Interface reactions and interphase formation

While chemical reactions ranging from interface bonding to compound formation are common in condensed matter systems, the electrochemical environment of energy storage systems poses a multiplicity of mechanisms for reactions that degrade the system, particularly during operation. As ions are driven between anode and cathode, they cause structural stress associated with volume changes in each of the materials, accompanied by direct phase change and/or chemical reaction in the electrode materials. Electrode voltages can decompose common liquid electrolytes, leading to interfacial layers such as the solid-electrolyte-interphase (SEI). While the SEI can partially suppress further degradation, it is can be unstable with respect to further charge/discharge cycles and underlying electrode stresses.
What is needed is a re-engineering of the electrode/electrolyte interface – a new interphase. This is true not only for existing battery chemistries but particularly to realize higher energy density batteries. A central example in the search for high energy anode materials, where Li has long been regarded as the ultimate choice, but its high chemical/electrochemical reactivity and tendency toward dendrite formation precludes its use for high performance batteries.

Synthesis of artificial interphases as protection layers

We have shown that thin coatings, produced by ALD or direct electrochemical reaction on high energy electrodes (Li, Si, and conversion materials), can significantly extend the working cycle life of electrode materials. This prescribes an opportunity to engineer thin multifunctional protection layers for electrodes, serving as interphases to transport ions while preventing degradation reactions, managing mechanical stress, and reducing voltages seen by the electrolyte.