Transition Metal-Doped Co-Free Layered Cathode for High-Performance Li-Ion Batteries

Abstract

Surging demand for high-energy-density cathodes based on Li(Ni x Co y Mn1−x−y )O2 (NCM) and Li(Ni x Co y Al1−x−y )O2 (NCA) for LIBs for EVs has tripled the price of Co in three years. As the price of Co rises rapidly, efforts to remove Co from the cathodes are increasing, but Co, even in minute amounts, plays an essential role in maintaining rate capability and structural stability while reducing cation mixing.1 So the realization of high-performance, Co-free layered cathodes poses a serious technical challenge. Recently, LiNi0.9Mn0.1O2 (NM90) was proposed as an alternative Ni-rich, Co-free cathode material.2 Although the long-term cycling stability of the NM90 is acceptable, its capacity is substantially less than that of a LiNi0.9Co0.05Mn0.05O2 (NCM90) when the NM90 is charged to a standard operating voltage (4.3 V) because the charging ends in the midst of the second hexagonal phase (H2) to the third hexagonal phase (H3) transition. In this study, we investigate to stabilizing the delithiated structure of an NM90 cathode at 4.4 V is proposed, namely, the introduction of a tertiary element into the cathode in combination with the modification of the electrolyte. The introduction of 1mol% Mo into NM90 accompanies increasing in the upper cut-off voltage to 4.4 V (versus Li+/Li) can help realize a half cell, delivering a capacity of 234 mAh g-1 that is comparable to that of NCM with similar Ni contents. The cycling stability of a full cell featuring the Li(Ni0.89Mn0.1Mo0.01)O2 (Mo–NM90) cathode is enhanced with a modified electrolyte (EF91, EMC:FEC = 9:1); retaining 86% of its initial capacity after 1,000 cycles while providing 880 Wh kgcathode −1. Mo–NM90 cathode is able to deliver a high capacity with cycling stability suitable for the long service life for electric vehicles at a reduced material cost, furthering the realization of a commercially viable Co-free cathode for LIBs. Reference s : [1] C. Delmas, I. Saadoune, A. Rougier, J. Power Sources, 44 (1993) 595-602.[2] A. Aishova, G.-T. Park, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 10 (2019) 1903179.