Accessing the full potential of aluminum alloy electrodes for Li-batteries: phase formation in the lithium-aluminum system

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Accessing the full potential of aluminum alloy electrodes for Li-batteries: phase formation in the lithium-aluminum system

Ghavidel, Mohammadreza Zamanzad; Feygin, Eliana M.; Kupsta, Martin; Le, Jon; Fleischauer, Mike

ELECTROCHEMICAL RESULTS

 Up to four distinct plateaus were present in voltage-capacity data. Plateaus are characteristic of co-existing phases.

 Voltage plateaus were often preceded by a nucleation overpotential. The nucleation overpotential decreased as the temperature increased.

 Some plateaus sagged significantly, indicating slow diffusion.

 Lithium electrochemically inserted in to aluminum foil at 60 _°C

forms three plateaus on insertion and removal. Subsequently

cooling the system to 30 °C cuts the capacity in half. The second

and third plateaus do not appear when testing at 30 °C.

MOTIVATION

Metal alloys have the potential to increase the capacity of lithium-ion batteries up to 50% over batteries made with standard graphite electrodes. Graphite stores lithium by intercalating lithium atoms between layers of graphine, and can store one Li per six carbon

atoms (~360 mAh g-1 _{or 0.17 Li/C). Metals store lithium via alloying}

reactions. Equilibrium phase diagrams suggest Al₄Li₉ should form

(2250 mAh g-1 _{or 2.25 Li/Al). However,} β-AlLi (1000 mAh g-1_{, 1 Li/Al)}

is the only Al-Li phase typically observed at standard temperatures. Here, we explore the factors influencing this discrepancy.

METHODS

SUMMARY

Aluminum is an abundant, promising electrode material for lithium-ion batteries. We can access three new Al-Li phases and double the storage capacity for lithium by increasing the operating temperature.

 Different phases of Li-Al were observed in the fully lithiated samples, depending on the insertion temperature.

STRUCTURAL+ELECTROCHEMICAL RESULTS

 Plateaus observed during (de)lithiation correspond to the growth

of the next Al-Li phase. Al ↔ β-AlLi ↔ Al₂Li₃ ↔ AlLi_2-x ↔ Al₄Li₉.

 Electrochemical results follow the thermal phase diagram.

 β-AlLi initially forms at temperatures above 50 ºC; measured and

expected capacities are in line (~1000 mAh g-1_{, 1 Li/Al). Large}

nucleation overpotentials are evident at most temperatures.

 Al₂Li₃ forms completely at temperatures above 60 ºC, measured

and expected capacities are in line (~1500 mAh g-1_{, 1.5 Li/Al).}

Nucleation barriers are not prominent above 50 ºC.

 AlLi_2-x forms partially at 60 ºC, and more fully above 90 ºC.

Measured capacities are ~300 mAh g-1 _{higher than expected,}

likely due to electrolyte breakdown at low potentials (~20 mV). Nucleation barriers are present.

 Al₄Li₉ partially forms at temperatures above 100 ºC. Nucleation

barriers and slow diffusion are prominent even at 150 ºC.

 Measured capacities on Li removal align with expected values.

CONCLUSION

 Lithium can be electrochemically inserted in to and removed from thick aluminum foil at moderate temperatures.

 Nucleation barriers and slow diffusion have large effects on the observed phases.

 Nucleation of β-AlLi was particularly challenging. This may be due

to the native surface oxide present on aluminum foil.

 Four different phases of Al-Li (β-AlLi, Al₂Li₃, AlLi_2-x, and Al₄Li₉) can

be electrochemically formed at temperatures above 100 ºC.

 Slow diffusion prevents the full capacity of Al₄Li₉ from being

realized, even at low current densities and high temperatures.

 Liquid electrolyte breakdown adds to the measured capacity at

potentials below 0.02 V vs. Li/Li+_.

 Phase transitions on lithium removal can be used to quantify the amount of electrolyte consumed.

FUTURE WORK

 Determining the limiting current density as a function of temperature on the nucleation of different Al-Li phases.

 Quantifying the diffusion coefficient of Li in different Al-Li phases.  Combining nucleation and diffusion insight to predict the

performance of all morphologies of aluminum alloy electrodes.

 Develop in-situ x-ray diffraction techniques to verify phases and

phase transitions without cooling the sample to room

temperature. Additional phases (-AlLi, Al₄Li₅) may be present.

Figure 1: Potential vs. capacity curves for Li-Al cells cycled at three different temperatures.

Mohammadreza Zamanzad Ghavidel,

Eliana M. Feygin,

Martin Kupsta,

Jon Le,

and Mike Fleischauer

1_{Department of Physics, University of Alberta, Edmonton, Alberta}

2_{National Research Council} – Nanotechnology Research Centre, Edmonton, Alberta

3_{Department of Physics, University of Waterloo, Waterloo, Ontario}

*zamanzad@ualberta.ca

Accessing the full potential of aluminum alloy electrodes for Li-batteries:

phase formation in the lithium-aluminum system

dHex dHexN dHex

Variable oligosaccharide chain (n=2-7) composed of Pen, dhex, Hex, HexA

T₁₈₉ , S₂₆₀ dHexNF

173Da

Figure 2: Potential vs. Capacity curves for Al foil cycled at 60 °C then

lithiated at 30 °C to 0.001 V vs. Li/Li+_.

Electro-chemistry

X-ray diffraction

s PP Figure 3: XRD patterns collected from aluminum samples lithiated to_{0.001 V vs. Li/Li+ at different temperatures.}

Figure 4: (A) Potential vs. capacity curves for Al-Li cells cycled at 100 °C

to specific potentials (as indicated). The data sets are self-consistent.

(B) XRD patterns from samples collected at potential specified in (A). Each insertion / removal data set was collected using a fresh Al foil.

Figure 5: Phase diagram of Al-Li (grey) and potential versus Li/Al ratio data (blue) collected at 100 ºC.

Figure 6: (top) Potential vs. capacity curves for Al foil lithiated at 120 °C

with different current densities. (bottom) Measured potential for the

β-AlLi ↔ Al₂Li₃ plateau at different temperatures and current densities.

Potential changes should be linear with 1/T for a given phase transition.

STRUCTURAL RESULTS

_{ELECTROCHEMICAL PHASE DIAGRAM}

variable temperature test chamber

 This is the first ever demonstration of the electrochemical