Ultrastable and High Energy Calcium Rechargeable Batteries Enabled by Calcium Intercalation in a NASICON Cathode

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 18; no. 14; pp. e2107853 - n/a
• Main Authors: Chen, Chunhong, Shi, Fangyi, Zhang, Shishi, Su, Yaqiong, Xu, Zheng‐Long
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-04-2022
• Subjects: Batteries; Ca ion batteries; Calcium ions; cathode materials; Cathodes; Diffusion barriers; Energy storage; Fluorine; Flux density; full cells; Intercalation; Ionic mobility; Nanotechnology; NASICON structure; Rechargeable batteries; Sodium
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202107853

Ca‐ion batteries (CIBs) have been considered a promising candidate for the next‐generation energy storage technology owing to the abundant calcium element and the low reduction potential of Ca2+/Ca. However, the large size and divalent nature of Ca2+ induce significant volume change and sluggish ion mobility in intercalation cathodes, leading to poor reversibly and low energy/power densities for CIBs. Herein, a polyanionic Na superionic conduction (NASICON)‐typed Na‐vacant Na1V2(PO4)2F3 (N1PVF3) with sufficient interstitial spaces is reported as ultra‐stable and high‐energy Ca ion cathodes. The N1PVF3 delivers exceptionally high Ca storage capacities of 110 and 65 mAh g‐1 at 10 and 500 mA g–1, respectively, and a record‐long cyclability of 2000 cycles. More interestingly, by tailoring the fluorine content in N1PVFx (1 ≤ x ≤ 3), the high working potential of 3.5 V versus Ca2+/Ca is achievable. In conjunction with Ca metal anode and a compatible electrolyte, Ca metal batteries with N1VPF3 cathodes are constructed, which deliver an initial energy density of 342 W h kg‐1, representing one of the highest values thus far reported for CIBs. Origins of the uncommonly stable and high‐power capabilities for N1PVF3 are elucidated as the small volume changes and low cation diffusion barriers among the cathodes.
The merits of covalent open framework with large tunnel sites, substantial Na interstitial vacancies, and fluorine‐rich phase indicate Na1V2(PO4)2F3 (N1VPF3) as an excellent candidate for Ca ion storage with high redox potentials. As a proof of concept, the N1VPF3 cathode demonstrates exceptionally high energy density and long‐term cyclic stability in Ca ion batteries.