Publications

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With current lithium ion batteries optimized for performance under relatively low charge rate conditions, implementation of XFC has been hindered by drawbacks including Li plating, kinetic polarization, and heat dissipation. This project will utilize model-informed design of 3-D hierarchical electrodes to tune key XFCrelated variables like 1) bulk porosity/tortuosity 2) vertical pore diameter, spacing, and lattice 3) crystallographic orientation of graphite particles relative to exposed surfaces 4) interfacial chemistry of the graphite surfaces through "artificial sEr' formation using ALD 5) current collector surface roughness (aspect ratio, roughness factor, etc.). A key aspect of implementing novel electrodes is characterizing them in relevant settings. For this project, ultimately led out of University of Michigan by Neil Dasgupta, that includes both coin cell and 2+ Ah pouch cell testing, as well as comparison testing against baselines. Sandia National Labs will be conducting detailed cell characterization on iterative versions/improvements of the model-based hierarchical electrodes, as well as COTS cells for baseline comparisons. Key metrics include performance under fast charge conditions, as well as the absence or degree of lithium plating. Sandia will use their unique high precision cycling and rapid EIS capabilities to accurately characterize performance and any lithium plating during 6C charging and beyond, coupling electrochemical observations with cell teardown. Sandia will also design custom fixturing to cool cells during rapid charge, to decouple any kinetic effects brought about by cell heating and allow comparisons between different cells and charge rates. Using these techniques, Sandia will assess HOH electrodes from the University of Michigan, as well as aiding in iterative model and electrode design.

Fast charging of lithium ion batteries is a critical enabler for mass EV adoption. Sandia National Laboratories (SNL) has been working with the University of Michigan to develop graphite anodes with novel 3D structures that facilitate faster charging while avoiding lithium plating, a main danger of unaided fast charging. SNL is using its unique high precision cycling capability, developed through ARPA-E funding, to characterize the ability of improved anodes to withstand fast charge and resist lithium plating, and the danger of lithium plating in present-day batteries.

Li deposition at the graphitic anode is widely reported in literature as one of the leading causes of capacity fade in lithium-ion batteries (LIBs). Previous literature has linked Li deposition resulting from low-temperature ageing to diminished safety characteristics, however no current research has probed the effects of Li deposition on the abuse response of well-characterized cells. Using overtemperature testing, a relationship between increased concentrations of Li deposition and exacerbated abuse response in 1 Ah pouch cells has been established. A novel Li deposition technique is also investigated, where cells with n:p < 1 (anode-limiting) have been cycled at a high rate to exploit Li+ diffusion limitations at the anode. Scanning Electron Microscopy of harvested anodes indicates substantial Li deposition in low n:p cells after 20 cycles, with intricate networks of Li(s) deposits which hinder Li+ intercalation/deintercalation. Peak broadening and decreased amplitude of differential capacity plots further validates a loss of lithium inventory to Li+ dissolution, and Powder X-ray Diffraction indicates Li+ intercalation with staging in anode interstitial sites as the extent of Li deposition increases. A cradle-to-grave approach is leveraged on cell fabrication and testing to eliminate uncertainty involving the effects of cell additives on Li deposition and other degradation mechanisms.

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One of the first milestones of the Behind the Meter Storage (BTMS) program was to develop testing protocols so that the state-of-the-art cell chemistries and form factors could be evaluated against BTMS aggressive performance and lifetime metrics. To help guide this conversation, a pack estimation calculation was run. At the time the team was assuming a worst-case scenario in which the battery alone would need to charge an electric vehicle in 15 minutes with no support from the grid. This calculation varied the amount of current applied by each string or module in the storage system and estimated how many cells (and estimated cost) would be needed to charge an electric vehicle in 15 minutes under the current applied.

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Since the last update, Sandia has performed additional testing on COTS baseline cells, as well as initial testing of University of Michigan baseline graphite anode cells. The COTS cell testing included an extreme stress test using 12C charging, as well as a non-cooled 6C charging test to determine the effectiveness of cooling plates. The Michigan cells were cycled with increasing charge rates to determine rate capability and possible propensity for lithium plating. The COTS cells are 5Ah NMC/Graphite pouches from Kokam with a modest 112 Wh/kg. The University of Michigan cells are NMC ~2.6Ah NMC/Graphite pouches made at the UM Battery Lab, and were designed with a more aggressive energy density. On the horizon, we will be testing additional cells from University of Michigan, including a baseline hard carbon anode cell. We will also disassemble the graphite anode cell, and continue to analyze the dQdV signals obtained during the graphite cell experiment to further understand evidence of possible plating. We also expect to receive cells with improved anodes for eventual testing against baselines.

With current lithium ion batteries optimized for performance under relatively low charge rate conditions, implementation of XFC has been hindered by drawbacks including Li plating, kinetic polarization, and heat dissipation. This project will utilize model-informed design of 3-D hierarchical electrodes to tune key XFC related variables like 1) bulk porosity/tortuosity 2) vertical pore diameter, spacing, and lattice 3) crystallographic orientation of graphite particles relative to exposed surfaces 4) interfacial chemistry of the graphite surfaces through "artificial sEr formation using ALD 5) current collector surface roughness (aspect ratio, roughness factor, etc.). A key aspect of implementing novel electrodes is characterizing them in relevant settings. For this project, ultimately led out of University of Michigan by Neil Dasgupta, that includes both coin cell and 2+ Ah pouch cell testing, as well as comparison testing against baselines. Sandia National Labs will be conducting detailed cell characterization on iterative versions/improvements of the model-based hierarchical electrodes, as well as COTS cells for baseline comparisons. Key metrics include performance under fast charge conditions, as well as the absence or degree of lithium plating. Sandia will use their unique high precision cycling and rapid EIS capabilities to accurately characterize performance and any lithium plating during 6C charging and beyond, coupling electrochemical observations with cell teardown. Sandia will also design custom fixturing to cool cells during rapid charge, to decouple any kinetic effects brought about by cell heating and allow comparisons between different cells and charge rates. Using these techniques, Sandia will assess HOH electrodes from the University of Michigan, as well as aiding in iterative model and electrode design.

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