Effect of micromechanical properties of commercial grade electrolytic copper foils on lithium-ion batteries

Abstract

As the carrier and electrical conduction component of positive and negative electrode materials, current collector plays an important role in lithium-ion batteries(LIBs). With the industrial application of silicon-doped anode materials with higher gram capacity, the huge volume change of silicon-doped anode materials puts forward higher requirements for the mechanical properties of copper foils(CFs). It is of great significance to study the effect of micromechanical properties on LIBs for the application screening of CFs. In this article, the effects of micromechanical properties of conventional tensile strength(CTS), high tensile strength(HTS) and ultra-high tensile strength(UHTS) commercial grade electrolytic CFs on LIBs were studied. The tensile strength of CTS, HTS and UHTS was 316.88 MPa, 464.74 MPa and 673.43 MPa, respectively; the elongation were 6.49 %, 5.38 % and 4.47 %, respectively. The surface morphology and XRD tests show that the microstructure such as grain size and dislocation density are the key factors affecting the mechanical properties of CFs. And under the same conditions, the main factors affecting bonding strength of electrode are microstrain and residual stress of CFs rather than surface roughness. The larger the microstrain and residual stress of CFs, the worse the interface bonding strength between CFs and coating materials, and the larger the corresponding interface charge transfer impedance, which is well confirmed by DCR and EIS. The charge-discharge test results show that the mutual stress between CFs and coating materials also have a great influence. The lower elastic modulus and microscopic stress of CFs can better eliminate the expansion pressure and contraction tension of coating materials, thereby reducing the resistance and overpotential in the process of lithium-ion diffusion, and achieving higher capacity under high rate system. The retention rates of three CFs after 500 cycles at 25℃ and 45℃ were 25-CTS(92.64 %), 25-HTS(90.63 %) 25-UHTS(89.11 %), and 45-CTS(82.17 %), 45-HTS(82.14 %), 45-UHTS(80.77 %), respectively, which indicates that the difference in mechanical properties of CFs have an important influence on long-term application of LIBs. The primary cause of the variation in electrochemical performance, aside from copper foil’s conductivity, is the phase interface shift brought on by the microstress of the material; and the overpotential caused by the phase interface force cannot be ignored.