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Increasing the areal capacity or electrode thickness in lithium ion batteries is one possible means to increase pack level energy density while simultaneously lowering cost. The physics that limit use of high areal capacity as a function of battery power to energy ratio are poorly understood and thus most currently produced automotive lithium ion cells utilize modest loadings to ensure long life over the vehicle battery operation. Here we show electrolyte transport limits the utilization of the positive electrode at critical C-rates during discharge; whereas, a combination of electrolyte transport and polarization lead to lithium plating in the graphite electrode during charge. Experimental measurements are compared with theoretical predictions based on concentrated solution and porous electrode theories. An analytical expression is derived to provide design criteria for long lived operation based on the physical properties of the electrode and electrolyte. Finally, a guideline is proposed that graphite cells should avoid charge current densities near or above 4 mA/cm2 unless additional precautions have been made to avoid deleterious side reaction.

The cost situation for lithium-ion batteries is one of the key limitations for the market potential of electric vehicles and has been covered by several authors from the industry and science sector. This work addresses the relation between active material properties, cell design and vehicle requirements. The results of this investigation show that the efficient use of the cell properties in the vehicle application will be decisive for the competitiveness of OEMs and battery suppliers. The center of the research is a cell model in which different active material properties, cell formats and electrode layouts can be implemented flexibly. Within a constant volume of a standardized cell housing the variation of the electrode loadings leads to relationships between the storable energy and the power of the cell. The costs determined for each specific cell design then allow describing the relation between the power to energy ratio of a cell and its energy specific costs for current and future materials. The optimal cost situation is reached when the P/E-ratio of the cell matches the required P/E-ratio of the storage system. In a broad vehicle portfolio this means a specific cell would be required for each car project. This potentially large number of cell types seems unfavorable for OEMs to handle. Therefore a genetic algorithm optimization is applied to determine the cost-optimal number and specifications of cells to address a certain vehicle portfolio. For these optimizations further restrictions such as voltage level limitations are considered as well. The tool derived from these considerations can support OEMs as well as cell &amp, material suppliers to find the optimal modular kit for their lithium-ion cell strategy considering individual customer requirements.