Solid-state lithium batteries are considered one of the most promising next-generation energy storage technologies owing to their safety and high energy density. The key to solid-state lithium battery advancement lies in the design and optimization of suitable solid-state electrolytes. Among various solid-state electrolytes, solid-state composite polymer electrolytes offer the combined benefits of solid inorganic electrolytes and solid polymer electrolytes. In particular, Li_{1 + x}Al_xTi_{2 − x}(PO₄)₃ (LATP)/polymer composite polymer electrolytes exhibit high ionic conductivity due to LATP and improved flexibility from the polymer matrix. These systems also demonstrate robust mechanical properties and excellent electrode contact. While recent reviews have primarily focused on the performance of LATP/polymer composite polymer electrolytes and the general effects of composite polymer electrolyte modifications for solid-state lithium battery applications, this review provides a concise overview of the Li⁺ transport mechanisms in LATP/polymer composite polymer electrolytes and strategies to enhance ionic conductivity. It highlights several modification approaches, including the use of fillers, additives, and LATP coatings, which markedly influence the performance of composite polymer electrolytes across different polymer matrices. Finally, the review addresses the challenges of LATP/polymer composite polymer electrolytes and outlines key research directions for developing advanced composite polymer electrolytes for high-performance solid-state lithium batteries.

FeS₂ cathode is promising for all-solid-state lithium batteries due to its ultra-high capacity, low cost, and environmental friendliness. However, the poor performances, induced by limited electrode-electrolyte interface, severe volume expansion, and polysulfide shuttle, hinder the application of FeS₂ in all-solid-state lithium batteries. Herein, an integrated 3D FeS₂ electrode with full infiltration of Li₆PS₅Cl sulfide electrolytes is designed to address these challenges. Such a 3D integrated design not only achieves intimate and maximized interfacial contact between electrode and sulfide electrolytes, but also effectively buffers the inner volume change of FeS₂ and completely eliminates the polysulfide shuttle through direct solid–solid conversion of Li₂S/S. Besides, the vertical 3D arrays guarantee direct electron transport channels and horizontally shortened ion diffusion paths, endowing the integrated electrode with a remarkably reduced interfacial impedance and enhanced reaction kinetics. Benefiting from these synergies, the integrated all-solid-state lithium battery exhibits the largest reversible capacity (667 mAh g⁻¹), best rate performance, and highest capacity retention of 82% over 500 cycles at 0.1 C compared to both a liquid battery and non-integrated all-solid-state lithium battery. The cycling performance is among the best reported for FeS₂-based all-solid-state lithium batteries. This work presents an innovative synergistic strategy for designing long-cycling high-energy all-solid-state lithium batteries, which can be readily applied to other battery systems, such as lithium-sulfur batteries.