Electrically conductive single-walled carbon nanotube network for reducing Li plating on Graphite/Silicon anode

Abstract

To overcome the chasm for electric vehicles, it is crucial to ensure fast charging times for LIBs (lithiumion batteries). However, the low working potential of graphite can lead to lithium plating issues during fast charging. Several trigger conditions can exacerbate lithium plating. Especially, sluggish Li-ion solid diffusion within graphite particles, high state of charge (SOC), and high loading of graphite electrodes are conditions that can trigger lithium plating. Introducing silicon into the anode can be a solution lithium plating problem. Silicon has a high theoretical capacity which can reduce electrode thickness with same areal capacity and relatively higher lithiation potential which can reduce the likelihood of lithium plating. However, using silicon remains challenging. The significant volume changes during charge/discharge can lead to particle pulverization, thick SEI layer formation, and contact loss between particles. To address these intrinsic problems of silicon, single-walled carbon nanotubes (SWCNTs) which are 1D conductive additive are being introduced. SWCNTs are be known to improve the stability of silicon by formation of stable and efficient electron conduction network in graphite-silicon composite electrode. However, how SWCNTs mitigate lithium plating in graphite-silicon composite anodes on full cell system has not been reported. Herein, we investigate the mechanism of Li plating depending on the dimension of conductive additive in graphite-silicon composite electrode. We investigate the correlation between the degradation of each active material that interacts electrochemically with lithium separately and SWCNTs by a methodology comprising differential plots and integral calculus. Additionally, we newly devised novel evaluation method as “intentional lithium plating cycle” in half cell system to evaluate the amount of lithium plating and suggested the mechanism of Li plating in graphite/silicon composite electrode depending on the type of conductive additive. As this method is conducted by half cell, we could establish charging conditions similar to those of a full cell. And we could investigate the role of SWCNT for reducing Li plating in graphite-silicon composite electrode by using incremental capacity analysis.