Advantages and disadvantages of Lithium Iron Phosphate batteries.

Lithium iron phosphate battery refers to a lithium ion battery that uses lithium iron phosphate as the positive electrode material. The cathode materials of lithium-ion batteries mainly include lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and so on.

Among them, lithium cobalt oxide is currently the cathode material used in most lithium-ion batteries. In terms of material principle, lithium iron phosphate is also an intercalation/deintercalation process, which is exactly the same as lithium cobaltate and lithium manganate.

It’s enough to know about lithium iron phosphate batteries!

 


1. Introduction

Lithium iron phosphate batteries are lithium-ion secondary batteries. One of its main uses is as a power battery. It has great advantages over NI-MH and Ni-Cd batteries.

 

The charging and discharging efficiency of lithium iron phosphate batteries is relatively high, and the charging and discharging efficiency can reach more than 90% in the case of rate discharge. The lead-acid battery is about 80%.

 


2. Eight advantages

 

Improvement of safety performance

The P-O bond in lithium iron phosphate crystal is stable and difficult to decompose. Even at high temperature or overcharge, it will not collapse and heat up like lithium cobalt oxide or form strong oxidizing substances, so it has good safety.

A report pointed out that in actual operation, a small part of the samples were found to burn in acupuncture or short-circuit experiments, but no explosion occurred. In the overcharge experiment, high voltage charging that was several times higher than the self-discharge voltage was used, and it was found that there were still Explosion phenomenon.

Nevertheless, its overcharge safety has been greatly improved compared with ordinary liquid electrolyte lithium cobalt oxide batteries.

 

Lifespan improvement

Lithium iron phosphate battery refers to a lithium ion battery that uses lithium iron phosphate as a positive electrode material.

The cycle life of a long-life lead-acid battery is about 300 times, the highest is 500 times, while the cycle life of a lithium iron phosphate power battery is more than 2000 times, and the standard charge (5 hour rate) use can reach 2000 times. Lead-acid batteries of the same quality are “new half a year, half a year old, and half a year for maintenance”, which is 1 to 1.5 years at most, while the lithium iron phosphate battery used under the same conditions will have a theoretical life of 7 to 8 years.

Comprehensive consideration, the performance-price ratio is theoretically more than 4 times that of lead-acid batteries. High-current discharge can quickly charge and discharge high current 2C. Under the special charger, the battery can be fully charged within 40 minutes of 1.5C charging, and the starting current can reach 2C, but lead-acid batteries have no such performance.

 

Good high temperature performance

The peak value of lithium iron phosphate electric heating can reach 350℃-500℃, while lithium manganate and lithium cobaltate are only around 200℃. Wide operating temperature range (-20C–+75C), with high temperature resistance, lithium iron phosphate electric heating peak can reach 350℃-500℃, while lithium manganate and lithium cobaltate are only around 200℃.

 

High capacity

It has a larger capacity than ordinary batteries (lead-acid, etc.). 5AH-1000AH (single)

 

No memory effect

Rechargeable batteries work under conditions that are often fully charged and not discharged, and their capacity will quickly fall below the rated capacity.

This phenomenon is called the memory effect. Like nickel-metal hydride and nickel-cadmium batteries, there is memory, but lithium iron phosphate batteries do not have this phenomenon.

No matter what state the battery is in, it can be charged and used at any time without having to discharge it before charging.

 

Light weight

The volume of the lithium iron phosphate battery of the same specification and capacity is 2/3 of the volume of the lead-acid battery, and the weight is 1/3 of the lead-acid battery.

 

Environmental friendly

The battery is generally considered to be free of any heavy metals and rare metals (the nickel-hydrogen battery requires rare metals), non-toxic (SGS certification), non-polluting, in line with European RoHS regulations, and is an absolute green battery certificate.

Therefore, the reason why lithium batteries are favored by the industry is mainly due to environmental protection considerations. Therefore, the battery has been included in the “863” national high-tech development plan during the “Tenth Five-Year Plan” period and has become a key national support and encouragement project.

With China’s accession to the WTO, China’s export volume of electric bicycles will increase rapidly, and electric bicycles entering Europe and the United States have been required to be equipped with pollution-free batteries.

 

However, some experts said that the environmental pollution caused by lead-acid batteries mainly occurred in the company’s irregular production process and recycling process. In the same way, lithium batteries belong to the new energy industry, but it cannot avoid the problem of heavy metal pollution.

Lead, arsenic, cadmium, mercury, chromium, etc. in the processing of metal materials may be released into dust and water. The battery itself is a kind of chemical substance, so there may be two kinds of pollution: one is the pollution of process excrement in the production engineering; the other is the pollution of the battery after it is scrapped.

 

Lithium iron phosphate batteries also have their shortcomings: for example, poor low-temperature performance, low tap density of the cathode material, and the volume of a lithium iron phosphate battery of equal capacity is larger than that of lithium-ion batteries such as lithium cobalt oxide, so it has no advantage in miniature batteries. When used in power batteries, lithium iron phosphate batteries, like other batteries, need to face battery consistency issues.

 

Comparison of power batteries

At present, the most promising cathode materials for power lithium-ion batteries are modified lithium manganate (LiMn2O4), lithium iron phosphate (LiFePO4) and lithium nickel cobalt manganate (Li(Ni,Co,Mn)O2) ternary Material.

Due to the lack of cobalt resources and the high content of nickel and cobalt and the large price fluctuations, it is generally believed that it is difficult to become the mainstream of power-type lithium-ion batteries for electric vehicles, but it can be compared with spinel manganese acid. Lithium is mixed and used within a certain range.

 

Industry Application

Carbon-coated aluminum foil brings technological innovation and industrial upgrading to the lithium battery industry

Improve the performance of lithium battery products and improve the discharge rate

With the increasing requirements of  battery manufacturers for battery performance, technicians generally agrees with new energy battery materials: conductive materials & conductive coated aluminum foil/copper foil.

Its advantage lies in: when processing battery materials, it often has high-rate charge-discharge performance, large specific capacity, but poor cycle stability, more serious attenuation, etc., so it has to be given up.

This is a magical coating that will improve the performance of the battery and bring it into a new era.

The conductive coating is composed of dispersed nano-conductive graphite coated particles. It can provide excellent static electrical conductivity and is a protective energy absorbing layer.

It can also provide good covering and protection performance. The coating is water-based and solvent-based, and can be applied to aluminum, copper, stainless steel, aluminum and titanium bipolar plates.

 

Carbon coating brings the following improvements to the performance of lithium batteries

1. Reduce the internal resistance of the battery and suppress the dynamic internal resistance increase during the charge-discharge cycle;

2. Significantly improve the consistency of the battery pack and reduce the battery composition cost;

3. Improve the adhesion of active materials and current collectors, and reduce the manufacturing cost of pole pieces;

4. Reduce polarization, improve rate performance, and reduce thermal effects;

5. Prevent the electrolyte from corroding the current collector;

6. The comprehensive factor further prolongs the service life of the battery.

7. Coating thickness: the conventional single-sided thickness is 1~3μm.

 

In recent years, Japan and South Korea have mainly developed power-type lithium-ion batteries using modified lithium manganese oxide and lithium nickel cobalt manganate ternary materials as cathode materials, such as Panasonic EV Energy Co., Ltd., Hitachi, Sony, New Kobe Electric, NEC, Sanyo Electric, Samsung, LG, etc.

 

The United States mainly develops power-type lithium-ion batteries using lithium iron phosphate as the cathode material, such as A123 System Company and Valence Company, but the major US automobile manufacturers choose manganese-based cathode material system power-type lithium-ion batteries in their PHEVs and EVs.

 

It is also said that the American company A123 is considering entering the field of lithium manganese oxide materials, while Germany and other European countries mainly adopt the method of cooperating with other countries’ battery companies to develop electric vehicles, such as Daimler-Benz and the French Saft alliance, and German Volkswagen and Japan’s Sanyo agreement cooperation Wait. At present, Volkswagen in Germany and Renault in France are also developing and producing power-type lithium-ion batteries with the support of their governments.

 

 


3. Disadvantages

Whether a material has application development potential, in addition to paying attention to its advantages, the more critical thing is whether the material has fundamental defects.

 

Lithium iron phosphate is now widely selected as the cathode material for power-type lithium-ion batteries in China. Market analysts such as governments, scientific research institutions, enterprises and even securities companies are optimistic about this material and regard it as the development direction of power-type lithium-ion batteries.

 

Analyzing the reasons, there are mainly the following two points:

First, affected by the research and development direction of the United States, Valence and A123 in the United States were the first to use lithium iron phosphate as the cathode material for lithium-ion batteries.

Secondly, there has not been a lithium manganate material with good high-temperature cycling and storage performance that can be used in power-type lithium-ion batteries in China.

However, lithium iron phosphate also has fundamental defects that cannot be ignored, which can be summarized as follows:

 

1) During the sintering process during the preparation of lithium iron phosphate, iron oxide may be reduced to elemental iron in a high-temperature reducing atmosphere.

Elemental iron can cause micro-short circuit of the battery, which is the most taboo substance in the battery.

This is also the main reason why Japan has not used this material as a positive electrode material for power-type lithium-ion batteries.

 

2) Lithium iron phosphate has some performance defects, such as low tap density and compaction density, resulting in low energy density of lithium ion batteries.

The low temperature performance is poor, even if it is nanometerized and carbon coated, it does not solve this problem.

When Dr. Don Hillebrand, director of the Energy Storage System Center of Argonne National Laboratory, talked about the low-temperature performance of lithium iron phosphate batteries, he described it as terrible.

Their test results on lithium iron phosphate lithium-ion batteries showed that lithium iron phosphate batteries were at low temperature. The electric vehicle cannot be driven at low temperature (below 0°C).

Although some manufacturers claim that the capacity retention rate of lithium iron phosphate batteries is good at low temperatures, that is when the discharge current is small and the discharge cut-off voltage is very low. In this situation, the device cannot start working at all.

 

3) The preparation cost of materials and the manufacturing cost of the battery are relatively high, the battery yield rate is low, and the consistency is poor.

Although the nanometerization and carbon coating of lithium iron phosphate improve the electrochemical performance of the material, it also brings other problems, such as a reduction in energy density, an increase in synthesis cost, poor electrode processing performance, and harsh environmental requirements. Although the chemical elements Li, Fe and P in lithium iron phosphate are abundant, and the cost is low, the cost of the prepared lithium iron phosphate product is not low.

Even if the previous research and development costs are removed, the process cost of the material is higher. The cost of preparing the battery will make the final unit energy storage cost higher.

 

4)Poor product consistency. At present, there is no lithium iron phosphate material factory in China that can solve this problem.

From the perspective of material preparation, the synthesis reaction of lithium iron phosphate is a complex multiphase reaction, including solid-phase phosphate, iron oxide and lithium salt, plus carbon precursor and reducing gas phase.

In this complex reaction process, it is difficult to ensure the consistency of the reaction.

 

5) Intellectual property issues. The earliest patent application related to lithium iron phosphate was obtained by FX MITTERMAIER & SOEHNE OHG (DE) on June 25, 1993, and the result of the application was announced on August 19 of the same year.

The basic patent of lithium iron phosphate is owned by the University of Texas, while the carbon coating patent is applied by Canadians. These two basic patents cannot be bypassed.

If royalties are included in the cost, the cost of the product will be further increased.

 

In addition, from the experience of R&D and production of lithium-ion batteries, Japan is the first country to commercialize lithium-ion batteries and has always occupied the high-end lithium-ion battery market.

Although the United States is leading in some basic research, so far there is no large-scale lithium-ion battery manufacturer.

Therefore, it is more reasonable for Japan to choose modified lithium manganate as the positive electrode material for power-type lithium-ion batteries.

Even in the United States, half of the manufacturers use lithium iron phosphate and lithium manganate as cathode materials for power-type lithium-ion batteries, and the federal government supports the research and development of these two systems at the same time.

In view of the above-mentioned problems of lithium iron phosphate, it is difficult to be widely used as a positive electrode material for power-type lithium-ion batteries in new energy vehicles and other fields.

If the problems of high temperature cycling and poor storage performance of lithium manganate can be solved, with its advantages of low cost and high rate performance, the application in power-type lithium-ion batteries will have huge potential.

 


4. Working principle and characteristics The full name of the lithium iron phosphate battery is lithium iron phosphate lithium ion battery, this name is too long, referred to as lithium iron phosphate battery.

Because its performance is particularly suitable for power applications, the word “power” is added to the name, that is, lithium iron phosphate power battery. Some people call it “Lithium Iron (LiFe) Power Battery”.

 

 

Significance

As of the time I added this entry (April 24, 2013), in the metal trading market, cobalt (Co) is the most expensive, and there is not much storage, nickel (Ni) and manganese (Mn) are cheaper, and iron (Fe) is the most expensive.

The price of the cathode material is also consistent with the price of these metals.

Therefore, the lithium ion battery made of LiFePO4 cathode material should be the cheapest. Another feature of it is that it does not pollute the environment.

 

As a rechargeable battery, the requirements are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, safety in use (not due to overcharge, overdischarge and short circuit Burning or explosion caused by improper operation), wide operating temperature range, non-toxic or less toxic, and non-polluting to the environment.

Lithium iron phosphate batteries using LiFePO4 as the positive electrode are good in these performance requirements, especially in high discharge rate discharge (5~10C discharge), discharge voltage is stable, safety (non-burning, non-explosive), and life (number of cycles) ).

It is the best in terms of no pollution to the environment, and is currently the best high-current output power battery.

 

Structure and working principle

The internal structure of the LiFePO4 battery is shown in Figure 1. On the left is LiFePO4 with olivine structure as the positive electrode of the battery. It is connected to the positive electrode of the battery by aluminum foil.

In the middle is a polymer separator, which separates the positive electrode from the negative electrode. The negative electrode of the battery composed of carbon (graphite) is connected to the negative electrode of the battery by copper foil.

Between the upper and lower ends of the battery is the electrolyte of the battery, and the battery is hermetically sealed by a metal casing.

 

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

 

Main performance

The nominal voltage of the LiFePO4 battery is 3.2V, the final charging voltage is 3.6V, and the final discharge voltage is 2.0V.

Due to the different quality and technology of the positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance.

For example, the battery capacity of the same model (standard battery in the same package) is quite different (10%-20%).

 

The main performance of lithium iron phosphate power battery is listed in Table 1. In order to compare with other rechargeable batteries, the performance of other types of rechargeable batteries is also listed in the table.

It should be noted here that lithium iron phosphate power batteries produced by different factories have some differences in various performance parameters; in addition, there are some battery performances that are not listed, such as battery internal resistance, self-discharge rate, charge and discharge temperature, etc.

 

There are big differences in the capacity of lithium iron phosphate power batteries, which can be divided into three categories: small ones from a few tenths to several milliamp-hours, medium-sized ones tens of milliamp-hours, and large-scale ones hundreds of milliamp-hours.

Similar parameters of different types of batteries also have some differences. Here we will introduce the parameters of a small standard cylindrical packaged lithium iron phosphate power battery that is currently widely used.

Its external dimensions: diameter 18mm, height 650mm (model 18650), its parameter performance is shown in Table 2.

 

Over discharge to zero voltage test

STL18650 (1100mAh) lithium iron phosphate power battery was used for over-discharge to zero voltage test. Test conditions: Fully charge a 1100mAh STL18650 battery with a 0.5C charge rate, and then discharge it with a 1.0C discharge rate until the battery voltage is 0C.

The 0V batteries are divided into two groups: one group is stored for 7 days, and the other group is stored for 30 days; after the storage expires, it is fully charged with a 0.5C charging rate, and then discharged with 1.0C.

Finally, compare the difference between the two zero-voltage storage periods.

 

The result of the test is that the battery has no leakage after 7 days of storage at zero voltage, with good performance, and the capacity is 100%; after storage for 30 days, there is no leakage, with good performance, and the capacity is 98%; the battery after 30 days of storage is subjected to 3 charge and discharge cycles. The capacity has returned to 100%.

 

This test shows that even if the battery is over-discharged (even to 0V) and stored for a certain period of time, the battery will not leak or be damaged.

This is a feature that other types of lithium-ion batteries do not have.

 

Features of lithium iron phosphate battery

Through the above introduction, LiFePO4 battery can summarize the following characteristics.

  • High efficiency output: standard discharge is 2~5C, continuous high current discharge can reach 10C, instant pulse discharge (10S) can reach 20C;
  • Good performance at high temperature: when the external temperature is 65 ℃, the internal temperature is as high as 95 ℃, and the temperature can reach 160 ℃ when the battery is discharged. The structure of the battery is safe and intact;
  • Even if the battery is damaged internally or externally, the battery does not burn or explode, and has the best safety;
  • Excellent cycle life, after 500 cycles, its discharge capacity is still greater than 95%;
  • There is no damage even after over-discharge to zero volts;
  • Can be charged quickly;
  • low cost;
  • No pollution to the environment.
  • Application of lithium iron phosphate power battery
  • Because lithium iron phosphate power batteries have the above-mentioned characteristics, and produce batteries with different capacities, they will soon be widely used. Its main application areas are:
  • Large-scale electric vehicles: buses, electric vehicles, tourist attractions and hybrid vehicles, etc.;
  • Light electric vehicles: electric bicycles, golf carts, small flat battery carts, forklifts, cleaning vehicles, electric wheelchairs, etc.;
  • Power tools: electric drills, electric saws, lawn mowers, etc.;
  • Remote control cars, boats, airplanes and other toys;
  • Energy storage equipment for solar and wind power generation;
  • UPS and emergency lights, warning lights and miner’s lamps (the best safety);
  • Replace the 3V disposable lithium battery and 9V nickel-cadmium or nickel-metal hydride rechargeable batteries in the camera (the same size);
  • Small medical equipment and portable equipment, etc.

 

Here is an application example of replacing lead-acid batteries with lithium iron phosphate power batteries. Using 36V/10Ah (360Wh) lead-acid battery, its weight is 12kg, it can walk about 50km with one charge, the number of charge is about 100 times, and the use time is about 1 year.

If the lithium iron phosphate power battery is used, the same 360Wh energy (12 10Ah batteries in series) is used, and its weight is about 4kg.

It can walk about 80km per charge, charge up to 1,000 times, and have a service life of 3 to 5 years.

Although the price of lithium iron phosphate power batteries is much higher than that of lead-acid batteries, the overall economic effect is better to use lithium iron phosphate power batteries, and they are lighter in use.

 


5. Battery performance

The performance of lithium-ion power batteries mainly depends on the positive and negative materials. Lithium iron phosphate has only appeared in recent years as a lithium battery material.

The Chinese development of large-capacity lithium iron phosphate batteries was in July 2005.

Its safety performance and cycle life are unmatched by other materials, and these are also the most important technical indicators of power batteries.

The 1C charge-discharge cycle life is up to 2000 times.

 

Single-cell battery will not burn or explode when overcharged at 30V.

Lithium iron phosphate cathode materials make large-capacity lithium-ion batteries easier to use in series.

 

To meet the needs of frequent charging and discharging of electric vehicles.

It has the advantages of non-toxic, non-polluting, good safety performance, wide source of raw materials, low price, and long life.

It is an ideal cathode material for a new generation of lithium-ion batteries.

 

This project belongs to the development of functional energy materials in high-tech projects, and is a key support field of the national “863” plan, “973” plan and the “Eleventh Five-Year” high-tech industry development plan.

 

The positive electrode of lithium-ion battery is lithium iron phosphate material, which has great advantages in safety performance and cycle life.

These are also one of the most important technical indicators of power batteries.

 

The 1C charging and discharging cycle life can reach 2000 times, puncture does not explode, and it is not easy to burn and explode when overcharged.

Lithium iron phosphate cathode material makes large-capacity lithium-ion batteries easier to use in series.

 


6. Research applications

Lithium iron phosphate battery

Recently, there have been successive reports about the progress of new batteries that are expected to replace traditional lithium batteries. We see the hope that mobile phones and tablets have longer battery life, but unfortunately most of them are still in the laboratory research stage.

It’s hard to say that it is put into commercial use on a large scale. In August 2012, the new energy company Deboch TEC.GmbH brought a new energy technology closer to reality: iron-containing lithium batteries.

 

The lithium iron phosphate battery technical white paper published by Deboch TEC.GmbH shows that after the use of composite nanomaterials, the energy density of a single cell of 32650 size (diameter 32mm/length 65mm) can be increased to 6000mAh, which is the same as the current industry’s 32650 size single cell 5000mAh Compared with the specifications, the same volume has increased by a full 1000mAh, which is as much as 20%. One cell can charge the iPhone 4S for almost 4 times.

 

What’s more gratifying is that when used in a single low-rate charge-discharge environment, this kind of battery still maintains about 80% after being cycled for up to 3000 times, while ordinary lithium batteries are recharged for about 500 times. NS.

According to the calculation of charging and discharging once every 3 days, it can be used continuously for 24 years, which is a veritable long-life battery.

 

This new type of battery technology can be widely used in various devices such as portable mobile power supplies, small UPS, notebook batteries, car batteries, and for different use environments, Deboch TEC.GmbH also uses different cell colors according to the difference in the number of cycles of charging : Gold for military-grade products, with 3000 cycles; blue for civilian cars, 2500 cycles; green, 2000 cycles, suitable for small portable mobile devices.

 

(source: internet, reference only)