Rational design of oxide/carbon composites to achieve superior rate-capability via enhanced lithium-ion transport across carbon to oxide. Issue 14 (21st March 2018)

• Record Type: Journal Article
• Authors: Jeong, Jun Hui; Kim, Myeong-Seong; Choi, Yeon Jun; Lee, Geon-Woo; Park, Byung Hoon; Lee, Suk-Woo; Roh, Kwang Chul; Kim, Kwang-Bum
• Is Part Of: Journal of materials chemistry. Volume 6:Issue 14(2018)
• Page Start: 6033
• Page End: 6044
• Publication Date: 2018-03-21
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c8ta00883c
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : The superior rate-capability of nano-perforated graphene wrapped Li4 Ti5 O12 composite indicate that lithium-ion transport across the carbon coating layer is critical to the rate capability of carbon-coated oxides. Abstract : Coating oxides with conductive carbon is a widely used strategy to improve the rate capability of oxides by enhancing their electronic conductivity. However, there is a growing concern that a carbon layer may hinder lithium-ion transport to oxides, thus limiting the rate capability. Nonetheless, this issue has not yet been thoroughly investigated, and whether lithium-ion transport across a carbon layer does indeed limit the rate capability remains unclear. To single out the effect of lithium-ion transport across a carbon layer on the rate capability, we propose the rational design and synthesis of nano-perforated graphene (NPG)-wrapped oxide composites using commercial Li4 Ti5 O12 (LTO) and LiFePO4 (both with a particle diameter of ∼70 nm), wherein the NPG has nano-perforations on the basal plane of graphene. As the number of nano-perforations in the composites increases, the rate capability significantly increases. For example, NPG-wrapped LTO shows a specific capacity of 117.9 mA h g −1 at 100C and could be stably charged–discharged even at 300C. The excellent rate capability is mainly due to the enhancement of lithium-ion transport through the nano-perforations of NPG. Cyclic voltammetry and impedance analyses reveal that the improved rate capability of NPG-wrapped LTO is closely associated with an increase in the area of electrochemically active sites of LTO in the composite due to the enhanced lithium-ion transport through the nano-perforations of NPG, indicating that lithium-ion transport across a carbon layer could limit the rate capability of oxides coated with highly conductive carbon. These salient results will provide further impetus to the design and synthesis of novel high-rate carbon-coated oxides.