Non-invasive detection and self-repair techniques for tomorrow's smart batteries : some approaches

Abstract

In this final lecture, we look at the importance of electrochemistry in harnessing blue energy, i.e. the energy derived from the mixing of liquids with different salt concentrations, such as freshwater and seawater via the phenomenon of osmosis. We began by recalling that osmotic pressure plays a fundamental role in many biological phenomena. Combined with capillarity, it is responsible, for example, for the absorption of water by plant roots, as well as for the upward movement of raw sap. Osmotic pressure triggers hemolysis, the destruction of red blood cells, and plasmolysis, the cellular state resulting from water loss. We have also pointed out that the phenomenon of osmosis is used to preserve meat with salt and fruit with sugar. So we understand why water rich in salts, such as that in the Dead Sea, is unsuitable for sustaining aquatic life.

The mixing flow of two waters of different concentrations is associated with a mixing entropy, and it was in 1954 that an English researcher (R.E. Pattle) proposed using this mixing energy and converting it into electricity. He demonstrated that the mixing energy associated with 1 ^m3 of salt water is equal to the energy that could be recovered from the fall of 1 ^m3 of water in a 250 m high waterfall. Based on such calculations, it is estimated that osmotic storage is superior to hydroelectric storage and, a priori, 1-2TW could be harvested worldwide if we took advantage of the various sources of salinity gradient (brines, wastewater). On the other hand, osmotic energy is much more difficult to recover than hydroelectric energy. It can be recovered by various processes known as i) delayed osmosis pressure (PRO), ii) reverse electrodialysis (RED) iii) or via an osmotic diffusion transport process developed by Lydéric Bocquet, which takes advantage of nano-fluidic technologies. Osmotic diffusion is a surface mechanism generated by an osmotic pressure gradient occurring in the first few nanometers of the pore surface. This osmotic concentration gradient at the pore surface leads to an ionic current known as osmotic diffusion. The energy potential of this new concept, which has already given rise to the creation of an SME called " SWEETCH Energie ", therefore depends on the nano-structuring of the membranes. It's also worth noting that energy recovery from different salinities can take place via a capacitor, in a four-stage cycle known as CAPMIX, which has a certain analogy with the thermodynamics of a four-stroke engine.

The reverse phenomenon of recovering mixing energy from concentration gradients is desalination via energy input. This is a major issue, given that water is still unavailable to one in seven people in the world. The current dominant technologies for water desalination are i) reverse osmosis, ii) distillation, and iii) electrodialysis, without forgetting desalination via capacitive de-ionization (e.g. via supercapacitors with multiple configurations). We'll also mention desalination batteries for Li recovery.

To sum up, blue energy is at first sight an attractive option. However, recovery technologies are problematic, with very limited yields. Numerous technological hurdles remain to be overcome before such energy can be taken into consideration in our energy mix.