In Situ Transmission Electron Microscopy Observation of the Lithiation–Delithiation Conversion Behavior of CuO/Graphene Anode

The electrochemical conversion behavior of metal oxides as well as its influence on the lithium-storage performance remains unclear. In this paper, we studied the dynamic electrochemical conversion process of CuO/graphene as anode by in situ transmission electron microscopy. The microscopic conversion behavior of the electrode was further correlated with its macroscopic lithium-storage properties. During the first lithiation, the porous CuO nanoparticles transformed to numerous Cu nanograins (2–3 nm) embedded in Li₂O matrix. The porous spaces were found to be favorable for accommodating the volume expansion during lithium insertion. Two types of irreversible processes were revealed during the lithiation–delithiation cycles. First, the nature of the charge–discharge process of CuO anode is a reversible phase conversion between Cu₂O and Cu nanograins. The delithiation reaction cannot recover the electrode to its pristine structure (CuO), which is responsible for about ∼55% of the capacity fading in the first cycle. Second, there is a severe nanograin aggregation during the initial conversion cycles, which leads to low Coulombic efficiency. This finding could also account for the electrochemical behaviors of other transition metal oxide anodes that operate with similar electrochemical conversion mechanism

Pt–Fe–Cu Ordered Intermetallics Encapsulated with N‑Doped Carbon as High-Performance Catalysts for Oxygen Reduction Reaction

Ternary platinum (Pt)-based ordered intermetallics represent a group of promising electrocatalysts in energy-conversion applications, because of their multielemental coupling that can potentially boost the activity and durability of the oxygen reduction reaction (ORR). Yet, the achievable catalysis performance is still susceptible to the inevitable transition metal leaching that can hardly be eliminated in an acidic environment. Herein, we report a nitrogen (N)-modified carbon (shell) encapsulated Pt–Fe–Cu ordered intermetallic nanoparticles (core) electrocatalyst for acidic ORR, where the Pt–Fe–Cu core presents a face-centered tetragonal (fct) phase. It is demonstrated that N-doped carbon shells can not only protect Pt–Fe–Cu cores from dissolution, agglomeration, coalescence, and Ostwald ripening but also enable the electronic structure regulation of the central Pt sites through the strong Fe–N coordination. The optimized Pt–Fe–Cu intermetallic with N-doped carbon shells delivers superior ORR activity and is more chemically stable over disordered Pt–Fe–Cu alloy, Pt–Fe–Cu intermetallics without a N-doped carbon shell, and commercial Pt/C, where the achievable ORR mass and specific activities are nearly 5-fold and 4-fold higher than those of commercial Pt/C in the acidic media, respectively

Lithiation Behavior of Individual Carbon-Coated Fe₃O₄ Nanowire Observed by in Situ TEM

Fe3O4 nanowires, as a typical transition-metal oxide (TMO), are being considered as promising anodes for lithium ion batteries (LIBs) due to their 1D structure and high specific capacity. However, their underlying mechanism and electrochemical behaviors are still poorly understood. Here, the dynamic behavior and the electrochemical reaction of the carbon-coated Fe3O4 (Fe3O4@C) nanowire have been investigated directly through assembling a nanoscale LIBs inside transmission electron microscope (TEM). The in situ TEM results reveal that the Fe3O4 nanowires undergo cracking and fracturing upon the first lithiation, but the carbon coatings still embrace the oxide cores well after lithiation and play a role in maintaining the mechanical and electrical integrity. Meanwhile the lithiation process involves the conversion of Fe3O4 nanowires to Fe nanograins and the formation of Li2O along the lithium ions diffusion direction. The delithiated product is FeO rather than the original phase of Fe3O4 after the first delithiation process. This irreversible phase conversion may be a major cause of capacity fading of the electrode in the first cycle. As for the Fe3O4 electrode, about 78% of the capacity loss can be attributed to the irreversible phase reaction in the first cycle. During the subsequent lithiation-delithiation cycles, the Fe3O4 electrode shows a reversible conversion between Fe and FeO nanograins, accounting for the good reversibility of Fe3O4 anodes for LIBs. Our in situ results provide important insights into the electrochemical behavior and conversion mechanism of TMO-based anodes in LIBs and are helpful for designing LIBs with outstanding performance

Lithiation Behavior of Individual Carbon-Coated Fe₃O₄ Nanowire Observed by in Situ TEM

Fe3O4 nanowires, as a typical transition-metal oxide (TMO), are being considered as promising anodes for lithium ion batteries (LIBs) due to their 1D structure and high specific capacity. However, their underlying mechanism and electrochemical behaviors are still poorly understood. Here, the dynamic behavior and the electrochemical reaction of the carbon-coated Fe3O4 (Fe3O4@C) nanowire have been investigated directly through assembling a nanoscale LIBs inside transmission electron microscope (TEM). The in situ TEM results reveal that the Fe3O4 nanowires undergo cracking and fracturing upon the first lithiation, but the carbon coatings still embrace the oxide cores well after lithiation and play a role in maintaining the mechanical and electrical integrity. Meanwhile the lithiation process involves the conversion of Fe3O4 nanowires to Fe nanograins and the formation of Li2O along the lithium ions diffusion direction. The delithiated product is FeO rather than the original phase of Fe3O4 after the first delithiation process. This irreversible phase conversion may be a major cause of capacity fading of the electrode in the first cycle. As for the Fe3O4 electrode, about 78% of the capacity loss can be attributed to the irreversible phase reaction in the first cycle. During the subsequent lithiation-delithiation cycles, the Fe3O4 electrode shows a reversible conversion between Fe and FeO nanograins, accounting for the good reversibility of Fe3O4 anodes for LIBs. Our in situ results provide important insights into the electrochemical behavior and conversion mechanism of TMO-based anodes in LIBs and are helpful for designing LIBs with outstanding performance

Lithiation Behavior of Individual Carbon-Coated Fe₃O₄ Nanowire Observed by in Situ TEM

Fe₃O₄ nanowires, as a typical transition-metal oxide (TMO), are being considered as promising anodes for lithium ion batteries (LIBs) due to their 1D structure and high specific capacity. However, their underlying mechanism and electrochemical behaviors are still poorly understood. Here, the dynamic behavior and the electrochemical reaction of the carbon-coated Fe₃O₄ (Fe₃O₄@C) nanowire have been investigated directly through assembling a nanoscale LIBs inside transmission electron microscope (TEM). The in situ TEM results reveal that the Fe₃O₄ nanowires undergo cracking and fracturing upon the first lithiation, but the carbon coatings still embrace the oxide cores well after lithiation and play a role in maintaining the mechanical and electrical integrity. Meanwhile the lithiation process involves the conversion of Fe₃O₄ nanowires to Fe nanograins and the formation of Li₂O along the lithium ions diffusion direction. The delithiated product is FeO rather than the original phase of Fe₃O₄ after the first delithiation process. This irreversible phase conversion may be a major cause of capacity fading of the electrode in the first cycle. As for the Fe₃O₄ electrode, about 78% of the capacity loss can be attributed to the irreversible phase reaction in the first cycle. During the subsequent lithiation-delithiation cycles, the Fe₃O₄ electrode shows a reversible conversion between Fe and FeO nanograins, accounting for the good reversibility of Fe₃O₄ anodes for LIBs. Our in situ results provide important insights into the electrochemical behavior and conversion mechanism of TMO-based anodes in LIBs and are helpful for designing LIBs with outstanding performance

Dual Passivation of Cathode and Anode through Electrode–Electrolyte Interface Engineering Enables Long-Lifespan Li Metal–SPAN Batteries

The reliability and durability of lithium metal (Li0)–sulfur batteries are largely limited by the undesired Li0 plating-stripping irreversibility and the detrimental polysulfide dissolution, yet approaches that can simultaneously address the above anodic and cathodic problems are scarce. Herein, we report the stable operation of a Li0-SPAN (sulfurized polyacrylonitrile) battery via an anode–cathode dual-passivation approach. By combination of a fluorinated localized high concentration electrolyte (LHCE) and a Li3N-forming additive (TMS-N3), robust and highly conductive electrode passivation layers are formed in situ on the surface of both the Li0 anode and the SPAN cathode. The resulting highly reversible, dendrite-free, and high-density Li0 plating morphology enables a high Coulombic efficiency of 99.4%. Advanced tender energy X-ray spectroscopy also reveals the eliminated Li2S formation and minimized polysulfide dissolution in SPAN cathodes, leading to a high capacity of 580 mAh/gSPAN and stable cycling with negligible capacity decay (0.7%) for 800 cycles. This electrode–electrolyte interphase engineering strategy has tackled the major limitations of Li–S batteries in both ether- and carbonate-based electrolyte systems and under a wide temperature range from −10 to +50 °C, thus providing insightful guidelines for the rational design of highly durable and high-energy-density Li0-S batteries

In Situ Visualization of Structural Evolution and Fissure Breathing in (De)lithiated H₂V₃O₈ Nanorods

Layered H2V3O8 material consisting of V3O8 layers features the elastic space for buffering volume change upon repeated ion (de)­intercalations. However, its ion transport and phase transformations still remain largely unknown due to lack of direct evidence. Here we employ in situ transmission electron microscopy to revisit this material carefully. Upon lithiation, the localized phase transformation from H2V3O8 to V2O3 via an intermediate VO2 phase was observed, and large structural fissures gradually formed. Unexpectedly, the large fissures were able to self-heal during delithiation with the VO2 phase as the delithiated product. The fissures could appear and disappear alternately upon subsequent (de)­lithiation, in which a stable and reversible phase transformation between V2O3 and VO2 phases was established. These unreported findings are expected to call for renewed attention to this electrode material for a more comprehensive understanding in rechargeable metal-ion batteries

In Situ Visualization of Structural Evolution and Fissure Breathing in (De)lithiated H₂V₃O₈ Nanorods

Layered H2V3O8 material consisting of V3O8 layers features the elastic space for buffering volume change upon repeated ion (de)­intercalations. However, its ion transport and phase transformations still remain largely unknown due to lack of direct evidence. Here we employ in situ transmission electron microscopy to revisit this material carefully. Upon lithiation, the localized phase transformation from H2V3O8 to V2O3 via an intermediate VO2 phase was observed, and large structural fissures gradually formed. Unexpectedly, the large fissures were able to self-heal during delithiation with the VO2 phase as the delithiated product. The fissures could appear and disappear alternately upon subsequent (de)­lithiation, in which a stable and reversible phase transformation between V2O3 and VO2 phases was established. These unreported findings are expected to call for renewed attention to this electrode material for a more comprehensive understanding in rechargeable metal-ion batteries

In Situ Visualization of Structural Evolution and Fissure Breathing in (De)lithiated H₂V₃O₈ Nanorods

Layered H2V3O8 material consisting of V3O8 layers features the elastic space for buffering volume change upon repeated ion (de)­intercalations. However, its ion transport and phase transformations still remain largely unknown due to lack of direct evidence. Here we employ in situ transmission electron microscopy to revisit this material carefully. Upon lithiation, the localized phase transformation from H2V3O8 to V2O3 via an intermediate VO2 phase was observed, and large structural fissures gradually formed. Unexpectedly, the large fissures were able to self-heal during delithiation with the VO2 phase as the delithiated product. The fissures could appear and disappear alternately upon subsequent (de)­lithiation, in which a stable and reversible phase transformation between V2O3 and VO2 phases was established. These unreported findings are expected to call for renewed attention to this electrode material for a more comprehensive understanding in rechargeable metal-ion batteries

In Situ Visualization of Structural Evolution and Fissure Breathing in (De)lithiated H₂V₃O₈ Nanorods

Layered H2V3O8 material consisting of V3O8 layers features the elastic space for buffering volume change upon repeated ion (de)­intercalations. However, its ion transport and phase transformations still remain largely unknown due to lack of direct evidence. Here we employ in situ transmission electron microscopy to revisit this material carefully. Upon lithiation, the localized phase transformation from H2V3O8 to V2O3 via an intermediate VO2 phase was observed, and large structural fissures gradually formed. Unexpectedly, the large fissures were able to self-heal during delithiation with the VO2 phase as the delithiated product. The fissures could appear and disappear alternately upon subsequent (de)­lithiation, in which a stable and reversible phase transformation between V2O3 and VO2 phases was established. These unreported findings are expected to call for renewed attention to this electrode material for a more comprehensive understanding in rechargeable metal-ion batteries