Electrolytes for Sodium Batteries: A Patent Landscape Analysis of Material Platforms and Their Transitions

Sodium batteries are attracting increasing attention as cost-effective alternatives to lithium-ion batteries, particularly for large-scale stationary energy storage.Their development has followed two technological pathways, high-temperature molten-sodium batteries and room-temperature sodium-ion batteries, which are fundamentally differentiated by their electrolyte systems.This review presents a comprehensive patent-based analysis of electrolyte chemistry, providing valuable insights into the evolution of sodium battery technologies.A title-based search yielded 9,563 patent families, which were consolidated based on their earliest priority dates.Candidate patents were screened using a two-stage workflow consisting of deterministic keyword filtering based on a bilingual dictionary, followed by large language model-assisted evaluation of complete patent claims.This process identified 1,068 patent families in which sodium electrolytes constituted the primary invention.The patent families were classified into three electrolyte categories: liquid, gel/polymer, and inorganic solid electrolytes.Patent activity was grouped into five segments, revealing three distinct development periods separated by a pronounced decline between 2005 and 2009.Liquid electrolytes accounted for 71.3% of filings in the most recent period, while inorganic solid electrolytes simultaneously reached their highest absolute filing level, indicating diversification rather than replacement.Within solid electrolytes, β/β″-alumina declined from 97.8% to 10.5% of filings, whereas NASICON-type oxides increased from zero to 41.1%, overtaking β/β″-alumina in the fourth period.Furthermore, applicant-and jurisdiction-level portfolios exhibited substantially greater specialization than suggested by aggregate trends, highlighting the importance of sub-type-level analysis for understanding technological evolution.