Layered lithium nickel oxide (LiNiO₂) is a promising cathode for high-energy lithium batteries, yet its conventional high-temperature solid-state (HS) synthesis inevitably involves an “ordered layered → disordered rocksalt → ordered layered” phase transformation, leading to structural defects and limited electrochemical performance. Here, we report a low-temperature reaction−high-temperature crystallization (LR-HC) strategy that decouples lithiation from crystallization, enabling topotactic conversion of Ni(OH)₂ into highly ordered LiNiO₂ while bypassing the detrimental rocksalt intermediate. The LR-HC product crystallized at 700°C for only 1 h exhibits an exceptionally low rocksalt phase content on the surface and delivers an initial discharge capacity exceeding 220 mAh g⁻¹ with an initial Coulombic efficiency above 90%. Remarkably, it retains 72.48% of its capacity after 200 cycles at 0.5C, far outperforming the HS counterpart (53.10%). Operando XRD during cycling further demonstrates that the enhanced stability originates from a reduced c-axis contraction (4.19% vs. 6.43%) and a more reversible H2-H3 phase transition. The LR-HC strategy also proves versatile for synthesizing other high-nickel layered oxides (e.g., Ni₉₅Co₅, Ni₉₅Mn₅), offering mechanistic insights into defect suppression and structural ordering for advanced cathode materials.

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) | SiOx-graphite (SiO-Gr.) battery chemistry is of intensive attention because its achievable practical energy density is approaching impressively 300 Wh Kg⁻¹. However, it still suffers rapid capacity fades during repeated cycles, both chemical, electrochemical and mechanical irreversibility contribute. A comprehensive understanding behind the fading behavior of the cell chemistry is required before fully realize the benefits of this chemistry. Herein, the in-situ thickness variation is introduced as a diagnostic technique and is performed on 5–55 Ah NCM811|SiO-Gr-Gr cells. With the help of Li reference electrode and in-situ X-ray diffraction device, the correspondence between thickness variation and the electrode potential is carefully investigated. Firstly, the NCM811|SiO-Gr-Gr cell is characterized with the maximum cell thickness at around 80% state-of-charge (SOC) in the discharge process, rather than at 100% SOC. Secondly, the electrochemical behaviors during rate charge/discharge are diagnosed, and a Li platting signal is resolved from thickness variation profile at 2C. This work confirms that the thickness monitoring is a nondestructive and informative complement to conventional diagnostic techniques for failure analysis of pouch cells.

Graphite is the dominant anode material for lithium-ion batteries; however, it still suffers from Li-plating when charging fast or at low temperature, and Li-plating is associated with performance fading and safety concerns. Herein, we clarify the mechanism of lithium evolution from graphite particles by over-lithiation cycle test, in-situ XRD, and titration gas chromatography. We observe that the graphite intercalation compounds (GICs, LiC₁₂ and LiC₆ e.g.) gradually become inactive and wrapped by dead lithium or side reaction sediments, while the rate of this degradation will be accelerated as the overpotential of Li-plating is decreased after initial Li metal nucleation. This understanding is contradictory to the popular one that the degradation of graphite anode after Li plating is mainly caused by the inferior SEI and dead Li induced hindering of Li-ion intercalation. The isolation of lithiated graphite particles leading to the fast vanishing of Li insertion/deintercalation process in graphite anodes. We further study the insertion/deintercalation vanishing process at low temperature and high rates, respectively. This work provides a insight on graphite anode degradation induced by Li-plating, and the new understanding can be used to guide the design of advanced materials and electrodes to avoid Li-plating and achieve extreme fast while safe charging.

Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance; thus, they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety. Moreover, the fluorinated electrolytes are widely used to form stable electrolyte interphase, due to their chemical reactivity with lithiated graphite or lithium. However, the influence of this reactivity on the thermal safety of batteries is seldom discussed. Herein, we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability, while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte. The reduction in fluorinated components (e.g., LiPF₆ and fluoroethylene carbonate (FEC)) by fully lithiated graphite accounts for a significant heat release during battery thermal runaway. The 13% of total heat is sufficient to trigger the chain reactions during battery thermal runaway. This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes, providing guidance on the concept of electrolyte design for safer lithium-ion batteries.

High-capacity lithium-containing alloy anodes (e.g., Li_4.4Si, Li_4.4Sn, and Li₃P) enable lithium-free cathodes (e.g., Sulfur, V₂O₅, and FeF₃) to produce next-generation lithium-ion batteries (LIBs) with high energy density. Herein, we design a Li₃P/C nanocomposite with Li₃P ultrafine nanodomains embedded in micrometer-scale porous carbon particles. Benefiting from the unique micro/nanostructure of the Li₃P/C nanocomposite, electrons transfer rapidly through the conductive pathway provided by the porous carbon framework and the volume change between Li₃P and P is confined in the nanopores of the carbon, which avoids the collapse of the whole Li₃P/C composite particles. As expected, the as-achieved Li₃P/C nanocomposite provided a high available lithium-ion capacity of 791 mAh/g (calculated based on the mass of Li₃P/C) at 0.1 C during the initial delithiation process. Meanwhile, the Li₃P/C nanocomposite showed 75% of its 0.5 C capacity at 6 C and stable cycling stability.