Metal Negatrode Supercapatteries: Advancements, Challenges, and Future Perspectives for High-Performance Energy Storage

Metal negatrode supercapattery (MNSC) is an emerging technology that combines the high energy storage capabilities of batteries with the high-power delivery of supercapacitors, thereby offering promising solutions for various applications, such as energy storage systems, electric vehicles, and portable electronics. This review article presents a comprehensive analysis of the potential of MNSCs as a prospective energy storage technology. MNSCs utilize a specific configuration in which the negatrode consists of a metal or metal-rich electrode, such as sodium, aluminum, potassium, or zinc, whereas the positrode functions as a supercapacitor electrode. The utilization of negatrodes with low electrochemical potential and high electrical conductivity is crucial for achieving high specific energy in energy storage devices, despite facing numerous challenges. The present study discusses the design and fabrication aspects of MNSCs, including the selection of appropriate metal negatrodes, electrolytes, and positrodes, alongside the fundamental operational mechanisms. Additionally, this review explores the challenges encountered in MNSCs and proposes solutions to enhance their performance, such as addressing dendrite formation and instability of metal electrodes.

Ultrahigh Energy Density and Long-Life Cyclic Stability of Surface-Treated Aluminum-Ion Supercapacitors

In this study, aluminum-graphene supercapacitors (denoted as aluminum-ion supercapacitors; ASCs), consisting of a battery-type aluminum anode, a capacitor-type graphene cathode, and ionic liquid 1-ethyl-3-methylimidazolium chloride (EMImCl) and aluminum chloride (AlCl₃) electrolyte, were prepared. This study primarily aimed to investigate the enhanced electrochemical performance of ASCs arising from changes in the surface oxide layer and morphology via electrochemical surface treatments, including electropolishing and electrodeposition of aluminum anodes. The ASC devices based on an electrodeposited anode at a current density of 3 A g^-1 exhibited a high specific capacity of 211 F g^-1 compared to that of the electropolished anode (∼186 F g^-1); these were 20 and 5.7%, respectively, higher than that of the pristine aluminum anode. In particular, the electrodeposited ASC delivered an energy density of 151 W h kg^-1 at a power density of 3,390 W kg^-1. Furthermore, a maximum power density of 11,104 W kg^-1 was achieved at an energy density of 124.3 W h kg^-1. These values are among the best as compared to those of previously reported aluminum-based supercapacitors, suggesting the potential feasibility of these ASCs with outstanding energy and power densities for next-generation energy storage devices.

Boosting capacitive performance of manganese oxide nanorods by decorating with three-dimensional crushed graphene

This work reports the rational design of MnO_x nanorods on 3D crushed reduced graphene oxide (MnO_x/C-rGO) by chemical reduction of Ni-incorporated graphene oxide (GO) followed by chemical etching to remove Ni. The resulting MnO_x/C-rGO composite synergistically integrates the electronic properties and geometry structure of MnO_x and 3D C-rGO. As a result, MnO_x/C-rGO shows a significantly higher specific capacitance (C_sp) of 863 F g^-1 than MnO_x/2D graphene sheets (MnO_x/S-rGO) (373 F g^-1) and MnO_x (200 F g^-1) at a current density of 0.2 A g^-1. Furthermore, when assembled into symmetric supercapacitors, the MnO_x/C-rGO-based device delivers a higher C_sp (288 F g^-1) than MnO_x/S-rGO-based device (75 F g^-1) at a current density of 0.3 A g^-1. The superior capacitive performance of the MnO_x/C-rGO-based symmetric device is attributed to the enlarged accessible surface, reduced lamellar stacking of graphene, and improved ionic transport provided by the 3D architecture of MnO_x/C-rGO. In addition, the MnO_x/C-rGO-based device exhibits an energy density of 23 Wh kg^-1 at a power density of 113 Wkg^-1, and long-term cycling stability, demonstrating its promising potential for practical application.

Emerging trends in anion storage materials for the capacitive and hybrid energy storage and beyond

Electrochemical capacitors charge and discharge more rapidly than batteries over longer cycles, but their practical applications remain limited due to their significantly lower energy densities. Pseudocapacitors and hybrid capacitors have been developed to extend Ragone plots to higher energy density values, but they are also limited by the insufficient breadth of options for electrode materials, which require materials that store alkali metal cations such as Li⁺ and Na⁺. Herein, we report a comprehensive and systematic review of emerging anion storage materials for performance- and functionality-oriented applications in electrochemical and battery-capacitor hybrid devices. The operating principles and types of dual-ion and whole-anion storage in electrochemical and hybrid capacitors are addressed along with the classification, thermodynamic and kinetic aspects, and associated interfaces of anion storage materials in various aqueous and non-aqueous electrolytes. The charge storage mechanism, structure-property correlation, and electrochemical features of anion storage materials are comprehensively discussed. The recent progress in emerging anion storage materials is also discussed, focusing on high-performance applications, such as dual-ion- and whole-anion-storing electrochemical capacitors in a symmetric or hybrid manner, and functional applications including micro- and flexible capacitors, desalination, and salinity cells. Finally, we present our perspective on the current impediments and future directions in this field.

Nonaqueous Rechargeable Aluminum Batteries: Progresses, Challenges, and Perspectives

For significantly increasing the energy densities to satisfy the growing demands, new battery materials and electrochemical chemistry beyond conventional rocking-chair based Li-ion batteries should be developed urgently. Rechargeable aluminum batteries (RABs) with the features of low cost, high safety, easy fabrication, environmental friendliness, and long cycling life have gained increasing attention. Although there are pronounced advantages of utilizing earth-abundant Al metals as negative electrodes for high energy density, such RAB technologies are still in the preliminary stage and considerable efforts will be made to further promote the fundamental and practical issues. For providing a full scope in this review, we summarize the development history of Al batteries and analyze the thermodynamics and electrode kinetics of nonaqueous RABs. The progresses on the cutting-edge of the nonaqueous RABs as well as the advanced characterizations and simulation technologies for understanding the mechanism are discussed. Furthermore, major challenges of the critical battery components and the corresponding feasible strategies toward addressing these issues are proposed, aiming to guide for promoting electrochemical performance (high voltage, high capacity, large rate capability, and long cycling life) and safety of RABs. Finally, the perspectives for the possible future efforts in this field are analyzed to thrust the progresses of the state-of-the-art RABs, with expectation of bridging the gap between laboratory exploration and practical applications.