A prussian blue analogue and its modification method and application

Abstract

This invention discloses a Prussian blue analogue, its modification method, and its applications, relating to the field of battery materials technology. The modification method of this invention includes the following steps: mixing the Prussian blue analogue to be treated with an electrolyte salt in an organic solvent, heating and refluxing, and extracting the solid product from the refluxed solution to obtain the Prussian blue analogue. The modification method of this invention effectively removes the water of crystallization within the crystal lattice of the Prussian blue analogue, while the added electrolyte salt facilitates the formation of [electrolyte salt + organic solvent]. + The structure effectively promotes the exchange of water of crystallization between the organic solvent and the Prussian blue analogue crystal, greatly improving the cycle stability and electrochemical performance of the Prussian blue analogue, making it suitable for the field of battery materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a Prussian blue analogue, a modification method and application thereof. BACKGROUND

[0002] Prussian blue analogues (PBAs) have great development potential due to their simple synthesis process, low cost, non-toxicity and easy scale production, and are the most common metal organic framework cathode materials in sodium ion batteries. Sodium ion batteries are considered as ideal electrochemical energy storage technology, and have broad application prospects in large-scale energy storage, low-speed electric vehicles and other fields. In sodium ion batteries, the cathode material plays a decisive role in its performance. Therefore, the development and improvement of Prussian blue analogues are of great significance to the development of sodium ion batteries. The ideal Prussian blue and Prussian blue analogue have a perfect framework structure, and as the cathode material of sodium ion batteries, they have the advantages of high capacity, high rate, long cycle life and small polarization voltage. However, the Prussian blue analogues prepared by the current method often have the problem of high content of crystallization water. The crystallization water in the Prussian blue analogue will promote the decomposition of the electrolyte and a series of side reactions, thereby corroding the electrode material and causing serious attenuation of the cycle life of the battery.

[0003] In the synthesis method of Prussian blue analogue, the traditional co-precipitation method has the advantages of low cost, non-toxicity and large-scale production. However, the solubility constant of Prussian blue analogue is extremely small, the nucleation and grain growth of the crystal occur almost simultaneously, the obtained product has irregular morphology and contains a large amount of crystallization water. The crystallization water will promote the decomposition of the electrolyte and a series of side reactions, thereby corroding the electrode material and causing serious attenuation of the cycle life of the battery.

[0004] In order to solve the problem of high content of crystallization water in the Prussian blue analogue prepared by the co-precipitation method, people usually use vacuum drying method to reduce the content of crystallization water. However, due to the low thermal stability of Prussian blue analogue, only low temperature drying can be used, and even vacuum drying can only remove a small amount of crystallization water in Prussian blue analogue, and it is difficult to obtain quasi-anhydrous or anhydrous samples. SUMMARY

[0005] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the purpose of the present application is to provide a modification method for the internal crystallization water of Prussian blue analogue, which forms an [electrolyte salt + organic solvent] structure by electrolyte salt and organic solvent, promotes the exchange of internal crystallization water of Prussian blue analogue by organic solvent, and effectively removes the crystallization water of Prussian blue analogue. +

[0006] ​The second aspect of the present application provides a Prussian blue analogue.

[0007] The third aspect of the present application provides a positive electrode material.

[0008] The fourth aspect of the present application provides a battery.

[0009] To achieve the above-mentioned object, the technical scheme adopted by the present application is as follows:

[0010] The first aspect of the present application provides a modification method of a Prussian blue analogue, comprising the following steps:

[0011] Mixing the Prussian blue analogue to be treated with an electrolyte salt in an organic solvent, heating and performing condensation reflux, extracting the solid product in the solution after reflux, and obtaining the Prussian blue analogue.

[0012] The present application, without destroying the crystal structure of the Prussian blue analogue, embeds the organic solvent into the crystal lattice of the Prussian blue analogue and exchanges it with the crystal water therein by means of condensation reflux, so as to replace the crystal water in the crystal lattice of the Prussian blue analogue, and obtains a Prussian blue analogue containing an organic solvent. The modification method of the present application effectively removes the crystal water in the crystal lattice of the Prussian blue analogue, greatly improves the cycle stability of the Prussian blue analogue, and improves the electrochemical performance of the material.

[0013] In addition, the modification method of the present application also adds an electrolyte salt, which is beneficial to form a structure of [electrolyte salt+organic solvent] + , so as to effectively promote the exchange of the organic solvent and the crystal water in the crystal lattice of the Prussian blue analogue.

[0014] The modification method of the Prussian blue analogue provided by the present application, compared with the ordinary heating method, condensation reflux is beneficial to avoid the volatilization of the organic solvent and promote the exchange of the organic solvent and the crystal water; compared with the existing technologies such as the solvothermal method, by adding the electrolyte salt and the organic solvent and adopting the condensation reflux method, the required Prussian blue analogue can be prepared without complex experimental devices and harsh experimental conditions such as high pressure.

[0015] In some embodiments of the present application, the molar ratio of the Prussian blue analogue to be treated to the electrolyte salt is 1:(2-10).

[0016] In some embodiments of the present application, the molar ratio of the Prussian blue analogue to be treated to the electrolyte salt is 1:(2-5).

[0017] In some embodiments of the present application, the reflux temperature is 100-180℃.

[0018] In some embodiments of the present application, the reflux temperature is 120-150℃.

[0019] In some embodiments of the present application, the reflux time is 5-100h.

[0020] In some embodiments of the present application, the reflux time is 40-50h.

[0021] In some embodiments of the present application, the reflux time is 45-50h.

[0022] According to different Prussian blue analog materials, the reflux temperature is 100-180℃, and the reflux time is 5-100h, which is beneficial to the exchange between the organic solvent and the crystal water in the crystal lattice of the Prussian blue analog. The whole reflux process can be carried out in an inert gas atmosphere or in an external environment.

[0023] In some embodiments of the present application, the organic solvent is an electrolyte solvent; specifically, an ester solvent and / or an ether solvent.

[0024] In some embodiments of the present application, the organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, and acetonitrile.

[0025] The present application further selects a battery electrolyte solvent as the organic solvent in the modification method of the present application, so that the commonly used battery electrolyte solvent is embedded into the crystal lattice of the Prussian blue analog and exchanged with the crystal water therein, thereby replacing the crystal water in the crystal lattice to obtain a Prussian blue analog containing the electrolyte solvent, which can further improve the cycle stability of the Prussian blue analog, further improve the electrochemical performance of the Prussian blue analog, and is more beneficial to be used as a battery electrode material.

[0026] In some embodiments of the present application, the electrolyte salt is an electrolyte sodium salt and / or an electrolyte lithium salt.

[0027] In some embodiments of the present application, the electrolyte salt is at least one of NaTFSI, NaFSI, NaFTFSI, NaPF6, NaBF4, NaClO4, LiTFSI, LiFSI, LiFTFSI, LiPF6, LiBF4, and LiClO4.

[0028] The present application further uses an electrolyte sodium salt to replace the alkali metal ions in the Prussian blue analog, so that the original K + or Na + is replaced by Na + or Li+ The Prussian blue analogues after replacement of the electrolyte sodium salt have greater advantages when used as positive electrode materials of sodium ion batteries or lithium ion batteries, and have excellent cycle stability.

[0029] The chemical formula of the Prussian blue analogue is A x M'[M"(CN)6]y(0)1-y·nH2O, 0

[0030] In some embodiments of the present application, the Prussian blue analogue to be treated is Na x FeFe(CN)6, K x FeFe(CN)6, K x NiFe(CN)6, Na x NiFe(CN)6, Na x CoFe(CN)6, Na x MnFe(CN)6, K x CoFe(CN)6, K x MnFe(CN)6, K

[0031] In some embodiments of the present application, the process of extracting the solid product in the solution after reflux includes the following steps:

[0032] The solution after reflux is centrifuged to obtain a centrifugal product, and the centrifugal product is dried, washed, centrifuged, and dried to obtain a Prussian blue analogue solid.

[0033] In some embodiments of the present application, the centrifugal product is vacuum dried at 60-150°C, and then repeatedly washed and centrifuged using a solvent, and then vacuum dried at 60-150°C for more than 12h.

[0034] In some specific embodiments of the present application, the solvent used for washing is at least one of acetonitrile, tetrahydrofuran, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and 1,3-dioxolane.

[0035] In some embodiments of the present application, the modification method of the Prussian blue analogue includes the following steps:

[0036] The Prussian blue analogue to be treated is A xM'M" (CN) 6 and electrolyte salt are uniformly mixed in a certain proportion; the obtained mixed powder is put into a reaction container, an organic solvent is added and stirring is continued so that the electrolyte salt is dissolved in the organic solvent; or the electrolyte salt is first dissolved in the organic solvent, then the Prussian blue analogue to be treated is added, and stirring is continued for mixing;

[0037] The reaction is heated to a suitable temperature under stirring and condensation reflux is carried out; after the reflux is completed, the reflux liquid is centrifuged, and the centrifuged product is vacuum dried; the vacuum-dried solid is washed with a solvent for multiple times and centrifuged; the washed solid is vacuum dried for more than 12 hours.

[0038] In some embodiments of the present application, the reaction container is connected with a condensation reflux device and a water separator.

[0039] The water separator is used to receive the crystallization water evaporated from the sample, so as to achieve the effect of water separation.

[0040] The purpose of vacuum drying the centrifuged product is to facilitate the subsequent treatment of the sample.

[0041] In some embodiments of the present application, the washing and centrifugation of the vacuum-dried solid are carried out in an inert environment.

[0042] The purpose of multiple washing and centrifugation is to wash away the residual reflux liquid and electrolyte salt, and vacuum drying after washing is to dry the organic solvent remaining on the surface of the sample.

[0043] The second aspect of the present application provides a Prussian blue analogue obtained by the modification method of the first aspect of the present application, wherein the mass content of crystallization water of the Prussian blue analogue is 0-2%.

[0044] The mass content of crystallization water of the Prussian blue analogue is generally more than 8%, and the modification method of the present application effectively removes the crystallization water in the crystal lattice of the Prussian blue analogue, so that the mass content of crystallization water is not more than 2%.

[0045] In some embodiments of the present application, the mass content of crystallization water of the Prussian blue analogue is 1.5-1.8%.

[0046] In some embodiments of the present application, the mass content of crystallization water of the Prussian blue analogue is 1.7-1.8%.

[0047] The third aspect of the present application provides a positive electrode material, which contains the Prussian blue analogue of the second aspect of the present application.

[0048] The fourth aspect of the present application provides a battery, which contains the Prussian blue analogue of the second aspect of the present application.

[0049] The internal crystal water of the Prussian blue analogue obtained by the modification method of the embodiment of the present application is replaced by an organic solvent, avoiding the decomposition of the crystal water and the occurrence of side reactions, thereby solving the problem of serious cycle life attenuation of the battery, and the Prussian blue analogue has excellent electrochemical performance, especially cycle stability, and is suitable for use in the field of battery materials and can improve the cycle life of the battery.

[0050] In some embodiments of the present application, the battery is a secondary battery.

[0051] In some embodiments of the present application, the battery is a sodium ion battery.

[0052] Compared with the prior art, the present application has at least the following technical effects:

[0053] (1) The modification method of the present application effectively removes the crystal water inside the lattice of the Prussian blue analogue, and the added electrolyte salt is beneficial to form a structure of [electrolyte salt + organic solvent], thereby effectively promoting the exchange of the organic solvent with the crystal water inside the Prussian blue analogue crystal, greatly improving the cycle stability of the Prussian blue analogue, and improving the electrochemical performance of the Prussian blue analogue. +

[0054] (2) The present application further improves the cycle stability of the Prussian blue analogue by further selecting an electrolyte sodium salt and an electrolyte solvent as the organic solvent, and has greater advantages when used as an electrode material of a sodium ion battery.

[0055] (3) The internal crystal water of the Prussian blue analogue obtained by the modification method of the present application is replaced by an organic solvent, avoiding the problem of serious cycle life attenuation of the battery caused by the existence of crystal water, and the Prussian blue analogue has excellent cycle stability and is suitable for use in the field of battery materials. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 The preparation flowchart of the modification method of the embodiment of the present application.

[0057] Figure 2 The experimental device diagram of the modification method of the embodiment of the present application.

[0058] Figure 3 K x NiFe(CN)6 and K x NiFe(CN)6-EC infrared spectrum of the embodiment 1 and the embodiment 5 of the present application.

[0059] Figure 4 K x NiFe(CN)6 and K x NiFe(CN)6-EC1:5 thermogravimetric curve of the embodiment 1 of the present application.

[0060] ​Figure 5 K is the embodiment of the present invention. x Thermogravimetric mass spectrum of NiFe(CN)6-EC1:5.

[0061] Figure 6 K is the embodiment of the present invention in Examples 1 and 5. x NiFe(CN)6 and K x Electrochemical performance diagram of NiFe(CN)6-EC.

[0062] Figure 7 Na is from Embodiment 2 of the present invention. x FeFe(CN)6 and Na x Infrared spectrum of FeFe(CN)6-EC1:5.

[0063] Figure 8 Na is from Embodiment 2 of the present invention. x FeFe(CN)6 and Na x Electrochemical performance diagram of FeFe(CN)6-EC1:5.

[0064] Figure 9 K is the embodiment of the present invention in Examples 3 and 4. x NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K x Infrared spectrum of NiFe(CN)6-DEGDME1:5.

[0065] Figure 10 K is the embodiment of the present invention in Examples 3 and 4. x NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K x Electrochemical performance diagram of NiFe(CN)6-DEGDME1:5.

[0066] Figure 11 K is the comparative example 1 of this invention. x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC1:0.

[0067] Figure 12 K is the comparative example 1 of this invention. x NiFe(CN)6 and K x Electrochemical performance diagram of NiFe(CN)6-EC1:0. Detailed Implementation

[0068] The content of the present invention will be further described in detail through specific embodiments below. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial channels or can be obtained by existing technical methods. Unless otherwise specified, the test or testing methods are conventional methods in the art.

[0069] The process of the modification method of the Prussian blue analogue in the following embodiments of the present invention is as Figure 1 shown, and the experimental device used for condensation reflux is as Figure 2 shown.

[0070] Example 1

[0071] This example provides a modification method of a Prussian blue analogue, which includes the following steps:

[0072] Uniformly mix the Prussian blue analogue K x NiFe(CN)6 (0 < x < 2) and the electrolyte salt NaTFSI in a molar ratio of 1:5; put the obtained mixed powder and a magnetic stirrer into a three-neck flask, and successively connect a glass water separator and a condenser above the three-neck flask; add an appropriate amount of organic solvent to the three-neck flask and continuously stir, and the organic solvent used is ethylene carbonate (EC); heat to 120 °C under stirring for condensation reflux, and the reflux time is 48 h; the whole reflux process is carried out in an inert gas atmosphere; after the reflux is completed, centrifuge the reflux liquid and put the centrifuged product into a drying oven for vacuum drying, and the drying temperature is 60 °C; transfer the solid obtained after vacuum drying to a glove box and wash and centrifuge it several times with the organic solvent acetonitrile; vacuum dry the washed solid for 24 h, and the vacuum drying temperature is 100 °C; after drying, obtain the Prussian blue analogue K x NiFe(CN)6-EC1:5.

[0073] Example 2

[0074] This example provides a modification method of a Prussian blue analogue. The difference from Example 1 is only that: replace the Prussian blue analogue K x NiFe(CN)6 with Na x FeFe(CN)6 to obtain Na x FeFe(CN)6-EC1:5; the reflux temperature is 140 °C and the reflux time is 48 h.

[0075] Example 3

[0076] This example provides a modification method of a Prussian blue analogue. The difference from Example 1 is only that: use the organic solvent ethylene glycol dimethyl ether (DME) to replace ethylene carbonate (EC) to obtain K x NiFe(CN)6-DME1:5.

[0077] Example 4

[0078] This example provides a method for modifying a Prussian blue analogue. The only difference from Example 1 is that the organic solvent diethylene glycol dimethyl ether (DEGDME) is used to replace ethylene carbonate (EC), resulting in K x NiFe(CN)6 - DEGDME 1:5.

[0079] Example 5

[0080] This example provides a method for modifying a Prussian blue analogue. The only difference from Example 1 is that the Prussian blue analogue K x NiFe(CN)6 (0 < x < 2) and the electrolyte salt NaTFSI are uniformly mixed at a molar ratio of 1:2, resulting in K x NiFe(CN)6 - EC 1:2.

[0081] Comparative Example 1

[0082] This comparative example provides a method for modifying a Prussian blue analogue. The only difference from Example 1 is that the electrolyte salt NaTFSI is not added, that is, the molar ratio of the Prussian blue analogue K x NiFe(CN)6 (0 < x < 2) to the electrolyte NaTFSI is 1:0, resulting in K x NiFe(CN)6 - EC 1:0.

[0083] Application Example

[0084] Using K x NiFe(CN)6 - EC 1:5, Na x FeFe(CN)6 - EC 1:5, K x NiFe(CN)6 - DME 1:5, K x NiFe(CN)6 - DEGDME 1:5, K x NiFe(CN)6 - EC 1:2, K x NiFe(CN)6 - EC 1:0 obtained from the above Examples 1 to 5 and Comparative Example 1 respectively as the positive electrode, sodium as the negative electrode, a DME (ethylene glycol dimethyl ether) solution of NaPF6 (NaPF6 concentration is 1 mol / L) as the electrolyte, and glass fiber as the separator to assemble a sodium ion battery for constant current charge and discharge testing; at the same time, using the same method, the Prussian blue analogue K x NiFe(CN)6, Na x FeFe(CN)6 as the positive electrode to assemble a sodium ion battery for constant current charge and discharge testing, and compare the performance improvement effect of the Prussian blue analogue obtained by the modification method of the present invention.

[0085] Result detection

[0086] The following is in conjunction with the appendix Figures 3-6 The effects of Embodiments 1 and 5 of the present invention and their application examples are described in detail below:

[0087] Figure 3 K is the embodiment of the present invention in Examples 1 and 5. x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC. Based on K x NiFe(CN)6:NaTFSI = 1:2 and 1:5 were refluxed to obtain K x NiFe(CN)6-EC1:2 and K x NiFe(CN)6-EC1:5. For the original sample K x For NiFe(CN)6, its infrared spectrum is at 3400 cm⁻¹ -1 and 1620cm -1 Strong absorption peaks appeared at these locations, corresponding to adsorbed water and coordinated water of the Prussian blue analogues, respectively. Meanwhile, K, after reflux using EC... x NiFe(CN)6-EC1:5 and K x NiFe(CN)6-EC1:2, its 3400cm -1 The adsorbed water peak disappears at K after EC reflux, indicating that the adsorbed water peak disappears at K. x NiFe(CN)6-EC does not contain adsorbed water; at the same time, 1620 cm -1 The coordination water peak at K almost completely disappeared, indicating that K x The content of crystal water within the NiFe(CN)6-EC lattice approaches 0. Furthermore, K... x NiFe(CN)6-EC at 2910 cm⁻¹ -1 1770cm -1 1460cm -1 New absorption peaks appeared at K, corresponding to the stretching vibrations of CH, C=O, and the bending vibrations of CH2 in the EC molecule, respectively. This indicates that the organic solvent EC is intercalated into K. x The NiFe(CN)6 crystal lattice is filled with NaTFSI, which replaces the water of crystallization. Adding a certain amount of NaTFSI is beneficial for forming [electrolyte salt + organic solvent]. + The structure promotes the exchange of water of crystallization between the organic solvent and the Prussian blue analogue crystal.

[0088] For K x NiFe(CN)6 and K xThermogravimetric analysis of NiFe(CN)6-EC can further quantitatively analyze its water molecule content, and the results are as follows: Figure 4 As shown. For the thermogravimetric curves of Prussian blue analogues, the mass loss at and below 200℃ mainly comes from the loss of adsorbed water and coordinated water. Thermogravimetric test results show that the original sample K x NiFe(CN)6 experiences a mass loss of 7.62% in the temperature range of 50–200℃, while K using EC for reflux... x The mass loss of NiFe(CN)6-EC1:5 in this temperature range is only 1.75%. This indicates that using EC to reduce K x Refluxing NiFe(CN)6 can significantly reduce its water of crystallization content.

[0089] Thermogravimetric-mass spectrometry (TGA-MS) analysis, by monitoring the gaseous products emitted during thermal decomposition, can infer the microscopic thermal reaction process of a sample, aiding in the qualitative and quantitative analysis of its composition. For Prussian blue analogues, decomposition occurs in the temperature range of 300–400 °C, accompanied by the formation of gaseous products such as (CN)₂ and HCN. Ethylene carbonate (EC) undergoes thermal decomposition at approximately 330–350 °C, with decomposition products including acetaldehyde (CH₃CHO), ethylene oxide (C₂H₄O), and carbon dioxide (CO₂). Figure 5 K is the embodiment of the present invention. x Thermogravimetric mass spectrum of NiFe(CN)6-EC1:5, from... Figure 5 It can be seen that the mass loss in the 300–400℃ temperature range mainly corresponds to the release of products with a charge ratio M / Z = 44. These products, with a charge ratio M / Z = 44, may be CH3CHO, C2H4O, or ionic fragments of CO2, all originating from the thermal decomposition of EC. Furthermore, some mass loss in the 300–400℃ temperature range may also originate from the escape of products with a charge ratio M / Z = 27 (HCN), which is one of the decomposition products of Prussian blue analogues. Clearly, K… x Thermogravimetric mass spectrometry results of NiFe(CN)6-EC1:5 indicate that EC can be embedded into K through reflux condensation. x The interior of NiFe(CN)6 lattice is consistent with the infrared test results.

[0090] Figure 6 K is the embodiment of the present invention in Examples 1 and 5. x NiFe(CN)6 and K x Electrochemical performance diagram of NiFe(CN)6-EC. K x NiFe(CN)6, K x NiFe(CN)6-EC1:2 and Kx Using NiFe(CN)6-EC1:5 as the positive electrode and sodium as the negative electrode, a NaPF6 DME (ethylene glycol dimethyl ether) solution (NaPF6 concentration 1 mol / L) was used as the electrolyte. A glass fiber separator was used to assemble the sodium-ion battery, and the battery was tested at 20 mA·g. -1 A constant current charge-discharge test was performed on the original sample K. x After 100 charge-discharge cycles, NiFe(CN)6 retained only 64% of its capacity; while K, using EC for reflux... x After 100 charge-discharge cycles, NiFe(CN)6-EC1:5 still retains 90% of its capacity. x The capacity retention of NiFe(CN)6-EC1:2 was 89%, and the cycle stability was significantly improved.

[0091] The following is in conjunction with the appendix Figures 7-8 The effects of Embodiment 2 of the present invention and its application examples are explained in detail below:

[0092] Figure 7 Na is from Embodiment 2 of the present invention. x FeFe(CN)6 and Na x Infrared spectrum of FeFe(CN)6-EC1:5. From Figure 7 As can be seen from this, the original sample Na x FeFe(CN)6 at 3600 cm -1 and 1620cm -1 Sharp absorption peaks appeared nearby, corresponding to Na. x The adsorbed water and coordinated water of FeFe(CN)6, and the original sample Na x FeFe(CN)6 has a high water content. Meanwhile, Na+ is refluxed using EC. x FeFe(CN)6-EC1:5, its 3400cm -1 The adsorbed water peak disappears at 1620 cm⁻¹ -1 The peak of coordinated water at 2900 cm⁻¹ weakened significantly, and then decreased further. -1 and 1150cm -1 A new absorption peak appeared nearby. This indicates that the organic solvent EC was able to intercalate into Na during reflux. x The FeFe(CN)6 crystal lattice effectively removes Na. x FeFe(CN)6 adsorbs water and replaces the water of crystallization inside the crystal lattice.

[0093] Figure 8 Na is from Embodiment 2 of the present invention. x FeFe(CN)6 and Na xElectrochemical performance diagram of FeFe(CN)6-EC1:5. Na x FeFe(CN)6 and Na x Using FeFe(CN)6-EC1:5 as the positive electrode and sodium as the negative electrode, a NaPF6 DME (ethylene glycol dimethyl ether) solution (NaPF6 concentration 1 mol / L) was used as the electrolyte. A glass fiber separator was used to assemble the sodium-ion battery, and the battery was tested at 20 mA·g. -1 A constant current charge-discharge test was performed on the original sample Na. x The high water content in FeFe(CN)6, which occupies some of the sodium ion insertion / extraction sites, results in an initial discharge capacity of only 105 mAh g. -1 Furthermore, after 100 charge-discharge cycles, the original sample Na... x The capacity retention of FeFe(CN)6 was only 57%. Meanwhile, the EC reflux sample Na... x The water of crystallization in FeFe(CN)6-EC1:5 has been replaced by EC, resulting in an initial discharge capacity of 131 mAh g. -1 It is significantly better than the original sample Na. x FeFe(CN)6. Meanwhile, after 100 charge-discharge cycles, Na... x The capacity retention rate of FeFe(CN)6-EC1:5 was 89%, and the cycling stability was significantly improved.

[0094] The following is in conjunction with the appendix Figures 9-10 The effects of Embodiment 3 of the present invention and its application examples are explained in detail below:

[0095] To demonstrate the general applicability of the modification method of the present invention, Examples 3 and 4 also used Prussian blue analogue K. x Taking NiFe(CN)6 as an example, and replacing the organic solvent from ethylene carbonate (EC) with ethylene glycol dimethyl ether (DME) and diethylene glycol dimethyl ether (DEGDME) respectively, a Prussian blue analog K containing an electrolyte solvent was prepared. x NiFe(CN)6-DME1:5 and K x NiFe(CN)6-DEGDME1:5. Figure 9 K is the embodiment of the present invention in Examples 3 and 4. x NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K x Infrared spectrum of NiFe(CN)6-DEGDME1:5. It can be seen that, compared with the original sample K... x Compared to NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K xNiFe(CN)6-DEGDME1:5 at 3400cm -1 The adsorbed water peak disappears at 1620 cm⁻¹ -1 The coordination water peaks at various locations showed varying degrees of attenuation. However, at 1000 cm⁻¹... -1 ~1400cm -1 Nearby, K x NiFe(CN)6-DME1:5 and K x A new absorption peak appeared in NiFe(CN)6-DEGDME1:5, corresponding to the characteristic absorption peaks of DME and DEGDME, respectively. This indicates that reflux using either DME or DEGDME can effectively remove K. x NiFe(CN)6 adsorbs water and replaces the water of crystallization inside its crystal lattice.

[0096] Figure 10 K is the embodiment of the present invention in Examples 3 and 4. x NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K x Electrochemical performance diagram of NiFe(CN)6-DEGDME1:5. The raw materials and assembly method used in the battery are the same as in Example 1, the only difference being that the positive electrode material is K. x NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K x NiFe(CN)6-DEGDME1:5. From Figure 10 As can be seen from this, compared with the original sample K x Compared to NiFe(CN)6, K using DME for reflux x After 100 charge-discharge cycles, NiFe(CN)6-DME1:5 retains 89% of its capacity, while K using DEGDME for reflow... x The capacity retention of NiFe(CN)6-DEGDME1:5 is 93%, and the cycle stability is significantly improved.

[0097] The following is in conjunction with the appendix Figures 11-12 The effects of Comparative Example 1 and its application examples of the present invention will be explained in detail below:

[0098] To demonstrate the role of electrolyte salts in the modification method of the present invention, Comparative Example 1 also used a Prussian blue analogue K. x Taking NiFe(CN)6 as an example, ethylene carbonate (EC) was used as the reflux solvent, and K was obtained by reflux without the addition of the electrolyte salt NaTFSI. x NiFe(CN)6-EC1:0. Figure 11 K is the comparative example 1 of this invention.x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC1:0. Compared with the original sample K. x Compared to NiFe(CN)6, K obtained by reflux without the addition of electrolyte salt NaTFSI x NiFe(CN)6-EC1:0 at 2910cm -1 1770cm -1 1420cm -1 And 1080cm -1 A new absorption peak appeared nearby, which can be attributed to the partial embedding of EC into K. x In the NiFe(CN)6 lattice; however, at 3400 cm⁻¹ -1 and 1620cm -1 A strong absorption peak still exists nearby, indicating that K x NiFe(CN)6-EC1:0 still contains a significant amount of adsorbed water and crystal water.

[0099] Figure 12 K is the comparative example 1 of this invention. x NiFe(CN)6 and K x Electrochemical performance graph of NiFe(CN)6-EC1:0. The battery assembly method and test conditions are the same as in Example 1. From... Figure 12 As can be seen from the data, the reflux sample K without the addition of the electrolyte salt NaTFSI... x After 100 charge-discharge cycles, the capacity retention of NiFe(CN)6-EC1:0 was only 69%, compared to the original sample K. x Compared to NiFe(CN)6, the cycling stability was not significantly improved. This indicates that the addition of a certain amount of the electrolyte salt NaTFSI can promote the exchange of water of crystallization between the organic solvent and the Prussian blue analog crystals, and improve its electrochemical performance.

[0100] In summary, the modification method for Prussian blue analogs provided by this invention can effectively remove the water of crystallization inside the Prussian blue analog lattice, while the added electrolyte salt facilitates the formation of [electrolyte salt + organic solvent]. + The structure effectively promotes the exchange of water of crystallization between the organic solvent and the Prussian blue analog crystal, greatly improving the cycle stability of the Prussian blue analog and enhancing its electrochemical performance. After being assembled into a sodium-ion battery as a positive electrode, the capacity retention rate still exceeds 85% after 100 charge-discharge cycles.

[0101] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for modifying a Prussian blue analogue, characterized in that, Includes the following steps: The Prussian blue analogue to be treated was mixed with an electrolyte salt in an organic solvent, heated and refluxed, and the solid product in the refluxed solution was extracted to obtain the Prussian blue analogue.

2. The modification method according to claim 1, characterized in that, The molar ratio of the Prussian blue analogue to be treated to the electrolyte salt is 1:(2~10).

3. The modification method according to claim 1, characterized in that, The reflux temperature is 100~180℃; And / or, the reflux time is 5~100h.

4. The modification method according to claim 1, characterized in that, The organic solvent is an ester solvent and / or an ether solvent.

5. The modification method according to claim 4, characterized in that, The organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, and acetonitrile.

6. The modification method according to claim 1 or 4, characterized in that, The electrolyte salt is a sodium electrolyte salt and / or a lithium electrolyte salt.

7. The modification method according to claim 6, characterized in that, The electrolyte salt is at least one of NaTFSI, NaFSI, NaFTFSI, NaPF6, NaBF4, NaClO4, LiTFSI, LiFSI, LiFTFSI, LiPF6, LiBF4, and LiClO4.

8. The modification method according to claim 1, characterized in that, The Prussian blue analogue to be treated is at least one selected from NaxFeFe(CN)6, KxFeFe(CN)6, KxNiFe(CN)6, NaxNiFe(CN)6, NaxCoFe(CN)6, NaxMnFe(CN)6, KxCoFe(CN)6, and KxMnFe(CN)6, wherein 0 <x<2。 9. The modification method according to claim 1, characterized in that, The process of extracting solid products from the refluxed solution includes the following steps: The refluxed solution was centrifuged to obtain a centrifuged product. The centrifuged product was dried, washed, centrifuged again, and dried to obtain a Prussian blue analogue solid.

10. A Prussian blue analogue obtained by the modification method according to any one of claims 1 to 9, characterized in that, The Prussian blue analogue has a water of crystallization content of 0-2% by mass.

11. A positive electrode material, characterized in that, The cathode material contains the Prussian blue analogue as described in claim 10.

12. A battery, characterized in that, The battery contains the Prussian blue analogue of claim 10.

Images