Composite Cathode Structure/Property Relationships

Abstract

Battery active materials are routinely evaluated via the electrochemical performance of their composite electrodes which are prepared with standard formulations and routine processing conditions. The relationship between electrochemical responses and these experimental variables are not commonly explored. Mechanical properties and their relationship to durability are almost never considered. We therefore offer some quite basic studies of the effects of formulation on these properties. Electrochemical and mechanical properties of composites across a broad formulation range are provided for the most common Li-Ion chemistry -LiCoO 2 electroactive particles with PVDF binders. Mechanical characterizations include evaluations of both the constituent materials and the porous electrode structures. We will show that composite electrode designs which optimize mechanical durability and ruggedness will degrade electrochemical performance for these LiCoO 2 /PVDF binder-based systems.

Cathode Structure/Property Relationships: Electrochemistry and Mechanics

“…Poor adhesion is not unexpected considering that metal oxide has high surface energy and binder is fluorinated, rendering it low surface energy. XPS of these samples is in agreement with this hypothesis, showing very little difference between pure HP PVDF and that blended with LiCoO 2 (2). Calendaring densifies the solid in all cases and decreases the both the total porosity and the size/shape of pores of both sizes.…”

“…Wet films were dried in dynamic vacuum at 80 °C for at least 2 hours before any measurement or further treatment. These films were often calendared as described previously (2).…”

Thermomechanical Polymer Binder Reactivity with Positive Active Materials for Li Metal Polymer and Li-Ion Batteries: An XPS and XPS Imaging Study

“…50,51 These polymer bridges can resist mechanical stress, but only up to a critical value that depends on how much they stick to the collector or particle's surface and also on their bulk strength. 8 The electrode cohesion and adhesion strengths generally increase with an increase of the binder content 52,53 or with an increase of the particle size. 54−57 This could be rationalized as the ratio of the binder mass to the total geometrical surface area of the active and conductive particles.…”

Direct reuse of aluminium and copper current collectors from spent lithium-ion batteries

“…The electrical conductivity decreases with increasing Al surface roughness, which is opposite to the adhesion strength. This is likely due to Al current collectors with a rougher surface trapping more PVDF binder at the Al/NMC622 interface and blocking the electrical conduction pathway, 44 reducing the contact conductivity. Thus, the rougher the Al surface, the lower the electrical conductivity.…”