No abstract

A dissolution–redeposition reaction mechanism of the MnO2 cathode is directly visualized in rechargeable aqueous zinc-ion batteries via in situ Raman microscopy. MnO2 is reduced to Mn3+ during the discharge process, followed by a disproportionation reaction to form Mn2+ and Mn4+. The dissolved Mn2+ plays an important role in the battery chemistry. During the following charge process, the redeposition of Mn2+ forms a species with high Zn-content on the surface of the MnO2 cathode in the high-potential window. Moreover, an effective method that allows in operando observation of Jahn–Teller distortion of manganese is provided for the first time. This method uses in situ Raman microscopy to reveal the correlation between Jahn–Teller distortion and Mn–O bond length change.

Solid polymer electrolytes (SPEs) have the potential to enhance the safety and energy density of lithium batteries. However, poor interfacial contact between the lithium metal anode and SPE leads to high interfacial resistance and low specific capacity of the battery. In this work, we present a novel strategy to improve this solid–solid interface problem and maintain good interfacial contact during battery cycling by introducing an adaptive buffer layer (ABL) between the Li metal anode and SPE. The ABL consists of low molecular-weight polypropylene carbonate , poly­(ethylene oxide) (PEO), and lithium salt. Rheological experiments indicate that ABL is viscoelastic and that it flows with a higher viscosity compared to PEO-only SPE. ABL also has higher ionic conductivity than PEO-only SPE. In the presence of ABL, the interface resistance of the Li/ABL/SPE/LiFePO4 battery only increased 20% after 150 cycles, whereas that of the battery without ABL increased by 117%. In addition, because ABL makes a good solid–solid interface contact between the Li metal anode and SPE, the battery with ABL delivered an initial discharge specific capacity of >110 mA·h/g, which is nearly twice that of the battery without ABL, which is 60 mA·h/g. Moreover, ABL is able to maintain electrode–electrolyte interfacial contact during battery cycling, which stabilizes the battery Coulombic efficiency.