Our Stories 09 Development of solid-state batteries

Story 09Leading the way to the practical use of electrolytes, developed to be safe and high performing, on the front-line of the competition to develop "solid-state batteries".

The lithium ion battery was released for the first time in 1991 in the world. It took the world's battery industry by storm, and is now used in EVs (electric vehicles), PHEVs (plug-in hybrid electric vehicles), HVs (hybrid vehicles) and for consumer use.
In 2009, when lithium ion batteries really became spreading, the competition to develop a revolutionary, next-generation battery had started, and the solid-state battery was regarded as the most promising successor to lithium ion batteries.
In solid-state batteries, the solid inorganic compound is used as electrolytes.
For NGK SPARK PLUG, this is a great chance to make use of our original technology cultivated in the ceramics industry.
It is anticipated that solid-state batteries will be released into the market in early 2020s.
Let's look at the current status of the development projects, leading the research into the most promising new fields.

Shishihara:A member who has been participated in the project since 2009 when it was established. As a team leader, he works on developing materials for electrolytes and electrodes, and designing batteries.

Takeuchi:A specialist in developing ceramic materials. Responsible for developing non-sintered type solid electrolytes.

Wadaguchi:The youngest member, who gives form to solid state batteries using specialized knowledge of battery design.

Adopting the solid oxide as the electrolytes to announce our entry into the coming battery development race.

Safe, high-capacity, high output, compact and light. The requirements for the next generation batteries will be higher.

In contrast to the conventional lithium ion batteries, which a liquid organic solvent is used as an electrolyte, inorganic solid electrolyte is used in solid-state batteries. Since the solid ceramics, which are chemically stable, are used for the electrolytes, they prevent ignitions triggered by the electrolytes that may flow out of the batteries. In addition, since the operating temperature range can be expanded and the energy density can be improved, they can help to involve the industry's academic side in the development competition for the practical use.

When we entered the solid-state battery development, other companies were entering likewise.
Shishihara, the team leader, comments, "The biggest challenge was how to compete with the companies who had started earlier. While other companies adopted sulfide as the electrolytes for solid-state batteries, we focused on oxide. Contacted with water, sulfide produces hydrogen sulphide gas which is harmful to human body. Whereas with oxide, there is no danger of combustion nor hazardous gases generation. We have set our goal to create our original safe batteries through developing our own composition using oxide."

Even we determined to take oxide as an electrolyte, its ion conductiviry was not good enough to be used as an electrolyte. It is necessary to improve the ion conductivity to a certain level, to be able to use oxide for practical use. It also needs to be sintered after shaping the oxide by increasing its density. We have begun to improve the performance of the oxide as an electrolyte.

Shishihara says, "We have the sintering technology to strengthen and increase the conductivity of ceramics, and the ability to replace certain elements with other elements. It was a huge advantage to be able to utilize the technology and knowledge cultivated by our senior engineers at the material development stage." 3 years after the establishment of the project, the original oxide solid electrolyte was developed. It had even reached the highest level of ion conductivity for an oxide material.

From sintering electrolytes to non-sintering electrolytes. A path to even better material development was found.

Even when you hit a dead end, changing your viewpoint can open up new possibilities.

Our first solid-state batteries were developed had both positive and negative electrodes on the sintered solid electrolytes. This is because lithium, the best anode material, was thought to be suitable for the sintered electrolytes. However, when it was sintered to the solid electrolyte, which was processed to be as thin as possible to reduce electric resistance, the material was warped and broken when being handled.
Since the project members could not see the advantages of sintered type solid batteries, they shifted to develop a method to mix the binding material with the electrolytes and connect them without sintering. Ceramics can be ceramics even though they are not sintered. They planned to make it a battery by just compressed it.

"The non-sintering technology was derived from the technology of the sintering type. The idea was developed by chance in 2015 when making the components for the sintering types", says Shishihara.

Takeuchi, who has been working on material development since entering the company, says: "We thought that the sintering types had a lot of potential, so changing direction was not easy for us to decide."
He continues, "We were uncertain at the beginning. It was surprising to hear from my senior, Shishihara, that the non-sintered types had a high ion conductivity. If it is sintered, since the interfaces connect, high ion conductivity will keep output high, although I could not imagine how it will become a battery if it is not sintered since it will simply just be a compressed powder."

The physical properties will increase if it is sintered, although the difficulty level and the cost will be increased. Whereas the non-sintered type can be made easily, and made to be large. Although the quality in some ways falls behind that of the sintered type batteries, as a manufacturer of oxide-based solid-state batteries, we can create our original electrolyte battery.
The members approached this unexpected new direction with a positive attitude, and accelerated the material development under Takeuchi's guidance.

A new power supported creation of a battery with understanding of the physical properties of solid electrolytes.

The material development accelerated, so did the technological development to make it function as a battery.

To make a thin material for the solid electrolytes, we were able to apply our technology of plastering a thin layer of slurry evenly onto the melting ceramic powder which is used in the process of making the semiconductor package. Next, we developed the electrodes that match the electrolytes. By using a material that can hold much electricity, we could minimize the resistance of the parts touching the electrolytes.
After completing this process, one battery cell is made. Laminating these cells and making them into packages, we finally forms a shape of battery.

We have reached the stage of releasing the trial product for demonstration in order to announce our research results to the public. Wadaguchi, the youngest member of our team showed his great ability then.
"The solid-state battery is also a very hot topic at universities. I was delighted to be assigned as one of the project members, since I had been conducting research for the best structure to maximize the quality of the battery. It did not work out well at first; there were many issues such as the film laminating not proceeding successfully and short circuits being detected. In addition, there was a lot of pressure involved in being responsible for creating the sample products."

"Wadaguchi is the key player in establishing the battery-making process. Based on advice from his seniors, he worked on making the sample product. At the exhibition held in 2016, people were surprised at our unique technology to compressed oxide-type solid-state battey without sintering it. Wadaguchi's contribution is necessary for further development", says Takeuchi, showing his high expectations on his junior colleague.
In fact, the results of Wadaguchi's efforts were widely used at the exhibition in 2017.

Solid electrolyte, electrode, and packaging. All of the developmental stages started to progress

We had to find something unique, that is "the NGK SPARK PLUG-style".

The most important point in differentiating ourselves from other companies is the establishment of technology to make solid electrolytes into batteries. Our strong points are to be able to compress thinly without sintering, making a package by putting it together with electrodes, and finally forming it into a battery; we have already applied for a patent for this.

We are working on developing the solid electrolytes since the quality needs to be improved for the purposes of practical use.
"We compress it by pressing instead of sintering. The structure of the electrolyte produced through this process is very important. We conduct research for practical applications, since the technology for improving the density of the electrolytes and for controlling the contact interface of the electrolytes is being required.", says Shishihara. He continues : "The research into and electrolytes has also reached the next level".
In the project team, we are focusing on materials that had previously been not available, since such materials are thought to react to organic electrolyte solution for lithium ion batteries. We can take advantege of it's feature; our electrolyte is not liquid but solid.

There are many challenges regarding material development. The output and ion conductvity need to be improved. We need to take firm steps forward, instead of rushing through it.

"We just continue to make progress every day. We produce new electrodes using new materials. We put it together with the electrodes and make it into a package, check to see if it works well as batteries. Although it is difficult, it is worth trying.", says Shishihara with a smile.

We aim to ship a practical sample at an early stage

Since we are working on something very new, new challenges turn up all the time. Nevertheless, all of our team members enjoy working on developing solid-state batteries.

"There are a lot of discoveries, things to learn, and it is an enjoyable process. Since our company's expectations are growing, we wish to release the materials in market as soon as possible, and continue our research into batteries, as there is a huge market", says Shishihara.

The safe and high-quality solid-state battery may become NGK SPARK PLUG's new business field since such batteries can be installed not only in automobiles but also for household electrics, smartphones, unmanned aircrafts and more, expanding their potential use.

All three members state, "We are confident in our belief that the oxide batteries made using our original non-sintered oxide electrolytes, that come in this size, are the very first from any company. We are eager to complete the sample product, and present it to the world".