What Are Semi-Solid State Batteries and Their Difference from Solid-State?
2025-02-26
It is an open secret that Toyota is spending a lot of energy on the development of solid-state batteries behind closed doors.
Once Toyota's solid-state batteries are successfully mass-produced, the range will directly reach 1,200km, even exceeding that of fuel vehicles, and the pain points of pure electric power will be solved at once.
Once Toyota's solid-state batteries are successfully mass-produced, the range will directly reach 1,200km, even exceeding that of fuel vehicles, and the pain points of pure electric power will be solved at once.
However, it seems that it will take some time for solid-state batteries to be mass-produced, but in the meantime, semi-solid statebatteries have been put into use.
So do you really understand semi-solid state batteries and solid-state batteries?
Today we will take you to understand from the perspective of engineers through 6 questions
1. What is a semi-solid state battery?
In a traditional lithium battery, the positive and negative electrodes are "energy warehouses", and the electrolyte is like a "channel" that allows lithium ions to move freely between the positive and negative electrodes. Therefore, it is also called a liquid battery.
As the name suggests, a semi-solid statebattery adopts a hybrid design of solid electrolyte and liquid electrolyte.
Specifically, the semi-solid statebattery has made innovations in electrode materials. It uses mud formed by mixing fine lithium compound particles with liquid electrolyte as electrode material. This hybrid design allows the battery to maintain the high safety of solid-state batteries while also having the high ion transmission rate of liquid batteries.
In addition, the structure of the semi-solid statebattery is also unique. It realizes the exchange of ions and the flow of current through two beams of positively and negatively charged mud flows and a water-permeable membrane.
2. What is the essential difference between semi-solid batteries and solid-state batteries?
Semi-solid statebatteries are similar in principle to solid-state batteries, but there are three significant differences.
First, the state of the electrolyte is different. Solid-state batteries use a completely solid electrolyte, while semi-solid batteries use a hybrid design of solid and liquid electrolytes.
Secondly, the upper limit of energy density is different.
Solid-state batteries usually have higher energy density because they use solid electrolytes. Of course, semi-solid statebatteries can also achieve higher energy density by optimizing electrode materials and structural design to meet the needs of most applications.
Third, since solid-state batteries use a new structure and materials, the production process is more complicated and the cost is higher than that of semi-solid statebatteries. Semi-solid statebatteries can, to a certain extent, draw on the production technology and equipment of traditional liquid batteries, reducing production costs and being more conducive to large-scale commercial applications.
3. How to distinguish between semi-solid/solid batteries?
Compared with liquid batteries, the biggest feature of semi-solid/solid batteries is the introduction of solid electrolytes. To replace the existing electrolyte + diaphragm battery structure.
But the structure of semi-solid batteries and solid-state batteries is different:
● Semi-solid batteries:
retain part of the electrolyte and diaphragm structure. Semi-solid batteries, in order to improve the conductivity, still retain a small amount of electrolyte while adding solid electrolytes, and therefore require diaphragms as a structure to separate the positive and negative electrodes. In addition, according to different technical routes, solid electrolytes also have a variety of structures such as granular and film-like.
● All-solid-state batteries:
No electrolyte is retained, and the diaphragm is uncertain. In all-solid-state batteries, the electrolyte will be completely replaced by solid electrolytes. Whether the diaphragm is replaced depends on different technical routes. In some solid-state battery technology solutions, the diaphragm is retained as a structure to support the pole piece; in other solutions, the diaphragm is completely eliminated.
"The two concepts of semi-solid and quasi-solid are the commonly accepted names in the industry. Generally, they are divided according to the proportion of liquid electrolyte in the battery cell: liquid (25wt%), semi-solid (5-10wt%), quasi-solid (0-5wt%) and full solid (0wt%)."
The corresponding percentages are also clearly divided, so once you have such a reference, it is actually clear at a glance.
4. What are the advantages of solid-state batteries?
Semi-solid batteries and solid-state batteries have four obvious advantages:
● First, they are safe.
There are two meanings here. First, the use of solid electrolytes makes the battery more compact and reduces the risk of liquid electrolyte leakage; second, the high stability of solid electrolytes also further improves the safety of the battery and reduces the possibility of explosion accidents during use. This actually solves the problem of lithium batteries being prone to "spontaneous combustion".
● Second, the energy density is high.
Due to the addition of solid electrolytes, the battery can store more energy in the same volume, thereby improving the endurance of the car.
● Third, the cycle life is long.
This is actually due to the stability of solid electrolytes, so it can better maintain its capacity and performance during long-term use, reducing the frequency and cost of battery replacement.
● Fourth, it has a wider range of applicability.
Compared with the problem that traditional liquid batteries may fail at extreme temperatures, solid-state batteries can work normally in a wider temperature range, which also makes it more feasible to use in extremely cold or hot environments.
5. What are the difficulties of solid-state batteries?
(1). Material selection and synthesis.
Semi-solid batteries require the use of special solid electrolytes and positive and negative electrode materials. The synthesis and selection of these materials need to take into account multiple factors such as battery performance, safety, and cost. At the same time, these materials need to have good ionic conductivity, chemical stability, and mechanical strength. How to be compatible with so many factors and conditions is a difficult problem!
(2). The production process is complex.
The manufacturing process of solid-state batteries involves multiple steps, including material preparation, electrode coating, electrolyte filling, battery packaging, etc. These steps require high-precision equipment and strict production control to ensure the quality and performance of the battery.
The quality of the production process directly affects the performance of the battery, so not all companies are capable of making solid-state batteries.
The quality of the production process directly affects the performance of the battery, so not all companies are capable of making solid-state batteries.
Summarize
The core difference between solid-state batteries and semi-solid statebatteries lies in the state of the electrolyte and the resulting performance characteristics. Solid-state batteries use all-solid-state electrolytes with outstanding safety and stability. The electrodes are made of pure metal or solid materials with high conductivity, low internal resistance, and high power density. They are suitable for high-end applications such as electric vehicles and drones.
Semi-solid batteries combine the advantages of liquid and solid electrolytes, are simple to prepare and low in cost. They wrap the liquid electrolyte with polymer materials to achieve richer electrochemical properties and are suitable for a wide range of energy storage devices and wearable devices. Both are new battery technologies that have significantly improved safety, energy density and cycle life compared to liquid batteries. When choosing, you need to weigh cost and performance based on specific application scenarios and needs to make the best decision.
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