Lithium negative electrode with functional protective layer and lithium sulfur battery

Abstract

The invention relates to a lithium negative electrode with a functional protective layer and a lithium sulfur battery. The lithium negative electrode is provided with a functional protective layer which is coated on the surface and includes a conductive polymer. In the lithium sulfur battery, the functional protective layer of the lithium negative electrode is contacted with an electrolyte, so that a stable interface is formed between the electrolyte and a base body of the lithium negative electrode.

Description

Technical field [0001] The invention belongs to the field of electrochemical technology, and specifically relates to a lithium negative electrode with a functional protective layer and a lithium-sulfur battery including the lithium negative electrode. Background technique [0002] With the development of society, mobile phones, portable computers, electric cars, digital cameras, I-pads and other portable electronic products are flooding people's lives. Among them, as the main energy storage device, lithium batteries have occupied a dominant position in small devices. However, as people's requirements for portable life increase, traditional lithium batteries can no longer meet human needs. Therefore, the next generation of lithium batteries with high specific energy, high safety, long service life and low cost are high expectations. [0003] The positive electrode is the key to increase the specific energy of the battery. The sulfur cathode has a theoretical specific capacity of 1...

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Problems solved by technology

[0006] The above measures start from the inside of the battery electrode structure. Although it can reduce the impact of the shuttle effect on battery performance to a certain extent, the materials used are complicated to prepare and costly, which is not convenient for large-scale production.

At the same time, the problems in the negative electrode of lithium-sulfur batteries are serious and complex, and there are few related studies

[0007] The problems of the negative electrode of lithium-sulfur batteries mainly include the following three aspects: First, because the Fermi energy level of metal lithium is low, metal lithium is unstable to the electrolyte, and the SEI film formed between them is unstable. , and will be consumed during the cycle, which will cause loss of electrolyte and lithium anode, so in order to match the sulfur cathode, the lithium anode of the lithium-sulfur battery must be excessive, reducing the energy density of the battery

In addition, like other batteries using metal lithium as the negative electrode, during the long-term charging and discharging process of the battery, the uneven deposition of lithium causes the growth of lithium dendrites, and the continuous growth of lithium dendrites may puncture the separator, resulting in safety hazards. sexual problems

At the same time, for lithium-sulfur batteries, lithium polysulfides, the intermediate products of the electrochemical reaction of the battery, will dissolve in the electrolyte, they will migrate to the lithium negative electrode and react with them to form insoluble and insulating lithium sulfide, the generation of lithium sulfide will not only cause The loss of active material will cause the battery capacity to decay, and will increase the polarization of the battery. At the same time, the positive and negative reactions between lithium polysulfide and lithium sulfide will occur simultaneously during charging, reducing the Coulombic efficiency of the battery.

[0008] There is very little research work on lithium anodes for lithium-sulfur batteries, but for ordinary lithium anodes, the relevant work is summarized as follows: Part of the work revolves around electrolyte additives, such as adding AlI to the electrolyte 3 , Li 2 CO 3 (J. Electrochem. Soc. 144(1997) 1709.), LiNO 3 (Journal of Power Sources196(2011)9839–9843), ionic liquids (J.Phys.Chem.C2013,117,4431-4440), etc., promote the formation of a more stable SEI film at the negative electrode during the electrochemical process, but these additives However, it will be gradually consumed in the electrochemical reaction process, so it is difficult to obtain very stable electrochemical performance, or the price is expensive, which affects the practical process of the battery; a part of the work is coated with a polymer on the surface of the lithium negative electrode (Journal of Power Sources244( 2013) 363-368), the presence of the polymer is beneficial to reduce the direct contact between the lithium negative electrode and the electrolyte, reduce the irreversible reaction between the lithium negative electrode and the electrolyte, and then obtain a relatively stable SEI film, but the non-conductive polymer Therefore, the migration of electron ions will still be delayed to a certain extent; in addition, the growth of Li on the surface of the lithium negative electrode 3 Li-ion conductors such as N (Journal of Power Sources 196 (2011) 8091–8097) or LiPON (Rare Metal Materials and Engineering 39 (2010) 1664-1667) can indeed solve the above three problems simultaneously to a large extent, however, growth The process is very complicated, and the reaction of Li3N with water in the air is very unstable, while the conductivity of LiPON is not high enough.

There are also some studies that introduce monomers such as pyrrole into the surface of lithium negative electrodes (Electrochimica Acta103(2013) 199–205), and obtain good results, but the preparation and design of materials are complex electrochemical processes, which are not conducive to large-scale applications

Although there have been literatures on the modification of pyrrole monomers to lithium anodes, pyrrole monomers have not been doped and oxidized, and are not conductive themselves. They can only stabilize SEI, but they will cause battery polarization. Suitable for lithium-sulfur batteries

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