Fast-charging of lithium-ion batteries is a critical requirement for wider adoption of electric vehicles. However, it is subject to several difficulties, such as inhomogeneous delithiation, local heating, and lithium plating. Various charging protocols have been developed to resolve these problems, most of which comprise the combinations of constant-current (CC) and constant-voltage (CV) charging steps. Although it is one of the two main components in conventional charging protocols, CV charging is usually applied in a restrictive manner only to supplement CC charging, and its potential implications as a fast-charging protocol have not yet been fully explored. Herein, we study the effects of a CV-only charging protocol on the fast-charging efficiency of high-rate LiNi_0.8Co_0.1Mn_0.1O₂ cathode particles prepared by ultrasonic spray pyrolysis. A 15 minute full-charging is achieved by a single CV charging step without a significant capacity loss in the early cycles. However, gradual degradation of specific capacity and charging efficiency was observed at later cycles. Based on electro- and physico-chemical analysis data, we propose a two-step CV charging protocol that can improve the cycle stability alleviating the damage to the cathode particles. By revisiting CV charging protocols, this work provides a better understanding of the CV charging process that can contribute to the design of new charging protocols with advanced fast chargeability.

A novel Mn-based Sp-DRX electrode engineered to initiate favorable early phase transitions, effectively delaying detrimental transitions to extend battery life.

Disordered rocksalt (DRX) cathodes are emerging as promising high-capacity materials for next-generation lithium-ion batteries due to their structural flexibility and compositional tunability. A recently discovered structural motif, known as the δ-phase, has drawn significant attention. This partially ordered, spinel-like structure forms progressively during electrochemical cycling, particularly in Mn-based DRX systems. The δ-phase contributes to improved electrochemical performance by enhancing capacity, rate capability, and cycling stability. In this review, we provide a comprehensive summary of recent advances in the understanding of δ-phase formation and its impact on DRX cathodes. We examine its structural characteristics, electrochemical behavior, and its role in enabling favorable Li-ion diffusion pathways through site energy homogenization and 0-TM percolation networks. Moreover, the thermodynamic and kinetic origins of δ-phase formation, which are governed by transition metal migration, oxidation states, and composition, are discussed based on both experimental and computational findings. Lastly, we highlight recent strategies to intentionally induce δ-phase formation, such as electrochemical pulse treatments and low-temperature annealing following chemical delithiation. These approaches enable faster and more controlled δ-phase development, suggesting a viable route toward practical DRX cathode implementation. Understanding and controlling the δ-phase will be pivotal in unlocking the electrochemical potential of DRX cathodes and accelerating the development of next-generation lithium-ion batteries.