Solid polymer nanocomposite electrolytes with improved interface properties towards lithium metal battery application at room temperature

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Erabhoina, Harimohan ; Rosenbach, Dominic ; Mohanraj, John ; Thelakkat, Mukundan:
Solid polymer nanocomposite electrolytes with improved interface properties towards lithium metal battery application at room temperature.
In: Electrochimica Acta. Bd. 387 (2021) . - 138455.
ISSN 0013-4686
DOI: https://doi.org/10.1016/j.electacta.2021.138455

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Abstract

Solid polymer electrolytes (SPEs) with good thermal, mechanical and electrochemical cycling stability are required for application in all-solid-state lithium metal batteries (LMBs) using non-intercalating Li metal anodes at room temperature. In this context, the polymer architecture plays a significant role in influencing the above parameters. Therefore, we studied systematically Poly(MA)m-graft-PEGME2k in comparison to the linear poly(ethylene oxide) (PEO) homopolymer as SPEs in all-solid-state LMBs using LiFePO4 as a cathode. Additionally, nanocomposite electrolytes using bottlebrush (SPNE1) and PEO (SPNE2) with improved mechanical and electrochemical properties were prepared by adding different amounts of TiO2 nanoparticles. Among them, the SPNE1-10 (with 10 wt TiO2) showed a homogenous distribution of nanoparticles throughout the polymer matrix, exhibited a good ionic conductivity of 3·10–5 at 25 ᴼC and 5.2·10–4 at 70 ᴼC, as well as a high electrochemical stability of up to 5.2 V vs. Li/Li+. Moreover, the symmetric Li/SPNE1-10/Li cells displayed a constant current up to 40 cycles without any fluctuations indicating good interfacial compatibility between the electrode and electrolyte. Furthermore, extended distribution of relaxation times (eDRT) studies provide evidence of a stable solid-electrolyte interface (SEI) layer formation, which is further supported by ex-situ X-ray photoelectron spectroscopy (XPS) analysis of the cycled lithium surface. The LMBs with the SPNE1-10 electrolyte delivered a high discharge capacity of 132 mAh g−1 at 70 ᴼC at a 0.2C. Even, when the current rate was increased to 2C, the cell maintained a good discharge capacity after 400 cycles. The SPNE1-10 nanocomposite based on the bottlebrush polymer outperforms considerably the SPNE2-10 consisting of linear PEO for the whole temperature range from 25 to 80 ᴼC enabling efficient all solid-state LMBs using SPEs below 70 ᴼC.