graphitic electrode. [ 8 ] Unfortunately, when applied in a dualgraphite battery, the EC molecules in the electrolyte can bind tightly with PF 6 − anions, and prevent the intercalation of these anions into the interlayer spaces of graphite positive electrodes. [ 9 ] Recently, with the developments of novel electrolyte formulas, several studies have reported signifi cantly improved reversibility of dual-carbon batteries. [ 10 ] Read et al. reported a reversible dual-graphite battery with simultaneous accommodation of Li + and PF 6 − in graphitic structures enabled by a high voltage electrolyte based on fl uorinated solvent and additive. [ 10a ] The battery demonstrated a reversible capacity of 60 mAh g −1 and a capacity retention of 62% after 50 cycles at C/7 rate. Rothermel et al. reported a dual-graphite battery based on a mixture of lithium bis-(trifl uoromethanesulfonyl)-imide (LiTFSI) and ionic liquid with SEI-forming additive. This electrolyte formula not only enabled stable TFSI − intercalation into the graphite positive electrode, but also allowed highly reversible intercalation of Li + into the graphite negative electrode. [ 10b ] Under an upper cut-off potential of 5.0 V, the full graphite battery presented a capacity of 97 mAh g −1 at a current rate of 10 mA g −1 , and 50 mAh g −1 at 500 mA g −1 , which shed light on the potential application of dual-ion batteries as an environmentally friendly energy storage technology.Herein, we report a novel aluminum-graphite dual-ion battery (AGDIB) in an ethyl-methyl carbonate (EMC) electrolyte with high reversibility and high energy density. It is the fi rst report on using an aluminum anode in dual-ion battery. The battery shows good reversibility, delivering a capacity of ≈100 mAh g −1 and capacity retention of 88% after 200 chargedischarge cycles at 2 C (1 C corresponding to 100 mA g −1 ). To the best of our knowledge, performance of the battery is among the best of reported dual-ion batteries.Figure 1 a schematically illustrates the initial and charged states of the AGDIB. Upon charging, PF 6 − anions in the electrolyte intercalate into the graphite cathode, while the Li + ions in the electrolyte deposit onto the aluminum counter electrode to form an Al-Li alloy. The discharge process is the reverse of the charge process, where both PF 6 − anions and Li + ions diffuse back into the electrolyte. The Al counter electrode acts as both the anode and the current collector, which greatly benefi ts the specifi c energy density and volumic energy density of the AGDIB. [ 11 ] Figure 1 b shows galvanostatic charge-discharge curves of the AGDIB, exhibiting a typical profi le of anion intercalation/deintercalation into/from graphite. The charge curve is mainly composed of three regions between 4.08 and 4.59 V (stage III), 4.59 and 4.63 V (stage II), and 4.63 and 5.0 V (stage I), each region corresponds to an anion intercalation stage of graphite, according to previous reports. [ 6e ] A dQ/dV differential curve of the battery is shown in the inset of Figure 1 b. Pe...

Calcium-ion batteries (CIBs) are attractive candidates for energy storage because Ca has low polarization and a reduction potential (-2.87 V versus standard hydrogen electrode, SHE) close to that of Li (-3.04 V versus SHE), promising a wide voltage window for a full battery. However, their development is limited by difficulties such as the lack of proper cathode/anode materials for reversible Ca intercalation/de-intercalation, low working voltages (<2 V), low cycling stability, and especially poor room-temperature performance. Here, we report a CIB that can work stably at room temperature in a new cell configuration using graphite as the cathode and tin foils as the anode as well as the current collector. This CIB operates on a highly reversible electrochemical reaction that combines hexafluorophosphate intercalation/de-intercalation at the cathode and a Ca-involved alloying/de-alloying reaction at the anode. An optimized CIB exhibits a working voltage of up to 4.45 V with capacity retention of 95% after 350 cycles.

In this work, combining both advantages of potassium-ion batteries and dual-ion batteries, a novel potassium-ion-based dual-ion battery (named as K-DIB) system is developed based on a potassium-ion electrolyte, using metal foil (Sn, Pb, K, or Na) as anode and expanded graphite as cathode. When using Sn foil as the anode, the K-DIB presents a high reversible capacity of 66 mAh g at a current density of 50 mA g over the voltage window of 3.0-5.0 V, and exhibits excellent long-term cycling performance with 93% capacity retention for 300 cycles. Moreover, as the Sn foil simultaneously acts as the anode material and the current collector, dead load and dead volume of the battery can be greatly reduced, thus the energy density of the K-DIB is further improved. It delivers a high energy density of 155 Wh kg at a power density of 116 W kg , which is comparable with commercial lithium-ion batteries. Thus, with the advantages of environmentally friendly, cost effective, and high energy density, this K-DIB shows attractive potential for future energy storage application.