Zinc-ion battery is a promising energy storage device, in which zinc metal cathode has been widely concerned because of its high theoretical capacity, high security and abundant resource storage. However, there are many problems in the process of cyclic charge and discharge, such as uneven deposition of zinc metal, corrosion and hydrogen evolution. Many researchers are working to solve these problems. The most common methods are the surface modification of zinc anode, the design of three-dimensional zinc metal anode and the regulation of electrolyte additives.
Recently, researchers proposed dextran as a multi-functional zinc ion battery electrolyte additive. Dextran is a complex, branched-chain glucan that is commonly used as an antithrombotic agent and is a major component of many eye drops. The experimental results and theoretical calculations show that dextran can effectively improve the electrochemical performance of zinc metal anode in the following four aspects. Firstly, dextran can be adsorbed on the surface of the zinc metal negative electrode to form a protective layer. Secondly, dextran can reduce the energy required in the desolvation process of hydrated zinc ions in the electrolyte. At the same time, dextran can induce deposition of zinc metal crystal face. In addition, dextran can also uniform the electric field distribution on the negative zinc electrode surface.
In this paper, scanning electron microscopy and light microscopy results show that dextran as an electrolyte additive can effectively promote the uniform deposition of metal zinc.
Secondly, it is proved by electrochemical results that dextran electrolyte additive can effectively inhibit the occurrence of metal zinc side reactions, and improve the cycle stability and coulomb efficiency of half cells.
In order to further prove that dextran additive can improve the electrochemical stability of zinc metal negative electrode, a symmetrical battery was assembled, and the cyclic stability of the symmetrical battery was tested under different discharge depths, currents and temperatures.
Then, through the experimental results and theoretical calculation, it is proved that dextran additive can be adsorbed on the surface of zinc metal negative electrode to form a protective layer and reduce the energy required for desolvation of hydrated zinc ions in the electrolyte. Dextran adsorbated on the negative zinc electrode surface can also induce the deposition of metal zinc (0002) crystal surface and even the electric field distribution on the zinc metal surface.
Finally, in order to prove that dextran additive can improve the electrochemical stability of zinc-ion batteries, vanadium pentoxide button battery and soft pack battery were assembled. For example, when the N/P ratio is as low as 2.18, buckle full batteries with dextran additives show higher cycle stability and discharge specific capacity at 1 Ag-1 current conditions. Soft-pack batteries with dextran additives also show improved cycle performance.
Based on the above experimental results and theoretical calculations, it is proved that dextran, which is cheap and non-toxic, can be used as a safe, effective and universal electrolyte additive for high performance zinc-ion batteries. Dextran can be adsorbed on the zinc metal negative electrode, limiting the reaction between free water and the zinc metal negative electrode and inhibiting the side reaction. Adsorptive dextran can also reduce the energy required for desolvation of hydrated zinc ions. At the same time, dextran can induce the deposition of zinc metal crystal surface and inhibit the growth of dendrites. In addition, the adsorbed dextran can even the electric field distribution on the surface of zinc metal.