Jolanta Światowska

Effect of Lithiation Potential and Cycling on Chemical and Morphological Evolution of Si Thin Film Electrode Studied by ToF-SIMS

Si thin films obtained by plasma enhanced chemical vapor deposition (PECVD) were used to investigate chemical and morphological modifications induced by lithiation potential and cycling. These modifications were thoughtfully analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling, which allows to distinguish the surface and bulk processes related to the formation of the solid electrolyte interphase (SEI) layer, and Li-Si alloying, respectively. The main results are a volume expansion/shrinkage and a dynamic behavior of the SEI layer during the single lithiation/delithiation process and multicycling. Trapping of lithium and other ions corresponding to products of electrolyte decomposition are the major reasons of electrode modifications. It is shown that the SEI layer contributes to 60% of the total volume variation of Si electrodes (100 nm). The apparent diffusion coefficient of lithium (DLi) calculated from the Ficks second law directly from Li-ion ToF-SIMS profiles is of the order of ∼5.9 × 10(-15) cm(2).s(-1). This quite low value can be explained by Li trapping in the bulk of electrode material, at the interfaces, continuous growth of the SEI layer and increase of SiO2 quantity. These modifications can result in limitation the ionic transport of Li.

Sealing of hard CrN and DLC coatings with atomic layer deposition

Atomic layer deposition (ALD) is a thin film deposition technique that is based on alternating and saturating surface reactions of two or more gaseous precursors. The excellent conformality of ALD thin films can be exploited for sealing defects in coatings made by other techniques. Here the corrosion protection properties of hard CrN and diamond-like carbon (DLC) coatings on low alloy steel were improved by ALD sealing with 50 nm thick layers consisting of Al2O3 and Ta2O5 nanolaminates or mixtures. In cross sectional images the ALD layers were found to follow the surface morphology of the CrN coatings uniformly. Furthermore, ALD growth into the pinholes of the CrN coating was verified. In electrochemical measurements the ALD sealing was found to decrease the current density of the CrN coated steel by over 2 orders of magnitude. The neutral salt spray (NSS) durability was also improved: on the best samples the appearance of corrosion spots was delayed from 2 to 168 h. On DLC coatings the adhesion of the ALD sealing layers was weaker, but still clear improvement in NSS durability was achieved indicating sealing of the pinholes.

Aging-induced chemical and morphological modifications of thin film iron oxide electrodes for lithium-ion batteries.

Spectroscopic (XPS, ToF-SIMS) and microscopic (SEM, AFM) analytical methods have been applied to iron oxide (∼Fe2O3) using a thin film approach to bring new insight into the aging mechanisms of conversion-type anode materials for lithium-ion batteries. The results show that repeated lithiation/delithiation causes both chemical and morphological modifications affecting the electrochemical performance. The SEI layer formed by reductive decomposition of the electrolyte remains stable in composition (mostly Li2CO3) but irreversibly thickens upon multicycling. Irreversible swelling of the material accompanied by penetration of the SEI layer and accumulation of non-deconverted material in the bulk of the oxide thin film occurs upon repeated conversion/deconversion. After initial pulverization of the thin film microstructure, grain growth and aggregation are promoted by multicycling. This leads to capacity increase in the first few cycles, but upon further cycling volume expansion and accumulation of non-deconverted material lead to deterioration of the electrode performances.

Novel Sulfur Host Composed of Cobalt and Porous Graphitic Carbon Derived from MOFs for the High-Performance Li–S Battery

A composite consisting of cobalt and graphitic porous carbon (Co@GC-PC) is synthesized from bimetallic metal-organic frameworks and employed as the sulfur host for high-performance Li-S batteries. Because of the presence of a large surface area (724 m2 g-1) and an abundance of macro-/mesopores, the Co@GC-PC electrode is able to alleviate the debilitating effect originating from the volume expansion/contraction of sulfur species during the cycling process. Our in situ UV/vis analysis indicates that the existence of Co@GC-PC promotes the adsorption of polysulfides during the discharge process. Density functional theory calculations show a strong interaction between Co and Li2S and a low decomposition barrier of Li2S on Co(111), which is beneficial to the following Li2S oxidation in the charge process. As a result, at 0.2C, the discharge capacity of the S/Co@GC-PC cathode is stabilized at 790 mAh g-1 after 220 cycles, much higher than that of a carbon-based cathode, which delivers a discharge capacity of 188 mAh g-1.

Lithium Battery Technologies: From the Electrodes to the Batteries

Abstract The metallic lithium is principally used in manufacturing ceramics, specialty glass (29%), rechargeable batteries (27%), high-temperature grease, continuous castings, polymers, aluminum alloys, and pharmaceuticals. Due to the huge increase of energy demand, the quantity of lithium for battery application is supposed to augment in the next future decades. It is then important to know the state of the art of lithium-ion batteries (LiBs). This chapter presents current LiB technologies with a particular focus on two principal components—positive and negative electrode materials. The positive electrode materials are described according to their crystallographic structure: layered, olivine, and spinel and the negative electrodes are classified according to their reactivity with lithium: intercalation, conversion, and alloying type materials. Some perspectives related to new materials for improved, higher energy density LiBs are presented. The electrode surface chemistry related to electrode/electrolyte interphase reactions, one of the most important factors influencing the electrochemical performance of LiBs, is also reported.