Understanding the Role of Temperature and Cathode Composition on Interface and Bulk: Optimizing Aluminum Oxide Coatings for Li-Ion Cathodes

Abstract

Surface coating of cathode materials with AlO has been shown to be a promising method for cathode stabilization and improved cycling performance at high operating voltages. However, a detailed understanding on how coating process and cathode composition change the chemical composition, morphology, and distribution of coating within the cathode interface and bulk lattice is still missing. In this study, we use a wet-chemical method to synthesize a series of AlO-coated LiNiCoMnO and LiCoO cathodes treated under various annealing temperatures and a combination of structural characterization techniques to understand the composition, homogeneity, and morphology of the coating layer and the bulk cathode. Nuclear magnetic resonance and electron microscopy results reveal that the nature of the interface is highly dependent on the annealing temperature and cathode composition. For AlO-coated LiNiCoMnO, higher annealing temperature leads to more homogeneous and more closely attached coating on cathode materials, corresponding to better electrochemical performance. Lower AlO coating content is found to be helpful to further improve the initial capacity and cyclability, which can greatly outperform the pristine cathode material. For AlO-coated LiCoO, the incorporation of Al into the cathode lattice is observed after annealing at high temperatures, implying the transformation from "surface coatings" to "dopants", which is not observed for LiNiCoMnO. As a result, AlO-coated LiCoO annealed at higher temperature shows similar initial capacity but lower retention compared to that annealed at a lower temperature, due to the intercalation of surface alumina into the bulk layered structure forming a solid solution.

Revealing electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries by in situ Fourier transform infrared spectroscopy

“…[5][6][7][8][9] While increasing Ni content in NMC from LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NMC111), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NMC622) to LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC811) can greatly increase initial discharge capacities, 5,6,10 the capacity retention decreases during cycling, 10,11 which is accompanied by earlier onset for gas (O 2 and CO 2 ) evolution. 10,12 Although the mechanistic details of electrolyte reactivity and reaction pathways on Ni-rich positive electrodes [13][14][15] are not well understood, modifying electrode surfaces by ceramic coatings such as Al 2 O 3 , [16][17][18][19][20] creating Ni-poor surfaces through concentration gradients [21][22][23][24] and introducing additives in the carbonate electrolytes [25][26][27][28][29][30] can greatly increase the capacity retention of Ni-rich electrodes, such as NMC811.…”

Development of Electrolytes for Single Crystal NMC532/Artificial Graphite Cells with Long Lifetime

“…[10][11][12][13][14][15][16][17][18][19][20][21] Recently, J. Li et al showed that single crystal Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 (NMC532) materials in NMC532/artificial graphite cells can have excellent long term lifetime with an electrolyte consisting of 2 wt% prop-1-ene-1,3 sultone (PES) + 1 wt % ethylene sulfate (DTD) + 1 wt% tris (trimethylsilyl) phosphite (TTSPi) in 1 M LiPF 6 in ethylene carbonate: ethyl methyl carbonate (3:7 by weight) (this electrolyte is called PES211 here). 22 During testing to 4.4 V at 40…”

Ni‐Rich/Co‐Poor Layered Cathode for Automotive Li‐Ion Batteries: Promises and Challenges

“…c) STEM images and cycle performance of pristine NCM523 and as‐coated NCM523. Reproduced with permission 201. Copyright 2017, American Chemical Society.…”