(Digital Presentation) An Initiator-Free and in-Situ Constructed Solid Electrolyte for High Energy Density Batteries with Si Anodes
Authors: Peng Xudong , Zhao Tim 
Published: September 2023

The emerging electrical applications and transportation electrification call for safe and energy-dense batteries with long lifespans and considerable power outputs. For the current graphite-majority LIBs, the anode takes up more than 30% of the mass ratio and around 50% of the volume ratio within the cell unit because of the low specific capacity of the graphite (theoretical capacity ~372 mAh g-1), leading to a low energy density around 200 Wh kg-1. Replacing the insertion-type graphite anode with the conversion-type Si anode (theoretical capacity ~3579 mAh g-1) [1] or the Li-metal anode (theoretical capacity ~3860 mAh g-1) could help reduce the mass and volume portion to less than 5% and 10%, respectively, which is thus of great significance for further promotion of the energy density (>350 Wh kg-1) at the cell level. Aside from the performance-related issues, the safety concerns of LIBs should also be well addressed. Therefore, solid state electrolytes have triggered worldwide interest in the past few years for its incomparable safety of anti-combustion and no leakage. Besides, the solid-state electrolytes could also boost the promotion of battery energy density.
However, most of the current research about solid-states electrolytes adopt Li-metal as the anode. Though solid-state Li-metal batteries (SSLMBs) are acclaimed to have the highest gravimetric specific energy density theoretically, it is challenged by several critical issues. First, the Li-metal anode could not well address the dendrite issue, which limits the critical current density (< 0.5 mA cm-2) and areal capacities (< 0.5 mA cm-2) of the battery [2]. Secondly, most of the reported SSLMBs are carried out at high-temperature (60℃ or above) or with incredibly huge pressure (fabrication at > 200 MPa; operation at > 50 MPa) [3][4], which is not realistic in the common scenarios. Besides, nearly all the reported SSLMBs are tested with large Li-excess (low reversibility of Li-plaiting and stripping) and limited cathode loadings (inefficient conductivity), leading to unacceptable energy densities of the cells.
Herein, we present that the Si-anode, which is not as widely as Li-metal studied in solid-state batteries, is a well-qualified candidate for the Li-metal for practical solid batteries. The pure Si anode (~2.1 mAh cm-2) with the solid electrolyte can be stably cycled at room temperature without external pressure for more than 150 cycles with no sharp capacity fade and a remained capacity over 1800 mAh g-1. The Si||LiFePO4 full cell adopting this electrolyte could achieves 120 stable cycles with high Coulombic efficiencies (>99.9%). This study shows that the in-situ polymerized solid electrolyte could be well matched with Si-anode for practical high energy density battery configuration.

Acknowledgement

The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrbative Region, China (Project No. R6005–20).

Reference

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Figure 1