Performance-Determining Factors for Si–Graphite Electrode Evaluation: The Role of Mass Loading and Amount of Electrolyte Additive

The mass loading of Si–graphite electrodes is often considered as a parameter of secondary importance when testing their electrochemical performance. However, if a sacrificial additive is present in the electrolyte to improve the electrochemical performance, the electrode loading becomes the battery cycle-life-determining factor. The correlation between mass-loading, electrolyte additive, and binder type was investigated by analyzing the cycling behavior of Si–graphite electrodes, prepared with water-based binders, with mass loading ranging from 3 to 9.5 mg cm$^{−2}$ and cycled with FEC electrolyte additive, while keeping electrolyte amount constant. A lower loading was obtained by keeping slurry preparation steps unchanged from binder to binder and resulted in a longer lifetime for some of the binders. When the final loading was kept constant instead, the performance became independent of the binder used. Since such results can lead to the misinterpretation of the influence of electrode components on the cycling stability (and to a preference of one binder over another in our case), we propose that a comparison of long-term electrochemical performance data of Si–graphite electrodes needs to be always collected by using the same mass-loading with the constant electrolyte and additive

Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 1: performance and gas evolution

Rendering the solid electrolyte interphase and the inter-particle connections more resilient to volume changes of the active material is a key challenge for silicon electrodes. The slurry preparation in a buffered aqueous solution offers a strategy to increase the cycle life and capacity retention of silicon electrodes considerably. So far, studies have mostly been focused on a citrate buffer at pH = 3, and therefore, in this study a series of carboxylic acids is examined as potential buffers for slurry preparation in order to assess which chemical and physical properties of carboxylic acids are decisive for maximizing the capacity retention for Si as active material. In addition, the cycling stability of buffer-containing electrodes was tested in dependence of the buffer content. The results were complemented by analysis of the gas evolution using online electrochemical mass spectrometry in order to understand the SEI layer formation in presence of carboxylic acids and effect of high proton concentration

Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 2: a photoelectron spectroscopy study

The mass loading of Si–graphite electrodes is often considered as a parameter of secondary importance when testing their electrochemical performance. However, if a sacrificial additive is present in the electrolyte to improve the electrochemical performance, the electrode loading becomes the battery cycle-life-determining factor. The correlation between mass-loading, electrolyte additive, and binder type was investigated by analyzing the cycling behavior of Si–graphite electrodes, prepared with water-based binders, with mass loading ranging from 3 to 9.5 mg cm-2 and cycled with FEC electrolyte additive, while keeping electrolyte amount constant. A lower loading was obtained by keeping slurry preparation steps unchanged from binder to binder and resulted in a longer lifetime for some of the binders. When the final loading was kept constant instead, the performance became independent of the binder used. Because such results can lead to the misinterpretation of the influence of electrode components on the cycling stability (and to a preference of one binder over another in our case), we propose that a comparison of long-term electrochemical performance data of Si–graphite electrodes needs to be always collected by using the same mass-loading with the constant electrolyte and additive

Potentiostatic lithium plating as a fast method for electrolyte evaluation in lithium metal batteries

One of the most crucial factors to enable metallic lithium anodes is having an electrolyte that allows stable and safe battery cycling, however, the commonly used carbonate electrolytes typically perform poorly, highlighting the need for the development of new electrolyte compositions. Evaluating potential electrolyte candidates is typically a lengthy procedure that does need time-consuming long-term cycling experiments. To speed this process up, we have investigated potentiostatic lithium plating, inspired from hydrogen-pumping performed for fuel cell performance evaluation, as a potential method for fast electrolyte suitability investigation. First, scanning electron microscopy was used to establish a link between lithium surface coverage and measured current response in a model carbonate electrolyte. Afterwards, a selection of carbonate and ether electrolytes was used for validation of our testing procedure, showing that individual, characteristic patterns can be distinguished. Apart from giving an insight into Li transport in each electrolyte, a correlation to physical electrolyte properties can be found. Consequently, our findings may be a first step towards using potentiostatic plating as a fast, easy and high-throughput method to investigate suitability of new electrolyte formulations for lithium metal batteries and beyond.ISSN:0013-4686ISSN:1873-385

Morphological Peculiarities from Lithium Plating and Stripping

Enabling metallic-Li negative electrodes is motivated by a significant increase of energy density, both gravimetric and volumetric (Fig. 1), despite the excess of metallic Li accounted to ensure a stable potential. The projected gain in energy density for post-Li-ion batteries with metallic Li is twice than that possible to achieve with graphite, whereas with current and potential positive electrodes of Li-ion batteries it is about 30 % [1]. However, Li-metal as an anode is prone to dendritic growth and, therefore, is considered an unsafe option. It has been under investigation since early 1970s and the interest declined with the invention of Li-ion battery technology, which was considered safer alternative. However, recently interest in the metallic Li has been again on a sharp rise [2]. There is still insufficient fundamental understanding about the fundamental principles, governing electrochemical lithium plating/stripping, which often results in dendrite growth, electrolyte consumption, other undesired effects. [3] The present study aims to gain a comprehensive fundamental understanding of metallic-Li behaviour upon plating/stripping. As a first step, we performed post-mortem SEM analysis during the first two cycles in various electrolytes, in addition to studying the cycling performance in Li–Cu and symmetric Li–Li cells. Our post-mortem SEM study revealed that Li plates sporadically, where some of the regions are preferred for plating, despite ‘dead’ Li agglomeration on those particular spots, while the other regions are free of Li deposits (Fig. 2). The most interesting morphological changes are obtained during the initial stages of stripping and plating

Identifying Pitfalls in Lithium Metal Battery Characterization

Over the past decade, there has been a revival of research activity on lithium metal batteries (LMBs) as these could be a solution for key challenges of electromobility and the energy revolution. While there is growing consensus in the scientific community that common reporting standards and testing conditions for LMBs have to be established, a vast majority of research activities on lithium metal use lab-dependant testing protocols. For that reason, this publication aims to shed light on various, potentially neglected aspects in battery assembly and testing. Firstly, the long-term cycling, regarding a range of experimental parameters, such as current density, capacity, electrolyte type and its quantity, as well as contribution of the electrode edges, is shown in both symmetric (Li||Li) and asymmetric (Cu||Li) configurations. The second part focuses on the reversibility of lithium thickness during cycling with and without protected electrode edges, investigated by operando dilatometry. By bringing the insights from this parameter study together, we aim to contribute to better experiment design for future LMB studies, as well as a better understanding for the failure mechanism of Li metal anodes

Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 1: performance and gas evolution

Rendering the solid electrolyte interphase and the inter-particle connections more resilient to volume changes of the active material is a key challenge for silicon electrodes. The slurry preparation in a buffered aqueous solution offers a strategy to increase the cycle life and capacity retention of silicon electrodes considerably. So far, studies have mostly been focused on a citrate buffer at pH = 3, and therefore, in this study a series of carboxylic acids is examined as potential buffers for slurry preparation in order to assess which chemical and physical properties of carboxylic acids are decisive for maximizing the capacity retention for Si as active material. In addition, the cycling stability of buffer-containing electrodes was tested in dependence of the buffer content. The results were complemented by analysis of the gas evolution using online electrochemical mass spectrometry in order to understand the SEI layer formation in presence of carboxylic acids and effect of high proton concentration

Prussian Blue Analogue-Sodium-Vanadium Hexacyanoferrate as a Cathode Material for Na-Ion Batteries

Sodium-ion (Na-ion) batteries have been attracting great interest because of a wide range of potential applications and sodium abundance. Yet, the performance of Na-ion electrode materials needs improvement to be able to compete with lithium-ion electrode materials. Here, sodium-vanadium hexacyanoferrate (NaVHCF) is investigated as a cathode active material in rechargeable Na-ion batteries. We explore the electrochemical performance of NaVHCF in a liquid organic electrolyte and demonstrate a high and very stable working potential of around 3.3 V vs Na+/Na, achieving excellent capacity retention of 73% after 200 cycles. Vanadium substitution in a Prussian blue crystal structure can improve the cycle life by acting as a pillar in interstitial spaces. These results represent a step forward in the development of cathode materials for Na-ion batteries.CIMELEP

Electrochemical impedance spectroscopy of a Li–S battery: Part 2. Influence of separator chemistry on the lithium electrode/electrolyte interface

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