Double-Holey-Heterostructure Frameworks Enable Fast, Stable, and Simultaneous Ultrahigh Gravimetric, Areal, and Volumetric Lithium Storage

Abstract

Deliberate design of advantageous nanostructures holds great promise for developing high-performance electrode materials for electrochemical energy storage. However, it remains a tremendous challenge to simultaneously gain high gravimetric, areal, and volumetric capacities as well as high rate performance and cyclability to meet practical requirements mainly due to the intractable insufficient ion diffusion and limited active sites for dense electrodes with high areal mass loadings. Herein we report a double-holey-heterostructure framework, in which holey Fe2O3 nanosheets (H-Fe2O3) are tightly and conformably grown on the holey reduced graphene oxide (H-RGO). This hierarchical nanostructure allows for rapid ion and electron transport and sufficient utilization of active sites throughout a highly compact and thick electrode. Therefore, the free-standing flexible H-Fe2O3/H-RGO heterostructure anode can simultaneously deliver ultrahigh gravimetric, areal, and volumetric capacities of 1524 mAh g–1, 4.72 mAh cm–2, and 2621 mAh cm–3, respectively, at 0.2 A g–1 after 120 cycles, and extraordinary rate performance with a capacity of 487 mAh g–1 (1.51 mAh cm–2) at a high current density of 30 A g–1 (93 mA cm–2) as well as excellent cycling stability with a capacity retention of 96.3% after 1600 cycles, which has rarely been achieved before.

A Universal Strategy toward Ultrasmall Hollow Nanostructures with Remarkable Electrochemical Performance

“…Theh ollow nanostructures have demonstrated great potential in electrochemical energy storage and conversion. However,t he performance still needs to improve and the understanding of size effect remains scarce.A saproof of concept, we studied the electrochemical performance of ultrasmall hollow Fe 2 O 3 nanoparticle on RGO (S-H-Fe 2 O 3 / RGO) composite as representative anode for the lithium-ion battery.F or comparison, we also fabricated the large hollow Fe 2 O 3 nanoparticle/RGO composite (L-H-Fe 2 O 3 /RGO) with an average size of 50 nm, which is typical size in previous studies (Supporting Information, Figure S12), [34][35][36][37][38] Figure S15).…”

Biological Metabolism Synthesis of Metal Oxides Nanorods from Bacteria as a Biofactory toward High‐Performance Lithium‐Ion Battery Anodes

“…In the first cycle, a well‐defined reduction peak located at ≈0.6 V is observed during the cathodic scanning, which is attributed to the Li + insertion into the crystal structure of Fe 2 O 3 and the reduction of Fe 2 O 3 (Fe 2 O 3 + 6 Li + + 6 e − ↔ 2 Fe + 3Li 2 O) as well as the formation of SEI layer . Meanwhile, a broad oxidation peak at ≈1.7 V in the first anodic scan is mainly ascribed to the two‐step oxidation process of Fe 0 to Fe 2+ and Fe 2+ to Fe 3+ . From the second cycle onward, the reduction peak shifts distinctly to the higher potential of ≈0.9 V, implying that the kinetics of the reduction process of Fe 3+ to Fe 0 are improved after the structure realignment and electrochemical activation during the first cycle .…”

“…[32] Meanwhile, a broad oxidation peak at ≈1.7 V in the first anodic scan is mainly ascribed to the two-step oxidation process of Fe 0 to Fe 2+ and Fe 2+ to Fe 3+ . [24,30] From the second cycle onward, the reduction peak shifts distinctly to the higher potential of ≈0.9 V, implying that the kinetics of the reduction process of Fe 3+ to Fe 0 are improved after the structure realignment and electrochemical activation during the first cycle. [46,47] Although the oxidation peak has a positive shift, it still locates around 1.7-1.8 V. Moreover, the intensities of reduction and oxidation peaks both decrease in the second cycle, particularly the reduction peak, which results from the formation of SEI layer on the surface of Fe 2 O 3 electrode during the initial lithiation process.…”

“…Iron-based oxides (e.g., α-Fe 2 O 3 , γ-Fe 2 O 3 , and Fe 3 O 4 ) as promising anode materials for LIBs have deserved soaring attention because of their much higher capacity than that of conventional graphite (372 mAh g −1 ), as well as nontoxicity, abundance, and low cost. [5,[19][20][21][22][23][24] Particularly, α-Fe 2 O 3 electrochemically reacted with Li + ions via the conversion mechanism (Fe 2 O 3 + 6Li + + 6e − ↔ 2Fe + 3Li 2 O) theoretically delivers an extremely high capacity of 1007 mAh g −1 . [22,25] However, restricted by dramatic volume expansion rate, low electronic conductivity, and unstable solid electrolyte interphase (SEI), α-Fe 2 O 3 suffers rapid capacity fading during the long-term cycling and inferior rate capability under high-current charge-discharge processes.…”

“…[26][27][28] So far, one effective approach to improve the cycle life and rate performance is to rationally design and fabricate delicate nanostructured α-Fe 2 O 3 that can not only shorten Li + diffusion pathways but also alleviate volume expansion. [19,[22][23][24]29,30] Although a variety of nanostructured α-Fe 2 O 3 including nanorods, [30][31][32] nanowires, [33] nanotubes, [34] nanosheets, [25,35] nanospheres, [36,37] and nanoparticles [27,28,[38][39][40] are widely verified to overcome the aforementioned issues in the past decades, the conventional physical/chemical synthetic methods extensively involve complex chemical reactions, high hazardous and expansive reagents, and high energy and time consumption, [5,16] which is a huge challenge for the largescale application of nanostructured α-Fe 2 O 3 anodes in LIBs.…”