Introduction

The growing energy crisis and environmental concerns caused by depletion of fossil fuels have been drastically promoting the development of renewable energy sources and storage
devices (1). The need for an efficient and sustainable way to store energy is an urgent necessity of the modern society. The large scale application of renewable energy production is limited by their intermittent production and by the inability to store the produced energy (currently less than one percent of the energy production can be stored), accordingly the development of efficient, low cost and environmental friendly electrochemical storage systems is fundamental for energy economy sustainability. The lithium ion technology, currently the power source of choice in portable electronic device, is the most mature technology. Unfortunately, due to the cost and somehow limited resources of lithium, the use of Li-ion batteries for large scale applications is nowadays under discussion (2).

Several other metal anode materials such as sodium, potassium, calcium, magnesium, and aluminum have been considered as suitable candidates for electrochemical storage devices, which are (see Figure 1) more abundant than lithium. Thus these materials are expected to reduce the cost of the alternative electrochemical storage systems and enable long-term sustainability. The most near to practical application is the sodium-ion system, due to the worldwide extensive research on sodium batteries in the last years (2).