RESUMEN
The development of potassium-ion batteries (PIBs) is challenged by the shortage of stable cathode materials capable of reversibly hosting the large-sized K+ (1.38 Å), which is prone to cause severe structural degradation and complex phase evolution during the potassiation/depotassiation process. Here, we identified that anionic doping of the layered oxides for PIBs is effective to combat their capacity fading at high voltage (>4.0 V). Taking P2-type K2/3Mn7/9Ni1/9Ti1/9O17/9F1/9 (KMNTOF) as an example, we showed that the partial substitution of O2- by F- enlarged the interlayer distance of the K2/3Mn7/9Ni1/9Ti1/9O2 (KMNTO), which becomes more favorable for fast K+ transition without violent structural destruction. Meanwhile, based on the experimental data and theoretical results, we identified that the introduction of F- anions effectively increased the redox-active Mn cationic concentration by lowering the average valence of the Mn element, accordingly providing more reversible capacity derived from the Mn3+/4+ redox couple, rather than oxygen redox. This anionic doping strategy enables the KMNTOF cathode to deliver a high reversible capacity of 132.5 mAh g-1 with 0.53 K+ reversible (de)intercalation in the structure. We expect that the discovery provides new insights into structural engineering for pursuing stable cathodes to facilitate the future applications of high-performance PIBs.
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.
RESUMEN
Hollow carbon nanospheres (HCNs) have found broad applications in a large variety of application fields. Unfortunately, HCNs are known for their tedious operations and are incompetent for scalable synthesis for those widely adopted nanocasting-based routes. Here, we report a facile and highly efficient method for the creation of hollow carbon structures by tuning the growth kinetics of its polymeric precursor. We identified that a controlled polymerization of Cu2+-poly(m-phenylenediamine) (Cu-PmPD) could form nanospheres with modulated inner chemical inhomogeneity, where the core of the particles was low in polymerization degree and water soluble, whereas the outer part was water insoluble. Therefore, a simple water washing of the prepared polymeric particles directly formed hollow nanospheres with a good control on the structural features including their cavity size and shell thickness. HCNs were formed through a following heat treatment and were able to exhibit promising potential as a stable anode material when tested in potassium-ion batteries.
RESUMEN
As lithium-ion batteries continue to climb to even higher energy density, they meanwhile cause serious concerns on their stability and reliability during operation. To make sure the electrode materials, particularly cathode materials, are stable upon extended cycles, surface modification becomes indispensable to minimize the undesirable side reaction at the electrolyte-cathode interface, which is known as a critical factor to jeopardizing the electrode performance. This Review is targeted at a precise surface control of cathode materials with focus on the synthetic strategies suitable for a maximized surface protection ensured by a uniform and conformal surface coating. Detailed discussions are taken on the formation mechanism of the designated surface species achieved by either wet-chemistry routes or instrumental ones, with attention to the optimized electrochemical performance as a result of the surface control, accordingly drawing a clear image to describe the synthesis-structure-performance relationship to facilitate further understanding of functional electrode materials. Finally, perspectives regarding the most promising and/or most urgent developments for the surface control of high-energy cathode materials are provided.
