Experimental Study on Combustion Characteristics of Electrolytes and Slurries for Semi-Solid Lithium-ion Flow Battery

Semi-solid lithium-ion flow battery (SSLFB) is a promising candidate in the field of large-scale energy storage. However, as a key component of SSLFB, the slurry presents a great fire hazard due to the extremely flammable electrolyte content in the slurry as high as 70 wt%–95 wt%. To evaluate the fire risk of SSFLB, the combustion experiments of electrolyte and slurry were conducted using cone calorimeter, and the critical fire parameters such as heat release rate (HRR), mass loss rate (MLR), and gas production were analyzed. This study firstly compared the combustion characteristics of electrolytes with the addition of different lithium salts (LiPF₆ and LiTFSI). The results showed that the peak HRR (pHRR) and peak MLR (pMLR) of LiTFSI-based electrolyte were reduced by 30.3% and 33.2%, respectively, compared with LiPF₆-based electrolyte. Also, LiTFSI-based electrolyte possessed a relatively lower toxic hazard. Overall, LiTFSI could reduce the fire hazard of the electrolyte compared with LiPF₆. Then, the combustion behaviour of slurries containing different electrode materials (Li₄Ti₅O₁₂, LiNi_0.8Co_0.1Mn_0.1O₂, LiFePO₄, and Graphite) was investigated. It was observed that the splashing occurred in the early stage combustion of slurries. The splashing of S-LTO and S-LFP was relatively violent, while only sporadic splashing occurred for S-NCM and S-graphite. Based on the pHRR and pMLR test results, the order of fire risk of the four slurries is determined as S-LTO > S-LFP > S-NCM > S-Graphite. The pHRR and pMLR of slurries other than S-LTO are lower than that of electrolyte, thus their fire risk is lower than electrolyte. The results of this study can provide a reference for the fire hazard evaluation and safety improvement of the SSFLB system.