Lithium‐ion batteries (LIBs) are promising candidates within the context of the development of novel battery concepts with high energy densities. Batteries with high operating potentials or high voltage (HV) LIBs (>4.2 V vs Li⁺/Li) can provide high energy densities and are therefore attractive in high‐performance LIBs. However, a variety of challenges (including solid electrolyte interface (SEI), lithium plating, etc.) and related safety issues (such as gas formation or thermal runaway effects) must be solved for the practical, widespread application of HV‐LIBs. Most of these challenges arise in the region between the electrodes: the electrolyte region. This review provides an overview of recent development and progress on the electrolyte region, including liquid electrolytes, ionic liquids, gel polymer electrolytes, separators, and solid electrolytes for HV‐LIBs applications. A focus on improving the safety of these systems, with some perspectives on their relative cost and environmental impact, is given. Overall, the new information is encouraging for the development of HV‐LIBs, and this review serves as a guide for potential strategies to improve their safety, allowing the development of HV‐LIBs, including solid‐state batteries, to be accelerated to practical relevance.

The initial formation cycles are critical to the performance of a lithium-ion battery (LIB), particularly in the case of silicon anodes, where the high surface area and extreme volume expansion during cycling make silicon susceptible to detrimental side reactions with the electrolyte. The solid electrolyte interface (SEI) that is formed during these initial cycles serves to protect the surface of the anode from a continued reaction with the electrolyte, and its composition reflects the composition of the electrolyte. In this work, ReaxFF reactive force field simulations were used to investigate the interactions between ether-based electrolytes with high LiTFSI salt concentrations (up to 4 mol/L) and a silicon oxide surface. The simulation investigations were verified with galvanostatic testing and post-mortem X-ray photoelectron spectroscopy, revealing that highly concentrated electrolytes resulted in the faster formation and SEIs containing more inorganic and silicon species. This study emphasizes the importance of understanding the link between electrolyte composition and SEI formation. This ReaxFF approach demonstrates an accessible way to tune electrolyte compositions for optimized performance without costly, time-consuming experimentation.

Herein, the room temperature gas sensing properties of a device fabricated based on an individual gold nanoparticles (AuNPs)-functionalized zinc oxide nanowire (ZnO NW) is reported. The Au-NPs/ZnO nanowires were deposited using the electrochemical approach in a classical three-electrode electrochemical cell. The dual beam focused ion beam/scanning electron microscopy (FIB/SEM) was used to integrate the single nanostructures into gas sensing nanodevices. The results are promising for future applications in monitoring H 2 gas for health care applications and clinical breath analysis.

In this work, an individual nanowire of zinc oxide (ZnO-NW), decorated with gold nanoparticles (Au-NPs/ZnO-NW), was integrated in a nanophotodetector using a dual beam focused electron/ion beam (FIB/SEM) system. Au-NPs/ZnO-NW arrays were synthesized by one-step electrochemical deposition at relative low-temperatures (90 °C). The nanodevice fabricated with a single nanowire Au-NPs/ZnO-NW demonstrated fast detection of UV radiation up to the operating temperature of 120 °C. The improved UV sensing properties of an individual Au-NPs/ZnO-NW compared to a single, undecorated, ZnO NW was explained based on the formation of Schottky barriers at the Au/ZnO NW interface, which resulted in a much more narrowed conduction channel and a lower dark current. These results prove that high-performance hybrid nanomaterials may possess superior electrical, optical and sensing properties and are of great interest for further fundamental studies.

Lithium ion batteries are one of the most promising secondary battery technologies with high gravimetrical and volumetric energy densities, enabling the path towards a green and environmentally friendly future. To further improve the energy density of the battery, much effort is spent in the development of new electrode materials, like silicon and sulfur, to replace the materials with limited specific capacity and critical environmental impact that are currently used. Silicon, with a specific capacity higher than pure lithium (4200 mAh/g vs. 3862 mAh/g [1]), is one of the most promising anode materials being cheap, earth-abundant and less dangerous compared to pure lithium metal anodes. Silicon offers the chance to replace state of the art graphite anodes, which have low specific capacity (372 mAh/g [1]). However, rechargeable silicon anodes still suffer from the intrinsic problems of silicon during cycling, making it unsuitable for battery applications. The huge volume expansion of 400% between the charged and discharged state lead to a pulverization of the silicon anode and consequently poor cycling stability. Since the 1990s many approaches like Si nanoparticles, nanowires or nanotubes, Si thin films or compounds with different metals, metal oxides or carbon lead to an improvement in cycling stability but so far with limited application in real batteries. [1] Here, we present a scalable top down approach where a defined porous micro-structure is etched into silicon wafers. The pores allow enough space in order to cope for the large volume expansion of Si during charging and discharging of the battery. In previous studies, it was already shown that Si microwire anodes could be cycled with 3150 mAh/g for hundreds of cycles without significant capacity. [2][3] Porous silicon can also be fabricated as thick thin films (>30 µm), possessing a defined and adjustable porosity, for use as electrodes with high areal capacity for lithium ion batteries. This generation of silicon anodes has the advantage that it can be processed with cheap silicon material in much larger scale. By the electrochemical top-down approach, the surface of a silicon wafer is porosified and transferred onto copper, which is used as current collector. The use of chemical and electrochemical copper deposition techniques, create a direct ohmic contact without the need of additional, inactive material that only adds to the weight of the anode. This study shows the performance of these porous silicon anodes. By using these anodes, the performance was shown to be almost constant from the 5th to the 100th cycle, with a capacity of 3150 mAh/g and columbic efficiencies around 99%.This novel electrode design is able to counteract the volume expansion problems, and already lead to promising results in the battery performance. To further increase the energy density of lithium ion batteries, cathode materials, like sulfur, are of great interest. Since sulfur is unlithiated, contrary to NMC, NCA and other cathode materials, lithium needs to be incorporated either in the silicon anode or in the cathode. With silicon present as a film, simple prelithiation strategies can be applied, according to Cui et al.[4]. By simply short-circuiting silicon and lithium in presence of an electrolyte, a silicon anode can be prelithiated. Varying time, concentration and other electrochemical and chemical parameters, it is possible to define a certain state of charge of the silicon anode. First results of this simple prelithation strategy demonstrate high capacities and high columbic efficiencies of the silicon anodes, already possible from the first charging cycle, offering the potential to be combined with lithium-free cathodes. [1] X. Zuo, J. Zhu, P. Müller-Buschbaum and Y. Cheng, "Silicon based lithium-ion battery anodes: A chronicle perspective review", 2019. [2] S. Hansen, E. Quiroga-González, J. Carstensen, R. Adelung and H. Föll, "Size-dependent physicochemical and mechanical interactions in battery paste anodes of Si-microwires revealed by Fast-Fourier-Transform Impedance Spectroscopy", Journal of Power Sources, vol. 349, pp. 1-10, 2017. [3] S. Hansen, E. Quiroga-González, J. Carstensen and H. Föll, "Size-dependent cyclic voltammetry study of silicon microwire anodes for lithium ion batteries", 2019. [4] N. Liu, L. Hu, M. McDowell, A. Jackson and Y. Cui, "Prelithiated Silicon Nanowires as an Anode for Lithium Ion Batteries", ACS Nano, vol. 5, no. 8, pp. 6487-6493, 2011.

Crystalline silicon is an ideal anode candidate for lithium ion batteries as it offers a high Li⁺ ion storage capacity, direct current pathway and is a stable and earth abundant element. In order to match the high theoretical energy density of silicon in lithium ion batteries a suitable cathode material is required. Sulfur based cathodes have a high theoretical storage capacity for application in lithium ion batteries, based on the conversion reaction of the cyclic S₈ molecule with lithium to form smaller lithium polysulfides up to Li₂S, and are also cheap and earth abundant. One of the major drawbacks of lithium sulfur cathode materials is the tendency of lithium polysulfides to be dissolved by the electrolyte, which causes the polysulfides to migrate away from the cathode, leading to an overall capacity loss. For application of porous silicon in a full cell lithium ion battery with sulfur it is important to understand the impact the presence of lithium polysulfides can have on the functionality of porous silicon as an anode. In this study porous silicon anodes with thicknesses of 6 µm and 12 µm were cycled in a half cell in the presence of varying concentrations of Li₂S₆ (0 M, 0.017 M and 0.083 M). For the electrolyte with 0.017 M Li₂S₆ the cycling behavior was comparable, or better, than the electrolyte with no polysulfides. The SEI layer formed on the surface of the porous silicon anodes was investigated ex situ with X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy after one, five and ten cycles. It was seen that in the first cycle lithium polysulfides are contained in the SEI and undergo an oxidation reaction to form sulfates over the following cycles. This leads to a more inorganic SEI layer in the presence of polysulfides, especially in the case of the 12 µm porous silicon, and long term cycling stability. The 12 µm porous silicon anode cycled in the presence of 0.083 M Li₂S₆ showed stable cycling behavior over one hundred cycles, with limited capacity loss and coulombic efficiencies of 96.2 % after one hundred cycles.