With the development of society, human beings need more and more energy. Traditional fossil energy can not only be regenerated, but excessive use has aggravated the deterioration of the environment. Although the current energy structure is basically based on fossil fuels, people have also learned the importance of making full use of renewable energy such as wind and solar energy. However, these energy sources are not continuous and require an energy storage device. The battery is very suitable as a device for storing electrical energy in the form of chemical energy. In particular, secondary batteries are used in modern mobile phones, watches, and even automobiles. In the development of batteries for decades, the performance is gradually optimized, and the high specific energy is the goal that people are constantly pursuing. Since lithium has a small specific gravity (M=6.94g/mol) and extremely low electrode potential (standard electrode potential -3.045V) in all metals, it is a metal with extremely high energy density, and the lithium battery system can theoretically obtain the largest. Energy density, so it logically entered the researcher's field of vision.
Lithium batteries are further divided into lithium primary batteries (also known as lithium primary batteries) and lithium secondary batteries (lithium rechargeable batteries), and were first proposed by Gilbert N. Lewis in 1912, which led people's attention to live metal batteries. . On the basis of lithium secondary batteries, lithium ion batteries have been developed. The general development process is shown in Figure 1.
Li-MnO2 battery (lithium primary battery) Li-MnO2 battery is an organic electrolyte battery that is widely used in lithium batteries. It is generally made of button type or cylindrical shape. The open circuit voltage is 3.5V and the load voltage is 2.8V. The energy can reach 200W·h/kg and 500W·h/L. The battery has a storage life of more than 10 years at normal temperature, and no gas is released during storage and discharge, and the safety performance is good.
Negative reaction: Li-e-→Li+
Positive electrode reaction: MnO2+Li++e-→MnOOLi
Battery reaction: Li+MnO2→MnOOLi
According to the above reaction, Li-MnO2 discharges Li + into the electrolyte solution, and the positive manganese dioxide is electronically reduced to trivalent manganese, and lithium ions enter the manganese dioxide lattice to form MnO 2 (Li), that is, MnOOLi. This type of battery is mainly used for low rate discharge. Its energy ratio is about 5 to 7 times that of a lead-acid battery. During the storage and discharge of the battery, no gas is released, and the self-discharge is small, and the internal pressure of the battery is not increased due to decomposition of the active material. The small and medium-sized battery is suitable for power supply of small electronic computers, cameras and small communication machines. The large-capacity battery is suitable for applications requiring high battery energy and long service life, so it can be used as an ideal power source for military applications.
Li-SOCl2 battery (lithium primary battery)
Li-SOCl2 battery is a relatively mature organic electrolyte battery. The open circuit voltage is as high as 3.6 ~ 3.7V, and the voltage is stable, the load voltage accuracy is high, and there is a higher specific energy. Table 1 gives a comparison of the cost of active materials for some commonly used small battery series. It can be seen that Li-SOCl2 batteries are the lowest cost among commonly used batteries.
The electrochemical expression of Li-SOCl2 battery is: (-)Li∣LiAlCl4-SOCl2∣C(+)
The electrolyte was a SOCl2 solution of LiAlCl4. SOCl2 is a solvent for the electrolyte and a positive electrode active material. Battery reaction:
The sulfur dioxide of the discharge product is partially dissolved in SOCl2, and a large amount of sulfur is precipitated and deposited in the positive carbon black, and LiCl is incompatible.
When the negative electrode lithium of this battery is in contact with SOCl2, the following reaction occurs.
Since the product LiCl forms a dense protective film which hinders the progress of the reaction, and since it is also a solid electrolyte membrane, ions are allowed to pass, so that the normal anode dissolution of the lithium electrode is not hindered.
However, there are two prominent problems with SOCl2 batteries, namely "voltage hysteresis" and "security issues." The voltage hysteresis is due to the production of LiCl, which covers the surface of the lithium anode in the form of a thin film, although it can prevent the battery from self-discharging, but causes a voltage lag. In addition, the longer the storage time, the higher the storage temperature, the thicker the film, and the more pronounced the hysteresis.
When the SOCl2 battery is short-circuited, it will cause a thermal reaction between Li and S:
Li2S reacts violently with SOCl2 at 145 degrees, causing an explosion.
Another cause of the explosion is that lithium deposited on the positive electrode forms dendrites, causing a short circuit. Li reacts with S, or SO2 can also react at the negative electrode, eventually producing Cl2O, a very unstable explosive substance.
Advantages and disadvantages of lithium batteries:
1. The energy is relatively high. With high storage energy density, it has reached 460-600Wh/kg, which is about 6-7 times of lead-acid battery;
2. It has a long service life and can last for more than 6 years. Lithium iron phosphate is a positive battery 1C (100% DOD) charge and discharge, and can be used for 10,000 times;
3. High rated voltage (single working voltage is 3.7V or 3.2V), which is equal to the series voltage of 3 nickel-cadmium or nickel-hydrogen rechargeable batteries, which is convenient for battery power packs; lithium battery can pass a new type of lithium battery regulator Technology, the voltage is adjusted to 3.0V, suitable for the use of small appliances;
4. With high power bearing capacity, lithium iron phosphate lithium ion battery for electric vehicles can achieve 15-30C charge and discharge capacity, which is convenient for high-intensity start-up acceleration;
5. The self-discharge rate is very low, which is one of the most outstanding advantages of the battery, generally can be 1% / month or less, less than 1 / 20 of the nickel-hydrogen battery;
6. Light weight, the weight in the same volume is about 1/6-1/5 of the lead acid product;
7. High temperature and low adaptability, can be used in the environment of -20 ° C - 60 ° C, after the process treatment, can be used in -45 ° C environment;
8. Green, no matter whether it is produced, used or scrapped, it does not contain any toxic and harmful heavy metal elements and substances such as lead, mercury and cadmium.
9. Production basically does not consume water, which is very beneficial for China that lacks water. Specific energy refers to the energy per unit weight or unit volume. The specific energy is expressed in Wh/kg or Wh/L. Wh is the unit of energy, W is watt, h is hour; kg is kilogram (weight unit), and L is liter (volume unit).
1. Lithium primary batteries have poor safety and there is a danger of explosion.
2. Lithium ion batteries of lithium cobalt oxide cannot be discharged at a large current, are expensive, and have poor safety.
3. Lithium-ion batteries need to protect the line to prevent the battery from being overcharged and discharged.
4. The production requirements are high and the cost is high.
5. There are restrictions on the use conditions, and the use of high and low temperature is dangerous.