ORIGINAL PAPER Synthesis and electrochemical properties of activated carbons and Li 4 Ti 5 O 12 as electrode materials for supercapacitors Mladen Mladenov & Kremena Alexandrova & Nartzislav V. Petrov & Boyko Tsyntsarski & Daniela Kovacheva & Nikolay Saliyski & Raicho Raicheff Received: 16 January 2011 /Revised: 26 April 2011 /Accepted: 28 April 2011 # Springer-Verlag 2011 Abstract New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li 4 Ti 5 O 12 , prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li 4 Ti 5 O 12 oxide composite as a positive electrode, and an organic electrolyte (LiPF 6 – dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000– 1,600 m 2 g -1 ) and texture parameters, as well as three types of organic electrolytes: Et 4 NBF 4 –propylene carbonate (PC), LiBF 4 –PC and LiPF 6 –DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g -1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g -1 for the asymmetric SC cell, with good cycleability for both super- capacitor systems, were obtained. Keywords Supercapacitors . Electrode materials . Organic electrolytes . Nanoporous carbons . Composite electrode . Hybrid capacitor Introduction In the last years, the electrochemical double-layer capaci- tors (supercapacitors) have attracted interest of many research groups worldwide, working in the field of chemical power sources, due to their potential applications as energy storage devices. When comparing different energy storage devices, the batteries show the highest energy density (up to 200 W h kg -1 ), but they have low power density (below 500 W kg -1 ) and a limited cycle life (usually less than 1,000 cycles). The electrochemical capacitors tend to have much lower energy density (up to 10 W h kg -1 ) compared to batteries, but they can provide high power capability (above 1,000 W kg -1 ), high reversibility (90–95% or more) and excellent cycling characteristics (usually more than 105 charge–discharge cycles). Other advantages of supercapacitors, compared with the rechargeable batteries, are their extremely low internal resistance, high output power, exceptionally low M. Mladenov (*) : K. Alexandrova : R. Raicheff Institute of Electrochemistry and Energy Systems, Bulgarian Academy of Sciences, Ak. G. Bonchev str. BL.10, 1113 Sofia, Bulgaria e-mail: mladen47@bas.bg N. V. Petrov : B. Tsyntsarski Institute of Organic Chemistry, Bulgarian Academy of Sciences, Ak. G. Bonchev str. BL.9, 1113 Sofia, Bulgaria D. Kovacheva : N. Saliyski Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Ak. G. Bonchev str. BL.11, 1113 Sofia, Bulgaria J Solid State Electrochem DOI 10.1007/s10008-011-1424-6