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Guo et al. Energy Mater. 2025, 5, 500041 https://dx.doi.org/10.20517/energymater.2024.214 Page 3 of 21

mechanics, and computational mathematics have provided a solid theoretical foundation for the design of
materials’ microstructures [25-27] . The maturity of computational methods such as Molecular Orbital (MO)
methods and Density Functional Theory (DFT) has significantly enhanced computational accuracy and
efficiency, enabling more precise predictions of material properties.

In this comprehensive review, we will present and discuss the recent advancements in the development of
lithium batteries based on polymer electrolytes. Given the plethora of review articles focusing on lithium
SPEs [28-30] , in this review, we will organize our exploration of the topic in the following manner to ensure it is
comprehensive and systematic: the surface modification strategies between polymer electrolytes and
electrodes; in-situ characterization techniques; and the advanced modeling methods. Ultimately, this review
will also elaborate on the bottlenecks hindering the development of polymer-based lithium batteries,
propose corresponding solutions, and simultaneously provide insights into the future direction of
development for this type of battery.

SURFACE MODIFICATION STRATEGY FOR LITHIUM SOLID-STATE BATTERY BASED ON
POLYMER ELECTROLYTES
Compared with other inorganic SEs, SPEs possess numerous advantages, including flexibility,
lightweightness, electrode compatibility, and ease of processing. These qualities make SPEs a powerful
strategy for developing high-energy-density lithium batteries. However, despite their promising attributes,
the lithium-ion conductivity of SPEs still urgently needs improvement. To address this issue, a significant
amount of effort and technical innovations have been dedicated to enhancing their conductivity [31,32] .
Considering the overall performance of the battery, the lithium-ion conductivity of SPEs is an important
parameter that determines the performance of SSBs. However, low charge transport kinetics and side
reactions occurring between electrodes and SPEs also have a serious impact on the battery’s output
performance [33-35] . Despite significant improvements in their surface contacts, there remains significant
potential for further enhancement when compared to liquid electrolytes. Generally, the poor interfacial
contacts initiate an increase in overpotential, which deteriorates the SSB performance and makes them not
comparable to liquid batteries. Thus, many researchers have been committed to improving the insufficient
surface contacts through various surface modification strategies [Figure 1], such as liquid lithium additives,
a quasi-solid layer, multi-layered SE, and direct coating methods. We will provide a comprehensive review
of the aforementioned four surface modification strategies based on previous research. These surface
modification strategies enhance ion transport efficiency, stabilize the surface, prevent dendrite growth, and
improve battery safety and durability.

Liquid lithium additives between SPE and electrodes
By adding liquid electrolytes between the electrode and the SPE, this type of SSB becomes a promising
candidate to replace the current lithium battery, owing to its advantages of benign interfacial contact and
the ability to create huge barriers against unwanted redox shuttles [36-38] . Kim et al. developed a hybrid
electrolyte that integrated a solid polyethylene terephthalate (PET) electrolyte with an organic liquid
electrolyte [LiPF in ethylene carbonate (EC), diethylcarbonate (DC) and dimethyl carbonate (DMC)],
6
which was sandwiched between the anode and the PET electrolyte [Figure 2A] . The active cathode
[38]
materials composed of In O -SnO (ITO) were coated on another surface of PET by vacuum sputtering
3
2
2
deposition. Because lithium-ions migrated much faster in the small amount of organic liquid electrolytes,
the solid-state cell exhibited a Coulombic efficiency of over 100% [Figure 2B]. During subsequent cycles, the
battery’s capacity stabilizes, as evidenced by the long-term cycling results which indicate an average
coulombic efficiency of approximately 110% over 1,278 cycles. The gravimetric capacity remained stable
-1
even at a higher charge rate (400 mA g ), four times the initial rate, suggesting good electrode interphase