What is an all-solid-state battery?
All-solid-state battery refers to a battery that is composed only of solids. Judging from the outside, conventional batteries may appear to use only solid metals, but they contain a liquid electrolyte inside. All-solid-state batteries are characterized by the fact that the electrolyte is also solid. By making the electrolyte, which is an important element for generating electricity, solid, there is a big difference from batteries that use liquid electrolytes.
By using a solid electrolyte, it is possible to achieve higher capacity and higher output than lithium-ion batteries. In addition, since no liquid material is used inside the battery, the battery can be used more safely.
The reason why all-solid-state batteries with such excellent performance have not become widespread is that solid materials that can conduct ions at high speed could not be developed. Although the effectiveness of all-solid-state batteries has been recognized for some time, it has been considered difficult to develop solid electrolytes with high ionic conductivity. However, in recent years, the development of effective materials has progressed, and the practical application of all-solid-state batteries has gained momentum.
With the increasing importance of electric vehicles and portable electronic devices in the future, all-solid-state batteries are expected to spread in earnest.
How does an all-solid-state battery work?
All-solid-state batteries are designed to conduct electricity by moving the ions inside the electrolyte to the positive electrode during discharging and to the negative electrode during charging. This mechanism is basically the same as a conventional lithium-ion battery, but the type of battery is determined by whether the electrolyte is liquid or solid. The materials used for the positive and negative electrodes are the same as lithium-ion batteries, so it is important to use a solid electrolyte.
The structure of the battery also differs depending on what kind of material is used for the electrolyte. When using a liquid electrolyte, a separator is required to separate the positive electrode liquid and the negative electrode liquid. Liquid electrolytes can mix rapidly, so a separator must be provided to control the operation. However, solid electrolytes do not mix, so there is no longer a need for separators. In all-solid-state batteries, the solid electrolyte between the positive and negative electrodes acts as a separator.
What type of all-solid-state battery?
- Bulk-type all-solid-state battery
All-solid-state batteries can be roughly divided into two types according to the manufacturing method.
A "bulk-type all-solid-state battery" uses powder, which is a collection of powders and grains, as electrodes and electrolytes. Although they use a solid electrolyte, they are structurally similar to lithium-ion batteries. Its function is greatly influenced by the quality of the constituent solid electrolyte.
Bulk-type all-solid-state batteries are used as batteries for electric vehicles, etc., because they can be manufactured to have large capacities that can store a lot of energy.
- Thin-film all-solid-state battery
A "thin film type all-solid-state battery" is an all-solid-state battery manufactured by stacking a thin film-like electrolyte on a vacuum electrode using a vapor phase method such as vacuum evaporation or sputtering.
Compared to bulk-type all-solid-state batteries, the amount of energy that can be stored is small, so it is not possible to create large-capacity batteries, but they are easy to manufacture and have a long cycle life. Therefore, it is suitable for small devices such as sensors that do not require a large battery capacity.
What are the advantages of all-solid-state batteries? About the difference from lithium-ion batteries
- Advantage 1: High degree of freedom in structure and shape
Conventional batteries have a liquid electrolyte. This liquid electrolyte may cause chemical burns if it comes into contact with the skin, and leakage from the container will cause a serious problem, so a strong container must be prepared. Even ordinary households need to be very careful when throwing away conventional batteries. However, since the electrolyte of all-solid-state batteries is solid, there is no need to worry about liquid leakage, and the degree of freedom in structure and shape is improved. By devising the structure and shape, it has become possible to enjoy various benefits such as improved functionality and expanded applications.
- Advantage 3: Resistant to heat and temperature changes
Lithium-ion batteries may not be usable depending on the ambient temperature, as the separator will melt at high temperatures, and the electrolyte will become more viscous at low temperatures, increasing the internal resistance.
All-solid-state batteries use a solid electrolyte that is less affected by temperature, so they have a wider operating temperature range than lithium-ion batteries and can withstand temperature changes. Therefore, all-solid-state batteries can operate even in places where the use of batteries has been avoided up until now.
- Advantage ④ High-speed charging and discharging
Batteries heat up when charging, especially when fast charging, a lot of heat is generated. In the case of lithium-ion batteries, problems such as deterioration of battery performance occur when used at high temperatures, so it is necessary to take the time to charge the battery while paying close attention.
However, all-solid-state batteries that can be used at high temperatures can be charged more rapidly than lithium-ion batteries. Furthermore, all-solid-state batteries, which can be multi-layered and consist of many small batteries inside, are suitable for charging in a short time. The charging time is said to be one-third that of lithium-ion batteries.
One application of all-solid-state batteries that is attracting attention is their use in electric vehicles, which are expected to become widespread in the future.
Electric vehicles currently being manufactured use lithium-ion batteries, which contain flammable organic solvents, and have been pointed out to be dangerous in the unlikely event of a fire. Lithium-ion batteries also have problems such as a long charging time and a narrow operating temperature range. For this reason, in order to make electric vehicles easier to use, batteries with higher performance than lithium-ion batteries are needed. All-solid-state batteries do not have flammable organic solvents, so the risk of fire can be reduced.
In addition to electric vehicles, it can also be used as a power source for electronic devices. Parts used in electronic devices are often soldered to electronic boards before use, but all-solid-state batteries can be soldered.
Taking advantage of the large capacity and high output of all-solid-state batteries, they are also being considered for installation in airplanes and ships. Many fields are looking forward to using batteries.
How safe are solid-state batteries?
The organic solvent used as the electrolyte in lithium-ion batteries evaporates easily, making it difficult to use in high-temperature conditions. I had to take precautions.
However, the electrolyte used in all-solid-state batteries has high heat resistance, so it can be used at high temperatures.
In addition, since lithium-ion batteries have the risk of worsening the environment due to liquid leakage, all-solid-state batteries that do not have the risk of liquid leakage can be said to be safer batteries for environmentally conscious societies. From now on, it is expected that all-solid-state batteries, which are superior not only in performance but also in safety, will become widespread.
What is the development status of all-solid-state batteries/challenges for commercialization?
All-solid-state batteries are being researched and developed so that they can be put into practical use within the next few years. As it is a key technology that will replace lithium-ion batteries in the future, many companies and universities are vigorously researching it, but there are still problems with solid electrolytes, electrode materials, and manufacturing processes. increase.
A challenge for solid electrolytes is the adhesion between solids. If the electrodes and the electrolyte are not in close contact at all times, the battery will not function properly. If the electrolyte is a liquid, it is relatively easy to create a state of close contact, but in the case of a solid electrolyte, it is necessary to devise ways to make the solids adhere to each other. Promising materials for solid electrolytes include sulfides and oxides, and the search for materials with particularly high ionic conductivity is also an issue.
The challenge for electrode materials is the need for more power storage. In order to improve the energy density of all-solid-state batteries, more efficient electrodes (positive and negative electrodes) are essential. Unless we develop electrodes that can store more power while keeping down the size and weight, the batteries will be inconvenient to use.
There are also manufacturing challenges. Several manufacturing methods are possible depending on the materials used, but the solid electrolyte of sulfide-based all-solid-state batteries deteriorates when exposed to moisture, so a dry room must be prepared. Since it requires manufacturing equipment different from conventional lithium-ion batteries, it is necessary to prepare large-scale equipment for mass production.
In order to create a battery that can replace lithium-ion batteries, we must overcome a number of challenges to manufacture better batteries.
summary
Although there are still some issues to be addressed for practical use, there are great expectations for the spread of all-solid-state batteries.
Batteries are sold at extremely low prices, so many people are not fully aware of their importance. Helps improve sexuality.
It is expected that there will be more opportunities to come into contact with all-solid-state batteries in the future, so it is important to be conscious of actively obtaining the latest information from now on.
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