Flexible energy storage devices are highly desirable in modern portable and wearable electronics. [1,2] All-solid-state flexible batteries are of particular interest for their highly compatible assembly with the existing electronic devices. [3,4] The flexible metal-air batteries, for instance, exhibiting a theoretical energy density of 8100 Wh kg −1 , have been considered as a promising clean energy conversion source to satisfy the demand of future energy storage systems. [5] As a typical requirement of metal-air batteries, the cathodic electrode undertakes the mission of oxygen reduction reaction (ORR) and significantly determines their final discharge performance. To date, the noble metal-based electrocatalysts have been widely used as the cathodic material due to their low activation energy for ORR. [6] However, their exorbitant price and lessthan-ideal durability in alkaline solution severely limited the wholesale application in the alkaline metal-air batteries. Therefore, developing novel nonprecious catalysts with highly-efficient ORR performance attracts great research attentions.Metals, metal oxides and their composites, [7,8] metal-free carbon materials, [9] and metal-N-C family [10,11] are widely studied nonprecious catalysts for ORR. The metal-free carbon materials have drawn particular interests due to their widespread pourability and excellent durability in alkaline solution, [12,13] yet the best performance is still limited by the insufficient active sites in the original pure products. Heteroatom doping of carbon materials is a unique approach to enhance the ORR activity since it can form abundant active sites. [14,15] With this regard, phosphorus (P) exhibits more negative electronegativity and stronger electron-donating ability compared to carbon, and thus the P-doped carbon materials are considered as highly potential catalysts for aqueous metal-air batteries. [16,17] Nevertheless, currently such P-doped carbon materials still exhibit a relatively poor ORR activity compared to the commercial Pt/C catalysts, ascribing to their unsatisfied structural geometry and relatively low doping level.Recently, N, S-doped carbon dots (P-CD), where mono-heteroatoms are doped into the highly stable sp 2 -hybridized graphite structure to form the covalent bonds, have been developed as a potential carbon architecture for ORR. [18] A common problem Carbon dots have been recognized as one of the most promising candidates for the oxygen reduction reaction (ORR) in alkaline media. However, the desired ORR performance in metal-air batteries is often limited by the moderate electrocatalytic activity and the lack of a method to realize good dispersion. To address these issues, herein a biomass-deriving method is reported to achieve the in situ phosphorus doping (P-doping) of carbon dots and their simultaneous decoration onto graphene matrix. The resultant product, namely P-doped carbon dot/graphene (P-CD/G) nanocomposites, can reach an ultrahigh P-doping level for carbon nanomaterials. The P-CD/G nanocomposites are fou...
The energy density of lithium-ion batteries can be increased by replacing the traditional graphite anode with a high capacity silicon anode. However, volume changes and interfacial instabilities cause a large irreversible capacity and a continual loss of lithium during cycling, which lead to rapid capacity loss. In this work, we add Li5FeO4 (LFO) to a LiNi0.5Mn0.3Co0.2O2 (NMC) cathode as a pre-lithiation additive, which increases the lithium inventory and extends the cycle life of Si-graphite/NMC full cells, and decreases the NMC particle degradation. LFO delivers a large 764 mAh g−1 LFO capacity below 4.7 V vs Li/Li+. By tuning the LFO content in Si-graphite/LFO-NMC full cells, we show higher capacity, improved retention, lower impedance, and superior rate performance compared to full cells without LFO. Post-test characterizations demonstrate that LFO inclusion in the cathode matrix leads to less NMC secondary particle segregation/cracking and a thinner surface reduced layer on the NMC particles. The beneficial effects of LFO endure after the lithium reserve has been exhausted, highlighting a lasting synergy between the lithium source and electrode active materials. This study introduces a new approach to simultaneously increase lithium inventory and reduce cathode degradation, and makes critical advances toward enabling Si anodes for lithium-ion batteries.
Metal fluorides usually have a large electronegativity and are promising electrode materials for high-power lithium-ion batteries. However, like other conversion-reaction-based materials, large volumetric expansions and large capacity losses in cycling are the major issues for metal fluorides. Here, we explore substitution of Ni with Cu for binary NiF2 and its effects on the electrochemical properties. By in situ transmission electron microscopy, the structural evolutions of several ternary metal fluorides with different Cu/Ni ratios are observed and correlated with their electrochemical properties. With increased Cu substitution from 0 to 25 wt %, the areal expansion during the first lithiation is reduced. Meanwhile, the fluorine loss (due to reaction irreversibility) in the delithiation cycle is also reduced. This provides an explanation for the advantage of Cu substitution for improved cycling stability and capacity. We believe that our observations provide insight into the development of better ternary metal fluorides as cathodes for high power density lithium-ion batteries.
Copper (Cu) is a catalyst broadly used in industry for hydrogenation of carbon dioxide, which has broad implications for environmental sustainability. An accurate understanding of the degeneration behavior of Cu catalysts under operando conditions is critical for uncovering the failure mechanism of catalysts and designing novel ones with optimized performance. Despite the widespread use of these materials, their failure mechanisms are not well understood because conventional characterization techniques lack the necessary time and spatial resolution to capture these complex behaviors. In order to overcome these challenges, we carried out transmission electron microscopy (TEM) with a specialized in situ gas environmental holder, which allows us to unravel the dynamic behavior of the Cu nanowires (NWs) in operando. The failure process of these nanoscale Cu catalysts under CO2 atmosphere were tracked and further rationalized based on our numerical modeling using phase-field methods.
This paper describes a new, high‐performance, Pb‐based nanocomposite anode material for lithium‐ion batteries. A unique nanocomposite structure of Pb@PbO core‐shell nanoparticles in a carbon matrix is obtained by using a simple high‐energy ball milling method using the low‐cost starting materials PbO and carbon black. Electrochemical performance tests show its excellent reversible capacity (≈600 mAh g−1) and cycle stability (92% retention at 100th cycle), which are one of the best values reported for Pb‐based anodes in the literature. Synchrotron X‐ray diffraction and absorption techniques revealed the detailed lithium storage mechanism that can be highlighted with the unexpectedly wide reversible Pb redox range (between Pb2+ and Pb4−) and the evolution of Zintl‐type LiyPb structures during the electrochemical lithium reaction. The results provide new insights into the lithium storage mechanism of these Pb‐based materials and their potential as low‐cost, high‐performance anodes.
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