For operation of an ion source in an intense ion beam diode, it is desirable to form a localized and robust source of high purity. A cryogenically operated ion source has great promise, since the ions are formed from a condensed high-purity gas, which has been confined to a relatively thin ice layer on the anode surface. Previous experiments have established the principles of operation of such an ion source, but have been limited in repetitive duration due to the use of short-lived liquid He cooling of the anode surface. We detail here the successful development of a “Cryo-Diode” in which the cooling was achieved with a closed-cycle cryo-pump. This results in an ion source design that can potentially be operated for an indefinite duration. Time-of-flight measurements with Faraday cups indicate that the resultant ion beam is of high-purity, and composed of singly charged ions formed out of the gas frozen out on the anode surface.

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Si has emerged as the most promising successor to graphite as an anode material in Lithium-ion batteries. Known to have nearly ten times the capacity of graphite, Si is increasingly being used to partially replace traditional graphite to raise the overall energy density of a cell. High nickel cathode chemistries such as NMC811 are also of particular interest due to its high specific capacity and low cobalt content, which drives down cost. Pairing these active materials is an obvious design choice, however it results in combining their respective drawbacks. Relative to lower nickel NMCs, NMC811 has been shown to be more reactive with carbonate electrolyte components and is known to be more violently reactive upon thermal decomposition. Si based materials swell dramatically upon lithiation, causing the SEI layer to break and reform with repeated cycling, consuming the electrolyte in the process. In combination, high energy density also implies increased safety concerns. To overcome these problems new electrolyte additives are needed. We report a new family of electrolyte additives designed to improve the robustness of the SEI and overall stability of the electrolyte system, which carries significance in improving cycle life and abuse tolerance in higher energy density cells. This is a tunable, drop-in solution to addressing the need for improving battery performance as well as safety. We demonstrate the effect of these additives on the SEI via analytical characterizations (SEM, XPS) and how it relates to improved long-term cycle life. The effect of additives on thermal decomposition at the material level is investigated via DSC and on the cell level via ARC, presenting a relationship between electrolyte design and inhibited electrode-electrolyte decomposition reactions. Novel electrolyte additives are thus shown to be a promising approach to resolving future high energy demand without compromising safety.

Lithium-ion batteries are an increasingly prevalent source of power in grid storage applications and electric powertrains, given its high energy density and extended cycle life. However, lithium-ion batteries carry significant safety risks and are a growing hazard due to possible fires that can be caused by overheating, physical cues (i.e., crushing or penetration of cell), overcharging and short-circuits. These risks are greatly increased when focus shifts from a single cell to either modules or packs, where an individual cell entering thermal runaway propagates to adjacent cells. In spite of multiple protections battery packs have in recent times been known to fail. It is well understood that thermal runaway occurs when the self-heating rate in the cell exceeds the heat dissipation out of the cell. This self-heating is the product of undesired side-reactions in the cell which are onset by abuse conditions such as excess heat, internal short circuits, etc. The key to inhibiting thermal runaway is to modify the cell such that the self-heating rate under abuse conditions is significantly reduced. Reducing the self-heating rate is important when considering battery packs that consist of many cells as is the case in electric vehicles, so that if one cell fails in a pack the thermal runaway does not propagate to adjacent cells. Our approach therefore is to modify the electrolyte system to reduce the overall cell self-heating rate. This is a tunable, drop-in solution to addressing the need for improving battery safety. The incorporation of NOHMs novel safe electrolyte formulation is shown to impact the abuse tolerance of cells on both the material level, i.e. the electrolyte-electrode interaction and on the cell level. The presented electrolyte systems demonstrate reduced overall energy and peak heat flow in the exotherm profiles of NMC cathode materials as well as lithiated graphite via differential scanning calorimetry (DSC). With this approach, we demonstrate significantly lower self-heating rates in an 18650 lithium-ion cell via an accelerating rate calorimeter (ARC). Using the self-heating rate data produced via ARC testing we developed a thermal runaway model to simulate thermal propagation in battery packs consisting of seven 18650 lithium-ion cells arranged in a honeycomb configuration. The self-heating rate is translated into thermal power generation for individual cells surrounding a ‘trigger cell’, a cell that has entered thermal runaway. The model suggests that changes in the electrolyte system as measured by ARC mitigates cell-to-cell thermal propagation in event of an individual cell thermal runaway (Figure 1). This simulation is then validated with a real pack by inducing thermal runaway in the center cell with a nail penetration test. NOHMs novel safe electrolyte development carries significance in not only safer individual cells but also in safer overall battery packs. Figure 1