Lithium-ion lithium-ion batteries have had a profound impact on daily life, commercial use of carbon negative lithium-ion battery is now basically close to its theoretical capacity, it is difficult to meet the portable electronic devices, electric vehicles and large-scale energy storage, etc. more and more High application requirements. Lithium metal has the largest theoretical energy density (3860mAhg? 1 or 2061mAhcm? 3) and the lowest electrochemical potential (relative to the standard hydrogen electrode of 3.04V) in the material that can be used as the negative electrode of the lithium battery, and is the next generation of high energy lithium Batteries such as Li-S and Li-air battery anode material of the best choice. However, the metal lithium anode in the practical application of easy to produce dendrites, to solve the problem of safety and stability of the current lithium metal anode research focus.
Recently, Prof. Cui Yi of the Department of Materials Science and Engineering at Stanford University published a review entitled "Reviving the lithium metal anode for high-energy batteries" at Nature Nano technology, which first summarizes the current understanding of the negative electrode of lithium metal Recent advances in material design and advanced characterization methods, and provide a reference for future research directions of metallic lithium negative electrodes.
Professor Cui Yi: the revival of the metal lithium anode for high energy batteries
Overview of the overview
1. Metal lithium negative challenges
Before the practical use of lithium metal anode, it needs to overcome its safety and cycle stability and other aspects of the challenges. During the charge-discharge cycle, lithium will be unevenly deposited to form dendrites and cause short-circuiting of the battery. At the same time, the low Kurun efficiency and the increasing lithium-over potential of the lithium will lead to a sharp decrease in capacity. In order to solve these problems, there is a need for a more in-depth understanding of interfacial chemistry, the behavior of lithium deposits, and the linkages between them.
1.1 Lithium surface solid electrolyte interface formation
Solid electrolyte interface (SEI) is the focus of battery research. Because Li + / Li has a high negative electrochemical potential, any electrolyte can be reduced on the lithium surface, through the passivation of SEI can solve this problem. However, the metal lithium anode on the SEI requirements are high, lithium on the SEI should have a high lithium ion conductivity and good electronic blocking ability, composition, morphology and ionic conductivity to be uniform. As the cycle of the intermittent interface is relatively large, but also requires SEI has good flexibility and even flexibility.
Alkyl lithium carbonate and ethers are two important electrolytes suitable for lithium negative electrodes. Improve the lithium anode in carbonate electrolytes, which is expected to replace the traditional carbon negative electrode and greatly improve the battery capacity. The development of lithium anode in ether electrolyte In the long run will be conducive to the development of Li-S and Li-air batteries. More importantly, the mechanism of the two electrolyte systems SEI is similar, and the discovery in a system can be applied to another system.
1.2 lithium dendrite growth theory
When the metal is electroplated with high current, such as Cu, Ni and Zn, the cation is gradually depleted, breaking the electric charge of the electrode surface to produce a space charge layer, resulting in uneven metal deposition, dendritic growth phenomenon occurs. However, in the lithium battery, the formation mechanism of lithium dendrites are different, need to consider the impact of interface chemistry. Lithium reduction electrode electrode potential is relatively high, will spontaneously form SEI layer on the surface. If the conductivity of the lithium ions of SEI is not uniform, it will lead to uneven nucleation. In addition, the volume changes in the cycle will cause SEI cracks, which in turn will exacerbate the uneven deposition of lithium. Lithium dendritic growth is a self-enhancing process.
1.3 Maximum relative volume change
All of the electrode material undergoes a volume change during the charge and discharge cycle, and even a commercial graphite electrode has a 10% volume change. For the metal lithium, because it is not the main body, the volume change is greater. From a practical point of view, the unilateral commercial electrode area capacity needs to reach 3mAhcm? 2, for lithium there will be 14.6μm volume change. This value will be even greater in the future, meaning that the movement of the lithium interface will reach tens of microns during the cycle.