What's primary battery? And, what's secondary battery?
Primary battery can be used only once. Secondary battery can be recharged for many times.
Are there many types of secondary batteries?
Yes. From low energy density to high, the major types include lead-acid (usually used in cars and UPS), Ni-Cd (often seen in cordless phone and power tools), Ni-MH (often seen in low-end mobile phone and high-end cordless phone and power tools), Li-ion and Li-polymer (often seen in mobile phone, PDA, digital camera, and laptop computer).
What's the difference between li-ion and li-polymer?
In terms technologies, their main difference is in battery packaging. Their positive and negative electrodes have similar chemical composition. Li-ion technology uses metal enclosure to limit the expansion of chemical materials over the battery's life. Li-polymer uses polymer fibers to tie the chemical materials together. So it can use soft materials for enclosure, such as plastic or aluminum foil. For a thickness of 3mm or less, li-polymer has advantage in capacity. For a thickness more than 3mm, li-ion has more advantages, especially in price.
What's the future of Ni-Cd, Ni-MH, and Li-ion?
Under the same weight or volume, Ni-Cd has only half of Ni-MH's capacity. In terms of price/performance, Ni-MH is better than Ni-Cd. Further more, Cadmium causes environmental concerns. So, more than half of Ni-Cd’s market has been replaced by Ni-MH. As a result, the Ni-Cd market is shrinking. On the other hand, Li-ion has about 50% more capacity than Ni-MH. For applications that have restrictive limitations in weight or volume (such as mobile phone, PDA, notebook computer), li-ion is taking over Ni-MH’s share. As a result, Ni-MH’s market is going flat. In terms of price performance (dollar per watt*hour), li-ion is about the same as Ni-MH. Since li-ion uses materials which are abundant on earth, it will become cheaper than Ni-MH in the long run. So, li-ion market is still growing rapidly.
Is it possible to use Ni-MH or Li-ion for UPS applications?
Most UPS uses lead-acid battery. Under the same energy capacity (Watt*hour), lead-acid battery is about 4 times bigger and 4 times cheaper than li-ion battery. The problem is that UPS requires 6CA~10CA discharge current. But lead-acid battery can provide only less than 1CA current if cycle life is not to be sacrified. As a result, after about 10 times of 6CA charge/discharge, lead-acid battery become dead. To increase its cycle life, UPS manufacturer must use bigger lead-acid battery (losing some advantage in price and getting worse in weight and volume) or use high C rate batteries, such as Ni-MH or Li-ion. So, a 6CA discharge rate li-ion or Ni-MH battery has the potential to dramatically change the cycle life and dimensions of future UPS.
What does 6CA discharge mean?
If the capacity of a battery is 7Ah (amper*hour), 6CA discharge means 6*7*A = 42A discharge. If the battery is 12Ah and the max discharge current is 5CA, the max discharge current will be 5*12*A = 60A.
What are the main specifications of rechargeable (secondary) batteries?
They include capacity (mA*hour), internal resistance(m Ohm), dimension, cycle life(times), maximum charge/discharge current (C), self discharge rate. There are other important specifications, e.g. under over charge whether it will explode.
Where can I buy Edan's product?
In Japan, please contact MCM Japan Ltd.. In China, please contact Edan China. In Taiwan and other countries, please contact Edan Taiwan.
What's the maximum instantaneous discharge current of Ni-MH battery cells?
The Ni-MH battery cell can be discharged at 5C~10C condition for several seconds. For example, an ED2000mA battery cell (capacity: 2Ah) can output 10A~20A current (2Ax5 ~ 2Ax10) if the discharge does not last for too long. This makes Ni-MH good for many high current applications, such as power hand tools and UPS.
What's the maximum fast discharge current of Ni-MH battery cells?
The Ni-MH battery can be discharged at 3C~5C condition for 12~20 minutes. For example, an ED1600AA battery cell (capacity: 1.6Ah) can continuously output 4.8A~8A current (1.6Ax3 ~ 1.6Ax5) for 12~20 minutes.
What the maximum discharge current of Li-ion battery?
About 1C for continuous discharge and 3C for instantaneous discharge. But these numbers can be changed by re-designing the battery.
What's the key components of a li-ion mobile phone battery pack?
There are three key components for a mobile phone battery pack: li-ion battery cell, protection circuit board, and plastic enclosure. Sometimes, a PTC (a multi-use current fuse, turn off when overcurrent) is added between the cell and PCB.
What's the cost structure and the key functions of the proteciton circuit board?
There are two ICs on the protection circuit board: the protection IC and the switch IC. The protection IC costs about US$0.15~0.5. And the switch IC, usually consists of two MOS FETs, is about US$0.2~0.3. There are another 5~7 R & C. So, roughly 20% costs is on the proteciton IC, 30% costs on the switch, and 15% costs on the others, 20% costs on labor and testing, another 15% is for overhead and profit margin. The key functions include over-current (include short circuit) protection, over-charge protection (limit the max voltage to about 4.25V), and over-discharge (limit the min voltage to about 3.0V) protection. The size of the proteciton circuit board is usually around 150 square milimeters (about 30mm * 5mm).
Why do we need proteciton circuit board for li-ion battery?
Lithium-ion battery operates between 3.0V and 4.2V. Outside this range, the capacity, life, and safety of the battery will degrade. When below 2.4V, the metal plates of the battery will be eroded, which may cause higher impedance, lower capacity and short circuit. When over 4.3V, the cycle life and capacity will be hurt. More over, lithium crystal will grow, which may eventually cause internal short circuit and explosion.
What kind of protections are needed for Ni-MH batteries, respectively?
In addition to the self-protections of the battery cells, a well designed charger and protection circuitry are also very important. For the protection circuitry, Ni-MH is much easier than li-ion. Usually it includes a polyswitch connected in serial with the batteries and a thermoresistor with one-end connected to the ground power line and the other end to charger control. When short circuit happens, the polyswitch will be heated up and the resistance will increase rapidly to stop the current. When the temperature cools down, it will resume the supply of the power. The thermoresistor is used by the charger. When the charger find that the battery temperature increases (through the increase of the thermoresistor's resistance), it will shut down the charging process. These two parts cost about US$0.2 together. So, it is much cheaper than the li-ion protection circuit board.
What's the difference between a charger and an adaptor? Why do we need a charger?
A charger consists of two parts: adaptor and changing controller. The charging controller takes the adaptor output as input and provides the battery cell constant current (when cell voltage < 4.2V) and constant voltage (when voltage reaches 4.2V). So, a charger will not over charge the battery cell. An adaptor, on the other hand, will put a lot of pressure on the protection circuit board. When a PCB fails to shut down the charging process, the cell will be over charged. Under such circumstances, gas and lithium will grow inside the cell. If there is a break on the enclosure causing explosive oxidation of the lithium or if the lithium crystal penaltrates the seperator and cuases short circuit, the cell may explode. So, a safe design must NOT put pressure on the PCB. Always use a charge to charge your battery pack.
Why are there so many explosions been reported in the mobile phone industry?
When an adaptor (not a charger) is used to charge a lithium-ion battery pack, the safety of the pack is relied on the protection circuit board heavily. When the PCB fails to shut down a charge, explosion may occur. Although the chances for the PCB to fail is very low (e.g., 1 out of 1 million), 350 million new mobile phones a year can make many cases.
Is it possible to make the lithium-ion cells resistive to short circuit and over charge?
Yes. Edan's cell can pass short circuit and 12V over charge. When the cell is short or when the PCB fails and the cell is over charged, the cell will become dead but it won't explode.