In a method of making a carbon fiber, polyacrylonitrile is dissolved into a first solvent, thereby generating a first solution. A plurality of cellulose nano-structures is dispersed in a second solvent, thereby generating a first suspension. The first suspension is mixed with the first solution, thereby generating a first mixture. The first mixture is spun so as to draw fibers from the first mixture. The fibers are stabilized and then the fibers are carbonized. A fiber includes an elongated carbonized polyacrylonitrile matrix. A plurality of carbonized cellulose nano-structures is in the carbonized polyacrylonitrile matrix.