Edge/basal/defect ratios in graphite and their influence on the thermal stability of lithium ion batteries

Abstract

Raw graphite can be processed industrially in large quanta but for the graphite to be useful in lithium ion batteries (LIB's) certain parameters needs to be optimized. Some key parameters are graphite morphology, active surface area, and particle size. These parameters can to some extent be manipulated by surface coatings, milling processes and heat treatment in various atmospheres. Industrial graphite materials have been investigated for use as anode material in LIB's and compared with commercial graphite. These materials have been exposed to two different milling processes, and some of these materials were further heat treated in nitrogen atmosphere above 2650 o C. BET combined with density functional theory (DFT) has been employed to study the ratio of basal to non-basal plane and to determine the relative amount of defects. Thermal properties have been investigated with differential scanning calorimetry (DSC). High ethylene carbonate (EC) content improved the thermal stability for graphite with high amount of edge/defect surface area, but showed no improvement of graphite with lower amount of edge/defects. High irreversible capacity loss (ICL) combined with low surface area improved the thermal properties. DFT combined with ICL could potentially be used as a tool to predict thermal stability.

Identifying the Association between Surface Heterogeneity and Electrochemical Properties in Graphite

“…Along with the adsorption-energy distribution (AED) of the graphite [ 28 , 29 , 30 , 31 ], values of the specific surface areas can be obtained ( Figure 1 a). The adsorption-potential energy of nitrogen has been obtained from the van der Waals force model, with the potential region at approximately 60 K for the basal plane, ~26 and ~44 K for the edge plane, and ~86 and 96 K for the defect site (by k B T where k B = 8.617 × 10 −5 eV K −1 ) [ 32 , 33 , 34 , 35 , 36 ].…”

“…We have also confirmed the cycle life with the pore volume of 1–10 nm in diameter, and the negative linear relationship of the cyclability according to the pore volume was more pronounced than the tendency according to the non-basal site ( Figure 5 b,c). The BJH method assumes that the pores are cylindrical, but since it is also applied to slit-shaped pores, pores of 1–10 nm appearing in graphite can be considered as defective sites, such as steps or surface roughness [ 32 , 33 , 34 ]. The pore distributions of graphite samples are shown in Figure S6 , and it can be shown that the non-basal sites are not perfectly proportional to the pore volume ( Figure S6c ).…”

“…The basal plane, having a higher areal carbon density, will adsorb nitrogen more strongly than the less dense edge plane. In contrast, lattice defects in the graphene layers enhance the adsorbent–adsorptive interactions and lead to higher adsorptive energy [ 32 , 33 , 34 ].…”

Modeling solid-electrolyte interfacial phenomena in silicon anodes

“…However, FEC may be reduced via two other multi-electron transfer mechanisms that result in the formation of either CO2 2-, F, and . CH2CHOor CO 2 (Fig. 2, left).…”

“…Lithium-ion batteries (LIBs) are suitable candidates to drive the technology to harvest a higher energy density to power portable devices and EVs. A typical electrochemical cell for this system includes graphitelithium cobalt oxide (LiCoO2) with lithium hexafluorophosphate (LiPF6) and organic solvents as the electrolyte mixture [1,2]. Graphite has replaced lithium metal as the anode electrode material due to the uncontrollable dendritic Li growth and limited Coulombic efficiency (C.E.)…”