Electrochemical Na-insertion/extraction properties of SnO thick-film electrodes prepared by gas-deposition

SnO thick-film electrodes for Na-ion battery anodes were prepared for the first time by a gasdeposition method, and we investigated the influence of fluoroethylene carbonate as an electrolyte additive on their anode performances. The SnO electrode showed high reversible capacities of 580 mA h g－1 and 260 mA h g－1 at the first cycle and at the 20th cycle, respectively, in an additive-free electrolyte. The cycle performance obtained was much higher than that of an Sn electrode. These results indicate that Na2O formed in the first Na-insertion process played a role as a matrix to alleviate a stress generated by drastic volumetric changes during alloying/dealloying reactions of Sn with Na. When we used fluorothylene carbonate as an additive, the SnO electrode achieved 250 mA h g－1 at the 50th cycle with a good capacity retention. The excellent cycle performance originates from a facile Na-ion transfer through a surface layer formed between the electrode and the electrolyte because the surface layer derived from additive prevents from making itself thicker by suppressing decompositionof the electrolyte.