A method for fabricating a silicon core/carbon shell material for an anode material of a lithium ion battery, comprising: providing silicon particles comprising a size in a range of 20 to 200 nm; providing a structure directing agent by mixing ethanol and water; mixing the silicon particles with the structure directing agent and a carbon source to form a reaction mixture comprising a ratio of the silicon particles and the carbon source within a range of 1:20 to 1:1 by weight, wherein the silicon particles are dispersed in ethanol to form silicon particle aggregation droplets; heating the reaction mixture by a hydrothermal process to form one or more silicon cores and one or more carbon shells, wherein each of the silicon cores comprises a plurality of silicon clusters formed from the silicon particle aggregation droplets, and is enclosed by the carbon shell; and calcinating the silicon cores enclosed by the carbon shell by a calcination process for further carbonizing the carbon shells; wherein the structure directing agent comprises a ratio of water to ethanol in a range of 40:1 to 30:1 by volume; wherein the reaction mixture comprises 0.01-0.2 g/mL of the silicon particles, 0.02-0.1 g/mL of the ethanol, and 0.05-1.2 g/mL of the carbon source; wherein the hydrothermal process is performed in an autoclave, and comprises a reaction temperature of 180-220°C, a reaction pressure of 1.5-3 atm, a reaction time of 8-24 hr, and a pH of 4-11; and wherein the calcination process comprises a first calcination process performed with a first calcination temperature of 350-420°C and a first calcination period of 2-4 hr, and a second calcination process performed with a second calcination temperature of 750-850°C and a second calcination period of 2-5 hr. providing silicon particles comprising a size in a range of 20 to 200 nm; providing a structure directing agent by mixing ethanol and water; mixing the silicon particles with the structure directing agent and a carbon source to form a reaction mixture comprising a ratio of the silicon particles and the carbon source within a range of 1:20 to 1:1 by weight, wherein the silicon particles are dispersed in ethanol to form silicon particle aggregation droplets; heating the reaction mixture by a hydrothermal process to form one or more silicon cores and one or more carbon shells, wherein each of the silicon cores comprises a plurality of silicon clusters formed from the silicon particle aggregation droplets, and is enclosed by the carbon shell; and calcinating the silicon cores enclosed by the carbon shell by a calcination process for further carbonizing the carbon shells; wherein the structure directing agent comprises a ratio of water to ethanol in a range of 40:1 to 30:1 by volume; wherein the reaction mixture comprises 0.01-0.2 g/mL of the silicon particles, 0.02-0.1 g/mL of the ethanol, and 0.05-1.2 g/mL of the carbon source; wherein the hydrothermal process is performed in an autoclave, and comprises a reaction temperature of 180-220°C, a reaction pressure of 1.5-3 atm, a reaction time of 8-24 hr, and a pH of 4-11; and wherein the calcination process comprises a first calcination process performed with a first calcination temperature of 350-420°C and a first calcination period of 2-4 hr, and a second calcination process performed with a second calcination temperature of 750-850°C and a second calcination period of 2-5 hr.