Micro/Nanoengineered α‐Fe₂O₃ Nanoaggregate Conformably Enclosed by Ultrathin N‐Doped Carbon Shell for Ultrastable Lithium Storage and Insight into Phase Evolution Mechanism

Abstract

The Fe-basedt ransitionm etal oxidesa re promising anode candidates for lithium storage consideringt heir high specific capacity,l ow cost, and environmental compatibility.H owever,t he poor electron/ion conductivity and significantv olumes tress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for a-Fe 2 O 3 have appearedi nm ost reports.Here, au niform micro/nano a-Fe 2 O 3 nanoaggregatec onformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-a-Fe 2 O 3 @NC)i sd esigned. The M/N porous balls combine the merits of secondary nanoparticles to shortent he Li + transportation pathways as well as alleviating volume expansion,a nd primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbons hell favors fast electron transfer and protects the electrode from electrolyte corrosion.T herefore, the M/N-a-Fe 2 O 3 @NC electrode delivers an excellent reversible capacity of 901 mA hg À1 with capacity retention up to 94.0 %a fter 200 cycles at 0.2 Ag À1 .N otably,t he capacityr ise does not happen during cycling. Moreover,t he lithium storagem echanism is elucidated by ex situ XRD and HRTEM experiments. It is verifiedt hat the reversible phase transformation of a$g occursd uring the first cycle, whereas only the a-Fe 2 O 3 phase is reversibly transformed during subsequent cycles. This study offersasimple and scalables trategy for the practical applicationo fhigh-performance Fe 2 O 3 electrodes. (140 mg) and dopamine (70 mg) were added to Tris-HCl buffer solution (10 mL, pH % 8.5) under stirring. Then, the mixture was stirred continuously for 24 hu nder an oxygen atmosphere. Afterwards, the resultant product was collected by centrifugation and rinsed several times with distilled water,

Graphitic Carbon-Doped Mesoporous Fe2O3 Nanoparticles for Long-Life Li-Ion Anodes

“…28 Then, in the first anodic scan process, a wide oxidation peak at around 1.70 V is 15,17,18 The first irreversible discharge capacity loss originates from the formation of SEI film, the decomposition of electrolyte, as well as the partial Li + extraction in the electrode. 30 In the subsequent 3rd and 5th cycles, the reversible discharge capacity of Fe 25 This result also proves that the Fe 2 O 3 /C 400 composite involves more graphitic carbon content, which can effectively mitigate the volume change of the electrode, thereby being conducive to enhance the long-life of the Fe 2 O 3 -based composite as an anode for LIBs. 31 Due to the volume expansion (∼196%) of the α-Fe 2 O 3 nanomaterial and structure collapse of the electrode induced by Li + -ion intercalation/deintercalation under high current densities, the capacity of LIBs rapidly decreases.…”

“…Meanwhile, the beginning discharge/charge capacity of Fe 2 O 3 /C 400 and Fe 2 O 3 /C 450 electrodes are 987/656 and 1219/885 mA h g –1 with the corresponding Coulombic efficiency being 66 and 73%. The low Coulombic efficiency is also reported in most other carbon-doped metal oxide materials. ,, The first irreversible discharge capacity loss originates from the formation of SEI film, the decomposition of electrolyte, as well as the partial Li + extraction in the electrode . In the subsequent 3rd and 5th cycles, the reversible discharge capacity of Fe 2 O 3 /C 400 and Fe 2 O 3 /C 450 materials can be basically stable at 670 and 863 mA h g –1 with the Coulombic efficiency being nearly 100%.…”

“…It can be calculated that there is no linear relationship between peak current intensity ( i ) and the square root of the scan rate (ν), indicating the presence of pseudocapacitance during the charge/discharge process. The pseudocapacitance contribution can be calculated from the equation below where the variable values of a and b are dependent on the intercept and slope of the line fitted by log i and log ν . Theoretically, b = 0.5 or 1 represents the extreme diffusion- or pseudocapacitive-controlled process.…”

“…It can be calculated that there is no linear relationship between peak current intensity (i) and the square root of the scan rate (ν), indicating the presence of pseudocapacitance during the charge/discharge process. The pseudocapacitance contribution can be calculated from the equation below 30 i av…”

Graphene‐Oxide‐Encapsulated Fe2O3 Nanoparticles with Different Dimensions as Lithium‐Ion Battery Anodes: The Morphology Effect of Fe2O3

“…(ii) The excessive generation of solid electrolyte interface layer (SEI) and undesirable side reactions subjoin while more electrolyte corrodes, leading to lower first coulomb efficiency [30] . (iii) The SEI film formed directly along the exterior of nano‐Fe 2 O 3 will also rupture with the volumetric variations in subsequent cycles, increasing the instability of the SEI film [31,32] . Fortunately, all these shortcomings could be relieved by being composited with carbon materials [33] …”