The structural and thermal stability are essential to understand the safety of Li4Ti5O12, but it is not fully understood. Here, the structural and thermal stability were investigated by the density functional theory (DFT) plane-wave pseudopotential technique and experimental method. Sub-micro Li4Ti5O12 particles were synthesized by a solid-state reaction. The calculated results of lattice parameters are highly coincident with the experimental values. XRD and Raman spectra demonstrate the formation of pure phase Li4Ti5O12. There is an amorphous phase and no phase transition when discharged to 0 V, which confirms that there is a certain reversible intercalation processes cycled below 1 V instead of a reduction–decomposition reaction. SEM shows that Li4Ti5O12 powder has a uniform, nearly cubic structural morphology with a narrow size distribution of about 500 nm. The low formation enthalpy (−6061.45 ± 4) indicates that Li4Ti5O12 has a high thermodynamic stability. The superior cycling performance at high rates cycled between 0 and 2.5 shows that Li4Ti5O12 has a very high structural stability. The high thermodynamic stability of Li4Ti5O12 is related to the strong covalent bonding characteristic between Ti and O according to the electron density difference diagram. DSC reveals that PF5 is the main species which damages the SEI layer.