A Common Amino Acid Could Tame the Biggest Problem Holding Back Zinc Batteries

Aqueous zinc-ion batteries have long been touted as one of the most promising alternatives to lithium-ion technology for grid-scale energy storage. They are cheap, non-flammable, and built around one of the most abundant metals on Earth. Yet a stubborn trio of failures—hydrogen gas evolution, runaway dendrite growth, and the buildup of inert corrosion byproducts—has kept them out of practical commercial use. Now, a team of researchers in China reports that a simple, naturally occurring amino acid called sarcosine may be able to tame all three problems at once, using nothing more than a dash of the additive in the battery’s water-based electrolyte.

The study, published in Frontiers in Chemistry by Zijing Wang and colleagues at Xi’an University of Science and Technology, Beijing University of Chemical Technology, and Yan’an University, combined first-principles calculations, spectroscopy, and electrochemical testing to unravel exactly how sarcosine stabilizes the zinc metal anode. The answer, they found, lies in a two-pronged mechanism: the molecule simultaneously restructures the water hydrogen-bond network in the electrolyte and preferentially adsorbs onto the zinc surface, reshaping the interface where the most damaging chemistry occurs.

The core challenge is thermodynamic. In an aqueous zinc-ion battery, the hydrogen evolution potential at pH 5 sits at −0.296 volts versus the standard hydrogen electrode, which is more positive than the zinc redox potential of −0.76 volts. That means water molecules are reduced before zinc ions can plate cleanly onto the anode, generating hydrogen gas, depleting the electrolyte, and corroding the metal. Meanwhile, hydroxide ions produced by water hydrolysis react with zinc sulfate to form insoluble, electrochemically inactive byproducts such as Zn4SO4(OH)6·xH2O, which roughen the electrode surface and accelerate dendrite formation. Left unchecked, these processes culminate in internal short circuits and battery failure.

Sarcosine, also known as N-methylglycine, is a naturally occurring, inexpensive, water-soluble, and biodegradable amino acid. Its compact molecular structure pairs an amino group with a carboxyl group, giving it two distinct chemical handles. Density functional theory calculations revealed a strong molecular polarization: the O–H and N–H hydrogens carry local positive electrostatic potential maxima of 46.21 and 40.57 kcal mol−1 respectively, making them powerful hydrogen-bond donors, while the carbonyl oxygen carries a negative potential of −38.97 kcal mol−1, providing an electron-rich anchor site for zinc ions and for binding to the zinc surface.

Molecular dynamics simulations showed that sarcosine does not dramatically rebuild the primary zinc solvation shell. In a baseline ZnSO4 electrolyte, each zinc ion coordinates with about 5.76 water molecules; adding sarcosine only nudges that number down to 5.74, with a weak Zn2+–O(Sar) coordination number of 0.06. Instead of displacing water from the inner shell, sarcosine works through weaker, subtler interactions—hydrogen bonding with water and preferential adsorption on the electrode. First-principles calculations confirmed that sarcosine binds to the Zn(002) surface with adsorption energies of −1.01 and −0.98 eV for two representative configurations, far stronger than water’s −0.31 eV. This means sarcosine outcompetes water for surface sites, physically blocking the direct adsorption and reduction of water molecules that drive hydrogen evolution and corrosion.

Spectroscopic evidence backed up the picture. Raman measurements of the O–H stretching region between 3,000 and 3,700 cm−1 deconvoluted the water population into three categories: strongly hydrogen-bonded free water at 3,230 cm−1, weakly hydrogen-bonded water at 3,450 cm−1, and non-hydrogen-bonded water at 3,620 cm−1. As sarcosine concentration increased, the fraction of active free water steadily shrank while the inert, additive-restricted fraction grew. Nuclear magnetic resonance confirmed the trend, with the deuterium peak of D2O shifting downfield from 4.702 ppm in neat solvent to 4.72 ppm in the 0.5 M sarcosine electrolyte, indicating progressively tighter binding of water molecules. Fourier-transform infrared spectroscopy showed the O–H stretching vibration shifting to higher wavenumbers and the sulfate vibration moving from 1081.6 to 1084.3 cm−1, both consistent with a weakened water network and reduced zinc–sulfate interaction.

The electrochemical consequences were dramatic. In Zn||Zn symmetric cells, the sarcosine-modified electrolyte sustained stable cycling for over 2,100 hours at 1 mA cm−2, while the baseline electrolyte failed after roughly 50 hours at the harsher condition of 5 mA cm−2 and 5 mAh cm−2. Zn||Cu half-cells achieved an average Coulombic efficiency of 99.7 percent over more than 1,200 cycles, compared with severe fluctuations and failure after about 200 cycles in the unmodified electrolyte. In situ optical microscopy revealed that zinc plating in the baseline electrolyte produced loose, black, dendritic deposits with visible gas bubbles, whereas the sarcosine-containing electrolyte maintained a smooth, flat surface throughout plating and stripping with no bubble formation.

Three-dimensional laser confocal microscopy quantified the improvement in surface morphology. After 100 cycles at 1 mA cm−2 and 1 mAh cm−2, the maximum surface height of zinc anodes cycled in the baseline electrolyte reached approximately 77 micrometers, while those cycled in the sarcosine electrolyte measured only 21 micrometers. After 5 hours of plating at 5 mA cm−2, the contrast was even starker: 118 versus 23 micrometers. Chronoamperometry showed that the deposition current in the baseline electrolyte rose continuously as new active sites formed and dendrites proliferated, while the sarcosine electrolyte reached a stable current quickly after nucleation, indicating uniform and controllable zinc deposition.

Kinetic measurements added further depth. Temperature-dependent electrochemical impedance spectroscopy and Arrhenius analysis showed that the activation energy for zinc deposition dropped from 34.2 kJ mol−1 in the baseline electrolyte to 30.01 kJ mol−1 with sarcosine, confirming a lowered energy barrier for zinc ion reduction. The nucleation overpotential increased from 33.4 to 42.5 millivolts, which paradoxically is beneficial: a higher nucleation barrier promotes the formation of more numerous, finer, and more evenly distributed zinc nuclei rather than coarse, dendritic growth. Tafel polarization measurements showed the corrosion current density falling from 5.42 to 1.11 mA cm−2, an approximately 80 percent reduction, while linear sweep voltammetry revealed that the hydrogen evolution onset potential shifted cathodically by 171 millivolts, from −1.073 to −1.244 volts, meaning substantially more energy is required to trigger gas evolution.

In full cells paired with a ZnI@CNT-AC cathode, the sarcosine electrolyte delivered higher specific discharge capacity across all tested rates and recovered nearly its original capacity when the current was reduced from 8 to 0.1 A g−1. After 24 hours of rest, the modified cell retained 96.87 percent of its capacity, compared with only 73.24 percent for the baseline cell—a stark demonstration of reduced self-discharge through suppressed parasitic reactions. Over 3,000 cycles at 1 A g−1, the full cell retained 90.6 percent of its initial capacity with Coulombic efficiency approaching 100 percent. The researchers note that further validation under high electrode loading, lean electrolyte, and limited zinc excess will be needed to confirm practical viability, but the strategy itself—a simple, green, low-cost amino acid additive that simultaneously tames water reactivity and reshapes the electrode interface—offers a compelling blueprint for the next generation of safe, durable aqueous zinc batteries.

Subject of Research: Sarcosine electrolyte additive for stabilizing zinc metal anodes in aqueous zinc-ion batteries

Article Title: Adsorption-dominated interfacial regulation by sarcosine via hydrogen-bond water modulation for stable Zn metal anodes

Article References: Wang, Z., Ju, H., Zhang, H., Yang, Y., Liu, H., Cao, B., Ding, J., & Xu, B. (2026). Adsorption-dominated interfacial regulation by sarcosine via hydrogen-bond water modulation for stable Zn metal anodes. Frontiers in Chemistry, 14, Article 1986660. https://doi.org/10.3389/fchem.2026.1986660

Image Credits: AI Generated

DOI: 10.3389/fchem.2026.1986660

Keywords: aqueous zinc-ion batteries, zinc metal anode, sarcosine, electrolyte additive, hydrogen evolution reaction, dendrite suppression, hydrogen-bond regulation, interfacial adsorption, energy storage, electrochemistry, density functional theory, zinc corrosion