Tailoring Cathode–Electrolyte Interface for High-Power and Stable Lithium–Sulfur Batteries

Abstract

Global interest in lithium–sulfur batteries as one of the most promising energy storage technologies has been sparked by their low sulfur cathode cost, high gravimetric, volumetric energy densities, abundant resources, and environmental friendliness. However, their practical application is significantly impeded by several serious issues that arise at the cathode–electrolyte interface, such as interface structure degradation including the uneven deposition of Li2S, unstable cathode–electrolyte interphase (CEI) layer and intermediate polysulfide shuttle effect. Thus, an optimized cathode–electrolyte interface along with optimized electrodes is required for overall improvement. Herein, we comprehensively outline the challenges and corresponding strategies, including electrolyte optimization to create a dense CEI layer, regulating the Li2S deposition pattern, and inhibiting the shuttle effect with regard to the solid–liquid–solid pathway, the transformation from solid–liquid–solid to solid–solid pathway, and solid–solid pathway at the cathode–electrolyte interface. In order to spur more perceptive research and hasten the widespread use of lithium–sulfur batteries, viewpoints on designing a stable interface with a deep comprehension are also put forth.

1. Introduction

Continuously increased demand but lack of energy has emerged as one of the most pressing issues confronting human society since the second industrial revolution [1]. Energy storage technology has flourished as a result of the tremendous growth in green energy production to offset the overconsumption of traditional fossil fuels [2–8]. Electrochemical energy storage has brought about great breakthroughs from the grid to every aspect of human life. Due to the superiorities of significant energy density and long-term cycling stability, lithium-ion batteries (LIBs) have played a vital role in most electronic portable devices since their first commercialization in 1991 by Sony Corporation [9–15]. Nevertheless, the energy density of LIBs while once regarded as high compared to capacitors and lead-acid batteries can hardly keep up with the contemporary ever-increasing energy storage demands because the theoretical specific capacities of cathodes like LiFeO4, LiCoO2, and LiMn2O4 are comparatively limited [16, 17]. Therefore, a number of energy storage alternatives “beyond LIBs” are investigated [18–21].

Lithium–sulfur batteries (LSBs) attracted widespread attention because of their potentially high theoretical energy density (2600 Wh kg−1) outperforming times the counterpart of conventional LIBs (LiCoO4:300 Wh kg−1) by approximately 8.6 [6, 26, 27]. As shown in Fig. 1a, the LSBs have wider operating temperature and much lower costs than LIBs. Moreover, together with the longer driving distance, the LSBs hold greater potential in commercial applications. Since LSBs and LIBs are both lithium-based batteries, the commercial application status of LSBs still could not compare with LIBs even regarding the unique merits of LSBs [28]. What blocks the application of LSBs requires deeper thinking and the underlying reason might trace back to its distinct working principle different from that of LIBs. The rocking chair-type battery like sodium-ion battery or LIBs mainly depends on the reverse intercalation and de-intercalation of Li+ from the cathode to anode during cycling and is therefore called a “rocking chair”-type battery [29–33]. Taking the LIB as an example with LiCoO2 cathode and graphite anode (Fig. 2a), the galvanostatic charge–discharge (GCD) curves and related chemical reactions that occur at electrodes can be presented in Fig. 2b, c, respectively. In comparison, the working principle of LSBs is much more complex and trickier, which not only has great differences in reactions at different stages but also involves complex solid–liquid–solid-phase revolution in conventional reaction pathway with two plateaus (Fig. 2e, ...).