A method for preparing a composite of particles of a high crystallinity carbon and a low crystallinity carbon, wherein: - low crystallinity carbon is characterized by wide-angle X ray diffraction measurements, i.e by an average lattice constant d= of 0.350 nm or more and a crystallite size L= in the direction of C axis of 25 nm or less; - high crystallinity carbon is characterized by wide-angle X ray diffraction measurements, i.e by an average lattice constant d= of 0.338 nm or less and a crystallinity size L= in the direction of C axis of 40 nm or more; the high crystallinity carbon is at least for 50% of its external surface embedded within or surrounded by matrix of the low crystallinity carbon; - high crystallinity carbon forms particles having a particle size ranging from 1 to 50 micrometers, said high crystallinity carbon particles being at least partially covered by particles of the low crystallinity carbon having a particle size ranging from 20 to 500 nm, said low crystallinity carbon particles being attached to the surface of said high crystallinity carbon particles, said method comprising the steps of: a) dispersing at least one carbon powder having high crystallinity and a polymeric substance in a solvent and mixing until evaporation of 40 to 60% of the solvent; b) conducting a first heat treatment phase up to a temperature of 225°C to 500°C and maintaining the temperature so as to pre-carbonise the resulting mixture; c) conducting a second heat treatment phase up to a temperature of 1000°C to 1250°C and maintaining the temperature so as to carbonize the resulting mixture; and d) conducting a final heat treatment phase up to a temperature of 2500°C to 2800°C and maintaining the temperature for at least 1 minute. - low crystallinity carbon is characterized by wide-angle X ray diffraction measurements, i.e by an average lattice constant d= of 0.350 nm or more and a crystallite size L= in the direction of C axis of 25 nm or less; - high crystallinity carbon is characterized by wide-angle X ray diffraction measurements, i.e by an average lattice constant d= of 0.338 nm or less and a crystallinity size L= in the direction of C axis of 40 nm or more; the high crystallinity carbon is at least for 50% of its external surface embedded within or surrounded by matrix of the low crystallinity carbon; - high crystallinity carbon forms particles having a particle size ranging from 1 to 50 micrometers, said high crystallinity carbon particles being at least partially covered by particles of the low crystallinity carbon having a particle size ranging from 20 to 500 nm, said low crystallinity carbon particles being attached to the surface of said high crystallinity carbon particles, a) dispersing at least one carbon powder having high crystallinity and a polymeric substance in a solvent and mixing until evaporation of 40 to 60% of the solvent; b) conducting a first heat treatment phase up to a temperature of 225°C to 500°C and maintaining the temperature so as to pre-carbonise the resulting mixture; c) conducting a second heat treatment phase up to a temperature of 1000°C to 1250°C and maintaining the temperature so as to carbonize the resulting mixture; and d) conducting a final heat treatment phase up to a temperature of 2500°C to 2800°C and maintaining the temperature for at least 1 minute.