In Situ TEM Experiments of Electrochemical Lithiation and Delithiation of Individual Nanostructures

Abstract

Understanding the microscopic mechanisms of electrochemical reaction and material degradation is crucial for the rational design of high-performance lithium ion batteries (LIBs). A novel nanobattery assembly and testing platform inside a transmission electron microscope (TEM) has been designed, which allows a direct study of the structural evolution of individual nanowire or nanoparticle electrodes with near-atomic resolution in real time. In this review, recent progresses in the study of several important anode materials are summarized. The consistency between in situ and ex situ results is shown, thereby validating the new in situ testing paradigm. Comparisons between a variety of nanostructures lead to the conclusion that electrochemical reaction and mechanical degradation are material specifi c, size dependent, and geometrically and compositionally sensitive. For example, a highly anisotropic lithiation in Si is observed, in contrast to the nearly isotropic response in Ge. The Ge nanowires can develop a spongy network, a unique mechanism for mitigating the large volume changes during cycling. The Si nanoparticles show a critical size of ∼ 150 nm below which fracture is averted during lithiation, and above which surface cracking, rather than central cracking, is observed. In carbonaceous nanomaterials, the lithiated multi-walled carbon nanotubes (MWCNTs) are drastically embrittled, while few-layer graphene nanoribbons remain mechanically robust after lithiation. This distinct contrast manifests a strong 'geometrical embrittlement' effect as compared to a relatively weak 'chemical embrittlement' effect. In oxide nanowires, discrete cracks in ZnO nanowires are generated near the lithiation reaction front, leading to leapfrog cracking, while a mobile dislocation cloud at the reaction front is observed in SnO 2 nanowires. This contrast is corroborated by ab initio calculations that indicate a strong chemical embrittlement of ZnO, but not of SnO 2 , after a small amount of lithium insertion. In metallic nanowires such as Al, delithiation causes pulverization, and the product nanoparticles are held in place by the surface Li-Al-O glass tube, suggesting possible strategies for improving electrode cyclability by coatings. In addition, a new in situ chemical lithiation method is introduced for fast screening of battery materials by conventional TEM. Evidently, in situ nanobattery experiments inside TEM are a powerful approach for advancing the fundamental understanding of electrochemical reactions and materials degradation and therefore pave the way toward rational design of high-performance LIBs.

Three-dimensional-networked NiCo2S4 nanosheet array/carbon cloth anodes for high-performance lithium-ion batteries

“…Because the NiCo 2 S 4 nanosheets have a thickness of 10 nm, it is challenging to visualize the lithium migration process by in situ TEM. [32][33][34] However, as shown by the selected area electron diffraction patterns (inserts in Figures 3b and d), the conversion of the NiCo 2 S 4 nanosheet from its original crystalline phase to an amorphous phase after 20 min can be considered indirect evidence of the lithiation process. Moreover, the detectable expansion of the NiCo 2 S 4 nanosheet itself indicates that lithiation occurred.…”

“…2,3 In this work, we carried 3D-networked NiCo 2 S 4 NSAs as anodes in LIBs R Zou et al out in situ TEM experiments to investigate mechanical strain in NiCo 2 S 4 nanosheets during their reaction with Li ions using a dual-probe biasing TEM holder (Nanofactory Instrument). 31,32 The configuration for in situ TEM measurements is shown schematically in Figure 3a. NiCo 2 S 4 nanosheets were decorated on the Cu wire probe, and a small piece of Li/Li 2 O was attached to the tip of the opposite W wire probe.…”

Chemomechanical modeling of lithiation-induced failure in high-volume-change electrode materials for lithium ion batteries

“…In contrast to the anisotropic swelling and surface fracture of cSi, lithiation of c-Ge, despite its similar crystalline structures to c-Si and large volume expansion (~250%), 7,87 proceeds isotropically, and the electrode remains tough without any sign of crack nucleation even for micron-sized c-GeNPs. 7,88 It has been shown that a-Si exhibits the similar tough behavior with a critical size on the order of microns, which may similarly stem from the isotropic swelling of a-Si.…”

In situ methods for Li-ion battery research: A review of recent developments

“…It therefore seems apparent that the method will continue to develop in the near future, also in terms of generating results that relate more to the world of real-life batteries. However, even in this stage a good consistency exists between the experimental data obtained by in situ TEM and other ex situ studies on bulk-type batteries [41].…”

“…However, many authors recognize the difference in configuration as well as testing methods, between the investigated nano-batteries and bulk-size batteries that are used in practice [41,42,44]. For instance, due to the required nano-sized configuration of the batteries, the contacts are very small and often non-optimized, inducing significant overpotentials during battery operation, which might influence their characteristics.…”