A method for preparing a Prussian blue-type sodium-ion battery cathode material with both high capacity and long cycle performance

Abstract

A method for preparing a Prussian blue-based sodium-ion battery cathode material with both high capacity and long cycle performance, belonging to the field of sodium-ion batteries, includes the following steps: Step 1, preparing a sodium ferrocyanide solution, denoted as solution A; Step 2, dissolving a transition metal divalent ferric salt, a doped metal salt, ascorbic acid, and a complexing agent in deionized water, denoted as solution B; Step 3, preparing an aqueous solution of the complexing agent, denoted as solution C; Step 4, simultaneously adding solutions A and B in equal molar amounts to solution C for a co-precipitation reaction, aging the solution to obtain a suspension, separating the suspension to obtain the Prussian blue-based sodium-ion battery cathode material with both high capacity and long cycle performance. This invention proposes a synthesis method that only requires co-precipitation through a combination of slow crystallization and ion doping to obtain a low-cost, non-toxic, harmless, simple preparation process, short production cycle, and Prussian blue-based sodium-ion cathode material with both high capacity and long cycle performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, specifically to a method for preparing a Prussian blue-based sodium-ion battery cathode material that combines high capacity and long cycle performance. Background Technology

[0002] Traditional energy sources rely heavily on fossil fuels, leading to energy shortages and a sharp increase in carbon emissions, resulting in serious environmental problems and the greenhouse effect. Renewable energy and new clean energy sources are considered an effective energy storage system to replace traditional fossil fuels and have received widespread attention. However, clean renewable energy has significant spatial and temporal impacts and cannot provide a stable and continuous energy supply at all times. Therefore, the development of low-cost, large-scale energy storage devices is receiving increasing attention and importance. Currently, lithium-ion battery energy storage devices are a relatively excellent energy storage method and are widely used in electronic products, high-power electric vehicles, energy storage power stations, and some smart grids. However, facing the huge future demand for energy storage, the abundance of lithium resources and their uneven geographical distribution are gradually becoming a hidden danger. Sodium, which is in the same group as lithium, has similar chemical properties, abundant reserves, and low cost. Moreover, seawater contains a large amount of sodium resources, and the geographical distribution is more even. In addition, the working principle of sodium-ion batteries is very similar to that of lithium batteries, both being typical rocking chair batteries. Therefore, sodium-ion batteries have greater advantages and potential in large-scale energy storage.

[0003] Currently, the main cathode materials used in sodium-ion batteries include layered transition metal oxides, Prussian blue / white materials, and polyanionic compounds. Transition metal oxides suffer from poor cycle stability due to the phase transition during sodium insertion / extraction, which easily disrupts the material's structure. Polyanionic compounds, with their oxygen and fluorine lattices, make sodium insertion / extraction relatively difficult, resulting in poor rate performance. Furthermore, both polyanionic compounds and layered transition metal oxides are generally synthesized using traditional solid-state sintering methods, requiring high-temperature processing and consuming significant energy, posing a challenge to the low-cost application of sodium-ion batteries.

[0004] Prussian blue / white materials, due to their open-framework structure and large interstitial ion channels, are simple to synthesize, inexpensive, and easily mass-produced. When used as cathode materials for sodium-ion batteries, their theoretical specific capacity can reach 170 mAh / g, exhibiting high specific capacity and a sodium storage potential typically above 3V. Because the entire framework structure possesses spacious three-dimensional diffusion channels, rapid ion insertion / extraction is easily achieved, resulting in good rate performance. Therefore, they are among the most promising commercially viable cathode materials for sodium-ion batteries.

[0005] However, practical research has revealed the following shortcomings in Prussian blue-based materials: First, Prussian blue prepared by co-precipitation typically has numerous vacancies, defects, and water of crystallization, resulting in low sodium content and consequently, low specific capacity. Second, even when using slow synthesis methods to synthesize Prussian blue with relatively low defects, low moisture content, and high sodium content, the cycling performance remains poor. For example, patent CN107364874A argues that the performance of materials synthesized by co-precipitation is poor, and therefore proposes improvements by using co-precipitation combined with high temperature and high pressure or spray drying. While this significantly improves capacity, the cycling performance of the material is not reflected. Patent CN107364875A employs a co-precipitation method, controlling the pH of the mixed solution with a pH adjuster to suppress metal ionization during the reaction. The hydrolysis of Prussian blue yields a high specific capacity and low charge-discharge plateau polarization as a cathode material for sodium-ion batteries. Although the capacity is improved, the cycling performance is still not fully realized. Patent CN111377462A uses a single-source synthesis method, which improves the capacity and cycling performance, but it is still far from being commercially viable. The material prepared using this method retains only 81.7% of its capacity after 500 cycles at 1C (100mA / g). Furthermore, the single-source method produces highly toxic NaCN, which is detrimental to industrial development. Therefore, developing a Prussian blue-based cathode material that combines high capacity, long cycling performance, safety, and low cost is of great significance for the practical industrial application of Prussian blue-based sodium-ion batteries. Summary of the Invention

[0006] This invention aims to solve the problem that existing Prussian blue materials cannot simultaneously achieve both high capacity and good cycle performance, thus limiting the widespread application of Prussian blue sodium-ion batteries. It provides a method for preparing a Prussian blue sodium-ion battery cathode material that combines high capacity and long cycle performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a Prussian blue-based sodium-ion battery cathode material with both high capacity and long cycle performance includes the following steps:

[0009] Step 1: Prepare a sodium ferrocyanide solution with a concentration of 0.05–0.6 mol / L, denoted as solution A;

[0010] Step 2: Dissolve the transition metal ferrous salt, the doped metal salt, ascorbic acid and the complexing agent in deionized water to prepare a mixed solution of transition metal ferrous salt and doped metal salt with a concentration of 0.05-3 mol / L, denoted as solution B. The molar ratio of doped metal salt to transition metal ferrous salt is not greater than 1:1.

[0011] Step 3: Prepare an aqueous solution of the complexing agent, denoted as solution C;

[0012] Step 4: Add solutions A and B to solution C in equal molar amounts simultaneously and carry out a co-precipitation reaction under stirring. After the reaction is completed, perform an aging treatment to obtain a suspension. Separate the suspension and wash and dry the obtained precipitate in sequence to obtain a Prussian blue sodium-ion battery cathode material with both high capacity and long cycle performance.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] This invention proposes a method for preparing Prussian blue-based sodium-ion cathode materials using a combination of slow crystallization and ion doping via co-precipitation. This method yields low-cost, non-toxic, and harmless materials with a simple preparation process, short production cycle, and high capacity and long cycle performance. When applied to the cathode of sodium-ion batteries, the resulting batteries exhibit excellent electrochemical performance, high specific capacity, and superior cycle performance. The prepared sodium-ion batteries achieve an initial discharge specific capacity of over 140 mAh / g, even reaching 145 mAh / g, at a 1C rate (140 mA / g). The capacity retention after 800 charge-discharge cycles at a 1C rate is over 80%, and even reaches 80.5% after 1200 charge-discharge cycles at a 1C rate. These are the best reported results for Prussian blue-based materials to date, combining both capacity and cycle performance. Furthermore, this method can be directly translated into industrial production. Therefore, the Prussian blue-based cathode materials prepared by this invention have excellent application prospects. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a reaction device for a Prussian blue sodium-ion battery cathode material that combines high capacity and long cycle performance in an embodiment of the present invention.

[0016] Figure 2 This is a graph showing the cycling performance of a sodium-ion half-cell using the Prussian blue sodium-ion battery cathode material prepared in Comparative Example 1 of this invention at a current density of 140 mA / g.

[0017] Figure 3 This is a graph showing the capacity retention of a sodium-ion half-cell using the Prussian blue sodium-ion battery cathode material prepared in Comparative Example 1 of this invention at a current density of 140 mA / g.

[0018] Figure 4 This is a graph showing the cycling performance of a sodium-ion half-cell using the Prussian blue sodium-ion battery cathode material prepared in Example 1 of this invention at a current density of 140 mA / g.

[0019] Figure 5This is a capacity retention diagram of the sodium-ion half-cell of the Prussian blue sodium-ion battery cathode material prepared in Example 1 of the present invention at a current density of 140 mA / g.

[0020] Figure 6 This is a graph showing the cycling performance of a sodium-ion half-cell using the Prussian blue sodium-ion battery cathode material prepared in Example 2 of this invention at a current density of 140 mA / g.

[0021] Figure 7 This is a graph showing the capacity retention of a sodium-ion half-cell using the Prussian blue sodium-ion battery cathode material prepared in Example 2 of this invention at a current density of 140 mA / g. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Specific Implementation Method 1

[0024] A method for preparing a Prussian blue-based sodium-ion battery cathode material with both high capacity and long cycle performance includes the following steps:

[0025] Step 1: Prepare a sodium ferrocyanide solution with a concentration of 0.05–0.6 mol / L, denoted as solution A;

[0026] Step 2: Dissolve the transition metal ferrous salt, the doped metal salt, ascorbic acid and the complexing agent in deionized water to prepare a mixed solution of transition metal ferrous salt and doped metal salt with a concentration of 0.05-3 mol / L, denoted as solution B. The molar ratio of doped metal salt to transition metal ferrous salt is not greater than 1:1.

[0027] Step 3: Prepare an aqueous solution of the complexing agent, denoted as solution C;

[0028] Step 4: Add solutions A and B equimolarly to solution C simultaneously, and carry out a co-precipitation reaction under stirring. After the reaction is complete, perform an aging treatment to obtain a suspension. Separate the suspension, and wash and dry the resulting precipitate sequentially to obtain a Prussian blue sodium-ion battery cathode material with both high capacity and long cycle performance, with the molecular formula Na. x Fe 1-y M yFe(CN)6·zH2O, where M is a metal element, and M is one or more of Ni, Mn, Mg, Al, and Zn. Here, 1.5 < x ≤ 2, 0 < y < 0.5, and 0 < z ≤ 4; at a 1C rate, the specific capacity of the sodium button cell can reach over 140 mAh / g, and at the same time, the cycle performance can reach over 800 cycles (on the premise that the capacity retention rate ≥ 80%).

[0029] Further, the doped metal salt is one or more of sulfates, nitrates, and chlorides of Ni, Mn, Mg, Al, and Zn.

[0030] Further, the divalent transition metal iron salt is a combination of one or more of iron sulfate, iron nitrate, and iron chloride.

[0031] Further, the complexing agent is at least one of trisodium citrate, citric acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, and tetrasodium ethylenediaminetetraacetate.

[0032] Further, the molar concentration of the complexing agent in both the B solution and the C solution is 0.1 - 3 mol / L.

[0033] Further, the pH of both the B solution and the C solution is controlled at pH = 5 - 7.

[0034] Further, before the B solution is added dropwise to the C solution, it is necessary to stir for 0.5 - 3 h to allow the complexation reaction between metal ions and the complexing agent.

[0035] Further, before the A solution, B solution, and C solution start to react, it is necessary to introduce a protective gas to remove oxygen in the water. The protective gas is at least one of nitrogen and argon.

[0036] Further, in step four, the temperature of the C solution is controlled at 0 - 80°C. The C solution also needs to maintain the temperature and stop stirring after the A solution and B solution are added dropwise, and then continue to stir until the reaction is complete. The reaction time is 2 - 24 h, and the aging time is 1 - 24 h.

[0037] Further, the separation method of the suspension is centrifugation, suction filtration, or pressure filtration. The drying process is vacuum drying, the vacuum degree is 100 Pa or less, the temperature is 120 - 170°C, and the time is 8 - 20 hours.

[0038] The preparation method of the present invention realizes the control of the reaction rate through the complexing effect of the complexing agent, enables the crystals to grow slowly, and obtains a Prussian blue cathode material with low defects, low moisture, high sodium content, and high capacity; at the same time, a certain proportion of metal ions are doped, making the synthesized Prussian blue cathode material more stable in the charge-discharge process, and the obtained Prussian blue sodium-ion battery cathode material has both high capacity and long cycle performance.

[0039] The present invention discloses a Prussian blue sodium-ion battery cathode material with both high capacity and long cycle performance. The synthesis process is simple, safe and free of toxic byproducts, and can be easily scaled up for industrial production.

[0040] Comparative Example 1

[0041] This comparative example provides a method for preparing a high-capacity Prussian blue-based sodium-ion battery cathode material, comprising the following steps:

[0042] Step 1: Dissolve 0.1 mol of sodium ferrocyanide decahydrate in 577 ml of deoxygenated deionized water to obtain reaction solution A;

[0043] Step 2: Dissolve 0.1 mol of ferrous sulfate heptahydrate, 0.6 mol of trisodium citrate dihydrate, 0.04 mol of citric acid monohydrate, and 4 g of ascorbic acid (VC) in 488 ml of deionized water to obtain reaction solution B.

[0044] Step 3: Dissolve 1 mol of trisodium citrate dihydrate and 0.067 mol of citric acid monohydrate in 600 ml of deoxygenated deionized water to obtain solution C;

[0045] use Figure 1 The apparatus shown is used for a coprecipitation reaction. Container A contains reaction solution A, container B contains reaction solution B, and container C contains solution C. Reaction solutions A and B are simultaneously added dropwise to reaction solution C through a silicone tube at a flow rate of 1.5 mL / min using a peristaltic pump. The stirrer in container C is maintained at 500 rpm. N2 is introduced into containers A, B, and C at a flow rate of 60 mL / min during the reaction. Solution C is maintained at 40°C, and the stirring speed is 500 rpm / min. After the addition of reaction solutions A and B is complete, stirring continues for 2 hours, followed by aging for 12 hours to obtain a suspension.

[0046] The suspension was centrifuged at 4500 rpm for 5 min, and the resulting precipitate was centrifuged and washed three times with deoxygenated deionized water. It was then placed in a vacuum oven at 100 Pa and dried at 120 °C for 12 hours to obtain the Prussian blue sodium-ion battery cathode material.

[0047] The Prussian blue sodium-ion battery cathode material prepared in this comparative example was mixed uniformly in a weight ratio of active material: carbon black: PVDF = 8:1:1, coated onto a 20µm aluminum foil current collector, dried, punched, pressed, weighed, and then placed in a vacuum oven with a vacuum degree below 50 Pa and dried at 120℃ for 15 hours. Afterward, it was removed and transferred to a glove box. A sodium-ion half-cell was assembled using glass fiber as the separator, 1 mol / L NaPF6, solvent EC:DEC = 1:1, and 5% FEC as the electrolyte, and its cycle performance was tested. Figure 2 , Figure 3 As shown, the initial discharge capacity of the material at a current density of 140 mA / g is 149 mAh / g, and the specific capacity retention rate is 80% after 80 cycles.

[0048] Example 1

[0049] This embodiment provides a method for preparing a Prussian blue-based sodium-ion battery cathode material that combines high capacity and long cycle performance, including the following steps:

[0050] Step 1: Dissolve 0.1 mol of sodium ferrocyanide decahydrate in 577 ml of deoxygenated deionized water to obtain reaction solution A;

[0051] Step 2: Add 0.07 mol of ferrous sulfate heptahydrate, 0.01 mol of manganese sulfate monohydrate, and 0.01 mol of anhydrous magnesium sulfate.

[0052] 0.005 mol aluminum sulfate octahydrate, 0.005 mol nickel sulfate hexahydrate, 0.6 mol trisodium citrate dihydrate, 0.04 mol citric acid monohydrate, and 4 g ascorbic acid (VC) were dissolved in 488 ml of deionized water to obtain reaction solution B.

[0053] Step 3: Dissolve 1 mol of trisodium citrate dihydrate and 0.067 mol of citric acid monohydrate in 600 ml of deoxygenated deionized water to obtain solution C.

[0054] use Figure 1 The apparatus shown is used for a coprecipitation reaction. Container A contains reaction solution A, container B contains reaction solution B, and container C contains solution C. Reaction solutions A and B are simultaneously added dropwise to reaction solution C through a silicone tube at a flow rate of 1.5 mL / min using a peristaltic pump. The stirrer in container C is maintained at 500 rpm. N2 is introduced into containers A, B, and C at a flow rate of 60 mL / min during the reaction. Solution C is maintained at 30°C, and the stirring speed is 500 rpm / min. After the addition of reaction solutions A and B is complete, stirring continues for 2 hours, followed by aging for 12 hours to obtain a suspension.

[0055] The suspension was centrifuged at 4500 rpm for 5 min, and the resulting precipitate was centrifuged and washed three times with deoxygenated deionized water. It was then placed in a vacuum oven at 100 Pa and dried at 120 °C for 12 hours to obtain the Prussian blue sodium-ion battery cathode material.

[0056] The Prussian blue sodium-ion battery cathode material prepared in this example was mixed uniformly in a weight ratio of active material: carbon black: PVDF = 8:1:1, coated onto a 20µm aluminum foil current collector, dried, punched, pressed, weighed, and then placed in a vacuum oven with a vacuum degree below 50 Pa and dried at 120°C for 15 hours. Afterward, it was removed and transferred to a glove box. A sodium-ion half-cell was assembled using glass fiber as the separator, 1 mol / L NaPF6, solvent EC:DEC = 1:1, and 5% FEC as the electrolyte, and its cycle performance was tested. Figure 4 , Figure 5 As shown, the initial discharge capacity of the material at a current density of 140 mA / g is 143.9 mAh / g, and the specific capacity retention rate is 80% after 800 cycles.

[0057] Example 2

[0058] This embodiment provides a method for preparing a Prussian blue-based sodium-ion battery cathode material that combines high capacity and long cycle performance, including the following steps:

[0059] Step 1: Dissolve 0.1 mol of sodium ferrocyanide decahydrate in 577 ml of deoxygenated deionized water to obtain reaction solution A;

[0060] Step 2: Dissolve 0.085 mol of ferrous sulfate heptahydrate, 0.015 mol of manganese sulfate monohydrate, 0.6 mol of trisodium citrate dihydrate, 0.4 mol of citric acid monohydrate, and 4 g of ascorbic acid (VC) in 488 mol of deionized water to obtain reaction solution B.

[0061] Step 3: Dissolve 1 mol of trisodium citrate dihydrate and 0.067 mol of citric acid monohydrate in 600 ml of deoxygenated deionized water to obtain solution C.

[0062] use Figure 1The apparatus shown is used for a coprecipitation reaction. Container A contains reaction solution A, container B contains reaction solution B, and container C contains solution C. Reaction solutions A and B are simultaneously added dropwise to reaction solution C through a silicone tube at a flow rate of 1.5 mL / min using a peristaltic pump. The stirrer in container C is set to a speed of 500 rpm. N2 is introduced into containers A, B, and C at a flow rate of 60 mL / min during the reaction. Solution C is maintained at 25°C, and the stirring speed is 500 rpm / min. After the addition of reaction solutions A and B is complete, stirring continues for 2 hours, followed by aging for 12 hours to obtain a suspension.

[0063] The suspension was centrifuged at 4500 rpm for 5 min, and the resulting precipitate was centrifuged and washed three times with deoxygenated deionized water. It was then placed in a vacuum oven at 100 Pa and dried at 120 °C for 12 hours to obtain the Prussian blue sodium-ion battery cathode material.

[0064] The Prussian blue sodium-ion battery cathode material prepared in this example was uniformly mixed according to the weight ratio of active material: carbon black: PVDF = 8:1:1, coated onto a 20µm aluminum foil current collector, dried, punched, pressed, weighed, and then placed in a vacuum oven with a vacuum degree below 50 Pa and dried at 120℃ for 15 hours. Afterwards, it was removed and transferred to a glove box. A sodium-ion half-cell was assembled using glass fiber as the separator, 1 mol / L NaPF6, solvent EC:DEC = 1:1, and 5% FEC as the electrolyte, and its cycle performance was tested. Figure 6 , Figure 7 As shown, the initial discharge capacity of the material at a current density of 140 mA / g is 145 mAh / g, and the specific capacity retention rate after 1200 cycles is 80.5%.

[0065] Comparative Example 1 describes a method for preparing a high-capacity Prussian blue sodium-ion battery cathode material. Electrical performance testing shows an initial discharge specific capacity of 149 mAh / g, indicating a high sodium content. However, its cycle performance is poor, only around 80 cycles, making industrial-scale application difficult. Examples 1 and 2, synthesized through a combination of slow crystallization and ion doping, achieve initial discharge specific capacities of 143.9 mAh / g and 145 mAh / g, respectively, also exhibiting high capacity. However, their cycle performance is significantly improved compared to the comparative example, reaching 800 and 1200 cycles, respectively, with a capacity retention rate ≥80%. These represent the best reported results for Prussian blue materials to date, combining both capacity and cycle performance. Furthermore, this method can be directly converted into industrial production. Therefore, the Prussian blue cathode material of this invention has excellent application prospects.

[0066] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a Prussian blue-based sodium-ion battery cathode material with both high capacity and long cycle performance, characterized in that, The method steps are as follows: Step 1: Dissolve 0.1 mol of sodium ferrocyanide decahydrate in 577 ml of deoxygenated deionized water to obtain reaction solution A; Step 2: Dissolve 0.07 mol of ferrous sulfate heptahydrate, 0.01 mol of manganese sulfate monohydrate, 0.01 mol of anhydrous magnesium sulfate, 0.005 mol of aluminum sulfate octahydrate, 0.005 mol of nickel sulfate hexahydrate, 0.6 mol of trisodium citrate dihydrate, 0.04 mol of citric acid monohydrate, and 4 g of ascorbic acid in 488 ml of deoxygenated deionized water to obtain reaction solution B; Step 3: Dissolve 1 mol of trisodium citrate dihydrate and 0.067 mol of citric acid monohydrate in 600 ml of deionized water to obtain reaction solution C; Step 4: Using a peristaltic pump, add reaction solutions A and B simultaneously and in equal volumes to reaction solution C through a silicone tube at a flow rate of 1.5 mL / min. Maintain the stirrer speed in the container at 500 rpm. During the reaction, introduce N2 into the container containing the three reaction solutions at a flow rate of 60 mL / min. Keep solution C at 30°C and maintain the stirring speed at 500 rpm / min. After reaction solutions A and B have been added, continue stirring for 2 hours, then allow to stand for 12 hours to age, obtaining a suspension. Step 5: Centrifuge the suspension at 4500 rpm for 5 min, and repeat the centrifugation and washing of the obtained precipitate with deoxygenated deionized water three times. Then place it in a vacuum oven with a vacuum degree of 100 Pa and dry it at 120°C for 12 hours to obtain the Prussian blue sodium-ion battery cathode material.

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