Into the Lab: Mechanical Engineering

A rechargeable battery is a component needed not only for electronic devices, but also for vehicles and renewable power systems such as solar and wind. One particular challenge in the implementation of electric and hybrid-electric vehicles is the development of batteries that provide the range and lifetime that drivers expect. The lithium ion battery has become the most preferred electrochemical energy storage device in vehicular applications because of its high energy density, power density and coulombic efficiency, or charge efficiency. Mechanical engineering faculty members Song-yul Choe and Jeffrey Fergus are leading an interdisciplinary team to investigate these batteries to increase their lifetimes, which could reduce costs for drivers, as well as conserve natural resources by placing more electric vehicles on the roadways.

When a cell is being charged and discharged, various interrelated processes take place inside a battery. Ions are transported in the liquid electrolyte and in the solid electrode materials, heat is generated and transferred and mechanical stresses are generated. At the same time, degradation processes occur in different cell components which may lead to poor performance or failure of the battery. The mechanisms by which these processes occur are not well understood. One of the major causes of degradation is the side reaction caused by reduction of the electrolyte. The side reaction, which takes place at the interface between the carbon anode and liquid electrolyte, consumes lithium ions and electrolyte solvents and produces deposits. The deposits cover electrode particles, which reduces the active area, as well as ionic conductivity. As a result, the energy capacity and power output of the battery decrease.

Choe and Fergus are focusing on understanding these mechanisms by testing battery performance using instruments developed by their team. The testing equipment is capable of measuring a battery’s current, voltage, temperature, heat generation, capacity, power and electrical impedance, while advanced control algorithms can be tested in real time by interfacing MATLAB with LabVIEW codes.

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