Microwave Synthesis of TiP2O7 assisted By Carbon-Coating As Anode Material for Aqueous Rechargeable Lithium Ion Batteries

Abstract

Aqueous rechargeable lithium ion batteries (ARLBs) are the promising candidates for long term energy storage [1]. TiP2O7 has been reported as a promising anode material for ARLBs due to its appealing and stable intercalation/deintercalation potential, [2,3]. Today, a traditional solid-state synthesis method has been reported to synthesize TiP2O7, which takes about 9 hours [4]. In previous work, a fast microwave synthesis method was applied to synthesize TiP2O7, which takes only 40 minutes [5]. The idea was informed by the report about microwave synthesis of NaTi2(PO4)2, which is an aqueous sodium ion batteries anode material [6]. In this work, more complete material characterizations and long-cycle tests have been conducted for both of 10% graphite-TiP2O7 composite and pure TiP2O7 electrode materials as prepared previously [5]. Figure 1a presents the X-ray diffraction patterns of graphite-TiP2O7 composite and pure TiP2O7, from which it can be demonstrated that crystalline TiP2O7 and graphite-TiP2O7 composite are produced. The Scherrer formula is used to calculate average crystal size of graphite-TiP2O7 composite and pure TiP2O7., which are 46.9nm and 37.4nm respectively. Figure 1b shows the surface morphology of pure TiP2O7 (top) and graphite-coated TiP2O7 composite (bottom)respectively. The surface of carbon coated TiP2O7 is much smoother than pure TiP2O7, which indicates graphite layer is coated and it may protect TiP2O7’s structure against dissolution during cycling. Figure 2a is the thermogravimetric analysis (TGA) of graphite-TiP2O7 composite, which shows 82.3% of active material exists in the composite. Figure 2b presents the stability of graphite-TiP2O7 composite under the rate of 0.5C. It also demonstrates that after coated with graphite, the electrode material gives much better electrochemical performance. Carbon coating is essential for electrode material synthesized through microwave method, which stabilized the material’s structure for better electrochemical performance. Figure 1 a) XRD patterns and b) SEM of Graphite-TiP2O7 composite and Pure TiP2O7. Figure 2 a) Thermogravimetric analysis of Graphite-TiP2O7 composite. b) Long-cycle tests on Graphite-TiP2O7 composite and Pure TiP2O7. Reference: Li W , Dahn J R , Wainwright D S . Rechargeable Lithium Batteries with Aqueous Electrolytes[J]. Science, 1994, 264(5162):1115-1118.Wang H, Huang K, Zeng Y, et al. Electrochemical properties of TiP2O7, and LiTi2(PO4)3, as anode material for lithium ion battery with aqueous solution electrolyte[J]. Electrochemical Acta, 2007, 52(9):3280-3285.Chen L , Gu Q , Zhou X , et al. New-concept Batteries Based on Aqueous Li+/Na+ Mixed-ion Electrolytes[J]. Scientific Reports, 2013, 3(6):1946.Wu W, Shanbhag S, Wise A, et al. High Performance TiP2O7 Based Intercalation Negative Electrode for Aqueous Lithium-Ion Batteries via a Facile Synthetic Route[J]. Journal of the Electrochemical Society, 2015, 162(9): A1921-A1926.Haosheng Song, Jiang Chang, Jinming Wu, Wei Wu, Jay Whitacre. Microwave Synthesized TiP2O7/Carbon Composites for Use in Aqueous Lithium-Ion Batteries. The Electrochemical Society - Meeting s, 13 Apr 2018, pp. 507.Wu W, Mohamed A, Whitacre J F. Microwave Synthesized NaTi2(PO4)3 as an Aqueous Sodium-Ion Negative Electrode[J]. Journal of the Electrochemical Society, 2013, 160(3): A497-A504. Figure 1