Q1. What are the differences between high C-rate and low C-rate lithium polymer (Li-Po) batteries.
In general, the differences lie in the materials made of the positive & negative terminals, the area density design, the electrolyte ingredient, the septum data and the density of inside pieces.
Q2. How is a Li-Po battery made?
When a Li-Po battery is made, five main aspects should be considered carefully: (1) Battery Pack should have sufficient strength, so that the polymer battery inside could be effectively protected from mechanical shocks; (2) The polymer cell should be fixed to the battery pack on its large surface area — no cell movement in the battery pack should be allowed; (3) No sharp edge components should be inside the pack containing the polymer battery, and meanwhile, sufficient insulation layer between wiring and the cell should be used to maintain multiple safety protection; (4) Ultrasonic welding is recommended for polymer tab connection to obtain low-resistance, high-reliability and light-weight properties; (5) Polymer packs should be designed carefully so that no shear force is applied, and also, no heat is generated even when leakage occurs for mishaps. PCM from electrolyte leakage should be isolated as perfectly as possible, and narrow distance between bare circuit patterns should be avoided.
Q3. What gases are generated in the formation process. Are they dangerous?
The generated gases include CO, CO2, H2, CH4 and so on. They are not dangerous because of low volume.
Q4. Why do we need formation process?
Organic solvents easily decompose on the negative electrodes during charging, leading to battery swelling, drop of cell capacity, and unsafety caused by active reaction. The purpose of the formation process is to form a solid layer called the solid electrolyte interphase (SEI), which is electrically insulating yet provides significant ionic conductivity. This interphase prevents further decomposition of the electrolyte after the second charging.
Q5. Why do Li-Po batteries bloat/swell?
The Li-Po batteries may bloat/swell due to the following reasons:
Normally, the maximum charge voltage is 4.2V for RC batteries. If the batteries were overcharged beyond 4.4V, electrolytic oxidation process would happen, which generates mass gas leading to battery swelling.
When discharging in high temperature or high C rate, the temperature of the inner part of the battery can be even higher, which gasify the electrolyte and results in swelling.
If short circuit happened, the cell voltage would drop very fast and the electrolyte would be reactive to generate gases, leading to battery swelling.
If sealed without proper processing, the battery cell would have water and air in, so that the electrolyte would be reactive to generate gases, leading to battery swelling.
Q6. What are the gases inside a swelling cell, and are they toxic/dangerous?
The gases vary depending on different situations:
1. If the gases were generated by electrolyte gas reaction, they would mainly be electrolyte solvent components, for example: EC, DMC, EMS and so on;
2. If the gases were generated by overcharging, they would mainly be H2, CO, CO2, CH4 and so on;
3, If the gas were generated by improper sealing, they would mainly be H2, C2, H2 and so on.
All of these gases are not dangerous due to low volume.
Q7. How many cycles should I expect for a RC Li-Po battery?
In general situation of lower c-rate discharging, the lifetime of a RC Li-Po battery should reach more than 500 cycles while its capacity remains 80%.
Q8. How should I dispose of my Li-Po batteries safely?
The waste batteries are better to be handled by professional recycling factories. If not, please dispose them into salty water, so that the cells can be oxidized slowly.
Q9. Why do I sometime get a dead cell in the pack? Why does the voltage fall?
The main reason for fast voltage dropping is that short circuit happens inside the cell.
During manufacturing process, different materials are mixed together and then coated. These materials are tiny powders mixed with binder; if some powders were dropped, it might penetrate the white diaphragm inside the cells and cause short circuit. Were such defective cells not picked out, their voltage would drop slowly day by day, so the customers would get dead cells in battery packs sometimes.
Another important reason is pack unbalance. During the charging and discharging process, the voltage of the worse cells would drop very fast if worked beyond what they can stand.
Q10. What is the maximum voltage before a battery explodes? Why does it explode?
Please charge a battery according to suppliers’ suggestion.For examples, the RC batteries’ max charge voltage is 4.2V. If they were charged under 4.3V, the ion would be pulled out from the cathode, leading to cycles life dropping; if they were charged under 4.4-4.5V, the electrolyte would be easily oxidized, resulting in cells swelling; if they were charged under 4.6V, the electrolyte’s oxidization would be very serious and the temperature would increase fast; if charged under 5.0V, the batteries would be burned or explode as the temperature inside would be very high and the reaction would be very active.
Q11. Do the Li-Po batteries need to be pre-cycled before I use it?
It is not necessary to do this because the manufactures have already done the formation processing for the cells. Their performance would be degraded if more cycling were performed.
Q12. Could I fast charge the Li-Po batteries, and if yes, under what conditions?
Please follow the suppliers’ suggestions and DO NOT fast charge the Li-Po batteries. If you need to do this under urgent conditions, please make sure to use a qualified balance charger. Frequent fast charging will shorten the batteries’ lifetime.
Q13. What are the Li-Po batteries’ maximum charging and discharging temperatures, and why?
In general, we follow these temperatures for RC Li-Po batteries:
Discharging: -20℃～60℃. If the temperature was too high, it would result in swelling; if the temperature was too low, it would be hard to release the capacity.
Charging: 0℃～45℃. Below 0℃ or above 45℃, the batteries may not only fail to be charged sufficiently, but also deteriorate in various ways.
Q14. If I puncture my battery, how should I dispose of it properly.
Please follow the same method as sated in Q8. The waste batteries are better to be handled by professional recycling factories. If not, please dispose them into salty water, so that the cells can be oxidized slowly.
Q15: What is PCM, and what main functions does it include?
To ensure peak batteries’ performance and their maximum cycle life, some polymer rechargeable batteries are required to be assembled in battery packs with a built-in protection circuit module (PCM). In such packs, thermistors for detecting status of battery temperature, thermostats, and temperature fuses are recommended to be provided as standard.
The PCM usually includes the these functions: Overcharge Protection, Over-discharge Protection, and Over-current Protection.
Q16: What functions and performance are required for Li-Po battery chargers?
1. The charging Voltage between the terminals must be 4.2±0.05V. In principle, it is desired to charge the Li-Po batteries at 4.2V. The specified tolerance is provided for variations in equipment, design and fabrication.
2. Charging current should be less than the maximum charging current listed in the specification. Charging with higher current than recommended may cause serious damage to the cell performance and safety features, leading to heat generation or leakage.
3. The charger should take into account that the temperature of polymer batteries will rise by approx. 5℃ while being charged at a strong current rate. After being switched to the constant voltage charging mode, the cell temperature will gradually decrease.
4. The charger must check the open-circuit voltage (OCV) of the battery pack before charging. When the OCV is measurable (that is to say, the PCM allows the battery to discharge ), the charging can be started immediately. If the OCV is not measurable (that is to say, the PCM prohibits the discharge), feed a small inspection current (0.01-0.07A) so as to release the battery from the discharge prohibition mode, and then check the battery pack voltage. If a voltage of 1.5V or more is detected, proceed to normal charging. If the OCV is not detected when the small inspection current is fed, the battery should be diagnosed as abnormal and charging should be avoided.
5. Whether or not a Li-Po battery is fully charged should be determined by detecting the charging current. A detected current of 0.1 mA indicates that the battery has been charged to 93% to 94% of its capacity.
6. Protection Features: (A) If the charging voltage gets out of the range of 1.5V - 4.3V, the battery should be deemed abnormal and charging should be avoided. (B) If the battery voltage remains at less than 1.5V for a specified time duration in the trickle-charging mode during battery check, the battery should be deemed abnormal and charging should be avoided. C) The Li-Po battery is not allowed for trickle charging, it is recommendable to provide the timer for safety purposes.
7. To prevent an over-voltage to the battery in the event of a malfunction in the power supply unit, select the unit equipped with over-voltage protection.
Q17. What discharging conditions do you recommend?
1. We Recommended a cut-off voltage as 3.0 V for standard series batteries.
2. The discharge rate should not exceed the maximum continuous discharge rate listed in the specifications.
3. The discharge temperature range should be -20℃ to +60℃. For maximum performance of our high-power series batteries, discharge temperature between 20℃ and 40℃ is recommended.
Q.18 How to Charge li-po battery
1. Charging Current: Charging current should be less than the maximum charging current listed in specifications. Charging with higher current than recommended may cause serious damage to cell performance and safety features , leading to heat generation or leakage.
2. Charging Voltage: Charging should be performed at a voltage less than that listed in specifications (4.20V/cell). Charging at above 4.25V—the absolute maximum voltage, must be strictly prohibited. The chargers used should have this voltage limitation function. Charging with higher voltage than specified is very dangerous, which may cause serious damage to the cell performance and safety features, leading to heat generation or leakage.
3. Charging Temperature: The cells should be charged within a range of temperatures listed in the specifications. Always let the batteries cool down to ambient temperature before charging.
4. Prohibition of Reverse Charging: Do not reverse the positive(+) and negative(-) terminals. Otherwise, the battery pack will be reverse-charged and abnormal chemical reactions may occur. Ecessively high current may flow during recharging, possibly leading to damage, overheating, smoke emission, bursting and/or ignition.
5. Use specific Li-Po charger only. DO NOT use a Ni-MH or Ni-Cd charger. It is your responsibility solely to ensure that the charger you purchased works properly.
6. Never charge batteries unattended. Always monitor charging process to assure batteries are being charged properly. Always charge the batteries in an isolated and safe area away from any flammable or/and combustible materials.
Q19. How to store Li-Po batteries if I will not use them for a while?
1. The cells shall be stored in an environment with low humidity free from corrosive gas and combustible material within a temperature range of -10 to 40℃.
2. It is recommended to strictly obey the first-in first-out (FIFO) principle through manufacturing and distribution of the product.
3. A higher cell voltage during storage will accelerate the deterioration of capacity, it is recommended to keep the cells at a lower voltage (about 3.8V/cell) throughout the period of storage. Storage for a long period may result in over-discharge, due to self-discharge of the cells. When you need to store batteries for more than one year, charge the cells at least once a year to about 3.8V/cell so as to prevent over-discharge.
Q20. What should be known with regard to handling of battery cells?
1. Aluminum Laminate Film: Easily damaged by sharp edge parts such as Ni-tabs, pins and needles, compared with metal-can-case Li-Po cells.
2. Cells may be damaged by heat above approximately 80℃. Sealing break may cause electrolyte leakage, possibly leading to short circuit and generation of very high current, especially for our high-power series cells, which sequently causes heating of the cells and may results in electrolyte leakage, smoke emission, ignition and/or explosion that are very dangerous. The polymer tabs may be easily short-circuited if put on conductive materials. An appropriate circuitry with PCM shall be employed to protect accidental short of the battery packs.
3. Mechanical Shock: Polymer has less mechanical endurance than metal can case of Lithium-ion cells. Falling, hitting and bending may cause degradation of polymer characteristics.
4. Handling of Tabs: the Polymer tabs are not so stubborn, especially for aluminum tabs at the positive terminal. DO NOT put much force on the polymer tabs. DO NOT bend tabs many times. Aluminum tabs may be torn off easily by shear force.
Q21. What should be known about assembling battery packs?
1. Shocks, high temperature or contacts of sharp-edge components should not be allowed in battery pack assembling process.
2. Soldering directly to polymer tabs is not recommended. When you solder directly to the polymer tabs, it is necessary to ensure not to apply too high welding temperature and too long welding time, to guarantee that the temperature transmitted to the cells is lower than 80℃. Temperature above 80℃ may cause damage to the polymer cells and degrade their performances.
3. In case that the battery packs are fixed by ultrasonic welding, it is necessary to ensure not to apply too much ultrasonic welding power to the polymer cell and electronic circuits such as PCM. Otherwise, it may cause serious damage to the cells and electronic circuit.
Q.22 What should be noticed about battery Life?
Batteries losing 20% of their capacity must be removed from service. Discharge the batteries to 3.0V/cell, ensure that output wires are insulated, and then wrap them in a bag for disposal properly.
Please comply with the following rules. Otherwise abnormal chemical reaction may occur, which may lead to the battery damage, overheat, emit smoke, burst and/or ignite:
1. Do not disassemble or modify the batteries.
2. Do not connect the positive (+) and negative (-) terminals with a metal object, such as wires or rings on your hand. Do not transport or store the batteries together with metal objects such as necklaces, hair pins , etc.
3. Do not incinerate or dispose the batteries in fire or heat it.
4. Do not use or leave the batteries near a heat source, such as fire or heater (80℃ or higher). Do not recharge the batteries near fire or in extremely hot weather.
5. Do not immerse the batteries in liquid such as water, seawater, drinks, etc., and do not get it wet.
6. Do not pierce the battery with a nail or other sharp objects, strike it with a hammer, or step on it . Do not strike and throw the battery packs.
7. Do not use an apparently damaged or deformed battery.
8. If a battery is damaged, gives off an odor, generates heat, becomes discolored/deformed , starts to balloon/swell up, or appears abnormal in any way during use, recharging or storage, immediately remove it from the equipment or charger, disconnect the battery, stop using it and observe it in a safe place for approximately 15minutes. The battery can still ignite even after 10minutes due to the delayed chemical reaction that may occur.
9. Never let the temperature transmitted to the cell higher than 80℃when directly solder the cell tabs to wire leads or devices. It is recommended to spot weld the cell tabs with the lead tabs with pre-soldered wiring. Otherwise, heat can melt down the insulation and damage its safety features.
10. Do not apply force to the connections if you cannot easily connect the battery terminals to the charger or other equipments. The positive (+) and negative (-) terminals are arranged in a particular orientation. Confirm that the terminals are correctly oriented.
11. Electrolyte is harmful. If a battery pack is damaged and the electrolyte gets into your eyes or contacts your skin/clothing, do not rub them. Instead, rinse your eyes and/or skin, wash it away with clean running water and immediately seek for medical attention. Otherwise, eye injury and skin inflammation may occur.
12. Do not use the battery packs for a purpose other than those are specified.
13. Do not mix batteries of different types, models, capacities, sizes, brands, charged and discharged, or new and old in the same assembly.
14. If charging operation fails to complete even when a specified recharging time has elapsed, immediately stop further recharging.
15. Do not put the batteries into a microwave oven or pressurized container.
1. Do not use or expose the batteries to intense sunlight or high temperature, such as in a car or in hot weather. Never recharge battery outside the specified temperature range of 0 to 45℃.
2. The battery packs incorporate built-in safety devices. Do not use them in a location where static electricity may be present. Otherwise, the safety of the devices can be damaged.
3. Store the batteries in a location where children cannot reach. Also, make sure that a child could not take out the battery packs from the charger or other equipments.
Q25. How to choose the best power for your device?
Step1. Please test the consumption of your device, such as average operating voltage and current, and then figure out the minimum capacity you need for the best performance according to the consumption and the expected operating time. For example, when the average operating current is 1200mA, the operating voltage is 6-8V and the operating time you expect is 1.5hours, the minimum capacity you need is 1200 mA X 1.5h=1800mAh, and two cells connected in series are needed to meet the operating voltage range.
Step 2. Then, please check the dimensions of the battery size in our specifications to find out which one should be fit for your device and meet your minimum capacity requirements. The below points should be taken into consideration when you choose the battery size:
1. If you are looking for a single cell with PCM, please consider approximately 1mm more space for the length of the pack.
2. We will apply a PCB for better connection when you are looking for two or more cells in a pack. Therefore, approximately 3mm should be added to the length of the packs. Also, the outer diameter of the lead wires should be taken into consideration.
3. Because the heat may be generated very fast during the high-rate discharge of our high-power series cells, we will leave approximately 1mm space between each battery layer in the pack for better release of the heat .Thus ,the thickness of the pack will be increased.