Mixing SiO_x materials with graphite materials has become a key technology to improve their performance, but it is still unclear what kind of graphite materials help to construct a stable electrode structure. The purpose of this study is to explore the effect of graphite morphology on the structure and performance of SiO_x/C composite electrodes (850 mAh g⁻¹). For the SiO_x/C59 composite electrode constructed by the lamellar graphite (C59) with a big aspect ratio and SiO_x particles, the SiO_x particles agglomerate in the pores of C59 particles. This uneven electrode structure could lead to excessive stress and strain of the electrode during cycling, which causes the anode electrode structure failure and cycling performance deterioration. While the small-size lamellar graphite (SFG15) with random orientation helps to construct stable electrode structure with uniform particle distribution and pore structure, which could reduce the stress and strain change of the electrode during cycling. Thus, the composite electrode (SiO_x/SFG15) exhibits better cycling performance compared with SiO_x/C59 composite electrode. This work reveals the structure-activity relationship of graphite morphology, electrode structure and the mechanical and electrochemical performance of the electrode, and provides a guide to the design and development of the high capacity SiO_x/C composite electrode structure.

The abrupt capacity rollover failure of medium-voltage lithium-rich manganese-based oxide (LRMO) batteries at elevated temperatures severely limits their practical application. This study systematically investigated the underlying failure mechanism of a 0.2Li₂MnO₃·0.8LiMn_0.33Ni_0.33Co_0.33O₂-graphite (LRMO-Gr) pouch cell cycled at 45 °C. Through combined differential voltage analysis, alternating current (AC) impedance measurements, and post-mortem characterization, we revealed that lithium plating on the anode surface acts as the primary trigger of rollover failure. This plating is driven by electrode saturation, which originates from the faster loss of the anode active material relative to the cathode. This imbalance stems from the structural degradation of a graphite anode induced by cathode-derived active lithium compensation and transition metal (TM) dissolution–migration–deposition. The migrated TMs and plated lithium further catalyze electrolyte decomposition, leading to gas evolution, electrode exfoliation, and rapid capacity collapse. These insights provide a fundamental basis for mitigating failure in high-energy LRMO-based batteries under realistic operating conditions.