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 put forward urgent requests for rechargeable batteries with higher energy/power density and longer lifespans. As such, next-generation Li-ion batteries (LiBs) are expected to meet these requirements. The possibility 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 oxygen and potentially initiate the formation of inactive crystal structures. LiBs mechanical and chemical degradation mechanisms can be extended by applying protective coatings to the cathode’s surface. Many studies explore atomic layer deposition (ALD) for this purpose. However, the complementary molecular layer deposition (MLD) technique might offer the benefit of depositing flexible hybrid coatings that can accommodate potential volume changes of the electrode during the battery cycling. This study reports the deposition of novel organic-inorganic films via the ALD-MLD method. Characterization analysis such as 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 by providing a longer life with a 93% capacity retention after 150 cycles (3.0-4.4 V vs. Li/Li+), while the uncoated one retained only 83% of its initial capacity. Moreover, in situ dilatometry showed irreversible volume change for uncoated NMC while it was mostly reversible for coated ones during the cycling. It revealed the dilation behavior of the electrode, resulting in crack formation, which is significantly suppressed for the coated samples. Stable cycling of Ni-rich cathode materials in crucial conditions such as high voltage windows and elevated temperatures is still extremely challenging. To evaluate this, in situ dilatometry was performed at elevated temperatures (40 °C and 55 °C) and higher voltage ranges (3.0-4.6 V). The results confirmed that in both conditions, the dilation behavior of the coated sample is still under control while the capacity is comparable to the uncoated sample. This revealed that the coatings present good lithium-ion kinetics and reduce electrolyte decomposition. Overall, this work showed the liability of the ALD-MLD films deposited on NMC electrodes to mitigate the degradation mechanisms and provides insight into a method that seems promising as a protective and elastic coating for future high-energy lithium-ion battery cathodes. Figure 1