Currently, three types of batteries are commonly used in new energy electric vehicles: lead-acid batteries, nickel-metal hydride batteries, and lithium-ion batteries. With the upgrading of electric vehicle battery technology, the development and application of lithium batteries are continuously expanding. So, what are the differences between lithium iron phosphate battery packs and lead-acid batteries? Which is better, lead-acid batteries or lithium iron phosphate batteries?
What is a lithium iron phosphate battery?
Lithium iron phosphate (LiFePO4) batteries are lithium-ion batteries that use lithium iron phosphate (LiFePO4) as the positive electrode material and carbon as the negative electrode material. A single cell has a rated voltage of 3.2V and a charging cut-off voltage of 3.6V~3.65V. Lithium iron phosphate batteries have advantages such as high operating voltage, high energy density, long cycle life, good safety performance, low self-discharge rate, and no memory effect.
During charging, some lithium ions in the lithium iron phosphate battery are released and transferred to the negative electrode via the electrolyte, where they embed into the carbon material. Simultaneously, electrons are released from the positive electrode and travel from the external circuit to the negative electrode, maintaining the chemical reaction balance. During discharging, lithium ions are released from the negative electrode and travel to the positive electrode via the electrolyte. At the same time, electrons are released from the negative electrode and travel from the external circuit to the positive electrode, providing energy to the surrounding environment.
What is a lead-acid battery?
A lead-acid battery is a type of rechargeable battery whose electrodes are primarily made of lead and its oxides, and whose electrolyte is a sulfuric acid solution. In the discharged state, the positive electrode is mainly composed of lead dioxide, and the negative electrode is mainly composed of lead; in the charged state, both the positive and negative electrodes are mainly composed of lead sulfate.
A single lead-acid battery cell has a nominal voltage of 2.0V, can discharge to 1.5V, and can be charged to 2.4V. In applications, six single lead-acid batteries are often connected in series to form a lead-acid battery with a nominal voltage of 12V. There are also 24V, 36V, and 48V batteries.
What are the differences between lithium iron phosphate battery packs and lead-acid batteries?
1. Size: Lead-acid batteries are relatively large, generally weighing around 15-30 kg; lithium iron phosphate batteries are relatively small, generally weighing around 2.5-3.0 kg.
2. Energy density ratio: In the same volume, the energy density of lithium iron phosphate batteries is 3 to 4 times that of lead-acid batteries, 2.5 times that of nickel-cadmium batteries, and 1.8 times that of nickel-metal hydride batteries. Therefore, with the same battery capacity, lithium-ion batteries are smaller and lighter than lead-acid, nickel-cadmium, and nickel-metal hydride batteries.
3. Lifespan: Lead-acid batteries have a cycle life of around 300 cycles. Lithium iron phosphate battery packs, at room temperature and 1C charge/discharge, retain over 80% capacity after 2000 cycles per cell, and their 3C cycle life exceeds 800 cycles. Lead-acid batteries are highly sensitive to environmental temperature; under harsh conditions, their lifespan does not exceed 5 years. Lithium iron phosphate batteries, under the same conditions, have a much longer lifespan.
4. Safety Performance: Lead-acid batteries can explode under strong impact, posing a threat to consumer safety. Lithium iron phosphate battery packs: Lithium iron phosphate batteries completely solve the safety hazards of lithium cobalt oxide and lithium manganese oxide. Lithium cobalt oxide and lithium manganese oxide can explode under strong impact, while lithium iron phosphate has undergone rigorous safety testing and will not explode even in severe collisions.
5. Temperature range: Lead-acid batteries can be used in a temperature range of -20℃ to 50℃ and have low self-discharge. Lithium iron phosphate battery packs have a peak thermal temperature of 350~500℃ and a wide operating temperature range (-20~+75℃), and can still discharge 100% even at high temperatures (60℃).
6. Charging efficiency: For lead-acid batteries, the charging time for a typical electric vehicle lead-acid battery charger is about 8-10 hours when the battery is 100% depleted. Due to the higher activity of lithium battery materials and electrolytes, lithium iron phosphate battery packs can be charged quickly, allowing for high-current 2C fast charging and discharging. With a dedicated charger, the battery can be fully charged in 40 minutes at 1.5C, and the starting current can reach 2C.
7. Regarding the absence of memory effect: Lead-acid batteries exhibit a memory effect; rechargeable batteries often operate under conditions where they are not fully discharged, causing their capacity to rapidly drop below the rated value. Lithium iron phosphate battery packs do not exhibit this phenomenon; the batteries can be charged and used immediately regardless of their state, without needing to be fully discharged before recharging.
8. In terms of green environmental protection: Lead-acid batteries in electric vehicles contain a large amount of lead, which will pollute the environment if not properly disposed of after disposal. Lithium iron phosphate materials do not contain any heavy metals or rare metals, are non-toxic, and do not cause pollution during production and use. They comply with European RoHS regulations and are considered green and environmentally friendly batteries, making them a hot topic of research and attention.
9. Usage and maintenance: Lead-acid batteries are prone to malfunctions, requiring frequent routine maintenance and increasing maintenance costs. Lithium iron phosphate battery packs, on the other hand, do not require frequent maintenance due to their stable performance; routine checks and tests are sufficient.
