Suppressing oxygen redox in layered oxide cathode of sodium-ion batteries with ribbon superstructure and solid-solution behavior

Abstract

Sodium-ion batteries (SIBs) are proved as one of the most acceptable candidates for replacing lithium-ion batteries in some fields by virtue of a similar “rocking chair” mechanism and the abundance of sodium. The voltage, rate performance, and energy density of these batteries are mainly determined by the cathodes. Hence, a Li-Ni-Co co-substituted P2-Na0.67[Li0.1(Mn0.7Ni0.2Co0.1)0.9]O2 (NLMNC) with ribbon superstructure is prepared with the aim of multi-ion synergistic modification. Owing to the addition of Ni and Co, the Jahn–Teller distortion of Mn can be suppressed corresponding with the improved structural stability, and a little bit of oxygen redox activities is triggered. When with the substitution of 10% Li, the X-ray diffraction (XRD) peaks of NLMNC show the ribbon superstructure at about 21° and 22°. The smooth charge/discharge profiles of the NLMNC cathode exhibit the solid-solution reaction. In addition, the platform at high voltage disappears corresponding with the existing oxygen redox activities being suppressed which may be related to the ribbon superstructure and the promotion of the Ni redox. Such NLMNC cathode can deliver a reversible discharge capacity of 123.5 mA h g–1 at 10 mA g–1. Even if the current density increases to 500 mA g–1, a reversible discharge capacity of 112.8 mA h g–1 still can be obtained. The distinguished cycling stability is related to the reversible migration of Li+ between the metal oxide layer and the interlayer and low volume change during cycling. It is also needing to be mentioned that the capacity retention of NLMNC cathode is about 94.4% (based on the highest discharge capacity) after 100 cycles. This work presents an effective route to develop high-performance cathodes for SIBs.