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What’s the life expectancy of an electric car battery

electric-car-battery

Many consumers who own new energy vehicles, as well as those who want to buy new energy vehicles, have had such a question in their minds, “If I buy a new energy vehicle, how long can I drive it?”

In the oil car era, most of the life of the car is linked to the engine, transmission and such big parts. For example, I often go to a repair shop has received a single more than 300,000 kilometers of BMW E70, because the transmission is not good for a long time, replace a new unit price is too expensive, and finally the owner can only tearfully give up.

To the electric car era, we are most concerned about life expectancy of an electric car battery, and the factors affecting the life of the battery. Because we all play with cell phones, computers, tablets over, in the memory, performance disadvantages show up before, often the battery is the first to collapse, which leads to everyone is extremely sensitive to the battery life.

electric-car-battery
electric car battery

As for battery life, we can always hear various voices on the network. Some car owners denounce car companies have no conscience, their cars only run a few tens of thousands of kilometers on the “serious decline”, there are car owners sunshine their own vehicle mileage, with the car for nearly ten years, mileage decline is very little. Why is this?

What should be the life expectancy of an electric car battery? What are the reasons for the serious decline in mileage? If you are also interested in these questions, let’s take a brief look below.

Why does the life of a power battery decay?

The chemical properties of lithium-ion batteries decide

First of all, we need to know one thing, new energy vehicles use ternary lithium batteries and lithium iron phosphate batteries, all belong to lithium-ion batteries. Whether you use it or not, the life of lithium-ion batteries will gradually decline, which is determined by its chemical properties.

How to understand the chemical properties? Simply put, lithium-ion batteries are charged and discharged through the chemical reaction of redox. When charging, the lithium metal at the positive electrode is oxidized into lithium ions, which run through the electrolyte and diaphragm to the negative electrode; when discharging, these lithium ions in turn run back to the positive electrode.

how-lithium-batteries-work
How lithium batteries work

As you can see, lithium ions are critical to battery life, but here’s the thing, not all lithium ions are guaranteed to run successfully to the finish line. Because over time, the electrolyte and other materials inside the battery will slowly deactivate and deteriorate, making the flow of lithium ions more and more resistance, resulting in reduced life.

In addition, just as there are fast cars and slow cars in the traffic, the lithium ions flow at different speeds, for example, when charging (especially fast charging), some lithium ions will be too late to be embedded in the negative electrode before saturation, resulting in deposition on the surface of the negative electrode to form lithium dendrites. This will also continue to deplete lithium ions, ultimately affecting lifespan.

Cycle life is the most influential factor

For these two situations of lithium-ion battery characteristics, the industry has summarized two concepts to define the life of the power battery, the first of which is the calendar life, and the other is the cycle life.

Let’s start with calendar life. As mentioned earlier, in the case of complete non-use, lithium-ion battery internal materials will also decline over time, and from the battery brand new factory to the capacity fell to the national standard stipulated the lower limit of time, is the calendar life.

However, we usually do not know the calendar life of the power battery, because this concept sounds like the “shelf life”, which is unfavorable to those consumers who do not use the car frequently and want to keep it for a long time. In addition, long term storage does not fit most consumers’ scenarios, which is why we don’t see much discussion about calendar life.

life-expectancy-of-an-electric-car-battery
Life expectancy of an electric car battery

However, if we must add a time limit to the calendar life, to know the life expectancy of an electric car battery.

The general calendar life of lithium-ion batteries, basically within 8-15 years, which can also be glimpsed from the battery warranty life of various car companies.

In contrast, cycle life is more mainstream. Its definition refers to the capacity of the battery can realize the total number of cycles before falling to the lower limit of the national standard time, and the battery is full of full discharge once, is a cycle. Theoretically, the cycle life of lithium ternary is around 800-1500 cycles, while lithium iron phosphate can reach around 2000-2500 cycles.

If the cycle life is 800-1500 times, does that mean electric cars cannot be used after charging 800-1500 times?

Not entirely correct. Cycle life refers to the total number of cycles a battery can achieve until its capacity drops to a specified lower limit. When the battery reaches 800-1500 cycles, its capacity may decrease to a certain extent, potentially resulting in the electric vehicle’s range becoming insufficient.
However, this does not mean the battery is completely unusable or the car cannot be used. The battery system of an electric vehicle typically continues to function after reaching its cycle life, but it may exhibit reduced range or performance.
At this stage, the owner may need to charge more frequently or consider replacing battery components to maintain the vehicle’s normal operation.

EV owners’ habits amplify the disadvantageous scenarios

Understanding Battery Cycle Life Factors

The current consumer discussion on battery life is mainly centered on cycle life, and based on the characteristics of lithium-ion batteries, the main reason for the actual cycle life varies greatly is actually the different habits of car owners, the impact of lithium ions inside the power battery.

EV-Charging-stations
EV Charging stations

Depth of Discharge: A Critical Factor

Nothing affects this more than the depth of discharge. For example, many people choose to drive long distances during the holiday season, and then at once deplete the battery from 100% to very extreme single digits, and then continue to fully charge, and so on.

Effects of Deep Discharge

This depth of discharge, which is infinitely close to 100%, will cause a large number of lithium ions to be discharged from the negative electrode structure, collapsing the original negative electrode structure, and the collapsed portion will react with the electrolyte – equivalent to a person’s wound slowly crusting over after a piece of flesh has been torn off by a wild animal. Although the wound is healed, that part of the flesh will not grow back.

Similarly, the negative electrode structure is reacting chemically with the electrolyte to form a layer of SEI film that serves as an insulator, and although the structure is temporarily stabilized, the volume that can hold lithium ions is smaller, and the capacity of the battery is reduced.

Effects of Deep Discharge

In addition to deep discharge, another factor that affects cycle life is temperature, as too high or too low a temperature can amplify the drawbacks of the SEI membrane. the creation of the SEI membrane itself consumes lithium ions, and the higher the temperature, the thicker the SEI membrane becomes, further limiting the performance of the lithium-ion battery.

Thermal Management and Battery Safety

At the same time as the temperature rises, the SEI film will also begin to react chemically with the nearby electrolyte and active materials, generating a large amount of heat. In the past, when new energy vehicle thermal management technology was immature, some trams suffered spontaneous combustion at high temperatures from here.

Ensuring Optimal Battery Performance

This also means that if we want to keep the SEI film out of trouble, we have to find a way to find a parking environment with a suitable temperature for new energy vehicles; however, the control of the battery temperature is also part of the BMS work of the car company, so those car companies that have a wealth of experience in the research and development of power batteries, theoretically, their BMS strategy is also more mature, and better able to help consumers to control the working temperature of the power battery.

Extreme-fast charging (XFC) doesn’t really have much of an effect

The above two points are actually the biggest factors affecting cycle life, but I guess there must be some people who will ask whether using extreme-fast charging (XFC) will affect the battery life. There is no need to worry about this, because the impact is not significant.

For example, in recent years, there is an international standard for the definition of supercharging, called extreme-fast charging(XFC), that is, the power battery energy density ≥ 200Wh/kg, charging pile power ≥ 400kw, the battery can be charged to 80% within 15 minutes. This standard is currently the industry’s recognized direction of development.

In China, head power battery suppliers like CATL, FinDreams Battery, Svolt, and Greater Bay Technology all have the ability to produce batteries that meet the XFC capability, and these batteries will be able to basically catch up with standard charging in terms of their lifespan when using supercharging.

The non-XFC standard batteries in the supercharging will not make much difference, because the supercharging is divided into charging intervals, and the BMS will also enter the constant voltage charging stage at the end, slowly saturating the battery, to avoid excessive lithium dendrites.

The example of Life expectancy of an electric car battery

Although the different habits of car owners will bring a certain degree of influence on the life of the power battery, but as consumers, we do not have to hold too much psychological pressure on the life of the power battery, let go of the heart to drive normally. Because in addition to the car company’s BMS support, the cycle life of the power battery itself, the actual longer than we thought.

Let’s take Xiaopeng P7 as an example, the nameplate of the power battery on the car, which mentions the implementation of the standard GB/T 31484/86-2015, which is China’s mandatory standard for battery life, and this standard requires that, after 1,000 charging and discharging cycles, the battery must ensure that the capacity of not less than 80% of the initial state.

Here, we assume that this Peng P7 is 2022 562E version, its NEDC range is 562km, then in the national standard 1,000 charging and discharging cycle, this car will be able to run 562 * 1,000 = 562,000 kilometers of the total NEDC mileage, and even if the actual range is halved, there are still 281,000 kilometers, enough to cover the majority of people’s car replacement cycle.

By the way, one more thing, car companies in the R & D cycle will generally have a verification process, which will be for the cycle life of the power battery under various conditions to ensure compliance with the national standard requirements, so this calculation is still very worthy of reference.

How do we maintain battery life?

Understanding Battery Life Factors

The last part of the sprawling talk a lot, and the actual impact of new energy vehicle power battery life is the main depth of discharge and battery temperature, in which the depth of discharge and the owner’s car habits have a lot to do with the temperature of the battery depends on the owner’s car environment, but also to test the car company’s BMS strategy.

How-do-we-maintain-battery-life
How do we maintain battery life

Consumer Initiatives for Battery Maintenance

In addition, for us ordinary consumers, if we want to maintain the battery life, the main way is to play our own initiative, by learning a more scientific way to use the car to achieve the goal.

For example, in deep-discharge scenarios, unless the situation is special, I suggest that we try not to “play the limit”, especially not like some automotive media, in order to test a so-called maximum range, deliberately drive a car to a completely dead battery, this is a gimmick far greater than the reference value.

Before the next charge, we would like to leave 10-20% of the remaining battery power, and do not have to pursue times full, only to 90-95% can be charged, this point for the ternary lithium batteries are more worth paying attention to, because its cycle performance is inherently inferior to lithium iron phosphate batteries.

Tesla-super-charging-station
Tesla super charging station

Consumer Initiatives for Battery Maintenance

Second is the working temperature of the power battery, in general, 15-35 degrees Celsius working temperature is the most suitable for lithium-ion batteries, so in the choice of parking lot scenery, four seasons of constant temperature and humidity of the basement is a better choice.

Of course, these are still too harsh for us consumers, after all, I bought the car is to serve me, why let me to accommodate the car? Therefore, the safest choice is still to buy those high-level new cars launched by mature manufacturers, these car companies not only have a relatively more mature BMS, in the battery heat dissipation will also be given to higher-cost program, through the structure, process to make up for the inherent shortcomings of lithium-ion battery materials.

Conclusion

To summarize, our concern about the life of the power battery is actually slightly redundant, because under the national standard, the mileage of many new energy vehicles is enough for us to use until the replacement of the car, and on this basis, the car company will also provide a variety of warranty policies about the battery.

As consumers, we can try to understand more about the scientific use of knowledge, such as trying to look at the manual, because it will talk about a lot of the correct way to use the car, and the reliability of this knowledge is certainly far greater than that you get from other entertainment platforms, which will be able to further ensure that the battery life.

As for car companies and EV charger manufacturers, I think they should also give more consideration to consumers, for example, car companies can put more emphasis on marketing to the after-sales part to provide consumers with more direct and effective car maintenance advice, rather than “hiding” these suggestions in the manual.

As a professional manufacturer of EV chargers, we will also release some useful knowledge about electric vehicles to help people recognize and use electric vehicles in a more comprehensive and scientific way. As a result, a lot of problems and troubles in choosing and using electric vehicles will be solved fundamentally.

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Leo Chen

Leo has rich experience in the field of EV charger industry.

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