A Low-Volatile and Durable Deep Eutectic Electrolyte for High-Performance Lithium-Oxygen Battery.

The lithium-oxygen battery (LOB) with a high theoretical energy density (∼3500 Wh kg-1) has been regarded as a strong competitor for next-generation energy storage systems. However, its performance is still far from satisfactory due to the lack of stable electrolyte that can simultaneously withstand the strong oxidizing environment during battery operation, evaporation by the semiopen feature, and high reactivity of lithium metal anode. Here, we have developed a deep eutectic electrolyte (DEE) that can fulfill all the requirements to enable the long-term operation of LOBs by just simply mixing solid N-methylacetamide (NMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at a certain ratio. The unique interaction of the polar groups in the NMA with the cations and anions in the LiTFSI enables DEE formation, and this NMA-based DEE possesses high ionic conductivity, good thermal, chemical, and electrochemical stability, and good compatibility with the lithium metal anode. As a result, the LOBs with the NMA-based DEE present a high discharge capacity (8647 mAh g-1), excellent rate performance, and superb cycling lifetime (280 cycles). The introduction of DEE into LOBs will inject new vitality into the design of electrolytes and promote the development of high-performance LOBs.

Three Birds with One Stone: An Integrated Cathode-Electrolyte Structure for High-Performance Solid-State Lithium-Oxygen Batteries.

Constructing solid-state lithium-oxygen batteries (SSLOBs) holds a great promise to solve the safety and stability bottlenecks faced by lithium-oxygen batteries (LOBs) with volatile and flammable organic liquid electrolytes. However, the realization of high-performance SSLOBs is full of challenges due to the poor ionic conductivity of solid electrolytes, large interfacial resistance, and limited reaction sites of cathodes. Here, a flexible integrated cathode-electrolyte structure (ICES) is designed to enable the tight connection between the cathode and electrolyte through supporting them on a 3D SiO2 nanofibers (NFs) framework. The intimate cathode-electrolyte structure and the porous SiO2 NFs scaffold combination are favorable for decreasing interfacial resistance and increasing reaction sites. Moreover, the 3D SiO2 NFs framework can also behave as an efficient inorganic filler to enhance the ionic conductivity of the solid polymer electrolyte and its ability to inhibit lithium dendrite growth. As a result, the elaborately designed ICES can simultaneously tackle the issues that limit the performance liberation of SSLOBs, making the batteries deliver a high discharge capacity and a long lifetime of 145 cycles with a cycling capacity of 1000 mAh g-1 at 60 °C, much superior to coventional SSLOBs (50 cycles).

Soluble and Perfluorinated Polyelectrolyte for Safe and High-Performance Li-O2 Batteries.

The severe performance degradation of high-capacity Li-O2 batteries induced by Li dendrite growth and concentration polarization from the low Li+ transfer number of conventional electrolytes hinder their practical applications. Herein, lithiated Nafion (LN) with the sulfonic group immobilized on the perfluorinated backbone has been designed as a soluble lithium salt for preparing a less flammable polyelectrolyte solution, which not only simultaneously achieves a high Li+ transfer number (0.84) and conductivity (2.5 mS cm-1 ), but also the perfluorinated anion of LN produces a LiF-rich SEI for protecting the Li anode from dendrite growth. Thus, the Li-O2 battery with a LN-based electrolyte achieves an all-round performance improvement, like low charge overpotential (0.18 V), large discharge capacity (9508 mAh g-1 ), and excellent cycling performance (225 cycles). Besides, the fabricated pouch-type Li-air cells exhibit promising applications to power electronic equipment with satisfactory safety.