2D composites with S doping into N-rich carbon nanosheets are fabricated, whose interlayer distance becomes large enough for Na insertion and diffusion. The large surface area and stable structure also provide more sites for Na adsorption, leading to high Na-storage capacity and excellent rate performance. Moreover, Faradaic reactions between Na and tightly bound S is beneficial for further improvement of Na-storage capacity.

For developing energy storage devices with both high energy and power density,l ithium-ion hybrid supercapacitors (LIHSs) are the optimal candidate to bridge the gap between lithium-ion batteries (LIBs) and conventional supercapacitors. AL IHS consists of ac apacitor-typec athode and aL IB-typea node.H owever,t he particle size of LIB-type anode materials shouldb ew ithin % 10 nm to overcome the sluggish ion diffusion in the bulk. In addition, capacitor-type cathodem aterials are required to possessh igh capacitance to match with LIB-type anodes. Meanwhile, pre-lithiation provesa ne ffective strategy to achieve high cell voltages and high energy density accordingly.I nt his review we first summarize the requirement on electrode materials for LIHSs, and then propose two levels of LIHSs with the clarification of true LIHSs according to the energy and power density.F inally,w egive an outlook for future LIHSs. SchoolofM aterialsS cience and Engineering NationalInstitute for Advanced MaterialsThe ORCID identification number(s)for the author(s)oft his article can be found under http://dx.