(Digital Presentation) Water-Soluble Binders That Enhance Electrochemical Sodium-Ion Storage Properties of NaTi2(PO4)3 Nanoparticle Anodes

Abstract

Sodium ion batteries (SIBs) have been considered as one of the most promising alternative to conventional lithium-ion batteries (LIBs) for next generation energy storage systems.1 , 2 In terms of anodes, commercial graphite only delivers a sodium-ion storage capacity of 31 mAh g−1.3 The polyanionic-type NaTi2(PO4)3 material is an attractive anode because of the crystal structure of a Na-super-ionic conductor (NASICON), high theoretical capacity, safety characterization and ‘zero-stress’ framework upon sodiation/desodiation.4 , 5 The primary role played by the binder is to link different types of small particles together and to ensure the active material adheres to the current collector, which has an important contribution to the electrical and mechanical behaviour of the electrode.6 , 7 Poly(vinylidene fluoride) (PVDF) is a common organic binder using N-methyl-2-pyrrolidone (NMP) as solvents. Sodium carboxymethyl cellulose (CMC) has been considered as an effective and green water-soluble binders. Styrene butadiene rubber (SBR) typically serves as an elastomer in water-soluble CMC binders and further increases binding force, adhesion, heat resistance, and flexibility of an electrode. The role of different binders on the structural/chemical stability of NaTi2(PO4)3 anode in SIBs has rarely been studied.Here, we synthesized NaTi2(PO4)3 nanoparticles using the hydrothermal method and explore the effects and influence of PVDF, CMC and CMC-SBR binders on the sodium-ion storage performance of NaTi2(PO4)3 anodes. Compared to traditional organic PVDF binder, water-soluble binders improved the cycling stability by increasing adhesion, flexibility, and mechanical properties between the active materials, conductive addictive and current collector. Notably, water-soluble binders show an important effect on the sodium storage mechanism of NaTi2(PO4)3 nanoparticles. The addition of SBR in the water-soluble binders further enhances the active materials areal specific capacity because of its better adhesion ability, reducing the overall quantity of binder polymer required for the electrode. This novel exploration of the effective combination of water-soluble CMC and SBR binders for NaTi2(PO4)3 anodes in SIBs not only provides an opportunity to enhance their electrochemical sodium storage properties, but may enables their practical application in high areal energy density sodium ion batteries in the future. References (1) Nayak, P. K.; Yang, L.; Brehm, W.; Adelhelm, P.: From Lithium-Ion to Sodium-Ion Batteries: Advantages, Challenges, and Surprises. Angew. Chem. Int. Ed. 2018, 57, 102-120.(2) Kim, S.-W.; Seo, D.-H.; Ma, X.; Ceder, G.; Kang, K.: Electrode Materials for Rechargeable Sodium-Ion Batteries: Potential Alternatives to Current Lithium-Ion Batteries. Adv. Energy Mater. 2012, 2, 710-721.(3) Doeff, M. M.; Ma, Y.; Visco, S. J.; De Jonghe, L. C.: Electrochemical insertion of sodium into carbon. J. Electrochem. Soc. 1993, 140, L169-L170.(4) Delmas, C.; Cherkaoui, F.; Nadiri, A.; Hagenmuller, P.: A nasicon-type phase as intercalation electrode: NaTi2(PO4)3. Mater. Res. Bull. 1987, 22, 631-639.(5) Chen, S.; Wu, C.; Shen, L.; Zhu, C.; Huang, Y.; Xi, K.; Maier, J.; Yu, Y.: Challenges and Perspectives for NASICON-Type Electrode Materials for Advanced Sodium-Ion Batteries. Adv. Mater. 2017, 29, 1700431.(6) Chen, H.; Ling, M.; Hencz, L.; Ling, H. Y.; Li, G.; Lin, Z.; Liu, G.; Zhang, S.: Exploring Chemical, Mechanical, and Electrical Functionalities of Binders for Advanced Energy-Storage Devices. Chem. Rev. 2018, 118, 8936-8982.(7) Bommier, C.; Ji, X.: Electrolytes, SEI Formation, and Binders: A Review of Nonelectrode Factors for Sodium-Ion Battery Anodes. Small 2018, 14, 1703576. Figure 1 (a) SEM image and (b) HRTEM image of NaTi2(PO4)3 nanoparticles with quasi-cubic architecture and hollow structure. (c) XRD analysis of the synthesized nanoparticles. (d) Specific capacity versus rate data using chronoamperometry (CA) method for NaTi2(PO4)3 nanoparticles anode of different binders. (Inset) Corresponding digital photos for NTP electrodes with different binders. (e) The first cycle in the cyclic voltammetric curve at a scan rate of 0.1 mV s-1 for NaTi2(PO4)3 nanoparticles anode. (f) Galvanostatic discharging and charging cycling stability at 0.2 C (1C = 133 mA g-1) for the NaTi2(PO4)3 nanoparticle anode with different binders. Figure 1