Journal
ACS ENERGY LETTERS
Volume 2, Issue 5, Pages 1122-1127Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsenergylett.7b00179
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Funding
- NSERC Canada
- Canada Research Chair programs
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Nonaqueous potassium-ion batteries have emerged as possible low-cost alternatives to Li-ion batteries for large-scale energy storage, owing to their ability to use graphitic carbon as the negative electrode. Positive electrode materials remain a challenge. Here, we report control of the crystal dimensions of the Prussian white hexacyanoferrate (HCF), K1.7Fe[Fe(CN)(6)](0.9), using solution chemistry to obtain either nano, submicron, or micron crystallites. We observe a very strong effect of crystallite size on electrochemical behavior. The optimal cathode material comprised of 20 nm crystallites delivers a close-to-theoretical reversible capacity of 140 mAh g(-1) with two well-defined plateaus at 4.0 and 3.2 V vs K/K+ upon discharge. Slightly inferior electrochemical behavior is observed for crystallites up to similar to 160-200 nm in diameter, but unlike the analogous Na HCFs, micron-sized crystals show very limited capacity. For the nanosized crystallites, however, the energy density of similar to 500 Wh kg(-1) is comparable to that of the best Na HCF cathode materials. At a relatively high current density of 100 mA g(-1) half-cells cycled with ethylene carbonate/diethyl carbonate (EC/DEC) and 5% fluoroethylene carbonate (FEC) demonstrate an initial discharge capacity of 120 mAh g(-1) with a capacity retention of 85% after 100 cycles and 65% after 300 cycles.
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