Direct Nano‐Synthesis Methods Notably Benefit Mg‐Battery Cathode Performance

Abstract

Rechargeable magnesium batteries are promising candidates for nextgeneration electrochemical energy storage, but their development is severely hindered by sluggish solid-state diffusion and significant desolvation penalties of the divalent cation. Studies suggest that nano-sized electrode materials alleviate these issues by shortening diffusion lengths and increasing electrode/electrolyte interaction. Here, the effect of particle size and synthetic methodology on the electrochemical performance of four sulfide cathode materials in Mg batteries is investigated: layered TiS 2 , CuS, spinel Ti 2 S 4 , and CuCo 2 S 4 . In these sulfide hosts, the direct preparation of nano-dimensional crystallites is critical to activate or improve electrochemistry. Even promising cathode materials can appear electrochemically inert when micron-sized particles are investigated (e.g., CuCo 2 S 4 ), and mechanical milling leads to surface degradation of active material which severely limits performance. However, nano-sized CuCo 2 S 4 prepared directly reaches a capacity nearly double that of ball-milled material and delivers 350 mAh g −1 at 60 °C. This work provides synthetic considerations which may be crucial in the discovery and design of novel Mg cathode materials, so that promising candidates are not overlooked. By extension, in oxide materials where Mg 2+ diffusion is expected to be much more sluggish, this factor is anticipated to be even more important when screening for new hosts.

Designing Nanostructured Metal Chalcogenides as Cathode Materials for Rechargeable Magnesium Batteries

“…These performance data reinforce the importance of interlayer expansion to facilitate Mg 2+ intercalation [34] and of nanostructuring to shorten Mg 2+ diffusion path inside the cathode. [18,103] Copper selenides were also studied to some extent. A cathode material of current interest is Cu 3 Se 2 due to its Cu +mediated cathode chemistry.…”

“…have shown that nanodimensional layered TiS 2 achieves more stable capacity retention as compared to micrometer‐sized TiS 2 because the smaller grains minimize cation trapping within the lattice and mitigate the volume change during cycling. [ 103 ] Micrometer‐sized TiS 2 exhibited large irreversible capacity (47%) during the initial cycle and a reversible capacity of 160 mAh g −1 at C/40 (1C = 1 Mg 2+ /TiS 2 ) and 60 °C. [ 39 ] This implies that there is substantial cation trapping in the cathode host.…”

“…Room temperature data were collected using APC/THF (where APC = all-phenyl complex), while capacity retention data at 60 °C were obtained with APC/G4 electrolyte. Reproduced with permission [103]. Copyright 2020, Wiley-VCH.…”

Recent Progress and Challenges in the Optimization of Electrode Materials for Rechargeable Magnesium Batteries

“…The third is drastically decreasing the particle size of the electrodes. [ 192–195 ] As reported in LIBs and NIBs, the nanostructured materials have several important advantages compared with the bulk ones, such as increased contact interface of electrolyte and electrode, and shorter diffusion lengths for electrons and ions. [ 196–199 ] In RMBs, using nanostructured composites is also an effective way to obtain a decreased route for Mg 2+ diffusion with better performance.…”

“…The third is drastically decreasing the particle size of the electrodes. [192][193][194][195] As reported in LIBs and NIBs, the nanostructured materials have several important advantages compared with the bulk ones, such as increased contact interface of electrolyte and electrode, and shorter diffusion lengths Figure 17. a) High energy XRD patterns of TiS 2 at different stages (stages 0-3 corresponding to the pristine TiS 2 , discharged to 1, 0.2, and 0 V, respectively).…”