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Page 8 of 10 Zhu et al. Energy Mater. 2025, 5, 500034 https://dx.doi.org/10.20517/energymater.2024.201

Figure 5. (A) Cycling performance and Coulombic efficiency of various LiFePO |LLZTO|Li full cells. (B-D) Corresponding 1st, 50th, and
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100th charge/discharge curves at 0.1C.

600 Li-symmetric cells before cycling [Figure 4D] are 800, 700, and 640 Ω, respectively. The similar
resistances indicate similar interfacial properties before cycling. After 1,500 cycles [Figure 4E], the LLZTO-
150 and LLZTO-300 Li-symmetric cells exhibit small resistances (180 and 99 Ω) due to the short-circuit,
while the total resistance of Li|LLZTO-600|Li is raised to 1,230 Ω caused by the interfacial degradation after
cycling.

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As shown in Figure 5A, the initial discharge capacity of LFP|LLZTO-150|Li [Figure 5B] is 158.9 mAh g ,
and the initial Coulomb efficiency (CE) is as high as 99.9%. However, the capacity decays severely in the
subsequent cycles. The overcharging occurs in the 78th cycle, and the capacity retention rate is only 83.4%
after 100 cycles. The initial discharge capacity of LFP|LLZTO-300|Li [Figure 5B] is 157.9 mAh g , and the
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initial CE is 96.3%. The reversible capacity remains at 143.8 mAh g after 150 cycles, and the capacity
retention rate is 91.1%. The initial discharge capacity of LFP|LLZTO-600|Li [Figure 5B] is 158.4 mAh g ,
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and the capacity retention rate after 150 cycles is 94.8%, which is the highest among all the full cells. This is
+
because the highest ionic conductivity facilitates the stable Li transport inside the cell, and the dense
morphology facilitates stable cathode/electrolyte/anode interfaces. In the 50th cycle [Figure 5C], the LFP|
LLZTO-150|Li cell exhibits the largest overpotential, even with severe voltage fluctuations in the 100th cycle
[Figure 5D]. The stable voltage plateaus and the lowest overpotential of LFP|LLZTO-600|Li confirm the
feasibility of enhancing the SLB performance by increasing the compaction pressure of SSEs.

CONCLUSIONS
In this paper, LLZTO pellets are prepared with different compaction pressures and sintered at 1,250 °C for
4 h showing various morphologies and compositions. The LLZTO-50 sample has a loose structure and
lower metal valance states, while the LLZTO-600 sample demonstrates the largest compactness (94%) and
the highest ionic conductivity (6.36 × 10 S cm ). As a result, the Li|LLZTO-600|Li symmetric cell exhibits
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the best performance, which can stably work for 1,500 cycles without short circuits. The reversible capacity
of the LFP|LLZTO-600|Li full cell is 158.4 mAh g , and the capacity retention rate is up to 94.8% after 150
-1
cycles, which is the highest among the samples. In summary, the different compaction pressure can regulate