(625a) Deconvolution of the Solid-Electrolyte Interphase Growth Patterns on Conversion-Based Transition Metal Oxides

Deconvolution of the solid-electrolyte
interphase growth patterns on conversion-based transition metal oxides

Benjamin Ngᵃ, Alessandro Palmieriᵇ, William E. Mustainᵃ*

ᵃDepartment of
Chemical Engineering, Swearingen Engineering Center, University of South Carolina,
Columbia

ᵇDepartment of
Chemical and Biomolecular Engineering. University of Connecticut, Storrs

A
paradigm shift, pushed forth by Sony in the 1990s, has fueled the
transformation of 21^st century portable electronics and motor vehicles
[1]. Traditional Li ion batteries are comprised of a graphitic anode, a lithium
metal oxide cathode, and LiPF₆/carbonate electrolyte. Unfortunately,
the high reversibility of graphite intercalation anodes is balanced by a
moderate specific energy density of ca. 150 Wh/kg[2], and the rise in power demand for data processing, multimedia,
automotive and other emerging applications means that new materials advances
are needed that enable a significant increase in the cell energy and power
density.

At
the cathode, materials that have capacities ca. 250 mAh/g
and stability up to 5V vs Li/Li⁺ have been recently shown. This relatively low cathode capacity does
limit what can be done at the anode due to an intrinsic “capacity penalty”[3] that occurs when the anode capacity is too high
relative to the cathode. Therefore, it
has been estimated that what is needed in the foreseeable future are anode
materials that are able to achieve capacities near 700 mAh/g.[4] This opens up
the periodic table to a wide number of available chemistries including metal
oxides (MOs) [4]. 

In
recent years, several metal oxide anode materials have been demonstrated that
have the ability to meet or exceed the 700 mAh/g
capacity target while showing excellent capacity retention in half cell
configurations. However, one limitation
for these materials in their transition to full cells has been capacity fade during
device life that is more rapid than in the half cell configuration. The two
most likely culprits for this fade have been identified as: 1) shifting of the
potential window at constant voltage during cycling; and 2) instability of the
solid electrolyte interphase (SEI) – with the former being most likely. Unfortunately, very little is currently known
about the formation of the SEI on these materials.

In
this work, our team will discuss the growth mechanisms of the SEI on variations
of NiO morphologies. It has been observed that the relatively poor
electronic conductivity of these materials leads to non-uniform distribution of
the SEI during cycling, which can cause clustering and vacancy formation due to
cohesive forces that act to agglomerate particles during cycling. We will show
how these formational patterns lead to SEI instability and subsequent utilization
of the finite amount Li in full cells. Lastly, we will discuss ways to control
the clustering effect and oxidation states of metal oxides through domain
confinement techniques.

References

1.    
T.
Nagaura, K. Tozawa, Prog. Batteries Sol. Cells, 9, (1990), 209.

2.    
M.M.
Thackeray, C. Wolverton and E.D. Isaacs, Energy and
Environmental Science, 5, (2012), 7854.

3.    
M.
Karulkar, R. Blaser, B. Kudla, Journal of Power Sources, 273, (2015), 1194.

4.    
N.
Spinner, L. Zhang and W.E. Mustain, J. Mat. Chem. A,
2(6) (2014) 1627.