The application of aqueous electrolytes is generally limited by their narrow electrochemical window (ECW), which sets an intrinsic limit on the practical voltage and energy density of fabricated energy storage devices. Herein, the coacervates of nano-ions are proposed as aqueous lithium-ion electrolytes with both high ion conductivity and broadened ECW. The hybrid complex coacervates of 1 nm nano-anions, metatungstate ([W 12 O 40 ] 8− ), and polyethylene glycol (PEG) are studied for their unique salt-hardening effect. The framework of random percolated nano-ions interweaved by PEG chains is demonstrated from small angle X-ray/neutron scattering (SAXS/SANS) and micro-rheology measurements. The introduced extra Li + can complex with the PEG backbone for strengthened PEG/nano-ion interaction. The relaxation dynamics follows the model of sticky reptation by treating the binding of Li + as effective stickers and this leads to the observed salt hardening effect, e.g., enhanced viscosity with the increased LiCl concentrations. This hybrid coacervate exhibits excellent ionic conductivity (∼0.027 S/cm), and the super-ionic nature of ion conduction is demonstrated employing fractional Walden rule. Suggested from diffusion ordered spectroscopy studies, the water molecules confined in the framework of the coacervates show hindered diffusive dynamics and this contributes to the extended ECW (∼2 V), demonstrating its potential application as aqueous lithium electrolytes.
Jiulong Che,Jian Zhang,Qing Lang,Jiayuan Yu,Yixiao Yang,Longqi Luo,Zhiyi Liu,Jiahui Ye,Gang Wang
Dual-ion batteries (DIBs) were demonstrated as a promising technology for large-scale energy storage due to their low cost, recyclability, and impressively fast charge capability. Graphite as a commonly used cathode material in DIBs, however, suffers from poor compatibility with commercial Li-ion electrolytes and graphite anodes, making it difficult to directly utilize the well-established infrastructure for Li-ion batteries. Herein, we report a small aromatic amine molecule 4,4′,4″-tris(diphenylamino)triphenylamine (N4) functioning as a compatible anion host in the EC-containing Li-ion electrolyte. With an average discharge voltage of 3.6 V (vs. Li+/Li), the N4 electrode delivers a reversible specific capacity of 108 mAh/g, which is much higher than 29 mAh/g for the graphite cathode at the same condition. The high capacity retention of 91.3% was achieved after 500 cycles at 1 A/g. The N4 electrode also exhibited good rate performance. Via different characterization techniques like Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, the energy storage mechanism of N4 was revealed as a conversion between amine and quaternary amine cations, accompanied by PF6−(de-)insertion. As consequences, the assembled N4||graphite DIB w showed a high discharge capacity of 90 mAh/g within 1.5–4.1 V, and good cycling stability with a 98% capacity retention after 40 cycles. Decent rate performance was achieved in the N4||graphite DIB as well. This work provides new insights into designing a compatible anion host for affordable DIBs.
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