Laser-synthesized metastable bismuth nanocrystals chemically bonded to reduced graphene oxide for excellent lithium storage

Abstract

The poor interface contact between Bi nanoparticles and reduced graphene oxide (rGO) hinders the transfer of ions/electrons for lithium-ion batteries. We propose an innovative approach for fabricating ultrafine bismuth nanocrystals chemically bonded to reduced graphene oxide (Bi-rGO) by liquid-phase pulsed laser irradiation followed by a solvothermal reaction with graphene oxide. Metastable Bi nanocrystals synthesized by a laser (5.5 nm) are then combined with graphene oxide in a solvothermal process, undergoing lattice restructuring and shrinking to a record-small size of 2 nm, which is the smallest reported for Bi/C composites as far as we know. The Bi nanocrystals are uniformly anchored onto rGO nanosheets by strong Bi—O—C bonds, which not only suppress particle aggregation but also establish efficient ion/electron transport channels and alleviate volume expansion during lithiation. As a result, the Bi-rGO-2 anode consisting of 2 nm Bi nanocrystals has an exceptional reversible capacity of 586.7 mAh g−1 over 500 cycles under a current density of 100 mA·g−1, nearly doubling that of a Bulk Bi/rGO composite anode (318 mAh·g−1). Theoretical calculations confirm a higher binding energy between Bi and rGO at small particle sizes, while kinetic analysis reveals accelerated Li+ diffusion. This work provides a scalable way to design high-performance alloy anodes through metastable nanocrystal engineering and covalent interface coupling.

1. Introduction

The rapidly escalating demand for electrification of transport and the expansion of grid storage systems has driven unprecedented advancements in lithium-ion battery (LIB) technology, particularly in energy/power density enhancements, thereby accelerating the critical development of high-power and high-capacity electrode materials[1]. The ideal anode materials, which serve as the foundation for achieving the high-power and high-capacity LIBs, should exhibit exceptional capacity, outstanding rate capability, prolonged cycle stability, and an appropriate voltage plateau[2]. Alloy anodes (e.g., Sb, Sn and Bi) have received widespread attention owing to their favorable operating potential, remarkable energy density, and superior electrical conductivity[3]. Bi and Li+ can form Li3Bi through an alloying reaction, which can obtain a mass-specific capacity of 385 mAh g−1 or a volume-specific capacity of 3800 mAh cm−3, becoming one of the ideal anode materials for LIBs[4]. Not only that, Bi also has a high redox reaction potential (0.5–0.75 V), which is conducive to inhibiting the dendrite formation and maintaining the safety of the batteries during charging and discharging, making it an ideal candidate for high-energy-density battery anodes[5].

Notwithstanding, like most known metal-based anodes, large volume expansion (215%) of Bi-based anodes can undesirably cause the pulverization of electrode material during the alloying and dealloying processes, which in turn results in a rapid capacity decay[6–7]. Additionally, the relatively low ion diffusion coefficient of Bi restricts the capacity and cycling performance of LIBs[8]. Various strategies have been attempted to solve these puzzles, such as controlling the size to nanometer level[9], combining Bi with other elements[10–11], and surface modification of Bi anodes[12]. Anchoring Bi particles on carbonaceous materials by stronger interactions has been validated as an effective strategy to buffer mechanical stress and alleviate volume expansion during the Li+ intercalation process while improving the transport capabilities of ions and electrons[13].