Nowadays, when designers choose batteries for new products, it is easy to think of lithium batteries, but they lack an in-depth understanding of how to choose suitable lithium batteries. Lithium is the lightest non-gaseous metal in nature. Its intrinsic potential is lower than that of any other metal. Therefore, compared with other kinds of batteries, the specific capacity (capacity per unit weight) and bulk density (capacity per unit volume) of lithium batteries are the highest and have incomparable advantages.
The internal resistance of lithium batteries is very high because the electrolyte inside the batteries is colloidal rather than aqueous. In addition, the extremely low moisture content and stable physical and chemical properties of the electrode materials also enable lithium batteries to work safely in a wide temperature range. Individual lithium batteries can operate at - 55 C and + 150 C. The rated output voltage of lithium battery is 2.7-3.6V.
Electrode Materials for Lithium Batteries
Different electrode materials will endow lithium batteries with different characteristics, which are mainly reflected in the following aspects:
Rating voltage, minimum voltage and maximum voltage;
Initial discharge current, average discharge current and maximum discharge current;
Continuous discharge performance and intermittent discharge performance;
The voltage fluctuation and discharge time in connection with minimum load and maximum load (discontinuous);
Environmental temperature range;
Maximum discharge current at the lowest operating temperature;
The shortest time when the voltage rises to the lower limit;
Storage time and storage conditions;
There are many kinds of lithium batteries, such as lithium-polyethylene, lithium-manganese dioxide, lithium-thionyl chloride, lithium-sulfur dioxide and lithium iodide batteries.
The output voltage of polyethylene battery is 2.8V, and its bulk density is relatively high. Cylindrical polyethylene battery uses spiral cathode and is sealed with artificial corrugated rubber. Although this structure is relatively solid, in some special circumstances, the battery life has not been exhausted, rubber sealing materials have been aging and damaged, resulting in leakage of active materials, causing accidents.
Compared with polyethylene lithium battery, LiMnO2 battery has more advantages in structure strength, bulk density, safety and output capacity, but its service life is only half of that of the former. The internal resistance of this battery is lower than that of other batteries, so it is very suitable for those devices which need high current continuous (or short-term) power supply.
The active substance of lithium iodide battery is entirely solid, so its safety is the best. The battery has an internal isolation layer, which can play a "self-healing" role when the shell is damaged by the impact of external forces. The biggest disadvantage of lithium iodide battery is that it has large internal resistance and is not suitable for small load equipment.
LiSO2 batteries are the most widely used batteries in military/aerospace fields. However, the bulk density of the battery is lower than that of LiMnO2 and polyethylene batteries, and its service life and bulk density are only half of that of LiSOCl2 batteries.
Among all lithium batteries, LiSOCl2 battery has the highest energy density and the longest service life, reaching 15-20 years. This kind of battery is especially suitable for equipment with small continuous supply current and large short supply current. Because of its long life and small self-discharge, the battery has excellent environmental resistance.
There are two common internal structures of LiSOCl2 batteries: spiral winding and cascade winding. In addition, the pulses plus battery also adopts a composite structure, i.e. a composite capacitor is added to the laminated winding structure.
In fact, all lithium batteries except LiSOCl2 batteries with cascade winding structure adopt spiral winding structure. The spiral winding structure can improve the load capacity, but compared with cascade winding structure, its capacity is smaller and self-discharge is more significant.
The stacked wound LiSOCl2 battery is especially suitable for equipment with low load current because of its high energy density, low self-discharge rate and service life of more than 10 years. The stacked winding structure has a large capacity and small volume, and can withstand the temperature range from - 55 to + 150 C. It also has good resistance to pressure, temperature and impact.
Composite Capacitance Battery with Short-term High Current Discharge
In recent years, equipment which needs short-term and high-current power supply have appeared, such as automobiles, GPS positioners, remote control monitors, measuring instruments and professional equipment in oceanography.
Usually, equipment requiring short-term high-current power supply has a relatively small continuous supply current (individual or even no), but its short-term power supply requirements often reach several amperes, lasting from a few seconds to 20 minutes.
The above requirements can be met by adding a composite capacitor to the stacked wound LiSOCl2 battery. Tadiran's pulses plus battery uses this technology. This composite lithium battery has been used by many remote monitoring devices. Some instruments that need to be used under harsh conditions require a battery life of up to 20 years, and ultimately this battery is also chosen.
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