RESUMO
Delithiation followed by lithiation of Li+-occupied (n-type) tetrahedral sites of cubic LiMn2O4 spinel (LMO) at ~4 [Formula: see text] (delivering ~100 mAh gLMO-1) has been used for energy storage by lithium ion batteries (LIBs). In this work, we utilized unoccupied (p-type) octahedral sites of LMO available for lithiation at ~3 [Formula: see text] (delivering additional ~100 mAh gLMO-1) that have never been used for LIBs in full-cell configuration. The whole capacity of amphi-redox LMO, including both oxidizable n-type and reducible p-type redox sites, at ~200 mAh gLMO-1 was realized by using the reactions both at 4 [Formula: see text] and 3 [Formula: see text]. Durable reversibility of the 3 V reaction was achieved by graphene-wrapping LMO nanoparticles (LMO@Gn). Prelithiated graphite (LinC6, n < 1) was used as anodes to lithiate the unoccupied octahedral sites of LMO for the 3 V reaction.
RESUMO
By coating nanoparticular lithium manganese oxide (LMO) spinel with a few layers of graphitic basal planes, the capacity of the material reached up to 220â mA h g(-1) at a cutoff voltage of 2.5â V. The graphitic layers 1)â provided a facile electron-transfer highway without hindering ion access and, more interestingly, 2)â stabilized the structural distortion at the 3â V region reaction. The gain was won by a simple method in which microsized LMO was ball-milled in the presence of graphite with high energy. Vibratory ball milling pulverized the LMO into the nanoscale, exfoliated graphite of less than 10â layers and combined them together with an extremely intimate contact. Abâ initio calculations show that the intrinsically very low electrical conductivity of the tetragonal phase of the LMO is responsible for the poor electrochemical performance in the 3â V region and could be overcome by the graphitic skin strategy proposed.