Rechargeable batteries are an integral component of energy-storage systems for electric vehicles and for grid storage (for example, for backup power during a power outage, as part of a microgrid and so forth.). Some such rechargeable battery systems include lithium metal and anode-free lithium batteries. Lithium metal and anode-free lithium batteries have certain advantages over traditional lithium ion batteries, as they are more energy dense. Anode-free cells are also less expensive and easier to assemble due to their lack of anode coating.
However, challenges with lithium metal and anode-free lithium batteries have prevented their wide spread adoption. Improving certain characteristics of lithium metal and anode-free battery systems will allow for more widespread use of such systems. For instance, developing electrolyte compositions that allow for commercially acceptable cycling performance of lithium metal and anode-free lithium batteries is critical to gaining adoption of such battery systems.
July 9, 2020, Tesla Motors Canada ULC published the patent 'Electrolytes with lithium difluoro (oxalato) borate and lithium tetrafluoroborate salts for lithium metal and anode-free cells.' It relates to rechargeable battery systems, and more specifically to the methods of improving capacity retention in lithium metal and anode-free lithium batteries and electrolyte solutions for use in such battery systems.
Until this patent, the general consensus in the industry is that an electrolyte with lithium difluoro(oxalato)borate ("LiDFOB") salt alone best increases the capacity retention of lithium metal and anode-free lithium cells.
FIG. 1 illustrates experimental data collected during charge-discharge cycling experiments in anode-free pouch-type cells at a charge rate of C/5 and discharge rate of C/2 at a cell stack pressure of about 10 psi, at 40.degree. C., and between voltage limits of 3.6V and 4.5V for: 1) 0.6M LiDFOB; 2) 0.6M LiDFOB+0.6M LiBF.sub.4; 3) 1.2M LiDFOB; and 4) 1M LiDFOB+0.4M LiBF.sub.4. | Tesla patent
This patent covers methods of improving capacity retention in anode-free lithium battery systems and electrolyte solutions for use in such battery systems. The present method and electrolyte solutions have been found to surprisingly provide for increased capacity retention of anode-free battery systems. More specifically, this disclosure describes that a combination of LiDFOB and lithium tetrafluoroborate ("LiBF.sub.4") as a dual salt for electrolytes in anode-free cells improves capacity retention during charge-discharge cycling.
Provided herein is a method of improving capacity retention in a lithium metal or anode-free rechargeable battery cell. The method includes providing to the battery cell a salt component including both lithium difluoro(oxalato)borate and lithium tetrafluoroborate and a solvent component.
Tesla continues to develop approaches to create energy-intensive, economical, long-life batteries. The company has already revolutionized the automotive industry, and soon the battery industry will face a breakthrough that will forever change it.