China News Service, Beijing, October 2 (Reporter Sun Zifa) How to efficiently screen trace doping elements for lithium-ion battery cathode materials? It has long attracted widespread attention in academia and industry.
Killing two birds with one stone to solve two major problems
The scientific research team of the Shenyang National Research Center for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, recently proposed a more targeted trace element screening method based on the underlying physical and chemical mechanisms, killing two birds with one stone and solving the two major problems of slow lithium ion running and unstable material structure.
This new material design strategy based on the laws of physical and chemical interactions of trace elements is expected to promote the development of lithium battery cathode materials from empirical trial and error to goal-oriented, accelerating the paradigm shift in material design. The relevant research paper was published online in the international professional academic journal "Nature Synthesis" on the night of October 1, Beijing time.
Schematic diagram related to the results of this research. Photo courtesy of Institute of Metal Research, Chinese Academy of Sciences
According to the scientific research team, how much electricity a lithium-ion battery can store, how quickly it charges and discharges, and how long it can be used largely depends on the cathode material. To further improve cathode material performance, researchers often incorporate small amounts of specific elements. Although the addition amount of these elements is often only about 1%, they can play a huge role in regulating the migration behavior of lithium ions and the crystal structure of the material, thereby affecting the capacity, rapid charge and discharge and cycle life of the battery.
However, among these 1% elements, who should we choose? Why choose? How to match different elements? become an urgent problem to be solved.
Faced with many candidate elements in the periodic table of elements, material research and development in the past relied heavily on existing experience and experimental results, and then tried one by one and repeatedly adjusted to find a suitable formula. This is a bit like stewing randomly. You may end up with a good dish, but it is not clear why it is good and what role the different ingredients play.
Two rulers filter four elements
In this study, the scientific research team focused on achieving fast transmission and strong structure of lithium battery cathode materials, and proposed a targeted screening method for trace doping elements. One type of elements is responsible for making lithium ions run more smoothly, and the other type of elements is responsible for making the material structure stronger.
These two effects are closely related to the ionic charge density and metal-oxygen bonding strength of the element respectively: Elements with lower charge density can reduce the obstacles encountered during the migration of lithium ions, making it easier for lithium ions to move quickly in the material; elements that are more strongly combined with oxygen can enhance the stability of the crystal skeleton, making the material less likely to undergo structural damage during repeated charge and discharge processes.
Based on these two rulers, the scientific research team screened out magnesium, calcium, titanium, and zirconium elements from many elements, and prepared a synergistically optimized cobalt-free and high-nickel cathode material with a content of each of the four elements close to 1%. The results show that under the joint action of multiple trace elements with a content close to 1%, the lithium ion transmission efficiency and material structural stability are simultaneously improved.
Electrochemical tests show that the material has excellent fast charge and discharge, long cycle and low temperature performance: it only takes 3 minutes of ultra-fast charging to reach nearly 80% of the battery capacity; after 350 cycles under 6 minutes of fast charge and discharge conditions, the capacity retention rate still reaches 82.4%. At the same time, the 5.74 ampere-hour battery made of this material can still achieve an energy density of 278.6 watt-hours per kilogram at a low temperature of -20°C, showing excellent low-temperature energy storage performance and providing a new material choice for the application of new energy vehicles and energy storage equipment in cold areas.
The scientific research team stated that this research work establishes design rules that can be followed for the selection of multiple trace elements, allowing material research and development to shift from relying on empirical trials to targeted selection, and provides new ideas for the precise design of high-performance lithium-ion battery cathode materials and other functional materials. (over)
