Influence of synthesis, dopants and cycling conditions on the cycling stability of doped LiNi0.5Mn1.5O4 spinels

Abstract

The high voltage LiNi0.5Mn1.5O4 spinel suffers from severe capacity fade when cycled against a graphitic anode as well as a relatively low theoretical capacity. Using metallic lithium as counter electrode, the stability is improved and the ability of the spinel structure to host 2 Li eq. can be used to improve the capacity. This leads to a theoretical specific energy of ∼1000 Wh kg−1. Unfortunately, the cycling of 2 Li eq. involves a phase transition from cubic to tetragonal associated with material degradation. In this work doping is used to improve capacity retention when cycling between 2.0 and 5.0 V. Initial capacities and stabilities are directly dependent on synthesis conditions and doping elements. Therefore, Fe- and Ti-doped spinels are compared with Ru- and Ti-doped spinels and tested at different cycling conditions. The cycling stability can be improved significantly by using reannealed material and by changing the discharge cutoff criteria. Thus a capacity of 190 mAh g−1 is achieved at a rate of C/2 with a capacity retention of ∼92% after 100 cycles. Furthermore, differences in the discharge behavior between the differently treated Ru- and Ti- doped materials are discussed based on the electrochemical behavior, the particle morphology and in-situ XRD analysis.