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"German Applied Chemistry" cyclohexanone refreshes the world record of organic positive electrode capacity of lithium ion battery

2019-05-23 来源:亚科官网
 
Recently, Chen Jun, a member of the Chinese Academy of Sciences and a professor at the School of Chemistry of Nankai University, designed and synthesized a high-capacity lithium-ion battery organic cathode material, cyclohexanone, which set a new world record for the capacity of organic cathode materials for lithium-ion batteries. Related research results were published in German Applied Chemistry.
The positive electrode is the "short board" of the lithium ion battery
Lithium-ion battery capacity, energy density and other performance by the positive limit, Chen Jun told reporters: "It can be said that the positive electrode is a 'short board' of lithium-ion batteries."
In addition, the existing lithium ion battery cathode material contains metal elements such as cobalt, and the synthesis process involves techniques such as beneficiation, smelting, and recycling, and there are problems such as lack of resources and environmental pollution. "Therefore, high-capacity, renewable, green, low-cost lithium battery cathode materials have become the research hotspot and focus in this field." Chen Jun said.
Organic electrode materials containing carbon, hydrogen, oxygen and other elements are considered to be promising next-generation lithium ion battery cathode materials due to their structural design, environmental friendliness and low cost. However, such materials still face problems such as low actual capacity (<600 mAh/g) and easy to dissolve in organic electrolytes, resulting in lower energy density, more serious capacity degradation, and shorter cycle life. Therefore, how to design and synthesize an organic positive electrode material with ultra-high capacity and solve its dissolution problem in an electrolyte is a challenge of a lithium ion battery.
The researchers targeted the cyclohexanone. The material consists of only six carbonyl groups, there are no non-electrochemically active structural units, and each carbonyl group can participate in the electrochemical reaction. Therefore, cyclohexanone exhibits the highest theory specific capacity (957 mAh/g) in many organic carbonyl cathode materials.
"The development of higher capacity lithium-ion battery cathode materials can continuously improve the energy density of the battery system, thereby increasing the battery operating time." Chen Jun said.
Breakthrough: increase material capacity and life
Among the many organic carbonyl cathode materials, although the cyclohexanone material has the highest theoretical capacity, it easily reacts with water to form a stable hydrate, and thus has not been successfully synthesized. After analysis and exploration, the researchers developed a new method of dehydration reaction, and successfully realized the synthesis of cyclohexanone material by precisely controlling the temperature and pressure of the dehydration reaction.
In addition, as for the positive electrode material, the length of the cycle life is an important factor in determining whether it can be practically applied. As an organic small molecule material, cyclohexanone is easily dissolved in a lithium ion electrolyte based on organic esters and ethers, resulting in a short cycle life.
In order to solve this problem, the team combined the principle of similar compatibility, using an ionic liquid-based electrolyte, and through series optimization, found that the greater polarity of the ionic liquid can greatly reduce the solubility of cyclohexanone.
The method effectively improves the cycle life of cyclohexanone and lays a foundation for further practical application of cyclohexanone. He said that synthesizing ultra-high capacity cyclohexanone materials and optimizing the matching electrolytes to improve material life are two major breakthroughs in this research.
Subsequently, the researchers studied the charge-discharge reaction mechanism and electrochemical performance of cyclohexanone in lithium ion batteries. The results show that the specific capacity of cyclohexanone can reach 902 mAh/g, which is the currently known organic electrode material. The highest capacity, assembled battery also reflects the characteristics of long cycle life.
The "peak" of lithium-ion batteries
The researchers said that lithium-ion batteries with cyclohexanone as the positive electrode can achieve higher battery capacity and longer life, and provide support for future applications of lithium-ion batteries in electric vehicles and energy storage grids.
In this study, the ultra-high capacity cyclohexanone cathode material was synthesized for the first time. The performance and charge-discharge mechanism of cyclohexanone in lithium ion battery were studied by theoretical calculation and experimental means. It is a work with original innovation. An important breakthrough in the field of sustainable energy storage technology in the future.
Chen Jun pointed out that the synthesis of cyclohexanone cathode materials for ultra-high-capacity lithium-ion batteries and the application of lithium-ion batteries have increased the energy density of organic cathode materials to a new level.
“Specifically, the energy density of cyclohexanone material is as high as 1533 Wh/kg, which is much higher than the current commercial lithium ion battery cathode materials, such as lithium cobalt oxide (about 600 Wh/kg). Other organic cathode materials reported in the current research." Chen Jun believes that the further optimization of high energy density cyclohexanone material containing only high abundance of carbon and oxygen is beneficial to its large-scale practical application for the future. New ideas for the design, fabrication and battery applications of high-capacity organic electrode materials.
Edited by Suzhou Yacoo Science Co., Ltd.