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Morphology Mechanics in Battery Anodes

出版	Pennsylvania State University, 2024
URL	http://books.google.com.hk/books?id=3OT10AEACAAJ&hl=&source=gbs_api

註釋Anode morphology affects battery lifespan and Coulombic efficiency (CE). Morphology evolution associated with volume change in silicon (Si) anodes and dendrite growth in zinc (Zn) aqueous batteries is investigated. Si is regarded as one of the most promising anode materials for lithium-ion batteries. Its high theoretical capacity (4000 mAh/g) has the potential to meet the demands of high-energy density applications, such as electric air and ground vehicles. The volume expansion of Si during lithiation is over 300%, indicating its promise as a large strain electrochemical actuator. A Si-anode battery is multifunctional, storing electrical energy and actuating through volume change by lithium-ion insertion. To utilize the property of large volume expansion, we design, fabricate, and test two types of Si anode cantilevers with bi-directional actuation: (a) bimorph actuator and (b) insulated double unimorph actuator. A transparent battery chamber is fabricated, provided with NCM cathodes, and filled with electrolyte. The relationship between state of charge and electrode deformation is measured using current integration and high-resolution photogrammetry, respectively. The electrochemical performance, including voltage versus capacity and CE versus cycle number, is measured for several charge/discharge cycles. Both configurations exhibit deflections in two directions and can store energy. In case (a), the largest deflection is roughly 35% of the cantilever length. Twisting and unexpected bending deflections are observed in this case, possibly due to back-side lithiation, non-uniform coating thickness, and uneven lithium distribution. In case (b), the single silicon active coating layer can deflect 12 passive layers. The cycle life and power density of Zn metal batteries depend on the anode electrodeposition morphology, including the formation of metal dendrites, and impedance, respectively. We investigate the influence of aqueous ZnSO4 electrolyte convection through a copper mesh anode on Zn electrodeposition morphology and current densities. Electrochemical experiments in a specially designed flow-through cell with a Zn metal cathode reveal that the electrolyte flow from the cathode through the anode improves Zn deposition morphology and reduces impedance at concentrations ranging from 0.01 to 1 mol/L. Small flow rates at millimeters per second double the current densities. The electrodeposition morphology and current density are positively impacted at Peclet number larger than 1. At these flow rates, the Zn plating is more smooth, compact, uniformly deposited around the wire, and dense than that in the stagnant electrolyte. Zn-Cu asymmetric cell cycling tests at 50 mA/cm2 show that flow-through electrolyte can significantly increase the cell lifespan from 18 cycles in static electrolyte to 1300 cycles at a flow rate of 0.5 mm/s. Numerical analysis illustrates that the flow-through electrolyte replenishes consumed zinc ions at the electrode surface and suppresses dendrite growth by maintaining a uniform current density distribution. Alkaline electrolyte flow through porous Zn anodes and Ni(OH)2 cathodes can overcome diffusion limits, reduce dendrite growth, and improve cycle life. Zinc deposition morphology improves with low flow rates electrolyte in KOH/ZnO electrolytes at current densities near the diffusion-limit regime. Zinc dendrites present without flow are suppressed by micrometer-per-second flow at concentrations ranging from 0.2 to 0.6 M ZnO dissolved in 6 M and 10 M KOH solutions. Zn-Cu asymmetric cell tests reveal that flowing electrolyte increases the lifespan by more than 6 times in the diffusion-limit regime by suppressing gas evolution and dendrite formation. Ni-Zn cell tests show that a flow-assisted battery cycles 1500 times with over 95% CE at 35 mA/cm2 current density and 7 mAh/cm2 charge capacity, increasing the battery lifespan by 17 times compared with a stagnant Ni-Zn cell. Flow-through electrolyte also stabilizes the Zn electrode in the over-limiting regime, achieving approximately 4 times increased lifespan and 297 cycles with over 90% CE at 52 mA/cm2. Thick electrodes suffer from underutilization of active materials due to ion transport limitation in thick porous structures. Flow-though electrolyte has been demonstrated to effectively improve cell electrochemical performances by improving ion transport with flow convection. A reduce-order electrolyte-enhanced single particle model with flow convection (ESPM-convection) is developed using Integral Method Approximation for electrolyte dynamics. The ESPM-convection model demonstrates that flow-through electrolyte can facilitate full utilization of active materials in thick electrode (>= 100 [mu]m) during intercalation at high C-rate (>= 1C) by maintaining uniform ion concentration distribution. The model exhibits less than 1% maximum percent error with the full-order COMSOL model in concentration and voltage profiles at 1C rate in graphite-NCM cells. In Li metal batteries, the ESPM-convection model indicates that flow uniforms ion concentration, and reduces impedance in Li-NCM cells with 12 [mu]m Li metal by reducing concentration overpotential.