Bulk antimony sulfide with excellent cycle stability as next-generation anode for lithium-ion batteries

Nanomaterials as anode for lithium-ion batteries (LIB) have gained widespread interest in the research community. However, scaling up and processibility are bottlenecks to further commercialization of these materials. Here, we report that bulk antimony sulfide with a size of 10-20 mu m exhibits a high capacity and stable cycling of 800 mAh g(-1). Mechanical and chemical stabilities of the electrodes are ensured by an optimal electrode-electrolyte system design, with a polyimide-based binder together with fluoroethylene carbonate in the electrolyte. The polyimide binder accommodates the volume expansion during alloying process and fluoroethylene carbonate suppresses the increase in charge transfer resistance of the electrodes. We observed that particle size is not a major factor affecting the charge-discharge capacities, rate capability and stability of the material. Despite the large particle size, bulk antimony sulfide shows excellent rate performance with a capacity of 580 mAh g(-1) at a rate of 2000 mA g(-1)

The influence of point defects on the entropy profiles of Lithium Ion Battery cathodes:a lattice-gas Monte Carlo study

In-situ diagnostic tools have become established to as a means to understanding the aging processes that occur during charge/discharge cycles in Li-ion batteries (LIBs). One electrochemical thermodynamic technique that can be applied to this problem is known as entropy profiling. Entropy profiles are obtained by monitoring the variation in the open circuit potential as a function of temperature. The peaks in these profiles are related to phase transitions, such as order/disorder transitions, in the lattice. In battery aging studies of cathode materials, the peaks become suppressed but the mechanism by which this occurs is currently poorly understood. One suggested mechanism is the formation of point defects. Intentional modifications of LIB electrodes may also lead to the introduction of point defects. To gain quantitative understanding of the entropy profile changes that could be caused by point defects, we have performed Monte Carlo simulations on lattices of variable defect content. As a model cathode, we have chosen manganese spinel, which has a well-described order-disorder transition when it is half filled with Li. We assume, in the case of trivalent defect substitution (M = Cr,Co) that each defect M permanently pins one Li atom. This assumption is supported by Density Functional Theory (DFT) calculations. Assuming that the distribution of the pinned Li sites is completely random, we observe the same trend in the change in partial molar entropy with defect content as observed in experiment: the peak amplitudes become increasing suppressed as the defect fraction is increased. We also examine changes in the configurational entropy itself, rather than the entropy change, as a function of the defect fraction and analyse these results with respect to the ones expected for an ideal solid solution. We discuss the implications of the quantitative differences between some of the results obtained from the model and the experimentally observed ones

Investigating changes in transport, kinetics and heat generation over NCA/Gr-SiOx battery lifetime

We present a study of battery ageing, comparing pristine, calendar-aged, and cycle-aged lithium-ion cells. Insight into degradation was obtained via differential voltage analysis and by estimating and tracking changes in a subset of electrochemical model parameters of the single particle model through inverse modelling. We show that both diffusion time and kinetic overpotential increase in cycle-aged cells, while calendar-aged cells experienced no diffusion time changes but some kinetic overpotential increase. The latter is also evident in 50% higher irreversible heat generation in cycle-aged cells. This study highlights the importance of updating battery model parameters during ageing

Direct observation of local chemical surface properties by scanning tunneling microscopy

Vapor deposited Pt films with a thickness locally varying between one and two atomic layers on Ru(0001) are studied as model surfaces with a well-defined lateral variation of the chemical properties. These are probed by reversible CO adsorption at 300 K and with CO pressures in the range p(CO)=10(-10) ... 10(-5) mbar under real-time STM observation. Upon exposure to 10-5 mbar CO, no densely packed adlayer is formed on the areas with a local thickness of one atomic layer, whereas a c(4x2) adlayer containing 0.5 CO molecules per surface atom is reversibly formed on areas with locally two atomic layers of Pt. Based on experimental and theoretical data points and parameters from the literature we calculate adsorption isotherms for Pt(111) and the two Ru(0001) supported Pt thin films at 300 K. For all three surfaces, STM observations on CO adsorption are found to be fully consistent with the respective isotherms

Segregation and stability in surface alloys:PdxRu 1-x/Ru(0001) and PtxRu1-x/Ru(0001)

The stability of PdRu/Ru(0001) and PtRu/Ru(0001) surface alloys and the tendency for surface segregation of Pd and Pt subsurface guest metals in these surface alloys is studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Atomic resolution STM imaging and AES measurements reveal that upon overgrowing the surface alloys with a 1-2 monolayer Ru film and subsequent annealing to the temperatures required for initial surface alloy formation, the Ru-covered Pd (Pt) atoms float back to the outermost layer. The lateral distribution of these species is also essentially identical to that of the initial surface alloys, before overgrowth by Ru. In combination, this clearly demonstrates that the surface alloys represent stable surface configurations, metastable only towards entropically favored bulk dissolution, and that there is a distinct driving force for surface segregation of these species. Consequences of these data on the mechanism for surface alloy formation are discussed. Floating in PtRu (PdRu) surface alloys on Ru(0001): The PtRu (PdRu)monolayer surface alloy layer is covered with the substrate metal Ru by means of physical vapour depositon. Subsequent annealing to temperatures necessary for surface alloy formation reconstitutes the original Pt (Pd) amount as well as the original atom distribution of the initial equilibrated alloy layer (see picture)

Short-range order in a metal - Organic network

Supramolecular assemblies on surfaces usually possess a long-range order controlled by the shape of the building blocks and the interactions between them. In this paper, we demonstrate that such a building block concept is applicable also for short-range ordered systems when used in combination with Monte Carlo (MC) techniques. Specifically, we focus on a structure that consists of a mixture of metal-organic complexes and organic trimers distributed on a hexagonal lattice. This distribution obeys a short-range order (SRO) governed by hydrogen bonds between the different types of lattice occupants. We show that this SRO, which is directly observed by scanning tunneling microscopy, can be predicted with high accuracy by MC simulations using pairwise interaction energy parameters which were determined by ab initio calculations

Segregation and stability in surface alloys:PdxRu 1-x/Ru(0001) and PtxRu1-x/Ru(0001)

The stability of PdRu/Ru(0001) and PtRu/Ru(0001) surface alloys and the tendency for surface segregation of Pd and Pt subsurface guest metals in these surface alloys is studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Atomic resolution STM imaging and AES measurements reveal that upon overgrowing the surface alloys with a 1-2 monolayer Ru film and subsequent annealing to the temperatures required for initial surface alloy formation, the Ru-covered Pd (Pt) atoms float back to the outermost layer. The lateral distribution of these species is also essentially identical to that of the initial surface alloys, before overgrowth by Ru. In combination, this clearly demonstrates that the surface alloys represent stable surface configurations, metastable only towards entropically favored bulk dissolution, and that there is a distinct driving force for surface segregation of these species. Consequences of these data on the mechanism for surface alloy formation are discussed. Floating in PtRu (PdRu) surface alloys on Ru(0001): The PtRu (PdRu)monolayer surface alloy layer is covered with the substrate metal Ru by means of physical vapour depositon. Subsequent annealing to temperatures necessary for surface alloy formation reconstitutes the original Pt (Pd) amount as well as the original atom distribution of the initial equilibrated alloy layer (see picture)

Growth of an oligopyridine adlayer on Ag(100) - a scanning tunnelling microscopy study

The growth behaviour of the oligopyridine derivative 2-phenyl-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl) pyridine-2-yl) pyrimidine (2,4'-BTP) on Ag(100) in the sub-monolayer regime was investigated by variable temperature scanning tunneling microscopy under ultra-high vacuum conditions. Over the entire coverage range, the molecules are adsorbed in a flat lying configuration, with preferential orientations with respect to the direction of the surface. The azimuth angles are derived using a previously introduced algorithm that fits the positions of the intramolecular N atoms geometrically to the underlying surface lattice ("points-to-lattice fit") [H. E. Hoster et al., Langmuir 2007, 23, 11570], indicating that the orientation of the admolecules and thus of the adllayer structure with respect to the Ag(100) surface lattice is determined by the 2,40-BTP - Ag(100) interaction, while intermolecular interactions are decisive for the structure of the adlayer. The results will be compared to other adsorption systems