Lithium ion battery for constructing and repairing positive electrode interface and preparation method of lithium ion battery

Abstract

The invention relates to a lithium ion battery for constructing and repairing a positive electrode interface and a preparation method thereof, a positive electrode material of the battery comprises a layered oxide, a nitrile group-containing polymer and a doped metal salt, the mass fraction of the nitrile group-containing polymer relative to the layered oxide is 0.5-2 wt.%, and the mass fraction of the doped metal salt relative to the layered oxide is 0.1-3 wt.%. Compared with the prior art, the stability of a positive electrode interface is enhanced, and the cycle performance of the positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof. Background Art

[0002] With the wide popularization of the new generation of artificial intelligence computing power, the demand for sustainable and portable energy is rising continuously. Among many energy solutions, lithium-ion batteries have attracted much attention due to their excellent energy density, long cycle life, and high efficiency. In lithium-ion batteries, layered oxide materials stand out because of their high theoretical capacity and large volume density, and become popular cathode materials. Although layered oxide materials can provide higher capacity, they have large repeated volume deformations during their operation, which cause damage to the interface layer and particle cracking, leading to a rapid decay of the electrochemical performance of the battery.

[0003] Patent CN114843500A discloses a method for constructing and applying a stable interface of a lithium-rich manganese-based cathode material for a lithium-ion battery, using fluorosilane as an additive to the electrolyte to remove hydrofluoric acid in the electrolyte, change the lithium-ion solvation structure, and simultaneously form a cathode electrolyte interface rich in lithium fluoride in-situ during the charge-discharge cycle. However, in this patent, fluorosilane cannot alleviate the problem of positive electrode volume expansion during the cycle, and there are limitations in the stability of the interface structure.

[0004] Patent CN113839092A discloses a dopable cathode metal salt-lithium salt composite additive and its application, using one or more of Mg 2+ 、Na + 、K + 、Al 3+ 、Zn 2+ 、Ni 2+ 、Cu 2+ 、Ca 2+ in the dopable cathode as metal cations of the metal salt additive; wherein, a solution of the dopable cathode metal salt additive and the lithium salt is uniformly coated on the cathode plate and the solvent is evaporated. However, this patent does not consider the problem that the passivation film on the cathode interface is prone to breakage during long cycles.

[0005] Patent CN118281215A discloses a method for constructing and repairing a titanium layer and synergistically regenerating waste lithium nickel cobalt manganese oxide cathode materials with a eutectic salt, mixing the lithium nickel cobalt manganese oxide cathode material and a titanium source evenly, and then adding a lithium source and mixing evenly to obtain a composite material; sintering the composite material in an oxidizing atmosphere in two stages and cooling to room temperature to obtain a regenerated waste lithium nickel cobalt manganese oxide cathode material with lithium supplementation and repair. However, the calcination method used in this patent has problems of high energy consumption and high cost, which is not conducive to its large-scale application.

[0006] Patent CN110224177A discloses a method and product for protecting a lithium metal / sodium metal anode. In any atmosphere, a type of interfacial modification material is pre-constructed on a battery separator to obtain a prefabricated separator. The interaction between the interfacial modification material and the lithium anode is stronger than the interaction with the separator. Perform the battery assembly process, wherein the side of the prefabricated separator with the interfacial modification material is closely attached to the metallic lithium anode, inject the electrolyte, and under the infiltration of the electrolyte, utilize the physical and chemical interaction between the interfacial modification material and metallic lithium, and the interfacial modification material spontaneously transfers from the separator to the surface of the metallic lithium anode, thereby automatically realizing the protection of the metallic lithium anode; wherein, the interfacial modification material includes polyacrylonitrile and its derivatives. Although this patent mentions that the interfacial modification material will spontaneously transfer from the separator to the surface of the metallic lithium anode, there are problems with the controllability of this transfer process, affecting the consistency and effectiveness of the protection of the lithium anode. Summary of the Invention

[0007] The object of the present invention is to provide a lithium-ion battery for constructing and repairing a positive electrode interface and its preparation method to overcome at least one defect existing in the above-mentioned prior art. The present invention enhances the stability of the positive electrode interface and improves the cycling performance of the positive electrode material.

[0008] The object of the present invention can be achieved by the following technical solutions:

[0009] One of the technical solutions of the present invention is to provide a lithium-ion battery for constructing and repairing a positive electrode interface. The positive electrode material of this battery includes a layered oxide, a nitrile group-containing polymer, and a doped metal salt. The mass fraction of the nitrile group-containing polymer relative to the layered oxide is 0.5 - 2 wt.%, and the mass fraction of the doped metal salt relative to the layered oxide is 0.1 - 3 wt.%.

[0010] As a preferred technical solution, the mass fraction of the doped metal salt relative to the layered oxide is 0.1 - 1.2 wt.%.

[0011] Furthermore, the layered oxide is selected from one of lithium cobaltate layered oxide (LCO), lithium-rich manganese-based layered oxide (LLO), and nickel-cobalt-manganese ternary layered oxide (NCM).

[0012] Furthermore, the nitrile group-containing polymer is selected from one or more of polyacrylonitrile (PAN), polyethylene glycol dicyanide (CN-PEG-CN), and polyarylether nitrile (PEN), and the molecular weight of the nitrile group-containing polymer is 4000 - 100000.

[0013] As a preferred technical solution, the molecular weight of the nitrile group-containing polymer is 70000 - 100000.

[0014] Furthermore, the cation of the doped metal salt is selected from Ca2+ , Mg 2+ , K + , Al 3+ , Zn 2+ One or more metal ions selected from, and the anions are selected from ClO4 - , NO3 - , SO4 2- One or more of them.

[0015] Furthermore, the electrolyte of the battery includes lithium hexafluorophosphate (LiPF6), an ester solvent, an ether solvent, and a boron-containing anion salt.

[0016] Furthermore, the ester solvent is selected from one or more carbonate solvents such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), and the ether solvent is selected from one or more fluoroether solvents such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), and ethylene glycol bis(trifluoroethyl ether) (D2). The concentration of lithium hexafluorophosphate is 0.5 - 2 mol·L -1 , and the volume ratio of the ester solvent to the ether solvent is (6 - 12):(1 - 3).

[0017] Furthermore, the boron-containing anion salt is selected from one or more boron-containing anion lithium salts such as lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB). The concentration of the boron-containing anion salt is 0 - 0.2 mol·L -1 .

[0018] As a preferred technical solution, the concentration of the boron-containing anion salt is 0.05 - 0.2 mol·L -1 .

[0019] One of the technical solutions of the present invention is to provide a preparation method of the lithium-ion battery for constructing and repairing the positive electrode interface, and this method includes the following steps:

[0020] S1. Dissolve the layered oxide, nitrile group-containing polymer, and doped metal salt in a positive electrode solvent, ultrasonically disperse, stir at low temperature, stir at high temperature until evaporated to dryness, and dry to obtain a layered oxide positive electrode material coated with a nitrile group-containing polymer-doped metal;

[0021] S2. Mix the positive electrode material, conductive agent, and binder in a dispersant, coat it on the surface of the current collector, and dry to obtain a positive electrode sheet;

[0022] S3. Mix lithium hexafluorophosphate and the boron-containing anion salt in an ester solvent and an ether solvent to obtain an electrolyte;

[0023] S4. Assemble the negative electrode sheet, electrolyte, separator, electrolyte and positive electrode sheet to obtain a lithium-ion battery with a constructed and repaired positive electrode interface.

[0024] Furthermore, in step S1, the positive electrode solvent is selected from one or more of ethanol, water, and dimethyl carbonate, and the mass / volume ratio of the layered oxide to the positive electrode solvent is (1 - 5 g):(10 - 30 mL).

[0025] The frequency of ultrasonic dispersion is 20 - 60 kHz, and the time is 20 - 60 min.

[0026] The temperature of low-temperature stirring is 20 - 60 °C, and the time is 2 - 8 h.

[0027] The temperature of high-temperature stirring is 60 - 100 °C, and the time is 0.5 - 2 h.

[0028] The drying temperature is 60 - 100 °C, and the time is 6 - 24 h.

[0029] As a preferred technical solution, in step S1, the temperature of ultrasonic dispersion is 20 - 40 °C.

[0030] The rotation speed of low-temperature stirring is 100 - 300 rpm.

[0031] The rotation speed of high-temperature stirring is 300 - 500 rpm.

[0032] Furthermore, in step S2, the conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and polytetrafluoroethylene (PTFE), the dispersant is selected from one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, and water, the mass ratio of the positive electrode material, conductive agent, and binder is (6 - 10):(1 - 3):(1 - 3), and the mass / volume ratio of the positive electrode material to the dispersant is (1 - 5 g):(1 - 3 mL).

[0033] The mixing temperature is 10 - 30 °C, and the time is 20 - 60 min.

[0034] The drying temperature is 60 - 100 °C, and the time is 2 - 5 h.

[0035] As a preferred technical solution, in step S2, the stirring rotation speed during mixing is 1000 - 2000 rpm.

[0036] The current collector is selected from one of aluminum foil and copper foil.

[0037] As a preferred technical solution, in step S3, the mixing temperature is 10 - 30 °C, and the time is 6 - 24 h.

[0038] As a preferred technical solution, the material of the negative electrode sheet in step S4 is selected from one of metallic lithium, graphite, and silicon-carbon composite, the separator is selected from one of polypropylene (PP) film, polyethylene (PE) film, and polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite film, and the ratio of the diameter of the electrode sheet to the volume of the electrolyte is (4-20 mm): (20-100 μL).

[0039] As a preferred technical solution, in step S4, the button battery is assembled in the order of the negative electrode shell, the spring sheet, the gasket, the negative electrode sheet, the electrolyte, the separator, the electrolyte, the positive electrode sheet and the positive electrode shell.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The positive electrode material of the present invention is coated with a high-voltage-resistant nitrile-containing polymer and an inorganic metal salt, and the coordination effect brought by the rich cyano (-CN) groups of the nitrile-containing polymer is utilized to achieve the enrichment of doped metal ions on the surface of the layered oxide positive electrode material, and the expansion property of the polymer is adapted to the volume change of the layered oxide positive electrode material during the cycle, which can effectively buffer the volume expansion of the layered oxide positive electrode material during the charge and discharge process; compared with lithium hexafluorophosphate (LiPF6), the hexafluorophosphate generated by doping metal ions is more inclined to preferentially decompose to form metal fluorides during the cycle; because metal fluorides have the characteristics of high hardness and high-voltage resistance, they can effectively resist the corrosion of hydrofluoric acid (HF) caused by high voltage, inhibit the dissolution of cobalt, and enhance the chemical stability of the positive electrode interface; in addition, doped metal ions can play the role of "support pillars" in the lattice, thereby improving the stability of the crystal structure in the layered oxide positive electrode material;

[0042] (2) When the pre-constructed metal fluoride-doped composite passivation film breaks after long-term cycling, part of the lithium hexafluorophosphate in the electrolyte of the present invention is replaced by a boron-containing anion salt, and the boron-containing anion salt is oxidized and decomposed at a high potential, and deposited on the surface of the positive electrode to form an oligomer with BO bonds, thereby constructing a new positive electrode electrolyte interface (CEI), thereby compensating for the failed positive electrode electrolyte interface film, significantly improving the cycle performance of the layered oxide positive electrode material, effectively alleviating the capacity loss caused by the instability of the surface interface structure of the layered oxide positive electrode material during the charge and discharge process, and improving the stability of long cycles;

[0043] (3) The method for constructing the positive electrode interface of the present invention is simple to operate, does not require calcination, and saves energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A comparison chart of the cycle performance of lithium-ion batteries in Examples 1 to 4 of the present invention and the comparative example;

[0045] Figure 2 This is the comparison chart of the cycle performance of the lithium-ion batteries with the construction and repair of the positive electrode interface in Embodiments 2, 5 to 7 of the present invention;

[0046] Figure 3 This is the comparison chart of the X-ray diffraction (XRD) test of the positive electrode sheets of the lithium-ion batteries after cycling in Embodiment 7 of the present invention and Comparative Example 1;

[0047] Figure 4 This is the enlarged view of the (003) peak of the XRD test comparison of the positive electrode sheets of the lithium-ion batteries after cycling in Embodiment 7 of the present invention and Comparative Example 1;

[0048] Figure 5 This is the X-ray photoelectron (XPS) spectrum of the positive electrode sheet of the lithium-ion battery with the construction and repair of the positive electrode interface in Embodiment 7 of the present invention after different etching times of cobalt element;

[0049] Figure 6 This is the XPS spectrum of the positive electrode sheet of the lithium-ion battery with the construction and repair of the positive electrode interface in Embodiment 7 of the present invention after different etching times of nitrogen element;

[0050] Figure 7 This is the XPS spectrum of the positive electrode sheet of the lithium-ion battery with the construction and repair of the positive electrode interface in Embodiment 7 of the present invention after different etching times of boron element;

[0051] Figure 8 This is the XPS spectrum of the positive electrode sheet of the lithium-ion battery with the construction and repair of the positive electrode interface in Embodiment 7 of the present invention after different etching times of magnesium element;

[0052] Figure 9 This is the XPS spectrum of the positive electrode sheet of the lithium-ion battery with the construction and repair of the positive electrode interface in Embodiment 7 of the present invention after different etching times of fluorine element. Detailed implementation manners

[0053] The present invention will be described in detail below with reference to specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0054] Unless otherwise specified, the equipment used in the following embodiments represents conventional equipment in the art; unless otherwise specified, the reagents used represent commercially available products or are prepared by conventional methods in the art. Those not described in detail in the following embodiments can be achieved by conventional experimental means in the art.

[0055] Embodiment 1:

[0056] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof, the specific steps are as follows:

[0057] S1. Dissolve 4 g of lithium cobaltate layered oxide (LCO), 0.04 g of polyacrylonitrile (PAN, molecular weight 85000), and 0.012 g of magnesium perchlorate (Mg(ClO4)2) in 20 mL of dimethyl carbonate (DMC). Place the mixed solution in an ultrasonic disperser and ultrasonically treat it at a frequency of 40 kHz at room temperature of 25°C for 30 min. Magnetically stir it at a speed of 200 rpm at a low temperature of 40°C for 4 h, and magnetically stir it at a speed of 400 rpm at a high temperature of 90°C for 1 h until it is evaporated to dryness. Dry it in a high-temperature oven at 80°C for 12 h to obtain 4.06 g of LCO powder coated with 1 wt.% PAN - 0.3 wt.% Mg(ClO4)2;

[0058] S2. Uniformly mix 4.06 g of LCO powder coated with 1 wt.% PAN - 0.3 wt.% Mg(ClO4)2, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. Add 1.5 mL of N-methylpyrrolidone (NMP), stir and defoam it at a speed of 1500 rpm at room temperature of 25°C for 30 min, coat it on the surface of the aluminum foil, and dry it in a high-temperature oven at 80°C for 3 h. Cut it to obtain a positive electrode sheet with a diameter of 10 mm;

[0059] S3. Weigh 0.308 g of lithium hexafluorophosphate (LiPF6) in a glove box and place it in a small glass bottle. Then add 0.8 mL of propylene carbonate (PC), 0.2 mL of ethylene carbonate (EC), 0.8 mL of DMC, and 0.2 mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to the bottle respectively, so that the concentration of LiPF6 is 1.0 mol·L -1 , and let it stand at room temperature of 25°C for 12 h to obtain an electrolyte;

[0060] S4. In a glove box filled with an argon atmosphere, assemble a CR2032 type button lithium-ion battery for constructing and repairing a positive electrode interface in the order of a negative electrode case, a spring piece, a stainless steel gasket, a metallic lithium negative electrode sheet with a diameter of 12 mm, 30 μL of electrolyte, a polypropylene (PP) separator, 30 μL of electrolyte, a positive electrode sheet with a diameter of 10 mm, and a positive electrode case.

[0061] Example 2:

[0062] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof are basically the same as those in Example 1, except that in step S1, 4 g of LCO, 0.04 g of PAN and 0.02 g of Mg(ClO4)2 are dissolved in DMC, and the mass fraction of added Mg(ClO4)2 relative to LCO is increased from 0.3 wt.% to 0.5 wt.%.

[0063] Example 3:

[0064] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof are basically the same as those in Example 1, except that in step S1, 4 g of LCO, 0.04 g of PAN and 0.028 g of Mg(ClO4)2 are dissolved in DMC, and the mass fraction of added Mg(ClO4)2 relative to LCO is increased from 0.3 wt.% to 0.7 wt.%.

[0065] Example 4:

[0066] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof are basically the same as those in Example 1, except that in step S1, 4 g of LCO, 0.04 g of PAN and 0.04 g of Mg(ClO4)2 are dissolved in DMC, and the mass fraction of added Mg(ClO4)2 relative to LCO is increased from 0.3 wt.% to 1.0 wt.%.

[0067] Example 5:

[0068] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof are basically the same as those in Example 2, except that in step S3, 0.277 g of LiPF6 and 0.0187 g of lithium tetrafluoroborate (LiBF4) are weighed, and the concentration of added LiPF6 is decreased from 1.0 mol·L -1 to 0.9 mol·L -1 , and the concentration of the newly added LiBF4 is 0.1 mol·L -1 .

[0069] Example 6:

[0070] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof are basically the same as those in Example 2, except that in step S3, 0.277 g of LiPF6 and 0.0287 g of lithium difluoro(oxalato)borate (LiDFOB) are weighed, and the concentration of added LiPF6 is decreased from 1.0 mol·L -1 to 0.9 mol·L -1 , and the concentration of the newly added LiDFOB is 0.1 mol·L -1 .

[0071] Example 7:

[0072] A lithium-ion battery for constructing and repairing a positive electrode interface and a preparation method thereof are basically the same as those of Example 2, except that in step S3, 0.277 g of LiPF6 and 0.0388 g of lithium bis(oxalato)borate (LiBOB) are weighed, and the concentration of added LiPF6 is reduced from 1.0 mol·L -1 to 0.9 mol·L -1 , and the concentration of the newly added LiBOB is 0.1 mol·L -1 .

[0073] Comparative Example 1:

[0074] A lithium-ion battery and a preparation method thereof are basically the same as those of Example 1, except that Mg(ClO4)2 and PAN are not added, denoted as Base.

[0075] Comparative Example 2:

[0076] A lithium-ion battery and a preparation method thereof are basically the same as those of Example 1, except that Mg(ClO4)2 is no longer added.

[0077] The above batteries are subjected to the following tests or experiments, and then the test or experimental results are analyzed.

[0078] Test Example 1:

[0079] In order to evaluate the influence of the doped metal content on the cycle stability of the layered oxide cathode material at high voltage, the batteries in Examples 1 to 4 and the comparative examples are subjected to charge and discharge tests in the voltage range of 3.0 - 4.6 V vs Li + / Li, and some test results are shown in Table 1.

[0080] As Figure 1 and shown in Table 1, the content of Mg(ClO4)2 in the batteries of Examples 3 and 4 is relatively high, and part of the Mg 2+ may drift to the lithium negative electrode. At the same time, Mg 2+ carries two units of positive charge and has a strong coordination effect with the solvent (such as EC / DMC), which may consume free solvent molecules, thereby affecting Li +The solvation and desolvation processes lead to a decrease in its initial capacity, but the discharge specific capacity retention rate after 200 weeks increases significantly; the initial capacity levels of the batteries in Examples 1 and 2 are similar, and the discharge specific capacity retention rate after 200 weeks is significantly higher than that of the batteries in the comparative example without the introduction of nitrile group-containing polymer and doped metal salt, indicating the effects of the polymer on alleviating volume expansion and the doped metal salt on inhibiting cobalt dissolution and enhancing stability; the content of Mg(ClO4)2 in the battery of Example 1 is low, and the protective effect on the positive electrode is relatively limited; the content of Mg(ClO4)2 in the battery of Example 2 is moderate, maintaining a high initial capacity and discharge specific capacity retention rate, so the electrochemical effect is the best.

[0081] Table 1 Comparison table of the electrochemical performance test discharge capacities of the lithium-ion batteries in Examples 1 to 4 and the comparative example

[0082]

[0083] Test Example 2:

[0084] To explore the repair effects of different boron-containing anion salts on constructing the positive electrode interface of metal fluoride, charge-discharge cycle tests were carried out on the batteries in Examples 2, 5 to 7 at a voltage range of 3.0 - 4.6V vs Li + / Li, and some test results are shown in Table 2.

[0085] As Figure 2 and shown in Table 2, the discharge specific capacity of the battery without the introduction of boron-containing anion salt in Example 2 decreased faster after 40 weeks compared with the batteries in Examples 5 to 7 with the introduction of boron-containing anion salt, and the electrochemical performance was relatively poor, indicating that the stability of the interface decayed to a certain extent; among the batteries in Examples 5 to 7, the battery in Example 7 had the highest discharge specific capacity retention rate after 200 weeks, and the electrochemical effect was the most significant, because LiBOB contains more boron, and its oxidation decomposition at high voltage can generate a higher content of B-O / B-F bonds, better repairing the damaged cathode electrolyte interface (CEI) film. The discharge specific capacity retention rates of the batteries in Examples 5 and 6 after 200 weeks were inferior to that of the battery in Example 7 due to the boron content, but the initial capacities of the batteries in Examples 5 to 7 were all higher than that of the battery in Example 2.

[0086] Table 2 Comparison table of the electrochemical performance test discharge capacities of the lithium-ion batteries in Examples 2, 5 to 7

[0087]

[0088] Test Example 3:

[0089] To more clearly analyze the structural effects of the present invention on the layered oxide cathode material, for 3.0 - 4.6V vsLi +The positive electrode plates of the battery in Example 7 and Comparative Example 1 after 200 cycles of Li / Li⁺ cycling were subjected to X-ray diffraction (XRD) tests.

[0090] As Figure 3 and Figure 4 shown, compared with the battery in Example 7 without cycling, the (003) peak of the battery in Comparative Example 1 after 200 cycles shifted towards a lower angle, indicating that the lattice distortion occurred due to the release of lattice oxygen and the dissolution of lithium cobaltate at high voltages; while the (003) peak of the battery in Example 7 after 200 cycles hardly shifted, indicating that the Mg 2+ doped metal ions played a role in alleviating lattice distortion and increased the stability of the interface structure.

[0091] Test Example 4:

[0092] To more clearly analyze the elemental distribution of the interface in the present invention, in-depth Ar + sputtering was used to perform a depth profile analysis on the battery in Example 7 after 200 cycles of 3.0 - 4.6V vs Li + / Li cycling.

[0093] As Figures 5 to 9 shown, when the etching time was short and the etching depth was shallow, the elements with a high CEI content near the surface of the battery in Example 7 were nitrogen, boron, magnesium, and fluorine, indicating that the outer passivation film was composed of a boron-containing polymer generated by the decomposition of PAN, MgF₂, LiBOB, and carbonate solvents; as the etching time increased and the etching depth gradually deepened, the peak of cobalt became more and more obvious. At this time, the CEI near the bulk phase was mainly composed of magnesium and fluorine elements, indicating that there was a dense inorganic passivation layer such as MgF₂ and LiF in this region; while a clear magnesium peak could still be seen in the deepest etched region, indicating that part of the magnesium entered the bulk phase of lithium cobaltate; by adding PAN + Mg(ClO₄)₂ to the positive electrode material and adjusting the lithium salt composition in the electrolyte, a CEI rich in organic matter on the outer layer and rich in inorganic matter on the inner layer was constructed, effectively stabilizing the lithium cobaltate interface at high voltages.

[0094] The present invention discloses a method for constructing and repairing the cathode interface of a lithium-ion battery, specifically designing a boron salt-containing repair-dopable metal fluoride composite passivation film. First, the present invention uses a coating method to achieve the enrichment of doped metal ions on the surface of the layered oxide cathode material through the rich cyano (-CN) groups in the nitrile group-containing polymer. The doped metal ions will produce a "strut effect", which can improve the stability of the crystal lattice. At the same time, during the cycling process, the metal hexafluorophosphate generated by the doped metal ions is easier to decompose into metal fluoride preferentially than lithium hexafluorophosphate (LiPF6). The high-voltage-resistant property of the metal fluoride is used to enhance the chemical stability of the cathode interface. Considering the possible damage to the cathode electrolyte interface (CEI) after long-term cycling, on this basis, a boron-containing anion salt is added to the electrolyte, and a boron-rich product is formed on the cathode surface through the oxidative decomposition of the boron-containing anion salt, effectively repairing the damaged cathode electrolyte interface. This design significantly improves the cycling performance of the layered oxide cathode material.

[0095] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A lithium-ion battery with a positive electrode interface construction and repair, characterized in that The positive electrode material of the battery includes a layered oxide, a nitrile group-containing polymer, and a doped metal salt. The mass fraction of the nitrile group-containing polymer relative to the layered oxide is 0.5 to 2 wt.%, and the mass fraction of the doped metal salt relative to the layered oxide is 0.1 to 3 wt.%.

2. The lithium-ion battery for constructing and repairing a positive electrode interface according to claim 1, wherein The layered oxide is selected from one of lithium cobaltate layered oxide, lithium-rich manganese-based layered oxide, and nickel-cobalt-manganese ternary layered oxide.

3. A lithium-ion battery for constructing and repairing a cathode interface according to claim 1, characterized in that, The nitrile group-containing polymer is selected from one or more of polyacrylonitrile, polyethylene glycol dicyanide, and polyarylether nitrile, and the molecular weight of the nitrile group-containing polymer is 4000 to 100000.

4. A lithium-ion battery for constructing and repairing a cathode interface according to claim 1, characterized in that, The cation of the doped metal salt is selected from Ca 2+ Mg 2+ , K + 、Al 3+ 、Zn 2+ One or more of, the anion is selected from ClO4 - 、NO3 - 、SO4 2- One or more of .

5. The lithium-ion battery for building and repairing a cathode interface according to claim 1, wherein The electrolyte of the battery includes lithium hexafluorophosphate, an ester solvent, an ether solvent, and a boron-containing anion salt.

6. The lithium-ion battery for constructing and repairing a cathode interface according to claim 5, wherein, The ester solvent is selected from one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. The ether solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and ethylene glycol bis(trifluoroethyl ether). The concentration of lithium hexafluorophosphate is 0.5 to 2 mol·L -1 , and the volume ratio of the ester solvent to the ether solvent is (6 to 12):(1 to 3).

7. A lithium-ion battery with a cathode interface construction and repair according to claim 5, characterized in that, The boron-containing anion salt is selected from one or more of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(oxalato)borate, and the concentration of the boron-containing anion salt is 0 to 0.2 mol·L -1 .

8. A method for preparing a lithium-ion battery with a positive electrode interface construction and repair as described in any one of claims 1 to 7, characterized in that, The method includes the following steps: S1. Dissolve the layered oxide, the nitrile group-containing polymer, and the doped metal salt in a positive electrode solvent, perform ultrasonic dispersion, stir at a low temperature, stir at a high temperature until dried, and dry to obtain the positive electrode material; S2. Mix the positive electrode material, the conductive agent, and the binder in a dispersant, coat the surface of the current collector, and dry to obtain the positive electrode sheet; S3. Mix lithium hexafluorophosphate and the boron-containing anion salt in the ester solvent and the ether solvent to obtain the electrolyte; S4. Assemble the negative electrode sheet, the electrolyte, the separator, the electrolyte, and the positive electrode sheet to obtain a lithium-ion battery with a positive electrode interface constructed and repaired.

9. The preparation method of a lithium-ion battery for constructing and repairing a positive electrode interface according to claim 8, wherein, In step S1, the positive electrode solvent is selected from one or more of ethanol, water, and dimethyl carbonate. The mass / volume ratio of the layered oxide to the positive electrode solvent is (1 to 5 g):(10 to 30 mL). The frequency of ultrasonic dispersion is 20 to 60 kHz, and the time is 20 to 60 min. The temperature of low-temperature stirring is 20 to 60 °C, and the time is 2 to 8 h. The temperature of high-temperature stirring is 60 to 100 °C, and the time is 0.5 to 2 h. The drying temperature is 60 to 100 °C, and the time is 6 to 24 h.

10. The preparation method of a lithium-ion battery for constructing and repairing a positive electrode interface according to claim 8, characterized in that, In step S2, the conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene. The binder is selected from one or more of polyvinylidene fluoride, polyvinyl alcohol, and polytetrafluoroethylene. The dispersant is selected from one or more of N-methylpyrrolidone, dimethyl carbonate, and water. The mass ratio of the positive electrode material, the conductive agent, and the binder is (6 to 10):(1 to 3):(1 to 3). The mass / volume ratio of the positive electrode material to the dispersant is (1 to 5 g):(1 to 3 mL). The mixing temperature is 10 to 30 °C, and the time is 20 to 60 min. The drying temperature is 60 to 100 °C, and the time is 2 to 5 h.

Images