Electrolytes For Li-ion Batteries Research Articles

High-voltage electrolyte design for a Ni-rich layered oxide cathode for lithium-ion batteries

LiNi0.8Co0.1Mn0.1O2 (NCM811) is one of the most promising cathode materials in high-energy-density Li-ion batteries (LIBs) because of its high capacity and low cost. However, it still suffers from irreversible capacity fading at high cut-off voltages. This is mainly because high voltage accelerates the hydrolysis reaction of lithium hexafluorophosphate with trace water to generate byproducts such as highly corrosive hydrogen fluoride (HF) resulting in an unstable cathode–electrolyte interface and continuous irreversible phase transitions. Here, we modify a conventional electrolyte by adding the dual additives of tetrabutyl titanate (TBT) and lithium difluoroxalate borate (LiDFOB) to form a stable Ti-, B-, and F-rich interfacial layer to eliminate the unfavorable cathode-electrolyte side reactions and suppress deleterious phase transitions. Additionally, TBT can stabilize the electrolyte by removing H2O/HF. With the synergistic effect of the dual additives, the cycling stability of NCM811 at high voltages is enhanced considerably. The Li∣NCM811 cell with dual additives exhibits a high capacity retention rate of 86% after 200 cycles at 1 C and a high cut-off voltage of 4.5 V. This strategy provides a reference for designing high-voltage electrolytes for LIBs.

Experimental and DFT analysis of structural, optical, and electrical properties of Li3xLa2/3-xTiO3 (3x = 0.1, 0.3 and 0.5) solid electrolyte

The perovskite material, lithium lanthanum titanate Li3xLa2/3-xTiO3 (LLTO) is one of the interesting prospects that may be employed as a solid-state inorganic electrolyte for Li-ion batteries. Here, three various formulations corresponding to: (i) 3x = 0.1 (Li0.1La0.63TiO3), (ii) 3x = 0.3 (Li0.3La0.57TiO3), and (iii) 3x = 0.5 (Li0.5La0.5TiO3) were synthesized using sol-gel method. The impacts of lithium concentration, calcination temperature, elemental composition, microstructure, optical properties, and conductivity of the ceramics were studied using a plethora of techniques. DFT calculations were performed on Li0.5La0.5TiO3 to get an in-depth understanding on the relationship between the structure –electronic– optical properties of LLTO materials. Our results show that the grain and crystallite sizes behave inversely proportional to the band gap. Maximum grain ionic conductivity on the order of 10−3S/cm and grain boundary ionic conductivity on the order of 10−6S/cm were obtained for both samples (3x = 0.3 and 3x = 0.5) at higher temperatures. The total density of states indicates that the titanium d-bands (Ti-d) and oxygen p–bands (O-p) form covalent Ti-O bond character. The formation of localized states is suggested to result in the lowering of the band gap energy, when lithium content is increased. Finally, the calculated mechanical properties show that LLTO (3x = 0.5) possess high elastic moduli as compared to other solid electrolytes.

LiBH4 as a Solid-State Electrolyte for Li and Li-Ion Batteries: A Review

In this paper, the methods used to enhance the conductivity of LiBH4, a potential electrolyte for the construction of solid-state batteries, are summarized. Since this electrolyte becomes conductive at temperatures above 380 K due to a phase change, numerous studies have been conducted to lower the temperature at which the hydride becomes conductive. An increase in conductivity at lower temperatures has generally been obtained by adding a second component that can increase the mobility of the lithium ion. In some cases, conductivities at room temperature, such as those exhibited by the liquid electrolytes used in current lithium-ion batteries, have been achieved. With these modified electrolytes, both lithium metal and lithium-ion cells have also been constructed, the performances of which are reported in the paper. In some cases, cells characterized by a high capacity and rate capability have been developed. Although it is still necessary to confirm the stability of the devices, especially in terms of cyclability, LiBH4-based doped electrolytes could be employed to produce solid-state lithium or lithium-ion batteries susceptible to industrial development.

Improved Ga-doped Li7La3Zr2O12 garnet-type solid electrolytes for solid-state Li-ion batteries

Improved Ga-doped Li7La3Zr2O12 garnet-type solid electrolytes for solid-state Li-ion batteries

Lithium Niobate for Fast Cycling in Li-ion Batteries: Review and New Experimental Results

Li-Nb-O-based insertion layers between electrodes and electrolytes of Li-ion batteries (LIBs) are known to protect the electrodes and electrolytes from unwanted reactions and to enhance Li transport across interfaces. An improved operation of LIBs, including all-solid-state LIBs, is reached with Li-Nb-O-based insertion layers. This work reviews the suitability of polymorphic Li-Nb-O-based compounds (e.g., crystalline, amorphous, and mesoporous bulk materials and films produced by various methodologies) for LIB operation. The literature survey on the benefits of niobium-oxide-based materials for LIBs, and additional experimental results obtained from neutron scattering and electrochemical experiments on amorphous LiNbO3 films are the focus of the present work. Neutron reflectometry reveals a higher porosity in ion-beam sputtered amorphous LiNbO3 films (22% free volume) than in other metal oxide films such as amorphous LiAlO2 (8% free volume). The higher porosity explains the higher Li diffusivity reported in the literature for amorphous LiNbO3 films compared to other similar Li-metal oxides. The higher porosity is interpreted to be the reason for the better suitability of LiNbO3 compared to other metal oxides for improved LIB operation. New results are presented on gravimetric and volumetric capacity, potential-resolved Li+ uptake and release, pseudo-capacitive fractions, and Li diffusivities determined electrochemically during long-term cycling of LiNbO3 film electrodes with thicknesses between 14 and 150 nm. The films allow long-term cycling even for fast cycling with rates of 240C possessing reversible capacities as high as 600 mAhg−1. Electrochemical impedance spectroscopy (EIS) shows that the film atomic network is stable during cycling. The Li diffusivity estimated from the rate capability experiments is considerably lower than that obtained by EIS but coincides with that from secondary ion mass spectrometry. The mostly pseudo-capacitive behavior of the LiNbO3 films explains their ability of fast cycling. The results anticipate that amorphous LiNbO3 layers also contribute to the capacity of positive (LiNixMnyCozO2, NMC) and negative LIB electrode materials such as carbon and silicon. As an outlook, in addition to surface-engineering, the bulk-engineering of LIB electrodes may be possible with amorphous and porous LiNbO3 for fast cycling with high reversible capacity.

Exploring the Effects of Dopamine and DMMP Additives on Improving the Cycle Boosting and Nonflammability of Electrolytes in Full-Cell Lithium-Ion Batteries (18650)

Concerns over recyclability, performance, and safety have grown as the use of commercial Li-ion batteries to meet our energy needs has increased. Electrolytes may aid in increased flammability, capacity loss, and safety. Dimethyl methyl phosphonate (DMMP), a flame retardant, and dopamine hydrochloride (DOP) are utilized to increase the cycle life and graphite anode compatibility. The optimal additive formulation (5% wt DMMP and 0.1% wt DOP) reduces inflammability and increases cycle life and reversible capacity (99.14%). Molecular dynamics simulations provide a comprehensive atomistic account of the dynamics of Li+ ion solvation in the electrolytes and in the presence of additives. Dopamine and DMMP increase the Li-ion solvation-free energy in the electrolyte formulation. While increasing the Li-ion conductivity, additive addition reduces the electrolyte viscosity and enables the formation of a smaller, stronger Li-DMMP-DOP complex than the larger Li-carbonate complex found in Li-neat electrolyte systems. When DMMP and DOP are added to the electrolyte, the carbonates are displaced from the Li-carbonate complex by these additives. The Li-ion solvating nature or compatibility was improved upon the addition of DMMP/DOP further aided by a faster diffusive behavior of the Li complex, which in part would be instrumental in enhancing the performance and safety of the battery electrolyte additive formulations. The modified electrolyte (DMMP 5% wt, DOP 0.1% wt) has a conductivity of 18.60 mS cm–1 and a low viscosity at 25 °C. This formulation was evaluated using graphite/NMC-532 cylindrical cells with commercial electrodes. The performance of the graphite/NMC-532 cells containing the modified electrolyte was comparable to those of regular electrolytes based on carbonates: ethylene carbonate/dimethyl carbonate/ethylmethylcarbonate (EC/DMC/EMC) (1:1:1) additions. These findings indicate that DOP and DMMP have a lower oxidation potential (4.3 V) than most commercial electrolytes (4.5 V), preventing cathode deterioration. These insights should pave the path for rational design of practical and cost-effective Li-ion battery electrolyte additive combinations aimed toward lower flammability and improved performance.

A review of mitigation strategies for li-ion battery thermal runaway

With its high energy density and long lifespan, li-ion battery (LIB) is now dominating the power source market for portable electronics such as smartphones, laptops, and electric vehicles. However, LIB electrolyte is flammable, and the diaphragm has low stability, making it easy to cause thermal runaway (TR). This paper reviews the research progress on TR propagation characteristics and prevention strategies. The study reviewed the analysis of practical measures of battery management systems, safety devices, flame retardants, electrolyte additives, and thermal absorption materials. It also discusses accidents related to TR of LIBs to emphasise the significance of TR to the entire accident investigation and analysis process. This paper can provide useful information on how to avoid TR-related accidents.

Inkjet-Printed Graphene-Modified Aluminum Current Collector for High-Voltage Lithium-Ion Battery

One of the problems plaguing the development of Li-ion batteries that can operate at high cell voltages (i.e., beyond 4.2 V; vs Li/Li+) is the corrosion of the cathode current collector, which causes electrochemical instability and impedance build-up. In this regard, here, we demonstrate the benefits of using inkjet printing technology to uniformly coat the Al current collector (AlCC) with a graphene layer to suppress the corrosion degradation of the current collector at the cathode side. The graphene ink is prepared via solvent exfoliation, and then a thin layer of graphene is coated (∼268 nm in thickness) via inkjet printing on AlCC, which is further annealed in Ar at 350 °C to enhance the electrical conductivity. The thickness and mass loading of the graphene film on Al foil is controlled by the number of printing cycles. The corrosion properties of the bare and printed graphene-coated AlCCs (Gr-AlCC) were evaluated by cyclic voltammetry within 1–5 V (vs Li/Li+) using a Li-ion battery electrolyte. This clearly showed the extensive corrosion degradation of the bare AlCC, which was, however, nearly completely suppressed in the presence of the printed graphene coating. Upon usage of these AlCCs for the galvanostatic cycling of homemade Li-NMC-based cathodes in Li “half” cells, the Gr-AlCC resulted in excellent cyclic stability pertaining to ∼90% capacity retention after 100 cycles (@C/5) despite the usage of 4.5 V as the upper cut-off. By contrast, the bare AlCC resulted in only ∼68% capacity retention under the same conditions. Furthermore, the usage of Gr-AlCC facilitated considerably superior rate capability and lower electrode impedance as compared to the bare AlCC counterpart. This highlights the importance of such passivation/protection of current collectors with conducting coatings and the utility of the scalable-cum-versatile inkjet printing technology for the same.

Advances on liquid electrolytes for Li-ion and Li metal batteries

Battery materials have been extensively studied in the past decades aiming to improve their capacity, energy density and power density. In this opinion review, materials that are used as liquid electrolytes are discussed, from organic, including ionic liquids, to aqueous based ones. Strategies as fluorinated organic solvents and low solvating organic solvents are highlighted, showing the recent progress, their impact on Li plating/stripping and on battery performance. Aqueous electrolyte with molecular crowding is also discussed, where Li+ solvation is controlled to be mostly by anions, which changes the nature of the solid electrolyte interphase. This opinion review aims to highlight the past two years of important reports on electrolyte for Li-ion and Li metal batteries.

Structural, electronic, and Li-ion mobility properties of garnet-type Li7La3Zr2O12 surface: An insight from first-principles calculations

Garnet-type Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte for Li-ion batteries, but Li-dendrite’s formation greatly limits the applications. In this paper, we systematically investigate the stability, electronic properties, and Li-ion mobility of the LLZO surface by the first-principles calculations. We consider the (110) and (001) slab structures with different terminations in the t- and c-LLZO. Our results indicate that both (110) and (001) surfaces prefer to form Li-rich termination due to their low surface energies for either t- or c-LLZO. Moreover, with the decrease of Li contents the stability of Li-rich surfaces is improved initially and degrades later. Unfortunately, the localized surface states at the Fermi level can induce the formation of metallic Li on the Li-rich surfaces. In comparison, Li/La-termination has a relatively low metallic Li formation tendency due to its rather low diffusion barrier. In fact, Li-ion can spontaneously migrate along path II (Li3 → Li2) on the Li/La–T(001) surface. In contrast, it is more difficult for Li-ion diffusion on the Li–T(001) surface, which has a minimum diffusion barrier of 0.50 eV. Interestingly, the minimum diffusion barrier decreases to 0.34 eV when removing four Li-ions from the Li–T(001) surface. Thus, our study suggests that by varying Li contents, the stability and Li-ion diffusion barrier of LLZO surfaces can be altered favorably. These advantages can inhibit the formation of metallic Li on the LLZO surfaces.

Implications of the Thermal Stability of FEC-Based Electrolytes for Li-Ion Batteries

Fluoroethylene-carbonate (FEC) is a common co-solvent for high-voltage cathodes and for silicon-based anodes in lithium-ion batteries. However, FEC has a limited thermal stability when used with LiPF6 as conductive salt, and its decomposition can trigger detrimental side reactions. Here, we will examine the reaction mechanism of FEC with LiPF6, confirming that vinylene-carbonate (VC) and HF are produced at elevated temperatures. By full-cell cycling at 45 °C in a T-cell setup with a micro-reference electrode (μ-RE), we can show by electrochemical impedance spectroscopy that these side reactions not only lead to an impedance increase of the anode and the cathode, but also trigger transition metal dissolution. By comparison of FEC and ethylene-carbonate (EC) as cyclic carbonate, we demonstrate that FEC has no advantage at high-voltage operation compared to EC, when employing cathode materials or cathode potentials for which no lattice oxygen is evolved. Finally, we use multi-layer pouch-cells to analyze the gassing of an EC- and FEC-based electrolyte upon extended charge/discharge cycling at 45 °C, showing that the latter leads to cell bulging upon extended charge/discharge cycling at 45 °C due to the oxidation of the VC formed by the thermal decomposition of FEC above ≈4.4 − 4.5 V vs. Li+/Li.

Solid electrolytes for Li-ion batteries via machine learning

In this work, machine learning (ML) techniques were employed to construct a predictive model that can be used to discover new solid state electrolytes (SE/SSE) for lithium ion batteries (LIBs). The model was built (with R2 = 0.97) based on a dataset constructed from previous works regarding ionic conductivity (IC) of solid electrolytes. After a suitable validation process, the ML-model was used to predict the IC of many compositions (∼30 K in Inorganic Crystal Structure Database (ICSD)). Interestingly, the predictions of this model, done on 145 compounds, were consistent with values of Li-phonon band center, which is used as an IC descriptor, this was then used to predict the IC vs temperature behavior of LiYS2 which is suggested as a promising SSE candidate in this work.

Towards N-rich solid polymer electrolytes for Li-ion batteries?

Solid polymer electrolytes (SPEs) are faced with many specifications to replace today's liquid organic electrolyte in Li-ion batteries, here BPEI based polymer is proposed as a new SPE.

Molecularly engineered linear organic carbonates as practically viable nonflammable electrolytes for safe Li-ion batteries

Concurrent modification of linear carbonates combining alkyl-chain extension and alkoxy substitution enables thermally stable high-performance batteries by decreasing volatility and increasing solvation ability simultaneously.

Single-oxygen linear ether (SOLE) based electrolytes for fast-charging and low-temperature Li-ion batteries

A series of electrolytes based on single-oxygen linear ether (SOLE) open up new avenues for designing novel LIB (Lithium-Ion Battery) electrolytes with improved charging and low-temperature performance.

Machine Learning Interatomic Potential to Investigate Fundamentals of Electrolytes for Li-ion Solid-State Batteries

Machine learning and deep learning are used to construct interatomic potential with superior performance by satisfying the accuracy of density functional theory (DFT) calculations while requiring computational resources comparable to those required for classical molecular dynamics simulations. In this study, the machine learning interatomic potential (MLIP) is successfully constructed using moment tensor potential (MTP) for predicting the ionic conductivity of Li-ion solid-state electrolytes with Li-Ge-P-X′ and Li-X″-P-S structures, where X′ = O, S, or Se and X″ = Ge, Si, or Sn. <i>Ab initio</i> molecular dynamics (AIMD) simulations are performed to construct the initial training database for MTP; the constructed MLIP exhibits excellent accuracy with an R<sup>2</sup> value of 0.98 for predicting the potential energy value. The excellent performance of MLIP is further validated by calculating the lattice constant and bulk modulus. Finally, the ionic conductivity is obtained by performing MTP-based molecular dynamics (MD); the predicted value exhibits good agreement with previous AIMD results. Further, MTP-MD evidently runs three orders of magnitude faster than AIMD. The obtained results clearly demonstrate that MLIP can be used to rapidly determine promising solid-state electrolytes with accuracy comparable to that of DFT while greatly reducing the computational cost.

High-voltage ionic liquid-based flexible solid polymer electrolyte for high-performance Li-ion batteries

Ionic liquid–solid polymer electrolyte membrane for sustainable battery technology.

Considering cell volume in dopant screening for improving Li-ion mobility in an amorphous LiPON solid-state electrolyte: an ab initio study.

Engineering of solid electrolytes of Li-ion batteries is carried out for achieving high levels of ionic conductivity and preserving low levels of electrical conductivity. Doping metallic elements into solid electrolyte materials composed of Li, P, and O is quite challenging due to instances of possible decomposition and secondary phase formation. To accelerate the development of high-performance solid electrolytes, predictions of thermodynamic phase stabilities and conductivities are necessary, as they would avoid the need to carry out exhaustive trial-and-error experiments. In this study, we demonstrated theoretical approach to increase the ionic conductivity of amorphous solid electrolyte by doping: cell volume-ionic conductivity relation. Using density functional theory (DFT) calculations, we examined the validity of the hypothetical principle in predicting improvements in stability and ionic conductivity with 6 candidate doping elements (Si, Ti, Sn, Zr, Ce, Ge) in a quaternary Li-P-O-N solid electrolyte system (LiPON) both in crystalline and amorphous phases. The doping of Si into LiPON (Si-LiPON) was indicated to stabilize the system and enhance ionic conductivity based on our calculated doping formation energy and cell volume change. The proposed doping strategies provide crucial guidelines for the development of solid-state electrolytes with enhanced electrochemical performances.

Effects of Li content on stability, electronic and Li-ion diffusion properties of Li<sub>3<i>x</i></sub>La<sub>(2/3)–<i>x</i></sub>†<sub>(1/3)–2<i>x</i></sub>TiO<sub>3</sub> surface

Li<sub>3<i>x</i></sub>La<sub>(2/3)–<i>x</i></sub>†<sub>(1/3)–2<i>x</i></sub>TiO<sub>3</sub>(LLTO) is a promising solid-state electrolyte for Li-ion batteries. We study the effect of Li content on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We consider both Li-poor and Li-rich LLTO surfaces. The results show that La/O/Li-terminated LLTO (001) is the most stable crystal surface. Further, LLTO (001) surface gives better stability when Li content is 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase . Electronic structure calculations infer that in both Li-poor and Li-rich LLTO(001) surfaces there occurs the transition from conductor to semiconductor with the increase of Li content. Besides, we find that Li-ion always keeps a two-dimensional diffusion path for different Li content. As Li content increases from 0.17 to 0.38 for Li-poor LLTO (001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li content increases from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for diffusion coefficient nor for diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li content is 0.40. Thus, our study suggests that by varying Li content, the stability, band gap, and Li-ion diffusion performance of LLTO (001) can be changed favorably. These advantages can inhibit the formation of lithium dendrites on the LLTO (001) surface.

Solvent and catalyst free vitrimeric poly(ionic liquid) electrolytes.

Polymer electrolytes (PEs) are a promising alternative to overcome shortcomings of conventional lithium ion batteries (LiBs) and make them safer for users. Introduction of self-healing features in PEs additionally leads to prolonged life-time of LIBs, thus tackling cost and environmental issues. We here present solvent free, self-healable, reprocessable, thermally stable, conductive poly(ionic liquid) (PIL) consisting of pyrrolidinium-based repeating units. PEO-functionalized styrene was used as a co-monomer for improving mechanical properties and introducing pendant OH groups in the polymer backbone to act as a transient crosslinking site for boric acid, leading to the formation of dynamic boronic ester bonds, thus forming a vitrimeric material. Dynamic boronic ester linkages allow reprocessing (at 40 °C), reshaping and self-healing ability of PEs. A series of vitrimeric PILs by varying both monomers ratio and lithium salt (LiTFSI) content was synthesized and characterized. The conductivity reached 10-5 S cm-1 at 50 °C in the optimized composition. Moreover, the PILs rheological properties fit the required melt flow behavior (above 120 °C) for 3D printing via fused deposition modeling (FDM), offering the possibility to design batteries with more complex and diverse architectures.