Lithium Ion Battery Separators

Targray carries Lithium-ion battery grade Polypropylene (PP) and Polyethylene (PE) Separators which play a critical role of separating the cathode from the anode. It is this separation of charge that allows the battery to generate electricity.

Separators are power-driven spacers and can be produced with fiberglass cloth or flexible plastic films made from nylon, polyethylene or polypropylene. It must be absorbent and slim to allow the charged lithium ions to pass without obstruction and it should take up the minimum of space allowed, leaving available space for the cathode active elements. The separators must be able to withstand penetration and branching moss-like crystalline minerals in order to prevent the electrodes from contamination. If the separator breaks down or is infiltrated, this will weaken high power cells end results.

During the charging cycle, the positively charged Lithium ions move from the cathode, through the Separator, to the anode. During discharge, the positively charged Lithium ions move from the anode, through the Separator, to the cathode while electrons move through the external load from the anode to the cathode, resulting in the current that provides power to the load. The Lithium ions move through the Separator via an Electrolyte solution.

Requirements for separators vary depending on the battery grade application. Producers of Lithium ion batteries using organic electrolytes should use microporous films as separators, as this will yield best results for performance, safety and costs. Factors to selecting the right separator are ¹:

• Electronic insulator
• Minimal electrolyte (ionic) resistance
• Mechanical and dimensional stability
• Sufficient physical strength to allow easy handling
• Chemical resistance to degradation by electrolyte, impurities, and electrode reactants and products
• Effective in preventing migration of particles or colloidal or soluble species between the two electrodes
• Readily wetted by electrolyte
• Uniform in thickness and other properties

Lithium Ion Battery Separator
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Process	PE / PP Single or Double Layer Dry Method
Pros	Uniformity in thickness Strong chemical resistance High wet ability, high EL absorption High MD tensile strength Thermal shutdown easy control (PE) Low cost (PE) Environmental friendly process Low contamination in product Thicker separator possible Competitive quotation Flexibility tailor-made products
Cons	Lower TD tensile strength (PE) Lower puncture rate (PE)

¹ Battery Separators, Chem. Rev 2001, 104, 4419-4462, Pankaj Arora and Zhengming (John) Zhang.