I. Battery rated capacity and rated voltage
1. Rated capacity
The minimum capacity a battery should be able to discharge under the specified design conditions (such as temperature, discharge rate, and termination voltage), expressed in amperes per hour (A/h), is represented by the symbol C. Capacity is significantly affected by the discharge rate, so the discharge rate is often indicated by an Arabic numeral in the lower right corner of the letter C, such as C20=50, which indicates a capacity of 50 A/h at a discharge rate of 20. The theoretical capacity of a battery can be precisely calculated based on the amount of active material used in the battery reaction formula and the electrochemical equivalent of the active material calculated according to Faraday's law. Due to potential side reactions in the battery and special design requirements, the actual capacity of a battery is often lower than its theoretical capacity.
2. Rated voltage
The typical operating voltage of a battery at room temperature, also known as the nominal voltage, serves as a reference when selecting different types of batteries. The actual operating voltage of a battery varies depending on usage conditions and is equal to the difference in equilibrium electrode potential between the positive and negative electrodes. It depends only on the type of active material in the electrodes, and not on the quantity of active material. Battery voltage is essentially a direct current voltage, but under certain special conditions, phase transitions in metal crystals or certain phase-forming films caused by electrode reactions can lead to minute voltage fluctuations; this phenomenon is called noise. The amplitude of the fluctuations is small, but the frequency range is wide, thus distinguishing it from self-excited noise in a circuit.
II. What are the differences between dry cell batteries and lithium batteries?
1. Dry cell batteries
Dry cell batteries are a type of voltaic cell that uses an absorbent (such as sawdust or gelatin) to make the contents a non-leaking paste. They are commonly used as power sources for flashlights, radios, and other electronic devices. After years of development, my country has made breakthroughs in dry cell battery technology, particularly in terms of specific energy, cycle life, and adaptability to high and low temperatures.
A dry cell is a chemical battery that generates direct current using a paste-like electrolyte (wet cells use a liquid electrolyte). Dry cells are disposable batteries and are the most common and portable batteries used in daily life. They can be used in many electrical appliances.
2. Lithium batteries
Lithium-ion batteries are a type of battery that uses lithium metal or lithium alloys as the positive/negative electrode material and a non-aqueous electrolyte solution. The earliest lithium metal battery was proposed and studied by Gilbert N. Lewis in 1912. In the 1970s, MS Whittingham proposed and began researching lithium-ion batteries. Due to the highly reactive chemical properties of lithium metal, its processing, storage, and use require very strict environmental controls. With the development of science and technology, lithium-ion batteries have become the mainstream technology.
Lithium batteries can be broadly classified into two categories: lithium metal batteries and lithium-ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth generation of rechargeable batteries, lithium metal batteries, was developed in 1996. They offer superior safety, specific capacity, self-discharge rate, and price-performance ratio compared to lithium-ion batteries. Due to their high technological requirements, only companies in a few countries produce lithium metal batteries.
3. The difference between dry cell batteries and lithium batteries
The commonly used AA and AAA batteries are dry cell batteries, while button batteries and mobile phone batteries are lithium batteries. The differences between the two are as follows:
a. Different materials
• Lithium-ion batteries: These are batteries that use manganese dioxide as the positive electrode material, lithium metal as the negative electrode material, and a non-aqueous electrolyte solution.
• Dry cell battery: A type of voltaic cell that uses an absorbent (such as sawdust or gelatin) to make the contents into a paste that does not spill out.
b. Different principles
• Lithium-ion batteries: They employ a spiral winding structure, with a very fine and highly permeable polyethylene film separating the positive and negative electrodes.
Dry cell batteries use a carbon rod as the positive electrode and a zinc canister as the negative electrode to convert chemical energy into electrical energy to supply the external circuit. In the chemical reaction, zinc is more reactive than manganese; zinc loses electrons and is oxidized, while manganese gains electrons and is reduced.
c. Different uses
• Lithium batteries: widely used in mobile phones, laptops, power tools, electric vehicles, backup power for streetlights, navigation lights, and small household appliances.
Dry cell batteries: Suitable for flashlights, transistor radios, tape recorders, cameras, electronic clocks, toys, etc., and also for various sectors of the national economy such as national defense, scientific research, telecommunications, navigation, aviation, and medicine.
