| Lithium-ion batteries were highly favored because of its high energy, long cycle life, low self-discharge, no memory effect and advantages of green industry. The lithium ion batteries as a new green energy have substituted for the lead-acid batteries in the market. With the expanding of its application, the safety of lithium batteries, especially the safety of large power batteries, has become the focus of attention.Internal lithium battery from the high activity material, under heat conditions are very prone to violent chemical reaction, generate a lot of heat, and even lead to "thermal runaway", causing a rapid temperature rise inside the battery. Especially in battery abuse(such as short circuit, vibration, extrusion, strong impact, over discharge and over charge etc.), the battery will smoke, fire, explosion, and even personal injury and so on. Battery shell as a battery pressure inside and outside of the carrier, the flame retardance, impact of dangerous situation occurs in the battery to the crucial role, so this paper focuses on the lithium battery shell safety promotion.Currently lithium batteries commonly used polypropylene(PP) material as the battery case material. PP material with heat, Chemical resistant, etc., is one of the few electrolyte corrosion resistant plastic material, so the industry is currently widely used battery case materials.However, the PP has low oxygen index, so it burns easily in air and releases a lot of heat and fast spreads the fire during combustion. In order to improve the retardant properties of the PP, the flame-retardants which can significantly improve the safety of the battery were usually added, and the combustion and explosion does not occur when the battery abused.This research focused on selecting excellent intumescent halogen-free flame retardants(IFR) which acid source was Ammonium polyphosphate(APP) to blend with PP. Adding a small amount of melamine cyanurate(MCA) in the IFR as a synergistic flame retardant was to improve its flame retardant property. The results showed that: With the gradually increase of the adding amount of the IFR, there was a rapid increasing stage of the oxygen index(LOI) of PP. When IFR content reached 25%, the LOI value remained unchanged. And the value of LOI had exceeded 30 when the IFR content came to 25%. Flame rating had reached UL94V-0. We could also see from the comparison data: When IFR content reached 25%, its fire-retardant property was equal to PP composited with Bromo-antimony oxide flame retardant system. It could meet flammability rating requirements of the lithium-ion battery cases.The glass fiber and the polyphenylene were added in order to improve the mechanical properties of PP. The PP grafted with functional acrylic Glycidyl was added to improve the interfacial bond strength of fire retardant, glass fiber and PP substrate. Impact testing machine, universal testing machine, scanning electron microscopy(SEM), water vapor permeability tester and melt index tester were used to analysis the mechanical properties, fracture surface, water permeability barrier properties of the electrolyte melt flow respectively rates and so on. The results showed that: the tensile strength and toughness of the material was effectively improved by adding the glass fiber and the polyphenylene. The interfacial bond strength was improved by adding the PP grafted with functional acrylic Glycidyl so that the mechanical performance is better. Compared with the PP composed of Bromo-antimony oxide flame retardant system, the tensile strength was slightly higher and the notched impact strength improved significantly. Its toughness was batter. There were no significant differences in the water permeability and electrolyte weather resistance of intumescent flame retardant polypropylene material compared with pure PP. |
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