An HBr‐assisted slow cooling method is developed for the growth of centimeter‐sized Cs4PbBr6 crystals. The obtained crystals show strong green photoluminescence with absolute photoluminescence quantum yields up to 97%. More importantly, the evolution process and structural characterizations support that the nonstoichiometry of initial Cs4PbBr6 crystals induce the formation of nanosized CsPbBr3 nanocrystals in crystalline Cs4PbBr6 matrices. Furthermore, high efficiency and wide color gamut prototype white light‐emitting diode devices are also demonstrated by combining the highly luminescent Cs4PbBr6 crystals as green emitters and commercial K2SiF6:Mn4+ phosphor as red emitters with blue emitting GaN chips. The optimized devices generate high‐quality white light with luminous efficiency of ≈151 lm W−1 and color gamut of 90.6% Rec. 2020 at 20 mA, which is much better than that based on conventional perovskite nanocrystals. The combination of improved efficiency and better stability with comparable color quality provides an alternative choice for liquid crystal display backlights.

To simultaneously achieve high compaction density and superior rate performance, a structure-gradient LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode material composed by a compacted core and an active-plane-exposing shell was designed and synthesized via a secondary co-precipitation method successfully. The tight stacking of primary particles in the core part ensures high compaction density of the material, whereas the exposed active planes, resulting from the stacking of primary nanosheets along the [001] crystal axis predominantly, in the shell region afford enhanced Li + transport. Thus, this structure-gradient Nirich cathode material shows a high compaction density with excellent electrochemical performances, especially the rate performance, exhibiting excellent rate capability (160 mA h g −1 at 10 C), which is 62% larger than that of the pristine material within 2.75−4.3 V (vs Li + /Li). Our work proposes a possible strategy for designing and synthesizing layered cathode materials with the required hierarchical structure to meet different application requirements.

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Limited cycling stability hampers the commercial application of Ni‐rich materials, which are regarded as one of the most promising cathode materials for Li‐ion batteries. Ni‐rich LiNi0.9Co0.06Mn0.04O2 layered cathode was modified with different amounts of LiTaO3, and the influences of fast‐ion conductor material on cathode materials were explored. Detailed analysis of the materials revealed the formation of a uniformly epitaxial LiTaO3 coating layer and a little Ta5+ doping into the lattice structure of Ni‐rich materials. The coating‐layer thickness increased with the amount of LiTaO3 added, protecting the electrode from erosion by electrolyte and suppressing undesired parasitic reactions on the cathode‐electrolyte interface. Meanwhile, the doped Ta5+ increased the interplanar spacing of materials, accelerating Li+ transfer. Using the positive synergistic effects of LiTaO3‐coating and Ta5+‐doping, improved capacity retentions of the modified materials, especially for 0.25 and 0.5 wt%‐coated Ni‐rich materials, were obtained after long‐term cycling, showing the potential applications of LiTaO3 modification. Further, the relations between one excessively thick coating layer and transfer of Li+/electron between the cathode and electrolyte was established, proving that very thick coating layers, even layers containing Li ions, have adverse effects on electrochemical performances. This finding may help to understand the roles of the coating layer better.

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