Development and Characterization of High-Performance Sodium-Ion Cells based on Layered Oxide and Hard Carbon

This paper reports the development and characterization of high-performance sodium-ion cells based on a starch-derived hard carbon anode and a mixed layered oxide cathode with the overall composition of P2/P3/O2-Na0.76Mn0.5Ni0.3Fe0.1Mg0.1O2. At first, both materials are tested in sodium-metal half cells to demonstrate the cycling performance. On the basis of this electrochemical characterization, the systematic development of sodium-ion cells is shown. Special attention is drawn towards activation, balancing, voltage range, as well as charging procedure. Important parameters such as energy and voltage efficiency, the influence of the constant voltage step at the end of the charge, as well as the potential and voltage profiles are discussed in greater detail. The developed sodium-ion cells show high specific energies (200–240 W h per kg of cathode and anode active materials), high average discharge voltages (3.3 V), high energy efficiencies, and extraordinary long-term cycling stability (e.g. 80 % capacity retention after 700 cycles). This performance underlines the beneficial combination of hard carbon and layered oxides and demonstrates sodium-ion batteries to be a promising energy-storage technology.