Silicon nanoparticles with atomic layer deposited zinc oxide (ZnO) coating show significantly improved electrochemical performance mainly because of enhanced mechanical integrity and stablized interface. These ZnO coated Si nanoparticles demonstrate stable cycling with a reversible capacity of 1500mAh/g over 260 cycles. With ZnO protected interface, these electrodes can achieve stable cycling with mass loading as high as 1.4mg/cm2. In-situ structural characterization is performed to illuminate the stabilizing mechanism of the ZnO coating during cycling. It is confirmed that the coating is mechanically robust to remain intact even though Si expands inside, and a battery electrode made of this Si/ZnO structure will undergo minimal structural damage upon cycling.