Nickel‐reiche Lithium‐Übergangsmetall‐Schichtverbindungen für Hochenergie‐Lithiumionenakkumulatoren

Abstract

Für Lithiumionenakkumulatoren mit hohen Energiedichten gibt es eine überaus große Nachfrage im Bereich tragbarer elektronischer Geräte und Elektrofahrzeuge. Weil die Energiedichten der Lithiumionenakkumulatoren vor allem vom verwendeten Kathodenmaterial abhängen, wird nach alternativen Kathodenmaterialien mit besserer Lithiumnutzung und höherer spezifischer Energiedichte intensiv geforscht. Insbesondere Ni‐reiche Lithium‐Übergangsmetalloxid‐Schichtverbindungen können höhere Kapazitäten als das klassische LiCoO2 bei geringeren Kosten bereitstellen. Sie gelten als besonders vielversprechend, aber sie bergen noch große Herausforderungen bezüglich Lebensdauer, Wärmestabilität und Sicherheit. Hier wird umfassend beschrieben, wie gezielte Veränderungen an der Struktur oder an den Grenzflächen in einer Leistungssteigerung von Ni‐reichen Kathodenmaterialien resultieren. Die zugrundeliegenden Mechanismen und die noch zu bewältigenden Herausforderungen werden ebenfalls diskutiert.

Learning from Electrochemical Data: Simple Evaluation and Classification of LiMO2‐type‐based Positive Electrodes for Li‐Ion Batteries

“…However, the complete absence of Mn 4+ and Ni 2+ in NCA is not favorable for its structural stability. It is assumed that small amounts of Mn 4+ and Ni 2+ ions (and thus the resulting Li + /Ni 2+ cation mixing) are even beneficial for structural stability, which is in accordance with the literature . Every LiMO 2 composition undergoes a characteristic structural transformation upon reaching the critical Li + ‐ion extraction amount .…”

“…As displayed in Figure , the implementation of additional Co 3+ to yield NMC442 and NMC111 results in increased structural stability relative to Co‐free NMC550 with regard to the reversible extractable amount of Li + ions. This leads to the conclusion that a decrease in undesired Ni 2+ ions is beneficial for the stability and specific energy of the resulting LiMO 2 material, even though this is associated with a decrease in beneficial Mn 4+ ions and with an increase in chemically instable Co 3+ …”

“…Mn 4+ is only present in combination with at least the same amount of divalent Ni (Ni 2+ ) within the LiMO 2 structure. According to crystal‐field theory, Mn 3+ and Ni 3+ undergo electron exchange, which results in Ni 2+ and desired Mn 4+ . In other words, the total capacity remains constant but there is a shift in electrons from Mn to Ni, which results in additional electrochemical activity of Ni and inactivity of Mn.…”

“…For the same LiMO 2 ‐type electrode material, the amount of extracted Li + is proportional to the applied charge cut‐off potential; thus, it can be concluded that the structural stability of LiMO 2 ‐type electrodes is primarily determined by the amount of extracted Li + ions . In the literature, the structural stability and stability versus transition‐metal dissolution of various, that is, not the same cathode materials, positive electrode material has been compared and discussed as a function of the applied charge cut‐off potential . However, a comparison between different LiMO 2 ‐type electrode materials with regard to their structural stability is only reasonable as a function of the amount of extracted Li + ions.…”

The Role of Zr Doping in Stabilizing Li[Ni0.6Co0.2Mn0.2]O2 as a Cathode Material for Lithium‐Ion Batteries

“…Owing to its simple concentration ratios of transition metal (TM) ions, the LNCM 211s tructure better describes the TM-ion disordered LNCM than the LNCM 622 structure fort he same size of supercells. 19 .T ov erify the validity of our interpretationont he XRD studies and investigate the influence of cation mixing on the layered LNCM structure, the free energy and detailed structuralchange accompanied by Ni-and Zr-ion migration into the Li-ion layer were compared.A st he Ni ion migrates more vigorously into the Li-ion layer compared with the Co and Mn ions, [6,7,46] only Niand Zr-ion migration were considered. For Zr-doped LNCM (Figure 6b), several Ni ions were replaced with Zr ions.…”