Effects of graphene with different sizes as conductive additives on the electrochemical performance of a LiFePO₄cathode

Abstract

This paper aims to demonstrate whether graphene nanosheets (GN) with different sizes as conductive additives are able to affect the electrochemical performance of a LiFePO 4 (LFP) cathode. The results of electrochemical measurements present that graphene nanosheets (GN) and Super-P (SP) used as conductive additives simultaneously could construct an effective electronic conducting network and achieve excellent electrochemical performance when compared with traditional carbon materials. A LFP with small-size GN shows better specific capacity and rate performance than those with medium-size and large-size GN, and the LFP with large-size GN displays a poor rate performance. The results indicate that the specific capacity and rate performance tend to worsen with the increase of the size of graphene, owing to the length of the lithium ion transport path being prolonged and the ionic conductivity decreasing greatly by the "barrier effect" of graphene.

Quantifying the factors limiting rate performance in battery electrodes

“…Shown in figure 3A are specific capacity versus rate data for anodes of GaS nanosheets mixed with carbon nanotubes at different mass fractions, Mf (ref 7 ). A clear improvement in rate performance can be seen as Mf, and hence the electrode conductivity, increases, indicating changes in  and n. We fitted data extracted from a number of papers 7,18,19,60,[62][63][64][65][66][67][68] to equation 2 and plotted  and n versus Mf in figures 3B and C. These data indicate a systematic drop in both  and n with increasing electrode conductivity. Figure 3B shows  to fall significantly with Mf for all data sets with some samples showing a thousand-fold reduction.…”

Choice for graphene as conductive additive for cathode of lithium-ion batteries

“…Although it has already been proved that graphene can play superior performance to the Super P as conductive additives for LIBs [11,15,23,25,29,30] , the effect of graphene for the practical application usually shows great difference. There are many factors affecting the effectiveness of the application of graphene additives, and one of the most important factors is the synthetic method for the graphene.…”

“…Graphene, as a typical two-dimensional planar material, possesses both excellent electronic conductivity ensuring high utilization efficiency of the carbon atoms for the electron transfer, and high flexibility enabling the good contact with active materials [19,20] . Therefore, it can form highly efficient and stable conducting network with low percolation threshold and improve the electrochemical performance of the electrode with even trace amount [15,21] , and has been regarded as a very promising conductive additive for both anode and cathode in LIBs [22][23][24][25] . However, it is also found that due to the planar structure in large size, graphene could block lithium ion transport by extending the ion diffusion path, especially at high charge/discharge rate [26,27] .…”

“…So far, many effort s have been made to investigate the affecting factors of graphene as additives on the performance of electrodes, including size [25] , defects [28] , addition amount [15,24,29,30] and surface chemistry of graphene [27,31] , as well as the size ratio of graphene to active materials [21,32] and the electrode thickness with graphene additives [33] . However, the synthetic method for the graphene using in the electrodes has attracted little attention.…”

Effects of Graphene Nanosheets with Different Lateral Sizes as Conductive Additives on the Electrochemical Performance of LiNi0.5Co0.2Mn0.3O2 Cathode Materials for Li Ion Batteries

“…The results indicated that the smallest size of graphene had better electrochemical performance (165 mAh•g −1 ). The specific capacity and rate performance of LiFePO 4 electrodes tend to worsen with increases of the size of graphene, because the length of ionic transport path got longer [46].…”