![]() ![]() ![]() T B is raised by reducing h and/or increasing T C during fast charging and reduced during rest and discharge by increasing h and/or reducing T C. 1a), e.g., increasing or reducing h by starting or stopping the coolant flow and/or changing T C by heating or cooling the coolant. (1) The first approach is system-level T B control using battery thermal management systems (BTMSs) 22, 24 by adjusting h and T C using coolant modulation (“CM” in Fig. Two heating strategies have been proposed/enacted for fast charging. Thus, elevating the battery temperature relies on the increased Q and T C and/or the reduced hA (see Supplementary Note 1 for the 3D transient electrochemical-thermal model). T C is the coolant temperature and h denotes the tunable thermal conductance per unit area between the battery and coolant, as illustrated in Fig. Treating the battery as a lumped thermal system (see Supplementary Note 1 for details on the validity of lumped model), the transient battery temperature can be written as \(\), where Q, A, T B, m, and C p are the transient heat generation, surface area, temperature, mass, and heat capacity of the battery, respectively. ![]() Among these approaches, heating strategies have shown promising results for existing high-energy-density LIBs and thus have the potential to enable XFC of EVs in the near term. Broadly, R&D efforts to develop XFC LIBs can be classified into four categories: the development of new electrolytes 11, 12, electrode materials 13, 14, 15, 16, 17, charge protocols 18, 19, or heating strategies (i.e., improving the kinetics by increasing the temperature before XFC) 20, 21, 22, 23, 24. Eliminating or mitigating lithium plating 8, 9, 10, which requires faster ion transport and kinetics in LIBs, is one of the greatest research and development (R&D) challenges remaining to enable XFC. Reducing the charge time to 15 min requires a charge rate of 6C for the constant-current stage of Constant Current Constant Voltage (CCCV) Charging, which can trigger lithium plating on graphite negative electrodes and cause dramatic capacity fade in LIBs. It is acknowledged that long XFC cycle life cannot be achieved in existing commercial high-energy-density lithium-ion batteries (LIBs) with graphite (C) negative electrodes and transition-metal oxide positive electrodes such as lithium cobalt oxide (LCO) 2. For a recharging experience comparable to that of gasoline vehicles, called extreme fast charging (XFC) of EVs, the United States Department of Energy (US DOE) has set a goal of 180 Wh/kg discharge specific energy, and <20% capacity loss in 500 XFC cycles 6, 7. Currently, the charge time to 80% state of charge (SOC) in EVs such as Tesla models with fast charging capabilities is >30 min 5. The long charge time (>30 min) of electric vehicles (EVs) compared with the refueling time of gasoline vehicles has been a major barrier to the mass adoption of EVs 1, 2, 3, 4. Finally, we also demonstrate the feasibility of integrating the XFC approach in a commercial battery thermal management system. These results are almost identical regarding operativity for the same battery type tested applying a 1 h of charge and 1 h of discharge, thus, meeting the XFC targets set by the United States Department of Energy. Without modifying cell materials or structures, the proposed XFC approach enables reliable battery operation by applying <15 min of charge and 1 h of discharge. We demonstrate that retaining the heat during XFC with the switch OFF boosts the cell’s kinetics while dissipating the heat after XFC with the switch ON reduces detrimental reactions in the battery. Here, to enable the XFC of commercial LIBs, we propose the regulation of the battery’s self-generated heat via active thermal switching. The mass adoption of electric vehicles is hindered by the inadequate extreme fast charging (XFC) performance (i.e., less than 15 min charging time to reach 80% state of charge) of commercial high-specific-energy (i.e., >200 Wh/kg) lithium-ion batteries (LIBs). ![]()
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