Determination of Lithium Diffusion Coefficients in Single Battery Active Material Particles by Using an AFM-Based Steady-State Diffusion Depolarization Technique

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In lithium-ion batteries (LIBs), the ambipolar diffusion coefficient of lithium in the active material particles of the composite electrodes is a key parameter for the battery performance. Because conventional intermittent titration techniques (PITT/GITT) for determining the Li diffusion coefficient do not yield reliable values for composite electrodes, it is important to develop alternative methods. Here, we present a novel AFM-based technique for determining the Li diffusion coefficient of single active material particles in composite electrodes. The technique is based on creating a local Li diffusion polarization around the AFM tip and by subsequently monitoring the depolarization by AFM-based surface potential measurements. The analysis of the measurement results is supported by 3D diffusion simulations. Measurements on a single LiCoO 2 particle inside a composite electrode yield a Li ambipolar diffusion coefficient of 8 × 10 –13 cm 2 /s at 25 °C, which is in good agreement with results obtained from PITT/GITT measurements on homogeneous LiCoO 2 thin films. The activation energy of the Li ambipolar diffusion coefficient is 0.41 eV.