Surface Layer Formation on Thin-Film LiMn[sub 2]O[sub 4] Electrodes at Elevated Temperatures

Abstract

Thin-film LiMn2O4 electrodes, which were exposed to pure dimethyl carbonate (DMC) or to a mixture of ethylene carbonate (EC) and DMC (1:1 by volume) containing 1 M LiPF6 at elevated temperatures, were studied by using X-ray diffraction, current-sensing atomic force microscopy (CSAFM), cyclic voltammetry, ordinary Raman spectroscopy, and surface-enhanced Raman spectroscopy (SERS). Thin, electronically insulating surface layers were detected by CSAFM and SERS on all electrodes. The surface layer formed by exposure to DMC at 70°C was uniform and preserved the electrode structure, however, it led to complete electrode deactivation, probably due to loss of surface electronic conductivity and slower lithium-ion transport rates through the surface layer. A similar surface layer was formed when the electrodes were exposed to EC­DMC­LiPF6, however, the layer formed at 70°C did not prevent LiMn2O4 decomposition and consequent electrode capacity loss. In this case, manganese dissolution was observed, accompanied by the formation of λ­MnO2. SER spectra of the surface layers suggest that they were formed as a result of DMC decomposition at the LiMn2O4 surface. The SER spectra displayed bands characteristic of Li-O-R, carbonate, and carboxyl groups. Derivatives of carbon-oxygen triple bonds or silver-carbon-oxygen groups, which are possibly a result of interactions between the surface layer and silver microparticles, were also detected. © 2001 The Electrochemical Society. All rights reserved.

Improvement of electrochemical performance of LiMn2O4 composite cathode by ox-MWCNT addition for Li-ion battery

“…SEI film is an insulator for electron and a good conductor for lithium ion which can freely insert and deinsert through. It has been reported 20 that the SEI film on the cathode is composed of various lithium salts, including lithium carbonate(Li 2 CO 3 ), lithium alkoxides (ROLi), and carboxylic lithium (RCO 2 Li). R ct and CPE2 are the charge transfer resistance and corresponding double-layer capacitance, respectively.…”

Characterization of SEI layers on LiMn2O4 cathodes with in-situ spectroscopic ellipsometry

“…Before the injection of the electrolyte into the cell, the surface of the LiMn 2 O 4 electrode was "bare" and reacted rapidly with the electrolyte. According to prior work by our group and others [12,16,17] , which readily dissolves into solution:…”

“…Thin-film LiMn 2 O 4 electrodes were prepared by spin-coating a homogeneous precursor solution onto well-polished Pt substrates (diameter 2.54cm) followed the same procedure reported in our previous paper [12]. There were no additives (including 5 binders) in the electrode; therefore possible side reactions were avoided.…”

“…Peled (1979) introduced the idea of the SEI layer on alkali and alkaline earth metals in organic electrolytes [1]. SEI layer formation has been observed for various electrode materials such as Li foil, carbon, and transition metal oxides [2][3][4][5][6][7][8][9][10][11][12]. The SEI layer plays a key role in the electrochemical performance and calendar life of Li-ion batteries because it prevents the electrode surface from further reacting with the electrolyte components, thereby increasing the cell impedance and decreasing its cycling efficiency [13].…”

Interfacial Reactions of Intercalation Electrodes in Lithium Ion Batteries

“…The intermediate reconstructed surfaces formed at the electrolyte soak could be stabilized by the readily-formed SEI layer until after the surface reconstruction is completed at the initial charge-discharge process. Previous studies of the LiMn 2 O 4 electrode, which were investigated based on ex situ techniques under accelerated aging conditions, 11,36 suggested the structural changes from the original spinel to A-MnO 2 structures accompanied with the SEI layer Electrochemistry, 83(9), 701-706 (2015) formation. However, the phase transition process of the LiMn 2 O 4 and the direct evidence of the association with the SEI formation have not been elucidated, because the initial process could not be detected using the accelerated aging samples.…”