Building ultraconformal protective layers on both secondary and primary particles of layered lithium transition metal oxide cathodes

A technological breakthrough on layered lithium transition metal oxide cathodes offers a promising design strategy for Ni-rich cathodes towards high-energy, long-life and safe lithium-ion batteries.  This new study reported by Prof. Chen Guohua and his research team of the PolyU Department of Mechanical Engineering was published in the high impact international journal “Nature Energy”.

Nature Energy Vol. 4, pages 484–494 (2019). 13 May 2019

Read more at https://onlinelibrary.wiley.com/doi/10.1002/er.4176.

Abstract

Despite their relatively high capacity, layered lithium transition metal oxides suffer from crystal and interfacial structural instability under aggressive electrochemical and thermal driving forces, leading to rapid performance degradation and severe safety concerns. Here we report a transformative approach using an oxidative chemical vapour deposition technique to build a protective conductive polymer (poly(3,4-ethylenedioxythiophene)) skin on layered oxide cathode materials. The ultraconformal poly(3,4-ethylenedioxythiophene) skin facilitates the transport of lithium ions and electrons, significantly suppresses the undesired layered to spinel/rock-salt phase transformation and the associated oxygen loss, mitigates intergranular and intragranular mechanical cracking, and effectively stabilizes the cathode–electrolyte interface. This approach remarkably enhances the capacity and thermal stability under high-voltage operation. Building a protective skin at both secondary and primary particle levels of layered oxides offers a promising design strategy for Ni-rich cathodes towards high-energy, long-life and safe lithium-ion batteries.

Fig. 1: The oCVD process and particle structural differences between different coatings.

Fig. 2: Surface characterization confirming the formation of PEDOT skin.

Fig. 3: TEM results confirming PEDOT coating on secondary/primary particles of NCM cathodes.

Fig. 4: In situ synchrotron HEXRD characterization of bare NCM111 and 60-PEDOT@NCM111 cathodes during charge–discharge.