Voltage profiles of the (a) LiNi0.5Mn1.5O4 solid-state lithium battery discharged at different rates. The battery was charged at C/10 before each discharge measurement. (Image: Green Car Congress)
Researchers from Oak Ridge National Laboratory recently presented a high-voltage (5V), long-lasting solid-state battery.
According to ORNL, this new cell can achieve an extremely long cycle life of over 10,000 cycles, while retaining more than 90% of its original capacity. Additionally, the Coulombic efficiency is near 100% on the first graph.
Is this the long awaited breakthrough?
"A high-voltage (5V) solid state battery has been demonstrated to have an extremely long cycle life of over 10,000 cycles. For a given size of battery, the energy stored in a battery is proportional to its voltage. Conventional lithium-ion batteries use organic liquid electrolytes that have a maximum operating voltage of 4.3 V. Operating a battery above this limit causes short cycle life and serious safety concerns."
"This work demonstrates that replacing the conventional liquid electrolyte with a ceramic solid electrolyte of lithium phosphorus oxynitride (Lipon) eliminates the limit of conventional lithium-ion batteries. A model battery of LiNi0.5Mn1.5O4/Lipon/Li has been operated over 10,000 cycles at a charge voltage to 5.1V. The solid state battery retains more than 90% of its original capacity after 10,000 cycles. Such a battery has a cycling lifetime of more than 27 years with a daily charge/discharge cycle, exceeding the lifetime of most devices and even vehicles. This work infuses new life into the existing chemistry of high-voltage lithium batteries."
Well...maybe, but we don't see a few important bits of data, which concerns us a little. The energy density value is missing and, on the second graph, we see that efficiency is falling down together with discharge rate.
At 2C rate (30-minute discharge), you can take just half the energy as at C/10 (10-hour discharge), which is not preferable. Old fashion liquid electrolyte lithium-ion batteries are almost as good at higher currents as at low, and we need this to be true of these batteries, especially those in electric cars. 2C is just about 50 kW from ~24 kWh battery pack in Nissan LEAF (which has an 80 kW motor).
Without maintaining efficiency at higher currents, the battery will waste all of the additional energy (if in fact energy density is higher).