Activating Oxygen Redox in Layered Na_xMnO₂ to Suppress Intrinsic Deficient Behavior and Enable Phase‐Transition‐Free Sodium Ion Cathode

Abstract

P2-type layered Na x MnO 2 cathode shows great potential in practical sodium ion batteries, especially for grid-level applications due to its ecofriendly and cost-effective sodium and manganese resources, and high theoretical specific capacity. However, several obstacles including severe phase transitions of P2-O2 and P2-P2′, low redox potential of Mn 3+ /Mn 4+ , disproportionation reaction and Jahn-Teller distortion of Mn 3+ , and deficient behavior have already hindered its practical applications. Herein, a Li, Cu co-doping strategy to tackle the mentioned obstacles by activating the oxygen redox is presented. The Li, Cu co-doped material exhibits solid solution reaction without any phase transitions as proved by in situ X-ray diffraction measurement and reduces the dissolution of active manganese element. With this modification treatment, it can dramatically raise the cycling stability from 30.4% to 80.1% after 150 cycles and simultaneously improves the deficient behavior due to the capacity contribution of oxygen redox at high voltage. More importantly, the coin-cell type sodium ion full cell assembled with this cathode and commercial hard carbon anode delivers a promising energy density of 225.1 Wh kg -1 .

Crystal Facet Design in Layered Oxide Cathode Enables Low-Temperature Sodium-Ion Batteries

“…The survey spectra (Figure S6a and S7a, Supporting Information) for both NCO-AC and NCO-O samples present all of the elements of Na, Cr, and O. The fitted peaks at 574.9, 575.6, 576.4, and 577.4 eV in Cr 2p 3/2 and the fitted peaks at 585.3 and 586.3 eV in Cr 2p 1/2 suggest the Cr species in NCO-AC is trivalent, as illustrated in Figure S6b (SI). , The O 1s XPS spectrum of NCO-AC is shown in Figure S6c (SI), where the peak at 529.2 eV can be ascribed to the typical lattice oxygen, the peaks at 531.3 and 533.1 eV are attributed to the oxygenated species, and the peak at a higher binding energy of 535.7 eV is assigned to the Na Auger. , The Na 1s peak (Figure S6d, Supporting Information) of NCO-AC located at 1071.5 eV is in accordance with the typical binding energy in layered oxide. , Meanwhile, the XPS results (Figure S7b–d, Supporting Information) for NCO-O reveal that the chemical state of Cr, O, and Na elements is no obvious difference between NCO-O and NCO-AC. In short, the difference between NCO-AC and NCO-O is the micromorphology and the exposure of the lattice facets.…”

W‐Doping Induced Efficient Tunnel‐to‐Layered Structure Transformation of Na0.44Mn1‐xWxO2: Phase Evolution, Sodium‐Storage Properties, and Moisture Stability

“…[ 21 ] Among the transition metal oxides, P2‐Na x MnO 2 stands in the spotlight owing to its low cost, environmental sustainability, and decent electrochemical performance. [ 22 ] And the structure of the P2 type system is more stable during Na ion insertion/removal compared to the O3 counterpart. [ 23 ] Nonetheless, the P2‐Na x MnO 2 compounds are still haunted by irreversible structural changes/phase transitions during cycling, insufficient electrochemical performances, and air/moisture instability.…”

Vanadium fluorophosphates: advanced cathode materials for next-generation secondary batteries

“…cannot withstand the conspicuous structural variations derived from the process of repeated Na + /K + (de)insertion, causing significant polarization and capacity degradation, resulting in an inferior electrochemical performance. [53][54][55][56] Furthermore, some olivine-type materials (e.g., NaFePO 4 and KFePO 4 ) endure sluggish diffusion kinetics for migration of Na + /K + and large lattice mismatch between NaFe-PO 4 (KFePO 4 ) and FePO 4 , leading to a poor rate performance and unsatisfactory lifespan. 57,58 Organic polymers have a low specific discharge capacity and poor cyclability due to their dissolution reactions with the electrolyte, which are difficult to meet the actual needs of rechargeable equipment.…”