Stabilized Positive Electrode Material to Enable High Energy/Power Density Lithium-Ion Batteries

Abstract

Recently, the large-scale deployment of electric vehicles (EVs) and stationary battery systems has putforward urgent requests for rechargeable batteries with higher energy/power density and longerlifespans. As such, next-generation Li-ion batteries (LiBs) are expected to meet these requirements. Thepossibility of using Ni-rich high-capacity cathode materials (NMC) can help to achieve that goal, however,they still suffer from significant capacity fade via several chemical and mechanical degradation modes.One is crack formation within secondary particles which leads to parasitic reactions that evolve oxygenand potentially initiate the formation of inactive crystal structures. LiBs mechanical and chemicaldegradation mechanisms can be extended by applying protective coatings to the cathode’s surface. Manystudies explore atomic layer deposition (ALD) for this purpose. However, the complementary molecularlayer deposition (MLD) technique might offer the benefit of depositing flexible hybrid coatings that canaccommodate potential volume changes of the electrode during the battery cycling. This study reportsthe deposition of novel organic-inorganic films via the ALD-MLD method. Characterization analysis suchas FTIR, XPS, SEM-EDS, and TEM confirmed the film deposition on the surface of the NMC electrode.Besides, the electrochemical results showed the enhancement of the coated electrode, as evidenced byproviding a longer life with a 93% capacity retention after 150 cycles (3.0-4.4 V vs. Li/Li+), while theuncoated one retained only 83% of its initial capacity. Moreover, in situ dilatometry showed irreversiblevolume change for uncoated NMC while it was mostly reversible for coated ones during the cycling. Itrevealed the dilation behavior of the electrode, resulting in crack formation, which is significantlysuppressed for the coated samples. Stable cycling of Ni-rich cathode materials in crucial conditions suchas high voltage windows and elevated temperatures is still extremely challenging. To evaluate this, in situdilatometry was performed at elevated temperatures (40 °C and 55 °C) and higher voltage ranges (3.0-4.6V). The results confirmed that in both conditions, the dilation behavior of the coated sample is still undercontrol while the capacity is comparable to the uncoated sample. This revealed that the coatings presentgood lithium-ion kinetics and reduce electrolyte decomposition. Overall, this work showed the liability ofthe ALD-MLD films deposited on NMC electrodes to mitigate the degradation mechanisms and providesinsight into a method that seems promising as a protective and elastic coating for future high-energylithium-ion battery cathodes. Figure 1