Designing Anion‐Type Water‐Free Zn²⁺ Solvation Structure for Robust Zn Metal Anode

Abstract

Rechargeable aqueous Zn batteries are potential for large‐scale electrochemical energy storage due to their low cost and high security. However, Zn metal anode suffers from the dendritic growth and interfacial hydrogen evolution reaction (HER), resulting in the deterioration of electrode/battery performance. Here we propose that both dendrites and HER are related to the water participated Zn2+ solvation structure‐Zn(H2O)62+ and thus can be resolved by transforming Zn(H2O)62+ to an anion‐type water‐free solvation structure‐ZnCl42−, which is achieved in traditional ZnSO4 aqueous electrolyte after adding chloride salt with a bulky cation (1‐ethyl‐3‐methylimidazolium chloride). The elimination of cation‐water interaction suppresses HER, while the electrostatic repulsion between Zn tips and the anion solvation structure inhibits dendrite formation. As a result, the electrolyte shows uniform Zn deposition with an average Zn plating/stripping Coulombic efficiency of ≈99.9 %, enabling a capacity retention of 78.8 % after 300 cycles in anode‐free Zn batteries with pre‐zincificated polyaniline as the cathode. This work provides a novel electrolyte design strategy to prevent HER and realize long‐lifespan metal anode.

Self-repairing interphase reconstructed in each cycle for highly reversible aqueous zinc batteries

“…1e ), which confirm the coexistence of Zn 2+ -O and Zn 2+ -N coordination in ZnSO 4 -C 3 N 4 QDs system, with bond lengths of 2.05 Å and 3.35 Å, respectively. The Zn 2+ -O pair in ZnSO 4 -C 3 N 4 QDs is slightly enlarged compared with that in ZnSO 4 (~1.94 Å) 22 , 35 , in accordance with the above XANES results. The weakened bonding strength between Zn 2+ and H 2 O reduces the proton activity and suppresses electrochemical water decomposition, as also evidenced by a gradually lower hydrogen evolution potential with increasing doses of C 3 N 4 QDs in the electrolyte (Supplementary Fig.…”

Strategies of regulating Zn2+solvation structures for dendrite-free and side reaction-suppressed zinc-ion batteries

“…In addition, the chloride salt with bulky cation (1-ethyl-3-methylimidazolium chloride, EMImCl) electrolytes was utilized to unlock the cation–water interaction, 211 release the bound water in [Zn(H 2 O) 6 ] 2+ , and form ZnCl 4 2− as an anion-type solvation structure in the electrolyte. As a result, the regulation of solvation structures significantly prevented the dendrite growth and other side reactions (Fig.…”

“…8h, this anion-type water-free Zn 2+ solvation structure electrolyte (ASE) presented a lower energy in the X-ray absorption near-edge structure (XANES) spectrum when compared with the pure ZnSO 4 electrolyte, demonstrating that the local structures of Zn 2+ ions were changed, and this new solvation structure in ASE donated more electrons to Zn 2+ and thus lowered the valence of Zn 2+ . 211 Furthermore, the Fourier transformation of the extended X-ray absorption fine structure (EXAFS) spectra of the ZnSO 4 electrolyte and ASE was conducted (Fig. 8i), a higher shift in the k space of ASE than that of the ZnSO 4 electrolyte was observed, indicated that Cl − squeezed out H 2 O and involved in the Zn 2+ coordination shell after introducing EMImCl into the ZnSO 4 electrolyte.…”

“…8i), a higher shift in the k space of ASE than that of the ZnSO 4 electrolyte was observed, indicated that Cl − squeezed out H 2 O and involved in the Zn 2+ coordination shell after introducing EMImCl into the ZnSO 4 electrolyte. 211 Moreover, the cationic surfactant-type electrolyte additive (tetrabutylammonium sulfate (TBA 2 SO 4 )) was also employed in aqueous ZIBs. 213 The DFT calculations revealed that the TBA + cation adsorbed onto the Zn(0002) surface and formed a TBA + cation layer on the anode surface (Fig.…”

“…The strategies of zinc-philic additives and the corresponding electrochemical performance are summarized in Table 3. 58,87,101,207–209,211,213,216–225 These zinc-philic additives can adsorb onto the zinc anode surface via physical/chemical adsorption to form a protective layer on the anode surface, which can effectively prevent the contact between H 2 O and zinc and guide the uniform zinc deposition. Besides, the adsorbed additive molecules promote the desolvation of Zn(H 2 O) 6 2+ by removing H 2 O molecules from the solvation sheath of Zn 2+ , which can suppress the HER, corrosion, and formation of by-products and zinc dendrites.…”