Dynamic spatial progression of isolated lithium during battery operations.

The increasing demand for next-generation energy storage systems necessitates the development of high-performance lithium batteries 1-3 . Unfortunately, current Li anodes exhibit rapid capacity decay and a short cycle life 4-6 , owing to the continuous generation of solid electrolyte interface 7,8 and isolated Li (i-Li) 9-11 . The formation of i-Li during the nonuniform dissolution of Li dendrites 12 leads to a substantial capacity loss in lithium batteries under most testing conditions 13 . Because i-Li loses electrical connection with the current collector, it has been considered electrochemically inactive or 'dead' in batteries 14,15 . Contradicting this commonly accepted presumption, here we show that i-Li is highly responsive to battery operations, owing to its dynamic polarization to the electric field in the electrolyte. Simultaneous Li deposition and dissolution occurs on two ends of the i-Li, leading to its spatial progression toward the cathode (anode) during charge (discharge). Revealed by our simulation results, the progression rate of i-Li is mainly affected by its length, orientation and the applied current density. Moreover, we successfully demonstrate the recovery of i-Li in Cu-Li cells with >100% Coulombic efficiency and realize LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC)-Li full cells with extended cycle life.