During charging and discharging, Li+ ions repeatedly insert and extract between the two electrodes: during charging, Li+ ions extract from the positive electrode, pass through the electrolyte, and insert into the negative electrode, leaving the negative electrode in a lithium-rich state; the reverse occurs during discharging. Batteries generally use lithium-containing materials as electrodes and are representative of modern high-performance batteries. Lithium-based batteries are divided into lithium-ion batteries and lithium-ion batteries. Mobile phones and laptops use lithium-ion batteries, which are commonly referred to as lithium-ion batteries, while true lithium-ion batteries are rarely used in everyday electronic products due to their high risk.
Lithium-ion batteries (Li-ion, Lithium Ion Battery): Lithium-ion batteries are widely used due to their advantages such as light weight, large capacity, and no memory effect. Many digital devices now use lithium-ion batteries as their power source, despite their relatively high price. Lithium-ion batteries have a very high energy density, with a capacity 1.5 to 2 times that of nickel-metal hydride batteries of the same weight, and a very low self-discharge rate. Furthermore, the near absence of a memory effect and the absence of toxic substances are also important reasons for their widespread use.
Use and maintenance of lithium-ion batteries:
Lithium-ion battery charging
It's important to note that lithium-ion batteries enter a dormant state after being stored for a period of time, at which point their capacity is lower than normal, and their usage time is shortened. However, lithium-ion batteries are easily activated; they can be activated and restored to normal capacity after just 35 normal charge-discharge cycles. Due to the inherent characteristics of lithium-ion batteries, they have virtually no memory effect. Therefore, no special methods or equipment are needed to activate a new lithium-ion battery in a user's mobile phone. A dedicated lithium-ion battery charger should be used to charge lithium-ion batteries. Lithium-ion battery charging uses a constant current/constant voltage method, initially charging with a constant current, and then switching to constant voltage charging near the termination voltage. For example, an 800mAh battery has a termination charging voltage of 4.2V. The battery is charged at a constant current of 800mA (1C charging rate). Initially, the battery voltage rises at a steep rate. When the battery voltage approaches 4.2V, the charging is switched to a constant voltage of 4.2V. The lithium-ion battery current gradually decreases, and the voltage change is minimal. When the charging current drops to 1/10C (approximately 80mA), it is considered nearly fully charged, and charging can be stopped (some chargers activate a timer after reaching 10C, ending charging after a set time). A charger designed for nickel-cadmium batteries (for three nickel-cadmium batteries) cannot be used to charge lithium-ion batteries (even though the rated voltage is the same, 3.6V). Due to the different charging methods, overcharging is likely to occur.
(1) Charging Voltage: The termination charging voltage when fully charged is related to the negative electrode material of the battery. Coke requires 4.1V, while graphite requires 4.2V. These are generally referred to as 4.1V and 4.2V lithium-ion batteries. It is important to note that a 4.1V battery cannot be charged with a 4.2V charger, otherwise there is a risk of overcharging (4.1V and 4.2V chargers use different charger ICs). Lithium-ion batteries have very high charging requirements, demanding a precise charging circuit to ensure charging safety. The tolerance for the termination charging voltage is 1% of the rated value (for example, the tolerance for charging a 4.2V lithium-ion battery is 0.042V). Overcharging will cause permanent damage to the lithium-ion battery.
(2) Charging Current: The charging current of lithium-ion batteries should be based on the battery manufacturer's recommendations, and a current-limiting circuit is required to prevent overcurrent (overheating). Commonly used charging rates are 0.25–1C, and the recommended charging current is 0.5C (C is the battery capacity; for example, a battery with a nominal capacity of 1500 mA·h would have a charging current of 0.5 * 1500 = 750 mA). During high-current charging, the battery temperature should be monitored to prevent damage or explosion due to overheating.
(3) Charging temperature: When charging the battery, the ambient temperature must not exceed the temperature range listed in the product characteristics table. The battery should be charged within the temperature range of 0 to 45°C, away from high temperature (above 60°C) and low temperature (-20°C) environments.
Overcharging, over-discharging, or overcurrent during charging or discharging can damage lithium-ion batteries or reduce their lifespan. To address this, various protective components and protection circuits composed of protection ICs have been developed and installed in the battery or battery pack to provide comprehensive protection. However, overcharging and over-discharging should be avoided as much as possible during use. For example, when a mobile phone battery is almost fully charged, it should be disconnected from the charger. Shallow discharge depth significantly improves cycle life. Therefore, do not wait until the phone displays a low battery warning signal before charging, and never continue using the phone when this signal appears, even if some residual capacity remains.
Lithium-ion battery discharge
Discharge termination voltage: The rated voltage of lithium-ion batteries is 3.6V (3.7V for some products), and the discharge termination voltage is 2.5-2.75V (the battery manufacturer provides the operating voltage range or the discharge termination voltage, and these parameters may vary slightly). The discharge termination voltage of the battery should not be less than 2.5V (n is the number of batteries connected in series). Continuing to discharge below the discharge termination voltage is called over-discharge, which will shorten the battery life and, in severe cases, lead to battery failure. When the battery is not in use, it should be charged to retain 20% of its capacity, then stored in moisture-proof packaging. The voltage should be checked and recharged every 3-6 months to ensure that the battery voltage is within the safe voltage range (above 3V).
Discharge Current: Lithium-ion batteries are not suitable for high-current discharge. Excessive discharge current will cause high internal temperatures, resulting in energy loss and reduced discharge time. If there are no protective components in the battery, overheating may occur, damaging the battery. Therefore, battery manufacturers specify a maximum discharge current, which should not be exceeded during use.
Discharge temperature: The discharge curves differ at different temperatures. The discharge voltage and discharge time of lithium-ion batteries also vary at different temperatures. Batteries should be discharged (operated) within a temperature range of -20℃ to +60℃.
Storage and transportation
Lithium-ion batteries can be stored in a clean, dry, and well-ventilated environment with a temperature of -5 to 35°C and a relative humidity of no more than 75%. They should be kept away from corrosive substances, fire and heat sources, and direct sunlight. The batteries should not be disassembled arbitrarily. For long-term storage, the battery charge should be maintained at 30% to 50% of its nominal capacity. It is recommended that stored batteries be charged every 6 months.
Batteries should be packed in boxes for transportation. During transportation, they should be protected from severe vibration, impact or squeezing, and protected from sun and rain. They can be transported by means of transportation such as automobiles, trains, ships, and airplanes.
Short circuit
Please pay attention to the safety issues related to lithium-ion batteries. Lithium-ion batteries are prone to short circuits during charging. Although most lithium-ion batteries have short-circuit protection circuits and explosion-proof wires, these circuits may not function under various circumstances. The effectiveness of the explosion-proof wires is also limited.
overcharge
All lithium-ion batteries, including polymer lithium-ion batteries and lithium iron phosphate batteries, are highly susceptible to overcharging. Prolonged charging increases the likelihood of an explosion. Lithium is chemically very reactive and easily combustible. During charging and discharging, the battery's internal temperature rises continuously, and the expansion of gases during activation increases internal pressure. If this pressure reaches a certain level, and the casing is damaged, the battery can rupture, leading to leakage, fire, or even an explosion. Therefore, extreme caution must be exercised when using lithium-ion batteries.
Charging Precautions
Overcharging and over-discharging lithium-ion batteries can cause permanent damage to both the positive and negative electrodes. Over-discharging causes the carbon layer structure of the negative electrode to collapse, preventing lithium ions from inserting during charging. Overcharging causes too many lithium ions to embed into the carbon structure of the negative electrode, resulting in some lithium ions being unable to be released. The amount of charge equals the charging current multiplied by the charging time. With a constant charging control voltage, the higher the charging current (the faster the charging speed), the less charge can be generated. Excessive charging speed and improper termination voltage control point can also lead to insufficient battery capacity. This is because some of the active materials at the battery electrodes do not have sufficient time to react before charging stops, and this insufficient charging phenomenon worsens with increasing cycle count.
Safety features of lithium-ion batteries:
Internationally, very strict standards have been established for assessing the safety performance of lithium-ion batteries. A qualified lithium-ion battery should meet the following safety performance requirements:
(1) Short circuit: No fire or explosion
(2) Overcharge: No fire or explosion.
(3) Hot box test: No fire or explosion (150℃ constant temperature for 10 min)
(4) Needle puncture: No explosion (pierce the battery with a Ф3mm nail)
(5) Flat plate impact: No fire or explosion (10kg weight dropped on the battery from a height of 1M)
Advantages of lithium-ion batteries:
(1) High voltage: The working voltage of a single cell is as high as 3.7-3.8V (3.2V for lithium iron phosphate), which is 3 times that of Ni-Cd and Ni-MH batteries.
(2) The actual specific energy that can be achieved is about 555Wh/kg, which means that the material can achieve a specific capacity of more than 150mAh/g (3-4 times that of Ni-Cd, 2-3 times that of Ni-MH), which is close to about 88% of its theoretical value.
(3) Long cycle life: Generally, they can reach more than 500 times, or even more than 1,000 times, and lithium iron phosphate batteries can reach more than 2,000 times. For electrical appliances with low current discharge, the service life of the battery will greatly increase the competitiveness of the appliance.
(4) Good safety performance, no pollution, and no memory effect. As the predecessor of Li-ion, the new lithium-ion battery has limited its application areas because lithium metal is prone to dendrite formation and short circuit. Li-ion does not contain elements such as cadmium, lead, and mercury that pollute the environment. A major drawback of Ni-Cd batteries with some processes (such as sintering) is the memory effect, which seriously restricts the use of the battery. However, Li-ion does not have this problem at all.
(5) The self-discharge rate of fully charged Li-ion at room temperature after one month of storage is about 2%, which is much lower than that of Ni-Cd (25-30%) and Ni-MH (30-35%).
(6) Fast charging: 1C charging for 30 minutes can reach more than 80% of the nominal capacity, while phosphorus iron batteries can reach 90% of the nominal capacity in 10 minutes.
(7) Operating temperature: The operating temperature is -25~45°C. With the improvement of electrolyte and positive electrode, it is expected to be extended to -40~70°C.
(6) Burning: No explosion (gas flame roasting battery)
Disadvantages of lithium-ion batteries:
(1) Aging: Unlike other rechargeable batteries, the capacity of lithium-ion batteries degrades slowly, depending on the number of uses and temperature. This degradation can be represented by a decrease in capacity or an increase in internal resistance. Because it is temperature-dependent, it is more noticeable in electronic products with high operating currents. Replacing graphite with lithium titanate appears to extend lifespan. Relationship between storage temperature and the rate of permanent capacity loss:
(2) Recycling rate: Approximately 1% of new products need to be recycled for various reasons.
(3) Not tolerant to overcharge: When overcharged, the excessive lithium ions will be permanently fixed in the crystal lattice and cannot be released, which can lead to a short battery life.
(4) Not tolerant to over-discharge: During over-discharge, too many lithium ions are de-intercalated or de-intercalated in the electrode, which can lead to lattice collapse and thus shorten the lifespan.
