A method for thermal repair modification of a prussian white type sodium-ion battery positive electrode material

Abstract

The application belongs to the field of production and preparation of sodium-ion battery positive electrode materials, and particularly relates to a hot repair modification method of Prussian white type sodium-ion battery positive electrode material, which comprises the following steps: taking sodium ferrocyanide as a repair agent, and adopting a hot repair method to obtain a Prussian white analog without defects and low crystallization water. The obtained manganese-based Prussian white analog presents a monoclinic structure, and has an elliptical flake shape with a particle size of 100-300 nm. The application removes crystallization water, repairs defects and supplements sodium through a low-temperature hot repair technology, so that a sodium-rich monoclinic structure crystal (LQMnHCF-R) with complete skeleton is obtained from a low-quality cubic manganese-based Prussian white analog (LQMnHCF), and the crystal exhibits good electrochemical sodium storage behavior. The application has a short process flow, low cost, and a repair agent which can be recycled and is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application relates to the field of sodium ion battery materials, in particular to a heat-repairing modification method of a Prussian white type sodium ion battery positive electrode material. BACKGROUND

[0002] Based on the double-carbon target of "carbon neutralization" and "carbon peak", the rapid growth of electric vehicle transportation, power grid application and electronic device sales promotes the development of rechargeable batteries. Moreover, the amount of materials required for stationary energy storage applications will put great pressure on the demand for raw materials. At present, the main sodium battery positive electrode materials mainly include polyanion compounds, Prussian white type compounds (PBAs) and layered transition metal oxides. Among them, Prussian white type sodium battery positive electrode materials gradually become the focus of research in the academic and industrial fields due to their unique open frame structure, rich sodium storage sites and large ion migration channels. In theory, Prussian white type sodium battery positive electrode materials are a kind of positive electrode material with high specific capacity and long cycle life. However, due to the influence of a large number of structural defects and crystal water in the material, the discharge capacity, cycle life and coulombic efficiency are often unsatisfactory. Therefore, developing efficient defect repair and crystal water removal strategies has become a hot spot in the research of Prussian white analogs.

[0003] At present, most of the research focuses on controlling defects and crystal water from the source, and reducing the content of defects and crystal water by chelating agent assisted method and the like to slow down the nucleation of crystals. Some researchers also try to solve the problem of crystal water in PBAs materials from the back end, such as vacuum dehydration. Goodenough et al. performed vacuum drying dehydration on MnFe-PBA at 100 DEG C for 30 h under high vacuum (Journal of the American Chemical Society, 2015, 137(7):2658-2664). The dehydrated MnFe-PBA showed high specific capacity (150 mAh g -1 ), excellent rate and cycle performance (75% capacity retention rate after 500 cycles). As can be seen, the electrochemical performance of PBAs can be greatly improved after dehydration. However, due to the large number of defects in the PBAs skeleton, water molecules in the air are easy to enter the PBAs skeleton again, especially the defect sites, and the electrochemical performance of the water-absorbed Prussian white decays quickly, which is not conducive to the industrial application of PBAs materials.

[0004] If the defects of PBAs can be repaired and the water absorption sites are reduced, the electrochemical sodium storage behavior and stability of PBAs are expected to be greatly improved, thereby promoting the application of PBAs in sodium ion batteries. We use a heat treatment defect repair technology to remove the crystal water in the unmodified Prussian white, and under the assistance of a repairing agent, the sodium ions and [Fe(CN)6]3- / 4- The sodium-rich high-crystallinity Prussian white positive electrode material is obtained by repairing defects in the skeleton into the skeleton of PBAs, and the commercialization of the sodium ion battery based on PBAs is expected to be further promoted. SUMMARY

[0005] In view of the problems in the prior art, the application provides a modification method of Prussian white and its analogs, and a low-temperature thermal repair technology is used to repair the defect structure of PBAs, so that the [Fe(CN)6] 3- / 4- The defects in the skeleton are repaired into the skeleton of PBAs, the integrity of the skeleton structure and the sodium storage amount are improved, and the storage stability and electrochemical performance of PBAs are improved. The material obtained after the thermal repair treatment has excellent characteristics of high capacity and high redox platform, and shows good electrochemical behavior. The method has a simple process, simple equipment, widely available raw materials, low cost of repair agent, and has very good industrialization prospect.

[0006] In order to achieve the above purpose, the application provides a modification method of Prussian white analogs, and the specific steps are as follows:

[0007] (1) Synthesis of water-containing and defect Prussian white analogs.

[0008] (2) The product in step (1) is mixed with a low-melting-point repair agent in a certain proportion.

[0009] (3) The mixture in step (2) is transferred to a tube furnace, and a protective gas is introduced, and the flow rate of the protective gas is 60 mlmin -1 .

[0010] (4) After the protective gas in step (3) is introduced into the tube furnace for 60 min, the reactants in the tube furnace are heated at a rate of 1-15 ℃ min -1 to 150-250 ℃, and then heat preservation for 3-24 h, and the protective gas is continuously introduced during heating and heat preservation.

[0011] (5) After step (4) is completed, the tube furnace is naturally cooled to room temperature, washed, dried, and the obtained material (LQMnHCF-R) has a monoclinic structure and almost no defects, and the water content in the material is only 9 wt%.

[0012] The water-containing and defect Prussian white analogues in the step (1) include one or more of water-containing and defect iron-based Prussian white analogues, water-containing and defect iron-manganese-based Prussian white analogues, water-containing and defect iron-cobalt-based Prussian white analogues, water-containing and defect iron-nickel-based Prussian white analogues, water-containing and defect iron-copper-based Prussian white analogues, water-containing and defect iron-zinc-based Prussian white analogues, water-containing and defect manganese-based Prussian white analogues, water-containing and defect manganese-cobalt-based Prussian white analogues, water-containing and defect manganese-nickel-based Prussian white analogues, water-containing and defect manganese-copper-based Prussian white analogues, water-containing and defect zinc-manganese-based Prussian white analogues, water-containing and defect nickel-based Prussian white analogues, water-containing and defect zinc-based Prussian white analogues, water-containing and defect cobalt-based Prussian white analogues, water-containing and defect vanadium-based Prussian white analogues, and water-containing and defect cerium-based Prussian white analogues.

[0013] The repairing agent in the step (2) includes sodium ferrocyanide and its hydrate.

[0014] The ratio of the defect Prussian white analogue and the repairing agent in the step (2) is 4-10:1, and the preferred ratio is 4:1.

[0015] The protective gas in the step (3) includes nitrogen, argon and hydrogen-argon mixed gas, and the preferred gas is hydrogen-argon mixed gas.

[0016] The heating rate in the step (4) is 1-15 ℃ / min -1 , and the preferred heating rate is 10 ℃ / min -1 , the target temperature of the heating is 150-250 ℃, and the preferred temperature is 160 ℃, and the holding time is 3-24 h, and the preferred holding time is 6 h.

[0017] The second aspect of the present application provides a sodium ion battery positive electrode material, which is prepared from the above-mentioned LQMnHCF-R material.

[0018] The preparation method of the above-mentioned sodium ion battery positive electrode is as follows: the LQMnHCF-R material, conductive carbon black (conductive agent) and sodium alginate (binder) are mixed according to 70:20:10 (wt%), the obtained mixture is fully ground and mixed uniformly in a mortar, is transferred to a 2 ml shock tube, several zirconium dioxide beads with a diameter of 3 mm are added, and is fully shocked to obtain a uniform slurry, which is coated on a carbon-coated aluminum foil and is placed in a vacuum drying box at 80 ℃ for vacuum drying for 12 h, so that the solvent is completely evaporated, and then the piece is cut, weighed, and the active material loading is calculated.

[0019] The third aspect of the present application provides the application of the above-mentioned LQMnHCF-R material in a sodium ion battery.

[0020] The method and the prepared modified Prussian white analogue positive electrode material have the following beneficial effects:

[0021] (1) In the modification process, under the action of low-temperature heating, the crystal water in the material escapes and is taken away by the flowing protective gas. The escaped crystal water is continuously taken away, reducing the water content in the furnace body, which helps the further escape of the crystal water in the crystal lattice. The reduction of the crystal water content in the material helps to reduce the adverse effects of the crystal water on the stability of the organic electrolyte during charging and discharging.

[0022] (2) While the crystal water escapes, the sodium ions and [Fe(CN)6] 3- / 4- enter the framework structure, realizing sodium supplementation and defect repair at the same time, which is efficient, fast and simple in process.

[0023] (3) The whole process does not involve many organic solvents, and the cost is low. After post-processing, the repair agent can be recycled, which is green and environmentally friendly.

[0024] (4) The sodium ion battery prepared by using such material as the positive electrode has higher redox potential, high reversible specific capacity and relatively long cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the XRD comparison chart of the series LQMnHCF and LQMnHCF-R materials of examples 1-2.

[0026] Figure 2 It is the TG comparison chart of the series LQMnHCF and LQMnHCF-R materials of examples 1-2.

[0027] Figure 3 It is the FTIR comparison chart of the series LQMnHCF and LQMnHCF-R materials of examples 1-2.

[0028] Figure 4 It is the Raman comparison chart of the series LQMnHCF and LQMnHCF-R materials of examples 1-2.

[0029] Figure 5 It is the SEM, element mapping and EDS chart of the LQMnHCF material of example 1.

[0030] Figure 6 It is the SEM, element mapping and EDS chart of the LQMnHCF-R material of example 2.

[0031] Figure 7 It is the XPS comparison chart of the series LQMnHCF and LQMnHCF-R of examples 1-2.

[0032] Figure 8 Galvanostatic charge-discharge plots for the series of LQMnHCF and LQMnHCF-R materials of Examples 1-2 at 10 mA g -1

[0033] Figure 9 CV plots for the series of LQMnHCF and LQMnHCF-R materials of Examples 1-2.

[0034] Figure 10 Cycle performance plots for the series of LQMnHCF and LQMnHCF-R of Examples 1-2 at 100 mA g -1

[0035] Figure 11 Rate capability plots for the series of LQMnHCF and LQMnHCF-R of Examples 1-2.

[0036] Figure 12 Rate capability plots for the LQMnHCF-R material of Example 2. DETAILED DESCRIPTION

[0037] The following further describes the present application in connection with specific embodiments, but does not limit the present application in any way. Any simple modification, equivalent change and modification made to the following examples according to the technical essence of the present application still falls within the scope of the technical solutions of the present application.

[0038] The test methods described in the following examples are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified. EXAMPLE

[0039] (1) Dissolve manganese sulfate (5 mmol) in 100 ml of deionized water, stir for 3 h, and record as solution A.

[0040] (2) Dissolve sodium ferrocyanide (5 mmol) in 100 ml of deionized water, stir for 3 h, and record as solution B.

[0041] (3) Pour the A solution into the B solution quickly, stir for 6 h, and age for 24 h. Then wash the lower precipitate with water and ethanol, and place it in a vacuum drying oven at 120 °C for vacuum drying for 12 h to collect a manganese-based Prussian white analogue (recorded as LQMnHCF) containing crystal water and defects.

[0042] ​​(4) Preparation of electrode: the LQMnHCF material in step (3), conductive carbon black (conductive agent) and sodium alginate (binder) were mixed according to 70:20:10 (wt%), the obtained mixture was transferred to a shaking tube, 6 3 mm zirconium dioxide beads were added and shaken thoroughly to obtain a uniform slurry, which was uniformly coated on a carbon-coated aluminum foil by a coating machine (MSK-AFA-I), and then placed in a vacuum drying oven at 100 ℃ for vacuum drying for 12 h, so that the solvent was completely evaporated, and then a piece cutting machine (MSK-T10) was used to cut the slurry into a circular electrode sheet with a diameter of 10 mm, weighed, and the active material mass was calculated to be ~1.5 mg.

[0043] (5) The negative electrode sheet was selected as a 12 mm diameter circular metal sodium sheet. The electrolyte was selected as a solution of NaClO4 dissolved in methyl ethyl carbonate and propylene carbonate (volume ratio 1:1) and 3 wt% of fluoroethylene carbonate additive, wherein the concentration of NaClO4 was 1 mol L -1 . The separator was selected as a glass fiber membrane (produced by Whatman).

[0044] (6) Electrochemical performance test: all battery assembly was completed in a glove box (O wt%≤0.01, H2O wt%≤0.01), the constant current charge-discharge test and long cycle test of R2032 button cell were realized by Neware CT4000, the test voltage window was 2-4.0 V, and the current density 1C=100 mA g -1 .

[0045] For comparison, LQMnHCF-R was prepared under the same conditions. Example

[0046] In this example, the powder obtained in Example 1 was mixed with sodium ferrocyanide according to a molar ratio of 1:4, and then transferred to a tube furnace. Hydrogen-argon mixed gas was passed at a rate of 60 ml min -1 . After 60 min of aeration, the reactants in the tube furnace were heated to 160 ℃ at a rate of 10 ℃ min -1 . After 6 h of heat preservation, the reaction was completed, the tube furnace was naturally cooled to room temperature, and then washed and dried to obtain a sodium-rich manganese-based Prussian white analogue (denoted as LQMnHCF-R) with a monoclinic structure and almost no defects, and the electrochemical performance thereof was tested.

[0047] Figure 1 As can be seen from the XRD comparison chart of the two products of Examples 1-2, after heat repair, the original cubic phase structure is changed to a monoclinic structure, and the peak intensity is increased.

[0048] Figure 2For the TG comparison of LQMnHCF and LQMnHCF-R of Example 1-2, it can be seen that the water content in the material is significantly reduced after the repair of the product, and the water content can be controlled at about 9.1% of the total weight of the material.

[0049] Figure 3 For the FTIR comparison of the two materials of Example 1-2, the intensity of the O-H peak belonging to water molecules in the sample LQMnHCF-R treated by heat repair is reduced.

[0050] Figure 4 For the Raman comparison of the two materials of Example 1-2, it can be seen that the peak shifts to the left with the increase of sodium source, indicating that there is more low-valence Mn in the material 2+ .

[0051] Figure 5 For the SEM, element mapping and EDS of LQMnHCF material of Example 1, it can be seen that the elements are uniformly distributed, and the size is about 100-300 nm.

[0052] Figure 6 For the SEM, element mapping and EDS of LQMnHCF-R material of Example 2, it can be seen that the elements are uniformly distributed, and the size is about 100-300 nm.

[0053] Figure 7 For the XPS comparison of the series of LQMnHCF and LQMnHCF-R materials of Example 1-2, Na, Fe, Mn, C, N and O elements can be detected.

[0054] Figure 8 For the galvanostatic charge-discharge comparison of the two materials of Example 1-2 at a current density of 10 mA / g, it can be seen that the sample LQMnHCF-R treated by heat repair has the highest specific capacity, higher working voltage and smaller polarization behavior.

[0055] Figure 9 For the CV comparison of the two materials of Example 1-2, the electrochemical redox platform of the sample LQMnHCF-R treated by heat repair is improved.

[0056] Figure 10 For the cycle performance comparison of the two materials of Example 1-2 at a current density of 100 mA g -1 , it can be seen that the capacity is improved after heat treatment and the original cycle stability is almost not lost.

[0057] Figure 11 For the rate performance comparison of the two materials of Example 1-2, it can be seen that even at 2000 mA g -1at high current densities, the material after the thermal repair treatment still maintains a capacity of 80 mAh g -1 .

[0058] Figure 12 For the rate charge-discharge curve of the LQMnHCF-R material of Example 2, it can be seen that as the current density increases, the curve shape of the charge-discharge does not change significantly, and the voltage polarization increases to a certain extent.

Claims

1. A method for thermal repair modification of Prussian white-based sodium-ion battery cathode material, characterized in that, The method comprises the following steps: (1) mixing low-melting-point repairing agent sodium ferrocyanide and its hydrate with unmodified Prussian white analog positive electrode material containing defects and crystal water in a molar ratio of 4-10:1; (2) The mixed powder obtained in step (1) is transferred into a tube furnace, and a protective gas is introduced at a flow rate of 60 ml / min -1 , and the protective gas comprises one of nitrogen, argon, and hydrogen-argon mixture. (3) After the protective gas in pipe furnace 60 min, the pipe furnace is heated at 1-50 ℃ min -1 to 150-250 ℃, and then kept for 3-24 h, and the protective gas is continuously inhaled during the heating and keeping; (4) after the heat preservation in step (3) ends, the tube furnace is naturally cooled to room temperature, washed, dried, and the modified Prussian white analog positive electrode material is obtained, wherein the modified Prussian white analog positive electrode material is a sodium-rich monoclinic phase crystal form.

2. The method for thermal repair modification of Prussian white-based sodium-ion battery cathode material according to claim 1, characterized in that, The Prussian white containing crystal water and defects in step (1) is one or several of the following: water-containing and defect-containing iron-based Prussian white analog material, water-containing and defect-containing iron-manganese-based Prussian white analog material, water-containing and defect-containing iron-cobalt-based Prussian white analog material, water-containing and defect-containing iron-nickel-based Prussian white analog material, water-containing and defect-containing iron-copper-based Prussian white analog material, water-containing and defect-containing iron-zinc-based Prussian white analog material, water-containing and defect-containing manganese-based Prussian white analog material, water-containing and defect-containing manganese-cobalt-based Prussian white analog material, water-containing and defect-containing manganese-nickel-based Prussian white analog material, water-containing and defect-containing manganese-copper-based Prussian white analog material, water-containing and defect-containing zinc-manganese-based Prussian white analog material, water-containing and defect-containing nickel-based Prussian white material, water-containing and defect-containing zinc-based Prussian white analog material, water-containing and defect-containing cobalt-based Prussian white analog material, water-containing and defect-containing vanadium-based Prussian white analog material, and water-containing and defect-containing cerium-based Prussian white analog material.

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