Towards high performance inorganic all-solid-state lithium-sulfur batteries: strategies for enhancing reaction kinetics and solid-solid contact

REVIEWS SCIENCE CHINA Materials mater.scichina.com link.springer.com Sci China Mater 2025, 68(5): 1530–1541 https://doi.org/10.1007/s40843-024-3276-3 Towards high performance inorganic all-solid-state lithium-sulfur batteries: strategies for enhancing reaction kinetics and solid-solid contact Zewei Huang1†, Liying Deng2†, Wangyang Li1, Jie Zhang1, Shuyu Liao1, Hong Zhang1* and Xinghui Wang1,3* ABSTRACT Inorganic solid electrolyte-based all-solid-state lithium-sulfur batteries (ASSLSBs) have garnered significant attention due to their inherent safety and higher energy density, making them a promising candidate for the upcoming lithium batteries. However, employing sulfur as the active material in all-solid-state composite cathodes introduces two critical challenges: sluggish electrochemical reaction kinetics and insufficient solid-solid contact between the sulfur, conductive additive, and solid electrolyte phases. These issues directly impact battery performance and hinder the commercialization of ASSLSBs. In this comprehensive review, the underlying causes of these issues are first discussed to gain a fundamental understanding of potential improvement directions. Subsequently, we summarize the recent progress in enhancing sulfur reaction kinetics and optimizing solid-solid contact. The fundamental principles, fabrication techniques, and resultant performance enhancement of diverse strategies are systematically categorized, summarized, and evaluated. Finally, the challenges and future outlook of advanced ASSLSB cathode research are discussed at the end of this review. Keywords: all-solid-state lithium-sulfur batteries, sulfur cathodes, cathode modifications, inorganic solid-state electrolytes INTRODUCTION Innovations in lithium-ion batteries (LIB) have revolutionized the fields of electric vehicles and consumer electronics, with insertion-type cathodes playing a dominant role in commercially available LIBs [1–5]. However, the energy density of traditional insertion-type cathodes coupled with graphite is gradually approaching their theoretical limit (170 W h kg−1 for LiFePO4 and 300 W h kg−1 for ternary cathode), which is not sufficient to meet market demands [6–8]. The two-electron redox reaction between sulfur and lithium provides high theoretical capacity, making lithium-sulfur (Li-S) batteries one of the most promising candidates for upcoming energy storage devices [9–12]. Specifically, the theoretical capacity of the lithium anode is 3860 mA h g−1, while that of the sulfur cathode is 1675 mA h g−1 [13,14]. Therefore, a maximum theoretical energy density of 2600 W h kg−1 is provided, and a fully packaged Li-S battery can achieve a high energy density up to 600 W h kg−1 [15–17]. Nevertheless, in commonly used ether-based liquid-state electrolytes (LEs), sulfur undergoes multistep electrochemical reactions, accompanied by the notorious drawback of the shuttle effect [18,19]. This phenomenon leads to a series of side reactions and a significant loss of active materials. Furthermore, the thermal instabilities and leakage-prone nature of LEs in the system pose potential safety risks [20–22]. Although there have been many attempts to suppress the shuttle effect by trapping soluble lithium polysulfides (LiPSs) and to improve the safety of LEs by adding flame retardants, fundamental solutions to the aforementioned challenges have yet to be achieved [23–28]. The introduction of inorganic solid-state electrolytes (ISEs) offers a promising solution to overcome the limitations. Currently, the ISEs utilized in all-solid-state lithium-sulfur batteries (ASSLSBs) primarily include sulfide-based, oxide-based, and halide-based electrolytes. Unlike gel electrolytes, some polymer electrolytes, or electrolytes that require interfacial wetting, the use of ISEs in place of separators and LEs typically results in the discharge curve of Li-S batteries transitioning from a dual plateau to a single plateau around 2.0 V (vs. Li/Li+) [29–34]. It is attributed to the absence of highly soluble long-chain LiPSs (Li2Sn, 4 ≤ n ≤ 8), which prevents the shuttle effect [35–37]. Moreover, ISEs exhibit superior thermal stability compared to LEs containing organic solvents, making them less susceptible to volatilization and leakage [38]. When ISEs replace porous electrode structures and separators, their relatively dense nature potentially facilitates a higher energy density [39,40]. Despite considerable progress in the development of ASSLSBs, there remain substantial challenges in the design and synthesis of high performance cathode, ISE, and anode, as well as the stabilization of their interfacial chemistry [41–43]. Particularly in the cathodes, the poor conductivity of sulfur and its significant volume change have become major concerns due to the absence of wetting by LEs [44,45]. In the solid-state system, the insulating properties of sulfur and its poor contact with ISEs are unfavorable for rapid electron and ion transport, leading to 1 College of Physics and Information Engineering, Institute of Micro-Nano Devices and Solar Cells, Fuzhou University, Fuzhou 350108, China Fujian Key Laboratory of Agricultural Information Sensing Technology, College of Mechanical and Electrical Engineering, Fujian Agriculture and Forestry University, Fuzhou 350002, China 3 Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou 213000, China † Equally contributed to this work. * Corresponding author (email: ; ) 2 1530 © Science China Press 2025 May 2025 | Vol.68 No.5 REVIEWS SCIENCE CHINA Materials sluggish reaction kinetics. Furthermore, the approximately 80% volume change of sulfur during cycling disrupts the solid-solid contact between the cathode and ISEs, ultimately leading to battery failure. These interconnected challenges hinder the realization of high performance ASSLSBs. To date, significant progress has been made in the mechanism research and performance optimization in inorganic ASSLSBs. In this review, we summarize the main challenges related to the cathode in inorganic ASSLSBs and their underlying causes. Distinct from other reviews, this article focuses on the problems of sulfur cathodes and their modification strategies, emphasizing the importance of improving reaction kinetics and maintaining close solid-solid contacts. From the perspectives of microscopic mechanisms and performance manifestations, we comprehensively summarize the latest progress in emerging strategies for optimizing solid-state sulfur cathodes, which encompasses the rational construction of conductive networks, the suppression of electrolyte decomposition, the catalysis of conversion reactions, the enhancement of interfaces and the mitigation of volume change (Fig. 1). Finally, we outline the opportunities and challenges faced by ASSLSBs, providing insights into future research prospects. Figure 1 Schematic diagram of the optimization strategies for sulfur cathodes in ASSLSBs. CHALLEN (...truncated)