Conversion-Type Anodes: Challenges, Mitigation Strategies, and Evaluation Guidelines

Conversion-type anode materials enable multi-electron redox reactions and therefore offer theoretical capacities beyond those of classical insertion-based anode materials such as graphite. However, their practical implementation is limited by multiple coupled penalties that evolve with cycling and electrode design. This review organizes recent progress in conversion-type anodes (including transition metal oxides, sulfides, selenides, and phosphides) around five recurring limitations: (i) voltage hysteresis and low round-trip energy efficiency, (ii) low initial Coulombic efficiency and cyclable-lithium inventory loss, (iii) interphase instability with continuous electrolyte reduction and dissolution-mediated cross-talk, (iv) chemo-mechanical damage leading to fracture, contact loss, and conductive network degradation, and (v) transport and accessibility limitations that intensify in thick, high-areal-loading electrodes under practical electrolyte amounts. We survey mitigation strategies spanning active-material and microstructure design, composite and processing controls, electrolyte design and formation protocols, and electrode-architecture design to improve ionic accessibility and reduce concentration polarization in thick electrodes. To reduce mechanistic overinterpretation, this review develops a coupled-penalty evaluation framework in which each section closes with an integrated interpretation and a validation checklist defining the evidence required for mechanistic claims. Overall, this review provides practical guidelines for distinguishing intrinsic conversion/reconversion pathway changes from electrode-level accessibility, resistance, interphase, and formation-history effects in conversion-type anodes.