Editors' Choice—Growth of Ambient Induced Surface Impurity Species on Layered Positive Electrode Materials and Impact on Electrochemical Performance

By N. Faenza, Lejandro Bruce, Zachary W. Lebens-Higgins, I. Plitz, N. Pereira, L. Piper, Glenn G. Amatuccia. 2017

161 citations recorded by the source corpus.

Surface impurity species, most notably Li 2 CO 3 , that develop on layered oxide positive electrode materials with atmospheric aging have been reported to be highly detrimental to the subsequent electrochemical performance. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) was used as a model layered oxide compound to evaluate the growth and subsequent electrochemical impact of H 2 O, LiHCO 3 , LiOH and Li 2 CO 3 . Methodical high temperature annealing enabled the systematic removal of each impurity specie, thus permitting the determination of each specie’s individual effect on the host material’s electrochemical performance. Extensive cycling of exposed and annealed materials emphasized the cycle life degradation and capacity loss induced by each impurity, while rate capability measurements correlated the electrode impedance to the impurity species present. Based on these characterization results, this work attempts to clarify decades of ambiguity over the growth mechanisms and the electrochemical impact of the specific surface impurity species formed during powder storage in various environments. The initial surface chemistry of Li-ion electrode materials plays a critical role in the development of in-situ derived interphases with the electrolyte and on the subsequent electrochemical performance. The surface chemistry can have a beneficial or destructive impact on performance relative to the bulk material. The principal challenge is controlling the variable surface chemistries which are induced by impurities during processing or material instability in an ambient at- mosphere. Impurity species on the surface of the electrochemically active materials have been shown to decrease both the electronic and ionic conductivities as well as reduce the amount of electrochemically viable lithium. 1,2 These consequences have a profound negative impact on the materials’ cycle life and energy density, resulting in significantly reduced cell performance. 3–5 The higher impedance has been proposed to create localized heating, which is known to increase the risk of catastrophically destroying the cell or igniting a liquid electrolyte. As a result, understanding the impact and controlling the surface impurities on positive electrode materials is of utmost im- portance to improve the functionality and safety of secondary lithium-ion 2 CO 3 layer is replaced by LiF, which is a product of the HF present in the electrolyte, and that this new surface layer significantly raises the electrode impedance. 16 Similar results were obtained for LiMn 2 O 416 , and NCA 15,35 positive electrodes. Our previous work demonstrates that layered oxide materials with higher contents of surface impurities have an amplified propensity for transition metal dissolution, likely caused by the increase of reduced transition metals that are at the Impurity

Subfields: Automotive Engineering, Electrical and Electronic Engineering

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