Boosting of reversible capacity delivered at a low voltage below 0.5 V in mildly expanded graphitized needle coke anode for a high-energy lithium ion battery

Abstract

The rate performance and cycle stability of graphitized needle coke (GNC) as anode are still limited by the sluggish kinetics and volume expansion during the Li ions intercalation and de-intercalation process. Especially, the output of energy density for lithium ion batteries (LIBs) is directly affected by the delithiation capacity below 0.5 V. Here, the mildly expanded graphitized needle coke (MEGNC) with the enlarged interlayer spacing from 0.346 to 0.352 nm is obtained by the two-step mild oxidation intercalation modification. The voltage plateau of MEGNC anode below 0.5 V is obviously broadened as compared to the initial GNC anode, contributing to the enhancement of Li storage below the low voltage plateau. Moreover, the coin full cell and pouch full cell configured with MEGNC anode exhibit much enhanced Li storage ability, energy density and better cycling stability than those full cells configured with GNC and commercial graphite anodes, demonstrating the practical application value of MEGNC. The superior anode behaviors of MEGNC including the increased effective capacity at low voltage and superior cyclic stability are mainly benefited from the enlarged interlayer spacing, which not only accelerates the Li ions diffusion rate, but also effectively alleviates the volume expansion and fragmentation during the Li ions intercalation process. In addition, the above result is further confirmed by the density functional theory simulation. This work provides an effective modification strategy for the NC-based graphite to enhance the delithiation capacity at a low voltage plateau, dedicated to improving the energy density and durability of LIBs.