Water-in-salt Electrolytes Research Articles

Aqueous Supercapacitor with Wide-Temperature Operability and over 100,000 Cycles Enabled by Water-in-Salt Electrolyte.

Supercapacitors are crucial in renewable energy integration, satellite power systems, and rapid power delivery applications for mitigating voltage fluctuations and storing excess energy. Aqueous electrolytes offer a promising solution for low-cost and safe supercapacitors. However, they still face limitations in cycle life and wide-temperature range performance. Here, we present a symmetric supercapacitor utilizing activated carbon electrodes and a "water-in-salt" electrolyte (WiSE) based on lithium perchlorate. The WiSE electrolyte exhibits an expanded electrochemical stability window, endowing the aqueous supercapacitor with remarkable stability and long cycle life of over 100,000 cycles at 500 mA g-1 with more than 91% capacity retention. Moreover, the supercapacitor demonstrates good rate capability and wide temperature operability ranging from -20 to 80 °C. The use of high concentrations of salt in the aqueous electrolyte contributes not only to the enhancement of supercapacitor performance and cycle life but also to the temperature stability range, enabling all-season operability.

Concurrently Improving both Mechanical and Electrochemical Performances of Quasi-Solid-State Electrical Double-Layer Capacitors by a Rational Design of Gel Polymer Electrolytes.

Aqueous poly(vinyl alcohol) (PVA) gel electrolyte-based quasi-solid-state electrical double-layer capacitors (QSEDLCs) have been extensively investigated in the past ten years, but challenges remain to fabricate the PVA gel electrolyte possessing both superior mechanical and outstanding electrochemical performances. Herein, we develop a strategy to address this issue by a rational design of PVA gel electrolytes, based on a combination of the freeze-thaw (FT) method and sodium perchlorate (NaClO4)-based water-in-salt (WIS) electrolyte. Our study demonstrates that either the FT method or the NaClO4-based WIS electrolyte can improve both the mechanical performance of the PVA gel electrolyte by increasing the crystallization of PVA chains and the electrochemical performance of the PVA gel electrolyte-based QSEDLC by different mechanisms. In comparison with the conventional solvent evaporation method, this work provides an effective strategy to concurrently improve both the mechanical and electrochemical performances of aqueous QSEDLCs.

Wide electrochemical stability window of NaClO4 water-in-salt electrolyte elevates the supercapacitive performance of poly(3,4-ethylenedioxythiophene)

Water-in-salt electrolytes (WiSEs) have emerged as the primary preference in the domain of aqueous-based supercapacitors, thanks to their wide electrochemical stability window (ESW > 1.23 V). Here, we have chemically synthesized a unique lettuce coral-like structure of tosylate doped-poly(3,4-ethylenedioxythiophene) (PEDOT-tos) and tested it for supercapacitor application in a 17 molal (m) NaClO4 WiSE, achieving an ESW of 1.9 V. The energy and power densities (Ed and Pd) of our PEDOT-tos supercapacitor are as high as 14 Wh kg-1 and 7210 W kg-1, respectively, with over 80 % capacitance retention after 10,000 continuous Galvanostatic charge-discharge cycles. The NaClO4 WiSE increases the Ed and Pd of PEDOT by several folds compared to traditional H2SO4 electrolyte. This work encourages the exploration of a suitable combination of a PEDOT-based composite material and WiSE for high-performance supercapacitors.

Are NaTFSI and NaFSI Salt-Based Water-in-Salt Electrolytes Structurally Similar or Different?

Water-in-salt electrolytes (WiSEs) are a promising class of electrolytes due to their wide electrochemical stability window and nonflammability. In this study, we explore the structural organization of sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and sodium bis(fluorosulfonyl)imide (NaFSI) salt-based aqueous electrolytes, covering dilute to highly concentrated regions, by employing an all-atom molecular dynamics simulation. For the NaTFSI-based electrolyte, we observe that Na+ ions are mostly surrounded by water molecules at all the salt concentrations due to the very strong interaction between them. While TFSI anions weakly coordinate with Na+ ions and other TFSI anions, they also mostly prefer to be surrounded by water molecules. These interactions were found to have moderate dependence on the concentration of the NaTFSI salt. For the NaFSI-based electrolyte, while the Na+-water interaction is stronger at lower salt concentrations, the number of nearest neighbor FSI anions is found to be more than that of water at higher concentrations (≥20 m). This is because the increase in the salt concentration leads to expulsion of water molecules from the solvation shell of Na+ ions and enhances the interaction between Na+ ions and oxygen atoms of FSI. At the highest salt concentration (solubility limit), the bulk-like water structure is completely disrupted and dominated by an anionic network in the FSI-based electrolyte. In contrast, water-water hydrogen bonding network is still present even in the highly concentrated TFSI-based electrolyte. The simulated X-ray scattering pattern displays a low-q peak, revealing the presence of an intermediate range ordering due to alternating anion-rich and water/Na+-rich regions in both the electrolytes. However, the characteristic length scale corresponding to the low-q peak decreases with increasing the salt content in both the electrolytes.

Waste PET bottles derived carbon black as electrode material for supercapacitor application

This study explores the conversion of polyethylene terephthalate (PET) waste into carbon black for its use in supercapacitors, offering a sustainable solution to waste management and energy storage needs. PET bottles were pyrolysed in an inert environment to produce carbon black. This plastic waste derived carbon was then characterised and used for electrode fabrication to explore its potential in supercapacitor applications. The supercapacitive properties of these electrodes were evaluated using cyclic voltammetry and charge–discharge techniques in various “Water-in-salt” electrolytes (WIS). WIS are the electrolytes in which the concentration of water is less than the concentration of salts by weight and volume. electrolytes. Sodium acetate (CH3COONa) exhibited the highest potential window and specific capacitance among the tested electrolytes. The derived carbon black demonstrated promising electrochemical performance, with a specific capacitance of 233 F/g and an energy density of 186.6 Wh/kg. These findings underscore the potential of carbon black derived from waste PET bottles as an effective material for supercapacitors, contributing to sustainable energy storage solutions and waste reduction.

Electrochemical and Cycle Analysis of Water-in-Salt K-Acetate Electrolyte Zn-Ion Batteries Under Commercially-Relevant Conditions

Water-in-salt electrolyte (WiSE) promises high-voltage battery technology with low fire risk. Here we assess potassium acetate (KAc) WiSE for Zn ion batteries under commercially relevant conditions. Rotating disc electrode analysis of WiSE degradation and Zn plating/deplating suggest a solid electrolyte interphase (SEI) layer dominates. Butler-Volmer kinetics and Koutecky-Levich mass-transfer are of secondary importance. Measurements of chemical potential reveal that bulk solvation of H2O (in KAc WiSE or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) WiSE) is an insignificant process compared to SEI blocking. Zinc cycling in KAc WiSE with practical rates (∼0.3 to 8.0 mA cm−2) and areal capacities (>20 mAh cm−2) shows dendrites are less prominent than in KOH, but the SEI layer suppresses the electrochemical reaction too much for commercial feasibility. Dilution or convection of the WiSE alleviates the SEI blocking effects. Cu substrate shows good Zn adhesion, but Ti, Sn, and Ni show poor adhesion. Cathodes made with Chevrel (Mo6S8) reversibly intercalate Zn2+ to form a novel battery technology when paired with Zn foil, but yield <1.0 V cell voltage. Cathodes made with zinc-containing Prussian blue analogues (ZnHCF or ZnMnHCF) yield a voltage near 2.0 V but don't cycle in the present KAc WiSE formulation. Future research directions for KAc WiSE are proposed, focussing on SEI dynamics and Prussian blue compatibility.

A systematic study of solvation structure of asymmetric lithium salts in water

Aqueous electrolytes are promising in large-scale energy storage applications due to intrinsic low toxicity, non-flammability, high ion conductivity, and low cost. However, pure water’s narrow electrochemical stability window (ESW) limits the energy density of aqueous rechargeable batteries. Water-in-salt electrolytes (WiSE) proposal has expanded the ESW to over 3 V by changing electrolyte solvation structure. The limited solubility and WIS electrolyte crystallization have been persistent concerns for imide-based lithium salts. Asymmetric lithium salts compensate for the above flaws. However, studying the solvation structure of asymmetric salt aqueous electrolytes is rare. Here, we applied small-angle x-ray scattering (SAXS) and Raman spectroscope to reveal the solvation structure of imide-based asymmetric lithium salts. The SAXS spectra show the blue shifts of the lower q peak with decreased intensity as the increasing of concentration, indicating a decrease in the average distance between solvated anions. Significantly, an exponential decrease in the d-spacing as a function of concentration was observed. In addition, we also applied the Raman spectroscopy technique to study the evolutions of solvent-separated ion pairs (SSIPs), contacted ion pairs (CIPs), and aggregate ions (AGGs) in the solvation structure of asymmetric salt solutions.

Improved Capacitive Performance of High‐Voltage Electric Double‐Layer Capacitors by Electrolyte Optimization Using Hierarchically Porous Carbon Electrodes

Advancement of the voltage window with stringent safety concerns is an imperative strategy to enhance the energy densities and output power delivery of electrical double‐layer capacitors (EDLCs). Solid‐state, water‐in‐salt (WIS), and ionic liquid‐based electrolytes are attractive and ideal choices for high‐voltage EDLCs due to their superior voltage window, electrochemical performance, and predominant safety aspects. Mindful of this, the current report demonstrates the electrochemical performance of new nanoporous carbon electrodes derived from waste dry leaves of Swietenia macrophylla with a high specific surface area (SSA) (1834 m2 g−1) in polymer–gel, WIS, and ionic liquids‐based electrolytes. Symmetric EDLC devices are fabricated using polymer gel solid‐state (PVA–Na2SO4), ionic liquids (EMIMBF4), and WIS (21 m LiTFSI) electrolytes with the electrochemical stability windows of (ESW) 2, 2.5, and 2 V, respectively. The assembled devices with Na2SO4/PVA, EMIMBF4, and 21 m LiTFSI (WIS) electrolytes‐based devices exhibit high energy densities of 40, 31, and 25 Wh kg−1 at 0.5 A g−1 and good output power delivery of 5, 6.23, and 3 kW kg−1 at 5 A g−1 with better cyclability features. Self‐discharging studies and systematic evaluation of high‐voltage EDLCs offer a sustainable method to develop high‐performance aqueous and diverse electrolyte‐based supercapacitors.

Sodium Triflate Water-in-Salt Electrolytes in Advanced Battery Applications: A First-Principles-Based Molecular Dynamics Study.

Offering a compelling combination of safety and cost-effectiveness, water-in-salt (WiS) electrolytes have emerged as promising frontiers in energy storage technology. Still, there is a strong demand for research and development efforts to make these electrolytes ripe for commercialization. Here, we present a first-principles-based molecular dynamics (MD) study addressing in detail the properties of a sodium triflate WiS electrolyte for Na-ion batteries. We have developed a workflow based on a machine learning (ML) potential derived from ab initio MD simulations. As ML potentials are typically restricted to the interpolation of the data points of the training set and have hardly any predictive properties, we subsequently optimize a classical force field based on physics principles to ensure broad applicability and high performance. Performing and analyzing detailed MD simulations, we identify several very promising properties of the sodium triflate as a WiS electrolyte but also indicate some potential stability challenges associated with its use as a battery electrolyte.

High‐Performance Co‐Solvent Engineering Electrolyte for Obtaining a High‐Voltage and Low‐Cost K+ Battery Operating from −25 to 50 °C

AbstractHigh‐safety potassium‐ion batteries (HPIBs) are highly intriguing owing to their green energy, low cost, high voltage, noncombustible, and simple assembly. However, most high‐voltage HPIBs use water‐in‐salt electrolytes (WISE), which lead to several problems, such as a high viscosity, which significantly reduces the performance and increases the cost of HPIBs, thus impeding their development. Unfortunately, studies regarding HPIB electrolytes remain limited, further limiting the development of HPIBs. Herein, a co‐solvent engineering electrolyte (4.0 m KOTf in a mixture of propylene carbonate (PC) and H2O with a volume ratio of 5.0:1.0) featuring low‐cost (1/4 of WISE) and high‐performance (45.43 mS cm−1) characteristics is proposed, which not only achieves a wide electrochemical stability window by reducing the activity of H2O, but also adjusts the solvation structure of K+. Consequently, the HPIBs assembled via co‐solvent engineering electrolyte demonstrated a high energy density of 88.05 Wh kg−1, and sufficiently operated at rates of 0.50–10.0 A g−1 over a wide temperature range (−25–50 °C). This study provides a promising means for developing high‐voltage HPIBs.

Wettability, imbibition and interdiffusion of lithium-based water-in-salt electrolytes in nanoporous carbon in relation to energy storage: A neutron radiography study

Superconcentrated lithium salt electrolytes, or lithium-based Water-in-Salt (WiS) electrolytes emerge as alternative electrolytes in supercapacitors and advanced batteries, such as the Li–O2 ones, especially when combined with a mesoporous carbon with very high surface area. In this work, we analyze the wettability, imbibition, and diffusivity of very concentrated lithium salts in a bimodal mesoporous carbon with pores of 5 nm and 25 nm in diameter. For the first time a neutron radiography technique is used to determine the imbibition and interdiffusion of lithium salts in mesoporous carbon. We found that a 20 m LiTFSI aqueous solution wets the surface of graphite and mesoporous carbon better than water. As a consequence, this WiS electrolyte is embedded rather fast in the mesoporous carbon by the action of capillary forces, exhibiting an intrinsic permeability K = (1.16 ± 0.03).10−18 m2. Finally, by resorting to the different cross-section of the 6Li and 7Li isotopes for the neutron capture, we could analyze the diffusion of LiCl in D2O confined in the mesoporous carbon. The interdiffusion coefficient of the confined LiCl is 5.0 10−7 cm2 s−1, corresponding to a tortuosity coefficient τ = 1.32. This moderate confinement effect results from the strong ion association of the LiCl that precludes the electrostatic interactions of Li+ ions with the negative charge on the pore walls. In summary, the combined properties of the lithium-based WiS electrolytes and the mesoporous carbon allow us to glimpse their use in supercapacitors and Li–O2 batteries.

Water‐in‐Polymer Salt Electrolyte for Long‐Life Rechargeable Aqueous Zinc‐Lignin Battery

Zinc metal batteries (ZnBs) are poised as the next‐generation energy storage solution, complementing lithium‐ion batteries, thanks to their cost‐effectiveness and safety advantages. These benefits originate from the abundance of zinc and its compatibility with non‐flammable aqueous electrolytes. However, the inherent instability of zinc in aqueous environments, manifested through hydrogen evolution reactions (HER) and dendritic growth, has hindered commercialization due to poor cycling stability. Enter potassium polyacrylate (PAAK)‐based water‐in‐polymer salt electrolyte (WiPSE), a novel variant of water‐in‐salt electrolytes (WiSE), designed to mitigate side reactions associated with water redox processes, thereby enhancing the cyclic stability of ZnBs. In this study, WiPSE was employed in ZnBs featuring lignin and carbon composites as cathode materials. Our research highlights the crucial function of acrylate groups from WiPSE in stabilizing the ionic flux on the surface of the Zn electrode. This stabilization promotes the parallel deposition of Zn along the (002) plane, resulting in a significant reduction in dendritic growth. Notably, our sustainable Zn‐lignin battery showcases remarkable cyclic stability, retaining 80% of its initial capacity after 8000 cycles at a high current rate (1 A g−1) and maintaining over 75% capacity retention up to 2000 cycles at a low current rate (0.2 A g−1). This study showcases the practical application of WiPSE for the development of low‐cost, dendrite‐free, and scalable ZnBs.

Optimization of the OPLS force field for “water-in-salt” electrolytes

Water-in-salt (WIS) electrolytes have attracted considerable interest in rechargeable batteries and supercapacitors, owing to their wide electrochemical stability window, non-flammability, and safety. A comprehensive understanding of the microstructure in WIS electrolytes provides a crucial theoretical foundation for their further development. In this work, the optimized potentials for liquid simulations (OPLS) force field parameters have been revisited by scaling atom charges to consider their ionic polarization. The ionic conductivity of different WIS electrolytes, calculated using the optimized force field, aligns well with the experimental observations. The polarization effects of ions exhibit augmentation as their size enlarges, which is caused by the enlargement of ion size inducing the asymmetry in the charge distribution. Additionally, the microstructures indicate that nitrates and perchlorates offer superior ionic conductivity, benefiting from a less ionic coordination number and lower viscosity. These insights could be of assistance in selecting force fields and comprehending the microstructure of WIS electrolytes.

Two-electron conversion nitroxide radicals-based electrode synergistically enhancing charge storage in water-in-salt electrolyte

Water-in-salt electrolytes (WISEs) are attractive in aqueous batteries due to their non-flammability, environmental friendliness, and wide electrochemical stability window. Stable nitroxide radicals with fast electron transfer rate and good cycling stability are promising electrode materials applied for WISEs, while their limited conductivity and high solubility in electrolytes are still challenges. Here, porous carbon with high specific area is used as conductive substrate for the deposition of 4-amino-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl), and MXene nanosheets are employed as their conductive binder to construct freestanding electrode with “hyacinth bean-like” structure. Nitroxide radicals undergo a two-step two-electron reversible redox reaction and MXene exhibits pseudocapacitive ion intercalation, leading to synergistically enhanced discharge capacity in WISE (19.8 m LiCl). The incorporated redox active nitroxide radicals in MXene/porous carbon-TEMPO electrode boost the surface pseudocapacity and the rationally designed three-dimensional structure further facilitates the ions diffusion and electrons transfer, endowing the composite electrode with fast charge storage kinetic. This work provides a promising potential for the design and fabrication of high-performance aqueous batteries.

A Water-in-Salt Electrolyte for Room-Temperature Fluoride-Ion Batteries Based on a Hydrophobic-Hydrophilic Salt.

Realizing room-temperature, efficient, and reversible fluoride-ion redox is critical to commercializing the fluoride-ion battery, a promising post-lithium-ion battery technology. However, this is challenging due to the absence of usable electrolytes, which usually suffer from insufficient ionic conductivity and poor (electro)chemical stability. Herein we report a water-in-salt (WIS) electrolyte based on the tetramethylammonium fluoride salt, an organic salt consisting of hydrophobic cations and hydrophilic anions. The new WIS electrolyte exhibits an electrochemical stability window of 2.47 V (2.08-4.55 V vs Li+/Li) with a room-temperature ionic conductivity of 30.6 mS/cm and a fluoride-ion transference number of 0.479, enabling reversible (de)fluoridation redox of lead and copper fluoride electrodes. The relationship between the salt property, the solvation structure, and the ionic transport behavior is jointly revealed by computational simulations and spectroscopic analysis.

Vehicular Motions Dominate the Ion Transport in Concentrated LiTFSI Aqueous Solutions?

Water-in-salt electrolytes (WiSEs) show great promise for applications in grid-scale energy storage. The design of high-performance WiSEs requires a comprehensive understanding of their microstructures and ion transport properties. In the present work, based on the CL&Pol force field, we have developed a polarizable force field (PFF) tailored for high-concentration LiTFSI aqueous solutions, which accurately reproduces the structural and dynamical properties. Unlike the literature, we do not observe the presence of bulk-like water in LiTFSI solutions exceeding 19 mol/kg. Furthermore, we find that the vast majority of Li(H20)n+ are short-lived, and thus, the structural motion rather than the vehicular motion is the main mode of ion transport. Our results have significant implications for understanding the ion dynamics in WiSEs. Additionally, further in-depth experimental analyses are imperative.

Designing hollow mesoporous carbon sphere for high-rate supercapacitor in water-in-salt electrolyte

The expansion of the operational voltage in supercapacitors (SCs) through the utilization of water-in-salt electrolytes (WISEs) has garnered considerable attention for achieving elevated energy density. However, the poor rate performance of assembled SCs persists due to the heightened viscosity of WISEs (e.g., 17.0 mol kg−1 NaClO4), so designing the porous structure of electrode materials to improve the rate performance of SC in WISEs has become a research focus. In this study, we present a straightforward approach to fabricate hierarchical porous carbon spheres, designing to expedite ion infilling and transport within WISE-based SCs. The hollow porous carbon is synthesized via one-step pyrolysis process, wherein the decomposition of inner colloid particles yields gases, while the outer resorcinol–formaldehyde resin carbonizes to form a spherical shell. In the WISE of 17.0 mol kg−1 NaClO4, the resulting symmetric SCs exhibit an operational voltage of 2.6 V and significantly improved rate capability with a capacitance retention of 47.7 % at 100 A g−1. Notably, the energy density can reach 31.0 Wh kg−1 at a power density of 2.4 kW kg−1. Even under high power density conditions of 120.0 kW kg−1, the energy density of 14.7 Wh kg−1 can remain. Additionally, the SC device manifests an impressive capacitance retention of 99.1 % after 20,000 cycles, showcasing exceptional cyclic stability. This research introduces a novel synthesis strategy for hierarchical porous carbon materials, enabling the development of high-rate SCs with both elevated energy density and power density.

Upgrading Cycling Stability and Capability of Hybrid Na‐CO2 Batteries via Tailoring Reaction Environment for Efficient Conversion CO2 to HCOOH

AbstractRechargeable Na‐CO2 batteries are considered to be an effective way to address the energy crisis and greenhouse effect due to their dual functions of CO2 fixation/utilization and energy storage. However, the insolubility and irreversibility of solid discharge products lead to poor discharge capacity and poor cycle performance. Herein, a novel strategy is proposed to enhance the electrochemical performance of hybrid Na‐CO2 batteries, using water‐in‐salt electrolyte (WiSE) to establish an optimal reaction environment, regulate the CO2 reduction pathway, and ultimately convert the discharge product of the battery from Na2CO3 to formic acid (HCOOH). This strategy effectively resolves the issue of poor reversibility, allowing the battery to exhibit excellent cycle performance (over 1200 cycles at 30 °C), especially under low‐temperature conditions (2534 cycles at −20 °C). Furthermore, density functional theory (DFT) calculations and experiments indicate that by adjusting the relative concentration of H/O atoms at the electrolyte/catalyst interface, the CO2 reduction pathway in the battery can be regulated, thus effectively enhancing CO2 capture capability and consequently achieving an ultra‐high discharge specific capacity of 148.1 mAh cm−2. This work effectively promotes the practical application of hybrid Na‐CO2 batteries and shall provide a guidance for converting CO2 into products with high‐value‐added chemicals.

Thermodynamic, Kinetic, and Transport Contributions to Hydrogen Evolution Activity and Electrolyte-Stability Windows for Water-in-Salt Electrolytes.

Concentrated water-in-salt electrolytes (WiSEs) are used in aqueous batteries and to control electrochemical reactions for fuel production. The hydrogen evolution reaction is a parasitic reaction at the negative electrode that limits cell voltage in WiSE batteries and leads to self-discharge, and affects selectivity for electrosynthesis. Mitigating and modulating these processes is hampered by a limited fundamental understanding of HER kinetics in WiSEs. Here, we quantitatively assess how thermodynamics, kinetics, and interface layers control the apparent HER activities in 20 m LiTFSI. When the LiTFSI concentration is increased from 1 to 20 m, an increase in proton activity causes a positive shift in the HER equilibrium potential of 71 mV. The exchange current density, io, derived from the HER branch for 20 m LiTFSI in 98% purity (0.56 ± 0.05 μA/cmPt2), however, is 8 times lower than for 20 m LiTFSI in 99.95% (4.7 ± 0.2 μA/cmPt2) and 32 times lower than for 1 m LiTFSI in 98% purity (18 ± 1 μA/cmPt2), demonstrating that the WiSE's impurities and concentration are both central in significantly suppressing HER kinetics. The ability and applicability of the reported methods are extended by examining additional WiSEs formulations made of acetates and nitrates.

Polyimide-Based Aqueous Potassium Energy Storage Systems Using Concentrated WiSE Electrolyte.

Aqueous batteries are considered as promising alternative power sources due to their eco-friendly, cost-effective, and nonflammable attributes. Employing organic-based electrode materials offers further advantages toward building greener and sustainable systems, owing to their tunability and environmental friendliness. In order to enhance the energy and power densities, superconcentrated aqueous electrolytes, such as water-in-salt electrolytes (WiSE), have renewed the interest in aqueous batteries due to their enhanced stability and much wider electrochemical stability window (>1.23 V) compared with the traditional aqueous electrolytes. Here, we present a perylene diimide-based electrode material (PDI-Urea) as an appealing anode for aqueous potassium energy storage systems and investigate their electrochemical performance in three WiSE electrolytes, namely, 30 M potassium acetate, 40 M potassium formate and 30 M potassium bis(fluorosulfonyl)imide (KFSI). To explore the potential of PDI-Urea for potassium-based electrochemical energy systems, we fabricated full cell devices such as aqueous potassium dual-ion battery (APDIB) and aqueous K-ion battery (AKIB) and studied their electrochemical properties with 30 M KFSI electrolyte. The full cell K-ion battery, using a PBA cathode, exhibited excellent electrochemical performance with good rate capability and impressive capacity retention of 91% upon 1000 cycles. Further, the reaction mechanism of the electrodes is systematically analyzed using ex-situ studies.