Operando Nanoindentation: A New Platform to Measure the Mechanical Properties of Electrodes during Electrochemical Reactions

Abstract

We present an experimental platform of operando nanoindentation that probes the dynamic mechanical behaviors of electrodes during real-time electrochemical reactions. The setup consists of a nanoindenter, an electrochemical station, and a custom fluid cell integrated into an inert environment. We evaluate the influence of the argon atmosphere, electrolyte solution, structural degradation and volumetric change of electrodes upon Li reactions, as well as the surface layer and substrate effects by control experiments. Results inform on the system limitations and capabilities, and provide guidelines on the best experimental practices. Furthermore, we present a thorough investigation of the elastic-viscoplastic properties of amorphous Si electrodes, during cell operation at different C-rates and at open circuit. Pure Li metal is characterized separately. We measure the continuous evolution of the elastic modulus, hardness, and creep stress exponent of lithiated Si and compare the results with prior reports. operando indentation will provide a reliable platform to understand the fundamental coupling between mechanics and electrochemistry in energy materials. photovoltaics, 7 and hydrogen storage. 8 The electrochemical reactions between the host material and guest species induce deformation, stress, fracture, and fatigue which cause ohmic and thermal resistance increase, and performance degradation. Likewise, mechanical stresses regulate mass transport, charge transfer, interfacial reactions, and consequently the potential and capacity of electrochemical systems. 9 In batteries, mechanical degradation compromises the performance of current technologies [10][11][12] and limits the implementation of high-capacity electrodes.13,14 Mechanics of both anode and cathode materials, such as diffusion-induced stresses, large deformation, plasticity, and fracture, have been extensively studied in recent years. [15][16][17][18][19][20] Nevertheless, the intimate coupling between mechanics and electrochemistry is far from complete understanding despite a considerable volume of existing studies. One major deficiency is the lack of reliable experimental tools to characterize the mechanical behaviors of electrodes under real electrochemical conditions. The operation of batteries is extremely sensitive to the work environment -a trace of oxygen and moisture can cause numerous side reactions. In contrast, most mechanical test equipment is open system with limited capability of environment control. As such, the mechanics and electrochemistry of batteries are often characterized separately. Recent studies propose that the mechanical response of materials at the chemical equilibrium states may differ from that under concurrent mechanical and chemical loads. 21,22 There is an urgent need for an experimental platform to probe the chemomechanical behaviors of electrodes in the course of electrochemical reactions. Current experimental tools have been able to provide valuable insight. Due to the generally small characteristic size and heterogen...

Mechanical breathing in organic electrochromics

“…Figure 2a shows the schematic of the methodology, where d film denotes the travel displacement of the tip when the contact between the tip and the film is detected, and d ITO represents the tip displacement down to the ITO substrate. To eliminate the effect of the liquid flow, all the electrodes are firmly attached to a homemade fluid cell 41 . The abrupt change in the contact stiffness when the tip approaches to the surface, Supplementary Fig.…”

Stress-Dependent Chemo-Mechanical Performance of Amorphous Si Anodes for Li-Ion Batteries upon Lithiation

“…We first study the mechanical deformation and failure of lithiated amorphous Si anodes a -Li x Si under different stress loading conditions and determine the critical ranges of external stresses in which a -Li x Si can deform without mechanical failure. As well understood in previous studies, lithiation results in the softening of Si anodes, owing to the formation of much weaker Li–Si bonds, , as well as the obvious brittle-to-ductile transformation in a -Li x Si systems. ,, We thus focus on the different phases of reference-state a -Li x Si in the Li concentration range of x = 0–3.6. It is indicated in Figure a1,a2 that a -Li x Si exhibits the unsymmetrical mechanical behavior under hydrostatic compression and tension.…”

A theory for coupled lithium insertion and viscoplastic flow in amorphous anode materials for Li-ion batteries

“…The stress-limiting role of plasticity has been recognised as a key element in preventing fracture of small-size electrodes (Zhao et al, 2011b). The composition dependence of the elastic modulus and hardness has been confirmed by nanoindentation studies (Hertzberg et al, 2011;Berla et al, 2015;Sitinamaluwa et al, 2017;de Vasconcelos et al, 2017), and further investigated using atomistic simulations (Shenoy et al, 2010;Zhao et al, 2011c;Cui et al, 2012). Recent molecular dynamics studies suggest that plastic deformation of a-LiSi involves local rearrangements of atoms in Shear Transformation Zones (STZs) involving mostly lithium atoms (Yan et al, 2017;Darbaniyan et al, 2020).…”

“…In the initial configuration, the concentration is C 0 , the disorder parameter is ξ 0 , and the sample is stress free. The elastic constants are set as E = 67 GPa and ν = 0.3, which are representative values for Li 2 Si (de Vasconcelos et al, 2017). We use b = 0.05 in the Drucker-Prager yield criterion (29), which is within the range of values reported by Zhao and Li (2009).…”