Lithium batteries that could be charged on exposure to sunlight will bring exciting new energy storage technologies. Here, we report a photorechargeable lithium battery employing nature-derived organic molecules as a photoactive and lithium storage electrode material. By absorbing sunlight of a desired frequency, lithiated tetrakislawsone electrodes generate electron–hole pairs. The holes oxidize the lithiated tetrakislawsone to tetrakislawsone while the generated electrons flow from the tetrakislawsone cathode to the Li metal anode. During electrochemical operation, the observed rise in charging current, specific capacity, and Coulombic efficiency under light irradiation in contrast to the absence of light indicates that the quinone-based organic electrode is acting as both photoactive and lithium storage material. Careful selection of electrode materials with optimal bandgap to absorb the intended frequency of sunlight and functional groups to accept Li-ions reversibly is a key to the progress of solar rechargeable batteries.
Although lithium–sulfur (Li–S) batteries are explored extensively, several features of the lithium polysulfides (LiPS) redox mechanism at the electrode/electrolyte interface still remain unclear. Though various in situ and ex situ characterization techniques have been deployed in recent years, many spatial aspects related to the local electrochemical phenomena of the Li-S electrode are not elucidated. Herein, we introduce the atomic-force-microscopy-based scanning electrochemical microscopy (AFM–SECM) technique to study the Li–S interfacial redox reactions at nanoscale spatial resolution in real time. In situ electrochemical and alternating current (AC) phase mappings of Li2S particle during oxidation directly distinguished the presence of both conducting and insulating regions within itself. During charging, the conducting part undergoes dissolution, whereas the insulating part, predominantly Li2S, chemically/electrochemically reacts with intermediate LiPS. At higher oxidation potentials, as-reacted LiPS turns into insulating products, which accumulate over cycling, resulting in reduction of active material utilization and ultimately leading to capacity fade. The interdependence of the topography and electrochemical oxidative behavior of Li2S on the carbon surface by AFM–SECM reveals the Li2S morphology–activity relationship and provides new insights into the capacity fading mechanism in Li–S batteries.
Nature-inspired solutions to energy storage are aimed at sustainability, cost-efficiency, and humanitarian issues surrounding current lithium ion battery (LIB) technologies. Tetrakislawsone (TKL), a tetramer derived from the natural tattooing dye henna, yields a promising cathode material for recyclable and environmentally friendly LIBs. Previously, small organic molecules as LIB materials have displayed precipitous capacity fading and poor cycling lifetimes due to their instability in organic electrolytes. Our study finds that tetrakislawsone exhibits stable gravimetric capacities exceeding 100 mAh g–1 for over 300 charge/discharge cycles owed to the coordination of four Li ions as well as the unique stability of lithium salts of TKL in electrolytes. The mechanistic investigation of metal ion binding was aided by DFT computations, solid-state NMR, and in situ spectroscopy studies revealing that the molecule adopts a nonplanar coordination geometry. This allows for reversible lithium ion binding between the carbonyl and hydroxyl functional groups of TKL subunits.
All-solid-state batteries using garnet-type solid-state electrolytes (SSEs) are promising candidates for safe, high energy density batteries due to their wide electrochemical stability window, high lithium-ion conductivity at room temperature, and the use of a lithium metal anode. However, garnet-type SSEs exhibit formidable challenges, including their instability in a moisture-containing atmosphere, high interfacial resistance, and the formation of lithium dendrites. Though several strategies have been deployed to alleviate the issues related to garnet-type SSEs against metallic lithium, most of the approaches fail to solve all the challenges. Herein, we demonstrate a surface modification strategy of the Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZT) garnet electrolyte by two-dimensional hexagonal boron nitride (h-BN) nanosheets to solve the interfacial issues. Detailed spectroscopic evidence elucidates that the h-BN interlayer effectively protects the LLZT from moisture-induced chemical degradation and suppresses the formation of adverse carbonate species for over 120 h in an open atmosphere. The h-BNcoated garnet SSE interface has shown a nearly 10-fold reduction in interfacial resistance value compared to the uncoated one and it exhibits stable lithium plating/stripping behavior for over 1400 cycles at 0.2 mA cm −2 . Advanced in situ Raman analysis reveals that the h-BN interlayers remain stable during cycling and inhibit the structural transformation of LLZT at the interface.
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