Low resistivity PPTC to improve Li-ion polymer battery packs

Since the technology was developed in the 1970s, LIBs have improved dramatically in terms of energy density, cost, durability, and safety.

The three main functional components in a lithium-ion battery cell are the anode (typically graphite), the cathode (typically lithium cobalt oxide), and a non-aqueous electrolyte (typically a lithium salt or organic solvent containing complexes of lithium ions).

The material choices affect a cell’s voltage, capacity, life, and safety. Li-ion cells are available in a cylindrical solid body, prismatic semi-hard plastic/metal case, or pouch form, which is also called Li-polymer.

Although pouch cells and prismatics have the highest energy density, they require some external means of containment to prevent an explosion when their State of Charge (SOC) is high (see Figure 1). Overheating is the main safety concern for lithium-ion cells.

Overheating causes thermal runaway of the cells, which can lead to cell rupture, re, or explosion. A deep discharge event could cause internal shorts in the cell, which would cause a short circuit upon charging.

Over-charging and deep discharge/short-circuit events create heat (generated by the anode of the cell) and oxygen (created by the cathode). Both of these effects can be dangerous to the cell and cause bloating (in the case of Li-polymer pouch cells), rupture, re, or even an explosion.

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