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

• Published in: Electrochimica acta 2021-08, Vol.387, p.138455, Article 138455
• Main Authors: Erabhoina, Harimohan, Rosenbach, Dominic, Mohanraj, John, Thelakkat, Mukundan
• Format: Article
• Language: English
• Subjects: Discharge; Electrochemical analysis; Electrolytes; Electrolytic cells; Ethylene oxide; Interfacial properties; Ion currents; Ionic conductivity; LiFePO4 cathode; Lithium batteries; Molten salt electrolytes; Nanocomposites; Nanoparticles; Photoelectrons; Polyethylene oxide; Polymers; Rheology; Room temperature; SEI layer; Solid electrolytes; Solid polymer Nanocomposite battery; Solid state; Stability; Titanium dioxide; X ray photoelectron spectroscopy
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2021.138455

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.