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Zhu et al. Energy Mater. 2025, 5, 500034 https://dx.doi.org/10.20517/energymater.2024.201 Page 7 of 10

Figure 4. Cycling performance at various current densities of (A) LLZTO-150, (B) LLZTO-300, and (C) LLZTO-600 Li-symmetric cells.
EIS of Li-symmetric cells (D) before cycling and (E) after 1,500 cycles.

dendrites start to grow along the grain boundary, resulting in a decrease in the “effective thickness” of the
SSEs and a large decrease in the internal resistance of the cell. In the subsequent cycles, the polarization
voltage stabilizes at 50 mV, exhibiting severe fluctuations up and down until the failure of the cell. Figure 4B
shows the voltage-time curves of Li|LLZTO-300|Li, in which the initial polarization voltage is ~80 mV and
the cells stably cycle at a current density of 0.2 mA cm without voltage fluctuations. In the 1,190 cycles, the
-2
overpotential is stable only with an average increase of 0.06 mV per cycle, which is only half of that in
Li|LLZTO-150|Li, indicating that the LLZTO-300 pellet has better stability to suppress Li dendrites. The Li|
LLZTO-300|Li cells short-circuit at 1,191 cycles, and the voltage decreases from 150 to 20 mV, indicating
that the Li dendrite growth has triggered a huge decrease in the internal resistance of the cell. As shown in
Figure 4C, the Li|LLZTO-600|Li symmetric cell has the longest cycle life associated with the highest ionic
conductivity and the largest compactness. The total resistances of LLZTO-150, LLZTO-300, and LLZTO-