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Despite good compatibility with Li metal, garnet solid electrolytes suffer from severe electron-attack-induced Li-metal penetration and large interfacial resistance. Here, a formic acid (HCOOH)-induced electron-blocking and lithiophilic interlayer is created via a spontaneous reaction with surface Li 2 CO 3 contamination on the garnet electrolyte (LLZTO) pellet. Unlike previous methods that involved immersing LLZTO in acidic solutions, this study employs a volatile small-molecule organic acid that is easily removable, condensed, and recyclable, thus circumventing the environmental drawbacks associated with acid waste. The Li symmetric cell assembled with HCOOH-treated LLZTO exhibits a low interfacial impedance (3 Ω cm 2 ) and a high critical current density (1.7 mA cm -2 ) at room temperature, enabling the cell to cycle continuously for over 1000 h at 0.2 mA cm -2 . Furthermore, under a stacking pressure of 2 MPa, stable lithium plating/stripping was achieved at a current density of 0.3 mA cm -2 with the assistance of HCOOH treatment. Additionally, the battery paired with a LiFePO 4 cathode delivers a high capacity of 151.7 mAh g -1 at 1 C and maintains 88.5% of the initial capacity after 500 cycles, suggesting the feasibility of this interfacial engineering strategy for garnet-based solid Li-metal batteries.

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as a promising candidate for next-generation energy storage systems. However, their practical applications are hindered by the slow kinetics of sulfur conversion and polysulfide shuttling. In particular, large-scale pouch cells show much poor cyclability. Here, we develop a high-efficiency catalyst of V-doped CoSe 2 by studying the binary CoSe 2 -VSe 2 system and confirming its effectiveness in accelerating polysulfide conversion. The coin cell tests reveal an initial capacity of 1414 mAh g -1 at 0.1 C and 1049 mAh g -1 at 1 C and demonstrate 1000 times cyclability with a decaying rate of 0.05% per cycle. Furthermore, the assembly and construction of pouch cells were optimized with monolithic three-dimensional (3D) electrodes and a multistacking strategy. Specifically, a 3D metallic scaffold (3MS) was developed to host V-doped CoSe 2 nanowires and sulfur. In addition, Janus microspheres of C@TiO 2 were synthesized to capture polar polysulfides with their polar part of TiO 2 and adsorb nonpolar sulfur with their nonpolar part of carbon. By integrating with 3MS, C@TiO 2 microspheres can block all ion channels of 3MS and only allow Li ions in and out. These integral designs and monolithic structures enable multistacking pouch cells with high cyclability. A high-loading pouch cell was demonstrated with a total capacity of 700 mAh. The cell can be cycled for 70 times with a capacity retention of 65.7%. In brief, this work provides an integral strategy of catalyst design and overall 3D assembly for practical Li-S batteries in a large pouch cell format.

Redox mediators (RMs) have become a significant point in the now-established Li-O 2 battery system to reduce the charging overpotential in the oxygen evolution process. Nevertheless, a major inherent barrier of the RM is the redox shuttling between the Li metal anode and mobile RM, resulting in the corrosion of Li and depletion of RM. In this study, taking iodide/triiodide as a model RM, we propose an effective strategy by immersing the Li metal anode in I 2 steam to create a 1.5 μm thick surface protective layer. The resultant ionic conductive LiI layer on the Li metal anode can not only suppress Li dendrite growth but also act as a buffer layer between the RM and bare Li. By combining the iodide/triiodide RM with the LiI protective layer, the Li-O 2 battery shows low and steady charge voltage plateaus of ∼3.6 V over 70 cycles. Importantly, the symmetrical cell using the LiI-protected Li electrode exhibited small Li plating/stripping overpotentials (∼20 mV, 480 h), far superior to that of the bare Li electrode (∼70 mV, 300 h). The in situ interfacial observation shows that dendrite growth on the Li metal can be effectively suppressed by optimizing the LiI protective layer.

The cycling performance of Li-O 2 batteries (LOBs), which is an important parameter determining the practical use of this advanced energy technology with ultrahigh energy density, is strongly affected by the nature of the oxygen electrocatalyst. As a good oxygen electrode, it should possess good activity for both the oxygen evolution reaction and the oxygen reduction reaction and superior stability under operating conditions. During the past, oxygen electrodes for LOBs were generally fabricated by loading noble metal nanoparticles on the surface of a porous carbon support. However, the nanoparticles could easily lose contact with the carbon support during the reversible liquid-gas-solid reactions that involve lithium ions, oxygen gas, and Li 2 O 2 . Herein, we reported a novel Ru-metal-organic framework (MOF)-derived carbon composite, characterized by stereoscopic Ru nanoparticle distribution within the carbon matrix, as an alternative oxygen catalyst of LOBs, enabling superior operational stability and favorable activity. More specifically, the battery demonstrated stable charge-discharge cycling for up to 800 times (∼107 days) at a current density of 500 mA g -1 with low discharge/charge overpotentials (∼0.2/0.7 V vs Li). A mechanism of regenerative surface was further proposed to explain the excellent cycling stability of the LOBs through the use of the Ru-MOF-C catalyst. These encouraging results imply an accessible solution to address issues related to the oxygen catalyst for the realization of practical LOBs.

The rechargeable Li-O2 batteries with high theoretical specific energy are considered to be a promising energy storage system for electric vehicle application. Because of the prohibitive cost, limited supply, and weak durability of precious metals, the developments of novel metal-free catalysts become significant. Herein, the graphitic-carbon nitride@carbon papers have been produced by a facile in situ method and explored as cathodes for Li-O2 batteries, which manifest considerable electrocatalytic activity toward oxygen reduction reaction and oxygen evolution reaction in nonaqueous electrolytes because of their improved electronic conductivity and high nitrogen content. The assembled Li-O2 batteries using graphitic-carbon nitride@carbon papers as cathodes deliver good rate capability and cycling stability with a capacity retention of more than 100 cycles.