The serpentine microchannel cold plate is widely used in the liquid cooling of lithium-ion batteries due to its high space utilization and excellent heat dissipation performance. Adding secondary channels to the serpentine microchannel can improve the cold plate's performance. The traditional parallelogram and herringbone secondary channels do not consider the changing state of fluid flow in the secondary channels. Based on the serpentine microchannel structures, the rhombus and circular secondary channel structures are proposed. And the influence of the fluid vortex inside the secondary channel on the performance of the cold plate is studied, and the performance is compared with that of the parallelogram and herringbone secondary channel structures. Then, the effect of the depression distance, width, relative position, and coolant flow velocity of the secondary channel on the performance of the cold plate is further studied by single-factor analysis using the 3D conjugative numerical simulation method. The results show that the parallelogram structure has the greatest heat transfer potential, and the rhombus structure has excellent performance in pressure drop and comprehensive performance. Compared with the original structure, the pressure drop of the optimized cold plate is reduced by 88.67%, and the overall performance is improved by 5.29 times.