High content anion(S/Se/P)doping assisted by defect engineering with fast charge transfer kinetics for high-performance sodium ion capacitors

The rate-determining process for sodium storage in TiO2 is greatly depending on charge transfer happening in the electrode materials owing to its inferior diffusion coefficient and electronic conductivity.Apart from reducing the diffusion distance of ion/electron,the increasement of ionic/electronic mobility in the crystal lattice is also very important for charge transport.Here,an oxygen vacancy(OV)engineering assisted in high-content anion(S/Se/P)doping strategy to enhance charge transfer kinetics for ultrafast sodium-storage performance is proposed.Theoretical calculations indicate that OV-engineering evokes spontaneous S doping into the TiO2 phase and achieves high dopant concentration to bring about impurity state electron donor and electronic delocalization over S occupied sites,which can largely reduce the migration barrier of Na+.To realize the speculation,high-content anion doped anatase TiO2/C composites(9.82 at%for S in A-TiO2–x-S/C)are elaborately designed.The optimized A-TiO2–x-S/C anode exhibits extraordinarily high-rate capability with 209.6 mAh g-1at 5000 mA g-1.The assembled sodium ion capacitors deliver an ultrahigh energy density of 150.1 Wh kg-1at a power density of 150 W kg-1when applied as anode materials.This work provides a new strategy to realize high content anion doping concentration,and enhances the charge transfer kinetics for TiO2,which delivers an efficient approach for the design of electrode materials with fast kinetic.

A Novel Hybrid Point Defect of Oxygen Vacancy and Phosphorus Doping in TiO_(2)Anode for High-Performance Sodium Ion Capacitor

Although sodium ion capacitors(SICs)are considered as one of the most promising electrochemical energy storage devices(organic electrolyte batteries,aqueous batteries and supercapacitor,etc.)due to the combined merits of battery and capacitor,the slow reaction kinetics and low specific capacity of anode materials are the main challenges.Point defects including vacancies and heteroatoms doping have been widely used to improve the kinetics behavior and capacity of anode materials.However,the interaction between vacancies and heteroatoms doping have been seldomly investigated.In this study,a hybrid point defects(HPD)engineering has been proposed to synthesize TiO_(2) with both oxygen vacancies(OVs)and P-dopants(TiO_(2)/C-HPD).In comparison with sole OVs or P-doping treatments,the synergistic effects of HPD on its electrical conductivity and sodium storage performance have been clarified through the density func-tional theory calculation and sodium storage characterization.As expected,the kinetics and electronic conductivity of TiO_(2)/C-HPD3 are significantly improved,resulting in excellent rate performance and outstanding cycle stability.Moreover,the SICs assembled from TiO_(2)/C-HPD3 anode and nitrogen-doped porous carbon cathode show outstanding power/energy density,ultra-long life with good capacity retention.This work provides a novel point defect engineering perspective for the development of high-performance SICs electrode materials.

MXene-Derived Defect-Rich TiO2@rGO as High-Rate Anodes for Full Na Ion Batteries and Capacitors

Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices.These devices’s rate ability is determined by the fast sodium ion storage behavior in electrode materials.Herein,a defective TiO2@reduced graphene oxide(M-TiO2@rGO)self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process.The employment of the MXene parent phase exhibits distinctive advantages,enabling defect engineering,nanoengineering,and fluorine-doped metal oxides.As a result,the M-TiO2@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism.The pseudocapacitance-dominated process leads to high capacity,remarkable rate ability,and superior cycling performance.Significantly,an M-TiO2@rGO//Na3 V2(PO4)3 sodium full cell and an M-TiO2@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO2@rGO.The sodium ion battery presents a capacity of 177.1 mAh g-1 at 500 mA g-1 and capacity retention of 74%after 200 cycles.The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg-1 and a maximum power density of 10,103.7 W kg-1.At 1.0 A g-1,it displays an energy retention of 84.7%after 10,000 cycles.

Sub-nanoscale Engineering of MoO_(2) Clusters for Enhanced Sodium Storage

Smart construction of battery-type anodes with high rate and good mechanical properties is significant for advanced sodium ion capacitors(SICs).Herein,a flexible film consisting of MoO_(2) subnanoclusters encapsulated in nitrogen-doped carbon nanofibers(MoO_(2) SCs@N-CNFs)is designed and synthesized via electrospinning toward SICs as anodes.The strong N-Mo interaction guarantees the stable yet uniform dispersion of high loading MoO_(2) SCs(≈40 wt.%)in the flexible carbonaceous substrate.The sub-nanoscale effect of SCs restrains electrode pulverization and improves the Na+diffusion kinetics,rendering better pseudocapacitance-dominated Na+-storage properties than the nanocrystal counterpart.The MoO_(2) SCs@N-CNFs paper with mass loadings of 2.2–10.1 mg cm^(−2) can be directly used as free-standing anode for SICs,which exhibit high reversible gravimetric/areal capacities both in liquid and quasi-solid-state electrolytes.The assembled flexible SICs competitively exhibit exceptional energy density and cycling stability.More significantly,the sub-nanoscale engineering strategy here is promisingly generalized to future electrode design for other electrochemical energy-related applications and beyond.

Nanotube-like hard carbon as high-performance anode material for sodium ion hybrid capacitors

Sodium ion hybrid capacitors（SIHCs） are of great concern in large-scale energy storage applications due to their good energy-and-power characteristic, as well as abundant reserves and low cost of sodium. However, the sluggish faradaic kinetics of anode materials severely limit the overall electrochemical performance of SIHC devices. Herein, we report an application of nanotube-like hard carbon（NTHC）anode material prepared by high-temperature carbonization（1150℃） of polyaniline（PANI） nanotubes for high-performance SIHCs. As a result, the assembled sodium ion half-cell with NTHC shows a high reversible capacity of 419.5 mA h g^-1at 0.05 A g^-1and a good rate performance of 74.6 mA h g^-1 at 2.5 A g^-1 in a potential window of 0-2 V（vs. Na/Na^＋）. On this basic, a SIHC using such NTHC as anode and a high-capacity activated carbon（APDC） as cathode is fabricated, which exhibits a high energy density of 133.0 W h kg^-1 at 2850 W kg^-1and still remains 100.9 W h kg^-1 at 14,250 W kg^-1. Within the potential range of 1.5-3.5 V, the SIHCs display an outstanding cycling stability tested at 2 A g^-1 with a good capacity retention of 82.5% even after 12,000 cycles.

High-performance nitrogen and sulfur co-doped nanotube-like carbon anodes for sodium ion hybrid capacitors

Sodium ion hybrid capacitors are of great concern in large-scale and cost-effective electrical energy storage owing to their high energy and power densities,as well as natural abundance and wide distribution of sodium.However,it is difficult to find a well-pleasing anode material that matches the high-performance cathode materials to achieve good energy and power output for sodium ion hybrid capacitors.In this paper,nitrogen and sulfur co-doped nanotube-like carbon prepared by a simple carbonization process of high sulfur-loaded polyaniline nanotubes is introduced as the anode.The assembled sodium ion half cell based on the optimal nanotube-like carbon delivers a high reversible capacity of ~304.8 mAh/g at 0.2 A/g and an excellent rate performance of ~124.8 mAh/g at 10 A/g in a voltage window of 0.01-2.5 V(versus sodium/sodium ion).For the hybrid capacitors assembled using the optimal nanotube-like carbon as the anode and high-capacity activated carbon as the cathode,high energy densities of ~100.2 Wh/kg at 250 W/kg and ~50.69 Wh/kg at 12,500 W/kg are achieved.

g-C_(3)N_(4) templated mesoporous carbon with abundant heteroatoms as high-rate anode material for dual-carbon sodium ion hybrid capacitors

Sodium ion hybrid capacitors(SIHCs)are regarded as advanced power supply systems.Nevertheless,the kinetics imbalance of cathode and anode suppresses the further performance improvement of SIHCs.The carbonaceous anode materials are promising and many strategies have been utilized to increase the capacity of sloping region or accelerate the reaction rate of plateau region.However,it is still challenging to simultaneously realize high mesopore/micropore volume ratio,large interlayer distance(>0.37 nm),and abundant and favorable heteroatoms-doping by a simple method.Herein,we report N,P,O ternarydoped mesoporous carbon(PNPOC-T,T=700,800 or 900)with large interlayer distance(~0.4 nm)as anode materials.The PNPOC-T were prepared by a simple in-situ polymerization of aniline and phytic acid on the exfoliated graphitic nitrogen carbide(g-C3N4)and subsequent carbonization.The obtained PNPOC-800 exhibits an excellent rate performance(101.5 mA·h·g^(-1) at 20 A·g^(-1)),which can be attributed to the high surface-controlled capacitive behavior ratio and rapid ion diffusion.The optimum SIHCs display a high energy density of 105.48 W·h·kg^(-1) and a high power density of 13.59 kW$kg1.Furthermore,the capacitance retention rate of SIHCs can reach 87.43%after 9000 cycles at 1 A·g^(-1).