Electrochemically Formed Na_xMn[Mn(CN)₆] Thin Film Anodes Demonstrate Sodium Intercalation and Deintercalation at Extremely Negative Electrode Potentials in Aqueous Media

Abstract

The development of electrode materials for Na-ion batteries has been substantially accelerated recently with respect to application in grid energy storage systems. Specifically, development of Na-ion batteries operating in aqueous media is considered more promising for this application due to safety issues. Many different types of cathode materials for aqueous Na-ion batteries have been proposed; however, the number and performance of contemporary anode materials are still insufficient for practical deployment. In this work, we demonstrate that electrochemically deposited Na x Mn­[Mn­(CN)6] thin films are very promising anode materials for aqueous Na-ion batteries. Na x Mn­[Mn­(CN)6] films exhibit (i) very low half-charge potential ca. −0.73 V vs SHE (ca. −0.93 V vs SSC) being one of the lowest among those reported in the literature for the electrode materials, which also inhibit hydrogen evolution reaction; (ii) a specific capacity of ca. 85 mA h g–1; and (iii) only ∼3% loss of capacity and high round-trip efficiency (99.6%) after 3,000 cycles. Surprisingly, the choice of the electrolyte composition has a very strong influence not only on the intercalation process but also on the long-term performance of battery anodes and their electrode surface morphology.

High‐Abundance and Low‐Cost Metal‐Based Cathode Materials for Sodium‐Ion Batteries: Problems, Progress, and Key Technologies

“…The open-framework structure endowed the material with structural integrity and the capability to accommodate multiple Na + ions, which guaranteed both fast kinetics and high capacity. [255]…”

“…Moreover, it exhibited a remarkable cycle life with 75% capacity retention after 100 cycles at 2 C (Figure e). The open‐framework structure endowed the material with structural integrity and the capability to accommodate multiple Na + ions, which guaranteed both fast kinetics and high capacity …”

A Cell for Controllable Formation and In Operando Electrochemical Characterization of Intercalation Materials for Aqueous Metal‐Ion Batteries

“…Figure shows typical cyclic voltammograms and EQCM data of the electrodeposition of NiHCF (Figure A,B) and MnHCM (Figure C,D) thin‐film electrodes . The characteristic increase in the peak current densities (indicated with green arrows) and the negative shift in the resonance frequencies of the quartz wafer substrates indicate that electrode material is being deposited onto the electrodes during the cycling.…”

“…These deposition solutions contained Na 2 SO 4 as a supporting electrolyte, as well as one hexacyanometallate complex ([Fe(CN) 6 ] 3− or [Mn(CN) 6 ] 3− ) and a transition metal cation (Ni 2+ or Mn 2+ ), that form the Prussian blue analogs NiHCF or MnHCM, respectively. The detailed procedures were adopted from Yun et al…”

“…The anode material MnHCM serves as an excellent example for challenges in investigating PBA‐based aqueous sodium‐ion batteries. It usually degrades rapidly in contact with oxygen . Thus, one cannot expose this electrode material to the atmosphere arbitrarily.…”