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Register a new userIn-operando quantitation of Li concentration for commercial Li-ion rechargeable battery using high-energy X-ray Compton scattering
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Compton scattering is one of the promising probe to quantitate of the Li under in-operando condition, since high-energy X-rays which have high penetration power into the materials are used as incident beam and Compton scattered energy spectrum have specific line-shape by the elements. We develop in-operando quantitation method of Li composition in the electrodes by using line-shape (Sparameter) analysis of Compton scattered energy spectrum. In this study, we apply S-parameter analysis to commercial coin cell Li-ion rechargeable battery and obtain the variation of S-parameters during charge/discharge cycle at positive and negative electrodes. By using calibration curves for Li composition in the electrodes, we determine the change of Li composition of positive and negative electrodes through S-parameters, simultaneously.
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Controlling nanostructure from molecular, crystal lattice to the electrode level remains as arts in practice, where nucleation and growth of the crystals still require more fundamental understanding and precise control to shape the microstructure of metal deposits and their properties. This is vital to achieve dendrite-free Li metal anodes with high electrochemical reversibility for practical high-energy rechargeable Li batteries. Here, cryogenic-transmission electron microscopy was used to capture the dynamic growth and atomic structure of Li metal deposits at the early nucleation stage, in which a phase transition from amorphous, disordered states to a crystalline, ordered one was revealed as a function of current density and deposition time. The real-time atomic interaction over wide spatial and temporal scales was depicted by the reactive-molecular dynamics simulations. The results show that the condensation accompanied with the amorphous-to-crystalline phase transition requires sufficient exergy, mobility and time to carry out, contrary to what the classical nucleation theory predicts. These variabilities give rise to different kinetic pathways and temporal evolutions, resulting in various degrees of order and disorder nanostructure in nano-sized domains that dominate in the morphological evolution and reversibility of Li metal electrode. Compared to crystalline Li, amorphous/glassy Li outperforms in cycle life in high-energy rechargeable batteries and is the desired structure to achieve high kinetic stability for long cycle life.
We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution x-ray Compton scattering. Application of our method to spinel LixMn2O4, a lithium ion battery cathode material, is discussed. The orbital involved in the lithium insertion and extraction process is shown to mainly be the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of a lithium ion battery.
Non-destructive determination of lithium distribution in a working battery is key for addressing both efficiency and safety issues. Although various techniques have been developed to map the lithium distribution in electrodes, these methods are mostly applicable to test cells. Here we propose the use of high-energy x-ray Compton scattering spectroscopy to measure the local lithium concentration in closed electrochemical cells. A combination of experimental measurements and parallel first-principles computations is used to show that the shape parameter S of the Compton profile is linearly proportional to lithium concentration and thus provides a viable descriptor for this important quantity. The merits and applicability of our method are demonstrated with illustrative examples of LixMn2O4 cathodes and a working commercial lithium coin battery CR2032.
The reversible heat in lithium-ion batteries (LIBs) due to entropy change is fundamentally important for understanding the chemical reactions in LIBs and developing proper thermal management strategies. However, the direct measurements of reversible heat are challenging due to the limited temperature resolution of applied thermometry. In this work, by developing an ultra-sensitive thermometry with a differential AC bridge using two thermistors, the noise-equivalent temperature resolution we achieve (10 uK) is several orders of magnitude higher than previous thermometry applied on LIBs. We directly observe reversible heat absorption of a LIR2032 coin cell during charging with negligible irreversible heat generation and a linear relation between heat generations and discharging currents. The cell entropy changes determined from the reversible heat agree excellently with those measured from temperature dependent open circuit voltage. Moreover, it is found that the large reversible entropy change can cancel out the irreversible entropy generation at a charging rate as large as C/3.7 and produce a zero-heat-dissipation LIB during charging. Our work significantly contributes to fundamental understanding of the entropy changes and heat generations of the chemical reactions in LIBs, and reveals that reversible heat absorption can be an effective way to cool LIBs during charging.
Compton scattering imaging using high-energy synchrotron x-rays allows the visualization of the spatio-temporal lithiation state in lithium-ion batteries probed in-operando. Here, we apply this imaging technique to the commercial 18650-type cylindrical lithium-ion battery. Our analysis of the lineshapes of the Compton scattering spectra taken from different electrode layers reveals the emergence of inhomogeneous lithiation patterns during the charge-discharge cycles. Moreover, these patterns exhibit oscillations in time where the dominant period corresponds to the time scale of the charging curve.
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