Manganese and Cobalt-Free Ultrahigh-Ni-Rich Single-Crystal Cathode for High-Performance Lithium Batteries.

Current commercial nickel (Ni)-rich Mn, Co, and Al-containing cathodes are employed in high-energy-density lithium (Li) batteries all around the globe. The presence of Mn/Co in them brings out several problems, such as high toxicity, high cost, severe transition-metal dissolution, and quick surface degradation. Herein, a Mn/Co-free ultrahigh-Ni-rich single-crystal LiNi0.94Fe0.05Cu0.01O2 (SCNFCu) cathode with acceptable electrochemical performance is benchmarked against a Mn/Co-containing cathode. Despite having a slightly lower discharge capacity, the SCNFCu cathode retaining 77% of its capacity across 600 deep cycles in full-cell outperforms comparable to a high-Ni single-crystal LiNi0.9Mn0.05Co0.05O2 (SCNMC; 66%) cathode. It is shown that the stabilizing ions Fe/Cu in the SCNFCu cathode reduce structural disintegration, undesirable side reactions with the electrolyte, transition-metal dissolution, and active Li loss. This discovery provides a new extent for cathode material development for next-generation high-energy, Mn/Co-free Li batteries due to the compositional tuning flexibility and quick scalability of SCNFCu, which is comparable to the SCNMC cathode.

Carbon nanostructure-reinforced SiCw/Si3N4 composite with enhanced thermal conductivity and mechanical properties.

Carbon nanostructures (CNS) as a kind of reinforcement material can remarkably enhance the mechanical and thermal properties of ceramics. This research presents an analysis of the influence of CNS on the thermal conductivity and mechanical properties of SiCw/Si3N4 composites. The SiCw/Si3N4 composites containing various types of CNS e.g. carbon nanofibers (CNF), multi-walled carbon nanotubes (MWCNT) and graphene nano-platelets (GNP) were fabricated by hot-press sintering. XRD analysis confirmed a complete transformation of α-Si3N4 to ß-Si3N4 and microstructural analysis shows a uniform distribution, as well as a pullout and bridging mechanism of CNS. The results revealed that the thermal conductivity and mechanical properties of SiCw/Si3N4 composites increased with the addition of CNS. Maximum values of fracture toughness (9.70 ± 0.8 MPa m1/2) and flexural strength (765 ± 58 MPa) have been achieved for the MWCNT-containing SiCw/Si3N4 composite, whereas the maximum values of Young's modulus (250 ± 3.8 GPa) and hardness (27.2 ± 0.9 GPa) have been achieved for the CNF-containing SiCw/Si3N4 composite. Moreover, thermal conductivity also improved with the addition of CNS and reached a maximum value of 110.6 W m-1 K-1 for the CNF-containing SiCw/Si3N4 composite. This work provides a useful approach for the fabrication of high-performance multifunctional composites for emerging engineering applications.

Enhanced thermal conductivity and mechanical properties of a GNP reinforced Si3N4 composite.

Graphene nanocomposites can significantly enhance the thermal conductivity and mechanical properties of ceramics at relatively low nano-filler addition. Herein, graphene nano-platelet reinforced Si3N4 (GNP/Si3N4) composites were prepared by hot press (HP) sintering using fluoride (AlF3, MgF2) sintering-additives. The microstructural properties revealed the enhanced crystallization degree and density of the GNP/Si3N4 composites with different concentrations of graphene nano-platelets (GNPs). These properties help to achieve a significantly improved thermal conductivity (from 82.42 to 137.47 W m-1 K-1) of the GNP/Si3N4 composites. The morphology of the composites shows a uniform distribution of GNP, whereas overlapping of GNPs (2 to 4 platelets) at the grain boundaries of Si3N4 was observed. The fracture toughness and Vickers hardness of the composites also increased with the increasing content of GNP. The toughening mechanism was similar in all composites with GNP addition in respect of pull out, crack deflection, crack branching and crack bridging.