Low-cost and high-performance lithium ion batteries (LIBs) are a key technology in these days. One promising candidate for cathodes is the layered nickel (Ni)-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) active material due to its high energy density, high specific capacity and lower material costs as well as social aspects concerning mining due to the diminished cobalt content. However, the lower thermal stability and higher sensitivity to H2O and CO2 result in a potential stronger performance degradation and lower safety. Therefore, process adaptions are inevitable. In this paper the current status and challenges of the entire cathode production process with NCM811 as active material are reviewed taking quality, cost and environmental aspects into account. General important aspects within the process are presented which are specially extended to NCM811 cathode production. Process recommendations are highlighted and innovative approaches like a water-based or solvent-free processing are discussed in comparison to conventional production technologies.
For batteries with high energy density and good fast-charge capability, NCM cathode active materials with ≥80 mol% nickel are promising due to their high specific capacities. Unfortunately, the increase in nickel content is accompanied by a high susceptibility to moisture. Therefore, nickel-rich NCM is coated or doped by the manufacturers to increase its stability. However, it is unclear if special requirements regarding ambient humidity must still be met during the whole production chain, or only after post-drying and during cell assembly. Therefore, the structure and properties of three different nickel-rich NCM active materials (one doped monocrystalline, two coated polycrystalline materials) processed at ambient atmosphere were investigated. At every process step, moisture content and microstructure were examined. Prior to cell assembly, two different post-drying procedures were applied and investigated. As validation, electrochemical tests were performed. Both polycrystalline cathodes demonstrated good physical and electrochemical properties, despite the ambient process atmosphere. Higher moisture reduction led to improved electrochemical performances at higher C-rates. Finally, a comparison between dry and normal atmosphere of the best performing material indicates that a production of high-quality nickel-rich electrodes at ambient atmosphere is possible if their exposure to moisture is short and well-designed post-drying techniques are applied.
The process step of drying represents one of the most energyintensive steps in the production of lithium-ion batteries (LIBs). [1,2] According to Liu et al., the energy consumption from coating and drying, including solvent recovery, amounts to 46.84% of the total lithium-ion battery production. [3] The starting point for drying battery electrodes on an industrial scale is a wet film of particulate solvent dispersions, which are applied to a current collector foil by slot-die coating. Conventional convective drying removes the solvent from the wet film and solidifies the layer as the drying time progresses (Figure 1). According to the state-of-the-art, electrodes are produced at a web speed of 25-80 m min À1 . [2,[4][5][6][7][8] The deviations in the coating/drying speeds are related to the constant improvement of the system technologies and the different coating thicknesses and types. For example, coatings can be applied intermittently or continuously. [9][10][11] Furthermore, double-sided coatings can be applied simultaneously or sequentially, meaning that the first side is dried first and then the second side. [4,6,7,12] In addition to the actual application methods, parameters such as mass loading and solids content determine the achievable drying rate. Pfleging et al. report typical coating speeds for thick electrodes of 30 m min À1 , whereas Mauler et al. assume that processing speeds of up to 100 m min À1 are realistic in the future. [6,7] However, the influence of the drying intensity on the structure of the electrode must be taken into account. Increasing the drying rate leads to a segregation of binder and carbon black particles contained in the formulation. [13,14] This results in a decrease in binder and carbon black at the interface between the current collector foil and the coating. Jaiser et al. divide the drying process into two different phases. During the first phase, the evaporation of the solvent leads to a shrinkage of the coated layer, the second starts once this shrinkage stops and the solvent is evaporated by capillary transport. The latter phase is mainly responsible for the binder migration. [15] For this reason, drying must be very gentle during this phase. Reducing the drying rate of anode slurries during this stage from 1.19 to 0.52 g m 2 s À1 leads to a 50% increase in adhesive strength. [15] Clearly, an elevation of the drying intensity and the associated production speed is not possible compromising electrode quality. [13,14] Regardless of the electrode parameters, however, throughput can be increased by lengthening the dryer. The difficulty here lies in handling very thin foils, which tend to wrinkle with an increase in dryer length and place new demands on the web tension controls. [4] To be able to increase production speeds and, thus, maximize throughputs, a carefully chosen
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