Functionally gradient materials for sustainable and high-energy rechargeable lithium batteries:Design principles,progress,and perspectives

Rechargeable lithium batteries with high-capacity cathodes/anodes promise high energy densities for nextgeneration electrochemical energy storage.However,the associated limitations at various scales greatly hinder their practical applications.Functional gradient material(FGM)design endows the electrode materials with property gradient,thus providing great opportunities to address the kinetics and stability obstacles.To date,still no review or perspective has covered recent advancements in gradient design at multiple scales for boosting lithium battery performances.To fill this void,this work provides a timely and comprehensive overview of this exciting and sustainable research field.We begin by overviewing the fundamental features of FGM and the rationales of gradient design for improved electrochemical performance.Then,we comprehensively review FGM design for rechargeable lithium batteries at various scales,including natural or artificial solid electrolyte interphase(SEI)at the nanoscale,micrometer-scale electrode particles,and macroscale electrode films.The link between gradient structure design and improved electrochemical performance is particularly highlighted.The most recent research into constructing novel functional gradients,such as valence and temperature gradients,has also been explored.Finally,we discussed the current constraints and future scope of FGM in rechargeable lithium batteries,aiming to inspire the development of novel FGM for next-generation high-performance lithium batteries.

Crack tip field in functionally gradient material with exponential variation of elastic constants in two directions

This paper presents an exact solution of the crack tip field in functionally gradient material with exponential variation of elastic constants. The dimensionless Poisson＇s ratios v0 of the engineering materials （iron, glass …… ） are far less than one; therefore, neglecting them, one can simplify the basic equation and the exact solution is easy to obtain. Although the exact solution for the case v0 ≠ 0 is also obtained, it is very complicated and the main result is the same with the case v0 = 0 （it will be dealt with in Appendix VII）. It has been found that the exponential term exp（ax ＋ by） in the constitutive equations becomes exp（ ax /2 ＋ by/2- kr /2 ） in the exact solution.

Different compositions of TC4/TC11 functional gradient materials interface by wire arc additive manufacturing

Titanium alloy is widely utilized in diverse industries due to its exceptional specific strength,making it a material with significant potential for advancement.Nevertheless,homogeneous materials are inadequate to meet the demands of various applications.Functional gradient materials(FGMs)have garnered increasing interest for their ability to tailor materials and structures.The continuous transition in FGMs often offers a more uniform and well-connected interface.However,there remains a lack of comprehensive research on the transition interface.In this study,TC4/TC11 double-alloy materials were produced using doublewire additive manufacturing.The wire feeding rates were adjusted to create materials with varying compositions.The grain morphologies,microstructures,and mechanical properties were examined.It was observed that as the TC11 content increased,the grain size decreased,theβcontent rose,the ultimate tensile strength improved,and the elongation decreased.Additionally,analysis of the fracture morphologies revealed that the dimples became smaller,indicating characteristics of ductile fracture.Following the solid solution aging heat treatment,it is observed that theαphase increases in size,and the mechanical properties are enhanced.These observations indicate that double-wire additive manufacturing can produce diverse interfaces.Furthermore,the heat treatment process has been shown to enhance the material properties,thus establishing an experimental foundation for FGMs.

Formation mechanism of inherent spatial heterogeneity of microstructure and mechanical properties of NiTi SMA prepared by laser directed energy deposition

Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.

Microstructures and Mechanical,Electrical,High-temperature Properties of Cu/Ti_2AlC FGM Fabricated by Hot-pressing

The microstructure and the electrical, thermal, friction, and mechanical properties of Cu/Ti_2AlC fabricated by hot-pressing at 900 ℃ for 1 h were investigated in the present work. Microstructural observations have shown that the plate-like Ti_2AlC grains distribute irregularly in the network of Cu grains, and well-structured, crack-free bonds between the layers. With the increase in the content of Ti_2AlC from layer A to layer D, the electrical resistivity increases from 1.381×10^（-7）Ω·m to 1.918 ×10^（-7）Ω·m, the hardness increases from about 980.27 MPa to about 2196.01 MPa, and the friction coefficient from above 0.20 reduces to about 0.15. Oxidation rate increases with the increases of temperature. Exfoliation was obviously observed on the surface of oxidation layer A. The surface of layer D was still intact and the spalling and other defects were not found. The mass decreases in the acid solution, and increases in the alkaline solution. The largest corrosion rate is found in 6.5% HNO_3 or 4% Na OH solution.

Dynamic stress analysis of functionally gradient material subject to SH waves

In this paper, the wave propagation in functionally graded materials (FGM) is studied by the elastic wave theory based on thewave problems in homogeneous media. The auxiliary function and modulus function are introduced to construct the displacementfield and density function. The displacement field, modulus function, and density function are connected to proposea design theory of special FGM. An analytical method for elastic wave propagation in inhomogeneous media with varyingmodulus and density is derived to provide theoretical references for material design and dynamic stress analysis under elasticwaves. Taking the problem of dynamic stress concentration caused by shallow buried elliptical cavity in half space designedunder SH waves as an example, the calculation results are obtained and analyzed. The results show that the dynamic stressconcentration is sensitive to the change of the inhomogeneity of the medium.