The results of studies on polymer electrolytes for metal-ion batteries are analyzed and generalized. Progress in this field of research is driven by the need for solid-state batteries characterized by safety and stable operation. At present, a number of polymer electrolytes with a conductivity of at least 10⁻⁴S cm⁻¹at 25 °C were synthesized. Main types of polymer electrolytes are described,viz., polymer/salt electrolytes, composite polymer electrolytes containing inorganic particles and anion acceptors, and polymer electrolytes based on cation-exchange membranes. Ion transport mechanisms and various methods for increasing the ionic conductivity in these systems are discussed. Prospects of application of polymer electrolytes in lithium- and sodium-ion batteries are outlined.The bibliography includes 349 references.

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

The Nafion-117 membranes in the Li⁺ form with pore-intercalated aprotonic organic solvents were prepared. The prepared materials were characterized by IR, impedance, and ⁷Li NMR spectroscopy. The solvent uptake of the membranes is shown to be controlled by the composition of organic solvents and their mixtures as well as by the conditions of the preliminary treatment of the initial membranes. For the Nafion-117 membrane, the degree of solvation can be improved by the preliminary treatment with alcohols, especially by the thermal treatment in methanol. Conductivity of the membranes is shown to increase with increasing content of the sorbed solvents. The best conductivity at 25 °C (2.5 × 10⁻³ and 1.6 × 10⁻³ S cm⁻¹) was attained for the electrolytes based on the Nafion-117 membrane in lithium form with sorbed ethylene carbonate-propylene carbonate and ethylene carbonate-dimethoxyethane mixtures, respectively.

All-solid-state lithium batteries are a promising alternative to commercially available lithium-ion batteries due to their ability to achieve high energy density, safety, and compactness. Electrolytes are key components of all-solid-state batteries, as they are crucial in determining the batteries’ efficiency. Herein, the structure of LiM₂(PO₄)₃ (M = Ti, Ge, Zr) and lithium-ion migration mechanisms are introduced as well as different synthetic routes and doping (co-doping), and their influence on conductivity is discussed. The effective methods of reducing electrolyte/electrode interface resistance and improving ion-conducting properties are summarized. In addition, different polymer/NASICON composites are considered. The challenges and prospects of practical applications of NASICON-type lithium phosphates as electrolytes for all-solid-state batteries are discussed.

Currently, all-solid-state lithium metal batteries are considered among the most promising energy storage devices, due to their safety and high energy density. Solid-state electrolytes, the key components of the batteries, are attracting increasing attention. This review presents an analysis of important recent advances in the field of lithium conducting solid-state electrolytes, including the mechanisms of conductivity, the main approaches to increase the conductivity, optimization of interfaces and ways to improve the stability for the main types of electrolytes, i.e., inorganic, polymer and composite materials. For solid inorganic electrolytes, high conductivity and stability have been achieved; however, the problems related the formation of dense thin films and formation of a reliable contact with electrode materials are still unsolved. Polymer electrolytes are characterized by lower conductivity, which is improved upon plasticization with aprotic solvents. Composite electrolytes, for which it is possible to achieve a combination of high conductivity and good mechanical properties along with stability, are considered as the most promising. The main problems in the field of solid electrolytes for all-solid-state lithium metal batteries and possible ways to solve them are outlined.The bibliography includes 661 references. Key words: solid-state lithium battery, inorganic electrolyte, polymer electrolyte, composite electrolyte, ionic conductivity, lithium conductivity, transference numbers