Highly Efficient, Cost Effective, and Safe Sodiation Agent for High‐Performance Sodium‐Ion Batteries

Abstract

The development of sodium-ion batteries has been hindered so far by the large irreversible capacity of hard carbon anodes and other anode materials in the initial few cycles, as sodium ions coming from cathode materials is consumed in the formation of the solid-electrolyte interface (SEI) and irreversibly trapped in anodes. Herein, the successful synthesis of an environmentally benign and cost-effective sodium salt (Na C O ) is reported that could be applied as additive in cathodes to solve the irreversible-capacity issues of anodes in sodium-ion batteries. When added to Na (VO) (PO ) F cathode, the cathode delivered a highly stable capacity of 135 mAh g and stable cycling performance. The water-stable Na (VO) (PO ) F cathode in combination with a water-soluble sacrificial salt eliminates the need for using any toxic solvents for laminate preparation, thus paving way for greener electrode fabrication techniques. A 100 % increase in capacity of sodium cells (full-cell configuration) has been observed when using the new sodium salt at a C-rate of 2C. Regardless of the electrode fabrication technique, this new salt finds use in both aqueous and non-aqueous cathode-fabrication techniques for sodium-ion batteries.

Nonaqueous Sodium‐Ion Full Cells: Status, Strategies, and Prospects

“…The self‐sacrificial electrode materials reported so far include NaN 3 , Na 3 P, Na 2 CO 3 , Na 2 C 4 O 4 , and Na 2 NiO 2 . Armand and his co‐workers have done a lot of forward‐looking efforts in this area . Thanks to the experience of lithium compensation, Singh et al first proposed the use of NaN 3 as a P2‐Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 cathode additive for sodium compensation in 2013 .…”

“…As a result, looking for environmentally friendly self‐sacrificial additives is the choice for sustainable development. Armand et al synthesized an environmentally friendly and economical organic Na 2 C 4 O 4 by a simple solution method . When used as a cathode additive, it exhibits an irreversible capacity of more than 230 mA h g −1 (theoretical capacity of 339 mA h g −1 ) with an oxidation potential about 3.6 V accompanied by the formation of CO 2 , C, and Na + .…”

“…a) Charge–discharge profiles of Na 3 V 2 O 2 (PO 4 ) 2 F, Na 3 V 2 O 2 (PO 4 ) 2 F/30 wt% Na 2 C 4 O 4 , Na 3 V 2 O 2 (PO 4 ) 2 F/30 wt% NaN 3 electrodes with Na‐CMC, and Na 3 V 2 O 2 (PO 4 ) 2 F/30 wt% Na 2 C 4 O 4 with PVDF, respectively. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

“…Armand and his co-workers have done a lot of forward-looking efforts in this area. [58,[183][184][185][186][187] Thanks to the experience of lithium compensation, Singh et al first proposed the use of NaN 3 as a P2-Na 2/3 [Fe 1/2 Mn 1/2 ] O 2 cathode additive for sodium compensation in 2013. [183] This concept stems from the fact that NaN 3 can generate irreversible capacity (theoretical capacity of 412 mA h g −1 ) over 270 mA h g −1 during the first cycle corresponding to a flat charge profile at 3.55 V versus Na + /Na.…”

“…Armand et al synthesized an environmentally friendly and economical organic Na 2 C 4 O 4 by a simple solution method. [58] When used as a cathode additive, it exhibits an irreversible capacity of more than 230 mA h g −1 (theoretical capacity of 339 mA h g −1 ) with an oxidation potential about 3.6 V accompanied by the formation of CO 2 , C, and Na + . In the half-cell, the discharge capacity of the electrode with Na 2 C 4 O 4 is increased from 105 to 135 mA h g −1 compared to the electrode without Na 2 C 4 O 4 , which is comparable to the NaN 3 additive (115 mA h g −1 ) (Figure 16a).…”