The growing demand for high-performance and safe energy storage systems in both stationary and automotive sectors has driven significant attention toward next-generation lithium-ion battery technologies [1]. Among these, semi-solid-state batteries (SSSBs) have emerged as a promising alternative, combining features of conventional lithium-ion batteries (LIBs) and all-solid-state batteries (ASSBs) to offer improved energy density and safety [2].
Despite the commercial maturity of LIBs, their limitations remain evident. For instance, lithium iron phosphate (LFP) cathodes suffer from relatively low energy density, which restricts their application in long-range electric vehicles [3]. On the other hand, Ni-rich cathode chemistries such as NMC, while offering high capacity, exhibit safety risks due to oxygen release at elevated states of charge, which can trigger uncontrollable thermal runaway (TR) [4].
ASSBs have been proposed as a solution to these issues; however, their progress toward large-scale commercialization has been slow [5]. Major obstacles include poor interfacial stability between solid electrolytes and electrodes, which leads to high resistance and capacity fading [6]. Although recent advances in electrolyte design have improved ionic conductivity [7], full-scale implementation is hindered by unresolved challenges in manufacturability and long-term performance [8]
SSSBs, often described as a hybrid between liquid and solid-state systems, present a unique compromise. By retaining partial liquid phases, they maintain high ionic conductivity and processability, while incorporating solid phases improves thermal and electrochemical stability [2]. As such, they are increasingly regarded as a candidate technology for bridging the gap between LIBs and ASSBs.
However, while their electrochemical performance has been studied, limited attention has been devoted to understanding their safety behaviour under misuse conditions, particularly in large-format cells [2]. One of the most critical safety threats in batteries is the onset of internal short circuits (ISCs), which can trigger TR [9]. The initiation of ISC is strongly dependent on factors such as electrode chemistry, cell design, and the abuse mechanism, including overcharge [10]. The recent investigation in [11] defined severe ISC as dV/dt ≥ – 0.1 V/s, and reported that for large format NMC LIBs, this severe ISC occur simultaneously with TR.
Addressing this current safety gap regarding SSSBs, this research redefines key warning onset criteria at different stages of overcharge, with particular emphasis on the electrochemical processes leading to ISC and TR. Therefore, providing insights that can support the development of safer SSSB cell.

Reference
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