Engineering a High-Voltage Durable Cathode/Electrolyte Interface for All-Solid-State Lithium Metal Batteries via In Situ Electropolymerization

Abstract

Poly­(ethylene oxide) (PEO)-based polymer electrolytes have been widely studied as a result of their flexibility, excellent interface contact, and high compatibility with a lithium metal anode. Owing to the poor oxidation resistance of ethers, however, the PEO-based electrolytes are only compatible with low-voltage cathodes, which limits their energy density. Here, a high-voltage stable solid-state interface layer based on polyfluoroalkyl acrylate was constructed via in situ solvent-free bulk electropolymerization between the LiNi0.8Mn0.1Co0.1O2 (NCM811) cathode and the PEO-based solid polymer electrolyte. The electrochemical oxidation window of the as-synthesized electrolyte was therefore expanded from 4.3 V for the PEO-based matrix electrolyte to 5.1 V, and the ionic conductivity was improved to 1.02 × 10–4 S cm–1 at ambient temperature and 4.72 × 10–4 S cm–1 at 60 °C as a result of the improved Li+ migration. This fabrication process for the interface buffer layer by an in situ electrochemical process provides an innovative and universal interface engineering strategy for high-performance and high-energy-density solid-state batteries, which has not been explicitly discussed before, paving the way toward the large-scale production of the next generation of solid-state lithium batteries.

Role of Interfaces in Solid‐State Batteries

“…[142] The buffer layers should exhibit good wettability with both cathodes and SE separators, strong adhesiveness (to ensure an intimate contact between cathodes and SE separators during cycling), high ionic conductivity, and chemical/electrochemical stability toward both cathodes and SE separators. [143][144][145][146] A high-voltage stable solid-state buffer layer based on polyfluoroalkyl acrylate was constructed via in situ solvent-free bulk electro-polymerization between an NCM811based cathode and a PEO-matrix SE. [144] The buffer layer widened the ESW to 5.1 V (vs Li/Li + ), which was much broader than that of the PEO matrix, and achieved a high ionic conductivity of 1.02 × 10 −4 S cm −1 at RT.…”

“…[143][144][145][146] A high-voltage stable solid-state buffer layer based on polyfluoroalkyl acrylate was constructed via in situ solvent-free bulk electro-polymerization between an NCM811based cathode and a PEO-matrix SE. [144] The buffer layer widened the ESW to 5.1 V (vs Li/Li + ), which was much broader than that of the PEO matrix, and achieved a high ionic conductivity of 1.02 × 10 −4 S cm −1 at RT. This buffer layer has advantages of excellent wettability and strong capability of protecting PEO, rendering intimate physical contact to the cathode/SE separator interface and substantially inhibiting the space charge effect.…”

Low-cobalt active cathode materials for high-performance lithium-ion batteries: synthesis and performance enhancement methods

“…, offer stable solid-electrolyte interfaces and improve the NCM811-based SSB performance. 226–229 Li et al have synthesized trifluoroethyl methacrylate (PTFEMA)–PEO by electropolymerization. 229 The PTFEMA layer modified the NCM811-electrolyte interface and plays the following roles: (i) offers undisrupted transport of Li + across the interface, (ii) mitigates the electrolyte oxidation at high voltage, (iii) prevents the microcrack formation and (iv) buffers the stress, generated by volume change in NCM811 particles during charge–discharge cycling.…”

Durable and Adjustable Interfacial Engineering of Polymeric Electrolytes for Both Stable Ni‐Rich Cathodes and High‐Energy Metal Anodes

“…[34,44] Moreover, the self-limited esterification reaction could help to create steady coordinating interactions with TM on NCM surfaces, according to the fact that the polyester as a binder additive is beneficial to the stability of Ni-rich NCM cathodes. [55] Examination of XPS results from SIP-NCM cathodes obtained from cycling at 4.4 V manifests that both characteristic peaks attributed to the adverse reactions are slightly elevated after 50 cycles (Figure S23, Supporting Information), probably catalyzed by high-valence Ni. [56] The results show that both oxidative decomposition and Al corrosion reaction reinforce each other, leading to significant deterioration of interfacial compatibility in the TiP case.…”

“…[65] For the cathode interface, a copolymer of acetal and anhydride is introduced into the coating inspired by the limited esterification in the SIP-derived coating, in which the ester-based groups in the copolymer chain contribute to the antioxidant degradation of SPEs. [43,55] It was evaluated by SIP-NCM622||Li full cells. With the copolymer additive, prolonged cycle life is achieved with high CEs of over 99%, even if the capacity decreases slightly after 100 cycles (Figure S30a, Supporting Information).…”