The changing battery market: progress, challenges and sustainability requirements

Technological advances in battery technology have played a crucial role in the development of electric cars and their ability to compete with gasoline or diesel powered vehicles. One of the most important parameters in the design of EV batteries is the power per kilogram, measured in watt-hours per kilogram. The most advanced batteries for EVs today use lithium, which allows an energy density of up to 250 Wh/kg and makes these batteries very competitive.

Historically, Asia has had a strong dominance in battery manufacturing, but in recent years, companies in the United States and Europe have also made progress in the market. Electric vehicle manufacturers and lithium battery producers have announced ambitious plans to increase production in the coming years. These efforts will significantly increase production capacity.

Need for efficiency gains for the sake of the environment

Although EVs compete well in performance and cost of ownership, car manufacturers must continue to streamline production processes to achieve the environmental sustainability they themselves want to achieve.

The production of an electric car battery generates carbon dioxide emissions equivalent to several thousand miles of driving in a car with an internal combustion engine. Calculations show that the production of a 100 kWh battery emits as much carbon dioxide as a gasoline-powered car does over about 6 000 miles of driving. For a diesel car, the emissions are equivalent to a full 15 000 miles of driving. While the production of an internal combustion engine has a major impact on the environment, we need to make the production of electric car batteries more efficient.

Part of the efficiency improvement is to increase quality and production capacity with existing resources, here filtration plays a major role. Filtration of, for example, impurities, particles and metal ions, can contribute to increased quality, production capacity and durability of batteries.

Battery build-up

In a battery cell, there are four basic components: anode, cathode, separator and electrolyte. Together these form a galvanic cell. The cathode is the negative electrode, while the anode is the positive one. Ions move through the electrolyte as a medium between the cathode and the anode. The role of the separator is to keep the anode and cathode separate, acting as a carrier and container for the electrolyte. When the battery charges or discharges, electrons transport from the anode to the cathode while ions pass through the electrolyte. 

The manufacturing process

The manufacturing process of a battery cell mainly consists of three parts, electrode manufacturing, cell assembly and electrolyte filling.

Two of the most critical parts of electrode manufacturing are stirring and coating. During stirring, you mix at least two active powder materials and add purified water as well as binding and solvent agents to create a so-called ”slurry”. Once you have formed a homogeneous and smooth slurry, you apply the mixture to thin film rolls in the coating step. It is one of the most important steps in manufacturing that affects the future performance of the battery. The coating needs to be smooth and fine with a thickness of between 5 and 25 μm on each side. This process has a particularly large impact on the overall production rate of the factory. This is followed by the final stages of electrode manufacturing: calendering, cutting and drying.

Stacking is a method in cell assembly where several layers of battery cells are stacked on top of each other. The stacking processes differ in principle between all manufacturers, but what is common is that anodes, cathodes and separators are stacked in turn.

Replenishing electrolyte is a time-critical process during battery manufacturing that also affects battery performance. Here you fill the fully assembled cells with electrolyte. You perform the process under vacuum and feed the electrolyte into the cells in several steps.

Filtration in battery manufacturing

There is a long list of applications in battery manufacturing where filters are used. We have so far identified 34 applications at our customers in Sweden (see picture below). Three applications where the filters are particularly critical and need to be changed frequently are when adding solvents and deionized water, during slurry agitation and during electrolyte filling.

• Solvents and water are often transported in stainless steel pipes, which can release metal ions that can contaminate the slurry if not filtered out.
• For the battery to be as efficient as possible, it is important that the slurry is homogeneous, in this process the filter selection is critical. The filter must allow the desired particles to pass through, while retaining oversized particles. This must be accomplished without clogging the filter and thereby shortening its life. Particles can be residues from previous parts of the process, or e.g. undissolved gel formed during slurry agitation.
• The electrolyte usually consists of lithium salts in organic solvents. These salts may not dissolve completely in the solvent and must therefore be removed by filtration.

Battery manufacturing processes using filters

We are committed to supporting the development of battery manufacturing in Sweden, and if there is even the slightest chance for us to contribute to a sustainable planet (albeit microscopically), we will do so. 

This text was written by Max Malm (max.malm@colly.se), CEO of Colly Flowtech.