Pressure-induced evolution of stoichiometries and electronic structures of host-guest Na-B compounds

Superionic and electride behaviors in materials,which induce a variety of exotic physical properties of ions and electrons,are of great importance both in fundamental research and for practical applications.However,their coexistence in hot alkali-metal borides has not been observed.In this work,we apply first-principles structure search calculations to identify eight Na-B compounds with host-guest structures,which exhibit a wide range of building blocks and interesting properties linked to the Na/B composition.Among the known borides,Na-rich Na9B stands out as the composition with the highest alkali-metal content,featuring vertex-and face-sharing BNa16 polyhedra.Notably,it exhibits electride characteristics and transforms into a superionic electride at 200 GPa and 2000 K,displaying unusual Na atomic diffusion behavior attributed to the modulation of the interstitial anion electrons.It demonstrates semiconductor behavior in the solid state,and metallic properties associated with Na 3p/3s states in the superionic and liquid regions.On the other hand,B-rich NaB7,consisting of a unique covalent B framework,is predicted to exhibit low-frequency phonon-mediated superconductivity with a T_(c) of 16.8 K at 55 GPa.Our work advances the understanding of the structures and properties of alkali-metal borides.

Nonlinear health evaluation for lithium-ion battery within full-lifespan

Lithium-ion batteries(LIBs), as the first choice for green batteries, have been widely used in energy storage, electric vehicles, 3C devices, and other related fields, and will have greater application prospects in the future. However, one of the obstacles hindering the future development of battery technology is how to accurately evaluate and monitor battery health, which affects the entire lifespan of battery use. It is not enough to assess battery health comprehensively through the state of health(SoH) alone, especially when nonlinear aging occurs in onboard applications. Here, for the first time, we propose a brand-new health evaluation indicator—state of nonlinear aging(SoNA) to explain the nonlinear aging phenomenon that occurs during the battery use, and also design a knee-point identification method and two SoNA quantitative methods. We apply our health evaluation indicator to build a complete LIB full-lifespan grading evaluation system and a ground-to-cloud service framework, which integrates multi-scenario data collection, multi-dimensional data-based grading evaluation, and cloud management functions. Our works fill the gap in the LIBs’ health evaluation of nonlinear aging, which is of great significance for the health and safety evaluation of LIBs in the field of echelon utilization such as vehicles and energy storage. In addition, this comprehensive evaluation system and service framework are expected to be extended to other battery material systems other than LIBs, yet guiding the design of new energy ecosystem.

Helium incorporation induced direct-gap silicides

The search of direct-gap Si-based semiconductors is of great interest due to the potential application in many technologically relevant fields.This work examines the incorporation of He as a possible route to form a direct band gap in Si.Structure predictions and first-principles calculations show that He and Si,at high pressure,form four dynamically stable phases of Si_(2)He(oP36-Si_(2)He,tP9-Si_(2)He,mC18-Si_(2)He,and mC12-Si_(2)He).All phases adopt host–guest structures consisting of a channel-like Si host framework filled with He guest atoms.The Si frameworks in oP36-Si2He,tP9-Si2He,and mC12-Si_(2)He could be retained to ambient pressure after removal of He,forming three pure Si allotropes.Among them,oP36-Si_(2)He and mC12-Si_(2)He exhibit direct band gaps of 1.24 and 1.34 eV,respectively,close to the optimal value(~1.3 eV)for solar cell applications.Analysis shows that mC12-Si_(2)He with an electric dipole transition allowed band gap possesses higher absorption capacity than cubic diamond Si,which makes it to be a promising candidate material for thin-film solar cell.