What are all-solid-state-batteries?

Generally, all-solid-state batteries do not use liquid electrolyte. Thus, they are considered to be safe, reliable, and long-life batteries. Among the next-generation of all-solid-state batteries, Maxell is committed to the development and mass production of the sulfide-based all-solid-state lithium-ion batteries, that have the special features of high output and high capacity^∗1, utilizing the technologies of design, development, and production of batteries, which are the foundation of our business.

The followings are detailed explanations of the all-solid-state batteries awaiting practical application.

Rechargeable batteries that do not use liquid electrolyte

The basis of chemical batteries was formed by means of trial and error to obtain high voltage batteries by combining two types of metals, since the invention of the voltaic cell around 1800.

After batteries were introduced to Japan in the 1800s, batteries were assembled by Japanese own. The batteries at that time had a problem of leakage of liquid electrolyte. "Dry-cell batteries" solved this problem, which were developed around the world. In Japan, a unique structure for dry-cell battery was invented, which uses carbon rods. It lead to today's dry-cell batteries structure, and it attracted attention from all over the world.

This is why Japan has become one of the world’s leading basis for battery development and manufacturing.

Even though various types of chemical batteries have been created, from the past to the present. Why are all-solid-state batteries needed?

A chemical battery converts its chemical energy into electrical energy, and it is mainly composed of three elements: a positive electrode, a negative electrode, and an electrolyte. Among these chemical batteries, disposable batteries are classified as "primary batteries" and batteries that can be recharged and used repeatedly are classified as "rechargeable batteries." Normally, both types of batteries adopt liquid as electrolytes.

Various liquid electrolytes are used with the type of batteries, aqueous electrolyte with less risk of ignition or electrolyte with flammable organic solvent etc.

"Lithium-ion batteries" are the most familiar rechargeable batteries to us.

The main components of lithium-ion batteries are positive and negative electrodes, a separator separating them, and liquid electrolyte. A metal compound containing lithium is used for the positive electrode, and a graphite that can store lithium ions is used for the negative electrode. The energy is stored (charged) and emitted (discharged) with lithium ions and electrons move back and forth between the positive and negative electrodes.

Lithium-ion batteries can be miniaturized and generally, they can discharge an electrical current at a wide range of temperatures from -20 to +60 deg. C. The batteries do not greatly deteriorate even after repeated charge and discharge cycles, and also carry large current at high voltage, so that they can drive mobile devices and electric vehicles repeatedly for a long time in various environments.

However, such a convenient lithium-ion batteries also have a week point. As highly flammable organic solvents are contained in the electrolyte, they may lead to a dangerous situation such as ignition, smoke generation, or heat generation, depending on the use conditions of the batteries.

If solid electrolytes are used in place of liquid electrolyte, that may solve this issue. The earliest commercially available battery using a solid electrolyte is the lithium-iodine battery that is used for cardiac pacemakers. It is possible to ensure high safety and long-term reliability by using solid electrolyte. It can be said that the battery is suitable for implantation in the body because of its safety; however, application has been restricted. Thus, it is also possible to compose a battery with excellent safety by an all-solid-state battery using solid electrolyte regarding the rechargeable lithium-ion battery. Using solid electrolytes for lithium-ion batteries can considerably improve their performance issues, such as battery life and heat resistance of +100 deg. C or more.

Advantages of Maxell’s all-solid-state batteries

Comparing the sulfide-based all-solid-state battery that is being developed by Maxell to the oxide-based all-solid-state battery that is already released in Japan, each has its advantages and disadvantages. Individual battery manufacturers are developing different types of all-solid-state batteries based on mass productivity and anticipated applications.

Maxell is developing sulfide-based all-solid-state batteries featuring mass productivity, high output and high capacity^∗1 that does not require high temperature sintering as seen in the manufacturing process of oxide-based all-solid-state batteries.

Moreover, Maxell’s all-solid-state batteries adopt (from among the various sulfide solid electrolytes) argyrodite type solid electrolyte, which is excellent for balancing mass productivity, stability, ionic conductivity, and formability. Using the electrolyte, increase in resistance is suppressed due to repeated charging/discharging or long-term storage, and we have succeeded in improving the discharge capacity under high loads after long-term cycles or long-term storage compared to existing batteries using liquid electrolyte.

Maxell has been developing and manufacturing lithium-ion batteries and micro batteries for many years based on the business with battery design, development, and manufacturing, which continues from the time of founding.

Maxell is developing all-solid-state batteries with high performance^∗2 and high reliability^∗3 by combining analog core technologies of "Mixing & Dispersion (mixing)", "Fine Coating (coating)", and "High Precision Molding & Forming (forming)" cultivated through our business and technology developed in collaboration with other companies, and moreover adding the newly developed process technologies.

Maxell is mass-producing ceramic-packaged all-solid-state batteries by utilizing factories, equipment, manufacturing technologies, and know-how of micro batteries and lithium-ion batteries within Japan.

• For more detailed technical information, please enter the customer information and refer to "All-solid-state Battery Documents Download".

Applications where Maxell’s all-solid-state battery is the best choice

Maxell’s all-solid-state batteries are the small-sized next-generation batteries that combine three features: safety^∗4, battery characteristics (life, capacity, output), and heat resistance

We believe that these batteries contribute to solving social issues such as declining birthrate and aging population, decreasing working population, and environmental conservation, and also provide additional value to the device equipped with the battery, where conventional lithium-ion batteries are unsuitable and primary batteries have been used, or for applications with safety issues depending on the usage condition if lithium-ion batteries are used.

Because of these features such as small size, high output, safety, long life^∗5, and high heat resistance^∗6, all-solid-state batteries are suitable for factory automation (FA), medical devices that require sterilization, wearable devices, etc.

For factory automation (FA), they can be repeatedly used even in an environment where high temperatures are expected, such as rotating joint parts of robots, and the frequency of maintenance such as battery replacement can be reduced.

With a medical device that requires sterilization, the device and the battery could not be sterilized at the same time in an autoclave that becomes hot. Simultaneous sterilization is enabled by using an all-solid-state battery with excellent heat resistance, and it becomes possible to maintain the sanitary conditions of medical devices, which had previously been a concern. With the declining birthrate and aging population, wearable sensors for biological monitoring are becoming more widespread, so, safety is required for batteries that are in close contact with the body.

• For details of the application, please refer to "Solving issues, adoption, and collaboration case studies".

Moreover, aspects essential for responding to future prospects are popularization of vehicles’ ADAS (advanced driving assistance system) and EVs. As autonomous driving progresses, the number of sensors in the vehicle increases. The small emergency backup batteries are expected to be mounted in many places such as the car body, doors, and seats, that can drive the sensors even if the main power supply fails due to a sudden accident, etc.

The batteries are also useful for sensing tire conditions. Primary batteries have been used due to charging issues; however, rechargeable batteries with higher capacity that can be repeatedly used in harsh environments are required due to the increase in sensing information.

Maxell develops technologies day-by-day through making products for these applications by combining the energy harvesting technology that convert natural energy to electric power with the all-solid-state battery.

• High output and high capacity: Characteristics equivalent to the rated capacity of 8 mAh and the maximum discharge current of 20 mA of Maxell’s coin type lithium-ion rechargeable battery (937 size) despite being an all-solid-state battery.
• High performance: Indicating high heat resistance, long life, and high safety.
• High reliability: Based on the result of comparison with Maxell’s liquid coin type lithium -ion rechargeable battery in an overdischarge storage test.
• Safety: No ignition or smoke generation is seen in various safety tests such as heating at +350 deg. C, nail penetration, and external short circuit.
• Long life: The predicted lifetime calculated from the acceleration factor is at the 20-year level, which is long compared to 5 years of life of general electronic components (for example, insulation parts).
• High heat resistance: It is possible to discharge up to +125 deg. C. The heat resistance is high compared to that of general lithium-ion batteries.