How long does the EV's in-vehicle battery last? What is an efficient charging method?The photo shows the charging port of the Nissan Leaf e +.

With the upcoming adoption of electric vehicles (EVs), many consumers may be wondering how long an in-vehicle battery will last. As an example of seeing related images, Nissan has given a warranty of 160,000 km for 8 years to a 30hWh lithium-ion battery in the latter half of the first "Leaf". The initial 24kWh specification was 100,000km for 5 years, which is a dramatic improvement in durability. Apart from the guideline, in practical use, the degree of deterioration changes depending on the charging method. Differences in charge / discharge between lithium ion and lead acid or nickel-metal hydride Lithium-ion batteries differ in charge / discharge method from conventional lead acid, nickel-metal hydride. In all conventional batteries, the metal of the electrode undergoes a chemical reaction due to the electrolyte, and when it is oxidized, it emits electrons to conduct electricity. That is, the metal of the electrode chemically changes to another metal. When charged, it is reduced and returned to the original metal. Since the metal of the electrode changes with each charge and discharge, the deterioration was quick. On the other hand, in the lithium ion battery, electricity flows only by passing lithium ions contained in the electrode back and forth between the positive electrode (+) and the negative electrode (-), so that the material of the electrode does not change. It will eventually deteriorate, but it will last longer than other batteries. With this in mind, a method different from lead acid or nickel-metal hydride for charging is a way to further suppress deterioration. Efficient charging of lithium-ion batteries Nickel-metal hydride, which was popular in hybrid vehicles (HVs), has the same characteristics as the nickel-cadmium (commonly known as NiCad) before that, so if you charge it before the stored power is used up, it will have a memory effect. It has the characteristic that it will not be fully charged to reach its original capacity. For this reason, it is recommended to use up the electricity as much as possible before charging. Some chargers have built-in controls that first discharge when power is still available and then start charging. Lead-acid batteries can provide stable performance when fully charged, so it is recommended to keep them fully charged at all times. Therefore, if you do not use the car for a long time, it is said that you should disconnect the electrode wiring. If it is left in a state where the electricity is used up, it will deteriorate. On the other hand, the lithium-ion battery may be charged even if the power is not used up. Also, if you keep the charge up to around 80% instead of 100% charge, it will last a long time. This applies not only to EVs but also to smartphones and laptop computers. EV is basically charged normally at home. Even on the go, when you stay for a few hours, such as at a work place where you stay for a relatively long time, at a shopping mall, or at a restaurant, you can charge the battery little by little with a low current, and even if it is not fully charged, the next route The best way to use it is to add it on the ground with normal charging. It is not appropriate to give priority only to the installation of quick chargers and aim for full charge after running out of electricity. However, this point is suitable because even quick charging can only charge up to about 80%. "Post-EV" batteries are also worth secondary use Next, EV batteries still have 60-70% capacity at the end of their lifespan. Unlike other electric products, cars frequently accelerate and decelerate, and the vertical range of current is large, so a battery that has consumed about 30% cannot exhibit sufficient performance in acceleration. On the other hand, general electric products such as smartphones are often used at a certain constant current consumption, which is called rated power, and do not require instantaneous current. Therefore, even a battery that has reached the end of its life with an EV can still be used for several years. For example, it can be used as a support battery to supplement the unstable power generated by renewable energy. The value remains in the battery after EV. The value of secondary use of batteries after EVs could further reduce the cost of EV batteries in the future. Regarding the transshipment of EV batteries, it is said that it will cost 700,000 to 800,000 yen to replace the battery of the first "Leaf". At the same time, the use of secondary batteries has begun. By using this, it is possible to replace the battery at about half the price. There is no point in worrying about the same idea as an engine car. Even if it is a battery after EV, the deterioration is not uniform, and the battery has a habit of producing only the performance that matches the cell with severe deterioration. Therefore, if the battery after EV is disassembled into cells, there are some cells that leave the capacity that can be used as EV. If you collect and assemble it, you can still run an EV. Nissan has already started this business. In addition, Honda and other manufacturers that sell EVs are developing recycling businesses. At the stage when EVs are finally becoming widespread, there is no point in worrying about the same idea as engine cars. There are ways to use EVs and how to extend their lives. And eight years later, 60% of domestic power generation will be decarbonized. The EV era is about to begin.

Response Naotsugu Mihori