Lithium-sodium ion capacitors: A new type of hybrid supercapacitors with high energy density

Controllable Synthesis of Heterogeneous ZnS/SnS2 Encapsulated in Hollow Nitrogen-Doped Carbon Microcubes as Anode for High-Performance Li-ion Capacitors

Li-ion capacitors (LICs) integrate the desirable features of lithium-ion batteries (LIBs) and supercapacitors (SCs), but the kinetic imbalance between the both electrodes leads to inferior electrochemical performance. Thus, constructing an advanced anode with outstanding rate capability and terrific redox kinetics is crucial to LICs. Herein, heterostructured ZnS/SnS2 nanosheets encapsulated into N-doped carbon microcubes (ZnS/SnS2@NC) are successfully fabricated. The sufficient ZnS/SnS2 heterostructure possesses abundant active sites, and the built-in electric field formed at the heterojunction interface can facilitate electron/ion migration. The interconnected hollow carbon layers could reduce the electron transfer resistance effectively and accommodate the volume change of SnS2, thereby maintaining the structural stability. Due to the synergy between multi-components, the ZnS/SnS2@NC anode demonstrates impressive Li storage performance with an excellent cyclic durablity (690 mAh g-1 at 0.5 A g-1 after 600 cycles) and considerable rate capability. Moreover, when matched with active carbon, the ZnS/SnS2@NC based LIC device delivers an admirable energy density of 134.1 Wh kg-1 and a high power output of 11,250 W kg-1, as well as remarkable capacity retention of 73.2 % after 6,000 cycles at 1.0 A g-1. The experimental results demonstrate the significance of optimized heterointerface engineering toward construction of electrode materials with high-performance for Li storage.

High-Performance Li-Ion and Na-Ion Capacitors Based on a Spinel Li4Ti5O12 Anode and Carbonaceous Cathodes

Lithium-ion hybrid capacitors (LICs) have become promising electrochemical energy storage systems that overcome the limitations of lithium-ion batteries and electrical double-layer capacitors. The asymmetric combination of these devices enhances the overall electrochemical performance by delivering simultaneous energy and power capabilities. Lithium titanate (Li4Ti5O12, LTO), a spinel zero-strain material, has been studied extensively as an anode material for LIC applications because of its high-rate capability, negligible volume change, and enhanced cycling performance. Here, the different synthetic methods and modifications of the intercalation-type LTO to enhance the overall electrochemical performance of LICs are mainly focused. Moreover, the cathodic part (i.e., the activated carbon derived from various sources, including natural products, polymers, and inorganic materials) is also dealt with as it contributes substantially to the overall performance of the LIC. Not only do the anode and cathode, but also the electrolytes have a substantial influence on LIC performance. The electrolytes used in LTO-based LICs as well as in flexible and bendable configurations are also mentioned. Overall, the previous work along with other available reports on LTO-based LICs in a simplified way is analyzed.

"Porous and Yet Dense" Electrodes for High-Volumetric-Performance Electrochemical Capacitors: Principles, Advances, and Challenges

With the ever-rapid miniaturization of portable, wearable electronics and Internet of Things, the volumetric performance is becoming a much more pertinent figure-of-merit than the conventionally used gravimetric parameters to evaluate the charge-storage capacity of electrochemical capacitors (ECs). Thus, it is essential to design the ECs that can store as much energy as possible within a limited space. As the most critical component in ECs, "porous and yet dense" electrodes with large ion-accessible surface area and optimal packing density are crucial to realize desired high volumetric performance, which have demonstrated to be rather challenging. In this review, the principles and fundamentals of ECs are first observed, focusing on the key understandings of the different charge storage mechanisms in porous electrodes. The recent and latest advances in high-volumetric-performance ECs, developed by the rational design and fabrication of "porous and yet dense" electrodes are then examined. Particular emphasis of discussions then concentrates on the key factors impacting the volumetric performance of porous carbon-based electrodes. Finally, the currently faced challenges, further perspectives and opportunities on those purposely engineered porous electrodes for high-volumetric-performance EC are presented, aiming at providing a set of guidelines for further design of the next-generation energy storage devices.