The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi 0.5 Co 0.2 Mn 0.3 O 2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0−4.6 V versus Li/Li + results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205−182 mAhg −1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and −CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack formation at the LiNi 0.5 Co 0.2 Mn 0.3 O 2 particles. The data provide a basic understanding of the interfacial stabilization mechanism on high-voltage layered oxide cathodes.

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High-capacity Li-rich layered composite oxide, xLi 2 MnO 3 • (1-x)LiMO 2 (M = Mn, Ni, Co), is a promising candidate cathode material for high-energy electrochemical energy storage. Enabling the high-performance of high-voltage cathode relies on an electrolyte breakthrough and the solid electrolyte interface (SEI) stabilization. In this study, the 0.6Li 2 MnO 3 • 0.4LiNi 0.45 Co 0.25 Mn 0.3 O 2 (Li 1.2 Mn 0.525 Ni 0.175 Co 0.1 O 2 , LMNC) cathode is operated at 2.5-4.8 V with 5 wt% fluorinated linear carbonate, di-(2,2,2 trifluoroethyl)carbonate (DFDEC), as a high-voltage electrolyte additive, for the first time and applied to a high-energy lithium-ion battery. The cathode with DFDEC outperforms that in electrolyte only, delivering a high capacity of 250 mAhg −1 with an excellent chargedischarge cycling stability at the rate of 0.2C. Upon the use of DFDEC, the cathode surface is effectively passivated by a stable SEI composed of DFDEC decomposition products, which inhibit a detrimental metal dissolution and structural cathode degradation. A full-cell based on the SEI-stabilized LMNC cathode and graphite anode successfully demonstrates doubled energy density (∼278 Whkg −1 ) compared to ∼136 Whkg −1 of a commercialized cell of graphite//LiCoO 2 and an excellent cycling stability.

The ammonia-free coprecipitation process using citric acid as a new chelating agent successfully produced a micro-sized spherical Ni0.5Co0.2Mn0.3(OH)2 precursor and a well-performed cathode active material LiNi0.5Co0.2Mn0.3O2 for Li-ion batteries.