TY - JOUR

T1 - Charge-transfer-induced lattice collapse in Ni-rich NCM cathode materials during delithiation

AU - Kondrakov, Aleksandr O.

AU - Geßwein, Holger

AU - Galdina, Kristina

AU - De Biasi, Lea

AU - Meded, Velimir

AU - Filatova, Elena O.

AU - Schumacher, Gerhard

AU - Wenzel, Wolfgang

AU - Hartmann, Pascal

AU - Brezesinski, Torsten

AU - Janek, Jürgen

PY - 2017/1/1

Y1 - 2017/1/1

N2 - Ni-rich LiNixCoyMnzO2 (NCM) cathode materials have great potential for application in next-generation lithium-ion batteries owing to their high specific capacity. However, they are subjected to severe structural changes upon (de)lithiation, which adversely affects the cycling stability. Herein, we investigate changes in crystal and electronic structure of NCM811 (80% Ni) at high states of charge by a combination of operando X-ray diffraction (XRD), operando hard X-ray absorption spectroscopy (hXAS), ex situ soft X-ray absorption spectroscopy (sXAS), and density functional theory (DFT) calculations and correlate the results with data from galvanostatic cycling in coin cells. XRD reveals a large decrease in unit cell volume from 101.38(1) to 94.26(2) Å3 due to collapse of the interlayer spacing when x(Li) < 0.5 (decrease in c-axis from 14.469(1) Å at x(Li) = 0.6 to 13.732(2) Å at x(Li) = 0.25). hXAS shows that the shrinkage of the transition metal-oxygen layer mainly originates from nickel oxidation. sXAS, together with DFT-based Bader charge analysis, indicates that the shrinkage of the interlayer, which is occupied by lithium, is induced by charge transfer between O 2p and partially filled Ni eg orbitals (resulting in decrease of oxygen-oxygen repulsion). Overall, the results demonstrate that highvoltage operation of NCM811 cathodes is inevitably accompanied by charge-transfer-induced lattice collapse.

AB - Ni-rich LiNixCoyMnzO2 (NCM) cathode materials have great potential for application in next-generation lithium-ion batteries owing to their high specific capacity. However, they are subjected to severe structural changes upon (de)lithiation, which adversely affects the cycling stability. Herein, we investigate changes in crystal and electronic structure of NCM811 (80% Ni) at high states of charge by a combination of operando X-ray diffraction (XRD), operando hard X-ray absorption spectroscopy (hXAS), ex situ soft X-ray absorption spectroscopy (sXAS), and density functional theory (DFT) calculations and correlate the results with data from galvanostatic cycling in coin cells. XRD reveals a large decrease in unit cell volume from 101.38(1) to 94.26(2) Å3 due to collapse of the interlayer spacing when x(Li) < 0.5 (decrease in c-axis from 14.469(1) Å at x(Li) = 0.6 to 13.732(2) Å at x(Li) = 0.25). hXAS shows that the shrinkage of the transition metal-oxygen layer mainly originates from nickel oxidation. sXAS, together with DFT-based Bader charge analysis, indicates that the shrinkage of the interlayer, which is occupied by lithium, is induced by charge transfer between O 2p and partially filled Ni eg orbitals (resulting in decrease of oxygen-oxygen repulsion). Overall, the results demonstrate that highvoltage operation of NCM811 cathodes is inevitably accompanied by charge-transfer-induced lattice collapse.

UR - http://www.scopus.com/inward/record.url?scp=85032706291&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.7b06598

DO - 10.1021/acs.jpcc.7b06598

M3 - Article

AN - SCOPUS:85032706291

VL - 121

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 39

ER -