One known drawback of Ni-containing layered cathodes is their poor first cycle efficiency of 85%–90%, upon cycling in a practical potential window. The poor first cycle efficiency is likely a result of surface overlithiation due to significant lithium ion diffusion limitation at this bulk state of charge, but the overlithiation properties of Ni-containing cathodes are currently insufficiently understood. This work focuses on one Ni-containing cathode, LixNi0.6Mn0.2Co0.2O2, and performs detailed characterization of its intercalation properties both in the poor cycling efficiency region as well as in the overlithiation region, where the bulk lithium ion content rises above the value of 1. The results of the study first demonstrate that it is possible to recover the capacity this cathode “loses” in the first cycle by lowering the applied potential. Then, they establish the possibility to overlithiate LixNi0.6Mn0.2Co0.2O2 cathodes by as much as 300 mAhg−1 relative to the pristine electrode. Through complementary characterization using ex situ X-ray diffraction and X-ray absorption spectroscopy both the structural changes and the oxidation state variations in the material throughout the overlithiation process are elucidated. The generated knowledge can be used in developing more accurate physics-based models of industrially-relevant batteries.

The impact of liquid electrolyte soaking on the interfacial resistance between garnet structured Li7La3Zr2O12 (LLZO) solid electrolyte and metallic lithium has been studied. Lithium carbonate (Li2CO3) formed by inadvertent exposure of LLZO to ambient conditions, is generally known to increase interfacial impedance and decrease lithium wettability. Soaking LLZO powders and pellets in electrolyte containing lithium tetrafluoroborate (LiBF4) shows a significantly reduced interfacial resistance and improved contact between lithium and LLZO. Raman spectroscopy, Xray diffraction (XRD), and soft X-ray absorption spectroscopy (XAS) reveal how Li2CO3 is continuously removed with increasing soaking time. On-line mass spectrometry (OMS) and free energy calculations show how LiBF4 reacts with surface carbonate to form carbon dioxide (CO2). Using a very simple and scalable process that does not involve heat-treatment and expensive 2 coating techniques, we show that the Li-LLZO interfacial resistance can be reduced by an order of magnitude.

Changes in nickel oxidation state of chemically delithiated Li0.3Ni0.8Co0.15Al0.05O2 (NCA) in bulk and surface after 35 days @ 80 °C are strongly depending on the type of polymer and lithium salt in the catholyte matrix.

Lithium plating is one of the most critical aging mechanisms that is harmful to the performance and safety of batteries. During fast charging, metallic lithium may be deposited on the Li-ion negative electrode when the surface overpotential drops below 0 V vs Li/Li+ under these conditions. This plating subsequently increases the rate of capacity fade (cyclable Li loss) and in extreme cases can result in dendrite growth through the separator. Experiments have shown that thermal and mechanical constraints could have significant effects on the performance and safety of lithium-ion batteries, including lithium plating [1-2].In this work, two models are used to study the thermal and mechanical effects on lithium plating in a NCM811/graphite cell. One is a 1D modified DualFoil model that solves the electrochemical equations and takes into account the mechanical effects caused by lithium intercalation and external pressure. The other one is a 3D electro-chemo-thermo-mechanical coupled model that couples the 1D modified DualFoil model with a 3D thermomechanical finite element model [3-5]. Our 1D results show that a lower temperature and mechanical deformation can both accelerate the occurrence of lithium plating, and that mechanical deformation is as important as thermal evolution. The 3D model is capable of capturing the inhomogeneity of temperature and mechanical environment in a cell during operation. Our 3D simulation results show that because of the mechanical constraints from the housing materials, localized tensile stress will appear in certain parts of the jellyrolls, and lithium plating is more likely to occur in these parts. We demonstrate that it is necessary to consider mechanical deformation during cell design, and show that our models can provide guidance for battery reliability.[1] John Cannarella, Craig B. Arnold, Stress evolution and capacity fade in constrained lithium-ion pouch cells, J. Power Source 245, 745-751 (2014).[2] Mathias Petzl, Michael Kasper, Michael A. Danzer, Lithium plating in a commercial lithium-ion battery – A low-temperature aging study, J. Power Source 275, 799-807 (2015).[3] Jake Christensen, David Cook, Paul Albertus, An Efficient Parallelizable 3D Thermoelectrochemical Model of a Li-Ion Cell, J. Electrochem. Soc. 160 (11), A2258-A2267 (2013).[4] Xiaoxuan Zhang, Markus Klinsmann, Sergei Chumakov, and et al., A Modified Electrochemical Model to Account for Mechanical Effects Due to Lithium Intercalation and External Pressure, J. Electrochem. Soc. 168, 020533 (2021).[5] Xiaoxuan Zhang, Sergei Chumakov, Xiaobai Li, and et al., An Electro-chemo-thermo-mechanical Coupled Three-dimensional Computational Framework for Lithium-ion Batteries, J. Electrochem. Soc. 167, 160542 (2020).

In this work we investigate the transition metal dissolution of the layered cathode material LiCoO 2 upon repeated fast-charging of three smartphone batteries from different manufacturers, using synchrotron micro X-ray fluorescence (μ-XRF). Using this spatially resolved technique, dissolution of Co and subsequent, location dependent, deposition on the anode is observed. μ-XRF mapping of selected parts of the anode electrode sheets, such as electrode folds and edges of the jelly roll, reveal the difference in the way Co is deposited on specific regions of the anode electrode. While some folds show no depositions, edges of the anode show gradually accumulating Co depositions. Careful quantification of the dissolved Co reveals that capacity loss scales with the amount of deposited Co on the anode; i.e., total Co loss from within the cathode. Soft X-ray absorption spectroscopy of the Co depositions on the anode shows that Co is mainly deposited in a reduced 2+ state. While optimization of the fast-charging protocol mitigates Li plating on the anode, no significant difference in the amount of deposited Co can be observed between an optimized and non-optimized fast-charging algorithm.

Nickel-based cathode materials have become an exciting alternative to the widely used LixCoO2 (LCO) for consumer electronics. The main advantages of this type of cathode materials over the LCO electrodes are a higher practical capacity and excellent safety characteristics.[1] Additionally, the tendency to increase the nickel content of these electrodes proves to be cost effective due to their lower cobalt content.[2] One known drawback of nickel-containing layered cathodes is their poor first cycle efficiency of 87-88.6% when cycled in the standard potential window of 2.8 V to 4.4V, whereas LCO cathodes reach a first cycle efficiency of 98%.[3] In this study, we focus on the electrochemical properties of LixNi0.6Mn0.2Co0.2O2 (NMC622) cathode materials. We start by demonstrating that it is possible to recover the capacity “lost” by the NMC622 electrode in the first cycle by increasing the applied overpotential, as was previously shown for other nickel-based cathodes, including LiNiO2, LiNi1/3Mn1/3Co1/3O2, and LiNi0.8Co0.10Al0.05O2.[3-4] We then establish through electrochemical measurements that it is possible to overlithiate the NMC622 cathode material by as much as 300 mAh/g relative to the pristine electrode. Finally, we complement our electrochemical characterization with ex-situ X-ray diffraction as well as soft and hard X-ray absorption spectroscopy experiments, to elucidate how the structure of the material and the oxidation states of the transition metals (nickel, cobalt, manganese) change throughout the overlithiation process. [1] Andre, D. et al. Future generations of cathode materials: An automotive industry perspective. J. Mater. Chem. A 3, 6709–6732 (2015). [2] Xu, J., Lin, F., Doeff, M. M. & Tong, W. A review of Ni-based layered oxides for rechargeable Li-ion batteries. J. Mater. Chem. A 5, 874–901 (2017). [3] Kang, S. H., Yoon, W. S., Nam, K. W., Yang, X. Q. & Abraham, D. P. Investigating the first-cycle irreversibility of lithium metal oxide cathodes for Li batteries. J. Mater. Sci. 43, 4701–4706 (2008). [4] Dahn, J. R., von Sacken, U. & Michal, C. A. Structure and electrochemistry of Li1+/-xNiOz and a new Li2Ni02 phase with the Ni (OH) 2 structure. Solid State Ionics 44, 87–97 (1990).

Ni-rich cathodes, such as nickel cobalt aluminum oxides (NCAs, LixNi0.80+0.15ε Co0.15(1−ε)Al0.05O2, 0 ≤ ε ≤ 1), are a class of cathode materials for lithium-ion batteries (LIBs), which are among the leading candidates for battery electric vehicle (BEV) applications. In this study we focus on an important, fundamental electrochemical property, the open-circuit potential function (OCP, U vs x), and investigate its relationship with the Ni stoichiometry. First, we demonstrate that published differential capacity curves (dQ/dU vs U) for Ni-rich NCA materials can be derived as a stoichiometric linear combination of differential capacities of the two end members, LixNi0.8Co0.15Al0.05O2 and LixNi0.95Al0.05O2. Subsequently, the OCP curves are obtained by taking the inverse of the integrated dQ/dU vs U curves, which match literature OCP curves. Then, we apply the same method to determine the composition of an unknown cathode extracted from a commercially available LIB. Lastly, we show that the identified relationship also holds true for the LixNi0.60+0.20ε Co0.20(1−ε)Mn0.20O2 family by demonstrating that the OCP curve of LixNi0.70Co0.10Mn0.20O2 can be predicted from a fractional combination of LixNi0.60Co0.20Mn0.20O2 and LixNi0.80Mn0.20O2. We anticipate that this methodology can be adapted to predict OCP curves for additional cathode families and used to validate the chemical composition of newly synthesized materials.

No abstract