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.

Influence of nano-mechanical evolution of Ti_(3)AlC_(2) ceramic on the arc erosion resistance of Ag-based composite electrical contact material

Al-containing MAX phase ceramic has demonstrated great potential in the field of high-performance low-voltage electrical contact material.Elucidating the anti-arc erosion mechanism of the MAX phase is crucial for further improving performance,but it is not well-understood.In this study,Ag/Ti_(3)AlC_(2) electrical contact material was synthesized by powder metallurgy and examined by nanoindentation techniques such as constant loading rate indentation,creep testing,and continuous stiffness measurements.Our results indicated a gradual degradation in the nano-mechanical properties of the Ti_(3)AlC_(2) reinforcing phase with increasing arc erosion times,although the rate of this degradation appeared to decelerate over arc erosion times.Specifically,continuous stiffness measurements highlighted the uneven mechanical properties within Ti_(3)AlC_(2),attributing this heterogeneity to the phase’s decomposition.During the early(1-100 times)and intermediate(100-1000 times)stages of arc erosion,the decline in the nano-mechanical properties of Ti_(3)AlC_(2) was primarily ascribed to the decomposition of Ti_(3)AlC_(2) and limited surface oxidation.During the later stage of arc erosion(1000-6200 times),the inner region of Ti_(3)AlC_(2) also sustained arc damage,but a thick oxide layer formed on its surface,enhancing the mechanical properties and overall arc erosion resistance of the Ag/Ti_(3)AlC_(2).

Enhanced conductivity and stability of Co_(0.98)Cu_(x)Mn_(2.02−x)O_(4)ceramics with dual phases and twin structures

Semiconductor materials with heterogeneous interfaces and twin structures generally demonstrate a higher concentration of carriers and better electrical stability.A variety of Cu-doped Co_(0.98)Cu_(x)Mn_(2.02−x)O_(4)(0≤x≤0.5)negative temperature coefficient(NTC)ceramics with dual phases and twin structures were successfully prepared in this study.Rietveld refinement indicates that the content of a cubic spinel phase increases with increasing Cu content.The addition of Cu can promote grain growth and densification.Atomic-level structural characterization reveals the evolution of twin morphology from large lamellae with internal fine lamellae(LIT lamellae)to large lamellae without internal fine lamellae(L lamellae)and the distribution of twin boundary defects.First-principles calculations reveal that the dual phases and twin structures have lower oxygen-vacancy formation energy than those in the case of the pure tetragonal and cubic spinel,thereby enhancing the transmission of carriers.Additionally,the three-dimensional charge-density difference shows that metal ions at the interface lose electrons and dwell in high valence states,thereby enhancing electrical stability of the NTC ceramics.Furthermore,the additional Cu ions engage in electron-exchange interactions with Mn and Co ions,thereby reducing resistivity.In comparison to previous Cu-containing systems,the Co_(0.98)Cu_(x)Mn_(2.02−x)O_(4)series exhibit superior stability(aging value≤2.84%),tunable room-temperature resistivity(ρ),and material constant(B)value(17.5Ω·cm≤ρ≤7325Ω·cm,2836 K≤B≤4315 K).These discoveries lay a foundation for designing and developing new NTC ceramics with ultra-high performance.

Preparation and arc erosion properties of Ag/Ti_2SnC composites under electric arc discharging

New Ag/Ti_2 SnC(Ag/TSC) composites with uniform microstructure were prepared by powder metallurgy. The superior wettability between Ag and Ti_2 SnC was confirmed with a contact angle of 14°. Arc erosion properties of Ag/10 wt%Ti_2 SnC(Ag/10 TSC) and Ag/20 wt%Ti_2 SnC(Ag/20 TSC) contacts were investigated under 400 V/100 A/AC-3 and compared with Ag/CdO contact.The Ag/10 TSC contact exhibited comparable arc erosion property to Ag/CdO contact. The fine arc erosion resistance was attributed to the good wettability between Ti_2 SnC and Ag,the good heat-conducting property of Ag/10 TSC, and the slight decomposition of Ti_2 SnC that absorbed part of electric arc energy. The excessive Ti_2 SnC significantly decreased the thermal conducting property of the Ag/20 TSC composite, resulting in the severe heat accumulation that decomposed Ti_2 SnC and deteriorated arc erosion property. The oxidation behavior of Ti_2 SnC under high electric arc temperature was also studied and then an arc erosion mechanism was proposed to get a comprehensive understanding on the arc erosion property of Ag/TSC composites.