Research On Zinc Anode And Its Surface/Interface Regulation In Aqueous Zinc Metal Battery

Renewable clean energy technologies have become the theme of today’s energy development.In addition to the pursue of high energy density and long cycle lifetime of the secondary batteries（such as commercial lithium-ion batteries）,the safety,environmental protection and low-cost of secondary batteries are also emphasized.Among them,aqueous zinc metal batteries（ZMBs）with abundant resources,safe and non-toxic is the most effective battery system that can break through these problems.The problems occurred at the zinc metal anode/electrolyte interface that affects the electrochemical performance of ZMBs can also be effectively alleviated.The ZMBs will become an important option for large-scale electrochemical energy storage.However,the commercial zinc plates mainly suffer from their low plating/stripping coulombic efficiencies（CEs）when using aqueous electrolyte.The side reactions（zinc dendrite,hydrogen evolution,by-product,etc.）at the anode/electrolyte interface（AEI）seriously affect the electrochemical performance of the battery,especially deteriorating the cycle life and CEs.There is a big gap between the main electrochemical performance indexes of the battery and the development of a new battery system.In this paper,Zn anode/electrolyte interface reaction and morphology evolution are regulated by surface coating,surface-preferred crystal plane regulation,alloying and electrolyte additive modulation.A series of related basic scientific issues are studied,the main research works and conclusions are shown as follows:（1）A new kind of Zn anode was prepared by coating a hydrophilic and multichannel Sc₂O₃ protective film on the commercial Zn plates.The density functional theory simulation and experimental results have proven that there is a great different dielectric constant between Zn anode and Sc₂O₃ and a charge separation over a considerable distance will be formed at the interfaces.A stratified adsorption effect was formed because the energy of H₂O adsorbed on Sc₂O₃-coated Zn anode is higher than the bare zinc.The smooth surface morphology of Sc₂O₃-coated Zn anode indicates a reversible deposition/stripping and the corresponding CE improved to～99.85%.The Sc₂O₃ coating with non-conductivity can hinder the direct contact between zinc anode and water molecules in the electrolyte,and can prevent H₂O from obtaining electrons and be decomposed into H₂ and OH^-on the anode surface,alleviating HER reaction and suppressing generation of Zn₄（OH）₆SO₄·H₂O by-product.Thus,the Sc₂O₃-coated Zn anode can run for more than 100 cycles without short circuit,more than one times higher than the commercial Zn plates.Sc₂O₃-coated Zn anode//MnO₂ full batteries can deliver higher storage capacity of 216.1 mAh g^-1 at 0.5 A g^-1.Sc₂O₃-coated Zn anode//NH₄V₄O₁₀ full batteries remain 82.4%capacity retention after 1000 cycles with 214.2 mAh g^-1 at 10 A g^-1.（2）A novel stable Zn|Sn alloy anode by modifying the composition and structure of matrix is designed via large-scale alloying strategy and technology optimization.This Zn|Sn alloy anodes possesses homogeneous second phase with the size about 1μm.Combined with theoretical analysis,Sn-contained second phases with localized electron effect can modulate the distribution of interfacial charge,constraining the reduction,diffusion and aggregation of hydrogen ions.The post-mortem/operando experimental proofs indicate that alloy anode displays a weaken hydrogen evolution reaction and a smooth surface without by-products and dendrite,in the sharp contrast to the bare one.Thus,the Zn|Sn alloy anode enables a long cyclic life of more than 2200-cycling and a high average coulombic efficiency of 97.53%in symmetric batteries.Zn|Sn anode//MnO₂ full batteries can deliver higher storage capacity of 216.1 mAh g^-1 after 500cycles at 0.5 A g^-1.Zn|Sn anode//NH₄V₄O₁₀ batteries remain 97.61%capacity retention after 1000 cycles with 241.3 mAh g^-1 at 10 A g^-1.（3）A highly stable and reversible Zn anode with preferentially exposed（002）basal plane was produced by the large rolling deformation.Compared to the commercial Zn plates with crystal plane orientation relative to（100）,the newly Zn anode mainly exposed（002）crystal plane orientation.Theoretical analysis indicates that due to the even interfacial charge density and stronger adsorption energies on parallel rather vertical direction on Zn（002）anode surface,Zn deposited uniformly along（002）crystal plane during the initial cycling process and grow laterally subsequently.The side reaction of Zn（002）anode can be effectively prevented owing to the strong catching ability of Zn atoms and high free energy for hydrogen evolution.The post-mortem/operando experimental techniques indicate that Zn anode with more（002）basal plane exposed exhibits free dendrites,no by-products and weak hydrogen evolution.Compared to the commercial Zn plates,the Zn（002）anode can enable a long cyclic life of more than 500 h and a high average coulombic efficiency of 97.71%for symmetric batteries.Zn|Sn anode//MnO₂ full batteries can maintain 1800 cycles at a current density of at 0.5 A g^-1.Even after rest for48 h,Zn|Sn anode//NH₄V₄O₁₀ full batteries remain a highly reversible specific capacity of nearly 116.3 mAh g^-1 after 1000 cycles.（4）The traditional zinc sulfate electrolyte was modified by using electrolyte additives.The results show that 2 M Zn SO₄/1 M NaClO₄ electrolyte is the optimum.The performance of the batteries improved a lot by simultaneously regulating the cation and anion in the electrolyte.The cation Na⁺restrains the Zn dendrite on the anode by electrostatic shield effect.The anion ClO₄^–is reduced to Cl^–to generate a protective layer on the Zn anode surface,providing a stable interface to decrease the Zn dendrite and H₂ evolution for long-term cycling.By introducing Na⁺and ClO₄^–in the aqueous Zn SO₄electrolyte,Zn//Zn symmetric cell shows durable and reversible Zn stripping/plating over 1500 h.when matched with the vanadium-based cathode,the full batteries exhibit the high capacity of 600 mAh g^–1 at 0.1 A g^–1 and long-term cycling performance over 5000 cycles with a capacity of 190 mAh g^–1 at 20 A g^–1.There are 90 pictures,17 tables and 204 references.