Tattooing Dye as a Green Electrode Material for Lithium Batteries

Lawsone (2‐hydroxy‐1,4‐naphthoquinone), a naturally derived red‐orange dye, is investigated as a promising cathode material for next‐generation lithium batteries. Lithium cells based on lawsone cathode display a high discharge capacity of 280 mA h g −1 (99% theoretical capacity), a high energy density of 664 W h kg −1 , and long life of 1000 cycles at 0.5 C along with good rate performance up to 5 C. These results represent significant improvements from previously reported organic cathode materials, and surpass those of conventional lithium batteries based on LiCoO 2 cathodes (140 mA h g −1 and 520 W h kg −1 , respectively). Its success stems from the unique 2D planar packing of lawsone molecules, with maximized overlap of adjacent p orbitals for redox active sites. The result is the simultaneous enhancement of electrical and ionic conductivities that are an order of magnitude higher than those of other synthetic quinones. Given that lawsone is derived from the henna plant and has long been used as a dye for human hair and skin, this work may open a new chapter in the design of future green batteries.