Stabilizing Na+ accessibility at high voltage
and accelerating
Na+ diffusivity are pressing issues to further enhance
the energy density of the Na3V2(PO4)3 (NVP) cathode for sodium-ion batteries (SIBs). Herein,
by taking a V/Cr solid-solution MXene as a precursor, a facile in-situ reactive transformation strategy to embed Cr-substituted
NVP (NVCP) nanocrystals in a dual-carbon network is proposed. Particularly,
the substituted Cr atom triggers the accessibility of additional Na+ in NVCP, which is demonstrated by an additional reversible
redox plateau at 4.0 V even under extreme conditions. More importantly,
the Cr atom alters the Na+ ordering at the Na2 sites with
an additional intermediate phase formation during charging/discharging,
thus reducing the energy barriers for Na+ migration. As
a result, Na+ diffusivity in NVCP accelerates to 2–3
orders of magnitude higher than that of NVP. Eventually, the NVCP
cathode exhibits extraordinarily high-rate capability (78 mA g–1 at 200 C and 68975 W kg–1), outstanding
cycle stability (over 1500 cycles at 10 C), excellent low-temperature
property, and full cell performance.
MXenes have attracted great attention in the fields of energy conversion and catalysis, and have proved to be an effective supporting material for single atom catalysts (SACs). In the present study, we investigated the catalytic activity of a series mono‐atomic transition‐metal atoms supported by MXenes M2NO2 for oxygen evolution reaction (OER) via first principle calculation. Particularly, single atom Cu site on Ti2NO2 having the lowest overpotentials of 0.24 V and bonding with the reaction intermediates moderately, is the most active SAC for OER. Energetically, Cu atom prefers to be mono‐atomically anchored on Ti2NO2 instead of aggregating. Plus, Cu anchoring enhance the electronic states around Fermi level. Additionally, ab‐initio molecular dynamics simulations show that Cu atom is anchored on Ti2NO2, stable and isolatable at 300 K. Studies on the small molecule adsorption on Cu‐Ti2NO2 further prove the potential applications of Cu−Ti2NO2 as active SACs for OER. Our results broaden the perception of MXenes and guide the exploration of non‐noble metal based OER electrocatalysts.
Structural superlubricity is a fascinating
physical phenomenon
that plays a significant role in many scientific and technological
fields. Here, we report the robust superlubricating state achieved
on the interface of relatively rotated graphdiyne (GDY) bilayers;
such an interface with ultralow friction is formed at nearly arbitrary
rotation angles and sustained at temperatures up to 300 K. We also
identified the reverse correlation between the friction coefficient
and size of the Moiré lattice formed on the surface of the
incommensurate stacked GDY bilayers, particularly in a small size
range. Our investigations show that the ultralow friction and the
reduction of the friction coefficient with the increase in size of
the Moiré lattice are closely related to the interfacial energetics
and charge density as well as the atomic arrangement. Our findings
enable the development of a new solid lubricant with novel superlubricating
properties, which facilitate precise modulation of the friction at
the interface between two incommensurate contacting crystalline surfaces.
Ni-rich layered cathodes with high energy densities reveal an enormous potential for lithium-ion batteries (LIBs), however, their poor stability and reliability have inhibited their application. To ensure their stability over extensive cycles at high voltage, surface/interface modifications are necessary to minimize the adverse reactions at the cathode-electrolyte interface (CEI), which is a critical factor impeding electrode performance. Therefore, this review provides a comprehensive discussion on the surface engineering of Ni-rich cathode materials for enhancing their lithium storage property. Based on the structural characteristics of the Ni-rich cathode, the major failure mechanisms of these structures during synthesis and operation are summarized. Then the existing surface modification techniques are discussed and compared. Recent breakthroughs in various surface coatings and modification strategies are categorized and their unique functionalities in structural protection and performance-enhancing are elaborated. Finally, the challenges and outlook on the Ni-rich cathode materials are also proposed.
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