A pouch cell is a type of lithium-ion battery, distinguishable by its flexible, soft casing rather than a rigid metal shell. This design allows the battery to be produced in various shapes, making it adaptable for diverse applications. Pouch cells are widely used in modern portable devices, consumer electronics, and electric vehicles, providing energy storage in a compact and lightweight format.
Anatomy of a Pouch Cell
A pouch cell’s internal structure resembles a series of stacked, flat layers, similar to a deck of cards. At its core are the electrodes: a positive cathode and a negative anode. The cathode is made from lithium metal oxides, such as lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (NMC), or lithium iron phosphate (LFP).
The anode is composed of graphite or silicon-carbon composites. Separating these two electrodes is a thin, porous membrane, made of polyethylene (PE) or polypropylene (PP), which prevents direct contact and short circuits while allowing ions to pass through. These stacked layers are saturated in a liquid electrolyte, a lithium salt dissolved in organic solvents, which facilitates the movement of lithium ions between the anode and cathode during charging and discharging. The entire assembly is then enclosed within a flexible, multilayered aluminum-laminate film. This outer pouch comprises three distinct layers: an outer nylon layer for shape stability, a middle aluminum layer acting as a moisture and UV barrier, and an inner polypropylene layer for heat sealing.
The Manufacturing Process
The manufacturing of pouch cells begins with the preparation of electrode sheets. Active materials for both the cathode and anode are mixed with binders and solvents to create a slurry. This slurry is then precisely coated onto thin metal foils—aluminum for the cathode and copper for the anode—before being dried to remove solvents and pressed to achieve uniform thickness.
Following electrode preparation, the sheets are cut into specific sizes, with integrated electrical tabs. These cut electrode pieces are then carefully stacked in an alternating sequence of anode, separator, and cathode layers. Electrical tabs from the stacked electrodes are subsequently welded together, using ultrasonic welding, to create reliable connections.
The stacked cell, sometimes called a “jelly roll,” is then inserted into a pre-formed pouch, created by punching a cup into the aluminum-laminate film. Electrolyte is injected into this pouch under a partial vacuum to ensure complete saturation of all internal layers. After initial sealing, the cell undergoes a formation step, involving controlled charging and discharging cycles that activate the materials and form a protective solid electrolyte interphase (SEI) layer on the electrodes. During this process, some gases are naturally generated, which are collected in a “gas bag” section of the pouch. This gas bag is later cut off, and the pouch is vacuum-sealed a final time, ensuring a compact and air-tight battery.
Common Applications of Pouch Cells
Pouch cells are widely adopted across various industries due to their adaptable form factor and energy density. In the realm of consumer electronics, they are a common power source for devices where space and weight are at a premium. This includes products such as smartphones, tablets, and laptops, where their thin, flat shape allows for sleek device designs.
Pouch cells also power drones, thanks to their lightweight nature, and are found in wearable devices like fitness bands and smart glasses, where their customizable shapes are advantageous. Beyond personal electronics, pouch cells are increasingly used in electric vehicles (EVs). Automakers such as Ford, Mercedes-Benz, Stellantis, Honda, Renault-Nissan, and Hyundai utilize pouch cells to maximize battery capacity within the available vehicle space. Their flexibility allows for more efficient packaging within the vehicle’s chassis, contributing to overall vehicle range and efficiency.
Performance Characteristics of Pouch Cells
Pouch cells offer several performance advantages, making them a preferred choice for many modern applications. Their lightweight design, resulting from the absence of a rigid metal casing, can reduce the overall weight of battery systems by up to 30% compared to traditional metal-cased formats. This characteristic contributes to higher energy density, ranging from 150 to 250 Wh/kg, making them efficient for portable devices and electric vehicles.
They also boast a high packaging efficiency, achieving 90% to 95% space utilization, allowing manufacturers to maximize energy storage in confined spaces. The flexible nature of the pouch cell means it can be custom-designed into various thin or irregular shapes, offering unparalleled adaptability for product design. Furthermore, their relatively large surface-to-volume ratio allows for better heat dissipation, aiding thermal management.
Despite these advantages, pouch cells do present certain considerations. They are susceptible to swelling over time due to gas generation, a byproduct of electrochemical reactions that can be accelerated by factors like overcharging or high temperatures. This expansion can deform the device housing if not accounted for in the design. Their soft outer casing also makes them physically more vulnerable to punctures or impact compared to rigid cylindrical or prismatic cells, necessitating additional external protection within the device or battery pack. While cylindrical cells are known for their mechanical stability and standardized sizes, and prismatic cells offer a balance of energy density and scalability, pouch cells are preferred for applications prioritizing lightweight, high packaging efficiency, and design flexibility.