Improving High-Rate Performance of Graphene Anode By Anchoring Titanium Nitride Nanoparticles in Lithium Ion Batteries

Abstract

Graphene based materials show superior properties as electrochemical capacitors, due to their unique two-dimensional structure and great intrinsic physical properties, such as high electrical conductivity and large surface area. However, their poor rate capability and cycling performance, because of failure of carbon structure, cannot meet the upward requirements for high-performance LIBs. Recently, there are tremendous efforts to improve graphene performance by doping various elements as conducting agent or decreasing crystallite size and increasing pore structure. In an attempt to improve cycling performance and high-rate capability of graphene anode, we intend to modify graphene structure by TiN nanoparticles. In this respect, a TiN/G nanocomposite has been prepared by using benzene as carbon source through partial decomposition under supercritical condition to form simultaneously TiN/C nanocomposite in one-step that has been followed by ammonia treatment at 1000 ˚C for 10 h to form nanocrystalline TiN/G composite as an anode for high-performance LIBs. Anchoring of TiN nanoparticles on graphene not only promotes the electrical conductivity along c-axis, but also suppresses the agglomeration of graphene sheets, resulting in the formation of a flexible porous texture. The fast electron and ion mixed transport capability at high current densities caused by enhancing the electrical conductivity, and the pore-transport system in the nanocomposite that would ensure the fast accessibility of the ions, promote the rate performance of TiN/G anode. In the active-inactive composite of G and TiN, the G acts as a reactant during the lithiation process to form LixC, which is enclosed by the TiN inactive matrix. The TiN in the composite electrode does not alloy with lithium but serves as an inactive matrix to support the intergrain electronic contact in the material. The highly efficient mixed conducting network and the internal defects between G layers induced by nitrogen doping lead to enhancement of rate capability and cycling performance of G sheets in such a way that demonstrates capacity retention of 112% after 250 cycles at charge/discharge (C/D) rate of 1.6 C (Fig. 1) with specific capacity of 325 mAh g-1. Meanwhile, TiN/G anode provides specific capacity of 381 mAh g-1 at C/D rate of 0.2 C. Interestingly, the synthesized TiN/G nanocomposite depicts rate-dependent behavior as it is shown in Fig. 2. By contrast, TiN/G anode shows specific capacity of 201 mAh g-1 when is cycled initially at lower rate (0.2 C) and is subsequently subjected to higher rate (1.6 C) (Fig. 2(a)), while it shows 317 mAh g-1when is cycled at higher rate (1.6 C) (Fig. 2(b)). Detailed characterization of the TiN/G nanocomposite and its performance as anode in LIBs will be presented. Furthermore, the possible mechanisms of the observed rate-dependent behavior of TiN/G anode will be discussed. Figure captions: Fig. 1. Cycling performance at C/D rate of 1.6 C using TiN/G electrode as an anode material. Fig. 2. Electrochemical performance of the TiN/G nanocomposite as anode in 1 M LiPF6-EC:DMC:DEC (vol. 1:1:1) electrolyte cycled between 3 and 0.005 V vs. Li+/Li: C/D curves cycled with (a) different rates as n=1@ 0.2 C, n=11 @ 1.6 C, (b) 1.6 C. Figure 1