Prussian blue analogue, modification method therefor, and use thereof

Abstract

A Prussian blue analogue, a modification method therefor, and a use thereof, relating to the technical field of battery materials. The modification method comprises the following steps: mixing a Prussian blue analogue to be processed and an electrolyte salt in an organic solvent, heating to perform condensation reflux, and extracting a solid product from the solution after reflux to obtain a Prussian blue analogue. The modification method effectively removes crystallized water within the lattice of a Prussian blue analogue, and the added electrolyte salt facilitates formation of a [electrolyte salt + organic solvent]+ structure, thereby effectively promoting the exchange between the organic solvent and the crystallized water within the Prussian blue analogue crystals. Hence, the cycling stability of the Prussian blue analogue is greatly improved, and the electrochemical performance thereof is enhanced, making the invention suitable for use in the field of battery materials.

Description

A Prussian blue analogue and its modification method and application Technical Field

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

[0002] Prussian blue analogues (PBAs) have great potential for development due to their simple synthesis, low cost, non-toxicity, and ease of scalable production. They are the most common metal-organic framework cathode materials for sodium-ion batteries. Sodium-ion batteries are considered an ideal electrochemical energy storage technology with broad application prospects in areas such as large-scale energy storage and low-speed electric vehicles. In sodium-ion batteries, the cathode material plays a decisive role in their performance. Therefore, the development and improvement of Prussian blue analogues are of great significance to the development of sodium-ion batteries. Ideal Prussian blue and its analogues possess a perfect framework structure and, as cathode materials for sodium-ion batteries, offer the advantages of high capacity, high rate capability, long cycle life, and low polarization voltage. However, Prussian blue analogues prepared by current methods often suffer from high crystalline water content. The crystalline water in Prussian blue analogues promotes electrolyte decomposition and triggers a series of side reactions, which corrode the electrode material and significantly reduce the battery's cycle life.

[0003] Among the traditional methods for synthesizing Prussian blue analogs, the coprecipitation method offers advantages such as low cost, non-toxicity, and scalability. However, the solubility constant of Prussian blue analogs is extremely small, and crystal nucleation and grain growth occur almost simultaneously, resulting in an irregular product morphology and the presence of a large amount of crystalline water. This crystalline water promotes the decomposition of the electrolyte and triggers a series of side reactions, which corrodes the electrode materials and significantly reduces the battery's cycle life.

[0004] To address the high crystalline water content in Prussian blue analogs prepared by the coprecipitation method, vacuum drying is commonly used to reduce the crystalline water content. However, due to the generally low thermal stability of Prussian blue analogs, drying can only be performed at relatively low temperatures. Even vacuum drying can only remove a small amount of crystalline water, making it difficult to obtain a quasi-anhydrous or even anhydrous sample.

[0005] Summary of the Invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention aims to provide a method for modifying the internal crystalline water of a Prussian blue analogue by forming [electrolyte salt + organic solvent] +structure, prompting the organic solvent to exchange the internal crystalline water of the Prussian blue analogue, thereby effectively removing the crystalline water of the Prussian blue analogue.

[0007] The second aspect of the present invention is to provide a Prussian blue analogue.

[0008] The third aspect of the present invention is to provide a positive electrode material.

[0009] A fourth aspect of the present invention is to provide a battery.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A first aspect of the present invention provides a method for modifying a Prussian blue analogue, comprising the following steps:

[0012] The Prussian blue analogue to be treated is mixed with an electrolyte salt in an organic solvent, heated for condensation reflux, and a solid product in the refluxed solution is extracted to obtain the Prussian blue analogue.

[0013] The present invention, without destroying the crystal structure of a Prussian blue analogue, embeds an organic solvent into the crystal lattice of the Prussian blue analogue through condensation reflux and exchanges the organic solvent with the crystalline water therein, thereby replacing the crystalline water in the Prussian blue analogue lattice, thereby obtaining a Prussian blue analogue containing an organic solvent. The modification method of the present invention effectively removes the crystalline water in the Prussian blue analogue lattice, greatly improving the cyclic stability of the Prussian blue analogue and the electrochemical performance of the material.

[0014] In addition, the modification method of the present invention also adds electrolyte salt, which is beneficial to the formation of [electrolyte salt + organic solvent] + structure, thereby effectively promoting the exchange of organic solvents and crystalline water inside the Prussian blue analogue crystals.

[0015] Compared with a conventional heating method, the modification method of the Prussian blue analog provided by the present invention uses condensation reflux to avoid the volatilization of the organic solvent and promote the exchange of the organic solvent and crystal water. Compared with existing technologies such as the solvothermal method, the present invention can prepare the desired Prussian blue analog by adding an electrolyte salt and an organic solvent and adopting a condensation reflux method, without the need for complex experimental equipment and relatively harsh experimental conditions such as high pressure.

[0016] In some embodiments of the present invention, the molar ratio of the Prussian blue analogue to be treated to the electrolyte salt is 1:(2-10).

[0017] In some embodiments of the present invention, the molar ratio of the Prussian blue analogue to be treated to the electrolyte salt is 1:(2-5).

[0018] In some embodiments of the present invention, the reflux temperature is 100-180°C.

[0019] In some embodiments of the present invention, the reflux temperature is 120-150°C.

[0020] In some embodiments of the present invention, the reflux time is 5 to 100 hours.

[0021] In some embodiments of the present invention, the reflux time is 40 to 50 hours.

[0022] In some specific embodiments of the present invention, the reflux time is 45 to 50 hours.

[0023] Depending on the material of the Prussian blue analog, the reflux temperature is between 100°C and 180°C, and the reflux time is between 5 and 100 hours, which is conducive to sufficient exchange of crystalline water between the organic solvent and the internal crystalline water of the Prussian blue analog. The entire reflux process can be carried out under an inert gas atmosphere or in an external environment.

[0024] In some embodiments of the present invention, the organic solvent is an electrolyte solvent; specifically, an ester solvent and / or an ether solvent.

[0025] In some embodiments of the present invention, the organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, and acetonitrile.

[0026] The present invention further selects a battery electrolyte solvent as the organic solvent in the modification method of the present invention, so that the commonly used battery electrolyte solvent is embedded in the crystal lattice of the Prussian blue analogue and exchanges with the crystalline water therein, thereby replacing the crystalline water in the crystal lattice, thereby obtaining a Prussian blue analogue containing the electrolyte solvent. This can further improve the cycle stability of the Prussian blue analogue, while further improving the electrochemical performance of the Prussian blue analogue, making it more conducive to use as a battery electrode material.

[0027] In some embodiments of the present invention, the electrolyte salt is an electrolyte sodium salt and / or an electrolyte lithium salt.

[0028] In some embodiments of the present invention, the electrolyte salt is at least one of NaTFSI, NaFSI, NaFTFSI, NaPF6, NaBF4, NaClO4, LiTFSI, LiFSI, LiFTFSI, LiPF6, LiBF4, and LiClO4.

[0029] The present invention further uses an electrolyte sodium salt to replace the alkali metal ions in the Prussian blue analogue, so that the original K + or Na + is replaced by Na + or Li + . The Prussian blue analogue after being replaced by the electrolyte sodium salt has greater advantages when used as the positive electrode material of a sodium ion battery or a lithium ion battery, and has excellent cycle stability.

[0030] The chemical formula of the Prussian blue analogue is A x M′[M″(CN)6]y(0)1-y·nH2O, 0 < x < 2, 0 < y < 1, where A is an alkali metal ion such as Li, Na, K, etc.; M′ and M″ are transition metal ions such as Fe, Co, Cu, Mn, Ni, etc.; (0) represents the vacancy defect of the Prussian blue analogue.

[0031] In some embodiments of the present invention, 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, at least one of them, where 0 < x < 2.

[0032] In some embodiments of the present invention, the process of extracting the solid product from the solution after refluxing includes the following steps:

[0033] Centrifuging the solution after refluxing to obtain a centrifuged product, and the centrifuged product is dried, washed, centrifuged, and dried to obtain a Prussian blue analogue solid.

[0034] In some examples of the present invention, after the centrifuged product is vacuum dried at 60 - 150 °C, it is washed and centrifuged repeatedly using a solvent, and then vacuum dried at 60 - 150 °C for more than 12 h.

[0035] In some specific examples of the present invention, the solvent used for washing is at least one of acetonitrile, tetrahydrofuran, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3 - dioxolane.

[0036] In some embodiments of the present invention, the modification method of the Prussian blue analogue includes the following steps:

[0037] The Prussian blue analog A to be treated x M′M″(CN)6 and an electrolyte salt are uniformly mixed in a certain proportion; the resulting mixed powder is placed in a reaction vessel, an organic solvent is added and continuously stirred to dissolve the electrolyte salt in the organic solvent; or the electrolyte salt is first dissolved in an organic solvent, and then the Prussian blue analogue to be treated is added and continuously stirred for mixing;

[0038] The method comprises heating the mixture to a suitable temperature under stirring to condense and reflux; centrifuging the reflux liquid after the reflux is completed, and vacuum drying the centrifuged product; washing the vacuum-dried solid with a solvent for multiple times and centrifuging the solid; and vacuum drying the washed solid for more than 12 hours.

[0039] In some embodiments of the present invention, the reaction vessel is connected to a condensation reflux device and a water separator.

[0040] The water separator is used to receive the crystallized water evaporated from the sample to achieve the effect of water separation.

[0041] The purpose of vacuum drying the centrifuged product is to facilitate subsequent processing of the sample.

[0042] In some embodiments of the present invention, the washing and centrifuging of the vacuum-dried solid is performed in an inert environment.

[0043] The purpose of multiple washing and centrifugation is to wash away the residual reflux liquid and electrolyte salts, and the vacuum drying after washing is to dry the organic solvent remaining on the surface of the sample.

[0044] The second aspect of the present invention provides a Prussian blue analogue obtained by the modification method of the first aspect of the present invention, wherein the mass content of crystal water of the Prussian blue analogue is 0-2%.

[0045] The mass content of crystal water of Prussian blue analogues is generally above 8%. The modification method of the present invention effectively removes the crystal water inside the crystal lattice of the Prussian blue analogues, and the mass content of crystal water does not exceed 2%.

[0046] In some embodiments of the present invention, the mass content of crystalline water of the Prussian blue analogue is 1.5-1.8%.

[0047] In some embodiments of the present invention, the mass content of crystalline water of the Prussian blue analogue is 1.7-1.8%.

[0048] The third aspect of the present invention provides a positive electrode material, wherein the positive electrode material contains the Prussian blue analogue according to the second aspect of the present invention.

[0049] A fourth aspect of the present invention provides a battery comprising the Prussian blue analogue according to the second aspect of the present invention.

[0050] The internal crystal water of the Prussian blue analogue obtained by the present invention is replaced by an organic solvent, thereby avoiding the decomposition of the crystal water and the occurrence of side reactions, which would otherwise cause a serious reduction in the cycle life of the battery. The invention has excellent electrochemical properties, especially cycle stability, is suitable for the field of battery materials, and can improve the cycle life of the battery.

[0051] In some embodiments of the present invention, the battery is a secondary battery.

[0052] In some embodiments of the present invention, the battery is a sodium ion battery.

[0053] Compared with the prior art, the present invention has at least the following technical effects:

[0054] (1) The modification method of the present invention effectively removes the crystal water inside the crystal lattice of the Prussian blue analogue, and the added electrolyte salt is conducive to the formation of [electrolyte salt + organic solvent] + structure, thereby effectively promoting the exchange of organic solvents and crystalline water inside the Prussian blue analogue crystals, greatly improving the cyclic stability of the Prussian blue analogues and improving the electrochemical properties of the Prussian blue analogues.

[0055] (2) The present invention further improves the cycle stability of the Prussian blue analogue by further selecting an electrolyte sodium salt and an electrolyte solvent as an organic solvent, which has greater advantages when used as an electrode material for sodium ion batteries.

[0056] (3) The internal crystal water of the Prussian blue analogue obtained by the present invention is replaced by an organic solvent, thereby avoiding the problem of serious attenuation of the battery cycle life caused by the presence of crystal water. The analogue has excellent cycle stability and is suitable for the field of battery materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG1 is a preparation flow chart of the modification method according to an embodiment of the present invention.

[0058] FIG2 is a diagram of an experimental setup for the modification method according to an embodiment of the present invention.

[0059] FIG3 is a diagram of K in Example 1 and Example 5 of the present invention. x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC.

[0060] FIG4 is a diagram of K in Example 1 of the present invention. x NiFe(CN)6 and K x Thermogravimetric curve of NiFe(CN)6-EC1:5.

[0061] FIG5 is a diagram of K in Example 1 of the present invention. x Thermogravimetric mass spectrum of NiFe(CN)6-EC1:5.

[0062] FIG6 shows K of Example 1 and Example 5 of the present invention. x NiFe(CN)6 and K x Electrochemical performance diagram of NiFe(CN)6-EC.

[0063] Figure 7 is a diagram of Na in Example 2 of the present invention. x FeFe(CN)6 and Na x Infrared spectrum of FeFe(CN)6-EC1:5.

[0064] FIG8 is a diagram of Na in Example 2 of the present invention. x FeFe(CN)6 and Na x Electrochemical performance diagram of FeFe(CN)6-EC1:5.

[0065] FIG9 is a diagram of K in Example 3 and Example 4 of the present invention. x NiFe(CN)6、K x NiFe(CN)6-DME1:5 and K x Infrared spectrum of NiFe(CN)6-DEGDME1:5.

[0066] FIG. 10 shows K of Example 3 and Example 4 of the present invention. x NiFe(CN)6、K x NiFe(CN)6-DME1:5 and K x Electrochemical performance diagram of NiFe(CN)6-DEGDME1:5.

[0067] Figure 11 is the K of Comparative Example 1 of the present invention x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC1:0.

[0068] Figure 12 is the K of Comparative Example 1 of the present invention x NiFe(CN)6 and K x Electrochemical performance diagram of NiFe(CN)6-EC1:0. DETAILED DESCRIPTION

[0069] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0070] The process of the modification method of the Prussian blue analogue in the following embodiments of the present invention is shown in Figure 1, and the experimental device used for condensation reflux is shown in Figure 2.

[0071] Example 1

[0072] This example provides a modification method of a Prussian blue analogue, including the following steps:

[0073] 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 to the top of 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 under 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 multiple 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.

[0074] Example 2

[0075] 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.

[0076] Example 3

[0077] 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.

[0078] Example 4

[0079] This example provides a modification method of a Prussian blue analogue. The difference from Example 1 is only that: use the organic solvent diethylene glycol dimethyl ether (DEGDME) to replace ethylene carbonate (EC) to obtain Kx NiFe(CN)6 - DEGDME 1:5。

[0080] Example 5

[0081] This example provides a method for modifying a Prussian blue analogue. The difference from Example 1 is only 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 to obtain K x NiFe(CN)6 - EC 1:2.

[0082] Comparative Example 1

[0083] This comparative example provides a method for modifying a Prussian blue analogue. The difference from Example 1 is only 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, and K x NiFe(CN)6 - EC 1:0 is obtained. [[ID=2'3]]

[0084] Application Example

[0085] Using the 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 WNiFe(CN)6 - EC 1:0 obtained in the above Examples 1 - 5 and Comparative Example 1 as the positive electrode, sodium as the negative electrode, a DME (ethylene glycol dimethyl ether) solution of NaPF6 (NaPF6 concentration is mole / L) as the electrolyte, and glass fiber as the separator to assemble a sodium ion battery for constant current charge - discharge testing; at the same time, using the same method, the Prussian blue analogue K x NiFe(CN)6, Na x FeFe(CN)6 of each example is used as the positive electrode to assemble a sodium ion battery for constant current charge - discharge testing, and the performance improvement effect of the Prussian blue analogue obtained by the modification method of the present invention is compared.

[0086] Result Detection

[0087] The following specifically describes the effects of Example 1, Example 5 and their application examples of the present invention with reference to Figures 3 - 6:

[0088] FIG3 is a diagram of K in Example 1 and Example 5 of the present invention. x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC. 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 3400cm -1 and 1620cm -1 Strong absorption peaks appeared at , corresponding to the adsorbed water and coordinated water of Prussian blue analogs. x NiFe(CN)6-EC1:5 and K x NiFe(CN)6-EC1:2, its 3400cm -1 The adsorption water peak at the end of the EC reflux x NiFe(CN)6-EC does not contain adsorbed water; at the same time, 1620 cm -1 The coordinated water peak at the position of K x The content of crystal water inside the NiFe(CN)6-EC lattice is close to 0. In addition, K x NiFe(CN)6-EC at 2910cm -1 、1770cm -1 、1460cm -1 New absorption peaks appeared at , which corresponded to the stretching vibration of CH, the stretching vibration of C=O and the bending vibration of CH2 in the EC molecule, which means that the organic solvent EC is embedded in the K x The addition of a certain amount of NaTFSI is beneficial to the formation of [electrolyte salt + organic solvent] + structure, thereby promoting the exchange of organic solvents with the crystal water inside the Prussian blue analog crystals.

[0089] K x NiFe(CN)6 and K x Thermogravimetric testing of NiFe(CN)6-EC can further quantitatively analyze the content of water molecules, and the results are shown in Figure 4. For the thermogravimetric curve of Prussian blue analogs, the mass loss at 200℃ and below is mainly due to the loss of adsorbed water and coordinated water. Thermogravimetric test results show that the original sample K x The mass loss of NiFe(CN)6 in the temperature range of 50-200℃ is 7.62%, while the mass loss of Kx The mass loss of NiFe(CN)6-EC1:5 in this temperature range is only 1.75%. x Reflux of NiFe(CN)6 can significantly reduce its crystal water content.

[0090] Thermogravimetric-mass spectrometry analysis technology monitors the gaseous products released during thermal decomposition, thereby inferring the microscopic thermal reaction process of the sample, which helps to qualitatively and quantitatively analyze the composition of the sample. For Prussian blue analogs, in the temperature range of 300-400°C, Prussian blue analogs will decompose, accompanied by the generation of gaseous products such as (CN)2 and HCN; while the thermal decomposition temperature of ethylene carbonate (EC) is about 330-350°C, and the decomposition products include acetaldehyde (CH3CHO), ethylene oxide (C2H4O), carbon dioxide (CO2), etc. Figure 5 is K of Example 1 of the present invention. x Thermogravimetric mass spectrum of NiFe(CN)6-EC1:5. As can be seen from Figure 5, the mass loss in the temperature range of 300-400℃ mainly corresponds to the release of the product with a mass-to-charge ratio of M / Z=44, and the product with a mass-to-charge ratio of M / Z=44 may be CH3CHO or C2H4O or ionic fragments of CO2, all of which are derived from the thermal decomposition of EC. In addition, some of the mass loss in the temperature range of 300-400℃ may be derived from the escape of the product with a mass-to-charge ratio of M / Z=27 (HCN), which is one of the decomposition products of Prussian blue analogues. Obviously, K x The thermogravimetric mass spectrometry results of NiFe(CN)6-EC1:5 showed that EC could be embedded into K by condensation reflux. x Inside the lattice of NiFe(CN)6, which is consistent with the infrared test results.

[0091] FIG6 shows K of Example 1 and Example 5 of the present invention. 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 K x NiFe(CN)6-EC1:5 was used as the positive electrode, sodium was used as the negative electrode, NaPF6 DME (ethylene glycol dimethyl ether) solution (NaPF6 concentration was 1 mol / L) was used as the electrolyte, and glass fiber was used as the separator to assemble the sodium ion battery. -1 The original sample K x After 100 charge and discharge cycles, the capacity retention rate of NiFe(CN)6 is only 64%; while the K xAfter 100 charge and discharge cycles, the capacity retention rate of NiFe(CN)6-EC1:5 can still reach 90%, K x The capacity retention rate of NiFe(CN)6-EC1:2 is 89%, and the cycle stability has been significantly improved.

[0092] The effects of Example 2 of the present invention and its application examples are described in detail below with reference to Figures 7 and 8:

[0093] Figure 7 is a diagram of Na in Example 2 of the present invention. x FeFe(CN)6 and Na x Infrared spectrum of FeFe(CN)6-EC1:5. As can be seen from Figure 7, the original sample Na x FeFe(CN)6 at 3600cm -1 and 1620cm -1 There are sharp absorption peaks near Na x The adsorbed water and coordinated water of FeFe(CN)6, and the original sample Na x The water content in FeFe(CN)6 is high. x FeFe(CN)6-EC1:5, its 3400cm -1 The adsorption water peak at 1620 cm -1 The peak of coordinated water at 2900 cm -1 and 1150cm -1 A new absorption peak appeared near the surface of the Na phase. This indicates that during the reflux process, the organic solvent EC can be embedded in the Na phase. x The interior of the FeFe(CN)6 lattice effectively removes Na x The adsorbed water of FeFe(CN)6 replaces the crystal water inside the lattice.

[0094] FIG8 is a diagram of Na in Example 2 of the present invention. x FeFe(CN)6 and Na x Electrochemical performance diagram of FeFe(CN)6-EC1:5. x FeFe(CN)6 and Na x FeFe(CN)6-EC1:5 was used as the positive electrode, sodium was used as the negative electrode, NaPF6 DME (ethylene glycol dimethyl ether) solution (NaPF6 concentration was 1 mol / L) was used as the electrolyte, and glass fiber was used as the separator to assemble the sodium ion battery. -1 The constant current charge and discharge test was carried out under the condition of xThe content of crystal water in FeFe(CN)6 is high and occupies a part of the space for sodium ion deintercalation, resulting in an initial discharge capacity of only 105 mAh g -1 , and after 100 charge and discharge cycles, the original sample Na x The capacity retention rate of FeFe(CN)6 is only 57%. x The crystal water in FeFe(CN)6-EC1:5 has been replaced by EC, and the initial discharge capacity reaches 131 mAh g -1 , which is significantly better than the original sample Na x FeFe(CN)6. At the same time, after 100 charge and discharge cycles, Na x The capacity retention rate of FeFe(CN)6-EC1:5 is 89%, and the cycle stability is significantly improved.

[0095] The effects of Example 3 of the present invention and its application examples are described in detail below with reference to Figures 9 and 10:

[0096] In order to demonstrate the universal applicability of the modification method of the present invention, Examples 3 and 4 also used the Prussian blue analog K x Taking NiFe(CN)6 as an example, the organic solvent was replaced from ethylene carbonate (EC) to ethylene glycol dimethyl ether (DME) and diethylene glycol dimethyl ether (DEGDME) to prepare a Prussian blue analogue K containing an electrolyte solvent. x NiFe(CN)6-DME1:5 and K x NiFe(CN)6-DEGDME1:5. Figure 9 shows the K of Examples 3 and 4 of the present invention. 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 the K x Compared with NiFe(CN)6, K x NiFe(CN)6-DME1:5 and K x NiFe(CN)6-DEGDME1:5 at 3400cm -1 The adsorption water peak at 1620 cm -1 The coordinated water peak at 1000 cm -1 ~1400cm -1 Nearby, K x NiFe(CN)6-DME1:5 and K xNiFe(CN)6-DEGDME1:5 showed new absorption peaks, corresponding to the characteristic absorption peaks of DME and DEGDME respectively. This shows that the use of DME or DEGDME for reflux can also effectively remove K x The adsorbed water of NiFe(CN)6 replaces the crystal water inside its lattice.

[0097] FIG. 10 shows K of Example 3 and Example 4 of the present invention. 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 of the battery are the same as those in Example 1, except that the positive electrode materials are K x NiFe(CN)6、K x NiFe(CN)6-DME1:5 and K x NiFe(CN)6-DEGDME1:5. As can be seen from Figure 10, compared with the original sample K x Compared with NiFe(CN)6, K x After 100 charge and discharge cycles, the capacity retention rate of NiFe(CN)6-DME1:5 can still reach 89%, while the K x The capacity retention rate of NiFe(CN)6-DEGDME1:5 is 93%, and the cycle stability is significantly improved.

[0098] The effects of Comparative Example 1 of the present invention and its application examples are described in detail below with reference to Figures 11 to 12:

[0099] In order to demonstrate the effect of electrolyte salt in the modification method of the present invention, Comparative Example 1 also uses Prussian blue analog K x NiFe(CN)6 was used as an example, and ethylene carbonate (EC) was used as the reflux solvent and K was obtained by reflux without adding electrolyte salt NaTFSI. x NiFe(CN)6-EC1:0. Figure 11 shows the K of Comparative Example 1 of the present invention. x NiFe(CN)6 and K x Infrared spectrum of NiFe(CN)6-EC1:0. Compared with the original sample K x Compared with NiFe(CN)6, K x NiFe(CN)6-EC1:0 at 2910cm -1 、1770cm -1 、1420cm -1 and 1080cm-1 A new absorption peak appears near the x In the NiFe(CN)6 lattice; however, at 3400 cm -1 and 1620cm -1 There is still a strong absorption peak near K x NiFe(CN)6-EC1:0 still contains a large amount of adsorbed water and crystallized water.

[0100] Figure 12 is the K of Comparative Example 1 of the present invention x NiFe(CN)6 and K x Electrochemical performance diagram of NiFe(CN)6-EC1:0. The battery assembly method and test conditions are the same as those in Example 1. As can be seen from Figure 12, the reflux sample K without the addition of electrolyte salt NaTFSI x After 100 charge-discharge cycles, the capacity retention rate of NiFe(CN)6-EC1:0 is only 69%, which is comparable to the original sample K x Compared with NiFe(CN)6, the cycling stability was not significantly improved. This indicates that the addition of a certain amount of electrolyte salt NaTFSI can promote the exchange of organic solvents with the crystal water inside the Prussian blue analogue crystals and improve its electrochemical performance.

[0101] In summary, the modification method of the Prussian blue analogue provided by the present invention can effectively remove the crystal water inside the crystal lattice of the Prussian blue analogue, and the added electrolyte salt is conducive to the formation of [electrolyte salt + organic solvent] + The structure of the Prussian blue analogue effectively promotes the exchange of organic solvents with the crystalline water inside the Prussian blue analogue crystals, greatly improving the cycle stability of the Prussian blue analogue and the electrochemical performance of the Prussian blue analogue. After being assembled into a sodium ion battery as a positive electrode, the capacity retention rate still exceeds 85% after 100 charge and discharge cycles.

[0102] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for modifying a Prussian blue analogue, characterized in that, It includes the following steps: Mix the Prussian blue analogue to be processed with an electrolyte salt in an organic solvent, heat for condensation reflux, and extract the solid product in the solution after reflux to obtain the Prussian blue analogue.

2. The modification method according to claim 1, wherein The molar ratio of the Prussian blue analogue to be processed 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 °C; And / or, the reflux time is 5-100 h.

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

5. The modification method according to claim 1 or 4, characterized in that, The electrolyte salt is an electrolyte sodium salt and / or an electrolyte lithium salt; And / or, the electrolyte salt is at least one of NaTFSI, NaFSI, NaFTFSI, NaPF6, NaBF4, NaClO4, LiTFSI, LiFSI, LiFTFSI, LiPF6, LiBF4, and LiClO4.

6. The modification method according to claim 1, wherein The Prussian blue analog to be processed 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)6K x CoFe(CN)6, K x at least one of MnFe(CN)6, where 0 < x < 2.

7. The modification method according to claim 1, characterized in that, The process of extracting the solid product in the solution after reflux includes the following steps:

8. A Prussian blue analogue obtained by the modification method according to any one of claims 1 to 7, characterized in that, Centrifuge the solution after reflux to obtain a centrifuged product, and the centrifuged product is dried, washed, centrifuged, and dried to obtain a Prussian blue analogue solid.

9. A cathode material, characterized in that, The mass content of the crystal water of the Prussian blue analogue is 0-2%.

10. A battery, characterized in that, The positive electrode material contains the Prussian blue analogue described in claim 8. The battery contains the Prussian blue analogue described in claim 8.

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