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Abstract: The instability of lithium (Li) metal anodes due to dendritic growth and low Coulombic efficiency (CE) hinders the practical application of high‐energy‐density Li metal batteries. Here, the systematic studies of improving the stability of Li metal anodes and the electrochemical performance of Li metal batteries through the addition of combinational additives and the optimization of solvent compositions in dual‐salt/carbonate electrolytes are reported. A dendrite‐free and high CE of 98.1% for Li metal anode is achieved. The well‐protected Li metal anode and the excellent cyclability and rate capability of the 4‐V Li metal batteries are obtained. This is attributed to the formation of a robust, denser, more polymeric, and higher ionic conductive surface film on the Li metal anode via the electrochemical reductive decompositions of the electrolyte components and the ring‐opening polymerization of additives and cyclic carbonate solvents. The key findings of this work indicate that the optimization of solvent compositions and the manipulation of additives are facile and effective ways to enhance the performances of Li metal batteries. [ABSTRACT FROM AUTHOR]

Abstract: The stability of various polymer binders was systematically investigated in the oxygen-rich environment required for the operation of Li–O2 batteries. Due to the coverage on air electrode surface by the discharge products and decomposition products of the electrolyte during the discharge process of Li–O2 batteries, the binder in the air electrode is hard to be detected making the evaluation of its stability problematic. Therefore, stability of the binder polymers against the reduced oxygen species generated during the discharge process was investigated by ball milling the polymers with KO2 and Li2O2, respectively. Most of the studied polymers are unstable under these conditions and their decomposition mechanisms are proposed according to the analyzed products. Polyethylene was found to exhibit excellent stability when exposed to superoxide and peroxide species and is suggested as a robust binder for air electrodes. In addition, the binding strength of the polymer significantly affects the discharge performance of Li–O2 batteries. [Copyright &y& Elsevier]

Abstract: The effects of six types of aprotic organic solvents on the discharge performance and discharge products in Li-O2 batteries are systematically investigated. A large amount of Li2O2 is identified in the air electrodes discharged in glyme-based electrolytes, while only a small amount of Li2O2 is detected in the air electrodes discharged in the electrolytes of nitrile, ionic liquid, phosphate, and sulfoxide. Li2CO3 and LiF are also found as byproducts whose compositions are related to the solvents. Li2CO3 is produced from oxidation and decomposition of the solvent, not from the oxidation of the carbon-based air electrode, as revealed by using a 13C-labeled carbon electrode and the solid-state 13C-magic angle spinning nuclear magnetic resonance technique. LiF in the discharge products can be attributed to the attack of superoxide radical anions to the Teflon binder and/or the F-containing imide salt. The formation of these byproducts will significantly reduce the Coulombic efficiency and cycle life of the Li-air batteries. Among the studied solvents, dibutyl diglyme is the suitable solvent for Li-O2 batteries based on its overall properties. However, better electrolytes that can ensure the formation of Li2O2 but minimize other reaction products need to be further investigated for long cycling rechargeable Li-air batteries. [Copyright &y& Elsevier]

Abstract: The Li–O2 chemistry in nonaqueous liquid carbonate electrolytes and the underlying reason for its limited reversibility was systematically investigated. X-ray diffraction data showed that regardless of discharge depth lithium alkylcarbonates (lithium propylenedicarbonate (LPDC), or lithium ethylenedicarbonate (LEDC), with other related derivatives) and lithium carbonate (Li2CO3) are constantly the main discharge products, while lithium peroxide (Li2O2) or lithium oxide (Li2O) is hardly detected. These lithium alkylcarbonates are generated from the reductive decomposition of the corresponding carbonate solvents initiated by the attack of superoxide radical anions. More significantly, in situ gas chromatography/mass spectroscopy analysis revealed that Li2CO3 and Li2O cannot be oxidized even when charged to 4.6V vs. Li/Li+, while LPDC, LEDC and Li2O2 are readily oxidized, with CO2 and CO released from LPDC and LEDC and O2 evolved from Li2O2. Therefore, the apparent reversibility of Li–O2 chemistry in an organic carbonate-based electrolyte is actually an unsustainable process that consists of (1) the formation of lithium alkylcarbonates through the reductive decomposition of carbonate solvents during discharging and (2) the subsequent oxidation of these same alkylcarbonates during charging. Therefore, a stable electrolyte that does not lead to an irreversible by-product formation during discharging and charging is necessary for truly rechargeable Li–O2 batteries. [Copyright &y& Elsevier]