Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Synergistic Degradation Mechanism in Single Crystal Ni-Rich NMC//Graphite Cells

Acknowledgments We acknowledge Diamond Light Source for time on beamline I09 under Proposals SI30201-1 and SI30201-2. This work is supported by the Faraday Institution under Grants FIRG044, FIRG024, and FIRG060.Peer reviewedPublisher PD

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Synergistic degradation mechanism in single crystal Ni-rich NMC//graphite cells

Oxygen loss at high voltages in Ni-rich NMC//graphite Li-ion batteries promotes degradation but increasing evidence from full cells has shown the depth of discharge choice can further accelerate aging i.e. synergistic degradation. In this letter, we employ cycling protocols of single crystal LiNi0.834Mn0.095Co0.071O2//graphite pouch cells to examine the origin of the synergistic degradation in terms of material degradation mechanisms. In regimes where oxygen loss is not promoted (V < 4.3 V), discharging to a lower cutoff voltage improves capacity retention despite significant graphite expansion occurring. In contrast, when NMC surface oxygen loss is induced (V > 4.3 V), the deeper depths of discharge lead to pronounced faster aging. Using a combination of post-mortem analysis and density functional theory we present a mechanistic description of evolution of the surface densification as a function of voltage and its impact on lithium-ion kinetics to explain the observed cycling results

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

Acknowledgements: We thank Ieuan Ellis and Paul Malliband from the Battery Scale Up facility at WMG for their assistance. This work is supported by the Faraday Institution under grant no. FIRG060, no. FIRG024, and no. FIRG061. We acknowledge Diamond Light Source for time on beamline I09 under proposal SI25355-5 and SI27494-2.Al-surface doped Ni-rich single crystal material translates into better capacity retention in long-term cycling at higher UCV and cycling temperature.</jats:p

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature †

Acknowledgements: We thank Ieuan Ellis and Paul Malliband from the Battery Scale Up facility at WMG for their assistance. This work is supported by the Faraday Institution under grant no. FIRG060, no. FIRG024, and no. FIRG061. We acknowledge Diamond Light Source for time on beamline I09 under proposal SI25355-5 and SI27494-2.The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants