(a) Galvanostatic cycling of CuHCF at various current densities between 0.6 and 1.4 V versus SHE showed a maximum specific capacity of 59.14 mAh g−1 centered at 0.946 V. (b) The cyclic voltammogram (1 mV s−1) of CuHCF in 1 M KNO3 shows no pH dependence. (c) The capacity retention of CuHCF at high current densities is greater than those of LiFePO4 and Li4Ti5O12, two commonly studied lithium ion electrodes. The theoretical specific capacity is used when calculating the fractional capacity retention of LiFePO4 and Li4Ti5O12. (d) Long-term cycling of CuHCF at a 17 C rate between 0.8 and 1.2 V versus SHE shows 83% capacity retention after 40,000 cycles, with 99.7% coulombic efficiency. Extra electrolyte was added to the cell after 25,000 cycles in response to evaporation (denoted by asterisk). (e) Impedance spectroscopy of CuHCF shows a charge transfer resistance of 1 Ω for 1 cm2 working electrodes. The impedance of the cell is dominated by electrolyte resistance. (f) The voltage hysteresis of CuHCF between the potentials observed at a half charge state during charging and discharging is lower than those of Li4Ti5O12, and comparable to those of LiFePO4 when normalized for current density. (g) The low voltage hysteresis of CuHCF results in round-trip energy efficiency comparable to recently reported lithium-ion half-cells.