Framework Doping of Ni Enhances Pseudocapacitive Na-Ion Storage of (Ni)MnO₂ Layered Birnessite

Abstract

We report a (Ni)­MnO2 layered birnessite material with a framwork doping of Ni ions as the cathode for much enhanced aqueous Na-ion storage. Characterized by neutron total scattering and pair distribution function (PDF) analysis, in situ XRD, in situ X-ray PDF, XANES, and XPS, the synergistic interaction between disordered [NiO6] and ordered [MnO6] octahedra contribute to the enhanced specific capacity and cycle life (63 mAh g–1 at 0.2 A g–1 after 2000 full-cell cycles). Electro-kinetic analysis and structural characterizations show that stable local structure is maintained by [MO6] octahedra during charge–discharge processes, while disordered [NiO6] octahedra significantly improve pseudocapacitive redox charge storage. This finding may pave a new way for designing a new type of low-cost and high performance layered electrode materials.

Atomic Engineering Catalyzed MnO2 Electrolysis Kinetics for a Hybrid Aqueous Battery with High Power and Energy Density

“…The Ni dopant exhibits a valence state of 3+, which is the same as reported (Ni)MnO 2 prepared via precipitation with a wet-chemistry method. [19] The elemental analysis determined elemental Ni composition at ~1.9 %, which is similar to the composition of catholyte. Additional supporting evidence regarding the morphology evolution and complete reversibility of the MnO 2 /Mn 2+ electrooxidation/electroreduction can be found in Fig.…”

Covalency Competition Induced Active Octahedral Sites in Spinel Cobaltites for Enhanced Pseudocapacitive Charge Storage

“…In order to confirm this point, we analyzed the bonding situation in the ternary {Co}[Co 2 ]O 4 , {Co}[Mn 2 ]O 4 , and {Zn}[Co 2 ]O 4 systems in detail by applying the concept of crystal orbital Hamilton populations (COHPs). Whereas Sun et al quantified the covalency by measuring the distance between the centers of metal d and oxygen p bands, [ 29 ] our calculations provide more accurate and reliable results. The COHP is described as the negative of density of states (DOS) multiplied by the corresponding Hamiltonian matrix elements.…”

“…One possible reason is that XPS is a surface sensitive technique, whereas XANES probes the bulk of the sample. [ 29 ] It is also possible that the complexity of the oxidation states in the transition metal 2p spectrum, as well as the lack of standardization, make it difficult to accurately determine the oxidation states of Co and Mn from only the XPS 2p 3/2 peak.…”

Degradation of Layered Oxide Cathode in a Sodium Battery: A Detailed Investigation by X‐Ray Tomography at the Nanoscale

“…In this regard, the survey spectra of Figure 5a reveal that both specimens have a complex chemistry and indicate a notable change in surface composition after cycling. Indeed, the spectrum of pristine NCAM shows the signatures of the main elements forming the oxide, i.e., Na, [46] Co, [47] Mn, Ni, [48] and O, [49] as well as those of F and C attributed to polymer binder (polyvinylidene fluoride, PVDF) and conductive agent (carbon black), [50,51] whilst the Al 2p doublet typically occurring at about a binding energy (BE) of 73 eV is marginally detected and evidenced in the selected region of Figure S8a in the Supporting Information. [52] The spectrum after cycling (Figure 5a) evidences a substantial raise of the sodium peaks along with a notable attenuation of the transition metal peaks, which may be causally related to formation of precipitates over the electrode surface as above described.…”