Designing Artificial Solid-Electrolyte Interphases for Single-Ion and High-Efficiency Transport in Batteries

Substrates able to rectify transport of ions based on charge and/or size are ubiquitous in biological systems. Electrolytes and interphases that selectively transport electrochemically active ions are likewise of broad interest in all electrical energy storage technologies. In lithium-ion batteries, electrolytes with single- or near-single-ion conductivity reduce losses caused by ion polarization. In emergent lithium or sodium metal batteries, they maintain high conductivity at the anode and stabilize metal deposition by fundamental mechanisms. We report that 20- to 300-nm-thick, single-ion-conducting membranes deposited at the anode enable electrolytes with the highest combination of cation transference number, ionic conductivity, and electrochemical stability reported. By means of direct visualization we find that single-ion membranes also reduce dendritic deposition of Li in liquids. Galvanostatic measurements further show that the electrolytes facilitate long (3 mAh) recharge of full Li/LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cells with high cathode loadings (3 mAh cm⁻²/19.9 mg cm⁻²) and at high current densities (3 mA cm⁻²). Less than three decades after its introduction, lithium-ion battery (LIB) technology dominates the market for portable electrical energy storage (EES) systems for consumer electronics and electric vehicles. Demand for more compact, lighter, more powerful EES solutions to meet needs for advanced electric vehicles and emergent autonomous robotics require more energy-dense lithium-metal batteries (LMBs) that utilize metallic Li anodes. We report on nanometer-thick artificial solid-electrolyte interphases (SEIs) composed of single-ion-conducting ionic polymers tethered to Li electrodes. The SEIs take advantage of synergistic processes for achieving high ionic conductivity, negligible ion polarization, and stable Li deposition. They also protect Li from parasitic reactions with liquid electrolytes, as well as from oxidative degradation on contact with ambient air, simultaneously improving cycling efficiency of LMBs and enabling LMB production using standard, dry-room-based, manufacturing. This article reports that high lithium transference number and high room temperature ionic conductivity can be simultaneously achieved in electrolytes by tethering nanometer-thick coatings of a single-ion conductor to an Li electrode. The protected electrode can be cycled stably at low and high currents.