Perspectives for next generation lithium-ion battery cathode materials

Transitioning to electrified transport requires improvements in sustainability, energy density, power density, lifetime, and approved the cost of lithium-ion batteries, with significant opportunities remaining in the development of next-generation cathodes. This presents a highly complex, multiparameter optimization challenge, where developments in cathode chemical design and discovery, theoretical and experimental understanding, structural and morphological control, synthetic approaches, and cost reduction strategies can deliver performance enhancements required in the near- and longer-term. This multifaceted challenge requires an interdisciplinary approach to solve, which has seen the establishment of numerous academic and industrial consortia around the world to focus on cathode development. One such example is the Next Generation Lithium-ion Cathode Materials project, FutureCat, established by the UK’s Faraday Institution for electrochemical energy storage research in 2019, aimed at developing our understanding of existing and newly discovered cathode chemistries. Here, we present our perspective on persistent fundamental challenges, including protective coatings and additives to extend lifetime and improve interfacial ion transport, the design of existing and the discovery of new cathode materials where cation and cation-plus-anion redox-activity can be exploited to increase energy density, the application of earth-abundant elements that could ultimately reduce costs, and the delivery of new electrode topologies resistant to fracture which can extend battery lifetime.</jats:p

Perspectives for next generation lithium-ion battery cathode materials

Transitioning to electrified transport requires improvements in sustainability, energy density, power density, lifetime, and approved the cost of lithium-ion batteries, with significant opportunities remaining in the development of next-generation cathodes. This presents a highly complex, multiparameter optimization challenge, where developments in cathode chemical design and discovery, theoretical and experimental understanding, structural and morphological control, synthetic approaches, and cost reduction strategies can deliver performance enhancements required in the near- and longer-term. This multifaceted challenge requires an interdisciplinary approach to solve, which has seen the establishment of numerous academic and industrial consortia around the world to focus on cathode development. One such example is the Next Generation Lithium-ion Cathode Materials project, FutureCat, established by the UK’s Faraday Institution for electrochemical energy storage research in 2019, aimed at developing our understanding of existing and newly discovered cathode chemistries. Here, we present our perspective on persistent fundamental challenges, including protective coatings and additives to extend lifetime and improve interfacial ion transport, the design of existing and the discovery of new cathode materials where cation and cation-plus-anion redox-activity can be exploited to increase energy density, the application of earth-abundant elements that could ultimately reduce costs, and the delivery of new electrode topologies resistant to fracture which can extend battery lifetime

Quantum evaporation from superfluid helium surfaces: Oblique incidence

We study the problem of surface scattering in (4)Helium at T = 0K. Starting with the microscopic superfluid theory of Beliaev [1] in a real space formulation [2] we derive an equation of motion for the quasiparticles valid in bulk helium, through the surface and in the vacuum. This equation contains the physics necessary to calculate the different evaporation probabilities, and, in particular, the formalism retains the diffuse nature of the surface of liquid helium and the non-locality of the helium-helium interaction. We solve the equation numerically and we present results for oblique incidence and for a range of quasiparticle energies

Magnetotransport theory in quantum dots: 3D-0D and 2D-0D tunneling and angular momentum selection rules

A study of magnetotransport through quantum dots is presented. The model allows one to analyze tunneling both from bulk-like contacts and from 2D accumulation layers. The fine features in the I-V characteristics due to the quantum dot states are known to be shifted to different voltages depending upon the value of the magnetic field. While this effect is also well reproduced by our calculations, in this work we concentrate on the amplitude of each current resonance as a function of the magnetic field. Such amplitudes show oscillations reflecting the variation of the density of states at the Fermi energy in the emitter. Furthermore the amplitude increases as a function of the magnetic field for certain features while it decreases for others. In particular, we demonstrate that the behavior of the amplitude of the current resonances is linked to the value of the angular momentum of each dot level through which tunneling occurs. We show that a selection rule on the angular momentum must be satisfied. As a consequence, tunneling through specific dot states is strongly suppressed and sometimes prohibited altogether by the presence of the magnetic field. This will allow to extract from the experimental curves detailed information on the nature of the quantum-dot wave functions involved in the electronic transport. Furthermore, when tunneling occurs from a two-dimensional accumulation layer to the quantum dot, the presence of a magnetic field hugely increases the strength of some resonant features. This effect is predicted by our model and, to the best of our knowledge, has never been observed. [S0163-1829(99)04007-2]

The effect of backflow on atom emission from the free surface of superfluid He-4 by rotons

We extend the theory of Sobnack and Inkson (Phys. Rev, Lett. 82 (1999) 3657) by including roton backflow semi-phenomenologically in the form of a backflow potential to examine the effect of backflow on the quantum evaporation of atoms from superfluid helium by rotons. We solve the resulting equations numerically and calculate the probabilities P-ra of atom (a) emission by both R+ and the negative group velocity R- rotons (r). We compare the results with the corresponding efficiencies when backflow is neglected and we comment on the improved agreement with experiments. (C) 2000 Elsevier Science B.V. All rights reserved

Mechanical properties of cathode materials for lithium-ion batteries

Mechanochemical degradation processes such as the fracture of cathode particles play a major role in limiting the service life of advanced lithium-ion batteries (LIBs). In order to help alleviate the degradation of battery performance, it is necessary to measure the relationship between the degradation of the mechanical properties of cathodes and their concomitant degradation of electrochemical performance. In this review, measurements of the mechanical properties of LIB cathode materials are summarized from the literature, along with the range of experimental methods used in their determination. Dimensional changes that accompany charge and discharge are compared for active materials of olivine, spinel, and layered atomic structures. The sensitivity of indentation hardness, Young's modulus and fracture strength to grain size, porosity, state of charge and charge/discharge history are critically reviewed and discussed with reference to the behavior of conventional, electrically inactive solids. This approach allows for the identification of microstructural properties that dictate the mechanical properties of LIB cathode materials.All authors acknowledge funding from the Faraday Institution project “FutureCat” (grant number FIRG017)

Fracture Testing of Lithium-Ion Battery Cathode Secondary Particles in-situ inside the Scanning Electron Microscope

Funder: Faraday Institution Next Generation Cathodes Project: FutureCat; Grant(s): FIRG017Fracture of cathode secondary particles is a critical degradation mechanism in lithium‐ion batteries. The microindentation strength of LiNi0.8Mn0.1Co0.1O2 secondary particles is measured in situ in the scanning electron microscope (SEM), enabling dynamical imaging of fracture. Crack propagation is intergranular between primary particles when induced by compressing between flat platens (analogous to calendaring), and with a cono‐spherical indenter (representing particle‐particle contact). Fracture occurs directly beneath the cono‐spherical tip and at the centre of secondary particles when compressed between flat platens. Finite element modelling of stress states provides insight into the dependence of fracture load upon cohesive strength and particle toughness. Secondary particle indentation strength decreases with increasing secondary particle size, with cycling, and with increasing state of charge. The indentation strength decrease is greatest in earlier stages of delithiation. The novel microindentation technique allows assessment of strength and toughness of different cathode morphologies, aiding prediction of optimal particle structure and processing conditions