High-Rate Charging of Zinc Anodes Achieved by Tuning Hydration Properties of Zinc Complexes in Water Confined within Nanopores

Rechargeable batteries constructed with high-energy-density metal anodes, such as zinc and lithium, often suffer from dendrite formation during high-rate charging, which can lead to short circuits and reduced battery life. Here we report a novel method of realizing high-rate charging of zinc anodes together with the suppression of zinc dendrite formation by remarkably accelerating the electrodeposition within the nanopores of a porous electrode. By tuning not only the affinity between the wall-surface of nanopores and water but also that between the zinc complex with polyvalent carboxylates and water, we can establish a condition under which a surface-induced phase transition (SIFT) occurs. With the occurrence of SIFT, the penetration of zinc complexes into the nanopores becomes quite fast toward the formation of a second phase within the nanopore where the concentration of zinc complexes is orders of magnitude higher than in the bulk solution. More specifically, we use a hydrophobic nanoporous electrode, zinc complexes that behave as hydrophobic solutes, and nanopores with a sufficiently small diameter. Due to the fast penetration originating from SIFT, high-rate charging of zinc anodes and the suppression of dendrite formation are simultaneously achieved by continuous deposition of zinc without the depletion of zinc complexes in the nanopores. It is emphasized that nanometer-sized pores play a crucial role for the present technique for high-rate charging: Pores with a diameter of similar to 3 nm induce SIFT, while mesopores several tens of nanometers in diameter do not. This behavior is in marked contrast with that exhibited in the absence of SIFT. Without SIFT, the supply of zinc complexes is made in accordance with the usual Fickian diffusion, zinc complexes are rapidly depleted within a nanopore, continuous high-rate charging is not possible, and matters become more serious as the nanopore diameter decreases.