Spinel Li4Ti5O12 has been considered as a promising alternative material to graphite for lithium ion batteries (LIBs) with improved safety and cycle life. Unfortunately, the destructive gas generation of Li4Ti5O12 and the associated cell swelling have been a major obstacle to the large-scale application of LIBs using Li4Ti5O12-based anodes. In this paper, we investigate the surface evolution of the anode in LiMn2O4//Li4Ti5O12/C cells and the role of formation potential on the gassing of LiMn2O4//Li4Ti5O12/C cells. It was found that an appropriate high potential formation protocol for LiMn2O4//Li4Ti5O12/C batteries can effectively inhibit the gassing and enhance the cycling performance of these LIBs. This is mainly because under high formation protocol, an artificial flexible solid-electrolyte interphase film can be formed on the surface of Li4Ti5O12/C, which further prevents electrolyte decomposition at the electrolyte//Li4Ti5O12/C interface.