Comparative performance of LiMn2O4 spinel compositions with carbon nanotubes and graphite in Li prototype battery

• Published in: Journal of solid state electrochemistry 2014, Vol.18 (8), p.2315-2324
• Main Authors: Apostolova, R., Peskov, R., Shembel, E.
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Electrochemistry; Energy Storage; Original Paper; Physical Chemistry
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-013-2350-6

We reported previously the superiority of electrochemical characteristics of the mechanical mixtures of micrometer LiMn 2 O 4 spinel with multiwall carbon nanotubes (MCNT) over those of spinel compositions with natural graphite in the prototypes of the Li-ion batteries. In the presented work, we extended the investigation of the kinetic and interfacial characteristics of the spinel in the redox reaction with the Li ion. Slow-rate scan cyclic voltammetry and impedance spectroscopy were used. Carbon electroconductive fillers, their nature, and particle sizes play the key role in the efficiency of the electrochemical transformation of spinel in Li-ion batteries. Electrodes based on the composition of the spinel and MCNT show a good cycling stability and efficiency at the discharge rate of 2C. Chemical diffusion coefficients of Li ion, which were determined in spinel composite with MCNT and graphite near potentials of peak activity in deintercalation/intercalation processes, change within one order of 10 −12  cm 2  s −1 . The value of this chemical diffusion coefficient for the composition of the spinel with MCNT and with graphite change within one order of 10 −12  cm 2  s −1 . The data of the impedance spectroscopy shows that the resistance of surface films on the spinel ( R s ) is low and does not considerably differ from R s in composites of the spinel with MCNT and graphite. The investigation shows that the resistance of charge transport ( R ct ) through the boundary of surface film/spinel composite is dependent on the conductive filler. Value of R ct in spinel electrode decreases by the factor of thousand in the presence of carbon filler. Exchange current of spinel electrode increases from the order of 10 −7 to 10 −4  A cm −2 under the influence of MCNT. At the potentials of maximum activity in deintercalation processes, exchange current of spinel composite electrode with MCNT is 2.2–3.0 times more than one of the composite with graphite. Determining role of the resistance of charge transport in electrode processes of spinel is established. The value of R ct is dependent on the resistance in contacts between spinel particles and also between particles and current collectors. Contact resistance decreases under the influence of MCNT with more efficiency than under the influence of graphite EUZ-M because of small the size of its particles with high surface area of the MCNT.