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A Breakthrough High Capacity Silicon Anode Technology

The Problem
Silicon (Si) is one of the most promising anode materials being considered for next generation, high energy and high power lithium ion batteries (LIBs). Graphite is currently the most widely used anode material, but Si has attracted great attention because of its natural abundance, non-toxicity, and very high theoretical specific capacity of nearly 4200 mAh/g about 10 times more capacity than conventional graphite anodes.

However, Si anodes suffer from large capacity fading and tremendous volume changes during lithium-ion charge-discharge cycling. The strains due to the huge volume changes actually pulverizes the Si material and eventually lead to electrode shattering and delamination, which adversely affect the battery performance and cycle life. These are the primary challenges to the commercial use of Si for battery anodes, which BioSolar intends to overcome.

Existing Si-based Anode Approaches To overcome the issues with Si, popular attempts over the recent years included fabrication of Si into nanoparticles, porous structures, composites with carbon or composites with intermetallic flexible matrix, and many others.

Nanoscale Si particles have been shown to reduce volume expansions and prevent particle cracking, which improves battery life. In addition, they allow for faster charging of the battery. Nevertheless, Si nanoparticles are expensive and not industry scalable yet.

Silicon Oxide (SiOx) based systems used for dilution of Si expansion stresses offer high capacity and long cycle life, but require high temperature synthesis process. They also suffer from low conductivity which requires carbon coating and surface treatments.

Si and carbon composite systems can mechanically protect the Si particles by a surrounding carbon matrix which maintains the electrical integrities. They can also be synthesized using low cost milling process and can be incorporated with existing graphite electrode systems. However, this approach has low matrix strength to prevent Si expansions, which results in short battery life.

All of the approaches to date have their own fundamental obstacles that need to be overcome before taking advantage of Si's full theoretical capacity.

BioSolar's Breakthrough Approach Anode based on Si-Alloy
We are focused on developing a unique and highly effective material and processing solutions to take maximum advantage of Si's full capacity.

BioSolar intends to commercialize a Si based anode material technology to significantly increase the energy density and cycle life of the current lithium-ion batteries. BioSolar's target is to design Si-Alloy materials with a capacity objective of 1500 mAh/g, which translates into to an anode with a capacity density of 1000 mAh/cm3 and a cell level volumetric energy density of 1000 Wh/L. As a point of reference, the lithium-ion batteries in a current Tesla Model S electric vehicle have an energy density of 676 Wh/L.

Our goal is to demonstrate a working high capacity anode for use by battery manufacturers to create the ultimate high capacity, high power, and fast charging and discharging lithium-ion battery.

BioSolar is currently funding a sponsored research program to develop its anode technology. The lead inventor of the technology is North Carolina A&T State University assistant professor Dr. Sungjin Cho, a lithium-ion battery expert with extended career in the battery industry prior to joining the University.

A Novel Polymer Cathode Technology
Why can't we use our iPhones for several days without charging, or drive our electric vehicles from Los Angeles to San Francisco without being stranded along the way due to a low battery? Wouldn't it be nice if you can fully recharge your electric car for a return trip back to Los Angeles while you are having lunch at San Francisco? When will we be able to purchase electric vehicles that cost about the same as conventional vehicles? The answer comes down to higher battery capacity, faster charging ability, and lower cost.

The Problem A battery contains two major parts, a cathode and an anode, that function together as the positive and negative sides. The overall capacity of the battery is determined by the combination of the storage capacity of its cathode as well as that of its anode. Today's state-of-the-art lithium-ion battery is limited by the storage capacity of its cathode, while the existing anode can store much more. Additionally, the materials used in batteries are still quite expensive.

The Solution - A Cathode based on Conductive Polymer Based on our patent-pending supercapacitor technology that uses a novel conductive polymer material, we are developing a high capacity cathode engineered from a conductive polymer. Instead of conventional cathodes that use lithium-ion intercalation chemistry, we exploit the fast redox-reaction properties of polymers to enable rapid charge and discharge.

Most lithium-ion batteries cannot retain more than 80% of its storage capacity after 1,000 charge-discharge cycles. The stable redox chemistry of our cathode material potentially can enable much longer life. Our laboratory experiments have shown that our cathode can cycle over 50,000 times without degradation in supercapacitors, and we believe that it can be very effective in batteries as well.

By enabling higher charge-discharge cycles, it may be possible to extend the life of lithium-ion batteries and further reduce the total cost of ownership. In certain applications such as off-grid solar energy storage where the batteries are fully charged and discharged daily, it is not cost-effective to use current lithium-ion batteries due to short replacement life.

Reducing the Cost of Storing Electrical Energy Materials account for more than 70% of the cost of a battery. In particular, the cathode material makes up 20-35% of the total materials costs. Therefore, lowering the cost of the cathode is an effective way to lowering the total battery cost.

Processing materials and time are additional cost drivers. Our cathode can be processed from water and eco-friendly solvents, which (i) eliminates the use of costly and toxic solvents, (ii) eliminates high temperature drying processes, and (iii) speeds up the production throughput.

Many analysts in the electric vehicle and solar industry consider $100 per kilowatt-hour (kWh) to be the "holy grail" price threshold. In the case of electric vehicles, $100/kWh will make them undeniably cost-competitive with gas-powered vehicles. And in the case of solar, it will finally be cost effective to store daytime solar electricity for nighttime use and be less reliant on, or completely independent of, the power grid.

Intellectual Property BioSolar jointly filed a number of patent applications with the University of California, Santa Barbara ("UCSB") for "High Capacity Cathode for Use In Supercapacitors and Batteries and Methods for Manufacturing Such Cathodes." The lead inventor of the technology is UCSB professor Dr. Alan Heeger, the recipient of a Nobel Prize in 2000 for the discovery and development of conductive polymers.