Hybrid Aqueous/Nonaqueous Water-in-Bisalt Electrolyte Enables Safe Dual Ion Batteries.

Dual ion batteries (DIBs) have recently attracted ever-increasing attention owing to the potential advantages of low material cost and good environmental friendliness. However, the potential safety hazards, cost, and environmental concerns mainly resulted from the commonly used nonaqueous organic solvents severely hinder the practical application of DIBs. Herein, a hybrid aqueous/nonaqueous water-in-bisalt electrolyte with both broad electrochemical stability window and excellent safety performance is developed. The lithium-based DIB assembled using KS6 graphite and niobium pentoxide as the active materials in the cathode and anode exhibits good comprehensive performance including capacity, cycling stability, rate performance, and medium discharge voltage. Initial capacities of ≈47.6 and 29.6 mAh g-1 retention after 300 cycles can be delivered with a medium discharge voltage of around 2.2 V in the voltage window of 0-3.2 V at the current density of 200 mA g-1 . Good rate performance for the battery can be indicated by 29.7 mAh g-1 discharge capacity retention at 400 mA g-1 . It is noteworthy that the coulombic efficiency of the battery can reach as high as 93.9%, which is comparable to that of the corresponding DIBs using nonaqueous organic electrolytes.

Sodium-Based Dual-Ion Battery Based on the Organic Anode and Ionic Liquid Electrolyte.

Combining the advantages of dual-ion batteries (DIBs) and sodium-ion batteries (SIBs), we herein develop a superior sodium-based dual-ion battery (Na-DIB) based on the PTCDA organic anode and ionic liquid (IL) electrolyte. The system shows the highest specific discharge capacity of 177 mAh g-1 at 0.5C and excellent capacity retention over 100% at 2C after 200 cycles. Notably, even at an ultrahigh rate of 20C, the battery still maintains a considerable capacity of 60 mAh g-1 with a coulombic efficiency (CE) close to 100 and 94% capacity retention after 1000 cycles. Moreover, the self-discharge of the system has been investigated and shown to have an extremely low value of 0.18% h-1. Consequently, this work presents an excellent Na-DIB system, which could be a promising candidate for large-scale applications.