Using Plasma Enhanced Chemical Vapor Deposition, one can prepare methylated amorphous silicon thin-layer anodes for Li-ion batteries exhibiting good cyclability. The properties of that material are investigated here in view of this target application. In comparison with pure amorphous silicon prepared in the same conditions, the improvement is twofold: longer lifetime, and capability of working with thicker electrodes. For example, capacity retention after 100 cycles of 150 nm thick layers with 10% carbon content is almost 70% larger than that of pure a-Si layers. The observed improvement is attributed to mechanical softening of amorphous Si by incorporation of CH3 groups.