Improving cycle life of layered lithium transition metal oxide (Li M O 2 ) based positive electrodes for Li ion batteries by smart selection of the electrochemical charge conditions

Abstract

Abstract Increasing the specific energy of a lithium ion battery and maintaining its cycle life is a predominant goal and major challenge for electrochemical energy storage applications. Focusing on the positive electrode as the specific energy bottleneck, cycle life characteristics of promising layered oxide type active materials (Li M O 2 ) has been thoroughly investigated. Comparing the variety of Li M O 2 compositions, it could be shown that the “Ni-rich” (Ni ≥ 60% for M in Li M O 2 ) electrodes expectably revealed best performance compromises between specific energy and cycle life at 20 °C, but only LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) could also maintain sufficient cycle performance at elevated temperatures. Focusing on NMC622, it could be demonstrated that the applied electrochemical conditions (charge capacity, delithiation amount) in the formation cycles significantly influence the subsequent cycling performance. Moreover, the insignificant transition metal dissolution, demonstrated by means of total X-ray fluorescence (TXRF) technique, and unchanged lithiation degree in the discharged state, determined by the measurement of the Li + content by means of the inductively coupled plasma optical emission spectroscopy (ICP-OES) technique, pointed to a delithiation (charge) hindrance capacity fade mechanism. Considering these insights, thoughtful modifications of the electrochemical charge conditions could significantly prolong the cycle life.