Mixing and Coating Procedure Development for LiNiCoAlO2 cathodes at Prototype Production Scale

Abstract

The use of high energy materials for Lithium ion batteries has given rise to the use of Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2, NCA) as viable cathode alternative to the traditionally used LiCoO2 (LCO). The expected usable specific gravimetric capacity of ~170mAh/g and a good cycle life with potential cost saving and less environmental impact compared to LCO make it interesting for commercial applications such as the automotive industry. Especially the use of NCA in electric vehicles is discussed by various major industrial players, with Panasonic and Tesla being on the forefront of this development. In conventional laboratory developments, small scale mixing and coin cell level testing is used to highlight novel material performance. However, this disguises the difficulties that some chemistries and electrode coating experience when scaled to levels that are closer to production. At the heart of academic electrode development is a small scale mixing of few grams of active material and standardised recipes of maximum 80% active material content in the mix. Whilst this is valuable for initial assessment, the manufacturing parameters do not translate well to large scale, industrially used electrode slurries, which would aim at active material contents of well above 90%. In addition, large scale development of slurries that have to be coated on several hundreds of meters has to consider coating adhesion properties and slurry viscosity for optimum coating. Furthermore, an optimised coating and calendering regime needs to be established in order to make the process viable for production. The presented work shows the correlation between several real world mixing recipes and procedures and their corresponding coating behaviour and electrochemical performance. Mixing has been done using a combination of small and large scale high torque, shear and energy mixers to process slurry volumes of up to 10L. This gives a processing procedures closer to production level when compared to conventional lab scale experiments. Coating parameters have been varied in terms of coating speed and drying conditions. Rheological properties of the mixes have been measured and the corresponding coating quality has been assessed using optical methods as well as adhesion tests. The coat weight uniformity is confirmed in situ during the coating process using ultrasonic absorption technology. The electrochemical performance of several electrode coatings has been determined using both a small scale conventional coin cell testing and a larger scale A5 sized pouch cell test for verification of coating quality and performance consistency. This work illustrates how this type of research is needed for any new electrode chemistry to be verified on production scale, before industrial entities can take up said material for implementation. In conclusion, this work highlights the challenges of scaling up electrode chemistries from lab scale to pre-production scale. NCA coatings have been prepared using several litres of slurry mix and A5 sized pouch cells have been manufactured in order to confirm electrochemical performance variation depending on coating and mixing parameters as well as overall coating consistency.