Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel‐based energy technologies. High‐energy lithium‐metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology‐based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.

promising anode candidates for highenergy rechargeable batteries. [1] Nevertheless, the uncontrolled dendrite formation and poor reversible Li plating/stripping efficiency long hinder its practical application. Fundamentally, the reactive nature of Li metal can spontaneously trigger side reactions with the electrolyte and form a passivation layer (called solid electrolyte interphase, SEI). [2] The chemical heterogeneity and mechanical instability of SEI are generally considered as the reasons for dendrites formation. [3] Therefore, manipulating the electrolyte chemistry is considered as the most effective method, for it can directly impact the properties of SEI and alter Li + deposition behavior. [4] In the electrolyte, Li + is solvated by solvents and anions to form the Li + solvation sheath. [5] The Li + solvation sheath can diffuse freely in bulk electrolyte, which has a higher probability of touching Li surface. Once touching Li metal surface, the solvent molecules and anions from the solvation sheath will be reduced by electrons and compose the main components of SEI, thereby modulating Li + transport and deposition behaviors. [6] Due to the diverse reactivity and proportion in the Li + solvation sheath, the contributions from solvents and anions to the interface chemistry are distinctly different. [7] For the dilute electrolytes (esters and ethers), more solvent molecules dominated the Li + solvation sheath due to high ratio of solvent/anions (e.g., 11.6:1 in 1 m lithium hexafluorophosphate (LiPF 6 )-ethylene carbonate (EC)/diethyl carbonate (DEC)). The reduction species in the SEI depend on the reactivity and proportion of the components (solvents and anions) in the Li + solvation sheath. [8] With a high proportion of solvent molecules in the solvation sheath, the as-obtained SEI was principally composed of solvent-derived organic species (ROLi, RCOOLi, and ROCO 2 Li), accompanied with few inorganic species (LiF, Li 2 S, and Li 2 O) mainly originating from anions. [4a,9] Such solvent-derived SEI with highly resistive nature can bring about sluggish transport and uneven charge distribution of Li + , resulting in notorious dendrite growth with low Coulombic efficiency (CE, 80%). [10] Inducing F atoms to the molecular structure of solvent can tune the reactivity of the Li + solvation sheath. [11] For instance, fluoroethylene carbonate (FEC) has a relatively smaller lowest unoccupied molecular orbital (LUMO) than EC, which can be preferentially reduced to form a SEI The spatial distribution and transport characteristics of lithium ions (Li + ) in the electrochemical interface region of a lithium anode in a lithium ion battery directly determine Li + deposition behavior. The regulation of the Li + solvation sheath on the solid electrolyte interphase (SEI) by electrolyte chemistry is key but challenging. Here, 1 m lithium trifluoroacetate (LiTFA) is induced to the electrolyte to regulate the Li + solvation sheath, which significantly suppresses Li dendrite formation and enables a high Coulombic efficiency of...

Higher efficiency, lower cost refrigeration is needed for both large and small scale cooling. Refrigerators using entropy changes during cycles of stretching or hydrostatically compression of a solid are possible alternatives to the vapor-compression fridges found in homes. We show that high cooling results from twist changes for twisted, coiled, or supercoiled fibers, including those of natural rubber, NiTi, and polyethylene fishing line. By using opposite chiralities of twist and coiling, supercoiled natural rubber fibers and coiled fishing line fibers result that cool when stretched. A demonstrated twistbased device for cooling flowing water provides a high cooling energy and device efficiency. Theory describes the axial and spring index dependencies of twist-enhanced cooling and its origin in a phase transformation for polyethylene fibers.Summary: Twist-exploiting mechanocaloric cooling is demonstrated for rubber fibers, fishing line fibers, and NiTi shape-memory wires.3

Comprehensive understanding of the Li deposition chemistry from Li+ to Li atom is crucial for suppressing dendrite formation and growth.