INTERFACE FUNCTIONAL LAYER AND PREPARATION METHOD THEREOF, AND LITHIUM-ION BATTERY

Abstract

This application relates to an interface functional layer and a preparation method thereof, and a lithium-ion battery, where the interface functional layer includes a cyclic ether compound, a lithium salt, an auxiliary agent and a ceramic powder in a mass ratio of 50-90:5-30:5-40:0-5. In this application, the interface functional layer is provided between a positive and/or negative electrode and a solid electrolyte, thereby inhibiting the uneven deposition of lithium-ions at interfacial gaps, reducing the interface impedance, and meanwhile improving the interfacial stability.

Claims

1. An interface functional layer, wherein the interface functional layer comprises a cyclic ether compound, a lithium salt, an auxiliary agent and a ceramic powder in a mass ratio of (50-90):(5-30):(5-40):(0-5).

2. The interface functional layer according to claim 1, wherein a thickness of the interface functional layer is 10 nm-10 μm.

3. The interface functional layer according to claim 2, wherein the thickness of the interface functional layer is 400 nm-800 nm.

4. The interface functional layer according to claim 1, wherein the ceramic powder has a particle size of 1 nm-900 nm.

5. The interface functional layer according to claim 2, wherein the ceramic powder has a particle size of 1 nm-900 nm.

6. The interface functional layer according to claim 3, wherein the ceramic powder has a particle size of 1 nm-900 nm.

7. The interface functional layer according to claim 4, wherein the particle size of the ceramic powder is 500 nm-600 nm.

8. The interface functional layer according to claim 5, wherein the particle size of the ceramic powder is 500 nm-600 nm.

9. The interface functional layer according to claim 6, wherein the particle size of the ceramic powder is 500 nm-600 nm.

10. The interface functional layer according to claim 1, wherein the cyclic ether compound is selected from 1,3-dioxolane and/or 1,4-dioxane; and/or, the lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(oxalate) borate, lithium difluoro(oxalate)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(malonato) borate, lithium malonate(oxalate) borate, lithium hexafluoroantimonate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl imidazole, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiC(SO.sub.2CF.sub.3).sub.3 and LiN(SO.sub.2F).sub.2; and/or, the auxiliary agent is selected from one or more of ethylene glycol dimethyl ether, dipropylene glycol dimethyl ether carbon, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate; and/or, the ceramic powder is selected from one or more of nano-hexagonal boron nitride, nano-alumina and nano-silicon dioxide.

11. The interface functional layer according to claim 2, wherein the cyclic ether compound is selected from 1,3-dioxolane and/or 1,4-dioxane; and/or, the lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(oxalate) borate, lithium difluoro(oxalate)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(malonato) borate, lithium malonate(oxalate) borate, lithium hexafluoroantimonate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl imidazole, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiC(SO.sub.2CF.sub.3).sub.3 and LiN(SO.sub.2F).sub.2; and/or, the auxiliary agent is selected from one or more of ethylene glycol dimethyl ether, dipropylene glycol dimethyl ether carbon, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate; and/or, the ceramic powder is selected from one or more of nano-hexagonal boron nitride, nano-alumina and nano-silicon dioxide.

12. The interface functional layer according to claim 3, wherein the cyclic ether compound is selected from 1,3-dioxolane and/or 1,4-dioxane; and/or, the lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(oxalate) borate, lithium difluoro(oxalate)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(malonato) borate, lithium malonate(oxalate) borate, lithium hexafluoroantimonate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl imidazole, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiC(SO.sub.2CF.sub.3).sub.3 and LiN(SO.sub.2F).sub.2; and/or, the auxiliary agent is selected from one or more of ethylene glycol dimethyl ether, dipropylene glycol dimethyl ether carbon, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate; and/or, the ceramic powder is selected from one or more of nano-hexagonal boron nitride, nano-alumina and nano-silicon dioxide.

13. The interface functional layer according to claim 4, wherein the cyclic ether compound is selected from 1,3-dioxolane and/or 1,4-dioxane; and/or, the lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(oxalate) borate, lithium difluoro(oxalate)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(malonato) borate, lithium malonate(oxalate) borate, lithium hexafluoroantimonate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl imidazole, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiC(SO.sub.2CF.sub.3).sub.3 and LiN(SO.sub.2F).sub.2; and/or, the auxiliary agent is selected from one or more of ethylene glycol dimethyl ether, dipropylene glycol dimethyl ether carbon, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate; and/or, the ceramic powder is selected from one or more of nano-hexagonal boron nitride, nano-alumina and nano-silicon dioxide.

14. A preparation method of the interface functional layer according to claim 1, comprising the following steps: mixing the cyclic ether compound, the lithium salt, the auxiliary agent and the ceramic powder evenly to obtain a mixed solution, attaching the mixed solution to a positive electrode, a negative electrode and/or a solid electrolyte, and performing a curing treatment to obtain the interface functional layer.

15. The preparation method of the interface functional layer according to claim 14, wherein the negative electrode is selected from at least one of a metal lithium negative electrode or a lithium alloy negative electrode, and the metal lithium is selected from one of molten metal lithium, lithium powder and lithium ribbon, and the lithium alloy is selected from one of Li—In alloy, Li—Al alloy, Li—Sn alloy, Li—Mg alloy and Li—Ge alloy.

16. The preparation method of the interface functional layer according to claim 14, wherein the mixing is performed under stirring, the stirring having a speed of 200-1000 rpm/min.

17. The preparation method of the interface functional layer according to claim 16, wherein the stirring is performed for 1-24 h.

18. The preparation method of the interface functional layer according to claim 14, wherein the attaching is performed by selecting from one or more of blade coating, spray coating, tape casting and soaking.

19. The preparation method of the interface functional layer according to claim 14, wherein a temperature of the curing treatment is 25-60° C.

20. A lithium-ion battery, prepared by means of winding or laminating a positive electrode, a solid electrolyte, and a negative electrode, wherein the interface functional layer according to claim 1 is further provided between the negative electrode and the solid electrolyte and/or between the positive electrode and the solid electrolyte.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1 is a schematic structural diagram of a metal lithium negative electrode sheet and an interface functional layer thereon according to Example 1 of the present application.

[0047] FIG. 2 is a schematic structural diagram of a solid electrolyte and an interface functional layer thereon in Example 4 of the present application.

[0048] FIG. 3 is a schematic structural diagram of a solid electrolyte and an interface functional layer thereon in Example 7 of the present application.

[0049] FIG. 4 is a microscopic morphology image of an interface functional layer in Example 3 of the present application.

[0050] FIG. 5 is a schematic diagram showing a comparison between AC impedance of the lithium-ion battery in Example 5 and AC impedance of the lithium-ion battery in Comparative Example 5 of the present application.

[0051] FIG. 6 is a cycle diagram of the symmetric lithium battery at a current density of 1 mA/cm.sup.2 in Example 8 of the present application.

DESCRIPTION OF EMBODIMENTS

[0052] This application will be described in further detail below with reference to specific embodiments. It should be understood that the following examples are only to exemplarily illustrate and explain this application, and should not be construed as limiting a protection scope of this application. All technologies implemented based on the above contents of this application are covered within the protection scope intended by this application.

[0053] The ceramic powders in the examples of this application were purchased from Kejing Chemical Co., Ltd., with a particle size of about 400-800 nm.

[0054] This application is described in detail below by specific examples.

[0055] The test methods for each example and comparative example are as follows.

1. AC Impedance at Room Temperature

[0056] AC impedance test for lithium-ion batteries

[0057] The electrochemical workstation with a model CHI600E from Shanghai Chenhua Instrument Co, Ltd. was used for battery testing, with a parameter setting: an amplitude of 10 mV, a frequency range of 0.1 Hz-3 MHz.

2. Cycle Test for Symmetric Lithium Batteries

[0058] Battery test equipment from Wuhan Landian Electronics Co. Ltd was used.

[0059] Test conditions: a constant current charge-discharge test for symmetric lithium batteries was carried out at a current density of 1 mA/cm.sup.2.

3. Cycle Life Test

[0060] The test instrument adopted was the battery test equipment from Wuhan Landian Electronics Co. Ltd.

[0061] Test conditions: in the case that the initial capacity is basically the same, the number of cycle when the capacity decays to 80% of the initial value was determined under a condition of 25° C. and 0.2 C/0.2 C.

4. Battery Short-Circuit Rate Test

[0062] During the cycle life test, the failure or short-circuit of battery is characterized by the battery failing to be charged and discharged normally, which is recorded as short-circuit. Short-circuit rate of battery=number of short-circuited battery/total number of measured battery×100%.

Example 1

[0063] Example 1 provides a metal lithium negative electrode containing an interface functional layer and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0064] 1. Preparation of the Metal Lithium Negative Electrode Containing an Interfacial Functional Layer

[0065] (1) 1,4-dioxane, lithium bis(difluorosulfonyl)imide (LiTFSI), polycarbonate (PC), and nanoboron nitride (BN) were fully mixed in a mass ratio of 79:9:10:2, and then placed in a beaker and stirred evenly with a rotation speed of 300 rpm for 15 h to form a homogeneous solution.

[0066] (2) After the stirring was completed, the homogeneous solution was uniformly coated on the surface of the metal lithium sheet by means of blade coating, so that the homogeneous solution fully covered and infiltrated into the metal lithium sheet.

[0067] (3) After a pretreatment for 15 minutes, a heating and curing treatment was performed on the metal lithium sheet, where the curing temperature was 45° C., to obtain a metal lithium negative electrode containing an interface functional layer. As shown in FIG. 1, the interface functional layer had a thickness of 500 nm.

[0068] 2. Preparation of Lithium-Ion Battery

[0069] A positive electrode sheet with an areal density of 6 mg/cm.sup.2 was obtained through coating with lithium cobalt oxide (91 wt %), Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.4O.sub.12 solid electrolyte (3.0 wt %), acetylene black (2.5 wt %), and polytetrafluoroethylene (3.5 wt %). The prepared positive electrode sheet, the Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.4O.sub.12 solid electrolyte and the metal lithium negative electrode containing the interface functional layer processed as above were assembled to prepare a soft-packed lithium-ion battery by using an existing lamination process.

Comparative Example 1

[0070] Comparative Example 1 provides a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0071] A positive electrode sheet with an areal density of 6 mg/cm.sup.2 was obtained through coating with lithium cobalt oxide (91 wt %), Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.4O.sub.12 solid electrolyte (3.0 wt %), acetylene black (2.5 wt %), and PVDF (3.5 wt %). The prepared positive electrode sheet, Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.4O.sub.12 solid electrolyte and the conventional metal lithium negative electrode which was untreated were assembled to prepare a soft-packed solid lithium-ion battery by using the existing lamination process.

Example 2

[0072] Example 2 provides a metal lithium negative electrode containing an interface functional layer and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0073] 1. Preparation of Li—In Alloy Negative Electrode Containing an Interfacial Functional Layer

[0074] (1) 1,3-dioxolane, lithium hexafluoroarsenate (LiAsF.sub.6), DME, and nano-alumina were fully mixed in a mass ratio of 68:12:23:3, then placed in a beaker and uniformly stirred for 8 h with a rotation speed of 600 rpm to form a homogeneous solution.

[0075] (2) After finishing stirring, the Li—In alloy was immersed in the homogeneous solution, so that the homogeneous solution fully covered and infiltrated into the Li—In alloy.

[0076] (3) After a pretreatment for 9 min, the Li—In alloy was taken out from the homogeneous solution, and heated and cured at a curing temperature of 35° C. to obtain a Li—In alloy negative electrode containing an interface functional layer, in which the interface functional layer had a thickness of 400 nm.

[0077] 2. Preparation of Lithium-Ion Battery

[0078] A positive electrode sheet with an areal density of 12 mg/cm.sup.2 was obtained through coating with LiNi.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2 (74 wt %), lithium phosphorus chlorine sulfide solid electrolyte (11 wt %), Super-P (9 wt %), and PVDF-HFP (6 wt %). The prepared positive electrode sheet, the lithium phosphorus chlorine sulfide solid electrolyte and the Li—In alloy negative electrode containing the interface functional layer processed as above were assembled to prepare a lithium-ion battery by using a mold.

Comparative Example 2

[0079] Comparative Example 2 provides a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0080] A positive electrode sheet with an areal density of 12 mg/cm.sup.2 was obtained through coating with LiNi.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2 (74 wt %), lithium phosphorus chlorine sulfide solid electrolyte (11 wt %), Super-P (9 wt %), and PVDF-HFP (6 wt %). The prepared positive electrode sheet, the lithium phosphorus chlorine sulfide solid electrolyte and the traditional Li—In alloy negative electrode were assembled to prepare a lithium-ion battery by using a mold.

Example 3

[0081] Example 3 provides a metal lithium negative electrode containing an interface functional layer and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0082] 1. Preparation of Li—Cu Composite Negative Electrode Containing Interfacial Functional Layer

[0083] (1) 1,4-dioxane, lithium trifluoromethanesulfonate (LiCF.sub.3SO.sub.3), EC/DEC with a system ratio of 1:1 were mixed uniformly in a mass ratio of 67:15:18 and placed in a beaker, and stirred uniformly with a rotation speed of 800 rpm for 2 h to form a homogeneous solution.

[0084] (2) Li—Cu composite tape was immersed in the stirred homogeneous solution, so that the homogeneous solution fully covered and infiltrated into the Li—Cu composite tape.

[0085] (3) After a pretreatment for 3 min, the Li—Cu composite tape was taken out from the homogeneous solution, and cured at a room temperature of 25° C. to obtain a Li—Cu composite negative electrode containing an interface functional layer, in which the interface functional layer had a thickness of 800 nm.

[0086] 2. Preparation of Lithium-Ion Battery

[0087] A positive electrode sheet with an areal density of 10 mg/cm.sup.2 was obtained through coating with lithium iron phosphate (85 wt %), polyethylene oxide polymer electrolyte (8%), CNT (5 wt %), and polyvinylidene fluoride (2 wt %). The prepared positive electrode sheet, the polyethylene oxide polymer electrolyte and the Li—Cu composite negative electrode containing an interface functional layer processed as above were assembled to obtain a soft-packed solid-state lithium-ion battery using the existing winding process.

Comparative Example 3

[0088] Comparative Example 3 provides a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0089] A positive electrode sheet with an areal density of 10 mg/cm.sup.2 was obtained through coating with lithium iron phosphate (85 wt %), polyethylene oxide polymer electrolyte (8%), CNT (5 wt %), and polyvinylidene fluoride (2 wt %). The prepared positive electrode sheet, the polyethylene oxide polymer electrolyte and Li—Cu composite negative electrode were assembled to obtain a soft-packed solid-state lithium-ion battery using the existing winding process.

Example 4

[0090] Example 4 provides a solid electrolyte containing an interface functional layer and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0091] 1. Preparation of the Solid Electrolyte Containing an Interfacial Functional Layer

[0092] (1) 1,3-dioxolane, lithium hexafluorophosphate (LiPF.sub.6), PC (Propylene carbonate)/DMM (Dipropyleneglycol dimethyl ether) with a volume ratio of 1:1, and nano-BN were fully mixed in a mass ratio of 56:18:23:3 and then placed in a beaker, and stirred uniformly with a rotation speed of 500 rpm for 1 h until to form a homogeneous solution.

[0093] (2) After the stirring is completed, the homogeneous solution was uniformly coated on a surface of the Li.sub.0.3La.sub.0.56TiO.sub.3 electrolyte that is close to the positive electrode by a way of tape casting, so that the homogeneous solution fully covered and infiltrated into the Li.sub.0.3La.sub.0.56TiO.sub.3 electrolyte near the positive electrode.

[0094] (3) After a pretreatment for 24 min, a curing treatment was performed on the Li.sub.0.3La.sub.0.56TiO.sub.3 electrolyte at room temperature of 55° C. to obtain the solid electrolyte containing an interface functional layer, as shown in FIG. 2, in which the thickness of the interface functional layer was 300 nm.

[0095] 2. Preparation of Lithium-Ion Battery

[0096] A positive electrode sheet with an areal density of 2.5 mg/cm.sup.2 was obtained through coating with LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2 (80 wt %), Li.sub.0.3La.sub.0.56TiO.sub.3 (5%), Ketjen Black (8 wt %), and polytetrafluoroethylene (7 wt %). The prepared positive electrode sheet, the solid electrolyte containing an interface functional layer and a metal lithium sheet were assembled to obtain a button battery, in which the interface functional layer was located between the positive electrode sheet and the solid electrolyte.

Comparative Example 4

[0097] Comparative Example 4 provides a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0098] A positive electrode sheet with an area density of 2.5 mg/cm.sup.2 was obtained through coating with LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2 (80 wt %), Li.sub.0.3La.sub.0.56TiO.sub.3 (5%), Ketjen Black (8 wt %), and polytetrafluoroethylene (7 wt %). The prepared positive electrode sheet, the Li.sub.0.3La.sub.0.56TiO.sub.3 oxide inorganic electrolyte and the metal lithium sheet were assembled to obtain a button battery.

Example 5

[0099] Example 5 provides a metal lithium negative electrode solid electrolyte containing an interface functional layer and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0100] 1. Preparation of the Solid Electrolyte Containing an Interfacial Functional Layer

[0101] (1) 1,3- dioxolane, lithium difluoro(oxalate)borate (LiDFOB), EC (Ethylene carbona)/DMC (Dimethyl carbonate) with a volume ratio of 1:1 were mixed uniformly in a mass ratio of 61:18:21 and then placed in a beaker, and stirred uniformly with a rotation speed of 600 rpm for 8 h to form a homogeneous solution.

[0102] (2) After the stirring was completed, the homogeneous solution was uniformly coated on a surface of Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO.sub.4).sub.3(LAGP) electrolyte by means of spray coating, so that the homogeneous solution fully covered and infiltrated into the Li.sub.1.5A.sub.0.5Ge.sub.1.5(PO.sub.4).sub.3(LAGP) electrolyte.

[0103] (3) After a pretreatment for 12 minutes, a heating and curing treatment was performed, where the curing temperature was 45° C., to obtain a solid electrolyte containing the Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO.sub.4).sub.3(LAGP) interface functional layer, in which the interface functional layer had a thickness of 500 nm.

[0104] 2. Preparation of Lithium-Ion Batteries

[0105] A positive electrode sheet with an areal density of 4 mg/cm.sup.2 was obtained through coating with lithium manganate (LiMnO.sub.2) (83 wt %), LAGP solid electrolyte (5 wt %), Ketjen black (6 wt %), and polyvinylidene fluoride (6 wt %). The prepared positive electrode sheet, the pretreated solid-state electrolyte containing Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO.sub.4).sub.3 interface functional layer and the metal lithium ribbon were assembled to prepare a soft-packed solid-state lithium-ion battery using the existing lamination process, in which the Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO4)3 interface functional layer was located between the solid electrolyte and the metal lithium ribbon.

Comparative Example 5

[0106] Comparative Example 5 provides a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0107] A positive electrode sheet with an areal density of 4 mg/cm.sup.2 was obtained through coating with lithium manganate (LiMnO.sub.2) (83 wt %), LAGP solid electrolyte (5 wt %), Ketjen black (6 wt %), and polyvinylidene fluoride (6 wt %). The prepared positive electrode sheet, traditional Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO4)3 solid electrolyte and the metal lithium ribbon were assembled to prepare a soft-packed solid lithium-ion battery using the existing lamination process, in which, the Li.sub.1.5Al.sub.0.5Ge.sub.1.5(PO.sub.4).sub.3 interface functional layer was located between the solid electrolyte and the metal lithium ribbon.

Example 6

[0108] Example 6 provides a solid electrolyte and a lithium-ion battery containing an interface functional layer, and the preparation method thereof. The method includes the following steps.

[0109] 1. Preparation of Solid Electrolyte Containing Functional Layers on its Both Sides

[0110] (1) 1,3-dioxolane, LiPF6/LiTFSI with a mass ratio of 2:1, EC/DEC (Diethyl carbonate)/DME (Dimethyl ether) with a volume ratio of 1:1:1 were mixed in a mass ratio of 51:18:31, and then placed in a beaker and stirred at a rotation speed of 500 rpm for 15 h to form a homogeneous solution.

[0111] (2) Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte sheet was immersed in the obtained homogeneous solution to ensure that the homogeneous solution fully covered and infiltrated into the Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte sheet.

[0112] (3) After a pretreatment for 19 minutes, the Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte sheet was taken out from the homogeneous solution and cured at 50° C. to obtain the solid electrolyte with interfacial functional layers on its both sides, in which each interfacial functional layer had a thickness of 1 μm.

[0113] 2. Preparation of Lithium-Ion Battery

[0114] A positive electrode sheet with an areal density of 3 mg/ cm.sup.2 was obtained through coating with LiNi.sub.0.6Co.sub.0.6Mn.sub.0.2O.sub.2 (72 wt %), Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte (11 wt %), Super-P (9 wt %), and PVDF-HFP (8 wt %). The prepared positive electrode sheet, Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte containing functional layers on its both sides and a metal lithium negative electrode were assembled to prepare a button-type lithium-ion battery using the existing process.

Example 7

[0115] Example 7 provides a solid electrolyte and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0116] 1. Preparation of Solid Electrolyte Containing Functional Layers on its Both Sides

[0117] (1) 1,3-dioxolane, LiPF.sub.6/LiTFSI with a mass ratio of 2:1, EC/DEC/DME with a volume ratio of 1:1:1 were mixed evenly in a mass ratio of 91:5:4, and then placed in a beaker and stirred at a rotation speed of 500 rpm for 15 h to form a homogeneous solution.

[0118] (2) Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte sheet was immersed in the obtained homogeneous solution to ensure that the homogeneous solution fully covered and infiltrated into the Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte sheet.

[0119] (3) After a pretreatment for 19 minutes, the Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte sheet was taken out from the homogeneous solution and cured at 50° C. to obtain a solid electrolyte containing interfacial functional layers on its both sides, in which each interfacial functional layer had a thickness of 600 nm.

[0120] 2. Preparation of Lithium-Ion Battery

[0121] A positive electrode sheet with an areal density of 3 mg/cm.sup.2 was obtained through coating with LiNi.sub.0.6Co.sub.0.6Mn.sub.0.2O.sub.2 (72 wt %), Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte (11 wt %), Super-P (9 wt %), and PVDF-HFP (8 wt %). The prepared positive electrode sheet, the Li.sub.6.4La.sub.3Zr.sub.1.4Ta.sub.0.6O.sub.12 solid electrolyte containing functional layers on its both sides and a metal lithium negative electrode were assembled to prepare a button-type lithium-ion battery using the existing process.

Example 8

[0122] Example 8 provides a metal lithium negative electrode containing an interface functional layer and a lithium-ion battery, and the preparation method thereof. The method includes the following steps.

[0123] 1. Preparation of a Metal Lithium Negative Electrode Containing an Interfacial Functional Layer

[0124] (1) 1,4-dioxane, LiPF.sub.6/LiFSI with a mass ratio of 1:1, DME, and nano-silica were mixed evenly in a mass ratio of 81:28:50:3 and placed in a beaker, stirred uniformly with a rotation speed of 1000 rpm for 1 h to form a homogeneous solution.

[0125] (2) A lithium ribbon containing a Cu current collector was immersed in the stirred homogeneous solution, so that the homogeneous solution fully covered and infiltrated into the lithium ribbon.

[0126] (3) After a pretreatment for 6 min, the lithium ribbon was taken out from the homogeneous solution, and cured at a room temperature to obtain the metal lithium negative electrode containing an interface functional layer, in which the interface functional layer had a thickness of 500 nm.

[0127] 2. Preparation of Lithium-Ion Battery

[0128] A positive electrode sheet with an areal density of 15 mg/cm.sup.2 was obtained through coating with lithium nickelate (Li.sub.2NiO.sub.2) (80 wt %), polyester polymer electrolyte (12 wt %), conductive carbon black (3 wt %), graphene (2 wt %), and polyvinylidene fluoride (3 wt %). The prepared positive electrode sheet, was stacked with the polymer electrolyte and a treated Cu current collector lithium ribbon containing a functional layer in sequence, and subjected to the existing winding process, to prepare a soft-packed lithium-ion battery.

[0129] The metal lithium negative electrode containing the interface functional layer in Example 8 was assembled into a symmetric lithium battery, and a cycle test was performed on the symmetric lithium battery, the results as shown in FIG. 6.

Comparative Example 6

[0130] Comparative Example 6 provides a metal lithium negative electrode and a lithium-ion battery. The difference between Comparative Example 6 and Example 8 only lies in that 1,4-dioxane, LiPF.sub.6/LiFSI (mass ratio 1:1), DME and nano-silica has a mass ratio of 45:4:6:13 in Comparative Example 6, with other preparation methods and parameters being the same.

Comparative Example 7

[0131] Comparative Example 7 provides a metal lithium negative electrode and a lithium-ion battery. The difference between Comparative Example 7 and Example 8 only lies in that 1,4-dioxane, LiPF.sub.6/LiFSI (mass ratio 1:1), DME and nano-silica has a mass ratio of 30:5:20:13 in Comparative Example 7, with other preparation methods and parameters being the same.

Comparative Example 8

[0132] Comparative Example 8 provides a metal lithium negative electrode and a lithium-ion battery. The difference between Comparative Example 8 and Example 8 only lies in that the 1,4-dioxane, LiPF.sub.6/LiFSI (mass ratio 1:1), DME and nano-silica has a mass ratio of 20:10:8:8 in Comparative Example 8, with other preparation methods and parameters being the same.

[0133] The AC impedance, cycle life, Coulomb efficiency and battery short-circuit rate of the lithium-ion batteries in Examples 1-8 and Comparative Examples 1-8 of this application were respectively tested at room temperature. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 AC impedance Coulomb Battery short- (Ω) at room Cycle life/cycle efficiency circuit rate temperature (0.2 C/0.2 C) (%) (%) Example 1 62 353 92.83% 0 Comparative 354 55 85.17% 0.4 Example 1 Example 2 103 243 89.86% 0 Comparative 321 132 83.93% 1.1 Example 2 Example 3 85 295 91.27% 0 Comparative 203 104 88.42% 0 Example 3 Example 4 66 382 94.57% 0 Comparative 538 149 82.93% 0.8 Example 4 Example 5 103 246 90.52% 0 Comparative 686 165 80.31% 2.3 Example 5 Example 6 95 175 92.33% 0 Example 7 110 412 90.84% 0 Example 8 82 260 91.10% 0 Comparative 332 121 88.43% 0.6 Example 6 Comparative 549 62 88.32% 0.5 Example 7 Comparative 522 47 85.64% 0.3 Example 8

[0134] As shown in Table 1, it can be seen from the comparison of the examples and the comparative examples that since an interface functional layer is provided between the positive electrode and the solid electrolyte and/or between the negative electrode and the solid electrolyte, the lithium-ion battery of this application has a lower interface impedance, and a higher cycle efficiency and cycle stability, and meanwhile has a battery short-circuit rate that is almost zero.

[0135] As shown in FIG. 5, compared with Comparative Example 5, the AC impedance at room temperature is smaller in Example 5, indicating that the battery in Example 5 has excellent interface performance and excellent overall performance.

[0136] As shown in FIG. 6, the symmetric lithium battery in Example 8 shows good stability in the voltage platform within 200 cycles without short circuit. It shows that there is good interface stability between the electrolyte and the negative electrode sheet that is prepared in Example 8 of this application, such that the growth of lithium dendrites can be well inhibited.

[0137] To sum up, by adjusting a composition and proportion of raw materials in the interface functional layer of this application, a grain boundary resistance and electrode interface performance can be improved, and the uneven deposition of lithium-ions at interface gaps can be inhibited, the interface impedance can be induced, and meanwhile the interface stability can be improved. The above-mentioned interface functional layer can be used for preparing a lithium-ion battery, such that the uneven deposition of lithium-ions at the interface gaps is inhibited, the interface impedance is reduced, and meanwhile the interface stability is improved. The lithium-ion battery of this application has higher cycle efficiency and cycle stability, with the battery short-circuit rate being almost zero.

[0138] The above description summarizes the features of several examples, which enables those skilled in the art to better understand various aspects of the application. Those skilled in the art can readily use this application as a basis for designing or modifying other compositions, so as to realize the same purposes and/or achieving the same advantages as those of the embodiments disclosed herein. Those skilled in the art can also understand that these equivalent examples do not deviate from the spirit and scope of the present application, and they can make various alterations, substitutions and modifications to the present application without departing from the spirit and scope of the present application. Although the methods disclosed herein have been described with reference to specific operations performed in a specific order, it should be understood that these operations may be combined, subdivided, or reordered to form equivalent methods without departing from the teachings of this application. Accordingly, unless specifically indicated herein, the order and grouping of operations are not limitations for this application.

[0139] The embodiments of this application have been described above. However, this application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.