Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteries

Chunyang Wang,Lili Han,Rui Zhang,Hao Cheng,Linqin Mu,Kim Kisslinger,Peichao Zou,Yang Ren,Penghui Cao,Feng Lin,Huolin L Xin

doi:10.1016/j.matt.2021.03.012

Abstract

Summary Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.

Highlights

Efforts to develop next-generation battery cells and modules that reduce battery cost, increase battery life, and improve its performance and safety are essential to deploying lithium-ion batteries (LIBs) in vehicles and grid power systems
LNO and a newly developed Ti/Mg codoped LNO7 layered cathodes were chosen as model materials, and both were charged to 4.4 V at 1.5 cycles for the study
The unidirectional streaking of the Bragg reflections along the [003] direction in the electron diffraction pattern (EDP) is present due to the formation of two-dimensional (2D) planar type defects parallel to the (003) planes

Summary

Introduction

Efforts to develop next-generation battery cells and modules that reduce battery cost, increase battery life, and improve its performance and safety are essential to deploying lithium-ion batteries (LIBs) in vehicles and grid power systems. Even though nickel-rich compounds, such as LiNi1ÀxÀyMnxCoyO2 (NMC) and LiNi1ÀxÀyCoxAlyO2 (NCA) materials, have dominated the cathode materials market for battery electric vehicles,[1,2,3] the high volatility of the cobalt price and the fact that cobalt is sourced from a single geopolitical region has made the elimination of cobalt from cathode chemistry a pressing need for the automotive industry. The extraction of Li from LNO causes a detrimental phase transformation that involves considerable volume shrinkage and thereby deteriorated capacity retention and structural stability.[16,19]

Results

Discussion

Conclusion