Li‐Rich Li[Li_1/6Fe_1/6Ni_1/6Mn_1/2]O₂ (LFNMO) Cathodes: Atomic Scale Insight on the Mechanisms of Cycling Decay and of the Improvement due to Cobalt Phosphate Surface Modification

Abstract

Lithium-rich Li[Li Fe Ni Mn ]O (0.4Li MnO -0.6LiFe Ni Mn O , LFNMO) is a new member of the xLi MnO ·(1 - x)LiMO family of high capacity-high voltage lithium-ion battery (LIB) cathodes. Unfortunately, it suffers from the severe degradation during cycling both in terms of reversible capacity and operating voltage. Here, the corresponding degradation occurring in LFNMO at an atomic scale has been documented for the first time, using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), as well as tracing the elemental crossover to the Li metal anode using X-ray photoelectron spectroscopy (XPS). It is also demonstrated that a cobalt phosphate surface treatment significantly boosts LFNMO cycling stability and rate capability. Due to cycling, the unmodified LFNMO undergoes extensive elemental dissolution (especially Mn) and O loss, forming Kirkendall-type voids. The associated structural degradation is from the as-synthesized R-3m layered structure to a disordered rock-salt phase. Prior to cycling, the cobalt phosphate coating is epitaxial, sharing the crystallography of the parent material. During cycling, a 2-3 nm thick disordered Co-rich rock-salt structure is formed as the outer shell, while the bulk material retains R-3m crystallography. These combined cathode-anode findings significantly advance the microstructural design principles for next-generation Li-rich cathode materials and coatings.

Inhibition of transition metals dissolution in cobalt-free cathode with ultrathin robust interphase in concentrated electrolyte

“…Our previous works indicated that voltage fade was significantly suppressed by replacing Co with Fe 35,36 . Unfortunately, the low coulombic efficiency during cycling has always existed but is rarely reported in Fe-substituted Li-rich cathode materials 20,[43][44][45] , which inevitably gives rise to poor cyclic performance and reduces battery life. In order to intuitively investigate the mechanism of low CE of LNFMO, the LNFMO electrodes were cycled in different concentrations of electrolyte at 0.1 C (20 mA g −1 ).…”

A Bifunctional-Modulated Conformal Li/Mn-Rich Layered Cathode for Fast-Charging, High Volumetric Density and Durable Li-Ion Full Cells

“…To ensure better interphase stability and improve the Li + diffusion, the surface of the MNC sample is firstly modified by a simple reported ionized solution coating method (ST-MNC) [ 40 ]. We chose Co-containing coating layers for the surface treatment considering that they contribute to improve the electrochemical performance of layered cathodes [ 26 , 40 ]. It has been reported that the using the completely ionized solution with lithium and cobalt acetate in ethanol to conduct the surface treatment could result in a stable Li x CoO 2 phase after heating treatment [ 40 ].…”

“…Among them, surface modification has been found to be effective as it can not only inhibit the phase transition and side reactions with the electrolytes or hydrogen fluoride, but also provide ion or/and electron highways in some cases [19][20][21][22][23][24][25][26]. Ion conductive coating materials such as Al 2 O 3 [21], AlF 3 [23,27], and phosphates [26] have been proved to facilitate ion diffusion and enhance the rate capability. Also, electron conductive materials such as carbon [22] and polypyrrole [25] have revealed the ability to accelerate charge transfer kinetics.…”

A Review of Lithium-Ion Battery Fire Suppression

“…LFP has a stable olivine structure and has attracted significant interest [12][13][14][15] due to low cost as it does not contain cobalt, has high average voltage and a low susceptibility to thermal runaway compared to NCM and LCO, providing a good balance between performance and safety [16][17][18]. To date, cathode materials with high capacity and voltage such as nickel- [19][20][21][22][23][24], manganese- [25] and lithium-rich [19,[25][26][27][28][29][30][31] materials, carbon-coated LFP nanospheres [32] and vanadium pentoxide [33] have been recognized. Higher contents of nickel and lithium increase the specific capacity of the cathode material but decrease thermal stability.…”