Investigation on the Application of Microporous Current Collector in Ultra-Fast Lithium-Ion Full Battery

Abstract

The widespread popularity of lithium-ion full batteries (LIFBs) has gradually demonstrated the need for fast charge and discharge. In this article, the application of microporous copper foil current collector (MC) and microporous aluminum foil current collector (MA) prepared by electrolytic etching in ultra-high rate LIFBs was studied. Compared with conventional copper foil current collectors (CC) and aluminum foil current collectors (CA), MC–MA has better electrical performance and safety performance in an ultra-high-rate system. The pore size of MC is mainly distributed in 2–10 μm, and MA is mainly distributed in 1–15 μm. Scanning electron microscope shows that the pore structure on MC–MA is a disordered pore. The formation of micropores weakens mechanical strength and elongation of the current collector. The strength of copper foil before and after pore-forming decreased from 317.77 to 305.21 MPa, and the elongation decreased from 5.4 to 2.26%. The strength of aluminum foil before and after pore-forming decreased from 287.24 to 237.83 MPa, and the elongation decreased from 3.16 to 1.74%. However, there was no significant change in the thickness and areal density before and after pore-forming. The formation of micropores increases the three-dimensional interface contact sites of the current collector, thereby improving adhesion strength and reducing the resistivity of the electrode. However, too many contact interfaces also face more side reactions, which also cause the self-discharge and high-temperature storage of MC–MA (0.033) to be slightly worse than that of CC–CA (0.030). The electrochemical results show that MC–MA has a larger specific capacity, better rate performance, and lower electrochemical impedance. The capacity retentions of MC–MA after 500 cycles at 5C and 10C were 84.81 and 76.96% and CC–CA were 81.85 and 62.43%, respectively. The capacity retentions of MC–MA and CC–CA are 84.20 and 73.78% after 500 cycles at 5C charge and 15C pulse discharge. The cell disassembly found that lithium dendrites were the main cause of the capacity decay. The excellent three-dimensional interface of micropore provides more reaction sites, and two-dimensional surface defects reduce current density distribution and realize uniform distribution of lithium ions at different phase interfaces. The micropore provides stress release space for volume expansion of charge and discharge and improves voltage hysteresis caused by compressive stress at the interface between the current collector and materials coating. In addition, due to pore structure changes in the elastic deformation ability and surface current density distribution of the current collector, the safety performance of LIFBs is improved.