Lithium-ion battery capacity refreshes "world record"

Lithium-ion batteries have been widely used in various types of portable electronic equipment, and are expected to be used in large-scale applications in electric vehicles, smart grids, and distributed energy storage. With the development of human society, as well as informationization, mobility, and intelligence, new high-capacity, long-life, low-cost, and high-security batteries are urgently needed to be developed.

Recently, the team of Chen Jun, an academician of the Chinese Academy of Sciences and a professor at Nankai University, designed and synthesized a kind of ultra-high capacity lithium-ion battery organic cathode material-cyclohexanone, which set a new world record for the capacity of lithium-ion battery organic cathode materials. Related results were published in "German Applied Chemistry".

The positive electrode is the "short board" of the lithium ion battery

The capacity and energy density of lithium-ion batteries are limited by the positive electrode. Chen Jun told the China Science Journal: "It can be said that the positive electrode is a 'short board' for lithium-ion batteries."

In addition, the existing cathode materials of lithium-ion batteries contain metal elements such as cobalt, and the synthesis process involves beneficiation, smelting, and recycling technologies. There are problems such as lack of resources and environmental pollution. "Therefore, high-capacity, renewable, environmentally friendly, low-cost lithium battery cathode materials have become the current research focus and focus in this field." Chen Jun said.

Organic electrode materials containing elements such as carbon, hydrogen, and oxygen are considered to be promising cathode materials for next-generation lithium-ion batteries due to their structural designability, environmental friendliness, and low cost. However, these materials still face problems such as low actual capacity (<600 mAh / g), easy dissolution in organic electrolytes, etc., resulting in lower energy density, severe capacity attenuation, and short cycle life. Therefore, how to design and synthesize an organic cathode material with ultra-high capacity and solve its dissolution in the electrolyte is a challenge for lithium ion batteries.

The researchers targeted cyclohexanone. The material is composed of only six carbonyl groups, there is no non-electrochemically active structural unit, and each carbonyl group can participate in electrochemical reactions. Therefore, cyclohexanone currently has the highest theoretical ratio among many organic carbonyl cathode materials Capacity (957 mAh / g).

"Developing higher capacity lithium-ion battery cathode materials can continuously improve the energy density of the battery system, thereby extending the working time of the battery." Chen Jun said.

Breakthrough: Improve the capacity and life of materials

Among many organic carbonyl cathode materials, although cyclohexanone has the highest theoretical capacity, it easily reacts with water to form stable hydrates, so it has not been synthesized. After analysis and exploration, the researchers developed a new method of dehydration reaction. By accurately controlling the temperature and pressure of the dehydration reaction, the synthesis of cyclohexanone material was successfully achieved.

In addition, as far as the cathode material is concerned, the length of the cycle life is an important factor that determines its practical application. As a small organic material, cyclohexanone is easily dissolved in lithium ion electrolytes based on organic esters and ethers, resulting in a short cycle life.

The first author of the paper, Lu Yong, Ph.D. of Nankai University, said in an interview with China Science News that in order to solve this problem, the team combined with the principle of similar miscibility and used an electrolyte based on ionic liquids. The polarity can greatly reduce the solubility of cyclohexanone.

Chen Jun pointed out that this method effectively improved the cycle life of cyclohexanone, and laid a foundation for the further practical application of cyclohexanone. He said that the synthesis of cyclohexanone with ultra-high capacity materials, and the optimization of matching electrolytes, to improve material life are the 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 discharge capacity of cyclohexanone can reach 902 mAh / g, which is currently known as an organic electrode material The highest capacity, the assembled battery has characteristics such as long cycle life.

New height of lithium ion battery

The researchers said that the lithium-ion battery with cyclohexanone as the positive electrode has the advantages of higher battery capacity and longer life, and provides support for future applications of lithium-ion batteries in electric vehicles, energy storage grids and other fields.

The reviewer of the paper believes that this research is the first synthesis of ultra-high capacity cyclohexanone and cathode materials, and the theoretical calculation and experimental means to study the performance and charge-discharge mechanism of cyclohexanone in lithium-ion batteries is an original Innovative work is an important breakthrough in the field of sustainable energy storage technology in the future.

Chen Jun pointed out that the synthesis of the ultra-high capacity lithium-ion battery cyclohexanone ketone cathode material and the application of lithium-ion battery exploration 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 currently commercially available cathode materials for lithium-ion batteries, such as lithium cobaltate (about 600 Wh / kg), and it is also high Other organic cathode materials reported in the current research. "Chen Jun believes that further optimization of high-energy density cyclohexanone materials containing only high-abundance carbon and oxygen elements will help realize their large-scale practical applications for the future. New ideas are provided for the design, preparation and battery application of high-capacity organic electrode materials.

Lynden A. Archer, a member of the American Academy of Engineering and a professor at Cornell University, said that this groundbreaking achievement has pushed the work in this field to the top. (â–  Our correspondent Xin Yu correspondent Ma Chao)

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