The addition of tungsten has been reported to greatly improve the capacity retention of Ni‐rich layered oxide cathode materials in lithium‐ion batteries. In this work, Ni(OH)2 precursors, coated with WO3 and also W‐containing precursors prepared by co‐precipitation followed by heat treatment with LiOH·H2O, are studied. Structural analysi s and electron microscopy show that W is incorporated as amorphous LixWyOz phases concentrated in all the grain boundaries between the primary particles of LiNiO2 (LNO) and on the surface of the secondary particles. Tungsten does not substitute for Ni or Li in the LNO lattice no matter how W is added at the precursor synthesis stage. Scanning electron microscopy (SEM) images show that adding W greatly suppresses primary particle growth during synthesis. In agreement with previous literature reports, cycling test results show that 1% W added to LNO can greatly improve charge–discharge capacity retention while also delivering a high specific capacity. The LixWyOz amorphous phases act as coating layer on both the primary and secondary particles, restrict primary particle growth during synthesis and increase the resistance of the secondary particles to microcracking.
Cation mixing in Li-based layered positive electrode materials has been reported to negatively affect the electrochemical performance and transport properties of intercalated Li. However, no previous reports have systematically correlated the impact of cation mixing (Ni atoms in the Li layer) on the electrochemical properties and Li transport. Herein, a series of Li-deficient LNO (Li1−xNi1+xO2) materials with different amounts of Ni in the Li layers ranging from ca. 1.5%–6.0% was intentionally prepared by varying the Li/Ni ratio during synthesis. An order of magnitude decrease in the Li chemical diffusion coefficient was found between samples with 1.5% and 6% Ni in the Li layer. A similar dependence of the diffusion constant on the amount of Ni in the Li layer was also observed in the Li-excess materials Li 1 + x Ni 0.5 Mn 0.5 1 − x O 2 for x = 0, 0.04, 0.08, 0.12, suggesting that, in general, larger amounts of Ni in the Li layer will lead to worse kinetics. This work quantitatively demonstrates that the amount of Ni in the Li layer needs to be carefully considered for the development of high-energy Ni-containing layered positive electrode materials as it directly affects overall electrochemical performance, phase transitions, and Li diffusion, leading to worse kinetics and seriously hindering rate capability.
Manganese dioxide (MnO) has been widely used as an active material for high-performance supercapacitors due to its high theoretical capacitance, high cycling stability, low cost, and environmental friendliness. However, the effect of its crystallographic phase on charge storage performances and mechanisms is not yet clear. Herein, MnO-based supercapacitors with different structures including nanospheres, nanorods, nanotubes, and nanosheets have been fabricated and investigated. Among such structures, δ-MnO nanosheets exhibit the highest specific capacitance of 194.3 F g at 1 A g when compared with other phases and shapes. The maximum specific energy of the δ-MnO nanosheet supercapacitor is 23.4 W h kg at 971.6 W kg and the maximum specific power is 4009.2 W kg at 15.9 W h kg with a capacity retention of 97% over 15 000 cycles. The δ-MnO nanosheet mainly stores charges via a diffusion-controlled mechanism at the scan rates of 10-100 mV s, whilst the α-MnO with different morphologies including nanospheres, nanorods, and nanotubes store charges via a non-faradaic or non-diffusion controlled process especially at fast scan rates (50-100 mV s). Understanding the charge storage performance and mechanism of the MnO nanostructures with different crystallographic phases and morphologies may lead to the further development of supercapacitors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.