Storage of renewable energy remains a significant challenge for the implementation of a future carbon neutral and sustainable society based on renewable energy. New technologies providing a paradigm shift for energy storage may likely be based on novel materials with new functionalities. This review provides new perspectives for rational design of functional materials for energy storage using dynamic, disorder or entropy effects as a design concept. These effects may be introduced into the solid state using complex anions such as BH4- or B12H122-. These dynamic effects may facilitate anion substitution and preparation of materials that may stabilize high temperature polymorphs at lower temperatures. This has provided new ion conductors for lithium batteries and perovskite type metal borohydrides, which can be modified to resemble the well-known useful metal halide photovoltaics. Completely new metal hydrides, which stores hydrogen and may also be ion conductors or have magnetic, optical or electronic properties may be designed and prepared. This review reveals extreme structural and compositional flexibility of metal hydrides and provides new inspiration for rational materials design towards multi-functionality.