Oxygen-regulated spontaneous solid electrolyte interphase enabling ultra-stable solid-state Na metal batteries.

Solid-state sodium metal batteries utilizing inorganic solid electrolytes (SEs) hold immense potentials such as intrinsical safety, high energy density, and environmental sustainability. However, the interfacial inhomogeneity/instability at the anode-SE interface usually triggers the penetration of sodium dendrites into the electrolyte, leading to short circuit and battery failure. Herein, confronting with the original nonuniform and high-resistance solid electrolyte interphase (SEI) at the Na-Na3Zr2Si2PO12 interface, an oxygen-regulated SEI innovative approach is proposed to enhance the cycling stability of anode-SEs interface, through a spontaneous reaction between the metallic sodium (containing trace amounts of oxygen) and the Na3Zr2Si2PO12 SE. The oxygen-regulated spontaneous SEI is thin, uniform, and kinetically stable to facilitate homogenous interfacial Na+ transportation. Benefitting from the optimized SEI, the assembled symmetric cell exhibits an ultra-stable sodium plating/stripping cycle for over 6600 h under a practical capacity of 3 mAh cm-2. Quasi-solid-state batteries with Na3V2(PO4)3 cathode deliver excellent cyclability over 500 cycles at a rate of 0.5 C (1 C = 117 mA cm-2) with a high capacity retention of 95.4%. This oxygen-regulated SEI strategy may offer a potential avenue for the future development of high-energy-density solid-state metal batteries.

A robust, highly reversible, mixed conducting sodium metal anode.

Sodium metal anode holds great promise in pursuing high-energy and sustainable rechargeable batteries, but severely suffers from fatal dendrite growth accompanied with huge volume change. Herein, a robust mixed conducting sodium metal anode is designed through incorporating NaSICON-type solid Na-ion conductor into bulk Na. A fast and continuous pathway for simultaneous transportation of electrons and Na+ is established throughout the composite anode. The intimate contact between Na-ion conducting phase and Na metallic phase constructs abundant two-phase boundaries for fast redox reactions. Further, the compact configuration of the composite anode substantially protects Na metal from being corroded by liquid organic electrolyte for the minimization of side reactions. Benefiting from the unique configuration, the composite anode shows highly reversible and durable Na plating/stripping behavior. The symmetric cells exhibit ultralong lifespan for over 700 h at 1 mA cm-2 with a high capacity of 5 mAh cm-2 and outstanding rate capability up to 8 mA cm-2 in the carbonate electrolyte. Full cells with Na3V2(PO4)3/C cathode demonstrate impressive cycling stability (capacity decay of 0.012% per cycle) and low charge/discharge polarization as well. This work provides new insights into rational design and development of robust sodium metal anode through an architecture engineering strategy for advanced rechargeable sodium batteries.