Electrochemical Performance of Li x Mn 2-Y Fe y O 4-Z Cl z Synthesized through in Situ Glycine Nitrate Combustion

Background: Lithium manganese oxide spinel is a potential candidate for lithium-ion battery cathodes due to its 3D network of lithium pathways within the structure, low toxicity, reasonable capacity, and low cost. However, this spinel suffers from capacity fading due to fracturing of the structure either through the Jahn-Teller distortion, alternative phase formation via non-stoichiometry, or loss of crystallinity. Historically, cycle life enhancements have been achieved through stabilization of the spinel structure via transition metal doping on the B-site of the lattice. Iron as a dopant is of interest due partly to its low toxicity but primarily its low cost. By adding the redox couple of this transition metal, this spinel can satisfy higher voltage (5.0 V) applications should compatible electrolytes be produced. While B-site doping has proven effective, this effort proposes to observe if cycle life can be even further enhanced in Li x Mn 2-y Fe y O 4 (LMFO) by also substituting anion dopants. Previously our group has incorporated chlorine and fluorine into the base LiMn 2 O 4 material using solid state processing methods and demonstrated cyclability to 32 cycles as a result of weakening the Li-O bond for easier extraction from the lattice. Others have also added chlorine and more commonly fluorine and demonstrated performance enhancements. However rather than incorporating the halide into the lattice, most studies focus on surface modification of the spinel. The present study intends to look more into the cycle life benefits of the less-studied chlorine incorporation into the bulk of an iron-doped spinel via in situ combustion synthesis of the material. Experimental : A glycine nitrate combustion method was used to synthesize iron doped chlorinated lithium manganese oxide spinel (LMFO-Cl). Stoichiometric amounts of Li(NO­ 3 ­) , Mn(NO­ 3 ) 2 ∙4H 2 O, FeCl 3 , and NH 2 CH 2 COOH (glycine, Alfa Aesar) in a 1:1 metal to glycine ratio were dissolved into the aqueous solution. The solution was heated to evaporate the water and form a gel, which was heated further to 250 °C when auto ignition occurs. The resultant ash was fired at 600 °C for two to six hours to achieve the desired phase. Material characterization was performed using X-ray diffraction, X-ray fluorescence, BET surface area analysis, thermogravimetric analysis, and scanning electron microscopy. Cathode materials were mixed with carbon black and Teflon in a ratio of 85:10:5 of active to carbon t