30-second summary
Lithium-ion Battery
A lithium-ion battery, also known as the Li-ion battery, is a type of secondary (rechargeable) battery composed of cells in which lithium ions move from the anode through an electrolyte to the cathode during discharge and back when charging.
There are several specific advantages to lithium-ion batteries. The most important advantages are their high cell voltage, high energy density, and no memory effect.
Lithium-ion batteries are used in many laptop computer batteries, cordless power tools, certain electric cars, electric kick scooters, most e-bikes, portable power banks, and LED flashlights.
The overall reaction during discharge is:
C6Li + CoO2 ⇄ C6 + LiCoO2
Lithium-ion Battery
A lithium-ion battery, also known as the Li-ion battery, is a type of secondary (rechargeable) battery composed of cells in which lithium ions move from the anode through an electrolyte to the cathode during discharge and back when charging.
The cathode is made of a composite material (an intercalated lithium compound) and defines the name of the Li-ion battery cell. The anode is usually made out of porous lithiated graphite. The electrolyte can be liquid, polymer, or solid. The separator is porous to enable the transport of lithium ions and prevents the cell from short-circuiting and thermal runaway.
Chemistry, performance, cost, and safety characteristics vary across types of lithium-ion batteries. Handheld electronics mostly use lithium polymer batteries (with a polymer gel as electrolyte), a lithium cobalt oxide (LiCoO2) cathode material, and a graphite anode, which offer high energy density.
Li-ion batteries, in general, have a high energy density, no memory effect, and low self-discharge. One of the most common types of cells is 18650 battery, which is used in many laptop computer batteries, cordless power tools, certain electric cars, electric kick scooters, most e-bikes, portable power banks, and LED flashlights. The nominal voltage is 3.7 V.
Note that non-rechargeable primary lithium batteries (like lithium button cells CR2032 3V) must be distinguished from secondary lithium-ion or lithium-polymer, which are rechargeable batteries. Primary lithium batteries contain metallic lithium, which lithium-ion batteries do not.
Characteristics of Lithium-ion Batteries
To compare and understand the capability of each battery, some important parameters are characteristic of each battery, also within a type of battery. These parameters are a reference when a battery is needed, and specific qualities are required since batteries are used in all types of devices and for infinite purposes.
Cell Voltage
The voltage of electric batteries is created by the potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction.
Almost all lithium-ion batteries work at 3.8 volts. In order to make current flow from the charger to the battery, there must be a potential difference. Therefore battery chargers or USBs for almost all smartphones provide a voltage of 5V.
Cut-off Voltage
The cut-off voltage is the minimum allowable voltage. It is this voltage that generally defines the “empty” state of the battery.
Li-ion battery has a higher cut-off voltage of around 3.2 V. Its nominal voltage is between 3.6 to 3.8 V; its maximum charging voltage can go to 4– 4.2 V max. The Li‑ion can be discharged to 3V and lower; however, with a discharge to 3.3V (at room temperature), about 92–98% of the capacity is used. Importantly, particularly in the case of lithium-ion batteries used in the vast majority of portable electronics today, a voltage cut-off below 3.2V can lead to chemical instability in the cell, resulting in a reduced battery lifetime.
Capacity
The coulometric capacity is the total Amp-hours available when the battery is discharged at a certain discharge current from 100% SOC to the cut-off voltage.
Almost all lithium-ion batteries work at 3.8 volts. Lithium-ion 18650 batteries generally have capacity ratings from 2,300 to 3,600 mAh.
C-rate of Battery
C-rate is used to express how fast a battery is discharged or charged relative to its maximum capacity. It has units h−1. A 1C rate means that the discharge current will discharge the entire battery in 1 hour.
Most li-ion batteries can only withstand a maximum temperature of 60°C and are recommended to be charged at a maximum of 45°C under a 0.5C charge rate. C rating for a 18650 battery is usually 1C, meaning we can consume a maximum of 2.85A from the battery.
Self-discharge
Batteries gradually self-discharge even if not connected and delivering current. This is due to non-current-producing “side” chemical reactions that occur within the cell even when no load is applied.
Li-ion rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5–2% per month. The rate increases with temperature and state of charge.
Degradation
Some degradation of rechargeable batteries occurs on each charge-discharge cycle. Degradation usually occurs because electrolyte migrates away from the electrodes or because active material detaches from the electrodes.
Most modern 18650 lithium-ion batteries, which are common for laptop batteries, have a typical cycle life of 300 – 500 (charge, discharge cycles). LFP batteries offer cycle life, which ranges from 2,700 to more than 10,000 cycles depending on conditions.
Depth of Discharge
Depth of discharge is a measure of how much energy has been withdrawn from a battery and is expressed as a percentage of full capacity. For example, a 100 Ah battery from which 40 Ah has been withdrawn has undergone a 40% depth of discharge (DOD).
For lithium-ion batteries, the cycle life of a cell strongly depends on the DOD. The loss of lithium ions and active electrode material is higher for larger DOD cycles. At high DODs, additional degradation mechanisms can occur, resulting in the decomposition and dissolution of cathode material and capacity fading.
