Li₃BO₃–Li₂CO₃: Rationally Designed Buffering Phase for Sulfide All-Solid-State Li-Ion Batteries

Abstract

Most inorganic solid electrolytes (SEs) suffer from narrow intrinsic electrochemical windows and incompatibility with electrode materials, which results in the below par electrochemical performances of all-solid-state Li-ion or Li batteries (ASLBs). Unfortunately, in-depth understanding on the interfacial evolution and interfacial engineering via scalable protocols for ASLBs to mitigate these issues are at an infancy stage. Herein, we report on rationally designed Li3BO3–Li2CO3 (LBO-LCO or Li3–x B1–x C x O3 (LBCO)) coatings for LiCoO2 in ASLBs employing sulfide SE of Li6PS5Cl. The new aqueous-solution-based LBO-coating protocol allows us to convert the surface impurity on LiCoO2 and Li2CO3, into highly Li+-conductive LBCO layers (6.0 × 10–7 S cm–1 at 30 °C for LBCO vs 1.4 × 10–9 S cm–1 at 100 °C for Li2CO3 or 1.4 × 10–9 S cm–1 at 30 °C for LBO), which also offer interfacial stability with sulfide SE. By applying these high-surface-coverage LBCO coatings, significantly enhanced electrochemical performances are obtained in terms of capacity, rate capability, and durability. It is elucidated that the LBCO coatings suppress the evolution of detrimental mixed conducting interphases containing Co3S4 and effectively passivate the interfaces by the formation of alternative interface phases.

Ni‐Rich Layered Cathode Materials with Electrochemo‐Mechanically Compliant Microstructures for All‐Solid‐State Li Batteries

“…The experimental data fitted with the equivalent circuit model (Figure S7, Supporting Information) indicate that the resistances of both the NCA80 and FCG75 SE layers remain constant ( R 1 + R 2 = 6–7 Ω) regardless of the number of cycles. These resistances are assigned as the grain and grain boundary resistances in the SE layer, respectively . The R 3 values are attributed to interfacial resistance, and that for NCA80 (39.6 Ω) dramatically increases at the first cycle, compared to that for FCG75 (2.6 Ω).…”

“…Additionally, it should be noted that the results herein for FCG75 were obtained with the bare sample. Further improvement in performance could be possible by intensive interfacial engineering, such as the application of protective coatings and/or the development of advanced SE materials with improved oxidation stability, which will be our next mission in future.…”

Computational Screening of Cathode Coatings for Solid-State Batteries

“…Oxides used to coat conventional cathode materials have shown varying degrees of effectiveness in SSBs. 21 They include, among others, Li 3 22 Li 3 BO 3 , 44 and Li 2 ZrO 3 , 45 most of which are metal oxides. Cathode coatings are used to isolate the SSEs from the low Li chemical potentials exerted by the cathode in its highly charged state, thereby preventing their electrochemical self-decomposition.…”

“…46 For SSBs, it is also desirable to consider the chemical compatibility of the coating with both the cathode and the SSE. In addition, the ionic conductivity, an important criterion for coating performance, 44,47 has often been neglected in the computational search for new coatings, presumably because of the high computational cost of ion conductivity predictions with ab initio techniques and the difficulty in integrating them with a high-throughput environment. 48,49 In this work, we conducted a high-throughput search for suitable materials for cathode coatings spanning a very wide range of chemistries.…”

Chemistry Design Towards a Stable Sulfide‐Based Superionic Conductor Li4Cu8Ge3S12

“…The thermodynamic stability against oxidation under high voltage still remains a key drawback of sulfide electrolytes today . Strategies such as the interface engineering could be applied to extend the electrochemical stability of the electrolyte …”