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Battery energy storage systems are widely used for renewable power generation and electric transportation systems. Bidirectional DC-DC converters (BDCs) are key components in such systems, enabling bidirectional power flow in battery charging and discharging modes. BDCs can be categorized into isolated and non-isolated. Non-isolated BDCs have lower volume, weight, and power losses, suitable for compact structures without needing galvanic isolation. In this paper, a comprehensive literature review is conducted for non-isolated BDCs, covering soft switching, current ripple reduction, high voltage gain and resiliency techniques. Soft switching aims to reduce switching losses and improve efficiency, including auxiliary circuits and non-auxiliary methods, such as interleaved structures, phase-shift modulation, and synchronous rectification. Current ripple reduction focuses on capacitive loop configurations, interleaved structures, and coupled inductor-based methods. Batteries are low-voltage power sources, BDCs can increase the output voltage to a level required by the applications through an appropriate voltage gain, and high voltage gain techniques include capacitor-based, magnetic-based, and combined networks, and mixed structures. Resiliency is explored to ensure reliable operations under adverse conditions. This review provides valuable insights into developing more efficient, reliable, and high-performance BDCs, addressing the evolving demands of modern energy systems. Future research directions in non-isolated BDCs are recommended in this paper.