Anion Defects Engineering of Ternary Nb-Based Chalcogenide Anodes Toward High-Performance Sodium-Based Dual-Ion Batteries

Highlights We developed an efficient and extensible strategy to produce the single-phase ternary NbSSe nanohybrids with defect-enrich microstructure. The anionic-Se doping play a key role in effectively modulating the electronic structure and surface chemistry of NbS2 phase, including the increased interlayers distance (0.65 nm), the enhanced intrinsic electrical conductivity (3.23 × 103 S m-1) and extra electroactive defect sites. The NbSSe/NC composite as anode exhibits rapid Na+ diffusion kinetics and increased capacitance behavior for Na+ storage, resulting in high reversible capacity and excellent cycling stability. Abstract Sodium-based dual-ion batteries (SDIBs) have gained tremendous attention due to their virtues of high operating voltage and low cost, yet it remains a tough challenge for the development of ideal anode material of SDIBs featuring with high kinetics and long durability. Herein, we report the design and fabrication of N-doped carbon film-modified niobium sulfur–selenium (NbSSe/NC) nanosheets architecture, which holds favorable merits for Na+ storage of enlarged interlayer space, improved electrical conductivity, as well as enhanced reaction reversibility, endowing it with high capacity, high-rate capability and high cycling stability. The combined electrochemical studies with density functional theory calculation reveal that the enriched defects in such nanosheets architecture can benefit for facilitating charge transfer and Na+ adsorption to speed the electrochemical kinetics. The NbSSe/NC composites are studied as the anode of a full SDIBs by pairing the expanded graphite as cathode, which shows an impressively cyclic durability with negligible capacity attenuation over 1000 cycles at 0.5 A g−1, as well as an outstanding energy density of 230.6 Wh kg−1 based on the total mass of anode and cathode. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01070-0.


S1 Calculation of b Value
The b value is applied to evaluate the pseudocapacitive behavior of electrode.According to the power-law relation between the sweep scan rate (v) and the peak current (i), Eqs.S1 and S2 can be provided: i = av b (S1) log(i) = blog(v) + log(a) (S2) in which the b-value of 0.5 or 1.0 indicates a fully diffusion-dominated or surfacecapacitive process, respectively.

S2 Calculation of Capacitive Contribution
Quantitatively, the capacitive-dominated contribution can be separated based on the current response (i) at a fixed voltage (v), according to the Eqs.S3 and S4: where k1 and k2 are adjustable parameters, the k1v stands for capacitive-controlled process, and the k2v 1/2 represents ionic-diffusion controlled process.

S3 Calculation of Na + Diffusion Coefficient (DNa+)
Galvanostatic intermittent titration technique (GITT) measurement during the 10th cycle is utilized to reveal the Na + diffusion coefficient (DNa+) in the WS2/C@CNTs cathode.By virtue of the linear relationship of the voltage variation (ΔEτ) and τ 1/2 (Fig. S27), the DNa+ can be determined based on the following Eq.S5: where τ is the duration of the current pulse; nm and Vm are the mole number (mol) and molar volume (cm 3 mol −1 ); S is the total contacting area between electrode and electrolyte; ΔEs is the voltage change between two adjacent equilibrium states; and ΔEτ is the voltage change induced by the galvanostatic charge/discharge.
S4 Calculation of the Specific Energy and Power (based on the total mass of both anode and cathode materials): The cell-level specific energy E and specific power P are calculated according to the following Eqs.S6, S7: where t (s) is the discharge time, I (A g -1 ) is charge/discharge current, Vmax (V) is the discharge potential excluding the IR drop and Vmin (V) is the potential at the end of discharge voltages, E is the specific energy (Wh kg -1 ) and P is the specific power (W kg -1 ).In order to obtain the optimized electrochemical performance, it was a key factor to balance the capacity between cathode and anode.The NbSSe/NC anode showed a specific capacity of around 420 mAh g -1 , and the EG cathode exhibited a specific capacity of around 100 mAh g -1 , thus the mass ratio of the EG cathode to NbSSe/NC anode was optimized to be 4:1 according to the charge balance Eq.S8: C cathode ×m cathode = C anode ×m anode (S8) where C (mAh g -1 ) and m (mg) are the specific capacity of both electrodes and the mass of active materials, respectively.Therefore, the mass ratio between cathode and anode was calculated to be 4:1.

Fig. S1
Fig. S1 Top and side view of the optimized structure of (a) NbSSe and (b) NbS2

Fig. S16
Fig. S16 Thermogravimetric analysis curves of NbSSe/NC Based on the transformation of NbSSe/NC after the TGA test as shown below, 10NbS 0.9 Se 0.9 + 30.5O 2 = 5Nb 2 O 5 + 9SO 2 ↑ + 9SeO 2 ↑ The carbon content in NbSSe/NC is calculated by equation： c=9.82% m represents the total mass of NbSSe/NC, c is the percentage composition of carbon in the NbSSe/NC.

Fig. S21 Nano
Fig. S21The GCD profiles of different rates for NbSSe/NC and NbS2/NC

Fig. S24
Fig. S24 The rate performance of NbSSe/NC and NbS2/NC electrodes

Fig. S25
Fig. S25 Log (i) versus log (v) plots at different redox peaks of the NbSSe/NC

Fig. S30
Fig.S30The SEM images and XRD data of EG cathode

Fig. S32
Fig. S32 CV and charge/discharge profiles (b,c) of the NbSSe/NC and EG half-cells

Fig. S33
Fig. S33 Average discharge voltage of the SDIB at 0.05 A g -1 over 200 cycles

Table S1
Contents of Nb, Se, S, and C in NbSSe/NC and NbS2/NC

Table S2
Comparison of electrochemical performances of anodes for Na-DIBs (the capacity is calculated based on the mass of cathode)