**1. Introduction**

Increasing energy consumption, rising human population and global warming has raised the necessity to progress alternative energy sources and Electrochemical Energy Storage (EES) devices for futuristic necessities. Further, intensifying demand on high-performance EES for portable microelectronic devices and hybrid electric vehicles has designed giant research thrust in the search for a novel diversity of energy storage devices [1–3]. Most of the modern microelectronic are intended to work on EES such as batteries, Supercapacitors and Hybrid Supercapacitors or Supercapbatteries. In particular, small-scale hybrid devices possessions have become vital requirements for diverse insistent purposes such as biomedical devices and portable electronics. With the intent, EES systems have been well-thought-out as an appropriate power sources for innumerable hands-on potential applications owing to the fast charging/discharging rate capability and exceptional stability. Instantaneously, extensive development in EES technology proposes to interest on the electrochemical performance of electrode materials,

electrolytes, and strategy of the devices [4–6]. To make specially, the active material should be sort out in a cost-effective manner for receiving high specific energy and specific power at low cost. However, to meet the greater necessities of upcoming systems, Researchers need to expand their performance by designing novel materials with high energy and power density concurrently. In the past few years, widespread activities have been defined to emphasize for the capable and simplistic progressions to fabricate thin, stretchable, and signifigant solid-state flexible batteries and supercapacitors, which are well thought-out as one of the opted candidates for most promising power sources in many of the portable and microelectronic applications [7–9].

The thin film energy storage devices like batteries and supercapacitors for satisfying the energy inevitabilities to balance both power and energy densities. In typical supercapbatteries contain two types of energy storage mechanism in a single device that which explicit pseudo capacitive (Faradaic) nature and other one is battery behavior [10, 11]. For emerging flexible thin film energy storage devices fabrication to form thin film electrodes there are variety of coating methods such as Electrochemical deposition (ED) [12], Physical Vapor Deposition (PVD) [13], Chemical Vapor Deposition (CVD) [14], sol–gel coating method, spray coatings, dip coating and innovative thin film coating systems such as Atomic Layer Deposition (ALD) [15] and Pulsed Laser Deposition (PLD) [16] have been employed in the noticeable arrival of thin flexible electrode assemblies. Frequently, the growth of micro and nanostructure coatings in thin film form are more suitable for flexible energy device applications and the most important benefits as the electrode is binder and conductive free in its structural design. This chapter deals with the electrochemical behavior of vanadium pentoxide (V2O5) and tungsten trioxide (WO3) thin films using PLD as well as thermal Evaporation technique used as different kind of Flexible thin film energy storage devices such as symmetric Supercapacitor and Supercapbatteries. Author demonstrated Transition metal oxides (TMOs) based thin film electrodes for flexible energy storage system rather than bulk electrodes. This chapter shows the recent influence of the TMO based thin films fabricated through PVD techniques for thin film Supercapacitors / Supercapbatteries. Also an example for anode (WO3) and cathode (V2O5) which based on the use of massive scale to micro / Nano scale structures to enhance the electrochemical properties of new energy systems with appropriate cost. This approach will be defined and delivered for enlightening device performances with extended cycle life of thin film Supercapacitors / Supercapbatteries based on the principal of electrochemical solid state redox reactions.

## **1.1 Thin film energy storage**

The expansion of flexible and portable electronics harmfully demands thin flexible and wearable energy storage devices (ESDs) that preserve both high energy and power density with their greater durability and flexibility to influence a vast wearable energy storage systems. Thus, extensive work have been devoted to emerging various types of flexible, stretchable and portable rechargeable supercapacitors (SCs) and batteries [17, 18]. Plentiful development has been accomplished in terms of thin film electrode material design and flexible device structure along with their electrochemical performance. With new type of ESDs, excluding outdated tests applied on supercapacitors, batteries and now supercapbatteries how to evaluate their "viability" and "portability" growths as a concern. Twisting and extending tests are the most used approaches to validate to the stability of flexible thin and stretchable energy storage devices, respectively [19, 20].

*Physicochemical Approaches for Thin Film Energy Storage Devices through PVD Techniques DOI: http://dx.doi.org/10.5772/intechopen.99473*

#### **1.2 Why thin film energy storage**

Since the scalability, a growth of micro electrochemical power sources with thin film structural design opens the approach for powering moderated devices such as electronic chip units, Biomedical implantable devices and credit card/ debit cards, and individual sensors systems. The technology of the thin film is useful for understanding the essential properties of the electrode active materials of energy storage system such as Supercapacitors along with lithium ion batteries (cathodes, anodes and solid state electrolytes) free of polymeric binder and carbonaceous preservative [21, 22]. More importantly in the form of thin film energy storage depends up on some specific features like morphology, size, thickness, pore volume etc., here author report why thin film energy storage device important requirement of society.


Additional imperative factor for the improved attention on thin-film battery resources is their applicability in micro-Lithium Ion Batteries (LIBs). The microscaling of devices is ongoing to compact the sizes of devices in addition to their energy demand, which makes many separate applications practicable, if micro-LIBs can be used for the power supply. These energy storage systems can be useful in different fields, such as biomedical implantable devices, laptops-on-chip, or micrometer-sized sensor systems.

#### *1.2.1 Supercapacitors*

Supercapacitors (SCs) have significant attention in past years owing to their high power density, long stability of cycle life and ability to bridge gap of the power and energy density between conventional capacitors, fuel cells and Lithium ion batteries (LIBs) Ragone plot of all kinds of energy storage is displayed in **Figure 1**. SCs retain extremely reversible ion adsorption /desorption on the surface of the electrode, nevertheless suffer with low energy density. An evolution of SC with its advantages of greater power density more than batteries, larger energy density delivers than the conventional capacitors, and exceptional durability, is playing an extraordinary role as a favorable candidate to come across this ongoing demand for high efficient EES and to throw out extended necessity on unsustainable fossil fuels [10, 23, 24].

**Figure 1.** *Ragone plot comparison with all kinds of energy storage system.*

Therefore, a single EES device, which can instantly provide high energy density and high power outputs with long lost, is an extremely desirable.

#### *1.2.1.1 Symmetric Supercapacitor*

Symmetric supercapacitor is typically assembled by two identical electrodes such as anode and cathode electrodes. The symmetric supercapacitors having limited operating voltage of an aqueous electrolyte up to 1.23 V being restricted by water decomposition, while using organic electrolyte whose voltage window can extend up to 2.7 V. Thin film supercapacitors (TFSCs) have materialized as a new class of electrochemical energy storage device and have considerable attention in recent years. TFSCs make their presence as one of the greatest hopeful energy storage devices attributable to their high power density, outstanding stability, light weight and are easy to handle. Nevertheless, the performance of predictable designs deteriorates extensively as a consequence of electrode and electrolyte exposure to atmosphere along with mechanical distortions for the case of flexible systems [25]. TFSCs are flexible and easily reconfigurable supercapacitors display great potential for application in portable electronics. Moreover, Flexible all-solid state supercapacitors are well-thought-out as a state-of-the art power supply for diminished electrical and electronic devices because they proficiently avoid the leakage of harmful electrolytes, which frequently happens in traditional aqueous electrolytebased supercapacitors [26, 27]. Numerous challenges limit their applications, such as the thin film composite fabrication process and the underprivileged interfacial compatibility among the electrode and the solid state electrolyte. In contrast to conventional SCs, flexible solid-state SCs have more than a few important benefits containing small size, low weight, exceptional reliability, and an extensive range of practical temperatures. TFSCs hold abundant promise for use as energy storage devices for flexible, stretchable and wearable electronics [7].

Recently the author group reported V2O5 thin film symmetric SC was fabricated using thermal evaporation technique shown in **Figure 2a**. In this work Ni foam substrate was used as a flexible current collector electrode, Flexible V2O5 thin film

*Physicochemical Approaches for Thin Film Energy Storage Devices through PVD Techniques DOI: http://dx.doi.org/10.5772/intechopen.99473*

**Figure 2.**

*(a) Schematic diagram of thermal evaporation technique; (b) photographic image V2O5 thin film annealed at 500°C at CSIR-CECRI, India; (c) AFM 3D topographical morphology of V2O5 thin film; (d) Ragone plot of V2O5 symmetric capacitors(Reprinted with permission from Ref. [46]. Copyright 2019 American Chemical Society) .*

electrodes were subjected to observed in a post annealing temperature at 500°C is shown in a **Figure 2b** (photographic image of Ni foam at CECRI, India). The V2O5 annealed at 500°C thin film was highly conducting nature owing to larger grain size, it is clearly indicated from the Atomic Force Microscopic 3D topographic image as shown in **Figure 2c**. Further author's group compared energy and power density of two symmetric V2O5 thin film devices such that As-prepared thin film electrode device (Cell-RT) and Annealed at 500°C thin film electrodes device (Cell A-500) is presented in **Figure 2d**. The cell A-500 delivered the maximum areal energy density around 0.7 μWhcm−2 which is fourteen times greater than as prepared cell-RT (0.05 μWh cm−2) [28]. Later author's group reported two symmetric thin film SCs using PLD, here this work V2O5 and WO3 thin film symmetric SCs was fabricated and successfully demonstrated various electrochemical investigation such as Cyclic Voltammogram (CV) and Galvanostatic Charge and Discharge (GCD). The CV curves of both V2O5 and WO3 symmetric SC devices is exposed **Figure 3a** and **c** reached the maximum voltage up to 1.2 V in a solid state PVA-KOH electrolyte, it is clearly indicated the decomposition appeared each devices above 1.0 V. To avoid this issue, author fixed the voltage window in GCD curve at different current densities of V2O5 and WO3 thin film symmetric SCs such as 1.0 V and 0.8 V as revealed in **Figure 3c** and **d** [28].

#### *1.2.1.2 Asymmetric Supercapacitor*

Potential window of the symmetric SCs be necessary more or less limitation due to similar materials (same potential widow) used for fabrication, this is one of important difficulty of symmetric SCs. On the way to overwhelm these

#### **Figure 3.**

*(a) CV curves V2O5 symmetric capacitor in different voltage window; (Reprinted with permission from Ref. [46]. Copyright 2019 American Chemical society) (b) GCD curves V2O5 symmetric capacitor in different current densities; (c) CV curves WO3 symmetric capacitor in different voltage window; (d) GCD curves V2O5 symmetric capacitor in different current densities (Reprinted with permission from Ref. [28]. Copyright 2020 Royal Society Chemistry).*

issues two dissimilar materials along with different potential widow based active materials are used in device fabrication for extending the voltage window. Asymmetric supercapacitors (ASCs) retain higher theoretical energy density than conventional symmetric SCs have complicated widespread consideration throughout the recent years. Still, there is a huge capacity gap between the two electrodes obviously restrict higher specific energy [29]. Flexible thin film electrodes capacity depends on mass, surface area and thickness of the films, can make the capacity balanced even though optimizing parameters such as weight, volume and thickness of the electrodes. One of the important footnote for several applications, in specific for portable micro electronic devices and hybrid vehicles, the volumetric specific energy is more important than gravimetric specific energy [30, 31].

#### *1.2.2 Batteries*

Conventional Li-ion batteries ensuring abound with limitations such that LIB constructed organic electrolytes are highly toxic, corrosive nature and only be handled with glow box atmospheric condition. To avoid this difficulties, solid state batteries (SSB) will be necessary the potential to progress the next generation of energy storage devices over the promises of greater energy density and healthier protection. The main perseverance of solid state electrolyte empowers

#### *Physicochemical Approaches for Thin Film Energy Storage Devices through PVD Techniques DOI: http://dx.doi.org/10.5772/intechopen.99473*

the predictable of flimsy lithium metal as the anode despite the fact replacing the frequently used inflammable organic electrolyte [32]. Even though the ionic conductivity of definite solid state electrolytes must come together taking place and in some incidents exceeded organic liquid electrolytes, their extensive application has remained inadequate by the excessive interfacial resistance sandwiched between the solid electrolyte and electrode [33, 34].
