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 dendrites¹² leads to a substantial capacity loss in lithium batteries under most testing conditions¹³. 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_0.5Mn_0.3Co_0.2O₂ (NMC)-Li full cells with extended cycle life.