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| 1. | The Introduction of Lithium Battery | |||
| Overview The lithium battery is divided into Li-SOCl2 battery and Li⌒MnO2 battery |
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| Li-SOCl2 battery The Li-SOCl 2 battery is the type with the highest specific energy, which can reach the level of 500Wh/kg . Its nominal voltage is 3.6v; when it discharges at the mediate current, the voltage is quite stable at 3~4 v(it can discharge stably with little changes within the 90% capacity). The battery can work at the range of -40C~ + 85C, while at -40C, the capacity is about 50% of the one at the normal temperature. The self-discharge rate is low( the annual one ?1% ), and the shelf life can reach as long as more than 10 years. |
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| Li⌒MnO2 battery The Li ⌒ MnO2 battery is the primary battery with the lithium as the negative electrode, the MnO2 as the positive electrode and the organic solvent as electrolyte. The main feature is the high voltage: the nominal voltage is 3v(2 times that of the common dry battery); the expiration discharge voltage is 2v, the specific capacity is high; the discharge voltage is stable and reliable; the shelf life is more than 3 years, the self discharge rate is low (the annual one ?2% ); the working temperature ranges from -20C to +60C. |
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| The battery can be made into different shapes
(rectangle, cylindrical and Coin) to meet the various requirements. The Coin Battery is often used in clocks, calculators, electron notepad, audiphone, electronic game machines, IC card, standby power sources, etc. |
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| Features | ||||
| Li-SOCl2
battery 3.6V rated voltage Highest specific capacity (500 wh/kg,1000wh/dm3); Nominal operating temperature range from -40C to +75C; Excellent low and high temperature characteristics; Low self-discharge(no more than 1%) rate; 10 years of shelf life; |
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| Li⌒MnO2
battery High voltage(3v); High energy density; Wide operation temperature range from -20C to +60C No voltage delay and low self discharge; High current discharge ; Excellent safety and no pollution; |
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| Applications | ||||
| Li-SOCl2 battery Real-time clockApparatus and instrumentCMOS memory backup power source Li⌒MnO2 battery Camera; Radio; Civil and military communication instruments; CMOS memory backup power source; |
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| 2. | Passivation, the important characteristic of Lithium battery | |||
| Cell passivation is an important characteristics of lithium battery that can be very difficult to understand for many batteries-users. This section discusses this phenomenon, and it gives suggestions on how to counteract the effects of passivation when using lithium batteries. | ||||
| Passivation | ||||
Passivation is a very thin, high resistant,self-assembled layer formed on the surface of the lithium anode. It is formed as a result of a chemical reaction between the battery electrolyte and the lithium anode. Without the passivation layer, this type of lithium battery would not exist because the lithium would discharge and degrade quite rapidly. An advantage of the passivation layer is it allows the battery to have a very low self discharge rate and extremely long shelf life. |
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| The most obvious affect of the passivation layer is voltage delay. Voltage delay will occur when a load is placed on the cell as illustrated in the following drawing: | ||||
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| After a load is applied to a cell, the high resistance of the passivation layer causes the cell's voltage to drop rapidily. The discharge reaction slowly removes the passivation layer thereby lowering the internal resistance of the cell. This in turn causes the cell's voltage to reach a peak value which should remain steady if other discharge conditions do not change. If the load increases after the cell's voltage stabilizes, then it may drop again until the passivation layer is fully removed. | ||||
| Once the load is removed or lowered, the passivation layer will reform, and voltage delay may be a factor when subsequent loads are applied. | ||||
| Several different factors may increase passivation thereby influencing the length and depth of voltage delay. They are: | ||||
| 1. | Current capability of cell - High loads on cells may cause voltage delay to increase. Conversely, voltage delay may be unnoticeable with very small loads. | |||
| 2. | Chemistry- Different variations in chemistry may influence passivation. | |||
| 3. | Length of storage - Generally, the longer a cell is in storage, the more passivation will grow on the anode surface. Thus, voltage delay may be higher for older cells of a given cell type. | |||
| 4. | Storage temperature - Higher storage temperatureincreases the amount of passivation. Storage of batteries in non-air-conditioned areas during the summer months in hot climates can cause adverse passivation problems. It is recommended that batteries be stored in climate controlled areas. | |||
| 5. | Discharge temperature - Just as high temperature storage may cause passivation effects,discharging batteries at very low temperatures may cause similar characteristics. | |||
| 6. | Prior discharge conditions - Partially discharging a cell and then removing the load increases the amount ofpassivation relative to when the cell was new. Thus, voltage delay on a second run may be more pronounced after the first use of the cellor battery. | |||
| In many cases, voltage delay caused by passivation does not affect users of lithium cells. However, we recommend that you evaluate the effect of passivation very carefully when selecting lithium batteries. Users of lithium cells should refer to each cell manufacturer's specific information on this subject. | ||||
| De-Passivation | ||||
| For some applications, passivation is not a factor, and users do not notice voltage delay when hooking up to the circuit. On the other hand, If the device cannot handle this drop in voltage (i.e., reset, turn-off,fail, etc.), then the cells must be "depassivated" prior to use. Depassivation is composed of placing a constant load on the cell for a period of time discharging a cell near the specified maximum continuous discharge rate. The purpose of this is to pre-condition the cell to where it does not drop below the minimum voltage of the deviceonce the load is applied. This is done by advancing the specified maximum continuous discharge to pass the point of the voltage drop in the above chart. | ||||