Solid polymer electrolytes in all-solid-state lithium metal batteries:From microstructures to properties

All-solid-state lithium(Li)metal batteries(ASSLMBs)are considered one of the most promising secondary batteries due to their high theoretical capacity and high safety performance.However,low room-temperature ionic conductivity and poor interfacial stability are two key factors affecting the practical application of ASSLMBs,and our understanding of the mechanisms behind these key problems from microscopic perspective is still limited.In this review,the mechanisms and advanced characterization techniques of ASSLMBs are summarized to correlate the microstructures and properties.Firstly,we summarize the challenges faced by solid polymer electrolytes(SPEs)in ASSLMBs,such as the low roomtemperature ionic conductivity and the poor interfacial stability.Secondly,several typical improvement methods of polymer ASSLMBs are discussed,including composite SPEs,ultra-thin SPEs,SPEs surface modification and Li anode surface modification.Finally,we conclude the characterizations for correlating the microstructures and the properties of SPEs,with emphasis on the use of emerging advanced techniques(e.g.,cryo-transmission electron microscopy)for in-depth analyzing ASSLMBs.The influence of the microstructures on the properties is very important.Until now,it has been difficult for us to understand the microstructures of batteries.However,some recent studies have demonstrated that we have a better understanding of the microstructures of batteries.Then we suggest that in situ characterization,nondestructive characterization and sub-angstrom resolution are the key technologies to help us further understand the batteries'microstructures and promote the development of batteries.And potential investigations to understand the microstructures evolution and the batteries behaviors are also prospected to expect further reasonable theoretical guidance for the design of ASSLMBs with ideal performance.

In-situ construction of a Mg-modified interface to guide uniform lithium deposition for stable all-solid-state batteries

Uniform lithium(Li)deposition in all-solid-state Li metal batteries is greatly influenced by the anode/electrolyte interface.Herein,a Mg-modified interface was constructed via the simple in-situ electrochemical reduction of Mg^(2+)from Mg(TFSI)_(2) in polyethylene oxide(PEO)and a Li bis(trifluoromethane)sulfoni mide(Li TFSI)formulae.As confirmed by cryogenic transmission electron microscopy,the anode/electrolyte interface exhibited hybrids consisting of crystalline Mg,Li_(2)O,and Li dots embedded in an amorphous polymer electrolyte.The crystalline Mg dots guided the uniform Li nucleation and growth,inducing a smoother anode/electrolyte interface compared with the pristine electrolyte.With 1 wt%Mg(TFSI)_(2) in the PEO-Li TFSI electrolyte,the Mg-modified electrolyte enabled the Li/Li symmetric cells with cycling performance of over 1700 and 1400 h at current densities of 0.1 and 0.2 m A cm^(-2),respectively.Moreover,the full LFP/Li cells using the novel Mg-modified electrolyte delivered a cycling lifespan of over 450 cycles with negligible capacity loss.

Mechanistic insights into the processes of the initial stage of electrolyte degradation in lithium metal batteries

The lithium(Li)metal batteries(LMBs)are considered one of the most promising next-generation batteries due to its extremely high theoretical specific capacity.However,there are a couple of issues,e.g.,the serious side reactions that occurred at the solid-liquid interface between the electrolyte and Li metal anode,hindering the broad commercialization of LMBs.Thus,a comprehensive understanding of the mechanisms underlying the decomposition of electrolytes is crucial to the design of LMBs.Herein,we utilize density functional theory simulations to explore the decomposition mechanism of electrolytes.The most commonly used ether electrolyte solvents,i.e.,1,2-dimethoxyethane(DME)and 1,3-dioxalane(DOL),based on suitable lithium salts,namely bis(trifluoromethanesulfonyl)imide(LiTFSI),are chosen to model the actual situations.We explicitly demonstrate that an electron-rich environment near the interface accelerates the decomposition of electrolytes.For ether electrolytes,we show that the LiTFSI degradation path is depending on the ratio of DOL to DME.In addition,the solvation structures of lithium-ion undergo a series of transformations upon electrolyte degradation,becoming thermodynamically more favorable and having a higher reduction potential in an electron-rich environment.Our finding provides new insights into the decomposition mechanisms of electrolytes and paves the way for the rational design of high-performance LMBs.

Considerable molecular interactions enable robust electrochemical properties:hydrogen bonds in lithium-ion batteries

Lithium-ion batteries(LIBs)have been in a dominant position in the new energy industry because of their excellent comprehensive performance.The performance of LIBs highly depends on the microstructures of the materials that constitute LIBs.Particularly,the relatively“weak”molecular interactions instead of the common-discussed strong chemical-bonding always affect the structures and the consequent properties of the components in LIBs.As a typical example,the hydrogen bonds,which widely exist inside LIBs,greatly improved the mechanical strength,lithium ion(Li^(+))transport rate and the intrinsic stabilities towards boosting performance of LIBs.This review starts from the interaction force between molecules,and especially summarizes the correlation between the formation of hydrogen bonds and the properties of the typical components in LIBs(cathode,anode,electrolyte,separator).In addition,how the formation of hydrogen bonds affects the performance of LIBs components is discussed.Finally,the strategies of combining hydrogen bonds with LIBs components in the future are prospected,which provide guidance for the rational design of high-performance LIBs.

Amorphous carbon-based materials as platform for advanced highperformance anodes in lithium secondary batteries

The growing concern for the exhaustion of fossil energy and the rapid revolution of electronics have created a rising demand for electrical energy storage devices with high energy density,for example,lithium secondary batteries(LSBs).With high surface area,low cost,excellent mechanical strength,and electrochemical stability,amorphous carbon-based materials(ACMs)have been widely investigated as promising platform for anode materials in the LSBs.In this review,we firstly summarize recent advances in the synthesis of the ACMs with various morphologies,ranging from zero-to three-dimensional structures.Then,the use of ACMs in Li-ion batteries and Li metal batteries is discussed respectively with the focus on the relationship between the structural features of the as-prepared ACMs and their roles in promoting electrochemical performances.Finally,the remaining challenges and the possible prospects for the use of ACMs in the LSBs are proposed to provide some useful clews for the future developments of this attractive area.