Abstract
Very high theoretical specific energies and abundant resource availability have emerged interest in primary Si–air batteries during the last decade. When operated with highly doped Si anodes and EMIm(HF)2.3F ionic liquid electrolyte, specific energies up to 1660 Wh kgSi−1 can be realized. Owing to their high-discharge voltage, the most investigated anode materials are langle 100rangle oriented highly As-doped Si wafers. As there is substantial OCV corrosion for these anodes, the most favorable mode of operation is continuous discharge. The objective of the present work is, therefore, to investigate the discharge behavior of cells with langle 100rangle As-doped Si anodes and to compare their performance to cells with langle 100rangle B-doped Si anodes under pulsed discharge conditions with current densities of 0.1 and 0.3 mA cm−2. Nine cells for both anode materials were operated for 200 h each, whereby current pulse time related to total operating time ranging from zero (OCV) to one (continuous discharge), are considered. The corrosion and discharge behavior of the cells were analyzed and anode surface morphologies after discharge were characterized. The performance is evaluated in terms of specific energy, specific capacity, and anode mass conversion efficiency. While for high-current pulse time fractions, the specific energies are higher for cells with As-doped Si anodes, along with low-current pulse fractions the cells with B-doped Si anodes are more favorable. It is demonstrated, that calculations for the specific energy under pulsed discharge conditions based on only two measurements—the OCV and the continuous discharge—match very well with the experimental data.Graphic abstract
Highlights
Increased demand on new battery technologies for electrical energy storage devices, possessing very high-theoretical energy densities and being abundant in terms of resource availability motivate the ongoing research on metal–air batteries progressively [1,2,3,4,5,6,7,8,9]
The intermittent discharge performance of Si–air cells under various current pulses with 0.1 and 0.3 mA cm−2 are shown in Figs. 1 and 2 for As ⟨100⟩ and B ⟨100⟩ Si anodes, respectively
Based on the results on mean voltages during discharge Edis, discharge currents Idis and times tdis, and mass changes Δmtot, the specific energies ws delivered by the Si–air cells under pulsed operation can be calculated according to ws = (Edis ⋅ Idis ⋅ tdis)∕Δmtot
Summary
Increased demand on new battery technologies for electrical energy storage devices, possessing very high-theoretical energy densities and being abundant in terms of resource availability motivate the ongoing research on metal–air batteries progressively [1,2,3,4,5,6,7,8,9]. Among the resource-efficient anode materials, the highest theoretical energy densities can be realized with aluminium and silicon; specific energies are 8091 Wh kgAl−1 and 8461 Wh kgSi−1 while energy densities are 21,845 Wh LAl−1 and 19,715 Wh LSi−1. Considering the resource efficiency, aluminium and silicon are most favorable with respect to their crustal abundance, which amounts to 1 04.9 and 1 05.5 ppm [10] and to their availability, as indicated by the annual production. In addition to high-specific energy and resource effectiveness, future energy scenarios based on fluctuating renewable energy supply require storage devices to be capable of being operated under dynamic conditions [12]. Regarding the performance point of view, it is advantageous to use the ionic liquid electrolyte which provides current densities one order of magnitude higher with corrosion being one order of magnitude lower than for the cells operated with KOH. The aqueous Si–air batteries are in a very early stage of development, so there is still a wide scope of improvements for this system [14,15,16,17]
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