High energy density lithium-ion batteries (LIBs) have continually been of great research interest amplified by the exponentially growing demand for electric vehicles.[1] Among the investigated systems, nickel-rich transition metal oxides appear very promising owing to their high specific capacity,[2] and low cobalt content, according to necessity of reducing the cobalt proportion in LIB cathodes due to its severe shortage and strong environmental and ecological concerns.[3] However, the increased nickel content also introduces previously overcome challenges of poor capacity retention and thermal stability due to the vulnerability of the nickel rich oxide towards interfacial side reactions.[4] Herein, a low volatility and non-flammable ionic liquid-based (IL) electrolyte[5] consisting of 0.8Pyr14FSI-0.2LiTFSI is employed to overcome those challenges faced by a Ni-rich LiNi0.8Co0.1Mn0.1O2 positive electrode. The cathode exhibits remarkable electrochemical performance in half-cell configuration, delivering a specific capacity of approximately 200 mAh g-1 and practically no capacity fading after 100 cycles at 0.1C at room temperature. After 600 cycles at 0.5C the cathode has an outstanding capacity retention of 97%, which is substantially higher than with the conventional organic carbonate-based electrolyte used for reference, attributed to a much more stable electrode-electrolyte interfacial layer. Even at elevated temperature (40 °C) the LiNi0.8Co0.1Mn0.1O2 in combination with the IL electrolyte offers a specific capacity of more than 200 mAh g-1 as well as a capacity retention around 99% after 100 cycles at 0.5C. To the best of our knowledge these results exceed the state-of-the-art performance reported for any Ni-rich positive electrode. Reference [1] W. Liu, P. Oh, X. Liu, M. J. Lee, W. Cho, S. Chae, Y. Kim, J. Cho, Angewandte Chemie 2015, 54, 4440.[2] S. H. A. Heist, and S. H. Lee, J . Electrochem . Soc 2019, 166 (6) A873-A879.[3] C.Vaalma, D. Buchholz, M. Weil, S. Passerini, Nature Review Materials 2018, 3, 18013.[4] U.-H. Kim, L.-Y. Kuo, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, ACS Energy Letters 2019, 4, 576.[5] G. A. Elia, U. Ulissi, S. Jeong, S. Passerini, J. Hassoun, Energy & Environmental Science 2016, 9, 3210.