Quantitative Operando ⁷Li NMR Investigations of Silicon Anode Evolution during Fast Charging and Extended Cycling

Abstract

The development and optimization of fast battery charging protocols require detailed information regarding lithium speciation inside a battery. Nuclear magnetic resonance (NMR) spectroscopy has the unique capability of identifying the Li phases formed in an anode during Li-ion cell operation and quantifying their relative amounts. In addition, both Li metal films and dendrites are readily detected and quantified. Here, our recently reported parallel-plate resonator radio frequency (RF) probe and the cartridge-type single-layer full cell were used to track the behavior of Si electrodes during cycling and during fast charging. The Li x Si compounds formed during electrochemical cycling exhibit an unexpected intrinsic nonequilibrium behavior at both slow and fast rates, evolving toward increasingly disordered local environments. The evolution with time of lithiated phases is nonlinear during both charging and discharging at constant current, unlike the case for pure graphite, and asymmetric between charge and discharge. During charging at rates of 1C, 2C, and 3C, metallic Li in both films and (to a lesser extent) dendritic forms are deposited on the Si anode. Part of the Li metal film formation is reversible, but a fraction remains on the electrode surface as dead Li, while all of the dendritic Li, even though formed in a considerably smaller amount, is entirely irreversible. Such performance-governing properties are critical to the development of fastcharging protocols for lithium-ion batteries (LIBs) and are exceptionally well evaluated and quantified by 7 Li magnetic resonance strategies such as those presented here.

Elucidations of Structure and Molecular Dynamics of Complex Polymers by State-of-the-Art Solid-State NMR Spectroscopy

“…All those challenges are closely related to the molecular details of polymer structures and dynamics, and ssNMR is expected to continue playing a key role in establishing their relationship with macroscopic properties and performance and thus for better design of high-performance materials as well as development of polymer theories. Besides, operando ssNMR techniques are very valued for revealing the transient structure or dynamic states at the molecular level during the stretching, shearing, and even battery charging process . Specifically, for polymer processing, it is desirable to develop new operando ssNMR techniques to capture the transient structure and dynamics information, which is crucial for optimizing processing parameters and eventually increasing final polymer products’ performance.…”

Novel Binder with Cross-Linking Reconfiguration Functionality for Silicon Anodes of Lithium-Ion Batteries

“…The development of electric vehicles limited by the capacity of graphite anode (372 mAh g –1 , LiC 6 ) has led to the emergence of range anxiety, necessitating the exploration of high-energy negative electrode materials . Silicon is recognized as a conceivable anode material for high-energy-density lithium-ion batteries owing to its high theoretical capacity (4200 mAh g –1 , Li 4.4 Si), low working potential, and abundant reserves. , Nevertheless, unlike the insertion/extraction mechanism of lithium-ion storage in graphite, silicon anodes undergo alloying/dealloying transformations during electrochemical reactions, leading to significantly higher volume expansion and shrinkage (>300%) upon cycling than the insertion/extraction process. This causes fragmentation of silicon electrodes, instability of the solid electrolyte interface (SEI), loss of electrical contact within the electrode film, and ultimately, a rapid deterioration of capacity, hindering the large-scale applicability of silicon anodes. , …”

Magnetic Force Dilatometry for Operando Coin Cell Electrochemical Dilation Measurements

“…6,7 In particular, operando and in situ characterization techniques have enabled researchers to probe these dynamic processes in real time, while simultaneously avoiding possible sample destruction or contamination issues associated with postmortem observations. A wide variety of techniques such as nuclear magnetic nuclear magnetic resonance (NMR), 8,9 X-ray photoemission spectroscopy (XPS), 10,11 Raman spectroscopy, 12,13 and electron microscopy, 14,15 among others, [16][17][18] have allowed for observing local chemical and structural changes at the electrode and interface levels. However, it is also critical to understand the dimensional changes (e.g., volume expansion) within the cell during cycling, which can be measured using techniques such as operando electrochemical dilatometry.…”