Battery Cell Quality Testing 350

18650

A standardized cylindrical battery cell with a diameter of 0.71 in. (18 mm) and a length of 2.56 in. (65 mm). 18650 battery cells are the most common type of lithium-ion cell.

AA

A standardized cylindrical battery cell with a diameter of 0.57 in. (14.51 mm) and a length of 1.99 in. (50.5 mm). AA battery cells are typically alkaline cells that output about 1.5 V.

alkaline cells

A type of battery cell that uses manganese dioxide in the cathode and a zinc anode in an alkaline electrolyte mixture. Alkaline cells are primary cells, meaning they must be discarded after one full discharge.

alternating current

AC. A flow of electricity that reverses direction at regularly recurring intervals of time. Alternating current is used in ACIR and EIS testing processes.

alternating current internal resistance

ACIR. The opposition to current that is detected when a low-amperage alternating current (AC) is applied to a battery cell circuit at a single frequency. Alternating current internal resistance actually tests battery impedance, or total electronic resistance, and is the most common type of resistance test.

amperage

A measurement that indicates the amount of current flowing in a circuit. Amperage is measured in amperes or amps.

anode

An electrode with a negative charge. In a battery, the anode sends current to the cathode.

area

The amount of space contained on a surface or within an enclosed object. Area is typically measured in square units.

basis weight

The mass per unit of area, which is used to create electrodes of a standard size. Basis weight is often measured in grams per square meter (g/m²)

burrs

A rough edge on a metal part created by cutting or machining. Burrs on battery electrodes can pierce the separator and lead to short circuits.

calendering

The process of compressing dried electrode coatings with heavy rollers to create an even thickness and improve atomic structure. Calendering is the fifth major step in battery cell electrode manufacturing.

cameras

A device used to capture still images, such as photographs, or moving images, such as videos. Cameras can capture surface data from in-process battery cell components and completed cells to detect surface anomalies.

cans

A protective metal cover that surrounds some battery cells. A can is typically cylindrical or prismatic and helps prevent cell swelling, bending, and damage.

capacity

The amount of energy a battery can provide. Capacity depends on battery materials and volume.

capacity test

A measurement of the time it takes for a fully charged battery to fully discharge. A capacity test, or load test, can help determine how different loads, operating conditions, and environmental conditions can affect battery capacity.

cathode

An electrode with a positive charge. In a battery, the cathode receives current from the anode.

cells

A single unit of a battery. Cells contain a cathode, an anode, and an electrolyte solution that react chemically to create electrical energy.

computer vision

A machine learning capability that enables an artificial intelligence to recognize visual patterns through a camera or on a screen. Computer vision can help manufacturers automate visual inspection tasks for quality control.

conformal coating

A process of coating a part, component, or device using spraying, dipping, or similar method. Conformal coatings are applied directly to the component's surface and conform to its shape.

corrosion

A process by which a material gradually degrades or wears away. Corrosion typically occurs when a material is exposed to atmosphere, moisture, or other substances.

current collector

An exceedingly thin sheet of metal used to provide structure and conductivity to a battery cell electrode. Current collector foils for lithium-ion battery cells are usually copper or aluminum.

cutting

An electrode cutting process that forms daughter rolls into the correct size and shape for cell assembly. Cutting, like slitting and notching, can be performed by laser cutting or mechanical cutting methods.

cylindrical

A type of rechargeable battery cell enclosed in a rigid, tube-shaped can. Cylindrical cells provide more power than prismatic cells and are common in high-performance applications.

delta OCV rate

A measurement of a battery's voltage drop over time when it is a rest. The Delta OCV rate method is used to examine a battery's self-discharge rate during end-of-line testing.

dielectric

Having little or no ability to conduct electricity. Dielectric materials are often used in protective coatings for electronic components.

digital multimeter

DMM. A device that can measure voltage, current, or resistance. A digital multimeter is the most versatile and common meter used today for electrical maintenance.

dimensions

A measurement of space, especially length, width, and height. Dimensions of battery cells and cell components are typically standardized and directly affect cell performance.

direct current

DC. Current that travels in one direction. Direct current does not reverse the direction of flow.

direct current internal resistance

DCIR. The opposition to current that is detected when a high-amperage direct current (DC) is applied to a battery circuit. Direct current internal resistance testing only tests resistor components in a battery circuit but provides more accurate information about a battery cell under normal operating conditions.

discharge rate

The speed at which a battery goes from fully charged to fully discharged. Discharge rates vary based on the type of battery, as well as load, temperature, and other operating conditions.

dry film thickness

The measured thickness of a coating material after it dries on the applied surface. Dry film thickness can be measured with a film thickness gauge or using automated measurement tools.

drying

The process of evaporating any liquid slurry ingredients or water from the electrode coating. Drying is the fourth major step in battery cell electrode manufacturing and cures active materials and binders to the current collector.

electric vehicle

EVs. A vehicle that is fully or partially propelled by an electric motor that draws its power from a battery. Electric vehicles, including hybrid electric vehicles, require high-energy, lightweight, rechargeable batteries.

electrical faults

Any condition that causes an abnormal flow of current in a circuit. Common types of electrical faults include open circuit faults and short circuit faults.

Electrochemical impedance spectroscopy

EIS. A testing method that measures opposition to current in a battery cell. Electrochemical impedance spectroscopy uses alternating current (AC) to measure impedance, similar to ACIR testing, but uses a range of AC frequencies.

electrode

A component within a circuit that conducts electricity. Electrodes have a positive or negative charge.

electrode tabs

A small strip of uncoated current collector foil that enables electrodes to be welded to each other and to other components in the finished battery. Welded tabs must be inspected to ensure they are free of spatter and meet weld specifications.

electrolyte

A conductive liquid, gel, ceramic, or other solid containing an acid, an alkaline, or a salt. The electrolyte in a battery connects the two electrodes.

electrolyte leakage testing

A vacuum chamber testing method that removes pressure from a vacuum chamber to detect leaking electrolyte vapor. Electrolyte leakage testing is typically used on all cell types near the end of cell production.

electronic resistance

Resistance to the flow of electricity caused by a battery cell's physical components. Electronic resistance expresses the resistance of the battery cell's resistors, protective covering, electrodes, and other components.

electrostatic discharge

ESD. A release of static electricity that occurs when two objects with different charges come into contact. Electrostatic discharge can harm equipment and technicians.

ellipsometer

A nondestructive testing device that uses reflected light to measure wet and dry film thickness. Ellipsometers can be used to determine dielectric coating film thickness.

energy density

The amount of energy that a battery can supply per unit of volume. Energy density is measured in watt-hours per liter (Wh/l).

film thickness gauge

A measurement device that measures dry film coating thickness when pressed into the coating material. Film thickness gauges are used to manually measure coating thickness.

foil enclosures

A battery cell container made from an exceedingly thin sheet of metal. A foil enclosure encases a pouch cell battery.

force tensiometers

An instrument that measures the surface tension of liquids. Force tensiometers can be used to determine if an electrode slurry coating is the correct thickness.

frequency

A measurement of the number of complete AC cycles in one second. Frequency is measured in hertz (Hz).

geometry

The measurement, properties, and relationships of the lines and points of an object that make up its shape. Geometry is used when measuring and designing parts.

helium

A light, colorless, nonflammable inert gas that is much lighter than air. Helium is forced into a battery cell within a vacuum chamber during helium leak testing.

helium leak testing

A vacuum chamber testing method that injects helium into a battery cell or other device to detect leakage. Helium leak testing is typically used on cylindrical and prismatic cells before adding the electrolyte.

IEEE 1625

A standard for rechargeable battery production that recommends inspections for burrs and is developed by the Institute of Electrical and Electronics Engineers (IEEE). IEEE 1625 is most specifically related to laptop batteries.

impedance

A measure of reactance and resistance in an alternating current (AC) circuit. Impedance is calculated to measure the total opposition to current flow in an AC circuit and is sometimes called total electronic resistance.

in-line inspection

The examination of a part during the production process. In-line inspection is typically required for efficient battery cell manufacturing processes.

Institute of Electrical and Electronics Engineers

IEEE. An international organization composed of engineers, scientists, and students in the electrical field. The Institute of Electrical and Electronics Engineers sets standards for the electronics and computer industries.

internal resistance

IR. The natural ohmic value of the electrodes in a battery. Internal resistance causes a battery's voltage to be lower with a load than without a load and to decrease over the course of discharge.

International Electrotechnical Commission

IEC. An international organization that prepares and publishes standards for electrical, electronic, and related technologies. The International Electrotechnical Commission is one organization that develops standards for battery safety, testing, and inspection.

ionic resistance

Resistance to the flow of electricity caused by a battery's chemical properties. Ionic resistance expresses the resistance of the battery's electrolyte, separator material, and other chemical resistance.

ions

A charged atom. Ions may lose their charges if they gain or lose electrons.

key quality characteristics

A measurable characteristic of a product that greatly impacts customer satisfaction. Monitoring key quality characteristics, such as battery cell chemistry, helps help manufacturers develop cell quality standards.

kilohertz

kHz. An alternating current frequency rating equal to 1000 hertz, or 1000 cycles per second. Kilohertz express how many times an alternating frequency current cycles per second.

laser welding

A welding process that uses a laser to heat base materials and create a weld. Laser welding is often used to connect battery tabs and seal battery cans or pouches.

Li-ion cell

Lithium-ion cell. A type of battery cell that uses lithium in the cathode and usually graphite as the anode. Li-ion cells are rechargeable cells, or secondary cells, meaning they can be recharged and discharged for multiple cycles before they must be discarded.

lithium-ion cells

Li-ion cells. A type of battery cell that uses lithium in the cathode and usually graphite as the anode. Lithium-ion cells are rechargeable cells, or secondary cells, meaning they can be recharged and discharged for multiple cycles before they must be discarded.

load

A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads are used to test battery's function when it is in operation.

load test

A measurement of the time it takes for a fully charged battery to fully discharge. A load test, or capacity test, can help determine how different loads, operating conditions, and environmental conditions can affect battery capacity.

mass

The amount of matter contained within an object. Mass describes an object's inertia independent of gravity and is measured in kilograms (kg).

mass loss

The process of a cell ejecting evaporated electrolyte and particulate matter from a battery due to overheating. Mass loss occurs due to thermal runaway.

mass spectrometer

A device that uses sensors to detect the presence and quantity of matter. Mass spectrometers are used in both helium leak testing and electrolyte leak testing.

matter

A substance that exists as a solid, liquid, or gas. Matter has both mass and volume.

microns

μm. A metric unit of measurement equal to one thousandth of a millimeter (0.000039 inches). Microns are used to measure electrode thickness.

mixing

The process of blending active materials, solvents, and other inactive materials to form an electrode slurry. Mixing is the second major step in battery cell electrode manufacturing, after pre-manufacturing.

nominal voltage

The maximum amount of voltage a battery can safely provide when fully charged. Nominal voltage is set by the manufacturer.

nondestructive testing

NDT. A category of inspection processes that evaluate a part's properties and performance using methods that do not damage or permanently alter the part. Nondestructive testing methods include visual testing, liquid penetrant testing, magnetic particle testing, eddy current testing, ultrasonic testing, and radiographic testing.

open circuit voltage

The amount of energy, in volts, that is currently available in a battery that is not connected to a load or charger. Open circuit voltage readings help determine a batterys self-discharge rate, state of charge, and state of health.

optical sensors

A type of sensor that detects the presence of an object through the use of a beam of light. Optical sensors can be used to inspect shape, thickness, or other physical properties to detect foreign objects and part anomalies.

particles

An extremely small portion of a material. Particles include everything from dust to metal powder.

pouch cells

A type of rechargeable battery cell enclosed in a flexible, multi-layer foil wrapper. Pouch cells are flexible, lightweight, and most common in portable devices like laptops and smartphones.

pressure

The amount of force applied on an object. Pressure is calculated by dividing force by the area.

primary

A battery that cannot be recharged. Primary cell batteries are usually dry-cell batteries.

prismatic

A type of rechargeable battery cell enclosed in a rigid, rectangular can. Prismatic cells are easy to stack and store more energy per cell than cylindrical cells.

radiography

A nondestructive inspection method that uses electromagnetic radiation in the form of X-rays and gamma rays to examine the inside of objects. Radiography uses radiation to measure the density of electrodes and determine the basis weight.

react

To undergo a change due to contact with another substance. When battery chemicals react, electrical energy is produced.

reactance

A measurement that includes both inductive resistance and capacitive resistance in an AC circuit. Reactance describes the resistive properties of capacitors and inductors in a circuit.

rechargeable

A battery that can be recharged. Rechargeable batteries, or secondary cell batteries, are usually wet-cell batteries.

scrap

Unusable material produced during a manufacturing process. Scrap is a waste product of manufacturing that can increase overall production costs.

self-discharge rate

The amount of energy a battery loses over a specific amount of time when it is not connected to a circuit. Self-discharge rate is usually expressed as a percentage of total energy lost per month.

separator

A film in a battery cell that provides a barrier between the anode and cathode. Separators allow ions to pass through when the battery is charging or discharging but prevent the flow of ions when the battery is not in use.

short circuits

An electrical fault in which current takes a shorter, unintended path between two conductors, interrupting the intended flow of electricity. A short circuit causes excess current flow.

software

A set of coded instructions or programs that control computer hardware functions and operations. Software is used to transfer and analyze surface data and to run computer vision algorithms used in vision systems.

spatter

Liquid metal droplets expelled during the welding process. Spatter can leave undesirable dots of metal on a workpiece surface.

specifications

A description of the essential physical and technical properties of a finished part. Specifications outline important information, including finished part dimensions and acceptable tolerance ranges.

spectroscopic ellipsometry

A nondestructive testing method that uses reflected light to measure wet and dry film thickness. Spectroscopic ellipsometry analyzes polarized light reflected off a surface to determine film thickness, surface roughness, and other characteristics.

state of health

SoH. A measurement of a battery's condition or performance compared to its original specifications that is based on voltage, internal resistance, and other conditions. State of health decreases over time due to several factors, including charge and discharge cycles, operating temperature, and damage to the battery.

surface anomalies

A flaw or irregularity present on the surface of a part or component. Surface anomalies can be detected automatically using computer vision systems.

thermal runaway

The process of a defective or damaged battery cell overheating and damaging nearby cells, causing them to also overheat. Thermal runaway can cause fires or explosions.

thickness sensors

An automated inspection tool that determines component thickness using a sensor above and below the measured component to calculate distance. Thickness sensors for battery electrode inspection typically use lasers to measure electrode thickness.

tolerances

An acceptable deviation from a desired dimension that meets specifications. Parts outside of required tolerances must be discarded or reworked.

ultrasonic measurement

A non-destructive inspection method that uses ultrasonic waves to examine the inside of objects. Ultrasonic measurement uses ultrasonic waves to measure the density of electrodes and determine the basis weight.

Underwriters Laboratories

UL. A private company that is certified to perform product safety testing and certification for the Occupational Safety and Health Administration (OSHA) and other government agencies. Underwriters Laboratories publishes safety testing standards for Li-ion batteries.

vacuum chamber

A sealed enclosure from which all air and gas is removed by a vacuum pump. Vacuum chambers are used to help detect leaks in a batter cell from flaws or damage.

vapor

A gas formed by boiling or evaporating a liquid. Electrolyte vapors exit a leaking battery cell during electrolyte leakage testing.

vision systems

A collection of advanced optical components that gathers data and forms an image, which is interpreted by a computer. Vision systems can be used to measure and inspect manufactured parts using the collected image data.

visual inspection

A visual assessment of surface defects. Visual inspection involves closely examining parts and components with the naked eye or using visual inspection tools.

voltage

A measure of electrical pressure or potential known as electromotive force. Voltage is measured in volts.

volts

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts measure voltage, which is also known as electromotive force.

volume

A measurement of the amount of space contained within a three-dimensional shape. Battery volume largely determines a battery's energy density.

weld penetration

The depth to which the arc heat melts the joint below the surface of the base metals. The weld penetration depth can affect the durability of the battery seal.

weld seam

A line along which two materials or components are joined together. Seams can be weaker and more prone to failure than solid areas.

welding

A joining process that uses heat, pressure, friction, or a combination of methods to fuse two materials together permanently. Welding processes can leave spatter that can affect the quality of battery components.

wet film thickness

The measured thickness of a coating material before it dries on the applied surface. Wet film thickness can be measured with tensiometers or other automated tools.

x-ray computed tomography

X-ray CT. An advanced radiographic, nondestructive testing method that creates a three-dimensional (3D) image of a part's interior and exterior out of multiple two-dimensional (2D) radiographs. X-ray computed tomography, which is sometimes referred to as micro-computed tomography (micro-CT), produces high-resolution images that show very fine part details.