Classification and safe use of lithium polymer batteries

A polymer lithium battery is a polymer lithium ion battery. Lithium-ion batteries are classified into a liquid lithium ion battery (Liquified Lithium-Ion Battery, abbreviated as LIB) and a polymer lithium ion battery (Polymer Lithium-Ion Battery, abbreviated as PLB), depending on the electrolyte material used in the lithium ion battery. 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 use of polymer colloidal electrolytes.

A. classification

Solid

The solid polymer electrolyte lithium ion battery electrolyte is a mixture of a polymer and a salt, and the battery has low 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

The lithium ion battery of the polymer positive electrode material uses a conductive polymer as a positive electrode material, and its specific capacity is relatively increased. 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 (Polymer Lithium-Ion Battery) battery is characterized by being compact, thin, and lightweight. Therefore, the market share of polymer batteries will gradually increase.

B. features

Polymer lithium ion batteries have the following characteristics:

1 shaping flexibility;

2 higher mass specific energy (3 times the MH-Ni battery);

3 electrochemical stability window width, up to 5V;

4 perfect safety and reliability;

5 longer cycle life, less capacity loss;

6 the volume utilization is high;

7 a wide range of applications.

C. considerations

Pay attention to short circuit conditions

Polymer lithium-ion batteries are prone to short-circuit conditions during charging. They include: internal short circuit and external short circuit, etc.

Although most lithium-ion batteries now have anti-short-circuit protection circuits and explosion-proof lines, in many cases, this protection circuit does not necessarily work under various conditions, and the explosion-proof line can play a limited role. .

Do not overcharge the second charge

Polymer lithium-ion batteries, if the charging time is too long, the possibility of expansion will increase.

The chemical properties of lithium are very active and easy to burn. When the battery is charged and discharged, the inside of the battery continues to heat up. The gas generated during the activation process expands, the internal pressure of the battery increases, and the pressure reaches a certain level. If the outer casing is scratched, it will rupture. It can cause leakage, fire, or even explosion. Polymer lithium-ion batteries only expand.

When you are using it, be sure to pay attention to safety.

D. principles

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:

(-)C|LiPF6—EC+DEC|Li Co O2 (+)

Rd

Positive electrode reaction (oxidation reaction): LiCoO2=Li1-xCoO2+xLi++xe------------ (2.1)

Negative reaction (reduction reaction): 6C+xLi++xe-=LixC6----------- (2.2)

Total battery reaction: LiCoO2+6C=Li1-xCoO2+LixC6----------- (2.3)

The principle of 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.

E. the outlook

At present, mobile phones have the following development trends:

(1) The mobile phone itself is developing in the direction of miniaturization and thinning to facilitate the carrying of consumers;

(2) The personalization of mobile phone design, the performance concept is no longer the original square shape, irregular shape curved surface design has become the mainstream of mobile phone design aesthetics;

(3) The use of color screens and mobile phone functions continues to increase. In order to miniaturize the mobile phone, battery reduction and thinning are the most effective ways. The thickness of the battery below 4mm has become the mainstream trend of thin mobile phone configuration. In terms of cost performance, this is the specialty of the polymer. The effective space left by the mobile phone with irregular shape, curve and curved surface design becomes an irregular shape. The liquid rectangular shape does not make efficient use of space and has a low capacity, and the laminated polymer can make the most efficient use of such irregular space to enlarge the capacity. Recently, the arc-shaped battery, trapezoidal battery, and backpack battery introduced by TCL Jinneng Company can increase the capacity of the mobile phone by more than 20% compared with the liquid battery with the corresponding specifications. More and more mobile phones are functioning, resulting in more and more power consumption. The battery capacity is required to increase accordingly. Polymer batteries have significant advantages without increasing the thickness of the battery. Similarly, notebook computers, Bluetooth headsets, PHS phones, mobile DVDs and other appliances are moving in the direction of mobile and portable, all equipped with liquid crystal display, and the functions are increasing, and the LCD screen is constantly increasing. These provide some opportunities for polymer lithium-ion batteries.

Polymer lithium-ion batteries have been matured and commercialized in the world for more than two years. Although sales volume is growing rapidly, its market share is still around 10%, which is incomparable with 90% of liquid lithium battery market share people's expectations. For various reasons, the price of polymers on the market is generally higher than that of liquid lithium batteries. However, because the competition mode of mobile appliances is quietly changing, especially the design value of polymer batteries for mobile appliances (such as 4mm) Polymer batteries are being recognized by more and more designers such as mobile phones and mobile DVDs. The polymer manufacturers are still confident that the polymer era will come. [6]

F. advantages and disadvantages

Advantage

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, 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 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 sufficient safety. Therefore, the protective circuit design of the polymer battery can be omitted by omitting the PTC and the fuse, thereby saving battery cost.

Disadvantage

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 over discharge will destroy the reversibility of the internal chemical substances of the battery, thus seriously affecting the life of the battery.

G. performance study

The properties of homopolymer polyvinylidene fluoride (PVdF), vinylidene fluoride and hexafluoropropylene binary copolymer (PVdF-HFP) as polymer lithium ion battery skeleton materials were compared. The research results show that PVdF can be used as the framework material of polymer lithium ion battery to obtain better performance than PVdF-HFP copolymer by appropriate technical means.

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