Lattice Analysis by Synchrotron Powder Diffraction on High Voltage Spinel LNMO

The high voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising material to increase the energy density of lithium ion batteries. A variety of research was done to investigate the material regarding its properties, synthesis and commercial viability. To investigate in detail the properties of the cathode material during the delithiation and lithiation, in situ measurements are a helpful tool to fully understand changes in the crystal structure, which can give important information how to further improve the electrochemical properties of the cathode material. Especially the 'ordered' crystal phase P 4332 and the 'unordered' F d3 ̅m, which can result from different temperature treatments during the synthesis process, need to be investigated to define the correlation between calcination temperatures, lattice parameters and electrochemical properties. The LNMO investigated was synthesized using a spray drying method. From a solution of acetate and nitrate salts precursors were produced which have been calcined under different conditions to support the crystallization into the ordered and unordered phase, respectively. First, the two powders were characterised by SEM analysis to investigate the crystal morphology. Then slurries (LiNi0.5Mn1.5O4, PVDF binder, carbon, NMP solvent) were prepared and cast on aluminium foil to prepare electrodes. The electrochemical properties of assembled test cells (capacity, cycle life, etc.) were measured. Customized coin cells were used for the in situ measurements. The in situ XRD were measured using the high energy, low-emittance synchrotron radiation source at the Petra III beamline P02.1 at the DESY in Hamburg. In our presentation we will correlate the synthesis temperatures, electrochemical properties and lattice parameters for the synthesized LNMOs. By deeply analysing the in situ measured diffraction patterns for the different state of charge we will fully demonstrate the phase transition for the different samples and correlate the lattice change to properties like the manganese(III) amount and the crystal phase. The manganese(III) amount is mostly dependent on the calcination temperature and therefore also on the received crystal phase. Furthermore, we will outline the influence on the degradation for the different samples. The degradation differences between the synthesized samples were investigated by analysing the cumulative charge and discharge capacity. The combination of those results will lead to a deeper understanding of the connection between the different influence factors for the cathode material.