Impact of cycling at low temperatures on the safety behavior of 18650-type lithium ion cells: Combined study of mechanical and thermal abuse testing accompanied by post-mortem analysis

The impact of cycling at low temperatures on the thermal and mechanical abuse behavior of commercial 18650-type lithium ion cells was compared to fresh cells. Post-mortem analyses revealed a deposition of high surface area lithium (HSAL) metal on the graphite surface accompanied by severe electrolyte decomposition. Heat wait search (HWS) tests in an accelerating rate calorimeter (ARC) were performed to investigate the thermal abuse behavior of aged and fresh cells under quasi-adiabatic conditions, showing a strong shift of the onset temperature for exothermic reactions. HSAL deposition promotes the reduction of the carbonate based electrolyte due to the high reactivity of lithium metal with high surface area, leading to a thermally induced decomposition of the electrolyte to produce volatile gaseous products. Nail penetration tests showed a change in the thermal runaway (TR) behavior affected by the decomposition reaction. This study indicates a greater thermal hazard for LIB cells at higher SOC and experiencing aging at low temperature

A high-capacity P2 Na 2/3 Ni 1/3 Mn 2/3 O 2 cathode material for sodium ion batteries with oxygen activity

Na2/3Ni1/3Mn2/3O2 with a P2 phase is investigated as a cathod material for sodium ion batteries. It delivers a high discharge capacity of 228 mAh g−1 within 1.5–4.5 V in half cells, which is much higher than the theoretical value of 172 mAh g−1. Metal K-edge X-ray absorption near edge spectroscopy results show that the Mn ions remain in 4 + oxidation state during sodiation/desodiation and the charge compensation is due to the Ni2+/Ni4+ redox. Soft X-ray absorption spectroscopy results reveals a gradient in the valence state of Ni ions from bulk to surface for the charged electrode, and a change in the integrated intensity of O K-edge peak after charging, strongly suggesting that part of the charge compensation takes place at the oxygen sites. In addition, the reduction of Mn ions on the surface is observed on the discharged electrode, which indicates that the carbonate-based electrolyte reacts with the cathode material, resulting in a fast capacity drop. By utilizing an ionic liquid (IL) electrolyte (1 M NaTFSI in Pyr14TFSI) to reduce the interfacial reactions, the discharge capacity of ∼200 mAh g−1 is retained