Many-Particle Li Ion Dynamics in LiMPO₄ Olivine Phosphates (M = Mn, Fe)

Abstract

LiMPO 4 (M = Mn, Fe) olivine phosphates are important materials for battery applications due to their stability, safety, and reliable recharge cycle. Despite continuous experimental and computational investigations, several aspects of these materials remain challenging, including conductivity dimensionality and how it maps onto Li pathways. In this work, we use a refined version of our finite temperature molecular dynamics “shooting” approach, originally designed to enhance Li hopping probability. We perform a comparative analysis of ion mobility in both materials, focused on many-particle effects. Therein, we identify main [010] diffusion channels, as well as means of interchannel couplings, in the form of Li lateral [001] hopping, which markedly impact the overall mobility efficiency as measured by self-diffusion coefficients. This clearly supports the need of many-particle approaches for reliable mechanistic investigations and for battery materials benchmarking due to the complex nature of the diffusion and transport mechanisms.

Effects of H2O on Improving the Performance of a Solid Composite Electrolyte Fabricated via an Air-Processable Technique

“…Note that the ICE of LFP-aSCE/Li battery reached as high as 98.6%, which can be ascribed to the improved Li + mobility in both LFP and aSCE layers at 50 °C. 34 The rate performance of LFP-aSCE/Li and LFP-aSCE/Li batteries is displayed in Figure 4e. As expected, the LFP-aSCE/Li battery showed largely improved electrochemical performance at various current rates compared with the LFP-iSCE/Li one, especially at 1.2, 2, and 3 C, although intensified polarization effect was found as well with increasing current rates (Figure 4f).…”

“…As shown in Figure d, a discharge capacity of 121 mAh g –1 at 0.2 C (180 cycles) and 132 mAh g –1 at 0.5 C (145 cycles) has been achieved, which well demonstrates the good thermal stability of the LFP-aSCE/Li batteries. Note that the ICE of LFP-aSCE/Li battery reached as high as 98.6%, which can be ascribed to the improved Li + mobility in both LFP and aSCE layers at 50 °C . The rate performance of LFP-aSCE/Li and LFP-aSCE/Li batteries is displayed in Figure e.…”

Ion Mobility in Crystalline Battery Materials

“…[115] These differences may be pinpointed to many factors, including the assumed uni-lateral nature of lithium ion diffusion in many theoretical works and the two phase coexistence/phase transformation during experiments. [109,116] Olivine materials are especially interesting as energy storage materials due to their high operating potentials and high capacity, but the scientific interest in the optimization of olivine structured compounds increased even further with the recent successful commercialization of LiFePO 4 . [117] Most of today's research focuses on either ridding this popular system from its known drawbacks, that is, their low energy density and slow rate performance or on the development of its derivative systems utilizing manganese, cobalt, or nickel.…”

“…[ 115 ] These differences may be pinpointed to many factors, including the assumed uni‐lateral nature of lithium ion diffusion in many theoretical works and the two phase coexistence/phase transformation during experiments. [ 109,116 ]…”

Optimizing the Electrochemical Performance of Olivine LiMnxFe1–xPO4 Cathode Materials: Ongoing Progresses and Challenges

“…However, they suffer from noticeable capacity decay, particularly at elevated temperatures . In contrast, olivine LiFePO 4 has been widely used due to its advantages of nontoxicity, pollution-free, low cost, and high safety and thermal stability characteristics since first being discovered in 1997. − Nevertheless, the limited operating voltage (3.4 V vs Li/Li + ) has impeded its capacity to fulfill the increasing need for higher energy density. − To address this issue, scholars have gradually turned their attention to LiMnPO 4 which shares the same structure as LiFePO 4 . Olivine LiMnPO 4 offers a higher operating voltage (4.1 V vs Li/Li + ) and thus increased energy density (701 Wh kg –1 ) of about 20% compared to LiFePO 4 (578 Wh kg –1 ) at the same specific capacity (170 mAh g –1 ). − Moreover, the operating voltage of LiMnPO 4 falls in the existing mature electrolyte system window, making it easier to popularize.…”