January_February_2022_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y / F E B R U A R Y 2 0 2 2 2 9 Argentina, China, and the U.S. As de- mand for Li increases, its extraction from alternative sources like seawater is also being considered. Whatever the sourcing method, the extracted lithium and other important battery element (e.g., iron, manganese, cobalt, and nick- el) compounds have varying degrees of elemental purity and require analysis to determine their composition. Li-ion batteries comprise a cath- ode, anode, electrolyte, and separator (Fig. 1). The cathode and electrolyte both require Li; compounds such as lithium iron phosphate (LFP) and lithi- um nickel cobalt aluminum oxide (NCA) are used for the cathode, while lithium hexafluorophosphate (LiPF 6 ) is used for the electrolyte. The purity of these materials is critical for meeting perfor- mance criteria such as achievable bat- tery power output, storage capacity, and maximum number of charging/dis- charging cycles. Elemental impurities can also af- fect the safety of Li-ion batteries; poor cathode and electrolyte purity can cause electrical shorting, rapid dis- charge, and overcharging. As such, Li- ion battery production is regulated to ensure sufficient quality and purity of materials. For example, the Chinese na- tional standard method, YS/T 789-2012, sets concentration limits for impurities in the range of < 1 mg/kg for a range of elements, including sodium, potas- sium, magnesium, copper, zinc, and lead [1] . Cathode and Anode Impurities. The composition of the cathode deter- mines the Li-ion battery’s properties, such as how much charge it can hold and how many times it can be charged and discharged. Li-ion battery cathodes are typically made from a mixed-met- al oxide base, such as nickel (Ni), co- balt (Co), or manganese (Mn) oxides, together with lithium. For example, manganese- and iron-containing cath- odes have a shorter lifespan than those based on other materials (e.g., cobalt), but they are cheaper to produce. These materials need to be high- ly purified and produced with a high degree of batch-to-batch composi- tion consistency in order to maintain optimum performance over multiple charging and discharging cycles. The presence of elemental impurities such as vanadium and sulfur disrupts battery performance and causes rapid degra- dation of the cathode materials. More- over, impurities from the cathode can build up on the opposing anode and are major sources of degradation products arising from interactions between the cathode and the electrolyte. Electrolyte Impurities. The elec- trolyte plays an important role in pro- viding the battery output and charging/ discharging cycle performance. The most common Li salt used in electro- lytes is LiPF 6 mixed with solvents like ethylene carbonate and dimethyl car- bonate. The presence of impurities such as water and transition metals in the electrolyte significantly degrades bat- tery performance. This can reduce the charge-carrying capacity of the battery and cause it to degrade faster during charging/discharging cycles. MONITORING ELEMENTAL PURITY The accurate determination and quantification of metal oxide elements and trace impurities in Li-ion battery materials is crucial for advancing and scaling up battery production, research, and development. As previously men- tioned, techniques available for this analysis include ICP-OES and ICP-MS. ICP-OES and ICP-MS methods are key to purity analysis in battery man- ufacturing, providing the robustness, sensitivity, detection limits, and high sample throughput needed to meet the demands for elemental analysis of bat- tery materials. These techniques have become an integral part of routine an- alytical workflows in many laborato- ries and can be easily implemented and operated by less-experienced an- alysts as well as experts. The latest generation of ICP-OES and ICP-MS in- struments provide complete solutions for all elemental analysis aspects of Li-ion battery research, development, and production. Fig. 1 — Components of lithium-ion batteries.