Here’s Honda’s Plan To Develop The Solid State Batteries The World Is Clamoring For

One of the many holy grails for the electric vehicle industry is the commercialization of solid-state batteries. The potential for improving energy density, reducing cost, and enhancing safety with solid-state cells is enticing for all involved. But there have been many challenges associated with this new type of cell.

Most automakers are either actively working on solid-state cells in-house or partnered with companies like QuantumScape, Factorial Energy, or SolidPower. Honda has been following the in-house development path and has just announced the completion of a pilot production factory in Japan. 

The cells that make up current batteries consist of five main components. There is the positively charged cathode, negatively charged anode, separator, electrolyte, and the package. In current-generation cells, the cathode and anode are sandwiched with a separator between them, stuffed into the package and the whole thing is filled with an electrolyte.

The electrolyte is a conductive medium that allows positively charged lithium ions to move back and forth between the cathode and anode. The separator is a polymer film that does what the name implies, keeping the anode and cathode from coming into contact and short-circuiting which can lead to thermal runaway and fires. 

One of the major challenges with batteries today is that the electrolyte materials are flammable and cobalt oxide used in many cell chemistries releases oxygen when overheated, such as when there is a short circuit. This release of oxygen internally is what makes it so hard to extinguish a battery fire. 

In a solid-state cell, the liquid electrolyte and separator are replaced with a layer of solid electrolyte that prevents the anode and cathode from making contact. This layer is also thinner than the liquid electrolyte, helping to enable more layers in a cell and thus higher energy density. Most of the companies developing solid-state cell technologies are claiming nearly double the energy density of current nickel-cobalt cathode lithium-ion cells, going from about 250 Wh/L to nearly 450-500 Wh/L. If this can be achieved, batteries could potentially be nearly half the size and weight while offering similar capacities or range could be nearly doubled. 

What is Honda doing?

So far, Honda isn’t sharing very much detail on the chemistry of its solid-state cells except to acknowledge that it is mostly experimenting with sulfide-based materials for the electrolyte. This is consistent with many other companies in this field including SolidPower and Factorial Energy. In general solid-state cells can be made with most of the existing cathode chemistries including nickel-manganese-cobalt and lithium iron phosphate. 

https://youtu.be/jkvo7_Qo9Ug

Where things get interesting for Honda is the work they are doing on the manufacturing process. Producing the cathode and anode typically consists of coating aluminum and copper foils respectively with a slurry paste. The slurry is usually mixed in large batches and applied to one side of the entire roll of foil. After drying, the foils are cut to the appropriate size for the cell format and the scraps are recycled. Honda has developed a continuous mixing system for the slurries and a process to apply only the amount needed to the foil for each electrode with a thin insulator frame around it to avoid short circuits. This should be a faster and more efficient process that removes cost from the production process. 

Once coated, the anode and cathode are sandwiched with the electrolyte layer and run through a series of rollers. The pressure from this rolling process helps to pack in the electrolyte material and ensure robust contact with the anode and cathode layers. Without this pressing, the electrolyte tends to have voids in it, which increases the internal resistance and limits the ability of the lithium ions to transit between the electrodes. 

The new pilot plant in Sakura City consists of three main buildings, one for cathode production and cell assembly, one for anode production, and the third for electrolyte activation and storage. The images and video provided by Honda seem to show the cells as typical long, rectangular pouch cells that are currently used by many EV manufacturers. They appear to be similar in size to those typically used in vehicles rather than just the small form factor coin or pouch cells typically used for bench testing. 

Honda is using the new facility to work out both the ideal material mixes as well as volume manufacturing processes for solid-state cells. At this point, since it is an R&D facility, Honda isn’t discussing the capacity of the new facility. However, at about 290,000 square feet, it is quite sizable and seems like it should be able to produce enough cells to conduct both lab and in-vehicle testing over the next several years with production starting in early 2025. 

Like most other developers of solid-state cells, Honda is targeting the late-2020s for high-volume production. At this point, there are no announced plans about whether Honda plans to pursue manufacturing entirely in-house or partner with an existing cell manufacturer. Honda has a joint venture in Ohio with LG Energy Solutions to produce current-generation cells for the new line of EVs that it plans to launch in late 2025. Since Honda also builds motorcycles and aircraft, the company also hopes to be able to utilize solid-state cells for those machines, which are even more size- and weight-sensitive than cars.