Lithium-ion batteries charge slowly in winter when it is cold, and their ions pass slowly though their electrolyte and separator membrane. This can be a real pain on cold mornings, and discourages many drivers from purchasing electric vehicles. Scientists at University of Michigan developed a method of rapidly-charging freezing lithium batteries in cold weather. We report their surprising findings here.
A Simple Modification Speeds Cold Lithium-Ion Charging
Electric vehicle charging becomes less efficient in freezing winter weather. A modified manufacturing method for lithium-ion batteries could ‘enable higher [driving]ranges and fast charging in cold weather’. The University of Michigan decided to resolve this puzzle in two stages:
- Drill ‘microscopic channels’ to admit ions.
- Apply a ‘stabilizing coating’ to one electrode.
The following summary highlights the challenges the scientists faced while achieving the above:
- The graphite particles on the anode are densely packed, creating convoluted paths for lithium-ion
- The trend towards thicker electrodes for greater stability, further increases this resistance during battery cycling.
- These factors create ‘significant concentration gradients’ which ‘significantly reduce’ anode ion-accessibility.
- This polarization causes regions of the graphite anode to become more negatively-charged, and condusive to lithium plating.
- This plating can combine with dendrite formation, causing loss of lithium inventory, capacity fade, and eventual cell failure.
Faster Pathways for Charging Cold Lithium-Ion Batteries
The researchers at University of Michigan improved lithium-ion battery charging performance, by creating new pathways through a graphite anode. They literally ‘blasted’ these 40-micron-diameter tunnels through, using lasers.
Doing so created spaces for lithium-ions to lodge faster, including deep in the graphite anode. This procedure accelerated battery charging at room temperature. However, cold charging remained inefficient.
The problem lay in the temporary coating that forms on the anode, in interaction with the electrolyte. The scientists found that this hardened ‘like butter’ when it was cold, and this created a ‘traffic jam’ of ions.
However, the team were able to resolve their remaining problem, by preventing the temporary coating. They achieved this by applying a 20-micron-coating of lithium borate-carbonate to the anode surface. And so they finally achieved their hope of rapidly-charging, freezing lithium batteries.
More Information
Winter and Electric Cars in Portland, Maine
Preconditioning Electric Car Batteries in Winter
Preview Image: Faster Charging With Modified Batteries
