Flexible Aqueous Rechargeable Metal-ion Batteries for Wearable Applications


Student thesis: Doctoral Thesis

View graph of relations



Awarding Institution
Award date28 Aug 2019


Flexible and wearable electronics are in explosive growth recently and considerable attention has been drawn to the corresponding indispensable energy storage devices. These electronics will bring significant change to human lifestyle due to the infinite possibilities they could offer, and high-tech companies have demonstrated how cutting-edge discoveries could be translated into real world. However, current commercially-available energy storage systems are intrinsically rigid because of their traditional stacking and packaging methods, which is a poor fit for wearable applications, thus having become a bottleneck for the further development of wearable electronics. Therefore, energy storage devices with high flexibility, superior durability, intrinsic safety, as well as good electrochemical performances are urgently desired in terms of boosting the practical applications of wearable electronics.

Lithium-ion batteries (LIBs) have long been commercialized and are believed to be one of the most promising candidates to power various electronics due to their high energy density. While they suffer from the risks of fires and explosions because of the employment of toxic and flammable organic electrolytes, especially when they are being used under pressure and deformations. To address these issues, we first report an aqueous lithium-ion battery (ALIB) based on carbon cloth substrates and polyvinyl alcohol-LiNO3 gel polymer electrolyte. With suppressed dissolution of LiV3O8 (LVO) anode, improved charge transfer resistance and buffered volume change during cycling by polypyrrole coating, the as-assembled LVO-based ALIB exhibits one of the best ever-reported cycle performances in aqueous electrolyte, retaining 98.7% and 79.8% of its capacity at 0.5 A g-1 after 100 and 500 cycles, respectively. It also demonstrates exceptional flexibility to sustain various deformations including bending, squeezing, twisting and folding because of the solid-state design. Moreover, the ALIB can be tailored into any desired shapes, and even be punched penetrative holes, exhibiting excellent safety. Thus, the creation of numerous tiny through-holes across the whole ALIB body is testified feasible, and a designed breathability catering to the demand of comfortability in wearable devices is thus realized.

Meanwhile, to facilitate the practical application of flexible energy storage devices, mechanical durability should be considered, which includes stability against dynamic mechanical stimuli as well as device-level toughness to ensure long-term usability. We present a mechanically durable zinc-ion battery based on a zinc anode, a MnO2 cathode, and a dual-crosslinked hydrogel electrolyte without the usage of separator. Compared to monovalent ALIB, this divalent aqueous zinc-ion battery (AZIB) system appears to be a more advantageous choice for wearable applications due to the intrinsic high capacity, high abundance, and low cost of zinc anode. The as-fabricated AZIB shows good electrochemical performances including a high specific capacity of 300.4 mAh g-1 at 0.11 A g-1 and 82% capacity retention after 500 charge-discharge cycles at 0.88 A g-1. Due to the effective energy dissipation of the hydrogel, the as-fabricated battery maintains a stable energy output when being dynamically deformed under severe mechanical stimuli. It can be vastly deformed into various shapes without electrochemical performance decay, showing excellent flexibility. It also exhibits super toughness that can endure two days’ treading pressure and survive 20 times of random run-over by cars on road. These demonstrations reveal its outstanding mechanical stability and durability, suggesting great potential in truly flexible and wearable applications.

Finally, to benefit the energy density and consistent power supply of wearable electronics, we develop a flexible aqueous zinc hybrid battery with flat and high-voltage discharge plateau. The employment of highly-concentrated electrolyte and hierarchically-structured lithium ion-intercalative LiVPO4F cathode enables a consistent discharge plateau of 1.9 V and a specific capacity of 146.9 mAh g-1, which contributes to an energy density of 235.6 Wh kg-1 at the power density of 320.8 W kg-1, having outperformed most reported ZIBs. This zinc hybrid battery can be integrated into various flexible devices as powerful energy supply by utilizing a highly-concentrated electrolyte-based hydrogel. The idea of designing such hybrid battery system offers a new strategy for developing high-voltage and high-energy aqueous batteries for wearable electronics.

In summary, various aqueous metal-ion battery systems with high flexibility, absolute safety, exceptional durability, and outstanding energy output capability are developed and comprehensively studied in this thesis, targeting at practical applications of wearable electronics. It is believed that the studies and strategies presented in the thesis can shed light on the design of flexible energy storage systems for future wearable electronics.