In Situ Imaging of Lithium-Ion Batteries Via the Secondary Ion Mass Spectrometry

Abstract

To develop lithium-ion batteries with a high rate-capability and low cost, the prevention o f capacity loss is one o f major challenges, which needs to be tackled in the lithium-ion battery industry. During electrochemical processes, lithium ions diffuse from and insert into battery electrodes accompanied with the phase transformation, whereas ionic diffusivity and concentration are keys to the resultant battery capacity. In the current study, we compare voltage versus capacity o f lithium-ion batteries at different current-rates (C-rates) discharging. Larger hysteresis and voltage fluctuations are observed in higher C-rate samples. We investigate origins o f voltage fluctuations by quantifying lithium-ion intensity and distribution via a time-of-flight secondary ion mass spectrometry (ToF-SIMS). The result shows that fo r fully discharged samples, lithium-ion intensity and distribution are not C-rate dependent, suggesting different lithium-ion insertion mecha nisms at a higher C-rate discharging might be solely responsible fo r the observed low frequency voltage fluctuation.

Critical lithiation for C-rate dependent mechanical stresses in LiFePO4

“…ANSYS Multiphysics (ANSYS, Inc., Canonsburg, Pennsylvania, USA) is used to develop a thermal-static coupling finite element model to investigate the diffusion-induced stresses under various C-rate conditions. A 10 μm×10 μm×10 μm cubic finite element model containing 1000 elements was developed per our previous study, in which a 10 μm×10 μm sputtering area was used to measure the lithium ion intensities in LiFePO 4 strip [28]. Various C-rates are chosen by assigning different mass fluxes J, where the 1 C model has J 1 C =0.225 W m −2 , the 2 C model has J 2 C =0.45 W m −2 , the 6 C model has J 6 C =1.35 W m −2 , and the 10 C model has J 10 C =2.25 W m −2 , respectively.…”

“…The maximum stress occurs on the particle surface during lithiation, explaining the experimentally observed particle fracture. Further, the voltage fluctuation is more noticeable in 10 C samples as compared to other ones with low C-rates, possibly suggesting that a different lithium insertion mechanism occurs at high C-rates [28]. Thus, to investigate strain energy under different C-rates may be helpful for explaining the observed voltage fluctuation.…”

Mechanical stresses at the cathode–electrolyte interface in lithium-ion batteries

“…In this study, a computational model integrating experimental results 32 and theoretical analysis 33 is developed through a multiphysics analysis. Multiphysics finite element models for a half-cell system (i.e., with electrolyte and cathode) are developed using ANSYS Multiphysics (ANSYS, Inc., Canonsburg, Pennsylvania, USA).…”

“…39,40 Ethylene carbonate (EC) is used as the electrolyte material in the finite element models because it has many beneficial properties such as high conductivity, high dipole moment (i.e., resulting in high ionic conductivity due to the dissociation of the lithium salt), yet high viscosity of electrolyte resulting in low fluidity (i.e., ionic movement). Since a commercial LiFePO 4 battery is a layered structure composed of a cathode strip and an anode strip with a separator between them, 32,41 one dimensional lithium-ion mass flux (J) along the y-axis is used as the driving force for the system (Fig. 1).…”

Composition and structure of porcine digital flexor tendon‐bone insertion tissues

“…The spectral information was obtained on a discrete basis at selected points. Complementarily, time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) can be used to obtain spatially continuous molecular mapping from the upper most monolayer of the tissue. In the past 20 years, TOF‐SIMS has been a widely used surface analysis technique for obtaining high‐quality spectra owing to its combination of high mass‐resolution (>10,000 M/ΔM), mass range (0–10,000 amu), spatial resolution (<300 nm), and simultaneous molecular mapping.…”