A higher energy and power of a lithium ion battery can be achieved with cathode materials operating at a higher voltage.[1, 2]
(NMC, with x + y + z = 1) with its most prominent protagonist LiNi1/3
("1/3-NMC") is regarded as one of the most competitive
cathode materials due to the combination of decent capacity, lesser thermal and electrochemical instability in the charged state and lower cost compared to the well-known LiCoO2
Using 4.3 V vs. Li/Li+
as upper cut-off potential, 1/3-NMC delivers a specific charge of ca. 150 mAh g-1
(at low C-rates) and shows stable cycling performance at
an average discharge potential of 3.86 V vs. Li/Li+
(= ca. 3.7 V cell voltage vs. graphite).
With increasing the cut-off potential from 4.3 to 4.6 V vs. Li/Li+
almost linear growth of the specific charge of ca. 190 mAh g-1
at a slightly higher potential of 3.95 V vs. Li/Li+
can be obtained.
at 4.6 V vs. Li/Li+
inevitably results in a rapid capacity decay. Various failure mechanisms have been discussed in literature so far, including: oxidative decomposition of
the conventional carbonate/LiPF6
increase of the overall battery impedance,
increased transition metal dissolution of the active material
in the electrolyte due to manganese disproportional reaction and acidic attack by HF,[4, 6]
oxygen release from the host structure,[7, 8]
or irreversible phase changes.
In order to solve the problems associated with instabilities at the cathode/electrolyte interface, two approaches are intensively discussed in literature. On the one hand, there is
the design of an electrolyte, which is thermodynamically stable vs. oxidation at the operation potential of the cathode. On the other hand, the addition of small amounts of film-forming
electrolyte additives or the application of surface coatings and modifications of the cathode/electrolyte interface, lead to kinetic stability.
Here we report on novel approaches
for new classes of electrolyte additives that improve the cycling stability of 1/3 NMC (used as model material for other high voltage cathode materials) at elevated cathode potentials,
i.e., metal cation additives and novel HF scavengers.
Parts of this work have been supported by BMW group.
-  R. Wagner; N. Preschitschek; S. Passerini; J. Leker; M. Winter, Journal of Applied Electrochemistry 2013, 43, 481.
-  A. Kraytsberg; Y. Ein-Eli, Advanced Energy Materials 2012, 2, 922.
-  H. Zheng; Q. Sun; G. Liu; X. Song; V. S. Battaglia, Journal of Power Sources 2012, 207, 134.
-  P. Niehoff; M. Winter, Langmuir 2013, 29, 15813.
-  J. Zhou; P. H. L. Notten, Journal of Power Sources 2008, 177, 553.
-  D. R. Gallus; R. Schmitz; R. Wagner; B. Hoffmann; S. Nowak; I. Cekic-Laskovic; R. W. Schmitz; M. Winter, Electrochimica Acta 2014, 134, 393.
-  F. La Mantia; F. Rosciano; N. Tran; P. Novák, Journal of the Electrochemical Society 2009, 156, A823.
-  J. Choi; A. Manthiram, Journal of the Electrochemical Society 2005, 152, A1714.
-  K. Xu, Chemical Reviews 2004, 104, 4303.