Negatively charged separators facilitating lithium-ion conduction to stabilize lithium metal anodes

Abstract

Lithium metal has been considered a promising anode material for lithium secondary batteries due to its low intercalation potential and high specific capacity. Nevertheless, the application of Li metal anodes on a large scale is still hampered by safety issues caused by the growth of uncontrollable Li dendrites during the repeated cycling process. From the viewpoint of the dendrite nucleation mechanism, constructing a negatively charged separator (NCS) to immobilize the anion within the electrolyte can suppress the free transport of the anion, which can prolong the formation of the space charge region. Thus, it can achieve the purpose of inhibiting lithium dendrite nucleation. Herein, based on polyvinylidene fluoride (PVDF) polymers, C–F groups with high-electronegativity in their molecular chains can immobilize anions in the electrolyte (PF₆⁻ ions) based on a strong bonding force. Furthermore, the as-prepared NCS displays a high porosity with an interconnected porous structure that facilitates ion transport, thus enabling selective and fast Li⁺ transport. The NCS constructed in this work exhibits a high Li⁺ conductivity of 0.37 mS cm⁻¹. As a result, Li/Li symmetric batteries with the NCS can achieve a long-term stable cycling of 2000 h at a high current density of 2 mA cm⁻². In addition, a full LiFePO₄/Li cell assembled using the NCS shows excellent rate capability and cycle stability. This work is expected to contribute to the development of dendrite-free lithium metal batteries through the construction of a NCS to regulate ion transport.