Lithium negative electrode with high-inertia interface modification layer, preparation method and lithium metal battery

Abstract

The invention relates to a lithium negative electrode with a high-inertia interface modification layer, a preparation method and a lithium metal battery, and belongs to the technical field of interface modification of lithium negative electrodes of lithium metal batteries. The thickness of the interface modification layer is 0.5-5 microns, and the interface modification layer is uniformly distributed on the surface of the lithium negative electrode; and the interface modification layer is made of polyborosiloxane with high chemical inertness. The interface modification layer has high ionic conductivity and chemical stability, can inhibit the reaction activity of the lithium negative electrode and the generation of surface lithium dendrites, and is beneficial to improving the cycling stability of the lithium metal battery; the invention also provides a preparation method of the lithium negative electrode with the high-inertia interface modification layer, and the high-inertia interface modification layer is uniformly prepared on the surface of the lithium negative electrode by adopting a solvent evaporation method and is used for protecting the lithium negative electrode and inhibiting the side reaction of the lithium negative electrode; the lithium metal battery is a button battery or a soft package battery.

Description

Technical Field

[0001] The present invention relates to a lithium negative electrode with a highly inert interface modification layer, a preparation method and a lithium metal battery, belonging to the technical field of lithium negative electrodes of lithium metal batteries. Background Art

[0002] The vigorous development of the new energy industry has put forward higher requirements for new energy storage technologies. Compared with pumped storage, flywheel storage, compressed air storage and other energy storage methods, electrochemical energy storage systems mainly convert chemical energy into electrical energy through redox reactions at positive and negative electrodes, and have the advantages of miniaturization, portability, convenience and high efficiency. Among them, lithium-ion batteries have a higher energy density (~250Wh kg -1 ) and good cycle stability, which can meet the needs of portable electronic devices, miniaturized special equipment and other fields, making it the current mainstream electrochemical energy storage system. However, with the higher endurance requirements of small devices and the rapid development of electric transportation, the capacity of traditional lithium-ion batteries has approached the theoretical limit (372mAh g for graphite negative electrode). -1 Theoretical specific capacity of lithium metal is very high (3862mAh g -1 ) and the lowest redox potential (-3.04Vvs.SHE). Lithium metal batteries (LMBs) with them as negative electrodes have the advantages of high voltage adaptability and high energy density. Promoting the practical development of lithium metal batteries is an important direction for future energy innovation.

[0003] However, due to the high redox activity of lithium metal anodes, the development of lithium metal batteries faces two major challenges: electrolyte side reactions and uncontrolled growth of lithium dendrites. Lithium metal has the lowest redox potential and spontaneously reacts with electrolyte components such as organic solvents and lithium salts to form a solid electrolyte interface (SEI) on the anode surface. The naturally formed SEI does not have a uniform and dense structure. During cycling, the SEI layer is easily broken by the stress associated with uneven lithium deposition. The exposed lithium beneath the layer continuously reacts with the electrolyte, leading to SEI thickening and electrolyte consumption. Furthermore, uneven lithium ion deposition easily induces lithium dendrite growth. Continuously expanding dendrites can easily penetrate the separator, causing a short circuit between the positive and negative electrodes, leading to battery failure or even thermal runaway. Furthermore, dendrite formation increases the specific surface area of ​​the electrode, exacerbating side reactions with the electrolyte. Furthermore, during cycling, dendrites are prone to breaking at their roots, forming "dead lithium," which results in battery capacity loss. Therefore, the development of lithium metal batteries must first address the issues of electrolyte side reactions and uncontrolled dendrite growth.

[0004] Constructing an artificial interface layer on the surface of the lithium negative electrode can isolate the direct contact between the electrode and the electrolyte, reduce the active lithium consumption and by-product accumulation caused by interface side reactions, and is an important strategy to improve the stability of the lithium negative electrode. However, due to the high redox activity of the lithium metal negative electrode, most interface layers are difficult to maintain long-term stability on the surface of metallic lithium. In addition, although alloy, inorganic and other interface layers have a rigid structure and good interface stability, the huge volume change of the lithium negative electrode can easily lead to the destruction and failure of the rigid interface layer. The organic flexible interface layer can achieve adaptive coverage of the lithium metal negative electrode, but its non-fixed ion transmission pathway limits the ion transmission kinetics. Therefore, developing a flexible interface layer with high ion transmission capacity and stability to lithium, taking into account the uniform deposition of lithium ions and suppressing interface side reactions, is a key strategy to achieve stable cycling of metallic lithium negative electrodes.

[0005] Siloxane-based materials contain high-energy silicon-oxygen bonds (Si-O) and rich organic groups, and have excellent flexibility, thermal and chemical stability. Applying them in battery research is expected to improve the problems currently faced by metal secondary batteries, such as negative electrode volume expansion, metal dendrite growth and low thermal safety. Summary of the Invention

[0006] In order to overcome the defects existing in the prior art, one of the purposes of the present invention is to provide a lithium negative electrode with a highly inert interface modification layer, which has high chemical stability and excellent ionic conductivity, can inhibit the reaction activity of the lithium negative electrode, promote the uniform deposition of lithium ions, and help improve the cycle stability of lithium metal batteries.

[0007] The second object of the present invention is to provide a method for preparing a lithium negative electrode with a highly inert interface modification layer; an interface modification layer with high chemical inertness is uniformly formed on the surface of the lithium negative electrode by a solvent volatilization method, which is used to protect the lithium metal negative electrode and effectively inhibit side reactions.

[0008] A third object of the present invention is to provide a lithium metal battery, wherein the negative electrode of the lithium metal battery is the lithium negative electrode with a highly inert interface modification layer as described in the present invention.

[0009] The objectives of the present invention are achieved through the following technical solutions.

[0010] A lithium negative electrode having a highly inert interface modification layer, wherein the thickness of the interface modification layer is 0.5 μm-5 μm, and the main body of the interface modification layer is polyborosiloxane;

[0011] The general structural formula of the polyborosiloxane is R1-[Si(R2R3)-O] n -B-R4R5, wherein n represents the degree of polymerization of the -Si(R2R3)-O- unit in the polyborosiloxane molecular chain, and is a positive integer ranging from 30 to 90;

[0012] R1 is a terminal group connected to Si, R1 is a methyl group, a hydroxyl group or a siloxane chain;

[0013] R2 and R3 represent side chains connected to silicon in the repeating unit, and R2 and R3 are independently methyl, phenyl or siloxane chains;

[0014] R4 and R5 represent side chains connected to the boron atom, and R4 and R5 are independently at least one of a hydroxyl group, a perfluoroalkyl group, a siloxane chain, and a long-chain alkyl group;

[0015] Preferably, in the general structural formula of the polyborosiloxane, the value of n is a positive integer of 50-70.

[0016] Preferably, in the polyborosiloxane structure, R1 is a methyl group or a siloxane chain, R2 and R3 are methyl groups, and R4 and R5 are siloxane chains, so as to avoid introducing active groups.

[0017] Preferably, the thickness of the interface modification layer is 2 μm-4 μm; if the thickness of the interface modification layer is too thin, it is difficult to ensure that the interface modification layer completely covers the lithium negative electrode, and if the thickness is too thick, it will lead to poor interface ion transport kinetics.

[0018] Preferably, lithium salt or organic macromolecular material with lithium ion transport properties is added to the interface modification layer to increase the ion transport capacity of the interface modification layer; in the interface modification layer, the mass fraction of lithium salt or organic macromolecular material is 10%-50%;

[0019] The lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6) and lithium trifluoromethanesulfonate (LiOTf).

[0020] The organic macromolecular material having lithium ion transport properties is at least one of polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and polyethylene carbonate (PEC).

[0021] A method for preparing a lithium negative electrode having a highly inert interface modification layer according to the present invention, the method being a solvent volatilization method;

[0022] Specifically, the method steps are as follows:

[0023] (1) In a glove box filled with argon, completely dissolving the polyborosiloxane in a diluent to form a homogeneous transparent dispersion;

[0024] In the dispersion, the mass fraction of polyborosiloxane is 0.2%-2%;

[0025] The diluent is at least one of tetrahydrofuran (THF), toluene, xylene, ethylene glycol dimethyl ether (DME), cyclohexane, and chlorobenzene;

[0026] (2) The dispersion obtained in step (1) is evenly dispersed on the surface of the lithium negative electrode, and allowed to stand at room temperature for 24 hours under normal pressure or vacuum to volatilize the diluent; during the solvent volatilization process, the polyborosiloxane gradually adheres to the lithium negative electrode, and finally forms an interface modification layer on the surface of the lithium negative electrode.

[0027] A lithium metal battery, wherein the lithium metal battery is a button battery or a soft pack battery, and the lithium metal battery is composed of a positive electrode, a negative electrode, a separator and an electrolyte;

[0028] Wherein, the negative electrode is the lithium negative electrode with a highly inert interface modification layer as described in the present invention;

[0029] The positive electrode is a positive electrode material commonly used in the field of lithium metal batteries in the prior art;

[0030] The diaphragm is a diaphragm material commonly used in the field of lithium metal batteries in the prior art;

[0031] The electrolyte is an electrolyte commonly used in the field of lithium metal batteries in the prior art.

[0032] Preferably, the positive electrode material is at least one of nickel-cobalt-manganese ternary material (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO) and sulfur-based materials; the nickel-cobalt-manganese ternary material includes NCM811, NCM622 and NCM523; the sulfur-based material includes elemental sulfur, sulfur-carbon composite material, sulfur-polymer composite material and sulfur-metal compound composite material;

[0033] The membrane material is a polyolefin porous membrane (PP, PE), a ceramic coating modified membrane (Al2O3, SiO2, ZrO2 coating membrane), or a polymer composite membrane (PVDF-based, PAN-based porous membrane);

[0034] The electrolyte is an ether liquid electrolyte (DOL / DME based), a high concentration carbonate electrolyte (HCE), a sulfone liquid electrolyte (TMS based), a PEO based polymer solid electrolyte, or an ionic liquid electrolyte (IL based).

[0035] Beneficial effects

[0036] (1) The present invention provides a lithium negative electrode with a highly inert interface modification layer, wherein the material of the highly inert interface modification layer is polyborosiloxane with high chemical and thermal stability. Unlike most interface modification layers, the interface modification layer of the present invention has high chemical stability and fast ion transport kinetics. The internal high bond energy Si-O bond gives the material excellent chemical and thermal stability, and it still has a stable composition and structure even on the surface of lithium metal. In addition, the dynamic association / dissociation of the BO covalent bond can give the siloxane molecular chain greater flexibility, which is beneficial to improving the adaptability of the interface layer. During the volume change of the lithium negative electrode dissolution / deposition, the structural integrity of the interface layer is guaranteed, and its intrinsic chemical inertness avoids side reactions on the surface of the metal lithium. The highly inert interface modification layer solves the problems of reactivity and volume change between the lithium negative electrode and the electrolyte.

[0037] (2) The present invention provides a lithium negative electrode having a highly inert interface modification layer, wherein the thickness of the highly inert interface modification layer is 0.5 μm–5 μm, and preferably the thickness of the interface modification layer is 2 μm–4 μm. The thickness of the interface modification layer significantly affects interfacial ion transport, and the interface modification material used in the present invention has poor ionic conductivity. A thicker interface layer significantly increases interfacial impedance, while a thinner interface layer cannot ensure complete coverage of the lithium negative electrode, affecting battery cycle performance. Therefore, the thickness of the interface modification layer must be appropriate, taking into account both lithium protection and rapid interfacial ion transport capabilities.

[0038] (3) The present invention provides a lithium negative electrode having a highly inert interface modification layer, wherein the main material of the interface modification layer is a lithium ion battery having a general structural formula of R1-[Si(R2R3)-O] n -B-R4R5 polyborosiloxane, using the high chemical stability imparted by the Si-O bond to inhibit the side reaction activity of the lithium negative electrode and maintain its own long-term stable existence; at the same time, the lithium salt or the organic macromolecular material with lithium ion transport properties can also be added to the interface modification layer to promote interfacial lithium ion transport while inhibiting the side reaction of the lithium negative electrode.

[0039] (4) The present invention provides a method for preparing a lithium negative electrode having a highly inert interface modification layer, wherein a uniform interface modification layer is constructed on the lithium negative electrode by a solvent evaporation method, the method comprising a static drop coating-natural evaporation method, a dynamic spin coating-forced evaporation method, a dip coating-gradient evaporation method, a vacuum-assisted-low-pressure evaporation method, and a heating-assisted-rapid evaporation method. The slow evaporation of the solvent can promote the adaptive adhesion of the siloxane material to the lithium negative electrode, forming a modification layer of uniform thickness, thereby preventing the lithium negative electrode from directly contacting the electrolyte.

[0040] (5) The present invention provides a lithium metal battery, wherein the negative electrode of the battery is the lithium negative electrode with a highly inert interface modification layer as described in the present invention. In order to solve the problem of high redox activity of the metal lithium negative electrode faced by lithium metal batteries, a highly chemically inert polyborosiloxane-based lithium negative electrode interface is constructed to achieve long-term stable circulation of the lithium metal negative electrode. The Si-O main chain structure of the polyborosiloxane makes the interface layer highly chemically and thermally stable, and induces the formation of an inorganic component-rich SEI, which suppresses the reaction activity of the lithium negative electrode and improves the interface stability. In addition, by adding the lithium salt or the organic macromolecular material with lithium ion transport properties to the polyborosiloxane interface modification layer, the interface ion transport network can be enriched, the interface lithium ion flux can be uniform, and the lithium deposition uniformity can be improved while suppressing the side reactions of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The infrared spectra of the highly inert interface modification material polyborosiloxane (PBS) and the condensation precursor polydimethylsiloxane (PDMS) of Example 1, wherein Wavenumber is translated as wave number and Transmittance is translated as transmittance;

[0042] Figure 2 is the ionic conductivity of the polyborosiloxane interface modification material of Example 1;

[0043] Figure 3 The infrared curves of the PBS matrix, lithium salt (LiTFSI) and the highly inert interface modification layer (PBSI) of Example 3, wherein Wavenumber is translated as wave number and Transmittance is translated as transmittance;

[0044] Figure 4 is the thickness of the highly inert interface modification layer of Example 4;

[0045] Figure 5 is the ionic conductivity of the polyborosiloxane interface modification material (PBSI) of Example 4;

[0046] Figure 6 The cycle performance of the lithium symmetric battery with a highly inert interface modification layer of Example 4, wherein Time is translated as time and Voltage is translated as voltage;

[0047] Figure 7 This is a cycle performance test of the lithium metal button battery with a lithium negative electrode highly inert interface modification layer of Example 8, wherein "Cycle Number" is translated as the number of cycles, "Specific Capacity" is translated as the specific capacity, and "Capacity Retention" is translated as the capacity retention rate;

[0048] Figure 8 This is a demonstration diagram of the lithium metal soft-pack battery with a highly inert interface modification layer in Example 11 lighting up an LED light sign. DETAILED DESCRIPTION

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. The methods described are all conventional methods unless otherwise specified, and the raw materials described can be obtained from public commercial channels unless otherwise specified.

[0050] Button cell assembly steps: Lithium symmetrical cells were assembled using CR2025 button cells, and full cells were assembled using CR2016 button cells. All assembly processes were performed in an argon-filled glove box. The assembly process was carried out in the order of anode, separator, electrolyte, and cathode. The lithium anode with a highly inert interface modification layer had a diameter of 12 mm, and the electrolyte volume added to all cells was 60 μL.

[0051] The assembly steps of the soft-pack battery are as follows: the lithium negative electrode (6cm*4cm*0.01cm) with a highly inert interface modification layer described in the present invention and the positive electrode (mass composition of positive electrode material: Super P:PVDF=8:1:1) are placed opposite each other, a diaphragm slightly larger than the electrode is used to separate the positive and negative electrodes, and an aluminum-plastic film is used to encapsulate the diaphragm. After liquid injection and heat sealing, a soft-pack battery with a lithium negative electrode having the highly inert interface modification layer is obtained.

[0052] Example 1

[0053] A lithium negative electrode with a highly inert interface modification layer, wherein the interface modification layer is uniformly distributed on the surface of the lithium negative electrode.

[0054] The material of the interface modification layer is polyborosiloxane with high chemical stability; the structural formula of the polyborosiloxane is R1-[Si(R2R3)-O] n -B-R4R5.

[0055] Wherein, n represents the degree of polymerization of -Si(R2R3)-O- units in the polyborosiloxane molecular chain, which is 30;

[0056] R1 is a terminal group connected to Si, and R1 is a methyl group;

[0057] R2 and R3 represent side chains connected to silicon in the repeating unit, and both R2 and R3 are methyl groups;

[0058] R4 and R5 represent side chains connected to the boron atom, and R4 and R5 are polysiloxane chains CH3-[Si(CH3CH3)-O] 60 -.

[0059] The polyborosiloxane described in this embodiment was prepared according to literature reports, and the steps are as follows:

[0060] Polydimethylsiloxane (PDMS) was used as a condensation precursor and boric acid (BA) as a cross-linking agent to synthesize polyborosiloxane (PBS) through a hydroxyl condensation reaction. Specifically, PDMS was mixed with a 0.05M boric acid aqueous solution at 30°C, and the proportion of boric acid in the reactants was controlled to be 2.58wt%. The temperature of the magnetic stirrer was then set to 170°C and the speed was set to 700rpm. The condensation process was carried out at high temperature. As the water evaporated and the precursor condensed completely, the system was converted from a solution to a viscoelastic gel. The obtained gel was vacuum dried in a 50°C oven for 12 hours to remove residual water and internal bubbles to obtain transparent polyborosiloxane.

[0061] Infrared spectrum shows Figure 1 ), 1008cm -1 The material has obvious Si-O peak, PBS matrix 1337cm -1 The obvious infrared peak at 3339cm corresponds to the stretching vibration of the BO bond, indicating that PDMS and boric acid are successfully cross-linked. -1 The broad peak of OH stretching vibration disappears, indicating that PDMS and boric acid are completely condensed.

[0062] A method for preparing a lithium negative electrode with a highly inert interface modification layer as described in this embodiment is a solvent volatilization method.

[0063] Specifically, the method steps are as follows:

[0064] (1) In an argon-filled glove box, the polyborosiloxane was added to tetrahydrofuran (THF), and the mixture was stirred and dissolved at 300 rpm at room temperature for 24 hours to form a homogeneous transparent dispersion, wherein the mass fraction of the polyborosiloxane in the dispersion was 2%;

[0065] (2) 20 μL of the dispersion was added dropwise to the surface of the lithium negative electrode, and then allowed to stand in a glove box for 24 h to naturally evaporate the solvent, thereby obtaining the lithium negative electrode with a highly inert interface modification layer as described in this embodiment.

[0066] A lithium metal battery is a button battery consisting of a positive electrode, a negative electrode, a separator and an electrolyte.

[0067] Wherein, the negative electrode is the lithium negative electrode with a highly inert interface modification layer as described in this embodiment;

[0068] The positive electrode material is lithium iron phosphate (LFP);

[0069] The diaphragm material is polypropylene diaphragm (PP);

[0070] The electrolyte is 1M LiTFSI-DOL / DME (volume ratio 1:1).

[0071] The lithium negative electrode with the highly inert interface modification layer prepared in Example 1 was tested using a scanning electron microscope. The thickness of the highly inert interface modification layer was 5 μm.

[0072] The lithium metal button battery prepared in Example 1 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a test temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical cell can be cycled for less than 200 h when the deposition capacity is high; when the 0.5 mA cm -2 Current density, 1mAh cm -2 The ionic conductivity of the polyborosiloxane interface modified material was further tested (attached Figure 2 ).

[0073] The test results show that the lithium metal button battery with a high inert interface modification layer on the negative electrode side of this embodiment can inhibit the side reaction with the electrolyte, but the low ionic conductivity of the interface layer (0.09mS cm -1 ) hinders the lithium ion transport kinetics, leading to increased polarization and rapid battery failure.

[0074] Example 2

[0075] Example 2 is based on Example 1, except that "the mass fraction of the polyborosiloxane in the dispersion is 2%" in Example 1 is replaced by "the mass fraction of the polyborosiloxane in the dispersion is 0.2%", and other conditions remain unchanged.

[0076] The lithium negative electrode with the highly inert interface modification layer prepared in Example 2 was observed in cross section. The thickness of the highly inert interface modification layer was 0.5 μm.

[0077] The lithium metal button cell prepared in Example 2 was subjected to constant current charge and discharge tests. The test instrument was a Xinwei CT-4008Tn battery test system and the test temperature was 30°C. When 0.5 mA cm -2 Current density, 0.5 mAh cm -2 The symmetrical battery can be cycled for about 400 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the deposition capacity is reached, the cycle life of the symmetrical battery is 200 hours. By reducing the thickness of the interface modification layer and lowering the lithium ion transmission resistance, the lithium metal button battery with the highly inert interface modification layer on the negative electrode side can exhibit a longer cycle life.

[0078] Example 3

[0079] Example 3 is based on Example 1, and lithium salt is added to the interface modification layer.

[0080] The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the mass fraction of the lithium salt in the interface modification layer is 10%.

[0081] Infrared spectrum shows Figure 3 ), 1338cm -1 and 1014cm -1 The stretching vibration peaks of BO bond and Si-O bond belonging to PBS matrix are shown at 1200 cm -1 and 1062cm -1 The stretching vibration peaks of CF bond and SNS bond of LiTFSI are shown at 1325 cm -1 The infrared peak of the S=O functional group shifts to a higher wave number of 1348 cm -1 This is mainly attributed to the attraction between the incompletely grafted B atoms in the PBS matrix and the lone pair electrons of the O atoms in the S=O functional groups in LiTFSI.

[0082] The lithium negative electrode with the highly inert interface modification layer prepared in Example 3 was tested using a scanning electron microscope. The thickness of the highly inert interface modification layer was 3 μm.

[0083] The lithium metal button battery prepared in Example 3 was subjected to constant current charge and discharge tests. The test instrument was a Xinwei CT-4008Tn battery test system and the test temperature was 30°C. When 0.5 mA cm -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 1000 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the capacity is deposited, the cycle life of the symmetrical battery is 500 hours. The lithium salt constructs an interfacial layer ion transport network, which can significantly improve the cycle life of the battery.

[0084] Example 4

[0085] Example 4 is based on Example 1, and lithium salt is added to the interface modification layer.

[0086] The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the mass fraction of the lithium salt in the interface modification layer is 50%.

[0087] The lithium negative electrode with a highly inert interface modification layer prepared in Example 4 was tested by scanning electron microscopy. The thickness of the highly inert interface modification layer was 3 μm (see Appendix 1). Figure 4 ).

[0088] The lithium metal button cell prepared in Example 4 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 2000 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the deposition capacity is reached, the cycle life of the symmetrical battery is 1350h (attached Figure 6 The lithium salt constructs an interfacial layer ion transport network, which improves the interfacial layer ion conductivity (1.76 mS cm -1 ), as attached Figure 5 As shown, the battery cycle life can be significantly improved.

[0089] Example 5

[0090] Example 5 is based on Example 1, and an organic macromolecular material with lithium ion transport properties is added to the interface modification layer.

[0091] The organic macromolecular material with lithium ion transport properties is polyethylene oxide (PEO), and the mass fraction of PEO in the interface modification layer is 5%.

[0092] The lithium negative electrode with the highly inert interface modification layer prepared in Example 5 was tested using a scanning electron microscope. The thickness of the highly inert interface modification layer was 3.1 μm.

[0093] The lithium metal button battery prepared in Example 5 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a test temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 800 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the capacity is deposited, the cycle life of the symmetrical battery is 400 hours. The organic macromolecular material with lithium ion transport properties promotes lithium ion transport at the interface, significantly improving the cycle life of the battery.

[0094] Example 6

[0095] Example 6 is based on Example 1, and an organic macromolecular material with lithium ion transport properties is added to the interface modification layer.

[0096] The organic macromolecular material with lithium ion transport properties is polyethylene oxide (PEO), and the mass fraction of PEO in the interface modification layer is 20%.

[0097] The lithium negative electrode with the highly inert interface modification layer prepared in Example 6 was tested using a scanning electron microscope. The thickness of the highly inert interface modification layer was 3.2 μm.

[0098] The lithium metal button cell prepared in Example 6 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 1200 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the capacity is deposited, the cycle life of the symmetrical battery is 600 hours. Increasing the mass fraction of the organic macromolecular material with lithium ion transport properties increases the proportion of lithium ion transport pathways at the interface and improves the cycle life of the battery.

[0099] Example 7

[0100] Example 7 is based on Example 1, except that "the positive electrode material is lithium iron phosphate (LFP)" in Example 1 is replaced by "the positive electrode material is nickel-cobalt-manganese ternary material (NCM)", and other conditions remain unchanged.

[0101] The lithium metal button cell prepared in Example 7 was subjected to constant current charge and discharge testing using a Xinwei CT-4008Tn battery testing system at 30°C. At a 1C rate, the lithium metal button cell with the highly inert interface modification layer for the lithium negative electrode retained 40% of its capacity after 500 cycles. This indicates that the highly inert interface modification layer, lacking a lithium ion transport network, has little effect on improving lithium metal battery performance.

[0102] Example 8

[0103] Example 8 is based on Example 1, except that "the positive electrode material is lithium iron phosphate (LFP)" in Example 1 is replaced by "the positive electrode material is nickel cobalt manganese ternary material (NCM)", and lithium salt is added to the interface modification layer, while other conditions remain unchanged.

[0104] The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the mass fraction of the lithium salt in the interface modification layer is 50%.

[0105] The lithium metal button battery prepared in Example 8 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a temperature of 30°C. When a 1C rate was used, the capacity retention rate of the lithium metal button battery with a lithium negative electrode high inert interface modification layer after 500 cycles was 56.1% (see Appendix). Figure 7 The rich lithium ion transport network provided by the lithium salt significantly improves the ion transport kinetics of the highly inert interface modification layer and promotes the coulombic efficiency of lithium ion insertion and extraction on the positive electrode side.

[0106] Example 9

[0107] Example 9 is based on Example 1, except that "the electrolyte is 1MLiTFSI-DOL / DME (volume ratio 1:1)" in Example 1 is replaced by "the electrolyte is 1M LiPF6-EC / DEC / DMC (volume ratio 1:1:1)", and lithium salt is added to the interface modification layer, while other conditions remain unchanged.

[0108] The lithium salt is lithium hexafluorophosphate (LiPF6), and the mass fraction of the lithium salt in the interface modification layer is 50%.

[0109] The lithium metal button cell prepared in Example 9 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 1300 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the deposition capacity is high, the symmetrical battery cycle life is 800 hours. Changing the type of lithium salt in the highly inert interface modification layer also constructs an intra-layer ion transport network, which can promote interface ion transport and improve battery cycle life.

[0110] Example 10

[0111] Example 10 is based on Example 1, except that "R2 and R3 are both methyl groups, and n is 30" in Example 1 is replaced by "R2 is a phenyl group, R3 is a siloxane chain, and n is 90", and other conditions remain unchanged.

[0112] The lithium negative electrode with the highly inert interface modification layer prepared in Example 10 was tested using a scanning electron microscope. The thickness of the highly inert interface modification layer was 3.2 μm.

[0113] The lithium metal button cell prepared in Example 10 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a test temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 400 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When depositing capacity, the symmetrical battery cycle life is 150 hours. Changing the composition of the highly inert interface modification layer does not affect the interface adaptive properties, but can inhibit the reactivity of the lithium negative electrode and improve the battery cycle life.

[0114] Example 11

[0115] Example 11 is based on Example 1, except that "R2 and R3 are both methyl groups, and n is 30" in Example 1 is replaced by "R2 is a phenyl group, R3 is a siloxane chain, and n is 90", and lithium salt is added to the interface modification layer, while other conditions remain unchanged.

[0116] The lithium salt is lithium hexafluorophosphate (LiPF6), and the mass fraction of the lithium salt in the interface modification layer is 50%.

[0117] The lithium negative electrode with the highly inert interface modification layer prepared in Example 11 was tested using a scanning electron microscope. The thickness of the highly inert interface modification layer was 3.2 μm.

[0118] The lithium metal button cell prepared in Example 11 was subjected to constant current charge and discharge tests using a Xinwei CT-4008Tn battery test system at a temperature of 30°C. -2 Current density, 0.5 mAh cm -2 The symmetrical battery can cycle for 1400 h when the deposition capacity is 0.5 mA cm -2 Current density, 1mAh cm -2 When the capacity is deposited, the cycle life of the symmetrical battery is 900 hours. By adding the lithium salt to the highly inert interface modification layer, the interface lithium ion transport kinetics can be improved, significantly improving the battery cycle life.

[0119] The lithium metal soft pack battery prepared in Example 11 was actually demonstrated (see Appendix Figure 8 ), the lithium metal soft-pack battery with a high-inertness interface modification layer can light up the LED signboard, showing the practical prospects of the high-inertness interface modification layer on the surface of the lithium negative electrode.

[0120] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium negative electrode having a highly inert interface modification layer, characterized in that: The thickness of the interface modification layer is 0.5 μm-5 μm, and the interface modification layer is evenly distributed on the surface of the lithium negative electrode; The general structural formula of the polyborosiloxane is R1-[Si(R2R3)-O] n -B-R4R5, wherein n represents the degree of polymerization of the -Si(R2R3)-O- unit in the polyborosiloxane molecular chain, and is a positive integer ranging from 30 to 90; R1 is a terminal group connected to Si, R1 is a methyl group, a hydroxyl group or a siloxane chain; R2 and R3 represent side chains connected to silicon in the repeating unit, and R2 and R3 are independently methyl, phenyl or siloxane chains; R4 and R5 represent side chains connected to the boron atom, and R4 and R5 are at least one of a hydroxyl group, a perfluoroalkyl group, a siloxane chain and a long-chain alkyl group, respectively and independently.

2. The lithium negative electrode having a highly inert interface modification layer according to claim 1, characterized in that: The thickness of the interface modification layer is 2 μm-4 μm.

3. A lithium negative electrode with a highly inert interface modification layer according to claim 1 or 2, characterized in that: In the general structural formula of the polyborosiloxane, the value of n is a positive integer of 50-70.

4. The lithium negative electrode having a highly inert interface modification layer according to claim 1, characterized in that: The interface modification layer further comprises a lithium salt or an organic macromolecular material having lithium ion transport properties; the mass fraction of the lithium salt or the organic macromolecular material in the interface modification layer is 10%-50%; The lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6) and lithium trifluoromethanesulfonate (LiOTf); The organic macromolecular material having lithium ion transport properties is at least one of polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and polyethylene carbonate (PEC).

5. A method for preparing a lithium negative electrode having a highly inert interface modification layer according to any one of claims 1 to 4, characterized in that: The method is a solvent volatilization method, and the steps are as follows: (1) In a glove box filled with argon, completely dissolving the polyborosiloxane in a diluent to form a homogeneous transparent dispersion; In the dispersion, the mass fraction of polyborosiloxane is 0.2%-2%; The diluent is at least one of tetrahydrofuran (THF), toluene, xylene, ethylene glycol dimethyl ether (DME), cyclohexane, and chlorobenzene; (2) The dispersion is evenly dispersed on the surface of the metal lithium negative electrode, and the dispersion is allowed to stand at room temperature for 24 hours under normal pressure or vacuum to volatilize the diluent, thereby forming an interface modification layer of the thickness on the surface of the lithium negative electrode.

6. A lithium metal battery, characterized in that: The lithium metal battery is a button battery or a soft pack battery, and the lithium ion battery is composed of a positive electrode, a negative electrode, a separator and an electrolyte; Wherein, the negative electrode is a lithium negative electrode with a highly inert interface modification layer as described in any one of claims 1 to 4.

7. A lithium metal battery according to claim 6, characterized in that: The positive electrode material is at least one of nickel-cobalt-manganese ternary material (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO) and sulfur-based materials; the nickel-cobalt-manganese ternary material includes NCM811, NCM622 and NCM523; the sulfur-based material includes elemental sulfur, sulfur-carbon composite material, sulfur-polymer composite material and sulfur-metal compound composite material; The membrane material is a polyolefin porous membrane (PP, PE), a ceramic coating modified membrane (Al2O3, SiO2, ZrO2 coating membrane), or a polymer composite membrane (PVDF-based, PAN-based porous membrane); The electrolytes are ether liquid electrolytes (DOL / DME based), high concentration carbonate electrolytes (HCE based), sulfone liquid electrolytes (TMS based), PEO based polymer solid electrolytes and ionic liquid electrolytes (IL based).

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