NOVELTY - Carbon nanotubes with surface carboxyl group are added to thionyl chloride. Anhydrous toluene solution of ethylene diamine is added. The reaction mixture is filtered, washed and vacuum-dried, to obtain carbon nanotubes with surface amino group. The carbon nanotubes are ultrasonically dispersed in deionized water, to obtain solution (A). Copper or aluminum is cleaned, immersed in solution (A), washed, and self-assembled to form 15-30 carbon nanotube layers. The copper/aluminum-deposited carbon nanotubes are compacted to obtain a composite collector.    USE - Preparation of composite collector for lithium ion redox flow batteries (claimed).    ADVANTAGE - The method provides composite collectors having excellent electroconductivity and low internal resistance. The obtained composite collector provides lithium redox flow batteries having an electrode material which is convenient to change. The battery also has high energy density and power density, and excellent energy-storage characteristics.    DETAILED DESCRIPTION - Multiwall carbon nanotubes are refluxed in sulfuric acid/nitric acid mixed solution for 5-10 hours at 70-80 degrees C, filtered, washed with deionized water, and vacuum-dried at 100 degrees C and -0.01 MPa or less for 5-10 hours to obtain carbon nanotubes with surface carboxyl group. The carbon nanotubes are then added to thionyl chloride and relfown at 75-80 degrees C for 10-15 hours. Residual thionyl chloride is evaporated and anhydrous toluene solution of ethylene diamine is added at 70 degrees C over 20-25 hours. The reaction mixture is then filtered, washed using ethanol and deionized water, and vacuum-dried at 50 degrees C for 18-26 hours, to obtain carbon nanotubes with surface amino group. The carbon nanotubes are ultrasonically processed for 3-5 hours and dispersed in deionized water, to obtain solution (A) of concentration 0.3-0.6 mg/ml. Copper or aluminum is cleaned by immersing in solution (B) for 30 minutes, taken out, washed with deionized water thrice, then immersed in solution (A) for 30 minutes, washed with deionized water thrice, and self-assembled to form 15-30 carbon nanotube layers on the surface. The copper/aluminum-deposited carbon nanotubes are compacted for 3-10 minutes at 1-10 MPa for 2-5 hours at 300-550 degrees C under reducing atmosphere, to obtain a composite collector.