A new pre-sodiation additive for sodium-ion batteries

We demonstrate the potential of diethylenetriamine penta-acetic acid salt (DTPA-5Na) as a sacrificing sodium supply source for blending with sodium-deficient tunnel-type Na0.44MnO2. Herein, we report that DTPA-5Na shows presodiation effects on the sodium-deficient cathode. With the addition of DTPA-5Na to the Na0.44MnO2 (polyvinylidene-fluoride-less) electrode, the charge capacity increased from ~58 to ~128 ​mAh g−1. Thus, the DTPA-5Na provides additional capacity (~70 ​mAh g−1), originating from the five sodium ions in the DTPA-5Na structure during oxidative reaction. Furthermore, DTPA-5Na/Na0.44MnO2//0.5 ​M NaPF6 in a PC:FEC (98:2 v/v.%)//hard carbon full cell exhibits a high coulombic efficiency close to 100% with long-term cycling performance. Interestingly, the increase in discharge capacity is shown to be associated with the electro-conducting nature of the C3N deposits formed on the surface of Na0.44MnO2. Our findings indicate that the introduction of DTPA-5Na as a sacrificing additive in a cathode material may provide a new opportunity to apply sodium-deficient cathode materials in practical sodium-ion batteries.