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In view of the requirements for high-energy lithium ion batteries (LIBs), hierarchically layered LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode materials have been prepared using a hydroxide coprecipitation method and subsequent high-temperature solid-state reaction. The diffraction results show that the synthesized NCM111 has a well-defined layered hexagonal structure. The initial specific discharge capacity of a Li/NCM111 cell is 204.5 mAh g-1 at a current density of 28 mA g-1 between 2.7 and 4.8 V. However, the cell suffers from poor capacity retention over extended charge-discharge cycles. The structural evolution of NCM111 electrode during electrochemical cycling is carefully investigated by in situ high-resolution synchrotron radiation diffraction. It is found that the nanodomain formation of a layered hexagonal phase H3 and a cubic spinel phase after charging to voltages above 4.6 V is the main source for the structural collapse in c direction and the poor cycling performance. This process is accompanied by the removal of oxygen, the transition metal (TM) migration and the crack generation in the nanodomains of the primary particles. These results may help to better understand the structural degradation of layered cathodes in order to develop high energy density LIBs. [ABSTRACT FROM AUTHOR]

In article number 1803094, Björn Schwarz, Xiushan Yang, Xiaodong Guo, Shulei Chou, Sylvio Indris and co‐workers describe the transformation processes (from spinel to rock‐salt to layered structure) observed during synthesis of Li‐rich Co‐free layered oxides that are used as cathode materials for Li‐ion batteries, on a single particle. These processes are driven by incorporation of Li and O into the Li‐free precursor. [ABSTRACT FROM AUTHOR]

As promising cathode materials, the lithium‐excess 3d‐transition‐metal layered oxides can deliver much higher capacities (>250 mAh g−1 at 0.1 C) than the current commercial layered oxide materials (≈180 mAh g−1 at 0.1 C) used in lithium ion batteries. Unfortunately, the original formation mechanism of these layered oxides during synthesis is not completely elucidated, that is, how is lithium and oxygen inserted into the matrix structure of the precursor during lithiation reaction? Here, a promising and practical method, a coprecipitation route followed by a microwave heating process, for controllable synthesis of cobalt‐free lithium‐excess layered compounds is reported. A series of the consistent results unambiguously confirms that oxygen atoms are successively incorporated into the precursor obtained by a coprecipitation process to maintain electroneutrality and to provide the coordination sites for inserted Li ions and transition metal cations via a high‐temperature lithiation. It is found that the electrochemical performances of the cathode materials are strongly related to the phase composition and preparation procedure. The monoclinic layered Li[Li0.2Ni0.2Mn0.6]O2 cathode materials with state‐of‐the‐art electrochemical performance and comparably high discharge capacities of 171 mAh g−1 at 10 C are obtained by microwave annealing at 750 °C for 2 h. Structural evolution from a precursor obtained by a hydroxide coprecipitation method to Co‐free Li‐excess layered Li[Li0.2Ni0.2Mn0.6]O2 (LLNMO) oxides is presented. The intermediate state consisting of coherent layered and spinel/rock‐salt‐type phases is observed directly on a single crystallite. A promising microwave‐assisted technique for preparing LLNMOs with high performance is proposed. The origin of oxygen incorporation during synthesis of LLNMOs is unraveled. [ABSTRACT FROM AUTHOR]