Commercial lithium-ion (Li-ion) batteries suffer from low energy density and do not meet the growing demands of the energy storage market. Therefore, building next-generation rechargeable Li and Li-ion batteries with higher energy densities, better safety characteristics, lower cost and longer cycle life is of outmost importance. To achieve smaller and lighter next-generation rechargeable Li and Li-ion batteries that can outperform commercial Li-ion batteries, several new energy storage chemistries are being extensively studied. In this review, we summarize the current trends and provide guidelines towards achieving this goal, by addressing batteries using high-voltage cathodes, metal fluoride electrodes, chalcogen electrodes, Li metal anodes, high-capacity anodes as well as useful electrolyte solutions. We discuss the choice of active materials, practically achievable energy densities and challenges faced by the respective battery systems. Furthermore, strategies to overcome remaining challenges for achieving energy characteristics are addressed in the hope of providing a useful and balanced assessment of current status and perspectives of rechargeable Li and Li-ion batteries.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries.

As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium-sulfur (Li-S) batteries. In this paper, a mesoporous nitrogen-doped carbon (MPNC)-sulfur nanocomposite is reported as a novel cathode for advanced Li-S batteries. The nitrogen doping in the MPNC material can effectively promote chemical adsorption between sulfur atoms and oxygen functional groups on the carbon, as verifi ed by X-ray absorption near edge structure spectroscopy, and the mechanism by which nitrogen enables the behavior is further revealed by density functional theory calculations. Based on the advantages of the porous structure and nitrogen doping, the MPNC-sulfur cathodes show excellent cycling stability (95% retention within 100 cycles) at a high current density of 0.7 mAh cm −2 with a high sulfur loading (4.2 mg S cm −2 ) and a sulfur content (70 wt%). A high areal capacity (≈3.3 mAh cm −2 ) is demonstrated by using the novel cathode, which is crucial for the practical application of Li-S batteries. It is believed that the important role of nitrogen doping promoted chemical adsorption can be extended for development of other high performance carbon-sulfur composite cathodes for Li-S batteries.

Nitrogen-Doped Mesoporous Carbon Promoted Chemical Adsorption of Sulfur and Fabrication of High-Areal-Capacity Sulfur Cathode with Exceptional Cycling Stability for Lithium-Sulfur Batteries

Li-ion batteries (LIBs), commercialized in 1991, have the highest energy density among practical secondary batteries and are widely utilized in electronics, electric vehicles, and even stationary energy storage systems. Along with the expansion of their demand and application, concern about the resources of Li and Co is growing. Therefore, secondary batteries composed of earth-abundant elements are desired to complement LIBs. In recent years, K-ion batteries (KIBs) have attracted significant attention as potential alternatives to LIBs. Previous studies have developed positive and negative electrode materials for KIBs and demonstrated several unique advantages of KIBs over LIBs and Na-ion batteries (NIBs). Thus, besides being free from any scarce/toxic elements, the low standard electrode potentials of K/K+ electrodes lead to high operation voltages competitive to those observed in LIBs. Moreover, K+ ions exhibit faster ionic diffusion in electrolytes due to weaker interaction with solvents and anions than that of Li+ ions; this is essential to realize high-power KIBs. This review comprehensively covers the studies on electrochemical materials for KIBs, including electrode and electrolyte materials and a discussion on recent achievements and remaining/emerging issues. The review also includes insights into electrode reactions and solid-state ionics and nonaqueous solution chemistry as well as perspectives on the research-based development of KIBs compared to those of LIBs and NIBs.

Research Development on K-Ion Batteries.

Aqueous zinc-ion batteries have rapidly developed recently as promising energy storage devices in large-scale energy storage systems owing to their low cost and high safety. Research on suppressing zinc dendrite growth has meanwhile attracted widespread attention to improve the lifespan and reversibility of batteries. Herein, design methods for dendrite-free zinc anodes and their internal mechanisms are reviewed from the perspective of optimizing the host-zinc interface and the zinc-electrolyte interface. Furthermore, a design strategy is proposed to homogenize zinc deposition by regulating the interfacial electric field and ion distribution during zinc nucleation and growth. This Minireview can offer potential directions for the rational design of dendrite-free zinc anodes employed in aqueous zinc-ion batteries.

Interfacial design of dendrite‐free zinc anodes for aqueous zinc‐ion batteries

Electrolytes are one of the vital constituents of electrochemical energy storage devices and their physical and chemical properties play an important role in these devices' performance, including capacity, power density, rate performance, cyclability and safety. This article reviews the current state of understanding of the electrode–electrolyte interaction in supercapacitors and battery–supercapacitor hybrid devices. The article discusses factors that affect the overall performance of the devices such as the ionic conductivity, mobility, diffusion coefficient, radius of bare and hydrated spheres, ion solvation, viscosity, dielectric constant, electrochemical stability, thermal stability and dispersion interaction. The requirements needed to design better electrolytes and the challenges that still need to be addressed for building better supercapacitive devices for the competitive energy storage market have also been highlighted.

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Electrolyte selection for supercapacitive devices: a critical review

Dendrite growth of metal anodes is one of the key hindrances for both secondary aqueous metal batteries and nonaqueous metal batteries. In this work, a freestanding Ti3C2Tx MXene@Zn paper is designed as both zinc metal anode and lithium metal anode host to address the issue. The binder-free Ti3C2Tx MXene@Zn paper exhibits merits of good mechanical flexibility, high electronic conductivity, hydrophilicity, and lithiophilicity. The crystal growth mechanism of Zn metal on common Zn foil and Ti3C2Tx MXene@Zn composite is also studied. It is found that the Ti3C2Tx MXene@Zn paper can effectively suppress the dendrite growth of Zn, enabling reversible and fast Zn plating/stripping kinetics in an aqueous electrolyte. Moreover, the Ti3C2Tx MXene@Zn paper can be used as a 3D host for a lithium metal anode. In this host, Zn is utilized as a nucleation agent to suppress the Li dendrite growth. The freestanding Ti3C2Tx MXene@Zn@Li anode exhibits superior reversibility with high Coulombic efficiency (97.69% over 600 cycles at 1.0 mA cm-2) and low polarization compared with the Cu@Li anode. These findings may be useful for the design of dendrite-free metal-based energy storage systems.

Flexible and Free-Standing Ti3C2Tx MXene@Zn Paper for Dendrite-Free Aqueous Zinc Metal Batteries and Nonaqueous Lithium Metal Batteries.

Commercial expanded graphite as a low-cost, long-cycling life anode for potassium-ion batteries with conventional carbonate electrolyte

Silicon is considered as one of the most favorable anode materials for next-generation lithium-ion batteries. Nanoporous silicon is synthesized via a green, facile, and controllable vacuum distillation method from the commercial Mg2Si alloy. Nanoporous silicon is formed by the evaporation of low boiling point Mg. In this method, the magnesium metal from the Mg2Si alloy can be recycled. The pore sizes of nanoporous silicon can be secured by adjusting the distillated temperature and time. The optimized nanoporous silicon (800 °C, 0.5 h) delivers a discharge capacity of 2034 mA h g–1 at 200 mA g–1 for 100 cycles, a cycling stability with more than 1180 mA h g–1 even after 400 cycles at 1000 mA g–1, and a rate capability of 855 mA h g–1 at 5000 mA g–1. The electrochemical properties might be ascribed to its porous structure, which may accommodate large volume change during the cycling process. These results suggest that the green, scalable, and controllable approach may offer a pathway for the commercializati...

Green, Scalable, and Controllable Fabrication of Nanoporous Silicon from Commercial Alloy Precursors for High-Energy Lithium-Ion Batteries

Silicon has been developed as the exceptionally desirable anode candidate for lithium-ion batteries (LIBs), attributing to its highest theoretical capacity, low working potential, and abundant resource. However, large volume expansion and poor conductivity hinder its practical application. Herein, we fabricate flexible, freestanding, and binder-free silicon/MXene composite papers directly as anodes for LIBs. The Silicon/MXene composite papers are synthesized via covalently anchoring silicon nanospheres on the highly conductive networks based on MXene sheets by vacuum filtration. This unique architecture can accommodate large volume expansion, enhance conductivity of composites, prevent restacking of MXene sheets, offer additional active sites, and facilitate efficient ion transport, which exhibits superior electrochemical performance with a high capacity of 2118 mAh·g–1 at 200 mA·g–1 current density after 100 cycles, a steady cycling ability of 1672 mAh·g–1 at 1000 mA·g–1 after 200 cycles, and a rate perf...

Yongling An

Papers

Flexible and Free-Standing Ti3C2Tx MXene@Zn Paper for Dendrite-Free Aqueous Zinc Metal Batteries and Nonaqueous Lithium Metal Batteries.

Commercial expanded graphite as a low-cost, long-cycling life anode for potassium-ion batteries with conventional carbonate electrolyte

Green, Scalable, and Controllable Fabrication of Nanoporous Silicon from Commercial Alloy Precursors for High-Energy Lithium-Ion Batteries

Flexible and Freestanding Silicon/MXene Composite Papers for High-Performance Lithium-Ion Batteries.

Vacuum distillation derived 3D porous current collector for stable lithium–metal batteries