High-Energy, Single-Ion-Mediated Nonaqueous Zinc-TEMPO Redox Flow Battery

Abstract

Two distinct advantages of nonaqueous redox flow batteries (RFBs) are the feasibility of building a high cell voltage (without a constraint of the water-splitting potential) and the operability at low temperatures (without a concern of freezing below 0 °C). However, electrochemically active organic redox couples are usually selectively soluble in specific nonaqueous solvents, and their solubility is relatively low (in contrast to that in aqueous solutions). The selective and low solubility of redox couples seriously constrict the practical energy density of nonaqueous RFBs. Herein, we present a hybrid nonaqueous RFB with a solid zinc anode and a liquid (2,2,6,6tetramethylpiperidin-1-yl)oxyl (TEMPO) cathode. Toward accessing a high solubility of the TEMPO cathode and to sufficiently accommodate the discharge products of a Zn anode, asymmetric electrolyte solvents, viz., propylene carbonate (PC) and acetonitrile (ACN), have, respectively, been employed at the cathode and anode. To prevent a mixing of the two asymmetric electrolyte solvents, a NASICON-type Na + -ion conductive solid-state electrolyte (SSE, Na 3 Zr 2 Si 2 PO 12 ) is employed to serve as a mediator-ion separator. The shuttling of Na + ions through the Na 3 Zr 2 Si 2 PO 12 SSE sustains the ionic charge balance between the two electrodes. The Zn-TEMPO nonaqueous cell with a stable energy density of ca. 12−18 Wh L −1 over 50 cycles was demonstrated.

Nonaqueous hybrid redox flow energy storage with a sodium–TEMPO chemistry and a single-ion solid electrolyte separator

“…27 According to our previous experience, propylene carbonate (PC) can serve as an ideal solvent for preparing a TEMPO catholyte (the solubility of TEMPO in PC can be up to ≈ 5.0 M). 21 Not only a highly concentrated TEMPO solution can be accessed with the PC solvent, but also a high-concentration NaClO 4 supporting electrolyte is achievable. Fig.…”

“…19,20 To improve the volumetric energy density/capacity, we demonstrated recently a hybrid redox flow battery by employing a solid Zn anode and a 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) liquid cathode. 21 Since the solid Zn anode can serve as a current collector (in addition to its major role as an active electrode) and the liquid electrolyte at the anode is actually not involved in scaling up the stored energy, the energy density of a hybrid flow battery (HFB) is mainly dependent on the storage capacity of the liquid TEMPO cathode. However, a Zn anode is not able to deliver a high cell voltage due to its relatively low electromotive force.…”

Recent advances in material chemistry for zinc enabled redox flow batteries

“…A possible solution is to introduce ion‐conducting interlayer like NASICON ceramic electrolyte that acts as separator and provides shuttled Na + to sustain charge balance within battery. [ 38 ] The ion transfer between two electrodes can be well adjusted and such strategy can match the requirement of different charge carriers. ResistanceThe separator is anticipated to be as thin as possible, then it can reduce the inner resistance of battery and thus improves the voltage efficiency of the flow battery. But the mechanical stability of porous membrane is insufficient to support a long‐last operation for RFBs.…”

Exploiting Self‐Healing in Lithium Batteries: Strategies for Next‐Generation Energy Storage Devices

“…[169] However, the diffusion of LMBs is hindered by two critical issues: random growth of lithium dendrites and anodic infinite volume change, which both lead to physical failures, cause serious safety concerns and jeopardize both coulombic efficiency and capacity retention. [170][171][172] Among the various solutions proposed in the literature, as artificial SEI fabrication or use of solid electrolytes, [173][174][175][176][177][178] also several self-healing approaches, summarized in Table 2, have been reported. In particular, the majority of papers that treat SH in lithium-metal batteries dealt with the management of uncontrolled dendritic growth in order to prevent dangerous shortages of the cell.…”