Optimization of Von Mises Stress Distribution in Mesoporous α‐Fe₂O₃/C Hollow Bowls Synergistically Boosts Gravimetric/Volumetric Capacity and High‐Rate Stability in Alkali‐Ion Batteries

Abstract

Hollow structures are often used to relieve the intrinsic strain on metal oxide electrodes in alkali-ion batteries. Nevertheless, one common drawback is that the large interior space leads to low volumetric energy density and inferior electric conductivity. Here, the von Mises stress distribution on a mesoporous hollow bowl (HB) is simulated via the finite element method, and the vital role of the porous HB structure on strain-relaxation behavior is confirmed. Then, N-doped-C coated mesoporous α-Fe 2 O 3 HBs are designed and synthesized using a multistep soft/hard-templating strategy. The material has several advantages: (i) there is space to accommodate strains without sacrificing volumetric energy density, unlike with hollow spheres; (ii) the mesoporous hollow structure shortens ion diffusion lengths and allows for high-rate induced lithiation reactivation; and (iii) the N-doped carbon nanolayer can enhance conductivity. As an anode in lithium-ion batteries, the material exhibits a very high reversible capacity of 1452 mAh g −1 at 0.1 A g −1 , excellent cycling stability of 1600 cycles (964 mAh g −1 at 2 A g −1 ), and outstanding rate performance (609 mAh g −1 at 8 A g −1 ). Notably, the volumetric specific capacity of composite electrode is 42% greater than that of hollow spheres. When used in potassium-ion batteries, the material also shows high capacity and cycle stability.

Polymer blend directed anisotropic self-assembly toward mesoporous inorganic bowls and nanosheets

“…Notably, bm -Nb 2 O 5 /C exhibits the highest rate capability among the previously reported metal oxide anodes (fig. S20A and table S4) ( 46 – 57 ). After galvanostatic cycles, the specific capacity could be recovered to 201 mA·hour g −1 when the current density was reset to 50 mA g −1 .…”

“…S22, A and B), thereby resulting in high volumetric capacity ( fig. S22C) (24). Furthermore, anisotropic morphology provides the short path length for electron/mass transport and increases the contact area between adjacent mesoporous bowls leading to enhanced charge transfer (6,20,25).…”

“…Conventional BCP-directed approaches for preparation of mesoporous inorganic particles mainly rely on the multistep procedures that use sacrificial silica templates (e.g., inverse opal) (16) or the solution-based systems such as emulsion and direct precipitation methods, which favorably generate isotropic spheres (or ill-defined shapes) because of a natural tendency to minimize total interfacial energy (17)(18)(19)(20). Thus, anisotropic morphologies can only be realized by breaking such intrinsic centrosymmetric arrangements; this breaking usually requires additional macroscale templates (for bowls, collapsed hollow polymers and concave substrates; and for 2D nanosheets, graphene and flat substrates/interfaces) (21)(22)(23)(24)(25). The kinetically controlled anisotropic growth on such templates has been also proposed (26,27).…”

Flowerlike Tin Diselenide Hexagonal Nanosheets for High-Performance Lithium-Ion Batteries

“…It is worth mentioning that the capacity fading in the initial 100 cycles can be ascribed to the repetitive volume expansion/contraction that can fracture the SEI layer and expose new active surfaces for SEI growth (Li et al, 2015 ). Subsequently, high-rate lithiation-induced mechanical degradation can effectively restructure the 3D SnSe 2 nanoflower and optimize the SEI, which was defined as reactivation, so the reversible capacity continuously increases during cycling (Qin et al, 2019 ).…”

Promise and reality of practical potassium‐based energy storage systems

“…, 45,46 transition metal chalcogenides (MoS 2 , MoSe 2 ), 47,48 transition metal nitrides (VN, Fe 2 N), 49 and transition metal phosphides (CoP, MoP). 50,51 The anode materials based on alloying reaction (P, Sn, Sb, and Bi) enable K + storage by forming alloys.…”