Rechargeable Lithium-Ion Battery with Halogen Inserted into Graphite Electrode

Abstract

The present disclosure provides a rechargeable lithium-ion battery comprising at least one lithium salt-graphite composite electrode. In particular, the present disclosure provides a rechargeable "double-salt-in-aqueous" lithium-ion battery having a high potential, wherein at least a portion of the lithium salt is phase-separated from the aqueous electrolyte and an anion-redox reaction occurs within the graphite lattice.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority of U.S. Provisional Application No. 62 / 814,618, filed on March 6, 2019, the entire content of which is incorporated herein by reference.

[0003] Statement Regarding Federally Sponsored Research

[0004] This invention was made with government support under DE - AR0000389 awarded by the Department of Energy, Advanced Research Projects Agency - Energy. The government has certain rights in this invention. Technical Field

[0005] The present invention relates to rechargeable lithium - ion batteries comprising a lithium - salt - graphite composite electrode. In particular, the present invention relates to a rechargeable "water - in - salt" lithium - ion battery having a high potential, in which at least a portion of the lithium salt is separated from the aqueous electrolyte. Background Art

[0006] Lithium - ion batteries are a useful and powerful energy storage option. Their use has expanded to a variety of products, including but not limited to portable electronic devices (such as computers, mobile phones, speakers, etc.) to hybrid and electric vehicles. Lithium - ion batteries have low maintenance costs, higher charge storage density and voltage, and better performance than typical lead - acid batteries because small lithium ions can be densely packed into the anode material.

[0007] Recent breakthroughs in aqueous electrolytes via the "water - in - salt" approach have significantly extended the electrochemical potential of lithium - ion batteries to the 3.0 - 4.0 V range and enabled high - voltage cathodes to be coupled with low - potential graphite anodes. However, the limited gravimetric capacity (<200 mAh / g) of intercalation cathodes based on lithium transition metal oxides constitutes a fundamental obstacle to achieving higher energy densities.

[0008] The intercalation cathode chemistries used in state - of - the - art lithium - ion batteries (LIBs) store electrical energy by accommodating Li + in their lattice and compensating for the charge through cationic redox reactions of transition metals (Ni, Co, Mn, Fe, etc.). They have excellent reversibility (long cycle life), but due to the large molar mass of each embedded Li + and potential structural instabilities upon over - de - lithiation, their capacity is generally (<200 mAh g –1 ). On the other hand, anion redox reactions (O / O 2- , S / S 2-etc.) are expected to achieve higher capacities by following conversion reaction mechanisms, but usually have extremely poor reversibility due to repeated destruction and reformation of the structure and the large volume changes accompanying each charge / discharge cycle. The low electron and ionic conductivities of these anion redox materials further exacerbate this problem.

[0009] Recently, a combination of cation and anion redox mechanisms in the host lattice has been discovered in lithium-excess transition metal oxide materials, where the oxygen layer participates in the battery reaction and makes a significant contribution to the overall capacity of the transition metal oxide. A lithium battery based on the occurrence of anion-redox reactions in the host lattice would be very attractive because it inherits both the high energy of the anion-redox conversion reaction and the excellent reversibility of the topology of insertion. PF6 in the electrolyte of the "dual-ion" battery - 、BF4 - 、TFSI - anions can be reversibly inserted into graphite. However, these redox reactions only occur on the graphite lattice rather than on the anions themselves, thus limiting the capacity to 120 mAh g -1 and below. The S / S n 2- and Br - / Br 3- redox of the cathode electrolyte is highly reversible, but these anions are only physically confined / adsorbed on the porous carbon, resulting in high self-discharge and low cycle life due to the unwanted shuttle reaction. Ideally, to avoid the shuttle reaction, the anion-cathode electrolyte should be phase-separated from the electrolyte, and the oxidized anions should be stabilized by insertion into a solid host. However, so far, no suitable anions, host lattices, and electrolytes have been found to support this ideal energy storage mechanism with sufficient capacity at high potentials.

[0010] Therefore, a suitable host lattice and electrolyte that provide higher capacity and / or high potential are needed. SUMMARY OF THE INVENTION

[0011] Some aspects of the present invention utilize halogen conversion-insertion chemistry in graphite to provide rechargeable high-potential and / or high-capacity lithium batteries. In a particular aspect of the present invention, a rechargeable lithium-ion battery (i.e., a lithium battery) is provided. The lithium battery includes: (i) a composite cathode comprising a lithium salt and graphite; (ii) an electrolyte; and (iii) an anode. In a particular embodiment, the composite cathode is configured such that the oxidation product of the lithium salt is inserted into or becomes inserted into the graphite. In other embodiments, the capacity of the lithium-ion battery is greater than 200 mAh / g, typically at least about 230 mAh / g, typically at least about 240 mAh / g, and most typically at least about 250 mAh / g. In still other embodiments, the energy density of the lithium-ion battery is at least about 400 Wh / kg, typically at least about 430 Wh / kg, typically at least about 460 Wh / kg, and most typically at least about 500 Wh / kg. When referring to a numerical value, the terms "about" or "approximately" are used interchangeably herein and refer to an acceptable error range of a particular value determined by a person of ordinary skill in the art. The determination of such a value will depend at least in part on how the value is measured or determined, such as the limitations of the measurement system, e.g., the precision required for a particular purpose. For example, in accordance with the practice in the art, the term "about" may mean within 1 standard deviation or more than 1 standard deviation. Alternatively, when referring to a numerical value, the term "about" may mean ±20% of the numerical value, typically ±10%, typically ±5%, and more typically ±1%. However, generally speaking, when describing a particular value in the present application and claims, unless otherwise specified, the term "about" refers to an acceptable error range of the particular value, typically within 1 standard deviation.

[0012] In other embodiments, the coulombic efficiency of the lithium battery is at least about 95%, typically at least about 98%, typically at least about 99%, and most typically at least about 99.9%.

[0013] In yet other embodiments, the lithium-ion battery has a potential relative to Li / Li + of at least about 4 V, typically at least about 4.1 V, typically at least about 4.15 V, and most typically at least about 4.2 V.

[0014] In some embodiments, the composite cathode comprises a plurality of lithium salts, such as lithium halide salts. In other embodiments, the composite cathode comprises lithium chloride, lithium bromide, lithium iodide, lithium fluoride, and other halogen salts or combinations thereof. In a particular embodiment, the composite cathode comprises a combination of lithium chloride and lithium bromide.

[0015] In a particular embodiment, the electrolyte comprises a fluoride-based electrolyte. Exemplary fluoride-based electrolytes useful in the lithium batteries of the present invention include, but are not limited to, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)borate (LiDFOB), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium nitrate (LiNO3), or an electrolyte separable from a lithium halide salt electrolyte, and mixtures thereof.

[0016] In another embodiment, the electrolyte comprises a water-in-salt electrolyte (WiBS), a high-concentration organic electrolyte, an all-solid-state ceramic electrolyte, an electrolyte separable from a lithium halide salt electrolyte, or a combination thereof.

[0017] Exemplary high-concentration organic electrolytes include, but are not limited to, 2 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) + 2 lithium difluoro(oxalato)borate (LiDFOB) in dimethoxyethane, 4 m lithium tetrafluoroborate (LiBF4) in ethylene carbonate (EC), 7 m lithium bis(fluorosulfonyl)imide (LiFSI) in fluoroethylene carbonate (FEC), and 2 m lithium tetrafluoroborate (LiBF4) in a 1:1 volume mixture of ethylene carbonate (EC) and propylene carbonate (PC).

[0018] Exemplary all-solid-state ceramic electrolytes include, but are not limited to, Li4(BH4)3I, Li4(BH4)3Br, Li4(BH4)3Cl, a LiBH4-LiBr-LiCl solid solution, Li2Al2SiP2TiO 13 (LASPT), Li7La3Zr2O 12 (LLZO), and a PEO–LiTFSI polymer electrolyte.

[0019] In other embodiments, the electrolyte is in the form of a hydrogel. In still other embodiments, the electrolyte further comprises poly(ethylene oxide), polyvinyl alcohol, polyacrylonitrile, poly(methyl methacrylate), polyacrylic acid, polytetrahydrofuran, poly(ethylene glycol) dimethacrylate, poly(ethylene glycol) diacrylate, 2-hydroxyethyl acrylate, poly(ethylene glycol) methyl ether, bisphenol A ethoxylate dimethacrylate, polyvinylpyrrolidone, and other hydrophilic polymers, or a combination thereof.

[0020] Another aspect of the present invention provides a method for preparing a lithium salt-graphite composite cathode for a rechargeable lithium-ion battery. In some embodiments, the lithium salt is embedded in the graphite. The method includes compressing a mixture of a lithium salt-graphite composite material and a polymer under conditions sufficient to produce a lithium salt-graphite composite cathode, whereby oxidation of the lithium salt causes the oxidation product of the lithium salt to be embedded within the graphite.

[0021] In some embodiments, the method further includes the step of mixing the lithium salt and the graphite and grinding the mixture to prepare the lithium salt-graphite composite material before mixing with the polymer. In a particular embodiment, the lithium salt includes two or more lithium salts, typically lithium halide salts.

[0022] In a particular embodiment, the lithium salt is a mixture of lithium bromide and lithium chloride. The molar ratio of lithium bromide to lithium chloride is about 5:1, typically about 3:1, typically about 2:1, and most often about 1:1.

[0023] In other embodiments, the mass ratio of the lithium bromide, the lithium chloride, and the graphite is about 2:0.25:2, typically about 2:0.5:2, and typically about 2:1:2.

[0024] In other embodiments, the polymer includes poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), alginic acid, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, or a mixture thereof. In a particular embodiment, the polymer includes PTFE.

[0025] In other embodiments, the mass ratio of the lithium salt-graphite composite material to the polymer is about 90:10, typically about 92:8, typically about 94:6, and most typically about 95:5.

[0026] Yet another aspect of the present invention provides a rechargeable lithium-ion battery, comprising: (i) a composite cathode comprising at least one lithium salt and graphite, wherein the composite cathode is configured such that oxidation of the lithium salt causes the oxidation product of the lithium salt to be embedded in the graphite; (ii) an aqueous electrolyte; (iii) an anode comprising a fluorinated polymer.

[0027] In some embodiments, the aqueous electrolyte comprises a water-in-bisalt electrolyte (WiBS). In a particular embodiment, the WiBS comprises lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)borate (LiDFOB), lithium hexafluoroarsenate (LiAsF6), an asymmetric ammonium salt (Me3EtN·TFSI), N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (pyr13TFSI), other ionic liquids, or mixtures thereof.

[0028] In other embodiments, the WiBS may further comprise an organic solvent. Suitable organic solvents include, but are not limited to, trimethyl phosphate, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), γ-butyrolactone (γ-BL), ethyl methyl carbonate, dimethoxyethane, diethylene glycol methyl ether, fluoroethylene carbonate (FEC), and derivatives thereof, as well as other organic solvents known to those skilled in the art or used in lithium-ion batteries. See, for example, Long et al., “Polymer electrolytes for lithium polymer batteries”, J. Mater. Chem. A, 2016, 4, pp. 10038–10069, the entire content of which is incorporated herein by reference. When an organic solvent is present, the amount of the organic solvent used relative to water is about 66 vol% or less (e.g., 2 or less:1), typically about 50 vol% or less (e.g., 1 or less:1), and typically about 20 vol% or less (e.g., 1 or less:4).

[0029] In other embodiments, at least a portion of the lithium salt is phase-separated from the aqueous electrolyte.

[0030] In other embodiments, the anode is protected by the fluorinated polymer. In some embodiments, the fluorinated polymer is a fluorinated ether polymer. In other embodiments, the fluorinated polymer comprises a highly fluorinated ether (HFE) polymer gel (e.g., 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, or mixtures thereof). Description of the Drawings

[0031] Figure 1Schematic illustration of the conversion-insertion mechanism occurring during the oxidation of the LBC-G composite in the WiBS aqueous gel electrolyte. A two-stage reaction involving the oxidation of Br (~4.0 V) and Cl (~4.2 V) and their subsequent insertion into the graphite structure. Discharge is the complete reverse of the charging process.

[0032] Figure 2 For a scan rate of 0.05 mVs -1 when the cyclic voltammogram of the LBC-G cathode is relative to Li / Li + from 3.2 to 4.9 V.

[0033] Figure 3 Galvanostatic charge / discharge curves of the LBC-G cathode at a current density of 80 mA g -1 . Inset: Discharge capacity retention and Coulombic efficiency.

[0034] Figure 4 Linear sweep voltammograms of a pure graphite electrode (only PTFE binder) on a Ti mesh current collector in LiBr3·H2O, LiCl3·H2O, and WiBS electrolytes, with an Ag / AgCl electrode as the reference, respectively, showing the oxidation of Br-, Cl-, and water at 1 mV / s, indicating no side reactions (including corrosion of the current collector and oxidation of graphite and water) before starting at ~4.0 V, 4.5 V, and 5.0 V relative to Li / Li + .

[0035] Figure 5 GITT characterization diagram of the LBC-G cathode at a current density of 80 mAg -1 . The red curve is the quasi-equilibrium potential at different lithiation / delithiation stages, which is composed of the average value of each open circuit voltage cycle during the charge / discharge process. Inset: Finite diffusion coefficient D of the reactants estimated from GITT and EIS measurements.

[0036] Figure 6 Nyquist plots of the LBC-G cathode obtained by EIS testing at different SOCs in a three-electrode cell. The dashed line is the fitting curve using the equivalent circuit. Inset: Full-scale plot.

[0037] Figure 7 In-situ Raman spectra (100–550 cm -1 ) of LBC-G during the entire charge-discharge cycle, showing the evolution of Br2 and BrCl intercalants. Red line: Free BrCl signal can only be detected after deliberately damaging the graphite matrix with a strong laser beam, further confirming the intercalation of BrCl. Quartz background removed.

[0038] Figure 8 Ex-situ Br K-edge XANES of the LBC-G composite during its first charge. Chemically intercalated Br2 and liquid Br2 were measured as control samples (dashed lines) in the same cell configuration.

[0039] Figure 9 Ex-situ Cl K-edge XANES of the LBC-G composite during its first charge.

[0040] Figure 10 Charge / discharge curves after the first charge of LBC-G composites with different LiBr / LiCl molar ratios at a current density of 80 mAg -1 are shown. The specific capacity was estimated from the weights of LiBr and LiCl.

[0041] The molar ratio was changed by reducing only certain portions of LiCl from the original LiBr / LiCl / graphite composite.

[0042] Figure 11 Charge / discharge curves after the first charge of LBC-G composites with different LiBr / LiCl molar ratios at a current density of 80 mAg -1 are shown. The specific capacity was estimated from the weights of LiBr and LiCl.

[0043] The molar ratio was changed by reducing only certain portions of LiBr from the original LiBr / LiCl / graphite composite.

[0044] Figure 12 In-situ Raman spectra (1200 - 2850 cm -1 ) of LBC-G during the entire charge / discharge cycle, showing the graphite structure evolution with the intercalation / deintercalation of Br2 and BrCl.

[0045] Figure 13 Ex-situ XRD of the LBC-G composite through the second cycle at different charge and discharge states. The θ-2θ scan mode was used for Cu Kα radiation in the reflection geometry Left: overall spectrum. Middle: enlarged range of 2θ (24° - 28°). Right: enlarged range of 2θ (48° - 60°). The peaks of the titanium current collector were used to calibrate the diffraction angle.

[0046] Figure 14 In-situ XRD patterns of the (00m + 1) peak of the LBC-G composite during the charge / discharge cycle, which were collected using high-energy X-ray radiation (wavelength of ) in the transmission geometry. Left: corresponding voltage curve. Right: two-dimensional contour and representative curve of the XRD pattern, showing the d-spacing of the graphite host during the intercalation / deintercalation process Continuous evolution. For convenience, the 2θ diffraction angle was converted to d-spacing (see Methods).

[0047] Figure 15 Ex-situ high-energy XRD patterns of the LBC-G composite (electrolyte and current collector removed) at 50% and 100% SOC. The high-energy transmission X-ray radiation was set perpendicular to most of the graphite flasks to show the in-plane structural features.

[0048] Figure 16A and 16B are the best-fit models of the Br EXAFS experimental data for phase II C7[Br]( Figure 16A , SOC = 50%) and phase I C 3.5 [Br 0.5 Cl 0.5 ( Figure 16B , SOC = 100%), respectively. The EXAFS spectra in R-space are uncorrected for phase, so the distances R in the two plots for the two phases are not comparable, but are both less than the actual values. Inset: In-plane configurations of phase II C7[Br] and phase I C 3.5 [Br 0.5 Cl 0.5 obtained from DFT simulations. Two sets of bond distances are marked as red lines (short) and blue lines (long).

[0049] Figure 17 Figure showing the typical charge-discharge voltage curves (3rd cycle) of two lithium-ion full cells with LBC-G cathodes consisting of graphite anodes protected by anhydrous LiBr / LiCl (blue) or LiBr / LiCl monohydrate (red) and HFE / PEO. Charging and discharging were carried out at 0.2C (44 mAg -1 for the LBC-G cathode) and 25 °C. The cell capacity was calculated based only on the cathode mass (above the X-axis) or based on the total mass of the cathode and anode including the binder and protective coating (below the X-axis).

[0050] Figure 18 Figure showing the discharge capacity (hollow circles) and Coulombic efficiency (semi-solid circles) of the full cell during cycling in a specific embodiment of the lithium-ion battery of the present invention, calculated based on the total mass of the cathode and anode.

[0051] Figure 19 Shows the discharge capacity calculated on the total anode and cathode mass at different rates for a specific embodiment of the LBC-G / graphite full cell of the present invention with different electrolyte / electrode (cathode + anode) mass ratios.

[0052] Figure 20Shows the galvanostatic charge / discharge curves of the LBC-G cathode in a 4 m LiBF4 / DME electrolyte at a current density of 80 mA g -1 current density.

[0053] Figure 21 Shows the galvanostatic charge / discharge curves of the LBC-G cathode in a polytetrafluoroethylene solid electrolyte at a current density of 80 mA g -1 current density. Detailed Description

[0054] Some aspects of the present invention provide a lithium battery having a capacity of at least about 200 mAh / g, typically at least about 210 mAh / g, typically at least about 220 mAh / g, more typically at least about 230 mAh / g and more typically at least about 240 mAh / g (total weight of the composite electrode). In other aspects of the present invention, there is provided a lithium battery having an average potential of at least about 4.0 V, typically at least about 4.1 V, and typically at least about 4.2 V (relative to Li / Li + ).

[0055] Such high-capacity and / or high-potential lithium batteries are possible because the inventors have discovered a new electrode in which a lithium salt is intercalated into graphite. Without being bound by any theory, it is believed that in the lithium batteries of the present invention, an anion-redox reaction occurs within the graphite lattice and the oxidized anions are stabilized by intercalation into the graphite lattice, thus avoiding problems associated with conventional batteries using intercalation cathode chemistries.

[0056] Conventional intercalation cathode chemistries used in lithium ion batteries (LIBs) store electrical energy by accommodating Li + in their lattice and charge compensation by cation redox reactions of transition metals (e.g., Ni, Co, Mn, Fe, etc.). They have excellent reversibility (long cycle life), but have relatively low capacity due to the large molar mass of each intercalated Li + and potential structural instability during over-deintercalation. In addition, it is believed that by providing an environment in which an anion-redox reaction of the battery occurs within the intercalation host, a high energy of the anion-redox conversion reaction and excellent reversibility from the topological structure mechanism of intercalation are generated.

[0057] For the sake of brevity and clarity, the present invention will now be described with reference to a composite electrode using a combination of graphite and a lithium halide salt, particularly lithium bromide and lithium chloride. However, it should be understood that the scope of the present invention is not limited to lithium salt-graphite composite electrodes. Generally, any combination of an electrode material and an anion salt can be used in the present invention, which provides an anion-redox reaction occurring within the lattice of the electrode material and stabilization of the oxidized anions within the lattice of the electrode material.

[0058] In some embodiments, the lithium-ion batteries of the present invention include a dual-salt water-in-salt (WiBS) electrolyte. It is believed that the WiBS electrolyte enables or enhances conversion-insertion reactions. As used herein, unless expressly stated or the context otherwise requires, a conversion reaction refers to an anionic oxidation reaction, such as the conversion of bromide ions to bromine gas or chloride ions to chlorine gas, or the conversion of a mixture of bromide and chloride ions to bromine gas, chlorine gas, and / or Br-Cl gas.

[0059] Some aspects of the present invention are based on the anion-redox reactions of halide anions (Br - and Cl - ). In particular, it is believed that both the anion-redox reactions of the halide anions and the resulting oxidation products remain embedded or trapped within the electrodes (e.g., graphite, lattice). In a specific embodiment of the present invention, a composite electrode containing graphite and an equimolar lithium halide salt (LiBr) 0.5 (LiCl) 0.5 -graphite (hereinafter denoted as LBC-G) is prepared as the active material. In some embodiments, the WiBS electrolyte is used in the lithium batteries of the present invention. It is believed that the highly concentrated WiBS electrolyte confines at least a portion of the hydrated LiBr and LiCl within the solid cathode matrix. It is believed that the anion-redox reactions, namely the oxidation of bromide anions and chloride anions to oxidation products, such as Br 0 and Cl 0 , occur within the graphite lattice, and the oxidation products are stabilized by insertion into the graphite structure.

[0060] Other aspects of the present invention provide a lithium-ion battery that utilizes high-density halide ion packing and a water-in-salt electrolyte to achieve a potential of over 4V in an aqueous battery. It is believed that the lithium salt within the graphite lattice is phase-separated from the aqueous electrolyte. Accordingly, other aspects of the present invention provide a rechargeable lithium-ion battery having at least a portion of the lithium salt phase-separated from the aqueous electrolyte. By phase-separating at least a portion of the lithium salt from the aqueous electrolyte, diffusion or shuttling of halide anions and oxidation products of halide anions is avoided, thereby significantly increasing the cycle life of the battery. When referring to a battery, the term "cycle life" is defined as the total number of charges while still maintaining a Coulombic efficiency of at least 99%, typically at least 99.5%, typically at least 99.9%. Alternatively, the term "cycle life" refers to the total number of charge-discharge cycles that a battery can undergo before its capacity drops or falls below about 80%, typically about 85%, typically about 90% of its theoretical capacity. When referring to a battery, the term "cycle" refers to the recharging of the battery, typically from about 5% or less of its charge to at least about 90% of its charge. Thus, one of ordinary skill in the art can readily determine the "cycle life" of a battery by discharging the battery to about 5% or less of its theoretical charge and recharging the battery to at least about 90% of its theoretical charge, and repeating the process until the Coulombic efficiency or capacity of the battery is below the amounts defined herein.

[0061] In some embodiments, the lithium battery of the present invention has a capacity retention of at least about 70%, typically at least about 75%, typically at least about 80%, more typically at least about 85%, more typically at least about 90% after 100 cycles.

[0062] In other embodiments, the lithium battery of the present invention has a capacity retention of at least about 80%, typically at least about 85%, typically at least about 90%, more typically at least about 95% after 100 cycles.

[0063] In other embodiments, the lithium battery of the present invention has a Coulombic efficiency of at least about 80%, typically at least about 85%, typically at least about 90%, more typically at least 95%, most typically at least about 98% throughout its cycle life. In other embodiments, the lithium battery of the present invention has a Coulombic efficiency of at least 99%, typically at least 99.5%, and typically at least 99.9% throughout its cycle life.

[0064] In additional embodiments, the lithium battery of the present invention has an energy density of at least about 250 Wh / kg -1 typically at least about 300 Wh / kg -1 typically at least about 350 Wh / kg -1 more typically at least about 400 Wh / kg -1 more commonly at least about 450 Wh / kg -1It should be understood that the scope of the present invention is not limited to these specific energy densities. In fact, the energy density of a particular battery of the present invention depends on a variety of factors, such as but not limited to lithium salts, anode materials, aqueous electrolytes, etc.

[0065] At a high de-lithiation / lithiation potential of 4.0–4.5 V versus Li / Li + , the calculated theoretical energy capacities of LiBr and LiCl are 309 mAh g -1 and 632 mAh g -1 respectively. These values of theoretical energy capacities and potentials are significantly higher than those of other anions, such as sulfur at ~2.2 V or oxygen at ~3.0 V. The reversible redox reactions of these halide anions followed by intercalation into graphite produced densely loaded stage-I intercalation compounds C 3.5 [Br 0.5 Cl 0.5 , with a corresponding total capacity of 243 mAh g -1 (based on the total mass of the LBC-G cathode). By coupling the LBC-G cathode with the protected graphite anode disclosed by the present inventors (see Yang, C. et al. 4.0 V Aqueous Li-Ion Batteries. Joule 2017, 1, 122-132), a 4.0 V-class aqueous full cell was fabricated, providing an energy density (460 Wh kg -1 ) even higher than that of most state-of-the-art LIBs (300-400 Wh kg -1 ). Such a previously unseen high energy density, together with the inherent safety of its aqueous nature and the much lower cost of the halide active materials compared to diverse transition metal oxides, is part of the many advantages of the rechargeable lithium-ion battery of the present invention.

[0066] Utilizing the anion-redox reactions of halide anions (Br - and Cl - ), a composite electrode containing graphite and equimolar lithium halide salts (LiBr) 0.5 (LiCl) 0.5 -graphite (hereinafter denoted as LBC-G) was prepared as the active material. The highly concentrated WiBS electrolyte confines the partially hydrated LiBr and LiCl within the solid cathode matrix, and upon oxidation, Br 0 and Cl 0 are stabilized by intercalation into the graphite structure. At a high de-lithiation / lithiation potential of 4.0–4.5 V versus Li / Li + , the theoretical capacity of LiBr is 309 mAh g -1 , and the theoretical capacity of LiCl is 632 mAh g -1, above sulfur at ~2.2 V or oxygen at ~3.0 V. The reversible redox reactions of these halide anions are then embedded in graphite to produce a densely loaded stage-I intercalation compound C 3.5 [Br 0.5 Cl 0.5 , corresponding to a total capacity of 243 mAh g -1 (based on the total mass of the LBC-G cathode).

[0067] By coupling the LBC-G cathode with the protected graphite anode disclosed by the present inventors (see Yang, C. et al. 4.0 V Aqueous Li-Ion Batteries. Joule 2017, 1, 122 - 132), a 4.0 V-class aqueous full cell was fabricated, providing an energy density (460 Wh kg -1 ) even higher than that of most state-of-the-art LIBs (300 - 400 Wh kg -1 ). Such a previously unseen high energy density, together with the inherent safety of its aqueous nature and the much lower cost of the halide active material compared to diverse transition metal oxides, is part of the many advantages of the rechargeable lithium-ion battery of the present invention.

[0068] This conversion-intercalation LBC-G chemistry is significantly different from the anions of all graphite-intercalation chemistries (e.g., PF6 - , BF4 - , TFSI - ) in at least two aspects: First, the LBC-G cathode stores the anion sources (Br - and Cl - ) in a high-density solid state rather than in a dilute liquid electrolyte. Thus, the capacity is not limited by salt solubility or electrolyte weight in principle. Second, during charging, the oxidizing species in LBC-G are bromide / chloride anions, and the graphite host remains almost intact, while the graphite cathode in a so-called "dual-ion" battery is oxidized by carrying electron holes, and the anion intercalants (PF6 - , BF4 - , TFSI - ) maintain their chemical states. Since the oxidation states of Br and Cl intercalants in graphite are close to zero, the small Coulombic repulsion between them results in a high-density graphite intercalation compound (GIC) of C 3.5 [H] (H = halogen) in sharp contrast to "dual-ion" batteries, where only intercalation compounds with general formulas C 24 + [X - or C 20 + [X - (X -= PF6 - , BF4 - , TFSI - etc.) diluted GICs with a capacity < 120 mAh g -1 . In addition, LBC-G chemistry is also different from traditional conversion cathodes such as transition metal halides (FeF2, CuF2, etc.) and anion redox couples (S / S n 2- , O / O 2- , Br3 - / Br - etc.). Compared with transition metal halides, the potential and energy of anion redox are much higher than those of transition metal cation redox. In addition, compared with the crystal reconstruction reaction in transition metal halides, the rate of halogen intercalation into graphite in LBC-G is also faster and more reversible, which is always accompanied by large kinetic hysteresis, large volume changes and irreversible particle disintegration. For anion redox couples (S / S n 2- , O / O 2- , Br3 - / Br - etc.), although the dissolution of intermediates also improves the reaction kinetics, the final charging products are usually deposited or adsorbed on the high-surface-area carbon matrix, resulting in side reactions, parasitic shuttle effects and low volumetric energy density. During the repeated cycling of LBC-G, the use of a super-concentrated WiBS electrolyte can confine the halide anions in the hydration layer that is thermodynamically immiscible with WiBS in the cathode solid composite, while the highly reactive oxidation products (BrCl, gaseous at room temperature) are effectively stabilized by intercalating into graphite, thus ensuring a high degree of reversibility of this conversion-intercalation chemistry.

[0069] The LBC-G composite cathode was prepared by mixing anhydrous LiBr and LiCl with graphite powder at a mass ratio of 2:1:2 (corresponding to a molar ratio of (LiBr) 0.5 (LiCl)0.5C 3.7 ). The electrochemical behavior of the LBC-G composite cathode was evaluated in a three-electrode cell, where activated carbon (about 50 times the mass of the working electrode) was used as the counter electrode, Ag / AgCl as the reference electrode, and a hydrogel polymer of 80 wt.% WiBS (21 mol kg -1 lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) - 7 mol kg -1Lithium trifluoromethanesulfonate (LiOTf) is dissolved in water and 20 wt.% polyethylene oxide (PEO) is used as the electrolyte. After exposure to the WiBS electrolyte (20 times the mass of the working electrode), the anhydrous LiBr-LiCl salt in LBC-G extracts trace water (about 2.4%) from the WiBS, forming a hydrated LiBr-LiCl layer on the LBC-G surface (the overall chemical formula of the hydrated salt is estimated to be LiBr·0.34H2O-LiCl·0.34H2O), which accelerates the redox reaction of halogens in the form of solvated anions. Figure 1 . At the same time, this hydrated salt layer undergoes thermodynamic phase separation from the bulk WiBS electrolyte and establishes a dynamic water balance. This liquefied layer allows Li + transport, but blocks the diffusion of halide ions and potential unwanted shuttling, as demonstrated by MD simulations and the extremely low chlorine and bromine contents (<32 ppm) detected by chromatographic analysis in the WiBS electrolyte that has been equilibrated with lithium chloride-lithium bromide solution for 500 hours.

[0070] The cyclic voltammogram of LBC-G ( Figure 2 ) and the charge / discharge curve ( Figure 3 ) respectively show two different reactions of Br + insertion at 4.0–4.2 V relative to Li / Li - and Cl + insertion at 4.2–4.5 V relative to Li / Li - , providing a highly reversible discharge capacity of 243 mAh g -1 (accounting for the total mass of the LBC-G composite material, including the LiBr / LiCl salt and graphite), where 82% remains unchanged after 230 cycles at a current density of 80 mA g -1 (0.2C), and the coulombic efficiency is 100% after the 80th cycle. The two-step redox reaction corresponds to:

[0071]

[0072]

[0073] where n is the molar ratio of carbon atoms to the halogen inserted in the GIC. During charging, Br - in the hydrated layer with a relatively low redox potential is first electrochemically oxidized to an oxidation state close to zero (Br 0 ) and inserted into the adjacent graphite interlayer to form Br2 GICs as C n [Br] (eq.1). After further charging, the oxidation of Cl - in the hydrated layer and the insertion of Cl 0The insertion of occurs at a higher potential (Equation 2), which has not been observed so far, to form the mixed insertion compound C n [BrCl]. The oxidation of each halogen involves an electron transfer and provides the same molar capacity for Br and Cl, respectively. Meanwhile, Li + flows out into the bulk electrolyte and is reduced at the anode. During discharge, the reverse reaction occurs, i.e., Cl and Br are sequentially removed from the graphite interlayer, reduced, and recombined with the returning Li + to form solid LiCl and LiBr crystals and liquefied halides outside the graphite matrix. Therefore, all the active materials LiCl and LiBr are well retained in the solid-state electrode without significant loss due to dissolution and shuttling. The thermodynamic reaction potential of LBC-G was confirmed by density functional theory (DFT) calculations. The fully charged product C 3.5 [Br 0.5 Cl 0.5 of the LBC-G composite achieves a theoretical storage capacity of 251 mAh g -1 at an average potential of ~4.2 V. In this conversion-insertion chemistry, the WiBS electrolyte plays a role in its electrochemical reversibility because its water molecules are not oxidized until the potential is 4.9 V relative to Li / Li +1 , thus enabling the oxidation / reduction reversibility of the halides at intermediate potentials (4.0–4.5 V). As Figure 4 shown, only the halogens are oxidized while the Ti current collector and graphite remain intact at the operating potential.

[0074] The galvanostatic intermittent titration technique (GITT) was used to examine the quasi-equilibrium potential and reaction kinetics at different stages. The quasi-equilibrium potential of Br - is ~4.05 V, and the quasi-equilibrium potential of the Cl - oxidation / insertion reaction is ~4.35 V ( Figure 5 ), while the total diffusion coefficient is estimated to be 10 -15 –10 -13 cm 2 s -1 (red and blue curves in the inset of Figure 5 ). The diffusion coefficient of the LBC-G cathode was also studied using electrochemical impedance spectroscopy (EIS), where the Nyquist plot ( Figure 6 ) shows two semicircles with characteristic frequencies of ~1250 Hz and ~20 Hz, respectively. The semicircle in the high-frequency range is attributed to the charge transfer resistance on the surface of the graphite matrix, while the semicircle in the intermediate-frequency range corresponds to the salt dissolution / precipitation in the hydration layer and the limited diffusion of reactants. The sloping tail in the low-frequency range is due to the halogen diffusion in the graphite. By fitting the Nyquist plot with an equivalent circuit, the apparent ionic diffusion coefficient of the reactants (including dissolution / precipitation) is estimated to be 6.85×10-15 to 2.07×10 -14 cm 2 s -1 ( Figure 5 (the green circles in the illustration of - Br - and Cl

[0075] LBC-G provides a practical weight capacity of 231 mAh g + at an average discharge voltage of 4.2 V vs. Li / Li -1 (total electrode weight), a volume capacity of 450 mAh mL -1 (total electrode volume), resulting in an extremely high energy density of 970 Wh kg -1 , almost twice that of Ni, Co, and Mn-based intercalation cathode materials, or comparable to sulfur conversion cathodes. However, the volume energy density of LBC-G is much higher than that of sulfur. LBC-G has high weight and volume energy densities, and its conversion-intercalation nature makes it one of the most useful cathode chemistries for lithium-ion batteries.

[0076] In-situ Raman spectroscopy (100 - 550 cm -1 ) was carried out to probe the intercalation mechanism of halogen species during the charge / discharge process of LBC-G ( Figure 7 ). When the state of charge (SOC) was from 0% to 50%, a characteristic peak (ω0 = 242 cm -1 ) was detected, which corresponded to the stretching mode of Br2 molecules intercalated in graphite. Further charging introduced a new characteristic peak for BrCl intercalation (ω0 = 310 cm -1 ), which was verified by a reference prepared by chemically intercalating BrCl into graphite. The peak intensity of the BrCl intercalant increased as LBC-G was charged to 4.5 V. Charge transfer in the graphene layer weakened the interatomic bonds of the halogen intercalants, resulting in a decrease in the frequency of free Br2 molecules (liquid) from 318 cm -1 to 242 cm -1 for the Br2 intercalant, and a decrease in the frequency of free BrCl molecules (gaseous) from 427 cm -1 to 310 cm -1 for the BrCl intercalant. It should be noted that during the charge / discharge process between 3.2 V and 4.5 V, no free Br2 or BrCl peaks were detected, unless the fully intercalated BrCl GIC was deliberately damaged with a high-intensity laser beam (red curve, Figure 7)。It is believed that all the halogen generated from the redox reaction of the halide anions is intercalated into the graphite structure rather than merely adsorbed on the surface of the graphite flakes. During the discharge process, a completely reversible change in the Raman spectrum was observed.

[0077] The oxidation states of the halogens at various SOCs, which reflect their redox reaction sequence in the LBC-G cathode, were monitored using ex-situ X-ray absorption near-edge structure (XANES) spectroscopy. For the Br K-edge, due to the 1s→4p transition within the Br atom, a distinct and sharp peak appeared at ~13473 eV, which emerged immediately after charging the LBC-G cathode. See Figure 8 。The intensity of this "white line" peak, which reflects the hole density in the Br 4p orbital, gradually increased with the blue shift of the absorption edge (1s→continuum, ~13480 eV). Apparently, Br - carried holes and was oxidized to Br 0 from the beginning of the charging process. Figure 9 ) For the Cl K-edge ( - ), only a single absorption edge at ~2825 eV (1s→continuum) was observed during the first charging plateau (SOC: 0%–50%), indicating that all Cl remained in the -1 oxidation state. The oxidation of Cl in the LBC-G cathode seems to occur only during the second charging plateau (SOC: 50%–100%), as evidenced by the appearance of its "white line" peak (~2821 eV), which is attributed to the 1s→3p transition within the Cl atom. Compared with the reference spectra of chemically intercalated Br2 in GIC and liquid Br2 ( Figure 8 the dashed line in 0 ), it is obvious that most of the Br was oxidized, but it did not fully reach Br 0 during the first charging plateau (SOC: 0%–50%). According to the distribution of the electron density in the DFT simulation, due to the charge transfer of the graphene layer, the oxidation state of Br remained at approximately -0.16 in the Br2 GIC at 50% SOC. The subsequently intercalated Cl tended to combine with the earlier intercalated Br, and due to its relatively lower electronegativity than Cl, the oxidation state of Br further increased approaching Br

[0078] This halogen conversion-intercalation mechanism in the LBC-G cathode is also supported by the charge / discharge curves of the LBC-G cathode at different LiBr and LiCl molar ratios. Figure 10 and 11 . The capacity ratio of the two charging / discharging plateaus is highly correlated with the LiBr / LiCl molar ratio in the LBC-G cathode, indicating that the two different potential plateaus are respectively attributed to the separate redox reactions of Br and Cl. At the low potential plateau (<4.25 V,Figure 10 ) At low rates ≤ 0.2C, the specific capacity calculated from the weight of LiBr in the LBC-G cathode is very close to the theoretical redox capacity of LiBr (309 mAh / g), while the high potential charge plateau (> 4.25 V), when calculated according to the weight of LiCl, is close to the theoretical redox capacity of LiCl (632 mAh / g, Figure 11 ). Interestingly, the Coulombic efficiency of the LBC-G cathode in the high voltage plateau increases with the increase of the LiBr / LiCl ratio, indicating that the 0 separate intercalation of Cl in graphite is not thermodynamically stable unless it is paired with Br 0 . This is because the most stable C n [Br / Cl] intercalation compound in graphite is achieved when the LiBr / LiCl ratio is close to 1:1. In sharp contrast, in the absence of the graphite host, pure (LiBr) 0.5 (LiCl) 0.5 can provide high oxidation ability during the initial charge, but the discharge ability is very low due to the loss of gaseous halogens. The carbon host can improve the reversibility and discharge capacity by surface adsorption of halogens, and the Coulombic efficiency further increases with its graphitization degree. It is believed that graphite intercalation provides a reversible and compact way to accommodate the oxidation products of halogens.

[0079] In-situ Raman spectroscopy (1200 - 2850 cm -1 ) shows the structural evolution of the graphite superlattice during the halogen intercalation process. Figure 12 . The number of GIC stages m provides important information, which is defined as the number of non-intercalated graphene layers between two nearest layers filled with the intercalated guest species. The graphite G band (1584 cm -1 ) gradually weakens and splits into a doublet (E 2g2 (b) mode and E 2g2 (i) mode) during halogen intercalation (charging), and evolves into the characteristic peak of the stage-II GIC structure at 50% SOC (at 1612 cm -1 , the G2 band of the E 2g2 (b) mode). At the fully charged state, the peak further shifts to 1631 cm -1 , indicating the stage-I GIC structure. In addition, the D band of graphite (1350 cm -1 ) disappears immediately after intercalation into graphite, which is a typical property of GIC. During the discharge process, a completely reversible change in the Raman spectrum is observed.

[0080] X-ray diffraction (XRD) spectra reveal the detailed evolution of the staged structure of the LBC-G cathode. The ex-situ XRD of the LBC-G cathode (reflection geometry, Figure 13)The mobile main peak at (00m + 1) and the secondary main peak at (002m + 2) during halogen insertion / extraction are shown, further confirming the reference pattern. A careful examination shows that when the SOC of LBC-G increases from 0% to 50%, the d-spacing of the main peak changes from that of pristine graphite (002) to that of stage-II Br2GIC Due to the slightly lower height of the insertion channels, it is believed that further insertion of Cl results in a gradual reduction of the d-spacing and finally reaches stage-I BrClGIC at 100% SOC in agreement with the insertion process revealed by Raman spectroscopy. In-situ XRD of the LBC-G cathode ( Figure 14 ) shows that the d-spacing of (00m + 1) undergoes a continuous shift during charge / discharge, indicating that the graphene interlayers gradually expand and accommodate halogen atoms. The complete reversal of the above process is again observed during discharge, indicating that the graphite structure is fully restored after deintercalation, which provides the basis for excellent reversibility. The formation of the GIC with the highest concentration in stage-I ensures the high capacity of the conversion-insertion chemistry of LBC-G. The reaction mechanisms proposed in Reactions 1 and 2 are confirmed by the consistency between the stage numbers of LBC-GIC and the corresponding charge / discharge capacities.

[0081] The in-plane configuration and coordination of the halogen intercalants in GIC provide a way to determine the optimal intercalation concentration of the LBC-G cathode chemistry. Since the in-plane insertion structure is independent of the intercalation concentration, the stoichiometry n of C n [Br] and C n [BrCl] always remains the same in each intercalation domain, regardless of the overall intercalation concentration. Ex-situ high-energy XRD (vertical incidence) of the LBC-G cathode (after removing the electrolyte and current collector) at 50% and 100% SOC ( Figure 15 ) shows multiple asymmetric and overlapping peaks instead of the intrinsic peaks of the graphene layers and PTFE binder, revealing a mild long-range ordering of the in-plane configuration of the intercalants. At 50% SOC, only three peaks at low diffraction angles can be indexed based on the single-crystal Br2 GIC reference, indicating the coexistence of multiple phases, local disorder, and structural strain. DFT simulations predict multiple possible in-plane configurations based on integer multiples of two stoichiometries n = 7 and 8, all of which reveal the nearest in-plane distances of the zig-zag polymer chains –Br–Br– or –Br–Cl– to be ( Figure 16A and 16B insets). Interestingly, all these models have very similar potentials (within 20 mV), indicating that the real material may be slightly disordered due to the coexistence of these idealized model structures, as demonstrated by the ex-situ XRD patterns ( Figure 15)。Molecular dynamics simulations predict that Br–Br contacts lead to overall structural disorder due to a slight excess of Br or interactions between adjacent intercalated chains. However, after an additional 100 ps of simulation under constant pressure conditions, no signs of deflation and subsequent graphite exfoliation were observed, even after a short annealing to 360 °C and relaxation back to 60 °C.

[0082] By fitting the Br extended X-ray absorption fine structure (EXAFS) of the LBC-G cathode at 50% and 100% SOC ( Figure 16A and 16B ), the most compatible models are C 7m [BrBr] and C 7m [BrCl], both with two sets of nearest in-plane distances (Br–X1 and Br–X2, X = Br or Cl), rather than the consistent distances of C 8m [BrBr] and C 8m [BrCl]. Due to the π-electron interaction with the graphene plane, the average of the nearest in-plane distances for the halogen intercalants is for Br–Br1, for Br–Br2, for Br–Cl1, for Br–Cl2, longer than the bond distances of Br2 and BrCl free molecules. However, these nearest in-plane distances are much shorter than those in alkali metal GIC - and large anion GICs (e.g., PF6 - , BF4 - , TFSI ), which makes the halogen intercalants have the highest in-plane density among all reported GICs. Without being bound by any theory, it is believed that this high-density packing is mainly due to the near-zero oxidation state of the halogen intercalants, which generates much lower Coulombic repulsion from the average effective charge of ~−0.16 per halogen atom, while the Coulombic repulsion in Li GIC is higher than +0.90, and that in large anion GICs is higher than −1.

[0083] An aqueous LIB full cell was constructed by using an aqueous gel electrolyte derived from WiBS and coupling the LBC-G cathode with a graphite anode protected by a highly fluorinated ether (HFE) polymer gel. A stable discharge capacity of 127 mAh / g (total anode and cathode mass) was obtained at an average voltage of 4.1 V at 0.2C ( Figure 17 ), and 74% of the initial capacity was retained over 150 cycles with an average Coulombic efficiency of 99.8% ( Figure 18)。A low self-discharge rate indicates that the ultra-concentrated hydrogel electrolyte effectively suppresses unwanted reactions, especially water decomposition and the loss of cathode halogen active materials.

[0084] Since forming a hydrated LiBr / LiCl layer by extracting 2.4 mol% of water from WiBS is important for achieving high power density, the mass ratio of WiSB electrolyte to the cathode may affect the rate performance of the LBC-G cathode. As Figure 19 shown in the upper part of, when the electrolyte / electrode (cathode + anode) mass ratio is reduced from 4:1 to 1:2, the rate performance is affected. Therefore, in some embodiments, the electrolyte / electrode ratio is about 1:1, typically about 2:1, typically about 4:1. On the other hand, a high ratio of electrolyte to electrode will reduce the energy density. One solution is to use lithium bromide and lithium chloride monohydrates (LiBr·H2O and LiCl·H2O) instead of their anhydrous salts when preparing the LBC-G cathode, which will eliminate the strong dependence on the WiBS electrolyte as a water source. The LBC-G cathode with monohydrates shows almost the same charge / discharge curve as the anhydrous cathode at a low rate of 0.2C, except for a slightly lower specific capacity ( Figure 17 and 18 ), which is due to the additional water brought by these monohydrates. However, the rate capability of the LiBr·H2O-LiCl·H2O-G / / G full cell is much higher than its anhydrous counterpart, while minimizing the influence of the electrolyte / electrode mass ratio. Since the performance of the battery constructed with LiBr-LiCl monohydrates is independent of the electrolyte weight, it is estimated that the energy density of such aqueous LIBs is about 460 Wh kg of the total mass of the cathode (containing monohydrates) and the anode -1 . Such an energy density has never been reported for any known aqueous battery, even higher than all known state-of-the-art non-aqueous LIBs. Even when counting the electrolyte weight, the full cell energy density can still reach 304 Wh kg -1 . It should be remembered that due to the aqueous nature, this high energy density has inherent safety and environmental insensitivity. This new aqueous cathode chemistry disclosed herein provides a battery with cost-effectiveness, safety, flexibility, and higher energy.

[0085] A non-aqueous LIB coin cell is constructed by using a high-concentration organic electrolyte and coupling the LBC-G cathode with a lithium anode. A high discharge capacity of 151 mAh / g (based on the cathode mass) was obtained at a current density of 80 mAg -1 ( Figure 20 ). Similar to the aqueous system, the two-stage reaction involves Br -1 (~3.6V) and Cl -1(~3.8 V) oxidation and their subsequent insertion into the graphite structure. The discharge capacity decreased to 83 mAh / g, corresponding to an initial Coulombic efficiency of 55%. The stable decay was mainly attributed to Br2 dissolution. For the Nafion solid electrolyte, Br2 dissolution can be effectively prevented, showing more stable charge-discharge performance( Figure 21 ).

[0086] Other objects, advantages, and novel features of the present invention will become apparent to those skilled in the art after examining the following embodiments of the present invention, which are not intended to be limiting. In the embodiments, the procedures constructively simplified to practice are described in the present tense, while the procedures performed in the laboratory are stated in the past tense.

[0087] Examples

[0088] Preparation of electrodes. For the three-electrode (LiBr) 0.5 (LiCl) 0.5 -graphite composite (denoted as sample LBC-G), which was obtained by uniformly mixing anhydrous LiBr (99.9%, Sigma-Aldrich), LiCl (99.9%, Sigma-Aldrich), and synthetic graphite powder( KS4, average particle size ~4.1 μm) by zirconia ball milling for 15 minutes. The molar ratio of LiBr / LiCl was 1:1, while the mass ratio of LiBr / LiCl / graphite was ~2:1:2. In the full cell containing LiBr / LiCl monohydrate, all procedures were the same except that anhydrous LiBr / LiCl was replaced with LiBr·H2O (99.95%, Sigma-Aldrich) and LiCl (99.95%, Sigma-Aldrich). By adjusting the composites (LiCl / graphite in LiCl-graphite was ~1:3; (LiBr) 0.5 (LiCl) 0.5 -Ti with LiBr / LiCl / titanium nanoflakes being ~2:1:60; (LiBr) 0.5 (LiCl) 0.5 -AC with LiBr / LiCl / activated carbon being ~2:1:9; (LiBr) 0.5 (LiCl) 0.5 -CB with LiBr / LiCl / graphite acetylene black being ~2:1:9), other control samples were obtained. The composite LBC-G cathode was fabricated by compressing the LBC-G composite and poly(vinylidene fluoride) (PTFE) on a titanium metal mesh (Alfa Aesar, 100 mesh) at a weight ratio of 95:5. The areal loading of the cathode material was ~38 mg cm -2。The thickness of the cathode is ~200 μm. A graphite anode is fabricated by using synthetic graphite powder ( particle size ~45.4 μm) and poly(vinylidene fluoride) (PTFE) on a stainless steel mesh (200 mesh) at a weight ratio of 9:1.

[0089] Preparation of the electrolyte. First, a liquid “dual-salt-in-water” aqueous electrolyte is prepared by dissolving 21 mol kg -1 LiTFSI (98%, TCI Co., Ltd.) and 7 mol kg - 1 LiOTf (99.996%, Sigma-Aldrich) in water (HPLC grade). An aqueous gel electrolyte is prepared by mixing 20 wt.% poly(ethylene oxide) (PEO, average M v ~600000, Sigma-Aldrich) with the WiBS electrolyte and heating it in a sealed glass mold at 80 °C for 1 h. After cooling to room temperature, a viscous semi-solid WiBS gel electrolyte is obtained, which can be shaped into any form at 50 °C.

[0090] Preparation of the HFE-PEO gel protective coating. Briefly, 1,1,2,2-tetrafluoroethyl-2',2',2'-trifluoroethyl ether (Daikin America or Apollo) is mixed with 0.5 M LiTFSI (denoted as LiTFSI-HFE gel) and 10 wt% PEO (Sigma-Aldrich) in a substance in HFE / FEC (volume ratio = 95:5), and heated at 70 °C for 5 min with stirring.

[0091] Preparation of chemical GIC as a reference sample. Chemically intercalated Br2 and BrCl GIC are synthesized as reference samples according to the reported procedures. For example, see Heald, S.M. & Stern, E.A. EXAFS study of Br2-graphite intercalation compounds. Synthetic Metals 1, 249-255, (1980); and Furdin, G., Bach, B. & Herold, A.A., C.R. Acad. Sci., Ser. C 271, 683, (1970). Briefly, Br2 and BrCl GIC are prepared by exposing graphite flakes ( KS4) to the vapors of highly concentrated Br2 (99.99%, Sigma-Aldrich) and BrCl gas in a well-sealed flask for 2 h. At -70 °C, BrCl is prepared by mixing Br2 with an equimolar amount of Cl2 obtained from the reaction of trichloroisocyanuric acid with hydrochloric acid.

[0092] Electrochemical measurements. In a three-electrode cell, the LBC-G electrode (or other reference electrode) serves as the working electrode, activated carbon serves as the counter electrode, and Ag / AgCl serves as the reference electrode. The mass ratio of the working electrode to the electrolyte is 1:20. Then, the three-electrode cell is subjected to constant-current charge / discharge at room temperature using a Land BT2000 battery test system (Wuhan, China). Cyclic voltammetry is performed using a CHI 600E electrochemical workstation. The GITT experiment is conducted in a three-electrode setup with the same electrode configuration. The cycling protocol consists of alternating 20-minute 0.2C current pulses with 120-minute OCV periods to reach the quasi-equilibrium potential. At different charge / discharge states, the apparent ionic diffusion coefficient (D) of the reactants in the LBC-G cathode is measured by GITT and estimated using the following relationship:

[0093]

[0094] where I is the applied constant current density, V m is the molar volume of partially hydrated LiBr / LiCl, F is the Faraday constant (96486 C mol -1 ), S is the contact area between the electrolyte and the active material, dE / dx is the slope of the coulometric titration curve of composition x, and dE / dt 1 / 2 can be obtained from the plot of the transient voltage versus the square root of time during the constant-current pulse. Four-point EIS measurements are performed using a Gamary 345 interface 1000, with a 5 mV perturbation and the required frequency range.

[0095] Using LBC-G as the cathode and a sulfur-carbon or graphite electrode as the anode, a full cell is assembled as a CR2032-type button cell. For the graphite anode cell, the cathode / anode mass ratio is set to 1.38:1. A titanium metal foil is applied between the cathode and the button cell case to prevent corrosion. The WiBS gel electrolyte is pressed into a film and applied as the electrolyte and separator in the button cell. The total mass ratio of the electrodes to the electrolyte ranges from 1:4 to 2:1. After assembly, the cell is heated to 50 °C for GPE self-healing. Then, the full cell is subjected to constant-current cycling at room temperature on a Land BT2000 battery test system (Wuhan, China).

[0096] The specific (weight or volume) energy density (E) of the full cell is calculated by the following formula

[0097] E = C × U (4)

[0098] where C is the specific (weight or volume) battery capacity and U is the average output battery voltage. The weight capacity C m is calculated by the following formula

[0099]

[0100] where C 电池 is the absolute battery capacity. M 阴极 is the total mass of the cathode, including LiBr, LiCl, graphite, and PTFE binder. M 阳极 is the total mass of the anode, including graphite, PTFE binder, and polymer passivation coating.

[0101] In-situ Raman and XRD studies. For in-situ Raman studies, the LBC-G full cell (button cell configuration) was charged and discharged at 0.1C. A quartz optical window (φ = 5 mm) was applied on the cathode side. Raman spectra were collected using a laser between 3500 and 60 cm -1 (wavelength = 532 nm) by Horiba JobinYvon LabramAramis. Four by four data points were collected to obtain a high signal-to-noise ratio.

[0102] For ex-situ X-ray diffraction (XRD) studies, after charging / discharging to a specific SOC at 0.1C, the LBC-G electrode (working electrode) was retrieved from the three-electrode cell. For in-situ X-ray diffraction (XRD) studies, a full cell (button cell configuration) was charged and discharged at 0.1C. Kapton windows (φ = 3 mm) were applied on both sides of the button cell, where the anode was deliberately placed to avoid the beam passing through the window. X-ray diffraction patterns were recorded on a Bruker D8 Advance X-ray diffractometer with CuKα radiation in grazing-incidence geometry. High-energy synchrotron XRD measurements were carried out on the 11-ID-C beamline at the Advanced Photon Source (APS) of Argonne National Laboratory. High-energy X-rays with a beam size of 0.2 mm × 0.2 mm and a wavelength of were used to obtain two-dimensional (2D) diffraction patterns in transmission geometry. X-ray patterns were recorded using a Perkin-Elmer large-area detector placed 1800 mm from the cell unit. The interval between subsequent diffraction patterns was 5 minutes. The obtained two-dimensional diffraction patterns were calibrated using a standard CeO2 sample and converted to one-dimensional patterns using Fit2D software.

[0103] The periodic repeat distance (I C ) and the intercalation channel height (d i ) of the GIC can be calculated using the following equations:

[0104]

[0105] where l is the index of the (00l) plane in the stacking direction, d obsis the observed value of the spacing between two adjacent planes in the XRD pattern and can be calculated from the diffraction angle according to Bragg's law. The d-spacing of pristine graphite is The intensity pattern is common for the m-th stage graphite intercalation compound (GIC), where the most prominent peak is (00m + 1). The d-spacing value of (00m + 1) is calculated from the XRD data according to Bragg's law, and the main phase of the observed GIC can be specified.

[0106] Ex-situ XANES and EXAFS studies. Ex-situ X-ray absorption spectroscopy (XAS) measurements were carried out on the same cell configuration used for in-situ XRD measurements. The experiments were conducted in the transmission mode at beamline 20-BM-B of the APS at Argonne National Laboratory. XANES measurements were performed at the K edges of bromine (13474 eV) and chlorine (2825 eV) to monitor the valence state changes of Br and Cl in the cathode, and the first derivative points of the XANES spectrum of Bi were used for energy calibration (L III -edge = 13419 eV). During the Cl measurement, the entire X-ray beam, sample, and detector were protected by helium gas. Reference spectra were collected for each in-situ spectrum, where a bismuth metal foil was placed in the reference channel. The EXAFS spectra were aligned, merged, and normalized using Athena. The coin cell was charged to a specific voltage with a constant current before the measurement.

[0107] The Athena program was first used to process the experimental X-ray absorption data to extract the normalized oscillation amplitude χ exp (k), and the photoelectron wave number k is given by where E0 is the absorption edge energy. The theoretically calculated χ th (k) is given by the EXAFS equation:

[0108]

[0109] where j represents the shell with the same backscattering, N j is the coordination number of the shell, f j is the backscattering amplitude, R j is the average distance, σ j is the mean square variation, δ j is the scattering phase shift, λ is the effective mean free path, is the amplitude reduction factor, and FEFF6 is used to calculate f j δ j and λ. The experimental data were fitted to refine the structural parameters, N j R j σ 2was completed using the Artemis program. The initial crystal structure for fitting was taken from the DFT-optimized phase II C7[Br] and phase I C 3.5 [Br 0.5 Cl 0.5 . was fixed at 1.0. Two ΔE values were used in the fitting, one for the Br-Br (or Cl) path and the other for the left Br-C path.

[0110] SEM imaging and specific surface area measurement. SEM of the cycled cathode was carried out in a Hitachi S-4700 operating at 5 kV. The specific surface area of the samples was characterized by N2 adsorption using a Micromeritics ASAP 2020 Porosimeter Test Station. Before testing, the samples were degassed at 180 °C (in vacuo) for 12 h. The specific surface area was calculated from the adsorption branch using the BET method.

[0111] Molecular dynamics simulations of LiBr in WiSE. MD simulations were carried out for aqueous solutions of 18 m (molal salt / kg solvent) LiBr and mixed salts (18 m LiBr + 21 m LiTFSI) at 363 K. The MD simulations used a previously modified CHARMM H2O force field 47 (force field 47 ) combined with the LiTFSI many-body polarization force field for APPLE&P in water, which was used to predict the ionic conductivity, self-diffusion coefficients of ions and water, viscosity, and density of LiTFSI-H2O, in excellent agreement with experiments over a wide range of salt concentrations from 5 m to 21 m.

[0112] A parallel version of an in-house developed MD simulation package was used for the MD simulations. The 18 m LiBr in the H2O simulation cell contained 448 LiBr and 1390 H2O molecules. The mixed salt MD simulation cell contained 1380 H2O, 512 LiTFSI, and 448 LiBr. All simulated (LiTFSI) n (LiBr) m (H2O) k complexes yielded large simulation cells of 70 and . The simulation box size was gradually reduced to For the mixed salt system at 363 K, NPT simulations were carried out for 2 ns at 363 K using a modified force field with increased repulsion between Br / Br and TFSI / TFSI anions in order to disperse them uniformly in the simulation box. After 9 ns of MD simulation in the NPT ensemble, LiBr(H2O) n was largely in agreement with LiTFSI(H2O) mDomain separation. This behavior indicates the initial stage of phase separation and is consistent with experimental observations.

[0113] The Ewald summation method is used in MD simulations to handle the electrostatic interactions between permanent charges with permanent charges and permanent charges with induced dipole moments of vectors with k = 6 3 using multi-time step integration, where the inner time step is 0.5 fs (bonded interactions); for all non-bonded interactions within the cutoff distance, the central time step is 1.5 fs, and for and all non-bonded interactions between the non-bonded cutoff distances of the smaller of -2 and 0.1×10 -4 fs, the outer time step is 3.0 fs. The reciprocal part of Ewald is only updated at the maximum of the multiple time steps. The Nose-Hoover thermostat and barostat are used to control the temperature and pressure, with the relevant frequencies being 10

[0114] The ability of MD simulations using the atomic dipole polarizable APPLE&P force field to predict the density and conductivity of 18 m LiBr in H2O was examined at 333 K. After 3 ns of equilibration in the NPT ensemble, 8 ns of MD simulations in the NVT ensemble predicted an electrolyte density of 1649 kg m -3 which is 0.8% higher than the experimental density of 1636.5 kg m -3 . 50 The ionic conductivity (σ) is obtained using the Einstein relation shown in the following equation:

[0115]

[0116] where e is the electronic charge, V is the volume of the simulation box, k B is the Boltzmann constant, T is the temperature, t is the time, z i and z j are the Li + and Br - charges, R i (t) is the displacement of ion i within time t, < > represents the overall average, and N is the number of diffusion times. Due to the finite size of the simulation cell, long-range hydrodynamic interactions limit the diffusion. The leading-order finite-size correction (FSC) for the self-diffusion coefficient is given by the following equation:

[0117]

[0118] where k Bis the Boltzmann constant, T is the temperature, L is the linear dimension of the simulation periodic cell, and is the viscosity. After FCS correction, the MD simulation predicts the conductivity of 18 m LiBr electrolyte to be 75 mS / cm, which is 30% lower than the experimentally determined conductivity of 98.89 mS / cm, but is accurate enough for high-concentration electrolytes.

[0119] DFT simulations of the embedding structure configurations. All calculations were performed using DFT with a plane-wave basis set and the projector augmented wave (PAW) method, as implemented in the Vienna Ab Initio Simulation Package (VASP). The Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) was used to calculate the exchange–correlation energy. An energy cutoff of 580 eV was used for the plane-wave basis, and the Brillouin zone was sampled using the Monkhorst–Pack scheme. The optB86b van der Waals density functional (vdW-DF) was used to correct the van der Waals energy to obtain accurate values of the layer spacing in all cases. Two possible configurations of C7[Br], C 3.5 [Br 0.5 Cl 0.5 and C8[Br], C4[Br 0.5 Cl 0.5 were considered. In these configurations, the Br and Cl atoms were randomly initialized. Geometric optimizations were carried out using the conjugate gradient method, with the convergence threshold set to 10 -5 eV for the energy and The charge difference map was obtained by subtracting the charge densities of graphite and Br (BrCl) from the charge density of C7[Br](C 3.5 [Br 0.5 Cl 0.5 ), respectively. The charge distribution on the atoms was determined using the Bader analysis method. The visualization of the structures was performed using VESTA software.

[0120] Embedding voltage step distribution simulations. For the core electrons, the embedding voltage curves were calculated using CP2K v5.1, with the dispersion correction (D3) PBE functional and a double-ζ (triple-ζ for bromides) short-range, molecule-optimized valence basis set and appropriate Goedecker–Teter–Hutter (GTH) pseudopotentials. The plane-wave energy cutoff was set to 1000 Ry, and the Brillouin zone was sampled only at the Γ point. The geometric and cell optimizations converged to a maximum change in atomic positions between 0.0005 au steps. The other convergence criteria were kept at default.

[0121] The relative to Li can be calculated from a series of energy calculations+ / Li embedding voltage (E int ), assuming the entropy contribution is negligible, is as follows:

[0122]

[0123] where n x is the number of anions, E(GrX) is the energy of embedding into the graphite channels, E(Gr) is the energy of pure graphite in the AB stacking, E desolv (LiX) is the desolvation energy of the LiX contact ion pair, using the cluster-continuum method (up to 8 explicit waters) in Gaussian calculations with PBEPBE+D3 / 6-31G(d), E gas (LiX) is the energy of the LiX contact ion pair in the battery, E b (Li) is the energy per lithium in bulk metal (-204.1894 eV / Li). For phases I-IV and VI, 12 layers of carbon are modeled. Phase V is modeled with 10 layers of carbon. Each layer consists of 112 carbon atoms.

[0124] The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to one or more forms disclosed herein. Although the description of the invention has included a description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention after understanding, for example, within the skill and knowledge of those skilled in the art. It is intended to obtain rights to include alternative embodiments within the scope permitted, including alternative, interchangeable, and / or equivalent structures, functions, scopes, or steps, whether or not such alternative, interchangeable, and / or equivalent structures, functions, scopes, or steps are disclosed herein, and it is not intended to disclose any patentable subject matter. All references cited herein are incorporated by reference in their entirety.

Claims

1. A rechargeable lithium-ion battery, comprising: Composite cathode comprising a variety of different lithium halide salts and graphite; Aqueous electrolyte, said aqueous electrolyte comprising a dual-salt-in-water electrolyte, a high-concentration organic electrolyte, an all-solid-state ceramic electrolyte, or a combination thereof; And An anode, wherein the rechargeable lithium-ion battery has a capacity greater than 200 mAh / g.

2. The rechargeable lithium-ion battery according to claim 1, wherein an oxidation product of the lithium halide salt is embedded in the graphite.

3. The rechargeable lithium-ion battery according to claim 1, wherein the composite cathode comprises lithium chloride salt and lithium bromide salt.

4. The rechargeable lithium-ion battery according to claim 1, wherein the composite cathode comprises lithium chloride, lithium bromide, lithium iodide, lithium fluoride, or a combination thereof.

5. The rechargeable lithium-ion battery according to claim 4, wherein the lithium halide salt comprises a combination of lithium chloride and a lithium salt.

6. The rechargeable lithium-ion battery according to claim 1, having an energy density of at least 400 Wh / kg.

7. The rechargeable lithium-ion battery according to claim 1, wherein the Coulombic efficiency of the rechargeable lithium-ion battery is at least 95%.

8. The rechargeable lithium-ion battery according to claim 1, wherein the rechargeable lithium-ion battery has a potential of at least 4 V relative to Li / Li + at least 4 V.

9. The rechargeable lithium-ion battery according to claim 1, wherein the dual-salt aqueous electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium hexafluoroarsenate, lithium perchlorate, lithium nitrate, or a mixture thereof.

10. A method for preparing a lithium salt-graphite composite cathode for a rechargeable lithium-ion battery, the method comprising compressing a mixture of a plurality of lithium halide salt-graphite composites and a polymer under conditions sufficient to prepare a lithium halide salt-graphite composite cathode comprising a plurality of lithium halide salts, whereby oxidation of the plurality of lithium halide salts causes an oxidation product of the plurality of lithium halide salts to be embedded in the graphite.

11. The method according to claim 10, the method further comprising a step of mixing a plurality of lithium halide salts and graphite and grinding the mixture to prepare the plurality of lithium halide salt-graphite composites before mixing with the polymer.

12. The method according to claim 11, wherein the plurality of lithium halide salts comprises lithium bromide and lithium chloride in a 1:1 molar ratio.

13. The method according to claim 12, wherein the mass ratio of the lithium bromide, the lithium chloride and the graphite is 2:1:

2.

14. The method according to claim 10, wherein the polymer comprises poly(vinylidene fluoride), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether or a mixture thereof.

15. The method according to claim 10, wherein the mass ratio of the lithium halide salt-graphite composite material to the polymer is 95:

5.

16. A rechargeable lithium-ion battery, comprising: Composite cathode comprising a variety of lithium halide salts and graphite, wherein the composite cathode is configured such that oxidation of the variety of lithium halide salts embeds the oxidation products of the variety of lithium halide salts into the graphite; Aqueous gel electrolyte, said aqueous gel electrolyte comprising a dual-salt-in-water electrolyte; and An anode comprising a highly fluorinated ether polymer.

17. The rechargeable lithium-ion battery according to claim 16, having an energy density of at least 400 Wh / kg.

18. The rechargeable lithium-ion battery according to claim 16, wherein the Coulombic efficiency of the battery is at least 95%.

19. The rechargeable lithium-ion battery according to claim 16, wherein the lithium-ion battery has a potential of at least 4 V relative to Li / Li + at least 4 V.

20. The rechargeable lithium-ion battery according to claim 16, wherein the dual-salt aqueous electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium hexafluoroarsenate, an asymmetric ammonium salt, N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide or a mixture thereof.

21. The rechargeable lithium-ion battery according to claim 16, wherein the hydrogel electrolyte further contains an organic solvent.

22. The rechargeable lithium-ion battery according to claim 21, wherein the organic solvent comprises trimethyl phosphate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate, γ-butyrolactone, ethyl methyl carbonate, dimethoxyethane, diethylene glycol methyl ether, fluoroethylene carbonate or a mixture thereof.

23. The rechargeable lithium-ion battery according to claim 16, wherein at least a portion of the plurality of lithium halide salts is phase-separated from the hydrogel electrolyte.

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