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Transition metal dissolution and degradation in nmc811-graphite electrochemical cells

Published version
Peer-reviewed

Type

Article

Change log

Authors

Xu, C 
Grey, CP 

Abstract

Nickel-rich lithium nickel-manganese-cobalt oxide cathodes, in particular Li(Ni0.8Mn0.1Co0.1)O2 (NMC811), are currently being commercialized as next generation cathode materials, due to their increased capacities compared to current materials. Unfortunately, the higher nickel content has been shown to accelerate cell degradation and a better understanding is needed to maximize cell lifetimes. NMC811/graphite cells were tested under stressed conditions (elevated temperature and cell voltages) to accelerate degradation focusing on transition metal (TM) dissolution from the cathode. Increasing the cell temperature, upper cut-off voltage (UCV) and number of cycles all accelerated capacity fade and diffraction studies showed that under stressed conditions, additional degradation mechanisms beyond lithium loss to the SEI are present. Significant TM dissolution and subsequent deposition on the graphite anode is seen, particularly at stressed conditions. The concentration of TMs in the electrolyte remained invariant with cycling conditions, presumably reflecting the limited solubility of these ions and emphasizing the role that TM deposition on the anode plays in continuing to drive dissolution. Significant deposits of metals from the cell casings and current collectors were also detected at all cycling conditions, indicating that corrosion and metal leaching can be as important as TM dissolution from the active material in some cell formats.

Description

Keywords

40 Engineering, 4016 Materials Engineering, 34 Chemical Sciences, 3406 Physical Chemistry

Journal Title

Journal of the Electrochemical Society

Conference Name

Journal ISSN

0013-4651
1945-7111

Volume Title

168

Publisher

The Electrochemical Society
Sponsorship
Faraday Institution (FIRG001)
Faraday Institution (FIRG001)
Faraday Institution (FIRG001)
Faraday Institution (FIRG001)
We thank Ms. Jennifer Allen, Prof. Mary Ryan and Dr Daniel Abraham for helpful discussions. We thank Stephen Young and Nigel Howard for assistance with the ICP-OES measurements. This work is supported by the Faraday Institution under grant no. FIRG001