Multifunctional Quasi-Solid-State Zinc–Sulfur Battery

Abstract

The introduction of structural energy storage devices into emerging markets, such as electric vehicles, is predominately hindered by weak energy density, safety concerns, and immaturity of the field in materials. Herein, fabrication and testing of a freeze-resistant, multifunctional quasi-solid-state zinc−sulfur battery (ZnS) are reported. To this end, an electrostatic spray coating technique was used to deposit a thin layer of sulfur on the highly porous, unidirectional activated carbon nanofibers (A-CNFs) as a load-bearing cathode. This technique could fill micro-and mesopores, and microsized channels with sulfur, achieving an extensive sulfur loading of 60 wt %. Several drawbacks of structural energy storage devices (applicability under varied climate conditions, poor electrochemical performance and mechanical properties) are addressed by initiating an antifreezing hydrogel electrolyte with a failure strain of over 200%. This electrolyte possesses ethylene glycol and an I 2 additive as an antifreezing agent and redox mediator, respectively. The as-assembled ZnS battery offers a high energy density of 283 Wh/kg based on the CNF-S cathode (149 Wh/ kg based on the ZnS cell) and mechanical properties beyond state-of-the-art structural energy storage devices with a tensile strength of 377 MPa, Young's modulus of 16.7 GPa, and energy-to-failure of 4.5 MJ/m 3 . The electrochemomechanical properties of the ZnS battery were also investigated to elucidate the effects of electrochemical energy storage on mechanical properties and vice versa. Overall, the ZnS battery outperforms state-of-the-art structural energy storage devices in terms of energy storage and load-bearing capabilities.

Fully integrated design of a stretchable kirigami-inspired micro-sized zinc–sulfur battery

“…In our recent article, 37 we proved an increase in the charge transfer resistance with the number of cycles, which was associated with the development of a surficial passivated layer caused by the side reactions with the formed SO 4 2− ions. This passivated layer and decrease in pH due to the formation of the SO 4 2− ions during initial cycles, limit the side charging reactions provided in Table S1 † 33,37 . A discharge capacity retention rate of 90% was achieved after 600 cycles and was increased in the successive 200 cycles.…”

“…2e shows that the coulombic efficiency increases sharply to 96% aer 50 cycles and slightly to 98% aer 800 cycles. In our recent article, 37 we proved an increase in the charge transfer resistance with the number of cycles, which was associated with the development of a surcial passivated layer caused by the side reactions with the formed SO 4 2− ions. This passivated layer and decrease in pH due to the formation of the SO 4 2− ions during initial cycles, limit the side charging reactions provided in Table S1.…”

“…They also showed that the discharge capacity decreases with the increase of sulfur content from 40 to 70 wt%, but samples with 40 wt% sulfur suffer severe side reactions at the voltage range of 1.4–1.6 V in the charging process. The possible side charge reactions are summarized in Table S1 † 33,37 . The formation of SO 4 2− can be considered as the primary deterioration reaction at the voltage range of 1.4–1.6 V. The formation of SO 4 2− ions, as shown in the Pourbaix diagram, 38 accelerates at higher pH.…”

“…The possible side charge reactions are summarized in Table S1. † 33,37 The formation of SO 4 2− can be considered as the primary deterioration reaction at the voltage range of 1.4-1.6 V. The formation of SO 4 2− ions, as shown in the Pourbaix diagram, 38 accelerates at higher pH. Since the surface of the activated carbon is decorated with O-H groups, they may increase the pH of the hydrogel by penetration and lead to the formation of more SO 4 2− ions and a plateau curve at 1.4-1.6 V in the charging process.…”

“…This passivated layer and decrease in pH due to the formation of the SO 4 2− ions during initial cycles, limit the side charging reactions provided in Table S1. † 33,37 A discharge capacity retention rate of 90% was achieved aer 600 cycles and was increased in the successive 200 cycles. The initial 10% capacity fading may be caused by abstruse oxygen and hydrogen evolution irreversible reactions, formation of SO 4 2− , side reactions, disproportionation, and dissociation in the stretchable Zn-S battery.…”