No abstract

High nickel content in LiNixCoyMnzO2 (NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high specific energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li1.4Y0.4Ti1.6(PO4)3 (LYTP) ion/electron conductive network which interconnects single-crystal LiNi0.88Co0.09Mn0.03O2 (SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g−1 after 500 cycles at 5 C rate in the 2.75-4.4 V range at 25 °C. Tests in Li-ion pouch cell configuration (i.e., graphite used as negative electrode active material) demonstrate capacity retention of 85% after 1000 cycles at 0.5 C in the 2.75-4.4 V range at 25 °C for the LYTP-containing SC-NCM88-based positive electrode.

Regulating nanocrystal composition with multiphase compounds is considered an efficient approach to enhance electrochemical performance and structure stability. Nevertheless, the thorough understanding of significant reaction mechanisms and insight into the reason of enhanced performance is still urgent. In this work, the bimetallic sulfide Bi 2 S 3 /MoS 2 heterogeneous with abundant phase boundaries is successfully fabricated. The in situ investigation of Na + -storage mechanism confirms that enormous phase boundaries are self-generated by composition optimization and rational structural design. More importantly, the full understanding of abundant phase boundaries on the enhanced electrochemical properties is explicitly unraveled by combining theoretical analysis and experimental results. It confirms that the interior self-built-in electric-field induced by phase boundaries can enhance the reaction kinetics and boost the charge transfer. Besides, the Bi/Na 2 S interface is well-maintained by the homogeneously distributed phase boundaries, effectively improving the conversion/alloying reversibility and keeping integrity without agglomeration and pulverization. As expected, the Bi 2 S 3 / MoS 2 composite exhibits superior rate capability and long-cycling stability (323.4 mAh g −1 after long-term 1200 cycles at ultrahigh rate of 10 A g −1 ). This strategy of constructing sufficient phase boundaries sheds light on the enhancement of reversibility and stability for other advanced conversion/ alloying-type anode materials.

Potassium‐ion batteries (PIBs) have appealed increasing attention due to the inexpensive K‐element resources and satisfactory electrochemical properties. Presently, there are still challenges for developing desirable anode materials. Two‐dimensional metal sulfides exhibit high specific capacity as host for PIBs, yet the dissolution and agglomeration of unstable reaction intermediate KxSy (K2S, K2S5) inescapability induces large loss of active ingredients and poor reactions reversibility, leading to inferior lifespan. Herein, polar polysulfide VS4 is introduced into SnS nanosheets with constructing layered VS4/SnS heterostructure anchored in graphene scaffold (VS4/SnS@C). In this framework, VS4 with unsaturated bridging (S2)2– can act as the anchoring sites to stabilize intermediates KxSy with efficient entrapment effects. Moreover, the heterostructure can maintain layered SnS and regulate the distribution of KxSy with high conversion reversibility. The reaction reversibility and intermediate absorptivity are enhanced, as confirmed by in situ X‐ray diffraction analysis and theoretical calculations. Consequently, the VS4/SnS@C electrode exhibits ultra‐long lifespans, which achieves a capacity of 168.4 mAh g–1 at 1 A g–1 after 6000 cycles. This strategy of heterostructure design facilitates the understanding of K‐storage mechanisms and significantly enhances the reaction reversibility, providing a thought to address the challenges in metal sulfide anodes toward the development of high‐performance PIBs.

A classical interatomic potential for uranium metal is derived within the framework of the charge optimized many body (COMB) formalism. The potential is fitted with a database obtained from experiment and density functional theory (DFT) calculations. The potential correctly predicts orthorhombic α-U to be the ground state. Good agreement with experimental values is obtained for the lattice parameters, nearest neighbor distances, and elastic constants. Molecular dynamics simulations also correctly show the anisotropy in the coefficient of thermal expansion and the temperature dependence of the nearest neighbor distances.