PNNL

Abstract

The high volatility of the cobalt price and geopolitical limitations of cobalt mining has made the elimination of cobalt (Co) a pressing need for the automotive industry. Owing to their high energy density and low-cost advantages, high-Ni and low-Co or completely Co-free layered cathodes become the most promising high-energy-density cathodes for next-generation lithium-ion batteries (LIBs). However, current high-Ni cathode materials, without exception, severely suffer from their intrinsic thermal and chemomechanical instabilities and insufficient cycle life. Here, by employing a novel compositional complex (“high-entropy”) doping strategy, we successfully fabricate a cobalt-free layered cathode that has extremely high termal and cycling stability. Combining in-situ synchrotron X-ray diffraction, transmission electron microscopy, and 3D nanotomography, we uncover that the cathode exhibits nearly zero volumetric change over a wide electrochemical window, resulting in significantly reduced lattice defects and local strain induced cracks in the cathode particles. In-situ heating experiments and mass spectroscopy reveal that the thermal stability of the new cathode is significantly improved compared with that of the state-of-the-art commercial cathode--NMC-811, reaching the level of the ultra-stable NMC-532. Owing to the dramatically increased thermal stability and zero-volumetric-change nature of the cathode, it exhibits extraordinarily improved capacity retention and cycle life (over 1000 cycles). This work, by resolving the long-standing safety and stability concerns on high-Ni and Co-free cathode materials, offers a highly promising strategy and commercially viable high-energy-density Co-free cathode for safe and long-life LIBs.