BaTiO3 Nanoparticle-Induced Interfacial Electric Field Optimization in Chloride Solid Electrolytes for 4.8 V All-Solid-State Lithium Batteries

Abstract

Chloride-based solid electrolytes are considered promising candidates for next-generation high-energy–density all-solid-state batteries (ASSBs). However, their relatively low oxidative decomposition threshold (~4.2 V vs. Li+/Li) constrains their use in ultrahigh-voltage systems (e.g., 4.8 V). In this work, ferroelectric BaTiO3 (BTO) nanoparticles with optimized thickness of ~50–100 nm were successfully coated onto Li2.5Y0.5Zr0.5Cl6 (LYZC@5BTO) electrolytes using a time-efficient ball-milling process. The nanoparticle-induced interfacial ionic conduction enhancement mechanism contributed to the preservation of LYZC's high ionic conductivity, which remained at 1.06 mS cm−1 for LYZC@5BTO. Furthermore, this surface electric field engineering strategy effectively mitigates the voltage-induced self-decomposition of chloride-based solid electrolytes, suppresses parasitic interfacial reactions with single-crystal NCM811 (SCNCM811), and inhibits the irreversible phase transition of SCNCM811. Consequently, the cycling stability of LYZC under high-voltage conditions (4.8 V vs. Li⁺/Li) is significantly improved. Specifically, ASSB cells employing LYZC@5BTO exhibited a superior discharge capacity of 95.4 mAh g−1 over 200 cycles at 1 C, way outperforming cell using pristine LYZC that only shows a capacity of 55.4 mAh g−1. Furthermore, time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy analysis revealed that Metal-O-Cl by-products from cumulative interfacial side reactions accounted for 6% of the surface species initially, rising to 26% after 200 cycles in pristine LYZC. In contrast, LYZC@5BTO limited this increase to only 14%, confirming the effectiveness of BTO in stabilizing the interfacial chemistry. This electric field modulation strategy offers a promising route toward the commercialization of high-voltage solid-state electrolytes and energy-dense ASSBs.

1. Introduction

All-solid-state batteries (ASSBs) offer enhanced safety over conventional lithium-ion systems by using non-flammable solid electrolytes (SEs) [1–3]. These SEs resist lithium dendrite propagation and have high oxidative stability, allowing for the use of high-capacity lithium metal anodes and ultra-high-voltage cathode materials [4–6]. ASSBs can achieve energy densities exceeding 500 Wh kg−1, making them ideal for applications like spacecraft propulsion, robotics, and next-gen electric vehicles [7–9]. However, developing commercially viable ASSBs require solid-state electrolytes with lithium-ion conductivities above 1 mS cm−1 at 25 °C and electrochemical stability over 4.5 V versus Li+/Li [10].

Inorganic solid electrolytes offer excellent ionic transport and broad electrochemical windows, making them suitable for advanced energy storage systems [11]. Key inorganic SE families include oxide-, chloride-, and fluoride-based systems, each with distinct anion-dependent electrochemical behaviors [12–14]. Fluoride electrolytes exhibit high oxidation resistance but limited ionic conductivity (<10−7 S cm−1 at 25 °C) [15]. Sulfide systems provide high ionic mobility but decompose above 2.3 V, restricting their application in high-voltage scenarios [16]. Chloride solid electrolytes (CSEs) balance voltage tolerance (~4.2 V) and ionic conduction (>1 mS cm−1) [17, 18], demonstrated by compositions like Li3InCl6 (LIC) and Li2.5Y0.5Zr0.5Cl6 (LYZC), which are compatible with commercial 4.3 V-class layered oxide cathodes (e.g., LiCoO2 (LCO), LiNi0.8Co0.1Mn0.1O2 (NCM811)) [19–21]. However, under extreme high-voltage conditions (>4.5 V) with high-nickel or Li-rich cathodes, CSEs are susceptible to accelerated electrochemical decomposition and interfacial degradation mechanisms [22, 23]. It is reported by Nazar et al. that L...