1. Approximately how much battery degradation will occur in an electric vehicle after 10,000 kilometers?
To be honest, there isn't a fixed figure for the rate of battery degradation after 10,000 kilometers of driving in an electric vehicle. It mainly depends on several factors, such as the type of battery, how the vehicle is used, driving habits, and charging mode.
Generally speaking, with normal driving and good charging habits, most electric vehicles will experience a battery capacity degradation of around 1% to 3% after 10,000 kilometers. For example, some models powered by lithium iron phosphate batteries may only experience a degradation of around 1% after 10,000 kilometers if properly maintained; while some vehicles using ternary lithium batteries may experience a slightly higher degradation, but it usually will not exceed 3%.
However, if you frequently drive aggressively, with rapid acceleration and braking, or rely on fast charging for extended periods, the battery will degrade faster, potentially by 5% or more after 10,000 kilometers. One car owner reported that his aggressive driving style and frequent use of fast charging stations resulted in a battery capacity reduction of approximately 6% after 10,000 kilometers, significantly higher than normal.
II. How does the degradation of electric vehicle batteries change over time?
The degradation of electric vehicle batteries varies over time, generally showing a trend of relatively slow degradation in the early stages and gradually accelerating degradation in the later stages.
In the first 2-3 years of a new car's battery life, the degradation rate is relatively stable, with an annual degradation of approximately 2%-5%. This is because the internal chemical active materials of the battery are still relatively stable during this stage, and the performance degradation of various materials is also relatively minor. However, as time goes on, starting from around the 4th or 5th year, the battery degradation rate will increase, potentially reaching 5%-8% per year. By the 8th to 10th year, if the battery continues to be used, the degradation rate may accelerate further, even reaching over 10% per year.
For example, some owners of a pure electric vehicle that was launched earlier reported that the vehicle's range on a full charge remained basically unchanged for the first 3 years; starting from the 4th year, they could clearly feel that the range on a full charge was decreasing, and by the 6th year, the range on a full charge was about 20% less than when the car was new.
III. What are the causes of battery degradation in electric vehicles?
(I) Internal Factors: Aging of Cathode Materials Different cathode materials exhibit different degradation characteristics after prolonged use. Lithium cobalt oxide cathodes, under prolonged operation or overcharging, experience lithium-ion over-extraction and cobalt-ion mixing, affecting battery performance. Lithium iron phosphate cathodes show varying corrosion rates and performance degradation speeds at different locations. Ternary materials, after long-term cycling, may experience structural collapse, cobalt-ion dissolution, and lithium-nickel mixing, all of which lead to battery capacity degradation. Aging of Anode Materials During the insertion and extraction of lithium ions into and out of the anode, volume changes occur in the anode material. Common graphite anodes are prone to structural changes after long-term charge-discharge cycles, leading to performance degradation. Furthermore, if the SEI film formed on the anode ruptures and regrows, it consumes active lithium ions, increasing interfacial resistance and also affecting battery performance. Aging of Electrolyte Decomposition Currently used lithium hexafluorophosphate electrolytes have less than ideal stability and are easily decomposed when exposed to high temperatures and moisture. Carbonate solvents have weak oxidation resistance and are prone to oxidative decomposition, producing side reactions, all of which contribute to electrolyte aging and affect normal battery operation. If the pores of the separator become blocked due to aging, or if its size and porosity change, it will affect the battery's internal resistance and capacity. Poor contact between the current collector (copper/aluminum foil) and the electrodes, or even corrosion, will lead to increased internal resistance and irreversible capacity increases. Over-discharge can also cause problems such as copper deposition, further damaging the battery.
(II) External Factors During charging and discharging, when the battery is in an unstable state of full charge or empty charge, or at extremely high or low SOC (State of Charge), the rate of side reactions in the battery's internal chemical system increases, which can easily lead to battery structural damage and performance degradation. To avoid this, battery management systems typically have a certain safety redundancy. At high temperatures, the activity of the battery's internal chemical system increases, accelerating the rate of side reactions and thus accelerating battery aging; while at low temperatures, battery activity decreases, and low-temperature lithium plating is more likely to occur. Generally, when the temperature reaches 55℃ and 0℃, the battery's cycle life and performance are significantly affected. For example, in hot summers, charging a vehicle immediately after it has been exposed to direct sunlight will accelerate battery degradation; in cold winters, the driving range of electric vehicles is generally shortened—these are all effects of temperature on the battery. High charge/discharge rates may cause lithium plating on the negative electrode surface, resulting in greater polarization and higher temperatures, leading to accelerated side reaction rates and faster cycle life degradation. Therefore, vehicles that frequently use fast charging often experience faster battery degradation than vehicles that primarily use slow charging. Battery systems, composed of numerous individual cells, are susceptible to the "weakest link" effect, making cell consistency crucial for performance. During use, battery capacity degradation is relatively gradual in the early stages but accelerates later. In the later stages, deteriorating cell consistency can accelerate the degradation of individual cells, thus affecting the performance of the entire battery system. Analysis and Improvement of Rapid Degradation in the Initial Stages of LFP Battery Cycles! – CN Know EV
IV. What measures can be taken to slow down battery degradation?
(I) Optimize Charging Strategy and Control Charging Limits: For daily charging, it is recommended to set the charging limit to 90%. Prolonged use at full charge (100% SOC) accelerates the degradation of the positive electrode material. For example, Tesla's "Daily Mode" defaults to a 90% charging limit. Simultaneously, avoid deep discharge; charge promptly when the battery level drops below 20%. Over-discharge leads to lithium plating on the negative electrode, damaging the battery. Owners can set low-battery reminders via a mobile app, such as an alert when the battery level reaches 30%. Reduce High-Frequency Fast Charging: While convenient and fast, fast charging draws a large current (e.g., 100-200A), and prolonged high-frequency use can shorten battery life by 20%-30%. Therefore, limit fast charging to once a week or less, prioritizing slow charging (AC charging station, current ≤32A). Furthermore, after fast charging, allow the battery to rest for 10-15 minutes until the temperature drops below 40℃ before driving to avoid further stress on the battery at high temperatures.
(II) Improve Driving and Energy Management: Drive gently and make good use of energy recovery. Sudden acceleration and braking can cause the battery to release or absorb a large amount of energy instantly, leading to a rapid increase in battery temperature and accelerated aging. It is recommended that the throttle opening not exceed 70% when accelerating, and the energy recovery intensity be adjusted to medium to high, such as using one-pedal mode, which can effectively reduce battery wear. Control High-Speed Driving Duration: When the vehicle speed exceeds 120km/h, the battery load will increase by more than 20%. Therefore, when traveling long distances, you can drive in segments and take a break every 2 hours to avoid the battery being under high load for a long time. Reasonable Load and Air Conditioning Use: Long-term full load of the vehicle will increase the burden on the battery. For every 100kg increase in vehicle weight, the range may decrease by about 5%. Therefore, try not to pile heavy objects in the trunk. Regarding air conditioning use, in winter, prioritize using seat/steering wheel heating, which saves 30% more energy than PTC air conditioning; in summer, after being exposed to the sun, open the windows for ventilation before turning on the air conditioning, which can reduce the energy consumption of the air conditioning and indirectly protect the battery.
(III) Environmental Temperature Control and High-Temperature Protection: When parking in summer, choose a shady spot, such as an underground garage or under a tree, to reduce the probability of the battery temperature exceeding 40°C. If fast charging is required, if the battery temperature is higher than 45°C before charging, turn on the air conditioning for 10 minutes (some models support remote temperature control) to lower the battery temperature before charging. Low-Temperature Handling: Before charging in winter, use the vehicle's preheating system to preheat the battery, such as BYD's "Battery Thermal Management System." In an environment of -20°C, preheating can improve charging efficiency by 30%. Meanwhile, when the temperature is below -10°C, use slow charging to 20% before switching to fast charging to reduce damage to the battery caused by hindered lithium-ion migration.
(IV) Important Considerations for Storage and Long-Term Idle Management: For short-term storage (1-2 weeks), charge the battery to 50%-60% before storage to avoid storing it fully charged or depleted. During storage, turn off the vehicle network to reduce standby power consumption. For long-term idle storage (>1 month), charge the battery to 30%-40% first, as excessive charge can easily lead to oxidation of the positive electrode material, while insufficient charge may cause lithium dendrite formation. It is recommended to recharge the vehicle using a slow charger every 2 months, charging it to 50%. In addition, when storing for a long time, disconnect the negative terminal of the low-voltage battery to avoid standby power consumption of the vehicle system (such as in sentry mode) and reduce frequent self-discharge of the main battery.
(V) Strengthen Battery Maintenance and System Optimization. Regularly check the cooling system. Replace the coolant (such as ethylene glycol aqueous solution) every 1-2 years to ensure the battery cooling system is working properly and avoid overheating due to insufficient coolant. Under normal circumstances, the battery temperature should be controlled between 25-40℃. Check the chassis battery protection plate annually. If the vehicle has been involved in any bottoming-out collisions, have the battery cells checked at a 4S shop in a timely manner. An internal resistance meter can be used to measure the impedance of a single cell to determine if the battery is damaged. Utilize BMS and OTA upgrades. Pay attention to the battery health (SOH) displayed on the vehicle system. Under normal circumstances, the annual degradation should not exceed 2%. If the degradation exceeds 5% within six months, contact after-sales service immediately. At the same time, update the vehicle system in a timely manner. Automakers usually optimize the battery management system (BMS) strategy through OTA upgrades. For example, Tesla reduced battery loss at low temperatures in its 2023 update.
