Why does understanding battery degradation matter?
Battery degradation is a key issue for manufacturers, energy providers, grid operators and battery owners, all of whom depend on energy storage for consistent power delivery, renewable energy integration and grid stabilization.
Degradation directly affects a battery’s performance and lifespan, making battery health management essential. Monitoring and managing battery health can mitigate degradation, ensuring that systems operate reliably and efficiently.
What causes battery degradation?
Battery degradation is a complex process influenced by multiple factors. Here's a brief breakdown of the causes:
Chemical wear and tear
Cyclic degradation
Every time a battery undergoes a charge and discharge cycle, its capacity diminishes slightly. The deeper the discharge, the more stress is placed on the battery. High charge rates and frequent use exacerbate this wear, leading to reduced capacity and performance over time.
Calendar aging
Even when not in use, batteries experience degradation due to internal chemical reactions. Calendar aging is the gradual loss of capacity over time and it's influenced by temperature and the state of charge at which the battery is stored. Batteries kept at high states of charge and in warmer environments age faster.
Overcharging and deep discharge
Frequently overcharging a battery (charging it to 100%) or discharging it to extreme levels (close to 0%) can lead to faster degradation. This is because overcharging leads to excessive voltage, which stresses the battery, while deep discharges put additional strain on the internal structure, leading to capacity loss and heat buildup.
Environmental factors
Temperature fluctuations
Extreme temperatures – both hot and cold – are harmful to battery health. High temperatures accelerate chemical reactions that degrade the battery's components, while cold temperatures can hinder the battery's ability to charge and discharge efficiently. Long-term exposure to temperature extremes can significantly shorten battery life.
Humidity and other external conditions
In industrial settings, external factors like humidity, dust and vibrations can affect battery health. For instance, excessive humidity can lead to the corrosion of battery components, while dust particles can interfere with battery connections and cooling mechanisms
Depth of Discharge (DoD)
It refers to the percentage of a battery’s capacity that has been used during a discharge cycle. For example, if a battery with a full charge is discharged to 30% of its total capacity, the DoD is 70%. Higher DoD typically leads to faster battery degradation, as deeper discharges put more stress on the battery's components
Degradation metrics and indicators
Battery degradation metrics are essential for understanding the long-term performance and reliability of lithium-ion batteries. Key indicators of battery degradation include:
Capacity fade
As a battery ages, its ability to store energy decreases. This reduction in capacity is often one of the first signs of degradation and can be observed through fewer hours of device operation or shorter driving ranges in electric vehicles (EVs).
Increased internal resistance
Degradation also causes an increase in internal resistance, which impacts the battery’s ability to deliver power efficiently. This results in slower charging/discharging rates and higher heat generation during use, further accelerating degradation. This ultimately results in a noticeable drop in battery efficiency.
State of Health (SOH)
SOH is a common metric to quantify a battery’s remaining useful life, representing the overall condition of the battery relative to its original capacity. Degradation models often use SOH to predict the battery's remaining lifespan.
Voltage drop
A degraded battery exhibits a lower voltage during operation, which can reduce its efficiency in delivering power to connected systems.
Cycle count
Lithium-ion batteries have a limited number of charge-discharge cycles. As the number of cycles increases, capacity and performance degrade due to chemical changes, electrode wear and electrolyte breakdown.
Monitoring these indicators helps in managing and prolonging battery life through practices like controlling operating temperatures, avoiding overcharging and using appropriate charging cycles.
Degradation rates of different types of batteries
Battery degradation rates vary depending on the type of battery used in energy storage systems (ESS), with the most common types being lithium-ion (Li-ion), lead-acid and flow batteries.
Lithium-ion batteries
These are the most widely used in ESS and typically degrade at a rate of 1–3% per year under standard operating conditions. However, this degradation rate can vary depending on several factors such as DoD, temperature and charging habits. For example, batteries cycled near 100% DoD degrade much faster than those cycled at 10% DoD. Typically, a 1–3% annual degradation rate assumes one full cycle per day at moderate temperatures. More frequent cycling or operation in extreme temperatures can accelerate this degradation further.
Lead-acid batteries
These degrade faster than lithium-ion batteries, with rates ranging from 4–6% annually. Their lifespan is also reduced by deep discharges and exposure to high temperatures.
Flow batteries
While newer and less prone to traditional degradation, flow batteries generally have a longer lifespan and lower degradation rates of around 1–2% per year, as they can handle deeper discharge cycles without significant capacity loss. However, their complexity and costs are higher.
Impact of battery degradation on energy management systems
Battery degradation has a significant impact on energy management systems (EMS), especially when integrated with EVs or battery energy storage systems (BESS). As batteries age, their capacity to store and deliver energy decreases, leading to a reduction in system efficiency and increasing operational costs.
Capacity loss
Battery degradation results in capacity fade, which lowers the energy available for use in EMS. This impacts the ability to meet energy demand, especially in grid-tied systems and reduces the driving range of EVs, causing inefficiencies in energy planning.
Increased resistance and power loss
As the battery’s internal resistance rises due to degradation, EMS experiences reduced power delivery efficiency. This can lead to longer charging times and less effective use of stored energy, which is crucial for peak shaving and grid stability applications. Reduced roundtrip capacities also limit energy arbitrage potential, as only a portion of stored energy can be resold, making it profitable only during large price spreads.
Higher costs
Frequent battery replacements or the need to over-provision storage to account for capacity loss can increase the overall cost of managing energy systems.
Grid instability risks
Degraded batteries in grid-connected systems reduce energy storage capacity and increase inefficiency. This can result in voltage fluctuations, overloading during peak demand and higher risks of unplanned outages. Additionally, increased internal resistance in aging batteries generates more heat, further accelerating degradation and impacting overall system reliability.
System reliability and lifecycle
Battery degradation reduces the reliability of energy management system by introducing uncertainties in power availability, affecting renewable energy integration and grid balancing tasks. Effective EMS solutions must incorporate predictive maintenance and real-time SOH monitoring to mitigate these effects.
Mitigating battery degradation
Mitigating battery degradation is critical for extending the lifespan of lithium-ion batteries, particularly in EVs and ESS. Here are several strategies to minimize degradation:
Smart charging practices
Maintaining the battery charge between 20% and 80% is one of the most effective ways to prevent overcharging and deep discharging, which accelerate degradation. Avoiding charging to 100% and discharging to 0% reduces stress on the battery’s chemistry. Another technique is to restrict cycling: by utilizing an optimization-based EMS, restrictions can be imposed on the battery operation to limit the daily number of cycles a battery undergoes, in order to slow down the calendar aging.
Temperature management
Lithium-ion batteries are highly sensitive to temperature. Keeping batteries within an optimal temperature range, generally between 15°C and 35°C, helps mitigate thermal stress. Active cooling or heating systems in EVs and ESS can significantly improve battery longevity.
Reducing charge rates
Fast charging generates excess heat and accelerates lithium plating, which contributes to battery wear. Slower charging rates, especially at high states of charge (SOC), can mitigate this effect.
Avoiding high-current discharges
High discharge rates increase the internal resistance of the battery and lead to more rapid capacity fade. Limiting high-current loads extends battery life.
Battery balancing and management systems
Employing advanced battery management systems (BMS) to monitor the state of charge (SOC), SOH and internal temperatures can prevent overcharging and over-discharging, thus optimizing battery performance and reducing wear.
Minimizing depth of discharge (DoD)
Frequent deep discharges are detrimental to battery health. By limiting the depth of discharge, the number of usable cycles of the battery can be extended.
Capacity expansion
Some strategies involve expanding the overall capacity of the battery system, either physical or virtual, so that even as degradation occurs, the system still meets the necessary performance thresholds.
These strategies, combined with predictive maintenance, ensure better long-term performance, reduce costs associated with battery replacement and contribute to more sustainable battery usage.
Future trends in battery longevity and degradation prevention
Advances in battery longevity and degradation prevention are increasingly centered around new materials and energy management technologies. Innovations like solid-state electrolytes and silicon anodes aim to enhance energy density and reduce degradation, while AI-driven BMSs optimize charging and discharging processes to extend battery life. Self-healing materials are also being explored to repair micro-cracks and slow down degradation.
The integration of energy management systems plays a critical role in prolonging battery life. EMS manages energy storage by optimizing the SoC and ensuring efficient cycles, which reduces the strain on batteries from renewable energy sources like wind and solar. These systems also support grid balancing, ensuring batteries perform at peak efficiency and avoid deep discharges that accelerate wear.
The push toward a circular economy includes advancements in battery recycling to recover valuable materials, as well as reducing waste and the environmental footprint. Modular battery systems that allow for individual cell replacements further extend overall battery life.
As Soner Candas, a software engineer from gridX, notes, “Innovative EMS solutions should not focus solely on ‘squeezing’ the highest possible economic value out of the batteries, but also keep a holistic view on its long-term state, both for economic and environmental reasons. As new use cases beyond self-sufficiency emerge, there will be arguments to operate the batteries even more frequently, so a careful evaluation of the cycling behavior is key.”
These innovations promise a future where batteries are more durable, efficient and environmentally sustainable.
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