A hollow graphene/conducting polymer composite fiber is created with high mechanical and electronic properties and used to fabricate novel fiber-shaped supercapacitors that display high energy densities and long life stability. The fiber supercapacitors can be woven into flexible powering textiles that are particularly promising for portable and wearable electronic devices.

The electrochemical performance of MnO 2 nanorods prepared by a precipitation reaction was investigated in 0.5 mol/L Li 2 SO 4 , Na 2 SO 4 , and K 2 SO 4 aqueous electrolyte solutions. Results show that at the slow scan rates, the nanorods show the largest capacitance (201 F/g) in Li 2 SO 4 electrolyte since the reversible intercalation/ deintercalation of Li + in the solid phase produces an additional capacitance besides the capacitance based on the absorption/desorption reaction. At fast scan rates they show the largest capacitance in the K 2 SO 4 electrolyte due to the smallest hydration radius of K + , highest ionic conductivity, and lowest equivalent series resistance (ESR). An asymmetric activated carbon (AC)/K 2 SO 4 /MnO 2 supercapacitor could be cycled reversibly between 0 and 1.8 V with an energy density of 17 Wh/kg at 2 kW/kg, much higher than those of the AC/K 2 SO 4 /AC supercapacitor and AC/Li 2 SO 4 /LiMn 2 O 4 hybrid supercapacitor. Moreover, this supercapacitor exhibits excellent cycling behavior with no more than 6% capacitance loss after 23 000 cycles at 10C rate even when the dissolved oxygen is not removed.

With the rapidly increasing interests on wearable electronics over the past decades, the limited energy density and nondeformable configuration of conventional 2D lithium-ion batteries (LIBs) have already become the dominant obstacles that are hindering the roads of wearable consumer electronics toward ubiquity. [1][2][3][4][5] Hence, it is urgent to develop an alternative highperformance flexible energy storage device to break through the inherent restrictions of rigid LIBs. [6][7][8] The Li-CO 2 battery, a newly conceptual metal-gas battery, has been considered as a promising candidate for the next-generation high-performance electrochemical energy storage system recently. [9,10] It possesses a high theoretical energy density via the four-electrons transfer reaction (4Li + + 3CO 2 + 4e − → 2Li 2 CO 3 + C, E° = 2.80 V vs Li + /Li) and provides a novel environmentally friendly approach to CO 2 fixing which is of great benefit to alleviate global warming. [11][12][13] Interestingly, the Li-CO 2 battery is also very attractive for aerospace exploration; for example, it may be a possible energy system for providing electricity on Mars where the atmosphere consists of 96% CO 2 gas. [14] In spite of the aforementioned favorable factors, very few reports in the literature related to flexible Li-CO 2 battery devices for wearable electronics have been reported so far. After systematical investigations, it is found that the main challenges of fabricating high-performance flexible Li-CO 2 battery devices lie in the following three aspects: (1) carbon nanophases (e.g., Ketjenblack, [9,10,15] CNTs, [11,16] graphene [17,18] ), which dominate those known Li-CO 2 battery catalysts, induce the formation of Li 2 CO 3 , a wide-bandgap insulator. [19,20] It results in a sluggish kinetics for CO 2 evolution so that a high charge potential of 4.2-4.6 V was commonly required to drive the degradation of Li 2 CO 3 in most previous Li-CO 2 batteries. [10,11,17] Such high potential not only increases the risk of electrolyte decomposition but also accelerates the oxidation of electrodes. [21,22] Meanwhile, originated from the incomplete decomposition, more and more solid carbonate species accumulated in the surface of cathode during cycling, leading to a distinct decrease on catalytic performance and even the rapid extension of impedance up to a "sudden death" of the battery. [20,23,24] Consequently, the majority of those reported Li-CO 2 batteries showed a negligibleThe rapid development of wearable electronics requires a revolution of power accessories regarding flexibility and energy density. The Li-CO 2 battery was recently proposed as a novel and promising candidate for nextgeneration energy-storage systems. However, the current Li-CO 2 batteries usually suffer from the difficulties of poor stability, low energy efficiency, and leakage of liquid electrolyte, and few flexible Li-CO 2 batteries for wearable electronics have been reported so far. Herein, a quasi-solidstate flexible fiber-shaped Li-CO 2 battery with low overpotential and ...