The 1st cycle Coulombic efficiency (CE) of LiNi1/3Co1/3Mn1/3O2 (NCM) at 4.6 V vs. Li/Li(+) has been extensively investigated in NCM/Li half cells. It could be proven that the major part of the observed overall specific capacity loss (in total 36.3 mA h g(-1)) is reversible and induced by kinetic limitations, namely an impeded lithiation reaction during discharge. A measure facilitating the lithiation reaction, i.e. a constant potential (CP) step at the discharge cut-off potential, results in an increase in specific discharge capacity of 22.1 mA h g(-1). This capacity increase during the CP step could be proven as a relithiation process by Li(+) content determination in NCM via an ICP-OES measurement. In addition, a specific capacity loss of approx. 4.2 mA h g(-1) could be determined as an intrinsic reaction to the NCM cathode material at room temperature (RT). In total, less than 10.0 mA h g(-1) (=28% of the overall capacity loss) can be attributed to irreversible reactions, mainly to irreversible structural changes of NCM. Thus, the impact of parasitic reactions, such as oxidative electrolyte decomposition, on the irreversible capacity is negligible and could also be proven by on-line MS. As a consequence, the determination of the amount of extracted Li(+) ("Li(+) extraction ratio") so far has been incorrect and must be calculated by the charge capacity (=delithiation amount) divided by the theoretical capacity. In a NCM/graphite full cell the relithiation amount during the constant voltage (CV) step is smaller than in the half cell, due to irreversible Li(+) loss at graphite.

In a lithium ion battery, balancing of active materials is an essential requirement with respect to safety and cycle life. However, capacity oversizing of negative electrodes is associated with decrease of specific energy/energy density. In this work, the required trade-off between maximized specific energy and minimized risk of lithium plating is thoroughly investigated by evaluating underlying potential/voltage curves. The adjustment of targeted state of charge (SOC) for both, positive and the negative electrode, can be achieved by intentional selection of only two parameters: negative/positive electrode active mass ratio and charge cutoff voltage. For investigation and controlling reasons, specific charge capacity reveals to be a simple but effective tool to indirectly predict electrode potentials. While cell kinetics/overvoltage are influenced by both electrodes, specific capacity losses are affected by a single electrode. The latter only correlate with negative electrode's BET surface area as long as specific capacity losses of negative electrodes are higher compared to positive electrodes. Based on these insights, a more systematic performance and safety optimized handling of the trade-off between specific energy and safety risk can be realized.

The practically available specific energy of Li ion batteries (LIB) is highly depending on the used specific charge/discharge current, since the respective overpotentials of each electrode affect the two vital specific energy parameters, specific capacity and voltage. Focusing on the positive composite electrode as the specific energy bottleneck, the overall nature of the overpotential is discussed for the LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) active material. It is shown that the characteristic overpotentials during charge (delithiation) and discharge (lithiation) is state of charge (SOC) and depth of discharge (DOD) dependent, respectively. It was demonstrated that the discharge characteristics are intertwined with the previous charge conditions, particularly with the charging time and the specific charge capacity. Increasing both in parallel can even lead to a deterioration of the subsequent specific discharge capacity. Furthermore, Li + transport pathways within the NCM composite electrode are discussed and their influence on the observed overpotential evaluated. Changes of the overpotential are found to be mainly associated with changes within the NCM crystal structure, which is experimentally supported by the correlation of the SOC dependent overpotential with the XRD determined c-axis lattice parameter. Consequently, the Li + transport within the active material is mostly responsible for limiting the practically available specific energy.

Increasing the operation voltage of electrochemical energy storage devices is a viable measure to realize higher specific energies and energy densities. A sufficient oxidative stability of electrolytes is the predominant requirement for successful high voltage applicability. The common method to investigate oxidative stability of LIB electrolytes is related to determination of the electrochemical stability window (ESW), on e.g. Pt or LiMnO electrodes. However, the transferability of the obtained results to practical systems is questionable for several reasons. In this work, we evaluated the validity of the potentiodynamic based ESW method by comparing the obtained data with the results of galvanostatic based techniques, applied on commercial positive electrodes. We demonstrated that the oxidative stabilities, determined by the two techniques, are in good accordance with each other. However, the investigation of electrolytes being incompatible to Li metal, renders conventional ESW measurements useless when metallic Li is used as counter - and reference electrode in the ESW setup. For this reason, we introduced an alternative setup based on LiTiO full cells. On the example of a butyronitrile-based electrolyte, we finally demonstrated that this electrolyte is not only reductively but also oxidatively less stable than common LiPF/organic carbonate based electrolytes.