Enabling dendrite-free and high-rate lithium anode with a self-standing anionic-MOF separator

Lithium dendrites are a major issue that restrict the commercialization of lithium metal batteries. It is well-accepted that lithium dendrite nucleation can be suppressed by improving the Li+ transference number based on the classical Sand's time principle. Here, a self-standing anionic metal–organic framework (MOF)-based functional separator with small pores is developed by simple doctor-blading to accelerate Li+ transport for an improved lithium metal anode. The design of this separator is based on the nano-confined channels of the MOF and negatively charged moieties (–SO3−) on the surface. Benefiting from the strong electrostatic interaction between the negatively charged nanochannels and ions within the liquid electrolyte, the anion transport is effectively suppressed, while the lithium-ion transmission is accelerated. Consequently, a high Li+ transference number of up to 0.85 is achieved within the liquid electrolyte, which enables ultra-stable Li plating/stripping on the lithium metal anode for over 4000 h at a high current density of 5 mA cm−2. This work is expected to provide new insight into the development of dendrite-free and high-rate lithium metal batteries.