Peter Lamp

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.

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.

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.