A gradient “Ceramic-in-Ionogel” electrolyte with tidal ion flow for ultra-stable lithium metal batteries

Composite solid-state electrolytes are considered as key components for safe and high-energy-density lithium metal batteries, given their superior mechanical properties and ion conductive kinetics. However, it still remains a challenge to simultaneously guarantee high ionic conductivity and excellent interfacial compatibility. Herein, a gradient “Ceramic-in-Ionogel” electrolyte with tidal ion flow is proposed for decoupling ionic conductivity and interfacial property. It is composed of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))/EMIMTFSI/Al2O3 (30 wt. %) layer (Ionogel-dual30) toward cathode and P(VDF-HFP)/EMIMTFSI/Al2O3 (50 wt. %) layer (Ionogel-dual50) to Li-metal anode. Ionogel-dual50 can provide a relatively large number of Al2O3 particles for the formation of AlF3 and Li3AlF6 after being offered electrons at lithium-metal anode and carbon-fluorine bond cleavage in TFSI-, resulting in rapid Li+ transfer and insulated electron transport at interface. Both simulation and experimental characterization suggest that the tidal-flow-like ion transport pathway can offer [Li+-NMP]-P(VDF-HFP) dominant pathway in Ionogel-dual30 and [Li(TFSI)x]+-Al2O3 interface dominant pathway in Ionogel-dual50, achieving a high ionic conductivity of 0.25 mS cm−1. Benefiting from these unique merits, the cycling performance of symmetric Li batteries was greatly improved with a lifetime of over 1000 h at 0.1 mA h cm−2. The effect of this gradient ionogel electrolyte could be well demonstrated in various full cells, evidenced by substantially enhanced cyclability under large current density (2 C), wide voltage range (3–4.5 V) and extreme conditions. This novel “Ceramic-in-Ionogel” electrolyte with tidal ion flow will accelerate the commercialization of high-energy-density lithium metal batteries.