Bi-containing Electrolyte Enables Robust and Li Ion Conductive Solid Electrolyte Interphase for Advanced Lithium Metal Anodes

Abstract

The notorious lithium dendrite growth, causing the safety concern, hinders the practical application of high-capacity Li metal anodes for rechargeable batteries. Here, a robust and highly ionic conductive solid electrolyte interphase (SEI) layer to protect Li metal anode is in-situ constructed by introducing trace additive of tetrapotassium heptaiodobismuthate (K₄BiI₇) into electrolyte. The K₄BiI₇-added electrolyte enables Li metal anode to display a stable cycling for over 600 cycles at 1.0 mA cm^-2/1.0 mAh cm^-2 and over 400 cycles at 5.0 mA cm^-2/5.0 mAh cm^-2. In situ optical microscopy observations also conform the suppression of Li dendrites at high current density. Moreover, the in-situ SEI layer modified Li anode exhibits an average Coulombic efficiency of 99.57% and less Li dendrite growth. The Li-S full sells with the modified electrolyte also show improved electrochemical performance. This research provides a cost-efficient method to achieve a highly ionic conductive and stable SEI layer toward advanced Li metal anodes.

Keywords: K4BiI7 additive; Li metal anode; dendrite suppression; ionic conductivity; solid electrolyte interphase.

Figure 1

(A) Voltage-time curves of Li|Li symmetrical cells at 1.0 mA cm⁻²/1.0 mAh cm⁻² and (B–D) the detailed magnified voltage-time curves at different cycling time. (E) Voltage-time curves of Li|Li symmetrical cells at 5.0 mA cm⁻²/5.0 mAh cm⁻² (F) Voltage-time curves of Li|Li symmetrical cells at different current densities.

Figure 2

In situ optical microscopy observations (captured from the videos) of the electrolyte–electrode interface during electrodeposition in (A) routine electrolyte and (B) modified electrolyte at an extremely high current density of 60 mA cm⁻² with 5 min per cycle. The capacity (mAh cm⁻²) of Li being electrodeposited on the electrodes is shown in the top middle of each image.

Figure 3

Typical constant current protocol and measured voltage vs. time plot of Li|Cu cells with (A) TE and (B) ME. (C) Average Coulombic efficiency of Li|Cu cells with different electrolytes.

Figure 4

TEM images of the (A) routine SEI and (C) modified SEI with SAED patterns inserted. High resolution TEM images of the (B) routine SEI and (D) modified SEI (crystal particles are marked out by dotted circle).

Figure 5

EIS of Li|Li cells with (A) TE and (B) ME at different cycling stages.

Figure 6

XPS spectra of (A) C 1s, O 1s, F 1s and (B) Bi 4f species at various depths of the modified SEI on Li anodes after 20 cycles in Li|Li batteries.

Figure 7

Electrochemical performance of Li|S full cells with different electrolyte. (A) Cycling performance of at 0.2C. (B) Rate capability. (C) Nyquist plots before cycling. CV curves for the initial three cycles of cells with (D) ME and (E) TE at a scan rate of 0.1 mV s⁻¹.