Electrochemical Investigations Of Sub-Micron Size And Porous Positive Electrode Materials Of Li-Ion Batteries

Abstract

A Comprehensive review of literature on electrode materials for lithium-ion batteries is provided in Chapter 1 of the thesis.

Chapter 2 deals with the studies on porous, sub-micrometer size LiNi1/3Co1/3O2 as a positive electrode material for Li-ion cells synthesized by inverse microemulsion route and polymer template route. The electromechanical characterization studies show that carbon-coated LiNi1/3Co1/3O2 samples exhibit improved rate capability and cycling performance. Furthermore, it is anticipated that porous LiNi1/3Co1/3O2 could be useful for high rates of charge-discharge cycling. Synthesis of sub-micrometer size, porous particles of LiNi1/3Co1/3O2 using a tri-block copolymer as a soft template is carried out. LiNi1/3Co1/3O2 sample prepared at 900ºC exhibits a high rate capability and stable capacity retention of cycling. The electrochemical performance of LiNi1/3Co1/3O2 prepared in the absence of the polymer template is inferior to that of the sample prepared in the presence of the polymer template.

Chapter 4 involves the synthesis of sub-micrometer size particles of LiMn2O4 in quaternary microemulsion medium. The electrochemical characterization studies provide discharge capacity values of about 100 mAh g-1 at C/5 rate and there is moderate decrease in capacity by increasing the rate of charge-discharge cycling. Studies also include charge-discharge cycling as well as ac impedance studies in temperature range from -10 to 40º C.

Chapter 5 reports the synthesis of nano-plate LiFePO4 by polyol route starting from two reactants, namely, FePO42H2O and LiOH.2H2O. The electrodes fabricated out of nano-plate of LiFePO4 exhibit a high electrochemical activity. A stable capacity of about 155 mAh g-1 is measured at 0.2 C over 50 charge-discharge cycles. Mesoporous LiFePO4/C composite with two sizes of pores is prepared for the first time via solution-based polymer template technique. The precursor of LiFePO4/C composite is heated at different temperatures in the range from 600 to 800ºC to study the effect of crystalllinity, porosity and morphology on the electrochemical performance. The compound obtained at 700ºC exhibits a high rate capability and stable capacity retention on cycling with pore size distribution around 4 and 46nm.

In Chapter 6, the electrochemical characterization of LiMn2O4 in an aqueous solution of 5 M LiNO3 is reported. A typical cell employing LiMn2O4 as the positive electrode and V2O5 as the negative electrode was assembled and the characterized by charge-discharge cycling in 5 M LiNO3 aqueous electrolyte. Furthermore, it is shown that Li+-ion in LiMn2O4 can be replaced by other divalent ions resulting in the formation of MMn2O4 (M = Ca, Mg, Ba and Sr) in aqueous M(NO3)2 electrolytes by subjecting LiMn2O4 electrodes to cyclic voltametry. Cyclic voltammetry and chronopotentiometry studies suggest that MMn2O4 can undergo reversible redox reaction by intercalation/deintercalation of M2+-ions in aqueous M(NO3)2 electrolytes.