Alternating Current Preheating And Fast Charging Of Lithium-Ion Batteries With Lithium Plating Prevention At Low Temperatures

The severe performance deterioration,especially in terms of charging acceptability,of lithium-ion batteries at low temperatures restricts the wide diffusion of electric vehicles.To solve the low-temperature charging problem,one strategy is to develop battery materials with superior low-temperature survivability.An alternative is to develop a combined preheating-charging protocol for today's lithium-ion batteries with graphite anode,which warms up the batteries before charging.Focusing on the combined preheating-charging strategy,this work studies on the alternating current preheating and fast charging methods of lithium-ion batteries with lithium plating prevention at low temperatures.The overarching question,namely the lithium plating mechanism and criterion,is scrutinized.Afterwards,the alternating current preheating and fast charging methods of lithium-ion batteries with lithium plating prevention are developed respectively.Then the viability of the combined preheating-charging protocol is evaluated.Firstly,lithium plating at low temperatures is examined.The amount of plated metallic lithium in a cell after low-temperature charging with a large current is quantitatively measured using ex-situ nuclear magnetic resonance experiments.An electrochemical model accounting for lithium plating as a side reaction is adopted.The electrochemical model is parameterized with experimental data including the open circuit voltage,discharging curves at different C-rates and temperatures,and especially the amount of plated metallic lithium.Utilizing the model,it is revealed that lithium plating commences when the potential difference across the electrode-electrolyte interface drops below the equilibrium potential of lithium plating reaction.This criterion of lithium plating lays the basis for developing alternating current preheating and fast charging methods with lithium plating prevention.Secondly,the alternating current preheating method with lithium plating prevention is developed.In the long run,a battery subjected to an alternating current will be heated only by the irreversible heat due to the Joule effect,which is corresponding to the real part of the cell impedance.An equivalent electrical circuit model is utilized to simulate the cell.Based on this equivalent electrical circuit,a heat generation rate model in frequency domain is developed.For the sake of preventing lithium plating,the maximum heating current amplitude as a function of frequency is determined at different temperatures,using the equivalent electrical circuit invoking the lithium plating constraint expressed in frequency domain.Taking advantage of the temperaturesensitivity of cell impedance,a temperature-adaptive alternating current preheating method of lithium-ion batteries with lithium plating prevention is developed.Thirdly,the direct current charging method with lithium plating prevention is developed.A thermal-electrochemical coupled model of lithium-ion batteries is adopted to describe the low-temperature charging process and the model is validated with experiments under various conditions.To prevent lithium plating,the maximum charging current as a function of the state of charge is obtained at different temperatures,using the thermal-electrochemical coupled model invoking the lithium plating constraint expressed in time domain.Then the direct current charging method with lithium plating prevention at low temperatures is further developed.Finally,based on the developed alternating current preheating method and direct current charging method,a combined preheating-charging protocol is proposed and evaluated.The effectiveness of lithium plating prevention of the developed alternating current preheating method and direct current charging method is experimentally checked,indicating that the preheating-charging protocol is safe and friendly to the cycle life of lithium-ion batteries.The time and energy costs of the combined preheating-charging protocol with different preheating-charging switching temperatures are investigated.It is concluded that the preheating-charging protocol can save much charging time at minor extra energy expense.