A METHOD FOR PREPARING NANOMETER-SIZED SURFACE FLUORINATED BATTERY MATERIALS

Abstract

A method uses mild fluorinating agents, such as hydrofluorocarbons—HCFs, perfluorocarbons—PFCs, hydrochlorofluorocarbons HCFCs and chlorofluorocarbons—CFCs, to fine-tune the fluorination process in battery material preparation in order to obtain uniform nanometer-sized surface fluoride coated battery materials. The use of a vertical flow-type tube reactor permits a fine-tuning of the fluorination process by accurately regulating the active gas or mixture of gases flow over battery materials using mass-flow regulators, and precisely setting the temperature with vertical rube furnace. Additionally, these fluorinating agents have slightly different reactivity, decomposing and reacting with battery materials at different temperatures, and therefore, offering additional parameter of fluorination fine-tuning. The method is scalable and can be easily adapted as an industrial solution. Moreover, all these gases are non-toxic, non-corrosive and non-flammable gases at room temperatures, hence, they are more convenient to handle than highly-toxic and highly-corrosive HF and F.sub.2 gases.

Claims

1-6. (canceled)

7. A method for preparing a nanometer-sized surface fluorinated battery material, which comprises the steps of: inserting the nanometer-sized surface fluorinated battery material into a vertically oriented flow-type tube reactor and placing the nanometer-sized surface fluorinated battery material on a porous support frit in absence of atmospheric conditions inside the vertically oriented flow-type tube reactor; associating the vertically oriented flow-type tube reactor with controllable heating to supply heat to an inner volume of the vertically oriented flow-type tube reactor; heating a battery active material to an extent in a range of 25 to 800° C. under an inert gas atmosphere supplied by at least a first gas supply line; and fluorinating a surface of the nanometer-sized surface fluorinated battery material at a controllable temperature using a fluorinating agent or a mixture thereof under a fluorinating gas or fluorinating gas mixture flow that is flooding the inner volume of the vertically oriented flow-type tube reactor at controllable flow rates.

8. The method according to claim 7, wherein the fluorinating gas or the fluorinating gas mixture flow is oriented vertically in the inner volume of the vertically oriented flow-type tube reactor.

9. The method according to claim 7, which further comprises providing LiNi.sub.0.50Co.sub.0.15Al.sub.0.05O.sub.2 and/or metallic lithium as the battery active material.

10. The method according to claim 7, wherein the fluorinating gas or the fluorinating gas mixture flow rates between 3 to 500 ml/min and are established for a time duration between 1 minute and 15 hours.

11. The method according to claim 7, wherein after a fluorination, cooling down the vertically oriented flow-type tube reactor under an inert gas flow.

12. The method according to claim 7, wherein the heating is achieved in a vertical tube furnace having the vertically oriented flow-type tube reactor inserted therein.

13. The method according to claim 7, which further comprises selecting the nanometer-sized surface fluorinated battery material from the group consisting of: a cathode active material, an anode active material, a solid electrolyte material and a current collector material.

14. The method according to claim 7, which further comprises selecting the fluorinating agent or the mixture thereof from the group consisting of: hydrofluorocarbons (HCFs), perfluorocarbons (PFCs), hydrochlorofluorocarbons (HCFCs), chlorofluorocarbons (CFCs), and CHF.sub.3.

Description

[0030] Preferred embodiments of the present invention are hereinafter described in more detail with reference to the attached drawings which depicts in:

[0031] FIG. 1 schematically the fluorination setup (a) and XPS surface analysis (b); and

[0032] FIG. 2 specific capacity vs. cycles graph exhibiting cycling performance of fluorinated and pristine NCA.

[0033] In the present invention, mild fluorinating agents, such as hydrofluorocarbons—HCFs, perfluorocarbons—PFCs, hydrochlorofluorocarbons—HCFCs and chlorofluorocarbons—CFCs, are used to enable the fine-tuning of the fluorination process in a controlled manner, resulting in a uniform nanometere-sized surface fluoride coated battery active materials. Particularly, the use of those mild fluorinating agents is considered here as a novel approach compared to the previous reported gases (e.g. elementary fluorine, HF gas and NF.sub.3) as the suggested gas-solid interfacial modification is achieved in a vertical flow type reactor, which allows an accurately regulating of the active gas or mixture of gases flow over battery materials using mass-flow regulators, and thereby precisely setting the temperature within the vertical tube furnace. Such a setup is both scalable and compatible with any industrials process. Moreover, subtle differences in reactivity (decomposition temperature) of these fluorinating agents offer an additional fine-tuning parameter of fluorination process. Furthermore, unlike the already reported strong gaseous fluorinating agents, the present gaseous mild fluorinating agents are non-toxic, non-corrosive and non-flammable gases at room temperatures, therefore, they are more convenient to handle than highly-toxic and highly-corrosive HF and F.sub.2.

[0034] It is known that the HCFs, PFCs, HCFCs and CFCs are all potent greenhouse gases and in addition the CFCs and HCFCs are ozone-depleting gases, which are phasing-out of production and use based on Montreal Protocol agreement. However, there are still vast world stock of these materials that could be used for fluorination of battery materials, and thus, in a controlled way braked down to “environmental-friendly” compounds. For example, the CHF.sub.3, one of the preferred mild fluorinating agent, is a large-volume (approximately 20 kilotons/year) side product in manufacturing polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), foams, fire-extinguishing agents and refrigerants. Therefore, there is a worldwide effort to convert or reuse this environmentally detrimental molecule and fluorination of battery materials could be one of the possible solutions.

[0035] The surface fluorination and inorganic fluoride coating is carried out in a vertical flow-type tube reactor consisting of silica or metal tube containing silica or metal porous frit, which allows to support the battery material in question (cathode, anode, solid electrolyte or current collector), but at the same time allow unobstructed gas flow. Metal of glass caps equipped with isolation valves allow the transfer of fluorinated material under inert atmosphere into the glove box. Mass flow controllers ensure the accurate concentration of active gas, to produce the gas mixtures and to exchange active gas with inert one after the fluorination period. The vertical tube furnace is equipped with high-precision temperature control unit. Mild fluorinating agents (active gases) such as HCFs, PFCs, HCFCs and CFCs, either in pure form or as a mixture with inert, e.g. Ar, gas (between 0 and 80% of inert gas), are feed into the flow-type tube reactor by mass flow controllers with a flow rate between 3 to 500 ml/min. Battery materials suspended on silica or metal porous frit are fluorinated/ fluoride coated in a temperature range between 50 and 800° C. The fluorination process for cathode material (e.g. transition metal oxides) is carried out in a temperature range between 100 and 800° C., anode materials (e.g. mantellic lithium) between 50 and 200° C., solid-electrolyte (e.g. Li.sub.3OCl) between 50 and 600° C., and current collector (e.g. Al and Cu metal between 150 and 800° C.

[0036] As an example, a LiNi.sub.0.80Co.sub.0.15Al.sub.0.05O.sub.2 (NCA) layered transition metal oxides battery cathode material was fluorinated with CHF3 gas (mild fluorination agent) at 300° C. in a vertical flow-type tube reactor as shown in FIG. 1a. The CHF.sub.3 gas was mixed with Ar gas in ratio of 1:1 by using mass flow controllers. Sample was fluorinated for 60 min with CHF.sub.3 gas. Afterwards, the sample was transferred into the Ar-filled glove box under inert atmosphere and thoroughly ground. The X-ray photoemission spectroscopy (XPS) clearly indicate formation of fluoride layer on the surface of cathode material after 60 min exposure to CHF.sub.3. The F is spectra of pristine (light-gray) and after 60 min fluorinated (dark-gray) NCA powders are shown in FIG. 1b).

[0037] All prepared samples were mixed with PVDF and Super C carbon in a 80:10:10 ratio in NMP solution to prepare a homogeneous slurry. The slurry was cast on an Al foil having a thickness of 200 μm. Afterwards, the slurries were dried in a vacuum oven at 80° C. over the night, cut into 13 mm electrodes with loading of active material between 3.8 to 5.3 mg/cm.sup.2, and dried at 120° C. over the night before storing them in Ar-filled glove box. The electrochemical cells were composed of cathode (described above), Celgard and glass-fibre separators, Li metal anode and electrolyte (1 M LiPF.sub.6 in ethylene carbonate: dimethyl carbonate, 1:1).

[0038] The electrochemical cells containing the fluorinated NCA material cycled at C/10 rate show superior specific capacity retention at higher cut-off potential (4.5 V and 4.9 V) and better long-cycling performance in comparison to pristine NCA as shown in FIG. 2.

[0039] Technical part:

[0040] Mild fluorinating agents, such as hydrofluorocarbons—HCFs, perfluorocarbons—PFCs, hydrochlorofluorocarbons—HCFCs and chlorofluorocarbons—CFCs, are convenient fluorinating agents, which enable a detailed fine-tuning of the fluorinating parameters, such as flow rate, concentration, temperature. In contrast to fluorine gas (usually used for cathode and anode materials fluorination), they are non-toxic, non-corrosive and non-flammable at room temperatures. Representative examples are CHF.sub.3 (R-23), CF.sub.4 (R-14), CCl.sub.3F (R-11), CCl.sub.2F.sub.2 (R-12), CClF.sub.3 (R-13), CHClF.sub.2 (R-22), CClF.sub.2CClF.sub.2 (R-114), CClF.sub.2CF.sub.3 (R-115), CF.sub.3CF.sub.3 (R-116), CF.sub.2CHClF (R-124), CHF.sub.2CHF.sub.2 (R-134) etc.

[0041] Suitable cathode materials are for example layered transition metal oxides, containing Mn, Fe, Co, Ni, Al, etc. with formulae Li.sub.1+xM1.sub.aM2.sub.bM3.sub.cO.sub.2 and Na.sub.1+xM1.sub.aM2.sub.bM3.sub.cO.sub.2 (x+a+b+c=1). Typical representatives are LiNi.sub.0.33Co.sub.0.33Mn.sub.0.33O.sub.2 (NCM111) , Ni-rich NCMs, such as LiNi.sub.0.85Co.sub.0.1Mn.sub.0.05O.sub.2,LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2 (NCM811), LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 (NCM622) , LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2 (NCM523) , Li-rich NCM; e.g. Li.sub.1.17 (Ni.sub.0.22Co.sub.0.12Mn.sub.0.6).sub.0.8302O.sub.2, LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2 (NCA) Na.sub.0.67Mn.sub.0.5Fe.sub.0.35Co.sub.0.15O.sub.2, Na.sub.0.67Mn.sub.0.6Fe.sub.0.25Al.sub.0.15O.sub.2 etc.; oxides, e.g. MnO.sub.2, V.sub.2O.sub.5, LiV.sub.3O.sub.8, etc.; Spinel oxides. such as LiMn.sub.2O.sub.4, LiMn.sub.1.5Ni.sub.0.5O.sub.4, LiMn.sub.1.5Cu.sub.0.5O.sub.4, LiCrMnO.sub.4, LiFeMnO.sub.4, etc.; Olivine-type phosphates, such as LiFePO.sub.4, LiMnPO.sub.4, LiNiPO.sub.4, LiCoPO.sub.4, etc.; Phosphates, such as Li.sub.3Ti.sub.2(PO.sub.4).sub.3, Li.sub.5Fe.sub.2(PO.sub.4).sub.3, Li.sub.3V.sub.2(PO.sub.4).sub.3, LiV.sub.2(PO.sub.4).sub.3, etc.; Sulfates, such as Li.sub.2Fe.sub.2(SO.sub.4).sub.3, Li.sub.2Fe(SO.sub.4).sub.2, Li.sub.2V.sub.2(SO.sub.4).sub.3, etc.; Hydroxi-phosphates/-sulfates, such as LiFeSO.sub.4(OH), LiCoPO.sub.4(OH), LiCrPO.sub.4(OH), LiFePO.sub.4(OH), etc.; Oxi-phosphates/-sulfates, such as LiVPO.sub.4O, Li.sub.5VO(PO.sub.4).sub.2, Li.sub.2VO(HPO.sub.4).sub.2, Li.sub.2VOP.sub.2O.sub.7, etc.).

[0042] The anode materials can be in general classified as carbonaceous, titanium oxides, metal oxides, alloys, metal phosphides/sulfides/nitrides and metals.

[0043] The first group are titanium oxides with Li.sub.4Ti.sub.5O.sub.12 (LTO) and TiO.sub.2 as representatives of this group. The second group are transition metal oxides, where the conversion mechanism is described with the following reaction: M.sub.xO.sub.y+2y Li.sup.++2y e.sup.−-->y Li.sub.2O+xM. The examples of the transition metal oxides are Fe.sub.2O.sub.3, Co.sub.3O.sub.4, MnO, CuO, NiO, SnO.sub.2, etc. The Si, Ge, Sn, Sb, etc. metals are forming alloys with Li and Na metal. These materials represent alloying anodes and the alloying mechanism follows the xLi.sup.++x e.sup.−+M-->Li.sub.xM formula. The fifth group are metal phosphides/ sulfides/ nitrides with MaXb formula, where M=Co, Ni, Mn, Fe, Cu, Cr, Mo, etc. and X=P, S, N. The last group are alkali (e.g. Li, Na and K), and alkaline earth (e.g. Mg and Ca) metals.

[0044] The oxide-type , sulfide-type, halides and solid-polymer-type ion conductors are three mayor groups of solid electrolytes. The oxide-type ion conductors can be further divided to perovskites with ABO.sub.3 formula, such as e.g. Li.sub.3xLa.sub.(2/3)−xTiO.sub.3; anti-perovskites, such as e.g Li.sub.3OCl, Li.sub.3OCl.sub.0.5Br.sub.0.5, Li.sub.3OCl.sub.0.05I.sub.0.5, Li.sub.3−2xMg.sub.xClO, etc.; NASICONs, such as Li.sub.1.3Al.sub.0.3Ti.sub.1.7(PO.sub.4).sub.3, Li.sub.l+xTi.sub.2−xSC.sub.x(PO.sub.4).sub.3, etc.; and garnets with Li.sub.5La.sub.3M.sub.2O.sub.12 (M=Nb, Ta) formula, such as Li.sub.5La.sub.3Nb.sub.2O.sub.12, Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, Li.sub.5+2xLa.sub.3Nb.sub.2−xY.sub.xO.sub.12, Li.sub.7La.sub.3Zr.sub.2O.sub.12, etc. The second type of ionic conductors are sulfide-type, which consist of thio-LISICONs with Li.sub.4−xM.sub.1−yM′.sub.yS.sub.4 (M=Si, Ge, and M′=P, Al, Zn, Ga) formula (e.g. LPS (Li.sub.3PS.sub.4), LGPSs (Li.sub.10GeP.sub.2S.sub.12), Li.sub.10SnP.sub.2S.sub.12, Li.sub.11Si.sub.2PS.sub.12, Li.sub.9.54Si.sub.1.74P.sub.1.44S.sub.11.7Cl.sub.0.3, Li.sub.10.35(Sn.sub.0.27Si.sub.1.08)P.sub.1.65S.sub.12, etc.), argyrodites with Li.sub.6PS.sub.5X (X=Cl, Br, I) formula (e.g. Li.sub.6PS.sub.5Cl, Li.sub.6PS.sub.5Br and Li.sub.6PS.sub.5I), LZPS with Li.sub.1+2xZn.sub.1−xPS.sub.4 formula, layered sulfides, such as Li[Li.sub.0.33Sn.sub.0.67S.sub.2], Li.sub.0.6[Li.sub.0.2Sn.sub.0.8S.sub.2], Li.sub.2SnS.sub.3, Li.sub.2Sn.sub.2S.sub.5 etc., and halide solid electrolyte materials Li.sub.3MX.sub.6 (X=Cl, Br, and I) (e.g. Li.sub.3YCl.sub.6,Li.sub.3YBr.sub.6), Li.sub.2Sc.sub.2/3Cl.sub.4 or Li.sub.3−xM.sub.1−xZrxCl.sub.6 (M=Y, Er) The solid-polymer-type ion conductors are subdivided to polyether-based containing crystalline alkali metal salts of poly(ethylene oxide), polycarbonate-based such as polyethylene carbonate bis(trifluoromethanesulfonyl)imide composite, and plastic-crystal-based for example nitrile based (N≡C—CH.sub.2—CH.sub.2—C≡N) polar crystalline plastic.

[0045] Electrochemical testing materials:

[0046] Conductive materials are for example Carbon black, acetylene black, Ketjen black, carbon fiber, graphite fine particles, natural graphite, artificial graphite, carbon nanotubes, fullerenes; metal powders, metal fibers, metal nanotubes, and conductive polymers (e.g. polyaniline, polyacetylene, polypyrrole, etc.), along with conductive material containing fluorine atoms (e.g. fluorocarbons).

[0047] Nonaqueous electrolyte comprise organic solvents and Li or Na salts. Organic solvents are for example organic carbonate based such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate and dibutyl carbonate. Ether based, such as tetrahydrofuran, 1,3-dioxane, dimethoxyethane, diethoxyethane, methoxyethoxyethane, methyldiglyme, dimethyl ether. Ester based electrolytes are for example methyl acetate and methyl butyrate. Nitriles such as acetonitrile benzonitrile. Other: N, N-dimethylformamide, dimethylacetamide, dimethylsulfoxide, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, γ-butyrolactone, γ-valerolactone, propiolactone, etc., and mixtures of those. Ionic salts such as LiPF.sub.6, LiBF.sub.4, LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3, LiC.sub.4F.sub.9SO.sub.3, LiAlO.sub.2, LiAlCl.sub.4, LiN(C.sub.xF.sub.2x−1SO.sub.2) etc. Along with their mixtures and Na analogues.

[0048] Binders used are vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene, styrene butadiene rubber-based polymer, etc., and mixtures of them.

[0049] Separators can be for instance glass fibers, polyester, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) or a combination of them.

[0050] Cathodes and anodes can be produced by thoroughly mixing cathode/ anode active material with conductive material(s) and binder in N-Methyl-2-pyrrolidone (NMP) solution/slurry. Then, casting the slurry on Al or Cu foil (current collector) for cathode and anode respectively and producing 50-350 μm thick film. Followed by vacuum drying at 80° C., punching the electrodes and additional vacuum drying at 120° C. before storing them inside Ar-filled glove box.

[0051] The electrochemical cells are produced by stacking cathode, separator soaked in nonaqueous electrolyte and anode inside the battery housing.