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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]

Allylboronic acid pinacol ester (ABPE) was investigated as shutdown overcharge additive to increase the intrinsic safety of lithium ion cells during operation at elevated charge cutoff potentials up to 4.5 V vs. Li/Li+. It was demonstrated that the additive had no negative influence on the cycling performance of LiNi1/3Co1/3Mn1/3O2 (NMC-111)/graphite full cells operated in a standard operation voltage range between 2.5 V and 4.2 V. Electrochemical impedance spectroscopy was used to study the influence of the electrolyte additive on the impedance before and after overcharge and concomitant cell shutdown. Thereby, an immense increase in the charge transfer resistance after electrode shutdown was observed, thus, hinting to the formation of a lithium ion-insulating layer on the positive electrode surface. To further elucidate the working principle of the shutdown additive, surface investigations by means of scanning electron microscopy and X-ray photoelectron spectroscopy were carried out. The existence of a surface layer consisting mainly of polymeric species was proven. The presented results open up a new family of compounds for overcharge protection. [ABSTRACT FROM AUTHOR]

In this work, non-graphitized carbon black and graphitized carbon blacks were analyzed with regard to their performance as conductive additives in high voltage spinel Cr-doped LiNi0.5Mn1.5O4 composite cathode electrodes. The degree of graphitization was investigated by X-ray diffraction. X-ray photoelectron spectroscopy was used to investigate the carbon black surface species and their alteration upon graphitization, as well as to the post mortem analysis of the composite cathodes. It was found that the cells with graphitized carbon blacks showed much longer cycling life. The depletion of the functional groups at the carbon black surface by graphitization apparently reduced the side reactions in the composite electrodes. Due to their superior performance, graphitized carbon black should be considered as substitute for the standard carbon black additives in the high voltage cathode electrodes. [ABSTRACT FROM AUTHOR]