Search

The electrochemical response of layered lithium transition metal oxides LiMO2 [M=Ni, Mn, Co; e. g., Li(Ni0.5Mn0.3Co0.2)O2 (NMC532)] with single‐crystalline architecture to slow and fast charging protocols and the implication of incomplete and heterogeneous redox reactions on the active material utilization during cycling were the subject of this work. The role of the active material size and the influence of the local microstructural and chemical ramifications in the composite electrode on the evolution of heterogeneous state of charge (SOC) distribution were deciphered. For this, classification‐single‐particle inductively coupled plasma optical emission spectroscopy (CL‐SP‐ICP‐OES) was comprehensively supplemented by various post mortem analytical techniques. The presented results question the impact of surface‐dependent failure mechanisms of single crystals for the evolution of SOC heterogeneity and identify the deficient structural flexibility of the composite electrode framework as the main driver for the observed non‐uniform active material utilization. [ABSTRACT FROM AUTHOR]

Porosity is frequently specified as only a value to describe the microstructure of a battery electrode. However, porosity is a key parameter for the battery electrode performance and mechanical properties such as adhesion and structural electrode integrity during charge/discharge cycling. This study illustrates the importance of using more than one method to describe the electrode microstructure of LiNi0.6Mn0.2Co0.2O2 (NMC622)-based positive electrodes. A correlative approach, from simple thickness measurements to tomography and segmentation, allowed deciphering the true porous electrode structure and to comprehend the advantages and inaccuracies of each of the analytical techniques. Herein, positive electrodes were calendered from a porosity of 44-18% to cover a wide range of electrode microstructures in state-of-the-art lithium-ion batteries. Especially highly densified electrodes cannot simply be described by a close packing of active and inactive material components, since a considerable amount of active material particles crack due to the intense calendering process. Therefore, a digital 3D model was created based on tomography data and simulation of the inactive material, which allowed the investigation of the complete pore network. For lithium-ion batteries, the results of the mercury intrusion experiments in combination with gas physisorption/pycnometry experiments provide comprehensive insight into the microstructure of positive electrodes. [ABSTRACT FROM AUTHOR]

Here we present the readily accessible amino acid 4,5-dimethoxy-2-nitrobenzyl- L -cysteine (DNC), as an ultra-low molecular weight gelator (MW = 316 g mol−1). Sonication of DNC in water or organic solvents as well as pH adjustment in water trigger gelation. A diverse set of stimuli (UV irradiation, oxidation, heat or pH change) induce a gel–sol transition. Moreover, the photo-triggered gel–sol transition was used to obtain a controlled cysteine release from the hydrogel. [ABSTRACT FROM AUTHOR]

Lithium ion battery cells operating at high‐voltage typically suffer from severe capacity fading, known as 'rollover' failure. Here, the beneficial impact of Li2CO3 as an electrolyte additive for state‐of‐the‐art carbonate‐based electrolytes, which significantly improves the cycling performance of NCM523 ∥ graphite full‐cells operated at 4.5 V is elucidated. LIB cells using the electrolyte stored at 20 °C (with or without Li2CO3 additive) suffer from severe capacity decay due to parasitic transition metal (TM) dissolution/deposition and subsequent Li metal dendrite growth on graphite. In contrast, NCM523 ∥ graphite cells using the Li2CO3‐containing electrolyte stored at 40 °C display significantly improved capacity retention. The underlying mechanism is successfully elucidated: The rollover failure is inhibited, as Li2CO3 reacts with LiPF6 at 40 °C to in situ form lithium difluorophosphate, and its decomposition products in turn act as 'scavenging' agents for TMs (Ni and Co), thus preventing TM deposition and Li metal formation on graphite. [ABSTRACT FROM AUTHOR]

Layered oxides, particularly including Li[NixCoyMnz]O2 (NCMxyz) materials, such as NCM523, are the most promising cathode materials for high‐energy lithium‐ion batteries (LIBs). One major strategy to increase the energy density of LIBs is to expand the cell voltage (>4.3 V). However, high‐voltage NCM∥ graphite full cells typically suffer from drastic capacity fading, often referred to as "rollover" failure. In this study, the underlying degradation mechanisms responsible for failure of NCM523∥ graphite full cells operated at 4.5 V are unraveled by a comprehensive study including the variation of different electrode and cell parameters. It is found that the "rollover" failure after around 50 cycles can be attributed to severe solid electrolyte interphase growth, owing to formation of thick deposits at the graphite anode surface through deposition of transition metals migrating from the cathode to the anode. These deposits induce the formation of Li metal dendrites, which, in the worst cases, result in a "rollover" failure owing to the generation of (micro‐) short circuits. Finally, approaches to overcome this dramatic failure mechanism are presented, for example, by use of single‐crystal NCM523 materials, showing no "rollover" failure even after 200 cycles. The suppression of cross‐talk phenomena in high‐voltage LIB cells is of utmost importance for achieving high cycling stability. [ABSTRACT FROM AUTHOR]

Graphite Lithium-Ion Cells: On the Beneficial Impact of Li2CO3 as Electrolyte Additive in NCM523 Graphite Lithium Ion Cells Under High-Voltage Conditions (Adv. Lithium carbonate, lithium difluorophosphate, lithium ion cells, lithium metal plating, rollover failure, electrolyte additives Keywords: electrolyte additives; lithium carbonate; lithium difluorophosphate; lithium ion cells; lithium metal plating; rollover failure EN electrolyte additives lithium carbonate lithium difluorophosphate lithium ion cells lithium metal plating rollover failure 1 1 1 03/13/21 20210311 NES 210311 In article number 2003756, Martin Winter, Tobias Placke, and co-workers address challenges related to the high-voltage operation of NCM523 graphite lithium-ion cells, suffering from transition metal (TM) dissolution/deposition, which subsequently induces capacity fading. [Extracted from the article]

Front Cover: Exploiting the Degradation Mechanism of NCM523 Graphite Lithium-Ion Full Cells Operated at High Voltage (ChemSusChem 2/2021) Keywords: lithium-ion batteries; degradation mechanisms; electrode materials; metal deposition; single-crystals EN lithium-ion batteries degradation mechanisms electrode materials metal deposition single-crystals 487 487 1 01/28/21 20210121 NES 210121 B The Front Cover b shows the cross-talk phenomena in high-voltage NCM523 graphite lithium ion battery cells, that is, the dissolution of transition metals (Mn, Co, Ni) from the NCM523 cathode and subsequent deposition at the graphite anode. Lithium-ion batteries, degradation mechanisms, electrode materials, metal deposition, single-crystals. [Extracted from the article]

Invited for this month′s cover is the group of Tobias Placke and Martin Winter at the MEET Battery Research Center (University of Münster). The image shows the failure mechanism of high‐voltage operated NCM523 || graphite lithium‐ion cells, that is, the dissolution of transition metals (Mn, Co, Ni) from the NCM523 cathode and subsequent deposition at the graphite anode, resulting in formation of Li metal dendrites. The Full Paper itself is available at 10.1002/cssc.202002113. [ABSTRACT FROM AUTHOR]