Cobalt-free nickel-rich layered oxides are considered as promising next-generation cathode materials for lithium-ion batteries (LIBs) due to their high capacity and controllable costs. However, the inferior cycling stability makes their application questionable. Herein, polycrystalline LiNi0.9Mn0.1O2 (PC-NM91) and single crystal LiNi0.9Mn0.1O2 (SC-NM91) were prepared by mixing the precursor with LiOH·H2O (and Li2SO4·H2O for SC-NM91). SC-NM91 with complete structure, uniform morphology, and good dispersion was successfully synthesized. The initial discharge capacity and Coulombic efficiency of both samples were similar. However, the capacity retention of SC-NM91 was 85.3% after 300 cycles at 1 C, while PC-NM91 showed only 65.8% under the same conditions. The proposed SC-NM91 cathode has better cycle stability than PC-NM91, especially under severe cycle conditions (4.5 V, 2 C, and 60 °C). The enhanced performance of SC-NM91 can be ascribed to the stronger structure, which prevents intergranular cracks, surface pulverization, disordered phase transition, and interface side reactions. In addition, it has a lower degree of Li+/Ni2+ mixing and fast Li+ diffusivity. This study provides insight into the role of single crystal structure in mitigating the performance degradation of Co-free Ni-rich cathodes and reveals that SC-NM91 can be a commercially available cathode material for high-energy LIBs.

Aqueous zinc-iodine (Zn-I 2 ) batteries are promising candidates for gridscale energy storage due to their safety and cost-effectiveness. However, the shuttle effect of polyiodides, Zn corrosion, and accumulation of by-products restrict their applications. Herein, a simple vermiculite nanosheets (VS) suspension electrolyte is designed for simultaneous confinement of polyiodides and stabilization of Zn anode. It is found that the generation of I 5 − as dominant intermediate and the precipitation reaction between I 5 − and alkaline by-products should cause irreversible iodine species loss. Benefiting from the high binding energy between polyiodides and silica-oxygen bonds of VS, dissolved polyiodides are effectively anchored on the surface of VS suspended in the bulk electrolyte to suppress the shuttle effect, which is confirmed by in situ Raman, Ultraviolet-visible characterizations and theoretical calculations. Furthermore, the self-assembly VS interfacial layer on the surface of Zn anode hinders side reactions induced by polyiodides. Meanwhile, the interlayer and surface excess negative charges of VS tend to be compensated by Zn 2+ from diffuse layer, which serves as ion accelerators for transferring Zn 2+ at the interface immediately, rendering dendrite-free Zn plating/stripping behavior. Consequently, the Zn-I 2 battery with VS electrolyte achieves an ultra-long lifespan of 40000 cycles with a negligible capacity decay at 20 C.

ZnÀ I 2 batteries stand out in the family of aqueous Zn-metal batteries (AZMBs) due to their lowcost and immanent safety. However, Zn dendrite growth, polyiodide shuttle effect and sluggish I 2 redox kinetics result in dramatically capacity decay of ZnÀ I 2 batteries. Herein, a Janus separator composed of functional layers on anode/cathode sides is designed to resolve these issues simultaneously. The cathode layer of Fe nanoparticles-decorated single-wall carbon nanotubes can effectively anchor polyiodide and catalyze the redox kinetics of iodine species, while the anode layer of cation exchange resin rich in À SO 3 À groups is beneficial to attract Zn 2 + ions and repel detrimental SO 4 2À / polyiodide, improving the stability of cathode/anode interfaces synergistically. Consequently, the Janus separator endows outstanding cycling stability of symmetrical cells and high-areal-capacity ZnÀ I 2 batteries with a lifespan over 2500 h and a high-areal capacity of 3.6 mAh cm À 2 .