A silicon-based active material composite comprising: particles with a silicon core and a shell of silicon oxide for surrounding the core, wherein the shell of silicon oxide is formed by oxidizing at least some of the silicon, wherein an amount of oxygen with respect to a total weight of the silicon and the silicon oxide is restricted to 9 wt% to 20 wt%, wherein the amount of oxygen is measured in an infrared ray detection method, wherein the silicon-based active material composite is produced by a method comprising: providing silicon particles; and oxidizing the silicon particles to form the silicon-based active material composite comprising particles with a silicon core and a shell of silicon oxide, wherein the shell of silicon oxide is obtained by oxidizing at least some of the silicon, wherein the oxidizing of the silicon particles is performed by chemically oxidizing the silicon particles in a liquid solvent containing oxygen, wherein the silicon particles comprise particles that are miniaturized through a grinding process or a pulverising process of coarse particles of silicon, wherein the grinding process or the pulverising process is performed on a slurry of the coarse particles of silicon and the liquid solvent containing oxygen, and at the same time, the silicon particles are chemically oxidized by at least one of compressive stress or shearing stress induced from the process. particles with a silicon core and a shell of silicon oxide for surrounding the core, wherein the shell of silicon oxide is formed by oxidizing at least some of the silicon, wherein an amount of oxygen with respect to a total weight of the silicon and the silicon oxide is restricted to 9 wt% to 20 wt%, wherein the amount of oxygen is measured in an infrared ray detection method, wherein the silicon-based active material composite is produced by a method comprising: providing silicon particles; and oxidizing the silicon particles to form the silicon-based active material composite comprising particles with a silicon core and a shell of silicon oxide, wherein the shell of silicon oxide is obtained by oxidizing at least some of the silicon, wherein the oxidizing of the silicon particles is performed by chemically oxidizing the silicon particles in a liquid solvent containing oxygen, wherein the silicon particles comprise particles that are miniaturized through a grinding process or a pulverising process of coarse particles of silicon, wherein the grinding process or the pulverising process is performed on a slurry of the coarse particles of silicon and the liquid solvent containing oxygen, and at the same time, the silicon particles are chemically oxidized by at least one of compressive stress or shearing stress induced from the process. providing silicon particles; and oxidizing the silicon particles to form the silicon-based active material composite comprising particles with a silicon core and a shell of silicon oxide, wherein the shell of silicon oxide is obtained by oxidizing at least some of the silicon, wherein the oxidizing of the silicon particles is performed by chemically oxidizing the silicon particles in a liquid solvent containing oxygen, wherein the silicon particles comprise particles that are miniaturized through a grinding process or a pulverising process of coarse particles of silicon, wherein the grinding process or the pulverising process is performed on a slurry of the coarse particles of silicon and the liquid solvent containing oxygen, and at the same time, the silicon particles are chemically oxidized by at least one of compressive stress or shearing stress induced from the process. <EOS>