Abstract
The role of the transition metal nature and Al2O3 coating on the surface reactivity of LiCoO2 and LiNi(1/3)Mn(1/3)Co(1/3)O2 (NMC) materials were studied by coupling chemisorption of gaseous probes molecules and X-ray photoelectron (XPS) spectroscopy. The XPS analyses have put in evidence the low reactivity of the LiMO2 materials toward basic gaseous probe (NH3). The reactivity toward SO2 gaseous probe is much larger (roughly more than 10 times) and strongly influenced by the nature of metal. Only one adsorption mode (redox process producing adsorbed sulfate species) was observed at the LiCoO2 surface, while NMC materials exhibit sulfate and sulfite species at the surface. On the basis of XPS analysis of bare materials and previous theoretical work, we propose that the acid-base adsorption mode involving the Ni(2+) cation is responsible for the sulfite species on the NMC surface. After Al2O3 coating, the surface reactivity was clearly decreasing for both LiCoO2 and NMC materials. In addition, for LiCoO2, the coating modifies the surface reactivity with the identification of both sulfate and sulfite species. This result is in line with a change in the adsorption mode from redox toward acid-base after Al/Co substitution. In the case of NMC materials, the coating induced a decrease of the sulfite species content at the surface. This phenomenon can be related to the cation mixing effect in the NMC.
Highlights
In the field of lithium ion battery, extensive studies have been carried out to improve the electrochemical performance of positive electrode materials
Crystallites size and shape were observed by a scanning electron microscopy (SEM) with Jeol Microprobe JAMP 9500F operating at the probe current of 1 × 10−10 A and 30 keV and a working distance of ∼20 mm
Concomitant theoretical studies have provided a clearer view of the adsorption mechanism of the SO2 gas probe on the LiCoO2 surface using density functional theory (DFT) calculations to explore the thermodynamically favorable SO2 adsorption modes on LiCoO2 and α-LiAlO2.14 This study demonstrates that the αLiAlO2 surface reactivity is governed by the Lewis basicity of surface oxide anions
Summary
In the field of lithium ion battery, extensive studies have been carried out to improve the electrochemical performance of positive electrode materials. Among the layered LiMO2 (M = 3d transition metal) with an α-NaFeO2 structural type, LiCoO2 started the field and dominated the Li-ion battery positive electrode material market due to its high energy density and cycling stability. LiCoO2 suffers from the high cost of cobalt, safety issues, and a rather low capacity Much research has been performed to explore alternative materials, including different cationic substitutions. Mixed transition metal oxides LiaNttixeMntnioxnC1o−16−2bxeOc2aus(e0.o3f3at≤tracxtive≤ch0a.r5a)ctehraisvteicsraencedivaewd idme uucshe depending on their composition. When these materials are charged to high voltages
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
