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Chen et al. Energy Mater. 2025, 5, 500064 https://dx.doi.org/10.20517/energymater.2024.163 Page 3 of 14

transition metals, minimize capacity loss at the cathode side, prevent interfacial side reactions, and improve
[29]
the oxidative stability of the electrolyte . Moreover, the protection of lithium metal anodes (LMA) using
ALD has shown effectiveness in facilitating lithium plating or acting as a physical barrier to constrain
[30]
lithium dendrite .

Regarding the ALD coating method, it has been extensively studied in liquid electrolyte-based batteries but
has been less documented in ASSBs, especially for the above PEO-based ones [31,32] . Besides, most of the
reported research about ALD coating approaches for lithium batteries is focused on the anode or cathode
side; the issues of anode/electrolyte interface and cathode/electrolyte interfaces have not sufficiently
investigated simultaneously [33,34] . In our opinion, a dual interface design via ALD in PEO-based ASSBs
should be studied to well address both the issues of dendrite growth for inherent soft nature of PEO-based
all-solid-state electrolytes (ASSEs) and the insufficient oxidation stability at a higher voltage. LLZO was
selected as the ceramic solid electrolyte to combine with PEO in forming the CSSE because this system has
been extensively studied in the literature and serves as an effective benchmark for comparing with our
ALD-modified CSSE system.

In this work, a dual interface design via ALD in PEO-based ASSBs is proposed for the first time. In detail, a
CSSE containing PEO, LLZO, and lithium bis (trifluoromethane-sulfonyl) imide (LiTFSI) (abbreviated as
LLZO/PEO/LiTFSI) is successfully fabricated through a simple solvent casting method. One side of the
cathode NCM811 and LMA is coated with an alucone thin layer using an ALD method. Then, the LLZO/
PEO/LiTFSI electrolyte is sandwiched by both alucone thin layer-coated cathode and anode to form the
ASSB (LMA-Alucone|LLZO/PEO/LiTFSI|Alucone-NCM811). Various advanced methods of representation
show that the alucone-coated interfaces can prevent electrochemical degradation of the cathode side and
facilitate lithium plating uniformly on the anode side. As a result, the assembled ASSB with the coated
interfaces shows significantly improved cycling stability even at low external pressure (< 1 mPa). In
comparison, the ASSB without ALD coating shows a significant capacity fade, and displayed micro-shorting
behavior after only 80 cycles. Overall, the fabrication strategy of coating electrode/electrolyte interfaces
through an ALD method in this work provides a new route to realize the robust interfaces in ASSBs, and
sheds light on the development of durable devices in the area of energy storage and conversion.

EXPERIMENTAL SECTION
Fabrication of the CSSE
Commercially available 99.99% purity LLZO with an average particle size of 500 nm was purchased from
MTI Corp. PEO (Mn = 400,000), LiTFSI and other common chemicals were purchased from Sigma-Aldrich
Inc. In the preparation of the CSSE, PEO and LiTFSI were weighed at a molecular ratio of 16:1, and further
dissolved in acetonitrile in the glovebox overnight to form a mixture. Then, LLZO powder was dissolved
into this mixture and stirred overnight. The obtained mixture was then cast onto the custom-made Teflon
plate (with film size desired) to form a film, which was slowly dried at 80 °C to obtain the final CSSE
(marked as LLZO/PEO/LiTFSI in this work, where the individual component mass ratio is 35:50:32). The
obtained thickness and diameter of the LLZO/PEO/LiTFSI film were about 100 μm and 18 mm,
respectively.

Cathode preparation and ALD coating
Cathode components of NCM811, Super-P, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio
of 90%, 5%, and 5%, respectively, and then pulverized with a high-shear mixer with the addition of N-
Methylpyrrolidone (NMP) solvent to make a homogeneous slurry. This cathode slurry was cast onto an
aluminum current collector using a doctor blade, which was then dried under vacuum at 90 °C for 24 h.