The energy storage of a battery can be divided into three virtual areas: a blank area that can be filled, a usable area that can provide energy, and an unused area, or rock area, due to use and aging, as shown in Figure 1.
Batteries decay from the time they are manufactured, and a new battery must provide 100% capacity, which most batteries in use cannot achieve.
As the usable area of the battery shrinks, the amount of energy that can be filled decreases, and the charging time gradually decreases. In most cases, battery capacity declines linearly due to cycle and aging. In addition, deep discharges put more stress on the battery than incomplete ones, so it's best not to drain the battery completely but to charge it frequently. For nickel-based batteries and smart batteries as calibration components, periodic deep discharge should be used to eliminate the "memory effect" of nickel-based batteries. Nickel-based lithium batteries can be fully charged and discharged for 300 to 500 weeks before their capacity decays to 80%.
Charge-discharge cycles are not the only cause of capacity decay, as storing lithium batteries at high temperatures can also cause capacity decay. A fully charged lithium-ion battery can lose 35% of its capacity when stored at 40 ° C (104°F) for a year without use. Super fast charging and discharging is also harmful to the battery, reducing the battery life by half, which is very obvious for single lithium batteries. Battery packs are high in specific energy, but are particularly subtle due to individual cell differences.
Device specifications are often based on new batteries, but this is a temporary phenomenon in the initial phase, not for long. Like an athlete, performance will gradually decline over time and, if left unchecked, will eventually lead to battery-related failures.
Batteries often need to calculate their capacity decay and final life. When the capacity decays to 80%, the battery pack needs to be replaced. The ultimate life limit of the battery pack should vary according to the application, the user's preference, and the company's guarantee. Since mechanical failures are rare, capacity decay is a good indicator for an eventual replacement plan, which can be achieved by checking the capacity of batteries in service every three months. In addition, technology is also being developed to characterize the operating state of the charger.
In addition to decay related to aging, sulfate and plate corrosion are the main factors affecting the decay of lead acid batteries. Sulfation is a thin film layer formed on the cathode plate when the battery stays at a lower rate of charge. If found in time, this can be eliminated by equalizing charging. The grid corrosion can be reduced by improving the charging state or using an optimized floating charging method.
In nickel-based batteries, the so-called unusable rock zone is usually caused by the formation of crystals of the active substance, also known as the "memory effect". Deep charge-discharge cycles often restore the battery to full capacity. Periodic discharge can also control the crystallization process, avoiding the harm to the diaphragm.
The aging of lithium ion batteries is the oxidation of internal materials, which is a part of the process of use and aging, and is naturally occurring and irreversible.
