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When to discard a li-ion battery
Li-ion battery end-of-life is conservatively rated by manufacturers to be 80% of the battery's original rated capacity. As the battery is repeatedly charged and discharged it gradually loses capacity in a fairly linear, but permanent manner. This lost capacity is the result of chemical degradation within the battery, and cannot be recaptured. Once the battery's operating life reaches an unacceptable level in the judgment of the user it should be replaced. Why do lithium-ion batteries have high energy density, power density and efficiency?
1. The reason for the high energy density of lithium ion batteries is that the voltage of lithium metal oxides used in the cathode, and graphite in the anode, is very high, in the range of 3.7 volts, which is three times greater than standard rechargeable chemistries such as NiCad and NiMH chemistries.
2. These materials are extremely compact in their physical structure and material properties allowing for high capacity in a very small space.
3. Construction techniques in cell building have optimized the weight and volume of electrode, separator and electrolyte components.
From a chemistry perspective:
The active components of lithium ion batteries are: lithitated metal oxide, serving as the cathode during discharge, and graphite, serving as the anode. These materials use carbon black as a conductive additive and PvDF polymer as a binder. Aluminum and copper metal foils serve as the current collectors separated by a polypropylene separator.
Lithium ion batteries have a nominal voltage of 3.7 volts, which is three times higher than NiMH and NiCad at 1.2 volts. For cells of the same capacity, three times the power is available through lithium ion chemistry as opposed to NiMH and NiCad. Also, lithium ion chemistry does not display the memory effect or self discharge rates of NiMH and NiCad chemistries.
Lithium-ion battery temperature range
Lithium-ion batteries can be operated at -40 degrees, but the cell impedance at that temperature will rise dramatically, resulting in significantly reduced output current. This is not harmful to the battery, but it will operate at a significantly lower voltage at any given current. Available capacity to a given cut-off voltage will also be reduced, perhaps to less than 20 percent of the capacity at 23 degrees C. The reason for the increase in impedance is that the liquid electrolyte becomes viscous at very low temperatures, which reduces its conductivity.
What does the term "1C" mean when used in specifications for rechargeable batteries?
The letter "C" refers to the rated Capacity of a rechargeable battery. For example, a battery with a rated capacity (C) of 1,000 mill amperes (mAh), can be charged or discharged at a current of 1,000 mA for one hour, which is referred to as a "1C" rate of charge or discharge. Similarly, if that same 1,000 mAh battery was charged or discharged at a current of 200 mA, you would be able to do so in 5 hours (1,000 divided by 5). This is called the C/5 rate.
Can a battery be used longer if it is kept in a cool area such as refrigerator?
A battery is to be kept in a place of low temperature and low humidity as a rule; however, a refrigerator is rather humid so the Lithium-ion battery which has instable property against moisture could be put in a danger.
What is Cell Impedance?
Inner Cell resistance is related to the maintaining of the current flow. If the resistance is high, voltage drop during discharge can occur which can affect the equipment.
About Lithium-ion and Lithium-polymer batteries
A Lithium-ion battery (LIB) employ lithium transition metal oxides as the cathode material and carbon as an anode material.
A Lithium Metal battery (LMB) employ lithium transition metal oxides as the cathode material and lithium metal as an anode material.
A Lithium polymer battery (LPB) uses a lithium metal as an anode material and SPE (Solid Polymer Electrolyte) as the electrolyte.
A Lithium-ion polymer battery (LIPB) empoly the LIB electrode, SPE instead of a separator and electrolyte.
Plastic Lithium Ion (PLI) battery is a new type lithium second battery developed by Bellcore, an American company. In Korea, Samsung SDI and Viable Korea are manufacturing PLI battery.
Advanced Lithium Battery (ALB) is a new type of battery using the LIB's manufacturing process and taking merits of LPB batteries. In Saehan-Enertech, Kokam, LG Chem, and Samsung SDI are manufacturing this type battery.
What is battery?
I.The concept of battery
Battery is a device to use electric energy which was once stored as a chemical energy and transformed back to the electric energy when necessary. That is to say, it is a device in which two different or same metal electrodes are put into the electrolyte. 'Discharge' is that an electric current flows out from a battery. On the contrary, 'charge' is that the electric current is taken into the battery. ' Charge' is to let electric energy in from the outside and have it cause chemical changes in opposition in order to pull the electric energy out to use again when necessary.
II.The components of a battery
- Cathode : the electrode of an electrochemical cell where reduction occurs.
- Anode : the electrode of an electrochemical cell where oxidation occurs.
- Electrolyte : a non-metallic medium, or a substance dissolved in solution which conducts the flow of ions between the cathode and anode
- Separator : a separation film used to prevent physical contact between the cathode and anode
III. The classification of Battery
- Primary cells are non rechargeable cells, in which the electrochemical reaction is irreversible. They contain only a fixed amount of the reacting compounds and are discharged only once.
ex) Alkaline Manganese Battery, Lithium primary Battery , Primary Zinc-Air Battery, Thermal Battery etc.
- Secondary cells are rechargeable several times. Only reversible electrochemical reactions offer such a possibility.
ex) Lead-acid Battery, Ni-Cd Battery, Ni-MH Battery, Na-S Battery, Li-ion Battery, Polymer Battery, etc. - Fuel cells, in contrast with the previous cells described above, operate in a continuous process. The reactants nowadays often hydrogen and oxygen- must be fed continuously into the cell from outside.
ex). DMFC, AFC, PEFC, PAFC, MCFC, SOFC etc.
- Physical battery : A battery that uses physical phenomena
ex) solar cells
Malfunction may be caused by the unstable Li-ion battery structure when it is overcharged or over discharged. Accordingly, a protection circuit is necessary to fend off this malfunction.
By monitoring voltage of each battery, charging or discharging is limited by breaking the current when the monitored voltage deviates from normal levels. The flow of current is cut off in the case when the current flow is excessive.
3. Function : control the pack
1) Prevention of overcharge
2) Prevention of over discharge
3) Prevention of over-voltaic current
1) Smart form : Over-charge+over-discharge+over-voltaic current+LED+Power Management
2) Dumb form : over-charge+over-discharge+over-voltaic current
A phenomenon that an active material is transformed into the discharge condition even in the state of open external current circuit is called ' self-discharge'. There is self-discharge in all the batteries. It is because that, in the battery system composed of different metals, a transfer of ions and electrons takes place on its own even though the electric current don't applied externally. There is very little self-discharge in the solid electrolyte system, but it is very notable in the liquid electrolyte system. It is also influenced by the surrounding temperature. Summer can have more influence over it than winter .
In the case of primary battery, the rate of self discharged are followed below:
Manganese battery : 10%/year
Alkaline battery : 5%/year
Lithium battery : 1%/year
The self-discharge rates of second battery are higher than those of primary battery. Particularly, the performances of second batteries are different depending on battery makers. It is because they form artificial, chemical structure in order to make it possible to use the battery many times. With this reason, there are differences of performance depending upon the battery makers although the variations are not big.
Here are some examples based on second batteries.
Ni-MH cell (Toshiba.) : 5 ~ 10%/month
Ni-Cd cell (Toshiba.) : 25 ~ 30%/month
Li-ion battery : 2%/month
Lead-acid Battery :
Pb-Sb alloy group : 25 ~ 30%/month
Pb-Ca alloy group : 2%/month
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