Lithium-ion batteries generally use lithium alloy metal oxides as the positive electrode material, graphite as the negative electrode material, and a non-aqueous electrolyte. Almost all the mobile phones we use daily employ lithium batteries, and most of the power sources in the currently popular electric vehicles are lithium iron phosphate batteries. So how are lithium batteries charged and discharged?
First, let's understand the structure of lithium batteries. Lithium batteries are generally composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The lithium batteries we commonly see in mobile phones are square, while the batteries in electric vehicle battery packs are generally round. Other shapes include stacked and wound types.
The four contacts on a typical mobile phone battery, besides the positive and negative terminals, are simply used to detect (or monitor) various information about the mobile phone battery.
The positive electrode of a lithium battery is generally lithium manganese oxide or lithium cobalt oxide, or lithium nickel cobalt manganese oxide. Electric bicycles commonly use lithium nickel cobalt manganese oxide (commonly known as ternary) or ternary + a small amount of lithium manganese oxide. The negative electrode is generally graphite, or carbon with a similar graphite structure. The separator between the positive and negative electrodes is a specially shaped polymer film with pore size that allows good ion permeability while also having electronic insulation, meaning that lithium ions can pass through freely, but electrons cannot.
The electrolyte plays a role in transporting charge between the positive and negative electrodes. It is generally a carbonate solvent containing dissolved lithium hexafluorophosphate, while a gel electrolyte is used for polymers.
When a lithium battery is charged, lithium ions are released from the positive electrode. The lithium ions pass through the electrolyte and the membrane, move to the negative electrode, and combine with electrons in the negative electrode. At this time, the chemical reaction that occurs at the positive electrode is LiCoO2=Li(1-x)CoO2+xLi++xe-(electrons), and the chemical reaction that occurs at the negative electrode is 6C+xLi++xe- = LixC6.
When a lithium battery discharges, the movement of lithium ions is exactly the opposite. Lithium ions enter the electrolyte from the negative electrode, pass through the separator, and finally reach the positive electrode, while electrons move from the negative electrode to the positive electrode from the external circuit (the direction of electron movement is opposite to the direction of current) and combine with the lithium ions at the positive electrode. This process allows the lithium battery to output electrical energy.
