Lithium batteries represent a category of batteries that utilize lithium metal or lithium alloy as the anode material, along with a non-aqueous electrolyte solution. The concept of a lithium metal battery was first introduced and examined by Gilbert N. Lewis in 1912. Later, in the 1970s, M.S. Whittingham initiated research on lithium-ion batteries. However, due to the highly reactive nature of lithium metal, its processing, storage, and application demand exceptionally high environmental standards, delaying its widespread use. Thanks to technological advancements, lithium batteries have now become prevalent.
Broadly, lithium batteries can be categorized into lithium metal batteries and lithium-ion batteries. Lithium-ion batteries, devoid of metallic lithium, are rechargeable. The fifth-generation rechargeable battery, the lithium metal battery, emerged in 1996. It surpasses lithium-ion batteries in terms of safety, specific capacity, self-discharge rate, and cost-effectiveness. Given its sophisticated technology, only a handful of companies globally manufacture this type of lithium metal battery.
Now, let’s delve into the lifespan of lithium batteries. Is it true that lithium-ion batteries can only undergo 500 charge-discharge cycles?
Many consumers have encountered the notion that lithium batteries have a lifespan of “500 cycles.” This implies that after 500 charge-discharge cycles, the battery reaches its end of life. Consequently, some individuals only charge their batteries when fully depleted, believing it prolongs their lifespan. However, this practice doesn’t significantly impact battery longevity. The “500 cycles” lifespan refers to one complete cycle of charging from empty to full and discharging back to empty, not individual charging instances.
A charging cycle signifies the complete process of discharging a battery from full to empty and then recharging it fully. For instance, if a lithium battery uses half its capacity on the first day and is fully charged afterward, and the same pattern continues the next day, it counts as one charging cycle, not two, despite two charging events. Therefore, several charges might be needed to complete a cycle. After each cycle, the battery’s capacity diminishes slightly, but this decrease is minimal. High-quality batteries can retain 80% of their original capacity after numerous cycles, allowing lithium-powered devices to function normally for two to three years. Ultimately, lithium batteries will need replacement.
The “500 cycles” figure is based on manufacturers achieving approximately 625 recharge cycles at a consistent discharge depth, such as 80%, equating to 500 cycles (80% * 625 = 500), disregarding capacity reduction. However, due to various real-life factors, especially fluctuating discharge depths during charging, “500 charging cycles” serve as a lifespan estimate.
In essence, the lifespan of lithium batteries correlates with the number of completed charging cycles, not individual charges. For example, if a lithium battery uses half its capacity daily and is fully charged afterward, it counts as one cycle, regardless of the number of charging instances. Each cycle slightly decreases the battery’s capacity, albeit minimally. High-quality batteries maintain 80% of their original charge after multiple cycles, explaining why lithium-powered devices function normally for years.
Typically, lithium batteries have a lifespan of 300 to 500 charging cycles. Assuming a full discharge provides Q electricity, lithium batteries can supply or replenish 300Q to 500Q of electricity over their lifespan, irrespective of capacity reduction per cycle. Thus, charging with half capacity each time allows for 600 to 1000 charges, and one-third capacity permits 900 to 1500 charges. Random charging frequencies yield varying results. In summary, regardless of charging methods, the total electricity replenished remains between 300Q and 500Q. Hence, lithium battery lifespan is linked to total charging capacity, not charging frequency. Deep and shallow discharge/charge impacts are relatively insignificant.
Actually, shallow discharge and charge are more beneficial for lithium batteries. Deep discharge and charge are only necessary for calibrating lithium batteries within product power modules. Therefore, lithium-powered products don’t require specific charging routines. Convenience prevails; charging can occur anytime without worrying about lifespan impacts.
Operating lithium batteries above the recommended 35°C temperature reduces their charge, shortening battery life. Charging at such temperatures exacerbates damage. Even storing batteries in hot environments deteriorates their quality. Thus, maintaining an optimal operating temperature is crucial for extending lithium battery lifespan.
When lithium batteries are exposed to low-temperature environments, specifically below 4°C, it becomes evident that their lifespan diminishes, and in some instances, original lithium batteries in phones fail to charge at all under such conditions. However, this concern is temporary. Unlike their behavior in high-temperature settings, as temperatures rise, the battery’s molecules warm up and swiftly regain their previous charging capacity.
To optimize the performance of lithium-ion batteries, frequent usage is crucial, ensuring that the electrons within remain in a constant state of flux. For infrequent users, it’s advisable to undertake a charging cycle and perform a power calibration once a month—this entails a complete discharge followed by a full recharge.
Technically termed a “charge-discharge cycle,” this metric does not equate to the “number of charges.” A cycle signifies the journey of a battery from full charge to complete depletion and back to full again. For instance, if your battery utilizes one-tenth of its capacity and then recharges fully, it constitutes one-tenth of a cycle. Ten such instances would constitute a full cycle. Similarly, starting from a full charge, using half, recharging fully, then using half again and recharging, equals one cycle despite two charging instances. Hence, the cycle’s measurement hinges on the accumulated electricity and is unrelated to the charging frequency.
The nominal number of charge-discharge cycles doesn’t imply obsolescence upon exhaustion but signifies a decline in the battery’s storage capacity after a specified number of cycles. For example, a lithium battery with a nominal charge-discharge cycle of “not less than 60% of nominal capacity after 500 cycles” implies a certain level of performance degradation post-500 cycles.
Lithium batteries do not have a set charging limit. Typically, reputable manufacturers’ batteries can endure at least 500 charge-discharge cycles with over 80% of their initial capacity retained, lasting about two years with daily charging. Generally, charging a mobile phone battery over 1000 times might lead to significant instability.
To maintain your mobile phone battery:
Fully charging it each time minimizes charging cycles and prolongs battery life.
Partial discharging is acceptable; charging is usually necessary when the battery level drops below 10%.
Always use the original charger to avoid universal charging incompatibilities.
Refrain from using your phone during charging.
Avoid overcharging by disconnecting once the battery is fully charged.
Experimental data confirms that lithium batteries’ lifespan progressively decreases with an increase in charging cycles. Typically, lithium batteries undergo 2000-3000 charging cycles.
Cycles represent usage, and our focus is on usage duration. To quantify rechargeable batteries’ longevity, we’ve defined the number of cycles. User behavior varies widely, and comparisons under differing conditions are invalid. Thus, standardizing the definition of cycle life is essential for comparison.
National standards stipulate the test conditions and requirements for lithium batteries’ cycle life: At an ambient temperature of 20°C ± 5°C, charge at 1C. When the battery’s terminal voltage reaches 4.2V, switch to constant voltage charging until the current drops to ≤1/20C, then discontinue charging. Allow the battery to rest for 0.5-1 hour before discharging at 1C current until it reaches 2.75V. After discharging, let it rest for another 0.5-1 hour before initiating the next cycle. If the continuous discharge time falls below 36 minutes twice, the battery’s life is deemed terminated, with a cycle count exceeding 300.
Interpreting the national standards:
- These regulationsmandate deep charging and discharging methods for testing cycle life.
- Lithium batteries’ cycle life, as per these guidelines, must exceed 60% capacity after ≥300 cycles.
Notably, varying cycle systems yield different cycle counts. For instance, altering only the constant voltage from 4.2V to 4.1V, while keeping other conditions constant, transforms the test into a non-deep charging method. Consequently, the cycle life increases by nearly 60%. Increasing the cut-off voltage to 3.9V for testing could multiply the cycle count.
It’s worth noting that each charge-discharge cycle slightly diminishes a lithium battery’s lifespan. The definition of a lithium battery’s charging cycle encompasses the battery’s full depletion and recharge, not just a single charging instance. Moreover, discussing cycle counts without considering the cycling conditions is futile, as cycle counts serve as a battery life assessment tool, not an end goal.
