A quasi-aggregation solvent design based on ionic liquid electrolyte realizes stable high-temperature potassium ion battery
By employing a quasi-aggregated solvation design of ionic liquid electrolytes, combined with phosphate ester TMP and Prussian blue cathode, the problems of thermal runaway and interfacial instability in potassium-ion batteries at high temperatures were solved, achieving high stability and high energy density performance in potassium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING FORESTRY UNIV
- Filing Date
- 2026-04-14
- Publication Date
- 2026-06-19
Smart Images
Figure CN122246228A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the fields of organic electrolyte technology and potassium-ion batteries, specifically relating to a quasi-aggregated solvation design based on ionic liquid electrolytes to achieve a stable high-temperature potassium-ion battery. Background Technology
[0002] Since the commercialization of lithium-ion batteries (LIBs), this technology has dominated energy storage solutions for consumer electronics, electric vehicles, and grid-scale energy storage systems. To meet the growing demand for energy storage, developing next-generation batteries with higher energy density, inherent safety, and lower manufacturing costs is crucial. Potassium-ion batteries (PIBs), which use high-voltage Prussian blue analogues (PBAs) as the positive electrode and graphite (Gr) as the negative electrode, leverage the abundant and inexpensive resources of potassium and its superior redox potential, promising to achieve competitive energy densities and thus becoming a highly promising alternative to LIBs.
[0003] Traditional carbonate electrolytes pose safety risks, such as a low thermal decomposition threshold (<60℃), high flammability, and a narrow electrochemical window (<4.3V vs. K). + The instability of the electrolyte (PBA) and its interface limits the practical application of PIBs. These defects also lead to severe degradation mechanisms, such as electrolyte decomposition at high voltages producing gaseous byproducts and high-resistivity interface layers; continuous side reactions at the electrodes accelerating capacity decay during long-cycle cycling; and a significantly increased risk of thermal runaway under high-temperature operation (especially in tropical climates or electric vehicle battery packs). Therefore, to fully realize the potential of PIBs in extreme application scenarios, it is urgent to develop safe electrolytes that combine high voltage, high temperature, and PBA interface compatibility.
[0004] Ionic liquids (ILs) possess high salt solubility, a wide electrochemical window, and excellent thermal stability, which can reduce the risk of thermal runaway in polyimide blocks (PIBs). N-propyl-N-methylpyrrolidone-onium bis(fluorosulfonyl)imide (Pyr) was employed. 13 When ionic liquid electrolytes (FSIs) are used as electrolytes, their high decomposition temperature of 300°C, wide electrochemical window of >4.5V, and ability to form anion-derived solid electrolyte interfaces (SEIs) enhance safety and cycling performance under extreme conditions. However, ionic liquid electrolytes (ILEs) suffer from slow kinetics and interfacial instability due to low ionic conductivity and excessive decomposition of organic cations. While introducing solvents such as carbonates can improve kinetics, it sacrifices safety and exacerbates interfacial problems. Introducing flame-retardant phosphate esters (such as TMP) is a better strategy, as it inhibits combustion while maintaining oxidative stability and synergistically reduces viscosity. Studies have shown that ionic liquid / phosphate ester systems can synergistically improve safety, such as TEP / [Pyr 13Systems such as [TFSI] have passed the UL-94V0 flame retardancy test for lithium metal batteries. Nevertheless, achieving solvation regulation of ILEs under extreme operating conditions to balance safety, capacity, and stability still faces fundamental challenges. Summary of the Invention
[0005] To address the aforementioned problems in existing technologies, the technical problem to be solved by this invention is to provide a quasi-aggregated solvation design based on ionic liquid electrolytes to achieve a stable high-temperature potassium-ion battery. The quasi-aggregated design regulates solvation through TMP, while simultaneously improving conductivity and interfacial compatibility, constructing an inorganic fluorine-rich electrode / electrolyte interface and reducing impedance, and using Prussian blue cathode to achieve highly stable cycling and activate Fe-C sites for potassium storage, enabling the full battery to operate stably under extreme conditions such as high temperature.
[0006] The technical solution to achieve the purpose of this invention is:
[0007] The aforementioned quasi-aggregated solvation design based on ionic liquid electrolyte to achieve a stable high-temperature potassium-ion battery is characterized in that the potassium-ion battery comprises a Prussian blue (PB) positive electrode, an electrolyte, and an untreated commercial flake graphite (Gr) negative electrode; the electrolyte is composed of potassium bisfluorosulfonylimide (KFSI) and N-propyl-N-methylpyrrolidone onium bisfluorosulfonylimide (Pyr 13 An ionic liquid electrolyte composed of FSI and trimethyl phosphate (TMP), wherein Pyr 13 The volume ratio of FSI to TMP is 9:1, and the total salt concentration is 1.0 M.
[0008] The aforementioned quasi-aggregated solvation design based on ionic liquid electrolyte to achieve a stable high-temperature potassium-ion battery is characterized by the use of KFSI at a specific molar concentration; and two solvents with different compositions: a pure ionic liquid solvent Pyr. 13 FSI and ionic liquid mixed solvent Pyr 13 FSI+TMP (volume ratio 9:1).
[0009] The aforementioned quasi-aggregated solvation design based on ionic liquid electrolyte to achieve a stable high-temperature potassium-ion battery is characterized by the following electrolyte preparation: KFSI at specific molar concentrations is dissolved in pure ionic liquid solvent Pyr in an argon-filled glove box (O2 < 0.01 ppm, H2O < 0.01 ppm). 13 FSI and ionic liquid mixed solvent Pyr 13 Different electrolytes were prepared in FSI+TMP (volume ratio 9:1) to obtain the target electrolyte. The salt concentration of all electrolytes was fixed at 1.0M.
[0010] The aforementioned quasi-aggregated solvation design based on ionic liquid electrolyte to achieve a stable high-temperature potassium-ion battery is characterized by the preparation of Prussian blue: Prussian blue (PB) is synthesized via a 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) containing 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.
[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0012] A quasi-aggregated solvation structure design principle for ionic liquid electrolytes is proposed. Trimethyl phosphate (TMP) with low dosage, low viscosity, strong solvation and flame retardant properties is introduced to stabilize the organic cations in the outer solvent sheath and locally promote the entry of anions into the inner solvent sheath, thereby improving the ionic conductivity and interfacial compatibility of the electrolyte.
[0013] By changing the formation mechanism of the cathode electrolyte interface from organic cation-dominated oxidation to fluorine-rich anion-dominated oxidation, a thin and dense interface layer rich in inorganic KF was constructed, which effectively suppressed interfacial side reactions and protected the structural integrity of the cathode material, thus improving the interface stability of the battery under extreme conditions such as high temperature.
[0014] Thanks to the synergistic effect between the stability brought by the quasi-aggregate design and the kinetic improvement caused by the increase in operating temperature, the PB cathode exhibits excellent cycle stability and rate performance at both room temperature and high temperature. In particular, after 500 cycles at 40℃, the capacity can be increased to 80.7mAh / g, and the ion transport impedance and charge transfer impedance are reduced.
[0015] This design activates intrinsically kineticly sluggish low-spin Fe-C sites in Prussian blue materials, enabling them to participate in deep potassium storage reactions under high voltage, contributing to capacity and energy density.
[0016] The PB||PILE||Gr full cell achieved an energy density of up to 269.6 Wh / kg and a power density of 609.9 W / kg at 60 °C, expanding the practical application of quasi-aggregated electrolytes under extreme conditions. Attached Figure Description
[0017] Figure 1 Electrochemical window, ionic conductivity and desolvation energy for quasi-aggregate solvated electrolyte (PILE) and pure ionic liquid electrolyte (ILE);
[0018] Figure 2 Fourier transform infrared spectra of PILE and TMP;
[0019] Figure 3 Raman spectra of PILE, ILE, and pure ionic liquid (IL), calculated coordination number f, and average coordination number n. FSI- and the distribution of solvation structures;
[0020] Figure 4 The following are performance cycle diagrams of Prussian blue cathode in different electrolytes at room temperature: a) Long-term cycle performance at high current, b) Charge-discharge curves of Prussian blue in PILE at different current densities, c) Rate performance of Prussian blue in PILE.
[0021] Figure 5 The following are performance cycle diagrams of Prussian blue in PILE at high temperatures: a) Comparison of capacity retention at different temperatures, b) Charge-discharge curves at 40℃, c) Long-cycle performance at 60℃.
[0022] Figure 6 The graph shows the long-cycle performance of the graphite anode in different electrolytes.
[0023] Figure 7 The cumulative capacity difference curves of the PB||PILE||Gr full cell at 20℃ and 60℃;
[0024] Figure 8 Figures showing the long-cycle performance of the PB||PILE||Gr full cell at different temperatures and current densities. Detailed Implementation
[0025] The present invention will be further described below with reference to specific embodiments.
[0026] Example 1
[0027] A quasi-aggregated solvation design based on an ionic liquid electrolyte enables a stable high-temperature potassium-ion battery. The potassium-ion battery includes a Prussian blue cathode, an electrolyte, and a commercially available flake graphite anode. The electrolyte is composed of potassium bisfluorosulfonylimide (KFSI) and N-propyl-N-methylpyrrolidone onium bisfluorosulfonylimide (Pyr 13 An ionic liquid electrolyte composed of FSI and trimethyl phosphate (TMP). The specific steps are as follows:
[0028] The preparation method of Prussian blue cathode includes the following steps:
[0029] (1) Preparation of solution A: Dissolve 16 mmol potassium citrate and 4 mmol ferrous sulfate heptahydrate in 100 mL of aqueous solution. (2) Preparation of solution B: Dissolve 4 mmol potassium hexacyanoferrate in 100 mL of aqueous solution. (3) Subsequently, under vigorous stirring, solution A was slowly added dropwise to solution B. After stirring for 12 hours, the mixture was aged for 12 hours and washed three times each with deionized water and anhydrous ethanol. The collected solid was then dried in a vacuum drying oven at 100 degrees Celsius for 12 hours.
[0030] Electrode preparation: The negative electrode is loaded on copper foil with 3500 mesh graphite: sodium alginate (SA) in a ratio of 9:1; the positive electrode is loaded on aluminum foil with Prussian blue: conductive carbon (Sp.): polyvinylidene fluoride (PVDF) in a ratio of 6:3:1.
[0031] The preparation of the quasi-aggregated solvated electrolyte is as follows:
[0032] In a glove box filled with argon atmosphere (moisture content less than 0.01 ppm, oxygen content less than 0.01 ppm), take 0.9 ml of N-methyl-N-propylpyrrolidone-onium bis(fluorosulfonyl)imide (Pyr 13 Add 1 mmol of potassium bis(fluorosulfonyl)imide (KFSI) to FSI, then add 0.1 mL of TMP, and stir well to obtain 1 mol / L KFSI / Pyr 13 FSI+TMP Quasi-aggregated solvated electrolyte (PILE).
[0033] The preparation of ionic liquid electrolytes is as follows:
[0034] In a glove box filled with argon atmosphere (moisture content less than 0.01 ppm, oxygen content less than 0.01 ppm), take 1 ml of Pyr 13 FSI was mixed with 1 mmol of potassium difluorosulfonamide and stirred until homogeneous to obtain 1 mol / L KFSI / Pyr. 13 FSI electrolyte (ILE).
[0035] Using PILE, graphite ||K half-cells were assembled to study the potassium storage performance of graphite in a quasi-aggregated solvated electrolyte.
[0036] Using an ILE, a graphite ||K half-cell was assembled to study the potassium storage performance of graphite in a pure ionic liquid electrolyte.
[0037] Using PILE, Prussian blue ||K half-cells were assembled to study the potassium storage performance of Prussian blue in a quasi-aggregated solvated electrolyte.
[0038] Using an ionic liquid electrolyte (ILE), a Prussian blue ||K half-cell was assembled to study the potassium storage performance of Prussian blue in the ionic liquid electrolyte.
[0039] Using PILE, Prussian blue||graphite full cells were assembled, and the potassium storage performance of the full cells in quasi-aggregated solvated electrolytes was studied.
[0040] Using an ionic liquid electrolyte (ILE), a Prussian blue || graphite full cell was assembled, and the potassium storage performance of the full cell in the ionic liquid electrolyte was studied.
[0041] The performance test results of the potassium-ion battery obtained from the above embodiments are as follows:
[0042] Figure 1 Electrochemical window, ionic conductivity, and desolvation energy for quasi-aggregate solvated electrolyte (PILE) and ionic liquid electrolyte (ILE). Figure 1 a indicates that pure ionic liquids remain stable above 5V, demonstrating that Pyr 13 FSI exhibits a wide electrochemical window; the response current of the ionic liquid electrolyte begins to increase at 4.3 V, while the current of the quasi-aggregated solvated electrolyte remains stable up to 5.0 V. This indicates that the quasi-aggregated solvated electrolyte possesses a wide electrochemical window, and this high oxidation stability helps the electrolyte to match the high-voltage cathode, achieving stable long-cycle performance. Figure 1 As shown in b, the quasi-aggregated solvated electrolyte exhibits an ionic conductivity of 5.4 mS / cm, compared to 3.9 mS / cm for the ionic liquid electrolyte. Simultaneously, its desolvation energy barrier is 76.7 kJ / mol, while that of the ionic liquid electrolyte is 90.5 kJ / mol. The PILE electrolyte enables rapid potassium ion transport within the electrolyte bulk phase and at the interface, and facilitates easier separation from the solvated structure, thus achieving rapid potassium storage kinetics.
[0043] Figure 2 Fourier transform infrared spectroscopy revealed characteristic peaks of POC in both TMP and PILE electrolytes. The POC peak in pure TMP solvent was mainly concentrated at 10¹³ cm⁻¹. -1 In phosphate ester-mediated ionic liquid electrolytes, this peak shifts to 1263 cm⁻¹. -1 This POC peak shift indicates that TMP has transitioned from a free state to a bound state, confirming a strong interaction between the introduced TMP and the electrolyte components in the outer solvated sheath.
[0044] Figure 3 Raman spectroscopy revealed the internal solvation structure of the electrolyte. Figure 3 As shown in a, in the range of 1200-1240cm -1 The Raman spectrum shifts to higher wavenumbers within the range, indicating that TMP enhances K... + With FSI - The solvation effect. Peak fitting shows it is located at 1215 cm⁻¹. -1 and 1220cm -1 The peaks correspond to FSI respectively - -Pyr 13 + and FSI - -K +Calculations show that K of ILE + Coordination FSI - The value of f is 0.351, n FSI- The value was 1.73; after introducing TMP, the f-value of PILE significantly increased to 0.417, n FSI- The increase to 2.05 indicates that TMP promotes more FSI. - It enters the inner solvated sheath layer. Figure 3 b, 680-760cm -1 Raman spectroscopy within the range revealed detailed solvation structures, with 722 cm⁻¹... -1 736cm -1 and 754cm -1 The peaks at each location are attributed to FSI. - -Pyr 13 + Contact ion pairs (CIPs) and aggregates (AGGs). The introduction of TMP enables FSI. - -Pyr 13 + The decrease in content, coupled with the increase in the content of contact ion pairs and aggregates, indicates that TMP exhibits quasi-aggregative behavior in the outer solvated sheath.
[0045] Figure 4 The cycling performance of the PB cathode in different electrolytes at room temperature was tested. Figure 4 As shown in Figure a, at a high current density of 200 mA / g, the PB in the PILE exhibits high specific capacity retention, maintaining a high specific capacity of 85.0 mAh / g even after 1100 cycles, with an average coulombic efficiency of 99.20%. In contrast, the PB cathode in the ILE shows severe capacity decay; after 500 cycles at 200 mA / g, the specific capacity of the PB cathode in the ILE is only 57.7 mAh / g, corresponding to a capacity retention of 70.60% and an average coulombic efficiency of 81.86%.
[0046] Figure 4 As shown in b and 4c, the PB cathode assembled with PILE electrolyte achieved a high reversible specific capacity of 95 mAh / g at a current density of 50 mA / g. When the current density increased to 100, 200, 400, and 600 mA / g, the capacity gradually decreased to 84, 77, 67, and 62 mAh / g, respectively. When the current density returned to the initial 50 mA / g, the reversible specific capacity recovered to 96 mAh / g, indicating that the PB cathode exhibits excellent rate performance in a quasi-crowded solvated electrolyte.
[0047] Figure 5 This study tested the cycling performance of the PB cathode in PILE electrolyte at high temperatures. Figure 5This study compared the capacity retention of the PB cathode in PILE electrolyte at 20℃ and 40℃ with increasing current density, relative to the value at 50 mA / g. At 40℃, the capacity retention of the PB cathode at current densities of 100, 200, 400, and 600 mA / g was 95.8%, 91.5%, 84.4%, and 81.7%, respectively, significantly higher than the corresponding values of 86.3%, 78.8%, 68.2%, and 63.5% at 20℃. Figure 5 As shown in b, the constant current charge-discharge curves of the PB cathode in PILE electrolyte with different number of cycles under the conditions of 40℃ and 50mA / g indicate that when the temperature rises to 40℃, the PILE electrolyte enables the PB cathode to achieve stable high-capacity cycling. Figure 5 As shown in Figure c, the PB cathode retains a high specific capacity of 136 mAh / g after 200 cycles in PILE electrolyte at 60 °C and 50 mA / g, with an average coulombic efficiency of 97.30%. Even at a high current density of 500 mA / g and an operating temperature of 60 °C, the PB cathode retains a high specific capacity of 69 mAh / g after 200 cycles in PILE electrolyte, corresponding to a capacity retention of 95.50% and an average coulombic efficiency of 99.54%. These stable and efficient potassium storage properties under extreme conditions strongly demonstrate the synergistic effect between the strong stability provided by the quasi-aggregated phosphate ester-mediated ionic liquid electrolyte and the significant kinetic improvement brought about by increased operating temperature.
[0048] Figure 6 The potassium storage performance of commercially available flake graphite as an anode was evaluated. After 30 cycles at a current density of 50 mA / g in PILE electrolyte, the graphite anode exhibited a stable high specific capacity of 291.4 mAh / g, significantly higher than the 206.8 mAh / g in ionic liquid electrolyte. This improved potassium storage specific capacity in PILE electrolyte further demonstrates the high compatibility between the designed phosphate ester-mediated ionic liquid electrolyte and the graphite anode.
[0049] Figure 7The evolution of potassium storage behavior under different operating temperatures was evaluated using cumulative dQ / dV curves with increasing cycle counts. At 20°C, the dQ / dV curve of the first cycle exhibited a pair of strong redox peaks at 3.01 / 3.38V, corresponding to the potassium storage reaction at high-spin Fe-N sites. With continuous cycling, the potential difference between the redox peaks gradually decreased, indicating that the reversibility of the potassium storage reaction continuously improved under the protection of the PILE electrolyte. No obvious redox peaks appeared in the high voltage range, indicating that the potassium storage utilization rate of low-spin Fe-C sites was extremely low under these conditions. At 60°C, in addition to the redox peaks related to potassium storage at high-spin Fe-N sites at low voltages of 3.00 / 3.17V, two additional pairs of redox peaks were clearly observed at high voltages of 3.76 / 4.00V and 3.23 / 3.41V, with slight potential shifts during cycling. This corresponds to the efficient potassium storage at low-spin Fe-C sites, contributing to high capacity and high energy density.
[0050] Figure 8 The graph shows the long-term cycling performance of the PB||PILE||Gr full cell at different temperatures and current densities. After 100 cycles at 50 mA / g and 20°C, the PB||PILE||Gr full cell exhibits a stable specific capacity of 72.8 mAh / g, corresponding to a high capacity retention of 90.3% and an average coulombic efficiency of 99.0%. At the same temperature and a high current density of 200 mA / g, the stable specific capacity of the PB||PILE||Gr full cell after 100 cycles significantly decreases to 45.7 mAh / g, corresponding to a capacity retention of 77.3% and an average coulombic efficiency of 98.8%. This decrease in potassium storage performance is mainly attributed to the exacerbated polarization problem caused by the increased operating current density. When the operating temperature rises to 60°C, the PB||PILE||Gr full cell maintains a high potassium storage specific capacity and excellent cycling stability even at a high current density of 200 mA / g. The full cell exhibited a stable specific capacity of 87.1 mAh / g after 100 cycles at 200 mA / g and 60°C, with a capacity retention of up to 90.2% and an average coulombic efficiency of 98.4%.
Claims
1. A quasi-aggregated solvation design based on ionic liquid electrolyte to achieve a stable high-temperature potassium-ion battery, characterized in that, The potassium-ion battery consists of a Prussian blue (PB) cathode, an electrolyte, and an untreated commercial flake graphite (Gr) anode; the electrolyte is composed of potassium bis(fluorosulfonyl)imide (KFSI) and N-propyl-N-methylpyrrolidone-onium bis(fluorosulfonyl)imide (Pyr 13 The electrolyte is an ionic liquid composed of Pyr13FSI and trimethyl phosphate (TMP), wherein the volume ratio of Pyr13FSI to TMP is 9:1 and the total salt concentration is 1.0M.
2. The stable high-temperature potassium-ion battery based on the quasi-aggregated solvation design of the ionic liquid electrolyte according to claim 1, characterized in that, Using KFSI at a specific molar concentration; two solvents with different compositions: the ionic liquid solvent Pyr was selected. 13 FSI and mixed solvent Pyr 13 FSI+TMP (volume ratio 9:1).
3. The stable high-temperature potassium-ion battery based on the quasi-crowded solvation design of the ionic liquid electrolyte according to claim 1, characterized in that, Electrolyte preparation: In an argon-filled glove box (O2 < 0.01 ppm, H2O < 0.01 ppm), KFSI at specific molar concentrations was dissolved in Pyr... 13 FSI and mixed solvent Pyr 13 Different electrolytes were prepared in FSI+TMP (volume ratio 9:1) to obtain the target electrolyte. The salt concentration of all electrolytes was fixed at 1.0M.