Ferrous Pyrophosphate Hollow Nanorods Enable Lithium Metal Batteries Under Low Negative/Positive Capacity Ratios

Abstract

ABSTRACT Lithium (Li) metal batteries (LMBs) exhibit a promising paradigm for their high energy density. However, their realization is still hindered by the inherent instability and excess of Li metal. Herein, we rationally design and synthesize ferrous pyrophosphate hollow nanorods encapsulated by an N‐doped carbon shell (Fe 2 P 2 O 7 @NC) as a Li host for Li metal anodes (LMAs). The Fe 2 P 2 O 7 @NC‐casted Cu electrode (Fe 2 P 2 O 7 @NC‐Cu) guides uniform Li deposition and suppresses volume expansion, enabling uniform Li plating and enhanced Coulombic efficiency. Time‐of‐flight secondary ion mass spectrometry and in‐depth X‐ray photoelectron spectroscopy analyses reveal that the existence of Fe 2 P 2 O 7 promotes the generation of LiF and Li 2 O in LMAs, thereby promoting uniform Li plating. The Fe 2 P 2 O 7 @NC‐Li electrode presents stable Li deposition/stripping with small voltage polarization for 1400 h at 1 mA cm −2 and 1 mAh cm −2 . Furthermore, a full cell coupled with a LiFePO 4 cathode, demonstrates consistent cycling stability, maintaining a capacity retention of 80.6% over 136 cycles at a low negative/positive capacity ratio of 1.5, highlighting the great potential of Fe 2 P 2 O 7 @NC for practical high‐energy‐density LMBs.