▎ 摘　　要

Graphite has been employed as anode material of lithium ion batteries due to its low cost, unique layered structure, and high conductivity; however, the small interlayer spacing and poor rate capability limit its application in sodium ion batteries. To address these issues, the interlayer spacing of graphene oxide (GO) was controllably enlarged through K+ and Ca2+ pillaring by the electrostatic interaction between the negatively charged GO sheets and the positively charged K+/Ca2+. The K+/Ca2+ pillared in the interlayers of GO can controllably expand the interlayer spacing from 0.78 to 1.01 nm by regulating the K+/Ca2+ concentrations. The K+/Ca2+-pillared GO (K+/Ca2+-GO) exhibits high Na+ ion storage performance because of expanded interlayer spacing, showing large Na+ ion diffusion coefficient (the largest DNa+ is 43.8 x 10(-15) cm(2) s(-1)) and high reversible specific capacity (199.3 mAh g(-1) at 0.1 A g(-1)). Meanwhile, the 2D layered structure of GO is stabilized by the pillar effects of K+/Ca2+ to realize a superior cycle stability of Na+ insertion/extraction. The relations between the interlayer spacing of K+/Ca2+-GO and rate capability are studied and an optimum interlayer spacing of K+/Ca2+-GO for high rate Na+ storage (0.84 nm and 1.01 nm for K+-GO and Ca2+-GO) is obtained. The results provide an essential reference for design of high rate 2D energy storage materials.