Developments of Low-Cost Aqueous Sodium-Ion Batteries with Prussian Blue Analogue Positive Electrodes for Solar Energy Storage Applications

Abstract

In this thesis, different aqueous sodium ion batteries are presented with various combinations of positive electrode, negative electrode and electrolyte, whereas the target application is the solar energy storage. Several Prussian blue analogues (PBAs) with multiple transition metal substitutions are utilized as positive electrodes, while diverse classes of redox active materials, namely functionalized carbons, vanadium based polyoxometalates, metal oxides, metal phosphates etc. are screened for negative electrodes. Herein, low-cost stainless steel current collectors are utilized, while optimized corrosion protective coatings are applied. The sodium ion prototype cells and devices with multiple electrode couples are assembled in both flooded and starved electrolyte configurations. The exploitation of hydrogels as electrolyte media is vividly emphasized in this thesis. However, all the developed prototype cells/devices are laboratory tested through specific capacity, Faradaic efficiency, rate capability, energy density, power density and cycle life at a wide range of working temperatures. Moreover, the prototype devices are also performance tested through the custom-built solar charging module as part of the feasibility assessments for solar energy storage applications. However, this thesis comprises eight chapters, and brief descriptions of each chapter are following. Chapter 1 elaborates the basic concepts of battery applications in renewable energy storage sectors. This chapter starts with the fundamental ideas of energy storage devices, namely batteries and supercapacitors, while their significances in our daily life are greatly discussed. The limitations of present battery technologies for solar energy storage are addressed, and the lacuna could be filled by the introduction of aqueous sodium ion batteries. The middle part of this chapter deals with the sodium ion electrochemistry and relevant active material screening. However, this chapter culminates with the wise selection of PBAs as positive electrode materials in sodium ion systems. Chapter 2 describes hybrid sodium ion batteries, wherewith Na2NiFe(CN)6 (Ni-PBA) positive electrode couples with functionalized carbon negative electrodes in starved electrolyte configuration. A 1 M Na2SO4 (aq.) solution is used as electrolyte, which is socked in porous adsorbent glass mat (AGM) separator. Chapter 3 demonstrates Na2CoFe(CN)6//NaV3O8 (Co-PBA//NVO) couple for successful sodium ion cells under pouch and prismatic cell configurations, whereas respective Na2SO4-AGM and Na2SO4- SiO2-hydrogel electrolytes are employed. Chapter 4 depicts the sodium ion cell with Na2MnFe(CN)6 (Mn-PBA) positive and commercial Fe2O3 negative electrodes in Na2SO4-SiO2-hydrogel electrolyte. This cell chemistry does not sustain well due to multiple performance limiting issues arising from both positive and negative electrodes. Chapter 5 emphasis on the limitations of Mn-PBA//Fe2O3 couple, and the legitimate solutions are addressed. Herein, Ni incorporation in Mn-PBA and Na-doping in Fe2O3 appreciably mitigate the problems of Mn-PBA//Fe2O3 couple. Therefore, a successful sodium ion cell is reported by coupling Na2Mn0.5Ni0.5Fe(CN)6 (MnNi-PBA) as positive and Na-doped Fe2O3 (NaxFe2O3) as negative electrodes in a novel hydrogel comprising carboxymethyl cellulose (CMC) and SiO2 in 1 M Na2SO4 (aq.). Chapter 6 demonstrates the performance studies of Na2Co0.5Ni0.5Fe(CN)6//Na3Ti2(PO4)3 (CoNiPBA//NTP) sodium ion cell in 1 M (aq.) Na2SO4-SiO2 hydrogel electrolyte. Chapter 7 represents the optimization studies of Ni/Co/Mn ratio in Na2NixCoyMnzFe(CN)6 system, while, Na2Ni0.33Co0.33Mn0.33Fe(CN)6 demonstrates augmented electrochemical performances. A sodium ion full cell is assembled with Na2Ni0.33Co0.33Mn0.33Fe(CN)6 positive and hydrogen Vanadate negative electrodes in Na2SO4-CMC-SiO2 hydrogel electrolyte. Chapter 8 introduces the high entropy PBAs (HE-PBAs: Na1.3Mn0.2Fe0.2Co0.2Ni0.2Cu0.2[Fe(CN)6]0.82‧2.2H2O and Na1.7Mn0.2Fe0.2Co0.2Ni0.2Zn0.2[Fe(CN)6]0.93‧1.4H2O) as positive electrodes in aqueous sodium ion cells. The Na2Mn0.2Fe0.2Co0.2Ni0.2Cu0.2Fe(CN)6 shows better charge storage performances, and is coupled with Na-incorporated CuFeO, derived from Na2CuFe(CN)6, in Na2SO4-CMC-SiO2 hydrogel electrolyte. However, the thesis is culminated with a concise description of future directions for PBAs based advanced sodium ion batteries for solar energy storage towards sustainable developments.