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.

Converting intercalation-type cathode in spent lithium-ion batteries into conversion-type cathode

The widespread applications of lithium-ion batteries(LIBs)generate tons of spent LIBs.Therefore,recycling LIBs is of paramount importance in protecting the environment and saving the resources.Current commercialized LIBs mostly adopt layered oxides such as LiCoO_(2)(LCO)or LiNi_(x)Co_(y)Mn_(1-x-y)O_(2)(NMC)as the cathode materials.Converting the intercalation-type spent oxides into conversion-type cathodes(such as metal fluorides(MFs))offers a valid recycling strategy and provides substantially improved energy densities for LIBs.Herein,two typical Co-based cathodes,LCO and LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NMC622),in spent LIBs were successfully converted to CoF_(2) and(Ni_(x)Co_(y)Mn_(z))F_(2) cathodes by a reduction and fluorination technique.The as converted CoF_(2) and(Ni_(x)Co_(y)Mn_(z))F_(2) delivered cell energy densities of 650 and 700 Wh/kg,respectively.Advanced atomic-level electron microscopy revealed that the used LCO and NMC622 were converted to highly phase pure Co metal and Ni_(0.6)Co_(0.2)Mn_(0.2) alloys in the used graphite-assisted reduction roasting,simultaneously producing the important product of Li_(2)CO_(3) using only environment friendly solvent.Our study provided a versatile strategy to convert the intercalation-type Co-based cathode in the spent LIBs into conversion-type MFs cathodes,which offers a new avenue to recycle the spent LIBs and substantially increase the energy densities of next generation LIBs.

锂沉积过程中固体电解质间相开裂与自愈合的原位观察

锂金属电池由于其超高的理论容量,被誉为是电池的"圣杯".然而,锂金属电池循环过程中树枝状或苔藓状锂的生长会使电池容量下降、电解液消耗、内部短路甚至起火爆炸.而直接追踪锂枝晶的生长仍然是一个巨大的挑战.本文报道了在CO_(2)气氛下利用环境电镜实时地观察了电化学诱导的锂沉积.研究发现单个锂沉积的形态强烈地受到固体电解质界面(SEI)开裂和自愈合的竞争过程的影响.当SEI膜的开裂速度超过自愈合时,锂晶须的定向生长占主导地位.相反地,当自愈大于裂纹时,圆形锂颗粒的各向同性生长将占主导地位.并且当SEI层是Li2O时,锂沉积的形貌只有球形,没有晶须的生成.因此,可以通过调节锂沉积速率和SEI成分来控制锂的形貌.本文还揭示了锂枝晶生长的一种新的"弱点"模式,这主要是由于在晶须截面上的Bardeen-Herring生长机制的作用.本研究对控制锂电池中锂枝晶的生长具有重要意义.