Radially aligned hierarchical columnar structure as a cathode material for high energy density sodium-ion batteries

Delivery of high capacity with good retention is a challenge in developing cathodes for rechargeable sodium-ion batteries. Here we present a radially aligned hierarchical columnar structure in spherical particles with varied chemical composition from the inner end (Na[Ni0.75Co0.02Mn0.23]O2) to the outer end (Na[Ni0.58Co0.06Mn0.36]O2) of the structure. With this cathode material, we show that an electrochemical reaction based on Ni2+/3+/4+ is readily available to deliver a discharge capacity of 157 mAh (g-oxide)−1 (15 mA g−1), a capacity retention of 80% (125 mAh g−1) during 300 cycles in combination with a hard carbon anode, and a rate capability of 132.6 mAh g-1 (1,500 mA g-1, 10 C-rate). The cathode also exhibits good temperature performance even at −20°C. These results originate from rather unique chemistry of the cathode material, which enables the Ni redox reaction and minimizes the surface area contacting corrosive electrolyte.