In this work, a conformally interfacial nanocoating strategy is introduced to enhance the lithium ion storage performance of LiNi 0.5 Mn 1.5 O 4 (LNMO). Stable cycling of LNMO is achieved through La 2 O 3 coating at both room and elevated temperatures. A series of La 2 O 3 -coated LNMO composites with various coating contents ranging from 0 to 3 wt% is prepared, and their electrochemical behaviors are systematically investigated. Among them, the 2 wt% La 2 O 3 -coated LNMO cathode presents the best comprehensive lithium ion storage performance; for instance, it retains more than 75% capacity retention after 500 cycles at room temperature and 93% capacity retention after 50 cycles at an elevated temperature of 55 °C with 1C rate. Moreover, the modified samples show more stable plateau potential than the pristine one during the cycling process. It is believed that the introduction of the La 2 O 3 nanocoating layer can effectively suppress side reactions between electrode and electrolyte, thus maintaining stable structure of electrode material and reducing polarization during cycling. Our work provides an effective approach to improve the electrochemical stability of LNMO high-potential cathode for future large-scale applications of enhanced lithium ion batteries with high energy density and long cycle life.
Due to the urgency of developing high energy density cathode materials in power batteries, as well as the high price and environmental unfriendliness of cobalt, researchers are working on ultra-high nickel low cobalt and ultra-high nickel cobalt-free layered cathode materials. However, the poor cyclic stability and rate performance of this material resulted from structural instability and severe surface/interface side reactions during cycling seriously hinder its practical application. In this paper, LiNi 0.9 Mn 0.1 O 2 (NM90) cathode material is modified by La 2 O 3 coating, and La 3+ doping caused by thermal diffusion is achieved simultaneously. The synergistic enhancement of the two modifications can effectively improve the layered structure and reduce surface/interface side reactions. The dual-modified material shows good structural stability, the La 2 O 3 coating does not fall off and the active material does not appear fragmentation and collapse after 100 cycles. At the same time, the dual-modified material also shows excellent electrochemical performance, with a capacity retention of 83.19% after 100 cycles at 1 C and a reversible capacity of 129.9 mAh g −1 at 10 C. The electrochemical mechanism reveals that the dual-modified material effectively reduces the charge transfer resistance and greatly increases the Li + diffusion coefficient. It will provide useful reference and technical support for the research of other electrode materials. Graphical abstract The NM90 and La 2 O 3 -coated NM90 particles have similar spherical morphology and are formed by the agglomeration of many primary particles; the surface of NM90 material is evenly coated by La 2 O 3 and No obvious boundary between La 2 O 3 and NM90 materials is found; LiNi 0.9 Mn 0.1 O 2 cathode material coated by 1wt% La 2 O 3 has the best cycle stability.
The major limitations of layered LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode materials are their severe capacity decay and marked impedance increase under a high cutoff voltage. Herein, a LiNi 0.5 Co 0.2 Mn 0.3 O 2 powder was successfully encapsulated by a compact and continuous La 2 O 3 thin layer via a facile freeze-drying method. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy , and X-ray photoelectron spectroscopy. The excellent thermal stability and favorable lithium ion conductivity of the La 2 O 3 -modified sample lead to a substantial improvement in its electrochemical performances. In particular, the coated sample exhibits a capacity retention of 80% at 1 C over 150 cycles, while that of the bare electrode is only 58% at a high cutoff voltage of 4.6 V. The alternating current impedance and cyclic voltammetry tests reveal that the La 2 O 3 coating can reduce the cell polarization and enhance the electrochemical activity of cathode materials .
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