Filippo Maglia

Future generations of cathode materials: an automotive industry perspective

Future generations of electrified vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium batteries is mandatory, maintaining at the same time similar, or improved, rate capability, lifetime, cost, and safety. Several new cathode materials have been claimed over the last decade to allow for this energy improvement. The possibility that some of them will find application in the future automotive batteries is critically evaluated here by first considering their theoretical and experimentally demonstrated energy densities at the material level. For selected candidates, the energy density at the automotive battery cell level for electric vehicle applications is calculated using an in-house developed software. For the selected cathodes, literature results concerning their power capability and lifetime are also discussed with reference to the automotive targets.

Electrode–Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights

Understanding reactions at the electrode/electrolyte interface (EEI) is essential to developing strategies to enhance cycle life and safety of lithium batteries. Despite research in the past four decades, there is still limited understanding by what means different components are formed at the EEI and how they influence EEI layer properties. We review findings used to establish the well-known mosaic structure model for the EEI (often referred to as solid electrolyte interphase or SEI) on negative electrodes including lithium, graphite, tin, and silicon. Much less understanding exists for EEI layers for positive electrodes. High-capacity Li-rich layered oxides yLi2-xMnO3·(1-y)Li1-xMO2, which can generate highly reactive species toward the electrolyte via oxygen anion redox, highlight the critical need to understand reactions with the electrolyte and EEI layers for advanced positive electrodes. Recent advances in in situ characterization of well-defined electrode surfaces can provide mechanistic insights and strategies to tailor EEI layer composition and properties.

High-energy-density lithium-ion battery using a carbon-nanotube–Si composite anode and a compositionally graded Li[Ni0.85Co0.05Mn0.10]O2 cathode

A fully operational practical Li-rechargeable battery system delivering unprecedented high energy density with excellent cycle life was proposed using the state-of-the-art cathode and anode technologies. Based on the simple ball-milling process, a carbon nanotube (CNT)–Si composite anode with extremely stable long-term cycling, while providing a discharge capacity of 2364 mA h g−1 at a tap density of 1.103 g cm−3, was developed. For the cathode, a two-sloped full concentration gradient (TSFCG) Li[Ni0.85Co0.05Mn0.10]O2 cathode, designed to obtain maximum possible discharge capacity by having a Ni-enriched core and to simultaneously ensure high chemical and thermal stability by having an outer Mn-enriched layer, yielded a discharge capacity of 221 mA h g−1. Integrating the CNT–Si composite and the TSFCG cathode in a full cell configuration, the full cell generated an energy density of 350 W h kg−1 with excellent capacity retention for 500 cycles at 1 C rate, satisfying the energy density limit imposed by the drive range requirement for EVs. The proposed battery system satisfied the demands for energy storage for vehicle applications in terms of energy density, power and cycle life.

Kinetic Study of Parasitic Reactions in Lithium-Ion Batteries: A Case Study on LiNi0.6Mn0.2Co0.2O2

The side reactions between the electrode materials and the nonaqueous electrolytes have been the major contributor to the degradation of electrochemical performance of lithium-ion batteries. A home-built high-precision leakage current measuring system was deployed to investigate the reaction kinetics between the delithiated LiNi(0.6)Mn(0.2)Co(0.2)O2 and a conventional nonaqueous electrolyte. It was found that the rate of parasitic reaction had strong dependence on the upper cutoff potential of the cathode material. The kinetic data also indicated a change of reaction mode at about 4.5 V vs Li(+)/Li.

Chemical versus Electrochemical Electrolyte Oxidation on NMC111, NMC622, NMC811, LNMO, and Conductive Carbon

We compare the stability of alkyl carbonate electrolyte on NMC111, -622, and -811, LNMO, and conductive carbon electrodes. We prove that CO2 and CO evolution onset potentials depend on the electrode material and increase in the order NMC811 < NMC111 ≈ NMC622 < conductive carbon ≈ LNMO, which we rationalize by two fundamentally different oxidation mechanisms, the chemical and the electrochemical electrolyte oxidation. Additionally, in contrast to the widespread understanding that transition metals in cathode active materials catalyze the electrolyte oxidation, we will prove that such a catalytic effect on the electrochemical electrolyte oxidation does not exist.

Future high-energy density anode materials from an automotive application perspective

Ramping up the full-electric vehicle market share heavily relies on the extension of electrical driving range, as well as on the reduction of charging time and cost. New Li-batteries should, at the same time, offer at least the same levels of power, lifetime and safety as the one nowadays available on the market. The achievement of these goals requires the development of new electrode materials with improved capacity, operating voltage, transport properties together with cycling and temperature stability. Several new anode materials have been proposed over the last decade. In this contribution we critically evaluate their chance to find application in the future automotive batteries. First, we discuss their properties at the materials level, subsequently, the energy density for selected candidates is calculated at the automotive battery cell level using an in-house developed software. If available, literature results concerning power capability and lifetime are also discussed with reference to the automotive targets.

Electrocatalytic transformation of HF impurity to H2 and LiF in lithium-ion batteries

AbstractThe formation of solid electrolyte interphase on graphite anodes plays a key role in the efficiency of Li-ion batteries. However, to date, fundamental understanding of the formation of LiF as one of the main solid electrolyte interphase components in hexafluorophosphate-based electrolytes remains elusive. Here, we present experimental and theoretical evidence that LiF formation is an electrocatalytic process that is controlled by the electrochemical transformation of HF impurity to LiF and H2. Although the kinetics of HF dissociation and the concomitant production of LiF and H2 is dependent on the structure and nature of surface atoms, the underlying electrochemistry is the same. The morphology, and thus the role, of the LiF formed is strongly dependent on the nature of the substrate and HF inventory, leading to either complete or partial passivation of the interface. Our finding is of general importance and may lead to new opportunities for the improvement of existing, and design of new, Li-ion technologies.Despite the central role that the solid electrolyte interphase plays on the efficiency of Li-ion batteries, little is known about its formation mechanism. It is now shown that LiF forms on graphite anodes as a result of the electrocatalytic transformation of HF impurities present in the electrolyte.

Chemical Reactivity Descriptor for the Oxide-Electrolyte Interface in Li-Ion Batteries

Understanding electrochemical and chemical reactions at the electrode-electrolyte interface is of fundamental importance for the safety and cycle life of Li-ion batteries. Positive electrode materials such as layered transition metal oxides exhibit different degrees of chemical reactivity with commonly used carbonate-based electrolytes. Here we employed density functional theory methods to compare the energetics of four different chemical reactions between ethylene carbonate (EC) and layered (LixMO2) and rocksalt (MO) oxide surfaces. EC dissociation on layered oxides was found energetically more favorable than nucleophilic attack, electrophilic attack, and EC dissociation with oxygen extraction from the oxide surface. In addition, EC dissociation became energetically more favorable on the oxide surfaces with transition metal ions from left to right on the periodic table or by increasing transition metal valence in the oxides, where higher degree of EC dissociation was found as the Fermi level was lowered into the oxide O 2p band.

Tuning mobility and stability of lithium ion conductors based on lattice dynamics

Lithium ion conductivity in many structural families can be tuned by many orders of magnitude, with some rivaling that of liquid electrolytes at room temperature. Unfortunately, fast lithium conductors exhibit poor stability against lithium battery electrodes. In this article, we report a fundamentally new approach to alter ion mobility and stability against oxidation of lithium ion conductors using lattice dynamics. By combining inelastic neutron scattering measurements with density functional theory, fast lithium conductors were shown to have low lithium vibration frequency or low center of lithium phonon density of states. On the other hand, lowering anion phonon densities of states reduces the stability against electrochemical oxidation. Olivines with low lithium band centers but high anion band centers are promising lithium ion conductors with high ion conductivity and stability. Such findings highlight new strategies in controlling lattice dynamics to discover new lithium ion conductors with enhanced conductivity and stability.

Systematic control of α-Fe2O3 crystal growth direction for improved electrochemical performance of lithium-ion battery anodes

α-Fe2O3 nanomaterials with an elongated nanorod morphology exhibiting superior electrochemical performance were obtained through hydrothermal synthesis assisted by diamine derivatives as shape-controlling agents (SCAs) for application as anodes in lithium-ion batteries (LIBs). The physicochemical characteristics were investigated via XRD and FESEM, revealing well-crystallized α-Fe2O3 with adjustable nanorod lengths between 240 and 400 nm and aspect ratios in the range from 2.6 to 5.7. The electrochemical performance was evaluated by cyclic voltammetry and charge–discharge measurements. A SCA test series, including ethylenediamine, 1,2-diaminopropane, 2,3-diaminobutane, and N-methylethylenediamine, was implemented in terms of the impact on the nanorod aspect ratio. Varied substituents on the vicinal diamine structure were examined towards an optimized reaction center in terms of electron density and steric hindrance. Possible interaction mechanisms of the diamine derivatives with ferric species and the correlation between the aspect ratio and electrochemical performance are discussed. Intermediate-sized α-Fe2O3 nanorods with length/aspect ratios of ≈240 nm/≈2.6 and ≈280 nm/≈3.0 were found to have excellent electrochemical characteristics with reversible discharge capacities of 1086 and 1072 mAh g−1 at 0.1 C after 50 cycles.