Hard carbon anode materials for hybrid sodium-ion/metal batteries with high energy density

Abstract

Interest in sodium-ion batteries (SIBs) as a lower-cost alternative to lithium-ion batteries (LIBs) is growing in both scientific and industrial fields. However, uneven premature sodium deposition and dendrite formation during cycling pose a serious safety threat, significantly limiting the application of SIBs. Achieving reversible and dendrite-free sodium metal deposition and dissolution on the anode surface is key to developing anode-less sodium batteries, the next generation of SIBs with energy densities comparable to those of LIBs. In anode-less systems, sodium ions not only intercalate into the anode's structure but also deposit on its surface, thereby multiplying the specific capacity. Here, we evaluate state-of-the-art hard carbon (HC) used in traditional SIBs as a potential anode material for anode-less sodium batteries. We present comprehensive research on sodium-ion/metal storage, depending on the type of carbon anode material, particle size and morphology of hard carbons, and the electrolyte and additives used. Half-cells with microspherical HC and a fluoroethylene carbonate-based electrolyte operated for over 3000 h, yielding an average discharge capacity of 550 mAh g−1, nearly twice that of HC in classic SIBs. Anode-less Na3V2(PO4)3||HC full cells demonstrated up to 25 % higher energy density and working potential compared to traditional full cells.