Vincent S. Battaglia

Optimization of Acetylene Black Conductive Additive and PVDF Composition for High-Power Rechargeable Lithium-Ion Cells

Fundamental electrochemical methods were applied to study the effect of the acetylene black (AB) and the polyvinylidene difluoride (PVDF) polymer binder on the performance of high-power designed rechargeable lithium-ion cells. A systematic study of the AB/PVDF long-range electronic conductivity at different weight ratios is performed using four-probe direct current tests, and the results are reported. There is a wide range of AB/PVDF ratios that satisfy the long-range electronic conductivity requirement of the lithium-ion cathode electrode; however, a significant cell power performance improvement is observed at small AB/PVDF composition ratios that are far from the long-range conductivity optimum of 1 to 1.25. Electrochemical impedance spectroscopy (EIS) tests indicate that the interfacial impedance decreases significantly with an increase in binder content. The hybrid power pulse characterization results agree with the EIS tests and also show improvement for cells with a high PVDF content. The AB to PVDF composition plays a significant role in the interfacial resistance. We believe the higher binder contents lead to a more cohesive conductive carbon particle network that results in better overall all local electronic conductivity on the active material surface and, hence, reduced charge-transfer resistance.

Effects of Various Conductive Additive and Polymeric Binder Contents on the Performance of a Lithium-Ion Composite Cathode

Fundamental electrochemical methods, cell performance tests, and physical characterization tests such as electron microscopy were used to study the effects of levels of the inert materials (acetylene black (AB), a nano-conductive additive, and polyvinylidene difluoride (PVDF), a polymer binder) on the power performance of lithium-ion composite cathodes. The electronic conductivity of the AB/PVDF composites at different compositions was measured with a four-point probe direct current method. The electronic conductivity was found to increase rapidly and plateau at a AB:PVDF ratio 0.2:1 (by weight), with 0.8:1 being the highest conductivity composition. AB:PVDF compositions along the plateau of 0.2:1, 0.4:1, 0.6:1 and 0.8:1 were investigated. Electrodes of each of those compositions were fabricated with different fractions of AB/PVDF to active material. It was found that at the 0.8:1 AB:PVDF, the rate performance improved with increases in the AB/PVDF loading, whereas at the 0.2:1 AB:PVDF, the rate performance improved with decreases in the AB/PVDF loading. The impedance of electrodes made with 0.6:1 AB:PVDF was low and relatively invariant.

Cathode Performance as a Function of Inactive Material and Void Fractions

Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 -based laminates of approximately the same loading and of varying levels of poly(vinylidene fluoride) (PVDF) binder and acetylene black (ratio held constant) were fabricated and calendered to different porosities, with the objective to investigate performance on a volume basis. The electronic conductivity of the laminates depends strongly on the inactive material content but not significantly on porosity. Electrochemical impedance spectroscopy studies found that charge-transfer resistance with calendering varied greatly with inactive material content. When the electrode contains low levels of inactive material (2% PVDF and 1.6% carbon), calendering significantly reduced the bulk resistance of the electrode. With high levels of inactive material (8% PVDF and 6.4% carbon), charge-transfer resistance increased with increased calendering. Above a certain level, depending on the overall composition, the inactive material reduces ionic transport to the active material surface. For a plug-in hybrid electric vehicle required to go 40 miles at an average rate of 20 miles/h with a 38 kW 10 s power-pulse capability, the cell chemistry studied is energy-limited. Therefore, based on the results of this study, the cathode should be compressed to 10% porosity with a minimal amount of inactive material.

Improved initial performance of Si nanoparticles by surface oxide reduction for lithium-ion battery application

Author(s): Xun, S; Song, X; Grass, ME; Roseguo, DK; Liu, Z; Battaglia, VS; Liu, G | Abstract: This study characterizes the native oxide layer of Si nanoparticles and evaluates its effect on their performance for Li-ion batteries. x-ray photoelectron spectroscopy and transmission electron microscopy were applied to identify the chemical state and morphology of the native oxide layer. Elemental and thermogravimetric analysis were used to estimate the oxide content for the Si samples. Hydrofluoric acid was used to reduce the oxide layer. A correlation between etching time and oxide content was established. The initial electrochemical performances indicate that the reversible capacity of etched Si nanoparticles was enhanced significantly compared with that of the as-received Si sample.

Insight into Iron Heat-Powder Combustion Products for Thermal Batteries: Core-Shell Structure and Semi-Conductive Properties

A mixture of Fe and KClO4 (84/16, wt/wt) was studied as an iron heat-powder. The combustion products were Fe, FeO, and KCl, which show semiconductor properties, with a conductivity on the order of 103 S cm−1. Based on energy-dispersive X-ray analysis (EDX) of samples from characterization tests, a core-shell structure of combustion products was discovered, where the core consisted of unreacted Fe and the shell of FeO. Transmission electron microscopy (TEM) images of the combustion products confirmed the thickness of the shell (~ 0.2 μm), consistent with the calculated value.