What is the typical battery life of a new energy vehicle?

Very long. To put it simply, if you quantify this for a 500km range vehicle, with a cycle life of 2,000 cycles, ideally you would be able to drive at least 1 million kilometres before the battery life is over. The above is the ideal situation, so based on actual statistics, Tesla's early model Model S/X, for example, throws around 85% of its usable battery capacity after 200,000 miles (320,000 km).

To understand battery life, it is important to first understand what battery life refers to. Battery life is generally referred to as Cycle Life and Calendar Life, with Working Condition Life as a reference in some standards. EOL (End Of Life) does not mean that the battery has decayed to 0% or is unusable, but rather that the total capacity of the battery falls to 80% (some tests and experiments use 70% as the base) of the original design capacity. For example, if the battery starts at 80% and is used up to 30%, i.e. 50% depth of discharge (DOD), then this will only count as 0.5 cycles, if the DOD is 20%, then it will only count as 0.2 cycles. 0.2 cycles.

According to experiments in a paper by Professor Ouyang Minggao of Tsinghua University, an academician of the Chinese Academy of Sciences, different DODs can significantly affect battery cycle life, with higher DODs accelerating battery decay, all other conditions being equal.

In other words, if only 40% of the vehicle's charge is used before each charge, e.g. 80%-40%, the battery cycle life is approximately three times longer than if it is used up from 100% every time; assuming a 400km range vehicle, the worst case 100% DOD, i.e. full and full charge every time, would result in approximately 1.04 million km of driving before the end of life; under the best case 40% The best case scenario of 40% DOD, where only 40% of the charge is used before each charge, would result in a range of approximately 3.2 million kilometres before the end of life.

Of course, DOD is not the only thing that affects cycle life, but also the charging rate and SOC (State Of Charge). In a paper from Chalmers University of Technology, Sweden, it is shown that the higher the charge rate, the lower the cycle life under the same conditions, e.g. in the second picture below, a charge at 4C (i.e. 15 minutes full) at 10% DOD will result in a cycle life of around 4000 cycles, while a charge at 1C (i.e. one hour full) under the same conditions will result in a cycle life of around around 7,000 cycles.

At the same time, the higher the SOC, the more it will be affected by the high charging rate and high DOD, which means, to put it bluntly, that deep discharge or fast charging under high charge conditions will accelerate the decay. And in the low SOC case, with a 10% DOD comparison, even with a fast charge at 4C rate, the battery only decays to 88.5% after 10,000 cycles; while in the higher SOC case, the cycle life decays considerably.

So the charging strategy for almost all brands of EVs is to charge at a very high rate when the charge is low, and to reduce the rate when charging to a higher rate to ensure that cycle life is not affected. Note, however, that the SOC must not be too low, otherwise it will instead accelerate battery degradation. Calendar life, on the other hand, refers to how long the battery will be left to reach EOL at different remaining charges (SOC, State Of Charge) when it is not used for a long period of time;

it is clear from the icon that it is important to try not to keep the SOC very high when the vehicle is left unused for a longer period of time; and calendar life does not only depend on the SOC but also on the battery temperature conditions.

In general, the optimum operating temperature range for the battery, which is the temperature range that guarantees calendar life, is the 15-35°C range.

Seeing this, many people may wonder why this result is somewhat different from the reality they hear, when looking at the experimental data, it seems that the cycle life is all around 2000-5000 cycles and the calendar life is at least 15-20 years. Because, in reality, there are many reasons for battery degradation. And not all of them are like the laboratory, where the effect of a particular environmental factor on the decay is measured with controlled variables.

The actual battery pack that is carried in the vehicle is subject to, but not limited to, the production of a large number of cells, testing, consistency, the hardware and software design of the pack, temperature control systems, etc. These variables cannot be constant in real life use scenarios.

So battery degradation, to a lesser extent, is the physical and chemical characteristics of the cells, to a greater extent, is the car companies in the battery system as a whole "kung fu". Back to the essence of battery degradation, that is, all the above mentioned factors that may affect the battery life, in fact, at the cell level, can be summarised as: Loss of Lithium Ion (LLI) and Loss of Active Matter (LAM) in the negative/positive electrode.

To put it more graphically, LAM is like the change in the water tank itself, and LLI is like the loss of water in the tank. In other words, the various factors mentioned above can cause LLI or LAM to occur in the battery, which in turn accelerates battery degradation.

In addition, battery degradation actually includes an increase in internal resistance and electrolyte consumption. This is because the increase in internal resistance leads directly to a decrease in the power of the battery and a decrease in the usable capacity of the battery; and electrolyte consumption is also a very important mode of degradation. While a small amount of electrolyte depletion has little effect on battery performance, too much electrolyte depletion can lead directly to a sudden drop in capacity. In summary,

Li-ion batteries are a very complex system with many different decay mechanisms, and just because the same recipe and case looks alike does not mean the same result. To extend the life of a battery, it needs to be carefully designed and optimisation methods based on computational models can be used to reduce the occurrence of internal side reactions. During the manufacturing process, it is important to ensure the quality of the battery, especially by controlling the homogeneity of the processes at the same time.

When using batteries, the temperature and voltage need to be controlled within the optimum operating range by designing the vehicle, the pack, the thermal management system and the battery management system algorithms, while the charging current needs to be very carefully controlled.

As far as each consumer is concerned, the simplest way to extend battery life is to use a battery, no matter what kind of battery it is (lithium iron phosphate needs to be filled for a certain period of time to calibrate the power calculation), without a full charge when not travelling long distances; usually use the car, if you have the conditions to use that charge, you don't have to use it until it is particularly low and then charge it, and you don't have to worry about frequent charging affecting the battery life, instead, you can often use the middle percentage of power to Instead, frequent use of the middle percentage can slow down battery decay.

Of course, many people have to recharge their batteries every time, partly because of their digital habits and partly because of the lack of convenience of charging stations. However, firstly, the lithium battery used in digital products is different from that used in electric cars. Its orientation is to meet the characteristics of high energy density and fast charging and discharging, at the expense of the battery life, which is generally at the end of 2-3 years, so electric cars do not need to follow this habit.

The second is the charging pile. At present, brands build their own charging, third-party charging and home charging are becoming more and more popular, so there is almost no need to worry about this problem.

Up to now, the number of Tesla's Supercharger stations open for use in mainland China has exceeded 1,300, with over 9,200 Supercharger piles, paired with over 700 destination charging stations and 1,800+ destination charging piles, covering over 360 cities and regions in mainland China. Finally, as for the control of temperature, charging speed, etc., it will be left to your trusted brand to consider. In other words, where you can least see, there is actually the most and most valuable technical strength hidden, and time is the best proof.