A Liquid‐Metal‐Enabled Versatile Organic Alkali‐Ion Battery

Despite the high specific capacity and low redox potential of alkali metals, their practical application as anodes is still limited by the inherent dendrite‐growth problem. The fusible sodium–potassium (Na–K) liquid metal alloy is an alternative that detours this drawback, but the fundamental understanding of charge transport in this binary electroactive alloy anode remains elusive. Here, comprehensive characterization, accompanied with density function theory (DFT) calculations, jointly expound the Na–K anode‐based battery working mechanism. With the organic cathode sodium rhodizonate dibasic (SR) that has negligible selectivity toward cations, the charge carrier is screened by electrolytes due to the selective ionic pathways in the solid electrolyte interphase (SEI). Stable cycling for this Na–K/SR battery is achieved with capacity retention per cycle to be 99.88% as a sodium‐ion battery (SIB) and 99.70% as a potassium‐ion battery (PIB) for over 100 cycles. Benefitting from the flexibility of the liquid metal and the specially designed carbon nanofiber (CNF)/SR layer‐by‐layer cathode, a flexible dendrite‐free alkali‐ion battery is achieved with an ultrahigh areal capacity of 2.1 mAh cm^?2. Computation‐guided materials selection, characterization‐supported mechanistic understanding, and self‐validating battery performance collectively promise the prospect of a high‐performance, dendrite‐free, and versatile organic‐based liquid metal battery.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

An All‐Stretchable‐Component Sodium‐Ion Full Battery

Stretchable energy‐storage devices receive considerable attention due to their promising applications in future wearable technologies. However, they currently suffer from many problems, including low utility of active materials, limited multidirectional stretchability, and poor stability under stretched conditions. In addition, most proposed designs use one or more rigid components that fail to meet the stretchability requirement for the entire device. Here, an all‐stretchable‐component sodium‐ion full battery based on graphene‐modified poly(dimethylsiloxane) sponge electrodes and an elastic gel membrane is developed for the first time. The battery exhibits reasonable electrochemical performance and robust mechanical deformability; its electrochemical characteristics can be well‐maintained under many different stretched conditions and after hundreds of stretching–release cycles. This novel design integrating all stretchable components provides a pathway toward the next generation of wearable energy devices in modern electronics.     

Calcium‐Ion Batteries: Current State‐of‐the‐Art and Future Perspectives

Recent developments in rechargeable battery technology have seen a shift from the well‐established Li‐ion technology to new chemistries to achieve the high energy density required for extended range electric vehicles and other portable applications, as well as low‐cost alternatives for stationary storage. These chemistries include Li–air, Li–S, and multivalent ion technologies including Mg²⁺, Zn²⁺, Ca²⁺, and Al³⁺. While Mg²⁺ battery systems have been increasingly investigated in the last few years, Ca²⁺ technology has only recently been recognized as a viable option. In this first comprehensive review of Ca²⁺ ion technology, the use of Ca metal anodes, alternative alloy anodes, electrolytes suitable for this system, and cathode material development are discussed. The advantages and disadvantages of Ca²⁺ ion batteries including prospective achievable energy density, cost reduction due to high natural abundance, low ion mobility, the effect of ion size, and the need for elevated temperature operation are reviewed. The use of density functional theory modeling to predict the properties of Ca‐ion battery materials is discussed and the extent to which this approach is successful in directing research into areas of promise is evaluated. To conclude, a summary of recent achievements is presented and areas for future research efforts evaluated.     

Clay‐Inspired MXene‐Based Electrochemical Devices and Photo‐Electrocatalyst: State‐of‐the‐Art Progresses and Challenges

MXene, an important and increasingly popular category of postgraphene 2D nanomaterials, has been rigorously investigated since early 2011 because of advantages including flexible tunability in element composition, hydrophobicity, metallic nature, unique in‐plane anisotropic structure, high charge‐carrier mobility, tunable band gap, and favorable optical and mechanical properties. To fully exploit these potentials and further expand beyond the existing boundaries, novel functional nanostructures spanning monolayer, multilayer, nanoparticles, and composites have been developed by means of intercalation, delamination, functionalization, hybridization, among others. Undeniably, the cutting‐edge developments and applications of clay‐inspired 2D MXene platform as electrochemical electrode or photo‐electrocatalyst have conferred superior performance and have made significant impact in the field of energy and advanced catalysis. This review provides an overview of the fundamental properties and synthesis routes of pure MXene, functionalized MXene and their hybrids, highlights the state‐of‐the‐art progresses of MXene‐based applications with respect to supercapacitors, batteries, electrocatalysis and photocatalysis, and presents the challenges and prospects in the burgeoning field.     

A Novel Potassium‐Ion‐Based Dual‐Ion Battery

In this work, combining both advantages of potassium‐ion batteries and dual‐ion batteries, a novel potassium‐ion‐based dual‐ion battery (named as K‐DIB) system is developed based on a potassium‐ion electrolyte, using metal foil (Sn, Pb, K, or Na) as anode and expanded graphite as cathode. When using Sn foil as the anode, the K‐DIB presents a high reversible capacity of 66 mAh g^?1 at a current density of 50 mA g^?1 over the voltage window of 3.0–5.0 V, and exhibits excellent long‐term cycling performance with 93% capacity retention for 300 cycles. Moreover, as the Sn foil simultaneously acts as the anode material and the current collector, dead load and dead volume of the battery can be greatly reduced, thus the energy density of the K‐DIB is further improved. It delivers a high energy density of 155 Wh kg^?1 at a power density of 116 W kg^?1, which is comparable with commercial lithium‐ion batteries. Thus, with the advantages of environmentally friendly, cost effective, and high energy density, this K‐DIB shows attractive potential for future energy storage application.     

Bioinspired,Spine‐Like,Flexible, Rechargeable Lithium‐Ion Batteries with High Energy Density

The rapid development of flexible and wearable electronics proposes the persistent requirements of high‐performance flexible batteries. Much progress has been achieved recently, but how to obtain remarkable flexibility and high energy density simultaneously remains a great challenge. Here, a facile and scalable approach to fabricate spine‐like flexible lithium‐ion batteries is reported. A thick, rigid segment to store energy through winding the electrodes corresponds to the vertebra of animals, while a thin, unwound, and flexible part acts as marrow to interconnect all vertebra‐like stacks together, providing excellent flexibility for the whole battery. As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery can be over 85% of that in conventional packing. A nonoptimized flexible cell with an energy density of 242 Wh L^?1 is demonstrated with packaging considered, which is 86.1% of a standard prismatic cell using the same components. The cell also successfully survives a harsh dynamic mechanical load test due to this rational bioinspired design. Mechanical simulation results uncover the underlying mechanism: the maximum strain in the reported design (≈0.08%) is markedly smaller than traditional stacked cells (≈1.1%). This new approach offers great promise for applications in flexible devices.     

Recent Development in Separators for High‐Temperature Lithium‐Ion Batteries

Lithium‐ion batteries (LIBs) are promising energy storage devices for integrating renewable resources and high power applications, owing to their high energy density, light weight, high flexibility, slow self‐discharge rate, high rate charging capability, and long battery life. LIBs work efficiently at ambient temperatures, however, at high‐temperatures, they cause serious issues due to the thermal fluctuation inside batteries during operation. The separator is a key component of batteries and is crucial for the sustainability of LIBs at high‐temperatures. The high thermal stability with minimum thermal shrinkage and robust mechanical strength are the prime requirements along with high porosity, ionic conductivity, and electrolyte uptake for highly efficient high‐temperature LIBs. This Review deals with the recent studies and developments in separator technologies for high‐temperature LIBs with respect to their structural layered formation. The recent progress in monolayer and multilayer separators along with the developed preparation methodologies is discussed in detail. Future challenges and directions toward the advancement in separator technology are also discussed for achieving remarkable performance of separators in a high‐temperature environment.     

Novel 3D Nanoporous Zn–Cu Alloy as Long‐Life Anode toward High‐Voltage Double Electrolyte Aqueous Zinc‐Ion Batteries

The recharge ability of zinc metal‐based aqueous batteries is greatly limited by the zinc anode. The poor cycling durability of Zn anodes is attributed to the dendrite growth, shape change and passivation, but this issue has been ignored by using an excessive amount of Zn in the past. Herein, a 3D nanoporous (3D NP) Zn–Cu alloy is fabricated by a sample electrochemical‐assisted annealing thermal method combined, which can be used directly as self‐supported electrodes applied for renewable zinc‐ion devices. The 3D NP architectures electrode offers high electron and ion transport paths and increased material loading per unit substrate area, which can uniformly deposit/strip Zn and improve charge storage ability. Benefiting from the intrinsic materials and architectures features, the 3D NP Zn–Cu alloy anode exhibits high areal capacity and excellent cycling stability. Further, the fabricated high‐voltage double electrolyte aqueous Zn–Br₂ battery can deliver maximum areal specific capacity of ≈1.56 mAh cm^?2, which is close to the level of typical commercial Li‐ion batteries. The excellent performance makes it an ideal candidate for next‐generation aqueous zinc‐ion batteries.     

Inkjet‐Printed Lithium–Sulfur Microcathodes for All‐Printed,Integrated Nanomanufacturing

Improved thin‐film microbatteries are needed to provide appropriate energy‐storage options to power the multitude of devices that will bring the proposed “Internet of Things” network to fruition (e.g., active radio‐frequency identification tags and microcontrollers for wearable and implantable devices). Although impressive efforts have been made to improve the energy density of 3D microbatteries, they have all used low energy‐density lithium‐ion chemistries, which present a fundamental barrier to miniaturization. In addition, they require complicated microfabrication processes that hinder cost‐competitiveness. Here, inkjet‐printed lithium–sulfur (Li–S) cathodes for integrated nanomanufacturing are reported. Single‐wall carbon nanotubes infused with electronically conductive straight‐chain sulfur (S@SWNT) are adopted as an integrated current‐collector/active‐material composite, and inkjet printing as a top‐down approach to achieve thin‐film shape control over printed electrode dimensions is used. The novel Li–S cathodes may be directly printed on traditional microelectronic semicoductor substrates (e.g., SiO₂) or on flexible aluminum foil. Profilometry indicates that these microelectrodes are less than 10 µm thick, while cyclic voltammetry analyses show that the S@SWNT possesses pseudocapacitive characteristics and corroborates a previous study suggesting the S@SWNT discharge via a purely solid‐state mechanism. The printed electrodes produce ≈800 mAh g^?1 S initially and ≈700 mAh g^?1 after 100 charge/discharge cycles at C/2 rate.     

Li‐Ion Cooperative Migration and Oxy‐Sulfide Synergistic Effect in Li14P2Ge2S16−6xOx Solid‐State‐Electrolyte Enables Extraordinary Conductivity and High Stability

Critical to the development of all‐solid‐state lithium‐ion batteries technology are novel solid‐state electrolytes with high ionic conductivity and robust stability under inorganic solid‐electrolyte operating conditions. Herein, by using density functional theory and molecular dynamics, a mixed oxygen‐sulfur‐based Li‐superionic conductor is screened out from the local chemical structure of β‐Li₃PS₄ to discover novel Li₁₄P₂Ge₂S₈O₈ (LPGSO) with high ionic conductivity and high stability under thermal, moist, and electrochemical conditions, which causes oxygenation at specific sites to improve the stability and selective sulfuration to provide an O‐S mixed path by Li‐S/O structure units with coordination number between 3 and 4 for fast Li‐cooperative conduction. Furthermore, LPGSO exhibits a quasi‐isotropic 3D Li‐ion cooperative diffusion with a lesser migration barrier (≈0.19 eV) compared to its sulfide‐analog Li₁₄P₂Ge₂S₁₆. The theoretical ionic conductivity of this conductor at room temperature is as high as ≈30.0 mS cm^?1, which is among the best in current solid‐state electrolytes. Such an oxy‐sulfide synergistic effect and Li‐ion cooperative migration mechanism would enable the engineering of next‐generation electrolyte materials with desirable safety and high ionic conductivity, for possible application in the near future.     

Porous Carbon Nanofibers Encapsulated with Peapod‐Like Hematite Nanoparticles for High‐Rate and Long‐Life Battery Anodes

Fe₂O₃ is regarded as a promising anode material for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) due to its high specific capacity. The large volume change during discharge and charge processes, however, induces significant cracking of the Fe₂O₃ anodes, leading to rapid fading of the capacity. Herein, a novel peapod‐like nanostructured material, consisting of Fe₂O₃ nanoparticles homogeneously encapsulated in the hollow interior of N‐doped porous carbon nanofibers, as a high‐performance anode material is reported. The distinctive structure not only provides enough voids to accommodate the volume expansion of the pea‐like Fe₂O₃ nanoparticles but also offers a continuous conducting framework for electron transport and accessible nanoporous channels for fast diffusion and transport of Li/Na‐ions. As a consequence, this peapod‐like structure exhibits a stable discharge capacity of 1434 mAh g^?1 (at 100 mA g^?1) and 806 mAh g^?1 (at 200 mA g^?1) over 100 cycles as anode materials for LIBs and SIBs, respectively. More importantly, a stable capacity of 958 mAh g^?1 after 1000 cycles and 396 mAh g^?1 after 1500 cycles can be achieved for LIBs and SIBs, respectively, at a large current density of 2000 mA g^?1. This study provides a promising strategy for developing long‐cycle‐life LIBs and SIBs.