Ni-rich layered oxides (LiNi x Mn y Co z O2, x ≥ 0.6, x + y + z = 1) are promising positive electrode materials for high energy density lithium-ion batteries thanks to their high specific capacity. However, large-scale application of Ni-rich layered oxides is hindered by its poor structural and interfacial stability, especially during cycling at a high cutoff potential (i.e., ≥ 4.3 V, versus Li+/Li). Herein, we demonstrate that lithium difluoro(oxalato)borate (LiDFOB) as a film-forming additive plays a dual role on the electrode|electrolyte interphase formation in a LiNi0.83Mn0.05Co0.12O2||graphite cell, meaning that it can not only be reduced on the graphite negative electrode but also oxidized on the nickel-rich oxide LiNi0.83Mn0.05Co0.12O2 positive electrode cycled at a high cutoff potential (4.4 V, versus Li+/Li) prior to typical carbonate-based electrolyte constituents. As a result, the addition of 1.5 wt % LiDFOB greatly reduces the polarization and improves the cycling stability of the LiNi0.83Mn0.05Co0.12O2||graphite cell, which shows a high discharge capacity of 198 mA h g–1, and more than 83.1% of the initial capacity was retained after 200 cycles at C/3 (the capacity retention obtained at the same cycling condition is only 59.9% for the cell without LiDFOB additive). Furthermore, the employ of LiDFOB additive also significantly suppresses the self-discharge of the LiNi0.83Mn0.05Co0.12O2||Li cell during high-temperature and long-term room-temperature storage at 4.4 V. These electrochemical performance enhancements could be attributed to the participation of LiDFOB in forming a stable and Li+ transfer favorable protective layer that is rich in inorganic boron, fluorine, and carbonate compounds on both the surface of the LiNi0.83Mn0.05Co0.12O2 positive electrode and the graphite negative electrode, thus suppressing the electrolyte decomposition on the positive electrode and negative electrode surfaces and decreasing the dissolution of transition-metal ions from the positive electrode bulk.
An ultrafine (6–7 nm) and well dispersed nano-SnO2/carbon nanotube hairball (SnO2/CNTH) composite material with a three-dimensional (3D) hierarchical structure is prepared by spray drying and solvothermal method. This composite material demonstrates much superior electrochemical performance over the bare SnO2 and an obviously improved Li-storage performance over the SnO2/CNT composite in respect to specific capacity, rate performance, and cycling stability. It exhibits a high reversible capacity of 1109.5 mAh g–1 at 0.1 A g–1, achieves a maximum reversible capacity of 1090.6 mAh g–1 when continuously cycled at 0.2 A g–1, and remains at a capacity of 809.2 mAh g–1 after 100 cycles with the capacity retention of 74.2%. The improved electrochemical performance is attributed to the increased conductivity and hence the enhanced electrode reactivity as well as the electrode stability due to the particular 3D hierarchical structure of the SnO2/CNTH composite. This structure can also address the large volume change upon cycling.
Nano‐TiNb2O7/multiwalled carbon nanotube and ketjen black (TiNb2O7/CNT‐KB) composite microspheres with porous three‐dimensional (3D) hierarchical heterostructure are fabricated by spray drying and solvothermal method. This composite material exhibits a high reversible charge specific capacity of 327.8 mAh g−1 at the current rate of 0.1 C and 151.1 mAh g−1 at 20 C rate. When it is cycled at a high current rate of 5 C for 1000 cycles, the charge capacity is dropped from the maximum value of 220.8 mAh g−1 (6th cycle) to the end value of 145.4 mAh g−1, with capacity retention of 65.9 %. The TiNb2O7/CNT‐KB composite material demonstrates much superior electrochemical performance over the bare TiNb2O7 material, and this result should be attributed to its particular porous 3D hierarchical structure, which possesses enhanced electrical conductivity as well as the ability for accommodating volume change and preventing particle aggregation of the electrode active material during the discharge and charge cycles.
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