To investigate the electrochemical performances of the designed Li
2.25Zr
0.75In
0.25Cl
6, LiNi
0.7Mn
0.2Co
0.1O
2/Li
2.25Zr
0.75In
0.25 Cl
6/Li
5.5PS
4.5Cl
1.5/In-Li solid-state battery was constructed. As shown in
Fig. 4a, the assembled battery delivers an initial discharge capacity of 150.0 mAh/g with a coulombic efficiency of 79.5% under 0.2 C between the voltage window of 3.0–4.3 V
vs. Li
+/Li
0 at room temperature. The discharge capacity quickly degrades below 82.8 mAh/g within 10 cycles. This poor cyclability is due to the rapid increase of Li
2.25Zr
0.75In
0.25Cl
6/Li
5.5PS
4.5Cl
1.5 electrolyte interface resistance in the middle frequency range during the first 10 cycles, as shown in
Fig. 4b. The ionic conductivity of solid electrolytes is significantly influenced by the temperature, a higher temperature yields faster lithium-ion mobility. When the operating temperature increase to 60 ℃, the solid-state battery shows a slightly larger initial discharge capacity of 155.0 mAh/g and higher coulombic efficiency of 82.5% and retains 88.0 mAh/g after 10 cycles (
Fig. 4a). EIS results confirm that smaller solid electrolyte associated interface resistances are achieved due to the increased operating temperatures (
Fig. 4b). Furthermore, the fabricated solid-state battery was also charged/discharged at a higher voltage window, between 3.0 and 4.5 V. It delivers a higher initial discharge capacity than that at a narrower voltage window, as shown in
Fig. 4c. A new charge plateau is observed at 4.3 V
vs. Li
+/Li
0, which may be associated with the side reaction between the active material and Li
2.25Zr
0.75In
0.25Cl
6. EIS results show a much larger cathode/solid electrolyte resistance in the same cycles due to the intense side reaction at a higher voltage window. Li
2.25Zr
0.75In
0.25Cl
6-based solid-state batteries show higher initial coulombic efficiencies at elevated temperature than at room temperature in different voltage windows, which may be attributed to the faster ionic mobility of the solid electrolyte. The faster lithium-ion migration rate in the cathode mixture due to the higher operating temperature can improve the reversibility, yielding enhanced coulombic efficiencies. Finally, to unravel the fast degradation of discharge capacities for the LiNi
0.7Mn
0.2Co
0.1O
2/Li
2.25Zr
0.75In
0.25Cl
6/Li
5.5PS
4.5Cl
1.5/Li-In solid-state batteries,
in-situ EIS was applied to evaluate resistance evolutions of the assembled battery during the first two cycles operating at the same conditions. As shown in Fig. S2 (Supporting information), the resistance in the high frequencies assigned to the contribution of Li
2.25Zr
0.75In
0.25Cl
6 electrolyte shows minor variations during the charge/discharge process of the first two cycles. In contrast, the semicircle sections in the middle and low frequencies reflect the total interface resistances, including cathode/Li
2.25Zr
0.75In
0.25Cl
6, Li
2.25Zr
0.75In
0.25Cl
6/Li
5.5PS
4.5Cl
1.5, and Li-In/Li
5.5PS
4.5Cl
1.5 interfaces, show intense variations during the initial charge process. The interfacial resistance appears when the battery is charged from 3.0 V to 3.3 V and significantly increases during the subsequent initial charge process till 3.7 V. During the first discharge process, the battery displays reduced interface resistance from 3.7 V to 3.0 V. Moreover, this battery exhibits much higher interfacial resistances during the 2
nd charging process compared with the 1
st charge process, suggesting a continuous interface degradation. As shown in Figs. S3a–d (Supporting information). A solid-state battery using LiNbO
3-coated LiNi
0.7Mn
0.2Co
0.1O
2 cathode and bilayer solid electrolyte layers was also constructed and showed similar fast degradation of capacity and large increase of interface resistance during cycling, indicating that the instability comes from the Li
2.25Zr
0.75In
0.25Cl
6/Li
5.5PS
4.5Cl
1.5 layer during cycling [
32]. As shown in Fig. S4 (Supporting information), the halide electrolyte layer and Li
2.25Zr
0.75In
0.25Cl
6/Li
5.5PS
4.5Cl
1.5 interface are easy to craze, which show an intense mechanical incompatibility.