Design Principles for Fluorinated Interphase Evolution via Conversion-Type Alloying Processes for Anticorrosive Lithium Metal Anodes

Intelligent Strategy of Lithium Metal Reconstruction through Generation of a Protective Layer and Regulating Lithium Deposition

Lithium metal has been considered as the most promising anode for next-generation batteries. However, its high reactivity with electrolyte and the growth of lithium dendrites hamper the application of lithium metal-based batteries. Herein, we demonstrate that lithium polyphosphides (LixPPs) can be dissolved in diethyl carbonate (DEC) and used as a reconditioner for generating a protective layer and regulating deposition of the Li metal anode. Since LixPPs are reduced prior to Li deposition in the lithiation process, their product can be a uniform and tight layer at the surface of the Li metal. The in situ-formed protection layer has superhigh Li ionic conductivity, and its thickness can be easily controlled by tuning the amount of LixPPs, thus facilitating the interface stability. The Li-Li symmetry batteries show stable cycling performance at 2 mA cm-2 and 1 mAh cm-2 over 5000 h. Interestingly, it exhibits a self-healing function on scratched Li metal.

Atomic Sn-incorporated subnanopore-rich hard carbon host for highly reversible quasi-metallic Li storage

The practical application of Li metal anodes has been hindered by severely irreversible side reactions for low Coulombic efficiency, uncontrollable growth of Li dendrites, and large volume change. Herein, we report subnanopore-rich carbon spheres encapsulated with Sn single atoms (Sn/CS@SC) as a Li host to address these challenges. Owing to the high Li affinity of Sn single atoms, Sn/CS@SC can promote storage of quasi-metallic Li within the inner void space other than direct plating of metallic Li on the outer surface. Moreover, the subnanopores with a strong spatial confinement effect can prevent the penetration of ester electrolyte for reduced side reactions. As expected, the Sn/CS@SC host demonstrates a high Coulombic efficiency of 99.8% over 600 cycles. Moreover, a full cell using a prelithiated Sn/CS@SC anode and LiNi0.8Co0.1Mn0.1O2 cathode shows high capacity retention (~80%) over 500 cycles at high current density.

In Operando Raman Spectroscopy Reveals Li-Ion Solvation in Lithium Metal Batteries

Inhomogeneous lithium (Li) deposition and unstable solid electrolyte interphase are the main causes of short cycle life and safety issues in Li metal batteries (LMBs). Developing a 3D structured matrix current collector and novel electrolyte are feasible strategies to tackle these issues. Ether-based electrolytes are widely used in LMBs. However, a fundamental understanding of Li-ion coordination and solvent remains incomplete. Here, lithiophilic Ag-Cu mesh is designed as the current collector to boost rapid Li-ion flux and Li metal nucleation. Meanwhile, dimethoxyethane (DME)/dioxolane (DOL) are used as complex solvents to enable lower interfacial resistance. The solvation structures at the interfaces of different collectors with different electrolytes are investigated. By applying in operando Raman spectroscopy, it is demonstrated that bis(trifluoromethylsulfonyl)imide TFSI-and DME molecules are highly coordinated with Li+ compared with DOL molecules. Furthermore, lithiophilic 3D Ag-Cu mesh tunes Li+ solvation/desolvation, resulting in a uniform deposition. The Ag-Cu mesh/Li symmetric cells demonstrate long-term cycling life up to 1200 h and Coulombic efficiency of 98.6% over 200 cycles at 1 mA cm-2. The Ag-Cu mesh/Li||LiNi0.8Co0.1Mn0.1O2 cells exhibit an initial discharge capacity of 208.7 mAh g-1 at 1.0 C with a capacity retention of 76.1% after 500 cycles.

CaF2 nanoparticles enabling LiF-dominated solid electrolyte interphase for dendrite-free and ultra-stable lithium metal batteries

The uncontrollable growth of Li dendrites and severe interfacial parasitic reactions on the Li anode are the primary obstacles to the practical application of lithium (Li) metal batteries. Effective artificial solid electrolyte interphase is capable of regulating uniform Li deposition and isolateing Li from electrolyte, thereby eliminating parasitic reactions. Herein, we rationally design a uniform LiF-dominated solid electrolyte interphase through an in-situ reaction between CaF2 nanoparticles and the Li anode, which allows dendrite-free Li deposition and restrains interfacial deterioration. Accordingly, the protective Li electrode demonstrated exceptional stability, sustaining over 6000 h at a current density of 2 mA cm-2 in symmetric cells and attaining over 1000 cycles with a low capacity decay rate of 0.015 % per cycle in coupling with LiFePO4 cathodes.

Design of an LiF-rich interface layer using high-concentration fluoroethylene carbonate and lithium bis(fluorosulfonyl)imide (LiFSI) to stabilize Li metal batteries

The development of high-energy-density Li metal batteries is limited by the uncontrollable growth of Li dendrites and an unstable Li/electrolyte interface during long-term Li plating/stripping. In this work, using high-concentration fluoroethylene carbonate (FEC) electrolyte, an LiF-rich interface layer was generated on the Li metal surface. This LiF-rich interface layer could effectively inactivate the high reactivity of the Li metal surface and suppress lithium dendrite growth, forming a uniform and dense structure at the Li/electrolyte interface to stabilize Li metal batteries. Owing to the enhanced interface stability offered by the high-concentration FEC electrolyte with LiFSI additive, the Li‖LiFePO4 cell presented high capacity retention (89.1%) after 200 cycles at 1C (165 mA g-1) and retained over 133.7 mA h g-1 at 10C rate, whereas only 115.0 mA h g-1 was achieved in the traditional carbonate ester electrolyte. The results show an obvious improvement in the cycle performance and rate capability of Li metal batteries containing a high-concentration FEC electrolyte with LiFSI as an additive.

Fluorine-Modulated MXene-Derived Catalysts for Multiphase Sulfur Conversion in Lithium-Sulfur Battery

Fluorine owing to its inherently high electronegativity exhibits charge delocalization and ion dissociation capabilities; as a result, there has been an influx of research studies focused on the utilization of fluorides to optimize solid electrolyte interfaces and provide dynamic protection of electrodes to regulate the reaction and function performance of batteries. Nonetheless, the shuttle effect and the sluggish redox reaction kinetics emphasize the potential bottlenecks of lithium-sulfur batteries. Whether fluorine modulation regulate the reaction process of Li-S chemistry? Here, the TiOF/Ti3C2 MXene nanoribbons with a tailored F distribution were constructed via an NH4F fluorinated method. Relying on in situ characterizations and electrochemical analysis, the F activates the catalysis function of Ti metal atoms in the consecutive redox reaction. The positive charge of Ti metal sites is increased due to the formation of O-Ti-F bonds based on the Lewis acid-base mechanism, which contributes to the adsorption of polysulfides, provides more nucleation sites and promotes the cleavage of S-S bonds. This facilitates the deposition of Li2S at lower overpotentials. Additionally, fluorine has the capacity to capture electrons originating from Li2S dissolution due to charge compensation mechanisms. The fluorine modulation strategy holds the promise of guiding the construction of fluorine-based catalysts and facilitating the seamless integration of multiple consecutive heterogeneous catalytic processes.

High-voltage electrosynthesis of organic-inorganic hybrid with ultrahigh fluorine content toward fast Li-ion transport

Hybrid materials with a rational organic-inorganic configuration can offer multifunctionality and superior properties. This principle is crucial but challenging to be applied in designing the solid electrolyte interphase (SEI) on lithium metal anodes (LMAs), as it substantially affects Li+ transport from the electrolyte to the anode. Here, an artificial SEI with an ultrahigh fluorine content (as high as 70.12 wt %) can be successfully constructed on the LMA using a high-voltage electrosynthesis strategy. This SEI consists of ultrafine lithium fluoride nanocrystals embedded in a fluorinated organic matrix, exhibiting excellent passivation and mechanical strength. Notably, the organic-inorganic interface demonstrates a high dielectric constant that enables fast Li+ transport throughout the SEI. Consequently, LMA coated with this SEI substantially enhances the cyclability of both half-cells and full cells, even under rigorous conditions. This work demonstrates the potential of rationally designed hybrid materials via a unique electrosynthetic approach for advanced electrochemical systems.

A 3D Hierarchical Host with Gradient-Distributed Dielectric Properties toward Dendrite-free Lithium Metal Anode

The conventional conductive three-dimensional (3D) host fails to effectively stabilize lithium metal anodes (LMAs) due to the internal incongruity arising from nonuniform lithium-ion gradient and uniform electric fields. This results in undesirable Li "top-growth" behavior and dendritic Li growth, significantly impeding the practical application of LMAs. Herein, we construct a 3D hierarchical host with gradient-distributed dielectric properties (GDD-CH) that effectively regulate Li-ion diffusion and deposition behavior. It comprises a 3D carbon fiber host modified by layer-by-layer bottom-up attenuating Sb particles, which could promote Li-ion homogeneously distribution and reduce ion concentration gradient via unique gradient dielectric polarization. Sb transforms into superionic conductive Li3Sb alloy during cycling, facilitating Li-ion dredging and pumps towards the bottom, dominating a bottom-up deposition regime confirmed by COMSOL Multiphysics simulations and physicochemical characterizations. Consequently, a stable cycling performance of symmetrical cells over 2000 h under a high current density of 10 mA cm-2 is achieved. The GDD-CH-based lithium metal battery shows remarkable cycling stability and ultra-high energy density of 378 Wh kg-1 with a low N/P ratio (1.51). This strategy of dielectric gradient design broadens the perspective for regulating the Li deposition mechanism and paves the way for developing high-energy-density lithium metal anodes with long durability.

Revealing the Distribution of Lithium Compounds in Lithium Dendrites by Four-Dimensional Electron Microscopy Analysis

Characterizing the microstructure of radiation- and chemical-sensitive lithium dendrites and its solid electrolyte interphase (SEI) is an important task when investigating the performance and reliability of lithium-ion batteries. Widely used methods, such as cryogenic high-resolution transmission electron microscopy as well as related spectroscopy, are able to reveal the local structure at nanometer and atomic scale; however, these methods are unable to show the distribution of various crystal phases along the dendrite in a large field of view. In this work, two types of four-dimensional electron microscopy diffractive imaging methods, i.e., scanning electron nanodiffraction (SEND) and scanning convergent beam electron diffraction (SCBED), are employed to show a new pathway on characterizing the sensitive lithium dendrite samples at room temperature and in a large field of view. Combining with the non-negative matrix factorization (NMF) algorithm, orientations of different lithium metal grains along the lithium dendrite as well as different lithium compounds in the SEI layer are clearly identified.

A corrosion inhibiting layer to tackle the irreversible lithium loss in lithium metal batteries

Reactive negative electrodes like lithium (Li) suffer serious chemical and electrochemical corrosion by electrolytes during battery storage and operation, resulting in rapidly deteriorated cyclability and short lifespans of batteries. Li corrosion supposedly relates to the features of solid-electrolyte-interphase (SEI). Herein, we quantitatively monitor the Li corrosion and SEI progression (e.g., dissolution, reformation) in typical electrolytes through devised electrochemical tools and cryo-electron microscopy. The continuous Li corrosion is validated to be positively correlated with SEI dissolution. More importantly, an anti-corrosion and interface-stabilizing artificial passivation layer comprising low-solubility polymer and metal fluoride is designed. Prolonged operations of Li symmetric cells and Li | |LiFePO4 cells with reduced Li corrosion by ~74% are achieved (0.66 versus 2.5 μAh h-1). The success can further be extended to ampere-hour-scale pouch cells. This work uncovers the SEI dissolution and its correlation with Li corrosion, enabling the durable operation of Li metal batteries by reducing the Li loss.

Near zero-strain silicon oxycarbide interphases for stable Li-ion batteries

We investigate silicon oxycarbide nanotubes that incorporate Si, SiC, and silicon oxycarbide phases, which exhibit near zero-strain volume expansion, leading to reduced electrolyte decomposition. The composite effectively accommodates the formation of c-Li15Si4, as validated by in situ TEM analyses and electrochemical tests, thereby proposing a promising solution for Li-ion battery anodes.

Self-Purifying Primary Solvation Sheath Enables Stable Electrode-Electrolyte Interfaces for Nickel-Rich Cathodes

Herein, we optimize the primary solvation sheath to investigate the fundamental correlation between battery performance and electrode-electrolyte interfacial properties through electrolyte solvation chemistry. Experimental and theoretical analyses reveal that the primary solvation sheath with a self-purifying feature can "positively" scavenge both the HF and PF5 (hydrolysis of ion-paired LiPF6), stabilize the PF6 anion-derived electrode-electrolyte interfaces, and thus boost the cycling performances. Being attributed with these superiorities, the NCM811//Li Li metal battery (LMB) with the electrolyte containing the optimized solvation sheath delivers 99.9% capacity retention at 2.5 C after 250 cycles. To circumvent the impact of excess Li content of Li metal on the performance of NCM811 cathode, the as-fabricated NCM811//graphite Li ion battery (LIB) also delivers a high-capacity retention of 90.1% from the 5th to the 100th cycle at 1 C. This work sheds light on the strong ability of the primary solvation sheath to regulate cathode interfacial properties.