The insufficient autonomy of Electric Vehicles (EVs), which is mainly due to the limited energy density of automotive batteries, can be addressed by increasing the specific energy and/or the average operating voltage of the active cell materials. LiMn1.5Ni0.5O4 (LNMO) is a top candidate active cathode material due to its access to a rare two-electron transition from Ni2+ to Ni4+ at two voltage plateaus near 4.7 V vs. Li+/Li, a theoretical capacity of 147 mAhg-1 and fast three-dimensional Li-ion diffusion paths within the cubic lattice. Furthermore, LNMO is a relatively low-cost material with fairly good charging rate capability, suitable for EV requirements. However, the employment of LNMO in next-generation Li-ion batteries is prohibited by phenomena related to structural stability due to manganese dissolution and electrolyte compatibility. Structural modification via the inclusion of suitable dopants and proper surface treatment constitute promising solutions to these problems. Materials development for more efficient automotive batteries is an urgent task. In this work, four research organizations have joined efforts to realize LNMO cathodes appropriate for EVs. Three partners in this team worked on the materials development, and the fourth partner worked on the benchmarking of the materials. We have exploited nine different synthesis technologies for the pristine LNMO. From the evaluated technologies, three have been identified as most promising and were optimized for the specific application: the co-precipitation, the sol-gel and the aerosol spray pyrolysis methods. Several calcination profile conditions of the produced powder were studied obtaining two LNMO spinel phases: the ordered (P4332) and the disordered (Fd-3m) with the latter identified as the most electrochemically active. Five dopants have been introduced into the most promising LNMO lattices with Fe and Al proven to be the best-performing ones. Twelve materials have been considered for the LNMO particle surface treatment, and the Al2O3 was evaluated as the one showing satisfactory cyclic stability. We have used Scanning and Transition Electron Microscopy (SEM/TEM), micro-Raman spectroscopy, X-Ray Powder Diffraction (XRD) and Particle Size Analysis (PSD) for the structural characterization of the products. The most promising compositions have been scaled up to quantities sufficient for the manufacture of battery cells used in the automotive sector. In this work, we will present the most significant results from the above developments including results from electrochemical performance tests of electrodes in half and full coin cells (HCC/FCC). At HCC and C/5 we managed to obtain a specific capacity of more than 130 mAh/g with about 10% irreversible capacity loss. In FCC (vs. graphite) and C/20 we have obtained materials with 118 mAh/g specific capacity and about 20 % irreversible loss. During cycling of FCCs at 1C, with the best performing material, we have attained about 80 % of the initial capacity after 100 charging/discharging cycles. Future developments should focus on increasing the cycling ability of the full-cell by optimising the active materials (both cathode and anode), the electrolyte as well as the electrode structure.
The different versions of the original document can be found in:
DOIS: 10.5281/zenodo.1483288 10.5281/zenodo.1483287