Graphite Anodes For Li-ion Batteries Research Articles

A novel modification approach for natural graphite anode of Li-ion batteries

To improve the rate capability and cyclability of natural graphite anode for Li-ion batteries, a novel modification approach was developed. The modification approach included two steps: (a) high-energy ball milling in a rotary autoclave containing alumina balls, H3 PO4 and ethanol; (b) coating with pyrolytic carbon from phenlic resin. The treated graphite shows obvious improvement compared with the original natural graphite in electrochemical properties such as cyclability and rate capability, especially at high current density. The primary reasons leading to the improvement in rate capability and cyclability are that the diffusion impedance of Li+ in graphite is reduced due to the fact that P filtered into graphite layers can mildly increase interlayer distances, and the fact that the structural stability of graphite surface is enhanced since the coated pyrolytic carbon can depress the co-intercalation of solvated lithium ion.

Poly(acrylonitrile-methyl methacrylate) as a non-fluorinated binder for the graphite anode of Li-ion batteries

Poly(vinylidene fluoride) (PVDF) has been a choice of the binder for both cathode and graphite anode in stateof-the-art Li-ion batteries [1, 2]. However, there is currently a demand to replace PVDF with non-fluorinated binder since at elevated temperatures the fluorinated polymers react with lithiated graphite (LixC6) and metal lithium to form more stable LiF and >C@CF– double bonds. In particular, the reaction of PVDF and metal lithium produces an enthalpy as high as 7180 J (g PVDF) [1]. It has been reported that in the presence of electrolytes, PVDF and lithiated graphite undergo a series of exothermic reactions, including (i) temperature-induced degradation of the solid electrolyte interface (SEI) at 120–140 C, (ii) reactions of lithiated graphite and electrolyte at 210–230 C, and (iii) dehydrofluorination of PVDF initiated by LixC6 at >260 C [1, 2]. Among these reactions, the last one is known to be very exothermic and is believed to be a potential source for the thermal runaway of Li-ion batteries under abuse conditions. Therefore, safety concerns with Li-ion batteries may arise from the use of PVDF in the graphite anode. To replace the rather reactive PVDF, we attempt to evaluate poly(acrylonitrile-methyl methacrylate) (AMMA) as a non-fluorinated binder for the graphite anode of Li-ion batteries. Differential scanning calorimetry (DSC) study has shown that the heat of reaction of the lithiated graphite and electrolyte can be reduced significantly by using AMMA instead of PVDF [3]. That is, total enthalpies for the reactions (as indicated by two exothermic peaks in DSC curves) of the fully lithiated graphite (MAG-10, Hitachi Chemical) and electrolyte (1.2 M LiPF6 3:7 EC/EMC) in the temperature range 280–340 C can be reduced to 1211 J (g AMMA) from 2699 J (g PVDF). In this paper, we will electrochemically evaluate AMMA as a binder of the graphite anode of Li-ion batteries. 2. Experimental details

Development of high performance graphite anodes for Li-ion batteries

Development of high performance graphite anodes for Li-ion batteries

IR Study of Ozone Modified Graphite Matrix

The oxidation of graphite powder was reported to enhance the capacity of graphite anodes in Li-ion batteries. Here we present IR-spectroscopic study of the graphite powder modified via oxidation by ozone with the subsequent LiOH or butyl-Li treatment compared to the results obtained by “wet” acid oxidation. Ozone treatment leads to the formation of ozonides, C-O-O-C, carboxylic and epoxy groups on graphite surface. Subsequent treatment of ozone modified graphite with LiOH eliminates the majority of C-O containing groups and yields only a few COOLi surface groups. Treatment of ozonated graphite with butyllithium appears to be more efficient.

Enhancement of Li doping/undoping reaction rate of carbonaceous materials by coating with an evaporated metal film

A novel method for enhancing the charge/discharge rate of the graphite anode of Li-ion batteries has been developed. The method involves covering the surface of the carbon material with a film of an appropriate metal. Simple vacuum evaporation was found to be effective in covering the entire surface of a carbon fiber sample. The metals examined were Ag, Au, Bi, In, Pb, Pd, Sn and Zn. All the metals exhibited a more or less rate-enhancing effect, but Ag, Sn and Zn were the most effective. The effect was dependent on the film thickness. The effects of heat-treatment were also studied with an eye toward obtaining a stable cycleability.