What is LiFePo4 battery

3.2V 20Ah lifepo4 battery

Lithium iron phosphate battery refers to a lithium-ion battery that uses lithium iron phosphate as a positive electrode material. Lithium iron phosphate batteries have the advantages of high safety, long cycle life, rate discharge, high-temperature resistance, etc., and are considered to be a new generation of lithium batteries.

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LiFePo4 battery

Features of lithium iron phosphate battery

  • Good safety performance, no explosion when punctured, no burning and no explosion when overcharged;
  • Good cycle life, the cycle life of lithium iron phosphate battery can reach more than 2000 times;
  • Good high-temperature performance, working temperature range -20°C to 70°C;
  • High tap density, higher capacity under the same conditions;
  • It can achieve 1C-5C fast charging capability, greatly shortening the charging time.

Application field

Power energy storage, special equipment, robots, AGV, rail transit, medical equipment, emergency backup, power communication, etc.

Advantages of lithium iron phosphate batteries

  • Good safety performance
    Safety comes from the stability of the cathode material and reliable safety design. The lithium iron phosphate battery pack has undergone strict safety tests and will not explode even in severe collisions.
  • Long cycle life
    The 1C cycle life of lithium iron phosphate batteries generally reaches 2,000 times, or even more than 3,500 times, while the energy storage market requires more than 4,000-5,000 times, which is higher than other types of lithium batteries.
  • Good high-temperature performance
    The thermal peak value of lithium iron phosphate battery can reach 350~500℃, the working temperature range is wide (-20~+75℃), and 100% capacity can still be released under high temperature (60℃).
  • Fast charging
    Using a special charger, the battery can be fully charged after 40 minutes of 1.5C charging.
  • Environment friendly
    The lithium iron phosphate battery is green, non-toxic, non-polluting, has a wide range of raw material sources and is cheap.

LiFePO4 battery voltage and capacity

1. LiFePO4 battery voltage

The nominal voltage of a single lithium iron phosphate battery is 3.2V, the charging voltage is 3.6V, and the discharge cut-off voltage is 2.0V.

The lithium iron phosphate battery pack achieves the voltage required by the device through the series combination of the cells, the battery pack voltage=N*the number of series. Commonly used lithium iron phosphate battery pack voltages are as follows:

  • 12V LiFePo4 battery
  • 24V LiFePo4 battery
  • 36V LiFePo4 battery
  • 48V LiFePo4 battery

2. LiFePO4 battery capacity

The capacity of the lithium iron phosphate battery pack is determined according to the capacity and quantity of the cells connected in parallel. Generally, it is determined according to the specific requirements of the electrical equipment. The more lithium-iron phosphate cells are connected in parallel, the greater the capacity.

Common lithium iron phosphate battery pack capacities are 10ah, 20ah, 40ah, 50ah, 100ah, 200ah, 400ah, etc.

LiFePO4 battery structure and working principle

1. LiFePO4 battery structure

As shown in the figure, the left side is LiFePO4 with olivine structure as the positive electrode of the battery, which is connected to the positive electrode of the battery by aluminum foil, and the middle is the polymer separator, which separates the positive electrode from the negative electrode, but the lithium-ion Li+ can pass through while the electron e- cannot. Pass, on the right is the negative electrode of the battery composed of carbon (graphite), which is connected to the negative electrode of the battery by a copper foil.

LiFePo4 cell structure
Internal structure diagram of lithium iron phosphate battery

2. The working principle of lithium iron phosphate battery

When LiFePO4 batteries are charged, the lithium ions Li+ in the positive electrode migrate to the negative electrode through the polymer separator; during the discharge process, the lithium ions Li+ in the negative electrode migrate to the positive electrode through the separator. Lithium-ion batteries are named after lithium ions migrate back and forth during charging and discharging.

LiFePO4 battery charger

1. LiFePO4 Battery Charging

It is recommended to use the CCCV charging method for charging the lithium iron phosphate battery pack, that is, constant current first and then constant voltage. The constant current is recommended to be 0.3C. Constant pressure recommends 3.65.

2. Are lithium iron phosphate batteries the same as lithium-ion battery chargers?

  • The charging methods of the two batteries are constant current and then constant voltage (CCCV), but the constant voltage points are different.
  • The nominal voltage of the lithium iron phosphate battery is 3.2V, and the charge cut-off voltage is 3.6V.
  • The nominal voltage of ordinary lithium batteries is 3.6V, and the charge cut-off voltage is 4.2V.

3. Charging LiFePO4 batteries with solar energy

The solar panel cannot directly charge the lithium iron phosphate battery, because the voltage of the solar panel is unstable, it cannot directly charge the lithium iron phosphate battery, a voltage regulator circuit is required, and the corresponding lithium iron phosphate battery charging circuit is also required to charge.

4. Using a generator to charge a lithium iron phosphate battery

The generator cannot directly charge the lithium iron phosphate battery, because the electricity from the generator is alternating current or pulsed direct current, and the charging of the lithium iron phosphate battery must be regulated direct current.

Lithium Iron Phosphate Battery and Lithium Ion Battery Comparison

SystemVoltageEnergy Density(Wh/kg)Work Temp(­°C)CycleSafetyEnvironment friendlyCost based on cycle
LiFePo43.2>120-20-60>2000SafeYes0.15-0.25 lower than SLA
Lead acid2.0>35-20-40>200SafeBad1
NiCd1.2>40-20-50>1000SafeNormal0.7
NiMH1.2>80-20-50>500SafeYes1.2-1.4
LiMnxNiyCoz023.7>160-20-50>500Better than LiCoO2Yes1.5-2.0
LiCoO23.7>200-20-50>500Unsafe w/o PCMYes1.5-2.0

Lithium iron phosphate battery and Li(NiCoMn)O₂ battery

Affected by the structure, lithium iron phosphate and ternary have their own advantages and disadvantages in performance, ternary has advantages in energy density and fast charging speed, and lithium iron phosphate has advantages in cycle life, safety and economy.

1. Material comparison

The negative electrode, electrolyte and separator of the two batteries are similar, and the biggest difference is the positive electrode material, which is named after that.

Positive electrode materialLiFePo4Li(NiCoMn)O₂
Abbreviate LFPNCM
Rated Voltage3.2V3.7V
Crystal formPeridot structureLayered structure
Li-ion deintercalation channelOne-dimensionalTwo-dimensional

2. Energy Density

From the cell level, the ternary battery has a higher energy density. The rated voltage and theoretical specific capacity (mAh/g) of the lithium iron phosphate cathode material are lower than those of the ternary battery, and its energy density has been developed to the “ceiling”.

Positive electrode materialRated Voltage(V)Theoretical specific capacity (mAh/g)Estimated actual specific capacity (mAh/g)Estimated response cell energy density (wh/kg)
LiFePo43.2170145170
NCM8113.7274195240
NCM5233.7274170210
NCM1113.7274145180

3. Charging efficiency

NCM lithium batteries have great advantages over lithium iron phosphate batteries in terms of charging efficiency.

When the NCM battery and the lithium iron phosphate battery are charged below 10C, there is no significant difference in the constant current ratio. When the rate is charged above 10C, the constant current ratio of the lithium iron phosphate battery decreases rapidly, and the charging efficiency decreases rapidly.

4. Cycle life

In theory, lithium iron phosphate has an advantage in life. The olivine crystal structure is more stable, the expansion is lower, and the electrochemical reaction is more stable.

5. Safety

Lithium iron phosphate batteries have unparalleled advantages in terms of safety. The positive electrode voltage is low, there is no oxygen-releasing thermal chain reaction similar to ternary, and the thermal stability temperature can reach above 300 °C, while the NCM battery is around 150-200 °C.

6. Economy

In terms of price, LiFePO4 currently has obvious advantages, the raw materials are relatively cheap, and the domestic industrial chain is relatively mature.

To reduce the price of ternary NCM batteries, cobalt is the key. Cobalt is mainly an associated ore, with small output and uneven distribution, and the price has continued to rise in recent years.

Cycle life and influencing factors of lithium iron phosphate battery

1. Lithium iron phosphate battery is used in normal temperature environment

Small current charge and discharge

In this field, if the lithium iron phosphate battery is used normally, the cycle life is basically more than 2000 times; for small lithium battery manufacturers, the quality of the lithium battery is slightly lower, and the cycle life is more than 1000 times;

  • High rate stable charge and discharge use

    Most of the applications of high-rate discharge are power-type lithium batteries, and most of them are used in applications that provide power to motors. Because most lithium iron phosphate batteries operate under high load conditions, the decay time of battery materials is accelerated, and the cycle life is about 800 times.
  • High rate unstable charge and discharge use

    The lithium iron phosphate battery used in this case will have a shorter lifespan, only about 300 times.

2. LiFePO4 battery used in high-temperature environment

The high-temperature performance of lithium iron phosphate batteries is not very mature at present. The operating temperature is -20°C to 125°C. This temperature range is the theoretical value, and the actual application temperature range is smaller.

  • Small current charge and discharge

    In this field, if the lithium iron phosphate battery is used normally, if the battery brand manufacturer is relatively strong and the quality is good, the cycle life is basically more than 1000 times; The cycle life of more than two times; because the use of high temperature, the damage to the battery is relatively large.
  • High rate stable charge and discharge use

    Since most lithium iron phosphate batteries operate under high load conditions, the decay time of battery materials is accelerated, and the cycle life is sharply reduced. Poor quality batteries may only have about 300 cycles; strong battery brand manufacturers, in The equipment technology and material application will be better, and the quality of the cell will be better, but the cycle life will be about 500 times.
  • High rate unstable charge and discharge use

    Unstable operation at high temperature and discharge rate will cause greater damage to the battery and a relatively low cycle life. Tests on the cells of several battery manufacturers have found that the battery is basically unusable after 250 to 300 times.

3. Lithium iron phosphate battery used in low-temperature environment

The low temperature environment has a greater impact on the performance of lithium iron phosphate batteries than high. According to the current market situation, lithium iron phosphate batteries work below -20 °C to -40 °C, and the life span is significantly reduced, and the cycle life is 300 times or so.

4. Factors affecting the cycle life of lithium iron phosphate batteries

  • Discharge

    When choosing a charger, it is best to use a charger with a correct termination of the charging device to prevent the lithium iron phosphate battery from shortening its service life due to overcharging. Generally speaking, slow charging can extend the life of the battery more than fast charging.
  • Depth of discharge

    The depth of discharge is the main factor affecting the life of the lithium iron phosphate battery. The higher the depth of discharge, the shorter the life of the lithium iron phosphate battery. In other words, as long as the depth of discharge is reduced, the service life of lithium iron phosphate batteries can be greatly extended. Therefore, we should avoid over-discharging lithium battery UPS to extremely low voltage.
  • Working environment

    If the lithium iron phosphate battery is used at high temperature for a long time, the electrode activity will be attenuated and the service life will be shortened. Therefore, it is a good way to prolong the life of the lithium iron phosphate battery by maintaining the appropriate operating temperature as much as possible.

Recycling of lithium iron phosphate batteries

Batteries that do not have cascade utilization value in retired lithium iron phosphate batteries and batteries after cascade utilization will eventually enter the dismantling and recycling stage. The difference between lithium iron phosphate battery and MCN material battery is that it does not contain heavy metals, and the recovery is mainly Li, P, and Fe. The added value of the recovered products is low, and a low-cost recovery route needs to be developed. There are mainly two recycling methods: fire method and wet method.

  • Fire recovery process

    The traditional fire recovery is generally high-temperature incineration of electrode sheets, which burns the carbon and organic matter in the electrode fragments, and the remaining ash that cannot be burned is finally screened to obtain fine powder materials containing metals and metal oxides.
  • Wet recycling process

    Wet recovery is mainly to dissolve the metal ions in the lithium iron phosphate battery through acid-base solution, and further use precipitation, adsorption, etc. to extract the dissolved metal ions in the form of oxides and salts. Most of the reaction processes use H2SO4, NaOH and H2O2 and other reagents.
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