Tesla Researchers Publish Hybrid lithium-Ion/Lithium Metal Cell Results Of Research Right Before Battery Day

Tesla's researchers in Canada have published the results of research on hybrid lithium-ion/lithium metal cells, which can be used to create an all-electric cars with a range extender. 

In order to increase the range of a car, some automakers, in addition to battery power, use gasoline internal combustion engines, which act as a generator to recharge the battery when there is a need to increase the range. But this mechanism is completely contrary to the Tesla mission, so the company is developing a similar concept, but at the same time it will be completely electric.

Researches in this direction are carried out by team from the University of Dalhousie in Canada. Tesla’s ‘Advanced Battery Research’ division, led by Jeff Dahn, has published a study that describes a new type of battery cell that takes advantage of both the longevity of lithium-ion cells and the high energy density of lithium metal cells:

Increasing the energy density of batteries will reduce the cost of electric vehicles and will increase the driving range. Replacing the graphite anode in conventional lithium-ion cells with lithium metal significantly increases the energy density. However, lithium metal anodes suffer from rapid loss of capacity and short cell life.

To develop a high energy density cell with longer lifetime, they propose a hybrid lithium-ion / lithium metal cell that is achieved by purposefully plating lithium metal on graphite. Although unwanted lithium plating is normally a degradation mechanism in conventional lithium-ion cells, researchers achieve reversible lithium plating on graphite with an optimized dual-salt electrolyte. Furthermore, since batteries are often not cycled to 100% of their capacity, these hybrid cells can be operated in lithium-ion mode with little degradation for the majority of their life with periodic fully charged lithium metal cycles for extended capacity.

Highlights:

• Cycling lithium metal on graphite enables hybrid lithium-ion / lithium metal cells
• Hybrid cells deliver 20% higher energy density than conventional lithium-ion cells
• Optimized electrolyte and pressure enable reversible lithium plating on graphite
• Cells can operate in lithium-ion mode with periodic lithium metal cycles

"A hybrid anode cell design is proposed involving lithium metal plating on top of graphite that provides a 20% increase in energy density over conventional lithium-ion cells. Pouch cells with hybrid graphite-lithium metal anodes cycled with conventional electrolytes fell below 80% capacity in under 15 cycles. However, with a dual-salt electrolyte and applied mechanical pressure optimized for lithium metal cycling, hybrid cells achieved over 150 full (100% utilization) cycles before falling below 80% capacity with a CE of 99.6% for lithium metal plating on graphite. We also found that intermittent high energy (100% utilization) cycles utilizing lithium metal can be dispersed among hundreds of conventional lithium-ion cycles where only the graphite is utilized. Operating the cell with this intermittent protocol shows minimal impact to the underlying graphite capacity. Therefore, these hybrid cells can operate well in “lithium-ion mode” with periodic high energy full cycles accessing the lithium metal capacity."

Tesla is making tremendous strides in the research and development of new batteries and electric power systems for cars, and today there is a lot of information that confirms this. Battery Day is likely to be full of reports on the company's achievements in this area.