Lithium-ion batteries are the dominant technology for energy storage in many types of devices. High power and large-scale applications such as electric vehicles and grid storage are pushing for increased storage capacity and charge cycle lifetimes. It is known that morphological changes in the electrode material are responsible for transport and irreversibility issues (1). To better understand the morphologies, we present a PiFM (Photoinduced Force Microscopy) study on lithium iron phosphate based nanomaterials demonstrating the presences of LiFePO4 and FePo4 and LixFePO4 intermediates. The LiFePO4 nanoparticles were synthesized using a solvothermal method and then partially delithiated either in a solution of 0.05M bromine in acetonitrile or electrochemically (2). Infrared Photo-induced Force Microscopy (IR PiFM) is based on an atomic force microscopy (AFM) platform that is coupled to a widely tunable mid-IR laser (3). PiFM measures the dipole induced on a sample with an excitation light source, by detecting the dipole-dipole force that exists between the sample and a metallic AFM tip. This interaction is strongly affected by the optical absorption spectrum of the sample, thereby providing a significant spectral contrast mechanism, which can be used to differentiate between chemical species. Due to the steep dipole-dipole force dependence on the tip-sample gap distance, PiFM spectral images surpass topographical spatial resolution, showcasing sub 10 nm spatial resolution despite the typical tip radius of metal-coated tips. The principles and the essential components of PiFM will also be presented with examples that highlight the nanoscale imaging and spectroscopic sensitivity inherent to the technique. In concert with the LiFePO4 studies, recent samples investigated with PiFM will be presented, including polymer blends, nano-fibers, polypeptides, block copolymers, organic, inorganic, and 2D materials.

Detecting the chemical phases of lithium and iron phosphate in nanoparticles with photoinduced force microscopy

253rd National Meeting (2017)

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