Initial reversibility and excellent capacity retention are the key requirements for the success of high-capacity electrode materials in high-performance Li-ion batteries and pose a number of challenges to development. Silicon has been regarded as a promising anode material because of its outstanding theoretical capacity. However, it suffers from colossal volume change and continuous formation of unstable solid electrolyte interphases during lithiation/delithiation processes, which eventually result in low initial Coulombic efficiency (ICE) and severe capacity decay. To circumvent these challenges, a new sandwich Si anode (SiO_x/Si/SiO_x) free from prelithiation is designed and fabricated using a combination of P-doping and SiO_x layers. This new anode exhibits high conductivity and specific capacity compared to other Si thin-film electrodes. Cells with SiO_x/Si/SiO_x anodes deliver the highest presently known ICE value among Si thin-film anodes of 90.4% with a charge capacity of 3534 mA h g⁻¹. In addition, the SiO_x layer has sufficient mechanical stability to accommodate the large volume change of the intervening Si layer during charge-discharge cycling, exhibiting high potential for practical applications of Si thin-film anodes.