Temperature-accelerated multiscale degradation in manganese-based blended-cathode pouch cells: evolution and origins of capacity loss

Understanding how dominant capacity-loss factors evolve under deeper cathode delithiation is critical for improving the capacity utilization and durability of lithium-ion batteries employing Mn-based blended cathodes. Here, 6.2 Ah graphite pouch cells with an NCM/LMFP/LRMO blended cathode were cycled between 3.0 and 4.3 V at 1 C at 25 and 45 ℃ and investigated using electrochemical diagnostics, ultrasonic inspection, and multiscale post-mortem characterization. The 25 ℃ cell retained 87.9% of its initial capacity after 1,200 cycles, whereas the 45 ℃ cell retained only 75.0% after 457 cycles. Electrochemical analysis indicates that capacity fading at 25 ℃ initially exhibits features consistent with reduced electrochemically accessible reaction capacity and LAM-related degradation, followed by increasingly evident LLI-related electrode slippage and ultimately a late-stage regime involving coupled LAM-related degradation, LLI, and impedance growth. At 45 ℃, this evolution is markedly compressed, with these degradation factors becoming strongly coupled within the first several hundred cycles. Multiscale characterization further links the accelerated degradation at elevated temperature to intensified interfacial parasitic reactions, cyclable-lithium and electrolyte consumption, gas generation, anode-material detachment, separator pore blockage, transport deterioration, and aggravated structural degradation of the layered NCM/LRMO components. In contrast, transition-metal dissolution and deposition do not increase commensurately with the accelerated capacity fading. These results demonstrate that elevated temperature primarily accelerates the onset and coupling of existing degradation processes rather than introducing fundamentally different failure mechanisms, highlighting electrolyte availability, interphase stability, and ion-transport integrity as key factors governing cell durability under deeper cathode utilization.