Understanding Inhomogeneous Reactions in Li‐Ion Batteries: Operando Synchrotron X‐Ray Diffraction on Two‐Layer Electrodes

Abstract

To understand inhomogeneous reactions perpendicular to the current collector in an electrode for batteries, a method combining operando synchrotron X‐ray diffraction and two‐layer electrodes with different porosities is developed. The two layers are built using two different active materials (LiNi0.80Co0.15Al0.05O2 and LiMn2O4), therefore, tracing each diffraction pattern reveals which active material is reacting during the electrochemical measurement in transmission mode. The results demonstrate that the active material close to the separator is obviously more active than that one close to the current collector in the case of low porosity electrodes. This inhomogeneity should be due to the rate‐limitation and especially to low average ionic conductivity of the electrolyte in the porous electrode because the current flows first mainly into the electrode regions close to the separator. The inhomogeneity is found to be mitigated by the adjustment of the electrode density and thus porosity. Hence, the novel operando method reveals a clear inhomogeneous reaction perpendicular to the current collector.

Li3BN2 as a Transition Metal Free, High Capacity Cathode for Li‐ion Batteries

“…Specifically, two clear trends are observed, that is, (i) the BN 2 1− peak becomes stronger after charge because BN 2 3− and BN 2 2− anions get oxidized, and (ii) both BN 2 1− and BN 2 2− peaks become weaker after discharge because BN 2 1− and BN 2 2− anions are reduced to become the BN 2 3− anion. As mentioned before, the presence of all three BN 2 anions in one sample is due to inhomogeneous charge/discharge in the electrode . Thus, the sXAS and XPS analyses are consistent in both the relative energy positions and the evolution of the lineshape, indicating that both the surface and bulk of α‐Li 3 BN 2 have the same redox mechanisms.…”

“…The first is that BN 2 3− , BN 2 2− and BN 2 1− anions are present in all samples even though their relative concentrations are changed. This is not a surprise since inhomogeneous charge/discharge is typical because not all the active particles are connected to conductive network and there is non‐uniform distribution of the active material . The second is the small shift in the binding energy of BN 2 3− , BN 2 2− and BN 2 1− anion peaks (≤0.5 eV) from one charge state to another.…”

“…This is not a surprise since inhomogeneous charge/discharge is typical because not all the active particles are connected to conductive network and there is non-uniform distribution of the active material. [30][31][32] The second is the small shift in the binding energy of BN 2 3À , BN 2 2À and BN 2 1À anion peaks (� 0.5 eV) from one charge state to another. One likely mechanism for this small shift is that the N1s peak of the BN 2 anion is not from an isolated NÀ BÀ N ion; instead, its binding energy may depend to a small extent on the overall Li site occupancy as well.…”

Combining operando synchrotron X-ray tomographic microscopy and scanning X-ray diffraction to study lithium ion batteries

“…3d). These findings imply that transport is limited by ionic diffusion rather than by electric conduction2829.…”

Charge Heterogeneity and Surface Chemistry in Polycrystalline Cathode Materials

“…[1][2][3][4][5] There are many factors, including the cell geometry, electrode thickness, porosity and cycling rate/history, that can affect the non-uniformity of the electrode both in-plane and perpendicular to the current collector. [6][7][8] For example, considerable structural heterogeneity was observed in LiFePO4 electrodes after high rate charging in prismatic or coin cells, by means of a synchrotron based micro-diffraction study. 9 Both electronic wiring and ionic diffusion pathways play key roles in affecting the non-equilibrium lithium distributions.…”