Mitigating Concentration Polarization through Acid-Base Interaction Effects for Long-Cycling Lithium Metal Anodes.

Lithium (Li) metal has attracted great attention as a promising high-capacity anode material for next-generation high-energy-density rechargeable batteries. Nonuniform Li+ transport and uneven Li plating/stripping behavior are two key factors that deteriorate the electrochemical performance. In this work, we propose an interphase acid-base interaction effect that could regulate Li plating/stripping behavior and stabilize the Li metal anode. ZSM-5, a class of zeolites with ordered nanochannels and abundant acid sites, was employed as a functional interface layer to facilitate Li+ transport and mitigate the cell concentration polarization. As a demonstration, a pouch cell with a high-areal-capacity LiNi0.95Co0.02Mn0.03O2 cathode (3.7 mAh cm-2) and a ZSM-5 modified thin lithium anode (50 µm) delivered impressive electrochemical performance, showing 92% capacity retention in 100 cycles (375.7 mAh). This work reveals the effect of acid-base interaction on regulating lithium plating/stripping behaviors, which could be extended to developing other high-performance alkali metal anodes.

Probing Hybrid LiFePO4/FePO4 Phases in a Single Olive LiFePO4 Particle and Their Recovering from Degraded Electric Vehicle Batteries.

The recycling of LiFePO4 from degraded lithium-ion batteries (LIBs) from electric vehicles (EVs) has gained significant attention due to resource, environment, and cost considerations. Through neutron diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, we revealed continuous lithium loss during battery cycling, resulting in a Li-deficient state (Li1-xFePO4) and phase separation within individual particles, where olive-shaped FePO4 nanodomains (5-10 nm) were embedded in the LiFePO4 matrix. The preservation of the olive-shaped skeleton during Li loss and phase change enabled materials recovery. By chemical compensation for the lithium loss, we successfully restored the hybrid LiFePO4/FePO4 structure to pure LiFePO4, eliminating nanograin boundaries. The regenerated LiFePO4 (R-LiFePO4) exhibited a high crystallinity similar to the fresh counterpart. This study highlights the importance of topotactic chemical reactions in structural repair and offers insights into the potential of targeted Li compensation for energy-efficient recycling of battery electrode materials with polyanion-type skeletons.

Metal/LiF/Li2O Nanocomposite for Battery Cathode Prelithiation: Trade-off between Capacity and Stability.

Lithium-ion batteries (LIBs) are currently dominating the portable electronics market and supplying power for electric vehicles and grid-level storage. However, lithium loss in the formation cycle at the anode side reduces the energy density of state-of-the-art LIBs with carbon anode materials. This situation will be even more severe for future LIBs using high-capacity Si-based anode materials. In this study, a transition metal-based nanocomposite with built-in lithium source was synthesized, featuring Fe nanodomains with a size of ∼5 nm uniformly dispersed in a hybrid Li2O and LiF matrix with intimate contact between them. The Fe/LiF/Li2O nanocomposite released a high Li-ion capacity of 550 mA h/g based on a multielectron inverse conversion reaction during the first-cycle charge process and exhibited better ambient stability than the counterpart with a pure Li2O matrix and also a lower lithium-extraction voltage and faster reaction kinetics than the counterpart with a pure LiF matrix. Serving as an additive to various cathodes (e.g., LiCoO2, LiFePO4, and LiNi1-x-yCoxMnyO2), the Fe/LiF/Li2O nanocomposite showed excellent lithium compensation effect. Using 4.8 wt % Fe/LiF/Li2O additive based on the total mass of the electrodes, a LiNi0.8Co0.1Mn0.1O2|SiO-graphite full cell with a high cathode mass loading of 20 mg/cm2 exhibited a high reversible capacity of 2.9 mA h/cm2 at 0.5 C after 100 cycles which is a 15% increase in comparison to the counterpart without the prelithiation additive. After the Fe/LiF/Li2O nanocomposite was immersed into the electrolyte and rested for 72 h, the content of iron metal in the electrolyte was negligible, indicating that this prelithiation additive was stable in the electrolyte and would not cause any side reactions, such as the shuttle of iron ions during cycling. The high "donor" Li-ion capacity, good ambient stability, and its compatibility with existing cathode materials and battery fabrication processes make the Fe/LiF/Li2O nanocomposite a promising cathode prelithiation additive to offset the initial lithium loss and improve the energy density of LIBs.

Locking Active Li Metal through Localized Redistribution of Fluoride Enabling Stable Li-Metal Batteries.

The creation of fluorinated interphase has emerged as an effective strategy for improving Li-metal anodes for rechargeable high-energy batteries. In contrast to the introduction of fluorine-containing species through widely adopted electrolyte engineering, a Li-metal composite design is reported in which LiF can locally redistribute on the Li-metal surface in liquid electrolytes via a dissolution-reprecipitation mechanism, and enable the formation of a high-fluorine-content solid electrolyte interphase (SEI). For validation, a Li/Li22 Sn5 /LiF ternary composite is investigated, where the as-formed LiF-rich SEI locks the active Li metal from corrosive electrolyte. The Li/Li22 Sn5 /LiF anode displays an impressive average Coulombic efficiency (ACE, ≈99.2%) at 1 mA cm-2 and 1 mAh cm-2 in a carbonate electrolyte and a remarkable cycling life of over 1600 h at 1 mA cm-2 and 2 mAh cm-2 . Applied to a LiCoO2 full cell with a high cathode areal capacity of 4.0 mAh cm-2 , a high capacity retention of ≈91.1% is realized for 100 cycles at 0.5 C between 2.8 to 4.5 V with a low negative/positive (N/P) ratio of 2:1. This design is conceptually different from the design employing the widely used fluorine-containing electrolyte additive and provides an alternative approach to realize reliable Li-metal batteries.

Regioselective hydrogenolysis of aryl ether C-O bonds by tungsten carbides with controlled phase compositions.

Evenly dispersed tungsten carbides with controlled phase compositions that exhibit an impressive capacity to carry out the regioselective hydrogenolysis of inert aryl ether C-O bonds instead of aliphatic C-O bonds to produce aromatic compounds are reported.