How machine vision empowers 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, the Tesla Model S, for example, which uses more than 7,600 lithium-ion cells. In the near future, such a large number of cells will not be considered typical, but will be considered strange.

The transition to green energy will require a corresponding increase in battery production and innovation over the coming decades. Lithium-ion batteries will become the workhorse of the green energy revolution in the near future, storing energy for everything from electric cars to airplanes to homes and commercial buildings.

There are three types of lithium-ion batteries: cylindrical, pouch, and prismatic (also called battery cans). Smartphones typically use pouch batteries, while most home appliances use cylindrical batteries.

Battery production is rising rapidly around the world. Tesla built its first "Gigafactory" in Sparks, Nevada, in 2015 to produce batteries. Another Tesla "Gigafactory" in Buffalo, New York, opened in 2017 and produces solar cells. The company plans to open two more factories in Berlin, Germany and Austin, the capital of Texas, in the coming years. European battery company Northvolt also plans to start large-scale construction of a Gigafactory in Skellefteå, Switzerland, in 2021.

The transition to green energy provides a long runway for new sectors in the global economy. As demand for solar cells and batteries increases, the manufacturing industry will benefit, and as new technologies develop, an industrial ecosystem will develop to support high growth and high productivity in the manufacturing industry. Lithium-ion batteries are currently at the forefront of an 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 batteries is very simple. Structurally, lithium-ion batteries have alternating cathode (positively charged) and anode (negatively charged) electrode sheets, separated by a separator. Liquid or solid electrolyte is injected between the electrode sheets to facilitate energy transfer between the cathode and anode sheets.

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 sheet is coated with specific materials to improve conductivity, efficiency and adhesion.

Active materials: Determine the capacity, voltage and characteristics of lithium-ion batteries. Cathode active materials usually include lithium cobalt oxide, lithium manganese oxide or lithium iron phosphate. Anode sheets are 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 the mixing of materials in the slurry so that the mixture can be coated on the electrode sheet.

In addition, the cathode 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 aromatic polyamide coating and then cut to size. Once the electrode sheets are stacked, they are placed in the battery case in one of 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 device being powered), an insulating layer between the outer shell and the electrode stack, gaskets, vents, and other components.

Cylindrical cells were one of the first mass-produced lithium-ion battery types. They consist of anode sheets, separators and cathode sheets stacked and wound in sequence. Cylindrical cells are well suited to automated production, and their shape allows the battery 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 the massive battery packs in Tesla cars.

Quality assurance of lithium-ion batteries using cameras

Although the manufacturing of lithium-ion batteries is simple in concept, consisting of a coated electrode stack and an electrolyte solvent, the actual production process is quite complex and sensitive. The thickness of the electrode coating has a great impact on the performance and even 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. Teledyne DALSA's Linea series of cameras, for example, can be installed on factory production lines and move freely during the manufacturing process to monitor the production of materials. Line scan cameras are ideal for inspecting electrode sheets because the process of electrode sheets from winding to coating to stacking runs at high speeds.

Laser profilers for inspection cameras cover the entire manufacturing process of lithium-ion batteries. These cameras can measure the thickness of electrode sheets and coatings, find surface defects on electrode sheets such as dents, scratches or bent edges, measure the dimensions of battery cases for cylindrical or pouch-shaped batteries, and monitor the welding quality of battery external terminals.

The potential of lithium-ion batteries

The ratio of electric vehicle sales to internal combustion engine vehicle sales generally predicts the dividing line for lithium-ion battery growth rates. Electric vehicles are expected to account for 10% of vehicle sales by 2025, rising to 28% in 2030 and 58% in 2040. For example, California, the most populous state in the United States and one of the largest economies in the world, has a goal of making all new cars and passenger vehicles sold in the state zero-emission by 2035.

Since battery storage is often paired with renewable energy, the growth of one directly predicts the adoption of the other. According to the U.S. Energy Information Administration (EIA), 70% of new energy capacity in the United States will come from renewable energy in 2021 (39% from solar and 31% from wind). Therefore, battery storage capacity will also rise that year, increasing four times more than in previous years. The world's largest solar cell will be put into operation in Florida at the end of 2021.

Battery manufacturers 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 their quality assurance processes and increase efficiency.