High-Performance All-Printed Flexible Micro-Supercapacitors with Hierarchical Encapsulation

Printed micro-supercapacitors(MSCs)have shown broad prospect in flexible and wearable electronics.Most of previous studies focused on printing the electrochemically active materials paying less attention to other key components like current collectors and electrolytes.This study presents an allprinting strategy to fabricate in-plane flexible and substrate-free MSCs with hierarchical encapsulation.This new type of“all-in-one”MSC is constructed by encapsulating the in-plane interdigital current collectors and electrodes within the polyvinyl-alcohol-based hydrogel electrolyte via sequential printing.The bottom electrolyte layer of this fully printed MSCs helps protect the device from the limitation of conventional substrate,showing excellent flexibility.The MSCs maintain a high capacitance retention of 96.84%even in a completely folded state.An optimal electrochemical performance can be achieved by providing ample and shorter transport paths for ions.The MSCs using commercial activated carbon as the active material are endowed with a high specific areal capacitance of 1892.90 mF cm^(-2)at a current density of 0.3 mA cm^(-2),and an outstanding volumetric energy density of 9.20 mWh cm^(-3)at a volumetric power density of 6.89 mW cm^(-3).For demonstration,a thermo-hygrometer is stably powered by five MSCs which are connected in series and wrapped onto a glass rod.This low-cost and versatile all-printing strategy is believed to diversify the application fields of MSCs with high capacitance and excellent flexibility.

Advances in doping strategies for sodium transition metal oxides cathodes:A review

The electrochemistry of cathode materials for sodium-ion batteries differs significantly from lithium-ion batteries and offers distinct advantages.Overall,the progress of commercializing sodium-ion batteries is currently impeded by the inherent inefficiencies exhibited by these cathode materials,which include insufficient conductivity,slow kinetics,and substantial volume changes throughout the process of intercalation and deintercalation cycles.Consequently,numerous methodologies have been utilized to tackle these challenges,encompassing structural modulation,surface modification,and elemental doping.This paper aims to highlight fundamental principles and strategies for the development of sodium transition metal oxide cathodes.Specifically,it emphasizes the role of various elemental doping techniques in initiating anionic redox reactions,improving cathode stability,and enhancing the operational voltage of these cathodes,aiming to provide readers with novel perspectives on the design of sodium metal oxide cathodes through the doping approach,as well as address the current obstacles that can be overcome/alleviated through these dopant strategies.

Direct mask-free fabrication of patterned hierarchical graphene electrode for on-chip micro-supercapacitors

Graphene-based electrodes with rational structural design have shown extraordinary prospect for en-hanced electrical double-layer capacitance of micro-supercapacitors(MSCs).Herein,a facile fabrication method for flexible planar MSCs based on hierarchical graphene was demonstrated by using a laser-treated membrane for electrode patterning,complemented with hierarchical electrode configuration tak-ing full advantages of size-determined functional graphene.The in-plane interdigital shape of MSCs was defined through vacuum filtration with the assistance of the functionalized polypropylene(PP)mem-brane.The hierarchical graphene films were built by macroscopic assembly based on size effect of differ-ent lateral sized graphene sheets(rGO-LSL).The sample of MSCs based on rGO-L SL(MSCs-LSL)exhibited excellent volumetric capacitance of 6.7 F cm^(−3) and high energy density of 0.37 mWh cm−3.The MSCs-LSL presented superb flexibility and cycling stability with no capacitance deteroriated after 2000 cycles.This newly developed fabrication strategy is of good scalability and designability to manufacture flexible elec-trode for MSCs with customized shapes,while the construction of hierarchical graphene can enlighten the structural design of analogous two-dimensional materials for potential advanced electronics.