A coating modification method of prussian blue analogues and application thereof

Abstract

The application discloses a coating modification method of Prussian blue analogues and application thereof, and belongs to the technical field of material modification. The coating modification method of Prussian blue analogues provided by the application comprises the following steps: mixing poly-3-hexylthiophene, Prussian blue analogues and a solvent, so that at least part of the poly-3-hexylthiophene coats the Prussian blue analogues, and the modified Prussian blue analogues are obtained after removing the solvent. The poly-3-hexylthiophene is used to coat the Prussian blue analogues, the crystal water is limited in the crystal structure, the crystal water cannot be removed in the use process, the structural stability of the modified Prussian blue analogues is effectively improved, the use performance of the Prussian blue analogues is improved, and the modified Prussian blue analogues obtained by the method have wide application in the preparation of battery positive electrode materials.

Description

Technical Field

[0001] This invention belongs to the field of material modification technology, and particularly relates to a coating modification method for Prussian blue analogues and its application. Background Technology

[0002] Prussian blue (PB) and its analogues (PBAs) have an open framework structure with large ion channels and voids in the lattice, making them among the few crystals capable of accommodating K+. + One of the host materials, which is very beneficial to K + Or Na + Rapid insertion and extraction. However, the main method for synthesizing Prussian blue analogues is currently co-precipitation in aqueous solution. This method inevitably produces a large amount of water of crystallization in the crystal. This water of crystallization participates in the battery cycle decomposition, causing an increase in the battery's internal resistance and leading to rapid capacity decay. At the same time, the water of crystallization repels K+ in the crystal. + Or Na + This leads to crystal defects. Current research suggests that reducing the water of crystallization content in the crystal, thereby improving the crystal completeness of Prussian blue analogues, plays a crucial role in enhancing their electrochemical performance.

[0003] Studies have reported that the molecular formula is K 0.220 Fe[Fe(CN)6] 0.805 • Prussian blue analogue (PBAs) cathode materials with 4.01H2O, during battery cycling, the water of crystallization in the above-mentioned PBA materials will change along with K. + Water is extracted and enters the electrolyte, where it is oxidized and decomposed at high potential. This not only affects the initial coulombic efficiency but also increases the battery's internal resistance, leading to capacity decay during cycles. Furthermore, the lattice stability of the material itself is affected by the extraction of crystal water. Other studies have shown that after synthesizing PBAs, they were dried at 100°C under vacuum and air conditions, respectively. The chemical formulas of the dried products are Na and Na, respectively. 1.89 Mn[Fe(CN)6] 0.97 ·0.3H2O and Na 1.89 Mn[Fe(CN)6] 0.97The water content of PBAs obtained by the two drying methods differed significantly, with the PBAs with lower water content exhibiting a reversible capacity of 150 mAh / g and excellent rate and cycle performance. This study indicates that thermal removal of interstitial water in PBAs significantly impacts their electrochemical performance. To date, research on PBAs has focused on reducing the water of crystallization, i.e., minimizing the water of crystallization content during synthesis to improve crystal integrity and thus enhance electrochemical performance. While it's difficult to completely avoid water of crystallization during PBA synthesis, and heating is the most direct method for removal, simply heating and drying may lead to unstable PBA crystal structures, affecting cycle performance. Furthermore, heating cannot completely remove all water of crystallization, failing to address the negative impact of water of crystallization on battery performance. Summary of the Invention

[0004] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a coating modification method for Prussian blue analogues, which stabilizes the crystal structure of PBAs, solves the negative problems caused by crystal water during use, and improves the performance of PBAs.

[0005] The second objective of this invention is to provide a modified Prussian blue analogue obtained by the above-described coating modification method.

[0006] The third objective of this invention is to provide an application of the above-mentioned modified Prussian blue analogue.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A first aspect of the present invention provides a method for coating modification of a Prussian blue analogue, comprising the following steps: mixing poly(3-hexylthiophene), a Prussian blue analogue and a solvent, such that at least a portion of the poly(3-hexylthiophene) coats the Prussian blue analogue, and removing the solvent to obtain the coated modified Prussian blue analogue.

[0009] The inventive concept of this invention differs from existing technologies that focus on reducing the water of crystallization content in materials. Instead, it takes a different approach, focusing on restricting the release of water of crystallization during use to prevent its impact on performance. Specifically, it uses poly(3-hexylthiophene) (P3HT) to coat PBAs, preventing the release of water of crystallization during battery cycling. This also stabilizes the PBA crystal structure and improves its electrochemical performance. Furthermore, the presence of water of crystallization in the crystal can also shield K... + Or Na + The interaction with structural anions increases the K of the material.+ or Na + diffusion ability to further improve the electrochemical performance of PBAs.

[0010] Preferably, the solvent includes at least one of chloroform, carbon disulfide, chlorobenzene, toluene, tetrahydrofuran, o-dichlorobenzene, p-dichlorobenzene or dimethylformamide; more preferably, the solvent includes at least one of chloroform, carbon disulfide, chlorobenzene or toluene; even more preferably, the solvent is selected from chloroform.

[0011] The solvent used in the present invention needs to have good solubility in poly(3-hexylthiophene), which is beneficial to the more sufficient dispersion of poly(3-hexylthiophene) and achieve a good coating effect on the Prussian blue analogues. Poly(3-hexylthiophene) has a large solubility in chloroform and can achieve a better coating effect in the present invention.

[0012] Preferably, the chemical formula of the Prussian blue analogue is A x M′[M″(CN)6] y ·nH2O, where 0 < x ≤ 2, 0 < y ≤ 1, 0 < n ≤ 4, A is an alkali metal element, and M′ and M″ are each independently a transition metal element.

[0013] Preferably, the alkali metal element includes at least one of Li, Na or K.

[0014] Preferably, the transition metal element includes at least one of Fe, Co, Cu, Mn or Ni.

[0015] In some specific embodiments of the present invention, in the chemical formula of the Prussian blue analogue, 0.5 ≤ x ≤ 2; in some specific embodiments of the present invention, in the chemical formula of the Prussian blue analogue, 1 ≤ x ≤ 2; non-limiting specific examples are that x is 1.2, 1.4, 1.5, 1.8 or 2.

[0016] In some specific embodiments of the present invention, in the chemical formula of the Prussian blue analogue, 0.2 ≤ y ≤ 1; in some specific embodiments of the present invention, in the chemical formula of the Prussian blue analogue, 0.5 ≤ y ≤ 1; non-limiting specific examples are that y is 0.6, 0.7, 0.8, 0.9 or 1.

[0017] In some specific embodiments of the present invention, in the chemical formula of the Prussian blue analogue, 0.2 ≤ n ≤ 3.5; in some specific embodiments of the present invention, in the chemical formula of the Prussian blue analogue, 1.5 ≤ n ≤ 3; non-limiting specific examples are that n is 1.8, 2, 2.3, 2.5 or 2.8.

[0018] In some specific embodiments of the present invention, the chemical formula of the Prussian blue analogue is K2FeFe(CN)6·2.3H2O.

[0019] Preferably, the mass ratio of the poly(3-hexylthiophene) to the Prussian blue analogue is 1:(10-35); more preferably 1:(15-25); even more preferably 1:(18-22); non-limiting examples include 1:19, 1:20 or 1:21.

[0020] Preferably, the mass ratio of the poly(3-hexylthiophene) to the solvent is 1:(15-25); more preferably 1:(18-22); non-limiting examples include 1:19, 1:20 or 1:21.

[0021] Preferably, in the coating modification method of the Prussian blue analogue, the mixing time is 0.1 to 20 hours; more preferably, it is 0.5 to 12 hours.

[0022] Preferably, in the coating modification method of the Prussian blue analogue, the solvent is removed by drying.

[0023] Preferably, the drying temperature is 60–100°C; more preferably 70–90°C; and even more preferably 75–85°C.

[0024] Preferably, the drying time is 5 to 30 hours; more preferably 8 to 25 hours; and even more preferably 10 to 20 hours.

[0025] In some specific embodiments of the present invention, the mixing specifically involves: first mixing poly-3-hexylthiophene with a solvent, and then adding a Prussian blue analogue for mixing.

[0026] First, thoroughly mix poly(3-hexylthiophene) and solvent, then add Prussian blue analogue. This helps to achieve a better coating effect on Prussian blue analogue.

[0027] A second aspect of the present invention provides a modified Prussian blue analogue prepared by the coating modification method described in the first aspect of the present invention.

[0028] Preferably, the modified Prussian blue analogue has a water content of 8–20 wt%; more preferably 9–18 wt%; and even more preferably 10–15 wt%.

[0029] A third aspect of the present invention provides the application of the modified Prussian blue analogue described in the first aspect of the present invention in the preparation of battery cathode materials.

[0030] Preferably, the battery comprises a potassium-ion battery or a sodium-ion battery.

[0031] The beneficial effects of this invention are as follows: This invention uses poly-3-hexylthiophene (P3HT) to coat Prussian blue analogues, confining the water of crystallization within the crystal structure so that it cannot escape during use. This effectively improves the structural stability of the modified Prussian blue analogue and also improves its performance. When the modified Prussian blue analogue obtained by the method of this invention is used as a battery cathode material, it prevents the water of crystallization from escaping during battery cycling. While stabilizing the crystal structure of the cathode material, it also solves the problem of oxidative decomposition caused by the water of crystallization entering the battery electrolyte, effectively improving the battery cycle performance. Therefore, the modified Prussian blue analogue of this invention has wide applications in the preparation of battery cathode materials.

[0032] Specifically, compared with the prior art, the present invention has the following advantages:

[0033] 1. The method of the present invention can be applied to PBA products containing a large amount of water of crystallization without changing their crystal structure. The method has a wide range of applications and is beneficial to fundamentally solve the adverse effects of water of crystallization on PBAs. When applied to the positive electrode of a battery, it has the advantages of good safety, low price, high capacity and high cycle life.

[0034] 2. When the modified Prussian blue analogue prepared in this invention is used as the positive electrode material for potassium-ion batteries or sodium-ion batteries, the presence of water of crystallization in the crystal can also shield K+. + Or Na + The interaction with structural anions increases the K of the material. + Or Na + Diffusion capability further enhances the electrochemical performance of cathode materials.

[0035] 3. The coating modification method of the present invention is simple, and the modified Prussian blue analogue obtained has good electrochemical performance and has wide application in the preparation of battery cathode materials, especially cathode materials for potassium-ion batteries or sodium-ion batteries. Attached Figure Description

[0036] Figure 1 This is a flowchart of the coating modification method for Prussian blue analogues in an embodiment of the present invention.

[0037] Figure 2 The images show the XRD patterns of samples from Example 1 and Comparative Examples 1-2.

[0038] Figure 3 The electrochemical performance graphs are for the samples of Examples 1-3 and Comparative Example 1.

[0039] Figure 4 The infrared spectra of the samples from Example 2 and Comparative Example 1 before and after the cyclic test are shown.

[0040] Figure 5Infrared spectra of the samples of Example 1 and Example 3 before and after cyclic testing. Detailed implementation manners

[0041] The content of the present invention will be further described in detail through specific examples below. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific data in the examples below. The raw materials, reagents or devices used in the following examples and comparative examples can be obtained from conventional commercial channels without special instructions, or can be obtained by existing known methods.

[0042] In some embodiments of the invention, the chemical formula of the Prussian blue analogue is A x M′[M″(CN)6] y ·nH2O, 0 < x ≤ 2, 0 < y ≤ 1, 0 < n ≤ 4, 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., and M′ and M″ can be the same or different. In some specific embodiments of the invention, the Prussian blue analogue further contains vacancy defects, and the number of vacancy defects is related to the number of [M″(CN)6], specifically 1 - y.

[0043] An embodiment of the present invention provides a method for coating and modifying a Prussian blue analogue. Taking potassium-based Prussian blue analogue (K2FeFe(CN)6·2.3H2O, KFF) as an example, P3HT@KFF is synthesized. The flow chart is as Figure 1 shown, and specifically includes the following steps:

[0044] A) Add poly(3-hexylthiophene) (P3HT) to chloroform and stir until it is completely dissolved to obtain a P3HT solution.

[0045] B) Add KFF powder to the P3HT solution and stir for 0.5 - 12 hours to obtain a suspension.

[0046] C) Centrifuge the obtained suspension to obtain a solid sample.

[0047] D) Put the solid sample into an oven and heat it for drying (dry at 80°C for more than 10 h) to obtain a dried P3HT@KFF sample.

[0048] The following will be further described in combination with specific examples and comparative examples.

[0049] Example 1

[0050] A method for coating modification of Prussian blue analogs, taking potassium-based Prussian blue analogs (K2FeFe(CN)6·2.3H2O, KFF) as an example, to synthesize P3HT@KFF, specifically including the following steps:

[0051] Poly(3-hexylthiophene) (P3HT) was added to chloroform and stirred at a mass ratio of 1:20 until fully dissolved. KFF powder was then added and stirred, with a P3HT to KFF mass ratio of 3:100. The mixture was stirred at room temperature (20–30°C) for 0.5–12 hours to obtain a suspension. The suspension was centrifuged to obtain a solid sample. The solid sample was then dried in an oven at 80°C for at least 10 hours to obtain dried P3HT@KFF. The sample prepared in this example is denoted as P3HT@KFF-3% or P3HT@KFF 80°C.

[0052] Example 2

[0053] A method for coating and modifying a Prussian blue analogue, differing from Example 1 in that the mass ratio of P3HT to KFF in this example is 1:20, while the other raw materials and preparation methods are the same as in Example 1. The sample obtained in this example is denoted as P3HT@KFF-5%.

[0054] Example 3

[0055] A method for coating and modifying a Prussian blue analogue, differing from Example 1 in that the mass ratio of P3HT to KFF in this example is 1:10, while the other raw materials and preparation methods are the same as in Example 1. The sample obtained in this example is denoted as P3HT@KFF-10%.

[0056] Comparative Example 1

[0057] The original potassium-based Prussian blue analogue (K2FeFe(CN)6·2.3H2O, KFF) was used as a control sample. Without any coating modification, the sample was dried in an oven at 80°C for at least 10 hours to obtain dried KFF. The sample prepared in this example is denoted as KFF or KFF 80°C.

[0058] Comparative Example 2

[0059] A method for coating modification of a Prussian blue analogue, differing from Example 1 in that the drying temperature of the solid sample is 150°C, while the other raw materials, amounts, and steps are the same as in Example 1. The sample obtained in this example is denoted as P3HT@KFF 150°C.

[0060] Performance testing

[0061] 1) Test the XRD patterns of the samples from Example 1 and Comparative Examples 1-2. Figure 2 The images show the XRD patterns of samples from Example 1 and Comparative Examples 1-2. Figure 2 It is evident that excessively high drying temperatures lead to material decomposition, and the sample in Comparative Example 2 no longer exhibits the Prussian blue phase. Since P3HT has high solubility in chloroform, chloroform was used as the solvent in Examples 1 and 2. Chloroform has a low boiling point, so a high drying temperature is unnecessary; 80°C is sufficient. If the temperature is too high, such as around 150°C, both the Prussian blue analogue crystals and P3HT may decompose, severely impacting material properties. Therefore, while increasing the drying temperature is beneficial for removing water of crystallization, maintaining the drying temperature within a certain range is more conducive to improving the overall performance of the material.

[0062] 2) The electrochemical performance of the samples in Example 1 and Comparative Examples 1-3 was tested. The test process is as follows: KFF of Comparative Example 1 and P3HT@KFF of Examples 1-3 were used as the positive electrode of the battery, potassium metal was used as the negative electrode of the battery, 0.8 mol / L KPF6 (solvent is ECDEC) was used as the electrolyte, and glass fiber was used as the separator. Potassium ion batteries were assembled and constant current charge-discharge tests were performed at 50 mA / g.

[0063] Figure 3 The electrochemical performance graphs for Examples 1-3 and Comparative Example 1 are shown. It can be seen that the capacity retention of sample KFF in Comparative Example 1 was only 41.12% after 200 charge-discharge cycles. In contrast, in Example 2, P3HT@KFF-5% coated with 5% P3HT achieved a capacity retention of 90.28% after 200 charge-discharge cycles, demonstrating significantly improved cycle stability. Examples 1 and 3 showed capacity retention of 81.33% and 76.05% respectively after 200 charge-discharge cycles, slightly lower than Example 2.

[0064] 3) Test the infrared spectra of the samples of Examples 1-3 and Comparative Example 1 (without cyclic testing), and perform cyclic performance testing on the samples using the performance test 1) method, and measure the infrared spectra of the samples after 10 cycles.

[0065] Figure 4 The images show the infrared spectra of the samples from Example 2 and Comparative Example 1 before and after the cyclic test. Figure 5The images show the infrared spectra of the samples from Examples 1 and 3 before and after the cycling test. KFF, P3HT@KFF-3%, P3HT@KFF-5%, and P3HT@KFF-10% represent the original samples before the cycling test, while KFF 10 cycles, P3HT@KFF-3% 10 cycles, P3HT@KFF-5% 10 cycles, and P3HT@KFF-10% 10 cycles represent the samples after 10 cycles of the cycling test. It can be seen that for the original samples KFF and P3HT@KFF before the cycling test, their infrared spectra are at 3400 cm⁻¹. -1 and 1620cm -1 Strong absorption peaks appeared at [values ​​missing], corresponding to adsorbed water and coordinated water of the Prussian blue analogues, respectively. As for the sample after cycling, after 10 cycles of KFF, its 3400 cm⁻¹ [value missing]... -1 The adsorption water peak at 1620 cm⁻¹ and 1620 cm⁻¹ -1 The decrease in the size of the coordination water peak at 3400 cm⁻¹ indicates that water participates in the reaction and disappears during the charge-discharge process of KFF; while for P3HT@KFF, the original sample and the sample after 10 cycles showed a smaller peak at 3400 cm⁻¹. -1 The adsorption water peak at 1620 cm⁻¹ and 1620 cm⁻¹ -1 The coordination water peak at the location did not change significantly. It can be seen that the coating modification in Examples 1 to 3 is not about reducing the water content in the crystal, but about confining it in the crystal so that it will not come out during battery cycling and affect battery performance. This coating modification method stabilizes the PBA crystal structure and solves the problem of oxidation decomposition caused by crystal water entering the battery electrolyte, effectively improving the battery cycle performance.

[0066] 4) The water content of the samples from Examples 1-3 and Comparative Example 1 (without cyclic testing) was tested, and the cyclic performance of the samples was tested using the performance test method 1). The water content of the samples after 10 cycles, as well as the initial charge-discharge specific capacity and the capacity retention rate after 200 cycles were determined. The results are recorded in Table 1.

[0067] Table 1. Performance of Samples from Examples 1-3 and Comparative Example 1

[0068]

[0069] As shown in Table 1, the coating modification of P3HT onto PBA crystals in Examples 1-3 does not reduce the water content in the crystals, but effectively improves the specific capacity and cycle performance of the battery. This is mainly because, in this invention, P3HT primarily functions to isolate water molecules from entering and exiting the battery, thereby improving battery performance. This is completely different from the existing approach of improving battery performance by reducing the water content of the crystals. Typically, PBA crystals contain water of crystallization. During battery operation, this water of crystallization enters the battery, leading to an increase in internal resistance. However, in Example 1, P3HT confines the water of crystallization within the PBA crystal lattice. During battery operation, the water of crystallization is confined within the lattice and does not negatively impact battery performance, thus achieving the goal of improving battery performance. Furthermore, the water of crystallization in the crystal also has a role in promoting improved battery performance; for example, it can shield K... + Or Na + The interaction with structural anions increases the K of the material. + Or Na + Diffusion capability further enhances the electrochemical performance of PBAs.

[0070] The method described in this invention can be applied to PBA products containing a large amount of water of crystallization without altering their crystal structure. The method has a wide range of applications and helps to fundamentally solve the adverse effects of water of crystallization on PBAs. When applied to battery cathodes, it offers advantages such as good safety, low cost, high capacity, and long cycle life. When the modified Prussian blue analogue prepared in this invention is used as the cathode material for potassium-ion or sodium-ion batteries, the presence of water of crystallization in the crystal can also shield K+. + Or Na + The interaction with structural anions increases the K of the material. + Or Na + The diffusion capability is improved, further enhancing the electrochemical performance of the cathode material. The coating modification method in the embodiments of the present invention is simple, and the resulting modified Prussian blue analogue exhibits excellent electrochemical performance, making it widely applicable in the preparation of battery cathode materials, especially cathode materials for potassium-ion or sodium-ion batteries.

[0071] In summary, this invention utilizes poly-3-hexylthiophene (P3HT) to coat Prussian blue analogues, confining the water of crystallization within the crystal structure and preventing its release during use. This effectively improves the structural stability of the modified Prussian blue analogue and enhances its performance. When used as a battery cathode material, the modified Prussian blue analogue obtained by this invention prevents the release of water of crystallization during battery cycling. While maintaining the stability of the cathode material's crystal structure, it also solves the problem of oxidative decomposition caused by water of crystallization entering the battery electrolyte, effectively improving battery cycle performance. Therefore, the modified Prussian blue analogue of this invention has wide applications in the preparation of battery cathode materials.

Claims

1. A method for coating modification of Prussian blue analogues, characterized in that, Includes the following steps: Mix poly(3 - hexylthiophene), a Prussian blue analogue, and a solvent so that at least a part of the poly(3 - hexylthiophene) coats the Prussian blue analogue, and obtain the coated and modified Prussian blue analogue after removing the solvent; the chemical formula of the Prussian blue analogue is A x M′[M′′(CN)6] y ·nH2O, 0 < x ≤ 2, 0 < y ≤ 1, 1.5 ≤ n ≤ 3, where A is an alkali metal element, and M′ and M′′ are each independently a transition metal element; the mass ratio of the poly(3 - hexylthiophene) to the Prussian blue analogue is 1:(15 - 25); the water content of the coated and modified Prussian blue analogue is 10 - 15 wt%; the alkali metal element includes at least one element selected from Li, Na, or K; the transition metal element includes at least one element selected from Fe, Co, Cu, Mn, or Ni; the way to remove the solvent is drying; the temperature of the drying is 60 - 100 °C; the time of the drying is 5 - 30 h.

2. The coating modification method according to claim 1, characterized in that, The solvent includes at least one of chloroform, carbon disulfide, chlorobenzene, toluene, tetrahydrofuran, o-dichlorobenzene, p-dichlorobenzene, or dimethylformamide.

3. The coating modification method according to claim 1, characterized in that, The mass ratio of the poly(3-hexylthiophene) to the solvent is 1:(15~25).

4. The coating modification method according to claim 1, characterized in that, The mixing time is 0.1 to 20 hours.

5. A modified Prussian blue analogue prepared by the coating modification method according to any one of claims 1 to 4; wherein the water content of the modified Prussian blue analogue is 10 to 15 wt%.

6. The application of the modified Prussian blue analogue as described in claim 5 in the preparation of battery cathode materials.

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