Hot Formation for Improved Low Temperature Cycling of Anode-Free Lithium Metal Batteries

Abstract

A new "hot formation" protocol is proposed to improve lower temperature cycling of lithium metal batteries. The cycling stability of anode-free pouch cells under low pressure (75 kPa) is shown to decline significantly as the cycling temperature is decreased from 40°C to 20°C. At low pressure and 40°C the initial morphology of the lithium anode is dense and columnar, far superior to that plated at 20°C. For "hot formation" two initial 40°C cycles (C/10 charge C/2 discharge) are conducted prior to extended low temperature (20°C) cycling. These two initial cycles have a surprisingly large impact; capacity retention to 80% is increased from only 18 cycles without hot formation to 60 cycles with hot formation at low pressure. When the applied pressure is increased to 1200 kPa, the hot formation (20°C cycling) cells show 85% capacity retention at 100 cycles. The benefits established during these two initial formation cycles are apparently carried forward to improve the longer term performance of lithium metal cells tested at room temperature.

Cycling Lithium Metal on Graphite to Form Hybrid Lithium-Ion/Lithium Metal Cells

“…This was shown to significantly improve the 20 C performance of anode-free lithium metal cells. 30 Similarly, Figure S5 shows that 20 C cycling of hybrid cells after hot formation can be sustained without increased degradation compared with cycling at 40 C.…”

Anode‐Free Full Cells: A Pathway to High‐Energy Density Lithium‐Metal Batteries

“…[ 67 ] Genovese et al reported the effects of a “hot formation” procedure, where the initial two cycles were carried out at an elevated temperatures of 40 °C. [ 69 ] They found that the high‐temperature formation cycles enable the deposited lithium metal to form dense, columnar growths, when compared with formation cycles carried out at 20 °C. This optimized high‐temperature formation procedure was applied in anode‐free Cu || NMC pouch full cells in conjunction with 75 kPa of stack pressure to realize drastically improved performance, with over 55% capacity retention at 100 cycles compared to the same retention at only 18 cycles in cells with the formation procedure carried at room temperature (LIRR = 99.4%).…”

What Can be Expected from “Anode‐Free” Lithium Metal Batteries?

“…Hot formation (>40 C) could extend cycle life to 200 cycles at 80% capacity retention combined with pressure application. [35] Pulsed charging procedures can also lead to enhanced compactness of Li metal deposition which is important in anode-free architectures. [36] A further consideration regarding the SEI formation is related to the cathode decomposition.…”