Revealing alkali metal ions transport mechanism in the atomic channels of Au@a-MnO_(2)

Understanding alkali metal ions’(e.g.,Li^(+)/Na^(+)/K^(+))transport mechanism is challenging but critical to improving the performance of alkali metal batteries.Herein using a-MnO_(2)nanowires as cathodes,the transport kinetics of Li^(+)/Na^(+)/K^(+)in the 2×2 channels of a-MnO_(2)with a growth direction of[001]is revealed.We show that ion radius plays a decisive role in determining the ion transport and electrochemistry.Regardless of the ion radii,Li^(+)/Na^(+)/K^(+)can all go through the 2×2 channels of a-MnO_(2),generating large stress and causing channel merging or opening.However,smaller ions such as Li^(+)and Na^(+)cannot only transport along the[001]direction but also migrate along the<110>direction to the nanowire surface;for large ion such as K^(+),diffusion along the<110>direction is prohibited.The different ion transport behavior has grand consequences in the electrochemistry of metal oxygen batteries(MOBs).For Li-O_(2)battery,Li^(+)transports uniformly to the nanowire surface,forming a uniform layer of oxide;Na^(+)also transports to the nanowire surface but may be clogged locally due to its larger radius,therefore sporadic pearl-like oxides form on the nanowire surface;K^(+)cannot transport to the nanowire surface due to its large radius,instead,it breaks the nanowire locally,causing local deposition of potassium oxides.The study provides atomic scale understanding of the alkali metal ion transport mechanism which may be harnessed to improve the performance of MOBs.

Enhanced electrochemical performance of nanoscale single crystal NMC811 modification by coating LiNbO_(3)

Single crystallization is an important strategy to resolve intergranular cracks and unnecessary side reactions with electrolytes in layered transition metal oxide cathodes LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811).Due to the limitations of high-temperature sintering and multi-step calcination,single crystal NMC811 generally shows irregular particles with a size of 2-3μm.However,the prolonged Li-ion diffusion pathway and the stress generated by the uneven de-/intercalation sluggish Li-ion diffusion kinetics,what is more,cause structural damage such as intragranular cracks.A slow Li extraction rate or particle size reduction will ameliorate the structural damage and improve the cycling stability.As the most promising cathodes for next-generation power batteries,NMC811 required fast charge performance and cycle stability.Particle size reduction appears to be the displacement option.Nanonization is an effective strategy to mitigate intragranular cracks of single crystal NMC811.However,the serious aggregation and increased specific surface area become new challenges.In this article,we synthesized monodisperse nanoscale single crystal NMC811 by molten salt method and modified the surface by LiNbO3 coating.The electrochemical performance shows that nanoscale single crystal NMC811 has faster kinetic and higher capacity retention,so the strategy of combining nanonization and surface coating is an alternative way to prepare high specific capacity and cycle stable single crystal NMC811.