A Figure of Merit for Fast-Charging Li-ion Battery Materials

Rate capability is characterized necessarily in almost all battery-related reports, while there is no universal metric for quantitative comparison. Here, we proposed the characteristic time of diffusion, which mainly combines the effects of diffusion coefficients and geometric sizes, as an easy-to-use figure of merit (FOM) to standardize the comparison of fast-charging battery materials. It offers an indicator to rank the rate capabilities of different battery materials and suggests two general methods to improve the rate capability: decreasing the geometric sizes or increasing the diffusion coefficients. Based on this FOM, more comprehensive FOMs for quantifying the rate capabilities of battery materials are expected by incorporating other processes (interfacial reaction, migration) into the current diffusion-dominated electrochemical model. Combined with Peukert's empirical law, it may characterize rate capabilities of batteries in the future.

Automated summary

The characteristic time of diffusion is proposed as a figure of merit to standardize the comparison of fast-charging battery materials by considering diffusion coefficients and geometric sizes. This indicator offers a way to rank the rate capabilities of battery materials and suggests methods to improve rate capability. Incorporating other processes into the current electrochemical model may lead to more comprehensive figures of merit for quantifying rate capabilities of battery materials.