On March 17, the reporter learned from the official website of the Chinese Academy of Sciences that the Chinese scientific research team pioneered the existence of H- ions on the negative side of the NCM ternary battery, which confirmed that this component has poor thermal compatibility with the electrolyte, which is The main trigger for inducing the chain exothermic reaction during the heating process of the battery. In addition, the detailed analysis of the thermal runaway path of the Li-S system will provide useful inspiration for the construction of the next generation of high specific energy and high safety battery systems.
It is understood that the relevant results were recently published in "Joule".
In the context of promoting carbon neutrality, accelerating the electrification of powertrains has become an inevitable trend in the development of new energy vehicles. As the key technology of new energy vehicle power system, lithium battery has become increasingly prominent with the increase of energy density, and battery thermal runaway phenomena such as spontaneous combustion and explosion occur frequently. Thermal runaway accidents have become constraints for further promotion and large-scale application of lithium-ion batteries. Therefore, improving battery safety has also become a prerequisite for the healthy and sustainable development of the new energy industry. Therefore, revealing the thermal runaway mechanism of the battery and developing a high-safety battery system have become the key issues that need to be solved urgently in the current battery field.
It is worth noting that the Solid State Energy System Technology Center of the Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences has been committed to building a lithium battery system with high specific energy and high safety, and has made a series of progress in recent years.
For the research and analysis of battery runaway, to trace the source, we must first understand the triggering reaction of the runaway. The researchers proved the existence of lithium metal anode lithium hydride (LiH) by titration-mass spectrometry, and quantitatively analyzed that the accumulation of LiH was negatively correlated with the cyclability of actual lithium metal batteries, revealing the failure of lithium metal batteries. Key mechanism (Angew. Chem. Int. Ed. 2021, 60, 7770–7776). At the same time, on the basis of fully summarizing the thermal stability and thermal characteristics of battery materials, the researchers proposed that the thermal compatibility between battery materials (electrode materials/electrolytes/additives, etc.) The thermal stability of the components cannot ensure the improvement of the overall safety performance of the battery (Energy Storage Mater., 2020, 31, 72–86).
In view of this, the team explored the failure mechanism of the ternary high nickel battery (NCM523) at the material-battery level through in-situ/ex-situ coupling methods, and pioneered the discovery of the existence of H- ions on the negative side of the NCM ternary battery. , confirming that this component has poor thermal compatibility with the electrolyte, which is the main trigger for inducing the chain exothermic reaction during the heating process of the battery. Moreover, through the self-designed in-situ detection device and method for thermal runaway gas shuttling of battery materials (CN202011538153.3), it is proved that H2 generated from the negative electrode side of graphite can shuttle to the positive electrode side, thereby accelerating the violent exothermic behavior and becoming the trigger for the battery. Key triggers for thermal runaway (Adv. Sci., 2021, 2100676).
In recent years, the anxiety of cruising range has put forward higher requirements on the energy density of lithium batteries, and the theoretical energy density of traditional lithium-ion batteries is approaching its limit (350 Wh/kg). Compared with graphite anodes, metallic lithium has extremely low electrode potential and extremely high theoretical specific capacity, and is considered to be a strong competitor for next-generation high-energy-density batteries. Lithium-sulfur (Li-S) batteries with lithium metal anode and sulfur cathode have become one of the most attractive battery systems due to their ultra-high theoretical energy density (2500 Wh/kg). However, the pace of research on its thermal safety assessment has lagged significantly. Researchers from the Center for Solid State Energy Systems have systematically studied the thermal compatibility of electrolyte/electrode in Li-S soft package, the effect of polysulfide shuttle on battery thermal safety, and the decomposition route of electrolyte, revealing the exothermic chain of Li-S battery. The reaction is initiated by the reaction of the sulfur cathode derivative with the electrolyte solvent and accelerated by the reaction of the lithium metal anode with the electrolyte and molten sulfur.
In addition, the researchers employed electrolyte systems with different thermal stabilities, including the inorganic all-solid-state electrolyte Li6PS5Cl, to study the characteristics during thermal runaway of Li-S batteries. It is found that the Li-S soft packs of different electrolyte systems all experience rapid thermal runaway in a relatively concentrated temperature range, and the use of the inorganic solid electrolyte Li6PS5Cl cannot prevent the thermal runaway of the Li-S soft packs. After a systematic in-situ-ex-situ interface analysis, it was found that this was mainly due to the crosstalk reaction of the positive and negative electrodes at high temperature due to the sublimation and melting of the sulfur cathode and the melting of the lithium metal in the anode in the Li-S system. The detailed analysis of the thermal runaway path of the Li-S system will provide useful inspiration for the construction of the next generation of high specific energy and high safety battery systems.
