Popular Science: The difference between lithium battery soft pack and hard pack

Introduction to lithium battery

A "lithium battery" is a type of battery using a lithium metal or a lithium alloy as a negative electrode material and using a nonaqueous electrolyte solution. Lithium metal batteries were first proposed and studied by Gilbert N. Lewis in 1912. In the 1970s, MSWhitTIngham proposed and began researching lithium-ion batteries. Due to the very active chemical properties of lithium metal, the processing, storage and use of lithium metal are very demanding on the environment. Therefore, lithium batteries have not been used for a long time. With the development of science and technology, lithium batteries have become the mainstream.

Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth-generation lithium-metal battery of rechargeable batteries was born in 1996, and its safety, specific capacity, self-discharge rate and performance price ratio are better than lithium-ion batteries. Due to its own high technical requirements, only a few companies in the country are producing such lithium metal batteries.

Lithium ion battery structure

Lithium-ion batteries are an alternative to metal lithium batteries that have appeared in the past few years. The main components of the batteries are positive and negative electrodes, electrolytes, separators and outer casings.

The positive electrode--- uses a carbon electrode capable of absorbing lithium ions. When discharging, lithium turns into lithium ion and leaves the anode of the battery to reach the cathode of the lithium ion battery.

The negative electrode----material selects an intercalable lithium compound whose potential is as close as possible to the lithium potential. For example, various carbon materials include natural graphite, synthetic graphite, carbon fiber, mesophase carbon, and the like, and metal oxides.

Electrolyte---a mixed solvent system of an alkyl carbonate such as ethylene carbonate, propylene carbonate and low viscosity diethyl carbonate of LiPF6.

Diaphragm---Polyene microporous membranes such as PE, PP or their composite membranes, especially PP/PE/PP three-layer membranes have low melting point and high puncture strength, which plays a role in heat insurance.

Enclosure---With steel or aluminum material, the cover assembly has the function of explosion-proof and power-off.

How lithium-ion batteries work

The working principle of lithium-ion battery refers to its charging and discharging principle.

When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure, and it has many micropores. The lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer, and the more lithium ions are embedded, the higher the charging capacity. The chemical reaction that occurs at this time is:

By the same token, when the battery is discharged (ie, the process we use the battery), the lithium ions embedded in the carbon layer of the negative electrode come out and move back to the positive electrode. The more lithium ions return to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to the discharge capacity. The chemical reaction that occurs at the negative electrode at this time is:

It is not difficult to see that during the charging and discharging process of a lithium ion battery, lithium ions are in a state of motion from a positive electrode to a negative electrode to a positive electrode. If we compare the lithium-ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like an excellent sportsman, running back and forth at both ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a cute name rocking chair battery.

Soft pack lithium battery introduction

The soft-pack lithium battery is simply a liquid lithium-ion battery with a polymer shell. The structure is packaged in aluminum plastic film, and in the case of a safety hazard, the soft pack battery will only burst at most.

Soft pack lithium battery parameters

Nominal voltage: 3.7V

Working voltage: 2.4~4.2V

Nominal capacity: 1250mAh

Standard discharge continuous current: 0.2C

Maximum discharge continuous current: 0.5C

Working temperature: Charging: 0~45°C

Discharge: -20~60°C

Product size: MAX9.5*35*52mm

Finished product internal resistance: ≤150mΩ

Over-discharge protection voltage 2.5±0.05V

Lead type: GB1007/24#, line length 55mm protection parameters: overcharge protection voltage / 4.325±0.025V per string

Over current value: 2~4A

Soft pack battery advantages

1. Good safety performance

The soft pack battery does not explode like a steel shell aluminum shell.

2. Light weight

The weight of the soft pack battery is 40% lighter than the equivalent capacity of the steel shell lithium battery, which is 20% lighter than the aluminum shell battery.

3. Large capacity

The soft pack battery has a capacity of 10 to 15% higher than the steel shell battery of the same size, and is 5 to 10% higher than the aluminum shell battery.

4. Small internal resistance

The internal resistance of the soft pack battery is smaller than that of the lithium battery. At present, the internal resistance of the domestic soft pack battery core can be as low as 35mΩ, which greatly reduces the self-consumption of the battery.

5. Flexible design

The shape of the soft pack battery can be customized according to the customer's needs, and a new battery model can be developed.

Shortcomings of soft pack batteries

The existing soft pack battery core models are few and cannot meet the market demand;

Developing new models is costly.

The difference between lithium battery soft bag and hard bag

The difference between the soft pack and the hard pack of the lithium battery mainly refers to the material of the lithium battery case. If there is a package on the outside, it is not easy to see, and the battery body must be seen. The weight of the steel case battery will be more important than the battery of the same volume. However, the aluminum case and the flexible package are not easy to distinguish, but the flexible package battery is softer than the aluminum case battery, and the handcuff is easily deformed.

The page contains the contents of the machine translation.