Advanced analytical electron microscopy for lithium-ion batteries

Abstract

Lithium-ion batteries are a leading candidate for electric vehicle and smart grid applications. However, further optimizations of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during battery operation. With the capability of resolving the structure and chemistry at an atomic resolution, advanced analytical transmission electron microscopy (AEM) is an ideal technique for this task. The present review paper focuses on recent contributions of this important technique to the fundamental understanding of the electrochemical processes of battery materials. A detailed review of both static (ex situ) and real-time (in situ) studies will be given, and issues that still need to be addressed will be discussed. NPG Asia Materials (2015) 7, e193; doi:10.1038/am.2015.50; published online 26 June 2015 INTRODUCTIONTo implement the commercialization of lithium-ion batteries in electric vehicles and smart grid systems, further improvements are required, especially with respect to the energy/power density, coulombic efficiency and cycle life. These parameters primarily depend on the diffusion of lithium-metal ions, electron transport, structure and chemical dynamics of the electrode/electrolyte materials, among others. During electrochemical cycling, significant changes in the material structure and elemental distributions occur, including ion relocation, lattice expansion/contraction, phase transition and structure/surface reconstruction. These changes could substantially influence ion and electron transport and affect the performance of the entire battery system. Understanding the structure-property relationships for each component and their synergistic behaviors during electrochemical processes is, therefore, essential for the design of new battery materials and the optimization of existing systems.Although many analysis techniques (for example, X-ray diffraction, X-ray absorption spectroscopy, neutron diffraction, nuclear magnetic resonance and so on) have been employed for such studies, most of them can acquire only spatially averaged information. Nevertheless, the structural and chemical evolution of battery materials upon electrochemical cycling can often be linked to specific nanofeatures, such as defects, interfaces and surfaces. As a result, techniques based on analytical transmission electron microscopy (AEM) are ideal tools to study these issues. The capability of AEM to precisely probe the structural/chemical evolutions at an ultrahigh spatial resolution frequently provides insight that cannot be obtained directly using macroscopic characterization methods.

Novel Solid Electrolytes for Li-Ion Batteries: A Perspective from Electron Microscopy Studies

“…These electron microscopy studies suggest that a reaction layer may frequently form between the solid electrolyte and cathode due to inter-diffusion. Unlike the solid electrolyte interface (SEI) in conventional LIBs, reaction layers at solid electrolyte/ electrode interfaces are usually detrimental rather than beneficial, as they typically impede the ionic transport (Qian et al, 2015).…”

Review—Promises and Challenges of In Situ Transmission Electron Microscopy Electrochemical Techniques in the Studies of Lithium Ion Batteries

“…[17][18][19][20] Achievements in the area of in situ microscopy in the past five years have brought material characterization techniques to the point where these questions may be studied. 21 Over 100 papers relating to the application of in situ TEM electrochemistry in LIB z E-mail: zhxie@cwnu.edu.cn; jzhang@gamry.com each year have been published according to an analysis by Web of Science.…”

“…14 Recently, in situ electrochemical transmission electron microscopy (TEM) techniques have been invented as a powerful tool to unveil the dynamic (real-time) electrochemical reaction processes and degradation mechanisms of electrode materials at atomic and nanoscale under typical operating conditions. [17][18][19][20] Achievements in the area of in situ microscopy in the past five years have brought material characterization techniques to the point where these questions may be studied. 21 Over 100 papers relating to the application of in situ TEM electrochemistry in LIB z E-mail: zhxie@cwnu.edu.cn; jzhang@gamry.com each year have been published according to an analysis by Web of Science.…”

Microstructure dynamics of rechargeable battery materials studied by advanced transmission electron microscopy

“…Moreover, a noticeable reduction in the Li signal has been observed in the EELS spectrum of the surface area (versus that of the bulk), a finding consistent with the observation that significant TM atoms occupy Li sites on the cycled surface. 17,18 A detailed explanation of the electronic origin in the migration of TM ions and surface reconstruction can be found in the 'TM cation migration and TM-O coordination' section.…”