This survey comprehensively reviews state-of-the-art research on non-isolated multi-port DC-DC converters for electric vehicle (EV) applications, emphasizing advancements in efficiency, reliability, and scalability. The analysis delves into key design parameters, including converter topologies, control strategies, efficiency optimization, and power density improvements. Innovative designs, such as coupled-inductor configurations, voltage multiplier circuits, and wide-range bidirectional buck-boost topologies, address critical EV requirements, including high voltage gain, low electromagnetic interference (EMI), and reduced component stress. Key techniques discussed include soft-switching methods and interleaved configurations, both of which enhance energy efficiency reaching up to 97.6% in select cases while mitigating thermal challenges. Bidirectional converters for regenerative braking and adaptive control strategies for dynamic power flow optimization are also evaluated for their contributions to improving system reliability. The integration of artificial intelligence, such as neural networks for maximum power point tracking (MPPT), and the use of advanced materials to enhance passive components underscore the innovative progress in this domain. Despite these advancements, challenges persist, including complex control strategies, increased device counts, and high initial costs. Multi-port architectures emerge as particularly promising for hybrid energy management, integrating multiple energy sources while minimizing hardware redundancy. By consolidating these findings, this survey highlights the transformative potential of non-isolated DC-DC converters for EV powertrain systems. Simultaneously, it identifies research gaps, paving the way for advancements in high-performance, cost-effective, and sustainable power conversion technologies.