Daniel Biro

The aim of manufacturing silicon‐carbon (Si/C) composites for lithium‐ion batteries is to embed silicon particles into a carbon matrix or shell, which results in improved electrical conductivities and cycling stability by avoiding the direct solid electrolyte interphase (SEI) formation on the silicon surfaces. In this study, we explore the production of Si/C composites containing one (single) and two (multiple) carbon shells, achieved through the carbonization of polyacrylonitrile. We thoroughly analyze the carbonization process of polyacrylonitrile and investigate the structural, physical, and electrochemical properties of the resulting Si/C composites. Our findings indicate that the increase of the carbon fraction and the second thermal treatment during the manufacturing of multiple carbon shells (MCS) have a significant impact on the conductivity of the powders, increasing it by one order of magnitude. We also discover that the MCS cover the silicon surface more effectively, as revealed through etching in a NaOH solution and subsequent elemental analysis. The MCS composite, containing 30 wt.% silicon, exhibits the best cycling performance in half‐cells at 0.5 C, with an initial capacity of 776 mAh g⁻¹ and a capacity retention of 83.0 % after 100 cycles.

For large‐scale energy‐storage systems, the aqueous rechargeable zinc–manganese dioxide battery (ARZMB) attracts increasing attention due to its excellent advantages such as high energy density, high safety, low material cost, and environmental friendliness. Still, the reaction mechanism and its influence on the electrolyte's pH are under debate. Herein, a pH buffer concept for ARZMB electrolytes is introduced. Selection criteria for pH buffer substances are defined. Different buffered electrolytes based on a zinc salt (ZnSO₄, Zn(CH₃COO)₂, Zn(CHOO)₂), and pH buffer substances (acetic acid, propionic acid, formic acid, citric acid, 4‐hydrobenzoic acid, potassium bisulfate, potassium dihydrogen citrate, and potassium hydrogen phthalate) are selected and compared to an unbuffered 2 mZnSO₄reference electrolyte using titration, galvanostatic cycling with pH tracking, and cyclic voltammetry. By adding buffer substances, the pH changes can be reduced and controlled within the defined operating window, supporting the Mn²⁺/MnO₂deposition/dissolution mechanism. Furthermore, the potential plateau during discharge can be increased from ≈1.3 V (ZnSO₄) to ≈1.7 V (ZnSO₄ + AA) versus Zn/Zn²⁺and the energy retention from ≈30% after 268 cycles (ZnSO₄) to ≈86% after 494 cycles (ZnSO₄ + AA). Herein, this work can serve as a basis for the targeted design of long‐term stable ARZMB electrolytes.

The energy transition is only feasible by using household or large photovoltaic powerplants. However, efficient use of photovoltaic power independently of other energy sources can only be accomplished employing batteries. The ever-growing demand for the stationary storage of volatile renewable energy poses new challenges in terms of cost, resource availability and safety. The development of Lithium-Ion Batteries (LIB) has been tremendously pushed by the mobile phone industry and the current need for high-voltage traction batteries. This path of global success is primarily based on its high energy density. Due to changing requirements, other aspects come to the fore that require a rebalancing of different technologies in the “Battery Ecosystem”. In this paper we discuss the evolution of zinc and manganese dioxide-based aqueous battery technologies and identify why recent findings in the field of the reaction mechanism and the electrolyte make rechargeable Zn-MnO₂ batteries (ZMB), commonly known as so-called Zinc-Ion batteries (ZIB), competitive for stationary applications. Finally, a perspective on current challenges for practical application and concepts for future research is provided. This work is intended to classify the current state of research on ZMB and to highlight the further potential on its way to the market within the “Battery Ecosystem”, discussing key parameters such as safety, cost, cycle life, energy and power density, material abundancy, sustainability, modelling and cell/module development.

In this paper, the multi-physical simulation workflow from electromagnetics to structural dynamics for a squirrel-cage induction machine is explored. In electromagnetic simulations, local forces and rotor torque are calculated for specific speed-torque operation points. In order to consider non-linearities and interaction with control system as well as transmission, time-domain simulations are carried out. For induction machines, the computational effort with full transient numerical methods like finite element analysis (FEA) is very high. A novel reduced order electro-mechanical model is presented. It still accounts for vibro-acoustically relevant harmonics due to pulse-width modulation (PWM), slotting, distributed winding and saturation effects, but is substantially faster (minutes to hours instead of days to weeks per operation point). The calculated forces acting on the stator teeth as well as the torque acting on the rotor are used as excitations of a structural representation of the electric machine. Selected aspects of the simulation workflow are validated by measurement results.

Upon immersion of a lithium (Li) anode into a diluted 0.05 to 0.20 M dimethoxyethane‐solution of the phosphoric acid derivative (CF₃CH₂O)₂P(O)OH (HBFEP), an artificial solid electrolyte interphase (SEI) is generated on the Li‐metal surface. Hence, HBFEP reacts on the surface to the corresponding Li salt (LiBFEP), which is a Li‐ion conducting inorganic coordination polymer. This film exhibits – due to the reversibly breaking ionic bonds – self‐healing ability upon cycling‐induced volume expansion of Li. The presence of LiBFEP as the major component in the artificial SEI is proven by ATR‐IR and XPS measurements. SEM characterization of HBFEP‐treated Li samples reveals porous layers on top of the Li surface with at least 3 μm thickness. Li−Li symmetrical cells with HBFEP‐modified Li electrodes show a three‐ to almost fourfold cycle‐lifetime increase at 0.1 mA cm⁻² in a demanding model electrolyte that facilitates fast battery failure (1 M LiOTf in TEGDME). Hence, the LiBFEP‐enriched layer apparently acts as a Li‐ion conducting protection barrier between Li and the electrolyte, enhancing the rechargeability of Li electrodes.

In this work, lithium‐ion battery full‐cells based on spruce‐derived hard carbon anodes and an electrochemical pre‐lithiation method are presented in combination with a detailed analysis of full‐cell operation and the lithiation state. The physical and electrochemical properties agree well with those of previous biomass‐derived hard carbon anodes. However, low initial coulombic efficiencies of 65 % represent one of the major challenges of the developed anodes with respect to full‐cell operation. To counteract the initial lithium loss, in‐situ electrochemical pre‐lithiation was conducted, allowing battery operation in the same cell setup without reassembly. Consequently, significantly increased capacities, cycle life, and first cycle coulombic efficiency were obtained in comparison to untreated anodes (195 mAh/g versus 150 mAh/g, state of health (SOH) 80 after 150 cycles versus 70 cycles, and 90 % versus 65 %). In summary, spruce‐based hard carbon has the potential to be an environmentally friendly alternative to standard graphite.

The reaction mechanisms (RM) during cycling of aqueous rechargeable Zn//MnO₂ batteries (ARZIBs) are still controversially discussed. The present study of different acidic electrolyte compositions (0.9 mM H₂SO₄, 0.5 M MnSO₄, 2 M ZnSO₄, 2 M ZnSO₄+0.5 M MnSO₄) and their pH behaviour is therefore designed as an alternative approach to investigate the RM. In operando pH tracking during cycling shows periodic pH changes for each electrolyte, highlighting the role of the pH‐relevant ions OH⁻ and H⁺ in the chemical processes, the major influence of MnO₂ deposition/dissolution mechanisms and the buffering behaviour of the zinc hydroxide sulphate (ZHS) precipitation. Innovative coupled cyclic voltammetry (CV) and pH measurements can link CV redox peaks to a pH change and a corresponding chemical reaction. It was found that a Zn²⁺ (de‐)intercalation has little or no influence on the capacity. The cycling of the SO₄²⁻‐free electrolyte 2 M Zn(CF₃SO₃)₂ underlines the pH‐dependant behaviour of the chemical processes. The results can contribute to the debate of RMs in ARZIBs and other aqueous battery chemistries by introducing a novel measurement technique.