Power cell capacity decay seriously affects endurance

From pure electric vehicles to computers, mobile phones and other electronic products, the battery life ability has always been highly concerned by consumers, even the recent Samsung note7 explosion. It has also been blamed by some experts for developers 'excessive pursuit of endurance and ignoring the safety risks of batteries. Battery-troubled companies are not alone. Recently, Microsoft Surface-Pro3's batteries have also experienced problems. Some users have reported that the Surface-Pro3, which is equipped with LGC batteries, has severely reduced its life after the upgrade.

Why does lithium ion battery capacity decay?

Lithium-ion batteries are the fastest developing secondary batteries after cadmium nickel batteries and hydrogen nickel batteries. The application of lithium-ion batteries depends to a large extent on the stability of their charge and discharge cycles. Like other secondary batteries, the capacity attenuation of lithium-ion batteries during the cycle process is inevitable.

Lithium-ion batteries have different embedding energy when they are embedded between two electrodes. In order to obtain the best performance of the battery, the capacity ratio of the two host electrodes should maintain a balance value. If the capacity ratio is too large or too small, it will cause the negative electrode material to be overcharged and there is a safety risk, or the negative pole can not be fully used.

For an ideal lithium-ion battery system, the capacity balance within its cycle does not change, and the initial capacity in each cycle is a certain value, but in fact the situation is much more complicated. Any side reaction that can produce or consume lithium ions or electrons may lead to a change in the battery capacity balance. Once the battery's capacity balance state changes, this change is irreversible and can be accumulated through multiple cycles. The performance of the battery has a serious impact.

In lithium ion batteries, in addition to the Redox reaction that occurs when lithium ions are deembedded, there are also a large number of side reactions, such as positive and negative electrode over-charging reactions, electrolyte decomposition, self-discharge, active substance dissolution, and metal lithium deposition. All of these will cause the battery internal capacity balance to be destroyed, resulting in permanent capacity loss of lithium batteries. In addition, external factors such as the extremely warm environment will also cause a temporary decrease in the capacity of lithium batteries.

Power cell decay seriously affects endurance.

In the past two years, China has vigorously promoted the development of new-energy automobile industry. However, in the initial stage of the development of emerging industries, some problems will always be exposed. The problem of power cell decay is also becoming a bottleneck that hinders the development of new-energy automobiles.

Low temperature is the battery killer. In the cold winter weather, lithium batteries of pure electric vehicles are normal due to reduced activity and the need to supply air-conditioning for a long period of time. In particular, the use of air-conditioning has greatly shortened the mileage of electric vehicles. This is because gasoline vehicles rely on engine cooling to provide warm air and will not increase fuel consumption. Electric vehicles need to consume more power because they do not have engine cooling. To heat up. That is one reason consumers complain about the generally inflated range of electric vehicles, even for Tesla's users. In Tesla's Norway, the world's second-largest market, there are plenty of cases of models users complaining of a sudden drop in mileage and trouble charging when temperatures fall below zero degrees. Tesla also admitted that when the temperature is below 0 degrees, ModelS will suffer from charging problems.

The difference of single battery and low level of BMS system cause battery decay. Power batteries are composed of a large number of single cells. According to the level of manufacturing of the battery manufacturer, the difference between individual cells in the battery is not the same. After repeated charge and discharge cycles of lithium batteries, the difference between the batteries will become more and more large.

Due to the overcharge and overdischarge protection of the BMS battery management system, the battery with the highest charge at the time of charging is full and stops charging, while other strings can not be filled; The battery with the lowest charge at the discharge stops discharging, and the other strings can not discharge the electricity; The "virtual power"(unusable power) of lithium battery packs has gradually increased, the actual effective power of lithium battery packs has greatly decreased, and the range of electric vehicles has continued to decline. If it is not balanced in time, the deeper the battery series discharge depth, the easier it is to shorten the life, and even the case of individual battery damage. However, many manufacturers do not understand the importance of BMS equilibrium function, and based on cost considerations, many electric car lithium battery packs BMS do not have equilibrium functions, or they are simply equipped with passive equilibrium functions. The difference between the batteries in the battery pack could not be repaired in time.

The owner of the vehicle used in the process of improper operation caused mileage attenuation. As mentioned above, overcharging and overloading can cause battery capacity to be reduced, the owner's charging time is too long, or the battery balance is not considered when driving until the car is in love, which will affect the range and service life of the power battery. In addition, since lithium batteries will not be self-discharge for a long time, this will also cause damage to power batteries. Therefore, when an electric car is not in use for a period of time, it needs to start the car at regular intervals to recharge the battery.

Power cell warranty is gradually being improved

At present, the vast majority of new energy vehicle products being sold in China have a lot of fuzzy areas and problems in terms of battery quality protection conditions. These problems, along with the increase of domestic new energy car product ownership and retention time, also gradually surfaced. Although domestic new energy vehicles have put forward terms of time and mileage for quality assurance of vehicles and key components, they have not explained the conditions for battery quality assurance. This has led consumers to purchase new energy vehicles and found that the battery decay problem has occurred. There have been many disputes with dealers.

Recently, the Beijing New Energy Automobile Industry Association issued the "Beijing Model Application of New Energy Minibus after-sales service specification(draft for consultation)". In the "Code", it is proposed that the warranty period for key parts such as power batteries and management systems, drive motors and their controllers, and vehicle controllers of new energy minibuses should not be less than 8 years or 120,000 kilometers, whichever is first arrived; Where a new energy passenger car has a product quality problem within 60 days from the date the seller invoices for the purchase of the car or within 3,000 kilometers(whichever is the first arrival), the main parts of the power battery or drive motor have product quality problems. Consumers can choose to replace power batteries and drive motors for free.

Battery China Network believes that at the beginning of the development of new energy vehicles in China, some problems are inevitable. With the improvement of the technology level of power battery manufacturers and vehicle enterprises, these problems will be gradually eased or solved. At present, China's power cell related quality assurance provisions are still under construction, the entire system needs to be improved, if necessary, can learn from the relevant regulations of Germany and other countries.

The page contains the contents of the machine translation.