Guo Weilin ¹, ZHOU Xiaoliang ^{1, 2}, LIU Limin ^{1, 2}, ZHANG Shuo ¹, WEN Kun ¹, YANG Qian ¹

(1. College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, Sichuan, China,

2. Tianfu Yongxing Laboratory, Chengdu 611130, Sichuan, China)

Extended Abstract:[Background and purpose] With the rapid development of energy storage technologies, all-solid-state sodium-ion batteries (ASSBs) have emerged as promising candidates for next-generation batteries, due to their potential for high energy density, safety and cost-effectiveness. However, one of the most significant challenges hindering the widespread adoption of ASSBs is the interface between the ceramic electrolyte and the metallic sodium electrode. Specifically, the interface between the ceramic electrolyte Na_3.4Zr₂Si_2.4P_0.6O₁₂ (NZSP) and the metallic sodium electrode has long been identified as a critical factor limiting the overall performance of these batteries. This interface is particularly problematic because it is prone to have defects that lead to high polarization during battery operation. High polarization, in turn, results in low capacity and poor cycling stability, which are detrimental to the practical application of ASSBs. To tackle these challenges, various strategies have been explored to optimize the interface between NZSP and the metallic sodium electrode.[Methods] One particularly innovative approach involves the introduction of a polymer film onto the surface of the NZSP electrolyte. Among the polymer films, polyethylene oxide (PEO) and polyethylene glycol diacrylate (PEGDA) have shown great promise. These polymers are chosen not only for their chemical compatibility with the ceramic electrolyte but also for their ability to enhance the interfacial properties between the electrolyte and the electrode. The introduction of the polymer film has multiple purposes. Firstly, it significantly enhances the interfacial wettability and contact between the NZSP electrolyte and the metallic sodium electrode. This improved contact is crucial because it allows ions to smoothly transport across the interface, thereby reducing the resistance that contributes to high polarization. Secondly, the polymer film acts as a protective barrier that effectively prevents unwanted side reactions at the interface. These side reactions, often involving the reduction of the electrolyte or the oxidation of the electrode, can lead to the formation of insulating layers or the consumption of active materials, both of which degrade battery performance.[Results] When a polymer film is applied to the surface of the NZSP electrolyte, the resulting Na/NZSP/Na symmetric battery demonstrates remarkable improvements in electrochemical performance and cycling stability. For instance, at current density of 0.01 mA·cm⁻², the polymer-coated symmetric battery can be stably cycled for up to 1,000 h, which is a significant enhancement as compared with the uncoated battery, which experiences a short circuit after operation for only 80 h. The ability to achieve such long-term stability is a major step forward in the development of ASSBs, as it addresses one of the primary concerns regarding their practical application.[Conclusions] The experimental results show that the Na/NZSP/Na symmetric cell coated with polymer film can be stably cycled for 1000 h at a current density of 0.01 mA·cm⁻², exhibiting excellent electrochemical performance and cycling stability, in contrast to the symmetric cell without polymer film, which was shorted after only 80 h. This result indicates that the introduction of polymer film provides an effective strategy for the interfacial optimization of all-solid-state sodium-ion batteries, which not only improves the performance of the batteries, but also lays the foundation for the commercial application of all-solid-state sodium-ion batteries.

Key words: ceramic electrolyte; NZSP; interface modification; sodium-ion battery