**2.2 Ceramic battery technology**

They are all solid-state batteries made up of ceramic materials as their electrolytes. The demand for high-density batteries has necessitated research into more technologies that will enhance the thermal stability, mechanical strength and wettability of solid-state battery manufacture. Enhancements at the metal electrodes and/or separator boundaries are made possible by the introduction of ceramic batteries to boast some of the desired properties needed for solid-state batteries. Ceramic-based flexible sheet electrolytes have been formed to improve the energy density of solid-state batteries by synthesizing flexible composite Al-doped LLZO sheet electrolyte [17], coating of Al2O3, SiO2 and TiO2 onto polyethylene membrane seperators [18]. They

**Figure 2.**

*Classification of printed battery technology.*

are used in cogeneration and fuel cell, electric vehicles, mobile devices and stationary storage applications [19].

#### **2.3 Lithium polymer battery technology**

This works on the principle of intercalation and de-intercalation of lithium ions from the positive electrode (cathode) to the negative electrode (anode) and vice versa through a solid-state electrolyte that provides the conductive medium. Lithiumpolymer batteries are lightweight, long-lasting and powerful solid-state batteries that can guarantee a constant energy supply [20]. They have a high energy density, flat voltage curves, low self-discharge and no memory effect from being discharged and charged again. The technology is used in laptop computers, personal electronics, cellular phones [21], notebooks and digital cameras. The polymer electrolyte may be in form of dry solid polymer electrolyte, polymer in-salt system, single-lithium-ion conducting electrolyte and gel polymer electrolyte [22].

#### **2.4 Nickel-metal hydride (NiMH) button battery technology**

This technology is an energy storage system that depends on charge/discharge reactions occurring between the nickel oxide-hydroxide cathode as the active material and the hydrogen-absorbing alloy anode [23]. This battery technology exhibits good tolerance to overcharge/discharge, high power capacity, very safe and compatible [24]. They are mainly used as power sources for hybrid electric vehicles, digital cameras and cell phones [25].

### **3. Deposition techniques**

Thin-film deposition techniques are used to modify the surface properties of solidstate thin-film batteries. The modification affects the battery characteristics such as energy density, conductivity, storage capacity, charging and discharge time, etc.

Thin-film battery deposition techniques are classified into physical and chemical deposition processes as shown in **Figure 3** [26]. In the chemical deposition process, a chemical reaction takes place before the product is deposited on the substrate while the physical deposition method involves only physical mixing and deposition of the mixture on the substrate without any chemical reaction [27]. The coating material in a physical deposition is always a solid while the coating materials in chemical deposition are always in gaseous form. Physical deposition techniques include thermal evaporation, sputtering, ion plating and arc vapor deposition while chemical deposition techniques include chemical vapor deposition, plating, sol-gel deposition, chemical bath deposition and spray pyrolysis deposition techniques [28].

#### **3.1 Physical deposition method**

This method includes thermal evaporation, molecular beam epitaxy, pulsed laser deposition, ion plating evaporation, cathodic arc deposition and sputtering techniques. In thermal evaporation, molten metals or metal oxides form vapor and are deposited on the substrate as it cools [29, 30]. Molecular beam epitaxy (MBE) is a deposition technique in which a single crystal layer is deposited in a single crystal substrate, using molecular beams in an ultra-high vacuum chamber [31]. It is used in *Thin-Film Batteries: Fundamental and Applications DOI: http://dx.doi.org/10.5772/intechopen.109734*

**Figure 3.** *Deposition techniques.*

multi-junction solar cell applications [32], Ga-FACE GaN electron devices [33], etc. Pulsed laser deposition (PLD) process is a technique where a high-power pulsed laser beam strikes a target, vaporizes it and deposits it as a thin film on a substrate [34]. It is useful for optical applications, especially for UV laser emission [35] and superconductor devices for electronic and medical applications [36].

#### **3.2 Chemical deposition method**

Chemical deposition of thin films involves the generation of the atoms, molecules or ions through a chemical means; transportation of the atoms or ions through a medium and condensation and cooling of the atoms, molecules or ions on the substrate [27]. Chemical methods include chemical vapor deposition (CVD), electrodeposition, electroless deposition, spray pyrolysis, ionic layer deposition, sol-gel technique, chemical bath, spray and spin coating as shown in **Figure 2**.

Spray pyrolysis is the process of depositing a thin film on a heated surface by spraying a solution on the heated substrate [37]. The solution reacts with the heated substrate to form a thin film on the surface of the substrate. Mostly used for manufacturing semi-conductor alloys and conductive glasses. Electrodeposition is a technique of coating a thin layer of metal on top of a different metal through electrolysis by reducing the cations of the material from the electrolyte and depositing it as a thin film on the substrate [38]. It is a major method for the production of rechargeable lithium-ion batteries [39, 40]. Electroless deposition is a thin-film coating technique without the application of external electric power. It is used for non-conducting substrates and its major application is in the metalizing of printed wiring boards [41]. Atomic layer deposition (ALD) is a chemical deposition technique where chemical precursors introduced on the surface of the substrate react to form ultra-thin film monolayers on the substrate surface. They find application in fuel cells, capacitors,

microelectronics and areas where highly uniform ultra-fine mono-layered thin films are required [42]. Sol-gel is a technique where metal alkoxides, used as precursors, are dissolved in a solvent (especially water or alcohol), heated and stirred to form a gel, which is condensed, dried and deposited on the substrate as a thin film [43]. The process involves hydrolysis, polycondensation, gelation, drying and crystallization [44].

#### **3.3 Deposition technique for cathode materials in thin-film batteries**

A cathode is a very important component of thin-film batteries. This electrode material facilitates the stability of the electrochemical reactions in the electrode/electrolyte interface. The material composition of the cathode determines the thermal stability and rate capacity of the battery. For a good and efficient battery system, there is always a good ion transport mechanism between the anode and the cathode through the electrolyte and the acquisition and flow of electrons through the external circuit during an electrochemical reaction. Different deposition methods have been used in the design and fabrication of cathode materials for different solid-state battery applications. Production of LiCoO2 cathode materials using radio frequency (RF) magnetron sputtering deposition technique for micro battery applications was studied by Jullien et al. [45], MoO3 thin-film cathodes using DC sputter deposition technique for Li-ion rechargeable battery applications [39] and V2O5 thin-film cathodes using radio frequency (RF) reactive sputtering technique for high-performance thin-film batteries (TFB) [46].

#### **3.4 Deposition technique for anode materials in thin-film batteries**

A good anode material should be a good conductor and reducing agent and possess a high electrical energy density. They are made from carbon (graphite), lithium metals, lithium alloys, titanium and its alloys, silicon and other metals. Several methods have been developed on good anode materials for solid-state thinfilm batteries for micro-mechanical system applications. Reto Pfenninger et al. [47] studied the electrodeposition of Li-garments on solid state anode. The group worked on metal oxide anodes of Li4Ti5O12 with good ionic conductivity and less Li-dendrite formation for microbattery applications [47]. Pulsed electrodeposition of Sn-Cu anodes has been studied and developed for enhanced cycle performance in micro battery applications [48, 49]. Spray deposition of silicon anode materials with high energy density for solid-state battery application was developed by Shin Kimura et al. [50]. Many researchers have fabricated different anode materials and their reports have shown that anodes fabricated with good properties have shown to exhibit better battery performances. Li4Ti5O12 anode thin film was deposited on a magnesium oxide (MgO) substrate using the pulse laser deposition (PLD) technique [47], pulsed laser deposition method was used to fabricate a silicon thin-film anode with iron sulphide for solid-state battery applications [51]. DC magnetron sputtering technique was reported by L. Baggetto et al. for Cu2Sb thin-film deposition for sodium ion (Na-ion) batteries because of excellent storage capacity, high-rate capacity, good reaction potential and decent cycling capacity retention [52]. Silicon/carbon (SiC) thin-film anode was fabricated using a radio frequency (RF) magnetic sputtering technique with improved cycling performance and high current density for thin-film battery applications.
