Novel Mesoporous Microspheres of Al and Ni Doped LMO Spinels and Their Performance As Cathodes in Secondary Lithium Ion Batteries

Abstract

1. Introduction – Lithium manganese oxides (LMO) based spinels are important cathode materials for Lithium ion batteries (LIBs). However the primary problem of these electrodes are that they suffer structural deformation owing to the Jahn-Teller distortion[1]. This reduces their lifetime and the efficiency of the battery greatly reduces with cycling. However, some improvement have been obtained by adding transition metals and/or modifying the surface area of the electrode materials. This abstract focuses on developing novel porous Ni and Al based LMO microstructures for LIB applications[2]. 2. Experimental fabrication – The LMO fabrication is done from their precursors. Initially MnCO3 microspheres are obtained from NaHCO3 and MnSO4.H2O precursors. This reaction is done in the liquid phase and once the two precursors are mixed, immediate formation of a white precipitate is noticed. Once this is obtained, the MnCO3 hollow spherical precursors are then reacted with LiOH by solid state reaction technique in stoichiometric amounts to obtain the LiAl0.1Mn1.9O4 (LAMO) and LiAl0.1Ni0.1Mn1.8O4 (LANMO) microspheres. 3. Results –Charge-discharge analysis have been performed at a constant current density of 0.5 mAcm-2by an Arbin instrument up to 4.5 V and discharged to 2V. The discharge curves follow the characteristic pattern of the LMO spinel based compounds. A phase changes is noticed during the discharge process, at ~ 4.1 V and ~ 2.75 V corresponding to the kink in the discharge. The second phase change at ~ 2.75 V is due to theJahn-Teller effect which produces a permanent deformation of the crystal lattice and steady loss of capacity. The maximum discharge capacity of the LAMO sample is 122.51 mAhg-1 and 75th cycle discharge capacity is 42.22 mAhg-1. The LANMO sample provides a 1st cycle discharge capacity of 140.49 mAhg-1 and a 75th cycle discharge capacity of 66.24 mAhg-1. The LANMO system is seen to be superior in performance as compared to the LAMO system. This is due to the stabilizing role that the added Ni has provided to the crystal lattice, improving the cathodes ability to perform stable intercalation. The performance of these electrodes is demonstrated in Figure 1(a-c). 4. Conclusions – This research provides an insight in to the study of spinels at relatively low voltages which is not so prevalent in the literature. Also a novel technique is used to produce highly porous LMO based spinel spheres which serve to have enhanced electrochemical capacity and cell performance.