context: A button-sized hybrid electrolyte cell (Fig. S4†), in which an ionic liquid-infiltrated NCM with a LLZTO electrolyte and a 20 μm–thick Li metal were respectively used as a cathode and a Li metal anode, was fabricated to check out the improvement of the electrochemical performance after laser-annealing treatment. For comparison, two kinds of LLZTO pellets were used: a polished pellet without laser treatment and a laser-treated pellet. In Fig. 6a and b, the Nyquist plots of the AC-impedance spectra from the samples obtained at an open circuit from the cells were compared. As shown in Fig. 6a and b, the ohmic losses calculated from the high-frequency intercept with the real axis were almost the same in the range of 3.2–4.0 Ω cm2 for both the cells. Based on the ohmic resistance, the ionic conductivities were expected to be in the range of 7.5–9.4 10−3 S cm−1 at 60 °C for the LLZTO pellets with and without laser treatment. These conductivity values are consistent with the reported values of Ta-doped LLZO and also with that value (∼8.6 × 10−3 S cm−1 at 60 °C) experimentally obtained from the Au-sputtered symmetric cells (Au/LLZTO/Au), as shown in Fig. S5a.† Thus, it can be inferred that the cathode and ionic liquid catholyte are not contributing significantly to the ohmic losses in these cells. Furthermore, the amorphous layer formed by laser irradiation had no significant effect on the ohmic resistance due to its low thickness of about 400 nm. The AC-impedance spectra of both cells consist of a depressed arc in the high-frequency range, a narrow line inclined at a constant angle to the real axis (Warburg impedance), and a capacitive line (blocking region) in the low-frequency range, which are typical features of a NCM-Li cell. The high-frequency arc could be associated with the charge-transfer reactions at the cathode and anode interface. Because the relaxation times for the cathodic and anodic reactions are generally overlapped over the high-frequency ranges for a NCM-Li full cell, it is difficult to separate the charge-transfer resistance at the Li-LLZTO interface from the resistance at the NCM-ionic liquid. The AC-impedance spectrum for Li/LLZTO/Li cell is also shown in Fig. S5b.† Considering that the electrochemical kinetics at the cathode would be almost the same for both cells, the variation in the high-frequency arc could be attributed to the charge-transfer resistance at the Li metal and LLZTO interface. The values of the overall interfacial resistance, Rct, were quantitatively determined from complex non-linear least-square (CNLS) fitting of the measured impedance spectra based on a typical equivalent circuit of the NCM-Li full cell. The Rct (Rc + Ra) value was reduced from ∼80 Ω cm2 to ∼26 Ω cm2 when the LLZTO surface was treated by a laser beam. In addition, as shown in Fig. S5c,† the electronic conductivity of LLZTO was significantly reduced by the laser treatment, which can originate from the formation of a wide band gap surface layer.