Lithium-ion batteries are widely used in modern consumer electronics, but their performance is not yet optimized for operations that require higher power and longevity, such as driving an electric vehicle. Meeting the battery performance demands of an increasingly high-tech world relies on investigating different electrode materials, which can combine different element compositions to form composites.
In a recent article in Advanced Energy Materials, Bei Long, Muhammad-Sadeeq Balogun, Yexiang Tong, Shuqin Song, and co-workers from Sun Yat-sen University, China, prepare a composite based on nickel nitride and sulfide nanosheets (Ni3N@Ni3S2) as the anode material for lithium ion batteries.
The composite was prepared by calcinating the precursor at 380 °C under ammonia followed by hydrothermal sulfuration at 180 °C for 8 hours, where adjusting the thiourea concentration controls the extent of sulfuration.
The first charge/discharge curves of the three samples were measured and reveal that the composite has the highest specific lithiation capacity at 1012 mA h g–1, followed by nickel sulfide (Ni3S2) and nitride (Ni3N) at 864 and 487 mA h g–1. During the second discharge cycle, the lithiation capacity for the composite drops to 583 mA h g–1, but this is still much higher than the nitride and sulfide alone. The capacity at less than 0.5 V during the first discharge cycle is 50.6% for the composite, which is much higher than its separated components, suggesting that a synergistic effect occurs as a result of the lattice mismatch.
Not only does this mismatch create more active sites and a large number of interfaces for energy storage, but the electrons are efficiently transferred from the p-type semiconductor (Ni3S2, in this case) to the n-type semiconductor (Ni3N). This “job-sharing” mechanism enables perfect separation of lithium ions and electrons.
The nickel sulfide/nitride (Ni3N@Ni3S2) composite also demonstrates the best cycle stability, retaining 74.5% of its performance in its second cycle after 200 cycles at a current density of 0.25 A g–1.The scanning electron microscopy (SEM) images of the electrodes revealed very little cracking of the composite after 200 cycles, and slightly more cracking for the bare nitride, indicating their durability. In contrast, the bare sulfide electrode was almost obliterated after cycling.
To find out more about this new type of composite for lithium ion batteries, please visit the Advanced Energy Materials homepage.