A Supercapacitor Architecture for Extreme Low‐Temperature Operation Featuring MXene/Carbon Nanotube Electrodes with Vertically Aligned Channels and a Novel Freeze‐Resistant Electrolyte

Abstract

The electrochemical performance of supercapacitors drops precipitously at extreme low temperatures due to a multitude of reasons, which includes electrolyte freezing, sluggish ion transport in the electrode and electrolyte, and high charge transfer resistance at electrode–electrolyte interfaces. To address high interface resistance, a new supercapacitor architecture is reported, in which MXene/carbon nanotube electrodes with vertically aligned channels are synthesized to reduce tortuosity and maximize the electrode–electrolyte contact area. These electrodes are fabricated using a directional‐freezing strategy, generating direct and fast ion transport pathways. Further, a freeze‐resistant electrolyte which shows high ionic conductivity is synthesized by designing a double‐crosslinked polymer network in a binary solvent consisting of ionic liquid and water, which exhibits an ultralow freezing temperature of −54 °C. An all‐in‐one supercapacitor is assembled by an integrated polymerization strategy to minimize interfacial resistances. The resulting device delivers a specific capacitance of 231 F g−1 at 2 mV s−1 and a maximum energy density of 10.17 Wh kg−1, while maintaining a capacitance retention of 92%, even at an extreme low temperature of −50 °C. The supercapacitor architecture developed in this study, demonstrates the feasibility of electrochemical energy storage at extreme low temperatures.

Antifreezing, Antidrying, and Conductive Hydrogels for Electronic Skin Applications at Ultralow Temperatures

“…Conductive hydrogels with three-dimensional (3D) networks can be applied as substrates of flexible electronic devices, such as smart energy storage equipment, wearable and portable sensors, and soft robots, because of their high flexibility and adjustable conductivities. − However, due to the inevitable freezing of the hydrogels and the sluggish electron and ion transport at low temperatures, , their ionic conductivity and flexibility reduce seriously, causing malfunction of the devices. Many efforts have been made to address this issue by weakening the hydrogen bonds between water molecules, − including the modification of polymer networks and the introduction of antifreezing agents (ionic liquids, etc.…”

Comparative Study of Electrochromic Supercapacitor Electrodes Based on PEDOT:PSS/ITO Fabricated via Spray and Electrospray Methods

“…The need to transition from traditional energy sources to renewable alternatives has spurred significant interest in the development of efficient energy storage devices. , In recent years, supercapacitors (SCs) have garnered substantial interest within the realm of energy storage systems, attributed to their rapid charge−discharge capabilities, impressive power density, and exceptional cycle stability . Another important topic, electrochromism refers to the reversible alteration of color induced by an applied voltage, a phenomenon driven by electrochemical redox reactions occurring within the electrochromic (EC) materials. − The charge injection and extraction occurring during the charge−discharge phases of the SC align with the chromatic transitions observed at various potentials, providing an effective indication of energy storage levels .…”

Proton Hydrogel-Based Supercapacitors with Rapid Low-Temperature Self-Healing Properties

“…26 Meanwhile, organic solvents also possess environmental hazards. 27 Additionally, integrating high concentrations of inorganic salts into hydrogels easily causes crystallization, resulting in the instability of hydrogels. At the same time, the high content of inorganic salts possesses corrosiveness on supercapacitors.…”

“…However, the addition of organic solvents such as glycerol, ethylene glycol, and dimethyl sulfoxide tends to suppress the dissociation of salts, causing poor conductivity of hydrogels . Meanwhile, organic solvents also possess environmental hazards . Additionally, integrating high concentrations of inorganic salts into hydrogels easily causes crystallization, resulting in the instability of hydrogels.…”