In order to reduce cost and increase energy density, it is critical to eliminate cobalt and increase nickel content in practicalLiNi 1−x−y Mn x Co y O 2 (NMC) and LiNi 1−x−y Co x Al y O 2 (NCA) cathodes. However, the implementation of cobalt-free, high-nickel layered oxide cathodes in lithium-ion batteries (LIBs) is hindered by the inherent issue of high surface reactivity with the electrolyte and microcrack formation during cycling. Herein, the origin of key parameters for microstructural engineering in cobalt-free LiNiO 2 (LNO) is comprehensively investigated with two representative dopants, B and Al. A notable difference in the segregation energy between B and Al results in different morphologies of LNO particles. The low solubility of B into the host structure leads to a surface-confined distribution of B, inhibiting the growth of primary particles, whereas the highly soluble Al facilitates primary particle growth. Recognition of this key parameter can help improve the cycle life of cobalt-free LIBs via microstructural engineering by increasing the aspect ratio inside the cathode particle. It is demonstrated that boron-doping in LNO (B-LNO) is the most effective dopant strategy for microstructural engineering of the primary particles. The B-LNO exhibits an excellent capacity retention of 81% in full cells after 300 cycles compared to both LNO and Al-doped LNO (Al-LNO).
Microstructural engineering is becoming notably important
in the
realization of cobalt-free, high-nickel layered oxide cathodes for
lithium-ion batteries since it is one of the most effective ways to
improve the overall performance by enhancing the mechanical and electrochemical
properties of cathodes. In this regard, various dopants have been
investigated to improve the structural and interfacial stabilities
of cathodes with doping. Yet, there is a lack of a systematic understanding
of the effects of dopants on microstructural engineering and cell
performances. Herein, we show controlling the primary particle size
by adopting dopants with different oxidation states and solubilities
in the host structure as an effective way for tuning the cathode microstructure
and performance. The reduction in the primary particle size of cobalt-free
high-nickel layered oxide cathode materials, e.g., LiNi0.95Mn0.05O2 (NM955), with high-valent dopants,
such as Mo6+ and W6+, gives a more homogeneous
distribution of Li during cycling with suppressed microcracking, cell
resistance, and transition-metal dissolution compared to lower-valent
dopants, such as Sn4+ and Zr4+. Accordingly,
this approach offers promising electrochemical performance with cobalt-free
high-nickel layered oxide cathodes.
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