Abstract
Sodium-ion batteries (SIBs) are emerging power sources for the replacement of lithium-ion batteries. Recent studies have focused on the development of electrodes and electrolytes, with thick glass fiber separators (~380 μm) generally adopted. In this work, we introduce a new thin (~50 μm) cellulose–polyacrylonitrile–alumina composite as a separator for SIBs. The separator exhibits excellent thermal stability with no shrinkage up to 300°C and electrolyte uptake with a contact angle of 0°. The sodium ion transference number, , of the separator is measured to be 0.78, which is higher than that of bare cellulose (: 0.31). These outstanding physical properties of the separator enable the long-term operation of NaCrO2 cathode/hard carbon anode full cells in a conventional carbonate electrolyte, with capacity retention of 82% for 500 cycles. Time-of-flight secondary-ion mass spectroscopy analysis reveals the additional role of the Al2O3 coating, which is transformed into AlF3 upon long-term cycling owing to HF scavenging. Our findings will open the door to the use of cellulose-based functional separators for high-performance SIBs.
Highlights
Lithium-ion batteries (LIBs) have received significant attention worldwide as major energy sources for electric vehicles and mobile devices, and the demand for LIBs is expected to increase in the near future (Mizushima et al, 1980; Amatucci et al, 1996; Winter et al, 1998; Mishra and Ceder, 1999; Sun et al, 2009; Jo et al, 2015)
There have been many reports on high-energy-density cathode materials with surface modification to prevent particle damage from the changing volume during charge/discharge, anode materials with high reversible capacity, and stable electrolytes under oxidizing environments (Yu et al, 2015; Hwang et al, 2017; Åvall et al, 2018; Kim et al, 2018; Sato et al, 2018; Suharto et al, 2018; Choi et al, 2019; Jo et al, 2019; Lee et al, 2019; Wang et al, 2020). In most of these studies, glass fibers (GF) have been widely used in most sodium-ion batteries (SIBs) because of their advantages over excellent wettability for ethylene carbonate and propylene carbonate, indicating high porosity (66%), large electrolyte uptake (360%), high ionic conductivity of electrolyte soaked in separator (3.8 mS cm−1), sodium ion transfer number (t+Na = 0.79) than polypropylene membrane (Zhu et al, 2016; Arunkumar et al, 2019)
The advantages of cellulose-based membranes for LIBs include their electrolyte uptake, thermal stability, and high ionic conductivity of electrolyte soaked in separator, which lead to high rate capability (Chiapponea et al, 2011)
Summary
Lithium-ion batteries (LIBs) have received significant attention worldwide as major energy sources for electric vehicles and mobile devices, and the demand for LIBs is expected to increase in the near future (Mizushima et al, 1980; Amatucci et al, 1996; Winter et al, 1998; Mishra and Ceder, 1999; Sun et al, 2009; Jo et al, 2015). A commercial cellulose–PAN membrane was compositized with Al2O3 particles by dip coating, where the addition of Al2O3 was anticipated to provide thermal stability and functionality during the electrochemical reaction with the electrolyte.
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