Hierarchically Porous N,S-Codoped Carbon-Embedded Dual Phase MnO/MnS Nanoparticles for Efficient Lithium Ion Storage

Synergistic Engineering of CoO/MnO Heterostructures Integrated with Nitrogen-Doped Carbon Nanofibers for Lithium-Ion Batteries

The integration of heterostructures within electrode materials is pivotal for enhancing electron and Li-ion diffusion kinetics. In this study, we synthesized CoO/MnO heterostructures to enhance the electrochemical performance of MnO using a straightforward electrostatic spinning technique followed by a meticulously controlled carbonization process, which results in embedding heterostructured CoO/MnO nanoparticles within porous nitrogen-doped carbon nanofibers (CoO/MnO/NC). As confirmed by density functional theory calculations and experimental results, CoO/MnO heterostructures play a significant role in promoting Li+ ion and charge transfer, improving electronic conductivity, and reducing the adsorption energy. The accelerated electron and Li-ion diffusion kinetics, coupled with the porous nitrogen-doped carbon nanofiber structure, contribute to the exceptional electrochemical performance of the CoO/MnO/NC electrode. Specifically, the as-prepared CoO/MnO/NC exhibits a high reversible specific capacity of 936 mA h g-1 at 0.1 A g-1 after 200 cycles and an excellent high-rate capacity of 560 mA h g-1 at 5 A g-1, positioning it as a competitive anode material for lithium-ion batteries. This study underscores the critical role of electronic and Li-ion regulation facilitated by heterostructures, offering a promising pathway for designing transition metal oxide-based anode materials with high performances for lithium-ion batteries.

Ni activated Mo2C by regulating the interfacial electronic structure for highly efficient lithium-ion storage

Regulating the electronic structure plays a positive role in improving the ion/electron kinetics of electrode materials for lithium ion batteries (LIBs). Herein, an effective approach is demonstrated to achieve Ni/Mo₂C hybrid nanoparticles embedded in porous nitrogen-doped carbon nanofibers (Ni/Mo₂C/NC). Density functional theory calculations indicate that Ni can activate the interface of Ni/Mo₂C by regulating the electronic structure, and accordingly improve the electron/Li-ion diffusion kinetics. The charge at the interface transfers from Ni atoms to Mo atoms on the surface of Mo₂C, illustrating the formation of an interfacial electric field in Ni/Mo₂C. The formed interfacial electric field in Ni/Mo₂C can improve the intrinsic electronic conductivity, and reduce the Li adsorption energy and the Li⁺ diffusion barrier. Thus, the obtained Ni/Mo₂C/NC shows an excellent high-rate capability of 344.1 mA h g^-1 at 10 A g^-1, and also displays a superior cyclic performance (remaining at 412.7 mA h g^-1 after 1800 cycles at 2 A g^-1). This work demonstrates the important role of electronic structure regulation by assembling hybrid materials and provides new guidance for future work on designing novel electrode materials for LIBs.

Rational Design of Space-Confined Mn-Based Heterostructures with Synergistic Interfacial Charge Transport and Structural Integrity for Lithium Storage

Manganese-based compounds are expected to become promising candidates for lithium-ion battery anodes by virtue of their high theoretical specific capacity and low conversion potential. However, their application is hindered by their inferior electrical conductivity and drastic volume variations. In this work, a unique heterostructure composed of MnO and MnS spatially confined in pyrolytic carbon microspheres (MnO@MnS/C) was synthesized through an integrated solvothermal method, calcination, and low-temperature vulcanization technology. In this architecture, heterostructured MnO@MnS nanoparticles (∼10 nm) are uniformly embedded into the carbonaceous microsphere matrix to maintain the structural stability of the composite. Benefiting from the combination of structural and compositional features, the MnO@MnS/C enables abundance in electrochemically active sites, alleviated volumetric variation, a rich conductive network, and enhanced lithium-ion diffusion kinetics, thus yielding remarkable rate capability (1235 mAh·g^-1 at 0.2 A·g^-1 and 608 mAh·g^-1 at 3.2 A·g^-1) and exceptional cycling stability (522 mAh·g^-1 after 2000 cycles at 3.0 A·g^-1) as a competitive anode material for lithium-ion batteries. Density functional theory calculations unveil that the heterostructure promotes the transfer of electrons with improved conductivity and also accelerates the migration of lithium ions with reduced polarization resistance. This combined with the enhancement brought by spatial confinement endows the MnO@MnS/C with remarkable lithium storage performance.

Polyvinylpyrrolidone assisted transformation of Cu-MOF into N/P-co-doped Octahedron carbon encapsulated Cu3P nanoparticles as high performance anode for lithium ion batteries

The large volume expansion and poor electrical conductivity of copper phosphide (Cu₃P) during the cycle limit their further application as anode of lithium-ion batteries. Therefore, polyvinylpyrrolidone (PVP) modified Cu₃(BTC)₂-derived (BTC = 1, 3, 5-Benzentricarboxylic acid) in-situ N/P-co-doped Octahedron carbon encapsulated Cu₃P nanoparticles (Cu₃P@NPC) are successfully prepared through a two-step process of carbonization and phosphating. The N/P-co-doped Octahedron carbon matrix improves the conductivity of Cu₃P and moderates the volume expansion during the lithiation/delithiation process. Meanwhile, the interaction between the Cu₃P and the doped carbon matrix is methodically explored by using density functional theory (DFT). Through the analysis of the partial charge density, the density of states and the Bader charge, and the calculation results verify the correctness of the experimental observation results, that is, Cu₃P@NPC has good electrochemical performance. The results show that Cu₃P@NPC, as the anode of Lithium-ion batteries, has excellent electrochemical performance: it exhibits satisfactory rate performance (251.9 mAh g^-1 at 5.0 A g^-1) and excellent cycle performance (336.4 mAh g^-1 at 1 A g^-1 over 1000 cycles). This article provides an effective strategy for the encapsulation of metal phosphide nanoparticles in a doped carbon matrix.

MnS@N,S Co-Doped Carbon Core/Shell Nanocubes: Sulfur-Bridged Bonds Enhanced Na-Storage Properties Revealed by In Situ Raman Spectroscopy and Transmission Electron Microscopy

Rational structure and morphology design are of great significance to realize excellent Na storage for advanced electrode materials in sodium-ion batteries (SIBs). Herein, a cube-like core/shell composite of single MnS nanocubes (≈50 nm) encapsulated in N, S co-doped carbon (MnS@NSC) with strong CSMn bond interactions is successfully prepared as outstanding anode material for SIBs. The carbon shell significantly restricts the expansion of the MnS volume in successive sodiation/desodiation processes, as demonstrated by in situ transmission electron microscopy (TEM) of one single MnS@NSC nanocube. Moreover, the in situ generated CSMn bonds between the MnS core and carbon shell play a significant role in improving the Na-storage stability and reversibility of MnS@NSC, as revealed by in situ Raman and TEM. As a result, MnS@NSC exhibits a high reversible specific capacity of 594.2 mAh g^-1 at a current density of 100 mA g^-1 and an excellent rate performance. It also achieves a remarkable cycling stability of 329.1 mAh g^-1 after 3000 charge/discharge cycles at 1 A g^-1 corresponding to a low capacity attenuation rate of 0.0068% per cycle, which is superior to that of pristine MnS and most of the reported Mn-based anode materials in SIBs.

Construction of Rich Conductive Pathways from Bottom to Top: A Highly Efficient Charge-Transfer System Used in Durable Li/Na-Ion Batteries at -20 °C

The construction of potential electrode materials with wide temperature property for high-energy-density secondary batteries has attracted great interest in recent years. Herein, a hybrid electrode, consisting of a nitrogen-doped carbon/α-MnS/flake graphite composite (α-MnS@N-C/FG), is prepared through a post-sulfurization route. In the α-MnS@N-C/FG composite, α-MnS nanoparticles wrapped by the N-C layer are uniformly embedded onto FG, forming a novel nanofoam structure. The as-obtained α-MnS@N-C/FG shows excellent lithium/sodium storage performance, with a specific capacity of 712 mA h g^-1 in the 700th cycle at 1.0 A g^-1 or 186.4 mA h g^-1 in the 100th cycle at 100 mA g^-1 using lithium or sodium foil as the counter electrode, respectively. Moreover, even operated at -20 °C, the α-MnS@N-C/FG can still attain a high specific capacity of 350 mA h g^-1 after 50 cycles at 100mA g^-1 for LIBs. This exceptional electrochemical response is attributed to the synergetic effect of the smart design of a hybrid nanofoam structure, in which the FG skeleton and N-C coating layer can significantly enhance the conductivity of the whole electrode from bottom to top. Accordingly, the enhanced redox kinetics endow the electrode with pseudocapacitive-dominated electrochemical behavior, leading to fast electrode reactions and robust structural stability in the whole electrode.

Temperature-Dependent Morphologies of Precursors: Metal-Organic Framework-Derived Porous Carbon for High-Performance Electrochemical Double-Layer Capacitors

In this work, three Cu metal-organic framework samples with tunable rhombic, squama, and trucated bipyramid morphologies have been synthesized at 0, 25, and 60 °C, respectively, and further employed as precursors to initially prepare Cu@C composites by the calcination-thermolysis procedure. Then Cu@C composites have been etched with HCl and subsequently activated with KOH to obtain activated porous carbon (APC-0, -25, and -60). Interestingly, APC-25 presents a loose multilevel morphology of cabbage and possesses the largest specific surface area (1880.4 m² g^-1) and pore volume (0.81 cm³ g^-1) among these APC materials. Consequently, APC-25 also exhibits the highest specific capacitance of 196 F g^-1 at 0.5 A g^-1, and the corresponding symmetric supercapacitor cell (SSC) achieves a remarkable energy density of 11.8 Wh kg^-1 at a power density of 350 W kg^-1. Furthermore, APC-25 shows excellent cycling stability, and the loss of capacitance is only 7.7% even after 10000 cycles at 1 A g^-1. Significantly, five light-emitting diodes can be lit by six SSCs, which proves that APC-25 can be used in energy storage devices.

Resorcinol-Formaldehyde Resin-Coated Prussian Blue Core-Shell Spheres and Their Derived Unique Yolk-Shell FeS2@C Spheres for Lithium-Ion Batteries

The practical applications of transition metal sulfides as electrode materials for lithium-ion batteries (LIBs) is greatly hindered by the fast capacity fading owing to the large volume expansion. To address this issue, construction of transition metal sulfide and carbon nanocomposites with unique yolk-shell structures is an effective strategy but also remains a great challenge. In this work, we reported a facile approach to synthesize the unique yolk-shell FeS₂@carbon (FeS₂@C) spheres via calcination treatment of the resorcinol-formaldehyde (RF) resin-coated Prussian blue (FeFe PB) core-shell spheres in Ar atmosphere and a subsequent sulfidation treatment. The synthetic method herein was quite simple and convenient. Such unique structure design could effectively prevent the large volume expansion and dissolution of the active materials in the electrolytes during lithiation. As expected, the yolk-shell FeS₂@C spheres exhibited good electrochemical performance as anode materials for LIBs, which displayed a high discharge capacity of 560 mA h g^-1 at 100 mA g^-1 for 100 cycles. When the current density increased to 1000 mA g^-1, a reversible discharge capacity of 269 mA h g^-1 was still retained after 500 cycles. The present work demonstrated an extraordinary synthetic strategy to construct transition metal sulfide and carbon nanocomposites with unique yolk-shell structure. In addition, this RF resin coating strategy can be further extended to synthesize other RF resin-coated PB analogue (PBA) core-shell nanostructures, demonstrating the generality of this RF resin coating strategy.

Bottom-Up Construction of Reduced-Graphene-Oxide-Anchored MnO with an Nitrogen-Doped Carbon Coating for Synergistically Improving Lithium-Ion Storage

Designing an advanced architecture to overcome the innate issue of MnO-based anode materials in terms of low electrical conductivity and severe volume change during cycling is still a challenge toward which more effort needs devoted. Here, an intriguing hybrid involving the architecture of reduced graphene oxide (RGO)-anchored MnO within an nitrogen-codoped carbon coating (RGO-MnO@NC) is reported via a simple and facile approach and regarded as a promising lithium-ion (Li⁺) anode material with high rate capacity, large specific capacity, and a long cycle lifespan simultaneously. The resulting porous conductive carbon layer could not only promote the electron/ion transfer but also alleviate the volume variation for retaining a relatively stable solid electrolyte interphase and prevent MnO from direct contact with the electrolyte to reduce unexpected lithium consumption. The existing internal voids offer the space to accommodate volume expansion in the lithiation/delithiation processes, and RGO could build a large conductive network for better electron transfer. Consequently, the RGO-MnO@NC electrode presents high Li⁺ storage capacity (699 mAh g^-1 at 0.1 A g^-1), excellent cycling performance (607 mAh g^-1 at 1 A g^-1 over 550 cycles), and a remarkable rate performance. Through kinetic analysis, it is revealed that RGO-MnO@NC exhibits an enhanced capacitive contribution for Li⁺ storage, showing a typical faradaic surface pseudocapacitive mechanism. This work proposes a new strategy to ameliorate the deficiency of the electrode material toward the conductivity and volume change for enhanced Li⁺ storage.