## 4 Electrodes and Electrolytes for SSTFBs
### Thin-film Electrodes
#### 4.1.1 Anodes  
Amorphous Li-metal thin films were previously deposited by thermal evaporation to serve as the anode for Li-V\({}_{2}\)O\({}_{5}\) cells and Li-LMO cells [336]. According to this work, the Li-V\({}_{2}\)O\({}_{5}\) cell was found to show a discharge capacity of 118 and 86 \(\upmu\)Ah/cm\({}^{2}\)\(\upmu\)m at room temperature with a current density of 2 and 40 \(\upmu\)A/cm\({}^{2}\), respectively. Compared to the Li-V\({}_{2}\)O\({}_{5}\), the Li-LMO cell showed a discharge capacity of 60 and 26 \(\upmu\)Ah/cm\({}^{2}\)\(\upmu\)m at room temperature with a current density of 2 and 40 \(\upmu\)A/cm\({}^{2}\), respectively. A couple of studies have shown the growth of amorphous silicon (\(\upalpha\)-Si) thin films via PLD and sputtering [337; 338; 339; 340]. Ohara et al. [339] reported the growth of amorphous Si thin films on Ni foils with a capacity of 3000 mAh/g at a 12 C charge rate with 1000 cycles. Park et al. [338] also grew an amorphous thin-film Si on stainless steel with PLD. The authors achieved a 96.7 \(\upmu\)Ah/cm\({}^{2}\) first discharge capacity and a 52.6 \(\upmu\)Ah/cm\({}^{2}\) first charge capacity. PLD-deposited amorphous Si thin films on stainless steel were also found to yield \(\sim\)20 \(\upmu\)Ah/cm\({}^{2}\) of capacity between 1 and 4 V up to 20 cycles by Xia et al. [337]. Multiple attempts have shown that graphene thin films can be deposited via CVD [341; 342; 343], sputtering [344] and PLD [345]. Reddy et al. [342] prepared N-doped graphene thin films for the anode  
Figure 11: Comparison of the volumetric and gravimetric energy density of solid-state thin-film batteries (SSTFBs) with other batteries [333; 334; 335]. via CVD. According to the authors, the films exhibited a reversible discharge capacity of 0.05 mAh/cm\({}^{2}\) under the current density of 5 \(\upmu\)A/cm\({}^{2}\) after 50 cycles. Saulnier et al. [341] fabricated a multilayered graphene (MLG) anode via CVD showing a discharge capacity of 250 mAh/g under the rate of 5 C.  
LTO thin films have been grown via PLD [346; 347; 348; 349], sputtering [350; 351], sol-gel [352; 353] and CVD processes [354]. Deng et al. [348] reported the growth of the (111)-oriented LTO thin films on Pt/Ti/SiO\({}_{2}\)/Si substrates via PLD, showing a discharge capacity of 157 mAh/g after 10 cycles with a constant current density of 10 \(\upmu\)A/cm\({}^{2}\). Cunha et al. [349] also used PLD to grow (001)-, (110)- and (111)-oriented epitaxial LTO thin films on (001), (110) and (111) SrTiO\({}_{3}\) (STO) substrates, respectively. The LTO films showed pyramidal, rooftop and flat surface morphology with \(<\)111\(>\) crystal facets, respectively. According to the authors, all three epitaxial thin films were found to exhibit high discharge capacities ranging from 280 to 310 mAh/g, which exceeds the theoretical value of 175 mAh/g. Among these three films with different crystallography orientations, the (100)-oriented films were found to show the highest discharge capacity due to its highest surface area. Using ion beam sputtering, Wunde et al. [350] reported the growth of the (111)-oriented LTO thin films, which showed a capacity ranging from \(\sim\)18 to 26 \(\upmu\)A/cm\({}^{2}\)\(\upmu\)m with different current density. The averaged diffusion coefficient for Li\({}^{+}\) was also reported as 3.27 \(\times\) 10\({}^{-16}\) m\({}^{2}\)/s. Thin films fabricated by sol-gel and CVD methods were polycrystalline with the (111) preferred orientation [353; 354]. The CVD thin films were found to have a better discharge capacity (\(\sim\)110 mAh/g) than the sol-gel thin films (\(\sim\)60 \(\upmu\)Ah/cm\({}^{2}\)\(\upmu\)m) under the current density of 10 \(\upmu\)A/cm\({}^{2}\). This result indicates that the performance of SSTFBs may also depend on the quality of thin films determined by the deposition technique. LNVO thin films with a reverse spinel structure were deposited via PLD [355; 356; 357] and RF sputtering [358]. Tang et al. [355] grew amorphous LNVO thin films via PLD on stainless steel substrates.