The energy transition to a renewable and sustainable generation will be the solution to reduce greenhouse gas emissions and thus achieve the European Commission´s goal of becoming the world´s first decarbonized economy.

This is why energy storage becomes indispensable, since it makes more flexible the intermittence of green energy generation systems (such as solar and wind), releasing energy when demand is high and storing it when demand is lower.

But how do we store energy?

The solution is to transform electrical energy into other types of energy that can be stored. In fact, many technologies allow transforming and storing that energy efficiently:

• Electrical energy, such as supercapacitors, which can store electrical charges inside them and release them extraordinarily quickly, generating very intense electrical currents.
• Mechanical energy, such as flywheels or hydraulic pumping, where companies like Iberdrola are world leaders in hydroelectric energy storage.
• Thermal energy, such as large-scale storage, for industrial processes, or storage for thermal management of electrical and electronic components.
• Chemical energy, such as hydrogen, although it is working to improve its efficiency, is the type of storage that has taken the lead in recent years because it will be key to decarbonize segments of the economy that are difficult to electrify.
• Electrochemical energy, with the clear example of batteries.

These two last types of energy storage -hydrogen and batteries- have been considered by the European Union as strategic values to make the transition to a competitive, sustainable and safe economy a reality.

In the case of hydrogen, the European Commission has just launched what has been called the "European Strategy for Hydrogen", a key commitment to decarbonize transport, building and industry, among other sectors, with a roadmap that leads to a situation of zero emissions in 2050.

On the other hand, the battery sector has seen how the strategic plan of the European Commission has led to the development of some relevant initiatives such as BatteRIes Europe and its derivatives Batteries 2030+ (with a long-term roadmap) or Horizon 2020 (with medium-term objectives), this last one with 4 CIC energiGUNE projects approved in the last year: SAFELiMOVE, HIGREEW, COFBAT, and 3beLIEVe. These initiatives will help consolidate Europe as one of the world leaders in the battery sector, promoting an industrial network that can reach 250,000 million euros in 2025.

Lithium-ion batteries

In this context of betting on electrochemical storage, there is a clear preponderance towards lithium-ion batteries.

Despite being one of the smallest elements in the periodic table, Lithium has a high electrochemical potential and is can accumulate large amounts of energy very efficiently. Furthermore, this type of battery has a low weight, making it ideal for mobility, as is the case with the electric vehicle.

Much of lithium batteries´ popularity was due to the expansion, from the 90s onwards, of the market for electronic devices (laptops, cell phones...). Moreover, in recent years due to its use in the electric automotive sector.

And although there are still some challenges to be faced in terms of safety, cost and useful life, it is considered that lithium batteries will continue to be a reference technology, at least until 2030.

In fact, the OECD (Organization for Economic Cooperation and Development) foresees a development of lithium batteries categorized in 4 phases:

• Phase 1: Consolidation of current batteries until 2025
• Phase 2: Penetration of the new generation of hybrid batteries, for example, combining the current lithium-ion with new rechargeable technologies, such as zinc-air or supercapacitors (two of the research lines on which we are already working at CIC energiGUNE) as a way to lower costs and develop competitive solutions in some applications.
• Phase 3: Development of what is known as advanced lithium, where solid electrolytes will become more relevant.
• Phase 4: Beginning of the beyond-lithium phase (post-Li).

This last phase is estimated to correspond to the 2030s; a challenging yet exciting stage, where there will not be a single technology that will cover all the applications, according to the different challenges that each of them has (cost, security, lifetime, energy density...). Instead, it will lead to the coexistence of different technologies such as metal-air, lithium-sulfur, redox flow... which, also, will specialize in different segments of storage: stationary, mobility, portability...

And even though lithium has come to stay, the great demand for this raw material, which is expected to be needed for the several existing applications, opens up new research streams such as sodium-ion.