Lithium Deposition-Induced Fracture of Carbon Nanotubes and Its Implication to Solid-State Batteries

Solid-state batteries: The critical role of mechanics

Solid-state batteries with lithium metal anodes have the potential for higher energy density, longer lifetime, wider operating temperature, and increased safety. Although the bulk of the research has focused on improving transport kinetics and electrochemical stability of the materials and interfaces, there are also critical challenges that require investigation of the mechanics of materials. In batteries with solid-solid interfaces, mechanical contacts, and the development of stresses during operation of the solid-state batteries, become as critical as the electrochemical stability to keep steady charge transfer at these interfaces. This review will focus on stress and strain that result from normal and extended battery cycling and the associated mechanisms for stress relief, some of which lead to failure of these batteries.

Design Strategies for Anodes and Interfaces Toward Practical Solid-State Li-Metal Batteries

Solid-state Li-metal batteries (based on solid-state electrolytes) offer excellent safety and exhibit high potential to overcome the energy-density limitations of current Li-ion batteries, making them suitable candidates for the rapidly developing fields of electric vehicles and energy-storage systems. However, establishing close solid-solid contact is challenging, and Li-dendrite formation in solid-state electrolytes at high current densities causes fatal technical problems (due to high interfacial resistance and short-circuit failure). The Li metal/solid electrolyte interfacial properties significantly influence the kinetics of Li-metal batteries and short-circuit formation. This review discusses various strategies for introducing anode interlayers, from the perspective of reducing the interfacial resistance and preventing short-circuit formation. In addition, 3D anode structural-design strategies are discussed to alleviate the stress caused by volume changes during charging and discharging. This review highlights the importance of comprehensive anode/electrolyte interface control and anode design strategies that reduce the interfacial resistance, hinder short-circuit formation, and facilitate stress relief for developing Li-metal batteries with commercial-level performance.

Superfast Mass Transport of Na/K Via Mesochannels for Dendrite-Free Metal Batteries

Fast ion diffusion in anode hosts enabling uniform distribution of Li/Na/K is essential for achieving dendrite-free alkali-metal batteries. Common strategies, e.g. expanding the interlayer spacing of anode materials, can enhance bulk diffusion of Li but are less efficient for Na and K due to their larger ionic radius. Herein, a universal strategy to drastically improve the mass-transport efficiency of Na/K by introducing open mesochannels in carbon hosts is proposed. Such pore engineering can increase the accessible surface area by one order of magnitude, thus remarkably accelerating surface diffusion, as visualized by in situ transmission electron microscopy. In particular, once the mesochannels are filled by the Na/K metals, they become the superfast channels for mass transport via the mechanism of interfacial diffusion. Thus-modified carbon hosts enable Na/K filling in their inner cavities and uniform deposition across the whole electrodes with fast kinetics. The resulting Na-metal anodes can exhibit stable dendrite-free cycling with outstanding rate performance at a high current density of up to 30 mA cm^-2 . This work presents an inspiring attempt to address the sluggish transport issue of Na/K, as well as valuable insights into the mass-transport mechanism in porous anodes for high-performance alkali-metal storage.

Growth and Performance of High-Quality SWCNT Forests on Inconel Foils as Lithium-Ion Battery Anodes

Large-scale production of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) on metal foils promises to enable technological advancements in many fields, from functional composites to energy storage to thermal interfaces. In this work, we demonstrate growth of high-quality (G/D > 6, average diameters ∼ 2-3 nm, densities > 10¹² cm^-2) VA-SWCNTs on Inconel metal for use as a lithium-ion battery (LIB) anode. Scale-up of SWCNT growth on Inconel 625 to 100 cm² exhibits nearly invariant CNT structural properties, even when synthesis is performed near atmospheric pressure, and this robustness is attributed to a growth kinetic regime dominated by the carbon precursor diffusion in the bulk gas mixture. SWCNT forests produced on large-area metal substrates at close to atmospheric pressure possess a combination of structural features that are among the best demonstrated so far in the literature for growth on metal foils. Leveraging these achievements for energy applications, we demonstrate a VA-SWCNT LIB anode with capacity >1200 mAh/g at 1.0C and stable cycling beyond 300 cycles. This robust synthesis of high-quality VA-SWCNTs on metal foils presents a promising route toward mass production of high-performance CNT devices for a broad range of applications.

Size-Dependent Chemomechanical Failure of Sulfide Solid Electrolyte Particles during Electrochemical Reaction with Lithium

The very high ionic conductivity of Li₁₀GeP₂S₁₂ (LGPS) solid electrolyte (SE) makes it a promising candidate SE for solid-state batteries in electrical vehicles. However, chemomechanical failure, whose mechanism remains unclear, has plagued its widespread applications. Here, we report in situ imaging lithiation-induced failure of LGPS SE. We revealed a strong size effect in the chemomechanical failure of LGPS particles: namely, when the particle size is greater than 3 μm, fracture/pulverization occurred; when the particle size is between 1 and 3 μm, microcracks emerged; when the particle size is less than 1 μm, no chemomechanical failure was observed. This strong size effect is interpreted by the interplay between elastic energy storage and dissipation. Our finding has important implications for the design of high-performance LGPS SE, for example, by reducing the particle size to less than 1 μm the chemomechanical failure of LGPS SE can be mitigated.