Deciphering Interfacial Chemical and Electrochemical Reactions of Sulfide‐Based All‐Solid‐State Batteries

Abstract

The success of ASSLBs could eventually eliminate the mileage anxiety and safety concerns of electric vehicles (EVs). To enable ASSLBs, various solid-state electrolytes have been intensively developed over the past decades, such as sulfide electrolytes (SEs), [1b,c,2] oxide electrolytes, [3] polymer-based electrolytes, [4] and emerging solid-state halide electrolytes (Li 3 MCl 6 , M = Y, In, Er, Sc, etc.). [5] Owing to the high ionic conductivity and soft mechanical properties of SEs, it is widely believed that SE-based ASSLBs will be a leading contender for large-scale energy storage, particularly for the fast-growing industry of electric vehicles.However, several challenges hinder the development of SE-based ASSLBs, including (1) moisture sensitivity and narrow electrochemical windows of SEs;(2) large interfacial resistance between electrodes and SEs that is caused by detrimental interfacial reactions; and (3) shortcircuits when lithium dendrites penetrate through thin SE separators. In recent years, various SEs have been synthesized with much-improved moisture stability, e.g., As-substituted Li 4 SnS 4 , [6] Sb-doped Li 10 GeP 2 S 12 , [7] and Li 6.6 Ge 0.6 Sb 0.4 S 5 I. [8] To fully realize the high energy density of ASSLBs, thin lithium metal is preferred, but lithium dendrite growth through the SE separator and SE reduction by Li metal needs to be addressed. Large interfacial resistance resulting from interfacial reactions is widely acknowledged as one of the main challenges in sulfide electrolytes (SEs)-based all-solid-state lithium batteries (ASSLBs). However, the root cause of the large interfacial resistance between the SEs and typical layered oxide cathodes is not fully understood yet. Here, it is shown that interfacial oxygen loss from single-crystal LiNi 0.5 Mn 0.3 Co 0.2 O 2 (SC-NMC532) chemically oxidizes Li 10 GeP 2 S 12 , generating oxygen-containing interfacial species. Meanwhile, the interfacial oxygen loss also induces a structural change of oxide cathodes (layered-to-rock salt). In addition, the high operation voltage can electrochemically oxidize SEs to form non-oxygen species (e.g., polysulfides). These chemically and electrochemically oxidized species, together with the interfacial structural change, are responsible for the large interfacial resistance at the cathode interface. More importantly, the widely adopted interfacial coating strategy is effective in suppressing chemically oxidized oxygencontaining species and mitigating the coincident interfacial structural change but is unable to prevent electrochemically induced non-oxygen species. These findings provide a deeper insight into the large interfacial resistance between the typical SE and layered oxide cathodes, which may be of assistance for the rational interface design of SE-based ASSLBs in the future.

Multiscale understanding of high-energy cathodes in solid-state batteries: from atomic scale to macroscopic scale

“…LiCoO 2 , Nirich layered oxides, LRLO, and Li-free cathodes) are enabling the construction of high-energy-dense SSBs [33]. Figure 3 schematically presents their properties in terms of volume change, specific capacity, rate capability, working voltage, cost, and cycle performance (in ascending order of specific capacity) [27,28,[39][40][41][42][43][44]. The upper cutoff voltage of commercial cathode material LiCoO 2 (LCO) was only 4.2 V vs. Li + /Li, which possesses only a specific capacity of 137 mAh g −1 [45].…”

2D Materials for All‐Solid‐State Lithium Batteries

“…Additionally, a few emerging advanced characterization technologies will be discussed that deepen the understanding of the structure-function relationship in 2DMs for ASSLBs. [47][48][49] Finally, future research directions are proposed to accelerate the technology developments, from the fundamental understanding of mechanisms to the improvement of materials and applications.…”

Challenges, interface engineering, and processing strategies toward practical sulfide‐based all‐solid‐state lithium batteries

“…The highly oxidized transition metal ions and O 2À in CAMs tend to induce and expedite the oxidative decomposition of sulfide SEs, which also makes the composition of CEI more complicated. 104,159 For example, Banerjee et al 145 successfully separated the interfacial chemical reactions from the electrochemical decomposition reactions of SEs and determined the corresponding reaction products at the initial state and the charged state of the cells by decoupling each effect, respectively. They employed XRD, Raman, XPS, and so on, to identify the interphase compositions and found that significant amounts of crystalline LiCl, Li 3 PO 4 , and Ni 3 S 4 were probed at the interfaces under the charged state, while the signals of these components were much weaker at the pristine state.…”

“…Moreover, the chemical reactions between CAMs and SEs will be exacerbated during electrochemical cycling. The highly oxidized transition metal ions and O 2− in CAMs tend to induce and expedite the oxidative decomposition of sulfide SEs, which also makes the composition of CEI more complicated 104,159 . For example, Banerjee et al 145 successfully separated the interfacial chemical reactions from the electrochemical decomposition reactions of SEs and determined the corresponding reaction products at the initial state and the charged state of the cells by decoupling each effect, respectively.…”