NiMH No.7 battery.Shanghai Silicate Institute has made progress in the research on the interface modification of the negative electrode of lithium metal batteries

　　Metal lithium has extremely high theoretical specific capacity and extremely low redox potential, and is expected to become the next generation anode material. When matched with conversion-reactive sulfur-based and fluorine-based cathodes, lithium metal batteries (LMBs) with energy densities as high as 500-900 Wh kg-1 are expected. However, the growth and spread of lithium dendrites at the negative terminal can easily lead to poor cycle stability of lithium metal batteries and pose a safety risk of battery short circuit; the extruded lithium dendrites may also damage the solid electrolyte interface (SEI) layer or form a "dead" "Lithium", as the specific surface area and porosity of the lithium metal anode increase, the consumption of electrolyte intensifies, and the SEI accumulates and becomes thicker, causing electrode passivation. These unfavorable factors will lead to an increase in battery impedance and overpotential, causing a decrease and fluctuation in Coulombic efficiency (CE), which seriously limits the development of lithium metal batteries. Adjusting the SEI components by adding low-content electrolyte additives is a simple and effective strategy to enhance the SEI film, improve the negative electrode interface, and thereby delay the growth of lithium dendrites. The enhancement effect of SEI depends on the degradation of the additives and the reducing Li surface. reaction process.

　　In view of the poor flexibility of the SEI layer with a single inorganic component and the complex construction operation of the existing organic-inorganic hybrid SEI layer, the team of Li Chilin, a researcher at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, proposed a simple and effective interface in-situ catalytic grafting. This strategy achieves high efficiency, stability and dendrite suppression for the negative electrode of lithium metal batteries. Relevant research was published in Advanced Functional Materials (Advanced Functional Materials, 2019, 1902220, DOI: 10.1002/adfm.201902220).

　　In this work, the research team used -OCH3 group-terminated liquid polydimethylsiloxane (PDMS-OCH3) as a graftable additive, and achieved its "grafting" on the surface of lithium metal through the action of electrochemical potential and electric field. ” and “fragment” reactions. The naturally existing thin layer "skin" of Li2O and LiOH on the surface of lithium metal can catalyze and activate the dissociation reaction of PDMS-OCH3 under the action of charge transfer. The broken macromolecules can be grafted onto the surface of lithium metal, while smaller molecules can Densified into inorganic LixSiOy fast ion conductor. Such an organic-inorganic hybrid interfacial phase (i.e., grafted SEI) is further enhanced by the high concentration of LiF injected during the electrochemical process. The combination of hard inorganic components of LiF and LixSiOy can provide fast ion channels and interfaces, achieve a homogenization effect of ion flow, and act as a barrier to hinder the growth of lithium dendrites; while the soft PDMS branches can enhance the flexibility and buffering of the entire SEI Effect. Using liquid PDMS-OCH3 as an additive in the carbonate system, the negative electrode under graft protection can give Li|Li symmetrical batteries a stable cycle of up to 1800 h, while achieving a small potential polarization of about 25 mV. Li|Cu asymmetric cells can still achieve Coulombic efficiencies as high as 97% under conditions of high current density and high areal capacity. In terms of lithium metal densification and SEI stabilization, liquid PDMS additives have more significant advantages than other solid silicone additives with weak grafting ability.

　　Recently, Li Chilin's team has made a series of progress in the research on the interface modification of the negative electrode of lithium metal batteries. It has proposed functional additives/fillers and conformal coating methods to design a stable artificial SEI layer, and was the first to propose a two-dimensional carbon-nitrogen polymer (C3N4). Strategies to enhance the electrolyte to inhibit the growth of lithium dendrites (ACS Appl. Mater. Interfaces2017, 9, 11615), and propose a method of in-situ plating of porous magnesium metal network to stabilize the reversible cycle of lithium anodes (ACS Appl. Mater. Interfaces2018, 10, 12678) , took the lead in proposing a way to achieve high ionic conductivity of a class of lithium-rich fluorine-based open-frame solid electrolytes and its homogenizing effect on lithium ion flow (Energy Storage Mater. 2018, 14, 100; ACS Appl. Mater. Interfaces 2018, 10, 34322), proposed a composite enhancement strategy using metal-organic framework (MOF) solid additives to trigger in-situ injection of high-concentration LiF into Zr-o-C-based SEI (ACS Appl. Mater. Interfaces2019, 11, 3869), and proposed the realization of conformal coating of sericin Methods for air-stabilizing lithium metal anodes and high-rate Li-S batteries (J. Power Sources2019, 419, 72), and proposing an alloy three-dimensional skeleton structure that can induce conformal coaxial deposition of lithium metal (ACS Appl. Energy Mater.2019, DOI : 10.1021/acsaem.9b00573).

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