Patent Application
20190312301
Lithium batteries, including lithium metal and lithium-ion batteries, continue to grow in commercial importance (sodium batteries, including sodium metal and sodium-ion batteries are also of commercial interest but less developed than the lithium counterparts). However, low energy density in the lithium-ion battery still remains as a major issue for handheld devices and vehicle applications. Searching for high capacity cathodes to enhance the total battery energy density has been a focus in battery research. Since the commercialization of rechargeable lithium battery in 1990s, several eminent cathodes including layered lithium metal oxide (LiMO2, M=Co, Ni, Mn), spinel structured LiM2O4 (M=Mn, NixMn1-x, and the like) and olivine lithium metal phosphate (LiMPO4, M=Fe, Co, Mn and the like) have dominated the energy markets ranging from portable electric devices to automotive propulsion. However, the insufficient cathode capacity less than 200 mAh g−1 (e.g., <145 mAh g−1 of commercialized LiCoO2) is much lower than that of carbon anode (e.g., about 372 mAh g−1 of natural graphite), which has always been the bottleneck in energy density enhancement. It is a great challenge which needs to be solved urgently. Although huge efforts based on solid-state chemistry have been paid for synthesizing new cathodes such as gradient nickel rich and lithium rich compounds with higher capacity, the durable cycle life and stable voltage plateau still warrant further investigation. Among the commonly used cathode materials, the olivine LFP (“lithium iron phosphate”) is an exceptional host for lithium ions storage because of its preponderant safety and rate capability (i.e. robust crystalline structure and large channels formed by the corner-connected octahedral FeO6 and tetrahedral PO4) over the layered oxide cathode. But the intrinsic low capacity is the major impediment for expanding their utilizations so that a theoretical capacity of 170 mAh g−1 is reached. Thus, it would be extremely attractive to enhance the capacity and cycle performance of LFP-based Li-ion battery for wider applications.
Prior art references include the text, Yoshio, Brodd, Kozawa (Eds.), Lithium-In Batteries, Science and Technologies, Springer, 2009 (“Yoshio text”), including chapters 4 and 19 which relate to electrolytes. See also U.S. Pat. Nos. 5,882,812 and 5,962,171 and U.S. Patent Publications 2013/010891 3 and 2014/0023936. See also Hayner et al., Annu. Rev. Chem. Biomol. Eng. 2012, 3: 445-71; Besenhard et al., J. Power Sources, 43-44, 413 (1993); and Wanger et al., J. Power Sources, 68, 328 (1997).
A need exists for better lithium-based battery devices providing higher energy densities and capacities.
Embodiments described herein include, for example, devices such as batteries and components thereof including, for example, compositions, separators, and electrodes, as well as methods of making and methods of using such batteries and components.
An aspect provided herein includes a battery comprising: at least one cathode, at least one anode, at least one battery separator, and at least one electrolyte disposed in the separator, wherein the anode is a lithium metal or lithium alloy anode or a lithiated anode adapted for intercalation of lithium ion, wherein the cathode comprises material adapted for reversible lithium extraction from and insertion into the cathode, and wherein the separator comprises at least one porous, electronically conductive layer and at least one insulating layer, and wherein the electrolyte comprises at least one polysulfide anion. Another aspect is a hybrid lithium ion-lithium sulfur battery.
In one embodiment, the polysulfide anion is from lithium polysulfide and the electrolyte comprises at least two organic solvents. In one embodiment, the polysulfide anion is from lithium polysulfide and the electrolyte comprises at least two lithium salts which are different than the lithium polysulfide.
In one embodiment, the porous, electronically conductive layer is a carbon layer. In one embodiment, the porous, electronically conductive layer is a carbon nanotube layer.
In one embodiment, the cathode is a layered material or a spinel material. In one embodiment, the cathode comprises lithium iron phosphate (LFP).
In one embodiment, the anode is an anode adapted for intercalation of lithium ion. In one embodiment, the anode comprises graphite.
In one embodiment, the polysulfide anion is from lithium polysulfide, wherein the porous, electronically conductive layer is a carbon layer, and wherein the cathode is a layered material or a spinel material.
Another embodiment is a battery comprising: at least one cathode, at least one anode, and at least one electrolyte, wherein the electrolyte comprises at least one polysulfide anion, wherein the battery is a lithium metal, a lithium ion, a sodium metal, or a sodium ion battery. In one embodiment for the sodium metal or sodium ion battery, the polysulfide anion is from sodium polysulfide.
In different embodiments, the batteries described herein can be in a charged or discharged state.
In selected embodiments, a strategy is provided based on, at least in part, using a polysulfide anion electrolyte for boosting the performance of the battery, such as an LFP Li-ion battery. This newly designed electrolyte, in selected embodiments, is able to lower the polarization and improve the cycle stability of a battery such as an LFP-based Li-ion battery. Meanwhile, the redox reaction potential of, for example, the polysulfide salt, Li2S8, falls in the voltage-window of, for example, LFP during the charge/discharge process, thus contributing additional voltage plateaus at around 2.0 V.
As a result, a completely new hybrid battery comprising, for example, Li/LFP and Li-S systems, was developed, which can deliver a high capacity of 442 mAh gLFP−1. The stability and rate capabilities of the preferred embodiments for the hybrid battery are also overwhelmingly better than current Li-ion battery.
Additional advantages for one or more embodiments are described or inherently provided hereinafter.
The polarization of battery using Li2S8-based electrolyte are about 347.9 mV, 364.9 mV, and 465.9 mV, significantly lower than 420.5 mV, 439.0 mV and 555.7 mV of commercial Li-ion battery electrolyte as increasing the scan rate from 0.075 mV s−1, 0.1 mV s−1 to 0.25 mV s−1. Also, the corresponding charge potentials of 3.61 V, 3.61 V and 3.65 V are much lower than 3.68 V, 3.69 V and 3.79 V of commercial Li-ion battery electrolyte.
Additional embodiments are provided in the following detailed description. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. Also, one aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment(s).
References cited herein are incorporated by reference.
Embodiments described herein can be described using terms such as “comprising,” “consisting essentially of,” and “consisting of” as known in the art.
A new strategy is provided in preferred embodiments of integrating a Li2S8-based electrolyte with Li-ion batteries to enhance their performance. Taking the olivine LiFePO4 (LFP) as an example, the polysulfide anion such as, for example, Li2S8 species in electrolytes results in lower polarization and superior cycle stability due to the low electrical impedance and fast lithium diffusion. Furthermore, the presence of S82−/S2− redox reaction from the Li2S8 species contributes extra capacity, making a new LFP/Li-S hybridized battery with a high energy density of 1124 Wh kgLFP−1 and a capacity of 442 mAh gLFP−1 over 500 cycles, which is far beyond all cathodes being used in current Li-ion battery technology. In preferred embodiments, the concept of introducing new redox species in electrolyte with a novel cell configuration for Li-ion battery is proposed, which serves as an efficient and scalable approach for obtaining higher density energy storage and conversion devices.
Some basic principles of batteries and electrochemical cells are described. Batteries may be divided into two principal types, primary batteries and secondary batteries. Primary batteries may be used once and are then exhausted. Secondary batteries are also often called rechargeable batteries because after use they may be connected to an electricity supply, such as a wall socket, and recharged and used again. In secondary batteries, each charge/discharge process is called a cycle. Secondary batteries eventually reach an end of their usable life, but typically only after many charge/discharge cycles.
Secondary batteries are made up of an electrochemical cell and optionally other materials, such as a casing to protect the cell and wires or other connectors to allow the battery to interface with the outside world. An electrochemical cell includes two electrodes, the positive electrode or cathode and the negative electrode or anode, an insulator separating the electrodes so the battery does not short out, and an electrolyte that chemically connects the electrodes.
In operation the secondary battery exchanges chemical energy and electrical energy. During discharge of the battery, electrons, which have a negative charge, leave the anode and travel through outside electrical conductors, such as wires in a cell phone or computer, to the cathode. In the process of traveling through these outside electrical conductors, the electrons generate an electrical current, which provides electrical energy.
At the same time, in order to keep the electrical charge of the anode and cathode neutral, an ion having a positive charge leaves the anode and enters the electrolyte and a positive ion also leaves the electrolyte and enters the cathode. In order for this ion movement to work, typically the same type of ion leaves the anode and joins the cathode. Additionally, the electrolyte typically also contains this same type of ion. In order to recharge the battery, the same process happens in reverse. By supplying energy to the cell, electrons are induced to leave the cathode and join the anode. At the same time a positive ion, such as Li+, leaves the cathode and enters the electrolyte and a Li+ leaves the electrolyte and joins the anode to keep the overall electrode charge neutral.
In addition to containing an active material that exchanges electrons and ions, anodes and cathodes often contain other materials, such as a metal backing to which a slurry is applied and dried. The slurry often contains the active material as well as a binder to help it adhere to the backing and conductive materials, such as a carbon particles. Once the slurry dries it forms a coating on the metal backing.
Unless additional materials are specified, batteries as described herein include systems that are merely electrochemical cells as well as more complex systems. Several important criteria for rechargeable batteries include energy density, power density, rate capability, cycle life, cost, and safety. The current lithium-ion battery technology based on insertion compound cathodes and anodes is limited in energy density. This technology also suffers from safety concerns arising from the chemical instability of oxide cathodes under conditions of overcharge and frequently requires the use of expensive transition metals.
Thicknesses of different components such as electrodes and separators can be adapted for the need. Surfaces can be adapted and treated for the need.
Batteries can be in a charged, partially charged, discharged, or partially discharged states.
Batteries can be incorporated into larger systems.
Batteries can include additional parts such as current collectors and external electrical circuitry.
The assembly of batteries is described elsewhere herein.
Hybrid batteries can be prepared which are based on more than one redox reaction. For example, herein a hybrid lithium ion-lithium sulfur battery is described which can comprise the electrolytes, separators, cathodes, and anodes described herein.
Electrolytes are known in the art. See, for example, Yoshio text, including chapters 4 and 19. They can be liquid, gel, or solid electrolytes. The electrolyte comprises at least one polysulfide anion. Polysulfide anions are known in the art, and metal polysulfides and polysulfide salts are known in the art. See, for example, U.S. Patent Publication 2015/0340738; 2014/0255797; 2014/0342214; and 2014/0023936. The electrolyte can comprise at least one solvent, preferably at least one organic solvent, preferably at least one aprotic solvent. Multiple solvents and/or multiple salts can be used in the electrolyte. One or more additives can also be used.
The polysulfide anion can be provided as a salt mixed into a larger electrolyte composition. The metal of the salt can be, for example, lithium, sodium, or magnesium, but preferably lithium polysulfide is used. Lithium polysulfide can be represented as Li2Sx wherein 2<x<8. In a preferred embodiment, the lithium polysulfide is represented as Li2S8.
Methods of forming polysulfide anions including lithium polysulfide are known in the art. For example, lithium can be mixed with sulfur and reacted.
Solvents as electrolytes are well-known in the art and can be aqueous or non-aqueous. However, non-aqueous solvents are preferred. Mixtures of solvents can be used. One or more organic solvents can be used, including one or more aprotic solvents, one or more etheric solvents, or one or more oxygenated solvents. Other examples of the one or more solvents include open-chain or cyclic carbonates, carboxylic acid esters, nitrites, ethers, sulfones, sulfoxides, lactones, dioxolanes, glymes, crown ethers, and any mixture thereof. Preferred examples of solvents include 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME).
Illustrative electrolyte solvents include, but are not limited to, acetals, ketals, sulfones, acyclic ethers, cyclic ethers, glymes, polyethers, dioxolanes, substituted forms of the foregoing, and blends or mixtures of any two or more such solvents. Examples of acyclic ethers that may be used include, but are not limited to, diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, 1,2-dimethoxypropane, and 1,3-dimethoxypropane. Examples of cyclic ethers that may be used include, but are not limited to, tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, and trioxane. Examples of polyethers that may be used include, but are not limited to, diethylene glylcol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (tetraglyme), higher glymes, ethylene glycol divinylether, diethylene glycol divinylether, triethylene glycol divinylether, dipropylene glycol dimethylether, and butylene glycol ethers. Examples of sulfones that may be used include, but are not limited to, sulfolane, 3-methyl sulfolane, and 3-sulfolene.
In some embodiments, the electrolyte solvent includes, but is not limited to, 1,2-dimethoxy ethane (DME), 1,3-dioxolane (DOL), tetraethyleneglycol dimethyl ether (TEGDME), tetrahydrofuran (THF), and tri(ethylene glycol)dimethyl ether. Mixtures of any two or more such solvents may also be used. For example, a mixture of DME:DOL is illustrated in the examples, but other mixtures may be used. Where a mixture of two of the solvents is used, the ratio of mixing may be from 1 to 99 of a first solvent and from 99 to 1 of a second solvent. In some embodiments, the ratio of the first solvent to the second solvent is from 10:90 to 90:10. In some embodiments, the ratio of the first solvent to the second solvent is from 20:80 to 80:20. In some embodiments, the ratio of the first solvent to the second solvent is from 30:70 to 70:30. In some embodiments, the ratio of the first solvent to the second solvent is from 40:60 to 60:40. In some embodiments, the ratio of the first solvent to the second solvent is about 1:1. For example, as illustrated in the examples, one mixture is that of DME:DOL at a ratio of about 1:1.
Additional lithium salts can be used which are not particularly limited including, for example, lithium bis(trifluoromethane)sulfonamide salt (LiTFSl) and lithium nitrate salt. Examples of additional lithium salts include LiBF4, LiPF6, and lithium bis-pentafluoroethanesulfonylimide (BETI).
The amounts of the electrolyte components, such as polysulfide and solvent, can be varied as known in the art.
A preferred electrolyte is prepared with use of, or comprises, lithium polysulfide (Li2S8), LiTFSI, and lithium nitrate as salt components and a solvent mixture of DOL and DME.
Battery separators are known in the art (e.g., see Yoshio text, including chapter 20) and can be, for example made from glass, polymers, or the like. They are porous and contain electrolyte in the pores. They can include an electrically insulating layer but allow the electrolyte to conduct ions. The separator can be made from, for example, a polymer such as a polyolefin such as polypropylene or polyethylene.
Suitable separators include those such as, but not limited to, microporous polymer films, glass fibers, paper fibers, and ceramic materials. Illustrative microporous polymer films include, but are not limited, nylon, cellulose, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene, or a blend or copolymer thereof. In some embodiments, the separator is an electron beam treated micro-porous polyolefin separator. In some embodiments, the separator is a shut-down separator. Other separators may include a microporous xerogel layer, for example, a microporous pseudo-boehmite layer as described in U.S. Pat. No. 6,153,337. Commercially available separators include those such as, but not limited to, Celgard® 2025 and 3501, and 2325; and Tonen Setela® E25, E20, and Asahi Kasei® and Ube® separators.
Separators of a wide range of thickness may be used. For example, the separator may be from about 5 microns to about 50 microns thick. In other embodiments, the separator is from about 5 microns to about 25 microns.
The battery separator can be made to be bifunctional. Examples of bifunctional separators are described in, for example, U.S. Patent Publication 2015/0318532 and Chung et al., J. Phys. Chem. Lett., 2014, 5(11), 1978-1983. Other examples are described in Zhu et al., Nano Energy, 20, 176-184 (2016) and Kannan et al., ECS Meeting Abstracts, MA 2015-01 239 (May 25, 2015).
In the bifunctional separator, for example, a porous, electronically conductive layer can be included in the structure along with the insulating layer. The layer can include materials such as carbon, carbon powder, carbon nanotubes, including multi-walled carbon nanotubes and interwoven carbon nanotubes, graphene, and other forms of carbon. The electronically conductive layer can include a polymeric binder if desired. The electronically conductive layer can be disposed on the cathode side of the separator.
Battery cathodes (positive electrodes) are generally known in the lithium battery art. See, for example, Yoshio text, including chapter 2. The cathode can be adapted for intercalation, extraction, insertion, or diffusion of the lithium cation. Transition metal oxides can be used. Spinel and layered materials can be used. An example is manganese spinel cathode material. Two- or three-dimensional diffusion of lithium ion can be used. Materials with layered structures include, for example, LiFePO4, LiCoO2, LiNiO2, LiCrO2, Li2MoO3, Li0.7MnO2, LiNi0.8CO0.2O2, LiNi0.8CO0.15O2, LiMn0.5Ni0.5O2, LiMn1/3Ni1/3Co1/3O2, LiMn0.4Ni0.4Co0.2O2, LiMn2O4, Li1.06, Mg0.06, Mn1.88O4, and LiAlMnO4. The cathode material can be doped if desired. For example, LiCoO2 can be doped with aluminum or magnesium. LiNiO2 can be doped with a foreign metal.
However, a particularly preferred embodiment is LiFePO4, particularly with the olivine structure.
As known in the art, conductive materials such as carbon and binder materials such as polymers can be used to construct an electrode including the cathode.
Anodes are also generally known in the lithium battery art. See, for example, Yoshio text, including Chapter 3. The anode can be a metallic lithium anode or an anode in which lithium ion is present. Alloys can be made including lithium with, for example, Sn, Si, Al, SB, SnB0.5Co0.5O3, or Li2.6Co0.4N.
As known in the art, conductive materials such as carbon and binder materials such as polymers can be used to construct an electrode including an anode. Lithiated carbon anodes can be used. Carbonaceous anodes can be used including graphite anodes.
Other embodiments for carbon anodes include, for example, spherical graphitized mesocarbon microbeads (MCMB), graphitized carbon fiber (MCF), pitch base graphite, and carbon-coated natural graphite.
Other embodiments include sodium metal and sodium ion batteries. For example, one embodiment provides for a battery comprising: at least one cathode, at least one anode, and at least one electrolyte, wherein the electrolyte comprises at least one polysulfide anion, wherein the battery is a lithium metal, a lithium ion, a sodium metal, or a sodium ion battery. In one embodiment, the battery is a lithium metal or a lithium ion battery, and in another embodiment, the battery is a sodium metal or a sodium ion battery.
Sodium metal and sodium ion batteries are known in the art. Such batteries are described in, for example, J. Sudworth, A. R. Tiley, Sodium Sulfur Battery, 1986; Lithium Batteries, Advanced Technologies and Applications (Eds. B. Scrosati et al.), Chapter 16, “Rechargeable Sodium and Sodium-Ion Batteries,” 2013. See also, Luo et al., ACS Cent. Sci., 2015, 1(8), 420-422; and Seh et al., ACS Cent. Sci., 2015, 1, 449-455.
For the sodium and sodium-ion embodiments, the anode, cathode, and electrolyte, and other aspects of the battery are adapted as known in the art to accommodate the use of sodium rather than lithium. The electrolyte can include an organic solvent such as one or more glymes (mono-, di-, or tetraglyme), and the sodium salt can be, for example, NaPF6, NaN(SO2CF3)2, NaN(SO2F)2, NaSO3CF3, or NaClO4.
Na2S8 can be prepared and used as the polysulfide anion.
The performance of the batteries can be tested by methods known in the art and use of the methods shown in the working examples. Performance parameters include, for example, energy density and/or capacity. While individual performance parameters are important, more important are combinations of performance parameters. For example, high energy density can be combined with high capacity.
In one embodiment, the energy density can be, for example, at least 1,000 Whkg−1, or at least 1,100 Whkg−1, wherein kg is linked to the cathode material such as an LFP cathode.
In one embodiment, the capacity can be, for example, at least 300 mAhg−1, or at least 400 mAhg−1, wherein g is linked to the cathode material such as an LFP cathode.
Testing can be done through a series of charge/discharge cycles and can be done, for example, for at least 100 cycles, or at least 250 cycles, or a least 500 cycles, or at least 1,000 cycles.
In one embodiment, the capacity can be, for example, at least 75 mAhg−1, or at least 125 mAhg−1, or at least 145 mAhg−1, after 500 cycles, wherein g is linked to the cathode material such as an LFP cathode.
The battery voltage can be, for example, at least 3 V, or at least 3.5 V, or at least 4 V.
Polarization performance can be lowered as reflected in lowering of charge voltage. Over-potential is lowered.
Cycle stability can be improved.
Cyclic voltammetry (CV) can be used to study the performance.
C-rate testing can be carried out including testing at, for example, 0.25C, 0.6C, 1.2C, 2.5C, 6C, and 12C, wherein one defines 1C as 1C=170 mAh g−1.
Buffer effects can be measured where voltage is maintained despite significant or full discharge.
The batteries can be made by methods known in the art and use of the methods shown in the working examples. See, for example, Yoshio text, chapter 8. Battery components to be assembled include, for example, the case or can, the positive terminal, the positive current collector, the positive active mass, the separator, the negative active mass, the negative current collector, and the negative terminal.
Different types of cells can be made including, for example, cylindrical cells, prismatic cells, polymer cells, and flat plate cells.
The cells can be assembled in a discharged condition and can be activated by charging. A solid electrolyte interface (SEI) can be formed.
Safety factors and external electrical circuits can be designed into the batteries.
Batteries can be used in many applications known in the art and developed in the future including energy storage, portable electrical devices, and vehicle or automotive propulsion. Biomedical applications are also important.
Additional embodiments are provided in the following working examples.
The electrolyte was composed of 1 M bis(trifluoromethane) sulfonimide lithium salt (LiTFSI) in 1,3-dioxolane (DOL)/1,2-dimethoxyethane (DME) (v/v, 1/1), 0.4 M LiNO3 and 0.05 M Li2S8. Since the redox reaction of Li2S8/Li2Sx (2≤x<8) is involved in the charge/discharge process, the separator was coated with multi-walled carbon nanotubes (MWCNTs) (
Different from the conventional electrolyte used for Li-ion battery, the Li2S8-based electrolyte used herein could largely enhance the overall capacity using the same volume of electrolyte. To understand the effect clearly, two other electrolytes were compared: (i) commercial Li-ion battery electrolyte (1 M LiPF6 in ethylene carbonate/dimethyl carbonate (EC/DMC)), and (ii) Li-S electrolyte without Li2S8 (1 M LiTFSl in DOL/DME with 0.4 M LiNO3).
The excellent performance using the Li2S8-based electrolyte showed here are not only the enhanced capacity but also the improved stability. In the C-rate test, the hybrid battery demonstrated high rate capabilities of 437, 381, 339, 288, 122 and 41 mAh g−1 at the rate of 0.25C, 0.6C, 1.2C, 2.5C, 6C and 12C respectively, and it could recover back to 340 mAh g−1 at 0.6C (
One should note that experimental results show that the overall cathode capacity decay with cycling in the hybrid battery is from the Li-S system, known as one issue in Li-S battery. This can be addressed by many approaches such as using a gel/solid electrolyte or blocking layer.
In addition to the above advantages, another benefit of using Li2S8-based electrolyte is the lower polarization for the charge and discharge of LFP.
The lower over-potential was further confirmed by the comparative cyclic voltammetry (CV) analysis, in which the oxidation peaks around 2.36 V and 3.60 V correspond to the conversion of Li2Sx to Li2S8/S8 and the extraction of lithium ions from LFP (
To interpret the phenomena, the lithium diffusion constant D (cm2 s−1) is calculated by the the Randles-Sevcik equation:
i
p=2.69×105 n3/2 A D1/2 C ν1/2
where ip indicates the peak current (A), n is the number of electron in the reaction (for LFP, n=1; for polysulfide, taking the first reduction peak at 2.4 V as example, n=2), A is the electrode area (1.33 cm2), u is the scanning rate (V s−1) and C is the variation of lithium-ion concentration in the electrolyte (mol cm−3). The plot of the normalized peak current (ip) with the square root of the scan rate (ν1/2) is displayed in
The stabilized resistance of hybrid battery using Li2S8-based electrolyte (i.e., 8 Ω) is lower than that in commercial electrolyte (i.e., 10 Ω) and that using Li-S electrolyte (i.e., 80 Ω). The additive of Li2S8 into Li-S battery electrolyte has significant effects to the final battery performance, apart from the capacity contribution. The role of Li2S8 can be described in our presented model: (i) First, soluble Li2Sx (x>6) can be formed at the end of charging, providing abundant free Li+ in electrolyte. (ii) In the charging process, the LFP cathode is positively charged. The dissociated/soluble Sx2− can gather around the LFP surface by electrostatic interaction and then the extracted Li+ can be quickly transported to electrolyte (
For the practical utilization of Li2S8-based electrolyte, the electrochemical behaviour of hybrid lithium ion battery versus graphite was studied in a full battery configuration (
In conclusion, an efficient electrolyte chemistry is reported to largely enhance the energy capacity and reduce the polarization of battery by using Li2S8-based electrolyte. A completely new hybrid LFP based lithium battery with an extremely high energy density of 1104 Wh kg−1 (i.e., 440 mAh gLFP−1), robust rate capacities and durable cycle performance was presented based on a novel cell configuration. In sum, success was achieved for LFP lithium ion battery versus lithiated graphite with higher capacity, better stability and durable cycle life over 500 cycles in Li2S8-based electrolyte.
Materials Preparation: The cathode was composed of 80 wt % LFP (purchased from Lausdeo, Taiwan), 10 wt % Super P carbon and 10 wt % polyvinylidene fluoride (PVDF) binder. In the preparation, the powders were mixed in 1-Methyl-2-pyrrolidinone (NMP) to form a uniform slurry and then casted on Al foil by doctor blade. Dried in vacuum oven at 80° C. for 12h and then punched to Φ13 mm circular electrode. The areal mass density of LFP was controlled at a high loading of 5.21 mg cm−2 close to practical application. For the CNTs modified separator, the mixture of CNT and PVDF binder with the mass ratio of 9/1 was dispersed into NMP, and then the slurry was casted on the glass fiber separator. The CNTs coated separator was dried first in vacuum oven at 120° C. for 12 h and then cut into Ø18 mm round discs before use. The electrolyte was prepared as below. Stoichiometric ratio of lithium metal pieces and sulfur powder (to form 0.05 M Li2S8) were dispersed in 40 mL 1, 3-dioxolane/1, 2-Dimethoxyethane (DOL/DME, v/v, 1/1) and stirred at 80° C. for 48 h. After the reaction, equivalent weight of bis(trifluoromethane) sulfonimide lithium salt (LiTFSI) and LiNO3 were added into the solution, giving rise to the electrolyte of 1 M LiTFSI in DOL/DME containing 0.4 M LiNO3 and 0.05 M Li2S8. The electrolyte without Li2S8 was prepared simply as the second step. The commercial electrolyte 1 M LiPF6 in ethylene carbonate and dimethyl carbonate (EC/DMC, 50/50, v/v) was purchased from Sigma-Aldrich.
Electrochemical measurements: The electrochemical tests were performed using 2032-type cells. The hybrid lithium ion battery has the configuration of LFP|CNTs modified separator| lithium metal, in which the electrolyte of 1 M LiTFSI, 0.4 M LiNO3, 0.05 M Li2S8 in DOL/DME was used. The amount of the electrolyte was 130 μL and the weight of sulfur was calculated based on the amount of Li2S8. For comparison, the lithium ion batteries with the 1 M LiPF6 in EC/DMC electrolyte were also tested. The batteries were assembled in Argon-filled glovebox in which the moisture and oxygen were strictly controlled below 0.5 ppm. Galvanostatic charge-discharge experiments were carried out by Arbin battery test instrument BT2043 within the voltage window of 1.8-3.6 V and 1.8-4.0V respectively. For the full battery configuration, lithiated graphite was used as anode, and the cut-off voltage was 1.8-3.75V. Cyclic Voltammetry (CV) and electrochemical impedance spectrum (EIS) were recorded by the BioLogic VMP3 under the scan rate 0.05-0.25 mV/s.
Characterizations: A Raman spectrum of electrolyte was carried out by a specific homemade glass tube battery and the spectrum was collected on a Witec alpha 300R Raman spectrometer at a 514 nm excitation wavelength. The interfacial morphology of CNTs-separator and LFP electrode were characterized by the field emission scanning electron microscope (FESEM, FEI Quanta 200), operated at 5 kV and 2.5 mA. The elemental distribution of sulphur, carbon, and LFP were analysed by the energy-dispersive X-ray (EDX) mapping, operated at 10 kV and 6 mA.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/053375 | 6/7/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62353277 | Jun 2016 | US |
