Electrochemical Energy Storage Devices
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As the world goes electric, storage of electricity is in urgent demand. Energy storage devices ranges from grid storage with the size of a parking lot to the small, light, stretchable wearable variants. Our group focuses on the latter, synthesizing new materials and devising new device architectures.
The battery-capacitor performance tradeoff has long been a standing dilemma, involving an undesirable sacrifice to either power or energy density. Microsupercapacitors (MSCs) can deliver energy quickly, but their energy density must be increased if they are to efficiently power flexible and wearable electronics, as well as larger equipment. Having to always use both batteries and capacitors for both capacity and speed in a given energy system is a roadblock to reducing system complexity, size, and cost. As is well-known, due to the operating principle based on physical absorption rather than a chemical reaction, MSCs suffer from drawbacks of insufficient areal energy density. But perhaps what is often overlooked is that MSCs also exhibit an undesirable sloped galvanostatic charge-discharge (GCD) output profile during the discharge process, while many applications demand a steady supply of a certain minimum voltage level.
An alternative approach encompassing a new combination of electrode materials and device structure is urgently needed to remove the aforementioned drawbacks, thereby truly combining the performance advantages of both MSCs and microbatteries. To this end, we have proposed an innovative device architecture, which we term the micro-redoxcapacitor (MRC). The MRC combines both ion intercalation (as in a capacitor) and solid-solid redox reaction (as in a battery). A major difference between our proposed MRC and the hybrid MSC is that the MRC implements both ion intercalation and redox reaction in a single electrode, the cathode, which to the best of our knowledge, has not been previously reported. To demonstrate the architecture and assess performance, we have prototyped the world's first MRC, consisting a MXene hybrid cathode, a Zn anode, and a polyacrylamide (PAM)/ZnCl2+NH4Cl hydrogel electrolyte.
We plan to further develop the new MRC paradigm, endowing it with more materials choices and efficient device implementations for a variety of applications requiring combined high power and energy densities, stretchability, and charge-discharge in excess of 10000 cycles.