The Role Of Defects On The Jahn-Teller Effect And Electrochemical Charge Storage In Nanometric Limn2o4 Material

Reducing the particle size to improve the electrochemical properties of LiMn2O4 has been a common practice along the last years claiming that, by doing this, the Jahn-Teller (JT) distortion in its 3 V region is reduced. However, only a few papers have proved actual links between the mitigation of the JT effect and particle size; therefore, the JT effect is often entangled with mechanical and kinetic improvements, which are also associated to diminishing the particle size. Regardless that, there is a consensus that reducing particle size positively impacts Li+ insertion into LiMn2O4, particularly in its 3 V plateau. On the other hand, defects have emerged as factors determining the electrochemical behaviours of LiMn2O4. Several works pointed out that certain defects such as Mn-i(tet), F and V colour centres, dislocations or voids, could improve the 3 V performance of the LiMn2O4 by decreasing the JT distortion. Nevertheless, the preponderant defect causing this enhancement has not yet been established. The present paper aims to determine, among Mn-i(tet), F and V centres as well as dislocations, which defect impacts the most on the JT transition, specific capacity and stability of nanometric LiMn2O4. The aforementioned defects were detected by HRTEM, XRD, UV-Vis as well as magnetic measurements. Their implications on the potential drop caused by the JT effect, specific capacity and stability were recorded by potentiometric and galvanostatic charge/discharge measurements. The results indicate that only Mnr-related defect reduces the JT distortion, increasing the stability and capacity within the 3 V region, especially when particle are small.