Composite Current Collectors and Aramid Separator Enabled Safer High-Nickel Batteries

The requirement on high energy density Li-ion batteries demands high energy chemistry system, this rise concerns on batteries’ safety issue. Battery non-active components, including current collectors and separator play important role in improving battery safety. Composite current collectors, which are consisted of a polymer layer between two plated thin metal layers, are widely treated as a solution to reduce safety concerns caused by high nickel layered cathode materials, e.g. LiNi_1-x-yCo_xMn_yO₂, LiNi_1-x-yCo_xAl_yO₂ and LiNi_1-x-y-zCo_xMn_yAl_zO₂ with Ni content higher than 0.8. In the meantime, composite current collectors can reduce most weight of current collectors and improve the cell’s gravimetric energy density without replacing cathode or anode materials. Moreover, high thermal stable separator could effectively prevent internal short circuit for it melts in higher temperature. In this work, we came up with a cell design which contains composite current collectors as positive/negative current collector and high thermal stable separator with aramid coating layers. This design improved separator breaking point by 84 °C while reduced current collector melting point by 900 °C, thereby it makes current collector shrinks earlier than separator break, this avoids internal short circuit by detaching cathode and anode coating layer when the separator is still in place. The design was applied in high nickel LiNi_0.91Co_0.03Mn_0.05Al_0.01O₂ cathode and graphite anode chemistry system with a thick coated electrode (4 mAh cm^-2, 21 mg cm^-2 per coating side). Pouch cell with 5 Ah nominal capacity was fabricated in this cell design. The electrochemical benefits and drawbacks by adopting positive or negative current collectors or both were evaluated, including the affection in cycling stability, cell resistance and rate performance. Nail penetration and thermal ramping was also adopted to evaluate the safety benefit of the design. The cell shows comparable electrochemical performance and improved cell safety after composite current collector and high thermal stable separator adoption.