Phosphate-based Electrolyte Research Articles

Monofluorinated Phosphate with Unique P-F Bond for Nonflammable and Long-Life Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) with conventional carbonate-based electrolytes suffer from safety concerns in large-scale applications. Phosphates feature high flame retardancy but are incompatible with graphite anode due to their inability to form a passivated solid electrolyte interphase (SEI). Herein, we report a monofluorinated co-solvent, diethyl fluoridophosphate (DEFP), featuring a unique P-F bond that allows a trade-off between safety and electrochemical performance in LIBs. The P-F bond in DEFP weakens ion-dipole interactions with Li+ ions, lowering the desolvation barrier, and simultaneously reduces the lowest unoccupied molecular orbital (LUMO) of DEFP, promoting the formation of a robust and inorganic-rich SEI. Additionally, DEFP exhibits improved thermal stability due to both robust SEI and the inherent flame-retardant properties of the P-F bond. Consequently, the optimized DEFP-based electrolyte exhibits improved cyclability and rate capacity in LiNi0.8Co0.1Mn0.1O2 || graphite full cells compared with triethyl phosphate-based electrolytes and commercial carbonate electrolytes. Even at a low E/C ratio of 3.45 g Ah-1, the 1.16 Ah NCM811||Gr pouch cells achieve a high capacity retention of 94.2% after 200 cycles. This work provides a promising approach to decouple phosphate safety and graphite compatibility, paving the way for safer and high-performance lithium-ion batteries.

Effect of SiO2-reinforcement and alkali treatment on the corrosion resistance of plasma electrolytic oxide coating on AZ31 magnesium alloy

Plasma electrolytic oxidation (PEO) produces an oxide coating containing pores and cracks lowering corrosion protection. The defects can be sealed by in-situ or post-treatment methods. This work compares the sealing effect of SiO2 particles and post-alkali treatment on the corrosion resistance of PEO coatings formed on AZ31 magnesium (Mg) alloy. PEO was conducted in a phosphate-based electrolyte containing 2 g/l nanoparticle SiO2 at a constant current density of 300 A/m2 for 10 min. The post-alkali treatment was performed in 0.5 M NaOH solution at 80 °C for 30 min. The corrosion resistance was evaluated using polarization, electrochemical impedance spectroscopy, and weight loss tests. The SiO2 particles were successfully embedded uniformly in the Mg3(PO4)2 coating, enhancing the coating compactness and stability. The reinforced coating exhibited ten times higher impedance modulus and lower corrosion current density. The post-alkali treatment improved corrosion resistance but not as high as the SiO2 reinforcement. The impedance modulus of the alkali-treated specimen increased five times, and the corrosion current density decreased three times of the base coating. The weight loss test consistently showed that the SiO2-reinforced coating generated lower mass loss during 14 days of immersion in simulated body fluid.

Thermal Runaway Characteristics of Ni-Rich Lithium-Ion Batteries Employing Triphenyl Phosphate-Based Electrolytes

Abstract Enhancing the safety performance of high-energy-density lithium-ion batteries is crucial for their widespread adoption. Herein, a cost-effective and highly efficient electrolyte additive, triphenyl phosphate (TPP), demonstrates flame-retardant properties by scavenging hydrogen radicals in the flame, thereby inhibiting chain reactions and flame propagation to enhance the safety performance of graphite/LiNi0.8Co0.1Mn0.1O2 (Gr/NCM811) pouch cells. The results reveal that the capacity retention of cells without flame retardants, and those with the addition of 1 wt%, 3 wt%, 5 wt%, and 10 wt% TPP is 96.4%, 92.1%, 84.15%, 40.8%, and 12.4% (at 1/2C 300 cycles), respectively. Furthermore, compared to cells without flame retardants, the highest temperature during thermal runaway (TR) decreases by 8.3%, 26.9%, 35.1%, and 38.8% with the addition of 1 wt%, 3 wt%, 5 wt%, and 10 wt% TPP, respectively. Through comprehensive analysis of the impact of flame-retardant additives on battery electrochemical performance and safety, it is determined that the optimal addition amount is 3 wt%. At this level, there are no significant flames during battery abuse, the triggering temperature for TR increases by 26.6 ℃, and the maximum temperature decreases by 157 ℃. Moreover, even after 300 cycles at 1/2C, a capacity of 814.5 mAh is retained, with a capacity retention rate of 84.1%. This study provides valuable insights into mitigating TR in high-energy-density power batteries.

Tri-anions regulated solvation structure in intrinsically nonflammable phosphate-based electrolytes for stable lithium metal batteries

The cycling instability and unsafety blocked the application of lithium metal batteries (LMB). Nonflammable solvents are hoped to improve the security of LMB; however, employing these solvents will irreversibly damage the cycling stability owing to incompatibility with Li metal. Herein, we regulated solvation structures in triethyl phosphate (TEP) through a simple Tri-anions strategy to achieve cycling stability and safety of LMB. Molecular dynamic simulation demonstrates that the solvation structure is well adjusted which can induce a powerful inorganic-rich solid electrolyte interface (SEI) to circumvent parasitic reactions between TEP solvents and Li anode as well as promote uniformly Li deposition. As a result, Li/LiNi0.8Co0.1Mn0.1O2 (NCM 811) cell has a capacity retention of 98.6 % after 300 cycles and Li/LiFePO4 (LFP) cell retains 75 % after 700 cycles. The novel electrolyte is expected to offer a promising approach for improving high safety and high-electrochemical-performance LMB.

Nonflammable Phosphate-Based Electrolyte for Safe and Stable Potassium Batteries Enabled by Optimized Solvation Effect.

Current potassium-ion batteries (PIBs) are limited in safety and lifetime owing to the lack of suitable electrolyte solutions. To address these issues, herein, we report an innovative non-flammable electrolyte design strategy that leverages an optimal moderate solvation phosphate-based solvent which strikes a balance between solvation capability and salt dissociation ability, leading to superior electrochemical performance. The formulated electrolyte simultaneously exhibits the advantages of low salt concentration (only 0.6 M), low viscosity, high ionic conductivity, high oxidative stability, and safety. Our electrolyte also promotes the formation of self-limiting inorganic-rich interphases at the anode surface, alongside robust cathode-electrolyte interphase on iron-based Prussian blue analogues, mitigating electrode/electrolyte side reactions and preventing Fe dissolution. Notably, the PIBs employing our electrolyte exhibit exceptional durability, with 80 % capacity retention after 2,000 cycles at high-voltage of 4.2 V in a coin cell. Impressively, in a larger scale pouch cell, it maintains over 81 % of its initial capacity after 1,400 cycles at 1 C-rate with high average Coulombic efficiency of 99.6 %. This work represents a significant advancement toward the realization of safe, sustainable, and high-performance PIBs.

Regulate the Solvation Structure and Interface by Nitrate in Phosphate-Based Electrolytes for 4.5V-Class Ni-Rich Batteries.

Phosphate-based electrolyte propels the advanced battery system with high safety. Unfortunately, restricted by poor electrochemical stability, it is difficult to be compatible with advanced lithium metal anodes and Ni-rich cathodes. To alleviate these issues, the study has developed a phosphate-based localized high-concentration electrolyte with a nitrate-driven solvation structure, and the nitrate-derived N-rich inorganic interface shows excellent performance in stabilizing the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode interface and modulating the lithium deposition morphology on the anode. The results show that the Li|| NCM811 cell has exceptional long-cycle stability of >80% capacity retention after 800 cycles at 4.3V, 1 C. A more prominent capacity retention rate of 93.3% after 200 cycles can be reached with the high voltage of 4.5V. While being compatible with the phosphate-based electrolyte with good flame retardancy and the good electrochemical stability of Ni-rich lithium metal battery (LMBs) systems, the present work expands the construction of anion-rich solvation structures, which is expected to promote the development of the high-performance LMBs with safety.

Electrolyte Design Chart Reframed by Intermolecular Interactions for High-Performance Li-Ion Batteries.

Developing advanced electrolytes has been regarded as a pivotal strategy for enhancing the electrochemical performance of batteries; however, the criteria for electrolyte design remain elusive. In this study, we present an electrolyte design chart reframed through intermolecular interactions. By combining systematic nuclear magnetic resonance, Fourier transform infrared measurements, molecular dynamics (MD) simulations, and machine-learning-assisted classifications, we establish semiquantitative correlations between electrolyte components and the electrochemical reversibility of electrolytes. We propose the equivalent increment of Li salt resulting from functional cosolvent and solvent-solvent interactions for effective electrolyte design and prediction. The controllable regulation of the electrolyte design chart by the properties of solvent-solvent interactions presents varying equivalent effects of increasing Li salt concentrations in different electrolyte systems. Based on this mechanism, we demonstrate highly reversible and nonflammable phosphate-based electrolytes for graphite||NCM811 full cells. The proposed electrolyte design chart, semiquantitatively determined by intermolecular interactions, provides the necessary experimental foundation and basis for the future rapid screening and prediction of electrolytes using machine-learning methods.

The growth behavior and performance of microarc oxidation coating on AZ91/Ti composite: Influence of Ti-reinforcement phase and electrolyte

Magnesium matrix composites with both high strength and ductility have been achieved by introducing pure Ti particles. However, the properties of the surfaces of the composites need to be improved by surface technology, such as micro-arc oxidation (MAO). In this study, we investigated the influence of the Ti-reinforcement phase on coating growth and evolution by subjecting both AZ91 alloy and AZ91/Ti composite to MAO treatment using silicate-based and phosphate-based electrolytes. Results revealed that the Ti-reinforcement phase influenced the MAO process, altering discharge behavior, and leading to a decreased cell voltage. The vigorous discharge of the Ti-reinforcement phase induced the formation of coating discharge channels, concurrently dissolving and oxidizing Ti-reinforcement to produce a composite ceramic coating with TiO2. The MAO coating on the AZ91/Ti composite exhibited a dark blue macromorphology and distinctive local micromorphological anomalies. In silicate electrolyte, a “volcano-like” localized morphology centered on the discharge channel emerged. In contrast, treatment in phosphate-based electrolyte resulted in a coating morphology similar to typical porous ceramic coatings, with visible radial discharge micropores at the reinforcement phase location. Compared to the AZ91 alloy, the coating on the AZ91/Ti composite exhibited lower thickness and higher porosity. MAO treatment reduced the self-corrosion current density of the AZ91/Ti surface by two orders of magnitude. The silicate coating demonstrated better corrosion resistance than the phosphate coating, attributed to its lower porosity. The formation mechanism of MAO coatings on AZ91/Ti composites in phosphate-based and silicate-based electrolytes was proposed.

Laser assisted electrodeposition of binary metallic alloys from water-based electrolytes: The case of palladium‑platinum

The present work investigates the applicability of laser assisted electrodeposition (LAE) to the plating of binary metallic alloys from aqueous solutions and in absence of any external polarization. PdPt was chosen as prototypical system and the deposition was carried out from phosphate-based electrolytes. The effect of electrolyte formulation and laser parameters on the composition, thickness and physical properties of the alloys was studied. In order to provide more insight on the LAE deposition process of alloys, the electrochemical properties of the electrolytes employed were correlated with the properties of the materials obtained. In analogy with standard alloy plating processes, a clear link between the currents observed for the reduction of the two single metals and the composition/thickness of the coated PdPt layers could be established. Compositionally tunable and continuous PdPt coatings were obtained and their chemical, morphological and mechanical properties were determined. Finally, the possibility to selectively deposit the PdPt alloy was demonstrated by patterning a complex figure.

Molecular-level design for a phosphate-based electrolyte for stable potassium-ion batteries

The safety and cycling stability of potassium-ion batteries are of paramount importance. This study investigates a class of phosphate electrolytes with different alkyl chains to understand the correlation between electrochemical properties and alkyl chains. Based on the traditional trimethyl phosphate, the impact of structural modifications on performance improvement was explored in a single-salt, single-solvent environment matched with 1 M bis(fluorosulfonyl)imide potassium salt (KFSI). The research findings indicate that appropriately altering the alkyl chain structure of the phosphate [1 M KFSI-tripropyl phosphate (TPP)] can enhance its electrochemical performance. Through characterization and calculations, it was revealed that TPP's weak solvation and steric hindrance properties favor the formation of a robust interphase on the electrode. Coupling with its excellent ion conductivity, the 1 M KFSI-TPP electrolyte enables good cycling stability of Kǁgraphite, KǁPrussian blue (PB), and PBǁgraphite full-cell configurations. This study provides essential guiding principles for electrolyte design and offers valuable insights into the molecular-level design of safe electrolytes.

Photocatalytically active Ag-doped TiO2 coatings developed by plasma electrolytic oxidation in the presence of colloidal Ag nanoparticles

The plasma electrolytic oxidation process of Ti foil in the presence of a colloidal solution of Ag nanoparticles was used for the synthesis of exceptionally photocatalytically active Ag-doped TiO2 coatings. UV–Vis absorption spectroscopy was applied to follow the changes in the surface plasmon resonance band of the Ag nanoparticles as a function of the Ag:PO43− ratio in a phosphate-based electrolyte solution. Transmission electron microscopy revealed the size of the Ag nanoparticles in the range of 3–12 nm. The XRD patterns of the Ag-doped TiO2 coatings confirmed the crystalline anatase TiO2 phase regardless of the dopant concentration and without metallic Ag or crystalline Ag oxide forms. The typical porous morphology of the Ag–TiO2 coatings was observed by scanning electron microscopy. A significantly improved photocatalytic activity of the Ag–TiO2 coatings in the degradation process of the insecticide lindane (gamma isomer of benzene hexachloride) and test molecule methyl orange compared to pure TiO2 was determined using the GC technique. The degradation efficiency of Ag-doped TiO2 coatings is higher for lindane than for methyl orange.

Effect of Pr(NO3)3 doping on the characteristics of TC4 micro-arc oxidation coatings

Micro-arc oxidation coatings were prepared on the surface of TC4 by adding different contents of rare-earth compound Pr(NO3)3 to the aluminate and phosphate-based electrolyte. The results showed that the change in oxidation voltage increased at first and then decreased with the raised of Pr(NO3)3 addition. At 0.05 g L−1, the oxidation voltage reached the maximum, the number of discharge micropores decreased, while the size increased, the thickness and hardness of the coatings reached the peak values. The coatings mainly included Al2TiO5, anatase, γ-Al2O3 and a little of Pr2O3. Pr(NO3)3-doped coatings showed excellent corrosion resistance in 3.5% NaCl electrochemical workstation and oilfield simulation fluid containing 5% NaCl, and the corrosion resistance of the coatings reached the best at 0.05 g L−1.

Improving the corrosion protection of plasma electrolysis-treated light metal by polymeric functionalization

Suppressing the rate of corrosive degradation has been the primary challenge in the widespread use of lightweight metals across a variety of potential applications because their native passive layer is still susceptible to chemical attacks in aqueous or humid environments. This work explores the roles of polyaniline in tandem with a TiO2 layer in improving the corrosion properties of pure Ti. The anodic TiO2 surface is a result of a plasma electrolysis treatment in a non-acidic, phosphate-based electrolyte. The emeraldine base form of the polymer is subsequently applied to modify the surface properties of the plasma-electrolyzed Ti samples to further protect the surface against polar species that might interact with TiO2. The deposition of the thin layer of polyaniline retains the original surface microstructure of the plasma electrolysis layer. Nevertheless, the presence of polyaniline successfully reduces the corrosion current density and passive current density of plasma-electrolyzed Ti by ~50%. The corrosion protection mechanism is explained in the context of equivalent circuit models based on impedance measurements.

Tuning the long-term corrosion behaviour of biodegradable WE43 magnesium alloy by PEO coating

Plasma electrolytic oxidation (PEO) coatings can control fast degradation of next-generation biodegradable magnesium alloys for biomedical applications. In this work, we studied the effect of a PEO coating on the long-term corrosion behaviour of medical-grade WE43 magnesium alloy. In vitro experiments were performed for periods of up to 4 weeks in an organic fluid Dulbecco's Modified Eagles' Medium (DMEM). The average corrosion rates were measured using the hydrogen evolution method, and the degradation of the mechanical integrity were quantified by tensile test. Susceptibility towards localized corrosion was evaluated by scanning electron microscopy (SEM) images of cross-sections. Moreover, energy-dispersive X-ray spectroscopy (EDS) mappings and X-ray diffraction (XRD) were utilised for analysing the corrosion layer. Experimental results reveal significant changes in the product layer formation due to the PEO coating in phosphate-based electrolyte. The porous morphology of the coating with an initial thickness of ∼20 ± 5 μm changed significantly during the corrosion process, and a growing Mg-O-rich layer of 32 μm after 28 days was detected at the substrate interface. In contrast to the non-coated control group, no carbon-enriched area was observed. These findings imply significant long-term corrosion protection of the PEO coating. The results provide valuable information for a better understanding of the in vitro degradation process in PEO-coated magnesium alloys.

Improving anti-corrosion properties AZ31 Mg alloy corrosion behavior in a simulated body fluid using plasma electrolytic oxidation coating containing hydroxyapatite nanoparticles

Orthopaedic implants often make use of magnesium and its alloys. These alloys are more mechanically compatible with bone tissue than other alloys, such as titanium, cobalt, and nickel, but a loss of implant mechanical strength can occur due to their low corrosion resistance. The plasma electrolytic oxidation (PEO) method was used to modify the surface of AZ31 magnesium alloy in this study. The effects of varying concentrations of hydroxyapatite (HA) nanoparticles (1, 3, and 5 g/l) on the morphology and corrosion characteristics of coatings were examined using phosphate-based electrolytes. The elemental composition was determined using Energy dispersive spectroscopy (EDS), elemental map analysis (MAP) and phase X-ray diffraction analysis (XRD). Field emission-SEM was employed to investigate the surface morphology and cross-section of the coatings. The corrosion characteristics of all samples were evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) in Ringer’s solution. The sample with 3 g/l HA showed the best anti-corrosion performance, as it had the smallest average pore size (8.7 µm), the thickest coating (22.5 µm) and the lowest corrosion current density (0.034 µA/cm2) among all the samples tested.

Structural regulation chemistry of lithium-ion solvation in nonflammable phosphate-based electrolytes for high interfacial compatibility with graphite anode

With the booming development of lithium-ion batteries, safety has become one of the most primary focuses of current researches. Although there are various approaches to enhance the safety of lithium-ion batteries, phosphate-based electrolyte holds the greatest potential for practical application due to their non-flammability. Nonetheless, its compatibility issue with the graphite anode remains a significant obstacle to its widespread use. Herein, an effective method is proposed to improve the compatibility of electrolyte with graphite (Gr) anode by rationally adjusting the proportion of lithium salt and solvent components to optimize the Li+ solvation structure. By slightly increasing the Li+/triethyl phosphate (TEP) ratio, TEP alone cannot fully occupy the inner solvation sheath and therefore less polar ethylene carbonate (EC) has to be recruited, and the solvation structure gradually changes from Li+–[TEP]4 to Li+–[TEP]3[EC] with the coexistence of EC and TEP. Simultaneously, EC molecules in the Li+–[TEP]3[EC] could be preferentially reduced on graphite compared to the TEP molecules, resulting in the formation of a uniform and durable solid-electrolyte interphase (SEI) layer. Benefiting from the optimized phosphate-based electrolyte, the Gr|Li battery exhibits a capacity retention rate of 96.8% after stable cycling at 0.5 C for 470 cycles which shows a longer cycle life than the battery with carbonate electrolyte (cycling at 0.5 C for 450 cycles). Therefore, this work provides the guidance for designing a non-flammable phosphate-based electrolyte for high-safety and long cycling-life lithium-ion batteries.

Nonfluorinated Antisolvents for Ultrastable Potassium-Ion Batteries.

A robust interface between the electrode and electrolyte is essential for the long-term cyclability of potassium-ion batteries (PIBs). An effective strategy for achieving this objective is to enhance the formation of an anion-derived, robust, and stable solid-electrolyte interphase (SEI) via electrolyte structure engineering. Herein, inspired by the application of antisolvents in recrystallization, we propose a nonfluorinated antisolvent strategy to optimize the electrolyte solvation structure. In contrast to the conventional localized superconcentrated electrolyte introducing high-fluorinated ether solvent, the anion-cation interaction is considerably enhanced by introducing a certain amount of nonfluorinated antisolvent into a phosphate-based electrolyte, thereby promoting the formation of a thin and stable SEI to ensure excellent cycling performance of PIBs. Consequently, the nonfluorinated antisolvent electrolyte exhibits superior stability in the K||graphite cell (negligible capacity degradation after 1000 cycles) and long-term cycling in the K||K symmetric cell (>2200 h), as well as considerably improved oxidation stability. This study demonstrates the feasibility of optimized electrolyte engineering with a nonfluorinated antisolvent, providing an approach to realizing superior electrochemical energy storage systems in PIBs.

Photocatalytic performance of Nd–TiO2 coatings: effect of voltage and frequency

Neodymium (Nd)–titanium dioxide (TiO2) micro-arc oxidation (MAO) coatings were formed in a phosphate-based electrolyte with the addition of neodymium (III) oxide (Nd2O3) using suitable voltages and frequencies. Scanning electron microscopy results revealed that the coatings varied with different voltages and frequencies. Furthermore, composition analysis showed the neodymium–titanium dioxide coatings were mainly composed of anatase and rutile phases. Meanwhile, the anatase content increased and then decreased. In addition, X-ray photoelectron spectroscopy results indicated that the titanium (Ti) 2p spin–orbit components of the neodymium–titanium dioxide coatings shifted toward a higher binding energy, suggesting that some of the neodymium (Nd3+) ions combined with the titanium dioxide lattice, leading to dislocation. Furthermore, photocatalytic experiment results showed that the photocatalytic activity of neodymium–titanium dioxide coatings can be greatly enhanced with a moderate amount of neodymium ions. However, an excessive amount of neodymium ions does not improve the photocatalytic activity further.

Effect of electrolyte composition on the surface characteristics of plasma electrolytic oxidation coatings over Ti[sbnd]40Nb alloy

The present work aims to develop corrosion-resistant and cytocompatible coatings on Ti40Nb alloy by the plasma electrolytic oxidation (PEO) process. Usually, PEO coatings on niobium substrate with superior surface characteristics are obtained using a silicate-based electrolyte system, and a phosphate-based electrolyte system is used for titanium substrate. Till date, electrolyte system composition is not optimised for the PEO coatings on Ti40Nb alloys. To study the influence of electrolyte composition on PEO coating properties over Ti40Nb alloy, three different concentrations of phosphate and silicate (75:25, 50:50, and 25:75) and a fixed amount of KOH were used, and their surface characteristics and corrosion properties were evaluated in this study. We found that coatings formed with an equal proportion of phosphate and silicate in an electrolyte system are dense, compact, thick and corrosion-resistant. A coating aimed for high bioactivity is also developed by adding hydroxyapatite (HA) nanoparticles to an equal proportion (50:50) electrolyte system. After the successful development of the PEO coatings over Ti40Nb alloy, its phase composition, surface morphological features, wettability, scratch resistance, and corrosion properties are examined. The cell viability and live/dead cell morphology of L-929 fibroblast cells were evaluated for untreated Ti40Nb alloy, PEO-treated Ti40Nb alloy, and Ti40Nb alloy PEO-treated with hydroxyapatite nanoparticles. All surface-modified samples exhibited better corrosion resistance than the untreated alloy. Ti40Nb alloy PEO treated with phosphate: silicate electrolyte system (50:50) exhibited better scratch resistance, higher wettability, bioactivity, favourable chemical composition, and surface morphological features than the other ratios of phosphate and silicate (25:75 and 75:25). Meanwhile, Ti40Nb alloy PEO treated with hydroxyapatite nanoparticles addition showed better cytocompatibility than without HA addition.

Methane synthesis from CO2 and H2O using electrochemical cells with polymer electrolyte membranes and Ru catalysts at around 120 °C: a comparative study to a phosphate-based electrolyte cell

A polymer-electrolyte electrochemical cell, equipped with a Ru/ZrO2 catalyst at 120 °C, converts CO2 and H2O into CH4 and O2 with a current efficiency of 85%.