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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.

Replacing liquid electrolytes with solid-state conductors is one of the key challenges to increasing the safety and energy density of next-generation Li secondary batteries. In this work, the NASICON-type Li1+xAlxZryTi2−x−y(PO4)3 with 0 ≤ x, y ≤ 0.2 solid electrolytes were synthesized using solid-state and sol-gel techniques at various sintering temperatures (800, 900, and 1000 °C). Their morphology and conducting properties were studied to determine the optimal dopant content and synthesis method. Li1.2Al0.2Zr0.1Ti1.7(PO4)3 and Li1.1Al0.1Zr0.2Ti1.7(PO4)3 prepared at 900 °C using a solid-state reaction exhibit the highest total conductivity at 25 °C (7.9 × 10−4 and 5.4 × 10−4 S cm−1, respectively), which is due to the optimal size of lithium transport channels, as well as the high density of these samples. The potential profile of Li|Li1.2Al0.2Zr0.1Ti1.7(PO4)3|Li cells was retained during cycling at a current density of 0.05 mA cm−2 for 100 h, indicating a high interfacial Li metal/electrolyte stability.

The effect of different nitrogen-doped carbon additives (carbon coating from polyaniline, N-doped carbon nanotubes, and N-doped carbon nanoparticles) on electrochemical performance of nanocomposites based on the olivine-type LiFePO4 was investigated. Prepared materials were characterized by XRD, SEM, TGA-MS, CHNS-analysis, IR-, Raman, and impedance spectroscopies. Polyaniline deposition on the LiFePO4 precursor with following annealing lead to the formation of a LiFePO4/C nanocomposite with a carbon coating doped with nitrogen. Due to nitrogen atoms presence in carbon coating, the LiFePO4/N-doped carbon nanocomposites showed enhanced conductivity and C-rate capability. The discharge capacities of the synthesized materials in LIBs were close to the theoretical value at 0.1 C and retained high values with increasing current density. At high C-rates, the best results were obtained for a more dispersed LiFePO4/C composite with carbon coating prepared from polyaniline previously in situ deposited on LiFePO4 precursor particles. Its discharge capacity reached 96, 84, 73, and 47 mAh g−1 at 5, 10, 20, and 60 C-rates, respectively.

The influence of different conductive additives (carbon nanofibers (CNFs), carbon nanoplatelets, and pyrolytic carbon from sucrose (Sucr) or polyvinylidene fluoride) on the morphology, electron conductivity, and electrochemical performance of LiFePO4-based cathodes was investigated to develop the most efficient strategy for the fabrication of high-rate cathodes. Pyrolytic carbon effectively prevents the growth of LiFePO4 grains and provides contact between them, CNFs provide fast long-range conductive pathways, while carbon nanoplatelets can be embedded in carbon coatings as high-conductive “points” which enhance the rate capability and decrease the capacity fading of LFP. The LiFePO4/CSucr/CNF showed better performance than the other cathodes due to the synergy of the high-conductive CNF network (the electronic conductivity was 1.3 × 10−2 S/cm) and the shorter Li+ ion path (the lithium-ion diffusion coefficient was 2.1 × 10−11 cm2/s). It is shown that the formation of composites based on LFP and carbon nanomaterials via mortar grinding is a more promising strategy for electrode material manufacturing than ball milling.

The possibilities of manufacturing batteries with Nafion 117 membranes in the Na+-form intercalated by mixtures of non-aqueous organic solvents used both as an electrolyte, separator, and binder were investigated. Electrochemical stability of various organic solvent mixtures based on N,N-dimethylacetamide, ethylene carbonate, propylene carbonate, and tetrahydrofuran were characterized. It was shown that a sodium battery based on a Nafion-Na membrane intercalated by mixture of ethylene carbonate and propylene carbonate with a Na3V1.9Fe0.1(PO4)3/C positive electrode is characterized by a discharge capacity of ≈110 mAh·g−1 (current density of 10 mA·g−1) at room temperature and shows the ability to cycle without degradation during 20 cycles. Batteries with Nafion membrane electrolytes, containing N,N-dimethylacetamide, were characterized using capacity fading during cycling, which is due to the interaction of N,N-dimethylacetamide and a negative sodium electrode.