INVESTIGATING SULFATION IN LEAD ACID BATTERIES RSR Technologies, East Penn Manufacturing, Argonne National Laboratory Tim Fister, Matthew Weimer, Eric Coleman, Pietro Papa-Lopes, Vojislav Stamenkovic, Nenad Markovic (ANL) Matthew Raiford, Tim Ellis (RSR Technologies) Subhas Chalasani, Kevin Smith (East Penn Manufacturing) ▪ Despite 100+ years of use, the energy density of lead acid batteries has considerable room for growth. EXAMPLE: HIGH RESOLUTION TOMOGRAPHY NEXT STEPS EXAMPLE: REAL-TIME X-RAY DIFFRACTION EXAMPLE: SURFACE SENSITIVE TECHNIQUES MOTIVATION APPROACH METHODS ▪ Initial goal: focus on dissolution of PbSO 4 at the negative Pb electrode. Improve reversibility by connecting growth/dissolution kinetics of PbSO 4 with its morphology. ▪ Phase I: simplify reaction by starting with lead metal electrodes. Develop operando diffraction, imaging, and spectroscopy methods. ▪ Phase II: Adapt these probes to model NAM pastes. ▪ Synchrotron-based diffraction and tomography: - In situ (high energy, up to 100 keV) - Real-time (Intensity = 10 10 - 10 13 photons/s) - Spatial resolution (10-1000 nm) ▪ Novel lab based tools: - In situ ICP/MS (part-per-trillion sensitivity) - In situ AFM, QCM (atomic scale growth/dissolution) ▪ World class battery fabrication/testing labs. ▪ Models and strategies for the DCA have been inferred from electrochemical testing and post-mortem characterization. Argonne has unique capability to measure changes in species and morphology of electrode/electrolyte species in working cell. ▪ Dynamic Charge Acceptance (DCA) plays a key role in the energy density and lifetime of batteries, especially during operation at partial state of charge. The major issues affecting DCA are: − Dissolution of PbSO 4 − Intraplate conductivity − Gassing of O 2 and H 2 Stable PbSO 4 Recharge Dissolution process Crystal Growth and Formation Discharge PbSO 4 Seeding Begins Left: CAD rendering of diffraction cell. Right: Computed tomography (CT) image of electrodeposited Pb. Advanced Photon Source CONCLUSIONS 2θ ▪ Single-shot powder diffraction (~0.5 s resolution) ▪ Easily measure the kinetics of sulfation/ desulfation AFM from the intial growth of PbSO 4 on BaSO 4 . We have solution and electrochemical AFM cells for watching these processes in situ. Top Top 250 μm Side Left: Cross section of a NAM paste during cycling. Note the change in porosity at the interior of the electrode. Al wire ▪ Surface diffraction and in situ atomic force microscopy provide atomic scale information on the nucleation and growth of PbSO 4 single crystal surfaces. ▪ Synchrotron-based diffraction and tomography can be used to follow 3D changes in morphology with μm resolution. ▪ CT scans are fast (< 1 min) and use high energy x-rays (60-100 keV) to penetrate through lead-based electrodes. 50 μm 300 μm Right: Electrodeposited lead before and after sulfation. Note the preferential redeposition of PbSO 4 on the face adjacent to the counter electrode. Schematic of single-shot powder diffraction and photo of in situ cell used for lead foils. Studies so far include: ▪ Extended voltammetry on lead foils. ▪ Self-discharge reactions (chemical sulfation) ▪ Formation/cycling on model paste electrodes. CV data Formation Crystal truncation rods (CTRs) are sensitive to electrolyte ordering near a charged surface. Our group has looked at hydration of 001-BaSO 4 (Bracco et al. JPCC 2017) and has begun work on PbSO 4 precipitation on barite. ▪ In situ ICP-MS combined with RDE provides part-per-trillion sensitivity to Pb and other species present in the electric double-layer during cycling. ANL studies seeding and formation mechanism (currently unknown) ANL studies dissolution Current data: Ex situ analysis of PbSO 4 ▪ The growth and dissolution of PbSO 4 in lead acid batteries is a multidimensional problem ranging from atomic scale changes at the charged interface to transport within a heterogeneous electrode. ▪ Argonne has developed tools capable of measuring sulfation during operation of a lead acid cell to validate and extend existing models based largely on electrochemistry alone. ▪ Further develop paste electrodes that are compatible for x-ray and ICP studies. ▪ Begin analogous studies on the positive electrode material. ▪ Incorporate modeling of crystal growth and continuum pack-level features. Right: Pb concentration measured in solution by ICP/MS during cyclic voltametry Chemical sulfation