Enhancing potassium-ion storage of Bi_(2)S_(3) through external–internal dual synergism: Ti_(3)C_(2)T_(x) compositing and Cu^(2+) doping

Potassium-ion batteries(PIBs)offer a cost-effective and resource-abundant solution for large-scale energy storage.However,the progress of PIBs is impeded by the lack of high-capacity,long-life,and fast-kinetics anode electrode materials.Here,we propose a dual synergic optimization strategy to enhance the K^(+)storage stability and reaction kinetics of Bi_(2)S_(3) through two-dimensional compositing and cation doping.Externally,Bi_(2)S_(3) nanoparticles are loaded onto the surface of three-dimensional interconnected Ti_(3)C_(2)T_(x) nanosheets to stabilize the electrode structure.Internally,Cu^(2+)doping acts as active sites to accelerate K^(+)storage kinetics.Various theoretical simulations and ex situ techniques are used to elucidate the external–internal dual synergism.During discharge,Ti_(3)C_(2)T_(x) and Cu^(2+)collaboratively facilitate K+intercalation.Subsequently,Cu^(2+)doping primarily promotes the fracture of Bi2S3 bonds,facilitating a conversion reaction.Throughout cycling,the Ti_(3)C_(2)T_(x) composite structure and Cu^(2+)doping sustain functionality.The resulting Cu^(2+)-doped Bi2S3 anchored on Ti_(3)C_(2)T_(x)(C-BT)shows excellent rate capability(600 mAh g^(-1) at 0.1 A g^(–1);105 mAh g^(-1) at 5.0 A g^(-1))and cycling performance(91 mAh g^(-1) at 5.0 A g^(-1) after 1000 cycles)in half cells and a high energy density(179 Wh kg–1)in full cells.

Enhanced reversibility of the magnetoelastic transition in(Mn,Fe)2(P,Si)alloys via minimizing the transition-induced elastic strain energy

Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)_(2)(P,Si)alloys by high-resolution transmission electron microscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density functional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)_(2)(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn_(1.15)Fe_(0.80)P_(0.45)Si_(0.55)alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)_(2)(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.

Large,low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

TiNiSi-type MnCoSi-based alloys show large magnetostriction during the magnetic-field-induced metamagnetic transition.However,the high critical field required to drive the transition directly hinders their potential applications.In this work,we systematically investigate the tricritical behavior and magnetostrictive effect in substituted MnCoSi alloys.Replacing Si with Sb or In,Co with Fe or Cu,and Mn with Co,which can simultaneously reduce the critical field and the temperature of tricritical point,are explored.Among the substituted MnCoSi alloys,Mn_(0.983)Co_(1.017)Si displays a temperature of a tricritical point of 250 K and a room-temperature critical field of 0.60 T,which is the lowest up to now.Profited from these optimizations,a large reversible magnetostrictive effect under low field is successfully realized at room temperature.In a field of 1 T,the magnetostriction of Mn_(0.983)Co_(1.017)Si alloy is close to 1000 ppm.Besides,a strong relation between critical field and valence electron concentration is revealed in the transition-metal-substituted MnCoSi alloys.Our work greatly enhances the low-field magnetostrictive performance of MnCoSi-based alloys and make them be of interest in potential applications.