Method for protecting an electrode, electrode and lithium battery

Abstract

This invention relates to the field of lithium battery technology, specifically to a method for protecting an electrode, an electrode, and a lithium battery. The electrode protection method includes placing a mixed solution containing cyclic anhydride and epoxy ether on the electrode surface, placing a catalyst on the electrode surface, and conducting an in-situ polymerization reaction to form a polymer protective layer on the electrode surface. The catalyst forms a coordination intermediate with trace amounts of water carried by the mixed solution, which then attacks the epoxy ether to form oxonium ions. The oxonium ions then attack the epoxy ether to form a homopolymer product of the epoxy ether, while simultaneously attacking the cyclic anhydride to open its ring. Finally, the two products alternately polymerize to form an ester-alt-ether structure, resulting in a high lithium-ion transference number. Ultimately, a high oxidation potential interface layer is synthesized on the electrode and electrolyte surfaces, greatly improving the stability of the lithium metal battery and extending its cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a method for protecting an electrode, an electrode, and a lithium battery. Background Technology

[0002] With the development of electronic products and new energy vehicles, the requirements for their energy (lithium batteries) are becoming increasingly stringent. Among them, lithium metal batteries are particularly important due to their low redox potential (-3.040V) and high energy density (3861mAh g / g). -1 This has made it one of the most ideal lithium battery systems for the next generation. Currently, the most commonly used cathode materials include ternary materials, lithium iron phosphate, and lithium-rich manganese-based materials.

[0003] Liquid lithium metal batteries are actually concentration cells, with the positive and negative electrodes composed of two different lithium-ion intercalation compounds. During charging, Li... + Lithium ions are extracted from the positive electrode, pass through the electrolyte, and then insert into the negative electrode. The negative electrode is in a lithium-rich state, while the positive electrode is in a lithium-poor state. Simultaneously, compensating charges are supplied to the lithium negative electrode from the external circuit to maintain charge balance. During discharge, the process is reversed. Under normal charge and discharge conditions, lithium ions insert and extract between the lithium material and the positive electrode, generally only causing changes in interlayer spacing and not damaging the crystal structure. However, when current flows through the electrodes, the phenomenon where the electrodes deviate from their equilibrium electrode potential is called battery polarization. Electrode polarization caused by anodic current is called anodic polarization; electrode polarization caused by cathode current is called cathodic polarization. The greater the current passing through a unit area of ​​the electrode, the more severe the deviation from the equilibrium electrode potential. Polarization can be divided into three types: electrochemical polarization, concentration polarization, and ohmic polarization. Electrochemical polarization, also known as activation polarization, is polarization caused by the electrochemical reaction rate of the positive and negative electrode active materials being lower than the electron movement rate, with a response time on the order of microseconds. Concentration polarization is caused by the consumption of reactants, resulting in the electrode surface not being replenished in time (or by the accumulation of certain products on the electrode surface, which cannot be dispersed in time). Ohmic polarization is polarization caused by the contact resistance between the electrolyte, electrode materials, separator resistance, and various components, and occurs instantaneously. If the polarization voltage remains abnormal, it will cause lithium ions to accumulate and crystallize at the negative electrode, which can shorten battery life in severe cases.

[0004] Research has summarized the causes of polarization as follows: 1. Electrolyte decomposition: Organic solvents in the electrolyte may decompose during charging and discharging, forming solid substances that adhere to the surfaces of the positive and negative electrodes, leading to polarization; 2. Battery aging: As the battery is used for longer periods, the internal materials age, producing oxides and other undesirable substances, resulting in polarization; 3. Lithium-ion accumulation: During charging and discharging, lithium ions may accumulate on the surfaces of the positive and negative electrodes, forming undesirable substances and causing polarization.

[0005] Currently, commonly used methods for optimizing battery polarization include: 1. Electrolyte improvement: reducing the electrolyte's antioxidant and reducing capabilities, and increasing the electrolyte's electrochemical window; 2. Improvement of battery charge / discharge regimes: designing charge / discharge currents and voltages that match different battery systems to avoid excessively high current densities and voltages causing more severe negative impacts on battery polarization; 3. Optimization of battery structure and materials: reducing battery polarization from the perspectives of battery structure design and electrode main and auxiliary materials; 4. Strengthening battery system design and monitoring: optimizing battery management systems, conducting real-time detection and control of battery operating status, and promptly identifying and addressing polarization problems; 5. At the battery manufacturing level: reducing the risk of polarization by improving battery manufacturing processes and addressing internal defects and adverse reactions. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defect of shortened battery life caused by positive and negative electrode polarization in the prior art, thereby providing an electrode protection method, an electrode, and a lithium battery.

[0007] The present invention provides a method for protecting an electrode, comprising placing a mixed solution containing cyclic anhydride and epoxy ether on the electrode surface, placing a catalyst on the electrode surface, and conducting an in-situ polymerization reaction to form a polymer protective layer on the electrode surface.

[0008] In this context, polymerization reaction refers to the polymerization reaction between epoxy ethers and epoxy ethers, or between cyclic anhydrides and epoxy ethers.

[0009] Further, the cyclic anhydride is one or more of the following: glutaric anhydride, cyclobutanetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 1,4-difluoro-2,3,5,6-phenyltetracarboxylic dianhydride, and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracenetetracarboxylic dianhydride; and / or, the epoxy ether is selected from di(2,3-epoxycyclopentyl) ether, 1,3-dioxolane, epoxy ether 1 with CAS number 6705-89-1, and epoxy ether 1 with CAS number 7010- The epoxy ether is selected from one or more of the following: 73-3 epoxy ether 2, finishing agent DTF-7 (CAS No. 5981-06-6), 1,3,6-trioxane, epoxy ether 3 (CAS No. 294-59-7), epoxy ether 4 (CAS No. 24194-62-5), epoxy ether 5 (CAS No. 295-42-1), and epoxy ether 6 (CAS No. 24471-99-6); and / or, the molar ratio of the epoxide anhydride to the epoxy ether is 5-100:5-100; and / or, the catalyst is selected from one or more of dichloromethane, dichloromethane-d, dichlorofluoromethane, and dichloromethane-13C; and / or, the volume ratio of the mixed solution to the catalyst in the same electrode area is 10-30:1.

[0010] Among them, the English name of epoxy ether 1 is 2,2'-Bi(1,3-dioxolane);

[0011] The English name of epoxy ether 2 is 1,3,6,9-tetraoxaspiro[4.4]nonane;

[0012] The English name for epoxy ether 3 is 1,3,6,9-tetraoxacycloundecane;

[0013] The English name for epoxy ether 4 is 1,3,6,9,12,15-hexaoxacycloheptadecane;

[0014] The English name for epoxy ether 5 is 1,3,6,9,12-pentaoxacyclotetradecane;

[0015] The English name for epoxy ether 6 is 1,4,6,9-tetraoxaspiro[4.4]nonane;

[0016] The CAS number for 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic dianhydride is 139162-14-4.

[0017] Furthermore, the mixed solution also includes a lithium source selected from lithium bis(trifluoromethanesulfonylimide) or a combination of a compound containing a bis(trifluoromethanesulfonylimide) anion and other lithium-containing compounds.

[0018] Bis(trifluoromethanesulfonylimide) anion, abbreviated as "TFSI" - ".

[0019] Further, the compound containing the bis(trifluoromethanesulfonyl)imide anion is selected from 1-butyl-4-methylpyridine bis(trifluoromethanesulfonyl)imide, N-octyl-4-methylpyridine bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, N-octyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt, 1-benzyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-methyl-3-n-octylimidazolium bis(trifluoromethanesulfonyl)imide, 1-benzyl-2,3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-butyl- The lithium compound is selected from one or more combinations of 2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexadecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; and / or, the other lithium-containing compound is selected from one or more combinations of lithium powder, lithium salt with CAS number 1186134-15-5, lithium salt with CAS number 33454-82-9, and lithium iodate with CAS number 546-89-4.

[0020] The Chinese name of the lithium salt with CAS number 33454-82-9 is lithium trifluoromethanesulfonate.

[0021] Furthermore, when the lithium source is lithium bis(trifluoromethanesulfonylimide), the molar ratio of lithium bis(trifluoromethanesulfonylimide), cyclic anhydride, and epoxy ether is 1:5 to 50:5 to 50; or, when the lithium source is a combination of a compound containing a bis(trifluoromethanesulfonylimide) anion and other lithium-containing compounds, the molar ratio of the compound containing the bis(trifluoromethanesulfonylimide) anion, other lithium-containing compounds, cyclic anhydride, and epoxy ether is 0.8 to 1.2:1:10 to 100:10 to 100.

[0022] Furthermore, the volume of the mixed solution used per unit area of ​​positive or negative electrode is 0.01–30 ml / cm². 2 The preferred concentration is 0.15–5 ml / cm³. 2 ;

[0023] The volume of the catalyst used per unit area of ​​positive or negative electrode is 0.01-10 ml / cm². 2 Preferably, the concentration is 0.01-1.7 ml / cm³. 2 .

[0024] Furthermore, the electrode is a positive electrode or a negative electrode; preferably, the active material of the positive electrode is one or more of the following: a cobalt-containing monolithic positive electrode material, a cobalt-containing binary positive electrode material, a cobalt-containing ternary positive electrode material, and a cobalt-free material;

[0025] More preferably, the unary cobalt-containing cathode material is one or more of lithium cobalt oxide and sodium cobalt oxide; the binary cobalt-containing cathode material is selected from lithium cobalt manganese oxide; the ternary cobalt-containing material is selected from one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; and the cobalt-free material is selected from one or more of lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, lithium aluminate, and lithium iron phosphate cathode materials.

[0026] Preferably, the negative electrode is lithium metal.

[0027] Furthermore, the in-situ polymerization reaction is carried out in an environment with an oxygen content of less than 100 ppm and a water content of less than 100 ppm; and / or, the polymerization reaction time is 4-36 h and the polymerization reaction temperature is 15-30 °C; and / or, the mixed solution and catalyst are sprayed sequentially onto the electrode surface using an injection pump.

[0028] The present invention also provides an electrode obtained after treatment with any of the electrode protection methods described above.

[0029] The present invention also provides a lithium battery comprising an electrode obtained after treatment by any of the electrode protection methods described above.

[0030] Before assembling the battery, one of the positive or negative electrodes is treated according to the electrode protection method described in this invention; or both the positive and negative electrodes are treated according to the electrode protection method described in this invention.

[0031] The moisture content of the purchased reagents can be between 0.01 and 100 ppm. If the moisture content is too high before preparation, molecular sieves can be added to remove water.

[0032] The technical solution of this invention has the following advantages:

[0033] 1. The electrode protection method provided by the present invention includes placing a mixed solution containing cyclic anhydride and epoxy ether on the electrode surface, placing a catalyst on the electrode surface, and conducting an in-situ polymerization reaction to form a polymer protective layer on the electrode surface. During the polymerization reaction, the catalyst first forms a coordination intermediate with trace amounts of water carried by the mixed solution itself, then attacks the epoxy ether to form oxonium ions, followed by the oxonium ions attacking the epoxy ether to form a homopolymer product of the epoxy ether, while simultaneously attacking the cyclic anhydride for ring opening. Finally, the two products alternately polymerize to form a polymer with an ester-alt-ether structure, which can react with Li + It forms multiple coordination configurations and has a large amount of Li+ Binding sites; the roles of the two complexing structures (Li + Complexes with two carbonyl groups on the polymer chain, Li + (Complexing with two carbonyl groups and one ether bond) results in a high lithium-ion transference number, ultimately synthesizing an interface layer with high oxidation potential on the electrode and electrolyte surfaces, which greatly improves the stability of lithium metal batteries and extends cycle life.

[0034] On the negative electrode surface, the polymer and Li + After complexation, the metal atomic orbital composition of the LUMO (lowest unoccupied molecular orbital) is suppressed, significantly reducing the polarity of the negative electrode. A lower LUMO energy level favors the entry of electrons into the electrode, resulting in stronger oxidation and a more positive potential. At the positive electrode surface, the increased electrode potential and the interaction between the gradually enriched anions and the polymer chain increase the HOMO (highest occupied molecular orbital) energy level, favoring the loss of electrons and resulting in stronger reduction and a more negative potential. Furthermore, the alternating ester and ether groups on the chain facilitate the dissociation of the lithium salt and maintain the Li... + The balanced complexation strength between the polymer and the polymer results in high conductivity.

[0035] 2. The electrode protection method provided by the present invention further includes a lithium source in the mixed solution, wherein the lithium source is selected from lithium bis(trifluoromethanesulfonylimide) or a combination of a compound containing a bis(trifluoromethanesulfonylimide) anion and other lithium-containing compounds, and the presence of alternating ester and ether groups on the polymer chain simultaneously promotes TFSI. - The conversion to LiF (lithium fluoride) involves alternating ester and ether groups on the polymer chain reacting with Li. + The multiple complexation sites and supramolecular interactions with TFSI enhance the stability of the lithium metal anode side, effectively suppressing lithium dendrite growth and extending the cycle life of the battery.

[0036] 3. The electrode protection method provided by the present invention controls the volume of the mixed solution used per unit area of ​​positive or negative electrode to be 0.01–30 ml / cm². 2 Especially 0.15~5ml / cm 2 The volume of the catalyst used per unit area of ​​positive or negative electrode is 0.01-10 ml / cm². 2 Especially 0.01-1.7 ml / cm 2 The resulting positive or negative electrode can better extend the cycle life of the battery. Detailed Implementation

[0037] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0038] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0039] Example 1

[0040] This embodiment provides a method for protecting electrodes, including the following steps:

[0041] (1) Preparation of mixed solution: Take 1,4,5,8-naphthalenetetraic acid dianhydride, di(2,3-epoxycyclopentyl) ether, 1-butyl-4-methylpyridine bis(trifluoromethanesulfonyl)imide and lithium salt (CAS:1186134-15-5) and mix them evenly in a molar ratio of 25:25:1:1 to prepare a mixed solution.

[0042] (2) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the positive electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 1.8 ml / min, and the volume of mixed solution sprayed per unit area is 0.18 ml / cm². 2 Then, dichlorofluoromethane is sprayed onto the front side of the positive electrode at a flow rate of 0.1 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.01 ml / cm². 2 Place the positive electrode sheet face up, flatten it, and let it stand at room temperature for 12 hours to complete the polymerization.

[0043] (3) Repeat step (2) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the positive electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 1.8 ml / min and 0.1 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 0.18 ml / cm², respectively. 2 and 0.01ml / cm 2 The positive electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 12 hours to complete polymerization, resulting in the processed positive electrode sheet.

[0044] (4) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the negative electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 1.8 ml / min, and the volume of mixed solution sprayed per unit area is 0.18 ml / cm². 2 Then, dichlorofluoromethane is sprayed onto the front side of the negative electrode at a flow rate of 0.1 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.01 ml / cm². 2 Place the negative electrode sheet face up, flatten it, and let it stand at room temperature for 12 hours to complete the polymerization.

[0045] (5) Repeat step (4) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the negative electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 1.8 ml / min and 0.1 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 0.18 ml / cm², respectively. 2 and 0.01ml / cm 2 The negative electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 12 hours to complete polymerization, resulting in the processed negative electrode sheet.

[0046] The positive electrode preparation method used in the above electrode protection method is as follows: A ternary material (molecular formula: LiNi) is prepared... 0.8 Co 0.1 Mn 0.1 O2), conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) are mixed uniformly at a mass ratio of 96.5:2.5:1.0:0.5 to prepare a lithium-ion battery positive electrode slurry. This slurry is coated onto aluminum foil for current collectors, dried at 85°C, and then cold-pressed. After trimming, cutting, and slitting, it is dried at 85°C under vacuum for 8 hours to produce a qualified lithium metal battery positive electrode sheet. The negative electrode sheet is prepared as follows: 8μm thick copper foil purchased commercially, and a copper-lithium composite strip with lithium coating on both sides (lithium thickness 30μm) are used. After trimming, cutting, and slitting, a qualified lithium metal battery negative electrode sheet is produced.

[0047] This embodiment also provides a method for preparing a lithium metal pouch battery: the positive electrode and negative electrode, after being treated by the electrode protection method of this embodiment, are stacked together with a separator to form a lithium metal battery with three positive and four negative electrodes, with a capacity of 2400mAh. An electrolyte (a mixed solution of ethylene glycol dimethyl ether (DEE) and tetrafluoroethyl tetrafluoropropyl ether (TTE) with a volume ratio of 1.0M lithium difluorosulfonyl imide (LiFSI) of 1:1) is injected to complete the battery fabrication.

[0048] Example 2

[0049] This embodiment provides a method for protecting electrodes, including the following steps:

[0050] (1) Preparation of mixed solution: Take 1,4,5,8-naphthalenetetraic acid dianhydride and di(2,3-epoxycyclopentyl) ether and mix them in a molar ratio of 25:25 to prepare a mixed solution.

[0051] (2) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the positive electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 1.8 ml / min, and the volume of mixed solution sprayed per unit area is 0.18 ml / cm². 2 Then, dichlorofluoromethane is sprayed onto the front side of the positive electrode at a flow rate of 0.1 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.01 ml / cm². 2 Place the positive electrode sheet face up, flatten it, and let it stand at room temperature for 12 hours to complete the polymerization.

[0052] (3) Repeat step (2) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the positive electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 1.8 ml / min and 0.1 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 0.18 ml / cm², respectively. 2 and 0.01ml / cm 2 The positive electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 12 hours to complete polymerization, resulting in the processed positive electrode sheet.

[0053] (4) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the negative electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 1.8 ml / min, and the volume of mixed solution sprayed per unit area is 0.18 ml / cm². 2 Then, dichlorofluoromethane is sprayed onto the front side of the negative electrode at a flow rate of 0.1 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.01 ml / cm². 2 Place the negative electrode sheet face up, flatten it, and let it stand at room temperature for 12 hours to complete the polymerization.

[0054] (5) Repeat step (4) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the negative electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 1.8 ml / min and 0.1 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 0.18 ml / cm², respectively. 2 and 0.01ml / cm 2The negative electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 12 hours to complete polymerization, resulting in the processed negative electrode sheet.

[0055] The positive electrode preparation method used in the above electrode protection method is as follows: A ternary material (molecular formula: LiNi) is prepared... 0.8 Co 0.1 Mn 0.1 O2), conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) are mixed uniformly at a mass ratio of 96.5:2.5:1.0:0.5 to prepare a lithium-ion battery positive electrode slurry. This slurry is coated onto aluminum foil for current collectors, dried at 85°C, and then cold-pressed. After trimming, cutting, and slitting, it is dried at 85°C under vacuum for 8 hours to produce a qualified lithium metal battery positive electrode sheet. The negative electrode sheet is prepared as follows: 8μm thick copper foil purchased commercially, and a copper-lithium composite strip with lithium coating on both sides (lithium thickness 30μm) are used. After trimming, cutting, and slitting, a qualified lithium metal battery negative electrode sheet is produced.

[0056] This embodiment also provides a method for preparing a lithium metal pouch battery: the positive electrode and negative electrode, after being treated by the electrode protection method of this embodiment, are stacked together with a separator to form a lithium metal battery with three positive and four negative electrodes, with a capacity of 2400mAh. An electrolyte (a mixed solution of ethylene glycol dimethyl ether (DEE) and tetrafluoroethyl tetrafluoropropyl ether (TTE) with a volume ratio of 1.0M lithium difluorosulfonyl imide (LiFSI) of 1:1) is injected to complete the battery fabrication.

[0057] Example 3

[0058] This embodiment provides a method for protecting electrodes, including the following steps:

[0059] (1) Preparation of mixed solution: Take 1,2,3,4-butanetetracarboxylic acid dianhydride, 1,3-dioxolane and lithium bis(trifluoromethanesulfonyl)imide in a molar ratio of 50:5:1 to prepare a mixed solution.

[0060] (2) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the positive electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 8.5 ml / min, and the volume of mixed solution sprayed per unit area is 0.85 ml / cm². 2 Then, dichlorofluoromethane is sprayed onto the front side of the positive electrode at a flow rate of 0.85 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.085 ml / cm². 2 Place the positive electrode sheet face up, flatten it, and let it stand at room temperature for 8 hours to complete the polymerization.

[0061] (3) Repeat step (2) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the positive electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 8.5 ml / min and 0.85 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 0.85 ml / cm², respectively. 2 and 0.085ml / cm 2 The positive electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 12 hours to complete polymerization, resulting in the processed positive electrode sheet.

[0062] (4) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the negative electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 8.5 ml / min, and the volume of mixed solution sprayed per unit area is 0.85 ml / cm². 2 Then, dichlorofluoromethane is sprayed onto the front side of the negative electrode at a flow rate of 0.85 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.085 ml / cm². 2 Place the negative electrode sheet face up, flatten it, and let it stand at room temperature for 8 hours to complete the polymerization.

[0063] (5) Repeat step (4) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the negative electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 8.5 ml / min and 0.85 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 0.85 ml / cm², respectively. 2 and 0.085ml / cm 2 The negative electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 12 hours to complete polymerization, resulting in the processed negative electrode sheet.

[0064] The positive electrode preparation method used in the above electrode protection method is as follows: A ternary material (molecular formula: LiNi) is prepared... 0.6 Co 0.2 Mn 0.2 O2), conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) are mixed uniformly at a mass ratio of 96.5:2.5:1.0:0.5 to prepare a lithium-ion battery positive electrode slurry. This slurry is coated onto aluminum foil for current collectors, dried at 85°C, and then cold-pressed. After trimming, cutting, and slitting, it is dried at 85°C under vacuum for 8 hours to produce a qualified lithium metal battery positive electrode sheet. The negative electrode sheet is prepared as follows: 8μm thick copper foil purchased commercially, and a copper-lithium composite strip with lithium coating on both sides (lithium thickness 30μm) are used. After trimming, cutting, and slitting, a qualified lithium metal battery negative electrode sheet is produced.

[0065] This embodiment also provides a method for preparing a lithium metal pouch battery: the positive electrode and negative electrode, after being treated by the electrode protection method of this embodiment, are stacked together with a separator to form a lithium metal battery with three positive and four negative electrodes, with a capacity of 2400mAh. An electrolyte (a mixed solution of ethylene glycol dimethyl ether (DEE) and tetrafluoroethyl tetrafluoropropyl ether (TTE) with a volume ratio of 1.0M lithium difluorosulfonyl imide (LiFSI) of 1:1) is injected to complete the battery fabrication.

[0066] Example 4

[0067] This embodiment provides a method for protecting electrodes, including the following steps:

[0068] (1) Preparation of mixed solution: Take 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, di(2,3-epoxycyclopentyl) ether, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and lithium trifluoromethanesulfonate and mix them in a molar ratio of 10:100:1:1 to prepare a mixed solution.

[0069] (2) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the positive electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 12.3 ml / min, and the volume of mixed solution sprayed per unit area is 1.23 ml / cm². 2 Then, dichlorofluoromethane was sprayed onto the front side of the positive electrode at a flow rate of 4.1 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.41 ml / cm². 2 Place the positive electrode sheet face up, flatten it, and let it stand at room temperature for 24 hours to complete the polymerization.

[0070] (3) Repeat step (2) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the positive electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 12.3 ml / min and 4.1 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 1.23 ml / cm², respectively. 2 and 0.41 ml / cm 2 The positive electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 24 hours to complete polymerization, resulting in the processed positive electrode sheet.

[0071] (4) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution is first sprayed onto one side of the negative electrode (hereinafter referred to as "front side") using a syringe pump at a flow rate of 12.3 ml / min, and the volume of mixed solution sprayed per unit area is 1.23 ml / cm². 2Then, dichlorofluoromethane was sprayed onto the front side of the negative electrode at a flow rate of 4.1 ml / min, resulting in a volume of dichlorofluoromethane sprayed per unit area of ​​0.41 ml / cm². 2 Place the negative electrode sheet face up, flatten it, and let it stand at room temperature for 24 hours to complete the polymerization.

[0072] (5) Repeat step (4) above, spraying the mixed solution and dichlorofluoromethane sequentially onto the other side of the negative electrode (hereinafter referred to as the "reverse side"). The flow rates of the mixed solution and dichlorofluoromethane are 12.3 ml / min and 1.23 ml / min, respectively, and the spray volume per unit area of ​​the mixed solution and dichlorofluoromethane is 4.1 ml / cm², respectively. 2 and 0.41 ml / cm 2 The negative electrode sheet is placed with the reverse side facing up, flattened, and left at room temperature for 24 hours to complete polymerization, resulting in the treated negative electrode sheet.

[0073] The positive electrode preparation method used in the above electrode protection method is as follows: A ternary material (molecular formula: LiNi) is prepared... 0.6 Co 0.2 Mn 0.2 O2), conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) are mixed uniformly at a mass ratio of 97.5:1.5:0.5:0.5 to prepare a lithium-ion battery positive electrode slurry. This slurry is coated onto aluminum foil for current collectors, dried at 70°C, and then cold-pressed. After trimming, cutting, and slitting, it is dried at 70°C under vacuum for 9 hours to produce a qualified lithium metal battery positive electrode sheet. The negative electrode sheet is prepared as follows: 8μm thick copper foil purchased commercially, and a copper-lithium composite strip with double-sided lithium coating (lithium thickness 30μm) are used. After trimming, cutting, and slitting, a qualified lithium metal battery negative electrode sheet is produced.

[0074] This embodiment also provides a method for preparing a lithium metal pouch battery: the positive electrode and negative electrode, after being treated by the electrode protection method of this embodiment, are stacked together with a separator to form a lithium metal battery with three positive and four negative electrodes, with a capacity of 2400mAh. An electrolyte (a mixed solution of ethylene glycol dimethyl ether (DEE) and tetrafluoroethyl tetrafluoropropyl ether (TTE) with a volume ratio of 1.0M lithium difluorosulfonyl imide (LiFSI) of 1:1) is injected to complete the battery fabrication.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing a lithium metal pouch battery, which is basically the same as that in Example 1. The only difference is that the positive and negative electrode sheets that have not been treated by the electrode protection method in Example 1 are used instead of the positive and negative electrode sheets that have been treated by the electrode protection method in Example 1. The other steps and conditions are the same as in Example 1.

[0077] Comparative Example 2

[0078] This comparative example provides a method for protecting an electrode, comprising the following steps:

[0079] (1) Preparation of polymerization solution:

[0080] First, 1,2,3,4-butanetetracarboxylic acid dianhydride, 1,3-dioxolane, and lithium bis(trifluoromethanesulfonyl)imide are mixed in a molar ratio of 50:5:1 to prepare mixed solution 1. Then, the mixed solution and dichlorofluoromethane are weighed in a volume ratio of 10:1 and stirred evenly to prepare mixed solution 2.

[0081] (2) In a glove box (oxygen content below 100 ppm, water content below 100 ppm), the above mixed solution 2 is sprayed onto one side (hereinafter referred to as "front side") of the positive and negative electrode plates using a syringe pump at a flow rate of 8.5 ml / min, and the volume of mixed solution 2 sprayed per unit area is 0.935 ml / cm². 2 Place the positive and negative electrode sheets face up, flatten them, and let them stand at room temperature for 8 hours to complete the polymerization.

[0082] (3) Spray mixed solution 2 onto the opposite side (hereinafter referred to as "reverse side") of the positive and negative electrode plates at a flow rate of 8.5 ml / min, with a spray volume of mixed solution 2 per unit area of ​​0.935 ml / cm². 2 The positive and negative electrode sheets were laid flat with their reverse sides facing up and left at room temperature for 8 hours to complete polymerization, resulting in the processed positive and negative electrode sheets.

[0083] This embodiment also provides a method for preparing a lithium metal pouch battery, which is basically the same as that in Example 3, except that the positive and negative electrode sheets treated in this comparative example are used instead of the positive and negative electrode sheets treated in Example 3.

[0084] Experimental Example 1

[0085] The lithium metal pouch batteries of each embodiment and comparative example were charged to 4.1V at room temperature with a current of 120mA, then charged to 4.25V with a current of 240mA, then charged at a constant voltage of 4.25V to the cutoff current (cutoff current set to 120mA), and then discharged to 2.8V with a current of 240mA. The initial charge and discharge capacity and efficiency were tested.

[0086] Coulombic efficiency and capacity retention test: At room temperature, the battery was charged to 4.25V at 1200mA, then charged at a constant voltage of 4.25V to the cutoff current (cutoff current set to 120mA), and discharged to 2.8V at 2400mA. The cycle count was set to 500. The discharge capacity CN per N cycles was obtained, and the capacity retention rate was calculated as CN / C1*100%, where C1 is the discharge capacity of the first cycle. In the cycle test data, the ratio of the discharge capacity per N cycles to the charge capacity per N cycles is the coulombic efficiency of the Nth cycle. The average coulombic efficiency from the first to the Nth cycles is the average coulombic efficiency over N cycles. The results are shown in Table 1. Experiments showed that for Comparative Examples 1-2, the cycle test was stopped before reaching 200 cycles when the capacity retention rate was below 80%. The maximum number of cycles with a capacity retention rate greater than 80%, as well as the capacity retention rate and average coulombic efficiency at that number of cycles, were recorded. The results are shown in Table 1.

[0087] Table 1. Results of the charge-discharge experiment

[0088]

[0089]

[0090] Note: For pouch lithium metal batteries, if the capacity retention rate is below 80% and the coulombic efficiency is below 98% during cycle testing, the battery testing will be stopped.

[0091] As can be seen from the table above, compared with Comparative Examples 1-2, the batteries obtained in Examples 1-4 of the present invention have significantly extended cycle life, especially Examples 1 and 3-4.

[0092] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for protecting an electrode, characterized in that, The method includes placing a mixed solution containing cyclic anhydride and epoxy ether on the electrode surface, placing a catalyst on the electrode surface, and conducting an in-situ polymerization reaction to form a polymer protective layer on the electrode surface; the polymerization reaction refers to the polymerization reaction between epoxy ethers or between cyclic anhydride and epoxy ether, and the electrode is a positive electrode or a negative electrode.

2. The electrode protection method according to claim 1, characterized in that, The cyclic anhydride is one or more of the following: glutaric anhydride, cyclobutanetetracarboxylic anhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 2,3,6,7-naphthalenetetracarboxylic anhydride, 1,2,3,4-butanetetracarboxylic anhydride, 1,2,3,4-cyclopentanetetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 2,3,3',4'-biphenyltetracarboxylic anhydride, 1,4-difluoro-2,3,5,6-phenyltetracarboxylic anhydride, and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic anhydride; and / or, the epoxy ether is selected from di(2,3-epoxycyclopentyl) ether, 1,3-dioxolane, epoxy ether 1 with CAS number 6705-89-1, and epoxy ether 1 with CAS number 7010-73- The epoxy ether 2 of 3, finishing agent DTF-7 with CAS number 5981-06-6, 1,3,6-trioxane, epoxy ether 3 with CAS number 294-59-7, epoxy ether 4 with CAS number 24194-62-5, epoxy ether 5 with CAS number 295-42-1, and epoxy ether 6 with CAS number 24471-99-6 are one or more of the following: and / or, the molar ratio of the epoxide anhydride to the epoxy ether is 5-100:5-100; and / or, the catalyst is one or more of dichloromethane, dichloromethane-d, dichlorofluoromethane, and dichloromethane-13C; and / or, the volume ratio of the mixed solution to the catalyst under the same electrode area is 10-30:

1.

3. The electrode protection method according to claim 1 or 2, characterized in that, The mixed solution also includes a lithium source selected from lithium bis(trifluoromethanesulfonylimide) or a combination of a compound containing a bis(trifluoromethanesulfonylimide) anion and other lithium-containing compounds.

4. The electrode protection method according to claim 3, characterized in that, The compound containing the bis(trifluoromethanesulfonyl)imide anion is selected from 1-butyl-4-methylpyridine bis(trifluoromethanesulfonyl)imide, N-octyl-4-methylpyridine bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, N-octyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt, 1-benzyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-methyl-3-n-octylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-benzyl-2,3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The lithium compound is selected from one or more combinations of 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexadecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; and / or, the other lithium-containing compound is selected from one or more combinations of lithium powder, lithium salt with CAS number 1186134-15-5, lithium salt with CAS number 33454-82-9, and lithium iodate.

5. The electrode protection method according to claim 3, characterized in that, When the lithium source is lithium bis(trifluoromethanesulfonylimide), the molar ratio of lithium bis(trifluoromethanesulfonylimide), cyclic anhydride, and epoxy ether is 1:5~50:5~50; or, when the lithium source is a combination of a compound containing a bis(trifluoromethanesulfonylimide) anion and other lithium-containing compounds, the molar ratio of the compound containing the bis(trifluoromethanesulfonylimide) anion, other lithium-containing compounds, cyclic anhydride, and epoxy ether is 0.8~1.2:1:10~100:10~100.

6. The method for protecting the electrode according to claim 1 or 2, characterized in that, The volume of the mixed solution used per unit area of ​​positive or negative electrode is 0.01~30 ml / cm². 2 ; The volume of the catalyst used per unit area of ​​positive or negative electrode is 0.01-10 ml / cm². 2 .

7. The electrode protection method according to claim 6, characterized in that, The volume of the mixed solution used per unit area of ​​positive or negative electrode is 0.15~5 ml / cm². 2 ; The volume of the catalyst used per unit area of ​​positive or negative electrode is 0.01-1.7 ml / cm². 2 .

8. The electrode protection method according to claim 1, characterized in that, The active material of the positive electrode is one or more of the following: cobalt-containing unary positive electrode material, cobalt-containing binary positive electrode material, cobalt-containing ternary positive electrode material, and cobalt-free material.

9. The electrode protection method according to claim 8, characterized in that, The unary cobalt-containing cathode material is one or more of lithium cobalt oxide and sodium cobalt oxide; the binary cobalt-containing cathode material is selected from lithium cobalt manganese oxide; the ternary cobalt-containing material is selected from one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; the cobalt-free material is selected from one or more of lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, lithium aluminate, and lithium iron phosphate cathode materials.

10. The electrode protection method according to claim 1, characterized in that, The negative electrode is lithium metal.

11. The method for protecting the electrode according to any one of claims 1-10, characterized in that, The in-situ polymerization reaction is carried out in an environment with an oxygen content of less than 100 ppm and a water content of less than 100 ppm; and / or, the polymerization reaction time is 4-36 h and the polymerization reaction temperature is 15-30 °C; and / or, the mixed solution and catalyst are sprayed onto the electrode surface sequentially using an injection pump.

12. The electrode obtained after being treated by the protection method of any one of claims 1-11.

13. A lithium battery, characterized in that, Electrodes obtained after being treated by the protection method for electrodes according to any one of claims 1-11.

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