Professor Ji Hengxing's research group at the University of Science and Technology of China (USTC), in collaboration with the University of California, Los Angeles (UCLA) and the Institute of Chemistry, Chinese Academy of Sciences (CAS), has made a major breakthrough in the research of new electrode materials for lithium-ion batteries.
They designed a black phosphorus composite material that makes it possible to combine the high capacity, fast charging, and long life of lithium-ion batteries. The results are published in the journal Science.
Electric cars are becoming more and more popular these days, but long charging times are a factor in consumers avoiding them.
While conventional fuel-efficient cars can travel 500 kilometers on a full tank of gas in just five minutes, the most advanced electric cars on the market today require an hour of charging to achieve the same effect.
The development of high-capacity lithium-ion batteries with fast charging capability has been an important goal for the electric vehicle industry. This latest research breakthrough at the University of Science and Technology of China brings mankind one step closer to that goal.
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Dr. Hongchang Jin, the first author of the paper, introduced: "In lithium-ion batteries, energy flows in and out of the battery through the chemical reaction between lithium ions and electrode materials, so the conductivity of electrode materials to lithium ions is the key to determining the charging speed; on the other hand, the amount of lithium ions accommodated by electrode materials per unit mass or volume is also an important factor."
Black phosphorus is an allotrope of white phosphorus, and its special laminar structure gives it strong ionic conductivity and high theoretical capacity, making it a highly promising electrode material for meeting fast-charging requirements.
However, black phosphorus is prone to structural damage from the edge of the layered structure, and the measured performance is much lower than theoretical expectations.
Therefore, Ji Hengxing's team adopts the strategy of "interface engineering" to connect black phosphorus and graphite through phosphorus-carbon covalent bonds, which stabilizes the material structure and enhances the lithium-ion conductivity inside the black phosphorus-graphite composite.
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The electrode material is coated with chemicals that are gradually broken down by the electrolyte during operation, which partially prevents lithium ions from entering the electrode material, just as dust on the surface of glass prevents light from penetrating.
The team used a thin polymer gel to make a dust coat to "wear" on the surface of the black phosphor-graphite composite, allowing lithium ions to enter.
"We used conventional process routes and technical parameters to make electrode sheets out of the black phosphorus composite. Laboratory measurements show that the electrode sheet can be recharged for 9 minutes to restore about 80 percent of its capacity, and can still maintain 90 percent capacity after 2,000 cycles." Xin Sen, co-senior author of the paper and a researcher at the Institute of Chemistry, Chinese Academy of Sciences, said.
"If mass production of this material can be achieved, matching cathode materials and other auxiliary materials can be found, and the design can be optimized for cell structure, thermal management, and lithium precipitation protection, a lithium-ion battery with an energy density of 350 watt-hours/kg and fast-charging capability will be expected."
Such a lithium-ion battery would enable an electric vehicle to travel close to 1,000 kilometers, compared to 650 kilometers for the Tesla Model S on a full charge. The fast-charging capability will take the user experience of the electric car up a notch.
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