Secondary batteries, also known as rechargeable battery, refers to the battery that can be activated by charging after the battery discharge and continue to use. The primary principle used by secondary batteries is the reversibility of chemical reactions. When the active substance in the battery is converted into electricity by a chemical reaction, the chemical system can be repaired by using electricity, and then the chemical reaction is converted into electricity again, so it is called a secondary battery.
- Lithium ion battery: Lithium-ion batteries are secondary batteries that rely on lithium ions moving between positive and negative electrodes. During the charging and discharging process, lithium ions inserts and disinserts back and forth between the two electrodes. When charging, lithium ions are disinserted from the positive electrode and inserted into the negative electrode through electrolyte, which is in a lithium-rich state. The positive electrode of lithium ion battery can be lithium manganese, lithium cobalt or lithium nickel manganese cobalt. The conducting collector uses electrolytic aluminum foil with a thickness of 10-20 microns. The membrane of a lithium-ion battery is a specially shaped polymer film with a microporous structure that allows lithium ions to pass freely, while electrons cannot. In addition, the cathode active material of lithium ion battery is graphite, and the conductive fluid collector uses electrolytic copper foil with thickness of 7-15 microns. The organic electrolyte of lithium ion battery is carbonate solvent with lithium hexafluorophosphate dissolved. The battery shell of lithium ion battery is divided into steel shell, aluminum shell, nickel plated iron shell, aluminum plastic film and others.
Figure 1. Working principle and main components of a lithium-ion battery.
- Ni-MH battery: Ni-MH battery can be divided into high voltage Ni-MH battery and low voltage Ni-MH battery, which is a mature product. The positive active substance of Ni-MH battery is Ni(OH)2 and negative active substance is metal hydride. Moreover, the electrolyte used by Ni-MH battery is 6mol/L potassium hydroxide solution. There are sintering type, pulping type, foamed nickel type, fiber nickel type and infiltration type for the active substance to form electrode sheet. The electrodes prepared by different processes have great differences in capacity and discharge performance. Therefore, the technological conditions need careful selection in the production of batteries according to the service conditions.
- Others: In addition to the above mentioned, secondary batteries also include other types, such as Ni-Ca battery, lead acid battery, lithium-sulfur battery and others. Ni-Ca battery can be charged and discharged more than 500 times and are economical and durable. Moreover, compared with other types of batteries, Ni-Ca battery can withstand overcharge or over discharge. Ni-Ca battery is a very ideal DC power supply battery because of its low internal resistance, which can be charged quickly and provide a large current for the load. A lead-acid battery is a type of battery in which the electrodes are mainly made of lead and its oxide and the electrolyte is a solution of sulfuric acid. In the discharge state of lead-acid battery, the main component of the positive electrode is lead dioxide, and the main component of the negative electrode is lead. In charge state, the main components of both anode and cathode are lead sulfate. In addition, lithium-sulfur battery are a new type of battery with high energy density emerging in recent years.
Figure 2. An example of lithium-sulfur battery.
- M. A. Navarra, K. Fujimura, M. Sgambetterra, A. Tsurumaki, S. Panero, N. Nakamura, H. Ohno, B. Scrosati, New Ether-functionalized Morpholinium- and Piperidinium-based Ionic Liquids as Electrolyte Components in Lithium and Lithium–Ion Batteries [J]. Chemsuschem, 2017.