## 4 Electrodes and Electrolytes for SSTFBs
### Thin-film Electrolytes  
As discussed earlier, the use of solid electrolytes can resolve the safety issues caused by liquid electrolytes in conventional LIBs. Furthermore, the use of thin-film solid electrolytes can provide the low ionic resistance by controlling material orientations, crystallinity and strain to build high power lithium-based batteries. Here, we mainly focus on progress in research on four thin-film solid electrolytes: NASICON, LiPON, perovskite and garnet electrolytes. LAGP and LATP are two of the most commonly used NASICON-type solid electrolytes in LIBs, due to their high ionic conductivities. Using various deposition techniques including RF \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{\begin{tabular}{c} **Crystalline** \\ **Structure** \\ \end{tabular} } & **Discharge** & \begin{tabular}{c} **Current** \\ **Density** \\ **Rate (C)** \\ \end{tabular} & \
\begin{tabular}{c} **Discharge** \\ **Density** \\ **(\(\upmu\)A/cm\({}^{2}\))** \\ \end{tabular} & \multirow{2}{*}{**Density**} & \multirow{2}{*}{
\begin{tabular}{c} **Capacity** \\ **(\(\upmu\)Ah/cm\({}^{2}\))** \\ \end{tabular} } & \multirow{2}{*}{**Ref.**} \\  & & & & & & & \\ \hline LCO\({}^{\text{a}}\) & (104) Epitaxial & 100 & & 23 & 5.03 & 13 & [373] \\ LCO\({}^{\text{a}}\) & (104) Epitaxial & 0.01 & & 90 & 5.03 & 45 & [373] \\ LCO\({}^{\text{b}}\) & Amorphous & & & 30 & **49** & 5.03 & 25 & [375] \\ LCO\({}^{\text{b}}\) & (100)-Oriented & & 30 & **120** & 5.03 & 61 & [375] \\ LCO\({}^{\text{c}}\) & Polycrystalline & & 0.5 & **50** & 5.03 & 25 & [377] \\ LiNi\({}_{0.5}\)Mn\({}_{0.25}\)Co\({}_{0.25}\)O\({}_{2}\)\({}^{\text{b}}\) & Polycrystalline & & **117** & 4.9 & 58 & [394] \\ LiNi\({}_{0.3}\)Mn\({}_{0.3}\)Co\({}_{0.3}\)O\({}_{2}\)\({}^{\text{b}}\) & Polycrystalline & 0.1 & & 127 & 4.9 & 62 & [392] \\ LiNi\({}_{0.5}\)Mn\({}_{0.5}\)Co\({}_{0.2}\)O\({}_{2}\)\({}^{\text{a}}\) & Polycrystalline & 0.5 & & 125 & 4.9 & 61 & [393] \\ LMO \({}^{\text{a}}\) & (100) Epitaxial & 0.7 & & 129 & 4.32 & 56 & [384] \\ LMO \({}^{\text{a}}\) & (100) Epitaxial & 13 & & 100 & 4.32 & 43 & [384] \\ LMO \({}^{\text{a}}\) & (100) Epitaxial & 33 & & 84 & 4.32 & 36 & [384] \\ LMO \({}^{\text{a}}\) & (110) Epitaxial & 0.7 & & 113 & 4.32 & 49 & [384] \\ LMO \({}^{\text{a}}\) & (110) Epitaxial & 13 & & 50 & 4.32 & 22 & [384] \\ LMO \({}^{\text{a}}\) & (111) Epitaxial & 0.1 & & 95 & 4.32 & 41 & [384] \\ LMO \({}^{\text{a}}\) & (111) Epitaxial & 13 & & 50 & 4.32 & 22 & [384] \\ LMO \({}^{\text{d}}\) & Amorphous & 0.1 & & 61 & 4.32 & 26 & [101] \\ LMO \({}^{\text{d}}\) & Polycrystalline & 0.1 & & 70 & 4.32 & 30 & [101] \\ LMO \({}^{\text{e}}\) & Polycrystalline & 100 & & **88** & 4.32 & 38 & [390] \\ LMO \({}^{\text{f}}\) & Polycrystalline & 50 & 80 & 4.32 & 35 & [391] \\ \hline \hline \end{tabular} Bold discharge capacity values in (mAh/g) are back-calculated from the data in (\(\upmu\)Ah/cm\({}^{2}\)\(\upmu\)m). Materials with superscript \(\upmu\), b, c, d, e and \(\upmu\) represent the corresponding thin films deposited by PLD, RF sputtering, atomic layer deposition (ALD), blade coating, sol–gel and CVD, respectively.  
\end{table} 
Table 7: Comparison of the discharge capacity among different cathode materials. sputtering [397; 398; 399], sol-gel [400] and aerosol deposition [401], LAGP and LATP thin films were implemented into SSTFBs. However, thin-film electrolytes fabricated by sol-gel cannot be fully densified due to the solution-based sol-gel method. Therefore, ionic conductivity for the pores in sol-gel-synthesized thin films also needs to be taken into account. Sun et al. [397] deposited LAGP thin films using RF sputtering with different deposition temperatures ranging from 50 to 600 \({}^{\circ}\)C, demonstrating an increase in ionic conductivity with increasing deposition temperatures up to 200 \({}^{\circ}\)C. In this study, the conductivity of the film deposited at 200 \({}^{\circ}\)C was found to be \(1.29\times 10^{-6}\) S/cm at room temperature.