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.

Enhanced sulfide chemisorption by conductive AI-doped ZnO decorated carbon nanoflakes for advanced Li-S batteries

Lithium-sulfur batteries have attracted significant attention recently due to their high theoretical capacity, energy density and cost effectiveness. However, sulfur cathodes suffer from issues such as shuttle effects, uncontrollable deposition of lithium sulfides species, and volume expansion of sulfur, which result in rapid capacity fading and low Coulombic efficiency. In recent years, metal-oxide nanostructures have been widely used in Li-S batteries, owing to their effective inhibition of the shuttle effect and controlled deposition of lithium sulfide. However, the nonconductive metal-oxides used in Li-S batteries suffer from extra diffusion process, which slows down the electrochemical reaction kinetics. Herein, we report the synthesis of carbon nanoflakes decorated with conductive aluminium-doped zinc oxide （AZO@C） nanoparticles, through a facile biotem- plating method using kapok fibers as both the template and carbon source. A sulfur cathode based on the AZO@C nanocomposites shows better electrochemical performance than those of cathodes based on ZnO and A1203 with poor conductivity, with a stable capacity of 927 mAh.g-1 at 0.1C （1C = 1,675 mA.g-1） after 100 cycles. A reversible capacity of 544 mAh.g-1 after 300 cycles was obtained even after increasing the current density to 0.5C, with a 0.039% capacity decay per cycle under a sulfur loading of 3.3 mg-cm-2. Moreover, a capacity of 466 mAh.g-1 after 100 cycles at 0.5C could still be obtained when the sulfur loading was increased to 6.96 mg.cm-2. The excellent electrochemical performance of the AZO@C/S composite can be attributed to its high conductivity of the polar AZO host, which suppresses the shuttle effect while simultaneously improving the redox kinetics in the reciprocal transformation of lithium sulfide species.