Formation of the Spinel Phase in the Layered Composite Cathode Used in Li-Ion Batteries

Abstract

Pristine Li-rich layered cathodes, such as Li(1.2)Ni(0.2)Mn(0.6)O(2) and Li(1.2)Ni(0.1)Mn(0.525)Co(0.175)O(2), were identified to exist in two different structures: LiMO(2)R3[overline]m and Li(2)MO(3)C2/m phases. Upon 300 cycles of charge/discharge, both phases gradually transform to the spinel structure. The transition from LiMO(2)R3[overline]m to spinel is accomplished through the migration of transition metal ions to the Li site without breaking down the lattice, leading to the formation of mosaic structured spinel grains within the parent particle. In contrast, transition from Li(2)MO(3)C2/m to spinel involves removal of Li(+) and O(2-), which produces large lattice strain and leads to the breakdown of the parent lattice. The newly formed spinel grains show random orientation within the same particle. Cracks and pores were also noticed within some layered nanoparticles after cycling, which is believed to be the consequence of the lattice breakdown and vacancy condensation upon removal of lithium ions. The AlF(3)-coating can partially relieve the spinel formation in the layered structure during cycling, resulting in a slower capacity decay. However, the AlF(3)-coating on the layered structure cannot ultimately stop the spinel formation. The observation of structure transition characteristics discussed in this paper provides direct explanation for the observed gradual capacity loss and poor rate performance of the layered composite. It also provides clues about how to improve the materials structure in order to improve electrochemical performance.

Rechargeable lithium batteries and beyond: Progress, challenges, and future directions

“…12 and LiFePO 4 that has an olivine-type structure. 13 Although NCA provides a slightly higher practical capacity (160-180 mAh/g) than LiCoO 2 , its thermal instability on delithiation due to the presence of the high valence Ni compromises the safety of Li-ion cells.…”

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

“…Due to the structural and chemical complexities of these layered structures, their fading mechanisms have not been fully resolved. Electron microscopy studies indicated that, in lithium and manganese-rich materials, the capacity fading and voltage decay were partially attributed to structural reconstruction inducing a transition from the layered structure to spinel and/or rock-salt structures at the surface and/or in the bulk 5,17,25,26 . A recent study investigated the atomic structure of Li 2 MnO 3 after partial delithiation and re-lithiation to enable improved understanding of lithium-rich/ manganese-rich materials 27 .…”

Study of the Failure Mechanisms of LiNi0.8Mn0.1Co0.1O2Cathode Material for Lithium Ion Batteries

“…19,22,23 However, to obtain such a capacity, these materials must be cycled over a wide potential range of 2.5-4.6 V (vs. Li + /Li), which may be challenging for the current carbonate-based electrolytes. Major issues such as large irreversible capacity (IRC), 19,33,34 voltage fade upon cycling 22,[35][36][37][38][39][40] and poor rate capability 22,41,42 have hindered the application of these materials. * Electrochemical Society Student Member.…”