Nanodiamonds Give Solid Electrolytes a Four-to-Five-Order Conductivity Boost
A pinch of diamond dust has helped transform two sluggish solid salts into substantially better ion conductors, according to research published in Ionics. The study examined whether nanodiamonds could improve the performance of organic ionic plastic crystals—materials that combine the mechanical advantages of solids with the molecular mobility needed to transport electrical charge. When added to tetraethylammonium tetrafluoroborate and tetrapropylammonium tetrafluoroborate, the carbon nanoparticles stabilized a high-temperature phase of the salts at room temperature and dramatically increased their ionic conductivity. At 150 °C, the best composite based on tetraethylammonium tetrafluoroborate reached 4.1 × 10−4 siemens per centimeter, while the tetrapropylammonium version reached 3.0 × 10−4 S/cm. Those values represent increases of four to five orders of magnitude compared with the unmodified salts. The findings could help researchers design solid electrolytes for future batteries, supercapacitors and other electrochemical devices, although the most conductive formulations still require elevated temperatures to reach their reported peaks.
Organic ionic plastic crystals, or OIPCs, are salts with an unusual structural personality. Like ordinary crystals, they remain solid and can be shaped into stable electrolyte layers. Yet, above a phase-transition temperature, their molecules or ions gain rotational and orientational freedom while the overall lattice remains intact. This partially disordered state is known as a plastic-crystal phase. The increased molecular motion can create pathways for ions to migrate through the material, allowing the crystal to conduct electricity without becoming a liquid. That combination is attractive for solid-state energy technologies because liquid electrolytes can leak, evaporate or contribute to safety problems, whereas conventional solids often transport ions too slowly. The central challenge is that many OIPCs reach useful conductivity only when heated. At lower temperatures, their ions are trapped in a more ordered structure, and the material’s resistance to charge transport rises sharply. The new work addresses that bottleneck by using nanodiamonds to alter both the structure and dynamics of the host salts.
The researchers, Ivan Stebnitskii and Yulia Mateyshina of the Institute of Solid State Chemistry and Mechanochemistry of the Siberian Branch of the Russian Academy of Sciences, focused on two tetrafluoroborate salts. The first, tetraethylammonium tetrafluoroborate, is written as Et4NBF4, where the positively charged tetraethylammonium ion is paired with the tetrafluoroborate anion BF4−. The second, tetrapropylammonium tetrafluoroborate, or Pr4NBF4, contains a larger tetrapropylammonium cation with the same anion. Changing the size of the organic cation can influence how ions pack, how readily the lattice becomes disordered and how easily charge moves through it. The team mixed each salt with different amounts of nanodiamond, a form of carbon consisting of diamond-like particles on the nanoscale. Rather than acting as a conventional conducting additive that carries electrons, the nanodiamond filler changes the environment through which the salt ions move. Its enormous surface area relative to its volume gives it extensive contact with the ionic crystal, potentially disrupting long-range order and creating defects or interfacial regions favorable to ion transport.
Several complementary techniques revealed how the filler changed the salts. Differential scanning calorimetry, or DSC, measures how much heat a material absorbs or releases as it passes through structural transitions. In these experiments, the thermal behavior indicated that nanodiamond doping stabilized the salts’ high-temperature plastic phase at room temperature. This is important because a phase that normally appears only after heating can provide the greater ionic mobility associated with the plastic state. X-ray diffraction supplied a structural counterpart to the thermal results. Sharp diffraction features generally indicate long-range crystalline order, whereas broadened or weakened features suggest disorder, reduced crystallite coherence or partial amorphization. The nanodiamond-containing samples showed evidence that the salts became partly amorphous, meaning that portions of their ordered lattice were disrupted without the entire material becoming a liquid. Infrared spectroscopy provided additional information by tracking changes in molecular vibrations and the local environment of the tetrafluoroborate ions. Together, the measurements point to a composite in which the nanodiamond particles interfere with the salt’s original packing and preserve a more dynamically disordered structure.
The conductivity improvement was strongly dependent on composition. For Et4NBF4, the maximum reported value—4.1 × 10−4 S/cm at 150 °C—occurred in a composite containing 50 percent nanodiamond by volume. For Pr4NBF4, the optimum was 40 vol% nanodiamond, producing 3.0 × 10−4 S/cm at the same temperature. The fact that conductivity peaked rather than increasing indefinitely with filler concentration is consistent with the competing effects present in a composite electrolyte. Adding nanoparticles can create more interfaces and disrupt unfavorable crystal order, but too much inert filler can dilute the ion-containing phase and interrupt continuous pathways through which ions migrate. Conductivity therefore depends on finding a balance between structural disorder and the amount of mobile salt available. The reported values are ionic rather than electronic conductivity: they describe the movement of charged species, principally the salt ions, under an electric field. In a battery or capacitor, this distinction matters because the electrolyte must transport ions while blocking electronic current between the electrodes.
The study’s most consequential result may be a broader design rule that emerged when the researchers compared these materials with related tetrafluoroborate-based OIPCs. Composite conductivity correlated with the melting point of the pure salt, not with its melting enthalpy. Melting point reflects the temperature at which a material loses its long-range crystal stability, while melting enthalpy measures the heat required to complete that transition. The two quantities describe different aspects of a solid: one is closely tied to transition temperature, while the other reflects the energetic magnitude of the transformation. The observed relationship suggests that salts with lower melting points are more readily driven into disordered, ionically mobile states when combined with nanodiamonds. In this respect, the composites behaved analogously to ionic liquids, whose transport properties are often linked to low melting points and weakly organized ionic structures. The result offers a practical screening strategy: when selecting candidate OIPCs for nanoparticle-based solid electrolytes, researchers may gain more by prioritizing salts with low melting temperatures than by choosing materials solely because they have a large melting enthalpy.
The nanodiamond effect is likely to involve more than one microscopic mechanism. At the interface between a nanoparticle and the ionic crystal, the regular arrangement of cations and anions can be strained or interrupted. Such disturbances may generate defects—local departures from ideal lattice order—that provide ions with additional sites or routes for hopping. Interfacial electric fields and changes in ion coordination could also alter the energy landscape for migration. Earlier work on nanoparticle-filled plastic crystals has considered space-charge effects, in which charge accumulates near an interface, and strain-induced defects, in which mechanical distortion modifies the lattice. The present study does not reduce the improvement to a single explanation; instead, its calorimetry, diffraction and infrared results establish that the filler changes the salt’s phase and structure as conductivity rises. The partially amorphous regions may be especially important because disordered materials generally offer a broader distribution of local environments, allowing some ions to move through lower-energy pathways. Determining the precise balance between bulk plastic-crystal transport and interfacial transport will require further measurements, particularly across temperature, composition and particle-size ranges.
The findings do not yet amount to a room-temperature battery electrolyte ready for commercial devices. The highest conductivities were measured at 150 °C, and the study reports no battery or supercapacitor prototype demonstrating cycling performance, power output, chemical compatibility or long-term stability. The authors also state that no datasets were generated or analyzed during the study, so the conclusions are based on the reported experimental characterization rather than a publicly deposited dataset. Even so, the work provides a direct route for improving a class of materials that has long faced a trade-off between solid mechanical form and sufficient ionic mobility. Nanodiamonds are chemically robust and can be dispersed through a salt matrix, while the two ammonium tetrafluoroborates offer a controlled way to examine how cation size affects the response. By showing that nanoparticle doping can stabilize a plastic phase and by linking composite conductivity to the melting point of the unfilled salt, the research turns an empirical materials trick into a potentially predictive design principle. Future solid-electrolyte development could use that principle to identify lower-melting OIPCs, optimize filler concentrations and seek formulations that retain enhanced transport closer to ordinary operating temperatures.
Subject of Research: Nanodiamond-doped organic ionic plastic crystal composite solid electrolytes
Subject of Research: Technology and Engineering
Article Title: Physico-chemical properties of composite electrolytes based on organic ionic plastic crystals: tetraethylammonium and tetrapropylammonium tetrafluoroborates doped with nanodiamonds
Article References: Stebnitskii, I., & Mateyshina, Y. (2026). Physico-chemical properties of composite electrolytes based on organic ionic plastic crystals: tetraethylammonium and tetrapropylammonium tetrafluoroborates doped with nanodiamonds. Ionics. https://doi.org/10.1007/s11581-026-07483-2
Image Credits: AI Generated
DOI: 10.1007/s11581-026-07483-2
Keywords: organic ionic plastic crystals, solid electrolytes, composite solid electrolytes, nanodiamonds, tetraethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate, ionic conductivity
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SCIENMAG. (August 27, 2026). Nanodiamond-Doped Ionic Crystals Could Enable Better Composite Electrolytes. https://scienmag.com/nanodiamond-doped-ionic-crystals-could-enable-better-composite-electrolytes/
SCIENMAG. “Nanodiamond-Doped Ionic Crystals Could Enable Better Composite Electrolytes.” Scienmag, 27 August 2026, https://scienmag.com/nanodiamond-doped-ionic-crystals-could-enable-better-composite-electrolytes/. Accessed 27 August 2026.
SCIENMAG. “Nanodiamond-Doped Ionic Crystals Could Enable Better Composite Electrolytes.” Scienmag. August 27, 2026. https://scienmag.com/nanodiamond-doped-ionic-crystals-could-enable-better-composite-electrolytes/
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