Electrolyte with compact solvation structure and high-energy-density potassium ion battery
By adopting a compact solvated structure electrolyte composed of bisfluorosulfonimide potassium salt and ternary mixed solvent, the problem of volume change and structural collapse of potassium ion batteries during potassium storage is solved, and the stable circulation and high energy density of graphite negative electrode are achieved.
Patent Information
- Application Number
- CN202510053192.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-13
- Publication Date
- 2025-06-17
AI Technical Summary
Existing potassium ion batteries have problems of volume changes and structural collapse during potassium storage, resulting in rapid capacity decay and insufficient cycle stability.
A compact solvation structure of the electrolyte solution was used to combine vinyl carbonate (EC), diethyl carbonate (DEC) and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imine (Pyr13FSI) as the ternary mixed solvent to form an electrolyte solution with low salt concentration, low viscosity and high ionic conductivity.
The stable circulation and high energy density of graphite negative electrode are achieved, the rapid storage capacity of potassium ions is improved, the thermal stability and safety of the electrolyte are enhanced, and the energy density of 200Wh/kg is achieved.
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Figure CN120165028A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the fields of electrolyte technology and potassium-ion batteries, and particularly relates to an electrolyte with a compact solvation structure and a high-energy-density potassium-ion battery. Background Art
[0002] Graphite, as the most promising anode candidate material in potassium-ion batteries (PIBs), undergoes significant volume changes during potassium storage due to the lack of a suitable electrolyte, and even structural collapse occurs during long-term cycling, resulting in rapid capacity decay and insufficient cycling stability. To further develop the application of graphite anodes in potassium-ion batteries, new electrolytes suitable for fast and stable potassium storage need to be developed.
[0003] The formation of the solid electrolyte interface (SEI) and interfacial kinetics are closely related to the solvation structure in the electrolyte. Electrolyte engineering is generally considered an effective method for rationally designing the solvation structure of the electrolyte and the SEI composition. Some feasible and convenient strategies for adjusting the solvation structure by optimizing potassium salts, solvents, and additives. Although significant progress has been made in the strategies of high-concentration salt electrolytes and locally high-concentration salt electrolytes in this regard, the slow reaction kinetics caused by high viscosity or low conductivity limit the rapid storage of potassium ions.
[0004] Ionic liquid-based electrolytes are a promising type of potassium-ion battery electrolyte due to their high safety, stable electrochemical window, environmental friendliness, etc. At the charged electrode, the solvation structure of the ionic liquid electrolyte allows cations and anions to participate in the formation of a protective SEI layer at the interface, and this interfacial chemistry can be adjusted and controlled. Graphite anodes based on ionic liquid electrolytes have good cycling stability, but there is still a certain gap between their specific capacity and the theoretical capacity. The combination of using ether solvents and ionic liquids as mixed solvents can form a denser interfacial layer to achieve high-voltage stability in lithium-ion batteries. However, most of these applications are concentrated in lithium-ion batteries. Summary of the Invention
[0005] Aiming at the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide an electrolyte with a compact solvation structure and a high-energy-density potassium-ion battery. This electrolyte simultaneously has a low salt concentration (0.8 M), low viscosity, high ionic conductivity, and safety. In addition, the electrolyte helps to form a solid electrolyte interface layer mainly composed of KF and accelerate the reaction kinetics on the anode surface, and at the same time, high-voltage stability can be achieved.
[0006] The technical solution for achieving the object of the present invention is:
[0007] A potassium-ion battery with a compact solvation structure electrolyte and high energy density, characterized in that the potassium-ion battery includes a Prussian blue positive electrode, an electrolyte, and a flake graphite negative electrode; the electrolyte is a compact solvation structure electrolyte of potassium bis(fluorosulfonyl)imide (KFSI).
[0008] In the potassium-ion battery with a compact solvation structure electrolyte and high energy density, the size of the graphite is 3500 mesh.
[0009] In the potassium-ion battery with a compact solvation structure electrolyte and high energy density, the preparation of Prussian blue: Prussian blue (PB) is synthesized by the co-precipitation method. An aqueous solution (100 mL) containing potassium citrate (16 mmol) and ferrous sulfate heptahydrate (4 mmol) is added dropwise to an aqueous solution (100 mL) of potassium hexacyanoferrate (4 mmol) at room temperature, stirred for 12 h, aged for 12 h, centrifuged, and dried under vacuum at 100 °C for 12 h to obtain PB.
[0010] In the potassium-ion battery with a compact solvation structure electrolyte and high energy density, an ionic liquid ternary mixed solvent is used: ethylene carbonate (EC), diethyl carbonate (DEC), and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr 13 FSI) is used as the solvent, and the ratio of the three solvents in the mixed solvent (ILED) is 3:3:2.
[0011] In the potassium-ion battery with a compact solvation structure electrolyte and high energy density, the preparation of the electrolyte: In a glove box filled with argon, KFSI is added to ILED, and after stirring evenly, a potassium-ion battery electrolyte is obtained, with a concentration of 0.8 mol / L.
[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0013] When preparing the electrolyte of the present invention, an ionic liquid with high conductivity and wide electrochemical window is mixed with a conventional ester-based solvent. The addition of the ionic liquid can improve the ionic conductivity and potassium ion transference number of the electrolyte, and change the solvation structure of the electrolyte through bis(fluorosulfonyl)imide anion (FSI - ) to endow the electrolyte with fast desolvation ability.
[0014] The electrolyte composition of the present invention contains a ternary mixed solvent. Based on the redox sequence, the electrolyte is controlled to derivatize a chemical component mainly composed of KF on the surface of the graphite negative electrode, realizing the stable cycling of the graphite negative electrode.
[0015] Through the regulation of the electrolyte, the present invention realizes the optimization of the potassium storage behavior of graphite, changing the original C-KC 36-KC 24 -KC 16 -The potassium storage process of KC8 is converted to C-KC 36 -(KC 24 +KC 16 )-KC8. This is beneficial to realizing rapid potassium storage in graphite.
[0016] Through the electrolyte optimization strategy, the present invention improves the limitation of the voltage window of the conventional low-concentration ester-based electrolyte. The optimized electrolyte enables the PB positive electrode to stably cycle at 2.0 - 4.4V.
[0017] The present invention realizes long-cycle cycling and excellent rate performance of the PB||Graphite full cell, enabling the full cell to have an energy density of 200 Wh / kg. Brief Description of the Drawings
[0018] Figure 1 For designing the conductivity, ion transference number, and desolvation energy of the compact solvation structure electrolyte, pure ionic liquid-based electrolyte, and conventional ester-based electrolyte;
[0019] Figure 2 For the differential scanning calorimetry curves and combustion schematic diagrams of the designed SCE and comparative electrolytes;
[0020] Figure 3 For the Raman spectra of different electrolytes regarding EC and FSI-;
[0021] Figure 4 For the cycling performance of graphite in different electrolytes: a long-cycle performance, b charge-discharge curves, c long-cycle performance of graphite in the designed electrolyte at high current;
[0022] Figure 5 For the rate performance diagram of graphite in different electrolytes;
[0023] Figure 6 For the cycling performance of Prussian blue in the designed electrolyte and conventional ester-based electrolyte: a charge-discharge curves and capacity difference curves of Prussian blue in the designed electrolyte, b long-cycle performance of Prussian blue in the designed electrolyte and conventional ester-based electrolyte;
[0024] Figure 7 For the long-cycle performance and rate performance diagram of the Prussian blue||Graphite full cell in the designed electrolyte;
[0025] Figure 8 For the long-cycle performance of the Prussian blue||Graphite full cell at a current density of 200 mA / g; Detailed Description of the Invention
[0026] Example 1
[0027] A potassium ion battery with a compact solvation structure electrolyte and a high energy density, the potassium ion battery includes a Prussian blue positive electrode, an electrolyte, and a flake graphite negative electrode; the electrolyte is a low-concentration ester-ionic liquid electrolyte of potassium bis(fluorosulfonyl)imide (KFSI). The specific steps are as follows
[0028] Preparation method of Prussian blue positive electrode, including the following steps:
[0029] (1) Preparation of solution A: Dissolve 16 mmol of potassium citrate and 4 mmol of ferrous sulfate heptahydrate in 100 mL of aqueous solution. (2) Preparation of solution B: Dissolve 4 mmol of potassium hexacyanoferrate in 100 mL of aqueous solution. (3) Subsequently, under vigorous stirring, slowly add solution A to solution B, stir for 12 h and then age for 12 h, and wash 3 times with deionized water and anhydrous ethanol respectively. The collected solid is dried in a vacuum drying oven at 100 °C for 12 h.
[0030] Preparation of electrode sheet: The negative electrode is loaded on the aluminum foil at a ratio of 3500-mesh graphite: sodium alginate (SA) = 9:1; the positive electrode is loaded on the aluminum foil at a ratio of Prussian blue: conductive carbon (Sp.): polyvinylidene fluoride (PVDF) = 6:3:1.
[0031] Preparation of the compact solvation structure electrolyte, specifically:
[0032] In a glove box filled with an argon atmosphere (moisture less than 0.01 ppm, oxygen less than 0.01 ppm), take 1.5 g of ethylene carbonate (EC) and 1.5 ml of diethyl carbonate (DEC) and stir and mix them. Take 3 ml of the mixed ester-based solution and 1 ml of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr 13 FSI), add 3.2 mmol of potassium bis(fluorosulfonyl)imide, and stir evenly to obtain a 0.8 mol / L KFSI / Pyr 13 FSI + EC + DEC compact solvation structure electrolyte (CSE).
[0033] Preparation of the ionic liquid electrolyte, specifically:
[0034] In a glove box filled with an argon atmosphere (moisture less than 0.01 ppm, oxygen less than 0.01 ppm), take 1 ml of Pyr 13 FSI, add 0.8 mmol of potassium bis(fluorosulfonyl)imide, and stir evenly to obtain a 0.8 mol / L KFSI / Pyr 13 FSI electrolyte (ILE).
[0035] Preparation of the low-concentration ester-based electrolyte, specifically:
[0036] In a glove box filled with an argon atmosphere (moisture less than 0.01 ppm, oxygen less than 0.01 ppm), 0.5 g of EC and 0.5 ml of DEC were taken and stirred and mixed. 0.8 mmol of potassium bis(fluorosulfonyl)imide was added to the mixed solvent, and after stirring evenly, a 0.8 mol / L KFSI / EC+DEC low-concentration ester-based electrolyte (BEE) was obtained.
[0037] Using BEE, a graphite||K half-cell was assembled to study the potassium storage performance of graphite in the low-concentration ester-based electrolyte.
[0038] Using ILE, a graphite||K half-cell was assembled to study the potassium storage performance of graphite in the pure ionic liquid electrolyte.
[0039] Using CSE, a graphite||K half-cell was assembled to study the potassium storage performance of graphite in the ionic liquid-based compact solvation structure electrolyte.
[0040] Using CSE, a Prussian blue‖K half-cell was assembled to study the potassium storage performance of Prussian blue in this electrolyte.
[0041] Using CSE, a Prussian blue||graphite full-cell was assembled to study the potassium storage performance of the full-cell in this electrolyte.
[0042] The performance test results of the potassium-ion battery obtained from the above examples are as follows:
[0043] Figure 1 a is the conductivity and ion transference number of the designed compact solvation structure electrolyte, pure ionic liquid-based electrolyte, and conventional ester-based electrolyte. As Figure 1 shown in a, CSE has the highest ionic conductivity (10.17 mS / cm), higher than 4.86 mS / cm of BEE and 2.17 mS / cm of ILE. The t of different electrolytes K + can be calculated by the potentiostatic polarization method. According to the calculation results, the t of CSE K + is 0.53, higher than that of BEE (0.43) or ILE (0.32). This difference can be attributed to the existence of a solvation structure mainly composed of CIP and AGG in CSE and the electrolyte maintaining a low viscosity. At the same time, according to the Arrhenius equation and the linear fitting results ( Figure 1 b), the Ea values (related to the K + desolvation energy barrier) of BEE, CSE, and ILE are 62.28, 53.04, and 93.06 kJ / mol respectively. The high ionic conductivity, high t K + and low desolvation energy of the CSE electrolyte allow K +It migrates rapidly in the electrolyte and is more easily separated from the solvation structure, thus enabling fast potassium storage kinetics.
[0044] Figure 2 Differential scanning calorimetry curves and combustion schematic diagrams of the designed SCE and reference electrolytes. As Figure 2 shown in a, ILE has very good thermal stability, with only one endothermic peak with a value of -101.83 J / g appearing at 280 - 325 °C. Due to the introduction of IL, the thermal stability of the CSE electrolyte is correspondingly enhanced. Compared with the BEE electrolyte, its endothermic peak shifts to a higher temperature, and the endotherm decreases to -80.31 J / g. The endotherm caused by the potassium salt and ionic liquid is approximately -147.61 J / g. The combustion experiment shows (2b) that ILE cannot be ignited, BEE has a bright flame at the maximum flame, while the flame of CSE becomes smaller. The above experiments show that this electrolyte with a compact solvation structure not only promotes the enhanced kinetic process but also helps to improve the thermal stability of the electrolyte, thus ensuring the safe operation of the battery.
[0045] Figure 3 Raman spectra of different electrolytes with respect to EC and FSI - The peaks in the range of 680 - 740 cm -1 are fitted into five peaks centered at 713, 717, 722, 730, and 740 cm -1 corresponding to free EC, solvated EC, free FSI - and the solvation structures of CIP and AGG, respectively. It can be clearly seen that compared with BEE, the peak areas corresponding to free EC and free FSI - decrease in the CSE electrolyte, and the proportions of the solvation structures of the CIP and AGG configurations increase to 49% and 21% respectively. Compared with ILE, its free FSI - also decreases relatively.
[0046] Figure 4Figure a shows the cycling performance of graphite in the above three electrolytes and a conventional 0.8 M KPF6 / EC+DEC (KCE) electrolyte. It can be clearly seen that the capacity fades rapidly in KCE, and after 190 cycles, the specific capacity is only 125 mA / g. When KPF6 is replaced with KFSI, both the cycling stability and the capacity retention rate are significantly improved. After 300 cycles, the graphite negative electrode still has a specific capacity of 136 mA / g. When using ILE, due to its good film-forming performance, the capacity decay after 300 cycles can be ignored. However, due to its poor fluidity and slow reaction kinetics, the specific capacity is only 220 mAh / g. Graphite has good capacity retention and a high initial capacity in CSE. After 300 cycles, the reversible capacity is still 252 mAh / g, and the average Coulomb efficiency is 99.5%.
[0047] Figure 4 Figure b shows the charge-discharge curves of graphite in four electrolytes. The main potential for potassium storage in graphite is between 0.5 V and 0.01 V, and the capacity in this part determines the potassium storage capacity of the electrode material.
[0048] Figure 5 Figure shows the rate performance of graphite in different electrolytes. Due to the high viscosity of ILE, it has low conductivity and potassium ion transference number, resulting in the inability to retain a high capacity at a large current density. KCE has a relatively good capacity retention rate. BEE has a high capacity at a small current density, but when the current density increases to 500 mA / g, the capacity decreases instead, which is also due to the slow ion transport kinetics of the electrolyte. Due to the low viscosity and high ion transport kinetics of CSE, graphite shows a high capacity at different current densities. Even at a current density of 500 mA / g, the specific capacity is still 150 mAh / g.
[0049] Figure 6 Figure a shows the charge-discharge curve and capacity difference curve of Prussian blue in the designed electrolyte. Prussian blue undergoes two-step potassium storage reactions in the CSE electrolyte, corresponding to 3.91 V / 4.17 V and 3.27 V / 3.49 V respectively. At the same time, Prussian blue can also achieve a specific capacity of 100 mAh / g in the CSE electrolyte. The high specific capacity and reaction potential are beneficial to achieving a high energy density. Figure 6 Figure b shows the long cycling performance of Prussian blue in CSE and KCE. Compared with the low specific capacity, low Coulomb efficiency, and rapid capacity decay of the positive electrode material in the conventional electrolyte. Prussian blue still has a specific capacity of 95 mAh / g and a Coulomb efficiency of 98% after 100 cycles in CSE, which ensures the stable cycling of the battery.
[0050] Figure 7a shows the long-term cycling performance of the Prussian blue||graphite full cell. After the capacity decays in the initial several cycles, the specific capacity remains stable, and even after 1450 cycles, there is still a specific capacity of 67 mAh / g and a capacity retention rate of 88%. According to Figure 7 the charge-discharge curves shown in b, it can be found that as the cycling progresses, the nature of the charge-discharge curves remains unchanged, and only partial capacity decay occurs. This also indicates that during the charge-discharge process, the structures of graphite and Prussian blue are not damaged. In addition, due to the fast ion transport kinetics of CSE, the Prussian blue||CSE||graphite full cell provides reversible capacities of 71, 65, 59, 51, and 53 mAh / g at current densities of 50, 100, 200, 400, and 600 mA / g, respectively, and when the current density is restored to 50 mA / g, there is still a specific capacity of 68 mAh / g. The good rate performance enables this potassium storage system to have the potential to achieve good power density.
[0051] Figure 8 Figure 6 shows the long-term cycling performance of the Prussian blue||graphite full cell at a current density of 200 mA / g. At a relatively high current density, this potassium storage system still has a specific capacity of 50 mAh / g and a capacity retention rate of 84.7% after 300 cycles.
Claims
1. A potassium ion battery with a compact solvated electrolyte and high energy density, characterized in that: The potassium ion battery includes a graphite negative electrode, a Prussian blue positive electrode, and a compact solvated structure electrolyte.
2. A potassium ion battery with a compact solvated structure electrolyte and a high energy density according to claim 1, characterized in that: The potassium salt used in the electrolyte is potassium bis(fluorosulfonyl)imide (KFSI).
3. A potassium ion battery with a compact solvated structure electrolyte and a high energy density according to claim 1, characterized in that: The ionic liquid is 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide salt.
4. A potassium ion battery with a compact solvated structure electrolyte and a high energy density according to claim 1, characterized in that: Preparation of the electrolyte: In a glove box filled with argon, 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide, ethylene carbonate and diethyl carbonate were mixed in proportion and then bis(fluorosulfonyl)imide potassium salt was added.
5. A potassium ion battery with a compact solvated structure electrolyte and a high energy density according to claim 1, characterized in that: Electrolyte concentration: Weigh different masses of salt to control the molar concentration, and the electrolyte concentration is configured to be 0.8 mol / L.
6. A potassium ion battery with a compact solvated structure electrolyte and a high energy density according to claim 1, characterized in that: The size of the graphite negative electrode used was 3500 mesh, and sodium alginate was used as a binder.
7. A potassium ion battery with a compact solvated structure electrolyte and a high energy density according to claim 1, characterized in that: Prussian blue was used as the positive electrode material, and Prussian blue was prepared by co-precipitation method.