Dual-phase nanostructuring of layered metal oxides for high-performance aqueous rechargeable potassium ion microbatteries

Inhibiting dissolution strategy achieving high-performance sodium titanium phosphate hybrid anode in seawater-based dual-ion battery

Aqueous sodium-ion batteries (ASIBs) show great promise as candidates for large-scale energy storage. However, the potential of ASIB is impeded by the limited availability of suitable anode types and the occurrence of dissolution side reactions linked to hydrogen evolution. In this study, we addressed these challenges by developing a Bi-coating modified anode based on a sodium titanium phosphate (NTP)-carbon fibers (CFs) hybrid electrode (NTP-CFs/Bi). The Bi-coating effectively mitigates the localized enrichment of hydroxyl anion (OH-) near the NTP surface, thus addressing the dissolution issue. Notably, the Bi-coating not only restricts the local abundance of OH- to inhibit dissolution but also ensures a higher capacity compared with other NTP-based anodes. Consequently, the NTP-CFs/Bi anode demonstrates an impressive specific capacity of 216.8 mAh/g at 0.2 mV/s and maintains a 90.7 % capacity retention after 1000 cycles at 6.3 A/g. This achievement sets a new capacity record among NTP-based anodes for sodium storage. Furthermore, when paired with a cathode composed of hydroxy nickel oxide directly grown on Ni foam, we assembled a seawater-based cell exhibiting high energy and power densities, surpassing the most recently reported ASIBs. This groundbreaking work lays the foundation for a potential method to develop long-life NTP-based anodes.

Benzoquinone-Lubricated Intercalation in Manganese Oxide for High-Capacity and High-Rate Aqueous Aluminum-Ion Battery

Aqueous aluminum-ion batteries are attractive post-lithium battery technologies for large-scale energy storage in virtue of abundant and low-cost Al metal anode offering ultrahigh capacity via a three-electron redox reaction. However, state-of-the-art cathode materials are of low practical capacity, poor rate capability, and inadequate cycle life, substantially impeding their practical use. Here layered manganese oxide that is pre-intercalated with benzoquinone-coordinated aluminum ions (BQ-AlxMnO2) as a high-performance cathode material of rechargeable aqueous aluminum-ion batteries is reported. The coordination of benzoquinone with aluminum ions not only extends interlayer spacing of layered MnO2 framework but reduces the effective charge of trivalent aluminum ions to diminish their electrostatic interactions, substantially boosting intercalation/deintercalation kinetics of guest aluminum ions and improving structural reversibility and stability. When coupled with Zn50Al50 alloy anode in 2 m Al(OTf)3 aqueous electrolyte, the BQ-AlxMnO2 exhibits superior rate capability and cycling stability. At 1 A g-1, the specific capacity of BQ-AlxMnO2 reaches ≈300 mAh g-1 and retains ≈90% of the initial value for more than 800 cycles, along with the Coulombic efficiency of as high as ≈99%, outperforming the AlxMnO2 without BQ co-incorporation.

Insights into Nano- and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano- and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy storage devices at all technology readiness levels. Due to various challenging issues, especially limited stability, nano- and micro-structured (NMS) electrodes undergo fast electrochemical performance degradation. The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement, even though it only occupies complementary and facilitating components for the main mechanism. However, extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies. This review will aim at highlighting these NMS scaffold design strategies, summarizing their corresponding strengths and challenges, and thereby outlining the potential solutions to resolve these challenges, design principles, and key perspectives for future research in this field. Therefore, this review will be one of the earliest reviews from this viewpoint.

The synthesis and application of crystalline-amorphous hybrid materials

Crystalline-amorphous hybrid materials (CA-HMs) possess the merits of both pure crystalline and amorphous phases. Abundant dangling bonds, unsaturated coordination atoms, and isotropic structural features in the amorphous phase, as well as relatively high electronic conductivity and thermodynamic structural stability of the crystalline phase simultaneously take effect in CA-HMs. Furthermore, the atomic and bandgap mismatch at the CA-HM interface can introduce more defects as extra active sites, reservoirs for promoted catalytic and electrochemical performance, and induce built-in electric field for facile charge carrier transport. Motivated by these intriguing features, herein, we provide a comprehensive overview of CA-HMs on various aspects-from synthetic methods to multiple applications. Typical characteristics of CA-HMs are discussed at the beginning, followed by representative synthetic strategies of CA-HMs, including hydrothermal/solvothermal methods, deposition techniques, thermal adjustment, and templating methods. Diverse applications of CA-HMs, such as electrocatalysis, batteries, supercapacitors, mechanics, optoelectronics, and thermoelectrics along with underlying structure-property mechanisms are carefully elucidated. Finally, challenges and perspectives of CA-HMs are proposed with an aim to provide insights into the future development of CA-HMs.

Superstable potassium metal batteries with a controllable internal electric field

Stable potassium metal batteries (PMBs) are promising candidates for electrical energy storage due to their ability to reversibly store electrical energy at a low cost. However, dendritic growth and large volume changes hinder their practical application. Here, referring to the morphology and structure of a virus, a bionic virus-like-carbon microsphere (BVC) was designed as the anode host for a PMB. A BVC with a three-dimensional structure can not only control the electric field, which can suppress dendrite formation, but can also provide a larger space to accommodate the volume change during the cycle progress. The designed potassium (K) metal anode exhibits excellent cycle life and stability (during 1800 h of repeated plating/stripping of K at a current density of 0.1 mA cm-2, K-BVC can realize a very stable K metal anode with low voltage hysteresis). Stable cyclability and improved rate capability can be realized in a full cell using Prussian blue over 400 cycles. This research provides a new idea for the development of stable K metal anodes and may pave the way for the practical application of next-generation metal batteries.

Vanadium Oxides with Amorphous-Crystalline Heterointerface Network for Aqueous Zinc-Ion Batteries

Rechargeable aqueous Zn-VO_x batteries are attracting attention in large scale energy storage applications. Yet, the sluggish Zn²⁺ diffusion kinetics and ambiguous structure-property relationship are always challenging to fulfil the great potential of the batteries. Here we electrodeposit vanadium oxide nanobelts (VO-E) with highly disordered structure. The electrode achieves high capacities (e.g., ≈5 mAh cm^-2 , 516 mAh g^-1 ), good rate and cycling performances. Detailed structure analysis indicates VO-E is composed of integrated amorphous-crystalline nanoscale domains, forming an efficient heterointerface network in the bulk electrode, which accounts for the good electrochemical properties. Theoretical calculations indicate that the amorphous-crystalline heterostructure exhibits the favorable cation adsorption and lower ion diffusion energy barriers compared to the amorphous and crystalline counterparts, thus accelerating charge carrier mobility and electrochemical activity of the electrode.

Flexible Ammonium-Ion Pouch Cells Based on a Tunneled Manganese Dioxide Cathode

Aqueous ammonium-ion (NH₄⁺) batteries are becoming the competitive energy storage candidate on account of their safety, affordability, sustainability, and intrinsically peculiar properties. Herein, an aqueous NH₄⁺-ion pouch cell is investigated based on a tunneled manganese dioxide (α-MnO₂) cathode and a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode. The MnO₂ electrode possesses a high specific capacity of ∼190 mA h g^-1 at 0.1 A g^-1 and displays excellent long cycling performance after 50,000 cycles in 1 M (NH₄)₂SO₄, which outperforms the most reported ammonium-ion host materials. Besides, a solid-solution behavior is revealed about the migration of NH₄⁺ in the tunnel-like α-MnO₂. The battery displays a splendid rate capacity of 83.2 mA h g^-1 even at 10 A g^-1. It also exhibits a high energy density of ∼78 W h kg^-1 as well as a high power density of ∼8212 W kg^-1 (based on the mass of MnO₂). What is more, the flexible MnO₂//PTCDA pouch cell based on the hydrogel electrolyte shows excellent flexibility and good electrochemical properties. The topochemistry results of MnO₂//PTCDA point to the potential practicability of ammonium-ion energy storage.

Interface Reversible Electric Field Regulated by Amphoteric Charged Protein-Based Coating Toward High-Rate and Robust Zn Anode

Metallic interface engineering is a promising strategy to stabilize Zn anode via promoting Zn²⁺ uniform deposition. However, strong interactions between the coating and Zn²⁺ and sluggish transport of Zn²⁺ lead to high anodic polarization. Here, we present a bio-inspired silk fibroin (SF) coating with amphoteric charges to construct an interface reversible electric field, which manipulates the transfer kinetics of Zn²⁺ and reduces anodic polarization. The alternating positively and negatively charged surface as a build-in driving force can expedite and homogenize Zn²⁺ flux via the interplay between the charged coating and adsorbed ions, endowing the Zn-SF anode with low polarization voltage and stable plating/stripping. Experimental analyses with theoretical calculations suggest that SF can facilitate the desolvation of [Zn(H₂O)₆]²⁺ and provide nucleation sites for uniform deposition. Consequently, the Zn-SF anode delivers a high-rate performance with low voltage polarization (83 mV at 20 mA cm^-2) and excellent stability (1500 h at 1 mA cm^-2; 500 h at 10 mA cm^-2), realizing exceptional cumulative capacity of 2.5 Ah cm^-2. The full cell coupled with Zn_xV₂O₅·nH₂O (ZnVO) cathode achieves specific energy of ~ 270.5/150.6 Wh kg^-1 (at 0.5/10 A g^-1) with ~ 99.8% Coulombic efficiency and retains ~ 80.3% (at 5.0 A g^-1) after 3000 cycles.

Unlocking the High Capacity Ammonium-Ion Storage in Defective Vanadium Dioxide

Aqueous ammonium-ion storage has been considered a promising energy storage competitor to meet the requirements of safety, affordability, and sustainability. However, ammonium-ion storage is still in its infancy in the absence of reliable electrode materials. Here, defective VO₂ (d-VO) is employed as an anode material for ammonium-ion batteries with a moderate transport pathway and high reversible capacity of ≈200 mAh g^-1 . Notably, an anisotropic or anisotropic behavior of structural change of d-VO between c-axis and ab planes depends on the state of charge (SOC). Compared with potassium-ion storage, ammonium-ion storage delivers a higher diffusion coefficient and better electrochemical performance. A full cell is further fabricated by d-VO anode and MnO₂ cathode, which delivers a high energy density of 96 Wh kg^-1 (based on the mass of VO₂ ), and a peak energy density of 3254 W kg^-1 . In addition, capacity retention of 70% can be obtained after 10 000 cycles at a current density of 1 A g^-1 . What's more, the resultant quasi-solid-state MnO₂ //d-VO full cell based on hydrogel electrolyte also delivers high safety and decent electrochemical performance. This work will broaden the potential applications of the ammonium-ion battery for sustainable energy storage.

A Flexible Aqueous Zinc-Iodine Microbattery with Unprecedented Energy Density

Currently, reported aqueous microbatteries (MBs) only show unsatisfactory electrochemical performance (≤120 mWh cm^-3 volumetric energy density and <1000 μWh cm^-2 areal energy density) and it remains challenging to develop durable aqueous MBs that can simultaneously offer both high volumetric and areal energy density. Herein, an in situ electrodeposition strategy is adopted to construct a flexible aqueous zinc-iodine MB (ZIDMB). Notably, the fabrication process well avoids the use of common additives (such as binders, conductive agents, and toxic solvent) and also bypasses subsequent time-consuming procedures such as grinding, coating, drying, etc., thus greatly simplifying the manufacture of the ZIDMB. Meanwhile, owing to the suppression of the shuttle effect of triiodide ions and the high ionic conductivity of the polyelectrolyte, the ZIDMB can simultaneously deliver record-high volumetric and areal energy densities of 1647.3 mWh cm^-3 and 2339.1 μWh cm^-2 , thus achieving values at least 13.5- and 2.3-fold better than those of best available aqueous MBs, respectively. This work affords an innovative strategy to construct an ideal micro-power-source for future miniaturized and integrated electronics.

Fast Ionic Storage in Aqueous Rechargeable Batteries: From Fundamentals to Applications

The highly dynamic nature of grid-scale energy systems necessitates fast kinetics in energy storage and conversion systems. Rechargeable aqueous batteries are a promising energy-storage solution for renewable-energy grids as the ionic diffusivity in aqueous electrolytes can be up to 1-2 orders of magnitude higher than in organic systems, in addition to being highly safe and low cost. Recent research in this regard has focussed on developing suitable electrode materials for fast ionic storage in aqueous electrolytes. In this review, breakthroughs in the field of fast ionic storage in aqueous battery materials, and 1D/2D/3D and over-3D-tunnel materials are summarized, and tunnels in over-3D materials are not oriented in any direction in particular. Various materials with different tunnel sizes are developed to be suitable for the different ionic radii of Li⁺ , Na⁺ , K⁺ , H⁺ , NH₄ ⁺ , and Zn²⁺ , which show significant differences in the reaction kinetics of ionic storage. New topochemical paths for ion insertion/extraction, which provide superfast ionic storage, are also discussed.

Photopatternable Porous Separators for Micro-Electrochemical Energy Storage Systems

The miniaturization of electrochemical energy storage (EES) systems, one of the key challenges facing the rapid expansion of the Internet-of-Things, has been limited by poor performance of the various energy-storage components at the micrometer scale. Here, the development of a unique photopatternable porous separator that overcomes the electrolyte difficulties involving resistive losses at small dimensions is reported. The separator is based on modifying the chemistry of SU-8, an epoxy-derived photoresist, through the addition of a miscible ionic liquid. The ionic liquid serves as a templating agent, which is selectively removed by solution methods, leaving the SU-8 scaffold whose interconnected porosity provides ion transport from the confined liquid electrolyte. The photopatternable separator exhibits good electrochemical, chemical, thermal, and mechanical stability during the operation of electrochemical devices in both 2D and 3D formats. For the latter, the separator demonstrates the ability to form conformal coatings over 3D structures. The development of the photopatternable separator overcomes the electrolyte issues, which have limited progress in the field of micro-EES.

Bioinspired Catechol-Grafting PEDOT Cathode for an All-Polymer Aqueous Proton Battery with High Voltage and Outstanding Rate Capacity

Aqueous all-polymer proton batteries (APPBs) consisting of redox-active polymer electrodes are considered safe and clean renewable energy storage sources. However, there remain formidable challenges for APPBs to withstand a high current rate while maximizing high cell output voltage within a narrow electrochemical window of aqueous electrolytes. Here, a capacitive-type polymer cathode material is designed by grafting poly(3,4-ethylenedioxythiophene) (PEDOT) with bioinspired redox-active catechol pendants, which delivers high redox potential (0.60 V vs Ag/AgCl) and remarkable rate capability. The pseudocapacitive-dominated proton storage mechanism illustrated by the density functional theory (DFT) calculation and electrochemical kinetics analysis is favorable for delivering fast charge/discharge rates. Coupled with a diffusion-type anthraquinone-based polymer anode, the APPB offers a high cell voltage of 0.72 V, outstanding rate capability (64.8% capacity retention from 0.5 to 25 A g-1 ), and cycling stability (80% capacity retention over 1000 cycles at 2 A g-1 ), which is superior to the state-of-the-art all-organic proton batteries. This strategy and insight provided by DFT and ex situ characterizations offer a new perspective on the delicate design of polymer electrode patterns for high-performance APPBs.

Design nanoporous metal thin films via solid state interfacial dealloying

Thin-film solid-state interfacial dealloying (thin-film SSID) is an emerging technique to design nanoarchitecture thin films. The resulting controllable 3D bicontinuous nanostructure is promising for a range of applications including catalysis, sensing, and energy storage. Using a multiscale microscopy approach, we combine X-ray and electron nano-tomography to demonstrate that besides dense bicontinuous nanocomposites, thin-film SSID can create a very fine (5-15 nm) nanoporous structure. Not only is such a fine feature among one of the finest fabrications by metal-agent dealloying, but a multilayer thin-film design enables creating nanoporous films on a wider range of substrates for functional applications. Through multimodal synchrotron diffraction and spectroscopy analysis with which the materials' chemical and structural evolution in this novel approach is characterized in details, we further deduce that the contribution of change in entropy should be considered to explain the phase evolution in metal-agent dealloying, in addition to the commonly used enthalpy term in prior studies. The discussion is an important step leading towards better explaining the underlying design principles for controllable 3D nanoarchitecture, as well as exploring a wider range of elemental and substrate selections for new applications.

Challenges and Strategies toward Cathode Materials for Rechargeable Potassium-Ion Batteries

With increasing demand for grid-scale energy storage, potassium-ion batteries (PIBs) have emerged as promising complements or alternatives to commercial lithium-ion batteries owing to the low cost, natural abundance of potassium resources, the low standard reduction potential of potassium, and fascinating K⁺ transport kinetics in the electrolyte. However, the low energy density and unstable cycle life of cathode materials hamper their practical application. Therefore, cathode materials with high capacities, high redox potentials, and good structural stability are required with the advancement toward next-generation PIBs. To this end, understanding the structure-dependent intercalation electrochemistry and recognizing the existing issues relating to cathode materials are indispensable prerequisites. This review summarizes the recent advances of PIB cathode materials, including metal hexacyanometalates, layered metal oxides, polyanionic frameworks, and organic compounds, with an emphasis on the structural advantages of the K⁺ intercalation reaction. Moreover, major current challenges with corresponding strategies for each category of cathode materials are highlighted. Finally, future research directions and perspectives are presented to accelerate the development of PIBs and facilitate commercial applications. It is believed that this review will provide practical guidance for researchers engaged in developing next-generation advanced PIB cathode materials.

A Durable Ni-Zn Microbattery with Ultrahigh-Rate Capability Enabled by In Situ Reconstructed Nanoporous Nickel with Epitaxial Phase

Powering device for miniaturized electronics is highly desired with well-maintained capacity and high-rate performance. Though Ni-Zn microbattery can meet the demand to some extent with intrinsic fast kinetic, it still suffers irreversible structure degradation due to the repeated lattice strain. Herein, a stable Ni-Zn microbattery with ultrahigh-rate performance is rationally constructed through in situ electrochemical approaches, including the reconstruction of nanoporous nickel and the introduction of epitaxial Zn(OH)₂ nanophase. With the enhanced ionic adsorption effect, the superior reactivity of the superficial nickel-based nanostructure is well stabilized. Based on facile miniaturization and electrochemical techniques, the fabricated nickel microelectrode exhibits 63.8% capacity retention when the current density is 500 times folded, and the modified hydroxides contribute to the great stability of the porous structure (92% capacity retention after 10 000 cycles). Furthermore, when the constructed Ni-Zn microbattery is measured in a practical metric, excellent power density (320.17 mW cm^-2 ) and stable fast-charging performance (over 90% capacity retention in 3500 cycles) are obtained. This surface reconstruction strategy for nanostructure provides a new direction for the optimization of electrode structure and enriches high-performance output units for integrated microelectronics.

Regulating Lattice-Water-Adsorbed Ions to Optimize Intercalation Potential in 3D Prussian Blue Based Multi-Ion Microbattery

Miniaturized energy storage device (MESD) is the core module in microscale electronic equipment, yet its electrochemical performance is far away from the actual requirements. The extensive research efforts have improved the performance of MESD via the fabrication techniques and material construction, while ignoring the expansion of optimization strategy in the combination of energy storage mechanism. Herein, the Prussian blue/Zn microbattery is reported with the regulation of lattice-water-adsorbed intercalated ion. The optimal charge transport of cathode is achieved via the optimization of 3D structure of microelectrode to maximize the electrochemical performance. Also, lattice-water-adsorbed ion storage mechanism is further investigated to guide the design of differential energy storage for cathode and anode. The Cu₃ (Fe(CN)₆ )₂ /Zn microbattery, with K⁺ inter/deintercalation in the cathode and Zn²⁺ deplating/plating in the anode, displays high capacity (0.281 mAh cm^-2 at 2.5 mA cm^-2 ), rate performance (0.181 mAh cm^-2 at 25 mA cm^-2 ), and cycling stability (77.6% capacity retention after 1500 cycles) enhanced by Cu²⁺ in the electrolyte. This highly efficient combination of fabrication process, active material, and multi-ion storage for microelectrode shows a high tolerance for optimization strategies, expanding the compatibility of optimization path for high-performance MESD.

Advanced High-Performance Potassium-Chalcogen (S, Se, Te) Batteries

Current great progress on potassium-chalcogen (S, Se, Te) batteries within much potential to become promising energy storage systems opens a new avenue for the rapid development of potassium batteries as a complementary option to lithium ion batteries. The discussion mainly concentrates on recent research advances of potassium-chalcogen (S, Se, Te) batteries and their corresponding cathode materials in this review. Initially, the development of cathode materials for four types of batteries is introduced, including: potassium-sulfur (K-S), potassium-selenium (K-Se), potassium-selenium sulfide (K-Se_x S_y ), and potassium-tellurium (K-Te) batteries. Next, critical challenges for chalcogen-based electrodes in devices operation are summarized. In addition, some pragmatic strategies are proposed as well to relieve the low electronic conductivity, large volumetric expansion, shuttle effect, and potassium dendrite growth. At last, the perspectives on designing advanced cathode materials for potassium-chalcogen batteries are provided with the goal of developing high-performance potassium storage devices.

Recent progress in sodium/potassium hybrid capacitors

Metal ion hybrid capacitors (MIHCs) have been recognized as one of the most promising power sources owing to their combined merits of high energy density in batteries and high power output in supercapacitors. The kinetics mismatch between the capacitor-type cathode and battery-type anode yet must be well addressed before implementing their practical feasibility. Here, we overview the recent progress in sodium and potassium ion hybrid capacitors (SIHCs and PIHCs) and discuss the major challenges and give an outlook on the future directions in this field. The fundamental knowledge and the history will be firstly introduced, and special emphasis is then laid on the development of a variety of electrode materials in recent years. The prospects of future research of MIHCs are finally proposed towards their practical applications. We wish that this feature article can not only educate newcomers starting their reasearch in this field, but also inspire experieced researchers to contribute to the development of high-performance MIHC devices.

Recent Advances in High-Performance Microbatteries: Construction, Application, and Perspective

High-performance miniaturized energy storage devices have developed rapidly in recent years. Different from conventional energy storage devices, microbatteries assume the main responsibility for micropower supply, functionalization, and characterization platforms. Evolving from the essential goals for battery design of high power density, high energy density, and long lifetime, further practical demands for microbatteries (MBs) have been raised for the microfabrication technique and device design. Numerous studies have generally focused on specific aspects of the microelectrode structures or certain microfabrication techniques, while the connection from techniques to functional applications is rarely involved. This Review generally fills such blanks from an application-oriented perspective. First, some basic micromachining techniques with different compatible features are summarized. Afterward, device designs including diversified battery reaction types, configuration, and assembly are highlighted, as well as microbatteries serving powering resources or further complicated functional systems. Finally, through providing the overall design concept based on requirements in application, this Review offers innovative insights for further development of microbatteries.

Recent advances in the template-confined synthesis of two-dimensional materials for aqueous energy storage devices

The template-confined synthesis strategy is a simple and effective methodology to prepare two-dimensional nanomaterials. It has multiple advantages including green process, controllable morphology and adjustable crystal structure, and therefore, it is promising in the energy storage realm to synthesize high-performance electrode materials. In this review, we summarize the recent advances in the template-confined synthesis of two-dimensional nanostructures for aqueous energy storage applications. The material design is discussed in detail to accommodate target usage in aqueous supercapacitors and zinc metal batteries. The remaining challenges and future prospective are also covered.

K0.38(H2O)0.82MoS2 as a universal host for rechargeable aqueous cation (K+, Na+, Li+, NH4+, Mg2+, Al3+) batteries

Rechargeable aqueous batteries have been widely investigated for large-scale energy storage in view of their high safety and low cost. While tremendous efforts have been devoted to the development of cathode materials, few have focused on the development of anode materials and only limited candidates such as V-based oxides and Ti-based polyanionic compounds have been explored. In this study, for the first time, we discover a hydrated compound of molybdenum based ternary sulfide K0.38(H2O)0.82MoS2 as a universal host for reversible intercalation of various hydrated cations (K+, Na+, Li+, NH4+, Mg2+, Al3+, etc.). It undergoes a two-phase reaction during the electrochemical process, showing a stable redox potential of around -0.1 V vs. Ag/AgCl to serve as an anode material and a specific capacity of over 50 mA h g-1 at a current density of 0.5 A g-1. The intercalation of larger hydrated cations during the discharge process results in a lower operation potential and wider interlayer spacing, which has been explained theoretically by Gibbs free energy analysis and valence bond theory. In particular, taking hydrated K+ insertion and extraction of K0.38(H2O)0.82MoS2 as an example, the ex situ XRD and XPS results demonstrate a reversible change in the phase structure and Mo3+/Mo4+ redox couple during the charge-discharge process. Our study provides a promising anode for aqueous batteries using K0.38(H2O)0.82MoS2 as a universal host.