The application of hard carbon with internal quasi-lithium metal deposition in high-energy Li-ion/Li-metal hybrid batteries

Abstract

The energy density of lithium-ion batteries (LIBs) with graphite as the negative electrode reaches the upper limit. The lithium ion/lithium metal hybrid batteries (HLBs) constructed by lowering the n/p of LIBs with graphite as the anodes effectively improves the energy density, but the massive plating of lithium metal (Li-M) on the surface of the graphite anode leads to rapid cell failure. In this paper, hard carbon (HC) is proposed as a better choice for anode in HLBs than that of graphite, and the difference in Li storage behaviors between HC and artificial graphite (AG) is systematically investigated. At low n/p, part of the “excess Li” is stored as quasi-lithium metal (Li-QM) in the sub-nanometer pores inside HC in a highly reversible way, which reduces Li-M plating on the surface of anodes, effectively increasing the cycle stability of HLBs. The HLBs with HC anode mass loading of 5.1 mg cm−2 and 7.8 mg cm−2 have 41.7% and 30.3% higher stack energy density compared to LIBs. Moreover, HLB-type pouch cells using HC anode with a mass loading of 7.8 mg cm−2 achieves high capacity retention of 81% after 450 cycles, while the capacity retention drops to 55% for the AG anode with the same mass loading.