ANALYSIS OF CAPACITY-RATE DATA FOR LITHIUM BATTERIES USING SIMPLIFIEDMODELS OF THE DISCHARGE PROCESS

Simplified models based on porous electrode theory are used to describ e the discharge of rep chargeable lithium batteries and derive analyti c expressions for the specific capacity against discharge rate in term s of the relevant system parameters. The resulting theoretical express ions are useful for design and optimization purposes and can also be u sed as a tool for the identification of system limitations from experi mental data. Three major cases are considered that are expected to hol d for different classes of systems being developed in the lithium batt ery industry. The first example is a cell with solution phase diffusio n limitations for the two extreme cases of a uniform and a completely nonuniform reaction rate distribution in the porous electrode. Next, a discharge dominated by solid phase diffusion limitations inside the I nsertion electrode particles is analysed. Last, we consider an ohmical ly-limited cell with no concentration gradients and having an insertio n reaction whose open-circuit potential depends linearly on state of c harge, The results are applied to a cell of the form Li/solid polymer electrolyte/LiyMn2O4 in order to illustrate their utility.