The voltage U o may be the same as U max in the previous stage, or it may be taken slightly higher. Some chargers follow this stage by a second constant-current stage (with a gradually increasing voltage) before continuing with the U-phase. This happens when the battery is charged to around 95% of its capacity. The U o-phase is concluded when the charge current goes below a threshold I min, after which the U-phase is entered. The voltage in the U o-phase is too high to be applied indefinitely (hence, overvoltage), but it allows charging the battery fully in a relatively short time. In this stage, the battery is continued being charged at a constant (over)voltage U o, but the charge current is decreasing. Stage 2 is called the U o-phase, constant-voltage boost stage, absorption stage, or topping charge. Some chargers may keep the voltage at U max for some time to allow the current to drop to 20% of the initial current value, before proceeding to the next stage. In case of a battery that is more than 80% full, this may happen immediately once the charger is switched on. Once the U max voltage is reached, typically when the battery is charged to 70–80% of its capacity, the charger enters the Uo-phase. The charger limits the maximum voltage to U max, a constant or temperature-dependent maximum, typically around 2.4 V per cell. As a result of this current, the battery absorbs a charge and its voltage rises. The charger provides a constant current, typically the maximum current that the charger is capable of producing. This phase occurs when an IUoU charger is connected to a deeply discharged battery.
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Thermal management strategies to both cool batteries during charging and preheat them in cold weather are acknowledged as critical, with a particular focus on techniques capable of achieving high speeds and good temperature homogeneities.Stage 1 is called the I-phase, constant-current stage, or bulk charge stage. Robust model-based charging optimisation strategies are identified as key to enabling fast charging in all conditions. The need to develop reliable onboard methods to detect lithium plating and mechanical degradation is highlighted. Finally, knowledge gaps are identified and recommendations are made for the direction of future research. Safety implications are explored, including the potential influence of fast charging on thermal runaway characteristics. Alternative fast charging protocols are presented and critically assessed. Special attention is paid to low temperature charging. The present paper reviews the literature on the physical phenomena that limit battery charging speeds, the degradation mechanisms that commonly result from charging at high currents, and the approaches that have been proposed to address these issues. Fast charging is a multiscale problem, therefore insights from atomic to system level are required to understand and improve fast charging performance. The high currents needed to accelerate the charging process have been known to reduce energy efficiency and cause accelerated capacity and power fade. While increasing numbers of car manufacturers are introducing electrified models into their offering, range anxiety and the length of time required to recharge the batteries are still a common concern.
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#CHARGING EQUIL NOTE PORTABLE#
In the recent years, lithium-ion batteries have become the battery technology of choice for portable devices, electric vehicles and grid storage.