A prussian blue analogue and a preparation method and application thereof

Abstract

The application discloses a Prussian blue analogue, a preparation method and application thereof, and belongs to the technical field of secondary battery materials. The preparation method of the Prussian blue analogue provided by the application comprises the following steps: in a mixed system of water and an organic solvent, a co-precipitation reaction is caused by transition metal salt and A Z M Ⅱ (CN)6, and a solvent thermal reaction is caused on the obtained mixture; wherein the range of Z is 2-4. The preparation method can effectively reduce the content of vacancy defects and crystal water of the obtained Prussian blue analogue, and finally improves the electrochemical performance. The application further provides the Prussian blue analogue prepared by the above preparation method, and application of the Prussian blue analogue.

Description

Technical Field

[0001] This invention relates to the field of secondary battery materials technology, and in particular to a Prussian blue analogue, its preparation method, and its application. Background Technology

[0002] Prussian blue analogues (PBAs) crystals possess an open framework and large diffusion channels, facilitating the insertion and extraction of alkali metal ions. They are also inexpensive and non-toxic, making them a promising electrode material for secondary batteries. A common synthesis method for Prussian blue analogues is co-precipitation, where two raw materials are separately dissolved in water to prepare precursor solutions, which are then added dropwise to each other. The two precursor solutions react to form a Prussian blue analogue precipitate. This process is vigorous; during the reaction, water molecules often embed into the Prussian blue analogue crystal, resulting in a large amount of water of crystallization (also known as coordinated water). Furthermore, due to the rapid reaction, the resulting crystal contains numerous vacancy defects. These vacancy defects reduce the specific capacity of the PBA cathode material, and the presence of water of crystallization leads to side reactions.

[0003] To address the aforementioned issues, related technologies typically involve adding chelating agents, such as potassium citrate or ethylenediaminetetraacetic acid, to the co-precipitation system. Chelating agents significantly reduce the precipitation reaction rate, resulting in better crystallinity and fewer vacancy defects. However, the effects of most chelating agents are currently limited, and the electrochemical performance of the synthesized Prussian blue analogs is not significantly improved. Other techniques aim to reduce the water of crystallization content by increasing the drying temperature and vacuum level of the co-precipitated Prussian blue analogs. However, Prussian blue analogs generally have low thermal stability, requiring relatively low drying temperatures. Therefore, heating methods are ineffective at removing water and may damage the material's structure.

[0004] However, experimental results show that the commonly used methods described above have very limited effect on improving the performance of Prussian blue analogues, especially their electrochemical performance. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for preparing Prussian blue analogues, which can effectively reduce the vacancy defects and the content of crystal water (also known as coordination water) in the obtained Prussian blue analogues, thereby improving their electrochemical performance.

[0006] The present invention also provides Prussian analogues prepared by the above-described method.

[0007] The present invention also provides applications of the aforementioned Prussian analogues.

[0008] According to an embodiment of a first aspect of the present invention, a method for preparing a Prussian blue analogue is provided, the method comprising reacting a transition metal salt and AZM in a mixture of water and an organic solvent. Ⅱ (CN)6 undergoes a coprecipitation reaction, and the resulting mixture is subjected to a solvothermal reaction; wherein Z ranges from 2 to 4.

[0009] The preparation method according to embodiments of the present invention has at least the following beneficial effects:

[0010] To reduce the water of crystallization content and vacancy defects within Prussian blue analogue crystals, this invention involves a co-precipitation reaction in a system containing an organic solvent, followed by a solvothermal reaction. This allows small molecules of the organic solvent to embed within the Prussian blue analogue crystals, replacing water molecules in their original positions, thereby reducing the water of crystallization content. Furthermore, compared to conventional aqueous systems, organic solvents can also reduce the rate of the co-precipitation reaction to some extent, reducing defects within the resulting Prussian blue analogue. Moreover, the embedding of small organic solvent molecules into the crystal lattice improves the thermal stability of the Prussian blue analogue crystals, thus allowing for a certain increase in drying temperature without damaging the material's structure, providing a basis for further reducing the water of crystallization content.

[0011] According to some embodiments of the present invention, the preparation method further includes solid-liquid separation of the mixture obtained from the solvothermal reaction and drying of the obtained solid product.

[0012] According to some embodiments of the present invention, the preparation method includes the following steps:

[0013] S1. In a mixture of water and organic solvent, the transition metal salt and A... Z M Ⅱ (CN)6 undergoes a coprecipitation reaction;

[0014] S2. The mixture obtained in step S1 is subjected to a solvothermal reaction;

[0015] S3. The mixture obtained from solid-liquid separation step S2;

[0016] S4. The solid product obtained from drying step S3.

[0017] According to some embodiments of the present invention, the transition metal salt and the A Z M Ⅱ The molar ratio of (CN)6 is 0.5 to 4:1. For example, it can be 1 to 3:1. Further, it can be about 0.75:1 or about 1.5:1.

[0018] According to some embodiments of the present invention, the organic solvent includes at least one selected from ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and acetonitrile. No strict limitation is made here; in production, solvents that are miscible with water and do not affect the transition metal salt, A... Z M Ⅱ (CN)6 soluble organic solvents can be used.

[0019] According to some embodiments of the present invention, the transition metal salt includes at least one selected from nickel, iron, cobalt, copper, and manganese salts. No strict limitation is imposed here; in production, any transition metal salt that can participate in the formation of Prussian blue analogues may be used.

[0020] Specifically, it can be at least one of NiCl2, FeCl2, CoCl2, MnCl2, and its water-containing compounds.

[0021] According to some embodiments of the present invention, the transition metal salt is a mixture of NiCl2 and FeCl2.

[0022] According to some embodiments of the present invention, the molar ratio of NiCl2 to FeCl2 is 1:0.8 to 1.2. For example, it can be approximately 1:1.

[0023] According to some embodiments of the present invention, the A Z M Ⅱ In (CN)6, A is at least one of an alkali metal and an alkaline earth metal ion. Specifically, it includes Li. + Na + K + Ca 2+ and Mg 2+ At least one of them.

[0024] According to some embodiments of the present invention, the A Z M Ⅱ In (CN)6, M Ⅱ It is a transition metal ion. Specifically, M... Ⅱ The price state is either +2 or +3.

[0025] According to some embodiments of the present invention, the A Z M Ⅱ In (CN)6, M Ⅱ For Fe 2+ Fe 3+ Mn 2+ Mn 3+ Co 2+ and Co 3+ One of them.

[0026] According to some embodiments of the present invention, the A Z M Ⅱ (CN)6 includes at least one of the following: K4Fe(CN)6, K3Fe(CN)6, K3Mn(CN)6, K4Mn(CN)6, K3Co(CN)6, Na3Fe(CN)6, Na4Fe(CN)6, Na3Mn(CN)6, Na4Mn(CN)6, and hydrates of the above substances. In actual production, A can participate in the formation of Prussian blue analogues. Z M Ⅱ (CN)6 can also be selected.

[0027] According to some embodiments of the present invention, the coprecipitation reaction includes A Z M Ⅱ A mixture of (CN)6-water-organic solvent and a transition metal salt-water-organic solvent are mixed. Specifically, the following steps are included:

[0028] A1. The A Z M Ⅱ (CN)6 dissolves in water and reacts with A Z M Ⅱ An organic solvent is added to an aqueous solution of (CN)6 to obtain A. Z M Ⅱ (CN)6-water-organic solvent mixture;

[0029] The transition metal salt is dissolved in water, and an organic solvent is added to the resulting aqueous solution of the transition metal salt to obtain the metal salt-water-organic solvent mixture;

[0030] A2. Under stirring conditions, the A Z M Ⅱ The (CN)6-water-organic solvent mixture and the transition metal salt-water-organic solvent mixture are mixed.

[0031] According to some embodiments of the present invention, the coprecipitation reaction includes A Z M Ⅱ (CN)6 aqueous solution and transition metal salt-water-organic solvent mixture are mixed. Specifically, the following steps are included:

[0032] B1. The A Z M Ⅱ (CN)6 dissolves in water to obtain A Z M Ⅱ (CN)6 aqueous solution;

[0033] The transition metal salt is dissolved in water, and an organic solvent is added to the resulting aqueous solution of the transition metal salt to obtain the metal salt-water-organic solvent mixture;

[0034] B2. Under stirring conditions, A Z M Ⅱ (CN)6 aqueous solution and the transition metal salt-water-organic solvent mixture are mixed.

[0035] According to some embodiments of the present invention, the coprecipitation reaction includes A Z M Ⅱ A mixture of (CN)6-water-organic solvent and an aqueous solution of a transition metal salt is mixed. Specifically, the following steps are included:

[0036] C1. The A Z M Ⅱ (CN)6 dissolves in water and reacts with A Z M Ⅱ An organic solvent is added to an aqueous solution of (CN)6 to obtain A. Z M Ⅱ (CN)6-water-organic solvent mixture;

[0037] The transition metal salt is dissolved in water to obtain an aqueous solution of the transition metal salt;

[0038] C2. Under stirring conditions, the A Z M Ⅱ The (CN)6-water-organic solvent mixture and the aqueous solution of the transition metal salt are mixed.

[0039] According to some embodiments of the present invention, the volume ratio of water to organic solvent in the water and organic solvent mixture is 1:3 to 10. That is, the coprecipitation reaction includes the mixture of the transition metal salt and the mixture containing A. Z M Ⅱ The amounts of water and organic solvent contained in each component of the (CN)6 mixture are not limited, as long as the overall proportions meet the above-mentioned range and allow the transition metal salt and A to react. Z M Ⅱ (CN)6 can be dissolved completely. Further, the transition metal salt and A... Z M Ⅱ Based on the premise that (CN)6 can be dissolved, the higher the proportion of the organic solvent, the better the performance of the resulting Prussian blue analogue.

[0040] According to some embodiments of the present invention, the volume ratio of water to organic solvent in the water and organic solvent mixture is 1:5 to 10.

[0041] According to some embodiments of the present invention, in steps A1, B1, and C1, the solute is first dissolved in water, and then an organic solvent is added. This can improve the solute's dissolution efficiency and reduce the difficulty of dissolution. If the solute is directly added to the mixture of water and organic solvent, the required water ratio may need to be increased, and the dissolution time may also need to be increased. This may be because the formation of hydrogen bonds between water and organic solvent reduces the solute's solubility.

[0042] According to some embodiments of the present invention, the dissolution in steps A1, B1, and C1 is carried out independently by stirring for 10 to 120 minutes. In actual production, this time is not strictly limited, as long as complete dissolution is achieved. For example, it can be approximately 60 minutes.

[0043] According to some embodiments of the present invention, in the dissolution steps A1, B1, and C1, if the resulting mixture contains an organic solvent, the organic solvent is added by dropping and then mixed after the dropping is completed; preferably, the dropping rate is 0.5–5 mL / min. This dropping rate has no significant effect on the performance of the prepared Prussian blue analogue, and can be adjusted according to the performance of the production equipment in actual production. Specifically, the dropping rate can be 2–3 mL / min.

[0044] The mixing process after the organic solvent is added involves stirring for 10–120 minutes. In actual production, this time does not need to be strictly limited, as long as thorough mixing is achieved. For example, stirring for 30–60 minutes is acceptable.

[0045] According to some embodiments of the present invention, in steps A2, B2 and C2, the mixing includes adding one mixture to another mixture and continuing to mix.

[0046] For example, it will include AZM Ⅱ A mixture of (CN)6 is added to a mixture including transition metal salts; or the addition is reversed. In this step, the addition rate is selected independently from 0.5 to 2 mL / min. This dropping rate is based on a system of 1 mL H2O and 10 mL organic solvent. If scaling up production, the addition rate needs to be adjusted according to the actual situation. A co-precipitation reaction occurs during the addition process. Within the above rate range, Prussian blue analogs with minimal crystal defects and optimal electrochemical performance can be obtained. Specifically, the addition rate can be approximately 1 mL / min.

[0047] According to some embodiments of the present invention, in steps A2, B2, and C2, the mixture is stirred continuously for 10 to 120 minutes. This allows the co-precipitation reaction to proceed fully.

[0048] In steps A2, B2, and C2, the stirring state and the rotation speed during continued stirring are between 300 r / min and 2000 r / min. In actual production, this stirring speed does not need to be strictly limited, as long as mass transfer is satisfied. For example, the specific rotation speed can be 1000–1500 r / min.

[0049] According to some embodiments of the present invention, in step S2, the temperature of the solvothermal reaction is 100–200°C. This allows the small molecules of the organic solvent to be fully embedded in the crystal lattice of the Prussian blue analogue. For example, the specific temperature could be approximately 120°C.

[0050] According to some embodiments of the present invention, in step S2, the duration of the solvothermal reaction is 4 to 100 hours.

[0051] According to some embodiments of the present invention, in step S2, the duration of the solvothermal reaction is 8–24 hours. Specifically, it can be approximately 10 hours. According to some embodiments of the present invention, in step S3, the solid-liquid separation also serves a cleaning function. Specifically, the mixture obtained in step S2 is mixed with water, and then solid-liquid separation is performed. The solid obtained from the solid-liquid separation is then mixed with water again, and solid-liquid separation is continued. This process is repeated until a cleaned solid product is finally obtained. This removes unreacted impurities adhering to the surface of the obtained solid product.

[0052] According to some embodiments of the present invention, in step S4, the drying includes sequentially performing blower drying and vacuum drying.

[0053] According to some embodiments of the present invention, the temperature of the forced-air drying is 60–120°C, and the duration is 2–10 hours. This removes moisture from the surface of the obtained Prussian blue analogue, resulting in a relatively dry powder, which facilitates subsequent crushing and further drying.

[0054] According to some embodiments of the present invention, the temperature of the blower drying is 70-80°C and the duration is 2-3 hours.

[0055] According to some embodiments of the present invention, the drying process further includes crushing between the blower drying and the vacuum drying.

[0056] According to some embodiments of the present invention, the vacuum drying temperature is 150–250°C, and the duration is 6–24 hours. This allows for the maximum removal of water of crystallization from the resulting Prussian blue analogue.

[0057] According to some embodiments of the present invention, the vacuum drying temperature is 180–210°C and the duration is 10–12 hours.

[0058] According to an embodiment of the second aspect of the present invention, a Prussian blue analogue prepared by the preparation method is provided, wherein the Prussian blue analogue has a water content of approximately 0.

[0059] Since the Prussian blue analogue employs all the technical solutions of the preparation methods described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Specifically, the Prussian blue analogue has a low defect density and a low water of crystallization content, thereby exhibiting superior electrochemical performance.

[0060] According to some embodiments of the present invention, the chemical formula of the Prussian blue analogue can be written as A X M I [M Ⅱ (CN)6] y Where A is an alkali metal or alkaline earth metal ion; M I M Ⅱ It is independently selected from transition metal ions; the value of X is between 0 and 2, and the value of y is approximately 0.94-1.0.

[0061] According to some embodiments of the present invention, the A X M I [M Ⅱ (CN)6] y In the middle, M I The price state is either +2 or +3.

[0062] According to some embodiments of the present invention, the A X M I [M Ⅱ (CN)6] y In the middle, M I For Ni 2+ Fe 2+ Fe 3+ Mn 2+ Mn 3+ Co 2+ Co 3+ Cu 2+ At least one of them.

[0063] M I and M Ⅱ They can be the same or different.

[0064] A X M I [M Ⅱ (CN)6] y In this context, the closer the value of y is to 1, the better the electrochemical performance of the Prussian blue analogue.

[0065] According to an embodiment of a third aspect of the present invention, a secondary battery is provided, wherein the raw materials for preparing the secondary battery include the Prussian blue analogue.

[0066] Since the secondary battery adopts all the technical solutions of the Prussian blue analogues in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments. The secondary battery has good cycle performance.

[0067] According to some embodiments of the present invention, the secondary battery includes at least one of a lithium-ion battery, a sodium-ion battery, and a potassium-ion battery. According to some embodiments of the present invention, the secondary battery includes a battery cell and an electrolyte soaking the battery cell.

[0068] According to some embodiments of the present invention, the battery cell includes a positive electrode and a negative electrode.

[0069] According to some embodiments of the present invention, the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises the Prussian blue analogue.

[0070] According to some embodiments of the present invention, the positive electrode further includes a conductive agent and a binder.

[0071] The conductive agent includes carbon black.

[0072] The adhesive includes PVDF.

[0073] The ratio of the positive electrode active material, conductive agent, and binder is 7–9.5:0.5–2:1.

[0074] According to some embodiments of the present invention, the method for preparing the positive electrode includes at least one of pressing into a sheet or coating into a sheet. The pressing into a sheet may not include a commonly used current collector; that is, the positive electrode active material, conductive agent, and binder are directly mixed and rolled.

[0075] According to some embodiments of the present invention, the negative electrode active material of the secondary battery includes at least one of elemental metals and carbonaceous materials.

[0076] According to some embodiments of the present invention, the carbonaceous material includes at least one of graphite and hard carbon. In actual production, no strict limitation is imposed here; any carbonaceous material that can provide sufficient lithium insertion and extraction performance can be used.

[0077] The metallic element includes at least one of lithium, sodium, and potassium.

[0078] According to some embodiments of the present invention, when the secondary battery is the sodium-ion battery, the active salt in the electrolyte of the secondary battery is at least one of NaPF6, NaFSI, NaTFSI and NaClO4.

[0079] According to some embodiments of the present invention, when the secondary battery is a lithium-ion battery, the active salt in the electrolyte of the secondary battery is at least one of LiPF6, LiClO4, LiFSI, LiTFSI, LiBF4 and LiAsF6.

[0080] According to some embodiments of the present invention, when the secondary battery is a potassium-ion battery, the active salt in the electrolyte of the secondary battery is at least one of KPF6, KFSI, and KTFSI.

[0081] According to some embodiments of the present invention, the concentration of the active salt in the electrolyte is 0.8 to 4 M, specifically about 1.0 M.

[0082] According to some embodiments of the present invention, the solvent of the electrolyte includes at least one of DME, Diglyme (diethylene glycol dimethyl ether), PC, DMC, EMC, EC and DEC.

[0083] According to some embodiments of the present invention, when the secondary battery is the potassium-ion battery, the capacity retention rate of the secondary battery is ≥78% after 400 cycles.

[0084] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0085] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0086] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0087] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0088] Figure 1 These are schematic flowcharts of embodiments 1 and 2 of the present invention;

[0089] Figure 2 These are the infrared spectra of the Prussian blue analogues obtained in Example 1 and Comparative Example 1 of this invention.

[0090] Figure 3 These are electrochemical performance graphs of the Prussian blue analogues obtained in Example 1 and Comparative Example 1 of this invention.

[0091] Figure 4This is the infrared spectrum of the Prussian blue analogue obtained in Comparative Example 2 of this invention.

[0092] Figure 5 This is a graph showing the electrochemical performance of the Prussian blue analogue obtained in Comparative Example 2 of this invention.

[0093] Figure 6 This is the infrared spectrum of the Prussian blue analogue obtained in Example 2 of the present invention.

[0094] Figure 7 This is an electrochemical performance diagram of the Prussian blue analogue obtained in Example 2 of the present invention.

[0095] Figure 8 This is an electrochemical performance diagram of the Prussian blue analogue obtained in Example 3 of the present invention. Detailed Implementation

[0096] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0097] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0098] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0099] Example 1

[0100] refer to Figure 1 In this embodiment, a Prussian blue analogue (chemical formula K2Ni[Fe(CN)6]) was prepared according to the following process:

[0101] S1. Material preparation and coprecipitation reaction:

[0102] A1. Mix 0.66 mmol K4Fe(CN)6 (CAS: 13943-58-3) (using an equal amount of K4Fe(CN)6·3H2O (CAS: 14459-95-1) can achieve similar results) with 1 mL of water and stir for 30-60 min to obtain an aqueous solution of K4Fe(CN)6. Add 10 mL of tetrahydrofuran (0.5-3 mL / min) to the aqueous solution of K4Fe(CN)6 and continue stirring for 30-60 min to obtain a K4Fe(CN)6-water-organic solvent mixture.

[0103] Mix 1 mmol of transition metal salt NiCl2 (CAS: 7718-54-9) (using an equal amount of NiCl2·6H2O (CAS#7791-20-0) can achieve similar results) with 1 mL of water and stir for 30-60 min to obtain an aqueous solution of transition metal salt. Add 10 mL of tetrahydrofuran to the aqueous solution of transition metal salt and continue stirring for 30-60 min to obtain a mixture of transition metal salt-water-organic solvent.

[0104] Under stirring conditions of 300-2000 rpm, add the K4Fe(CN)6-water-organic solvent mixture to the transition metal salt-water-organic solvent mixture at a rate of 0.5-2 mL / min. After addition, continue stirring for 60 min to promote the co-precipitation reaction.

[0105] S2. The mixture obtained in step S1 is subjected to a solvothermal reaction; specifically, it is heated at 120°C for 8 hours.

[0106] S3. Washing and solid-liquid separation:

[0107] After mixing the mixture obtained in step S2 with water, centrifuge, remove the supernatant, and repeat the process to finally obtain a solid product.

[0108] S4. Drying:

[0109] Dry the solid at 80℃ for 2 hours, then grind the solid into powder and dry it under vacuum at 200℃ for 12 hours to obtain the final product.

[0110] In this embodiment, if a range value appears, it indicates that the parameter falls within this range and has no significant impact on the performance of the resulting Prussian blue analogue. The appearance of a range value is due to instrument error and human error caused by operator error. During the operation of this embodiment, the actual value set is the median of the corresponding range.

[0111] Example 2

[0112] refer to Figure 1In this embodiment, a Prussian blue analogue (K2Ni) was prepared according to the process described above. 0.5 Fe 0.5 [Fe(CN)6]), the specific steps differ from those in Example 1 as follows:

[0113] In A1, the preparation method for the transition metal salt-water-organic solvent mixture is as follows:

[0114] Mix 0.5 mmol of transition metal salt NiCl2 (CAS: 7718-54-9) (using an equimolar amount of NiCl2·6H2O (CAS#7791-20-0) can achieve similar results) with 0.5 mmol of transition metal salt FeCl2 (CAS: 7705-08-0) and 1 mL of water and stir for 30-60 min to obtain an aqueous solution of transition metal salt. Add 10 mL of tetrahydrofuran to the aqueous solution of transition metal salt and continue stirring for 30-60 min to obtain a mixture of transition metal salt-water-organic solvent.

[0115] Example 3

[0116] refer to Figure 1 In this embodiment, a Prussian blue analogue (chemical formula Na2Co[Fe(CN)6]) was prepared using the following process:

[0117] S1. Material preparation and coprecipitation reaction:

[0118] A1. Mix 0.66 mmol of Na4Fe(CN)6 (CAS:13601-19-9) (using an equimolar amount of Na4Fe(CN)6·10H2O (CAS#:14434-22-1) can achieve similar results) with 1 mL of water and stir for 30-60 min to obtain an aqueous solution of Na4Fe(CN)6. Add 10 mL of tetrahydrofuran (0.5-3 mL / min) to the aqueous solution of Na4Fe(CN)6 and continue stirring for 30-60 min to obtain a mixture of Na4Fe(CN)6-water-organic solvent.

[0119] Mix 1 mmol of transition metal salt CoCl2 (CAS: 7646-79-9) (using an equal amount of CoCl2·6H2O (CAS: 7791-13-1) can achieve similar results) with 1 mL of water and stir for 30-60 min to obtain an aqueous solution of transition metal salt. Add 10 mL of tetrahydrofuran to the aqueous solution of transition metal salt and continue stirring for 30-60 min to obtain a mixture of transition metal salt-water-organic solvent.

[0120] Under stirring conditions of 300-2000 rpm, add the Na4Fe(CN)6-water-organic solvent mixture to the transition metal salt-water-organic solvent mixture at a rate of 0.5-2 mL / min. After addition, continue stirring for 60 min to promote the co-precipitation reaction.

[0121] S2. The mixture obtained in step S1 is subjected to a solvothermal reaction; specifically, it is heated at 120°C for 8 hours.

[0122] S3. Washing and solid-liquid separation:

[0123] After mixing the mixture obtained in step S2 with water, centrifuge, remove the supernatant, and repeat the process to finally obtain a solid product.

[0124] S4. Drying:

[0125] Dry the solid at 80℃ for 2 hours, then grind the solid into powder and dry it under vacuum at 200℃ for 12 hours to obtain the final product.

[0126] Comparative Example 1

[0127] This comparative example prepared a Prussian blue analogue, which differs from Example 1 in that:

[0128] (1) Replace the organic solvent in step A1 with water.

[0129] (2) Since the Prussian blue analogue prepared in water has poor heat resistance, the vacuum drying temperature in step S4 is 80°C.

[0130] Comparative Example 2

[0131] This comparative example prepared a Prussian blue analogue, which differs from Example 1 in that:

[0132] (1) Replace the organic solvent in step A1 with water.

[0133] (2) Between steps S1 and S2, the mixture obtained in step A2 is subjected to solid-liquid separation, the volume V of the obtained filtrate is recorded, and the obtained solid and V volume of tetrahydrofuran are mixed, and the solid-tetrahydrofuran mixture is used as raw material for the solvothermal reaction in step S2.

[0134] Application Example 1

[0135] This application example uses the Prussian blue analogues of Examples 1-2 and Comparative Examples 1-2 as the positive electrode material to provide a potassium-ion battery, specifically:

[0136] The preparation steps for the positive electrode are as follows: Prussian blue analogue, conductive agent carbon black, and binder PVDF are thoroughly ground in a mortar at a mass ratio of 7:2:1. The mixture is then coated onto aluminum foil using a coating method to form a positive electrode sheet. Both the preparation of the coating slurry and the coating method can employ commercially available techniques, and these methods will not significantly affect the performance of the resulting potassium-ion battery.

[0137] The negative electrode is potassium.

[0138] The electrode solution is a DME solution containing 1M KPF6.

[0139] The diaphragm is a commercially available PP diaphragm.

[0140] Application Example 2

[0141] This application example uses the Prussian blue analogue from Example 3 as the positive electrode material to provide a sodium-ion battery, specifically:

[0142] The preparation steps for the positive electrode are as follows: Prussian blue analogue, conductive agent carbon black, and binder PVDF are thoroughly ground in a mortar at a mass ratio of 7:2:1. The mixture is then coated onto aluminum foil using a coating method to form a positive electrode sheet. Both the preparation of the coating slurry and the coating method can employ commercially available techniques, and these methods will not significantly affect the performance of the resulting sodium-ion battery.

[0143] The negative electrode is a sodium plate;

[0144] The electrolyte is an EC:DEC solution containing 1M NaClO4.

[0145] The diaphragm is a commercially available PP diaphragm.

[0146] Test case

[0147] This test example first tested the infrared spectra of the Prussian blue analogues obtained in Examples 1-3 and Comparative Examples 1-2. The spectra at 3400 cm⁻¹... -1 and 1640cm -1 The absorption peak at 3400 cm⁻¹ corresponds to the stretching vibration of interstitial water (HOH) and the bending vibration of coordinated water (OH). The results show that in the Prussian blue analogues obtained in Examples 1-2, the absorption peak at 3400 cm⁻¹ corresponds to the stretching vibration of interstitial water (HOH) and the bending vibration of coordinated water (OH). -1 The disappearance of the stretching vibration peak of the interstitial water HOH at the 1640 cm⁻¹ indicates that the interstitial water within the crystal has been removed. -1The bending vibration peak of the coordinated water OH group almost disappeared, indicating that the internal coordinated water content was close to zero. This shows that the preparation method provided by the present invention can indeed embed small organic solvent molecules into the Prussian blue lattice through co-precipitation and solvothermal reactions, thereby significantly reducing the water content in the Prussian blue analogue and potentially improving its electrochemical performance. The infrared spectrum of Example 3 is similar to that of Examples 1 and 2. In the Prussian blue analogue obtained in Comparative Example 1, both regions have strong absorption peaks, indicating that the interstitial water and coordinated water content in its crystal is very high. The parameter results of Comparative Example 2 are similar to those of Comparative Example 1. The reason may be that in Comparative Example 2, a large amount of water was already encapsulated in the Prussian blue analogue during the co-precipitation process, and because the water molecules are very small, they are difficult to be replaced by the organic solvent in the subsequent solvothermal process. Specific characterization results are as follows. Figure 2 , Figure 4 and Figure 6 As shown.

[0148] This test also evaluated the electrochemical performance (or cycle performance) of the potassium-ion battery obtained in Application Example 1 and the sodium-ion battery obtained in Application Example 2. Specifically, the test voltage range was 2-4.5V, with a charge-discharge configuration. The current was 60mA. -1 The Prussian blue analogue was tested at room temperature (25°C). The results showed that the Prussian blue analogue obtained in Comparative Example 1 retained only about 50% of its capacity after 75 cycles. The Prussian blue analogue obtained in Comparative Example 2 retained only about 33% of its capacity after 100 cycles. The Prussian blue analogue obtained in Example 1 retained 78% of its capacity after 400 cycles. The first-cycle discharge specific capacity of the Prussian blue analogue obtained in Example 2 was approximately 75 mAh g⁻¹. -1 After 100 cycles, the discharge specific capacity is approximately 72 mAh g. -1 Sodium-ion batteries showed that the discharge specific capacity of the Prussian blue analogue obtained in Example 3 was ≥165 mAh g. -1 This demonstrates that the preparation method provided by this invention, by adjusting the preparation process, yields a Prussian blue analogue with low defect density and low water content, thereby improving its electrochemical performance, especially its cycling performance. Specific test results are as follows... Figure 3 , Figure 5 and Figures 7-8 As shown.

[0149] Since the Prussian blue analogues provided by this invention have excellent electrochemical properties, it is expected that they will have broad application prospects in the fields of power batteries, energy storage batteries and 3C batteries.

[0150] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing a Prussian blue analogue, characterized in that, The preparation method includes, in a mixture of water and an organic solvent, reacting a transition metal salt and A... Z M Ⅱ (CN)6 undergoes a coprecipitation reaction, and the resulting mixture is subjected to a solvothermal reaction; wherein Z ranges from 2 to 4; The volume ratio of water to organic solvent in the water and organic solvent mixture is 1:3~10; The organic solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and acetonitrile; The solvothermal reaction is carried out at a temperature of 100~200℃ for a duration of 4~100h.

2. The preparation method according to claim 1, characterized in that, The preparation method further includes solid-liquid separation of the mixture obtained from the solvothermal reaction and drying of the obtained solid product.

3. The preparation method according to claim 2, characterized in that, The drying process includes sequential blowing drying and vacuum drying.

4. The preparation method according to claim 3, characterized in that, The temperature of the blower drying is 60~120℃, and the duration is 2~10h.

5. The preparation method according to claim 3, characterized in that, The vacuum drying temperature is 150~250℃, and the duration is 6~24h.

6. The preparation method according to claim 1, characterized in that, The coprecipitation reaction includes A Z M Ⅱ A mixture of (CN)6-water-organic solvent and a mixture of transition metal salt-water-organic solvent.

7. The preparation method according to claim 1, characterized in that, The coprecipitation reaction includes A Z M Ⅱ (CN)6 aqueous solution and transition metal salt-water-organic solvent mixture are mixed.

8. The preparation method according to claim 1, characterized in that, The coprecipitation reaction includes A Z M Ⅱ A mixture of (CN)6-water-organic solvent and an aqueous solution of transition metal salt.

9. The preparation method according to any one of claims 1 to 8, characterized in that, The transition metal salt includes at least one of nickel salt, iron salt, cobalt salt, copper salt, and manganese salt.

10. A Prussian blue analogue prepared by the method according to any one of claims 1 to 9, characterized in that, The Prussian blue analogue contains 0% water of crystallization.

11. A secondary battery, characterized in that, The raw materials for preparing the secondary battery include the Prussian blue analogue as described in claim 10.

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