Encapsulating Multielectron CoCO₃ Spindle-like Nanoclusters in 3D Ascorbic Acid Preintercalated Porous Ti₃C₂T_x MXene Architectures toward Superior Lithium Storage

Developing advanced transition-metal carbonate anode materials with superior electrochemical reaction kinetics has great potential for high-performance alkali-metal-ion-based electrochemical energy storage. However, the low conductivity, poor structural stability, and sluggish reaction kinetics hinder their practical applications. Taking advantage of the benefits of multielectron conversion reactions of cobalt carbonate (CoCO3) and rich surface-active reaction sites of 3D porous ascorbic acid (AA)-preintercalated Ti3C2Tx (AA-Ti3C2Tx) hybrids, we elaborately fabricated the CoCO3/AA-Ti3C2Tx architectures with CoCO3 spindle-like nanoclusters homogeneously distributed in 3D porous AA-Ti3C2Tx hybrids. The AA-Ti3C2Tx hybrids with the enlargement of the interlayer spacing and higher active surface area not only provide unblocked ionic/electronic channels for charge transfer and diffusion and prevent the restacking of CoCO3 spindle-like nanoclusters in the cycling process but also significantly strengthen both fast kinetics and long-term stability. Furthermore, the CoCO3 spindle-like nanoclusters could efficiently shorten the Li+ diffusion path length and offer more exposed redox sites to boost capacity utilization. As a result, the CoCO3/AA-Ti3C2Tx anode displays an ultrahigh reversible capacity of 987.6 mA h g(-1) at 200 mA g(-1) after 200 cycles and an outstanding rate performance (547.2 mA h g(-1) at 2000 mA g(-1) after 500 cycles). Especially, ex situ and in situ characterizations demonstrate that CoCO3/AA-Ti3C2Tx undergoes reversible evolution for proceeding with the deep decomposition of C1- -> C4+ during the lithiation process. Impressively, the full battery (CoCO3/AA-Ti3C2Tx//LCO) with a CoCO3/AA-Ti3C2Tx anode achieves a satisfying energy density of 742.1 mA h g(-1) at 200 mA g(-1) and a low capacity decay rate. Our research may encourage further the elaborate design of advanced transition-metal carbonates-based architectures toward high-performance rechargeable batteries.