Francis Amalraj Susai

In this work, we continued our systematic investigations on synthesis, structural studies, and electrochemical behavior of Ni-rich materials Li[Ni_xCo_yMn_z]O₂ (x + y + z = 1; x ≥ 0.8) for advanced lithium-ion batteries (LIBs). We focused, herein, on LiNi_0.85Co_0.10Mn_0.05O₂ (NCM85) and demonstrated that doping this material with high-charge cation Mo⁶⁺ (1 at. %, by a minor nickel substitution) results in substantially stable cycling performance, increased rate capability, lowering of the voltage hysteresis, and impedance in Li-cells with EC-EMC/LiPF₆ solutions. Incorporation of Mo-dopant into the NCM85 structure was carried out by in-situ approach, upon the synthesis using ammonium molybdate as the precursor. From X-ray diffraction studies and based on our previous investigation of Mo-doped NCM523 and Ni-rich NCM811 materials, it was revealed that Mo⁶⁺ preferably substitutes Ni residing either in 3a or 3b sites. We correlated the improved behavior of the doped NCM85 electrode materials in Li-cells with a partial Mo segregation at the surface and at the grain boundaries, a tendency established previously in our lab for the other members of the Li[Ni_xCo_yMn_z]O₂ family.

This work continues our systematic study of Li- and Mn- rich cathodes for lithium-ion batteries. We chose Li₂MnO₃ as a model electrode material with the aim of correlating the improved electrochemical characteristics of these cathodes initially activated at 0 °C with the structural evolution of Li₂MnO₃, oxygen loss, formation of per-oxo like species (O₂²⁻) and the surface chemistry. It was established that performing a few initial charge/discharge (activation) cycles of Li₂MnO₃ at 0 °C resulted in increased discharge capacity and higher capacity retention, and decreased and substantially stabilized the voltage hysteresis upon subsequent cycling at 30 °C or at 45 °C. In contrast to the activation of Li₂MnO₃ at these higher temperatures, Li₂MnO₃ underwent step-by-step activation at 0 °C, providing a stepwise traversing of the voltage plateau at >4.5 V during initial cycling. Importantly, these findings agree well with our previous studies on the activation at 0 °C of 0.35Li₂MnO₃·0.65Li[Mn_0.45Ni_0.35Co_0.20]O₂ materials. The stability of the interface developed at 0 °C can be ascribed to the reduced interactions of the per-oxo-like species formed and the oxygen released from Li₂MnO₃ with solvents in ethylene carbonate–methyl-ethyl carbonate/LiPF₆ solutions. Our TEM studies revealed that typically, upon initial cycling both at 0 °C and 30 °C, Li₂MnO₃ underwent partial structural layered-to-spinel (Li₂Mn₂O₄) transition.

This presentation summarizes the recent studies in Bar-Ilan University of materials for positive electrodes of Li-ion batteries. The materials included lithiated oxides of Ni-based family Li[Ni-Co-Mn]O₂ (layered, R-3m space group) and of Li,Mn-rich layered-layered xLi₂MnO₃ ^.(1-x)LiMO₂ (M=Ni, Co, Mn), 0Mn. It was concluded from XPS studies that the modified stable and less resistive interface on the Al-doped particles comprised the Li⁺-ion conducting centers like LiAlO₂, AlF₃, etc., which promote, to some extent, the Li⁺ transport to the bulk and therefore facilitate the electrochemical reactions [2]. We discuss also the following issues: ab-initio calculations of the preferential substitution of Zr⁴⁺ at Mn, Co or Ni sites; influence of Zr⁴⁺ and Mo⁶⁺ ions on the Li⁺/Ni²⁺ mixing, charge distribution, the lattice constants, as well as partial layered-to-spinel structural transformation and thermal characteristics of cathode materials in reactions with solutions. In case of Li,Mn-rich cathode materials, we used thin surface coatings, as well as gas treatment with ammonia at 400 °C to stabilize these materials. The AlF₃-coated electrodes exhibit stable charge-discharge behavior providing higher capacities and lower fade upon prolonged cycling at 60 °C. It has been found that electrodes comprising the AlF₃-coated material exhibited higher reversible capacities of ∼250 mAh/g at a C/5 rate, more stable cycling behavior, higher lithium storage capability at 60 ^oC, and lower impedance measured during Li-deinteraclation comparing to electrodes prepared from the uncoated material. An important finding is that Li_x[MnNiCo]O₂ /AlF₃ materials revealed much higher thermal stability both in the pristine (lithiated) and cycled (delithiated) states than their uncoated counterparts [1]. Ammonia treatment of Li,Mn-rich materials for 2 h improves discharge capacity, lowers capacity and mean voltage fading during cycling. The mechanism of the ammonia treatment will be discussed. Further work will explore full cell studies with graphite anodes to confirm if NH₃ treatment can indeed improve the likelihood of commercialization of the above materials [3]. Fig : 1 Discharge capacity of the electrodes comprising NH₃-treated and untreated Li,Mn-rich 0.35Li₂MnO₃·0.65LiNi_0.35Mn_0.45Co_0.20O₂ materials. The treatment was performed for 1, 2 and 4 hours, as indicated. References : [1] S. F. Amalraj, M. Talianker, B. Markovsky et al. J. Electrochem. Soc. 160 (2013) A2220. [2] D. Aurbach, O. Srur-Lavi, C. Ghanty et al. J. Electrochem. Soc. 162 (2015) A1014. [3] Evan M. Erickson, Hadar Sclar, Florian Schipper, B. Markovsky et al., Adv. Energy Mater., 7, (2017) 1700708 Figure 1

Amongst a number of different cathode materials, the layered nickel-rich LiNi_yCo_xMn_1−y−xO₂ and the integrated lithium-rich xLi₂MnO₃·(1 − x)Li[Ni_aCo_bMn_c]O₂ (a + b + c = 1) have received considerable attention over the last decade due to their high capacities of ~195 and ~250 mAh·g⁻¹, respectively. Both materials are believed to play a vital role in the development of future electric vehicles, which makes them highly attractive for researchers from academia and industry alike. The review at hand deals with both cathode materials and highlights recent achievements to enhance capacity stability, voltage stability, and rate capability, etc. The focus of this paper is on novel strategies and established methods such as coatings and dopings.