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Page 4 of 10 Zhu et al. Energy Mater. 2025, 5, 500034 https://dx.doi.org/10.20517/energymater.2024.201

Figure 1. (A) XRD patterns of various LLZTO pellets. (B) Calculated grain size and micro-strain of various LLZTO pellets. Cross-section
SEM images and related optical photos of (C) LLZTO-50, (D) LLZTO-150, (E) LLZTO-300, and (F) LLZTO-600 pellets.

the incomplete sintering of the grains. For the LLZTO-300 pellet [Figure 1E], the grains have close contact
with each other, and the ceramic is thoroughly densified after sintering. Most of the grain boundaries
disappear due to the complete fusion of grains, leaving only a few small pores. For the LLZTO-600 pellet
[Figure 1F], the tight contact between grains leads to the densest morphology with absent grain boundaries
and few pores.

Based on the energy difference and peak intensity of La 3d peaks of the LLZTO-50 [Figure 2A], the La
elements primarily exist in a form similar to metal oxides. The Ta 4f peaks of LLZTO-50 consist of splitting
peaks [Figure 2B], indicating the dominance of Ta oxides. In contrast, the Ta 4f peaks of LLZTO-600 shift
3+
to higher binding energy, implying greater oxidation of Ta in the high-pressure pellets. Similarly, the Zr 3d
peaks of LLZTO-600 also shift to higher binding energy [Figure 2C], suggesting a higher valence of Zr in the
high-pressure pellets. The Li 1s peak of LLZTO-50 and LLZTO-600 [Figure 2D] are similar, except for the
larger peak area in LLZTO-600, indicating reduced Li loss and complete sintering in high-pressure pellets.
These results imply that higher compactness may lead to concentrated oxygen, promoting the stable
oxidation of transition metals and increased Li content in SSEs.