New Progress on Negative Materials of Lithium-ion Battery

In recent years, lithium-ion batteries have been widely used in portable electronic equipment, electric vehicles and energy storage power stations. However, commercial lithium-ion batteries with graphite as the negative electrode have not been able to meet people's needs for high energy density, long cycle life and fast charging and discharging. Therefore, the development of new negative electrode materials to replace traditional graphite materials has become the focus of research in this field.

The conversion lithium storage mechanism shows that the theoretical capacity of the transition metal oxides is between 700 and 1000 mAhg-1, and in the actual test, most transition metal oxides will have a "supercapacity" phenomenon with reversible capacity greater than the theoretical capacity. The study found that the solid electrolyte interface(SEI) membrane components(such as Li2CO3, LiOH, LiAc, etc.) on the surface of the active material undergo reversible decomposition and generation under the catalysis of the transition metal, thereby achieving more lithium ions and electrons. Release and storage. According to the conversion mechanism, the layered base cobalt acetate(LHCA) is converted to Co nanocrystals, LiOH, and LiAc after being charged with lithium, which is very similar to the components of the SEI membrane described above. This means that LHCA may provide much higher capacity than the conversion mechanism, that is, LiOH and LiAc will provide additional capacity under the catalysis of Co nanocrystals. Inspired by this, the research team of Zhejiang University of Technology and Nankai University conducted nanocrystallization and compounding of LHCA and conducted in-depth research on its lithium storage behavior.

The team prepared ultra-thin LHCA nanoparticles by a simple solvent heat method, which allowed the nanoparticles to be loaded face to face on the surface of graphene. The LHCA/graphene composite exhibits high capacity, excellent cyclic stability, and doubling performance. In 1A? After the current density of the G-1 circulates for 200 weeks, its reversible capacity is about 1050mAh? G-1, in 4A? After the current density of the G-1 circulates for 300 weeks, the reversible capacity can still be maintained at 780mAh? G-1, much higher than the theoretical capacity calculated according to the conversion mechanism(about 460mAh? G-1). The authors also confirmed the mutual transformation of acetate and acetaldehyde during the cycle process through Fourier transform infrared spectroscopy, and proposed a new mechanism for lithium storage involving the electrochemical catalytic conversion of Co nanoparticles to OH groups.

Layered alkali salts are a large family. The study of the lithium storage properties of LHCA in this work opens a window for such materials to be used for energy storage. In addition, the successful preparation of regular morphology Nano layered alkali salts and their composite materials has also expanded the understanding of the morphology of the material and potential applications(especially in the fields of energy storage, magnetism and ion exchange). More importantly, the research results provide new ideas for the design and development of the next generation of energy storage materials, and at the same time help us to further understand the contribution of SEI membrane components(especially LiOH and LiAc) to lithium storage.

This achievement was recently published in AdvancedFusionalMaterials. Associate Professor Suliwei of Zhejiang University of Technology and Heijinpei Wanglianbang of 2016 doctoral students are co-authors, and Professor Zhouzhen of Zhejiang University of Technology and Professor Li Guozheng of Nankai University are communication authors.

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