Design Considerations to Improve Transport in Porous Electrodes for Lithium-Ion Batteries
- PDF / 368,137 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 95 Downloads / 155 Views
Design Considerations to Improve Transport in Porous Electrodes for Lithium-Ion Batteries Rajeswari Chandrasekaran1, Andrew Drews1, Apoorv Shaligram2, Jeffrey Sakamoto2 1 Research and Advanced Engineering, Ford Motor Company, Dearborn, Michigan - 48124. 2 Michigan State University, East Lansing, Michigan. ABSTRACT The relationship between tortuosity and porosity and its influence on effective transport properties in lithium-ion cells was analyzed. The variation in cell performance with changes in component thicknesses, porosities and tortuosities was investigated. Optimal, novel electrode designs are developed to improve their rate capability even at higher active material loadings. INTRODUCTION A lithium-ion cell sandwich comprises of three porous regions: the positive and the negative electrodes and the separator. The composite porous electrodes consist of solid active insertion material particles, binder, inert conductive carbon and the void volume in all three regions of the cell is filled with electrolyte. To increase the driving range of electric vehicles powered by lithium-ion cells (with present chemistries of active materials), thicker electrodes are needed to maximize the energy contenti. However, simply increasing the thickness of conventional porous electrodes can lead to increased charge and mass transport limitations. In addition, solid phase diffusion limitations may also exist within the micron-sized active material particles. Moreover, at low temperatures, cell performance is further inhibited by the reduced bulk transport properties. All these can reduce the charge-discharge performance at medium to high rates in high energy cells. The rate limitations may be more pronounced during charge than discharge [1]. This is a significant concern because the cells must be able to accept full charge safely and efficiently at high rates to meet customer expectations. The US DOE (Department of Energy) has established aggressive fast charge goals [2] of 10 minutes (~ 6C rate) to charge a 24 kWh battery pack used in an electric vehicle with 100-mile range and roughly 30 minutes (2C rate) for a 300mile range electric vehicle. Some of the approaches that can help avoid liquid phase transport limitations in lithium-ion cells ii include higher electrode porosity and novel electrode designs. Simply increasing porosity may improve liquid phase transport, but will also reduce the matrix phase electronic path and the amount of active material for the same volume, resulting in a lower energy density at the cell level. This implies that the ability of commercial lithium-ion cell chemistries to meet the USABC (United States Advanced Battery Consortium) goals for energy storage systems for advanced electric vehicles is further reduced. An alternate approach is to enhance the effective transport properties by reducing tortuosity for the same porosity. In this work, firstly, we describe our preliminary theoretical analysis of this approach. Secondly, we provide quick methodologies to estimate the different limitations in poro
Data Loading...
