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.
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.
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