RESUMEN
Sodium-ion batteries (SIBs) are promising candidates for large-scale electric energy storage with abundant sodium resources. However, their development is challenged by the availability of satisfactory cathode materials with stable framework to accommodate the transportation of large-sized Na+ (1.02 Å), whose continuous insertion/extraction can easily cause irreversible volumetric deformation in the crystalline material, leading to inevitable structural failure and capacity fading. Here, different from the previous synthesis efforts targeting at Na+ containing compounds, we unveil the possibility of achieving a highly reversible sodiation/desodiation process by resorting to a K+-based layered metal oxide formulated as K0.5Mn0.7Fe0.2Ti0.1O2 (KMFT), which is a P2 type in structure with a wide interlayer spacing to sit K+ (1.38 Å). We demonstrate that an initial K+/Na+ exchange can introduce Na+ into the lattice while a small amount of K+ remains inside, which plays a significant role in ensuring enlarged channels for a fast and stable Na+ diffusion. The KMFT electrode delivers a high initial discharge capacity of 147.1 mA h g-1 at 10 mA g-1 and outstanding long cycling stability with capacity retention of 71.5% after 1000 cycles at 500 mA g-1. These results provide a new design strategy for the development of stable SIBs cathodes to facilitate their future applications.
RESUMEN
Potassium ion batteries (KIBs) have emerged as a promising energy storage system, but the stability and high rate capability of their electrode materials, particularly carbon as the most investigated anode ones, become a primary challenge. Here, it is identified that pitch-derived soft carbon, a nongraphitic carbonaceous species which is paid less attention in the battery field, holds special advantage in KIB anodes. The structural flexibility of soft carbon makes it convenient to tune its crystallization degree, thereby modulating the storage behavior of large-sized K+ in the turbostratic carbon lattices to satisfy the need in structural resilience, low-voltage feature, and high transportation kinetics. It is confirmed that a simple thermal control can produce structurally optimized soft carbon that has much better battery performance than its widely reported carbon counterparts such as graphite and hard carbon. The findings highlight the potential of soft carbon as an interesting category suitable for high-performance KIB electrode and provide insights for understanding the complicated K+ storage mechanisms in KIBs.
