Homogenous coating of Li^(+)conductive Li_(5)AlO_(4)on single-crystalline nonstoichiometric Li_(1.04)Ni_(0.92)Al_(0.04)O_(2)for rechargeable lithium-ion batteries

Cobalt-free,nickel-rich LiNi_(1-x)Al_(x)O_(2)(x≤0.1)is an attractive cathode material because of high energy density and low cost but suffers from severe structural degradation and poor rate performance.In this study,we propose a molten salt-assisted synthesis in combination with a Li-refeeding induced aluminum segregation strategy to prepare Li_(5)AlO_(4)-coated single-crystalline slightly Li-rich Li_(1.04)Ni_(0.92)Al_(0.04)O_(2).The symbiotic formation of Li_(5)AlO_(4)from reaction between molten lithium hydroxide and doped aluminum in the bulk ensures a high lattice matching between the Ni-rich oxide and the homogenous conductive Li_(5)AlO_(4)that permits high Li^(+)conductivity.Benefiting from mitigated undesirable side reactions and phase evolution,the Li_(5)AlO_(4)-coated single-crystalline Li_(1.04)Ni_(0.92)Al_(0.04)O_(2)delivers a high specific capacity of220.2 mA h g^(-1)at 0.1 C and considerable rate capability(182.5 mA h g^(-1)at 10 C).Besides,superior capacity retention of 90.8%is obtained at 1/3 C after 100 cycles in a 498.1 mA h pouch full cell.Furthermore,the particulate morphology of Li_(1.04)Ni_(0.92)Al_(0.04)O_(2)remains intact after cycling at a cutoff voltage of 4.3 V,whereas slightly Li-deficient Li_(0.98)Ni_(0.97)Al_(0.05)O_(2)features intragranular cracks and irreversible lattice distortion.The results highlight the value of molten salt-assisted synthesis and Li-refeeding induced elemental segregation strategy to upgrade Ni-based layered oxide cathode materials for advanced Li-ion batteries.

Experimental behavior and fracture prediction of a novel high-strength and high-toughness steel subjected to tension and shear loading tests

In this study,laboratory testing and numerical simulation methods are used to investigate the mechanical behavior and perform fracture prediction of a novel high-strength and high-toughness steel with a negative Poisson's ratio(NPR)effect under combined tensile-shear loading conditions.A test device capable of meeting different tensile-shear combination test angles is designed and manufactured,wherein the mechanical experiments on the NPR(Negative Poisson's Ratio)steel specimens are carried out at various testing angles.Q235 steel and MG400 steel are used as experimental control groups.The results show that the mechanical deformation of NPR steel is significantly better than that of Q235 steel and MG400 steel.Its tensile-shear test curve has no yield plateau and it has quasi-ideal elastic-plastic mechanical properties.The loading direction gradually changes from tension-dominated to shear-dominated as the tension-shear angle increases,and the strength and deformation of the specimens show a decreasing trend.Based on the laboratory test results,a finite element numerical model of NPR steel is established.A series of numerical simulations are carried out under the conditions of different tension and shear angles and the average stress triaxiality and fracture strain data are obtained.The fracture data of NPR steel are fitted using the Johnson-Cook fracture criterion,and the Johnson-Cook fracture parameters under the tensile-shear test conditions of NPR steel are thus obtained.The numerical simulation verifies that the fracture model can accurately predict the tensile-shear fracture behavior of NPR steel.