Analysis

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In recent years, with the gradual improvement of China's new energy automobile industry chain, enterprises in the power battery industry have also completed early technology accumulation, and stepped out of a number of leading enterprises with both technical strength and capital scale, such as Contemporary Ampere Technology Co., Ltd. and BYD. After the white list of 20 19 power battery was cancelled, it officially participated in the global wrestling with top enterprises in LG Chem, Panasonic and other countries.

Compared with other types of batteries such as lead acid, lithium-ion batteries have the characteristics of light weight, high specific energy and long life, and gradually become the main battery type in the field of new energy vehicles. According to the data, since the lithium-ion power battery was applied to new energy vehicles in 2008, the actual energy density of the power battery has been fully increased by more than 2.5 times compared with the original 100 Wh/kg. On the other hand, while the current battery technology is progressing, it gradually approaches the upper limit of the energy density of the traditional theory of positive and negative materials, separators and electrolyte power batteries, and it is difficult to improve it, while the solid-state battery technology is in this field.

Solid-state battery, that is, all-solid lithium secondary battery. In the traditional liquid lithium-ion power battery system, the materials used for the anode and cathode largely determine the charging capacity of the battery itself, that is, the energy density. Electrolyte and separator exist in the battery structure as lithium ion transmission media. In the structure of solid-state battery, because its solid electrolyte can not only conduct lithium ions, but also play the role of diaphragm, materials such as electrolyte, electrolyte salt diaphragm and binder polyvinylidene fluoride can be omitted in solid-state battery. At the same time, because its solid electrolyte is generally stable in structure, electrolyte is not easy to leak, easy to package and has a wide working range, its safety and operability have also been significantly improved.

At present, the mainstream solid-state batteries in the market can be divided into three types according to the different electrolytes: polymer, sulfide and oxide. Among them, polymer electrolyte belongs to organic electrolyte, and the latter two belong to inorganic electrolyte.

Polymer solid state: At present, POE and its derivative materials are the main route of polymers, which have good high-temperature performance. Relatively speaking, although the ionic conductivity of PEO-based electrolytes has improved at a high temperature above 60 degrees, its mechanical properties have declined at this time because the polymers are in a molten state. In the greenhouse, polymer has high mechanical strength, but its conductivity is not high. Therefore, it is one of the urgent problems to find the balance between the conductivity and mechanical strength of polymers. In addition, the electrochemical window of polymer is generally narrow, and the electrolyte is easily electrolyzed when the potential difference is too large (>: 4V), which makes the upper limit of polymer performance low. Other types of polymer electrolytes, such as PVCA, have relatively stable chemical window (4.5V) and relatively suitable ionic conductivity, but VC is too expensive to be commercialized on a large scale.

Sulfide solid state: the comprehensive performance of sulfide electrolyte solid state battery is the best among the three batteries at present, with soft texture and even higher ionic conductivity than traditional liquid electrolyte. However, sulfide electrolyte easily reacts with oxygen in water and air to produce toxic gases such as H2C, which invisibly increases its manufacturing difficulty and greatly increases its manufacturing cost, thus limiting its large-scale commercial use to some extent. In addition, sulfide electrolyte has problems in interfacial contact and contact stability between anode and cathode. Although electric double layer electrolyte technology has been designed in industry to improve it to some extent, it still cannot be completely eliminated.

Solid oxide: At present, the most promising oxide electrolytes are garnet, LISICON and NASICON, among which garnet electrolyte has higher ionic conductivity at room temperature (10-3S/cm). However, the wettability of garnet electrolyte to lithium metal is poor, and lithium dendrites are easy to occur when the battery is deposited unevenly during continuous charge and discharge cycles, which has certain safety hazards. However, research shows that this problem can be effectively solved by inserting polymer or gel electrolyte as buffer layer or sputtering substances that can form alloy layer with lithium. LISICON-type materials have high conductivity, but are sensitive to H2O and CO2, so they are unstable in air and have poor stability to lithium metal. At present, doping zirconium can prevent phase separation and greatly improve its stability. NASICON has good performance, stable structure, simple synthesis and strong conductivity. However, the raw materials of this electrolyte are precious metals such as germanium and titanium, which makes its large-scale application difficult.

On the whole, in the current mainstream solid-state battery system, sulfide solid-state batteries have extremely high requirements on the production environment due to their own manufacturing process and cost problems, and are prone to produce harmful gases such as H2C, which has serious safety hazards. Therefore, although it has the best performance, it is difficult to industrialize. However, polymers have the problems of poor charging rate, extremely low energy density and can only work normally above 60 degrees, so it is difficult to be used as power batteries. The comprehensive performance, cost and relatively low technical difficulty of oxide solid-state batteries are undoubtedly more likely to become the main technical route of solid-state batteries in the future.