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We report on interphase modification by in situ generated protons (H+) via electropolymerization. The protons are released from oxidative electropolymerization of indole-3-carboxylic acid (InAc) us...

The ever-increasing demand for electrical energy storage technologies triggered by the demands for consumer electronics, stationary energy storage systems and especially the rapidly growing market of electro mobility boosts the need for cost-effective, highly efficient and highly performant rechargeable battery systems. After the successful implementation of lithium ion batteries (LIBs) in consumer electronics and electric vehicles, there is still a need for further improvements in terms of energy and power densities, safety, cost and lifetime. In the last decades, a large battery research community has evolved, developing all kinds of new battery materials, e.g., positive and negative electrode active materials for different cell chemistries, electrolytes, related auxiliary (inactive) materials and their constituents. Different battery cell setups, including so-called “half-cell”, “symmetrical-cell” and “full-cell” setups as well as two-electrode or three-electrode configurations, are described in the literature to be used in the laboratory for the electrochemical characterization of battery components like electrode materials and electrolytes. Typically, all cell setups display certain limitations or issues concerning their application for the parameter determination of battery materials. In this review article, we highlight the advantages but also the limitations of different cell setups, with special focus on two- and three-electrode configurations with or without the help of “auxiliary” excess capacity Li metal electrodes. We point out possible mistakes and/or misinterpretations and give the reader recommendations, i.e., a guide for the right choice of the cell setup/configuration appropriate for the intended aim of the electrochemical investigation.

In this work, carbon nanospheres (CS) are prepared by hydrothermal synthesis using glucose as precursor, followed by a subsequent carbonization step. By variation of the synthesis parameters, CS pa...

Pre-lithiation of anode materials can be an effective method to compensate active lithium loss which mainly occurs in the first few cycles of a lithium ion battery (LIB), due to electrolyte decomposition and solid electrolyte interphase (SEI) formation at the surface of the anode. There are many different pre-lithiation methods, whereas pre-lithiation using metallic lithium constitutes the most convenient and widely utilized lab procedure in literature. In this work, for the first time, solid state nuclear magnetic resonance spectroscopy (NMR) is applied to monitor the reaction kinetics of the pre-lithiation process of graphite with lithium. Based on static 7Li NMR, we can directly observe both the dissolution of lithium metal and parallel formation of LiCx species in the obtained NMR spectra with time. It is also shown that the degree of pre-lithiation as well as distribution of lithium metal on the electrode surface have a strong impact on the reaction kinetics of the pre-lithiation process and on the remaining amount of lithium metal. Overall, our findings are highly important for further optimization of pre-lithiation methods for LIB anode materials, both in terms of optimized pre-lithiation time and appropriate amounts of lithium metal.

Active lithium loss (ALL) resulting in a capacity loss (QALL), which is caused by lithium consuming parasitic reactions like SEI formation, is a major reason for capacity fading and, thus, for a reduction of the usable energy density of lithium-ion batteries (LIBs). QALL is often equated with the accumulated irreversible capacity (QAIC). However, QAIC is also influenced by non-lithium consuming parasitic reactions, which do not reduce the active lithium content of the cell, but induce a parasitic current. In this work, a novel approach is proposed in order to differentiate between QAIC and QALL. The determination of QALL is based on the remaining active lithium content of a given cell, which can be determined by de-lithiation of the cathode with the help of the reference electrode of a three-electrode set-up. Lithium non-consuming parasitic reactions, which do not influence the active lithium content have no influence on this determination. In order to evaluate this novel approach, three different anode materials (graphite, carbon spheres and a silicon/graphite composite) were investigated. It is shown that during the first charge/discharge cycles QALL is described moderately well by QAIC. However, the difference between QAIC and QALL rises with increasing cycle number. With this approach, a differentiation between “simple” irreversible capacities and truly detrimental “active Li losses” is possible and, thus, Coulombic efficiency can be directly related to the remaining useable cell capacity for the first time. Overall, the exact determination of the remaining active lithium content of the cell is of great importance, because it allows a statement on whether the reduction in lithium content is crucial for capacity fading or whether the fading is related to other degradation mechanisms such as material or electrode failure.

In this work, silicon/carbon composites are synthesized by forming an amorphous carbon matrix around silicon nanoparticles (Si-NPs) in a hydrothermal process. The intention of this material design is to combine the beneficial properties of carbon and Si, i.e., an improved specific/volumetric capacity and capacity retention compared to the single materials when applied as a negative electrode in lithium-ion batteries (LIBs). This work focuses on the influence of the Si content (up to 20 wt %) on the electrochemical performance, on the morphology and structure of the composite materials, as well as the resilience of the hydrothermal carbon against the volumetric changes of Si, in order to examine the opportunities and limitations of the applied matrix approach. Compared to a physical mixture of Si-NPs and the pure carbon matrix, the synthesized composites show a strong improvement in long-term cycling performance (capacity retention after 103 cycles: ≈55% (20 wt % Si composite) and ≈75% (10 wt % Si composite)), indicating that a homogeneous embedding of Si into the amorphous carbon matrix has a highly beneficial effect. The most promising Si/C composite is also studied in a LIB full cell vs a NMC-111 cathode; such a configuration is very seldom reported in the literature. More specifically, the influence of electrochemical prelithiation on the cycling performance in this full cell set-up is studied and compared to non-prelithiated full cells. While prelithiation is able to remarkably enhance the initial capacity of the full cell by ≈18 mAh g−1, this effect diminishes with continued cycling and only a slightly enhanced capacity of ≈5 mAh g−1 is maintained after 150 cycles.

In order to meet the sophisticated demands for large-scale applications such as electro-mobility, next generation energy storage technologies require advanced electrode active materials with enhanced gravimetric and volumetric capacities to achieve increased gravimetric energy and volumetric energy densities. However, most of these materials suffer from high 1st cycle active lithium losses, e.g., caused by solid electrolyte interphase (SEI) formation, which in turn hinder their broad commercial use so far. In general, the loss of active lithium permanently decreases the available energy by the consumption of lithium from the positive electrode material. Pre-lithiation is considered as a highly appealing technique to compensate for active lithium losses and, therefore, to increase the practical energy density. Various pre-lithiation techniques have been evaluated so far, including electrochemical and chemical pre-lithiation, pre-lithiation with the help of additives or the pre-lithiation by direct contact to lithium metal. In this review article, we will give a comprehensive overview about the various concepts for pre lithiation and controversially discuss their advantages and challenges. Furthermore, we will critically discuss possible effects on the cell performance and stability and assess the techniques with regard to their possible commercial exploration.

Lithium consuming parasitic reactions which induce active lithium loss (ALL) are a major reason for capacity fading in lithium ion batteries (LIBs).[1, 2] As a consequence of capacity fading, the usable energy density is reduced. Typically, the ALL is set equal to the accumulated irreversible capacity (sum of the differences between charge and discharge capacity in each cycle, AIC). However, regarding the AIC it is known that it includes all parasitic reactions which generate a parasitic current. Hence, the AIC cannot be directly equated with ALL. Due to this, we proposed a novel approach in the following named as IRLC method, which is based on the remaining active lithium content of the cell, in order to determine the ALL with a higher accuracy. Therefore, a cell with a three electrode set-up is cycled and afterwards the positive electrode is de-lithiated with help of the former reference electrode in order to obtain the remaining active lithium content. Finally, the ALL can be calculated by using the remaining and the initial active lithium content. In order to evaluate the IRLC method we investigated different anode materials. It can be shown that within the first cycles the ALL can be described moderately well with help of AIC. However, with increasing cycle number the difference between ALL and AIC increases, most likely attributed to the fact that the impact of SEI formation and repair becomes smaller in comparison to other parasitic reactions which do not consume lithium. Furthermore, one additional advantage of the IRLC method is that it allows a statement whether the reduction of lithium content is crucial for capacity fading or whether the fading is related to host material losses or other degradation mechanisms e.g. a higher charge transfer resistances due to a growing SEI film. 1. Krueger, S., et al., How Do Reactions at the Anode/Electrolyte Interface Determine the Cathode Performance in Lithium-Ion Batteries? Journal of the Electrochemical Society, 2013. 160(4): p. A542-A548. 2. Vetter, J., et al., Ageing mechanisms in lithium-ion batteries. Journal of Power Sources, 2005. 147(1-2): p. 269-281.

A major disadvantage of anode materials, in particular high-capacity materials like silicon, is the high irreversible lithium loss attributed to solid electrolyte interphase (SEI) formation triggered by electrolyte decomposition. For this reason, pre-lithiation of anode materials is getting more attention. However, therefore the exact amount of irreversible lithium loss is needed. Even if the SEI formation presents the major part of lithium loss, there are some other parasitic reactions which can lead to irreversible lithium loss, e.g., positive electrode degradation or the reaction of lithium ions with water. In addition, there are also some parasitic reactions which do not change the active lithium content of the cell but still possess an impact on the capacity or are able to transfer lithium ions out of the electrolyte into the electrodes. Typically, the irreversible lithium loss is set equal with the accumulated irreversible capacity (sum of the differences between charge and discharge capacity in each cycle). It can be shown that this approach possesses a relatively low accuracy and one can only get an acceptable estimation of the first cycles. With increasing cycle number, the determination of the irreversible lithium loss with help of the accumulated irreversible capacity becomes more inaccurate because the impact of SEI formation and regeneration becomes smaller in comparison to other parasitic reactions. In this work, a novel approach is investigated in order to determine the irreversible lithium loss with high accuracy. Therefore, “pseudo full cells” are built, while the term “pseudo full cell” refers to a cell with an oversized cathode (in terms of capacity). These cells are cycled like “real” full cells and afterwards the positive electrode is de-lithiated with help of the reference electrode in order to determine the remaining active lithium content of the cell. Finally, the exact amount of irreversible lithium loss can be determined as difference between initial and remaining active lithium content.