Dielectric Polarization in Inverse Spinel‐Structured Mg₂TiO₄ Coating to Suppress Oxygen Evolution of Li‐Rich Cathode Materials

Abstract

High‐energy Li‐rich layered cathode materials (≈900 Wh kg−1) suffer from severe capacity and voltage decay during cycling, which is associated with layered‐to‐spinel phase transition and oxygen redox reaction. Current efforts mainly focus on surface modification to suppress this unwanted structural transformation. However, the true challenge probably originates from the continuous oxygen release upon charging. Here, the usage of dielectric polarization in surface coating to suppress the oxygen evolution of Li‐rich material is reported, using Mg2TiO4 as a proof‐of‐concept material. The creation of a reverse electric field in surface layers effectively restrains the outward migration of bulk oxygen anions. Meanwhile, high oxygen‐affinity elements of Mg and Ti well stabilize the surface oxygen of Li‐rich material via enhancing the energy barrier for oxygen release reaction, verified by density functional theory simulation. Benefited from these, the modified Li‐rich electrode exhibits an impressive cyclability with a high capacity retention of ≈81% even after 700 cycles at 2 C (≈0.5 A g−1), far superior to ≈44% of the unmodified counterpart. In addition, Mg2TiO4 coating greatly mitigates the voltage decay of Li‐rich material with the degradation rate reduced by ≈65%. This work proposes new insights into manipulating surface chemistry of electrode materials to control oxygen activity for high‐energy‐density rechargeable batteries.

Fluorinated Aromatic Diluent for High‐Performance Lithium Metal Batteries

“…In addition, the XPS spectra of NCM523 cathodes after 15 cycles ( Figure S17) revealed that triple-DMC/1,2-dfBen contributed to the formation of ac athode electrolyte interphase (CEI) layer containing -CF 3 and LiF. [30] Cycling tests were carried out by galvanostatically cycling the cells at 0.1 C(1C= 3mAcm À2 )for the first two cycles and then at 0.5 Cfor subsequent cycles ( Figure 5). Thecapacity of the cell with 1m LiPF 6 in EC/DEC decreased abruptly after only 17 cycles,which is attributed to the depletion of Li metal.…”

Interfacial Degradation and Optimization of Li‐rich Cathode Materials†

“…In addition to the spinel‐like surface, inverse spinel structure has also been reported recently. Chen's group [ 105 ] constructed a stable interphase of Mg 2 TiO 4 on the surface of commercial Li‐rich materials. The cell volume change caused by oxygen release for the modified material was reduced, as shown in Figure 7B.…”

“…(B) In situ XRD results of fully charged LR and LR@MTO. Reproduced with permission from Ref [105]. Copyright 2020 WILEY‐VCH.…”

Mechanochemical Synthesis and Structure of Lithium Tetrahaloaluminates, LiAlX4 (X = Cl, Br, I): A Family of Li-Ion Conducting Ternary Halides

“…Equally, use of LiAlBr 4 and LiAlI 4 with high voltage cathodes might be enabled with an appropriate coating of the positive electrode to prevent SSE decomposition. 37 , 38 Further investigations into various half- and full-cell architectures and their performance are currently underway and will be reported elsewhere.…”