1/3 Mn 1/3 )O 2 (NCM111), morphologies such as preferentially oriented crystals in the particles, [2] nanobrick morphology, [3] one-dimensional hierarchical microrods, [4] and hierarchically structured particles [5][6][7][8][9] were investigated. The latter is achieved by forming secondary particles with open intraparticle pore structure from assembled primary particles. The advantages of such structures are higher rate capability and improved cycling stability, due to a larger interface between active material and electrolyte, smaller diffusion paths and lower mechanical stress during cycling. By modifying the particle morphology of commercial compact materials in a few additional process steps, a comparison can be made between the commercial starting material and the produced structured material. This approach was applied in the work of Wagner et al. [9] by grinding, spray drying and calcination commercial NCM111. The influences of the process parameters in the production of such structures on the electrochemical properties as a function of the particle morphology were investigated. The optimum sintering temperature was found to be between 850 and 900 C, resulting in primary particle diameters of 350 and 550 nm. It is the optimum between the demands of the ionic conductivity of the primary particles and the electrical conductivity of the secondary particles. During the sintering process, the primary particles grow, which aggravates ion diffusion but increases the electrical conductivity due to sinter necks. The specific capacity was improved from 20 to 100 mAh g À1 at 10C for the original and the structured particles, respectively. [9]

Previous investigations on porous NCM particles with shortened diffusion paths and an enlarged interface between active material and electrolyte showed improved rate capability and cycle stability compared to compact particles. Due to the additional intragranular porosity of the active material, the pore structure of the overall electrode, and, as consequence, the ionic transport in the pore phase, is altered. In addition, the particle morphology influences the ohmic contact resistance between the current collector and electrode film. These effects are investigated using impedance spectroscopy in symmetrical cells under blocking conditions. The ionic resistance and the tortuosity of the electrodes are determined and analyzed by a transmission line model. Tortuosity is higher for porous particles and increases more during calendering. This limits the options for densifying these electrodes to the same level as with compact particles. In a further approach, the method is used to explain the drying related performance differences of these electrodes. At higher drying rates, the contact and the ionic resistance of electrodes with compact particles increases more strongly as for electrodes with porous particles. These investigations provide new insights into the ion transport behavior and enable a better understanding of the impact of the electrode processing condition.