Although lithium-ion batteries are used as electrochemical energy storage in various applications, further improvements regarding the efficiency, cyclability, power-, and energy density are desirable to match the increasing demand of energy storage in the future. In order to improve such properties, detailed knowledge about the charge transport in individual battery components and across the phase boundaries is required. Important quantities describing the charge transport in materials for electrochemical applications are the ionic and the electronic partial conductivity.
As most active cathode electrode materials, Li(NixCoyMn1-x-y)O2 (NCM) is a layered transition metal oxide. The most intensively studied NCM composition consists of an equimolar content of Nickel, Cobalt and Manganese (NCM 111). In these structures lithium ions are intercalated in the inter-slab position between layers of oxygen coordinated transition metal ions.
NCM is mostly used in form of a porous network of nanometer sized primary particles which form spherical secondary particles with diameters on the micrometer scale to provide short diffusion pathways for faster charge transport and higher (dis-)charge currents. To get a better understanding of the intrinsic transport processes in this complex structure and to optimize the electrochemical performance it is necessary to study the ionic and electronic transport processes in pristine secondary particles.
To study ionic and electronic partial conductivities of secondary particles systematically, single spherical NCM 111 with diameters between 5 µm and 30 µm have been positioned on a predefined position on a photolithographically patterned substrate. The substrates were put into a specially designed electrochemical cell, which allows to contact the particles individually and under controlled pressure. Electrochemical impedance spectroscopy has been performed on several single NCM 111. By correlating the measured resistance with the nanoparticles’ diameter the electronic conductivity of the secondary particles could be determined using a simple model.
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