Recyclable and more environmentally friendly, University of Maryland discovers new active materials for lithium-ion batteries

by:CTECHi     2021-08-12

Lithium Grid News: Due to the increasing demand for rechargeable lithium-ion batteries (LIBs), environmental friendliness and sustainability have become key factors for electrode materials. However, manufacturing inorganic electrode materials such as LiCoO2 and graphite consumes a lot of energy and releases a lot of CO2. In addition, used batteries may cause more serious environmental problems by leaking toxic heavy metals in cobalt-based electrodes into soil and water. In order to circumvent environmental and sustainability challenges, the development of energy-saving, sustainable and recyclable battery materials is of great significance.

[Introduction]

Recently, Wang Chunsheng's team at the University of Maryland designed a new chemical substance based on the electrochemical conversion of nitro compounds to azo compounds for high-performance lithium-ion batteries. Select 4-nitrobenzoic acid lithium salt (NBALS) as the model nitro compound, and systematically study the structure, lithiation/delithiation mechanism and electrochemical performance of nitro compound. The initial capacity of NBALS at 0.5C is 153mAh g-1, and it maintains a capacity of 131mAh g-1 after 100 cycles. Detailed characterization showed that during the initial electrochemical lithiation process, the nitro group in the crystalline NBALS was irreversibly reduced to an amorphous azo compound. Subsequently, the azo compound is reversibly lithiated/delithiated with high electrochemical performance in the charge/discharge cycle. The lithiation/delithiation mechanism of azo compounds is also verified by directly using azo compounds as electrode materials, which exhibit electrochemical performance similar to nitro compounds and at the same time have higher initial coulombic efficiency. Related results were published on Adv. Mater. with the title 'Azo Compounds Derived from Electrochemical Reduction of Nitro Compounds for High Performance Li-Ion Batteries'.

Figure 1 The working principle of organic molecules in lithium ion batteries

In the NN reaction, two nitro groups are reduced by lithium ions to azo groups to form Li2O

Figure 2 Electrochemical performance of NBALS in lithium-ion batteries

a) Constant current charge/discharge curve

b) 0.1 mV s-1 Cyclic voltammogram

c) The relationship between the delithiation ability and the coulombic efficiency and the number of cycles at a current density of 0.5C

d) Rate performance

Figure 3 Spectral analysis

a) Raman spectra of the NBALS electrode before and after 1 cycle

b) 1 Mass spectra of NBALS electrodes before and after one cycle

c) XRD spectra of NBALS electrodes before and after one cycle

d) Diagram of reduction from NBALS to azo compounds And calculations

[Summary]

This work is a new type of active material for high-performance LIBs using azo compounds synthesized from the lithiation of nitro compounds. Detailed characterization shows that during the initial lithiation process, nitro compounds are irreversibly transformed into azo compounds and Li2O with low ICE. The discovery of nitro and azo compounds used in organic electrodes provides new opportunities for high-performance LIBs.

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