Detailed explanation of lithium iron phosphate battery advantages and disadvantages

Lithium iron phosphate batteries full name is the lithium iron phosphate lithium-ion batteries, the name was too long, referred to as lithium iron phosphate batteries.Because of its performance is particularly suitable for power applications, to join in the name of "power" two words, namely lithium iron phosphate power battery.Also some people called it "lithium iron (LiFe) power battery.

The working principle of

Lithium iron phosphate batteries, refers to the use of lithium iron phosphate as the anode material of lithium ion batteries.Lithium ion battery anode materials mainly have cobalt acid lithium, lithium manganese acid lithium, nickel, ternary material, lithium iron phosphate, etc.The cobalt acid lithium is at present most of the lithium ion battery cathode material.

meaning

Metals trading market, cobalt (Co) is the most expensive, and the storage capacity is not much, nickel (Ni), manganese (Mn) cheaper, and more iron (Fe) storage.The price of the anode materials is consistent with the the prices of these metals market.Therefore, the use of LiFePO4 cathode material of lithium ion batteries should be quite cheap.Another feature of it is environmental protection free from contamination to the environment.

As the requirements of the rechargeable batteries are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, large current charge and discharge, electrochemical stability, use of safety (did not charge, discharge and short circuit caused by improper operation, such as the combustion or explosion), wide working temperature range, non-toxic or less poison, no pollution to the environment.Adopting LiFePO4 as anode of lithium iron phosphate batteries are good on these performance requirements, particularly in large discharge rate discharge (5 ~ 10 c discharge), stable discharge voltage, security, not burning, not an explosion, and life (cycles), on the environment pollution-free, it is the best, is currently the best large current output power battery.

The structure and working principle

LiFePO4 as the positive pole of the battery, connected to the battery positive electrode by aluminum foil and polymer is among the diaphragm, which separates the positive and negative, but lithium ion Li and electronic e - cannot pass, right is composed of carbon (graphite) battery cathode, the copper foil and negative connection of the battery.Between the top and bottom side is the battery electrolyte battery, the battery by the metal casing airtight packaging.

LiFePO4 battery when charging, the anode of lithium ion Li by polymer membrane to the cathode migration;In the process of discharge, the cathode of lithium ion Li through the diaphragm to the positive transfer.Lithium ion battery is due to the lithium ion migration and named after the back and forth during charging and discharging.

The main performance

LiFePO4 battery's nominal voltage is 3.2 V, termination of charging voltage is 3.6 V, termination voltage is 2.0 V.Because of the various manufacturers adopt positive and negative electrode materials and electrolyte material quality and process is different, its performance will be some difference.For example the same models (the same kind of packaging standard cell), the battery capacity has a bigger difference (10% ~ 20%).

Here to explain that different factory production of iron phosphate lithium power battery in various performance parameters will have some difference;In addition, there are some battery performance was not included in, such as battery internal resistance, self-discharge rate, temperature of the charge and discharge, etc.

Lithium iron phosphate power battery capacity has a bigger difference, can be divided into three categories: small zero a few to several mah, medium of dozens of mah, large hundreds of mah.The same parameters of different types of batteries also have some differences.

Over discharge to zero voltage test:

Using STL18650 (1100 mah) lithium iron phosphate power battery discharge to zero voltage test.Test conditions: 0.5 C charge rate will be filled with 1100 mah STL18650 batteries, and then use 1.0 C discharge rate discharge to the battery voltage is 0 C.Then to 0 v battery is divided into two groups: a group for seven days, another group of 30 days;Deposit matures with 0.5 C charge rate is full, and then use 1.0 C discharge.Finally comparing two zero voltage storage period the difference between different.

Test result, zero voltage battery for seven days without leakage, good performance, the capacity is 100%;For 30 days, no leakage, the performance good, capacity is 98%;For 30 days after the battery to do 3 times charge and discharge cycle, capacity and up to 100%.

This test shows that the lithium iron phosphate battery discharge even seen (or even to 0 v), and deposit a certain time, battery leakage, damage.This is other kinds of lithium ion battery has no features.

advantage

1, the improvement of safety performance

Lithium iron phosphate crystals in P - solid O key, difficult to decompose, even in high temperature or overcharge when also won't like cobalt acid lithium structure collapse fever or strong oxidizing substances, thus having good security.A report pointed out that the practice of acupuncture or short circuit experiment found combustion phenomenon in a small number of samples, but no one explosion occurred, and overcharge experiments using several times greatly beyond their discharge voltage of high voltage charging, found that there are explosive.Even so, the overcharge safety than common liquid electrolyte cobalt acid lithium batteries, has been greatly improved.

2, the improvement of the life

Lithium iron phosphate battery refers to the use of lithium iron phosphate as the anode material of lithium ion battery.

Long life cycle life of lead-acid battery in around 300, the highest is 500 times, and lithium iron phosphate power battery, cycle life reached more than 2000 times, the standard charging rate (5 hours) to use, can reach 2000 times.With the quality of the lead-acid battery is "new half a year, half a year, maintenance, maintenance and half year old", at most 1-1.5 years, while the lithium iron phosphate batteries used under the same conditions, the theory of life will reach 7 ~ 8 years.Comprehensive consideration, the price performance ratio in theory for lead-acid battery more than four times.Large current discharge can be as big 2 C fast charge and discharge current, under the special charger, 1.5 C can make battery charging 40 minutes, starting current can be up to 2 C, lead-acid battery is the performance.

3, high temperature performance is good

Lithium iron phosphate can reach 350 ℃ to 500 ℃ and the electric peak and cobalt acid lithium manganese acid lithium only at about 200 ℃.Wide range of operating temperature (20 c - 75 - c), have a high temperature resistant properties of lithium iron phosphate can reach 350 ℃ to 500 ℃ heating peak lithium cobalt and lithium manganese acid and acid only at about 200 ℃.

4, large capacity

Studying the rechargeable battery in often filled with not to put out under the conditions of work, capacity quickly is lower than the rated capacity values, this phenomenon is called memory effect.Memory like nickel metal hydride, nickel cadmium battery, and lithium iron phosphate batteries do not have this phenomenon, the battery no matter in what condition, can use increases with the increasing charge, do not need to first put the recharging.

5, light weight

The same specification of lithium iron phosphate battery capacity volume is two-thirds the size of lead-acid battery, weight is the 1/3 of lead-acid batteries.

6, the environmental protection

Lithium iron phosphate batteries generally do not contain any heavy metals and rare metals (nickel metal hydride battery of rare metals), non-toxic (through the SGS certification), no pollution, comply with European RoHS, for absolute green battery certificate.So the lithium battery is favored by the industry, mainly environmental considerations, so the battery and listed in the "863" during the tenth five-year national high-tech development plan, has become the national key support and encourage the development of project.With China's accession to the WTO, Chinese exports of electric bikes will increase rapidly, and into Europe and the United States of electric bicycle has asked equipped with battery from pollution.

But experts say, lead-acid battery caused by environmental pollution, mainly in non-standard production process and recycling.By the same token, the lithium battery belongs to new energy industry is good, but it can't avoid the problem of heavy metal pollution.In the metal material processing such as lead, arsenic, cadmium, mercury, chromium is likely to be released into the dust and the water.The battery itself is a kind of chemicals, so is likely to produce two kinds of pollution: one is the production engineering process of waste pollution;2 it is scrapped after the battery pollution.

Lithium iron phosphate battery also has its disadvantages: low temperature performance is poor, for example, tap density is small, the anode materials such as volume of lithium iron phosphate battery capacity than cobalt acid lithium and other lithium ion battery, so don't have an advantage in terms of micro cells.And when used for power battery, lithium iron phosphate batteries and other batteries, battery consistency issues needs to face.

disadvantages

Is a kind of material has great potential application development, in addition to focus on its merits, even more crucial is whether the material has fundamental flaws.

Domestic now generally choose the lithium iron phosphate as power type lithium ion battery cathode material, from the government, scientific research institutions, enterprises, and even markets such as securities analysts are bullish on this material, as the development direction of power type lithium ion battery.Analysis its reason, mainly has the following two points: first is influenced by American research direction, the Valence and the A123 company do early adoption of lithium iron phosphate lithium ion battery cathode material.Followed by the domestic has not been prepared for use with power type lithium ion battery has good high temperature cycle and storage performance of manganese acid lithium materials.But there are also nots allow to ignore the fundamental flaws of lithium iron phosphate, it mainly include the following:

1, in the preparation of lithium iron phosphate sintering process, the reduction of iron oxide under high temperature and reducing atmosphere is the possibility of elemental iron.Elemental iron can cause cell micro short circuit, is the most taboo in the battery material.This is Japan has not the material as the main reason of power type lithium ion battery cathode material.

2, lithium iron phosphate has some defects on the performance, such as low tap density and compaction density, leading to a lower energy density of lithium-ion batteries.Low temperature performance is poorer, even if the nano and carbon coating to solve this problem.Argonne national laboratory, Dr. DonHillebrand, director of the center for energy storage system when it comes to the lithium iron phosphate battery performance at low temperature with terrible to describe, their type of lithium iron phosphate lithium ion battery test results show that shows that the lithium iron phosphate battery at low temperature (below 0 ℃) could not make the electric car.Although there is also a manufacturer claims that the lithium iron phosphate battery capacity in low temperature retention is good, but it's a small discharge current and discharge cut-off voltage is very low.Under this condition, the equipment can't start the job.

The preparation of 3, the material cost and battery manufacturing cost is higher, battery low yield, poor consistency.Lithium iron phosphate nano and carbon coated despite the electrochemical properties of the material, but also brought other problems, such as lower energy density and the rising cost of synthesis, electrode processing performance is poor and demanding to the environment and other problems.Although the lithium iron phosphate chemical elements in the Li, Fe and P is very rich, and a low cost, but the preparation of lithium iron phosphate product cost is not low, even with previous research and development costs, the process of the material cost and high cost of batteries, will make the final unit cost of energy storage battery is higher.

4, poor product consistency.At present domestic has not been a lithium iron phosphate material factory can solve this problem.From the Angle of material preparation, the synthetic reaction of the lithium iron phosphate is a complex multiphase reaction, has a solid phosphate, iron oxide and lithium salt, plus the precursor and carbon reduction aerosols.In the process of the complex reaction, it is difficult to ensure consistency of response.

5, intellectual property rights.Is the foundation of the lithium iron phosphate all patents by the United States at the university of Texas, and carbon coated by Canadian patent application.The two basic patent is not around the past, if royalties on the cost of calculation, the product cost will be further improved.

In addition, from the perspective of the experience of development and production of lithium ion battery, Japan is the country of the first commercial lithium-ion batteries, and high-end lithium ion battery has dominated the market.Although in some basic research on the leading and the United States, but so far not a single large lithium-ion battery production enterprises.As a result, Japan choose modified lithium manganese acid as power type lithium ion battery cathode material more makes sense.Even in the United States, use and lithium manganese acid lithium iron phosphate as the manufacturer of power type lithium ion battery cathode material is also a half, the federal government is also support for the development of the two systems.In view of the problems existing in the lithium iron phosphate, difficult as power type lithium ion battery cathode material in the field of new energy vehicles for a wide range of applications.If you can solve the manganese acid lithium storage high temperature cycle and difficult problems of poor performance, with its advantage of low cost and high performance ratio in the application of power type lithium ion battery will have great potential.

The page contains the contents of the machine translation.