Do Zinc Dendrites Exist in Neutral Zinc Batteries: A Developed Electrohealing Strategy to In Situ Rescue In‐Service Batteries

Abstract

The dendritic issue in aqueous zinc‐ion batteries (ZBs) using neutral/mild electrolytes has remained an intensive controversy for a long time: some researchers assert that dendrites severely exist while others claim great cycling stability without any protection. This issue is clarified by investigating charge/discharge‐condition‐dependent formation of Zn dendrites. Lifespan degradation (120 to 1.2 h) and voltage hysteresis deterioration (134 to 380 mV) are observed with increased current densities due to the formation of Zn dendrites (edge size: 0.69–4.37 µm). In addition, the capacity is also found to remarkably affect the appearance of the dendrites as well. Therefore, at small current densities or loading mass, Zn dendrites might not be an issue, while the large conditions may rapidly ruin batteries. Based on this discovery, a first‐in‐class electrohealing methodology is developed to eliminate already‐formed dendrites, generating extremely prolonged lifespans by 410% at 7.5 mA cm–2 and 516% at 10 mA cm–2. Morphological analysis reveals that vertically aligned Zn dendrites with sharp tips gradually become passivated and finally generate a smooth surface. This developed electrohealing strategy may promote research on metal dendrites in various batteries evolving from passive prevention to active elimination, rescuing in‐service batteries in situ to achieve elongated lifetime.

Highly Reversible Zn Anode Enabled by Controllable Formation of Nucleation Sites for Zn‐Based Batteries

“…The nonuniform and dented surface of the bare Zn anode can be observed from the cross‐sectional SEM images (Figure S8a,b, Supporting Information). After 100 cycles, it is noteworthy that the dendrite formation can be obviously observed on the bare Zn anode at high current density even in the mild electrolyte, which is consistent with the previous reported results 39. Considering the large polarizations and the short cycle life of the bare Zn anode in Figure 4, it can be speculated that these serious cracks can be the indication of the severe Zn corrosion caused by the occurrence of HER and shape change due to the uncontrollable nucleation.…”

“…Surface coating layer on anode acts as a protective layer to decrease the contact area between electrode and electrolyte, suppressing the HER and Zn corrosion during cycling. Zhi's group developed a porous nano‐CaCO 3 coating to achieve uniform Zn stripping/plating, and it is also found that the Zn dendrites formation would be facilitated with increased current densities, where the electrohealing methodology can be expected to eliminate already‐formed dendrites 38,39. The electrolyte optimization positively influences the performance of Zn anode by forming a smooth absorbed layer or decreasing the active of H 2 O in the electrolyte, leading to the dendrite‐free anode and guaranteeing the long cycle life of battery.…”

A Sieve‐Functional and Uniform‐Porous Kaolin Layer toward Stable Zinc Metal Anode

“…Structure optimization strategies such as Zn/CNT, [ 3 ] Zn@ZnO‐3D, [ 4 ] Cu foam@Zn [ 5 ] were introduced to accelerate uniform Zn 2+ deposition and alleviate the dendrite issue in neutral electrolyte. [ 6 ] Ion‐conductive polymer electrolytes can effectively restrain the growth of Zn dendrites and alleviate the dissolution of active materials owing to their limited water content. [ 7 ] A kind of “water‐in‐salt” ultrahigh concentration electrolyte of 1 m Zn(TFSI) 2 + 20 m LiTFSI was designed to reduce the H 2 O molecules that surround Zn 2+ , wherefore it could effectively suppress the Zn dendrites and side reactions, [ 8 ] which was also achieved by using ZnCl 2 ·2.33H 2 O, [ 9 ] 30 m ZnCl 2 , [ 10 ] Zn(CF 3 SO 3 ) 2 , [ 11 ] “water‐in‐deep eutectic solvent” of urea electrolyte.…”

A Long‐Cycling Aqueous Zinc‐Ion Pouch Cell: NASICON‐Type Material and Surface Modification

“…At a rate of 0.1 A g −1 , a reversible discharge capacity of 73 mAh g −1 could be maintained after 100 cycles. More importantly, at the relatively high rate of 0.2 A g −1 , although the capacity is rapidly decreased at the initial stage (probably due to the lattice distortion and the information of zinc dendrites), it is stabilized at around 40 mAh g −1 from the 50th to 1000th cycles with almost no capacity fading (Figure g and Figure S1). Such stable performance is superior to that of most reported aqueous zinc‐ion pouch cells…”