High-density cathode structure of independently acting Prussian-blue-analog nanoparticles: a high-power Zn-Na-ion battery discharging ∼200 mA cm-2 at 1000C

Sustainable societies demand ultrahigh-power batteries to discharge explosive electricity. Herein, we use current densities (mA cm(-2)) to measure high power when comparing different laboratory-scale loading amounts (several mg cm(-2)) of redox-active materials. Current densities are improved by increasing discharge currents (A g(-1)) in conjunction with loading amounts. However, maintaining the theoretical capacities of cathodes at ultrahigh rates of >= 100C remains challenging. Independently acting nanoparticles (NPs) are most effective in boosting the C-rate capabilities of cathodes by improving sluggish kinetics via shortened ion-diffusion length. Therefore, we fabricate aggregation-free cathodes through the one-step filtration of independently water-dispersed surface-modified NPs of Prussian-blue analogs (metal hexacyanoferrates (MHCFs), M = Zn, Cu, and Mn) along with single-walled carbon nanotubes. ZnHCF NPs are densely stacked between 1.0 and 1.3 g cm(-3) while maintaining nanometer-scale spaces around each NP. These spaces are filled with electrolyte solutions, enabling the NPs to act independently. In Zn-Na-ion batteries, an unprecedented charge/discharge rate mismatch between cathodes and Zn-foil anodes is investigated by changing the loading amounts of NPs. The low-loading amounts of <= 0.50 mg cm(-2) achieve synchronized charge/discharge profiles ranging from 100 (1.64) to 1000C (operating voltage, 1.53 V) with retained discharge capacities of >= 97%. Furthermore, we demonstrate the ability to conduct at least 150 000 charge/discharge cycles at 400C. At a high loading amount of 3.0 mg cm(-2), the capacity charged to the theoretical value at 300C is almost fully discharged at 1000C/66 A g(-1) with high-power outputs of 198 mA cm(-2)/246 mW cm(-2). In Ragone plots, Zn-Na/K-ion batteries using MHCFs exhibit ultrahigh-power densities of 10(4)-10(5) W kg(-1) with energy densities of 90-200 W h kg(-1). The unique cathode structure thereby shows a promising avenue for overcoming the tradeoff between densifying NPs and increasing current densities for future ultrahigh-power batteries.