With the rapid development of electric vehicles and the energy storage industry，the production scale of high-rate batteries such as lithium batteries expands continuously，and the efficiency and power density of direct current converters in the battery formation process become research hot spots in the industry.In view of the shortcomings of traditional high-gain direct current converters，such as the high voltage stress of high-voltage side devices，the large current stress of low-voltage side devices，and the low efficiency and power density，a high-gain direct current converter topology suitable for the intermediate stage of the battery formation power supply system is proposed.A circuit structure in which two symmetrical half-bridge LLC resonant converters based on gallium nitride devices are connected in series on the high-voltage side and in parallel on the low-voltage side is adopted，which realizes automatic voltage sharing on the high-voltage side and automatic current sharing on the low-voltage side and reduces device stress.Furthermore，the height of the converter is reduced，and the power density is improved through the interleaved complementary modulation strategy and planar magnetic technology.Finally，a finite element simulation model and a 2 kW experimental platform are built to complete the simulation and experimental verification.