Designing a hybrid electrode toward high energy density with a staged Li⁺ and PF₆ ^- deintercalation/intercalation mechanism.

Abstract

Existing lithium-ion battery technology is struggling to meet our increasing requirements for high energy density, long lifetime, and low-cost energy storage. Here, a hybrid electrode design is developed by a straightforward reengineering of commercial electrode materials, which has revolutionized the "rocking chair" mechanism by unlocking the role of anions in the electrolyte. Our proof-of-concept hybrid LiFePO₄ (LFP)/graphite electrode works with a staged deintercalation/intercalation mechanism of Li⁺ cations and PF₆ ^- anions in a broadened voltage range, which was thoroughly studied by <i>ex situ</i> X-ray diffraction, <i>ex situ</i> Raman spectroscopy, and <i>operando</i> neutron powder diffraction. Introducing graphite into the hybrid electrode accelerates its conductivity, facilitating the rapid extraction/insertion of Li⁺ from/into the LFP phase in 2.5 to 4.0 V. This charge/discharge process, in turn, triggers the in situ formation of the cathode/electrolyte interphase (CEI) layer, reinforcing the structural integrity of the whole electrode at high voltage. Consequently, this hybrid LFP/graphite-20% electrode displays a high capacity and long-term cycling stability over 3,500 cycles at 10 C, superior to LFP and graphite cathodes. Importantly, the broadened voltage range and high capacity of the hybrid electrode enhance its energy density, which is leveraged further in a full-cell configuration.