Electrolytes

Archer discovered that adding certain halide salts to liquid electrolytes creates nanostructured surface coatings on lithium battery anodes that hinder the development of dendritic structures that grow within the battery cell and typically lead to a decline in performance and overheating.^[28] This study was conducted by modeling metal electrodeposition using density functional theory and continuum mechanics.

By adding tin to a carbonate-based electrolyte, Archer's group observed the instantaneous formation of a nanometer-thick interface that shields the anode and prevents dendrite formation, but keeps it electrochemically active.^[29] Lithium can rapidly alloy with the added tin, which makes the lithium deposition during recharging more uniform. As a result, a lithium anode with a tin interface had a battery life cycle of more than 500 hours at 3 mA/cm², as opposed to 55 hours without the protective interface. Tin requires minimal amounts of specialized equipment and processing. In a cheaper sodium anode, battery lifetime could be improved from less than 10 to more than 1,700 hours.

Another way of preventing dendrite growth in batteries that Archer investigated was the addition of large polymers to the liquid electrolyte. The consistency of the liquid is altered: it becomes viscoelastic, which suppresses electroconvection and therefore prevents flow in patterns that enable dendrite formation.^[30] Archer also investigated the polymerization of a previously liquid electrolyte inside the electrochemical cell, which can improve the contact between the electrolyte and electrodes.^[31]

Membranes

Another way of inhibiting dendrite growth that Archer investigated is the incorporation of a porous nanostructured membrane, which prevents the formation of subsurface structures in the lithium electrode.^[32][33] The key nanoscale organic hybrid materials (NOHMs) were formed by grafting polyethylene oxide onto silica, subsequently cross-linked with polypropylene oxide to create strong, porous membranes. The intermediate porosity allows liquid electrolytes to flow but prevents dendrites from passing through. The incorporation of such membranes does not require significant changes in battery design. Archer's group found that such a porous electrolyte effectively lengthens the route along which ions travel between anode and cathode and thus increases the life of the anode.^[34] Additionally, the porous polymer membrane is softer than the metal, but can nonetheless act as an effective separator suppressing dendritic growth due to its tortuos nanostructure.

Archer investigated how tethering anions to the separator membrane in a battery can stabilize an electrochemical cell, which uses reactive metals as electrodes. The electric field at the metal electrode is reduced, which enhances stability during battery recharging even at higher currents, where usually a depletion zone forms due to ion migration, which in turn initiates dendrite growth. This depletion zone can be neutralized by permanently tethering anions to the membrane, which ultimately prevents battery failure. The method can be applied to lithium batteries, but also to batteries made of sodium or aluminum.^[35]

Anodes

In exploring alternative materials to lithium to be used in batteries, Archer discovered a way of treating aluminum films to prevent the formation of an aluminum oxide layer that prevents electrical charge transfer.^[36] The aluminum is coated with an ionic liquid containing chloride ions and a small nitrogen-containing organic compound. This treatment erodes existing aluminum oxide and prevents the formation of additional oxide.

Archer's research uncovered a way to build a low-cost zinc-anode battery with epitaxy by growing zinc on graphene, which creates a very stable, high-density energy storage in a reversible manner due to its electrochemical inertness.^[37][38]

Archer studied electrochemical cells that can both capture carbon dioxide and produce electricity.^[39][22] These devices consist of an aluminum foil anode, a porous and electrically conductive cathode, which allows for carbon dioxide and oxygen to pass through, and a liquid electrolyte bridging the anode and cathode through which molecules can diffuse. In experiments, such electrochemical cells generated 13 Ampere hours for each gram of captured carbon and converted carbon dioxide into aluminum oxalate, which can then be converted into oxalic acid.