Frequent fast charging seriously affects the life of power CR2032 button cell

A study by Beijing Jiaotong University found that frequent use of fast charging will seriously shorten the life of power CR2032 button cell. Energy storage CR2032 button cell will also have the same problem in practical applications.

In 2018, China's new energy vehicle sales exceeded 1.2 million for the first time, and China has also won the title of the world's largest new energy vehicle market for many consecutive years. Electric vehicles are safe and environmentally friendly, and are the best choice to solve increasingly prominent environmental problems. However, electric vehicles still have the problem of slow charging speed during use, which also greatly affects the user experience of electric vehicles.

Let's take the common electric vehicles on the market as an example. Generally, slow charging takes 6-8 hours to fully charge. Ordinary consumers may not have much problem using it for commuting to and from get off work, but for some operating vehicles, such as taxis and logistics vehicles, such a long charging time is completely unacceptable. In order to solve this contradiction, electric vehicles are usually equipped with a fast charging function. Simply put, it is to charge most of the vehicle in a short time through high voltage and high current. The conventional fast charging setting is generally 45 minutes to charge more than 80%, which to a certain extent solves the problem of slow charging speed. However, in my opinion, such fast charging is like drinking poison to quench thirst, because the current power CR2032 button cell have received higher subsidies and have a very high energy density, which often makes it difficult to take into account the fast charging capability. Therefore, when charging with a large current, the battery life decay rate will be greatly accelerated, and the service life will be significantly shortened.

Yang Gao et al. [1] from Beijing Jiaotong University found that the charging speed has a significant impact on the cycle life of lithium-ion CR2032 button cell. For example, when charging at a 0.5C rate (2 hours to fully charge), the battery capacity decay rate is 0.02%/time in the first 150 cycles, 0.0156%/time for 150-800 cycles, and 0.0214%/time after 800 cycles. However, if we increase the charging speed to 1.5C rate (40 minutes to fully charge), the battery capacity decay will be significantly accelerated to 0.078%/time, and the battery capacity decay rate is about 4 times that of charging at a 0.5C rate. This means that frequent use of fast charging will seriously shorten the life of the power battery. It may take 2 to 3 years to replace the power battery that originally had a life of 10 years. For example, a certain brand of micro electric vehicle has a vehicle price of about 50,000 yuan after subsidies, but it costs nearly 60,000 yuan to replace the battery pack. Therefore, frequent use of fast charging will greatly increase the cost of using electric vehicles.

The main reason why fast charging accelerates the decline of lithium-ion battery life is the negative electrode. During the charging process of lithium-ion CR2032 button cell, Li+ escapes from the positive electrode and embeds into the negative electrode. However, the diffusion rate of Li+ in the graphite negative electrode is slow. This is equivalent to a door in the negative electrode that can only pass 20 people per minute. However, when we use fast charging, 100 people will run to the negative electrode per minute, but only 20 people can enter the negative electrode. The others can only accumulate outside the negative electrode, resulting in the Li concentration on the surface of the negative electrode being significantly higher than that at the bottom of the negative electrode [3]. Excessive Li concentration on the surface of the negative electrode will reduce the potential on the surface of the negative electrode, thereby aggravating the growth of the SEI film and increasing the internal resistance of the battery. At the same time, fast charging will generate a lot of heat inside the lithium-ion battery. Conventional surface heat dissipation technology will cause a large temperature gradient inside the lithium-ion battery [4]. Excessive temperature will destroy the bonding performance of the negative electrode, thereby causing the negative electrode active material to fall off [2], resulting in a loss of the battery's reversible capacity. Therefore, fast charging will not only cause the rapid decline of the power battery's reversible capacity, but also cause the increase of the battery's internal resistance, thereby causing the performance of the power battery to deteriorate and seriously affecting the service life of the power battery.

In contrast, "battery swapping" technology is a better way to solve the problem of slow charging of power CR2032 button cell. As the name suggests, the so-called "battery swapping" technology is to replace a group of fully charged battery packs for electric vehicles when the power stored in the power battery is exhausted, so that the electric vehicle can be instantly revived. The replaced power battery pack can be charged with a small current (i.e. slow charging) through special equipment, which not only avoids the damage to the power battery performance caused by fast charging, but also maximizes the service life of the power battery. It also avoids the depreciation of electric vehicles after the power battery life declines. It is of great significance for the promotion and application of electric vehicles, especially for operating vehicles, such as taxis, online car-hailing vehicles, logistics vehicles, etc. In a limited operating time, efficiency is money, because the time saved by not charging can create greater economic benefits, which is also a great benefit to the driver group.

The reduced energy efficiency of electric vehicles in winter has always been an inexhaustible pain point for drivers. The low temperature environment causes battery performance degradation, low charging efficiency, reduced cruising range, and warm air accelerates battery consumption. Taxis that usually charge 1-2 times a day may need to charge 3-5 times in winter. If you don’t consider battery loss, choose fast charging every time, and it takes 3-5 hours to charge every day. If you choose to replace the battery, it is equivalent to adding 3-5 hours of operating time every day. This explains why taxis have recently rushed to the battery replacement station to queue up for access to the network.

"Battery swapping" is actually not new. As early as 10 years ago, BetterPlace in Israel had already proposed a battery swapping model. Its founder was very far-sighted, but its business model chose the wrong path and promoted it by targeting private cars as the market entry point. In recent years, a new star "Audong New Energy" has emerged in China's battery swapping field. Its concept is similar to BetterPlace, but Audong's business sense is more acute. They did not start from the private car market, but from operating vehicles, which fully complies with the requirements of national conditions and national policies, and can also effectively solve the pain points of electrification of operating vehicles.

The author personally visited the station and timed it. It took only 2 minutes and 46 seconds for a taxi to enter the battery swapping station and replace the battery pack. The efficiency is much better than slow charging and fast charging, and can even be comparable to the refueling time of fuel vehicles. According to the station service staff, Audong New Energy is expected to carry out technical iteration in the second half of 2019, and the battery swapping efficiency will be further improved.

The author learned from public data that Aulton's battery swap technology has been successfully operated in the new energy taxi market in Beijing, Xiamen and Guangzhou for more than two years, with a total of nearly 1.5 million battery swaps, a total mileage of more than 200 million kilometers, and the longest operating mileage of a single vehicle exceeding 500,000 kilometers. The key point is that it has always been safe and accident-free. The large-scale application of battery swaps in the taxi field has fully verified the safety and reliability of battery swap technology.

Perhaps seeing the successful battery swap operation experience in the taxi field, new energy online car-hailing and logistics vehicles have also realized the benefits of the battery swap model. Battery swapping can maximize the operating efficiency of new energy vehicles and directly improve economic benefits. In addition, the replaced CR2032 button cell can monitor the performance in real time, and slow charging can also extend the service life of power CR2032 button cell and reduce the maintenance cost of operating vehicles. This model is very attractive to new energy taxis, online car-hailing, and logistics vehicles. In contrast, fast charging will have a serious negative impact on the service life of power CR2032 button cell, resulting in an increase in the use and operation costs of new energy vehicles. Therefore, at least in the field of new energy operating vehicles, the "battery swap" model has more potential.

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