The effect of Li(Ni0.9Co0.05Mn0.05)O2 on improving electrical properties of semi-conductive LDPE/EVA/CB composites

The conductive mechanism of the semiconductor shielding layer between the conductive core and the insulation layer of high-voltage direct current (HVDC) cables includes tunneling and over-diffusion theories; however, the ethylene vinyl acetate copolymer (EVA) matrix in the semi-conductive composite material expands when heated, leading to a break in the carbon black (CB) conductive networks, which results in an increase in resistivity and the formation of the positive temperature coefficient (PTC) effect. The addition of materials with negative temperature coefficient (NTC) properties can weaken the PTC effect while absorbing some free electrons to enhance the suppression of space charge injection into the insulating layer. Li(Ni0.9Co0.05Mn0.05)O2 (NCM) was prepared by sol–gel method, which was melted and mixed with low-density polyethylene (LDPE), EVA, and CB, and pressed and molded to obtain modified semi-conductive composites. The semiconducting composites were measured by resistivity, thermal stimulation depolarizing current method (TSDC), and pulsed electroacoustic method (PEA). The results showed that the composites had the best performance when the NCM doping was 2 wt%.