Battery Cell Assembly 347

active materials

AMs. A substance that contributes to the electrochemical reactions that enable a battery to charge and discharge. Active materials for lithium-ion battery cells include lithium metal oxides, graphite, and silicon.

adhesives

A chemical material used to bond two objects together. Adhesives can be applied to separators to prevent them from slipping out of place during winding.

aging

A cell finishing process during which completed battery cells are repeatedly charged, discharged, and tested in a temperature-controlled storage area. Aging can last several weeks, requires large amounts of storage space, and typically includes repeated charging, discharging, and testing.

anode

The negative electrode in a battery. The anode in a lithium-ion battery is usually made of copper with graphite or silicon active materials.

automated

A system or process that does not require human intervention to operate. Automated technology can improve efficiency and accuracy during battery cell assembly, while reducing the risk of errors or contamination from human technicians.

automated testing racks

An all-in-one battery storage system that also charges batteries and facilitates battery testing. Automated testing racks are used in sophisticated battery aging processes to minimize human handling.

burrs

A rough, sharp edge remaining on the edge of a battery electrode. Burrs from cutting during electrode manufacturing can damage the enclosure during packaging.

canning

The process of placing wound electrodes into a protective covering and welding it shut. Canning is sometimes used to describe the packaging process for prismatic and cylindrical cells.

cans

A protective metal cover that surrounds some battery cells. Cans are typically cylindrical or prismatic and help prevent cell swelling, bending, and damage.

capacity

The amount of energy a battery can store. Capacity is determined by the battery's materials and size.

carbon dioxide

A heavy, colorless, odorless gas composed of carbon and oxygen. Carbon dioxide is one of several gases produced as a byproduct of formation in lithium-ion batteries.

cathode

The positive electrode in a battery. The cathode in a lithium-ion battery is usually made of aluminum with lithium oxide active materials.

cell assembly

The process of preparing and combining battery cell components, which generally includes winding, packaging, and filling. Cell assembly is the second stage of battery cell manufacturing and comes after electrode manufacturing.

cell chemistry

The chemical composition of materials in a battery cell. Cell chemistry influences the cell's design and manufacturing processes.

cell finishing

The process of allowing a solid-electrolyte interface layer to form and reserving time for the battery to mature and be tested. Cell finishing is the last step of cell assembly but is often separated into its own stage because it is a multi-step process that includes formation, degassing, aging, and testing.

cell geometry

The specific shape, dimensions, and design of a battery cell. Cell geometry impacts the type of enclosure the battery will have, how finished electrodes will fit into it, and whether electrodes will be folded, stacked, or wound.

ceramic

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramic electrolytes and coatings are emerging technologies for rechargeable batteries.

cleanroom

An enclosed space in which temperature, humidity, contamination, and air pressure are controlled and maintained. Cleanrooms are important for preventing the contamination of sensitive electronics.

conductive

Able to convey electricity. The conductivity of a battery cell electrode can be altered by any microscopic flaws or contamination.

consumes

Irreversibly uses up. The anode of an Li-ion battery consumes lithium and electrolyte ions during the first charging cycle, which slightly reduces the battery's capacity until the SEI forms.

current

The flow of electricity. Current strength is called amperage and is measured in amperes (A).

current collectors

An exceedingly thin sheet of metal used to provide structure and conductivity to a battery cell electrode. Current collectors for lithium-ion battery cells are usually copper or aluminum and are coated with conductive active materials like lithium and graphite.

cycle life

The total number of times a rechargeable battery can be discharged and recharged before it must be replaced. Cycle life depends on the battery's design, materials, and operating conditions.

cylindrical cells

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

degassing

The controlled release of built-up gases from a pouch cell battery. Degassing uses a lance to pierce the battery and a vacuum pump to remove gas.

discharged

Forced or allowed to naturally lose stored electrical energy. Batteries are repeatedly discharged during aging.

dry room

A type of cleanroom that maintains lower humidity levels, typically below 1 percent. A dry room prevents ionic contamination in battery cell manufacturing.

electrochemical reaction

A process that converts chemical energy into electrical energy. An electrochemical reaction in Li-ion batteries causes the formation of the solid-electrolyte interface as well as unwanted gas.

electrode manufacturing

The process of fabricating electrodes for battery cells, which generally includes pre-manufacturing, mixing, coating, drying, calendering, and slitting, cutting, and notching. Electrode manufacturing is the first stage of battery cell manufacturing and comes before cell assembly and cell finishing.

electrode stacking machines

An automated piece of equipment that uses rollers to move and position electrodes. Electrode stacking machines are used to perform the winding technique of rolling.

electrodes

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

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.

enclosing

The process of placing wound electrodes into a protective covering and welding it shut. Enclosing is sometimes used to describe the packaging process for prismatic and cylindrical cells.

end-of-line

EOL. Occurring after all major production steps and immediately before a product is stored, shipped, or sold. End-of-line procedures, like testing, are a final opportunity for manufacturers to ensure battery quality, safety, and performance.

energy density

The amount of energy that a battery can supply per unit of volume. Energy density is often measured in kilowatt-hours per liter (kWh/L).

ethylene

A flammable hydrocarbon gas. Ethylene is one of several gases produced as a byproduct of formation in lithium-ion batteries.

filling

A cell assembly step during which liquid electrolyte is added to the enclosed battery cell. Filling uses liquid injection machines to add pre-determined amounts of electrolyte.

foil

An exceedingly thin sheet of metal. Foil wrappers are used to enclose pouch cell batteries.

formation

A cell finishing process during which filled batteries are charged for the first time and the solid-electrolyte interface (SEI) forms. Formation causes the protective SEI layer to form on the anode but also produces gases, which must be removed from pouch cells.

fumes

A cloud of particles suspended in a gas. Fumes created by battery fires are toxic.

gases

A fluid state of matter that has no fixed shape or volume. Gases like ethylene, carbon dioxide, and hydrogen are produced during formation.

gels

A semisolid composed of a solid dispersed in a liquid. Gel electrolytes are an emerging rechargeable battery technology.

graphite

A soft, black form of carbon that conducts electricity. Graphite is a common active material for lithium-ion battery cell anodes.

heat press

A piece of equipment that uses heat and pressure to create a seal. A heat press is sometimes used to secure the layers of an electrode stack to keep them aligned during later cell assembly steps.

high-frequency sound waves

An acoustic vibration caused by the movement of energy that occurs at a rate higher than what is perceivable by human hearing. High-frequency sound waves are used to form permanent joints during ultrasonic welding.

high-temperature

HT. An environmental condition in which battery cells are aged at elevated ambient temperatures. High-temperature conditions are approximately 86-122°F (30-50°C).

humidity

The presence of water vapor in the air. Humidity during cell assembly can cause ionic contamination.

hydrogen

A colorless, odorless gas that is the most abundant element on the planet. Hydrogen is one of several gases produced as a byproduct of formation in lithium-ion batteries.

internal resistance

IR. The resistance within a battery or voltage source that causes a voltage drop when current flows through it. 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.

internal short circuits

ISCs. The unwanted flow of current between electrodes in a cell that occurs when they unintentionally connect. Internal short circuits can lead to increased temperatures and thermal runaway.

inventory

A quantity of goods held in stock. Inventories of finished batteries must be carefully managed during the lengthy aging process.

ions

A charged atom or molecule. An ion can be either positive or negative depending on whether it has a shortage or surplus of electrons.

ISCs

Internal short circuits. The unwanted flow of current between electrodes in a cell that occurs when they unintentionally connect. ISCs can lead to increased temperatures and thermal runaway.

jellyrolls

The group of electrode and separator layers that is formed during winding. Jellyrolls are a commonly used term for any roll or stack formed during rolling, stacking, or Z-folding.

lance

A solid, needle-like device with a sharp point. A lance is used to pierce enclosed battery cells so gases can escape during degassing.

laser alignment systems

A device that uses an intense beam of coherent, collimated, monochromatic light to aid robots in positioning tasks. Laser alignment systems can be used to precisely position electrodes during battery cell packaging.

laser welding

A welding process that uses an intense beam of light to permanently bond two separate components together. Laser welding is a noncontact welding method used during battery cell manufacturing.

Li-ion

Lithium ion. A type of rechargeable battery cell that uses a lithium compound in the cathode and, usually, carbon in the form of graphite in the anode. Li-ion battery cells are widely used in portable electronics and electric vehicles.

liquid injection machine

A piece of automated equipment used to precisely deliver a pre-determined volume of liquid electrolyte to an enclosed battery. A liquid injection machine uses hollow, needle-like injectors.

lithium compounds

A substance composed of molecules of lithium and another chemical element. Lithium compounds build up on the anode during formation and become the solid-electrolyte interface.

lithium oxide

A solid, white compound formed when lithium combines with oxygen. Lithium oxide active materials are used to coat cathodes in lithium-ion batteries.

lithium-ion

Li-ion. A type of rechargeable battery cell that uses a lithium compound in the cathode and, usually, carbon in the form of graphite in the anode. Lithium-ion battery cells are widely used in portable electronics and electric vehicles.

mandrel

A cylindrical rod around which electrode layers are wound for stability. A mandrel is most likely to be used during jellyroll rolling.

mass

A measure of the amount of matter in an object. The mass of a battery in kilograms (kg) can be used to determine its energy density in watt-hours per kilogram (Wh/kg).

misalignments

A condition in which electrodes and/or separator sheets are positioned incorrectly. Misalignments during winding can cause electrodes to contact each other and result in ISCs.

nonconductive

Unable to convey electrical energy. Nonconductive materials like polymer must be used for separators in rechargeable batteries.

normal-temperature

NT. An environmental condition in which battery cells are aged at roughly room temperature. Normal-temperature conditions are approximately 71.6°F (22°C).

open circuit voltage

OCV. The difference of electrical potential between the positive and negative terminals of a battery when not connected to a load. Open circuit voltage tests can determine a battery's state of charge (SoC) and state of health (SoH).

optical sensors

A type of sensor that detects the presence of an object through the use of a beam of light. Optical sensors are used by vision systems to position electrodes during battery cell packaging.

packaging

The process of placing a wound electrode into a protective covering and welding it shut. Packaging is sometimes called enclosing or canning during production of prismatic and cylindrical cells.

pores

An opening or void in a material. Pores between particles in the electrode coating fill with electrolyte in a process called wetting.

pouch cells

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

power

The rate at which a device converts energy from one form to another, such as converting electrical energy into light or movement. Power is measured in watts (W).

prismatic cells

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

pump

A mechanical device used to move fluids in a pneumatic or hydraulic system. A pump uses a vacuum to remove gases during degassing without wasting electrolyte.

rechargeable battery

A battery that can be recharged. A rechargeable battery, or secondary cell battery, is charged by running electrical current back through it to restore its chemical energy.

resistance welding

A welding process that uses the heat of electrical resistance to permanently join two separate components together. Resistance welding is a contact welding method used during battery cell manufacturing, most commonly for manufacturing cylindrical cells.

robots

A programmable machine used to perform a variety of complex, repetitive tasks. Robots are used in automated assembly lines to enable a higher degree of accuracy and precision than human assemblers.

rollers

A rotating, cylindrical drum. Rollers in an electrode stacking machine move and position electrodes into stacks when performing winding by rolling.

rolling

A winding technique that creates a tight spiral of electrodes and separator layers. Rolling is best for cylindrical cells but is also sometimes used for prismatic cells.

roll-pressing

A process that uses the pressure of rollers to evenly distribute electrolyte in pouch cell batteries. Roll-pressing is an optional step that can improve filling in pouch cells.

secondary cell battery

A battery that can be recharged. A secondary cell battery, or rechargeable battery, is charged by running electrical current back through it to restore its chemical energy.

SEI

Solid-electrolyte interface. A protective layer of solid lithium compounds that builds up on the surface of the anode during formation. The SEI covers the entire surface of the anode, which prevents the anode from continuously consuming ions and maintains the battery's capacity.

separator

A film in a battery cell that provides a barrier between the anode and cathode. Separators are made from nonconductive materials like plastics and are stacked between anodes and cathodes to prevent internal short circuits.

silicon

A lustrous gray, semi-metallic semiconductor material. Silicon is a common active material for lithium-ion battery cell anodes.

solid-electrolyte interface

SEI. A protective layer of solid lithium compounds that builds up on the surface of the anode during formation. The solid-electrolyte interface covers the entire surface of the anode, which prevents the anode from continuously consuming ions and maintains the battery's capacity.

solids

A non-flowing form of a substance. Some substances, like ceramics, are solid at room temperature, while others, such as water, are solid when frozen.

spatter

The liquid metal droplets expelled during welding processes, especially traditional contact welding processes. Spatter can cause particulate contamination of battery components.

stacking

A winding technique that layers individual electrode and separator sheets. Stacking is best for prismatic and pouch cell batteries.

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. Tabs are welded together during the packaging phase of cell assembly.

terminals

A conductive point within a circuit to which other components can be attached. Terminals have a negative or a positive charge.

thermal conductivity

A material's ability to act as a medium for conveying heat. Thermal conductivity in battery cells can be improved by tightly winding electrodes, which creates more surface area through which heat can dissipate.

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 if not detected and stopped.

ultrasonic welding

A welding process that uses high-frequency sound waves to permanently join two separate components together. Ultrasonic welding is a noncontact welding method used during battery cell manufacturing.

vacuum

A space with negative air pressure created by removing air with suction. A vacuum can create suction to speed up wetting during filling and remove gases during degassing.

vacuum grippers

A device that uses flexible suction cups and controlled airflow to attach to parts. Vacuum grippers allow robots to perform tasks such as handling and moving delicate electrode sheets.

vision systems

A collection of advanced optical components that collects data and forms an image, which is interpreted by a computer. Vision systems can be used to precisely position electrodes during battery cell packaging.

volume

A measure of the amount of space a three-dimensional object or substance occupies. A pre-determined volume of liquid electrolyte is delivered to batteries by liquid injection machines during filling.

welding

The process of permanently joining two or more materials using heat, pressure, or friction. Welding is used to connect electrode tabs and other components during battery cell manufacturing.

wetting

The process of saturating an electrode with an electrolyte. Wetting occurs during the filling stage of cell assembly when the electrolyte is added to the battery.

winding

The process of layering electrodes and separators to create a stack or roll that matches the size and shape of the finished battery cell. Winding may also be called rolling, stacking, folding, or other terms, depending on the cell geometry and processes used.

Z-folding

A winding technique that layers electrode sheets between one continuous separator sheet. Z-folding folds the separator back and forth over the electrodes in a zigzag and is best for prismatic and pouch cell batteries.