Issue 41, 2022

Surface reduction in lithium- and manganese-rich layered cathodes for lithium ion batteries drives voltage decay

Abstract

Li- and Mn-rich layered oxides (Li1.2Ni0.2Mn0.6O2) are actively pursued as high energy and sustainable alternatives to the current Li-ion battery cathodes that contain Co. However, the severe decay in discharge voltage observed in these cathodes needs to be addressed before they can find commercial applications. A few mechanisms differing in origin have been proposed to explain the voltage fade, which may be caused by differences in material composition, morphology and electrochemical testing protocols. Here, these challenges are addressed by synthesising Li1.2Ni0.2Mn0.6O2 using three different hydrothermal and solid-state approaches and studying their degradation using the same cell design and cycling protocols. The voltage fade is found to be similar under the same electrochemical testing protocols, regardless of the synthesis method. X-ray absorption near edge, extended X-ray absorption fine structure spectroscopies, and energy loss spectroscopy in a scanning transmission electron microscope indicate only minor changes in the bulk Mn oxidation state but reveal a much more reduced particle surface upon extended cycling. No spinel phase is seen via the bulk structural characterisation methods of synchrotron X-ray diffraction, 7Li magic angle spinning solid state nuclear magnetic resonance and Raman spectroscopy. Thus, the voltage fade is believed to largely result from a heavily reduced particle surface. This hypothesis is further confirmed by galvanostatic intermittent titration technique analysis, which indicates that only very small shifts in equilibrium potential take place, in contrast to the overpotential which builds up after cycling. This suggests that a major source of the voltage decay is kinetic in origin, resulting from a heavily reduced particle surface with slow Li transport.

Graphical abstract: Surface reduction in lithium- and manganese-rich layered cathodes for lithium ion batteries drives voltage decay

Supplementary files

Article information

Article type
Paper
Submitted
19 jun 2022
Accepted
23 set 2022
First published
28 set 2022
This article is Open Access
Creative Commons BY license

J. Mater. Chem. A, 2022,10, 21941-21954

Surface reduction in lithium- and manganese-rich layered cathodes for lithium ion batteries drives voltage decay

B. Wen, F. N. Sayed, W. M. Dose, J. K. Morzy, Y. Son, S. Nagendran, C. Ducati, C. P. Grey and M. F. L. De Volder, J. Mater. Chem. A, 2022, 10, 21941 DOI: 10.1039/D2TA04876K

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