PNNL

Abstract

Stationary electric energy storage devices (rechargeable batteries) have gained increasing prominence due to great market needs, such as smoothing availability of renewable energy resources and supporting the reliability of the electric grid. However, stationary application of conventional lithium ion battery technologies is rather limited for the frequency regulation due to its high cost and limited life cycle. With regard to raw materials avilability, sodium based batteries are better positioned than lithium batteries due to the abandent resource of sodium in the earth’s crust. The sodium-nickel chloride (Na-NiCl2) battery, one of the most attractive stationary battery technologies, is hindered from further market penetration by its high material cost (Ni cost) and fast material degradation at its high operating temperature. Here, we demonstrate a design of a core–shell microarchitecture cathode—nickel-coated graphite—with a graphite core to maintain electrochemically active surface area and structural integrity of the electron percolation pathway while using 40% less Ni than conventional Na-NiCl2 batteries. An initial energy density of 133 Wh/kg (at ~C/4) and energy efficiency of 94% are achieved at an intermediate temperature of 190°C. More importantly, the battery degradation rate is as low as 0.005% per cycle, which is equivalent to maintaining 80% of the initial discharge energy after more than 3,000 cycles.