Comparison of polymer lithium battery and lithium iron phosphate battery

Comparison of polymer lithium battery and lithium iron phosphate battery

Polymer lithium battery overview

A polymer lithium battery generally refers to a polymer lithium ion battery.

Lithium-ion batteries are classified into Lithified Lithium-Ion Battery (LIB) and Polymer Lithium-Ion Battery (PLB) or Plastic Lithium Ion Battery (PlasTIcLithium IonBatteries) referred to as PLB). The positive and negative materials used in the polymer lithium ion battery are the same as the liquid lithium ions. The positive electrode material is divided into lithium cobaltate, lithium manganate, ternary material and lithium iron phosphate material, and the negative electrode is graphite. The working principle of the battery is also basically Consistent. The main difference is that the electrolyte is different. The liquid lithium ion battery uses a liquid electrolyte, and the polymer lithium ion battery is replaced by a solid polymer electrolyte. The polymer can be either "dry" or "colloidal". Most of the current polymer gel electrolytes are used.

Polymer lithium battery classification:

Solid:

The solid polymer electrolyte lithium ion battery electrolyte is a mixture of a polymer and a salt. The battery has high ionic conductivity at normal temperature and can be used at normal temperature.

Gel:

The gel polymer electrolyte lithium ion battery adds an additive such as a plasticizer to the solid polymer electrolyte to increase the ionic conductivity and allow the battery to be used at normal temperature.

Polymer:

Since the solid electrolyte is used instead of the liquid electrolyte, the polymer lithium ion battery has the advantages of being thinner, arbitrarily aread, and arbitrarily shaped compared with the liquid lithium ion battery, so that the battery casing can be fabricated from the aluminum-plastic composite film, thereby It can improve the specific capacity of the whole battery; the polymer lithium ion battery can also use the polymer as the positive electrode material, and its mass specific energy will be more than 20% higher than the current liquid lithium ion battery. The polymer lithium ion (PolymerLithium-IonBattery) battery is characterized by being compact, thin, and lightweight. Therefore, the market share of polymer batteries will gradually increase.

Principle of polymer lithium battery:

Lithium-ion batteries currently have two types of liquid lithium-ion batteries (LIB) and polymer lithium-ion batteries (PLB). Among them, the liquid lithium ion battery refers to a secondary battery in which the Li+ intercalation compound is a positive electrode or a negative electrode. The positive electrode is made of lithium compound LiCoO2, LiNiO2 or LiMn2O4, and the negative electrode is made of lithium-carbon interlayer compound LixC6. The typical battery system is:

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The principle of a polymer lithium ion battery is the same as that of liquid lithium. The main difference is that the electrolyte is different from liquid lithium. The main structure of the battery includes three elements: positive electrode, negative electrode and electrolyte. The so-called polymer lithium ion battery means that at least one or more of the three main structures use a polymer material as a main battery system. In the polymer lithium ion battery system currently developed, polymer materials are mainly used for the positive electrode and the electrolyte. The positive electrode material includes a conductive high molecular polymer or an inorganic compound used in a general lithium ion battery, and the electrolyte can use a solid or colloidal polymer electrolyte or an organic electrolyte. Generally, a lithium ion technique uses a liquid or a colloidal electrolyte, so it is required the sturdy secondary package accommodates flammable active ingredients, which adds weight and limits size flexibility.

A new generation of polymer lithium-ion batteries can be thinned in shape (ATL battery can be as thin as 0.5 mm, compared to the thickness of a card), arbitrarily aread and arbitrarily shaped, greatly improving battery design The flexibility to match the product requirements to a battery of any shape and capacity provides device developers with some design flexibility and adaptability in their power solutions to maximize their product performance. At the same time, the unit energy of the polymer lithium ion battery is 20% higher than the current general lithium ion battery, and its capacity and environmental performance are better than those of the lithium ion battery.

Advantages and disadvantages of polymer lithium battery:

Advantages:

1. The operating voltage of the single cell is as high as 3.6v~3.8v, which is much higher than the 1.2V voltage of Ni-MH and Ni-Cd batteries.

2. The capacity density is large, and the capacity density is 1.5 to 2.5 times or higher of the nickel-hydrogen battery or the nickel-cadmium battery.

3. Self-discharge is small, and its capacity loss is small after being placed for a long time.

4. Long life, normal use of its cycle life can reach more than 500 times.

5. There is no memory effect. It is not necessary to empty the remaining power before charging, which is convenient to use.

6. Good safety performance

The polymer lithium battery is made of aluminum-plastic flexible packaging, which is different from the metal casing of the liquid battery. Once the safety hazard occurs, the liquid battery is easy to explode, and the polymer battery can only be air-blasted at most.

7. Small thickness, can be made thinner

Ultra-thin, the battery can be assembled into a credit card. Ordinary liquid lithium battery adopts the method of customizing the outer casing and plugging the positive and negative materials. The thickness is 3.6mm or less. There is a technical bottleneck. The polymer battery core does not have this problem. The thickness can be less than 1mm, which is in line with the current demand of mobile phones.

8. Light weight

A battery using a polymer electrolyte does not require a metal shell as a protective outer package. The weight of the polymer battery is 40% lighter than the steel shell lithium battery of the same capacity specification, which is 20% lighter than the aluminum shell battery.

9. Large capacity

The polymer battery has a capacity of 10-15% higher than that of the same size steel shell battery, which is 5-10% higher than that of the aluminum shell battery. It is the first choice for color screen mobile phones and MMS mobile phones. Nowadays, the new color screen and MMS mobile phones on the market are mostly used. Polymer batteries.

10. Small internal resistance

The internal resistance of the polymer battery core is smaller than that of the general liquid battery. At present, the internal resistance of the domestic polymer battery core can even be less than 35mΩ, which greatly reduces the self-consumption of the battery and prolongs the standby time of the mobile phone. The level of integration with the international. This polymer lithium battery that supports large discharge currents is an ideal choice for remote control models and is the most promising alternative to nickel-metal hydride batteries.

11. Shape can be customized

Manufacturers are not limited to standard shapes and can be economically made to the right size. Polymer batteries can increase or decrease the thickness of batteries according to customers' needs. Develop new battery models, which are cheap, open cycle is short, and some can even be customized according to the shape of mobile phones to make full use of battery casing space and upgrade batteries. Capacity.

12. Good discharge characteristics

The polymer battery uses a colloidal electrolyte, which has a smooth discharge characteristic and a higher discharge platform than a liquid electrolyte.

13. The protection board is simple in design

Due to the use of polymer materials, the battery core does not ignite or explode, and the battery core itself has enough safety. Therefore, the protective circuit design of the polymer battery can be omitted by omitting the PTC and the fuse, thereby saving battery cost.

Disadvantages:

1. The battery cost is high and the electrolyte system is difficult to purify.

2. It is necessary to protect the line control. Overcharge or overdischarge will destroy the reversibility of the internal chemical substances of the battery, thus seriously affecting the life of the battery.

Second, lithium iron phosphate battery overview

The lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material. The positive electrode materials of lithium ion batteries mainly include lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and the like. Among them, lithium cobaltate is the positive electrode material used in most lithium ion batteries.

The space structure of lithium iron phosphate battery:

For the positive electrode material of LiFePO4, the raw material source is wider, the cycle life is longer, the safety index is also high, and the environmental pollution is small. It has a very strong comprehensive performance in many positive electrode materials, and has been the preparation of the positive electrode of lithium ion battery. Hot material, in the development of recent years, LiFePO4 cathode material has reached a practical level, and even began formal commercial application, LiFePO4 is an olivine structure, the spatial structure is shown in Figure 1, its theoretical specific capacity is 170mAhh, when the lithium ion battery is charged, an oxidation reaction occurs, and the lithium ion FeO6 layer is released, flows into the electrolyte, and finally reaches the negative electrode. In the external circuit, the electron reaches the negative electrode at the same time, and the iron changes from the divalent iron ion to the ferric Ion., an oxidation reaction takes place. The discharge process is reversed from the charging process, and a reduction reaction occurs.

Lithium iron phosphate battery works:

The lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material. The positive electrode materials of lithium ion batteries mainly include lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and the like. Among them, lithium cobaltate is the positive electrode material used in most lithium ion batteries.

Meaning

In the metal trading market, cobalt (Co) is the most expensive, and the storage amount is small. Nickel (Ni) and manganese (Mn) are relatively cheap, while iron (Fe) is stored in a large amount. The price of the cathode material is also consistent with the price of these metals. Therefore, a lithium ion battery made of a LiFePO4 positive electrode material should be relatively inexpensive. Another feature of it is that it is environmentally friendly and non-polluting.

The requirements for rechargeable batteries are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, and safety during use (no overcharge, overdischarge, and short circuit) Such as improper operation caused by burning or explosion), wide operating temperature range, non-toxic or less toxic, no pollution to the environment. Lithium iron phosphate battery using LiFePO4 as positive electrode has good performance requirements, especially in large discharge rate discharge (5~10C discharge), stable discharge voltage, safety (no combustion, no explosion), and life (cycle number)), it is the best for the environment, it is the best high current output power battery.

Structure and working principle

LiFePO4 is used as the positive electrode of the battery. It is connected to the positive electrode of the battery by aluminum foil. The middle is a polymer separator. It separates the positive electrode from the negative electrode, but the lithium ion Li can pass and the electron e- cannot pass. The right side is composed of carbon (graphite). The negative electrode of the battery is connected by a copper foil to the negative electrode of the battery. 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 toward the negative electrode through the polymer separator; during the discharge, the lithium ion Li in the negative electrode migrates toward the positive electrode through the separator. Lithium-ion batteries are named after the lithium ions migrate back and forth during charging and discharging.

LiFePO4 internal structure

Main performance

The nominal voltage of the LiFePO4 battery is 3.2V, the termination charging voltage is 3.6V, and the termination discharge voltage is 2.0V. Due to the quality and process of the positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the same model (standard battery of the same package) has a large difference in battery capacity (10% to 20%).

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

Lithium iron phosphate power batteries have large differences in capacity and can be divided into three categories: small fractions to a few milliamperes, medium tens of milliampere-hours, and large-scale hundreds of milliampere-hours. There are some differences in the same parameters for different types of batteries.

Over discharge to zero voltage test:

The STL18650 (1100mAh) lithium iron phosphate power battery was used for over-discharge to zero voltage test. Test conditions: A 1100 mAh STL 18650 battery was charged at a charging rate of 0.5 C, and then discharged at a discharge rate of 1.0 C until the battery voltage was 0 C. The batteries placed in 0V 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 filled with a charging rate of 0.5 C, and then discharged with 1.0 C. Finally, compare the differences between the two zero voltage storage periods.

The result of the test is that the battery has no leakage after 7 days of zero voltage storage, and the performance is good, the capacity is 100%; after 30 days of storage, there is no leakage, the performance is good, the capacity is 98%; after 30 days of storage, the battery is further charged and discharged for 3 times. The capacity is restored to 100%.

This test shows that even if the lithium iron phosphate battery is over-discharged (even to 0V) and stored for a certain period, the battery will not leak or be damaged. This is a characteristic that other types of lithium-ion batteries do not have.

Third, polymer lithium battery and lithium iron phosphate battery

Lithium polymer batteries (Li-polymer) are produced by replacing a conventional liquid organic electrolyte with a polymer electrolyte based on a lithium ion battery. The polymer electrolyte can be used as a medium for conducting ions, and can also be used as a separator, and the reactivity with lithium metal is extremely low, thereby effectively avoiding the phenomenon that the lithium ion battery is easily burned and easily leaked. And since the lithium ion polymer battery adsorbs the liquid organic electrolyte on a polymer matrix, it is called a colloidal electrolyte, and the electrolyte is neither a free electrolyte nor a solid electrolyte, so that the lithium polymer battery not only has The excellent performance of the liquid lithium ion battery can also be made into any shape and size, and the ultra-thin product makes it suitable for a wide range of applications and good development prospects. In addition, the safety is better than that of a lithium-ion battery. If it is heated during use, it will only swell or burn without exploding.

The lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material. The long-life lead-acid battery has a cycle life of about 300 times, and the highest is 500 times of lithium iron phosphate battery, while the lithium iron phosphate power battery has a cycle life of more than 2,000 times. The standard charge (5-hour rate) can be used up to 2000 times. The same quality lead-acid battery is "new half year, old half year, maintenance and maintenance for half a year", up to 1~1.5 years, and lithium iron phosphate battery will be used under the same conditions, it will reach 7~8 years. Comprehensive consideration, the performance price ratio will be more than 4 times that of lead-acid batteries.

In addition, polymer lithium battery (3.7v) is light in weight and higher in voltage than lithium iron phosphate (3.2v). The temperature resistance coefficient is lower than lithium iron phosphate.

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