UC Riverside

Energy storage technologies have developed rapidly in recent years due to their functions in grid regulation, energy transformation, and economic benefits. Among them, lithium-ion battery energy storage has been widely commercialized owing to its advantages including modularized design, rapid response, and high efficiency. The significant problem with lithium batteries at present is safety considerations because of the flammable organic components contained in the electrolyte. In addition, lithium battery energy storage is far from meeting global energy demand in the next few decades.

Aqueous Zinc-ion batteries have been widely studied due to their low toxicity, low cost, and high safety. The advantage of pure metal anodes over intercalated anodes is that they take full advantage of their high theoretical capacity in the metallic state (820mAh/g) and low electrochemical potential (−0.762V vs. SHE). However, the current major challenge for zinc metal anodes is dendrite growth, which potentially causes anode corrosion and further affects the reversibility of the anode.

In this research, we focus on investigating the functions of electrolyte additive - vanillin (C8H8O3) that improves the reversibility of the zinc metal anode. Computation- ally, we use ab initio density functional theory (DFT) calculation to explain the roles that vanillin plays in displacing water from the solvation shell of Zn ions in the electrolyte with and without the effect of the zinc surface. In addition, by integrating the experimental results on the potential vanillin decomposition, we investigate the binding energy preferences and charge transfer among electrolyte molecules with various vanillin derivatives. Furthermore, through molecular dynamics (MD) simulation, we explained the self-assembly mechanism with respect to the initial vanillin orientation placement at the zinc metal anode surface. Later, we investigated the Gaussian Process Regression (GPR) informed Bayesian Inference method to accelerate the exploration of the self-assembly process of finding the global minimum energy configuration without consuming additional computing resources by cooperating with the auxiliary force results.

In summary, the experimental results from our collaboration group show a boost in Coulombic efficiency from 95.38% to 99.34% by the electrolyte additive vanillin. Computationally we demonstrated that there exists a strong driving force for vanillin to replace one water molecule of zinc solvation shell in the highly concentrated electrolyte. In addition, the product of vanillin decomposition H-C8H8O3-Cl binds more strongly to the zinc metal anode than vanillin itself which further reveals that H-C8H8O3-Cl molecules create a passivation layer inhibiting hydrogen evolution reaction. Last but not least, the established Gaussian Process Regression approach provides landscape scanning at the early stage to inform the potential wells’ position so that the following downhill search optimization can be accelerated, and to make the informed decision on the initial structure configuration inputted into traditional DFT and/or MD relaxation to avoid performing many costly minimization calculations.