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Introduction to the latest technology of lithium batteries
The graphite negative electrode density of traditional lithium-ion batteries is relatively low. In order to pursue high density, new negative electrode materials such as silicon carbon and silicon oxygen have become new hotspots pursued by enterprises. However, silicon oxide may have low initial efficiency and require lithium supplementation. During the initial charging and discharging process of liquid lithium-ion batteries, the electrode material reacts with the electrolyte at the solid-liquid interface, forming a passivation layer covering the surface of the electrode material. This passivation layer is an interface layer with the characteristics of solid electrolyte. It is an electronic insulator but an excellent conductor of Li+. Li+can be freely embedded and detached through this passivation layer. Therefore, this passivation film is called “solid electrolyte interface” (SEI film for short) (positive electrode also has a layer of film, but at this stage it is believed that its impact on the battery is far less than the SEI film on the negative electrode surface [2]). The lithium replenishment process for silicon carbon negative electrode is to pre coat a layer of lithium metal on the surface of the silicon carbon negative electrode, which is in close contact with the negative electrode. After pouring the electrolyte, the coating reacts with the negative electrode and embeds into the negative electrode particles, pre storing a portion of lithium ions inside the negative electrode to compensate for the Li ions consumed during the first charge discharge or cycle process due to the formation or repair of SEI film. Compared to the high difficulty and high investment negative electrode lithium replenishment process, positive electrode lithium replenishment appears much simpler. The typical positive electrode lithium replenishment process involves adding a small amount of high-capacity positive electrode material to the positive electrode slurry. During the charging process, excess Li elements are extracted from these lithium rich positive electrode materials and embedded into the negative electrode to supplement the irreversible capacity of the first charge and discharge. Through this complex lithium replenishment process, the density of negative electrode materials can be increased. At present, it is not known what specific technology Zhiji Automobile will use, but it is basically a foregone conclusion that Zhiji Automobile will apply this high-end lithium battery.
Finally, let’s take a look at the last step in improving the energy density of battery cells – the electrolyte.
Electrolyte – Solid State Battery&Jelly Battery
On December 8th local time, QuantumScape, a startup supported by Volkswagen and Bill Gates, announced its latest solid-state battery and stated that the battery will be put into production in 2024. This type of solid-state battery has significant improvements compared to traditional lithium-ion batteries: they can increase the range of electric vehicles by 80%. Next, let’s explore what solid-state batteries are and their benefits.
While improving the energy density of batteries, the safety of batteries must be considered. Fundamentally eliminating the safety hazards of lithium-ion batteries still lies in improving the safety of battery materials. But for positive electrode materials, these two aspects are contradictory. For example, as mentioned earlier, increasing nickel content can improve energy density, but increasing nickel content means reduced safety Is there any way to enhance the safety of batteries from other aspects, so as to increase energy density more confidently? At this point, we need to consider from the perspective of electrolytes. Numerous studies have shown that liquid electrolytes are involved in most of the reactions during the thermal runaway process of batteries, greatly reducing the initial reaction temperature of the battery and lowering the threshold for thermal runaway. Therefore, improving electrolyte safety is one of the most effective methods to achieve battery safety [3]. The physical properties of liquid electrolytes determine that they cannot avoid leakage and are not conducive to reducing battery volume and increasing energy density. Therefore, in order to improve energy density and safety, the solidification of electrolytes has become a trend. We refer to batteries with solid-state electrodes and electrolytes as solid-state batteries. Solid state battery cells without liquid inside not only have higher safety, but also can be assembled in series and parallel first, reducing the material used for packaging shells. The PACK design is greatly simplified, which also improves the energy density of battery groups.
