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The increase of specific energy of current Li ion batteries via further increase of the cell voltage, for example, to 4.5 V is typically accompanied by a sudden and rapid capacity fade, known as "rollover" failure. This failure is the result of Li dendrite formation triggered in the course of electrode cross‐talk, that is, dissolution of transition metals (TMs) from the cathode and deposition on the anode. It is shown herein, that the elimination of ethylene carbonate (EC) from a state‐of‐the‐art electrolyte, that is, from 1.0 m LiPF6 in a 3:7 mixture of EC and ethyl methyl carbonate prevents this failure in high‐voltage LiNi0.5Co0.2Mn0.3O2||graphite cells, even without any electrolyte additives. While the oxidative stability on the cathode side is similar in both electrolytes, visible by a decomposition plateau at 5.5 V versus Li|Li+ during charge, the anode side in the EC‐free electrolyte reveals significantly less TM deposits and Li metal dendrites compared to the EC‐based electrolyte. The beneficial effect of EC‐free electrolytes is related to a significantly increased amount of degraded LiPF6 species, which effectively trap dissolved TMs and suppress the effect of detrimental cross‐talk, finally realizing rollover‐free performance under high voltage conditions. [ABSTRACT FROM AUTHOR]

Li-Ion Batteries: Understanding the Outstanding High-Voltage Performance of NCM523||Graphite Lithium Ion Cells after Elimination of Ethylene Carbonate Solvent from Conventional Electrolyte (Adv. Conventional electrolytes, ethylene carbonate-free, high voltage, Li ion batteries, rollover fading Keywords: conventional electrolytes; ethylene carbonate-free; high voltage; Li ion batteries; rollover fading EN conventional electrolytes ethylene carbonate-free high voltage Li ion batteries rollover fading 1 1 1 04/19/21 20210415 NES 210415 In article number 2003738, Martin Winter, Tobias Placke, Johannes Kasnatscheew and co-workers report that a simple elimination of ethylene carbonate (EC) from conventional electrolytes counterintuitively boosts the high voltage performance in Li-ion batteries. [Extracted from the article]

Previous studies have shown that electrolyte additives based on metals and semimetals (LiBOB, Mg(TFSI) 2 , Al(TFSI) 3 ) as well as additives containing trimethylsiloxyl (TMS) groups as ligands can have positive impact on the cycling performance of lithium ion battery cells due to solid electrolyte interphase (SEI) and/or cathode electrolyte interphase (CEI) film forming properties and/or scavenging properties towards acidic impurities. In this study, both active functionalities (metal core and trialkylsiloxy based ligands) were combined into one using Al, Ti and B as metal cores combined with TMS ligands (M(TMS) x ). All investigated additives M(TMS) x were able to improve the cycling performance regarding Coulombic efficiency, energy efficiency and capacity retention of LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111)/Li half-cells and NCM111/graphite full-cells at high potentials (>4.3 V vs. Li/Li + ). The formed CEI was studied by means of electrochemical impedance spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The obtained results indicate that the investigated additives are either actively incorporated into the formed CEI layer (in case of Al, Ti as metal core) or interacting with decomposition products (in case of B as metal core) resulting in lower charge-transfer impedance and hence improved long-term cycling behavior. [ABSTRACT FROM AUTHOR]