Single crystal cathode materials have better cycling stability than the polycrystalline ones, since they own smaller specific surface area and better mechanical strength, thus suffering from reduced contact with electrolyte and suppressed generation of cracks during long-term cycling. Consequently, in this work, the single crystal Li-rich materials were synthesized using a molten salt method towards solving the problem of fast capacity decline. We investigated the role of calcination temperature on the structure and performance of synthesized Li-rich materials, and found out that higher temperature is beneficial to the particle growth and structural stability, but it also leads to lattice shrinkage and increased Li2MnO3 phase, which deteriorated the electrochemical performance. Therefore, the calcination temperature is one of the most important parameters in the synthesis of single crystal lithium rich materials, and it is necessary to determine the optimal calcination temperature to achieve a balance between capacity and cycle stability
The development of high-capacity cathode materials is one of most effective strategies to improve the energy density of Li-ions batteries. Layered Li-rich manganese-based cathode materials have attracted much attention from researchers due to their ultra-high specific capacity (>250 mAh g-1) and low cost. However, Li-rich cathode materials still suffer some drawbacks especially its poor cycle performance due to the necessary high operation voltage, which accelerated structural deterioration toward inactive rock-salt phase and greatly limit their practical application. Herein, Ru are proposed as a doping element to substitute TM in Li1.2Ni0.2Mn0.6O2 as a prototype materials. The XRD and EDS mapping results indicate the Ru has been successfully doped in the layered structure and can restrain the structural degradation during cycling. The electrochemical tests present that the Li-rich cathode with 1 wt% Ru-doping displays the highest capacity retention with nearly no capacity fade over 40 cycles. This work should shed light on the structural and electrochemical enhancement of lithium-rich cathode materials for the most advanced Li ions batteries.
Micron-silicon possess dense morphology and high tap density, which can improve volume and area capacity while maintaining a large specific capacity. In addition, the cost of micron silicon is low, and compared to nano silicon, it has more potential for large-scale industrialization. However, micron-silicon will suffer huge volume expansion during the charge-discharge process, which causes the active material to fall off from the fluid collector, resulting in rapid capacity degradation; In addition, the edges and corners of micro-silicon are easy to crack the surface solid-electrolyte interface (SEI), resulting in the repeated generation of SEI, which further restricts the cyclic stability of the electrode. In this work, we added a lithium source to in-situ convert the silicon oxide on the surface of micron-silicon into lithium orthosilicate (Li4SiO4) protective layer. The lithium orthosilicate coating can not only effectively alleviate the volume expansion of the silicon anode during the charging and discharging process, but also effectively avoid the direct contact between the micron silicon and the electrolyte as a protective layer, which can reducing the surface side reaction of the electrode. The prepared electrode displays a high reversible specific capacity of 1075.3 mAh g-1 after 100 cycles at 0.3C.
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