RESUMO
Lithium (Li) metal, a typical alkaline metal, has been hailed as the "holy grail" anode material for next generation batteries owing to its high theoretical capacity and low redox reaction potential. However, the uncontrolled Li plating/stripping issue of Li metal anodes, associated with polymorphous Li formation, "dead Li" accumulation, poor Coulombic efficiency, inferior cyclic stability, and hazardous safety risks (such as explosion), remains as one major roadblock for their practical applications. In principle, polymorphous Li deposits on Li metal anodes includes smooth Li (film-like Li) and a group of irregularly patterned Li (e.g., whisker-like Li (Li whiskers), moss-like Li (Li mosses), tree-like Li (Li dendrites), and their combinations). The nucleation and growth of these Li polymorphs are dominantly dependent on multiphysical fields, involving the ionic concentration field, electric field, stress field, and temperature field, etc. This review provides a clear picture and in-depth discussion on the classification and initiation/growth mechanisms of polymorphous Li from the new perspective of multiphysical fields, particularly for irregular Li patterns. Specifically, we discuss the impact of multiphysical fields' distribution and intensity on Li plating behavior as well as their connection with the electrochemical and metallurgical properties of Li metal and some other factors (e.g., electrolyte composition, solid electrolyte interphase (SEI) layer, and initial nuclei states). Accordingly, the studies on the progress for delaying/suppressing/redirecting irregular Li evolution to enhance the stability and safety performance of Li metal batteries are reviewed, which are also categorized based on the multiphysical fields. Finally, an overview of the existing challenges and the future development directions of metal anodes are summarized and prospected.
RESUMO
Manganese dioxide (MnO2) with a conversion mechanism is regarded as a promising anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity (â¼1223 mA h g-1) and environmental benignity as well as low cost. However, it suffers from insufficient rate capability and poor cyclic stability. To circumvent this obstacle, semiconducting polypyrrole coated-δ-MnO2 nanosheet arrays on nickel foam (denoted as MnO2@PPy/NF) are prepared via hydrothermal growth of MnO2 followed by the electrodeposition of PPy on the anode in LIBs. The electrode with â¼50 nm thick PPy coating exhibits an outstanding overall electrochemical performance. Specifically, a high rate capability is obtained with â¼430 mA h g-1 of discharge capacity at a high current density of 2.67 A g-1 and more than 95% capacity is retained after over 120 cycles at a current rate of 0.86 A g-1. These high electrochemical performances are attributed to the special structure which shortens the ion diffusion pathway, accelerates charge transfer, and alleviates volume change in the charging/discharging process, suggesting a promising route for designing a conversion-type anode material for LIBs.
RESUMO
Aqueous batteries are promising energy storage systems but are hindered by the limited selection of anodes and narrow electrochemical window to achieve satisfactory cyclability and decent energy density. Here, we design aqueous hybrid Na-Zn batteries by using a carbon-coated Zn (Zn@C) anode, 8 M NaClO4 + 0.4 M Zn(CF3SO3)2 concentrated electrolyte coupled with NASICON-structured cathodes. The Zn@C anode achieves stable Zn stripping/plating and improved kinetics without Zn dendrite formation due to the porous carbon film facilitating homogeneous current distribution and Zn deposition. Furthermore, the concentrated electrolyte offers a large electrochemical window (â¼2.5 V) and permits stable cycling of cathodes. As a result, the hybrid batteries exhibit extraordinary performance including high voltage, high energy density (100-150 Wh kg-1 for half battery and 71 Wh kg-1 for full battery), and excellent cycling stability of 1000 cycles.