Evaluation of Battery Raw Materials
Lithium-ion batteries are composed of positive electrode materials, negative electrode materials, separators, and electrolyte solution. Individual completed batteries are referred to as cells and assemblies of multiple cells packaged together are referred to as modules. The evaluation of batteries requires an extremely wide variety of methods because batteries are assembled from a variety of materials, such as ceramics, polymers, and an electrolyte solution, because they involve electrochemical changes due to charge-discharge cycles, and also because they are difficult to handle due to their sensitivity to air and moisture. Therefore, batteries require multifaceted evaluations using a wide variety of analytical instruments. For safety reasons, reliability testing and safety evaluations that involve physical destruction are essential.
Positive electrodes are typically created by applying a slurry mixture of positive electrode active materials, a binder, conductive additives, and other materials onto aluminum foil, and then drying and press forming the coated foil. Positive electrode materials typically consist of a ternary (NMC) or lithium iron phosphate (LFP) cathode material, polyvinylidene fluoride (PVDF) as a binder, carbon black or other such substance as a conductive additives, and n-methylpyrrolidone (NMP) as a solvent.
Because the raw materials can affect the energy density, safety, service life, and other performance characteristics of batteries, it is important to evaluate their particle properties, thermal properties, composition, and other characteristics.
Negative electrodes are typically created by applying a slurry mixture of negative electrode active materials, a binder, conductive additives, and other materials onto copper foil, and then drying and press forming the coated foil. Negative electrode materials typically consist of graphite,
styrene-butadiene rubber (SBR) or carboxymethylcellulose (CMC) as a binder, carbon black or other such substance as a conductive additives, and water as a solvent.
Because the raw materials can affect the energy density, safety, service life, and other performance characteristics of batteries, it is important to evaluate their particle properties, thermal properties, composition, and other characteristics.
Separators consist of a porous membrane used to separate positive electrodes from negative electrodes. Whereas ions can normally pass back and forth through the pores, the pores close up if the battery becomes hot. Thus, the separators serve to prevent uncontrolled heating. Separators are mainly made of polyethylene or other polyolefin polymer. It is important to evaluate the physical and thermal properties of separators and their composition, because separators must not obstruct lithium ion movement during charging-discharging and must be electrically insulative and mechanically strong in order to prevent short-circuiting between positive and negative electrodes.
The electrolyte is the substance located between the positive and negative electrodes that includes the ions that serve as a carrier. For liquid lithium-ion batteries, the electrolyte is referred to as an electrolyte solution, which consists of a mixture of ethylene carbonate (EC) or other organic solvent, lithium hexafluorophosphate (LiPF6) or other lithium salt, and vinylene carbonate (VC) or other additive. Because the electrolyte solution status can affect battery performance, it is important to evaluate its composition.
For all-solid-state batteries, three types of solid electrolytes, referred to as oxide-based, sulfide-based, and polymer-based electrolytes, are typically used. Because the status of solid electrolytes can affect battery performance, it is important to evaluate their particle, surface, and thermal properties as well as their chemical composition and other characteristics.
The electrodes included in batteries are made from a variety of materials, such as active materials, conductive additives, and binders. Consequently, the networks for conducting electrons and ions formed by such materials in electrodes have a major influence on battery performance. Furthermore, because the status of those networks can vary due to charge-discharge cycles, detailed analysis of the factors that affect long-term battery performance and safety is necessary. Therefore, it is important to evaluate the physical properties and composition of electrodes, a process that includes evaluating electrode conductivity before and after charging-discharging, evaluating the SEI layer formed by charging-discharging, and controlling the quantities of residual organic solvents contained in electrode slurries.