LiMn2O4

LiMn2O4 is a lithium manganese oxide with a spinel crystal structure used as a cathode material in some lithium-ion batteries. In the spinel framework, Li+ ions occupy tetrahedral 8a sites while Mn ions reside in octahedral 16d sites within a close-packed oxide lattice of oxygen. The manganese is present in mixed valence, typically Mn3+ and Mn4+, giving an average oxidation state of +3.5.

Electrochemistry and performance: LiMn2O4 operates at about 4.0 V versus Li/Li+. The theoretical capacity for a full one-electron transfer per formula unit is 148 mAh/g. Practical capacities are commonly in the 110–120 mAh/g range, and the material often exhibits good rate capability due to three-dimensional lithium diffusion pathways in the spinel structure. The voltage profile and capacity can be influenced by particle size, morphology, and dopants.

Challenges and improvements: The presence of Mn3+ can cause Jahn-Teller distortions during cycling, contributing to structural instability and capacity fade. Mn dissolution into the electrolyte further degrades performance, especially at elevated temperature or high voltage. These issues are mitigated by doping with other metals (for example Ni, Co, Cr, or Fe), surface coatings (such as Al2O3 or ZrO2), and by synthesizing nanoscale or highly crystalline particles to improve stability and lifespan.

Synthesis and variants: LiMn2O4 can be prepared by solid-state reactions, sol-gel methods, or co-precipitation. Doping and compositional adjustments lead to variants that balance cost, safety, rate capability, and cycle life.

Applications: Historically used as a cost-effective, relatively safe cathode material with good high-rate performance. It has been largely superseded in high-energy applications by other cathode chemistries, but remains of interest for low-cost or fast-ch charging cells.