Nickel-rich layered oxides have been identified as the most promising commercial cathode materials for lithium-ion batteries (LIBs) for their high theoretical specific capacity. However, the poor cycling stability of nickel-rich cathode materials is one of the major barriers for the large-scale usage of LIBs. The existing obstructions that suppress the capacity degradation of nickel-rich cathode materials are as a result of phase transition, mechanical instability, intergranular cracks, side reaction, oxygen loss, and thermal instability during cycling. Core–shell structures, oxidating precursors, electrolyte additives, doping/coating and synthesizing single crystals have been identified as effective methods to improve cycling stability of nickel-rich cathode materials. Herein, recent progress of surface modification, e.g. coating and doping, in nickel-rich cathode materials are summarized based on Periodic table to provide a clear understanding. Electrochemical performances and mechanisms of modified structure are discussed in detail. It is hoped that an overview of synthesis and surface modification can be presented and a perspective of nickel-rich materials in LIBs can be given.

The capacitance loss caused by slow electron and ion migration kinetics in thick electrode with high-mass loading has been regarded as a great challenge in the field of electrochemical energy storage. Herein, we demonstrate a facile electrochemical deposition method for coating the heterostructured Ti₃C₂T_x/WO_x onto flexible carbon cloth (Ti₃C₂T_x/WO_x@CC). In the Ti₃C₂T_x/WO_x heterojunction, the mixed-valence WO_x core provides abundant active sites for H⁺ ions accommodation, while Ti₃C₂T_x shell can not only prevent peeling off the thick WO_x but also act as an interconnected conductive network. The Ti₃C₂T_x/WO_x@CC flexible electrode with an ultrahigh mass loading of 34.9 mg·cm⁻² exhibits a high areal capacitance of 5.73 F·cm⁻² at 5 mA·cm⁻² and excellent rate capability. Notably, the Ti₃C₂T_x/WO_x@CC electrode under such a high mass loading still delivers a gravimetric capacitance of 164 F·g⁻¹ and areal capacitance of Ti₃C₂T_x/WO_x@CC electrode increases linearly with the WO_x mass loading. Furthermore, a symmetrical supercapacitor assembled with Ti₃C₂T_x/WO_x@CC electrode exhibits a good areal energy density of 96.8 μWh·cm⁻² at a power density of 1.5 mW·cm⁻². This work verifies high mass loading of active materials per unit electrode area for charge storage of supercapacitors in limited space, indicating the great potential in the development of commercially available thick metal-oxide film supercapacitors.