Analysis of Lithium Iron Phosphate

Lithium iron phosphate battery, also known as lithium iron phosphate lithium-ion battery, 

is abbreviated as lithium iron phosphate power battery due to its excellent performance as a power source. 

People prefer to refer to it more colloquially as a "lithium iron (LiFe) power battery".

The working principle of lithium iron phosphate batteries is based on their material composition. 

It is a lithium-ion battery made of lithium iron phosphate as the positive electrode material. 

Meanwhile, the positive electrode materials of lithium-ion batteries mainly include lithium cobalt oxide, 

lithium manganese oxide, lithium nickel oxide, ternary materials, lithium iron phosphate, etc. 

Among them, the vast majority of lithium-ion batteries use lithium cobalt oxide as the positive electrode material. 

However, given that cobalt is a precious metal with limited reserves, 

lithium iron phosphate batteries are increasingly being valued due to their material cost advantages and environmental performance.

As a rechargeable battery, the requirements for lithium iron phosphate batteries include high capacity, high voltage output, 

good charge discharge cycle performance, stable output voltage, ability to charge and discharge high currents, good electrochemical stability, 

safe use, wide operating temperature range, and no pollution to the environment. 

Lithium iron phosphate batteries have shown good performance in these requirements, 

especially in high discharge rate discharge (5-10C discharge), stable discharge voltage, 

safety (non combustion, non explosion), lifespan (number of cycles), and environmental pollution-free advantages.

However, despite the excellent performance of lithium iron phosphate batteries in many aspects, there are still some potential problems. 

The discussion on these issues will be elaborated in subsequent articles.

In the wave of technological development and the advancement of battery technology, 

lithium iron phosphate batteries are undoubtedly a new type of battery with development potential. 

Despite its many advantages, with the joint efforts of researchers and engineers, 

its shortcomings will gradually be improved to meet our energy needs and protect the planet while providing efficient electricity.

Firstly, although lithium iron phosphate batteries have high safety and environmental friendliness, their voltage is slightly inferior, only around 3.2V, 

which still has certain shortcomings compared to other types of lithium-ion batteries. 

This may prevent it from fully realizing its potential in situations that require high voltage output.

Secondly, the conductivity of lithium iron phosphate batteries is relatively low. 

Although this can be improved by adding conductive agents or optimizing the electrolyte, it undoubtedly increases its production difficulty and cost. 

Therefore, lithium iron phosphate batteries rely heavily on advances in production technology to address their performance issues.

The third issue is the low capacity of lithium iron phosphate batteries. 

Although its performance in terms of safety and stability is impeccable, in practical applications, we often focus more on its energy storage and usage time. 

Perhaps this drawback can be compensated for in certain applications, such as electric vehicles with ample space, 

but on some compact but long-term devices, this issue may affect their effectiveness.

Fourthly, lithium iron phosphate batteries may experience performance degradation in extreme temperature environments (extremely high or low temperatures). 

Even though current battery technology allows for safe operation within a certain temperature range, 

temperature dependence remains a major challenge affecting the large-scale application of lithium iron phosphate batteries.

Finally, although lithium iron phosphate batteries have a long charge discharge cycle life, 

they still experience a gradual decrease in discharge capacity after prolonged use, which directly affects the user's experience.

Although these problems exist, with the development of technology, they may all be solved. 

Although lithium iron phosphate batteries are not yet perfect, their unique advantages are enough to show us their enormous potential and possibilities. 

As long as we continue to explore and innovate, we may achieve more breakthroughs in this field and make the world a better place through our efforts.

In summary, lithium iron phosphate batteries have become a widely used battery in many electronic devices due to their superior performance and relatively affordable price. 

Its emergence has had a profound impact on our way of life and has become a landmark product of this era.

Preparation method and research of lithium iron phosphate

The performance of LiFePO4 cathode material depends to some extent on the morphology, particle size, 

and atomic arrangement of the material, so the preparation method is particularly important. 

At present, there are mainly solid-phase and liquid-phase methods, among which solid-phase methods include high-temperature solid-phase reaction method, 

carbon thermal reduction method, microwave synthesis method, and pulsed laser deposition method; Liquid phase method includes sol gel method, 

hydrothermal method, precipitation method and solvothermal method.

1. High-temperature solid-phase method

1) Lithium carbonate and lithium hydroxide are used as lithium sources, while ferrous oxalate, ferrous oxalate, iron oxide, 

and iron phosphate are used as iron sources. 

The phosphate ions mainly come from ammonium dihydrogen phosphate.

2) The typical process flow is: after ball milling and drying the raw materials, 

they are heated to a certain temperature in an inert or reducing atmosphere in a muffle furnace or tube furnace at a certain heating rate, 

reacted for a period of time, and then cooled.

3) The advantages of high-temperature solid-phase method are simple process and easy industrialization, 

but the product particle size is difficult to control, uneven distribution, irregular morphology, 

and requires the use of inert gas protection during the synthesis process.

2. Carbon thermal reduction method

1) This method is an improvement of the high-temperature solid-phase method, which directly uses high valent iron oxides such as Fe2O3, LiH2PO4, 

and carbon powder as raw materials, mixes them in a stoichiometric ratio, 

and sinter them at 700 ℃ for a period of time in an argon atmosphere in a box type sintering furnace, 

and then naturally cools them to room temperature.

2) The initial charge and discharge capacity of the experimental battery made using this method is 151mAh/g. 

This method is currently being applied by a few companies. Due to its simple and controllable production process and the use of one-time sintering,

 it provides another way for LiFePO4 to move towards industrialization.

3) The material prepared by this method has lower capacity and rate performance compared to traditional high-temperature solid-phase methods.

3. Hydrothermal synthesis method

1) Synthesis of LiFePO4 using Na2HPO4 and FeCl3, followed by hydrothermal synthesis of LiFePO4 with CH3COOLi.

2) Compared with the high-temperature solid-phase method, the hydrothermal synthesis method has a lower temperature of about 150-200 degrees, 

a reaction time of only about 1/5 of the solid-phase reaction, and can directly obtain lithium iron phosphate without the need for inert gas. 

The product has the advantages of small grain size and uniform phase, making it particularly suitable for the field of high power discharge. 

However, this synthesis method is prone to Fe dislocation in the formation of olivine structure, which affects the electrochemical performance. 

Additionally, the hydrothermal method requires high-temperature and high-pressure equipment, making industrial production more difficult.

4. Liquid-phase co precipitation method

The raw materials of this method are evenly dispersed, and the precursor can be synthesized under low temperature conditions; 

Add LiOH to a mixed solution of (NH4) 2Fe (SO4) and H3PO4 to obtain a co precipitate. 

After filtration and washing, perform heat treatment under an inert atmosphere to obtain LiFePO4; 

The product exhibits good cycling stability, and Japanese companies have adopted this technology route, 

but due to patent issues, it has not yet been widely applied.

5. Atomization pyrolysis method

The atomization pyrolysis method is mainly used for synthesizing precursors. 

The raw materials and dispersants are stirred at high speed to form a slurry, 

and then subjected to pyrolysis reaction in an atomizing drying device to obtain the precursor, which is then burned to obtain the product.

6. Oxidation-reduction method

This method can obtain electrochemically excellent nanoscale lithium iron phosphate powder, 

but its process is complex and cannot be mass-produced, only suitable for laboratory research.

manufacturing process

1. Synthesis method: There are mainly two methods for synthesizing lithium iron phosphate: chemical method and physical method. 

Chemical methods use compounds of iron, phosphorus, lithium, and oxygen as raw materials

 and prepare them through high-temperature solid-state reactions; 

The physical laws are prepared using a physical mixing method.

2. Preparation of positive and negative electrodes: 

The positive and negative electrodes are mainly composed of active substances, conductive agents, and binders. 

After mixing the active substance with conductive agent and binder evenly, 

it is coated on a metal foil and processed into electrode sheets through drying, rolling, and cutting.

3. Battery assembly: Assemble the positive and negative electrode plates with materials 

such as separators and electrolytes to make lithium iron phosphate power batteries.

7、 Cost analysis

1. Material cost: The main costs of lithium iron phosphate cathode materials include raw materials such as iron, phosphorus, lithium, and carbon. 

Among them, iron and phosphorus have abundant reserves and relatively low prices; Lithium is relatively scarce and expensive.

2. Manufacturing cost: The manufacturing cost of lithium iron phosphate batteries mainly includes electrode production, battery assembly, and testing. 

The manufacturing cost is closely related to the production scale, and as the production scale expands, the average cost will gradually decrease.

3. Other costs: Other costs include research and development costs, transportation costs, and sales expenses. 

These costs will directly or indirectly affect the total cost of lithium iron phosphate batteries.

Ternary lithium vs. lithium iron phosphate

The core of lithium batteries is the positive electrode material. 

Ternary lithium batteries generally use nickel cobalt aluminum or nickel cobalt manganese as the positive electrode material, 

while lithium iron phosphate batteries use lithium iron phosphate as the positive electrode, 

both of which use graphene as the negative electrode material

The principle of charging and discharging is the same. 

Electrolyte is poured between the positive and negative electrodes, with a separator inserted in between. 

During operation, the liquid electrolyte acts as a non active medium to allow lithium ions to move between the positive and negative electrodes

Charging is the process of transferring lithium ions from the positive electrode to the negative electrode, 

while discharging is the process of transferring lithium ions from the negative electrode to the positive electrode. 

During this process, an electric current is generated to provide electrical power for the car. 

When all the lithium ions run to the positive electrode, it means that the battery is dead. 

At this time, an external power source needs to be connected to the positive electrode to "send" the lithium ions back to the negative electrode. 

When all the lithium ions reach the negative electrode, it also means that the battery is fully charged

To measure the quality of a power battery, it is generally evaluated comprehensively from five aspects: energy density, 

safety performance, cycle life, temperature resistance, and battery cost

Their respective advantages and disadvantages

If we simply compare the energy density, the advantages of ternary lithium batteries are even more obvious. 

Due to the active metals such as nickel and cobalt in the positive electrode material, 

not only is the energy density higher, but the charging speed is also faster

But it is precisely because of this discussion on lithium iron phosphate that the safety of ternary lithium batteries is worse. 

The decomposition temperature of the positive electrode material is only 200 ℃, 

while that of lithium iron phosphate batteries is as high as 700 ℃. 

Once the battery experiences thermal runaway, the safety performance of lithium iron phosphate batteries is significantly better

In addition, in terms of cycle life, ternary lithium batteries need to undergo approximately 2500 cycles to decay to 80% capacity, 

while lithium iron phosphate batteries can reach a maximum of over 5000 cycles

In terms of temperature resistance, ternary lithium batteries are even better. 

At temperatures as low as minus 20 degrees Celsius, ternary lithium batteries can release 70% of their electrical energy, 

while lithium iron phosphate batteries only release about 50%.