Graphene‐functionalised Olivine Lithium Manganese Phosphate Derivatives for High Performance Lithium‐ion Capacitors

Boron-Catalyzed Graphitization Carbon Layer Enabling LiMn0.8 Fe0.2 PO4 Cathode Superior Kinetics and Li-Storage Properties

The poor electrode kinetics and low conductivity of the LiMn_0.8 Fe_0.2 PO₄ cathode seriously impede its practical application. Here, an effective strategy of boron-catalyzed graphitization carbon coating layer is proposed to stabilize the nanostructure and improve the kinetic properties and Li-storage capability of LiMn_0.8 Fe_0.2 PO₄ nanocrystals for rechargeable lithium-ion batteries. The graphite-like BC₃ is derived from B-catalyzed graphitization coating layers, which can not only effectively maintain the dynamic stability of the LiMn_0.8 Fe_0.2 PO₄ nanostructure during cycling, but also plays an important role in enhancing the conductivity and Li⁺ migration kinetics of LiMn_0.8 Fe_0.2 PO₄ @B-C. The optimized LiMn_0.8 Fe_0.2 PO₄ @B-C exhibits the fastest intercalation/deintercalation kinetics, highest electrical conductivity (8.41 × 10^-2 S cm^-1 ), Li⁺ diffusion coefficient (6.17 × 10^-12 cm² s^-1 ), and Li-storage performance among three comparison samples (B-C0, B-C6, and B-C9). The highly reversible properties and structural stability of LiMn_0.8 Fe_0.2 PO₄ @B-C are further proved by operando XRD analysis. The B-catalyzed graphitization carbon coating strategy is expected to be an effective pathway to overcome the inherent drawbacks of the high-energy density LiMn_0.8 Fe_0.2 PO₄ cathode and to improve other cathode materials with low-conductivity and poor electrode kinetics for rechargeable second batteries.

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn₂O₄/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn₂O₄/MWCNTs preparation involved initial synthesis of Mn₃O₄ and CuMn₂O₄ precursors followed by an energy efficient reflux growth method for the CuMn₂O₄/MWCNTs. The CuMn₂O₄/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g^-1 at 0.5 A g^-1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g^-1 at 0.5 A g^-1 current load. Stability studies showed that after 6000 cycles, the CuMn₂O₄/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte.

Sustainable Hydrothermal and Solvothermal Synthesis of Advanced Carbon Materials in Multidimensional Applications: A Review

The adoption of green technology is very important to protect the environment and thus there is a need for improving the existing methods for the fabrication of carbon materials. As such, this work proposes to discuss, interrogate, and propose viable hydrothermal, solvothermal, and other advanced carbon materials synthesis methods. The synthesis approaches for advanced carbon materials to be interrogated will include the synthesis of carbon dots, carbon nanotubes, nitrogen/titania-doped carbons, graphene quantum dots, and their nanocomposites with solid/polymeric/metal oxide supports. This will be performed with a particular focus on microwave-assisted solvothermal and hydrothermal synthesis due to their favourable properties such as rapidity, low cost, and being green/environmentally friendly. These methods are regarded as important for the current and future synthesis and modification of advanced carbon materials for application in energy, gas separation, sensing, and water treatment. Simultaneously, the work will take cognisance of methods reducing the fabrication costs and environmental impact while enhancing the properties as a direct result of the synthesis methods. As a direct result, the expectation is to impart a significant contribution to the scientific body of work regarding the improvement of the said fabrication methods.