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Battery Applications


Introduction

We are investigating a variety of electrode materials for applications in lithium-ion, sodium-ion and magnesium-ion batteries. For lithium-ion based systems, materials under investigation include intercalation compounds such as LiFePO4, Li-Ni-Co-Al-O (NCA), LiMnO2, TiO2-B and Nb2O5; conversion materials such as VS4, NbS3, FeF3 and RuO2; and alloying materials such as P, Ge and Si. Additionally, we study potential alternatives to the conventional lithium-ion battery systems including metal-air, sodium-ion and divalent magnesium-ion batteries. In this "beyond lithium" research, we study, among others, lithium-air, sodium-air, NaMnO2, Na-Fe-SO4, Na-hard carbons, Na-P, Na-Sn, Na-Sb, Mg-Bi, Mg6MnO8 and Mg electrolytes. We utilize an array of advanced characterisation tools and theoretical techniques to understand complex reaction mechanisms in these battery systems and to develop new materials.

List of selected publications:

"Materials' Methods: NMR in Battery Research", O Pecher, J Carretero-Gonzalez, KJ Griffith and CP Grey, Chem. Mater. (2017) 29, 213 (DOI: 10.1021/acs.chemmater.6b03183)

Lithium Ion Batteries (LIBs)

Rechargeable lithium-ion batteries recently celebrated their 25th anniversary as commercial products. However, mobile technologies, electric vehicles, safety, cost, sustainability and large-scale storage all provide the impetus for research into new battery materials and mechanisms. We are interested in a wide variety of commercial and next-generation cathode and anode materials, solid electrolytes for all-solid state batteries, and Li dendrite growth mechanisms.

In our group, laboratory-based and synchrotron/neutron diffraction methods are used extensively to understand the changes in average structure that occur during electrochemical discharge/charge reactions. Lithium has two NMR active isotopes, 6Li and 7Li, that provide direct insight into the local environment and dynamics of lithium in topotactic or conversion/alloying electrodes. The application of two-dimensional exchange spectroscopy or variable-temperature relaxation measurements enables quantitative analysis of lithium ion motion and often yields information on diffusion pathways and mechanisms. In alloying and conversion electrodes, the amorphous nature of starting materials and intermediates often hinders diffraction studies but NMR and Pair Distribution Function (PDF) analysis are sensitive to local structure and can be used for phase identification. Ab initio calculations of phase space and/or NMR parameters frequently guide and support experimental studies. Indeed, in these complex systems, several complementary techniques must often be applied to provide a detailed understanding of the changes that occur and an accurate description of the phases present in a lithium-ion battery during lithiation and delithiation cycles.

List of selected publications:

"Sustainability and In Situ Monitoring in Battery Development", CP Grey and JM Tarascon, Nature Mater. (2017) 16, 45 (DOI: 10.1038/nmat4777)

"Preventing Structural Rearrangements on Battery Cycling: A First-Principles Investigation of the Effect of Dopants on the Migration Barriers in Layered Li0.5MnO2", ID Seymour, DJ Wales and CP Grey, J. Phys. Chem. C (2016) 120, 19521 (DOI: 10.1021/acs.jpcc.6b05307)

"High-rate Intercalation without Nanostructuring in Metastable Nb2O5 Bronze Phases", KJ Griffith, AC Forse, JM Griffin and CP Grey, J. Am. Chem. Soc. (2016) 138, 888 (DOI: 10.1021/jacs.6b04345)

"Unraveling the Complex Delithiation Mechanisms of Olivine-Type Cathode Materials, LiFexCo1-xPO4", FC Strobridge, H Liu, M Leskes, OJ Borkiewicz, KM Wiaderek, PJ Chupas, KW Chapman and CP Grey, Chem. Mater. (2016) 28, 2676 (DOI: 10.1021/acs.chemmater.6b00319)

Sodium Ion Batteries (NIBs)

Lithium-ion batteries can reach higher energy density and operating voltages than their sodium analogues and have been the focus of rechargeable battery research over the past three decades. Demand for lithium is set to soar; not only for the growing portable electronics market, but also for electric vehicle (EV) and hybrid electric vehicle (HEV) applications, and for large-scale energy storage of intermittent renewable energy generating technologies, such as wind, solar and wave power.  There are concerns that the cost of LIBs will increase on the long-term in light of the projected orders-of-magnitude increase in lithium usage in batteries, to a point where the technology is not economically effective. Low-cost, safe, high power and high capacity battery materials that are not resource-limited must be found. The use of Na instead of Li in intercalation electrode materials for Na-ion batteries could mitigate the feasible shortage and rising cost of lithium, due to the huge availability of sodium and its low price. NIBs are an obvious choice for large-scale renewable energy storage applications, for which high energy density also becomes less critical but instead high per-cycle energy efficiency is particularly important.
Since NIBs have been explored considerably less than their Li analogues the major challenge is finding and optimizing electrode materials with good enough electrochemical properties to meet the demands of energy storage applications. We use a range of structural probes to characterize the charging behavior of potential electrode materials, with a view to understanding and improving their electrochemical performance.  
23Na MAS solid-state NMR provides detailed insight into the actual local environments experienced by electrochemically active species in sodium-ion battery materials. A reliable assignment of NMR spectral features is a prerequisite to understand the variations in spectra on electrochemical cycling and can be facilitated by comparison to NMR parameters obtained by hybrid Hartree-Fock / Density Functional Theory (DFT) calculations.
The use of diffraction probes such as high resolution powder X-ray and neutron diffraction, and pair distribution function analysis of total scattering data can give complementary information about average and local structure, and can be combined with 23Na MAS solid-state NMR and computational studies to build a comprehensive structural picture of charging behavior in potential electrode materials. 

List of selected publications:

"Investigating Sodium Storage Mechanisms in Tin Anodes: A Combined Pair Distribution Function Analysis, Density Functional Theory, and Solid-State NMR Approach", JM Stratford, M. Mayo, PK Allan, O Pecher, OJ Borkiewicz, KM Wiaderek, KW Chapman, CJ Pickard, AJ Morris and CP Grey, J. Am. Chem. Soc. (2017), ASAP (DOI: 10.1021/jacs.7b01398)

"Mechanistic Insights into Sodium Storage in Hard Carbon Anodes using Local Structure Probes", JM Stratford, PK Allan, O Pecher, PA Chater and CP Grey, Chem. Commun. (2016), 52, 12430 (DOI: 10.1039/c6cc06990h)

"Insights into the Nature and Evolution upon Electrochemical Cycling of Planar Defects in the β-NaMnO2 Na-ion Battery Cathode: An NMR and First-Principles Density Functional Theory Approach", RJ Clément, DS Middlemiss, ID Seymour, AJ Ilott and CP Grey, Chem. Mater. (2016), 28, 8228 (DOI: 10.1021/acs.chemmater.6b03074)

"Sodium Intercalation Mechanism of 3.8 V Class Alluaudite Sodium Iron Sulfate", G Oyama, O Pecher, KJ Griffith, SI Nishimura, R Pigliapochi, CP Grey and A Yamada, Chem. Mater. (2016), 28, 5321 (DOI: 10.1021/acs.chemmater.6b01091)

Lithium-Air

The lithium-air battery is, in principle, a promising candidate for use as an energy storage system. Theoretically, it can store up to 3,505W.h.kg-1 (approaching an order of magnitude more than a conventional lithium ion battery) based on the reaction (in non-aqueous electrolytes) of lithium and oxygen to form lithium peroxide and including the weight of the reactants. In practice the development of the battery is still at initial stages with operating cells falling short of their promising potential. Among the challenges to be addressed are the identification of stable electrolyte systems, inert and porous cathode materials and efficient catalytic species. These targets can only be realised with a careful analysis of the electrochemical products formed during the operation of the cell.
In our lab we apply multi-nuclear solid state NMR spectroscopy, supported by other techniques such as electron microscopy and X-ray diffraction, to monitor the evolution of electrochemical processes in the battery and gain insight on the performance of various electrolytes, cathode materials and potential catalysts. NMR is a unique and powerful tool in the study of this system as it is sensitive to the entire bulk of the cathode and can detect both crystalline and amorphous materials.

List of selected publications:

"Cycling Li-O2 batteries via LiOH formation and decomposition", T Liu, M Leskes, W Yu, AJ Moore, L Zhou, PM Bayley, G Kim and CP Grey, Science (2015) 350, 530 (DOI: 10.1126/science.aac7730)

"Direct Detection of Discharge Products in Lithium–Oxygen Batteries by Solid-State NMR Spectroscopy", M Leskes, NE Drewett, LJ Hardwick, PG Brice, GR Goward and CP Grey, Angew. Chem. Int. Ed. (2012) 51, 8560 (DOI: 10.1002/anie.201202183)

Magnesium Ion Batteries

Multivalent ions such as Mg2+, Ca2+, Al3+, are interesting in the context of rechargeable batteries as they could lead to batteries with increased gravimetric (by weight) and volumetric (by size) capacity. This relatively new field presents many challenges and all components - cathode, anode, electrolyte, casing - require optimised materials.

In collaboration with the Wright group in the Department of Chemistry, we have been investigating the performance and degradation mechanism of new electrolyte systems based on magnesium hexafluorophosphate. We also use 25Mg NMR and DFT to understand reaction mechanisms in positive and negative electrode materials for magnesium-ion batteries.

List of selected publications:

"Insights into the Electrochemical Performances of Bi Anodes for Mg Ion Batteries using 25Mg Solid State NMR Spectroscopy", Z Liu, J Lee, G Xiang, HFJ Glass, EN Keyzer, SE Dutton and CP Grey, Chem. Commun. (2017) 53, 743 (DOI: 10.1039/c6cc08430c)

"A Systematic Study of 25Mg NMR in Paramagnetic Transition Metal Oxides: Applications to Mg-ion Battery Materials", J Lee, ID Seymour, AJ Pell, SE Dutton, and CP Grey, Phys. Chem. Chem. Phys. (2016) 19, 613 (DOI: 10.1039/c6cp06338a)

"Mg(PF6)2-Based Electrolyte Systems: Understanding Electrolyte-Electrode Interactions for the Development of Mg-Ion Batteries", EN Keyzer, HFJ Glass, Z Liu, PM Bayley, SE Dutton, CP Grey and DS Wright, J. Am. Chem. Soc. (2016) 138, 8682 (DOI: 10.1021/jacs.6b04319)

Solid Electrolyte Interphase (SEI)

The formation of a stable SEI is critical to the long term capacity retention of lithium-ion batteries. Lithium is consumed in its formation resulting in irreversible capacity loss, and its growth is correlated with increased cell impedance. We are systematically studying SEI formation on battery materials including silicon-carbon composite electrodes and silicon nanowires.

In addition to NMR, classical and quantum mechanical modelling of molecular and interfacial interactions important for understanding the SEI.

List of selected publications:

"Solid Electrolyte Interphase Growth and Capacity Loss in Silicon Electrodes", AL Michan, G Divitini, AJ Pell, M Leskes, C Ducati and CP Grey, J. Am. Chem. Soc. (2016) 138, 7918 (DOI: 10.1021/jacs.6b02882)

"Fluoroethylene Carbonate and Vinylene Carbonate Reduction: Understanding Lithium-Ion Battery Electrolyte Additives and Solid Electrolyte Interphase Formation", AL Michan, BS Parimalam, M Leskes, RN Kerber, T Yoon, CP Grey and BL Lucht, Chem. Mater. (2016) 28, 8149 (DOI: 10.1021/acs.chemmater.6b02282)

"C-13 Solid State NMR Suggests Unusual Breakdown Products in SEI Formation on Lithium Ion Electrodes", N Leifer, MC Smart, GKS Prakash, L Gonzalez, L Sanchez, KA Smith, P Bhalla, CP Grey, SG Greenbaum, J. Electrochem. Soc. (2011) 158, A471 (DOI: 10.1149/1.3559551)