Summary
Lithium‐ion pouch cells are widely used in electric vehicles because of their high energy density than other structures. There is an unavoidable external surface pressure between the cells in the process of packing and driving of electric vehicles. The influence of external surface pressure on the main properties of the lithium‐ion pouch cell has been studied, which is of great significance to packing batteries and reusing retired cells. In this study, a testing device applied for the measurement of constant external surface pressures of lithium‐ion pouch cells was first proposed and the different pressure stress‐strain distribution on the external surface of cells under semirigid material pads were analyzed by simulation. The effects of pressure on the capacity, internal resistance, and open circuit voltage of fresh and aged LiNixCoyMnzO2 (NCM) lithium‐ion pouch cells are analyzed through experiments under 1 Mpa external surface pressure. The results show that the internal resistance of fresh cells tends to decrease. The average percentage of the maximum reduction of internal resistance is 13.28%. The experiments also demonstrate that the capacity of aging cells increased by 2.3%. Irreversibility of capacity improvement indicates applying appropriate external surface pressure can improve the secondary utilization efficiency of aging cells.
Monocrystalline silicon wafer is the most important raw material in chip manufacturing, wire sawing is the most common processing method of monocrystalline silicon wafer. The residual stress generated by cutting affects the subsequent polishing costs directly, as well as the fracture strength and mechanical integrity of the monocrystalline silicon wafer, thus affecting the service performance. In this paper, the generation mechanism of residual stress was analyzed based on diamond wire sawing technology. Then, based on D-P plastic constitutive model, the magnitude and distribution of residual stress of monocrystalline silicon chip under different process parameters were simulated by ABAQUS simulation software. Finally, the experiment of ultrasonic vibration assisted diamond wire sawing monocrystalline silicon and blind hole drilling method detection were conducted, the strain values before and after drilling in three directions were measured by strain gauge rosette, and the residual stress was calculated by combining with mathematical theory, and the experimental results verified the validity of the finite element model. The experimental results showed that residual compressive stress remains on the surface of silicon wafer in both conventional wire sawing and ultrasonic vibration assisted wire sawing. The residual compressive stress increases with the increase of the axial speed of wire saw, decreases with the increase of the wire saw feed speed, and fluctuates with the increase of the workpiece rotation speed. The residual compressive stress on the surface of the silicon wafer by ultrasonic vibration assisted wire sawing is larger than that by conventional wire sawing. The variation trend of simulation and experiment results is consistent, which provides theoretical support for the subsequent processing of monocrystalline silicon wafers.
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