Next Generation Low-Cost NMP/PVDF-Free Fast-Charging Ni-Rich NMC Cathode Electrodes for High Power Energy Storage Device Applications

Abstract

Longer range, faster charging, safer, and more durable and affordable batteries are required in order to promote the shift to an EV society powered by renewable energy. However, the current battery performance is limited by the conventional PVDF-NMP processing based cathode, which has lower electrical and ionic conductivity. The high molecular weight PVDF binders are the main cause of non-uniform porosity distribution, material agglomeration in active layer, and poor electrical conductivity. This problem is more prominent in high mass loading thick cathodes (>5 mg/cm2) that are required in high energy density battery designs. For examples, these cathode electrodes are not compatible with fast charging as they have high impedance and do not allow moderate to high C-rates in both charge and discharge.Nanoramic has re-invented how electrodes are manufactured by completely removing high molecular weight polymers such as PVDF and the toxic NMP solvent from the active layer of electrode. This dramatically improves Li-ion battery and Li-metal battery cell performance while decreasing the cost of manufacturing and the capital expenditures related to mixing, coating and drying, NMP solvent recovery, and calendering. In the Neocarbonix™ electrodes, a 3D nanocarbon matrix works as a mechanical scaffold for the electrode active material and mimics the polymer chain entanglement. The engineered surface chemistry of the nanocarbon materials, active materials (NMC), and the current collector promotes excellent mechanical stability for the resulting electrode architecture. As opposed to PVDF polymer, the 3D nanocarbon matrix is highly electrically conductive, allows for significantly thicker cathode active layer while improving the electrical conductivity of the electrode. By using eco-friendly solvents that are easily evaporated, the electrode throughput is higher, and more importantly, the energy consumption from electrode drying process is reduced by 30% due to reduction of temperature from 150 ⁰C-180 ⁰C required by the NMP to 60-70 ⁰C.In the Neocarbonix cathode electrodes the 3D carbon matrix is formed during a proprietary slurry preparation: high aspect ratio 1D and 2D carbon materials are properly dispersed and chemically functionalized using a 2-step proprietary slurry preparation process. The chemical functionalization is designed to form an organized self-assembled structure with the surface of active material particles (e.g. NMC particles). The so formed slurry is usually based on low-boiling point environmental green solvents for Ni-Rich NMC cathodes and are very easily evaporated and handled.After coating and drying, the electrodes undergo a calendering to control the density and porosity of the active material. In NMC811 cathode electrodes, densities of ≥3.6 g/cc and ≤20% porosity can be achieved. Depending on mass loading and battery cell requirements, the porosity can be optimized. Nanoramic projects a reduction in $/kWh of up to 20% with such cathode design. Figure below displays the preliminary results comparing the Neocarbonix (NX) NMP-PVDF free Ni-Rich NMC cathode electrodes with the conventional PVDF based NMC cathode electrodes in Li-Metal based half pouch cells (Li metal is the counter electrodes). Preliminary data shows that NX electrodes can maintain 62-66% capacity retention under 7C-Rate while the PVDF based electrodes can only maintain ~39% of initial capacity, which proves 27% improvement under high C-Rate discharge power performance. Also the NX NMC622 electrodes shows excellent fast-charging capability with 87.1% charge capacity within 15 mins constant current (CC) region fast-charge. Even for the higher areal loading NMC811 cathode (5.2-5.6 mAh/cm2) under 3.4C-Rate fast-charging, NX NMC811 displays 77.3% capacity retention within 17 mins CC region fast-charge, while the PVDF NMC811 control electrode only shows 35.9% capacity retention under 3.4C-Rate fast-charging, which proves that high capacity loading ~5.6 mAh/cm2 Neocarbonix Ni-rich NMC cathode can improve >2X in high-rate 15mins fast-charging capability compared with conventional PVDF electrodes in the electric vehicle (EV) applications. Figure 1