The introduction of Li-ion batteries (LIBs) has revolutionized our daily lives by enabling portable electronics and electromobility. However, the rapidly increasing demand for LIBs has led to a significant strain on the raw materials essential for Li-based energy storage systems and raised questions about their future price, availability, and, most importantly, the sustainability of their use. Calcium metal is an excellent candidate for next-generation batteries due to its low redox potential of −2.87 V (vs. standard hydrogen electrode, SHE) and high anode capacity. However, the development of Ca batteries is hampered by both a lack of practical electrolytes and cathode hosts. Significant progress has been made in recent years, particularly in the area of electrolytes that enable the reversible Ca metal plating/stripping and cathode materials that do not undergo traditional ion insertion mechanisms, such as organics and sulfur. Despite the progress, significant challenges still stand in the way of practical Ca battery application.

In this review, we aim to highlight the key obstacles that Ca metal batteries have to overcome on the way to practical viability. Improving Ca metal plating/stripping beyond 99% efficiency and developing highly reversible Ca²⁺ ion cathode hosts may require fundamentally different approaches than those currently in use. At the same time, computational modeling support can go a long way to improve our understanding of Ca electrochemistry and accelerate exploration of the available chemical space. When conducting studies on electrochemical Ca cells, researchers might be unaware of challenges connected with cell setups and electrolyte preparation that can affect experimental results. Therefore, complementary characterization techniques and comparisons across different cell setups are required to avoid erroneous conclusions and accelerate the development of Ca battery technology.