Rational Design of a Piezoelectric BaTiO 3 Nanodot Surface‐Modified LiNi 0.6 Co 0.2 Mn 0.2 O 2 Cathode Material for High‐Rate Lithium‐Ion Batteries

Piezoelectric 1T Phase MoSe2 Nanoflowers and Crystallographically Textured Electrodes for Enhanced Low-Temperature Zinc-Ion Storage

Transition metal dichalcogenides (TMDs) are regarded as promising cathode materials for zinc-ion storage owing to their large interlayer spacings. However, their capabilities are still limited by sluggish kinetics and inferior conductivities. In this study, a facile one-pot solvothermal method is exploited to vertically plant piezoelectric 1T MoSe₂  nanoflowers on carbon cloth (CC) to fabricate crystallographically textured electrodes. The self-built-in electric field owing to the intrinsic piezoelectricity during the intercalation/deintercalation processes can serve as an additional piezo-electrochemical coupling accelerator to enhance the migration of Zn²⁺ . Moreover, the expanded interlayer distance (9-10 Å), overall high hydrophilicity, and conductivity of the 1T phase MoSe₂  also promoted the kinetics. These advantages endow the tailored 1T MoSe₂ /CC nanopiezocomposite with feasible Zn²⁺ diffusion and desirable electrochemical performances at room and low temperatures. Moreover, 1T MoSe₂ /CC-based quasi-solid-state zinc-ion batteries are constructed to evaluate the potential of the proposed material in low-temperature flexible energy storage devices. This work expounds the positive effect of intrinsic piezoelectricity of TMDs on Zn²⁺ migration and further explores the availabilities of TMDs in low-temperature wearable energy-storage devices.

Elucidating the cation hydration ratio in water-in-salt electrolytes for carbon-based supercapacitors

The solvation of cations is one of the important factors that determine the properties of electrolytes. Rational solvation structures can effectively improve the performance of various electrochemical energy storage devices. Water-in-Salt (WIS) electrolytes with a wide electrochemically stable potential window (ESW) have been proposed to realize high cell potential aqueous electrochemical energy storage devices relying on the special solvation structures of cations. The ratio of H₂O molecules participating in the primary solvation structure of a cation (a cation hydration ratio) is the key factor for the kinetics and thermodynamics of the WIS electrolytes under an electric field. Here, acetates with different cations were used to prepare WIS electrolytes. And, the effect of different cation hydration ratios on the properties of WIS electrolytes was investigated. Various WIS electrolytes exhibited different physicochemical properties, including the saturated concentration, conductivity, viscosity, pH values and ESW. The WIS electrolytes with a low cation hydration ratio (<100%, an NH₄-based WIS electrolyte) or a high cation hydration ratio (>100%, a K-based WIS electrolyte and a Cs-based WIS electrolyte) exhibit more outstanding conductivity or a wide ESW, respectively. SCs constructed from active carbon (AC) and these WIS electrolytes exhibited distinctive electrochemical properties. A SC with an NH₄-based WIS electrolyte was characterized by higher capacity and better rate capability. SCs with a K-based WIS electrolyte and a Cs-based WIS electrolyte were characterized by a wider operating cell potential, higher energy density and better ability to suppress self-discharge and gas production. These results show that a WIS electrolyte with a low cation hydration ratio or a high cation hydration ratio is suitable for the construction of power-type or energy-type aqueous SCs, respectively. This understanding provides the foundation for the development of novel WIS electrolytes for the application of SCs.