Impact of Metallic Impurities on the Synthesis and Properties of NMC Cathode Material Obtained by Co-Precipitation

Abstract

Among the different factors that influence lithium-ion batteries (LIB) performances, the properties of the cathode active material (CAM) play a crucial role. The composition, the crystallinity and also the particle size and morphology of these materials are part of the major parameters governing the CAM behaviour. These parameters are strongly dependent of the synthesis method, especially in the case of the hydroxide precursor of the layered LiNixMnyCozO2 [1].One of the most widely spread synthesis method of such precursors is the synthesis by co-precipitation, where metal salts of Ni, Mn and Co are precipitated together in a continually-stirred tank reactor (CSTR) in carefully controlled pH- and temperature conditions[2]. Any parameter of the co-precipitation must be precisely tuned to obtain the desired material, as highlighted in the figure here after.Considering the increasing presence of wanted (coating/doping)[3] and unwanted (impurities after recycling)[4] elements in the co-precipitation process, extensive knowledge of their impact on it is of great interest. Therefore, the synthesis of NixMnyCoz(OH)2 was conducted by co-precipitation with the controlled addition of increasing amounts of elements such as Cu and Al.The effects of these additions were investigated by thoroughly characterizing the morphology of the obtained hydroxides with the help of SEM, BET, particle size distribution and porosity measurements. The composition of the synthesized hydroxides was determined by the ICP-OES technique. The possible influence on the further step of CAM synthesis, i.e. calcination, was followed by in-situ X-Ray thermodiffraction and the electrochemical performances were assessed by galvanostatic cycling the obtained CAM in lithium half-cells. This helped to evidence the varying impact of the added elements, depending on their concentration in the synthesis process.This work is supported by the German Ministry for Economy and Climate Protection (BMWK).