(696c) Highly Energy Dense Cu-Intercalated Birnessite/Zn Battery for Grid Applications

Manganese
dioxide (MnO₂) and zinc (Zn) are one of the most abundant, safest
and cheapest materials available. Together, they are found in common household
batteries like Duracell, Energizer, etc. as small cylindrical alkaline cells.
These cells or batteries are used as primary batteries, i.e., as single use
batteries, where the entire capacity of the battery is delivered once and then
discarded. The disadvantage of primary batteries is that it takes a lot of
energy to produce the battery than the energy that can be actually obtained
from it, and also, it creates environmental waste. However, the manufacturing
of primary cells has still been rampant due to the cost of manufacturing MnO₂-Zn
cells being very cheap. In terms of improving the overall energy efficiency,
reducing waste and maintaining its cost advantage, it makes good sense,
economically and environmentally, to make MnO₂-Zn cells
rechargeable. However, the main deterrent to this direction has been the
fundamental material and chemical problems of the main raw components, i.e.,
MnO₂ and Zn.

Manganese
dioxide can theoretically deliver a capacity of approximately 617mAh/g. It
delivers this capacity through a 2 electron electrochemical reaction (each
electron providing around 308mAh/g). MnO₂ has been found to be
rechargeable when the capacity has been limited to around 5-10% of the
617mAh/g. It suffers a crystal structure breakdown as more of the capacity is
accessed, and it inherently forms electrochemical irreversible phases. If the
entire 2 electron capacity can be accessed then theoretically it can reach
energy density numbers near lithium-ion batteries. Similar problems are
associated with the zinc electrode, where higher utilization of its capacity
causes dendrite formation, shape change and formation of inactive zinc oxides
that ultimately lead to electrode failure. These are the main deterrent to a
cheap and safe battery that could be a disruptive technology in the energy
storage field.

In this
presentation, we report the breakthrough of reversibly accessing the 2^nd
electron capacity of MnO₂ by using its layered polymorph called birnessite mixed with bismuth oxide (Bi-birnessite)
and intercalating the layers with Cu ions (1). Bi-birnessite’s
undergo conversion reactions in alkaline electrolyte and ultimately form
electro-inactive hausmannite (Mn₃O₄)
because of its poor charge transfer characteristics. Intercalating the layers
of Bi-birnessite with Cu ions is shown to improve its
charge transfer characteristics dramatically and regenerate its layered
structure reversibly for thousands of cycles as shown in Figure 1. We also
present a case of Cu-intercalated Bi-birnessite’s
applicability in practical batteries by cycling the material at high areal
capacities (10-29mAh/cm²) for thousands of cycles at C-rates that
are of interest in the battery community.

For
true applicability in practical energy dense batteries its
pairing with a Zn anode is essential. The use of Zn anodes has also presented
problems as it is the source of zincate ions in electrolyte that react with the
cathode, MnO₂, to form electro-inactive phase called haeterolite (ZnMn₂O₄). The best
reported cycle life data for high depth-of-discharge (DOD) birnessite
cathodes with Zn anodes had been 50 cycles till our recent publication, which
showed over 90 cycles achieving 140Wh/L.

In
this presentation, we also report the effect of zincate ions on the
Cu-intercalated Bi-birnessite cathodes beyond 100
cycles (2). The Cu-intercalated Bi-birnessite
cathodes when paired with Zn anodes are shown to deliver 160Wh/L and cycle
reversibly for over 100 cycles. The Cu ions play an important role in
mitigating the detrimental effect of zincate ions in the 100 cycles; however,
the zincate ions eventually poison the cathode to form ZnMn₂O₄.
The mechanism through which ZnMn₂O₄ is formed is
presented in detail with the aid of electroanalytical and spectroscopic
methods.  A solution of trapping the
zincate ions is also presented, where the membrane that is used successfully
traps the zincate ions from interacting with the cathode and thus, extend cycle
life to over 900 cycles as shown in Figure 2. This is the best reported cycle
life data with a manganese dioxide cathode accessing the near 2^nd
electron capacity paired with Zn anodes.

Figure 1. (a) Volumetric
energy density of a Cu-intercalated Bi-birnessite/Zn
cell. Inset shows the first 5 cycles of the cell. (b) Energy density comparison
of different energy storage systems. (c) Specific capacity (mAh/g)
vs cycle number for the Cu-intercalated Bi-birnessite
against a sintered Ni counter electrode. Insets show specific cycle discharge
curves for different wt.% loadings of MnO₂.

Figure
2. A Cu-intercalated Bi-birnessite cathode paired
with Zn anode achieving cycle life greater than 900 cycles with specialized
membrane.

References:

1] Yadav, G.
G.; Gallaway, J. W.; Turney,
D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S. “Regenerable
Cu-intercalated MnO₂ layered cathode for highly cyclable
energy dense batteries” Nat. Commun. 8, 14424 (2017).

2] Yadav, G. G.; Wei, X; Huang,
J.; Gallaway, J. W.; Turney,
D. E.; Nyce, M.; Secor, J.;
Banerjee, S., Journal of Materials Chemistry A, 5, 15845 (2017)