电动汽车电池退化的解释

电动汽车电池退化的解释

最近在我们的AVID学习播客中,滚球体育app最新版我们谈到了电池退化的话题以及如何确定电池车的健康状态。我们的听众特别想知道,他们是否可以做些什么来最大限度地降低他们的新电动汽车的电池退化。首先,这可能有助于理解我们所说的电动汽车电池的退化以及它是如何发生的。

退化

电动车电池组由数百个锂电池电池组成,当EV通过一个良好的新电池组构建时,它具有一定的容量,但在使用中,随着时间的推移,这种容量会慢慢减少,这被称为退化。在EV世界中,通常认为当电池达到其原始容量的80%时,它不适合使用,因此在40kWh包中,这将降低到32kWh的容量。请记住,千瓦时是能量存储的单位,并等于1kW的功率为1小时。意思是40kWh电池需要5.7小时才能从7kW充电器充电。宝马仍然表达了AMP时间(AH)的电池容量,这是一个类似的测量单位,并将AMP小时转换为KWH,您必须将AH值乘以Pack KW =伏X放大器的电压。BMW更喜欢该测量单位,因为电压根据电池组的充电状态而变化。许多电动车报告了电池的健康参数状态,我们已经有一些狂热的技术播客听众询问了关于这个问题。滚球体育app最新版健康状况由电池管理系统(BMS)计算,比较将电池从充电曲线上的一个点移动到另一个电量的电池所需的实际电荷量VS当电池是新的量。这是通过精确地测量通过库仑计数的电流来准确地测量流入包装的电流,同时充电和包装的电压并将其比较到外表表。包的充电状态简单地基于电池电压,锂电池具有S曲线,其中电池电压随着电荷状态而变化,但随着细胞降低,将电池移动到其充电时需要更少的充电 curve which is indicated by the state of health. This gradual reduction in capacity over time is a key design consideration when developing EV battery systems. With a huge amount of investment going into making sure this does not happen too quickly. There are several mechanisms that cause degradation in the cell, such as lithium plating and dendrite formation, and the growth of the solid electrolyte interface (SEI) layer and copper and carbon stripping. These mechanisms are due to the electrochemistry in a lithium battery and all result in the loss of active material inside the battery cell and the formation of inactive compounds. So a key question is what causes or can accelerate these degradation mechanisms?

电池管理和冷却系统

电池管理系统
狂热的滚球体育app最新版BMS.
电动汽车电池组中的BMS是一个复杂的管理和测量系统,用于保护电池,确保它不会被损坏。例如,如果BMS检测到电池温度过高,它将限制给电池充电的速率。这是背后的充电器门问题与日产聆风。因为目前的Leaf电池都是被动冷却的,从电池中获得热量的能力是相当有限的。当充电或放电电池硬,它会导致电池发热,由于电流和电池的内部阻抗给予欧姆加热,即电流的平方x电阻。BMS正在监测电池温度,并将看到这种情况的发生。为了保证电池不被损坏,就会减慢充电速率,直到温度下降。如果天气炎热,从电池组中获取热量的能力将进一步降低,这意味着当环境温度较高时,汽车更有可能限制充电速率。包括2019年65kWh版Leaf在内的许多电动汽车在上市时都采用了主动液体冷却,有时甚至使用车辆的空调制冷系统来实现电池过冷。这确保即使环境温度非常高,电池温度可以保持在其最佳水平低于环境温度。 Obviously, this comes at a cost of a more complex system and the energy required to operate the refrigeration and cooling systems. So in most cases, the BMS is working to ensure there is no excessive damage caused to the battery pack, but it does have an operating window in which it will allow the pack to operate. If as an owner of the vehicle you really wanted to ensure you maximised the life of the battery by preventing degradation there are steps that you could take. Degradation mechanisms happen more readily at elevated temperatures, rapid charging, and hard driving will result in raised pack temperatures due to the high current flows. If the EV is equipped with a subcooling system that utilises the A/C refrigeration system this should not make much difference to the pack temperatures, although it will have an impact on efficiency as we need energy to operate this chilling system which you would see in a reduced driving range and increased charge times. However, if the EV is equipped with only a basic liquid cooling system or a passive cooling system minimising activity that would cause the pack to be in the upper quartile of its operating temperature range will result in improved degradation performance. For example, if the option is there to slow charge (3-7kw) overnight when the ambient temperature is preferable this should be done in preference to fast charging during the day. Degradation also occurs more readily at higher SoC levels, meaning there is some sense to the commonly heard advice about not keeping your car battery continually topped up to 100% i.e. plugging in every time you park the car. You should never top the battery up if it is not necessary. In reality, manufacturers are generally finding that battery system degradation is lower than they had been predicting. This is due to actual real-world vehicle use being easier on the battery than the prediction models. Transient, stop-start driving in real-world traffic with lower acceleration rates and average speeds allow the battery opportunity to cool down and the relatively infrequent use of fast chargers because of the convenience of simply plugging in overnight.

神话

还有一些关于电动汽车电池与温度有关的误解,可以用本白皮书中已经提到的一些内容来解释。例如,在低温条件下,需要能量为乘员加热舱室,这将使用电池的能量,这将减少驾驶里程,但不会减少电池容量。只不过,不是所有的能量都被用来驱动车辆,其中一些也被用来加热乘客。在非常低的温度下,电池本身需要加热才能充电。这意味着给汽车充电需要更长的时间因为一些能量被用来加热电池系统而不是进入电池,电池容量没有实际变化。在ICE车辆中,发动机冷却时效率更低,但一旦达到温度,发动机通常会产生足够的余热,即使在最冷的日子里也能让乘客保持温暖。在高温环境下,需要能量来运行空调系统,以冷却舱室、乘客,可能还需要根据车辆的不同来冷却电池。再次,这将减少驾驶范围,但不会压缩容量。在较高的环境温度下,充电过程中会使用能量来冷却电池组,这将降低电池组充电的速度,但对电池组来说不是问题。在这种情况下,它与ICE车辆没有太大区别,后者会在炎热的天气使用更多的燃料来驱动空调系统。 Improved performance can be achieved by minimising solar gain while the car is parked, windscreen blinds and tinted glass will help this. Also making full use of preconditioning features to bring the car to temperature while plugged in so it does not drain energy from the car’s battery which would affect the battery range.

概括

总而言之,电池退化比制造商预测的要少得多,这主要是因为电动汽车在现实世界中的使用并不像制造商在开发这些汽车时考虑的测试周期那样积极。此外,大量的资金已经被用于确保退化被绝对地最小化。有几件事你可以做,以确保你个人可以进一步减少这一点,如避免在炎热的天气环境温度高时快速充电,明智地驾驶你的汽车,不要咄咄逼人,随时使用3-7千瓦的充电器充电。所有这些都将有助于你的电池长期。滚球体育app最新版狂热学习电动汽车技术播客封面艺术

附加信息

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关于作者

瑞安·莫恩

瑞安·莫恩

AVID Technology Group Ltd.董事总滚球体育app最新版经理。滚球体育app最新版AVID总部位于英格兰东北部,是重型高性能汽车电气化动力系统设计和制造的领导者。