Reliability and life prediction of rechargeable batteries

Reliability and life prediction of rechargeable batteries

① Forecast of battery life
The prediction of battery life is not only difficult but also expensive. In addition, the battery life depends on the number of charge and discharge cycles, the materials used and the type of operation (intermittent or constant). The life expectancy of lead-acid batteries for start-up, lighting, and ignition (SLI) applications is relatively simple, because the design of lead-acid batteries is fully mature, and the material costs and maintenance procedures are fully known. For batteries that use solid electrodes and special all-solid materials, the life expectancy is more complicated. As mentioned earlier, life prediction strictly depends on the materials used in the cathode and anode, the characteristics of the materials, and the maintenance procedures and schedules used. Research on rechargeable batteries used in electric vehicles and hybrid vehicles has shown that predicting the life or reliability of battery systems is both expensive and extremely difficult. It is worth noting that, for reasonable accuracy, it needs to test a known full-size battery system or battery pack in various weather and driving conditions in the past few years. The high degree of uncertainty stems from the structure of the electric vehicle battery, which usually requires 100 or more electrochemical cells connected in series. In addition, with the changes in the manufacturing process between the batteries and the temperature changes between the batteries and the batteries during use, it is extremely difficult to maintain the electrical performance balance of so many batteries during the service life of the batteries.
Various levels of system control and maintenance plans need to reach a balance point, and may also include some combination of thermal management systems, periodic overcharging, and active electronic systems to maintain the state of charge of the battery within its expected operating range. In short, the actual effect of such changes means that the life of such rechargeable battery systems is also highly variable and unpredictable.

battery life

②Reliability and failure mechanism of rechargeable batteries
The reliability of any equipment or system, such as rechargeable batteries, strictly depends on the probability of zero failure reliability over a period of time and the failure rate of the related components included. In this case, the anode and the electrode are the main components, because after a long-lasting electrochemical process, the surface of the anode and the electrode will decompose. It is necessary to determine the failure mechanism of rechargeable batteries, especially since many rechargeable batteries are used in military and satellite applications. In commercial applications, the failure mechanism is easy to determine, and corrective steps can be taken without interrupting the operation of any equipment or system. The measurement of component reliability includes the calculation of the failure rate under working conditions within a specified time interval and the analysis of failure modes. Because the battery consists of two basic components in series, the reliability of these two components must be considered. The reliability of a component or device can be estimated by the mathematical theory of reliability. On the basis of this theory, the reliability of the battery can be calculated by exponential failure rate (λ).
R(t) =[e-λt]

In the formula: R(t) is the reliability of zero failure within time t; λ is the sum of the failure rates of the anode (A) and the electrode (C), which can be expressed as
λ=[λAc]
In the formula: λA is the failure rate of the anode; λC is the failure rate of the electrode.
Some key applications, such as reconnaissance satellites or covert communications, must consider satellite redundancy. This requires a system component, such as the battery charge controller, which is considered the smallest unit, to provide the necessary redundant functions to achieve continuous operation on the satellite.
The reliability of a simple battery composed of an anode and an electrode can be expressed as
RB(t) = [RA(t)RC(t)]
Where: RA is the reliability of the anode at time t; RC is the reliability of the electrode at time t.

Reliability and life prediction of rechargeable batteries
Battery reliability