Building a better lithium-ion battery is a challenge for researchers worldwide. The object of much of the research is to find improved, nonflammable, materials for the electrolyte.

The electrolyte, whether liquid or solid, serves to insulate the flow of electrons between anode and cathode and promote the flow of ions. The basic battery circuit is that electrons move from the negative terminal out of the battery through a load, and return to the battery’s positive terminal, the cathode. When the electrons leave the anode, positively charged lithium ions move across the electrolyte to the cathode.

In rechargeable batteries, the cycle can be reversed and the lithium ions are conserved. Typical lithium-ion batteries use liquid electrolytes, which are less stable, more flammable, and more volatile than solid polymers. Thus, research is focused on finding the best solid polymer electrolytes.

Adding lithium salts to polyethylene oxide (PEO) is a technique that has been used to create a solid electrolyte. The salt contains lithium cations, positively charged ions that move back and forth in the battery, and some negatively charged anions to balance the charge.

However, the PEO conducts lithium ions poorly in comparison to liquid electrolytes. This means the ions travel slowly to the cathode thereby limiting the current the battery can produce. It also conducts the anions too quickly, which creates a loss in battery voltage.

A team of researchers at the California Institute of Technology has been searching for a solid electrolyte that would conduct lithium ions more quickly than PEO. They developed a simulation protocol to screen electrolyte materials initially trying a set of 500 diverse classes of polymers.

For their search they used Oak Ridge National Laboratory’s Titan supercomputer. That enabled them to run hundreds of simulations – each consisting of thousands of atoms – on possible new electrolytes. The simulations ran on timescales ranging from a femtosecond to a microsecond – a span of nine orders of magnitude.

They achieved surprisingly good results using Lewis-acidic polymers, which not only conducted the anions more slowly than PEO, but also conducted the positive lithium ions more quickly. The simulations showed that these polymers may be capable of producing an eight-fold increase in desired lithium conduction and a marked decrease in the unwanted anion conduction.