According to foreign media reports, scientists at Argonne National Laboratory in the United States have made new progress in the research and development of high-capacity lithium-ion batteries, which can meet the growing demand for batteries.

With the increasing number of electric vehicles on the road, people are increasingly dependent on consumer electronic products. The demand for high-capacity lithium-ion batteries or lithium-ion batteries that can store a large amount of electricity is also rising.

One of the ways to increase the total capacity of Li ion battery is to increase the energy capacity of anode or cathode. In the past few decades, the most advanced lithium-ion batteries have been made of graphite anode. The energy capacity of graphite is fixed, which means that its capacity will not decay, and the material will not crack, even after 1000 charge discharge cycles. However, the theoretical energy capacity of graphite is too low to meet the increasing energy demand of today’s society.

In a new study, a team led by researchers at the U.S. Department of energy’s Argonne National Laboratory demonstrated a higher capacity anode material. The composite was originally developed for sodium ion batteries, and commercial sodium ion batteries are used less than lithium-ion batteries. Therefore, this research attempts to apply this material to lithium-ion batteries.

The United States has made new progress in the research and development of high-capacity lithium-ion batteries

Recently, two materials have been at the forefront of anode research for next generation batteries silicon and phosphorus. In theory, the energy capacity of silicon and phosphorus is at least 10 times that of graphite, which can exceed the energy capacity requirements of lithium-ion batteries. According to Khalil amine, an outstanding researcher and senior materials scientist at Argonne National Laboratory, there are two problems with silicon. One is that during charging, silicon will expand in a large area when it is lithiated, which may lead to the fracture of this anode material, resulting in the loss of battery energy capacity.

The second problem concerns the initial coulomb efficiency (ice). When the battery completes a complete charge discharge cycle, theoretically, the battery charge output should be consistent with the charge input. However, due to the reaction between lithium and anode material, some energy in the charge output will be lost. In order to develop practical lithium-ion batteries, the ratio of output charge to input charge should be more than 90%, that is, the coulomb efficiency should reach 90%. However, the coulomb efficiency of Li ion battery with silicon anode is less than 80%, which makes this kind of battery not practical.

So researchers at Argonne National Laboratory studied two kinds of phosphorus: black phosphorus and red phosphorus. “Phosphorus has a high energy capacity and a high coulomb efficiency of more than 90 percent,” the researchers said Coulomb efficiency higher than 90% means that there is almost no side reaction between anode material and electrolyte, and lithium loss is not much in the initial charge discharge cycle.

Therefore, the team independently developed anode composite materials, which are mainly composed of black phosphorus and conductive carbon compounds, among which black phosphorus is a conductor with high theoretical capacity. To make the composite, the researchers also ground large pieces of phosphorus and conductive carbon into micron sized particles to increase the density of the anode.

When measuring the life cycle of the battery, i.e. how many times it can be charged and discharged, the researchers used the advanced photon source (APS) of Argonne National Laboratory and the center for nanomaterials (CNM), both of which are affiliated to the office of scientific user facilities of the Ministry of energy. Using APS on-site storage ring light source X-ray diffraction and CNM on-site scanning electron microscope, the team can observe the changes of anode phase and volume when the battery is repeatedly charged and discharged.

After proving the stability of the black phosphorus composite, the team developed a composite made of red phosphorus. Although black phosphorus has better conductivity than red phosphorus, it is too expensive for market application. After using economical red phosphorus composite material, the stability of the battery is similar to that of black phosphorus battery, and it also has high coulomb efficiency and high actual capacity.

At present, the team is studying composite materials mainly made of red phosphorus, and the materials also show promising results.

Editor in charge: Tzh

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