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Chen et al. Energy Mater. 2025, 5, 500064 https://dx.doi.org/10.20517/energymater.2024.163 Page 5 of 14

RESULTS AND DISCUSSION
Structural analysis of the ASSB with dual interface design
The structure of the proposed ASSB with dual interface design is presented in Figure 1. It can be seen that
the ASSB has a “sandwich” configuration and the thin layers of alucone are coated on both the cathode and
anode surfaces. The purpose of the alucone coating layers is to prevent electrochemical degradation
reactions between the CSSE of LLZO/PEO/LiTFSI and NCM811 cathode, as well as the side reactions
between the CSSE and LMA.

ALD was carried out with 15 cycles of deposition, resulting in a thickness of alucone coating layer of ~2 nm.
The coated cathode is depicted in Figure 1B, which shows that the active material is uniformly distributed
and protected by the coated alucone layer. A SEM image of the NCM811 cathode without alucone coating is
presented for comparative analysis, as shown in Supplementary Figure 1. Similarly, LMA is coated with the
same material, as revealed by the SEM image in Figure 1C(i), and EDS data in Figure 1C(ii) and (iii), which
indicates a uniform ALD coating of alucone. The coin cell-shaped CSSE film is composed of PEO, LLZO
and LiTFSI in a mixed matrix as shown in Figure 1D and E. It can be seen that the film is uniform and
flexible, and its mechanical properties can be favorable for enabling low-pressure cells with good wettability.

Both the chemical environment and molecular interactions in the critical components including LLZO/
PEO/LiTFSI film and alucone-coated NCM811 cathode were further investigated by XPS and XAS. In
detail, XPS was used to characterize the LLZO/PEO/LiTFSI film and understand how LiTFSI was dissolved
into the material, as shown in Figure 2A-D. All XPS spectra were calibrated and corrected based on
adventitious carbon. The C 1s signal shows a typical PEO structure with CH - and (-OCH -CH ) groups at
2 n
2
2
~284.8 and 286.6 eV, and CF functionality at ~293.0 eV [Figure 2A], which indicates that the LiTFSI has
3
broken down and reacted with the carbon atoms from the PEO . This is also supported by the S 2p and
[35]
F 1s XPS data, namely the peaks of CF (688.7 eV), LiF (685.2 eV), LiTFSI (168.9 and 170.1 eV), and Li S O
x y
3
z
(167.1 and 168.3 eV), which show the dissociation of lithium salt [Figure 2B and C], and this is also
[36]
confirmed by the Li 1s XPS as displayed in Supplementary Figure 2 . In the O 1s signal [Figure 2D], the
presence of C-O bonds is observed, which aids in the formation of a stable and structurally ordered solid
electrolyte interphase (SEI) layer on the electrode surface. The formed SEI layer enhances its structural
[37]
stability by forming hydrogen bonds or electrostatic interactions with the ions from the electrolyte . The
dissociation of lithium salt could also subsequently facilitate the reduction of Li -TFSI pairs towards much
-
+
+
[38]
more liberated Li , further promoting the migration and transformation of lithium .
In addition to the structural analysis for LLZO/PEO/LiTFSI film by XPS, the cathode side with or without
an alucone coating layer was detected through XAS, which included both X-ray absorption near edge
structure (XANES) and extended X-ray absorption fine structure (EXAFS) sections and was very
[39]
informative on both the oxidation and coordination states of metal species . Specifically, the XAS results of
the alucone-coated and pristine NCM811, along with their k -weighted R space transformation, are
3
displayed in Figure 2E and F. The absorption energy (E ) of the Co K-edge slightly shifts to higher energy,
0
indicating that the alucone coating can slightly alter the surface status of NCM811. The slight shift to higher
E is likely due to the Al-O-Co bonding, causing the Co to be more electron deficient [40,41] . This is further
0
verified in the R space of the XAS spectra [Figure 2F], which shows slight bonding changes, particularly at
~1 Å, indicating the change of Co-O bonding [42,43] .
As observed, the alucone-coated cathode tends to show a slightly lower electronic conductivity than the
pristine one without coating, which stems from the electronically insulating nature of the alucone, while the
ionic conductivity stays more or less the same. This is because the alucone layer is sufficiently thin, which