Fluorinated Interface Layer with Embedded Zinc Nanoparticles for Stable Lithium-Metal Anodes

Progress in Modeling and Applications of Solid Electrolyte Interphase Layers for Lithium Metal Anodes

The increasing demand for high-specific-energy lithium batteries has stimulated extensive research on the lithium metal anode owing to its high specific capacity and low electrode potential. However, the lithium metal will irreversibly react with the electrolyte during the first cycling process, forming an uneven and unstable solid electrolyte interphase (SEI) layer, which results in the non-uniform deposition of Li ions and thus the formation of lithium dendrites. This could cause a battery short circuit, resulting in safety hazards such as thermal runaway. In addition, the continuous rupture and repair of the SEIs during the repeated charge/discharge processes will constantly consume the active lithium, which leads to a significant decrease in battery capacity. An effective strategy to address these challenges is to design and construct ideal artificial SEIs on the surface of the lithium metal anode. This review analyzes and summarizes the mathematical modeling of SEI, the functional characteristics of SEIs with different components, and finally discusses the challenges faced by artificial SEIs in practical applications of lithium metal batteries and future development directions.

Recent Progress on Advanced Flexible Lithium Battery Materials and Fabrication Process

Flexible energy storage devices have attracted wide attention as a key technology restricting the vigorous development of wearable electronic products. However, the practical application of flexible batteries faces great challenges, including the lack of good mechanical toughness of battery component materials and excellent adhesion between components, resulting in battery performance degradation or failure when subjected to different types of deformation. It is imperative to develop flexible batteries that can withstand deformation under different conditions and maintain stable battery performance. This paper reviews the latest research progress of flexible lithium batteries, from the research and development of new flexible battery materials, advanced preparation processes, and typical flexible structure design. First, the types of key component materials and corresponding modification technologies for flexible batteries are emphasized, mainly including carbon-based materials with flexibility, lithium anode materials, and solid-state electrolyte materials. In addition, the application of typical flexible structural designs (buckling, spiral, and origami) in flexible batteries is clarified, such as 3D printing and electrospinning, as well as advanced fabrication techniques commonly used in flexible materials and battery components. Finally, the limitations and coping strategies in the practical application of flexible lithium batteries are discussed, which provides new ideas for future research.

Probing the Mechanically Stable Solid Electrolyte Interphase and the Implications in Design Strategies

The inevitable volume expansion of secondary battery anodes during cycling imposes forces on the solid electrolyte interphase (SEI). The battery performance is closely related to the capability of SEI to maintain intact under the cyclic loading conditions, which basically boils down to the mechanical properties of SEI. The volatile and complex nature of SEI as well as its nanoscale thickness and environmental sensitivity make the interpretation of its mechanical behavior many roadblocks. Widely varied approaches are adopted to investigate the mechanical properties of SEI, and diverse opinions are generated. The lack of consensus at both technical and theoretical levels has hindered the development of effective design strategies to maximize the mechanical stability of SEIs. Here, the essential and desirable mechanical properties of SEI, the available mechanical characterization methods, and important issues meriting attention for higher test accuracy are outlined. Previous attempts to optimize battery performance by tuning SEI mechanical properties are also scrutinized, inconsistencies in these efforts are elucidated, and the underlying causes are explored. Finally, a set of research protocols is proposed to accelerate the achievement of superior battery cycling performance by improving the mechanical stability of SEI.

Long-Lifespan Lithium Metal Batteries Enabled by a Hybrid Artificial Solid Electrolyte Interface Layer

Lithium metal batteries based on metallic Li anodes have been recognized as competitive substitutes for current energy storage technologies due to their exceptional advantage in energy density. Nevertheless, their practical applications are greatly hindered by the safety concerns caused by lithium dendrites. Herein, we fabricate an artificial solid electrolyte interface (SEI) via a simple replacement reaction for the lithium anode (designated as LNA-Li) and demonstrate its effectiveness in suppressing the formation of lithium dendrites. The SEI is composed of LiF and nano-Ag. The former can facilitate the horizontal deposition of Li, while the latter can guide the uniform and dense lithium deposition. Benefiting from the synergetic effect of LiF and Ag, the LNA-Li anode exhibits excellent stability during long-term cycling. For example, the LNA-Li//LNA-Li symmetric cell can cycle stably for 1300 and 600 h at the current densities of 1 and 10 mA cm^-2, respectively. Impressively, when matching with LiFePO₄, the full cells can steadily cycle for 1000 times without obvious capacity attenuation. In addition, the modified LNA-Li anode coupled with the NCM cathode also exhibits good cycling performance.

Synergy of an In Situ-Polymerized Electrolyte and a Li3N-LiF-Reinforced Interface Enables Long-Term Operation of Li-Metal Batteries

The long-term operation of a Li-metal anode remains a great challenge due to the severe dendrite growth in an organic liquid electrolyte. To protect a Li-anode surface from continuous corrosion by an electrolyte, a consistent and robust solid electrolyte interface (SEI) is an essential prerequisite. This work proposes a secure gel polymer electrolyte, which is in situ constructed via a facile polymerization process of vinylidene carbonate inside Li-metal batteries. The liquid components that are not involved in polymerization are well entrapped in the poly(vinyl carbonate) framework, leading to a high oxidative stability of up to 4.5 V (vs Li/Li+). A Li3N-LiF-reinforced SEI resulting from the reduction of fluoroethylene carbonate and lithium nitrate additives has a synergistic effect on the suppression of Li-dendrite growth. The densely packed Li deposition behavior is revealed by in situ/ex situ microscopic observations. Steady cycling of over 2500 h with a relatively low voltage hysteresis is achieved by the Li||Li symmetric cells. A Coulombic efficiency above 96% upon long-term cycling is available for the asymmetric Li||Cu cells. The smooth operation of batteries with commercial LiFePO4 cathodes further indicates that the SEI with homogeneity in composition and structure prompts Li deposition with alleviative dendrites.

In Situ Construction a Stable Protective Layer in Polymer Electrolyte for Ultralong Lifespan Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SLMBs) are attracting enormous attention due to their enhanced safety and high theoretical energy density. However, the alkali lithium with high reducibility can react with the solid-state electrolytes resulting in the inferior cycle lifespan. Herein, inspired by the idea of interface design, the 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide as an initiator to generate an artificial protective layer in polymer electrolyte is selected. Time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy reveal the stable solid electrolyte interface (SEI) is in situ formed between the electrolyte/Li interface. Scanning electron microscopy (SEM) images demonstrate that the constructed SEI can promote homogeneous Li deposition. As a result, the Li/Li symmetrical cells enable stable cycle ultralong-term for over 4500 h. Moreover, the as-prepared LiFePO4 /Li SLMBs exhibit an impressive ultra-long cycle lifespan over 1300 cycles at 1 C, as well as 1600 cycles at 0.5 C with a capacity retention ratio over 80%. This work offers an effective strategy for the construction of the stable electrolyte/Li interface, paving the way for the rapid development of long lifespan SLMBs.