Battery Degradation and Countermeasures

Created on 10.15

I. Causes of Battery Degradation in Electric Vehicles

(I) Internal Factors

Degradation and Aging of Cathode Materials

Different cathode materials exhibit distinct degradation characteristics after long-term service. When cathodes operate for extended periods or are over-charged, excessive lithium-ion de-intercalation and cobalt-ion mixing may occur, impairing battery performance. Corrosion rates and performance degradation rates vary across different sites of the cathode. After long-term cycling, ternary materials may suffer structural collapse, cobalt-ion dissolution, and lithium-nickel mixing, all of which trigger battery capacity degradation.

Degradation and Aging of Anode Materials

Volume variation takes place in anode materials during lithium-ion intercalation and de-intercalation. For conventional graphite anodes, structural changes tend to occur upon repeated charge-discharge cycles, leading to performance degradation. In addition, cracking and regrowth of the SEI film on the anode will consume active lithium ions and raise interfacial resistance, which also deteriorates battery performance.

Decomposition and Aging of Electrolyte

Commonly-used electrolytes have limited stability and are prone to decomposition under high-temperature and humid conditions. Carbonate-based solvents feature poor oxidation resistance and are susceptible to oxidative decomposition and side reactions, which age the electrolyte and disrupt normal battery operation.

Degradation and Aging of Separators, Copper and Aluminum Foils

Pore clogging, dimensional change and porosity variation of separators will alter battery internal resistance and capacity. Poor contact or corrosion of current collectors (copper and aluminum foils) with electrodes elevates internal resistance and increases irreversible capacity. Copper deposition may even occur under over‑discharge conditions, causing further damage to batteries.

(II) External Factors

Charge-Discharge Range

When batteries stay in unstable fully-charged or fully-discharged states, or operate at extremely high or low State of Charge (SOC), side-reaction rates of internal chemical systems rise, which may damage battery structures and degrade performance. Battery management systems (BMS) usually reserve certain safety margins to mitigate such risks.

Ambient Temperature

High-temperature conditions boost the activity of internal chemical systems and accelerate side reactions, thus speeding up battery aging. Under low-temperature circumstances, battery activity declines and lithium plating may emerge. Generally, battery cycle life and performance are markedly affected at 55 °C and 0 °C. For instance, charging immediately after vehicle exposure to scorching summer sun accelerates battery degradation; electric vehicles commonly suffer reduced driving range in cold winter, reflecting temperature-induced battery impacts.

Charge-Discharge Rate

High-rate charge-discharge may induce lithium plating on anode surfaces, produce severe polarization and higher temperature, accelerate side reactions and shorten cycle life. Accordingly, batteries of vehicles frequently using fast charging usually degrade faster than those relying mainly on slow charging.

Cycle Number and Cell Consistency

A battery system is assembled from numerous single cells and subject to the “wooden-bucket short-board effect”, so cell consistency is critical to overall performance. In service, battery capacity degrades moderately in the early stage and accelerates in the later phase. Deteriorated cell consistency in later cycles may expedite degradation of individual cells and further undermine the performance of the whole battery system.

II. Measures to Mitigate Battery Degradation

(I) Optimize Charging Strategies

Set Upper and Lower Charging Limits

For daily-use charging, it is recommended to cap the state of charge at 90%. Keeping the battery at 100% SOC for prolonged periods accelerates cathode material degradation. For instance, the "Daily Mode" of Tesla sets the default charging upper limit at 90%. Meanwhile, deep discharge shall be avoided; timely charging is required when the state of charge drops below 20%. Over-discharge triggers lithium plating on the anode and damages the battery. Vehicle owners may set low-battery alerts via mobile APPs, for example, triggering an alarm when the remaining charge reaches 30%.

Reduce Frequent Fast‑charging

Though fast charging delivers convenience with high current (100‑200 A), frequent long‑term application may shorten battery service life by 20%‑30%. Fast‑charging frequency should be limited to no more than once per week, and slow charging (AC chargers with current ≤32 A) is preferred. After fast‑charging completion, allow a 10‑15 min rest period for the battery temperature to drop below 40 °C before driving, so as to prevent the battery from sustaining heavy loads under high‑temperature conditions.

(II) Improve Driving Habits and Energy Management

Moderate Driving and Rational Use of Energy Recovery

Sharp acceleration and hard braking cause instantaneous massive electric energy release or absorption, leading to sharp battery temperature rise and accelerated aging. It is advised to keep the accelerator opening below 70% during acceleration, and set the energy‑recovery intensity to medium‑high level (e.g. one‑pedal mode), which effectively mitigates battery loss.

Limit High-speed Driving Duration

Battery load increases by over 20% when the driving speed exceeds 120 km/h. For long-distance trips, drive in segments and take a break every two hours to prevent the battery from operating under sustained heavy loads.

Reasonable Load and Air-conditioner Operation

Long‑term full‑load driving adds burden to the battery. Every 100 kg increase in vehicle curb weight may reduce driving range by approximately 5%. Therefore, avoid storing heavy cargo in the trunk. For air‑conditioning usage: prioritize seat / steering‑wheel heating in winter, which consumes 30% less power than PTC heating. After vehicle exposure to intense summer sunlight, open windows for ventilation before turning on the air‑conditioner to cut air‑conditioner energy consumption and indirectly protect the battery.

(III) Environmental Temperature Control

High-temperature Protection

In summer, park vehicles in shaded locations such as underground garages or under tree canopies to minimize instances where battery temperature rises above 40 °C. If fast-charging is needed while battery temperature exceeds 45 °C, turn on cabin refrigeration for 10 minutes (remote temperature control is supported on some vehicle models) to cool down the battery prior to charging.

Low-temperature Countermeasures

Before charging in winter, activate the vehicle-mounted battery preheating function via the battery thermal management system (e.g. BYD's system). Preheating can boost charging efficiency by 30% under −20 °C ambient conditions. When ambient temperature falls below −10 °C, perform slow-charging first until SOC reaches 20%, then switch to fast-charging, to reduce battery damage caused by hindered lithium-ion migration.

(IV) Storage and Long-term Idling Management

Short-term Storage (1-2 weeks)

Charge the battery to 50%-60% before storage; neither full-charge nor zero-charge storage is allowed. Turn off on-board network services during parking to cut standby power consumption.

Long‑term Idling (> 1 month)

Charge the battery to 30%‑40%. Excessively high SOC facilitates cathode oxidation, while excessively low SOC may induce lithium dendrite formation. Perform supplementary slow‑charging up to 50% SOC every two months. Besides, disconnect the negative terminal of the low‑voltage auxiliary battery during long‑term parking to eliminate standby power draw from on‑board systems (e.g. Sentry Mode) and reduce frequent self‑discharge of the main traction battery.

(V) Battery Maintenance and System Optimization

Periodically Inspect the Cooling System

Replace coolant (e.g. ethylene‑glycol aqueous solution) every 1‑2 years to guarantee proper operation of the battery cooling system and avoid battery overheating caused by insufficient coolant. Ideally, battery temperature shall be maintained within 25‑40 °C.

Annual Inspection of Under‑body Battery Shield

If the vehicle has suffered undercarriage impact, go to authorized 4S service centers promptly to inspect cell conditions. An internal‑resistance tester can measure single‑cell impedance to identify potential battery damage.

Leverage BMS and OTA Firmware Updates

Keep track of State of Health (SOH) displayed on the on‑board system. Normal annual battery degradation should not exceed 2%. Contact after‑sales service if degradation exceeds 5% within half a year. Meanwhile, install timely OTA updates for vehicle infotainment systems. Automakers usually optimize BMS strategies via OTA upgrades. For example, a Tesla update released in 2023 reduced battery loss under low‑temperature scenarios.

In summary, understanding battery-degradation mechanisms and adopting proper mitigation measures can extend battery service life, cut operating costs and enhance driving experience. Hope every EV user can become a battery-care expert and keep vehicles in sound condition. Feel free to share your experience or questions concerning EV batteries in the comment section.