Detailed explanation of the three major technical routes of solid-state batteries
Abstract: According to different electrolytes, solid-state batteries can be divided into three major technical routes, namely polymers, oxides and sulfides. polymer. In summary, the sulfide route suffers from its own production process and cost issues and serious safety hazards, while the polymer route has factors such as poor charging rate and harsher working temperature zone. Oxide may become the future solid-state battery technology. Mainstream.
In recent years, with the gradual improvement of my country’s new energy vehicle industry chain, companies in the power battery industry have also completed early technological accumulation, and have emerged from a group of leaders with both technical strength and capital scale represented by the Ningde era and BYD. After the cancellation of the power battery whitelist in 2019, the company officially participated in the global competition with LG Chem, Panasonic and other top companies in various countries.
Compared with other types of batteries such as lead-acid batteries, lithium-ion batteries have gradually become the main battery type in the field of new energy vehicles because of their light weight, high specific energy, and long life. According to data, since the application of lithium-ion power batteries in new energy vehicles in 2008, the actual energy density of current power batteries has increased by more than 2.5 times compared with the original 100WH/KG. While the current battery technology continues to improve, it is also gradually approaching the upper limit of the theoretical energy density of traditional positive and negative materials, separators, and electrolyte power battery systems. It is difficult to increase it. Solid-state battery technology provides the industry for exploration in this field. New possibilities.
Solid-state batteries are all solid-state lithium secondary batteries. In the traditional liquid lithium-ion power battery system, the materials used in the positive and negative electrodes largely determine the battery’s own charge capacity, that is, the energy density, and the electrolyte and diaphragm are the lithium ion transmission media. In the battery structure. In the structure of solid-state batteries, because the solid-state electrolyte can conduct lithium ions and can also act as a separator, in solid-state batteries, materials such as electrolyte, electrolyte salt diaphragm and binder polyvinylidene fluoride can be used. Omitted. At the same time, due to the overall structure of the solid electrolyte is relatively stable, and the electrolyte is not easy to leak, easy to package and wide working range, so the safety and operability have also been significantly improved.
At present, the mainstream solid-state batteries on the market can be divided into three types according to different electrolytes: Polymer, Sulfide and Oxide. Among them, polymer electrolytes are organic electrolytes, and the latter two are inorganic electrolytes.
Polymer Solid State: The current mainstream route for polymers is poly-POE and its derivative materials. This material has good high-temperature performance, but relatively, PEO-based electrolytes have improved ion conductivity at high temperatures above 60 degrees. , But at this time because the polymer is in a molten state, its mechanical properties are reduced. In the greenhouse, the polymer has higher mechanical strength, but its electrical conductivity is not high. Therefore, finding the balance point between polymer conductivity and mechanical strength is one of the urgent problems in the industry. In addition, polymers generally have a narrow electrochemical window, and electrolytes are easily electrolyzed when the potential difference is too large (>4V), which makes the upper limit of polymer performance lower. Other types of polymer electrolytes, such as PVCA, have a relatively stable chemical window (4.5V) and relatively suitable ionic conductivity. However, the high price of VC makes it difficult to commercialize on a large scale.
Sulfide Solid State: The comprehensive performance of the sulfide electrolyte solid state battery is currently the best among the three batteries. Its texture is relatively soft, and it has even higher ionic conductivity than the traditional liquid electrolyte. However, the sulfide electrolyte is very easy to interact with the air. The water, oxygen, etc. react to produce toxic gases such as H2C, which invisibly increases the difficulty of its manufacture and greatly increases the manufacturing cost, thus limiting its large-scale commercial use to a certain extent. In addition, the sulfide electrolyte has problems in the interface contact between the positive and negative electrodes and the contact stability. Although the electric double layer electrolyte technology has been designed in the industry to improve it to a certain extent, it still cannot be completely eliminated.
Oxide Solid State: At present, the most promising oxide type electrolytes are GARNET type, LISICON type and NASICON type. Among them, the GARNET type electrolyte has a higher room temperature ionic conductivity (10-3S/cm). However, the GARNET electrolyte has poor metal lithium wettability. When the battery is deposited unevenly during the continuous charge and discharge cycle, it is easy to produce lithium dendrites, which poses certain safety risks. However, studies have shown that this problem can be effectively solved by inserting polymers or gel electrolytes as buffer layers, or sputtering materials that can form an alloy layer with lithium. The LISICON type material has high conductivity, but is sensitive to H2O and CO2, so it is unstable in the air and has poor stability to metal lithium. Currently, zirconium can be doped to prevent the appearance of phase separation and greatly improve its stability. NASICON has relatively good performance, with a relatively stable structure, simple synthesis, and strong electrical conductivity. However, the electrolyte raw material contains precious metals such as germanium and titanium, making it difficult to apply on a large scale.
Source: "Research Status and Prospects of All-Solid State Lithium Battery Technology" Xu Xiaoxiong et al., Tianfeng Securities, "Review of the Latest Development of Solid Metal Lithium Battery" Duan Hui et al.
In summary, in the current mainstream solid-state battery system, the sulfide solid-state battery has extremely strict production environment requirements due to its own manufacturing process and cost issues. At the same time, it is prone to produce harmful gases such as H2C, which poses serious safety risks. The best, but the industrialization is more difficult, and the polymer has poor charging rate, extremely low energy density, and at the same time, it can only work normally above 60 degrees, so it is also difficult to use as a power battery. The relatively comprehensive performance and cost of oxide solid-state batteries, and the relatively low technical difficulty, are undoubtedly more likely to become the main technical route for solid-state batteries in the future.