Interfacial built-in electric field and crosslinking pathways enabling WS_(2)/Ti_(3)C_(2)T_(x) heterojunction with robust sodium storage at low temperature

Developing efficient energy storage for sodium-ion batteries(SIBs)by creating high-performance heterojunctions and understanding their interfacial interaction at the atomic/molecular level holds promise but is also challenging.Besides,sluggish reaction kinetics at low temperatures restrict the operation of SIBs in cold climates.Herein,cross-linking nanoarchitectonics of WS_(2)/Ti_(3)C_(2)T_(x) heterojunction,featuring built-in electric field(BIEF),have been developed,employing as a model to reveal the positive effect of heterojunction design and BIEF for modifying the reaction kinetics and electrochemical activity.Particularly,the theoretical analysis manifests the discrepancy in work functions leads to the electronic flow from the electron-rich Ti_(3)C_(2)T_(x) to layered WS_(2),spontaneously forming the BIEF and“ion reservoir”at the heterogeneous interface.Besides,the generation of cross-linking pathways further promotes the transportation of electrons/ions,which guarantees rapid diffusion kinetics and excellent structure coupling.Consequently,superior sodium storage performance is obtained for the WS_(2)/Ti_(3)C_(2)T_(x) heterojunction,with only 0.2%decay per cycle at 5.0 A g^(-1)(25℃)up to 1000 cycles and a high capacity of 293.5 mA h g^(-1)(0.1A g^(-1)after 100 cycles)even at-20℃.Importantly,the spontaneously formed BIEF,accompanied by“ion reservoir”,in heterojunction provides deep understandings of the correlation between structure fabricated and performance obtained.

Boosted electrochemical performance of Na_(3)V_(2)(PO_(4))_(3) at low temperature through synergistical F substitution and construction of interconnected nitrogen-doped carbonaceous network

Benefitting from its unique NASICON-type framework,the Na_(3)V_(2)(PO_(4))_(3)(NVP)cathodes have aroused extensive interest and have been deemed as the promising cathode candidate for sodium-ion batteries(SIBs).Unfortunately,the poor electronic conductivity,combined with the undesirable volume variations,seriously hinders the practical application of NVP cathode,especially at low temperatures.Herein,a dual-strategy,F substitution accompanied by V vacancies and the construction of three-dimensional(3D)nitrogen-doped carbonaceous frameworks(NC),were employed for the NVP cathode(F-NVP/C@3DNC).The former can remarkably decrease the particle size and enhance Na^(+)migration capability,increasing the ionic conductivity.Meanwhile,the electronic connection and effective buffering can be obtained from the latter,strengthening the electrode integrity.Consequently,up to 100 cycles at 0.1 A g^(-1),a reversible capacity of 113.8 mAh g^(-1),approaching the theoretical value(117 mAh g^(-1)),is demonstrated,accompa-nied by impressive capacity retentions at 1.0(93.75%after 4800 cycles)and 20.0 A g^(-1)(92.7%after 1000 cycles).More importantly,even at-20℃,a superior specific capacity(102.6 mAh g^(-1) after 100 cycles at 0.1 A g^(-1))and high capacity retention(86.6%at 20.0 A g^(-1) up to 1000 cycles)can still be obtained simul-taneously.Significantly,the design of F-NVP/C@3DNC provides insights for the fabrication of polyanion cathodes for applications at low temperatures with modified structure stability and reaction kinetics.