Discussion on cycle life of lithium iron phosphate battery and influencing factors of life
ONE. Cycle life of lithium iron phosphate battery
Lithium iron phosphate batteries have a long cycle life, which can generally reach more than 2000 times. This means that under normal conditions of use, after multiple charge and discharge cycles, the battery can still maintain a high capacity and performance.
Its long cycle life is mainly due to the following aspects:
Stable chemical structure: lithium iron phosphate has a stable olivine structure, which changes little in structure during charging and discharging, and is not easy to collapse and damage, thus ensuring the long-term stability of the battery.
Good safety performance: lithium iron phosphate battery is relatively safe in the case of overcharge, overdischarge, short circuit, etc., and is not easy to occur dangerous situations such as thermal runaway, which reduces the battery life shortened due to safety problems.
High temperature resistance: Compared with other types of lithium batteries, lithium iron phosphate batteries can work at higher temperatures, and high temperatures have relatively little impact on battery life.
TWO, the factors affecting the life of lithium iron phosphate battery
Depth of charge and discharge
Shallow charging and shallow discharge can prolong battery life. When the battery is only partially charged and discharged each time, that is, when the depth of charge and discharge is shallow, the chemical reaction inside the battery is relatively mild, and the structure of the electrode material changes little, which can extend the cycle life of the battery. For example, the battery charge and discharge range is controlled between 20% and 80%, compared to each full and empty, the battery life can be significantly improved.
Deep charging and deep discharge will shorten battery life. If the battery is often fully filled and emptied, that is, the depth of charge and discharge is large, the electrode material inside the battery will bear greater stress, easily leading to structural damage and capacity attenuation. For example, in some application scenarios that require high battery capacity, frequent deep charging and deep discharge may cause the battery to decrease significantly in a short period of time.
Charge and discharge ratio
Low rate charge and discharge helps extend life. Charge and discharge with a lower current, charge and discharge rate is small, the chemical reaction inside the battery is slower, less heat is generated, and the damage to the electrode material is also small. For example, in some energy storage systems, the use of low rate charge and discharge can make the life of lithium iron phosphate batteries reach several years or even longer.
High rate charge and discharge will reduce life. When rapid charging and discharging with high current is carried out, the charging and discharging ratio is large, and more heat will be generated inside the battery, which may lead to the acceleration of the structural change of the electrode material and the increase of side reactions, thus shortening the life of the battery. For example, in the fast charging mode of electric vehicles, although charging time can be saved, frequent use of high rate charging may adversely affect battery life.
temperature
The right temperature extends battery life. When the lithium iron phosphate battery works in a certain temperature range, the performance is more stable and the life is longer. Generally speaking, 20℃ -35 ℃ is a more suitable working temperature range. In this temperature range, the chemical reaction rate inside the battery is moderate, and the activity and stability of the electrode material is good. For example, lithium iron phosphate batteries used in indoor environments are usually able to maintain good life performance.
Both high and low temperatures affect life span. The high temperature will accelerate the chemical reaction inside the battery, resulting in aging and capacity attenuation of the electrode material. At the same time, high temperatures may also cause safety problems, such as thermal runaway. For example, in the hot summer, if the battery is in a high temperature environment for a long time, the life will be significantly shortened. At low temperatures, the performance of the battery will be reduced, the charge and discharge ability will be weakened, and charging at low temperatures may lead to the formation of lithium dendrites, causing irreversible damage to the battery. For example, in the cold winter, the range of electric vehicles will be significantly reduced, and battery life may also be affected.
Battery management system
A good battery management system (BMS) is essential to extend battery life. The BMS can monitor the battery voltage, current, temperature and other parameters in real time, and carry out reasonable charge and discharge control of the battery according to these parameters. For example, when the battery temperature is too high, the BMS can start the cooling system to reduce the battery temperature; When the battery is overcharged or overdischarged, the BMS can cut off the charge and discharge circuit in time to protect the battery. In addition, BMS can also ensure that the state of each single battery in the battery pack is consistent by means of balanced charging, so as to avoid affecting the life of the entire battery pack due to excessive differences in single batteries.
Imperfect BMS can shorten battery life. If the BMS function is not perfect, can not accurately monitor and control the status of the battery, it may lead to the battery overcharge, overdischarge, overheating, etc., thus accelerating the aging and damage of the battery. For example, the battery management system used in some low-end electronic products may not be accurate enough, which is easy to cause problems in the use of the battery and shorten the battery life.
Storage condition
Proper storage can preserve battery life. When the lithium iron phosphate battery is not used for a long time, it should be stored in a dry, cool, ventilated environment, and maintain a certain state of electricity. In general, it is more appropriate to store the battery at a state of 40%-60% charge. This can avoid damage to the battery due to excessive self-discharge, and also reduce the capacity attenuation of the battery during storage. For example, some spare batteries can maintain good performance after a long time if they are stored correctly.
Poor storage conditions can reduce battery life. If the battery is stored in a state of high temperature, humidity, full charge or empty power, it will accelerate the aging and capacity decay of the battery. For example, if the battery is placed in direct sunlight or in a high temperature environment, the battery may have problems such as bulging and leakage. When the battery is fully charged or drained for a long time, the activity of the electrode material will be reduced, affecting the performance and life of the battery.
