Amphiphilic Bottlebrush Polymeric Binders for High-Mass-Loading Cathodes in Lithium-Ion Batteries

In contrast to noteworthy advancements in cathode active materials for lithium-ion batteries, the development of cathode binders has been relatively slow. This issue is more serious for high-mass-loading cathodes, which are preferentially used as a facile approach to enable high-energy-density Li-ion batteries. Here, amphiphilic bottlebrush polymers (BBPs) are designed as a new class of cathode binder material. Using poly (acrylic acid) (PAA) as a sidechain, BBPs are synthesized through ring-opening metathesis polymerization. The BBPs are amphiphilic in nature owing to the hydrophilic PAA sidechains and hydrophobic polynorbornene (PNB) backbones. The PNB backbone allows process compatibility with nonaqueous solvent-based commercial cathode fabrication, while the PAA sidechain provides strong adhesion between cathode active layers and metallic current collectors. Moreover, the PAA sidechain simultaneously chelates transition metal ions dissolved from cathode active materials (LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811)) particles which are chosen as a model material. Driven by the well-balanced amphiphilicity and bottlebrush-based structural uniqueness of the BBP binder, the resulting NCM811 cathode exhibits uniform electron/ion conduction networks and dimensional stability. Notably, a high-mass-loading (27 mg cm⁻², corresponding to 5.2 mAh cm⁻²) NCM811 cathode with stable cyclability is achieved with an extremely low content (1 wt%) of the BBP binder.