关键词: 磷化镍, 氮磷共掺杂碳, 储锂

Abstract:

In recent years, the nickel-based phosphide has drawn great attention because of its low intercalation/deintercalation platform and lower polarization compared to sulfides and oxides as anodes for next-generation high-energy lithium-ion batteries. The Ni₂P anode can deliver high theoretical specific capacity of 542 mAh·g^-1, but it subject to a conversion reaction mechanism, which make them unsuitable for commercial applications. The agglomeration of Ni₂P nanoparticles during material fabrication and the structural deterioration of electrode associated with large volume change during charge-discharge process lead to poor cycle stability and low utilization of active materials. Meanwhile, the low intrinsic conductivity of Ni₂P is also sluggish electrochemical reaction kinetics. Herein, we design a facile and viable approach to synthesize Ni₂P/NPC composites with a stable structure to address these issues. This new approach entails synthesis of Ni₂P/NPC by a N and P co-doped carbon framework with ionic liquids assistance during synthesis. This stable composite structure can serve as anode material of lithium ion batteries with good electrochemical performance. The Ni₂P/NPC composites were prepared by one-step method using ionic liquids as carbon and nitrogen sources, while sodium hypophosphite and nickel acetate as phosphorus and nickel sources, respectively. The results of SEM and TEM show that Ni₂P nanoparticles were uniformly distributed on the N and P co-doped carbon framework. When the Ni₂P/NPC composite was used as an anode material of lithium ion batteries, the discharge specific capacities were 377.7, 294.1, 265.4, 211.7 and 187.5 mAh·g^-1 at 0.1, 0.5, 1, 3 and 5 A·g^-1, respectively. When the current density returned to 0.1 A·g^-1, the discharge specific capacity reached 368.1 mAh·g^-1. The Ni₂P/NPC structure could be kept stable at high rate, showing excellent rate performance. The fabricated Ni₂P/NPC anode delivered the discharge specific capacity of 301.8 mAh·g^-1 with the capacity retention of 80.7% after 200 cycles at 0.5 A·g^-1. Finally, CV curves confirmed that the lithium storage of Ni₂P/NPC colud be controlled by diffusion process and capacitance behavior.

Key words: nickel phosphide, nitrogen and phosphorous co-doped carbon, lithium storage