A PROTECTIVE LAYER FOR A METAL ELECTRODE AND LITHIUM BATTERY COMPRISING THE SAME

Abstract

An electrode for a lithium battery contains a metal layer coated with a coating layer containing an organic binder and a metal compound. The metal compound is selected from aluminium oxide, silicon dioxide, zirconium oxide, mixed oxides including zirconium, mixed oxides including aluminium, lithium zirconium phosphate, and mixtures thereof. The metal compound is made of aggregates of primary particles with a number mean primary particle size d.sub.50 of 5 nm-100 nm, obtained by a pyrogenic process. The weight ratio of the metal compound to the organic binder in the coating layer is from 0.1 to 10.

Claims

1: An electrode for a lithium battery, comprising a metal layer coated with a coating layer comprising an organic binder, and a metal compound selected from the group consisting of aluminium oxide, silicon dioxide, zirconium oxide, a mixed oxide comprising zirconium, a mixed oxide comprising aluminium, lithium zirconium phosphate, and a mixture thereof, wherein the metal compound consists of aggregates of primary particles with a number mean primary particle size d.sub.50 of 5 nm-100 nm obtained by a pyrogenic process, and wherein a weight ratio of the metal compound to the organic binder in the coating layer is from 0.1 to 10.

2: The electrode according to claim 1, wherein the metal compound comprises the mixed oxide comprising zirconium, and wherein the mixed oxide comprising zirconium further comprises one or several elements selected from the group consisting of Li, Na, K, Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Mn, B, Al, Ga, In, Fe, Sc, Y, La, Ti, Zr, Hf, Ce, Si, Ge, Sn, Pb, V, Nb, Ta, Mo, and W.

3: The electrode according to claim 1, wherein the metal compound comprises the mixed oxide comprising zirconium, and wherein the mixed oxide comprising zirconium is a compound of a general formula Li.sub.aZr.sub.bM.sub.cO.sub.0.5a+2b+d (I), wherein 1.5≤a≤15, 0.5≤b≤3.0, 0≤c≤5, d=0.5c for M=Na, K; d=c for M=Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Mn; d=1.5c for M=B, Al, Ga, In, Fe, Sc, Y, La; d=2c for M=Ti, Zr, Hf, Ce, Si, Ge, Sn, Pb; d=2.5c for M=V, Nb, Ta; and d=3c for M=Mo, W.

4: The electrode according to claim 1, wherein the coating layer further comprises a lithium salt selected from the group consisting of lithium hexafluorophosphate (LiPF.sub.6), lithium bis 2-(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium perchlorate (LiClO.sub.4), lithium tetrafluoroborate (LiBF.sub.4), Li.sub.2SiF.sub.6, lithium triflate, Lithium bis(perfluoroethylsulfonyl)imide (LiN(SO.sub.2CF.sub.2CF.sub.3).sub.2), lithium nitrate, lithium bis(oxalate)borate, lithium-cyclo-difluoromethane-1,1-bis(sulfonyl)imide, lithium-cyclo-hexafluoropropane-1,1-bis(sulfonyl)imide, and a mixture thereof.

5: The electrode according to claim 1, wherein the metal compound is surface treated with a surface treatment agent selected from the group consisting of an organosilane, a silazane, an acyclic polysiloxane, a cyclic polysiloxane, and a mixture thereof.

6: The electrode according to claim 1, wherein the metal compound has a number mean aggregate particle size d.sub.50 of 20 nm-1 μm.

7: The electrode according to claim 1, wherein the weight ratio of the metal compound to the organic binder in the coating layer is from 1 to 6.

8: The electrode according to claim 1, wherein the organic binder is selected from the group consisting of poly(vinylidene fluoride), copolymer of vinylidene fluoride and hexafluoropropylene, poly(vinyl acetate), poly(ethylene oxide), poly(methyl methacrylate), poly(ethyl acrylate), poly(vinyl chloride), poly(urethane), poly(acrylonitrile), copolymer of ethylene and vinyl acetate, carboxyl methyl cellulose, poly(imide), poly(dimethylsiloxane), poly(ethylene oxide), and a mixture thereof.

9: The electrode according to claim 1, wherein the metal layer comprises at least one material selected from the group consisting of lithium, aluminium, copper, silver, gold, nickel, iron, steel, stainless steel, titanium, or a metal alloy thereof.

10: The electrode according to claim 1, wherein a thickness of the metal layer is 0.5 μm-500 μm.

11: The electrode according to claim 1, wherein a thickness of the coating layer is 0.5 μm-100 μm.

12: A process for producing the electrode as defined in claim 1, comprising: (1) preparing a mixture comprising: the organic binder, the metal compound selected from the group consisting of aluminium oxide, silicon dioxide, zirconium oxide, a mixed oxide comprising zirconium, a mixed oxide comprising aluminium, lithium zirconium phosphate, and a mixture thereof, wherein the metal compound consists of aggregates of primary particles with a number mean primary particle size d.sub.50 of 5 nm-100 nm and is obtained by a pyrogenic process, and optionally, a solvent, wherein the weight ratio of the metal compound to the organic binder is from 0.1 to 10: (2) coating the mixture prepared in (1) on a surface of the metal layer, to obtain the coating laver; and (3) optionally, drying and/or curing the coating layer prepared in (2).

13: The process according to claim 12, wherein the solvent used in (1) is selected from the group consisting of 1,2-dimethoxyethane, diethyl ether, tetrahydrofuran, dioxane, bis (2-methoxyethyl) ether, pentane, hexane, heptane, octane, decane, toluene, ethanol, isopropanol, N-Methyl-2-pyrrolidone, triethyl phosphate, dimethyl sulfoxide, methyl ethyl ketone, methyl isobutyl ketone, benzaldehyde, N,N-dimethylformamide, dimethylacetamide, acetonitrile, cyclohexanone, ethyl acetate, propylene carbonate, ethylene carbonate, diethylene glycol monomethyl ether, triethylene glycol methyl ether, acetylacetone, acetone, and a mixture thereof.

14: A method of constructing a battery, comprising: providing the electrode according to claim 1 as a constituent in a lithium metal or lithium ion battery.

15: A battery comprising the electrode according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] FIG. 1a shows polarized voltages with different metal compounds at the current density of 0.1 mA/cm.sup.2 in liquid electrolytes.

[0092] FIG. 1b shows polarized voltages with different metal compounds at the current density of 0.5 mA/cm.sup.2 in liquid electrolytes.

[0093] FIG. 1c shows polarized voltages with materials from examples 12a-14a at the current densities of 0.05 (cycle 1-5) to 0.1 (cycle 5-9) mA/cm.sup.2 in hybrid solid electrolytes.

[0094] FIG. 1d shows polarized voltages with materials from examples 12a-14a at the current densities of 0.25 (cycle 1-5) to 0.5 (cycle 5-9) mA/cm.sup.2 in hybrid solid electrolytes.

[0095] FIG. 2 (A) shows plating and stripping cycles for the example 6a.

[0096] FIG. 2 (B) shows plating and stripping cycles for the example 5a.

[0097] FIG. 2 (C) shows plating and stripping cycles for the example 4a.

[0098] FIG. 3 shows cycle performance of the Li—Cu asymmetric cells.

[0099] FIG. 4 (A) shows a SEM image for the electrode from example 8b indicating the volume expansion ratio of the electrode in comparison to the reference without alumina-polymer coating (reference value 100%).

[0100] FIG. 4 (B) shows a SEM image for the electrode from example 7b indicating the volume expansion ratio of the electrode in comparison to the reference without alumina-polymer coating (reference value 100%).

[0101] FIG. 4 (C) shows a SEM image for the electrode from example 4b indicating the volume expansion ratio of the electrode in comparison to the reference without alumina-polymer coating (reference value 100%).

EXAMPLES

Metal Compound Samples

[0102] AEROXIDE Alu 130 is a fumed alumina with BET=130 m.sup.2/g supplied by Evonik Operations GmbH.

[0103] TAMICON® TM-DAR (referred to as “TM-DAR” below) is an (alpha) alumina oxide with BET=14.5 m.sup.2/g supplied by Taimei Chemicals Co., Ltd.

[0104] (Alpha) aluminum oxide powder with BET=3.9 m.sup.2/g supplied by US Research Nanomaterials, Inc. is referred to as “USR” below.

[0105] Evonik ZrO.sub.2 is a fumed zirconium oxide with BET=40 m.sup.2/g supplied by Evonik Operation GmbH.

[0106] LLZO precursor particle is a fumed aluminum doped lithium lanthanum zirconium oxide particle with a BET of about 28 m.sup.2/g supplied by Evonik Operations GmbH.

[0107] Cubic LLZO particle is a fumed and calcined aluminum doped lithium lanthanum zirconium oxide particle with a BET of about 0.4 m.sup.2/g supplied by Evonik Operations GmbH.

[0108] Evonik ball milled (BM) c-LLZO (referred to as “BM c-LLZO” below) is a fumed, calcined and ball milled aluminum doped lithium lanthanum zirconium oxide particle with a BET of about 10 m.sup.2/g supplied by Evonik Operations GmbH.

[0109] NEI LLZO (referred to as “NEI LLZO” below) is a cubic phase aluminum doped lithium lanthanum zirconium oxide with BET of about 4.8 m.sup.2/g supplied by NEI Corporation, Physical properties of tested metal compound particles are summarized in Table 1.

TABLE-US-00001 TABLE 1 Physical properties of the tested metal compound particles BET, Average primary Crystal Metal compounds [m.sup.2/g] particle size, [nm] structure AEROXIDE ® Alu 130 130 15-25 Beta & gamma (alumina) TM-DAR (alumina) 14.5  80-100 Alpha USR (alumina) 3.9 400-500 Alpha Evonik ZrO.sub.2 40 20-50 Tetragonal & monoclinic Evonik LLZO precursor 28 20-50 Pyrochlore particle La.sub.2Z.sub.2O.sub.7 + Li.sub.2CO.sub.3 NEI LLZO 4.8 Approx. 1000 Cubic phase Evonik c-LLZO 0.4 Approx. 10000 Cubic phase Evonik BM c-LLZO 10 Approx. 100-1000 Cubic phase

[0110] Preparation of the Coated Electrode Sheets

Example 1a

[0111] A copper foil with a thickness of 12 μm covered with a lithium metal layer with a thickness of 100 μm was provided. AEROXIDE® Alu 130 particles were dispersed in 1,2-dimethoxyethane (DME), to obtain a first solution with a solid content of 40 wt %. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) (supplier: Sigma-Aldrich, weight average molecular weight (Mw) about 400,000 g/mol) was also dissolved in DME, to obtain a second solution with a solid content of 5 wt %. Both the first and the second solution were stirred vigorously for several hours and then mixed together under stirring in such a ratio to produce a mixture with a 1:1 ratio (by weight) of alumina to PVDF-HFP polymer. This mixture was coated on the lithium metal layer by solvent casting method: the raw mixture slurry was stirred by a magnet stirrer in a 20 mL sample vial followed by coating by pen brush at one time. After heating at 70° C. for 30 min on a hot plate, an electrode sheet having artificial solid electrolyte interphase (ASEI) layer with a thickness of about 10 μm was obtained.

Example 1b

[0112] The same as described in example 1a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 2a

[0113] The same as described in example 1a with the only difference that the mixture comprising a 1:1 (weight ratio) mixture of alumina particles TM-DAR and PVDF-HFP was used for coating of the electrode sheet.

Example 2b

[0114] The same as described in example 2a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 3a

[0115] The same as described in example 1a with the only difference that the mixture comprising a 1:1 (weight ratio) mixture of alumina particles USR and PVDF-HFP was used for coating of the electrode sheet.

Example 3b

[0116] The same as described in example 3a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 4a

[0117] The same as described in example 1a with the only difference that the mixture comprising a 4:1 (weight ratio) mixture of alumina particles AEROXIDE® Alu130 and PVDF-HFP was used for coating of the electrode sheet.

Example 4b

[0118] The same as described in example 4a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 5a

[0119] The same as described in example 1a with the only difference that the mixture comprising a 4:1 (weight ratio) mixture of alumina particles TM-DAR and PVDF-HFP was used for coating of the electrode sheet.

Example 5b

[0120] The same as described in example 5a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 6a

[0121] The same as described in example 1a with the only difference that the mixture comprising a 4:1 (weight ratio) mixture of alumina particles USR and PVDF-HFP was used for coating of the electrode sheet.

Example 6b

[0122] The same as described in example 6a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 7a

[0123] The same as described in example 1a with the only difference that the mixture comprising a 6:1 (weight ratio) mixture of alumina particles TM-DAR and PVDF-HFP was used for coating of the electrode sheet.

Example 7b

[0124] The same as described in example 7a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 8a

[0125] The same as described in example 1a with the only difference that the mixture comprising a 6:1 (weight ratio) mixture of alumina particles USR and PVDF-HFP was used for coating of the electrode sheet.

Example 8b

[0126] The same as described in example 8a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 9a

[0127] The same as described in example 4a with the only difference that the mixture comprising a 4:1 (weight ratio) mixture of ZrO.sub.2 particles and PVDF-HFP was used for coating of the electrode sheet.

Example 10a

[0128] The same as described in example 4a with the only difference that the mixture comprising a 4:1 (weight ratio) mixture of Evonik LLZO precursor particle and PVDF-HFP was used for coating of the electrode sheet.

Example 10b

[0129] The same as described in example 10a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 11a

[0130] The same as described in example 4a with the only difference that the mixture comprising a 6:1 (weight ratio) mixture of NEI LLZO and PVDF-HFP was used for coating of the electrode sheet.

Example 11b

[0131] The same as described in example 11a with the differences that the copper foil without a lithium metal layer was used instead of lithium deposited copper foil as the electrode sheet and acetone as a solvent was used instead of 1,2-dimethoxyethane (DME) for the dispersion of oxide particles and to dissolve Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the coating formulation.

Example 12a

[0132] A copper foil (with a thickness of 10 μm) having a lithium metal layer (with a thickness of 100 μm) was provided. PVDF-HFP was dissolved in DME, obtaining the first solution (with a solid content of 5 wt %). AEROXIDE® Alu 130 (alumina particles) was dispersed into the first solution (the mixtures were stirred vigorously for several hours) with 50 wt % alumina particles and 50 wt % PVDF-HFP obtaining the final slurry (with a solid content of 9.5 wt %). The mixture was coated on the lithium metal layer with brush by solvent casting. After baking at 70° C. for 30 min on hot plate for removing DME, both the electrodes were then covered by hybrid solid electrolyte film (details are described in Li—Li symmetrical cell fabrication in a solid (hybrid) polymer electrolyte) for the coin cell assembling.

Example 13a

[0133] The same as described in example 12a with the only difference that lithium bis (fluorosulfonyl) imide (LiFSI, supplied by Kishida Chemical Co., Ltd.) was dissolved into the second slurry with continued stirring for 1 minute. The mixture was dripped onto the lithium metal layer, then covered by hybrid solid electrolyte film. The other side of film was also dripped by the mixture, and then quickly covered with another lithium metal electrode.

Example 14a

[0134] Both the lithium metal electrodes without protective layer were covered by hybrid solid electrolyte film (details are described in Li—Li symmetrical cell fabrication in a solid (hybrid) polymer electrolyte) for the coin cell assembling.

[0135] The used in examples 1a,b-14 a,b weight ratios of metal compound particles to PVDF-HFP are summarized in Table 2-1 and Table 2-2.

TABLE-US-00002 TABLE 2-1 Preparation of the electrode sheets coated with metal compound particles in liquid electrolyte. Oxide particle:PVDF-HFP ratio (by weight) Metal compounds 1:1 4:1 6:1 Coated layer Li Cu Li Cu Li Cu onto AEROXIDE ® Example Example Example Example Not available Alu 130 1a 1b 4a 4b TM-DAR Example Example Example Example Example Example 2a 2b 5a 5b 7a 8b USR Example Example Example Example Example Example 3a 3b 6a 6b 8a 8b Evonik ZrO.sub.2 Example 9a Evonik LLZO Example Example precursor 10a 10b NEI LLZO Example Example 11a 11b

TABLE-US-00003 TABLE 2-2 Preparation of the electrode sheets coated with metal compound particles in solid (hybrid) polymer electrolyte. Metal compound:PVDF-HFP:LiFSI ratio (by weight) Without protective Metal compound layer 1:1:0 1:1:16 Solid (hybrid) Evonik BM c-LLZO: (PEO + LiTFSI) ratio (by polymer electrolyte weight) = 3:7 AEROXIDE ® Example 14a Example 12a Example 13a Alu 130

[0136] Li—Li Symmetrical Cell Fabrication in Liquid Electrolyte

[0137] A 1 M lithium bis(trifluoromethanesulfonyl)imide (supplier: KISHIDA, >99.9%) solution in 1:1 vol./vol. 1,3-dioxolane (supplier: Sigma-Aldrich, 99.8%):1,2-dimethoxyethane (supplier: KISHIDA, 99.9%) containing 1 wt % lithium nitrate (supplier: Sigma-Aldrich, stored in a glovebox for a week) was used as an electrolyte composition. The first coated electrode sheet, a polypropylene-polyethylene-polypropylene (PP/PE/PP) separator (Celgard® 2320, supplier: Celgard) with a thickness of about 10-20 μm, and the second (identical to the first one) electrode sheet were placed in sequence (metal compound coating layer of each electrode sheet was faced toward the separator) and sealed within an CR2320 coin cell.

[0138] Li—Li Symmetrical Cell Fabrication in Solid (Hybrid) Polymer Electrolyte

[0139] Weighted Evonik ball milled c-LLZO was ground, milled with polyethylene oxide (PEO, purchased from Sigma-Aldrich) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, purchased from Kishida Chemical Co., Ltd). Weighted LLZO to obtain a paste-like material, which was then annealed at 100° C. for overnight, successively hot-pressed at 100° C. between Teflon substrates for a desired thickness. The molar ratio of [O]:[Li] was set as 15:1. This hybrid solid electrolyte (HSE) was used as separator as well as the solid electrolyte. The first coated electrode sheet, HSE with a thickness of about 110 μm, and the second (identical to the first one) electrode sheet were placed in sequence (metal compound coating layer of each electrode sheet was faced toward the separator) and sealed within an CR2320 coin cell.

[0140] Electrochemical Tests (Cell Cycling Tests)

[0141] Electrochemical cycling tests were carried out using CR2032-type coin cells on Arbin BT2000 battery testers at room temperature. Voltage vs. time(cycles) profiles during galvanostatic cycling of Li—Li cells are related to electrode stability and failure. Voltage profiles of Li stripping and plating in a Li—Li symmetric cell were measured at a current density of 0.1 mAh/cm.sup.2 and 0.5 mAh/cm.sup.2.

[0142] The procedure for Li—Li symmetric cell tests curried out at room temperature was as follows:

[0143] Rest 10 sec.

[0144] a. Charge 0.1 mA/cm.sup.2 for 5 h, record every 5 min, then rest 10 min;

[0145] b. Discharge 0.1 mA/cm.sup.2 for 5 h, record every 5 min, then rest 10 min;

[0146] Repeat a. and b. for 5 cycles

[0147] c. Charge 0.5 mA/cm.sup.2 for 1 h, record every 30 sec., then rest 10 min;

[0148] d. Discharge 0.5 mA/cm.sup.2 for 1 h, record every 30 sec., then rest 10 min;

[0149] Repeat c. and d. for 5 cycles

[0150] e. Charge 1 mA/cm.sup.2 for 0.5 h, record every 15 sec., then rest 10 min;

[0151] f. Discharge 1 mA/cm.sup.2 for 0.5 h, record every 15 sec., then rest 10 min;

[0152] Repeat a. b. for 5 cycles

[0153] The determination of the voltage profiles with different alumina particles showed the lowest polarization voltage for systems comprising AEROXIDE® Alu130 alumina particles as FIG. 1a and FIG. 1a with the current density of 0.1 mA/cm.sup.2 and 0.5 mA/cm.sup.2. (Table 3: example 1a vs examples 2a and 3a; example 4a vs. examples 5a and 6a).

[0154] As to the alumina particles:polymer ratio, the voltage profile with the compounding ratio of AEROXIDE® Alu130 alumina particles to the PVDF-HFP=4:1 (FIG. 1, Table 3, example 4a) showed the lowest polarization voltage and the flattest profile among all the tested alumina samples and alumina particles:polymer ratios.

TABLE-US-00004 TABLE 3-1 The results of the polarized voltage measurements for the electrodes coated with metal compound/PVDF-HFP in the liquid electrolyte. Polarized voltage Polarized voltage at 0.1 mA/cm.sup.2 at 0.5 mA/cm.sup.2 Example 1a 15 mV 30 mV Example 2a 25 mV 50 mV Example 3a 30 mV 55 mV Example 4a 15 mV 25 mV Example 5a 25 mV 45 mV Example 6a 30 mV 45 mV Example 7a 25 mV 35 mV Example 8a 30 mV 40 mV Example 9a 10 mV 20 mV Example 10a 15 mV 30 mV Example 11a 30 mV 40 mV

[0155] The coated electrode sheets of examples 4a, 5a, and 6a which compounding ratio of alumina particles and PVDF-HFP=4:1, were further cycled at the current density of 1 mA/cm.sup.2 and plating and stripping capacity of 0.5 mAh/cm.sup.2 to compare the cycling performance of the examples of Li—Li symmetric cells (example 4a: FIG. 2 (C); example 5a: FIG. 2 (B); example 6a: FIG. 2 (A)). It was not possible to continue the cycling with the electrodes of example 5a and 6a containing the alumina particles TM-DAR and USR. This indicates that the lithium dendrite formation was not prevented. On the other hand, the sample 4a was able to continue the cycling over 200 cycles and also showed the stable polarized voltage profile. That indicates that the lithium dendrite formation was mitigated.

TABLE-US-00005 TABLE 3-2 The results of the polarized voltage measurements for the electrodes coated with metal compound/PVDF- HFP in the hybrid solid electrolyte. Polarized Polarized Polarized Polarized voltage at voltage at voltage at voltage at 0.05 0.1 0.25 0.5 mA/cm.sup.2 mA/cm.sup.2 mA/cm.sup.2 mA/cm.sup.2 Example 12a 250 mV  300 mV  not not without Li measurable measurable salt Example 13a 15 mV 30 mV not not with LiFSI measurable measurable Example 14a 50 mV 90 mV 300 mV 500 mV without the protective layer

[0156] Li—Cu Asymmetrical Cell Fabrication

[0157] In order to further analyze the coulombic efficiency using the protection layer, Li—Cu asymmetrical cells were fabricated.

[0158] 1 M lithium bis(trifluoromethanesulfonyl)imide (KISHIDA, >99.9%) solution in 1:1 v/v 1,3-dioxolane (supplier: Sigma-Aldrich, 99.8%):1,2-dimethoxyethane (supplier: KISHIDA, 99.9%) containing 1 wt % lithium nitrate (supplier: Sigma-Aldrich, stored in a glovebox for a week) was used as an electrolyte composition. The first coated electrode sheet, a polypropylene-polyethylene-polypropylene (PP/PE/PP) separator (Celgard® 2320, supplier: Celgard) with a thickness of about 10-20 μm, and the second (identical to the first one) electrode sheet were placed in sequence (metal compound coating layer of each electrode sheet was faced toward the separator) and sealed within an CR2320 coin cell.

[0159] Cycling Tests

[0160] The cycling tests using Li—Cu asymmetric cells were performed for the examples of 1b, 2b, 3b, 4b, 7b, 8b, 10b and 11 b. Coulombic efficiency was measured.

[0161] The Procedure for Li—Cu Asymmetric Cell CE.sub.avg. Tests was as Follows:

[0162] a. Discharge 0.5 mA/cm.sup.2 for 10 h, record every 3 min;

[0163] b. Charge 0.5 mA/cm.sup.2 for 10 h, record every 3 min;

[0164] Repeat a. and b. for 2 cycles

[0165] Discharge 0.5 mA/cm.sup.2 for 10 h, record every 3 min;

[0166] Charge 0.5 mA/cm.sup.2 for 2 h, record every 3 min;

[0167] a. Discharge 0.5 mA/cm.sup.2 for 2 h, record every 3 min;

[0168] b. Charge 0.5 mA/cm.sup.2 for 2 h, record every 3 min;

[0169] Repeat a. and b. for 11 cycles

[0170] Discharge 0.5 mA/cm.sup.2 for 2 h, record every 3 min;

[0171] Charge 0.5 mA/cm.sup.2 until >1V, record every 3 min.

[0172] The Procedure for Li—Cu Asymmetric Cell CE Cycling Tests was as Follows:

[0173] a. Discharge 0.5 mA/cm.sup.2 for 2 h, record every 3 min;

[0174] b. Charge 0.5 mA/cm.sup.2 until >1V, record every 3 min;

[0175] Repeat a. and b.

[0176] In all cases, using alumina-polymer coatings provided an improved coulombic efficiency of the electrodes when compared with the uncoated electrode material (reference). With the increased alumina particles to polymer weight ratio, as well as using the smaller size of alumina particles, particularly, with fumed alumina of example 4b, the coulombic efficiency of Li—Cu asymmetric cells was improved significantly (FIG. 3, Table 4).

TABLE-US-00006 TABLE 4 Coulombic efficiency and volume expansion of Li—Cu asymmetric cells in the liquid electrolyte. Coulombic Volume Electrode efficiency, [%] expansion, [%] Reference without protective 75.60% 100%  layer Example 1b 95.80% Example 2b 89.20% Example 3b 87.60% Example 4b 99.90% 10% Example 7b 99.00% 30% Example 8b 90.90% 50% Example 10b 92.10% Example 11b 93.30%

[0177] The measurement of the volume expansion ratio was done by SEM analyses. The thickness changes before (10 μm) and after 10 cycles were measured at the current density of 0.5 mA/cm.sup.2 and the capacity of 2 mAh/cm.sup.2 and analysed in SEM images for the cells in comparison to the reference without alumina-polymer coating (reference value 100%). Volume expansion ratios of the electrodes from examples 8b, 7b and 4b are shown in FIGS. 4 (A), 4 (B) and 4 (C), respectively.

[0178] The Procedure for Li Expansion Test on Cu Foil was as Follows:

[0179] a. Discharge 0.5 mA/cm.sup.2 for 4 h, record every 1 min;

[0180] b. Charge 0.5 mA/cm.sup.2 until >1V, record every 1 min;

[0181] c. Discharge 0.5 mA/cm.sup.2 for 4 h, record every 1 min.

[0182] For the electrode of example 4b, this value was minimized down to 10%, whereas the electrodes from examples 7b and 8b with higher alumina:polymer weight ratio but other than in example 4b alumina types, provided volume expansion ratios of 30% and 50%, respectively (Table 4).