Li-ion Battery Basic

Bi-Cell

A bi-cell is a cell, the basic unit of a battery, where multiple electrodes and separators are combined. It has a laminated structure with the same electrodes at the sides, like in cathode/separator/anode/separator/cathode or anode/separator/cathode/separator/anode.

Cell, modules, and battery packs

A high-voltage battery system in hybrid and electric vehicles comprises individual cells, modules, and packs configured in series and parallel arrangements. A cell represents the smallest packaged unit of a battery, typically providing a voltage ranging from one to six volts. A module, on the other hand, comprises several cells connected either in series or in parallel. Finally, a battery pack is formed by interconnecting these modules, once more, in series or parallel configurations.

Current Collector

A thin layer of about 10μm planted in the battery. It helps ions travel during charging and discharging

Active materials

Active materials in a battery are the materials that participate in the electrochemical charge and discharge reaction. These materials include: Electrolyte: A chemical paste that separates the anode and cathode. It also transforms chemical energy into electrical energy. Positive and negative electrodes: These include the anode and cathode. Other components of a battery include separators and current collectors. Active materials react chemically to produce electrical energy when the cell discharges. During the charging process, the material returns to its original state. Anode active materials (AAM) are usually made from carbon-based materials like graphite, silicon, or a combination of both. Graphite is the most commonly used anode material because of its low cost, high electrical conductivity, and stable structure.

Lithium-ion - LFP cathode

Another alternative for the cathode of the Li-ion batteries is the use of lithium iron phosphate. Although the performance of this kind of battery is generally lower than the NMC type, it is preferred by some manufacturers because of its higher service life and the cheaper and more common materials used. The specific energy density is lower here because of two main factors.

Battery Classifications

Batteries, even those of the same chemical composition, can vary significantly. The primary trade-off in battery design centers around power and energy capabilities. Batteries can either excel in high power or high energy capacity, but it is challenging to optimize both simultaneously. Manufacturers frequently categorize batteries based on these distinctions. Another commonly used classification is "High Durability," denoting battery chemistries that have been adjusted to extend battery lifespan at the cost of power and energy output.

Current

Current is the flow of electrical charges passing through a conductor. For instance, a current of 1 ampere corresponds to the flow of 6 trillion electrons per second. The electric current can be seen as the flow rate in a pipe. The rated current of a battery corresponds to the maximum current that it can provide continuously.

Dendrites

Dendrites are tree-shaped crystals formed as lithium ions deposit on the Surface of the anode during the charging of a lithium-ion battery. Using lithium-ion batteries, "lithium-crystals" that look like sharp tree branches could deposit on the anode surface during charging. Dendrites are considered one of the main reasons for undermining the life and stability of lithium-ion batteries. Dendrites on the electrode of a battery could reduce the energy efficiency and lifespan of the battery as they block the smooth movement of lithium ions that travel actively between the cathode and anode.

Secondary and Primary Cells

Despite the terminology, batteries used in hybrid, plug-in, and electric vehicles are categorized as secondary batteries. Primary batteries are those that cannot be recharged, whereas secondary batteries are rechargeable.

Cathode Active Materials

The cathode active materials hold lithium ions and send them to the anode as a battery charge. Cathode active materials are responsible for battery capacity and output. To make one, different materials are combined considering their properties and needs, resulting in LCO (Lithium cobalt oxide), LMO (Lithium manganese oxide), NCM (Lithium nickel cobalt manganese oxide), NCA (Lithium nickel cobalt aluminum oxides), and LFP (Lithium iron phosphate).

Anode Active Materials

When batteries discharge, the anode active materials in the anode store the lithium ions delivered from the cathode and release them to produce energy. Graphite is the most widely used ingredient for anode active materials since it offers stability when lithium ions travel (charging and discharging). These days, energy-dense silicon is increasingly replacing graphite to improve the performance of the anode.