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2019-03-14 来源:亚科官网

 In recent years, with the rapid development of consumer electronics equipment, electric vehicles, portable medical electronic equipment, power storage base stations, and aerospace, higher requirements have been placed on rechargeable lithium-ion battery energy storage systems, namely, higher energy density, longer cycle life, etc. Lithium cobaltate (LCO) plays an important role in the cathode material of lithium ion batteries.

Compared with other positive electrode materials, lithium cobaltate has a high compact density and excellent electrochemical performance, but its actual capacity is only half of the theoretical capacity. Studies have shown that lithium cobaltate can release more reversible capacity at high voltages. Then, is it possible to achieve a stable cycle of lithium cobaltate material at high voltage to cope with the craving for high-energy energy storage systems in energy storage fields such as consumer electronics and electric transportation?

Recently, the Lu Yingying team of Zhejiang University and the Houlong L. Zhuang team of Arizona State University have cooperated to modify the interface of Lithium Cobaltate with hydrothermal-assisted Li, Al and F-based hybrid modification strategies to prepare a ultra high voltage lithium cobalt oxide material LAF-LCO with high performance.

Although high-voltage lithium cobalt oxide batteries have the advantages of high-pressure solid density and high energy density, lithium cobalt oxide materials also face many challenges under high-voltage operating conditions, such as the occurrence and activity of positive electrode materials and electrolyte side reactions, dissolution of Co element, unstable structure of positive electrode material, etc. In addition, it is worth noting that at 4.6V ultra-high voltage, lithium cobaltate will undergo structural phase transition from O3 to H1-3. At this time, the lithium ion diffusion rate of the lithium cobaltate crystal is significantly lowered, so that the concentration gradient is rapidly increased, thereby causing a large internal stress difference, eventually causing destruction of the crystal structure, resulting in the phase transition becoming "irreversible". This problem is particularly serious in the surface structure of lithium cobaltate crystals. This is also one of the main reasons limiting the stable circulation of lithium cobaltate at ultra high voltage (4.6 V).

The ultra-high voltage lithium cobalt oxide material developed by the Lu Yingying team of Zhejiang University and the Houlong L. Zhuang team of Arizona State University provides a feasible solution to the above problems. They designed a hybrid interface modification strategy of Li, Al, F, and synthesized a new high-voltage LAF-LCO material by simple hydrothermal method. The mixed modified interface protective layer constructed by the above method can be divided into a surface coating layer and a surface layer doped layer. On the one hand, the surface coating layer is electrochemically stable, which can effectively avoid direct contact between the electrolyte and the positive electrode material, inhibit the occurrence of interfacial side reactions, and reduce the loss of active Co; on the other hand, Li-Al-Co-O-F surface layer doping the heterogeneous layer has a stable crystal structure, and at the same time broadens the Li+ transmission channel, alleviates the strain of the surface structure, and contributes to the reversible progress of the lithium cobaltate O3 to H1-3 phase transition. Finally, the LAF-LCO material exhibits good cycle stability and excellent electrochemical performance. Under the cycle conditions of 4.6 V and 27.4 mA g-1, the discharge specific capacity of the battery using LAF-LCO material was as high as 170.7 mAhg-1 after the cycle of 200 cycles, and the capacity retention rate was 81.8%. The control battery was only 68.2 mAh g-1, and the capacity retention rate was 32.8%.

The LAF-LCO material exhibits excellent high voltage cycling performance, making the high voltage lithium cobalt oxide battery system one of the strong candidates for the next generation of high specific energy battery systems. At the same time, in view of the simple and cheap preparation method, it provides a feasible idea for the industrial application of high-voltage lithium cobaltate materials, and has potential commercial value, and is expected to be widely used in portable consumer electronics, unmanned aerial vehicles and high-energy storage such as aerospace.

Edited by Suzhou Yacoo Science Co., Ltd.