A team from Nanjing University in China, using a titanium nitride (TiN) nanotube array as the substrate, has synthesized a high-performance composite tin anode (TiN@Sn) for Li-ion batteries.
The structured electrode delivers a capacity of 795 mAh gSn−1 (Sn basis) and 1812 mAh cmel-3 (electrode basis). The long-term cycling shows only 0.04% capacity decay per cycle. A paper on their work appears in the Journal of Power Sources.
Because of the high specific capacity, tin has been considered one promising anode material. However, the large volume change induces cracks during cycling. The fractured surface reacts with cyclable lithium atoms and forms the solid electrolyte interphase (SEI), which may electronically isolate the active particles during repeated cycling, resulting in the capacity decay. To minimize the adverse effects caused by the volume change, a mechanically and chemically stable support is usually used to hold the active materials and accept the strain caused during lithiation and delithiation.
… For high capacity anode materials, large particles or thick film are usually inclined to fracture, while small particles or thin film are more stable. Using thin film structures are able to improve cyclability but may decrease the volumetric energy density because of the relatively low loading per unit volume. The volume ratio of active materials, void, and scaffold should be rationally designed to maximize the volumetric capacity and cyclability.
… It remains a challenge to obtain both the good cyclability of thin film and high volumetric capacity of electrodes with large t/D ratios. Here, we present a TiN@Sn composite anode with metallic nanotubes array and nano-sized tin as the supporting scaffold and anode materials, respectively.—Pu et al.
|Schematic illustration of (a) the design concept on the pore size (D) and active material thickness (t), (b) the active layer fracture during cycling, and (c) the fabrication procedure of TiN@Sn nanotubes array. Pu et al. Click to enlarge.|
To create the TiN nanotube array, the team anodized Ti foil in an aqueous solution containing 50 vol% ethylene glycol, 0.2 M ammonium fluoride, and 0.5 M phosphoric acid. The obtained amorphous TiO2 nanotubes array were crystallized in air at 450 ˚C. After heat treatment at 800 ˚C in ammonia atmosphere, TiO2 was converted to TiN.
The researchers then electroplated metallic tin into the TiN nanotube array. A series of galvanostatic pulses were applied between the TiN nanotubes array and a Sn counter electrode; the Sn thickness was controlled by the pulse number.
The TiN nanotubes provide mechanical supports and accommodate the volume expansion caused by lithiating the tin; the metallic TiN is also able effectively to conduct electrons and accelerate the Li-ion transport.
In addition to delivering the high volumetric capacity, after 400 cycles at 200 mA g-1, a TiN@Sn anode delivered a capacity of 616 mAh g-1, losing nearly 0.04% of its initial capacity per cycle.
The good cyclability of thin film and high energy density of thick electrodes are combined in our TiN nanotubes array-supported tin anodes. More importantly, the route we developed in this work could also be applied to other high capacity materials (such as Si, Sb, MnO, Co3O4, SnO2, etc), which need extra space and good electron conducting pathway.—Pu et al.
Jun Pu, Hongxiu Du, Jian Wang, Wenlu Wu, Zihan Shen, Jinyun Liu, Huigang Zhang (2017) “High-performance Li-ion Sn anodes with enhanced electrochemical properties using highly conductive TiN nanotubes array as a 3D multifunctional support,” Journal of Power Sources, Volume 360, Pages 189-195 doi: 10.1016/j.jpowsour.2017.05.111.