将硅纳米颗粒限域在多壳层空心球:一种提升循环稳定性的有效策略

单质硅是一种有潜力的高容量锂离子电池负极材料.然而,受限于充放电过程中巨大的体积膨胀,其循环性能并不理想.在这个工作中,我们设计了一种独特的三组分复合负极材料(Si/Cr_(2)O_(3)/C),其中Si纳米颗粒被限域在碳包覆的氧化铬多层空心球(MSHSs)中.得益于Cr_(2)O_(3)/C基体的体积变化缓冲能力与优异的结构稳定性,将Si纳米颗粒封装在MSHSs中可以有效地提高其电化学性能.合理的结构设计赋予了Si/Cr_(2)O_(3)/C三组分复合材料高的可逆容量(在100 mA g^(-1)的电流密度下,比容量为1351 mA h g^(-1))和稳定的循环性能(在500 mA g^(-1)的电流密度下,循环300次后比容量保持在716 mA h g^(-1)).这一工作提出了一种多壳层空心结构设计的新思路,以解决硅基负极材料循环性差的瓶颈.

Revealing structural degradation in layered structure oxides cathode of lithium ion batteries via in-situ transmission electron microscopy

Transition metal oxides with layered structure have been widely used as cathode materials for lithium-ion batteries(LIBs)which have relatively high energy density,large capacity and long life.However,in the long-term electrochemical cycle,the inevitable degradation of performance of LIBs due to structural degradation in cathodes severely restricts their large-scale practical applications.Understanding the underlying mechanism of structural degradation is the most critical scientific problem.Recently,in situ transmission electron microscopy(TEM)has become a useful tool to study the structural and compositional evolutions at atomic scale in electrochemical reactions,which provided a unique and in-depth understanding of the structural degradation.In this review,we discuss the recent advances in the in situ TEM,focusing on its role in revealing the structural degradation mechanisms in the four key places:(1)the interface between the cathodes and electrolyte;(2)the cathode surface;(3)the particle interior and(4)those induced by thermal effect.The insight gained by the in-situ TEM which is still developing at its fast pace is unique and expected to provide guidance for designing better layered cathode materials.

Embedding tin disulfide nanoparticles in twodimensional porous carbon nanosheet interlayers for fast-charging lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries have attracted significant attention for their high specific capacity,non-toxic and harmless advantages.However,the shuttle effect limits their development.In this work,small-sized tin disulfide(SnS_(2))nanoparticles are embedded between interlayers of twodimensional porous carbon nanosheets(PCNs),forming a multi-functional nanocomposite(PCN-SnS_(2))as a cathode carrier for Li-S batteries.The graphitized carbon nanosheets improve the overall conductivity of the electrode,and the abundant pores not only facilitate ion transfer and electrolyte permeation,but also buffer the volume change during the charge and discharge process to ensure the integrity of the electrode material.More importantly,the physical confinement of PCN,as well as the strong chemical adsorption and catalytic reaction of small SnS_(2)nanoparticles,synergistically reduce the shuttle effect of polysulfides.The interaction between a porous layered structure and physical-chemical confinement gives the PCN-SnS_(2)-S electrode high electrochemical performance.Even at a high rate of 2 C,a discharge capacity of 650 mA h g^(-1)is maintained after 150 cycles,underscoring the positive results of SnS_(2)-based materials for Li-S batteries.The galvanostatic intermittent titration technique results further confirm that the PCN-SnS_(2)-S electrode has a high Li+transmission rate,which reduces the activation barrier and improves the electrochemical reaction kinetics.This work provides strong evidence that reducing the size of SnS_(2)nanostructures is beneficial for capturing and reacting with polysulfides to alleviate their shuttle effect in Li-S batteries.

Unraveling the reaction mechanisms of electrode materials for sodiumion and potassium‐ion batteries by in situ transmission electron microscopy

Sodium ion batteries(SIBs)and potassium ion batteries(PIBs)have caught numerous attention due to the low cost and abundant availability of sodium and potassium.However,their power density,cycling stability and safety need further improvement for practical applications.Investigations on the reaction mechanisms and structural degradation when cycling are of great importance.In situ transmission electron microscopy(TEM)is one of the most significant techniques to understand and monitor electrochemical processes at an atomic scale with real-time imaging.In this review,the current progress in unraveling reaction mechanisms of electrode materials for SIBs and PIBs via in situ TEM is summarized.First,the importance of in situ TEM is highlighted.Then,based on the three types of electrochemical reaction,i.e.,intercalation reac-tion,conversion reaction and alloying reaction,the structural evolution and reaction kinetics at atomic resolution,and their relation to the electrochemical performance of electrode materials are reviewed and described in detail.Fi-nally,future directions of in situ TEM for SIBs and PIBs are proposed.Therefore,the in‐depth understanding revealed by in situ TEM will give an instructive guide in rational design of electrode materials for high performance electrode materials of SIBs and PIBs.