Nonaqueous Potassium-ion Batteries Research Articles

Prussian Blue Analogues Cathodes for Nonaqueous Potassium‐Ion Batteries: Past, Present, and Future

AbstractRecently, potassium‐ion batteries (PIBs) have emerged as a new energy storage system, offering a complementary solution to lithium‐ion batteries due to their cost‐effectiveness and significantly high theoretical energy density, making them suitable for large‐scale grid energy storage applications. The critical challenge PIBs face is the scarcity of appropriate high‐capacity cathode materials. Among the various contenders, Prussian blue analogs (PBAs) stand out. The appeal of PBAs arises from their simple synthesis, economic viability, and a stable, open framework conducive to the insertion/extraction of large‐size K+. This review aims to provide an overview of current research progress on PBAs as cathode materials in nonaqueous PIBs. A comprehensive examination of the crystal structure and electrochemical reaction mechanisms of PBAs is undertaken, with a focus on prevalent optimization strategies in PIBs. Subsequent sections delve into designing and developing potassium‐based full cells architectures incorporating PBAs. The discourse culminates in a discussion on the requirements for transitioning PBAs PIBs from a laboratory setting to commercial production, aiming to chart a course for the development of advanced PIBs.

Enhancing the Electrochemical Properties of the Layered-Type K0.4V2O5 Cathode Materials through Cationic Metal Substitution in K Sites

Layered-type K0.4V2O5 have been widely investigated as cathode materials for potassium-ion batteries (PIBs) due to their high specific capacity. [1,2] However, sluggish intercalation kinetics of K ions into their crystal structure generally result in drastic capacity fading and poor power capability. [3] Here, we present significantly enhanced K-ion storage performances of the layered-type K0.4V2O5 cathode enabled by substitution of cationic metal for K-site. Density functional theory calculations data indicates that cationic metal prefer to occupy the K-site than transition metal layer. During charge and discharge process, inactive cationic metal acts as a pillar, thereby suppressing the irreversible phase transition and structural deterioration. In addition, cationic metal creates vacancies at k site, improving K-ion diffusion kinetics. Compared to K0.4V2O5, the modified cathode demonstrated the better cycling stability and power capability. A insitu X-ray diffraction and X-ray absorption near edge structure was used to verify role of cationic metal in improving electrochemical performance of the K0.4V2O5 cathode. Deng, X. Niu, G. Ma, Z. Yang, L. Zeng, Y. Zhu, L. Guo. Layered Potassium Vanadate K0.5V2O5 as a Cathode Material for Nonaqueous Potassium Ion Batteries, Adv. Func. Mater. 28 (2018) 1800670.Yang, Z. Liu, L. Deng, L. Tan, X. Niu, M. M. S. Sanad, L. Zeng, Y. Zhu. A Non-Topotactic Redox Reaction enabled K2V3O8 as a High Voltage Cathode Material for Potassium-Ion Batteries, Chem. Commun. 55 (2019) 14988–14991.Q. Fu, A. Sarapulove, L. Zhu, G. Melinte, A. Missyul, E. Welter, X. Luo, M. Knapp, H. Ehrenberg, S. Dsoke. In Operando Study of Orthorhombic V2O5 as Positive Electrode Materials for K-Ion Batteries, J. Energy Chem. 62 (2021) 627–636.

Fundamental investigations on the ionic transport and thermodynamic properties of non-aqueous potassium-ion electrolytes

Non-aqueous potassium-ion batteries (KIBs) represent a promising complementary technology to lithium-ion batteries due to the availability and low cost of potassium. Moreover, the lower charge density of K+ compared to Li+ favours the ion-transport properties in liquid electrolyte solutions, thus, making KIBs potentially capable of improved rate capability and low-temperature performance. However, a comprehensive study of the ionic transport and thermodynamic properties of non-aqueous K-ion electrolyte solutions is not available. Here we report the full characterisation of the ionic transport and thermodynamic properties of a model non-aqueous K-ion electrolyte solution system comprising potassium bis(fluorosulfonyl)imide (KFSI) salt and 1,2-dimethoxyethane (DME) solvent and compare it with its Li-ion equivalent (i.e., LiFSI:DME), over the concentration range 0.25–2 molal. Using tailored K metal electrodes, we demonstrate that KFSI:DME electrolyte solutions show higher salt diffusion coefficients and cation transference numbers than LiFSI:DME solutions. Finally, via Doyle-Fuller-Newman (DFN) simulations, we investigate the K-ion and Li-ion storage properties for K∣∣graphite and Li∣∣graphite cells.

Fast-Charging Nonaqueous Potassium-Ion Batteries Enabled by Rational Construction of Oxygen-Rich Porous Nanofiber Anodes.

Practical applications of carbon anodes in high-power potassium-ion batteries (PIBs) were hampered by their limited rate properties, due to the sluggish K+ transport kinetics in the bulk. Constructing convenient ion/electron transfer channels in the electrode is of great importance to realize fast charge/discharge rates. Here, cross-linked porous carbon nanofibers (inner porous carbon nanotubes and outer soft carbon layer) modified with oxygen-containing functional groups were well designed as anodes to realize robust de-/potassiation kinetics. The novel anode delivered excellent rate capabilities (107 mAh g-1 at 20 A g-1 and 78 mAh g-1 at 40 A g-1) and superior cycling stability (76% capacity retention after 14,000 cycles at 2 A g-1). In situ XRD measurement, in situ Raman spectra, and galvanostatic intermittent titration verified its surface-dominated potassium storage behavior with fast de-/potassiation kinetics, excellent reversibility, and rapid ion/electron transport. Moreover, theoretical investigation revealed that the carboxyl groups in the carbon offered additional capacitive adsorption sites for K+, thus significantly enhancing the reversible capacity. Surprisingly, a full cell using the anode and perylene-3,4,9,10-tetracarboxylic dianhydride cathode achieved an outstanding power density of 23,750 W kg-1 and superior fast charge/slow discharge performance.

Understanding the Effect of Interplanar Space and Preintercalated Cations of Vanadate Cathode Materials on Potassium-Ion Battery Performance.

Nonaqueous potassium-ion batteries (KIBs) have been regarded as a promising alternative energy system to lithium-ion batteries, due to the abundance of the K resource and unique electrochemical properties. However, exploring suitable KIB cathode materials remains a great challenge, owing to the much larger size of the K ion than that of the Li ion. Here, a series of layered vanadates have been developed as cathodes for KIBs to elucidate the key factors that determine the electrochemical performance of KIBs, including the interlayer distance between adjacent (100) planes (d100) and preintercalated cations. Compared to NH4V3O8 nanowires with a d100 of 7.80 Å, (NH4)0.5V2O5 nanowires with a wider d100 of 9.52 Å show a faster K+ diffusion and much higher reversible capacity. The preintercalation of potassium ions into V-O slabs is also crucial to the stability of the structure of vanadates, which leads to better electrochemical cycling stability in K0.5V2O5 than that in (NH4)0.5V2O5 and NH4V3O8 nanowires. These findings reveal the great potential of the vanadate cathode in future KIBs and provide a new direction to rationally design a stable layered intercalation compound for practical KIBs.

Origin of anomalous high-rate Na-ion electrochemistry in layered bismuth telluride anodes

Summary van der Waals layered metal chalcogenide Bi2Te3 has shown exceptional capacity and rate capability in alkali-ion batteries but the underlying reaction mechanism with Li+, Na+, and K+ remains undiscovered. It is unexpected that Na+ electrochemistry outperforms Li+ and K+ at high current densities. Here, in situ transmission electron microscopy is used to uncover nanoscale transformations during lithiation, sodiation, and potassiation, which follows two-step conversion and alloying reactions with Li+ and Na+, and three-step intercalation-conversion-alloying reactions with K+. Counterintuitively, sodiation exhibits the highest reaction kinetics, and its origin can be elucidated by first-principles and finite-element simulations in two aspects. The lower interfacial strain accommodation energy between Bi2Te3 and its Na-conversion products allows more facile sodiation phase transformation than Li- and K-ion reactions. The higher electrochemo-mechanical stress concentration at the concave-shaped sodiation reaction front facilitates continued Na-ion diffusion and reaction propagation. These fundamental insights are essential for fast-charging alkali-ion batteries.

Crystal, interfacial and morphological control of electrode materials for nonaqueous potassium-ion batteries

In the existing battery system, non-aqueous potassium-ion batteries (PIBs) have attracted considerable interest and exhibited a broad application prospect in the prospective large-scale energy storage due to the abundant and cost-effective resources, fast K-ion conductivity in electrolyte and low standard reduction potential of K+/K. After tremendous efforts for ideal electrode materials and full-cells assembly technologies, the comprehensive performance of PIBs including K-ion diffusion kinetics, K storage capacity and reversibility, has made great progress. This review features our current understanding and the development status of PIBs from the perspective of crystal, interfacial and morphological control on electrode materials for nonaqueous PIBs, including i) the correlation between the lattice structure of electrode material (interlayer spacing, lattice parameter, etc.) and the K+ storage/transfer, ii) K+ transfer/reaction kinetics in two-phase interface and the relationship between phase interface and structural stability and iii) the development status and law of the relationship between morphology and volume strain or K+/electron transfer rate. The summary and perspectives aim to address the crucial issues and explore high-performance PIBs, which may provide a guidance for other energy storage devices. Future research hotspots and other key issues that need to be addressed are outlined.

Hierarchical two-atom-layered WSe2/C ultrathin crumpled nanosheets assemblies: Engineering the interlayer spacing boosts potassium-ion storage

Nonaqueous potassium-ion batteries (KIBs) represent a potential low-cost and source-abundant alternative to lithium-ion batteries (LIBs). The critical challenge of the electrode materials for KIBs mainly lies in the structural degradation and slow kinetics caused by the large-size K ions. Herein, we report the engineering of interlayer spacing of two-atom-layered WSe2/C ultrathin crumpled nanosheet assemblies (denoted as WSNC) to achieve optimal electrochemical performance as an anode for KIBs via an oleylamine-assisted solvothermal strategy. Individual crumpled nanosheets with two atomic layer thickness are hierarchically assembled to curb the agglomeration, enhance the cycling stability and the resistance to mechanical stress. Notably, the expanded interlayer spacing (from 0.651 to 0.755 nm) of WSe2 can provide more active sites, reduce its volume expansion and accelerate ion diffusion during the intercalation/deintercalation of K ions, thus increasing the specific capacity and simultaneously boosting the structural stability and reaction kinetics. Besides, the nitrogen-doped carbon coating can further improve the electronic conductivity of WSe2 and strengthen the structural stability. Further in-situ characterizations and density functional theory (DFT) computations indicate that the WSNC shows reverisible intercalation/deintercalation and conversion mechanism, as well as a low diffusion barriers and slight volume change during the intercalation of K ions. As expected, WSNC delivers a high capacity of 384 mAh g−1 over 200 cycles at 0.1 A g−1, superior rate capability, and excellent cycling stability up to 500 cycles at high rates.

The Rise of Prussian Blue Analogs: Challenges and Opportunities for High‐Performance Cathode Materials in Potassium‐Ion Batteries

Potassium‐ion batteries (PIBs) are emerging as one of the potential alternatives to lithium‐ion batteries for next‐generation rechargeable battery systems. Nevertheless, the lack of suitable cathode materials with high capacity hinders their practical applications. Recently, Prussian blue analogs (PBAs) cathode materials stand out as promising candidates for PIBs. Their unique crystal structure with open 3D frameworks and large interstitial voids favors fast K+ intercalation without causing drastic volume expansion, which is the prerequisite for high‐rate and long‐term battery operation. Herein, a fundamental review on the development and advance of PBAs cathode materials is presented for PIBs with in‐depth elucidation of their crystal structures, chemical compositions, and electrochemical performances. Particularly, the unique and prominent advantages of PBAs in both aqueous and nonaqueous PIBs are highlighted. In addition, to bridge the current gap from the laboratory to future commercialization, potential improvement strategies are proposed to overcome the present drawbacks. Finally, perspectives and new insights are provided for further exploration and research in PBAs for better PIBs.

Quantifying the cost effectiveness of non-aqueous potassium-ion batteries

Non-aqueous K-ion batteries currently attract intensive interest as a promising candidate for electrochemical energy storage with potentially lower cost than Li-ion batteries. In this paper, a total battery cost and annual battery cost analysis of K-ion batteries is presented, with a comparison to a lithium-ion reference battery. Our analysis shows that all models of K-ion batteries considered will have a higher total cost than the reference Li-ion battery, unless the coulombic efficiency of K-ion batteries could be made superior to existing Li-ion batteries. Therefore, in our opinion K-ion battery research should focus on increasing battery lifetime. This is probably true for all beyond-Li-ion cell chemistries.

Superior potassium-ion storage properties by engineering pseudocapacitive sulfur/nitrogen-containing species within three-dimensional flower-like hard carbon architectures

Rechargeable non-aqueous potassium-ion batteries have been regarded as one of ideal candidates for large-scale electric energy storage applications. However, the achievement of high reversible capacity and rate capability is still a great challenge. In this work, an extraordinary S-/N-/O- multielement-doped three-dimensional (3D) flower-like hard carbon architecture is firstly proposed as promising anode material for low-cost potassium-ion batteries. The 3D flower-like architecture not only provides abundant exposed surface-active sites but acts as highly conductive interconnected network for electron transport. More encouragingly, the introduction of highly reactive -N-Cx-S- species has been revealed to show highly reversible pseudo-capacitive charge storage behavior, inherently enlarging the slope reversible capacity to the highest value of 423 mAh g−1 at low current density of 0.05 A g−1. As well, benefitted from the structural and compositional advantages, an unprecedented rate capability (251 mAh g−1 at 1.0 A g−1) and stable cycling stability (362 mAh g−1 after 300 cycles at 0.5 A g−1) has been obtained, which outperforms most of carbonaceous materials for K-ion storage. Our present work not only provide new understandings on surface/conversion-synergistic driven K-ion storage mechanisms but offer effective material engineering strategies for improving the properties of potassium-ion batteries.

Emerging polyanionic and organic compounds for high energy density, non-aqueous potassium-ion batteries

This review focuses on the state-of-the-art development of emerging polyanionic and organic compounds to achieve high energy density of non-aqueous potassium-ion batteries.

Improving Potassium-Ion Batteries by Optimizing the Composition of Prussian Blue Cathode

Prussian blue and its analogues are considered as superior cathode materials for nonaqueous potassium-ion batteries because of their three-dimensional open framework structure, high stability, and ...

One-Pot Formation of Sb-Carbon Microspheres with Graphene Sheets: Potassium-Ion Storage Properties and Discharge Mechanisms.

Low-cost rechargeable batteries are ardently required for large-scale energy storage applications. In this regard, nonaqueous potassium-ion batteries (KIBs) are ascendant candidates due to the abundance of potassium resources, yet their energy density and cycle stability are insufficient for practical use. In this study, we report the Sb-based multicomposite comprising Sb nanoparticles, amorphous carbon (C), and reduced graphene oxide (rGO) as an anode material for KIBs. By adopting the tartaric acid as a carbon source and a chelating agent simultaneously, a multicomposite electrode with uniform and fine-sized Sb particles is realized. The Sb-C-rGO multicomposite exhibits a reversible capacity of 310 mAh g-1 at 0.5 A g-1 and 79% of it is retained after 100 cycles. Electrochemical tests show that the capacity fading in the Sb-C-rGO cell is attributed to the side reactions in the K metal and electrolyte, rather than the degradation of Sb nanoparticles. Furthermore, the formation of the metastable product is elucidated by Ostwald's step rule and density functional theory calculations. The present synthesis approach and the understanding of the failure and working mechanisms provide general insight into developing the alloying-type electrode materials for rechargeable batteries.

Influence of KPF6 and KFSI on the Performance of Anode Materials for Potassium-Ion Batteries: A Case Study of MoS2.

Recently, nonaqueous potassium-ion batteries (KIBs) are attracting because of increasing interest due to the abundance of potassium resources, but the systematic study about the effects of electrolyte's salt on the electrochemical performance of electrode materials is still insufficient. Here, it is shown that the capacity retention and Coulombic efficiency of commercial micrometric MoS2 can be remarkably improved by simply using potassium bis(fluorosulfonyl)imide (KFSI) over potassium hexafluorophosphate (KPF6) dissolved in ethylene carbonate/diethyl carbonate as the electrolyte. By constructing various cell configurations, it is discovered that the degradation of MoS2||K half-cells in KPF6-containing electrolyte originates from the failure of the MoS2 electrode. The solid electrolyte interphase (SEI) layer formed on MoS2 during cycling was systematically investigated by using a series of characterizations. It is found that a stable, protective, and KF-rich SEI layer is formed on MoS2 in the KFSI-containing electrolyte, while an unstable, KF-deficient, and organic species-rich SEI layer is formed in the KPF6-containing electrolyte. Finally, the origins of such differences are discussed, which will provide new insights into further exploration of novel electrolytes for KIBs.

Characterising the Structure and Electrochemical Behaviour of Manganese Hexacyanochromate: Highlighting the Role and Importance of Structural Water at Low Potentials.

In recent years Prussian blue analogue materials have received much attention as battery materials. Two distinct transition metal sites connected through cyanide ligands create an open-framework structure containing interstitial sites capable of containing a range of alkali metal cations.1 Compositional control, as well as defect and water content, allow tunability of many properties. They show excellent electrochemical properties and are some of the most promising candidate cathode materials for sodium- and potassium-ion batteries.2 Operating in both aqueous and organic electrolytes they have shown high rate capability and extremely long cycle lives attributed to negligible change in lattice constant on cycling and fast ionic mobility.3 A majority of current literature focuses on hexacyanoferrate's as cathode materials, operating at around 0.8 V vs. SHE. However, to utilise the excellent properties in a full cell you need an anode with comparable cycle life and kinetics. Through exchanging Fe with Mn, manganese hexacyanomanganate had a redox couple at 0 V vs. SHE. This, in combination with copper hexacyanoferrate produced a full cell with an average discharge voltage of 1 V and long cycle life.4 Efforts to produce lower potential PBA materials have often resulted in loss of the cubic structure and reversible capacity ascribable to a conversion-type mechanism.5 In this work we investigate manganese hexacyanochromate as a low potential PBA material. Through substitution of Cr into the structure we have lowered the reduction potential to -0.86 V vs. SHE, whilst operating in a high voltage aqueous electrolyte. This is the lowest reduction potential reported with the confirmation that the open-framework structure is maintained, and reversible capacity arises from sodium insertion into the material. Two types of water in the structure are characterised through high resolution XRD, TGA and FTIR, and the crucial role water plays in electrochemical activity and structural integrity is highlighted. It was found that when operating in a non-aqueous electrolyte the material is dehydrated and during electrochemical reduction the crystalline structure is lost. This study isolates the important role water plays within the structure and that it is vital to consider when investigating low potential PBA materials for alkali-ion batteries. Hurlbutt, K., Wheeler, S., Capone, I. & Pasta, M. Prussian Blue Analogs as Battery Materials. Joule (2018). doi:10.1016/J.JOULE.2018.07.017Song, J. et al. Removal of interstitial H2O in hexacyanometallates for a superior cathode of a sodium-ion battery. J. Am. Chem. Soc. 137, 2658–2664 (2015).Wessells, C. D., Huggins, R. a & Cui, Y. Copper hexacyanoferrate battery electrodes with long cycle life and high power. Nat. Commun. 2, 550 (2011).Pasta, M. et al. Full open-framework batteries for stationary energy storage. Nat. Commun. 5, 3007 (2014).Deng, L. et al. Investigation of the Prussian Blue Analog Co3[Co(CN)6]2 as an Anode Material for Nonaqueous Potassium-Ion Batteries. Adv. Mater. 1802510 (2018). doi:10.1002/adma.201802510 Figure 1

Potassium Metal as Reliable Reference Electrodes of Nonaqueous Potassium Cells.

Potassium metal electrochemical cells are widely utilized to examine potassium insertion materials for nonaqueous potassium-ion batteries. However, large polarization during K plating-stripping and unstable rest potential are found at the potassium electrodes, which leads to an underestimation of the electrochemical performance of insertion materials. In this study, the electrochemical behavior of K-metal electrodes is systematically investigated. Electrolyte salts, solvents, and additives influence the polarization of K metals. Although a highly concentrated electrolyte of 3.9 M KN(SO2F)2/1,2-dimethoxyethane realizes the smallest polarization of 25 mV among all the electrolytes investigated in this study, the polarization of K metals is still larger than those of Li and Na metals. The issue of inaccurate rest potential is solved by pretreating the K electrodes with a plating-stripping process, which is essential in evaluating the intrinsic electrode performance of potassium insertion materials.

Rhombohedral Potassium-Zinc Hexacyanoferrate as a Cathode Material for Nonaqueous Potassium-Ion Batteries.

Rhombohedral potassium-zinc hexacyanoferrate K1.88Zn2.88[Fe(CN)6]2(H2O)5 (KZnHCF) synthesized using a precipitation method is demonstrated as a high-voltage cathode material for potassium-ion batteries (PIBs), exhibiting an initial discharge capacity of 55.6 mAh g-1 with a discharge voltage of 3.9 V versus K/K+ and a capacity retention of ∼95% after 100 cycles in a nonaqueous electrolyte. All K ions are extracted from the structure upon the initial charge process. However, only 1.61 out of 1.88 K ions per formula unit are inserted back into the structure upon discharge, and it becomes the reversible ion of the second cycle onward. Despite the large ionic size of K, the material exhibits a lattice-volume change (∼3%) during a cycle, which is exceptionally small among the cathode materials for PIBs. The distinct feature of the material seems to come from the unique porous framework structure built by ZnN4 and FeC6 polyhedra linked via the C≡N bond and a Zn/Fe atomic ratio of 3/2, resulting in high structural stability and cycle performance.

Recent Progresses and Prospects of Cathode Materials for Non-aqueous Potassium-Ion Batteries

Rechargeable potassium-ion batteries (KIBs) are potential alternatives to lithium-ion batteries for application in large-scale energy storage systems due to their inexpensive and highly abundant resources. Recently, various anode materials have been investigated for use in KIBs, especially the traditional graphite anodes which have already been successfully applied in KIBs. In contrast, the appropriate cathode materials which are able to accommodate large K ions are urgently needed. In this review, a comprehensive summary of the latest advancements in cathode materials for non-aqueous KIBs in terms of capacity, cycle life and energy density will be presented, as well as K-storage mechanisms. In addition, various strategies to improve K-storage performance will be provided through combining insights from the study of material structures and properties and thus bring low-cost non-aqueous KIBs a step closer to application in sustainable large-scale energy storage systems.

Investigation of the Prussian Blue Analog Co3 [Co(CN)6 ]2 as an Anode Material for Nonaqueous Potassium-Ion Batteries.

Nonaqueous potassium-ion batteries (KIBs) are attracting increasing attention as a potential low-cost energy-storage system due to the abundance of potassium resources. Here, cobalt hexacyanocobaltate (Co3 [Co(CN)6 ]2 ), a typical Prussian blue analog (PBA), is reported as an anode material for nonaqueous KIBs. The as-prepared Co3 [Co(CN)6 ]2 exhibits a highly reversible capacity of 324.5 mAh g-1 at a current density of 0.1 A g-1 , a superior rate capability (221 mAh g-1 at 1 A g-1 ), and a favorable long-term cycling stability (200 cycles with 82% capacity retention). Based on a series of characterizations, it is found that potassiation/depotassiation in Co3 [Co(CN)6 ]2 proceeds via solid-state diffusion-limited K-ion insertion/extraction process, in which both carbon- and nitrogen-coordinated cobalt are electrochemically active toward K-ion storage. Finally, the reaction pathway between potassium and Co3 [Co(CN)6 ]2 is proposed. The present study provides new insights on further exploration of PBAs as high-performance electrode materials for KIBs.