Superstructure and Correlated Na+ Hopping in a Layered Mg-Substituted Sodium Manganate Battery Cathode are Driven by Local Electroneutrality

Acknowledgments ARTICLE SECTIONSJump To E.N.B. acknowledges funding from the Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018 (EP/S515334/1). J.D.B. acknowledges funding from the Faraday Institution (EP/S003053/1, FIRG016). The authors also thank the Science and Technology Facilities Council (STFC) and ISIS Neutron and Muon source for neutron data (experiment no.: RB2010350). Additional thanks are given to the staff scientists at beamline I11 of the Diamond Light Source for synchrotron data using block allocation group time under proposal CY34243. This work also utilized the ARCHER UK National Supercomputing Service via our membership in the UK’s HEC Materials Chemistry Consortium, funded by the EPSRC (EP/L000202). The research was also carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, through the U.S. Department of Energy, Office of Basic Energy Sciences, Contract DE-AC02-98CH10866. E.N.B. would also like to thank A. Van der Ven and M.A. Jones for illuminating discussions.Peer reviewedPublisher PD

Probing Jahn-Teller Distortions and Antisite Defects in LiNiO2 with 7Li NMR Spectroscopy and Density Functional Theory

A.R.G.-S. and C.S.C. contributed equally to this work. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.Peer reviewe

Structural origins of voltage mysteresis in the Na-Ion cathode P2-Na0.67[Mg0.28Mn0.72]O2 : A combined spectroscopic and density functional theory study

Funding Information: E.N.B. acknowledges funding from the Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018 and is also grateful for use of the ARCHER UK National Supercomputing Service via our membership in the UK’s HEC Materials Chemistry Consortium, funded by the EPSRC (EP/L000202). Research was also carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, through the U.S. Department of Energy, Office of Basic Energy Sciences, Contract DE-AC02-98CH10866. P.J.R. thanks the Northeast Centre for Chemical Energy Storage (NECCES), an Energy Frontier Research Centre funded by the US Department of Energy, Office of Basic Energy Sciences, award DE-SC0012583. M.A.J. is grateful for the financial support of the EPSRC Centre for Doctoral Training (CDT) in Nanoscience and Nanotechnology Award EP/L015978/1. J.L. was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (no. 2019R1A6A1A10073437). E.N.B. also wishes to thank Dr M.F. Groh for assistance with setting up capillary XRD measurements. Publisher Copyright: ©Peer reviewedPublisher PD

Oxygen hole formation controls stability in LiNiO2 cathodes

Ni-rich lithium-ion cathode materials achieve both high voltages and capacities but are prone to structural instabilities and oxygen loss. The origin of the instability lies in the pronounced oxidation of O during delithiation: for LiNiO2, NiO2, and the rock salt NiO, density functional theory and dynamical mean-field theory calculations based on maximally localized Wannier functions yield a Ni charge state of ca. +2, with O varying between −2 (NiO), −1.5 (LiNiO2), and −1 (NiO2). Calculated X-ray spectroscopy Ni K and O K-edge spectra agree well with experimental spectra. Using ab initio molecular dynamics simulations, we observe loss of oxygen from the (012) surface of delithiated LiNiO2, two surface O⋅− radicals combining to form a peroxide ion, and the peroxide ion being oxidized to form O2, leaving behind two O vacancies and two O2− ions. Preferential release of 1O2 is dictated via the singlet ground state of the peroxide ion and spin conservation

Strengthening the Magnetic Interactions in Pseudobinary First-Row Transition Metal Thiocyanates, M(NCS)2.

Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with high operating temperatures. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese(II) thiocyanate, Mn(NCS)2, and iron(II) thiocyanate, Fe(NCS)2. Using magnetic susceptibility measurements on these materials and on cobalt(II) thiocyanate and nickel(II) thiocyanate, Co(NCS)2 and Ni(NCS)2, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, θ, from 29 K for Ni(NCS)2 to -115 K for Mn(NCS)2-a consequence of more diffuse 3d orbitals, increased orbital overlap, and increasing numbers of unpaired t2g electrons. We elucidate the magnetic structures of these materials: Mn(NCS)2, Fe(NCS)2, and Co(NCS)2 order into the same antiferromagnetic commensurate ground state, while Ni(NCS)2 adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that significantly stronger exchange interactions can be realized in these thiocyanate frameworks by using earlier TMs.EPSRC NPIF 2018 fund Laboratory Directed Research and Development Program of Oak Ridge National Laboratory NSERC of Canada PGSD fund Trinity College, Cambridge School of Chemistry, University of Nottingham Hobday Fellowship EPSRC Strategic Equipment Grant EP/M000524/

17O NMR Spectroscopy in Lithium-Ion Battery Cathode Materials: Challenges and Interpretation.

Modern studies of lithium-ion battery (LIB) cathode materials employ a large range of experimental and theoretical techniques to understand the changes in bulk and local chemical and electronic structures during electrochemical cycling (charge and discharge). Despite its being rich in useful chemical information, few studies to date have used 17O NMR spectroscopy. Many LIB cathode materials contain paramagnetic ions, and their NMR spectra are dominated by hyperfine and quadrupolar interactions, giving rise to broad resonances with extensive spinning sideband manifolds. In principle, careful analysis of these spectra can reveal information about local structural distortions, magnetic exchange interactions, structural inhomogeneities (Li+ concentration gradients), and even the presence of redox-active O anions. In this Perspective, we examine the primary interactions governing 17O NMR spectroscopy of LIB cathodes and outline how 17O NMR may be used to elucidate the structure of pristine cathodes and their structural evolution on cycling, providing insight into the challenges in obtaining and interpreting the spectra. We also discuss the use of 17O NMR in the context of anionic redox and the role this technique may play in understanding the charge compensation mechanisms in high-capacity cathodes, and we provide suggestions for employing 17O NMR in future avenues of research.E.N.B. acknowledges funding from the Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018. E.N.B. would also like to thank K.R. Bassey for assistance with figure preparation and invaluable advice and discussions

Graphite anodes for Li-ion batteries – an electron paramagnetic resonance investigation

Graphite is the most commercially successful anode material for lithium (Li) ion batteries: its low cost, low toxicity and high abundance make it ideally suited for use in batteries for electronic devices, electrified transportation and grid-based storage. The physical and electrochemical properties of graphite anodes have been thoroughly characterised. However, questions remain regarding its electronic structure and whether the electrons occupy localised states on Li or delocalised states on C, or an admixture of both. In this regard, electron paramagnetic resonance (EPR) spectroscopy is an invaluable tool for characterising the electronic states generated during electrochemical cycling as it measures the properties of the unpaired electrons in lithiated graphite. In this work, ex situ variable-temperature (10-300 K), variable frequency (9-441 GHz) EPR was carried out to extract the g-tensors and linewidths, and understand the effect of metallicity on the observed EPR spectra of charged graphite at four different states of lithiation. We show that the increased resolution offered by EPR at high frequencies (>300 GHz) enables up to three different electron environments of axial symmetry to be observed, revealing heterogeneity within the graphite particles and the presence of hyperfine coupling to 7Li nuclei. Importantly, our work demonstrates the power of EPR spectroscopy to investigate the local electronic structure of graphite at different lithiation stages, paving the way for this technique as a tool for screening and investigating novel materials for use in Li-ion batteries.T.I. and C.P.G. were supported by an ERC Advanced Investigator Grant for C.P.G. (EC H2020 835073). E.N.B. was supported by the Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018. K.M. was supported by the Faraday Institution Degradation Project (FIRG001 and FIRG024). The Pulsed EPR measurements were performed at the Centre for Pulse EPR at Imperial College London (PEPR), supported by the EPSRC grant EP/T031425/1

Graphite Anodes for Li-Ion Batteries: An Electron Paramagnetic Resonance Investigation.

Graphite is the most commercially successful anode material for lithium (Li)-ion batteries: its low cost, low toxicity, and high abundance make it ideally suited for use in batteries for electronic devices, electrified transportation, and grid-based storage. The physical and electrochemical properties of graphite anodes have been thoroughly characterized. However, questions remain regarding their electronic structures and whether the electrons occupy localized states on Li, delocalized states on C, or an admixture of both. In this regard, electron paramagnetic resonance (EPR) spectroscopy is an invaluable tool for characterizing the electronic states generated during electrochemical cycling as it measures the properties of the unpaired electrons in lithiated graphites. In this work, ex situ variable-temperature (10-300 K), variable-frequency (9-441 GHz) EPR was carried out to extract the g tensors and line widths and understand the effect of metallicity on the observed EPR spectra of electrochemically lithiated graphites at four different states of lithiation. We show that the increased resolution offered by EPR at high frequencies (>300 GHz) enables up to three different electron environments of axial symmetry to be observed, revealing heterogeneity within the graphite particles and the presence of hyperfine coupling to Li nuclei. Importantly, our work demonstrates the power of EPR spectroscopy to investigate the local electronic structure of graphite at different lithiation stages, paving the way for this technique as a tool for screening and investigating novel materials for use in Li-ion batteries.T.I. and C.P.G. were supported by an ERC Advanced Investigator Grant for C.P.G. (EC H2020 835073). E.N.B. was supported by the Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018. K.M. was supported by the Faraday Institution Degradation Project (FIRG001 and FIRG024). The Pulsed EPR measurements were performed at the Centre for Pulse EPR at Imperial College London (PEPR), supported by the EPSRC grant EP/T031425/1

Probing Jahn-Teller distortions and antisite defects in LiNiO2 with 7Li NMR spectroscopy and Density Functional Theory

The long- and local-range structure and electronic properties of the high-voltage lithium-ion cathode material for Li-ion batteries, LiNiO2, remain widely debated, as are the degradation phenomena at high states of delithiation, which limit the more widespread use of this material. In particular, the local structural environment and the role of Jahn-Teller distortions are unclear, as are the interplay of distortions and point defects, and their influence on cycling behaviour. Here, we use ex-situ 7Li NMR measurements in combination with density functional theory (DFT) calculations to examine Jahn-Teller distortions and anti-site defects in LiNiO2. We calculate the 7Li Fermi contact shifts for the Jahn-Teller distorted and undistorted structures, the experimental 7Li room temperature spectrum being ascribed to an appropriately weighted time-average of the rapidly fluctuating structure comprising, collinear, zigzag and undistorted domains. The 7Li NMR spectra are sensitive to the nature and distribution of anti-site defects, and in combination with DFT calculations of different configurations, we show that the 7Li resonance at approximately -89 ppm is characteristic of separated Li – Ni antisite defects, these and the anti-site defect with Li in next-nearest Li-Ni neighbour configurations accounting for approximately 1/3 and 2/3, respectively of the total anti-site defect concentrations at room temperature in the pristine material. Via ex-situ 7Li MAS NMR, X-ray diffraction and electrochemical experiments, we identify the 7 Li spectral signatures of the different crystallographic phases on delithiation. The results imply fast Li-ion dynamics in the monoclinic phase and indicate that the hexagonal H3 phase near the end of charge is largely devoid of Li.This work was supported by the Faraday Institution degradation project (FIRG011, FIRG020). This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 957189 (BIGMAP). The project is part of BATTERY 2030+, the large-scale European research initiative for inventing the sustainable batteries of the future, funded by the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 957213. A.R.G.-S. gratefully acknowledges funding from the German National Academy of Sciences Leopoldina. We thank Teresa Insinna for fruitful discussions. Generous computing resources were provided by the Sulis HPC service (EP/T022108/1)