The differences of polymer lithium battery and lithium iron phosphate battery

A, An overview of the Polymer lithium battery

Polymer lithium battery generally refers to Polymer lithium ion batteries。

According to the electrolyte materials that are used in lithium ion batteries, lithium ion batteries are divided into liquid lithium ion battery (Liquified Lithium – Ion Battery, LIB for short) and polymer lithium ion battery (Polymer Lithium – Ion Battery, for PLB) or plastic lithium ion battery (PlasTIcLithiumIonBatteries, for PLB).Is used in the polymer lithium ion battery cathode materials and liquid lithium ion is the same, the anode materials are divided into cobalt acid lithium, manganese acid lithium, ternary material and lithium iron phosphate material, negative extremely graphite, working principle of the battery is almost the same. Their main difference is that the different electrolytes, liquid lithium ion battery using liquid electrolyte, polymer lithium ion battery with solid polymer electrolyte as a substitute for, the polymer can be "dry", also can be "colloidal", at present most of the polymer gel electrolyte.

 Polymer lithium battery categories:

Solid:

Solid polymer electrolyte of lithium ion battery electrolyte for the polymer with a mixture of salt, the battery the ionic conductivity at room temperature is high, can be used at room temperature.

Gel:

Gel polymer electrolyte for lithium ion batteries is in solid polymer electrolyte adding plasticizer and other additives, thus improve the ionic conductivity, the battery can be used at room temperature.

Polymer:

By using solid electrolyte instead of liquid electrolyte, compared with the liquid lithium ion batteries, polymer lithium ion battery has can thin shape is changed, any area with arbitrary shape, etc, so can use lu: su composite membrane manufacturing battery shell, which can improve the specific capacity of the battery; Polymer lithium ion battery can also be used polymer as the anode material, its quality than the energy will be more than 20% higher than that of the liquid lithium ion battery. Polymer lithium ion (PolymerLithium - IonBattery) battery has the characteristics of miniaturization, thin, lightweight. Therefore, polymer battery in the market will gradually increase.

Polymer lithium battery principle:

Lithium ion battery has liquid lithium ion battery (LIB) and polymer lithium ion battery (PLB).Among them, the liquid lithium ion battery is refers to the Li + embedded compounds for positive and negative secondary battery. The anode with lithium compound LiCoO2, LiNiO2 or LiMn2O4, carbon anode with lithium - LixC6 interlayer compounds, the typical battery system for:

Principle and liquid lithium polymer lithium ion battery is the same, and the main difference is that the electrolyte is different from liquid lithium. The main structure consists of the positive and negative battery electrolyte three elements. So-called polymer lithium ion battery is said in the three main structure at least one or more than one use of polymer materials as the main battery system. But in the current development of polymer lithium ion battery systems, polymer materials are mainly used in the anode and electrolyte. Anode materials include conductive polymer or lithium ion batteries used in inorganic compounds commonly, use solid electrolyte or colloidal polymer electrolytes, or organic electrolyte, lithium ion technology commonly used liquid or gel electrolyte, so need to accommodate combustible solid secondary packaging, the active ingredient, this increases the weight, in addition also limits the size of flexibility.

 A new generation of polymer lithium ion battery in shape can be thin shape is changed (ATL battery can reach 0.5 mm, the thinnest phase in the thickness of the card) and arbitrary shape, arbitrary area, greatly improving the battery design flexibility, which can meet the needs of the product, made into any shape and the capacity of the battery, for the equipment on the power supply solution developers provide some design flexibility and adaptability, in order to maximize the optimization of its product performance. At the same time, polymer lithium ion battery energy per unit of a 20% increase over the current general lithium ion battery, its capacity, and environmental performance is lithium ion battery, there are some improvement.

Lithium polymer batteries advantages and disadvantages:

Advantages:

1. Single cells working voltage of 3.6 v to 3.8 v is much higher than nickel-metal hydride and nickel cadmium battery voltage of 1.2 v.

2. Large capacity density, the volume density is 1.5 ~ 2.5 of nimh battery or nickel cadmium battery times, or even higher.

3. Small self-discharge, placed in a long time after its capacity loss is very small.

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

5. No memory effect, not empty battery before charging, easy to use.

6. Good safety performance

Lithium-ion polymer battery with aluminum composite flexible packaging in the structure, different from liquid metal case of batteries, in the event of a safety hazard, liquid batteries easy explosion, gas drum and polymer batteries will only at most.

7. Thickness is small, can do more thin

Ultra-thin, batteries could assemble into a credit card. Ordinary liquid lithium electricity use custom shell, after the plug is cathode materials, the method of thickness of 3.6 mm the following technical bottlenecks, polymer batteries, there is no this problem, the thickness can be below 1 mm, can meet the demand of current mobile direction.

8. Light weight

Batteries with polymer electrolytes do not require a metal casing to protect them. Specifications of steel shell polymer battery weight is equal capacity lithium electric light 40%, a 20% aluminum battery light.

9. Large capacity

Polymer battery is the same size of the steel shell battery capacity, 10 to 15% more than high aluminum battery 5 ~ 10%, be the first choice of the color screen mobile phones and MMS, now on the market a new color and MMS phones are mostly used polymer batteries.

10. Small resistance

The internal resistance of the polymer batteries is less than liquid batteries, the current domestic internal resistance of the polymer batteries can even do below 35 m Ω, greatly reduced the battery power consumption, extend the standby time of mobile phone, can reach with international level. The support of large discharge current polymer li-ion battery, the ideal choice of remote control model to become the most promising alternative products of nimh batteries.

11. The shape can be customized

Manufacturers need not limited to the standard shape, able to make the appropriate economic size. Polymer battery can increase or decrease the thickness of the batteries according to the customer's demand, the development of new batteries models, price cheap, open mold cycle is short, some even can be tailored according to the mobile phone shape, to make full use of the battery shell space, improve battery capacity.

12. The discharge characteristics

Polymer battery using gel electrolyte, compared to liquid electrolyte, colloid electrolyte with smooth discharge characteristics and higher discharge platform.

13. Simple protection board design

Because of using polymer materials, batteries, no fire, no explosion, batteries itself has enough safety, therefore, polymer battery protection circuit design can consider omitting PTC and fuse, thereby saving the cost of battery.

Disadvantages:

1. The cost is high, the battery electrolyte system purification difficulties.

2. The need to protect line control, overcharge or discharge will make chemical battery internal reversible destroyed, thus seriously affect the battery life.

Second, an overview of the Lithium iron phosphate batteries

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.

lithium iron phosphate battery space structure:

For LiFePO4 cathode material, and its relatively wide raw material sources, long cycling life, safety index is high, less pollution to the environment, in numerous positive electrode material reflects the very strong comprehensive performance, has always been the hot spot of the preparation of lithium ion battery anode material, in recent years, under the development of type LiFePO4 cathode material has reached a practical level, and even began to formal commercial application of LiFePO4 is olivine structure, spatial structure as shown in figure 1, the theoretical specific capacity is 170 mahh, when lithium ion battery recharged, oxidation reaction happens, lithium ion released between FeO6 level, flow into the electrolyte, finally arrived at the cathode, the external circuit, electronic at the same time arrived at the cathode, iron can be from ferrous iron ion to ferric iron ions, oxidation reaction. Is contrary to the charging process, the discharge process is the reduction reaction.

Lithium iron phosphate batteries work principle:

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 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.

When the LiFePO4 battery is charged, lithium Li in the positive electrode migrates to the negative electrode through the polymer membrane. During the discharge process, lithium Li in the negative electrode migrates to the positive electrode through the membrane. Lithium ion battery is due to the lithium ion migration and named after the back and forth during charging and discharging.

LiFePO4 internal structure

The main performance

LiFePO4 battery's nominal voltage is 3.2 V, termination of charging voltage is 3.6 V, and 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 Lithium iron phosphate power battery in various performance parameters will have some differences; 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 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.

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