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Inexpensive and Stable - the Salt Water Battery

Research on the water electrolyte: Empa researcher Ruben-Simon Kühnel connecting a test cell to the charger with the concentrated saline solution. The stability of the system is determined in several charging and discharging cycles. (Empa)

Research on the water electrolyte: Empa researcher Ruben-Simon Kühnel connecting a test cell to the charger with the concentrated saline solution. The stability of the system is determined in several charging and discharging cycles. (Empa)

January 29, 2018 | Source: Phys Org, phys.org, 9 January 2018, Rainer Klose

Water could form the basis for future particularly inexpensive rechargeable batteries. Empa researchers have succeeded in doubling the electrochemical stability of water with a special saline solution. This takes us one step closer to using the technology commercially.

In the quest to find safe, low-cost batteries for the future, eventually we have to ask ourselves a question: Why not simply use water as an electrolyte? Water is inexpensive, available everywhere, non-flammable and can conduct ions. However, water has one major drawback: It is chemically stable only up to a voltage of 1.23 volts. In other words, a water cell supplies three times less voltage than a customary lithium ion cell with 3.7 volts, which makes it poorly suited for applications in an electric car. A cost-effective, water-based battery, however, could be extremely interesting for stationary electricity storage applications.

Ruben-Simon Kühnel and David Reber, researchers in Empa's Materials for Energy Conversion department, have now discovered a way to solve the problem: The salt containing electrolyte has to be liquid, but at the same time it has to be so highly concentrated that it does not contain any "excess" water.

For their experiments, the two researchers used the special salt sodium FSI (precise name: sodium bis(fluorosulfonyl)imide).