Construction Of Gradient Lithiophilic/Sodiophilic Metallic Electrodes And Its Application In Advanced Batteries

The development of new high specific energy and high safety batteries is the focus of academic and industrial circles,and the development of high specific energy,safe and stable electrodes is fundamental.Lithium and sodium metal anode are known as the’holy grail’in secondary batteries.There have high theoretical specific capacity of3862 m Ah/g or 1166 m Ah/g and the lower potential（-3.04 V or-2.71 V vs SHE）,which are the most promising next-generation metal anode materials.However,before lithium/sodium metal are applied to the anodes of the battery,several key problems should be overcome.（1）The uneven plating/stripping of lithium or sodium ions are easy to generate dendrites and’dead lithium or dead sodium’,which may penetrate the separator and cause potential safety hazards;（2）The high activity of lithium/sodium metal are easy to react chemically and electrochemically with the electrolyte,resulting in irreversible consumption of lithium/sodium,thereby reducing the energy density of lithium or sodium metal batteries;（3）Lithium/sodium metal batteries are prone to obvious volume changes during charge and discharge,which brings great challenges to battery structure design.To meet these problems,in this paper,on the one hand,starting from the design of multi-level gradient pore metal-based electrode structure,combined with three-dimensional macroporous conductive skeleton and microporous lipophilic alloy layer,lithium ions are induced to deposit preferentially at the bottom of metal-based electrode,which alleviates and inhibits the growth of dendrites and highly regulates the reversible lithium deposition/stripping process.On the other hand,an integrated metal composite electrode strategy for the preparation of high melting point metal mixed liquid metal is proposed,which effectively improves the electrode volume expansion and high activity of lithium in lithium metal batteries,and achieves reversible lithium storage performance.Finally,the development of metal-based batteries with high specific energy and high safety was realized,optimizing the battery device integration process,and the application of alloy electrodes in new scenarios of biological batteries（Na-O₂）was further explored.The specific research contents are as follows:First of all,a multi-level gradient pore Cu Sn Al@Cu foam composite electrode was designed and developed by magnetron sputtering technology using Sn-based lithiophilic alloy materials.A continuous micro-pore-sized lithiophilic alloy layer was constructed by chemical dealloying technology.Through structural design and composition optimization,an integrated metal electrode with pore gradient and lithiophilic gradient was obtained.The optimal matching relationship with different content of stored lithium was studied to induce Li⁺to deposit away from the dangerous area near the separator/anode,regulate the process of lithium deposition with different content and inhibit dendrite growth.Achieve’bottom-up’dense deposition of less lithium metal electrodes.It effectively regulates the deposition mode of lithium ions,and also suppresses and improves the problem of electrode materials volume expansion in lithium metal batteries.By using the differential phase contrast（DPC）,the principle of’bottom-up growth’mode is revealed by observing the electric field distribution in the electrode.The effective integration of three-dimensional porous current collector and porous metal electrode materials is realized.Then,a design strategy of self-healing alloy anode with high melting point metal mixing is proposed to reduce the surface tension of liquid metal anode and improve the contact between alloy layer and current collector interface.The gallium-based liquid alloy material with good lithium storage performance is selected,and the nano-sized tungsten powder is introduced to physically mix with it,thereby reducing the fluidity and surface tension of the gallium-based liquid metal,so that it can be directly used as an electrode material,and the best mixing ratio of the two is selected.This gallium-based liquid metal mixture was uniformly dispersed on commercial Cu foil to obtain a new LM-W10/CF integrated metal composite electrode.Due to the small surface tension and large viscosity of the liquid metal mixture,the electrode forms a close contact interface with the current collector,which realizes the reversible storage of lithium metal and the uniform plating/stripping on the electrode surface,and has excellent self-healing function and lithium storage capacity.By studying the optimal matching relationship with different content of lithium storage,the internal reasons of nano-tungsten powder changing the physical properties of gallium-based liquid metal are deeply studied,and the best scheme suitable for lithium metal battery system is proposed.Finally,in order to meet the needs of high specific energy,high safety and long life implantable power supply,a new high safety and high stability Na-based alloy anode was prepared based on the work of electrode structure design and material development under combining the previous two chapters.We proposed a new implantable and flexible Na-O₂ battery design,which could realize stable operation in vivo and in vitro.The structure consists of Na-based alloy anode,ion-selective separator,nanoporous gold cathode catalyst,dissolved oxygen in body fluid as cathode active material,and the outer packaging is encapsulated by a biocompatible and flexible electrospinning polymer.The Na-O₂ battery can convert dissolved oxygen in the body from chemical energy to electrical energy.The cathode side of the battery is designed as an open structure,which can directly obtain a large amount of dissolved oxygen from the organism to continuously provide energy for the battery.It is expected to increase the battery life of the existing implanted battery by more than 3times.The electrochemical performance of the battery in vitro and in vivo was systematically studied.The results of the discharge products of the Na-O₂ battery and the biochemical indicators,immunohistochemistry,and subcutaneous local tissue inflammation of the organism during the battery implantation showed that it had a negligible effect on the organism,and the capillaries wrapped around the battery during the battery implantation were in good condition,which could continuously provide oxygen for the implanted Na-O₂ battery.The advantage of the battery is its high discharge voltage and good biocompatibility,which can meet the needs of most implantable electronic devices.The new implantable Na-O₂ battery developed is also the first battery in the same battery to completely change the concept of implantable battery,and also lays the foundation for the development of high specific energy and high safety biomedical batteries.