Mechanistic Probing of Encapsulation and Confined Growth of Lithium Crystals in Carbonaceous Nanotubes

Abstract

Encapsulation of lithium in the confined spaces within individual nanocapsules is intriguing and highly desirable for developing high‐performance Li metal anodes. This work aims for a mechanistic understanding of Li encapsulation and its confined growth kinetics inside 1D enclosed spaces. To achieve this, amorphous carbon nanotubes are employed as a model host using in situ transmission electron microscopy. The carbon shells have dual roles, providing geometric/mechanical constraints and electron/ion transport channels, which profoundly alter the Li growth patterns. Li growth/dissolution takes place via atom addition/removal at the free surfaces through Li+ diffusion along the shells in the electric field direction, resulting in the formation of unusual Li structures, such as poly‐crystalline nanowires and free‐standing 2D ultrathin (1–2 nm) Li membranes. Such confined front‐growth processes are dominated by Li {110} or {200} growing faces, distinct from the root growth of single‐crystal Li dendrites outside the nanotubes. Controlled experiments show that high lithiophilicity/permeability, enabled by sufficient nitrogen/oxygen doping or pre‐lithiation, is critical for the stable encapsulation of lithium inside carbonaceous nanocapsules. First‐principles‐based calculations reveal that N/O doping can reduce the diffusion barrier for Li+ penetration, and facilitate Li filling driven by energy minimization associated with the formation of low‐energy Li/C interfaces.

Visualizing the failure of solid electrolyte under GPa-level interface stress induced by lithium eruption

“…As {110} planes of b.c.c. metals have the lowest surface energy, they are therefore preferentially exposed on the surface of Li crystals, consistent with previous TEM observations 26 , 27 . Besides, the low-energy Li {002} and {112} planes prevailed alternately on the lower growing facet to adapt to the uneven LLZO surface, so as to minimize the overall energy of the expanding-Li|LLZO system.…”

“…We present a simple demonstration in Fig. 4i, j , where the amorphous carbon nanotube (a-CNT) serves as a Li host between LLZO and CC 27 . Li metal can quickly fill the cavity of a-CNT through Li + (or Li 0 atoms 31 ) diffusion along the carbon shells with an estimated current density of 200 mA cm −2 (Supplementary Movie 7 ), still much faster than the cases in Figs.…”

An Encapsulation‐Based Sodium Storage via Zn‐Single‐Atom Implanted Carbon Nanotubes

“…The above results indicate that the use of Zn SA -HCNT as a sodiophilic substrate for sodium metal anodes can significantly improve the metal sodium deposition and stripping process, and our work is also superior to other recently published works (Figure 4d). This profit from the reduction of the diffusion barrier of sodium ions by the sodiophilic Zn single atoms, [14] and the abundant pores and defect sites on the carbon shells derived from ZIF provide a diffusion path for sodium ions. The results of Tafel curve also prove this conclusion (Figure S21, Supporting Information).…”

“…[13] Reliable sodiphilic doping sites can facilitate Na + penetrating into the tube and form a sodium-carbon interface with carbon as much as possible to minimize system energy. [14] Nevertheless, sodium ions are difficult to react with carbon and cannot be inserted into graphene interlayers of CNFs (or CNTs) like lithium ions, making it unable to construct suitable Na + diffusion pathways. [15] Hence, it is extremely important to design a suitable geometric space and the sodiophilicity wall embedded with appropriate sodiophilic sites to reduce the diffusion barrier of Na + for realizing high reversible Na encapsulation.…”

Enhanced Cyclability of Lithium Metal Anodes Enabled by Anti-aggregation of Lithiophilic Seeds

“…For a better understanding of this issue, another type of carbon spheres, N-HPCSs decorated with Ag nanoparticles (denoted as Ag@N-HPCSs, where Ag is a commonly used alloying-type seed material [12–14] ) was adopted for comparative studies. As illustrated in Figure S14, in situ TEM observation of Li deposition on these two types of carbon spheres was conducted using a dry-cell nanobattery setup (see Methods). − Figure a and Movie S4 depict the plating/stripping process on a single Ag@N-HPCS. Clearly, most of the Ag nanoparticals somewhat expanded due to the alloying reaction with Li during plating (pointed by the yellow arrowheads), and some particles dissolved in the Li metal (leaving behind the vacancies pointed by the white arrowheads) and even aggregated to form a larger particle (indicated by the red circles).…”