## 2 Electrodes and Electrolytes for Lithium-Based Batteries
### Solid Electrolytes  
Due to the lack of liquid electrolytes with electrochemical windows above 5 V, until now, the selection of electrode materials has been limited. However, recent advances in developing inorganic solid electrolytes have demonstrated the possibility of using other electrode materials. Ideal inorganic solid electrolytes are required to have thermal/chemical stability, high ionic conductivity and long \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **Doping** & **Discharge Rate (C)** &
\begin{tabular}{c} **Initial Discharge** \\ **Capacity (mAb/g)** \\ \end{tabular} & **Ref.** \\ \hline LCO & Ba, Ti & 0.2 & 190.5 & [128] \\ LCO & La, Al & 0.1 & 190 & [129] \\ LMO & Y & 0.5 & 120 & [138] \\ LMO & Ce & 1 & 101 & [139] \\ LNVO & & 0.02 & 80 & [141] \\ LNVO & & 0.1 & 30 & [142] \\ NMC-811 & Ta & 0.067 & 212 & [157] \\ LiNi\({}_{0.83}\)Co\({}_{0.11}\)Mn\({}_{0.6}\)O\({}_{2}\) & 1 & 200 & [158] \\ NMC-811 & LiPO\({}_{4}\)-AlPO\({}_{4}\)-Al(PO\({}_{3}\))\({}_{3}\) & 0.1 & 218 & [171] \\ Li\({}_{1.14}\)Ni\({}_{0.14}\)Co\({}_{0.14}\)Mn\({}_{0.54}\)O\({}_{2}\) & La(PO\({}_{3}\))\({}_{3}\) & 0.1 & 286 & [172] \\ NMC-811 & LiTa\({}_{2}\)PO\({}_{8}\) & 0.1 & 231 & [173] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of the discharge capacity among different cathode materials. Figure 5: Crystal structure of Ni-rich LiNi\({}_{1-2y}\)Mn\({}_{y}\)Co\({}_{y}\)O\({}_{2}\) (NMC) (y \(\leq\) 0.1). Reprinted from ref. [165] with permission of Elsevier. cycle life. Table 3 shows a summary of ionic conductivities for several solid inorganic electrolytes. In particular, oxide materials, which present excellent stability in ambient conditions, are promising solid electrolytes for SSBs. In this section, we mainly focus on the chronological research progress of oxide electrolytes from their introduction to the field, in addition to two representative non-oxide solid-state electrolytes, anti-perovskites and sulfides. The NASICON structure, standing for Na\({}^{+}\) superionic conductors, was reported by Hangman et al. in 1968 [199]. It has a rhombohedral structure (space group R-3c) made of the framework of octahedra (MO\({}_{6}\), M = divalent to pentavalent transition metal ions) and tetrahedra (XO\({}_{4}\), X = P, Si, As). Two MO\({}_{6}\) octahedra and three PO\({}_{4}\) tetrahedra share oxygen atoms, which are assembled to form a 3D network structure. This structure provides a 3D interconnected conduction pathway for mobile ions, most commonly Na\({}^{+}\) or Li\({}^{+}\)[200]. The NASICON structure can have a wide range of compositional varieties, leading to varied ionic conductivities. The most promising NASICON-type Li\({}^{+}\) conductors are LiTi\({}_{2}\)(PO\({}_{4}\))\({}_{3}\) and LiGe\({}_{2}\)(PO\({}_{4}\))\({}_{3}\) with Al substitutions. Arbi et al. [174] reported the synthesis of Li\({}_{1+x}\)Al\({}_{x}\)Ti\({}_{2-x}\)(PO\({}_{4}\))\({}_{3}\) (LATP) and Li\({}_{1+x}\)Al\({}_{x}\)Ge\({}_{2-x}\)(PO\({}_{4}\))\({}_{3}\) (LAGP) conductors (\(0\leq x\leq 0.5\)) giving conductivities of \(3.4\times 10^{-3}\) S/cm (LATP, x = 0.2) and \(10^{-4}\) S/cm (LAGP, x = 0.2) at room temperature. By enhancing the crystallization of LAGP, Thokhom et al. [175] reported a conductivity of \(4.22\times 10^{-3}\) S/cm at room temperature. Although its high ionic conductivity is attractive, the instability of LATP in contact with Li metal due to the reduction of Ti\({}^{4+}\) requires an additional protective  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Category**} & \multirow{2}{*}{**Electrolyte**} & \multicolumn{2}{c}{**Ionic**} & \multirow{2}{*}{**Activation**} & \multirow{2}{*}{**Temperature**} & \multirow{2}{*}{**Ref.