The Ishikawa diagram, also termed the fishbone or cause-and-effect diagram, offers a comprehensive view of factors influencing a specific problem.
In the domain of lithium-ion batteries, the Ishikawa diagram can provide an overview of the myriad factors causing their degradation (reference: Harting et. al.*).
Calendar Ageing: Ambient temperature profoundly impacts battery lifespan. Storing batteries at high temperatures speeds up internal chemical reactions, resulting in capacity loss or even damage. Additionally, the state of charge (SoC) during storage influences degradation rates. Extended storage at full charge, especially in warm conditions, intensifies degradation.
Cycle Number: Every charge-discharge cycle contributes to lithium-ion battery degradation. As the number of cycles grows, the rate of degradation can turn nonlinear, suggesting that as batteries approach their life's end, they may degrade even faster.
Environmental Conditions: The environment plays a crucial role in battery longevity. Operating a battery at high temperatures, or cycling temperatures, hastens degradation. Humidity, by letting moisture seep into the battery, poses the risk of short circuits. Mechanical stresses, like physical impacts, can cause internal damage, curtailing battery life. Even when batteries are not in use, their storage temperature affects health, necessitating effective cooling systems to stave off overheating.
Manufacturing: Production processes and their consistency shape battery longevity. Electrode defects or variations in manufacturing can yield batteries with disparate aging behaviors. Such inconsistencies highlight the importance of stringent quality control measures during battery production.
Cyclic Ageing: The manner in which a battery is charged and discharged bears significant influence on its lifespan. Fast charging, though time-efficient, can heat up and degrade the battery more rapidly. Similarly, high-power or rapid discharges place undue strain on the battery. Habitual cycling at extreme states of charge (SoCs) or continually depleting batteries to low SoCs can accelerate degradation. Overcharging, or pushing a battery beyond its capacity, can induce overheating and other adverse effects.
Components: The integrity of battery components is central to its performance. Over time, the degradation of the electrolyte can curtail the battery’s capacity. Breakdowns at the interfaces between components can hamper performance. The separator, a pivotal component, can, when compromised, lead to internal shorts. Furthermore, the breakdown of anode or cathode materials diminishes the battery's energy storage capabilities.
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