A trifluoromethyl substitution strategy significantly enhances the emission efficiency and suppresses device-efficiency roll-off for TADF emitter by creating hydrogen bonds, avoiding π–π stacking, and regulating excited-state alignment.

A single-crystalline Ni-rich (SCNR) cathode with a large particle size can achieve higher energy density,and is safer,than polycrystalline counterparts.However,synthesizing large SCNR cathodes ( ＞5 μm) without compromising electrochemical performance is very challenging due to the incompatibility between Ni-rich cathodes and high temperature calcination.Herein,we introduce Vegard's Slope as a guide for rationally selecting sintering aids,and we successfully synthesize size-controlled SCNR cathodes,the largest of which can be up to 10 μm.Comprehensive theoretical calculation and experimental characterization show that sintering aids continuously migrate to the particle surface,suppress sublattice oxygen release and reduce the surface energy of the typically exposed facets,which promotes grain boundary migration and elevates calcination critical temperature.The dense SCNR cathodes,fabricated by packing of different-sized SCNR cathode particles,achieve a highest electrode press density of 3.9 g cm-3 and a highest volumetric energy density of 3000 Wh L-1.The pouch cell demonstrates a high energy density of 303 Wh kg-1,730 Wh L-1 and 76％ capacity retention after 1200 cycles.SCNR cathodes with an optimized particle size distribution can meet the requirements for both electric vehicles and portable devices.Furthermore,the principle for controlling the growth of SCNR particles can be widely applied when synthesizing other materials for Li-ion,Na-ion and K-ion batteries.

Composite particle with high speed channels for delivering lithium is a promising candidate for the high performance electrode in electric vehicles. However, it still suffers from poor rate capability due to the long diffusion pathway caused by large particle size. Inspired by the efficient transporting ability of the hierarchical structure in tree roots, we design the channel structure to improve the rate capability using a diffuse interface model. This model enables us to simulate the fast lithium diffusion along the channel network and the electrochemical reaction on the particle surface. Our results demonstrate that two microstructure features of the channel network can efficiently enhance the rate capacity: One is the gradient distribution of the channel density with a higher channel density near the surface than that in the center; the other is the orientation of the channel structure parallel to lithium flux from the particle surface. The root-inspired hierarchical channel network displaying these two features can improve the capacity retention at large C-rates. Furthermore, our study can offer an efficient tool that can rationalize the topology design of channel structure in the purpose of achieving a high rate capability.

Lithium cobalt oxides (LiCoO2) possess a high theoretical specific capacity of 274 mAh g–1. However, cycling LiCoO2-based batteries to voltages greater than 4.35 V versus Li/Li+ causes significant structural instability and severe capacity fade. Consequently, commercial LiCoO2 exhibits a maximum capacity of only ~165 mAh g–1. Here, we develop a doping technique to tackle this long-standing issue of instability and thus increase the capacity of LiCoO2. La and Al are concurrently doped into Co-containing precursors, followed by high-temperature calcination with lithium carbonate. The dopants are found to reside in the crystal lattice of LiCoO2, where La works as a pillar to increase the c axis distance and Al as a positively charged centre, facilitating Li+ diffusion, stabilizing the structure and suppressing the phase transition during cycling, even at a high cut-off voltage of 4.5 V. This doped LiCoO2 displays an exceptionally high capacity of 190 mAh g–1, cyclability with 96% capacity retention over 50 cycles and significantly enhanced rate capability. Lithium cobalt oxides are used as a cathode material in batteries for mobile devices, but their high theoretical capacity has not yet been realized. Here, the authors present a doping method to enhance diffusion of Li ions as well as to stabilize structures during cycling, leading to impressive electrochemical performance.