As lithium-ion battery (LIB) use rises, recycling becomes imperative. Efficiently overdischarging LIBs for residual energy extraction is crucial for safe recycling. Our study analyzes the electrochemical behavior during overdischarge for positive electrode materials, including LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiFePO4 (LFP), LiCoO2 (LCO), and LiMn2O4 (LMO). Electrochemical evaluations involve half cells and full cells subjected to constant current overdischarge beyond normal operating ranges. In positive electrode half-cells, a material-dependent conversion reaction was observed, while full cells exhibited similar behaviors during overdischarge to 0 V due to increasing voltage at the negative electrode. Distinct electrochemical variations emerged under forced discharge below 0 V, particularly in the NCM series, showing a gradual voltage decrease to −2 V followed by an internal short circuit. In contrast, LFP, LCO, and LMO swiftly stabilized near 0 V, attributed to the lower initial Coulombic efficiency of NCM materials leading to an early rise in negative electrode potential. To recycle used lithium-ion batteries (LIBs), it’s crucial to optimize conditions that ensure both efficient and safe overdischarge, considering the characteristics of positive electrode materials.

This paper presents the development of an isothermal battery calorimeter (IBC) for analyzing the thermal characteristics of high-capacity lithium-ion pouch cells used in electric vehicles. The IBC incorporated a Peltier module to maintain an isothermal environment within the test cell, and a PID control was employed for the operation. A Positive-Thermal-Coefficient (PTC) heater was used to calibrate the IBC and determine the heat generation rate of the battery during operation. The heat generation rate of a lithium-ion battery (LIB) was measured under various load conditions, including constant current discharge and driving profiles. The results were compared with those of conventional methods, such as equivalent electric circuit model (EECM)-based simulation and inverse heat analysis. This comparison demonstrated that the IBC accurately captured the thermal behavior of the pouch cell, which exhibited changes in the state of charge (SOC), similar to the inverse heat analysis. Additionally, the IBC effectively identified specific regions with significant heat generation, thus facilitating in the detection of serious heat problems within the battery under driving load conditions. Although a time delay in the heat generation rate was observed in the IBC, owing to the thermal inertia of the Peltier module, this issue could be mitigated by reducing the thermal mass of the module.

Lithium-sulfur batteries (LSBs) have been considered promising candidates for next-generation energy storage devices owing to their high energy density, low price, and environment-friendly characteristics. However, their commercialization has been hindered by the "shuttle effect", which occurs during the charge/discharge cycles and leads to poor cycling performance and low coulombic efficiency. Here, we synthesized flower-shaped hollow VOOH spheres on the carbon nanotube (CNT) network, which were used as the multifunctional sulfur host materials for the first time in LSBs. These VOOH spheres can chemically and physically confine polysulfides as well as catalyze their redox conversion; additionally, their hollow structure can effectively accommodate the volume change during cycling. Moreover, the CNTs among spheres can improve the conductivity of the host material and increase the number of active sites for interfacial reactions. Accordingly, when used as a cathode material, VOOH@CNTs/S composites exhibited a large specific discharge capacity of 1414.63 mAh/g at 0.1 C and excellent cycling stability. At a low current density of 0.5 C, VOOH@CNTs/S exhibited a capacity decay of 0.044% per cycle after 100 cycles. Importantly, at an ultrahigh current density of 5 C, a specific capacity as high as 455.09 mAh/g could be still be delivered after 1000 cycles, corresponding to a superior capacity retention of 90.46% and an ultralow capacity decay of 0.009% per cycle. These findings open up a new material for the practical application of LSBs with ultrafast charge/discharge property and long-lasting cyclic stability.