## 3 Results and Discussion
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Sample** & \(b\)**-Value (Avg.)** & **Dominant Mechanism** & **Diffusivity** & **Interpretation** \\ \hline
1 & \(\sim\)0.52–0.53 & Diffusion-controlled & High (\(\sim\)10\({}^{-9}\) cm\({}^{2}\)/s) & Fast ion transport aligns with diffusion-limited kinetics \\ \hline
2 & \(\sim\)0.54 & Mostly diffusion, minor capacitive & Low (\(\sim\)10\({}^{-10}\) cm\({}^{2}\)/s) & Low diffusivity causes sluggish kinetics, limited surface contribution \\ \hline
3 & \(\sim\)0.58 & Mixed with capacitive & Moderate (\(\sim\)10\({}^{-9}\) cm\({}^{2}\)/s) & Capacitive contribution increases due to fast surface reaction in liquid system \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The summary table comparing the electrochemical characteristics of the three battery samples based on \(b\)-value analysis and Li-ion diffusivity. Although cross-sectional SEM/EDS analysis would provide the direct evidence of the LFP/LATP interface structure, attempts to prepare intact cross-sections were hindered by interfacial delamination and cracking during mechanical polishing, due to the brittle nature of sintered LATP. The surface SEM images indicate significant grain coarsening in LATP sintered at 1000 \({}^{\circ}\)C, consistent with excessive densification. This structural evolution is likely to reduce interfacial compliance and limit Li-ion transport, as also supported by the reduced diffusivity values. These findings align with those of the previous reports which state that excessive sintering can suppress beneficial grain boundary conduction and lead to brittle interfaces [29; 30]. Further investigation using cross-sectional SEM or focused ion beam analysis is planned to validate this hypothesis. In summary, the SEM images reveal that a moderately porous, well-adhered interface (Sample 1) supports fast Li-ion diffusion and diffusion-limited kinetics, leading to high-rate performance. Excessively dense morphology (Sample 2) impairs interfacial transport, lowering diffusivity and electrochemical efficiency. Meanwhile, surface smoothing and interphase formation (Sample 3) encourage surface-driven kinetics, reflected in higher  
Figure 5: SEM images showing morphological evolution of AC-EPD LFP electrodes under different cycling and interfacial conditions. (**a**) As-deposited LFP electrode before cycling. (**b**) LFP after cycling in contact with liquid electrolyte (1 M LiPF\({}_{6}\) in EC/DEC). (**c**) LFP after cycling with LATP solid electrolyte sintered at 900 \({}^{\circ}\)C. (**d**) LFP after cycling with LATP sintered at 1000 \({}^{\circ}\)C.  
\(b\)-values and acceptable diffusivity, albeit with less structural integrity than solid-state counterparts. Thus, morphology is a direct indicator of electrochemical performance, especially in systems where solid-solid interfaces govern charge transport. Overall, these images highlight the critical role of the electrode/electrolyte interface--whether liquid or solid--and processing temperature on the structural integrity and surface stability of LFP electrodes. Solid-state interfaces, especially with optimized LATP processing, may offer improved morphological stability compared to liquid electrolytes, though high-temperature sintering can also induce unintended surface modifications. In this study, LATP pellets were sintered at 900 \({}^{\circ}\)C and 1000 \({}^{\circ}\)C to intentionally produce two distinct interfacial microstructures for comparative analysis. The lower temperature (900 \({}^{\circ}\)C) typically leads to less-densified LATP with higher interfacial resistance, while the higher temperature (1000 \({}^{\circ}\)C) may result in coarsened grains and potential interface degradation. These boundary conditions were selected to represent limiting cases rather than an exhaustive sintering profile, aiming to elucidate the impact of interface quality on electrochemical performance.