Interpretation of Ningde era solid-state battery patents

by:CTECHi     2021-09-12
There are many side reactions at the interface between metallic lithium and liquid electrolyte, the uneven and unstable distribution of SEI film leads to poor cycle life, and the uneven deposition and dissolution of metallic lithium lead to the uneven formation of lithium dendrites and pores, thereby causing safety problems. Lithium dendrites grow slowly in solid electrolytes, are difficult to penetrate, have poor flammability, and have higher safety. However, the important problem lies in low conductivity, which has become a bottleneck in the commercial application of solid-state batteries. Existing solid electrolytes can be divided into three categories according to the material system: sulfides, oxides and polymers. Among them, in the 'sulfide' route, the current Ningde era, Qingtao, Toyota, Honda, Panasonic, Samsung, etc. all have technical layouts. On January 19, the State Intellectual Property Office published two patents for solid-state batteries from the Ningde era: a method for preparing a solid electrolyte, a sulfide solid electrolyte sheet and a method for preparing the same. The patent documents show that the former patent is to improve the conductivity of the solid electrolyte; the latter patent is to improve the conductivity of the solid electrolyte sheet, the energy density of the battery and the cycle performance. 'A method for preparing a solid electrolyte' is as follows: a method for preparing a solid electrolyte The lithium precursor is selected from one or more of Li2S and LiX; wherein X is selected from F, Cl, Br, and I The central atom ligand is selected from at least one of P2S5, SiS2, GeS2, B2S3, and Al2S3. This preparation method uses borate as the doping raw material to modify the sulfide solid electrolyte to obtain a solid electrolyte co-doped with B and O. The reason why the element distribution test results of solid electrolytes can improve the conductivity is that the doping of B element can reduce the binding use of anions to lithium ions and improve the transmission capacity of lithium ions; O element can be partially doped instead of S element. The mixed anion effect can improve the conductivity of lithium ions, and can inhibit the formation of a space charge layer at the interface between the oxide cathode and the sulfide electrolyte, and reduce the interface impedance. It can be seen from the figure below that the incorporation of 1% borate can increase the conductivity of the electrolyte. The impedance spectrum of the solid electrolyte. At the same time, the patent utilizes the property of borate to form a uniformly dispersed solution in the solvent. During the doping modification process, a sufficient gap between the raw material of the electrolyte and the borate to be doped is realized. mix. In addition, the borate can be completely decomposed at the phase forming temperature of the sulfide electrolyte, reducing the introduction of impurities or residual reactants, so that the ionic conductivity of the prepared sulfide solid electrolyte is significantly improved, which is beneficial to the energy of the all-solid battery The play of density. The sulfide solid electrolyte sheet supplied by another patent includes a sulfide electrolyte material and a boron element doped in the sulfide electrolyte material. According to the patent, the important use of introducing boron into the sulfide solid electrolyte is to reduce the binding and uniform distribution, specifically: 1. Boron can effectively reduce the binding use of anions to lithium ions and improve the transmission capacity of lithium ions; 2. The boron element is evenly distributed in the sulfide solid electrolyte, the doping uniformity and conductivity of the solid electrolyte are improved, and the surface roughness of the solid electrolyte sheet is significantly improved, which is beneficial for lithium ions in the sulfide solid electrolyte sheet and lithium The diffusion process of the metal anode interface reduces the interface impedance and improves the cycle performance of the battery. Optical microscope picture of surface roughness test of solid electrolyte sheet On January 9, NIO announced a 150kWh battery pack, which can achieve an energy density of 360Wh/kg, and is scheduled to be delivered in the fourth quarter of 2022. However, its battery supplier has not yet been announced, and the industry speculates that it may be Ningde Times, Qingtao, Weilan, and Huineng Technology. Zeng Yuqun, chairman of CATL, revealed in 2019 that, with regard to cutting-edge technologies such as solid-state batteries, CATL will continue to invest in cutting-edge research and product development. According to the high-tech lithium battery tracking, CATL has many years of technical reserves in the field of solid-state batteries. As early as 2016, CATL revealed its research and development progress in the field of solid-state batteries, and its involvement in polymer and sulfide systems. At that time, regarding the development of the sulfide system, Ningde Times gave important strategies including: improving the interface compatibility between the positive electrode and the solid electrolyte, developing hybrid processes, doping and modifying sulfides, and developing all-solid-state battery manufacturing processes (such as Uniform coating, hot pressing) and so on. It can be seen that the above strategies are also reflected in these two patents. CATL has accumulated years of research and development in the field of solid-state batteries. It is worth looking forward to whether it can accelerate the commercialization of solid-state batteries.
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