The world's new energy policy is to reduce CO2 emissions and transition to low-carbon energy production, and thus green alternative energy and electric vehicles must be a top priority. This demands for large-scale energy storage systems, and therefore superior rechargeable batteries in terms of energy/power density are now required at a substantially lower cost. The next-generation batteries need to have high specific capacity and operating voltage, fast-charge ability, high safety, wide operating temperatures, long cycle life, and most importantly, environmental friendliness. Increasing needs in high energy density and superior power density will require the design and development of novel functional redox-active materials as electrodes. The limited excess to lithium resources will also require the discovery of new electrochemistry beyond lithium-ion battery (LIB) technology. New post-Li-ion batteries (PLIBs) based on the monovalent and multivalent charge carriers, such as Na+, Mg2+, and Zn2+, have the promise to deliver higher specific capacity and energy density at a lower cost. However, in order to materialize these new energy storage technologies, several challenges must be overcome and complete understanding of redox mechanisms must be achieved.