title: Layered Na-Ion Cathodes with Outstanding Performance Resulting from the Synergetic Effect of Mixed P- and O-Type Phases.
abstract: Herein, the synthesis of new quaternary layered Na-based oxides of the type NaxMnyNizFe0.1Mg0.1O2(0.67≤x≤ 1.0; 0.5≤y≤ 0.7; 0.1≤z≤ 0.3) is described. The synthesis can be tuned to obtain P2- and O3-type as well as mixed P-/O-type phases as demonstrated by structural, morphological, and electrochemical properties characterization. Although all materials show good electrochemical performance, the simultaneous presence of the P- and O-type phases is found to have a synergetic effect resulting in outstanding performance of the mixed phase material as a sodium-ion cathode. The mixed P3/P2/O3-type material, having an average elemental composition of Na0.76Mn0.5Ni0.3Fe0.1Mg0.1O2, overcomes the specific drawbacks associated with the P2- and O3-type materials, allowing the outstanding electrochemical performance. In detail, the mixed phase material is able to deliver specific discharge capacities of up to 155 mAh g-1(18 mA g-1) in the potential range of 2.0-4.3 V. In the narrower potential range of 2.5-4.3 V the material exhibits high average discharge potential (3.4 V versus Na/Na+), exceptional average coulombic efficiencies (>99.9%), and extraordinary capacity retention (90.2% after 601 cycles). The unexplored class of P-/O-type mixed phases introduces new perspectives for the development of layered positive electrode materials and powerful Na-ion batteries.
authors.affiliation: Helmholtz Institute Ulm (HIU) Helmholtzstrasse 11 89081 Ulm Germany; Karlsruhe Institute of Technology (KIT) P.O. Box 3640 76021 Karlsruhe Germany.
authors.forename: Marlou
authors.initials: M
authors.lastname: Keller
authors.affiliation: Helmholtz Institute Ulm (HIU) Helmholtzstrasse 11 89081 Ulm Germany; Karlsruhe Institute of Technology (KIT) P.O. Box 3640 76021 Karlsruhe Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Buchholz
authors.affiliation: Helmholtz Institute Ulm (HIU) Helmholtzstrasse 11 89081 Ulm Germany; Karlsruhe Institute of Technology (KIT) P.O. Box 3640 76021 Karlsruhe Germany.
authors.forename: Stefano
authors.initials: S
authors.lastname: Passerini
keywords: O‐type phases; P‐type phases; layered structures; sodium cathodes; sodium ion batteries