Science and Technology of Electrically Conductive Nitrogen-Ultrananocrystalline Diamond (N-UNCD)-Coated Natural Graphite-Copper Anode for New Long Life Lithium Ion Battery

摘要

Although Li-ion batteries (LIBs) are powering electric cars (GM's Volt), problems still exist in terms of performance, mainly because current LIBs feature natural graphite (NG)-based anodes, which exhibit large irreversible capacity loss and short charging-discharging cycling life induced by chemical reactions between Li-ion inserted NG and organic electrolyte. This report shows that this problem is overcome by using a novel nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) encapsulated NG/copper complex anodes. N-UNCD films (～5-10 nm grain size) exhibit electrically conductive grain boundaries induced by nitrogen incorporation into the boundaries, satisfying carbon sp2 dangling bonds and providing electrons for conduction. In addition, N-UNCD films provide excellent chemical inertness, electronic/lithium ionic conductivity, and excellent lithium ions permeation between the electrolyte and the N-UNCD encapsulated NG matrix of NG/Cu anodes. N-UNCD enables robust solid electrolyte interphase (SEI) formed by anode/electrolyte chemical reactions and suppresses stress induced cracks of the SEI and NG particles and the subsequent loss of anode conductivity. X-ray diffraction and chemical analysis proved the integrity of N-UNCD/NG/Cu anodes and provided understanding of the new robust anode performance to enable next generation LIBs with potentially 10x longer life and superior performance than current LIBs.