Carbon‐Based Dual‐Ion Battery with Enhanced Capacity and Cycling Stability

Abstract

A high cycling stability of dual‐ion batteries is greatly challenging, as the size required for inserting anions matches only insufficiently with the interlayer spacing of graphite which is often used as positive electrode. Herein, an activated expanded graphite (AEG) electrode is successfully prepared via KOH treatment. The loose structure of AEG accommodates the volume expansion caused by anion intercalation, and the large specific surface area facilitates the immersion of electrolyte ions to afford more energy density. Thus, the cycling stability is largely enhanced without losing capacity. Matching with activated carbon as negative electrode and an ionic liquid electrolyte, the assembled dual‐ion battery achieves an energy density of 43 Wh kg−1 at the power density of 756 W kg−1 within a working window of 0–3.6 V. Specifically, the energy density retains 83 % after 50 cycles. Such effective and low‐cost electrode optimization opens up a new route toward full enhancement on the cycling performance of positive electrodes for dual‐ion batteries.

Facilitating Tetrafluoroborate Intercalation into Graphite Electrodes from Ethylmethyl Carbonate‐Based Solutions

“…It is known that there is a strong affinity between Li + and propylene carbonate (PC) [9] which is the main cause of the structure destruction of graphite anode when PC-based electrolyte solutions are used in Li-ion battery. [4,10] Hence PC is employed here as an effective "cation acceptor" . [4,10] Hence PC is employed here as an effective "cation acceptor" .…”

“…[8] Also, using PC as the co-solvent has been proven feasible in dual-ion battery systems. [4,10] Hence PC is employed here as an effective "cation acceptor" . As exhibited in Figure 4(a), even a very small amount of PC is added into the solution (n(PC): n(Li + ) = 1 : 3 in the solution), the specific capacity jumps to a much higher value, and then specific capacity value levels off until the molar ratio of PC to Li + is above 3.…”

Electrolytes for Dual‐Carbon Batteries

“…The most common electrolytes for DCBs are organic carbonates and ionic liquid (IL) solvents paired with various inorganic/organic salts such as LiPF 6 , NaPF 6 , and n‐butyl pyridinium [PF 6 ] . Their concentration is usually set to be between 0.5 and 2 mol L −1 to ensure high ionic conductivity and low viscosity.…”

“…Frustratingly, it still exhibited a poor average CE of ∼90 % during cycles, suggesting poor compatibility between the carbonaceous electrode and the carbonate electrolyte. Apart from inorganic salts, the organic salts (ionic liquids) dissolved in carbonate solvents have also been invested as DCB electrolytes ,,,,. These batteries usually show relatively low reversible capacity (∼30 mAh g −1 ) and low discharge voltages (∼2.5 V), which may be ascribed to the poor compatibility between the large cations and carbon anodes.…”

“…The most common electrolytes for DCBs are organic carbonates and ionic liquid (IL) solvents paired with various inorganic/ organic salts such as LiPF 6 , NaPF 6 , and n-butyl pyridinium [PF 6 ]. [26][27][28][29][30][31][32][33][34][35][36][37][38] Their concentration is usually set to be between 0.5 and 2 mol L À 1 to ensure high ionic conductivity and low viscosity. These electrolytes, however, suffer from severe decomposition on carbonaceous cathodes and/or anodes because of the superior catalytic activity of the defects in carbonaceous materials, [39][40][41] causing unsatisfactory Coulombic efficiency (CE) and inferior cycling performance of DCBs.…”