Nanoscale Voltage Enhancement at Cathode Interfaces in Li-ion Batteries

TL;DR

This study investigates how interfaces in Li-ion battery cathodes influence lithium intercalation voltages, revealing a nanoscale voltage enhancement mechanism driven by electron transfer, strain, and dipole screening, with implications for advanced cathode design.

Contribution

The paper introduces a detailed analysis of interfacial effects on Li intercalation energetics, demonstrating a nanoscale voltage enhancement mechanism in cathode interfaces.

Findings

Voltage remains constant in high-voltage material and decays linearly in low-voltage material across interfaces.

Voltage enhancement occurs over 0.5-9nm depending on interfacial dipole screening.

Mechanisms include electron transfer, strain, and interfacial dipole screening.

Abstract

Interfaces are ubiquitous in Li-ion battery electrodes, occurring across compositional gradients, regions of multiphase intergrowths, and between electrodes and solid electrolyte interphases or protective coatings. However, the impact of these interfaces on Li energetics remains largely unknown. In this work, we calculated Li intercalation-site energetics across cathode interfaces and demonstrated the physics governing these energetics on both sides of the interface. We studied the olivine/olivine-structured LixFePO4/LixMPO4 (x=0 and 1, M=Co, Ti, Mn) and layered/layered-structured LiNiO2/TiO2 interfaces to explore different material structures and transition metal elements. We found that across an interface from a high- to low-voltage material the Li voltage remains constant in the high-voltage material and decays approximately linearly in the low-voltage region, approaching the Li voltage of the low-voltage material. This effect ranges from 0.5-9nm depending on the interfacial dipole screening. This effect provides a mechanism for a high-voltage material at an interface to significantly enhance the Li intercalation voltage in a low-voltage material over nanometer scale. We showed that this voltage enhancement is governed by a combination of electron transfer (from low- to high-voltage regions), strain and interfacial dipole screening. We explored the implications of this voltage enhancement for a novel heterostructured-cathode design and redox pseudocapacitors.