High-performance sodium-ion full cell using tunnel and layered-type composite cathode

Abstract

Na_0.44MnO₂(NMO) powders are synthesized by auto combustion. At lower calcination temperature, carbothermal reductive environment preserves lamellar Birnessite type slab of NMO. A stress induced mechanism is proposed to explain the splitting of the lamellar nanosheet to NMO rods. TEM analyses confirm that the diffusion distance for Na⁺ ion extraction is much shorter than the growth direction to facilitate the extraction of Na⁺ from NMO lattice. Due to facile extraction of Na⁺ ions, remarkable 1st charge capacity ∼96 mAhg⁻¹ is obtained in NMO cathode. Composite of NMO and TiO₂ coated Na(Ni_1/3Fe_1/3Mn_1/3)O₂ (NFM) is made as a novel cathode for Na ion rechargeable cells. At 1C the discharge capacity of 0.7 NMO–0.3 NFM composite is reported to be 113 mAhg⁻¹ with a capacity retention of ∼80 % after 100 cycles. The composite cathode also exhibits superior rate performance with a discharge capacity ∼66 mAhg⁻¹ at 15C rate. In a voltage window of 1.0–4.0V, the discharge capacity of hard carbon and 0.7NMO – 0.3NFM full cell is measured to be 133 mAhg⁻¹ and 109 mAhg⁻¹ at 0.1 and 1C respectively. After 100 cycles, at 1C rate, we have reported 80 % capacity retention of the full cell.