Here we find that Nano-Si powder can catalyze the esterification reaction of citric acid and ethanol to form a highly viscous gel, which is carbonized to obtain a typical core-shell structured Si@C nanocomposite. The carbon layer is a dense micropore carbon layer and is uniformly coated on the surface of the Si particles, which can effectively prevent electrolyte permeation and acts as a mechanically frame to limit the silicon volume change. An optimum carbon weight is about 11%, the thickness of the carbon layer is about 4–7 nm. A diffusion-controlled behavior and a pseudocapacitive effect during the (de)lithiation processes can work together to provide significant electrochemical characteristics for Si@C-TC, which makes Si@C-TC electrode exhibits the initial charge capacity of 1854 mAh g−1 (667 mAh cm−3, CE of 72.3%) at 0.1 A g−1 and the capacity of 1131 mAh g−1 (407 mAh cm−3) over 200 cycles at 0.5 A g−1. This work provides an in-depth understanding of the effects of carbon layer in Si@C structure, and the obtained views are very important for the selection of the carbon layer in high performance Si@C electrodes.