Xiangyun Song

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.

Three-dimensional biomimetic mineralization of dense hydrogel templates.

An electric-current-assisted method was used to mineralize dense hydrogels and create hydroxyapatite/hydrogel composites with unique hierarchical structures. The microstructure of the final material can be controlled by the mineralization technique and the chemistry of the organic matrix. A hydroxyapatite/hydrogel composite was obtained with a large inorganic content (approximately 60% of the weight of the organics). After being heated to 1050 degrees C, the sintered inorganic phase has a very uniformly distributed porosity and its Brunauer-Emmett-Teller (BET) surface area is 0.68 m(2)/g.

Preparation and Capacity-Fading Investigation of Polymer-Derived Silicon Carbonitride Anode for Lithium-Ion Battery

Polymer-derived silicon carbonitride (SiCN) materials have been synthesized via pyrolyzing from five poly(silylcarbondiimide)s with different contents of carbon (labeled as 1–5#). The morphological and structural measurements show that the SiCN materials are mixtures of nanocrystals of SiC, Si3N4, and graphite. The SiCN materials have been used as anodes for lithium-ion batteries. Among the five polymer-derived SiCN materials, 5#SiCN, derived from dichloromethylvinylsilane and di-n-octyldichlorosilane, has the best cycle stability and a high-rate performance at the low cutoff voltage of 0.01–1.0 V. In lithium-ion half-cells, the specific delithiation capacity of 5#SiCN anode still remains at 826.7 mA h g–1 after 100 charge/discharge cycles; it can even deliver the capacity above 550 mA h g–1 at high current densities of 1.6 and 2 A g–1. In lithium-ion full cells, 5#SiCN anode works well with LiNi0.6Co0.2Mn0.2O2 commercial cathode. The outstanding electrochemical performance of 5#SiCN anode is attributed to two factors: (1) the formation of a stable and compact solid electrolyte interface layer on the anode surface anode, which protects the electrode from cracking during the charge/discharge cycle; and (2) a large amount of carbon component and the less Si3N4 phase in the 5#SiCN structure, which provides an electrochemical reactive and conductive environment in the SiCN structure, benefit the lithiation/delithiation process. In addition, we explore the reason for the capacity fading of these SiCN anodes.

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

Optimization of Acetylene Black Conductive Additive and Polyvinylidene Difluoride Composition for High Power Rechargeable Lithium-Ion Cells G. Liu a,z , H. Zheng a,c , V. S. Battaglia a , A. S. Simens b,d , A. M. Minor b , and X. Song a a Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA b National Center for Electron Microscopy, Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA c On Leave from Henan Normal University, Henan Provence, China d Present Address: Material Science and Engineering Department, Stanford University, Stanford, 94305, USA z Corresponding Author: Gao Liu Lawrence Berkeley National Laboratory 1 Cyclotron Rd., MS 70R108B Berkeley, CA 94720 Office Phone: (510) 486-7207 Office Fax: (510) 486-7303 E-mail: Gliu@lbl.gov