Sulfate-Containing Composite Based on Ni-Rich Layered Oxide LiNi0.8Mn0.1Co0.1O2 as High-Performance Cathode Material for Li-ion Batteries

Enabling Aqueous Processing of Ni-Rich Layered Oxide Cathode Materials by Addition of Lithium Sulfate

Aqueous processing of Ni-rich layered oxide cathode materials is a promising approach to simultaneously decrease electrode manufacturing costs, while bringing environmental benefits by substituting the state-of-the-art (often toxic and costly) organic processing solvents. However, an aqueous environment remains challenging due to the high reactivity of Ni-rich layered oxides towards moisture, leading to lithium leaching and Al current collector corrosion because of the resulting high pH value of the aqueous electrode paste. Herein, a facile method was developed to enable aqueous processing of LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811) by the addition of lithium sulfate (Li₂ SO₄ ) during electrode paste dispersion. The aqueously processed electrodes retained 80 % of their initial capacity after 400 cycles in NCM811||graphite full cells, while electrodes processed without the addition of Li₂ SO₄ reached 80 % of their capacity after only 200 cycles. Furthermore, with regard to electrochemical performance, aqueously processed electrodes using carbon-coated Al current collector outperformed reference electrodes based on state-of-the-art production processes involving N-methyl-2-pyrrolidone as processing solvent and fluorinated binders. The positive impact on cycle life by the addition of Li₂ SO₄ stemmed from a formed sulfate coating as well as different surface species, protecting the NCM811 surface against degradation. Results reported herein open a new avenue for the processing of Ni-rich NCM electrodes using more sustainable aqueous routes.

Probing the Ni(OH)2 Precursor for LiNiO2 at the Atomic Scale: Insights into the Origin of Structural Defect in a Layered Cathode Active Material

In lithium ion batteries (LIBs), the layered cathode materials of composition LiNi_{1- x - y} Co_x Mn_y O₂  are critical for achieving high energy densities. A high nickel content (>80%) provides an attractive balance between high energy density, long lifetime, and low cost. Consequently, Ni-rich layered oxides cathode active materials (CAMs) are in high demand, and the importance of LiNiO₂ (LNO) as limiting case, is hence paramount. However, achieving perfect stoichiometry is a challenge resulting in various structural issues, which successively impact physicochemical properties and result in the capacity fade of LIBs. To better understand defect formation in LNO, the role of the Ni(OH)₂  precursor morphology in the synthesis of LNO requires in-depth investigation. By employing aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and precession electron diffraction, a direct observation of defects in the Ni(OH)₂  precursor preparedis reported and the ex situ structural evolution from the precursor to the end product is monitored. During synthesis, the layered Ni(OH)₂  structure transforms to partially lithiated (non-layered) NiO and finally to layered LNO. The results suggest that the defects observed in commercially relevant CAMs originate to a large extent from the precursors, hence care must be taken in tuning the co-precipitation parameters to synthesize defect-free Ni-rich layered oxides CAMs.

Improved Electrochemical Behavior and Thermal Stability of Li and Mn-Rich Cathode Materials Modified by Lithium Sulfate Surface Treatment

High-energy cathode materials that are Li- and Mn-rich lithiated oxides—for instance, 0.35Li2MnO3.0.65LiNi0.35Mn0.45Co0.20O2 (HE-NCM)—are promising for advanced lithium-ion batteries. However, HE-NCM cathodes suffer from severe degradation during cycling, causing gradual capacity loss, voltage fading, and low-rate capability performance. In this work, we applied an effective approach to creating a nano-sized surface layer of Li2SO4 on the above material, providing mitigation of the interfacial side reactions while retaining the structural integrity of the cathodes upon extended cycling. The Li2SO4 coating was formed on the surface of the material by mixing it with nanocrystalline Li2SO4 and annealing at 600 °C. We established enhanced electrochemical behavior with ~20% higher discharge capacity, improved charge-transfer kinetics, and higher rate capability of HE-NCM cathodes due to the presence of the Li2SO4 coating. Online electrochemical mass spectrometry studies revealed lower CO2 and H2 evolution in the treated samples, implying that the Li2SO4 layer partially suppresses the electrolyte degradation during the initial cycle. In addition, a ~28% improvement in the thermal stability of the Li2SO4-treated samples in reactions with battery solution was also shown by DSC studies. The post-cycling analysis allowed us to conclude that the Li2SO4 phase remained on the surface and retained its structure after 100 cycles.