Noncrystalline Nanocomposites as a Remedy for the Low Diffusivity of Multivalent Ions in Battery Cathodes

Abstract

Rechargeable batteries using multivalent metals are among the most promising next-generation battery systems due to their high capacity, high safety, and low cost compared with lithium-ion batteries. However, strong cation−anion interaction degrades diffusion in solid cathodes, an effect that must be mitigated to yield practical multivalent metal batteries. We show that a highly defective iron phosphate−carbon composite prepared by ultracentrifugation serves as a reversible insertion/deinsertion for magnesium ions with, and operates beyond, a 2-V cell voltage at room temperature. A composite of noncrystalline particles that embeds the surrounding carbon structure enhances the magnesium-ion diffusion in the solid phase with stability for cycle life. X-ray absorption spectroscopy, transmission electron microscopy with energy-dispersive X-ray spectroscopy, and high-energy X-ray scattering measurements demonstrate magnesium-ion insertion and extraction in the defective iron phosphate without conversion reactions. This work suggests promising applications for highly defective structures as intercalation hosts for multivalent ions.

In Situ/Operando (Soft) X‐ray Spectroscopy Study of Beyond Lithium‐ion Batteries

“…[31] Similar work to study the olivine-type Mg x FePO 4 (x = 0-0.4) at the Fe K-edge were reported very recently. [96,97] In Figure 10a, the edge according to the Fe 1s to Fe 4p and to the continuum state was identified for FePO 4 . [98] With increasing of inserted Mg 2+ , the XANES shifted to lower energy region, implicating the Fe ions in FePO 4 were reduced.…”

“…To make electric vehicles feasible, it is imperative to understand considerably new battery chemistries with higher energy densities than the lithium ion, designated as “beyond lithium‐ion” batteries. [ 2,4–8 ] Examples include Li‐air, [ 9 ] Li‐S, [ 10,11 ] Na‐ion [ 12–16 ] batteries, and multivalent‐ion batteries including Mg‐ion, [ 17–38 ] Zn‐ion, [ 39,40 ] and Ca‐ion batteries. [ 17 ]…”

“…This article is intended to provide a succinct overview of the recent development of in situ/operando X‐ray spectroscopy and its application in the fundamental and applied research of beyond lithium‐ion batteries. A summary of in situ/operando XAS on various beyond lithium‐ion batteries, including Mg‐ion, [ 17–38 ] Zn‐ion, [ 39,40 ] Ca‐ion, [ 17 ] Li‐S, [ 10,11 ] and Na‐ion [ 12–16 ] batteries, will be discussed in the next section, followed by a brief presentation of several papers employed RIXS and scanning transmission X‐ray microscopy (STXM) for applications in the beyond lithium‐ion battery field. In addition, a perspective on the future problems to solve with the assistance of in situ/operando soft X‐ray spectroscopies will be discussed.…”

“…d) Fourier transform magnitudes from EXAFS oscillation at the Fe K-edge of highly defective FePO 4 and crystalline FePO 4 . Reproduced with permission [96,97]. Copyright 2020 American Chemical Society.…”

First-Principles Plane-Wave-Based Exploration of Cathode and Anode Materials for Li and Na-ion Batteries involving Complex Nitrogen-based Anions

“…For comparability, all structures with different computational setup were recalculated including the proper vander-Waals corrections (DFT-D3). The respective reaction enthalpy Δ r was estimated from total energies 84,168 of the involved components, 114,139,169 Since the reaction enthalpies turned out to be positive for all five combinations, these dicyanamide materials rather have a cathodic character than an anodic one if in contact with LiFePO4 and NaFePO4. Furthermore, dicyanamides show unexpected electrochemical flexibility because upon calculating reaction enthalpies if combined with LiFePO4F, Na2FePO4F and NaFePO4F (and the respective FePO4F phases) 141,144,170 as given in scheme 2, dicyanamides salts do show anodic character when reacting with LiFePO4F and NaFePO4F (reactions 6, 8, 10, 11 and 13) while behaving as cathodes in combination with Na2FePO4F (reactions 7, 9 and 12).…”