Recipient Organization
EVOSEER LLC
566 N 9TH ST
LARAMIE,WY 820723315
Performing Department
(N/A)
Non Technical Summary
There is increasing need for transportation decarbonization and rising consumer interest in electric vehicles (EVs), but higher cost and lower range compared to internal combustion engine vehicles have severely restricted consumer adoption of EVs. These range and cost limitations are due to the low gravimetric energy density and high cost of current lithium batteries (LiBs). Evoseer's innovation is a novel technology for the production of cathodes to enable next-generation lithium batteries (LiBs) based on lithium-sulfur (Li-S) chemistry.LiBs, of which there is one predominant chemistry in commercial use and many more under investigation, generally function by moving Li ions between two electrodes: an anode and a cathode. Li is stored in a high energy state in the anode and, as the battery discharges, Li ions and electrons flow from the anode to the cathode. The flow of electrons generates the current that the battery ultimately produces. Current commercial LiBs use graphite as the anode material due to the ability of graphite to reversibly intercalate lithium. Current cathodes also use intercalation chemistry, with cobalt, nickel, and aluminum oxides being the most commonly used cathode materials. Currently used cathode chemistries adequately stabilize lithium but the high mass of these metal oxides significantly reduces performance of the battery cell. Nickel and cobalt also have the disadvantages of cost and availability. The high cost of nickel and cobalt contributes significantly to the overall cost of LiBs, with cathode materials accounting for 35-37% of total LiB cell production cost. There also are serious concerns about the availability of cobalt as the growth of the electric vehicle market increases LiB demand, with over 60% of world cobalt production occurring in the Democratic Republic of the Congo. Current lithium batteries using graphite anodes and metal oxide cathodes have energy densities of 160-260 Wh·kg-1 on a full cell basis, and further increases in gravimetric energy density beyond 350 Wh·kg-1 are likely not possible with current electrode materials due to the limited number of crystallographic sites available for insertion of lithium ions. Thus, new battery chemistries are necessary to significantly increase battery gravimetric energy density.Lithium-sulfur (Li-S) chemistry has been suggested as a replacement for current LiBs. Li-S batteries have the potential to double the capacity of current LiBs while utilizing inexpensive and widely available sulfur rather than expensive cobalt and nickel. To date, Li-S chemistry has not been commercialized due to technical issues, primarily due to unwanted diffusion of sulfur within these batteries. Evoseer has created a wood-derived monolithic cathode that is vapor-infiltrated with sulfur to produce high energy density batteries at low cost while utilizing readily available forest biomass. Evoseer's cathodes have the potential to double the performance of lithium batteries while lowering cost.
Animal Health Component
20%
Research Effort Categories
Basic
0%
Applied
20%
Developmental
80%
Goals / Objectives
Goal: The goal of this project is to produce high-capacity lithium sulfur batteries utilizing monolithic wood-derived cathodes. Current lithium batteries suffer from low specific energies and high cost, mainly due to the limitations of current cathode chemistries. This project aims to produce high-capacity, low-cost batteries utilizing wood feedstocks to overcome the limitations of current lithium batteries.Objectives:1. Optimization of biomass-derived graphitic carbon scaffold. Evoseer aims to produce a wood-derived carbon scaffold as the basis for our Li-S cathodes. This process involves forming wood biomass to the rough dimensions of the desired cathode, addition of FeCl3 to promote catalytic graphitization, heat treatment to 1,200 °C, and removal of residual iron. The resultant graphitic disc is desired to have a high specific surface area (>400 m2/g) in order to allow for significant sulfur addition to pores, high electrical conductivity (>1,000 S/m) in order to allow for the carbon scaffold to act as the current collector, and high graphitic content (>40%) to likewise provide minimal electrical resistance within the cathode.2. Loading of cathode with sulfur at 35% by mass. Cathodes will be loaded using a high temperature and pressure process. Loosely bound sulfur will be removed by heating sulfur infiltrated disks to 150°C under vacuum. Sulfur loading of disks will be analyzed using elemental analysis.3. Achievement of cathode capacity of 300 mAh/g after 100 cycles. Coin cells will be constructed using produced cathodes and cycled on a battery tester. Achievement of at least 300 mAh/g after 100 cycles will be used as the benchmark for validating the cathodes. This value provides a gravimetric energy density equivalent to the highest performance commercial metal oxides and a greater gravimetric energy density when considering that binder, conductivity additive, and current collectors are eliminated in Evoseer's cathodes.
Project Methods
Optimization of biomass-derived graphitic carbon scaffoldEvoseer will utilize both lodgepole pine and aspen as feedstocks for our carbon scaffolds. Trees will be harvested from Medicine Bow National Forest in Wyoming. Tree trunks will be cut into 4 cm thick sections with a chainsaw, and a hole saw will then be used to remove cores 1.9 cm in diameter and 4 cm in length. A band saw will then be used to cut the cores into discs of 1.9 cm diameter by 5 mm thickness. Cores will then be leached in 1% acetic acid solution for 24 hours to remove mineral content. After drying, cores will then be soaked in 1M FeCl3 solution for 24 hours to load cores with FeCl3. Metallic iron and FeCl3 have been show to catalytically graphitize biomass with appropriate heat treatment, and graphitized biomass has been shown to be an excellent material for lithium battery electrodes. Iron-loaded biomass discs will pyrolyzed in N2 at 500 °C for 1 hour and then graphitized by heat treatment at 1,200 °C in nitrogen for 1 hour in a controlled atmosphere muffle furnace. The surface area and pore characteristics of the carbon scaffolds will be tailored through addition of small amounts of oxidizer for short durations during pyrolysis and/or heat treatment.Following heat treatment, discs will be soaked in 37% HCl for 2 hours to remove iron. Graphite content will then be evaluated by Raman spectroscopy, and electrical conductivity will be assessed using a two-probe technique. Finished discs will be analyzed by physisorption (BET analysis) to determine their pore size distribution and surface area. Desired attributes are high specific pore volume with most volume existing at small pore widths, with roughly 1 nm pores being typical of many activated carbons. Carbon discs will be optimized for these characteristics by modifying the process parameters of the pyrolysis and heat treatment steps, particularly gas environment and residence time.During the pyrolysis and heat treatment steps, the discs shrink as mass is lost. The initial 19 cm diameter by 5 mm thickness is sufficiently large such that heat-treated discs will still be slightly larger than required for coin cell usage. Discs will be sanded down to the appropriate size, approximately 17 mm diameter by 1 mm thickness, for battery construction.Loading of cathodes with sulfur at 35% by massGraphitized wood-derived carbon discs will be placed in a stainless steel reactor of 1.9 cm inner diameter by 30 cm length along with powdered sulfur. Half of the discs will be placed in the bottom of the reactor such that they are in contact with liquid sulfur while the other half will be placed in the top of the reactor such that they will have contact only with sulfur vapor. The reactor will be heated to 100 °C for 1 hour under vacuum to remove any gases adsorbed onto the carbon scaffold discs. The reactor will then be heated to the test temperature (maximum 850 °C) and held for a prescribed length of time, with test temperature and time to be optimized. At the conclusion of the test, the reactor will be cooled to room temperature. Discs will be removed from the reactor and heated in a vacuum oven at 150 °C to remove any loosely bound sulfur that would interfere with battery cycling. The parameters of sulfur infiltration temperature and treatment time will be examined to determine how to maximize the sulfur loading that can be achieved, as well as the preferred phase of infiltration (liquid or vapor).Sulfur-loaded discs will be analyzed by thermogravimetric analysis (TGA) to examine how strongly sulfur is bound within the pore structure of carbon scaffold. Sulfur typically evaporates at 446 °C, and observation of mass loss at higher temperatures demonstrates that sulfur is strongly bound to the carbon scaffold. Discs will be analyzed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) to examine the distribution of sulfur within the disc, with particular attention paid to the amount of sulfur across the depth of the disc.Achievement of cathode capacity of 300 mAh/g after 100 cyclesCoin cells will be constructed using Li foil as the anode and Celgard 2340 separator. Electrolyte will be composed of a 50/50 vol/vol% solution of 1,3-dioxolane (DOL) and dimethoxyethane (DME) containing 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.3M LiNO3. A DOL/DME binary mixture is commonly used as electrolyte in Li-S cells as these compounds are more inert to reactions with polysulfides compared to conventional electrolytes. LiTFSI is used as the primary electrolyte salt as LiTFSI is able to form a stable solid electrolyte interface (SEI) on lithium metal anodes. LiTFSI has the additional advantages of high dissociation and diffusivity in DOL/DME mixtures allowing for fast cycling rates. LiNO3 is added as a secondary lithium salt as LiNO3 has been shown to from a passivation layer on Li metal anodes that helps to hinder the polysulfide shuttle, resulting in greater charge/discharge efficiency and long cycle life. Coin cell batteries will be constructed using lithium foil as the anode and Evoseer's biomass-derived cathodes. Cells will be constructed under argon and then cycled between 2.7 and 1.5 V at C/3 on an Arbin battery tester. Achievement of at least 300 mAh/g after 100 cycles will be used as the benchmark for validating the cathodes. This value provides a gravimetric energy density equivalent to the highest performance commercial metal oxides and a greater gravimetric energy density when considering that binder, conductivity additive, and current collectors are eliminated in Evoseer's cathodes.