NSRRC Activity Report 2023

060 NSRRC ACTIVITY REPORT 2023 Another studies by the same team also used XAS to analyze electrode materials. Currently, commercial lithium-ion batteries mostly use graphite as the anode material. Lithium ions are embedded in the graphite after passing through the electrolyte. The development of lithium metal batteries actually preceded that of lithium ion batteries. However, due to the high activity of lithium metal, lithium metal often passes through the electrolyte and reaches the cathode, causing a short circuit. Because the structure of lithium metal batteries only requires a very thin lithium component as an anode, they display improved overall energy density and have been the subject of many studies. The research team synthesized a novel electrolyte, 3D-SIPE-LiFPA, to use in lithium metal batteries. This electrolyte is combined with a NCM811(LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) cathode to make a full lithium metal battery, and the control group LiPF 6 electrolyte was used for comparison. Lithium metal battery research often focuses on improving cycle life; however, the thermal stability of the battery is often neglected. The research team conducted several thermal tests on different electrolytes. A significant enhancement of the safety characteristics of the soft pack battery was achieved using 3D-SIPE-LiFPA as an electrolyte, since it reduces the heat released by the lithium anode. When cycled in 3D-SIPE-LiFPA, the decrease in the oxidation state from Ni 3+ to Ni 2+ was significantly suppressed. Similarly, the transition of Co 3+ to Co 2+ , as well as the transition of Mn 4+ to Mn 3+ and Mn 2+ ( Figs. 2(a)−2(c) ) were also greatly inhibited when using 3D-SIPE-LiFPA. The O K-edge XAS spectra ( Fig. 2(d) ) in the bulk structure-affected TFY showed a lower Ni 2+ content when using 3D-SIPE-LiFPA, in line with the Ni L-edge XAS result. XAS, along with other analyses, provide a clearer picture of the interfacial reaction. The interfacial layer of the F3D-SIPE-LiFPA-derived cathode prevents the reduction of the Co ion valence state and inhibits the dissolution of the transition metal and destruction of the crystal structure. XAS is sensitive to the element valence, bonding, and material structure. With the combination of TEY and TFY, it provides considerable validation of the reaction mechanisms at the lithium battery material interface. (Reported by Fan-Hsiu Chang) This report features the work of Guanglei Cui and his collaborators published in Angew. Chem.Int. Ed. 62 , e2023026 (2023) and Energy Enivron. Sci. 16 , 2591 (2023). TLS 11A1 (Dragon) MCD, XAS • XAS, XMCD • Materials Science, Batteries Fig. 2 : (a–c) Ni, Co, Mn L 3,2 -edge XAS spectra in the TEY mode and (d) O K-edge XAS spectra in the TFY mode of the measured NCM811 cathodes: pristine (black line), cycled in 3D-SIPE-LiFPA (green line), and cycled in 1 M LiPF 6 EMC/FEC electrolyte (yellow line). The measured NCM811 cathodes were harvested from NCM811/Li LMBs (50 μm, 3.7 mA h cm −2 , 2.8–4.3 V) after 50 cycles. [Reproduced from Ref. 1]