution A is ≥0.3M (e.g., Examples 6, 11-12, 16-17), the capacity enhancement per unit mass is ≤18mAh / g (except for 20.9mAh / g in Example 6, due to Co³).+ (Partial restoration compensates for some performance loss), and the voltage efficiency is ≤62% (except for Example 6).

[0128] From the perspective of price adjustment, for Co-based PBA, Co 3+ The PBA materials prepared by partial reduction (reduction rate controlled at 1 / 3-2 / 3) (Examples 3-6) showed significantly higher energy storage performance than those prepared by no reduction (Examples 1-2) and complete reduction (Example 16). This is because, without reduction treatment, Co... 3+ Excessive oxidizing power leads to an imbalance in electron transfer and poor reversibility, resulting in decreased efficiency. Furthermore, excessive reduction of Co... 3+ All converted to Co 2+ This leads to a weakening of the coordination ability between cobalt ions and cyanide ions, resulting in a further decrease in crystal structure stability. For Ni-based PBA, the optimal valence state strategy is to "keep Ni²+ unoxidized" (Example 8). In this state, Ni²+... + In a stable state, with suitable coordination bond strength, complete crystal structure, and high utilization of active sites, the prepared nickel-based PBA material exhibits good compatibilization performance and voltage efficiency; when Ni² + Partial oxidation (Ni³) + :Ni² + =0.3:1 (Examples 9-10, Example 17) Ni³ + An excessively high proportion disrupts the coordination balance and reduces the number of active sites. While Example 7 uses Ni² + It remains in an unoxidized state, but its cyanide ion concentration is too low, while Example 17 not only has its Ni³ + The high proportion of Ni² and the excessively high concentration of cyanide ions resulted in poor energy storage performance of the products in both examples; while reducing Ni²... + oxidation ratio (Ni³) + :Ni² + =0.1:1 (Examples 11-12), possibly due to the high cyanide concentration in solution A of Examples 11-12, which easily leads to agglomeration, the energy storage performance of the PBA material did not show an improvement. In Example 18, solution A had suitable cyanide concentration and Ni²... + The oxidation ratio is low, and the energy storage performance of PBA material is better than that of the product prepared in Example 8 at a low cyanide concentration.

[0129] From the perspective of the metal elements used to construct the three-dimensional network crystal structure of PBA, Examples 13-15 employed a bimetallic system and valence state synergistic regulation, resulting in a significant improvement in the compatibility of the products compared to those prepared using a single metal system. This is mainly due to the variable valence characteristics of Co (Co²+ / Co³+) providing a rapid electron transfer channel, while the stable valence state of Ni (Ni²+) ensures structural stability, avoiding the fluctuations in the three-dimensional network crystal structure of a single Co-based system and the slow electron transfer of a single Ni-based system. The mixed coordination network formed by Co-Ni and cyanide ions is more compact than that of a single metal, increasing the number of active sites and improving the compatibility. Simultaneously, the bimetallic synergistic effect compensates for the insufficient number of active sites at low concentrations. Under the bimetallic synergistic effect, high-performance PBA energy storage materials can be prepared even at relatively low cyanide concentrations (0.06-0.12M).

[0130] In summary, this invention directly uses potassium cobalt cyanide or potassium nickel cyanide to prepare Fe-free PBA via a "coordination method," which significantly outperforms the ion exchange method. However, excessively high cyanide ion concentrations (>0.3M) or Co... 3+ Not reduced or fully reduced or Ni 2+ Oxidation will lead to a decrease in the performance of PBA. At the same time, experiments have shown that the energy storage performance of PBA materials constructed by bimetallic systems is better than that of single metal systems.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an Fe-free Prussian blue analogue, PBA, characterized in that, The preparation steps include the following: S1. Preparation of precursor solution Preparation of solution A: Dissolve one or both of hexacyanocobalaminate and tetracyanonitrile completely in water to prepare a solution with a concentration of 0.02-0.5M; after the solution A is prepared, adjust the valence state of M in solution A. The total concentration of cyanide ions in solution A is ≤0.3M; and, When the metal M in solution A is Co, the valence state control includes adding sodium sulfite or potassium sulfite to solution A to [Co(CN)6]. 3- China Co 3+ Partial restoration was performed, with a restoration rate of 1 / 3 to 2 / 3. When the metal M in solution A is Ni, either maintain Ni at a +2 valence or add an oxidant to solution A, controlling the amount of oxidant added to reduce the Ni content in the tetracyanonitrile. 3+ :Ni 2+ Molar ratio ≤ 0.3:1; When the metal M in A is a combination of Co and Ni, the valence state control includes adding a reducing agent to solution A to reduce the Co in hexacyanocobalamate. 3+ To partially reduce to Co 2+ and Ni in tetracyanonitrile +2 The price remains at +2. Preparation of solution B: Dissolve the vanadium salt in sulfuric acid solution or a mixed solution of sulfuric acid and hydrochloric acid to prepare a solution with a vanadium ion concentration of 0.08-2M; S2. While stirring, pour solution A (volume ratio 1:1) into solution B, continue stirring rapidly for 20-40 minutes, then let it stand for aging for 12-24 hours. Centrifuge to separate the precipitate, wash, and vacuum dry to obtain the Fe-free Prussian blue analogue PBA powder.

2. The production method according to claim 1, characterized by, In S1, the valence state control includes using a reducing agent or an oxidizing agent or an external chemical workstation to lower or raise the valence state of the M ions in solution A; the reducing agent is at least one of sodium thiosulfate, potassium thiosulfate, sodium sulfite, potassium sulfite, sodium metabisulfite, potassium metabisulfite, ascorbic acid, and hydrazine hydrate; the oxidizing agent is at least one of hydrogen peroxide and potassium permanganate.

3. The preparation method according to claim 1, characterized in that, In S1, when the metal M in the solution is Co or Ni, its concentration is 0.06-0.20M; when solution A contains both hexacyanocobalaate and tetracyanonate, the molar ratio of hexacyanocobalaate to tetracyanonate is 3:1 to 1:3, and the total cyanide concentration is ≤0.12M.

4. The production method according to claim 1 or 2, characterized by, In S1, after solution B is prepared, the valence state of vanadium ions in solution B is also controlled. The control methods include: adding oxidizing or reducing agents to solution B to increase or decrease the valence state of vanadium ions, or using electrolysis to increase or decrease the valence state of vanadium ions.

5. The preparation method according to claim 4, characterized in that, In S1, when preparing solution B, the vanadium salt is dissolved in a mixed solution of sulfuric acid and hydrochloric acid with a total concentration of 1.8-2.2M, and the concentration of hydrochloric acid in the mixed solution is ≥0.

6. The preparation method according to claim 4, characterized in that, In S1, the vanadium salt is vanadium oxysulfate.

7. The preparation method according to claim 4, characterized in that, In S1, the vanadium salt is a vanadium salt containing divalent vanadium ions, trivalent vanadium ions, or pentavalent vanadium ions obtained by reduction or oxidation treatment of vanadium oxysulfate solution. Alternatively, the vanadium salt is a vanadium salt containing divalent, trivalent, or tetravalent vanadium ions, prepared by reduction reaction using vanadium pentoxide, ammonium metavanadate, vanadium oxychloride, or vanadium chloride as raw materials.

8. The production method according to claim 1 or 2, characterized by, In the mixed system composed of solution A and solution B obtained in S2, the molar ratio of Co:V is 1:2-1:3 or the molar ratio of Ni:V is 1:2.5-1:5, or the molar ratio of Co+Ni to V is 1:

3.

9. A bulk PBA solid energy storage material, characterized in that, It is a block formed by uniformly compounding Fe-free Prussian blue analog PBA powder, a conductive agent, and a binder with the preparation method described in any one of claims 1-8.

Images