A lithium iron phosphate (LiFePO4) battery is a lithium-ion battery that uses lithium iron phosphate (LiFePO4) as the positive electrode material and carbon as the negative electrode material. The rated voltage of a single cell is 3.2V, and the charging cut-off voltage is 3.6V~3.65V. Because its performance is particularly suitable for power applications, the word "power" is added to its name, hence lithium iron phosphate power battery. It is also sometimes called a "lithium iron (LiFe) power battery."
Lithium iron phosphate (LFP) batteries are a type of lithium battery, similar to those used in our mobile phones. They are named for their positive electrode material, which is primarily a compound of phosphorus, iron, and lithium. Below, we will introduce the advantages and disadvantages of this new material in detail.
Advantages of lithium iron phosphate batteries
1. Improved safety performance
The PO bonds in lithium iron phosphate crystals are stable and difficult to decompose. Even at high temperatures or under overcharge, they do not collapse and generate heat or form strong oxidizing substances like lithium cobalt oxide, thus exhibiting good safety. Reports indicate that in actual operation, a small number of samples showed combustion in nail penetration or short-circuit tests, but no explosions were observed. However, in overcharge tests using voltages several times higher than their discharge voltage, explosions were still observed. Nevertheless, its overcharge safety is significantly improved compared to ordinary liquid electrolyte lithium cobalt oxide batteries.
2. Improved lifespan
Long-life lead-acid batteries have a cycle life of around 300 cycles, with a maximum of 500 cycles. Lithium iron phosphate (LFP) batteries, on the other hand, have a cycle life exceeding 2000 cycles, and can reach 2000 cycles under standard charging (5-hour rate) conditions. Lead-acid batteries of the same quality typically last only 1-1.5 years – "new for six months, old for six months, and then another six months of maintenance" – while LFP batteries, under the same conditions, theoretically have a lifespan of 7-8 years. Considering all factors, the performance-price ratio is theoretically more than four times that of lead-acid batteries. LFP batteries also offer high-current discharge and fast charging/discharging capabilities, allowing for 2C fast charging and discharging. With a dedicated charger, a 1.5C charge can fully charge the battery within 40 minutes, and the starting current can reach 2C – capabilities that lead-acid batteries lack.
3. Good high-temperature performance
Lithium iron phosphate (LFP) has a peak thermal conductivity of 350℃-500℃, while lithium manganese oxide and lithium cobalt oxide are only around 200℃. It has a wide operating temperature range (-20℃ to 75℃) and high-temperature resistance.
4. Large capacity
When a battery is frequently operated under conditions where it is fully charged but not fully discharged, its capacity will rapidly drop below its rated capacity. This phenomenon is called the memory effect. Nickel-metal hydride and nickel-cadmium batteries exhibit this memory effect, while lithium iron phosphate batteries do not. Lithium iron phosphate batteries can be charged and used immediately regardless of their state, without needing to be fully discharged before recharging.
6. Lightweight
A lithium iron phosphate battery of the same capacity is 2/3 the volume of a lead-acid battery and 1/3 the weight of a lead-acid battery.
7. Environmental protection
Lithium iron phosphate batteries are generally considered to be free of any heavy metals and rare metals (nickel-metal hydride batteries require rare metals), non-toxic (SGS certified), pollution-free, and compliant with European RoHS regulations, making them absolutely green and environmentally friendly batteries. Therefore, the main reason lithium batteries are favored by the industry is their environmental benefits. Consequently, this type of battery was included in the "863" National High-Tech Development Program during the "15th Five-Year Plan" period, becoming a key project supported and encouraged by the state.
Lithium iron phosphate batteries also have their drawbacks: for example, poor low-temperature performance, low tap density of the cathode material, and a larger volume for a lithium iron phosphate battery of the same capacity compared to lithium-ion batteries such as lithium cobalt oxide, thus lacking advantages in micro-batteries. When used in power batteries, lithium iron phosphate batteries, like other batteries, face the challenge of battery consistency.
Disadvantages of lithium iron phosphate batteries
Whether a material has potential for application and development depends not only on its advantages, but more importantly on whether it has fundamental defects.
1. The tap density of the positive electrode of lithium iron phosphate battery is low, generally between 0.8 and 1.3, and the volume is large.
2. Poor conductivity, slow lithium-ion diffusion rate, and low actual specific capacity during high charge and discharge cycles.
3. Lithium iron phosphate batteries have poor low-temperature performance.
4. A single lithium iron phosphate battery has a long lifespan, around 2000 cycles, but a lithium iron phosphate battery pack has a short lifespan, generally around 500 cycles.
Currently, the most common lithium batteries on the market are lithium cobalt oxide (LiCoO2) and lithium manganese oxide. As a type of lithium battery, lithium iron phosphate is mainly used in the power system field, such as electric steam, automobiles, military aerospace, power tools, and uninterruptible power supplies. It has attracted much attention due to its excellent structural stability and safety performance, and has a longer service life, making it more suitable for use in the power system field.
