Next Generation Batteries
Next Generation Batteries (NGBs), or sometimes 'post - lithium batteries', is a collective name for batteries that are being researched and developed due to the limited availability of lithium and other substances in lithium-ion batteries, such as graphite and cobalt. The development of NGBs aims to provide batteries with energy density, longer service life, low cost, versatile uses and reduced / no lithium content.
High-performance batteries are needed for the development of electric vehicles, portable electronics and greener energy storage systems. The term post-lithium batteries may seem somewhat confusing as it still includes lithium-based batteries, but post-lithium refers to technologies developed after the lithium-ion battery, which was commercialized in 1991 by Sony. 
Batteries such as lead-acid, nickel metal hydride (NiMH), nickel cadmium, ZEBRA, and sodium sulfur, and others do therefore most often not count as NGB. Typical NGBs are based on sodium (Na), magnesium (Mg), calcium (Ca), aluminium (Al), etc.
Different types of next generation batteries
With examples from today's lithium batteries, lithium-ion batteries are cells where lithium ions are intercalated at the anode, typically into graphite. Lithium-metal batteries, on the other hand, have an anode of pure lithium where lithium is plated on the surface. A collective name for both concepts is lithium battery, but sometimes this name (a little confusing) is also used for only lithium metal batteries or lithium-ion batteries. The same applies to NGB: sodium / sodium-ion, magnesium / magnesium-ion, aluminium / aluminium-ion, etc. In addition to this basic rule, there is also NGB where the cathode is specified: lithium-sulfur (Li-S), lithium-oxygen, or more commonly lithium-air, Li-O2. These sulfur and air batteries are also available in variants where Li has been replaced with Na, Mg, Ca, or Al.
Sodium-ion batteries (Na-ion batteries) are based on the same technology as lithium-ion batteries (Li-ion batteries) but have Na+ as a charge carrier instead of Li+. During discharge, electrons migrate from the negative electrode (anode) to the positive electrode (cathode) via an external circuit. Na+ smooths out the charge differences that form and therefore migrates to the positive electrode inside the cell. Sodium is the fourth most abundant element in the Earth's crust and has an inexpensive and non-energy-intensive extraction process. 
Sodium does not form alloys with aluminum which allows aluminum current collectors, while Li-ion batteries must use copper current collectors - which are considerably heavier and above all more expensive. The challenges for Na-ion batteries are mainly to find suitable anode materials. Unfortunately, graphite used in Li-ion batteries cannot be used in Na-ion batteries - instead other anode materials are investigated, such as hard carbons, often with lower capacity. Today both Tiamat, France and Faradion, UK, commercialize the sodium-ion battery technology.
Lithium-sulfur batteries (Li-S) have attracted great interest due to a high theoretical energy density and because sulfur is cheap, commonly found and has a low environmental impact. The Li-S batteries consist of an electrode of sulfur and one of lithium metal. The main challenges with Li-S batteries are low practical energy density, decreasing capacity and low electrical conductivity of sulfur - sulfur is an insulator.  It is counteracted by working with high-surface carbon-sulfur composites on the carbon as anodes.  Decreasing capacity is a consequence of "shuttling" - which is a process where sulfur in the cathode during discharge forms polysulfides which dissolve in the electrolyte and during charging react with the anode.  The shuttling effect can be counteracted by i) oxidizing the polysulfides before they reach the anode, ii) cover the anode with a protective layer, or iii) prevent the polysulfides from entering the electrolyte by using nano-porous carbon cathodes. Higher concentrations of salt in the electrolyte have also been shown to reduce the shuttling effect, but this also increases the cost of the battery. 
NGBs based on di- or trivalent metals can exchange more than one electron per cation. This results in high theoretical energy density. These technologies are based on inexpensive and commonly used metals such as magnesium, calcium and aluminium. The major challenge for rechargeable multivalent batteries is the service life of the number of recharges and recharges. Multivalent batteries may play an important role in future large-scale energy storage. 
The magnesium ion, Mg2+, can carry two charges per atom, and as an anode material, magnesium has closer to the double volumetric capacity compared to lithium.  Magnesium is the eighth most abundant element in the Earth's crust and is inexpensive. Mg2+ has approximately the same radius as Li+, which in theory implies that the same cathode material used in Li-ion batteries could also work for Mg batteries, but this has proved difficult to apply in practice when Mg2+ tends to react with the cathode and form MgO which impairs the reversibility of the reaction and thus the number of times the battery can be recharged . Mg2+ has low diffusion in solids, which impairs the battery's ability to high power output. Analogous to the Li-ion battery, a new solid phase is formed in the interface between electrolyte and anode (SEI) on the Mg metal. SEI in Mg batteries often results in Mg ions poorly and therefore new electrolytes are also needed.
The calcium ion, Ca2+, has two charges per atom just like Mg2+ and the element is the fifth most abundant in the Earth's crust.  Two of the most promising properties of Ca batteries is the faster diffusion of Ca2+ as compared to Mg2+ and that the potential is much closer to lithium metal. The latter means that the cell voltage can be largely the same but with much higher capacity in the electrodes especially the negative. A major challenge for Ca batteries just as for the other multivalent batteries is to find compatible positive electrode materials. Another problem is finding electrolytes where the battery can operate at room temperature together with calcium metal. 
Aluminium is cheap and the third most abundant element in the Earth's crust. Al3+ can carry three charges per atom, which has the advantage that the battery has a high theoretical energy density. Al does not react with air which means that the production of Al batteries does not pose risks, as the production of Li batteries does.
The main challenges of Al-ion batteries consist in finding electrode materials that work with Al3+, as well as the limited range of electrolytes available. Graphite electrodes are capable of intercalating Al3+, but as the electrolyte produces AlCl4− anions, they will be intercalated simultaneously. This results in the amount of electrolyte constituting a limiting factor for the capacity of the battery which lowers the energy density. Unfortunately, Al-ion batteries cannot copy the technology of a Li-ion battery because Al3+ would react strongly and irreversibly with the cathode.
Al-organic batteries use a technology where the anode consists of Al and the cathode of organic material.  Other multivalent metals also use this technology. These have the advantage of high theoretical capacity and that they can be manufactured at room temperature, which lowers the environmental impact of the batteries. However, this development has some way to go before it can be industrialized.
Energy storage on the electricity grid
In order to increase the amount of renewable energy available, large-scale energy storage opportunities are needed to be introduced on the electricity grid. Solar cells can only produce energy during the day and wind power is dependent on weather conditions. NGB has the opportunity to play a major role in the expansion of renewable energy on the electricity grid. These NGBs do not necessarily have high energy density, but should be cheap, durable and have low maintenance requirements. When multivalent batteries have increased in maturity, they have good potential to match the characteristics demanded for large-scale energy storage.
The transport sector is responsible for about 30% of the World's Carbon dioxide in Earth's atmosphere emissions. Electric vehicles may be the solution, but this requires that the batteries used have a reduced environmental impact. Cars, buses, trucks, boats and aircraft are vehicles that could be electrically driven on a larger scale when better technologies than lithium-ion batteries are available. The challenge with batteries in electric vehicles is to find batteries with higher energy density so that longer driving distances without stopping for charging can be achieved. Batteries that are able to recharge quickly without losing capacity are also sought after.
Recycling (as alternative to NGBs)
Related to the introduction of NGBs, another way to reduce the lithium consumption is through recycling. Recupyl in France and Accurec in Germany are examples of companies exploring the opportunities . Current recycling methods of Li-ion batteries do not recover any lithium at all. The most common industrial recovery methods are pyrolysis and pyrometallurgy. The focus is there on seizing cobalt, nickel, copper and the rest becomes slag with lithium and alloys. Cobalt is the most valuable metal on the list and its price affects the profitability of recycling. Previously, it has not been profitable to recycle lithium, which has reduced companies' efforts to do so. 
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