Understanding the Influence of Nanocarbon Conducting Modes on the Rate Performance of Lifepo4 Cathode in Lithium Ion Batteries

Abstract

We report on an efficient and practical conducting mode built up by ternary conductive additive for boosting the electrochemical performance of LiFePO₄ cathode in lithium ion batteries. The influence on the conductivity, rate capability as well as the continuous conductive paths of the resulting electrode is investigated. Carbon nanotubes (CNTs) with long-range electronic conduction are ultimately homogeneously dispersed (mono-dispersed) in electrode slurry, which connect the short-range conductive regions together formed by graphene sheets. Importantly, CNTs could provide more open channels for electrons and ions transportation, compared with the blocking function of graphene sheets. Herein, it is found that low contents of graphene sheet are unable to build up continuous conductive networks thus causing degraded rate capability compared with higher contents of them. Low-content graphene regions are then bridged by mono-dispersed CNTs to construct a complete conductive network, enable the hybrids having both an improved electrically conductivity and an electrons/ions open channels. Furthermore, combining a small number of carbon black as supplementary conducive point, an efficient and practical conducting mode called "plane-to-line-to-point" is demonstrated. Such conducting mode can construct both short-range/long-range electronic conduction and open ions channels, while also having conductive points all over the uncovered area of LiFePO₄ cathode.

Keywords: Lithium ion batteries, Conductive additive, LiFePO4 cathode, Carbon nanotubes, graphene, electrons/ions open channels