## 3 Results and Discussion
Overall, these results demonstrate that the sintering condition of LATP has a substantial impact on the performance of all-solid-state batteries, with optimized conditions (900 \({}^{\circ}\)C) enabling superior rate capability and cycling stability through improved electrode-electrolyte interfacial contact. Figure 2: (**a**) Rate performance of AC-EPD LFP electrodes in three cell configurations: Sample 1 (Li/LATP (900 \({}^{\circ}\)C)/LFP), Sample 2 (Li/LATP (1000 \({}^{\circ}\)C)/LFP), and Sample 3 (Li/LiPF\({}_{6}\)/LFP), cycled at 1C, 2C, 5C, and returned to 1C. (**b–d**) Corresponding charge–discharge voltage profiles at various C-rates for (**b**) Sample 1, (**c**) Sample 2, and (**d**) Sample 3. From the comparison of the cycling performance in the Supporting Information (Figure S1), the LATP 900 \({}^{\circ}\)C and 1000 \({}^{\circ}\)C samples both exhibit stable cycling behavior over repeated cycles (500 cycles), although the 900 \({}^{\circ}\)C sample shows a higher initial capacity. This difference is likely due to better interfacial contact and lower resistance in the 900 \({}^{\circ}\)C-sintered LATP, which enhances lithium-ion transport. In contrast, the 1000 \({}^{\circ}\)C sample, while more densely sintered, may have poorer interfacial compliance, resulting in lower capacity. However, both samples maintain similar long-term stability, suggesting that their bulk structures remain intact and chemically stable throughout cycling. The comparison of \(b\)-values for the three LFP-based samples, derived from CV at various scan rates, provides insight into the dominant charge storage mechanisms operating in each system [27; 28]. The \(b\)-value, obtained from the slope of log(current) versus log(scan rate), indicates whether the process is diffusion-controlled (\(b\approx 0.5\)) or surface-capacitive (\(b\approx 1.0\)). Sample 1, which uses LATP sintered at 900 \({}^{\circ}\)C, shows \(b\)-values of 0.53 (anodic) and 0.52 (cathodic), as seen in Figure 3a,b. These values are very close to 0.5, indicating that the redox process is predominantly diffusion-controlled. The near-symmetric CV curves and stable peak separation further suggest efficient Li\({}^{+}\) intercalation/deintercalation and good electrode-electrolyte interfacial contact. This result aligns well with the excellent rate performance observed earlier, confirming the favorable ion transport dynamics in this solid-state configuration. Sample 2, paired with LATP sintered at 1000 \({}^{\circ}\)C, exhibits similar \(b\)-values of 0.51 (anodic) and 0.57 (cathodic) in Figure 3c,d. Although still diffusion-dominated, the cathodic value is marginally higher, indicating a slightly more capacitive contribution during discharge. In contrast, Sample 3, using a liquid electrolyte (1 M LiPF\({}_{6}\)), shows the highest \(b\)-values--0.58 (anodic) and 0.56 (cathodic)--as shown in Figure 3e,f. These values reflect a more significant contribution from surface capacitive processes, likely due to enhanced ion mobility and electrolyte wetting at the interface. The sharper, more symmetric CV peaks support this interpretation, pointing to fast surface redox activity and a more pronounced pseudocapacitive effect. In other words, all three systems show charge storage predominantly governed by diffusion, but to varying extents. Sample 1 demonstrates the most ideal solid-state interfacial kinetics, Sample 2 reveals limitations due to high-temperature sintering, and Sample 3 benefits from surface-dominated processes in liquid electrolytes. This comparison underscores how electrolyte type and interface quality critically influence the charge storage behavior in LFP electrodes. It is also important to note that the broader redox peaks observed in CV curves for the solid-state cells (Samples 1 and 2) relative to the liquid electrolyte cell (Sample 3) arise from a combination of factors including higher interfacial resistance, lower ionic conductivity of LATP, and limited solid-solid contact at the LFP/LATP interface.