(i). Seawater battery: 

Seawater batteries (SWBs) could be a promising contender for large-scale implementation as their eco-friendly and use of abundant seawater as sources of Na-ions or active materials. This SWB can convert chemical energy into electrical energy, often represented as reversible like rechargeable metal (Li/Na)-air batteries. But unlike rechargeable metal (Li/Na)-air/O2 batteries, SWB typically utilizes the Na-ions, hydroxide ions, H2O molecules, and dissolved oxygen present in the seawater for the repeated charge-discharge process.

Related Publications: 

1. Development of coin-type cell and engineering of its compartments for rechargeable seawater batteries, J Han, SM Hwang, W Go, S. T. Senthilkumar, D Jeon, Y Kim. Journal of Power Sources, 2018, 374, 24-30. (Link)

2. Seawater battery performance enhancement enabled by a defect/edge- rich, oxygen self-doped porous carbon electrocatalyst, S. T. Senthilkumar, Sung O. Park, Junsoo Kim, Soo Min Hwang, Sang Kyu Kwak and Youngsik Kim. Journal of Materials Chemistry A, 2017, 5, 14174-14181. (Link)

3. Emergency of Rechargeable Seawater Battery, S. T. Senthilkumar; W. Go; J. Han; L. P.Thi Thuy; K. Kishor; Y.Kim; Y. Kim. Journal of Materials Chemistry A, 2019,7, 22803-22825 (Review article). (Link)

(ii). Hybrid electrolyte Na-ion battery: 

Aqueous rechargeable sodium-ion batteries (ARSBs) have attracted much attention as a promising alternative owing to advantages such as low cost, green, and safety. However, one of the primary disadvantages of ARSBs is that they deliver a relatively low energy density owing to the limited working voltage (∼2 V) due to the decomposition of water. So, the enhancement of cell voltage has been a major challenge. However, the working voltage of ARSBs can be improved by using NASICON (Na3Zr2Si2PO12) as the solid electrolyte, which separates the moisture-sensitive Na metal anode (in a non-aqueous electrolyte) from the aqueous electrolyte (water).

(iii). Hybrid electrolyte Na-ion Flow battery: 

Redox flow battery (RFB) technologies have become a significant role in the future in storing electrical energy produced from intermittent renewable energies such as solar, wind, and hydroelectric powers. However, the development of high-energy-density RFB remains challenging. The energy density can be increased in two ways; (i) using high concentration and increasing cell voltage. Na-aqueous-catholyte RFB (NaAqRFB) could be a potential contender for high-density electrical energy storage. NASICON (Na3Zr2Si2PO12) is employed as a solid electrolyte in the NaAqRFB to separate the Na anode and a flowable aqueous catholyte. In NaAqRFB, the Na-metal anode can offer a high capacity and lower redox potential, which is key to increasing the cell voltage and energy density. The use of an aqueous flowing catholyte in NaAqRFB could decouple the energy and power. 

(i). Fiber-type weaveable supercapacitor:

Flexible fiber electronic devices have attracted extensive research interest in the past few years due to their unique features and potential applications in next-generation wearable electronics and smart textiles. Various fiber-type energy storage devices are highly demanded to store or power the available fiber electronic devices. Among them, supercapacitors (SCs) act as a promising candidate that can offer long cycle life, high power density, safety, etc.

Supercapacitors (SCs) are a promising field in energy storage devices. In the last few decades, different types of carbon-based materials with suitable surface modifications, metal oxides, metal hydroxides, conducting polymers, and their various composites, have been used as electrodes to improve the energy performance of SCs. In addition, different technologies like asymmetric and hybrid systems have also been introduced. Interestingly, another alternative approach has been proposed recently by a few research groups, wherein electrolytes (liquid and polymer) can enhance the performance of the SCs via redox reactions at the electrode-electrolyte interface by introducing redox additives or mediators in the electrolytes. The main advantage of this new technique is its safe and straightforward preparation method and cost-effectiveness compared to the preparation of some active electrode materials. Hence, it is believed that identifying suitable redox additives or species in electrolytes will be a hotspot in the field of SCs in the coming years.