Li + -Ion Extraction/Insertion of Ni-Rich Li 1 + x (Ni y Co z Mn z ) w O 2 (0.005 < x < 0.03; y :z = 8:1, w  1) Electrodes: In Situ XRD and Raman Spectroscopy Study Chandan Ghanty,* [a] Boris Markovsky,* [a] Evan M. Erickson, [a] Michael Talianker, [b] Ortal Haik, [a] Yosef. Tal-Yossef, [a] Albert Mor, [a] Doron Aurbach, [a] Jordan Lampert, [c] Aleksei. Volkov, [c] Ji-Yong Shin, [c] Arnd. Garsuch, [c] Frederick Francois Chesneau, [c] and Christoph Erk [c] 1. Introduction Recently, lithiated transition-metal oxides LiNi x Co y Mn z O 2 (x + y + z = 1) with moderate (x = 0.3–0.5) or high (x = 0.6–0.8) nickel contents for positive electrodes in Li-ion batteries have received significant attention from research communities, owing to their relatively high capacity and low cost compared to, for instance, LiCoO 2 . As a result, Li–Ni–Co–Mn–O 2 ternary systems of the R-3m space group have been developed. Among the members of this ternary family, the Li- Ni 0.8 Co 0.1 Mn 0.1 O 2 cathode material with a high nickel content has been reported to show discharge capacities of around 200 mAh g 1 with scattered cyclability and rate capabilities. [1] Several research groups, for instance, [2] have shown that NCM (Ni,Co,Mn) cathode materials with high Ni contents (x > 0.6) possess the advantages of mono-metal oxides LiCoO 2 , LiNiO 2 , or LiMnO 2 , and exhibit higher capacities as well as lower toxici- ties. At the same time, the electrochemical behavior of such cathode materials depends strongly on the synthesis method, particle morphology and size, crystallinity, purity, and cation mixing. [1a] Poor thermal stability of Ni-rich NCM is also a possi- ble concern for its practical application. Ni-rich NCM cathode materials are known to undergo structural phase transforma- tions during Li + extraction/insertion (charge/discharge) and the implications of these transformations on electrochemical performances are poorly understood. Moreover, there are not many direct investigations on Ni-rich NCM cathode materials to detect the above phenomena by using in situ techniques [3] and, hence, further scientific analysis is necessary to under- stand the limitations of these materials for electric vehicle (EV) and hybrid EV applications. In situ XRD measurements were used to study LiNiO 2 , Li- Co 0.2 Ni 0.8 O 2 , [4] LiNi 0.5 Co 0.3 Mn 0.2 O 2 , [5] as well as LiNi x Co y Mn z O 2 com- pounds with various Co contents [6] of layered-type structures. An interesting finding in Ref. [5] is that the formation of hexag- onal phase H3 from hexagonal phase H2 upon Li + extraction from moderately Ni-rich LiNi 0.5 Co 0.3 Mn 0.2 O 2 electrodes is the main source of the poor electrochemical cycling behavior. These authors concluded that the suppression of hexagonal phase H3 (at 4.7 V) can result in long-term cyclability and a high reversible capacity. For spinel-type materials, Zaghib and co-workers [7] recently studied phase evolution in 5 V spinel LiMn 1.5 Ni 0.5 O 4 cathodes doped with various metals (Co, Al, Cu, Mg) by using in situ XRD measurements. They demonstrated that partial substitution of Ni with Co resulted in the best elec- We present the results of our in situ X-ray diffraction (XRD) and Raman spectroscopy measurements for the first Li-ion extrac- tion/insertion (charge/discharge) processes of nickel-rich Li 1 +x (Ni y Co z Mn z ) w O 2 (0.005 < x < 0.03; y :z = 8:1, w is nearly 1) electrodes in Li cells. These cells were of a special design that provide in situ (at-work) measurements during electrochemical polarization and can be used for regular cycling tests of practi- cal Li-battery electrodes. By using XRD measurements, it was established that, upon Li + extraction, these cathode materials demonstrate structural transformations of the hexagonal phase (space group R-3m) H1 to another hexagonal phase H2 (with a lower Li-ion content in the lattice) and to domains compris- ing both of these two phases, coexisting at potentials E  4.2– 4.3 V. The above phases differ by the a and c lattice constants, which is in agreement with literature results. Evolution of the lattice constants with the electrode potential upon charge/dis- charge is shown to be in correlation with the differential ca- pacity dQ/dE versus E plots and with some Raman parameters calculated from complementary in situ studies of these cath- ode materials by Raman spectroscopy. [a] Dr. C. Ghanty, Prof. B. Markovsky, Dr. E. M. Erickson, Dr. O. Haik, Dr. Y. Tal-Yossef, A. Mor, Prof. D. Aurbach Department of Chemistry Bar-Ilan University, Ramat-Gan, 52900 (Israel) E-mail : chandanghanty@gmail.com markovskyboris22@gmail.com [b] Prof. M. Talianker Department of Materials Engineering Ben-Gurion University of the Negev Beer-Sheva 84105 (Israel) [c] Dr. J. Lampert, Dr. A. Volkov, Dr. J.-Y. Shin, Dr. A.Garsuch, Dr. F.F. Chesneau, Dr. C. Erk BASF SE, GCN/E Ludwigshafen am Rhein, 67056 (Germany) An invited contribution to a Special Issue on In Situ Monitoring of Fuel Cell and Battery Processes ChemElectroChem 0000, 00,0–0  0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 & These are not the final page numbers! ÞÞ These are not the final page numbers! ÞÞ Articles DOI: 10.1002/celc.201500160