A sustainable shift from internal combustion engine (ICE) vehicles to electric vehicles (EVs) is essential to achieve a considerable reduction in emissions. The production of Li-ion batteries (LIBs) used in EVs is an energy-intensive and costly process. It can also lead to significant embedded emissions depending on the source of energy used. In fact, about 39% of the energy consumption in LIB production is associated with drying processes, where the electrode drying step accounts for about a half. Despite the enormous energy consumption and costs originating from drying processes, they are seldomly researched in the battery industry. Establishing knowledge within the LIB industry regarding state-of-the-art drying techniques and solvent evaporation mechanisms is vital for optimising process conditions, detecting alternative solvent systems, and discovering novel techniques. This review aims to give a summary of the state-of-the-art LIB processing techniques. An in-depth understanding of the influential factors for each manufacturing step of LIBs is then established, emphasising the electrode structure and electrochemical performance. Special attention is dedicated to the convection drying step in conventional water and N-Methyl-2-pyrrolidone (NMP)-based electrode manufacturing. Solvent omission in dry electrode processing substantially lowers the energy demand and allows for a thick, mechanically stable electrode coating. Small changes in the electrode manufacturing route may have an immense impact on the final battery performance. Electrodes used for research and development often have a different production route and techniques compared to those processed in industry. The scalability issues related to the comparison across scales are discussed and further emphasised when the industry moves towards the next-generation techniques. Finally, the critical aspects of the innovations and industrial modifications that aim to overcome the main challenges are presented.

The LiNixMn1-x-yCoyO2 (NMC) is a widely used cathode material in lithium-ion batteries (LIBs) due to its high capacity. By enabling water-based cathode processing, the cost and environmental impact of LIBs will be reduced substantially. However, the water compatibility of Ni-containing materials has been problematic due to lithium (Li)-leaching, corrosion of the aluminium (Al) current collector, and lack of aqueous dissoluble binders. For the first time, we demonstrated that NMC111 cathodes with comparable specific capacities to the standard polyvinylidene fluoride/N-methyl-2-pyrrolidone (PVDF/NMP)-processed cathodes can be formulated in water using lignin as binder material. Rheology measurements revealed that less solvent is needed to obtain the same slurry viscosity when replacing the NMP solvent with water. Cycling voltammetry and differential scanning calorimetry revealed that lignin is electrochemically inactive between 2.5-4.5 V and thermally stable up to 152 oC, respectively. Drying the cathode coatings at 50 oC allowed for a controlled evaporation rate as surface cracks and binder migration detected using scanning electron microscopy diminished. The lignin binder provided strong cohesion forces to the carbon black (CB) and the NMC111 particles, and the use of carbon(C)-coated Al-foil (C-Al) further increased the coating's mechanical strength. Scratch tests revealed that calendaring magnified the nature of the initial mechanical strength, intensifying a poor adhesion of the coating to the Al-foil and strong cohesion between the particles. While calendering and pore removal improved the rate performance for PVDF-cathodes (85:10:5 wt % NMC:CB:binder), the rate capability of lignin-cathodes (80:11:9 wt %) decreased with lower porosity (from 53 to 0 %) and higher mass loading (9.7 mg/cm2). Particle deformation and extensive pore-blocking at high carbon contents created a Li+-transfer barrier across the cathode/electrolyte surface, decreasing the rate performance. Cathodes using a CMC/lignin-binder mix (2:7 wt% ratio) and C-Al foil (75 % capacity retention) electrochemically outperformed those with the commercial CMC/SBR mix and plain Al-foil (35 % capacity retention) at a high C-rate (5 C). Of all the aqueous produced cathodes, the uncalendered with pure lignin-binder, C-Al foil, dried at 50 oC, and a mass loading of 7.4 mg/cm2 showed the highest capacity retention at 5 C (60 %). Additionally, the lignin-cathodes have poor electrolyte wetting abilities and need longer exposure time before cycling and additional formation cycles compared to the PVDF-cathodes. Lignin-cathodes with the smallest lignin/CB matrix (90:5:5 wt% NMC:CB:binder) wetted for 35 days with 5 formation cycles at C/10 showed similar initial discharge capacity and capacity retention (154 mAh/g and 89 %) as 85:10:5 PVDF-based cathodes (153 mAh/g and 93 %) after 100 cycles at C/2.

The cost and environmental impact of Li-ion batteries can be reduced through aqueous processing of cathode materials. Here, we used aqueous processing to prepare lignin-based NMC111 cathodes for Li-ion batteries with enhanced rate capability.

By enabling water-based cathode processing, the energy-intensive N-methyl-2-pyrrolidone (NMP) recovery step can be eliminated, reducing the cost and environmental impact of LIBs. Aqueous processing of the high capacity Ni-containing LiNixMn1−x−yCoyO2...

The evaporation of N-Methyl-2-Pyrrolidone (NMP) solvent during the large-scale production of LiNixMn1−x−yCoyO2 (NMC) cathodes usually occurs in convection ovens. This paper aims to close the gap between the industrial convection drying method and the conventional vacuum oven typically used at the laboratory scale. Multiple studies focus on modeling convection dryers to reduce energy consumption, but few have studied their impact on the cathode quality experimentally and compared them to vacuum-dried cathodes. A convection oven designed for LIB electrode drying was developed to investigate the influence of drying kinetics on the formation of small electrode surface cracks (<1400 μm2) and binder migration. The drying kinetics were revealed through thermogravimetric analysis (TGA) at drying temperatures of 50 and 100 °C and hot air velocities of 0.5 and 1 m/s. Even at these relatively low drying rates, structural differences were detected when comparing the two drying methods, illustrating the importance of implementing drying conditions that represent the industry process in laboratories. Surface cracking increased with drying rates, and cathodes with multiple cracks after calendering obtained a higher discharge capacity at discharge currents >C/2. An alternative surface analysis with less sample preparation was sufficient for determining the relative change in binder migration.