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Advantages and disadvantages of lithium iron phosphate batteries

Apr. 09, 2022

Advantages and disadvantages of lithium iron phosphate batteries

Lithium Iron Phosphate (LFP) is a rechargeable lithium-ion battery. Among them, lithium iron phosphate is used as the positive electrode material, and graphite is used as the negative electrode. LFP batteries have a larger specific capacity than traditional lithium-ion batteries. However, the energy density is lower than that of conventional lithium-ion batteries. This is because the operating voltage of the LFP battery is low.

LFPs are widely used due to their advantages of long-term stability, low toxicity, and low cost. It is now widely used in vehicle and utility scale stationary applications.

Depth of discharge of lithium iron phosphate battery

When a Li-Ion battery is discharged, the energy extracted determines the depth of discharge of the battery. Assuming a 100 Ah battery. With 50 Ah of this battery, the depth of discharge is 50%. Depending on the type of battery used, the depth of charge determines the number of cycles the battery can be cycled.

Lithium iron phosphate batteries can perform the largest number of charge and discharge cycles depending on the technology used inside. Therefore, LFP batteries are ideal for stationary energy storage systems and all applications requiring long life. The number of cycles for an LFP depends on several factors, one of which is the depth of discharge (DOD). Under optimal conditions, the lifetime "cycle count" of the LFP battery decreases as the DOD increases.

Lithium phosphate battery weight and space

LFP batteries are used for high power APP applications that require long life. LFP batteries can produce high discharge current, do not explode, and have a long cycle life. But its energy density is lower than that of conventional lithium-ion batteries. The LFP battery is rated to operate at 3.2V. Considering the long cycle life, LFP batteries have the lowest cost of all Li-ion batteries. In most lead-acid batteries, the reciprocating efficiency from 100% discharge to 0% discharge to 100% discharge is about 80%. In LFP cells, the reciprocating efficiency is 92%. The Battery Management System (BMS) fully controls all parameters of the battery and provides optimum safety and performance.

LFP batteries can save up to 70% space and 70% weight. This is a battery suitable for small applications such as electric vehicles where space, weight and size are important. Compared to lead-acid batteries, LFP batteries are only 40% of their weight.

Lithium iron phosphate battery cycle times

The battery voltage of the lithium iron phosphate battery is 3.2V or 3.3V. The end-of-charge voltage of an LFP battery is typically 3.6V to 3.65V. Their discharge voltage values are between 2.8V and 2.5V. LFP has high cycle stability, so it can cycle 1,000 to 2,000 cycles more than conventional lithium-ion batteries. Also, LFP cells do not release oxygen when an error occurs. In this way, the LFP battery will be very safe as the risk of explosion and fire is minimized. The cycle life of lithium iron phosphate batteries is very long, reaching 2000 charge/discharge cycles. Since the crystal structure of iron phosphate does not break under repeated packing and unpacking of lithium ions during charging and discharging, LFP batteries have a long cycle life.

A full charge of the LFP requires two stages;

Charge the battery to around 60% with constant current (CC)

When the charging voltage reaches 3.65V per cell, change the constant current ( CC ) to the constant voltage ( CV ).

Compared with conventional lithium-ion batteries, LFP batteries have a wider overcharge margin. This way, LFP cells can be safely overcharged to a maximum of 4.2 volts per cell. However, it's good to know that higher voltages destroy the organic electrolyte inside the LFP cell. Due to the safety factor inside LFP batteries, performance and safety are widely used in important devices and applications.

The LFP battery is a non-aqueous battery with a rated voltage of 3.2V during discharge. Their specific capacity exceeds 145 Ah/kg. Therefore, the gravimetric energy density of the LFP battery is 130 Wh/kg. These all make lithium iron phosphate batteries a more ideal choice in technical equipment.

LFP batteries have a certain discharge voltage. During discharge, the discharge voltage was maintained at around 3.2V. Constant voltage allows LFP cells to deliver almost full power before the discharge point.

LFP batteries do not require voltage regulation circuitry. Lithium phosphate batteries are safer than traditional lithium-ion batteries. It is not easy to catch fire during charging or discharging. Dissipation of overcharge energy occurs as heat in most batteries, but lithium iron phosphate batteries do not decompose at high temperatures.

After being stored on the shelf for nearly a year, the energy density of lithium iron phosphate batteries is basically the same as at the beginning due to the gradual decrease in energy density.