High Voltage Lithium Batteries Research Articles

Investigation of the Roles of Functional Solvents in Performance Stability of High Voltage Lithium Batteries

Li-ion batteries (LIBs) have become prevalent for portable and large-scale applications, such as personal electronic devices, unmanned aircraft systems, electric vehicles, and power grids.1 However, LIBs are approaching an asymptotic limit in specific energy (~250 Wh kg-1 at cell level); therefore, they are insufficient to meet future applications that require higher battery specific energies.2 Ni-rich cathodes, such as LiNi0.8Co0.1Mn0.1O2 (NMC811), have the potential to provide much higher specific energies for next-generation LIBs (e.g., >350 Wh kg-1) and, therefore, are considered the most promising low-cost cathode materials.3 Nevertheless, Ni-rich cathode based LIBs with conventional carbonate solvent based electrolytes face severe technical challenges, especially when cycled at high upper cutoff voltages, due to electrolyte decomposition, parasitic oxidation reactions at the electrolyte/cathode interface, irreversible phase changes in the cathodes, and dissolution of transition metals into electrolytes.4 Therefore, R&D efforts are needed to tackle the above technical challenges of Ni-rich cathode based LIBs before they become commercially viable.In our previous study,5 a ternary of fluorinated solvents was used to formulate a high voltage stable electrolyte (HVE) which was used in Ni-rich cathode based, high-voltage lithium batteries. These HVE-based batteries demonstrated a significant improvement in cycle stability when operated at a charge cutoff voltage of 4.5 V (vs Li/Li+). In this study, we investigated the roles of single-solvents and co-solvents in the cycle stability of the high-voltage lithium batteries. Several families of organic solvents, such as fluorinated carbonates and organosilicon based solvents were investigated. Our preliminary data showed that some unique combinations of the functional solvents could lead to exceptionally stable cycle performance in the high-voltage lithium batteries. We will discuss possible fundamental mechanisms responsible for the observed performance stability of the high-voltage lithium batteries using ex-situ XPS, density functional theory calculations, and other characterization techniques. References (1) Li, J.; Fleetwood, J.; Hawley, W. B.; Kays, W. From materials to cell: state-of-the-art and prospective technologies for lithium-ion battery electrode processing. Chemical Reviews 2021, 122 (1), 903-956.(2) Khan, F. N. U.; Rasul, M. G.; Sayem, A.; Mandal, N. K. Design and optimization of lithium-ion battery as an efficient energy storage device for electric vehicles: A comprehensive review. Journal of Energy Storage 2023, 71, 108033.(3) Xue, W.; Huang, M.; Li, Y.; Zhu, Y. G.; Gao, R.; Xiao, X.; Zhang, W.; Li, S.; Xu, G.; Yu, Y. Ultra-high-voltage Ni-rich layered cathodes in practical Li metal batteries enabled by a sulfonamide-based electrolyte. Nature Energy 2021, 6 (5), 495-505.(4) Yang, J.; Liang, X.; Ryu, H.-H.; Yoon, C. S.; Sun, Y.-K. Ni-Rich Layered Cathodes for Lithium-Ion Batteries: From Challenges to the Future. Energy Storage Materials 2023, 102969.(5) Poches, C.; Razzaq, A. A.; Studer, H.; Ogilvie, R.; Lama, B.; Paudel, T. R.; Li, X.; Pupek, K.; Xing, W. Fluorinated High-Voltage Electrolytes To Stabilize Nickel-Rich Lithium Batteries. ACS Applied Materials & Interfaces 2023, 15 (37), 43648-43655. Acknowledgement This work was supported by the following funding sources. The Larry and Linda Pearson Endowed Chair at the Department of Mechanical Engineering, South Dakoda School of Mines and Technology. The Naval Air Warfare Center Weapons Division, China Lake, CA under Contract No N6893622C0017. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Naval Air Warfare Center Weapons Division, China Lake, CA. TP acknowledges the support from the SDBOR Governor Research Center for the Electrochemical Energy Storage and NASA EPSCOR-80NSSC23M0072.

Solid polymer electrolytes regulated by ion-dipole interactions for high voltage lithium batteries

Solid polymer electrolytes (SPEs) with wide electrochemically stable window and high lithium-ion transference number (tLi+) are a requirement for high energy density lithium batteries. Here, we construct a copolymer electrolyte (PDA) with ether-ester bifunctional groups that exhibits a low highest occupied molecular orbital (HOMO) energy level by in situ polymerization. Compared to the poly(1,3-dioxolane) (PDOL) pure polyether electrolyte, the weakening of the ion-dipole interaction between lithium salt and polymer in the PDA electrolyte promotes the formation of a “weak solvation” structure. Therefore, the electrolyte achieves high oxidative stability (4.6 V vs. Li+/ Li with a standard leakage current of 10 μA), high Li+ transference number (0.60), and importantly, derives a stable LiF-rich composition on high voltage cathode surface. Which ultimately enables stable cycling of Li||LiNi0.5Co0.2Mn0.3O2 (NCM523) batteries at a range of 3.0–4.3 V. This work provides a fundamental understanding of the design of antioxidant SPEs to achieve high energy density lithium batteries.

Ionic Liquids as Cathode Additives for High Voltage Lithium Batteries

AbstractTwo oxalatoborate ionic liquids (ILs), which are commonly utilized as electrolyte additives that form a protective layer on the cathode surface, are investigated for the first time as electrode additives. Cathodes based on LiNi0.5Mn1.5O4 (LNMO) containing 3 wt % ILs, i. e., “IL‐enriched cathodes”, exhibit capacity values above 120 mAh/g with high Coulombic efficiencies throughout cycling over 200 times. A cathode without ILs also exhibits a capacity of 119 mAh/g but its Coulombic efficiency becomes low and unstable after 109 cycles. In addition, when 0.3 M ILs are added to conventional carbonate‐based electrolytes, the battery cycle life improves but there is a reduction in the capacity probably due to low ionic conductivity of the electrolyte mixtures. Post‐mortem analyses of electrodes retrieved from cycled cells highlight less electrolyte decomposition and less cathode corrosion, enabled by using the IL as the additive in LNMO, which are confirmed by a particle shape with smooth surface identical to the fresh cathode. The study demonstrates that oxalatoborate ILs can be used as the electrode additive, and this provides a new concept for cathode formulations for high performance batteries with a small amount of ILs.

Polymer-based electrolytes for high-voltage solid-state lithium batteries

Increasing the charging cut-off voltage of lithium batteries is a feasible method to enhance the energy density. However, when batteries operate at high voltages (> 4.3 V), the degradation of liquid organic carbonate electrolyte is accelerated and may cause safety hazards. Polymer-based electrolytes with inherently high safety and good electrochemical stability can prevent the electrolyte degradation in high-voltage solid-state lithium batteries. This paper provides a comprehensive and in-depth review of the design strategies, recent developments, and scientific challenges associated with polymer-based electrolytes for high-voltage applications. Emphases are placed on the interfacial compatibility between electrolytes and cathodes, such as mechanical contacts and interface chemical stability, which are critical to the lifespan of high-voltage lithium batteries. Moreover, guidelines for the future development of high-voltage solid-state lithium batteries are also discussed.

Insights into lithium inventory quantification of LiNi0.5Mn1.5O4–graphite full cells

A systematic methodology for the quantification of lithium inventory is developed and the degradation mechanisms of high-voltage lithium batteries are revealed.

Stabilizing Ni-rich layered cathode for high-voltage operation through hierarchically heterogeneous doping with concentration gradient

High-nickel LiNixMnyCo1-x-yO2 (NMC) cathodes have demonstrated superior energy density, yet their stability is compromised under high voltage conditions. To address this, we propose a strategy of heterogeneous doping with a concentration gradient, specifically through Sr–Zr co-modification. We synthesized Ni-rich NMC particles featuring several micron-sized secondary particles composed of micron-sized primary grains. This design aims to harness the structural robustness of single-crystalline grains and the favorable diffusion kinetics of polycrystalline secondary particles. Systematic characterization using a combination of electrochemical measurements and synchrotron analytics reveals an intriguing pattern of hierarchically heterogeneous Sr–Zr co-doping. It demonstrates a depth-dependent concentration gradient at the secondary particle level and competing dopant segregation over the buried grain boundaries. This unique characteristic creates opportunities for enhancing battery performance, particularly by optimizing precursors and implementing advanced modulation techniques. We also investigate the dissolution and precipitation of the cathode's transition metal cations upon high-voltage cycling. These insights suggest that a tailored compositional variation can be a viable approach to effectively design the next-generation high-Ni NMC cathode materials for high-voltage lithium batteries.

Mechanism of Bilayer Polymer-Based Electrolyte with Functional Molecules in Enhancing the Capacity and Cycling Stability of High-Voltage Lithium Batteries.

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) are favorable for all-solid-state lithium metal batteries (ASSLBs) to ensure safety and enhance energy density. However, their narrow work windows and unstable electrode/electrolyte interfaces hinder their practical application in high-voltage ASSLBs. Although introducing additives in SPEs has been proven to be effective to address the above issues, it could hardly optimize both cathode and anode interfaces by an individual additive. Herein, heterogeneously double-layer SPEs are constructed with two typical additives (LiPO2F2 and LiFSI), which are used to modify the LiNi0.6Co0.2Mn0.2O2 (NCM)-cathode/electrolyte interface (CEI) and lithium-anode/solid electrolyte interface (SEI), and further understand their respective mechanism in enhancing the capacity and cycling stability of ASSLBs. Specifically, LiPO2F2 not only leads to a uniform CEI layer to prevent the oxidation decomposition of PEO and LiTFSI but also ensures fast Li+ diffusion at high voltage (>3.9 V), improving the rate performances and life spans of the cells. The LiFSI contributes to a stable SEI layer with rich LiF, suppressing the growth of lithium dendrites and maximizing the specific capacity for ASSLBs. Integrating the advantages of the two functional molecules, the optimized ASSLB displays an excellent capacity of 141.4 mAh g-1 at 1C and an outstanding capacity retention of 81.6% after 400 cycles when using the NCM cathode, even reaching 154.2 mAh g-1 at 0.1 mA cm-2 with a high mass loading (6.4 mg cm-2). Additionally, the bilayer SPEs also match well with a LiFePO4 electrode with a high mass loading of 11.0 mg cm-2, displaying a high capacity of 155.7 mAh g-1 at 0.1 mA cm-2.

Polymer-in-Salt Electrolyte from Poly(caprolactone)-graft-polyrotaxane for Ni-Rich Lithium Metal Batteries at Room Temperature.

Solid-state lithium batteries with solid polymer electrolytes have recently attracted extensive attention due to their promising potential in high energy density and safety. However, the principal issues plaguing the solid polymer electrolytes are their restricted ionic conductivities at ambient temperature and the limited tolerance to the widely used high-voltage cathodes (such as LiNi0.8Mn0.1Co0.1O2, NCM811), thus limiting their practical applications seriously. In this regard, a superior polymer-in-salt solid electrolyte from poly(caprolactone)-graft-polyrotaxane (PGPE) is developed for high-voltage lithium batteries operated at room temperature. The PGPE displays remarkable electrochemical properties at room temperature, with an exceptional ionic conductivity of 4.89 × 10-4 S cm-1 and a lithium-ion transference number of approximately 0.64, stemming from the rapid segmental motions of PCL sidechains by the enhanced dynamics of the cyclic molecules along the axial polymer chain of polyrotaxane. More importantly, the PGPE demonstrates a high electrochemical oxidation voltage of ∼4.7 V, suggesting the excellent electrochemical stability of PGPE against the NCM811-based cathode. Owing to the dense LiF-rich CEI self-generated on the NCM811 particles in the cathode, the transition metal ion diffusion is successfully constrained and the PGPE is well protected from continuous decomposition. The PGPE also shows superior interfacial stability between the metallic Li and the electrolyte. As a result, the all-solid-state NCM811|PGPE|Li cell exhibits superior discharge capacity (196 mAh g-1) and extraordinary long-term cycling stability (74% capacity retention at 150 cycles) at 30 °C.

A scalable one-pot strategy for the development of polymer electrolytes adaptable to room-temperature high-voltage lithium batteries

Poly(ethylene oxide) (PEO) polymer electrolytes (PEs) have been commercially applied in LiFePO4||Li solid-state lithium batteries (SSLBs). However, it remains challenging to develop PEO-based PEs applicable to the high-voltage SSLBs with higher energy density, owing to the poor electrochemical stability of PEO. Herein, we report a scalable strategy for fabricating PEO-based PEs with high-voltage compatibility, by exploiting a new mechanism to stabilize the cathode-electrolyte interface in the high-voltage SSLBs. The protocol only involves a one-pot synthesis procedure to covalently crosslink the PEO chains, in the presence of high-content lithium bis(trifluoromethylsulphonyl)imide (LiTFSI) salts and N,N-dimethylformamide (DMF). LiTFSI-DMF supramolecular aggregates are formed and firmly embedded in the polymer network, endowing the PE with high room-temperature ionic conductivity. The dissociated and highly concentrated TFSI− anions can enter the Helmholtz layer close to the high-voltage cathode, leading to the formation of a thin and homogeneous cathode electrolyte interface (CEI), mainly composed of LiF, on the cathode. The CEI with high electrochemical stability can effectively stabilize the cathode-electrolyte interface, enabling long-term stable cycling of the high-voltage LiCoO2||Li and nickel-rich NCM622||Li batteries at room temperature. The simplicity and scalability of the strategy makes the reported PEO-based PE potentially applicable in high-voltage SSLBs in practice.

Design Guidelines for Sulfonyl/Sulfamoyl Fluoride Electrolyte Additives for Modulation of Lithium Anode Coulombic Efficiency

Owing to its high theoretical capacity (3860 mAh/g, over 10 times that of graphite) and its lowest theoretical electrochemical potential (-3.04 V vs SHE), Li metal is an ideal anode material for improving the capacity of rechargeable Li batteries [1]. However, the practical application of the Li anode is severely hindered by its high reactivity with standard electrolyte compositions, which results in limited Coulombic efficiency (CE) in those electrolytes (for instance, 85-90% with 1 M LiPF6 EC:DEC [2]). Strategies to improve CE have focused on electrolyte engineering, including development of highly concentrated electrolytes (HCE) and more recently, local high-concentration electrolytes (LHCE) [3]. A feature shared by these strategies is the promotion of contact-ion pairing, which enhances anion contributions to the solid electrolyte interphase (SEI). Among the best-performing salts are fluorinated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), which are believed to promote stable inorganic-rich SEIs and correlate with higher CE [4]. A second strategy of interest is to pursue development of additives incorporated at relatively low concentrations (e.g., 2-5 wt%) that can favorably alter the SEI, such as carbonates (e.g., vinylene carbonate (VC) [5] and fluoroethylene carbonate (FEC) [6]), sulfates (e.g., ethylene sulfate (DTD) and 1,3-propanesulfonate (PS) [7]), and borates (e.g., lithium difluoro(oxoalate) borate (LiDFOB) [8] and tris (2,2,2-trifluoroethyl) borate (TTFEB) [9]). An advantage of this strategy is the possibility to ultimately lower reliance on high fluorinated salt concentrations, which are costly and can be corrosive towards the Al current collector, and potentially expand the versatility of available electrolyte frameworks having competitive CE. However, compared to the principles developed for salt and solvent selection in HCE and LHCE, the mechanism behind successful additive activation needs elucidation.In this work, we examined the potential of "FSI-like," neutral sulfonyl/sulfamoyl fluorides (R-SO2F and R-R’-NSO2F, Figure 1) as functional additives for Li cycling, motivated by their structural similarity to the high-performance FSI- anion. The examined baseline electrolytes include high-CE systems consisting of LiFSI dissolved in various solvents: fluoroethylene carbonate (FEC, 1 and 4 M salt), 1,2-dimethoxyethane (DME, 4 M), and dimethyl carbonate (DMC, 6 M). The ability for each additive to coordinate with Li+ was first examined by NMR, with trends rationalized in part by supporting microcalorimetry data on the degree of solvent coordination strength. We relate these to CE and cycling outcomes in each electrolyte. Interestingly, we find that additives have negligible effect on CE in FEC-based electrolytes, whereas significant impacts were observed in DME and DMC. We relate these diverse outcomes to the SEI chemical compositions and gases evolved during galvanostatic cycling, as characterized by X-ray photoelectron spectroscopy (XPS) and gas chromatography (GC), which help to rationalize competitive reactions among solvent, anion, and additive. Unfortunately, additives had a negative-to-neutral impact on CE in these systems. Thus, we finally examined a LiPF6 in carbonate electrolyte, 1 M LiPF6 in EC/DMC (LP40), where we hypothesized that competitive reduction of coordinating additives over problematic carbonate solvent would lead to performance gains. Indeed, significant improvements (up to 94%, compared to baseline 89% over the initial 50 cycles) in CE were observed for two additives, with their structural advantages further discussed. Overall, our findings provide insights into the effects of sulfonyl/sulfamoyl fluoride additive structures on Li metal cyclability and the compositions of baseline electrolytes whose electrochemical cycling stability can be effectively modulated by these additives. Xu, W., et al., Lithium metal anodes for rechargeable batteries. Energy & Environmental Science, 2014.7(2):p.513-537.Genovese, M., et al., Combinatorial methods for improving lithium metal cycling efficiency. Journal of The Electrochemical Society, 2018.165(13):p.A3000.Hobold, G.M., et al., Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes. Nature Energy, 2021.6(10):p.951-960.Suo, L., et al., Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries. Proceedings of the National Academy of Sciences, 2018.115(6):p.1156-1161.Aurbach, D., et al., On the use of vinylene carbonate (VC) as an additive to electrolyte solutions for Li-ion batteries. Electrochimica acta, 2002.47(9):p.1423-1439.Markevich, E., et al., Fluoroethylene carbonate as an important component in electrolyte solutions for high-voltage lithium batteries: role of surface chemistry on the cathode. Langmuir, 2014.30(25):p.7414-7424.Han, B., et al., Poor Stability of Li2CO3 in the Solid Electrolyte Interphase of a Lithium ‐Metal Anode Revealed by Cryo ‐Electron Microscopy. Advanced Materials, 2021.33(22):p.2100404.Liu, J., et al., Lithium difluoro (oxalato) borate as a functional additive for lithium-ion batteries. Electrochemistry communications, 2007.9(3):p.475-479.Ma, Y., et al., Enabling reliable lithium metal batteries by a bifunctional anionic electrolyte additive. Energy Storage Materials, 2018.11:p.197-204. Figure 1. (a) Sulfonyl/sulfamoyl fluoride chemical structures and (b) R-S and S-F bond lengths calculated by density functional theory. Figure 1

Interface Engineering Via Fluorinated Solid Electrolytes for All-Solid-State Li Batteries

Solid electrolytes (SEs) are vital for all-solid-state batteries (ASSBs) since they replace the flammable liquid electrolytes to make the ASSBs safer and compacter.1 In order to boost the energy density of ASSBs, a practical SE is not only expected possessing high ionic conductivity, but also good compatibility with both cathode and anode to allow the use of high-voltage cathode and Li metal.2, 3 However, most of the developed SEs show limitations on directly contact with either high-voltage cathode materials or Li metal. As such, SE modification is required to address the interfacial issues between SE and electrodes.In this work, fluorinated sulfide- and halide-based SEs are proposed to stabilize the SE/Li metal and SE/high-voltage cathode interfaces, respectively. Our results firstly show that fluorinated argyrodite Li6PS5Cl (LPSCl) can enhance the interfacial stability toward the Li metal anode.4 The in-situ formed interface between Li and LPSCl1−xFx are of highly fluorinated and condense, which enables ultrastable Li plating/stripping behavior over 250 hrs at a high current density of 6.37 mA cm−2 and a cutoff capacity of 5 mAh cm−2. The Li metal treated by the LPSCl1−xFx SE is then demonstrated to deliver good durability and rate capability in full cells. Other than anode side improvement, F is introduced into a superionic conductor Li3InCl6 to widen the oxidation limit to over 6 V (vs. Li/Li+).5 Both experimental and computational results identify that F-containing passivating interphases are generated to contribute to the enhanced oxidation stability of Li3InCl6-xFx and stabilization the surface of cathodes at high cut-off voltages. The optimized composition Li3InCl4.8F1.2 is directly matched with bare high-voltage LiCoO2, enabling ASSBs to stably operate at room temperature at a cut-off voltage of 4.8 V (vs Li/Li+). Our studies provide a new strategy of interface engineering by introducing F in SEs, realizing the good compatibility between SE and electrodes and opening up the applications of ASSBs. Re ferences Manthiram, A., Yu, X. W., Wang, S. F. Lithium battery chemistries enabled by solid-state electrolytes. Nat. Rev . Mater. 2, 1-16 (2017).Wang, C. H., Liang, J. W., Zhao, Y., Zheng, M. T., Li, X. N., Sun, X. L. All-solid-state lithium batteries enabled by sulfide electrolytes: from fundamental research to practical engineering design. Energy Environ. Sci. 14, 2577-2619 (2021).Li, J. C., Ma, C., Chi, M. F., Liang, C. D., Dudney, N. J. Solid Electrolyte: the Key for High-Voltage Lithium Batteries. Adv. Energy Mater. 5, 1401408 (2015).Zhao, F. P., et al. Ultrastable Anode Interface Achieved by Fluorinating Electrolytes for All-Solid-State Li Metal Batteries. ACS Energy Lett. 5, 1035-1043 (2020).Zhang, S. M., et al. Advanced High-Voltage All-Solid-State Li-Ion Batteries Enabled by a Dual-Halogen Solid Electrolyte. Adv. Energy Mater. 11, 2100836 (2021).

Lithium difluorophosphate–modified PEO-based solid-state electrolyte for high-voltage lithium batteries

Lithium difluorophosphate–modified PEO-based solid-state electrolyte for high-voltage lithium batteries

Gradient trilayer solid-state electrolyte with excellent interface compatibility for high-voltage lithium batteries

Solid-state electrolytes (SSEs) are considered as promising alternatives for liquid electrolytes to achieve high energy density and safe lithium metal batteries. However, their practical utilization is limited owing to low ionic conductivity and insufficient interface stability. Here, a unique gradient trilayer SSE (20 µm) is designed to improve compatibility of anode/electrolyte/cathode interfaces and enhance structural integration to provide continuous Li+ transport channels. One side anti-oxidation polymer layer improves the high-voltage tolerance for electrolyte/cathode interface, and the other side anti-reduction polymer layer provides soft interfacial contact and compatibility with Li-metal anode. Remarkably, the ultrathin porous membrane as host allows the fully penetration of two different polymers to form a gradient middle layer, providing excellent structural integration and fast Li+ transport. Thus, the Li||Li symmetric cells with gradient trilayer electrolyte can stably operate over 2500 h under 0.1 mA cm−2. The LiNi0.8Co0.1Mn0.1O2||Li solid-state batteries with gradient trilayer electrolyte deliver over 107 mAh g−1 capacity after 1000 cycles at 0.5C. This work provides a novel strategy to significantly enhance multilayer SSE with gradient interface in solid-state lithium-metal batteries.

A Janus-faced, perovskite nanofiber framework reinforced composite electrolyte for high-voltage solid lithium-metal batteries

High-voltage solid lithium-metal batteries (HVSLMBs) are not only energy denser but also safer than state-of-the-art lithium-ion batteries. However, the narrow electrochemical stability windows and low ionic conductivities of polymer solid electrolytes severely hinder the practical application of this type of battery. To simultaneously address these issues, we propose and fabricate a thin yet mechanically strong composite solid electrolyte by forming a layer of a reduction-tolerant polyethylene glycol diacrylate (PEGDA) and oxidation-resistant poly(vinylidene fluoride) (PVDF) within the perovskite nanofiber framework. The unique Janus-faced design enables stable and intimate contact with the lithium metal anode and high-voltage cathode, while the perovskite inorganic electrolyte Li0.33La0.557TiO3 (LLTO) nanofiber framework endows the membrane with a high ionic conductivity of 0.1 mS cm−1 at room temperature (25 °C) and excellent mechanical strength with the thickness of as low as 24 μm. When paired with a high-voltage LiNi0.8Co0.1Mn0.1O2 cathode, the solid lithium battery can deliver a reversible discharge capacity of as high as 176 mAh g−1 at 0.2C at room temperature. This work offers a novel, effective strategy to develop high-performance solid electrolytes for next-generation high-voltage lithium batteries.

Pseudo Over Saturated Electrolyte for High Voltage Lithium Batteries

Pseudo Over Saturated Electrolyte for High Voltage Lithium Batteries

Stable lithium metal batteries enabled by localized high-concentration electrolytes with sevoflurane as a diluent

A localized high concentration electrolyte, prepared using sevoflurane as a diluent in carbonate, promotes the formation of highly robust LiF-rich solid-electrolyte interphases on both Li-metal anodes and NMC811 cathodes, leading to long-life high-voltage lithium batteries.

Safe gel polymer electrolytes for high voltage Li-batteries

Gel polymer electrolytes (GPEs), based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), 1 M LiPF6 in ethylene carbonate/dimethyl carbonate (EC/DMC), so called LP30, and 1‑butyl‑1-methylpyrrolidinium hexafluorophosphate ([Py14]PF6), have been developed to improve inherent safety of the electrolyte for high voltage lithium batteries. Dry PVdF-HFP membranes, prepared with EC/DMC, were soaked in LP30 in addition to its mixtures with 30 wt% and 50 wt% [Py14]PF6 to obtain GPEs. Non-flammable character and mechanical stability enhanced via physical crosslinks of the GPEs are demonstrated with flammability tests and rheological measurements, respectively. Lithium ion conduction property in the GPEs is evaluated by means of both electrochemical impedance spectroscopy and NMR spectroscopy (Pulsed Field Gradient-PFG and relaxation time). Galvanostatic charge and discharge cycles of lithium metal batteries having LiNi0.5Mn1.5O4 as a high voltage cathode demonstrate improved electrochemical performance with coulombic efficiency above 99% and high specific capacity above 110 mAh g − 1 at C/5 throughout 150 cycles, when the GPE containing LP30 with 30 wt% [Py14]PF6 is used. The capacity retention is sufficiently high compared to the GPE without [Py14]PF6, confirming that the IL is a highly promising additive for improving battery life.

Lithium Borate Ester Salts for Electrolyte Application in Next‐Generation High Voltage Lithium Batteries

AbstractThe atmospheric instability and the corrosive tendency of hexafluorophosphate [PF6]− and fluorosulfonylimide [FSI]− based lithium salts, respectively, are among the major impediments towards their application as electrolytes in high voltage lithium batteries. Herein a new class of Li salts is introduced and their electrochemical behavior is explored. The successful synthesis and characterization are reported, including the crystal structure, of lithium 1,1,1,3,3,3‐(tetrakis)hexafluoroisopropoxy borate (LiBHfip). The oxidative stability of electrolytes of this salt in an ethylene carbonate:dimethyl carbonate mixture (v/v, 50:50) is found to be 5.0 V versus Li+/Li on various working electrodes, showing substantial improvement over a LiPF6 based electrolyte. Moreover, a high stability of an aluminum substrate is observed at potentials up to 5.8 V versus Li+/Li; in comparison, a LiFSI based electrolyte shows prominent signs of Al corrosion above 4.3 V versus Li+/Li. Cells tested with high voltage layered LiNi0.8Mn0.1Co0.1O2 (NMC811) and spinel LiMn2O4 (LMO) cathodes show stable cycling over 200 cycles with capacity retention of 76% and 90%, respectively. The LMO|Li cell maintains this same low capacity fade rate for 1000 cycles even after the salt has been exposed for 24 h to atmospheric conditions (water content ≈0.57 mass%).

LiF and LiNO3 as synergistic additives for PEO-PVDF/LLZTO-based composite electrolyte towards high-voltage lithium batteries with dual-interfaces stability

Solid electrolytes with desirable properties such as high ionic conductivity, wide electrochemical stable window, and suitable mechanical strength, and stable electrode–electrolyte interfaces on both cathode and anode side are essential for high-voltage all-solid-state lithium batteries (ASSLBs) to achieve excellent cycle stability. In this work, a novel strategy of using LiF and LiNO3 as synergistic additives to boost the performance of PEO-PVDF/LLZTO-based composite solid electrolytes (CSEs) is developed, which also promotes the assembled high-voltage ASSLBs with dual-interfaces stability characteristic. Specifically, LiF as an inactive additive can increase the electrochemical stability of the CSE under high cut-off voltage, and improve the high-voltage compatibility between cathode and CSE, thus leading to a stable cathode/CSE interface. LiNO3 as an active additive can lead to an enhanced ionic conductivity of CSE due to the increased free-mobile Li+ and ensure a stable CSE/Li interface by forming stable solid electrolyte interphase (SEI) on Li anode surface. Benefiting from the improved performance of CSE and stable dual-interfaces, the assembled NCM622/9[PEO15-LiTFSI]-PVDF-15LLZTO-2LiF-3LiNO3/Li cell delivers a high rate capacity of 102.1 mAh g−1 at 1.0 C and a high capacity retention of 77.4% after 200 cycles at 0.5 C, which are much higher than those of the ASSLB assembled with additive-free CSE, with only 60.0 mAh g−1 and 52.0%, respectively. Furthermore, novel cycle test modes of resting for 5 h at different charge states after every 5 cycles are designed to investigate the high-voltage compatibility between cathode and CSE, and the results suggest that LiF additive can actually improve the high-voltage compatibility of cathode and CSE. All the obtained results confirm that the strategy of using synergistic additives in CSE is an effective way to achieve high-voltage ASSLBs with dual-interfaces stability.

High-performance polymer electrolyte membrane modified with isocyanate-grafted Ti3+ doped TiO2 nanowires for lithium batteries

The Ti3+ doped TiO2 nanowires were grafted by tolylene-2,4- diisocyanate (TDI) and applied as a modifier for the preparation of organic–inorganic hybrid electrolyte in high performing lithium batteries. The PEO-based polymer electrolyte was optimized at different organic–inorganic ratios and exhibited excellent lithium-ion conductivity of 1 × 10−4 S·cm−1 at 30 °C when adding 8% TDI-TiO2 nanowires, outstanding electrochemical stability with a wide electrochemical window up to 5.5 V at 60 °C and a high lithium-ion transport number of 0.36. The LiFePO4|PTTNW8%|Li cells deliver excellent rate capability and cycling performance, with a high initial discharge capacity up to 151 mAh·g−1 at 60 °C at 0.1 C rate and excellent capacity retention of 91% after 100th cycle. NCM811|PTTNW8%|Li high-voltage lithium batteries were also demonstrated at a 50 °C, which displayed a superior cycling performance. Therefore, the prepared PEO-TDI-TiO2 electrolyte is a promising polymer electrolyte for solid- state lithium batteries.