Technology. Organosilicon (OS) Electrolytes for Li-ion Batteries

Current Li-ion electrolytes are unstable above 60 degrees C and at charge voltages above 4.3 volts. They also exhibit flashpoints around 35 degrees C, and are the major source of the energy released during an extreme Li-ion cell failure. Given these significant limitations, current electrolytes are impeding the development of advanced Li-ion batteries for all applications, including portable products, electric drive vehicles (EDVs), and utility scale use.

In general, OS compounds are environmentally friendly, non-flammable, high temperature materials. These characteristics make OS materials well-suited for use as electrolytes, binders, and coatings in energy storage devices. Recently, the need for improved electrolytes in energy storage devices has led Silatronix to focus on development of unique OS materials for these applications, especially for Li-ion battery products. OS electrolytes are compatible with all lithium (Li) based electrochemical systems, including non-rechargeable batteries, Li-ion, Li-air, and Li-battery/capacitors. The process of designing OS electrolytes into a Li battery involves limited changes in the cell design, and these electrolytes can be incorporated into production operations with existing manufacturing processes and equipment.

As with past silicone material developments, a wide range of variables can be manipulated to “engineer” customized electrolytes to meet specific Li-ion battery application requirements. The basic structure and characteristics of an OS compound for use as a Li-ion electrolyte are described below and shown in Figure 1.

Figure 1: Structure of an OS electrolyte compound

Structure of an OS electrolyte compound

  • Siloxane backbone provides thermal and electrochemical voltage stability
  • Polyethylene oxide (PEO) chain allows dissolution of lithium salts
  • Functional groups and structure can be modified to control overall electrolyte properties
    • Conductivity, flash point, viscosity, thermal stability, voltage stability, capacity, and cost

Based on the need for improved electrolytes in Li-ion batteries, Silatronix is developing a novel class of OS based liquid solvents to replace the carbonate based solvent system in traditional Li-ion batteries. Silatronix is using the versatility of silicone chemistry to development unique silicone materials for use as electrolytes. The OS solvent system has the potential to provide significant improvements in performance and abuse tolerance in Li-ion batteries.

  • Thermal stability up to 100 degrees C for longer life at elevated temperatures
  • Electrolyte flash points in excess of 100 degrees C for improved safety in abuse conditions
  • Voltage stability up to 5.0 volts to allow use of high voltage cathode materials to achieve higher energy density
  • Reduced battery failure rates to be consistent with the requirements for large scale Li batteries used in EDV and grid storage applications
  • Compatibility with materials currently in use in Li-ion batteries for ease of adoption in current designs

In its development effort, Silatronix has established a rigorous methodology to identify the failure mechanisms associated with solvent instability within electrolyte formulations. This work has led to a unique understanding of the structure of OS compounds and the underlying affect their characteristics have on the performance of OS electrolytes in Li-ion batteries. With this knowledge, Silatronix has been able to target development of specific classes of OS molecules which are capable of improving the safety, thermal stability, and voltage stability of Li-ion electrolytes. Several of the patent pending molecules developed at Silatronix exhibit dramatic performance improvements compared with previously explored OS based electrolyte solvents, including ionic conductivity and electrolyte salt compatibility. Using the results of this mechanistic approach, Silatronix has engaged discussions with numerous lithium battery producers.

The Company is currently developing customized OS based electrolyte blends to meet the requirements of specific applications in the industrial, military, and consumer product markets. These efforts should lead to the commercialization of Silatronix initial OS electrolyte products. However, these products will only represent the first steps in the development of OS electrolytes. By capitalizing on the versatility of silicone chemistry, Silatronix intends to pursue a development process that identifies new OS compounds that continually improve the performance of Li-ion batteries, and meets the evolving requirements of future energy storage systems such as non-rechargeable Li batteries, capacitors, and Li-air batteries. Just as silicone chemistry versatility has enabled the evolution from Silly Putty in the 1940s, to thousands of silicone products today, Silatronix intends to continually “engineer” new OS electrolyte products to grow the market and expand its commercial opportunities.