水系锌离子电池的稳定性优化策略

Stability Optimization Strategy of Aqueous Zinc Ion Batteries

随着全球的环境恶化日益加剧,如何提高可再生能源的利用效率逐渐受到人们的关注。其中,水系锌离子电池相比锂离子电池及其他离子电池,在安全性和低成本等方面表现较为出色而成为当前研究热点。然而,水系锌离子电池面临着阴极材料的性能衰减、锌阳极的枝晶、副反应以及电解液消耗等问题,导致循环稳定性低,使其应用受到极大的限制。目前,针对水系锌离子电池循环稳定性低的优化策略方面还没有得到系统的总结和归纳。本文针对循环稳定性的优化这一问题,从阴极的空位、掺杂、包覆、复合和阳极的3D结构、表面改性、无锌金属设计还有电解液的离子诱导、去溶剂化结合水、原位固体电解质界面(SEI)以及隔膜和集流体的材料设计等角度,分别对水系锌离子电池阴极材料、锌阳极和电解液等方面进行了系统性的总结。并且,本文还提出了相关优化策略仍需探究的机制、适用材料体系等问题,最后对未来的研究方向做出展望。

The deterioration of climate and environment caused by fossil energy consumption was becoming more and more serious,which made the efficient utilization of renewable energy particularly important.In the research system of high-efficiency energy storage devices,lithium-ion batteries had been widely used in various electronic devices and new energy vehicles because of their high capacity and wide voltage window,but there were still some problems such as high cost and poor safety at present.In contrast,the high safety,low cost and low redox potential of aqueous zinc ion battery showed its application advantages in the field of large-scale energy storage,which had become a hot research direction in recent years.However,the problem of cycle stability attenuation of aqueous zinc ion battery hadn’t been completely solved.For cathode materials,the irreversible structure collapse in the process of electrochemical reaction was one of the main reasons for the performance degradation of aqueous zinc ion batteries.Specifically,the cathode materials of the battery would dissolve in varying degrees in the process of electrochemical reaction,and some materials would be transformed into composite products with different structures in the case of proton co-intercalation,which might cause irreversible damage to the material structure.In addition,the conversion reaction was accompanied by the change of pH,and the side reaction would consume the electrolyte and cause the attenuation of capacity.For the anode of the battery,zinc deposition was inevitably accompanied by competitive hydrogen evolution due to thermodynamic and kinetic factors,and the electrolyte consumption and gas expansion caused by hydrogen evolution directly damaged the cycle life of the battery.Secondly,the Zn^(2+) adsorbed on the anode diffused two-dimensional(2D)along the surface,accumulated at the preferential nucleation position and formed the initial protrusion,and the subsequent Zn^(2+) tended to deposit at the existing protrusion,which led to dendrite growth and easy to cause battery short circuit.In addition,the inert side reaction products covered on the electrode surface would further hinder the reversible deposition of Zn^(2+).For the above stability problems,the current optimization strategies could be summarized from the perspectives of cathode/anode,electrolyte and separator.For the optimization of cathode stability,vacancy defect modification,doping modification,surface coating and composite materials could be used.The introduction of vacancy defects in the cathode system was conducive to the insertion/desorption and adsorption/desorption of H+/Zn^(2+).In the doping modification strategy,the doping of multivalent metal ions effectively reduced the formation energy to promote the process of Zn^(2+) insertion/removal and diffusion,and enhanced the binding bond energy,which was conducive to the reversible phase transition of the structure.The surface coating of cathode material was to modify the electrode/electrolyte interface to inhibit the volume change caused by dissolution and phase transformation of cathode material.The cathode was composed of different material structures in the form of synergy and complementarity,which was also a direction to improve the stability of cathode materials.Moreover,the optimization strategy of anode stability included the optimization of zinc anode geometry,the modification of anode surface and the design of zinc free metal anode.Among them,the geometric structure of zinc anode was designed in the direction of high electroactive specific surface area and uniform porosity,which was conducive to the uniform adsorption of Zn^(2+) to alleviate the growth of zinc dendrites.The modification on the anode surface was to form a protective layer to prevent the uneven deposition of zinc and the corrosion of zinc by side reactions.In addition,the use of zinc free metal anode strategy fundamentally avoided the uneven zinc deposition of zinc metal anode,but it had high requirements for the structural stability,coulomb efficiency and capacity of the material,and the research scope was limited.Furthermore,the optimization strategies of electrolyte to electrode stability could be divided into inducing zinc deposition,removing bound water from Zn^(2+) solvated structure and in-situ forming solid electrolyte interphase(SEI)film on the surface of zinc anode.The electrolyte additive that produced competitive anodic adsorption with Zn^(2+) was introduced to induce the uniform deposition of Zn^(2+),and the additive that reduced the water activity of the electrolyte could effectively inhibit the generation of hydrogen evolution side reaction.In addition,compared with the SEI film manually coated on the anode surface,the SEI film produced by introducing additives based on the difference of adsorption was more compact and could effectively inhibit the dendritic growth and side reactions of the anode.In addition,the optimization strategy of the diaphragm could adjust the orderly transport of ions by adding functional layers to promote the reversibility of Zn^(2+) dissolution/deposition,and inhibit the growth of large dendrites by designing a structure with uniform porosity and high mechanical strength.However,the above optimization schemes would need further analysis in terms of qualitative/quantitative and material system.And in practical application,factors such as environment and cost occupied a certain weight,which were also the key directions of optimization researches in the future.