How machine vision is enabling the future of lithium-ion batteries

Lithium-ion batteries used in electric vehicles and solar power systems will be the driving force behind the green revolution.

Take the typical electric car Tesla Model S, which uses more than 7,600 lithium-ion batteries. In the near future, this use of a large number of batteries will not be considered typical, but rather strange.

How machine vision is enabling the future of lithium-ion batteries

The transition to green energy in the coming decades will require a corresponding increase in battery production and innovation. Lithium-ion batteries will be the workhorse of the green energy revolution in the not too distant future, storing energy for just about everything from electric cars to planes to homes and commercial buildings.

Lithium-ion batteries come in three types: cylindrical, pouch, and square (also known as battery cans). Smartphones typically use pouch cells, while most home appliances use cylindrical cells.

Battery production around the world is climbing rapidly. Tesla built its first “gigafactory” in Sparks, Nevada, in 2015 to make batteries. Tesla’s other “gigafactory” in Buffalo, New York, opened in 2017 and mainly produces solar cells. The company plans to open two more plants in the next few years in Berlin, Germany, and Austin, Texas. European battery company Northvolt also plans to start large-scale construction of a gigafactory in SkellefteĆ„, Switzerland, in 2021.

The transition to green energy provides a long runway for new industries in the global economy. Manufacturing will benefit as demand for solar cells and storage batteries increases, and as new technologies develop, industrial ecosystems will develop to support high growth and high productivity in manufacturing. Lithium-ion batteries are currently at the forefront of the ecological and economic revolution.

How Lithium-Ion Batteries are Made

Although the importance of lithium-ion batteries is self-evident, conceptually, the structure of lithium-ion batteries is very simple. Structurally, the cathode (positively charged) and anode (negatively charged) electrode sheets of a lithium-ion battery are alternately stacked, with each layer separated by a separator. Liquid or solid electrolytes are injected between the electrode sheets to promote energy transfer between the cathode sheets and the anode sheets.

How machine vision is enabling the future of lithium-ion batteries

The structure of a lithium-ion battery. Compared to metal batteries, lithium-ion batteries are more stable during operation and charging. Lithium-ion batteries typically have twice the energy density of nickel-cadmium batteries, but they tend to be heavier than other batteries.

The cathode sheet is usually made of aluminum foil, while the anode sheet is usually made of copper foil. Each piece is coated with a specific material to improve conductivity, efficiency and adhesion.

Active material: determines the capacity, voltage and characteristics of lithium-ion batteries. Cathode active materials typically include lithium cobalt oxide, lithium manganate oxide, or lithium iron phosphate. The anode sheet is usually coated with some kind of carbon material, such as graphite or lithium titanate.

Adhesive: Used to adhere the mixture to the foil.

Solvent: Promotes mixing of the materials in the slurry so that the mixture can be applied to the electrode sheet.

In addition, the cathode also contains a conductive agent to reduce the internal resistance of the battery and improve conductivity.

The separator between the electrodes is made of a porous polyolefin film material that is coated with an aramid coating and then cut to size. When the electrode sheets are stacked, the electrode sheets will be placed into the battery case in one of the following three main forms (cylindrical, pouch or square). Depending on the shape and characteristics of the battery, the battery case will include external positive and negative terminals (to connect to the powered device), insulation between the case and the electrode stack, gaskets, vents, and other components.

How machine vision is enabling the future of lithium-ion batteries

Cylindrical cells, one of the first mass-produced types of lithium batteries, consist of anode sheets, separators and cathode sheets stacked and wound in sequence. Cylindrical cells are ideal for automated production, and their shape allows the cells to withstand higher levels of internal pressure without deforming. Cylindrical cells are commonly used in medical devices, laptops, electric bicycles and power tools, and are part of Tesla’s massive battery packs.

Quality Assurance of Li-Ion Batteries Using Cameras

Although the fabrication of lithium-ion batteries is conceptually simple, consisting of a coated electrode stack and an electrolyte solvent, the actual production process is rather complex and sensitive. The coating thickness of the electrode has a great influence on the performance and even the stability of the battery.

Line scan cameras with machine learning algorithms can help automate and optimize the quality assurance phase of lithium-ion battery manufacturing. Take Teledyne DALSA’s Linea series of cameras, for example. This line scan camera can be installed on a factory production line and can be moved freely during the manufacturing process to monitor the production of materials. Line scan cameras are ideal for inspecting electrode sheets because the electrode sheets run at high speeds from winding to coating to stacking.

How machine vision is enabling the future of lithium-ion batteries

The inspection camera’s laser profiler covers the entire manufacturing process of lithium-ion batteries. These cameras can measure the thickness of electrode sheets and coatings, look for surface defects on electrode sheets such as dents, scratches or bent edges, measure the dimensions of battery casings for cylindrical or pouch cells, and monitor the quality of soldering on the battery’s external terminals.

How machine vision is enabling the future of lithium-ion batteries

The development potential of lithium-ion batteries

The ratio of EV sales to diesel vehicle sales often predicts the dividing line for lithium-ion battery growth rates. Electric vehicles are expected to account for 10 percent of vehicle sales by 2025, after which the share will increase to 28 percent and 58 percent in 2030 and 2040, respectively. For example, California, the most populous state in the U.S. and one of the largest economies in the world, has a goal of achieving zero emissions for all new and passenger vehicles sold in the state by 2035.

Since battery energy storage is often paired with renewable energy sources, the growth of one energy source directly predicts the adoption of the other. According to the U.S. Energy Information Administration (EIA), 70 percent of new energy capacity in the U.S. in 2021 will come from renewable energy sources (39 percent from solar and 31 percent from wind). As a result, battery storage capacity will also rise in the year, quadrupling compared to previous years. The world’s largest solar cell will be operational in Florida by the end of 2021.

Battery makers need to prepare for future demand for lithium-ion batteries. The use of line scan cameras, laser profilers and machine learning will help battery manufacturers optimize quality assurance processes and increase efficiency.

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