Is it universal that the layered-spinel structure can improve electrochemical performance?

Abstract

The introduction of spinel phase to form the layered-spinel structure (LSS) is an effective way to improve the electrochemical performance of Li- and Mn-rich layered oxides (LMR). But is this structure universal for all LMR systems? In this work, different Mn/Ni ratio systems with the LSS are discussed in detail. It is found that, high discharge capacity (200.8 mA h g−1 at 1C rate; 1C = 250 mA h g−1) as well as high capacity-retention (94% at 1C rate after 100 cycles) can be achieved by forming the LSS for low-Ni system (Mn/Ni = 5.0). However, the capacity retention decreases severely in the high-Ni system (Mn/Ni = 3.5, 2.6). For example, when the ratio of Mn/Ni is 3.5, the capacity-retention of the layered-spinel sample was only 65.8%, compared to the 83% of the original LMR sample. The Ex-situ XRD, XPS, and HRTEM results demonstrate that the introduction of spinel phase in high-Ni system accelerates the transition and collapse of the crystal structure. This work provides guidance for optimizing the proportions of elements and the design of structures for the LMR.