A N, S co-doped carbon produced from soybean pods for use as the anode in sodium-ion batteries

Subsequently, the mixtures were thermally treated at 800 °C under a nitrogen atmo sphere to facilitate nitrogen and sulfur co-doping. The resulting samples were denoted as NS-PHC-1, NS PHC-2 and NS-PHC-3 according to the respective thiourea ratios.2The surface morphology and internal structure of PHC and NS-PHC were characterized by transmis sion electron microscopy (TEM) and scanning elec tron microscopy (SEM). The crystalline structure of the hard carbon materials was analyzed using X-ray diffraction spectroscopy (XRD) and Raman spectro scopy.

The surface elemental composition and chem ical states were examined by X-ray photoelectron spectroscopy (XPS). The specific surface area and pore size distribution of the materials were determ ined using Brunauer-Emmett-Teller (BET).3 Electrochemical tests The prepared hard carbon material, conductive carbon black, and binder were thoroughly mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 8∶1∶1 to form a homogeneous slurry.

The resulting slurry was uniformly coated onto copper foil and sub sequently dried for 8 h in a blast drying oven fol lowed by a vacuum oven. The dried anode electrodes were then punched into 12 mm discs with an active material mass loading of approximately 0.4 0.8 g cm−2. The electrodes were assembled into CR2032 coin-type cells using sodium metal as the ref erence electrode.

All assembly processes were con ducted in an argon-filled glove box ( H2 O and O2 < 0.01×10−6, v/v). The electrolyte consisted of 1 mol L−1 NaPF6 dissolved in a 1∶1 (v/v) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), with 1.0% (mass fraction) ethylene carbonate (EC) addit ive, and a Celgard2400 microporous membraneserved as the separator. Galvanostatic charge-dis charge (GCD) tests, rate capability measurements, and long-cycle evaluations were performed using a LAND battery testing system within a voltage window of 0.01–3.0 V. Cyclic voltammetry (CV) and electro chemical impedance spectroscopy (EIS) were carried out on a CHI760E electrochemical workstation (Shanghai Chenhua, China) at scan rates ranging from 0.2 to 1.0 mV s−1 over a voltage range of 0.005–3.0 V. The galvanostatic intermittent titration technique (GITT) was conducted in the range of 0.01–3.0 V at a current density of 0.05 A·g−1, with each current pulse lasting 20 min and a relaxation interval of 40 min