Lai Chenying, Chen Jiewei, Knight James C, Manthiram Arumugam, Navrotsky Alexandra
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California Davis, One Shields Ave., Davis, CA, 95616, USA.
McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St. Stop C0400, Austin, TX, 78712, USA.
Chemphyschem. 2016 Jul 4;17(13):1973-8. doi: 10.1002/cphc.201600120. Epub 2016 Apr 1.
The formation enthalpies from binary oxides of LiMn2 O4 , LiMn2-x Crx O4 (x=0.25, 0.5, 0.75 and 1), LiMn2-x Fex O4 (x=0.25 and 0.5), LiMn2-x Cox O4 (x=0.25, 0.5, and 0.75) and LiMn1.75 Ni0.25 O4 at 25 °C were measured by high temperature oxide melt solution calorimetry and were found to be strongly exothermic. Increasing the Cr, Co, and Ni content leads to more thermodynamically stable spinels, but increasing the Fe content does not significantly affect the stability. The formation enthalpies from oxides of the fully substituted spinels, LiMnMO4 (M=Cr, Fe and Co), become more exothermic (implying increasing stability) with decreasing ionic radius of the metal and lattice parameters of the spinel. The trend in enthalpy versus metal content is roughly linear, suggesting a close-to-zero heat of mixing in LiMn2 O4 -LiMnMO4 solid solutions. These data confirm that transition-metal doping is beneficial for stabilizing these potential cathode materials for lithium-ion batteries.
采用高温氧化物熔体溶液量热法测定了LiMn₂O₄、LiMn₂₋ₓCrₓO₄（x = 0.25、0.5、0.75和1）、LiMn₂₋ₓFeₓO₄（x = 0.25和0.5）、LiMn₂₋ₓCoₓO₄（x = 0.25、0.5和0.75）以及LiMn₁.₇₅Ni₀.₂₅O₄在25°C时由二元氧化物形成的焓，发现这些焓均为强放热。增加Cr、Co和Ni的含量会使尖晶石在热力学上更稳定，但增加Fe的含量对稳定性没有显著影响。对于完全取代的尖晶石LiMnMO₄（M = Cr、Fe和Co），由氧化物形成的焓随着金属离子半径和尖晶石晶格参数的减小而变得更放热（意味着稳定性增加）。焓随金属含量的变化趋势大致呈线性，表明LiMn₂O₄ - LiMnMO₄固溶体中的混合热接近于零。这些数据证实，过渡金属掺杂有利于稳定这些潜在的锂离子电池正极材料。
