ABSTRACT
Si anodes are of great interest for next-generation Li-ion batteries due to their exceptional energy density. One of the problems hindering the adoption of this material is the presence of electrolyte decomposition reactions that result in capacity fade and Coulombic inefficiency. This work studies the influence of the decomposition layer in Si on its electrochemical performance using thermogalvanic profiling, a non-destructive in operando technique. This is accomplished by comparing thermogalvanic profiles of uncoated thin-film Si to those of lithium phosphorus oxynitride (LiPON)-coated Si, in which decomposition reactions are inhibited. Through a combination with physico-chemical methods including scanning electron microscopy and time-of-flight secondary ion mass spectrometry, the thermogalvanic profiles are found to contain signatures that reflect the nature of the decomposition layer. More specifically, this decomposition layer appears to gradually develop a passivating function during the first electrochemical cycles. Thermogalvanic profiles collected at later cycles indicate that this passivating behavior is eventually lost, causing the observed capacity degradation. The identification of a passivating regime in Si is highly relevant for the development of high-capacity Li-ion batteries. In addition, the use of thermogalvanic profiles to track the properties of decomposition layers could be of interest for monitoring the formation or degradation of battery cells.
ABSTRACT
The lifetime of lithium-ion batteries can be extended by applying protective coatings to the cathode's surface. Many studies explore atomic layer deposition (ALD) for this purpose. However, the complementary molecular layer deposition (MLD) technique might offer the benefit of depositing hybrid coatings that are flexible and can accommodate potential volume changes of the electrode during charging and discharging of the battery. This study reports the deposition of titanium carboxylate thin films via MLD. The structure and stability of the hybrid films are studied by using Fourier transform IR spectroscopy. The electrochemical properties of two titanium carboxylate films and a "titanicone" MLD film, deposited by using TDMAT and glycerol, are evaluated on top of a TiO2, TiN, and LiMn2O4 electrode. The coatings are found to present good lithium-ion kinetics and to reduce electrolyte decomposition. Overall, the titanium carboxylate films deposited in this work seem promising as protective and elastic coatings for future high-energy lithium-ion battery cathodes.
