3D Graphene Nanoflake/Vertically Aligned Carbon Nanotube/CoAl Layered Double Oxide Composites for High-Performance Lithium-Ion Batteries

Abstract

Using a urea-assisted precipitation method, we synthesized CoAl-layered double hydroxide (LDH) nanosheets that were uniformly aligned perpendicular to the surface of the silicon wafer. Then, a carbon nanocomposite consisting of vertically aligned carbon nanotubes (VACNTs) and graphene nanoflakes (GNFs) was prepared by plasma-enhanced chemical vapor deposition (PECVD) using LDH as the catalyst precursor. After heat treatment, LDH formed a layered double oxide (LDO). The VACNTs were attached to both sides of the LDO nanosheets, while GNFs were uniformly distributed on the VACNTs’ surface. Next, the three-dimensional (3D) GNF/VACNT-LDO material was used as a conductive agent for the LiFePO₄ cathode with a practical commercialized state-of-the-art cathode recipe of lithium-ion batteries. The results showed that the cathode had a high specific capacity and excellent cycling stability. The discharge specific capacity was as high as 168.6 mAh g^–1 at a current rate of 0.2 C. Amazingly, when the current rate was increased to 10 C, the discharge capacity reached 105.3 mAh g^–1, which was much higher than that with the conventional conductive agent Super P (65.1 mAh g^–1). After 500 cycles at 0.5 C current density, the discharge specific capacity was still 118.2 mAh g^–1, with a capacity retention rate of 72.7% and an average capacity loss of only 0.089 mAh g^–1 per cycle. The excellent rate performance and cycling stability of the LFP cathode are largely attributed to the GNF/VACNT-LDO. The unique 3D conductive network constructed by GNF/VACNT-LDO can greatly increase the electron transport rate and accelerate the shuttling of Li⁺ between the electrolyte and the electrode material.