Polymer‐Templated Formation of Polydopamine‐Coated SnO2 Nanocrystals: Anodes for Cyclable Lithium‐Ion Batteries

Well‐controlled nanostructures and a high fraction of Sn/Li₂O interface are critical to enhance the coulombic efficiency and cyclic performance of SnO₂‐based electrodes for lithium‐ion batteries (LIBs). Polydopamine (PDA)‐coated SnO₂ nanocrystals, composed of hundreds of PDA‐coated “corn‐like” SnO₂ nanoparticles (diameter ca. 5 nm) decorated along a “cob”, addressed the irreversibility issue of SnO₂‐based electrodes. The PDA‐coated SnO₂ were crafted by capitalizing on rationally designed bottlebrush‐like hydroxypropyl cellulose‐graft‐poly (acrylic acid) (HPC‐g ‐PAA) as a template and was coated with PDA to construct a passivating solid‐electrolyte interphase (SEI) layer. In combination, the corn‐like nanostructure and the protective PDA coating contributed to a PDA‐coated SnO₂ electrode with excellent rate capability, superior long‐term stability over 300 cycles, and high Sn→SnO₂ reversibility.     

Revealing an Interconnected Interfacial Layer in Solid‐State Polymer Sodium Batteries

Replacing the commonly used nonaqueous liquid electrolytes in rechargeable sodium batteries with polymer solid electrolytes is expected to provide new opportunities to develop safer batteries with higher energy densities. However, this poses challenges related to the interface between the Na‐metal anode and polymer electrolytes. Driven by systematically investigating the interface properties, an improved interface is established between a composite Na/C metal anode and electrolyte. The observed chemical bonding between carbon matrix of anode with solid polymer electrolyte, prevents delamination, and leads to more homogeneous plating and stripping, which reduces/suppresses dendrite formation. Full solid‐state polymer Na‐metal batteries, using a high mass loaded Na₃V₂(PO₄)₃ cathode, exhibit ultrahigh capacity retention of more than 92 % after 2 000 cycles and over 80 % after 5 000 cycles, as well as the outstanding rate capability.     

Electrolyte Chemistry Enables Simultaneous Stabilization of Potassium Metal and Alloying Anode for Potassium‐Ion Batteries

Alloying anodes are promising high‐capacity electrode materials for K‐ion batteries (KIBs). However, KIBs based on alloying anodes suffer from rapid capacity decay due to the instability of K metal and large volume expansion of alloying anodes. Herein, the effects of salts and solvents on the cycling stability of KIBs based on a typical alloying anode such as amorphous red phosphorus (RP) are investigated, and the potassium bis(fluorosulfonyl)imide (KFSI) salt‐based carbonate electrolyte is versatile to achieve simultaneous stabilization of K metal and RP electrodes for highly stable KIBs. This salt‐solvent complex with a moderate solvation energy can alleviate side reactions between K metal and the electrolyte and facilitate K⁺ ion diffusion/desolvation. Moreover, robust SEI layers that form on K metal and RP electrodes can suppress K dendrite growth and resist RP volume change. This strategy of electrolyte regulation can be applicable to other alloying anodes for high‐performance KIBs.     

Water‐Mediated Synthesis of a Superionic Halide Solid Electrolyte

To promote the development of solid‐state batteries, polymer‐, oxide‐, and sulfide‐based solid‐state electrolytes (SSEs) have been extensively investigated. However, the disadvantages of these SSEs, such as high‐temperature sintering of oxides, air instability of sulfides, and narrow electrochemical windows of polymers electrolytes, significantly hinder their practical application. Therefore, developing SSEs that have a high ionic conductivity (>10^?3 S cm^?1), good air stability, wide electrochemical window, excellent electrode interface stability, low‐cost mass production is required. Herein we report a halide Li⁺ superionic conductor, Li₃InCl₆, that can be synthesized in water. Most importantly, the as‐synthesized Li₃InCl₆ shows a high ionic conductivity of 2.04×10^?3 S cm^?1 at 25 °C. Furthermore, the ionic conductivity can be recovered after dissolution in water. Combined with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode, the solid‐state Li battery shows good cycling stability.     

Spatiotemporal Changes of the Solid Electrolyte Interphase in Lithium‐Ion Batteries Detected by Scanning Electrochemical Microscopy

The solid electrolyte interphase (SEI) in lithium‐ion batteries separates the highly reductive lithiated graphite from reducible electrolyte components. It is critical for the performance, durability, and safe operation of batteries. In situ imaging of the SEI is demonstrated using the feedback mode of scanning electrochemical microscopy (SECM) with 2,5‐di‐tert‐butyl‐1,4‐dimethoxy benzene as mediator. The formation of the SEI is indicated by a decrease of the mediator regeneration rate. Prolonged imaging of the same region revealed fluctuation of the passivating properties on time scales between 2 min and 20 h with an inhomogeneous distribution over the sample. The implications of the approach for in situ assessment of local SEI properties on graphite electrodes are discussed with respect to studying the influence of mechanical stress on SEI reliability and the mode of action of electrolyte additives aiming at improving SEI properties.     

Fluoroethylene Carbonate Enabling a Robust LiF‐rich Solid Electrolyte Interphase to Enhance the Stability of the MoS2 Anode for Lithium‐Ion Storage

As a high‐capacity anode for lithium‐ion batteries (LIBs), MoS₂ suffers from short lifespan that is due in part to its unstable solid electrolyte interphase (SEI). The cycle life of MoS₂ can be greatly extended by manipulating the SEI with a fluoroethylene carbonate (FEC) additive. The capacity of MoS₂ in the electrolyte with 10 wt % FEC stabilizes at about 770 mAh g^?1 for 200 cycles at 1 A g^?1, which far surpasses the FEC‐free counterpart (ca. 40 mAh g^?1 after 150 cycles). The presence of FEC enables a robust LiF‐rich SEI that can effectively inhibit the continual electrolyte decomposition. A full cell with a LiNi_0.5Co_0.3Mn_0.2O₂ cathode also gains improved performance in the FEC‐containing electrolyte. These findings reveal the importance of controlling SEI formation on MoS₂ toward promoted lithium storage, opening a new avenue for developing metal sulfides as high‐capacity electrodes for LIBs.     

Water‐Induced Growth of a Highly Oriented Mesoporous Graphitic Carbon Nanospring for Fast Potassium‐Ion Adsorption/Intercalation Storage

A highly oriented mesoporous graphitic carbon nanospring (OGCS) with graphitic layers that are perpendicular to the axis is prepared by hydrothermal treatment of epoxy resin at 500 °C and annealing at 1400 °C. Water plays an important role in not only forming the graphitic carbon nanospring with a high [002] orientation and a large amount of active edge‐plane sites, but also in the generation of the mesoporous structure, which facilitate fast K‐ion adsorption and diffusion. In situ and ex situ measurements confirm that OGCS undergoes K‐adsorption in mesopores and then K‐intercalation in the graphite layer to form KC₈ with a low discharge voltage. The spring‐like nanostructure can expand one‐dimensionally along the axial direction to accommodate the volume variation. The OGCS electrode thus shows a much better K‐storage performance than that of unoriented graphitic carbon.     

Enhanced Lithium‐Ion Conductivity of Polymer Electrolytes by Selective Introduction of Hydrogen into the Anion

The anion chemistry of lithium salts plays a pivotal role in dictating the physicochemical and electrochemical performance of solid polymer electrolytes (SPEs), thus affecting the cyclability of all‐solid‐state lithium metal batteries (ASSLMBs). The bis(trifluoromethanesulfonyl)imide anion (TFSI^?) has long been studied as the most promising candidate for SPEs; however, the Li‐ion conductivities of the TFSI‐based SPEs still remain low (Li‐ion transference number: ca. 0.2). In this work, we report new hydrogen‐containing anions, conceived based on theoretical considerations, as an electrolyte salt for SPEs. SPEs comprising hydrogen‐containing anions achieve higher Li‐ion conductivities than TFSI‐based ones, and those anions are electrochemically stable for various kinds of ASSLMBs (Li–LiFePO₄, Li–S, and Li–O₂ batteries). This opens up a new avenue for designing safe and high‐performance ASSLMBs in the future.     

4.5 V High‐Voltage Rechargeable Batteries Enabled by the Reduction of Polarization on the Lithium Metal Anode

Lithium metal is used to achieve high‐energy‐density batteries due to its large theoretical capacity and low negative electrochemical potential. The introduction of quasi‐solid electrolytes simultaneously overcomes the safety problems induced by the liquid electrolytes and the high interfacial resistance issues confronted by all solid‐state electrolytes. In‐depth investigations involving interfacial behaviors in quasi‐solid lithium metal batteries are inadequate. Herein an ultrathin Li₃OCl quasi‐solid‐state electrolyte layer (500 nm thickness) is used to cover a lithium anode. The polarization of the anode is remarkably reduced by introducing the Li₃OCl quasi‐solid‐state electrolyte. In contrast to the decomposition of solvents in a standard electrolyte (EC‐DEC,1.0 m LiPF₆), the established quasi‐solid‐state electrolyte interfaces can significantly inhibit the decomposition of solvents when the cut‐off voltage is 4.5 V.     

A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A facile microwave method was employed to synthesize NiCo₂O₄ nanosheets as electrode materials for lithium‐ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller methods. Owing to the porous nanosheet structure, the NiCo₂O₄ electrodes exhibited a high reversible capacity of 891 mA h g^?1 at a current density of 100 mA g^?1, good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo₂O₄ nanosheets demonstrated a specific capacitance of 400 F g^?1 at a current density of 20 A g^?1 and superior cycling stability over 5000 cycles. The excellent electrochemical performance could be ascribed to the thin porous structure of the nanosheets, which provides a high specific surface area to increase the electrode–electrolyte contact area and facilitate rapid ion transport.     

A Porous Network of Bismuth Used as the Anode Material for High‐Energy‐Density Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are plagued by a lack of materials for reversible accommodation of the large‐sized K⁺ ion. Herein we present, the Bi anode in combination with the dimethoxyethane‐(DME) based electrolyte to deliver a remarkable capacity of ca. 400 mAh g^?1 and long cycle stability with three distinct two‐phase reactions of Bi? KBi₂?K₃Bi₂?K₃Bi. These are ascribed to the gradually developed three‐dimensional (3D) porous networks of Bi, which realizes fast kinetics and tolerance of its volume change during potassiation and depotassiation. The porosity is linked to the unprecedented movement of the surface Bi atoms interacting with DME molecules, as suggested by DFT calculations. A full KIB of Bi//DME‐based electrolyte//Prussian blue of K_0.72Fe[Fe(CN)₆] is demonstrated to present large energy density of 108.1 Wh kg^?1 with average discharge voltage of 2.8 V and capacity retention of 86.5 % after 350 cycles.     

A Hydrostable Cathode Material Based on the Layered P2@P3 Composite that Shows Redox Behavior for Copper in High‐Rate and Long‐Cycling Sodium‐Ion Batteries

Low‐cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium‐ion batteries. Biphasic Na_0.78Cu_0.27Zn_0.06Mn_0.67O₂ obtained via superficial atomic‐scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium‐ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X‐ray diffraction coupled with electron‐energy‐loss spectroscopy, a possible Cu^2+/3+ redox reaction mechanism has now been revealed.