Electrolyte Design for In Situ Construction of Highly Zn²⁺‐Conductive Solid Electrolyte Interphase to Enable High‐Performance Aqueous Zn‐Ion Batteries under Practical Conditions

Abstract

Rechargeable aqueous Zn‐ion batteries promise high capacity, low cost, high safety, and sustainability for large‐scale energy storage. The Zn metal anode, however, suffers from the dendrite growth and side reactions that are mainly due to the absence of an appropriate solid electrolyte interphase (SEI) layer. Herein, the in situ formation of a dense, stable, and highly Zn2+‐conductive SEI layer (hopeite) in aqueous Zn chemistry is demonstrated, by introducing Zn(H2PO4)2 salt into the electrolyte. The hopeite SEI (≈140 nm thickness) enables uniform and rapid Zn‐ion transport kinetics for dendrite‐free Zn deposition, and restrains the side reactions via isolating active Zn from the bulk electrolyte. Under practical testing conditions with an ultrathin Zn anode (10 µm), a low negative/positive capacity ratio (≈2.3), and a lean electrolyte (9 µL mAh−1), the Zn/V2O5 full cell retains 94.4% of its original capacity after 500 cycles. This work provides a simple yet practical solution to high‐performance aqueous battery technology via building in situ SEI layers.

Tuning the Electrolyte Solvation Structure to Suppress Cathode Dissolution, Water Reactivity, and Zn Dendrite Growth in Zinc‐Ion Batteries

“…The E a1 calculated on the interphase under the Zn(OTf) 2 ‐H 2 O electrolyte (Figure S27, Supporting Information) was 55.6 kJ mol −1 , much larger than that for the Zn(OTf) 2 ‐TEP‐H 2 O electrolyte (17.2 kJ mol −1 , Figure S28, Supporting Information), indicating the lower energy barrier for Zn 2+ diffusion through the polymeric inorganic layer than via the OTf‐hydrate. Moreover, the Zn(OTf) 2 ‐H 2 O electrolyte leads to a low transference number () in the cycled Zn/Zn symmetric battery, which is known to cause an ion gradient at the electrolyte and electrode interface and can assist the dendrite growth, [ 12 ] while the Zn(OTf) 2 ‐TEP‐H 2 O electrolyte had a much higher of 0.76 (Figure S29, Supporting Information). Therefore, the electron insulating property as well as the low energy barrier for ion diffusion of the poly‐inorganic SEI under the Zn(OTf) 2 ‐TEP‐H 2 O electrolyte can block electron transfer and enable the deposition of Zn 2+ beneath the interfacial layer, thus inhibiting dendrite growth.…”

“…As evaluated in Figure S26 in the Supporting Information, the electrical resistivity (ρ) of the Zn electrode with this poly-interphase was measured to be 1.3 × 10 4 Ω cm, which is lower than for the bare Zn metal (ρ = 7.9 × 10 4 Ω cm) and the cycled Zn with OTf-hydrate (ρ = 2.0 × 10 3 Ω cm). The activation energy (E a1 ) representing the transport process of Zn 2+ through the interphase on the Zn surface was obtained by fitting the semicircles ( ) in the cycled Zn/Zn symmetric battery, which is known to cause an ion gradient at the electrolyte and electrode interface and can assist the dendrite growth, [12] while the Zn(OTf) 2 -TEP-H 2 O electrolyte had a much higher t + Zn 2 of 0.76 (Figure S29, Supporting Information). Therefore, the electron insulating property as well as the low energy barrier for ion…”

“…On the anode side, the parasitic H 2 evolution during Zn deposition is inevitable, since water is thermodynamically unstable at the Zn deposition potential. [12] The evolution of H 2 changes the local pH environment and triggers the formation of passivation layers such as Zn(OH) 2 and ZnO, which become barriers against ion/electron diffusion, reduce the Zn utilization, and promote Zn dendrite growth. Therefore, it is necessary to inhibit these side reactions of H 2 O in aqueous electrolyte to enable good Zn electrode reversibility.…”

A Universal Compensation Strategy to Anchor Polar Organic Molecules in Bilayered Hydrated Vanadates for Promoting Aqueous Zinc‐Ion Storage

“…In the full cells, three‐dimensional nitrogen doped carbon nanofiber film@Zn (3DN‐C@Zn) serves as dendrite‐free anode to replace common Zn foil anode, which often suffers from Zn dendrites in traditional aqueous electrolyte because of the unhomogeneous Zn deposition. [ 39–45 ] 3DN‐C@Zn was obtained through electrodepositing Zn on 3DN‐C, where 3DN‐C was prepared by combining electrospinning technique with pyrolysis process (Figure S15 and S16). 3DN‐C displays hydrophilic property, as reflected by the contact angle (almost 0 o ) between 3DN‐C and water (Figure S17).…”

Current Advances on Zn Anodes for Aqueous Zinc‐Ion Batteries

“…This opens facile routes of synthesizing in situ SEI by novel electrolyte design. Addition of 0.025 M Zn(H 2 PO 4 ) 2 into 1 M Zn(OTf) 2 enables the formation of a dense and uniform SEI, which was identified to be Zn 3 (PO 4 ) 2 ⋅ 4H 2 O (Figure 5A) [75] . A composite SEI made of Zn 3 (PO 4 ) 2 and ZnF 2 was designed via an in situ method using KPF 6 (Figure 5B) [76] .…”