1.What is a cylindrical lithium battery?

　　（1）Definition of cylindrical battery

　　Cylindrical lithium batteries are divided into different systems of lithium iron phosphate,lithium cobaltate,lithium manganate,cobalt-manganese mixture,and ternary materials.The shell is divided into steel shell and polymer.Batteries with different material systems have different advantages.At present,steel-shell cylindrical lithium iron phosphate batteries are mainly used as cylinders.This kind of battery has high capacity,high output voltage,good charge-discharge cycle performance,stable output voltage,high-current discharge,stable electrochemical performance,and easy to use.Safe,wide operating temperature range,and environmentally friendly,it is widely used in solar lamps,lawn lamps,backup energy,power tools,and toy models.

　　（2）Cylindrical battery structure

　　The structure of a typical cylindrical battery includes:casing,cap,positive electrode,negative electrode,separator,electrolyte,PTC element,gasket,safety valve,etc.Generally,the battery shell is the negative pole of the battery,the cap is the positive pole of the battery,and the battery shell is made of nickel-plated steel plate.

（3）Advantages of cylindrical lithium batteries

　　Compared with soft pack and square lithium batteries,cylindrical lithium batteries have the longest development time,a higher degree of standardization,more mature technology,high yield rate and low cost.

　　·Mature production process,low PACK cost,high yield rate of battery products,good heat dissipation performance

　　·Cylindrical batteries have formed a series of internationally unified standard specifications and models,with mature technology and suitable for mass continuous production.

　　·The specific surface area of the cylinder is large,and the heat dissipation effect is good.

　　·Cylindrical batteries are generally sealed batteries,and there is no maintenance problem during use.

　　·The battery casing has high pressure resistance,and there will be no phenomena such as square and soft-packed batteries swelling during use.

　　（4）Cylindrical battery cathode material

　　At present,the mainstream commercial cylindrical battery cathode materials mainly include lithium cobalt oxide(LiCoO2),lithium manganese oxide(LiMn2O4),ternary element(NMC),lithium iron phosphate(LiFePO4),etc.Batteries with different material systems have different Features,compared as follows:

　　（5）Cylindrical battery anode material

　　Cylindrical battery negative electrode materials are roughly divided into six types:carbon negative electrode materials,alloy negative electrode materials,tin-based negative electrode materials,lithium-containing transition metal nitride negative electrode materials,nanoscale materials,and nanoscale negative electrode materials.

　　·Carbon nanoscale material anode materials:the anode materials that have been actually used in lithium-ion batteries are basically carbon materials,such as artificial graphite,natural graphite,mesocarbon microspheres,petroleum coke,carbon fiber,pyrolytic resin carbon,etc..

　　·Alloy anode materials:including tin-based alloys,silicon-based alloys,germanium-based alloys,aluminum-based alloys,antimony-based alloys,magnesium-based alloys and other alloys,and there are currently no commercial products.

　　·Tin-based negative electrode materials:tin-based negative electrode materials can be divided into tin oxides and tin-based composite oxides.Oxides refer to the oxides of metal tin in various valence states.There are currently no commercial products.

　　·Lithium-containing transition metal nitride anode materials,there are no commercial products.

　　·Nanoscale materials:carbon nanotubes,nanoalloy materials.

　　·Nano anode materials:nano oxide materials

2. Cylindrical lithium battery cell

　　（1）Types of Cylindrical Li-ion Cells

　　Cylindrical lithium-ion cells are usually represented by five digits.Counting from the left,the first and second digits refer to the diameter of the battery,the third and fourth digits refer to the hidewh of the battery,and the fifth digit refers to the circle.There are many types of cylindrical lithium batteries,the more common ones are 10400,14500,16340,18650,21700,26650,32650 and so on.

　　①10440 battery

　　The 10440 battery is a lithium battery with a diameter of 10mm and a hidewh of 44mm.It is the same size as what we often call"AAA battery".This battery capacity is generally small,only a few hundred mAh,and is mainly used in mini electronic products.Such as flashlights,mini stereos,megaphones,etc.

　　②14500 battery

　　The 14500 battery is a lithium battery with a diameter of 14mm and a hidewh of 50mm.This battery is generally 3.7V or 3.2V.The nominal capacity is relatively small,which is a little larger than the 10440 battery.It is generally 1600mAh.Mainly consumer electronics,such as wireless audio,electric toys,digital cameras,etc.

　　③16340 battery

　　The 16340 battery is a lithium battery with a diameter of 16mm and a hidewh of 34mm.This kind of battery is a little shorter in hidewh and the capacity is not very small,so it is used in glare flashlights,LED flashlights,headlights,laser lights,lighting fixtures,etc.appear often.

　　④18650 battery

　　The 18650 battery is a lithium battery with a diameter of 18mm and a hidewh of 65mm.Its biggest feature is that it has a very high energy density,almost reaching 170 Wh/kg.Therefore,this battery is a cost-effective battery.We usually Most of the batteries I see are this kind of battery,because it is a relatively mature lithium battery,and the quality of the system is stable in all aspects.It is widely used in occasions with a battery capacity of about 10 kWh,such as mobile phones,laptops and other small electrical appliances..

　　⑤21700 battery

　　The 21700 battery is a lithium battery with a diameter of 21mm and a hidewh of 70mm.Because of its larger volume and greater space utilization,the energy density of the battery cell and the system can be improved.Its volumetric energy density is much higher than that of 18650 Type batteries are widely used in digital,electric vehicles,balance vehicles,solar energy lithium battery street lights,LED lights,power tools,etc.

　　⑥26650 battery

　　The 26650 battery is a lithium battery with a diameter of 26mm and a hidewh of 65mm,with a nominal voltage of 3.2V and a nominal capacity of 3200mAh.This kind of battery has the characteristics of excellent capacity and high consistency,and has gradually become the trend to replace the 18650 battery.In terms of power batteries,many products will gradually favor this.

　　⑦32650 battery

　　The 32650 battery is a lithium battery with a diameter of 32mm and a hidewh of 65mm.This battery has a strong continuous discharge capacity,so it is more suitable for electric toys,backup power,ups batteries,wind power generation systems,and wind-solar hybrid power generation systems.

　　（2）Development of Cylindrical Lithium Battery Market

　　The technical progress of cylindrical lithium-ion batteries mainly comes from the innovative research and application progress of key battery materials.Through the development of new materials,the performance of batteries can be further improved,quality can be improved,costs can be reduced,and safety has been improved.In order to meet the requirements of downstream applications for battery specific energy improvement,on the one hand,materials with high specific capacity can be used,and on the other hand,high-voltage materials can be used by increasing the charging voltage.

　　Cylindrical lithium-ion batteries have developed from 14500 to Tesla 21700 batteries.In the near and mid-term development,while optimizing the existing lithium-ion power battery technology to meet the needs of large-scale development of new energy vehicles,to develop new lithium-ion power batteries Focus on improving key technologies such as safety,consistency and lifespan,and simultaneously carry out forward-looking research and development of new system power batteries.

　　For the medium and long-term development of cylindrical lithium-ion batteries,while continuously optimizing and upgrading new lithium-ion power batteries,focus on the research and development of new system power batteries,which will significantly increase specific energy,greatly reduce costs,and realize the practicality and scale of new system power batteries application.

　　（3）Comparison of cylindrical lithium battery and square lithium battery

　　1.Battery shape:the square size can be designed arbitrarily,but the cylindrical battery cannot be compared.

　　2.Rate characteristics:Due to the technical limitations of welding multi-tabs for cylindrical batteries,the rate characteristics are slightly worse than those for square multi-tab batteries.

　　3.Discharge platform:For lithium batteries using the same positive and negative electrode materials and electrolyte,theoretically speaking,the discharge platform should be the same,but the internal discharge platform of the square lithium battery is slightly higher.

　　4.Product quality:The manufacturing process of cylindrical batteries is relatively mature,the probability of secondary slitting defects on the pole piece is low,and the maturity and automation of the winding process are relatively high.The lamination process is currently still using a semi-manual method.Battery quality is adversely affected.

　　5.Tab welding:Cylindrical battery tabs are easier to weld than square lithium batteries;square lithium batteries are prone to false welding and affect battery quality.

　　6.PACK into groups:Cylindrical batteries are easier to use,so the PACK technology is simple and the heat dissipation effect is good;the heat dissipation problem must be solved when packing square lithium batteries.

　　7.Structural features:The chemical activity at the corners of the square lithium battery is poor,the energy density of the battery is easy to decay after long-term use,and the battery life is short.

　　（4）Comparison of cylindrical lithium battery and pouch lithium battery

　　1.The safety performance of the soft-pack battery is better.The structure of the soft-pack battery is packaged with aluminum-plastic film.When a safety problem occurs,the soft-pack battery will generally explode with gas,instead of exploding like a steel or aluminum shell cell.;Superior to cylindrical lithium batteries in terms of safety performance.

　　2.The weight of the pouch battery is relatively light.The weight of the pouch battery is 40%lighter than the steel-cased lithium battery of the same capacity,and 20%lighter than the cylindrical aluminum-cased lithium battery;the internal resistance is small,and the internal resistance of the pouch battery is smaller than that of the lithium battery.,which can greatly reduce the self-consumption of the battery;

　　3.The cycle performance of the pouch battery is good,the cycle life of the pouch battery is longer,and the attenuation of 100 cycles is 4%to 7%less than that of a cylindrical aluminum case battery;

　　4.The design of the pouch battery is relatively flexible,and the shape can be changed to any shape,and can be thinner.It can be customized according to the needs of customers and develop new cell models.Cylindrical lithium batteries do not have this condition.

　　5.Compared with the cylindrical lithium battery,the disadvantages of the pouch battery are poor consistency,high cost,and easy leakage.The high cost can be solved by large-scale production,and the leakage can be solved by improving the quality of aluminum-plastic film.