Improved Electrochemical Performance in Advanced Lithium-Ion Batteries with Porocarb® As Functional Additive
Authors: Rohde Michael , Büttner Niklas , Kuhn Andreas , Moerseburg Erik , Weingarth Daniel , Becker Joerg , Pihan Sascha , Michaud-Bernlochner Julie , Samuelis Dominik , Hucke Thomas 
Published: February 2020

Electric vehicles face significant battery related challenges such as driving range, recharge time, durability, and cycle life. New concepts for improved and advanced battery technologies are required in order to increase driving range and durability, while simultaneously decreasing recharging time, weight, and cost. In recent years, new cell designs have been developed specifically for large scale applications in the automotive and stationary storage sectors.

A new electrode concept is to supplement with Heraeus Porocarb® porous particles as a functional additive to assure optimal mass transport of lithium ions by locally enhancing the effective diffusivity in the volume of the calendared electrode. Thereby achieving higher energy densities with improved cycle life and durability. Heraeus Porocarb is an electrochemically inert carbon with low specific surface with a unique porosity profile with distinct pore size regime. Its fully interconnected macropores allow for rapid ion transport, while the mesopores locally store electrolyte promoting mass transport and the pulse response of the cell.

Heraeus Porocarb can be implemented into lithium-ion battery electrodes in two different ways. More conventionally, a percolation-type approach can be taken for Porocarb particles which are smaller than the active material particles. Due to the interconnected and surface-accessible pore network in Porocarb, ionic percolation sets in at the same time as electronic transport, and local improvement of the porosity evolves into a globally interconnected transport pathway of Li+ions with low tortuosity.

The second electrode concept is an imprinting-type approach where the Porocarb particles used are larger and the active material is not only slightly imprinted but to a certain degree embedded in the Porocarb after calendaring. Due to the large contact area, very low resistances can be achieved in between the carbon and the active material, which alleviates contact resistance degradation and delamination, thereby extending cycle lifetime of the electrode.

The properties of Heraeus Porocarb will be presented with electrochemical data showing the enhanced performance and the so-called “Porocarb effect.”

This effect can be seen in lithium ion full cells by adding Porocarb in small quantities to the cathode. Therefore a representative cathode recipe were used, with an active material (NMC-111) content of 93 wt.%, 3 wt.%  PVDF binder, 2.5 wt.% carbon black and 1.5 wt.% Porocarb. Reference cells were using a graphite instead of Porocarb. Two different cathode loadings were chosen: 120 g/m2 and 240 g/m2representing high-power and high-energy cell designs, respectively. The unique porous structure of Porocarb increases significantly the kinetics in the electrode and overcomes easily the drawbacks of the low rate capability of high energy cell.

Figure 1