1. Understanding of lithium batteries
The so-called lithium-ion battery refers to a secondary battery composed of two compounds that can reversibly intercalate and deintercalate lithium ions as positive and negative electrodes. People call this kind of lithium-ion battery with a unique mechanism that relies on the transfer of lithium ions between the positive and negative electrodes to complete the charging and discharging work of the battery. It is vividly called "rocking chair battery", commonly known as "lithium battery".
According to the appearance of lithium batteries: square lithium batteries (such as commonly used mobile phone battery cells) and cylindrical lithium batteries; according to lithium battery outsourcing materials: aluminum shell lithium batteries, steel shell lithium batteries, soft pack batteries; according to lithium battery Positive and negative electrode materials (additives) of the battery: Lithium oxide (LiCoO2) battery or lithium manganese oxide (LiMn2O4), lithium iron phosphate battery (LiFePO4), disposable manganese dioxide lithium battery; another method: lithium ion LIB , polymer PLB;
2. Lithium battery advantages
(1) The energy ratio is relatively high. It has a high storage energy density, which has reached 460-600Wh/kg, which is about 6-7 times that of lead-acid batteries;
(2) Long service life. The service life can reach more than 6 years, and the battery with lithium iron phosphate as the positive electrode is charged and discharged at 1C (100DOD), and it has a record of being able to use 10,000 times;
(3) The rated voltage is high (the working voltage of a single unit is 3.7V or 3.2V). Approximately equal to the series voltage of 3 nickel-cadmium or nickel-metal hydride rechargeable batteries, which is convenient to form a battery power pack;
(4) With high power capacity. Among them, the lithium iron phosphate lithium-ion battery used in electric vehicles can reach 15-30C charge and discharge capacity, which is convenient for high-intensity start-up acceleration;
(5) The self-discharge rate is very low. This is one of the most prominent advantages of this battery. At present, it can generally be achieved for less than 1/month, less than 1/20 of Ni-MH batteries; and there is no memory effect;
(6) Light weight. The weight of the same volume is about 1/5-6 of the lead-acid product;
(7) High and low temperature adaptability. It can be used in the environment of -20 ℃ - 60 ℃, and can be used in the environment of -45 ℃ after technical treatment;
(8) Green and environmental protection. Regardless of production, use and scrapping, it does not contain or produce any toxic and harmful heavy metal elements and substances such as lead, mercury, and cadmium.
(9) The production basically does not consume water. It is very beneficial to our country which is short of water.
3. Disadvantages of lithium batteries
(1) Lithium primary batteries have poor safety and may explode.
(2) The lithium-ion battery of lithium cobalt oxide cannot be discharged with a large current, and its safety is poor.
(3) Lithium-ion batteries need to protect the circuit to prevent the battery from being overcharged and discharged
(4) After a period of storage without use, some of its capacity will be permanently lost.
(5) The production requirements are high and the cost is high.
4. Lithium battery technical terms
(1) Battery capacity: The capacity of the battery is determined by the amount of active material in the battery, usually expressed in milliampere hours (mAh) or (Ah). For example, 1 000 mAh can be discharged with a current of 1 A for 1 h, which converts to a charge of about 3600 C.
(2) Nominal voltage: The potential difference between the positive and negative poles of the battery is called the nominal voltage of the battery. The nominal voltage is determined by the electrode potential of the plate material and the concentration of the internal electrolyte. Under normal circumstances, the unit lithium ion battery is 3.6V, and the lithium iron phosphate battery is 3.2V.
(3) End-of-charge voltage: When the rechargeable battery is fully charged, the active material on the plate has reached saturation, and the voltage of the battery will not rise when charging is continued. The voltage at this time is called the end-of-charge voltage. The lithium ion battery is 4.2 V, and the lithium iron phosphate battery is 3.55-3.60 V.
(4) End-of-discharge voltage: The end-of-discharge voltage refers to the minimum voltage allowed when the battery is discharged. The end-of-discharge voltage is related to the discharge rate. Generally speaking, the unit lithium-ion battery is 2.7 V, and the lithium iron phosphate battery is 2.0-2.5 V.
(5) Internal resistance of the battery: The internal resistance of the battery is determined by the resistance of the plate and the impedance of the ion flow. During the charging and discharging process, the resistance of the plate is constant, but the impedance of the ion flow will vary with the concentration of the electrolyte and the charge changes with the increase or decrease of ions. Generally speaking, the internal resistance of the unit lithium-ion battery is 80~100 mΩ, and the lithium iron phosphate battery is <20mΩ.
(6) Self-discharge rate: refers to the percentage of the total capacity of the battery that automatically loses power when the battery is not in use for a period of time. Generally, at room temperature, the self-discharge rate of lithium-ion batteries is only 5% to 8% per month.