Here are the highlights from Session 1 – Energy Generation and Storage of the recent IEEE San Francisco Bay Area Nanotechnology Council Symposium:
Dr. Dania Ghantous, V.P. Technology of Qnovo: “Lithium-Ion Batteries: Opportunities and Challenges”
Dr. Ghantous provided an overview of lithium-Ion (Li-ion) battery technology and market since Qnovo is still in “stealth mode”. She did say that battery life, charge time, and cost are challenges they are working on from an electronics perspective. (Cleantech Insights does provide this summary of Qnovo’s focus.)
Li-ion batteries have been around for over twenty years with mobile phones and laptop computers being the drivers for the technology. As costs decrease along with increased demand for the benefits of Li-ion technology (higher voltages, higher energy density, and no memory effects) volume adoption is occurring in everything from power tools to electric vehicles. Unfortunately there is no Moore’s Law for batteries and performance improvements are incremental. For example cells have gone from 1 Ah in 1990 to 2.6 Ah today (using lithium cobalt cathodes) and are predicted to go as high as 4 Ah in a few years. Clearly these are improvements but not on the order of Moore’s Law.
Beyond the selection of basic materials used for the cathode, anodes, and electrolytes which determine the electrochemical reaction, the design of the cells is specific to the intended application. The cells are then combined with electronics which manage the cell (including safety to avoid overcharging and potential explosions) to form a battery pack. A typical laptop has a six cell battery pack while a car might have 100’s of cells grouped in packs.
Particle size of the materials can be selected depending on the cell application. For example, if the cell is intended for extended / long term energy storage larger particles are desired, while if high power demands are required typically smaller particles are desired. However, most of the materials in use today are particles that are 10 µm or larger – clearly not nanotechnology.
Some of the initial nanotechnology used in batteries includes reduction of the particle size to enable faster diffusion (reducing charge / recharge time), increasing the surface area (providing higher capacity), and avoiding structural change to the electrochemical cell (resulting in longer life / greater number of charges). These are all areas of active research and some initial commercialization of nanotechnology has been done for anode (such as lithium-titanate) materials.
Dr. Ghantous closed by discussing the role that ARPA-E has taken to bridge the gap between basic research (universities) and development / commercialization (what venture capitalists and companies will fund). Over the last two years ARPA-E has provided approximately $70 M to fund battery-related research – i.e. applied research with a majority of it focused on the consumer space especially electric vehicles.
Dr. Herman Lopez, Director of Materials Development of Envia Systems: “High Capacity Cathode for Consumer Electronics Application”
Dr. Lopez started by describing Envia’s startup in 2007 and recent funding including ARPA-E, US Advanced Battery Consortium (General Motors, Ford, & Chrysler), and a $17 M Series C in January including $7 M from GM. They are currently focused on qualify their High Capacity Manganese Rich (HCMR) cathode battery technology for the next Chevy Volt. Their HCMR technology is based upon work that started at Argonne National Laboratory using two nano-engineered layered composite materials to form the cathode. By using this structure, they are displacing expensive cobalt with inexpensive manganese to increase the energy density of lithium-ion cells.
Since their cathode has twice the energy density of existing commercially available cathodes, they are now concentrating on improving the performance of the anode using nanotechnology. They need to match the performance of their cathode in order to achieve cell performance of over 400 Wh/kg at less than $125 / kWh. Currently the state of the art is 80 to 180 Wh/kg at a cost of $250 – 350 / kWh.
During the question period he explained that their business model is to be a materials company. However, they have learned they need to be able to do all the work (design cells, formulate anodes & cathodes, etc.) since customers would not initially be successful with just receiving the materials. As such they have a cell development facility in Jiaxing China to build prototype quantities of cells.
Professor Ali Shakouri, Department of Electrical Engineering, UC Santa Cruz: “Nanostructured Materials for Direct Conversion of Heat Into Electricity”
Professor Shakouri started with this motivation: total world-wide energy consumption is forecasted to rise while at the same time we need to reduce the equivalent carbon dioxide (CO2e) per person to avoid global warming. Unfortunately, green / renewable energy and nuclear sources will not grow fast enough to keep up with demand and displace large amounts of traditional energy sources.
Taking a closer look at energy flows in the Sankey diagram above from Lawrence Livermore National Laboratory (LLNL) shows the amount of energy lost as heat. United States transportation consumes 26.98 Quads (10^15 BTU or 1.055 x 10^18 joules of energy per Quad) – 94% of it from petroleum – but looses 20.23 Quads as rejected heat for a total efficiency of only 25%. Similarly electrical generation uses 38.19 Quads and rejects 26.10 Quads for an efficiency of 32%.
He maintains that converting heat back to productive energy is necessary if we are to make significant changes in overall energy efficiency. The thermoelectric figure of merit ZT = S^2 * sigma * T / kappa. Where S is the Seebeck coefficient, sigma is electrical conductivity, and kappa is the thermal conductivity. Unfortunately, material properties are inter-related: most electrical conductors are good thermal conductors and vice-versa. Therefore, we haven’t made much progress since the 1950s and everything below ZT=1 was developed between 1950 and 1960.
Most of the small number of improvements in ZT since then have been the results of nano-scale engineering of which he provided examples. When you change atoms using quantum mechanics, you can fundamentally change the nature of the material. And when you are in the 10 to 15 nm scale materials behave substantially different than bulk. One of the challenges is how to measure temperatures at nano-scale which they solved by measuring light reflection of liquid crystals using a heterodyne technique. They are able to now measure with an accuracy of 0.08 C in 100 ns.
Professor Shakouri also described his team’s work with erbium arsenic (ErAs) where the islands within the lattice structure allow thermal vibration. This material has a 2 to 3 nm particle size and they use self assembly to form the structures. To produce a small square they were able to grow the thickness at a rate of 1 to 1.5 µm / hour. However, they needed 100 µm overall thickness to achieve ZT=1.33 at 800 C so this process is very time consuming and expensive.
In order to make cost effective solutions, one needs to increase the efficiency further (higher ZT) or decrease the cost to produce or both to achieve the desired cost per Watt. Even though these are costly structures, the use of a heat spreader to concentrate the heat may allow the use of higher cost but smaller area devices. This is similar to how concentrator photovoltaic (CPV) solar systems work and achieve the desired cost effectiveness.
Note: copies of presentations are archived here when they become available.