Three-dimensional stable lithium metal anode with nanoscale lithium islands embedded in ionically conductive solid matrix

Abstract

Rechargeable batteries based on lithium (Li) metal chemistry are attractive for next-generation electrochemical energy storage. Nevertheless, excessive dendrite growth, infinite relative dimension change, severe side reactions, and limited power output severely impede their practical applications. Although exciting progress has been made to solve parts of the above issues, a versatile solution is still absent. Here, a Li-ion conductive framework was developed as a stable "host" and efficient surface protection to address the multifaceted problems, which is a significant step forward compared with previous host concepts. This was fulfilled by reacting overstoichiometry of Li with SiO. The as-formed Li_xSi-Li₂O matrix would not only enable constant electrode-level volume, but also protect the embedded Li from direct exposure to electrolyte. Because uniform Li nucleation and deposition can be fulfilled owing to the high-density active Li domains, the as-obtained nanocomposite electrode exhibits low polarization, stable cycling, and high-power output (up to 10 mA/cm²) even in carbonate electrolytes. The Li-S prototype cells further exhibited highly improved capacity retention under high-power operation (∼600 mAh/g at 6.69 mA/cm²). The all-around improvement on electrochemical performance sheds light on the effectiveness of the design principle for developing safe and stable Li metal anodes.

Keywords: 3D composite; Li metal; electrolyte proof; high-power output; overlithiation.

Fig. 1.

Synthetic procedures and stripping/plating behavior of as-obtained electrode. (A) Schematic showing the open-framework configuration of Li metal anode with stable host, where the scaffold is coated by metallic Li. In this case, Li metal faces directly with the liquid electrolyte, which brings about excess SEI formation at the early stage. (B) Schematic illustration of the electrolyte-proof configuration where the majority of Li is embedded in a Li-ion conductive scaffold. After immersing into electrolytes, SEI only forms on the outer surface while the embedded Li domains remain intact. (C–H) Digital photo images (C–E) and corresponding SEM images (F–H) showing the pristine (C and F) LCNE after stripping 8 mAh/cm² (D and G) and LCNE after plating 8 mAh/cm² of Li back (E and H). (I–K) Cross-section SEM images of pristine LCNE (I), LCNE after stripping 8 mAh/cm² of Li (J), and electrode after stripping and plating back 8 mAh/cm² of Li (K). The current density was set at 2 mA/cm² for all of the above characterizations.

Fig. 2.

Characterization on morphology of Li deposited on different Li metal electrodes after 20 cycles. (A and B) Low-magnification (A) and magnified (B) SEM images showing the Li deposition behavior on Li foil (B) after 20 cycles. (C and D) Low-magnification (C) and magnified (D) SEM images showing the Li deposition behavior on LCNE after 20 cycles. The current density was fixed at 1 mA/cm² for both Li stripping and plating processes. The stripping/plating capacity was 1 mAh/cm².

Fig. 3.

Electrochemical characteristics of Li stripping/plating and their mechanisms. (A and B) Time-dependent Nyquist plots showing the impedance evolution of symmetric cells with LCNE (A) and Li foil (B) electrodes. (C) Typical stripping/plating voltage profile of the Li foil (black) and LCNE (red) of the first galvanostatic cycle. (D) Schematic shows the initial stripping/plating barrier (corresponding to barrier I in C), plating barrier (corresponding to barrier II in C), and further stripping barrier (corresponding to barrier III in C). (E) Voltage profile of Li foil symmetric cell (black) and LCNE symmetric cell (red) at the 1st, 2nd, 10th, and 100th cycle. The current density and the areal capacity were fixed at 1 mA/cm² and 1 mAh/cm², respectively.

Fig. 4.

Electrochemical performance of LCNE symmetric cell. (A) Voltage profile of Li foil symmetric cell (red) and that of LCNE symmetric cell (blue) at different rate various from 0.5 to 5 mA/cm². (B) The voltage profiles of Li foil symmetric cells (red) and LCNE symmetric cells (blue) at various current densities of 1 mA/cm² (Top), 5 mA/cm² (Middle), and 10 mA/cm² (Bottom). Stripping/plating capacity is fixed at 1 mAh/cm².

Fig. 5.

Rate capability of Li–S batteries with different Li electrodes. (A and B) Voltage profile of Li–S batteries with LCNE (A) and Li foil (B) as negative electrodes. Mass loading of S is fixed at 2 mg/cm². C rate is various from 0.2 to 2 C (6.69 mA/cm²). (C) Capacity retention of Li–S batteries at different C rate with LCNE (red) and Li foil (black) as negative electrodes.