Adsorption and Reaction Branching of Molecular Carbonates on Lithiated C(0001) Substrates

Abstract

The desorption and interactions of ethylene carbonate (EC) and dimethyl carbonate (DMC) with clean and lithiated graphite substrates were measured by temperature-programmed desorption (TPD) and reaction (TPR) methods under UHV conditions. Both EC and DMC interact weakly with the clean C(0001) surface with adsorption energies of 0.60 ± 0.06 and 0.64 ± 0.05 eV, respectively. Addition of Li+ to the C(0001) substrate significantly increases the binding energies of molecular carbonates, and the range of measured values is indicative of EC solvation of lithium ions. EC undergoes complete decomposition on metallic Li films. Organolithium products were quantified by TPR, and the amount of lithium carbonate product was determined by detailed mass balance analysis. Decomposition of 1.5 L of EC resulted in the formation of 0.64 ± 0.12 L of lithium ethylene dicarbonate, 0.40 ± 0.05 L of lithium ethylene glycolate, and 0.5 ± 0.2 L of lithium carbonate. The branching ratio at the immediate EC–metallic lithium interface was determined as 70.% organolithium products vs 30% inorganic lithium product.

Interaction of Ultrathin Films of Ethylene Carbonate with Oxidized and Reduced Lithium Cobalt Oxide—A Model Study of the Cathode|Electrolyte Interface in Li‐Ion Batteries

“…In the present case, reaction with lithium atoms has to be considered as well, if these become mobile at the interface at elevated temperatures. Therefore, Li‐containing decomposition products such as Li 2 CO 3 , ROCO 2 Li, lithium ethylene dicarbonate (CH 2 OCO 2 Li) 2 , and Li 2 O have to be considered as well . We also have to take into account that besides these decomposition products Li could reside on the surface as a complexed cation (Li + (EC) n ) .…”

“…Therefore, Li‐containing decomposition products such as Li 2 CO 3 , ROCO 2 Li, lithium ethylene dicarbonate (CH 2 OCO 2 Li) 2 , and Li 2 O have to be considered as well . We also have to take into account that besides these decomposition products Li could reside on the surface as a complexed cation (Li + (EC) n ) . For the present XPS analysis, we consider potential decomposition products containing CO, COC, and CC (CH) bonds, which according to the literature results in C 1s BEs of ≈288, ≈287, and ≈284–285 eV, respectively …”

“…One possible way to determine the initial stages of the SEI formation at the EEI at the atomic/molecular level involves the use of surface science techniques, studying the interaction of individual components of electrolytes, such as the typical key component EC (or other electrolyte components like ionic liquids), with well‐defined model electrodes under idealized ultrahigh‐vacuum (UHV) conditions, which is focus of the ongoing work in our laboratory. Following a previous study on the interaction of EC with Li‐free and lithiated highly oriented pyrolytic graphite (HOPG) as model for the anode, we here report the results of a similar type of study on the interaction of EC with well‐defined LiCoO 2 electrode surfaces, both fully oxidized LiCoO 2 and partly reduced LiCoO 2− δ surfaces, as models for the cathode.…”

“…Before presenting and discussing the results, we will briefly summarize results of previous work on the interaction of EC with model electrode surfaces, which are relevant for this report. Song et al determined by temperature‐programmed desorption that desorption of a monolayer of EC adsorbed on HOPG sets in closely below 200 K, showing zero‐order desorption kinetics (adsorption energy ≈0.60 eV) . In addition, they demonstrated that adsorbed EC, deposited at 100 K on a metallic lithium (Li 0 ) film, decomposes upon annealing to 600 K, forming presumably lithium ethylene dicarbonate (CH 2 OCO 2 Li), lithium ethylene glycolate (ROCO 2 Li), and lithium carbonate (Li 2 CO 3 ) decomposition products .…”

“…Song et al determined by temperature‐programmed desorption that desorption of a monolayer of EC adsorbed on HOPG sets in closely below 200 K, showing zero‐order desorption kinetics (adsorption energy ≈0.60 eV) . In addition, they demonstrated that adsorbed EC, deposited at 100 K on a metallic lithium (Li 0 ) film, decomposes upon annealing to 600 K, forming presumably lithium ethylene dicarbonate (CH 2 OCO 2 Li), lithium ethylene glycolate (ROCO 2 Li), and lithium carbonate (Li 2 CO 3 ) decomposition products . This was derived from desorption of fragments like C 2 H 4 , C 2 H 4 O, and CO 2 , upon heating (possible products of the above Li‐containing species).…”