18650 Battery Voltage is a vital parameter of 18650 Lithium Battery. To master basic knowledge of 18650 battery voltage plays an important role of scientifically charging& discharging and protecting 18650 battery. This article tries to establish 18650 battery voltage system through explaining following parameters:

1. work voltage, also called rated voltage of 18650 battery. This voltage is 3.7V, which equals voltage of Ni-Cd or Ni-MH battery in three-series configuration. Some domestic lithium battery manufacturers might design 3.6V work voltage.

2. Limit charge voltage: maximum limit to 18650 battery voltage, which is 4.2V. 18650 battery charge is a process with voltage rising from 3.7V to 4.2V. After completion of this process, continuous discharge could cause battery overcharge.

3. Discharge cutoff voltage: that is, the minimum work voltage under which continuous discharge is unsuitable. This cutoff voltage is 2.75V. if battery discharge below cutoff voltage, over discharge occurs, which could destroy 18650 battery electrode structure, cause irreversible reaction of li ions and affect 18650 battery lifetime.

Due to severe damage of overcharge and over discharge to 18650 battery, electric circuit protection is equipped on 18650 battery to automatically stop charge& discharge when upper and lower voltage limits reach.

Battery packs could be assembled with 18650 battery in series, parallel and series& parallel ways.

1. 18650 Battery Pack in parallel form: capacity equals sum of battery cell capacity; voltage is same with rated voltage of single voltage. For instance, for 18650 battery pack assembled with two 2000mAh cells in parallel, voltage is 3.7V and capacity 4400mAh.

2. 18650 battery pack in series combination: capacity remains unchanged; voltage is sum of 18650 battery cell voltage. Take 18650 battery pack in three-series form for example, voltage is 11.1V whereas capacity remains 2200mAh.

3. 18650 battery pack in series& parallel way: for example, for 18650 lithium battery Pack in three-series and two-parallel combination, voltage is 11.1V and capacity is 4400mAh.

The above 11.1V is also work voltage of 18650 after series& parallel combination. Besides, charge limit voltage and discharge cutoff voltage varies as per series number. For instance, charge limit voltage of three-series& two-parallel battery pack is 12.6V whereas cutoff voltage is 8.25V.

Therefore, different battery combination ways have generated diverse 18650 capacity. Owing to different capacity and voltage, 18650 batteries are used in more fields.

Since its birth, 18650 battery application has been rapidly expanded with technological progress and market development. Japanese companies have made remarkable contribution to expand its applications. 

During 1990s, Sony was the first to declare the birth of lithium-ion battery. Since then, 18650 battery, as the earliest lithium-ion battery, had fast replaced Ni-MH battery. Thus last century, 18650 battery was completely used on portable electronic products.

Since 21st century, Lithium Battery had taken a predominant position in the portable electronic product market. Between 2004 and 2007, Sony, Panasonic, Samsung, etc focused on increasing capacity of 18650 battery from the previous 600mAh to 2900mAh. In this period, 18650 battery was mainly used on laptops.

After 2007, Japan’s Sanyo Electric used 18650 battery on emergency portable power. Afterwards, Battery Packs made up of two or more 18650 batteries was launched, bringing forth storage 18650 battery for solar power and wind power, and power supply 18650 battery for electric motorcycles and light power cars.

Due to domestic frequent contingencies, Sanyo Electric launched emergency power used for electricity cutoff caused by natural disasters. For example, battery system made up of 321 18650 batteries can continuously work two and half hours. Reconstruction after Japan’s earthquake has fully reflected use of 18650 battery.

Seeing Sanyo’s outstanding achievement on 18650 battery, Panasonic and Sony also broadened 18650 battery packs on previous laptop to household Storage Battery and EV products. In the same period, Sony developed LiFePo4 18650 battery. Panasonic, Sony and Sanyo have turned to development of high-capacity 18650 battery for electric vehicles.

Currently, 18650 battery has widely used on EV as well as cell phones, laptops, power tools, street lights. At present,Japan companies are still developing 18650 battery with capacity over 3000mAh to further expanded its use, however, it is commonly believed that 18650 battery’s R&D should be oriented on reducing its current battery cost.

Discharge cutoff voltage is a vital parameter concerning Lithium Ion Battery lifetime. Therefore, this concept meaning should be made clear. 

Lithium ion battery cutoff voltage means that it is not suitable to discharge any longer if lithium ion battery Voltage reaches a certain value otherwise, partial capacity of lithium ion battery will be irreversible or even battery will be seriously damaged. Generally rated voltage of current single lithium ion battery is 3.7V and cutoff voltage 2.75V. Yet considering following two cases, manufacturers might raise cutoff voltage to 3.0V: one case is to use battery more safely; the other is relevant to specific electric devices and operating environment. Of course, on the contrary, producers may reduce cutoff voltage to 2.5V or 2.4V. There is no cutoff voltage less than 2.4V.  

In case discharge operating temperature scope is -20~60℃, lithium batteries with 2.75V cutoff voltage is able to continue discharging, however discharge with voltage lower than 2.5V is not allowed because discharge loss between 2.75V to 2.5V might be partial but discharge lower than 2.5V will lead to serious damage to battery. 

Lithium ion Battery Pack, often called multi-cell lithium batteries, also has cutoff voltage, which should not be less than 2.75*n (n is serial battery number). Take 6-cell lithium Battery Pack used on laptops for example, discharge cutoff voltage of this lithium battery with 3S2P combination is 2.75V*3=8.25V and 2.5V*3=7.5V is not allowed in practical use.  Actually, due to high lithium-ion battery price, both single lithium battery or multi-cell lithium battery are equipped with PCM or protection IC so that batteries will send a signal to electric devices in case of reaching cutoff voltage. 

Same with all rechargeable batteries, charge time for 18650 battery equals the ratio of rated capacity to charge current. However, because of internal resistance of Lithium Battery during charge, charge time of 18650 battery should consider resistance overcome factor.

As per the resistance extent, a factor has been designed as comparison value of rechargeable battery charge time. Through long-term experiment, this factor has briefly turned into a ratio of charge current to rated capacity. Thus the above 18650 battery has become: 18650 battery charge time=rated capacity/charge current*factor.

According to national standard, battery better be charged under a current not higher than 0.2C. Based on this standard, the above factor is set 1.2. In fact, due to high capacity of 18650 Lithium Battery and different features of lithium battery charger from different manufacturers, usually this factor is set 1.5 during battery charge time calculation. Basically battery chargers are designed under this theory. For example, usually 18650 battery capacity is 1800-2600mAh. On the basis of the above formula, charger choice and 18650 battery charge time (under 0.2C discharge) should be so follow:

For 1800mAh battery, approximate 7.5-hour charge time with 350mA charger (1800÷350×1.5).

For 2200mAh battery, approximate 8.25-hour charge time with 400mA charger (8.5 hrs if 350mA charger used).

For 2600mAh battery, around 7.8-hour charge time with 500mA charger (2600÷500×1.5).

Considering different charger design, there are three alternative factors: 1.2, 1.3 and 1.5. The small the factor, the shorter the charge time will be.

Practically, 18650 battery charge time is set with PCM and protection IC during design. All that customers have to do is to use under the user instruction. Besides, it would be the best to stop charging after the color change of charger indicator because overcharge arising from too long charge time will damage charger and 18650 battery.

What is the process of Lithium-ion Battery Customization Process?

What parameters should customer provide for lithium ion battery customization?

1.      Battery shape and size

2.      Battery operating voltage and cut-off voltage

3.      Battery capacity

4.      Working current ,i.e. continuous and peak discharge&charge current

5.      Temperature type, i.e. working environment of battery

6.      Choice of PCM/BMS, ordinary or intelligent with communication

7.      Input and output ports(connectors)

8.      Wire type and length

We will consider material sources, battery performance, battery process, economic indicators, environmental issues before providing customer best solutions.

What service we can provide?

Battery customization:

One-to-one customization

Customize 3.7V~60V Lithium ion battery pack

Customize 10W~2000W special power supply

Customize 20W~20000W intelligent charger

Manufacturing:

Battery daily output: 350,000pcs

Multi-model, multi-batch and quick response

High quality customized battery pack fully meet personalized and diversified needs of users

Quality System:

Company ISO9001,ISO14001 approved

Battery in line with CE,CB,UL,UN38.3,KC,REACH,ROHS and other global certification

Product traceability system provides accurate data information for after-sales service.100% full inspection shipment

Logistic transportation:

Good cooperation with professional battery forwarder

Provide a variety of air shipment, ocean shipment and door to door shipment.

After-sales service:

24H response-72H proposing solutions-lifelong maintenance

Provide battery testing, battery installation, battery troubleshooting and other technical support.

Notice about lithium ion battery customization

1.      Lithium battery customization is different from COTS(Commercial off-the-shelf) products. It has independent research and development&design for different products, so in the customization process, mold cost, development cost and product proofing cost required.

2.      Research and development time is directly related to the new product launch. General R&D time for lithium-ion battery pack customization is about 15~30days.

Energy density refers to the amount of energy stored in a certain unit of space or mass of matter. The energy density of a battery is the average unit volume or mass of electrical energy released by the battery. The energy density of batteries is generally divided into two dimensions: weight energy density and volume energy density

What is energy density?

Energy density refers to the amount of energy stored in a certain unit of space or mass of matter. The energy density of a battery is the average unit volume or mass of electrical energy released by the battery. The energy density of batteries is generally divided into two dimensions: weight energy density and volume energy density.

Battery weight energy density=battery capacity × Discharge platform/weight, basic unit is Wh/kg (watt hours/kg)

Battery volume energy density=battery capacity × Discharge platform/volume, basic unit is Wh/L (watt hours/liter)

The higher the energy density of a battery, the more electricity stored per unit volume or weight.

How to improve energy density?

The adoption of new material systems, the precise adjustment of lithium battery structures, and the improvement of manufacturing capabilities are the three stages for R&D engineers to perform well. Below, we will explain from both individual and system dimensions.

——Single energy density mainly relies on breakthroughs in chemical systems

1. Increase battery size

Battery manufacturers can achieve the effect of battery capacity expansion by increasing the original battery size. Our most familiar example is that Tesla, a well-known electric vehicle company that was the first to use Panasonic 18650 batteries, will replace them with a new 21700 battery.

However, the phenomenon of battery cells becoming overweight or growing is only a symptom, not a cure. The ultimate solution is to find key technologies to improve energy density from the positive and negative electrode materials and electrolyte components that make up the battery cell.

2. Chemical system transformation

As mentioned earlier, the energy density of a battery is controlled by its positive and negative electrodes. Due to the fact that the energy density of negative electrode materials is much higher than that of positive electrodes, increasing energy density requires continuous upgrading of positive electrode materials.

High nickel positive electrode

Ternary materials generally refer to the nickel cobalt manganese lithium oxide family, and we can change the performance of batteries by changing the proportion of nickel, cobalt, and manganese.

In the figure, the silicon carbon negative electrode

The specific capacity of silicon based negative electrode materials can reach 4200mAh/g, which is much higher than the theoretical specific capacity of 372mAh/g of graphite negative electrode, making them a powerful substitute for graphite negative electrode.

At present, using silicon carbon composite materials to enhance the energy density of batteries has become one of the recognized development directions for lithium-ion battery negative electrode materials in the industry. Tesla's Model 3 uses silicon carbon negative electrodes.

In the future, if we want to go further and break through the single cell 350Wh/kg barrier, industry peers may need to focus on lithium metal negative electrode battery systems, but this also means changes and improvements in the entire battery manufacturing process. From several typical ternary materials, it can be seen that the proportion of nickel is increasing, while the proportion of cobalt is decreasing. The higher the nickel content, the higher the specific capacity of the battery cell. In addition, due to the scarcity of cobalt resources, increasing the proportion of nickel will reduce the use of cobalt.

3. System energy density: improving the grouping efficiency of battery packs

The grouping test of battery packs is the ability of battery "Siege Lions" to deploy individual cells and modules, which requires safety as a prerequisite and maximizes the use of every inch of space.

There are several ways to slim down battery packs.

3.1 Optimize layout structure

From the perspective of external dimensions, the internal layout of the system can be optimized to make the internal components of the battery pack more compact and efficient.

topological optimization

We achieve weight reduction design through simulation calculations while ensuring rigidity, strength, and structural reliability. Through this technology, topology optimization and morphology optimization can be achieved, ultimately helping to achieve lightweight of the battery box.

3.2 Material selection

We can choose low-density materials, such as the battery pack cover, which has gradually shifted from a traditional sheet metal cover to a composite material cover, which can reduce weight by about 35%. For the lower box of the battery pack, it has gradually shifted from a traditional sheet metal solution to an aluminum profile solution, reducing weight by about 40% and achieving significant lightweight effects.

3.3 Integrated vehicle design

The integrated design of the entire vehicle and the structural design of the entire vehicle should be considered comprehensively, and structural components should be shared and shared as much as possible, such as anti-collision design, to achieve ultimate lightweight

Batteries are a comprehensive product, and if you want to improve one aspect of performance, you may sacrifice other aspects of performance. This is the understanding foundation of battery design and development. Power batteries are specialized for vehicles, so energy density is not the only measure of battery quality.

Lithium Polymer Battery is one type of Lithium ion Battery. Compare to other lithium ion batteries, it is advantageous on high energy density, small size, thin, and high safety, cost efficient etc. It is a new type battery.

Advantage,

Ultra-thin: could be assembled in credit card.

Flexible sharp: manufacturer doesn’t need to limit to standard sharp, could make different size to fit.

Lightweight: polymer Lithium Battery doesn’t need metal case for out package.

Improve safety factor, more stable in over charge, leakage ratio low down.

Disadvantage,

Compared with primary battery, production cost for lithium polymer battery is higher. It has no standard sharp. Most of them are applicable to high capacity consume market.

All rechargeable lithium batteries need to be protected. It requires protection from over-charge, over-discharge, over-current, short circuit, over-temperature, ect.

Main function of PCM:

a. Over charge protection, stop charge once reach to certain voltage, in another word, MOS that controls overcharge be cut off, stop charge.

b. Over discharge protection, stop load discharge when voltage drop to certain voltage, MOS that controls over discharge be cut off, stop discharge, it’s opposite with over charge monitor.

c. Over current protection, stop load discharge when over current too large, aim to protect battery and MOS, make sure the safety of battery when working; and PCM will auto recover.

d. Short circuit. Principle as below, protect IC, core of protect chip, judge from sample Battery Voltage, send control message to MOS, manage chip; MOS, switch of PCM circuit.

Main PCM supplier:

Demand of global market about 100 million per month

a. A grade market, 40 million per month, main protect IC manufacturer SEIKO, RICOH, MITSUMI; MOSFET manufacturer, SANYO, AO.

b. B grade market, 40 million per month, main protect IC manufacturer FORTUNE, NEOTEC, VIMICTO; MOSFET manufacturer, SAMHOP, CETSEMI, SOUTHSEASEMI, MAXTEK, ANPEC.

c. C grade market, 20 million per month, main protect IC manufacturer SILAN, SINGEN, JWK; MOSFET manufacturer ZHUHAI NANKER, SINGEN, JWK.

PCM Circuit for 3.7V battery pack:

PCM Circuit for 7.4V battery pack:

PCM Circuit for 11.1V battery pack:

PCM Circuit for 14.8V battery pack:

Physical image for PCM:

                                                       PCM for 3.7V 18650 battery

                                                             PCM for 7.4V battery pack

                                                     PCM for 7.4V battery pack with temperature control   

                                                               PCM for 11.1V battery pack

                                            PCM for 11.1V battery pack with SM-Bus communication

                                                                          PCM for 14.8V battery pack

Partial PCM showed.

Our professional engineer will recommend suitable PCM according to the specs provided by you, such as pulse&continuous working current, discharge cut-off voltage, product name,ect.

Welcome to share us more information. We are glad to help you in further.

Be caution when assemble Lithium battery in serial and Parallel

Lithium battery in serial or parallel combination sounds simple, while to avoid quality problem, there is something you need to know.

Before combination, it requires to match battery with similar voltage, impedance and capacity. Voltage difference below 10mV, impedance difference less than 5mΩ and capacity difference less than 20mA.

If the voltage and capacity difference is big, lower voltage or zero voltage might happen. Because some lithium battery cell might be over-charged, while some are not fully charged when recharge. At the same time, some battery might be over discharged while some are not fully discharged. This will also do harm to the battery for long term.

Never use new and old battery in one combination. And do not mix cells with different brand or different capacity. Make sure use the same type of battery when combination.

Our professional team usually match the battery before combination. If you will assemble at your end, then please advise how many pieces in one battery pack. We will match according to your quantity.

1.      Main material for Lithium ion battery:

Lithium ion battery mainly consists of five parts: Shell, anode, cathode, separator, electrolyte

At present, the main enclosures are:

Steel: cylindrical battery, square battery

Aluminum: square battery, cylindrical battery

Aluminum plastic film: polymer battery

1.1   Anode

Main material used for anode: LiCoO2, LiMnNiCoO2,LiMnO2,LiFePO4

Positive pole structure of lithium ion battery (see view) ：

1.1   Cathode

There are two kinds of cathode materials: graphite and lithium titanate

Graphite: At present, more than 99% of lithium batteries use this cathode material, with a capacity of 300-360mAh/g and a compaction density of 1.45-1.7g/cm3. It is mainly divided into natural graphite, artificial graphite and mesophase carbon microspheres.

The cathode substrate is copper foil.

Lithium titanate: At present, only a few manufacturers are developing and applying it. Because of its excellent cycle performance, it is promising in the field of power batteries. At present, the problem is also very obvious. The charge discharge expansion is large. After being applied to lithium batteries, the voltage decreases by 1.0-1.2V compared with graphite.

Negative pole structure of lithium ion battery (see view):

1.1   Separator

There are two main types of diaphragms: wet diaphragm and dry diaphragm

Wet membrane: PP/PE/PP three-layer membrane represented by TONEN, ENTEK, ASAHI

Dry process diaphragm: PE single-layer diaphragm represented by CLGARD and UBE

Domestic manufacturers include wet Buddha plastic Jinhui PE, dry Grayne PP, etc. Their manufacturing methods are different from the above two

At present, the thickness of commonly used diaphragm is 12 μ m，16 μ m，20 μ m，25 μ m，30 μ m. In addition to the above, ceramic diaphragms are being used, which are based on the above diaphragms and coated with a layer of metal oxides, Al2O3, SiO2, etc. Such diaphragms are gradually used in high energy density and power batteries due to their strong puncture resistance and flame retardancy.

Material: single layer PE (polyethylene) or Three layer composite PP (polypropylene)+PE+PP

Thickness: 0.016 ～ 0.020mm for single layer

The third floor is generally 0.020 ～ 0.025mm

1.1   Electrolyte

(1) Solid polymer electrolyte: mainly used for making solid state batteries, which is still in the laboratory stage

(2) Gel polymer electrolyte: It is mainly used to make gel polymer batteries. At present, only a few companies use this electrolyte.

(3) Liquid electrolyte: at present, most batteries use this electrolyte;

Solvent: mainly carbonate, such as EC, PC, DMC, DEC, EMC, MPC, etc;

Solute: mainly LiPF6, others LiAsF6, LiBF4;

Additives: adding a small amount can significantly improve a certain performance or several performance of the battery, such as VC, PS, etc;

2.      Working principle of lithium ion battery

During the charging and discharging process of lithium-ion battery, Li+is embedded and de embedded back and forth between the two electrodes, which is known as "rocking chair battery".

When charging the battery, Li+is dis embedded from the positive electrode and embedded into the negative electrode through the electrolyte. The negative electrode is in a lithium rich state. The opposite is true when discharging.

Positive reaction：LiCoO₂==== Li_1-xCoO₂ + x Li+ + xe

Negative reaction：6C + x Li+ + x e- === Li_xC₆
Total reaction：LiCoO₂ + 6C ==== Li_1-xCoO₂ + Li_xC₆

3.      Classification of lithium ion battery from shape

Prismatic, cylindrical, polymer

4.      Main application for lithium ion battery

l  Mobile lighting flashlight flashlight, HID flashlight, HID portable searchlight, diving light, emergency lighting, high-power LED lighting, film and television lighting equipment, etc.

l  Medical instruments and equipment portable monitor, transcranial Doppler blood flow analyzer, ECG monitor, portable X-ray system, B-ultrasound instrument, respirator, infusion pump, blood gas/electrolyte analyzer, pulmonary function detector, rehabilitation instrument, etc.

l  Military security monitoring industrial detection and measurement instruments Military wireless communication, PDL digital control radio, chemical agent detector, satellite positioning and navigator, wireless intelligent alarm, wireless monitor, communication cable detector, mapping instrument, etc.

l  Portable printer, POS machine, automatic order machine, walkie talkie, wireless handheld monitor, wireless baby monitoring camera, GPS positioning system, handheld data terminal, portable projector, barcode scanner, etc.

l  Electric tools toys electric cars rechargeable electric drills, screwdrivers, circular saws, reciprocating saws, sandpaper machines, rechargeable round forest tools, rechargeable electric scissors, rechargeable cutting machines, aviation and navigation models, electric wheelchair bicycles, golf carts, etc.

l  Communication digital IT portable industrial control computer, PDA handheld computer, notebook, electronic reader, learning machine, electronic dictionary, digital camera, video camera, wireless music player, wireless headset, PSP game machine, etc.

l  ODM/OEM battery mobile power combination battery intelligent cleaner, intelligent robot, intelligent toilet, warm clothing, wireless transmitter, air humidifier, solar energy charger, mobile power, backup photography power, etc.

Small battery used for：Bluetooth earphone，MP3，MP4

Medium battery used for：Cellphone，GPS，Digital camera/DV

Big battery used for：DVD，tablet

Other battery pack：RC toy，E-bike，power tool

We are professional battery solution provider. If you need help for power solution, please feel free to contact us.

It usually takes about 2~3working days.

SUJOR aim to provide customer medium higher level quality product, every battery from us will be strictly follow up at least five steps quality control reflected in R&D process, incoming control process, production process, prior-shipment control and after-sales service process.

If you have further doubt on battery formation, please contact us.