Effects of Atmospheric Gases on Li Metal Cyclability and Solid-Electrolyte Interphase Formation.

For Li-air batteries, dissolved gas can cross over from the air electrode to the Li metal anode and affect the solid-electrolyte interphase (SEI) formation, a phenomenon that has not been fully characterized. In this work, the impact of atmospheric gases on the SEI properties is studied using electrochemical methods and ex situ characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The presence of O2 significantly improved the lithium cyclability; less lithium is consumed to form the SEI or is lost because of electrical disconnects. However, the SEI resistivity and plating overpotentials increased. Lithium cycled in an "air-like" mixed O2/N2 environment also demonstrated improved cycling efficiency, suggesting that dissolved O2 participates in electrolyte reduction, forming a homogeneous SEI, even at low concentrations. The impact of gas environments on Li metal plating and SEI formation represents an additional parameter in designing future Li-metal batteries

Noninvasive In Situ NMR Study of "Dead Lithium" Formation and Lithium Corrosion in Full-Cell Lithium Metal Batteries.

Capacity retention in lithium metal batteries needs to be improved if they are to be commercially viable, the low cycling stability and Li corrosion during storage of lithium metal batteries being even more problematic when there is no excess lithium in the cell. Herein, we develop in situ NMR metrology to study "anode-free" lithium metal batteries where lithium is plated directly onto a bare copper current collector from a LiFePO4 cathode. The methodology allows inactive or "dead lithium" formation during plating and stripping of lithium in a full-cell lithium metal battery to be tracked: dead lithium and SEI formation can be quantified by NMR and their relative rates of formation are here compared in carbonate and ether-electrolytes. Little-to-no dead Li was observed when FEC is used as an additive. The bulk magnetic susceptibility effects arising from the paramagnetic lithium metal were used to distinguish between different surface coverages of lithium deposits. The amount of lithium metal was monitored during rest periods, and lithium metal dissolution (corrosion) was observed in all electrolytes, even during the periods when the battery is not in use, i.e., when no current is flowing, demonstrating that dissolution of lithium remains a critical issue for lithium metal batteries. The high rate of corrosion is attributed to SEI formation on both lithium metal and copper (and Cu+, Cu2+ reduction). Strategies to mitigate the corrosion are explored, the work demonstrating that both polymer coatings and the modification of the copper surface chemistry help to stabilize the lithium metal surface.A.B.G acknowledges the support from the Royal Society (RP/R1/180147) and EPSRC-EP/M009521/1. C.V.A acknowledges financial support from the TomKat Center Postdoctoral Fellowship in Sustainable Energy at Stanford, and a Visiting Fellowship from Corpus Christi College at the University of Cambridge. S.M thanks the Blavatnik Cambridge Fellowships. C.P.G thanks the EU/ERC for an Advanced Fellowship. A.B.G thanks the NanoDTC Cambridge for travel funding

3D nano-rheology microscopy : Operando nanomapping of 3D mechanical nanostructure of SEI in Na-ion batteries

The Solid Electrolyte Interphase (SEI) is a nanoscale thickness passivation layer that is formed as the product of electrolyte decomposition through a combination of chemical and electrochemical reactions in the cell and defines the fundamental battery properties - its capacity, cycle stability and safety. While local mechanical properties of SEI hold a clue to its performance, their operando characterisation is difficult as one has to probe nanoscale surface features in electrochemical environment that are also dynamically changing. Here, we report novel 3D nano-rheology microscopy (3D-NRM) that uses a tiny (sub-nm to few nm) lateral dithering of the sharp SPM tip at kHz frequencies to probe the minute sample reaction forces. By mapping the increments of the real and imaginary components of these forces, while the tip penetrates the soft interfacial layers, we obtain the true 3D nanoscale structure of sub–m thick layers [1]. 3D-NRM allows to elucidate the key role of solvents in SEI formation and predict the conditions for building SEI for robust, safe and efficient Li-ion and Na-ion batteries. Here, we discuss the extension of these studies on smooth HOPG and inhomogeneous and rough copper anodes as sodium ion battery electrodes. Essentially, the new approach allows nanoscale characterisation of SEI with a few nm precision on the electrodes with 1000 nm roughness, and quantitatively evaluate the real and imaginary parts of the elastic moduli over the whole thickness of SEI layer. The observation of the change in moduli and the tip-surface distance helps to evaluate the growth of SEI as a function of the electrolyte, additives, electrode material and charge-discharge rate. We believe that such evaluation of key interfacial nanomechanical properties of SEI will allow us to develop the electrochemically and mechanically robust SEI surface passivation layer and the development of efficient and safe rechargeable batteries

Toward an Understanding of SEI Formation and Lithium Plating on Copper in Anode-Free Batteries.

Funder: Blavatnik Family Foundation"Anode-free" batteries present a significant advantage due to their substantially higher energy density and ease of assembly in a dry air atmosphere. However, issues involving lithium dendrite growth and low cycling Coulombic efficiencies during operation remain to be solved. Solid electrolyte interphase (SEI) formation on Cu and its effect on Li plating are studied here to understand the interplay between the Cu current collector surface chemistry and plated Li morphology. A native interphase layer (N-SEI) on the Cu current collector was observed with solid-state nuclear magnetic resonance spectroscopy (ssNMR) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies showed that the nature of the N-SEI is affected by the copper interface composition. An X-ray photoelectron spectroscopy (XPS) study identified a relationship between the applied voltage and SEI composition. In addition to the typical SEI components, the SEI contains copper oxides (Cu x O) and their reduction reaction products. Parasitic electrochemical reactions were observed via in situ NMR measurements of Li plating efficiency. Scanning electron microscopy (SEM) studies revealed a correlation between the morphology of the plated Li and the SEI homogeneity, current density, and rest time in the electrolyte before plating. Via ToF-SIMS, we found that the preferential plating of Li on Cu is governed by the distribution of ionically conducting rather than electronic conducting compounds. The results together suggest strategies for mitigating dendrite formation by current collector pretreatment and controlled SEI formation during the first battery charge

Selective NMR observation of the SEI–metal interface by dynamic nuclear polarisation from lithium metal

Funder: Oppenheimer Foundation, Cambridge. Blavatnik Cambridge Fellowships.Abstract: While lithium metal represents the ultimate high-energy-density battery anode material, its use is limited by dendrite formation and associated safety risks, motivating studies of the solid–electrolyte interphase layer that forms on the lithium, which is key in controlling lithium metal deposition. Dynamic nuclear polarisation enhanced NMR can provide important structural information; however, typical exogenous dynamic nuclear polarisation experiments, in which organic radicals are added to the sample, require cryogenic sample cooling and are not selective for the interface between the metal and the solid–electrolyte interphase. Here we instead exploit the conduction electrons of lithium metal to achieve an order of magnitude hyperpolarisation at room temperature. We enhance the 7Li, 1H and 19F NMR spectra of solid–electrolyte interphase species selectively, revealing their chemical nature and spatial distribution. These experiments pave the way for more ambitious room temperature in situ dynamic nuclear polarisation studies of batteries and the selective enhancement of metal–solid interfaces in a wider range of systems

Effects of Atmospheric Gases on Li Metal Cyclability and Solid-Electrolyte Interphase Formation.

For Li-air batteries, dissolved gas can cross over from the air electrode to the Li metal anode and affect the solid-electrolyte interphase (SEI) formation, a phenomenon that has not been fully characterized. In this work, the impact of atmospheric gases on the SEI properties is studied using electrochemical methods and ex situ characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The presence of O2 significantly improved the lithium cyclability; less lithium is consumed to form the SEI or is lost because of electrical disconnects. However, the SEI resistivity and plating overpotentials increased. Lithium cycled in an "air-like" mixed O2/N2 environment also demonstrated improved cycling efficiency, suggesting that dissolved O2 participates in electrolyte reduction, forming a homogeneous SEI, even at low concentrations. The impact of gas environments on Li metal plating and SEI formation represents an additional parameter in designing future Li-metal batteries

Research data for "Investigating the effect of a fluoroethylene carbonate additive on lithium deposition and the solid electrolyte interphase in lithium metal batteries using in situ NMR spectroscopy"

This dataset contains the raw data files required to run the mathematical model of isotope exchange and raw data files for EIS spectra simulation along with corresponding MATLAB codes for both. See the README files within the dataset for more information

Lithium Air Batteries – Tracking Function and Failure

The lithium-air battery (LAB) is arguably the battery with the highest energy density, but also a battery with significant challenges to be overcome before it can be used commercially in practical devices. Here, we discuss experimental approaches developed by some of the authors to understand the function and failure of lithium-oxygen batteries. For example, experiments in which nuclear magnetic resonance (NMR) spectroscopy was used to quantify dissolved oxygen concentrations and diffusivity are described. 17O MAS NMR spectra of electrodes extracted from batteries at different states of charge (SOC) allowed the electrolyte decomposition products at each stage to be determined. For instance, the formation of Li2CO3 and LiOH in a DME solvent and their subsequent removal on charging was followed. Redox mediators have been used to chemically reduce oxygen or to chemically oxidise Li2O2 in order to prevent electrode clogging by insulating compounds, which leads to lower capacities and rapid degradation; the studies of these mediators representing an area where NMR and electron paramagnetic resonance (EPR) studies could play a role in unravelling reaction mechanisms. Finally, recently developed coupled in-situ NMR and electrochemical impedance spectroscopy (EIS) are used to characterise the charge transport mechanism in lithium symmetric cells and to distinguish between electronic and ionic transport, demonstrating the formation of transient (soft) shorts in lithium-oxygen common electrolytes. More stable solid electrolyte interphases are formed under oxygen atmosphere, which help stabilises the lithium anode on cycling.JE and CPG acknowledge support from a Royal Society Research Professorship for CPG (grant no. RP\R1\180147). JE and CPG also acknowledge support from an ERC Advanced Investigator Grant for CPG (grant no. EC H2020 ERC 835073). GH acknowledges support from a Faraday Institution grant (grant no. FIRG060). JBF gratefully acknowledge funding by the Faraday Institute through the LiSTAR (FIRG014, FIRG058). SM gratefully acknowledge funding by the Faraday Institute through the NEXGENNa (FIRG018)

Spiers Memorial Lecture: Lithium air batteries - tracking function and failure.

Acknowledgements: JE and CPG acknowledge support from a Royal Society Research Professorship for CPG (grant no. RP\R1\180147). JE and CPG also acknowledge support from an ERC Advanced Investigator Grant for CPG (grant no. EC H2020 ERC 835073). GH acknowledges support from a Faraday Institution grant (grant no. FIRG060). JBF gratefully acknowledges funding by the Faraday Institute through LiSTAR (FIRG014, FIRG058). SM gratefully acknowledges funding by the Faraday Institute through NEXGENNa (FIRG018). LB acknowledges support from the EPSRC through the NanoDTC (grant no. EP/S022953/1).The lithium-air battery (LAB) is arguably the battery with the highest energy density, but also a battery with significant challenges to be overcome before it can be used commercially in practical devices. Here, we discuss experimental approaches developed by some of the authors to understand the function and failure of lithium-oxygen batteries. For example, experiments in which nuclear magnetic resonance (NMR) spectroscopy was used to quantify dissolved oxygen concentrations and diffusivity are described. 17O magic angle spinning (MAS) NMR spectra of electrodes extracted from batteries at different states of charge (SOC) allowed the electrolyte decomposition products at each stage to be determined. For instance, the formation of Li2CO3 and LiOH in a dimethoxyethane (DME) solvent and their subsequent removal on charging was followed. Redox mediators have been used to chemically reduce oxygen or to chemically oxidise Li2O2 in order to prevent electrode clogging by insulating compounds, which leads to lower capacities and rapid degradation; the studies of these mediators represent an area where NMR and electron paramagnetic resonance (EPR) studies could play a role in unravelling reaction mechanisms. Finally, recently developed coupled in situ NMR and electrochemical impedance spectroscopy (EIS) are used to characterise the charge transport mechanism in lithium symmetric cells and to distinguish between electronic and ionic transport, demonstrating the formation of transient (soft) shorts in common lithium-oxygen electrolytes. More stable solid electrolyte interphases are formed under an oxygen atmosphere, which helps stabilise the lithium anode on cycling.JE and CPG acknowledge support from a Royal Society Research Professorship for CPG (grant no. RP\R1\180147). JE and CPG also acknowledge support from an ERC Advanced Investigator Grant for CPG (grant no. EC H2020 ERC 835073). GH acknowledges support from a Faraday Institution grant (grant no. FIRG060). JBF gratefully acknowledge funding by the Faraday Institute through the LiSTAR (FIRG014, FIRG058). SM gratefully acknowledge funding by the Faraday Institute through the NEXGENNa (FIRG018)

Spiers Memorial Lecture: Lithium air batteries – tracking function and failure

Acknowledgements: JE and CPG acknowledge support from a Royal Society Research Professorship for CPG (grant no. RP\R1\180147). JE and CPG also acknowledge support from an ERC Advanced Investigator Grant for CPG (grant no. EC H2020 ERC 835073). GH acknowledges support from a Faraday Institution grant (grant no. FIRG060). JBF gratefully acknowledges funding by the Faraday Institute through LiSTAR (FIRG014, FIRG058). SM gratefully acknowledges funding by the Faraday Institute through NEXGENNa (FIRG018). LB acknowledges support from the EPSRC through the NanoDTC (grant no. EP/S022953/1).Here, we discuss experimental approaches developed by some of the authors to understand the function and failure of lithium–oxygen batteries.</jats:p