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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]

We report on the reversible (de)intercalation of TFSI− anions from a Mg‐based ionic liquid electrolyte, Mg(TFSI)2 in Pyr14TFSI, in graphite ∥ activated carbon hybrid dual‐ion capacitor (DIC) cells. The role of different pseudo reference electrodes (PREs) including Ag‐wire and Li metal is discussed regarding the comparability of different battery cells. We show that an Ag‐wire PRE is not suitable for the designated purpose, while the use of a Li metal PRE results in high reproducibility. Mg‐based DIC cells are compared with cells based on pure Pyr14TFSI and LiTFSI‐Pyr14TFSI electrolytes, and with graphite ∥ Li metal dual‐ion cells employing LiTFSI‐Pyr14TFSI. At 5.2 V vs. Li|Li+, Mg‐containing DIC cells reveal an improved performance compared to Li‐based cells, i. e. higher capacity (87 vs. 85 mAh g−1) and higher Coulombic efficiency (98 vs. 96 %). These results may pave the way to further studies and performance improvements of Mg‐based batteries and to hybrid DIC chemistries with other cations, especially multi‐valent ones. [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]

A major challenge for longer life lithium ion batteries is the irreversible loss of active lithium during the first charge/discharge cycles, which consequently reduces the practical energy density in cells without lithium ion excess. This degradation mechanism is especially detrimental for high-capacity anodes with low first cycle Coulombic efficiency. The present study aims for overcoming this challenge by pre-lithiating the high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) positive electrode material with a simple and easily scalable chemical process via stirring LNMO particles with Li metal in boiling pentanol. The subsequent structural and electrochemical analysis proves the electrochemical accessibility of the “extra” lithium and long-term cycling stability. Charging/discharging the material in LNMO || graphite (C) and LNMO || silicon/carbon (Si/C) cells demonstrates positive effects on discharge capacity, energy and capacity retention. Furthermore, the additional active lithium is used to increase the specific capacity of the cells by including the lower potential region of LNMO through application of a lower cell cutoff voltage of 2.4 V. Comparing “standard” LNMO || C with pre-lithiated LNMO || Si/C cells (both charged/discharged at standard cutoff voltages of 3.0 and 4.95 V), improvements in specific energy of >21% can be identified. [ABSTRACT FROM AUTHOR]

PEO-based solid polymer electrolytes typically show limited capability for the suppression of Li metal dendrites, which is mainly attributed to their low mechanical strength. To tackle this issue, we improved the mechanical strength of a ternary solid polymer electrolyte (TSPE: PEO-LiTFSI-Pyr14TFSI) by integratingCelgard 2500 separator as a high modulus domain. The Celgard-reinforced TSPE (CgTSPE) presents a significantly higher elastic modulus (223MPa) than TSPE (0.2MPa) at 60°C, which in result leads tomore lithium anode utilization. Specifically, the Columbic efficiency of Li electrodeposition/dissolution during cycling in Li|CgTSPE|Cu cells (90%) is distinctly higher than in Li|TSPE|Cu (30%). Furthermore, the cycling of Li||Li symmetric cells with CgTSPE displays an improved cycling stability, due to the presence of Celgard, in which high surface area lithium (HSAL), e.g., dendrite formation is suppressed. Operando electrochemical dilatometry (ECD) analysis as well as post mortem surface analysis with SEM reveal the formation of "dead lithium" and cavities under an areal capacity utilization of 5 mAh/cm2. It is also suggested by the cycling behavior of the Li||Li cell with high areal capacity utilization that lithium surface treatment is required to completely eliminate the formation of "dead lithium" and of cavities. [ABSTRACT FROM AUTHOR]

Effective SEI Formation via Phosphazene-Based Electrolyte Additives for Stabilizing Silicon-Based Lithium-Ion Batteries (Adv. Keywords: electrolyte additives; lithium-ion batteries; phosphazene compounds; silicon anodes; solid electrolyte interphase EN electrolyte additives lithium-ion batteries phosphazene compounds silicon anodes solid electrolyte interphase 1 1 1 07/18/23 20230708 NES 230708 B Lithium-Ion Batteries b The cover shows cyclic fluorinated phosphazene compounds as additional stabilizing additives in a state-of-the-art electrolyte for SiO SB I x i sb /C-based lithium ion battery cells. Electrolyte additives, lithium-ion batteries, phosphazene compounds, silicon anodes, solid electrolyte interphase. [Extracted from the article]