Lithium-enriched graphite anode surfaces investigated using nuclear reaction analysis.

Non-destructive Li nuclear reaction analysis techniques were used to profile the Li distribution at the surface of graphitic Li-ion battery anodes. These techniques show that Li concentrations are elevated within 300 nm of the anode surface, even in fully delithiated states. The surface region, which includes the solid electrolyte interphase, contains at least 60% of the total Li irreversibly lost during formation and cycling.

Kinetic Study of Parasitic Reactions in Lithium-Ion Batteries: A Case Study on LiNi(0.6)Mn(0.2)Co(0.2)O2.

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.

Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction.

This Review is focused on ion-transport mechanisms and fundamental properties of solid-state electrolytes to be used in electrochemical energy-storage systems. Properties of the migrating species significantly affecting diffusion, including the valency and ionic radius, are discussed. The natures of the ligand and metal composing the skeleton of the host framework are analyzed and shown to have large impacts on the performance of solid-state electrolytes. A comprehensive identification of the candidate migrating species and structures is carried out. Not only the bulk properties of the conductors are explored, but the concept of tuning the conductivity through interfacial effects-specifically controlling grain boundaries and strain at the interfaces-is introduced. High-frequency dielectric constants and frequencies of low-energy optical phonons are shown as examples of properties that correlate with activation energy across many classes of ionic conductors. Experimental studies and theoretical results are discussed in parallel to give a pathway for further improvement of solid-state electrolytes. Through this discussion, the present Review aims to provide insight into the physical parameters affecting the diffusion process, to allow for more efficient and target-oriented research on improving solid-state ion conductors.

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.

Size-dependent electrocatalytic activity of gold nanoparticles on HOPG and highly boron-doped diamond surfaces.

Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between < 1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.