Plasma-Assisted Mechanochemistry to Covalently Bond Ion-Conducting Polymers to Ni-Rich Cathode Materials for Improved Cyclic Stability and Rate Capability

Nickel-rich cathode materials in lithium-ion batteries are in the spotlight for high energy capacity, but they have the disadvantage of poor long-term stability due to interfacial phase changes and side reactions. We introduce a plasma-assisted mechanochemical composite process for covalently bonding polyvinylidene fluoride (PVDF) with high ionic conductivity to LiNi_0.8Co_0.1Mn_0.1O₂(NCM811) particles in the dry-state electrode fabrication process. When plasma and mechanical friction are applied simultaneously, chemically inert PVDF is firmly and uniformly coated on NCM811 particles with a unique Ni-C covalent bond acting as an excellent cathode-electrolyte interface to inhibit transition metal dissolution and parasitic side reactions. In addition, PVDF has excellent ion conductivity and elasticity, so structural stability against the repetitive volume change can be achieved without interfering with lithium-ion transport. The PVDF-bonded Ni-rich cathode exhibits a high specific capacity of 215.2 mAh g^-1at 0.5 C, improved rate capability of 165.9 mAh g^-1at 5 C, and excellent cycle stability with a capacity retention of 83.6% after 300 cycles. This approach can maximize the electrochemical performance of conventional materials through one simple plasma-assisted composite process that controls the surface properties of cathode materials in the dry state.